TH ADV. COMMUNICATION LAB 6 SEM E&C • the line-coded signal can directly be put on a transmission line, in the form of variations of the voltage or current (often using differential signaling). • the line-coded signal (the "base-band signal") undergoes further pulse shaping (to reduce its frequency bandwidth) LINE CODING and then modulated (to shift its frequency bandwidth) to create the "RF signal" that can be sent through free space. Line coding consists of representing the digital signal to be • the line-coded signal can be used to turn on and off a light transported by an amplitude- and time-discrete signal that is in Free Space Optics, most commonly infrared remote optimally tuned for the specific properties of the physical channel control. (and of the receiving equipment). The waveform pattern of • the line-coded signal can be printed on paper to create a voltage or current used to represent the 1s and 0s of a digital bar code. data on a transmission link is called line encoding. The common • the line-coded signal can be converted to a magnetized types of line encoding are unipolar, polar, bipolar and spots on a hard drive or tape drive. Manchester encoding. • the line-coded signal can be converted to a pits on optical For reliable clock recovery at the receiver, one usually imposes a disc. maximum run length constraint on the generated channel Unfortunately, most long-distance communication sequence, i.e. the maximum number of consecutive ones or channels cannot transport a DC component. The DC zeros is bounded to a reasonable number. A clock period is component is also called the disparity, the bias, or the DC recovered by observing transitions in the received sequence, so coefficient. The simplest possible line code, called unipolar that a maximum run length guarantees such clock recovery, because it has an unbounded DC component, gives too while sequences without such a constraint could seriously many errors on such systems. hamper the detection quality.

Most line codes eliminate the DC component — such codes After line coding, the signal is put through a "physical channel", are called DC balanced, zero-DC, zero-bias or DC equalized either a "transmission medium" or "data storage medium". etc. There are two ways of eliminating the DC component: Sometimes the characteristics of two very different-seeming channels are similar enough that the same line code is used for • Use a constant-weight code. In other words, design each them. The most common physical channels are: transmitted code word such that every code word that contains some positive or negative levels also contains enough of the opposite levels, such that the average level • AMI over each code word is zero. For example, Manchester • Modified AMI codes : B8ZS, B6ZS, B3ZS, HDB3 code and Interleaved 2 of 5. • 2B1Q • Use a paired disparity code. In other words, design the • 4B5B receiver such that every code word that averages to a • 4B3T negative level is paired with another code word that • 6b/8b encoding averages to a positive level. Design the receiver so that • Hamming Code either code word of the pair decodes to the same data • 8b/10b encoding bits. Design the transmitter to keep track of the running • 64b/66b encoding DC buildup, and always pick the code word that pushes • 128b/130b encoding the DC level back towards zero. For example, AMI, 8B10B, • Coded mark inversion (CMI) 4B3T, etc. • Conditioned Diphase • Eight-to-Fourteen Modulation (EFM) used in Compact Disc Line coding should make it possible for the receiver to • EFMPlus used in DVD synchronize itself to the phase of the received signal. If the • RZ — Return-to-zero synchronization is not ideal, then the signal to be decoded will • NRZ — Non-return-to-zero not have optimal differences (in amplitude) between the various • NRZI — Non-return-to-zero, inverted digits or symbols used in the line code. This will increase the • Manchester code (also variants Differential Manchester & error probability in the received data. Biphase mark code) • Miller encoding (also known as Delay encoding or Modified It is also preferred for the line code to have a structure that will Frequency Modulation, and has variant Modified Miller enable error detection. encoding) • MLT-3 Encoding Note that the line-coded signal and a signal produced at a • Hybrid Ternary Codes terminal may differ, thus requiring translation. • Surround by complement (SBC) A line code will typically reflect technical requirements of the • TC-PAM transmission medium, such as optical fiber or shielded twisted Optical line codes: pair. These requirements are unique for each medium, because each one has different behavior related to interference, • Carrier-Suppressed Return-to-Zero distortion, capacitance and loss of amplitude. • Alternate-Phase Return-to-Zero

[EDIT ] COMMON LINE CODES NON-RETURN-TO-ZERO mechanisms for bit synchronization when a separate clock signal is not available. From Wikipedia, the free encyclopedia NRZ-Level itself is not a synchronous system but rather an Jump to: navigation, search encoding that can be used in either a synchronous or asynchronous transmission environment, that is, with or without an explicit clock signal involved. Because of this, it is not strictly necessary to discuss how the NRZ-Level encoding acts "on a clock edge" or "during a clock cycle" since all transitions happen in the given amount of time representing the actual or implied integral clock cycle. The real question is that of sampling--the

The binary signal is encoded using rectangular pulse amplitude high or low state will be received correctly provided the modulation with polar non-return-to-zero code transmission line has stabilized for that bit when the physical line level is sampled at the receiving end. In telecommunication, a non-return-to-zero (NRZ) line code is a binary code in which 1's are represented by one significant However, it is helpful to see NRZ transitions as happening on the condition (usually a positive voltage) and 0's are represented by trailing (falling) clock edge in order to compare NRZ-Level to some other significant condition (usually a negative voltage), other encoding methods, such as the mentioned Manchester with no other neutral or rest condition. The pulses have more code, which requires clock edge information (is the XOR of the energy than a RZ code. Unlike RZ, NRZ does not have a rest clock and NRZ, actually) and to see the difference between NRZ- state. NRZ is not inherently a self-synchronizing code, so some Mark and NRZ-Inverted. additional synchronization technique (for example a run length limited constraint, or a parallel synchronization signal) must be CONTENTS used to avoid bit slip. • 1 Unipolar Non-Return-to-Zero Level For a given data signaling rate, i.e., bit rate, the NRZ code • 2 Bipolar Non-Return-to-Zero Level • requires only half the bandwidth required by the Manchester 3 Non-Return-to-Zero Space • 4 Non-Return-to-Zero Inverted code. (NRZI) • 5 See also When used to represent data in an asynchronous communication • scheme, the absence of a neutral state requires other 6 References

[EDIT ] UNIPOLAR NON-RETURN-TO-ZERO LEVEL Main article: On-off keying An example of this is RS-232, where "one" is −5V to −12V and "zero" is +5 to +12V. "One" is represented by one physical level (such as a DC bias on the transmission line). [EDIT ] NON-RETURN-TO-ZERO SPACE

"Zero" is represented by another level (usually a positive voltage).

Non-Return-to-Zero Space

"One" is represented by no change in physical level. In clock language, "one" transitions or remains high on the "Zero" is represented by a change in physical level. trailing clock edge of the previous bit and "zero" transitions or remains low on the trailing clock edge of the previous bit, or just In clock language, the level transitions on the trailing clock edge the opposite. This allows for long series without change, which of the previous bit to represent a "zero." makes synchronization difficult. One solution is to not send bytes without transitions. Disadvantages of an on-off keying are the This "change-on-zero" is used by High-Level Data Link Control waste of power due to the transmitted DC level and the power and USB. They both avoid long periods of no transitions (even spectrum of the transmitted signal does not approach zero at when the data contains long sequences of 1 bits) by using zero- zero frequency. See RLL bit insertion. HDLC transmitters insert a 0 bit after five contiguous 1 bits (except when transmitting the frame delimiter [EDIT ] BIPOLAR NON-RETURN-TO-ZERO LEVEL '01111110'). USB transmitters insert a 0 bit after six consecutive 1 bits. The receiver at the far end uses every transition — both "One" is represented by one physical level (usually a negative from 0 bits in the data and these extra non-data 0 bits — to voltage). maintain clock synchronization. The receiver otherwise ignores these non-data 0 bits. "Zero" is represented by another level (usually a positive voltage). [EDIT ] NON-RETURN-TO-ZERO INVERTED (NRZI) In clock language, in bipolar NRZ-Level the voltage "swings" from positive to negative on the trailing edge of the previous bit clock cycle. Example NRZI encoding From Wikipedia, the free encyclopedia

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In telecommunication, Manchester code (also known as Phase NRZ-transition occurs for a zero Encoding, or PE) is a line code in which the encoding of each data bit has at least one transition and occupies the same time. Non return to zero, inverted (NRZI) is a method of mapping a It therefore has no DC component, and is self-clocking, which binary signal to a physical signal for transmission over some means that it may be inductively or capacitively coupled, and transmission media. The two level NRZI signal has a transition at that a clock signal can be recovered from the encoded data. a clock boundary if the bit being transmitted is a logical 1, and does not have a transition if the bit being transmitted is a logical Manchester code is widely used (e.g. in Ethernet; see also RFID). 0. There are more complex codes, such as 8B/10B encoding, that use less bandwidth to achieve the same data rate but may be "One" is represented by a transition of the physical level. less tolerant of frequency errors and jitter in the transmitter and receiver reference clocks. "Zero" has no transition.

Also, NRZI might take the opposite convention, as in Universal CONTENTS Serial Bus (USB) signalling, when in Mode 1 (transition when signalling zero and steady level when signalling one). The • 1 Features transition occurs on the leading edge of the clock for the given • 2 Description 2.1 Manchester encoding as phase-shift keying bit. This distinguishes NRZI from NRZ-Mark. o o 2.2 Conventions for representation of data • 3 References However, even NRZI can have long series of zeros (or ones if transitioning on "zero"), so clock recovery can be difficult unless • 4 See also some form of run length limited (RLL) coding is used on top. Magnetic disk and tape storage devices generally use fixed-rate [EDIT ] FEATURES RLL codes, while USB uses bit stuffing, which is efficient, but results in a variable data rate: it takes slightly longer to send a Manchester code ensures frequent line voltage transitions, long string of 1 bits over USB than it does to send a long string of directly proportional to the clock rate. This helps clock recovery. 0 bits. (USB inserts an additional 0 bit after 6 consecutive 1 bits.) The DC component of the encoded signal is not dependent on MANCHESTER CODE the data and therefore carries no information, allowing the signal to be conveyed conveniently by media (e.g. Ethernet) which • A 0 is expressed by a low-to-high transition, a 1 by high- usually do not convey a DC component. to-low transition (according to G.E. Thomas' convention -- in the IEEE 802.3 convention, the reverse is true). [EDIT ] DESCRIPTION • The transitions which signify 0 or 1 occur at the midpoint of a period. • Transitions at the start of a period are overhead and don't signify data.

Manchester code always has a transition at the middle of each bit period and may (depending on the information to be transmitted) have a transition at the start of the period also. The direction of the mid-bit transition indicates the data. Transitions at the period boundaries do not carry information. They exist only to place the signal in the correct state to allow the mid-bit transition. The existence of guaranteed transitions allows the An example of Manchester encoding showing both conventions signal to be self-clocking, and also allows the receiver to align correctly; the receiver can identify if it is misaligned by half a bit Extracting the original data from the received encoded bit (from period, as there will no longer always be a transition during each Manchester as per 802.3): bit period. The price of these benefits is a doubling of the bandwidth requirement compared to simpler NRZ coding original data XOR clock = Manchester value schemes (or see also NRZI). 0 0 0 In the Thomas convention, the result is that the first half of a bit 0 1 1 period matches the information bit and the second half is its complement. 1 0 1

1 1 0 [EDIT] MANCHESTER ENCODING AS PHASE-SHIFT KEYING

Summary: Manchester encoding is a special case of binary phase-shift keying (BPSK), where the data controls the phase of a square • Each bit is transmitted in a fixed time (the "period"). wave carrier whose frequency is the data rate. Such a signal is easy to generate. [EDIT] CONVENTIONS FOR REPRESENTATION OF DATA From Wikipedia, the free encyclopedia

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Encoding of 11011000100 in Manchester code (as per G. E. A universal asynchronous receiver/transmitter (usually Thomas) abbreviated UART and pronounced /ˈjuːɑrt/) is a type of There are two opposing conventions for the representations of "asynchronous receiver/transmitter", a piece of computer data. hardware that translates data between parallel and serial forms. UARTs are commonly used in conjunction with communication The first of these was first published by G. E. Thomas in 1949 and standards such as EIA RS-232, RS-422 or RS-485. The universal is followed by numerous authors (e.g., Tanenbaum). It specifies designation indicates that the data format and transmission that for a 0 bit the signal levels will be Low-High (assuming an speeds are configurable and that the actual electric signaling amplitude physical encoding of the data) - with a low level in the levels and methods (such as differential signaling etc) typically first half of the bit period, and a high level in the second half. For are handled by a special driver circuit external to the UART. a 1 bit the signal levels will be High-Low. A UART is usually an individual (or part of an) integrated circuit The second convention is also followed by numerous authors used for serial communications over a computer or peripheral (e.g., Stallings) as well as by IEEE 802.4 (token bus) and lower device serial port. UARTs are now commonly included in speed versions of IEEE 802.3 (Ethernet) standards. It states that microcontrollers. A dual UART, or DUART, combines two UARTs a logic 0 is represented by a High-Low signal sequence and a into a single chip. Many modern ICs now come with a UART that logic 1 is represented by a Low-High signal sequence. can also communicate synchronously; these devices are called USARTs (universal synchronous/asynchronous If a Manchester encoded signal is inverted in communication, it is receiver/transmitter). transformed from one convention to the other. This ambiguity can be overcome by using differential Manchester encoding. CONTENTS UNIVERSAL ASYNCHRONOUS RECEIVER/TRANSMITTER • 1 Transmitting and receiving serial data o 1.1 Character framing standards for voltage signaling are RS-232, RS-422 and RS-485 o 1.2 Receiver from the EIA. Historically, the presence or absence of current (in o 1.3 Transmitter o 1.4 Application current loops) was used in telegraph circuits. Some signaling • 2 Synchronous transmission schemes do not use electrical wires. Examples of such are optical • 3 History fiber, IrDA (infrared), and (wireless) Bluetooth in its Serial Port • 4 Structure • 5 Special receiver conditions Profile (SPP). Some signaling schemes use modulation of a carrier o 5.1 Overrun error signal (with or without wires). Examples are modulation of audio o 5.2 Underrun error signals with phone line modems, RF modulation with data radios, o 5.3 Framing error o 5.4 Parity error and the DC-LIN for power line communication. o 5.5 Break condition • 6 UART models Communication may be "full duplex" (both send and receive at • 7 See also the same time) or "half duplex" (devices take turns transmitting • 8 References and receiving). • 9 External links [EDIT] CHARACTER FRAMING [EDIT ] TRANSMITTING AND RECEIVING SERIAL DATA

See also: Asynchronous serial communication

The Universal Asynchronous Receiver/Transmitter (UART) takes Each character is sent as a logic low start bit, a configurable bytes of data and transmits the individual bits in a sequential number of data bits (usually 7 or 8, sometimes 5), an optional fashion. At the destination, a second UART re-assembles the bits parity bit, and one or more logic high stop bits. The start bit into complete bytes. Each UART contains a shift register which is signals the receiver that a new character is coming. The next five the fundamental method of conversion between serial and to eight bits, depending on the code set employed, represent the parallel forms. Serial transmission of digital information (bits) character. Following the data bits may be a parity bit. The next through a single wire or other medium is much more cost one or two bits are always in the mark (logic high, i.e., '1') effective than parallel transmission through multiple wires. condition and called the stop bit(s). They signal the receiver that the character is completed. Since the start bit is logic low (0) and The UART usually does not directly generate or receive the the stop bit is logic high (1) then there is always a clear external signals used between different items of equipment. demarcation between the previous character and the next one. Separate interface devices are used to convert the logic level signals of the UART to and from the external signaling levels. [EDIT] RECEIVER External signals may be of many different forms. Examples of All operations of the UART hardware are controlled by a clock interrupt. Since full-duplex operation requires characters to be signal which runs at a multiple (say, 16) of the data rate - each sent and received at the same time, practical UARTs use two data bit is as long as 16 clock pulses. The receiver tests the state different shift registers for transmitted characters and received of the incoming signal on each clock pulse, looking for the characters. beginning of the start bit. If the apparent start bit lasts at least one-half of the bit time, it is valid and signals the start of a new [EDIT] APPLICATION character. If not, the spurious pulse is ignored. After waiting a further bit time, the state of the line is again sampled and the Transmitting and receiving UARTs must be set for the same bit resulting level clocked into a shift register. After the required speed, character length, parity, and stop bits for proper number of bit periods for the character length (5 to 8 bits, operation. The receiving UART may detect some mismatched typically) have elapsed, the contents of the shift register is made settings and set a "framing error" flag bit for the host system; in available (in parallel fashion) to the receiving system. The UART exceptional cases the receiving UART will produce an erratic will set a flag indicating new data is available, and may also stream of mutilated characters and transfer them to the host generate a processor interrupt to request that the host processor system. transfers the received data. In some common types of UART, a Typical serial ports used with personal computers connected to small first-in, first-out FIFO buffer memory is inserted between modems use eight data bits, no parity, and one stop bit; for this the receiver shift register and the host system interface. This configuration the number of ASCII characters per second equals allows the host processor more time to handle an interrupt from the bit rate divided by 10. the UART and prevents loss of received data at high rates.

Some very low-cost home computers or embedded systems [EDIT] TRANSMITTER dispensed with a UART and used the CPU to sample the state of an input port or directly manipulate an output port for data Transmission operation is simpler since it is under the control of transmission. While very CPU-intensive, since the CPU timing was the transmitting system. As soon as data is deposited in the shift critical, these schemes avoided the purchase of a costly UART register after completion of the previous character, the UART chip. The technique was known as a bit-banging serial port. hardware generates a start bit, shifts the required number of data bits out to the line,generates and appends the parity bit (if [EDIT ] SYNCHRONOUS TRANSMISSION used), and appends the stop bits. Since transmission of a single character may take a long time relative to CPU speeds, the UART USART chips have both synchronous and asynchronous modes. will maintain a flag showing busy status so that the host system In synchronous transmission, the clock data is recovered does not deposit a new character for transmission until the separately from the data stream and no start/stop bits are used. previous one has been completed; this may also be done with an This improves the efficiency of transmission on suitable channels since more of the bits sent are usable data and not character Depending on the manufacturer, different terms are used to framing. An asynchronous transmission sends no characters over identify devices that perform the UART functions. Intel called the interconnection when the transmitting device has nothing to their 8251 device a "Programmable Communication Interface". send; but a synchronous interface must send "pad" characters to MOS Technology 6551 was known under the name maintain synchronization between the receiver and transmitter. "Asynchronous Communications Interface Adapter" (ACIA). The The usual filler is the ASCII "SYN" character. This may be done term "Serial Communications Interface" (SCI) was first used at automatically by the transmitting device. Motorola around 1975 to refer to their start-stop asynchronous serial interface device, which others were calling a UART. [EDIT ] HISTORY [EDIT ] STRUCTURE Some early telegraph schemes used variable-length pulses (as in Morse code) and rotating clockwork mechanisms to transmit A UART usually contains the following components: alphabetic characters. The first UART-like devices (with fixed- • length pulses) were rotating mechanical switches (commutators). a clock generator, usually a multiple of the bit rate to allow These sent 5-bit Baudot codes for mechanical teletypewriters, sampling in the middle of a bit period. • and replaced morse code. Later, ASCII required a seven bit code. input and output shift registers • When IBM built computers in the early 1960s with 8-bit transmit/receive control • characters, it became customary to store the ASCII code in 8 bits. read/write control logic • transmit/receive buffers (optional) Gordon Bell designed the UART for the PDP series of computers. • parallel data bus buffer (optional) Western Digital made the first single-chip UART WD1402A • First-in, first-out (FIFO) buffer memory (optional) around 1971; this was an early example of a medium scale integrated circuit. [EDIT ] SPECIAL RECEIVER CONDITIONS

An example of an early 1980s UART was the National [EDIT] OVERRUN ERROR Semiconductor 8250. In the 1990s, newer UARTs were developed with on-chip buffers. This allowed higher transmission speed An "overrun error" occurs when the receiver cannot process the without data loss and without requiring such frequent attention character that just came in before the next one arrives. Various from the computer. For example, the popular National devices have different amounts of buffer space to hold received Semiconductor 16550 has a 16 byte FIFO, and spawned many characters. The CPU must service the UART in order to remove variants, including the 16C550, 16C650, 16C750, and 16C850. characters from the input buffer. If the CPU does not service the UART quickly enough and the buffer becomes full, an Overrun A "break condition" occurs when the receiver input is at the Error will occur. "space" level for longer than some duration of time, typically, for more than a character time. This is not necessarily an error, but [EDIT] UNDERRUN ERROR appears to the receiver as a character of all zero bits with a framing error. An "underrun error" occurs when the UART transmitter has completed sending a character and the transmit buffer is empty. Some equipment will deliberately transmit the "break" level for In asynchronous modes this is treated as an indication that no longer than a character as an out-of-band signal. When signaling data remains to be transmitted, rather than an error, since rates are mismatched, no meaningful characters can be sent, but additional stop bits can be appended. This error indication is a long "break" signal can be a useful way to get the attention of commonly found in USARTs, since an underrun is more serious in a mismatched receiver to do something (such as resetting itself). synchronous systems. Unix-like systems can use the long "break" level as a request to change the signaling rate, to support dial-in access at multiple [EDIT] FRAMING ERROR signaling rates.

A "framing error" occurs when the designated "start" and "stop" Phase-shift keying (PSK) is a digital modulation scheme that bits are not valid. As the "start" bit is used to identify the conveys data by changing, or modulating, the phase of a beginning of an incoming character, it acts as a reference for the reference signal (the carrier wave). remaining bits. If the data line is not in the expected idle state when the "stop" bit is expected, a Framing Error will occur. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of [EDIT] PARITY ERROR phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of A "parity error" occurs when the number of "active" bits does not bits forms the symbol that is represented by the particular agree with the specified parity configuration of the USART, phase. The demodulator, which is designed specifically for the producing a Parity Error. Because the "parity" bit is optional, this symbol-set used by the modulator, determines the phase of the error will not occur if parity has been disabled. Parity error is set received signal and maps it back to the symbol it represents, when the parity of an incoming data character does not match thus recovering the original data. This requires the receiver to be the expected value. able to compare the phase of the received signal to a reference signal — such a system is termed coherent (and referred to as [EDIT] BREAK CONDITION CPSK). Alternatively, instead of using the bit patterns to set the phase of o 6.3 Example: Differentially-encoded BPSK • 7 Channel capacity the wave, it can instead be used to change it by a specified • 8 See also amount. The demodulator then determines the changes in the • 9 Notes phase of the received signal rather than the phase itself. Since • 10 References this scheme depends on the difference between successive phases, it is termed differential phase-shift keying (DPSK). DPSK can be significantly simpler to implement than ordinary [EDIT ] INTRODUCTION PSK since there is no need for the demodulator to have a copy of There are three major classes of digital modulation techniques the reference signal to determine the exact phase of the used for transmission of digitally represented data: received signal (it is a non-coherent scheme). In exchange, it produces more erroneous demodulations. The exact • Amplitude-shift keying (ASK) requirements of the particular scenario under consideration • Frequency-shift keying (FSK) determine which scheme is used. • Phase-shift keying (PSK)

All convey data by changing some aspect of a base signal, the CONTENTS carrier wave (usually a sinusoid), in response to a data signal. In • 1 Introduction the case of PSK, the phase is changed to represent the data o 1.1 Definitions signal. There are two fundamental ways of utilizing the phase of • 2 Applications a signal in this way: • 3 Binary phase-shift keying (BPSK) o 3.1 Implementation • o 3.2 Bit error rate By viewing the phase itself as conveying the information, • 4 Quadrature phase-shift keying (QPSK) in which case the demodulator must have a reference o 4.1 Implementation signal to compare the received signal's phase against; or o 4.2 Bit error rate • By viewing the change in the phase as conveying o 4.3 QPSK signal in the time domain o 4.4 Variants information — differential schemes, some of which do not . 4.4.1 Offset QPSK (OQPSK) need a reference carrier (to a certain extent). . 4.4.2 π/4–QPSK . 4.4.3 SOQPSK . 4.4.4 DPQPSK A convenient way to represent PSK schemes is on a constellation • 5 Higher-order PSK diagram. This shows the points in the Argand plane where, in this o 5.1 Bit error rate context, the real and imaginary axes are termed the in-phase • 6 Differential phase-shift keying (DPSK) and quadrature axes respectively due to their 90° separation. o 6.1 Differential encoding o 6.2 Demodulation Such a representation on perpendicular axes lends itself to straightforward implementation. The amplitude of each point Q(x) will give the probability that a single sample taken from a along the in-phase axis is used to modulate a cosine (or sine) random process with zero-mean and unit-variance Gaussian wave and the amplitude along the quadrature axis to modulate a probability density function will be greater or equal to x. It is a sine (or cosine) wave. scaled form of the complementary Gaussian error function:

In PSK, the constellation points chosen are usually positioned with uniform angular spacing around a circle. This gives . maximum phase-separation between adjacent points and thus the best immunity to corruption. They are positioned on a circle The error-rates quoted here are those in additive white Gaussian so that they can all be transmitted with the same energy. In this noise (AWGN). These error rates are lower than those computed way, the moduli of the complex numbers they represent will be in fading channels, hence, are a good theoretical benchmark to the same and thus so will the amplitudes needed for the cosine compare with. and sine waves. Two common examples are "binary phase-shift keying" (BPSK) which uses two phases, and "quadrature phase- [EDIT ] APPLICATIONS shift keying" (QPSK) which uses four phases, although any number of phases may be used. Since the data to be conveyed Owing to PSK's simplicity, particularly when compared with its are usually binary, the PSK scheme is usually designed with the competitor quadrature amplitude modulation, it is widely used in number of constellation points being a power of 2. existing technologies.

[1][2] [EDIT] DEFINITIONS The wireless LAN standard, IEEE 802.11b-1999 , uses a variety of different PSKs depending on the data-rate required. At the For determining error-rates mathematically, some definitions will basic-rate of 1 Mbit/s, it uses DBPSK (differential BPSK). To be needed: provide the extended-rate of 2 Mbit/s, DQPSK is used. In reaching 5.5 Mbit/s and the full-rate of 11 Mbit/s, QPSK is employed, but • Eb = Energy-per-bit has to be coupled with complementary code keying. The higher- • Es = Energy-per-symbol = nEb with n bits per symbol speed wireless LAN standard, IEEE 802.11g-2003 [1] [3] has eight • Tb = Bit duration data rates: 6, 9, 12, 18, 24, 36, 48 and 54 Mbit/s. The 6 and 9 • Ts = Symbol duration Mbit/s modes use OFDM modulation where each sub-carrier is • N0 / 2 = Noise power spectral density (W/Hz) BPSK modulated. The 12 and 18 Mbit/s modes use OFDM with • Pb = Probability of bit-error QPSK. The fastest four modes use OFDM with forms of • Ps = Probability of symbol-error quadrature amplitude modulation. Because of its simplicity BPSK is appropriate for low-cost passive Constellation diagram example for BPSK. transmitters, and is used in RFID standards such as ISO/IEC 14443 which has been adopted for biometric passports, credit BPSK (also sometimes called PRK, Phase Reversal Keying, or cards such as American Express's ExpressPay, and many other 2PSK) is the simplest form of phase shift keying (PSK). It uses two applications[4]. phases which are separated by 180° and so can also be termed 2-PSK. It does not particularly matter exactly where the Bluetooth 2 will use π / 4-DQPSK at its lower rate (2 Mbit/s) and constellation points are positioned, and in this figure they are 8-DPSK at its higher rate (3 Mbit/s) when the link between the shown on the real axis, at 0° and 180°. This modulation is the two devices is sufficiently robust. Bluetooth 1 modulates with most robust of all the PSKs since it takes the highest level of Gaussian minimum-shift keying, a binary scheme, so either noise or distortion to make the demodulator reach an incorrect modulation choice in version 2 will yield a higher data-rate. A decision. It is, however, only able to modulate at 1 bit/symbol (as similar technology, IEEE 802.15.4 (the wireless standard used by seen in the figure) and so is unsuitable for high data-rate ZigBee) also relies on PSK. IEEE 802.15.4 allows the use of two applications when bandwidth is limited. frequency bands: 868–915 MHz using BPSK and at 2.4 GHz using OQPSK. In the presence of an arbitrary phase-shift introduced by the communications channel, the demodulator is unable to tell which Notably absent from these various schemes is 8-PSK. This is constellation point is which. As a result, the data is often because its error-rate performance is close to that of 16-QAM — differentially encoded prior to modulation. it is only about 0.5 dB better[citation needed] — but its data rate is only three-quarters that of 16-QAM. Thus 8-PSK is often omitted from [EDIT] IMPLEMENTATION standards and, as seen above, schemes tend to 'jump' from QPSK to 16-QAM (8-QAM is possible but difficult to implement). The general form for BPSK follows the equation:

[EDIT ] BINARY PHASE-SHIFT KEYING (BPSK)

This yields two phases, 0 and π. In the specific form, binary data is often conveyed with the following signals:

f or binary "0" for binary "1"

where fc is the frequency of the carrier-wave.

Hence, the signal-space can be represented by the single basis function

Constellation diagram for QPSK with Gray coding. Each adjacent symbol only differs by one bit.

Sometimes this is known as quaternary PSK, quadriphase PSK, 4- where 1 is represented by and 0 is represented by PSK, or 4-QAM. (Although the root concepts of QPSK and 4-QAM . This assignment is, of course, arbitrary. are different, the resulting modulated radio waves are exactly the same.) QPSK uses four points on the constellation diagram, The use of this basis function is shown at the end of the next equispaced around a circle. With four phases, QPSK can encode section in a signal timing diagram. The topmost signal is a BPSK- two bits per symbol, shown in the diagram with gray coding to modulated cosine wave that the BPSK modulator would produce. minimize the bit error rate (BER) — sometimes misperceived as The bit-stream that causes this output is shown above the signal twice the BER of BPSK. (the other parts of this figure are relevant only to QPSK). The mathematical analysis shows that QPSK can be used either [EDIT] BIT ERROR RATE to double the data rate compared with a BPSK system while maintaining the same bandwidth of the signal, or to maintain the [5] The bit error rate (BER) of BPSK in AWGN can be calculated as : data-rate of BPSK but halving the bandwidth needed. In this latter case, the BER of QPSK is exactly the same as the BER of BPSK - and deciding differently is a common confusion when or considering or describing QPSK.

Since there is only one bit per symbol, this is also the symbol Given that radio communication channels are allocated by error rate. agencies such as the Federal Communication Commission giving a prescribed (maximum) bandwidth, the advantage of QPSK over [EDIT ] QUADRATURE PHASE-SHIFT KEYING (QPSK) BPSK becomes evident: QPSK transmits twice the data rate in a given bandwidth compared to BPSK - at the same BER. The engineering penalty that is paid is that QPSK transmitters and Hence, the signal constellation consists of the signal-space 4 receivers are more complicated than the ones for BPSK. points However, with modern electronics technology, the penalty in cost is very moderate.

As with BPSK, there are phase ambiguity problems at the The factors of 1/2 indicate that the total power is split equally receiving end, and differentially encoded QPSK is often used in between the two carriers. practice.

Comparing these basis functions with that for BPSK shows clearly [EDIT] IMPLEMENTATION how QPSK can be viewed as two independent BPSK signals. Note that the signal-space points for BPSK do not need to split the The implementation of QPSK is more general than that of BPSK symbol (bit) energy over the two carriers in the scheme shown in and also indicates the implementation of higher-order PSK. the BPSK constellation diagram. Writing the symbols in the constellation diagram in terms of the sine and cosine waves used to transmit them: QPSK systems can be implemented in a number of ways. An illustration of the major components of the transmitter and receiver structure are shown below.

This yields the four phases π/4, 3π/4, 5π/4 and 7π/4 as needed.

This results in a two-dimensional signal space with unit basis functions

Conceptual transmitter structure for QPSK. The binary data stream is split into the in-phase and quadrature-phase The first basis function is used as the in-phase component of the components. These are then separately modulated onto two signal and the second as the quadrature component of the orthogonal basis functions. In this implementation, two sinusoids signal. are used. Afterwards, the two signals are superimposed, and the resulting signal is the QPSK signal. Note the use of polar non- return-to-zero encoding. These encoders can be placed before for However, in order to achieve the same bit-error probability as binary data source, but have been placed after to illustrate the BPSK, QPSK uses twice the power (since two bits are transmitted conceptual difference between digital and analog signals simultaneously). involved with digital modulation. The symbol error rate is given by:

.

Receiver structure for QPSK. The matched filters can be replaced with correlators. Each detection device uses a reference If the signal-to-noise ratio is high (as is necessary for practical threshold value to determine whether a 1 or 0 is detected. QPSK systems) the probability of symbol error may be approximated: [EDIT] BIT ERROR RATE

Although QPSK can be viewed as a quaternary modulation, it is easier to see it as two independently modulated quadrature carriers. With this interpretation, the even (or odd) bits are used [EDIT] QPSK SIGNAL IN THE TIME DOMAIN to modulate the in-phase component of the carrier, while the odd The modulated signal is shown below for a short segment of a (or even) bits are used to modulate the quadrature-phase random binary data-stream. The two carrier waves are a cosine component of the carrier. BPSK is used on both carriers and they wave and a sine wave, as indicated by the signal-space analysis can be independently demodulated. above. Here, the odd-numbered bits have been assigned to the As a result, the probability of bit-error for QPSK is the same as for in-phase component and the even-numbered bits to the BPSK: quadrature component (taking the first bit as number 1). The total signal — the sum of the two components — is shown at the bottom. Jumps in phase can be seen as the PSK changes the phase on each component at the start of each bit-period. The topmost waveform alone matches the description given for BPSK above. Timing diagram for QPSK. The binary data stream is shown beneath the time axis. The two signal components with their bit Signal doesn't cross zero, because only one bit of the symbol is assignments are shown the top and the total, combined signal at changed at a time the bottom. Note the abrupt changes in phase at some of the bit- Offset quadrature phase-shift keying (OQPSK) is a variant of period boundaries. phase-shift keying modulation using 4 different values of the The binary data that is conveyed by this waveform is: 1 1 0 0 0 1 phase to transmit. It is sometimes called Staggered quadrature 1 0. phase-shift keying (SQPSK).

• The odd bits, highlighted here, contribute to the in-phase component: 1 1 0 0 0 1 1 0 • The even bits, highlighted here, contribute to the quadrature-phase component: 1 1 0 0 0 1 1 0

[EDIT] VARIANTS

[EDIT ] OFFSET QPSK (OQPSK)

Difference of the phase between QPSK and OQPSK

Taking four values of the phase (two bits) at a time to construct a QPSK symbol can allow the phase of the signal to jump by as much as 180° at a time. When the signal is low-pass filtered (as is typical in a transmitter), these phase-shifts result in large Timing diagram for offset-QPSK. The binary data stream is shown amplitude fluctuations, an undesirable quality in communication beneath the time axis. The two signal components with their bit systems. By offsetting the timing of the odd and even bits by one assignments are shown the top and the total, combined signal at bit-period, or half a symbol-period, the in-phase and quadrature the bottom. Note the half-period offset between the two signal components will never change at the same time. In the components. constellation diagram shown on the right, it can be seen that this [EDIT ] Π/4–QPSK will limit the phase-shift to no more than 90° at a time. This yields much lower amplitude fluctuations than non-offset QPSK and is sometimes preferred in practice.

The picture on the right shows the difference in the behavior of the phase between ordinary QPSK and OQPSK. It can be seen that in the first plot the phase can change by 180° at once, while in OQPSK the changes are never greater than 90°.

The modulated signal is shown below for a short segment of a random binary data-stream. Note the half symbol-period offset between the two component waves. The sudden phase-shifts Dual constellation diagram for π/4-QPSK. This shows the two occur about twice as often as for QPSK (since the signals no separate constellations with identical Gray coding but rotated by longer change together), but they are less severe. In other 45° with respect to each other. words, the magnitude of jumps is smaller in OQPSK when This final variant of QPSK uses two identical constellations which compared to QPSK. are rotated by 45° (π / 4 radians, hence the name) with respect to one another. Usually, either the even or odd symbols are used to select points from one of the constellations and the other symbols select points from the other constellation. This also reduces the phase-shifts from a maximum of 180°, but only to a maximum of 135° and so the amplitude fluctuations of π / 4– QPSK are between OQPSK and non-offset QPSK.

One property this modulation scheme possesses is that if the modulated signal is represented in the complex domain, it does not have any paths through the origin. In other words, the signal does not pass through the origin. This lowers the dynamical [EDIT ] SOQPSK range of fluctuations in the signal which is desirable when engineering communications signals. The license-free shaped-offset QPSK (SOQPSK) is interoperable with Feher-patented QPSK (FQPSK), in the sense that an On the other hand, π / 4–QPSK lends itself to easy demodulation integrate-and-dump offset QPSK detector produces the same and has been adopted for use in, for example, TDMA cellular output no matter which kind of transmitter is used[1]. telephone systems. These modulations carefully shape the I and Q waveforms such The modulated signal is shown below for a short segment of a that they change very smoothly, and the signal stays constant- random binary data-stream. The construction is the same as amplitude even during signal transitions. (Rather than traveling above for ordinary QPSK. Successive symbols are taken from the instantly from one symbol to another, or even linearly, it travels two constellations shown in the diagram. Thus, the first symbol smoothly around the constant-amplitude circle from one symbol (1 1) is taken from the 'blue' constellation and the second symbol to the next.) (0 0) is taken from the 'green' constellation. Note that magnitudes of the two component waves change as they switch The standard description of SOQPSK-TG involves ternary between constellations, but the total signal's magnitude remains symbols. constant. The phase-shifts are between those of the two previous [EDIT ] DPQPSK timing-diagrams.

Dual-polarization quadrature phase shift keying (DPQPSK) or dual-polarization QPSK - involves the polarization multiplexing of two different QPSK signals, thus improving the spectral efficiency by a factor of 2. This is a cost-effective alternative, to utilizing 16-PSK instead of QPSK to double the spectral the efficiency.

[EDIT ] HIGHER-ORDER PSK Timing diagram for π/4-QPSK. The binary data stream is shown beneath the time axis. The two signal components with their bit assignments are shown the top and the total, combined signal at the bottom. Note that successive symbols are taken alternately from the two constellations, starting with the 'blue' one. ,

,

and

and are jointly- Gaussian random variables. Constellation diagram for 8-PSK with Gray coding.

Any number of phases may be used to construct a PSK constellation but 8-PSK is usually the highest order PSK constellation deployed. With more than 8 phases, the error-rate becomes too high and there are better, though more complex, modulations available such as quadrature amplitude modulation (QAM). Although any number of phases may be used, the fact that the constellation must usually deal with binary data means that the number of symbols is usually a power of 2 — this allows an equal number of bits-per-symbol.

[EDIT] BIT ERROR RATE Bit-error rate curves for BPSK, QPSK, 8-PSK and 16-PSK, AWGN channel. For the general M-PSK there is no simple expression for the This may be approximated for high M and high Eb / N0 by: symbol-error probability if M > 4. Unfortunately, it can only be obtained from:

.

The bit-error probability for M-PSK can only be determined exactly once the bit-mapping is known. However, when Gray where coding is used, the most probable error from one symbol to the next produces only a single bit-error and , For example, in differentially-encoded BPSK a binary '1' may be . transmitted by adding 180° to the current phase and a binary '0' by adding 0° to the current phase. Another variant of DPSK is (Using Gray coding allows us to approximate the Lee distance of Symmetric Differential Phase Shift keying, SDPSK, where the errors as the Hamming distance of the errors in the decoded encoding would be +90° for a '1' and -90° for a '0'. bitstream, which is easier to implement in hardware.) In differentially-encoded QPSK (DQPSK), the phase-shifts are 0°, The graph on the left compares the bit-error rates of BPSK, QPSK 90°, 180°, -90° corresponding to data '00', '01', '11', '10'. This (which are the same, as noted above), 8-PSK and 16-PSK. It is kind of encoding may be demodulated in the same way as for seen that higher-order modulations exhibit higher error-rates; in non-differential PSK but the phase ambiguities can be ignored. exchange however they deliver a higher raw data-rate. Thus, each received symbol is demodulated to one of the M points in the constellation and a comparator then computes the Bounds on the error rates of various digital modulation schemes difference in phase between this received signal and the can be computed with application of the union bound to the preceding one. The difference encodes the data as described signal constellation. above. Symmetric Differential Quadrature Phase Shift Keying (SDQPSK) is like DQPSK, but encoding is symmetric, using phase [EDIT ] DIFFERENTIAL PHASE-SHIFT KEYING (DPSK) shift values of -135°, -45°, +45° and +135°. This article may require cleanup to meet Wikipedia's quality standards. Please improve this article if you The modulated signal is shown below for both DBPSK and DQPSK can. The talk page may contain suggestions. (May 2009) as described above. In the figure, it is assumed that the signal starts with zero phase, and so there is a phase shift in both signals at t = 0. [EDIT] DIFFERENTIAL ENCODING

Main article: differential coding

Differential phase shift keying (DPSK) is a common form of phase modulation that conveys data by changing the phase of the carrier wave. As mentioned for BPSK and QPSK there is an ambiguity of phase if the constellation is rotated by some effect in the communications channel through which the signal passes. Timing diagram for DBPSK and DQPSK. The binary data stream is This problem can be overcome by using the data to change above the DBPSK signal. The individual bits of the DBPSK signal rather than set the phase. are grouped into pairs for the DQPSK signal, which only changes

every Ts = 2Tb. Analysis shows that differential encoding approximately doubles system. This channel will, in general, introduce an unknown the error rate compared to ordinary M-PSK but this may be phase-shift to the PSK signal; in these cases the differential overcome by only a small increase in Eb / N0. Furthermore, this schemes can yield a better error-rate than the ordinary schemes analysis (and the graphical results below) are based on a system which rely on precise phase information. in which the only corruption is additive white Gaussian noise(AWGN). However, there will also be a physical channel [EDIT] DEMODULATION between the transmitter and receiver in the communication

th Call the received symbol in the k timeslot rk and let it have

phase φk. Assume without loss of generality that the phase of the

carrier wave is zero. Denote the AWGN term as nk. Then

.

The decision variable for the k − 1th symbol and the kth symbol is

the phase difference between rk and rk − 1. That is, if rk is

BER comparison between DBPSK, DQPSK and their non- projected onto rk − 1, the decision is taken on the phase of the differential forms using gray-coding and operating in white noise. resultant complex number:

For a signal that has been differentially encoded, there is an obvious alternative method of demodulation. Instead of demodulating as usual and ignoring carrier-phase ambiguity, the where superscript * denotes complex conjugation. In the absence phase between two successive received symbols is compared of noise, the phase of this is θk − θk − 1, the phase-shift between and used to determine what the data must have been. When the two received signals which can be used to determine the differential encoding is used in this manner, the scheme is known data transmitted. as differential phase-shift keying (DPSK). Note that this is subtly different to just differentially-encoded PSK since, upon reception, The probability of error for DPSK is difficult to calculate in the received symbols are not decoded one-by-one to general, but, in the case of DBPSK it is: constellation points but are instead compared directly to one another.

which, when numerically evaluated, is only slightly worse than

ordinary BPSK, particularly at higher Eb / N0 values. th Using DPSK avoids the need for possibly complex carrier- At the k time-slot call the bit to be modulated bk, the recovery schemes to provide an accurate phase estimate and differentially-encoded bit ek and the resulting modulated signal can be an attractive alternative to ordinary PSK. mk(t). Assume that the constellation diagram positions the symbols at ±1 (which is BPSK). The differential encoder In optical communications, the data can be modulated onto the produces: phase of a laser in a differential way. The modulation is a laser which emits a continuous wave, and a Mach-Zehnder modulator which receives electrical binary data. For the case of BPSK for example, the laser transmits the field unchanged for binary '1', where indicates binary or modulo-2 addition. and with reverse polarity for '0'. The demodulator consists of a delay line interferometer which delays one bit, so two bits can be compared at one time. In further processing, a photo diode is used to transform the optical field into an electric current, so the information is changed back into its original state.

The bit-error rates of DBPSK and DQPSK are compared to their non-differential counterparts in the graph to the right. The loss for using DBPSK is small enough compared to the complexity reduction that it is often used in communications systems that would otherwise use BPSK. For DQPSK though, the loss in performance compared to ordinary QPSK is larger and the BER comparison between BPSK and differentially-encoded BPSK system designer must balance this against the reduction in with gray-coding operating in white noise. complexity.

So ek only changes state (from binary '0' to binary '1' or from

[EDIT] EXAMPLE: DIFFERENTIALLY-ENCODED BPSK binary '1' to binary '0') if bk is a binary '1'. Otherwise it remains in its previous state. This is the description of differentially-encoded BPSK given above.

The received signal is demodulated to yield ek = ±1 and then the

Differential encoding/decoding system diagram. differential decoder reverses the encoding procedure and produces: since binary subtraction is the same as Given a fixed bandwidth, channel capacity vs. SNR for some binary addition. common modulation schemes

b Therefore, bk = 1 if ek and ek − 1 differ and bk = 0 if they are the Like all M-ary modulation schemes with M = 2 symbols, when same. Hence, if both ek and ek − 1 are inverted, bk will still be given exclusive access to a fixed bandwidth, the channel decoded correctly. Thus, the 180° phase ambiguity does not capacity of any phase shift keying modulation scheme rises to a matter. maximum of b bits per symbol as the SNR increases.

Differential schemes for other PSK modulations may be devised TIME-DIVISION MULTIPLEXING along similar lines. The waveforms for DPSK are the same as for differentially-encoded PSK given above since the only change From Wikipedia, the free encyclopedia between the two schemes is at the receiver. Jump to: navigation, search The BER curve for this example is compared to ordinary BPSK on Time-division multiplexing (TDM) is a type of digital or the right. As mentioned above, whilst the error-rate is (rarely) analog multiplexing in which two or more signals or bit approximately doubled, the increase needed in Eb / N0 to streams are transferred apparently simultaneously as sub- overcome this is small. The increase in Eb / N0 required to channels in one communication channel, but are physically overcome differential modulation in coded systems, however, is taking turns on the channel. The time domain is divided into larger - typically about 3 dB. The performance degradation is a several recurrent timeslots of fixed length, one for each sub- result of noncoherent transmission - in this case it refers to the channel. A sample byte or data block of sub-channel 1 is fact that tracking of the phase is completely ignored. transmitted during timeslot 1, sub-channel 2 during timeslot 2, etc. One TDM frame consists of one timeslot per sub-channel plus a synchronization channel and sometimes error correction channel before the synchronization. After the last sub-channel, error correction, and synchronization, the cycle starts all over again with a new frame, starting with the second sample, byte or data block from sub-channel 1, etc.

CONTENTS

• 1 Application examples • 2 TDM versus packet mode communication • 3 History In its primary form, TDM is used for circuit mode communication o 3.1 Transmission using Time Division Multiplexing (TDM) with a fixed number of channels and constant bandwidth per • 4 Synchronous time division multiplexing (Sync TDM) channel. • 5 Synchronous digital hierarchy (SDH) • 6 Statistical time-division multiplexing (Stat TDM) Bandwidth Reservation distinguishes time-division multiplexing • 7 See also • 8 Notes from statistical multiplexing such as packet mode communication (also known as statistical time-domain • 9 References multiplexing, see below) i.e. the time-slots are recurrent in a fixed order and pre-allocated to the channels, rather than APPLICATION EXAMPLES scheduled on a packet-by-packet basis. Statistical time-domain multiplexing resembles, but should not be considered the same • The plesiochronous digital hierarchy (PDH) system, also as time-division multiplexing. known as the PCM system, for digital transmission of several telephone calls over the same four-wire copper In dynamic TDMA, a scheduling algorithm dynamically reserves a cable (T-carrier or E-carrier) or fiber cable in the circuit variable number of timeslots in each frame to variable bit-rate switched digital telephone network data streams, based on the traffic demand of each data stream. • The SDH and synchronous optical networking (SONET) Dynamic TDMA is used in network transmission standards, that have surpassed PDH. • • The RIFF (WAV) audio standard interleaves left and right HIPERLAN/2 ; • stereo signals on a per-sample basis Dynamic synchronous Transfer Mode ; • • The left-right channel splitting in use for stereoscopic IEEE 802.16a . liquid crystal shutter glasses [EDIT ] HISTORY TDM can be further extended into the time division multiple access (TDMA) scheme, where several stations connected to the Time-division multiplexing was first developed in telegraphy; see same physical medium, for example sharing the same frequency multiplexing in telegraphy: Émile Baudot developed a time- channel, can communicate. Application examples include: multiplexing system of multiple Hughes machines in the 1870s.

• The GSM telephone system For the SIGSALY encryptor of 1943, see PCM. • The Tactical Data Links Link 16 and Link 22 In 1962, engineers from Bell Labs developed the first D1 Channel Banks, which combined 24 digitised voice calls over a 4-wire [EDIT ] TDM VERSUS PACKET MODE COMMUNICATION copper trunk between Bell central office analogue switches. A channel bank sliced a 1.544 Mbit/s digital signal into 8,000 higher order multiplex, four TDM frames from the immediate separate frames, each composed of 24 contiguous bytes. Each lower order are combined, creating multiplexes with a bandwidth byte represented a single telephone call encoded into a constant of n x 64 kbit/s, where n = 120, 480, 1920, etc.[2] bit rate signal of 64 Kbit/s. Channel banks used a byte's fixed position (temporal alignment) in the frame to determine which [EDIT ] SYNCHRONOUS TIME DIVISION MULTIPLEXING call it belonged to.[1] (SYNC TDM)

[EDIT] TRANSMISSION USING TIME DIVISION MULTIPLEXING There are three types of (Sync TDM): T1, SONET/SDH (see (TDM) below), and ISDN[4].

In circuit switched networks such as the public switched [EDIT ] SYNCHRONOUS DIGITAL HIERARCHY (SDH) telephone network (PSTN) there exists the need to transmit multiple subscribers’ calls along the same transmission medium. Plesiochronous digital hierarchy (PDH) was developed as a [2] To accomplish this, network designers make use of TDM. TDM standard for multiplexing higher order frames.[2][3] PDH created allows switches to create channels, also known as tributaries, larger numbers of channels by multiplexing the standard [2] within a transmission stream. A standard DS0 voice signal has Europeans 30 channel TDM frames.[2] This solution worked for a a data bit rate of 64 kbit/s, determined using Nyquist’s sampling while; however PDH suffered from several inherent drawbacks [2][3] criterion. TDM takes frames of the voice signals and which ultimately resulted in the development of the Synchronous multiplexes them into a TDM frame which runs at a higher Digital Hierarchy (SDH). The requirements which drove the bandwidth. So if the TDM frame consists of n voice frames, the development of SDH were these:[2][3] bandwidth will be n*64 kbit/s.[2] • Be synchronous – All clocks in the system must align with Each voice sample timeslot in the TDM frame is called a channel . a reference clock. [2] In European systems, TDM frames contain 30 digital voice • Be service-oriented – SDH must route traffic from End [2] channels, and in American systems, they contain 24 channels. Exchange to End Exchange without worrying about Both standards also contain extra bits (or bit timeslots) for exchanges in between, where the bandwidth can be [2] signalling (see Signaling System 7) and synchronisation bits. reserved at a fixed level for a fixed period of time. • Allow frames of any size to be removed or inserted into an Multiplexing more than 24 or 30 digital voice channels is called SDH frame of any size. higher order multiplexing.[2] Higher order multiplexing is • Easily manageable with the capability of transferring accomplished by multiplexing the standard TDM frames.[2] For management data across links. example, a European 120 channel TDM frame is formed by • Provide high levels of recovery from faults. multiplexing four standard 30 channel TDM frames.[2] At each • Provide high data rates by multiplexing any size frame, therefore extremely fast.[2] Modern optic fibre transmission limited only by technology. makes use of Wavelength Division Multiplexing (WDM) where • Give reduced bit rate errors. signals transmitted across the fibre are transmitted at different wavelengths, creating additional channels for transmission.[2][3] SDH has become the primary transmission protocol in most PSTN This increases the speed and capacity of the link, which in turn [2][3] networks. It was developed to allow streams 1.544 Mbit/s and reduces both unit and total costs.[2] above to be multiplexed, in order to create larger SDH frames [2] known as Synchronous Transport Modules (STM). The STM-1 [EDIT ] STATISTICAL TIME-DIVISION MULTIPLEXING frame consists of smaller streams that are multiplexed to create (STAT TDM) a 155.52 Mbit/s frame.[2][3] SDH can also multiplex packet based [2] frames e.g. Ethernet, PPP and ATM. STDM is an advanced version of TDM in which both the address of the terminal and the data itself are transmitted together for While SDH is considered to be a transmission protocol (Layer 1 in better routing. Using STDM allows bandwidth to be split over 1 the OSI Reference Model), it also performs some switching line. Many college and corporate campuses use this type of TDM functions, as stated in the third bullet point requirement listed to logically distribute bandwidth. above.[2] The most common SDH Networking functions are these: If there is one 10MBit line coming into the building, STDM can be • SDH Crossconnect – The SDH Crossconnect is the SDH used to provide 178 terminals with a dedicated 56k connection version of a Time-Space-Time crosspoint switch. It (178 * 56k = 9.96Mb). A more common use however is to only connects any channel on any of its inputs to any channel grant the bandwidth when that much is needed. STDM does not on any of its outputs. The SDH Crossconnect is used in reserve a time slot for each terminal, rather it assigns a slot Transit Exchanges, where all inputs and outputs are when the terminal is requiring data to be sent or received. connected to other exchanges.[2] • SDH Add-Drop Multiplexer – The SDH Add-Drop Multiplexer This is also called asynchronous time-division multiplexing[4] (ADM) can add or remove any multiplexed frame down to (ATDM), in an alternative nomenclature in which "STDM" or 1.544Mb. Below this level, standard TDM can be "synchronous time division multiplexing" designates the older performed. SDH ADMs can also perform the task of an SDH method that uses fixed time slots. Crossconnect and are used in End Exchanges where the channels from subscribers are connected to the core PSTN PULSE-CODE MODULATION network.[2] From Wikipedia, the free encyclopedia SDH network functions are connected using high-speed optic fibre. Optic fibre uses light pulses to transmit data and is (Redirected from PCM) Jump to: navigation, search [EDIT ] MODULATION

"PCM" redirects here. For other uses, see PCM (disambiguation).

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals, which was invented by Alec Reeves in 1937. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems. A PCM stream is a digital representation of an analog signal, in which the magnitude of the analogue signal is sampled regularly at Sampling and quantization of a signal (red) for 4-bit PCM uniform intervals, with each sample being quantized to the nearest value within a range of digital steps. In the diagram, a sine wave (red curve) is sampled and quantized for pulse code modulation. The sine wave is sampled at regular PCM streams have two basic properties that determine their intervals, shown as ticks on the x-axis. For each sample, one of fidelity to the original analog signal: the sampling rate, which is the available values (ticks on the y-axis) is chosen by some the number of times per second that samples are taken; and the algorithm. This produces a fully discrete representation of the bit depth, which determines the number of possible digital values input signal (shaded area) that can be easily encoded as digital that each sample can take. data for storage or manipulation. For the sine wave example at right, we can verify that the quantized values at the sampling CONTENTS moments are 7, 9, 11, 12, 13, 14, 14, 15, 15, 15, 14, etc. Encoding these values as binary numbers would result in the • 1 Modulation following set of nibbles: 0111 • 2 Demodulation (23×0+22×1+21×1+20×1=0+4+2+1=7), 1001, 1011, 1100, • 3 Limitations • 4 Digitization as part of the PCM 1101, 1110, 1110, 1111, 1111, 1111, 1110, etc. These digital process values could then be further processed or analyzed by a purpose- • 5 Encoding for transmission specific digital signal processor or general purpose DSP. Several • 6 History • 7 Nomenclature Pulse Code Modulation streams could also be multiplexed into a • 8 See also larger aggregate data stream, generally for transmission of • 9 References multiple streams over a single physical link. One technique is • 10 Further reading called time-division multiplexing, or TDM, and is widely used, • 11 External links notably in the modern public telephone system. Another technique is called Frequency-division multiplexing, where the inherent losses in the system compensate for the artifacts — or signal is assigned a frequency in a spectrum, and transmitted the system simply does not require much precision. The along with other signals inside that spectrum. Currently, TDM is sampling theorem suggests that practical PCM devices, provided much more widely used than FDM because of its natural a sampling frequency that is sufficiently greater than that of the compatibility with digital communication, and generally lower input signal, can operate without introducing significant bandwidth requirements. distortions within their designed frequency bands.

There are many ways to implement a real device that performs The electronics involved in producing an accurate analog signal this task. In real systems, such a device is commonly from the discrete data are similar to those used for generating implemented on a single integrated circuit that lacks only the the digital signal. These devices are DACs (digital-to-analog clock necessary for sampling, and is generally referred to as an converters), and operate similarly to ADCs. They produce on their ADC (Analog-to-Digital converter). These devices will produce on output a voltage or current (depending on type) that represents their output a binary representation of the input whenever they the value presented on their inputs. This output would then are triggered by a clock signal, which would then be read by a generally be filtered and amplified for use. processor of some sort. [EDIT ] LIMITATIONS [EDIT ] DEMODULATION There are two sources of impairment implicit in any PCM system: To produce output from the sampled data, the procedure of • modulation is applied in reverse. After each sampling period has Choosing a discrete value near the analog signal for each passed, the next value is read and a signal is shifted to the new sample leads to quantization error, which swings between value. As a result of these transitions, the signal will have a -q/2 and q/2. In the ideal case (with a fully linear ADC) it is significant amount of high-frequency energy. To smooth out the uniformly distributed over this interval, with zero mean 2 signal and remove these undesirable aliasing frequencies, the and variance of q /12. • signal would be passed through analog filters that suppress Between samples no measurement of the signal is made; energy outside the expected frequency range (that is, greater the sampling theorem guarantees non-ambiguous than the Nyquist frequency fs / 2). Some systems use digital representation and recovery of the signal only if it has no filtering to remove some of the aliasing, converting the signal energy at frequency fs/2 or higher (one half the sampling from digital to analog at a higher sample rate such that the frequency, known as the Nyquist frequency); higher analog filter required for anti-aliasing is much simpler. In some frequencies will generally not be correctly represented or systems, no explicit filtering is done at all; as it's impossible for recovered. any system to reproduce a signal with infinite bandwidth, As samples are dependent on time, an accurate clock is required PCM with linear quantization is known as Linear PCM (LPCM).[1] for accurate reproduction. If either the encoding or decoding clock is not stable, its frequency drift will directly affect the Some forms of PCM combine signal processing with coding. Older output quality of the device. A slight difference between the versions of these systems applied the processing in the analog encoding and decoding clock frequencies is not generally a major domain as part of the A/D process; newer implementations do so concern; a small constant error is not noticeable. Clock error in the digital domain. These simple techniques have been largely does become a major issue if the clock is not stable, however. A rendered obsolete by modern transform-based audio drifting clock, even with a relatively small error, will cause very compression techniques. obvious distortions in audio and video signals, for example. • DPCM encodes the PCM values as differences between the Extra information: PCM data from a master with a clock current and the predicted value. An algorithm predicts the frequency that can not be influenced requires an exact clock at next sample based on the previous samples, and the the decoding side to ensure that all the data is used in a encoder stores only the difference between this prediction continuous stream without buffer underrun or buffer overflow. and the actual value. If the prediction is reasonable, fewer Any frequency difference will be audible at the output since the bits can be used to represent the same information. For number of samples per time interval can not be correct. The data audio, this type of encoding reduces the number of bits speed in a compact disk can be steered by means of a servo that required per sample by about 25% compared to PCM. • controls the rotation speed of the disk; here the output clock is Adaptive DPCM (ADPCM) is a variant of DPCM that varies the master clock. For all "external master" systems like DAB the the size of the quantization step, to allow further reduction output stream must be decoded with a regenerated and exact of the required bandwidth for a given signal-to-noise ratio. • synchronous clock. When the wanted output sample rate differs Delta modulation is a form of DPCM which uses one bit per from the incoming data stream clock then a sample rate sample. converter must be inserted in the chain to convert the samples In telephony, a standard audio signal for a single phone call is to the new clock domain. encoded as 8,000 analog samples per second, of 8 bits each, giving a 64 kbit/s digital signal known as DS0. The default signal [EDIT ] DIGITIZATION AS PART OF THE PCM PROCESS compression encoding on a DS0 is either μ-law (mu-law) PCM (North America and Japan) or A-law PCM (Europe and most of the In conventional PCM, the analog signal may be processed (e.g., rest of the world). These are logarithmic compression systems by amplitude compression) before being digitized. Once the where a 12 or 13-bit linear PCM sample number is mapped into signal is digitized, the PCM signal is usually subjected to further an 8-bit value. This system is described by international standard processing (e.g., digital data compression). G.711. An alternative proposal for a floating point representation, with 5-bit mantissa and 3-bit radix, was abandoned. Where circuit costs are high and loss of voice quality is Another technique used to control ones-density is the use of a acceptable, it sometimes makes sense to compress the voice scrambler polynomial on the raw data which will tend to turn the signal even further. An ADPCM algorithm is used to map a series raw data stream into a stream that looks pseudo-random, but of 8-bit µ-law or A-law PCM samples into a series of 4-bit ADPCM where the raw stream can be recovered exactly by reversing the samples. In this way, the capacity of the line is doubled. The effect of the polynomial. In this case, long runs of zeroes or ones technique is detailed in the G.726 standard. are still possible on the output, but are considered unlikely enough to be within normal engineering tolerance. Later it was found that even further compression was possible and additional standards were published. Some of these In other cases, the long term DC value of the modulated signal is international standards describe systems and ideas which are important, as building up a DC offset will tend to bias detector covered by privately owned patents and thus use of these circuits out of their operating range. In this case special standards requires payments to the patent holders. measures are taken to keep a count of the cumulative DC offset, and to modify the codes if necessary to make the DC offset Some ADPCM techniques are used in Voice over IP always tend back to zero. communications. Many of these codes are bipolar codes, where the pulses can be [EDIT ] ENCODING FOR TRANSMISSION positive, negative or absent. In the typical alternate mark inversion code, non-zero pulses alternate between being positive Main article: Line code and negative. These rules may be violated to generate special symbols used for framing or other special purposes. Pulse-code modulation can be either return-to-zero (RZ) or non- return-to-zero (NRZ). For a NRZ system to be synchronized using See also: T-carrier and E-carrier in-band information, there must not be long sequences of identical symbols, such as ones or zeroes. For binary PCM [EDIT ] HISTORY systems, the density of 1-symbols is called ones-density.[2] In the history of electrical communications, the earliest reason Ones-density is often controlled using precoding techniques such for sampling a signal was to interlace samples from different as Run Length Limited encoding, where the PCM code is telegraphy sources, and convey them over a single telegraph expanded into a slightly longer code with a guaranteed bound on cable. Telegraph time-division multiplexing (TDM) was conveyed ones-density before modulation into the channel. In other cases, as early as 1853, by the American inventor Moses B. Farmer. The extra framing bits are added into the stream which guarantee at electrical engineer W. M. Miner, in 1903, used an electro- least occasional symbol transitions. mechanical commutator for time-division multiplex of multiple telegraph signals, and also applied this technology to telephony. He obtained intelligible speech from channels sampled at a rate produced all bits simultaneously by using a fan beam instead of a above 3500–4300 Hz: below this was unsatisfactory. This was scanning beam. TDM, but pulse-amplitude modulation (PAM) rather than PCM. The National Inventors Hall of Fame has honored Bernard M. In 1926, Paul M. Rainey of Western Electric patented a facsimile Oliver [7] and Claude Shannon [8] as the inventors of PCM,[9] as machine which transmitted its signal using 5-bit PCM, encoded described in 'Communication System Employing Pulse Code by an opto-mechanical analog-to-digital converter.[3] The Modulation,' U.S. Patent 2,801,281 filed in 1946 and 1952, machine did not go into production. British engineer Alec Reeves, granted in 1956. Another patent by the same title was filed by unaware of previous work, conceived the use of PCM for voice John R. Pierce in 1945, and issued in 1948: U.S. Patent communication in 1937 while working for International Telephone 2,437,707. The three of them published "The Philosophy of PCM" and Telegraph in France. He described the theory and in 1948.[10] advantages, but no practical use resulted. Reeves filed for a French patent in 1938, and his U.S. patent was granted in 1943. Pulse-code modulation (PCM) was used in Japan by Denon in 1972 for the mastering and production of analogue phonograph The first transmission of speech by digital techniques was the records, using a 2-inch Quadruplex-format videotape recorder for SIGSALY vocoder encryption equipment used for high-level Allied its transport, but this was not developed into a consumer communications during World War II from 1943. In 1943, the Bell product. Labs researchers who designed the SIGSALY system became aware of the use of PCM binary coding as already proposed by [EDIT ] NOMENCLATURE Alec Reeves. In 1949 for the Canadian Navy's DATAR system, Ferranti Canada built a working PCM radio system that was able The word pulse in the term Pulse-Code Modulation refers to the to transmit digitized radar data over long distances.[4] "pulses" to be found in the transmission line. This perhaps is a natural consequence of this technique having evolved alongside PCM in the late 1940s and early 1950s used a cathode-ray coding two analog methods, pulse width modulation and pulse position [5][6] tube with a plate electrode having encoding perforations. As modulation, in which the information to be encoded is in fact in an oscilloscope, the beam was swept horizontally at the represented by discrete signal pulses of varying width or sample rate while the vertical deflection was controlled by the position, respectively. In this respect, PCM bears little input analog signal, causing the beam to pass through higher or resemblance to these other forms of signal encoding, except that lower portions of the perforated plate. The plate collected or all can be used in time division multiplexing, and the binary passed the beam, producing current variations in binary code, numbers of the PCM codes are represented as electrical pulses. one bit at a time. Rather than natural binary, the grid of Goodall's The device that performs the coding and decoding function in a later tube was perforated to produce a glitch-free Gray code, and telephone circuit is called a codec. OPTICAL FIBER [EDIT] OPTICAL FIBER COMMUNICATION

Main article: Fiber-optic communication An optical fiber or optical fibre is a thin, flexible, transparent fiber that acts as a waveguide, or "light pipe", to transmit light Optical fiber can be used as a medium for telecommunication between the two ends of the fiber. The field of applied science and networking because it is flexible and can be bundled as and engineering concerned with the design and application of cables. It is especially advantageous for long-distance optical fibers is known as fiber optics. Optical fibers are widely communications, because light propagates through the fiber with used in fiber-optic communications, which permits transmission little attenuation compared to electrical cables. This allows long over longer distances and at higher bandwidths (data rates) than distances to be spanned with few repeaters. Additionally, the other forms of communication. Fibers are used instead of metal per-channel light signals propagating in the fiber have been wires because signals travel along them with less loss and are modulated at rates as high as 111 gigabits per second by NTT,[15] also immune to electromagnetic interference. Fibers are also [16] although 10 or 40 Gbit/s is typical in deployed systems.[17][18] used for illumination, and are wrapped in bundles so they can be Each fiber can carry many independent channels, each using a used to carry images, thus allowing viewing in tight spaces. different wavelength of light (wavelength-division multiplexing Specially designed fibers are used for a variety of other (WDM)). The net data rate (data rate without overhead bytes) per applications, including sensors and fiber lasers. fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in Optical fiber typically consists of a transparent core surrounded commercial dense WDM systems as of 2008). The current by a transparent cladding material with a lower index of laboratory fiber optic data rate record, held by Bell Labs in refraction. Light is kept in the core by total internal reflection. Villarceaux, France, is multiplexing 155 channels, each carrying This causes the fiber to act as a waveguide. Fibers which support 100 Gbit/s over a 7000 km fiber.[19] Nippon Telegraph and many propagation paths or transverse modes are called multi- Telephone Corporation have also managed 69.1 Tbit/s over a mode fibers (MMF), while those which can only support a single single 240 km fiber (multiplexing 432 channels, equating to 171 mode are called single-mode fibers (SMF). Multi-mode fibers Gbit/s per channel).[20] Bell Labs also broke a 100 Petabit per generally have a larger core diameter, and are used for short- second kilometer barrier (15.5 Tbit/s over a single 7000 km distance communication links and for applications where high fiber).[21] power must be transmitted. Single-mode fibers are used for most communication links longer than 1,050 meters (3,440 ft). For short distance applications, such as creating a network within Joining lengths of optical fiber is more complex than joining an office building, fiber-optic cabling can be used to save space electrical wire or cable. The ends of the fibers must be carefully in cable ducts. This is because a single fiber can often carry cleaved, and then spliced together either mechanically or by fusing them together with heat. Special optical fiber connectors much more data than many electrical cables, such as 4 pair Cat- are used to make removable connections 5 Ethernet cabling.[vague] Fiber is also immune to electrical interference; there is no cross-talk between signals in different particularly useful feature of such fiber optic sensors is that they cables and no pickup of environmental noise. Non-armored fiber can, if required, provide distributed sensing over distances of up cables do not conduct electricity, which makes fiber a good to one meter. solution for protecting communications equipment located in high voltage environments such as power generation facilities, or Extrinsic fiber optic sensors use an optical fiber cable, normally a metal communication structures prone to lightning strikes. They multi-mode one, to transmit modulated light from either a non- can also be used in environments where explosive fumes are fiber optical sensor, or an electronic sensor connected to an present, without danger of ignition. Wiretapping is more difficult optical transmitter. A major benefit of extrinsic sensors is their compared to electrical connections, and there are concentric ability to reach places which are otherwise inaccessible. An dual core fibers that are said to be tap-proof.[22] example is the measurement of temperature inside aircraft jet engines by using a fiber to transmit radiation into a radiation [EDIT] FIBER OPTIC SENSORS pyrometer located outside the engine. Extrinsic sensors can also be used in the same way to measure the internal temperature of Main article: Fiber optic sensor electrical transformers, where the extreme electromagnetic fields present make other measurement techniques impossible. Fibers have many uses in remote sensing. In some applications, Extrinsic sensors are used to measure vibration, rotation, the sensor is itself an optical fiber. In other cases, fiber is used to displacement, velocity, acceleration, torque, and twisting. A solid connect a non-fiberoptic sensor to a measurement system. state version of the gyroscope using the interference of light has Depending on the application, fiber may be used because of its been developed. The fiber optic gyroscope (FOG) has no moving small size, or the fact that no electrical power is needed at the parts and exploits the Sagnac effect to detect mechanical remote location, or because many sensors can be multiplexed rotation. along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes A common use for fiber optic sensors are in advanced intrusion detection security systems, where the light is transmitted along along the fiber through each sensor. Time delay can be the fiber optic sensor cable, which is placed on a fence, pipeline determined using a device such as an optical time-domain or communication cabling, and the returned signal is monitored reflectometer. and analysed for disturbances. This return signal is digitally processed to identify if there is a disturbance, and if an intrusion has occurred an alarm is triggered by the fiber optic security Optical fibers can be used as sensors to measure strain, system. temperature, pressure and other quantities by modifying a fiber so that the quantity to be measured modulates the intensity, ] PRINCIPLE OF OPERATION phase, polarization, wavelength or transit time of light in the fiber. Sensors that vary the intensity of light are the simplest, An optical fiber is a cylindrical dielectric waveguide (nonconducting waveguide) that transmits light along its axis, by since only a simple source and detector are required. A the process of total internal reflection. The fiber consists of a o 8.2 Cellular telephone (phones and modems) core surrounded by a cladding layer, both of which are made of o 8.3 Wi-Fi dielectric materials. To confine the optical signal in the core, the o 8.4 Wireless energy transfer refractive index of the core must be greater than that of the o 8.5 Computer interface devices cladding. The boundary between the core and cladding may • 9 Categories of wireless implementations, devices and either be abrupt, in step-index fiber, or gradual, in graded-index standards fiber • 10 See also • 11 References • 12 Further reading WIRELESS • 13 External links From Wikipedia, the free encyclopedia [EDIT ] INTRODUCTION In telecommunications, wireless communication may be used to transfer information over short distances (a few meters as in Handheld wireless radios such as this Maritime VHF radio television remote control) or long distances (thousands or transceiver use electromagnetic waves to implement a form of millions of kilometers for radio communications). The term is wireless communications technology. often shortened to "wireless". It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, Wireless operations permits services, such as long range personal digital assistants (PDAs), and wireless networking. Other communications, that are impossible or impractical to implement examples of wireless technology include GPS units, garage door with the use of wires. The term is commonly used in the openers and or garage doors, wireless computer mice, keyboards telecommunications industry to refer to telecommunications and headsets, satellite television and cordless telephones. systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc.) which use some form of energy (e.g. radio frequency (RF), infrared light, laser CONTENTS light, visible light, acoustic energy, etc.) to transfer information without the use of wires.[1] Information is transferred in this • 1 Introduction manner over both short and long distances. • 2 Wireless services • 3 Wireless networks • 4 Modes [EDIT ] WIRELESS SERVICES • 5 Cordless • 6 History o 6.1 Photophone The term "wireless" has become a generic and all-encompassing 6.2 Early wireless work o word used to describe communications in which electromagnetic o 6.3 Radio • 7 The electromagnetic spectrum waves or RF (rather than some form of wire) carry a signal over • 8 Applications of wireless technology o 8.1 Security systems part or the entire communication path. Common examples of connect via satellite. A wireless transmission method is a logical wireless equipment in use today include: choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless • Professional LMR (Land Mobile Radio) and SMR technology: (Specialized Mobile Radio) typically used by business, industrial and Public Safety entities. • To span a distance beyond the capabilities of typical • Consumer Two way radio including FRS Family Radio cabling, Service, GMRS (General Mobile Radio Service) and Citizens • To provide a backup communications link in case of band ("CB") radios. normal network failure, • The Amateur Radio Service (Ham radio). • To link portable or temporary workstations, • Consumer and professional Marine VHF radios. • To overcome situations where normal cabling is difficult or • Cellular telephones and pagers: provide connectivity for financially impractical, or portable and mobile applications, both personal and • To remotely connect mobile users or networks. business. • Global Positioning System (GPS): allows drivers of cars and [EDIT ] MODES trucks, captains of boats and ships, and pilots of aircraft to ascertain their location anywhere on earth. Wireless communication can be via: • Cordless computer peripherals : the cordless mouse is a • common example; keyboards and printers can also be radio frequency communication, • linked to a computer via wireless. microwave communication, for example long-range line-of- • Cordless telephone sets: these are limited-range devices, sight via highly directional antennas, or short-range not to be confused with cell phones. communication, or • • Satellite television : Is broadcast from satellites in infrared (IR) short-range communication, for example from geostationary orbit. Typical services use digital remote controls or via Infrared Data Association (IrDA). broadcasting to provide multiple channels to viewers. Applications may involve point-to-point communication, point-to- multipoint communication, broadcasting, cellular networks and [EDIT ] WIRELESS NETWORKS other wireless networks.

Wireless networking (i.e. the various types of unlicensed 2.4 GHz [EDIT ] CORDLESS WiFi devices) is used to meet many needs. Perhaps the most common use is to connect laptop users who travel from location The term "wireless" should not be confused with the term to location. Another common use is for mobile networks that "cordless", which is generally used to refer to powered electrical or electronic devices that are able to operate from a portable [EDIT] EARLY WIRELESS WORK power source (e.g. a battery pack) without any cable or cord to limit the mobility of the cordless device through a connection to Main article: Wireless telegraphy the mains power supply. David E. Hughes, eight years before Hertz's experiments,

Some cordless devices, such as cordless telephones, are also transmitted radio signals over a few hundred yards by means of wireless in the sense that information is transferred from the a clockwork keyed transmitter. As this was before Maxwell's work cordless telephone to the telephone's base unit via some type of was understood, Hughes' contemporaries dismissed his wireless communications link. This has caused some disparity in achievement as mere "Induction". In 1885, T. A. Edison used a the usage of the term "cordless", for example in Digital Enhanced vibrator magnet for induction transmission. In 1888, Edison Cordless Telecommunications. deployed a system of signaling on the Lehigh Valley Railroad. In 1891, Edison obtained the wireless patent for this method using inductance (U.S. Patent 465,971). [EDIT ] HISTORY

In the history of wireless technology, the demonstration of the [EDIT] PHOTOPHONE theory of electromagnetic waves by Heinrich Hertz in 1888 was [2][3] Main article: Photophone important. The theory of electromagnetic waves was predicted from the research of James Clerk Maxwell and Michael The world's first, wireless telephone conversation occurred in Faraday. Hertz demonstrated that electromagnetic waves could 1880, when Alexander Graham Bell and Charles Sumner Tainter be transmitted and caused to travel through space at straight invented and patented the photophone, a telephone that lines and that they were able to be received by an experimental conducted audio conversations wirelessly over modulated light apparatus.[2][3] The experiments were not followed up by Hertz. beams (which are narrow projections of electromagnetic waves). Jagadish Chandra Bose around this time developed an early In that distant era when utilities did not yet exist to provide wireless detection device and helped increase the knowledge of electricity, and lasers had not even been conceived of in science millimeter length electromagnetic waves.[4] Practical applications fiction, there were no practical applications for their invention, of wireless radio communication and radio remote control which was highly limited by the availability of both sunlight and technology were implemented by later inventors, such as Nikola good weather. Similar to free space optical communication, the Tesla. photophone also required a clear line of sight between its transmitter and its receiver. It would be several decades before Further information: Invention of radio the photophone's principles found their first practical applications [EDIT] RADIO in military communications and later in fiber-optic communications. Main article: History of radio [EDIT] SECURITY SYSTEMS

The term "wireless" came into public use to refer to a radio Wireless technology may supplement or replace hard wired receiver or transceiver (a dual purpose receiver and transmitter implementations in security systems for homes or office device), establishing its usage in the field of wireless telegraphy buildings. early on; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband [EDIT] CELLULAR TELEPHONE (PHONES AND MODEMS) Internet. It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as Perhaps the best known example of wireless technology is the "wireless remote control" or "wireless energy transfer", cellular telephone and modems. These instruments use radio regardless of the specific technology (e.g. radio, infrared, waves to enable the operator to make phone calls from many ultrasonic) used. Guglielmo Marconi and Karl Ferdinand Braun locations worldwide. They can be used anywhere that there is a were awarded the 1909 Nobel Prize for Physics for their cellular telephone site to house the equipment that is required to contribution to wireless telegraphy. transmit and receive the signal that is used to transfer both voice and data to and from these instruments. [EDIT ] THE ELECTROMAGNETIC SPECTRUM [EDIT] WI-FI Light, colors, AM and FM radio, and electronic devices make use Main article: Wi-Fi of the electromagnetic spectrum. In the US, the frequencies that are available for use for communication are treated as a public Wi-Fi is a wireless local area network that enables portable resource and are regulated by the Federal Communications computing devices to connect easily to the Internet. Commission. This determines which frequency ranges can be Standardized as IEEE 802.11 a,b,g,n, Wi-Fi approaches speeds of used for what purpose and by whom. In the absence of such some types of wired Ethernet. Wi-Fi hot spots have been popular control or alternative arrangements such as a privatized over the past few years. Some businesses charge customers a electromagnetic spectrum, chaos might result if, for example, monthly fee for service, while others have begun offering it for airlines didn't have specific frequencies to work under and an free in an effort to increase the sales of their goods.[5] amateur radio operator were interfering with the pilot's ability to land an airplane. Wireless communication spans the spectrum [EDIT] WIRELESS ENERGY TRANSFER from 9 kHz to 300 GHz. (Also see Spectrum management) Main article: Wireless energy transfer [EDIT ] APPLICATIONS OF WIRELESS TECHNOLOGY Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of • List of emerging technologies interconnecting wires. • Short-range point-to-point communication : Wireless microphones, Remote controls, IrDA, RFID (Radio [EDIT] COMPUTER INTERFACE DEVICES Frequency Identification), Wireless USB, DSRC (Dedicated Short Range Communications), EnOcean, Near Field Answering the call of customers frustrated with cord clutter, Communication many manufactures of computer peripherals turned to wireless • Wireless sensor networks : ZigBee, EnOcean; Personal area technology to satisfy their consumer base. Originally these units networks, Bluetooth, TransferJet, Ultra-wideband (UWB used bulky, highly limited transceivers to mediate between a from WiMedia Alliance). computer and a keyboard and mouse, however more recent • Wireless networks : Wireless LAN (WLAN), (IEEE 802.11 generations have used small, high quality devices, some even branded as Wi-Fi and HiperLAN), Wireless Metropolitan incorporating Bluetooth. These systems have become so Area Networks (WMAN) and Broadband Fixed Access ubiquitous that some users have begun complaining about a lack (BWA) (LMDS, WiMAX, AIDAAS and HiperMAN) of wired peripherals.[who?] Wireless devices tend to have a slightly slower response time than their wired counterparts, however the MICROWAVE TRANSMISSION gap is decreasing. Initial concerns about the security of wireless keyboards have also been addressed with the maturation of the From Wikipedia, the free encyclopedia technology.

[EDIT ] CATEGORIES OF WIRELESS IMPLEMENTATIONS, DEVICES AND STANDARDS

• Radio communication system • Broadcasting • Amateur radio • Land Mobile Radio or Professional Mobile Radio: TETRA, P25, OpenSky, EDACS, DMR, dPMR • Communication radio • Cordless telephony :DECT (Digital Enhanced Cordless Telecommunications) The atmospheric attenuation of microwaves in dry air with a • Cellular networks : 0G, 1G, 2G, 3G, Beyond 3G (4G), Future precipitable water vapor level of 0.001 mm. The downward wireless spikes in the graph correspond to frequencies at which microwaves are absorbed more strongly, such as by oxygen wide band of frequencies around 60 GHz, the radio waves are molecules strongly attenuated by molecular oxygen in the atmosphere. The electronic technologies needed in the millimeter wave band are Microwave transmission refers to the technology of also much more difficult to utilize than those of the microwave transmitting information by the use of radio waves whose band. wavelengths are conveniently measured in small numbers of centimeters, by using various electronic technologies. These are called microwaves. This part of the radio spectrum ranges across CONTENTS frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These • 1 Properties correspond to wavelengths from 30 centimeters down to 1.0 cm. • 2 Uses • 3 Parabolic (microwave) antenna In the microwave frequency band, antennas are usually of • 4 Microwave power transmission o 4.1 History convenient sizes and shapes, and also the use of metal o 4.2 Common safety concerns waveguides for carrying the radio power works well. o 4.3 Proposed uses Furthermore, with the use of the modern solid-state electronics o 4.4 Current status • 5 Microwave radio relay and traveling wave tube technologies that have been developed o 5.1 How microwave radio relay links are formed since the early 1960s, the electronics used by microwave radio o 5.2 Planning considerations transmission have been readily used by expert electronics o 5.3 Over-horizon microwave radio relay o 5.4 Usage of microwave radio relay systems engineers. o 5.5 Microwave link . 5.5.1 Properties of microwave links Microwave radio transmission is commonly used by . 5.5.2 Uses of microwave links o 5.6 Tunable microwave device communication systems on the surface of the Earth, in satellite • 6 See also communications, and in deep space radio communications. Other • 7 References parts of the microwave radio band are used for radars, radio • 8 External links navigation systems, sensor systems, and radio astronomy.

The next higher part of the radio electromagnetic spectrum, [EDIT ] PROPERTIES where the frequencies are above 30 GHz and below 100 GHz, are • called "millimeter waves" because their wavelengths are Suitable over line-of-sight transmission links without conveniently measured in millimeters, and their wavelengths obstacles • [clarification needed] range from 10 mm down to 3.0 mm. Radio waves in this band Provides good bandwidth are usually strongly attenuated by the Earthly atmosphere and particles contained in it, especially during wet weather. Also, in • Affected by rain, vapor, dust, snow, cloud, mist and fog, [EDIT ] MICROWAVE POWER TRANSMISSION heavy moisture, depending on chosen frequency (see rain fade) Microwave power transmission (MPT) is the use of microwaves to transmit power through outer space or the [EDIT ] USES atmosphere without the need for wires. It is a sub-type of the more general wireless energy transfer methods. • Backbone or backhaul carriers in cellular networks. Used to link BTS-BSC and BSC-MSC. [EDIT] HISTORY • Communication with satellites Following World War II, which saw the development of high- • Microwave radio relay links for television and telephone power microwave emitters known as cavity magnetrons, the idea service providers of using microwaves to transmit power was researched. In 1964, William C. Brown demonstrated a miniature helicopter equipped with a combination antenna and rectifier device called a rectenna. The rectenna converted microwave power into electricity, allowing the helicopter to fly.[1] In principle, the rectenna is capable of very high conversion efficiencies - over 90% in optimal circumstances.

Most proposed MPT systems now usually include a phased array microwave transmitter. While these have lower efficiency levels they have the advantage of being electrically steered using no [EDIT ] PARABOLIC (MICROWAVE) ANTENNA moving parts, and are easier to scale to the necessary levels that

Main article: Parabolic antenna a practical MPT system requires.

A parabolic antenna is a high-gain reflector antenna used for Using microwave power transmission to deliver electricity to radio, television and data communications, and also for communities without having to build cable-based infrastructure is radiolocation (radar), on the UHF and SHF parts of the being studied at Grand Bassin on Reunion Island in the Indian electromagnetic spectrum. The relatively short wavelength of Ocean. electromagnetic radiation at these frequencies allows reasonably [EDIT] COMMON SAFETY CONCERNS sized reflectors to exhibit the desired highly directional response for both receiving and transmitting. The common reaction to microwave transmission is one of Wireless Power Transmission (using microwaves) is well proven. concern, as microwaves are generally perceived by the public as Experiments in the tens of kilowatts have been performed at dangerous forms of radiation - stemming from the fact that they Goldstone in California in 1975[3][4][5] and more recently (1997) at are used in microwave ovens. While high power microwaves can Grand Bassin on Reunion Island.[6] In 2008 a long range be painful and dangerous as in the United States Military's Active transmission experiment successfully transmitted 20 watts 92 Denial System, MPT systems are generally proposed to have only miles from a mountain on Maui to the main island of Hawaii.[7] low intensity at the rectenna. [edit] Microwave radio relay Though this would be extremely safe as the power levels would be about equal to the leakage from a microwave oven, and only slightly more than a cell phone, the relatively diffuse microwave beam necessitates a large rectenna area for a significant amount of energy to be transmitted.

Research has involved exposing multiple generations of animals to microwave radiation of this or higher intensity, and no health issues have been found.[2]

[EDIT] PROPOSED USES Heinrich-Hertz-Turm in Germany

Main article: Solar power satellite Microwave radio relay is a technology for transmitting digital and analog signals, such as long-distance telephone calls and the MPT is the most commonly proposed method for transferring relay of television programs to transmitters, between two energy to the surface of the Earth from solar power satellites or locations on a line of sight radio path. In microwave radio relay, other in-orbit power sources. MPT is occasionally proposed for radio waves are transmitted between the two locations with the power supply in [beam-powered propulsion] for orbital lift directional antennas, forming a fixed radio connection between space ships. Even though lasers are more commonly proposed, the two points. Long daisy-chained series of such links form their low efficiency in light generation and reception has led transcontinental telephone and/or television communication some designers to opt for microwave based systems. systems.

[EDIT] CURRENT STATUS [EDIT] HOW MICROWAVE RADIO RELAY LINKS ARE FORMED Danish military radio relay node

[EDIT] PLANNING CONSIDERATIONS

Because of the high frequencies used, a quasi-optical line of sight between the stations is generally required. Additionally, in order to form the line of sight connection between the two stations, the first Fresnel zone must be free from obstacles so the radio waves can propagate across a nearly uninterrupted path. Obstacles in the signal field cause unwanted attenuation, and are as a result

Relay towers on Frazier Mountain, Southern California only acceptable in exceptional cases. High mountain peak or ridge positions are often ideal: Europe's highest radio relay Because a line of sight radio link is made, the radio frequencies station, the Richtfunkstation Jungfraujoch, is situated atop the used occupy only a narrow path between stations (with the Jungfraujoch ridge at an altitude of 3,705 meters (12,156 ft) exception of a certain radius of each station). Antennas used above sea level. must have a high directive effect; these antennas are installed in elevated locations such as large radio towers in order to be able to transmit across long distances. Typical types of antenna used in radio relay link installations are parabolic reflectors, shell antennas and horn radiators, which have a diameter of up to 4 meters. Highly directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances.

Multiple antennas provide space diversity

Obstacles, the curvature of the Earth, the geography of the area and reception issues arising from the use of nearby land (such as in manufacturing and forestry) are important issues to consider when planning radio links. In the planning process, it is essential that "path profiles" are produced, which provide information about the terrain and Fresnel zones affecting the transmission path. The presence of a water surface, such as a lake or river, in the mid-path region also must be taken into consideration as it can result in a near-perfect reflection (even modulated by wave or tide motions), creating multipath distortion as the two received signals ("wanted" and "unwanted") swing in and out of phase. Multipath fades are usually deep only in a small spot and a narrow frequency band, so space and frequency diversity schemes were usually applied in the third quarter of the 20th century.

The effects of atmospheric stratification cause the radio path to bend downward in a typical situation so a major distance is possible as the earth equivalent curvature increases from Portable microwave rig for television news 6370 km to about 8500 km (a 4/3 equivalent radius effect). Rare events of temperature, humidity and pressure profile versus [EDIT] OVER-HORIZON MICROWAVE RADIO RELAY height, may produce large deviations and distortion of the In over-horizon, or tropospheric scatter, microwave radio relay, propagation and affect transmission quality. High intensity rain unlike a standard microwave radio relay link, the sending and and snow must also be considered as an impairment factor, receiving antennas do not use a line of sight transmission path. especially at frequencies above 10 GHz. All previous factors, Instead, the stray signal transmission, known as "tropo - scatter" collectively known as path loss, make it necessary to compute or simply "scatter," from the sent signal is picked up by the suitable power margins, in order to maintain the link operative receiving station. Signal clarity obtained by this method depends for a high percentage of time, like the standard 99.99% or on the weather and other factors, and as a result a high level of 99.999% used in 'carrier class' services of most technical difficulty is involved in the creation of a reliable over telecommunication operators. horizon radio relay link. Over horizon radio relay links are therefore only used where standard radio relay links are unsuitable (for example, in providing a microwave link to an island).

[EDIT] USAGE OF MICROWAVE RADIO RELAY SYSTEMS

During the 1950s the AT&T Communications system of microwave radio grew to carry the majority of US Long Distance telephone traffic, as well as intercontinental television network A microwave link is a communications system that uses a signals. The prototype was called TDX and was tested with a beam of radio waves in the microwave frequency range to connection between New York City and Murray Hill, the location transmit video, audio, or data between two locations, which can of Bell Laboratories in 1946. The TDX system was set up between be from just a few feet or meters to several miles or kilometers New York and Boston in 1947. The TDX was improved to the TD2, apart. Microwave links are commonly used by television which still used klystrons, and then later to the TD3 that used broadcasters to transmit programmes across a country, for solid state electronics. The main motivation in 1946 to use instance, or from an outside broadcast back to a studio. microwave radio instead of cable was that a large capacity could be installed quickly and at less cost. It was expected at that time Mobile units can be camera mounted, allowing cameras the that the annual operating costs for microwave radio would be freedom to move around without trailing cables. These are often greater than for cable. There were two main reasons that a large seen on the touchlines of sports fields on Steadicam systems. capacity had to be introduced suddenly: Pent up demand for long [EDIT ] PROPERTIES OF MICROWAVE LINKS distance telephone service, because of the hiatus during the war years, and the new medium of television, which needed more • Involve line of sight (LOS) communication technology bandwidth than radio. • Affected greatly by environmental constraints, including rain fade Similar systems were soon built in many countries, until the • Have limited penetration capabilities 1980s when the technology lost its share of fixed operation to • Sensitive to high pollen count newer technologies such as fiber-optic cable and optical radio • Signals can be degraded during Solar proton events [8] relay links, both of which offer larger data capacities at lower cost per bit. Communication satellites, which are also microwave [EDIT ] USES OF MICROWAVE LINKS radio relays, better retained their market share, especially for television. • In communications between satellites and base stations • As backbone carriers for cellular systems At the turn of the century, microwave radio relay systems are • In short range indoor communications being used increasingly in portable radio applications. The technology is particularly suited to this application because of [EDIT] TUNABLE MICROWAVE DEVICE lower operating costs, a more efficient infrastructure, and provision of direct hardware access to the portable radio A tunable microwave device is a device that works at radio operator. frequency range with the dynamic tunable capabilities, especially an electric field. The material systems for such a device usually [EDIT] MICROWAVE LINK have multilayer structure. Usually, magnetic or ferroelectric film on ferrite or superconducting film is adopted. The former two are has a much higher data bandwidth than the data being used as the property tunable component to control the working communicated. frequency of the whole system. Devices of this type include tunable varators, tunable microwave filters, tunable phase An analogy to the problem of multiple access is a room (channel) shifters, and tunable resonators. The main application of them is in which people wish to talk to each other simultaneously. To re-configurable microwave networks, for example, reconfigurable avoid confusion, people could take turns speaking (time division), wireless communication, wireless network, and reconfigurable speak at different pitches (frequency division), or speak in phase array antenna.[9][10] different languages (code division). CDMA is analogous to the last example where people speaking the same language can CODE DIVISION MULTIPLE ACCESS understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users From Wikipedia, the free encyclopedia is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can Code division multiple access (CDMA) is a channel access communicate. method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply CONTENTS CDMA), which use CDMA as an underlying channel access • 1 Uses method. • 2 Steps in CDMA Modulation • 3 Code division multiplexing (Synchronous CDMA) One of the basic concepts in data communication is the idea of o 3.1 Example • 4 Asynchronous CDMA allowing several transmitters to send information simultaneously o 4.1 Advantages of asynchronous CDMA over other over a single communication channel. This allows several users techniques 4.2 Spread-spectrum characteristics of CDMA to share a band of frequencies (see bandwidth). This concept is o • 5 See also called Multiple Access. CDMA employs spread-spectrum • 6 References technology and a special coding scheme (where each transmitter • 7 External links is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division [EDIT ] USES multiple access (FDMA) divides it by frequency. CDMA is a form One of the early applications for code division multiplexing is in of spread-spectrum signalling, since the modulated coded signal GPS. This predates and is distinct from cdmaOne. • The Qualcomm standard IS-95, marketed as cdmaOne. • The Qualcomm standard IS-2000, known as CDMA2000. This standard is used by several mobile phone companies, including the Globalstar satellite phone network. • CDMA has been used in the OmniTRACS satellite system for transportation logistics.

[EDIT ] STEPS IN CDMA MODULATION

CDMA is a spread spectrum multiple access[1] technique. A spread spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. Spreading code is a pseudo-random code that has a narrow Ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated Each user in a CDMA system uses a different code to modulate code runs at a much higher rate than the data to be transmitted. their signal. Choosing the codes used to modulate the signal is Data for transmission is combined via bitwise XOR (exclusive OR) very important in the performance of CDMA systems. The best with the faster code. The figure shows how spread spectrum performance will occur when there is good separation between signal is generated. The data signal with pulse duration of Tb is the signal of a desired user and the signals of other users. The XOR’ed with the code signal with pulse duration of Tc. (Note: separation of the signals is made by correlating the received bandwidth is proportional to 1 / T where T = bit time) Therefore, signal with the locally generated code of the desired user. If the the bandwidth of the data signal is 1 / Tb and the bandwidth of signal matches the desired user's code then the correlation the spread spectrum signal is 1 / Tc. Since Tc is much smaller function will be high and the system can extract that signal. If than Tb, the bandwidth of the spread spectrum signal is much the desired user's code has nothing in common with the signal larger than the bandwidth of the original signal. The ratio Tb / Tc the correlation should be as close to zero as possible (thus is called spreading factor or processing gain and determines to a eliminating the signal); this is referred to as cross correlation. If certain extent the upper limit of the total number of users the code is correlated with the signal at any time offset other supported simultaneously by a base station.[2] than zero, the correlation should be as close to zero as possible. This is referred to as auto-correlation and is used to reject multi- path interference.[3]

In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes). [EDIT ] CODE DIVISION MULTIPLEXING (SYNCHRONOUS CDMA)

Synchronous CDMA exploits mathematical properties of orthogonality between vectors representing the data strings. For example, binary string 1011 is represented by the vector (1, 0, 1, 1). Vectors can be multiplied by taking their dot product, by summing the products of their respective components. If the dot product is zero, the two vectors are said to be orthogonal to each other (note: if u = (a, b) and v = (c, d), the dot product u·v = ac + bd). Some properties of the dot product aid understanding of how W-CDMA works. If vectors a and b are orthogonal, then and:

An example of four mutually orthogonal digital signals.

Each user in synchronous CDMA uses a code orthogonal to the Start with a set of vectors that are mutually orthogonal. others' codes to modulate their signal. An example of four (Although mutual orthogonality is the only condition, these mutually orthogonal digital signals is shown in the figure. vectors are usually constructed for ease of decoding, for example Orthogonal codes have a cross-correlation equal to zero; in other columns or rows from Walsh matrices.) An example of orthogonal words, they do not interfere with each other. In the case of IS-95 functions is shown in the picture on the left. These vectors will be 64 bit Walsh codes are used to encode the signal to separate assigned to individual users and are called the code, chip code, different users. Since each of the 64 Walsh codes are orthogonal or chipping code. In the interest of brevity, the rest of this to one another, the signals are channelized into 64 orthogonal example uses codes, v, with only 2 bits. signals. The following example demonstrates how each user's signal can be encoded and decoded. Each user is associated with a different code, say v. A 1 bit is represented by transmitting a positive code, v, and a 0 bit is [EDIT ] EXAMPLE represented by a negative code, –v. For example, if v = (1, –1) and the data that the user wishes to transmit is (1, 0, 1, 1), then the transmitted symbols would be (1, –1, 1, 1) ⊗ v = (v0, v1, –v0, – (1, –1, –1, 1, 1, –1, 1, –1) + (–1, –1, –1, –1, 1, 1, 1, 1) = (0, – v1, v0, v1, v0, v1) = (1, –1, –1, 1, 1, –1, 1, –1), where ⊗ is the 2, –2, 0, 2, 0, 2, 0) Kronecker product. For the purposes of this article, we call this constructed vector the transmitted vector. This raw signal is called an interference pattern. The receiver then extracts an intelligible signal for any known sender by Each sender has a different, unique vector v chosen from that combining the sender's code with the interference pattern, the set, but the construction method of the transmitted vector is receiver combines it with the codes of the senders. The following identical. table explains how this works and shows that the signals do not interfere with one another: Now, due to physical properties of interference, if two signals at Ste a point are in phase, they add to give twice the amplitude of Decode sender0 Decode sender1 p each signal, but if they are out of phase, they subtract and give a code0 = (1, –1), signal = (0, – code1 = (1, 1), signal = (0, –2, signal that is the difference of the amplitudes. Digitally, this 0 2, –2, 0, 2, 0, 2, 0) –2, 0, 2, 0, 2, 0) behaviour can be modelled by the addition of the transmission vectors, component by component. 1 decode0 = pattern.vector0 decode1 = pattern.vector1

decode0 = ((0, –2), (–2, 0), (2, decode1 = ((0, –2), (–2, 0), (2, 2 If sender0 has code (1, –1) and data (1, 0, 1, 1), and sender1 has 0), (2, 0)).(1, –1) 0), (2, 0)).(1, 1) code (1, 1) and data (0, 0, 1, 1), and both senders transmit decode0 = ((0 + 2), (–2 + 0), decode1 = ((0 – 2), (–2 + 0), simultaneously, then this table describes the coding steps: 3 (2 + 0), (2 + 0)) (2 + 0), (2 + 0))

Ste data0=(2, –2, 2, 2), meaning data1=(–2, –2, 2, 2), meaning Encode sender0 Encode sender1 4 p (1, 0, 1, 1) (0, 0, 1, 1) 0 code0 = (1, –1), data0 = (1, code1 = (1, 1), data1 = (0, 0, 0, 1, 1) 1, 1) Further, after decoding, all values greater than 0 are interpreted 1 encode0 = 2(1, 0, 1, 1) – (1, encode1 = 2(0, 0, 1, 1) – (1, as 1 while all values less than zero are interpreted as 0. For 1, 1, 1) 1, 1, 1) example, after decoding, data0 is (2, –2, 2, 2), but the receiver = (1, –1, 1, 1) = (–1, –1, 1, 1) interprets this as (1, 0, 1, 1). Values of exactly 0 means that the 2 signal0 = encode0 ⊗ code0 signal1 = encode1 ⊗ code1 sender did not transmit any data, as in the following example:

= (1, –1, 1, 1) ⊗ (1, –1) = (–1, –1, 1, 1) ⊗ (1, 1) Assume signal0 = (1, –1, –1, 1, 1, –1, 1, –1) is transmitted alone. = (1, –1, –1, 1, 1, –1, 1, –1) = (–1, –1, –1, –1, 1, 1, 1, 1) The following table shows the decode at the receiver:

Because signal0 and signal1 are transmitted at the same time into the air, they add to produce the raw signal: Ste Decode sender0 Decode sender1 On the other hand, the mobile-to-base links cannot be precisely p coordinated, particularly due to the mobility of the handsets, and code0 = (1, –1), signal = (1, – code1 = (1, 1), signal = (1, –1, 0 require a somewhat different approach. Since it is not 1, –1, 1, 1, –1, 1, –1) –1, 1, 1, –1, 1, –1) mathematically possible to create signature sequences that are 1 decode0 = pattern.vector0 decode1 = pattern.vector1 both orthogonal for arbitrarily random starting points and which make full use of the code space, unique "pseudo-random" or decode0 = ((1, –1), (–1, 1), (1, decode1 = ((1, –1), (–1, 1), (1, 2 –1), (1, –1)).(1, –1) –1), (1, –1)).(1, 1) "pseudo-noise" (PN) sequences are used in asynchronous CDMA systems. A PN code is a binary sequence that appears random decode0 = ((1 + 1), (–1 – 1),(1 decode1 = ((1 – 1), (–1 + 1),(1 3 + 1), (1 + 1)) – 1), (1 – 1)) but can be reproduced in a deterministic manner by intended receivers. These PN codes are used to encode and decode a data0 = (2, –2, 2, 2), meaning data1 = (0, 0, 0, 0), meaning 4 (1, 0, 1, 1) no data user's signal in Asynchronous CDMA in the same manner as the orthogonal codes in synchronous CDMA (shown in the example above). These PN sequences are statistically uncorrelated, and When the receiver attempts to decode the signal using sender1's the sum of a large number of PN sequences results in multiple code, the data is all zeros, therefore the cross correlation is equal access interference (MAI) that is approximated by a Gaussian to zero and it is clear that sender1 did not transmit any data. noise process (following the central limit theorem in statistics). Gold codes are an example of a PN suitable for this purpose, as [EDIT ] ASYNCHRONOUS CDMA there is low correlation between the codes. If all of the users are received with the same power level, then the variance (e.g., the See also: Direct-sequence spread spectrum and near-far problem noise power) of the MAI increases in direct proportion to the The previous example of orthogonal Walsh sequences describes number of users. In other words, unlike synchronous CDMA, the how 2 users can be multiplexed together in a synchronous signals of other users will appear as noise to the signal of interest system, a technique that is commonly referred to as code and interfere slightly with the desired signal in proportion to division multiplexing (CDM). The set of 4 Walsh sequences shown number of users. in the figure will afford up to 4 users, and in general, an NxN All forms of CDMA use spread spectrum process gain to allow Walsh matrix can be used to multiplex N users. Multiplexing receivers to partially discriminate against unwanted signals. requires all of the users to be coordinated so that each transmits Signals encoded with the specified PN sequence (code) are their assigned sequence v (or the complement, –v) so that they received, while signals with different codes (or the same code arrive at the receiver at exactly the same time. Thus, this but a different timing offset) appear as wideband noise reduced technique finds use in base-to-mobile links, where all of the by the process gain. transmissions originate from the same transmitter and can be perfectly coordinated. Since each user generates MAI, controlling the signal strength is adjacent channels will interfere, but decrease the utilization of an important issue with CDMA transmitters. A CDM (synchronous the spectrum. CDMA), TDMA, or FDMA receiver can in theory completely reject arbitrarily strong signals using different codes, time slots or Flexible Allocation of Resources frequency channels due to the orthogonality of these systems. Asynchronous CDMA offers a key advantage in the flexible This is not true for Asynchronous CDMA; rejection of unwanted allocation of resources i.e. allocation of a PN codes to active signals is only partial. If any or all of the unwanted signals are users. In the case of CDM, TDMA, and FDMA the number of much stronger than the desired signal, they will overwhelm it. simultaneous orthogonal codes, time slots and frequency slots This leads to a general requirement in any asynchronous CDMA respectively is fixed hence the capacity in terms of number of system to approximately match the various signal power levels simultaneous users is limited. There are a fixed number of as seen at the receiver. In CDMA cellular, the base station uses a orthogonal codes, timeslots or frequency bands that can be fast closed-loop power control scheme to tightly control each allocated for CDM, TDMA, and FDMA systems, which remain mobile's transmit power. underutilized due to the bursty nature of telephony and packetized data transmissions. There is no strict limit to the [EDIT] ADVANTAGES OF ASYNCHRONOUS CDMA OVER number of users that can be supported in an asynchronous OTHER TECHNIQUES CDMA system, only a practical limit governed by the desired bit Efficient Practical utilization of Fixed Frequency Spectrum error probability, since the SIR (Signal to Interference Ratio) varies inversely with the number of users. In a bursty traffic In theory, CDMA, TDMA and FDMA have exactly the same environment like mobile telephony, the advantage afforded by spectral efficiency but practically, each has its own challenges – asynchronous CDMA is that the performance (bit error rate) is power control in the case of CDMA, timing in the case of TDMA, allowed to fluctuate randomly, with an average value determined and frequency generation/filtering in the case of FDMA. by the number of users times the percentage of utilization. Suppose there are 2N users that only talk half of the time, then TDMA systems must carefully synchronize the transmission times 2N users can be accommodated with the same average bit error of all the users to ensure that they are received in the correct probability as N users that talk all of the time. The key difference timeslot and do not cause interference. Since this cannot be here is that the bit error probability for N users talking all of the perfectly controlled in a mobile environment, each timeslot must time is constant, whereas it is a random quantity (with the same have a guard-time, which reduces the probability that users will mean) for 2N users talking half of the time. interfere, but decreases the spectral efficiency. Similarly, FDMA systems must use a guard-band between adjacent channels, due In other words, asynchronous CDMA is ideally suited to a mobile to the unpredictable doppler shift of the signal spectrum because network where large numbers of transmitters each generate a of user mobility. The guard-bands will reduce the probability that relatively small amount of traffic at irregular intervals. CDM (synchronous CDMA), TDMA, and FDMA systems cannot recover either spread its energy over the entire bandwidth of the signal the underutilized resources inherent to bursty traffic due to the or jam only part of the entire signal.[4] fixed number of orthogonal codes, time slots or frequency channels that can be assigned to individual transmitters. For CDMA can also effectively reject narrowband interference. Since instance, if there are N time slots in a TDMA system and 2N users narrowband interference affects only a small portion of the that talk half of the time, then half of the time there will be more spread spectrum signal, it can easily be removed through notch than N users needing to use more than N timeslots. Furthermore, filtering without much loss of information. Convolution encoding it would require significant overhead to continually allocate and and interleaving can be used to assist in recovering this lost deallocate the orthogonal code, time-slot or frequency channel data. CDMA signals are also resistant to multipath fading. Since resources. By comparison, asynchronous CDMA transmitters the spread spectrum signal occupies a large bandwidth only a simply send when they have something to say, and go off the air small portion of this will undergo fading due to multipath at any when they don't, keeping the same PN signature sequence as given time. Like the narrowband interference this will result in long as they are connected to the system. only a small loss of data and can be overcome.

Another reason CDMA is resistant to multipath interference is [EDIT] SPREAD-SPECTRUM CHARACTERISTICS OF CDMA because the delayed versions of the transmitted pseudo-random Most modulation schemes try to minimize the bandwidth of this codes will have poor correlation with the original pseudo-random signal since bandwidth is a limited resource. However, spread code, and will thus appear as another user, which is ignored at spectrum techniques use a transmission bandwidth that is the receiver. In other words, as long as the multipath channel several orders of magnitude greater than the minimum required induces at least one chip of delay, the multipath signals will signal bandwidth. One of the initial reasons for doing this was arrive at the receiver such that they are shifted in time by at military applications including guidance and communication least one chip from the intended signal. The correlation systems. These systems were designed using spread spectrum properties of the pseudo-random codes are such that this slight because of its security and resistance to jamming. Asynchronous delay causes the multipath to appear uncorrelated with the CDMA has some level of privacy built in because the signal is intended signal, and it is thus ignored. spread using a pseudo-random code; this code makes the spread Some CDMA devices use a rake receiver, which exploits spectrum signals appear random or have noise-like properties. A multipath delay components to improve the performance of the receiver cannot demodulate this transmission without knowledge system. A rake receiver combines the information from several of the pseudo-random sequence used to encode the data. CDMA correlators, each one tuned to a different path delay, producing a is also resistant to jamming. A jamming signal only has a finite stronger version of the signal than a simple receiver with a single amount of power available to jam the signal. The jammer can correlator tuned to the path delay of the strongest signal.[5] Frequency reuse is the ability to reuse the same radio channel Telecommunications Standards Institute (ETSI) in response to the frequency at other cell sites within a cellular system. In the FDMA earlier CDPD and i-mode packet switched cellular technologies. It and TDMA systems frequency planning is an important is now maintained by the 3rd Generation Partnership Project consideration. The frequencies used in different cells must be (3GPP).[1][2] planned carefully to ensure signals from different cells do not interfere with each other. In a CDMA system, the same frequency It is a best-effort service, as opposed to circuit switching, where a can be used in every cell, because channelization is done using certain quality of service (QoS) is guaranteed during the the pseudo-random codes. Reusing the same frequency in every connection. In 2G systems, GPRS provides data rates of 56- [3] cell eliminates the need for frequency planning in a CDMA 114 kbit/second. 2G cellular technology combined with GPRS is system; however, planning of the different pseudo-random sometimes described as 2.5G, that is, a technology between the [4] sequences must be done to ensure that the received signal from second (2G) and third (3G) generations of mobile telephony. It one cell does not correlate with the signal from a nearby cell.[6] provides moderate-speed data transfer, by using unused time division multiple access (TDMA) channels in, for example, the Since adjacent cells use the same frequencies, CDMA systems GSM system. GPRS is integrated into GSM Release 97 and newer have the ability to perform soft handoffs. Soft handoffs allow the releases. mobile telephone to communicate simultaneously with two or more cells. The best signal quality is selected until the handoff is GPRS usage charging is based on volume of data, either as part complete. This is different from hard handoffs utilized in other of a bundle or on a pay as you use basis. An example of a bundle cellular systems. In a hard handoff situation, as the mobile is up to 5 GB per month for a fixed fee. Usage above the bundle telephone approaches a handoff, signal strength may vary cap is either charged for per megabyte or disallowed. The pay as abruptly. In contrast, CDMA systems use the soft handoff, which you use charging is typically per megabyte of traffic. This is undetectable and provides a more reliable and higher quality contrasts with circuit switching data, which is typically billed per signal.[6] minute of connection time, regardless of whether or not the user transfers data during that period. GENERAL PACKET RADIO SERVICE

CONTENTS From Wikipedia, the free encyclopedia • 1 Technical overview General packet radio service (GPRS) is a packet oriented o 1.1 Services offered mobile data service on the 2G and 3G cellular communication o 1.2 Protocols supported systems global system for mobile communications (GSM). The o 1.3 Hardware o 1.4 Addressing service is available to users in over 200 countries worldwide. • 2 Coding schemes and speeds GPRS was originally standardized by European o 2.1 Multiple access schemes o 2.2 Channel encoding GPRS supports the following protocols:[citation needed] o 2.3 Multislot Class . 2.3.1 Multislot Classes for GPRS/EGPRS . 2.3.2 Attributes of a multislot class • internet protocol (IP). In practice, built-in mobile browsers • 3 Usability use IPv4 since IPv6 is not yet popular. • 4 See also • point-to-point protocol (PPP). In this mode PPP is often not • 5 References supported by the mobile phone operator but if the mobile • 6 External links is used as a modem to the connected computer, PPP is used to tunnel IP to the phone. This allows an IP address to [EDIT ] TECHNICAL OVERVIEW be assigned dynamically to the mobile equipment. • X.25 connections. This is typically used for applications See also: GPRS Core Network like wireless payment terminals, although it has been removed from the standard. X.25 can still be supported [EDIT] SERVICES OFFERED over PPP, or even over IP, but doing this requires either a network based router to perform encapsulation or GPRS extends the GSM circuit switched data capabilities and intelligence built in to the end-device/terminal; e.g., user makes the following services possible: equipment (UE). • "Always on" internet access When TCP/IP is used, each phone can have one or more IP • Multimedia messaging service (MMS) addresses allocated. GPRS will store and forward the IP packets • Push to talk over cellular (PoC/PTT) to the phone even during handover. The TCP handles any packet • Instant messaging and presence—wireless village loss (e.g. due to a radio noise induced pause). • Internet applications for smart devices through wireless application protocol (WAP) [EDIT] HARDWARE • Point-to-point (P2P) service: inter-networking with the Internet (IP) Devices supporting GPRS are divided into three classes:

If SMS over GPRS is used, an SMS transmission speed of about 30 Class A SMS messages per minute may be achieved. This is much faster than using the ordinary SMS over GSM, whose SMS transmission Can be connected to GPRS service and GSM service (voice, speed is about 6 to 10 SMS messages per minute. SMS), using both at the same time. Such devices are known to be available today. [EDIT] PROTOCOLS SUPPORTED Class B Can be connected to GPRS service and GSM service (voice, models have connector for external antenna. Modems can be SMS), but using only one or the other at a given time. added as cards (for laptops) or external USB devices which are During GSM service (voice call or SMS), GPRS service is similar in shape and size to a computer mouse, or nowadays suspended, and then resumed automatically after the GSM more like a pendrive. service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B. [EDIT] ADDRESSING

Class C A GPRS connection is established by reference to its access point name (APN). The APN defines the services such as wireless Are connected to either GPRS service or GSM service application protocol (WAP) access, short message service (SMS), (voice, SMS). Must be switched manually between one or multimedia messaging service (MMS), and for Internet the other service. communication services such as email and World Wide Web A true Class A device may be required to transmit on two access. different frequencies at the same time, and thus will need two In order to set up a GPRS connection for a wireless modem, a radios. To get around this expensive requirement, a GPRS mobile user must specify an APN, optionally a user name and password, may implement the dual transfer mode (DTM) feature. A DTM- and very rarely an IP address, all provided by the network capable mobile may use simultaneous voice and packet data, operator. with the network coordinating to ensure that it is not required to transmit on two different frequencies at the same time. Such mobiles are considered pseudo-Class A, sometimes referred to as [EDIT ] CODING SCHEMES AND SPEEDS "simple class A". Some networks are expected to support DTM in The upload and download speeds that can be achieved in GPRS 2007. depend on a number of factors such as:

• the number of BTS TDMA time slots assigned by the operator • the channel encoding used. • the maximum capability of the mobile device expressed as a GPRS multislot class Huawei E220 3G/GPRS Modem [EDIT] MULTIPLE ACCESS SCHEMES USB 3G/GPRS modems use a terminal-like interface over USB 1.1, 2.0 and later, data formats V.42bis, and RFC 1144 and some The multiple access methods used in GSM with GPRS are based coding scheme (CS-1) is used when the mobile station (MS) is on frequency division duplex (FDD) and TDMA. During a session, further away from a BTS. a user is assigned to one pair of up-link and down-link frequency channels. This is combined with time domain statistical Using the CS-4 it is possible to achieve a user speed of multiplexing; i.e., packet mode communication, which makes it 20.0 kbit/s per time slot. However, using this scheme the cell possible for several users to share the same frequency channel. coverage is 25% of normal. CS-1 can achieve a user speed of The packets have constant length, corresponding to a GSM time only 8.0 kbit/s per time slot, but has 98% of normal coverage. slot. The down-link uses first-come first-served packet Newer network equipment can adapt the transfer speed scheduling, while the up-link uses a scheme very similar to automatically depending on the mobile location. reservation ALOHA (R-ALOHA). This means that slotted ALOHA (S- In addition to GPRS, there are two other GSM technologies which ALOHA) is used for reservation inquiries during a contention deliver data services: circuit-switched data (CSD) and high-speed phase, and then the actual data is transferred using dynamic circuit-switched data (HSCSD). In contrast to the shared nature of TDMA with first-come first-served scheduling. GPRS, these instead establish a dedicated circuit (usually billed per minute). Some applications such as video calling may prefer [EDIT] CHANNEL ENCODING HSCSD, especially when there is a continuous flow of data Channel encoding is based on a convolutional code at different between the endpoints. code rates and GMSK modulation defined for GSM. The following The following table summarises some possible configurations of table summarises the options: GPRS and circuit switched data services. Codin Spee TDMA g d Technolog Download Upload Timeslots schem (kbit/s y (kbit/s) (kbit/s) e ) allocated

CS-1 8.0 CSD 9.6 9.6 1+1

CS-2 12.0 HSCSD 28.8 14.4 2+1

CS-3 14.4 HSCSD 43.2 14.4 3+1 20.0 (Class 8 & CS-4 20.0 GPRS 80.0 4+1 10 and CS-4)

40.0 (Class 10 GPRS 60.0 3+2 The least robust, but fastest, coding scheme (CS-4) is available and CS-4) near a base transceiver station (BTS), while the most robust EGPRS 236.8 59.2 (Class 8, 4+1 (EDGE) 10 and MCS-9) i.e. when the best EDGE modulation and coding scheme can be EGPRS 118.4 (Class 10 used, 5 timeslots can carry a bandwidth of 5*59.2 kbit/s = 296 177.6 3+2 (EDGE) and MCS-9) kbit/s. In uplink direction, 3 timeslots can carry a bandwidth of 3*59.2 kbit/s = 177.6 kbit/s.[5]

[EDIT] MULTISLOT CLASS [EDIT ] MULTISLOT CLASSES FOR GPRS/EGPRS Multisl The multislot class determines the speed of data transfer Downli Uplin Activ ot nk TS k TS e TS available in the Uplink and Downlink directions. It is a value Class between 1 to 45 which the network uses to allocate radio 1 1 1 2 channels in the uplink and downlink direction. Multislot class with values greater than 31 are referred to as high multislot classes. 2 2 1 3

3 2 2 3 A multislot allocation is represented as, for example, 5+2. The first number is the number of downlink timeslots and the second 4 3 1 4 is the number of uplink timeslots allocated for use by the mobile 5 2 2 4 station. A commonly used value is class 10 for many 6 3 2 4 GPRS/EGPRS mobiles which uses a maximum of 4 timeslots in downlink direction and 2 timeslots in uplink direction. However 7 3 3 4 simultaneously a maximum number of 5 simultaneous timeslots 8 4 1 5 can be used in both uplink and downlink. The network will 9 3 2 5 automatically configure the for either 3+2 or 4+1 operation depending on the nature of data transfer. 10 4 2 5

11 4 3 5 Some high end mobiles, usually also supporting UMTS also support GPRS/EDGE multislot class 32. According to 3GPP TS 12 4 4 5 45.002 (Release 6), Table B.2, mobile stations of this class 30 5 1 6 support 5 timeslots in downlink and 3 timeslots in uplink with a 31 5 2 6 maximum number of 6 simultaneously used timeslots. If data traffic is concentrated in downlink direction the network will 32 5 3 6 configure the connection for 5+1 operation. When more data is 33 5 4 6 transferred in the uplink the network can at any time change the 34 5 5 6 constellation to 4+2 or 3+3. Under the best reception conditions, [EDIT ] ATTRIBUTES OF A MULTISLOT CLASS operators. With these enhancements the active round-trip time can be reduced, resulting in significant increase in application- Each multislot class identifies the following: level throughput speeds.

• the maximum number of Timeslots that can be allocated FM BROADCASTING IN INDIA on uplink • the maximum number of Timeslots that can be allocated From Wikipedia, the free encyclopedia on downlink • the total number of timeslots which can be allocated by In the mid-nineties, when India first experimented with private the network to the mobile FM broadcasts, the small tourist destination of Goa was the • the time needed for the mobile phone to perform adjacent fifth place in this country of one billion where private players got cell signal level measurement and get ready to transmit FM slots. The other four centres were the big metro cities: Delhi, • the time needed for the MS to get ready to transmit Mumbai, Kolkata and Chennai. These were followed by stations in • the time needed for the MS to perform adjacent cell signal Bangalore, Hyderabad, Jaipur and Lucknow. level measurement and get ready to receive • the time needed for the MS to get ready to receive. Indian policy currently states that these broadcasters are assessed a One-Time Entry Fee (OTEF), for the entire license The different multislot class specification is detailed in the Annex period of 10 years. Under the Indian accounting system, this B of the 3GPP Technical Specification 45.002 (Multiplexing and amount is amortised over the 10 year period at 10% per annum. multiple access on the radio path) Annual license fee for private players is either 4% of revenue share or 10% of Reserve Price, whichever is higher. [EDIT ] USABILITY Earlier, India's attempts to privatise its FM channels ran into The maximum speed of a GPRS connection offered in 2003 was rough weather when private players bid heavily and most could similar to a modem connection in an analog wire telephone not meet their commitments to pay the government the amounts network, about 32-40 kbit/s, depending on the phone used. they owed. Latency is very high; round-trip time (RTT) is typically about 600- 700 ms and often reaches 1 s. GPRS is typically prioritized lower CONTENTS than speech, and thus the quality of connection varies greatly. • 1 Content Devices with latency/RTT improvements (via, for example, the • 2 FM stations in New Delhi extended UL TBF mode feature) are generally available. Also, • 3 FM stations in MUMBAI • 4 FM stations in Bangalore network upgrades of features are available with certain • 5 FM stations in chennai [EDIT ] FM STATIONS IN MUMBAI • 6 Market view • 7 List of FM radio Stations in India • Radio City 91.1 • Big FM 92.7 • 8 Current allocation process • Red FM 93.5 • Radio One 94.3 [EDIT ] CONTENT • Win FM 94.6 (The Station is closed) • Radio Mirchi 98.3 News in not permitted on private FM, although the Federal • AIR FM Gold 100.7 Minister for Information-Broadcasting (I. and B. Ministry, Govt. of • Fever 104 FM 104.0 India) says this may be reconsidered in two to three years. • Meow 104.8 Nationally, many of the current FM players, including the Times • AIR FM Rainbow 107.1 of India, Hindustan Times, Mid-Day, and BBC are essentially • Mumbai One newspaper chains or media, and they are already making a • Gyan Vani strong pitch for news on FM. • Radio MUST • Radio Jamia 90.4 FM [EDIT ] FM STATIONS IN NEW DELHI

[EDIT ] FM STATIONS IN BANGALORE • AIR FM Rainbow / FM-1 (107.1 MHz) • AIR FM Gold /FM-2 (Early Morning till Midnight) (106.4 MHz) Main article: List of FM radio stations in Bangalore • AIR Rajdhani/Gyanvani Channel (Non-Regular broadcast) (105.6 MHz) • Radio City 91.1 FM - Kannada • Meow FM (104.8 MHz) • Radio Indigo 91.9 FM - English • Fever 104 (104 MHz) • Big 92.7 FM - Kannada • Radio Mirchi FM (98.3 MHz) • Red FM 93.5 FM - Kannada • Hit FM (95 MHz) • Radio One FM (94.3 MHz) [EDIT ] FM STATIONS IN CHENNAI • Red FM (93.5 MHz) • Big FM (92.7 MHz) • AIR FM - RAINBOW • Radio City (91.1 MHz) • AIR FM - GOLD • Delhi University Educational Radio (Available only in • Hello FM (106.4), University area) (DU Radio FM) (90.4 MHz) • suryan FM , • Aaha FM, • Big FM , Antennas at a ham operator's station. • radio city FM , • radio mirchi FM , Amateur radio or ham radio is a hobby that is practised by over [1] • Radio-1 FM. 16,000 licenced users in India. Licences are granted by the Wireless and Planning and Coordination Wing (WPC), a branch of

[EDIT ] MARKET VIEW the Ministry of Communications and Information Technology. In addition, the WPC allocates frequency spectrum in India. The India's new private FM channels could also change the Indian Wireless Telegraphs (Amateur Service) Rules, 1978 lists [2] advertising scenario. Traditionally, radio accounts for 7% to 8% five licence categories: of advertiser expenditures around the world. In India, it is less To obtain a licence in the first four categories, candidates must than 2% at present.[citation needed] pass the Amateur Station Operator's Certificate examination conducted by the WPC. This exam is held monthly in Delhi, [EDIT ] LIST OF FM RADIO STATIONS IN INDIA Mumbai, Kolkata and Chennai, every two months in Ahmedabad, See also: List of FM radio stations in India Nagpur and Hyderabad, and every four months in some smaller cities.[3] The examination consists of two 50-mark written [EDIT ] CURRENT ALLOCATION PROCESS sections: Radio theory and practice, Regulations; and a practical test consisting of a demonstration of Morse code proficiency in [4] In FM Phase II — the latest round of the long-delayed opening up sending and receiving. After passing the examination, the of private FM in India — some 338 frequencies were offered of candidate must clear a police interview. After clearance, the WPC which about 237 were sold.[citation needed] The government may go grants the licence along with the user-chosen call sign. This [5] for rebidding of unsold frequencies quite soon. In Phase III of FM procedure can take up to one year. This licence is valid for up [6] licensing, smaller towns and cities will be opened up for FM radio. to five years.

Reliance and South Asia FM (Sun group) bid for most of the 91 Each licence category has certain privileges allotted to it, cities, although they were allowed only 15% of the total allocated including the allotment of frequencies, output power, and the frequencies. Between them, they have had to surrender over 40 emission modes. This article list the various frequencies allotted licenses. to various classes, and the corresponding emission modes and input DC power. LIST OF AMATEUR RADIO FREQUENCY BANDS IN INDIA CONTENTS

From Wikipedia, the free encyclopedia 14.350 • 1 Allotted spectrum • 18.068– 2 Emission designations 7 17 m HF • 3 Licence categories 18.168 o 3.1 Short Wave Listener 21.000– o 3.2 Grade II Restricted 7 15 m HF o 3.3 Grade II 21.450 o 3.4 Grade I 24.890– o 3.5 Advanced Grade 7 12 m HF 24.990 • 4 See also • 5 Notes 28.000– 7 10 m HF 29.700 • 6 References 8 144–146 2 m VHF

[EDIT ] ALLOTTED SPECTRUM 9 434–438 70 cm UHF

1260– The following table lists the frequencies that amateur radio 9 23 cm UHF 1300 operators in India can operate on. 3300– 10 9 cm SHF 3400 • Band refers to the International Telecommunication Union (ITU) radio band designation 5725– 10 5 cm SHF • Frequency is measured in megahertz 5840 • Wavelength is measured in metres and centimetres • Type refers to the radio frequency classification [EDIT ] EMISSION DESIGNATIONS Ban Frequenc Waveleng Typ d y (MHz) th e Main article: Types of radio emissions

1.820– 6 160 m MF The International Telecommunication Union uses an 1.860 internationally agreed system for classifying radio frequency 3.500– 7 80 m HF signals. Each Type of radio emission is classified according to its 3.700 bandwidth, method of modulation, nature of the modulating 3.890– 7 80 m HF signal, and Type of information transmitted on the carrier signal. 3.900 It is based on characteristics of the signal, not on the transmitter 7.000– used. 7 40 m HF 7.100

7 14.000– 20 m HF An emission designation is of the form BBBB 123 45, where • Electronic telegraphy, intended to be decoded by BBBB is the bandwidth of the signal, 1 is a letter indicating the machine (radio teletype and digital modes) Type of modulation used, 2 is a digit representing the Type of • Frequency modulation, • modulating signal, 3 is a letter corresponding to the Type of Single channel containing digital information, F2B using a subcarrier, information transmitted, 4 is a letter indicating the practical details of the transmitted information, and 5 is a letter that • Electronic telegraphy, intended to be decoded by machine (radio teletype and digital modes) represents the method of multiplexing. The 4 and 5 fields are • Frequency modulation, optional. For example, an emission designation would appear F3E • Single channel containing analogue information, read as 500H A3E, where 500H translates to 500 Hz, and A3E is • the emission mode as permitted. Telephony (audio) • Frequency modulation, F3C • Single channel containing analogue information, The WPC has authorized the following emission modes:[7] • Facsimile (still images) Emission Details • Single-sideband with full carrier, H3E • Single channel containing analogue information, • Single channel containing digital information, no subcarrier, A1A • Telephony (audio) • Single-sideband with suppressed carrier (e.g. • Aural telegraphy, intended to be decoded by ear, Shortwave utility and amateur stations), such as Morse code J3E • Single channel containing analogue information, • Single channel containing digital information, using a subcarrier, A2A • Telephony (audio) • Single-sideband with reduced or variable carrier, • Aural telegraphy, intended to be decoded by ear, • Single channel containing analogue information, such as Morse code R3E • Double-sideband amplitude modulation (AM • Telephony (audio) A3E radio),

• Single channel containing analogue information, [EDIT ] LICENCE CATEGORIES • Single channel containing analogue information, A3X • None of the other listed types of emission [EDIT] SHORT WAVE LISTENER • Single channel containing analogue information, A3F[nb 1] The Short Wave Listener's Amateur Wireless Telegraph Station • Video (television signals) • Frequency modulation , Licence allows listening on all amateur radio frequency bands, F1B • Single channel containing digital information, no but prohibits transmission. The minimum age is 12.[8] subcarrier, 1.820– A1A, A2A, A3E, H3E, J3E, [EDIT] GRADE II RESTRICTED 6 160 m MF 50 1.860[nb 4] R3E

3.500– A1A, A2A, A3E, H3E, J3E, The Restricted Amateur Wireless Telegraph Station Licence 7 80 m HF 50 3.700[nb 4] R3E licence requires a minimum score of 40% in each section of the written examination, and 50% overall.[9] The minimum age is 12 3.890– A1A, A2A, A3E, H3E, J3E, 7 80 m HF 50 years.[8] The licence allows a user to make terrestrial 3.900 R3E radiotelephony (voice) transmission in two VHF frequency bands. 7.000– A1A, A2A, A3E, H3E, J3E, 7 40 m HF 50 The maximum power allowed is 10 W.[2] 7.100 R3E 14.000– A1A, A2A, A3E, H3E, J3E, Ban Frequen Waveleng Typ Powe 7 20 m HF 50 Emission 14.350 R3E d cy (MHz) th e r (W) 18.068– 8 144–146 2 m VHF A3E, H3E, J3E, R3E, F3E 10[nb 2] A1A, A2A, A3E, H3E, J3E, 7 18.168[nb 17 m HF 50 5] R3E 434– 9 70 cm UHF A3E, H3E, J3E, R3E, F3E 10[nb 2] 438[nb 3] 21.000– A1A, A2A, A3E, H3E, J3E, 7 15 m HF 50 21.450 R3E

[EDIT] GRADE II 24.890– A1A, A2A, A3E, H3E, J3E, 7 12 m HF 50 24.990 R3E

The Amateur Wireless Telegraph Station Licence, Grade–II licence 28.000– A1A, A2A, A3E, H3E, J3E, 7 10 m HF 50 requires the same scores as the Grade II Restricted, and in 29.700 R3E addition a demonstration of proficiency in sending and receiving A1A, A2A, A3E, H3E, J3E, 8 144–146 2 m VHF 10[nb 2] Morse code at five words a minute.[9] The minimum age is 12 R3E years.[8] The licence allows the user to make radiotelegraphy 434– A1A, A2A, A3E, H3E, J3E, 9 70 cm UHF 10[nb 2] (Morse code) and radiotelephony transmission in 11 frequency 438[nb 3] R3E bands. The maximum power allowed is 50 W.

A Grade II licence holder can only be authorized the use of radio [EDIT] GRADE I telephony emission on frequency bands below 30 MHz on submission of proof that 100 contacts have been made with The Amateur Wireless Telegraph Station Licence, Grade–I other amateurs operators using CW (Morse code).[2] requires a minimum of 50% in each section of the written examination, and 55% overall, and a demonstration of Ban Frequen Waveleng Typ Powe Emission proficiency in sending and receiving Morse code at 12 words a d cy (MHz) th e r (W) minute.[9] The minimum age is 14 years.[8] The licence allows a user to make radiotelegraphy and radiotelephony transmission in A3X, A3F 14 frequency bands. The maximum power allowed is 150 W. In A1A, A2A, A3E, H3E, R3E, [nb 2] addition, satellite communication, facsimile, and television 8 144–146 2 m VHF J3E, F1B, F2B, F3E, F3C, 25 A3X, A3F modes are permitted.[2] A1A, A2A, A3E, H3E, R3E, 434– Ban Frequen Waveleng Typ Powe 9 70 cm UHF J3E, F1B, F2B, F3E, F3C, 25[nb 2] Emission 438[nb 3] d cy (MHz) th e r (W) A3X, A3F A1A, A2A, A3E, H3E, R3E, 1.820– 1260– A1A, A2A, A3E, H3E, R3E, 6 160 m MF J3E, F1B, F2B, F3E, F3C, 150 [nb 3] [nb 2] 1.860[nb 4] 9 1300 23 cm UHF J3E, F1B, F2B, F3E, F3C, 25 A3X, A3F [nb 6] A3X, A3F A1A, A2A, A3E, H3E, R3E, 3.500– A1A, A2A, A3E, H3E, R3E, 3300– [nb 2] 7 [nb 4] 80 m HF J3E, F1B, F2B, F3E, F3C, 150 10 9 cm SHF J3E, F1B, F2B, F3E, F3C, 25 3.700 3400[nb 3] A3X, A3F A3X, A3F

A1A, A2A, A3E, H3E, R3E, A1A, A2A, A3E, H3E, R3E, 3.890– 5725– 7 80 m HF J3E, F1B, F2A, F3E, F3C, 150 10 5 cm SHF J3E, F1B, F2B, F3E, F3C, 25[nb 2] 3.900 5840[nb 3] A3C, A3F A3X, A3F A1A, A2A, A3E, H3E, R3E, 7.000– 7 40 m HF J3E, F1B, F2B, F3E, F3C, 150 7.100 A3X, A3F [EDIT] ADVANCED GRADE

A1A, A2A, A3E, H3E, R3E, 14.000– The Advanced Amateur Wireless Telegraph Station Licence is the 7 20 m HF J3E, F1B, F2B, F3E, F3C, 150 14.350 A3X, A3F highest licence category. To obtain the licence, an applicant must be 18 years of age.[8] pass an advanced electronics 18.068– A1A, A2A, A3E, H3E, R3E, 7 18.168[nb 17 m HF J3E, F1B, F2B, F3E, F3C, 150 examination, along with the Rules and Regulations section and 5] A3X, A3F Morse code sending and receiving at 12 words per minute.[9] The maximum power permitted is 400 W in selected sub-bands.[2] A1A, A2A, A3E, H3E, R3E, 21.000– 7 15 m HF J3E, F1B, F2B, F3E, F3C, 150 21.450 Ban Frequen Waveleng Typ Powe A3X, A3F Emission d cy (MHz) th e r (W) A1A, A2A, A3E, H3E, R3E, 24.890– A1A, A2A, A3E, H3E, R3E, 7 12 m HF J3E, F1B, F2B, F3E, F3C, 150 1.820– 24.990 6 160 m MF J3E, F1B, F2B, F3E, F3C, 150 A3X, A3F 1.860[nb 4] A3X, A3F 7 28.000– 10 m HF A1A, A2A, A3E, H3E, R3E, 150 29.700 J3E, F1B, F2B, F3E, F3C, 7 3.500– 80 m HF A1A, A2A, A3E, H3E, R3E, 150 3.700[nb 4] J3E, F1B, F2B, F3E, F3C, A3X, A3F A1A, A2A, A3E, H3E, R3E, 5725– [nb 2] 10 [nb 3] 5 cm SHF J3E, F1B, F2B, F3E, F3C, 25 A1A, A2A, A3E, H3E, R3E, 5840 3.890– A3X, A3F 7 80 m HF J3E, F1B, F2B, F3E, F3C, 150 3.900 A3X, A3F 400 W sub-bands A1A, A2A, A3E, H3E, R3E, 7.000– Ban Frequen Waveleng Typ Powe 7 40 m HF J3E, F1B, F2B, F3E, F3C, 150 Emission 7.100 d cy (MHz) th e r (W) A3X, A3F A1A, A2A, A3E, H3E, R3E, A1A, A2A, A3E, H3E, R3E, 3.520– 14.000– 7 [nb 4] 80 m HF J3E, F1B, F2B, F3E, F3C, 400 7 20 m HF J3E, F1B, F2B, F3E, F3C, 150 3.540 14.350 A3X, A3F A3X, A3F A1A, A2A, A3E, H3E, R3E, 3.890– 18.068– A1A, A2A, A3E, H3E, R3E, 7 80 m HF J3E, F1B, F2B, F3E, F3C, 400 [nb 3.900 7 18.168 17 m HF J3E, F1B, F2B, F3E, F3C, 150 A3X, A3F 5] A3X, A3F A1A, A2A, A3E, H3E, R3E, A1A, A2A, A3E, H3E, R3E, 7.050– 21.000– 7 40 m HF J3E, F1B, F2B, F3E, F3C, 400 7 15 m HF J3E, F1B, F2B, F3E, F3C, 150 7.100 21.450 A3X, A3F A3X, A3F A1A, A2A, A3E, H3E, R3E, A1A, A2A, A3E, H3E, R3E, 14.050– 24.890– 7 20 m HF J3E, F1B, F2B, F3E, F3C, 400 7 12 m HF J3E, F1B, F2B, F3E, F3C, 150 14.150 24.990 A3X, A3F A3X, A3F A1A, A2A, A3E, H3E, R3E, A1A, A2A, A3E, H3E, R3E, 14.220– 28.000– 7 20 m HF J3E, F1B, F2B, F3E, F3C, 400 7 10 m HF J3E, F1B, F2B, F3E, F3C, 150 14.320 29.700 A3X, A3F A3X, A3F A1A, A2A, A3E, H3E, R3E, 21.100– A1A, A2A, A3E, H3E, R3E, 7 15 m HF J3E, F1B, F2B, F3E, F3C, 400 21.400 8 144–146 2 m VHF J3E, F1B, F2B, F3E, F3C, 50 A3X, A3F A3X, A3F

A1A, A2A, A3E, H3E, R3E, 434– 9 70 cm UHF J3E, F1B, F2B, F3E, F3C, 25[nb 2] 438[nb 3] A3X, A3F

1260– A1A, A2A, A3E, H3E, R3E, 9 1300[nb 3] 23 cm UHF J3E, F1B, F2B, F3E, F3C, 25[nb 2] [nb 6] A3X, A3F

3300– A1A, A2A, A3E, H3E, R3E, 10 9 cm SHF 25[nb 2] 3400[nb 3] J3E, F1B, F2B, F3E, F3C, A3X, A3F