International Journal of Research (IJR) e-ISSN: 2348-6848, p- ISSN: 2348-795X Volume 2, Issue 4, April 2015 Available at http://internationaljournalofresearch.org

Modulation of Signals Akshay dutt (16195); Anosh Justin (16199) & Gautam saini (16211) Department of ECE Dronacharya College of Engineering Khentawas, Farrukh Nagar-123506 Gurgaon, Haryana Email- [email protected] ABSTRACT This paper addresses the technique of rapidly A (from modulator–demodulator) can updating the weights of an adaptive filter to perform both operations. cancel non-stationary interference. This method The aim of digital is to transfer is used, for example, in radar systems that a digital bit stream over an receive coherent multipath interference, known analog bandpass channel, for example over as "hot clutter" or "terrain scattered jamming". the public switched telephone network (where We develop a framework for understanding how a bandpass filter limits the frequency range to this rapid weight updating (inadvertently) 300–3400 Hz), or over a limited radio frequency modulates signals. Two principal types band. of modulation are studied: random induced by finite-length The aim of analog modulation is to transfer training sets and non- an analog baseband (or lowpass) signal, for randommodulations induced by the coherence of example an audio signal or TV signal, over an the interference. Our framework is then used to analog bandpass channel at a different frequency, assess the impact of these modulations on the for example over a limited radio frequency band overall performance of various well-known or a cable TV network channel. jammer multipath mitigation algorithms. Several Analog and digital modulation techniques for controlling this modulation are facilitate frequency division (FDM), proposed. where several low pass information signals are

transferred simultaneously over the same shared physical medium, using separate KEYWORDS channels (several different carrier frequencies). modulation; signal modulation; pulse modulation; bandwidth; carrier signal The aim of digital baseband modulation methods, also known as line coding, is to transfer a digital bit stream over a baseband INTRODUCTION channel, typically a non-filtered copper wire such In electronics and , modulati as a serial bus or a wired local area network. on is the process of varying one or more The aim of pulse modulation methods is to properties of a periodic waveform, called transfer a narrowband analog signal, for example the carrier signal, with a modulating signal that a phone call over a wideband baseband channel typically contains information to be transmitted. or, in some of the schemes, as a bit stream over another digital transmission system. In telecommunications, modulation is the process of conveying a message signal, for example a In music synthesizers, modulation may be used to digital bit stream or an analog audio signal, inside synthesise waveforms with an extensive overtone another signal that can be physically transmitted. spectrum using a small number of oscillators. In Modulation of a sine waveform transforms this case the carrier frequency is typically in the a baseband message signal into a passband signal. same order or much lower than the modulating waveform. See for example frequency A modulator is a device that performs modulation synthesis or ring modulation modulation. synthesis A demodulator (sometimes or demod) is a device that performsdemodulation, the inverse of modulation.

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International Journal of Research (IJR) e-ISSN: 2348-6848, p- ISSN: 2348-795X Volume 2, Issue 4, April 2015 Available at http://internationaljournalofresearch.org

carrier signal are chosen from a finite number of ANALOG MODULATION M alternative symbols (themodulation alphabet). METHODS In analog modulation, the modulation is applied continuously in response to the analog information signal. Common analog modulation techniques are:

(AM) (here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal) Schematic of 4 baud (8 bit/s) data link containing  Double-sideband modulation (DSB) arbitrarily chosen values.  Double-sideband modulation with A simple example: A telephone line is designed carrier (DSB-WC) (used on the AM for transferring audible sounds, for example radio broadcasting band) tones, and not digital bits (zeros and ones).  Double-sideband suppressed-carrier Computers may however communicate over a transmission (DSB-SC) telephone line by means of , which are  Double-sideband reduced carrier representing the digital bits by tones, called transmission (DSB-RC) symbols. If there are four alternative symbols  Single-sideband modulation (SSB, or (corresponding to a musical instrument that can SSB-AM) generate four different tones, one at a time), the  SSB with carrier (SSB-WC) first symbol may represent the bit sequence 00,  SSB suppressed carrier modulation the second 01, the third 10 and the fourth 11. If (SSB-SC) the modem plays a melody consisting of 1000  Vestigial sideband modulation (VSB, or tones per second, the is 1000 VSB-AM) symbols/second, or baud. Since each tone (i.e.,  Quadrature amplitude symbol) represents a message consisting of two modulation (QAM) digital bits in this example, the bit rate is twice the symbol rate, i.e. 2000 bits per second. This is  , which is similar to the technique used by dialup modems approximately constant envelope as opposed to DSL modems.  (FM) (here the According to one definition of digital signal, the frequency of the carrier signal is varied modulated signal is a digital signal, and in accordance to the instantaneous according to another definition, the modulation is amplitude of the modulating signal) a form of digital-to-analog conversion. Most  (PM) (here the phase textbooks would consider digital modulation shift of the carrier signal is varied in schemes as a form of digital transmission, accordance with the instantaneous synonymous to data transmission; very few amplitude of the modulating signal) would consider it as analog transmission. DIGITAL MODULATION FUNDAMENTAL METHODS DIGITAL MODULATION In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital METHODS modulation methods can be considered as digital- The most fundamental digital modulation to-analog conversion, and the techniques are based on keying: corresponding or detection as analog-to-digital conversion. The changes in the  PSK (phase-shift keying): a finite number of phases are used.

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International Journal of Research (IJR) e-ISSN: 2348-6848, p- ISSN: 2348-795X Volume 2, Issue 4, April 2015 Available at http://internationaljournalofresearch.org

 FSK (frequency-shift keying): a finite called equivalent lowpass signal or equivalent number of frequencies are used. baseband signal is a complex-valued  ASK (amplitude-shift keying): a finite representation of the real-valued modulated number of amplitudes are used. physical signal (the so-called passband  QAM (quadrature amplitude modulation): a signal or RF signal). finite number of at least two phases and at These are the general steps used by least two amplitudes are used. the modulator to transmit data: In QAM, an inphase signal (or I, with one example being a cosine waveform) and a 1. Group the incoming data bits into quadrature phase signal (or Q, with an example codewords, one for each symbol that will being a sine wave) are amplitude modulated with be transmitted. a finite number of amplitudes, and then summed. 2. Map the codewords to attributes, for It can be seen as a two-channel system, each example amplitudes of the I and Q channel using ASK. The resulting signal is signals (the equivalent low pass signal), equivalent to a combination of PSK and ASK. or frequency or phase values. In all of the above methods, each of these phases, 3. Adapt pulse shaping or some other frequencies or amplitudes are assigned a unique filtering to limit the bandwidth and form pattern of binary bits. Usually, each phase, the spectrum of the equivalent low pass frequency or amplitude encodes an equal number signal, typically using digital signal of bits. This number of bits comprises processing. the symbol that is represented by the particular 4. Perform digital to analog conversion phase, frequency or amplitude. (DAC) of the I and Q signals (since today all of the above is normally If the alphabet consists of alternative achieved using digital signal processing, symbols, each symbol represents a message DSP). consisting of N bits. If the symbol rate (also 5. Generate a high frequency sine carrier known as the baud rate) is symbols/second waveform, and perhaps also a cosine (or baud), the data rate is bit/second. quadrature component. Carry out the modulation, for example by multiplying For example, with an alphabet consisting of 16 the sine and cosine waveform with the I alternative symbols, each symbol represents 4 and Q signals, resulting in the equivalent bits. Thus, the data rate is four times the baud low pass signal being frequency shifted rate. to the modulated pass band signal or RF In the case of PSK, ASK or QAM, where the signal. Sometimes this is achieved using carrier frequency of the modulated signal is DSP technology, for example direct constant, the modulation alphabet is often digital synthesis using a waveform table, conveniently represented on a constellation instead of analog signal processing. In diagram, showing the amplitude of the I signal at that case the above DAC step should be the x-axis, and the amplitude of the Q signal at done after this step. the y-axis, for each symbol. 6. Amplification and analog band pass filtering to avoid harmonic distortion and MODULATOR AND periodic spectrum DETECTOR PRINCIPLES At the receiver side, the demodulator typically performs: OF OPERATION PSK and ASK, and sometimes also FSK, are 1. Band pass filtering. often generated and detected using the principle 2. Automatic gain control, AGC (to of QAM. The I and Q signals can be combined compensate for attenuation, for into a complex-valued signal I+jQ (where j is example fading). the imaginary unit). The resulting so

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International Journal of Research (IJR) e-ISSN: 2348-6848, p- ISSN: 2348-795X Volume 2, Issue 4, April 2015 Available at http://internationaljournalofresearch.org

3. Frequency shifting of the RF signal to the equivalent baseband I and Q signals, or LIST OF COMMON to an intermediate frequency (IF) signal, DIGITAL MODULATION by multiplying the RF signal with a local oscillator sine wave and cosine wave TECHNIQUES frequency (see the super The most common digital modulation techniques heterodyne principle). are: 4. Sampling and analog-to-digital conversion (ADC) (Sometimes before or  Phase-shift keying (PSK): instead of the above point, for example  Binary PSK (BPSK), using M=2 by means of under sampling). symbols 5. Equalization filtering, for example  Quadrature PSK (QPSK), using M=4 a matched filter, compensation for symbols multipath propagation, time spreading,  8PSK, using M=8 symbols phase distortion and frequency selective  16PSK, using M=16 symbols fading, to avoidintersymbol  Differential PSK (DPSK) interference and symbol distortion.  Differential QPSK (DQPSK)

6. Detection of the amplitudes of the I and  Offset QPSK (OQPSK) Q signals, or the frequency or phase of  π/4–QPSK the IF signal.  Frequency-shift keying (FSK): 7. Quantization of the amplitudes, frequencies or phases to the nearest  Audio frequency-shift keying (AFSK) allowed symbol values.  Multi-frequency shift keying (M-ary 8. Mapping of the quantized amplitudes, FSK or MFSK) frequencies or phases to codewords (bit  Dual-tone multi-frequency (DTMF) groups).  Amplitude-shift keying (ASK) 9. Parallel-to-serial conversion of the  On-off keying (OOK), the most common codewords into a bit stream. ASK form 10. Pass the resultant bit stream on for  M-ary vestigial sideband modulation, for further processing such as removal of example 8VSB any error-correcting codes.  Quadrature amplitude modulation (QAM) - a combination of PSK and ASK:

like QAM a As is common to all digital communication combination of PSK and ASK.[citation systems, the design of both the modulator and needed] demodulator must be done simultaneously. Digital modulation schemes are possible because  Continuous phase modulation (CPM) the transmitter-receiver pair have prior methods: knowledge of how data is encoded and  Minimum-shift keying (MSK) represented in the communications system. In all  Gaussian minimum-shift digital communication systems, both the keying (GMSK) modulator at the transmitter and the demodulator  Continuous-phase frequency-shift at the receiver are structured so that they perform keying (CPFSK) inverse operations.  Orthogonal frequency-division multiplexing (OFDM) modulation: Non-coherent modulation methods do not require a receiver reference clock signal that is phase  Discrete multitone (DMT) - including synchronized with the sender carrier wave. In this adaptive modulation and bit-loading. case, modulation symbols (rather than bits,  characters, or data packets)  Trellis coded modulation (TCM), also known are asynchronously transferred. The opposite as trellis modulation is coherent modulation.  Spread-spectrum techniques:

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International Journal of Research (IJR) e-ISSN: 2348-6848, p- ISSN: 2348-795X Volume 2, Issue 4, April 2015 Available at http://internationaljournalofresearch.org

 Direct-sequence spread waveforms, and sometimes QAM demodulators spectrum (DSSS) are used to receive the signals put out by these  Chirp (CSS) according switching amplifiers. to IEEE 802.15.4a CSS uses pseudo- stochastic coding AUTOMATIC DIGITAL  Frequency-hopping spread spectrum (FHSS) applies a special MODULATION scheme for channel release RECOGNITION (ADMR)  SIM31 (SIM) New digital Mode SIM31 Automatic digital modulation recognition in SIM63 takes SWL Tunisian intelligent communication systems is one of the MSK and GMSK are particular cases of most important issues in software defined continuous phase modulation. Indeed, MSK is a radio and cognitive radio. According to particular case of the sub-family of CPM known incremental expanse of intelligent receivers, as continuous-phase frequency-shift automatic modulation recognition becomes a keying (CPFSK) which is defined by a challenging topic in systems rectangular frequency pulse (i.e. a linearly and computer engineering. Such systems have increasing phase pulse) of one symbol-time many civil and military applications. Moreover, duration (total response signalling). blind recognition of modulation type is an important problem in commercial systems, OFDM is based on the idea of frequency-division especially in software defined radio. Usually in multiplexing (FDM), but the multiplexed streams such systems, there are some extra information are all parts of a single original stream. The bit for system configuration, but considering blind stream is split into several parallel data streams, approaches in intelligent receivers, we can reduce each transferred over its own sub-carrier using information overload and increase transmission some conventional digital modulation scheme. performance.[1] Obviously, with no knowledge of The modulated sub-carriers are summed to form the transmitted data and many unknown an OFDM signal. This dividing and recombining parameters at the receiver, such as the signal helps with handling channel impairments. OFDM power, carrier frequency and phase offsets, is considered as a modulation technique rather timing information, etc., blind identification of than a multiplex technique, since it transfers one the modulation is a difficult task. This becomes bit stream over one communication channel using even more challenging in real-world scenarios one sequence of so-called OFDM symbols. with multipath fading, frequency-selective and OFDM can be extended to multi-user channel time-varying channels.[2] access method in theorthogonal frequency- division multiple access (OFDMA) and multi- There are two main approaches to automatic carrier code division multiple access (MC- modulation recognition. The first approach uses CDMA) schemes, allowing several users to share likelihood-based methods to assign an input the same physical medium by giving different signal to a proper class. Another recent approach sub-carriers or spreading codes to different users. is based on feature extraction. Of the two kinds of RF power PULSE MODULATION amplifier, switching amplifiers (Class D amplifiers) cost less and use less battery power METHODS than linear amplifiers of the same output power. Pulse modulation schemes aim at transferring a However, they only work with relatively narrowband analog signal over an analog constant-amplitude-modulation signals such as baseband channel as a two-level signal by angle modulation (FSK or PSK) and CDMA, but modulating a pulse wave. Some pulse modulation not with QAM and OFDM. Nevertheless, even schemes also allow the narrowband analog signal though switching amplifiers are completely to be transferred as a digital signal (i.e. as unsuitable for normal QAM constellations, often a quantized discrete-time signal) with a fixed bit the QAM modulation principle are used to drive rate, which can be transferred over an underlying switching amplifiers with these FM and other digital transmission system, for example

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International Journal of Research (IJR) e-ISSN: 2348-6848, p- ISSN: 2348-795X Volume 2, Issue 4, April 2015 Available at http://internationaljournalofresearch.org some . These are not modulation schemes in the conventional sense since they are .Adaptive DPCM (ADPCM) not channel coding schemes, but should be considered as source coding schemes, and in some cases analog-to-digital conversion techniques. REFRENCES Analog-over-analog methods: [1.] M. Hadi Valipour, M. Mehdi  Delta modulation (DM or Δ-modulation) Homayounpour and M. Amin  Delta-sigma modulation (∑Δ) Mehralian, Automatic digital modulation recognition in presence of noise using  Continuously variable slope delta SVM and PSO, in Proceedings of 2012 modulation (CVSDM), also Sixth International Symposium on called Adaptive-delta modulation (ADM) Telecommunications (IST), pp. 378-382,  Pulse-density modulation (PDM) Nov 2012, Tehran, Iran.  Pulse-amplitude modulation (PAM)  Pulse-width modulation (PWM) AND Pulse- [2.] Dobre, Octavia A., Ali Abdi, Yeheskel depth modulation (PDM) Bar-Ness, and Wei Su. Communications,  Pulse-position modulation (PPM) IET 1, no. 2 (2007): 137-156. (2007). "Survey of automatic modulation Analog-over-digital methods: classification techniques: classical approaches and new trends" (PDF). IET Communications: 137–156.3.Ke-Lin Du and M. N. S. Swamy (2010). Wireless .Pulse-code modulation (PCM) Communication Systems: From RF Subsystems to 4G Enabling .Differential PCM (DPCM) Technologies. Cambridge University Press. p. 188. ISBN 978-0-521-11403-5.

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