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Telematics Chapter 3: Physical Layer Telematics User Server watching with video Chapter 3: Physical Layer video clip clips Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Data Link Layer Data Link Layer Data Link Layer Physical Layer Physical Layer Physical Layer Univ.-Prof. Dr.-Ing. Jochen H. Schiller Computer Systems and Telematics (CST) Institute of Computer Science Freie Universität Berlin http://cst.mi.fu-berlin.de Contents ● Design Issues ● Theoretical Basis for Data Communication ● Analog Data and Digital Signals ● Data Encoding ● Transmission Media ● Guided Transmission Media ● Wireless Transmission (see Mobile Communications) ● The Last Mile Problem ● Multiplexing ● Integrated Services Digital Network (ISDN) ● Digital Subscriber Line (DSL) ● Mobile Telephone System Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.2 Design Issues Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.3 Design Issues ● Connection parameters ● mechanical OSI Reference Model ● electric and electronic Application Layer ● functional and procedural Presentation Layer ● More detailed ● Physical transmission medium (copper cable, Session Layer optical fiber, radio, ...) ● Pin usage in network connectors Transport Layer ● Representation of raw bits (code, voltage,…) Network Layer ● Data rate ● Control of bit flow: Data Link Layer ● serial or parallel transmission of bits Physical Layer ● synchronous or asynchronous transmission ● simplex, half-duplex, or full-duplex transmission mode Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.4 Design Issues Transmitter Receiver Source Transmission System Destination NIC NIC Input Abcdef djasdja dak jd ashda kshd akjsd asdkjhasjd as kdjh askjda Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.5 Theoretical Basis of Data Communication Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.6 Signal Parameters ● The variable physical property of the signal which represent the data ● Spatial signals ● The values are functions of the space, i.e., memory space ● Time signals ● The values are functions of the time, i.e., S = S(t) ● Classification of signals (based on time and value space) ● Continuous-time, continuous-valued signals ● Discrete-time, continuous-valued signals ● Continuous-time, discrete-valued signals ● Discrete-time, discrete-valued signals Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.7 Types of Signals Time Continuous Discrete S(t) S(t) Analog Signal t t Continuous Value S(t) S(t) Digital Signal t t Discrete Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.8 Periodic and Digital Signals ● Periodic signals are the simplest S(t) signals S(t T) S(t) t ● Parameters of periodic signals: t ● Period T ● Frequency f =1/T T ● Amplitude S(t) S(t) ● Phase j t ● Examples: j ● Sine wave 2p ● Phase difference j S(t) ● Square wave t T Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.9 Composite Signals T1 Component with low frequency t (fix amplitude) Tn Component with high frequency t (fix amplitude) Composite voice signal with mixed frequencies and amplitudes. t Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.10 Composite Signals sin(2pft) ● A signal is made up of many frequencies 1 ● Example: s (t) sin(2pft) sin(2p (3 f )t) 3 ● Components of the signal are sine waves of frequencies f and 3f 1 sin(2p (3 f )t) ● Observations 3 ● Second frequency is multiple of the first one, which is denoted fundamental frequency ● The period of the composite signal is equal to the period of the 1 fundamental frequency sin(2pft) sin(2p (3 f )t) 3 Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.11 Composite Signals: Domain Concepts ● Frequency Domain Time Domain ● Specifies the constituent frequencies ● Spectrum of a signal is the range of frequencies it contains ● In the example from f to 3f ● The absolute bandwidth of the signal is the width of the spectrum Frequency Domain ● In the example 2f ● Many signals have infinite bandwidth ● Effective bandwidth ● Most energy is contained on a narrow band of frequencies Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.12 Composite Signals: Medium ● What can a medium transport? Attenuation (dB) ● A medium transports always a limited frequency-band. 1 Cutoff Frequencies 0 ● Bandwidth -1 ● Bandwidth in Hz [1/s] -2 ● Frequency range which can be transmitted over a medium -3 ● Bandwidth is the difference of the -4 highest and lowest frequency which Bandwidth -5 can be transmitted ● The cutoff is typically not sharp 0 1 2 3 4 Frequency (kHz) Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.13 Composite Signals ● Relationship between data rate 1 0 1 0 and bandwidth ● Square wave ● positive pulse 1-bit ● negative pulse 0-bit ● Duration of a pulse is ½ f ● Data rate is 2f bits per second Data 1 Data 2 ● Question ● What are the frequency components? Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.14 Composite Signals ● Relationship between data rate and bandwidth ● Signal made of: f, 3f, and 5f 1 1 sin( 2pft) sin(2p3 ft) sin(2p5 ft) 3 5 ● Signal made of: f, 3f, 5f, and 7f 1 1 1 sin( 2pft) sin(2p3 ft) sin(2p5 ft) sin(2p 7 ft) 3 5 7 ● Square waves can be expressed as 4 1 s(t) A sin(2pkft) p k k1,k odd 1 0 1 0 ● Infinite number of components ● Amplitude of the k-th component is only 1/k ● What happens if k is limited? Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.15 Effect of Bandwidth on a Digital Signal Bits: 0 1 0 0 0 0 1 0 0 0 Ideal, requires infinite Bit rate 2000 bps 1/400 s bandwidth! Bandwidth 500 Hz 1. Harmonic Bandwidth 900 Hz 1.+2. Harmonics Bandwidth 1300 Hz 1.-3. Harmonics Bandwidth 1700 Hz 1.-4. Harmonics Bandwidth 2500 Hz 1.-5. Harmonics t Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.16 Composite Signals ● Relationship between data rate and bandwidth ● Example 1 1 0 ● f = 106 Hz = 1 MHz ● The fundamental frequency ● Bandwidth of the signal s(t) (5×106 Hz) – (1×106 Hz) = 4 MHz ● T = 1/f = 1/106s = 10-6s = 1µs ● 1 bit occurs every 0.5µs 1 1 Data rate = 2 bit × 106 Hz = 2 Mbps s(t) sin(2pft) sin(2p3 ft) sin(2p5 ft) 3 5 ● Example 2 ● f = 2 MHz ● Bandwidth (5×2MHz) – (1×2MHz) = 8 MHz ● T = 1/f = 0.5µs ● 1 bit occurs every 0.25µs Data rate = 2 bit × 2 MHz = 4 Mbps Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.17 Symbol Rate 1 2 3 4 5 6 7 8 S(t) t T Takt Example: 1s Symbol rate 5 baud [1/s] Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.18 Binary and Multilevel Digital Signals ● Binary digital signal ● A digital signal with two possible values, e.g., 0 and 1 ● Multilevel digital signal ● A digital signal with more than two possible values, e.g., DIBIT = two bits per coordinate value (quaternary signal element) ● The number of discrete values which a signal may have are denoted as follows ● n = 2 binary ● n = 3 ternary ● n = 4 quaternary ● ... ● n = 8 octonary ● n = 10 denary Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.19 Multilevel Digital Signal Signal steps (amplitude value) 11 +2 10 +1 t 01 -1 00 -2 Quaternary 01 10 11 00 01 01 10 00 00 00 01 00 00 code Time 1 2 3 4 5 6 7 8 9 10 11 12 13 Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.20 Symbol rate vs. Data rate ● Symbol rate v (modulation rate, digit rate) ● The number of symbol changes (signaling events) made to the transmission medium per second ● Unit 1/s = baud (abbrv. bd) ● Data rate (Unit bps, bit/s) ● For binary signals Data rate [bps] = v [baud] ● Each signaling event codes one bit ● For multilevel signals (n possible values) Data rate [bps] = v × ld(n) ● DIBIT 1 baud = 2 bps (quaternary signal) ● TRIBIT 1 baud = 3 bps (octonary signal) Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 3: Physical Layer 3.21 Units of Bit Rates Name of bit rate Symbol Multiple Explicit Bit per second bps 100 1 Kilobit per second kbps 103 1,000 Megabit per second Mbps 106 1,000,000 Gigabit per second Gbps 109 1,000,000,000 Terabit per second Tbps 1012 1,000,000,000,000 Petabit per second Pbps 1015 1,000,000,000,000,000 Do not confuse with binary prefixes ● 1 byte = 8 bit (also called octet in telco standards) ● today 8 bit, term coined in 1956 by Werner Buchholz, in general a unit of digital data to describe a group of bits as the smallest amount of data that a processor could process ● 1 kbyte = 210 byte = 1024 byte In this case kilo = 1024 ● Typically 2x in storage technology, 10x in transmission technology Univ.-Prof.
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