Signal Encoding TechniquesSlide 2Coding TerminologyCoding DesignClock Recovery CircuitDigital Signal Encoding FormatsMulti-level Binary EncodingBi-phaseScramblingSignal SpectrumDigital Data Analog SignalsFrequency Shift Keying (FSK)Phase-Shift Keying (PSK)Multi-level PSKQAMAnalog Data, Digital SignalsNonlinear EncodingCompandingDelta ModulationAnalog Data, Analog SignalsSummaryReading AssignmentHomeworkSolution to Chapter 5 HomeworkChapter 3 Homework: Grading5-1©2005 Raj JainCSE473sWashington University in St. LouisSignal Encoding Signal Encoding TechniquesTechniquesRaj Jain Washington UniversitySaint Louis, MO [email protected] slides are available on-line at:http://www.cse.wustl.edu/~jain/cse473-05/5-2©2005 Raj JainCSE473sWashington University in St. Louis1. Coding Terminology and Design issues2. Digital Data, Digital Signal: AMI, Manchester, etc.3. Digital Data, Analog Signals: ASK, FSK, PSK, QAM4. Analog Data, Digital Signals: PCM, Companding5. Analog Data, Analog Signals: AM, FMOverview5-3©2005 Raj JainCSE473sWashington University in St. LouisCoding TerminologyCoding TerminologySignal element: Pulse (of constant amplitude, frequency, phase)Unipolar: All positive or All negative voltageBipolar: Positive and negative voltageMark/Space: 1 or 0Modulation Rate: 1/Duration of the smallest element =Baud rateData Rate: Bits per secondData Rate = Fn(Bandwidth, signal/noise ratio, encoding)PulseBit+5V0-5V+5V0-5V5-4©2005 Raj JainCSE473sWashington University in St. LouisCoding DesignCoding Design1. Pulse width indeterminate: Clocking2. DC, Baseline wander3. No line state information4. No error detection/protection5. No control signals6. High data rate7. Polarity mix-up  Differential (compare polarity)0 1 0 0 0 1 1 1 0 0 0 0 0ManchesterNRZIClockNRZBits+5V0-5V5-5©2005 Raj JainCSE473sWashington University in St. LouisClock Recovery CircuitClock Recovery CircuitSquarerReceivedSignalClocktd/dtPre FilterPhase LockLoopttt5-6©2005 Raj JainCSE473sWashington University in St. LouisDigital Signal Encoding FormatsDigital Signal Encoding FormatsReturn-to-Zero (RZ)0 = Remain at zero, 1 = +ve for ½ bit durationNonreturn-to-Zero-Level (NRZ-L)0 = high level, 1 = low levelNonreturn to Zero Inverted (NRZI)0 = no transition at beginning of interval (bit time)1 = transition at beginning of interval RZ5-7©2005 Raj JainCSE473sWashington University in St. LouisMulti-level Binary EncodingMulti-level Binary EncodingBipolar-AMI:0 = no line signal1= +ve or -ve for successive 1’sPseudo-ternary:0 = +ve or -ve for successive 0’s1= no line signalNo advantage over AMI1. No loss of sync with 1’s2. zeros are a problem3. No net dc component4. Error detectionNoise  violation5. Two bits/Hz6. 3 dB higher S/N7. 2b/Hz. Not 3.16 b/Hz5-8©2005 Raj JainCSE473sWashington University in St. LouisBi-phaseBi-phaseManchester: Used in Ethernet0 = High to low transition in middle 1 = Low to high transition in middle Differential Manchester: Used in Token RingAlways a transition in middle 0 = transition at beginning 1= no transition at beginning 1. No DC2. Clock sync3. Error detection4. 1 bit/Hz, 5. baud rate = 2  bit rate5-9©2005 Raj JainCSE473sWashington University in St. LouisScramblingScramblingBipolar with 8-Zero Substitution (B8ZS): Same as AMI, except eight 0’s replaced w two code violations0000 0000 = 000V 10V1High Density Bi-polar w 3 Zeros (HDB3): Same as AMI, except that four 0’s replaced with one code violation0000 = 000V if odd number of ones since last substitution 100V otherwise5-10©2005 Raj JainCSE473sWashington University in St. LouisSignal SpectrumSignal Spectrum5-11©2005 Raj JainCSE473sWashington University in St. LouisDigital Data Analog SignalsDigital Data Analog SignalsA Sin(2ft+)ASKFSKPSKUsed in 300-1200 bps modemsUsed in Optical Nets5-12©2005 Raj JainCSE473sWashington University in St. LouisFrequency Shift Keying (FSK)Frequency Shift Keying (FSK)Less susceptible to errors than ASKUsed in 300-1200 bps on voice grade lines1170±100 2125±1005-13©2005 Raj JainCSE473sWashington University in St. LouisPhase-Shift Keying (PSK)Phase-Shift Keying (PSK)Differential PSK: 0 = Same phase, 1=Opposite phaseA cos(2ft), A cos(2ft+) Quadrature PSK (QPSK): Two bits11=A cos(2ft+45°), 10=A cos(2ft+135°), 00=A cos(2ft+225°), 01=A cos(2ft+315°)Sum of two signals 90° apart in phase (In-phase I , Quadrature Q), Up to 180° phase difference between successive intervalsOrthogonal QPSK (OQPSK): Q stream delayed by 1 bitPhase difference between successive bits limited to 90° 111000 01015-14©2005 Raj JainCSE473sWashington University in St. LouisMulti-level PSKMulti-level PSK9600 bps Modems use PSK with 4 bits4 bits  16 combinations4 bits/element  1200 baud12 Phases, 4 with two amplitudes5-15©2005 Raj JainCSE473sWashington University in St. LouisQAMQAMQuadrature Amplitude and Phase ModulationQAM-4, QAM-16, QAM-64, QAM-256Used in DSL and wireless networksBinary QAM-401100001 11QAM-16IQIQIQ5-16©2005 Raj JainCSE473sWashington University in St. LouisAnalog Data, Digital SignalsAnalog Data, Digital SignalsSampling Theorem: 2  Highest Signal Frequency4 kHz voice = 8 kHz sampling rate8 k samples/sec  8 bits/sample = 64 kbpsQuantizing Error with n bits: S/N = 6.02n +1.76 dB5-17©2005 Raj JainCSE473sWashington University in St. LouisNonlinear EncodingNonlinear EncodingLinear: Same absolute error for all signal levelsNon-linear: More steps for low signal levels5-18©2005 Raj JainCSE473sWashington University in St. LouisCompandingCompandingReduce the intensity range by amplifying weak signals more than the strong signals inputOpposite is done at output5-19©2005 Raj JainCSE473sWashington University in St. LouisDelta ModulationDelta Modulation1 = Signal up one step, 0 = Signal down one stepLarger steps  More quantizing noise, Less slope overhead noiseHigher sampling rate = Lower noise, More bits11111111000000000010101010111015-20©2005 Raj JainCSE473sWashington University in St. LouisAnalog Data, Analog SignalsAnalog Data, Analog SignalsAmplitude Modulation (AM)Frequency Modulation (FM)Phase Modulation (PM)Both FM and PM are special cases of angle modulation5-21©2005 Raj JainCSE473sWashington University in St. LouisSummarySummaryCoding: Higher data rate, error control, clock synchronization, line state indication, control