Data TransmissionOverviewTransmission TerminologyLine DuplexityAnalog vs Digital SignalsPeriodic vs AperiodicExamples of Periodic SignalsFrequency, Period, and PhaseSine WaveWavelengthTime and Frequency DomainsFrequency Domain ConceptsSignal with DC ComponentFrequency Components of Square WaveData vs SignalAnalog Data Example: Speech and MusicAnalog Data Example 2: TelevisionVideo SignalAttenuation and Dispersion (Delay Distortion)Digital TransmissionDecibelsNoiseNoise (Cont)Channel CapacityShannon's TheoremThermal NoiseSummaryReading AssignmentHomework3-1©2005 Raj JainCSE473sWashington University in St. LouisData Data TransmissionTransmissionRaj JainProfessor of CSE Washington University in Saint LouisSaint Louis, MO [email protected] slides are available on-line at:http://www.cse.wustl.edu/~jain/cse473-05/3-2©2005 Raj JainCSE473sWashington University in St. LouisOverviewOverviewTime Domain and Frequency DomainDecibels Data vs SignalAttenuation, Delay Distortion, Noise, Capacity3-3©2005 Raj JainCSE473sWashington University in St. LouisTransmission TerminologyTransmission TerminologyGuided Media: Wire, Fiber , coaxUnguided Media: Air, Vacuum, sea waterDirect LinkPoint to Point vs Point to MultipointT RT RTR1 R2 R33-4©2005 Raj JainCSE473sWashington University in St. LouisLine DuplexityLine DuplexitySimplex: Transmit or receive, e.g., TelevisionHalf-Duplex: Transmit and receive alternately, e.g., Police RadioFull Duplex: Transmit and receive simultaneously, e.g., TelephoneT RT/R T/R3-5©2005 Raj JainCSE473sWashington University in St. LouisAnalog vs Digital SignalsAnalog vs Digital SignalsAnalog:Digital:3-6©2005 Raj JainCSE473sWashington University in St. LouisPeriodic vs AperiodicPeriodic vs AperiodicPeriodic: Signal pattern repeats over timeAperiodic: Not periodicTS(t+T) = s(t) for all tPeriod = T3-7©2005 Raj JainCSE473sWashington University in St. LouisExamples of Periodic SignalsExamples of Periodic SignalsSine Wave:Square Wave:3-8©2005 Raj JainCSE473sWashington University in St. LouisFrequency, Period, and PhaseFrequency, Period, and PhaseA Sin(2ft + ), Period T=1/f, Frequency in Hertz3-9©2005 Raj JainCSE473sWashington University in St. LouisSine WaveSine WavePeak Amplitude (A): Maximum strength of signal in voltsFrequency (f): Hertz (Hz) or cycles per secondPeriod = time for one repetition (T)T = 1/fPhase (): Relative position in time3-10©2005 Raj JainCSE473sWashington University in St. LouisWavelengthWavelengthDistance occupied by one cycleDistance between two points of corresponding phase in two consecutive cyclesWavelength = Assuming signal velocity v = vTf = vc = 3*108 m/s (speed of light in free space) = 300 m/sDistanceAmplitude3-11©2005 Raj JainCSE473sWashington University in St. LouisTime and Frequency DomainsTime and Frequency DomainsFrequencyAmplitudeFrequencyAmplitudeFrequencyAmplitudef3fAAf 3fA/3A/33-12©2005 Raj JainCSE473sWashington University in St. LouisFrequency Domain ConceptsFrequency Domain ConceptsFundamental Frequency: All other frequency components are multiple of fundamental frequency fPeriod = 1/fSpectrum: Range of frequenciesAbsolute Bandwidth: Width of the spectrum Absolute Bandwidth = 3f-f = 2fEffective Bandwidth: Narrow band of frequencies containing most of the energyDC Component: Constant or zero frequencyA+B sin (2ft+)3-13©2005 Raj JainCSE473sWashington University in St. LouisSignal with DC ComponentSignal with DC Component3-14©2005 Raj JainCSE473sWashington University in St. LouisFrequency Components of Square WaveFrequency Components of Square WaveFreq.AmplitudeAmplitudeFrequencyfA3f 5fA/3A/5Freq.f 3fA/35fA/57fA/7 … A/k sin (2kft)3-15©2005 Raj JainCSE473sWashington University in St. LouisData vs SignalData vs SignalTelephoneModemCODECDigital TransceiverAnalogDigitalDataSignalAnalogDigitalAnalogAnalogDigitalDigitalData SignalMediumData3-16©2005 Raj JainCSE473sWashington University in St. LouisAnalog Data Example: Speech and MusicAnalog Data Example: Speech and Music3-17©2005 Raj JainCSE473sWashington University in St. LouisAnalog Data Example 2: TelevisionAnalog Data Example 2: Television30 Screens/secInterlacing: Odd lines every 1/60 sand even lines every 1/60 s483 lines/screen3-18©2005 Raj JainCSE473sWashington University in St. LouisVideo SignalVideo SignalUSA - 483 lines scanned per frame at 30 frames per second525 lines but 42 lost during vertical retraceSo 525 lines x 30 scans = 15750 lines per second63.5s per line11s for retrace, so 52.5 s per video lineMax frequency if line alternates black and whiteHorizontal resolution is about 450 lines giving 225 cycles of wave in 52.5 sMax frequency of 4.2MHz3-19©2005 Raj JainCSE473sWashington University in St. LouisAttenuation Attenuation and Dispersion (Delay Distortion)and Dispersion (Delay Distortion)D i s t a n c e3-20©2005 Raj JainCSE473sWashington University in St. LouisDigital TransmissionDigital TransmissionRepeaters are used to regenerate digital signalSignal attenuation is overcomeNoise is not amplifiedLow cost LSI/VLSI technologyLonger distances over lower quality linesCapacity utilizationHigh bandwidth links economicalHigh degree of multiplexing easier with digital techniquesSecurity & Privacy: Encryption3-21©2005 Raj JainCSE473sWashington University in St. LouisDecibelsDecibelsAttenuation = Log10 PinPoutExample 1: Pin = 10 mW, Pout=5 mWAttenuation = 10 log 10 (10/5) = 10 log 10 2 = 3 dBExample 2: Pin = 100mW, Pout=1 mWAttenuation = 10 log 10 (100/1) = 10 log 10 100 = 20 dBBelPinPoutdecibelAttenuation = 10 Log10 VinVoutdecibelAttenuation = 20 Log103-22©2005 Raj JainCSE473sWashington University in St. LouisNoise Noise Additional signals inserted between transmitter and receiverThermal Noise:Due to thermal agitation of electronsUniformly distributedWhite noiseIntermodulation Noise:Signals that are the sum and difference of original frequencies sharing a medium3-23©2005 Raj JainCSE473sWashington University in St. LouisNoise (Cont)Noise (Cont)Crosstalk Noise: A signal from one line is picked up by anotherImpulse Noise: Irregular pulses or spikese.g., External electromagnetic interferenceShort durationHigh amplitude3-24©2005 Raj JainCSE473sWashington University in St. LouisChannel
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