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Data Encoding

Data Encoding. Encoding scheme. Analog data, Analog signal. Analog data, Digital signal. digital. analog. analog. voice. Telephone. CODEC. Digital data, Digital signal. Digital data, Analog signal. analog. digital. digital. digital. Modem. Digital transmitter.

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Data Encoding

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  1. Data Encoding

  2. Encoding scheme Analog data, Analog signal Analog data, Digital signal digital analog analog voice Telephone CODEC Digital data, Digital signal Digital data, Analog signal analog digital digital digital Modem Digital transmitter

  3. Encoding and Modulation x(t) x(t) g(t) g(t) Encoder Decoder digital or analog digital t s(f) s(t) m(t) Modulator Demodulator m(t) digital or analog analog f fc fc

  4. Why encoding? • Three factors determine successfulness of receiving signal • S/N • data rate • bandwidth • More factor can be used to improve • encoding scheme

  5. Encoding evaluation factors • Signal spectrum • Clocking • Error detection • Signal interference& noise immunity • Cost and complexity

  6. Digital data, Digital signal 0 1 0 0 1 1 0 0 0 1 1 NRZ NRZI Bipolar -AMI Pseudoternary Manchester Differential Manchester

  7. Scrambling techniques 1 1 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1 0 Bit value Bipolar-AMI 0 0 0 V B 0 V B B8ZS 0 0 0 V B 0 0 V B 0 0 V HDB3

  8. Spectral density 1.5 B8ZS,HDB3 NRZ-L, NRZI 1 AMI, Pseudoternary Mean square voltage per unit bandwidth 0.5 Manchester, Differential Manchester 0 0 1 0.5 1.5 -0.5 Normalized frequency (f/r)

  9. Digital data, Analog signal • Tranmitting digital data through PSTN • Modem is used to convert digital data to analog signal and vice versa

  10. Modultion techniques 0 0 1 1 0 1 0 0 0 1 0 ASK FSK PSK

  11. ASK Vd(t) Vc(t) VASK(t) Signal power frequency spectrum Frequency fc fc+f0 fc+3f0 fc-3f0 fc-f0

  12. FSK vd(t) Data signal v1(t) Carrier 1 v2(t) Carrier 2 vFSK(t) Signal power frequency spectrum Frequency f1 f2

  13. PSK Data Signal vc(t) • bit rate = signaling rate Carrier vc(t) Phase coherent vPSK(t) Differential vPSK(t) 180=0 0=1 phase diagram

  14. Multilevel modulation method 10 11 00 01 • bit rate = n x signaling rate 0 +90 +180 +270

  15. 1 Multilevel modulation method +90?01 +180?11 0?00 +270?11 4-PSK phase diagram 16-QAM phase diagram

  16. Analog data, Digital signal • Two principle techniques used • PCM • DM PCM signal PAM signal Sampling clock Sampling Circuit Quantizer and compander Analog voice signal Digitized voice signal

  17. PCM • Sampling signal based on nyquist theorem Original signal 3.9 4.2 3.4 3.2 2.8 PAM pulse 1.2 4 4 PCM pulse with quantized error 3 3 3 1 011 100 011 011 001 100 PCM output 011100011011001100

  18. A B C D PCM Conversion process Sampling clock PCM signal PAM signal Sampling Circuit Quantizer and compander Analog voice signal Digitized voice signal D B A C

  19. Strong signal Weak signal Nonlinear encoding Quantizing level 15 15 14 14 13 13 12 12 11 11 10 10 9 8 9 8 7 7 6 5 6 4 5 3 4 3 2 2 1 1 0 0 Without nonlinear encoding With nonlinear encoding

  20. 11 10 01 00 00 01 10 11 Companding process 11 10 01 • Implement nonlinear encoding via companding process • Companding = Compressing Expanding 00 11 10 01 00 11 10 01 00 segment codes (+) 11 10 01 00 11 10 01 00 11 10 01 00 11 10 01 00 segment codes (-) 11 10 01 00 linear quantization interval Compressor circuit Linear ADC Linear DAC Expander circuit Network vi vo vi vo

  21. Analog Data, Analog signal • Use Modultion techniques • Need a high frequency for effective tranmission • Modulation permits frequency division multiplex

  22. AnalogModulation Amplitude-modulated wave Carrier Frequency-modulated wave Modulating sine-wave signal Phase-modulated wave

  23. AM Spectrum upper sideband carrier lower sideband M(f) Discrete carrier term Lower sideband Upper sideband 0 fc - B fc fc + B f • each sideband contains the complete spectrum of s(t) !

  24. AM power saving • SSB (Single ideband) • DSBSC (Double sideband supresses carrier) • VSB (Vestigial sideband)

  25. FM and PM Carrier Modulating sine-wave signal Amplitude-modulated (DSBTC) wave Phase-modulated wave Frequency-modulated wave

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