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ECE 4371, Fall, 2009

ECE 4371, Fall, 2009. Zhu Han Department of Electrical and Computer Engineering Class 10 Sep. 24 th , 2009. 0111. 0110. 0100. 0101. Resolution= 1 part in 2 n. 0011. 0010. 0001. 0000. 1111. 1110. 1100. 1010. 1101. 1011. 1001. PCM. 0000. 0110. 0111. 0011. 1100. 1001.

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ECE 4371, Fall, 2009

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  1. ECE 4371, Fall, 2009 Zhu Han Department of Electrical and Computer Engineering Class 10 Sep. 24th, 2009

  2. 0111 0110 0100 0101 Resolution= 1 part in 2n 0011 0010 0001 0000 1111 1110 1100 1010 1101 1011 1001 PCM 0000 0110 0111 0011 1100 1001 1011 Numbers passed from ADC to computer to represent analogue voltage

  3. Noise consideration in PCM systems (Channel noise, quantization noise)

  4. Noise consideration in PCM systems

  5. Differential Encoding • Encode information in terms of signal transition; a transition is used to designate Symbol 0 Regeneration (reamplification, retiming, reshaping ) 3dB performance loss, easier decoder

  6. Linear Prediction Coding (LPC) Consider a finite-duration impulse response (FIR) discrete-time filter which consists of three blocks : 1. Set of p ( p: prediction order) unit-delay elements (z-1) 2. Set of multipliers with coefficients w1,w2,…wp 3. Set of adders (  )

  7. For convenience, we may rewrite the Wiener-Hopf equations The filter coefficients are uniquely determined by

  8. Linear adaptive prediction (If for varying k is not available)

  9. Differentiating (3.63), we have Substituting (3.71) into (3.69)

  10. Reduce the sampling rate Block diagram illustrating the linear adaptive prediction process.

  11. Differential Pulse-Code Modulation (DPCM) Usually PCM has the sampling rate higher than the Nyquist rate. The encode signal contains redundant information. DPCM can efficiently remove this redundancy. 32 Kbps for PCM Quality

  12. From (3.74) Differential Pulse-Code Modulation (DPCM) Input signal to the quantizer is defined by:

  13. Processing Gain

  14. Adaptive Differential Pulse-Code Modulation (ADPCM) Need for coding speech at low bit rates , we have two aims in mind: 1. Remove redundancies from the speech signal as far as possible. 2. Assign the available bits in a perceptually efficient manner. Adaptive quantization with backward estimation (AQB).

  15. 8-16 kbps with the same quality of PCM ADPCM Adaptive prediction with backward estimation (APB).

  16. Coded Excited Linear Prediction (CELP) • Currently the most widely used speech coding algorithm • Code books • Vector Quantization • <8kbps • Compared to CD 44.1 k sampling 16 bits quantization 705.6 kbps 100 times difference

  17. Time-Division Multiplexing Figure Block diagram of TDM system.

  18. DS1/T1/E1 • Digital signal 1 (DS1, also known as T1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is a widely used standard in telecommunications in North America and Japan to transmit voice and data between devices. E1 is used in place of T1 outside of North America and Japan. Technically, DS1 is the transmission protocol used over a physical T1 line; however, the terms "DS1" and "T1" are often used interchangeably. • A DS1 circuit is made up of twenty-four DS0 • DS1: (8 bits/channel * 24 channels/frame + 1 framing bit) * 8000 frames/s = 1.544 Mbit/s • A E1 is made up of 32 DS0 • The line data rate is 2.048 Mbit/s which is split into 32 time slots, each being allocated 8 bits in turn. Thus each time slot sends and receives an 8-bit sample 8000 times per second (8 x 8000 x 32 = 2,048,000). 2.048Mbit/s • History page 274

  19. Synchronization • Super Frame

  20. Synchronization • Extended Super Frame

  21. T Carrier System Twisted Wire to Cable System

  22. Fiber Communication

  23. Delta Modulation (DM)

  24. DM System: Transmitter and Receiver.

  25. Slope overload distortion and granular noise The modulator consists of a comparator, a quantizer, and an accumulator. The output of the accumulator is

  26. Slope Overload Distortion and Granular Noise ( differentiator )

  27. Delta-Sigma modulation (sigma-delta modulation) The modulation which has an integrator can relieve the draw back of delta modulation (differentiator) Beneficial effects of using integrator: 1. Pre-emphasize the low-frequency content 2. Increase correlation between adjacent samples (reduce the variance of the error signal at the quantizer input ) 3. Simplify receiver design Because the transmitter has an integrator , the receiver consists simply of a low-pass filter. (The differentiator in the conventional DM receiver is cancelled by the integrator )

  28. delta-sigma modulation system.

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