Ee 551 451 fall 2006 communication systems
This presentation is the property of its rightful owner.
Sponsored Links
1 / 27

EE 551/451, Fall, 2006 Communication Systems PowerPoint PPT Presentation


  • 83 Views
  • Uploaded on
  • Presentation posted in: General

EE 551/451, Fall, 2006 Communication Systems. Zhu Han Department of Electrical and Computer Engineering Class 13 Oct. 3 rd , 2006. Pulse Code Modulation (PCM). Pulse code modulation (PCM) is produced by analog-to-digital conversion process. Quantized PAM

Download Presentation

EE 551/451, Fall, 2006 Communication Systems

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Ee 551 451 fall 2006 communication systems

EE 551/451, Fall, 2006Communication Systems

Zhu Han

Department of Electrical and Computer Engineering

Class 13

Oct. 3rd, 2006


Pulse code modulation pcm

Pulse Code Modulation (PCM)

  • Pulse code modulation (PCM) is produced by analog-to-digital conversion process. Quantized PAM

  • As in the case of other pulse modulation techniques, the rate at which samples are taken and encoded must conform to the Nyquist sampling rate.

  • The sampling rate must be greater than, twice the highest frequency in the analog signal,

    fs > 2fA(max)

  • Telegraph time-division multiplex (TDM) was conveyed as early as 1853, by the American inventor M.B. Farmer. The electrical engineer W.M. Miner, in 1903.

  • PCM was invented by the British engineer Alec Reeves in 1937 in France.

  • It was not until about the middle of 1943 that the Bell Labs people became aware of the use of PCM binary coding as already proposed by Alec Reeves.

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Pulse Code Modulation

Figure The basic elements of a PCM system.

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Encoding

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Virtues, Limitations and Modifications of PCM

Advantages of PCM

1. Robustness to noise and interference

2. Efficient regeneration

3. Efficient SNR and bandwidth trade-off

4. Uniform format

5. Ease add and drop

6. Secure

DS0: a basic digitalsignaling rate of 64 kbit/s. To carry a typical phone call, the audio sound is digitized at an 8 kHz sample rate using 8-bit pulse-code modulation.4K baseband, 8*6+1.8 dB

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

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

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

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 (  )

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Reduce the sampling rate

Block diagram illustrating the linear adaptive prediction process.

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

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

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Processing Gain

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

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).

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

8-16 kbps with the same quality of PCM

ADPCM

Adaptive prediction with backward estimation (APB).

EE 541/451 Fall 2006


Coded excited linear prediction celp

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

EE 541/451 Fall 2006


Time division multiplexing

Time-Division Multiplexing

Figure Block diagram of TDM system.

EE 541/451 Fall 2006


Ds1 t1 e1

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

EE 541/451 Fall 2006


Synchronization

Synchronization

  • Super Frame

EE 541/451 Fall 2006


Synchronization1

Synchronization

  • Extended Super Frame

EE 541/451 Fall 2006


T carrier system

T Carrier System

Twisted Wire to Cable System

EE 541/451 Fall 2006


Fiber communication

Fiber Communication

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Delta Modulation (DM)

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

DM System: Transmitter and Receiver.

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Slope overload distortion and granular noise

The modulator consists of a comparator, a quantizer, and an accumulator. The output of the accumulator is

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

Slope Overload Distortion and Granular Noise

( differentiator )

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

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 )

EE 541/451 Fall 2006


Ee 551 451 fall 2006 communication systems

delta-sigma modulation system.

EE 541/451 Fall 2006


Adaptive delta modulation

Adaptive Delta Modulation

  • Adaptive adjust the step size according to frequency, figure 6.21

  • Out SNR

    • Page 286-287

    • For single integration case, (BT/B)^3

    • For double integration case, (BT/B)^5

  • Comparison with PCM, figure 6.22

    • Low quality has the advantages.

    • Used in walky-talky

EE 541/451 Fall 2006


Questions

Questions?

EE 541/451 Fall 2006


  • Login