Objectives to study, implement and analyse a typical analogue source (speech) encoding technique a prerequisites




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EXPERIMENT 1: SOURCE ENCODING




OBJECTIVES

To study, implement and analyse a typical analogue source (speech) encoding technique
A PREREQUISITES


A knowledge of the sampling theorem, quantisation noise and linear prediction. Please refer to the experimental guide for an outline of the preparatory work that has to be completed before this experiment is attempted. This work must be done in the lab book that has been specified for this purpose. For evaluation purposes, an extract of the relevant examples and results must be taken from the lab book and submitted in the form of a preliminary report to be handed in for evaluation on the scheduled date (usually a few days before the day on which the experiment has to be performed - see lab time table in study guide).


B REFERENCES


[1] B.P. Lathi and Z. Ding, Modern Digital and Analog Communication Systems, Fourth Edition, Oxford University Press, 2010.

[2] J.G. Proakis and M. Salehi, Communication Systems Engineering - 2nd edition, Prentice-Hall, 2002 - Chapter 6.

[3] S. Haykin, Communication Systems, 3rd edition, Wiley, 1994.

[4] H. Taub and D.L. Schilling, Principles of Communication Systems, McGraw-Hill, 1971.1

[5] D. Jones, “Delta modulation for voice transmission”, Electronic Engineering, January 1978.


C PREPARATION AND PRELIMINARY REPORT


  1. Study the references below:




  1. [1] Chapter 6 §6.6 and 6.7.

  2. as well as the corresponding material in [3] and [4]. Find at least one additional reference of your own on Delta Modulation and include as an addendum to your preliminary report.

  3. Additional lab notes (to be handed out during the first lab lecture – refer to lab schedule)

  4. Study and describe the principles of operation of a -mod and familiarise yourself with the purpose of each parameter and component. Describe with the help of the necessary expressions and sketches, the concepts slope overload and granular (quantisation) noise.




  1. Do the following problems from the given references to gain insight into the theoretical and functional

characteristics of a -mod.


From [4]: (i) Problem 6.20 (identical to Problem 1 of list or summary of delta-modulator problems).

(ii) The signal m(t)=Msinot is to be encoded by means of a -mod. If the step size S and

sampling frequency fs are selected so as to ensure that neither slope overload nor

step-size limiting occurs, show that fs > 3 fo (see Prob 3 in list of delta-modulator problems).

(iii) Analyse the Delta-PCM modulator in Appendix I. Use MATLAB to generate and

plot all the waveforms at the critical points in Figure 6.33-3 below.


  1. Analyse the Delta-mod circuit in Fig 1 and design it according to the specifications in E. Use a clock speed of 16 to 32 kHz for this purpose. Assume analog speech or music as input with a bandwidth of

approximately 5 kHz.

D REQUIRED EQUIPMENT


Oscilloscope, spectrum analyser, signal generator(s), power sources, voltmeters etc. In addition, it is required from the student to build up his own modules wherever required or where these building block are not provided as part of the laboratory equipment. For this purpose each student will have to acquire his own set of basic electronic lab tools2 which should accompany him/her to each practical session.


E EXPERIMENTAL PROCEDURE




Figure 1 Block diagram of simple linear -modulator


1. Build and test the simple linear -mod shown in the figure in your own time.


2. Determine the step response of the -mod for various clock frequencies and time constants RC (design for clock frequencies between 16 and 32 kHz).


3. Determine the relationship between the clock speed fc [units?] and bit speed, fb [units?]. How does the clock signal differ from the bit stream at the output of the -mod? Also compare their respective spectra.


4. Demonstrate slope overload and granular (quantisation) noise and explain what effect a change in clock frequency fc and time constant RC will have on these phenomena.


5. Demonstrate step-size-limiting


6. Study the frequency spectra at the critical nodes in the -mod circuit diagram. Attempt to point out basic relationships between these spectra (from a signal processing viewpoint, considering the functional diagram of the -mod in Figure 1 above).


7. Test your -mod’s with a speech signal as input. Bring your own cassette player for this purpose. (NB! Pre-amplification may be necessary to obtain an m(t) with suitable amplitude).


8. Remember to document all observations and findings in your lab book for future reference. Note that this will be your only reference during tests and the exam!

F EVALUATION


This experiment will be evaluated as follows:


1. Preliminary Report, Lab book with preparation, solution of problems and -mod design

20%

2. Formal lab: Delta-Mod demonstration and lab book with final results, observations and conclusions.

60%

3. Optical Mark Reader Lab Test

20%

TOTAL:

100%


APPENDIX I



1The authors of this book were actively involved with the earlier developments of the -modulator concept.

2 Sharp muzzled pliers, side cutter, soldering iron, screw driver, basic electronic components, connection wire, set of oscilloscope probes etc.

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