Performance of Digital Communication Lab

8/17/2019 Performance of Digital Communication Lab

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1.0. Objective1.1. To study the performance of digital communication system when it

is corrupted by noise.1.2. To study the performance of digital communication system when it

is under the inuence of inter-symbol interference (ISI) only.1.. To study the performance of digital communication system when it

is both under the inuence of inter-symbol interference (ISI) and

corrupted by noise.

2.0. Theory

In communication systems! the wa"eform present at the recei"er

(user) is un#nown until after it is recei"ed otherwise! no information would

be transmitted and there would be no need for the communication

system. $ore information is communicated to the recei"er when the user

is %more surprised& by the message that was transmitted. That is! the

transmission of information implied the communication of messages that

are not #nown ahead of time (a priori). 'oise limits our ability to

communicate. If there were no noise! we could communicate messages

electronically to the outer limits of the uni"erse by using an innitely small

amount of power.

The two primary considerations in the design of a communication systemare as follows

1. The performance of the system when it is corrupted by noise. The

performance measure for a digital system is the probability of error

of the output signal. *or analog systems! the performance measure

is the output signal-to-noise ratio.

2. The channel bandwidth that is re+uired for transmission of the

communication signal.

There are numerous ways in which the information can be

demodulated (reco"ered) from the recei"ed signal that has been corrupted

by noise. Some recei"ers pro"ide optimum performance! but most do not.

,ften a suboptimum recei"er will be used in order to lower the cost. In

addition! some suboptimum recei"ers perform almost as well as optimum

ones for all practical purposes.


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Figure 1. eneral binary communication system.

*igure 1 shows a general bloc# diagram for a binary communication

system. The recei"er input r(t) consists of the transmitted signal s(t) plus

channel noise n(t). *or baseband signalling! the processing circuits in the

recei"er consist of low-pass ltering with appropriate amplication. *or

bandpass signalling! such as ,,! /0S and *S! the processing circuits

normally consist of a super heterodyne recei"er containing a mier! an I*

amplier and a detector. These circuits produce a baseband signalling

analog output r(t).

The analog baseband wa"eform r(t) is sampled at the cloc#ing time

t 3 t 4 nT to produce the samples r(t 4 nT)! which are fed into a

threshold de"ice (a comparator). The threshold de"ice produces the binary

serial-data wa"eform m(t).

3.0. Equipments.1. 0ersonal 5omputer (05)

.2. $atlab Software

4.0. Saety !recaution6.1. $a#e sure all the e+uipment is turn o7 after the eperiments is

done.6.2. $a#e to put bac# all the e+uipment to its place.6.. 8o not conduct eperiment with wet hand.6.6. 9lways wear lab coat.


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".0. !roce#ure:.1. 0art 1

a) The following $atlab function $-le are gi"en which represents a

basic digital communication system that transmits an 9mplitude

Shift eying (9S) signal n the presence of nose in the channel1. test;noise2. binse+;t. binse+;det

The function of these les is eplained n the result.

b) The main specications for the 9S signal (bit rate! sampling

fre+uency! "oltage amplitude! number of bits in a pac#et and

number of pac#ets) is identied in the les.c) The 2 missing les is created before the system is eecuted. The

les are1. a function to generate bytes of pseudorandom binary se+uence.2. a !16 and 1 CD with "oltage

amplitude 3 1 and bit rate 3 1.. /it rate 32! ! 6 and : bitsEsec with "oltage amplitude 31 and

sampling fre+uency 3 16. Two graph is plotted with is a graph of /?@ against each of the

"arying parameters for both theoretical and measured /?@s and

a graph of /?@ against S'@ (d/) for each of the "arying

parameter for theoretical and measured /?@s. The results for each graph is comment.

:.2. 0art 2a) /y going bac# to its original state! the performance of the system if

it is under the inuence of inter-symbol interference (isi) without

noise is considered and the coding of the program is identied and

changed.b) The step (d)! (e) and (f) is repeated and comment.


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:.. 0art a) The performance of the system if it is under the inuence of both isi

and noise is considered and the coding of the program is identied

and changed.

b) The step (d)! (e) and (f) is repeated and comment.c) The o"erall results obtained in 0art 1! 0art 2 and 0art is compared

and contrasted.

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Performance of Digital Communication Lab