performance of digital communication lab
TRANSCRIPT
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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.