14-02-2013, 04:51 PM
PERFORMANCE EVALUATION OF DIRECT SEQUENCE
SPREAD SPECTRUM SCHEME
PERFORMANCE EVALUATION OF DIRECT SEQUENCE.docx (Size: 29.21 KB / Downloads: 18)
PROGRAM:
clc
clear
% Generating the bit pattern with each bit 20 samples long
b=round(rand(1,30));
pattern=[];
for k=1:30
if b(1,k)==0
sig=-ones(1,20);
else
sig=ones(1,20);
end
pattern=[pattern sig];
end
subplot(4,1,1)
plot(pattern);
axis([-1 620 -1.5 1.5]);
title('Original Bit Sequence');
% Generating the pseudo random bit pattern for spreading
d=round(rand(1,120));
pn_seq=[];
carrier=[];
t=[0:2*pi/4:2*pi]; % Creating 5 samples for one cosine
for k=1:120
if d(1,k)==0
sig=-ones(1,5);
else
sig=ones(1,5);
end
c=cos(t);
carrier=[carrier c];
pn_seq=[pn_seq sig];
end
% Spreading of sequence
spreaded_sig=pattern.*pn_seq;
subplot(4,1,2)
plot(spreaded_sig)
axis([-1 620 -1.5 1.5]);
title('Spreaded signal');
% BPSK Modulation of the spreaded signal
bpsk_sig=spreaded_sig.*carrier; % Modulating the signal
subplot(4,1,3);
plot(bpsk_sig)
axis([-1 620 -1.5 1.5]);
title('BPSK Modulated Signal');
%Demodulation and Despreading of Received Signal
figure
rxsig=bpsk_sig.*carrier;
demod_sig=[];
for i=1:600
if rxsig(i)>=0
rxs =1;
else
rxs =-1;
end
demod_sig=[demod_sig rxs];
end
subplot(3,1,1)
plot(demod_sig)
axis([-1 620 -1.5 1.5]);
title('Demodulated Signal')
despread_sig=demod_sig.*pn_seq;
subplot(3,1,2)
plot(despread_sig)
axis([-1 620 -1.5 1.5]);
title('Despreaded data')
%Bit error rate vs signal to noise ratio
data=randint(1,96);
for i=1:96
if data(i)==0
data(i)=-1;
end
end
y=kron(data,ones(1,8));
f=50;prand=[];
t=linspace(1,1/f,768);
d=[-1 -1 1 1 1 -1 1 -1];
for i=1:96
prand=[prand d];
end
signal=y.*cos(2*pi*f*t);
transmit1=signal.*prand;