This document contains code for performing various digital signal processing and modulation techniques, including: - PCM and demodulation of sampled signals - Delta modulation and adaptive delta modulation of signals - Generation of ASK, FSK, and PSK modulated signals using a random binary sequence and adding AWGN noise - Calculation of the bit error rate for the three modulation schemes over varying SNR levels - Implementation of direct sequence spread spectrum modulation and demodulation using a pseudo-random sequence.

1. PCM AND Demodulation
clc
A=input('enter the Amplitude of the
signal')
fm= input('enter the Frequency of the
signal')
fs= input('enter the sampling frequency of
the signal')
n=4
t=0:1/(100*fm):1;
x=A*cos(2*pi*fm*t);
%---Sampling-----
ts=0:1/fs:1;
xs=A*cos(2*pi*fm*ts)
%--Quantization---
x1=xs+A
x1=x1/(2*A)
L=(-1+2^n) % Levels
x1=L*x1
xq=round(x1)
%----Encoding---
y=[];
for i=1:length(xq)
d=dec2bin(xq(i),n);
y=[y double(d)-48];
end
%----Decoding---
q=char(reshape( y, n, numel(y)/n ) + '0').'
index=bin2dec(q)
subplot(4,1,3)
plot(index);
figure(1)
subplot(3,1,1)
plot(t,x,'linewidth',2)
title('Original signal and its samples')
ylabel('Amplitute')
xlabel('Time t(in sec)')
hold on
stem(ts,xs,'r')
hold off
legend('Original Signal', 'Sampled Signal');
subplot(3,1,2)
stairs(y)
title('Encoding')
ylabel('Binary Signal')
xlabel('bits')
axis([0 length(y) -1 2])
grid
subplot(3,1,3)
plot(index)
xlabel('index')
ylabel('amplitude')
title('recovered signal')
clc;
clear all;
close all;
%Delta modulation
Delta modulation (vary step size to
check granular noise and slope
%overload noise)
A=input('enter the amp of sin signal=')
f=input('enter the freq of sin signal=')
t=0:0.005:1/f;
x=A*sin(2*pi*f*t);
del=0.1 %step size is fixed
y=[0];
xr=0;
for i=1:length(x)-1
if xr(i)<=x(i)
%d=1;
xr(i+1)=xr(i)+del;
else
%d=0;
xr(i+1)=xr(i)-del;
end
%y=[yd]
end
figure(1)
plot(x)
hold on
stairs(xr)
title('delta modulation')
hold off
adaptive modulation
clc
A=input('enter the amp of sin signal =')
f=input('enter the freq of sin signal
=')
t=0:0.005:1/f;
x=A*sin(2*pi*f*t);
del=0.3 %step size is fixed
y=[0];
xr=[0.1];
for i=1:length(x)-1
if (x(i)-xr(i)>0)
if (x(i)-xr(i)<=0.3)
%d=1;
xr(i+1)=xr(i)+del;
elseif(x(i)-xr(i))>0.3&&(xr(i)-
x(i))<=0.6
xr(i+1)=xr(i)+2*del
elseif(x(i)-xr(i))>0.6&&(xr(i)-
x(i))<=0.9
xr(i+1)=xr(i)+3*del
elseif(x(i)-xr(i))>0.9&&(xr(i)-
x(i))<=1.2
xr(i+1)=xr(i)+4*del
end
else
if(x(i)-xr(i))>=-0.3&&(x(i)-
xr(i))<0
%d=0;
xr(i+1)=xr(i)-del;
elseif(x(i)-xr(i))>=-0.6&&(x(i)-
xr(i))<-0.3
xr(i+1)=xr(i)-2*del

2. elseif(x(i)-xr(i))>=-0.9&&(x(i)-
xr(i))<-0.6
xr(i+1)=xr(i)-3*del
elseif(x(i)-xr(i))>=-1.2&&(x(i)-
xr(i))<-0.9
xr(i+1)=xr(i)-4*del
end
end
xr=[xr xr(i+1)]
end
figure(1)
plot(x)
hold on
stairs(xr)
title('delta modulation')
hold off
function ASK_FSK_PSK(n)
n=200;
b=randint(1,n);
f1=1; f2=2;
t=0:1/30:1-1/30;
%ASK
sa1=sin(2*pi*f1*t);
E1=sum( sa1.^2);
sa1=sa1/sqrt(E1);
sa0=0*sin(2*pi*f1*t);
%FSK
sf0=sin(2*pi*f1*t);
E=sum(sf0.^2);
sf0=sf0/sqrt(E);
sf1= sin(2*pi*f2*t);
E=sum(sf0.^2);
sf0=sf0/sqrt(E);
%PSK
sp0=-sin(2*pi*f1*t)/sqrt(E1);
sp1=sin(2*pi*f1*t)/sqrt(E1);
%Modulation
ask=[ ]; psk=[ ]; fsk=[ ];
for i=1:n
if b(i)==1
ask=[ask sa1];
psk=[psk sp1];
fsk=[fsk sf1];
else
ask=[ask sa0];
psk=[psk sp0];
fsk=[fsk sf0];
end
end
figure(1)
subplot(4,1,1);
stairs(0:10,[b(1:10)
b(10)],'linewidth',1.5)
axis([0 10 -0.5 1.5])
title('Message bits');
grid on
subplot(4,1,2);
tb=0:1/30 :10 -1/30;
plot(tb,ask(1:10*30),'b','linewidth',1.5
);
title ('ASK Modulation');
grid on
subplot(4,1,3);
plot (tb,
fsk(1:10*30),'r','linewidth',1.5);
title('FSK Modulation');
grid on
subplot(4,1,4);
plot (tb,
psk(1:10*30),'k','linewidth',1.5)
title('PSK Modulation');
grid on
%AWGN
for snr=0:20
askn=awgn(ask,snr);
pskn=awgn(psk,snr);
fskn=awgn(fsk,snr);
%Detection
A=[ ]; F=[ ]; P=[ ];
for i= 1: n
% ASK Detection
if sum(sa1.*askn(1+30*(i-1):30*i))>0.5
A=[A 1];
else
A=[A 0];
end
% FSK Detection
if sum(sf1.*fskn(1+30*(i-1):30*i))>0.5
F=[F 1];
else
F=[F 0];
end
% PSK Detection
if sum(sp1.*pskn(1+30*(i-1):30*i))>0.5
P=[P 1];
else
P=[P 0];
end
end
%BER
errA=0; errF=0; errP=0;
for i=1: n
if A(i)==b(i)
errA=errA;
else
errA =errA+1;
end
if F(i)==b(i)
errF=errF;
else
errF =errF+1;
end
if P(i)==b(i)
errP=errP;
else
errP =errP+1;
end
end
BER_A(snr+1)=errA/n;
BER_F(snr+1)=errF/n;
BER_P(snr+1)=errP/n;
end

3. figure(2)
subplot(4,1,1);
stairs(0:10,[b(1:10) b(10)],
'linewidth', 1.5)
axis ([0 10 -0.5 1.5]);
grid on
title('Received signal after AWGN
chaneel')
subplot(4,1,2);
tb=0:1/30:10-1/30;
plot(tb,askn(1:10*30),'b','linewidth',
1.5)
title('Received ASK signal');
grid on
subplot(4,1,3);
plot(tb,fskn(1:10*30),'r','linewidth',1.
5)
title('Received FSK signal');
grid on
subplot(4,1,4);
plot(tb,pskn(1:10*30),'k','linewidth',1.
5)
title('Received PSK signal');
grid on
figure(3)
semilogy(0:20,BER_A,'b','linewidth',2)
title('BER vs SNR')
grid on
hold on
semilogy(0:20,BER_F,'r','linewidth',2)
semilogy(0:20,BER_P,'k','linewidth',2)
xlabel('Eo/No(db)')
ylabel('BER')
hold off
legend('ASK','FSK','PSK');
DSSS PROGRAM
clc;
close all;
clear all;
b=input('Enter the input Bits');
pnseq=input('Enter pn 7 bit sequence');
%ln=length(b);
% converting bit 0 to -1
for i=1:length(b)
if b(i)==0
b(i)=-1
end
end
% Generating the bit sequence with each
bit 8 samples long
k =1
bb =0
for i=1:length(b)
for j=1:7
bb(k)=b(i);
j=j+1;
k=k+1;
end
i=i+1;
end
pnseq1 =[]
for i=1:length(b)
pnseq1 =[pnseq1 pnseq]
end
%len=length(bb);
for i=1:length(pnseq1)
if pnseq1(i)== 0
pnseq1(i)= -1;
end
end
for i=1:length(bb)
bbs(i)=bb(i).*pnseq1(i);
end
dsss=[];
t=0:0.1:2*pi;
c1=sin(t);
c2=sin(t+pi);
for k=1:length(bb)
if bbs(1,k)== -1
dsss=[dsss c2];
else
dsss=[dsss c1];
end
end
subplot(4,1,1)
stairs(bb)
axis([0 length(bb) -2 2]);
xlabel('index')
ylabel('amplitude')
title('binary data')
subplot(4,1,2)
stairs(pnseq1)
axis([0 length(pnseq1) -2 2]);
xlabel('index')
ylabel('amplitude')
title('pn sequence')
subplot(4,1,3)
stairs(bbs)
axis([0 length(bbs) -2 2]);
xlabel('index')
ylabel('amplitude')
title('spread sequence')
subplot(4,1,4)
plot(dsss)
axis([0 length(dsss) -2 2]);
xlabel('index')
ylabel('amplitude')
title('direct sequence spread spectrum')