MATLAB Program for Frequency Hopping Spread Spectrum(FHSS) using BPSK m file

Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is used as a multiple access method in the code division multiple access (CDMA) scheme frequency-hopping code division multiple access (FH-CDMA).

Each available frequency band is divided into sub-frequencies. Signals rapidly change ("hop") among these in a predetermined order. Interference at a specific frequency will only affect the signal during that short interval. FHSS can, however, cause interference with adjacent direct-sequence spread spectrum (DSSS) systems.

A sub-type of FHSS used in Bluetooth wireless data transfer is adaptive frequency-hopping spread spectrum (AFH).

MATLAB Program:

% Frequency Hopping Spread Spectrum

clc;

clear all;

close all;

% Generation of bits

N=20;

s=randint(1,N);   % Generating N bits

signal=[]; 

carrier=[];

T=180;

t=0:2*pi/(T-1):2*pi;     % Creating T samples for one cosine

subplot(5,1,1);

stem(s);

set(gca,'XTick',1:N,'XLim',[0.66 N+0.33]);    %Setting axis limits and scale for the graph

title('Binary information');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% Generation of bit pattern/bit stream(Polar NRZ type)

for k=1:N

     if s(1,k)==0

         sig=-ones(1,T);    % T no.of MINUS ONES for bit 0

     else

         sig=ones(1,T);     % T no.of ONES for bit 1

     end

     c=cos(t);  

     carrier=[carrier c];

     signal=[signal sig];

end

subplot(5,1,2);

stairs(signal);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);      %Setting axis limits and scale for the graph

title('Original Bit Sequence');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% BPSK Modulation of the signal

bpsk_sig=signal.*carrier;   % Modulating the signal

subplot(5,1,3);

plot(bpsk_sig);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);

title('BPSK Modulated Signal');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% Preparation of 6 new carrier frequencies

t1=0:2*pi/8:2*pi;

t2=0:2*pi/9:2*pi;

t3=0:2*pi/17:2*pi;

t4=0:2*pi/35:2*pi;

t5=0:2*pi/89:2*pi;

t6=0:2*pi/179:2*pi;

c1=cos(t1);

c1=[c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1];

c2=cos(t2);

c2=[c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2 c2] ;

c3=cos(t3);

c3=[c3 c3 c3 c3 c3 c3 c3 c3 c3 c3] ;

c4=cos(t4);

c4=[c4 c4 c4 c4 c4];

c5=cos(t5);

c5=[c5 c5];

c6=cos(t6);

% Random frequency hops to form a spread signal

spread_signal=[];

spread=[];

for n=1:N

    c=randint(1,1,[1 6]);

    spread=[spread c];

    switch(c)

        case(1)

            spread_signal=[spread_signal c1];

        case(2)

            spread_signal=[spread_signal c2];

        case(3)

            spread_signal=[spread_signal c3];

        case(4)

            spread_signal=[spread_signal c4];

        case(5)       

            spread_signal=[spread_signal c5];

        case(6)

            spread_signal=[spread_signal c6];

    end

end

display('Spreading Code :');

display(spread);

subplot(5,1,4);

plot(1:N*T,spread_signal);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);

title('Spreading Code with 6 frequencies');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% Spreading BPSK Signal into wider band with total of 12 frequencies

freq_hopped_sig=bpsk_sig.*spread_signal;

subplot(5,1,5);

plot(1:N*T,freq_hopped_sig);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);

title('Frequency Hopped Spread Spectrum Signal');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% Receiver Side

figure;

subplot(3,1,1);

plot(1:N*T,freq_hopped_sig);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);

title('Frequency Hopped Spread Spectrum Signal');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% Demodulated BPSK Signal

demod_psk=freq_hopped_sig.*spread_signal;

subplot(3,1,2);

plot(demod_psk);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);

title('Demodulated BPSK Signal');

ylabel('Amplitude(V)');

xlabel('Time(s)');

% Demodulated Binary Signal

demod_sig=[];

for j=0:T:N*T-1

     if demod_psk(j+1)<0

         sig=-ones(1,T);

     else

         sig=ones(1,T);

     end

     demod_sig=[demod_sig sig];

end

subplot(3,1,3);

stairs(demod_sig);

set(gca,'XTick',0:T:N*T,'XLim',[-60 N*T+60],'YLim',[-1.5 1.5]);      %Setting axis limits and scale for the graph

title('Demodulated Binary Signal');

ylabel('Amplitude(V)');

xlabel('Time(s)');

OUTPUT