EXPERIMENT - 9
AIM:
Understanding and Demonstrating Frequency Hopping Spread Spectrum
APPARATUS REQUIRED:
MATLAB 2023b
THEORY: -
Frequency Hopping Spread Spectrum (FHSS) is a wireless communication technique that enhances
signal security and reduces interference by rapidly switching the carrier frequency over a wide range of
frequencies. In FHSS, the transmitter and receiver "hop" between different frequency channels in a
synchronized manner, following a predetermined pattern known only to them.
The primary advantage of FHSS is its resistance to jamming and interception. Since the signal transmits
over multiple frequencies in a pseudo-random order, unauthorized users have difficulty intercepting or
disrupting communication without knowing the hopping pattern. Additionally, FHSS reduces the impact
of interference by spreading the signal across a wide bandwidth, which makes it less susceptible to noise
or other signals operating on a single frequency.
FHSS is widely used in military communications, Bluetooth, and early versions of Wi-Fi. The system's
ability to maintain communication integrity in noisy environments and enhance privacy makes it ideal
for secure and reliable wireless communication. However, it requires synchronization between
transmitter and receiver, adding complexity to the system design.
FHSS has a wide range of applications and is commonly employed in military communications, where
secure transmission is critical, as well as in consumer technologies like Bluetooth and early versions of
Wi-Fi. The technique's ability to ensure communication integrity, even in noisy or hostile environments,
along with its contribution to enhanced privacy, makes it particularly suitable for secure and dependable
wireless communication.
Vanshika Sharma A2305121004
However, FHSS does introduce some complexity in system design, as it requires precise synchronization
between the transmitter and receiver to ensure they hop together in a coordinated manner. Maintaining
this synchronization adds to the design challenges but is necessary for the technique's effectiveness in
secure communication scenarios.
4o
CODE:
% Frequency Hopping Spread Spectrum
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
clc clear
% Generation of bit pattern
s=round(rand(1,25)); % Generating 20 bits
signal=[]; carrier=[];
t=[0:2*pi/119:2*pi]; % Creating 60 samples for one cosine
for k=1:25 if s(1,k)==0
sig=-ones(1,120); % 120 minus ones for bit 0
else
sig=ones(1,120); % 120 ones for bit 1
end c=cos(t); carrier=[carrier c];
signal=[signal sig];
end subplot(4,1,1);
plot(signal);
axis([-100 3100 -1.5 1.5]); title('\bf\it
Original Bit Sequence');
% BPSK Modulation of the signal
bpsk_sig=signal.*carrier; % Modulating the signal
subplot(4,1,2); plot(bpsk_sig) axis([-100 3100 -1.5
1.5]);
title('\bf\it BPSK Modulated Signal');
% Preparation of 6 new carrier frequencies
t1=[0:2*pi/9:2*pi]; t2=[0:2*pi/19:2*pi];
t3=[0:2*pi/29:2*pi];
t4=[0:2*pi/39:2*pi];
t5=[0:2*pi/59:2*pi];
t6=[0:2*pi/119:2*pi]; c1=cos(t1);
Vanshika Sharma A2305121004
c1=[c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1 c1];
c2=cos(t2); c2=[c2 c2 c2 c2 c2 c2];
c3=cos(t3); c3=[c3 c3 c3 c3];
c4=cos(t4); c4=[c4 c4 c4]; c5=cos(t5);
c5=[c5 c5]; c6=cos(t6);
% Random frequency hopps to form a spread signal
spread_signal=[]; for
n=1:25
c=randint(1,1,[1 6]);
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 subplot(4,1,3)
plot([1:3000],spread_signal); axis([-100
3100 -1.5 1.5]);
title('\bf\it Spread Signal with 6 frequencies');
% Spreading BPSK Signal into wider band with total of 12 frequencies
freq_hopped_sig=bpsk_sig.*spread_signal;
subplot(4,1,4)
plot([1:3000],freq_hopped_sig); axis([-
100 3100 -1.5 1.5]); title('\bf\it Frequency
Hopped Spread Spectrum Signal');
% Expressing the FFTs
figure,subplot(2,1,1)
plot([1:3000],freq_hopped_sig); axis([-
100 3100 -1.5 1.5]);
title('\bf\it Frequency Hopped Spread Spectrum signal and its FFT'); subplot(2,1,2);
plot([1:3000],abs(fft(freq_hopped_sig)))
OUTPUT:
Vanshika Sharma A2305121004
RESULT:
Hence, we have successfully demonstrated Frequency hopping spread spectrum.
CRITIRIA TOTAL MARKS MARKS OBTAINED COMMENTS
Concept (A)
Implementation (B)
Performance (C)
Total
Vanshika Sharma A2305121004
