BPSK modulation. Calculate and plot the one-sided amplitude spectrum of the BPSK-modulated signal

A sequence of alternating “1” and “-1” bits are BPSK-modulated onto a carrier. The bit duration is 1 μs, and the carrier frequency is 1.5 GHz.

Calculate and plot the one-sided amplitude spectrum of the BPSK-modulated signal

(use Matlab®). Clearly label all axes and frequency domain components.

Now, this is my code.

%% BPSK modulation

clc

close all

clear

% Sequence of alternating "1" and "-1" bits of BPSK

t=-1:0.0001:1;

% bit duration is 1 μs

T=10^-6 ;

fm=1/T;

% Carrier frequency is 1.5 GHz

fc=1.5*10^9;

% Function for computing the one-sided amplitude spectrum of BPSK-modulated signal

s = (cos(2*pi*fm.*t)) .* cos(2*pi*fc.*t)

subplot(2,2,1);plot(t,s,'linewidth',2);

title('One-sided Amplitude Spectrum of the BPSK-modulated signal')

xlabel('time in microseconds');ylabel('Signal Amplitude');

grid;

My question is the plot. This plot dont make sense. The plot should be like a sine wave? How i can plot the frequency and time?

Thanks in advances for any guindances,im a beginner using matlab.

Answer 1

[Swetha Polemoni]

Hi,

Following code snippet is for generating sequence of 1 and -1

N=100;  % number of symbols
x= randi([0,1],N,1); 
BPSK=2*x-1; % sequence of 1 and -1

For better understading BPSK modulation implementation in Matlab refer this.

For implementation of single sided amplitude spectrum in Matlab refer this .

This might help you.