Explaining BPSK Demodulation ?

Hi everyone,

I've a simple question (or it should be one).

I have a sequence, let's say it is u = [1 1 0]. I've modulate it using BPSK as u_BPSK = [-1 -1 1]. I've sent it through AWGN channel using the command I found on the internet.

y = u_BPSK + sqrt(N0/2)*(randn(size(u_BPSK))+i*randn(size(u_BPSK)));

where N0 is the noise power spectral density:

N0 = 1/(10^(SNRdB/10));

I just want to understand how this type of demodulation.

Thanks in advance.

Answer 1

[Hari]

Hi Jason,

I understand that you want to know how to perform BPSK demodulation on a sequence that has been transmitted through an AWGN channel. You have already modulated the sequence using BPSK and added noise to it.

Understanding BPSK Demodulation: BPSK demodulation involves detecting the transmitted bits from the received noisy signal. The process is simple: if the received signal is greater than zero, the bit is '1'; otherwise, it is '0'.

Noise Addition in the Channel: You added noise using the equation

y = u_BPSK + sqrt(N0/2)*(randn(size(u_BPSK))+i*randn(size(u_BPSK)));

This simulates the effect of an AWGN channel.

Demodulation Process:

First, you need to strip the imaginary part (if any) because BPSK is a real-valued modulation scheme.

Then, make a decision based on the sign of the real part of the received signal.

Begin by removing any imaginary components.

y_real = real(y);

Next, demodulate by checking the sign of the real part.

u_demodulated = y_real > 0;

Convert logical array to binary.

u_demodulated = double(u_demodulated);

Final Output: The demodulated sequence should match the original sequence, barring any errors introduced by the noise.

Refer to the documentation of "BPSK Modulation" for more details: https://www.mathworks.com/help/comm/ref/comm.bpskmodulator-system-object.html

Refer to the documentation of "AWGN Channel" for more details: https://www.mathworks.com/help/comm/ref/comm.awgnchannel-system-object.html

Refer to the documentation of "randn" function for more details: https://www.mathworks.com/help/matlab/ref/randn.html

Hope this helps!

[Jason Hathaway]

Many thanks Hari for getting back on this after all these years. 😁

I have asked this question when I was working on one project during university. Time flies!

Thanks again!