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From: Yaseen Al-Hasan on 1 Aug 2010 06:03
Hi , I have the following problem:
I receive
the same BER for all varying SNR values (BER around 50%).

May somebody give me an advice?

My code is:

clc; clear; close all
% Create Rayleigh fading channel object.
chan = rayleighchan(1/10000,100);

% Generate data and apply fading channel.
M = 2; % BPSK modulation order
tx = ones(1,50000); % Random bit stream
pskSig = pskmod(tx,M); % BPSK signal
fadedSig = filter(chan,pskSig); % Effect of channel

% Compute error rate for different values of SNR.
SNR = 0:2:20; % Range of SNR values, in dB.
for n = 1:length(SNR)
rxSig = awgn(fadedSig,SNR(n)); % Add Gaussian noise.
rx = pskdemod(rxSig,M); % Demodulate.
% Compute error rate.
% Ignore first sample because of DPSK initial condition.
[nErrors, BER(n)] = biterr(tx(2:end),rx(2:end));
end

% Compute theoretical performance results, for comparison.
BERtheory = berfading(SNR,'psk',M,1);

% Plot BER results.
semilogy(SNR,BERtheory,'b-',SNR,BER,'r*');
legend('Theoretical BER','Empirical BER');
xlabel('SNR (dB)'); ylabel('BER');
title('Binary DPSK over Rayleigh Fading Channel');


thanks
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