PSK Modulation performance in rayleigh channel

Hi dear friends:

I intend to simulate the performance of PSK modulation in rayleigh channel. First I used the example of Matlab for DPSK which is:

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

% Generate data and apply fading channel.
M = 2; % DBPSK modulation order
hMod = modem.dpskmod('M', M);       % Create a DPSK modulator
hDemod = modem.dpskdemod(hMod);     % Create a DPSK demodulator
                                        % using the modulator
tx = randi([0 M-1],50000,1);        % Generate a random bit stream
dpskSig = modulate(hMod, tx);       % DPSK modulate the signal
fadedSig = filter(chan,dpskSig);    % Apply the channel effects

% Compute error rate for different values of SNR.
SNR = 0:2:20; % Range of SNR values, in dB.
numSNR = length(SNR);
BER = zeros(1, numSNR);
for n = 1:numSNR
   rxSig = awgn(fadedSig,SNR(n));   % Add Gaussian noise
   rx = demodulate(hDemod, rxSig);  % Demodulate
   reset(hDemod);
   % Compute error rate.
   [nErrors, BER(n)] = biterr(tx,rx);
end

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

the output for this code is sensible and it fits the theoretical curve.

But when I edit the code to do the simulations for psk modulation like bellow:

hMod = modem.pskmod('M', M);       
hDemod = modem.pskdemod(hMod);

This time I get an approximately flat line as the BER curve. I don't know what's wrong with it?! It will be very appreciated if you help me with this tricky problem.

Answer 1

[Deepak Rathore]

Dear This is due to not using the channel estimation or equalizer. DPSK not require but bpsk, qpsk and qam require the channel compensation at the receiver.

[KARTEEK RAMBATLA]

sir, why does DPSK donot need channel estimation. I would like to know the outlines of the mathematical treatment.Also,how to perform channel estimation (idea). what is the affect of rayleigh channel specifications over the performance.

[Shahzad Ahmed]

because you do not need to synchronization for DPSK i guess

[Yashar]

Thank you very much for your answer to my question.

[ABDUL]

which is the best channel estimation or equalizer that can be used for m-ary psk for implementing the BER of the M-ary psk systems

Regards

Abdul Azeez

[Mohamed]

Thanks, that saved my life!