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PSK Modulation performance in rayleigh channel

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Yashar
Yashar on 3 Nov 2012
Commented: KARTEEK RAMBATLA on 20 Feb 2016
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.

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Answers (1)

Deepak Rathore
Deepak Rathore on 21 Apr 2013
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.

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KARTEEK RAMBATLA
KARTEEK RAMBATLA on 20 Feb 2016
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.

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