ber plot for qpsk in rayleigh channel changes every time I simulate

[vaidehihoshing]

Plot of ber vs ebno for qpsk in rayleigh channel using the object rayleighchan changes for each simulation. Why does this happen? My code is as follows:

% Create Rayleigh fading channel object.

chan = rayleighchan(1/10000,0);

% Generate data and apply fading channel.

M = 4; % QPSK modulation order

hMod = modem.pskmod('M', M,'InputType','bit'); % Create a QPSK modulator

hDemod =modem.pskdemod('M',M,'OutputType','bit','DecisionType','hard decision'); % Create a QPSK demodulator

tx = randsrc(50000,1,[0 1]); % Generate a random bit stream

dpskSig = modulate(hMod, tx); % QPSK modulate the signal

fadedSig = filter(chan,dpskSig); % Apply the channel effects

% Compute error rate for different values of SNR.

SNR = 0:2:40; % Range of SNR values, in dB.

numSNR = length(SNR);

BER = zeros(1, numSNR);

for n = 1:numSNR

rxSig = awgn(fadedSig,SNR); % Add Gaussian noise
rx = demodulate(hDemod, rxSig); % Demodulate
% Compute error rate.
[nErrors, BER] = biterr(tx,rx);
end

% Compute theoretical performance results, for comparison.

% Plot BER results.

semilogy(SNR,BER,'r*');

legend('Empirical BER');

xlabel('SNR (dB)'); ylabel('BER');

title('Binary QPSK over Rayleigh Fading Channel');