single Relay simulation using QAM

[amana]

Hi all
I have code for single link (source- destination) using QAM simulation to produce BER curve. however I need to add relay node between source and destination and produce BER curve. can anyone help me with this please
here is the code (matlab)

M = 16;                     % Size of signal constellation
k = log2(M);                % Number of bits per symbol
n = 10^6;                    % Number of bits to process
nSyms = n/k;                % Number of symbols

hMod = modem.qammod(M);         % Create a 16-QAM modulator
hMod.InputType = 'Bit';         % Accept bits as inputs
hMod.SymbolOrder = 'Gray';         % Accept bits as inputs
hDemod = modem.qamdemod(hMod);  % Create a 16-QAM based on the modulator

x = randi([0 1],n,1); % Random binary data stream
tx = modulate(hMod,x);

EbNo = 0:10; % In dB
SNR = EbNo + 10*log10(k);

rx = zeros(nSyms,length(SNR));
% Simulation bit error rate
bit_error_rate = zeros(length(SNR),1);
for i=1:length(SNR)
    rx(:,i) = awgn(tx,SNR(i),'measured');
end

% Demodulation
rx_demod = demodulate(hDemod,rx);
for i=1:length(SNR)
    [num,bit_error_rate(i)] = biterr(x,rx_demod(:,i));
end

% fprintf('\nThe Gray coding bit error rate = %5.2e,  based on %d errors\n', ...
%     bit_error_rate(i), num)

% Theoritical bit error rate

theoryBer = (1/k)*3/2*erfc(sqrt(k*0.1*(10.^(EbNo/10))));
figure;
semilogy(EbNo,theoryBer,'ro-',EbNo, bit_error_rate, 'b*');
grid on;
legend('theory', 'simulation ');
xlabel('Eb/No, dB');
ylabel('Bit Error Rate');
title('Bit error probability curve for 16-QAM modulation');

Thanks in advance