%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % All rights reserved by Krishna Pillai, http://www.dsplog.com % The file may not be re-distributed without explicit authorization % from Krishna Pillai. % Checked for proper operation with Octave Version 3.0.0 % Author : Krishna Pillai % Email : krishna@dsplog.com % Version : 1.0 % Date : 14th December 2008 % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Script for computing the BER for BPSK modulation in a % Rayleigh fading channel with 2 Tx, 2Rx MIMO channel % Maximum Likelihood equalization
clear N = 10^6; % number of bits or symbols Eb_N0_dB = [0:25]; % multiple Eb/N0 values nTx = 4; nRx = 4; for ii = 1:length(Eb_N0_dB)
% Transmitter
ip = rand(1,N)>0.5; % generating 0,1 with equal probability
s = 2*ip-1; % BPSK modulation 0 -> -1; 1 -> 0
sMod = kron(s,ones(nRx,1)); %
sMod = reshape(sMod,[nRx,nTx,N/nTx]); % grouping in [nRx,nTx,N/NTx ] matrix
h = 1/sqrt(2)*[randn(nRx,nTx,N/nTx) + j*randn(nRx,nTx,N/nTx)]; % Rayleigh channel
n = 1/sqrt(2)*[randn(nRx,N/nTx) + j*randn(nRx,N/nTx)]; % white gaussian noise, 0dB variance
% Channel and noise Noise addition
y = squeeze(sum(h.*sMod,2)) + 10^(-Eb_N0_dB(ii)/20)*n;
% Maximum Likelihood Receiver
% ----------------------------
% if [s1 s2 ] = [+1,+1 ]
sHat1 = [1 1];
sHat1 = repmat(sHat1,[1 ,N/2]);
sHat1Mod = kron(sHat1,ones(nRx,1));
sHat1Mod = reshape(sHat1Mod,[nRx,nTx,N/nTx]);
zHat1 = squeeze(sum(h.*sHat1Mod,2)) ;
J11 = sum(abs(y - zHat1),1);
% if [s1 s2 ] = [+1,-1 ]
sHat2 = [1 -1];
sHat2 = repmat(sHat2,[1 ,N/2]);
sHat2Mod = kron(sHat2,ones(nRx,1));
sHat2Mod = reshape(sHat2Mod,[nRx,nTx,N/nTx]);
zHat2 = squeeze(sum(h.*sHat2Mod,2)) ;
J10 = sum(abs(y - zHat2),1);
% if [s1 s2 ] = [-1,+1 ]
sHat3 = [-1 1];
sHat3 = repmat(sHat3,[1 ,N/2]);
sHat3Mod = kron(sHat3,ones(nRx,1));
sHat3Mod = reshape(sHat3Mod,[nRx,nTx,N/nTx]);
zHat3 = squeeze(sum(h.*sHat3Mod,2)) ;
J01 = sum(abs(y - zHat3),1);
% if [s1 s2 ] = [-1,-1 ]
sHat4 = [-1 -1];
sHat4 = repmat(sHat4,[1 ,N/2]);
sHat4Mod = kron(sHat4,ones(nRx,1));
sHat4Mod = reshape(sHat4Mod,[nRx,nTx,N/nTx]);
zHat4 = squeeze(sum(h.*sHat4Mod,2)) ;
J00 = sum(abs(y - zHat4),1);
% finding the minimum from the four alphabet combinations
rVec = [J11;J10;J01;J00];
[jj dd] = min(rVec,[],1);
% mapping the minima to bits
ref = [1 1; 1 0; 0 1; 0 0 ];
ipHat = zeros(1,N);
ipHat(1:2:end) = ref(dd,1);
ipHat(2:2:end) = ref(dd,2);
% counting the errors
nErr(ii) = size(find([ip- ipHat]),2);
end
simBer = nErr/N; % simulated ber EbN0Lin = 10.^(Eb_N0_dB/10); theoryBer_nRx1 = 0.5.*(1-1*(1+1./EbN0Lin).^(-0.5)); p = 1/2 - 1/2*(1+1./EbN0Lin).^(-1/2); theoryBerMRC_nRx2 = p.^2.*(1+2*(1-p));
close all figure semilogy(Eb_N0_dB,theoryBer_nRx1,'bp-','LineWidth',2); hold on semilogy(Eb_N0_dB,theoryBerMRC_nRx2,'kd-','LineWidth',2); semilogy(Eb_N0_dB,simBer,'mo-','LineWidth',2); axis([0 25 10^-5 0.5]) grid on legend('theory (nTx=1,nRx=1)', 'theory (nTx=1,nRx=2, MRC)', 'sim (nTx=2, nRx=2, ML)'); xlabel('Average Eb/No,dB'); ylabel('Bit Error Rate'); title('BER for BPSK modulation with 2x2 MIMO and ML equalizer (Rayleigh channel)');
