www.gusucode.com > MIMO与SISO仿真程序 > MIMO-OFDM/all code/MIMO_v9_4_2x2_STBC_offset.m

    clc; clear all; close all

data = 2^16;                                    % data points

n_fft = 64;                                     % fft size
    
n_cp = 16;                                      % cyclic prefix

snr = [0:1:35];
errors = zeros(size(snr));
ber = zeros(size(snr));
%%
binary_data = round(rand(data,1));              % generate data
h = [randn()+randn()*1i, randn()+randn()*1i; randn()+randn()*1i, randn()+randn()*1i];
%%
for mod_value = 1:3
% bits per symbol
if mod_value == 1
    symbols = 2;   
elseif mod_value == 2
    symbols = 4;
else 
    symbols = 6;
    while floor(length(binary_data)/symbols) ~= length(binary_data)/symbols
    binary_data = [binary_data; zeros(1,1)];                                    %padding for symbol mapping
    end
    while floor(length(binary_data)/symbols/n_fft) ~= length(binary_data)/symbols/n_fft
    binary_data = [binary_data; zeros(6,1)];                                    %padding for subcarriers mapping
    end
end

mod_method = 2^symbols;       
                                                
mod_data = qammod(binary_data,mod_method,'unitaveragepower',true,'inputtype','bit');
%mod_data = mod_data./abs(mod_data);
%% STBC
% [x1 -x2* ; x2 x1*]
STBC = zeros(2*length(mod_data),1);
for i = 0:(length(mod_data)/2-1)
    STBC(4*i+1) = mod_data(2*i+1);
    STBC(4*i+2) = mod_data(2*i+2);
    STBC(4*i+3) = -conj(mod_data(2*i+2));
    STBC(4*i+4) = conj(mod_data(2*i+1));
end

STBC = reshape(STBC.',2,length(mod_data));
%% splitting up the data between the transmitters
Tx1 = STBC(1,:);
Tx2 = STBC(2,:);

% while floor(length(Tx1)/64) ~= length(Tx1)/64
%     Tx1 = [Tx1 zeros(1,1)];
%     Tx2 = [Tx2 zeros(1,1)];
% end


%% IFFT
%S/P
Xk1 = reshape(Tx1,n_fft,length(Tx1)/n_fft);
Xk2 = reshape(Tx2,n_fft,length(Tx2)/n_fft);

Xn1 = ifft(Xk1);
Xn2 = ifft(Xk2);
%% Cyclic prefix
Xn1_cp = [Xn1((end - n_cp + 1):end,:);Xn1];  
Xn2_cp = [Xn2((end - n_cp + 1):end,:);Xn2]; 


%% P/S
xn1 = Xn1_cp(:);
xn2 = Xn2_cp(:);
%% Channel

for k = 1:length(snr)
yn11 = xn1*h(1,1);            % y time, receiver 
yn21 = xn2*h(2,1);

yn12 = xn1*h(1,2);
yn22 = xn2*h(2,2);

% add noise

yn11 = awgn(yn11,snr(k),'measured');
yn21 = awgn(yn21,snr(k),'measured');
yn12 = awgn(yn12,snr(k),'measured');
yn22 = awgn(yn22,snr(k),'measured');

% delay added to 

delay = 0;

% adding delay to first transmitter
yn11 = [zeros(delay,1);yn11];
yn21 = [yn21; zeros(delay,1)];

yn12 = [yn12; zeros(delay,1)];
yn22 = [yn22; zeros(delay,1)];

% superposition of two received signals at receiver
yn1 = yn11 + yn21;                    % y(1) = h1*x1 + h2*x2 ; y(2) = -h2* x1* + h1 * x2*
yn2 = yn12 + yn22;

yn1 = yn1(1:end-delay);
yn2 = yn2(1:end-delay);

%% S/P
yn1_sp = reshape(yn1,n_fft+n_cp,length(Xn1_cp));
yn2_sp = reshape(yn2,n_fft+n_cp,length(Xn1_cp));
%% remove cyclic prefix
yn1_rcp = yn1_sp((n_cp + 1):end,:);
yn2_rcp = yn2_sp((n_cp + 1):end,:);

%% DFT
Yk1_block = fft(yn1_rcp);
Yk2_block = fft(yn2_rcp);

Yk1 = Yk1_block(:);              % transform 64 subchannels back into 1 stream
Yk2 = Yk2_block(:);

%% STBC decoding
abs_h = sum(sum(abs(h).^2));
% assume perfect channel estimation
H = [ conj(h(1,1)) , conj(h(1,2)), h(2,1), h(2,2) ; ...         % pseudo inverse
    conj(h(2,1)), conj(h(2,2)), -h(1,1) , -h(1,2)]./ abs_h;

X_hat1 = zeros(length(Tx1)/2,1);
X_hat2 = zeros(length(Tx2)/2,1);

X = zeros(length(Tx1)/2,1);

for i = 0:length(Yk1)/2-1
Yk1(2*i+2) = conj(Yk1(2*i+2));
Yk2(2*i+2) = conj(Yk2(2*i+2));

X_hat1(i+1) = H(1,1)*Yk1(2*i+1) + H(1,2)*Yk2(2*i+1) + H(1,3)*Yk1(2*i+2) + H(1,4)*Yk2(2*i+2);       
X_hat2(i+1) = H(2,1)*Yk1(2*i+1) + H(2,2)*Yk2(2*i+1) + H(2,3)*Yk1(2*i+2) + H(2,4)*Yk2(2*i+2);

X(2*i+1) = X_hat1(i+1);
X(2*i+2) = X_hat2(i+1);

end

%% demodulate
X_demod = qamdemod(X,mod_method,'unitaveragepower',true,'outputtype','bit');
%output = reshape(X_demod.',size(binary_data));
output = X_demod(:).';
%%

errors(mod_value,k) = 0;
for i = 1:length(binary_data)
    if output(i) ~= binary_data(i)
        errors(mod_value,k) = errors(mod_value,k) + 1;
    end
end
ber(mod_value,k) = errors(mod_value,k)/length(binary_data);

end

semilogy(snr,ber(mod_value,:),'-');
title('STBC for 2x2 System with No Time Offset'); legend('4QAM','16QAM','64QAM');
xlabel('E_b/N_o (dB)'); ylabel('BER'); grid on; hold on
end