sttc_test_2x2.m

基于MIMO通信系统中的各种空时编译码算法

% 2X2 STTC,QPSK,4 states
%% initialization
clear all;
close all;
clc;
frame_length=10000;
original_bits=randint(frame_length,2);
code_matrix(:,:,1)=[0 0 0 0;
                    1 1 1 1;
                    2 2 2 2;
                    3 3 3 3];
code_matrix(:,:,2)=[0 1 2 3;
                    0 1 2 3;
                    0 1 2 3;
                    0 1 2 3];
%% STTC coding
orig_num=bi2de(original_bits,'left-msb'); % 0~3
sig_sttc=zeros(2,length(orig_num));
now_num=1;
for ii=1:length(orig_num)
    next_num=orig_num(ii,1)+1;  % 1~4
    sig_sttc(:,ii)=reshape(code_matrix(now_num,next_num,:),2,1);
    now_num=next_num;
end
sig_sttc=qammod(sig_sttc,4);
%% channel matrix
% you can modify the channel to a 2*2*length matrix, in which '2*2' means Nr*Nt
H=zeros(2,2,frame_length);
for n=1:2
    H(n,:,:)=(randn(size(sig_sttc))+j*randn(size(sig_sttc)))/sqrt(2); %Raylaigh channel
end
received_sig=zeros(size(sig_sttc));
for n=1:length(sig_sttc)
    received_sig(:,n)=reshape(H(:,:,n),2,2)*sig_sttc(:,n);
end
%% viterbi algorithm
survivors=zeros(4,frame_length);
s_temp=survivors;
distance=zeros(4,1); % Euclidian distance
d_temp=distance;
d_q=zeros(1,4);
% snr=20db
received_sig=received_sig+sqrt(2/(10^(20/10)))*(randn(size(received_sig))+j*randn(size(received_sig)));
for p=1:4 
    X_e=qammod(reshape(code_matrix(1,p,:),2,1),4);
    distance(p,1)=sum(abs(received_sig(:,1)-reshape(H(:,:,1),2,2)*X_e).^2);
    survivors(p,1)=p-1;
end
for n=2:frame_length
    for p=1:4 % check state_p
        for q=1:4 % check state_q to state_p
            X_e=qammod(reshape(code_matrix(q,p,:),2,1),4);
            d_q(q)=sum(abs(received_sig(:,n)-reshape(H(:,:,n),2,2)*X_e).^2)+distance(q,1);
        end
        [v in]=min(d_q);
        d_temp(p,1)=v;
        s_temp(p,1:n)=[survivors(in,1:(n-1)) p-1];
    end
    distance=d_temp;
    survivors=s_temp;
end
[v in]=min(distance);
decoded_num=survivors(in,:);
decoded_num=decoded_num.';
decoded_bits=de2bi(decoded_num,'left-msb');
[err_num ber]=biterr(original_bits,decoded_bits);
ber