vblast_test.m

基于MIMO通信系统中的各种空时编译码算法

clear all;
clc;
%% initialization
Nt=2;
Nr=2;
M=4;
tx_bits=randint(15000,1);
%% modulation
layered_bits=reshape(tx_bits,Nt,[]);
layered_sym=zeros(Nt,length(layered_bits)/log2(M));
for n=1:Nt
    temp=bi2de(reshape(layered_bits(n,:),log2(M),[]).','left-msb');
    layered_sym(n,:)=qammod(temp,M).';
end
sym_length=length(layered_sym);
P_mean=mean(abs(qammod((0:M-1),M)).^2);
%% transmit
H=(randn(Nr,Nt,sym_length)+j*randn(Nr,Nt,sym_length))/sqrt(2);
EbNo=0:10:30;
ber=zeros(size(EbNo));
rec_sig=zeros(Nr,sym_length);
for n=1:sym_length
    rec_sig(:,n)=H(:,:,n)*layered_sym(:,n);
end
SNR=EbNo+10*log10(log2(M));
%% AWGN
for rr=1:length(SNR)
sigma=sqrt(0.5*P_mean/(Nt*10^(SNR(rr)/10)));
awgn_sig=rec_sig+sigma*(randn(size(rec_sig))+j*randn(size(rec_sig)));
decoded_sym=zeros(size(layered_sym));
%% Successive Interference Cancellation
for n=1:sym_length
    H_save=reshape(H(:,:,n),Nr,Nt);
    H_temp=H_save;
    r=awgn_sig(:,n);
    G=pinv(H_save);
    [g0 k]=min(sum(abs(G).^2,2));
    for ii=1:Nt  % k must be stored!!!
        kk(ii)=k;
        w=G(k,:);
        y=w*r;
        decoded_sym(k,n)=y;
        r=r-y*H_save(:,k);
        H_temp(:,k)=zeros(Nr,1);
        G=pinv(H_temp);
        for ki=1:ii
           G(kk(ki),:)=inf;
        end
        [g0 k]=min(sum(abs(G).^2,2));
    end
end
%% de-qammod
rec_layered_num=qamdemod(decoded_sym,M);
rec_layered_bits=zeros(size(layered_bits));
for n=1:Nt
    rec_layered_bits(n,:)=reshape(de2bi(rec_layered_num(n,:).',log2(M),'left-msb').',1,[]).';
end
rx_bits=reshape(rec_layered_bits,1,[]).';
[num_err ber(rr)]=biterr(rx_bits,tx_bits);
end
%% plot
semilogy(EbNo,ber,'r-o');
xlabel('Eb/No');
ylabel('Bit Error Rate');
title('VBLAST');
grid on;
hold on;