ofdm.m

stbc_ofdm(time)

function [Pb]=ofdm(snr_in_dB)
%----------------------------------------------------------------------
%本程序在时域里对ofdm的性能进行仿真
%----------------------------------------------------------------------
M = 512000;       % number of bits    
N = 512;         % FFT/IFFT point number
G = 128;         % CP point number
NumOfBlock = M/N;               % the number of the OFDM block
Eb=1;				  	        % energy per bit
snr=10^(snr_in_dB/10);	 	  	% signal to noise ratio
sgma=sqrt(Eb/(2*snr));	  	  	% noise standard variance
%---------------------------------------------------------------------
%采用的信道为6条径的指数衰落信道，抽样间隔为20ns
%---------------------------------------------------------------------
atten_power = exp(-[0:5]);
path_delay = [0:5]*20; 
aver_power=atten_power/sum(atten_power);%进行功率归一化
% generation of the data source
temp = rand(1,M); 
dsource = 2.*(temp>=0.5) - 1;          
s = sqrt(Eb).*dsource;                
% 对频域的信号进行IFFT变换，转化到时域分析
time_temp = sqrt(N)*ifft(reshape(s,N,NumOfBlock));
x = vertcat(time_temp(N-G+1:N,:),time_temp);%加上循环前缀克服多经衰落
x = reshape(x,1,(N+G)*NumOfBlock);
%  AWGN
n = sqrt(sgma)*(randn(1,(N+G)*NumOfBlock)+j*randn(1,(N+G)*NumOfBlock));
h = zeros(length(path_delay),NumOfBlock);
for k=1:6
    h(k,:) = sqrt(aver_power(k)/2)*(randn(1,NumOfBlock) +j*randn(1,NumOfBlock));
end    
for k=1:6
    H(k,:)=reshape(repmat(h(k,:),N+G,1),1,(N+G)*NumOfBlock);
end
Y=zeros(1,(N+G)*NumOfBlock);
for k=1:1:6
    C=H(k,:).*x;
    Y=Y+horzcat(zeros(1,path_delay(k)),C(1:(N+G)*NumOfBlock-path_delay(k)));
end
r=Y+n;
y=reshape(r,N+G,NumOfBlock);%去掉循环前缀，把接收的信号进行DFT变换，转化到频域
freq_y=fft(y(G+1:N+G,:))/sqrt(N);
freq_y1=reshape(freq_y,1,N*NumOfBlock);
h_time=zeros(N,NumOfBlock);
%----------------------------------------------------------------------
%把信道进行DFT变换转移到频域
for i=1:1:6
h_time(path_delay(i)+1,:)=h(i,:);
end
h_freq=fft(h_time)./sqrt(N);
h1_freq=reshape(h_freq,1,N*NumOfBlock);
%-----------------------------------------------------------------------
z = freq_y1./h1_freq;%对接收的信号进行均衡
 
% detection 
decis = 2.*(real(z)>=0)-1;  % real(z)<0 ==> -1 or real(z)>=0 ==> +1
%  probability of error calculation
NumOfBitError = sum(decis ~= dsource);         	         
Pb = NumOfBitError / M;