channel.m

瑞利衰落信道下

%adds the  AWGN and the channel fades and gives the channel output 
%inputs:in_vec (complex symbol vector), alpha (complex fades) 
% snr_db, length (length of the vectors)
%output: out_vec -- complex channel output of size length 

function [out_vec] = channel(in_vec, alpha, snr_db, length)
   
    snr = 10^(snr_db/10);
    sigma = 1/sqrt(2*snr); %snr=1/(2*sigma^2)
    nu_vec = sigma*(randn(length,1)+j*randn(length,1));
    %AWGN of size length with complex variance (2*sigma^2)
    
    for ii=1:length;
        out_vec(ii) = in_vec(ii)*alpha(ii)+nu_vec(ii);
    end