function [H, H_f]=create_channel(Mt, Mr, A, N);% function [H, H_f]=create_channel(Mt, Mr, A, N);%%   A - vector containing the power-delay profile (real values)%   Mt - number of Tx antennas%   Mr - number of Rx antennas%   N - number of vector symbols to be sent in a single OFDM symbol Tx%       ie: N MIMO transmissions in one OFDM symbol% This is for Rayleigh frequency-selective fading, which assumes complex% Gaussian matrix elements with in-phase and quadrature components independent.% Assume iid matrix channel elements, and further, independent channel taps% define the channel tapsH_int = 1/sqrt(2)*(randn(Mr*length(A),Mt) + j*randn(Mr*length(A),Mt));H_int2=[];for i = 1:length(A)    H_int2 = [H_int2;sqrt(A(i))*H_int((i-1)*Mr+1:i*Mr,:)];end%h_f = fft(H_int2',64);%%H = H_int2';H_int2 = [H_int2;zeros((N-length(A))*Mr,Mt)];H_f = zeros(Mr,Mt*(N-16));for i = 1:Mt    for j = 1:Mr        h_f = fft(H_int2(j:Mr:(N-16-1)*Mr+j,i));        for k = 1:(N-16)            H_f(j,i+(k-1)*Mt) = h_f(k);        end    endend% every Mr row block is the channel at time = ( 1, 2, ... N)H=[H_int2];for i = 1:N-1    H=[H,[zeros(Mr*i,Mt);H_int2(1:(N-i)*Mr,:)]];end