channel.m

MIMO and VBLAST( please see the documentation)

function varargout = channel(sig,ch_conf,fading,varargin)

%CHANNEL MIMO channel model.
%   SIG_OUT = CHANNEL(SIG_IN,FADING,SNR) corrupts input signal
%   SIG_IN by the desired type of channel fading. Possible values
%   for FADING are 'None'|'AWGN'|'Rayleygh'. A signal-to-noise 
%   ratio in decibels must be set unlike a 'None' fading is chosen.
%   Fading is assumed to be quasistatic and flat. 
%
%   NOTE: When a 'None' option is chosen than there are no noise in
%         the MIMO channel, however the direct signals will be
%         combined at the receiver input.
%
%   [SIG_OUT,CH_COEFS] = CHANNEL(SIG_IN,FADING,SNR) same as above
%   but returns a matrix of complex path fading. This may be useful
%   when performing data detection.
%
%   [SIG_OUT,CH_COEFS] = CHANNEL(SIG_IN,FADING,SNR,'EchoOn') turns
%   the function echo on.
%
%   See also DETECT, EST.

%   Copyright 2001-2002 Kamil Anis, [e-mail]
%   Dept. of Radioelectronics, 
%   Faculty of Electrical Engineering
%   Czech Technical University in Pragu
%   $Revision: 2.0 $  $Date: 2002/10/23 17:33:28 $
%   --
%   <additional stuff should go here>

[sig_length,space_dim,frames] = size(sig);
sig_pwr = varargin{1};
snr = varargin{2};
symb_time = varargin{3};
smplper = varargin{4};

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% BODY BEGIN %%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

sigma_ch = 1;
esr = symb_time * sigma_ch ^2 * ch_conf(1) * sig_pwr;
n0 = esr / (10 ^ (0.1 * snr));
sigma = sqrt(2 * n0 / smplper);
const = sqrt(2);

switch fading
case 'Rayleigh'
  ch_coefs = (randn(ch_conf(1),ch_conf(2),frames) +...
    i * randn(ch_conf(1),ch_conf(2),frames)) / const;

  ch_noise = (randn(sig_length,space_dim,frames) +...
    i * randn(sig_length,space_dim,frames)) * sigma / const;

case 'AWGN'
  ch_coefs = ones(ch_conf(1),ch_conf(2),frames);

  ch_noise = (randn(sig_length,space_dim,frames) +...
    i * randn(sig_length,space_dim,frames)) * sigma / const;

case 'None'
  ch_coefs = ones(ch_conf(1),ch_conf(2),frames);

  ch_noise = zeros(sig_length,space_dim,frames);
end

% signal mixture
for k = 1:frames % no 3D arrays multiplication is available
    sig_add(:,:,k) = sig(:,:,k) * ch_coefs(:,:,k);
end

sig_corr = sig_add + ch_noise;
varargout = {sig_corr,ch_coefs};

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% BODY END %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if (isempty(varargin) == 0) & (varargin{end} == 'EchoOn')
	[indent,gap,name] =  iprompt('CHANEL:');
	
	switch fading
	case 'None'
      str2 = [''];
	otherwise
      str1 = num2str(snr);
      str2 = [' ,SNR -> ',str1,' [dB]'];
	end
	
	disp(' ');
	disp([name,gap,'Channel fading -> ',fading,str2,'.']);
	disp(' ');
end