channel_simulator.m

il s a GSM channel simulation

function [ r ] = channel_simulator(I,Q,OSR)
% CHANNEL_SIMULATOR:
%           This function is intended as an skeleton for channel 
%           simulator implementations, and is not to be considderd
%           as an actual channel simulator. It does however provide
%           a mean for making the GSMsim package produce detection 
%           errors. Substitute this function with userdefined 
%           functions.
%
% SYNTAX:   channel_simulator(I,Q,OSR)
%
% INPUT:    I:      The inphase signal as produced by the modulator.
%           Q:      The quadrature signal as it is produced by the
%                   modulator .
%           OSR:    The over sampling ratio, defined as f_s/r_b. This
%                   parameter is not used in the incuded channel_simulator
%                   function, but is passed to the function for future
%                   use.
%
% OUTPUT:   r:      The received signal, as predicted by the channel
%                   simulator.
%
% WARNINGS: Do not use this function for scientific purposes.
% 
% AUTHOR:   Jan H. Mikkelsen / Arne Norre Ekstr鴐
% EMAIL:    [e-mail] / [e-mail]
%
% $Id: channel_simulator.m,v 1.6 1998/02/12 10:56:13 aneks Exp $

% THE CHANNEL SIMULATOR INCLUDED IN THE GSMsim PACKAGE ONLY ADD
% NOISE, AND SHOULD _NOT_ BE USED FOR SCIENTIFIC PURPOSES.
% 
% SUBSTITUTE THE NEXT LINES WITH A LINE CONTAINING A CHANNEL SIMULATION.
% HERE WE SIMPLY ADD NOISE OF VARIANCE Var TO THE MODULATED SIGNAL. NOTE
% THAT THIS NOISE IS ONLY BANDLIMITED BY THE SAMPLERATE.
% 
I=2;
Var=0.02;
FACTOR=sqrt(Var);
samples=length(I);
random=randn(1,2*samples);
r= I + j.*Q + random(1:samples).*FACTOR;
r= r + random(samples+1:2*samples).*FACTOR.*j;