channel.m

这是一个关于完成QAM调制的Matlab示例程序

function [rxMsg] = Channel(modMsg,avgSnr,sampsPerSymbol,RAYLEIGH,SLOWFADE)
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% function [rxMsg] = Channel(modMsg,gammaBar)
% This function models the transmission channel.  As such, it will
% take modMsg, apply noise and fading, and return rxMsg.
%
% modMsg = modulated message from the transmitter.  Assumed to be 
%          an integer number of symbols, aligned to first sample.
% avgSnr = average received SNR desired, in dB
% sampsPerSymbol = samples per symbol.
% rxMsg = modulated message with AWGN, Rayleigh fading applied.
%         Rayleigh fading is constant over a single symbol, and 
%         currently independent from symbol to symbol.
%         To simplify things at the receiver, the signal power
%         shall remain constant, as is the case with AGC.  This
%         means that instead of fading the signal, the noise
%         is scaled by 1/fading.
%
% RAYLEIGH = boolean value for Rayleigh fading. If = nonzero value
%            (==1), then Rayleigh fading will be applied.  Else, just awgn.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if (RAYLEIGH)
	% Complex Gaussian noise
	noiseVect = randn(size(modMsg)) + j*randn(size(modMsg));
	
	fadeVectLength = (length(modMsg)/sampsPerSymbol);
    if (SLOWFADE)
	    fadeVect(1:fadeVectLength,1) = (1/sqrt(2))*abs(randn + j*randn);
    else
		% Modelling Rayleigh fading as the envelope of complex noise
		% Right now, every symbol has independent fading.  May have to consider
		% correlation time later.
		%fadeVectLength = (length(modMsg)/sampsPerSymbol);
		fadeVect = (1/sqrt(2))*abs(randn(1,fadeVectLength) + j*randn(1,fadeVectLength));
		%fadeVect = ones(1,fadeVectLength);
    end
	
	noiseToSigVoltRatio = 10.^(-avgSnr/20);
	for ii = 1:fadeVectLength
        symbolSamples = (ii-1)*sampsPerSymbol+(1:sampsPerSymbol);
        noiseVect(symbolSamples) = noiseVect(symbolSamples)/fadeVect(ii);
	end
	
	rxMsg = modMsg + noiseToSigVoltRatio*noiseVect;
else
    rxMsg = awgn(modMsg,avgSnr,10*log10(2));
end

return