receivefilter.m

simulation module for visual wireless sensor network

% ------------------------------------------------------------------------------------------------------%
% ReceiveFilter(..) - The 'Matched Filter' used in DigiComm.
% -----------------------------------------------------------
% This is usually the matched filter used in digital communication systems, but with the flexibility 
% that the actual filter coeffecients can be specified in the routine. This filter does two things :
% 1. Does the filtering of the actual received waveform using the filter coefficients specified.
% 2. Does the Sampling of the waveform at each signalling interval to retrieve the I and Q symbols.
%
% Inputs :
% ---------
% I_RxWaveform, Q_RxWaveform - The I and Q received waveforms.
% hReceiveFilter - The FIR filter coefficients used to perform 'matched' filtering. (usually this will
% be the same as the transmit filter coeffients inorder to enable matched filtering).
% numSamplesPerSymbol - The number of samples used to represent a symbol. This will be useful for 
% sampling the filtered waveform.
%
% Outputs :
% -----------
% I_Symbols, Q_Symbols - The Received I and Q symbols.
%
% ------------------------------------------------------------------------------------------------------%

function [I_RxSymbols,Q_RxSymbols] = ReceiveFilter(I_RxWaveform,Q_RxWaveform,hReceiveFilter,numSamplesPerSymbol)

% Do the matched filtering first.
I_FilterOutput = conv(I_RxWaveform,hReceiveFilter);
Q_FilterOutput = conv(Q_RxWaveform,hReceiveFilter);

% It's assumed here that the transmit and the receive filters are of the same length.
% In actual it is ((Nt+Nr-1)-1)/2 = (Nt-1) = (Nr-1) (if Nt = Nr).
N_FilterTrailer = length(hReceiveFilter)-1;

% Convert to a symbol stream, taking into account the trailers due to the transmit and
% receive filter impulse responses.
SymbolRange = N_FilterTrailer+1:length(I_FilterOutput)-N_FilterTrailer;
I_RxSymbols = WaveformToSymbol(I_FilterOutput(SymbolRange),numSamplesPerSymbol);
Q_RxSymbols = WaveformToSymbol(Q_FilterOutput(SymbolRange),numSamplesPerSymbol);