www.pudn.com > ofdm_matlab.rar > imagerx.m
%COFDMRD This script reads a COFDM waveform from a .WAV file and decodes it.
% This script is the complement to the COFDMWAV script.
% This script read the WAV file given the extracts the first frame
% in the file. This frame is decoded and compared with the known data
% sent by the COFDMWAV script.
%
% The wavefile to be decoded is expected to be a 16bit windows .WAV file
% call RX.WAV
%
% The data expected is that generated using genrand.m, having the
% random seed set to 123456 before it is generated.
%
% Copyright (c) July 1997 Eric Lawrey
%================
% Modified:
% 29/7/97 11:00am cofdmwav.m
% Modified simtxrx.m so that it would just generate the output of the
% COFDM transmitter, and store the result in a wav file.
%
% 29/7/97 11:30am cofdmwav.m
% Changed it so that a wav file of multiple frames could be generated.
%
% 29/7/97 11:48am cofdmrd.m
% Modifed cofdmwav.m so that it now decodes the wav sound file.
%
% 2/8/97 10:25pm imagerx.m
% Fixed an algorithum error for picking the starting time of the frames.
% I was using the normal start time, as for single frame simulations, which
% meant that only early frame start time errors could only with out causing
% error. This was fixed by picking the start time early by 1/4 of the
% guard time (1/2 the time of the cyclic extension of the symbol), thus
% allowing a start time error of +- 1/4 guard time.
%
% 3/8/97 2:00pm imagerx.m
% Added the option of compressing the contrast of the picture
% to help prevent roll over of intensity when sending 8bits/word.
% Also added data averaging, allowing duplicates of data to
% be sent and recombined to reduce the phase error. This works,
% except for it giving errors for black pixels.
%
% 12/8/97 10:30pm imagerx.m
% Made many changes to the structure of the program. It can now receive
% random data, pictures, and general binary files. Both the random data
% and picture transmission appears to mostly work, however the
% data padding for data sets which are not multiples of the number of
% carriers doesn't work yet.Also a common setting script is now used
% for both the transmitter and receiver. This is settings.m.
%
% 17/8/97 2:00 pm imagetx.m
% Moved the calculation of the carriers to use into the settings
% script.
%======================================================
% External functions required to run this script:
% wread16.m (from the Matlab web site)
% calcerr.m
% settings.m
% rddatatx.m
% findfrm.m
% receive.m
% convbase.m
% bmpread.m
% bmpwrite.m
% wrimage.m
% wavwrite.m
clear all;
flops(0);
tic; %Measure the time it takes to run the simulation
settings %Setup the link parameters
%=====================
%Read in the .wav file
%=====================
SignalIn = wavread(rxwavfile);
%======================================================
%Read in the picture to be received to check for errors
%======================================================
%Read the picture with no data averaging to get just the picture data
%[Datatx,h,w] = rdimage(filename,PictureComp);
rddatatx %Read the data which was transmitted. This sets up data
%transmitted (DataIn) and Datatx, and the height (h) and width (w)
%of the original data
TotNoData = h*w;
NoData = h*w;
switch guardtype
case 1
%Zeroed guard period
FrameGap = ifftsize+guardtime*2;
zerotime = guardtime;
case 2
FrameGap = ifftsize+guardtime;
zerotime = 0;
case 3
FrameGap = ifftsize+3*guardtime/2;
zerotime = guardtime/2;
end
if SymbPerFrame ~= 0,
SampPerFrame = (SymbPerFrame+1)*(ifftsize+guardtime);
SignalLeft = SignalIn;
Finished = 0;
AllData = [];
AllDiff = [];
First = 1;
if fileknown == 0,
%Don't know how many frames so estimate from the number of samples
NumFrames = floor((length(SignalIn)/(SampPerFrame)));
disp(['Estimating the number of frames as : ' int2str(NumFrames)]);
else
NumFrames = ceil(((TotNoData*(OutWordSize/wordsize))...
*DataAvg/NumCarr)/SymbPerFrame);
end
for k = 1:NumFrames,
disp(['Decoding Frame : ', num2str(k)]);
%FrameCount = FrameCount+1;
if First == 1,
First = 0;
Signal = SignalLeft(1:min(SampPerFrame*1.1,length(SignalLeft)));
Scale = ([0:length(Signal)-1]/length(Signal)*mean(abs(Signal))).';
Signal = Signal+Scale;
else
Signal = SignalLeft(1:min(FrameGap*3,length(SignalLeft)));
end
FrameStart = findfrm(Signal, FrameGap, quickrate,zerotime);
FrameStart = FrameStart - guardtime/4;
Signal =SignalLeft(FrameStart:...
min(FrameStart+SampPerFrame,length(SignalLeft)));
if k == NumFrames,
Finished = 1;
NoData = TotNoData;
else
SignalLeft = SignalLeft(...
FrameStart+SampPerFrame-FrameGap*1.5:length(SignalLeft));
plot(SignalLeft);
TotNoData = TotNoData - SymbPerFrame*NumCarr/...
(OutWordSize/wordsize)/DataAvg;
NoData = floor(SymbPerFrame *NumCarr/(OutWordSize/wordsize)/DataAvg);
end
[Datarx, DiffPhRx] = receive(Signal,ifftsize,carriers,...
wordsize,guardtype,guardtime,DataAvg,NoData);
AllDiff = [AllDiff DiffPhRx];
AllData = [AllData Datarx];
end
DiffPhRx = AllDiff;
Datarx = AllData;
else
TotalWords = ceil((h*w*(OutWordSize/wordsize)*DataAvg)/NumCarr)*NumCarr;
%===============================================================
%Try to detect the start of a frame by envelop detection & filtering
%===============================================================
%Calc number of samples in a frame, no including the frame sync guard period
SampPerFrame=((TotalWords/NumCarr)+1)*(ifftsize+guardtime);
%Calc number of sample in a frame guard period
SampPerFrmGrd = FrameGuard;
disp('Searching for start of frame');
disp(' -Filtered Signal');
%FrameGap = ifftsize+3*guardtime/2;
%zerotime = guardtime/2;
FrameStart = findfrm(SignalIn(1:length(SignalIn)/2), FrameGap, quickrate,zerotime);
FrameStart = FrameStart - guardtime/4;
%cut out one frame to decode
BaseSignal = SignalIn(FrameStart:FrameStart+SampPerFrame)/(2^15);
disp('Decoding COFDM frame');
%===============================
%Decode the received COFDM frame
%===============================
[Datarx, DiffPhRx] = receive(BaseSignal,ifftsize,carriers,...
wordsize,guardtype,guardtime,DataAvg,NoData);
end
if (size(Datatx) == size(Datarx)),
[PhError, Summary] = calcerr(Datatx,Datarx,DiffPhRx,wordsize);
disp(['BER = ',num2str(Summary(1)),' RMS phase error = ' num2str(Summary(2)),...
' Total number of errors = ', num2str(Summary(3))]);
else
disp('WARNING: Length of received data does not match the transmitted length');
disp(['length of transmitted data : ' int2str(length(Datatx))]);
disp(['length of received data : ' int2str(length(Datarx))]);
end
Datarx = convbase(Datarx, wordsize, OutWordSize);
if DataType == 2,
[x2,map] = bmpread(infile);
%outfile = [outfile, num2str(SNR), 'db.bmp'];
x=wrimage(Datarx,h,w,outfile,PictureComp);
figure(1);
image(x);
colormap(map);
title('Received image');
figure(2);
image(x2-1);
colormap(map);
title('Original Transmitted image');
figure(3);
colormap(map);
image((x2-x)*8+128);
title('Error in received image (Contrast Enhanced)');
%errorfile = [errorfile, num2str(SNR), 'db.bmp'];
bmpwrite(((x2-x)*8+128),map,errorfile);
RmsAmpErr=mean(std(x2-1-x)); %RMS amplitude error of the picture
RmsAmp = mean(std(x2)); %RMS amplitude of the original picutre
SNRpic = 20*log10(RmsAmp/RmsAmpErr);
disp(['SNR of the received image : ', num2str(SNRpic), ' dB']);
elseif DataType == 3,
if OutWordSize == 8,
DataSize = 'integer*1';
elseif OutWordSize == 16,
DataSize = 'integer*2';
else
error('OutWordSize no valid for sending binary files, must be 8 or 16');
end
fid = fopen(outfile,'wb');
fwrite(fid,Datarx,DataSize);
fclose(fid);
elseif DataType == 4,
wavwrite(Datarx/(2^(OutWordSize)+1),fs,OutWordSize,outfile);
end
disp(['Total Time: ' num2str(toc) 'sec']);
disp(['Total FLOPS: ' num2str(flops)]);
disp(['Process Speed : ' num2str(flops/toc) ' flops/sec']);