www.pudn.com > ofdm_matlab.rar > imagetx.m

%IMAGETX This script produces a wav file of a COFDM frame suitable for 
%	a playing as a COFDM signal generator. 
%	It generates a signal which consists of a number of frames, each 
%	separated by a frame guard time of one symbol period. The signal is 
%	zero during this period. 
% 
%	This transmission uses a simple synchronisation method. A null 
%	symbol (no signal) is added as a synchronisation symbol at the 
%	start of each frame. An envelop detector, in combination with a  
%	moving average of the envelop is used to find this null symbol. 
%	The transistion from the null symbol to the first OFDM symbol in 
%	the frame (i.e the phase reference) is used to synchronise the 
%	receiver. No additional fine tunning is performed. 
% 
%	A pre and post signal is added to the OFDM signal, to allow synchronisation 
%	of the first frame. The post signal is to allow for tolerances in the 
%	total number of samples. The pre signal is just a set of tones, not an OFDM signal. 
%	I guess I was too lasy to do any thing more complicatied. 
% 
%	No link layer has been added to the transmission. Data is simply padded 
%	with zeros, so that the number of data words requires an integral number of 
%	OFDM symbols. The number of data words sent is extracted from the original 
%	data at the receiver using rddatatx.m. The original data is loaded at the 
%	receiver so that it can be compared with the received data. This allows 
%	the Bit Error Rate (BER) and phase error to be calculated. The original data 
%	loaded at the receiver also allow the number of transmitted data words to be found. 
%	 
% 
%	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. 
%	31/7/97	8:44am	rdimage.m 
%	Modified cofdmwav.m so that it now uses a bmp file as it data source 
% 
%	3/8/97	2:00pm imagetx.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 imagetx.m 
%	Made many major changes to the software so that multiple data 
%	types can be transmitted. Including random data, pictures, and 
%	general binary files. 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: 
%	settings.m 
%	rddatatx.m 
%	channel.m 
%	wavwr.m		(from the Matlab web site) 
%	transmit.m 
%	rdimage.m 
%	rddatatx.m		(Script to read in the data to transmit) 
 
clear all; 
flops(0); 
tic;			%Measure the time it takes to run the simulation 
settings		%Initialize all the setting required 
 
rddatatx	%read in the data to transmit. This could be random data, an image 
		%or a general binary file. 
 
 
FrameSig = zeros(1,FrameGuard);		%Generate the blank period between frames 
TimeSignal = []; 
if SymbPerFrame ~= 0, 
	%==================================== 
	%Generate a set of tones for the pre and post signals 
	f = 0.25;	%Frequency 0.5 = nyquist rate 
	N = (ifftsize+guardtime)*8; 
	Header = sin(0:f*2*pi:f*2*pi*(N-1)); 
	f = 0.117; 
	Header = Header + sin(0:f*2*pi:f*2*pi*(N-1)); 
	%==================================== 
 
	TimeSignal = []; 
	NumCarr = length(carriers); 
	NoDataWords = length(Datatx)*DataAvg; 
	numbsymb = ceil(NoDataWords/NumCarr); 
 
	%Check if the number of symbols required will require multiple frames 
	if numbsymb > SymbPerFrame, 
		%========================= 
		%Multiple Frames		 
		%========================= 
		Dataleft = Datatx; 
		while length(Dataleft) > 1, 
 
			AmountData = min(SymbPerFrame*NumCarr/... 
				DataAvg,length(Dataleft)); 
			FrameData = Dataleft(1:AmountData); 
			Dataleft = Dataleft(AmountData+1:length(Dataleft)); 
			%=========================================================== 
			%Generate one frame of the COFDM signal from data to be sent 
			%=========================================================== 
			BaseSignal = transmit(FrameData,ifftsize,carriers,... 
 		 		wordsize,guardtype,guardtime,windowtype,DataAvg); 
			TimeSignal = [TimeSignal FrameSig BaseSignal]; 
		end 
		SigPow = std(BaseSignal); %calc the signal power of the OFDM signal  
					  % so the the header power can be scaled to match 
		TimeSignal = [SigPow*Header TimeSignal FrameSig SigPow*Header]; 
	else	 
		%========================= 
		%Single Frame 
		%========================= 
		BaseSignal = transmit(Datatx,ifftsize,carriers,... 
	 		wordsize,guardtype,guardtime,windowtype,DataAvg); 
		SigPow = std(BaseSignal); 
		Header = SigPow*Header; 
		TimeSignal = [Header FrameSig BaseSignal FrameSig Header]; 
	end 
else 
	%========================================= 
	%Single Frame but generated multiple times 
	%========================================= 
	%If SymbPerFrame == 0 and NoFrames is greater than 1 then 
	%the frame generated from the data is copied multiple times 
	BaseSignal = transmit(Datatx,ifftsize,carriers,... 
	 		wordsize,guardtype,guardtime,windowtype,DataAvg); 
	%Concatenate all the frames together 
	for k = 1:NoFrames, 
		TimeSignal = [TimeSignal BaseSignal FrameSig]; 
	end 
end 
%Generate a very simple multipath model (i.e 2 tap filter) 
%Multi can be set to any impluse function for more complicated 
%multipath modelling 
Multi = zeros(Delay,1); 
Multi(1) = 1; 
Multi(Delay) = MultiMag; 
 
%Apply a simulated channel model to the data 
%See channel for more detail 
TimeSignal = channel(TimeSignal, Comp, SNR, Multi); 
 
 
%================= 
%Scale the signal 
%================= 
MaxSig = max(abs(TimeSignal(N:length(TimeSignal)-N))); %Find the max of the OFDM signal 
						  %removing the header and trailer before 
						  %finding the maximum 
RMSSig = std(TimeSignal(N:length(TimeSignal)-N)); 
if (FullScaleFlag==1) 
	TimeSignal = TimeSignal*FullScale/MaxSig; 
	RMSSig = RMSSig/MaxSig*FullScale; 
	MaxSig = FullScale; 
else 
	TimeSignal = TimeSignal*sqrt(TxSignalPow)/RMSSig; 
	ind = find(abs(TimeSignal)>0.9999);		%Clip the signal to -1 to +1 
	TimeSignal(ind) = ones(size(ind)).*sign(TimeSignal(ind))*0.9999; 
	%Recalculate the Maximum and the RMS signal 
	MaxSig = max(abs(TimeSignal(N:length(TimeSignal)-N)));  
	RMSSig = std(TimeSignal(N:length(TimeSignal)-N)); 
end 
%============================== 
%Save the signal as a .WAV file 
%============================== 
wavwrite(TimeSignal,Fs,res,txwavfile); 
 
%====================== 
% Display some results 
%====================== 
disp(['Max Signal Level: ' num2str(MaxSig)]); 
disp(['RMS Signal Level: ' num2str(RMSSig)]); 
disp(['Peak to RMS power ratio : ' num2str(20*log10(MaxSig/RMSSig)) 'dB']); 
disp(['Total Time: ' num2str(toc) 'sec']); 
disp(['Total FLOPS: ' num2str(flops)]); 
disp(['Process Speed : ' num2str(flops/toc) ' flops/sec']);