www.pudn.com > ofdm_matlab.rar > Transmit.m
function BaseSignal = transmit(Datatx,ifftsize,carriers,...
wordsize,guardtype,guardtime,windowtype,DataAvg)
%TRANSMIT Generates a COFDM waveform from an input data.
% function BaseSignal = transmit(DataIn,ifftsize,carriers,...
% wordsize,guardtype,guardtime,windowtype,DataAvg)
%
% This function generates a COFDM time waveform based on the input parameters
% and the data given. The data is transmformed into a single frame COFDM signal.
% This for the simulation of a COFDM phone system.
% INPUTS:
% ========
% Datatx : Data to transmit in the wordsize given. eg. for wordsize = 2
% Data is from 0-3, for wordsize = 8, data is from 0-255
% The data should be a single row vector. See convbase.m to
% convert from 8bit data to the required wordsize.
% e.g. datatx = convbase(datain, 8, wordsize);
% ifftsize : Size of ifft to use for generating the waveform
% carriers : Which carriers to use for the transmission
% wordsize : Number of bits to transmit on each carrier eg. 2 => QPSK
% 1 => BPSK, 4 => 16PSK, 8 => 256PSK.
% Must be one of: 1,2,4 or 8
% guardtype : What type of guard period to use
% Options:
% 0 = No Guard period
% 1 = zero level guard period
% 2 = cyclic extension of end of symbols
% 3 = same as 2 but with the first half of the guard period = zero
% guardtime : Number of sample to use for the total guard time
% windowtype : Type of window to apply to the time waveform of the symbol
% Options:
% 0 = No windowing
% 1 = Hamming window
% DataAvg : Data Averaging. Number of repeats to send of each data word, so
% that the repeats can be combined at the receiver to reduce the
% phase error, and thus to BER. DataAvg = 1 (No duplication)
%
% OUTPUTS:
% ========
% BaseSignal : This is the output time signal for the COFDM waveform. The format
% of the output is a row vector.
% Datatx : Data transmitted. This is the input data (DataIn) converted to
% the number base used for transmission, based on wordsize.
%
% Copyright (c) Eric Lawrey 1997
%
% See: RECEIVE, RDFILE.
%===============================
% External Functions Used :
% None
%===============================
% Modifications:
% 8/6/97 Redo of the previous simulation script. (based on distort.m)
% 15/6/97 Continuing work on this function, currently not finished
% 16/6/97 Continued work on function, it is now finished and works, but not all
% the features have been tested.
% I have tested the windowing and the zeroed guard period. The code has also
% been optimized a bit and runs ~10 times faster then it used to, plus
% it can handle much bigger files (tested upto 87kbytes, wordsize=4), in 35sec
% It appears to work as a function.
% The function needs to be changed so that it does not read the file directly
% but instead get the data as input.
% 17/6/97 Modified the function so that it does read the input file from within
% the transmit function. This is so that the file can be read else where
% then split up into smaller frames, then processed by transmit.
% Fixed up some logical errors in the program, and removed the output phase
% variable as it can be easily calculated from the data being transmitted.
% 12/8/97 Changed the input requirements for Datatx. It is now DataIn which is a
% serial vector of byte data. The base conversion, reshaping of the data
% into symbols, and padding of the input data is done by transmit.m. I also
% data averaging that send duplicates of the data words. The duplicates are
% sent as the very next data word. (No the best spreading, but easy to do).
%====================
% Initialization
%====================
%rand('seed',3567);
NumCarr = length(carriers); %find the number of carriers
%=====================
% Apply Data Averaging
%=====================
%Duplicate data to be transmitted, duplicate each dataword having the next carrier
%also transmitting the same data word. This will not give the best diversity
%performance but is the easiest to implement.
DataOut = zerohold(Datatx,DataAvg);
%=============
% Pad the Data
%=============
%Format the input serial data stream into symbols
%Reshape the data to fit the number of carriers
numsymb = ceil(length(DataOut)/NumCarr);
%If the data length is not a multiple of the number of carrier the pad the data
%with zeros
if length(DataOut)/NumCarr ~= numsymb,
DataPad = zeros(1,numsymb*NumCarr);
DataPad(1:length(DataOut)) = DataOut;
DataOut = DataPad;
end
clear DataPad;
%==============================
% Reshape the data into symbols
%==============================
DataOut = reshape(DataOut,NumCarr,numsymb)'; %Reshape the data into symbols
numsymb = size(DataOut,1)+1; %find the total number of symbols
%including the phase reference symbol
%========================================
% Convert to DQPSK & add phase reference
%========================================
PhaseRef = round(rand(1,NumCarr)*(2^wordsize)+0.5); %generate random phase ref.
DPSKdata = zeros(size(DataOut,1)+1,size(DataOut,2));
DPSKdata(1,:) = PhaseRef;
for k = 1:numsymb-1
DPSKdata(k+1,:)=rem((DataOut(k,:) + DPSKdata(k,:)-1),(2^wordsize))+1;
end
%clear DataOut;
%=====================================
%Find the required spectrums
%=====================================
[X,Y] = pol2cart(DPSKdata*(2*pi/(2^wordsize)),ones(size(DPSKdata)));
CarrCmplx = X+i*Y;
NegCarriers = ifftsize-carriers+2; %find the bins for the negative frequency carriers
TxSpectrums = zeros(numsymb,ifftsize);
for k = 1:numsymb
%Place the carriers used into the full spectrum
TxSpectrums(k,carriers) = CarrCmplx(k,:);
TxSpectrums(k,NegCarriers) = conj(CarrCmplx(k,:));
end
clear NegCarriers;
%==================================
%Find the time waveform using IFFT
%==================================
BaseSignal = real(ifft(TxSpectrums'));
clear TxSpectrums; %Save Memory
%=================================
%Window the signal
%=================================
if windowtype==1
window = hamming(ifftsize); %make window
window2 = zeros(ifftsize,numsymb);
for k = 1:numsymb-1
window2(:,k) = window;
end
BaseSignal = window2.*BaseSignal; %window the waveform
clear window2; %save memory
clear window;
end
%=================================
%Add a Guard Period
%=================================
if guardtype~=0
if guardtype == 1 %if guard period is just a zero transmission
BaseSignal=[zeros(guardtime,numsymb);BaseSignal];
elseif guardtype == 2
EndSignal = size(BaseSignal,1); %Find the number of columns in the BaseSignal
BaseSignal=[BaseSignal((EndSignal-guardtime+1):EndSignal,:); BaseSignal];
elseif guardtype == 3
EndSignal = size(BaseSignal,1); %Find the number of columns in the BaseSignal
BaseSignal=[zeros(guardtime/2,numsymb); ...
BaseSignal((EndSignal-guardtime/2+1):EndSignal,:); BaseSignal];
end
end
BaseSignal = reshape(BaseSignal,1,size(BaseSignal,1)*size(BaseSignal,2));