paprofdmbpsk.m

Code for calculating reduced PAPR through SLM

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% Author	: Krishna
% Email		: [e-mail]
% Version	: 1.0
% Date		: 24 February 2008
% Modified by	: Subhasis
% Version	: 1.0
% Date		: April 20, 2009
% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Script for computing the per symbol peak to average PAPR for 
% an OFDM transmit waveform (loosely based on IEEE 802.11A 
% specifications) 
% Further, Cumulative Distribution Function (CDF) plots of the 
% PAPR is captured

clear
nFFTSize = 64;
% for each symbol bits a1 to a52 are assigned to subcarrier 
% index [-26 to -1 1 to 26] 
subcarrierIndex = [-26:-1 1:26];
subcarriersymIndex = [-30:-27 27:30];
subcarriersymIndex_new = [-28:-27 27:28];
nBit = 10000; 
ip = rand(1,nBit) > 0.5; % generating 1's and 0's
nBitPerSymbol = 52;

nSymbol = ceil(nBit/nBitPerSymbol);

% BPSK modulation
% bit0 --> -1
% bit1 --> +1
ipMod = 2*ip - 1; 
ipMod = [ipMod zeros(1,nBitPerSymbol*nSymbol-nBit)];
ipMod = reshape(ipMod,nSymbol,nBitPerSymbol);

st = zeros(nSymbol*80,1);%[];
st_slm = zeros(nSymbol*80,1);%[];
paprSymbol = zeros(nSymbol,1);
paprSymbol_slm = zeros(nSymbol,1);
min = 10000;

seqs1 = zeros(256,8);
for i=0:255
seqs1(i+1,:) = 2*bitget(i,8:-1:1)-ones(1,8);
end

%% conventional SLM, all possible 8 element sequences (total 256)

for ii = 1:nSymbol

fprintf(1,'%d\n',ii);
min = 1000;

for seq=0:255

R = seqs1(seq+1,:);
S = ones(nFFTSize/8,1)*R;
Q = S(:)';
Q = bitrevorder(Q);

inputiFFT = zeros(1,nFFTSize);

symboliFFT = zeros(1,nFFTSize);

% assigning bits a1 to a52 to subcarriers [-26 to -1, 1 to 26]
inputiFFT(subcarrierIndex+nFFTSize/2+1) = ipMod(ii,:);

% assigning bits R(1:8) to subcarriers [-30 to -27, 27 to 30]
symboliFFT(subcarriersymIndex+nFFTSize/2+1) = R(:);

% shift subcarriers at indices [-26 to -1] to fft input indices [38 to 63]
inputiFFT = fftshift(inputiFFT);
symboliFFT = fftshift(symboliFFT);

% doing iFFT
outputiFFT = 64*ifft(Q.*inputiFFT,nFFTSize);
symboliFFT = 64*ifft(symboliFFT,nFFTSize);

outputiFFT = outputiFFT + symboliFFT;

% adding cyclic prefix of 16 samples 
outputiFFT_with_CP = [outputiFFT(49:64) outputiFFT];

% computing the peak to average power ratio for each symbol
meanSquareValue = outputiFFT*outputiFFT'/length(outputiFFT);
peakValue = max(outputiFFT.*conj(outputiFFT));

if(min > peakValue/meanSquareValue) 
    min = peakValue/meanSquareValue;
    outputiFFT_with_CP_min = outputiFFT_with_CP;
end;

end

paprSymbol_slm(ii) = min;

% concatenating the symbols to form the final output
st_slm((ii-1)*80+1:ii*80) = outputiFFT_with_CP;

end

%% plotting

close all
paprSymboldB = 10*log10(paprSymbol);
paprSymboldB_slm = 10*log10(paprSymbol_slm);
[n x] = hist(paprSymboldB,0:0.1:15);
[n_slm x] = hist(paprSymboldB_slm,0:0.1:15);
plot(x,[1-cumsum(n)/nSymbol; 1-cumsum(n_slm)/nSymbol],'LineWidth',2)
xlabel('papr, x dB')
ylabel('Probability, X <=x')
title('CCDF plots of PAPR from an IEEE 802.11a Tx with BPSK modulation')
grid on