%% simulation of OFDM through multipath channel
%% the time resolution is ts=1/Fs=0.078us
%% GSM TU channel: six rays
%% power dB----->value delay(us)
%% -3.0 0£®1897 0
%% 0 0£®3785 0.2
%% -2.0 0£®2388 0.5
%% -6.0 0£®0951 1.6
%% -8.0 0£®0600 2.3
%% -10.0 0£®0379 5.0
clear
error=zeros(1,100);
frame_total=100;
N=2048; %% number of subcarriers
G=120; %% length of guard interval
multipath=[sqrt(0.1897) 0 sqrt(0.3785) 0 0 sqrt(0.2388) 0 0 0 0 sqrt(0.0951) 0 0 0 0 sqrt(0.06) 0 0 0 0 0 0 sqrt(0.0379)]; %% power
multipath_channel=zeros(1,length(multipath));
EN=2:2:18;
r=zeros(1,length(EN));
for snr=1:length(EN)
en = 10^((EN(snr))/10);
sigma = 1/sqrt(2*en);
for frame_temp=1:frame_total
multipath_channel=multipath.*(randn(1,length(multipath_channel))+j*randn(1,length(multipath_channel)))*sqrt(0.5); %% rayleigh fading
fdata=2*round(rand(1,N))-1; %% BPSK data
tdata=ifft(fdata,N)*sqrt(N); %% OFDM modulation
tdata_guard=[zeros(1,G) tdata];[tdata(N-G:N) tdata]; %% add guard interval,cyclic prefix
tdata_chan=filter(multipath_channel,[1],tdata_guard);;%% passing through the multipath channel
tdata_chan_dguard=tdata_chan(G+1:N+G); %% discard the guard interval
fdata_rev_channel=fft(tdata_chan_dguard,N)/sqrt(N); %% OFDM channel estimation demodulate
fchan_est=fdata_rev_channel./fdata; %% frequency channel fading facor
h=[multipath_channel,zeros(1,N+G-length(multipath))];
fchan_est1=fft(h,N);
%fchan_est1=fchan_1(:)+conj([fchan_1(G+1:N),zeros(1,G)]');
figure
plot([1:2048],fchan_est,'r',[1:2048],fchan_est1,'b')
le=length(tdata_chan);
noise=sigma*(randn(1,le)+j*randn(1,le));
tdata_chan1=tdata_chan+noise; %% add the AWGN
tdata_chan_dguard1=tdata_chan1(G+1:N+G); %% discard the guard interval
fdata_rev=fft(tdata_chan_dguard1,N)/sqrt(N);
fdata_rev1=fdata_rev.*conj(fchan_est);%% channel compensation
error(snr)=error(snr)+sum(sign(real(fdata_rev1))~=fdata);
end
end
ber=error(1:length(EN))/(N*frame_total)
r= 10.^(EN/10);
pb=0.5*(1-sqrt(r./(1+r)))
figure
semilogy(EN,ber,'b-*',EN,pb,'r-^')
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