implementing rayleighchan in OFDM

Hi everbody,

I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". I
have very limited time, if you can help me I will be grateful to
you....

I can implement the OFDM structure in AWGN channel, it works very
well..

But when i try to implement the system in a "rayleighchan", I obtain
very bad BER results.

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N=3D256 ;   % carriers
GI=3DN/4;    % Guard =C4=B1nterval=3DCyclic prefix
DataBit =3D randint(N,1,2);   % obtain 0 and 1's
DataMod =3D qammod(DataBit,2);   % obtain modulated symbols (BPSK)

Ifft=3DIfft (DataMod, N);    %Take ifft of the symbols
x_t =3D [Ifft(N- GI + 1 : N);Ifft];

%Here x_t enters the channel

%CHANNEL

pathgains=3D[1,0.63,0.1,0.01];
gain=3D 10*log10(pathgains);    % convert to dB

pathdelays=3D[0,0.2,0.4,0.6]*1E-6;
samplingtime=3D0.2E-6;
fdoppler=3D50 ; % 50 Hz
chan=3Drayleighchan(samplingtime,fdoppler,pathdelays,gain);

chan.ResetBeforeFiltering=3D0;

y_t=3Dfilter(chan,x_t);
.=2E...
.=2E..

------------------------------------

I have some questions:

1) Which parameters determine the sampling time of  x_t and sampling
time of the channel parameters? (It is a basic question sorry but I am
confused...)

(I think sampling time=3D0.2E-6 and x_t's sampling rate are not
correlated in my code, may be it is the problem)

2) I do not determine any parameters like ;  carrier frequency =3D2
MHz , OFDM symbol duration =3D 200us  etc...
May I determine them, then how i can I put them in the code...(Again
it is a basic question sorry but I am confused...)

2)If i use only "chan=3Drayleighchan(samplingtime, fdoppler)"  then
there is no problem, BER results are good...So am I choosing wrong
pathdelays and samplingtime or am I doing wrong channel
estimation&equalization?

3) How can I get channel impulse response? (Because chan.PathGains
gives the path gains , not channel impulse response complex values)

4)I am taking chan.ResetBeforeFiltering=3D0 but not sure about it, am I
doing this wrong?


Burkay Etiler