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.

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


N=256 ; % carriers
GI=N/4; % Guard ınterval=Cyclic prefix
DataBit = randint(N,1,2); % obtain 0 and 1's
DataMod = qammod(DataBit,2); % obtain modulated symbols (BPSK)

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

%Here x_t enters the channel

%CHANNEL

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

pathdelays=[0,0.2,0.4,0.6]*1E-6;
samplingtime=0.2E-6;
fdoppler=50 ; % 50 Hz
chan=rayleighchan(samplingtime,fdoppler,pathdelays,gain);

chan.ResetBeforeFiltering=0;

y_t=filter(chan,x_t);
......
.....

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

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=0.2E-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 =2
MHz , OFDM symbol duration = 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=rayleighchan(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=0 but not sure about it, am I
doing this wrong?


Burkay Etiler

.

Relevant Pages

  • Re: question on FIR channel
    ... My target sampling rate is, for example, 50MHz, i.e., the sampling ... But my channel taps do not fall on integer units of the sampling ... so what you're trying to do is scale an existing FIR design from an FIR ... Carefully examine just how accurate the delays can be measured/specified. ...
    (comp.dsp)
  • Re: Nyquist Sampling
    ... By sampling say a 3.1 kHz band-limited voice channel at the Nyquist rate ...
    (comp.dsp)
  • implementing rayleighchan in OFDM
    ... I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". ... I can implement the OFDM structure in AWGN channel, ... Which parameters determine the sampling time of x_t and sampling ... it is a basic question sorry but I am confused...) ...
    (sci.math.num-analysis)
  • implementing rayleighchan in OFDM
    ... I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". ... I can implement the OFDM structure in AWGN channel, ... Which parameters determine the sampling time of x_t and sampling ... it is a basic question sorry but I am confused...) ...
    (comp.dsp)
  • implementing rayleighchan in OFDM
    ... I am doing my M.SC thesis on the topic "ICI cancellation in OFDM". ... I can implement the OFDM structure in AWGN channel, ... Which parameters determine the sampling time of x_t and sampling ... it is a basic question sorry but I am confused...) ...
    (sci.math.symbolic)