Space-Time decoding in multipath MIMO-OFDM system

Hello,

I'm working on a MIMO-OFDM system simulation in Matlab. I assume a 3 tap multipath channel. My question concerns the Space-Time decoding block at the receiver side.
When decoding a ST coded signal, ussually a pseudo inverse of a channel matrix H has to be calculated (zero forcing, MMSE, SIC, OSIC algorithms). In a single tap channel this is a trivial problem. However, my problem is that I have three matrices, each presenting one tap, delayed in time. I don't really know how to calculate the inverse directly. Should I use only the matrix for the first tap, with the highest mean power(and hence aproximate the channel state information at the receiver), or is there any better, more precise way (but more complex of course)?

Thanks, Tine Start a New Thread

Hello,
>
>I'm working on a MIMO-OFDM system simulation in Matlab. I assume a 3 tap multipath channel. My question concerns the Space-Time decoding block at the receiver side.
>When decoding a ST coded signal, ussually a pseudo inverse of a channel matrix H has to be calculated (zero forcing, MMSE, SIC, OSIC algorithms). In a single tap channel this is a trivial problem. However, my problem is that I have three matrices, each presenting one tap, delayed in time. I don't really know how to calculate the inverse directly. Should I use only the matrix for the first tap, with the highest mean power(and hence aproximate the channel state information at the receiver), or is there any better, more precise way (but more complex of course)?
>
>Thanks, Tine

Hi,

Even if the time domain channel has multiple taps, assuming that the time domain channel response duration is less than the cyclic prefix, the effect of channel can be compensated by a single-tap frequency domain equalizer.

Does that help?

Regards,
Krishna
http://dsplog.blogspot.com Start a New Thread

Hello,
for MIMO -OFDM, at the Tx and Rx we use IFFT
and FFT repectively for each antenna branch. At the Rx
after FFT, each we can write as flat fading component.
Hence, even though the channel is multipath
(Selective), after FFT it is flat fading MIMO model.
Hence u can use the stD. MIMO detectors.
HTH,
-SaiRamesh.

--- t...@ijs.si wrote:

> Hello,
>
> I'm working on a MIMO-OFDM system simulation in
> Matlab. I assume a 3 tap multipath channel. My
> question concerns the Space-Time decoding block at
> the receiver side.
> When decoding a ST coded signal, ussually a pseudo
> inverse of a channel matrix H has to be calculated
> (zero forcing, MMSE, SIC, OSIC algorithms). In a
> single tap channel this is a trivial problem.
> However, my problem is that I have three matrices,
> each presenting one tap, delayed in time. I don't
> really know how to calculate the inverse directly.
> Should I use only the matrix for the first tap, with
> the highest mean power(and hence aproximate the
> channel state information at the receiver), or is
> there any better, more precise way (but more complex
> of course)?
>
> Thanks, Tine
> Start a New Thread

Hello,
At the Rx once the FFT operation is done u need
to multiply it by the FFT of the channel (freq. domain
equalization). So this is equalivalent to the MIMO
flat fading channel model, hence u can use
conventional MIMO detection techniques. So each H is
the fft of the channel, so u will have different
realizationas of H (depends on the size of the FFT)
for each symbol, hence erogoic.

HTH,
-SaiRamesh.
--- Tine Celcer wrote:

> Hi,
>
> Thank you for the response. I am aware of the things
> that you mentioned, my
> concern is, with the channel matrix I should use for
> the ST decoding, when I
> have to calculate the pseudo inverse (for Zero
> Forcing for example).
>
> My channel is composed of three matrices of size
> Ntr, which in combination
> with the appropriate delay represent channel
> response for each tap. Now, at
> the receiver side I need a single matrix
> representing channel response, for
> which I have to calculate a pseudo inverse. My
> problem is which matrix
> should I use. I'm thinking, maybe I could use only
> the first tap matrix,
> since the other two are considerably attenuated, and
> I wouldn't make such a
> big mistake.
>
> Tine
>
>
>
>
>
> -----Original Message-----
> From: nammi sairamesh [mailto:s...@yahoo.com]
>
> Sent: Monday, October 08, 2007 2:19 AM
> To: t...@ijs.si; m...
> Subject: Re: [matlab] Space-Time decoding in
> multipath MIMO-OFDM system
>
> Hello,
> for MIMO -OFDM, at the Tx and Rx we use
> IFFT
> and FFT repectively for each antenna branch. At the
> Rx
> after FFT, each we can write as flat fading
> component.
> Hence, even though the channel is multipath
> (Selective), after FFT it is flat fading MIMO model.
> Hence u can use the stD. MIMO detectors.
> HTH,
> -SaiRamesh.
> --- t...@ijs.si wrote:
>
> > Hello,
> >
> > I'm working on a MIMO-OFDM system simulation in
> > Matlab. I assume a 3 tap multipath channel. My
> > question concerns the Space-Time decoding block at
> > the receiver side.
> > When decoding a ST coded signal, ussually a pseudo
> > inverse of a channel matrix H has to be calculated
> > (zero forcing, MMSE, SIC, OSIC algorithms). In a
> > single tap channel this is a trivial problem.
> > However, my problem is that I have three matrices,
> > each presenting one tap, delayed in time. I don't
> > really know how to calculate the inverse directly.
> > Should I use only the matrix for the first tap,
> with
> > the highest mean power(and hence aproximate the
> > channel state information at the receiver), or is
> > there any better, more precise way (but more
> complex
> > of course)?
> >
> > Thanks, Tine
> >
>
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