Q) MIMO-OFDM better than AWGN performance. Why..

Hello. It's very shameful to ask this stupid question...but, if anyone
woule help, can we have some discussion please?

1) I have a MIMO-OFDM simulator. My problem is that, for example, if I use
Alamouti's 2-by-2 diversity scheme, then my MIMO-OFDM curve in
freq-selective channel works partially better than SISO QPSK curve in
gaussian channel. The two curves also intersect. 

2)It seems that the problem is coming from the MIMO part of my program,
not the OFDM part. I'm sure about this.

3) But actually, looking at the Alamouti's paper 'Simple Transmit
Diversity Technique for wireless communicatons', even there, a diversity
curve shows better BER than gaussian channel performance.

4) Can I have some advice, please? I've spend so much time on this, with
no clue. 

Thank you very much. 

On Wed, 21 Feb 2007 04:53:30 -0600, "lsw00kor" <lsw00kor@hotmail.com>
wrote:

>Hello. It's very shameful to ask this stupid question...but, if anyone
>woule help, can we have some discussion please?
>
>1) I have a MIMO-OFDM simulator. My problem is that, for example, if I use
>Alamouti's 2-by-2 diversity scheme, then my MIMO-OFDM curve in
>freq-selective channel works partially better than SISO QPSK curve in
>gaussian channel. The two curves also intersect. 
>
>2)It seems that the problem is coming from the MIMO part of my program,
>not the OFDM part. I'm sure about this.
>
>3) But actually, looking at the Alamouti's paper 'Simple Transmit
>Diversity Technique for wireless communicatons', even there, a diversity
>curve shows better BER than gaussian channel performance.
>
>4) Can I have some advice, please? I've spend so much time on this, with
>no clue. 
>
>Thank you very much. 

It's not clear to me what you're comparing.   A MIMO system by nature
will often have better performance than a SISO system, which is why
they're useful.

The performance comparison of a MIMO system in a faded channel
compared to a SISO system in AWGN will depend a lot on the channel
model used for the MIMO system.

Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org