Alamouti STBC

Discuss 2Tx. 1Rx transmit diversity scheme called Alamouti Space Time Block Coding (STBC)

Description

A simple Space Time Code, suggested by Mr. Siavash M Alamouti in his landmark October 1998 paper - A Simple Transmit Diversity Technique for Wireless Communication, offers a simple method for achieving spatial diversity with two transmit antennas.

Since the estimate of the transmitted symbol with the Alamouti STBC scheme is identical to that obtained from MRC, the BER should be same as that for MRC. However, there is a small catch. With Alamouti STBC, we are transmitting from two antenna’s. Hence the total transmit power in the Alamouti scheme is twice that of that used in MRC. To make the comparison fair, we need to make the total trannsmit power from two antennas in STBC case to be equal to that of power transmitted from a single antenna in the MRC case.

With this scaling, we can see that BER performance of 2Tx, 1Rx Alamouti STBC case has a roughly 3dB poorer performance that 1Tx, 2Rx MRC case.

For theoretical details on 2 transmit, 1 receive Alamouti STBC coding and its equalization, please check
http://www.dsplog.com/2008/10/16/alamouti-stbc/

• MATLAB release: MATLAB 7 (R14)
• Other Files: license.txt, ; script_ber_alamouti_stbc_code_bpsk_rayleigh_channel.m

[Yi Xiao]

Very good! Clear codes and explanation.

Only one question, why we need these lines:
    yHat = sum(hEq.*yMod,1)./hEqPower;
    yHat(2:2:end) = conj(yHat(2:2:end));

I mean, if the decision rule is: ipHat = real(yHat)>0;
Then
yHat = sum(hEq.*yMod,1)
will be enough for everything.
Why do we need to divide it by the power of the channel and do the conjugate for
h2*y1 -h1y2* ?
I am a little bit confused here.

[Krishna Sankar M]

@Yi Xiao: Well, for BPSK constellation, you are right - one need not divide by the channel power. However, for higher order modulations one needs to take care of the scaling factor such that the constellation boundaries can be defined correctly. Hence provided the equation for the general case. Hope this helps.

[Yi Xiao]

Thank u, it helps a lot. By the way, could u please recommend me some paper or articles that talk about the scaling factor problem for Alamouti's code in higher order modulation?

I am studing on Alamouti's paper and I can get the same simulation result when using BPSK but not for QPSK, ur code inspires me alot and I want to learn more about scaling factor u mentioned.

Thanks again.

[PRAVEENA]

 

[Krishna Sankar M]

@Yi Xiao: The channel power is indeed the scaling factor, no?

[Shanar]

Hi Mate
This is really good work just I have simple question in my mind, can i emplement your code to work on IEEE802.16 transmitter receiver?
Thanks in advance