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aw03r's blog

Visualization of Bayesian Detection in MIMO Systems

The animated graphic on the right illustrates the possible channel output states of a 2x3 real-valued MIMO system using BPSK modulation. Additionally the Bayesian decision boundary is provided.

 

EXIT Chart Analysis When Considering Wideband Channels

EXIT charts under wide-band fading conditions can be generated in the following to ways:

    1. Only take a snap-shot of the channel, which would correspond to the AWGN EXIT chart

    2. Assume uncorrelated fading so that the resultant EXIT chart reflects the average behavior of the system.

The first option is not very useful since it does not really account for the Rayleigh fading. The second option appears attractive in the first place but is in my opinion not meaningful to analyze receivers. The reason is that in wide-band communication systems we would like to be able to exploit the freq. domain diversity of the channel. However, if uncorrelated fading is considered full diversity is already obtained in the time domain and the freq. domain diversity in fact only contributes interference. What would be of interest is some sort of EXIT chart representation for block-fading channels. The only way I could think of generating them is as follows:

    1. Generate channel realization and record the EXIT curve

    2. Repeat step 1 until the fading statistics are satisfied

    3. Average all EXIT functions by taking into account the fading PDF

Also it sounds easy, step three is in-fact rather complicated since you need to evaluated the probability of each channel realization. The problem seems to be closely related to the channel capacity versus outage probability issue.

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