Receivers and CQI Measures for MIMO-CDMA Systems in Frequency-Selective Channels

We investigate receiver designs and CQI (channel quality indicator) measures for the jointly encoded (JE) and separately encoded (SE) types of MIMO transmission. For the JE transmission, we develop a per-Walsh code joint detection structure consisting of a front-end linear filter followed by joint symbol detection among all the streams. We derive a class of filters that maximize the so-called constrained mutual information, and show that the conventional LMMSE and MVDR equalizers belong to this class. This constrained mutual information also provides us with a CQI measure describing the MIMO link quality, similar to the notion of generalized SNR. Such a measure is essential for both link adaptation and also to provide a means of link-to-system mapping. For the case of SE transmission, we extend the successive decoding algorithm of per-antenna rate control (PARC) to multipath channels, and show that in this case successive decoding achieves the constrained mutual information. Meanwhile, similar to the case of JE schemes, we also derive proper CQI measures for the SE schemes.

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