Constellation randomization (CoRa) for outage performance improvement on MIMO channels

This work studies a new concept, "constellation randomization" (CoRa), for performance improvement of transmission over quasi-static (block fading) multidimensional ("MIMO") channels with small signal constellations. The motivation behind CoRa is to reduce some of the mutual information penalty associated with the use of a finite input alphabet for signalling on a static, possibly ill-conditioned, channel. We show, both via information-theoretic considerations, and via Monte-Carlo simulation of the frame-error-rate (FER) of a coded system, that CoRa can offer a lower outage probability than a conventional spatial multiplexing system that uses a fixed signal constellation. In our examples the improvement offered by CoRa is comparable to that offered by linear (complex-field) precoding. This is interesting, because the performance gain of CoRa comes at virtually no computational expense.