On the existence of the Mazo-limit on MIMO channels

Mazo, in 1975, showed that the signaling rate of a linear modulation can be significantly higher than the maximum rate for orthogonal signaling without any loss of minimum square Euclidean distance. In subsequent literature the highest such rate is referred to as the Mazo-limit. In this letter we ask whether there exists a Mazo-limit also on MIMO channels. The answer is yes, but it applies to the largest pairwise error probability rather than to minimum square Euclidean distance. Moreover, it occurs at exactly the same rate as in the AWGN case. As a special case results for single-input single-output fading channels are obtained.