Performance limits in fading MIMO channels

The multiple-input multiple-output (MIMO) channel is typically modeled as a randomly varying fading channel. Therefore the channel capacity is also a random variable and can vary from zero to infinity in a Rayleigh channel. Given this random nature of the channel capacity when the transmitter does not have channel knowledge, any signaling rate it chooses to use may not be supported by the channel with a finite probability, leading to a transmission error even when ideal channel coding for that chosen rate is employed. Therefore, in the absence of channel knowledge, the packet (or block) error rate (PER) is equal to the outage of capacity for the specified signaling rate. We study the fundamental limits on packet error rate versus signaling rate versus average SNR and the performance tradeoffs therein. We then examine such tradeoffs for several specific space-time coding schemes have. been. proposed that maximize either rate or diversity. These coding schemes modify the achievable capacity of the channel and therefore also the corresponding performance tradeoffs.