On the Diversity and Multiplexing Tradeoff in MIMO Fading Channels with Two-Way Training and Power Control

We analyze the achievable diversity-multiplexing tradeoff (DMT) in MIMO fading channels with two-way channel training. We first consider a typical training scenario, where the transmitter transmits training symbols followed by data symbols, and the receiver performs channel estimation using the training symbols and then uses the imperfect channel estimates to decode the data symbols. It turns out that as long as the training power is equal to the data power, the obtained DMT based on imperfect channel state information at receiver (CSIR) is the same as the original DMT result with perfect CSIR given in Zheng and Tse´s seminal work. We further extend our analysis to two-way training scenarios, with single and multiple training rounds. Our results show that two-way training together with power control further significantly improves the achievable diversity gain. In particular, we show that if the multiplexing gain is larger than a certain value, no training can help get any diversity and therefore the achievable diversity is zero.