Fundamental tradeoffs in MIMO wireless systems

Summary form only given. The use of multiple-input multiple-output (MIMO) antenna systems leads to dramatic improvements in capacity and link reliability of wireless systems. Focusing on the coherent case where the channel is unknown at the transmitter and perfectly known at the receiver, the leverages offered by MIMO channels can be summarized as follows: 1) spatial multiplexing gain increases spectral efficiency by opening up multiple spatial data pipes in the frequency band of operation for no additional power expenditure; 2) diversity gain improves link reliability by providing multiple (ideally) independently fading signal paths between transmitter and receiver; 3) interference canceling gain reduces co-channel interference and hence increases cellular system capacity by using the spatial degrees of freedom to out undesired interfering signals; and 4) array gain improves coverage by improving the received signal-to-noise ratio (SNR) through coherent combining of the signals arriving at the receive antenna array. While there is a wide variety of space-time signaling techniques available realizing various combinations of the above mentioned MIMO gains, little is known about the underlying fundamental tradeoffs and relations between the different gains. Understanding these tradeoffs is paramount in the design of MIMO wireless transceiver algorithms. The purpose of this talk is to introduce a simple information-theoretic framework establishing the existence of fundamental tradeoffs and relations between MIMO gains and subsequently quantifying them. The resulting tradeoff curves provide valuable insights into the question of how much of each of the MIMO gains can be realized concurrently.