TABLE OF CONTENTS In this section we focus on the capacity of single-user MIMO channels. While most wireless systems today support multiple users, single-user results are still of much interest for the insight they provide and their application to channelized systems where users are allocated orthogonal resources (time, frequency bands, etc.). MIMO channel capacity is also much easier to derive for single-users than for multiple users. Indeed, single-user MIMO capacity results are known for many cases where the corresponding multi-user problems remain unsolved. In particular, very little is known about multi-user capacity without the assumption of perfect channel state information at the transmitter (CSIT) and at the receiver (CSIR). While there remain many open problems in obtaining the single-user capacity under general assumptions of CSI and CDI, for several interesting cases the solution is known. This section will discuss fundamental capacity limits for single-user MIMO channels with a particular focus on special cases of CDI at the transmitter as well as the receiver. We begin with a description of the channel model and the different CSI and CDI models we consider, along with their motivation.
Consider a transmitter with M T transmit antennas and a receiver with M R receive antennas. The channel can be represented by the M R M T matrix H of channel gains h ij representing the gain from transmit antenna j to receive antenna i. The M R 1 received signal
