Diversity achievable by joint channel diagonalization through multi-user MIMO smart antennas

Through use of multiple antennas at base and mobile receivers, a joint channel diagonalization (JCD), capable of transmitting multiuser signal streams into orthogonal space, has recently been proposed for downlink communications, thereby making orthogonal space division multiplexing (OSDM) possible. In this paper, we consider an OSDM (or JCD) system for communication from a base station (BS) employing N transmit antennas to N mobile stations (MS), each with 2 receiving antennas, in frequency flat fading channels. At each mobile subscriber, co-channel interference (CCI) from other users can be completely eliminated by simply a maximum ratio combiner (MRC), irrespective of the number of users. The resulting OSDM system reduces a multiuser system into multiple uncoupled single-user systems with diversity. The focus of this paper is to quantify the diversity achievable by JCD, and to empirically model the distribution of the resultant channel gain. Simulation results show that about 0.5 diversity orders in terms of receiving power and 0.3 diversity orders in terms of reducing the variance of received signal energy, can be gained for every additional user accommodated in the system. Results also reveal that the distribution of the resultant channel gain can be well approximated by the Nakagami-m distribution.