Optimal Multi-User MISO Solution with Application to Multi-User Orthogonal Space Division Multiplexing5

Rights ©2003 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. Absrracr-In this paper, we shall show that for a nr-element base station (BSI communicating with M (5 nT) single-element mobile stations (MS) (or multiuser MISO) orthogonally in the spatial domain, the optimization problem is equivalent to the least squares (LS) problem for an underdetermined linear system. We then prove that the optimal BS antenna weights can be expressed as the pseudo-inverse of the multiuser channel matrix. This solution decomposes the multiuser system into many single-user systems with maximal resultant channel responses. The average of the squared channel response (defined as channel gain) and the inverse of the normalized variance of the squared channel response (defined as diversity order) are derived for performance analysis. It is found that every individual user of the resulting system behaves like a single-user system with nT-M+1 reception diversity. Finally, by applying the solution on a multiuser MIMO antenna system (i.e., with multiple antennas at the MS as well), an iterative approach is proposed to perform multiuser orthogonal space division multiplexing (OSDM) in the downlink.