Nonlinear multiuser precoding for non-connected decision regions

Spread spectrum CDMA systems suffer from interference in frequency-selective channels. By applying multiuser transmission (MUT) methods in the base station in conjunction with smart antennas, the interference can be mitigated and the downlink (DL) cell capacity can be substantially increased while keeping the complexity of the battery operated mobile devices within a limit. Besides linear multiuser transmission, known as zero forcing joint transmission and transmit Wiener filters, the nonlinear Tomlinson Harashima precoding (THP) was proposed. The contribution of this paper is the extension of THP with a search algorithm exploiting the degrees of freedom given by the equivalent non-connected decision regions. The simulation environment is similar lo the 3GPP TDD CDMA standard extended with the HSDPA mode.