Multichannel LMS and RLS algorithms for cancelling MAI and ISI before transmission in TDD/CDMA downlink

A novel transmitter based multiuser detection scheme for the TDD/CDMA downlink is presented. The method assumes knowledge of the channel at the transmitter. This is feasible under the time division duplex (TDD) mode where the channel is assumed to be the same on uplink and downlink and can be estimated at the base station from the uplink. The portable unit´s structure is significantly simplified since no channel estimation, equalisation or multiuser detection is required. The novelty is that the base station performs an emulation of the mobile receiver and adaptively sets the filters that pre-equalise the transmitted signals, reducing multiple access and multipath intersymbol interference. The theoretical analysis is supported with simulation results which show that the proposed technique increases the system´s capacity, compared with other recently published methods, and maintains low computational cost.