Downlink MIMO multiuser detection with interference subspace rejection

We proposed recently a new technique for multiuser detection in CDMA networks, denoted interference subspace rejection (ISR), and evaluated its performance on the uplink. This paper extends its application to the downlink (DL). On the DL the information about interference is sparse, e.g., spreading factor (SF) and modulation of interferers may not be known, which makes the task much more challenging. We present three new ISR variants, which require no prior knowledge of the interfering users. The new solutions are applicable to MIMO systems and can accommodate any modulation, coding, spreading factor, and connection type. A new dynamic power-assisted channelization code allocation (DACCA) technique significantly reduces implementation complexity at the receiving mobile. Simulations under practically reasonable conditions suggest that increased user capacities and data-rates are attainable with downlink interference subspace rejection (DLISR) and system capacity increases linearly with the number of antennas. Capacity gains are at least 3 dB over the single-user detector and increase to 8 dB for high data-rates with 16-QAM.