Multiuser precoding and power allocation in downlink of cooperative CDMA networks

In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA) systems, where a set of Mobile Terminals (MT) cooperate with the purpose of improving their downlink communications reliability with Base Station (BS). For combating Multiple-Access Interference (MAI) as well as transferring complexity and spatial processing from the mobile terminals to the transmitter of BS, multiuser transmitter precoding is considered. In addition to multiuser precoding based on Minimum Mean-Square Error (MMSE) criterion for mitigating MAI, the proper transmission power control strategy under a fixed total power constraint is proposed and analyzed. Compared with equal transmission power assigning, where BS and cooperative terminals transmit with the same power, the proposed power allocation scheme leads to a significant performance gain at the destination. Finally, simulation results demonstrate acceptable performance for the proposed multiuser precoding algorithms and power allocation schemes in synchronous DS-CDMA systems.