Time and Power Allocation Optimization for Multiple Relay Transmission in MIMO System

The scenario that base station (BS) transmits downlink data to two users with the assistance of two relays is considered in this paper. BS and relays have multiple antennas. The relays transmit to the users using the same frequency and time resources. Multi-user SDMA scheme and cooperative interference avoidance scheme are adopted in the first hop and the second hop, respectively, to reduce the interference generated when transmitting to or from the two relays simultaneously. Time allocation optimization and power allocation optimization are studied based on the joint usage of the two schemes. The optimal time allocation for the two hops is derived. The power allocation scheme at the base station is studied. Because it is difficult to solve the power allocation optimization problem directly, a suboptimal power allocation solution is proposed, which matches the two-hop transmission capacities of both the two relay links. The suboptimal power allocation solution can be realized by numerical iteration, and its simplified method is proposed to reduce complexity. Simulation results show that the performance of the simplified method is very close to the suboptimal power allocation solution, and the proposed time and power allocation methods effectively enhance the system throughput.