Downlink energy-efficient multiuser beamforming with individual SINR constraints

Transmit beamforming in multiuser wireless systems is typically designed to minimize the transmit power subject to signal-to-interference-plus-noise ratio (SINR) constraints, or maximize the SINR with a total transmit power constraint. However, transmit power is only one part of the total power consumption during the transmission. Circuit power, incurred by devices and signal processing, also needs to be taken into account. In this paper, we consider energy efficiency as the objective function, which can be defined as the number of information bits per unit energy usage. We design the beamforming vectors to maximize energy efficiency with individual SINR constraints for each user. A zero-gradient-based energy-efficient multiuser downlink beamforming algorithm is developed which optimizes the normalized beamforming vectors and the transmitted powers jointly for each user. A simpler method of power allocation among users, with the normalized beamforming vectors given, is also described when the interference among users can be eliminated. Based on this power allocation approach, an additional iterative beamforming algorithm is presented. Simulation results show the advantages of the proposed energy-efficient multiuser beamforming algorithms over traditional downlink beamforming schemes.