Energy Optimization Algorithms for MIMO-OFDM Based Downlink C-RAN System

In this paper, we consider a green communication design in a multiple-input-multiple-output orthogonal frequency-division multiplexing-based downlink cloud radio access network system with per-user quality of service constraints and remote antenna units (RAUs) power constraints. Two problems are solved in this paper: a total transmits power minimization problem and a total network consumption minimization problem. The first problem is to minimize the total transmit power of RAUs by designing beamforming. While the other is to minimize the total network consumption by beamforming and switching off unnecessary RAUs, which is a joint design of sparse beamforming and RAU selection. It is a mixed integer nonlinear programming problem and hard to deal with. Approximations are made to convert the problems into convex ones by using the difference of convex programming and a mixed ℓ
₁
/ℓ
₂
-norm. Then, the iterative algorithms are proposed to solve the problems. The simulation results show that by using proposed algorithms, the transmit power consumption and the network power consumption can be significantly reduced. Meanwhile, the number of active RAUs can be effectively decreased.