Queue‐aware energy minimisation through sparse beamforming in C‐RAN

This paper considers the queue‐aware optimal energy minimisation sparse beamforming design (QESB)in a downlink cloud radio access network (C‐RAN) system where multi‐RRHcommunicates with multi‐user through a central computing cloud via digitalfront‐haul links. The problem is formulated as the joint optimisation problem ofthe transmission energy consumption, system queue length and front‐haul costwith sparse beamforming design. As we know, the beamforming design adaptive toboth QSI and CSI is challenging because of the high complexity. Apart fromprevious works that take queue length as constraints, in this paper we directlyminimise the queue length state involved joint optimisation problem with SINRconstraints. A smooth function is proposed to approximate the l 0 ‐norm function which is discrete andnon‐convex. To overcome the challenge due to the non‐convexity of theoptimisation problem, the semidefinite relaxation (SDR) technology is utilisedto convert the primitive problem into the difference of convex (DC) programmingproblem, and convex and concave procedure (CCP) algorithm is used to induce thesparsity of the beamforming control. The simulation results show that the schemeproposed by this paper can obtain a good tradeoff between system energyconsumption, queue length and front‐haul cost with SINR constraints in C‐RANsystem.