Energy-efficient precoding design for cloud radio access networks

In cloud radio access network, a baseband unit (BBU) performs the baseband processing for a cluster of low-power low-cost remote radio heads (RRHs) that are connected to the BBU through low-latency fronthaul links. In this study, the authors study the optimisation of two energy-efficient compression and precoding strategies which take transmit power constraint, fronthaul capacity constraint and user specific rate constraint into account. To overcome the non-convexity nature of the original problem, they first transform the objective of the original problem into a parameterised subtractive form and obtain an approximate convex problem via the successive convex approximation. Then, an effective optimisation algorithm with provable convergence is designed to solve the effective problem. Numerical results reveal that the proposed scheme outperforms the conventional maximum sum rate and minimum total power consumption schemes in terms of the energy-efficiency criterion. In particular, compression after precoding strategy outperforms compression before precoding strategy when both of their RRHs perform the same user scheduling, while the opposite conclusion can be drawn otherwise.