An uplink-downlink duality for cloud radio access network

摘要

Uplink-downlink duality refers to the fact that the Gaussian broadcastchannel has the same capacity region as the dual Gaussian multiple-accesschannel under the same sumpower constraint. This paper investigates a similarduality relationship between the uplink and downlink of a cloud radio accessnetwork (C-RAN), where a central processor (CP) cooperatively serves multiplemobile users through multiple remote radio heads (RRHs) connected to the CPwith finite-capacity fronthaul links. The uplink of such a C-RAN modelcorresponds to a multipleaccess relay channel; the downlink corresponds to abroadcast relay channel. This paper considers compression-based relaystrategies in both uplink and downlink C-RAN, where the quantization noiselevels are functions of the fronthaul link capacities. If the fronthaulcapacities are infinite, the conventional uplinkdownlink duality applies. Themain result of this paper is that even when the fronthaul capacities arefinite, duality continues to hold for the case where independent compression isapplied across each RRH in the sense that when the transmission and compressiondesigns are jointly optimized, the achievable rate regions of the uplink anddownlink remain identical under the same sum-power and individual fronthaulcapacity constraints. As an application of the duality result, the powerminimization problem in downlink C-RAN can be efficiently solved based on itsuplink counterpart.