Abstract-Uplink-downlink duality refers to the fact that the Gaussian broadcast channel has the same capacity region as the dual Gaussian multiple-access channel under the same sumpower constraint. This paper investigates a similar duality relationship between the uplink and downlink of a cloud radio access network (C-RAN), where a central processor (CP) cooperatively serves multiple mobile users through multiple remote radio heads (RRHs) connected to the CP with finite-capacity fronthaul links. The uplink of such a C-RAN model corresponds to a multipleaccess relay channel; the downlink corresponds to a broadcast relay channel. This paper considers compression-based relay strategies in both uplink and downlink C-RAN, where the quantization noise levels are functions of the fronthaul link capacities. If the fronthaul capacities are infinite, the conventional uplinkdownlink duality applies. The main result of this paper is that even when the fronthaul capacities are finite, duality continues to hold for the case where independent compression is applied across each RRH in the sense that when the transmission and compression designs are jointly optimized, the achievable rate regions of the uplink and downlink remain identical under the same sum-power and individual fronthaul capacity constraints. As an application of the duality result, the power minimization problem in downlink C-RAN can be efficiently solved based on its uplink counterpart. As a promising candidate for the future 5G standard, cloud radio access network (C-RAN) enables a centralized processing architecture, using multiple relay-like base stations (BSs), named remote radio heads (RRHs), to serve mobile users cooperatively under the coordination of a central processor (CP). The practically achievable throughput of C-RAN is largely constrained by the finite-capacity fronthaul links between the RRHs and the CP. In the literature, a considerable amount of effort has been dedicated to the study of efficient fronthaul techniques [1] . In the uplink, the compression-based strategy can be used, where each RRH samples, quantizes and forwards its received signals to the CP over its fronthaul link such that each user's messages can be jointly decoded [2] . Likewise, in the downlink, the CP can pre-form the beamforming vectors, then compress and transmit the beamformed signals via the fronthaul links to RRHs for coherent transmission [3] . This paper focuses on these compression-based strategies and reveals an uplink-downlink duality for C-RAN. Information theoretically, the uplink of C-RAN model corresponds to a multiple-access relay channel, while the downlink corresponds to a broadcast relay channel. When the fronthaul links have infinite capacities, the C-RAN model reduces to a multiple-access channel (MAC) in the uplink, and a broadcast
Very recent work has also established uplinkdownlink duality for compression-based strategies for cloud radio access networks REF .
An uplink-downlink duality for cloud radio access network
2016 IEEE International Symposium on Information Theory (ISIT)
2016 IEEE International Symposium on Information Theory (ISIT)
Computer Science Mathematics