On the Capacity of Cloud Radio Access Networks

Uplink and downlink cloud radio access networks are modeled as two-hop K-user L-relay networks, whereby small base-stations act as relays and are connected to a central processor via orthogonal links of finite capacity. Simplified versions of noisy network coding and distributed decode forward are used to establish inner bounds on the capacity region for uplink and downlink communications, respectively. Through a careful analysis, the uplink inner bound is shown to achieve the cutset bound on the capacity region universally within O(log L) bits per user. The downlink inner bound achieves the cutset bound with a slightly looser gap of O(log(KL)). These tight per-user gap results are extended to the situations in which the nodes have multiple antennas.