Flexible Functional Split in C-RAN with Renewable Energy Powered Remote Radio Units

Functional split is a promising technique to reduce the fronthaul rate requirement in cloud radio access networks (C-RAN). Different functional split schemes have different processing costs and fronthaul transmission rates. To maximize the throughput while satisfying the average fronthaul rate constraint in C- RAN with renewable powered Remote Radio Units (RRUs), we first explore the offline problem of selecting the optimal functional split scheme, jointly with the corresponding user data transmission duration and transmission power. We find that in each interval between successive energy arrivals, at most two functional split schemes should be selected, and the two schemes have the same transmission power. We further analyze the scenario with one instance of energy arrival and two candidate functional split schemes, and derive the closed-form expressions of the optimal transmission power and transmission duration for each scheme. Based on the analysis of the special case, a heuristic online algorithm is then proposed, which has similar performance with the optimal offline policy, as validated by simulations.