A Novel HARQ Pooling Scheme for Improved Multi-Connectivity in 5G Cloud RAN

5G Radio Access Network (RAN) is expected to support HetNets and cloud technologies natively to provide scalable high capacity. Specifically, smaller transmission time intervals in 5G coupled with increased propagation delay due to the fronthaul between the baseband unit (BBU) and the remote radio head (RRH) result in variable HARQ (Hybrid Automatic Repeat Request) round trip times. Therefore, HARQ design is one of the challenging aspects in realizing such an architecture because it needs to factor in non-ideal and non-uniform fronthaul latencies across cells. In this paper, we address this design problem using a novel HARQ process pooling scheme for UEs operating in multi-connectivity mode. The HARQ processes of a UE are pooled and shared across different carriers, instead of having independent HARQ processes for each carrier. We further propose a dynamic and adaptive split of the HARQ processes across carriers to enable independent scheduling and transmission from each of the carriers such that the UE's throughput is maximized. We evaluate the proposed algorithm using system simulations and show that our scheme provides superior system performance.