Multi-connectivity for Mobility Robustness in Standalone 5G Ultra Dense Networks with Intra-frequency Cloud Radio Access

Capacity and ultra-reliable communication are some of the requirements for 5th Generation (5G) networks. One of the candidate technologies to satisfy capacity requirement is standalone Ultra Dense Networks (UDN). UDNs are characterized by fast change of received signal strength that creates mobility challenges in terms of increased change of serving cell(s), e.g. handover, and connection failures such as handover failures and radio link failures. Handover procedures and connection failures create service interruptions for the users. Existing solutions focus on achieving mobility robustness in dense small cells by using Macro cells as mobility anchor. This paper presents a low layer multi-connectivity scheme for standalone UDN aiming at ultra-reliable communication, that is free of connection failures, without leveraging the Macro cell as mobility anchor. The problem of configuring and managing the set of serving cells, that are involved in multi-connectivity for each user, is formulated. By using numerical method, feasible scheme for configuring and managing the set of serving cells is derived. With support of elaborated simulation, performance of the proposed multi-connectivity solution is evaluated in a challenging mobility scenario that consists of mix of slow and fast users. It is shown that radio link failures are resolved with low signaling overhead by using the derived scheme for configuring and managing a set of serving cells.