Hierarchical Mobility via Relaying in Dense Wireless Networks

This paper proposes a novel relaying-based approach for managing mobility in dense cellular networks. Dense deployment of base stations will have small cells, necessitating frequent handovers. Moreover, small cell solutions such as femtocells may lack low-delay backhaul connections to the operator core´s network where handover procedures are coordinated. As a result, handover delays can be large, impacting signal quality severely. The proposed relay-based hierarchical mobility scheme forwards data over-the-air to other base stations close to mobile as the mobile moves but before the network point of attachment can be switched. Hybrid ARQ and randomized beamforming are used to opportunistically gain the benefits of relays with no explicit coordination between the relay base stations and the source or mobile. Thus, the protocol is attractive for high-speed dynamic environments and can be implemented with minimal messaging overhead. A simulation of the protocol in a 3GPP Long-Term Evolution (LTE) cellular system with dense cells and high-speed mobiles shows the ability of the protocol to mitigate short-term rate outages during handover with significant improvements for delay sensitive applications.