Two-Step Handover for LTE HetNet mobility enhancements

Through the study on “HetNet mobility enhancements for LTE”, it was observed that handover (HO) performance in heterogeneous networks (HetNets) deployments is not as good as in pure macro deployments. It also showed that high speed user equipment (UE) suffers much higher handover failure (HOF) rate than low speed UE. The major cause of HOF is the failure of handover command transmission from source eNodeB (eNB) to UE. There is the tradeoff between optimizing HO parameters to reduce HOF and increased ping-pongs. This makes HO performance optimization an intricate problem. In this paper, we propose a solution that improves HO performance with regard to HOF rate and ping-pong at the same time. It consists of early HO preparation and ping-pong avoidance. The early HO preparation helps to relieve HOF problems with expedited transmission of HO command message. But this premature HO command causes increased ping-pong rate. The ping-pong avoidance delays HO execution to suppress unnecessary HOs. This solution also improves to help with recovery from radio link failure (RLF).