Towards Studying the Two-Tier Intra-Frequency X2 Handover Based on Software-Defined Open LTE Platform

The next generation cellular systems are rapidly evolving from a homogeneous macrocell deployment to a heterogeneous deployment of macrocells overlaid with femtocells, which is referred to as heterogeneous networks (HetNets). In macro-femto HetNets, the handover issue is more important than that in macrocell networks. On one hand, more frequent handovers are triggered because the coverage range of the femtocell is small, and the multiple femtocells are overlaid with macrocells. On the other hand, some schemes, such as load balancing, aimed at improving network performance, will also cause frequent handover in macro-femto HetNets. Therefore, the study on handover is of great importance, especially in macro-femto HetNets. In this paper, based on the software-defined open long-term evolution (LTE) platform, we propose an analytical model to study the two-tier intra-frequency X2 handover in realistic macrocell-femtocell HetNets scenario. Specifically, we first construct the software-defined open LTE platform. Based on the open LTE platform, we then characterize the relation between the handover failure and the ping-pong rates in a macro-femto HetNets scenario as a function of the relevant system parameters such as the time-to-trigger, user equipment velocity, etc. Finally, we derive the handover failure and ping-pong rates in closed-form expressions. The handover experiment results have verified the accuracy of our analytical derivations, which shed new light on key aspects of the handover process in macro-femto HetNets.