CoPS: Context Prefetching handover scheme on 4G outdoor small cell testbed

Mobility enhancements of small-cell networks in the IEEE/3GPP standard meeting is an important issue, where the mobility robustness is aimed at the prevention and solution of connection failure/exceptions that occur as a result of uncertain channel condition or aggressive mobility. Although exception handling, such as uncontrolled handover and connection re-establishment, is supported in a 4G wireless network system, it still results in a lengthy yet acceptable handover duration. Notably, the results from commercial 4G cellular systems show that the preparation phase period accounting for 19% of the controlled handover duration is long and prone to uncompleted handover. In this work, we propose a Context Prefetching handover Scheme (CoPS) for 4G broadband wireless access networks in order to effectively reduce the lengthy preparation phase period in the controlled handover procedure without any modifications on user side. We also propose two triggering mechanisms according to the mobility scenario for a trade-off between the overhead and the benefit of prefetching. We implement CoPS and the triggering mechanisms on a WiMAX small-cell network platform of outdoor small cell base-stations. Our field trial results show significant improvements of CoPS in a reduction of the preparation phase period by 78% as well as a reduction of handover duration by 17% and in negligible resource occupation overhead. The proposed solutions also can be introduced into existing LTE infrastructures.