Cell-pair specific optimization of the inter-RAT handover parameters in SON

The Long Term Evolution (LTE) network will be at first deployed in some areas with high user traffic overlaying with legacy radio access technologies (RATs) such as the second generation (2G) or third generation (3G) mobile system. Consequently, the user equipments (UEs) will be handed over from LTE to 3G network and vice versa. Having robust and error-free handovers between different RATs is one of the most prominent self-organizing network (SON) use cases where the handover thresholds of the base stations in both networks have to be automatically optimized. Currently, the thresholds of measurement event B2 triggering the handover of the UEs from LTE to another RAT are defined by the 3^rd Generation Partnership Project (3GPP) as cell-specific, and therefore, they cannot be differentiated with respect to each neighboring target cell. In this paper, we analyze the difference between optimizing a single handover threshold in a cell-specific and cell-pair specific ways. Based on this analysis, we investigate three new alternative configuration paradigms for the inter-RAT handover thresholds along with those considered by 3GPP. The performance of the SON-based algorithm optimizing the inter-RAT handover thresholds is evaluated for each configuration paradigm. The simulation results have shown that the three alternative configuration paradigms outperform those used by 3GPP. Among the three configuration paradigms, we propose the one which extends the current 3GPP approach and configures the threshold corresponding to the handover target cell in measurement event B2 as cell-pair specific instead of cell-specific.