Inter-eNB Coordination-Free Algorithm for Mobility Robustness Optimization in LTE HetNet

Mobility Robustness Optimization (MRO), i.e. self-optimization of handover (HO) parameters, is a key driver for expanding Heterogeneous Networks (HetNet) while suppressing the need for drive tests. 3GPP Long Term Evolution (LTE) has introduced a scheme for MRO that enables the eNB, i.e. a base station, to detect HO failures while coordinating with other eNBs via the X2-interface (X2-Intf). However, neighboring eNBs do not always have X2-Intf because of technical constraints. In this paper, we propose an inter-eNB coordination-free algorithm for MRO. The algorithm adjusts the Cell Individual Offset (CIO) on the basis of ping-pong HOs and HO failures that are detected by monitoring HO related signaling via interfaces other than X2-Intf. LTE HetNet simulations confirmed that the algorithm was resistant to the detection error of HO failures and its HO performance was comparable to that of an algorithm using X2-Intf. Moreover, the proposed algorithm reduced the total number of HO failures from pico cells by 33% while keeping the ping-pong HO rate at an acceptable level, even with quasi-optimal default settings. The HO performance from the macro cells always had good quality, irrespective of whether the proposed algorithm was used or not.