Co-existence of enhanced inter cell interference co-ordination and mobility robustness optimization

Enhanced Inter-Cell Interference Co-ordination (eICIC) enables expanding the range of small cells (and thereby better Macro cell offloading) by protecting users in the expanded area through blanking subframes in the Macro cells. Range expansion is achieved by modifying the handover parameters. However, those handover parameters are already modified by the existing feature Mobility Robustness Optimization (MRO). The interaction between MRO and eICIC is particularly challenging since real deployments face a mixture of Rel. 10/11 users (which are able to perfectly exploit eICIC) and legacy Rel. 8/9 users. Furthermore, the details of the eICIC impact on mobility (failures) is not very well explored, in particular due to the lack of simulation tools capable of investigating both eICIC and MRO at the same time. In Release 11, there was a proposal for a new feature which enables proper interaction between MRO and eICIC in the presence of both Rel. 8/9 and Rel. 10/11 users. The feature allows setting up separate MRO statistics for Rel. 8/9 users and for Rel. 10/11 users. The paper presents comparison of this new feature with simpler workarounds. The results were created with a system level simulator which has elaborated mobility and eICIC model. The main conclusions are that mobility problems also exist for Rel. 10/11 users, and simple workaround solutions cannot solve the interaction problem.