Mobile speed sensitive handover in a mixed cell environment

As mobile cellular radio systems evolve into personal communications, a mixed cell architecture is introduced to successfully meet the increasing user capacity requirements and to preserve the system integrity. Cells of different sizes co-exist in a two-layer structure comprising: micro cells on the lower layer and macro (umbrella) cells on the upper layer. This paper reports on a mobile speed sensitive handover criterion, which allows sufficient differentiation between slow and fast-moving mobiles in a mixed cell environment. Based upon this criterion, handovers from umbrella into micro cells can be avoided for fast moving mobiles. Correspondingly, slow-moving subscribers are "dropped" from the umbrella into an underlaid micro cell and remain served by the micro-cell-layer, while those who tend to increase their speed over a given threshold are "steered" towards the umbrella-cell-layer. The new technique is compared with a standard handover strategy by means of emulations on measured propagation data in different deployment scenarios. The results indicate that utilizing the mobile speed sensitive handover in a mixed cell environment, the system performance can be significantly improved with respect to both handover load in the fixed network and forced call terminations.