Mobility-Aware Access Strategy in Multi-User HetNets

For the user moving with high velocity in heterogeneous networks (HetNets), two aspects that cause performance degradation should be considered, one is the channel aging, the other is the handoffs. Nevertheless, only one of these two aspects is involved for performance evaluation in most of researches. In this letter, the optimal access scheme determination is investigated considering these two aspects caused by user mobility. Firstly, the vertical and horizontal handoff probability in HetNets are analyzed. Then the closed-form expressions of coverage probability considering the channel aging for both open access and closed access are derived. Combining the handoff probability and the coverage probability, a fixed data rate scheme is adopted to determine the optimal access strategy. Numerical results verify our analysis, and show that open access performs better than closed access in dense femto-tier base stations (FBSs), whereas closed access is suggested in relatively sparse FBSs. Further, for a large bias factor, the optimal access strategy depends on both the signal-to-interference ratio threshold and the user velocity.