With the recent emergence of 5G era, heterogeneous cellular networks (HCNs)have invoked a popular research interest. In this paper, we provide acomprehensive analysis for multiantenna transmissions in a multi-tier downlinkHCN. We first propose a reliability-oriented threshold-based mobile associationpolicy, where each user connects to the strongest base station from which thisuser can obtain the largest truncated long-term received power. Under ourmobile association policy, we derive analytical expressions for the exactoutage probability of an arbitrary randomly located user, along withcomputationally convenient lower and upper bounds. Asymptotic analysis on theoutage probability shows that introducing a large access threshold into mobileassociation significantly decreases the outage probability. We furtherinvestigate the spectrum efficiency and the energy efficiency of the HCN. Ourtheoretic analysis and numerical validations show that both the spectrum andenergy efficiencies can be improved by properly choosing the access threshold.
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