Energy Efficiency Analysis of Cache-Enabled Two-Tier HetNets Under Different Spectrum Deployment Strategies

Heterogeneous networks (HetNets) consisting of macrocells overlaid with small cells (e.g. femtocell, picocell, microcell, and relay) are conceived as an appealing technology to cope with the explosive growth of service traffic in future cellular networks. However, the backhaul limitation has become a bottleneck in HetNets, which affects the network performance and users' quality of experience. Wireless edge caching that caches popular contents at the network edge (e.g., base stations (BSs)) can effectively unblock the bottleneck and further unleash the potential of HetNets. In this paper, considering a cache-enabled two-tier HetNet, we resort to the stochastic geometry theory to model and analyze the energy efficiency performance of the HetNet with closed-access policy under cochannel and orthogonal channel deployment scenarios. Specifically, the exact closed-form expressions of outage probability, throughput and energy efficiency are derived, respectively. Numerical results show that the larger small-cell local cache capability may not always lead to higher network energy efficiency due to the caching power cost. The results also show that with a given cache capacity for small cells, there exists an optimal small BS density that maximizes the network energy efficiency.