Caching popular contents at base stations (BSs) can reduce the backhaul costand improve the network throughput. Yet whether locally caching at the BSs canimprove the energy efficiency (EE), a major goal for 5th generation cellularnetworks, remains unclear. Due to the entangled impact of various factors on EEsuch as interference level, backhaul capacity, BS density, power consumptionparameters, BS sleeping, content popularity and cache capacity, anotherimportant question is what are the key factors that contribute more to the EEgain from caching. In this paper, we attempt to explore the potential of EE ofthe cache-enabled wireless access networks and identify the key factors. Byderiving closed-form expression of the approximated EE, we provide thecondition when the EE can benefit from caching, find the optimal cache capacitythat maximizes the network EE, and analyze the maximal EE gain brought bycaching. We show that caching at the BSs can improve the network EE when powerefficient cache hardware is used. When local caching has EE gain over notcaching, caching more contents at the BSs may not provide higher EE. Numericaland simulation results show that the caching EE gain is large when the backhaulcapacity is stringent, interference level is low, content popularity is skewed,and when caching at pico BSs instead of macro BSs.
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