Analysis of Delay and Energy Efficiency in Fog Radio Access Networks with Hybrid Caching

In this paper, delay and energy efficiency (EE) are investigated in three-tier fog radio access networks (F-RANs) with hybrid caching. By using tools from stochastic geometry, we firstly derive tractable expressions of delay for coded cached, non-partitioned cached and uncached files. Then, we derive tractable expressions of EE by jointly considering power consumed in circuits, transmissions and backhaul links. To balance delay and EE, the corresponding multi-objective optimization problem is formulated to obtain the optimal hybrid caching strategy. Numerical results show the flexibility of the proposed optimal hybrid caching strategy in delay-sensitive and EE-sensitive scenarios, and that fog access point (F-AP) density has a more significant impact on delay-sensitive scenarios than EE-sensitive scenarios.