Energy-Aware Cross-Layer Offloading in Fog-RANs Using Network Coded Device Cooperation

This paper studies a Fog Radio Access Network (F-RAN) architecture that utilises the increasing storage and device-to-device communication capacities of users' smart devices (referred to as F-UEs) in order to reduce the time that the central processing unit (referred to as BBU) has to spend to serve these F-UEs and thus, increases the system's capacity. Indeed, these F-UEs can employ these capacities in cooperatively serving each other's file requests, as long as the F-UEs have the files in their storage, rather than always receiving them through the BBU. In addition, network coding (NC) can be employed to minimize the communications among the F-UEs and from the BBU to further offload the BBU resources and reduce the energy consumed in F-UEs' cooperation. This paper develops an algorithm for scheduling the file encoding and transmissions both among half-duplex F-UEs and from the BBU to minimise the consumed time-frequency resources from the BBU given constraints on the energy consumed by each F-UE for their cooperation to help preserve their battery life. The influence of the energy constraint on BBU offloading is investigated and the performance of the system under a variety of settings is evaluated through extensive simulations. The benefit of using NC is shown and the ability of the F-UEs to transmit with different power levels is also studied and shown to considerably impact the number of cooperating F-UEs and the BBU offloading.