In this work, we propose a cross-layer approach for cloud offloading using network coding enabled fog radio access networks. Exploiting prior popular file downloads by clients, network coding was previously employed to send more efficient coded files from both edge nodes and the cloud, thus achieving further upper-layer offloading gains. The proposed cross-layer approach in this paper extends the study towards achieving actual cloud physical-resource offloading, by considering the download rates of each client from the cloud in the coding-based offloading process. We first formulate the cross- layer cloud offloading problem as an optimization problem over an opportunistic network coding graph, and prove its NP-hardness. We then devise a heuristic algorithm to efficiently solve the problem by dividing it into two subproblems, which are solved sequentially by a greedy vertex search and a sorted greedy coloring algorithms. Simulation results show a superior performance of our proposed cross-layer cloud offloading scheme compared to the traditional upper-layer scheme. Furthermore, the suggested heuristic achieves a close cloud offloading performance to the optimal cross-layer solution.
