Delivery Latency Regions in Fog-RANs with Edge Caching and Cloud Processing.

A Fog Radio Access Network (F-RAN) is a cellular wireless system that enables content delivery via edge caching, i.e., storage of popular content at the edge nodes (ENs), and cloud processing. The existing information-theoretic analyses of F-RAN systems, and special cases thereof, make the assumption that all files in the content library are equally relevant, and hence all users' requests should be guaranteed the same delivery latency (i.e., transmission time). In practice, it is generally desirable to provide different latency levels as a function of the users' requests, e.g., based on the current popularity ranking of the contents. This paper studies the problem of characterizing the region of delivery latencies for all possible users' requests under a per-EN cache capacity constraint. For the case with two ENs and two users, the latency region is characterized in the high-SNR regime in terms of the Normalized Delivery Time (NDT) metric, introduced in prior work.