Fundamental Limits of Distributed Caching in D2D Wireless Networks

TL;DR

This paper analyzes the fundamental limits of distributed caching in D2D wireless networks, revealing that coded multicast gain and spatial reuse do not combine to improve throughput scaling laws.

Contribution

It demonstrates that combining coded caching with D2D spatial reuse does not yield additional throughput scaling benefits, contrary to intuition.

Findings

Coded multicast gain and spatial reuse gain do not cumulate in throughput scaling.

Both gains achieve the same scaling law behavior independently.

No further scaling law improvement is possible by combining both techniques.

Abstract

We consider a wireless Device-to-Device (D2D) network where communication is restricted to be single-hop, users make arbitrary requests from a finite library of possible files and user devices cache information in the form of linear combinations of packets from the files in the library (coded caching). We consider the combined effect of coding in the caching and delivery phases, achieving "coded multicast gain", and of spatial reuse due to local short-range D2D communication. Somewhat counterintuitively, we show that the coded multicast gain and the spatial reuse gain do not cumulate, in terms of the throughput scaling laws. In particular, the spatial reuse gain shown in our previous work on uncoded random caching and the coded multicast gain shown in this paper yield the same scaling laws behavior, but no further scaling law gain can be achieved by using both coded caching and D2D spatial reuse.