Mobility-Aware Content Placement for Device-to-Device Caching Systems

TL;DR

This paper investigates how user mobility influences optimal content placement in D2D caching networks, proposing a submodular optimization approach and deriving closed-form solutions for high mobility scenarios.

Contribution

It introduces a mobility-aware content placement framework that adapts to user movement, utilizing submodular optimization and providing closed-form solutions for high mobility cases.

Findings

Greedy algorithm achieves near-optimal solutions.

Optimal placement caches partial popular contents in high mobility.

Formulation minimizes average BS data load considering user mobility.

Abstract

User mobility has a large effect on optimal content placement in D2D caching networks. Since a typical user can communicate neighboring users who stay in the D2D communication area of the typical user, the optimal content placement should be changed according to the user mobility. Under consideration of randomness of incoming and outgoing users, we formulate an optimization problem to minimize the average data load of a BS. It is proved that minimization of the average data load of a BS can be transformed to maximization of a monotonic submodular function with a matroid constraint, for which a greedy algorithm can find near-optimal solutions. Moreover, when motions of neighboring users are rapid, the optimal content placement is derived in closed-form, aided by reasonable approximation and relaxation. In the high mobility regime, the optimal content placement is shown to cache partial amounts of the most popular contents.