Mobility Increases the Data Offloading Ratio in D2D Caching Networks

TL;DR

This paper models user mobility in D2D caching networks using an alternating renewal process and demonstrates that increased user speed improves data offloading ratios, providing analytical expressions and validation through simulations.

Contribution

It introduces a novel model for contact durations using an alternating renewal process and analytically shows mobility enhances data offloading in D2D caching networks.

Findings

Data offloading ratio increases with user speed.

The beta distribution approximates communication time well.

Simulation confirms the analytical results.

Abstract

Caching at mobile devices, accompanied by device-to-device (D2D) communications, is one promising technique to accommodate the exponentially increasing mobile data traffic. While most previous works ignored user mobility, there are some recent works taking it into account. However, the duration of user contact times has been ignored, making it difficult to explicitly characterize the effect of mobility. In this paper, we adopt the alternating renewal process to model the duration of both the contact and inter-contact times, and investigate how the caching performance is affected by mobility. The data offloading ratio, i.e., the proportion of requested data that can be delivered via D2D links, is taken as the performance metric. We first approximate the distribution of the communication time for a given user by beta distribution through moment matching. With this approximation, an accurate expression of the data offloading ratio is derived. For the homogeneous case where the average contact and inter-contact times of different user pairs are identical, we prove that the data offloading ratio increases with the user moving speed, assuming that the transmission rate remains the same. Simulation results are provided to show the accuracy of the approximate result, and also validate the effect of user mobility.