最新东南大学研究生英语雅思写作下学期大作业

On the Delay of Geographical Caching Methods in Two-Tiered Heterogeneous Networks

Abstract

We consider a hierarchical network that consists of mobile users, a two-tiered cellular network (namely small cellsand macro cells) and central routers, each of which follows a Poisson point process (PPP). In this scenario, small cells with limited-capacity backhaul are able to cache content under a given set of randomized caching policies and storage constraints. Moreover, we consider three different content popularity models, namely fixed content popularity, distance-dependent and load-dependent,in order to model the spatio-temporal behavior of users’ content request patterns. We derive expressions for the average delay of users assuming perfect knowledge of content popularity distributions and randomized caching policies. Although the trend of the average delay for all three content popularity models is essentially identical, our results show that the overall performance of cached-enabled heterogeneous networks can be substantially improved, especially under the load dependentcontent popularity model.

Besides, Because of the limitation of research conditions, the total network delay, network cost and optimization of network parameters are not analyzed.

Keywords: edge caching, Poisson point process, stochastic geometry, mobile wireless networks, 5G

Introduction

It is known that content caching in 5G heterogeneous wireless networks improves the system performance, and is of high importance in limited-backhaul scenarios. Most existing literature focuses on the characterization of key performance metrics neglecting the backhaul limitations and the spatio-temporal content popularity profiles. In this work, we analyze the gains of caching in heterogeneous network deployment, and consider the average delay as a performance metric.

Firstly we use passion point process (PPP) method to build the model. This heterogeneous network consists of mobile terminals (users), cache-enabled small base stations (SBSs), macro base stations (MBSs)

and central routers. In this network setting, a user may experience delays due to downlink transmissions, backhaul and caches.

Moreover, in order to capture the spatio-temporal content access patterns of users, we suppose fixed content popularity, distance-dependent and load-dependent content popularities. Assuming that the content popularity distribution is perfectly known at the small base stations, we explore three different caching policies based on content-popularity and randomization. And finally, we draw our conclusion.

Methodology

First, our Research objective is to get the average delay in a cache-enabled two-tiered cellular network modeled by stochastic geometry, the figure one is an illustration of the considered system model, the methodology part including the following parts.

The first is the topology, the central routers, MBSs, SBSs, USERs are modeled by the independent PPP models, the second is the signal model, for the tractability for the problem, we assume that the typical user experience the rayleigh fading and the standard power law path loss, also we assume that the network is interference-limited, that is to say the interference power dominates over the noise power.

Then it is the caching model, when a user has a content request, we assume that the request is drawn from a continuous zipf distribution, in the function, there is a content popularity parameter, based on this parameter, we have three caching models, Fixed means that the content popularity is identical for all users, all SBSs observe the same distribution, Distance-dependent means that each user has a distance-dependent steepness factor ,the factor is related to the average distance between the SBS and its users.

Based on the caching models, here we consider three caching policies: StdPop means the SBSs cache the most popular content from the catalogue, the Unirand means the contents are cached uniformly at random, the MixPop policy means that part storage cache the most popular contents, the other part cache the content at random.