Coded Caching In Large-scale Wireless Small-cell Networks

The global mobile data traffic has undergone a fundamental shift from voices and messages to rich content distributions,such as video streaming and application downloads.However,the current wireless network architecture is unable to support the fastgrowing mobile data traffic.Since the edge resources in wireless network are closer to the user and can quickly perceive the users' states,they can be applied to alleviate the pressure of the wireless core network.By prefetching popular contents during offpeak times at the edge of wireless networks,wireless caching can alleviate peak-hour network congestion,provide traffic offloading,and improve users' quality of experience.Coded caching is able to exploit the accumulated cache size and hence superior to uncoded caching by distributing different fractions of a file in different nodes.This work investigates the model,analysis,and optimization of coded caching in a large-scale small-cell network(SCN),mainly including the static and moving users' states.The locations of small base stations(SBSs)are modeled by stochastic geometry.We first propose a static content delivery framework,where multiple SBSs that cache different coded packets of a desired file transmit concurrently upon a user request and the user decodes the signals using successive interference cancellation(SIC).The performance of coded caching is characterized by two performance metrics,average fractional offloaded traffic(AFOT)and average ergodic rate(AER),for which a closed-form expression and a tractable expression are derived,respectively,in the high signal-to-noise ratio region.We then formulate the coded cache placement problem for AFOT maximization as a multiple-choice knapsack problem(MCKP).By utilizing the analytical properties of AFOT,a greedy but optimal algorithm is proposed.We also consider the coded cache placement problem for AER maximization.By converting this problem into a standard MCKP,a heuristic algorithm is proposed.In the second part,we find that user mobility can further increase the cache access opportunity and exploit the accumulated cache size in wireless small-cell networks(SCNs).A moving user whose trajectory as the Random waypoint(RWP)mobility model can receive coded packets of the requested file from the SBSs within the coverage radius without error before a delay constraint.To maximize AFOT,another coded cache placement problem is formulated as a multiple-choice knapsack problem and a greedy-based optimal algorithm is proposed to solve it.In this work,we can conclude that coded caching can use the accumulated cache size of different network nodes to cache different packets and serve users,which achieves better performance than uncoded caching.To satisfy different performance requirements,we will design different coding coefficients.Coding coefficients does not need to be too large approaching the upper bound of the coding cache performance when users are static.Coding coefficients should increase to regain the performance gain when users are moving.