Cache-at-relay: energy-efficient content placement for next-generation wireless relays

Uploading and downloading content have recently become one of the major reasons for the growth of Internet traffic volume. With the increasing popularity of social networking tools and their video upload/download applications, as well as the connectivity enhancements in wireless networks, it has become a second nature for mobile users to access on-demand content onthe-go. Urban hot spots, usually implemented via wireless relays, answer the bandwidth need of those users. On the other hand, same popular contents are usually acquired by a large number of users at different times, and fetching those from the initial content source each and every time, make inefficient use of network resources. In-network caching provides a solution to this problem by bringing contents closer to the users. Although in-network caching has been previously studied from latency and transport energy minimization perspectives, energy-efficient schemes to prolong User Equipment (UE) lifetime have not been considered. To address this problem, we propose the Cache-At-Relay (CAR) scheme which utilizes wireless relays for in-network caching of popular contents with content access and caching energy minimization objectives. CAR consists of three Integer Linear Programming (ILP) models, namely Select Relay (SER), Place Content (PCONT) and Place Relay (PREL) which respectively solve content access energy minimization, joint minimization of content access and caching energy and joint minimization of content access energy and relay deployment cost problems. We have shown that PREL significantly minimizes the content access energy consumption of UEs while PCONT provides a compromise between the content access and the caching energy budgets of the network.