Coded Caching Clusters with Device-to-Device Communications

We consider a geographically constrained caching community where popular data files are cached on mobile terminals and distributed through Device-to-Device (D2D) communications. Further, to ensure availability, data files are protected against user mobility, or churn, with erasure coding. Communication and storage costs (in units of energy) are considered. We focus on finding the coding method that minimizes the overall cost in the network. Closed-form expressions for the expected energy consumption incurred by data delivery and redundancy maintenance are derived, and it is shown that coding significantly decreases the overall energy consumption – by more than 90% in a realistic scenario. It is further shown that D2D caching can also yield notable economical savings for telecommunication operators. Our results are illustrated by numerical examples and verified by extensive computer simulations. Index Terms Device-to-Device Communications, Regenerating Codes, Wireless Caching, Markov Processes, Distributed Data Storage J. Pääkkönen and O. Tirkkonen are with the Department of Communications and Networking, Aalto University, Finland. A. Barreal and C. Hollanti are with the Department of Mathematics and Systems Analysis, Aalto University, Finland. (Emails: [email protected]) The authors are financially supported by the Academy of Finland under Grants #276031, #282938, #283262 and #284725, the Finnish Funding Agency for Technology and Innovations under grant 2383/31/2014, as well as a grant from the Finnish Foundation for Technology Promotion. The support from the ESF COST Action IC1104 is gratefully acknowledged. Parts of this work were presented at IEEE GLOBECOM 2013 [1] and MACOM 2015 [2].