NOMA Assisted Wireless Caching: Strategies and Performance Analysis

This paper investigates the coexistence of two important enabling techniques for future wireless networks, non-orthogonal multiple-access (NOMA) and wireless caching, and we show that the use of NOMA ensures that the two caching phases, content pushing and content delivery, can be more effectively carried out, compared to the conventional orthogonal multiple-access (OMA) based case. Two NOMA caching strategies are developed, namely the push-then-delivery strategy and the pushand-delivery strategy. In the push-then-delivery strategy, the NOMA principle is applied in the content pushing and content delivery phases, respectively. The presented analytical framework demonstrates that the push-then-delivery strategy not only significantly improves the cache hit probability, but also considerably reduces the delivery outage probability, compared to the OMA strategy. The push-anddelivery strategy is motivated by the fact that some users’ requests cannot be accommodated locally and the base station has to serve them directly. The key idea of the push-and-delivery strategy is to merge the content pushing and delivery phases, i.e., the base station pushes new content to local servers while simultaneously serving the users. We show that this strategy can be straightforwardly extended to Z. Ding and H. V. Poor are with the Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA. Z. Ding is also with the School of Computing and Communications, Lancaster University, Lancaster, UK (email: [email protected], [email protected]). P. Fan is with the Institute of Mobile Communications, Southwest Jiaotong University, Chengdu, China (email: [email protected]). G. K. Karagiannidis is with the Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece (email: [email protected]). R. Schober is with the Institute for Digital Communications, Friedrich-Alexander-University Erlangen-Nurnberg (FAU), Germany (email: [email protected]).