Outage analysis of a content-based user pairing in NOMA.

This article proposes an opportunistic online caching strategy (OOCS) capable of updating cached content even when the traffic load of a non-orthogonal multiple access (NOMA)-enabled heterogeneous network (HetNets) is at its peak. The macro base station (MBS) has an opportunity to update cached content when none of the user-requested files are cached. The OOCS selects a file from the historical record based on a newly proposed metric called the <italic>Cache Index</italic>, which takes into account the popularity of the contents and the backhaul latency. Furthermore, we propose a content-based user pairing strategy for NOMA and analyse the outage performance of the HetNets. [ABSTRACT FROM AUTHOR]