Cache-Aided Non-Orthogonal Multiple Access: The Two-User Case

Abstract

In this paper, we propose a cache-aided non-orthogonal multiple access (NOMA)\nscheme for spectrally efficient downlink transmission. The proposed scheme not\nonly reaps the benefits associated with NOMA and caching, but also exploits the\ndata cached at the users for interference cancellation. As a consequence,\ncaching can help to reduce the residual interference power, making multiple\ndecoding orders at the users feasible. The resulting flexibility in decoding\ncan be exploited for improved NOMA detection. We characterize the achievable\nrate region of cache-aided NOMA and derive the Pareto optimal rate tuples\nforming the boundary of the rate region. Moreover, we optimize cache-aided NOMA\nfor minimization of the time required for completing file delivery. The optimal\ndecoding order and the optimal transmit power and rate allocation are derived\nas functions of the cache status, the file sizes, and the channel conditions.\nSimulation results confirm that, compared to several baseline schemes, the\nproposed cache-aided NOMA scheme significantly expands the achievable rate\nregion and increases the sum rate for downlink transmission, which translates\ninto substantially reduced file delivery times.\n