Extending the Optimality Range of Multi-Antenna Coded Caching with Shared Caches

摘要

This work considers the cache-aided multiple-input single-output broadcast channel (MISO BC) where an L-antenna transmitter serves K receiving users, each assisted by one of Λ < K caches with normalized capacity γ. For this setting it was known that in the range of L ∈ [K/Λ, Kγ], one can achieve a Degrees-of-Freedom (DoF) performance of L + Kγ. This very restrictive constraint that L ≤ Kγ excluded shared- cache settings with a large number of antennas from achieving the maximum DoF; for the more realistic regime of L > Kγ, all existing coded caching schemes suffer substantially reduced caching or multiplexing gains.Our work provides a novel coded caching scheme that achieves the exact best known, near optimal, DoF L+Kγ, and does so even if L > Kγ, thus covering an important hole in identifying the optimal performance for the multi-antenna shared-cache problem. Therefore, our work reveals that shared-cache systems with many transmit antennas can also enjoy both full multiplexing gains (L) as well as full caching gains (Kγ) despite the sharing of the caches. A side benefit of this scheme is its applicability in multi-antenna settings with dedicated users caches, where it can offer the advantage of reducing the subpacketization without sacrificing the DoF performance.