The work identifies the performance limits of the multiple-input single-output broadcast channel where cache- aided users coincide with users that do not have caches. The main contribution is a new algorithm that employs perfect matchings on a bipartite graph to offer full multiplexing as well as full coded-caching gains to both cache-aided as well as cache-less users. This performance is shown to be within a factor of at most 3 from the optimal, under the assumption of linear one- shot schemes. An interesting outcome is the following: starting from a single- stream centralized coded caching setting with normalized cache size γ, then every addition of an extra transmit antenna allows for the addition of approximately 1/γ extra cache-less users, at no added delay costs. For example, starting from a single-stream coded caching setting with γ = 1/100, every addition of a trans- mit antenna, allows for serving approximately an additional 100 more cache-less users, without any increase in the overall delay. Finally the work reveals the role of multiple antennas in removing the penalties typically associated to cache-size unevenness, as it shows that the performance in the presence of both cache-less and cache-aided users, matches the optimal (under uncoded cache placement) performance of the corresponding symmetric case where the same cumulative cache volume is split evenly across all users.
Full coded caching gains for cache-less users
ITW 2018, IEEE Information Theory Workshop, 25-29 November 2018, Guangzhou
Systèmes de Communication
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