Adding transmitters dramatically boosts coded-caching gains for finite file sizes

In the context of coded caching in the K-user BC, our work reveals the surprising fact that having multiple (L) transmitting antennas, dramatically ameliorates the long-standing subpacketization bottleneck of coded caching by reducing the required subpacketization to approximately its Lth root, thus boosting the actual DoF by a multiplicative factor of up to L. In asymptotic terms, this reveals that as long as L scales with the theoretical caching gain, then the full cumulative (multiplexing + full caching) gains are achieved with constant subpacketization. This is the first time, in any known setting, that unbounded caching gains appear under finite file-size constraints. The achieved caching gains here are up to L times higher than any caching gains previously experienced in any single- or multiantenna fully-connected setting, thus offering a multiplicative mitigation to a subpacketization problem that was previously known to hard-bound caching gains to small constants. The proposed scheme is practical and it works for all values of K, L and all cache sizes. The scheme's gains show in practice: e.g. for K = 100, when L = 1 the theoretical caching gain of G = 10, under the original coded caching algorithm, would have needed subpacketization S1 = K G
= 100 10
> 1013, while if extra transmitting antennas were added, the subpacketization was previously known to match or exceed S1. Now for L = 5, our scheme offers the theoretical (unconstrained) cumulative DoF dL = L + G = 5 + 10 = 15, with subpacketization SL = K/L G/L
= 100/5 10/5
= 190. The work extends to the multi-server and cache-aided IC settings, while the scheme's performance, given subpacketization SL = K/L G/L
, is within a factor of 2 from the optimal linear sum