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

Lampiris, Eleftherios; Elia, Petros
IEEE Journal on Selected Areas in Communications, Vol. 36, N°6, June 2018

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

Systèmes de Communication
Eurecom Ref:
© 2018 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.