Graduate School and Research Center in Digital Sciences

# Bridging two extremes: Multi-antenna coded caching with reduced subpacketization and CSIT

Lampiris, Eleftherios; Elia, Petros

SPAWC 2019, 20th IEEE International Workshop on Signal Processing Advances in Wireless Communications, Special Session on Cache-aided Communication Networks, 2-5 July 2019, Cannes, France

Two long-standing bottlenecks of coded caching are the exponentially large file sizes that are needed to achieve a maximal caching gain, and - when multiple transmit antennas are involved - the large CSIT feedback costs needed for such caching gains to materialize. Recent results have addressed these two bottlenecks individually, allowing significant reductions in both. In the Multiple-Input-Single-Output (MISO) BC with $L$ antennas, the subpacketization constraint was shown to be as small as the L-th root of the single-antenna case, while maintaining the full Degrees-of-Freedom performance, but requiring feedback from all active users. On the other hand, another result showed that the feedback cost can be reduced to feedback from only $L$ users, but that method required a very high subpacketization. In this work we make progress towards combining the advantages of both worlds by proposing a near-optimal multiantenna coded caching algorithm that incurs a minimal feedback cost, untangled from the number of users, and simultaneously achieving an exponentially reduced subpacketization compared to the single-stream case. In particular - in the context of the L-antenna MISO BC with $K$ single-antenna receivers equipped with caches of normalized size $\gamma$ - the new algorithm achieves a DoF of $(L+K\gamma)(1-\gamma)$ using feedback from only $L$ users, while also reducing subpacketization by a multiplicative factor of $\left(\frac{L+K\gamma}{1+K\gamma}\right)^{K\gamma}$ compared to the single-antenna case, achieving subpacketization reductions exponential to the number of antennas.

 Title: Bridging two extremes: Multi-antenna coded caching with reduced subpacketization and CSIT Type: Conference Language: English City: Cannes Country: FRANCE Date: July 2019 Department: Communication systems Eurecom ref: 5880 Copyright: © 2019 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. Bibtex: @inproceedings{EURECOM+5880, doi = {http://dx.doi.org/10.1109/SPAWC.2019.8815564}, year = {2019}, title = {{B}ridging two extremes: {M}ulti-antenna coded caching with reduced subpacketization and {CSIT}}, author = {{L}ampiris, {E}leftherios and {E}lia, {P}etros}, booktitle = {{SPAWC} 2019, 20th {IEEE} {I}nternational {W}orkshop on {S}ignal {P}rocessing {A}dvances in {W}ireless {C}ommunications, {S}pecial {S}ession on {C}ache-aided {C}ommunication {N}etworks, 2-5 {J}uly 2019, {C}annes, {F}rance}, address = {{C}annes, {FRANCE}}, month = {07}, url = {http://www.eurecom.fr/publication/5880} } See also: