4 research outputs found
On Multi-Server Coded Caching in the Low Memory Regime
In this paper we determine the delivery time for a multi-server coded caching
problem when the cache size of each user is small. We propose an achievable
scheme based on coded cache content placement, and employ zero-forcing
techniques at the content delivery phase. Surprisingly, in contrast to previous
multi-server results which were proved to be order-optimal within a
multiplicative factor of 2, for the low memory regime we prove that our
achievable scheme is optimal. Moreover, we compare the performance of our
scheme with the uncoded solution, and show our proposal improvement over the
uncoded scheme. Our results also apply to Degrees-of-Freedom (DoF) analysis of
Multiple-Input Single-Output Broadcast Channels (MISO-BC) with cache-enabled
users, where the multiple-antenna transmitter replaces the role of multiple
servers. This shows that interference management in the low memory regime needs
different caching techniques compared with medium-high memory regimes discussed
in previous works
Resolving the Feedback Bottleneck of Multi-Antenna Coded Caching
Multi-antenna cache-aided wireless networks have been known to suffer from a
severe feedback bottleneck, where achieving the maximal Degrees-of-Freedom
(DoF) performance required feedback from all served users. These costs matched
the caching gains and thus scaled with the number of users. In the context of
the -antenna MISO broadcast channel with receivers having normalized
cache size , we pair a fundamentally novel algorithm together with a
new information-theoretic converse, and identify the optimal tradeoff between
feedback costs and DoF performance, by showing that having CSIT from only
served users implies an optimal one-shot linear DoF of . As a side
consequence of this, we also now understand that the well known DoF performance
is in fact exactly optimal. In practice, the above means that we
are now able to disentangle caching gains from feedback costs, thus achieving
unbounded caching gains at the mere feedback cost of the multiplexing gain.
This further solidifies the role of caching in boosting multi-antenna systems;
caching now can provide unbounded DoF gains over multi-antenna downlink
systems, at no additional feedback costs. The above results are extended to
also include the corresponding multiple transmitter scenario with caches at
both ends.Comment: 16 pages, partially presented in ISIT 2018, submitted on Transactions
on Information Theor
Fundamental Limits of Stochastic Shared Caches Networks
The work establishes the exact performance limits of stochastic coded caching
when users share a bounded number of cache states, and when the association
between users and caches, is random. Under the premise that more balanced
user-to-cache associations perform better than unbalanced ones, our work
provides a statistical analysis of the average performance of such networks,
identifying in closed form, the exact optimal average delivery time. To
insightfully capture this delay, we derive easy to compute closed-form
analytical bounds that prove tight in the limit of a large number of
cache states. In the scenario where delivery involves users, we conclude
that the multiplicative performance deterioration due to randomness -- as
compared to the well-known deterministic uniform case -- can be unbounded and
can scale as at
, and that this scaling vanishes when
. To alleviate this adverse effect of
cache-load imbalance, we consider various load balancing methods, and show that
employing proximity-bounded load balancing with an ability to choose from
neighboring caches, the aforementioned scaling reduces to , while when
the proximity constraint is removed, the scaling is of a much slower order
. The above analysis is extensively
validated numerically.Comment: 40 pages, 12 figure
Low-Complexity High-Performance Cyclic Caching for Large MISO Systems
Multi-antenna coded caching is known to combine a global caching gain that is
proportional to the cumulative cache size found across the network, with an
additional spatial multiplexing gain that stems from using multiple
transmitting antennas. However, a closer look reveals two severe bottlenecks;
the well-known exponential subpacketization bottleneck that dramatically
reduces performance when the communicated file sizes are finite, and the
considerable optimization complexity of beamforming multicast messages when the
SNR is finite. We here present an entirely novel caching scheme, termed
\emph{cyclic multi-antenna coded caching}, whose unique structure allows for
the resolution of the above bottlenecks in the crucial regime of many transmit
antennas. For this regime, where the multiplexing gain can exceed the coding
gain, our new algorithm is the first to achieve the exact one-shot linear
optimal DoF with a subpacketization complexity that scales only linearly with
the number of users, and the first to benefit from a multicasting structure
that allows for exploiting uplink-downlink duality in order to yield optimized
beamformers ultra-fast. In the end, our novel solution provides excellent
performance for networks with finite SNR, finite file sizes, and many users