4,705 research outputs found

    Multi-Antenna Coded Caching for Multi-Access Networks with Cyclic Wrap-Around

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    This work explores a multiple transmit antenna setting in a multi-access coded caching (MACC) network where each user accesses more than one cache. A MACC network has KK users and KK caches, and each user has access to r<Kr < K consecutive caches in a cyclic wrap-around manner. There are LL antennas at the server, and each cache has a normalized size of M/N≀1M/N \leq 1. The cyclic wrap-around MACC network with a single antenna at the server has been a well-investigated topic, and several coded caching schemes and improved lower bounds on the performance are known for the same. However, this MACC network has not yet been studied under multi-antenna settings in the coded caching literature. We study the multi-antenna MACC problem and propose a solution for the same by constructing a pair of arrays called caching and delivery arrays. We present three constructions of caching and delivery arrays for different scenarios and obtain corresponding multi-antenna MACC schemes for the same. Two schemes resulting from the above constructions achieve optimal performance under uncoded placement and one-shot delivery. The optimality is shown by matching the performance of the multi-antenna MACC scheme to that of an optimal multi-antenna scheme for a dedicated cache network having an identical number of users, and each user has a normalized cache size of rM/NrM/N. Further, as a special case, one of the proposed schemes subsumes an existing optimal MACC scheme for the single-antenna setting.Comment: 11 pages (double column), 3 Figure

    Combinatorial Multi-Access Coded Caching: Improved Rate-Memory Trade-off with Coded Placement

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    This work considers the combinatorial multi-access coded caching problem introduced in the recent work by Muralidhar \textit{et al.} [P. N. Muralidhar, D. Katyal, and B. S. Rajan, ``Maddah-Ali-Niesen scheme for multi-access coded caching,'' in \textit{IEEE Inf. Theory Workshop (ITW)}, 2021] The problem setting consists of a central server having a library of NN files and CC caches each of capacity MM. Each user in the system can access a unique set of r<Cr<C caches, and there exist users corresponding to every distinct set of rr caches. Therefore, the number of users in the system is (Cr)\binom{C}{r}. For the aforementioned combinatorial multi-access setting, we propose a coded caching scheme with an MDS code-based coded placement. This novel placement technique helps to achieve a better rate in the delivery phase compared to the optimal scheme under uncoded placement, when M>N/CM> N/C. For a lower memory regime, we present another scheme with coded placement, which outperforms the optimal scheme under uncoded placement if the number of files is no more than the number of users. Further, we derive an information-theoretic lower bound on the optimal rate-memory trade-off of the combinatorial multi-access coded caching scheme. Finally, using the derived lower bound, we show that the first scheme is optimal in the higher memory regime, and the second scheme is optimal if N≀(Cr)N\leq \binom{C}{r}.Comment: 15 pages and 5 figure
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