In this paper, we propose a scheme for the problem of cache-aided multi-user private information retrieval with small caches, in which $K$ users are connected to $S$ non-colluding databases via shared links. Each database contains a set of $N$ files, and each user has a dedicated cache of size equivalent to the size of $M$ files. All the users want to retrieve a file without revealing their demands to the databases. During off-peak hours, all the users will fill their caches, and when required, users will demand their desired files by cooperatively generating query sets for each database. After receiving the transmissions from databases, all the users should get their desired files using transmitted data and their cache contents. This problem has been studied in [X. Zhang, K. Wan, H. Sun, M. Ji and G. Caire, \tqt{Fundamental limits of cache-aided multiuser private information retrieval}, IEEE Trans. Commun., 2021], in which authors proposed a product design scheme. In this paper, we propose a scheme that gives a better rate for a particular value of $M$ than the product design scheme. We consider a slightly different approach for the placement phase. Instead of a database filling the caches of all users directly, a database will broadcast cache content for all users on a shared link, and then the users will decide unitedly which part of the broadcasted content will be stored in the cache of each user. This variation facilitates maintaining the privacy constraint at a reduced rate.

翻译：本文针对小缓存场景下的缓存辅助多用户私有信息检索问题提出了一种方案。在该问题中，$K$个用户通过共享链路连接到$S$个非共谋数据库。每个数据库包含$N$个文件，每个用户拥有容量相当于$M$个文件大小的专用缓存。所有用户需在不向数据库泄露其需求的前提下检索一个文件。在非高峰时段，所有用户填充其缓存；当需要时，用户通过协作生成每个数据库的查询集来请求所需文件。接收数据库传输后，所有用户应能利用传输数据及缓存内容获取所需文件。该问题已在[X. Zhang, K. Wan, H. Sun, M. Ji and G. Caire, \tqt{Fundamental limits of cache-aided multiuser private information retrieval}, IEEE Trans. Commun., 2021]中研究，作者提出了乘积设计方案。本文针对特定$M$值提出了一种优于乘积设计方案的方案。我们在缓存放置阶段采用了略有不同的方法：不再是数据库直接填充所有用户的缓存，而是由数据库通过共享链路广播缓存内容，然后用户联合决定将广播内容的哪些部分存储到每个用户的缓存中。这种变化有助于在更低的速率下维持隐私约束。