The Advantages of Grouping Method for Repeated Requests in Coded Caching Recently, coded caching has been widely studied due to its ability of significantly reducing the amount of transmissions (i.e., rate) during peaktraffic time. While to achieve this rate, each file is divided into a number of packets, which is even exponentially increasing with users. In practice, we prefer to design a coded caching scheme to achieve smaller rate with lower packet number. In order to reduce the packet number, the well known grouping method has been proposed by Shanmugam et al. in 1 and generated by Cheng et al. in 2. However, the rate of the scheme obtained by grouping method is very large since there is no multicasting gain generated between different user groups. Thus, many other schemes have been investigated from other perspective. In this paper, we will show that when some files are requested more than once, the scheme obtained by grouping method has a smaller rate and smaller packet numbers than that of some other improved schemes.

On the Fundamental Limit of Coded Caching Systems with a Single Demand Type Caching is a technique to reduce the communication load in peak hours by prefetching contents during offpeak hours. Recently MaddahAli and Niesen introduced an information theoretic framework for coded caching, and showed that significant improvement can be obtained compared to uncoded caching. Considerable efforts have been devoted to identify the precise information theoretic fundamental limit of such systems, however the difficulty of this task has also become clear. One of the reasons for this difficulty is that the original coded caching setting allows multiple demand types during delivery, which in fact introduces tension in the coding strategy to accommodate all of them. In this paper, we seek to develop a better understanding of the fundamental limit of coded caching by investigating single demand type systems. We first show that in the canonical threeuser threefile systems, such single demand type systems already provide important insights. Motivated by these findings, we focus on systems where the number of users and the number of files are the same, and the demand type is when all files are being requested. A novel coding scheme is proposed, which provides several optimal memorytransmission operating points. Outer bounds for this class of systems are also considered, and their relation with existing bounds is discussed.