On the Placement Delivery Array Design for Coded Caching Scheme in D2D Networks

The coded caching scheme is an efficient technique as a solution to reduce the wireless network burden during the peak timesin a Device-to-Device (D2D in short) communications. In a coded caching scheme, each file block should be divided into Fpackets. It is meaningful to design a coded caching scheme with the rate and F as small as possible, especially in the practice forD2D network. In this paper we first characterize coded caching scheme for D2D network by a simple array called D2D placementdelivery array (DPDA in shot). Consequently some coded caching scheme for D2D network can be discussed by means of anappropriate DPDA. Secondly we derive the lower bounds on the rate and F of a DPDA. According these two lower bounds, weshow that the previously known determined scheme proposed by Ji et al., ( IEEE Trans. Inform. Theory, 62(2): 849-869,2016)reaches our lower bound on the rate, but does not meet the lower bound on F for some parameters. Finally for these parameters,we construct three classes of DPDAs which meet our two lower bounds. Based on these DPDAs, three classes of coded cachingscheme with low rate and lower F are obtained for D2D network.