# User-Information-Aware D2D Multicast File Distribution Mechanism
### System Model  
In the existing D2D multicast communication system, the time domain is not fully considered in distribution for user service requests. Actually, most of the users access the video at any time during the day. For the high popularity videos, the same video in the same area more likely be transmitted multiple times at different times by using existing D2D multicast communication technology. Therefore, there are a large number of redundant transmissions of the traditional D2D multicast content distribution system, the spectrum efficiency and energy efficiency of the system still can be improved.  
The users requesting video at the current moment are called service requesters, and the potential service requesters are defined as the users presenting the same video demands with service requesters but no initiate service requests at this moment. The distribution of users within the cell is shown as Figure 1, where the blue dots and red dots represent the requesters and the potential requesters, respectively. The cell is divided into the grid based on the grid-based clustering deduced in [23]. In the same grid, the users needing the video distribution service at this moment form the D2D multicast cluster, so the distance between every two users should be less than the D2D communication radius.  
Figure 1 also shows the distribution of users within a grid and the D2D multicast scene in the grid. In this grid, there are \(n\) service requesters and \(m\) potential service requesters, denoted by the set \(U_{R}=\{u_{r1},u_{r2},\ldots,u_{m}\}\) and the set \(U_{P}=\left\{u_{p1},u_{p2},\ldots,u_{pm}\right\}\), respectively. The users set in the grid is constituted by requesters and potential requesters, denoted by the set \(U=U_{R}\cup U_{P}\). In the traditional D2D multicast system, the members of the D2D multicast cluster are formed by service requesters, and an advisable user is selected as the cluster head from the service requesting users. However, the traditional mechanism fails to give full play to the advantages of D2D multicast communication, and the performance of the system can be further promoted.  
If the video is pushed to the potential service requesters when it is distributed to the service requesters, the throughput of the system will be significantly improved due to increased number of D2D multicast receivers, thereby the energy efficiency and spectrum efficiency will be improved  
Figure 1: Grid-based clustering method and the D2D multicast scene in the grid.  
greatly. Besides, the QoE of potential service requesters will be also improved by the suitable video push service. In fact, due to the differences of user's interest, the residual energy of user's device, and the status of user's device, the willingness of each potential requesters to accept the pushed video is very different. What's more, the channel quality and the social relationship strength among users also affect the transmission performance of the system. Therefore, the selection of both potential service requesters and the cluster head is the key to improve the transmission performance of D2D multicast file distribution mechanism. The purpose of this paper is to accurately predict the service requests of potential service requesters and formulate appropriate clustering and cluster head selection schemes to achieve system throughput, energy efficiency and spectrum efficiency improvement.