# User-Information-Aware D2D Multicast File Distribution Mechanism
## 2 Related Works  
In the traditional cellular communication system, an enormous number of users with the same video demands separately obtain the required content from the base station using their respective allocated bandwidth, so the base station needs to send duplicate content over different links as the multiple users initiate the same service request. Obviously, the base station performs a vast number of redundant transmissions, resulting in low video transmission efficiency, and the amount of redundancy is proportional to the popularity of the transmitted content. D2D multicast content distribution as a potential technology to reduce redundant transmissions and improve the resource utilization, has received extensive attention and research in recent years. As mentioned in Section 1, the improvement on performance in D2D multicast communication is influenced by selecting suitable clustering, cluster head selection methods and data distribution mechanisms. In the D2D multicast communication, the cluster head node is responsible for relaying data, so the transmission performance of the content distribution system is mainly determined by the capability of the cluster head node. And the capability of cluster head includes two aspects, physical and social. In order for all receivers to receive all data correctly, the transmission rate of D2D multicast communication is determined by the receiver with the worst channel quality, i.e., the multicast communication performance is subject to the worst SINR of the receivers. In [15], with consideration of the difference of link quality, a SINR constraint-based intra-cloud D2D multicast retransmission algorithm is proposed. The link cost model is built in the proposed algorithm, limiting the number of multicast retransmissions, and selecting the appropriate cluster head by traversing the link quality matrix. The proposed algorithm reduces the link consumption, and the spectrum efficiency can be improved. The efficient Tx user selection algorithm is proposed in [16], in which the number of stable links for each node in the cluster is calculated by the link quality information about nodes, and then the user with the largest number of stable links is selected as the cluster head. The throughput of D2D multicast communication have improved by maximizing the number of members in the cluster. This algorithm reduces interference in D2D multicast transmissions, increasing the throughput of more than 5% of edge users by at least 50%. The above studies only consider the physical information. In fact, numerous studies have confirmed that the social relationship between users has a significant impact on the performance of wireless communications [17; 18]. Cluster head nodes forward data for other users in the system, so cluster head nodes are frequently referred to as relay nodes. The relay nodes will cause a large amount of storage, calculation, and energy burden as providing services for other users. In addition, different users have various file or video demands, so it is very likely that the relay nodes will cooperate negatively. The stability of D2D links can be affected by the users' selfishness, mobility and degree of intimacy between users. Insufficient intensity of social relationships between users can even lead to frequent breaks in D2D links, severely reducing the ability in D2D communication and the user's experience quality. Therefore, it is necessary to integrate social domain information and social network research methods into the research of D2D multicast communication. The social-aware file-sharing mechanism is proposed in [19], users with the same documentation requirements are divided into the same D2D multicast cluster, and then the cluster is selected by the social relationships and trust degrees of users. In the proposed mechanism, the influence of users' social relationships to wireless communication is fully considered, user's experience quality has improved greatly, and the transmission time delay and the burden of base station have reduced.