# Social-Aware-Based Resource Allocation for NOMA-Enhanced D2D Communications
## 1 Introduction  
Recently, a growing mobile devices and multimedia applications have largely accelerated people's requirement for low-latency and high-rate data transmission and aggravated core network pressure. Device-to-device (D2D) communication enables users to communicate through a direct connection without the base station, which effectively improves spectrum utilization and system throughput. Therefore, D2D communication is considered to be a promising technology for next-generation communication system [1, 2]. In D2D communication, resource allocation has a huge impact on system performance which has caused widespread concern. In Reference [3], the Nash bargaining game was applied to D2D resource allocation in order to improve the throughput of users. In Reference [4], cooperative and noncooperative games were applied to allocate transmit power for D2D users. In Reference [5], a channel allocation mechanism for D2D users based on Kuhn-Munkres (KM) algorithm was proposed, then D2D users' transmit power was optimized in order to reduce interference. In Reference [6], cellular, D2D, and relay users formed a student-project matching model to improve the system throughput. However, the above algorithms only consider one-to-one D2D communication with orthogonal multiple access (OMA). Many-to-one D2D communication has not been considered to further improve the system throughput through nonorthogonal multiple access (NOMA). NOMA enables multiple users to communicate on the same channel. It further improves the spectrum utilization and increases the system throughput. Reference [7] studied resource allocation for D2D communication assisted by NOMA under the scenario of a D2D transmitter and multiple D2D receivers (one-to-many). It optimized D2D user's throughput while ensuring cellular user'squality of service (QoS). Reference [8] modeled the resource allocation under NOMA-based D2D as the Nash bargaining game and used the Karush-Kuhn-Tucker (KKT) condition to solve the power optimization problem. Reference [9] solved the joint channel and power optimization problem of D2D-NOMA system to reduce the system interference through optimizing the total transmit power. Reference [10] proposed a joint resource allocation method, which used KM algorithm and KKT conditions to achieve NOMA-enabled D2D resource allocation. Reference [11] used the differential evolution (DE) algorithm to allocate channels and power for D2D users under NOMA to achieve maximum energy efficiency while ensuring all users' QoS. However, the above solutions have only considered one-to-many scenario, and have not considered D2D communication with multiple D2D transmitters and one D2D receiver (many-to-one). In the practical environment, when a user needs to get some contents, he can request contents from multiple users around him to reduce the backhaul burden. At this time, many-to-one D2D communication could be implemented. However, one-to-many D2D communication is commonly studied in current papers and many-to-one D2D communication has not been studied in any paper as we know. This paper considers the cellular uplink network in which independent channels are allocated to different cellular users. D2D users are classified into D2D content requesters and D2D content providers. They form D2D clusters to communicate with NOMA by reusing cellular users' uplink channels. In each D2D cluster, multiple D2D content providers send contents to a D2D content requester at the same time. We propose a joint optimization method which combines channel and power optimization while ensuring all the users' QoS on each channel. The main contributions of this paper can be summarized as follows:  
* Social relationships among D2D users are considered. One D2D content requester form a D2D cluster with multiple D2D content providers according to social relationship and other factors. NOMA is used to realize many-to-one D2D communication.