Social-Aware Peer Discovery for D2D Communications Underlaying Cellular Networks With emerging demands for local area services, device-to-device (D2D) communication is conceived as a vital component for the next-generation cellular networks to improve spectral reuse, bring hop gains, and enhance system capacity. Ripening these benefits depends on efficiently solving several main technical problems, among which peer discovery aiming to probe the D2D communication contacts is critically challenging. In this paper, we propose a social-aware peer discovery scheme for D2D communications, which exploits social network characteristics for assisting the ad hoc peerdiscovery. In this scheme, the D2D users in the network are first divided into groups according to their social metrics of community and centralities, and then optimal beacons probing rate with constant intervals is decided for each group of users. Through extensive simulations with real human mobility traces, we demonstrate the effectiveness of our proposed scheme, which significantly increases thepeer discovery ratio and enhances the data transmission performance compared with the existing schemes.