### Related Work
They used adaptive neuro-fuzzy inference system architecture for relay selection and a particle swarm optimization algorithm is used for power allocation with the aim to maximize network energy efficiency. However, social information is not utilized to select a relay. [PERSON] et al. [13] proposed social-trust and power-efficient relay selection (STRS) scheme for D2D communications underlaying distributed shared network, which takes into account physical and social information of users. In their scheme, initially candidate relay users are selected using location and social trust information. Then among the candidate relay devices, a device having lowest power consumption is selected as a relay. Unlike References [1; 18; 13], we aim to maximize throughput by selecting a relay transmitting at a high power and minimize the energy consumption by limiting the number of probes for the selection of a relay. [PERSON] et al. [19] proposed social-aware energy efficient relay selection (SERS) scheme for cooperative D2D communications. Social trust, encounter history and node energy consumption are utilized for the selection of a relay. They formulated power control game that maximizes data rate while minimizing energy consumption and interference. The energy consumption and network interference is minimized by using social distance as the penalty coefficient. Similar to Reference [19], we measure the average throughput that can be achieved by our proposed schemes. [PERSON] et al. [20] developed an algorithm to select relays for content dissemination in multi-hop D2D communications called PSRS which minimizes power consumption. They used frequency/duration of interaction for sharing/downloading of content and social reciprocity to quantify social relationship value. [PERSON] et al. [21] proposed relay selection scheme for multi-hop D2D communication in which two devices are selected as candidate relays. The relay is selected by the BS and instantaneous SINR and neighbour discovery is done by D2D pair. When one of the devices is unable to relay, the second device is selected as a relay. The relays are chosen among the available devices which satisfy SINR threshold, battery power threshold, reliability and buffer requirements. Their scheme increases success probability and network throughput of D2D communications. [PERSON] et al. [22] proposed multicasting in cooperative D2D communications using social-aware relay selection. Both the propagation link conditions and social-trust level are used while selecting a relay to minimize end-to-end content delivery delay. While References [20; 21; 22] present schemes for D2D, none of them probes to know the physical condition of the path from the relay to the destination and do not consider the time/cost involved for probing during the selection of a relay. The following papers are closely related to our work. [PERSON] et al. [8] developed a relay selection technique for cooperative D2D communications that leverages social trust among mobile users while selecting a relay. Social and physical distances are used for analysis of cooperative D2D communications. Their assumption is that a mobile device having high social trust for a source device relays data for the source at a high transmission power. When the mobile users do not have social relationship, relaying is done using social reciprocity. Their study shows that a relay selection based on social trust and/or social reciprocity can significantly improve average throughput of D2D communications. The improvement in the system increases with the increment in number of users. Their proposed mechanism can provide up to 122% performance gain over the case without D2D cooperation. [PERSON] et al. [5] proposed an optimal stopping relay selection scheme to enhance throughput of D2D communications in a distributed network. The average contact duration and common friends are used to represent social relationship weight coefficient. The candidate relay nodes are filtered using social threshold.