Social-Aware Based Secure Relay Selection in Relay-Assisted D2D Communications

Relay-assisted transmission could effectively enhance the performance of Device-to-Device(D2D)communications when D2D user equipments(UEs)are too far away from each other or the quality of D2D channel is not good enough for direct communications.Meanwhile,security is one of the major concerns for proximity services.The secure relay selection problem for D2D communications underlaying cellular network is studied in this paper.Firstly,we define a relay selection area and derive the closed-form of outage probability in D2D links using a Poisson Point Process(PPP)method.Next,in the defined relay selection area,we propose a secure relay selection scheme for the relay-assisted D2D communication system by exploiting the social relation as a security factor.Simulation results show that the scheme based on social relation can greatly improve the security performance of relay-assisted D2D communications.

Social-aware device-to-device communications underlaying cellular networks

This article put forward a resource allocation scheme aimming at maximizing system throughtput for devide-to- device （D2D） communications underlying cellular network. Firstly, user closeness is defined and calculated through social information including friendship, interest similarity and communication strength to represent the willingness of user to share the spectrum resource with others. Then a social-aware resource allocation problem is formulated to maximize the system throughput while guaranteeing the quality of service （QoS） requirements of both D2D pairs and cellular users （CUs）. Then the complicate problem is decomposed into three subproblems. Firstly the admissible D2D pairs are determined and then the power of both CUs and D2D pairs is efficiently allocated. Finally CUs and D2D pairs are matched to reuse the spectrum resource in consideration of both user closeness and physical conditions. Simulation results certify the effectiveness of the proposed scheme which significantly enhances the system throughput compared with the existing algorithms.

Performance bounds for Nash equilibria in submodular utility systems with user groups

It is shown that for a valid non-cooperative utility system,if the social utility function is submodular,then any Nash equilibrium achieves at least 1/2 of the optimal social utility,subject to a function-dependent additive term.Moreover,if the social utility function is nondecreasing and submodular,then any Nash equilibrium achieves at least 1/(1+c)of the optimal social utility,where c is the curvature of the social utility function.In this paper,we consider variations of the utility system considered by Vetta,in which users are grouped together.Our aim is to establish how grouping and cooperation among users affect performance bounds.We consider two types of grouping.The first type is from a previous paper,where each user belongs to a group of users having social ties with it.For this type of utility system,each user’s strategy maximises its social group utility function,giving rise to the notion of social-aware Nash equilibrium.We prove that this social utility system yields to the bounding results of Vetta for non-cooperative system,thus establishing provable performance guarantees for the social-aware Nash equilibria.For the second type of grouping we consider,the set of users is partitioned into l disjoint groups,where the users within a group cooperate to maximise their group utility function,giving rise to the notion of group Nash equilibrium.In this case,each group can be viewed as a new user with vector-valued actions,and a 1/2 bound for the performance of group Nash equilibria follows from the result of Vetta.But as we show tighter bounds involving curvature can be established.By defining the group curvature cki associated with group i with ki users,we show that if the social utility function is nondecreasing and submodular,then any group Nash equilibrium achieves at least 1/(1+max1≤i≤l cki)of the optimal social utility,which is tighter than that for the case without grouping.As a special case,if each user has the same action space,then we have that any group Nash equilibrium achieves at least 1/(1+ck∗)of the optimal social utility,where k∗is the least number of users among the l groups.Finally,we present an example of a utility system for database-assisted spectrum access to illustrate our results.