Joint relay selection and resource allocation for energy-efficient D2D cooperative communications using matching theory

Device-to-device (D2D) cooperative relay can improve network coverage and throughput by assisting users with inferior channel conditions to implement multi-hop transmissions. Due to the limited battery capacity of handheld equipment, energy efficiency is an important issue to be optimized. Considering the two-hop D2D relay communication scenario, this paper focuses on how to maximize the energy efficiency while guaranteeing the quality of service (QoS) requirements of both cellular and D2D links by jointly optimizing relay selection, spectrum allocation and power control. Since the four-dimensional matching involved in the joint optimization problem is NP-hard, a pricing-based two-stage matching algorithm is proposed to reduce dimensionality and provide a tractable solution. In the first stage, the spectrum resources reused by relay-to-receiver links are determined by a two-dimensional matching. Then, a three-dimensional matching is conducted to match users, relays and the spectrum resources reused by transmitter-to-relay links. In the process of preference establishment of the second stage, the optimal transmit power is solved to guarantee that the D2D link has the maximized energy efficiency. Simulation results show that the proposed algorithm not only has a good performance on energy efficiency, but also enhances the average number of served users compared to the case without any relay

Resource Allocation and Relay Selection for Collaborative Communications

Abstract-We investigate the relay selection problem in a network where users are able to collaborate with each other; decode and forward the messages of each other along with their own messages to the destination. We study the performance obtained from collaboration in terms of 1) increasing the achievable rate, 2) saving the transmit energy, and 3) reducing the resource (timebandwidth) requirement. To ensure fairness, we assume that the transmit energy to the rate ratio is fixed for all users. We allocate resource optimally for the proposed collaborative protocol (CP) and compare the result with the non-collaborative protocol (NCP) where users transmits their messages directly to the destination. The collaboration gain allows us 1) to decide whether to collaborate or not and 2) to select one relay among the possible relay users. We show that a considerable gain can be obtained if the direct source-destination channel gain is significantly smaller than those of alternative links. We demonstrate that a rate and energy improvement of up to 1 + η k k+1 η can be obtained, where η is the environment path loss exponent and k is the ratio of the rates of involved users. We also show that the collaboration is only beneficial for the middle range rate ratio