IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY (ACCEPTED) 1 An Energy-Efficient Uncoordinated Cooperative Scheme with Uncertain Relay Distribution Intensity

Abstract-Due to signal fading and user mobility in wireless networks, quality-of-service (QoS) provisioning for wireless services becomes more challenging. As a promising technique, cooperative communications make use of the broadcasting nature of wireless medium to facilitate data transmission, and thereby reduce energy consumption. However, in many studies on wireless cooperative diversity, it is often assumed that the number of relays or the relay distribution intensity is known a priori. In this paper, we relax such assumption and propose an algorithm to estimate the relay intensity for a backoff-based cooperative scheme, where the relays are distributed as a homogeneous Poisson point process (PPP). It is proved that the algorithm can converge to an optimal solution with the minimum estimation error. Based on the estimated relay intensity, we further investigate a distributed energy saving strategy, which selectively turns off some relays to reduce energy consumption while maintaining the required transmission success probability. The performance of the proposed cooperative scheme is analytically evaluated with respect to the collision probability. The numerical and simulation results demonstrate the high accuracy and efficiency of the intensity estimation algorithm and also validate the theoretical analysis. Moreover, the proposed cooperative scheme exhibits significant energy saving and satisfactory transmission performance, which offers a good match to accommodate green communications in wireless networks. Index Terms-Cooperative wireless networks, distributed relaying, intensity estimation, energy efficiency

Dynamic service selection and bandwidth allocation in IEEE 802.16m mobile relay networks

Cooperative relay network will be supported in IEEE 802.16m to improve the coverage and performance of mobile broadband wireless access service. In this paper, we jointly consider the problem of dynamic service selection and bandwidth allocation in IEEE 802.16m mobile relay networks. Specifically, the advanced mobile stations (AMSs) perform the selection of advanced base station (ABS) and transmission mode (i.e., direct transmission or relay-cooperation transmission) for a better service quality. The ABSs allocate the bandwidth for different transmission modes to maintain the desired queue level at base stations and user distribution for satisfying performance requirements. This problem is challenging when the strategies of both ABSs and AMSs influence each other and the decisions are made dynamically. To address this problem, a two-level dynamic game framework based on an evolutionary game and a differential game is developed. Since the mobile stations can adapt their strategies according to the received service quality, the dynamic service selection is modeled as an evolutionary game at the lower level. At the upper level, a differential game is formulated for a dynamic bandwidth allocation of base stations and a closed-loop Nash equilibrium is obtained as the solution. Viewing the fluctuation of traffic flow rate as disturbance, the robust bandwidth allocation strategy design is performed. Both stochastic optimal control and H_∞ optimal control approaches are adopted for average performance and worst-case performance design, respectively