Abstract-Vehicle-to-roadside (V2R) communications enable vehicular networks to support a wide range of applications for enhancing the efficiency of road transportation. While existing work focused on non-cooperative techniques for V2R communications between vehicles and roadside units (RSUs), this paper investigates novel cooperative strategies among the RSUs in a vehicular network. We propose a scheme whereby, through cooperation, the RSUs in a vehicular network can coordinate the classes of data being transmitted through V2R communications links to the vehicles. This scheme improves the diversity of the information circulating in the network while exploiting the underlying content-sharing vehicle-to-vehicle communication network. We model the problem as a coalition formation game with transferable utility and we propose an algorithm for forming coalitions among the RSUs. For coalition formation, each RSU can take an individual decision to join or leave a coalition, depending on its utility which accounts for the generated revenues and the costs for coalition coordination. We show that the RSUs can self-organize into a Nash-stable partition and adapt this partition to environmental changes. Simulation results show that, depending on different scenarios, coalition formation presents a performance improvement, in terms of the average payoff per RSU, ranging between 20.5% and 33.2%, relative to the noncooperative case. Keywords: Vehicle-to-roadside communications, coalitional game theory, coalition formation game, vehicular networks. I. INTRODUCTION Recent advances in the integration of communication and sensor technologies have triggered the deployment of numerous attractive applications for road transportation systems. In this regard, networks of connected vehicles constitute the main building block of intelligent transportation systems (ITS) and are the basis for a diversity of applications that can enhance the safety and comfort of road transportation (e.g., through providing road traffic condition, remote vehicle monitoring, accident prevention, payment services, security applications etc.) [1] . In order to support different ITS applications, both vehicle-to-roadside (V2R) communications and vehicleto-vehicle (V2V) communications need to be supported in vehicular networks. On one hand, V2R communications allow the vehicles to connect, through their on-board units (OBUs), to the roadside units (RSUs) belonging to one or several service providers, in order to download (or upload) various types of data related to a variety of applications. On the other hand, V2V communications enable a group of vehicles to communicate and exchange information for different purposes. Existing work has already explored various aspects of V2R and V2V communications. For instance, in [2], a lowcomplexity scheme for packet scheduling for downlink and uplink transmissions over V2R communication links (between an RSU and multiple OBUs) is proposed. The authors in [3] propose an IEEE 802.16-based protocol for data communication between a cluster of vehicles and an RSU. Further, an experimental testbed for traffic congestion detection and emergency warning using V2R and V2V communication is presented in [4] . In [5] , the authors propose a non-cooperative Bit Torrent-based approach for data distribution between the RSUs and the OBUs of the vehicles as well as a Nash bargaining solution for V2V data exchange. Multiple antenna techniques are proposed in [6] for enhancing the performance of V2R communications. The work in [7] studies a protocol, using time sharing for inter-vehicle message delivery with short and deterministic delay bounds in a V2V ad hoc network. The objective of the work in [7] is to improve the safety of vehicular networks. In addition, the work in [8] proposes an effective protocol, comprising congestion control policies, mechanisms for service differentiation, and methods for emergency warning dissemination using V2V communications. Further, the use of V2V communications and cooperation among sensor-equipped vehicles is studied in [9] for proactive urban data monitoring. Other aspects of V2R and V2V communication such as routing, security, channel modeling, and authentication are studied in [10]-[16]. Most of the existing work in vehicular networks have focused on communication technologies for V2R or V2V communication, content-sharing through V2V cooperation as well as on non-cooperative data delivery between the RSUs and the OBUs of the vehicles through V2R communications. Nonetheless, one challenging aspect of vehicular networks that remains unexplored is the design of cooperative strategies among the RSUs for improving the diversity of the data circulating in the network as well as for exploiting the data exchange capabilities of the underlying V2V networks. By exploring the possibilities of content-sharing between the vehicles, the RSUs in a vehicular network can cooperate in order to coordinate the classes of data that they will transmit to their served vehicles. For example, instead of non-cooperartively sending information on the traffic of the same geographical location to their served vehicles, two RSUs can cooperate to send
In REF , a coalitional game was proposed for cooperative data service among the base stations in vehicular networks.
Coalition Formation Games for Distributed Cooperation Among Roadside Units in Vehicular Networks
IEEE Journal on Selected Areas in Communications (JSAC), 2010
Mathematics Computer Science