IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 55, NO. 3, MAY2006 865 A Cross-Layer Multihop Data Delivery Protocol With Fairness Guarantees for Vehicular Networks Gökhan Korkmaz, Student Member, IEEE, Eylem Ekici, Member, IEEE, and Füsun Özgüner, Member, IEEE Abstract—In this paper, a new cross-layer communication pro- tocol for vehicular Internet access along highways is introduced. The objective of the new Controlled Vehicular Internet Access (CVIA) protocol is to increase the end-to-end throughput while achieving fairness in bandwidth usage between road segments. To achieve this goal, the CVIA protocol eliminates contention in relaying packets over long distances. CVIA creates single-hop vehicle clusters and mitigates the hidden node problem by dividing the road into segments and controlling the active time of each segment. Using an analytical throughput estimation model, the protocol parameters are fine-tuned to provide fairness among road segments. Simulation results confirm that the proposed CVIA pro- tocol provides higher throughput and better fairness in multihop data delivery in vehicular networks when compared with purely IEEE 802.11-based protocols. Index Terms—Computer networks, internet, protocols, road vehicle, wireless LAN. I. I NTRODUCTION A S MOBILE wireless devices became the essential parts of our lives, “anytime, anywhere” connectivity gains a growing importance. Inasmuch as an average user spends hours in the traffic everyday, Internet access from vehicles is in great demand. Proposals and prototypes for vehicles supporting Internet access exist in the literature, such as The Network Vehicle [1] and Web on Wheels [2]. In addition to these smart vehicles, the feasibility of vehicle to Internet connection is also investigated in [3]. The FleetNet project [4] investigates the integration of the Internet and vehicular networks. This integration requires mo- bility support, efficient communication, discovery of services, and support of legacy applications. The proposed architecture contains stationary Internet gateways (IGWs) along the road with two interfaces connecting vehicular networks to the In- ternet [5]. Vehicles communicate with distant IGWs via multi- hopping. This architecture is useful not only to connect vehicles to other networks but also to connect isolated vehicle groups to each other [6]. FleetNet uses an IPv6-based addressing solution to address the vehicles. Two approaches to solve the service discovery problem have been proposed in [7] and [8]. However, Manuscript received August 1, 2005; revised November 23, 2005 and December 2, 2005. This work was supported by OKI Electric Ind. Co. Ltd. The review of this paper was coordinated by Prof. Y. Fang. The authors are with the Department of Electrical and Computer En- gineering, The Ohio State University, Columbus, OH 43210 USA (e-mail: korkmazg@ece.osu.edu; ekici@ece.osu.edu; ozguner@ece.osu.edu). Digital Object Identifier 10.1109/TVT.2006.873838 in these proposals, there are no specific solutions to move data over multiple hops. End-to-end throughput is one of the key parameters for vehicular Internet access systems employing an infrastructure along the road. Although Dedicated Short Range Communica- tion (DSRC) systems use the IEEE 802.11 protocol as their medium access control (MAC) layer, multihopping with the IEEE 802.11 protocol suffers from several problems, leading to low throughput and starvation of packets originating from vehicles far away from gateways. In this paper, we introduce a new cross-layer protocol for vehicular Internet access along highways called Controlled Vehicular Internet Access (CVIA) protocol. The proposed protocol divides the time into slots and the service area of the gateway into segments. The CVIA protocol controls time slots the vehicles are allowed to transmit in, how the vehicles access the channel, and to which vehicles the packets are sent. The CVIA protocol functions span MAC and network layers. The objective of the new protocol is to increase the end-to-end throughput while achieving fairness in bandwidth usage between road segments. To achieve this objective, the CVIA protocol eliminates contention in relaying packets over long distances by forming single-hop clusters on-the-fly. Once vehicles send their packets using contention-based methods in single-hop clusters, packets are relayed to their destinations without contention. II. CVIA PROTOCOL A. Preliminaries In this paper, we consider a vehicular network that accesses the Internet through fixed IGWs along the road. Although the wireless interface of these gateways has a limited wireless coverage, their range can be increased with multihop communi- cation. As a result, a gateway can communicate with a vehicle at a distance several times longer than its physical transmission range. The range of a gateway where it provides Internet access service is called the virtual transmission radius (VTR). We assume that gateways send periodic service announcements to indicate the availability of the service in their service area. We also assume that the uplink and the downlink packets are transmitted over two frequency-separated channels. Vehicles are assumed to be equipped with Global Posi- tioning System (GPS) devices used for time synchronization and obtaining vehicle positions. Vehicle positions obtained via GPS are exchanged among one-hop neighbors. When a vehicle enters the VTR of a gateway, it registers itself with the gateway. 0018-9545/$20.00 © 2006 IEEE