# Intersection-Based Link-Adaptive Beaconless Forwarding in Urban Vehicular Ad-Hoc Networks
## 1 Introduction  
Remote monitoring of vehicles moving in urban traffic environment significantly contribute to various applications in the field of telemedicine, road safety and mobile surveillance. Remote monitoring applications for road traffic environment generally involve data transfer from a moving vehicle to a static remote infrastructure. The data to be transferred include still images, signals from various physiological sensors, audio and video. Vehicular ad-hoc network (VANET) aims at achieving intelligent transportation system (ITS) and offers an ideal platform to enable remote monitoring applications in road traffic environment. In such network, all vehicles are equipped with wireless sensors and onboard units to allow wireless communication between the vehicles and the infrastructure [1]. Communications in VANET can be broadly classified into four types: in-vehicle, vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I) and more recently vehicle-to-broadband cloud (V2B) communication [2]. Wireless access in vehicular environments (WAVE) [3] architecture comprising the IEEE 802.11p and IEEE 1609.x communication standards is used in VANETs. IEEE 802.11p is an approved amendment of IEEE 802.11 [4] focusing mainly on the physical andmedium access control (MAC) sublayers whereas IEEE 1609.x comprises various communication standards that operate in the middle layers of the protocol stack to support safety applications. Wireless communication required to facilitate remote monitoring applications in urban traffic environment faces significant challenges. Specifically, it has to cope with general vehicular environment constraints such as mobility and density variations [5; 6; 7]. In addition, urban traffic environment has its own constraints such as drastic speed decays, presence of road intersections and traffic signals [8; 9]. Apart from this, wireless communication also needs to support different data rate requirements for various data types such as images, physiological signals, audio and video that need to be transferred in remote monitoring applications. The above mentioned constraints give rise to significant hurdles while developing routing solutions in urban VANETs. Routing protocols that use geographic information and make routing decisions on the fly are well suited for VANET environment. One of such routing techniques is the receiver-based data forwarding, where the intermediate vehicles upon data reception, decide whether or not to forward the data packet. The decision is usually based on certain characteristics of intermediate vehicle, previous relay vehicle and destination, with the most commonly used characteristic being geographic information. Receiver-based data forwarding techniques mainly comprise two key features: forwarding zone and waiting time criteria. Forwarding zone criterion limits the number of vehicles eligible for data forwarding based on their presence in the forwarding zone. Eligible vehicles then contend for the forwarding rights by setting their timers based on a certain waiting time criterion. A vehicle with the shortest waiting time wins the contention and forwards the data packet, while other contending vehicles cancel their timer and discard the data packet upon reception of duplicate data packet. Although receiver-based schemes are well suited for dynamic environments, they result in significant end-to-end (ETE) delay [5]. This is due to their waiting time criterion, where the relay vehicles are required to wait for certain time for each data packet before forwarding it further. The work in [10; 11] minimize this issue by allowing a relay vehicle that wins the contention to directly forward any incoming data packet without any waiting time for certain duration. This duration is usually based on the position and speed information of the vehicles. This helps in reducing the ETE delay, as relay vehicles do not have to perform relay selection for every incoming data packet.