978-1-4799-0059-6/13/$31.00 ©2014 IEEE. ZLS: A Next-door Lightweight QoS Aware Location Service Technique for VANET on Highways Maaz Rehan 1,3 , Halabi Hasbullah 1 , Omer Chughtai 2,3 , Waqas Rehan 4 1 Computer Information Science Department, Universiti Teknologi PETRONAS, Malaysia 2 Electrical Electronics Engineering Department, Universiti Teknologi PETRONAS, Malaysia 3 COMSATS Institute of Information Technology, Pakistan 4 Institute of Telematics, University of Lübeck, Germany maaz_g01945@utp.edu.my , halabi@petronas.com.my , omer_g01947@utp.edu.my , rehan@itm.uni-luebeck.de Abstract—In VANET, a Location service technique comprises of location update and location request. In location update, a destination vehicle advertises its services and location to a set of vehicles called location servers. In location request, a source vehicle queries location servers in its broadcast range about the location and services of destinations. During location update, separate control messages are exchanged to periodically update location servers which create delay and congestion in the network. Similarly, after location request, pre-loaded digital maps at source vehicle are used to find the shortest path towards destination which does not give vehicle density on road at that moment in time. Other than digital maps, Dijkstra or Bellmen ford algorithms at source or intermediate nodes are also used to find shortest path, which is a computationally time consuming activity leading to an extra delay during path finding and before packet transmission. We therefore propose QoS and traffic density aware location service technique called ZoomOut Location Service (ZLS). We have implemented ZLS in NS2.33. The simulation results for highway traffic show that ZLS updates its location servers in a uni-cast fashion such that the location servers have up-to-date information of advertised services and destination position. Similarly, a source can reach destination in the quickest possible way by sending uni-cast messages without using digital map or shortest path finding algorithms.Keywords—location service; next-door location server; next-door destination discovery; ZoomOut; VANET; QoS aware. I. INTRODUCTION Vehicular ad hoc network (VANET) is a highly mobile network with random vehicular speeds where the position of vehicles is aligned to roads. There are two components of VANET: the static Road Side Unit (RSU) and the On Board Unit (OBU) installed inside vehicles. Both OBUs and RSUs operate at general purpose 5.9GHz radio frequency band using Dedicated Short Range Communications (DSRC) with a data rate of up to 27mbps and a communication range of around 1km [1]. DSRC supports vehicles with a speed of 120mph [2]. In geographic or position based VANET, the speed and position of each vehicle is periodically broadcast via 1-hop HELLO broadcast so that, vehicles within the broadcast range can update the changing position of each sender [3, 4]. A vehicle, after receiving 1-hop HELLO broadcast packet, adds an entry in its neighbour table for the sender. As long as HELLO is kept receiving, the entry in the neighbour table is refreshed with new position, speed and any other information sent in the broadcast packet. For a specific period of time, if HELLO broadcast is not received to the vehicle maintaining the neighbour table, the entry is purged from the table. Normally vehicular speeds on highways range from 80km to 120km. When a new vehicle joins VANET network on a highway, it does not know about the set of services that are being offered by the VANET fleet at that point in time. There may be some services being offered by the highway authority like Internet and location based services. Providing these services by the authority is possible via the fixed Road Side Units (RSUs). The installation of an RSU is worth USD 3000$/RSU [5] and provides a coverage of 1km due to DSRC. This can be very costly on a very long highway as it requires the installation of many RSUs. Therefore, services like Internet, games, movies, books and inter alia can easily be offered by the vehicles on highway. Our work therefore, focuses on the vehicle to vehicle (V2V) communication. Normally, when a vehicle wishes to use the services offered by a destination vehicle, it needs to first fetch the up- to-date coordinates of the destination vehicle and then it computes the shortest path towards destination. The same is done at the intermediate vehicles as well. Hence, providing an up-to-date position of destination along with the services is a task that demands careful design. The location service technique in VANET is therefore a two-step process: location update and location request, Fig. 1. When a destination vehicle advertises its location along with the set of services to some specific vehicles called Locations Servers (LS), the process itself is called Location Update (LU). This process is iterative which means one location server relays the message to vehicles nearby and as a result some other vehicle becomes location server and this process goes on till the end of VANET fleet. Now, when a source vehicle queries its nearest location server(s) about the available services and the position of their advertiser (the destination), it is called Location Request (LR). Both LU and LR are delicate tasks so they need careful design. Since VANET is a shared wireless network, so control and data packets are transmitted in broadcast fashion. At one time only one vehicle is sending the control or data packet and all others are receiving. As a result of frequent control messages, network throughput will decrease and over network delay will also increase. Similarly, since vehicles on highways are moving very fast, therefore, an improper next or previous hop