An enhanced vertical handover decision algorithm designed for vehicular networks Johann M´arquez-Barja, Carlos T. Calafate, Juan-Carlos Cano and Pietro Manzoni 1 Abstract — Nowadays automotive industry is taking advantage of the latest developments offering On-Board Units, which are powered by advanced processors, GPS de- vices, sensors, and multiple wireless access technolo- gies such as Wi-Fi, WiMAX and UMTS. Users within vehicular networks will be able to access content from the Internet at high speeds while moving from one place to another, switching among multiple access points with heterogeneous coverage areas, as well as with different Quality of Service (QoS) levels of- fered. To maintain data connections alive in such dy- namic conditions, Vertical Handover techniques are required. In this paper we present a Vertical Han- dover Decision Algorithm designed for dynamic envi- ronments. The decision making process is optimized by combining networking information, obtained by the services of the IEEE 802.21 standard, with ge- olocation, map information, surround context infor- mation and route calculation, thereby improving the handovers’ performance. Keywords — Vertical handover, IEEE 802.21, Wi-Fi, WiMAX, UMTS, ns-2, GPS, vehicular networks. I. Introduction Due to the wide deployment of wireless broadband systems, nowadays vehicles are being improved to use telecommunications not only for sending safety- related messages, but also for infotainment services. Therefore, the QoS must be guaranteed in order to fulfill the application requirements. Different solu- tions in the Vehicular Networks (VNs) area have been proposed, but they only consider a single wire- less technology as the main underlying network, as is the case of Universal Mobile Telecommunica- tions System (UMTS) due to its wide coverage area, or IEEE 802.11 in the Vehicular Ad-hoc Network (VANET) case. However, when considering mul- tiple wireless access network candidates to hand over to, a Vertical Handover Decision Algorithm (VHDA) must evaluate the most suitable network among them in order to maintain connectivity with the highest quality possible. The automotive indus- try is taking advantage of the latest developments of the different embedded systems and communication technologies, thus building fully featured On-Board Units (OBUs) powered by fast and reliable processor units, Global Positioning System (GPS) based nav- igation systems, Wireless Fidelity (Wi-Fi), UMTS, and even Worldwide interoperability for Microwave Access (WiMAX) interfaces to reinforce the com- munication system of the vehicles [1]. Since there are different alternatives for communication among vehicles, and between the vehicles and the infras- 1 Universitat Polit` ecnica de Val` encia, Cam´ ı de Vera, s/n, 46022 Valencia, Espa˜ na. {jomarba, calafate, jucano, pman- zoni}@disca.upv.es tructure, on highways and metropolitan areas, the industry must face the downside issues when het- erogeneous wireless technologies are used in highly dynamic environments such as VNs. Therefore, in order to provide continuous communication among heterogeneous wireless networks while maintaining certain QoS levels, the IEEE 802.21 standard [2] has been released. In this paper we propose a novel VHDA called MACHU (Multi-ACcess network Handover Algorithm for vehicUlar environments), which combines GPS-based geolocation, map information, surround context information and route calculation, with the functionality of the IEEE 802.21 standard. For the decision-making process, MACHU takes ad- vantage of both current and future geolocation of the vehicle (within the route and map layout), along with the networking information provided by the different services of the IEEE 802.21 standard. The purpose is to choose the most suitable access network along the route when following the pathway from one location to another. The rest of this paper is organized as follows: Sec- tion II presents related proposals found in the liter- ature. An overview of the Vertical Handover (VHO) process and the IEEE 802.21 standard is provided in Section III. The design and considerations of MACHU are presented in Section IV. Section V describes the simulation environment used for the evaluation of the VHDA, while Section VI presents the experimentation results. Finally, Section VII presents the conclusions of this research work, as well as the future work. II. Related Work Horizontal handovers assisted by GPS informa- tion have been already studied and proposed by different authors [3], [4] presenting the advantages of geolocation within a single type of wireless net- work. Recently, works considering GPS support for the decision-making process when performing VHO among multiple access technologies were presented. Ylianttila et al. [5] proposed using the GPS in order to manage the current location of the mobile device to hand over among Wi-Fi and UMTS cells, perform- ing the decision-making based on the Received Signal Strength (RSS). A more recent proposal is presented by Gu et al. [6] using a Position Prediction Mechanism (PPM) in order to predict the future position of the mo- bile device, and obtaining network information for the decision-making process from the advertisement packets. However, authors propose predicting the