Proactive Caching and Forwarding Schemes for Seamless Handover in IEEE WAVE Networks

The IEEE Wireless Access for Vehicular Environment (WAVE) standard consists of the IEEE 802.11p and the IEEE 1609 specifications supporting fast link establishment as well as broadband data communication in vehicular environment. Although the standard has been widely accepted by industry as well as highway authorities in many countries to be used for the radio communication infrastructure of the next-generation Intelligent Transport System (ITS), it remains open for further enhancements such as seamless handover support. This paper presents two proactive caching and forwarding schemes for seamless handover in IEEE WAVE networks: one for straight highway sections and the other for crossroads and junctions. Practical and efficient handover procedures, based on the proposed schemes, are also presented. Specifically, an on-board unit (OBU) informs the old road-side unit (RSU) about its departure from the coverage area such that the old RSU can forward the buffered packets to candidate RSUs for proactive caching. In handover scenarios around crossroads and junctions, the IEEE 802.11f Move-notify message is used by the new RSU to request the rest of candidate RSUs to purge the cached packets in order to prevent the waste of radio resource. Simulation results show that the proposed schemes outperform conventional schemes. 1. Introduction Thanks to the recent advances in various technologies including wireless communication, sensors, controllers, and hardware and software platforms, traveling in a car is becoming safer than ever as vehicles and roads are always connected and cooperatively exchange safety-related information. The IEEE WAVE is a suite of specifications for wireless access in ITS which comprises of the IEEE 802.11p and the IEEE 1609 supporting fast link establishment as well as broadband data communication of the maximum 27？Mbps between an OBU installed in a car moving at the maximum speed of 200？Km/h and an RSU deployed along roadways [1]. According to the specification of IEEE WAVE, the size of a safety-related application message is limited by a WAVE short message (WSM), which is defined to be 1,400 bytes. This allows the transmission of a WAVE message to be completed while a vehicle moves under the radio coverage of a single RSU. As a result, handover has been excluded from the specification. On the other hand, multimedia applications such as live highway CCTV video clips and Internet browsing, in which a sequence of multiple MAC protocol data units (MPDUs) is transmitted, require handover. Consequently, a growing amount of interest is being