Cross-layer design vehicle-aided handover scheme in VANETs

The requirement for in-vehicle passengers to access Internet multimedia services has risen recently. As a consequence, Vehicle Ad hoc NETwork (VANET) has gained much attention, and is regarded as a promising solution for providing in-vehicle Internet service through inter-vehicle and infrastructure communication. A new developed wireless network technique, termed WiMAX Mobile Multihop Relay (MMR), provides a good communication framework for a VANET formed from vehicles on high-speed freeways. Applying MMR WiMAX allows some public transportation vehicles to act as relay vehicles (RVs) to provide Internet access to passenger vehicles. However, the standard handover procedure of mobile or MMR WiMAX suffers long delay due to the lack of information about the next RV. This study presents a cross-layer fast handover scheme, called vehicular fast handover scheme (VFHS), where the physical layer information is shared with the MAC layer, to reduce the handover delay. The key idea of VFHS is to utilize oncoming side vehicles (OSVs) to accumulate physical and MAC layers information of passing through RVs and broadcast the information to vehicles that are temporarily disconnected, referred to as disconnected vehicles (DVs). A DV can thus perform a rapid handover when it enters the transmission range of one of approaching RVs. The effectiveness of VFHS is verified using ns2 simulations. Simulation results indicate that VFHS significantly decreases handover latency and packet loss. Copyright c ⃝ 2009 John Wiley & Sons, Ltd.