A location aware based handoff algorithm in V2I system of railway environment

By taking advantage of the regularity of train track, a high-data-rate access system based on 802.11 network is proposed for passengers to surf on Internet when they are travelling on the railway or subway. The system mainly consists of a gateway with multi-antennas on the train, terminals in the train and access points (APs) along the track. Then, a location aware based handoff algorithm (LAB-HA) is proposed to shorten the time on handoff, avoid the signaling storm and decrease the packet loss ratio caused by frequent handoff. In LAB-HA, numbers of handoff procedures between lots of terminals with passengers and APs along the way can be replaced by the only one handoff procedure between the gateway and APs. The LAB-HA algorithm contains three parts. Firstly, creating and maintaining a table of APs which contains the location information for handoff process. The candidate location area for handoff is selected by statistical learning, where the probability of successful handoff is nearly 100%. Secondly, the gateway is authenticated. Only when the gateway moves into an extended service set (ESS) at first time, it sends the authentication request packet to the new AP. Finally, the gateway on the train detects its location information by GPS periodically while moving. If it moves into the candidate area, the handoff process is triggered. The table is then updated by the result whether the handoff is successful or not. Simulation results reveal that LAB-HA can reduce the handoff latency dramatically compared with fast BSS transition (FT) in the 802.11 standard, and LAB-HA is more reliable while it provides higher throughput. LAB-HA can be used in wireless access network based on 802.11 for data transmission in some special scenes, such as subway or railway.