Fast Handoff Mechanism Study Of Mine Locomotive Mobile Communication Network

The frequently occurred mine accidents not only cause great losses of lives and economic in our country, but also lead a serious social impact. The development and operation of the mine rail locomotive unmanned system contribute to reduce these accidents caused by incorrect scheduling and operating. Simultaneously, operation of the mine rail locomotive unmanned system can reduce the number of staff who work under mine and can also reduce the number of casualties caused by these accidents, will have a tremendous economic and social benefits.In order to achieve the development of mine rail locomotive unmanned system, the model of mobile network besides the rail locomotive should be built to support the communication between locomotive and server on the ground. The mobile network besides the rail locomotive is based on IEEE 802.11. Because of the limited coverage of AP, the moving locomotive will lead to the problem of handoff. In the thesis, the WLAN based on IEEE 802.11 standard is introduced and handoff mechanism is studied. The handoff consists of three phases:scan, authentication and re-association. More than 90% of handoff delay is caused by the scan phase, so reducing delay in the scan phase is the key to reducing the handoff delay and keeping the data transmission safe in the system.According to the handoff delay caused by mobile node on locomotive moving from one AP to another one, two different kinds of handoff mechanisms are proposed:beacon synchronization and channel estimation based handoff mechanism of underground mine wireless network and multi-site information sharing based handoff mechanism of underground mine wireless network, In the former, the model of wireless network underground mine based on IEEE 802.11 standard is built, and beacon synchronization and channel estimation based handoff mechanism of underground mine wireless network is presented to reduce the channel staying time and the number of scanned channels with the way of beacon synchronization and using neighbor list of APs. The simulation validates that delay of the mechanism could be reduced to satisfy the requirement of real-time·communication system, reduces at least 70% of the handoff delay than hard handoff mechanism. In the latter, in order to reduce signal multipath interference because of mine tunnel reflecting wireless signal the wireless network model besides rail is improved, the using of directional antenna can reduce interference with directional transmission signal. Working with the same power, the AP with directional antenna has the farther signal coverage. Increasing the density of access points are arranged ensures communication uninterrupted when single AP fails. There may be more than a locomotive which work at the same rail at same time, so the mechanism of multi-site information sharing is proposed, the locomotive moving in front shares the information about handoff to the locomotive behind, mobile node on the locomotive behind omit the channel scanning stage and the handoff delay is reduced.