高速移动环境下IEEE 802.11 MAC层切换方案

Wireless Handoff Scheme in IEEE 802.11 MAC Layer for High-Speed Mobile Communications

高速移动的无线节点在接入点间切换时,切换延迟较大,丢包率较高.该文结合地铁无线通信环境对切换延迟和丢包问题进行研究,改变了扫描信道的顺序,有效降低了切换延迟.在此基础上提出一种数据链路层的缓冲算法——Layer2-Buff,为移动节点设立专用缓冲区,以缓存切换过程中没有正常发送的数据帧,用于实现平滑切换功能.测试结果表明,Layer2-Buff算法无需修改网络层及上层协议栈,在地铁无线通信环境中可实现自动列车控制系统的零丢包.该算法已在地铁信号系统中得到应用.

Mobile station performs a handoff when it moves out of the range of one access point and tries to connect to the next. The delay and lost packets caused by the handoff process affect the network quality of service. Taking subway wireless communication system as an application scenario, the number of channels used is reduced, which decreases the scan delay effectively. An algorithm called Layer2-Buff is proposed to solve the problem of lost packets, which sets up buffers for STA, and used to save data that cannot be sent successfully. Test results show that Layer2-Buff reduces the packet loss rate to zero in an automatic train control system, and extra delay to the network is tolerable. This algorithm has been applied to a pre-research project of subway signal systems.