The Research Of Monitor Method In Metro Wireless AP Signal Quality

As the rail transit operation control system to the systematic, network, information, intelligence and integration of communication signals, wireless communication has become the key technology of rail transit signaling system. Wireless AP(Access Point) as an essential part of the wireless local area network(WLAN) communication, whose quality directly effect the communication signal system running.The platform screen door linkage system of Shanghai metro line 2 adopt a redundant wireless AP equipment, the maintenance staff used to use spectrum analyzer, the wireless signal analyzer detect the signal quality of AP periodically, but cannot achieve the real-time monitoring and predict fault. At present, only all AP fails, can management system alarm, meanwhile, the signal auxiliary system cannot work normally, also the platform screen door. Even impact the normal running of the subway. Therefore, it is necessary to do some further research about the signal transmission mode and signal quality monitoring method of AP equipment.This paper according to the standard of 802.11 wireless technology adopted by Shanghai metro line 2 wireless AP and the new technology of WLAN Mesh. Aimed at the characteristics of 2.4 GHz open frequency band signal can be freely received. use independent research and development of monitoring software, collect the interaction signal between the train and the platform AP, through the study of signal intensity, the interference source, AP packet retransmission rate and other case of influence communication, combined with wireless AP MAC information, transmission rate, channel information. By using the method of process detection and logical deduction judge the working status of AP equipment, make subway maintenance staff accurately locate faults AP, so that they can execute maintenance with purpose. Finally, reduce maintenance costs and improve the work efficiency and quality of operations.The study is on the basis of site investigation, then analysis its feasibility and the reliability, summarizes the technical route, comb research emphasis and difficulties, and then focuses on realization method. From hardware structure to software algorithm, even to the system layer, several key problems had been solved independently during the process of research, made a number of breakthroughs such as grasped the packets feature and interaction mechanism between the train and the platform, summed up the foundation of judging signal quality of AP, discovered the method of obtain and MAC address filter of data link layer packet, fulfilled the development of USB wireless network card Monitor mode, realized the remote upgrade of program based on Arm and can start up automatic when powered on, developed the server application which has the function of asynchronous services, formulated the communication protocol between client and server. Obtained good monitoring effect.