Research On The Effect Of WIFI Signal On Equipments In Train

With the development of high speed mobile communication and Internet technology, people are increasingly reliable to information technology and the Internet service has been people’s Rigid Demand individually in the 21th century, promoting Internet service based on WIFI technology on train has been the key to improve passengers’ experience during travel time. Under the background, this thesis did the research on the electromagnetic compatibility between WIFI signal and vehicular equipment.Firstly, this thesis introduced the entire structure of WIFI system on train, and described how to build, maintain WLAN system and how train’s WLAN can connect to Internet. Based on WIFI equipment’s operating process and characteristic, the thesis presented WIFI physical layer protocol——802.11 protocol briefly.The WLAN on train is built with WIFI technology to cover carriage by WIFI signal, and WIFI signal strength should be strong enough to support the communication. This thesis did research on radiation characteristic of WIFI equipment. Combined with carriage’s characteristic, this thesis also studied WIFI antenna layout and path loss of radio, and calculated distribution of WIFI signal strength in carriage. Through studying transmission characteristic of WIFI technology, this thesis confirmed that signal strength can support communication.In the aspect of electromagnetic compatibility, this thesis analyzed the electromagnetic compatibility of WIFI equipment and tested it to confirm the equipment’s electromagnetic compatibility can meet the national standards. The interference from WIFI signal to vehicle equipment mainly results from slot on shielding box of vehicle equipment. Based on theory of slot antenna, this thesis derived the expression of field distribution in box; what’s more, this thesis derived the approximate expression of field distribution in shielding box and plot the distribution in shielding box.In the aspect of electromagnetic slot leakage, this thesis simulated the numerical model of shielding box. With the simulation, radiation characteristic of slot antenna, influence factors of slot leakage, field distribution inside shielding box, the effects of dielectric-slab on field distribution are analyzed and studied. In addition, this thesis analyzed the overall distribution characteristics, field distribution characteristic on each plane, standing wave and shielding efficiency of shielding box in different situation, then obtained the conclusion:dielectric-slab in shielding box make electromagnetic energy well-distributed in shielding box, so that peak level of field strength descends. This thesis proposes a way of evaluating shielding efficiency based on radiation power. Compared with ways based on electric field or magnetic field, it reduces the uncertainty of result, gets rid of the individual difference of reference point’s shielding efficiency, result evaluated through the new way is more objective.This thesis briefly studied the communication characteristics of WIFI transmission system, and obtained the relationship between WIFI system error rate and signal noise ratio, the results verified the availability of WIFI signal intensity in the train. Finally, through the conclusions, this thesis proposed some recommends avoiding interference and reducing the impact of WIFI signal on the vehicle equipment.