Research On The Train Positioning Method For Subway Based On Visible Light Communication And Received Signal Strength Indication

At present,subway is one of the mainstream public transport tools in metropolitan areas.CBTC(Communication Based Train Control)systems are the prevailing operation control systems of subway.The accurate position information of train obtained by positioning technology is an important basis for CBTC systems to control the safe and efficient train running.However,the existing train positioning methods have some problems,such as low data transmission rate between train and wayside equipment,error accumulation in positioning results,high investment cost,easily disturbed signal,occupying scarce spectrum resources,restricted application in tunnel environment and so on.VLC(Visible Light Communication)has the characteristics of no need to apply for spectrum certificates,fast transmission rate,and taking into account the functions of lighting and communications.Meanwhile,the positioning technology using VLC has the characteristics of safe,high accuracy,green transport and so on.In terms of the mainstream tunnel scenarios and operation characteristics of trains,a train positioning method based on VLC and RSSI(Received Signal Strength Indication)was proposed to make up for the existing train positioning technologies.Firstly,VLC theory and train positioning theory based on VLC were summarized,according to the tunnel scenarios of subway and LED light source with Lambert model,and the VLC channel model,train positioning model with VLC and train moving model were constructed.Secondly,the train positioning method based on VLC-RSSI was designed.The linear distance d between a LED lamp installed on the tunnel wall and the train was obtained by using RSSI value,and the horizontal distance r between the train and the lamp was obtained by using the spatial geometric relationship,the position information of LED was obtained by IM/DD(Intensity Modulation with Direct Detection)method,and the train positioning result was fitted by trilateral positioning principle and least square method.Thirdly,the observation model and the error model of train positioning were established based on VLC-RSSI,and the real-time positioning and error analysis for a running train were done.The principles of Kalman filtering and Newton interpolation were analyzed,the state equation and measurement equation of system were established.Then,taking RSSI values as observation,the UKF(Unscented Kalman Filter)was used to optimize the train positioning results.In the optimization process,the Newton interpolation method was introduced to re-estimate the RSSI measurement value with coarse error,to reduce the influence of noise and coarse RSSI measurement value on train positioning accuracy.Finally,according to the real line data and equipment parameters from Chengdu Metro Line 1,an experimental platform was built to validate the effectiveness of the train location method based on VLC-RSSI and the rationality of using Newton-UKF algorithm to optimize the train location results.The experimental results show that the average positioning error of the proposed VLC-RSSI method is 13.46 cm,and taking RSSI value as observation,Newton-UKF algorithm is used to optimize the train positioning results,and the average positioning accuracy is 4.98 cm.The positioning accuracy of the proposed method meets the requirements of IEEE1474.1 for CBTC systems,the train positioning method based on VLC-RSSI can also be used as the reliable support for vehicle-to-vehicle communication and FAO(Full Automatic Operation)in urban rail transit,which has broad application prospects.