Research On Multi-target Indoor Ultrasonic Three-dimensional Positioning System

Geographical location is one of the critical foundations of human behaviors,and indoor area is where people spend longest time daily.Therefore,it is an important task for us to successfully combine the indoor location with the user data or the information that the user is interested in.Indoor positioning will surely become one of the most major applications in the mobile Internet era.Ultrasound indoor positioning have many advantages including accurate positioning,simple layout,strong anti-interference,low cost,etc.But it is difficult to synchronize with high-precision timing.In addition,a conventional ultrasonic positioning system generally uses several fixed nodes as transmitting ultrasonic nodes,and a targeted node(unknown node)as a signal receiving node.In order to avoid locating crosstalk between multiple signals received by the target node,a certain coordination algorithm is also required.Based on the research of ultrasonic indoor positioning across the world,a new scheme of ultrasonic positioning is proposed.Firstly,the target node to be located sends unidirectional infrared signals and ultrasonic signals to multiple fixed nodes(referred to as "double "One-way method).Infrared signals is used as the ultrasonic timing signal timing superscript.Following this way,there will be no multi-channel signal crosstalk;Secondly,multi-fixed-node receiving signal detection part concentrated in a FPGA to achieve high-precision ultrasonic timing synchronization.Multi-channel signal is easy to process and the structure is simple and clear.Finally,based on the original traditional positioning algorithm,combining least square method and Taylor series expansion improves the positioning accuracy.Through the above methodology,the design of ultrasonic indoor positioning algorithm studied in this paper can reach the accuracy of centimeter level,which is of high reference value in practical application.The main work and innovation of the thesis are as follows:1)Design the "double" unidirectional method ultrasonic measuring circuit for transmitter and infrared circuit for driver and signal processing circuit for receiver,as well as FPGA-based high-precision synchronous timing processing module and FPGA and STM32 communication module.2)The response and delay of the ultrasonic/infrared signal processing circuit in the ultrasonic ranging process are analyzed.The errors introduced by the delay of the device itself are corrected.The positioning accuracy is improved,which lays the foundation for precise ultrasound positioning.3)Several commonly used localization algorithms are analyzed:the advantages and disadvantages are analyzed for absolute time method(TOA),time difference based method(TDOA),arrival based approach(AOA),received signal strength(RSSI).On top of this,an optimization algorithm is proposed,that is,the least square method is combined with the Taylor series expansion positioning algorithm to further improve the positioning accuracy of the target.4)The design adds the infrared synchronization signal sent by the positioning target point to the coded information,and injects a random delay to the infrared information transmission interval to achieve the multi-target non-interference positioning.