Research On Application Of LoRa Communication Technologies In Differential Global Positioning System

With the continuous development of GPS technology,the GPS standard positioning accuracy which reach tens or even several tens of meters can not meet user's demand for high-precision positioning.Differential GPS technologies which use the spatial and time correlation of GPS observation error can improve the positioning accuracy obviously,it has been widely applied.At present,the pseudorange differential GPS and carrier phase differential GPS are used most widely in differential GPS field,their positioning accuracy can reach sub-meters and centimeters level separately.Although conventional differential GPS devices have high positioning precision,the high price is difficult for ordinary users to accept.Inexpensive differential GPS devices have horizontal positioning precision in 4to 5 meters,which can not fulfill the high-precision positioning requirements of consumers.Hence,considering positioning accuracy,universality,hardware price,low-cost differential GPS positioning system: pseudorange differential GPS and carrier phase differential GPS to satisfy the demands in different positioning precision situations for different users are designed and implemented.Besides,traditional differential data transmission involves radio stations in early and 4G networks in nowadays.The radio station is complex and costly to install,though 4G networks possess fast transmission speed and low time delay,the reliability of data transmission can not be guaranteed in mountain areas in which 4G is not covered or the signal is poor.Therefore,LoRa wireless communication technology with low power consumption and long transmission distance is applied as the data communication in the differential positioning system.The main research contents in this paper are introduced as follows:1.The main resources of GPS positioning errors are introduced and the basic positioning principles of single-frequency pseudorange differential and carrier phase differential are expounded;Two standard differential message protocol for RTCM 2.3and RTCM 3.2 are introduced.2.The technical advantages of LoRa is highlighted and the reason for choosing LoRa is explained.The hardware selection and circuit design of the LoRa are completed.The communication performance including output spectrum,receiving sensitivity,data transmission rate,time delay and power consumption are studied and tested.The datatransmission protocol applicable to this paper is designed.3.The design of network pseudorange differential GPS and the pseudorange differential GPS based on autonomous encoding RTCM 2.3 message are completed.RTCM 2.3 standard differential message is obtained by Ntrip protocol.The original observation data and navigation data in UBX format can be decoded and the satellite coordinates are calculated in real time,the programming for RTCM 2.3 differential message encoding is designed.Finally,different embedded devices are built to realize two different pseudorange differential positioning...4.The design of network carrier phase differential GPS and the carrier phase differential GPS based on autonomous encoding RTCM 3.2 message are completed.RTCM 3.2 standard differential message is obtained by Ntrip protocol.The decoding of UBX format data and the programming design of RTCM 3.2 differential message encoding are completed.Finally,different embedded devices are built to realize two different carrier phase differential positioning.