Real-Time Kinematic andHigh Accuracy NavigationWith Low-Cost GPS Receivers

摘要

Today's high accuracy applications demand the mostrnaccurate ranging information obtainable with satelliternnavigation systems, the carrier beat phase observable.rnCommon practice is to utilize high-performance (dualfrequency)rngeodetic-type GPS receivers for these applicationsrncosting about US$10,000 each. Instead, the massmarketrnand the private user segemnt demand low-costrn(< US$100), low weight and volume GPS receivers.rnFurthermore, there are many GPS-related scientificrnapplications where GPS receivers have to be modified andrnwhich also require high ranging accuracies. Most often thernonly possible way is to use receiver experimental kitsrnbased on low-cost chipsets allowing broad control over thernreceiver’s control loops and digital signal processing.rnTherefore, the important question arises whether low-costrnreceivers are capable of fulfilling the stringentrnrequirements of high accuracy applications (typicallyrn< 10 cm) and how they distinguish from high-endrnreceivers.rnThe Institute of Flight Guidance and Control (IFF) hasrnstudied a typical GPS receiver kit based on the PLESSEYrn(now: MITEL Corp.) chipset due to its research activitiesrnon the fields of low-cost pseudolite systems and highrnprecision integrated GPS/IMU systems intended forrnautomated vehicle guidance. When starting with thernsingle-frequency receiver kit only poor pseudorange accuracies were available and any real carrier beat phasernwas missing. Thus a high precision carrier beat phase hadrnto be developed. Additionally, a high precisionrnpseudorange was implemented by carrier smoothingrntechnique which tremendously reduces the effects of largerncode noise and multipath.rnTwo low-cost GPS receivers with the developed softwarernwere operated in a differential mode and compared with arnpair of high-end dual-frequency receivers. The tests showrnthat low-cost GPS receivers are even suitable for real-timernkinematic (RTK) high accuracy positioning.