Research On Pseudolite Realtime Indoor Positioning And Its Implementation

GNSSs have the many merits like continuous positioning, all-weather and highprecision, but in rooms and undergrounds and some shielding environments, GNSSsignals attenuate a lot and visible satellites reduce, which causes poor positioningaccuracy or makes it impossible to locate, and thus limits GNSSs applications.Pseudolite can satisfy the requirements of indoor and some other special positioningscenarios, which not only serves as a self-positioning system, but also could act as anauxiliary tool to enhance outdoor GNSS performances to achieve seamless positioning.The purposes and major points of this paper are to design a universal GNSSpseudolite including all bands and adjustable output power, then a realtime software-defined receiver is design to analyze its signal to implement realtime positioning. Firstfor its wide bands and programmable features then new signal systems can easilyapplied to pseudolite transmitter to study and verify the design. Followed by adjustablepower, near-far problem and multipath will be reduced to some extent. At last,modifying a software-defined pseudolite receiver to analyse signal structure andhardware design to get a better transmitter, and then a pseudolite realtime indoorpositioning system will be set up.This paper studies the research on realtime indoor pseudolite positioning. Basedon the principle similarities between signal structure of pseudolite and GNSS satellite,some analyses on RF signal structure of pseudolite are made at first, and thenlocalization methods are explored, like asynchronous clock double difference method,synchronous clock signal difference and double difference method, at the same time,the conditions and processes and their differences are described in detail.The pseudolite positioning precision and errors are discussed. At first, the effectsof psedolite to GNSSs on GDOP have been proved, and then the optimal geometriclayout of indoor pseudolite on principle is analysised, some simulations about actualoptimal geometric layout have been performed, at last, some errors in pseudolitepositionings are discussed like near-far problem, multi-path and nonlinearity.The hardware structure of pseudolite transmitter is improved, the hardware designprinciple is introduced first and modules are stated respectively, the transmitter has a wide bandwith ranging form800MHz to2500MHz including all GNSS signals, andpower tuning is necessary for mitigating multi-path and near-far problem.A software-defined pseudolite receiver (SDR) based on multi-threads is designedand the internal implementation processes are discussed in detail and then somechanges different from GPS are modified. Finally taken USRP1and DBSRX or GN3Sas RF front-end, the procedure of modification, compilation and running of SDR arestated.Each module tests and overall tests of pseudolite transmitter have been done, andthe SDR has also been tested by GPS satellites and pseudolite transmitter which verifythe rationality of transmitter and SDR. In the end, the SDR have tested the positioningeffect of indoor pseudolite system.