Assisted GNSS Positioning using State Space Corrections

Abstract: Classical GNSS based positioning has accuracy limitations due to many sources oferror. The error sources range from clock errors and orbit errors toerrors due to variations in atmospheric propagation delays. One way to improve GNSSpositioning is to generate real time corrections using a GNSS reference network.The corrections can then be distributed through the mobilenetwork and be delivered in real time to the device that should position itself.  This thesis aims to develop a positioning engine utilizing statespace representation corrections (SSR). The thesis also has the goal to develop methods for combiningpseudorange measurements with carrier-phase measurements, in the case when SSR correctionsare used. The static and dynamic performance ofthe positioning engine will be evaluated. Also, the  SSR correction format itself, willalso be evaluated and different levels of SSR corrections will be compared. The proposed combined positioning engine uses SSR correctionsand single-difference measurements. Through this, all majorerror sources on the satellite side, device side and in the atmosphere, are removedexcept for an integer ambiguity in the carrier phase measurement. This ambiguityis handled by tracking the GNSS receiver's position along with the integerambiguities in an extended Kalman filter (EKF). Experiments show that usingreal-time SSR corrections leads to a significant improvement in global absolutepositioning for simple GNSS receivers using only a single measurement frequencyand only using pseudorange measurements. For a more advanced receiver capable ofcarrier phase measurements, experiments together with simulation resultsshow that using the proposed combined positioning engine, improves the positioningperformance even further.