Research On GNSS Performance Enhancement

Since Global Navigation Satellite System (GNSS) has been widely used today, every aspect of social life has a high and growing dependence on GNSS. Meanwhile, its shortages are increasingly emphasized, including: availability, integrity and accuracy. Lack of availability is reflected in the limited signal coverage in urban and indoor scenarios due to user‐satellite geometry and signal shielding; current integrity performance does not meet the highly demanding requirements of safety‐of‐life related applications; insufficient accuracy is reflected by the user requirements of higher accuracy PNT service, while maintaining low cost. Way towards GNSS performance enhancement has become the hot and important research topic and is also one of the working emphasis of GNSS providers. A dedicated subgroup on service performance enhancement has been established within the International Committee on GNSS to provide the opportunity of discussion and possible solutions.This dissertation discusses the above three primary parameters for GNSS performance enhancement: researches the pseudolite system and its applications to improve the signal coverage and availability; proposes the Satellite Autonomous Integrity Monitoring and autonomous ephemeris improvement methods using inter‐satellite links and inter‐satellite rangings to improve the integrity and accuracy. The dissertation also proposed a novel optical time‐difference‐of‐arrival based positioning system and its algorithms, to cover the deficit of GNSS indoor uses. The primary contributions are presented:(1) A through research of pseudolite system and related issues including compatibility and solution.(2) Research of pseudolite network solution, proposal of a novel stand‐alone positioning algorithm using asynchronous pseudolites.(3) Design and implementation the pseudolite transmitter and relevant software; implementation of a pseudolite positioning demonstration system.(4) Research of GNSS integrity, proposal of Satellite Autonomous Integrity Monitoring (SAIM) method using inter‐satellite ranging.(5) Research and proposal of satellite autonomous broadcast ephemeris improvement method using inter‐satellite ranging.(6) On the basis of comparison of different physical quantities and principles, research and proposal of time‐difference‐of‐arrival positioning in optical band; discuss of the relevant theories and implementation issues.The key technologies and innovations in the research focus on the following points:(1) Proposed the stand‐alone positioning algorithm using asynchronous pseudolites and the required initialization approaches along with the simulated validation. The proposed algorithm exploited new application areas, and has the potential to be used in the extended field of signal‐of‐opportunity (SOOP). (2) Designed an entire set of pseudolite demonstration system including the transmitter and software, which can be either used to construct a positioning system with values of practical usages, or to research and validate pseudolite techniques and algorithms with.(3) Proposed the Satellite Autonomous Integrity Monitoring (SAIM) approach based on inter‐satellite links. The approach can be used to improve the system integrity along with others methods such as ground based integrity monitoring and Receiver Autonomous Integrity Monitoring (RAIM).(4) Proposed the satellite autonomous broadcast ephemeris improvement approach based on inter‐satellite links. The approach can improve the User Ranging Error (URE) significantly without reliance of ground stations.(5) Proposed a novel indoor positioning approach in optical band. The advantages of optical band and its features are discussed. System design, ranging codes and receiver scheme are also discussed.On the basis of above discussion, the following conclusions are summarized:(1) Pseudolite can be used as the augmentation and supplement to GNSS and play an important part in urban/indoor scenarios, providing equivalent or better performance with regard to GNSS.(2) By using the inter‐satellite ranging capability of modern navigation satellites, the proposed SAIM algorithm can monitor the integrity risk autonomously and improve the system integrity; the proposed autonomous broadcast ephemeris improvement algorithm can significantly improve the URE from1.05m to0.34m.(3) The novel indoor positioning approach in optical band has a lot of advantages including high accuracy and free of electromagnetic interference, and is of great application potential.