Advanced Signal Processing in Multi-mode Multi-frequency Receivers for Positioning Applications

The demands for positioning services are increasing steadily since the first Global Navigation Satellite Systems (GNSS), NAVSTAR Global Positioning System, also known as GPS was introduced in the early 80s. The increasing demands for positioning services have accelerated the advent of other satellite-based systems, such as the Russian GLONASS, the European Galileo and the Chinese Compass/Beidou-2 system. However, the GNSS fail to provide accurate positioning solution indoors, which is one of the demanding environments. Therefore developing indoor positioning techniques has become a very important topic, mainly in terms of continuity of services and seamless localization. This has led to many theoretical and experimental studies in this field using a wide range of techniques, from purely GNSS approach to methods employing networks of physical sensors or Wireless Local Area Networks (WLAN). These systems, together with satellite­ based ones, all have their advantages, but they also face different challenges. Most of these are related to the physical channel containing various error sources that affect the quality of the received signal and degrade the receiver's positioning performance. The users will benefit from having multiple systems with more satellites and different positioning methods available. In this way, the positioning performance against the errors and challenges will be superior to having only a single system. This can be realized by the multi-mode multi-frequency receiver, which is able to process jointly the new signals, modulations and frequencies introduced in modem positioning systems. The work presented in this thesis focuses on the signal processing part for research and development of such a receiver and outlines the potential capability of the future receivers for positioning applications. More specifically, this thesis studies the narrowband interference effects on the future GNSS signals in both single-frequency and multi­ frequency receivers, makes a performance analysis of dual-frequency ionosphere delay estimation methods under strong multipath errors and presents an optimized multi­ correlator based multipath mitigation technique for future GNSS signals. In addition, the performance of four multipath mitigation techniques under time-varying, measurement­ based channel models is compared. Finally, a new Non-Line-of-Sight identification based on non-GNSS signal is proposed for improving the path-loss modeling based indoor positioning in multi-mode multi-frequency receivers. This thesis consists of an introductory part with live chapters and a compendium of six original publications ([I] - [VI]), attached as appendices.