High-precision positioning plays a pivotal role in intelligent transportation systems by enabling reliable navigation, automated intersection management and high-precision platooning for autonomous vehicles in large-scale, unfamiliar environments. However, existing loosely or tightly coupled integration solutions of Global Navigation Satellite System (GNSS), Inertial Navigation System (INS), and Visual System can be challenged by the limited availability of GNSS signals, which will affect their ability to consistently achieve robust high-precision positioning in harsh environments. In this work, we propose a multi-sensor (GNSS/INS/Vision) ultra-tightly coupled system with GNSS carrier phase long coherent integration tracking (MUT-LCI). At the signal processing level, MUT-LCI utilizes the multi-sensor sensed dynamics to assist GNSS signal tracking loops and realizes extended coherent integration periods up to 300 milliseconds, improving the availability of GNSS carrier phase observations in highly challenging environments significantly. The data fusion of the GNSS RTK/INS/Vision is conducted using a Multi-state Constraint Kalman Filter (MSCKF). To evaluate the performance of the proposed MUT-LCI system, we conducted experiments using an intelligent transportation wheeled robot platform in harsh environments, including areas covered by dense tree canopies and surrounded by tall buildings. The results demonstrate that the proposed MUT-LCI system achieves precise GNSS carrier phase signal tracking in highly challenging environments, enabling continuous RTK fixed solutions and providing reliable centimeter-level positioning accuracy.

The carrier phase measurements of the global navigation satellite system (GNSS) exhibit degraded accuracy and availability in challenging environments, thereby hindering their effective use for intelligent transportation applications. In this paper, an inertial navigation system (INS) aided GNSS signal tracking architecture with long coherent integration periods is proposed to provide accurate and continuous carrier phase observations in challenging environments. In order to implement efficient long coherent integration, a GNSS real time kinematic (RTK)/INS ultra-tight integration algorithm is designed to compensate for the dynamics induced by the receiver-satellite relative motion, and a multichannel cooperative loop with a specialized discriminator is proposed to eliminate the negative effects due to the receiver oscillator instability. Meanwhile, an accurate open loop tracking strategy is designed to sustain the integer ambiguity during a signal blockage, improving the continuity of the carrier phases. Initial blockage test shows that the open loop strategy can keep the carrier phase error below 90 degrees for over 40 seconds. Moreover, an INS based cumulative cycle slip decision variable (CCSDV) is proposed to detect the carrier phase cycle slips accurately. Finally, field vehicle tests were carried out using a (micro-electro-mechanical system) MEMS IMU. It turns out the proposed architecture significantly improves the accuracy and continuity of the carrier phase observations and it can provide superior positioning performance with a small amount of GNSS single frequency observations and a long RTK baseline.

Global navigation satellite systems (GNSS) like GPS but also Galileo, GLONASS, and Beidou represent an important infrastructure to our society. They provide position and timing for numerous applications. A GNSS is a rather complex system consisting of around 30 satellites, a number of monitor stations, plus a control center. Billions of GNSS receivers represent the user segment. The receivers and the monitor stations receive a weak satellite radio signal and thus are susceptible to interference like jamming or spoofing. This paper outlines the core operation principles of satellite navigation to describe those kind of interference and to analyze the impacts. Different types of interference attacks result in different effects at the target receiver. The attack schemes are categorized within this paper. Reported incidents are summarized as well as the potential impact of GNSS vulnerability on critical infrastructure. Well known countermeasures at user receiver level or at system level are outlined and discussed for their suitability. The political and socioeconomic context of GNSS vulnerability is described emphasizing the large impact of a potential disruption of the GNSS service.

Deep indoor scenarios are one of the most challenging areas of application for Global Navigation Satellite Systems (GNSS) in personal navigation devices. Especially severe signal attenuation, as well as heavy multipath constrain the use of GNSS in this environment. The project DINGPOS is focusing on the development of a platform for pedestrian users which can acquire and track GNSS signals also under most adverse indoor signal conditions. The main idea of the concept is the extension of the coherent signal integration time of the GNSS receiver to the length of several seconds, which increases the correlation gain significantly. To facilitate this goal, a very long and very precise signal replica is needed. Therefore the system must reproduce the user motion, the navigation message data bits and the satellite constellation precisely. Hence, the system uses a sensor suite of several state of the art indoor positioning sensors and innovative fusion algorithms. The integrating element of the system is a software receiver using Ultra-Tightly Coupling (UTC) implemented by vector tracking. The presented work was performed under the ESA funded contract DINGPOS, ESTEC Ctr. No. 20834.

This paper summarizes what is needed to achieve a real-time -157 dBm GPS C/A signal acquisition sensitivity in ASIC and software receiver implementations for a cold and a warm start. Two receivers (one ASIC receiver working in the time domain and one PC software receiver working in the frequency domain) are implemented in a highly efficient way. The algorithms are outlined here and are tested with a GNSS signal simulator. Both use the same RF front end, operate on identical 2-bit samples and produce identical correlation results. The sensitivity comparison is completed by including some new commercial GPS chip evaluation boards in the test runs. We demonstrate the importance of narrow band and strong signal interference mitigation and investigate the role of the coherent integration time length as an important trade-off parameter.