Abstract
Ubiquitous navigation requires timely, uninterrupted and accurate estimate of receiver’s position at all times, in all environments and for all modes of transportation and it is highly dependent on satellite availability, geometry and accurate positioning estimation. However, the availability, continuity and accuracy of a GNSS can be severely affected in a highly dynamic environment due to blockage, fading and multipath. This results in positioning information inaccurate, unreliable and sometimes unavailable. This paper presents a study on the potential vulnerabilities that can affect a multi-constellation multi-frequency GNSS receiver in low to highly dynamic multipath environments such as clear line-of-sight, partially and highly obstructed environments to characterize the distortions/anomalies which could significantly affect the satellite signals and their impact on positioning and navigation. The multi-constellation multi-frequency GNSS receiver configuration in this paper is set to GPS, GLONASS, Galileo and BeiDou for the first time at full capacity and performance comparison is made with the GPS based on satellite availability, blockage, continuity, precision and accuracy parameters. These parameters are then used in this paper to detect and characterize the type of environment for the multi-constellation GNSS receiver without using any external aiding devices or sensors. Based on environment detection and characterization, a new Adaptive Environment Navigation (AEN) based GNSS receiver design is proposed which can work in real time and has achieved an overall availability and accuracy factor of 94% in highly dynamic multipath/NLOS environment along with a reduction in the blockage coefficient, $\beta $ , by almost 11% resulting in more accuracy and precision than the standard multi-constellation GNSS receiver where the availability factor was found to be 57% only.
Highlights
The rapid urbanization in the developed/developing countries brought several challenges for the cities to cope with issues related to administrative, infrastructure, logistics and transportation
Keeping in view the challenges faced by the satellite-based navigation systems, this paper presents a comprehensive study on the potential vulnerabilities that can affect the global navigation satellite system (GNSS) performance in low and high dynamic multipath environment such as clear open-sky view, partially degraded environment having both LOS and NLOS signals and high multipath environment having little or no LOS signal reception [31]
The Adaptive Environment Navigation (AEN) method starts by acquiring and tracking all visible satellites in order to estimate the positioning and navigation parameters. It calculates the blockage factor, continuity factor, position DOP (PDOP) and satellites visibility to check for Circular Error Probable (CEP) and Distance Root Mean Square (DRMS) to characterize the working environment into three distinct categories i.e., nominal/standard, partially degraded and highly dynamic multipath environment based on the set minimum performance level indicators Table 5 which can be used by the receiver to decide, when to initiate the adaptive tracking in case the working conditions have been changed
Summary
The rapid urbanization in the developed/developing countries brought several challenges for the cities to cope with issues related to administrative, infrastructure, logistics and transportation. The average positioning error in case of PPP is less than one meter in clear open-sky [6] This level of accuracy cannot be achieved in obstructed environments even if the receiver is equipped with additional error modelling [29], because there are significant chances of navigation services being interrupted or their performance reduced due to signal blockage and MP/NLOS [7], [9], [30] leading to inaccurate positioning solution. A series of field experiments has been carried out with different working modes and different observation conditions using four major characteristics of a GNSS that has never been done before, i.e., Availability, Signal Characteristics, Service Continuity and Accuracy These characteristics are studied in detail through blockage coefficient, satellite availability, loss of signal lock and standard quality (accuracy and precision) measures for positioning and navigation such as Distance Root Mean Square (DRMS), VOLUME 8, 2020. The last section, i.e., Section VI, talks about the proposed navigation receiver design based on Adaptive Environment Navigation (AEN) Algorithm
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