Cloud-Based Single-Frequency Snapshot RTK Positioning

Abstract

With great potential for being applied to Internet of Things (IoT) applications, the concept of cloud-based Snapshot Real Time Kinematics (SRTK) was proposed and its feasibility under zero-baseline configuration was confirmed recently by the authors. This article first introduces the general workflow of the SRTK engine, as well as a discussion on the challenges of achieving an SRTK fix using actual snapshot data. This work also describes a novel solution to ensure a nanosecond level absolute timing accuracy in order to compute highly precise satellite coordinates, which is required for SRTK. Parameters such as signal bandwidth, integration time and baseline distances have an impact on the SRTK performance. To characterize this impact, different combinations of these settings are analyzed through experimental tests. The results show that the use of higher signal bandwidths and longer integration times result in higher SRTK fix rates, while the more significant impact on the performance comes from the baseline distance. The results also show that the SRTK fix rate can reach more than 93% by using snapshots with a data size as small as 255 kB. The positioning accuracy is at centimeter level when phase ambiguities are resolved at a baseline distance less or equal to 15 km.

A Method to Determine Secondary Codes and Carrier Phases of Short Snapshot Signals

“…Fortunately for carrier-phase measurements, the fact that they are fractional values does not impact the positioning results as their integer parts are expected to be solved in the navigation filter through the Integer Ambiguity Resolution (IAR) procedure. However, it is vital to perform the global time tag determination step as described in Liu et al (2021) in order to have accurate information about the satellite transmission times of these measurements.…”

“…1. To compute an accurate tiered code delay, which will leave a resolution of a full secondary code period for the navigation filter to determine the global time tag of the observables as described in Liu et al (2021); only when accurate SCI values are known can the satellite transmission time be properly computed and the satellite coordinate errors can be within an acceptable range. 2.…”

“…Although Medina et al (2020) pointed out that the main factor that impacts the realization of instantaneous RTK fixes is the code measurement quality, this is under the assumption that the carrier-phase measurements are free from anomalies and their quality are only related to the C/N 0 and acquisition configurations. In practice, as shown in Liu et al (2021), snapshot processing may encounter carrier-phase anomalies that lead to errors of half a cycle when the so-called data bit ambiguity (DBA) issue occurs. The main objective of the present work is to tackle such challenges properly so that valid carrier-phase measurements can be generated and the SRTK technique can be implemented to achieve snapshot positioning with centimeter-level accuracy.…”

“…More specifically, for the first block, an open-loop batch processing architecture has to be used since the traditional closed-loop sequential tracking architecture requires longer signal recordings (Linty, 2015;Liu et al, 2021). For the second block, a coarse time navigation filter has to be applied because the accurate satellite transmission times are not known.…”

Precision-Aided Partial Ambiguity Resolution Scheme for Instantaneous RTK Positioning

“…This work focuses on PAR solutions for snapshot estimation, i.e., non-recursive estimation for which only the observations received at a time instant are considered. This case is particularly relevant for safety-critical vehicular applications, for which high availability of precise positioning is required in an instantaneous manner [7][8][9][10]. Thus, PAR identifies a subset of ambiguities to fix upon certain criteria, e.g., success rate maximization, failure rate minimization, etc.…”