Optimal Independent Baseline Searching for Global GNSS Networks

Abstract

An n-station continuously operated global navigation satellite system (GNSS) network contains n-1 independent baselines. Baseline structure is critical to positioning accuracy, and the final result is dependent on the baseline selection strategies. The baseline length and amount of common observations are the primary principles for baseline selection. However, there are few discussions about the optimal strategy to determine the independent baseline of a huge GNSS network. To enhance the performance of the multibaseline solution, a comparison is drawn between the conventional method and a weighting strategy. Observations from continuous stations distributed globally within the International GNSS Service (IGS) are explored. At first, two conventional principles for baseline selection are tested. Subsequently, a weightingschemeisdevelopedtoexploit thesetwo strategies. The enhanced method improves nearly 10% external accuracy compared with the classical methods, which can be verified from the experiment on January 1, 2012. Lastly, the network experiment is extended to the whole year of 2012 to increase statistical significance. It is therefore revealed that the novel weighting strategy (WEIGHT), with an equal chance of two conventional strategies, mitigates 0.4%-3.0% three-dimensional (3D) coordinate error of the whole year. Also, an analysis of the probability of gross errors indicates that WEIGHT exhibits better performance. Unlike the conventional view, it is shown that a proper weight of OBS-MAX and SHORTEST could form a better coordinate calculation result and a lower gross error rate. In conclusion, these experiments suggest a proposed method that synthetically considers the length of total stations and the total number of observations, and it is verified that WEIGHT is a better choice for searching independent baselines

Pseudolites to Support Location Services in Smart Cities: Review and Prospects

“…A study has identified the concept that the constellation optimization of pseudolites can influence the pseudolite positioning error [123]. The essence of constellation optimization is to make a larger number of satellites observable in more space to improve positioning precision [124,128]. The effectiveness of a multi-objective particle swarm-based approach for the deployment optimization of pseudolite systems is discussed [129].…”

An Observation Density Based Method for Independent Baseline Searching in GNSS Network Solution

“…The data was processed with the Bernese software developed at the Astronomical Institute of the University of Bern (AIUB). Detailed descriptions or flow charts of data processing with Bernese can be found in the Bernese manual [8] or other publications [12,14,[16][17][18]. The products were downloaded and used following the website (https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/GNSS_product_holdings.ht ml, Weihai, China, 1 June 2018) and the instruction of Bernese [8].…”

“…WEIGHT is a synthesis of these two strategies. In this process, a normalization is introduced since the dimensions of OBS-MAX (number) and SHORTEST (meter) are not consistent [14]. Unfortunately, WEIGHT is still an empirical operation lacking theoretical support.…”

“…Then, SHORTEST and OBS-MAX should be fully equivalent. However, the statistics show that they are not consistent [14], i.e., on various days, the baselines generated by different methods could ultimately lead to different solution precision, which violates the assumption that the two methods are equivalent. This means that the number of observations does not necessarily increase as the baseline becomes shorter.…”

“…A scheme of setting up weights (WEIGHT) between SHORTEST and OBS-MAX has been proposed [14]. The WEIGHT method was demonstrated to be of higher positioning precision than that of SHORTEST and OBS-MAX.…”