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1

Characterizing positioning errors when using the second-generation Australian satellite-based augmentation system

Khaki Mehdi, El-Mowafy Ahmed

Artificial Satellites : Journal of Planetary Geodesy

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2020

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Vol. 55, No. 1

1--15

EN

Fault detection and exclusion (FDE) is the main task for pre-processing of global navigation satellite system (GNSS) positions and is a fundamental process in integrity monitoring that is needed to achieve reliable positioning for applications such as in intelligent transport systems. A widely used method is the solution separation (SS) algorithm. The FDE in SS traditionally builds the models assuming positioning errors are normally distributed. However, in urban environments, this traditional assumption may no longer be valid. The objective of this study is to investigate this and further examine the performance of alternative distributions, which can be useful for FDE modelling and thus improved navigation. In particular, it investigates characterization of positioning errors using GNSS when the Australian satellite-based augmentation system (SBAS) test bed is used, which comprised different positioning modes, including single-point positioning (SPP) using the L1 global positioning system (GPS) legacy SBAS, the second-generation dual-frequency multi-constellation (DFMC) SBAS service for GPS and Galileo, and, finally, precise point positioning (PPP) using GPS and Galileo observations. Statistical analyses are carried out to study the position error distributions over different possible operational environments, including open sky, low-density urban environment, and high-density urban environment. Significant autocorrelation values are also found over all areas. This, however, is more evident for PPP solution. Furthermore, the applied distribution analyses applied suggest that in addition to the normal distribution, logistic, Weibull, and gamma distribution functions can fit the error data in various cases. This information can be used in building more representative FDE models according to the work environment.

2

Optimization of satellite combination in kinematic positioning mode with the aid of genetic algorithm

Srinuandee P., Satirapod C., Ogaja C., Lee H. K.

Artificial Satellites : Journal of Planetary Geodesy

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2012

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Vol. 47, No. 2

35--46

EN

The basis of high precision relative positioning is the use of carrier phase measurements. Data differencing techniques are one of the keys to achieving high precision positioning results as they can significantly reduce a variety of errors or biases in the observations and models. Since GPS observations are usually contaminated by many errors such as the atmospheric biases, the receiver clock bias, the satellite clock bias, and so on, it is impossible to model all systematic errors in the functional model. Although the data differencing techniques are widely used for constructing the functional model, some un-modeled systematic biases still remain in the GPS observations following such differencing. Another key to achieving high precision positioning results is to fix the initial carrier phase ambiguities to their theoretical integer values. To obtain a high percentage of successful ambiguity-fixed rates, noisy GPS satellites have to be identified and removed from the data processing step. This paper introduces a new method using genetic algorithm (GA) to optimize the best combination of GPS satellites which yields the highest number of successful ambiguity-fixed solutions in kinematic positioning mode. The results indicate that the use of GA can produce higher number of ambiguity-fixed solutions than the standard data processing technique.

3

A new algorithm for long baseline kinematic positioning with dual frequency GPS/GNSS receivers

Isshiki H., Wang J.

Artificial Satellites : Journal of Planetary Geodesy

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2006

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Vol. 41, No. 4

117--135

EN

Smoothing pseudo ranges with ionosphere-free combinations of phase ranges can be useful for long rang positioning, since this new smoothing process can significantly remove the effect of ionosphere delays in positioning applications. The smoothing process can be conducted without being affected by cycle slips, though it uses phase ranges. Therefore, it can provide a robust precise positioning solution which is not affected by cycle slips. The multipath effects may also be reduced, if the averaging interval taken is long enough. If the low frequency noise components and the hardware biases in pseudo ranges are reduced, the positioning performance with the smoothed pseudo ranges may be promising. In future GNSS receivers, both the noises and the hardware biases in pseudo ranges will be significantly reduced. Then, the positioning based on the proposed algorithm will be very useful.