American Society of Civil Engineers

An initial characterization and performance assessment of the COMPASS/BeiDou-2 regional navigation system is presented. Code and carrier phase measurements on up to three frequencies have been collected in March 2012 with a small regional network of monitoring stations. The signal and measurement quality are analyzed and compared with the Japanese Quasi Zenith Satellite System. A high level of stability is demonstrated for the inter-frequency carrier phase biases, which will facilitate the application of triple-frequency undifferenced ambiguity resolution techniques in future precise point positioning applications. The performance of the onboard Rubidium frequency standards is evaluated in comparison to ground-based hydrogen masers and shown to be well competitive with other GNSS satellite clocks. Precise orbit and clock solutions obtained in post-processing are used to study the presently achievable point positioning accuracy in COMPASS/BeiDou-2-only navigation. Finally, the benefit of triple-frequency measurements and extra-wide-lane ambiguity resolution is illustrated for relative positioning on a short baseline.

Initial assessment of the COMPASS/BeiDou-2 regional navigation satellite system

Integrity is one criteria to evaluate GNSS performance, which was first introduced in the aviation field. It is a measure of trust which can be placed in the correctness of the information supplied by the total system. In recent years, many GNSS-based applications emerge in the urban environment including liability critical ones, so the concept of integrity attracts more and more attention from urban GNSS users. However, the algorithms developed for the aerospace domain cannot be introduced directly to the GNSS land applications. This is because a high data redundancy exists in the aviation domain and the hypothesis that only one failure occurs at a time is made, which is not the case for the urban users. The main objective of this paper is to provide an overview of the past and current literature discussing the GNSS integrity for urban transport applications so as to point out possible challenges faced by GNSS receivers in such scenario. Key differences between integrity monitoring scheme in aviation domain and urban transport field are addressed. And this paper also points out several open research issues in this field.

/pdf/gnss-position-integrity-in-urban-environments-a-review-of-1ved0w5512.pdf

GNSS Position Integrity in Urban Environments: A Review of Literature

Siloxane removal from landfill and digester gas – A technology overview

This paper describes a method of processing Global Positioning System (GPS) observations to achieve undifferenced ambiguity resolution. Dual-frequency carrier phase and pseudorange measurements are processed by specifying separate oscillator parameters for the carrier phase and pseudorange measurements. Carrier phase estimates of the oscillator errors are arbitrarily biased with respect to the pseudorange estimates, and ambiguity parameters are constrained to be integer-valued. A network solution is necessary to compute the satellite code and phase clocks required as fixed parameters in single-user Precise Point Positioning (PPP) solutions. In the PPP results presented here, the LAMBDA method was used to optimally resolve ambiguities at each epoch. Only a small improvement in position error is gained with 5-minute static processing over 24 hours. However, there is a significant reduction in convergence time, and with 30-second static processing after 60 minutes, 90% of solutions approach 2 cm horizontal error, compared to 10 cm for standard PPP.

/pdf/undifferenced-gps-ambiguity-resolution-using-the-decoupled-5y57j1buc4.pdf

Undifferenced GPS Ambiguity Resolution Using the Decoupled Clock Model and Ambiguity Datum Fixing

The principle of positioning with the Global Positioning System (GPS) is based on determining the distance of at least four GPS satellites to a receiver. For that purpose the so-called code measurements can be used, so that the position of the receiver can be determined up to several meters. In order to allow for navigation with centimeter accuracy, it is however required to use the very precise carrier phase measurements, since the phase of the carrier wave of the GPS signal can be measured up to several millimeters. Unfortunately, a receiver can only measure the phase of the carrier A¢â¬â that is the fraction of the wavelength at the time of arrival. The wavelength is approximately 20 centimeters, and it is not known how many complete waves have preceded the one at the time of arrival. Therefore the phase measurements are called ambiguous. And that brings the problem of 'integer ambiguity resolution'. The goal of this research has been to set up a procedure for ambiguity resolution, such that there is a sound theoretical foundation for the estimation as well as the validation procedure. Until now that was not the case. Different approaches have been considered, and it was shown that an optimal method can be set up, based on the new principle of Integer Aperture estimation. But there are also alternative methods, which are computationally more attractive, and for which it has been shown that their solution is close to optimal. Furthermore, it has been shown that the principle of Integer Aperture estimation gives a theoretical foundation for the traditional validation procedures, as used until now. The result of this research is, that there is now a complete theory available, which gives a solution to the problem of integer ambiguity resolution. This allows for the first time to make inferences on the statistical reliability of the estimated ambiguities. This is an important step, since for many applications not only precision but also reliability is a very important measure in order to decide whether or not one can safely use the navigation system.

/pdf/the-gnss-integer-ambiguities-estimation-and-validation-34aaxqz0e0.pdf

The GNSS integer ambiguities: Estimation and validation

The performance of the popular ambiguity ratio test is analyzed. Based on experimental and simulated data, it is demonstrated that the current usage of the ratio test with fixed critical value is not sustainable in light of the enhanced variability that future global navigation satellite system (GNSS) ambiguity resolution will bring. As its replacement, the model-driven ratio test with fixed failure rate is proposed. The characteristics of this fixed-failure rate ratio test are described, and a performance analysis is given. The relation between its critical value and various GNSS model parameters is also studied. Finally, a procedure is presented for the creation of fixed failure rate look-up tables for the critical values of the ratio test.

The ratio test for future GNSS ambiguity resolution

Integer carrier phase ambiguity resolution is the key to fast and high-precision global navigation satellite system (GNSS) positioning and application Apart from integer estimation, also acceptanc

The GNSS ambiguity ratio-test revisited: a better way of using it

Integer carrier phase ambiguity resolution is the process of resolving unknown cycle ambiguities of doubledifferenced carrier phase data as integers, and it is a prerequisite for rapid and high-precision global navigation satellite system positioning and navigation. Besides integer estimation, integer ambiguity resolution also involves validation of the integer estimates. In this contribution a new ambiguity resolution method is presented, based on the class of integer aperture estimators, which for the first time reveals an overall approach to the combined problem of integer estimation and validation. Furthermore, it is shown how the different discrimination tests that are currently in use in practice can be cast into the framework of the new approach.

/pdf/new-global-navigation-satellite-system-ambiguity-resolution-yqicyxk89u.pdf

New Global Navigation Satellite System Ambiguity Resolution Method Compared to Existing Approaches

The problem of integer estimation has drawn a lot of attention in the past decade, and is now often considered solved. However, a parameter resolution theory cannot be considered complete without rigorous measures for validating the parameter solution.

Sandra Verhagen

Papers

The GNSS integer ambiguities: Estimation and validation

The ratio test for future GNSS ambiguity resolution

The GNSS ambiguity ratio-test revisited: a better way of using it

New Global Navigation Satellite System Ambiguity Resolution Method Compared to Existing Approaches

Integer ambiguity validation: an open problem?