GPS/GALILEO/GLONASS Hybrid Satellite Constellation Simulator – GPS Constellation Validation and Analysis A. Constantinescu, R. Jr. Landry Ecole de technologie supérieure, Montréal, Canada GPS/Galileo/GLONASS Satellite Constellation simulator, BIOGRAPHY the so-called project titled Software Defined Simulator Aurelian Constantinescu received an Aerospace (SDS). Engineering Degree from the Polytechnic University of Bucharest (Romania) in 1992. He has received also a The development of an accurate hybrid constellation Master’s Degree in 1993 and a PhD in 2001 in Control simulator is a key point in any GNSS Signal Generator from the Polytechnic National Institute of Grenoble simulator. The use of a Radio Frequency (RF) or (France). He worked as a post-doctoral researcher at the Intermediate Frequency (IF) signal generator simulator Launch Division of the French Space Agency (CNES) in for performance testing of GNSS receivers is obvious, Evry (France), on the control of conventional launchers. allowing a repeatable and a completely controlled test Since 2002 he is a post-doctoral researcher in the environment which ensures the efficiency of the Electrical Engineering Department of Ecole de development of any GNSS receiver. The use of such a technologie superieure (ETS), Montreal (Canada). His simulator allows also characterizing the receiver’s research interests in the last 2 years include Global behavior in unusual or unexpected conditions. Navigation Satellite Systems (GPS and Galileo) and The SDS project results showing the capabilities of the Indoor Positioning Systems. hybrid GNSS constellation are presented, such as René Jr. Landry received a PhD degree at SupAéro / Paul- worldwide simulated availability and accuracy for various Sabatier University and a Post Doc in Space Science at GPS, Galileo and GLONASS possible combinations. the National French Space Industry (CNES), both at Spatial and temporal performances are presented and Toulouse, France, in 1997 and 1998 respectively. Since compared. The following parameters are considered in 1999, Professor Landry is involved in receiver design and order to evaluate the performance of the hybrid GNSS the problem of navigation and telecommunication signal navigation system compared to different satellite interferences for the Canadian Navigation and constellations combinations: visibility and various Communication Industries. One of his major interest Dilution Of Precision (DOP) parameters. concerns the development of New Innovative Mitigation In this paper, the validation of the GPS satellite Techniques for GNSS Receiver Robustness Design constellation is emphasized, the generation of the GPS including those of electronic Inertial Navigation System constellation being done using either almanacs or based on low cost MEMS. He is actually working on broadcast ephemeris. In order to do so, comparisons with several digital signal processing applications in Anti- results obtained either from other existing satellite Jamming, receiver design, Indoor Navigation and Inertial constellation simulators, from real GPS receivers or from Navigation Systems. precise ephemeris are done. Different parameters defining the satellite constellation configurations are considered ABSTRACT for the validation, such as coordinates of the satellites, The advent of the European Galileo navigation system, elevation, azimuth and visibility. the modernization of the American GPS and the update of the Russian GLONASS satellite constellation will lead to 1. INTRODUCTION an improved Global Navigation Satellite System (GNSS). The performance of any GNSS is characterized by its Availability, reliability and accuracy are key parameters availability, accuracy, continuity and integrity. For in evaluating GNSS performance. In order to completely example, the existing GPS constellation does not provide understand the benefits that will bring Galileo, and the the accuracy and reliability necessary for some update of GLONASS, it is necessary to evaluate the applications. performance improvement using a hybrid ION 61st Annual Meeting/ The MITRE Corporation & Draper Laboratory, 27-29 June 2005, Cambridge, MA 733 With a 27-satellite constellation and multiple open and the SDS simulator are presented. Spatial and temporal encrypted signals, Galileo is designed to provide Europe results are presented and compared, for only GPS, Galileo with a GNSS capability similar to that available from the or GLONASS and for several possible combinations, in U.S. Global Positioning System. The modernization of order to emphasize the interest of using a hybrid GNSS GPS, the advent of the European Galileo system and the constellation. GPS almanac, broadcast and precise update of GLONASS will lead to a multi frequency civil ephemeris are also presented. The results obtained are GNSS. The use of Galileo with the actual or the presented, analyzed and validated. modernized GPS and the updated GLONASS systems A number of papers have been dedicated to the study of will increase the number of GNSS navigation satellites the hybrid GPS/Galileo constellations and to the gain currently available and will provide better accuracy, obtained using the Galileo satellite navigation system ([3- availability and reliability than those obtained with only 5]). A study of hybrid modernized GPS and Galileo GPS, only Galileo or only GLONASS systems. number of satellites and satellite geometry systems is Three of the main advantages of the deployment of a presented in [6]. Availability, accuracy and reliability for hybrid GNSS constellation are greater availability, a hybrid GPS/Galileo system are compared to only GPS integrity and accuracy. and Galileo by means of HDOP and VDOP in [7]. This paper presents the performance of the hybrid Complete GNSS simulators are also used in order to GPS/Galileo/GLONASS satellite navigation system evaluate the gain of the Galileo system compared to the compared to those of various combinations of existing GPS (see [8, 9]). GPS/Galileo/GLONASS. The main goal of the paper is The paper is organized as following: In Section 2 the the validation of the SDS GPS satellite constellation GPS, Galileo and GLONASS constellation parameters are simulator. The generation of the GPS is implemented by introduced. Section 3 is dedicated to some of the using either GPS almanac or broadcast ephemeris data. In performance evaluation parameters considered in the SDS order to validate the generation of the GPS satellite simulator (availability, accuracy). Section 4 is dedicated constellation, the results obtained are first compared to to the presentation of the SDS simulator, while the those generated by using other simulators already almanac and ephemeris data used in the GPS simulator existent, such as the Chinalake interactive satellite are presented in Section 5. Some spatial and temporal predictor (see [1]). Visibility, elevation and azimuth results obtained with the SDS simulator are presented in parameters available from the Chinalake simulator are Section 6. The main part of the paper is presented in used for performance evaluation. As the positions of the Section 7 and it concerns the GPS constellation satellites are not provided by the Chinalake simulator, real validation. The last section is dedicated to some data from a GPS receiver has been used, which allowed conclusions and remarks. validating the SDN GPS constellation simulator from the 2. GNSS CONSTELLATIONS PARAMETERS satellites positions point of view. The GPS satellites positions have been also compared to precise ephemeris 2.1. GPS Constellation Parameters data, which has allowed us to validate the SDS simulator. The GPS constellation comprises 24 satellites situated on The results are presented and analyzed afterwards. nearly circular orbits, with a radius of 26561.75 km and a The latest available values of RAAN, mean anomalies period of 11 h 58 min (half of a mean sidereal day). The and semi-major axis of the orbit have been considered for satellites are situated on 6 orbital planes (named A the Galileo satellite navigation system, even if the through F) inclined at 55° relative to the equatorial plane problem of the initial offsets of GPS and Galileo orbital (4 satellites per orbit, named 1 through 4). The satellite planes is still open. Previous results obtained with a planes are equally spaced in longitude relative to the GPS/Galileo version of the simulator may be found in [2]. vernal equinox, but the satellites themselves in each plane are not equally spaced. The GPS constellation parameters The SDS simulator is a powerful tool which gives access may be found in [10, 11] and additional information in to any computed variables, such as availability, satellites [10, 12-14]. positions, receiver trajectory, elevation, azimuth, GDOP, PDOP, HDOP, VDOP and TDOP values, Doppler 2.2. Galileo Constellation Parameters frequency, etc. The simulator gives to the user the The space segment of Galileo consists of 27 Mean Earth possibility to parameterize the simulation, to choose the Orbiting (MEO) satellites, distributed over 3 orbital results desired (spatial, temporal), as well as to choose the planes (named A through C) with a period of 14 h 21 min position (fixed) or a desired trajectory for the receiver. (3/5 of the mean sidereal day). There are 9 satellites per In this paper, the constellations parameters of the GPS, orbit, named 1 through 9. The Galileo constellation Galileo and GLONASS systems are briefly reviewed, as parameters are presented in Table 1. No information has well