The Impact of Current and Future Global Navigation Satellite Systems on Precise Carrier Phase Positioning

Transcription

1 The Impact of Current and Future Global Navigation Satellite Systems on Precise Carrier Phase Positioning R.Murat Demirer R.Murat Demirer( CORS Project) 1

2 Potential Applications of the Global Positioning Systems R.Murat Demirer ( CORS Project) 2

3 GPS R.Murat Demirer ( CORS Project) 3

4 Functions & Products of the GPS Segments R.Murat Demirer ( CORS Project) 4

5 The GPS Satellite Constellation R.Murat Demirer ( CORS Project) 5

6 The GNSS (Global Navigation Satellite System) From ancient times people's effort for positioning and navigation has never been stopped Currently there are two GNSS systems in operation: the United States' Global Positioning System (GPS) and the Russian's Global Orbiting Navigation Satellite System (GLONASS) Europe's Gallieosystem, another promising GNSS, will reach its full operational capacity in 2010 R.Murat Demirer ( CORS Project) 6

7 Principles of RTK Satellite Navigation Navigation -is a process of determination Where I am now? -> current position and velocity Radionavigation-user (passive) receives signals transmitted by satellites (GPS, GLONASS, Galileo) R.Murat Demirer ( CORS Project) 7

8 Main Characteristics of GPS, GLONASS & Galileo R.Murat Demirer ( CORS Project) 8

9 The main idea of Navigation: triangulation Different signal structure, different carrier frequency, different satellite orbit, they share the similar idea to locate the user: triangulation. The theory of triangulation is simple: as long as the receiver can measure the radial distance between itself and several radio transmitter, and the position of all the transmitters, the user's location can be determined by the intersection of all the spheres centered the transmitters. R.Murat Demirer ( CORS Project) 9

10 How GPS works. The idea of the GPS system is that the user is located at the intersection of the four spheres A b s o l u t e P o s i t i o n i n g G e o m e t r i c P o s i t i o n f r o m R a n g e O b s e r v a t i o n s R.Murat Demirer ( CORS Project) 10

11 Main features Each satellite broadcasts signals on two carriers: the major carrier L1 with frequency f1 = MHz, and the secondary carrier L2 with frequency f2 = MHz. Two pseudorandom noise (PRN) codes are modulated on the two base carriers. The first code is the coarse acquisition code (C/A code) which is available for civilian use with the Standard Positioning Service (SPS). The second code is the precision code (P code or Y code) for military use and designated as the Precision Positioning Service (PPS). The P-code is modulated on both carriers L1 and L2, whereas the C/A code is modulated upon only L1. R.Murat Demirer ( CORS Project) 11

12 The three types of measurements can be obtained from GPS receivers based on the GPS signals Pseudo range Measurements: These are derived from the PRN codes Carrier Phase Measurements: These are obtained by measuring the phase of theincoming carrier (L1 and/or L2), and the range to a satellite can be computedby measuring an ambiguous number of cycles Doppler Measurements: The derivative of the carrier phase measurement is thedoppler shift due to the relative motion between the receiver and the GPS satellite R.Murat Demirer ( CORS Project) 12

13 GNSS Observations R.Murat Demirer ( CORS Project) 13

14 R.Murat Demirer ( CORS Project) 14

15 Distance Measurement Using GNSS 1. Satellite positions are known 2. Each satellite transmits a different code 3. Time measurements rely on an accurate time reference (clock) 4. Satellite and user clocks should be synchronized 5. The differences between generated and received codes corresponds to the time difference 6. Several error sources affect the measurement accuracy R.Murat Demirer ( CORS Project) 15

16 Schematic Presentation of GNSS Codes & Carrier R.Murat Demirer ( CORS Project) 16

17 The signals has three parts: Carrier wave with fl1 and fl2 Navigation Data (50 bps) Spreading Sequence R.Murat Demirer( CORS Project) 17

18 The GPS signal transmitted from the satellite can be modeled There are three component: C/A code on L1, P(Y) code on L1 and P(Y) code on L2 R.Murat Demirer ( CORS Project) 18

19 Comparison of the Present GPS Signals and the Post-Modernization GPS R.Murat Demirer ( CORS Project) 19

20 Signal transmitted from satellite k R.Murat Demirer ( CORS Project) 20

21 Generation of GPS Signals at the satellites R.Murat Demirer ( CORS Project) 21

22 C/A Code Generator R.Murat Demirer ( CORS Project) 22

23 Carrier Phase and Pseudo-range Measurement Pseudo-range measurement is noisy but unambiguous. The carrier phase measurement is the difference between the phases of the local generated carrier signal and the phase of the carrier from the input signal of each satellite. Carrier phase measurement is cleaner but ambiguous because it only contains the information of the change of the carrier cycles between the time that phase lock was achieved until the present time. R.Murat Demirer ( CORS Project) 23

24 Sources of Range Measurement Errors R.Murat Demirer ( CORS Project) 24

25 Measurement Simulation Diagram R.Murat Demirer ( CORS Project) 25

26 Simulation Approach R.Murat Demirer ( CORS Project) 26

27 The basic observation equations for GPS satellite positioning at pseudo range and carrier phase measurements from a receiver A to a GPS satellite ior k The geometrical range between satellite and receiver is computed as

28 Model equations GPS Carrier Phase measurements (Lachapelle 2003) R.Murat Demirer ( CORS Project) 28

29 The carrier phase based double difference observable in meters (Lachapelle 2003) R.Murat Demirer ( CORS Project) 29

30 R.Murat Demirer ( CORS Project) 30

31 Time scale representation of GNSSS 31 R.Murat Demirer ( CORS Project)

32 Linearization of observation Equation 32 Nonlinear term Linearization starts by finding an initial position for the receiver Earth(0,0,0) R.Murat Demirer ( CORS Project)

33 33 The partial derivatives in Taylor expansion Linearized observation equation where R.Murat Demirer ( CORS Project)

34 Using Least Squares Method 34 Observations: m 4 unique solution R.Murat Demirer ( CORS Project)

35 Kalman Filter Equations (from Brown et al. 1992) 35 A Kalman filter estimation algorithm has been used to estimate the unknown states in a sequential fashion Like standard least squares estimation, the Kalman filter is based on an optimality criterion of minimizing the squared estimation residuals. R.Murat Demirer ( CORS Project)

36 Kalman Filter Approach 36 Kalman Gain R.Murat Demirer ( CORS Project)

37 Keplerian Orbit Elements 37 GM= M 3 /s 2 R.Murat Demirer ( CORS Project)

38 Orbit Estimation Strategy 38 R.Murat Demirer ( CORS Project)

39 Ephemeris Parameters 39 R.Murat Demirer ( CORS Project)

40 40 Necessary variables for determining geometric coordinates of satellite k at t j R.Murat Demirer ( CORS Project)

41 Troposphericmodels According to Parkinson et al. (1995), simple troposphere models remove about 90% of the troposphere error on an undifferenced measurement. Some examples of effective troposphere models include the Saastamoinenmodel (Saastamoinen, 1972), the UNB3 model (Collins et al. 1996) and the Modified Hopfield Model (Goad et al. 1974), while mapping function can be found in Neill (1996), Lanyi(1984), and Ifadis(2000) R.Murat Demirer ( CORS Project) 41

42 Hopfield Model (total tropospheric error D at zenith) N Refractivity P pressure T.temperature 2-5 meters error at zenith 25 meters at low elevation R.Murat Demirer ( CORS Project) 42

43 TroposphericDelay versus Humidity for Satellites with 5 and 80 Degree Elevation Angles R.Murat Demirer ( CORS Project) 43

44 Ionosphere delay the ionosphere delay is treated as a state to be estimated. Since the ionosphere delay is highly correlated with the initial carrier phase ambiguity, a pseudo-observation is used to enable the ionosphere delay state to converge R.Murat Demirer ( CORS Project) 44

45 Ionosphericdelay R.Murat Demirer ( CORS Project) 45

46 GNSS User Range Error Budget R.Murat Demirer ( CORS Project) 46

47 Real Accuracy of Position Determination R.Murat Demirer ( CORS Project) 47

48 GNSS Positioning Accuracy R.Murat Demirer ( CORS Project) 48

49 GN S S E r r o r S o u r c e s R.Murat Demirer ( CORS Project) 49

50 GPS Modifications (GPS III) R.Murat Demirer ( CORS Project) 50

51 Why do We Need the Augmentations? R.Murat Demirer ( CORS Project) 51

52 Differential Navigation R.Murat Demirer ( CORS Project) 52

53 Comparison of Normal and Differential GNSS R.Murat Demirer ( CORS Project) 53

54 Potential Applications R.Murat Demirer ( CORS Project) 54

55 Galileo R.Murat Demirer ( CORS Project) 55

56 Galileo Signal Structure and Services ( Hein et al. 2002) R.Murat Demirer ( CORS Project) 56

57 Positioning Scenarios Galileo will also transmit freelyavailable satellite navigationsignals on three frequencies and is scheduled to be fully operational as early as 2008 (Wibberley, 2004) the impact that the new signals will have on precise kinematic positioning R.Murat Demirer ( CORS Project) 57

58 Galileo Services R.Murat Demirer ( CORS Project) 58

59 Potential Services of Galileo System R.Murat Demirer ( CORS Project) 59

60 GPS and Galileo Together Enhanced geometry of a combined GPS/Galileo system greatly improve the ability to estimate ionosphere delays quickly and precisely R.Murat Demirer ( CORS Project) 60

61 GPS and Galileo systems in an integrated manner The L1/E1 ( MHz) andl5/e5a ( MHz) frequency bands will be shared. This will allow the systems tobe used together because receiver manufacturers will be able to use the same receiverfront-ends for multiple signals. This will keep the cost of future dual-system receiverseconomically viable. However, the systems will remain autonomous by keeping the GPSand Galileo control segments completely separate R.Murat Demirer ( CORS Project) 61

62 Heterogeneous Double Differences Homogenous Double Differences R.Murat Demirer ( CORS Project) 62

63 PseudorangeMeasurement Covariance Matrix for GPS/Galileo Triple- Frequency Data R.Murat Demirer ( CORS Project) 63

64 Developing Near Real-Time Kinetic Algorithms for estimating accurate position using GPS carrier phase observations Tointroduce a new RTK mathematical model To develop real-time kinetic algorithms defined on a dynamical model (H) for increasing accuracy of coordinates of moving vehicle. To identify the relationship between problems sourced by orbit, ionosphore, troposphere as well as multipath (fading) and antenna phase center variations (z) on a dynamical model (RK) by competing with other estimators To develop new techniques that can be applied to a wide range of problems like Autonomous Helicopter Landing, missile navigation in the RK model. To evaluate performance of accuracy of centimeters of some duration of seconds R.Murat Demirer ( CORS Project) 64

65 Diagram of Finite-Difference Nonlinear Filtering The Ito equation characterizes how target states and their probability densities evolve in time due to deterministic and random target motion effects. R.Murat Demirer ( CORS Project) 65

66 What will be the goals with GPS and Galileo systems together in future? 1. To describe and demonstrate effective processing techniques for GNSS data from multiple systems and on multiple frequencies; 2. To show the impact that current and future GNSS signals will have on the ability to estimate ionosphere delays and GPS signal fading effects 3. To provide a realistic and quantitative analysis of the reliability of ambiguity resolution with current and future GNSS signals; 4. To elucidate the benefits of using linear combinations of GNSS data and to test various optimally chosen combinations for better accuracy for example dual-system scenario using triple-frequency GPS and triple-frequency Galileo measurements together; 5. To develop a realistic mathematical model for simulation of future GNSS measurements R.Murat Demirer ( CORS Project) 66

67 GPS Array Monitors Deformation of the Earths Crust Daniel Abrams Institution Name: University of Illinois at Urbana-Champaign The earths crust bends or deforms before it breaks, just as a stick bends before it breaks across your knee. When the earths crust breaks, it is called an earthquake. Deformation of the earth between earthquakes invisible to scientists Relative movements of less than 3mm between two points separated by hundreds of kilometers can now be measured by GPS. Networks of GPS stations currently monitor the relatively rapid movement of the earths plates and the slower deformations due to the interaction of two plates at their boundaries. The ability of GPS to measure both small and slow deformations naturally leads to its use in studying the problems of earthquakes and attendant seismic hazard. Preliminary results suggest that deformations may be occurring inside the seismic zone, and these deformations are consistent with the types expected based on the earthquake activity, models for stress Improvements in the measurement of this deformation over the next few years will help in developing better explanations for the causes of New Madrid earthquakes and will contribute to improvements in seismic hazard estimation. R.Murat Demirer ( CORS Project) 67

68 Seismic instrumentation network R.Murat Demirer ( CORS Project) 68

69 Defense Application A Block 50 F-16D of the Eglin based 46th Test Wing carrying a pair of EDGE test weapons during captive carry trials. One bomb is measuring its position using standard GPS, the other is using differential GPS updates datalinkedto the F-16 from a ground station, using an encrypted channel. The bomb using DGPS achieved accuracies as high as 3.5 ft in horizontal position (USAF). R.Murat Demirer ( CORS Project) 69