1. GNSS Basics

2. Objective of Training Course Outline: A. GPS basics B. GNSS basics
C. SBAS
D. GBAS
E. NTRIP
F. Cell vs. Radio
G. Guidance performance
H. Post class test

3. Acronyms GPS – Global Positioning System (USA)
GNSS – Global Navigation Satellite System
Encompasses all signals
DGPS – Differential Global Positioning System
RTK – Real Time Kinematic
CORS – Continuous Operating Reference Station
NTRIP – Network Transport of RTCM via Internet Protocol
VRS – Virtual Reference Station
WAAS – Wide Area Augmentation System

4. What is GNSS? Encompasses all satellite navigation sources
GPS (USA) – 32 current
GLONASS (Russian Federation) – 29 current
Galileo (European Union) – 4 current, 30 planned
COMPASS/BeiDou (China) – 16 current (basic regional service in China currently available, expanding to regional Asia/Pacific offering in next 2 years)
WAAS/EGNOS/MSAS
OMNISTAR®
Note: as of June 6, 2013

5. What is GPS? GPS = The Global Positioning System
A collection of a satellites
Minimum of 24 satellites, 32 in orbit
Provide accurate position worldwide
Backbone of today’s technology
Orbit at 12,550miles (20,200km)
Copied from “GPS Navstar User’s Overview” prepared by GPS Joint Program Office, 1984

6. Why GPS? Effective tool Provides accurate positioning Free
Available 24/7/365

7. Who Can Use GPS? Operated by US Air Force Paid for by US taxpayers
Free of charge
Available Worldwide

8. How Does GPS Work? Satellites used as reference to calculate position
GPS receiver times radio signal from satellites
Uses time delay to measure distance to satellite
Requires 4 satellites for 3 dimensional position
Latitude, Longitude, and Altitude

9. How Does GPS Work?
GPS Satellites have very expensive, very accurate atomic clocks
Accurate to Hz
All GPS satellites send a “Tick” at the same time
GPS receivers have cheaper, less accurate, but consistent, quartz clocks
The receiver can “hear” the “ticks” from each of the satellites
The “ticks” are delayed from each satellite depending on how far away they are from the GPS receiver
The GPS receiver calculates how long the signal is delayed from each satellite

10. How to Measure Time Psuedo Random Code
Receiver “syncs” code and determines lag time.
Lag Time

11. How Does GPS Work? How far away from the storm are we?
See lightning
Count the number of seconds until you hear thunder
Divide by 5
Estimates the distance from the storm
Distance = Velocity X Time
Speed
Speed of light is 186,282 miles/second (300,000km/sec)
Time
GPS receiver has calculated how long each signal from each satellite is delayed
Receiver measures delays to within a few billionths of a second
Equivalent to a few feet (1-2m) at the speed of light

12. How Does GPS Work?

13. GPS Signals L1 L2 1575.42 MHz 1227.6 MHz L1 L2 Wavelength 19 cm 24 cm
Code
C/A P(y)
P (y)
Message
Navigation L1
MHz
MHz L2

14. GNSS Error Sources Orbit Error Satellite Clock Error Îonosphere
Troposphere
Receiver Clock Error
Multipath

15. GNSS Positioning

16. Satellite Position Matters
DOP – Dilution of Precision
Spread out = low DOP (good)

17. Satellite Position Matters
Poor VDOP
Bunched up = High VDOP (bad)

18. Satellite Position Matters
Poor HDOP
Low Horizon = High HDOP (bad)

19. Satellite Visibility

20. GPS Satellite Visibility

21. GPS + GLONASS Satellite Visibility

22. GPS Satellite Visibility
5° Elevation
20° Elevation

23. GPS + GLONASS Satellite Visibility
5° Elevation
20° Elevation

24. Trimble Planning Software

25. Resources Trimble Planning Software – on laptop
Requires updated almanac
Trimble Planning Software – online
Space Weather and Satellite Update

26. So when do I need GLONASS?
Multiple GPS losses during the day
Operate around trees and obstacles
Require high elevation mask
Require reduced DOP
To reduce convergence time
Others

27. How do I get GLONASS? Capable receiver OmniSTAR G2 CenterPoint RTX
RTK with GLONASS capable base station

28. GPS Accuracy Autonomous GPS accurate to 30ft (10m)
Increase accuracy with Differential GPS (DGPS)
Types of DGPS
Space Based Augmentation System (SBAS)
WAAS, EGNOS, OMNISTAR®, RTX, John Deere StarFireTM
Ground Based Augmentation System (GBAS)
RTK, CORS, NTRIP, Trimble CenterPointTM VRS, TopCon TopNet, Leica
Look at each in detail

29. DGPS Measuring Accuracy
Dynamic (pass to pass) – 15 minutes
Static (repeatable) – >24 hours
Repeatable performance, playing with statistics
1 Sigma – 66%
2 Sigma – 95%
Trimble quotes at 2 Sigma

30. DGPS DGPS reference station measures GPS signal error
Compiles correction message
Broadcasts correction from ground station or satellite
Mobile receiver uses correction to compute position

31. WAAS/EGNOS

32. The Origins of WAAS
The Federal Aviation Administration (FAA) and the Department of Transportation (DOT) are developing WAAS for use in precision flight approaches.
WAAS satellite coverage only available in North America.
There are no ground reference stations in South America
Even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit.
Other governments are developing similar satellite-based differential systems.
Asia: Japanese Multi-Functional Satellite Augmentation System (MSAS)
Europe:Euro Geo-stationary Navigation Overlay Service (EGNOS).

33. How Does WAAS/EGNOS Work?
WAAS Satellite

34. North America WAAS

35. WAAS - Current Status TeleSat CRE107º W PRN 138 (Active 7/11/07)
Inmarsat AMR 98º W PRN 133 (Active Nov 2010)
Intelsat CRW 133º W PRN 135 (Active 11/9/06)

36. EGNOS/Galileo

37. RangePoint™ RTX™

38. What is RangePoint™ RTX™ ?
RangePoint™ RTX™ is a global, satellite-delivered correction service for broad-accuracy applications exclusive to Trimble GNSS receivers
Features
15cm (6-inch) pass-to-pass accuracy
50cm (20-inch) repeatable accuracy
Supports GPS, GLONASS
Global coverage area
1-5 minute convergence
Customer Activated

39. Target Market
Precision Agriculture customers that require reliable 6”/15 cm pass-to-pass accuracy
Entry-level customers that are interested in more positioning reliability from extra satellite constellations
Customers currently using WAAS, EGNOS, or Autonomous corrections
Customer-types currently buying competitor DGPS-level guidance in regions where no other entry-level, “free” service exists
Customers located across the globe

40. OMNISTAR HP/XP/G2

41. OMNISTAR HP / XP / G2
OmniSTAR is a dual frequency (L1/L2) GPS augmentation service that can measure the true Ionospheric error at the reference station and user location, substantially eliminating this effect in positioning accuracy.
Utilizes a Convergence process to develop a positional solution.
Requires minutes to reach 30cm (11.8”) estimated accuracy.
Requires at least minutes to full convergence.
First Convergence after new subscription may take 45 minutes
Convergence starts over after a power cycle.

42. OMNISTAR Convergence Horizontal Displacement Vs. Time
50cm (19.7 inches)
30cm (11.8 inches)
Meters
The position eventually reaches a point where the system is incapable of improving.

43. OMNISTAR XP, G2, and HP
OMNISTAR XP inch pass to pass accuracy Long term (Static) accuracy is +/ in (20cm) Available worldwide XP can go 120 seconds without update from OMNISTAR 3 day trials available OMNISTAR G2 GNSS Uses both GPS and GLONASS satellites, better coverage around trees, and faster convergence OMNISTAR HP 2- 4 inch pass to pass accuracy Long term (Static) accuracy is +/ in (10 cm) Available in most land areas - Uses the 4 closest OMNISTAR Reference stations. HP can go 60 seconds without update from OMNISTAR

44. RTX Fast Restart Allows instantaneous re-convergence
After any period of time
Based on previous position solution

45. SBAS Possible Problems
Shadow effect from South facing obstructions

46. CenterPoint™ RTX™

47. Convergence Times of RTX
Two types:
Fast Convergence < 1 min
Standard Convergence < 30 min
Standard Convergence
Standard receiver convergence time varies based on:
GNSS constellation health
Multipath
Proximity to obstructions
Receivers can converge to:
30 cm position in ~10 minutes
20 cm in 15 minutes
10 cm in 30 minutes
Full accuracy (3.8cm) in < 30 minutes

48. North America RTX Fast Coverage

49. Coverage Map for DCM-300 Modem

50. Coverage Map via Satellite

51. RTX Beams

52. RTK / CORS / CenterPoint VRS™ Real Time Kinematics

53. RTK Correction via Radio
GPS Signal
Correction Signal over radio
Rover
Base Station

54. Tracking only GPS satellites
RTK Operation Modes:
Tracking only GPS satellites
Corrections from Base Station received- Initialization started
Initialization Complete – typically less than 2 min after first correction received
Autonomous
RTK Float
RTK Fix

55. RTK Range vs. Radio Range
8 Mile radius will provide Sub-inch accuracy
1cm + 1ppm baseline distance
Average base station covers 100,000 acres
Coverage area may have to be supplemented with Repeaters in order to get range, depending on terrain

56. 8 Mile Range Explained RTK Accuracy Green paint won’t resolve this
At base station
10 mm + 1 ppm = mm
.39 inches
At 10 km (6 miles) from base station
10 mm + 1 ppm or 10 mm + 10 mm = 20 mm
0.79 inches
At 20 km (12 miles) from base station
10 mm + 1 ppm or 10 mm + 20 mm = 30 mm
1.18 inches
At 30 km (18 miles) from base station
10 mm + 1 ppm or 10 mm + 30 mm = 40 mm
1.57 inches
Green paint won’t resolve this

57. AgGPS 542 GNSS Base 220 channel receiver
GLONASS standard on all configurations
Integrated 900 or 450 MHz Radio
Illuminated front display
L2C & L5 GPS support
Galileo compatible in advance

58. Base Station – Rules to Follow
Location, location, location
Consider obstacles
Trees
Buildings
Terrain
View of sky
Desire for repeatability
Solid structure
Wind impact
Frost impact
Weight/load impact

59. Radio Range Dependent on Antenna height Antenna type Antenna gain
Radio wattage
Terrain
Desire for repeatability
Rover antenna
Rover location

60. Impact of Higher Gain 2 km
Normal Beam
High Gain
2 km

61. 900MHz vs. 400MHz 900 Pros 900 Cons Common in NA and AUS
Free, no subscription
Low power, 1 Watt
Low heat
Little interference
900 Cons
Absorbed by foliage
Limited range
Low saturation

62. 900MHz vs. 400MHz 400 Pros 400 Cons Required in EU Penetrates trees
Up to 10 Watts
High saturation
400 Cons
Requires license
Power consumption
High heat
Interference

63. Good or Bad? X X X X X

64. Good or Bad? X X

65. Trimble SNB900 Repeater Radio
LED front panel display
Simple user interface
Internal battery good for 10 hours
Spread spectrum 900MHz radio
License free operation in US, Canada, Australia and New Zealand

66. Repeater Usage

67. Repeater Usage

68. What is CenterPoint VRS?
CenterPoint VRS = Virtual Reference Station
A Trimble proprietary cellular RTK system.
Cellular RTK is similar to traditional RTK systems in that a base station receiver and vehicle (rover) receiver are required for a complete solution. What is different is how the corrections are physically delivered to the vehicle.
To receive a cellular RTK correction two separate infrastructure components must be in place:
Must have regionally available cellular RTK network: either VRS or CORS.
Reliable cell phone connection to the internet.

69. Cellular vs. Radio Link
Cellular RTK customer requires two-way cellular data connection with local cellular carrier to operate autoguidance system.
Rover sends its position via DCM-300 modem (installed on the vehicle) to the RTK corrections server.
Server receives user's position data from rover and calculates the appropriate corrections for that location.
For a CORS network, the corrections are generated at the nearest or specified base station.
Cellular RTK requires a continuous data connection via cell modem.
If cellular connection is lost, the rover loses corrections.
Cellular signal availability is affected by the local cell coverage and peak cell network usage (voice typically has priority over data).
With traditional RTK Arrays, correction is delivered directly from a local base station via a dedicated radio link (450mhz or 900mhz) to the vehicle.

70. CORS CORS = Continually Operating Reference Stations
Federally-maintained community GPS base stations that provide carrier phase and code range measurements for real-time and post-processing differential correction.
Functions to assure that all navigation and positioning in the US is performed using a common coordinate system.
Uses software and a centralized server to model for error, but uses single baseline distance from nearest CORS base.

71. CORS vs. Network RTK
In network RTK, a service provider supports a network of reference stations distributed across a specific area.
Reference stations provide GPS data over Internet to a central NTRIP server.
GPS corrections are calculated on this NTRIP server for a customer’s specific location.
CORS is similar to network RTK, but the reference stations are not networked together.
User is linked to the closest CORS site, and the user's accuracy depends on their distance from the site, just like traditional, single baseline RTK.
Customers using CORS must switch base stations (mount points) as they move through the network.

72. Single Baseline RTK (450 mhz UHF, 900 mhz, or internet-based CORS) compared to a network of reference stations like VRS.

73. Trimble RTK xFill™

74. Trimble RTK xFill™
RTX™ technology used to extend RTK fixed state for up to 20 minutes
Designed to keep users operating during times of RTK comms interruptions
Radio Link Blockage
Weak Radio Link
Busy Cellular Network
Poor Cellular Signal
Precision degrades at 0.7cm per minute*

75. xFill Example

76. Auto Guidance – DGPS (3 Feet)
WAAS/EGNOS
Broad acre seeding
Spraying

77. Auto Guidance – DGPS (3 Feet)
WAAS/EGNOS
Tillage/Fertilization

78. Auto Guidance - DGPS (<12”)
XP/HP/G2
Row marker Replacement

79. Auto Guidance - RTK (Sub-Inch)
Repeatability – Strip Tillage

80. Auto Guidance - RTK (Sub-Inch)
Accuracy – Seed Bed Preparation
Drip Irrigation tape

81. Correction Services Portfolio
Accuracy
CenterPoint RTX
CenterPoint RTK/VRS
OmniSTAR XP,G2,HP
<1”/2.5 cm
CenterPoint RTX
CenterPoint RTK/VRS
OmniSTAR XP,G2,HP
<1”/2.5 cm
<1.5”/3.8 cm
<1.5”/3.8 cm
3-4”/
8-10 cm
3-4”/
8-10 cm
6”/15 cm
pass-to-pass
RangePoint RTX
SBAS/WAAS/EGNOS/OmniSTAR VBS
40”/1 m

82. Guidance in Agriculture
Factors affecting performance
Satellite Constellation & Geometry
Atmospheric Conditions- ionosphere, troposphere, solar flare activity
GPS Receiver & Antenna Quality
Correction Sources
Multi-path
Filtering & Smoothing
Terrain Compensation for Pitch, Roll, and Yaw
Guidance System Settings – Calibration
Vehicle setup/configuration
Tractor weight
Steering linkage
Hydraulic flow
Tire pressure

83. Questions?