Global Navigation Satellite Systems gnss about Glonass, gps modernization and Galileo

Global Navigation Satellite Systems GNSS

• About Glonass, GPS Modernization and Galileo

Global Navigation Satellite Systems

Introduction to Glonass

• GLONASS

• Russian satellite navigation system
• positioning by measuring distances to satellites with known positions
• Not operational (anymore)
• first launch in 1982 (GPS in 1978)
• complete constellation in 1996 (GPS in 1993)
• present constellation (14) satellites (GPS 28 satellites)
• Modernization plan:
• Modernized Glonass-M and new Glonass-K
• next launch: 25 December 2005 (3 Satellites)
• 18 operational satellites in 2007

GLONASS satellite constellation

GLONASS-GPS integration (1)

• GLONASS+GPS = 44 navigation satellites

• >= 8 satellites @ 15+ degrees elevation

• (GPS >= 4 satellites)

GLONASS-GPS Integration (2)

• Visibility of satellites

• Delft

• 06/11/1998

• 0 deg. cut off

GLONASS-GPS Integration (3)

• better precision for single point positioning
• lower update rate for DGLONASS corrections

GLONASS-GPS Integration (4)

• Single point positioning

• 1000 epochs

• GPS 10 SVs

• GLONASS 7 SVs

GLONASS-GPS integration (problems)

• Different definition of time

• GLONASS and GPS system time do not match

GLONASS Space Segment (1)

• GLONASS GPS

• 24 satellites 24

• 3 orbit planes 6

• 64,8° inclination 55°

• 11h16m orbit period 11h58m

GLONASS Space Segment (2)

GLONASS Control Segment (1)

• Main task

• predict satellite orbits and clock behavior

• Components

• System Control Center

• planning and coordination of activities

• Phase Control System

• monitor satellite clocks by comparing satellite signals with system time

• Telemetry, Tracking and Command Stations

• computation of satellite orbits by radar distance measurement,

• communication, control segment for the satellites,

• monitoring of satellite signals

GLONASS Control Segment (2)

• Telemetry, Tracking and Command stations

• Because of the geographic location of TT&C stations it

• is system integrity is difficult to maintain

GLONASS Control Segment (3)

GLONASS User Segment

• development of user segment

• GLONASS in 1993 released for international civil use
• “all-in-view” single frequency receivers available since 1996
• “all-in-view” dual frequency receivers available since 1998

• receiver manufacturers

• Ashtech, JPS/TPS, 3S Navigation (single & dual freq.)
• Novatel, MAN Technologie, Zeiss, Dasa (single freq.)

GLONASS signal structure (1)

• Components of GLONASS and GPS signals

• carrier
• two carriers (L1- and L2-frequency band)
• PRN-code bi-phase modulation
• two PRN-code modulations (C/A- and P-code)
• data modulation
• two types of data: satellite orbit en clock & system almanac

GLONASS signal structure (2)

• Difference GLONASS and GPS signals

• carrier + PRN-code modulation

• also: GPS PRN-codes are transmitted with a higher chip-rate than GLONASS PRN-codes

GLONASS signal structure (3)

• carrier frequencies

• k : channel number

• 1998 : k= 1 …24

• >2005 : k= -7…4

• (some) anti-podale satellites use the same channel

GLONASS functional/stochastical model (1)

• using different carrier frequencies results in

• hardware delays that do not cancel out

• phase ambiguities cannot be determined directly

• important for relative positioning

• lower chip-rate for the PRN-code results in

• lower precision (higher standard.dev.) for the observations

• But, GLONASS has no S/A or A-S!

GLONASS functional/stochastical model (2)

• (simplified) observation equations

GLONASS functional/stochastical model (3)

• Double Difference pseudo range

• 3500 C/A code pseudo ranges measured on a zero baseline

• Double Difference : differences between receivers and satellites

• elimination of clock errors

• Zero baseline : two receivers connected to the same antenna

• elimination of geometry

GLONASS functional/stochastical model (4)

• Double Difference phase

• 3500 phase measurements on a zero baseline

• mean for phase in cycles

• correction clock errors with clock estimates in double diff.

• standard deviation for phase in meters

• elimination clock errors in double differences

IGEX-98 / IGLOS (1)

• International GLONASS-GPS network

IGEX-98 / IGLOS (2)

IGEX-98 / IGLOS (3)

IGEX-98 / IGLOS (4)

IGEX-98 / IGLOS (5)

Global Positioning System (GPS) Modernization

GPS Modernization Goals

• GPS signal upgrade

• Military M-code
• C/A code on L2
• New civil signal on L5
• More signal power

• Backward compatibility

• Keep the GPS constellation healthy

• Ensure the right strategy to design and field the best GPS System for the user’s needs in the long term

Modernized Signal Evolution

GPS satellites

Launch schedule for GPS satellites

Availability of new GPS signals

Block IIR- Modified Satellites

Block IIF Satellites

GPS Operational Control Segment

GPS III Program

The 4 GALILEO arguments

GALILEO for the benefits of the Citizens

Service Definition Study

Service Definition from Application Performance

GALILEO Services

Galileo added value

• Under control of civilian authorities

• Technological improvements

• New technology (improved signals)
• More frequencies and signals
• More ground stations for tracking and orbit determination
• Better choice of satellite orbits

• Integrity service for “safety of life” applications

• Integration (“interoperable”) with GPS

• combined GPS and Galileo receivers
• twice the number of satellites
•  this is the probably the single most important contribution to accuracy and reliability

Galileo status

• Official go-ahead on 26 March 2002

• Galileo System Test Bed (GSTB-V1) delivered in 2004

• Implementation Galileo ground segment using GPS satellites
• 10x better than GPS

• First experimental satellite in 2005 (GSTB-V2) Launch 28 Dec 2005

• First four “operational” satellites in 2006-2007 (IOV)

• Operational in 2009-2010 (officially 2008)

• EGNOS (GPS/GLONASS Integrity Service) on geostationairy satellites

• EGNOS operational in 2005 (slight delay; wind-up, operational 2006)

• EGNOS integrated with GALILEO starting 2008 (GEO service available until 2015)

GPS versus Galileo

• GPS Satellites:

• 24 nominal (27 operational)
• circular orbits 26,561 km
• Orbit period 11h58m (1/2)
• inclination 550 , 6 orbit planes

• GPS Signals (3+5):

• Two frequencies (L1=1575.42 MHz and L2=1227.60 MHz)
• Civil signal on L1 (C/A)
• Military signals on L1 and L2 (P(Y))
• Planned modernisation (+5):
• Third frequency (L5=1176.45 MHz)
• New civil signals on L2 and L5
• Plus two new military signals

GNSS frequency allocations

GPS Signals

GALILEO Signals

Linear combinations (GPS)

Linear combinations (GALILEO)

GPS/Galileo ambiguity resolution

Impact of GALILEO & GPS+

• Individually:

• Improved observations, especially on L5/E5

• Improved ionosphere free linear combinations

• Use of L5/E5 instead of L2: 2.98  2.59 (24%)
• Three frequencies: 2.98  2.55/2.50 (27%/30%)

• Third frequency for ambiguity resolution

• When combined:

• More and better distributed observations

• Will benefit ambiguity resolution
• Will benefit height, zenith delay and clock estimation

• Tested in a simulation experiment

Simulation Experiment

Number of Satellites in View

Standard deviation (Kinematic)

Standard deviation (Static)

Standard deviation ZTD

Conclusion GPS + GALILEO

• Improved measurements (code & phase) for both GPS and GALILEO

• Improved ionosphere free linear combinations

• Use of L5/E5 instead of L2: 2.98  2.59 (24%)
• Three frequencies: 2.98  2.55/2.50 (27%/30%)

• Improved height when used together

• Kinematic (moving) receiver 73.1  35.7 mm (76%)
• Static receiver 2.9  1.7 mm (65%)

• Improved zenith delays when used together

• Kinematic (moving) receiver 19.1  7.9 mm (83%)
• Static receiver 4.5  2.9 mm (58%)