Present and Future Global Navigation Satellite Systems (GNSS)

Present and Future Global Navigation 

Satellite Systems (GNSS) 

Earth Observation with Satellite Positioning Techniques - Lecture 1 

GNSS Training 18-29 May 2009, GEO2TECDI, Bangkok, Thailand 

Hans van der Marel 

Edited and presented by Wim J.F. Simons 

Delft University of Technology 

Faculty of Aerospace Engineering 

The Netherlands 

1

Contents – Lecture 1 

Present and future Global Navigation Satellite Systems 

• Introduction to satellite navigation 

• GPS and GLONASS 

• GPS Modernization, Galileo, Compass, … 

• Basics of signal processing and the promises of new signals 

• Issues of accuracy, integrity, continuity and availability 

• GNSS augmentations 

• Present and future applications 

But not in 

this order 

2 

GEO2TECDI – Bangkok, May, 2009 – GNSS Lecture 2

Principle of Satellite navigation 

Satellite transmits: 

• Time code (atomic clock) *) 

• Message with position and 

satellite clock error 

Satellite 

Receiver computes: 

• time difference between 

satellite and receiver clock 

pseudo range 

• coordinates receiver (3) and 

receiver clock error (1) **) 

x s 

p s r 

e s r 

x r 

c dt r 

3 

Receiver 

*) GPS 

• 1 civilian signal (L1-C/A) 

• 2 military signals L1-P(Y), L2-P(Y) 

**) From 4 or more satellites 

Earth 


Standard GNSS Point Positioning Algorithm 

Wanted (4 unknown parameters): 

• receiver position (x,y,z) 

• receiver clock error (dt) 

Satellite 

Can be computed from: 

1. Measured pseudo-ranges on L1 *) 

e s r 

Receiver 

2. Broadcast ephemeredes (data message) 

x r 

satellite position and clock error 

ionospheric delay (for L1) 

Earth 

3. Tropospheric delay model 

*) We can only measure the distance to a satellite, not the 3-D vector! 

x s 

p s r 

c dt r 

4 

We need 4 or more satellites, more satellites is better (redundancy)! 

Least Squares Adjustment 


Global Navigation Satellite Systems 

GPS 

GLONASS 

Space Based Augmentation Systems: 

WAAS, EGNOS, MSAS, GAGAN, SDCM 

GALILEO 

IRNSS 

COMPASS 

QZSS 

5 


GPS: Present Status 

Signals: 

– Two frequencies (L1 and L2) 

– C/A-code on L1 

– P-code (encrypted) on L1 and L2 

Satellite constellation: 

– 24 nominal satellites (28 operational) 

– Block II/IIA/IIR satellites (until 2014) 

– Orbital period 11 hour 58 min 

– 6 orbital planes, 55 o inclination 

– 20,200 km altitude 

6 


NAVSTAR GPS Block II Satellite 

solar panels 

antenna for ground 

control 

array of 12 helix 

antennas 

7 


NAVSTAR GPS Block IIR and IIF 

satellites Block IIR 

Block IIF 

> 2009? 

Last 8 of the IIR series retrofitted 

with CS code on L2; First 

retrofitted IIR launched 

December 2005 

8 


GPS Satellite Ground Tracks 

90 

60 

30 

0 

−30 

−60 

−90 

−180 −150 −120 −90 −60 −30 0 30 60 90 120 150 180 

nearly circular orbits 

orbital period 11 h 58 m 

20,200 km altitude 

inclination 55 0 

6 orbital planes 

9 


GPS Satellite Visibility in Delft 

11 

Satellite (PRN) 

31 

30 

29 

27 

26 

25 

24 

23 

22 

21 

19 

18 

17 

16 

15 

14 

13 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

8.7 8.8 8.9 9 9.1 9.2 9.3 9.4 9.5 

Time [sec] 

x 10 5 

Number of satellites 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 

Number of visible satellites 

8.7 8.8 8.9 9 9.1 9.2 9.3 9.4 9.5 

Time [sec] 

x 10 5 

24 hour period 

Elevation cut-off 

angle 10 o 

1-Dec-1999 

10 


80 

60 

40 

20 

0 

270 

−20 

−40 

−60 

−80 

GPS Skyplot (azimuth and elevation) for Delft 

300 

240 

3 

210 

330 

17 

21 19 21 

27 23 

24 29 7 

25 

4 

10 

22 

31 

26 

9 

15 

8 

30 16 13 

15 

5 

1418 

6 

31 

27 

0 

−50 0 50 

180 

15 

30 

45 

60 

75 

90 

119 

17 

3 

21 

21 2 

150 

30 

23 

23 

22 

60 

10 

4 

2924 

729 

25 

120 

90 

Elevation (deg) 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

Elevation versus time plot 

23 

31 

21 

29 

3 

2 

15 

14 

7 

25 

1 

16 

4 

18 

22 

24 

19 

13 

27 

10 

17 

2 

7 

23 

8.7 8.8 8.9 9 9.1 9.2 9.3 9.4 9.5 

Time [sec] 

x 10 5 

Skyplot (polar plot of azimuth 

and elevation) 

24 hour period 

Elevation cut-off angle 10 o 

1-Dec-1999 

26 

8 

9 

21 

5 

29 

4 

30 

24 

6 

25 

1 

10 

22 

17 

3 

11 

2321 

31 

19 

27 

15 

29 


80 

60 

40 

20 

0 

270 

−20 

−40 

−60 

−80 

300 

240 

More GPS Skyplots… 

210 

330 

23 

29 7 

24 

2 

25 

27 

4 

10 

22 

31 

26 

3 

9 

15 30 13 16 8 

North Pole 

19 1 

221 

17 

0 

27 

26 

−50 0 50 

180 

6 

15 

30 

45 

60 

75 

90 

15 31 

14 5 186 

27 

150 

30 

18 

14 5 

816 

13 30 15 

8 9 9 

3 

26 

31 

22 

23 

10 

4 

25 

24 

21 729 

23 

321 

2 

117 

19 

60 

120 

90 

80 

60 

40 

20 

0 

270 

−20 

−40 

−60 

−80 

300 

240 

3 

2 

9 

210 

330 

519 

14 181 

617 

27 

21 

30 13 

21 16 815 

29 

23 

7 

2926 

24 31 25 22 

25 

410 

1-Dec-1999, 24h period 

Equator 

0 

−50 0 50 

180 

15 

23 

30 

45 

60 

75 

90 

6 

17 

150 

30 

9 

5 

30 

60 

120 

90 

12 


GPS Signal Components 

• All signals and time information are coherently derived from the same clock 

with a frequency of f0=10.23 MHz 

• cesium and rubidium clocks (two each) 

• clock stability better than 10-13 

• To compensate for relativistic effects a frequency offset of 4.55 10-3 Hz is applied 

• Two carrier frequencies 

• L1 frequency 1575.42 Mhz (154*f0) L1 wavelength 19.05 cm 

• L2 frequency 1227.60 Mhz (120*f0) L2 wavelength 24.45 cm 

• Binary bi-phase modulation (spread spectrum modulation) with two Pseudo 

Random Noise (PRN) code sequences 

• Coarse/Aquisition (C/A) code on L1 with 1.023 bits/sec (0.1*f0) [1 ms long] 

• Precision (P) code on L1 and L2 with 10.23 bits/sec (f0) [ 7 days long] 

In case of Anti-Spoofing (A-S) the P-code is encrypted by a secret W-code, 

resulting in the classified Y-code 

A-S was enabled on Monday 31 January 1994 0h00m 

• The PRN codes are combined with a broadcast message (50 bits/sec) 

13 


GEOCENTER 

Principle of one-way ranging: 

Satellite clock generates signal 

Receiver clock detects signal arrival 

Pseudo Range 

∆t 

P I 

j 

= c ∆t = || r I -r j || 

Carrier Phase 

Code arriving from satellite 

Replica generated in receiver 

Time delay (Pseudo 

Range measurement) 

Doppler shifted carrier from satellite 

Carrier generated in receiver 

Carrier beat signal 

GPS measurements 

PROBLEM: 

The two clocks must keep the same time 

P I 

j 

= -λϕ i 

j 

= || r I -r j || - λA i 

j 

14 


Examples of GPS Receivers 

PC card module 

Harisons dream.. 

handheld 

Geodetic receiver with radio 

link 

15 


Geodetic GPS Receivers 

• Requirements for a geodetic receiver: 

• must be able to measure integrated carrier phase data 

• must have data recording capability (typically RAM) 

• must have downloading capability (RS-232, USB, TCP/IP) 

• may be single-frequency (L1) or dual-frequency (L1&L2) 

• Dual-frequency receivers must be able to cope with A-S. 

• Measurements are usually stored/downloaded in a proprietary data format 

• Raw measurements can be converted into the Receiver Independent Exchange 

Format (RINEX) 

• by the receiver, or 

• using special converter software (manufacturer, TEQC, …) 

• Read/write data stream in RTCM-SC104 format (D-GPS/RTK) over serial port, 

build in radio-link, or via TCP/IP using the NTRIP protocol [optional for $$] 

16 


RINEX: Receiver INdependent EXchange format 

• Different file types 

• Observation file: pseudo range and carrier phase data 

• Navigation file: broadcast ephemeredes 

• Meteo file: optional meteorological data 

Each file contains the necessary meta data, such as station name, receiver and 

antenna type, type of measurements, operator, date, approximate station 

coordinates, etc. 

• Naming convention . (example: delf204e.04o) 

4let: 

4 letter abbreviation for the station/vehicle name 

doy: 

day of the year (1…365) 

yy: 

last two digits of the year 

s: session number 0 complete day 

a…x identify the hour of the day 

t: RINEX file type (o=observation, n=navigation, m=meteo) 

17 


Anti-Spoofing (A-S) 

• On block II satellites P-code is replaced by a secret Y-code (actually the 

P-code is encrypted) 

• To prevent military receivers from tracking "false" GPS satellites and to 

prevent jamming 

• Only (military) receivers with the appropriate "key" can use the Y-code 

• Two frequency GPS receivers cope with A-S in the following way 

Signal squaring on L2: L1 code & phase, L2 half wavelength phase 

Cross-correlation: L1 code & phase, Y2-Y1 code & L2-L1 phase 

P/W tracking: L1 code & phase, L2 code & phase 

Anti-Spoofing will always result in some loss of information, even if 

they can cope with A-S, the signal-to-noise ratio is worse than w/o A-S! 

• A-S was enabled on Monday 31 January 1994 0h00m, 

occasionally off for testing and other purposes 

18 


Selective Availability (SA) – 1990-2000 

• Intentional degradation of satellite signals by 

"Dithering" of satellite clock (through adding periodic errors to the satellite 

clock with periods of 5-7 minutes) 

Introducing deliberately errors in the broadcast ephemerides 

Classified algorithm and characteristics 

• To provide 100 m horizontal and 170 m vertical accuracy (95% 

confidence level) for C/A-code navigation 

• Ways to mitigate the negative effects for positioning 

Military receivers are able to overcome SA 

Use Glonass instead 

☺ Can be overcome by differential GPS operation (much better than absolute 

positioning) 

• Implemented on all block II satellites, but not block I, although it is 

was off on some block II satellites 

• Was operational from March 1990 until May 2nd 2000 (none during the 

1st Gulf war), switched off on May 2nd at 4:05 UTC!! 

19 


Selective Availability (SA) 

60 

GPS Pseudo Range error (2 May 2000, 3:00-5:00 UTC) 

Range Error [meters] 

Range error (meters) 

40 

20 

0 

-20 

-40 

SA turned off May 2 nd 2000 

4:05 UTC 

-60 

3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 

Time (Hours) 

20 


GPS Services 

SPS/SA: 

SPS 

PPS 

Standard Positioning Service (SA on) 

Standard Positioning Service (SA off) 

Precise Positioning Service (military only) 

1-freq. 

2-freq. 

SBAS 

DGPS 

PPP 

CP&RTK 

Satellite Based Augmentation System (global) 

- GPS alike signal from Geostationary Satellite 

- Corrections / Integrity flag / Protection levels 

Differential GPS (regional corrections) 

Precise Point Positioning (global) 

1/2-freq. 

Carrier Phase & Real Time Kinematic 

1 freq. 

21 


Accuracy (1σ) of GPS Services 

22 


GPS PRN 23 Anomaly, 1 Jan, 2004 

500 

400 

300 

200 

100 

East, North and Up differences − delf001s.04r 

Not noticed by US for 3 hours 

Picked up by EGNOS 

North 

East 

Up 

[m] 

0 

−100 

−200 

−300 

−400 

satellite PRN23 included (default) 

at 18:30 (UT) 

3 min. 

−500 

100 110 120 130 140 150 160 170 180 190 200 

Number of epochs 

at 10 seconds interval 

23 


GPS Modernization 

Signal upgrade: 

– Third L5 frequency (1176.45 MHz) 

– Military M-code (on L1 and L2) 

– Civil signals on L2 and L5 

– More signal power 

Satellite constellation upgrade: 

– Upgrade Block IIR satellites (2005>): 

– C/A like code on L2 (now 5 sats) 

– M-code on L1 and L2 

– New Block IIF satellites (2009?): 

– C/A-code on L2 

– M-code on L1 and L2 

– New L5 signal 

1 Block IIR with 

L5 in 2008 

24 


Modernized Signal Evolution 

Present Signal 

L5 

P(Y) 

L2 

P(Y) 

L1 

C/A 

New Civil General 

Utility Signal 

P(Y) 

C/A 

P(Y) 

C/A 

Civil Safety of Life 

Applications and 

New Military 

Signals 

1176 MHz 

P(Y) 

M 

C/A 

P(Y) 

M 

C/A 

1227 MHz 1575 MHz 

25 


GPS satellites 

Block I 

Launch: 1978-1985 

In use unil: 1995 

Expected life: 5 years 

Weight: 

759 kg 

Block II/IIA/IIR/IIR-M 

Launch: 1989-2003 2007 

In use until: 2014 2017 

Expected life: 7.5/7.5/10 years 

Weight: 

1660/1816/2032 kg 

Block IIF 

Launch: starting 2005 2009 

In use until: ? 

Expected life: 15 years 

Weight: ? 

26 


GEO2TECDI – Bangkok, May, 2009 – GNSS Lecture 2 

27

GLO bal’naya 

NA igatsionnaya 

S putnikova 

S istema 

28 


Introduction to Glonass 

GLONASS 

Russian satellite navigation system 

Not operational (anymore) 

first launch in 1982 (GPS in 1978) 

complete constellation in 1996 (GPS in 1993) 

in 2005: 14 satellites remaining 

(GPS 28 satellites) 

GLONASS is rebuilding 

Modernized Glonass-M (> 2003) and new Glonass-K (> 2009) 

Extended lifetime for Glonass-M (7 years) and Glonass-K (10 years) 

Several new launches in 2006, 2007 

18 operational satellites in 2008, plan for 24 satellites by 2010 

new signals and regional augmentation planned 

29 


1 Jan 2000 

1 Jan 1999 

GLONASS satellite constellation 

30 

24 

22 

20 

18 

16 

14 

12 

10 

8 

6 

4 

2 

0 

1 Jan 1982 

1 Jan 1983 

1 Jan 1984 

1 Jan 1985 

1 Jan 1986 

1 Jan 1987 

1 Jan 1988 

1 Jan 1989 

1 Jan 1990 

1 Jan 1991 

1 Jan 1992 

1 Jan 1993 

1 Jan 1994 

1 Jan 1995 

1 Jan 1996 

1 Jan 1997 

1 Jan 1998 



31

GLONASS Space Segment (2) 

skyplot - 8 days 

ground tracks - 8 days 

80 

330 

0 

15 

30 

90 

60 

30 

60 

40 

300 

45 

60 

60 

30 

20 

75 

0 

270 

90 

90 

0 

−20 

−30 

−40 

240 

−60 

120 

−60 

−80 

210 

−50 0 50 

180 

150 

GPS PRN 1 

−90 

−180 −150 −120 −90 −60 −30 0 30 60 90 120 150 180 

GLONASS slot 1 

32 


GLONASS signal structure (2) 

Difference GLONASS and GPS signals 

carrier + PRN-code modulation 

GLONASS: satellites transmit the same PRN-code on 

different carrier frequencies 

GPS: 

satellites transmit different PRN-codes on 

the same carrier frequency 

also: GPS PRN-codes are transmitted with a higher 

chip-rate than GLONASS PRN-codes 

33 



34

The 4 GALILEO arguments 

- European independence and sovereignty 

- Industrial politics 

Political 

Social 

- Better and new services for the citizens 

- Improved safety of transport systems 

- Environmental benefits 

Economic 

Technological 

- Technological lead to European industry 

- Explore synergy of a number of technologies 

- Global market shares 

- Global competitiveness of all segments 

of the Value Chain 

- Employment 

- Efficiency of transport industry 

35 


GALILEO Services 

Navigation Services 

Open Access Service (OS) 

Consumer market, e.g. car navigation systems 

Commercial Service (CS) 

Commercial and Professional applications (geodesy) 

Improved accuracy (3 frequencies) and integrity 

Public Regulated Service (PRS) 

“Safety of life” services (SAS) 

Govermental services (PRS) 

Free 

Not Free! 

Original plan, 

now abandoned 

Financed by government and industry - 

Public Private Partnership (PPP) 

36 


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 

37 


Galileo status 

GIOVE-B in 

2008 

• 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 -> 2009-2010 (IOV) 

• Operational in 2008 -> 2009-2010 -> 2012-2013 

GIOVE-A 

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

• EGNOS operational in 2005 (slight delay; wind-up, operational 2007) 

• EGNOS integrated with GALILEO in future (GEO service available until 

2015?) -> EGNOS MRS 

38 


GALILEO In Flight Configuration 

Navigation payload: 70-80 Kg / 850 W 

Search and Rescue (SAR) 

transponder: ca. 20 kg 

Overall Spacecraft: 

650 Kg / 1.5 kW class 

Launcher Options: 

Ariane, Proton, Soyuz, …... 

39 


GALILEOALILEO DATA 

Walker 27/3/1 

Constellation 

altitude ~23616 km 

SMA 29993.707 km 

inclination 56 degrees 

27 + 3 satellites in three 

Medium Earth Orbits (MEO) 

• period 14 hours 4 min 

• ground track repeat about 10 days 

40 


GPS versus Galileo 

GPS Satellites: 

24 nominal (27 operational) 

circular orbits 26,561 km 

Orbit period 11h58m (1/2) 

inclination 55 0 , 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 

Galileo Satellites: 

27 nominal + 3 active spare 

circular obits 29,600 km 

Orbital period 14h05m (10/17) 

inclination 56 0 , 3 orbit planes 

Galileo Signals (10): 

Four frequencies (L1, L5(E5a), E5b= 

1207.14 MHz, E6=1278.75) 

Open service (OS) on L1, E5a and 

E5b, data+pilot channel, 6 signals 

Public Regulated (PRS), “safety of life” 

(SAS) and commercial (CS) services 

on e.g. E6, 4 signals 

Integrated integrity service 

41 


First Galileo measurements in Delft 

Giove A 

Septentrio AsteRx1 

GPS 

C/A code noise vs SNR 

Giove B 

Giove B 

Giove A 

42 


COMPASS 

43 


IRNSS 

44 


QZSS 

45

Present and Future Global Navigation Satellite Systems (GNSS)

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