Simulation and Measurements on BeiDou-2 Positioning Performance

Stanford PNT Symposium 2011 Simulation and Measurements on BeiDou-2 Positioning Performance Mingquan LU Department of Electronic Engineering Tsinghua University Nov. 17, 2011

Outline 1. BeiDou Overview 2. Current Status of BeiDou-2 3. Simulated Positioning Performance of BeiDou-2 4. Measured Positioning Performance of Current BeiDou-2 5. Conclusions

1. BeiDou Overview BeiDou, known as COMPASS, is China s satellite navigation program, began development in 1980 s. According to the three-step strategy, BeiDou program will be developed gradually, from Phase I, Phase II to Phase III. Phase I Phase II Phase III

1. BeiDou Overview BeiDou Phase I (BeiDou-1, Replaced) BeiDou Satellite Navigation Demonstration System, known as BeiDou-1, consists of 3 GEO satellites, provides RDSS (Radio Determination Satellite Service) service in China since 2003. After more than 7 year s operation, BeiDou-1 has been replaced by BeiDou-2 in 2010.

1. BeiDou Overview BeiDou Phase II (BeiDou-2, Deploying) BeiDou Satellite Navigation System (Regional), known as BeiDou-2, consists of 14 satellites (5 GEO, 5 IGSO and 4 MEO), transmits 3 frequencies, 5 signals. BeiDou-2 will provide RNSS (Radio Determination Satellite Service, PNT service) and RDSS services to users in Asia-Pacific region by 2012.

1. BeiDou Overview BeiDou Phase III (Scheduled) BeiDou Satellite Navigation System (Global), consists of 35 satellites (30 MEO satellites and 5 GEO), and transmits 3 frequencies, and more signals. The scheduled system will provide worldwide RNSS (PNT) service and upgraded regional RDSS service by 2020.

1. BeiDou Overview The Perspective of BeiDou The development of BeiDou program goes smoothly and rapidly. BeiDou-1 has been replaced, BeiDou-2 is being deployed, the global system is scheduled. In the near future, BeiDou, together with GPS, Glonass and Galileo, will provide worldwide PNT service, as well as regional RDSS service. BeiDou will become one of the most important part of the national information infrastructure of China.

Outline 1. BeiDou Overview 2. Current Status of BeiDou-2 3. Simulated Positioning Performance of BeiDou-2 4. Measured Positioning Performance of Current BeiDou-2 5. Conclusions

2. Current Status of BeiDou-2 Constellation of BeiDou-2 The nominal constellation of BeiDou-2 consists of 14 satellites, including 5 GEO, 5 IGSO and 4 MEO satellites. Orbit GEO IGSO MEO Semi-major Axis (km) 42164 42164 27878 Eccentricity 0 0 0 Inclination (deg) RAAN (deg) Argument Perigee (deg) Mean Anomaly (deg) Satellite Number Table 1 BeiDou-2 constellation 0 55 55 158.75E 180E 210.5E 240E 260E 218E 98E 338E 218E 98E 0 0 0 0 218E:0 98E:120 338E:240 218E:337 98E:97 5 5 4 0E,120E 105 150 270 315

2. Current Status of BeiDou-2 Signals and Services of BeiDou-2 (RNSS only) 3 frequencies: B1, B2, B3 5 signals, B1 I/Q, B2 I/Q, B3 2 services: open and authorized PNT service Table 2 Signals and services of BeiDou-2

2. Current Status of BeiDou-2 Launch history of BeiDou-2 9 satellites have been launched, including 1 MEO, 4 GEO and 4 IGSO satellites. The latest launch is in July, this year. 5 or more satellites will be launched by the end of next year. Table 3 The Launch History of BeiDou-2 Date SV Orbit 1 2007.04.14 MEO ~21,500km 2 2009.04.15 GEO In-orbit Maintenance 3 2010.01.17 GEO 144.5 E 4 2010.06.02 GEO 84 E 5 2010.08.01 IGSO Intersecton Node:118 E 6 2010.11.01 GEO 160 E 7 2010.12.18 IGSO Intersecton Node:118 E 8 2011.04.10 IGSO Intersecton Node:118 E 9 2011.07.27 IGSO Intersecton Node:95 E

2 Current Status of BeiDou-2 Constellation status Total in orbit: 9 satellites Operational: 6 satellites (3 GEO+3 IGSO) In maintenance: 2 satellites (1 MEO+1GEO) In test: 1 satellite (1 IGSO, latest launch)

2 Current Status of BeiDou-2 The Initial Operational Capability (IOC) of BeiDou-2 By July 2011, there are 6 operational satellites in orbit. The minimal number of visible satellites is 4 (3 GEO+1 IGSO) in China. BeiDou-2 is able to provide initial PNT service for users in China.

Outline 1. BeiDou Overview 2. Current Status of BeiDou-2 3. Simulated Positioning Performance of BeiDou-2 4. Measured Positioning Performance of Current BeiDou-2 5. Conclusions

3. Simulated Positioning Performance of BeiDou-2 3.1 Simulation items distributions of Positional Dilution of Precision (PDOP) PDOP distribution for BeiDou-2. PDOP distribution for GPS. PDOP for BeiDou-2 + GPS. distributions of Visible Satellite Number (VSN). VSN distribution for BeiDou-2. VSN distribution for GPS. VSN distribution for BeiDou-2 + GPS.

3. Simulated Positioning Performance of BeiDou-2 3.2 Simulation conditions Constellations: BeiDou-2: constellation of 12 satellites (5+3+4 ) (lack of new 14 satellites constellation (5+5+4 ) ephemerides) GPS: the current constellation Simulation period: 24 hours Simulation Region: 55 S55 N, 50 E180 E (Coverage of BeiDou-2). Mask angle: 5 Statistical probability: 95%

3. Simulated Positioning Performance of BeiDou-2 3.3 Simulation Results (1) -- Distribution of PDOP and VSN for BeiDou-2 Fig. 1 Distribution of PDOP for BeiDou-2 Fig. 2 Distribution of VSN for BeiDou-2 18

3. Simulated Positioning Performance of BeiDou-2 3.3 Simulation Results (2) -- Distribution of PDOP and VSN for GPS Fig. 3 Distribution of PDOP for GPS Fig. 4 Distribution of VSN for GPS 19

3. Simulated Positioning Performance of BeiDou-2 3.3 Simulation Results (3) -- Distribution of PDOP and VSN for BeiDou-2 + GPS (combined) Fig. 5 Distribution of PDOP for BeiDou-2+ GPS Fig. 6 Distribution of VSN for BeiDou-2+GPS 20

3. Simulated Positioning Performance of BeiDou-2 3.3 Simulation Results (4) -- The Statistics of the PDOP and VSN Distribution for BeiDou-2, GPS and BeiDou-2 + GPS Table 4 Statistics of PDOP and VSN for BeiDou-2, GPS and BeiDou-2+GPS Constellation PDOP(95%) Visible Satellite Number(95%) Max Min Mean Max Min Mean BeiDou-2 14.0000 2.7418 6.3348 8.0000 3.0000 6.0709 GPS 2.4327 1.7157 2.0421 10.0000 8.0000 8.7440 BeiDou-2 + GPS 1.7624 1.1094 1.3840 19.0000 12.0000 15.6651 21

3. Simulated Positioning Performance of BeiDou-2 3.3 Simulation Results (5) -- Average PDOP and VSN for some cities in China: Harbin, Beijing, Kashi and Sanya

3. Simulated Positioning Performance of BeiDou-2 3.3 Simulation Results (5) -- Average PDOP and VSN for some cities in China Table 5 Average PDOP and VSN for some cities in China ( Harbin, Beijing, Kashi and Sanya) Constellation Average PDOP Average VSN Harbin Beijing Kashi Sanya Harbin Beijing Kashi Sanya BeiDou-2 2.33 2.26 3.19 2.20 8.08 8.33 7.33 8.83 GPS 1.66 1.70 1.61 1.58 9.50 9.25 9.67 10.17 BeiDou-2 + GPS 1.17 1.20 1.25 1.14 17.58 17.58 17 19

3. Simulated Positioning Performance of BeiDou-2 3.4 The expected positioning performance of BeiDou-2 (in most areas of China) The expected availability: there are at least 6 or 7 visible satellites. The expected accuracy: since the PDOP is from 2 to 4, assuming the ranging error is 1m, the designed positioning accuracy (10m) can be reached.

Outline 1. BeiDou Overview 2. Current Status of BeiDou-2 3. Simulated Positioning Performance of BeiDou-2 4. Measured Positioning Performance of Current BeiDou-2 5. Conclusions

4. Measured Positioning Performance of Current BeiDou-2 Constellation 4.1 Measurement of Signal Quality for BeiDou-2 4.2 Measurement of Pseudorange Single Point Positioning For BeiDou-2 For GPS For BeiDou-2 + GPS

4.1 Measurement of Signal Quality for BeiDou-2 Measurement Conditions Measurement site: Tsinghua campus, Beijing, China. Observation period: 4 hours, April 2, 2011. Received signals: BeiDou-2 B1(I) signals for 3 GEO satellites (SV 1, 3, 4) and 2 IGSO satellites (SV 6, 7). 27

4.1 Measurement of Signal Quality for BeiDou-2 Measurement Results For GEO, the signal carrier-to-noise ratio is stable. For IGSO, the carrier-to-noise ratio degrades rapidly as the elevation is low. Fig. 7 C/N0 and Elevation of BeiDou-2 SV-1 (GEO) 28 Fig. 8 C/N0 and Elevation of BeiDou-2 SV-6 (IGSO)

4.2 Measurement of Pseudorange Single Point Positioning Measurement Conditions 29 Measurement site: Zibo, Shandong Province, China. Measurement period: 3.5 hours, Sept 29, 2011. Received signals: B1(I) for 3 GEO satellites (SV 1, 3, 4) and 2 IGSO satellites (SV 7, 8), and GPS L1 C/A signals for all visible satellites. Mask angle: 10 PVT Solutions: Satellite selection is not used. Simple least-squares method is used. BeiDou-2 measurements and GPS measurements have the same weight.

4.2 Measurement of Pseudorange Single Point Positioning VSN and PDOP Distribution of BeiDou-2 The average VSN for BeiDou-2 is 5. The average PDOP for BeiDou-2 is 6.915. Fig. 9 PDOP distribution for BeiDou-2 Fig. 10 VSN distribution for BeiDou-2

4.2 Measurement of Pseudorange Single Point Positioning Positioning accuracy of BeiDou-2Topocentric (a) North (b) East (c) Up Fig. 11 Positioning accuracy of BeiDou-2Topocentric NEU

4.2 Measurement of Pseudorange Single Point Positioning Positioning accuracy of BeiDou-2 The N, E, U error in RMSE is 10.229m, 4.674m and 22.059m, respectively Table 6 Statistics of the Positioning accuracy of BeiDou-2Topocentric Max. Min. Mean RMSE North 15.007 m 2.596 m 9.766 m 10.229 m East 1.937 m -8.924 m -3.724 m 4.674 m Up 6.853 m -35.536 m -18.810 m 22.059 m

4.2 Measurement of Pseudorange Single Point Positioning VSN and PDOP Distribution of GPS The average VSN for GPS is more than 7 The average PDOP for GPS is 2.296 Fig. 12 PDOP distribution for GPS Fig. 13 VSN distribution for GPS

4.2 Pseudorange Single Point Positioning Positioning accuracy of GPSTopocentric (a) North (b) East (c) Up Fig. 14 Positioning accuracy of GPSTopocentric NEU

4.2 Pseudorange Single Point Positioning Positioning accuracy of GPS The N, E, U error in RMSE is 4.433m, 3.713m and 9.23m, respectively. Table 7 Statistics of the Positioning accuracy of GPSTopocentric Max. Min. Mean RMSE North 9.304 m 0.147 m 3.760 m 4.433 m East -1.002 m -5.574 m -3.555 m 3.713 m Up 4.315 m -16.772 m -7.396 m 9.234 m

4.2 Pseudorange Single Point Positioning VSN and PDOP Distribution of BeiDou-2 + GPS The average VSN for BeiDou-2 + GPS is more than 13. The average PDOP for BeiDou-2 + GPS is 2.231. Fig. 15 PDOP distribution for BeiDou-2 + GPS Fig. 16 VSN distribution for BeiDou-2 + GPS

4.2 Pseudorange Single Point Positioning The positioning accuracy for BeiDou-2 + GPSTopocentric. (a) North (b) East (c) Up Fig. 17 Positioning accuracy of BeiDpu-2 + GPSTopocentric NEU

4.2 Pseudorange Single Point Positioning The positioning accuracy for BeiDou-2 + GPS The N, E, U error in RMSE is 3.671, 3.389 and 9.445 respectively. Table 8 Statistics of the Positioning accuracy of BeiDou-2 + GPSTopocentric Max. Min. Mean RMSE N 5.199 m 1.815 m 3.591 m 3.671 m E -1.457 m -4.538 m -3.310 m 3.389 m U 1.783 m -14.032 m -7.902 m 9.445 m

4.2 Pseudorange Single Point Positioning The comparison of positioning accuracy for BeiDou-2, GPS and BeiDou-2 + GPS Table 9 Comparison of Positioning accuracy in RMSE of BeiDou-2, GPS, and BeiDou-2 + GPS (Topocentric BeiDou-2 GPS BeiDou-2+GPS North 10.229 m 4.433 m 3.671 m East 4.674 m 3.713 m 3.389 m Up 22.059 m 9.234 m 9.445 m

4.2 Pseudorange Single Point Positioning Summary of the measurement results The quality of the current BeiDou-2 signals is high enough (about 45 db-hz) for positioning. The PDOP and the SVN of the current BeiDou-2 are acceptable, BeiDou-2 has the ability to provide initial PNT service. If BeiDou-2 and GPS are combined, the positioning accuracy can be improved significantly, which is more accurate than BeiDou-2 only. Compared to GPS only, the positioning accuracy of the combined system is also slightly improved.

Outline 1. BeiDou Overview 2. Current Status of BeiDou-2 3. Simulated Positioning Performance of BeiDou-2 4. Measured Positioning Performance of Current BeiDou-2 Constellation 5. Conclusions

5 Conclusions (1) Current BeiDou-2 is able to provide initial PNT service There are 6 operational satellites (3 GEO and 3 IGSO satellites) in orbit. The received signals have high enough C/N0 for applications. The relative large PDOP of the current constellation results in relative low positioning accuracy. Although still in test, Beidou-2 is able to provide initial PNT services in China and surrounding areas. 42

5 Conclusions 2BeiDou-2 and GPS combined receivers provide better positioning performance, due to more visible satellites, smaller PDOP, and improved positioning accuracy. 3Since BeiDou-2 is still under construction, the positioning performance presented here is just the measurements for the current status, which does not represent the final status of BeiDou-2.

Stanford PNT Symposium 2011 Thanks for Your Attention! Prof. Mingquan LU lumq@tsinghua.edu.cn GNSS Lab Department of Electronic Engineering Tsinghua University