One Decade of WAAS Lessons - How Would We Have Done It Differently, If Given Another Chance

Transcription

1 One Decade of WAAS Lessons - How Would We Have Done It Differently, If Given Another Chance Tim Schempp, WAAS Technical Director Dr. Kenneth Kung, Sr. Principal Engineering Fellow November 18, 2011 The contents of this material reflect the views of the authors and/or Raytheon and do not necessarily reflect the views of the FAA or the DOT. Neither the Federal Aviation Administration nor the Department of Transportation makes any warranty or guarantee, or promise, expressed or implied, concerning the content or accuracy of the views expressed herein. Copyright 2011 Raytheon Company. All rights reserved. Customer Success Is Our Mission is a registered trademark of Raytheon Company.

2 Agenda Recent System Performance WAAS Architecture Interoperability Reliability as we move towards the future Testing User/Ground Interface Page 2

3 WAAS LPV Service LPV Service Attribute Requirement Alert Limit VAL=50m / HAL=40m Accuracy 95%: VPE=20m / HPE=16m Integrity per approach Continuity per approach Availability 0.99 to Time to Alert 6.2 Seconds Decision Height As low as 250 feet Page 3

4 WAAS LPV Service % of CONUS/A Alaska with 100% Ava ailability CRW Switch Zombie Satellite (CRW) CRE Switch Zombie Sat+CRE Switch Over+PRN 12 Out 0 10/7/11 9/6/11 8/6/11 7/6/11 6/5/11 5/5/11 4/4/11 3/4/11 2/1/11 1/1/11 % of CONUS with LPV service % of Alaska with LPV Service Lab Data Feed Outage Ionospheric Storm Page 4

5 WAAS LPV Service CRW CRW AMR Page 5

6 WAAS Architecture L2 GPS GPS L1 GPS GEO L1 & L5 L1 GEO w/ WAAS Message Generator Message L1 & L2 GPS L1 & L5 GEO Message Processor GEO Uplink System (1 pair per GEO) Reference Station WRS 1-38 User Dual Ring Terrestrial Communication Network WAAS Message Com mparator Wide Area Master Station 1-3 Page 6

7 WAAS Architecture Page 7

8 WAAS Architecture Processor Generator Generator Processor Generator Processor Processor Generator Generator Processor Generator Processor Operations and Maintenance Console Operations and Maintenance Console Page 8

9 Time To Alarm X X+1 X+2 X+3 X+4 X+5 X+6 Failure Reference Stn Master Station Co omparator Uplink Station Processor Generator X second time to alarm Measurements sampled at a one second rate, allows for the probability that a failure occurred an instant after the last sample. Message takes one second to transmit from the GEO and 0.2 seconds to downlink. Page 9

10 Time To Alarm Master Station + Uplink Station + Processor Processor1 Compa arator Generator Reduces hardware (No master station, ti no second correction processor) Simpler Each station monitors message stream of its attached GEO Switchover accomplished via a uplink to uplink interface Reduced Processing Load Low risk for field testing a build and cutting over new builds Page 10

11 Time To Alarm Failure Reference Stn Master Station + Uplink Station + Processor Processor1 Generator X+5.2 Page 11

12 Interoperability Inmarsat WAAS EGNOS GAGAN MSAS Page 12

13 Reliability Reliability Features Every sub system has a backup Three independent receivers with one acting as a hot standby Dual GEO coverage is critical. Vulnerabilities Common mode Master Station Failure Common mode GPS Failure CRW@133 W AMR@98 W CRE@107 W Constellation Weakness Jamming Page 13

14 Reliability Common Mode Failure GPS GEO L1 & L5 GEO L1 & L5 L1 & L2 GPS L2 GPS L1 GPS L1 GEO w/ WAAS Message Generator Message Message Processor GEO Uplink System (1 pair per GEO) Reference Station User WAAS Message Dual Ring Terrestrial Communication WRS 1-38 Wide Area Master Station 1-3 Network Page 14

15 Reliability Common Mode Failure L5 GPS GPS L1 GPS GEO L1 & L5 L1 GEO w/ WAAS Message Generator Message L1 & L2 GPS L1 & L5 GEO Message Processor GEO Uplink System (1 pair per GEO) Reference Station User L1 WAAS Message L5 WAAS Message Compara ator WRS 1-38 Single Frequency Wide Area Master Station 1-3 Compara ator Dual Frequency Wide Area Master Station 1-3 Page 15

16 Reliability Common Mode Failure GPS Galileo GEO L1 & E5 Galileo L1 & L5 GPS L1 & L5 GEO L1/L5 GPS L1/E5 L1 & L5 L1 G enerator mparator Co GPS GPS GPS Corr Processor Reference Station L1,L5,E5+ GEO Msg User nal rator L5 Sig Gener Compa arator Galileo Galileo Galileo Corr Processor Multi Constellation GEO Uplink System (1 pair per GEO) WRS 1-38 Page 16

17 Testing Processor Generator Generator Processor Generator Processor Processor Generator Generator Processor Generator Processor Operations and Maintenance Console Operations and Maintenance Console Co omparator Co omparator or Comparat Page 17

18 WAAS Messages The ionospheric uncertainty bound (GIVE) is broadcast using 4 bits according to a look up table. A GIVEI of 12 supports LPV service. A GIVEI of 13 or higher does not supports LPV service Constant GIVE % of CONUS with LPV Service % % % Page 18

19 WAAS Messages Message?? UDRE and GIVE Quantization Table Data content Bits used Range of values Resolution For each of 16 quantization values numbered 0 to 15 GIVE Quantization step i* to 9.6m 0.3m For each of 16 quantization values numbered 0 to 15 UDRE Quantization step i* to 64m 0.25m Spare 4 The 0 th GIVE Quantization value is GIVE Quantization step 0. The i th GIVE Quantization value is GIVE Quantization value i-1 plus GIVE Quantization step i. *The one sigma version of the i th GIVE Quantization value is (GIVE Quantization value i)/3.29 The GIVE Quantization value of an entry with a GIVE Quantization step of 9.3 is 45. The GIVE Quantization value of an entry with a GIVE Quantization step of 9.6 is Not Monitored The 0 th UDRE Quantization value is UDRE Quantization step 0. The i th UDRE Quantization value is UDRE Quantization value i-1 plus UDRE Quantization step i. *The one sigma version of the i th UDRE Quantization value is (UDRE Quantization value i)/3.29 The UDRE Quantization value of an entry with a UDRE Quantization step of is 150. The UDRE Quantization value of an entry with a UDRE Quantization step of is Not Monitored. The UDRE Quantization value of an entry with a UDRE Quantization step of 64 is Don t Use Page 19

20 WAAS Messages flt udre udre UDRE is dependent on user location. UDRE comes from a static look up table In WAAS, UDRE inflates the satellite uncertainty, UDRE, for users away from reference stations. Imagine the opposite scenario where the covariance matrix and UDRE was the satellite uncertainty and UDRE inflates the uncertainty until a new message is broadcast. In that case all of the UDRE would be near 1 (0.95,1.05,1.10,1.15 ) Page 20

21 The Ionosphere 11/20/03 WAAS Time: Vertical )6 ionospheri ic delay (m) 7 m 20m 3 m Page 21

22 Conclusion WAAS Architecture provides a backup for every sub system. Common mode failure is the weak point. Need to consider this carefully as we transition to dual frequency and multi- constellation SBAS. Interoperability is the key to providing world wide LPV200 service. Need to continue international working groups and work together to make sure that standards are as unambiguous as possible. Don t lock down the user/ground interface before you build the ground system. Don t build the ground system without buy in from the user community. WAAS should have a GEO for testing. Leverage the lessons learned from the past decade along with the maturity of the single frequency system to ensure a smooth transition to dual frequency WAAS. Page 22

23 WAAS Availability w/geo Ranging Maximum, With GEO Ranging 20m 25m Maximum 30m 35m LPV200 40m 45m 50m LPV 65m Page 23

24 WAAS Availability with critical GPS satellite outages Maximum, Without GEO Ranging PRN 10,14,28 outage 20m 25m Maximum 30m 35m LPV200 40m 45m 50m LPV 65m Page 24