Galileo Integrity Concept user level

Transcription

1 Galileo Integrity Concept user level Presented at The Technical Universtiy of Munich Andrew Simsky, Frank Boon

2 GPS integrity provided by SBAS (1/2) WAAS/EGNOS define Safety-Of-Life on top of GPS RTCA DO229 defines MOPS for SBAS : SBAS transmits UERE components Receiver performs UERE variance geometry propagation Receiver computes Protection Levels HPL = K H *d major VPL = K V *d up d = G σ UERE Geometry matrix Computed UERE. User checks Protection Levels against Alarm Limits June 8, 2010 Septentrio 2

3 GPS integrity provided by SBAS (2/2) Protection Levels (PL) based on bias-free models Normal operation: Navigation Error (NE) < PL Misleading information: NE > PL PL > AL -> alarm raised PL > AL, but NE < AL (false alarm, unavailable epoch) HMI = Hazardous Misleading Information HMI: NE > AL but PL < AL (missed detection!) HMI information condensed in Stanford Plot Protection Level versus Position Error accumulated Not available to navigation user SOL service accepted if Protection Level overbounds Error Widely accepted for WAAS/EGNOS validation June 8, 2010 Septentrio 3

4 Stanford plot in Septentrio s GUI June 8, 2010 Septentrio 4

5 Galileo Carriers : E5a,b Galileo Carriers & Services MHz MHz E6-A,B MHz MHz L1-A,B MHz MHz Galileo services : Open L1-B, E5a F/NAV modulation Safety Of-Life L1-B/E5b I/NAV modulation Commercial E6-B C/NAV modulation Publicly Regulated L1-A/E6-A G/NAV modulation Galileo developments at Septentrio: GETR: GIOVE A, B Test User Receiver (TUR), under ESA contract: all services Commercial AsteRx receivers: open, SOL June 8, 2010 Septentrio 5

6 Galileo Navigation Message Navigation message content : Ephemeris Almanac all, but not C/NAV all, but not C/NAV NeQuick (SingleFreq ionosphere model) all, but not C/NAV Galileo System Time (GST-UTC, GST-GPS) all, but not C/NAV Satellite Health & Clock (3 sets to handle) all, but not C/NAV Commercial Data (content yet unknown) only C/NAV Integrity I/NAV (& G/NAV) Navigation message characteristics: F/NAV E5a, 5 bps,10 second pages Requires 5 pages : TTFF 50 sec Longer TTFF than GPS Drawback of FEC encoding I/NAV L1-B/E5b, 250 bps, 2 second pages Requires 5 pages Interleaved over two freq : TTFF between 6 and 15 sec June 8, 2010 Septentrio 6

7 Galileo SOL, system level: Galileo Integrity Information Galileo Signal In Space Accuracy SISA : SIS Accuracy = std (SISE), 4D error of orbit&clock) 8 bits : 126 levels, rest reserved 1,2,4,16 cm bins with 6 m bound Transmitted for L1/E5a, L1/E5b, L1-A/E6-A Analogue of URA for GPS; URA is rougher Galileo Satellite Integrity monitoring SISMA : SIS Monitored Accuracy = std (SISE - SISEest) 4 bits : 14 levels (5.2 m bound), Not monitored, Satellite Not OK Not encrypted but protected with time-dependent authentication key Integrity info = SISMA + Integrity flag -> Integrity threshold is computable Nominal page / alert page Alert page transmitted in case of detected failures ( 1 sec for dual-freq. users) Integrity info linked to ephemeris issue IODnav June 8, 2010 Septentrio 7

8 Galileo Safety-Of-Life, user level: Navigation Warning Algorithm 3 operational modes defined over 15 sec interval nominal operations do-not-initiate new navigation procedure abort current navigation procedure : integrity ok : integrity at risk : integrity failure Input SISA, SISMA, Satellite Geometry Alarm Limits (user application) Output Probability of Hazardous or Misleading Information (P HMI ) event Defined by Galileo SIS-ICD as either vertical or horizontal error exceeds alarm limit without warning to user Introduces concept Set of Critical Satellites Navigation mode indication for next interval Parts of NWA could be used for future Galileo MOPS MOPS under costruction, EUROCAE (analog of RTCA) June 8, 2010 Septentrio 8

9 Galileo SoL integrity requirements Integrity risk: 2.0e-7 in any 150 sec Continuity risk: 8.0e-6 in any 15 sec Availability of service 99.5% (GPS/SBAS 95%) Time to alert: 5.2 sec HAL: 12 m VAL: 20m New integrity concept is based on the computation of the probability of HMI. This algorithm is called HPCA and must be implemented by the receiver. Pfailure = Pfailure in fault-free conds + Pfailure if one-sat fault*pfault of this sat June 8, 2010 Septentrio 9

10 Probability of Failure in fault-free conditions Vertical Limit exceeded Horizontal Limit exceeded P failure VAL fault free = 1 erf + 2 σ up e HAL 2 2ξ 2 Horizontal STD Vertical STD June 8, 2010 Septentrio 10

11 One satellite is faulty Assume that satellite (i) had an undetected bias Use computed std(errors) affected by failure Use computed Maximal Undetectable Bias per satellite repeated N times for all sats Left side of biased Alarm Limit Right side of biased Alarm Limit P 1 VAL G = 1 erf ' i 2 2σ u [ i] B VAL + G[ i] + 1 erf vertical i error> VALi ' i 2σ u B i Non-central ChiSquare with 2 DOF Increased std(error) due to sat failure P HAL 2 ( G[ 1, i] B ) + ( G[ 2, i] B ) 2 horizontal 2 i error> HALi = χnc, f = 2, '2 ' 2 ξi ξi i 2 June 8, 2010 Septentrio 11

12 Total probability: add components Add all individual failure possibilities to bias free failure Assume probability of satellite failure during 150 sec interval Example : p satfailure = P HMI = P failure + n i= 1 p satfailure ( vertical horizontal P P ) undetectedbias> VAL + undetectedbias> HAL Unbiased failure Sum of all non-zero mean biases Predicted P HMI compared to Probability Threshold for 150 sec interval Example : P HMI = June 8, 2010 Septentrio 12

13 Concept of critical satellites For all satellites: Repeat HPCA computation w/o one satellite If Pfailure < threshold -> is critical If a critical satellite sets -> don t initiate (integrity at risk) Navigation Warning Algorithm Generate HPCA & CSPA output HPCA failure : abort navigation mode CSPA failure : don t initiate Otherwise : nominal condition June 8, 2010 Septentrio 13

14 Thank you for your attention! website: June 8, 2010 Septentrio 14 COMMERCIAL IN CONFIDENCE