ICAO policy on GNSS, GNSS SARPs and global GNSS developments

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ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
ICAO policy on GNSS,
GNSS SARPs
and global GNSS developments
Jim Nagle
jnagle@icao.int
Chief, Communication, Navigation and Surveillance Section
ICAO
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Presentation
overview
􀀴 Introduction
􀀴 GNSS developments in ICAO
􀀴 ICAO policy on GNSS
􀀴 Basic technical principles
􀀴 GNSS elements
􀀴 GNSS performance requirements
􀀴 Future evolution
􀀴 GNSS implementation in States
􀀴 GNSS and PBN
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Introduction - ICAO
:
􀀴Convention (Chicago, 1944) and Annexes
􀀴UN Specialized Agency
􀀴189 Contracting States
􀀴Assembly (ordinarily every 3 years)
􀀴Council – 36 States
􀀴Air Navigation Commission – 19 members
􀀴Air Navigation Bureau
􀀴Standards, Recommended Practices (SARPs)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Introduction - ICAO
Mexico
Lima
Paris
Dakar
Nairobi
Cairo
Bangkok
ICAO
HQ
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Introduction – GNSS
􀀴 The theoretical definition:
􀂾 “GNSS. A worldwide position and time determination system
that includes one or more satellite constellations, aircraft
receivers and system integrity monitoring, augmented as
necessary to support the required navigation performance for
the intended operation.” [from ICAO Annex 10, Volume I]
􀀴 The practical foundation:
􀂾 1994/1996: US and Russia offer to ICAO to provide GPS (Global
Positioning System)/GLONASS (GLObal NAvigation Satellite
System) service for the foreseeable service on a continuous
worldwide basis and free of direct user fees
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS developments in ICAO
􀀴 1991: 10th Air Navigation Conference:
􀂾 The Air Navigation Commission requests the initiation of an agreement
between ICAO and GNSS-provider States concerning quality and
duration of GNSS
􀀴 1993: ICAO GNSS Panel established
􀂾 Primary task: to develop SARPs in support of aeronautical applications
of GNSS
􀀴 1994/1996: GPS/GLONASS offers from US/Russia
􀀴 1999: GNSSP completes the development of GNSS SARPS (applicable
2001)
􀀴 2002 – today: GNSSP (subsequently renamed NSP) develops GNSS
SARPs enhancements
􀀴 2003: 11th Air Navigation Conference:
􀂾 The Conference recommends a worldwide transition to GNSS-based air
navigation
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
ICAO policy on GNSS
􀀴 1994: Statement of ICAO policy on CNS/ATM systems implementation and
operation approved by the ICAO Council:
􀂾 “GNSS should be implemented as an evolutionary progression from
existing global navigation satellite systems, including the United States’
GPS and the Russian Federation’s GLONASS, towards an integrated
GNSS over which Contracting States exercise a sufficient level control
on aspects related to its use by civil aviation. ICAO shall continue to
explore, in consultation with Contracting States, airspace users and
service providers, the feasibility of achieving a civil, internationally
controlled GNSS”
􀀴 1998: Assembly resolutions A32-19 (“Charter on the Rights and Obligations
of States Relating to GNSS Services”) and A32-20 (“Development and
elaboration of an appropriate long-term legal framework to govern the
implementation of GNSS”)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
The GPS/GLONASS offers
􀀴 GPS offer (1994):
􀂾 GPS standard positioning service to be made available on a
continuous worldwide basis and free of direct user fees for the
foreseeable future. At least 6 years notice prior to termination.
􀀴 GLONASS offer (1996):
􀂾 GLONASS standard accuracy channel to be provided to the
worldwide aviation community for a period of at least 15 years
with no direct charges collected from users.
􀀴 Both offers accepted by ICAO Council
􀀴 Offers reiterated at various occasions, most recently February 2007
(180th Session of the ICAO Council)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Basic technical principles (1)
􀀴 The aircraft computes its position by “trilateration”
􀀴 A simplified geometrical explanation:
􀂾 the aircraft computes distances d1, d2 and d3 from three
satellites whose positions P1, P2 and P3 are known;
􀂾 knowing distances from, and positions of, three satellites,
it is a simple geometrical problem to derive the position of
the aircraft:
􀂾 the position of the aircraft is the intersection of the three spheres of
radius d1, d2 and d3 and centers respectively P1, P2 and P3
􀂾 (there are actually two intersection points, but typically only one of
them is “reasonable”)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Basic technical principles (2)
􀀴 How does the aircraft know the position of the satellites?
􀂾 the satellite position information is broadcast by the satellites themselves
as a part of the navigation message transmitted by each satellite
􀀴 How does the aircraft compute its distance from the satellites?
􀂾 messages sent by the satellites are time-tagged with the time of
transmission;
􀂾 by comparing the time the message is received and the time the
message was sent, the aircraft can measure the time taken by the
message to travel from the satellite to the aircraft;
􀂾 knowing the speed at which messages travel (the speed of light), and
the time taken, the aircraft can compute the distance travelled by the
message (or “range”), as follows:
􀂾 speed = distance/time, hence > distance= speed x time
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Basic technical principles (3)
􀀴 Some complications:
􀂾 the simplified geometrical explanation assumes that time reference used
by the satellites and by the aircraft are the same
􀂾 however, this is not the case – the satellites carry “precise” clocks
(atomic clocks), whereas the aircraft typically carries a relatively
imprecise (and less expensive) quartz clock
􀂾 hence, the “range” computed by the aircraft based on the equation
shown above is not the “true” range – it is a “pseudorange”
􀂾 Example: a 1 μs (microsecond) synchronization error between clocks corresponds to a 300
m error in range measurement
􀂾 Solution: the clock error is resolved by using a fourth additional satellite
to provide additional information to estimate aircraft clock error and thus
derive “true range” information
􀂾 Instead of three equations in three unknowns (the three position
coordinates of the aircraft), the aircraft receiver solves four equations in
four unknowns (the three position coordinates and the clock error)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements: GPS
􀀴 Nominal constellation: 24 satellites (30 active as of March
2007)
􀀴 Six orbital planes
􀀴 Near-circular, 20,200 km altitude (26,600 km radius) 12-hour
orbits
􀀴 First experimental satellite launched in 1978, operational in
1995
􀀴 Managed by the US National Space-Based Positioning,
Navigation, and Timing (PNT) Executive Committee
􀀴 Standard positioning service (SPS) frequency: 1 575.42 MHz
􀀴 Selective availability (SA) discontinued in 2000
􀀴 ICAO Annex 10, Volume I, section 3.7.3.1
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements: GLONASS
􀀴 Nominal constellation: 24 satellites (fewer active as of March
2007)
􀀴 Three orbital planes
􀀴 Near-circular, 19,100 km altitude (25,500 radius) 11:15-hour
orbits
􀀴 First experimental satellite launched in 1982, operational in
1995, subsequent decline (plans to restore full operational
capability by 2010)
􀀴 Operated by the Ministry of Defence of the Russian
Federation
􀀴 Channel of standard accuracy (CSA) frequencies: 1602 MHz
± 0.5625n MHz
􀀴 ICAO Annex 10, Volume I, section 3.7.3.2
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements:
augmentation systems
􀀴 Three (and a half) ICAO GNSS augmentation
systems:
􀂾 aircraft-based augmentation system (ABAS)
􀂾 satellite-based augmentation system (SBAS)
􀂾 augmentation system (GBAS)
>ground-based regional augmentation system (GRAS)
􀀴 Purpose: to overcome inherent limitations in the
service provided by the core constellations
ground-based
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements: ABAS
􀀴 ABAS: aircraft-based augmentation system
􀀴 The basic element of ICAO GNSS
􀀴 Purpose: to augment/integrate GNSS information with on-board
aircraft information
􀀴 Required to ensure that performance meets Annex 10 requirements
(Volume I, Table 3.7.2.4-1)
􀀴 Uses redundant satellite range measurements (and/or barometric
information) to detect faulty signals and alert the pilot
􀀴 Receiver-autonomous integrity monitoring (RAIM) – five satellites
required (or four + baro)
􀀴 Fault detection and exclusion (FDE) – six satellites required (or five
+ baro)
􀀴 RAIM/FDE availability: are sufficient redundant measurements
available?
􀀴 ICAO Annex 10, Volume I, section 3.7.3.3
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements: SBAS (1)
􀀴 SBAS: satellite-based augmentation system
􀀴 Augments core satellite constellations by providing ranging, integrity and
correction information
􀀴 The information is broadcast via geostationary satellites, in the same band
as the core constellations
􀀴 SBAS elements:
􀂾 a network of ground reference stations that monitor satellite signals
􀂾 master stations processing reference stations data and generating
SBAS signals
􀂾 uplink stations to send the messages to the geostationary satellites
􀂾 transponders on the satellites to broadcast SBAS messages
􀀴 SBAS (where supported) provides higher availability of GNSS services and
lower minima than ABAS
􀀴 Approach procedures with vertical guidance (APV-I and -II)
􀀴 Developments to achieve Cat-I-like minima are underway
􀀴 ICAO Annex 10, Volume I, section 3.7.3.4
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements: SBAS (2)
􀀴 Wide Area Augmentation System (WAAS) - commissioned for
safety-of-life use in 2003
􀀴 European Geostationary Navigation Overlay Service (EGNOS) -
initial operations started in 2005
􀀴 Multi-functional Transport Satellite (MTSAT) Satellite-based
Augmentation System (MSAS) - satellites launched in 2005-2006
􀀴 GPS aided Geostationary Earth Orbit (GEO) Augmented Navigation
(GAGAN) - to be completed in 2008
􀀴 SBAS coverage area vs service area:
􀂾 SBAS coverage area: GEO satellite signal footprint
􀂾 SBAS service area: service area established by a State within
SBAS coverage area
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS elements: GBAS/GRAS
􀀴 GBAS: ground-based augmentation system
􀀴 Operates in the VHF NAV band (108 – 117.975 MHz)
􀀴 Supports precision approach service (currently up to CAT I) and
optionally positioning service
􀀴 Precision approach service provides “ILS-like” deviation guidance
for final approach segments
􀀴 Can support multiple runways
􀀴 GRAS: ground-based regional augmentation system
􀂾 an extension of GBAS to provide regional coverage down to
APV service
􀀴 ICAO Annex 10, Volume I, section 3.7.3.5
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS signal-in-space
performance requirements
􀀴 Accuracy – The difference between the estimated and actual
aircraft position
􀀴 Integrity – A measure of the trust which can be placed in the
correctness of the information supplied by the total system. It
includes the ability of the system to alert the user when the system
should not be used for the intended operation (alert) within a
prescribed time period (time-to-alert)
􀀴 Continuity – The capability of the system to perform its function
without unscheduled interruptions during the intended operation
􀀴 Availability – The portion of time during which the system is
simultaneously delivering the required accuracy, integrity and
continuity
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS signal-in-space performance
requirements (Annex 10, Vol.I)
Typical operation
Accuracy
horizontal
95%
Accuracy
vertical
95%
Integrity
Time-to-alert
Continuity
Availability
En-route 3.7 km
(2.0 NM)
N/A 1 – 1 × 10–7/h 5 min 1 – 1 × 10–4/h
to 1 – 1 × 10–8/h
0.99 to
0.99999
En-route,
Terminal
0.74 km
(0.4 NM)
N/A 1 – 1 × 10–7/h 15 s 1 – 1 × 10–4/h
to 1 – 1 × 108/h
0.99 to
0.99999
Initial approach,
Intermediate approach,
Non-precision approach (NPA),
Departure
220 m
(720 ft)
N/A 1 – 1 × 10–7/h 10 s 1 – 1 × 10–4/h
to 1 – 1 × 10–8/h
0.99 to
0.99999
Approach operations with
vertical guidance (APV-I)
16.0 m
(52 ft)
20 m
(66 ft)
1 – 2 × 10–7
per
approach
10 s 1 – 8 × 10–6
in any 15 s
0.99 to
0.99999
Approach operations with
vertical guidance (APV-II)
16.0 m
(52 ft)
8.0 m
(26 ft)
1 – 2 × 10–7
per
approach
6 s 1 – 8 × 10–6
in any 15 s
0.99 to
0.99999
Category I precision approach 16.0 m
(52 ft)
6.0 m to 4.0 m
(20 ft to 13 ft)
1 – 2 × 10–7
per
approach
6 s 1 – 8 × 10–6
in any 15 s
0.99 to
0.99999
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS signal-in-space performance
requirements (Annex 10, Vol.I)
Typical operation Horizontal alert limit Vertical alert limit
En-route (oceanic/continental
low density)
7.4 km
(4 NM)
N/A
En-route (continental) 3.7 km
(2 NM)
N/A
En-route,
Terminal
1.85 km
(1 NM)
N/A
NPA 556 m
(0.3 NM)
N/A
APV-I 40 m
(130 ft)
50 m
(164 ft)
APV- II 40.0 m
(130 ft)
20.0 m
(66 ft)
Category I precision approach 40.0 m
(130 ft)
15.0 m to 10.0 m
(50 ft to 33 ft)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Future evolution
􀀴GPS and GLONASS evolution (GPS
L5/ GLONASS L3 signals)
􀀴Galileo
􀀴GBAS support of Cat II/III landing
operations
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS implementation
in States
􀀴 Elements to be addressed for a State implementing GNSS
operations:
􀂾 planning and organization
􀂾 procedure development
􀂾 airspace considerations
􀂾 aeronautical information services
􀂾 system safety analysis
􀂾 certification and operational approvals
􀂾 anomaly/interference reporting
􀂾 vulnerability
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Implementation planning
􀀴 Planning to be coordinated on a regional / wide area basis
(common requirements)
􀀴 Coordination through ICAO and its regional bodies (PIRGs)
􀀴 Bilateral/multilateral coordination as necessary
􀀴 Establish a GNSS implementation team, involving users and
appropriate multidisciplinary expertise
􀀴 Sample team Terms of Reference: ICAO GNSS Manual (Doc
9849) Appendix C
􀀴 GNSS plan to include the development of a business case
􀀴 Training requirements
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Procedures development
􀀴 ICAO PANS-OPS (Doc 8168) contains the design criteria for
GNSS procedures
􀀴 Departure, arrival, approach procedures using “basic GNSS”
receiver (ABAS) and/or SBAS/GBAS receiver
􀀴 Includes procedures for “APV” (approach procedure with
vertical guidance):
􀂾 APV/Baro-VNAV
􀂾 APV with SBAS (LPV: localizer performance with vertical
guidance)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Airspace considerations
􀀴 Accurate oceanic en-route airspace
(no conventional navaids available)
􀀴 Lateral separation reductions enabled by ADS
(GNSS-based) in non-radar 􀀴 Continental en-route and terminal airspace: RNAV
arrival and departure procedures reduce delays
and less workload
􀀴 Terminal, approach/departure airspace: support to
aerodromes not served adequately by conventional
navaids
navigation in airspace
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Aeronautical information services
􀀴 State’s Aeronautical information publication (AIP)
to cover these aspects:
􀂾 Description of GNSS services
􀂾 Information about the approval of GNSS-based
operations
􀂾 World Geodetic System – 1984 (WGS-84)
coordinate system
􀂾 Airborne navigation database
􀂾 Status monitoring and NOTAM
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
WGS-84
􀀴 Coordinate system adopted by ICAO to be used in
support of GNSS
􀀴 ICAO Annex 4, 11, 14 and 15
􀀴 Using different coordinate systems is a hazard
􀀴 Transition path to WGS-84:
􀂾 mathematical transformation of existing
coordinate
􀂾 resurvey (preferred option)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Airborne navigation database
􀀴 Safety of GNSS navigation depends on the
integrity of the data in the airborne navigation
database
􀀴 Data originates with States
􀀴 Quality of the position data must be retained
throughout the data chain
􀀴 Manual entry into the airborne database not
permitted
􀀴 EUROCAE/RTCA standards (DO-200A/ED-76 and
DO-201A/ED77)
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
System safety assessment
􀀴Annex 11: safety assessment before
making significant safety-related changes to
ATC system
􀀴Systematic analysis of hazards and
mitigations during all phases of system’s life
cycle
􀂾GNSS safety plan
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Certification and operational approvals
􀀴 State responsibility to authorize GNSS operations
in its airspace
􀀴 Approval document: for aircraft with certified
equipment and approved flight manual
􀀴 Specifies any limitations on proposed operations
􀀴 VFR use or IFR use
􀀴 GNSS alone or with other systems
􀀴 Airworthiness certification based on
RTCA/EUROCAE documents
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Anomaly reporting
􀀴 Anomaly: GNSS service interference)
􀀴 Pilot to report to ATC asap requesting special
handling as required and file complete report in
accordance with State procedures
􀀴 Controllers to record information of the occurrence,
to identify other GNSS-equipped aircraft that may
be affected, and to forward information to
designated authority
􀀴 National focal point unit to information
outage (may be due to
collect anomaly-related
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
Vulnerability
􀀴 Potential for interference is the main vulnerability
􀀴 Receiver interference mask specifies the level of interference that can be
tolerated
􀀴 Several interference sources (eg microwave links within L1 band in some
States)
􀀴 Unintentional vs intentional interference
􀀴 States should:
􀂾 assess sources of vulnerability and develop mitigations (technical,
procedural back-up)
􀂾 provide effective spectrum management and protection of GNSS
frequencies to reduce the possibility of unintentional interference
􀂾 use on-board mitigation techniques (eg inertial)
􀂾 consider selective retention of conventional navaids as part of an
evolutionary transition
􀂾 take full advantage of new GNSS signals and constellations
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
GNSS and PBN
ALL PBN Navigation specifications are
based on GNSS either as the primary
navigation infrastructure or as one
element of the infrastructure
ATMB–CAAC Workshop on GNSS Beijing, 16-17 April 2007
END
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