Satellite Based Augmentation Systems - SBAS Lecturer: Michael O'Grady
Course: MSc Ubiquitous & Multimedia Systems
Unit: Context Sensitive Service Delivery
Lecture: SBAS
Satellite Based Augmentation Systems - SBAS Lecturer: Michael O'Grady
Course: MSc Ubiquitous & Multimedia Systems
Unit: Context Sensitive Service Delivery
Lecture: SBAS
Objectives
Outline current developments in Satellite Based Augmentation Systems (SBASs)
Satellite - Current Developments
Global Navigation Satellite System (GNSS)
Aims to resolve the conflict between civilian and military demands
seeks to provide position readings to within 3 metres
Two phases
GNSS-1
Resolves most technical issues
Political issues still remains
Introduces Satellite Based Augmentation Systems (SBASs)
GNSS-2
Seeks to provide a global infrastructure for positioning and timing
Both GPS and GLONASS have successfully demonstrated both the feasibility and the usefulness of satellite-based navigation techniques. However there are still a number of issues, both technical and political, that need resolution. For example, neither system is considered accurate enough for use in aviation situations, which require very exact position readings in real-time, e.g. for landing at times of poor visibility. This situation has received considerable attention and a number of systems are being developed to augment GPS. From a political perspective, both GPS and GLONASS were developed for military purposes and remain under military control. The conflict between civilian demands and military demands has given rise to a number of issues, most of which are of a legal nature [Lar01]. To overcome these obstacles, plans for a Global Navigation Satellite System (GNSS) were put in place, the implementation of which will be take place in two phases termed GNSS-1 and GNSS-2 [LB00].
GNSS-1 - EGNOS
European Geostationary Navigation Overlay System (EGNOS)
Developed by
European Commission
Eurocontrol
European Space Agency
Coverage area includes
all Europe, Africa and the Middle East
parts of Asia and South America
Uses INMARSAT-3 satellites for broadcasting correctional and integrity data
Scheduled for launch in 2006
A joint project of the European Space Agency (ESA), the European Commission (EC) and Eurocontrol, the European Organisation for the safety of Air Navigation, EGNOS [BMV99] [URL25] is Europe’s first venture into satellite navigation and will provide similar functionality to WAAS. It will augment both GPS and GLONASS signals and in contrast to WAAS, which is only available in the US, EGNOS will provide coverage for all of Europe, Africa, the Middle East, parts of Asia and parts of South America. It consists of a network of ground stations and uses INMARSAT-3 satellites for broadcasting correctional and integrity data. Though test signals are currently being broadcast, EGNOS will not be fully operational until 2004.
GNSS-1 - WAAS
Wide Area Augmentation System (WAAS)
Designed by the Federal Aviation Authority (FAA)
Designed to provide precise navigational services to aircraft for the duration of flight
Network of 25 ground stations spread across the USA
INMARSAT-3 used to broadcast connections
same frequency as GPS signal
Receiver must be WAAS enabled
Currently being deployed
Developed by the FAA, WAAS [FAA97] is intended to provide aircraft with precise navigational services for the duration of its flight. The key component of WAAS is a network of 25 ground reference stations spread across the USA. These receive and process GPS data, after which the corrections are transmitted to INMARSAT-3 (International Maritime Satellite Organisation) geostationary satellites. These broadcast the information on the same frequency as the GPS signal to WAAS-enabled GPS receivers onboard the aircraft. Accuracy can be increased from 100m to less than 3m. WAAS is scheduled to become operational in late 2003.
GNSS-1 - LAAS
Local Area Augmentation System (LAAS)
intended to operate when WAAS cannot
I.e when visibility is less than 1 km
Deployed in the immediate vicinity of airports
Will only broadcast data to aircraft in sight of the corresponding ground reference station
Intended to operate when WAAS cannot, namely in circumstances where visibility is less than 1 km, LAAS [FAA99] is designed to work in the immediate vicinity of airports. It will only broadcast GPS correction data to aircraft that are in sight of the corresponding ground reference station.
GNSS-1 - MSAS
Multifunctional Transport Satellite Augmentation System (MSAS)
Services include
Navigation
Meteorology
Architecture
24 ground stations
2 satellites
Features
Area covered include most Asia/Pacific air space
Compatible with EGNOS and WAAS
Developed solely by Japan
Multifunctional Transport Satellite Augmentation System (MSAS)
Designed for both navigation and meteorological purposes, MSAS [KKI01] will consist of two geostationary satellites and 24 ground stations. Though difficulties were encountered in the project, it is hoped to be fully operational by 2004. MSAS is comparable to both WAAS and EGNOS and, like EGNOS, is compatible with WAAS. Though MSAS is being developed by Japan, it is planned to cover most of the Asia/Pacific air space and is scheduled to become operational in 2005.
GNSS – Developments
India
GAGAN
China
SNAS
Canada
CWAAS
EGNOS - Services
GEO Ranging
GPS-like signals
GMSS Integrity Channel
Signal integrity information
Wide Area Differential (WAD)
Differential corrections
EGNOS - ARCHITECTURE
Four Segments
Space
Ground
User
Support Facilities
EGNOS Diagram
EGNOS – Space Segment
Three Geostationary transponders
INMARSAT-3 AOR-E
INMARSAT-3 AOR-W
ESA ARTEMIS
EGNOS Ground Segment - RIMS
Ranging and Integrity Monitoring Stations (RIMS)
GPS, GLONASS, EGNOS(!)
34 stations (mainly in Europe)
GPS/GLONASS/EGNOS receiver
Atomic clock
Network access
RIMS tasks
Pseudorange measurements
Demodulate SIS messages
Mitigate multipath & interference
Verify signal integrity
Packet & transmit data to MCC
EGNOS Ground Segment - MCC
Mission/Master Control Centre (MCC)
4 stations in Europe
Monitoring & control of EGNOS
Real-time software processing
MCC tasks
Integrity determination
Pseudo-range corrections for each satellite
Ionospheric delay
Generate Satellite (EGNOS) ephemeris
EGNOS Ground Segment - NLES
Navigation Land Earth Station (NLES)
Two for each satellite (EGNOS)
1 primary
1 backup
One for Test & Validation
NLES Tasks
Generate GPS-like signal
Generate GIC signal (GNSS Integrity Channel)
Generate Wide Area Differential (WAD) signal
Transmit signals to GEO (EGNOS)
EGNOS Ground Segment - EWAN
EGNOS Wide Area Network
Links all EGNOS ground-based components
EGNOS – User Segment
EGNOS Receiver
Uses
Civil Aviation
Land
Marine
EGNOS – Support Facilities
Support for
Development
Operations
Verifications
SISNet
Signal In Space over the Internet (SISNet)
Provides EGNOS signal over standard TCP/IP connection
User Requirements
PDA/mobile phone
Wireless data connection e.g. GPRS
GPS card/receiver
Why SISNet?
Recall …
Geostationary orbits
Low elevation angles
So…………
Consider
In urban canyon?
At high latitudes?
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