GNSS Conference 8th Feb 05

1
The Bluffers Guide to GNSS Past, Present and
Future
David Park IESSG, University of Nottingham
2
Whats Coming Up?

• What is Satellite Positioning?
• Introduction to GPS
• How Does it Work?
• Introduction to Galileo (Europes GPS)
• Common Jargon Acronyms Explained
• SatNav in the Rail Environment
• Likely Operational Issues
• Areas of probable research and cooperation

3
What is Satellite Positioning?
4
What is GPS?

• GPS Global Positioning System
• GPS is the only Fully Operational SatNav system
• Designed and operated by US Government
• A GPS Receiver Provides Position, Velocity,
  Acceleration and Time Information
• Works Almost Anywhere on Earth, BUT . . .
• Only Works Outdoors

5
What does a GPS Satellite Look Like?
6
How Does GPS Work?

• 24 or more GPS Satellites in Orbit (currently 29)
• Each Satellite is 20,000 km above the Ground
• Each GPS Satellite Continuously transmits a
  signal
• If we know where the satellites are . . . AND
• We calculate the distance from each satellite to
  our receiver (using time) . . . THEN
• We can work out our position (min 4 satellites
  reqd)

7
Comparing GPS Performance

• Performance Accuracy Receiver
  Price Basic 10m 75 -
  1000
• Intermediate 1m 125 -
  2000
• Advanced 0.01m 2000 - 25000
• Also possible to use GPS to measure long term
  movements with accuracy of 1mm (Scientific
  users only)

8
Galileo
Europes very own SatNav
9
So what is Galileo?

• Europe wants (needs?) its own global positioning
  system
• Politics (including issues of sovereignty)
• Industry / Commerce
• Galileo is Europes GPS
• Cost 6 8 Billion Euros
• Fully Operational by 2008 (?)
• (Partially) Funded via PFI, it is expected that a
  range of services and signals will be offered

10
Other Satellite Positioning Systems

• A number of Satellite Positioning Systems are
  planned / in production including
• EGNOS/WAAS (now)
• QZSS (2008?)
• GALILEO (2008?)
• GPS III (2012?)
• GLONASS (???!)
• Chinese System (2012)

11
Common Jargon and Acronyms Explained
12
First the Easy Ones . . .

• GNSS
• Global Navigation Satellite System Generic Term
• GPS
• Global Positioning System US
• DGPS
• Differential GPS (1 metre, or less, real time)
• RTK GPS
• Real Time Kinematic GPS (centimetres, real time)
• L1, L2, L5, E1, E5b . . .
• Refers to the various frequencies at which GNSS
  signals are transmitted (eg L1 1.575 GHz)
• More frequencies Better performance

13
Probably also need to know . . .

• Augmentation System(s)
• For operational reasons, GPS is often augmented
  with complementary position systems (eg INS,
  odometer, LORAN, imagery)
• Some form of Communications is usually required .
  . .
• But what range, bandwidth, latency, etc?
• Coordinate Systems (eg WGS84)
• All raw GPS coordinates / positions are
  presented in the WGS84 global coordinate system.
  
• Positions may then be transformed into local
  coordinate systems (eg for local UK use) or all
  systems can work in WGS84.
• There will probably be differences between the
  same position presented in different coordinate
  systems.

14
May also hear mention of . . .

• Integrity
• Integrity describes the level of trust that can
  be placed in the information provided by the
  navigation system. It includes the ability of the
  navigation system to provide timely and valid
  warnings to users when the system must not be
  used for a particular operation
• Availability
• Availability is defined as the percentage of time
  during which a service is available for use
  (taking into account all outages etc). A service
  is available if accuracy integrity requirements
  are satisfied
• Continuity
• The continuity of a navigation system may be
  defined as The systems ability to perform its
  function without nonscheduled interruptions
  during the intended period of operation.

15
SatNav in the Rail Environment
16
Vulnerability

• Although GPS is now used for many applications,
  the GPS signal is very vulnerable
• Easy to Jam
• Relatively easy to transmit False, GPS-like
  signals
• Also possible for GPS Receivers to Fail
• Users should mitigate with simple tools and
  rules
• Carry a spare receiver
• Always have alternative / additional back-ups
• BE AWARE OF THIS ISSUE!

17
Potential Augmentations
18
Potential Operational Constraints
19
Multi-Disciplinary Approach Required

• Positioning is just one (critical!) element
• We also need to consider (in an effective way)
• Human Factors, Societal Issues, Legal Issues
• Including driver acceptance, institutional
  legislation, certification, etc
• Engineering Issues
• Hardware Robustness
• Communications
• Awareness and Expertise of Rails unique issues,
  attitudes and requirements

20
To conclude . . .

• Great Potential for Position as an Enabling Tool
• Employee Safety, Safety Critical, Value-Added
• Plenty of issues to address
• Technical, commercial, societal, etc
• What we need are
• Strong Intra/Inter University Links
• More Multi-disciplinary Research
• Basic research overseas, mapped back to EU?
• Effective, long-term relationship between
  academia, industry, institutions and the railway

21
Thank You