GPS: Applications to Distributed Systems and Networks

1
GPS Applications to Distributed Systems and
Networks

• Raj Jain The Ohio State UniversityColumbus, OH
  43220Jain_at_ACM.Org http//www.cse.ohio-state.edu/
  jain/

2
(No Transcript)
3
Overview

• Principles of operation
• Current applications
• Potential applications
• Obstacles
• Current products and manufacturers

4
Executive Summary

• Precise determination of location, velocity,
  direction, and time.
• Price is falling rapidly and applications are
  growing
• Goal was to survey current applications
• Most efforts are in providing navigational
  guidance to drivers
• Only two non-navigational applications
• Identified many new applications of GPS for
  distributed computing and networking
• A few obstacles to GPS deployment
• Detailed lists of GPS products, addresses of
  manufacturers
• Sources for further information

5
Introduction

• Space-based radio positioning system
• Provide
• time
• three-dimensional position
• velocity
• First conceived after the launch of Sputnik 1 in
  1957
• Measuring the frequency shifts in the small
  bleeps ??Distance

6
Principles of Location Determination

• Broadcast signals allow computing the distance
  from the satellite
• Distance from one satellite ? Any point on the
  circle (sphere)
• Distance from two satellites ? Two points
  (circle)Ridiculous answer can be eliminated
• Distance from three satellites ? One point (two
  points)
• Distance from four satellites ? One point

7
NAVSTAR

• Constellation of 24 satellites (Three are spare)
• Orbiting at a height of 10,900 nautical miles
• Orbital period of 12 hours
• Planned life span of 7.5 years
• Orbits inclined 55 degrees to the equatorial
  plane
• Provide a minimum of four satellites in good
  geometric positions
• Up to 10 GPS satellites are usually seen
• Each satellites carries several cesium clocks
• Positional accuracy of 100 m, Timing accuracy of
  300 ns
• Frequency accuracies of a few parts in 1012

8
NAVSTAR (Cont)

• Two L band frequencies, L1 (1575.42 MHz) and L2
  (1227.6 MHz)
• L1 carries a precise (P) code and a
  coarse/acquisition (C/A) code
• L2 carries the P code
• The P code is encrypted (also known as Y code)
• Only the C/A code is available to civilian users
• Space vehicle (SV) number Assigned in order of
  launch
• Two services SPS and PPS

9
Standard Positioning Service (SPS)

• Sandard level of positioning and timing accuracy
• Available to any user on a continuous worldwide
  basis
• 100 m horizontal accuracy
• 156 meter vertical accuracy
• 167 ns time accuracy

10
Precise Positioning Service (PPS)

• Can only be accessed by authorized users with
  cryptographic equipment and keys
• US and Allied military and approved civil users
• Accuracy
• 17.8 meter horizontal
• 27.7 m vertical
• 100 ns time

11
Selective Availability (SA)

• Intentional degradation by DOD to limit accuracy
• For non-US military and government users
• Accuracy of C/A code reduced from 30 m to 100 m

12
(No Transcript)
13
Differential GPS (DGPS)

• Method of eliminating errors in a GPS receiver
• Assumes most of the errors seen by GPS receivers
  are common errors
• Caused by clock deviation, selective
  availability, drift from predicted orbits,
  multipath error, internal receiver noise and
  changing radio propagation conditions in the
  ionosphere
• Use a base station with known location to
  determine error
• Use the error to correct the location of rovers
• Continuous broadcast ? real-time DGPS
• Post-processing correction (Used in surveying)
• Offers accuracies of few m

14
Accurate Time using GPS

• GPS Time Within 1 ?s of UTC. Began on January
  6, 1980
• No leap seconds ? Lags behind UTC
• Constant offset of 19 s with the International
  Atomic Time
• Time accuracy from GPS signals
• Better than 340 ns (95 probability) using SPS
• 100 ns using PPS
• Inexpensive GPS receivers operating at known
  positions ? accuracy of about 0.1 ?s with only
  one satellite in view
• With more sophisticated techniques, one ns is
  possible (globally)
• Requires advanced preparation, coordination of
  the two sites and tracking of specific satellites
  during specific time periods

15
Accurate Time using GPS

• Time accuracy from GPS signals
• Better than 340 ns (95 probability) using SPS
• 100 ns using PPS
• Inexpensive GPS receivers operating at known
  positions ? accuracy of about 0.1 ?s with only
  one satellite in view
• With more sophisticated techniques, one ns is
  possible (globally)
• Requires advanced preparation, coordination of
  the two sites and tracking of specific satellites
  during specific time periods

16
Current Applications of GPS

• Frequency Counters
• Intelligent Vehicle Highway Systems (IVHS)
• Car Navigation Systems
• Geographic Information Systems (GIS)
• Emergency Systems Backpacking
• Aviation
• GPS Aides for the Blind
• Astronomical Telescope Pointing
• Atmospheric Sounding using GPS Signals
• Tracking of Wild Animals
• Recorded Position Information
• Airborne Gravimetry

17
Commercial Efforts

• Trimble Bell Atlantic, Trimble IBM, PacTel
  Cellular Wireless Wireless Solutions Inc
• Vehicle tracking and location devices
• Ford
• GPS based car alarms to locate stolen cars,
• Traffic control, Vehicle tracking, Vehicle
  recovery, Navigation, Mapping
• Avis Testing GPS in rental cars in NYC area
• As a navigational aid
• DeTeMobil
• GPS receivers in all cars in Germany
• Pay tolls using smart cards and GSM digital phone

18
Current Distributed Systems and Networking
Applications

• Network delays in DA-30
• SONET Synchronization

19
Network Delays

• Wandel Goltermann Inc.
• DA-30 Internetwork Analyzer uses GPS to make
  latency measurements between Ethernet LANs linked
  by a WAN
• GPS boards lock into the GPS time signal
  broadcasts
• S/W conducts latency trials
• Accurate to within 150 ?s
• Requires two kits priced at 6,750 each
• Ref Government Computer News, March 21, 1994,
  vol. 13, no. 6, p.64.

20
SONET Clock Distribution

• Multiple bit streams to a single network element
  ? Need synchronized clocks
• CCITT Recommendation G.811 ? Long term frequency
  departure
• Building Integrated Timing Supply (BITS) is
  Bellcore's clock-system specification ?
  Multi-level hierarchy
• Stratum 1 (ST-1) is the highest quality clock
• BITS allows LORAN/Rubidium ST1 clock systems
• ATT's primary reference clock (PRC) uses GPS
  signals for long term timing accuracy
• Rubidium oscillators provide short-term stability
• Ref Telephony, August 24, 1992, pp. 50-54.

21
Potential Applications to Distributed Systems
and Networks

• Time applications
• Position Applications

22
Time Applications

• Circuit Switching Using Synchronized Clocks
• Synchronous Slotted Systems
• Clock Synchronization in Distributed System
• Database Synchronization
• Connectionless Real-time Communication
• Real-Time Communications
• One-Way Delay
• Delay based routing
• Time to Live

23
Circuit Switching Using Synchronized Clocks

• Synchronized clocks ? circuit switching easy
• Precompute switching schedule
• Similar to synchronized lights on roads

24
Synchronous Slotted Systems

• Slotted systems are less sensitive to distance
  bandwidth product
• More suitable for high speed or long distance
  networks
• Slotted architectures for all-optical,
  multi-gigabit networks
• Need clock synchronization
• GPS clocks an all-optical ARPA research project

25
Clock Synchronization in Distributed System

• Clock difference
• Currently NTP, OSF-DTS, DECdts, Fuzzbal, timed
• Future GPS clocks (1 ns) at least in timeservers
• Ordering of events (e.g., FCFS scheduling)
• Consistent update of replicated data
• At most once receipt of messages
• Authentication tickets in some systems (e.g.,
  Kerberos)
• Ensuring atomicity
• Expiration of privileges
• Prearranged synchronization
• Ordering multi-version objects

26
Database Synchronization

• Synchronization after a failure or a disconnected
  operation
• Use logs with timestamp to decide the order of
  actions
• More precise clocks ? less conflicts

27
Connectionless Real-time Communication

• Delay guarantees on IP-like networks ? Need
  deadline scheduling
• GPS ? Deadline timestamp on the packet
• Similarly, scheduling subtasks of real-time tasks

28
One-Way Delay

• Currently, clock differences one-way
  delays??Can't measure one-way delay
• Round-trip delays used instead
• Example ATM networks ABR parameters are
  fn(delay)
• GPS synchronized clocks at source and
  destination? exact one-way delay between source
  and destination and to every switch can be
  measured with a single timestamp.

29
Delay based routing

• Internet uses link delays for routing
• Accurate measurement is difficult ? approximate
  or round-trip delay used
• GPS provided exact one-way delay can be used

30
Time to Live

• Helps remove old packets from the networks
• Currently, the time-to-live field is decremented
  by 500 ms regardless of actual delay
• With GPS synchronized clock, exact time-to-live
  possible

31
Diagnostics/Maintenance of system clocks

• A GPS frequency calibrator can be used to
  periodically check crystals in various equipment

32
Time and Frequency Alternatives

• National Institute of Standards and Technology
  (NIST)
• WWV and WWVH radio broadcasts (accurate to 1 ms)
• WWWVB broadcasts (2 to 3 parts in 1011)
• US Naval Observatory (USNO)
• Loran-C (LOng RAnge Navigation)
• Land based radio navigation system
• Frequency accuracies of 1 part in 1012, Time
  better than 1 ?s
• Both USNO and NIST provide
• Telephone voice messages (accuracy 30 ms)
• Computer modem time transfer (several ms)
• Remote synchronization of time bases (10-9).

33
Position Applications

• Resource Location
• Location Adaptive Protocols
• Handoffs in Wireless Networks
• Prescheduled Hand-overs Based on Velocity and
  Direction
• Adaptive Transmission Power Control Algorithm
• Directional Antennas
• Temporary Cell Partitioning for Congestion
  Avoidance
• Peer-to-peer Routing with Limited Range Receivers
• Email Delivery Based on Geographic Location
• Distributed Robot Control and Navigation
• Equipment Location Marking for Maintenance Crew

34
Resource Location

• Digitized maps and GPS locations
• Find the nearest printer or fileserver
• Prescheduling possible

35
Location Adaptive Protocols

• Currently, networking is location transparent
• Service decisions do not use location
• In many applications, knowing location helps
• Examples Home vs Office vs Car. Electronic Fence.

36
Home vs Office vs Car

• Different physical medium wire, ISDN, modem,
  cellular, or radio
• Different bandwidth bandwidth, cost, and error
  characteristics
• Mobile computing decisions fn(GPS
  location)Example Which files to fetch for home
  vs other town

37
Electronic Fence

• Company confidential papers stay within physical
  walls
• GPS provides electronic fence for electronic
  information
• Information usable only if computer is within the
  corporate boundary

38
Handoffs in Wireless Networks

• Inter-cell (change base) or intra-cell (change
  channel)
• Decision by base or by mobile unit
• Currently use signal strengthBetter to use
  position
• Avoids passive listening to beacons
• Simplifies handoff

39
Prescheduled Uninterrupted Handoffs

• Signal strength ? Difficult to predict future
• GPS location, velocity, and direction ? Future
  predictable
• Handoff ? Interruption in service as the packets
  sent to the previous base have to be forwarded to
  the new base
• Prediction ? Prenegotiate the hand-over with all
  parties

40
Adaptive Transmission Power Control Algorithm

• Battery lifetime is important for mobile
  computing
• Little hope for exponential increase in lifetime
• Need to save battery usage
• Optimize transmission power
• Nearby base ? transmit less power
• Also allow frequency reuse in the same cell

41
Directional Antennas

• Transmission in all directions ? most of the
  energy wasted
• GPS ? less power
• Particularly helpful for satellite communication
• Also allow better packing density - more users
  for the same space
• Provides the minimum radiated RF pattern for
  covert communications.
• Can talk to the least busy base unit even if it
  is not closest unit

42
Temporary Cell Partitioning for Congestion
Avoidance

• Cell splitting Dividing a cell to form new cells
• Allows reuse of spectrum and helps in reducing
  congestion
• Requires prior preparation and usually a
  permanent change
• GPS ? dynamic, quick, temporary splitting
  feasible
• Can also be used in case of base station failures

43
Peer-to-peer Routing with Limited Range Receivers

• Civilian wireless communication uses base units
• Military communication ? no pre-existing
  infrastructure? Better to use peer-to-peer
  communication
• Position, heading, velocity, as well as, digital
  terrain topology information can be used for
  optimum routing

44
Email Delivery Based on Geographic Location

• Name, addresses, route, and physical position are
  not related
• Multicast/anycast to a particular geographic
  location
• For example, "to all police cars near Stanford
  university on route 101"

45
Distributed Robot Control and Navigation

• Intelligent robots can use position and
  environment information
• Unmanned vehicles can navigate effectively.

46
Equipment Location Marking for Maintenance Crew

• Service requesters (mobile or stationary) provide
  GPS location
• Maintenance crew carry GPS to locate the equipment

47
Current Limitations of GPS

• Selective Availability degrades achievable
  accuracies
• Temporary outage of the receiver as the receiver
  passes under obstructions? GPS for performance
  not for operation
• Systems should continue to work without the GPS
• Like cache memories

48
Details of Selected Products

• Trimble's Mobile GPS Card Type II PCMCIA GPS
  sensor by Trimble (995). 3 channels tracking up
  to 8 satellites. 100 m accuracy. Acquisition time
  of less than 30 s and re-acquisition rate of 2-3
  s.
• Trimble's Mobile GPS Gold Card
  Differential-ready (1,595). Provides 2-5 m
  accuracy in real-time.
• Trimble's Mobile GPS Intelligent Sensor 100
  Low-end sensor 395
• Rockwell's NavCard PCMCIA GPS sensor
• Mobile Computing Kit Includes pen-based TelePad,
  Proxim's RangeLAN, cellular phone, Trimble GPS,
  FotoMan Plus camera, ScanMan, AudioMan (7,299).

49
GPS Software Applications

• GPS for windows (1,995) By Peacock Systems
• City Streets for Windows 99.95 by Road Scholar
  software
• Streets on a Disk By Kylnas Engineering
  (22595/county)
• Map'n'GO (50) 3CS Software.
• NCompass 3.0 for Windows - real time GPS
• Zagat-Axxis CityGuide by Axxis Software.
• MapInfo for Windows 3.0 MapInfo Corp.
• Atlas GIS for Windows 2.0 By Strategic Mapping
  Inc.
• GISPlus for PC By Caliper Corp.
• Maptech Professional Marine Chart S/W (1,290)
  by Resolution Mapping Inc.

50
Summary

• Cheap PCMCIA receivers for 300-400 ? Growing
  applications
• Currently mostly for navigational guidance to
  drivers
• SONET and Wolter and Golderman's DA-30 network
  analyzer
• Many many potential applications
• Main obstacles Antennas must point to open sky

51
References Books

• Jeff Hurn, Differential GPS Explained, Trimble
  Navigation, 1993.
• Jeff Hurn, GPS A Guide to the Next Utility,
  Tremble Navigation, 1988.
• David Wells et al., Guide to GPS Positioning
  (ISBN 0-920-114-73-3), Canadian Associates,
  1986.
• Tom Logsdon, Navstar Global Positioning System,
  Van Nostrand Reinhold, 1992.
• Hoffmann-Wellenhof, et al, Global Positioning
  System, Theory and Practice, 3rd Edition,
  Springer-Verlag.
• Ackroyd and Robert Lorimer, Global Navigation-A
  GPS users guide, 2nd Edition, Loyds of London,
  1994.

52
References On-Line

• Michael Heflin, Global GPS Time Series.''
  http//sideshow.jpl.nasa.gov/mbh/series.html
• Peter H. Dana, An Overview of the Global
  Positioning System (GPS),'' http//wwwhost.cc.utex
  as.edu/ftp/pub/grg/gcraft/notes/gps/gps.html
• Hal Mueller, Hal Mueller's GPS Sources,''
  http//www.zilker.net/hal/geoscience/gps.html
• John T. Beadles, Introduction to GPS
  Applications,'' http//www.einet.net/editors/john-
  beadles/introgps.htm

53
ThankYou!
54
GPS Standards

• NMEA-0183 Data format standard for
  communications between ship-borne navigationGPS
  receivers output this format but do not accept
  it.
• RTCM-104 Radio Technical Commission for Maritime
  (RTCM) Services standard for DGPS
  operation.Version 2 used by many beacon systems
  (including the US Coast Guard system)Version 2.1
  includes additional information for the transfer
  of real-time kinematic data

55
Other Radio Navigation Systems

• GLONASS Russian 24 satellites
• LORAN-C LOng RAnge Navigation
• TRANSIT First satellite system
• Timation
• Low-Altitude Satellites

56
LOng-RAnge Navigation (LORAN-C)

• Ground-based radio navigation
• Two versions
• Loran C for civilian users
• Loran D for military
• A master and up to four secondary transmitting
  stations
• Radio pulses centered on 100 kHz
• Difference in arrival time ? position
• Range Over 1500 kilom from master stations
• Accuracy 100 to 500 m
• Better than 30 m on shorter range

57
GLONASS

• Russian
• 24 satellites
• Precise (P) code and a coarse/acquisition (C/A)
  code
• P code is encrypted for military use
• C/A code is available for civilian use

58
TRANSIT

• First operational satellite navigation system
• Developed by the Johns Hopkins Applied Physics
  Laboratory
• Used Doppler shift of a radio signal transmitted
  from the satellite
• Limitations
• Two dimensional
• Mutual interference ? Max five satellites
• Satellites visible for only limited periods of
  time

59
Timation

• Developed in 1972 by the Naval Research
  Laboratory (NRL)
• Satellites intended to provide time and frequency
  information
• Initially used quartz crystal oscillators
• Later atomic clocks
• Acted as a GPS technology demonstrator.

60
Low-altitude Satellites

• Experiments are also being
• Poposals to place GPS tansmitters on low altitude
  satellites
• Would greatly reduce the cost

61
Time Synchronization Techniques

• Absolute time synchronization
• Receiver picks up the signals from a single GPS
  satellite
• Accuracies of about 100 ns (with S/A off) and 300
  ns (with S/A on)
• Clock fly-over
• Satellite swings up over two sites
• Yields a clock synchronization error of around 50
  ns
• Common view mode
• Two distant sites have line-of-site to the same
  satellite at the same time.
• Yields synchronization errors of 10 ns or less
• Multi-satellite common view mode
• Four or more satellites that are being observed
  simultaneously from the two different clock sites
• Can achieve synchronization errors as small as 1
  ns

62
Frequency Counters

• Accurate frequency counters, time interval
  counters, frequency calibrators and phase
  comparators can be built using the GPS technology
• GPS clock module Stellar GPS Corp (now
  Absolute Time Corp)
• L1 C/A GPS receiver optimized for frequency and
  time
• Provides a stable 10 MHz reference frequency
• RMS pulse-to-pulse jitter of 1 ns for 1 pps
  output
• Frequency/timing offset measurements (timing
  resolution is 5 ns and frequency resolution of
  10-12

63
Intelligent Vehicle Highway Systems (IVHS)

• To improve highway safety
• Ease traffic congestion
• Reduce harmful environmental effects

64
Car Navigation Systems

• GPS receiver digital maps
• Provides location and directions

65
Geographic Information Systems (GIS)

• GPS receiver Digital maps Cellular networks
• Permit state and local governments
• Efficiently coordinate roadway maintenance and
  construction in rural areas
• Provide efficient ways of maintaining roadway
  databases
• Maintain accident inventories

66
Emergency Systems

• Emergency system communicates the position to the
  base
• car alarms with GPS to locate stolen cars

67
Aviation

• Aircraft safety systems
• Air traffic control
• Can plot aircraft altitude to a pitch of 0.1
  degree
• Zero visibility landing
• Will reduce the manpower in the control tower and
  cockpit

68
GPS Aides for the Blind

• Real time GPS along with digitized maps and audio
  capability
• To provide useful navigational capabilities

69
Astronomical Telescope Pointing

• Observe the occultation of stars by asteroids
• To determine the sizes and shapes of asteroids
• Need mobile telescopes placed in the predicted
  path of the shadow
• Odetics GPStar 325 receiver feeds coordinates to
  a computer
• Timing signals are used to time the event
• Ref Mark Trueblood In the Shadow of the
  Asteroid,'' GPS World Vol 4, no. 11, November
  1993, pp. 22-30.

70
Atmospheric Sounding using GPS Signals

• Observe planetary atmospheres
• Mariner and Voyager's radio signals transected a
  planets atmosphere
• Detected phase changes in the radio signals
• Can estimate atmospheric refractivity, density,
  pressure temperature and humidity.

71
Tracking of Wild Animals

• To track animals and for studying their nomadic
  patterns
• Animals are equipped with GPS receivers and with
  wireless transmitters
• Position is transmitted to the control station

72
Recorded Position Information

• To track executives
• To determine charges (highway toll)
• To search for stolen items (cars)
• To study the migratory patterns (animals)
• To validate legal claims

73
Airborne Gravimetry

• To accurately position airplanes in flight
• Its vertical acceleration and tilt can be
  monitored with GPS
• Airborne gravimetric data can be used for natural
  resource exploration

74
Other Uses

• Surveying
• Navigation of missiles
• Electric power synchronization
• Census taking
• Backpacking emergency systems
• Natural resource management

75
Commercial Efforts (Cont)

• Seiko Communications
• Global wireless information services using FM
  radio.
• Includes differential GPS data.
• Fujitsu
• The Car Marty vehicle multimedia device (2,640),
• Consists of a system box, a CD player, and a 5.6"
  color TV
• Sony Mobile Electronics and Etak Inc.
• Computerized navigation system for automobiles
  (2,200)
• PCMCIA GPS receiver on laptop computers
• Info on restaurants, hotels, entertainment and
  shopping
• Includes a CD-ROM (for map), a GPS antenna, a 5"
  color LCD display

76
Commercial Efforts (Cont)

• Toshiba Developed a portable navigation system
• Tusk Inc Tusk 386 - an all terrain supertablet
  pen computer with GPS.
• Penstuff Trimble Navigation
• Combine GPS technology with pen computers
• Developed GPS standard for PenPoint
• Record location in terms of latitude, longitude
  and altitude
• Motorola
• Cellular Positioning Emergency Messaging Unit
• Communicates GPS-determined vehicle position and
  status
• Also traxar Hand-held navigational computer.

77
TrueClock

• Marketing term like ATT's True Voice''
• Products implementing GPS clock marked True
  Clock''

78
GPS Products and Services

• 200 million (sold) in 1992. Could reach 500M in
  1995
• Include receivers, modems, simulators, range
  finders, robotic systems, and navigation modules.
• GPS Receivers and Stations
• Land Vehicle Receivers
• Mapping Receivers
• Aircraft Receivers
• Miscellaneous Receivers
• OEM receivers
• PC Card (PCMCIA) Receivers
• Shipboard Receivers

79
Products (cont)

• Spacecraft Receivers
• Surveying Receivers
• Timing Receivers
• Modems
• Satellite Simulators
• Laser Range Finders
• Robotic Total Stations
• Navigation Modules
• Scientific GPS Software Suites
• DGPS Correction Signal Services
• Addresses of GPS Equipment Manufacturers. See
  report.

80
GPS S/W (Cont)

• GPSez and GPSpac for Windows (1,290) by General
  Engineering and Systems S.A.
• GPS MapKit XV By DeLorme Mapping. It links GPS
  to maps.
• GPS Signal Simulation software Accord Software
  and Systems. (495). Platform to experiment with
  various modules of signal processing section of a
  GPS receiver.