Chapter 18 GPS and Location-Based Services

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Chapter 18GPS and Location-Based Services

• Yu-Chee Tseng
• cs.nctu.edu.tw

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10 Applications of LBS
(week 2)

• 10 applications that make the most of location
  (Wired Magazine, www.wired.com, 17.02)

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1. Drive Fast, Avoid Cops

• Trapster (iPhone, BlackBerry)
• report red-light cameras, speed cameras, cops
  hiding,

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2. Sleep Easy, Well Wake You Up

• iNap (iPhone)
• Linked to Google map. As long as your GPS gets
  signal, it will wake you up at designated
  destinations.

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3. Target and Tag Location Game

• JOYity (Android)
• 3 location-savvy games (e.g., when a tag is
  within 80 feet, press trackball on your phone to
  execute the tag)

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4. Call a Cab

• Cab4Me (Android)

5. Scan a Barcode, Find a Deal

• ShopSavvy (Android)
• help you to find a cheaper deal somewhere else

6. See the World, Googles Eyes

• Google Earth (iPhone)

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7. Train Your Phone to Know Its Place

• Locale (Android)
• turn off your ringtone at programmed places
• can also change your wallpaper and disable WiFi
  at programmed areas.

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8. Look Up! Be a Stellar Student.

• GoSkyWatch (iPhone)
• to get the name of a star, just point the back of
  your phone toward it (thanks to iPhones
  accelerometer)

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9. Dark Alley? Call for Help.

• SafetyNet (Android)
• Use its map to select bad neighborhood areas.
• When you are in these areas, your mobile phone
  will enter watchdog mode.
• If trouble arises, just shake the handset, and
  your phone will start sending your location to
  your friends/families every 30 sec., take a
  picture, turn on speaker, and dial 911.

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10. Find Public Bathrooms!

• SitOrSquat (iPhone, BlackBerry)

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Introduction to GPS
(week 2)
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GPS????

• GPS consists

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GPS????

• Space segment
• ???24??????
• ?????????(20200km)??????,?????????55?,??????????
• ???????15???,????48????
• ??????????
• GPS????
• ??3-D??
• ????20,200??
• ????11hr 58min
• ????24?/ 6??
• ????55
• ????WGS 84

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GPS????

• ???????????
• ??Time of arrival (ToA)?????
• ??(D) ??(V) x ??(T)

??
?t
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GPS????

• ?????
• ?????????,???????????????????????????????,????????
  ????????
• ????(x,y)?????,???A?B?C???????r1?r2?r3,???????????
  (x,y)?

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GPS???? (?)

• Position calculation
• ???????????
• ?????????????

????http//videos.howstuffworks.com/hsw/13268-dis
covering-math-gps-and-triangulation-video.htm
(341)
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GPS??

• GPS ???????????????
• ??????(Standard Positioning Service,SPS)
• ??GPS L1 ??,??C/A ?(Coarse Acquisition Code)
• ?????12.8 ??(95)
• ?????40ns??(95)
• ??????(Precise Positioning Service,PPS)
• ??????????????
• ??GPS L1 ?L2 ????P(y) ?
• ???????????11.8 ??(95)
• ??????????????12.6??(95)
• ?????40ns ??(95)

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GPS?? (?)

• C/A ??????GPS ?????,?P(y) ???????????????????L2?L2
  C ????????L5(1176.45 MHz),???????L1 ?L2??M ??
• ?????L ?????????????

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GPS?? (?)

• GPS signals
• L1 carrier 1575.42MHz, L2 carrier 1227.6 MHz
• PRN (pseudo random noise) ??????
• C/A (coarse acquisition) code, P (precise) code

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Navigation messages

• System time and clock correction values
• Its own highly accurate orbital data (ephemeris)
• Approximate orbital data for all other satellites
  (almanac)
• System health, etc.

Need 25 different frames
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Almanac data
From http//www.navcen.uscg.gov/gps/current/curre
nt.alm
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????????

• Global Navigation Satellite System (GNSS)
• Global Positioning System (United State)
• Full operational
• GLONASS (Russian)
• Restored to full operation
• Galileo (European Union)
• Initial deployment phase
• BeiDou (Peoples Republic of China)
• Expand regional to global
• QZSS(Quasi-Zenith Satellite System) (Japan)

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LBS(Location-Based Service)
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LAB????

• LBS ?????????
• ??????????????????,??GPS ????
• ???????GSM?3G ?WiFi?????????????????,????????????,
  ??????????(Mobile Location Based ServiceMLBS)???
• LBS ??????????
• ????
• ???????????
• ????

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LBS????

• ????
• ????
• ???????????
• ????????
• ?????????
• ????????????

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• AGPS?DGPS??

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AGPS??

• A-GPS ???????????,???
• ???A-GPS(Online A-GPS)????,??????????????????????
  ???
• ???A-GPS(Offline A-GPS)???A-GPS ????????????GPS
  ???,????????????

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AGPS????

• A-GPS (Assisted GPS)
• ?GPS??????????
• ???GPS startup performance
• ?????signaling(control plane)?????(user
  plane)??Navigation messages

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DGPS????

• ?????(SA)??????,??GPS ???????,DGPS(Differential
  GPS,????????)???????,????????????????
• DGPS???GPS??????,????????????(Reference
  Station)????????????????(Differential
  Correction),????????GPS ?????????????

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GPS ? A-GPS ????
GPS A-GPS
???? ???????? ? ??????????????,??????? ???????? ?????????????? ??????????????????
??? ????? 5-30m?? ???????? 5-15m?
???? ??? (Cold Start) ???? 30 ? 15 ????? ????? (Cold Start),8 ?????????
??? ????? ????