Indoor Radio Positioning Systems


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Indoor Radio Positioning Systems

  1. 1. Indoor Radio Positioning Systems Naveed Rasheed April 2009
  2. 2. CONTENTS Introduction to Positioning   Positioning Theory Methods  Information required  Comparisons  Indoor Radio Positioning  Why?  Problems  Options  Discussion and Challenges 
  3. 3. INTRODUCTION TO POSITIONING There are basically two types of positioning systems  Where am I? the user wants to know his/her position  Where are you? the system wants to know a target position  Position information is required for many applications  Military  Everyday emergencies  Driving Directions  Location based services (LBS) 
  4. 4. Positioning can be achieved using radiowaves, ultrasound, and infrared. The advantages of using radiowaves is longer range suitablility for non-line-of-sight positioning.
  5. 5. POSITIONING THEORY Positioning methods:   Triangulation  Trilateration  Multileration  Fingerprinting Information required for positioning:   Time of arrival (ToA)  Time difference of arrival (TDoA)  Angle of arrival (AoA)  Received signal strength (RSS)
  6. 6. POSITIONING METHOD: TRIANGULATION Triangulation can be used to find the location of an  object C (such as a ship); Using the angle α at A, angle β at B and the distance  between A and B, we can find the coordinates of C – the position of C. Two angles and one distance are required for a 2D or  3D space.
  7. 7. POSITIONING METHOD: TRILATERATION Trilateration uses the known locations of reference points and  the distance between the object and each reference point. To accurately and uniquely determine the relative location of the object, 3 reference points are needed for a 2D plane and 4 points are required for a 3D space. r2 r1 r3 C
  8. 8. POSITIONING METHOD: MULTILATERATION Multilateration, also known as hyperbolic positioning, is the  process of locating an object by accurately computing the time difference of arrival (TDoA) of a signal emitted from the object to three or more receivers. R3 Generally 4 receivers are needed for a 2D C R1 plane; R2 5 receivers are needed for a 3D space. R4
  9. 9. POSITIONING METHOD: FINGERPRINTING Fingerprinting: the location is estimated by comparing the  measured results with that in a database. The information of comparison could be the signal strength,  profile, and angle of arrival. Simple algorithm.  Prior measurements. 
  10. 10. POSITIONING METHOD COMPARISON Method Triangula- Trilateration Multi- Finger- tion lateration printer RSS (and At least 4 Information One At least 3 phase, or TDoAs required distance & ToAs without AoA even AoA) two angles without AoA information information Advantages Fewer Rx Simple No sync Simple required (2), positioning between Tx positioning no sync req. algorithms and Rx alg and sys Drawbacks High AoA High sync Sync Prior meas. accuracy req. for Tx between Tx Large data requirement and Rx req. base, accuracy
  11. 11. INDOOR RADIO POSITIONING SYSTEMS Why do we need indoor radio positioning systems?  Because the outdoor systems (such as GPS) don’t work indoors!  Because there are many possible attractive positioning  applications in security, asset tracking, navigation, health care. What are the problems?  Multi-path effects  Attenuation 
  12. 12. What options do we have  Cellular radio based systems? The precision is not very  good. COMPANY SYSTEM ENVIRONMENT REPORTED ACCURACY Nokia GSM Urban / Suburban 67% CPS GSM Suburban 69% KSI AOA IS-136 67% VTT GSM Suburban 67% US Wireless AMPS Light Urban / Suburban 67%
  13. 13. WiFi/WLAN/Network based systems? A possibility, but the  accuracy could be a problem
  14. 14. Ultra-Wide Band (UWB) based systems? Seems to be the  best option for most applications
  15. 15. UWB signals are relatively immune to multipath effects 
  16. 16. POSITIONING SYSTEM It consists of many tags (T) and base stations (BS) at known locations which are connected to the Monitoring Centre (MC) BS BS T T T MC BS T T BS BS
  17. 17. BS BS Data Ethernet Tag Switch MC BS BS Clock Ethernet 17
  18. 18. DISCUSSIONS AND CHALLENGES A number of systems have been developed, but they only work well provided that there is a LOS path which means that we need to deploy a lot of BS, the cost could be very high!
  19. 19. Base stations:  Resource allocation and anti-collision are two of the major  issues to be considered Synchronisation of BS  Base station locations and deployment  Pathloss and radio coverage: they are functions of building materials and frequency: the higher the frequency, the higher the loss (hence the smaller the coverage). Through wall positioning is extremely challenging.