This document discusses indoor radio positioning systems. It begins with an overview of positioning methods such as triangulation, trilateration, multilateration and fingerprinting. It then discusses challenges with indoor positioning like multipath effects and attenuation. It evaluates options for indoor positioning systems including cellular, WiFi, and ultra-wide band (UWB) systems. UWB seems the best option due to its ability to mitigate multipath effects. The document concludes with challenges for deploying indoor positioning systems at scale, such as cost of deploying many base stations and issues with base station resources, synchronization, locations and coverage.

1. Indoor Radio Positioning Systems
Naveed Rasheed
April 2009

2. CONTENTS
Introduction to Positioning

 Positioning Theory
Methods

Information required

Comparisons

Indoor Radio Positioning

Why?

Problems

Options

Discussion and Challenges


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. 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. 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. 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. 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. 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. 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. 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. 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. 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. WiFi/WLAN/Network based systems? A possibility, but the

accuracy could be a problem

14. Ultra-Wide Band (UWB) based systems? Seems to be the

best option for most applications

15. UWB signals are relatively immune to multipath effects


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. BS
BS
Data
Ethernet
Tag
Switch
MC
BS
BS
Clock Ethernet
17

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. 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.

20. SUPPORT AND GUIDANCE OF
Dr. YI HUANG
IS ACKNOWLEDGED