Wireless Indoor Positioning Techniques

Rilind BallazhiSupervisor: Prof. Dr. Károly Farkas

Communication Systems SeminarFS 2012

Wireless Indoor Positioning Techniques 1

Agenda

• Introduction

• Positioning Techniques

• Positioning Algorithms

• Measurement Techniques

• Positioning Systems

• Comparison of the Systems

• Summary and Conclusion

• Discussion

Communication Systems Seminar

Agenda

• Introduction

• Discussion

Introduction

• High demand in recent years

• Used in many applications

Objectives:

• Investigate the techniques and systems of wireless indoor positioning

• Compare the different indoor positioning systemsCommunication Systems Seminar

Mobile Terminal

Base Stations

Propagated Signal Location metrics: TOA, AOA...

Positioning Algorithm

Location coordinates

Display System

Reference Point

Received Signal

Agenda

• Introduction

• Discussion

Positioning Techniques

Positioning TechniquesPositioning Algorithms

• Triangulation

• Trilateration

• Scene Analysis

• Proximity

• Triangulation

• Trilateration

• Scene Analysis

• Proximity

• Estimates an object by computing angles relative to multiple reference points

• The object to be located is used as a fixed point of a triangle

• Usually AOA used for angle measurement

• Triangulation

• Trilateration

• Scene Analysis

• Proximity

• Estimates the position of an object by measuring its distances from multiple reference points

• The distance is computed by multiplying the radio signal velocity and the travel time

• Usually TOA and TDOA used for distance measuring

• Triangulation

• Trilateration

• Scene Analysis

• Proximity

• Type of algorithms that first collect features of a scene and then estimate the location of an object by matching

• Two stages:• offline• online

• Received Signal Strength is commonly used in Scene Analysis

• RSS could be affected by diffraction, reflection and scattering

• Fingerprinting-based positioning algorithms• probabilistic methods• k-nearest neighbor• neural networks• support vector machine (SVM)• smallest M-vertex polygon (SMP)

• Triangulation

• Trilateration

• Scene Analysis

• Proximity

• Provides symbolic relative location information

• Relies upon a dense grid of antennas, having a well-known position

• If mobile target detected by a single antenna• mobile target collocated with the single antenna

• If mobile target detected by multiple antennas• collocation with the one with the highest RSS

• RSS is commonly used in proximity

• Simple to be implemented

Positioning TechniquesMeasurement Techniques

• Angle of Arrival (AOA)

• Time of Arrival (TOA)

• Time Difference of Arrival (TDOA)

• Received Signal Strength (RSS)

• Target object can be found by intersection of several pairs of angle direction lines • Commonly referred as direction finding (DF)

• At least two reference Points (A and B) and two angles used, in order to derive the 2D location of the target

• No time synchronization between measuring points

• Requirement of large and complex hardware

Source: H. Liu, H. Darabi, P. Banerjee, J. Liu; “Survey of Wireless Indoor Positioning Techniques and Systems”, IEEE Transactions on Systems, November 2007

• Time taken by the signal to go from the source mobile target to the measuring unit

• The distance from the mobile target to the measuring unit is directly proportional to the propagation time

• All transmitters and receivers in the system have to be precisely synchronized

• For 2D positioning, at least three reference points needed

• Determines the relative position of the mobile transmitter by examining the difference in time at which the signal arrives at multiple measuring units

• The transmitter must lie on a hyperboloid

• The hyperboloid equation is:

• (xi,yi,zi) and (xj,yj,zj) are fixed receivers; (x,y,z) is the coordinate of the target object

• Target location estimated by the intersection of two or more TDOA measurements

• RSS presents the strength of the received signal

• The core idea is to establish a one-to-one relationship between the received signal strength from several reference nodes and the current position of the mobile.

• RSS needs a radio map to be created in the coverage area

• Radio map collects the vectors of signal strengths for each reference node

• Model stored in a central location

Agenda

• Introduction

• Discussion

Positioning Systems

• Fixed Indoor Positioning Systems

• Infrared Positioning Systems

• Ultrasonic Positioning Systems

• RF Positioning Systems

• Ultra Wideband Systems

• Optical Indoor Positioning Systems

• Pedestrian Indoor Positioning Systems• Beauregard’s System

• FootSLAM

• Fischer’s System

• Bat System

Positioning SystemsFixed Indoor Positioning Systems

Infrared signals used for signal transmission

• Active Badge system

• Objects tracked by a badge, which emits a unique identifier every 15 sec.

• Each location in the building covered by a network with IR sensors

• Central server for collecting the data from IR sensor• Principle used: Trilateration and TOA

Source: J. Xiao, Z. Liu, Y. Yang, D. Liu, X. Han, “Comparison and Analysis of Indoor Wireless Positioning Techniques”, 2011 International Conference on Computer Science and Service System (CSSS 2011), Nanjing, China, June, 2011

Ultrasonic beacons used for signal transmission

• Active Bat system

• Cricket system

• Users and objects are tagged with ultrasonic tags identified as “bats”• Signal receivers mounted across the ceiling • A large number of receivers required

Source: J. Xiao, Z. Liu, Y. Yang, D. Liu, X. Han, “Comparison and Analysis of Indoor Wireless Positioning Techniques”, 2011 International Conference on Computer Science and Service System (CSSS 2011), Nanjing, China, June, 2011

• Cricket systemconsists of Cricket nodes:• beacons: are fixed, attached to the ceiling• listeners: attached to the target objects or people

• Beacons transmit periodically a message to the listener• Listener uses these information to determine its position

Source: Priyantha, N. B; The cricket indoor location system: PhD Thesis, Massachusetts Institute of Technology. 199 p, June 2005

• Radio Frequency used for signal transmission

• RFID systems consists of RFID readers and RFID tags

RF based systems:

• LANDMARC• RADAR• SpotON

RF based systems:

• RFID active tag• RFID reader with 8 power levels, placed in known positions• Extra fixed location reference tags used to help location calibration

Source: Lionel M.NI, Yunhao Liu, Iu Cho Lau, Abhıshek P. Patil; LANDMARC: Indoor Location Sensing Using Active RFID

RF based systems:

• Signal strength information collected at multiple receiver location triangulated to find user coordinates

• RSS information is collected during the off-line phase and real-time phase

Source: J. Hightower, R. Want and G. Borriello; SpotON: An indoor 3D location sensing technology based on RF signal strength,UW CSE00-02-02, February 2000

RF based systems:

• Based on RSS

• Object Tags and Base Stations connected serially

• Server processor maps the RSS values

• UWB is based on sending ultrashort pulses• UWB systems transmit a signal over multiple bands of frequencies simultaneously• Signal transmission for a much shorter duration

UWB based systems:

• Ubisense systemconsist of:• Tags: Are carried by persons or targeted objects• Fixed sensor infrastructure: Sensors placed in the building• Location management platform: Processes and distributes

the location information to applications

• Cellular System Architecture

• Positioning of objects with a system installed in the building and a mobile sensors (i.e. camera) carried by the user• Used for locating robots within an indoor environment

Proposed system:• CLIPS (Camera and Laser based Indoor Positioning System)

• The laser device is oriented toward the ceiling and laser beams are on the ceiling• The camera device acts as mobile device and tracks the laser beams

Source: Tilch,S.Mautz,R., Current investigations at the ETH Zurich in optical indoor positioning. IEEE Positioning Navigation and Communication (WPNC) conference, 2010

Positioning SystemsPedestrian Indoor Positioning Systems

• Beauregard’s System

• FootSLAM

• Bat System

• FootSLAM

• Bat System

• Pedestrian Dead Reckoning (PDR) approach used

• Helmet mounted sensors

• Algorithm used consist of two steps:• step detection and estimation• heading detection and estimation

Source: S. Beauregard, A helmet-mounted pedestrian dead reckoning system, in 4th International Forum on Applied Wearable Computing, 2006

• FootSLAM

• Bat System

• System uses foot mounted Inertial Measurement Unit (IMU)

• It builds 2D map of the building, without prior knowledge of the building structure

• The more times places are visited within the building, the better information or map built in regards of the place

• PDR approach used

Source: Robertson, P., Angermann, M, Krach, B., Simultaneous Localization and Mapping for Pedestrians using only Foot-Mounted Inertial Sensors. In Proc. UbiComp 2009, ACM (2009) 93-96

• FootSLAM

• Bat System

• Combination of Ultrasound beacons and foot mounted inertial sensors• Two types of errors: heading error and distance error

• Ultrasound beacons for providing better accuracy and less heading error in PDR approach are used

Source: “Ultrasound-aided Pedestrian Dead Reckoning for Indoor Navigation”, http://www2.parc.com/isl/projects/MELT08/ProgramSlides/poster1_3_fischer.ppt.pdf

• FootSLAM

• Bat System

• Combination of a foot mounted Inertial Measurement Unit, a detailed building model and a particle filter for providing absolute positioning to reduce complexity

• Initialization of the localization algorithm using WiFi signal strength

• Unknown Initial position and orientation of the user

• Position of the pedestrian at time k is estimated when knowing his position at time k-1

Source: O. Woodman and R. Harle. Pedestrian localisation for indoor environments. In Proc. of the UbiComp 2008, Seoul, South Korea, Sept. 2008

Agenda

• Introduction

• Discussion

Comparisons

Positioning System Accuracy Signal Principle Range Cost Data rate

Active Badge 7cm Infra Red T/TOA 5 m moderate 0.1 Hz

Active Bats 9 cm Ultrasound T/TOA 50 m moderate 75 Hz

Cricket 2 cm Ultrasound T/TOA 10 m low 1 Hz

Dolphin 2 cm Ultrasound T/TOA Room moderate 20 Hz

Radar 2-3 m RF R/RSS Room moderate 4 Hz

Wave LAN 3 m RF R/RSS Room moderate 4 Hz

UWB 10 cm RF T/TOA 15 m moderate 1 Hz

LANDMARC 1-2 m RF R/RSS 50 m moderate 70 Hz

SpotOn 3 m RF R/RSS Room low 2 Hz

CLIPS 0.5 mm Camera images Image process 36 m2 high 30 Hz

Comparison of fixed indoor positioning systems

Comparisons [2]

Positioning System Technique Accuracy 2D/3D Range Robustness

Beauregard’s PDR 10 m 2D Room1. No change in

heading2. No drift caused by

FootSLAM PDR 1-3 m 3D 2 mImproves with larger number of visits to

locations in the building

Fischer’s US + PDR < 1 m 3D 3 m1. No harsh light

2. Not noisy environment LOS

Bat System Wifi + PDR 0.5 m 3D building Existence of WiFi

Comparison of pedestrian indoor positioning systems

Agenda

• Introduction

• Discussion

Summary and Conclusion

• Indoor positioning is a huge area, with many applications

• Various indoor positioning techniques

• Many improvements can be carried for different systems

• Fixed indoor positioning systems have a better accuracy compared to the pedestrian positioning systems

Comparisons [3]Thank you for your attention!

Comparisons [3] Questions

Discussion

• Which of the presented indoor positioning systems you think have more need for improvement? Fixed or pedestrian indoor positioning systems?

• Which of the presented systems you think are most promising systems for the future?

• Do you think that a combination of different techniques can increase the performance of indoor positioning systems?

• Is something you are missing in your daily life, and you would like to have such a system? What kind of systems would match to solve this problem?

Wireless Indoor Positioning Techniques

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