1896 1920 1987 2006

Survey on indoor positioning systems

(IPS)Zhou Haihang 0150332004

Bai Xuanyu 115033910088

Zheng Shengan 0140339027 

Brian A. Ignacio Reyes 115030990049

Huan Yang 0140339011

Jin Yan 015033910010

Tian Tan 0150332007

Ivan M. Peñaranda Soria 115030990048

OutlineBusiness background• Trend• ApplicationsIPS approaches• Technical approaches• Positioning approaches

• Fingerprinting• Triangulation• Trilateration• Connection based positioning

Business Background1

Business backgroundThe indoor location market is growing

rapidly•At least 130 companies are working on

indoor maps, tracking and navigation technologies and services.

•Indoor location market is expected to grow fast and potential benefits are seen in every level (consumer, service provider, operator and supplier).

•There are individual players like Google and also group of players like Nokia lead In-location alliance (including at&t, intel, CISCO, microsoft)

•http://www.in-location-alliance.com/

Market expectations: Example on Advertising

ABI Research proposes that by 2017 up to 4$ billion would be spent on indoor positioning based advertising.

This is just one service example but indicates the expected potential of IPS

technology.

Applications

Airports Universities Stadiums

Some IPS use scenarios

IDTechEx: The addressable market is around $10B with healthcare expected to be the first to expand.

Navigation• Finding places in large office buildings, university buildings,malls,

museums, hospitals• Emergency situations: navigation of rescue personality and

localization of peoplePeople and property tracking – patients, kids, visitors, travellers• Example: Baggage tracking in airports• Logistic – cargo and container tracking in warehouses, harbours,

airports etc.• Device (Factories, Offices & Hospitals) and items tracking (keys,

wallets, bag, laptops etc.)User applications• Social applications: Finding people.• Shopping, indoor parking assistanceAdvertising• Advertising based on where you are.

Unlimited applications

•Take advantage of position with cellphones, tablets, Smart watches, etc.

• Display specific menus and options depending of the location of user.

• Focused advertising

• Better maps for specific places, ability to save places for reference or directions.

• Statistics of interest for the application owner.

Some companies working with IPS

IPS approaches2

Problem definition

Wirelessly locate objects or people inside a building in real time.Indoor Positioning Systems (IPS)Real-time Locating Systems (RTLS)

Criteria

AccuracyCoverageAvailabilityUpdate rateCosts and System Complexity

Technical IPS approachesTerminal based IPS:•Most commercial products use terminal based

IPS since it can be easily implemented without permission/support from network.

Infrastructure based IPS:•Current infrastructure based IPS products use

either dedicated IPS infrastructure or existing WiFi networks.

Hybrid IPS (terminal and infrastructure based):

•Combine all available IPS information (WiFi, BT, geomagnetic information, intertia sensor

• information)

Positioning approaches

Connection based positioning

In simple methods called as Cell of Origin or Cell Identity terminal simply uses the location of the serving wireless node.

To run this positioning system just a database of station IDs and locations is needed.

The position is determined by measuring the signal strengths from different stations.

• It is assumed that the closest station is the station from which the strongest incoming signal on the device is received.

• Terminal just send the ID of the serving station to the IPS database. Then the database will send the location of the station to the terminal.

Connection based positioning

Connection based positioning

Advantages•No complicated algorithms•Easy to implement•Low cost

Disadvantages•Low accuracy – room level•Identification problem

Trilateration/multilaterationThese methods assume that signal strength and/or time delay is

directly proportional to the distance between the user terminal and the base station.

• When this assumption holds it is a simple geometrical exercise to compute the location of the user terminal provided that signals from at least three separate base stations can be reliably received.

The challenge for a trilateration method is in the determination of the distance between the base station and the user terminal.

• Methods that are based on time measurements assume accurate synchronization between the base stations and the user terminal.

• Methods that are based on the signal strength have problems with interference and multipath propagation effects.

• Well‐known methods for distance estimation are ToA, TdoA and RSSI/SNR.

Time of arrive (ToA)

Time difference of arrive (TdoA)

lUsing relative Arrival time measurements at each receiving sensor

Example:

TDoAc-a= Txc – Txa = 10^-8s

TDoAb-a = Txb – Txa = 10^-7s

Received Signal Strength Indicator

• PR: Received signal strength at the receiver• PT: Transmitted power strength at the emitter• GT GR: Antenna gains of transmitter and receiver• d: Distance• P: The path loss factor The path loss factor (P) is related to the environmental conditions P = 2 for free spaceP > 2 for environments with multipathP ≈ (4 - 6) for typical indoor environments

Example•The RSSI pattern is shown below.• 3 WiFi routers• 9 references points

•Q: Where is M(1.2, 2.6, 4.5) in this pattern?

5

2 1

3

4 1

1

4 2

5

2 1

2

3 3

1

3 3

3

1 2

1

1 3

1

2 5

1

2 3

Example (Continuation)

•Q: Where is M(1.2, 2.6, 4.5) in this pattern?

A: Measured RSSI of Wifi one is 1.2.• Red zone (referenced RSSI of Wifi one is 1) are possible locations.

5

2 1

3

4 1

1

4 2

5

2 1

2

3 3

1

3 3

3

1 2

1

1 3

1

2 5

1

2 3

Example (Continuation)

•Q: Where is M(1.2, 2.6, 4.5) in this pattern?

•A: Measured RSSI of Wifi two is 2.6.• Green zone (referenced RSSI of Wifi two is 3) are possible locations.

5

2 1

3

4 1

1

4 2

5

2 1

2

3 3

1

3 3

3

1 2

1

1 3

1

2 5

1

2 3

Example (Continuation)

•1

•Q: Where is M(1.2, 2.6, 4.5) in this pattern?

•A: Measured RSSI of Wifi three is 4.5.• Blue zone (referenced RSSI of Wifi two is 5) are possible locations.• The intersection of three zones is the location of M.

5

2 1

3

4 1

1

4 2

5

2 1

2

3 3

1

3 3

3

1 2

1

1 3

1

2 5

1

2 3

TriangulationBase stations measure the angle of

arrival(AoA) for the received signal from user terminal.

Location of the terminal is computed using the known locations of the base stations and AoA measurements.

Needs directive antennas and thus, challenging to implement

•Special infrastructures needed.

Triangulation

Angle of Arrival / Direction of Arrival

AoA/DoAMore sensors = Higher accuracy

Fingerprint based approachBased on spatial differences in the radio

environment.Fingerprint based methods include two

phases.• Off-line Phase• A fingerprint database is build by collecting signal

strengths from all identified base stations at pre-defined locations.

• Several measurements are collected at each location and e.g. the median signal strength values are calculated.

• The values are inserted into a radio environment map.

• On-line Phase• User terminal that desire to define location

measure the signal strengths from surrounding base stations and compared result with the radio environment radio map.

• Usually many measurements are needed to define the location from the radio environment map.

Example of fingerprinting

Example: google3

The big player: Google

Due to Google business approach the user reach in general is of great importance.

Google provides IPS map database and location functions through Android

•http://maps.google.com/help/maps/indoormaps/

Did you know that Google uses your Android to collect location based information?

Automated multiradio fingerprinting

Automated fingerprintingAndroid Location Services check

periodically user location using GPS, 3GPP Cell-ID, and Wi-Fi to locate your device.

When location is defined, user’s Android phone will send back Wi-Fi access points' Service set identifier (SSID) and Media Access Control (MAC) data.

As a result Google can aggregate radio fingerprinting information taking advantage of users that employ Android based location services.

Not only Google does this. It's common practice for location database vendors.

LimitationsThe bottleneck in the Google approach is that

accurate user location is needed before measured radio fingerprinting information is useful

Usually best reference location is obtained through GPS

• automated indoor fingerprinting is difficult due to lack of GPS

• either manual fingerprinting or other location reference information is needed indoors

• manual fingerprinting is not possible without access to indoor premises (then, of course, access to indoor maps can be limited)

• Some development attempts have been done to use inertia sensors to provide reference location: location known when entering the building and inertia sensors used to update location. Accuracy of this method decreases with distance that user moves

References[1] Z. Zhang Indoor LocalizationCSI Wireless Networks and Mobile Computing, University of Ottawa.

[2] S. Sullivan Indoor Localization Primer Local Social. Place London (2014).

Thank you for your attention.