INDOOR GEOLOCATIONINDOOR GEOLOCATION

PRESENTED BYD.LAKSHMI SOUJANYA09951A0418ECE IV A

Introduction Indoor geolocation is an important and novel emerging technology

for commercial, public safety and military applications.

In commercial applications for residential and nursing homes there is an increasing need for indoor geolocation systems to track people with special needs, the elderly, and children who are away from visual supervision, to locate in-demand portable equipment in hospitals, and to find specific items in warehouses.

In public safety and military applications, indoor geolocation systems are needed to track inmates in prisons, and navigating policeman, firefighters and soldiers to complete their missions inside buildings

These incentives have initiated interest in modeling the radio channel for indoor geolocation, development of new technologies, and emergence of first generation indoor geolocation products

GPS is a worldwide space based radio navigation system that works with the help of a constellation of 24 satellites and their base stations.

It employs signal timing to determine position of a mobile station, which acts, as the receiver and orbiting satellites are transmitters

An Enhanced 9-1-1 system provides a three-digit dialing, no-coin requirement from pay telephones and intelligent routing to the Public Safety Answering Point (PSAP) that handles the area where the phone is located and is able to display the caller's address and telephone number at the PSAP for the dispatcher's reference.

In general, 9-1-1 is an emergency number for any police, fire or medical incident

Global Positioning System (Gps) And E-911 Services

The architecture of indoor geolocation systems also can be roughly grouped into two main categories: handset based architecture and network-based architecture

In network-based architecture the geolocation base stations extract location metrics of the mobile station and relay this information to a central control station.

The control station, calculating the metrics it receives, keeps track of the mobile station.

In handset-based architecture, the mobile station estimates self-position by measuring received radio signals from multiple fixed base stations

System Architecture

Wireless Geolocation Systems

The basic function of a wireless geolocation system is to gather a particular information about the position of a mobile station (MS) and process that information to form a location estimate

The main elements of the system are a number of location sensing devices that measure metrics related to the relative position of a mobile station with respect to a known fixed station, a positioning algorithm that processes metrics reported by location sensing terminals to estimate the location coordinates of MS, and a display system that illustrates the location of MS to users.

The location metrics may indicate the approximate arrival direction of the signal or the distance between the MS and FS

Geolocation systems attempt to locate an MS by measuring the signals traveling between the MS and a set of fixed stations (FS's).

The signal measurements are first used to determine the length or direction of the path, and then the MS position is derived from known geometric relationships.

It is important to note that line-of-sight (LOS) propagation is necessary for accurate location estimates.

The indoor radio propagation channel is characterized as site-specific, severe multipath, and low probability for availability of a line of sight (LOS) signal propagation path between transmitter and receiver.

The most important impact on location accuracy is due to the range/direction estimation error.

The two major sources of errors that come under this category, in the measurement of location metrics in indoor environments are multipath fading and no LOS (NLOS) conditions due to shadow fading

Geolocation Process

In systems using RSS geolocation technique, nearness of an MS to fixed detection devices is used to determine its position.

RSS techniques estimate the location of an MS by measuring the power transmitted by it.

Simple geometric relationships are then used to form the location estimate, based on the RSS measurements and the known positions of the BS's.

Once the power transmitted by a mobile terminal is known, measuring received signal strength at receiver will provide the distance between the transmitter and the receiver using a known mathematical model for radio signal path loss with distances.

The measured distance will determine a circle, centered at the receiver, on which the mobile transmitter must lie.

Three RSS measurements will provide a position fix for the mobile

RSS Geolocation

The AOA geolocation method uses simple triangulation to locate the transmitter.

The receiver measures the direction of received signals (i.e. angle of arrival) from the target transmitter using directional antennas or antenna arrays.

Simple geometric relationships arc then used to form the location estimate, based on the AOA measurements and the known positions of the BS's.

With the AOA method, a position fix requires a minimum of two BS's in a 2-D plane.

Multipath propagation, in the form of scattering near and around the MS and BS, will affect the measured AOA.

As a result, more that two receivers are normally needed to improve the location accuracy

AOA Geolocation

Time of Arrival

Time Difference of Arrival

Time-Based Location

TOA/TDOA Geolocation

TRADITIONAL TECHNIQUES – In the indoor radio channel, it is difficult to accurately measure

AOA and RSS so that most of the independent indoor positioning systems mainly use TOA based techniques.

– With reliable TOA based measurements, simple geometrical triangulation methods can be used to find the location of Ms.

– Due to estimation errors of distances at BS receivers caused by inaccurate TOA measurements, the geometrical triangulation technique can only provide a region of uncertainly instead of a single position fix, for estimated location of the MS.

– To obtain an estimate of the location coordinates in the presence of measurement errors of location metrics, a variety of direct and iterative statistical positioning algorithms have been developed to solve the problem by formulating it into a set of nonlinear

equations

Positioning Algorithms

PATTERN RECOGNITION TECHNIQUES– For indoor geolocation applications, the service area is restricted to

inside and close vicinity of a building, and nowadays the building floor plan is normally accessible as an electronic document.

– The availability of electronic building floor plans is one of the features of indoor applications that can be exploited in positioning algorithms

– Another unique feature of indoor application is that the size of coverage area is much smaller than outdoor applications.

– This makes it possible to conduct comprehensive planning of placement of sensors

– Operation of Geolocation Technique is based on 2 phases:– - Off-Line phase (Phase of data collection) or

Learning phase– - Real-Time phase (Phase of user's position location)

So-called tags, physical devices associated with the people and assets being tracked, which should be as small and light as possible for the widest applicability.

Tags that are inexpensive, for broad appeal and applicability, and therefore far simpler in design than GPS receivers.

An infrastructure that tracks thousands of tags, whereas in GPS, a mobile device must determine its own location in reference to an infrastructure.

Accuracy of 10 meters for most indoor applications, though some require 2-meter accuracy or better.

Counteraction of indoor multipath effects, a challenge when combined with the higher accuracy requirement.

Goals Of An Indoor Positioning System

Since the invention of the microprocessor a variety of short-range radio-based technologies have been employed to track items indoors.

They identify objects with a sensor having a range of a few centimeters to about 3 meters, depending on the technology

A newer technology, radio frequency identification (RFID), has been emerging over the past decade as a substitute for bar codes.

Detectable up to about 3 meters away, RFID tags are identified as they pass fixed sensors.

As the tags pass within range of an interrogator (tag reader), their circuitry is charged either inductively or electro magnetically.

Industry exploits them for a wide variety of purposes and as a replacement for bar codes.

Evidently, current RFID offerings were designed to cover doorways, where a read range of 3 meters is adequate

Existing Short-range Technologies

A variety of products can be read from a distance of 15 meters or more

If a receiver is in range, it detects the tag's presence and notifies a software application.

If the tag signal is not received when expected, the system triggers an alarm

A mature instance of this technology is produced by BI Inc., Boulder, Colo., for Electronic Home Arrest Monitoring (EHAM).

The systems monitor the homes of persons under court-ordered supervision, to check whether they are there or not.

A radio-frequency transmitter fastened around the client's ankle emits a signal, and a field-monitoring device picks it up

Current Mid-range Technologies

The U.S. Department of Defense also deploys a tagging system, based on high-end tag technology developed by Savi Technology, Mountain View, Calif.

Containers of the kind usable on any form of transport have two-way radio tags attached to them, and their contents recorded in the tag's memory

Several products for identifying locations of objects employ infrared technology, called IR1D.

The tags periodically transmit their identification codes by emitting infrared light to readers installed throughout the facility.

The tag prices are relatively high, and installation is complicated by the large number of readers required to ensure a line of sight to every possible tag.

Users also complain about reliability. Nonetheless, IRID systems are currently being sold, mostly for health care applications

The 3D-iD system was envisioned as the equivalent of a GPS for a location fixed by boundaries—a building, say, or a parking lot, or an amusement park; hence the term local positioning system (LPS).

The system uses the concepts of GPS, but with a proprietary infrastructure to communicate with inexpensive tags

In GPS, each satellite transmits a unique code, a copy of which is created in real time in the user-set receiver by the internal electronics.

The receiver then gradually time-shifts its internal code until it corresponds to the received code—an event called lock-on.

Once locked on to a satellite, the receiver can determine the exact timing of the received signal in reference to its own internal clock

In real GPS receivers, the internal clock is not quite accurate enough

The 3D-iD system design

A 3D-iD system requires its own indoor antenna infra-structure

The system is organized as cells within a building.

Each cell is handled by a cell controller, which is attached to up to 16 antennas by means of coaxial cables.

Both the cell controller and the tag are designed to comply with FCC Part 15 regulations so that no license is needed for operation.

In operation, the cell controller quickly cycles among antennas, determining distances to whichever of them are in range of the tag.

Once this is done for at least three antennas, the tag's location in space can be estimated

Without developments in four parallel underlying technologies, 3D-iD technology would not have been practical

Even though buildings and updating the signature database are much easier in indoor environments than in wide urban areas, the major drawback of pattern recognition techniques still lies in substantial efforts needed in generation and maintenance of the signature database in the view of the fact that working environment changes constantly.

DrawbackDrawback

Conclusion Indoor geolocation is an emerging technology that needs a

scientific foundation.

To provide such a foundation we need to characterize the radio propagation features that impact the performance of indoor geolocation systems.

The challenge for TOA-based systems is to develop a signaling system and infrastructure that is inexpensive to design and deploy, complies with frequency regulations, and provides a comprehensive coverage for accurate ranging.

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