The document provides information about the Global Positioning System (GPS) and indoor geolocation systems. It describes how GPS uses satellites and receivers to determine location based on triangulation of distance measurements. It then discusses challenges with indoor geolocation and describes common techniques used like received signal strength, angle of arrival, and time of arrival measurements along with related positioning algorithms and use of floor plan data.

1. Global Positioning System
• Introduction
• The Global Positioning System (GPS) is a satellite-based navigation
system developed and operated by the US Department of Defense.
GPS permits land, sea and airborne users to determine their three-
dimensional position, velocity and time. This service is available to
military and civilian users around the clock, in all weather, anywhere
in the world.
• A transmitter high above the Earth sending a high-frequency radio
wave with a special coded signal can cover a large area and still
overcome much of the "noise" encountered on the way to the ground.
This is the main principle behind the GPS system

2. GPS Elements
GPS has 3 parts:
• The space segment
• The user segment
• Control segment.
• The space segment consists of 24 satellites, each in its own orbit 11,000 nautical
miles above the Earth.
• The user segment consists of receivers, which you can hold in your hand or
mount in your car.
• The control segment consists of ground stations (five of them, located around the
world) that make sure the satellites are working properly.

3. Cont…

4. Working of G PS
• The principle behind GPS is the measurement of distance (or "range")
between the receiver and the satellites. The satellites also tell us
exactly where they are in their orbits above the Earth. Four satellites
are required to compute the four dimensions of X, Y, Z (position) and
Time. GPS receivers are used for navigation, positioning, time
dissemination, and other research.

5. Cont…

6. Cont…
It works something like this: If we know our exact distance from a
satellite in space, we know we are somewhere on the surface of an
imaginary sphere with radius equal to the distance to the satellite radius.
If we know our exact distance from two satellites, we know that we are
located somewhere on the line where the two spheres intersect. And, if
we take a third measurement, there are only two possible points where
we could be located. By taking the measurement from the fourth
satellite we can exactly point out our location.

7. Sources of GPS signal errors
• Ionosphere Troposphere delays
• Signal multi path
• Orbital Errors
• Number of satellites visible
• Satellite geometry/shading

8. Limitations
• GPS can provide worldwide, three-dimensional positions, 24 hours a
day, in any type of weather. However, the system does have some
limitations. There must be a relatively clear "line of sight" between the
GPS antenna and four or more satellites. Objects, such as buildings,
overpasses, and other obstructions, that shield the antenna from a
satellite can potentially weaken a satellite's signal such that it becomes
too difficult to ensure reliable positioning. These difficulties are
particularly prevalent in urban areas. The GPS signal may bounce off
nearby objects causing another problem called multi path interference.

9. Applications
We can find the uses and applications of GPS in the following fields:
• Aircrafts and bombers
• Military operations and weapon systems
• Police, Fire and Emergency service
• Automobile Manufacturers
• Mapping and Surveying companies

10. Part 2
INDOOR GEOLOCATION

11. 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

12. System Architecture
 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

13. Wireless Geolocation Systems

14. Cont…
• 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

15. Geolocation Process
• 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

16. RSS Geolocation
• 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

17. AOA 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

18. TOA/TDOA Geolocation
• Time of Arrival
• Time Difference of Arrival
• Time-Based Location

19. Positioning Algorithms
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

20. Cont…
• 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)