TECHNOLOGIES FOR WIRELESS
GEOLOCATION
GBS
• GBS – Geolocation base station (obtain
location parameters of mobile station directly
or indirectly).
• BTS – Base transceiver subsystem
• BSC – Base station controller
BSC
BTS
GBS
WIRELESS GEOLOCATION
• GEOLOCATION – Location based service to
mobile user.
• GBS – RECEIVER
• MS – TRANSMITTER
• LOCATION OF GBS - (Xi , Yi) -> KNOWN
• LOCATION OF MS – (Xm , Ym) -> TO BE FOUND
TECHNIQUES TO DETERMINE THE LOCATION OF AN MS
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
DIRECTION-BASED
• Direction is determined from the AOA (angle of
arrival) of received signal.
• Receiver(GBS) measures the direction of the
received signal from the target transmitter (MS)
using directional antennas / antenna array.
• Accuracy depends on where the transmitter is
located with respect to the receiver.
• More than 2 receivers are needed for accuracy.
GBS1
AOA TECHNIQUE
GBS2
DISADVANTAGES
CAUSE
EFFECT
LOS path may be blocked
buildings, walls and cause
errors.
Not suitable for indoor
geolocation system.
Requires expensive array
antennas at the
receiver(GBS) to track the
direction of arrival of signal.
Not suitable for low cost
indoor applications.
APPLICATION
• Can be used in next generation cellular system
where smart antennas are used to increase
capacity.
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
DISTANCE BASED
• Distance between the MS and GBS can be
determined using parameters such as
i. Time of arrival
ii. Signal strength
iii. Signal phase
DISTANCE-BASED
GBS1
d1
GBS2
GBS3
d3
d2
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
ARRIVAL TIME METHOD
• Arrival time method uses 2 ways of identifying
the distance :
i. Time of arrival (TOA)
ii. Time difference of arrival (TDOA)
TOA
• It is based on the
propagation time of
signal from a MS to
multiple GBSs.
• It provides circles
centered on the mobile
or fixed transceiver.
TDOA
• It is the difference in
TOA used to locate the
mobile.
• It provides hyperbolas
on which the
receiver(GBS) must be
located at foci.
TOA
TDOA
• Requires knowledge of
the transmit time of
transmitter.
• Does not require transit
time.
• Hence strict time
synchronization
between MS and the
GBSs is required.
• Requires time
synchronization only
among all GBSs.
RLS ALGORITHM
• It is used when there are errors in the distance
measurements.
• Let the distance di from the i th GBS ,
di=c*
where c – velocity of light
– time taken by the signal
to reach the GBS.
• Location of i th GBS – (xi , yi)
• Location of mobile – (x , y)
• We have N equations of the form:
fi(x , y)= (x-xi)^2 + (y-yi)^2-di^2=0
for i= 1,2,3,……,N.
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
SIGNAL STRENGTH METHOD
• If the transmitted power is known, measuring the
RSS (received signal strength) at the GBS can
provide an estimate of the distance.
• Distance is determined using a circle, centered on
the receiver(GBS), on which the mobile transmitter
must lie.
• Accuracy can be improved by using premeasured
RSS contours and by using fuzzy logic algorithm.
ADVANTAGES
• Low complexity
receiver
DISADVANTAGES
• Very unreliable due to
shadow fading
(fluctuations around the
mean value and
expected value caused
due to signal being
blocked from GBS).
• GBS do not distinguish
between signal strength
in los path and
reflected path.
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
RECEIVED SIGNAL PHASE METHOD
• Reference receivers (GBSs) measure the
carrier phase.
ADVANTAGES:
• Differential GPS can improve location accuracy from
about 20m to within 1m.
DISADVANTAGES:
• Ambiguity resulting from periodic property of the
signal phase.
• Multipath condition causes more errors.
APPLICATION
• Used in indoor geolocation system, along with
TOA/TDOA or RSS method to fine- tune the
location of MS.
GEOLOCATION
TECHNIQUES
DIRECTION BASED
DISTANCE BASED
ARRIVAL TIME
METHOD
SIGNAL
STRENGTH
METHOD
RECEIVED
SIGNAL PHASE
METHOD
FINGERPRINTING BASED
FINGERPRINTING-BASED
• Develops a “signature database” of a location
grid in specific service areas.
• The received signal is measured as a vehicle
moves along this grid in specific areas and
recorded in signature database.
• When another vehicle moves in the same
area, the signal received from it is compared
with the entry in the database, thus its
location is determined.
APPLICATOON
• Can be used in indoor applications.
THANK YOU