GBS GBS Geolocation base station obtain location parameters of mobile station directly or indirectly BTS Base transceiver subsystem BSC Base station controller BSC BTS ID: 602968
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TECHNOLOGIES FOR WIRELESS GEOLOCATIONSlide2
GBS
GBS
– Geolocation base station (obtain location parameters of mobile station directly or indirectly).BTS – Base transceiver subsystemBSC – Base station controller
BSC
BTS
GBSSlide3
WIRELESS GEOLOCATION
GEOLOCATION
– Location based service to mobile user.GBS – RECEIVER MS – TRANSMITTER LOCATION OF GBS - (Xi , Yi) -> KNOWNLOCATION OF MS – (Xm , Ym) -> TO BE FOUNDSlide4
TECHNIQUES TO DETERMINE THE LOCATION OF AN MSSlide5Slide6
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.Slide7
GBS1
GBS2
AOA TECHNIQUESlide8
DISADVANTAGES
CAUSE
LOS path may be
blocked buildings, walls and cause errors. Requires expensive array antennas at the receiver(GBS) to track the direction of arrival of signal.
EFFECT
Not suitable for
indoor geolocation system.
Not suitable for low cost indoor applications.Slide9
APPLICATION
Can be used in next generation cellular system where
smart antennas
are used to increase capacity.Slide10Slide11
DISTANCE BASED
Distance between the MS and GBS can be determined using parameters such as
Time of arrival
Signal strengthSignal phaseSlide12
DISTANCE-BASED
GBS1
GBS3
GBS2
d1
d2
d3Slide13Slide14
ARRIVAL TIME METHOD
Arrival time method uses 2 ways of identifying the distance :
Time of arrival (
TOA)Time difference of arrival (TDOA) Slide15
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. Slide16
TOA
Requires knowledge of the transmit time of transmitter.
Hence strict time synchronization between MS and the GBSs is required.
TDOA
Does not require transit time.
Requires time synchronization only among all GBSs. Slide17
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. Slide18
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.
Slide19Slide20
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. Slide21
ADVANTAGES
Low complexity
receiver
DISADVANTAGESVery 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. Slide22Slide23
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.Slide24
APPLICATION
Used in indoor
geolocation
system, along with TOA/TDOA or RSS method to fine- tune the location of MS.Slide25Slide26
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. Slide27
APPLICATOON
Can be used in indoor applications.Slide28
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