TECHNOLOGIES FOR WIRELESS GEOLOCATION GBS GBS Geolocation base

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.

GBS 1 AOA TECHNIQUE GBS 2

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 GBS 1 d 1 GBS 2 GBS 3 d 2

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 20 m to within 1 m. 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