gsm_slides5631

GSM-NetworkGSM-Positioning

RestrictionsSignallingSystem#7

Conclusion

GSM-PositioningOutdoorpostioning: Technologies, Characteristics and Limitations

Bohdan [email protected]

19. Februar 2009

Bohdan Dulya GSM-Positioning



Conclusion

Possible scenario

Example: a person is in an accident but precise location isunknown.How can the rescue team to find location of this person?One possible solution: 911-operator localize the mobile phone ofthis person via GSM-positioning.




Conclusion

Motivation

Why GSM-positioning?

existent infrastrukture

widespread technologie




Conclusion

GSM-Network

Mobile Station (MS)

Base Tranceiver Station (BTS)

Base Station Controller (BSC)

Mobile Switching Center (MSC)

Visitor Location Register (VLR)

Home Location Register (HLR)

Authentication Center (AuC)




Conclusion

Timing AdvanceAngle Of ArrivalRound-Trip-Time-of-FlightTime Difference Of ArrivalEnhanced Observed Time Difference

GSM-Positioning

Positioning architecturea

mobile-based (a)

network-based (b)

hybrid (c)

aLSC - location service center




Conclusion


Cell Of Origin (COO)

Position of mobile phone is theposition of cell, in which themobile phone is registeredCell size 100 m-35 km

precision: 100 m-35 km




Conclusion


COO with Cell Sector (COO CS)

Extension of COO:position of mobile phone is theposition of cell and sector, inwhich the mobile phone isregistered

Mostly 3 sectors ever 120degree




Conclusion


COO with Cell Sector (COO CS)





Conclusion


COO with CS and Received Signal Strength

Extension of COO CS:measuring the signal strengthof mobile phone in the sector





Conclusion


generally

COO and modifications of this

+ simple method

+ only one cell required

+ low modification on network

- precision




Conclusion


generally

COO and modifications of this

passive self-positioning possible

active positioning from BTS only when mobile phone is

”active“

BTS can”activate“ the mobile phone with

”stille sms“




Conclusion


Timing Advance (TA)

Timing advance value - whensend MS the signal to BTS

value 0 to 63 (equates0 m-35 km)

one unit 3,69 µs equates550 m




Conclusion


Angle Of Arrival (AOA)

Measuring the AOA of a signalfrom BTS at MS orthe AOA of a signal from MSat BTS

better precision50 m-150 m

extension required(antenna with anglemeasurement unit)

only”active“ mobile

phone

only remote positioning




Conclusion


Round-Trip-Time-of-Flight (RToF)

Measuring the propagation time -the time of travel of signal betweenBTS and MSBTS sent a signal and wait for aresponse from MS




Conclusion


Round-Trip-Time-of-Flight (RToF)

Signal from minimum 3BTS required

Precision is dependent ondelay time on BTS/MS

50 m-150 m

mobile phone must be

”active“




Conclusion


Time Difference Of Arrival (TDOA)

MS sent simultaneous signalsto two or more BTSEach BTS compute the timedifference and convert this todistance to MS




Conclusion


Enhanced Observed Time Difference (EOTD)

Two or more BTS sentsimultaneous signals to MSMS compute the timedifference of each BTS andconvert this to distance toBTS




Conclusion


TDOA & EOTD

BTS must be exactly synchronised

time delay of 1µs involve 150 m inaccuracy

bias error possible when unsynchronised

passive positioning possible




Conclusion

Falsifikation of signal

Abbildung: Reflection Abbildung: Refraction




Conclusion

Falsifikation of signal

Abbildung: Dispersion Abbildung: Flexion




Conclusion

SignallingSystem#7

SignallingSystem#7 (SS7)

Standardprotokoll of digital phonenetwork

no authentication built in

Mobile Application Part (MAP) - part of SS7 that specifiesadditional signalling




Conclusion

SignallingSystem#7




Conclusion

SignallingSystem#7

Successful request returns

IMSI (International MobileSubscriber Identity)

”global title“ of MSC you are

using

user error if phone is notavailable




Conclusion

SignallingSystem#7




Conclusion

SignallingSystem#7

New 3GPP standard will fix this problem − >”home routing“




Conclusion

Precision of GSM-Positioning

Method PrecisionCell of Origin (COO) 100 m - 35 km

COO with Cell Sector 100 m - 35 km

COO with CS and Received Signal Strength 100 m - 20 km

Angle Of Arrival (AOA) 50 m - 150 m

Round-Trip-Time-of-Flight (RToF) 50 m - 150 m

Time Difference Of Arrival (TDOA) 50 m - 150 m

Enhanced Observed Time Difference (EOTD) 50 m - 150 m

Precision of GSM-Positioning




Conclusion

Questions???


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