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Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID) • Cell Global Identity with Timing Advance (CGI/TA)
• Cell ID and Round Trip Time (RTT- similar to TA)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)• Conclusions
Mobile Positioning
Category 1
Category 2
Handset-Based Network-BasedNetwork-Based
MS-Based Network Assisted
MS-Assisted Network Based
Pure Network Based
Multilateral n/a n/a AoA, ToA or TDoA
UnilateralEOTD, AFLT, IPDL-OTDOA, RX-Level
EOTD, AFLT, IPDL-OTDOA, RX-Level
Rx-Level
BilateralCell Coverage, CI+RTD
n/aLF, Cell Coverage, CI+RTD
Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID) • Cell Global Identity with Timing Advance (CGI/TA)
• Cell ID and Round Trip Time (RTT- similar to TA)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)• Conclusions
Cell Global Identity (CGI) - I• A Cell-ID (CID) is a number which is associated with a
specific cell located in the radio tower to which your terminal is connected. (also sector information can be utilized)
• MNOs have DB which may be used for mapping coordinates and Cell-IDs to provide location information.
Cell-ID=1234, MCC=244, MNC=05
Lat=64° 55' 45" N Lon=25° 21' 30" E
(ICAO: EFOU)
MNO Server and Cell-ID DB
Cell Global Identity (CGI) - II• So this sounds just great?
• Let´s just get the Cell-ID and make query about corresponding coordinate pair and then we will know our location.
• Good, but... We would know only geographical coordinates of serving cell as well as sector.
• ... The issue is that the location of cells is not public information.
• The operators keep this private for many reasons including:• Security and other policies• Extra revenue income
Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID) • Cell Global Identity with Timing Advance (CGI/TA)
• Cell ID and Round Trip Time (RTT- similar to TA)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)
• Conclusions
CGI-TA (Timing Advance)• Improvement to basic Cell-ID based positioning.
• TA is an existing parameter to avoid overlapping of bursts transmitted by several MSs at the same time
• For positioning purposes the TA is an estimate of the absolute distance between MS and serving BTS
• Quantized into 64 levels, each level corresponds ~550m
CGI CGI-TA
Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID)
• Cell Global Identity with Timing Advance (CGI/TA)• Cell ID and Round Trip Time (RTT)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)
• Conclusions
Cell ID and RTT• RTT (Round Trip Time) is a UMTS ‘TA-like’ improvement
for Cell ID positioning.
• As the TA was providing accuracy of about 550m the RTT measurements can achieve 80m and even (theoretically) about 5 m (based on 1/16 chip resolution in RTT reporting.
• But…
• Unfortunately (mainly) propagation effects are degrading the accuracy.
• Also cell separation causes difference in accuracy
Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID)
• Cell Global Identity with Timing Advance (CGI/TA)• Cell ID and Round Trip Time (RTT)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)
• Conclusions
E-CGI (Enhanced CGI)• Accuracy Improvement to CGI-TA
• Consists of CGI + TA(RTT) + NMR (Network Management Record)
• Usage of received signal levels (RXLEV) refine and add reliability to positioning.
Scenario (sectors, angle, cell separation)
Accuracy
3/65°, 3km 1400 m
3/65°, 1km 440 m
6/65°, 1km 163 m
6/35°, 1km 158 m
Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID)
• Cell Global Identity with Timing Advance (CGI/TA)• Cell ID and Round Trip Time (RTT)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)
• Conclusions
Assisted GPS (A-GPS)• Enhanced version of GPS. • Retrieves assistance data over a data connection (like
GPRS or 3G).• Assistance data reduces the time, known as Time To First
Fix (TTFF), a GPS enabled device requires to find its current position. • It can supply orbital data or almanac for the GPS satellites to the
GPS receiver, enabling the GPS receiver to lock to the satellites more rapidly in some cases.
• The device captures a snapshot of the GPS signal, with approximate time, for the server to later process into a position
Topics
• Mobile Positioning
• Cell Global Identity (CGI aka. CID)
• Cell Global Identity with Timing Advance (CGI/TA)• Cell ID and Round Trip Time (RTT)
• Enhanced CGI (E-CGI aka. E-CID)
• Assisted GPS (A-GPS)• Conclusions
Conclusions•Cell ID based positioning methods (CGI, CGI-TA/RTT, E-CGI) provide cheap
positioning possibilities everywhere where cell coverage is available
• Network itself provides all needed factors
• No additional changes in e.g. mobile terminal
• => High integration level possible
•Accuracy varies quite much between tens of meters up to kilometer level because of variance in:
• Cell separation• Sectoring schemes
• Used method and system (e.g. GSM or UMTS)
• => Still provides adequate accuracy for non-critical applicatons
•Assisted GPS provides much higher accuracy but also some issues:
• Lower integrity due to demand for GPS chip in terminal
• Costs... A-GPS network services typically provided by terminal vendor
• => Still best solution (IMO) because of precision and extension
References[1] Adusei I. K. Et al. Mobile Positioning Technologies in Cellular Networks: An Evaluation of their
Performance Metrics, http://www.cs.nccu.edu.tw/~ttsai/mobilecomm_ttsai/papers/1239adus.pdf , Referred
2010-04-10[2] TuruePosition Corporate, http://www.trueposition.com/web/guest/e-cid , Referred
2010-04-15[3] Mobile Network Codes, http://en.wikipedia.org/wiki/Mobile_Network_Code , Referred
2010-04-10[4] MobiForge, http://mobiforge.com/developing/story/adding-location-a-non-gps-phone-
introducing-cellid , Referred 2010-04-13[5] Nikolai D., Mobile Positioning Solutions for GSM, Alcatel R&I, 2002, http://
www.docstoc.com/docs/21589926/Mobile-Positioning-Solutions-for-GSM , Referred 2010-04-15
[6] Borkowski J., Performance of Cell ID+RTT Hybrid Positioning Method for UMTS, http://www.cs.tut.fi/tlt/RNG/publications/docs/location/MScJakub.pdf , Referred 2010-04-15
[7] Djuknic G.M. (Bell Laboratories) , Richton R.E. (Lucent Technologies), Geolocation and Assisted GPS, http://cens.ucla.edu/~mhr/cs219/location/djunkic01.pdf , Referred 2010-04-16