Mobile Positioning

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Mobile Positioning

Jussi Kangasoja 2010-4-19

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Topics

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Mobile Positioning

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Cell Global Identity (CGI aka. CID)

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Cell Global Identity with Timing Advance (CGI/TA)

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Cell ID and Round Trip Time (RTT- similar to TA)

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Enhanced CGI (E-CGI aka. E-CID)

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Assisted GPS (A-GPS)

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Conclusions

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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

Unilateral EOTD, AFLT, IPDL- OTDOA, RX-Level

EOTD,

AFLT, IPDL- OTDOA, RX-Level

Rx-Level

Bilateral Cell Coverage, CI

+RTD n/a LF, Cell Coverage, CI

+RTD

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Topics

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Mobile Positioning

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Cell Global Identity (CGI aka. CID)

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Conclusions

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Cell Global Identity (CGI) - I

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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)

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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

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Cell Global Identity (CGI) - II

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So this sounds just great?

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Let´s just get the Cell-ID and make query about

corresponding coordinate pair and then we will know our location.

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Good, but... We would know only geographical coordinates of serving cell as well as sector.

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... The issue is that the location of cells is not public information.

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The operators keep this private for many reasons including:

• Security and other policies

• Extra revenue income

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Topics

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Mobile Positioning

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Cell Global Identity with Timing Advance (CGI/TA)

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Conclusions

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CGI-TA (Timing Advance)

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Improvement to basic Cell-ID based positioning.

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TA is an existing parameter to avoid overlapping of bursts transmitted by several MSs at the same time

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For positioning purposes the TA is an estimate of the absolute distance between MS and serving BTS

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Quantized into 64 levels, each level corresponds ~550m

CGI CGI-TA

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Topics

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Mobile Positioning

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Cell ID and Round Trip Time (RTT)

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Conclusions

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Cell ID and RTT

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RTT (Round Trip Time) is a UMTS ‘TA-like’ improvement for Cell ID positioning.

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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.

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^But…

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Unfortunately (mainly) propagation effects are degrading the accuracy.

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Also cell separation causes difference in accuracy

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Topics

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Mobile Positioning

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Cell ID and Round Trip Time (RTT)

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Enhanced CGI (E-CGI aka. E-CID)

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Conclusions

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E-CGI (Enhanced CGI)

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Accuracy Improvement to CGI-TA

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Consists of CGI + TA(RTT) + NMR (Network Management Record)

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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

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Cell ID -based

Cell size Round area ~550m

Round area + sector ~550m

<500m

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Topics

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Mobile Positioning

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Assisted GPS (A-GPS)

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Conclusions

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Assisted GPS (A-GPS)

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Enhanced version of GPS.

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Retrieves assistance data over a data connection (like GPRS or 3G).

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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

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Assisted GPS (A-GPS)

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Accurate within 50 meters indoors and 15 meters outdoors

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Topics

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Mobile Positioning

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Conclusions

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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

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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

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Thanks (anyway)

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Bonus

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Open Cell ID (non-profit approach)

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Saunalahti Dashboard (active)

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Sonera - Missä olet? (R.I.P. 2006)

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Elisa Paikannin (R.I.P. 2006)

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Google Latitude (active)