Mobile Positioning. Jussi Kangasoja

Transcription

1 Mobile Positioning Jussi Kangasoja

2 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

3 Mobile Positioning Category 1 Handset-Based Network-Based Category 2 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

4 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

5 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. Lat=64 55' 45" N Lon=25 21' 30" E (ICAO: EFOU) Cell-ID=1234, MCC=244, MNC=05 MNO Server and Cell-ID DB

6 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

7 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

8 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

9 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

10 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

11 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

12 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

13 Cell ID -based Cell size Round area ~550m Round area + sector ~550m <500m

14 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

15 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

16 Assisted GPS (A-GPS) Accurate within 50 meters indoors and 15 meters outdoors

17 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

18 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

19 References [1] Adusei I. K. Et al. Mobile Positioning Technologies in Cellular Networks: An Evaluation of their Performance Metrics, Referred [2] TuruePosition Corporate, Referred [3] Mobile Network Codes, Referred [4] MobiForge, Referred [5] Nikolai D., Mobile Positioning Solutions for GSM, Alcatel R&I, 2002, Referred [6] Borkowski J., Performance of Cell ID+RTT Hybrid Positioning Method for UMTS, Referred [7] Djuknic G.M. (Bell Laboratories), Richton R.E. (Lucent Technologies), Geolocation and Assisted GPS, Referred

20 Thanks (anyway)

21 Bonus Open Cell ID (non-profit approach) Saunalahti Dashboard (active) Sonera - Missä olet? (R.I.P. 2006) Elisa Paikannin (R.I.P. 2006) Google Latitude (active)