Locatability in Mobile Networks

1. Locatability in Mobile Networks Harsha Nagesh Integrated Network Research Dept. Bell Labs, Lucent Technologies harsha@research.bell-labs.com Joint work with Vishy Poosala, Anurag Srivastava, Yuh Jye Chang, Mansoor Alicherry

2. Talk Outline • Industry drivers • Cellular Location Tracking Techniques • Design for Locatability • iLocator – Novel Location Service

3. Drivers • GPS infrastructure worth 10 Billion built for smart weapons program • Enhanced-911 for Wireless Networks (E112 in EU) • FCC ruling to enhance emergency services • ANI (automatic number identification) across PSTN (wire-line and wireless) • Phase I completed in Oct 2001 • Basic ANI with cell Id/sector information of mobile • Phase II spread over 4 years, to be completed by 2005 • Each SP has a deployment proposal approved by FCC, including technology choice and location % coverage of handsets issued • Handset Based - within 50m for 67% of calls, within 150m for 95% of calls • Network Based - within 100m for 67% of calls, within 300m for 95% of calls • TTFF (time-to-first-fix) location is 30s, with first estimate in 7s

4. Location Services • Location services present a significant revenue opportunity • Expected market size of $7-8B by 2007-08 • Compelling applications: fleet tracker, restaurant finder, buddy alerts, teen-tracking, coupons, dating, games • What is required to make LBS a reality ?

5. Keys to LBS Takeoff • Service Providers • Standards based access to network resident information • Location, Presence Parlay gateways • Convergence across wire-line and wireless networks • Usage based charging • Locatability – outdoor, indoor, cities, etc • Application Developers • Easy deployment across multiple service providers, device technologies • Consumers • Compelling applications • Mass market cell phones with programmability • Java, Brew, Symbian based • Fine grained privacy knobs

6. Location Tracking Background • Basic geometric distance between the mobile and a reference point, with known location • Signals travel with speed of light, c • Three dimensions to location computation • Physical-layer technique – Angle of Arrival, Time of Arrival, Time Difference of Arrival, Hybrid • Computation Model - Network Based, Mobile Based, Hybrid • Synchronization – or lack of among entities involved in location measurements

7. A B Base Station Fixed Known Location Mobile TOA Mobile Angle of Arrival (AoA) Multi-path effects make AoA less effective Time of Arrival (ToA)

8. Time Difference of Arrival (TDoA) • dT - Time difference of Signal • Measured at the mobile, with synchronized transmission at A,B • Measured at A and B for signal transmitted by mobile • Multiple pairs of reference points, leads to solving non-linear hyperbolic equations c*dT = sqrt{ (XA - x)2 + (YA - y)2 } - sqrt{ (XB - x)2 + (YB - y)2 }

9. Wireless Networks • Cell-ID and Cell-ID variants - GSM, GPRS, and WCDMA • E-OTD (Enhanced Observed Time difference) - GSM/GPRS • OTDOA (Observed Time Difference of Arrival) - WCDMA • A-GPS (Wireless Assisted GPS) - GSM, GPRS and WCDMA • Hybrid (combinations of A-GPS and other standards) - GSM, GPRS, and WCDMA

10. CDMA Location Architecture • MSC – Routes 911 calls with mobile details and capabilities • MPC – Stores, retrieves location data, selects appropriate PDE, PSAP, sends routing digits to MSC • PDE – Calculates location based on data from SRS (Satellite Reference Service), MPC

11. CDMA Link Tri-Lateration • TDOA technique requires visibility of mobile at 3 or more BS • Reverse link has visibility problems at 3 BS due to power control • Forward Link TDOA • Each BS broadcasts the a PN sequence with a known unique offset • MS uses sliding window correlation to find out pair-wise pilot signal phase offset differences • BS uses the phase difference TDOA to locate the mobile • MSC determines location technique • Legacy CDMA MS use Enhanced Forward Link Trilateration (EFLT) • Lower accuracy using Pilot Signal strength (about 244m) • IS-801 compliant MS use Advanced Forward Link Trilateration (AFLT), Assisted GPS (AGPS) or Hybrid solutions • Higher accuracy using Pilot Phase measurements (about 15m) or GPS assistance

12. CDMA Network Design • Automated design tools to minimize drive tests • Design for a given capacity (blocking probability) maximize coverage • Forward link pilot Ec/Io for every mobile is above a threshold • Model the Network as a mesh with nodes representing MS • Optimize capacity-coverage tradeoff points • Determine the power, tilt, azimuth of each antenna through non-linear optimization and analytical differentiation • Capacity-Coverage Intuition • Power controlled MS is distance (coverage) limited to ensure good signal reception at the BS which is interference limited

13. Low Coverage High Coverage High Pilot Pollution in Center => Large Coverage Hole Reduced Pilot Pollution in Center: => Small Coverage Holes Cells have equal traffic load => High Effective Network Capacity Traffic load unbalanced => Small Effective Network Capacity High Capacity Low Capacity Ocelot CDMA Capacity-Coverage Tradeoff Network coverage and network capacity cannot be optimized at the same time Large Antenna Tilt Small

14. Dolphin: Locatability Analysis and Design • 100% geographic coverage does not translate to 100% location coverage • Location tracking using trilateration poses stronger requirements • Must be covered by at least three base stations • Significantly increases interference – pilot pollution • In CDMA this translates to a capacity-coverage-locatability trade-off • Harder than coverage • Non-trivial to assess the locatability of a network • Drive-by testing is expensive, not flexible, not exhaustive • CDMA Development Group Specifies detailed test scenarios • Dolphin Software • Assessing locatabilityin the current network • Design keeping in mind capacity – coverage – locatability metrics

15. Screenshot of Dolphin Locatability Assessment Red: Locatable Region Grey: Non-locatable Region

16. Location Everywhere • GPS still doesn’t work well indoors and in NY city canyons • Location access everywhere seamlessly through applications • mobile network, wi-fi hotspots for indoor and outdoor environments • New Ideas • Design for location coverage and assess location accuracy • Push sampled GPS signals indoor to work with standard AGPS mobiles • Radio-Star is Bell-Labs indoor wireless solution • Extending coverage inside buildings by encapsulating CDMA/GSM in gigabit-Ethernet frames and using low power antennas • Explore GPS-repeaters in to fill city GPS canyons

17. Hybrid Locatability • Leverage short range supplementary radio (ex. Bluetooth) to compute location autonomously • Distributed computation using both proximity and non-proximity constraints • Especially useful when not all mobiles are GPS capable or have GPS visibility • Globecom 04 (Vishy Poosala, Harsha Nagesh, Chitra Phadke, Mansoor Alicherry, Sumesh Philip)

18. iLocator – Location Based Service • A location and presence-based track & alert application offering multiple services • Tracks people/events/enterprises and displays their positions on a map and Alerts when they are in the user’s vicinity • People: Like Instant Messenger, maintains a buddy list and informs about buddies entering or leaving a configurable distance around the user • Events: Alerts if there is a concert / sale / traffic-jam near user’s location • Enterprises: Display all the preferred restaurants etc. in user’s vicinity • Alert Me:Alert through SMS when the callee becomes available • e.g. John is calling Mary, Mary is busy or has no coverage, network SMS’es John when Mary is again able to receive calls • Provides privacy: users control from the handset who can track them • Supports SMS’ing from within the application

19. Value Proposition • Realize revenues out of the E-911 infrastructure • Prompt more calls and SMSes, complete more calls with Alert Me • The AOL Effect: entice other uses to join the network to interact with their buddies • Before inter-carrier location exchange becomes a reality, first mover advantage for service providers • Convergence: Works across cellular and wifi networks • Mass Market – works on any phone, any location technology, any network

20. Technical Details • Works on top of any Parlay Network Gateway • Works on any wireless network • GSM, CDMA, iDEN, TDMA • HTTP transport needed to support GUI application • Works with any location-tracking mechanism • GPS, Triangulation, Cell Number, User-specified • Works on any phone • Adapts to handset capabilities – screen size, stylus, color • Works on any phone through SMSes • JVM needed for map display (Java phones, BREW, iDEN) • Scales with number of users • Software challenges - strict limit on resident memory, adaptability to 100’s of handsets, J2ME implementations, etc

21. HLR MSC iLocator Network Diagram and Call Flow Web pages for Privacy Policies, Event registrations • iLocator refresh request • Get Locatable Buddies based on permissions • Eliminate duplicates from multiple clients and request ISG for buddy locations, nearby enterprises, filter based on policies (UL and US) • Fetch the map based on current location and device parameters • Return map with buddy information and user status internet HTTP Map Server 4 HTTP over air link HTTP 1 5 Mobile Network iLocator Server & Proxy * HTTP CORBA/Parlay APIs 2 3 Packet-IN Database ISG Mobile Network

22. Internet/Intranet Internet/Intranet Content Providers MiLife™ Intelligent Services Gateway XML GW ISG Parlay/OSA/PAM API’s CHAM PAM MSG DIR* FW PM UL US CC/UI ANSI/MAP SMPP ANSI/MAP XML/LIF SMTP/IMAP4 LDAP JTAPI MSC SMSC HLR GMLC MSGServer SurePay LSS SIP Other Lucent/Non-Lucent Services Intelligent Services Gateway Operater Applications 3rd Party Applications MiLife™ Intelligent Services Gateway Provides standard set of APIs and hides Network complexities XML GW ISG Parlay/OSA/PAM API’s CHAM PAM MSG DIR* FW PM UL US CC/UI ANSI/MAP SMPP ANSI/MAP XML/LIF SMTP/IMAP4 LDAP JTAPI MSC SMSC HLR GMLC MSGServer SurePay LSS SIP Other Lucent/Non-Lucent Services

23. Conclusion • Design for capacity-coverage-locatability is hard, but important to be E-911 compliant fully • Compelling mass market applications that works across service provider networks and technologies important for LBS to take off • iLocator is a novel service that service providers can leverage to increase ARPU and lock in customers