Locatability in Mobile Networks
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Locatability in Mobile Networks. Harsha Nagesh Integrated Network Research Dept. Bell Labs, Lucent Technologies [email protected] Joint work with Vishy Poosala, Anurag Srivastava, Yuh Jye Chang, Mansoor Alicherry. Talk Outline. Industry drivers

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Locatability in Mobile Networks

Harsha Nagesh

Integrated Network Research Dept.

Bell Labs, Lucent Technologies

[email protected]

Joint work with Vishy Poosala, Anurag Srivastava, Yuh Jye Chang, Mansoor Alicherry


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Talk Outline

  • Industry drivers

  • Cellular Location Tracking Techniques

  • Design for Locatability

  • iLocator – Novel Location Service


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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


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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 ?


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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


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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


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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)


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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 }


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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


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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


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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


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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


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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


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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


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Screenshot of Dolphin

Locatability Assessment

Red: Locatable Region

Grey: Non-locatable Region


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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


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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)


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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


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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


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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


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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


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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


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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


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