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Bluetooth Indoor Location Management (BILM) Krishna Kumar Bhoutika May 2003
Personal information management Calendar, appointments etc. Network capability Wireless, cellular network Synchronization, emails etc. Mobile Computing Evolution More • Context-awareness • Smart applications Level of user intervention Less
Context ? • Intuitively: • If applications on mobile device could gather hints about what is expected of them • Save a lot of user input • Improved user experience • Formal definition: • ”Context is the set environmental state and settings that either determines an applications behavior or in which an application event occurs and is interesting to the user.”
Computing Context Network connectivity Communication cost Comm. bandwidth Nearby resources User Context User profile User mood Other’s presence Environmental Context Lighting Noise level Traffic conditions Weather Physical Context Time, Date Location Computing, user and env. context recorded over time gives context history. Context Classification
Context-mediation • In a device-mediated communication, most of this context information is not captured and hence lost. • An external support infrastructure/framework is required to provide context information.
Goal • An indoor support infrastructure for context aware applications • Location support • Enhanced service-discovery support • Limited mobility support • Current work: Bluetooth based location support framework.
Outline • Definition of Location • Why location information is important? • Basic location estimation techniques • Overview of existing systems • Bluetooth Location-management • Bluetooth overview • IP over Bluetooth • Current work • Work in progress
(x) known position 5 mtrs. (x+5) unknown position What is Location? • Estimate of the geographical position of a mobile device. • Expressed in latitude, longitude and altitude • Presented in well-defined universal format • Indoor Location: Position of a mobile node relative to the known position of another node. Distance estimation. • Location changes when people or devices or objects move.
Why Location is Important? • Support Location-aware application • Navigation • Object tracking • Network of nodes • Event origins • Evaluate network coverage • Assistance with routing
Finding Services: Printing service Display service Phone service Example usage • Finding People: • Friends in neighborhood • Business associates • Information: • Advertising • Information dissemination (MOTD) • Localized information • Restaurant menu, tourist information (Museum) • Tracking: • People, Kids • Goods • Resources
Medium • Three major signaling medium • Radio Frequency: • WiFi, HomeRF, Bluetooth • Infra Red • Ultra Sound 128+
Basic Concepts: Distance Estimation • Three major distance estimation techniques • Radio Signal Strength Indicator (RSSI) Uses RSSI readings and wireless propagation model Signal strength becomes weaker as you move further from the transmitter. Gives rough estimate of distance. Radio signal is not uniform. Fading & Multipath affect measurements
Basic Concepts: Distance Estimation 2. Time of Arrival (TOA) Absolute time measurements Starting time of the transmission has to be known All base stations synchronized with an atomic clock d1 d2 Example: GPS d3 Used with radio, IR, acoustic, ultrasound
Basic Concepts: Distance Estimation • Time difference of arrival (TDOA) Uses relative time measurements rather than absolute time measurements used by TOA Hyperbola d3-d2 = constant d3 Example. Airport radar systems GSM TDOA: accuracy 60-200 meters d2 d1 Hyperbola d1-d2 = constant
Basic Concepts: Distance Estimation 3. Angle of arrival (AOA) Measure angles of signals as they arrive Possible location α1 α2 Beacon 2 Beacon 1 Measured with directive antennas or arrays VOR (Very high frequency omni directional range) system used for aircraft navigation and some military battlefield systems is an example of an AOA system.
Existing System • Outdoor • GPS – GLONASS - GALILEO (Satellite) • COO: Cell of origin (Cellular system) • E911 Emergency Location System (Cellular system) • Indoor • ActiveBadge (IR) • ActiveBat (Ultrasound, RF) • Cricket, Cricket Compass (Ultrasound, RF) • 3D-ID (RF proximity) • RADAR (WiFi, Radio map)
Two views Location infrastructure view Who is there ? Devices within range ? Mobile Terminal View Where am I ? Transmitters within range ? Location calculated by : Mobile Terminal (MT) Infrastructure (IF) MT / IF assisted IF / MT assisted Location Management
Bluetooth Location-Management Framework • Device discovery • Process of joining the support infrastructure • Inquiry: Devices in range • Paging : Connection and synchronization • Service Discovery • Searching and browsing • Service UUID • Location Discovery • Enhanced Location Based Service Discovery Learn about clock offset and dev. address
Cordless Bluetooth Baby monitors 802.11a, b Unused LANs Microwave oven 802.11g Bluetooth Overview • ISM band divided into 79 freq. channels: • 2.402 - 2.480 GHz of 1 MHz each • FHSS: 1600 hops/sec • Reduces interference • Channel divided into 625 µs time slots • 1 Mb/s rate, 10+ meter range • Point to Multipoint • Master to slave communication • Service discovery mechanism • Native support for voice (Time Division Duplex scheme)
Scatternet Piconets Master BT Topology Master / Slave Slave Piconet ScatterNet Bluetooth Piconet and Scatternet formation
Bluetooth Addressing • BT device address (BD_ADDR) • 48-bit IEEE MAC address • 3-bit active member address (AM_ADDR) • Maximum 8 active members in a piconet • All zero broadcast address • 8-bit parked member address (PM_ADDR) • 255 parked members • 3 low power modes • Sniff : Reduced listening, Keeps AMA, communication during specified Sniff time slots • Hold : Keeps AMA, Do other things or sleep • Park : Release AMA, Gets PMA, Keeps synced to piconet
Link Manager Handles physical Link Setup and Control Baseband Low level processing of packets. Inquiry and page scan Active, Hold, Sniff, Park state management, Freq. Hop calculation Radio Bluetooth Protocol Stack Simplified protocol architecture High Level Applications APIs Standards Host Application(s) Legacy APIs UDP TCP AT Commands OBEX IP Adaptation RFCOMM, BNEP Adaptation Host (PC, …) L2CAP Logical link control for each separate connection Performs Segmentation, Reassembly of packets Multiplexing of High Level Applications, QoS HCI Core Host Controller (BT Module)
Each Bluetooth device supports one or more profiles A profile represents a default solution for a usage model Vertical slice through the protocol stack Basis for interoperability between devices from different vendors Profile List Generic Access Profile Service Discovery Application Profile Cordless Telephony Profile Intercom Serial Port Profile Headset Profile Dial-up Networking Profile Fax Profile LAN Access Profile Generic Object Exchange Profile Object Push Profile File Transfer Profile Synchronization Profile And more coming BT Profile
Protocol Stack & Profiles Protocol Stack with profiles Simplified protocol stack
IP over Bluetooth Quick Solution: Use PPP over Virtual Serial Link
Current: Bluetooth PAN • Test bed: Private IP Network over Bluetooth eth0 Linux Kernel 2.4.20 BlueZ Bluetooth Stack 802.1d Ethernet Bridge Socket Bluetooth CompactFlash Cards D-Link DBT120 USB Dongles bnep0: 0.0.0.0 bnep1: 0.0.0.0 master1 br0: 10.0.0.1 bnep0: 10.0.0.3 bnep0: 10.0.0.2 slave1 slave2
Work in Progress • Hot-plugging : Spontaneous network formation • Average device discovery time • Average service discovery time • Effects of multiple piconets • Location support
References • Bluetooth core specification v1.1 • Bluetooth BNEP profile specification • Dynamic Location Discovery in Ad-Hoc Networks: http://nesl.ee.ucla.edu/projects/ahlos/reports.htm • BlueZ Bluetooth stack: http://bluez.sourceforge.net • Tutorial: BluetoothVs. 802.11 http://www.winlab.rutgers.edu/~pravin/publications/papers/T3-Bluetooth.zip • Location Based Services: https://doc.telin.nl/dscgi/ds.py/Get/File-23319/location_based_services.pdf