Using Bluetooth Low Energy for Location

Transcript

1. Using Bluetooth Low Energy for Location
   

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2. What is BLE?
   Bluetooth Low Energy
   Originally designed by Nokia as Wibree (2001)
   Bluetooth Smart
   

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3. Why has BLE been so Successful?
   Rapid adoption by vendors
   Apple
   Samsung
   Simple design
   Cheap in comparison to Wifi, Zigbee, 3g/4g
   Open Specification*
   

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4. But is it really Bluetooth?
   Current specification is 4.1, comprised of
   Bluetooth classic
   Bluetooth smart (BLE)
   Not at all compatible with each other
   

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5. Network Topology
   Broadcasts
   Fast and simple to do using advertising packets
   No security
   Connections
   Transmit data in both directions, similar to a socket
   Security*
   

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6. Security
   BLE has in-band key exchange
   SIG invented their own key exchange protocol
   Has fundamental weaknesses
   

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7. BLE Location
   

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8. BLE Location
   Quickly determine location within a home
   Do this accurately otherwise users will be annoyed
   Keep the costs down
   

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9. How to locate BLE devices?
   Standard method is to use Received Signal Strength
   Indicator (RSSI)
   A measurement of power present in a received signal
   Calculated for each frame
   Can be used to estimate distance once calibrated*
   

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11. The challenges with RSSI
    There is no standardised relationship of any particular
    physical parameter to the RSSI reading.
    Vendors and chipset makers provide their own
    accuracy, granularity, and range for the actual power
    Requires testing each receiver to estimate distance..
    

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12. RSSI based Location in
    practice
    1 m ± 1 m
    5 m ± 5m
    10 ± 10m
    

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13. Multipath and RSSI
    RSSI is easily varied by multipath
    Phenomenon which results in radio signals reaching
    the receiving antenna by two or more paths
    Varies building to building
    Can be mitigated by antenna diversity
    

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14. Positioning techniques
    

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15. Example Space
    Bedroom
    Bedroom
    Combined Living / Kitchen
    

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16. Trilateration
    Is the process of determining absolute or relative locations of
    points by measurement of distances
    Used in global positioning systems
    Enables location of BLE
    Uses 3 or more fixed way points or beacons
    Gather RSSI from these fixed way points to calculate location
    Requires lots of way points to work effectively
    

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17. Fingerprinting
    Uses fixed way points
    Preferably one per room
    Walls or divisions help
    Apply a gradient filter for smoothing the RSSI
    Enhanced by calibration of a space*
    

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18. Observations
    RSSI based positioning is hard
    Trilateration didn’t work for us
    Way to much variance in values
    Smoothing didn’t help
    Fingerprinting working for room level location*
    Requires lots of data and Maths to improve accuracy
    

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19. Hardware
    Important to have a stable and known group of devices
    reporting RSSI
    TI CC2540 / CC2541 (8051)
    http://www.ti.com/sensortag
    TI Wilink8 which combines wifi/bluetooth/ble
    Nordic Semiconductors nRF51822 (ARM)
    

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20. Future Work
    Move from RSSI to Channel State Information (CSI)
    Fine Grained metric full of frequency domain
    information
    Requires access to the Baseband Controller
    Smarter way points
    

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