Lightning A fast and lightweight acoustic localization protocol

							                                                 Lightning:
       A fast and lightweight acoustic localization protocol using low-end wireless
                                     micro-sensors.




                  Qixin Wang, Rong Zheng, Ajay Tirumala, Xue
                               Liu and Lui Sha.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala           Power Point created by Qixin Wang and Ajay Tirumala
               Outline of the presentation
  •     Demand
  •     Observations and Solution Heuristics
  •     Protocol Details
  •     Theorems and Experiment Results
  •     Demo Video
  •     Conclusion


Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                                                 Demand

  • Want a fast, deterministic (i.e.O(1)
    response time) acoustic event localization
    scheme.
  • Fits low-end wireless micro-sensor
    networking.
  • Proximity localization, i.e. electing the
    closest sensor, is good enough.


Dec 8th, RTSS 2004, Presented by Ajay Tirumala            Power Point created by Qixin Wang and Ajay Tirumala
                                          Observations
  • Sound sources are often directional and of
    unknown intensities. This implies:
          – Intensity-based localization is not desirable.
          – Time-Of-Arrival (TOA) is a more reliable metric. When
            sensors are densely deployed, Line-Of-Sight to the
            closest sensor can usually be guaranteed, therefore
            earliest TOA  closest sensor.
  • Radio (RF) wave travels much faster than
    acoustic wave.
          – When a lightning strikes, people see the lightning
            before hearing the rumbling of the thunder.

Dec 8th, RTSS 2004, Presented by Ajay Tirumala     Power Point created by Qixin Wang and Ajay Tirumala
                              Solution Heuristic I
  • When sound reaches the closest sensor,
    the closest sensor should immediately
    announce the event (via RF broadcast) to
    all other sensors and suppress them even
    before they hear the sound.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                                            Observation
  • Immediate Data Packet (DP) RF
    broadcast is not practical, because of
    collisions.
          – To think several sensors, all almost the same
            distance to the sound source, try to broadcast
            data packets at almost the same time.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala      Power Point created by Qixin Wang and Ajay Tirumala
                             Solution Heuristic II
  • Do NOT use data packet broadcast,
    broadcast RF burst instead.

        RF burst is not susceptible to overlapping.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                                            Observation
  • If there are multiple closest sensors, there
    can be multiple election winners.
  • How to guarantee every time there is only
    one winner?




Dec 8th, RTSS 2004, Presented by Ajay Tirumala      Power Point created by Qixin Wang and Ajay Tirumala
                         Solution Heuristics III
  • Color the sensors, to differentiate RF burst
    duration, to break ties.
          – It is proven, with regular sensor layout and
            proper coloring, it is guaranteed to always
            elect one winner sensor.
          – (To be included in our upcoming publications)
            Empirically, even with random sensor layout
            and without coloring, the number of winners is
            still well limited.

Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                                                 Remark
  • Heuristics I, II and III lead to the design of
    Basic Lightning Protocol.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala        Power Point created by Qixin Wang and Ajay Tirumala
                                            Observation
  • Energy cost is a concern.
          – Currently, a sensor has to have RF on all the
            time to listen to possible RF bursts.
            Remember a sensor to be suppressed
            receives RF burst before hears the sound.
  • How to have RF module sleep during most
    of the time and only be turned on when
    there is an acoustic event?

Dec 8th, RTSS 2004, Presented by Ajay Tirumala      Power Point created by Qixin Wang and Ajay Tirumala
                         Solution Heuristics IV
  • RF Sleep during usual time.
  • When hears a sound, turn on RF and RF listen
    for Δdefer sec, to make sure all other sensors that
    can hear the sound have turned on their radios.
    Then carry out the same procedure as Basic
    Lightning Protocol.
  • Equivalent to the sound takes place Δdefer sec
    later in real-world, and Basic Lightning Protocol
    is deployed.

Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                                                 Remark
  • Heuristics IV leads to the design of
    Energy-Efficient Lightning Protocol.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala        Power Point created by Qixin Wang and Ajay Tirumala
                   Basic Lightning Protocol
  • Regular sensor layout with
    certain coloring
  • All sensors are initially in RF-                               Beep recognized
    listen mode                                  RF Listen
                                                                                              RF burst

  • Beep recognized:                                                                          for i.Tburst

          – broadcast RF burst without                           Timer expires
            backoff for iTburst.                    Burst
                                                    recognized
          – Listen for RF bursts for Tb.
                 • No other burst recognized
                   “elected”                                  Supressed Burst recognized
                 • Other burst recognized –                  Set reset timer
                   ”supressed”
                                                                                           Post burst listen
  • During RF listen
          – RF burst recognized                       Timer expires

                 • Enter supressed mode
  • Reenter RF listen mode after                                 Elected
                                                                               No burst recognized

    basic timer expires.                                     set reset timer



Dec 8th, RTSS 2004, Presented by Ajay Tirumala               Power Point created by Qixin Wang and Ajay Tirumala
       Energy-efficient lightning protocol
  • All sensors initially in RF                                  Beep recognized
    sleeping                                     RF Sleeping
                                                                                          RF listen for
                                                                                             defer
  • When beep is recognized
          – Listen for RF bursts but defer                     Timer expires
            bursting for Δdefer                                            Burst
                                                                           recognized
          – If no burst is recognized,
            transmit RF burst without
            backoff，for iTburst sec.                        Supressed Burst recognized              RF burst
                                                           Set reset timer
          – Post burst RF listen                                                                    for i.Tburst
                 • No other burst recognized
                   “elected”
                                                       Timer expires
                 • Other burst recognized –
                   ”suppressed”
          – If burst is recognized in RF                                      No burst recognized   Post burst listen
            listen – enter suppressed mode                     Elected
                                                           set reset timer
  • When reset timer expires,
    return to RF Sleeping mode


Dec 8th, RTSS 2004, Presented by Ajay Tirumala                 Power Point created by Qixin Wang and Ajay Tirumala
                                       Key Properties
     • Theorem 1,2: Both Basic and Energy-Efficient
       Lightning Protocol elect a unique winner with
       deterministic localization distance error.
     • Corollary 1,2: Both have a short and O(1) time
       bound for the election.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                               Experiment results




  • Implemented on U.C. Berkeley MICA Motes
  • Directional Sound Source


Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                               Experiment results
  • Comparable, or even
    better accuracy than
    ideal (no pkt loss)
    data packet based
    localization.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                             Experiment Results
                 60

                 50

                 40                                                     Lightning
                                                                        Color 4 (ms)
                 30                                                     DP - Closest
                                                                        First (ms)
                 20                                                     DP - Any first
                                                                        (ms)
                 10

                    0
                           Max              Min   Mean


  • Fast: in the sense that the Upper Bound of
    Lightning Protocol Election Delay is shorter than
    the Lower Bound of Data Packet Election
    Protocol

Dec 8th, RTSS 2004, Presented by Ajay Tirumala           Power Point created by Qixin Wang and Ajay Tirumala
                             Experiment Results




  • Deterministic Election Delay, while data packet
    localization’s election delay are random due to
    MAC contention.

Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                             Experiment Results
  Number of bursts in                            1      2                       >2
  lightning protocol
  % of localization trials                       81.4   18.6                    0



  • O(1) broadcasts
          – Theoretical: Guaranteed to be <= 4.
          – Experiment: Never more than 2.




Dec 8th, RTSS 2004, Presented by Ajay Tirumala              Power Point created by Qixin Wang and Ajay Tirumala
                Demo video (Qixin Wang)




  URL: http://www-rtsl.cs.uiuc.edu/papers/LightningDemo.html
  See reference [13]
Dec 8th, RTSS 2004, Presented by Ajay Tirumala   Power Point created by Qixin Wang and Ajay Tirumala
                                                 Conclusion
  • Fast and Deterministic:
          – O(1) election delay.
          – O(1) number of broadcasts.
  • Lightweight:
          – only involves simple comparison (<>) operation;
          – no clock synchronization needed;
          – simple network stack.
  • Comparable, or even better localization accuracy than ideal data
    packet scheme.
  • Robust:
          – Immune to RF broadcast overlapping;
          – Handles directional sound source
  • Energy Efficient:
          – only turns on RF module when there is an acoustic event.



Dec 8th, RTSS 2004, Presented by Ajay Tirumala           Power Point created by Qixin Wang and Ajay Tirumala
                                                 Thank you!




Dec 8th, RTSS 2004, Presented by Ajay Tirumala           Power Point created by Qixin Wang and Ajay Tirumala