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

Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower 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 8 th, RTSS 2004, Presented by Ajay TirumalaPower 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 Δ defer 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 Δ defer sec later in real-world, and Basic Lightning Protocol is deployed.

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

Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala Basic Lightning Protocol Regular sensor layout with certain coloring All sensors are initially in RF- listen mode Beep recognized: –broadcast RF burst without backoff for iT burst. –Listen for RF bursts for T b. No other burst recognized “elected” Other burst recognized – ”supressed” During RF listen –RF burst recognized Enter supressed mode Reenter RF listen mode after basic timer expires. RF Listen Beep recognized RF burst for i.T burst Post burst listen Burst recognized Supressed Set reset timer No burst recognized Elected set reset timer Timer expires Burst recognized Timer expires

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

Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower 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 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala Experiment results Implemented on U.C. Berkeley MICA Motes Directional Sound Source

Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower 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 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala Experiment Results 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 8 th, RTSS 2004, Presented by Ajay TirumalaPower 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 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala Experiment Results O(1) broadcasts –Theoretical: Guaranteed to be <= 4. –Experiment: Never more than 2. Number of bursts in lightning protocol 12> 2 % of localization trials

Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala Demo video (Qixin Wang) URL: See reference [13]

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