Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala...
-
Upload
dora-wilkins -
Category
Documents
-
view
217 -
download
0
Transcript of Dec 8 th, RTSS 2004, Presented by Ajay TirumalaPower Point created by Qixin Wang and Ajay Tirumala...
Dec 8th, RTSS 2004, Presented by Ajay Tirumala Power 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 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-
listen mode• Beep recognized:
– broadcast RF burst without backoff for iTburst.
– Listen for RF bursts for Tb.• 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 recognizedRF burst
for i.Tburst
Post burst listen
Burst recognizedSupressedSet reset timer
No burst recognizedElected
set reset timer
Timer expiresBurst recognized
Timer expires
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 sleeping
• When beep is recognized– Listen for RF bursts but defer
bursting for Δdefer
– If no burst is recognized, transmit RF burst without backoff , for iTburst 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 recognizedRF listen for
defer
Post burst listen
Burst recognizedSupressedSet reset timer
No burst recognizedElected
set reset timer
Timer expires
Timer expires
Burst recognized
RF burst
for i.Tburst
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
• Fast: in the sense that the Upper Bound of Lightning Protocol Election Delay is shorter than the Lower Bound of Data Packet Election Protocol
0
10
20
30
40
50
60
Max Min Mean
LightningColor 4 (ms)
DP - ClosestFirst (ms)
DP - Any first(ms)
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
• O(1) broadcasts– Theoretical: Guaranteed to be <= 4.– Experiment: Never more than 2.
Number of bursts in lightning protocol
1 2 > 2
% of localization trials 81.4 18.6 0
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.