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The Chinese Univ. of Hong KongDept. of Computer Science & Engineering
A Sensibility-Based Sleeping Configuration Protocol for
Dependable Wireless Sensor Networks
Chen XinyuGroup Meeting
2005-01-28
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Outline
Introduction Neighboring-sensor field sensibility Sensibility-based sleeping configuration
protocol Performance evaluations Conclusions
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Wireless Sensor Networks
Composed of a large number of sensor nodes
Sensors communicate with each other through short-range radio transmission
Sensors react to environmental events and relay collected data through the dynamically formed network
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Applications Environment
monitoring Military
reconnaissance Physical security Traffic surveillance Industrial and
manufacturing automation
Distributed robotics …
Ossama Younis and Sonia Fahmy: Distributed Clustering in Ad-hoc Sensor Networks: A Hybrid, Energy-Efficient Approach (InfoCom2004)
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Requirements
Maintaining coverage• Every point in the region of interest should be
sensed within given parameters
Extending system lifetime• The energy source is usually battery power
• Battery recharging or replacement is undesirable or impossible due to the unattended nature of sensors and hostile sensing environments
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Requirements (Cont’d)
Fault tolerance• Sensors may fail or be blocked due to physical
damage or environmental interference• Produce some void areas which do not satisfy
the coverage requirement Scalability
• High density of deployed nodes• Each sensor must configure its own operational
mode adaptively based on local information, not on global information
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Approach: Coverage Configuration
Coverage configuration is a promising way to extend network lifetime by alternately activating only a subset of sensors and scheduling others to sleep according to some heuristic schemes while providing sufficient coverage in a geographic region
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Concerns
A good coverage-preserved and fault-tolerant sensor configuration protocol should have the following characteristics:• It should allow as many nodes as possible to turn their
radio transceivers and sensing functionalities off to reduce energy consumption, thus extending network lifetime
• Enough nodes must stay awake to form a connected network backbone and to preserve area coverage
• Void areas produced by sensor failures and energy depletions should be recovered as soon as possible
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Two Sensing Models
Boolean sensing model (BSM)• Each sensor has a certain sensing range, and
can only detect the occurrences of events within its sensing range
General sensing model (GSM)• Capture the fact that signals emitted by a
target of interest decay over the distance of propagation
• Exploit the collaboration between adjacent sensors
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Discussions for the BSM
Each sensor has a deterministic sensing radius
Allow a geometric treatment of the coverage problem
Miss the attenuation behavior of signals Ignore the collaboration between adjacent
sensors in performing area sensing and monitoring
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Problem Formulation for the GSM
Point Sensibility s(Ni, p): the sensibility of a sensor Ni for an event occurring at an arbitrary measuring point p
: the energy emitted by events occurring at point p : the decaying factor of the sensing signal d(Ni, p) : the distance between senosr Ni and point p
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All-Sensor Field Sensibility (ASFS)
Suppose we have a “background” distribution of n sensors, denoted by N1, N2, …, Nn, in a deployment region A
All-Sensor Field Sensibility for point p
With a sensibility threshold , the point p is covered if Sa(p) ≥
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Discussions for the ASFS
Need a sink working as a data fusion center
Produce a heavy network load in multi-hop sensor networks
Pose a single point of failures
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Neighboring-Sensor Field Sensibility (NSFS)
Treat each sensor as a sensing fusion center Each sensor broadcasts its perceived field
sensibility Each sensor only collects its one-hop neighbors’
messages
Transform the original global coverage decision problem into a local problem
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Responsible Sensing Region (RSR)
Voronoi diagram• Partition the deployed region into a set of
convex polygons such that all points inside a polygon are closet to only one particular node
The polygon in which sensor Ni resides is its Responsible Sensing Region i
• If an event occurs in i, sensor Ni will receive the strongest signal
• Open RSR and closed RSR
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Pessimistic Scan Region
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Connectivity Requirement
Considering only the coverage issue may produce disconnected subnetworks
Simple connectivity preservation
• Evaluating whether Ni’s one-hop neighbors will remain connected through each other or through its two-hop neighbors when Ni is removed
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Ni’s Sleeping Candidate Condition
: Responsible Sensing Region of Nj
: the two-hop confined region of Ni
: communication path between Nj and Nk
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Optimistic Scan Region
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uncertain I
Sensibility-Based Sleeping Configuration Protocol (SSCP)
onsleeping
ready-to-sleeping
ready-to-on
Tround
eligible / STATUS
ineligible
Tround
TwaitTwait
eligible / STATUS
ineligible / STATUS
uncertain II
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Performance Evaluation with ns-2
Boolean sensing model• ESS: extended sponsored sector
•Proposed by Tian et. al. of Univ. of Ottawa, 2002
•Consider only the nodes inside the RSR of the evaluated node
General sensing model• SscpP: SSCP with the pessimistic scan region
• SscpO: SSCP with the optimistic scan region
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Bridge between BSM and GSM
Ensured-sensibility radius
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Default Parameters Setting
The deployed area is 50m x 50m = 1, = 3, = 0.001 (r = 10m) R = 12 m The number of deployed sensor: 120 Power Consumption:
• Tx (transmit) = 1.4W, Rx (receive) = 1W, Idle = 0.83W, Sleeping = 0.13W
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Performance Evaluation (1)
Sleeping sensor vs. communication radius
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Performance Evaluation (2) Network topology
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Performance Evaluation (3)
Sleeping sensor vs. sensor number
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Performance Evaluation (4)
Sleeping sensor vs. sensibility threshold
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Performance Evaluation (5)
Network lifetime vs. live sensor when the MTBF is 800s, R is 12m
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Performance Evaluation (6)
-coverage accumulated time•The total time during which or more percentage of the deployed area satisfies the coverage requirement
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Conclusions
Propose NSFS with the GSM• transform a global decision problem to a
local one
• exploit the cooperation between adjacent sensors
Develop SSCPs to build dependable wireless sensor networks
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Q & A
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