communication support for location- centric collaborative signal processing in sensor networks...
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Communication Support for Location-Centric Collaborative
Signal Processing in Sensor Networks
Parmesh RamanathanUniversity of Wisconsin, Madison
Acknowledgements:K.-C. Wang, K. K. Saluja, T. Clouqueur
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What is a sensor network? A large ad hoc network of low-cost,
smart devices Devices communicate over
wireless channels Devices can sense only a small
area around them Need collaboration among devices to
carry out most meaningful tasks
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Sensor Network Characteristics Commands/queries are typically issued to
a geographic region and not to specific nodes Compute the average temperature in a region Are there any unidentified objects in a given
region? Track an object within a region
Only devices in the specified geographic region need to participate in executing a command/query
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Ad Hoc Wireless LANs Nodes are the addressable entities Commands are issued to specific
nodes Typical challenge is to how to
maintain ongoing interactions between a given set of nodes even as they move
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Open Question What is the best programming
abstraction and the underlying communication support suited for sensor networks?
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Prior Work Programming abstraction
Subscribe-Publish model [USC/ISI/MIT/LL]
Communication support Directed Diffusion [USC/ISI]
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Subscribe-Publish Model Nodes disseminate the attributes of the
information they need (Subscribe) Nodes also disseminate the attributes of
the information they can provide (Publish)
An interaction between nodes is established when there is match between their respective subscription and publication
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Directed Diffusion Nodes diffuse interest messages identifying
the attributes of the information they need Nodes with the data respond over one or
more routes identified by the interest messages
Reinforcement messages are used to converge a good route
Intermediate nodes may use filters to aggregate information as it passes through the network
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Our Programming AbstractionLocation-centric Computing
All nodes are aware of their current location Addressable entity is a geographic region Regions play the traditional role of a node A region must be created before a command
or query can be issued Each region has a manager region responsible
for coordinating intra-region activities Each node maintains the list of regions to
which it belongs and participates only in the activities of its regions
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Location-centric Model
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Location-centric Communication Primitives
Data exchange primitives Motivated by the well-known
distributed computing library called MPI 1.1
Send, Receive, Reduce, Barrier, Multicast, Broadcast,…
Administrative primitives Create region and delete region
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Location-centric Communication PrimitivesExample: SN_Send Sends a message from a node to all
nodes in the addressed region Used to send commands and dataExample: SN_Reduce Aggregates data within a region at the
manager region Aggregation is in the form of min,
max, average, sum, …
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Location-based Routing Each node maintains a routing table
identifying next hop to reach a destination region
Routing entry for a region is created on demand using RouteRequest (RREQ) and RouteReply (RREP)
RREQ and RREP use an approach similar to Location-aided Routing [Vaidya] to limit the scope of flooding
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Location-Based Routing: Inter-Region
Send:1. message
sent from a source node to a region.
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Location-Based Routing: Inter-Region
Send:1. message
sent from a source node to a region.
2. Message flooded to all nodes in the region.
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Target Detection and Trackingt=0
t=20
t=60
t=40
81 sensors evenly spaced over 800mx800m square area
Target emits power sensible within 100m
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Location-centric solution
Create region(s) at expected entry area(s)
Send detect & track command to the region(s)
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Location-centric solutionManager
Nodes in the region use Reduce to aggregate sensor readings
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Location-centric solution
Predict the track and create the next region Initiate detection & tracking in the created region
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Subscribe/Publish Solution I
Each node subscribes to track info from neighboring nodes
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Subscribe/Publish solution
Duplicate copies of track info from same node are suppressed.
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Subscribe/Publish solution
Track info from different nodes are not suppressed.
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Regional Subscribe/Publish Solution
subscribe
subscribesubscrib
e
subscrib
e
Each node subscribes to track info from neighboring regions.
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Regional Solution with Subscribe/Publish Model
Track info propagates to subscribers using directed diffusion
Data suppression more effective.
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Evaluation We implemented the three
approaches in ns-2. Counted the total number of
messages exchanged for the tracking scenario Routing messages Application payload
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Initial Results
010002000300040005000600070008000
Message count
Loc-Cen SP-I SP-II
PayloadRouting
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Summary Collaboration in sensor networks are quite
different from that in conventional wireless ad hoc networks
Compared performance of two different approaches for collaboration in sensor networks
Initial results show that a location-centric based approach is better in terms of number of messages for target tracking application
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Ongoing Work Physical and link layer aware
communication schemes to improve energy and bandwidth usage
Incorporate fault-tolerance in sensor fusion algorithms
Develop collaborative signal processing algorithms for typical sensor network applications