1. CMPSCI 791L: Sensor Networks Experiences Building a Real Distributed Sensor Network Victor R. Lesser Computer Science Department University of Massachusetts, Amherst September 12, 2003

2. Acknowledgements Bryan Horling Bryan Horling Roger Mailler Roger Mailler Jiaying Shen Jiaying Shen Dr. Regis Vincent (SRI) Dr. Regis Vincent (SRI) http://mas.cs.umass.edu/~bhorling/papers/02-14.ps.gz http://mas.cs.umass.edu/~bhorling/papers/02-14.ps.gz http://mas.cs.umass.edu/~bhorling/papers/00-49.ps.gz http://mas.cs.umass.edu/~bhorling/papers/00-49.ps.gz

3. Outline An example DSN problem An example DSN problem Issues in Distributed Resource Allocation Issues in Distributed Resource Allocation An example of one approach An example of one approach

4. Distributed Sensor Network Challenge Problem Small 2D Doppler radar units (30’s) –Scan one of three 120  sectors at a time Commodity Processor associated with each radar Communicate short messages using one of 8 radio channels Triangulate radars to do tracking

5. Representative of Distributed Sensor Network Issues Need for Coordination/Distributed Resource Allocation Need for Coordination/Distributed Resource Allocation Multiple sensors need to collaborate on tasks Multiple sensors need to collaborate on tasks View objects of interest from multiple angles with different types of sensors View objects of interest from multiple angles with different types of sensors Sensing time windows need to be closely aligned Sensing time windows need to be closely aligned Environmental Dynamics Environmental Dynamics Sensor configuration changes as target moves Sensor configuration changes as target moves Potential for Resource Overloads Potential for Resource Overloads Multiple target in overlapping sensor regions Multiple target in overlapping sensor regions Limited Communication Channels Limited Communication Channels

6. Representative of DSN Issues, cont. Soft Real-time Soft Real-time Limited time window for sensing Limited time window for sensing Must anticipate where target is moving in order to effectively allocate sensor resources Must anticipate where target is moving in order to effectively allocate sensor resources Time for coordination affects time for sensing Time for coordination affects time for sensing Distribution: communication latency/limited bandwidth precludes global knowledge/control Distribution: communication latency/limited bandwidth precludes global knowledge/control distributed data fusion distributed data fusion Scalability: need to be able to handle large numbers of sensor nodes Scalability: need to be able to handle large numbers of sensor nodes Robustness: local failures should not induce global collapse Robustness: local failures should not induce global collapse Handle uncertain information, sensor/processor/communication failures Handle uncertain information, sensor/processor/communication failures

7. Real-Time Tornado Tracking supercomputers Internet2 radar Fractional T1 (100K) 802.11b (0,1,2,4Mb) Legend

8. Weather/Computation/ Sensor Integrated Control radars signal processing Quality Control (clutter removal, de-aliasing) Hazardous Weather Detection algorithms Retrieval of 3D wind, other fields Assimilation, Multiple Doppler analysis (more Compete gridding Determine initial conditions for near-term dynamic forecasting models (NWP) Resource database weather-algorithm-provided utility functions Control: what to sense, when

9. How to Allocate Processing/Sensing Tasks Avoid processing overloads Avoid processing overloads Avoid communication overloads Avoid communication overloads Have information/processing co-located Have information/processing co-located Avoid failure of network based on single location failure Avoid failure of network based on single location failure Allocate sensing so that as many targets can be tracked with reasonable fidelity Allocate sensing so that as many targets can be tracked with reasonable fidelity Allocate processing/sensing so that real-time constraints can be met Allocate processing/sensing so that real-time constraints can be met

10. Additional Questions What tasks can be assigned statically which have to be dynamically allocated What tasks can be assigned statically which have to be dynamically allocated When do static and dynamically made decisions need to be revisited When do static and dynamically made decisions need to be revisited What is the appropriate context for making these decision What is the appropriate context for making these decision What decisions can be made locally What decisions can be made locally What decisions need to made with in a non-local context What decisions need to made with in a non-local context Is this context fixed or dynamically evolved Is this context fixed or dynamically evolved

11. Sensor Processing Issues Integrating Target Acquisition with Target Tracking Integrating Target Acquisition with Target Tracking Re-acquiring lost targets Re-acquiring lost targets Data-Correlation Issues Data-Correlation Issues Recognizing which data belongs to which target Recognizing which data belongs to which target Handling Uncertainty in Sensor Information Handling Uncertainty in Sensor Information How to make resource allocation issues in face of faulty sensor data How to make resource allocation issues in face of faulty sensor data

12. Tasks, Processes and Agents Issue of Autonomy -- Locus of Control Issue of Autonomy -- Locus of Control How much leeaway is allowed in what goals to pursue, how to do them, who to interact with, what resources to use, … How much leeaway is allowed in what goals to pursue, how to do them, who to interact with, what resources to use, … Where are these decisions being made Where are these decisions being made How decentralized are these decisions How decentralized are these decisions How dynamic/context-dependent these decisions are How dynamic/context-dependent these decisions are

13. Soft vs. Hard Real-Time There are not catastrophic effects if events are occasionally not interpreted correctly There are not catastrophic effects if events are occasionally not interpreted correctly If lose sight of target for a few time steps and then reacquire generally okay If lose sight of target for a few time steps and then reacquire generally okay Computation/Sensing after the deadline may still have some value Computation/Sensing after the deadline may still have some value Reduction in certainty of target location Reduction in certainty of target location

14. How to Evaluate a Sensor Network Communication Locality Communication Locality Information and Processing Bottlenecks Information and Processing Bottlenecks Organizational Control Overhead Organizational Control Overhead Overall Effectiveness Overall Effectiveness ……. ……. What’s Best -- Multi-attributed Evaluation?

15. One Approach from an MAS perspective Decompose environment to form a partitioned organization. Decompose environment to form a partitioned organization. Each partition (sector) will contain a set of sensor nodes, each with its own controlling agent. Each partition (sector) will contain a set of sensor nodes, each with its own controlling agent. Individual sectors are relatively autonomous. Individual sectors are relatively autonomous. Specialize members of the agent population to dynamically take on multiple, different goals/roles. Specialize members of the agent population to dynamically take on multiple, different goals/roles. Individual agents become “managers” of different aspects of the problem. Individual agents become “managers” of different aspects of the problem. Managers form high-level plans to address their goals, and negotiate with other nodes to achieve them. Managers form high-level plans to address their goals, and negotiate with other nodes to achieve them.

16. Sectored-Based Agent Organization Agents Multiplex among Different roles Sector Manager Tracking Manager Tracking Agent Scanning Agent

17. Organizationally-Structured Communication among Agents DrA DrQ DrR TB RR TD PT C RB PC DA TB U ES Sector Manager Tracking Manager Scanning Agent Tracking Agent

18. Managing Conflicted Resources: Sensors, Processors, Communication Sensors Sensors Conflicting Scanning Tasks from different Sector Managers Conflicting Scanning Tasks from different Sector Managers Locally resolved by agent connected to sensor -- SRTA agent Locally resolved by agent connected to sensor -- SRTA agent Tracking Tasks wanting same sensor resources Tracking Tasks wanting same sensor resources Negotiation among track managers -- SPAM protocol Negotiation among track managers -- SPAM protocol Communication Communication Communication Degradation due to lack of Locality Communication Degradation due to lack of Locality Track manager migration among sectors Track manager migration among sectors Communication Channel Overload Communication Channel Overload Sector manager assignment of track manager roles Sector manager assignment of track manager roles Processors Processors Data Fusion Overload/Knowledge locality Data Fusion Overload/Knowledge locality Sector manager assignment of data fusion/track manager roles Sector manager assignment of data fusion/track manager roles Multiplexing Roles -- SRTA agent Multiplexing Roles -- SRTA agent

19. Centralizing Information in Sector Manager Handling Data Correlation with Multiple Tracks Targets are represented by uncertainty bounds Targets are represented by uncertainty bounds Bounds are affected by speed of target and age of supporting measurements Bounds are affected by speed of target and age of supporting measurements Bounds are shared with sector manager, who in turn shares them with other track managers Bounds are shared with sector manager, who in turn shares them with other track managers Sector manager Sector manager Uses target uncertainty bounds to determine if new target detections (from scanning) are known targets Uses target uncertainty bounds to determine if new target detections (from scanning) are known targets Data from known target detections are used to focus attention of relevant track manager Data from known target detections are used to focus attention of relevant track manager Track managers Track managers Uses amplitude lobe intersections to estimate position in times of need Uses amplitude lobe intersections to estimate position in times of need Prevents data fusion if estimated resolved position is within another target’s bounds Prevents data fusion if estimated resolved position is within another target’s bounds Throws out ambiguous measurements which intersect another target’s bounds Throws out ambiguous measurements which intersect another target’s bounds

20. Fault Tolerance Node information is propagated through the use of directory services (x, y, orientation, etc.). Node information is propagated through the use of directory services (x, y, orientation, etc.). Sensors provide sector managers with their information. Sensors provide sector managers with their information. Track managers query sector managers for sensor details. Track managers query sector managers for sensor details. This information is cached for future use at each step This information is cached for future use at each step The directory held in sector manager maintains historical query information The directory held in sector manager maintains historical query information New data are analyzed for relevance to those queries New data are analyzed for relevance to those queries Relevant information is automatically propagated to the query source Relevant information is automatically propagated to the query source This process quickly updates agents’ beliefs, allowing them to adapt to change This process quickly updates agents’ beliefs, allowing them to adapt to change

21. Major Issues in This Approach What is an appropriate organization for agents What is an appropriate organization for agents Scalability and Robustness Scalability and Robustness Self-Organization and Adaptation Self-Organization and Adaptation What is the protocol for distributed resource allocation What is the protocol for distributed resource allocation Soft Real-Time, Graceful Degradation, Efficient Soft Real-Time, Graceful Degradation, Efficient What is the structure of an agent architecture that supports What is the structure of an agent architecture that supports Agents functioning in an organizational context Agents functioning in an organizational context Agents implementing complex distributed resource protocols Agents implementing complex distributed resource protocols Agents operating under soft real-time constraints Agents operating under soft real-time constraints

22. Some Final Thoughts Can not isolate one set of issues from another Can not isolate one set of issues from another Strict layering of issues does not seem to work Strict layering of issues does not seem to work There is no one best approach There is no one best approach Very sensitive to characteristics/capabilities of sensors, quality of sensor data, the character of required sensor fusion, amount and type of processing required, system objectives, communication and processing capabilities, environment … Very sensitive to characteristics/capabilities of sensors, quality of sensor data, the character of required sensor fusion, amount and type of processing required, system objectives, communication and processing capabilities, environment …