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Coverage Density as a Dominant Property of Large-Scale Sensor Networks

Coverage Density as a Dominant Property of Large-Scale Sensor Networks. Osher Yadgar & Sarit Kraus. Growing needs of Large-scale Sensor Networks. Measure the hardness of a given large-scale sensor network problem,

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Coverage Density as a Dominant Property of Large-Scale Sensor Networks

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  1. Coverage Density as a Dominant Property ofLarge-Scale Sensor Networks Osher Yadgar & Sarit Kraus

  2. Growing needs of Large-scale Sensor Networks • Measure the hardness of a given large-scale sensor network problem, • Compare a given system to other large-scale sensor networks in order to extract a suitable solution, • Predict the performance of the solution, and • Derive the value of each system property from the desired performance of the solution, the problem constraints, and the user's preferences.

  3. Large-scale Agent Systems ? • Thousands of agents ? (Ogston 03, Turner & Jennings 00, …) • Hundreds of agents ? (Ortiz 04, Scerri 04, …) • Dozens of agents ? (Bult 04, …) • Sensor coverage ? (Gage 92, Batalin 02, …) Coverage Density: What is the context ? What is the problem space ? Tradeoffs: time, money, accuracy, survivorability, etc.

  4. Coverage Density intuition • Coverage Density defines the time needed to cover the problem space. • There may be an overlap of agent coverage such that, for example, a value of 100% Coverage Density does not reflect coverage of all the controlled area. • Given a limited budget, the system designer should consider whether to use many cheap sensors or a small number of expensive sensors.

  5. Definition of the Coverage Density • Let A be a set of n agents such that whereas • Let be the area covered by the sensor of agent at a given time t. The agent may detect objects in this area at time t. • Let agent coverage be the average area covered by the sensor of agent such that . • Let total coverage be the average area covered by the sensors of all the agents such that . • Let Z be the size of the controlled area. • Coverage Density is the total coverage divided by the size of the controlled area such that .

  6. Using the Coverage Density • Environment: a large number of real-time tasks/objects and a large number of mobile agents in a given geographical area. • Main issues: • Resource management in a large scale environment. • How the agents should be distributed over the area? • How agents should process local information, derived from possibly noisy sensors, to provide a partial solution? • How partial solutions should be integrated into global solution?

  7. ANTS (Autonomous Negotiating Teams) related challenge • Environment: Targets and Doppler sensors. • Goal: Form an information map of targets in a controlled area as a function of time. • Large scale environment • Mobility

  8. Challenges • Large scale environment; • Mobile sensor Dopplers; • Real time response; • No clock synchronization; • No close cooperation between the sensors; • Limit the information exchange; • Fault tolerant;

  9. Doppler sensors’ properties • A radar is based on the Doppler effect with a wide beam of 120 degrees. • Provides information only about an arc that the detected target may be located on and the velocity towards the sensor (radial velocity) • A single Doppler measurement cannot be used to establish the exact velocity • Intersection method

  10. Organizational Structure • Hierarchic structure of groups based on geographical areas; the base level consists of the sensor Dopplers. • Each level controls the level below it. It • processes the information obtained from the level below it • forms an estimation of the information map of its zone • reports to it group leader.

  11. Hierarchy Example • Entities • Sampler agent • Group Leader agent • Data Structures • Capsule • InfoMap • GoalGenerate a map of targets as a function of time.

  12. Hierarchy of Group Leaders Level 4: 1 Zone Group Leader Level 3: 4 Zone Group Leaders Level 2: 16 Zone Group Leaders Level 1: 64 Sampler Group Leaders

  13. Simulation environment • 150 computers X 4 months = 50 years of CPU • Z= 400,000,000 square meters. • There are 5,000 Sampling and 85 Group Leader agents. • Each Doppler sensor has initial random location and velocity that is up to 50 kilometers per hour. • Range of interaction: 50 meters. • Sensing time: 10 seconds. • Moving time: 5 seconds.

  14. Simulation environment • At any given time, there are 1,000 targets in the area. Each target had an initial random location on the border and an initial random velocity, with a speed limit of 50 kilometers per hour (13.9 meters per second). • Targets leave the area when reaching the boundaries of the zone. Each target that leaves the area causes a new target to appear at a new location on the border. • A target stays a random time period in the area. • For 7 simulated days total of 13,635 targets.

  15. Conclusions • Coverage Density defines the time needed to cover an area equal to the size of the controlled zone. • We have shown that there is a strong correlation between the Coverage Density of a system and its behavior. • We introduced a way to achieve the same system results with different preferences. • As a result, a system designer may find it easier to achieve a certain level of system performance under given specific constraints, such as budget limits.

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