CHAPTER 4: Cooperation in Wireless Ad-Hoc and Sensor Networks

1. CHAPTER 4:Cooperation in Wireless Ad-Hoc and Sensor Networks J. Barbancho, D. Cascado, J. L. Sevillano, C. León, A. Linares and F. J. Molina In M. S. Obaidat and S. Misra (Eds.) Cooperative Networking (Wiley)

2. 1.Introduction • Characteristics of a Wireless Ad-Hoc Sensor Network (WAdSN) • Nodes with tiny size, limited radio range, low resources and autonomy, etc. • Different roles: data source, data sink and gateway. • Cooperation in WAdSN: two paradigms • Data transport paradigm: Cooperation limited to an exchange of information. • Cooperative paradigm: cooperation understood as a distributed way to achieve an objective

3. 2. Cooperation in WAdSN: Synchronization, Localization and Calibration Important issues in WAdSN: • Time synchronization reduces energy waste • Avoids collisions through reservation and scheduling • Avoids idle listening switching off the radio during the inactive periods • Facilitates cooperation and data fusion (time stamping) • Localization: • Allows location stamping of sensed data • Facilitates data aggregation (e.g. sensors in the same area) • Calibration: • Needed to combine data from several sensors

4. 2. Cooperation in WAdSN: Synchronization, Localization and Calibration SLC (Synchronization/Localization/Calibration): concepts closely related to each other: • Calibration: mapping the output of a sensor to a well-defined scale. • Time synchronization: special case considering the hardware clock as the sensor. • Localization: • RRS (Receiver Signal Strength) requires calibration of the receivers • TDoA (Time Difference of Arrivals) requires time synchronization • SLC should be performed periodically, specially in WAdSN

5. 2. Cooperation in WAdSN: Synchronization, Localization and Calibration SLC share similar techniques/classes: • External vs. Internal • External: provides absolute SLC information • Internal: only relative information • Continuous vs. On demand • Continuous: maintain SLC at all times • On demand: only during active periods. Can be event or time triggered. • Master-slave vs. Peer to peer • Master-slave: masters are reference nodes while slaves estimate their SLC with respect to the masters • Peer to peer: reference nodes are not required

6. 2. Cooperation in WAdSN: Routing • Routing requires cooperation among nodes, specially in WAdSN (ad-hoc deployment, lack of global addressing, etc.) • Some methods are based on the introduction of Artificial Intelligence techniques • A directed graph is used to represent the communication links among all nodes (Network Backbone Formation) • QoS parameters are used to dynamically select the routing path

7. 2. Cooperation in WAdSN: Routing • Example: Sensor Intelligence Routing (SIR) Network Backbone Formation • wij: weight. V := {r, vi}i and T := V −{r}. • d(vi): distance from the base station r to a node vi • p(vj): subset of nodes which are predecessors or successors of node vj. • p: path from the root node to vj

8. 2. Cooperation in WAdSN: Data Aggregation and Fusion • Data Fusion reduces the number of packets transmitted, and therefore power consumption • Additionally, it allows selecting routes with better energy and bandwidth efficiency: • Address-centric routing (a) • Data-centric routing (b)

9. 2. Cooperation in WAdSN: Data Aggregation and Fusion Data Fusion can be described by means of the Joint Directors of Laboratories (JDL) model: • Level 0: Source preprocessing. • Level 1: Object refinement. • Level 2: Situation refinement. • Level 3: Impact assessment. • Level 4: Process refinement. • Level 5: Cognitive refinement.

10. 2. Cooperation in WAdSN: Data Aggregation and Fusion Example application: WAdSN to estimate water level in flood zones of the National Park of Doñana. A Self-Organized Map (SOM) is executed in every node, trained with historical data. • Level 0: The SOM receives data from environmental sensors • Level 1: State of the water level is identified • Level 2: Data aggregators • Level 3: • Level 4: • Level 5: Biologists interpret the results at the Doñana Biological Station Only changes in the state (water level) are sent

11. 3. Research lines for WAdSN:Introduction • A WAdSN is difficult to manage with devices only implementing MAC & PHY. • Synchronization, calibration, location… • Upper layers are a good place to implement these strategies. • Middleware • Multi-agent systems • Artificial neural networks

12. 3. Research lines for WAdSN:Middleware • Heterogeneity is a problem for WAdSN nodes, leads to incompatibility: • Different hardware, OpSys, Network… • Solution: an abstraction layer between OpSys and hardware: middleware. • Common interface for client/server communication • Service discovering • Service description • Common language to write applications

13. 3. Research lines for WAdSN:Middleware Architectures: • Distributed tuples: L2IMBO, LINDA • Remote procedure call: Java Remote Method Invocation, Modula-3, XML-RPC, .NET Remoting • Message-oriented: Advanced Message Queuing Protocol, Java Message Service • Object request broker: DCOM, CORBA, COM

14. 3. Research lines for WAdSN:Middleware • Middleware is a solution designed for large distributed system. Why to use it? • In WadSN, resources are very limited. • Design principles for WAdSN middleware must consider: • Distributed by nature. • Limited by low machine resources. • Focused on energy saving. • Dynamic availability and quality of data collected from the environment. • Constrained applications quality of services.

15. 3. Research lines for WAdSN:Middleware Design principles: • Data-centric • Distributed and collaborative algorithms • Support of data aggregation • Lightweight • Cluster based architecture • Virtual-machine abstraction and • Common language to write applications Examples: • Cougar, SINA. AutoSec, DSWare, Impala, Milan, Mires, COCA Drawbacks: • No solid functionality, no support to time and location in measurements,

16. 3. Research lines for WAdSN:Multi-Agent Systems • Agent: is an entity located in one environment, capable of performing flexible and autonomous actions to achieve its goals. • Agents reside in the WAdSN nodes: • Gathering information • Taking actions based on collected information • Interact with other agents • Move to other sensors if required

17. 3. Research lines for WAdSN:Multi-Agent Systems Agents are supported by a middleware architecture in order to take access to: • Local services of the platform • Agent discovery and maintenance • Agent=code + data + state + meta-information. • Common language to develop agents • Reactivity to changes • Asynchronous operation • Autonomy about their own actions • Communications with other agents • Collaboration and cooperation with other agents • Mobility to migrate between nodes Examples • IMPALA, Agilla, MASIF.

18. 3. Research lines for WAdSN:Artificial Neural Networks (ANN) ANN can be used … • When no algorithm exists to solve a specific task, but the solution can be expressed on the basis of a rich set of input examples. • For classification • For pattern recognition Features of ANN • Robustness against noise • Easy to parallelize and distribute • Lightweight

19. 3. Research lines for WAdSN:Artificial Neural Networks (ANN) • Artificial Neuron: is an entity whose output is defined as a function of a set of weighted inputs • This output can be codified as a number within a range or as a series of spikes distributed in time

20. 3. Research lines for WAdSN:Artificial Neural Networks (ANN) Neurons are arranged in layers • Feed-fordward ANN • Recurrent ANN Training before operation (simple and fast algorithm) • Supervised • Not supervised • Reinforcement

21. 3. Research lines for WAdSN:Artificial Neural Networks (ANN) • How can an ANN be implemented in a WAdSN? • One node, one neuron • Nodes serve as input layer of the network. Further layers can be implemented in another place • Suitable for pattern recognition, classification, or predictions • One node, one ANN • Each ANN trained to solve an specific problem of the WAdSN • Suitable for routing optimization, self-calibration, insertion of new nodes.

22. 4. Final Remarks • Cooperation in WAdSN is a collaborative action between network nodes • Implemented in upper layers of OSI model • Basic services for cooperation • Synchronization, localization and calibration • Middleware makes cooperation easier • Cooperation implemented regardless hardware of network technology • Multi-agent systems are a evolution of middleware • Designed to large systems. Difficult to implement in WAdSN yet.