1. Wireless sensor and actor networks: research challenges 2004 4. 6 Ian. F. Akyildiz, Ismail H. Kasimoglu bwlee@mmlab.snu.ac.kr

2. MMLAB2 Contents Introduction WSAN –WSN vs. WSAN –WSAN architecture –Sensor, actor component –Sensor-actor coordination –Actor-actor coordination Research Challenges –Transport –Routing –MAC –Cross layering Conclusion

3. MMLAB3 Introduction WSAN (wireless sensor and actor networks ) –Observing physical world (sensor)  processing the data  making decisions based on the observations  performing appropriate actions (actor) –Application Battle field surveillance Microclimate control in building Nuclear, biological and chemical attack detection Home automation Environmental monitoring

4. MMLAB4 WSN vs WSAN In WSN (wireless sensor network) –Communication between sensor and sink In WSAN –Sensor-actor and actor-actor communication –Unique characteristic Node heterogeneity Real-time requirement Deployment Coordination Mobility Due to the above difference new research about WSAN is required

5. MMLAB5 WSAN physical architecture (a) automated vs. (b) semi-automated architecture

6. MMLAB6 Automated Architecture Why do we focus on Automated architecture –Low latency –Low energy consumption –Long network lifetime Event information always passes through the sensor nodes which are within one hop from the sink

7. MMLAB7 The component of sensors and actors (a) sensor (b) actor

8. MMLAB8 Effective sensor-actor coordination Main problems which should be investigated for sensor- actor coordination are 1.Which sensors communicate with which actors Single- actor(SA) vs. multi- actor(MA) 2.How this communication occurs 3.What are the requirement of this communication To consume low energy To support real-time traffic

9. MMLAB9 Application Example Robots

10. MMLAB10 Effective sensor-actor coordination Single actor Main challenge –How to determine that single actor –The selection requires the coordination between sensor nodes –Criteria Distance Energy Action range of actor node –Actor perform the action without coordinating other actors

11. MMLAB11 Effective sensor-actor coordination Multi-actor No need for coordination between the sensors Cluster may be constructed Criteria –Low latency –Minimum energy path –Action regions of actors can cover the entire event area

12. MMLAB12 Effective sensor-actor coordination Single-actor(SA) –Strong point Action can be done immediately after receiving event information No needs for actor-actor coordination –Weak point Need for sophisticated coordination among all sensors in the event area Multi-actor(MA) –Strong point Sensor may coordinate with sensors within neighbor Actors can figure out the event center –Weak point Actor-actor negotiation is required So which one is more efficient?

13. MMLAB13 Effective actor-actor coordination Few number of actor nodes, power capacities of actors are higher than sensor nodes  ad-hoc network Actor-actor communication can occur if… –The actor receiving sensor data can not act on the event area –One actor is not sufficient –Multiple actors receive the same event information Which actors should execute which actions?  How should multi-actor task allocation be done –Single-actor task (SAT) vs. multi-actor task (MAT) –Centralized decision (CD) vs. distributed decision (DD)

14. MMLAB14 WSAN protocol architecture Management plane –Responsible for monitoring and controlling a sensor/actor node –Provide information needed by coordination plane to make decision –Power management, Mobility management, Fault management Coordination plane –Decides how the node should act on the data from communication plane –Provides node to be modeled as a social entity Communication plane –Enables the information exchange among the nodes of the network –Produce a change in the state of the network

15. MMLAB15 Research challenges in each layer Transport layer –Need for unified transport protocol –Sensor-actor communication case Every individual report doesn’t have to reach the actor with perfect accuracy  event reliability Must support real time issue Must construct event reliability metrics which involve real-time property –Actor-actor communication case Every message between actors should be reliable transmission  conventional reliability Must support real time issue –There is no solution to support real time issue and reliability at the same time

16. MMLAB16 Research challenges in each layer Routing layer –Sensor-actor communication To provide robustness to node and link failure, multi-path routing would be recommended It result in congestion around actor node  data aggregation Optimal aggregation point along the path depends on application routing protocol must support real-time communication  prioritization –Actor-actor communication Well known routing protocol can be used (e.g. AODV, DSR) Must provide timely actions and adaptability to different application

17. MMLAB17 Research challenges in each layer MAC layer –Actors may be mobile  WSAN MAC protocol should maintain network connectivity between sensor and mobile actor –Sensor-actor communication Sensor-actor coordination and actor-actor coordination Timeliness should be considered –Contention based protocol? –TDMA? –Collision free real-time protocol? –Actor-actor communication Current MAC protocol should be improved to support real-time traffic –Should consider adaptation to mobility, coordination between sensors and actors

18. MMLAB18 Research challenges in each layer Cross- layering –The suboptimality and inflexibility of each layer result in poor performance for WSAN –In congestion situation MAC layer react locally by exponential back-off Transport layer lower the transmission rate –Optimization of packet size Routing layer point of view : the longer distance, the shorter packet size has advantage MAC layer point of view : the shorter packet size, the more collision –Optimization of transmission power Relative to both channel condition (physical) and delay constraints (application) – weak link connectivity (actor-actor case) Physical layer increase transmission power, what if the actor moves fast?

19. MMLAB19 Conclusion WSANs have different property from WSN in that –Node heterogeneity, real-time requirement, mobility etc. –Actor-actor communication is required as well as actor-sensor communication WSAN architecture has 3 plane –Communication, management, coordination There are many research challenges in each layer Each layer have common requirements and highly dependent so cross layer approach can be much more effective