Wireless Embedded Systems ( x) Ad hoc and Sensor Networks

Transcription

1 Wireless Embedded Systems ( x) Ad hoc and Sensor Networks Chaiporn Jaikaeo Department of Computer Engineering Kasetsart University Materials taken from lecture slides by Karl and Willig

2 Typical Wireless Networks Base stations connected to wired backbone Mobile nodes communicate wirelessly to base stations

3 Ad hoc Networks Networks without pre-configured infrastructure require no hubs, access points, base stations are instantly deployable can be wired or wireless wired wireless multi-hop wireless Initially targeted for military and emergency applications

4 Ad hoc Mode IEEE already provides support for ad hoc mode Computers can be connected without an access point Only work with single hop

5 Possible Applications for Ad hoc Networks Factory Floor Automation Disaster recovery Car-to-car communication

6 Characteristics of Ad hoc Networks Heterogeneity sensors, PDAs, laptops Limited resources CPU, bandwidth, power Dynamic topology due to mobility and/or failure Mobile Ad hoc Networks (MANETs) C B A

7 Sensor Networks Participants in the previous examples were devices close to a human user, interacting with humans Alternative concept: Instead of focusing interaction on humans, focus on interacting with environment Network is embedded in environment Nodes in the network are equipped with sensing and actuation to measure/influence environment Nodes process information and communicate

8 Traditional Sensors sensor field Network Data loggers Local monitoring Remote monitoring

9 Wireless Sensors Sensors communicate with data logger via radio links sensor field Network radio link Remote monitoring

10 Wireless Sensor Networks Wireless sensors + wireless network Sensor nodes (motes) deployed and forming an ad hoc network Requires no hubs, access points Instantly deployable Sensor node/mote Sensor network Gateway Targeted applications Emergency responses Remote data acquisition Remote monitoring Internet

11 WSN Platforms Most are based on IEEE (Wireless Low-Rate Personal Area Network) and many others

12 WSN Application Examples Agriculture Humidity/temperature monitoring Civil engineering Structural response Disaster management Environmental sciences Habitat monitoring Conservation biology

13 WSN in Telemetry Applications Browser sensor sensor wireless sensor node Sensor field Information Server GPRS Network or Internet Gateway

14 Landslide Monitor Real deployment scenario

15 Roles of Participants in WSN Sources of data: Measure data, report them somewhere Typically equip with different kinds of actual sensors Sinks of data: Interested in receiving data from WSN May be part of the WSN or external entity, PDA, gateway, Actuators (actors): Control some device based on data, usually also a sink WSN = WASN

16 Classifying Application Types Interaction patterns between sources and sinks classify application types Event detection Periodic measurement Function approximation Edge detection Tracking

17 Deployment Options Dropped from aircraft Random deployment Well planned, fixed Regular deployment Mobile sensor nodes Can move to compensate for deployment shortcomings Can be passively moved around by some external force (wind, water) Can actively seek out interesting areas

18 Maintenance Options Feasible and/or practical to maintain sensor nodes? Replace batteries Unattended operation Impossible but not relevant Energy supply Limited from point of deployment Some form of recharging / energy scavenging

19 Characteristic Requirements Type of service of WSN Not simply moving bits like another network Rather: provide answers (not just numbers) Geographic scoping are natural requirements Quality of service Fault tolerance Lifetime: node/network Scalability Wide range of densities Programmability Maintainability

20 Required Mechanisms Multi-hop wireless communication Energy-efficient operation Both for communication and computation, sensing, actuating Auto-configuration Manual configuration just not an option Collaboration & in-network processing Nodes in the network collaborate towards a joint goal Pre-processing data in network (as opposed to at the edge) can greatly improve efficiency

21 Required Mechanisms Data centric networking Focusing network design on data, not on node identifies (id-centric networking) To improve efficiency Locality Do things locally (on node or among nearby neighbors) as much as possible Exploit tradeoffs E.g., between invested energy and accuracy

22 MANET vs. WSN - Similarities MANET Mobile Ad hoc Network Self-organization Energy efficiency (Often) Wireless multi-hop

23 MANET vs. WSN - Differences Equipment: MANETs more powerful Application-specific: WSNs depend much stronger on application specifics Environment interaction: core of WSN, absent in MANET Scale: WSN might be much larger (although contestable) Energy: WSN tighter requirements, maintenance issues

24 MANET vs. WSN - Differences Dependability/QoS: in WSN, individual node may be dispensable (network matters), QoS different because of different applications Addressing: Data centric vs. id-centric networking

25 Enabling Technologies for WSN Cost reduction For wireless communication, simple microcontroller, system on chip, sensing, batteries Miniaturization Some applications demand small size Smart dust as the most extreme vision Energy scavenging Recharge batteries from ambient energy (light, vibration, )

26 Conclusion MANETs and WSNs are challenging and promising system concepts Many similarities, many differences Both require new types of architectures & protocols compared to traditional wired/wireless networks In particular, application-specificness is a new issue

27 Demonstration

28 Sensor Modules IWING-MRF modules from IWING LAB 250 kbps 2.4GHz IEEE MHz Atmel ATMega328P microcontroller Additional light and temperature sensors

29 Scenario Monitor station Sensor nodes measuring light intensity