Presented by:
Abhimanyu kumar

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Ad hoc and Sensor NetworksChapter
1: Motivation & Applications
Give an understanding what ad hoc & sensor networks are good for, what their intended application areas are
Commonalities and differences
Differences to related network types
Limitations of these concepts
Infrastructure-based wireless networks
Typical wireless network: Based on infrastructure
E.g., GSM, UMTS, …
Base stations connected to a wired backbone network
Mobile entities communicate wirelessly to these base stations
Traffic between different mobile entities is relayed by base stations and wired backbone
Mobility is supported by switching from one base station to another
Backbone infrastructure required for administrative tasks
Infrastructure-based wireless networks – Limits?
What if …
No infrastructure is available? – E.g., in disaster areas
It is too expensive/inconvenient to set up? – E.g., in remote, large construction sites
There is no time to set it up? – E.g., in military operations
Possible applications for infrastructure-free networks
Factory floor automatio
Solution: (Wireless) ad hoc networks
Try to construct a network without infrastructure, using networking abilities of the participants
This is an ad hoc network – a network constructed “for a special purpose”
Simplest example: Laptops in a conference room – a single-hop ad hoc network
Problems/challenges for ad hoc networks
Without a central infrastructure, things become much more difficult
Problems are due to
Lack of central entity for organization available
Limited range of wireless communication
Mobility of participants
Battery-operated entities
No central entity ! self-organization
Without a central entity (like a base station), participants must organize themselves into a network (self-organization)
Pertains to (among others):
Medium access control – no base station can assign transmission resources, must be decided in a distributed fashion
Finding a route from one participant to another
Limited range ! multi-hopping
For many scenarios, communication with peers outside immediate communication range is required
Direct communication limited because of distance, obstacles, …
Solution: multi-hop network
Mobility ! Suitable, adaptive protocols
In many (not all!) ad hoc network applications, participants move around
In cellular network: simply hand over to another base station
Battery-operated devices ! energy-efficient operation
Often (not always!), participants in an ad hoc network draw energy from batteries
Desirable: long run time for
Individual devices
Network as a whole
! Energy-efficient networking protocols
E.g., use multi-hop routes with low energy consumption (energy/bit)
E.g., take available battery capacity of devices into account
How to resolve conflicts between different optimizations?
Outline
Infrastructure for wireless?
(Mobile) ad hoc networks
Wireless sensor networks
Applications
Requirements & mechanisms
Comparison
Wireless 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 it wirelessly
! Wireless sensor networks (WSN)
Or: Wireless sensor & actuator networks (WSAN)
WSN application examples
Disaster relief operations
Drop sensor nodes from an aircraft over a wildfire
Each node measures temperature
Derive a “temperature map”
Biodiversity mapping
Use sensor nodes to observe wildlife
Intelligent buildings (or bridges)
Reduce energy wastage by proper humidity, ventilation, air conditioning (HVAC) control
Needs measurements about room occupancy, temperature, air flow, …
Monitor mechanical stress after earthquakes
WSN application scenarios
Facility management
Intrusion detection into industrial sites
Control of leakages in chemical plants, …
Machine surveillance and preventive maintenance
Embed sensing/control functions into places no cable has gone before
E.g., tire pressure monitoring
Precision agriculture
Bring out fertilizer/pesticides/irrigation only where needed
Medicine and health care
Post-operative or intensive care
Long-term surveillance of chronically ill patients or the elderly
WSN application scenarios
Logistics
Equip goods (parcels, containers) with a sensor node
Track their whereabouts – total asset management
Note: passive readout might suffice – compare RF IDs
Telematics
Provide better traffic control by obtaining finer-grained information about traffic conditions
Intelligent roadside
Cars as the sensor nodes
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: Control some device based on data, usually also a sink
Structuring WSN application types
Interaction patterns between sources and sinks classify application types
Event detection: Nodes locally detect events (maybe jointly with nearby neighbors), report these events to interested sinks
Event classification additional option
Periodic measurement
Function approximation: Use sensor network to approximate a function of space and/or time (e.g., temperature map)
Edge detection: Find edges (or other structures) in such a function (e.g., where is the zero degree border line?)
Tracking: Report (or at least, know) position of an observed intruder (“pink elephant”)
Deployment options for WSN
How are sensor nodes deployed in their environment?
Dropped from aircraft ! Random deployment
Usually uniform random distribution for nodes over finite area is assumed
Is that a likely proposition?
Well planned, fixed ! Regular deployment
E.g., in preventive maintenance or similar
Not necessarily geometric structure, but that is often a convenient assumption
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
Maintenance options
Feasible and/or practical to maintain sensor nodes?
E.g., to replace batteries?
Or: unattended operation?
Impossible but not relevant? Mission lifetime might be very small
Energy supply?
Limited from point of deployment?
Some form of recharging, energy scavenging from environment?
E.g., solar cells
Outline
Infrastructure for wireless?
(Mobile) ad hoc networks
Wireless sensor networks
Applications
Requirements & mechanisms
Comparison
Characteristic requirements for WSNs
Type of service of WSN
Not simply moving bits like another network
Rather: provide answers (not just numbers)
Issues like geographic scoping are natural requirements, absent from other networks
Quality of service
Traditional QoS metrics do not apply
Still, service of WSN must be “good”: Right answers at the right time
Fault tolerance
Be robust against node failure (running out of energy, physical destruction, …)
Lifetime
The network should fulfill its task as long as possible – definition depends on application
Lifetime of individual nodes relatively unimportant
But often treated equivalently
Characteristic requirements for WSNs
Scalability
Support large number of nodes
Wide range of densities
Vast or small number of nodes per unit area, very application-dependent
Programmability
Re-programming of nodes in the field might be necessary, improve flexibility
Maintainability
WSN has to adapt to changes, self-monitoring, adapt operation
Incorporate possible additional resources, e.g., newly deployed nodes
Required mechanisms to meet requirements
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
Required mechanisms to meet requirements
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 far as possible
Exploit tradeoffs
E.g., between invested energy and accuracy
Outline
Infrastructure for wireless?
(Mobile) ad hoc networks
Wireless sensor networks
Comparison
MANET vs. WSN
Many commonalities: Self-organization, energy efficiency, (often) wireless multi-hop
Many differences
Applications, equipment: MANETs more powerful (read: expensive) equipment assumed, often “human in the loop”-type applications, higher data rates, more resources
Application-specific: WSNs depend much stronger on application specifics; MANETs comparably uniform
Environment interaction: core of WSN, absent in MANET
Scale: WSN might be much larger (although contestable)
Energy: WSN tighter requirements, maintenance issues
Dependability/QoS: in WSN, individual node may be dispensable (network matters), QoS different because of different applications
Data centric vs. id-centric networking
Mobility: different mobility patterns like (in WSN, sinks might be mobile, usual nodes static)
Wireless fieldbuses and WSNs
Fieldbus:
Network type invented for real-time communication, e.g., for factory-floor automation
Inherent notion of sensing/measuring and controlling
Wireless fieldbus: Real-time communication over wireless
! Big similarities
Differences
Scale – WSN often intended for larger scale
Real-time – WSN usually not intended to provide (hard) real-time guarantees as attempted by fieldbuses
Enabling technologies for WSN
Cost reduction
For wireless communication, simple microcontroller, sensing, batteries
Miniaturization
Some applications demand small size
“Smart dust” as the most extreme vision
Energy scavenging
Recharge batteries from ambient energy (light, vibration, …)
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