Architectures and Applications
for Wireless Sensor Networks
(01204525)
Network Architecture
Chaiporn Jaikaeo
chaiporn.j@ku.ac.th
Department of Computer Engineering
Kasetsart University
Materials taken from lecture slides by Karl and Willig
Outline
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Network scenarios
Optimization goals
Design principles
Service interface
Gateway concepts
2
Typical Views of WSN
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Self-organizing mobile ad hoc networks
(MANETs)
Peer-to-peer networks
Multi/mobile agent systems and swarm
intellegence
3
Sensor Network Scenarios
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Sources: Any entity that provides
data/measurements
Sinks: Nodes where information is required
Source
Source
Sink
Sink
Source
Sink
Internet
4
Single-Hop vs. Multi-hop
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Multi-hop networks
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Send packets to an intermediate node
Intermediate node forwards packet to its destination
Store-and-forward multi-hop network
Store & forward
multi-hopping NOT
the only possible
solution

E.g., collaborative
networking,
network coding
Sink
Source
Obstacle
5
Multi-hopping Always Efficient?
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Obvious idea: Multi-hopping is more energyefficient than direct communication

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Suppose we put a relay at distance d/2
Energy for distance d is reduced from cd to
2c(d/2)

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c - some constant
 - path loss coefficient ( 2)
Usually wrong, or over-simplified

Need to take constant offsets for powering
transmitter, receiver into account
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Multiple Sinks, Multiple sources
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Different sources of mobility
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Node mobility
Sink mobility
Event mobility
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Sink Mobility
Request
Propagation
of answers
Movement
direction
9
WSN Event Mobility
10
Outline
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Network scenarios
Optimization goals
Design principles
Service interface
Gateway concepts
11
Goal: Quality of Service
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QoS in WSN is more complicated
(compared to MANET)
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Event detection/reporting probability
Event classification error, detection delay
Probability of missing a periodic report
Approximation accuracy (e.g, when WSN constructs a
temperature map)
Tracking accuracy (e.g., difference between true and
conjectured position of the pink elephant)
Related goal: robustness

Network should withstand failure of some nodes
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Goal: Energy efficiency

Many definitions
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Energy per correctly received bit
Energy per reported (unique) event
Delay/energy tradeoffs
Network lifetime

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Time to first node failure
Network half-life (how long until 50% of the nodes
died?)
Time to partition
Time to loss of coverage
Time to failure of first event notification
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Sharpening the Drop
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Sacrifice long lifetimes in return for an
improvement in short lifetimes
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Goal: Scalability
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Network should be operational regardless of
number of nodes
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Typical node numbers difficult to guess
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At high efficiency
MANETs: 10s to 100s
WSNs: 10s to 1000s, maybe more
Requiring to scale to large node numbers has
serious consequences for network architecture

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Might not result in the most efficient solutions for
small networks!
Carefully consider actual application needs before
looking for scalable solutions
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Outline
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Network scenarios
Optimization goals
Design principles
Service interface
Gateway concepts
16
Distributed Organization
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WSN participants should cooperate in
organizing the network
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Potential shortcomings
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Centralized approach usually not feasible
Not clear whether distributed or centralized
organization achieves better energy efficiency
Option: “limited centralized” solution
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Elect nodes for local coordination/control
Perhaps rotate this function over time
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In-Network Processing
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WSNs are expected to provide information
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Gives additional options
E.g., manipulate or process the data in the
network
Main example: aggregation
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Apply aggregation functions to a collection tree
in a network
Typical functions: minimum, maximum,
average, sum, …
Not amenable functions: median
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Aggregation Example
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1
3
1
1
6
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Signal Processing
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Another form of in-network processing
E.g.,
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Exploit temporal and spatial correlation
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Edge detection
Tracking/angle detection of signal source
Observed signals might vary only slowly in time
Signals of neighboring nodes are often quite
similar
Compressive sensing
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Adaptive Fidelity
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Adapt data processing effort based on
required accuracy/fidelity
E.g., event detection
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When event occurs, increase rate of message
exchanges
E.g., temperature

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When temperature is in acceptable range, only
send temperature values at low resolution
When temperature becomes high, increase
resolution and thus message length
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Data Centric Networking
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Interactions in typical networks are
addressed to the identities of nodes
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In WSN, specific source of events might not
be important
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Known as node-centric or address-centric
networking paradigm
Several nodes can observe the same area
Focus on data/results instead
 Data-centric networking
 Principal design change
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Implementation Options
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Publish/subscribe (NDN – Named Data
Networking)
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Nodes can publish data, can subscribe to any
particular kind of data
Once data of a certain type has been
published, it is delivered to all subscribers
Databases
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SQL-based request
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Other Design Principles
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Exploit location information
Exploit activity patterns
Exploit heterogeneity
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By construction
By evolution
Cross-layer optimization of protocol stacks
for WSN
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Goes against grain of standard networking
Promises big performance gains
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Outline
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Network scenarios
Optimization goals
Design principles
Service interface
Gateway concepts
25
Interfaces to Protocol Stacks
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The world’s all-purpose network interface: sockets
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Good for transmitting data from one sender to one receiver
Not well matched to WSN needs (ok for ad hoc networks)
App as another component
Well-designed interface
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Outline
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Network scenarios
Optimization goals
Design principles
Service interface
Gateway concepts
27
Gateways in WSN/MANET
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Allow remote access to/from the WSN
Bridge the gap between different interaction
semantics
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E.g., data vs. address-centric networking
Need support for different radios/protocols
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WSN to Internet Communication
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E.g., deliver an alarm message to an Internet host
Issues
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Need to find a gateway (integrates routing & service discovery)
Choose “best” gateway if several are available
How to find Alice or Alice’s IP?
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Internet to WSN communication
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How to find the right WSN to answer a need?
How to translate from IP protocols to WSN
protocols, semantics?
Remote requester
Gateway
nodes
Internet
Gateway
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WSN tunneling
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Use the Internet to “tunnel” WSN packets
between two remote WSNs
Internet
Gateway
nodes
Gateway
31
6LoWPAN
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IPv6 over Low-power Wireless Personal
Area Networks
Nodes communicate using IPv6 packets
An IPv6 packet is carried in the payload of
IEEE 802.15.4 data frames
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Example 6LoWPAN Systems
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Summary
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Network architectures for WSNs look quite
different from typical networks in many aspects
Data-centric paradigm opens new possibilities for
protocol design
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