© university of cancun, mexico1 chapter 14: energy efficient next generation communications 1 jason...
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© University of Cancun, Mexico 1
Chapter 14: Energy Efficient Next Generation
Communications
1Jason B. Ernst
1University of Guelph, Canada
HANDBOOK ON GREEN INFORMATION AND COMMUNICATION SYSTEMS
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Outline
Introduction
Applications and Networks
Architectures, Techniques and Protocols
Trends, Limitations, Challenges and Open Problems
Conclusions & Future Directions
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Introduction
Motivation for Green Communications Energy as a Resource
• Limited Spectrum availableLimited Spectrum available
• Unlicensed spectrum saturated (802.11abgn Wi-Fi, Unlicensed spectrum saturated (802.11abgn Wi-Fi,
Bluetooth, Zigbee, Microwave Ovens, Cordless Telephones …Bluetooth, Zigbee, Microwave Ovens, Cordless Telephones …
etc.)etc.)
• Interference between competing technologiesInterference between competing technologies
• Particularly troublesome in dense network deploymentsParticularly troublesome in dense network deployments
• ““Cognitive RadioCognitive Radio”” techniques to use licensed spectrum on techniques to use licensed spectrum on
demand when not in usedemand when not in use
• Limits of information transmission – Limits of information transmission – ““Shannon LimitShannon Limit””
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Introduction
Motivation for Green Communications Handheld & Battery Powered Devices
• Batteries are heavy & expensive componentBatteries are heavy & expensive component
• Reducing energy consumption allows smaller or cheaper Reducing energy consumption allows smaller or cheaper
power or increased lifetimepower or increased lifetime
• Many devices have multiple technologies (Wi-Fi, Bluetooth, Many devices have multiple technologies (Wi-Fi, Bluetooth,
Cellular), so choosing the best technology to reduce Cellular), so choosing the best technology to reduce
consumption in particular cases is importantconsumption in particular cases is important
• Potential to extend overall lifetime of the network (in WSN or Potential to extend overall lifetime of the network (in WSN or
MANETs)MANETs)
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Introduction
Motivation for Green Communications Potential Health Effects
• Recent studies showing evidence for and against the health Recent studies showing evidence for and against the health effects on humans of wireless exposureeffects on humans of wireless exposure
• Are models for exposure accurate?Are models for exposure accurate?• Are standards for exposure keeping people safe?Are standards for exposure keeping people safe?
Reduced Interference & Contention• Interference and contention implemented poorly can be Interference and contention implemented poorly can be
inefficientinefficient• Collisions require retransmissions, using more energyCollisions require retransmissions, using more energy• As the number of hops increase, without caching, the As the number of hops increase, without caching, the
retransmissions become cumulative and successful retransmissions become cumulative and successful communication becomes more unlikelycommunication becomes more unlikely
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Applications and Networks
Wireless Sensor (WSN) & Mobile Ad Hoc Networks (MANETs) Sensor nodes are often dropped randomly MANETs can also have random topologies and node
placement Both WSN and MANETs cannot rely on infrastructure Geographically may be dense or sparse in some
areas Nodes are often battery powered, have low
processing and memory capability WSN focuses on transporting data to collection points MANET traffic may travel to and from Internet or
between peers
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Applications and Networks
Heterogeneous Wireless Networks (HWNs)
“Convergence Networks”
Use multiple technologies, ex: Bluetooth, Wi-Fi, 3G,
4G, Satellite
Each individual technology is optimized without
considering inter-operability
Traffic may have the ability to select a more energy
efficient route by selecting which technology to
transmit over when several are available
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Applications and Networks
Delay Tolerant Networks
Useful when network partitioning is possible (WSNs
or MANETS
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Applications and Networks
Delay Tolerant Networks
Often employs caching at individual hops so
retransmission is not required across all hops, only at
those where the data was lost
Can also employ scheduled transmission if some
nodes appear on a predictable timeline (ex: orbits,
bus schedules etc.)
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Applications and Networks
Interplanetary & Intergalactic Networks Communication in space has several challenges Line of sight is often interrupted (planets and orbits) There are often not many links and routes to choose
from Energy is limited, often solar powered Weight is limited (rules out large batteries, and
generally limits how much communication equipment and processing may be done)
Some traffic must be reliable (firmware updates, orbit corrections)
Other traffic may not be reliable (streaming video)
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Applications and Networks
Alternative Energy Networks These networks are not powered by a typical
electrical grid Solar, wind, tidal, etc. Power may come in bursts, may or may not be stored
in batteries Communication may be intermittent when power is
unreliable
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Applications and Networks
Military, Emergency and Disaster Scenarios Communication networks for these applications may
be integrated with aerial drones, uavs, rovers, trained dogs, soldiers, medics, police offers, heavy equipment (tanks, planes etc) which require light and compact devices for mobilty
Again cannot rely on electrical grid
Must be secure and reliable
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Applications and Networks
Developing Countries and Rural Access Networks Internet access in these areas is extremely expensive Also necessary to provide education, emergency
services and communication Should provide a tradeoff between performance and
cost
In developing countries, a van physically drives between villages collecting emails which are sent opportunistically when the van returns to the city where infrastructure exists
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Architectures, Techniques & Protocols
Topology Control
Many very different techniques to control the layout
or arrangement of nodes in the network
Shut some nodes off completely periodically
Using a variety of cell sizes (smaller cells in dense
areas so that fewer nodes are handled by one access
point)
Adjust power levels dynamically to reduce neighbor
connections (making routing choices easier)
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Architectures, Techniques & Protocols
Power Control
Related to topology control, but not always done to
control the layout of the network
May also be used to reduce destructive interference
Can be performed in conjunction with transmission
schedules and compatibility matrices (used to
determine which nodes may transmit at once without
interfering – due to distance)
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Architectures, Techniques & Protocols
Repeater and Relay Nodes
Can be used to reduce the distance required for long
hops, reducing the transmission power
Especially useful in networks where battery life
should be conserved
Similarly, special indoor antennas can be used within
buildings so that mobile devices can use lower power
when inside
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Architectures, Techniques & Protocols
Caching, Clustering and Data Aggregation
Similar to repeater and relay nodes, cluster heads
can be used to perform similar functionality
Nodes elect cluster heads within a nearby area and
send all traffic through this node
The cluster head can then transmit several nodes’
traffic in burst
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Architectures, Techniques & Protocols
Caching, Clustering and Data Aggregation
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Architectures, Techniques & Protocols
Caching, Clustering and Data Aggregation
This reduces long hops to the destination, and avoids
contention – reducing retransmissions
Techniques can also be used to switch cluster heads
in the event the current cluster head is low on
battery to keep the network “alive” longer
Particularly useful in WSN and MANETs
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Architectures, Techniques & Protocols
Energy-Aware Handover Techniques Traditional handover focuses on horizontal handovers
(switching AP due to mobility) With modern devices, vertical handover must also be
considered(switching access technology due to mobility or changing network conditions)
Choice becomes more complex since this is a cost and overhead associated with handover
Using the correct information such as capacity, transmission energy, congestion, battery life can lead to improved efficiency
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Architectures, Techniques & Protocols
Access Point Selection
Typically based solely on signal strength when
choosing between multiple Aps
More recent solutions propose considering
congestion level, capacity etc.
It is also possible to avoid using the infrastructure
and form small ad hoc networks that relay eventually
back to an AP
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Architectures, Techniques & Protocols
Energy-Efficient Routing Algorithms
Particularly effective in WSNs
Consider a “data-centric” approach rather than
“destination-centric” approach
Query based routing, for example:
• “Give me periodic reports about animal location in region A
every t seconds”
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Architectures, Techniques & Protocols
Energy-Efficient Transport Protocols In some application it may be worthwhile to tradeoff
reliability for energy-efficiency
One way to encourage green communication is to prioritize traffic from other “green networks” who make energy efficiency a priority
Another way is to encourage protocols which attempt to reduce re-transmissions, ie avoid protocols like UDP which may cause many retransmission by flooding into the network without any feedback
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Architectures, Techniques & Protocols
Energy-Efficient Transport Protocols Removing the end-to-end requirement of traditional
protocols and use a store-and-forward approach
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Architectures, Techniques & Protocols
Energy-Efficient Medium Access Protocols When combined with certain routing approaches
such as Directed Diffusion (data-centric) it may be beneficial to abandon using automatic repeat requests (ARQ) in MAC protocols and assume that reliability is handled at higher layers
When links are periodically poor, using ARQ will reduce higher layer retransmissions (ie retransmission across every hop)
Trade-off between each decision, dynamically switch between strategies?
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Trends, Limitations, Challenges & Open Problems
Integration of specific solutions for targeted applications, networks and architectures into a complete green strategy / framework
Joint optimization across existing wireless technologies Existing networks are optimized without
interoperability in mind Need to optimize with respect to interaction for
converging network solutions
Standardization
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Conclusions & Future Directions
Apply known green techniques from specific networks and applications to more general networks
Combine approaches where possible, for ex) Data centric routing + link layer ARQ disabled
Extend horizontal handover techniques to vertical When multiple access technologies are available, make
choice based on:• Capacity, Congestion level, Energy requirements etc. so that Capacity, Congestion level, Energy requirements etc. so that
retransmission and contention are reducedretransmission and contention are reduced
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Thanks for your attention!