© University of Cancun, Mexico1 Chapter 14: Energy Efficient Next Generation Communications 1 Jason...

© 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


Outline

Introduction

Applications and Networks

Architectures, Techniques and Protocols

Trends, Limitations, Challenges and Open Problems

Conclusions & Future Directions


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””


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)


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



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



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



Delay Tolerant Networks

Useful when network partitioning is possible (WSNs

or MANETS



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.)



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)



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



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



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


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)



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)



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



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




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



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



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



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”



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



Energy-Efficient Transport Protocols Removing the end-to-end requirement of traditional

protocols and use a store-and-forward approach



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?


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


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


Thanks for your attention!

© University of Cancun, Mexico1 Chapter 14: Energy Efficient Next Generation Communications 1 Jason...

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