energy conservation in wireless communication systems with relays

27th December, 2011Science City, Kolkata

Aniruddha Chandra

Telecommunications, School of Engineering & Technology,Asian Institute of Technology, Bangkok, Thailand.

[email protected]

Energy Conservation in Wireless Energy Conservation in Wireless Communication Systems with RelaysCommunication Systems with Relays

2/41A. Chandra - Energy Conservation with Relays

OutlineOutline

Introduction

Energy Conservation

Basics of Relaying

Modelling

Case Study

Summary


OutlineOutline

Introduction - Paradigm shift in wireless system design

- Energy consumption by telecomm industry

Energy Conservation

Basics of Relaying

Modelling

Case Study

Summary


IntroductionIntroduction

Paradigm Shift in Wireless System Design

Meteoric growth in wireless usage:

- Demand for coverage extension.

- Demand for higher capacity.

- Demand for better QoS.

Traditional design:

- New infrastructure deployment, Complement old ones with Relay.

- Femtocell, SDMA, MIMO.

- Adaptive modulation, coding, equalization, diversity.

Increase in energy costs and greater awareness of impact on environment:

- New energy-efficiency oriented design perspective.

- Value power consumption as much as BW, delay, or throughput.


Energy Consumption by Telecomm Industry

Some statistics on environmental impact:

- A cellular network (medium sized) ~ Energy for 1,70,000 homes.

- About 3% of the energy consumption, 2% of CO2 emissions.

- The figures are going to double in next 5 years.

- Energy from electricity grid, runs on fossil-fuel.

- Backup diesel generators for unreliable electric supply.

Objects in Mirror are Close than

they Appear




Some statistics on cost incurred for power:

- Powering the BSs accounts for half of the total OpEx.

- Diesel cost has doubled since 2008.

- Even the operators don’t care about environment, they care about ….




Cost Components:

Energy Components:

- Top three energy consuming components,

feeder network, RF conversion, and climate

control (e.g., air conditioning).


Energy consumption at a typical macro BS (normalized)


OutlineOutline

Introduction

Energy Conservation - Various means

Basics of Relaying

Modelling

Case Study

Summary


Energy ConservationEnergy Conservation

Various Means

Power efficient wireless nodes:

- Low power architecture ~ Clock gating, Power saving modes.

- Improved display, Enhanced battery life.

Energy optimized software:

- Improved modem software and OS, application driven power management.

Efficient communication strategies:

- Energy efficient routing.

- Handling idle modes.

- Emerging techniques ~ Multi-antenna, Relay, Cognitive radio etc.

F. Shearer, Power Management in Mobile Devices, Elsevier, 2008.


OutlineOutline

Introduction

Energy Conservation

Basics of Relaying - What is a relay and Why use a relay?

- Modes of operation

- Relaying protocols

Modelling

Case Study

Summary


Basics of RelayingBasics of Relaying

What is a Relay?

A simple repeater: receive, boost, and re-send a signal.

Cellular Network: different node, carrier owned infrastructure, tree topology.

IEEE 802.16j (mobile multihop relay).

Sensor Network: identical node, subscriber equipment, mesh topology.

IEEE 802.15.5 (WPAN mesh), IEEE 802.11s (WLAN mesh).

Base Station(BS)

Relay Station (RS)

Mobile Terminal(MT)

Cellular Network Sensor Network

Relay #1

Relay #2 DestinationSource


Basics of RelayingBasics of Relaying

Why Use a Relay?

Network performance improvement

- Radio range extension

- Service for coverage holes

- Improve QoS

- Reduce Tx energy requirement

- Capacity enhancement

- Load balancing between the

neighbouring cells

Cost benefit

- Use relays to lower CapEx

- Temporary coverage

BS

MT #3

MT #1

MT #2

RS #2

RS #3

RS #1

Traditional service boundary

Capacity enhancement through replacing low rate, unreliable links with multiple high rate, reliable links

Traditional direct transmission

Cooperative transmission

BS-RS link

RS-MS link

Coverage/ radio range extension

A. Chandra, C. Bose, and M. K. Bose, “Wireless relays for next generation broadband networks,” IEEE Potentials, vol. 30, no. 2, pp. 39-43, Mar.-Apr. 2011.


Modes of OperationModes of Operation

Direct Path vs. Relayed Path

Co-operative Strategies

Relay

DestinationSource

Relay

DestinationSource

1st time slot

2nd time slot

× ××

K. J. Ray Liu, A. K. Sadek, W. Su, and A. Kwasinski, Cooperative Communications and Networking, Cambridge University Press, 2009.

Relay

DestinationSource

Relay

DestinationSource

1st time slot

2nd time slot


Relaying ProtocolsRelaying Protocols

Forwarding Strategy

Amplify and Forward (AF)

- Layer #1 relaying: Relays act as analog repeaters.

Decode and Forward (DF)

- Layer #2 relaying: Relays act as digital regenerative repeaters.

Compress and Forward (CF)

- Hybrid solution: Relays quantize and compress (source coding).

Relay

DestinationSource

Amplify and Forward

Relay

DestinationSource

Decode and Forward

Relay

DestinationSource

Compress and Forward


Relaying ProtocolsRelaying Protocols

Protocol Nature

Fixed protocol

- Relays always forward a processed version of their received signals.

Adaptive protocol

- Relays autonomously decide whether or not to forward.

Feedback protocol

- Relays provide redundancy only when explicitly requested by destination.

H. Katiyar, A. Rastogi, and R. Agarwal, “Cooperative communication: A review,” IETE Tech. Review, vol. 28, no. 5, pp. 409-417, Sep.-Oct. 2011.


OutlineOutline

Introduction

Energy Conservation

Basics of Relaying

Modelling - Power consumption at Rx/ Tx

- Energy consumed per bit

- Effect of fading

Case Study

Summary


ModellingModelling

Assumptions

Receiver

- Heterodyne, Hartley & Weaver, Zero IF, Low IF.

Baseband Signal Processing

- Source Coding, Pulse Shaping, Digital Modulation blocks are omitted.

Uncoded System

- No Error Correction Code (ECC) blocks are included.

Multiple Antennas

- Multiple RF processing blocks.


ModellingModelling

Power Consumption at Receiver

Block Diagram

Components

P. -I. Mak, S. -P. U, and R. P. Martins, Analog-baseband Architectures and Circuits for Multistandard and Low-voltage Wireless Transceivers, Springer, 2007.

B. Leung, VLSI for Wireless Communications, 2nd ed., Springer, 2011.

Image rejection

filter

Channel selection

filterMixer IFAAntenna ADC

LO

LNA

Band selection

filter

synfilADCIFAmixLNARx PPPPPPP


ModellingModelling

Power Consumption at Transmitter

Block Diagram

Components

Image rejection

filter

Channel selection

filter Mixer PAAntennaDAC

LO

synfilmixDACTx PPPPP

TxPAtotalTx PPP ,

TPA PP

PT → RF transmit power.

ξ → Peak-to-average ratio.

η → Drain efficiency.


ModellingModelling

RF Transmit Power

Friis Free Space Formula

For Terrestrial Transmission

Considering Link Margin and Noise Figure

G

dPP

GGdP

P

RT

RTT

R

22

2

4

4

PR → Received power.

d → Distance between Tx and Rx.

λ → Signal wavelength.

G → Combined antenna gain.

where G = GT GR.

G

dPP

n

RT

24

FL

n

RT NMG

dPP

24

n → Path loss exponent (2 ≤ n ≤ 4).

ML → Link margin.

NF → Noise figure.


ModellingModelling

Energy Consumed per Bit

Total Circuit Power Consumption

RxTxFL

n

R PPNMG

dP

2

4

where, Eb → Received energy per bit, Rb → Bit rate, and PR = Eb Rb.

RxtotalTxC PPP ,

RxTxPA PPP

RxTxT PPP

RxTxFL

n

bb PPNMG

dRE

2

4


ModellingModelling

Energy Consumed per Bit

Consumption per Bit

Bit Rate (Rb)

- When no pulse shaping is used, Rb = 2B, where B = System BW.

Received Energy per Bit (Eb)

- This parameter determine the BER floor and QoS.

b

C

R

PE

b

RxTxFL

n

b R

PPNM

G

dE

2

4


ModellingModelling

Ensuring a Fixed BER

Consider the Modulation Scheme

- For BPSK modulation, the BER is

Consider the Target BER

- Target BER is application specific, e.g. for voice applications, Pe ≤ 10-3.

Calculate Required Eb

0

erfc2

1

N

EP b

e

3

0

10erfc2

1

N

Eb

231-0 102erfc NEb


ModellingModelling

Effect of Fading

Statistics of Received SNR

- For Rayleigh fading

Outage Probability

- For a target SNR (γo),

- Target SNR is determined by the required data rate.

exp1

f

0Pr O

0

0

df

0exp1


ModellingModelling

Target SNR Calculation

Ergodic Capacity: Shannon’s Formula

- For reliable communication

Outage Probability

ob BR 1log2

0exp1O

12 BRo

b

12exp1

BRb

0

3exp1

NEb


ModellingModelling

Energy Consumed per Successful Bit

Effective Data Rate

Energy Consumption per Bit

ORR beffb 1,

effb

Csuc R

PE

,

OR

P

b

C

1

O

E

1


ModellingModelling

One More Equation …

… and you’ll lose rest of your audience!


ModellingModelling

Research Challenges

Relay: To Use or Not to Use

- Always cooperate, or use relay only when the direct link fails?

Relay Placement

- If relay node is not collinear, is there any boundary region to place it?

Relay Selection

- If there are many relay nodes, how many and which ones to select?

Other Issues

- Multiple antennas at relay, distributed STC etc.


OutlineOutline

Introduction

Energy Conservation

Basics of Relaying

Modelling

Case Study - Relay placement: Collinear model

- Relay placement: Non-linear model

Summary


Modelling for RelayModelling for Relay

Statistics of S-R-D Link

Outage Probability

Energy Consumption per Bit in S-R Link

Energy Consumption per Bit in R-D Link

0exp1DRRS OO DRRSRSDRS OOOO 1

b

RxTxFL

nRS

bb

RSCRS R

PPNM

G

dE

R

PE

2, 4

b

RxTxFL

nDR

bb

DRCDR R

PPNM

G

dE

R

PE

2, 4


Modelling for RelayModelling for Relay

Statistics of S-R-D Link

Energy Consumption per Bit in S-R-D Link

- Outage in S-R path, , probability

- No outage in S-R path, , probability

- Average energy consumption

Effective Data Rate

Energy Consumption per Successful Bit

DRRSDRS EEE RSDRS EE .RSO

.1 RSO

DRRSRSRSRSDRS EEOEOE 1

DRSbeffb ORR 1,

DRS

DRSsuc O

EE

1


Relay PlacementRelay Placement

Collinear Model

Relay DestinationSource

Direct Path(Reference level)

Relayed Path

42.2 m (Optimum location)

Direct Path vs. Relayed Path



Non-linear Model



Non-linear Model

Source Relay Destination

?



Non-linear Model

Source

Relay

Destination


OutlineOutline

Introduction

Energy Conservation

Basics of Relaying

Modelling

Case Study

Summary


SummarySummary

Energy efficient perspective for wireless systems.

Various means to reduce energy consumption.

Use of wireless relays is one of them.

A single collinear relay may save upto 35% energy.

For non-linear setup, an energy efficient region may be found to place the relay.

Many open problems, we need you!


Read More About ItRead More About It

Green Communication

1. G. Y. Li et al., “Energy efficient wireless communications: Tutorial, survey, and open issues,” to appear in IEEE Wireless Commun. Magz.

Modelling Energy Consumption

1. S. Cui, A. Goldsmith, and A. Bahai, “Energy-efficiency of MIMO and cooperative MIMO techniques in sensor networks,” IEEE J. Sel. Areas Commun., vol. 22, no. 6, pp. 1089-1098, Aug. 2004.

2. G. G. de Oliveira Brante, M. T. Kakitani, and R. D. Souza, “On the energy efficiency of some cooperative and non-cooperative transmission schemes in WSNs,” Proc. IEEE CISS, Baltimore, MD, Mar. 2011, pp. 1-6.


Thank You AllThank You All

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Hua Hin

Bangkok

Science City

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AcknowledgementsAcknowledgements

This talk won’t be possible without …

The support of Conference Organizers

Encouragements

Permissions

My research group

Prof. Richard D. Souza UTFPR - Parana,Curitiba, Brazil.

Prof. Joyanta Kr. RoyPrincipal, NIT& Program Chair, ICCIA.

Dr. P. VenkateswaranAssoc. Prof., ETCE Deptt., & Secretary, IEEE ComSoc.

Mr. Biswajit Ghosh Lecturer, IT, FIEM, Kolkata& Ph.D. student.

Mr. Anirban Ghosh Master’s student,NIT Durgapur.


Thank You!

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