energy conservation in wireless communication systems with relays
DESCRIPTION
Two hour tutorial presented at IEEE ICCIA held in Kolkata in 2011.TRANSCRIPT
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27th December, 2011Science City, Kolkata
Aniruddha Chandra
Telecommunications, School of Engineering & Technology,Asian Institute of Technology, Bangkok, Thailand.
Energy Conservation in Wireless Energy Conservation in Wireless Communication Systems with RelaysCommunication Systems with Relays
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2/41A. Chandra - Energy Conservation with Relays
OutlineOutline
Introduction
Energy Conservation
Basics of Relaying
Modelling
Case Study
Summary
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3/41A. Chandra - Energy Conservation with Relays
OutlineOutline
Introduction - Paradigm shift in wireless system design
- Energy consumption by telecomm industry
Energy Conservation
Basics of Relaying
Modelling
Case Study
Summary
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4/41A. Chandra - Energy Conservation with Relays
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.
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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
IntroductionIntroduction
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6/41A. Chandra - Energy Conservation with Relays
Energy Consumption by Telecomm Industry
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 ….
IntroductionIntroduction
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Energy Consumption by Telecomm Industry
Cost Components:
Energy Components:
- Top three energy consuming components,
feeder network, RF conversion, and climate
control (e.g., air conditioning).
IntroductionIntroduction
Energy consumption at a typical macro BS (normalized)
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8/41A. Chandra - Energy Conservation with Relays
OutlineOutline
Introduction
Energy Conservation - Various means
Basics of Relaying
Modelling
Case Study
Summary
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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.
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10/41A. Chandra - Energy Conservation with Relays
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
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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
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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.
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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
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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
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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.
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OutlineOutline
Introduction
Energy Conservation
Basics of Relaying
Modelling - Power consumption at Rx/ Tx
- Energy consumed per bit
- Effect of fading
Case Study
Summary
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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.
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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
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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.
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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.
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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
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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
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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
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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
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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
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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
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ModellingModelling
One More Equation …
… and you’ll lose rest of your audience!
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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.
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OutlineOutline
Introduction
Energy Conservation
Basics of Relaying
Modelling
Case Study - Relay placement: Collinear model
- Relay placement: Non-linear model
Summary
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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
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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
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Relay PlacementRelay Placement
Collinear Model
Relay DestinationSource
Direct Path(Reference level)
Relayed Path
42.2 m (Optimum location)
Direct Path vs. Relayed Path
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Relay PlacementRelay Placement
Non-linear Model
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Relay PlacementRelay Placement
Non-linear Model
Source Relay Destination
?
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Relay PlacementRelay Placement
Non-linear Model
Source
Relay
Destination
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36/41A. Chandra - Energy Conservation with Relays
OutlineOutline
Introduction
Energy Conservation
Basics of Relaying
Modelling
Case Study
Summary
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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!
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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.
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Thank You AllThank You All
… travelling around the Globe!
Hua Hin
Bangkok
Science City
Presenting talks in conferences ensure …
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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.