Download - Green wireless communication with relays
01 August, 2012Bangalore, India
Aniruddha Chandra
Electronics & Communication Engineering Department, National Institute of Technology, Durgapur.
Green Wireless Communication Green Wireless Communication with Relayswith Relays
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Green Communication =
Energy Efficient Communication
A new timely idea
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OutlineOutline
Energy Efficiency – Why?
Energy Efficiency – How?
Basics of Relaying
Case Study
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OutlineOutline
Energy Efficiency – Why?
Energy Efficiency – How?
Basics of Relaying
Case Study
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Energy EfficiencyEnergy Efficiency
Why?
Traditional perspective:
- Reduced Tx power → reduced reliability.
- To maintain QoS, Tx rate should be reduced.
Ecological perspective:
- Reduce greenhouse gas emission.
Economical perspective:
- Reduce OPEX cost.
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Energy EfficiencyEnergy Efficiency
Traditional Perspective
Value BW most:
- Ever increasing subscriber base.
- Strict spectrum regulations.
- R&D focus on BW efficient radio access techniques.
- These complex techniques demand more processing power.
A typical MIMO-OFDM Tx Rx ckt
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Energy EfficiencyEnergy Efficiency
Traditional Perspective
What about energy?
- Battery powered mobile terminals → limited energy.
- Limited energy → limited reliable data rate.
BER vs. SNR curves (M = 16) BW efficiency vs. power efficiency
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Energy EfficiencyEnergy Efficiency
Ecological Perspective
2007 statistics on environmental impact:
- A cellular network ~ Energy for 1,70,000 homes.
- 3% of the energy consumption.
- 2% of CO2 emission.
- The figures are going to triple by 2020.
Objects in Mirror are Close than
they Appear
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Energy EfficiencyEnergy Efficiency
Sources of Greenhouse Gas Emission
Operation of radio access network:
- RF transmission.
- Fossil fuel powered BS.
- Charging of devices.
Device/ equipment
production.
Backbone network
operation.
A. Fehske et al. “The global footprint of mobile communications: the ecological and economic perspective,” IEEE Commun. Magz., 49 (8), 55-62, 2011.
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Energy EfficiencyEnergy Efficiency
Economical Perspective
Decreasing revenue:
- Vodafone annual ARPU decreased from € 30 (2000) to € 16 (2009).
Increasing fuel cost:
- Diesel cost has doubled since 2008.
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Energy Consumption
Cost components:
Energy components:
- Feeder network.
- RF conversion.
- Climate control (e.g., air conditioning).
Energy EfficiencyEnergy Efficiency
Energy components for BS
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Energy EfficiencyEnergy Efficiency
Energy Cost Calculation
Revenue generated:
- No. of subscribers per cell site ~ 800.
- ARPU ~ 3$ / month.
- Monthly revenue ~ 800 x 3$ = 2400 $.
Cost for energy:
- Energy cost ~ 0.20 $/ kWh.
- Power requirement per BS ~ 1.7 kW.
- Cost per month ~ 30 (days) x 24 (hours) x 1.7 x 0.20 $ = 244 $.
10% of total revenue (even before tax, interest, depreciation)!
BSSubscriber
Subscriber
Cell site
Power plant
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OutlineOutline
Energy Efficiency – Why?
Energy Efficiency – How?
Basics of Relaying
Case Study
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Energy Savings in Base Stations
Improvements in PA:
- Linear PAs → 90% wastage.
- DPD, Doherty, GaN based PA.
Power saving mode:
- Sleep mode, discontinuous Tx/ Rx.
Optimization:
- BS placement, cell size.
Energy EfficiencyEnergy Efficiency
V. Mancuso et al. “Reducing costs and pollution in cellular networks,” IEEE Commun. Magz., 49 (8), 55-62, 2011.
Z. Hasan et al. “Green cellular networks: a survey, some research issues and challenges,” IEEE Commun. Surveys Tuts., 13 (4), 524-40, 2011.
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Energy Savings in Base Stations
Renewable energy:
- Sustainable bio-fuel.
- Solar energy.
- Wind energy.
New BS architecture:
- Short, low power RF cable between Amp. & Ant.
- Feeder less site.
Reduce no. of BS?
Energy EfficiencyEnergy Efficiency
C. Lubritto et al. “Energy and environmental aspects of mobile communication systems,” Energy, 36 (2), 1109-14, 2011.
Solar powered BS (Italy)
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New Communication Strategies
MIMO / beamforming:
- Diversity.
- More sectors per cell site.
Cognitive radio:
- Find unused spectrum, BW traded off for power.
Use a third node:
- Reduce effective transmission distance.
Energy EfficiencyEnergy Efficiency
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OutlineOutline
Energy Efficiency – Why?
Energy Efficiency – How?
Basics of Relaying
Case Study
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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)/ 802.11s (WLAN mesh).
Base Station(BS)
Relay Station (RS)
Mobile Terminal(MT)
Relay #1
Relay #2 DestinationSource
Cellular network Sensor network
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Basics of RelayingBasics of Relaying
Why Use a Relay?
Save Tx energy:
- Reduced transmission distance.
Performance improvement:
- Enhance QoS, capacity, range.
- Load balancing.
CapEx benefit:
- Temporary coverage, gradual rollout.
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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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
Basics of RelayingBasics of Relaying
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Decoding at Relay
Amplify and forward:
- Relays act as analog repeaters.
Decode and forward:
- Relays act as digital regenerative repeaters.
Compress and forward:
- Relays quantize and compress.
Relay
DestinationSource
Relay
Basics of RelayingBasics of Relaying
DestinationSource
Relay
DestinationSource
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Resource Allocation
Persistent transmission:
- Relays always forward a processed version of their received signals.
Selective relaying:
- Relays autonomously decide whether or not to forward.
Incremental relaying:
- 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.
Basics of RelayingBasics of Relaying
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OutlineOutline
Energy Efficiency – Why?
Energy Efficiency – How?
Basics of Relaying
Case Study
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Relay PlacementRelay Placement
Collinear Model
Relay DestinationSource
Direct Path(Reference level)
Relayed Path
42.2 m (Optimum location)
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Relay PlacementRelay Placement
Non-linear Model
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Relay PlacementRelay Placement
Non-linear Model
Source Destination
Relay
?
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Relay PlacementRelay Placement
Energy Ratio
Source Destination
Relay
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Open Problems
Relay - To use or not to use:
- Always cooperate, or use relay only when the direct link fails?
Relay selection:
- If there are many relay nodes, how many and which ones to select?
Other issues:
- Multiple antennas at relay, distributed STC etc.
Relay PlacementRelay Placement
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SummarySummary
Value energy.
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,” IEEE Wireless Commun. Magz., 18 (6), 28-35, 2011.
Modelling Energy Consumption
1. S. Cui et al., “Energy-efficiency of MIMO and cooperative MIMO techniques in sensor networks,” IEEE JSAC, 22 (6), 1089-98, 2004.
2. G. G. de Oliveira Brante et al., “Energy efficiency analysis of some cooperative and non-cooperative transmission schemes in wireless sensor networks,” IEEE TCOM, 59 (10), 2671-77, 2011.