green wireless communication with relays

01 August, 2012Bangalore, India

Aniruddha Chandra

Electronics & Communication Engineering Department, National Institute of Technology, Durgapur.

[email protected]

Green Wireless Communication Green Wireless Communication with Relayswith Relays

2/31A. Chandra - Green wireless communication with relays

Green Communication =

Energy Efficient Communication

A new timely idea


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Energy Efficiency – Why?

Energy Efficiency – How?

Basics of Relaying

Case Study


OutlineOutline



Basics of Relaying

Case Study


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.



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



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



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



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.



Economical Perspective

Decreasing revenue:

- Vodafone annual ARPU decreased from € 30 (2000) to € 16 (2009).

Increasing fuel cost:

- Diesel cost has doubled since 2008.


Energy Consumption

Cost components:

Energy components:

- Feeder network.

- RF conversion.

- Climate control (e.g., air conditioning).


Energy components for BS



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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Basics of Relaying

Case Study


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.


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.


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?


C. Lubritto et al. “Energy and environmental aspects of mobile communication systems,” Energy, 36 (2), 1109-14, 2011.

Solar powered BS (Italy)


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.



OutlineOutline



Basics of Relaying

Case Study


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



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.


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



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


DestinationSource

Relay

DestinationSource


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.



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Basics of Relaying

Case Study


Relay PlacementRelay Placement

Collinear Model

Relay DestinationSource

Direct Path(Reference level)

Relayed Path

42.2 m (Optimum location)



Non-linear Model



Non-linear Model

Source Destination

Relay

?



Energy Ratio

Source Destination

Relay


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.



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!


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.


Thank You!

[email protected]

green wireless communication with relays

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