2011 ULTRA Program: Green Radio

Prof. Jinho Choi

College of Engineering

Swansea University, UK

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Outline

1. Introduction

2. Energy Metric in Wireless

3. Candidate Technologies

4. Concluding Remarks

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1. Introduction

• Need of Green Radio: Every 5 years the traffic demands is expected to double meaning the current 2% CO2 emission could be larger if we do not do anything. So it is better now to work on energy efficient schemes and algorithms.

• This prediction would be modest as Smart Phones increase traffics a lot in recent years.

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Increasing Wireless Traffics

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Green Radio Research Activities

• Energy efficiency– To reduce CO2 emission (Green Radio)– For better battery life– To minimise operation costs– For better performance, mobility, and services

• Current status for Green Radio– In UK, Mobile VCE plays a key role in developing

green radio technologies– In Europe, EU-funded EARTH project is flagship

project on energy efficient cellular networks– In China, Green Radio Excellence in Arch. & Tech.

(GREAT) project is running.

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In EU and China

• Vodafone: – Energy consumption per unit in 2011 lower by 40% than that of

2005– Lower power consumption and improve EE

• T-Mobile:– CO2 emission in 2010 lower 50% than 1995– Initiate CO900 project

• China Mobile:– “Green Action Programme” starts up now!– Power consumption per traffic in 2010 lower 40% than 2005– Lower power consumption, save source, CO area and cost,

waste recycle

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2. Energy Metric in Wireless

• Spectral efficiency is the most popular measure.

Frequency (Hz)

Channel Channel Channel

Hz

sec per bits

Bandwidth

Rate Data Efficiency Spectral

Spectral Efficiency is a measure for how fast data sequences can be transmitted for a given bandwidth.

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Spectral Efficiency (1)

• This measure has been adopted in many data communication system designs.

• Data rate is decided as

Data rate = Spectral efficiency Bandwidth

• Thus, if spectral efficiency is 2, for a data rate of 10 M bits per second, the required bandwidth is 5 MHz.

• The higher spectral efficiency, the better utilization of bandwidth is expected.

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Spectral Efficiency (2)

• Spectral efficiency is the number of floors for a building.

4 < 8

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Spectral Efficiency and Energy Efficiency

• In fact, spectral efficiency is NOT right measure in the context of green radio.

• Joules per bit (J/b) is a candidate.

Rate Data

Power

TimeRate Data

TimePower Bit perEnergy

• Energy per bit should be low for better energy efficiency.• Data rate increases with transmission power. Thus, the

energy per bit is a function of transmission power.

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Energy Efficiency versus TX Power

No transmission is the most energy efficient ??

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Energy Efficiency

• The previous result shows that no transmission is the best for energy efficiency.

• This is a natural consequence: for zero CO2 emission, no human activities are the best (human beings are bad for environment).

• Although this conclusion could be right, it is not meaningful.

• Thus, energy efficiency should be considered with transmission time delay – wait until you are close to a base station.

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Energy Efficient Life in Mobile Comm.

• Wait until you are close to a base station

Do not talk!

Talk now!

As the distance is longer, a high transmission power is required. Thus, it is better to transmit signal when the distance is closer.

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3. Candidate Technologies

• There are various technologies for green radio in cellular systems:– Cell size optimization– Cooperative communications– Interference management

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Cell Size Does Matter (1)

• Small Cells or Large Cells

Less system overhead (e.g., handover)

Less TX power

Better for users of high mobility

Better for users of low mobility

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Cell Size Does Matter (2)

• Scalable and Flexible Structure via Relay• It also help to increase area capacity and cell edge capacity

Relay

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Multicell Cooperation

• Interference management/alignment– This is crucial for energy efficiency

• Without multicell cooperation, it is not easy to manage intercell interference and particularly cell edge capacity

• But, multicell cooperation introduces extra signaling load

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Cooperative PHY (1)

• Users at cell edges– Cell reuse factor of 1 causes inter-cell interference

problem.– In CoMP, the cell reuse factor becomes 1.

interference

interference

Competition

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Cooperative PHY (2)

• Joint coding to avoid inter-cell interference• Actively use cooperative communication techniques

Jointly encoded or modulated signals for both users

Cooperation

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Cooperative Relay (1)

• To support users far away from BSs

• Depending on the mobility of users, we may use beamforming or STC.

Relay

Relay

Relay

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Cooperative Relay (2)

• With CoMP

• This approach suits for medium/high mobility users when distributed STC is employed.

Relay

Relay

Relay Relay

Relay

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4. Concluding Remarks

• As mobile traffics increases rapidly, more energy consumption is expected in the near future.

• To reduce energy consumption, Green Radio is very important.

• At a system-level, we expect 10 – 100 times energy saving.

• Furthermore, various applications should also be developed for green radio.