2011 ULTRA Program: Green Radio Prof. Jinho Choi College of Engineering Swansea University, UK.
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Transcript of 2011 ULTRA Program: Green Radio Prof. Jinho Choi College of Engineering Swansea University, UK.
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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.