2011 ULTRA Program: Green Radio Prof. Jinho Choi College of Engineering Swansea University, UK
Outline • Introduction • Energy Metric in Wireless • Candidate Technologies • Concluding Remarks
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.
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.
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
2. Energy Metric in Wireless • Spectral efficiency is the most popular measure. Channel Channel Channel Frequency (Hz) Spectral Efficiency is a measure for how fast data sequences can be transmitted for a given bandwidth.
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.
Spectral Efficiency (2) • Spectral efficiency is the number of floors for a building. 4 < 8
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. • 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.
Energy Efficiency versus TX Power No transmission is the most energy efficient ??
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.
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.
3. Candidate Technologies • There are various technologies for green radio in cellular systems: • Cell size optimization • Cooperative communications • Interference management
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
Relay Cell Size Does Matter (2) • Scalable and Flexible Structure via Relay • It also help to increase area capacity and cell edge capacity
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
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
Cooperative PHY (2) • Joint coding to avoid inter-cell interference • Actively use cooperative communication techniques Jointly encoded or modulated signals for both users Cooperation
Relay Relay Relay 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 Relay Relay Cooperative Relay (2) • With CoMP • This approach suits for medium/high mobility users when distributed STC is employed.
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.