Chapter 21: Overview of Energy Saving Techniques for Mobile and Wireless Access Networks

1. HANDBOOK ON GREEN INFORMATION AND COMMUNICATION SYSTEMS Chapter 21: Overview of Energy Saving Techniques for Mobile and Wireless Access Networks 1 Diogo Quintas, 1Oliver Holland, 1Hamid Aghvami, and 2Hanna Bogucka 1Centre for Telecommunications Research, King’s College London 2Poznan University of Technology, Poland

2. Carbon Footprint of Mobile Networks • Embodied Energy • Energy spent on manufacturing, installation and decommission of equipment • Operational Energy • Energy spent on the day to day operation of the equipment • Operational Energy is the dominant part of the energy consumption… but, • As systems become more efficient the Embodied Energy will be dominant Figure 1: Contribution to the carbon footprint of mobile wireless networks [1]

3. Operational Energy • There are three main components of energy consumption by access equipment: • Power Amplifiers • Cooling • Baseband Processing • Other circuitry • The total power consumption has a load and RF power variant part AND a fixed consumption Figure 2: Operational energy consumption breakdown [2]

4. Operational Energy Modeling • Linear models scaling with the average RF power consumption and load have been proposed in the literature, modeling a Omni-directional BS* [3]: • * - The total power typically scales linearly with the number of PA’s and sectors

5. Embodied Energy • Estimatives for the embodied energy of a base station set the total cost as 75GJ [7] • Semiconductor manufacure is the dominant factor in the embodied energy of mobile equipment Figure 3: Embodied energy consumption breackdown [7]

6. Towards a Life Cycle Perspective • To evaluate the enviormental impact of a new system design it is critical to have in mind the full life cycle‘s energy consumption • Facilitating the comparison between two systems/techniques with different life expectancie‘s (or time frames...) the full life cycle‘s energy consumption must be scaled into an energy cost per unit of time (usually measured in years)

7. Extending the Life Cycle • Modular equipment with multiple reusable parts • Parts of High end equipment could be reused in lower end equipement after reaching their end of life. • Reconfigurable chips • New technology could then be deployed by a simple reconfiguration of the chip • Recycling valuable raw material • In practice this is already done...

8. Improving Hardware • Improvements on hardware design are the most effective way of reducing the operational energy consumption • Base station equipment consuming just 500W has been released by manufacturers • Little understanding of the impact of the new design paradigms in the manufacture phase

9. Power Amplifiers • Three promising designs/techniques: • Doherty Amplifiers • Envelope Tracking • Digital Pre-distortion • Together these are expected to yield efficiency rates of up to 50% [8] • Comercial PA‘s have been anounced with an efficiency rate of 45%

10. Processors • Power consumption of a processor varies quadraticaly with the voltage and linearly with the clock frequency • Dynamicaly adaptin the frequency and undervolting the processor leads to significant power savings • Multi core arquitechtures allow a fine-grained control off the power consumption

11. Micro Sleep Modes • Switch off signaling during some timeslots • Power down the processor (under voltage) • Switch off the PA (DTX) • Ensure that the power consumption scales with the effective load (i.e. the instantaneous load).

12. Whole System Design • Component level efficiency improvements can only reduce the operational power costs • There are fundamental limits to achievable efficiency gains by better designs • They do little to improve the Energy Consumption/Capacity trade off • The whole system has to be taken into consideration • Network dimensioning • Alternative networking paradigms • Spectrum management

13. “Green” Radio Interface • Theoretical capacity of current modulation schemes are pushing us closer to the Shannon bound. • As the bound is approached the number of base stations to provide capacity is reduced... • However, these new techniques require complex DSP, increasing both the embodied and operational energy of processors. • Simpler techniques are needed that still achieve capacity...

14. System Dimensioning • Smaller cells tend to consume less RF power - however more base stations are needed to cover the same area • The fixed energy costs increase linearly with the number of access routers • For smaller micro base stations the embodied starts to dominate the Life Cycle consumption Figure 8: Energy consumption per year to cover a 20 sq km area, with and without embodied energy

15. Multi Hop Networks • Multi hop networking can effect a reduction by: • Increasing the capacity density of the network • Decreasing the RF power levels in the network • However, relays can be inthemselves power hungry • The embodied energy of relays could be a problem.

16. Relay Aided Networks • The operational power consumption can be reduced up to a factor of 10 depending on the required capacity density • Extrapolating from an economic analysis, if relays have an life cycle cost of less than 6% of a base station then energy is saved • Relay switch off paterns can further reduce the life cycle costs of these networks.

17. Mobile Ad-Hoc Networks • Delay tolerant applications can use Mobile Ad-Hoc networks • Traffic can be shifted from the access network to the Ad-Hoc network, reducing the capacity density required • Effects on the energy efficiency are highly dependent on the spatial and temporal characteristics of delay tolerant traffic...

18. Dynamic Spectrum Management • Utilizing the available spectrum bands in a more intellegent way can reduce energy consumption by: • Moving users or traffic from one band to another switching off all radio equipment in one of the bands • Adjusting sectorisation patterns allowing the switching off of some sectors • Moving users or traffic between bands to allow subsets of cells to be switched off • Enabling the switching off radio equipment in single band scenarios

19. Alternative Source of Energy • Grid access is an increasingly important issue as mobile networks grow in emerging markets • On-site generation has to be used, bypassing the need for a grid (and associated losses...) • Coupled with an effective reduction of the power consumption of access networks, renewable energy is an option to reduce the carbon footprint

20. Suitability Of Wind and Solar Power • Macro sites have more space to deploy power generating equipment • BUT... consume much more power. • Energy yields from renewable source can be volatile, with clear seasonal patterns Figure : Energy availability throughout the year in London, United Kingdom. Data from

21. Conclusion • There are several techniques that can improve the access network‘s energy efficiency spanning several design dimensions: • Component level energy efficient design • Network planning • Spectrum management • Renewable energy • Little research has been done from a life cycle prespective – recent energy efficient research has been focusing on the operational energy reduction • There is a risk of shifting the energy consumption of the operational phase to the manufacture phase.

22. Selected References [1] T. Edler, “Green base stations how to minimize co2 emission in operator networks.” in Next Generation Networks and Base stations Conference, Bath, UK, 2008. [2] H. Karl, “An overview of energy-efficiency techniques for mobile communication System,” TU Berlin, Tech. Rep., 2003. [3] O. Arnold, F. Richter, G. Fettweis, and O. Blume, “Power consumption modeling of different base station types in heterogeneous cellular networks,” in Future Network and Mobile Summit 2010 [4] M. Deruyck, E. Tanghe, W. Joseph, and L. Martens, “Modelling and optimization of power consumption in wireless access networks,” Comp Comms, In Press, Corrected Proof, 2011. [5] W. Guo and T. OFarrell, “Green cellular network: Deployment solutions, sensitivity and tradeoffs,” in WiAd 2011, Jun 2011. [6] L. Saker and S. Elayoubi, “Sleep mode implementation issues in green base stations,” in PIMRC 2010, sept. 2010, pp. 1683 –1688. [7] I. Humar, X. Ge, L. Xiang, M. Jo, M. Chen, and J. Zhang, “Rethinking energy efficiency models of cellular networks with embodied energy,” Network, IEEE, vol. 25, no. 2, pp. 40 –49, march-april 2011. [8] L. Correia, D. Zeller, O. Blume, D. Ferling, Y. Jading, I. Go anddor, G. Auer, and L. Van Der Perre, “Challenges and enabling technologies for energy aware mobile radio networks,” Comm Mag, IEEE, vol. 48, no. 11, pp. 66 –72, november 2010.

23. Thanks for your attention!