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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
The last decade has witnessed an unprecedented development and growth in global wireless communications systems, technologies and network "traffic" generated over network infrastructures. This book presents state-of-the-art energy-efficient techniques, designs and implementations that pertain to wireless communication networks such as cellular networks, wireless local area networks (WLANs) and wireless ad hoc networks (WAHNs) including mobile ad hoc networks (MANETs), and wireless sensor networks (WSNs) as they are deployed across the world to facilitate "always on" reliable high-speed wireless access from anywhere, at anytime to accommodate the new paradigm of the "Internet of Things" (IoT). The pervasive and exponential growth of Wi-Fi and the impact of bandwidth-intensive applications on the energy consumption of Wi-Fi-enabled devices are discussed along with energy harvesting as an advantageous option to power WAHNs. The book aims to serve as a useful reference for researchers, students, regulatory authorities, and educators.
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Seitenzahl: 191
Veröffentlichungsjahr: 2013
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Contents
Preface
1 Energy Efficiency in Cellular Networks
1.1. Overview of cellular communication networks
1.2. Metrics for measuring energy efficiency in cellular wireless communication systems
1.3. Energy efficiency in base stations
1.4. Energy-efficient cellular network design
1.5. Interference management and mitigation
1.6. Enabling technologies
2 Energy Efficiency in Wireless Ad Hoc Networks
2.1. Overview of wireless ad hoc networks
2.2. Metrics for measuring energy efficiency in wireless ad hoc networks
2.3. Energy losses in wireless ad hoc networks
2.4. Energy efficiency in wireless sensor networks
2.5. Mobile ad hoc networks (MANETs)
3 Energy Efficiency in Wireless Local Area Networks
3.1. Overview of wireless local area networks
3.2. Energy consumption metrics for WLANs
3.3. Energy efficiency in WLANs
3.4. Energy efficiency strategies in IEEE 802.11n
4 Energy Harvesting in Wireless Sensor Networks
4.1. Energy harvesting
4.2. Harvesting techniques
4.3. Energy harvesting storage devices
4.4. Power management for EH-WSN
4.5. Conclusion
5 Future Challenges and Opportunities
5.1. Energy efficiency in cellular networks
5.2. Energy efficiency in ad hoc networks
5.3. Energy efficiency in WLAN
5.4. Energy harvesting in wireless sensor networks
5.5. Energy efficiency for wireless technologies for developing countries
Bibliography
List of Acronyms
Index
First published 2013 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27–37 St George’s RoadLondon SW19 4EUUK
www.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ07030USA
www.wiley.com
©ISTE Ltd 2013
The rights of Oswald Jumira & Sherali Zeadally to be identified as the author of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Library of Congress Control Number: 2012947510
British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISSN: 2051-2481 (Print)
ISSN: 2051-249X (Online)
ISBN 978-1-84821-444-6
Preface
Over the last decade, there has been an unprecedented development and growth in wireless communication systems and technologies worldwide. The need to communicate and the modes of communication have evolved and become ubiquitous, pervasive and affordable. We have seen an exponential increase in the number of users accessing services and applications over the Internet using different types of portable and non-portable devices. As a result, network traffic generated over these network infrastructures has grown significantly. Other factors responsible for the increase in network traffic include:
Furthermore, affordable wireless communication access technologies and systems that include long-term evolution (LTE), worldwide interoperability for microwave access (WiMAX) and high-speed wireless fidelity (Wi-Fi) have been developed and deployed across the world to facilitate “always on”, reliable high-speed wireless access from anywhere, at anytime. Also, the new paradigm of the “Internet of Things” (IoT) has been a huge motivation for the development of efficient and reliable wireless communication systems and technologies [IOT 12]. The IoT refers to the networked interconnection of everyday objects, which relies on sensors, actuators, radio frequency identification (RFID) and other devices (cellular) for the collection of information from the surrounding environment and which is stored at distributed data storage systems and platforms for analysis and dissemination.
As a result, energy efficiency in wireless networks is an area that is currently attracting the attention of mobile wireless network operators, wireless technology device manufacturers, network users and governments. Standardization organizations such as the International Telecommunications Union (ITU) and the Third-Generation Partnership Project (3GPP) [3GP 10, ITU 10] are also advocating energy-efficient wireless communication networks and devices. The motivations driving the interest of different stakeholders toward energy efficiency in the wireless communications networks ecosystem include:
Wireless technology device manufacturers: there is a growing demand for the design of cost-effective energy-efficient wireless networking hardware, devices and systems to reduce energy consumption.
Mobile wireless network operators: operators would like to offer energy-efficient, affordable, consistent and high-quality services to their users.
Network users: there is a strong need for increased device/node lifetime due to the fact that mobile portable devices (laptops, cell phones, tablets, smartphones, etc) and sensors traditionally make use of constrained finite energy sources such as batteries.
Governments: policy and regulatory frameworks in many countries have become environmentally “green” and energy focused as the international community strives to address the challenges associated with global warming.
Energy efficiency in wireless networking is not just about the amount of energy consumed by various wireless networking equipment and operations alone. A comprehensive energy-efficient wireless networking solution needs to take into account the entire product lifecycle spanning from manufacturing to operation to disposal and recycling [WAN 08] of products. However, a detailed discussion of energy efficiency issues in the area of information communication technology (ICT) products’ lifecycle is beyond the scope of this book.
The goal of this book is to present state-of-the-art energy-efficient methods, designs and implementations that have been deployed in recent years in various types of wireless networks. It aims to serve as a useful reference for researchers, students, regulatory authorities and educators. In addition, we hope the book will be valuable to industry researchers, designers and engineers willing to keep themselves up-to-date in the field of energy-efficient wireless communication technologies.
The book is also intended to guide newcomers in the area of energy-efficient wireless networks in acquiring a deeper knowledge and a thorough understanding of the challenges and opportunities for innovative energy conservation ideas and future trends in wireless networks.
In this book, we discuss energy-efficient techniques that pertain to wireless communication networks such as cellular networks, wireless local area networks (WLANs) and wireless ad hoc networks (WAHNs) including mobile ad hoc networks (MANETs) and wireless sensor networks (WSNs). Cellular networks are normally deployed with careful network planning and rely on radio base stations (RBSs) to provide access to different types of services. WLANs are based on the IEEE 802.11 standard, which is the de facto standard for WLAN. In the infrastructure mode, a WLAN offers wireless access to wireless stations through an access point (AP) that acts like an RBS. Unlike cellular networks, WLANs require no network planning to deploy APs. Sensors (also known as motes) are hardware devices that respond to a measurable physical stimulus (such as thermal energy, electromagnetic energy, acoustic energy, pressure, magnetism or motion) to produce electrical signals. A network of sensors that communicate using the wireless medium is termed as a WSN. A MANET is a self-configuring infrastructureless network of portable devices connected wirelessly. Each device in a MANET is free to move independently in any direction, and therefore connectivity with other devices changes frequently. Such networks may operate by themselves or may be connected to the Internet. Although satellite networks also constitute a part of the wireless industry, the discussion on such networks is not given in this book.
The book is organized as follows. In Chapter 1, we describe recent techniques and strategies that have been proposed to enable deployment of energy-efficient cellular wireless networks. We present cooperative relaying and cognitive radio-based strategies for improving energy efficiency in wireless cellular network deployment.
In Chapter 2, we present energy-efficient networking schemes that are currently in use and have been proposed for WAHNs such as MANETs and WSNs. We describe research and industrial developments that have characterized the growth in interest in ad hoc networks.
In Chapter 3, we present recent developments in energy-efficient networking strategies and techniques for WLANs. The pervasive and exponential growth of Wi-Fi and the impact of bandwidth-intensive applications of the energy consumption of Wi-Fi-enabled devices are also presented in this chapter.
Chapter 4 discusses energy harvesting as an advantageous option to power WAHNs. The chapter also presents energy harvesting techniques for WAHNs and in particular for WSNs.
Chapter 5 discusses some of the future challenges and opportunities of energy-efficient wireless networks and concludes with some final remarks.
We would like to thank Professor Abdelhamid Mellouk for his great encouragement and feedback throughout the preparation of this book. We would also like to express our deepest gratitude to Alexandra Toulze, Raphael Menasce and the editorial staff at ISTE Ltd for their continuous support that led to the preparation of this book.
Last but not least, a special thank you to our families and friends for their constant encouragement, patience, sacrifice and understanding throughout this project.
We would welcome and appreciate your feedback, and we hope you enjoy reading this book.
Oswald JUMIRA and Sherali ZEADALLYOctober 2012
1
Energy Efficiency in Cellular Networks
In this chapter, we discuss recent energy efficiency techniques and solutions that have been proposed and deployed in cellular networks. We focus mainly on the energy-efficient cellular network hardware systems that include a base station (BS) system and energy-efficient cellular network design and deployment strategies.
1.1. Overview of cellular communication networks
The world has seen an exponential growth in the number of mobile subscribers and the number of portable devices (six billion cell phones worldwide [ERI 12]). In addition, data rates for mobile broadband access are improving and several projects have been initiated to address energy efficiency in cellular networks. The Green Radio project, formulated in 2007, aims to secure 100-fold reductions in energy requirements for the delivery of high data rate services in the cellular network industry [MOB 12]. The members of the project are pursuing energy reduction from two different perspectives [MOB 12]. The first perspective is to investigate design alternatives for reducing energy consumption in the existing cellular network infrastructures. The second perspective is to study the novel techniques that can be used in BSs or handsets to reduce energy consumption. To address the challenge of increasing energy efficiency in future wireless communication networks and thereby maintain profitability, it is crucial to consider various paradigm-shifting technologies such as energy-efficient wireless architectures and protocols, efficient BS redesign, opportunistic network access or cognitive radio, cooperative relaying and heterogeneous network deployment based on smaller cells.
We have seen the evolution of mobile communication from the first-generation mobile communication networks in the early 1990s to the current fourth-generation mobile communication networks. Almost all the mobile service providers now strive to deliver 3G and 4G services that are based on packet-switching systems, whereas in some areas the popular second-generation (2G) network, Global System for Mobile Communications (GSM), is still extensively used. Services advertised as 3G are required to meet the International Mobile Telecommunications-2000 (IMT-2000) technical standard, including standards for reliability, speed (data transfer rates) and offer voice, data and multimedia applications (3D gaming, video calls and video conferencing), specified by the International Telecommunications Union (ITU) [CHE 10]. Many services advertised as 3G provide higher speeds than the minimum technical requirements for a 3G service. Recent 3G releases, often called 3.5G and 3.75G, also provide mobile broadband access of several megabits per second to smartphones and mobile modems on laptop computers. The following standards are typically branded 3G: Universal Mobile Telecommunications Systems (UMTS), Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) radio interfaces, Wideband Code Division Multiple Access (WCDMA) radio interface, High-Speed Packet Access+ (HSPA) and Code Division Multiple Access 2000 (CDMA2000). The first release of the Third-Generation Partnership Project (3GPP) Long-Term Evolution (LTE) standard does not completely fulfill the ITU 4G requirements called IMT-Advanced. The first LTE release is not backward compatible with 3G, but is a pre-4G or 3.9G technology, however, sometimes branded as “4G” by the service providers. LTE-Advanced, which is an incremental version of LTE, is a 4G technology. WiMAX is another technology marketed as 4G.
Most of these developments in wireless communication systems have been driven by the need for high-speed and data-oriented networks, which cater for bandwidth-hungry applications and services without much consideration for quality of service (QoS) and energy efficiency.
Figure 1.1 shows all the network components of a mobile cellular network. A typical cellular network consists of three main elements:
Figure 1.2 shows a breakdown of power consumption in a typical cellular network and gives us an insight into the possible research avenues for reducing energy consumption in wireless communications.
Figure 1.2 illustrates the fact that a reduction in energy consumption of the BS system will lead to significant energy improvements for wireless cellular networks. The radio network itself contributes 80% to the network operator’s entire energy consumption. Several studies have also shown that the power drain per user of the mobile handset is much lower than that of the BS component, making the latter a major focus of research [HAN 11].
Figure 1.1.Mobile cellular networks
Figure 1.2.Power consumption of a typical wireless cellular network [HAN 11]
1.2. Metrics for measuring energy efficiency in cellular wireless communication systems
It is important to understand the meaningful metrics that identify the gains achieved through the introduction of energy-efficient strategies in cellular communication networks. A more comprehensive taxonomy of energy efficiency metrics is presented in [CHE 10], but there are two important metrics that are mainly used for comparison in communication systems. These metrics are the energy consumption rating (ECR) and energy consumption gain (ECG). ECR measures the consumed energy per information bit that is successfully transported over the network and is measured in joules per bit [CHE 10]. ECG is a relative measure mostly used for comparing two different systems and is the ration of energy consumed by the baseline systems and the energy consumed by the system under test [CHE 10].
Although the energy efficiency metrics at the component and equipment level are fairly straightforward to define, it is more challenging to define metrics at a system or network level [CHE 10]. Due to the intrinsic difference between various communication systems and performance measures, it is important to have different metrics. In the future, energy efficiency metrics must also consider deployment costs such as site construction, backhaul and QoS requirements such as transmission delay along with spectral efficiency in order to assess the true efficiency of the system. Once a consensus is reached on a set of standard energy metrics, there will not only be an acceleration of the research activities in energy-efficient communication, but also a way toward standardization.
The specific objectives of various projects [ICT 12a, FP7 12, ICT 12b] are to investigate and develop innovative methods to reduce the total energy needed to operate a radio access network (BS) and to identify appropriate energy-efficient radio architectures. To minimize the energy consumption of cellular architectures and networks and keep the emission of CO2 to a minimum level, further investigations are required. In the following sections, some of the strategies and techniques that have been recently proposed to improve energy efficiency in cellular networks are presented. The focus is on energy efficiency in various components of a cellular network.
1.3. Energy efficiency in base stations
The number of BSs worldwide has increased to many millions in recent years and has led to a large increase in the energy consumption for cellular operators. BS equipment manufacturers have begun to offer a number of eco- and cost-effective solutions to reduce the power demands of BSs and to support off-grid BSs with renewable energy resources. Radio Resource Management (RRM) is a system-level approach that controls parameters such as transmit power, channel allocation, data rates, handover criteria, modulation schemes and error coding schemes. The objective is to utilize the limited radio spectrum resources and radio network infrastructure as efficiently as possible. Traditionally, RRM did not consider system energy efficiency, but it is now being enhanced to take into consideration the energy aspect. Nokia Siemens Networks Flexi Multiradio Base Station, Huawei Green Base Station and Flexenclosure Esite Solutions [CHE 11, HUA 09, FLE 12] are a few examples of efforts to reduce the energy consumption of BSs. The overall efficiency of the BS, in terms of power drawn from its supply in relation to its radio frequency (RF) power output, depends on the power consumption of its various components including the core radio devices. Figure 1.3 shows the power consumption distribution in a BS system.
Figure 1.3.Power consumption distribution in base stations [HAN 11]
A BS typically consists of the following components that are shown in Figure 1.4:
BSs also contain some other ancillary equipment, providing facilities such as connection to the service provider’s network and climate control system. A climate control system is a system that is used to control the weather conditions (usually temperature) within an infrastructure where the BS equipment is stored. The system is composed of an air-conditioning and ventilation system. The energy consumption of a typical BS can be reduced by improving the BS hardware design, and by including additional software and system features to optimize between energy consumption and performance. To make the BS design more energy efficient, all the BS components need to operate efficiently.
Figure 1.4.Base station architecture
Some of the techniques used to improve the BS energy efficiency are given in the following:
a) Energy-efficient power amplifiers
PAs are used to increase the power level of an input signal without altering the content of the signal. A PA dominates the energy consumption of a BS. Its energy efficiency depends on its operating frequency band, the type of modulation technique in use and its operating environment [LOU 07]. A PA consumes almost 50% of the energy in the BS. Approximately 80–90% of this consumed energy is wasted as heat, which, in turn, requires air conditioners, thereby adding even more to the energy costs. The total efficiency of a currently deployed amplifier, which is the ratio of AC power input to generated RF output power, is generally in the range from 5% to 20%, depending on the standard (i.e. GSM, UMTS, CDMA) and the equipment’s condition [CLA 08].
Modern BSs are inefficient because of their need for PA linearity and high peak-to-average power ratios (PAPR). PA linearity is the linear relationship between input power and output power, which, in an ideal amplifier, would be precisely related by the gain of the amplifier. The modulation schemes used in communication standards such as WCDMA/HSPA and LTE are characterized by strongly varying signal envelopes with PAPR that exceeds 10 dB. To achieve high linearity, PAs need to operate well below saturation in order to maintain the quality of radio signals, and this results in low power efficiency [COR 10]. Depending on their PA technology (e.g. Class-A/B amplifiers with digital predistortion) and implementation, the component-level efficiency of modern amplifiers for CDMA and UMTS systems is in the order of approximately 30–40% [CLA 08]. Because cellular technologies have reached their limits with Class-A/B power amplifiers, PAs based on special architectures such as digital pre-distorted Doherty-architectures and aluminum gallium nitride (GaN)-based amplifiers are now used to deliver higher power efficiency levels [CLA 08].
Additional improvements in energy efficiency can be done by shifting to switch-mode PAs from the traditional analog RF-amplifiers. Compared to standard analog PAs, switch-mode PAs use less electric current and dissipate less energy. While amplifying a signal, a switch-mode amplifier turns its output transistors on and off at an ultrasonic rate [CLA 08]. The switching transistors produce no electric current when they are switched off and produce no voltage when switched on, which results in highly efficient power supply. It is expected that the overall component efficiency of these energy-efficient devices could be approximately 70% [CLA 08].
b) Energy-aware cooperative BS power management
One way to improve BS energy efficiency is to shut down BS during low traffic or cell zooming [NIU 10, MAR 10]. Cell zooming is a technique through which BSs can adjust the cell size according to the network or traffic situation, in order to balance the traffic load, while reducing the energy consumption. When a cell gets congested with an increased number of users, it can zoom itself in, whereas the neighboring cells with the less amount of traffic can zoom out to cover those users that cannot be served by the congested cell. Cells that are unable to zoom in may even go to sleep to reduce energy consumption, whereas the neighboring cells can zoom out and help serve the mobile users cooperatively.
Traffic load in cellular networks causes significant fluctuations in space and time because of various factors (e.g. user mobility). During daytime, traffic load is generally higher in office areas compared to residential areas, while it is the other way around during the night. Therefore, a static cell size deployment is not optimal with the fluctuating traffic conditions. For next-generation cellular networks based on multi-hop and relay strategies, limited cell size adjustment called “cell-breathing” is currently used in CDMA networks. With cell breathing, a cell under heavy load or interference reduces its size through power control and the mobile user is handed off to the neighboring cells [NIU 10]. More network-level power management is required where multiple BSs can coordinate each other. As the operation of a BS consumes a considerable amount of energy, selectively letting BSs go to sleep based on their traffic load can help save a significant amount of energy. When some cells are switched off or in sleep mode, the radio coverage can be guaranteed by the remaining active cells by filling in the gaps created. Such concepts of self-organizing networks (SONs) have been introduced in the 3GPP standard (3GPP TS 32.521) [NIU 10] to add network management and intelligence features so that the network is able to optimize, reconfigure and repair itself in order to reduce the costs and improve the network performance and flexibility [3G 09].
