IEEE Journal of Selected Topics in Quantum Electronics, "Special Issue on Green Photonics", vol.17, no.2, 2011
This special issue covers the major issues related to energy for optical systems and networks spanning from optical interconnects to wide area networks with contributions from leading experts.

IEEE Journal on Selected Areas in Communications (JSAC), Special Issue on "Energy-Efficient Wireless Communications", vol. 29, no. 8, September 2011.
This special issue is the first one of IEEE Journal on Selected Areas in Communications (JSAC) focusing on energy-efficient wireless communications, which spans a broad spectrum of various timely topics relevant to the energy-efficiency issues and challenges, bringing together the state-of-the-art research results and industrial applications within the energy-efficient wireless communications.

IEEE Wireless Communications, Feature Topics Issue on "Green Radio Communication Networks", vol. 18, no. 5, October 2011.
This special issue provides a detailed overview of the state of the art in energy efficient wireless networks. The special issue contains some articles that address techniques that can improve the energy efficiency of individual base stations, such as base station sleep modes and distributed antenna technologies. It also contains articles that address network management perspectives to reduce energy consumption and to exploit renewable energy resources. There are also two review articles provided by the UK funded Green Radio project and the European funded EARTH project.

IEEE Network Magazine, Special Issue on "Energy Efficient Networks", vol. 25, no. 2, 2011.
An early and broad scope special issue covering the essential energy issues in wireline and wireless core and access networks.

Computer Networks, Special Issue on "Green Communication Networks", v. 56, 10, 2317-2550, July 2012
A comprehensive snapshot of the state of the art in this rapidly evolving and expanding field including both wireless and wireline networks.

IEEE Communications Magazine, Feature Topics Issue on Green Communications, “Energy Efficiency in Communications“,   vol. 48, no. 11, November 2010
This is the very first one of the three reoccurring Feature Topic issues of IEEE Communications Magazine in sequence (November 2010, June and August 2011) devoted to energy efficiency improvement, which aims to provide a holistic overview of the state-of-the-art in the relevant fundamental technology challenges, essential frameworks, international research programs, global regulation, industrial standardization, and smart grids applications for energy-efficient green communications in the coming environment-friendly & sustainable development era.

IEEE Communications Magazine, Feature Topics Issue on Green Communications, “Energy Efficiency in Communications: Part II“, vol. 49, no.6, June 2011
This is the second part of the three reoccurring Feature Topic issues of IEEE Communications Magazine on energy efficiency for green communications, which in particular is dedicated to the latest advances in various energy-efficient fixed and wireless communications and networking technologies for highlighting the increasingly global interests in the technical potentials and approaches to mitigating energy consumption and the consequential environmental influences.

IEEE Communications Magazine, Feature Topics Issue on Green Communications, "Energy Efficiency in Communications: Part III“, vol. 49, no. 8, August 2011
This Feature Topic issue is the finale of the “Energy Efficiency in Communications” series within IEEE Communications Magazine (November 2010, June and August 2011), which specifically covers the recent advancements and developments from networking architectures, communications protocols and algorithms to various typical practical applications (e.g., testbed, deployment and standards, etc.) in energy-efficient communications, reflecting the cutting-edge research trends as well as the newest practical needs.

Bell Labs Technical Journal, Special Issue on "Green Information and Communications Technology (ICT) for Eco-Sustainability", vol. 15, no. 2, September 2010
This issue of Bell Labs Technical Journal provides a broad ranging review of recent research related to all aspects of energy efficiency and communications systems. Articles cover a diverse range of topics from energy efficient wireless communications, improvements in wired and optical communications technologies, energy scavenging concepts through to smart grid systems.

EURASIP Journal on Wireless Communications and Networking, Special Issue on "Green Radio", January 2013
Having been listed as “Highly Accessed” by the EURASIP Journal on Wireless Communications and Networking, this special issue focuses on the green radio networks aiming at reducing the ever-growing energy requirements for wireless communications and radio access networks (RAN). In concrete, this special issue includes 17 papers dealing with various key topics that covers network considerations (both indoor and outdoor scenarios), cell layout adaptation, efficient techniques for radio resource management and optimal transmission, cognitive radio networks with environment learning & information exchange, and electronic components optimization.

David JC MacKay, "Sustainable Energy - Without the Hot Air", UIT Cambridge Ltd., 1 edition, February 20, 2009
This book provides a tutorial level introduction to issues around energy provision, from the point of view of a physics professor. It is scientifically rigorous and dispassionate analysis of future energy issues, looking in particular at the challenges facing energy provision in the United Kingdom.

E. Hossain, V.K. Bhargava, and G. P. Fettweis (Eds.), "Green Radio Communication Networks," Cambridge University Press, August 27, 2012 (440 book pages)
The very first book in this field of green communications presents the state-of-the-art research on green wireless communications. It gathers all the key concepts and techniques used in energy-efficient wireless communications in one reference book. The book contains 17 chapters that cover 5 different aspects of green radio communications and networking issues. The aspects discussed in this book include communication architectures and models, physical communications techniques, base station power-management techniques, wireless access techniques for green radio networks, and green radio test-bed, experimental results and standardization activities.

J. Wu, S. Rangan, H. Zhang (Eds.), "Green Communications: Theoretical Fundamentals, Algorithms and Applications," CRC Press, September 20, 2012 (840 book pages)
This is the second published book in the field of the green communications technologies. This is the first comprehensive published book effort on green communications covering broad topics of green wireless communications, green wireline communications, general relevant green topics and applications in one book using a research perspective. This book provides comprehensive coverage in an all-inclusive panoramic style on the broad areas of all relevant green communications and computing topics including general issues, theoretic concepts and algorithms, wireless communications, wireline communications, optical networking infrastructures, virtualization techniques, device- and system-level implementation details, standardizations, smart grids, data centers, cloud computing and cloud-RAN, video communications and quality of services, content distribution networks and applications. This book provides the state of art research surveys, and discusses the relevant research challenges and directions. This book is suitable for encouraging graduate students and academic and industrial researchers, engineers as well as regulatory practitioners and governmental policy makers to take up this emerging research field. Comment 2: From FPGAs, smart grids, cognitive radio to cloud computing with focus on both wireless and wireline communications, this edited book provides a broad understanding of energy consumption, energy efficiency and energy-saving strategies for a wide range of communication systems.

O. Tamm, C. Hermsmeyer, A. Rush, “Eco-Sustainable System and Network Architectures for Future Transport Networks”, Bell Labs Technical Journal, vol.14, no.4, p.311 2010
This paper discusses energy consumption in core optical internet functions such as data transport, aggregation and switching. The paper addresses the fact that current internet traffic volumes are increasing rapidly, meaning that the internet is forecast to consume an increasing proportion of total energy use. The paper studies the energy consumption of internet devices as at 2008 and also forecasts energy consumption trends in these devices up until 2020.

P. Grover, P.; K. Woyach, and A. Sahai, “Towards a Communication-Theoretic Understanding of System-Level Power Consumption,” IEEE JSAC, Special Issue on Energy-Efficient Wireless Communications, vol. 29, no. 8, pp. 1744 - 1755, Sept. 2011
The authors give a theoretical point of view on how to minimize the total power in a communication system. This article provides a well-investigated theoretical framework that considers the required decoding power as well as the transmit power. The model is examined from two perspectives – for an isolated point-to-point link, and a collection of interfering non-cooperating links.

P. Mahadevan, P. Sharma, S. Banerjee, P. Ranganathan, “A Power Benchmarking Framework for Network Devices”, Lecture Notes in Computer Science, vol. 5550, p.795, 2009
An important property of any communications device is its capability to scale energy consumption according to the current traffic load. This paper studies a number of wired routers to assess their energy consumption properties at different traffic loads to assess their relative efficiency. The paper also defines a novel metric called energy proportionality index (EPI) which is a simple measure to show how effectively a particular device can scale its energy consumption with traffic load.

B. Wang, S. Singh, “Computational Energy Cost of TCP”, INFOCOM 2004, Vol.2, p.785, 2004
The authors perform measurements on three different systems and two different platforms to study the energy cost of TCP (Transmission Control Protocol). They analyze these measurements for separate TCP functions at both the sender and receiver. Then, some software approaches are presented to re- duce the energy cost of TCP processing by between 20% and 30% in most cases. These results can be used by researchers to study node-level energy cost models and the energy consumption in wireless networks including.

M. Gupta, S. Singh, “Greening of the Internet”, ACM SIGCOMM 2003, p.19, 2003
This paper is a premier work on studying the energy consumption of networking devices in the internet, such as Hubs, switches, and Routers, and how to modify the already deployed architectures and protocols in the internet to save energy in these devices. The authors first discuss why it is important to consider the energy consumption of networking devices in the internet. Next, identifying “sleeping” technique as the most appropriate way of energy conservation, new protocols followed by necessary architecture changes are suggested to put more networking devices into sleep at a given time.

A. A. Nasir, X. Zhou,  S. Durrani, and R. A. Kennedy, “Relaying Protocols for Wireless Energy Harvesting and Information Processing”, IEEE Trans. Wireless Commun., vol. 12, no. 7, pp. 3622 - 3636, Mar. 2013
For an amplify-and-forward (AF) relaying network, two different relaying protocols are studied in this paper to concurrently harvest energy and process information at the relay. The relay node harvests from RF signals and using that harvested energy, it forwards information from source to destination node. The paper derives the ergodic capacity and outage probability expressions. By numerical analysis, this paper also gives some practical insights into system design parameters, such as energy harvesting time, power splitting ratio, source transmission rate, source to relay distance, noise power, and energy harvesting efficiency.

X. Zhou, R. Zhang, and C. K. Ho, “Wireless Information and Power Transfer: Architecture Design and Rate-Energy Tradeoff,” IEEE Trans. Comm., vol. 61, no. 11, pp. 4754-4767, Nov. 2013
The paper proposes a general receiver operation, namely, dynamic power splitting (DPS), which splits the received signal with adjustable power ratio for energy harvesting and information decoding, separately. Three special cases of DPS are investigated. The paper proposes two types of practical receiver architectures, namely, separated versus integrated information and energy receivers. The integrated receiver integrates the front-end components of the separated receiver, thus achieving a smaller form factor. The rate-energy tradeoff for the two architectures are characterized by a so-called rate-energy region. The optimal transmission strategy is derived to achieve different rate-energy tradeoffs.

L. Venturino, A. Zappone, C. Risi, and S. Buzzi, “Energy-Efficient Scheduling and Power Allocation in Downlink OFDMA Networks With Base Station Coordination,”  IEEE Trans. Wireless Commun., vol.14, no. 1, pp. 1-14, Jan. 2015
This paper focuses on energy-efficient resource allocation for downlink transmissions in an orthogonal frequency division multiple access (OFDMA) system. It optimizes the power allocation and scheduling in a cluster of coordinated base stations. This paper shows that maximizing energy efficiency implies maximizing spectral efficiency for small values of maximum transmit power.

Y. Yao, Q. Cao, and A. V. Vasilakos, “EDAL: An Energy-Efficient, Delay-Aware, and Lifetime-Balancing Data Collection Protocol for Heterogeneous Wireless Sensor Networks,” IEEE/ACM Trans. Netw., vol. 23, no. 3, pp. 810-823, Jun. 2015
The work in this paper stems from the authors’ insight that recent research efforts on open vehicle routing (OVR) problems are based on similar assumptions and constraints compared to sensor networks. Therefore, it may be feasible that one could adapt these techniques in such a way that they will provide valuable solutions to certain tricky problems in the wireless sensor network (WSN) domain. To demonstrate that this approach is feasible, the authors develop one data collection protocol called EDAL, which stands for Energy-efficient Delay-aware Lifetime-balancing data collection. The algorithm design of EDAL leverages one result from OVR to prove that the problem formulation is inherently NP-hard. The authors develop EDAL to be closely integrated with compressive sensing.

C. Fang, F. R. Yu, T. Huang, J. Liu, and Y. Liu, “A Survey of Green Information-Centric Networking: Research Issues and Challenges,”  IEEE Commun. Surveys Tuts., vol. 17, no. 3, pp. 1455-1472, Third Quarter 2015
To better cope with the Internet usage shift from host-centric end-to-end communication to receiver-driven content retrieval, innovative information-centric networking (ICN) architectures have been proposed. With the explosive increase in global network traffic, the energy efficiency issue in ICN is a growing concern. A number of approaches have been proposed to address the energy-efficiency issue in ICN. In this paper, the authors present a brief survey on some of the works that have been already done to achieve green ICN and discuss some research issues and challenges. They identify several important aspects of green ICN, i.e., overview, energy efficiency metrics, network planning, enabling technologies, and challenges.

C. Liu, B. Natarajan, and H Xia, “Small Cell Base Station Sleep Strategies for Energy Efficiency”, IEEE Trans. Veh. Technol., vol. 65, no. 3, pp. 1652-1661, March 2016
Using a stochastic geometry-based heterogeneous cellular network (HCN) model, the authors of this paper derive coverage probability, average achievable rate, and energy efficiency (EE) in heterogeneous K-tier wireless networks with different sleep modes for small cells. They try to maximize EE under a random sleeping policy and a strategic sleeping policy, with constraints on both coverage probability and wake-up times. Due to the nonconvexity of EE, the authors propose an alternative low-complexity near-optimal solution by maximizing the lower bound of EE. They use an alternating iterative approach to solve the resulting multivariable optimization problem.

G. Han, J. Jiang, M. Guizani, J. J. P. C Rodrigues, “Green Routing Protocols for Wireless Multimedia Sensor Networks,” IEEE Wireless Commun., vol. 23, no. 6, pp. 140-146, Nov. 2016
This paper presents a detailed survey of existing routing protocols for wireless multimedia sensor networks (WMSNs), which are classified into two categories based on network structures. The performance of existing routing protocols is compared. Future research issues of green routing protocols in WMSNs are presented and discussed.

P. Somavat, V. Namboodiri, “Energy Consumption of Personal Computing Including Portable Communication Devices”, Journal of Green Engineering, Vol.1, No.4, p.447, 2011
This paper presents a detailed investigation of the overall energy consumption of computing devices at 2010, looking at mobile devices such as mobile phones and laptops as well as the energy consumption of network side including internet connections, data centers and desktop computers. They also discuss their results in the broader context of total energy consumption in different countries and provide recommendations for improving energy saving in future devices and networks.

B. Puype, W. Wereecken, D. Colle, M. Pickavet, P. Demeester, “Multilayer traffic engineering for energy efficiency”, Photonic Network Communications, Apr. 2011, DOI 10.1007/s11107-010-0287-6
This paper investigates how multilayer traffic engineering helps in improving network energy efficiency, and how the power requirement in the network can be modeled for the multilayer traffic engineering (MLTE) algorithm. Then the paper discuss two case studies where the merits of MLTE for energy efficiency are shown.

K. Hinton, J. Baliga, M. Feng, R. Ayre, R. Tucker, “Power Consumption and Energy Efficiency of the Internet”, IEEE Network, March/April, p.6, 2011
An excellent introduction and high level overview of the main energy issues for the data networks that make up the Internet including access and core technologies.

J. Baliga, R. Ayre, K. Hinton, W. Sorin, R. Tucker, “Energy Consumption in Optical IP Networks”, IEEE/OSA Jour. Lightwave Technol., vol.27, no.13, p.2391, 2009
First detailed bottom up approach to understanding energy use in communication networks considering wireline networks from access to the core.

R. Tucker, R. Parthiban, J. Baliga, K. Hinton, R. Ayre, W. Sorin, “Evolution of WDM Optical IP Networks: A Cost and Energy Perspective”, IEEE/OSA Jour. Lightwave Technol. vol.27, no.3, p.243, 2009
This paper reviewed technologies and architectures for wavelength-division multiplexing (WDM) optical IP networks from the viewpoint of capital expenditure and network energy consumption. The paper showed how requirements of the low cost and low energy consumptions could influence the choices of switching technologies.

D. Kilper, K. Guan, K. Hinton, R. Ayre, “Energy Challenges in Current and Future Optical Transmission Networks”, Proc. IEEE, vol.100, no.5, p.1168 2012
Provides an overview of energy use in optical systems for core networks and describes trends and research related to energy and scaling of optical networks.

A. Dejonghe, B. Bougard, S. Pollin, J. Craninckx, A. Bourdoux, L. Ven der Perre, and F. Catthoor, "Green reconfigurable radio systems," IEEE Signal Processing Magazine, vol. 24, no. 3, pp. 90-101, May 2007
The authors present the concept of green reconfigurable radio system as a flexible energy-efficient alternative to overcome spectrum scarcity and mitigate the growing gap between the available battery energy and the rapidly increasing energy requirements of future radios. An energy-aware cross-layer radio management framework is also presented for different case studies to show the gains achieved by cross-layer optimization and problem partitioning. The Software Defined Radio and its role in enabling Cognitive Radio are also discussed.

Amor Nafkha, Pierre Leray, Yves Louet, and Jacques Palicot, “Moving a Processing Element from Hot to Cool Spots: Is This an Efficient Method to Decrease Leakage Power Consumption in FPGAs?,” the Chapter 8 of "Green Communications-Theoretical Fundamentals, Algorithms and Applications, edited by J. Wu, S. Rangan, and H. Zhang, CRC Press, September 2012
This book chapter is dedicated to the significant implementation issue of leakage power consumption in FPGA systems. In Particular, this chapter has heavily focused on FPGA’s temperature and static power consumption, possibility to move the Processing Element from a hot spot to a cooler one, and dynamic power consumption management using DPR (dynamic partial reconfiguration), so as to reduce the leakage power consumption of the FPGA systems.

J. Joung, C. K. Ho, K. Adachi, and S. Sun, “A Survey on Power-Amplifier-Centric Techniques for Spectrum- and Energy-Efficient Wireless Communications,” IEEE Commun. Surveys Tuts., vol. 17, no. 1, 315-333, First Quarter 2015
This paper provides a survey on techniques to improve the spectrum and energy efficiency of wireless communication systems. Recognizing the fact that power amplifier (PA) is one of the most critical components in wireless communication systems and consumes a significant fraction of the total energy, the authors take a bottom-up approach to focus on PA-centric designs. In the first part of the survey, fundamental properties of the PA, such as linearity and efficiency are introduced. Next, the detrimental effects of the signal non-linearity and power inefficiency of the PA on the spectrum efficiency (SE) and energy efficiency (EE) of wireless communications are introduced. In the last part, known mitigation techniques from three perspectives are surveyed: PA design, signal design and network design.

H. Matthews, T. Morawski, A. Nagengast, G. O’Reilly, D. Picklesimer, R. Sackett, P. Wu, “Planning Energy-Efficient and Eco-Sustainable Telecommunications Networks”, Bell Labs Technical Journal, vol.15, no.1, p.215, 2010
A detailed overview of energy efficiency issues in future communications networks is described and presented. The paper addresses technical means to save energy as well as investigating alternative energy sources such as solar or wind. The paper also develops a simple business model to show the financial impact of energy savings on a network operator.

Y. Chen, S. Zhang, S. Xu, G. Li, “Fundamental Trade-offs on Green Wireless Networks” IEEE Communications Magazine, June, p.30, 2011
A significant work proposing a framework for green radio research and integrating the fundamental issues that are currently dispersed. Using four fundamental tradeoffs, namely deployment efficiency-energy efficiency, spectrum efficiency-energy efficiency, bandwidth-power, and delay-power tradeoffs, the authors demonstrate how key network performance/cost indicators are tied together. 

G. Auer, V. Giannini, I. Godor, P. Skillermark, M. Olsson, M. Imran, D. Sabella, M. Gonzalez, O. Blume, A. Fehske, “How Much Energy Is Needed to Run a Wireless Network?”, IEEE Wireless Communications, vol. 49, no. 6, October, 2011
In this important work, within the Energy Aware Radio and Network Technologies (EARTH) project, a general energy efficiency evaluation framework (E3F) is developed to quantify the energy efficiency for operation of cellular radio networks. E3F stands out among existing energy efficiency evaluation schemes by taking into account various base station types, as well as long term traffic models and large scale deployment models.

A. Fehske, G. Fettweis, J. Malmodin, G. Biczok, “The Global Footprint of Mobile Communications” The Ecological and Economic Perspective”, IEEE Communications Magazine, August, p.55, 2011
This is an important paper in which the carbon footprint of mobile communication systems is comprehensively classified and quantified. The ecological and economic implications of this carbon footprint are also discussed. It is predicted in this paper that three orders of magnitude more traffic can be supported with the same energy consumption as of today, if the technologies designed to reduce the energy consumption are implemented quickly.

J. Baliga, R. Ayre, K. Hinton, R. Tucker, “Energy Consumption in Wired and Wireless Access Networks”, IEEE Communications Magazine, vol. 49, no. 6, June 2011
This article presents a detailed all-inclusive analysis of energy consumption in various representative wired and wireless access networks, which includes the energy consumption of DSL, HFC networks, passive optical networks, fiber to the node, point-to-point optical systems, UMTS (W-CDMA), and WiMAX. In particular, this article also points out the advantage of future optical access networks holding the potential as one of the most energy-efficient access technologies.

D.Q. Feng, C.Z. Jiang, G.B. Lim, L. J. Cimini, Jr., G. Feng, and G. Y. Li, “A Survey of Energy-Efficient Wireless Communications”, IEEE Communications Surveys and Tutorials, vol. 15, no. 1, 2013, pp. 167 - 178
This is one of the very early introductive papers that provides a comprehensive survey covering various broad aspects of energy-efficient wireless communications and networks, which first outlines the technical roadmaps of several representative international projects for energy-efficient wireless networks and then introduces the state-of-the-art research on energy-efficient wireless networks including energy-efficiency metric, network deployment strategies, network resource management, relay and cooperative communications, MIMO and OFDM technologies, as well as cross-layer optimizations for developing energy-efficient wireless networks.

A. Bianzino, C. Chaudet, D. Rossi, J. Rougier, “A Survey of Green Networking Research”, IEEE Communications Surveys and Tutorials, vol.14, no.1, pp. 3-20, 2012
As a comprehensive survey on green networking research, the authors focus on surveying the previous research on reducing the energy consumption in the wired networks. The article discusses four main techniques to reduce the energy waste including Adaptive Link Rate, Interface-Proxying, Energy-Aware Infrastructure, and Energy-Aware Applications. It also provides the open problems to each technique as well as a further perspective for research.

Y. Zhang, P Chowdhury, M. Torniatore, B. Mukerjee, “Energy Efficiency in Telecom Optical Networks”, IEEE Communications Surveys and Tutorials, vol.12, no.4, pp. 441, 2010
This is a very comprehensive survey on research activities for improving energy efficiency in optical networks. It first explained the energy issues in core, metro, and access network domains and provided a survey on the standardization efforts for making optical networks be more energy-efficient. The detailed technologies for designing green core, metro and access networks were summarized afterwards. This paper is a one-stop reference for energy-efficient optical networks.

R. Bolla, R. Bruschi, F. Davoli, F. Cucchietti, “Energy Efficiency of the Future Internet: A Survey of Existing Approaches and Trends in Energy-Aware Fixed Network Infrastructures”, IEEE Communications Surveys and Tutorials, vol.13, no.2, p.223, 2011
This paper provided a survey on existing technologies for designing energy-aware fixed network infrastructures, discussed the reasons for energy wastes in current network infrastructures, explained the concepts for low-energy networking from different perspectives, and also forecasted green technologies in future Internet.

J. Baliga, R. Ayre, K. Hinton, R. S. Tucker, "Architectures for Energy Efficient IPTV Networks" in Proc. OFC/NFOEC, 2009
Pioneering analysis of the energy trade-off between transport and storage in content distribution.

L. Chiaraviglio, M. Mellia, F. Neri, “Reducing power consumption in backbone networks” in Proc. IEEE ICC 2009.
This is an important work on reducing power consumptions in backbone networks by switching off network nodes and links strategically. The paper proved that the problem itself falls in the class of capacitated multi-commodity flow problems and proposed a few heuristics to solve it.

D. Kilper, et al., "Power Trends in Communication Networks," IEEE J. Sel. Top. Quantum Electron., vol. 17, no. 2, p. 275, 2011.
A detailed bottom up assessment of commercial wireline and wireless network energy trends using a transaction based service model.

F. Richter, A. Fehske, and G. Fettweis, "Energy efficiency aspects of base station deployment strategies for cellular networks," in Proc. IEEE Vehicular Technology Conference Fall (VTC 2009-Fall), 2009
This paper provides a detailed mathematical model that demonstrates that the choice of cell size has a significant impact on the energy consumption of a wireless network. Their results suggest that for a given network there is an optimal cell size that minimizes energy consumption.

L. Correia, D. Zeller, O. Blume, D. Ferling, Y. Jading, I. Godor, G. Auer, and L. Van der Perre, "Challenges and enabling technologies for energy aware mobile radio networks," IEEE Communications Magazine, vol. 48, pp. 66-72, November 2010
This is one of the early papers presenting a holistic approach for energy efficient mobile radio networks. The authors describe a framework for energy efficiency evaluation, identifying the levels that need to be addressed, namely, component level, link level and network level.

Z. Niu, Y. Wu, J. Gong, and Z. Yang, "Cell zooming for cost-efficient green cellular networks," IEEE Communications Magazine, vol. 48, no. 11, pp. 74-79, 2010
The concept of adjusting cell sizes by varying transmission power levels to match traffic loads is investigated in this paper. The key contribution is to show that by adjusting the transmit power, a wireless network can provide good coverage for high traffic conditions and save significant energy consumption under lower traffic conditions by reducing base station transmit power or switching them off (sleep mode).

C. Han, T. Harrold, S. Armour, I. Krikidis, S. Videv, P. Grant, H. Haas, J. Thompson, I. Ku, C. Wang, et al., "Green radio: radio techniques to enable energy-efficient wireless networks," IEEE Communications Magazine, vol. 49, no. 6, pp. 46-54, 2011
This is an important paper that describes the approach being taken in the Mobile VCE project to study novel approaches to reducing the energy consumption of wireless links, particularly in improving the design and operation of wireless base stations.

B. Badic, T. O'Farrrell, P. Loskot, and J. He, "Energy efficient radio access architectures for green radio: Large versus small cell size deployment," in IEEE Vehicular Technology Conference Fall (VTC 2009-Fall), 2009, pp. 1-5, Sept. 2009
The authors study the relation between the energy consumption performance and reducing the cell size in cellular radio access networks. Energy consumption ratio and energy consumption gain are used to evaluate this performance when the cell size is reduced for a certain user density and service area. They investigate two different architectures where sleep mode is used in one of them along with a small-cell deployment. These two architectures aim to increase the energy consumption gain and reduce energy consumption ratio while maintaining a given Quality-of-Service.

S. Zhou, J. Gong, Z. Yang, Z. Niu, and P. Yang, "Green mobile access network with dynamic base station energy saving," in Proc. ACM MobiCom, vol. 9, 2009
This is one of the very early papers on base station (BS) energy saving issues within the mobile cellular access networks, which deals with dynamically turning off certain BSs when the network traffic is low and implements the centralized and decentralized power saving algorithms while paying specific attention to the cellular coverage guarantee.

E. Oh, B. Krishnamachari, X. Liu, and Z. Niu, "Toward dynamic energy-efficient operation of cellular network infrastructure," IEEE Communications Magazine, vol. 49, no. 6, pp. 56-61, 2011
This is a significant work which discusses how dynamic operation of base stations can contribute to significant energy savings in cellular networks. The idea is to turn off redundant base stations when they are under low traffic condition. Some open issues associated with implementing energy efficient dynamic operation of base stations are also discussed.

Z. Hasan, H. Boostanimehr, and V. Bhargava, "Green cellular networks: A survey, some research issues and challenges," IEEE Communications Surveys Tutorials, vol. 13, no. 4, pp. 524-540, 2011
This is a premier work identifying the methods to improve the power efficiency of cellular networks while also exploring some research issues and challenges and suggesting techniques to enable an energy efficient or “green” cellular network. The authors also present a research vision to make future technologies such as cognitive radio and cooperative relaying more energy efficient.

 M. Marsan and M. Meo, "Energy efficient management of two cellular access networks," ACM SIGMETRICS Performance Evaluation Review, vol. 37, no. 4, pp. 69-73, 2010
The article addresses an interesting energy-aware cooperative management technique for two-operator cellular access networks. It proposes to switch off the networks whose traffic is very low while allowing their users to use one of the cooperating networks as roaming customers. The authors show that with different switching patters a substantial amount of energy could be saved.

K. Chen, C. Cui, Y. Huang, and B. Huang, "C-RAN: A Green RAN Framework," the Chapter 11 of Green Communications-Theoretical Fundamentals, Algorithms and Applications, edited by J. Wu, S. Rangan, and H. Zhang, CRC Press, September 2012
From industrial perspective, this book chapter introduces the motivation, the concept, advantages, challenges, framework, architecture, and up-to-date research and deployment status of C-RAN (Centralized processing, Cooperative radio, Cloud, and Clean infrastructure Radio Access Network) approaches, first announced by China Mobile Communications Corporation in April 2010. C-RAN offers a new paradigm in base stations architecture that aims to reduce the number of cell sites while increasing the base station deployment density. The C-RAN concept lowers operating expenses and simplifies the deployment process. By centralizing all the active electronics of multiple cell sites, at one location, energy, real-estate and security costs may be minimized.

P. Rost and G. Fettweis, , “Green communications in cellular networks with fixed relay nodes,” Chapter 11 in Cooperative Cellular Wireless Network, Cambridge, 2011.
This is a leading work which identifies relaying technique as a candidate to increase the spatial frequency reuse in cellular networks in order to meet higher data rate demands while reducing the energy consumption level.

R. Bolla, F. Davoli, R. Bruschi, K. Christensen, F. Cucchietti, and S. Singh, "The potential impact of green technologies in next-generation wireline networks: Is there room for energy saving optimization?," IEEE Communications Magazine, vol. 49, no. 8, pp. 80-86, August 2011
According to results from ECONET European project, this paper analyzes the feasibility of energy efficiency improvements in green wireline networking through adapting the performance and energy absorption to meet actual workload and operational requirements.

K. Son, H. Kim, Y. Yi, and B. Krishnamachari, "Base station operation and user association mechanisms for energy-delay tradeo s in green cellular networks," IEEE Journal on Selected Areas in Communications, vol. 29, no. 8, pp. 1525-1536, 2011
Facing the ever-growing energy-efficiency challenge of wireless cellular networks, a theoretical framework for base-station (BS) energy saving has been thoroughly developed in this paper, which integrates the dynamic BS operation mechanisms with the relevant mobile terminal/user association processes, in order to realize a total network cost minimization allowing for a flexible tradeoff between the low-level performance and the energy consumption while obtaining optimal energy-efficient user association.

G. Li, Z. Xu, C. Xiong, C. Yang, S. Zhang, Y. Chen, and S. Xu, "Energy-efficient wireless communications: tutorial, survey, and open issues," IEEE Wireless Communications, vol. 18, pp. 28-35, December 2011
An analysis of the basic mathematical trade-offs concerning energy efficiency are explored and discussed. The paper also studies how multiple antenna links and cooperative or relay communications can improve the energy efficiency of wireless communications systems.

I. Humar, X. Ge, L. Xiang, M. Jo, M. Chen, and J. Zhang, "Rethinking energy efficiency models of cellular networks with embodied energy," IEEE Network Magazine, vol. 25, no. 2, pp. 40-49, March-April 2011
Unlike most of research in literature, which only considers the operating energy, the authors discuss the effect of embodied energy on the energy efficiency of cellular networks. It is shown that the embodied energy accounts for a significant amount of the energy waste and cannot be neglected when compared to the operating energy. This encourages researches, operators, and manufacturers to reconsider their models for base station energy consumption.

Tomas Edler and Susanne Lundberg, “Energy efficiency enhancements in radio access networks”, Ericsson Review, No 1, 2004
One of the first publications to study the energy consumption of wireless radio base stations. It drew attention to the inefficiencies in base station design and to the importance of modeling of base station components.

Meshkati, F., Poor, H.V. ; Schwartz, S.C, “Energy-Efficient Resource Allocation in Wireless Networks”, IEEE Signal Processing Magazine, May 2007, vol 24, no. 3, pp 58-68.
This paper explores energy efficient resource allocation strategies with a focus on the uplink from mobile terminals to base stations. The paper considers a variety of resource allocation and power control strategies, including those based around game theory concepts.

C.E. Jones, K.M. Sivalingam, P. A. Agrawal and J.Y.H. Cheng Chen, “A Survey of Energy Efficient Network Protocols for Wireless Networks”, Wireless Networks 7, 343–358, 2001
As one of the pioneering works on energy efficiency in wireless networks, [8] provides a comprehensive survey of recent research in energy efficient and low-power design within all layers of the protocol stack of the wireless networks. Besides the energy savings at the physical layer, the article focuses on the higher layers (starting from the data link layer up to the application layer). The article shows the importance of focusing on all the protocol layers instead of the typical power conservation research at the physical layer only in which most of energy savings have been already achieved.

Arnold, O., Richter, F. ; Fettweis, G. ; Blume, O., “Power consumption modeling of different base station types in heterogeneous cellular networks”, Future Network and Mobile Summit, 2010, 16-18 June 2010, pp 1-8.
Modelling the relationship between transmitted radio frequency power and the overall power consumption of radio base stations is important for analyzing the overall energy consumption of wireless networks. This is an important paper that studies these issues in detail and proposes realistic power consumption models.

L. Le, D. Niyato, E. Hossain, D. Kim, D. Hoang, "QoS-Aware and Energy-Efficient Resource Management in OFDMA Femtocells," IEEE Transactions on Wireless Communications, vol. PP, no. 99, pp.1-15, 2013
As one of the premier works on energy-efficient design of two-tier cellular wireless networks, the authors develop a unified mathematical model to solve the problem of cross-layer resource allocation and admission control for OFDMA-based two-tier femtocell networks. In the presence of both co-tier and cross-tier interferences, this model considers the Quality-of-Service requirements of the macrocell and femtocell users in terms of average data rates and blocking probabilities. They propose a distributed power adaptation algorithm that improves the energy efficiency of the system.

Hoydis, J.; Kobayashi, M.; Debbah, M., "Green Small-Cell Networks," IEEE Vehicular Technology Magazine, vol. 6, no. 1, pp.37-43, March 2011
As a more economical and energy-efficient alternative to increasing the density of base stations to meet the expected traffic demands in future networks, the authors introduce the concept of green small-cell networking. The challenges related to the optimal system design and a large system analysis are presented in this article. This is an important work in the area of green cellular wireless networks.

Fallahi, A.; Hossain, E., "Distributed and Energy-Aware MAC for Differentiated Services Wireless Packet Networks: A General Queuing Analytical Framework," IEEE Transactions on Mobile Computing, vol.6, no.4, pp.381-394, April 2007
The authors develop a novel analytical model to analyze the trade-off between the Quality-of-Service and the energy efficiency of a distributed and energy-aware wireless medium access control (MAC) protocol considering ser- vice differentiation between two different types of services. They take the impact of non-ideal wireless channel condition as well as the bursty traffic arrival process and non-saturation MAC buffer state into account. For this general model, the authors present some applications to integrate more realistic considerations into it.

Tao Chen, Yang Yang, Honggang Zhang, Haesik Kim, and Kari Horneman, "Network Energy Saving Technologies for Green Wireless Access Networks," IEEE Wireless Communications, Feature Topics Issue on Green Radio Communication Networks, vol. 18, no. 5, pp. 30-38, October 2011
This article presents a timely overview of the network energy saving studies within the framework of 3GPP LTE standardization activities. In particular, by classifying the network energy saving technologies into the time, frequency, and spatial domains, this article strengthens the whole-scale networking solutions involving multiple networks/systems as the most promising technologies toward green wireless access networks.

S. Aleksic, "Analysis of Power Consumption in Future High-Capacity Network Nodes", IEEE/OSA Journal of Optical Communications and Networking, vol. 1, no. 3, pp. 245-258, August 2009
As an important work on improving energy-efficiency in wireless networks, the authors address the significance of exploiting the dependencies between different protocol layers of ad hoc wireless networks in designing these layers when there is a constraint on the energy. The challenges and applications of ad hoc wireless networks as well as cross-layer design are also presented. The article summarizes the design issues at the radio link, network, and application layers.

A. J. Goldsmith and S. B. Wicker, “Design Challenges for Energy Constrained Ad Hoc Wireless Networks,” IEEE Wireless Communications. Mag., vol. 9, no. 4, pp. 8–27, Aug. 2002.
As an important work on improving energy-efficiency in wireless networks, the authors address the significance of exploiting the dependencies between different protocol layers of ad hoc wireless networks in designing these layers when there is a constraint on the energy. The challenges and applications of ad hoc wireless networks as well as cross-layer design are also presented. The article summarizes the design issues at the radio link, network, and application layers.

E. Jorswieck, H. Boche, S. Naik, "Energy-Aware Utility Regions: Multiple Access Pareto Boundary," IEEE Trans. Wireless Communications, vol. 9, no. 7, pp. 2216-2226, July 2010
Based on the difference of the individual capacity and a weighted power penalty term, this paper puts forward a novel definition and the relevant model of energy-aware utility function for energy-efficient resource allocation and transmit optimization in the multiuser communication systems, for which the energy-aware utility region and the closed form expression for its Pareto boundary, the maximum sum utility problem in MIMO multiple-access channel, and the relevant efficient algorithm have been theoretically analyzed.

J. Wu, “Green Wireless Communications: From Concept to Reality,” IEEE Wireless Communications, vol. 19 , no. 4,, August 2012
From industry perspective, this article provides a concise and high-level overview in green wireless communications on the relevant statuses and recent advances of the research and development, which not only summarizes the broad topics in general green wireless communications but also systematically covers various typical aspects of energy-efficient cellular system infrastructure, energy efficiency approaches for base station equipment and environmental temperature control, as well as state-of-art energy efficiency efforts in industrial sectors like 3GPP and Cloud RAN.

Q. Zhao and L. Tong, “Energy Efficiency of Large-scale Wireless Networks: Proactive Versus Reactive Networking”, IEEE JSAC, vol. 23, no. 5, May 2005
This paper presents an analytic approach to characterize energy consumption of large-scale wireless networks including ad-hoc sensor networks, focusing on the total energy consumption of two representative networking scenarios (i.e. proactive and reactive networking), and specifically taking into account the energy consumption of nodes at various operating states like transmitting, listening, and sleeping mode.

E. Oh , K. Son, and B. Krishnamachari, “Dynamic Base Station Switching-On/Off Strategies for Green Cellular Networks,” IEEE Trans. Wireless Commun., vol. 12, no. 5, pp. 2126-2136, May 2013
The paper investigates dynamic base station (BS) switching to reduce energy consumption in wireless cellular networks. It formulates a general energy minimization problem pertaining to BS switching that is known to be a difficult combinatorial problem and requires high computational complexity as well as large signaling overhead. The paper proposes a practically implementable switching-on/off based energy saving algorithm (SWES) that can be operated in a distributed manner with low computational complexity. The paper proposes three other heuristic versions of SWES that use the approximate values of network-impact as their decision metrics. The algorithms reduce the total energy consumption up to 50-80%.

Y. S. Soh, Tony Q. S. Quek, M. Kountouris, and H. Shin, “Energy Efficient Heterogeneous Cellular Networks,” IEEE J. Sel. Areas Commun., vol. 31, no. 5, pp. 840-850, May 2013
This paper investigates the design and the associated tradeoffs of energy efficient cellular networks through the deployment of sleeping strategies and small cells. Using a stochastic geometry based model, it derives the success probability and energy efficiency in homogeneous macrocell (single-tier) and heterogeneous K-tier wireless networks under different sleeping policies. It formulates the power consumption minimization and energy efficiency maximization problems, and determines the optimal operating regimes for macrocell base stations.

J. Wu, Y. Zhang, M. Zukerman, and E. K.-N. Yung, “ Energy-Efficient Base-Stations Sleep-Mode Techniques in Green Cellular Networks: A Survey,” IEEE Commun. Surveys Tuts., vol. 17, no. 2, pp. 803-826, Second Quarter 2014
In this survey, the authors first present facts and figures that highlight the importance of green mobile networking and then review existing green cellular networking research with particular focus on techniques that incorporate the concept of the “sleep mode” in base stations. This approach takes advantage of changing traffic patterns on a daily or weekly basis and selectively switches some lightly loaded base stations to low energy consumption modes. As base stations are responsible for the large amount of energy consumed in cellular networks, these approaches have the potential to save a significant amount of energy. However, it is noticed that certain simplifying assumptions made in the published papers introduce inaccuracies. This review discusses these assumptions and show that considering this effect may lead to noticeably lower benefit than in models that ignore this effect.

R. Q. Hu and Y. Qian, “An Energy Efficient and Spectrum Efficient Wireless Heterogeneous Network Framework for 5G Systems,” IEEE Commun. Mag., vol. 52, no. 5, pp. 94-101, May 2014
In this article the authors explore a system framework of cooperative green heterogeneous networks for 5G wireless communication systems. They first survey the state-of-the-art on spectrum efficiency (SE), energy efficiency (EE), and quality of service (QoS) based mobile association, multi-layer interference management and power control, network wide cooperation and dynamic resource allocation for heterogeneous wireless networks. They also present the system framework of cooperative green heterogeneous networks, which aims at balancing and optimizing SE, EE, and QoS in heterogeneous wireless networks. They discuss the design principles and show some preliminary performance results on the tradeoffs among SE, EE, and QoS. Finally, the authors identify the technical challenges that remain in the cooperative green heterogeneous network design.

K. Davaslioglu and E. Ayanoglu, “Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks,” IEEE Commun. Surveys Tuts., vol. 16, no. 4, pp. 2065-2091, Fourth Quarter 2014
The authors describe the sources of the inefficiencies in cellular wireless networks. First, results of the studies on how much Carbon footprint such networks generate are presented. The authors also discuss how much more mobile traffic is expected to increase so that this Carbon footprint will even increase tremendously more. They then discuss specific sources of inefficiency and potential sources of improvement at the physical layer, as well as at higher layers of the communication protocol hierarchy. They consider most of the energy inefficiency in cellular wireless networks is at the base stations, and thus, they discuss multi-tier networks and point to the potential of exploiting mobility patterns in order to use base station energy judiciously. They then investigate potential methods to reduce this inefficiency and quantify their individual contributions.

S. Buzzi, C.-L. I, T. E. Klein, H. V. Poor, C. Yang, and A. Zappone, “A Survey of Energy-Efficient Techniques for 5G Networks and Challenges Ahead,” IEEE J. Sel. Areas Commun., vol. 34, no. 4, pp. 697-709, Apr. 2016
This survey provides an overview of energy-efficient wireless communications, reviews seminal and recent contribution to the state-of-the-art and discusses the most relevant research challenges to be addressed in the future.

S. Zhang, Q. Wu, S. Xu, G. Y. Li, “Fundamental Green Tradeoffs: Progresses, Challenges, and Impacts on 5G Networks,” IEEE Commun. Surveys Tuts., vol. 19, no. 1, pp. 33-56, First Quarter, 2017
This paper provides a comprehensive overview on the extensive on-going research efforts and categorizes them based on the fundamental green tradeoffs. It focuses on research progresses of 4G and 5G communications, such as orthogonal frequency division multiplexing and non-orthogonal aggregation, multiple input multiple output, and heterogeneous networks. It discusses potential challenges and impacts of fundamental green tradeoffs.

Q. Wu, G. Y. Li, W. Chen, D. W. K. Ng, R. Schober, “An Overview of Sustainable Green 5G Networks,” IEEE Wireless Commun., vol. 24, no. 4, pp. 72-80, Aug. 2017
Various 5G techniques target the reduction of the energy consumption without sacrificing the quality of service. Meanwhile, energy harvesting technologies, which enable communication transceivers to harvest energy from various renewable resources and ambient radio frequency signals for communication have drawn significant interest from both academia and industry. In this article, the authors provide an overview of the latest research on both green 5G techniques and energy harvesting for communication. In addition, some technical challenges and potential research topics for realizing sustainable green 5G networks are also identified.

L. Wang, Y. Xiao, “A Survey of Energy-Efficient Scheduling Mechanisms in Sensor Networks”, Mobile Networks and Applications, October 2006, Volume 11, Issue 5, pp 723-740
This is a comprehensive survey on power consumption and energy saving issues in the field of sensor networks, with specific emphasis on various energy-efficient scheduling mechanisms. Corresponding to different typical sensor networking scenarios under the constraints of energy saving and limited lifetime, this survey provides in-depth yet panoramic description on a number of key aspects within sensors networks like sensors detection model, sensing area, transmission range, failure model, time synchronization, ability to obtain location and distance information, distributed non-hierarchical/hierarchical networks structure and sensor deployment strategy.

Devarajan, R.; Jha, S.C.; Phuyal, U.; Bhargava, V.K., "Energy-Aware Resource Allocation for Cooperative Cellular Network Using Multi-Objective Optimization Approach," IEEE Transactions on Wireless Communications, vol.11, no.5, pp.1797-1807, May 2012
This is a pioneering work to use multi-objective optimization approach to jointly optimize and keep a balance between the power consumption and throughput in a multiuser, multi-relay cooperative cellular system. In this paper, quality-of-service for the end users is guaranteed in terms of end-to-end signal-to-noise ratio using more realistic channel model assuming the presence of channel estimation errors. The authors also proposed an algorithm to enhance fairness among end users.

D. W. K. Ng, E. S. Lo, and R. Schober, “Energy-Efficient Resource Allocation in Multi-Cell OFDMA Systems with Limited Backhaul Capacity,” IEEE Trans. Wireless Commun., vol. 11, no. 10, pp. 3618 - 3631, Oct. 2012
This paper studies the resource allocation problem in a multi-cell orthogonal frequency division multiple access (OFDMA) system composed of cooperative base stations. It formulates the problem as a non-convex problem considering the limited backhaul capacity. Then it converts it into a subtractive form where in each iteration, a suboptimal semi-orthogonal user selection policy is computed. The paper also proves the zero duality gap using perturbation function and uses dual decomposition method to derive closed-form of the power allocation problem. Convergence and the trade-off between energy efficiency, network capacity, and backhaul capacity are shown via simulations.

S. Bayhan, and F. Alagoz, “Scheduling in Centralized Cognitive Radio Networks for Energy Efficiency,” IEEE Trans. Veh. Technol., vol. 62, no. 2, pp. 582-595, Feb. 2013
This paper focuses on scheduling in cognitive radio networks (CRNs) considering diversity among the queues of the cognitive radio users as well as channel capacity. It formulates a nonlinear integer programming (NLP) scheduling problem and provides an energy-efficient heuristic algorithm. The paper also studies important system performance metrics such as energy efficiency and successful transmission probability of the designed scheduler.

Y. Luo, J. Zhang, and K. B. Letaief, “Optimal Scheduling and Power Allocation for Two-Hop Energy Harvesting Communication Systems,” IEEE Trans. Commun., vol. 12, no. 9, pp. 4729-4741, Sep. 2013
This paper investigates the application of relaying to improve the performance of an energy-harvesting system composed of a harvesting source and a non-harvesting half-duplex relay. The key contribution of this paper is the application of directional water-filling (DWF) in two-hop systems and derivations of the main properties of the optimal solutions.

J. Tang, W. P. Tay, and T. Q. S. Quek, “Cross-Layer Resource Allocation with Elastic Service Scaling in Cloud Radio Access Network,” IEEE Trans. Commun., vol. 14, no. 9, pp. 5068 - 5081, Sep. 2015
This paper proposes a cross-layer model of resource allocation for a cloud radio access network (C-RAN) to minimize the power consumption in the system. After formulating the problem as a mixed-integer nonlinear programming (MINLP), it relaxes the original problem into an extended sum-utility maximization (ESUM) problem. To solve this, two approaches are given along with a low-complexity Shaping-and-Pruning (SP) algorithm with an objective to obtain a sparse solution. Simulation results show that the proposed resource allocation is more energy efficient compared to the greedy selection and successive selection algorithms.

M. Peng, K. Zhang, J. Jiang, J. Wang , and W. Wang, “Energy-Efficient Resource Assignment and Power Allocation in Heterogeneous Cloud Radio Access Networks,” IEEE Trans. Wireless Commun., vol. 64, no. 11, pp. 5275 - 5287, Nov. 2015
Heterogeneous cloud radio access network (H-CRAN) architecture is presented in this paper to improve spectral and energy efficiency of communications. This paper formulates the problem of user association with remote radio heads (RRHs) in this H-CRAN to mitigate inter-tier interference and improve energy efficiency. It also formulates an energy-efficient non-convex problem for resource assignment and power allocation. Closed-form expressions for energy-efficient resource allocation are obtained using Lagrange dual decomposition.

H. Wang, J. Wang, G. Ding, L. Wang, T. A. Tsiftsis, and P. K. Sharma, “Resource Allocation for Energy Harvesting-Powered D2D Communication Underlaying UAV-Assisted Networks,” IEEE Trans. Green Comm. Netw., vol. 2, no. 1, pp. 14-24, Mar. 2018
This paper investigates the resource allocation problem in a drone-assisted network where the drone itself acts as an energy source for device-to-device (D2D) pairs. It maximizes system throughput considering a harvest-transmit-store model, which is a non-convex problem. Using Lagrangian relaxation technique, this paper analytically shows the exclusiveness in the behavior of all D2D pairs at different time slots. The paper designs an efficient algorithm to solve this problem suboptimally where D.C. (difference of two convex functions) programming and golden section method are jointly used.

D. Miller, “Device Requirements for Optical Interconnects to Silicon Chips”, Proc. IEEE, vol.97, no.7, pp. 1166 - 1185, 2009
A clear and thorough analysis of the scalability and energy efficiency requirements for board and chip level interconnects and the corresponding targets for and potential of optical technologies.

R. Tucker, “The Role of Optics and Electronics in High-Capacity Routers” Jour Lightwave Technol. vol.24, no.12, pp. 4655 - 4673, 2006
This paper discussed the designing of high-capacity routers with the emphasis on the usages of optics and electronics. It also covered the energy-consumption problem and provided some ideas on how to improve the energy-efficiency of high-capacity routers.

R. Keys, “Power Dissipation in Information Processing”, Science, vol.168, p.796, 1970
An early classic paper comparing electronic processing energy limits with optics, pneumatics, and neurons.

U. Lee, I. Rimac, D. Kilper, V. Hilt, “Toward Energy-Efficient Content Dissemination”, IEEE Network, March/April, vol. 25, no. 2, pp.14-19, 2011
A review of content dissemination networks and analysis of the potential energy efficiency benefits.

R. Tucker, K. Hinton, “Energy Consumption and Energy Density in Optical and Electronic Signal Processing”, IEEE Photonics Journal, vol.3, no.5, p.812, 2011
This paper compared the energy consumption and energy density in optical and electronic signal processing, and provided some practical models for future research in these areas.

K. Hinton, G. Raskutti, P. Farrell, R. Tucker, “Switching Energy and Device Size Limits on Digital Photonic Signal Processing Technologies”, IEEE Jour. Quantum Electron., vol. 14, no. 3, pp. 938 - 945, 2008
This paper derived the relationship between the device size and power consumption of photonic signal processing devices through using device-specific models for photonic signal processing using semiconductor optical amplifiers, periodically poled lithium niobate, and highly nonlinear fibers.

R. Tucker, "Green Optical Communications -- Part I: Energy Limitations in Transport," IEEE J. Sel. Top. Quantum Electron., vol. 17, no. 2, pp. 261-274, 2011.
A detailed analysis of energy limitations for transport in optical communications considering key practical and fundamental constraints. First of a two part analysis that is essential reading for understanding energy limitations in optical networks.

R. Tucker, "Green Optical Communications -- Part 2: Energy Limitations on Networks," IEEE J. Sel. Top. Quantum Electron., vol. 17, no. 2, p. 261, 2011.
A detailed analysis of energy limitations for optical networks considering key practical and fundamental constraints. Second of a two part analysis that is essential reading for understanding energy limitations in optical networks.

K.-L. Lee, B. Sedighi, R. S. Tucker, H. Chow, and P. Vetter, "Energy Efficiency of Optical Transceivers in Fiber Access Networks," J. Opt. Comm. Netwking, vol. 4, no. 9, pp. 59-68, 2012.
This paper proposes a model on the power consumptions of different transceivers and demonstrates how various electronic and photonic technologies could help improve the energy efficiencies. Then it shows how the energy efficiency is related to the network topology.

A. V. Krishnamoorty, et al., "Progress in Low-Power Switched Optical Interconnects," IEEE J. Spec. Top. Quantum Electron., vol. 17, no. 2, pp. 357-376, 2011
A comprehensive review of the key progress and targets for optical devices and interconnects in terms of energy, bandwidth, and footprint.

A. Morea, et al., "Power Management of Optoelectronic Interfaces for Dynamic Optical Networks," in Proc. European Conference on Optical Communications, Geneva, 2011.
This paper proposed a protocol enhancement to manage the power state of optoelectronic interfaces in automatically reconfigurable optical networks. This paper proposed an enhancement of current GMPLS signaling protocol enabling the dynamic power management of optoelectronic devices in the optical layer.

K. Guan, D. C. Kilper, G. Atkinson, “Evaluating the Energy Benefit of Dynamic Optical Bypass for Content Delivery,” in Proc. IEEE INFOCOM Green Communications Workshop, 2011
Establishes the potential and metrics for using dynamic optical bypass to achieve energy efficiency including the trade-off between transmission and content storage.

R. S. Tucker, “Green Optical Communications—Part I: Energy Limitations in Transport,” IEEE J. Sel. Topics Quantum Electron., vol. 17, no. 2, pp. 245-260, March/April 2011
This is the first of two papers that explore the fundamental limits on energy consumption in optical communication systems and networks. The objective of these papers is to provide a framework for understanding how this growth in energy consumption can be managed. This paper (Part I) focuses on the energy consumption in optically amplified transport systems. A key focus of both papers is an analysis of the lower bound on energy consumption. This lower bound gives an indication of the best possible energy efficiency that could ever be achieved. The lower bound on energy in transport systems is limited by the energy consumption in optical amplifiers, and in optical transmitters and receivers. The performance of an optical transport system is ultimately set by the Shannon bound on receiver sensitivity, and depends on factors such as the modulation format, fiber losses, system length, and the spontaneous noise in optical amplifiers. Collectively, these set a lower bound on the number of amplifiers required, and hence, the amplifier energy consumption.

R. S. Tucker, “Green Optical Communications—Part II: Energy Limitations in Networks,” IEEE J. Sel. Topics Quantum Electron., vol. 17, no. 2, pp. 261-274, March/April 2011
This is Part II of a two-part paper that explores the fundamental limitations on energy consumption in optical communications. It explores the lower bound on energy consumption in optical switches and networks, analyzes the energy performance of a range of switching devices, and presents quantitative models of the lower bounds on energy consumption in these devices. These models are incorporated into a simple model of a global switched network and the lower bound on total network energy consumption is estimated.  The paper finds that the theoretical lower bounds on transport energy identified in Part I and the switching energy in this paper are more than three orders of magnitude lower than predicted by a “business-as-usual” analysis.

C. Kachris, K. Kanonakis, and I. Tomkos, ”Optical Interconnection Networks in Data Centers: Recent Trends and Future Challenges,” IEEE Commun. Mag., vol. 51, no. 9, pp. 39-45, Sep. 2013
This article provides an update on recent developments in the field of ultra-high capacity optical interconnects for intra data center network (intra-DCN) communication. Several recently proposed architectures and technologies are examined and compared, while future trends and research challenges are outlined.

X. Fan, W. Weber, L. Barroso, “Power Provisioning for a Warehouse-sized Computer”, Proc. ACM International Symposium on Computer Architecture, ISCA, 2007
This paper presents in-depth investigation and analyses on the basic characteristics of aggregate power usage in the scenario of large collections of computing servers for different classes of applications, which highlights the potential opportunities for maximizing the deployed power capacity usage within datacenters and provides power management schemes to reduce peak power and energy consumption.

A. Berl, E. Gelenbe, M. di Girolamo, G. Giuliani, H de Meer, M. Dang, K. Pentikousis, “Energy-Efficient Cloud Computing”, The Computer Journal, vol. 53, no. 7, p. 1045, 2010
This paper describes cloud computing as an inherently energy-efficient ICT technology for achieving significant energy savings, especially taking into account various key aspects of computing hardware, system operation and networking infrastructure in the context of cloud computing while identifying the relevant arising research challenges when such energy-saving techniques are applied in cloud computing environments.

J. Baliga, R. Ayre, K. Hinton, R. Tucker, “Green Cloud Computing: Balancing Energy in Processing, Storage, and Transport” Proc. the IEEE, vol. 99, no. 1, pp. 149-167, 2011
Seminal work analyzing the balance of network processing, storage, and transport from an energy perspective. Identifies key issues and determines metrics for energy efficient cloud computing.

J. Baliga, R. W. A. Ayre, K. Hinton, R. S. Tucker, “Green Cloud Computing: Balancing Energy in Processing, Storage, and Transport,” Proc. IEEE, vol. 99, no. 1, pp. 149-167, Jan. 2011
In this paper, the authors present an analysis of energy consumption in cloud computing. The analysis considers both public and private clouds, and includes energy consumption in switching and transmission as well as data processing and data storage. The authors show that energy consumption in transport and switching can be a significant percentage of total energy consumption in cloud computing. Cloud computing can enable more energy-efficient use of computing power, especially when the computing tasks are of low intensity or infrequent. However, under some circumstances cloud computing can consume more energy than conventional computing where each user performs all computing on their own personal computer.

E. Baccarelli, N. Cordeschi, A. Mei, M. Panella, M. Shojafar, and J. Stefa, “Energy-Efficient Dynamic Traffic Offloading and Reconfiguration of Networked Data Centers for Big Data Stream Mobile Computing: Review, Challenges, and a Case Study,” IEEE Netw., vol. 30, no. 2, pp. 54-61, March/April, 2016
This position paper formalizes the paradigm of big data stream mobile computing, discusses its most significant application opportunities, and outlines the major challenges in performing real-time energy-efficient management of the distributed resources available at both mobile devices and Internet-connected data centers. The performance analysis of a small-scale prototype is also included in order to provide insight into the energy vs. performance tradeoff that is achievable through the optimized design of the resource management modules. Performance comparisons with some state-of-the-art resource managers are provided.

J. Shuja, K. Bilal, S. A. Madani, M. Othman, R. Ranjan, P. Balaji, and S. U. Khan, “Survey of Techniques and Architectures for Designing Energy-Efficient Data Centers,” IEEE Syst. J., vol. 10, no. 2, pp. 507-519, Jun. 2016
In this survey, the authors discuss research issues related to conflicting requirements of maximizing quality of services (QoSs) (availability, reliability, etc.) delivered by the cloud services while minimizing energy consumption of the data center resources. The authors present the concept of inception of data center energy-efficiency controller that can consolidate data center resources with minimal effect on QoS requirements.  Software- and hardware-based techniques and architectures for data center resources such as server, memory, and network devices that can be manipulated by the data center controller to achieve energy efficiency are discussed.

M. Gursoy, D. Qiao, and S. Velipasalar, "Analysis of Energy Efficiency in Fading Channels Under QoS Constraints," IEEE Transactions on Wireless Communications, vol. 8, no. 8, pp. 4252-4263, August 2009.
This paper employed the effective capacity formulation, rather than the Shannon capacity, to fundamentally analyze the spectral efficiency-bit energy tradeoff in the low-power and wideband regimes under QoS constraints.

J.-M. Liang, J.-J. Chen, H.-H. Cheng, and Y.-C. Tseng, “An Energy-Efficient Sleep Scheduling With QoS Consideration in 3GPP LTE-Advanced Networks for Internet of Things,” IEEE J. Emerg. Sel. Topics Circuits Syst., vol. 3, no. 1, pp. 13-22, Mar. 2013
This paper addresses the discontinuous reception/transmission (DRX/DTX) optimization, by asking how to maximize the sleep periods of devices while guaranteeing their quality-of-service (QoS), especially on the aspects of traffic bit-rate, packet delay, and packet loss rate in Internet-of-Things (IoT) applications. Efficient schemes to optimize DRX/DTX parameters and schedule devices’ packets with the base station are proposed. The key idea of the schemes in the paper is to balance the impacts between QoS parameters and DRX/DTX configurations. Simulation results show that the schemes can guarantee traffic bit-rate, packet delay, and packet loss rate while saving energy of user equipment.

Z. Zhao, M. Peng, Z. Ding, W. Wang, and H. V. Poor, “Cluster Content Caching: An Energy-Efficient Approach to Improve Quality of Service in Cloud Radio Access Networks,” IEEE J. Sel. Areas Commun., vol. 34, no. 5, pp. 1207-1221, May 2016
In cloud radio access networks (C-RANs), a substantial amount of data must be exchanged in both backhaul and fronthaul links, which causes high power consumption and poor quality of service (QoS) experience for real-time services. To solve this problem, a cluster content caching structure is proposed in this paper, which takes full advantages of distributed caching and centralized signal processing. In particular, redundant traffic on the backhaul can be reduced because the cluster content cache provides a part of required content objects for remote radio heads (RRHs) connected to a common edge cloud. Tractable expressions for both effective capacity and energy efficiency performance are derived, which show that the proposed structure can improve QoS guarantees with a lower cost of local storage. Furthermore, the joint design of resource allocation and RRH association is optimized, and two distributed algorithms are accordingly proposed.

D. Grace, J. Chen, T. Jiang, and P. Mitchell, "Using Cognitive Radio to Deliver 'Green' Communications," in Proc. International Conference on Cognitive Radio Oriented Wireless Networks and Communications, 2009. CROWNCOM '09. 4th , June 2009
This is the first paper concretely investigating various effective approaches of realizing green cognitive radio concept and functionalities. In particular, this paper is dedicated to exploiting the basic trade-off of spectrum (bandwidth) availability and power(energy) efficient modulation by introducing greater intelligence into the devices for a balance of spectrum-efficiency and energy-efficiency, meanwhile reducing the complexity overall of cognitive radio systems during spectrum sensing by virtue of reinforcement based learning.

J. Palicot, "Cognitive Radio: An Enabling Technology for the Green Radio Communications Concept," in Proc. the 2009 ACM International Conference on Wireless Communications and Mobile Computing: Connecting the World Wirelessly, IWCMC '09, pp. 489-494, 2009
As the very first work on proposing cognitive radio approaches for meeting green communications concept and needs, this paper not only deals with the applications of cognitive radio functionalities to various scenarios of energy-efficient networks, protocols, devices and energy management, but also addresses the potential electromagnetic waves pollution and the corresponding threat to sustainable development considering human aspects both from the social and the health point of views.

G. Gur and F. Alagoz, "Green Wireless Communications via Cognitive Dimension: An Overview," IEEE Network, vol. 25, no. 2, pp. 50-56, 2011
This is the first comprehensive overview on cognitive green wireless communications, which especially highlights the two fundamental features of cognitive radio systems in the context of green communications, namely: taking advantage of cognitive radio functionalities for improving energy-efficiency and cognitive radio self-operation with energy-efficiency.

Hasan, Z.; Bansal, G.; Hossain, E.; Bhargava, V., "Energy-Efficient Power Allocation in OFDM-Based Cognitive Radio Systems: A Risk-Return Model," IEEE Transactions on Wireless Communications, vol.8, no.12, pp.6078-6088, December 2009
This is one of the first papers to address energy efficiency of cognitive wireless networks. The authors propose an energy-efficient power allocation scheme to maximize the expected transmission rate for OFDM-based cognitive radio systems while taking into account the reliability of the available sub-bands, sub-band power constraints, and total allowed interference limit to the adjacent primary user bands.

S. Lee, R. Zhang, K. Huang, “Opportunistic Wireless Energy Harvesting in Cognitive Radio Networks,” IEEE Trans. on Wireless Commun., vol. 12, no. 9, pp. 4788-4799, Sep. 2013
This paper proposes a novel method for wireless networks coexisting where low-power mobiles in a secondary network, called secondary transmitters (STs), harvest ambient RF energy from transmissions by nearby active transmitters in a primary network, called primary transmitters (PTs), while opportunistically accessing the spectrum licensed to the primary network. It considers a stochastic-geometry model in which PTs and STs are distributed as independent homogeneous Poisson point processes (HPPPs) and communicate with their intended receivers at fixed distances. Each PT is associated with a guard zone to protect its intended receiver from ST’s interference, and at the same time delivers RF energy to STs located in its harvesting zone. Based on the proposed model, the transmission probability of STs and the resulting spatial throughput of the secondary network are analyzed. The optimal transmission power and density of STs are derived for maximizing the secondary network throughput under the given outage-probability constraints in the two coexisting networks, which reveal key insights to the optimal network design.

S. Bu and F. R. Yu, “Green Cognitive Mobile Networks With Small Cells for Multimedia Communications in the Smart Grid Environment,” IEEE Trans. Veh. Technol., vol. 63, no. 5, pp. 2115-2126, Jun. 2014
This paper studies green cognitive mobile networks with small cells in the smart grid environment. Unlike most existing studies on cognitive networks, where only the radio spectrum is sensed, cognitive networks in this paper sense not only the radio spectrum environment but also the smart grid environment, based on which power allocation and interference management for multimedia communications are performed. The problems of electricity price decision, energy-efficient power allocation, and interference management are treated as a three-stage Stackelberg game. A homogeneous Bertrand game with asymmetric costs is used to model price decisions made by the electricity retailers. A backward induction method is used to analyze the proposed Stackelberg game. Simulation results show that the proposed scheme can significantly reduce operational expenditure and CO2 emissions in cognitive mobile networks with small cells for multimedia communications.

X. Huang, T. Han, and N. Ansari, “On Green-Energy-Powered Cognitive Radio Networks,” IEEE Commun. Surveys Tuts., vol. 17, no. 2, pp. 827-842, Second Quarter 2015
This paper surveys the energy-efficient cognitive radio (CR) techniques and the optimization of green-energy-powered wireless networks. Existing works on energy-aware spectrum sensing, management, and sharing are investigated. The state of the art of the energy-efficient CR-based wireless access network is discussed in various aspects, such as relay and cooperative radio and small cells. To optimize and adapt the usage of green energy according to the opportunistic spectrum availability, the paper discusses research challenges in designing CR networks that are powered by energy harvesters.

B. Heile, "Smart Grids for Green Communications," IEEE Wireless Communications, vol. 17, pp. 4-6, June 2010
The author states some of the work done to manage the smart grids effectively to meet the targeted carbon footprint. This is an important work from industrial point of view.

H. Farhangi, "The Path of the Smart Grid," IEEE Power & Energy, vol. 8, no. 1, pp. 18-28, Jan. 2010
This paper provided a precise high level view and roadmap of the transition from traditional power grids to smart grids as well as the strong impact and relevance to the ICT. The author described the current status and limitations of conventional power grids and looked forward to the potential enhancements through the evolution of smart grid technologies and relevant standardizations. The author also pointed out the challenges and potential problems to be combated during the global transitions to smart grids.

S. Bu, F. R. Yu, Y. Cai, and X. P. Liu, “When the Smart Grid Meets Energy-Efficient Communications: Green Wireless Cellular Networks Powered by the Smart Grid,” IEEE Trans. on Wireless Commun., vol. 11, no. 8, pp. 3014-3024, Aug. 2012
In this paper, the authors consider energy-efficient communications and the dynamics of the smart grid in designing green wireless cellular networks. Specifically, the dynamic operation of cellular base stations depends on the traffic, real-time electricity price, and the pollutant level associated with electricity generation. Coordinated multipoint (CoMP) is used to ensure acceptable service quality in the cells whose base stations have been shut down. The active base stations decide on which retailers to procure electricity from and how much electricity to procure. The problem is formulated as a Stackelberg game, which has two levels: a cellular network level and a smart grid level. Simulation results show that the smart grid has significant impacts on green wireless cellular networks, and the proposed scheme can significantly reduce operational expenditure and CO2 emissions in green wireless cellular networks.

M. Erol-Kantarci and H. T. Mouftah, “Energy-Efficient Information and Communication Infrastructures in the Smart Grid: A Survey on Interactions and Open Issues,” IEEE Commun. Surveys Tuts., vol. 17, no. 1, pp. 179-197, First Quarter 2015
The paper provides a comprehensive survey on the smart grid-driven approaches in energy-efficient communications and data centers, and the interaction between smart grid and information and communication infrastructures. The paper provides background information on the smart grid and continues with surveying smart grid-driven approaches in energy-efficient communication systems, followed by energy, cost and emission minimizing approaches in data centers, and the corresponding cloud network infrastructure. It discusses the open issues in smart grid-driven information and communication technologies.

H. Chao, Y. Chen, J. Wu, "Power Saving for Machine to Machine Communications in Cellular Networks", in Proc. IEEE Globecom International Workshop on Machine-to-Machine Communications, Dec. 2011
This paper is a pioneer work in systematically proposing efficient power saving mechanisms on simultaneously considering all three aspects machine-to machine devices, radio access networks and core networks for machine-to-machine communications in cellular systems. With the significant power savings in the machine-to-machine communications and the minimal impact in legacy human-to-human communications, the new proposal in this paper includes the new sleep state, the new three-layer machine-to machine paging solution, and the modified signaling flow for the core network. The authors have provided both qualitative and quantitative analysis for the proposed comprehensive solutions.

C. Zhu, V. C. M. Leung, L. Shu, and E. C.-H. Ngai, “Green Internet of Things for Smart World,” IEEE Access, vol. 3, pp. 2151-2162, Nov. 2015
This paper discusses various technologies and issues regarding green Internet-of-Things (IoT). Particularly, an overview regarding IoT and green IoT is performed first. Then, the hot green information and communications technologies (ICTs) (e.g., green radio frequency identification, green wireless sensor network, green cloud computing, green machine to machine, and green data center) enabling green IoT are studied, and general green ICT principles are summarized. Furthermore, the latest developments and future vision about sensor cloud, which is a novel paradigm in green IoT, are reviewed and introduced, respectively. Finally, future research directions and open problems about green IoT are presented.

U. Raza, P. Kulkarni, and M. Sooriyabandara, “Low Power Wide Area Networks: An Overview,” IEEE Commun. Surveys Tuts., vol. 19, no. 2, pp. 855-873, Second Quarter 2017
This review paper presents the design goals and the techniques, which different low power wide area (LPWA) technologies exploit to offer wide-area coverage to low-power devices at the expense of low data rates. It surveys several emerging LPWA technologies and the standardization activities carried out by different standards development organizations (e.g., IEEE, IETF, 3GPP, ETSI) as well as the industrial consortia built around individual LPWA technologies (e.g., LORa Alliance, WEIGHTLESS-SIG, and DASH7 alliance).

Aman Kansal, Jason Hsu, Sadaf Zahedi, Mani B. Srivastava, "Power Management in Energy Harvesting Sensor Networks", ACM Transactions on Embedded Computing Systems, vol. 6, no. 4, September 2007
This paper discussed issues in power management for energy-harvesting sensor networks. The authors pinoeerly developed abstractions to characterize the complex time varying nature of such sources with analytically tractable models and use them to address key design issues. The authors also develop distributed methods to efficiently use harvested energy.

Chin Keong Ho, Rui Zhang, "Optimal Energy Allocation for Wireless Communications With Energy Harvesting Constraints", IEEE Transactions on Signal Processing, vol. 60, no. 9, pp. 4808-4818, Sept. 2012
In this paper, the authors considered maximizing the throughput through the the energy allocation over a finite horizon. Two types of side information (SI) on the channel conditions and harvested energy are assumed to be available: causal SI (of the past and present slots) or full SI (of the past, present and future slots). Through the use of dynamic programming and convex optimization techniques, the structural results for the optimal energy allocation were obtained. In the case of the unlimited energy storage and the full SI, the authors prove the optimality of a water-filling energy allocation solution where the so-called water levels follow a staircase function.

S. Sudevalayam, P. Kulkarni, "Energy Harvesting Sensor Nodes: Survey and Implications", IEEE Communications Surveys & Tutorials, vol. 13, no. 3, Third Quarter 2011
pp. 443 - 46
In this paper, the authors have made a timely survey on various aspects of energy harvesting sensor systems- architecture, energy sources and storage technologies. This paper also has investigated some insights into implications of recharge opportunities on node-level operations and design of sensor network applications and solutions.

J.P. Barton, D.G. Infield, "Energy Storage and Its Use with Intermittent Renewable Energy", IEEE Transactions on Energy Conversion, vol. 19, no. 2, pp. 441-448, June 2004
This paper discusses on the connection of wind generators at locations where the level of embedded renewable generation (ERG) would be limited by the voltage increase. Short-term storage offers only a small increase in the amount of electricity that could be absorbed by the network. Storage over periods of up to one day delivers greater energy benefits, but is significantly more expensive. This paper compare different feasible electricity storage technologies for their operational suitability over different time scales. This paper also investigate the value of storage regarding to the power rating and energy capacity so as to adapt appropriate sizing.

S. Luo, R. Zhang, and T. J. Lim, “Optimal Save-Then-Transmit Protocol for Energy Harvesting Wireless Transmitters,” IEEE Trans. Wireless Commun., vol. 12, no. 3, pp. 1196 - 1207, Mar. 2013
This paper considers an energy-harvesting system with two rechargeable energy storage devices. These are half-duplex in nature and unable to charge and discharge at the same time. This paper introduces a save-then-transmit protocol and evaluates its energy efficiency. Finally, it derives the optimal save-ratio to minimize outage probability. The paper also extends the protocol for networks with multiple transmitters.

D. W. Kwan Ng, Ernest S. Lo, and R. Schober, “Energy-Efficient Resource Allocation in OFDMA Systems with Hybrid Energy Harvesting Base Station,” IEEE Trans. Wireless Commun., vol. 12, no. 7, pp. 3412-3427, Jul. 2013
This paper designs a resource allocation algorithm for an orthogonal frequency division multiple access (OFDMA) network composed of hybrid energy harvesting base stations. It formulates a non-convex optimization problem considering the uncertainties in the energy arrivals and channel gains in presence of finite energy storage. Using the techniques of time-sharing and non-linear fractional programming, the paper devises an asymptotically optimal iterative algorithm. Finally, an online algorithm using stochastic dynamic programming is also given. The paper also proposes a suboptimal low complexity algorithm which achieves a close enough energy efficiency of the optimal algorithm.

S. Lee, R. Zhang, K. Huang, “Opportunistic Wireless Energy Harvesting in Cognitive Radio Networks,” IEEE Transactions on Wireless Communications, vol. 12, no. 9, pp. 4788 - 4799, Sep. 2013
Self-sustainability of the wireless networks by harvesting from ambient energy sources is studied in this paper using a stochastic geometry framework. It considers independent homogeneous Poisson point processes for spatial distributions of primary and secondary transmitters. The paper derives the optimal power and density of the secondary transmitters in order to maximize the throughput of the secondary network under some given outage-probability constraints.

B. Gurakan, O. Ozel, J. Yang, and S. Ulukus, “Energy Cooperation in Energy Harvesting Communications,” IEEE Trans. Comm., vol. 61, no. 12, pp. 4884 - 4898, Dec. 2013
This paper coins the term “energy cooperation” to improve performance of an energy-harvesting communication system where the energy arrival profiles are not certain. It derives the policies to manage energy to maximize the throughput of the system using Lagrangian formulation and KKT optimality conditions. This paper also proposes a directional water-filling algorithm to control the flow of harvested energy optimally in two dimensions: in time and among users.

D. W. K. Ng, E. S. Lo, and R. Schober, “Wireless Information and Power Transfer: Energy Efficiency Optimization in OFDMA Systems,” IEEE Trans. Wireless Commun., vol. 12, no. 12, pp. 6352 - 6370, Dec. 2013
This paper studies the resource allocation algorithm design with an objective to maximize the energy efficiency of the orthogonal frequency division multiple access (OFDMA) systems. It considers simultaneous wireless information and power transfer (SWIPT) technique and uses power splitting (for both fixed and arbitrary splitting ratio) to concurrently harvest energy and decode information. Finally, the paper formulates the problem as a non-convex optimization problem and solves it using fractional programming and dual decomposition methods. The solution reveals the trade-off between energy efficiency and system capacity.

Q. Shi, L. Liu, W. Xu, and R. Zhang, “Joint Transmit Beamforming and Receive Power Splitting for MISO SWIPT Systems,” IEEE Trans. Wireless Commun., vol. 13, no. 6, pp. 3269-3280, Jun. 2014
This paper studies a multi-user multiple-input single-output (MISO) downlink system for simultaneous wireless information and power transfer (SWIPT), in which a set of single antenna mobile stations (MSs) receive information and energy simultaneously via power splitting (PS) from the signal sent by a multi-antenna base station (BS). It aims to minimize the total transmission power at BS by jointly designing transmit beamforming vectors and receive PS ratios for all MSs under their given signal-to-interference-plus-noise ratio (SINR) constraints for information decoding and harvested power constraints for energy harvesting. It derives the sufficient and necessary condition for the feasibility of the formulated problem. Next, it solves this non-convex problem by applying the technique of semidefinite relaxation (SDR). It proves that SDR is indeed tight for this problem and thus achieves its global optimum. Finally, it proposes two suboptimal solutions of lower complexity than the optimal solution based on the principle of separating the optimization of transmit beamforming and receive PS, where the zero-forcing (ZF) and the SINR-optimal based transmit beamforming schemes are applied, respectively.

S. Ulukus, A. Yener, E. Erkip, O. Simeone, M. Zorzi, P. Grover, and K. Huang, “Energy Harvesting Wireless Communications: A Review of Recent Advances,” IEEE J. Sel. Areas Commun., vol. 33, pp. 360-381, Mar. 2015
This paper summarizes recent contributions in the broad area of energy harvesting wireless communications. It provides the current state of the art for wireless networks composed of energy harvesting nodes, starting from the information-theoretic performance limits to transmission scheduling policies and resource allocation, medium access, and networking issues. The emerging related area of energy transfer for self-sustaining energy harvesting wireless networks is considered in detail covering both energy cooperation aspects and simultaneous energy and information transfer. Various potential models with energy harvesting nodes at different network scales are reviewed, as well as models for energy consumption at the nodes.

Z. Ding, C. Zhong, D. W. K. Ng, M. Peng, H. A. Suraweera, R. Schober, and H. V. Poor, “Application of Smart Antenna Technologies in Simultaneous Wireless Information and Power Transfer,” IEEE Commun. Mag., vol. 53, no. 4, pp. 86-93, Apr. 2015
This article focuses on the application of advanced smart antenna technologies to simultaneous wireless information and power transfer (SWIPT), including multiple-input multiple-output and relaying techniques. These smart antenna technologies have the potential to significantly improve the energy efficiency and also the spectral efficiency of SWIPT. Different network topologies with single and multiple users are investigated, along with some promising solutions to achieve a favorable trade-off between system performance and complexity. A detailed discussion of future research challenges for the design of SWIPT systems is also provided.

S. Bi, C. K. Ho, and R. Zhang, “Wireless Powered Communication: Opportunities and Challenges,” IEEE Commun. Mag. , vol. 53, no. 4, pp. 117-125, Apr. 2015
The combination of wireless energy and information transmissions raises many new research problems and implementation issues that need to be addressed. This article provides an overview of state-of-the-art RF-enabled WET technologies and their applications to wireless communications, highlighting the key design challenges, solutions, and opportunities ahead.

A. H. Sakr, and E. Hossain “Cognitive and Energy Harvesting-Based D2D Communication in Cellular Networks: Stochastic Geometry Modeling and Analysis,” IEEE Trans. Comm., vol. 63, no. 5, pp. 1867-1880, May 2015
This paper analyzes cognitive and energy harvesting-based device-to-device (D2D) communication in cellular networks where the cognitive transmitters harvest energy from ambient interference.

O. Ozel, K. Tutuncuoglu, S. Ulukus, and A. Yener, “Fundamental Limits of Energy Harvesting Communications,” IEEE Commun. Mag., vol. 53, no. 4, pp. 126-132, Apr. 2015
This paper surveys recent results in energy-harvesting communications and points to open problems that could be of interest to a broad set of researchers in the fields of communication theory, information theory, signal processing, and networking. In particular, it reviews capacities of energy harvesting links with infinite-sized, finite-sized, and no batteries at the transmitter.

S. Guruacharya and E. Hossain, “Self-Sustainability of Energy Harvesting Systems: Concept, Analysis, and Design,” IEEE Trans. Green Comm. Netw., vol. 2, no. 1, pp. 175-192, Mar. 2018
Studying the self-sustainability of a system via the usage of ambient energy harvesting is the main focus of this paper. It describes mathematically the notions of the eventual energy outage and self-sustainability. This paper considers a harvest-store-consume system where energy arrival follows a stochastic process and the energy consumption rate is fixed. It derives the necessary condition for a system to achieve self-sustainability using random walk theory. Using integral equations, this paper also gives the general formulas for self-sustainability probability and then finds its upper bound for using martingales.