Special Issue on Green Communications: Part Ⅰ

With the development of communication systems, computer networks, and other information and communication technology （ICT） infrastructures, challenges in communications and efficient communications for green technologies are rising in recent years. In order to reduce the environmental problems thereby creating a sustainable environment, there is an urgent need for new models, algorithms, methodologies, platforms, tools, devices, and systems. Hence, green computing and communications solutions should be effectively and practically designed with more renewable energy, higher energy efficiency, lower greenhouse gas emission, and environmental friendly materials.

Independent Vector Analysis Based Blind Interference Reduction and Signal Recovery for MIMO IoT Green Communications

In application to time convolutive mixing model or frequency domain blind separation model for wireless receiving applications,frequency domain independent component analysis(FDICA)has been a very popular method but with adverse random permutation ambiguity influence.In order to solve this inherent problem in FDICA assisted multiple-input multiple-output orthogonal frequency-division multiplexing(MIMO-OFDM)based the Internet of Thing(IoT)systems,this paper proposes an new detection mechanism,named independent vector analysis(IVA),for realizing blind adaptive signal recovery in MIMO IoT green communication to reduce inter-carrier interference(ICI)and multiple access interference(MAI).IVA jointly implements separation work for different frequency bin data while the FDICA deals with it separately.In IVA,the dependencies of frequency bins can be exploited in mitigating the random permutation problem.In addition,multivariate prior distributions are employed to preserve the inter-frequency dependencies for individual sources,which can result in separation performance enhancement.Simulation results and analysis corroborate the effectiveness of the proposed method.

Green resource allocation for mobile edge computing

We investigate the green resource allocation to minimize the energy consumption of the users in mobile edge computing systems,where task offloading decisions,transmit power,and computation resource allocation are jointly optimized.The considered energy consumption minimization problem is a non-convex mixed-integer nonlinear programming problem,which is challenging to solve.Therefore,we develop a joint search and Successive Convex Approximation(SCA)scheme to optimize the non-integer variables and integer variables in the inner loop and outer loop,respectively.Specifically,in the inner loop,we solve the optimization problem with fixed task offloading decisions.Due to the non-convex objective function and constraints,this optimization problem is still non-convex,and thus we employ the SCA method to obtain a solution satisfying the Karush-Kuhn-Tucker conditions.In the outer loop,we optimize the offloading decisions through exhaustive search.However,the computational complexity of the exhaustive search method is greatly high.To reduce the complexity,a heuristic scheme is proposed to obtain a sub-optimal solution.Simulation results demonstrate the effectiveness of the developed schemes.

Spectrum and energy efficient multi-antenna spectrum sensing for green UAV communication

Unmanned Aerial Vehicle(UAV)communication is a promising technology that provides swift and flexible ondemand wireless connectivity for devices without infrastructure support.With recent developments in UAVs,spectrum and energy efficient green UAV communication has become crucial.To deal with this issue,Spectrum Sharing Policy(SSP)is introduced to support green UAV communication.Spectrum sensing in SSP must be carefully formulated to control interference to the primary users and ground communications.In this paper,we propose spectrum sensing for opportunistic spectrum access in green UAV communication to improve the spectrum utilization efficiency.Different from most existing works,we focus on the problem of spectrum sensing of randomly arriving primary signals in the presence of non-Gaussian noise/interference.We propose a novel and improved p-norm-based spectrum sensing scheme to improve the spectrum utilization efficiency in green UAV communication.Firstly,we construct the p-norm decision statistic based on the assumption that the random arrivals of signals follow a Poisson process.Then,we analyze and derive the approximate analytical expressions of the false-alarm and detection probabilities by utilizing the central limit theorem.Simulation results illustrate the validity and superiority of the proposed scheme when the primary signals are corrupted by additive non-Gaussian noise and arrive randomly during spectrum sensing in the green UAV communication.

Green Concerns in Federated Learning over 6G

As Information,Communications,and Data Technology(ICDT)are deeply integrated,the research of 6G gradually rises.Meanwhile,federated learning(FL)as a distributed artificial intelligence(AI)framework is generally believed to be the most promising solution to achieve“Native AI”in 6G.While the adoption of energy as a metric in AI and wireless networks is emerging,most studies still focused on obtaining high levels of accuracy,with little consideration on new features of future networks and their possible impact on energy consumption.To address this issue,this article focuses on green concerns in FL over 6G.We first analyze and summarize major energy consumption challenges caused by technical characteristics of FL and the dynamical heterogeneity of 6G networks,and model the energy consumption in FL over 6G from aspects of computation and communication.We classify and summarize the basic ways to reduce energy,and present several feasible green designs for FL-based 6G network architecture from three perspectives.According to the simulation results,we provide a useful guideline to researchers that different schemes should be used to achieve the minimum energy consumption at a reasonable cost of learning accuracy for different network scenarios and service requirements in FL-based 6G network.

Green Air-Ground Integrated Heterogeneous Network in 6G Era

The research of three-dimensional integrated communication technology plays a key role in achieving the ubiquitous connectivity,ultra-high data rates,and emergency communications in the sixth generation(6G)networks.Aerial networking provides a prom⁃ising solution to flexible,scalable,low-cost and reliable coverage for wireless devices.The integration of aerial network and terrestrial network has been an inevitable paradigm in the 6G era.However,energy-efficient communications and networking among aerial net⁃work and terrestrial network face great challenges.This paper is dedicated to discussing green communications of the air-ground integrated heterogeneous network(AGIHN).We first provide a brief introduction to the characteristics of AGIHN in 6G networks.Further,we analyze the challenges of green AGIHN from the aspects of green terrestrial networks and green aerial networks.Finally,several solutions to and key technologies of the green AGIHN are discussed.

Optimal Cost-Aware Paradigm for Off-Grid Green Cellular Networks in Oman

Green wireless networks or energy-efficient wireless networks have gained popularity as a research topic due to the ecological and economic concerns of cellular operators.The specific power supply requirements for the cellular base station,such as cost-effectiveness,efficiency,sustainability,and reliability,can be met by utilizing the technological advances in renewable energy.There are numerous drivers for the deployment of renewable energy technologies and the transition towards green energy.Renewable energy is free,clean,and abundant in most locations throughout the year.Accordingly,this work proposes a novel framework for energy-efficient solar-powered base stations for the Oman site,specifically for off-grid locations where fuel transportation for diesel generator(DG)is a serious concern.To demonstrate the effectiveness of the proposed system for off-grid sites,the Hybrid Optimization Model for Electric Renewables optimization software is adapted by considering real-time conditions and its technical feasibility.Different cost factors such as capital cost,salvage cost,replacement cost,operational,and maintenance cost of PV panels,inverters,and batteries also undergo extensive analysis.From the observed results,the total net present cost(NPC)of the proposed system is$27,887,while the net NPC of the DG is estimated at$32,900.Remarkably,the proposed scheme can potentially achieve considerable savings in the operational expenditure at approximately 15.24%.Indeed,these outcomes can provide profound economic,technical,and ecological benefits to the cellular operators of Oman.It also ensures a sizeable reduction in greenhouse gas that supports sustainable green wireless network deployment in remote areas.

Powering Mobile Networks with Optimal Green Energy for Sustainable Development

Green wireless networking is an emerging area for many societies,especially academia and industry,in light of economic and ecological perspectives.Empowering wireless infrastructures exploiting green power sources can enhance sustainability due to the adverse effects of conventional power sources and atmospheric circumstances.Moreover,the specific power supply requirements for a base station(BS),such as cost effectiveness,efficiency,sustainability,and reliability,can be met by utilizing technological advances in renewable energy.Numerous drivers and motivators are involved in the deployment of renewable energy technologies and the transition toward green energy.Renewable energy is free,clean,and abundant in most locations throughout the year.In this work,a sustainable optimal stand-alone solarpowered model envisioning green cellular BSs for urban locations in Oman is proposed.This model can extend 24 h uninterrupted power supply support to a cellular BS that fully utilizes an integrated storage device.The system analysis is conducted using a hybrid optimization model for electric renewables(HOMER)based on actual prevailing conditions of the regions and their technical feasibility.The results showed can be achieved operational expenditure savings up to 16%.These outcomes provide a huge benefit to the cellular operators of Oman economically,technically,and ecologically.

Toward Optimal Cost-Energy Management Green Framework for Sustainable Future Wireless Networks

The design of green cellular networking according to the trafc arrivals has the capability to reduce the overall energy consumption to a cluster in a cost-effective way.The cell zooming approach has appealed much attention that adaptively ofoads the BS load demands adjusting the transmit power based on the trafc intensity and green energy availability.Besides,the researchers are focused on implementing renewable energy resources,which are considered the most attractive practices in designing energy-efcient wireless networks over the long term in a cost-efcient way in the existing infrastructure.The utilization of available solar can be adapted to acquire cost-effective and reliable power supply to the BSs,especially that sunlight is free,available everywhere,and a good alternative energy option for the remote areas.Nevertheless,planning a photovoltaic scheme necessitates viability assessment to avoid poor power supply,particularly for BSs.Therefore,cellular operators need to consider both technical and economic factors before the implementation of solar-powered BSs.This paper proposed the usercentric cell zooming policy of solar-powered cellular base stations taking into account the optimal technical criteria obtained by the HOMER software tool.The results have shown that the proposed system can provide operational expenditure(OPEX)savings of up to 47%.In addition,the efcient allocation of resource blocks(RBs)under the cell zooming technique attain remarkable energy-saving performance yielding up to 27%.

5G Green Mobile Communication Networks

With the popularization of wireless multimedia communications,the wireless traffic is predicated to be increased more than 1000time in the next decade.Some new technologies,e.g.,massive multi.input multi.output antennas,millimeter wave and small

Green indoor optical wireless communication systems:Pathway towards pervasive deployment

The Optical Wireless Communication(OWC)offers the high capacity of optical fiber communication with the flexibility of wireless communication.Since it works in the optical region of the ElectroMagnetic(EM)spectrum,it guarantees safety and security which are critical in radio and microwave frequency communication.The principal objective of this paper is to analyze the indoor OWC systems on these guaranteed features,and safety and security are jointly denoted by the term green.The high obstacle impermeability of optical signals and their directivity strengthen the security of indoor OWC data transmission.The confidentiality and authenticity of optical wireless data can also be preserved with the Quantum Key Distribution(QKD).This paper provides a technological overview and a review of literature about the OWC system that helps to identify the challenges in the path of a ubiquitous deployment of green wireless communication systems.Significant advancements in the sources and detectors are discussed together with the coding,modulation and multiplexing techniques for making highly robust OWC links.The ubiquitous deployment of green OWC necessitates the development of optical transmitters and receivers,performance enhancement techniques,incorporation of uplink and energy harvesting abilities,and safety and security enhancement techniques.Hence,a special emphasis is placed on these aspects and their challenges towards the green implementation.Furthermore,the paper explores some significant indoor applications based on the OWC that have great impacts on the Next Generation Networks(NGN)and the Internet of Things(IoT).

Ecological Concept and Green Communication:Path Innovation of Xi Jinping's Ecological Civilization Thought in External Communication

Xi Jinping's ecological civilization is an important part of socialist ideology with Chinese characteristics in the new era,and it is also a highlight of foreign dissemination of Xi Jinping's socialism with Chinese characteristics.The green,balanced and sustainable concept contained in it also brings a lot of enlightenment to the innovation of external communication methods.It can be said that ecological civilization is a red line.The thought of ecological civilization affects the national governance ability,the modernization of national governance and the cross-cultural construction of national image.In a sense,the modernization of national governance should also be reflected in the cultivation of national ecological civilization quality,the overall ecological civilization of the country and the external green(ecological)communication,guidance,influence and credibility of socialist ecological civilization.Under the guidance of green(ecological)concept,the idea of ecological civilization of General Secretary Xi Jinping,including the whole socialist ideology with Chinese characteristics,will be in a great situation of"letting a hundred of flowers bloom and a hundred of schools of thought contend"in external communication of the new era.

Energy Efficiency in ARQ-Based Multi-Hop Systems and the Tradeoff with Throughput

The minimum energy per bit(EPB)as the energy efficiency(EE)metric in an automatic retransmission request(ARQ)based multi-hop system is analyzed under power and throughput constraints.Two ARQ protocols including type-I(ARQ-I)and repetition redundancy(ARQ-RR)are considered and expressions for the optimal power allocation(PA)are obtained.Using the obtained optimal powers,the EE-throughput tradeoff(EETT)is analyzed and the EETT closed-form expressions for both ARQ protocols and in arbitrary average channel gain values are obtained.It is shown that how different throughput requirements,especially the high levels,affect the EE performance.Additionally,asymptotic analysis is made in the feasible high throughput values and lower and upper EETT bounds are derived for ARQ-I protocol.To evaluate the EE a distributed PA scenario,as a benchmark,is presented and the energy savinggain obtained from the optimal PA in comparison with the distributed PA for ARQ-I and ARQ-RR protocols is discussed in different throughput values and node locations.

A dynamic incentive and reputation mechanism for energy-efficient federated learning in 6G

As 5G becomes commercial,researchers have turned attention toward the Sixth-Generation(6G)network with the vision of connecting intelligence in a green energy-efficient manner.Federated learning triggers an upsurge of green intelligent services such as resources orchestration of communication infrastructures while preserving privacy and increasing communication efficiency.However,designing effective incentives in federated learning is challenging due to the dynamic available clients and the correlation between clients'contributions during the learning process.In this paper,we propose a dynamic incentive and reputation mechanism to improve energy efficiency and training performance of federated learning.The proposed incentive based on the Stackelberg game can timely adjust optimal energy consumption with changes in available clients during federated learning.Meanwhile,clients’contributions in reputation management are formulated based on the cooperative game to capture the correlation between tasks,which satisfies availability,fairness,and additivity.The simulation results show that the proposed scheme can significantly motivate high-performance clients to participate in federated learning and improve the accuracy and energy efficiency of the federated learning model.

Green UAV communications for 6G: A survey

Unmanned Aerial Vehicles(UAVs) have received a wide range of attention for military and commercial applications. Enhanced with communication capability, UAVs are considered to play important roles in the Sixth Generation(6G) networks due to their low cost and flexible deployment. 6G is supposed to be an all-coverage network to provide ubiquitous connections for space, air, ground and underwater. UAVs are able to provide air-borne wireless coverage flexibly,serving as aerial base stations for ground users, as relays to connect isolated nodes, or as mobile users in cellular networks. However, the onboard energy of small UAVs is extremely limited. Thus,UAVs can be only deployed to establish wireless links temporarily. Prolonging the lifetime and developing green UAV communication with low power consumption becomes a critical challenge.In this article, a comprehensive survey on green UAV communications for 6G is carried out. Specifically, the typical UAVs and their energy consumption models are introduced. Then, the typical trends of green UAV communications are provided. In addition, the typical applications of UAVs and their green designs are discussed. Finally, several promising techniques and open research issues are also pointed out.

Reliable and Energy-Aware Job Offloading at Terahertz Frequencies for Mobile Edge Computing

In this paper,we co-design the transmission power and the offloading strategy for job offloading to a mobile edge computing(MEC)server at Terahertz(THz)frequencies.The goal is to minimize the communication energy consumption while providing ultra-reliable low end-to-end latency(URLLC)services.To that end,we first establish a novel reliability framework,where the end-to-end(E2E)delay equals a weighted sum of the local computing delay,the communication delay and the edge computing delay,and the reliability is defined as the probability that the E2E delay remains below a certain pre-defined threshold.This reliability gives a full view of the statistics of the E2E delay,thus constituting advancement over prior works that have considered only average delays.Based on this framework,we establish the communication energy consumption minimization problem under URLLC constraints.This optimization problem is non-convex.To handle that issue,we first consider the special single-user case,where we derive the optimal solution by analyzing the structure of the optimization problem.Further,based on the analytical result for the single-user case,we decouple the optimization problem for multi-user scenarios into several sub-optimization problems and propose a sub-optimal algorithm to solve it.Numerical results verify the performance of the proposed algorithm.

Adaptive Cell Zooming Strategy Toward Next-Generation Cellular Networks with Joint Transmission

The Internet subscribers are expected to increase up to 69.7%(6 billion)from 45.3%and 25 billion Internet-of-things connections by 2025.Thus,the ubiquitous availability of data-hungry smart multimedia devices urges research attention to reduce the energy consumption in the fifthgeneration cloud radio access network to meet the future traffic demand of high data rates.We propose a new cell zooming paradigm based on joint transmission(JT)coordinated multipoint to optimize user connection by controlling the cell coverage in the downlink communications with a hybrid power supply.The endeavoring cell zooming technique adjusts the coverage area in a given cluster based on five different JT schemes,which will help in reducing the overall power consumption with minimum inter-cell interference.We provide heuristic solutions to assess wireless network performances in terms of aggregate throughput,energy efficiency index(EEI),and energy consumption gain under a different scale of network settings.The suggested algorithm allows efficient allocation of resource block and increases energy and spectral efficiency over the conventional location-centric cell zooming mechanism.Extensive system-level simulations show that the proposed framework reduces energy consumption yielding up to 17.5%and increases EEI by 14%.Subsequently,a thorough comparison among different JT-based load shifting schemes is pledged for further validation of varying system bandwidths.

Optimization Analysis of Sustainable Solar Power System for Mobile Communication Systems

Cellular mobile technology has witnessed tremendous growth in recent times.One of the challenges facing the operators to extend the coverage of the networks to meet the rising demand for cellular mobile services is the power sources used to supply cellular towers with energy,especially in remote.Thus,switch from the conventional sources of energy to a greener and sustainable power model became a target of the academic and industrial sectors in many fields;one of these important fields is the telecommunication sector.Accordingly,this study aims to find the optimum sizing and technoeconomic investigation of a solar photovoltaic scheme to deploy cellular mobile technology infrastructure cleanly and sustainably.The optimal solarpowered system is designed by employing the energy-balance procedures of the HOMER software tool.The problem objective is considered in terms of cost,but the energy system is constrained to meet the power demand reliably.Process simulations were performed to determine the optimum sizing,performance and monetary cost of the power system,using long-term meteorological datasets for a case study site with defined longitude(31◦25E)and latitude(30◦06N).From the observed results,the total net present cost(NPC)of the proposed system is$28,187.Indeed,these outcomes can provide profound economic,technical,and ecological benefits to cellular operators.It also ensures a sizeable reduction in greenhouse gas that supports sustainable green wireless network(WN)deployment in remote areas.

UEs Power Reduction Evolution with Adaptive Mechanism over LTE Wireless Networks

At present, the major drawback for mobile phones is the issue of power consumption. As one of the alternatives to decrease the power consumption of standard, power-hungry location-based services usually require the knowledge of how individual phone features consume power. A typical phone feature is that the applications related to multimedia streaming utilize more power while receiving, processing, and displaying the multimedia contents, thus contributing to the increased power consumption. There is a growing concern that current battery modules have limited capability in fulfilling the long-term energy need for the progress on the mobile phone because of increasing power consumption during multimedia streaming processes. Considering this, in this paper, we provide an offline meaning sleep-mode method to compute the minimum power consumption comparing with the power-on solution to save power by implementing energy rate adaptation(RA) mechanism based on mobile excess energy level purpose to save battery power use. Our simulation results show that our RA method preserves efficient power while achieving better throughput compared with the mechanism without rate adaptation(WRA).

A Methodology to Measure the Environmental Impact of ICT Operating Systems across Different Device Platforms

A new methodology was created to measure the energy consumption and related green house gas （GHG） emissions of a computer operating system （OS） across different device platforms. The methodology involved the direct power measurement of devices under different activity states. In order to include all aspects of an OS, the methodology included measurements in various OS modes, whilst uniquely, also incorporating measurements when running an array of defined software activities, so as to include OS application management features. The methodology was demonstrated on a laptop and phone that could each run multiple OSs, results confirmed that OS can significantly impact the energy consumption of devices. In particular, the new versions of the Microsoft Windows OS were tested and highlighted significant differences between the OS versions on the same hardware. The developed methodology could enable a greater awareness of energy consumption, during both the software development and software marketing processes.