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Two-dimensional numerical simulations based on an immersed boundary method are performed for the two-foil system with varying spacings, and a staggered arrangement with a spacing normalized by chord length (X d / D , Y d / D) = (2.0 , 2.5) is found to be the most favorable for energy harnessing with the efficiency enhancement of nearly 40% for the downstream foil. By scrutinizing the mean flow characteristics and the instantaneous wake dynamics, it is revealed that convective flow acceleration and vortex impingement in synchronized timing with foil motion are the two primary mechanisms that contribute to significant efficiency improvement. Based on the staggered arrangement for the two-foil system, a V-shape formation is further proposed for the multiple-foil system and verified with the highest efficiency of energy harnessing up to nearly twice that of a single foil. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) is considered as a promising technology, which can effectively control the phase of signals with low-cost reflective elements. In this paper, we investigate the RIS-assisted D2D communication system under Nakagami- $m$ fading. Overlay mode and underlay mode are discussed respectively. To characterize the performance of proposed communication system, we propose novel closed-form analytical expressions for outage probability under two modes, respectively. Based on the analytical results, we derive the diversity order of outage probability. We show that under overlay D2D mode, the diversity order depends on the number of elements and fading parameters. For the underlay D2D case, 0 diversity order is obtained due to the existence of interference. Furthermore, we study the ergodic achievable rate for each mode and the corresponding tight bounds are derived in closed form. High SNR slopes achieved by users under two modes are also discussed. We observe a high SNR slope of order 1 for overlay D2D mode and 0 for underlay D2D mode. In addition, we also investigate the energy efficiency (EE) of the considered system. Numerical results show that the optimal phase shift proposed in our paper enhance system performance effectively comparing to the traditional D2D communication and random phase shift scheme. Significant EE gains can be obtained for low to middle SNR region by passive reflectors with reconfigurable phase. Unlike relay system, the nearer RIS to the D2D transmitter/receiver, the better performance is obtained. [ABSTRACT FROM AUTHOR]

The mechanism of Coordinated Multi-Point (CoMP) can improve the spectral efficiency of the 4G and 5G cellular network, and also can reduce transmitting power of base stations (BSs). However, CoMP requires a large amount of energy due to extra signal processing and backhaul traffic. In this paper, an energy-efficient algorithm based on optimal dynamic clustering mechanism (ODCEM) for CoMP networks is proposed, which aims to minimize the overall network energy consumption. In the ODCEM, cells are pre-ordered in descending order according to their traffic load increments. The cell with lowest load increment is selected to switch off. Then, users in selected cell are handed over to other neighboring cells if quality of service (QoS) for users can be guaranteed. After that, the selected cell is switched off to conserve network energy. The remaining cells in each CoMP cluster will be evaluated after the previous order is updated. The simulation results show that the energy efficiency of ODCEM schemes is significantly higher than that of fixed CoMP algorithm in terms of SINR and traffic loads. Furthermore, the ODCEM algorithm can achieve better energy efficiency with lower computational complexity according to the performance evaluation of user association and BS switching off. [ABSTRACT FROM AUTHOR]

Highlights • Formulating a maximization model of expected social welfare by given a classification of smart home applications. • Representing operating process of household appliances by Markov decision process. • Dividing the optimization problem into two sub-problems in terms of users and energy supplier. • Solving the maximization model with distributed algorithms. • Simulation studies are given to show performance of the proposed algorithm. Abstract Demand side management (DSM) aims to match power demand to supply through cutting the peak and filling the valley. It is one of the most important factors in smart grid. The real-time pricing (RTP) scheme is an ideal method to adjust power balance between supply and demand. Considering the classification of smart home appliance (SHA) and the correlation of power consumption among users, a social welfare maximization model is proposed based on Markov decision process (MDP) in the research. A probabilistic transfer matrix has been introduced to characterize the elastic appliance in smart home. Several state transfer functions have been utilized to reflect the operating process of the semi-elastic appliance also. In this way, the specific characteristics of SHA can be fully embodied. In order to improve computing efficiency and protect the user's privacy, this project divides the optimization into two subproblems in terms of users and energy supplier (ES). At user side, a modified simulated annealing RTP algorithm is developed to solve the optimization problem. Also, at ES side, the dual sub-gradient method is used to solve the convex optimization problem in the paper. Finally, the simulation results validate the rationality and feasibility of the optimization model by the decentralized RTP algorithm. [ABSTRACT FROM AUTHOR]

In this letter, we consider a multiuser mobile-edge computing (MEC) system with latency constraint. In order to meet the latency requirement and save energy consumption, each user can partially offload the task to the MEC server for edge computing. Data compression is applied to compress the offloaded data before transmission to reduce the data size. The problem of jointly optimizing computation offloading, data compression and resource allocation to minimize energy consumption under the latency constraint and finite MEC computation capacity is considered. We transform the non-convex problem into a convex one and apply convex optimization to solve it. The simulation results demonstrate that our proposed scheme significantly outperforms the benchmark schemes. [ABSTRACT FROM AUTHOR]

For us to meet the green and reliable communication requirement by the forthcoming fifth generation mobile networks, this paper focuses on a secrecy constrained device-to-device (D2D) underlay massive multiple-input multiple-output hybrid network, where the D2D user (DU) and cellular user (CU) links are exposed to passive malicious eavesdroppers. The D2D transmitters harvest the power from the signals of dedicated power beacons (PBs), but also the ambient radio frequency (RF) interference of CUs. The signals of PBs are known previously at the receivers of both the D2D and cellular users but are not known at eavesdroppers so that it can be regarded as an artificial noise. For the interested hybrid networks, we first present an energy-harvesting scheme based on the inversion power control where the power received at the corresponding receiver is higher than the receiver's sensitivity. Then, by modeling the locations of network elements as Poisson point process and applying stochastic geometry, we derive the sufficient probability that a typical D2D transmitter harvests sufficient energy to establish communication links. Finally, with the derived sufficient probability, we evaluate the performance of the CUs and DUs in the achievable ergodic rate and the secrecy outage probability. Both the analytical and simulated results show that precious power of network is saved because of the ambient RF interference exploited, and the secrecy of both D2D and cellular links is improved simultaneously because of the signal of PBs modeled as artificial noises at CUs and DUs. [ABSTRACT FROM AUTHOR]

Combining with finite field network coding, relay ordering is significant for the transmission reliability of multiple-source multiple-relay wireless sensor networks. However, it leads to severe energy consumption and is harmful to the lifetime of the network. To overcome the drawback of relay ordering and achieve desired trade-off between energy efficiency and transmission reliability, a residual energy-activated forwarding protocol is proposed in this article. In the protocol, by considering the unique characteristics of relay ordering–finite field network coding, a novel metric is proposed to jointly formulate both energy consumption and transmission reliability into one optimization problem. Based on this, the appropriate numbers of cooperative relays are selected to reduce energy consumption. Furthermore, by solving the proposed optimization problem in various cases, the optimization process is transferred to three sub-problems, and the corresponding strategy is developed to maximize the proposed metric accordingly. Extensive simulation results verify the superiority of the proposed protocol in both energy efficiency and transmission reliability. [ABSTRACT FROM AUTHOR]

Cell-free massive multiple-input multiple-output (MIMO) has been regarded as a promising technology due to high spectral efficiency. However, as large number of access points (APs) are deployed with fibers connecting to the central processing unit, the increase of energy consumption and hardware cost raise concerns. The reconfigurable intelligent surface (RIS) with impressing potential for low energy and cost finds a way to solve this problem. In this paper, we investigate the performance of the cell-free massive MIMO system with a RIS. As RIS can only reflect signals from the front, user equipments (UEs) and APs are divided into two categories according to their relative position with the RIS, i.e., one is on the reflection area of the RIS and the other is not. A closed-form approximation of the UE achievable downlink rate is derived. Based on it, we obtain the optimal RIS position and phase shift that can maximize the UE sum rate, through alternating optimization method. It is found that compared with the cell-free massive MIMO system without RIS, to achieve the same rate performance, the number of required AP in the RIS-assisted system can be significantly reduced. Moreover, as the RIS component increases, the number of required AP can be reduced almost linearly without rate reduction, which means the hardware and energy cost can be greatly cut down. Furthermore, from our simulation results, we can see that when users are densely distributed, the optimal location of the RIS should be closer to users. When users are uniformly distributed, the optimal position of RIS is close to the central position. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the blue top-emitting organic light-emitting devices (TEOLEDs) with different metal anodes are fabricated. The effect of different anode materials on the spectra and efficiency of blue TEOLEDs is studied. We demonstrate that Al is a more suitable anode material for blue TEOLEDs due to its larger phase shift on reflectance (PSR) than the other common metal materials, such as Ag and Au. The influence of light outcoupling layer (LOL) on the transmittance and PSR of cathode is also investigated to obtain the optimum condition for devices. Angle-independent electroluminescence (EL) spectra are obtained in blue TEOLEDs for each metal anode but the device with Al anode possesses higher efficiency and much thicker organic layers, which is beneficial to the lifetime of the device. These results offer a practicable platform for the realization of TEOLEDs based full-color displays and lightings. [Copyright &y& Elsevier]