1,474 publications from this institution
In this paper, we study the optimal node placement problem in wireless powered communication networks (WPCNs), where the wireless devices (WDs) harvest the radio frequency energy transferred by dedicated energy nodes (ENs) in the downlink, and use the harvested energy to transmit data to information access points (APs) in the uplink. In particular, we are interested in minimizing the deployment cost on ENs and APs, while satisfying the energy harvesting and communication performance requirements of the WDs. Specifically, we first study the optimal placement of ENs given fixed AP locations, where an efficient greedy algorithm is proposed to tackle the non-convexity of the problem. Based on the obtained results, we further propose an alternating optimization method that jointly optimizes the placements of ENs and APs. Simulation results show that the proposed methods can effectively reduce the network deployment cost to guarantee the given performance requirements, which is a key consideration in the future applications of WPCNs.
A novel sterically hindered chiral cyclic phosphoric acid derived from l-tartaric acid was designed and synthesized based on highly regioselective cyclosulfitation of chiral 1,1,4,4-tetraphenylbutanetetraol. The asymmetric Biginelli reaction catalyzed by this newly synthesized chiral phosphoric acid was examined, and enantioselectivities up to 99% ee was obtained.
In this letter, we study efficient channel estimation and passive beamforming designs for a double-intelligent reflecting surface (IRS) aided single-user communication system, where a user communicates with an access point (AP) via the cascaded user-IRS 1-IRS 2-AP double-reflection link. First, a general channel estimation scheme is proposed for the system under any arbitrary inter-IRS channel, where all coefficients of the cascaded channel are estimated. Next, for the typical scenario with a line-of-sight (LoS)-dominant inter-IRS channel, we propose another customized scheme to estimate two signature vectors of the rank-one cascaded channel with significantly less channel training time than the first scheme. For the two proposed channel estimation schemes, we further optimize their corresponding cooperative passive beamforming for data transmission to maximize the achievable rate with the training overhead and channel estimation error taken into account. Numerical results show that deploying two cooperative IRSs with the proposed channel estimation and passive beamforming designs achieves significant rate enhancement as compared to the conventional case of single IRS deployment.
Wireless energy transfer (WET) has attracted significant attention recently for providing energy supplies wirelessly to electrical devices without the need of wires or cables. Among different types of WET techniques, the radio frequency (RF) signal enabled far-field WET is most practically appealing to power energy constrained wireless networks in a broadcast manner. To overcome the significant path loss over wireless channels, multi-antenna or multiple-input multiple-output (MIMO) techniques have been proposed to enhance the transmission efficiency and distance for RF-based WET. However, in order to reap the large energy beamforming gain in MIMO WET, acquiring the channel state information (CSI) at the energy transmitter (ET) is an essential task. This task is particularly challenging for WET systems, since existing channel training and feedback methods used for communication receivers may not be implementable at the energy receiver (ER) due to its hardware limitation. To tackle this problem, in this paper we consider a multiuser MIMO system for WET, where a multiple-antenna ET broadcasts wireless energy to a group of multiple-antenna ERs concurrently via transmit energy beamforming. By taking into account the practical energy harvesting circuits at the ER, we propose a new channel learning method that requires only one feedback bit from each ER to the ET per feedback interval. The feedback bit indicates the increase or decrease of the harvested energy by each ER between the present and previous intervals, which can be measured without changing the existing hardware at the ER. Based on such feedback information, the ET adjusts transmit beamforming in different training intervals and at the same time obtains improved estimates of the MIMO channels to ERs by applying a new approach termed analytic center cutting plane method (ACCPM).
This letter studies the pilot contamination (PC) problem for massive multiple-input multiple-output (MIMO) networks with coexisting terrestrial users and unmanned aerial vehicles (UAVs). Due to the strong line-of-sight (LoS) air-to-ground channels between UAVs and base stations (BSs), UAVs usually cause a more severe PC issue as compared to the traditional terrestrial users. To mitigate the PC caused by UAVs, we propose a low-complexity distributed scheme by exploiting the full-dimensional beamforming of massive MIMO BSs and the angle-dependent LoS channels between them and high-altitude UAVs. Numerical results show the effectiveness of the proposed pilot decontamination scheme and the significant signal-to-interference-plus-noise ratio (SINR) gains in both the uplink and downlink after pilot decontamination.
This paper reports the use of dual-microcantilevers coupled by cruciform overhang to enhance the mass sensitivity for minor mass detection. Driven by a piezoactuator in air, each cantilever of the structure can resonate in two different modes (in-phase and out-of-phase modes), and the resonant amplitude-ratios are compared before and after a mass adding. Using this sensing strategy, the cross-shaped overhang of the coupled system, by weakening the coupling effect between the two cantilevers, provides two orders of magnitude enhancement in mass sensitivity without scaling down the cantilevers.
Entering the low-carbon economy area,shipping enterprises must combine their own industry characteristics with low-carbon concept for direct the comprehensive operation to meet more opportunities and higher requirements.By recognizing the status quo of human resources management in shipping groups under the current conditions,the paper analysis the significance of putting the low-carbon ideas into the human resources management with the perspectives of job analysis,recruitment,training,performance evaluation,compensation management,labor relations,and make use of green human resource management and other new concepts and methods to guide human resource management innovation in shipping companies in low-carbon economic environment.
The energy cost of cellular networks is ever increasing to match the surge of wireless data traffic, and savings in this cost is important to reduce the operational expenditure of wireless operators in the future. Recent advancements in renewable energy integration and two-way energy flow in smart grid provide potential new solutions to save cost. However, they also impose challenges, especially on how to use the stochastically and spatially distributed renewable energy harvested at cellular BSs to reliably supply time- and space-varying wireless traffic over cellular networks. To overcome these challenges, in this article we present three approaches, energy cooperation, communication cooperation, and joint energy and communication cooperation, in which different BSs bidirectionally trade or share energy via the aggregator in smart grid, and/or share wireless resources and shift loads with each other to reduce the total energy cost.
The paper briefly investigates the importance of power control of HVDC (high voltage direct current) control system in the HVDC projects and focus on the actual analysis and research on the realization of automatic power control in HVDC transmission. It has the important guiding significance for the implementation of automatic power control in HVDC transmission.
This paper is concerned with adaptive and robust video streaming over lossy networks. A general system is described which is compatible with virtually all application settings. The delivery procedure is optimized within a rate-distortion framework with the aid of an efficient real-time end-to-end distortion estimation algorithm. The estimate fully accounts for the effects of (prior) quantization, packet loss and error propagation, as well as error concealment. It features high accuracy and low complexity, and requires a small amount of pre-computed side information. It is shown that various error-resilient schemes can be optimized within the proposed framework. In particular, unequal error protection through forward error control is employed in the simulations to demonstrate the achievable performance gains.
The conventional Gaussian multiple-input multiple-output (MIMO) broadcast channel (BC)- multiple-access channel (MAC) duality has previously been applied to solve non-convex BC capacity computation problems. However, this conventional duality approach is applicable only to the case in which the base station (BS) of the BC is subject to a single sum-power constraint. An alternative approach is the minimax duality, established by Yu in the framework of Lagrange duality, which can be applied to solve the per-antenna power constraint case. This paper first extends the conventional BC-MAC duality to the general linear transmit covariance constraint (LTCC) case, and thereby establishes a general BC-MAC duality. This new duality is then applied to solve the BC capacity computation problem with multiple LTCCs. Moreover, the relationship between this new general BC-MAC duality and the minimax duality is also presented, and it is shown that the general BC-MAC duality has a simpler form. Numerical results are provided to illustrate the effectiveness of the proposed algorithm.
EMTP off-line simulation is conducted by using certain HV fault phase selection algorithm.The correctness of the fault phase selection algorithm is verified through the simulation of different fault and 4 kinds of transitional resistance states.At last,the practicability of algorithm is verified through data check algorithm of fault occurred in the real operation of power system.
A newly designed two‐dimensional planar inverted‐F antenna (PIFA) that achieves a substantially enhanced dual‐band impedance bandwidth is presented. It employs a proposed series‐resonant feed structure, which consists of two series resonators. The enhanced dual‐band impedance bandwidth is realised based on the appropriate increase of the impedance levels of the two series resonators. This increase is sufficient to cover wide use in mobile handsets of 698–960 MHz for the low band and 1710–2690 MHz for the high band with a VSWR < 3.
