220 research outputs found
Joint optimization of relay selection and transmission scheduling for UAV-aided mm wave vehicular networks
No full textTo deal with the explosive growth of mobile traffic, millimeter-wave (mmWave) communications with abundant bandwidth resources have been applied to vehicular networks. As mmWave signal is sensitive to blockage, we introduce the unmanned aerial vehicle (UAV)-aided two-way relaying system for vehicular connection enhancement and coverage expansion. How to improve transmission efficiency and to reduce latency time in such a dynamic scenario is a challenging problem. In this paper, we formulate the joint optimization problem of relay selection and transmission scheduling, aiming to reduce transmission time while meeting the throughput requirements. To solve this problem, two schemes are proposed. The first one is the random relay selection with concurrent scheduling (RCS), a low-complexity algorithm implemented in two steps. The second one is the joint relay selection with dynamic scheduling (JRDS), which fully avoids relay contentions and exploits potential concurrent ability, to obtain further performance enhancement over RCS. Through extensive simulations under different environments with various flow numbers and vehicle speeds, we demonstrate that both RCS and JRDS schemes outperform the existing schemes significantly in terms of transmission time and network throughput. We also analyze the impact of threshold selection on achievable performance
Throughput maximization for intelligent refracting surface assisted mmWave high-speed train communications
Get PDFWith the increasing demands from passengers for data-intensive services, millimeter-wave (mmWave) communication is considered as an effective technique to release the transmission pressure on high-speed train (HST) networks. However, mmWave signals encounter severe losses when passing through the carriage, which decreases the quality of services on board. In this article, we investigate an intelligent refracting surface (IRS)-assisted HST communication system. Herein, an IRS is deployed on the train window to dynamically reconfigure the propagation environment, and a hybrid time division multiple access-nonorthogonal multiple access scheme is leveraged for interference mitigation. We aim to maximize the overall throughput while taking into account the constraints imposed by base station beamforming, IRS discrete phase shifts and transmit power. To obtain a practical solution, we employ an alternating optimization method and propose a two-stage algorithm. In the first stage, the successive convex approximation method and branch and bound algorithm are leveraged for IRS phase shift design. In the second stage, the Lagrangian multiplier method is utilized for power allocation. Simulation results demonstrate the benefits of IRS adoption and power allocation for throughput improvement in mmWave HST networks.</p
Nitrogen Transfer Is Enhanced By AMF Fungi In A Faba Bean/Wheat Intercropping
Get PDFIntercropping is an agricultural practice that can offer several benefits allowing a better native resources use efficiency and, consequently, a restraint of the auxiliary inputs and often a greater production compared to the monocultures (Brooker et al. 2015). Several authors observed that, in a legume/non-legume mixture, one of the benefits could be the N transfer (up to 80 % of the non-legume N demand; Thilakarathna et al. 2016). The transfer may occur via different pathways: legume rhizodeposition, plant tissue decomposition and direct transfer through arbuscular mycorrhizal fungi (AMF) (Bedoussac et al. 2015). The latter, can simultaneously establish symbiotic relationship with different plant species creating a common mycorrhizal network, which serve as a preferential pathway for exchange among plants (He et al. 2003). However, contrasting results have been reported about the contribution of the AMF on N transfer; for instance, Li et al. (2009) showed that N transfer from mung bean to rice increased from 5.4% to 15.7% due to hyphal linkage, whereas Ikram et al. (1994) showed no significant differences with or without AMF inoculum. This experiment aimed to investigate the role of AMF on N transfer from faba bean to durum wheat grown in mixture, using the stem 15N injecting method
Applications of machine learning in wireless communications
No full textThis detailed and comprehensive reference considers how to combine the disciplines of wireless communications and machine learning. Coverage includes channel modelling, signal estimation and detection, energy efficiency, cognitive radios, wireless sensor networks, vehicular communications and wireless multimedia communications
Cardiac manifestations of Wegener's granulomatosis: Case report and review of the literature
No full textSummaryWegener's granulomatosis, first characterized as a clinical syndrome in 1936, is a rare form of vasculitis of the small- and medium-sized blood vessels affecting mainly the upper and lower respiratory tracts as well as the kidneys. This review article describes the case of a 45-year-old man who developed aortic regurgitation and third degree heart block secondary to Wegener's granulomatosis. He subsequently presented to our institution 3 years later with pulmonary hemorrhage. The ensuing literature review reveals that historically clinical cardiac involvement in Wegener's has been rare, particularly with valvular lesions. However, recent literature has shown an increase in reported cases of cardiac valvular lesions in Wegener's. The presented case report along with recently reported case reports highlight the morbidity and mortality associated with such cardiac lesions. We believe routine cardiovascular supervision including echocardiography and electrocardiograms are important for the screening and monitoring of patients with Wegener's granulomatosis
Broadband Channel Long Delay Cluster Measurements and Analysis at 2.4GHz in Subway Tunnels
Get PDFThe delay caused by the reflected ray in broadband communication has a great influence on the communications in subway tunnel. This paper presents measurements taken in subway tunnels at 2.4 GHz, with 5 MHz bandwidth. According to propagation characteristics of tunnel, the measurements were carried out with a frequency domain channel sounding technique, in three typical scenarios: line of sight (LOS), Non-line-of-sight (NLOS) and far line of sight (FLOS), which lead to different delay distributions. Firstly IFFT was chosen to get channel impulse response (CIR) h(t) from measured three-dimensional transfer functions. Power delay profile (PDP) was investigated to give an overview of broadband channel model. Thereafter, a long delay caused by the obturation of tunnel is observed and investigated in all the scenarios. The measurements show that the reflection can be greatly remained by the tunnel, which leads to long delay cluster where the reflection, but direct ray, makes the main contribution for radio wave propagation. Four important parameters: distribution of whole PDP power, first peak arriving time, reflection cluster duration and PDP power distribution of reflection cluster were studied to give a detailed description of long delay characteristic in tunnel. This can be used to ensure high capacity communication in tunnel
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