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A vactrain (or vacuum tube high-speed flying train) is considered as a novel proposed rail transportation approach in the ultra-high-speed scenario. The maglev train can run with low mechanical friction, low air resistance, and low noise mode at a speed exceeding 1000 km/h inside the vacuum tube regardless of weather conditions. Currently, there is no research on train-to-ground wireless communication system for vactrain. In this paper, we first summarize a list of the unique challenges and opportunities associated with the wireless communication for vactrain, then analyze the bandwidth and Quality of Service (QoS) requirements of vactrain’s train-to-ground communication services quantitatively. To address these challenges and utilize the unique opportunities, a leaky waveguide solution with simple architecture but excellent performance is proposed for wireless coverage for vactrains. The simulation of the leaky waveguide is conducted, and the results show the uniform phase distribution along the horizontal direction of the tube, but also the smooth field distribution at the point far away from the leaky waveguide, which can suppress Doppler frequency shift, indicating that the time-varying frequency-selective fading channel could be approximated as a stationary channel. Furthermore, the train-to-ground wireless access architectures based on leaky waveguide are studied and analyzed. Finally, the moving scheme is adopted based on centralized, cooperative, cloud Radio Access Network (C-RAN), so as to deal with the extremely frequent handoff issue.

Hyperloop is envisioned as a novel transportation way with merits of ultra-high velocity and great traveling comforts. In this paper, we present some concepts on the key technologies dedicated to the train-to-ground communication system based on some prevailing fifth-generation communication (5G) technologies from three aspects: wireless channel, network architecture, and resource management. First, we characterize the wireless channel of the distributed antenna system (DAS) using the propagation-graph channel modelling theory. Simulation reveals that a drastic Doppler shift variation appears when crossing the trackside antenna. Hence, the leaky waveguide system is a promising way to provide a stable receiving signal. In this regard, the radio coverage is briefly estimated. Second, a cloud architecture is utilized to integrate several successive trackside leaky waveguides into a logical cell to reduce the handover frequency. Moreover, based on a many-to-many mapping relationship between distributed units (DUs) and centralized units (CUs), a novel access network architecture is proposed to reduce the inevitable handover cost by using the graph theory. Simulation results show that this scheme can yield a low handover cost. Then, with regards to the ultra-reliable and low latency communication (uRLLC) traffic, a physical resource block (PRB) multiplexing scheme considering the latency requirements of each traffic type is exploited. Simulation presents that this scheme can maximize the throughput of non-critical mission communication services while guaranteeing the requirements of uRLLC traffic. Finally, in terms of the non-critical mission communication services, two cache-based resource management strategies are proposed to boost the throughput and reduce the midhaul link burden by pre-fetching and post-uploading schemes. Simulation demonstrates that the cache-based schemes can boost the throughput dramatically.

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Cloud radio access network (C-RAN) is considered as a promising architecture for 5G with advantages of green energy, convenient resources allocation. In this paper, we explore the feasibility of C-RAN for high-speed railway (HSR) scenarios. A novel phenomenon of group handover is defined in the extensively and densely distributed railway network and we present a resource migration cost with a closedform expression to depict the group handover. To reduce the cost, we propose a novel connection relationship between the remote radio head (RRH) and the baseband unit (BBU) pool. Based on this, we establish a flexible network so as to allocate the resource dynamically and formulate a graph by abstracting the RRH-BBU and BBU-BBU mapping relationship. Then the minimization of resource migration cost along the high-speed train (HST) routine is converted into the shortest path problem (SPP). By using the modified Floyd-Warshall algorithm, the SPP can be solved with high efficiency compared with the conventional algorithm. Finally, the simulation result shows that the proposed mechanism can decrease the resources migration cost significantly. INDEX TERMS Cloud radio access network, group handover, graph theory, high-speed railway communication, RRH-BBU mapping.

Wireless channel modeling is regarded as a pivotal research topic, since the analysis and evaluation of the wireless communication system requires a reliable model of the channel impulse response (CIR). This paper presents a novel and practical study on the position-based radio propagation channel for high-speed vactrains in the vacuum tube scenarios using the propagation graph channel modeling theory. Based on the Lambertian scattering pattern, the propagation graph channel modeling method considers the diffusion effect of radio waves. A multiple-input multiple-output (MIMO) wideband system channel is emulated for obtaining the virtual channel data. During the emulation process, the line-of-sight (LoS), single-bounced and double-bounced components are considered to yield the virtual CIR. Then, small-scale fading properties such as K factor, time delay spread (DS), and Doppler frequency feature are parameterized particularly, which presents dynamic variances at different train locations. Moreover, the simulation performance analysis of the MIMO system focuses on the ergodic capacity and the singular value spread (SVS). The corresponding results indicate a MIMO capacity performance degradation in this scenario. The proposed model can facilitate the reliable simulation and evaluation of MIMO systems for the high-speed vactrains in the vacuum tube scenarios.

Increasing use of large commercial wind turbines motives energy efficiency improvement and fatigue load mitigation in wind turbines. Advanced control methods designed with remote sensing techniques are considered as promising solutions. In this paper, we design a radial basis function neural network feedforward control based on light detection and ranging (LIDAR) measurement. In this control method, the measurements of wind-speed disturbance from LIDAR are used to train weights online in a neural network for optimizing the blade pitch angle and electromagnetic torque in a wind turbine, which is helpful in tracking the maximum wind energy and alleviate fatigue loads. The effectiveness of the proposed controller is validated with the National Renewable Energy Laboratory's typical three-blade wind turbine.

Purpose This paper aims to propose a hybrid force/position control algorithm based on the stiffness estimation of the unknown environment. A frequency-division control scheme is developed to improve the applicability and reliability of the robot in welding, polishing and assembly. Design/methodology/approach The stiffness estimation algorithm with time-varying forgetting factors is used to improve the speed and accuracy of the unknown environmental estimation. The sensor force control and robot position control are adopted in different frequencies to improve system stability and communication compatibility. In the low frequency of sensor force control, the Kalman state observer is used to estimate the robot’s joints information, whereas the polynomial interpolation is used to ensure the smoothness of the high frequency of robot position control. Findings Accurate force control, as well as the system stability, is attained by using this control algorithm. Practical implications The entire algorithm is applied to a six-degrees-of-freedom industrial robot, and experiments are performed to confirm its applicability. Originality/value The frequency-division control strategy guarantees the control stability and improves the smoothness of the robot movement.