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.

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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.

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This study aims to investigate the risk factors associated with impaired pulmonary diffusing capacity among patients with noncystic fibrosis bronchiectasis (NCFB) and compare the predictive value of several scoring systems for the impairment in these patients. Between July 2019 and June 2021, patients who were admitted to the hospital and diagnosed with NCFB were included in this study. Clinical data were collected and analyzed retrospectively. A total of 175 NCFB patients were included in the analysis. Multivariate logistic regression analysis revealed that impaired pulmonary diffusing capacity diagnosed by carbon monoxide diffusing capacity (DLCO) <80% prediction was associated with age, Reiff score, body mass index (BMI), comorbid chronic obstructive pulmonary disease (COPD), and interstitial lung disease (ILD). Disease duration, frequency of exacerbation, hemoglobin level, and COPD were independent risk factors for impaired pulmonary diffusing capacity diagnosed by DLCO/alveolar volume (VA) <80% prediction. Age, Reiff score, and smoking status were independent risk factors for decreased VA diagnosed by VA <80% prediction. The areas under the curve (AUC) for discrimination of DLCO <80% prediction were 0.822 (0.760–0.885) for Bronchiectasis Severity Index (BSI), 0.787 (0.718–0.856) for FACED, 0.795 (0.729–0.863) for E-FACED, and 0.767 (0.694–0.839) for modified Medical Research Council (mMRC) scores; the AUC for discrimination of DLCO/VA <80% prediction was 0.803 (0.727–0.880) for BSI, 0.752 (0.669–0.835) for FACED, 0.757 (0.676–0.839) for E-FACED, and 0.762 (0.679–0.845) for mMRC, respectively. The BSI had the largest AUC, but the differences between those scoring systems had no statistical significance ( P = 0.181 for DLCO <80% prediction and P = 0.105 for DLCO/VA <80% prediction). The mMRC score (up to 2 grades) showed a high specificity for discriminating diffusing dysfunction (88.3% for DLCO <80% prediction and 76.1% for DLCO/VA <80% prediction). In NCFB patients, several factors such as age, Reiff score, BMI, exacerbation frequency, disease duration, and comorbid COPD and ILD were associated with impaired pulmonary diffusing capacity, which requires more attention in managing those patients. In addition, several scoring methods, including a simple index of mMRC, showed a comparable and moderate performance for predicting pulmonary diffusing impairment and would facilitate the systematic evaluation of the diffusing capacity of NCFB patients.

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