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Underwater Optical Wireless Communication (UOWC) is an up-and-coming technology to support the perception layer of the Internet of Underwater Things (IoUT). However, UOWC channel behaviors can lead to a reduction of IoUT network reliability, while UOWC sensor nodes usually face with the issue of energy limitation. In this paper, we propose a retransmission scheme, which utilizes probing packets and energy harvesting mechanism to solve these issues. The scheme could provide more reliable transmission and energy efficiency for UOWC-based IoUT networks. To investigate the performance of the proposed scheme, we provide an analytical framework based on a two-dimensional Markov chain model. The Monte-Carlo simulation is used to validate the correctness of our analysis. From numerical results, we highlight the advantages of our scheme in comparison with the conventional one. We also determine appropriate values of network parameters to optimize the network performance.

Objectives: The COVID-19 pandemic may impact cigarette smokers’ behaviors. Among smokers, perceptions about the risks of contracting COVID-19 and the severity of COVID-19 illness likely vary, and perceptions may be associated with individual smoking behavior. Our study measured smokers’ perceptions of COVID-19 risks and their association with smoking and quitting outcomes. Methods: A sample of 1,223 U.S. adult cigarette smokers participated in an online survey in October-November 2020 to assess their COVID-19-related risk perceptions and changes in smoking, readiness to quit, and quit attempts during the COVID-19 pandemic. Results: More smokers believed smoking could increase the severity of COVID-19 (43.6%, 95% CI: 40.1, 47.3) than believed smoking makes them more susceptible to COVID-19 (20.0%, 95% CI: 17.2, 23.0.). While there were no associations between perceptions of COVID-19 susceptibility and smoking behaviors or intentions, perceptions of greater smoking-related COVID-19 severity were associated with both higher likelihood of smoking increases (aOR: 2.16, 95% CI: 1.19, 3.93) and greater readiness to quit smoking (aOR: 1.65, 95% CI: 1.18, 2.30). Greater perceptions of general COVID-19 severity were associated with higher likelihood of smoking reductions (aOR: 1.12, 95% CI: 1.02, 1.22), greater readiness to quit smoking (aOR: 1.14, 95% CI: 1.07, 1.22), and higher likelihood of making a quit attempt (aOR: 1.12, 95% CI: 1.04, 1.22). Conclusions: Smokers’ perceptions about COVID-19 severity are related to their smoking behavior and likelihood of making a quit attempt. Providing smokers with accurate information on the relationship between smoking and the severity of COVID-19 may alter smoking behaviors.

Supported by IEEE 802.15.7 standardization activities, visible local area network (VLAN) has been gaining popularity in recent years. Specified in the standard are physical (PHY) and uplink medium access control (MAC) layers of VLAN. However, there is a lack of studies on the MAC performance analysis and improvement under the effects of PHY transmission errors in the literature. We thoroughly analyze the MAC for various performance metrics taking into account PHY transmission errors due to different VLC physical factors. We also consider MAC enabling frame retransmissions as a solution to PHY transmission errors. Numerical results show that, first, MAC performance is critically affected by PHY transmission errors and, second, frame retransmissions, with a proper setup, could considerably improve the performance.

High-altitude airborne platforms interconnected by free-space optical communications (FSOCs) have recently emerged as a promising solution for establishing wireless networks for rural and remote areas. The performance of FSOC system is severely degraded by the angle-of-arrival (AoA) fluctuation and pointing error. The precise alignment between the optical transmitter and receiver can be achieved by using the pointing, acquisition, and tracking (PAT), but it should work within the tight constraints of airborne platforms on size, weight, and power. It is also highly desirable that the PAT operates rapidly (e.g., without iteration for optimization) since the airborne platforms can be on the fast move. We propose a rapid and computation power-efficient adaptive beam control technique, where the beam sizes are adjusted without iterations at both the transmitter and receiver using nonmechanical variable-focus lenses, to mitigate the deleterious effects of AoA fluctuation and pointing error simultaneously. For this purpose, we provide the closed-form expressions about the optimum beam sizes at the transmitter and receiver for the outage probability. We carry out Monte Carlo simulations to validate the accuracy of our theoretical derivations. We show that the airborne FSOC system using the adaptive beam control technique outperforms the system having fixed beam sizes over wide ranges of AoA fluctuation and pointing error.

In this paper, we study a cross-layer analysis framework for the performance evaluation of TCP over millimeter-Wave (mmWave) fading channels in the fifth-generation (5G) cellular networks, when the truncated incremental redundancy hybrid automatic repeat request (IR-HARQ) scheme and adaptive modulation and coding (AMC) are employed. Specifically, the throughput performance of TCP Cubic, which is one of the most widely deployed TCP variants in the Internet, is investigated. For this purpose, the mmWave fading channel, approximated by Nakagami-m distribution, is captured by a finite-state Markov chain (FSMC) to develop a transmission loss model. A loss-based TCP model, which is analyzed based on the transmission loss model, is then used to analytically derive the TCP throughput performance. The numerical results quantitatively show the effect of different parameters/settings of AMC, IR-HARQ, blockages and mmWave fading channels on the TCP performance and support the optimal selection of parameters to maximize the system throughput. Monte Carlo simulations are also performed to validate the analytical results.

Free-space optical communications (FSOCs) have recently emerged as a promising solution for various communication scenarios. However, the pointing, acquisition, and tracking (PAT) is a technically challenging issue, especially in airborne FSOC systems. In this paper, we present an adaptive beam control technique combined with beaconless PAT using a variable focus lens. By using the lens whose focal length can be tuned electrically, we facilitate the coarse PAT by enlarging the beam size and also mitigate the adverse effects of pointing errors by adjusting the beam divergence angle adaptively to the link conditions. The major benefit of the proposed scheme is that the beam control can be implemented in a simple and compact manner, without relying on mechanical movements. We carry out a proof-of-concept experimental demonstration of the proposed scheme for a 10-Gb/s free-space optical link over 104 m. The demonstration shows that the probability of PAT success can be improved considerably by using the proposed scheme. It also shows that the proposed scheme could result in a system loss reduction of 6.4 dB and improve the tolerance to pointing errors up to 500 μrad for a target bit-error ratio of 10−3. The response time of the lens is measured to be

Aim. Diabetes in children is becoming more prevalent in some countries. However, in most countries, little is known about the epidemiology of this disease. This study is aimed at estimating the prevalence of type 1 and type 2 diabetes and prediabetes among children in Vietnam and examining factors associated with the conditions. Methods. A total of 2880 students aged 11-14 years old were recruited for the survey, using a school-based and nationally representative sampling frame. Capillary blood samples of participants were collected to measure fasting glucose level, using glucose meter OneTouch Verio Pro+. Diabetes and impaired fasting plasma glucose were initially diagnosed based on the cut-off points of the American Diabetes Association criteria. Diabetes status and type of diabetes of participants were confirmed at a hospital. Additionally, anthropometric and blood pressure measurements were conducted following a standardized procedure. Multivariate logistic regression was used to examine the association between outcome and independent variables. Results. The overall prevalence of diabetes among the participants was 1.04‰ (three cases), with 2 cases (0.75‰) diagnosed with type 1 diabetes (one known and one newly diagnosed) and 1 case newly diagnosed with type 2 diabetes (0.35‰). The prevalence of impaired fasting glucose was 6.1%. Body mass index, place of residence, and age were found to be significantly associated with the impaired fasting glucose condition in participants. Conclusion. The prevalence of type 1 and type 2 diabetes in children in Vietnam is lower than that in some other countries reported recently. However, there is a high prevalence in impaired fasting glucose, requiring attention from policymakers to take action to prevent the occurrence of the epidemic of type 2 diabetes in children in the future.

The impact of atmospheric turbulence is one of the most challenging issues for the widespread deployment of free-space optical (FSO) communication systems. To enhance the systems' performance, adaptive-rate (AR) transmission and automatic repeat request (ARQ) have been separately considered at the physical and data link control layers. This paper introduces a framework of cross-layer design, analysis, and optimization for FSO communication systems, in which ARQ and AR transmission are jointly integrated to further improve the overall system performance over atmospheric turbulence channels. Two cross-layer designs are considered: 1) AR and standard ARQ and 2) AR and ARQ with frame combining. In addition, we newly develop a Markov chain model-based cross-layer analysis to evaluate system performance. System performance metrics, including spectral efficiency, maximum expected number of transmissions, and outage probability, are analytically studied under the presence of atmospheric turbulence. In numerical results, how the cross-layer designs significantly outperform conventional ones is quantitatively shown. Furthermore, we discuss a cross-layer optimization of selecting the ARQ persistence level for the tradeoff between the spectral efficiency and the number of transmissions.