Sensing-Assisted Communication in Vehicular Networks with Intelligent Surface

The recent development of integrated sensing and communications (ISAC) technology offers new opportunities to meet high-throughput and low-latency communication as well as high-resolution localization requirements in vehicular networks. However, considering the limited transmit power of the road site units (RSUs) and the relatively small radar cross section (RCS) of vehicles with random reflection coefficients, the power of echo signals may be too weak to be utilized for effective target detection and tracking. Moreover, high-frequency signals usually suffer from large fading loss when penetrating vehicles, which seriously degrades the quality of communication services inside the vehicles. To handle this issue, we propose a novel sensing-assisted communication mechanism by employing an intelligent omni-surface (IOS) on the surface of vehicles to enhance both sensing and communication (S&C) performance. To this end, we first propose a two-stage ISAC protocol, including the joint S&C stage and the communication-only stage, to fulfill more efficient communication performance improvements benefited from sensing. The achievable communication rate maximization problem is formulated by jointly optimizing the transmit beamforming, the IOS phase shifts, and the duration of the joint S&C stage. However, solving this ISAC optimization problem is highly non-trivial since inaccurate estimation and measurement information renders the achievable rate lack of closed-form expression. To handle this issue, we first derive a closed-form expression of the achievable rate under uncertain location information, and then unveil a sufficient and necessary condition for the existence of the joint S&C stage to offer useful insights for practical system design. Moreover, two typical scenarios including interference-limited and noise-limited cases are analyzed.Comment: IEEE Transactions on Vehicular Technology, 2023. arXiv admin note: text overlap with arXiv:2211.0420

Dtn and non-dtn routing protocols for inter-cubesat communications: A comprehensive survey

CubeSats, which are limited by size and mass, have limited functionality. These miniaturised satellites suffer from a low power budget, short radio range, low transmission speeds, and limited data storage capacity. Regardless of these limitations, CubeSats have been deployed to carry out many research missions, such as gravity mapping and the tracking of forest fires. One method of increasing their functionality and reducing their limitations is to form CubeSat networks, or swarms, where many CubeSats work together to carry out a mission. Nevertheless, the network might have intermittent connectivity and, accordingly, data communication becomes challenging in such a disjointed network where there is no contemporaneous path between source and destination due to satellites’ mobility pattern and given the limitations of range. In this survey, various inter-satellite routing protocols that are Delay Tolerant (DTN) and Non Delay Tolerant (Non-DTN) are considered. DTN routing protocols are considered for the scenarios where the network is disjointed with no contemporaneous path between a source and a destination. We qualitatively compare all of the above routing protocols to highlight the positive and negative points under different network constraints. We conclude that the performance of routing protocols used in aerospace communications is highly dependent on the evolving topology of the network over time. Additionally, the Non-DTN routing protocols will work efficiently if the network is dense enough to establish reliable links between CubeSats. Emphasis is also given to network capacity in terms of how buffer, energy, bandwidth, and contact duration influence the performance of DTN routing protocols, where, for example, flooding-based DTN protocols can provide superior performance in terms of maximizing delivery ratio and minimizing a delivery delay. However, such protocols are not suitable for CubeSat networks, as they harvest the limited resources of these tiny satellites and they are contrasted with forwarding-based DTN routing protocols, which are resource-friendly and produce minimum overheads on the cost of degraded delivery probability. From the literature, we found that quota-based DTN routing protocols can provide the necessary balance between delivery delay and overhead costs in many CubeSat missions

Traffic pattern prediction in cellular networks.

PhDIncreasing numbers of users together with a more use of high bit-rate services complicate radio resource management in 3G systems. In order to improve the system capacity and guarantee the QoS, a large amount of research had been carried out on radio resource management. One viable approach reported is to use semi-smart antennas to dynamically change the radiation pattern of target cells to reduce congestion. One key factor of the semi-smart antenna techniques is the algorithm to adjust the beam pattern to cooperatively control the size and shape of each radio cell. Methods described in the literature determine the optimum radiation patterns according to the current observed congestion. By using machine learning methods, it is possible to detect the upcoming change of the traffic patterns at an early stage and then carry out beamforming optimization to alleviate the reduction in network performance. Inspired from the research carried out in the vehicle mobility prediction field, this work learns the movement patterns of mobile users with three different learning models by analysing the movement patterns captured locally. Three different mobility models are introduced to mimic the real-life movement of mobile users and provide analysable data for learning. The simulation results shows that the error rates of predictions on the geographic distribution of mobile users are low and it is feasible to use the proposed learning models to predict future traffic patterns. Being able to predict these patterns mean that the optimized beam patterns could be calculated according to the predicted traffic patterns and loaded to the relevant base stations in advance

PROGNOSTIC MODELING FOR RELIABILITY PREDICTIONS OF POWER ELECTRONIC DEVICES

The applications of semiconductor power electronic devices, including power and RF devices, in industry have stringent requirements on their reliability. Power devices are subject to various types of failure mechanisms under various stressors. Prognostics and health management (PHM) allows detecting signs of failures, providing warnings of failures in advance, and performing condition-based maintenance. There is a pressing need to develop a robust prognostic model to detect anomalous behavior and predict the lifetime of devices that can be applicable to different types of power transistors. In the present dissertation, a comprehensive prognostic model for remaining useful life (RUL) prediction of semiconductor power electronic devices is developed. The model consists of an anomaly detection module and a RUL prediction module including a non-linear system process model describing the evolution of parametric degradation, and a measurement model. The anomaly detection module uses principal component analysis (PCA) for dimensionality reduction and feature extraction, as well as k-means clustering to establish baseline clusters in the feature space. The novel singular-value-weighted distance (SVWD) is developed as the distance measure in the feature space, based on which Fisher criterion (FC) is used for anomaly probability calculation. The system process model incorporates variables concerning loading conditions and physics-of-failure of devices, and uses particle filter (PF) approach for process model training and RUL prediction. For PF methodology, a novel resampling technique, called MHA-replacement resampling, is developed to solve the particle degeneracy in classic PF techniques and sample impoverishment in traditional resampling techniques. The developed prognostic model is first implemented on IGBT modules for validation. It was reported that the module package of power transistors was susceptible to various types of fatigue-related failure modes due to coefficient of thermal expansion (CTE) mismatches under temperature/power cycles introducing thermomechanical stresses. The physics-of-failure "driving variable" is derived from Paris equation. The model is validated on several time-series IGBT module degradation data under power cycles from literature sources, based on SIR particle filter for RUL prediction with good accuracy. Then the model is implemented on GaN HEMTs, a representative of wide-bandgap semiconductor power devices. GaN HEMTs are susceptible to degradation mechanisms such as ohmic contact inter-diffusion that leads to voiding in the field plate at high temperature under RF accelerated life tests (ALTs). The time-series data of the physics-of-failure "driving variable" is obtained from diffusion computation in Mathematica with the temperature prole coming from COMSOL thermal simulation. The RUL prediction results based on SIR lter are also satisfactory for GaN HEMTs. For each type of device, the new resampling technique is validated through performance benchmarking against state-of-the-art resampling techniques. Another reliability threat for GaN HEMTs, especially in aerospace and nuclear applications, is the degradation due to radiation effect on the device performance. Gamma radiation has been found to lead to generation of defects in AlGaN/GaN layers, which form complexes acting as carrier traps, thus reducing carrier density and current. EPC GaN HEMTs are irradiated under a wide range of Gamma ray doses and critical DC characteristics are recorded before and after radiation to quantify their shifts during the irradiation. Future work needed to allow implementation of the developed prognostic model for RUL estimation is proposed

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

Development of maintenance framework for modern manufacturing systems

Modern manufacturing organizations are designing, building and operating large, complex and often ‘one of a kind’ assets, which incorporate the integration of various systems under modern control systems. Due to such complexity, machines failures became more difficult to interpret and rectify and the existing maintenance strategies became obsolete without development and enhancement. As a result, the need for more advanced strategies to ensure effective maintenance applications that ensures high operation efficiency arise. The current research aims to investigate the existing maintenance strategies, the levels of machines complexity and automation within manufacturing companies from different sectors and sizes including, oil and gas, food and beverages, automotive, aerospace, and Original Equipment Manufacturer. Results analysis supports in the development of a modern maintenance framework that overcome the highlighted results and suits modern manufacturing assets using systematic approaches and utilisation of pillars from Total productive maintenance (TPM, Reliability Centred Maintenance (RCM) and Industry 4.0

Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields

Innovations in Road, Railway and Airfield Bearing Capacity – Volume 1 comprises the first part of contributions to the 11th International Conference on Bearing Capacity of Roads, Railways and Airfields (2022). In anticipation of the event, it unveils state-of-the-art information and research on the latest policies, traffic loading measurements, in-situ measurements and condition surveys, functional testing, deflection measurement evaluation, structural performance prediction for pavements and tracks, new construction and rehabilitation design systems, frost affected areas, drainage and environmental effects, reinforcement, traditional and recycled materials, full scale testing and on case histories of road, railways and airfields. This edited work is intended for a global audience of road, railway and airfield engineers, researchers and consultants, as well as building and maintenance companies looking to further upgrade their practices in the field

A Random Trajectory Approach for the Development of Nonstationary Channel Models Capturing Different Scales of Fading

This paper introduces a new approach to developing stochastic nonstationary channel models, the randomness of which originates from a random trajectory of the mobile station (MS) rather than from the scattering area. The new approach is employed by utilizing a random trajectory model based on the primitives of Brownian fields (BFs), whereas the position of scatterers can be generated from an arbitrarily 2-D distribution function. The employed trajectory model generates random paths along which the MS travels from a given starting point to a fixed predefined destination point. To capture the path loss, the gain of each multipath component is modeled by a negative power law applied to the traveling distance of the corresponding plane wave, whereas the randomness of the path traveled results in large-scale fading. It is shown that the local received power is well approximated by a Gaussian process in logarithmic scale, even for a very limited number of scatterers. It is also shown that the envelope of the complex channel gain follows closely a Suzuki process, indicating that the proposed channel model superimposes small-scale fading and large-scale fading. The local power delay profile (PDP) and the local Doppler power spectral density (PSD) of the channel model are also derived and analyzed.acceptedVersionnivå