Sharing of the frequency bands between radar and communication systems has attracted substantial attention, as it can avoid under-utilization of otherwise permanently allocated spectral resources, ...thus improving efficiency. Further, there is increasing demand for radar and communication systems that share the hardware platform as well as the frequency band, as this not only decongests the spectrum, but also benefits both sensing and signaling operations via the full cooperation between both functionalities. Nevertheless, the success of spectrum and hardware sharing between radar and communication systems critically depends on high-quality joint radar and communication designs. In the first part of this paper, we overview the research progress in the areas of radar-communication coexistence and dual-functional radar-communication (DFRC) systems, with particular emphasis on application scenarios and technical approaches. In the second part, we propose a novel transceiver architecture and frame structure for a DFRC base station (BS) operating in the millimeter wave (mmWave) band, using the hybrid analog-digital (HAD) beamforming technique. We assume that the BS is serving a multi-antenna user equipment (UE) over a mmWave channel, and at the same time it actively detects targets. The targets also play the role of scatterers for the communication signal. In that framework, we propose a novel scheme for joint target search and communication channel estimation, which relies on omni-directional pilot signals generated by the HAD structure. Given a fully-digital communication precoder and a desired radar transmit beampattern, we propose to design the analog and digital precoders under non-convex constant-modulus (CM) and power constraints, such that the BS can formulate narrow beams towards all the targets, while pre-equalizing the impact of the communication channel. Furthermore, we design a HAD receiver that can simultaneously process signals from the UE and echo waves from the targets. By tracking the angular variation of the targets, we show that it is possible to recover the target echoes and mitigate the resulting interference to the UE signals, even when the radar and communication signals share the same signal-to-noise ratio (SNR). The feasibility and efficiency of the proposed approaches in realizing DFRC are verified via numerical simulations. Finally, the paper concludes with an overview of the open problems in the research field of communication and radar spectrum sharing (CRSS).
In the immersive communications systems, video information is stringently delivered for extended reality applications. Since users may demand various immersive experience and have different levels of ...view prediction accuracy, the two-tier 360-degree video delivery frame structure with dynamic transmission time interval duration needs to be designed appropriately. To maximize the system's quality of experience, two new frame structures and power control are proposed. Meanwhile, the synchronous and asynchronous cases with different computational complexities are addressed. The results demonstrate the effectiveness of the proposed design and indicate that flexible frame structure is beneficial for multiuser immersive communications.
The disturbance propagation mechanism is crucial for the preventive, corrective, and in-extremis control of power grids. This paper proposes a novel non-uniform frame structure model for power system ...disturbance propagation analysis. A general state transition model of the power grid is derived from the electromechanical wave propagation process. This is further used together with the Gaussian function to derive the non-uniform heterogeneous inertial continuum model, where the non-uniform parameters of the inertia are estimated using the state transition model. The proposed non-uniform frame structure model can be integrated with the electromechanical wave equation to study the disturbance propagation process. These novel developments allow us to tackle the inertial loss and uniform homogenous assumption in existing models. Extensive comparison results carried out on both the chain grid and the IEEE 118-bus system demonstrate that the proposed model can achieve 5- and 3-times accuracy improvements of the state-of-the-art SHU-FSM and ISHU-FSM models, respectively.
The parameters of physical layer radio frame for 5th generation (5G) mobile cellular systems are expected to be flexibly configured to cope with diverse requirements of different scenarios and ...services. This paper presents a frame structure and design, which is specifically targeting Internet of Things (IoT) provision in 5G wireless communication systems. We design a suitable radio numerology to support the typical characteristics, that is, massive connection density and small and bursty packet transmissions with the constraint of low-cost and low complexity operation of IoT devices. We also elaborate on the design of parameters for random access channel enabling massive connection requests by IoT devices to support the required connection density. The proposed design is validated by link level simulation results to show that the proposed numerology can cope with transceiver imperfections and channel impairments. Furthermore, the results are also presented to show the impact of different values of guard band on system performance using different subcarrier spacing sizes for data and random access channels, which show the effectiveness of the selected waveform and guard bandwidth. Finally, we present system-level simulation results that validate the proposed design under realistic cell deployments and inter-cell interference conditions.
•A unified damage model to describe the level of damage as well as the spatial distribution of damage.•Local vibration modes caused by complete loss of one part of one or more members.•Fail-safe ...optimization problems with millions of local stress constraints.•Solving the fail-safe optimization problems with a working-set method.
In conventional fail-safe optimization of frame structures the damage is usually modelled as complete removal of one or more members. We propose and incorporate two additional types of damage models into the fail-safe design problem. The first describes thickness degradation caused e.g. by corrosion. The second describes severe local damage by removal of a part of a member that causes a gap and free ends in the member. The latter damage model can cause undesirable local vibration modes. By combining the two damage models, local thickness degradation in a part of a member can be modelled. The considered design problem minimizes structural mass and includes local stress constraints and limits on eigenfrequencies. Besides the new damage models, a working-set algorithm is applied on the fail-safe optimization problem to reduce the computational cost. Numerical experiments on two-dimensional frame structures illustrate that the working-set algorithm can effectively handle the relatively large number of constraints and damage scenarios in fail-safe optimization.
Accurate estimates of the electromechanical disturbance propagation in a power system play an important role in taking preventive, corrective, and in-extremis control actions. This paper proposes an ...analytical method for disturbance propagation investigation based on the electromechanical wave theory. A frame structure model is developed that allows us to derive an analytical relationship between the disturbance propagation and the turbine-generator inertia, the line reactance, bus voltage, and disturbance source frequency. In addition, the disturbance attenuation and the degree of disturbance propagation are studied. Numerical results performed on a multi-machine chain network and the IEEE 118-bus test system demonstrate the effectiveness of the developed method.
•Review of the state-of-art on progressive collapse.•Focus on frame structures (reinforced concrete, steel,...).•The influence of triggering events on progressive collapse is discussed.•Robustness ...techniques are compared.•Emphasis on the open or unsolved issues is paid.
This paper reviews the state-of-art in progressive collapse studies on framed building structures. Such types of failure start with a local damage which extension increases, up to the whole structure. First, emphasis is placed on the current techniques to study collapse propagation, i.e., numerical, experimental and analytical. In particular, the various numerical methods found in the literature are reported and discussed and the experimental studies and technologies involved in the laboratory tests are listed and compared. As reviewed, the method of analysis depends on the collapse mechanism and the triggering event. Thus, an in-depth review of the collapse typologies is proposed. Pure and mixed progressive collapse mechanisms are discussed and debated. The various triggering events, their modeling and their effects on the framed structures are examined. Details on the available literature on multi-hazard scenarios are provided. Finally, robustness techniques against progressive collapse are summarized, compared and contrasted. The paper concludes with an ambitious comprehensive list of open questions and issues covering different aspects of future needs.
Structural health monitoring (SHM) and Non-destructive Damage Identification (NDI) using responses of structures under dynamic excitation have an imperative role in the engineering application to ...make the structures safe. Interpretations of structural responses known as inverse problems are emerging topics with a large body of works in the literature. They have been widely solved with Machine Learning (ML) techniques such as Artificial Neural Network (ANN), Deep Neural Network (DNN), Adaptive Network-based Fuzzy Inference System (ANFIS), and Support Vector Machine (SVM). Nonetheless, these approaches can precisely predict the inverse problems of civil structures (e.g., truss or frame systems) with low damage levels, which have to wait until the structures reach certain damage or deteriorate level. The issue is related to the fact that most of the real structures have very low damage levels during their routine maintenances and usually be neglected due to limitations of the current techniques. This paper proposes a combination of Particle Swarm Optimization and Support Vector Machine (PSO-SVM) for damage identifications. The proposed approach is inspired by the effective searching capability of PSO, which can eliminate the redundant input parameters and robust SVM technique to classify damage locations effectively. In other words, natural frequencies and mode shapes extracted from the numerical examples of truss and frame structures are used as input parameters in which the redundant parameters might lead to reduction of the accuracy in the predicting models. The proposed PSO-SVM shows superior accuracy prediction in both damage locations and damage levels compared to the other ML models. It also substantially outperforms other ML models through validated cases of low damage levels.
The whale optimization algorithm (WOA) is a recently developed swarm-based optimization algorithm inspired by the hunting behavior of humpback whales. This study attempts to enhance the original ...formulation of the WOA in order to improve solution accuracy, reliability and convergence speed. The new method, called enhanced whale optimization algorithm (EWOA), is tested in sizing optimization problems of truss and frame structures. The EWOA is compared with WOA and other metaheuristic methods developed in literature in four optimization problems of skeletal structures. Numerical results demonstrate the efficiency of the EWOA and WOA with the former algorithm being more efficient than its standard version.
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