Search results

This paper aims to study the encounter issues of the Tethered-Space Net Robot System (TSNRS) with non-target objects on orbit during the maneuver, including the collision issues with small space debris and the obstacle avoidance from large obstacles.

For the collision of TSNRS with small debris, the available collision model of the tethered net and its limitation is discussed, and the collision detection method is improved. Then the dynamic response of TSNRS is studied and a closed-loop controller is designed. For the obstacle avoidance, the variable enveloping circle of the TSNRS has coupled with the artificial potential field (APF) method. In addition, the APF is improved with a local trajectory correction method to avoid the overbending segment of the trajectory.

The collision model coupled with the improved collision detection method solves the detection failure and speeds up calculation efficiency by 12 times. Collisions of TSNRS with small debris make the local thread stretch and deforms finally making the net a mess. The boundary of the disturbance is obtained by a series of collision tests, and the designed controller not only achieved the tracking control of the TSNRS but also suppressed the disturbance of the net.

This paper fills the gap in the research on the collision of the tethered net with small debris and makes the collision model more general and efficient by improving the collision detection method. And the coupled obstacle avoidance method makes the process of obstacle avoidance safer and smoother.

The work in this paper provides a reference for the on-orbit application of TSNRS in the active space debris removal mission.

This paper aims to tele-operate the movement of an unmanned aerial vehicle (UAV) in the obstructed environment with asymmetric time-varying delays. A simple passive proportional velocity errors plus damping injection (P-like) controller is proposed to deal with the asymmetric time-varying delays in the aerial teleoperation system.

This paper presents both theoretical and real-time experimental results of the bilateral teleoperation system of a UAV for collision avoidance over the wireless network. First, a position-velocity workspace mapping is used to solve the master-slave kinematic/dynamic dissimilarity. Second, a P-like controller is proposed to ensure the stability of the time-delayed bilateral teleoperation system with asymmetric time-varying delays. The stability is analyzed by the Lyapunov–Krasovskii function and the delay-dependent stability criteria are obtained under linear-matrix-inequalities conditions. Third, a vision-based localization is presented to calibrate the UAV’s pose and provide the relative distance for obstacle avoidance with a high accuracy. Finally, the performance of the teleoperation scheme is evaluated by both human-in-the-loop simulations and real-time experiments where a single UAV flies through the obstructed environment.

Experimental results demonstrate that the teleoperation system can maintain passivity and collision avoidance can be achieved with a high accuracy for asymmetric time-varying delays. Moreover, the operator could tele-sense the force reflection to improve the maneuverability in the aerial teleoperation.

A real-time bilateral teleoperation system of a UAV for collision avoidance is performed in the laboratory. A force and visual interface is designed to provide force and visual feedback of the slave environment to the operator.

THE airborne Eros II Collision Avoidance System (CAS) designed and produced by McDonnell Douglas Corporation is actuated when the computer calculates the aircraft is within 25 sec of or ½ mile of another aircraft whichever event occurs first. At the same time, the pilot of one of the aircraft gets a command to climb while the pilot of the other aircraft is instructed to descend, thus avoiding a potential mid‐air collision.

The purpose of this paper is to introduce an orthogonal frequency‐division multiplexing (OFDM)‐based 2‐phase physical‐layer feedback space (PFS) for distributed relay selection (RS) in virtual multiple‐input multiple‐output (VMIMO) systems. The proposed method is evaluated with numeric and simulation results.

Unlike minislots used in current MAC layer feedback, the authors introduce physical‐layer feedback space (PFS) which hosts one‐bit for each candidate relay (CR), for instance, a 48‐subcarrier OFDM symbol hosts 48 bits. In the two‐phase feedback procedure, each CR firstly hears the invitation and respond between cluster heads (CH) of upper‐/down‐stream cluster and decides whether to be a qualified relay or not. Then if it is qualified, it randomly selects one subcarrier and sends a pre‐equalized one‐bit feedback. The upper‐stream CH evaluate all feedbacks in PFS, then selects all or a subset of relays with successful feedback and broadcasts its decision to all nodes. Although the number of successful feedbacks (NSF) drops as number of CR increases (NCR), 7∼8 CR can be selected with high probability when NCR is triple that of total subcarriers (48).

In current literature, several traditional MAC layer feedback mechanisms are designed for relay selection in virtual MIMO (VMIMO) system most of which are based upon feedback minislots. For such methods, the number of active nodes should be estimated first and known to all participating nodes to choose optimal feedback possibility to obtain best successful feedback possibility. Furthermore, each minislot should include unique identification of candidate relay thus such methods can NOT be referred as one‐bit feedback. In the new method, though OFDM subcarriers play the same role as minislots, they are exactly one‐bit fashioned and occupies only multiple OFDM symbols which is much shorter than that in current methods.

By using physical‐layer feedback space, exactly only one‐bit is required for each candidate relay to send its feedback, and the overall overhead introduced for all of them is K‐bit provided by the required PFS, which spans only fixed duration of the PFS, which is one or more OFDM symbols. Therefore, the proposed scheme can greatly reduce overhead and feedback delay during relay selection.

In order to obtain visually appealing simulation results with smooth cloth surfaces, high resolution meshes are required. Since cloth simulation with high resolution meshes is very time consuming, subdivision of a reusable model is preferred. The purpose of this paper is to adopt an approach for the subdivision of a reusable model, using different subdivision methods.

In order to obtain visually pleasing reusable garment model, the authors subdivide the model after the conversion to reusable garment model. Two meshes are employed, of which the coarse mesh is used to convert to deformable model while the subdivided mesh, i.e. the refined mesh, is for pleasing modeling results. The modified loop subdivision and modified butterfly subdivision scheme is adopted for the optimization of determining which is more suitable for the reusable model. The authors adopt an algorithm for resolving the collisions happened after the subdivision.

A 3D reusable garment model obtained from previous work was tested. The experimental results validate this method as a useful and effective approach to resolve collisions after the subdivision process.

The paper presents an approach for the subdivision of a reusable model, using different subdivision methods.

A huge variety of devices accumulates as well distributes a large quantity of data either with the help of wired networks or wireless networks to implement a wide variety of application scenarios. The spectrum resources on the other hand become extremely unavailable with the development of communication devices and thereby making it difficult to transmit data on time.

The spectrum resources on the other hand become extremely unavailable with the development of communication devices and thereby making it difficult to transmit data on time. Therefore, the technology of cognitive radio (CR) is considered as one of the efficient solutions for addressing the drawbacks of spectrum distribution whereas the secondary user (SU) performance is significantly influenced by the spatiotemporal instability of spectrum.

As a result, the technique of the hybrid filter detection network model (HFDNM) is suggested in this research work under various SU relationships in the networks of CR. Furthermore, a technique of hybrid filter detection was recommended in this work to enhance the performance of idle spectrum applications. When compared to other existing techniques, the suggested research work achieves enhanced efficiency with respect to both throughputs as well as delay.

The proposed HFDNM improved the transmission delay at 3 SUs with 0.004 s/message and 0.008 s/message when compared with existing NCNC and NNC methods in case of number of SUs and also improved 0.02 s/message and 0.08 s/message when compared with the existing methods of NCNC and NNC in case of channel loss probability at 0.3.

In regarding to operational efficiency and safety improvements, multiple tower crane service scheduling problem is one of the main problems related to tower crane operation but receives limited attention. The current work presents an optimization model for scheduling multiple tower cranes' service with overlapping areas while achieving collision-free between cranes.

The cooperative coevolutionary genetic algorithm (CCGA) was proposed to solve this model. Considering the possible types of cross-tasks, through effectively allocating overlapping area tasks to each crane and then prioritizing the assigned tasks for each crane, the makespan of tower cranes was minimized and the crane collision avoidance was achieved by only allowing one crane entering the overlapping area at one time. A case study of the mega project Daxing International Airport has been investigated to evaluate the performance of the proposed algorithm.

The computational results showed that the CCGA algorithm outperforms two compared algorithms in terms of the optimal makespan and the CPU time. Also, the convergence of CCGA was discussed and compared, which was better than that of traditional genetic algorithm (TGA) for small-sized set (50 tasks) and was almost the same as TGA for large-sized sets.

This paper can provide new perspectives on multiple tower crane service sequencing problem. The proposed model and algorithm can be applied directly to enhance the operational efficiency of tower cranes on construction site.

Cross-layer approach in media access control (MAC) layer will address interference and jamming problems. Hybrid distributed MAC can be used for simultaneous voice, data transmissions in wireless sensor network (WSN) and Internet of Things (IoT) applications. Choosing the correct objective function in Nash equilibrium for game theory will address fairness index and resource allocation to the nodes. Game theory optimization for distributed may increase the network performance. The purpose of this study is to survey the various operations that can be carried out using distributive and adaptive MAC protocol. Hill climbing distributed MAC does not need a central coordination system and location-based transmission with neighbor awareness reduces transmission power.

Distributed MAC in wireless networks is used to address the challenges like network lifetime, reduced energy consumption and for improving delay performance. In this paper, a survey is made on various cooperative communications in MAC protocols, optimization techniques used to improve MAC performance in various applications and mathematical approaches involved in game theory optimization for MAC protocol.

Spatial reuse of channel improved by 3%–29%, and multichannel improves throughput by 8% using distributed MAC protocol. Nash equilibrium is found to perform well, which focuses on energy utility in the network by individual players. Fuzzy logic improves channel selection by 17% and secondary users’ involvement by 8%. Cross-layer approach in MAC layer will address interference and jamming problems. Hybrid distributed MAC can be used for simultaneous voice, data transmissions in WSN and IoT applications. Cross-layer and cooperative communication give energy savings of 27% and reduces hop distance by 4.7%. Choosing the correct objective function in Nash equilibrium for game theory will address fairness index and resource allocation to the nodes.

Other optimization techniques can be applied for WSN to analyze the performance.

Game theory optimization for distributed may increase the network performance. Optimal cuckoo search improves throughput by 90% and reduces delay by 91%. Stochastic approaches detect 80% attacks even in 90% malicious nodes.

Channel allocations in centralized or static manner must be based on traffic demands whether dynamic traffic or fluctuated traffic. Usage of multimedia devices also increased which in turn increased the demand for high throughput. Cochannel interference keep on changing or mitigations occur which can be handled by proper resource allocations. Network survival is by efficient usage of valid patis in the network by avoiding transmission failures and time slots’ effective usage.

Literature survey is carried out to find the methods which give better performance.

Purpose – This chapter reviews planning and design approaches for cycle traffic in order to direct future thinking towards the critical aspects of network design that will have a beneficial impact on the utility and nature of the environment for cycling.

Approach – This chapter provides a critique of the approach of adopting a so-called hierarchy of solutions frequently adopted in western countries with low levels of cycling use.

Findings – The guiding principle for designing routes for cycle traffic is that the bicycle is a vehicle capable of speed and, as a consequence, links and junctions need to be designed according to appropriate geometric design standards. In addition, owing to the nature of the cycle and rider combination, the oft repeated Dutch characteristics for good design for cycle traffic of coherence, directness, attractiveness, safety and comfort remain firm.

Practical implications – The practical implications of the outcomes from the chapter are a method of approach for planning infrastructure for cycle traffic which starts with an analysis of demand and works through to the creation of suitable networks for cycle traffic which are grounded in, and extended from, suitably regulated existing highway networks.

Social implications – An extensive transport system suitable in nature for cycle traffic will attract a wide base of users and consequently allow for the benefits of cycling to be captured.

Value of chapter – The value of the chapter rests in its emphasis on the need to treat cycling as a distinct transport mode and, consequentially, planning and engineering needs to be undertaken in a way conducive to providing the basic necessary infrastructure for such a distinct mode.