An efficient multitarget tracking algorithm for car applications

A new and efficient tracking algorithm for vehicle collision warning and collision avoidance systems using car radar is proposed. The target-to-measurement data association is accomplished using the decision logic algorithm based on order statistics. The simulation and experimental results are presented to demonstrate its performance.     

Hierarchical Longitudinal Controller for Rear-End Collision Avoidance

Rear-end collision is a very serious problem in modern traffic situations, and there have been a great number of research reports on the longitudinal control method for road vehicles. In many cases, however, the control problem is formulated under platoon configuration and for some predictable noncollision situations. For predictable collision situations, regional and hierarchical approaches have been employed, but these approaches render difficulties due to ignorance for modeling error and logical error in a decision process. In this paper, the vehicle control for collision avoidance is studied with two control objectives, i.e., minimization of the safety distance error and regulation of the relative velocity between two vehicles. For this, a longitudinal controller using terminal sliding mode (TSM) with hierarchical structure is proposed for rear-end collision avoidance. The TSM is employed to achieve convergence in finite time, while the hierarchical approach is used for the system to accommodate the intelligence of the driver to handle various situations. The effectiveness of the proposed control scheme is verified by software simulations     

一种新的通用航空机载防撞逻辑设计方法

由于机载防撞系统(TCAS)是针对具有较大垂直高度变化率的大型飞机设计的,系统设定条件和与之相关的解脱建议并不能适用于通航飞机.针对通用航空的防撞问题,提出了一种基于马尔可夫决策过程(MDP)的防撞逻辑设计方法.首先,将飞机空中相遇过程的动态模型转换为离散转移函数;然后,基于防撞系统结果事件末端效用函数进行MDP建模,采用动态规划方法导出了最优防撞逻辑的迭代方程;最后,给出了通航飞机最优化防撞逻辑的设计流程并对最优防撞逻辑进行了计算机仿真.仿真结果表明,通过调整效用比参数可以在保证安全性能的同时有效降低系统告警率.在垂直相遇高度小于30 m的相遇过程占比高达18%的情况下,当告警率大于0.85时系统的碰撞概率仅为2.88×10-4左右.该设计方法对我国在低空空域通用飞机防撞系统的研究具有一定的参考价值.     

24 GHz active retrodirective antenna array

A 24 GHz active Van Atta planar antenna array proposed for increasing the vehicle radar echo in a vehicle collision avoidance system is designed and demonstrated. The antenna array contains two parallel linear sub-arrays. Each sub-array is composed of four receiving microstrip antennas, four transmitting microstrip antennas and four transistor amplifiers. At the angles of -40°<&thetas;<40°, except those very close to the specular direction (&thetas;=0°), the measured backscattering field levels of the fabricated array have variations <3 dB and are at least 10 dB higher than those of a metal plate of the same size     

A Resilient and Scalable Flocking Scheme in Autonomous Vehicular Networks

Vehicular Ad hoc NETworks (VANET) is emerging as a highly promising technology, which aims to provide road safety, environment protection and personal-oriented services. The vehicle ad hoc wireless communications form an indispensable part of truly ubiquitous communications networking. VANET is formed by spontaneously moving autonomous vehicles with the self-organization and self-management capability. In this paper, we focus on the decentralized coordination of multiple unmanned vehicles such that they can freely move and adaptively cooperate in a complex environment. During this procedure, flocking is one of the key operations and requirements. Here, flocking refers to the formation and maintenance of a desired pattern by a group of mobile vehicles without collision during movement. We propose a resilient and scalable flocking scheme for a group of vehicles, which follows the leader–followers moving pattern. In the absence of obstacles, a collision avoidance algorithm is presented to maintain a desired distance among vehicles. This will ensure information completeness and is significant in certain mission critical situations without collision between a unmanned vehicle and its neighboring vehicles. In the presence of obstacles in an environment, this algorithm is able to avoid collision between a vehicle and its neighbor (either a neighboring vehicle or a neighboring obstacle). Theoretical proof has been presented to demonstrate the effectiveness and correctness of the algorithm to guarantee collision-free. In addition, with increasing number of vehicles, the performance of the proposed flocking scheme performs without increasing the processing overhead, which demonstrates the desirable scalability.     

Nonlinear brake control for vehicle CW/CA systems

A brake control law for vehicle collision warning/collision avoidance (CW/CA) systems has been proposed in the paper. The control law has been designed for optimized safety and comfort. A solenoid-valve-controlled hydraulic brake actuator system for the CW/CA systems has been investigated. A nonlinear computer model and a linear model of the hydraulic brake actuator system have been developed. Both models were found to represent the actual system with good accuracy. Uncertainties in the brake actuator model have been considered in the design of the control law for the robustness of the controller. The effects of brake control on CW/CA vehicle response has been investigated via simulations. The simulations were performed using a complete nonlinear vehicle model. The results indicate that the proposed brake control law can provide the CW/CA vehicles with an optimized compromise between safety and comfort     

面向车辆盲区防撞系统的交通目标智能检测

交通目标智能检测是车辆盲区智能防撞系统中的基础技术,该技术的研究和应用对降低交通事故损失具有重要意义。本文面向车辆盲区防撞系统设计的检测模型,其在基础模型中融合了两个性能提升策略。将该模型应用于国内和国外道路场景检测数据集,以验证模型在所有范围和近距离目标的检测性能。实验结果表明该模型可以对近距目标表现出较高的检测精度,且具有较高的检测速度,因此该模型可适用于车辆低速启动或者转弯时智能盲区防撞系统对交通目标的检测需求。      

Millimeter wave backscatter measurements in support of collision avoidance applications

Millimeter-wave short range radar systems have unique advantages in surface navigation applications, such as military vehicle mobility, aircraft landing assistance, and automotive collision avoidance. In collision avoidance applications, characterization of clutter due to terrain and roadside objects is necessary in order to maximize the signal-to-clutter ratio (SCR) and to minimize false alarms. The results of two types of radar cross section (RCS) measurements at 95 GHz are reported in this paper. The first set of measurements presents data on the normalized RCS (NRCS) as well as clutter distributions of various terrain types at low grazing angles of 5° and 7.5°. The second set of measurements presents RCS data and statistics on various types of roadside objects, such as metallic and wooden sign posts. These results are expected to be useful for designers of short-range millimeter-wave collision avoidance radar systems.     

A frequency hopping method for spatial RFID/WiFi/Bluetooth scheduling in agricultural IoT

Currently, a variety of wireless modules are purposed for different criteria in the area of the agricultural internet of things; however, there is a lack of appropriate methods enabling these wireless modules to operate in the same frequency band. The goal of this paper is to make a very thorough quantitative analysis on the theoretical maximum collision time and collision probability of WiFi or Bluetooth network with RFID interferers. We propose the interference avoidance scheme which requires the knowledge of the theoretical maximum collision time and collision probability between RFID and WiFi/Bluetooth packets. This scheme generates an optimal channel based on the current usage of the adjacent frequency channels thereby reducing the interference. We also propose two solutions from this scheme: a frequency hopping combined with white space exploitation method and an intelligent frequency hopping scheme; for maintaining a quality connection of the WiFi or Bluetooth network in the presence of heavy RFID interferers. We implement a hybrid backscatter-based RFID architecture in existence of the WiFi/Bluetooth infrastructure for efficient operations within the 2.4 GHz ISM band. Results obtained are very encouraging and indicate that quantifying the maximum collision time and collision probability is a vital step for the interference avoidance scheme, which can be adopted in the avoidance of the interference from RFID modules.

     

A Wireless MAC Protocol with Collision Detection

The most popular strategies for dealing with packet collisions at the medium access control (MAC) layer in distributed wireless networks use a combination of carrier sensing and collision avoidance. When the collision avoidance strategy fails, such schemes cannot detect collisions and corrupted data frames are still transmitted in their entirety, thereby wasting the channel bandwidth and significantly reducing the network throughput. To address this problem, this paper proposes a new wireless MAC protocol capable of collision detection. The basic idea of the proposed protocol is the use of pulses in an out-of-band control channel for exploring channel condition and medium reservation and achieving both collision avoidance and collision detection. The performance of the proposed MAC protocol has been investigated using extensive analysis and simulations. Our results show that, as compared with existing MAC protocols, the proposed protocol has significant performance gains in terms of node throughput. Additionally, the proposed protocol is fully distributed and requires no time synchronization among nodes.     

民机空中交通警戒与防撞系统目标跟踪算法

空中交通警戒与防撞系统(TCAS)是航空电子综合环境监视系统的一个重要组成部分,它能有效降低空中飞行器间的碰撞威胁,对于提高飞行安全有着非常重要的意义。TCAS是一种不依赖地面设备的空中交通防撞系统。它能够探测在其领域内装有空中交通管制应答机的飞机,向驾驶员报告潜在的相撞目标。目标跟踪是TCAS的一个重要模块,能提供目标的飞行状态信息,并对目标的未来飞行状态进行预测。对空中目标进行稳定、高精确度的跟踪是目标跟踪模块的重要任务。本文介绍了基于扩展卡尔曼和交互式多模型(IMM-EKF)的目标跟踪算法,实现对目标的精确跟踪。通过仿真验证,证明算法能实现精确的目标跟踪,对防止空中相撞起到了积极作用。     

Collision avoidance in TV white spaces: a cross-layer design approach for cognitive radio networks

One of the most promising applications of cognitive radio networks (CRNs) is the efficient exploitation of TV white spaces (TVWSs) for enhancing the performance of wireless networks. In this paper, we propose a cross-layer design (CLD) of carrier sense multiple access with collision avoidance (CSMA/CA) mechanism at the medium access control (MAC) layer with spectrum sensing (SpSe) at the physical layer, for identifying the occupancy status of TV bands. The proposed CLD relies on a Markov chain model with a state pair containing both the SpSe and the CSMA/CA from which we derive the collision probability and the achievable throughput. Analytical and simulation results are obtained for different collision avoidance and SpSe implementation scenarios by varying the contention window, back off stage and probability of detection. The obtained results depict the achievable throughput under different collision avoidance and SpSe implementation scenarios indicating thereby the performance of collision avoidance in TVWSs-based CRNs.     

Saturation throughput analysis of a carrier sensing based MU-MIMO MAC protocol in a WLAN under fading and shadowing

In wireless local area networks (WLANs), the traditional carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol cannot use the full benefits from multiuser multiple-input multiple-output (MU-MIMO) technique due to random medium access of the users. In this paper, we propose a carrier sensing based MAC protocol for a MU-MIMO based WLAN with full utilization of MU-MIMO technique. By modeling the WLAN system under the proposed MAC protocol as a discrete time Markov chain, we develop an analytical model for computing the saturation throughput in presence of path loss, Rayleigh fading and log-normal shadowing. The analytical model is then validated via simulation. By means of numerical and simulation results, we demonstrate that the proposed MAC protocol significantly improves throughput performance than the traditional CSMA/CA MAC protocol. Further, we compare the performance of the proposed MAC protocol with a MU-MIMO MAC protocol called Uni-MUMAC protocol and find that the proposed MAC protocol performs better than the Uni-MUMAC protocol. We also explore the effect of some of the network and wireless channel parameters on the performance of the proposed MAC protocol.

     

Vision-Based Target Tracking and Collision Avoidance for Two Autonomous Robotic Fish

A new type of vision-based autonomous robotic fish capable of 3-D locomotion is developed in this paper. Based on our robotic fish prototype, the forces and moments acting on its fins and body are analyzed, and the governing motion equations are derived. We further investigate a decentralized control method in target-tracking and collision-avoidance task for two autonomous robotic fish. Most of previous work on the task strategies of autonomous robots is focused on terrestrial robots and seldom deals with underwater applications due to the uncertainties and complexity in a hydro environment. To address this challenge in such an underwater task, a situated-behavior-based decentralized control is employed on each robotic fish according to its visual data. On dealing with motion planning of the fish during target tracking and collision avoidance, a control law by a combination of an attractive force toward a target and a repulsive force for collision avoidance is utilized. Experimental results of the task performed by two autonomous robotic fish validate the effectiveness of the proposed method.     

Energy Efficient Target Tracking with Collision Avoidance in WSNs

Wireless sensor network (WSN) is one of the most evolving technologies. WSN involves collecting, processing, transferring and storing information about objects with the help of sensor nodes. Tracking and detection of targets is one of the most attractive applications of WSN in surveillance systems. To resolve the problem of target tracking, it is essential to deploy a system model. It has been observed that clustering algorithms play an important role in cluster head selection, but they consume significant amount of energy. In this paper an energy efficient system model is deployed with a novel target tracking algorithm to track the target around the vicinity of the WSN. As there is more possibility of collision proximate to the base station, a new collision avoidance method is introduced. The lifetime of the network on the basis of congestion around the sink node, packet density and path loss are also measured efficiently.

     

Safe Navigation of a Mobile Robot Considering Visibility of Environment

We present one approach to achieve safe navigation in an indoor dynamic environment. So far, there have been various useful collision avoidance algorithms and path planning schemes. However, those algorithms possess fundamental limitations in that the robot can avoid only ldquovisiblerdquo ones among surrounded obstacles. In a real environment, it is not possible to detect all the dynamic obstacles around the robot. There are many occluded regions due to the limited field of view. In order to avoid collisions, it is desirable to exploit visibility information. This paper proposes a safe navigation scheme to reduce collision risk considering occluded dynamic obstacles. The robot's motion is controlled by the hybrid control scheme. The possibility of collision is dually reflected to path planning and speed control. The proposed scheme clearly indicates the structural procedure on how to model and to exploit the risk of navigation. The proposed scheme is experimentally tested in a real office building. The experimental results show that the robot moves along the safe path to obtain sufficient field of view. In addition, safe speed constraints are applied in motion control. It is experimentally verified that a robot safely navigates in dynamic indoor environment by adopting the proposed scheme.     

A Novel Dynamic Obstacle Avoidance Algorithm Based on Collision Time Histogram

Robot path planning in uncertain dynamic environment is a hot issue in the field of Unmanned ground vehicle (UGV). Starting from the practical demands of UGV, we propose a novel dynamic obstacle avoidance al-gorithm based on Collision time histogram (CTH). Given current steering angle, an effective collision check model, which is called Collision check circles (CCC), is firstly cal-culated. The local environment information is then com-bined with CCC to generate the proposed CTH. The non-holonomic nature of the vehicle is embedded in this pro-cess. Finally, the proposed algorithm calculates the execut-ing steering angle by considering both the CTH and the target point. Extensive experiments and comparisons are conducted to evaluate the performance of the proposed al-gorithm. Simulation experiments are firstly conducted to verify its feasibility. Furthermore, real-world experiment is conducted to verify its effectiveness. Experimental results demonstrate the practical value of the proposed algorithm.     

Enhanced EDCA with Deterministic Transmission Collision Resolution for Real-Time Communication in Vehicular Ad Hoc Networks

The collision prevention system is one of most important research issues on vehicle safety technology. Sending worming messages within the right time and reliable transmission will get prevention of a possible vehicle accident. The communication standards of vehicular networks (VANET) are unable to guarantee the delivery of critical messages within tight deadlines. Indeed, the transmission collisions are handled with probabilistic manner that can reduce the transmission latency; however, it is inept to predict an upper bound value of this delay to verify the deadline. In this paper, we propose a medium access protocol that ensures the delivery of critical messages within a deadline. It is a hard real-time system with delay constant guarantee. We are focusing on improving the EDCA medium access protocol to prioritize critical messages and to get access to the transmission channel within a predictable communication delay. We create a new enhanced access protocol that is compatible with the IEEE 802.11p VANET standards and adapted to real-time communication requirements related to the vehicle collision avoidance problem.     

Receiver-Initiated Collision Avoidance in Wireless Networks

Many medium-access control (MAC) protocols for wireless networks proposed or implemented to date are based on collision-avoidance handshakes between sender and receiver. In the vast majority of these protocols, including the IEEE 802.11 standard, the handshake is sender initiated, in that the sender asks the receiver for permission to transmit using a short control packet, and transmits only after the receiver sends a short clear-to-send notification. We analyze the effect of making the collision-avoidance handshake, receiver initiated and compare the performance of a number of receiver-initiated protocols with the performance of sender-initiated collision avoidance protocols. Analytical and simulation results show that the best-performing collision avoidance MAC protocol based on receiver-initiated or sender-initiated collision avoidance is one in which a node with data to send transmits a dual-purpose small control packet inviting a given neighbor to transmit and asking the same neighbor for permission to transmit. The receiver-initiated protocols we present make use of carrier sensing, and are applicable to either baseband or slow frequency-hopping radios in which an entire packet can be sent within the same frequency hop (which is the case of frequency hopping spread spectrum (FHSS) commercial radios).     

Sliding-Mode Formation Control for Cooperative Autonomous Mobile Robots

This paper considers the control of a group of autonomous mobile robots. A coordinated control scheme based on a leader–follower approach is developed to achieve formation maneuvers. First and second order sliding-mode controllers are proposed for asymptotically stabilizing the vehicles to a time-varying desired formation. The latter controller, based on the relative motion states, eliminates the need for measurement or estimation of the leader velocity. It enables formation stabilization using a vision system carried by the followers and ensures the collision avoidance from the initial time instance. Experimental investigation has been conducted using a test bench made of three nonholonomic mobile robots in order to demonstrate the effectiveness of the proposed strategy.