A new MAC protocol design based on TDMA/FDD for QoS support in WATM networks

Several wireless networking solutions have been developed to provide different types of services for various end user applications. Currently, wireless networking infrastructures are not suitable for multimedia applications each requiring a different QoS support with various traffic parameters. Due to the success of ATM technology in the wired network, WATM concept and related researches are of importance in the information technology area. Main objective of WATM, which promises seamless transmission of different traffics such as voice, data and video over wireless medium, is to implement high bit rate and QoS guaranteed data transfer, already well achieved by ATM technology over wired medium. To support QoS guaranteed data transfer over error-prone and low bandwidth wireless medium, an effective MAC protocol must be designed and utilized. In this paper, a new TDMA/FDD based MAC protocol, maintaining QoS requirements of real-time wireless multimedia applications, is proposed. The main contribution of this study is the new guarantee-based scheduling algorithm used in the proposed MAC to support required level of QoS guarantee for all multimedia traffic types in wireless medium. Computer modeling and simulation of the new approach providing CBR, VBR, ABR and UBR ATM services are realized using OPNET Modeler. Simulation results are also presented together with comparisons those of a WATM counterpart which uses PRMA/DA MAC protocol.     

A Distributed Deployment Strategy for Multi-Agent Systems Subject to Health Degradation and Communication Delays

This paper presents a distributed deployment algorithm for a network of autonomous agents. The main goal is to perform a coverage task when the sensor effectiveness of each agent varies during the mission. It is also assumed that the agents are subject to communication delays induced by communication faults. To improve the overall performance and guarantee the collision avoidance, the guaranteed multiplicatively-weighted Voronoi (GMW-Voronoi) diagram is introduced. A distributed coverage control is then provided to drive agents in such a way that the coverage performance function is minimized over the regions assigned to agents. The effectiveness of the proposed algorithm is evaluated by simulations.     

WSN in cyber physical systems: Enhanced energy management routing approach using software agents

Recently, the cyber physical system has emerged as a promising direction to enrich the interactions between physical and virtual worlds. Meanwhile, a lot of research is dedicated to wireless sensor networks as an integral part of cyber physical systems. A wireless sensor network (WSN) is a wireless network consisting of spatially distributed autonomous devices that use sensors to monitor physical or environmental conditions. These autonomous devices, or nodes, combine with routers and a gateway to create a typical WSN system. Shrinking size and increasing deployment density of wireless sensor nodes implies the smaller equipped battery size. This means emerging wireless sensor nodes must compete for efficient energy utilization to increase the WSN lifetime. The network lifetime is defined as the time duration until the first sensor node in a network fails due to battery depletion. One solution for enhancing the lifetime of WSN is to utilize mobile agents. In this paper, we propose an agent-based approach that performs data processing and data aggregation decisions locally i.e., at nodes rather than bringing data back to a central processor (sink). Our proposed approach increases the network lifetime by generating an optimal routing path for mobile agents to transverse the network. The proposed approach consists of two phases. In the first phase, Dijkstra’s algorithm is used to generate a complete graph to connect all source nodes in a WSN. In the second phase, a genetic algorithm is used to generate the best-approximated route for mobile agents in a radio harsh environment to route the sensory data to the base-station. To demonstrate the feasibility of our approach, a formal analysis and experimental results are presented.     

阈交方法在无线网络业务分析中的应用

与有线计算机网络相比,由于无线网络的有限带宽和可变信道,使得无线网络提供业务 服务的QoS保证比有线网络来说更加困难。在提供QoS保证方面一个重要的因素是网络业务预报, 通过对无线网络业务超阈值数据采用方差分析法构造阈值v的偏差函数,为阈值选取提供一定的依 据,通过对无线网络业务到达数据对阈值穿越强度的计算验证了该方法在阈值选取方面的有效性。 可以根据该阈值更好地实现对无线网络业务的预报。     

基于ARMA预测的无线监控系统可靠传输机制

无线监控网络易受衰减、多径、盲区等不利因素影响,经常出现局部节点负载过大而导致拥塞现象的发生,导致数据可靠传输得不到保障.从拥塞控制角度,提出了一种基于拥塞预知的改进的拥塞控制算法.该算法基于主动避免拥塞的设计思想,在选取路由时考虑链路质量指标LQI,并依据ARMA预报算法获得未来时刻的网络流量预报值,由此判断节点的拥塞程度以便预先采取措施,最终实现拥塞自适应控制.实验结果表明,该算法能提升无线监控系统数据传输的可靠性,并能显著提高吞吐量.     

基于移动代理的无线传感器网络节点定位算法

研究了无线传感器网络节点定位算法及移动代理技术。在DV-Hop算法的基础上采用移动代理技术,并限制未知节点接收移动代理的个数和移动代理的传播跳数,减少了节点信息收发和存储量,降低了网络流量及节点负载。     

A 3D reactive collision avoidance algorithm for underactuated underwater vehicles

Avoiding collisions is an essential goal of the control system of autonomous vehicles. This paper presents a reactive algorithm for avoiding obstacles in a three‐dimensional space, and shows how the algorithm can be applied to an underactuated underwater vehicle. The algorithm is based on maintaining a constant avoidance angle to the obstacle, which ensures that a guaranteed minimum separation distance is achieved. The algorithm can thus be implemented without knowledge of the obstacle shape. The avoidance angle is designed to compensate for obstacle movement, and the flexibility of operating in 3D can be utilized to implement traffic rules or operational constraints. We exemplify this by incorporating safety constraints on the vehicle pitch and by making the vehicle seek to move behind the obstacle, while also minimizing the required control effort. The underactuation of the vehicle induces a sway and heave movement while turning. To avoid uncontrolled gliding into the obstacle, we account for this movement using a Flow frame controller, which controls the direction of the vehicle's velocity rather than just the pitch and yaw. We derive conditions under which it is ensured that the resulting maneuver is safe, and these results are verified trough simulations and through full‐scale experiments on the Hugin HUS autonomous underwater vehicle. The latter demonstrates the performance of the proposed algorithm when applied to a case with unmodeled disturbances and sensor noise, and shows how the modular nature of the collision avoidance algorithm allows it to be applied on top of a commercial control system.     

A systolic parallel simulation system for dynamic traffic assignment: SPSS-DTA

This paper presents a new approach to solve dynamic traffic assignment problems. The approach employs a mixed method of real-time simulation and off-line optimization. The fundamental approach to the simulation is systolic parallel processing based on autonomous agent modeling. Agents continuously act on their own initiatives and access to database to get the status of the simulation world. In particular, existing models and algorithms were incorporated in designing the behavior of relevant agents such as car-following and headway distribution. Simulation is based on predetermined routes between centroids that are computed off-line by a conventional optimal path-finding algorithm such as the Frank-Wolf algorithm. Iterating the cycles of optimization and simulation, the proposed system will provide a practical and valuable traffic assignment. Gangnam-Gu district in Seoul, Korea is selected as the target area for the modeling. It is expected that real-time traffic assignment services can be provided on the Internet soon.     

城市交叉口车辆速度与交通信号协同优化控制

为了降低城市交通中的行车延误与燃油消耗,针对人类驾驶车辆与自动驾驶车辆混合交通环境,提出一种基于交通信息物理系统(TCPS)的车辆速度与交通信号协同优化控制方法.首先,综合考虑路口交通信号、人类驾驶车辆、自动驾驶车辆三者之间的相互影响,设计一种适用于自动驾驶车辆与人类驾驶车辆混合组队特性的过路口速度规划模型;其次,针对车辆速度规划单一应用时的局限性,即无法减少车辆路口通行延误且易出现无解情况,提出一种双目标协同优化模型,能够综合考虑车辆速度规划与路口交通信号控制,同时降低车辆燃油消耗与路口平均延误.由于双目标优化问题求解的复杂性,设计一种遗传算法-粒子群算法混合求解策略.基于SUMO的仿真实验验证了所提出方法的有效性.     

长链型无线传感器网络QoS路由优化的研究*

针对输电线路监测系统对无线传感器网络实时性和可靠性要求较高的特点,在抽象出的长链型传感器网络QoS路由模型中把网络带宽、时延、跳数、收包率作为链路约束,寻求网络中的最优数据传输路径。考虑到基本蚁群算法存在收敛速度慢、易陷入局部最优等缺陷,提出一种用自适应蚁群算法求解最优路径的方法。仿真结果表明,改进的算法通过自适应地调整信息素挥发因子,能够快速地找到满足约束的最优路径,网络规模越大其优势越明显,保证了用于输电线路监测的无线传感器网络数据传输的服务质量。     

一种新的移动ad hoc网络中带宽保证的路由算法

移动adhoc网络(Mobileadhocnetworks)是一种由无线移动主机/节点组成的动态自治网络。移动adhoc网络在军事和民用方面都有很大的应用前景。在移动adhoc网络中进行有QoS保证的路由选择有重要的意义。论文讨论了移动adhoc网络中的路由选择、QoS保证,并提出了一种新的带宽保证的路由算法ABGR。ABGR以受限扩散路由方法为基础,采用多种机制避免在全网中进行扩散,同时在路由选择的过程中考虑路径稳定性和节点的电能受限问题。     

A topology-transparent MAC scheduling algorithm with guaranteed QoS for multihop wireless network

Due to its character of topology independency, topology-transparent medium access control (MAC) scheduling algorithm is very suitable for large-scale mobile ad hoc wireless networks. In this paper, we propose a new topologytransparent MAC scheduling algorithm, with parameters of the node number and the maximal nodal degree known, our scheduling algorithm is based on a special balanced incomplete block design whose block size is optimized by maximizing the guaranteed throughput. Its superiority over typical other scheduling algorithms is proven mathematically with respect to the guaranteed throughput, the maximal transmission delay, and also the minimal transmission delay. The effect of inaccuracy in the estimation of the maximal nodal degree on the guaranteed throughput is deduced mathematically, showing that the guaranteed throughput decreases almost linearly as the actual nodal degree increases. Further techniques for improving the feasibility of the algorithm, such as collision avoidance, time synchronization, etc., are also discussed.     

结合状态机和动态目标路径的无人驾驶决策仿真

目的 决策系统是无人驾驶技术的核心研究之一。已有决策系统存在逻辑不合理、计算效率低、应用场景局限等问题,因此提出一种动态环境下无人驾驶路径决策仿真。方法 首先,基于规则模型构建适于无人驾驶决策系统的交通有限状态机;其次,针对交通动态特征,提出基于统计模型的动态目标路径算法计算状态迁移风险;最后,将交通状态机和动态目标路径算法有机结合,设计出一种基于有限状态机的无人驾驶动态目标路径模型,适用于交叉口冲突避免和三车道换道行为。将全速度差连续跟驰模型运用到换道规则中,并基于冲突时间提出动态临界跟车距离。结果 为验证模型的有效性和高效性,对交通环境进行虚拟现实建模,模拟交叉口通行和三车道换道行为,分析文中模型对车流量和换道率的影响。实验结果显示,在交叉口通行时,自主车辆不仅可以检测冲突还可以根据风险评估结果执行安全合理的决策。三车道换道时,自主车辆既可以实现紧急让道,也可以通过执行换道达成自身驾驶期望。通过将实测数据和其他两种方法对比,当车流密度在0.20.5时,本文模型的平均速度最高分别提高32 km/h和22 km/h。当车流密度不超过0.65时,本文模型的换道成功率最高分别提升37%和25%。结论 实验结果说明本文方法不仅可以在动态城区环境下提高决策安全性和正确性,还可以提高车流量饱和度,缓解交通堵塞。     

自动驾驶车辆在无信号交叉口右转驾驶决策技术研究

利用深度强化学习（deep reinforcement learning,DRL）技术实现自动驾驶决策已成为国内外研究热点,现有研究中的车辆交通流缺乏随机性与真实性,同时自动驾驶车辆在环境中的有效探索具有局限性。因此利用TD3算法进行自动驾驶车辆在无信号交叉口下的右转驾驶决策研究,首先在Carla仿真平台中开发无信号交叉口的训练与测试场景,并添加交通流管理功能,提高系统训练和测试随机性。其次,为了提高自动驾驶车辆的探索性,对TD3算法中的Actor网络进行改进,为目标动作添加OU噪声。最后使用通行成功率和平均通行时间评估指标评价自动驾驶行为决策。结果表明,在不同交通流场景下,改进后的TD3算法通行成功率与基于DDPG算法控制的车辆相比平均提升6.2%,与基于规则的AEB模型相比平均提升23%。改进后的TD3算法不仅能够探索更多可能,而且其通行决策表现更加突出。     

无线Mesh网络混合策略的接口角色决定*

针对无线Mesh网络混合策略的接口角色决定问题至今尚未定论,定义了接口角色决定问题,并证明了该问题是NP难题。为了在合理的时间内解决接口角色决定问题,提出了一种近似1/2算法。该算法在维持原拓扑结构的情况下,最大限度地提高了接口间可切换对的总数量,从而帮助节点找到更多路径以避免干扰、平衡传输负载。同时,也确保了节点之的连通性。所定义的问题有利于提高网络吞吐量,该算法优于现有方法。     

Motion planning of autonomous vehicles in a non-autonomous vehicle environment without speed lanes

Planning is one of the key problems for autonomous vehicles operating in road scenarios. Present planning algorithms operate with the assumption that traffic is organised in predefined speed lanes, which makes it impossible to allow autonomous vehicles in countries with unorganised traffic. Unorganised traffic is though capable of higher traffic bandwidths when constituting vehicles vary in their speed capabilities and sizes. Diverse vehicles in an unorganised exhibit unique driving behaviours which are analysed in this paper by a simulation study. The aim of the work reported here is to create a planning algorithm for mixed traffic consisting of both autonomous and non-autonomous vehicles without any inter-vehicle communication. The awareness (e.g. vision) of every vehicle is restricted to nearby vehicles only and a straight infinite road is assumed for decision making regarding navigation in the presence of multiple vehicles. Exhibited behaviours include obstacle avoidance, overtaking, giving way for vehicles to overtake from behind, vehicle following, adjusting the lateral lane position and so on. A conflict of plans is a major issue which will almost certainly arise in the absence of inter-vehicle communication. Hence each vehicle needs to continuously track other vehicles and rectify plans whenever a collision seems likely. Further it is observed here that driver aggression plays a vital role in overall traffic dynamics, hence this has also been factored in accordingly. This work is hence a step forward towards achieving autonomous vehicles in unorganised traffic, while similar effort would be required for planning problems such as intersections, mergers, diversions and other modules like localisation.     

On the complexity and algorithm of grooming regular traffic in WDM optical networks

In SONET/WDM networks, a high-speed wavelength channel is usually shared by multiple low-rate traffic demands to make efficient use of the wavelength capacity. The multiplexing is known as traffic grooming and performed by SONET Add-Drop Multiplexers (SADM). The maximum number of low-rate traffic demands that can be multiplexed into one wavelength channel is called grooming factor. Since SADMs are expensive, a key optimization goal of traffic grooming is to minimize the total number of SADMs in order to satisfy a given set of traffic demands. As an important communication traffic pattern, all-to-all traffic has been widely studied for the traffic grooming problem. In this paper, we study the regular traffic pattern, which is considered as a generalization of the all-to-all traffic pattern. We focus on the Unidirectional Path-Switched Ring (UPSR) networks. We prove that the traffic grooming problem is NP-hard for the regular traffic pattern in UPSR networks, and show that the problem does not admit a Fully Polynomial Time Approximation Scheme (FPTAS). We further prove that the problem remains NP-hard even if the grooming factor is any fixed value chosen from a subset of integers. We also propose a performance guaranteed algorithm to minimize the total number of required SADMs, and show that the algorithm achieves a better upper bound than previous algorithms. Extensive simulations are conducted, and the empirical results validate that our algorithm outperforms the previous ones in most cases. In addition, our algorithm always uses the minimum number of wavelengths, which are precious resources as well in optical networks.     

Distributed on-demand address assignment in wireless sensornetworks

Sensor networks consist of autonomous wireless sensor nodes that are networked together in an ad hoc fashion. The tiny nodes are equipped with substantial processing capabilities, enabling them to combine and compress their sensor data. The aim is to limit the amount of network traffic, and as such conserve the nodes' limited battery energy. However, due to the small packet payload, the MAC header is a significant, and energy-costly, overhead. To remedy this, we propose a novel scheme for a MAC address assignment. The two key features which make our approach unique are the exploitation of spatial address reuse and an encoded representation of the addresses in data packets. To assign the addresses, we develop a purely distributed algorithm that relies solely on local message exchanges. Other salient features of our approach are the ability to handle unidirectional links and the excellent scalability of both the assignment algorithm and address representation. In typical scenarios, the MAC overhead is reduced by a factor of three compared to existing approaches     

Scheduling multimedia services in a low-power MAC for wireless andmobile ATM networks

This paper describes the design and analysis of the scheduling algorithm for energy conserving medium access control (EC-MAC), which is a low-power medium access control (MAC) protocol for wireless and mobile ATM networks. We evaluate the scheduling algorithms that have been proposed for traditional ATM networks. Based on the structure of EC-MAC and the characteristics of wireless channel, we propose a new algorithm that can deal with the burst errors and the location-dependent errors. Most scheduling algorithms proposed for either wired or wireless networks were analyzed with homogeneous traffic or multimedia services with simplified traffic models. We analyze our scheduling algorithm with more realistic multimedia traffic models based on H.263 video traces and self-similar data traffic. One of the key goals of the scheduling algorithms is simplicity and fast implementation. Unlike the time-stamped based algorithms, our algorithm does not need to sort the virtual time, and thus, the complexity of the algorithm is reduced significantly     

Cooperative distributed target tracking algorithm in mobile wireless sensor networks

The paper proposes a cooperative distributed target tracking algorithm in mobile wireless sensor networks.There are two main components in the algorithm:distributed sensor-target assignment and sensor motion control.In the key idea of the sensor-target assignment,sensors are considered as autonomous agents and the defined objective function of each sensor concentrates on two fundamental factors:the tracking accuracy and the tracking cost.Compared with the centralized algorithm and the noncooperative distrib...