Maintaining Optimal Communication Chains in Robotic Sensor Networks using Mobility Control

This paper presents a decentralized mobility control algorithm for the formation and maintenance of an optimal cascaded communication chain between a lead sensor-equipped robot and a control station, using a team of robotic vehicles acting as communication relays in an unknown and dynamic RF environment. The gradient-based controller presented uses measurements of the signal-to-noise ratio (SNR) field of neighbor communication links, as opposed to relative position between nodes, as input into a localized performance function. By using the SNR field as input into the control system, the controller is reactive to unexpected and unpredictable changes in the RF environment that is not possible with range-based controllers. Since the operating environment is not known a priori to deployment of a robotic sensor network, an adaptive model-free extremum seeking (ES) algorithm, that uses the motion of the relays to estimate the performance function gradient, is presented to control the motion of 2D nonholonomic vehicles acting as communication relays using the gradient-based controller. Even without specific knowledge of the SNR field, simulations show that the ES decentralized chaining controller using measurements of the SNR field, will drive a team of robotic vehicles to locations that achieve the global objective of maximizing capacity of a cascaded communication chain, even in the presence of an active jamming source.

Multicast Communication in Ad Hoc Networks with Directional Antennas

This paper investigates the benefits and impacts of using directional antennas for multicast communications in ad hoc networks. In terms of signal reception, directional antennas have shown considerable improvement in the performance of all aspects over omni-directional antennas, especially over dense networks with heavy traffic load. In addition, we have found that transmitting multicast packets directionally to known neighboring group members or forwarders can help reduce the average end-to-end packet delay and increase the overall throughput. However, directional transmission of unacknowledged data transfers may result in lower performance in terms of packet delivery ratio than omni-directional transmission in any carrier sensing MAC protocols under moderate load due to the effect from the hidden terminal problem. Both analytical results and simulation results, as well as an acknowledgment mechanism to improve the successful delivery rate of multicast data packets, are presented. Prepared through collaborative participation in the Communications and Networks Consortium sponsored by the U.S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon.     

Two-Way Cooperative Quantum Communication with Partial Entanglement Analysis

In this paper, we describe an improved cooperative two-way quantum communication scheme that works in a forward-and-backward fashion. In this scheme, partial entanglement analysis based on five-qubit entangled Brown state allows for the simultaneous exchange of arbitrary unknown states between Alice and Bob （with the help of trusted Charlie）. Security is guaranteed because opposing unknown states are transmitted by performing the suitable recovery operations in a deterministic way or, in the case of irregularities, no results are generated. The current two-way quantum communication scheme can also be extended to transmit arbitrary unknown states. This is done in a probabilistic way by using two-way quantum teleportation based on the generalized Brown-like state.     

纠缠交换的量子回路实现

自从量子纠缠态及隐性传态理论提出以来,量子纠缠技术和隐性传态技术得到了迅速发展.量子隐性传态在技术上保证了量子通信的绝对安全,量子隐性传态是基于量子纠缠交换提出的.文章阐述了量子隐形传态及量子纠缠交换的基本理论,给出了一种基于Bell态实现量子纠缠交换的量子回路,该回路结构简单,易于实现.     

基于纠缠度计算的低轨道量子卫星通信切换算法

为了解决低轨道(Low Earth Orbit, LEO) 量子卫星通信的越区切换问题,提出了基于纠缠度计算的量子卫星通信切换算法。在卫星与终端距离和量子噪声的作用下,得出了环境与量子系统消相干后两粒子系统的纠缠度,并且系统始终选择与终端纠缠度最大的卫星进行切换。仿真结果表明,LEO卫星在700km和1400km轨道上在一定纠缠度下的切换成功率可达到95%以上,这很好的实现了量子卫星的平稳切换,对于构建未来全球量子通信系统及其标准的制定有着重要的技术支撑作用。     

Jaynes-Cumming模型中几种量子纠缠测量熵的比较

通过求解二能级Jaynes-Cummings模型,得到J-C模型中原子与光场的约化密度矩阵,并通过原子与光场的约化密度矩阵计算量子线性熵、von Neumann熵与原子Wehrl熵,给出熵随时间的演化关系,利用上述三种量子熵分别对量子纠缠进行测量,并分析系统量子熵与系统量子布洛赫球面结果的关系,研究发现上述三种熵随时间演化结果相似,都可以作为量子纠缠的测量理想的工具。     

Channel Adaptive Shortest Path Routing for Ad Hoc Networks

1　IntroductionAdhocnetworksareformedwithoutrequiringthepreexistinginfrastructureorcentralizedadminis tration ,incontrasttocellularnetworks.Asidefromtheoriginalmilitaryapplication ,ithasapplicationinpublicsafetyandcommercialareas,butadaptiveprotocolsarerequiredinorderforthemtodoso .Twoimportantcharacteristicsofacommunicationlinkinadhocnetworksareitsunreliabilityanditsvariability .Thelinksinsuchanetworkareunreli ablebecauseoffading ,interference,noise,andper hapsthefailureofthetransmittingorrec…     

DV Based Positioning in Ad Hoc Networks

Many ad hoc network protocols and applications assume the knowledge of geographic location of nodes. The absolute position of each networked node is an assumed fact by most sensor networks which can then present the sensed information on a geographical map. Finding position without the aid of GPS in each node of an ad hoc network is important in cases where GPS is either not accessible, or not practical to use due to power, form factor or line of sight conditions. Position would also enable routing in sufficiently isotropic large networks, without the use of large routing tables. We are proposing APS – a localized, distributed, hop by hop positioning algorithm, that works as an extension of both distance vector routing and GPS positioning in order to provide approximate position for all nodes in a network where only a limited fraction of nodes have self positioning capability.     

一种解决ad hoc网络中自私节点安全问题的方法

移动ad hoc网络（MANET）路由和分组转发功能需要节点间的相互合作，自私节点为节约能量而不参与合作，将会影响网络的正常工作．因此本文将针对自私节点危害和解决方法展开分析，并提出一种改进解决方法——基于可信任中心服务器和邻居监测的合作增强机制，该方法不但能够激励节点间的相互合作，而且有效地解决了自私节点改变用户身份的欺骗攻击．最后，仿真结果表明这种合作增强机制对自私节点安全问题是有效的，并且易于实用化．     

Extending Global IP Connectivity for Ad Hoc Networks

Ad hoc networks have thus far been regarded as stand-alone networks without assumed connectivity to wired IP networks and the Internet. With wireless broadband communications and portable devices with appropriate CPU, memory and battery performance, ad hoc connectivity will become more feasible and demand for global connectivity through ad hoc networking is likely to rapidly grow. In this paper we propose an algorithm and describe a developed prototype for connectivity between an ad hoc network running the ad hoc on-demand distance-vector protocol and a wired IP network where mobile IP is used for mobility management. Implementation issues and performance metrics are also discussed.     

Minimum-Energy Broadcasting in Static Ad Hoc Wireless Networks

Energy conservation is a critical issue in ad hoc wireless networks for node and network life, as the nodes are powered by batteries only. One major approach for energy conservation is to route a communication session along the route which requires the lowest total energy consumption. This optimization problem is referred to as Minimum-Energy Routing. While the minimum-energy unicast routing problem can be solved in polynomial time by shortest-path algorithms, it remains open whether the minimum-energy broadcast routing problem can be solved in polynomial time, despite the NP-hardness of its general graph version. Recently three greedy heuristics were proposed in [11]: MST (minimum spanning tree), SPT (shortest-path tree), and BIP (broadcasting incremental power). They have been evaluated through simulations in [11], but little is known about their analytical performances. The main contribution of this paper is a quantitative characterization of their performances in terms of approximation ratios. By exploring geometric structures of Euclidean MSTs, we have been able to prove that the approximation ratio of MST is between 6 and 12, and the approximation ratio of BIP is between 13/3 and 12. On the other hand, we show that the approximation ratio of SPT is at least n/2, where n is the number of receiving nodes. To the best of our knowledge, these are the first analytical results for the minimum-energy broadcasting problem.     

An End-to-End Bandwidth Allocation Algorithm for Ad Hoc Networks

Bandwidth-guaranteed QoS service in ad hoc networks is a challenging task due to several factors such as the absence of the central control, the dynamic network topology, the hidden terminal problem and the multihop routing property. An end-to-end bandwidth allocation algorithm was proposed in [Lin and Liu, 15] to support the QoS service in ad hoc networks. However, without exploring the global resource information along the route, the performance of that algorithm is quite limited. In addition, it also incurs significant control overhead. We develop a new algorithm for end-to-end bandwidth calculation and assignment in ad hoc networks which utilizes the global resource information along the route to determine the available end-to-end bandwidth. Our method also employs the topology-transparent scheduling technology to reduce the control overhead. The proposed algorithm can be efficiently utilized in a distributed manner. Both theoretical analysis and simulation results show that our end-to-end bandwidth allocation scheme can significantly improve the network capacity compared with the existing method.     

Performance Evaluation of Routing Protocols for Ad Hoc Wireless Networks

A mobile ad hoc network is a collection of autonomous mobile nodes that communicate with each other over wireless links. Such networks are expected to play an increasingly important role in future civilian and military settings, being useful for providing communication support where no fixed infrastructure exists or the deployment of a fixed infrastructure is not economically profitable and movement of communicating parties is possible. However, since there is no stationary infrastructure such as base stations, mobile hosts need to operate as routers in order to maintain the information about the network connectivity. Therefore, a number of routing protocols have been proposed for ad hoc wireless networks. In this paper, we study and compare the performance of the following routing protocols AODV, PAODV (preemptive AODV), CBRP, DSR, and DSDV. A variety of workload and scenarios, as characterized by mobility, load and size of the ad hoc network were simulated. Our results indicate that despite its improvement in reducing route request packets, CBRP has a higher overhead than DSR because of its periodic hello messages while AODV's end-to-end packet delay is the shortest when compared to DSR and CBRP. PAODV has shown little improvements over AODV.     

Mobility Management for Hierarchical Wireless Networks

In this paper, we consider the mobility management in large, hierarchically organized multihop wireless networks. The examples of such networks range from battlefield networks, emergency disaster relief and law enforcement etc. We present a novel network addressing architecture to accommodate mobility using a Home Agent concept akin to mobile IP. We distinguish between the physical routing hierarchy (dictated by geographical relationships between nodes) and logical hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). The performance of the mobility management scheme is investigated through simulation.     

ABRP: Anchor-based Routing Protocol for Mobile Ad Hoc Networks

Ad hoc networks, which do not rely on any infrastructure such as access points or base stations, can be deployed rapidly and inexpensively even in situations with geographical or time constraints. Ad hoc networks are attractive in both military and disaster situations and also in commercial uses like sensor networks or conferencing. In ad hoc networks, each node acts both as a router and as a host. The topology of an ad hoc network may change dynamically, which makes it difficult to design an efficient routing protocol. As more and more wireless devices connect to the network, it is important to design a scalable routing protocol for ad hoc networks. In this paper, we present Anchor-based Routing Protocol (ABRP), a scalable routing protocol for ad hoc networks. It is a hybrid routing protocol, which combines the table-based routing strategy with the geographic routing strategy. However, GPS (Global Positioning System) (Kaplan, Understanding GPS principles and Applications, Boston: Artech House publishers, 1996) support is not needed. ABRP consists of a location-based clustering protocol, an intra-cell routing protocol and an inter-cell routing protocol. The location-based clustering protocol divides the network region into different cells. The intra-cell routing protocol routes packets within one cell. The inter-cell routing protocol is used to route packets between nodes in different cells. The combination of intra-cell and inter-cell routing protocol makes ABRP highly scalable, since each node needs to only maintain routes within a cell. The inter-cell routing protocol establishes multiple routes between different cells, which makes ABRP reliable and efficient. We evaluate the performance of ABRP using ns2 simulator. We simulated different size of networks from 200 nodes to 1600 nodes. Simulation results show that ABRP is efficient and scales well to large networks. ABRP combines the advantages of multi-path routing strategy and geographic routing strategy—efficiency and scalability, and avoids the burden—GPS support.     

无线自组织网络TCP速率联合调制

TCP在无线自组织网络中受到信道竞争和队列拥塞的双重影响,因而不能准确地调节数据发送速率从而降低了传输性能。本文针对该问题提出一种基于对信道竞争和排队拥塞联合检测的TCP速率调制策略。实验结果显示,本策略在吞吐量和端到端时延上均明显提高了TCP的性能。     

无线自组织网络极限信道容量增长规律研究

 为了分析和提高无线自组织网络的吞吐能力,提出了无线自组织网络的极限信道容量增长规律(capacity scaling laws)的一般表达式,研究发现单个节点的策略决定了整个无线自组织网络的吞吐能力,证明了使得整个网络吞吐能力最大化的最优策略的存在性。进一步通过应用博弈论,推导得出最优策略,并验证其满足纳什均衡且是演化稳定策略。     

An Approach for Modestly Directional Communications in Mobile Ad Hoc Networks

Directional antennas are a promising technology for use in mobile ad hoc environments. By consuming smaller volumes than omni directional antennas, directional antennas enable significant increases in network capacity by allowing more simultaneous transmissions to occur within a multihop wireless network. In this paper, we present some of the challenges that face asynchronous directional channel access schemes and describe how these problems can be avoided by taking a synchronous approach. We describe a communications system architecture that enables modestly directional sectored antennas to be effectively exploited in a mobile ad hoc environment. A key part of this architecture is the Directional Synchronous Unscheduled Multiple Access (DSUMA) protocol. By making intelligent decisions regarding the enabling/disabling of sector antennas, DSUMA provides an increased density of transmissions while insuring that collisions do not occur. Our results indicate how the number of sectors per node affects performance in terms of spatial reuse, the likelihood of collisions, and overall network capacity.     

Distributed Power Control for Energy Efficient Routing in Ad Hoc Networks

In this paper, distributed power control is proposed as a means to improve the energy efficiency of routing algorithms in ad hoc networks. Each node in the network estimates the power necessary to reach its own neighbors, and this power estimate is used both for tuning the transmit power (thereby reducing interference and energy consumption) and as the link cost for minimum energy routing. With reference to classic routing algorithms, such as Dijkstra and Link State, as well as more recently proposed ad hoc routing schemes, such as AODV, we demonstrate by extensive simulations that in many cases of interest our scheme provides substantial transmit energy savings while introducing limited degradation in terms of throughput and delay.     

Connectivity Based k-Hop Clustering in Wireless Networks

In this paper we describe several new clustering algorithms for nodes in a mobile ad hoc network. The main contribution is to generalize the cluster definition and formation algorithm so that a cluster contains all nodes that are at distance at most k hops from the clusterhead. We also describe algorithms for modifying cluster structure in the presence of topological changes. We also proposed an unified framework for most existing and new clustering algorithm where a properly defined weight at each node is the only difference in otherwise the same algorithm. This paper studied node connectivity and node ID as two particular weights, for k=1 and k=2. Finally, we propose a framework for generating random unit graphs with obstacles.