Handling asymmetry in power heterogeneous ad hoc networks

Traditional MAC and routing protocols, which are primarily designed for homogeneous networks wherein all nodes transmit with the same power, suffer performance degradations when employed in power heterogeneous networks. The observed degradations are due to link asymmetry, which arises as high power nodes that do not sense the transmissions of low power nodes can potentially initiate transmissions that interfere with the low power communications. Link layer asymmetry in power heterogeneous networks not only disrupts the functioning of the routing protocol in use, but also results in unfairness in medium access. In this paper, we develop a cross-layer framework to effectively address the link asymmetry problem at both the MAC and the routing layers. At the MAC layer, the framework intelligently propagates low power control messages to the higher power nodes, so as to preclude them from initiating transmissions while there are low power communications in progress within their sensing range. At the routing layer, the framework facilitates the efficient use of unidirectional links. We perform extensive simulations to study the performance of our proposed framework in various settings, and show that the overall throughput in power heterogeneous networks is enhanced by as much as 25% over traditional layered approaches. In addition, we show that our schemes are also beneficial in power homogeneous settings, as they reduce the extent of false link failures that arise when the IEEE 802.11 MAC protocol is used. In summary, our framework offers a simple yet effective and viable approach for medium access control and for supporting routing in power heterogeneous ad hoc networks.     

A quality based routing protocol for wireless mesh networks

Wireless mesh networks can provide low-cost solutions for extending the reach of wireless access points by using multi-hop routing over a set of stationary wireless routers. The routing protocol for these networks may need to address quality considerations to meet the requirements of the user. In this paper, we present a quality based routing protocol for wireless mesh networks that tries to maximize the probability of successful transmissions while minimizing the end-to-end delay. The proposed routing protocol uses reactive route discoveries to collect key parameters from candidate routes to estimate the probability of success and delay of data packets transmitted over them. To achieve accurate route quality assessments, a new route quality metric is proposed that uses performance models of data packet transmissions as opposed to estimating route quality from the transmission of control packets, which have different transmission characteristics. These models are developed after careful evaluations of multi-hop wireless transmissions and validated by computer simulations. Relevant parameters that can be used to assess the route quality metric using these models are explained. Extensive performance evaluations of the proposed quality based routing protocol are presented and its benefits in comparison to some other known routing protocols are discussed.     

车载传感器网络的研究进展

车载传感器网络是一种建立在车载自组织网络基础上的以数据为中心的新型移动传感器网络。与传统传感器网络不同的是,车载传感器网络中的节点是高速移动的,从而导致网络间歇连通、拓扑结构变化频繁,网络中数据的传输只能依靠节点间机会性的传递,严重影响了这种以数据为中心的网络中的数据传输的性能。对目前车载传感器网络的研究现状进行了分析讨论,同时结合延迟容忍网络和机会网络思想,给出了车载传感器网络的研究方向。     

On the capacity of multi-packet reception enabled multi-channel multi-interface wireless networks

Multi-packet reception (MPR) offers increased number of concurrent transmissions, which improves the capacity of wireless Ad hoc networks. By equipping each node with multiple wireless interfaces, the transmissions can be separated into different channels and the throughput can be increased. Combining these two technologies, this work studies the capacity of wireless networks wherein each node is equipped with multiple interfaces and each interface can decode at most k concurrent transmissions within its receiving range.     

基于概率传输的无线传感网数据汇聚方案

针对传统无线传感网数据汇聚中通信开销较大的问题,提出了基于概率传输的无线传感网数据汇聚方案。由于簇内节点有限,汇聚误差难以避免,在可容忍汇聚误差下,簇内节点按概率进行数据发送,可有效减少簇内消息传输量,降低通信开销。同时,采取狄克逊准则对小样本中的粗大误差进行剔除提供高的簇内汇聚可靠性。实验结果表明,在可容忍误差下进行概率发送可有效降低簇内消息传输量,所提方案的簇内数据汇聚通信开销约为传统方案的27.5%;概率发送的汇聚误差与所有节点进行数据发送的汇聚误差基本在同一水平,都是传感器网络可接受的。     

基于节点间信息事件分析的CDMA无线Ad Hoc网络传输性能研究

CDMA无线Ad Hoc网络节点间的并发信息传送所造成的节点间相互干扰是影响网络传输性能的主要因素之一.文中从CDMA无线Ad Hoc网络的节点间的信息流量角度研究了CDMA无线Ad Hoc网络的传输性能和吞吐量性能,以节点间信息事件图为工具研究了节点间干扰对网络传输性能的影响,并证明了节点间信息流量成功传输的一个充分条件,最后对结果进行了仿真并给出了节点间信息流量的一个拟合方程.     

A passive tree-based backbone construction scheme for MANETs

Backbone-based broadcast schemes are effective in alleviating the broadcast storm problem in mobile ad hoc networks (MANETs). However, periodically hello packets used to maintain a backbone usually lead to extra control overhead. In this paper, passive tree-based backbone construction scheme (PTBCS) is proposed as a backbone construction scheme for MANETs. Different from other schemes, each node in PTBCS determines its role by intercepting packet transmissions in the air during a special waiting period. Hence, its most remarkable advantage is that there are no periodical packet transmissions specially for backbone construction. The property that the nodes selected by PTBCS make up a connected dominating set (CDS) of the network is proven with several ideal assumptions. Simulation results show that PTBCS is effective when compared with some other typical backbone construction schemes.     

基于P2P的CDN网络中紧急消息广播技术

向基于P2P方式连接的CDN网络中的所有节点广播紧急消息,泛洪技术可以满足快速和可达这两个指标,但同时会在网络中产生大量冗余的消息广播,效率低下,使网络负荷产生一个短时的波峰.提出泛洪技术的两种改进方案,即WFES和WFESN技术,在不降低泛洪技术快速和可达的前提下提高了广播效率,改善了网络负荷的性能.     

分布式混合压缩感知无线传感器网络数据收集

在传感器网络数据收集过程中,降低网络传输量对于网络传输效率和生命周期的延长具有重要意义。结合压缩感知思想,设计了一种分布式混合压缩感知的无线传感器网络数据收集方法。首先通过基于k-means++的方法均匀聚类形成簇,各簇进行基于混合压缩感知的分布式数据收集,完成后通过建立骨干树将数据传输至sink节点。仿真结果表明,在给定的仿真工况下（压缩率为10,节点数为800）,与最短路径树混合压缩感知和最优树混合压缩感知算法相比,分别能减少40%和10%以上的传输量,与不使用混合压缩感知的收集方法相比减少70%以上的传输量;同时,节点传输量标准差由14.07和14.37和降低至11.85,置信区间大小由322.66和131.75降低至39.12,证明网络鲁棒性和负载均衡度均有提升。     

Data networks are mostly empty and for good reason

If you think data networks run at full capacity, think again. Most run at three to five percent in an average week. In fact, corporate data networks in the US are lightly utilized, with much lower average use than the Internet backbones. But low utilization is not necessarily a problem. It may in fact be the most efficient solution in terms of total system cost. Given the nature of the beast, there may be no way around it; utilization will stay low as long as data networks must accommodate bursty transmissions, users concentrate traffic during regular business hours, and network administrators have to provide spare capacity for the rapid introduction of new services     

A NEW DISTRIBUTED LOCATION-BASED ROUTING ALGORITHM FOR WIRELESS SENSOR NETWORKS

Searching and routing procedures are important in order to ensure communication in wireless sensor networks (WSN). Although naive flooding-based searching is simple to implement, it costs a high number of message transmissions and results in high energy consumption. In this study, we propose a new distributed location-based routing algorithm for WSN. Our goal was to decrease the number of message transmissions and to increase coverage by constructing relay zones. Directed broadcast, relay zone, and broadcast suppression constitute the backbone of our algorithm. We compared our algorithm with a flooding-based approach, and saw that our algorithm performs much better for several parameters.     

基于冗余小波变换的可扩展视频多描述编码

视频图像信息在不可靠信道上传输将引起丢包、误码以及延时等现象,严重影响了重建视频图像的质量;另外,在网络带宽、信道条件以及用户需求不同的传输环境下,迫切希望对视频图像进行可扩展性编码。将多描述编码技术与视频小波技术相结合,提出了一种新的视频编码方法,为解决上述问题提供一种新途径,实验仿真结果说明了这一方法的可行性与有效性。     

Delay-bounded data gathering in urban vehicular sensor networks

Vehicular sensor networks are an emerging network paradigm, suitable for various applications in vehicular environment making use of vehicles’ sensors as data sources and Inter-Vehicle Communication systems for the transmissions. We present a solution, based on vehicular sensor networks, for gathering data from a certain geographic area while satisfying with a specific delay bound. The method leverages the time interval during which the query is active in order to make the gathering process efficient, properly alternating data muling and multi-hop forwarding strategies like in delay-bounded routing protocols. Simulations show that our proposed solution succeeds in performing efficient data gathering outperforming other solutions.     

Network Security: Important Issues

In current times, sending confidential data over the Internet is becoming more commonplace every day. Some people and organizations, e.g. commercial banks, are completely dependent on electronic transmission of confidential data. Computer networks are the transport medium for these electronic data transmissions. Hackers mostly target networks as their primary point of infiltration, whether it is internal or external from a private network. What should one know about the security of networks these days? How should security be implemented to safeguard a network? How should security be managed? This article will address the above questions and will give an idea of where we stand with network security in current times.     

A direction-based geographic routing scheme for intermittently connected mobile networks

In an intermittently connected mobile network, a complete routing path from a source to a destination cannot be guaranteed most of the time. Therefore, traditional routing methods for mobile ad hoc networks are not applicable in such a network. Current approaches for intermittently connected mobile networks are primarily based on redundant transmission and single-copy opportunistic routing. However, they incur either high overhead due to excessive transmissions, or long delay due to incorrect path choices during forwarding. In this paper, we propose a direction-based geographic (DIG) routing scheme for intermittently connected mobile networks. Relying on geographic location information, the packets are routed in a path approximately to the shortest path from the source node to the destination, which significantly reduces the overhead in redundant transmission and decreases the transmission delay in the single-copy opportunistic routing. Theoretical analysis and trace-driven experimental results show that DIG provides low transmission delay with low overhead in comparison with the schemes in the redundant transmission and single-copy opportunistic routing.     

MANET中一种基于多信道的按需路由及其仿真

在移动自组织（Ad hoe）网络多信道环境下,现有路由协议不能充分利用多信道的特点。针对多信道Ad hoe网提出一种新路由协议,使节点对间能互不影响的并发传送数据。以提高网络容量。简单介绍了现有的按需距离矢量路由协议（AODV）及信道分配原理,对此路由协议进行微小修改,通过增加信道索引表项,动态交互信道信息等机制,提出一种多信道按需路由协议AODV—MC,并与现有的按需路由协议进行了相关的对比仿真实验。仿真结果说明。AODV—MC相对其他按需路由协议能更好的适应多信道环境,在网络开销增加极小的情况下。明显地减少了丢包率,提高了网络吞吐量。     

A multi-layer experimental study of multimedia and QoS communication in wireless mesh networks

A significant issue in Mesh networks is to support multimedia transmissions while providing Quality of Service (QoS) guarantees to mobile users. For real-time multimedia streaming, unstable throughput or insufficient bandwidth will incur unexpected delay or jitter, and it remains difficult to provide comprehensive service guarantees for a wireless mesh environment. In this paper, we target the problem of providing multimedia QoS in wireless mesh networks. We design and implement a campus test-bed for supporting multimedia traffic in mobile wireless mesh networks, and investigate in detail some possible improvements on a number of layers to enable multimedia transmission over wireless networks with QoS support. We first study a number of improvements of some existing routing protocols to support multimedia transmissions. Some new admission control and rate control mechanisms are studied and their performance gains are verified in our experiments. In our new cross-layer adaptive rate control (CLARC) mechanism, we adaptively change the video encoder’s output bit rate based on the available network bandwidth to improve the quality of the received video. We also design a mobile gateway protocol to connect the MANET to Internet and a wireless LAN management protocol to automatically manage WLAN to provide some QoS.     

无线多媒体传感器网络并发传输性能建模及实验评估

针对无线多媒体传感器网络（wireless multimedia sensor network,WMSN）在多路视频并发传输性能方面缺乏定量化评估的问题,对WMSN的并发性能进行了建模分析与实验验证．首先利用排队论和概率论原理构造了一个基于IEEE 802.11的WMSN数据链路层延迟模型,为实验提供理论依据．而后实验测量了基于IEEE 802.11的WMSN在不同网络拓扑下,不同因素（如距离、跳数、并发视频数）对视频评价指标（延迟、抖动、信道利用率）的影响．理论及实验结果表明,IEEE 802.11协议仅能支持四路以下视频并发传输,不适合高并发视频传输,亟待开展WMSN专属协议及算法的研究．     

Optimal data aggregation tree in wireless sensor networks based on improved river formation dynamics

The restricted energy of nodes is one of the most important challenges in wireless sensor networks. Since data transmissions among nodes consume most of the nodes' energy, thus, minimizing the unnecessary transmissions reduces the consumed energy. One of the sources of this problem is the redundancy of raw data that can be eliminated at the aggregation points. As a result, data aggregation can be considered as an effective strategy to tackle the mentioned issue and to optimize the communication energy consumption. In this paper, the sensor nodes are organized in a tree structure, and the data aggregation are done in intermediate nodes at the junction of tree branches. One of the main characteristics of tree protocols is reduction of energy consumption through optimizing the structure of a data aggregation tree. For this, this paper proposes to apply a swarm intelligent algorithm named river formation dynamics. The simulation results show that the proposed algorithm outperforms in comparison to the famous ant colony optimization algorithm in terms of network lifetime. Simulations show that the proposed algorithm makes nearly 4% and 50% improvement in lifetime of wireless sensor networks than ant colony optimization and shortest path routing, respectively.     

On the energy balance problem in distributed sensor networks

We investigate the problem of how to achieve energy balanced data propagation in distributed wireless sensor networks. The energy balance property guarantees that the average per sensor energy dissipation is the same for all sensors in the network, throughout the execution of the data propagation protocol. This property is crucial for prolonging the network lifetime, by avoiding early energy depletion of sensors.We survey representative solutions from the state of the art. We first present a basic algorithm that in each step probabilistically decides whether to propagate data one-hop towards the final destination (the sink), or to send it directly to the sink. This randomized choice trades-off the (cheap, but slow) one-hop transmissions with the direct transmissions to the sink, which are more expensive but bypass the bottleneck region around the sink and propagate data fast. By a detailed analysis using properties of stochastic processes and recurrence relations we precisely estimate (even in closed form) the probability for each propagation option necessary for energy balance.The fact (shown by our analysis) that direct (expensive) transmissions to the sink are needed only rarely, shows that our protocol, besides energy balanced, is also energy efficient. We then enhance this basic result by surveying some recent findings including a generalized algorithm and demonstrating the optimality of this two-way probabilistic data propagation, as well as providing formal proofs of the energy optimality of the energy balance property.