自适应高效无线传感器网络时间同步优化算法

针对无线传感器网络全网多跳自适应时间同步效率低的问题,在接收端与接收端同步模型基础上,该文提出一种自适应高效无线传感器网络时间同步优化算法(AEO)。首先,双节点同步时,从节点接收来自参考节点的同步消息并进行确认,在同步周期结束后通过拟合估计和数据更新完成时间修正,构建交互参数同步包,并与主节点进行信息交换完成同步过程。其次,全网同步时,建立Voronoi多边形拓扑结构,认定拓扑结构中参考节点和邻域节点身份(ID),参考节点覆盖区域间通过邻域节点交换同步信息,实现自适应多区域节点联合时间同步。仿真结果表明该算法在双节点时间同步中能够保证同步误差较小,网络能耗较低;同时,Voronoi拓扑相较于其他典型拓扑,在连通效率和收敛时间方面均有所改进。     

Wirelessly Synchronized One‐Way Ranging Algorithm with Active Mobile Nodes

In this letter, we propose a one‐way ranging algorithm that is based on wireless synchronization with measured timestamps and clock frequency offsets. In our proposed algorithm, an active mobile node initiates a ranging procedure by transmitting a ranging frame, and the anchor nodes report their timestamps for the received ranging frame to a reference anchor node. The synchronization of a pair of nodes is provided with instantaneous time information, and the corresponding difference of distances can be calculated.     

Distributed Routing Based on Minimum End‐to‐End Delay for OFDMA Backhaul Mobile Mesh Networks

In this paper, an orthogonal frequency division multiple access (OFDMA)‐based minimum end‐to‐end delay (MED) distributed routing scheme for mobile backhaul wireless mesh networks is proposed. The proposed scheme selects routing paths based on OFDMA subcarrier synchronization control, subcarrier availability, and delay. In the proposed scheme, OFDMA is used to transmit frames between mesh routers using type‐I hybrid automatic repeat request over multipath Rayleigh fading channels. Compared with other distributed routing algorithms, such as most forward within radius R, farthest neighbor routing, nearest neighbor routing, and nearest with forwarding progress, simulation results show that the proposed MED routing can reduce end‐to‐end delay and support highly reliable routing using only local information of neighbor nodes.     

rDFD: reactive distributed fault detection in wireless sensor networks

Generally, fault detection approaches pursue high detection accuracy, but neglect energy consumption due to the high volume of messages exchanged. Therefore, in this work we propose a reactive distributed scheme for detecting faulty nodes. The scheme is able to detect transient and permanent faulty nodes accurately by exchanging fewer messages. In existing fault detection schemes, nodes exchange too many messages after every specific interval to detect suspicious node. However, in the proposed scheme comparatively much less messages are exchanged within a limited geographical area around the suspicious node only and that too when the node suspects its own readings. In the proposed scheme, each node exploits the temporal correlation in its own readings to detect any suspicious behavior. In order to confirm its status, the suspicious node communicates with its immediate neighbors who may be locally good or possible faulty with a certain level of confidence. Thus, the scheme utilizes the strength of both spatial and temporal correlation to find faulty nodes. Also, a confidence level is assigned to each correlated neighbor of suspicious node in order to enhance the detection accuracy. The ns-2 based simulation results show that our scheme performs better by reducing communication overhead and by detecting faulty nodes with high accuracy as compared to existing approaches.     

基于定向收发的水声通信网络邻节点发现机制

针对水声通信网络邻节点发现困难的问题,该文提出一种基于定向收发的邻节点发现机制。该机制中节点只采用定向方式发送和接收信号,能够避免增益不对称引起的隐藏终端问题,增加网络覆盖范围;时间被划分为邻节点发现时隙和侦听回复时隙,发现时隙中节点发送HELLO信号,然后接收邻节点回复的REPLY信号,侦听回复时隙中节点侦听源节点发送的HELLO信号,然后回复REPLY信号,节点通过基于竞争的HELLO/REPLY两路握手以直接发现和间接发现两种方式完成邻节点发现,能够克服“聋”节点问题,提升邻节点发现效率。仿真结果表明,在不同的网络节点密度与发射天线波束扇区数目条件下,该邻节点发现机制相比随机两路邻节点发现机制,邻节点平均发现时延更短,邻节点发现率更高。     

On a joint temporal-spatial multi-channel assignment and routing scheme in resource-constrained wireless mesh networks

Use of multiple orthogonal channels can significantly improve network throughput of multi-hop wireless mesh networks (WMNs). In these WMNs where multiple channels are available, channel assignment is done either in a centralized manner, which unfortunately shows a poor scalability with respect to the increase of network size, or in a distributed manner, where at least one channel has to be dedicated for exchanging necessary control messages or time synchronization has to be utilized for managing the duration of data packet transmission, causing excessive system overhead and waste of bandwidth resource. In this paper, we first formulate multi-channel assignment as a NP-hard optimization problem. Then a distributed, heuristic temporal-spatial multi-channel assignment and routing scheme is proposed, assuming every wireless node in the network is equipped with a single-radio interface. Here the gateway node is set to use all the channels sequentially in a round-robin fashion. This temporal scheme ensures all the nodes that need to directly communicate with the gateway node shall have a fair access to it. For those non-gateway nodes, a spatial scheme where channels are assigned based on their neighbors’ channel usage is adopted to exploit parallel communications and avoid channel interference among nodes. Furthermore, since the routing factors, including channel usage of neighbor nodes, node hop count, node memory size, and node communication history, are all considered along with the channel assignment, network performance, measured by packet delivery latency, channel usage ratio, and memory usage ratio, tends to be considerably enhanced. The simulation results have confirmed that, compared with a couple of well-known multi-channel assignment schemes, such as LCM [21] and ROMA [15], the proposed scheme shows substantial improvement in network throughput with a very modest collision level. In addition, the proposed scheme is highly scalable as the algorithm complexity is only linearly dependent on the total number of channels that are available in the network and the number of neighbors that a network node directly connects to.     

Compromise‐Resistant Pairwise Key Establishments for Mobile Ad hoc Networks

This letter presents a pairwise key establishment scheme that is robust against the compromise of nodes in mobile ad hoc networks. Each node establishes local keys with its neighbor nodes that are at most three hops away at network boot‐up time. When any two nodes establish a pairwise key, they receive the secret information from the nodes on the route between them, and construct the pairwise key using the secret information. Here, the local keys are utilized by the nodes on the route to send the secret information securely. The simulation results have proven that the proposed scheme provides better security than the key pre‐distribution‐based scheme.     

Protocol design and data detection for two‐way relay networks with fractional asynchronous delays

In wireless two‐way relay systems, it is difficult to achieve perfect timing synchronization among different nodes. In this paper, we investigate relaying protocol design and data detect schemes for asynchronous two‐way relaying systems to combat the intersymbol interference caused by asynchronous transmission. We consider fractional asynchronous delays and two schemes are proposed based on cyclic prefixed single carrier block transmission, namely, the receiver frequency domain equalization scheme and relay synchronization and network coding (RSNC) scheme. In the receiver frequency domain equalization scheme, the relay simply amplifies the received signal and forwards to the two source nodes, and fractionally spaced frequency domain equalizer (FS‐FDE) is employed at the receiver to recover the transmit data. In the RSNC scheme, the asynchronous signals are resynchronized with an FS‐FDE at the relay node. The output signals of FS‐FDE are then demodulated and network coded before forwarding to the two source nodes. In this RSNC scheme, data detection at the source nodes is the same as that in synchronous networks because the asynchronous signals have already been synchronized at the relay node. Simulation results show that the performance of both schemes is almost the same as in the perfect synchronized two‐way relaying systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Cluster‐Based Trust Evaluation Scheme in an Ad Hoc Network

This paper presents a new trust evaluation scheme in an ad hoc network. To overcome the limited information about unfamiliar nodes and to reduce the required memory space, we propose a cluster‐based trust evaluation scheme, in which neighboring nodes form a cluster and select one node as a cluster head. The head issues a trust value certificate that can be referred to by its non‐neighbor nodes. In this way, an evaluation of an unfamiliar node's trust can be done very efficiently and precisely. In this paper, we present a trust evaluation metric using this scheme and some operations for forming and managing a cluster. An analysis of the proposed scheme over some security problems is also presented.     

一种基于邻域信息的多信道自适应建网算法

为实现多信道无线自组网的高效建网,针对节点难以感知全网拓扑、其他所有节点的可用频谱以及无法获得同步信息的实际场景,提出了一种基于邻域信息的多信道自适应建网算法。该算法首先设计基于邻域信息的建网策略,使节点能够以自身信息为基础,充分利用可用信道情况、邻居簇首情况等有限的邻域信息进行自适应决策,以建立分簇结构的网络;然后提出基于最大熵原理的信道质量评价算法和基于多头绒泡菌模型的邻居簇首评价算法,分别对节点的可用信道和邻居簇首进行排序,指导节点在建网过程中选择合理的信道和簇首。仿真结果表明,所提建网算法能够使节点在实际场景通信受限的条件下以较小的通信开销完成建网,建立的网络在公共信道数量和簇规模方面也取得了较好的均衡。     

Routing in the frequency domain

The design of single transceiver based multi-channel multi-hop wireless mesh networks focuses on the trade-off between rapid neighbor synchronization and maximizing the usage of all available channels. Existing designs are confined to the MAC layer and scale poorly as the network grows in coverage and density. We recently proposed Dominion as a cross-layer architecture that includes both medium access control and routing. Dominion eliminates the need for neighbor synchronization at the MAC layer and pushes the intelligence up the network stack. At the MAC layer, a node switches channels according to a deterministic schedule which guarantees that a node converges with each of its neighbors periodically. At the network layer, the channel-hopping aware routing substrate routes traffic along the frequency domain, i.e., packets along a multi-hop route generally traverse via multiple channels. In this paper, we present the complete design, analysis and evaluation of Dominion and make four new contributions. Firstly, we extend Dominion to support goal-oriented routing: source nodes can locally choose to maximize throughput or minimize end-to-end latency without requiring any changes in the network. Secondly, we describe a technique that eliminates intra-flow interference. In absence of extrinsic interference, Dominion now allows network flows to maintain constant throughput and deterministic end-to-end latencies irrespective of distance. Thirdly, via theoretical modeling and analysis, we provide expected throughput and end-to-end latencies for network flows. Finally, via extensive QualNet simulations we show that Dominion achieves 1064% higher throughput than IEEE 802.11 while being 299% fairer.     

Detouring dynamic routing holes in stationary wireless sensor networks in the presence of temporarily misbehaving nodes

In this work, we propose a scheme, named BRIDGE , to bypass dynamic routing holes arising in stationary wireless sensor networks in the presence of temporarily misbehaving nodes such as dumb 1 , 2 or transfaulty nodes. The affected nodes behave normally after the resumption of favorable environmental conditions. Therefore, both dumb and transfaulty behaviors of sensor nodes are dynamic in nature. The nodes in these networks get temporarily isolated from the network, when they behave as dumb or transfaulty. Because of the presence of nodes with such behavior, dynamic communication holes may occur in the network, which are formed or removed and thus increase or decrease in size with time. Connectivity re‐establishment procedures can mitigate holes by re‐connecting isolated nodes with the network after activating the intermediate sleep nodes, adjusting the communication range of intermediate nodes, or by using an alternative communication mode. However, such procedures cannot always re‐establish connectivity because of the lack of neighbor nodes in reduced or adjusted communication range. Therefore, routing schemes using greedy forwarding approaches need to bypass holes to avoid the data packets from getting stuck at the boundary nodes and efficiently delivering them to the sink. However, the existing hole avoidance schemes consider holes as static. The proposed scheme, BRIDGE , detects hole boundary and bypasses routing traffics in the dynamic hole scenario. In the proposed scheme, a boundary node selects the next hop based on the minimum distance from all the neighbor nodes to the destination node, although this minimum distance is more than the distance to the destination from the node itself. Simulation results show that the performance of the proposed scheme degrades with the increase in hole area. Copyright © 2015 John Wiley & Sons, Ltd.     

Neighbor caching in multi-hop wireless ad hoc networks

We propose a neighbor caching strategy to overcome the overhead of multi-hop wireless communications. Neighbor caching makes a node able to expand its caching storage instantaneously by storing its data in the storage of idle neighbors. We also present the ranking based prediction that selects the most appropriate neighbor which data can be stored in. The ranking based prediction is an adaptive algorithm that adjusts the frequency of neighbor caching and makes neighbor caching flexible according to the idleness of nodes.     

Mobility control for achieving optimal configuration in wireless sensor networks

Recent work in wireless sensor networks, or simply called WSNs, has drawn attention to the mobility capability of each node. In Stojmenovic and Lin (IEEE Trans Parallel Distrib Syst 12: 1023–1032, 2001), it is proved that the optimal positions of the relay nodes along a single active flow must lie entirely on the line between the source and destination with each node spaced evenly along such a line. Based on this, we propose two practical solutions to control the relay nodes in WSNs to approach their optimal positions in the local relative coordinate system. One uses one-hop neighbor information and the other one uses two-hop neighbor information. Basically, each relay node will approach the midpoint on the line composed of neighbors. For the latter control scheme, we also discuss its different implementation with outdated two-hop neighbor information (lagged by one-round neighbor information exchange and update). This is an improvement since given nodes only reuse the two-hop neighbor information previously saved at its one-hop neighbors and does not require any extra neighbor information collection. All the new methods prevent oscillations by demanding minimal moving distance per round (MDPR), otherwise the node does not move. Unlike the one presented in Goldenberg et al. (Proceedings of the 5th ACM International Symposium on Mobile Ad Hoc Networking and Computing (Mobihoc’04), pp 163–174 2004) using only one-hop neighbor information, our methods will converge more quickly. The experimental results show a substantial improvement on the speed of achieving the optimal configuration and the total moving distance of nodes.     

Sensor fault detection algorithm based on credibility and neighbor-cooperation

To effectively detect whether a node was failure,one of the effective sensor fault detection methods was to compare historical data of suspicious node with its neighbors.The key points of this method were identification of suspicious nodes,as well as decision problem of sending timing for fault diagnosis messages.To this end,a sensor fault detection algorithm was presented based on credibility and neighbor-cooperation.Firstly,a credibility model to determine whether nodes are suspicious was established.Then suspicious nodes send fault diagnosis requests to neighbor nodes based on neighbor-cooperation.The sending timing was determined by equal probability time window.Finally,it could finish classification of fault condition and state judgment based on diagnosis responds of neighbor nodes.Simulation experiments show that this algorithm can achieve higher fault detection rate with less fault diagnosis times and low data congestion probability.     

Incremental Adaptive Strategies Over Distributed Networks

An adaptive distributed strategy is developed based on incremental techniques. The proposed scheme addresses the problem of linear estimation in a cooperative fashion, in which nodes equipped with local computing abilities derive local estimates and share them with their predefined neighbors. The resulting algorithm is distributed, cooperative, and able to respond in real time to changes in the environment. Each node is allowed to communicate with its immediate neighbor in order to exploit the spatial dimension while limiting the communications burden at the same time. A spatial-temporal energy conservation argument is used to evaluate the steady-state performance of the individual nodes across the entire network. Computer simulations illustrate the results.     

STS_4e: Secure Time Synchronization in IEEE802.15.4e Networks

IEEE802.15.4e networks adopt time-synchronized medium access control protocols which enables highly reliable and ultra-low power industrial wireless networks. In these networks, nodes use timeslot to communicate which need a high-precision time synchronization. In hostile environments, the time synchronization protocol may be destroyed by external, compromise or pulse-delay attacks. In this paper, we present a secure time synchronization for IEEE802.15.4e networks called STS_4e which includes a secure single-hop pair-wise time synchronization and a secure cluster-wise time synchronization. The secure pair-wise time synchronization adopts message integrity authentication mechanism to defend against external attacks and threshold filter algorithm to defend against compromise and pulse-delay attacks. The secure cluster-wise time synchronization adopts packet-based key chain to improve µTESLA broadcast authentication mechanism which can well balance the delay of disclosed keys and the length of key chain. Finally, we implement the STS_4e scheme on OpenMoteSTM node running OpenWSN. The results show that the proposed scheme can successfully defend against time synchronization attacks as well as the low energy consumption.     

Optimal Sleep/Wake Scheduling for Time-Synchronized Sensor Networks With QoS Guarantees

We study sleep/wake scheduling for low-duty cycle sensor networks. Our work explicitly considers the effect of synchronization error. We focus on a widely used synchronization scheme and show that its synchronization error is nonnegligible and using a conservative guard time is energy wasteful. We formulate an optimization problem that aims to set the capture probability threshold for messages from each individual node such that the expected energy consumption is minimized, and the collective quality of service (QoS) over the nodes is guaranteed. The problem is nonconvex. Nonetheless, we are able to obtain a solution with energy consumption that is provably at most 37% larger than the optimal solution. Simulations demonstrate the efficacy of our solution.     

Secure and Energy-Efficient Traffic-Aware Key Management Scheme for Wireless Sensor Network

In Wireless Sensor Network (WSN), a sensor node may communicate with a small set of neighbor sensor nodes. Existing key management schemes, did not consider this communication between these nodes. They establish shared keys for all pairs of neighbor sensor nodes. When the number of sensor nodes in WSN is augmented, large number of keys is to be loaded in each sensor node, which in turn causes supplementary energy consumption. If any two close sensor nodes are seldom in the active-state the assignment of shared keys may be gratuitous, since they may be hardly exploited.In this paper, based on this information, secure and Energy-Efficient Traffic Aware key Management (EETKM) is developed for WSN. This determines shared keys for active sensors which takes part in the direct communication. In order to broadcast keys without retransmission or acknowledgements, the proposed scheme gives an efficient Re-keying mechanism. The proposed scheme attains high connectivity which is shown through numerical results. The proposed scheme is applied for various routing protocols and the simulation results shows the stronger resilience, low energy consumption and increased delivery ratio.     

DS/FH通信系统的跳频同步技术研究

同步是DS/FH混合通信系统的关键技术之一。根据跳频系统中对同步的要求,介绍了一种适用于DS/FH混合扩频通信系统的跳频同步方法,采用同步字头和精准时间相结合的方法实现跳频同步。对同步性能进行了分析,结果表明该跳频同步方法同步时间短,捕获概率高。