一种低开销的无线传感器网络时间同步算法

低开销是无线传感器网络时间同步算法的重要技术要求之一.为了降低同步过程中的通信开销,提出了一种基于部分广播的低开销无线传感器网络时间同步算法.算法基于TPSN算法的分层思想,利用节点的距离信息,选撵当层节点的部分相邻节点进行下一层的等级广播,从而有效地降低同步过程中的通信开销.分析了在不同的网络节点密度下广播信息包数与等级广播距离的关系,得到了不同网络节点密度下的最优等级广播距离.仿真结果表明,与TPSN算法相比,在相同的同步精度下,算法能显著地降低高密度无线传感器网络时间同步的开销.     

WSN中有效的最小单位圆集覆盖算法*

针对具有不同传输半径的无线传感器网络覆盖与广播数据转发问题,提出了一种以最小单位圆覆盖集作为广播数据转发集的算法。该算法能有效计算出覆盖范围的轮廓集,具有最优的时间复杂度O(n log n)。对每个节点,该算法以其最少数量的邻居节点子集实现所有邻居节点的覆盖,并证明了该算法找到的最小单位圆覆盖集与其轮廓集是相等的。详细的仿真实验及与现有算法的比较表明,提出的覆盖算法不仅以最少数量的节点实现了网络覆盖与广播数据转发,同时延长了网络生命期。     

一种改进的井下无线传感器网络广播算法

针对现有的井下无线传感器网络广播算法能耗较高的问题,提出了一种改进的无线传感器网络前向广播算法。该算法中,转发节点可根据自身位置,选择优先节点转发信息,大大减少了无线传感器网络中需要转发的冗余信息量,从而降低了网络能耗。仿真结果表明,该算法在网络节点密度达到一定值时,满足网络接收率要求,且能够限制转发的信息总量,有效降低了无线传感器网络能耗。     

一种基于转发优先及流量分级的无线传感器网络退避算法

基于无线传感器网络的特点,提出了一种新的基于转发优先和流量分级的退避算法,该算法根据节点自身可获取的网络信息将网络流量判定为不同的级别,并依此改变退避窗口的大小;该算法还赋予转发节点一定的信道竞争优势,使得当前的通信业务可以优先地进行下去。通过理论分析和仿真实验,证实该算法能够有效地降低节点冲突率和额外的能量开销,减少传输延时,提高系统吞吐量,从而提高无线传感器网络的性能。     

基于反向生成CDS树的无线传感器网络拓扑控制算法研究

拓扑控制是无线传感器网络中一种有利于节约能量、延长网络生命周期的策略。作为一种著名的基于CDS树的拓扑控制机制,A3算法的目标是在保证网络连通和通信覆盖的前提下,通过关闭一些非必要节点来获得一个次优连通支配集(CDS)。针对A3算法在构建连通支配集时通信开销较大的问题,提出了一种基于叶节点反向生成CDS树的改进型算法A3G。该算法利用反向拓扑方法来寻找连通支配集,减少了节点间的信息交换。仿真结果显示,相对于A3算法和一些其他著名的拓扑控制算法,A3G算法在活动节点数和能效方面具有明显的优越性。     

低开销的无线传感器网络下行路由协议

下行路由是无线传感器网络路由的一个重要组成部分.利用分布式编址算法为每个节点分配一个下行地址,在转发下行报文时,中间节点利用目的地址即可确定下一跳节点,从而可以通过单播转发实现基站到单个传感器节点的下行通信.在TinyOS上实现了编址算法和下行路由,仿真结果表明和基于广播转发的下行路由协议相比,该协议可以大幅减少报文转发次数,降低了路由开销.同时,因为减少了通信冲突,该下行路由协议对上行数据传输的影响也较小,适合那些既需要上行通信也需要频繁进行下行通信的无线传感器网络使用.     

无线传感器网络中基于异构节点的覆盖控制算法

研究了无线传感器网络中基于异构节点的优化覆盖控制问题.异构无线传感器网络由两类能力不同的节点组成,包括普通节点和超级节点.对普通节点采用基于状态轮转的覆盖控制算法,对超级节点采用基于路由表的转发策略.通过两类节点的协作使得网络达到覆盖与连通的目的.模拟结果表明,在具有相同初始能量的情况下,该算法与SHHN-HS算法相比能够延长网络生命期.     

不可靠通信环境下无线传感器网络最小能耗广播算法

在实际的通信环境中,由于噪声、报文冲突、信号衰减等因素的影响,无线传感器网络节点间信息交换往往是不可靠的.广播是无线传感器网络中广泛使用的操作,如何在不可靠通信环境下实现能量高效的广播算法,对提高整个无线传感器网络的性能具有重要的理论和应用价值.研究了不可靠通信环境下的无线传感器网络最小能耗广播问题,首先,分析了相邻节点之间最小能耗通信模型,并给出了保证节点接收概率不低于P^*的最优发送半径;然后,讨论了多跳转发策略与节点位置信息之间的关系.在此基础上,提出了一种基于PSO的最小生成树广播算法,通过优化各节点的发送半径,在保证所有节点都能以不低于P^*的概率接收到广播数据包的前提下,实现广播操作的总能耗最小.实验结果表明：所提出的广播算法不仅可使每一个节点的接收概率不小于P^*,而且广播总能耗比改进后的BIP算法要小,具有较好的性能.     

高密度且信号涵盖范围不规则的WSN广播算法研究

广播在无线传感器(WSN)协议中有着广泛的应用,但简单泛洪广播将带来广播风暴问题,在节点稠密的网络中尤为严重.借鉴DCB(double-covered broadcast)算法的节点双重覆盖思想,提出适合在节点高密度且信号涵盖范围不规则无线传感器网络的改进广播算法,简称为SDCB(sensor double-covered broadcast)算法.算法考虑在节点间不对称链路存在情况下,有效利用局部邻居节点信息减轻广播风暴,使广播有效进行,同时考虑低能量节点的处理来平衡网络耗能.最后在NS2平台上对SDCB算法进行仿真,并与DCB算法进行分析、比较.仿真结果表明,SDCB算法有较高的广播送达率、较低的节点转发率以及较低的广播时延.     

基于通信与感知覆盖的WSNs节点调度算法

在随机部署的无线传感器网络中通常包含覆盖与通信冗余节点,这些节点不仅会造成大量的能量浪费,同时影响网络的性能。因此,如何对网络中的覆盖与通信冗余节点进行有效的调度是无线传感器网络研究的一个重要课题。提出了一种基于蜂窝模型的分布式节点调度算法(RCSC)。在蜂窝结构的基础上,RCSC算法通过添加"桥梁节点"和填补"空洞"来进一步优化工作节点集,使得整个网络达到全"通信覆盖"和全"感知覆盖"。最后,RCSC算法结合LEACH协议,对网络中的节点进行动态调度。经试验仿真证明,由RCSC算法构建出的网络拓扑中的工作节点数少且稳定,从而减少了由于冗余数据通信导致的额外能量消耗,延长了网络生存时间。     

一种跨层协助的Ad hoc无线网络广播策略

在Ad hoc无线网络中，对全网范围进行广播有着广泛的应用。而Ad hoc网络节点资源、网络资源严重受限，广播引起的广播风暴问题加剧了资源的消耗。本文提出一种跨层协助的广播策略，该策略利用一跳邻节点的信息和物理层、数据链路层的信息统一在MAC设置退避时间，并根据发送节点密度自适应调整退避的时间，减少转播冗余、冲突发生的概率和延迟，确保了广播的可达性。仿真结果也表明提高了广播的效率。     

无冲突的无线传感器网络广播算法

无线传感器网络的节点众多,各种资源严重受限,广播引起的冗余转播加剧了资源的消耗,因而慎重选择转播节点非常关键.提出了一种无冲突的广播策略,该策略利用邻节点能量和度等信息构建最小连通树,减少了转播节点的数量,同时对最小连通树中的节点的转播进行调度,避免冲突的发生.该策略减少网络中节点的能量消费、延长了网络寿命,同时确保了广播的可达性.仿真结果表明该算法提高了广播的效率.     

一种能量高效的Ad hoc无线网络广播算法

广播在Ad hoc无线网络中有着广泛的应用,而Ad hoc网络节点资源、网络资源严重受限,广播引起的广播风暴问题加剧了资源的消耗。提出了一种能量高效的无冲突的广播策略,该策略利用所有两跳邻节点的剩余能量和度等信息选择前向转播节点,并将前向转播节点分为相互不干扰的独立子集,统一为独立子集设置退避时间,避免冲突的发生。该策略平衡了网络中节点的能量消费、延长了网络寿命,同时减少了广播延迟和转播冗余,确保了广播的可达性。仿真结果也表明提高了广播的效率。     

基于区域划分的连通支配集协议

针对规模较大、节点分布密集的无线传感器网络容易产生冗余数据包以及信号冲突,导致过多的节点能量消耗,加速死亡过程等问题,在深入研究现有的分布式连通支配集构造算法的基础上,提出基于区域划分的连通支配集协议——RPMPR协议.RPMPR协议中每个节点针对网络拓扑信息,对邻居节点进行区域划分,在各区域内选择中继转发节点集,并以节点的度作为选择支配节点的依据,构建覆盖全网的连通支配集.仿真实验结果表明,RPMPR协议充分考虑网络拓扑信息,显著减小连通支配集规模,同时支配节点分布更为均匀.     

Extended Dominating Set and Its Applications in Ad Hoc Networks Using Cooperative Communication

We propose a notion of an extended dominating set where each node in an ad hoc network is covered by either a dominating neighbor or several 2-hop dominating neighbors. This work is motivated by cooperative communication in ad hoc networks whereby transmitting independent copies of a packet generates diversity and combats the effects of fading. We first show the NP-completeness of the minimum extended dominating set problem. Then, several heuristic algorithms, global and local, for constructing a small extended dominating set are proposed. These are nontrivial extensions of the existing algorithms for the regular dominating set problem. The application of the extended dominating set in efficient broadcasting is also discussed. The performance analysis includes an analytical study in terms of approximation ratio and a simulation study of the average size of the extended dominating set derived from the proposed algorithms.     

MANET adaptive structured P2P overlay

This paper presents an efficient structured P2P overlay over MANET which better matches to the physical network in term of routing. This feature is achieved by locally building up the minimum-spanning tree (MST) at each peer using the information of the peer’s logical neighbors which are either directly connected (1-hop) or 2-hops away. Using this interconnection structure among the peers, we design a new algorithm to distribute the contents information in the overlay by partitioning the identifier (ID) space among the peers. In this algorithm, each peer maintains a disjoint portion of the ID space. The ID space at a peer may be non-contiguous and each contiguous part is consecutive to the ID space of its directly connected neighbor peers. To route the file-lookup query, each peer builds up a binary search tree (BST) using the knowledge of the ID space of itself and of its directly connected neighbor peers. Simulation results show that our approach outperforms the existing approaches in term of routing overhead, average file-discovery delay, false-negative ratio and average path-stretch value.     

Loop-free hybrid single-path/flooding routing algorithms withguaranteed delivery for wireless networks

In a localized routing algorithm, each node makes forwarding decisions solely based on the position of itself, its neighbors, and its destination. In distance, progress, and direction-based approaches'(reported in the literature), when node A wants to send or forward message m to destination node D, it forwards m to its neighbor C which is closest to D (has best progress toward D, whose direction is closest to the direction of D, respectively) among all neighbors of A. The same procedure is repeated until D, if possible, is eventually reached. The algorithms are referred to as GEDIR, MFR, and DIR when a common failure criterion is introduced: The algorithm stops if the best choice for the current node is the node from which the message came. We propose 2-hop GEDIR, DIR, and MFR methods in which node A selects the best candidate node C among its 1-hop and 2-hop neighbors according to the corresponding criterion and forwards m to its best 1-hop neighbor among joint neighbors of A and C. We then propose flooding GEDIR and MFR and hybrid single-path/flooding GEDIR and MFR methods which are the first localized algorithms (other than full flooding) to guarantee the message delivery (in a collision-free environment). We show that the directional routing methods are not loop-free, while the GEDIR and MFR-based methods are inherently loop free. The simulation experiments, with static random graphs, show that GEDIR and MFR have similar success rates, which is low for low degree graphs and high for high degree ones. When successful, their hop counts are near the performance of the shortest path algorithm. Hybrid single-path/flooding GEDIR and MFR methods have low communication overheads. The results are also confirmed by experiments with moving nodes and MAC layer     

Sparse structures for searching and broadcasting algorithms over internet graphs and peer-to-peer computing systems

In a broadcasting problem, a message is sent from a source to all the other nodes in the network. Blind flooding is a classical mechanism for broadcasting, where each node retransmits received message to all its neighbors. Despite its important advantages, an increase in the number of requests or the network size or density produces communication overheads that limit the scalability of blind flooding, especially in networks with dynamic topologies. Theoretically optimal solution is based on minimal spanning trees (MST), but its construction is expensive. We discuss here protocols based on local knowledge and newly proposed sparse structures. In weighted RNG (Relative Neighborhood Graph), messages are forwarded only on links which are not the ‘longest’ in any triangle. In weighted RNGQ, messages are forwarded to links which are not the longest in any triangle or quadrangle. Each node constructs weighted MST based on its 2-hop knowledge. Weighted LMST (Localized LMST) preserves only edges that are selected by both endpoints, and messages are forwarded on these links. Any available metric, such as delay, reliability, reputation etc. can be used as weight. Analysis and simulation show that weighted RNG performs better than existing Flooding and Rumor Mongering (or Gossip) schemes. The parameterless weighted LMST, MST, RNG and RNGQ (RNG over Quadrangle) based broadcasting schemes are compared, showing overall advantage for LMST. We also hint that a number of existing protocols can be simplified by applying concept from this article.     

对IEEE 802.11 MAC层协议公平性改进的研究

Ad Hoc网络中基于IEEE 802.11的MAC层协议采用CSMA/CA机制,通过侦听只能获取一跳范围内节点的信息,存在隐终端问题,影响了网络流调度的公平性.文中对IEEE 802.11提出了一种修改方案,该方案通过邻居结点间的信息交换,使网络中每个节点具有其二跳范围内所有结点的信息,以发现网络中的隐终端,提高网络流调度的公平性.对比仿真实验结果表明,修改后的IEEE 802.11与原协议的网络吞吐量基本相当,但具有更好的公平性.     

Constructing minimum extended weakly-connected dominating sets for clustering in ad hoc networks

Motivated by cooperative communication in ad hoc networks, Wu et al. proposed extended dominating set (EDS) where each node in an ad hoc network is covered by either a dominating neighbor or several 2-hop dominating neighbors, and defined two types of dominating sets: extended strongly connected dominating set (ECDS) and extended weakly connected dominating set (EWCDS), according to the success of a broadcast process. An EWCDS is an effective method for clustering. In this paper, we extend the dominative capabilities of nodes such that each forward node dominates not only itself and its regular neighbors fully, but also its quasi-neighbors partly. Based on this extension, three novel algorithms to find EWCDSs in ad hoc networks are proposed. The correctness and performance of our algorithms are confirmed through theoretical analysis and comprehensive simulations.