无线自组织网中VoIP性能研究

目前,VoIP技术及其业务迅速发展,在无线自组织网络中有广泛的应用,有必要对于VoIP在无线自组网中的传输进行分析研究。利用NS-2作为仿真工具对G.711编码标准下多跳无线自组织网中VoIP的传输进行仿真,使用802.11MAC层协议和AODV路由层协议。实验结果表明,无线自组织网络环境下VoIP系统性能(包括丢包率、时延等)受到多跳影响。     

Integration of mobility and intrusion detection for wireless ad hoc networks

One of the main challenges in building intrusion detection systems (IDSs) for mobile ad hoc networks (MANETs) is to integrate mobility impacts and to adjust the behaviour of IDSs correspondingly. In this paper, we first introduce two different approaches, a Markov chain‐based approach and a Hotelling's T² test based approach, to construct local IDSs for MANETs. We then demonstrate that nodes' moving speed, a commonly used parameter in tuning IDS performances, is not an effective metric to tune IDS performances under different mobility models. To solve this problem, we further propose an adaptive scheme, in which suitable normal profiles and corresponding proper thresholds can be selected adaptively by each local IDS through periodically measuring its local link change rate, a proposed unified performance metric. We study the proposed adaptive mechanism at different mobility levels, using different mobility models such as random waypoint model, random drunken model, and obstacle mobility model. Simulation results show that our proposed adaptive scheme is less dependent on the underlying mobility models and can further reduce false positive ratio. Copyright © 2006 John Wiley & Sons, Ltd.     

Efficient broadcast for wireless ad hoc networks with a realistic physical layer

In this paper, we investigate the low coverage problem of efficient broadcast protocols in wireless ad hoc networks with realistic physical layer models. To minimize energy consumption, efficient protocols aim to select small set of forward nodes and minimum transmission radii. In ideal physical layer model, nodes within forward nodes’ transmission ranges can definitely receive packets; therefore energy efficient protocols can guarantee full coverage for broadcasting. However, in networks with a realistic physical layer, nodes can only receive packets with probability. We present an analytical model to show that the transmission radii used for nodes can be used to establish a tradeoff between minimizing energy consumption and ensuring network coverage. We then propose a mechanism called redundant radius, which involves using two transmission radii, to form a buffer zone that guarantees the availability of logical links in the physical network, one for broadcast tree calculation and the other for actual data transmission. With this mechanism, we extend well-known centralized protocols, BIP and DBIP, and corresponding localized protocols, LBIP and LDBIP. The effectiveness of the proposed scheme in improving network coverage is validated analytically and by simulation.     

The diameter of mobile ad hoc networks

With the prevalence of mobile devices, it is of much interest to study the properties of mobile ad hoc networks. In this paper, we extend the concept of diameter from static ad hoc network to mobile ad hoc network, which is the expected number of rounds for one node to transmit a message to all other nodes in the network, reflecting the worst end‐to‐end delay between any two node. Specifically, we investigate the diameter of identically and independently mobility model in cell‐partitioned network and random walk mobility model in two‐dimensional torus network, achieving the boundary , when (k=Ω(n)), and O(k log2k), respectively, where n is the number of nodes and k is the number of cells of network and especially under random walk mobility model . A comparison is made among the diameter of mobile ad hoc networks under identically and independently mobility model, random walk mobility model and static ad hoc network, showing that mobility dramatically decreases the diameter of the network and speed is an essential and decisive factor of diameter. Copyright © 2016 John Wiley & Sons, Ltd.     

Gamma random waypoint mobility model for wireless ad hoc networks

Random waypoint (RWP) mobility model is widely used in ad hoc network simulation. The model suffers from speed decay as the simulation progresses and may not reach the steady state in terms of instantaneous average node speed. Furthermore, the convergence of the average speed to its steady state value is delayed. This usually leads to inaccurate results in protocol validation of mobile ad hoc networks modeling. Moreover, the probability distributions of speed vary over the simulation time, such that the node speed distribution at the initial state is different from the corresponding distribution at the end of the simulation. In order to overcome these problems, this paper proposes a modified RWP mobility model with a more precise distribution of the nodes' speed. In the modified model, the speeds of nodes are sampled from gamma distribution. The results obtained from both analysis and simulation experiments of the average speed and the density of nodes' speed indicate that the proposed gamma random waypoint mobility model outperforms the existing RWP mobility models. It is shown that a significant performance improvement in achieving higher steady state speed values that closely model the pre‐assumed average speeds are possible with the proposed model. Additionally, the model allows faster convergence to the steady state, and probability distribution of speed is steady over the simulation time. Copyright © 2012 John Wiley & Sons, Ltd.     

Energy efficient broadcast routing in mobile ad hoc networks

In this paper, we address the problem of broadcast routing in mobile ad hoc networks from the viewpoint of energy efficiency. In an ad hoc wireless network, each node runs on a local energy source which has a limited energy lifespan. Thus, energy conservation is a critical issue in ad hoc networks. One approach for energy conservation is to establish routes which require lowest total energy consumption. This optimization problem is referred as the minimum‐energy broadcast routing problem (MEBRP). In this paper, we propose new efficient algorithms for the construction of energy‐efficient trees for broadcast in mobile ad hoc networks. These algorithms exploit the broadcast nature of the wireless channel, and address the need for energy‐efficient operations. Empirical studies show that our algorithms are able to achieve better performance than algorithms that have been developed for MEBRP. Copyright © 2004 John Wiley & Sons, Ltd.     

Robust position-based routing for wireless ad hoc networks

We consider a wireless ad hoc network composed of a set of wireless nodes distributed in a two dimensional plane. Several routing protocols based on the positions of the mobile hosts have been proposed in the literature. A typical assumption in these protocols is that all wireless nodes have uniform transmission regions modeled by unit disk centered at each wireless node. However, all these protocols are likely to fail if the transmission ranges of the mobile hosts vary due to natural or man-made obstacles or weather conditions. These protocols may fail because either some connections that are used by routing protocols do not exist, which effectively results in disconnecting the network, or the use of some connections causes livelocks. In this paper, we describe a robust routing protocol that tolerates up to roughly 40% of variation in the transmission ranges of the mobile hosts. More precisely, our protocol guarantees message delivery in a connected ad hoc network whenever the ratio of the maximum transmission range to the minimum transmission range is at most .     

无线ad hoc网络多性能指标基本性能边界

在无线ad hoc网络中,基本性能边界对路由算法和资源分配协议的分析和评价具有重要的意义。对无线ad hoc网络多性能指标基本性能边界进行了研究,包括理论上最优的性能边界和实际可以得到的性能边界。提出了一种稳定状态(steady state)下的网络基本性能指标分析模型。该模型考虑了无线网络广播特性和无线信道干扰,可同时分析多个性能指标,包括：吞吐量、端到端延迟和能量消耗。基于该模型,针对ad hoc网络中最常见的多流—单/双中继拓扑分析基本性能指标,求解多目标优化问题得到基本性能边界。仿真结果验证了模型的准确性,均方根误差小于10-3量级。     

Analysis of broadcasting delays in vehicular ad hoc networks

High mobility of nodes in vehicular ad hoc networks (VANETs) may lead to frequent breakdowns of established routes in conventional routing algorithms commonly used in mobile ad hoc networks. To satisfy the high reliability and low delivery‐latency requirements for safety applications in VANETs, broadcasting becomes an essential operation for route establishment and repair. However, high node mobility causes constantly changing traffic and topology, which creates great challenges for broadcasting. Therefore, there is much interest in better understanding the properties of broadcasting in VANETs. In this paper we perform stochastic analysis of broadcasting delays in VANETs under three typical scenarios: freeway, sparse traffic and dense traffic, and utilize them to analyze the broadcasting delays in these scenarios. In the freeway scenario, the analytical equation of the expected delay in one connected group is given based on statistical analysis of real traffic data collected on freeways. In the sparse traffic scenario, the broadcasting delay in an n‐vehicle network is calculated by a finite Markov chain. In the dense traffic scenario, the collision problem is analyzed by different radio propagation models. The correctness of these theoretical analyses is confirmed by simulations. These results are useful to provide theoretical insights into the broadcasting delays in VANETs. Copyright © 2010 John Wiley & Sons, Ltd.     

Energy-aware on-demand routing protocols for wireless ad hoc networks

Energy use is a crucial design concern in wireless ad hoc networks since wireless terminals are typically battery-operated. The design objectives of energy-aware routing are two folds: Selecting energy-efficient paths and minimizing the protocol overhead incurred for acquiring such paths. To achieve these goals simultaneously, we present the design of several on-demand energy-aware routing protocols. The key idea behind our design is to adaptively select the subset of nodes that are required to involve in a route-searching process in order to acquire a high residual-energy path and/or the degree to which nodes are required to participate in the process of searching for a low-power path in networks wherein nodes have transmission power adjusting capability. Analytical and simulation results are given to demonstrate the high performance of the designed protocols in energy-efficient utilization as well as in reducing the protocol overhead incurred in acquiring energy-efficient routes. Baoxian Zhang received his B.S., M.S., and Ph.D. degrees in Electrical Engineering from Northern Jiaotong University, Beijing, China in 1994, 1997, and 2000, respectively. From January 2001 to August 2002, he was working with Department of Electrical and Computer Engineering at Queen’s University in Kingston as a postdoctoral fellow. He is currently a research scientist with the School of Information Technology and Engineering (SITE) of University of Ottawa in Ottawa, Ontario, Canada. He has published over 40 refereed technical papers in international journals and conference proceedings. His research interests include routing algorithm and protocol design, QoS management, wireless ad hoc and sensor networks, survivable optical networks, multicast communications, and performance evaluation. He is a member of the IEEE. Hussein Mouftah joined the School of Information Technology and Engineering (SITE) of the University of Ottawa in September 2002 as a Canada Research Chair (Tier 1) Professor in Optical Networks. He has been with the Department of Electrical and Computer Engineering at Queen’s University (1979-2002), where he was prior to his departure a Full Professor and the Department Associate Head. He has three years of industrial experience mainly at Bell Northern Research of Ottawa, now Nortel Networks (1977-79). He has spent three sabbatical years also at Nortel Networks (1986-87, 1993-94, and 2000-01), always conducting research in the area of broadband packet switching networks, mobile wireless networks and quality of service over the optical Internet. He served as Editor-in-Chief of the IEEE Communications Magazine (1995-97) and IEEE Communications Society Director of Magazines (1998-99) and Chair of the Awards Committee (2002-2003). He is a Distinguished Speaker of the IEEE Communications Society since 2000. Dr. Mouftah is the author or coauthor of five books, 22 book chapters and more than 700 technical papers and 8 patents in this area. He is the recipient of the 1989 Engineering Medal for Research and Development of the Association of Professional Engineers of Ontario (PEO), and the Ontario Distinguished Researcher Award of the Ontario Innovation Trust. He is the joint holder of the Best Paper Award for a paper presented at SPECTS’2002, and the Outstanding Paper Award for papers presented at the IEEE HPSR’2002 and the IEEE ISMVL’1985. Also he is the joint holder of a Honorable Mention for the Frederick W. Ellersick Price Paper Award for Best Paper in the IEEE Communications Magazine in 1993. He is the recipient of the IEEE Canada (Region 7) Outstanding Service Award (1995). Also he is the recipient of the 2004 IEEE Communications Society Edwin Howard Armstrong Achievement Award, and the 2004 George S. Glinski Award for Excellence in Research of the Faculty of Engineering, University of Ottawa. Dr. Mouftah is a Fellow of the IEEE (1990) and Fellow of the Canadian Academy of Engineering (2003).     

无线自组网个体移动模型分析

应用Palm积分分析随机点模型、随机方向模型和随机游走模型的平稳速度分布,证明速度衰减问题源于各个移动周期内速度和持续时间的相关性.应用Palm积分和几何概率分析随机点模型和随机方向模型的平稳节点分布,证明这2种模型具有非均匀节点分布特征.应用中心极限定理证明无边界区域随机游走模型的轨迹端点成正态分布.结果表明时间型随机游走模型是最合理的个体移动模型.     

Localized broadcast incremental power protocol for wireless ad hoc networks

We investigate broadcasting and energy preservation in ad hoc networks. One of the best known algorithm, the Broadcast Incremental Power (BIP) protocol, constructs an efficient spanning tree rooted at a given node. It offers very good results in terms of energy savings, but its computation is centralized and it is a real problem in ad hoc networks. Distributed versions have been proposed, but they require a huge transmission overhead for information exchange. Other localized protocols have been proposed, but none of them has ever reached the performances of BIP. In this paper, we propose and analyze an incremental localized version of this protocol. In our method, the packet is sent from node to node based on local BIP trees computed by each node in the broadcasting chain. Local trees are constructed within the k-hop neighborhood of nodes, based on information provided by previous nodes, so that a global broadcasting structure is incrementally built as the message is being propagated through the network. Only the source node computes an initially empty tree to initiate the process. Discussion and results are provided where we argue that k = 2 is the best compromise for efficiency. We also discuss potential conflicts that can arise from the incremental process. We finally provide experimental results showing that this new protocol obtains very good results for low densities, and is almost as efficient as BIP for higher densities.     

Predicting group partitions in mobile ad hoc networks

Group mobility is prevalent in many mobile ad hoc network applications such as disaster recovery, military actions, etc., and group partitions are unavoidable in such kinds of dynamic networks. Group partition may occur when mobile nodes move in diverse mobility patterns and causes the network to be partitioned into disconnected components. It may result in severe link disconnections, which then interrupt intergroup communications. By examining the group mobility pattern, we can predict the possibility of network partitions, and thus minimize the amount of communication disruptions. In this paper, we introduce a system for predicting potential group partitions in mobile ad hoc networks. On the basis of historical group mobility information, a quadratic regression model is formulated to predict the direction and speed of a group's movement. A group's micromovement is ignored and is replaced by significant linear displacement to measure its mobility to improve the prediction accuracy. We also discuss the notion of safe distance between adjacent groups, based on which the time duration before the occurrence of group partitioning can be measured. Experimental results show that our proposed prediction method demonstrates its effectiveness and efficiency in group partition predictions such that remedial actions can be taken in advance to avoid network disconnection. Copyright © 2011 John Wiley & Sons, Ltd.     

Statistical estimation of link availability and its impact on routing in wireless ad hoc networks

In this paper, an analytical framework is developed and validated via simulation for statistical estimation of the evolution of the separation between a pair of mobile nodes in an ad hoc network. Simulation results demonstrate that path selection based on minimization of the product of the link statistic significantly outperforms minimum‐hop and fixed threshold‐based ‘path‐stability’ schemes. A hierarchical mobility model integrating the dynamic effects of velocity, group movement and geographic scope is used to generalize the results. Another significant result is the performance enhancements hold in large networks irregardless of the assumptions used for statistical estimation. The effect of merging many independent groups appears to restore independent mobility. Finally, results show that at the highest mobility levels, 90% of the longest surviving paths fail within 60 s. None of the strategies approach this optimal value. This important result suggests that optimal predictive mechanisms alone are insufficient to ensure scalable routing in ad hoc networks. Copyright © 2004 John Wiley & Sons, Ltd.     

Adding sense of spatial locality to routing protocols for mobile ad hoc networks

Recently, there has been an increasing interest in mobile ad hoc networks. In a mobile ad hoc network, each mobile node can freely move around and the network is dynamically constructed by collections of mobile nodes without using any existing network infrastructure. Compared to static networks, it faces many problems such as the inefficiency of routing algorithms. Also, the number of control packets in any routing algorithm increases as the mobile speed or the number of mobile nodes increases. Most of the current routing protocols in ad hoc networks broadcast the control packets to the entire network. Therefore, by reducing the number of control packets, the efficiency of the network routing will be improved. If we know where the destination is, we can beam our search toward that direction. However, without using global positioning systems, how can we do this? Define the range nodes as the 1‐hop or 2‐hop neighbors of the destination node. In this paper, we propose using the range nodes to direct our searches for the destination. It can be combined with the existing routing protocols to reduce the control overhead. We show through simulations that AODV and DSR combined with the range node method outperforms the original AODV and DSR routing protocols in terms of control packets overhead. We also show that the delay introduced in find range nodes is insignificant. Copyright © 2006 John Wiley & Sons, Ltd.     

Lifetime optimization for reliable broadcast and multicast in wireless ad hoc networks

In this paper, we consider the reliable broadcast and multicast lifetime maximization problems in energy‐constrained wireless ad hoc networks, such as wireless sensor networks for environment monitoring and wireless ad hoc networks consisting of laptops or PDAs with limited battery capacities. In packet loss‐free networks, the optimal solution of lifetime maximization problem can be easily obtained by tree‐based algorithms. In unreliable networks, we formulate them as min–max tree problems and prove them NP‐complete by a reduction from a well‐known minimum degree spanning tree problem. A link quality‐aware heuristic algorithm called Maximum Lifetime Reliable Broadcast Tree (MLRBT) is proposed to build a broadcast tree that maximizes the network lifetime. The reliable multicast lifetime maximization problem can be solved as well by pruning the broadcast tree produced by the MLRBT algorithm. The time complexity analysis of both algorithms is also provided. Simulation results show that the proposed algorithms can significantly increase the network lifetime compared with the traditional algorithms under various distributions of error probability on lossy wireless links. Copyright © 2012 John Wiley & Sons, Ltd.     

一种高效的无线自组网全网可靠广播协议

现有大部分的无线自组网广播协议采用最小虚拟骨干子网进行全网广播,能最小化广播的总发送次数。但是,由于未考虑无线链路的不可靠性,这些协议在实际网络中的广播效率并不高。为此,提出了一种高效的全网可靠广播协议（ENWRB）,该协议采用网络编码技术减少单跳广播的重传次数,并通过一种基于链路感知的虚拟骨干网选择算法产生更高效的广播骨干网。仿真结果表明,在确保所有节点成功接收广播消息的相同前提下,ENWRB协议的效率显著高于HCA(Hierarchical CDS-based Algorithm)协议。     

无线自组网中基于离散粒子群优化的睡眠调度感知最小功率广播

针对当网络使用睡眠调度并且节点的传输功率连续可调节时的最小功率广播调度问题,首先给出了一种计算节点内部最优发送调度的递归方法,然后提出了一种构造最小功率广播调度的离散粒子群算法。该算法搜索最优广播树结构,并融合基于最小广播功率增量的贪心算法和基于启发式调整广播树结构的局部优化算法以提高收敛速度和求解质量。模拟实验结果表明所提算法能够有效地减少广播功率。     

Slot allocation strategies for delay sensitive traffic support in asynchronous ad hoc wireless networks

Supporting real‐time traffic in ad hoc wireless networks is considered as a challenging problem. Existing bandwidth reservation mechanisms assume a TDMA environment where achieving time synchronisation is expensive in terms of resources. Heuristics that exist for slot allocation schemes assume a CDMA over TDMA model in order to alleviate the presence of hidden terminals. Slot allocation strategies in the presence of hidden terminals assume significance in a single channel system for supporting delay sensitive traffic. In this paper, we propose three heuristics for the slot allocation process in asynchronou single channel multihop wireless networks in the presence of hidden terminals. The heuristics we propose are the early fit reservation (EFR), minimum bandwidth‐based reservation (MBR) and position‐based hybrid reservation (PHR). The EFR heuristic assigns bandwidth link‐by‐link in the forward path. The MBR heuristic allocates bandwidth to the links in the increasing order of free conn‐slots. The PHR heuristic assigns bandwidth for every link proportional to its position in the path. Simulation studies show that EFR performs better in terms of delay characteristics. MBR provides better call blocking performance at the cost of high end‐to‐end delay. PHR provides a better delay performance compared to MBR and better call blocking performance comparedto EFR. Copyright © 2004 John Wiley & Sons, Ltd.     

TCP performance over mobile ad hoc networks: a quantitative study

In this paper, we study the performance of the transmission control protocol (TCP) over mobile ad‐hoc networks. We present a comprehensive set of simulation results and identify the key factors that impact TCP's performance over ad‐hoc networks. We use a variety of parameters including link failure detection latency, route computation latency, packet level route unavailability index, and flow level route unavailability index to capture the impact of mobility. We relate the impact of mobility on the different parameters to TCP's performance by studying the throughput, loss‐rate and retransmission timeout values at the TCP layer. We conclude from our results that existing approaches to improve TCP performance over mobile ad‐hoc networks have identified and hence focused only on a subset of the affecting factors. In the process, we identify a comprehensive set of factors influencing TCP performance. Finally, using the insights gained through the performance evaluations, we propose a framework called Atra consisting of three simple and easily implementable mechanisms at the MAC and routing layers to improve TCP's performance over ad‐hoc networks. We demonstrate that Atra improves on the throughput performance of a default protocol stack by 50%–100%. Copyright © 2004 John Wiley & Sons, Ltd.