基于网络编码的无线多跳网络生存时间优化研究

在能量有限的无线网络中,网络生存时间往往需要尽量延长.针对网络生存时间优化问题,综合考虑了随机拓扑环境中的无网络编码场景、双向网络编码场景和侦听网络编码场景,结合功率控制模型、数据流个数、业务需求分布和每个节点的初始能量,使用内点方法对这些场景下的网络生存时间进行评估和优化.仿真结果说明了在弱功控情况下,网络编码可提高生存时间增益,该增益和计算开销都随数据流个数的增加而增加,而业务需求分布和节点初始能量对生存时间性能影响可忽略,另外也说明了双向网络编码对生存时间的改进性能与侦听网络编码相似,而计算开销更低.     

无线多跳网络基于位势博弈的传输调度方法*

为了进一步提高无线多跳网络的吞吐量,采用物理干扰模型,考虑链路速率可以随信干噪比(signal tointerference plus noise ratio,SINR)动态可调,提出了基于位势博弈的传输调度算法。通过设计合适的位势函数,使得纳什均衡点的存在性和收敛性都得到保证。同时,每个参与者在最小化自己支付的同时,使全局函数达到最优。仿真结果表明,该算法具有较好的吞吐量性能,而且有较快的收敛速度。     

Fine grained load balancing in multi-hop wireless networks

In this paper we address the problem of local balancing in multi-hop wireless networks. We introduce the notion of proactive routing: after a short pre-processing phase in which nodes build their routing tables by exchanging messages with neighbors, we require that nodes decide the relay of each message without any further interaction with other nodes. Besides delivering very low communication overhead, proactive routing protocols are robust against some well known active attacks to network routing. In this framework, we develop a proactive routing protocol that is able to balance the local load. Experiments show that our protocol improves network lifetime up to 98% and that it delivers a network that is more robust against attacks that have the goal of getting control over a large part of the network traffic.     

无线多跳网络视频流的联合源编码优化算法

由于网络媒体的共享性和不可靠性,对无线多跳网络中视频流的支持面临更大的技术挑战.研究了视频流优化问题并提出了一种联合源网络编码机制.该机制将视频流的源分段,并分为不同的世代,以达到视频流质量的最大化.算法首先分析世代规模对网络性能如源速率、编码效率和解码延时的影响,然后为了使源速率较大,在源端产生较多数据分组,并设计一种联合网络编码机制确定各个中间节点发送到网络中分组的最佳数量,使视频流的质量达到最高.仿真实验结果表明,在世代规模合适的情况下,使用所提联合源编码机制可以增强无线多跳网络视频流的性能.     

支持多媒体业务的新型无线多跳网络MAC协议*

提出了一种单信道无线多跳网络同步媒体接入控制协议—M-TDMA。基于信道预约,协议采用分类调度机制以满足多媒体业务中各类业务的服务质量需求。协议采用信道使用列表（CUL）、预约控制时隙、划分竞争期和非竞争期等措施维护预约信道,降低分组冲突率,提高信道使用率。分析结果表明,协议在保证分组传输可靠性的同时,传输时延较低,能够较好地支持多媒体业务的服务质量需求。     

Model-based approach for available bandwidth prediction in multi-hop wireless networks

We present a complete and practical analytical model for the IEEE 802.11-based multi-hop wireless networks.The features of our model are that it first takes into account the realistic problems both from the physical and MAC (Media Access Control) layers in multi-hop wireless networks,including packet collisions,neighboring interference,hidden node problems,capture effects,non-ideal channels,non-saturated situations and multi-rate sending scenarios,which makes the analytical results more accurate.Second,it r...     

多跳无线网络中基于模型的可用带宽预测

文中首先针对基于IEEE802.11协议的多跳无线网络,建立了一个更完整、实用的分析模型.相对于以往的工作,该模型具有3个突出特点:(i)它从物理层和MAC层上考虑了多跳无线网络中更真实的情况,包括节点周围的干扰、隐藏节点问题、捕获效应、真实的信道环境、非饱和节点以及多速率发送等,从而使得基于该模型的分析结果更准确;(ii)它将网络中业务的带宽需求映射到了模型的参数中,从而可以方便地对带宽敏感业务进行建模分析;(iii)它可以预测性地分析当某一特定带宽的业务进入网络后网络性能的表现.然后,基于该模型提出和验证了端到端可用带宽预测的迭代算法.该算法可以预测新业务进入网络后,一些对可用带宽估计起关键作用的网络参数的变化,因而可以获得更准确的可用带宽信息.该迭代算法收敛速度快且易于实现,具有很好的应用前景.     

一种基于IEEE 802.11e的多跳无线网络拥塞控制协议

多跳无线网络中网络拥塞的出现将严重降低网络的性能。基于802.11e提供的区分业务类型的信道接入优先级机制,提出了一种对尽力而为(best-effort)类型业务动态调整其优先级进行网络拥塞控制的协议。该算法的主要思想是对发生网络拥塞的节点提升其业务流传输的优先级使其获得更多的传输机会以缓解拥塞状况,并对严重的网络拥塞状况采取反向施压的策略降低上游节点业务流的转发速率。仿真结果表明,该算法有效地提高了网络重负载情况下的吞吐量。     

Modeling and performance analysis of ad hoc broadcasting schemes

Broadcasting is a technique widely used for distributing control packets in ad hoc networks. The traditional flooding scheme has been proven to unnecessarily consume network capacity and may lead to severe packet collisions in high-density networks. New schemes have been proposed for alleviating this so-called broadcast storm problem and their efficiencies are usually analyzed and compared by ns-2 simulations. However, little work has been done on mathematical modeling and rigorous analysis. In this paper, we focus on two popular ad hoc broadcasting schemes and provide their detailed analysis in one-dimensional and two-dimensional ideal networks. The statistical results obtained have revealed new relationships between network parameters and the performance metrics. These results are useful for optimally setting network parameters in designing protocols. It is also expected that the analytical methods developed will lay a solid foundation for the development of mathematical models for other ad hoc broadcast and multicast schemes.     

无线传感器网络中多跳时间同步算法的研究

提出了一种基于簇型的多跳时间同步算法——CBTS。利用Leach算法将网络划分成不同的簇,在此基础上把节点间的时间同步分为水平同步和垂直同步两个阶段来完成。在水平同步阶段,通过构建基站与簇头节点的层次拓扑结构,采用双向消息交换同步机制来完成簇头节点与基站的时间同步。在垂直同步阶段,采用双向消息交换和参考广播相结合的同步机制,来完成簇头节点和簇成员之间的时间同步,并利用最小方差线性拟合的方法估计了节点的时钟偏差,提高了时钟同步的精度,最终实现了整个网络节点的时间同步。经过仿真测试,证明该算法具有较低的消息交换开销和不错的同步精度。     

Modeling multiple hop wireless networks with varying transmission power and data rate

Wireless multi-hop networks can vary both the transmission power and modulation of links. Those two parameters provide several design choices, which influence the performance of wireless multi-hop networks, e.g. minimize energy consumption, increase throughput, reduce contention, and maximize link quality. However, only network-wide metrics are considered in previous works. Further, per-flow performance metrics, such as the end-to-end energy consumption and latency, have not been studied. Those parameters directly impact the experience of users, which should be considered in capacity and performance studies. Our model incorporates per-flow metrics while also considering fading, contention, hidden terminals and packet error probabilities. We instantiate the model into an IEEE 802.11 multi-hop scenario, and evaluate common routing decisions such as maximizing link quality, maximizing data rate or minimizing the transmission power.     

On supporting high-throughput routing metrics in on-demand routing protocols for multi-hop wireless networks

Researchers have proposed routing metrics other than hop count, such as ETX (expected transmission count) and ETT (expected transmission time), to find routes with high throughput. These metrics are inherently suitable to be used in source routing protocols such as DSR, because link state information needs to be collected for the calculation of the shortest path. In this paper, we propose an efficient and generalized approach called accumulated path metric (APM) for supporting high-throughput metrics (HTMs) in on-demand routing protocols. One advantage of APM is that it is able to find the shortest path, in terms of a particular metric, without collecting topology information and without running a shortest-path algorithm. This will significantly simplify the existing design of supporting HTMs in DSR. We present a proof of the correctness of APM. Moreover, we address the problem of duplicate RREQ (route request) transmissions with existing HTM schemes and present a broadcast ordering (BO) technique to suppress unnecessary RREQ transmissions. We study the performance of APM and BO in both AODV and DSR, and the results verify the effectiveness of the proposed approaches.     

Comparison of efficient random walk strategies for wireless multi-hop networks

Wireless multi-hop networks have drawn great attention from research and business communities, since they suit well diverse application scenarios, such as environmental monitoring, military support in hostile environments and emergency applications. However, this challenging communication paradigm requires solutions able to fit specific requirements in terms of resource constrains, node mobility and quality of service. Random Walks (RWs) are probabilistic approaches to perform distributed operations, such as data search and retrieval. They are effective and have relatively small overhead compared to classic schemes, such as flooding. To further improve performance of RWs, hybrid solutions may be employed. Such strategies increase system performance at the cost of additional energy consumption. In this work, we propose two novel schemes that exploit local topological information in order to increase the hybrid RW protocols performance. Through simulations, we compare hybrid protocols with a traditional RW solution, studying their performance in static and mobile scenarios. An analysis of the trade-off between the number of node revisits and energy consumption allows to identify the more fitting protocols for different application scenarios in wireless multi-hop networks. Advantages and drawbacks of different RW strategies are highlighted, along with research challenges that need to be investigated in the future.     

Performance analysis of ad-hoc routing in heterogeneous clustered multi-hop wireless networks

This paper analyzes the performance of clustered decode-and-forward multi-hop relaying (CDFMR) wireless Rayleigh fading networks, and sheds light on their design principles for energy and spectral efficiency. The focus is on a general performance analysis (over all SNR range) of heterogeneous wireless networks with possibly different numbers of relays in clusters of various separations. For clustered multi-hop relaying systems, hop-by-hop routing is known as an efficient decentralized routing algorithm which selects the best relay node in each hop using local channel state information. In this article, we combine hop-by-hop routing and cooperative diversity in CDFMR systems, and we derive (i) a closed-form expression for the probability distribution of the end-to-end SNR at the destination node; (ii) the system symbol error rate (SER) performance for a wide class of modulation schemes; and (iii) exact analytical expressions for the system ergodic capacity, the outage probability and the achievable probability of the SNR (power) gain. We also provide simple analytical asymptotic expressions for SER and the outage probability in high SNR regime. Numerical results are provided to validate the correctness of the presented analyses.     

The balance of routing energy consumption in wireless sensor networks

In order to tackle the energy hole problem of sensor networks, the non-uniform node deployment strategy was presented recently. For achieving the expected performance of this deployment method, nodes need to transmit data to the sink node by selecting a node in the adjacent inner region decided by the deployment strategy. Since nodes near the outer boundary of a region will be covered by more nodes, the random selection method will cause the unbalanced energy consumption problem. In this paper, this issue is rigorously studied and a region constraint selection scheme is proposed based on the analytical result. By combining the region constraint strategy and the maximum energy node selection mechanism, a hybrid scheme is presented. Numerical and simulation results show that the region constraint scheme can achieve acceptable performance improvements over the random scheme and the hybrid mechanism also gains better performance in comparison to the maximum energy node selection scheme.     

An effective scheduling scheme for multi-hop multicast in wireless mesh networks

With the utilization of concurrent transmission strategy, a throughput-enhanced scheduling scheme is devised for multicast service in wireless multi-hop mesh networks. Since the performance of a multicast mechanism is constrained in a wireless setting due to the interference among local wireless transmissions, the interference relationships are first characterized by introducing a graph transformation method. Based on the graph transformation, the multicast scheduling problem is converted to the graph coloring problem, and then a capacity greedy algorithm is designed to provide concurrent transmission scheduling so that the demanded multicast transmission rate can be achieved. Moreover, the necessary and sufficient conditions of multicast schedulable feasibility are derived. Through corresponding simulations, it is shown that the proposed strategy can enhance the throughput of wireless multi-hop multicast systems significantly.     

Symbol-level reliable broadcasting of sensitive data in error-prone wireless networks

Reliable packet transmission over error-prone wireless networks has received a lot of attention from the research community. In this paper, instead of using simple packet retransmissions to provide reliability, we consider a novel retransmission approach, which is based on the importance of bits (symbols). We study the problem of maximizing the total gain in the case of partial data delivery in error-prone wireless networks, in which each set of bits (called symbols) has a different weight. We first address the case of one-hop single packet transmission, and prove that the optimal solution that maximizes the total gain has a round-robin symbol transmission pattern. Then, we extend our solution to the case of multiple packets. We also enhance the expected gain using random linear network coding. Our simulation results show that our proposed multiple packets transmission mechanism can increase the gain up to 60%, compared to that of a simple retransmission. Moreover, our network coding scheme enhances the expected total gain up to 15%, compared to our non-coding mechanism.     

无线传感器网络中数据分发方案的研究

无线传感器网络是由大量具有感知、计算和通信能力的能量有限的微型传感器节点组成。为了建立有效的数据传输路径,节约能耗和带宽,延长网络生存期,设计能量有效的数据分发方案是至关重要的。针对无线传感器网络中节点是否可移动的三种情况,分析了目前提出的主要数据分发方案。     

SURF: A distributed channel selection strategy for data dissemination in multi-hop cognitive radio networks

In this paper, we propose an intelligent and distributed channel selection strategy for efficient data dissemination in multi-hop cognitive radio network. Our strategy, SURF, classifies the available channels and uses them efficiently to increase data dissemination reliability in multi-hop cognitive radio networks. The classification is done on the basis of primary radio unoccupancy and of the number of cognitive radio neighbors using the channels. Through extensive NS-2 simulations, we study the performance of SURF compared to four related approaches. Simulation results confirm that our approach is effective in selecting the best channels for efficient communication (in terms of less primary radio interference) and for highest dissemination reachability in multi-hop cognitive radio networks.