车用自组网自适应单跳广播协议

在车用自组织网的单跳广播协议中,隐藏/暴露节点是影响广播信息成功分发的关键因素,媒体接入控制层的竞争窗口是影响吞吐量性能的关键因素.首先建模分析广播信息成功接收率、吞吐量与节点密度、竞争窗口之间的关系,然后针对车用自组织网的节点密度动态变化特征提出基于多目标优化的自适应可靠单跳广播协议.仿真研究结果表明,该协议通过自动调整节点竞争窗口可以在保证广播信息可靠分发的同时优化网络吞吐量.     

HM-MAC:一种支持广播的多信道传感器网络MAC协议

针对单Radio多信道MAC协议需要全网时间同步、占用大量正交信道、多信道隐终端较多以及单跳多信道广播数据大量丢失等问题,提出了一种基于竞争的多信道MAC协议--HM-MAC.该协议无需全网时间同步,通过动态预约技术降低了正交信道占用量,利用握手机制减少了多信道隐终端数目,同时,HM-MAC采用基于概率的广播发送者协调机制,减少了广播数据丢失,提高了广播效率.在理论上分析了所用信道数目、多信道隐终端数目以及广播效率等性能参数.实验结果表明:HM-MAC可以有效地解决多信道隐终端数目较多的问题,显著地提高了广播效率和网络吞吐量.     

一种基于跳变预约的多信道自组网MAC协议

文章提出了一种新的基于跳变预约的AdHoc网络多信道媒体接入协议(NHRMC),它综合了基于ATIM窗口的同步机制和基于等级的信道预约算法,有效地解决了多跳网络环境下隐终端问题。吞吐量性能分析和仿真实验结果表明,与IEEE802.11DCF的RTS/CTS机制相比,在一定假设条件下,网络的性能得到了明显的改善。     

基于状态响应的分组预约多址接入协议研究

为了克服经典PRMA-HS协议中的双稳态问题和分组发送允许概率的静态性缺点,提出了一种基于状态响应的改进型分组预约多址接入协议.该协议能够利用卫星基站反馈信息,根据系统状态实时调整分组发送允许概率,使系统始终处在最佳状态.利用计算机对理想信道和随机误差信道条件下的协议性能进行了仿真,实验结果表明,采用状态响应机制能够克服经典PRMA-HS协议的双稳态问题,提高了协议的稳定性,增加了系统容量,降低了分组丢弃率.     

无线网络中的多跳协作机制*

现有的协作机制过度地依赖于信道状态信息,而无线信道状态瞬时变化,使得信道状态信息在实践中很难获取。提出一种新的多跳协作机制,该机制不依赖信道状态信息,而是充分利用无线网络的广播特性,使得系统中的节点缓存其前面节点发送的信号,并对接收到的信号进行最大比合并,恢复原信号再转发。通过理论分析以及仿真分析验证所提方案的可行性和有效性,并与多跳非协作机制进行比较,仿真结果表明,多跳协作机制可以获得额外的分集增益,有效地提高了交付率以及增大系统中的端到端的平均吞吐量。     

基于预约和反馈的无线传感器网络MAC协议研究

针对无线传感器网络中对通信实时性要求较高的应用环境,引入信道预约机制和反馈机制到S-MAC协议,提出了一种低时延的RF-MAC协议。该协议在有数据需要发送时先预约信道,各节点根据预约时间表进行数据传输。采用在数据传输过程中向源节点发送反馈信息的方法,实现后续数据的提前发送。通过仿真实验表明:RF-MAC协议有效地降低了数据传输的时延,同时改善了丢包率和网络吞吐量。     

基于RS纠删码的无线传感器网络信息分发协议性能评价

无线传感器网络中,传感器节点的能量、存储和计算能力有限,且无线传感器网络具有数据链路不对称、拓扑易变化等特点,设计节能可靠的网络协议是困难的。设计良好的网络协议不仅能降低网络的负载,还有助于节省传感器节点的能量,从而延长网络的生存周期。在无线传感器网络操作系统TinyOS平台上实现了基于RS纠删码的信息分发协议,并理论分析了在单跳情况下的协议性能,最后在仿真环境TOSSIM上模拟比较了在多跳、多路径情况下该信息分发协议和洪泛分发协议的性能。模拟仿真表明,提出的基于RS纠删码的信息分发协议明显减少了发送方发送数据包的数量,同时提高了节点的报文接收率,从而达到了降低网络能耗的目的。     

基于多步信道预约机制的多址接入协议研究

无线自组织网络(Ad Hoc网络)中实时业务的传输需要网络协议提供较为可靠的服务质量保证(Qos保证),而现有多址接入协议一般未能提供较好的Qos支持。在单步信道预约思想的基础上,提出了一种基于更为可靠的多步信道预约机制的多址接入协议,其利用实时业务分组的周期性特点,对无线信道资源进行多步预约,从而保证了实时业务的可靠传输。仿真实验表明,相较于单步信道预约机制,多步信道预约机制对网络的多址接入性能有较好的改进。     

一种事件驱动型WSN状态监测信息路由协议

为了均衡无线传感器网络(WSN)中各节点的能量消耗,提出了一种基于分簇路由算法思想的网络自身健康状态信息传输路由协议——事件驱动型状态监测信息路由协议（ED-SMIR）。在ED-SMIR协议中,簇内节点根据能量消耗速度的大小,采用单跳和多跳轮换的方式,簇头到sink节点的路由,采用多跳的方式。仿真实验表明,与LEACH和EDBCM协议相比,ED-SMIR消耗的能量更少,可以均衡整个网络的能量并有效延长网络的生存时间。     

一种新的拓扑无关的按需分配多信道自组网MAC协议

本文针对节点具有多个可用信通的自组网,提出了一种与拓扑无关的多信道MAC接入协议,协议采用按需预约的方式进行动态的信道分配,通过携带在信道预约消息中的节点邻居状态信息实现节点信道状态的更新。该协议所需信道数与网络的拓扑和度无关,克服了拓朴相关的多信道MAC协议不适用于节点密集的应用场合的问题。在协议开销增加很小的情况下,每个节点只需要一部半双工收发信机就能够实现在多个信道上高效的数据收发,不需要节点间的时钟同步,极大地降低了对网络节点设备的硬件要求,具有良好的应用前景。仿真结果表明,协议在网络总吞吐量、端到端时延等方面具有优良的性能。     

Repetition-based cooperative broadcasting for vehicular ad-hoc networks

In vehicular ad hoc networks, most of critical applications involved with safety rely on reliable broadcast communications with low latency. Recently, repetition-based protocols have been proposed to meet the requirements of timeliness and reliability for broadcasting. In these protocols, a sender repeatedly retransmits the broadcast message during the lifetime of the message. However, existing protocols face serious problems such as deterioration of the signal quality caused by wireless fading. In particular, since excessive repetitions might cause network congestion and waste channel resources, reliability of broadcasting should be achieved with as small a number of repetitions as possible. In this paper, we therefore propose a novel repetition-based broadcast protocol which exploits a cooperative diversity technique (called RB-CD) making a small number of repetitions robust for wireless fading. To support this cooperative diversity, neighboring nodes transmit the same message almost simultaneously (that is, using the same repetition pattern for each other) in order to form a virtual antenna array. The virtual antenna array achieves a diversity gain at the receivers. In the RB-CD protocol, the virtual antenna array consists of the source and some of its neighbors (called relays) which participate in repeating the transmission of a broadcast message. In addition, a new distributed relay selection algorithm is introduced in the RB-CD protocol. From the ns-2 simulation results, we verified that RB-CD provides a more reliable broadcasting service due to its capability of exploiting cooperative diversity.     

多跳远程量子态制备

多跳远程量子态制备在量子无线网络、长距离量子信息传输中有重要价值。融合多跳隐形传态和远程态制备的思想，提出一个多跳远程任意单量子态制备协议。在每一跳中都以三粒子非最大纠缠GHz态为量子信道，利用远程态制备方法，原始单量子态通过中间节点逐跳被制备，每跳恢复的态被用着下一跳被制备的态。通过对单跳和两跳制备的分析，获得了[n]跳制备后方案成功的概率。在协议中，仅涉及到Pauli算子、单粒子测量和前馈策略，因此该方案易于物理实现。     

基于平均跳距的水下传感器网络节点定位算法

在分析DV-Hop定位算法优缺点的基础上,针对其平均跳距误差大的不足,提出一种基于平均跳距的水下传感器网络节点定位算法. 该算法对平均跳距进行两次改进. 首先,锚节点利用边界锚节点和其一跳邻居的锚节点计算平均每跳距离. 其次,未知节点收到各锚节点的平均距离广播分组包,根据其到各锚节点的跳数按权重比例公式计算出最终的平均每跳距离. 仿真实验表明,经过两次改进,该算法优于传统DV-Hop定位算法,提高了定位精确度.     

Using an evolutionary algorithm to optimize the broadcasting methods in mobile ad hoc networks

A mobile ad hoc network (MANET) is a collection of mobile nodes communicating through wireless connections without any prior network infrastructure. In such a network the broadcasting methods are widely used for sending safety messages and routing information. To transmit a broadcast message effectively in a wide and high mobility MANET (for instance in vehicular ad hoc network) is a hard task to achieve. An efficient communication algorithm must take into account several aspects like the neighborhood density, the size and shape of the network, the use of the channel. Probabilistic strategies are often used because they do not involve additional latency. Some solutions have been proposed to make their parameters vary dynamically. For instance, the retransmission probability increases when the number of neighbors decreases. But, the authors do not optimize parameters for various environments. This article aims at determining the best communication strategies for each node according to its neighborhood density. It describes a tool combining a network simulator (ns-2) and an evolutionary algorithm (EA). Five types of context are considered. For each of them, we tackle the best behavior for each node to determine the right input parameters. The proposed EA is first compared to three EAs found in the literature: two well-known EAs (NSGA-II and SPEA2) and a more recent one (DECMOSA-SQP). Then, it is applied to the MANET broadcasting problem.     

Delay-sensitive routing in multi-rate MANETs

A mobile ad hoc network (MANET) is a collection of mobile hosts, which can communicate by the aid of intermediate mobile hosts without utilizing a fixed infrastructure and centralized administration. Many MANET standards, such as 802.11a, 802.11b, and 802.11g, can be operated at various rates for Quality-of-Service (QoS) constrained multimedia communication to more efficiently use the limited resources of MANETs. Since the radio channel is shared among neighbors in MANETs, calculating one-hop delays and determining delay-sensitive routes using the IEEE 802.11 MAC are still two challenging problems. In this paper, we first exploit the busy/idle ratio of the shared channel to estimate one-hop delay based on varied data rates. Then by the aid of the estimated delay, a multi-rate routing protocol is proposed for selecting data rates and determining a route for admitting a flow with a requested delay. In MANETs, when a host is transmitting data packets, its neighbors are blocked (i.e., forbidden to send packets) since it shares the radio channel with its neighbors. We adopt the strategy by selecting the combination of data rates and a route in order to minimize the total blocking time to all hosts of the network for maximizing the network’s capacity, which is the number of flows admitted by the network. Simulation results show that the proposed method obtains a more precise one-hop delay than a very recent work, and the proposed protocol admits more flows than an existing protocol.     

PaderMAC: Energy-efficient machine to machine communication for cyber-physical systems

Wireless sensor nodes typically switch between sleep and wake periods. This poses a rendezvous problem on message senders and recipients. X-MAC, a state of the art sensor network medium access control (MAC) protocol, solves this problem by sending a strobe of short preambles from the message sender until the message recipient wakes up. Upon wake-up, the recipient receives the next strobe, signals the message sender that it is ready to receive, and the message transmission can take place. In sink oriented communication, geographic greedy routing, and link reversal routing, a forwarding node may have more than one potential next hop forwarding node. X-MAC does not support such opportunistic communication patterns. Instead it requires the sender to name the recipient explicitly. However, preamble length can be saved when message transmission starts as soon as the first one of the set of potential next hop nodes is waken up by a preamble. This requires PaderMAC, a new MAC protocol, where the decision on the next hop node is shifted from the sender to the receiver. This work specifies the PaderMAC protocol, explains the implementation of that protocol using TinyOS and the MAC layer architecture (MLA), describes a contribution to the MLA which is useful also for other MAC layer implementations, and presents the results of a testbed and theoretical performance study. The testbed study compares PaderMAC in conjunction with opportunistic routing to X-MAC in conjunction with path-based routing and shows how PaderMAC reduces the preamble length, better balances the load and further improves the end-to-end latency within the network.     

改进的DV-Hop定位算法研究

传统DV-Hop定位算法只考虑最近一个锚节点估计的平均跳距值,而单个锚节点估计的平均跳离值无法准确地反映网络的实际平均跳距.为此,提出一种基于加权处理的平均跳距估计算法,考虑多个锚节点估计的平均跳距值,根据距离未知节点的跳数和环境影响因素进行加权,使网络平均跳距的估计更加准确,从而提高定位精度.仿真结果表明,与DV-Hop算法的平均跳距估计算法相比,该算法能更准确地估计平均跳距,提高了定位精度.     

Asynchronous reservation protocol for variable-sized messages in a WDM-based local network

In this paper, we propose and analyse an asynchronous reservation protocol for a very high-speed optical LAN using a passive star topology. Each node is equipped with a single tunable transmitter and a single tunable receiver, both of which are tunable over a range of wavelengths. A separate channel, called the control channel, is used to coordinate message transmissions on the other channels, called data channels. We consider random and idle selection schemes for the data channel selection strategy. The proposed protocol can efficiently support variable-sized messages. It is operated asynchronously, i.e. data channels are not slotted and the control channel is slotted with the size of a control packet. Also, the protocol is scalable, hence the network can accommodate a variable number of nodes. Any new node can join the network without network reinitialization. Moreover, with the protocol one can avoid destination conflicts. We analyse its performance by using the equilibrium point analysis (EPA) method, and validate the results by simulation. According to the numerical results, the asynchronous protocol achieves higher throughput than the synchronous one.