多跳蜂窝网互连性研究

将Ad Hoc网络与蜂窝网融合首要解决的问题是Ad Hoc如何接入蜂窝网,多数方案使用的是移动IP。提出了一种基于扩展Ad Hoc路由协议的多跳转发网络方案。Ad Hoc多种路由协议中可以实现Ad Hoc网络与蜂窝网互连的只有DSDV,但在移动场景中的低性能限制了它的发展。AODV是Ad Hoc路由协议中最有前途的协议,但它并不支持Ad Hoc节点接入基站的路由搜索。研究对AODV协议进行改进,以使它能支持移动节点到固定基站以及有线网络的寻路。     

Ad Hoc移动骨干网分层路由协议的研究

为了解决Ad Hoc网络的可扩充性问题,分级结构在Ad Hoc网络中的应用得到了广泛的研究.文中提出了一种适用于移动Ad Hoc网络中的多频分级结构--移动骨干网的分层路由协议Layered-AODV.该协议结合了网络多频分级的结构特点在各级采用不同的按需路由策略以降低全网冗余路由信息的传播,提高了网络的可扩展性.仿真结果表明,该协议能够有效减少移动Ad Hoc网络中的路由开销,端到端传播时延,并能有效地提高网络业务的性能,在一定程度上能够解决随着Ad Hoc网络规模扩大而网络性能下降的问题.     

基于跨层的加权自组网路由协议的设计及实现

以优化的链路状态路由（Optimized Link State Routing,OLSR）协议为原型,为无线移动自组织网络（Mobile Ad Hoc Networks,MANETs）设计了基于跨层的速率自适应的加权路由协议。该协议充分考察无线信道的时变性质,在路由计算过程中通过跨层信息共享节点的邻居关系及获取节点的当前发送速率,削减了协议的开销。将无线链路的速率与跳数相结合,设计了一种新的路由度量规则。仿真结果表明,提出的加权路由协议能够显著降低网络层的路由开销,提升网络吞吐量,降低端到端时延。     

一种适用于多跳Ad Hoc网络的增强型协作多址接入协议

 针对多跳Ad Hoc网络提出一种增强型协作多址接入协议.该协议联合考虑数据传输速率和隐藏终端对协作网络性能的影响,通过优化协议的握手规则和协同节点的选择策略,从而在不引入开销的条件下,有效提高了网络的饱和吞吐量并降低了业务的接入时延.另外,基于对节点行为及其所处状态概率的分析,本文建立了协作多址协议在多跳Ad Hoc网络中的饱和吞吐量分析模型,并给出相应的理论分析结果.最后,通过在多跳Ad Hoc网络中的大量仿真,评估了所提增强型协作多址接入协议和分析模型的性能.仿真结果表明:相对于已有的协作多址协议该协议能够有效提高网络的饱和吞吐量.此外,仿真结果和理论分析结果能够很好的匹配,从而也证明了分析模型的正确性和有效性.     

移动代理技术在Ad Hoc无线网络中的应用研究

Ad Hoc无线网络是一组具有路由和转发功能的移动节点组成的一个多跳的临时性自治系统,是一种无中心的无线网络。现有的主动路由协议或者按需路由协议都不能很好地满足Ad Hoc网络的需要。介绍了Ad Hoc无线移动网络和移动代理技术。在分析了现有的2种路由协议后,提出了在按需路由协议中加入移动代理技术来增强Ad Hoc无线网络的性能。在这些结果的基础上,提出了移动代理通信协议。     

Ad Hoc 网络按需路由协议性能分析

无线移动Ad Hoc网络作为可移动分布式多跳无线网络，没有预先确定的网络拓扑或网络基础设施以及集中控制。为了在这样的网络中促进通信，路由协议主要用于在节点之间发现路径。Ad Hoc网络路由协议的主要目的是网络拓扑的动态变化任意两个节点之间建立一个使得通信总费用和带宽消费最少的正确和有效的通信路径。使用OPNET仿真软件对AODV、DSR协议这两种典型无线移动Ad Hoc网络按需路由协议的参数和性能进行了详细比较和分析。     

基于OPNET的MAODV仿真技术分析

移动Ad Hoc网络是指由一组带有无线收发装置的移动节点组成的一个多跳的、不需要固定中心接入点或者基站支持的自治系统。对移动Ad Hoc网络多播路由中的MAODV协议进行理论分析,采用OPNET软件对该协议在AdHoc网络中的分组投递速率和延迟等关键参数进行仿真统计,并分析了节点移动速率对路由协议性能的影响。     

移动代理在MANET路由协议中的应用研究

移动Ad Hoc网络(MANET)是由移动节点组成的分布式异构网络,其路由协议的研究是该领域的焦点之一。本文分析了现有移动Ad Hoc网络两类路由协议的优缺点,接着提出将移动代理应用于AODV路山协议的方案,最后给出了初步的仿真结果。仿真结果表明,通过移动代理的漫游更新途经节点路由表,可以在网络负载增加不人的情况下,减少路由发起数,降低端到端的数据传输延迟。     

基于优先级的多路径AODV路由协议的实现

Ad Hoc网络是一个多跳临时性无中心的网络,它不需要现有的基础设施,并且节点在通信时可以随意移动。由于其网络拓扑经常发生变化,稳定的路由协议在Ad Hoc网络中就显得尤为重要。本文提出了基于AODV的改进路由协议M-AODV。M-AODV可以保存多个前往目的节点的不相交路径,并且根据路由的优先级进行路径选择。通过仿真试验可以看出,M-AODV比AODV协议在路由负载、丢包率等性能上有较好的效果。     

Ad Hoc网络中一种基于灰色关联算法的路由协议

针对移动Ad Hoc网络中节点任意移动、网络拓扑频繁变化导致以最小跳数作为路由选择机制的AODV路由协议面临频繁连接中断而造成网络QoS下降的问题,文章综合节点的剩余电量、剩余队列长度和源节点到目的节点的跳数三个跨层信息,提出一种基于灰色关联算法的改进AODV路由协议(GRA-AODV)。仿真结果显示:相比于改进前的AODV协议,改进之后的GRA-AODV(Gray Relevance AlgorithmAODV)协议在稍微增加路由开销的情况下,具有更低的平均端到端时延和更低的分组丢失率,在拓扑频繁变化的移动Ad Hoc网络中具有较好的鲁棒性。     

A Queueing Analysis of Two ARQ Protocols

In every data communication system, a procedure must be provided to allow for the retransmission of data when errors are detected. The receiving node is required to make a (positive/negative) acknowledgment (ACK/NACK) to the sending node. Until an acknowledgment is received, a "copy" of the message must be retained at the sending node. If an ACK is received, the space assigned to the "copy" is released. If either a NACK or no acknowledgment is received in a suitable interval of time, retransmission is required. Different protocols specifying how the nodes recover from a transmission error can be defined. In this paper, we present a queueing analysis of the two ARQ (automatic repeat request) protocols-block and select ARQ-for a (slotted) concentrator network node.     

A High-Throughput MAC Protocol for Wireless Ad Hoc Networks

One way to improve the throughput of a wireless ad hoc network at the media access (MAC) layer is to allow as much as possible concurrent transmissions among neighboring nodes. In this paper, we present a novel high-throughput MAC protocol, called Concurrent Transmission MAC(CTMAC), which supports concurrent transmission while allowing the network to have a simple design with a single channel, single transceiver, and single transmission power architecture. CTMAC inserts additional control gap between the transmission of control packets (RTS/CTS) and data packets (DATA/ACK), which allows a series of RTS/CTS exchanges to take place between the nodes in the vicinity of the transmitting or receiving node to schedule possible multiple, concurrent data transmissions. To safeguard the concurrent data transmission, collision avoidance information is included in the control packets and used by the neighboring nodes to determine whether they should begin their transmissions. Also, to isolate the possible interference between DATA packets and ACK packets, a new ACK sequence mechanism is proposed. Simulation results show that a significant gain in throughput can be obtained by the CTMAC protocol compared with the existing work including the IEEE 802.11 MAC protocol.     

Window flow control with error-checking scheme in quasi-cut-throughswitching network with noisy channels

Two acknowledgement (ACK) schemes for window flow control, full and partial ACK schemes, are investigated in conjunction with two error-checking schemes at every node or at the store-and-forward nodes only, in a quasi-cut-through switching network with noisy channel. It is shown that with respect to power and delay, the full ACK scheme performs better than the partial ACK scheme. On the other hand, in terms of throughput, the opposite holds. This reflects a tradeoff between throughput and delay in the contention system. Thus, the two ACK schemes can effectively be used to meet alternative user requirements for services in different application areas. The full ACK scheme yields better delay and throughput performance than that of conventional flow-controlled packet switching     

基于跳到跳信息的卫星网络传输控制协议研究

设计了一种适用于卫星网络的传输控制协议TPSN。该协议使用异步跳到跳确认,快速恢复成段丢失数据,并采用基于检测窗口的端到端选择性否定应答(SNACK)机制,减少协议控制信息,保证数据可靠传输。在跳到跳可靠性保证机制基础上传输网络负载,实现在避免网络拥塞条件下高效利用网络带宽资源,并保证具有不同端到端往返时延的异种数据流之间的公平性。仿真结果表明TPSN能够在长延迟、误码率高、链路频繁切换的卫星网络中保证高效的带宽利用、可靠的数据传输以及各数据流之间的公平。     

Using TCP rate control for queue input‐output rate matching

In explicit TCP rate control, the receiver's advertised window size in acknowledgment (ACK) packets can be modified by intermediate network elements to reflect network congestion conditions. The TCP receiver's advertised window (i.e. the receive buffer of a TCP connection) limits the maximum window and consequently the throughput that can be achieved by the sender. Appropriate reduction of the advertised window can control the number of packets allowed to be sent from a TCP source. This paper evaluates the performance of a TCP rate control scheme in which the receiver's advertised window size in ACK packets are modified in a network node in order to match the generated load to the assigned bandwidth in the node. Using simulation and performance metrics such as the packet loss rates and the cumulative number of TCP timeouts, we examine the service improvement provided by the TCP rate control scheme to the users. The modified advertised windows computed in the network elements and the link utilization are also examined. Copyright © 2002 John Wiley & Sons, Ltd.     

面向GEO卫星网络的多速率多播拥塞控制机制

针对GEO卫星网络带宽时延积较大、拥塞控制机制不完善的问题,提出了一种面向GEO卫星网络的多速率多播拥塞控制机制MMCCM_GEO.首先,在保证接收端请求速率最大化的前提下,将GEO卫星网络中的多速率多播问题转化为非线性优化问题,并采用改进的模拟退火算法对其求解,得到了最优的接收端请求速率.其次,通过采用代理节点实现反馈信息的汇集与丢失数据的恢复,有效地解决了反馈内暴及数据恢复问题.仿真结果表明,与目前GEO卫星网络中典型的多速率多播拥塞控制机制相比,本文的拥塞控制机制有效地提高了数据吞吐量和带宽利用率,降低了GEO卫星网络中的数据传输时延,同时也具备了更好的可扩展性.     

TCP transmission rate control mechanism based on channel utilization and contention ratio in AD hoc networks

In ad hoc networks, both contention and congestion can severely affect the performance of TCP. In our work, we first show that the over-injection of conventional TCP window mechanism results in severe contentions, and medium contentions cause network congestion. Furthermore, introducing two metrics, channel utilization (CU) and contention ratio (CR), we characterize the network status. Then, based on these two metrics, we propose a new TCP transmission rate control mechanism based on Channel utilization and Contention ratio (TCPCC). In this mechanism, each node collects the information about the network busy status and determines the CU and CR accordingly. The CU and CR values fed back through ACK are ultimately determined by the bottleneck node along the flow. The TCP sender controls its transmission rate based on the feedback information. Simulation results show that the proposed TCPCC mechanism significantly outperforms the conventional TCP mechanism and the TCP contention control mechanism in terms of throughput and end-to-end delay.     

Sleep scheduling with expected common coverage in wireless sensor networks

Sleep scheduling, which is putting some sensor nodes into sleep mode without harming network functionality, is a common method to reduce energy consumption in dense wireless sensor networks. This paper proposes a distributed and energy efficient sleep scheduling and routing scheme that can be used to extend the lifetime of a sensor network while maintaining a user defined coverage and connectivity. The scheme can activate and deactivate the three basic units of a sensor node (sensing, processing, and communication units) independently. The paper also provides a probabilistic method to estimate how much the sensing area of a node is covered by other active nodes in its neighborhood. The method is utilized by the proposed scheduling and routing scheme to reduce the control message overhead while deciding the next modes (full-active, semi-active, inactive/sleeping) of sensor nodes. We evaluated our estimation method and scheduling scheme via simulation experiments and compared our scheme also with another scheme. The results validate our probabilistic method for coverage estimation and show that our sleep scheduling and routing scheme can significantly increase the network lifetime while keeping the message complexity low and preserving both connectivity and coverage.     

Delivery time analysis of a low Earth orbit satellite network forseamless PCS

The message delivery time on a low Earth orbit (LEG) satellite network is analyzed. The LEO network is assumed to be seamless and virtual cut-through switching is proposed for use. Equations to calculate the message delivery time and the probability of a message being delivered successfully using no more than a time delay bound for LEO networks, varying in size and connectivity, are derived. The message delivery times of different LEO networks, varying in network connectivity, are compared. Numerical examples show that with the probability of successful delivery =0.99 and the probability of cut-through =0.5, an 8×8 LEO network with six crosslinks per node can deliver messages 40% faster than with four crosslinks per node for communicating satellites, separated by D hops, where D is the network diameter     

DCMA: A Label Switching MAC for Efficient Packet Forwarding in Multihop Wireless Networks

This paper addresses the problem of efficient packet forwarding in a multihop, wireless "mesh" network. We present an efficient interface contained forwarding (ICF) architecture for a "wireless router," i.e., a forwarding node with a single wireless network interface card (NIC) in a multihop wireless network that allows a packet to be forwarded entirely within the NIC of the forwarding node without requiring per-packet intervention by the node's CPU. To effectively forward packets in a pipelined fashion without incurring the 802.11-related overheads of multiple independent channel accesses, we specify a slightly modified version of the 802.11 MAC, called data driven cut-through multiple access (DCMA) that uses multiprotocol label switching (MPLS)-like labels in the control packets, in conjunction with a combined ACK/RTS packet, to reduce 802.11 channel access latencies. Our proposed technique can be used in combination with "frame bursting" as specified by the IEEE 802.11e standard to provide an end-to-end cut-through channel access. Using extensive simulations, we compare the performance of DCMA with 802.11 DCF MAC with respect to throughput and latency and suggest a suitable operating region to get maximum benefits using our mechanism as compared to 802.11