基于UWB的Ad hoc无线网络研究

文中对以超宽带UWB通信技术为基础的Ad hoc无线网络进行研究,重点分析了网络中媒体接入控制MAC协议,其中主要的研究集中在对无线资源的管理控制(RRC)上,最后给出实用功能模型和工作过程;而对网络路由协议则采用按需路由AODV协议,它具有单点通信、多点通信和广播三种通信方式,文中对单点通信进行讨论.总之,采用此MAC协议和AODV协议的Ad hoc无线网络能较好的支持UWB通信.     

基于多节点数据检测的无线接入协议设计

移动自组织网络在专用通信领域中得到广泛重视,如何提高其媒体接入效率是研究的热点。文中针对移动自组织网络中多节点共享资源时媒体接入的频谱利用率和接入效率问题,基于多用户检测理论设计和实现了多节点共享物理资源的媒体接入协议,与传统CSMA/CA协议相比,提高了节点并发传输数量,频谱效率改善可达4.28倍。     

水声网络全双工定向碰撞避免媒体接入控制协议

近年来水声网络(UAN)技术飞速发展,但仍然面临诸多严峻挑战,能量效率成为水声网络的首要考虑因素。此外,水声信道传播时延大且可用带宽受限,严重制约了水声通信技术的可靠性和有效性,进而限制了水声网络的整体性能。定向通信技术可以有效改善上述情况,通过波束聚焦能力将声波能量聚集在一定角度范围内,获得比全向通信更高的通信范围和信噪比,提升整个网络的能耗效率和空间复用率。但该技术需要对目的节点的位置具备先验知识,且会面临“聋节点”问题,因此该文提出一个水声网络全双工定向碰撞避免(FDDCA)媒体接入控制(MAC)协议,通过装备两个分别处于不同工作频带的全向换能器和定向换能器解决“聋节点”问题,并通过降低节点的冲突域解决了“暴露终端”问题。仿真结果表明,与水下Aloha(UW-Aloha)和时隙地面多址接入(S-FAMA)协议相比,FDDCA在多汇聚节点的网络拓扑下吞吐量分别提升了140%和400%,网络能效上节省了90%和94%。     

IEEE802.11与高级红外无线AIr MAC协议的性能比较

红外线作为室内通信无线传输媒质,具有低成本、低功耗等特点.本文描述 了IEEE 802.11红外局域网媒质访问控制协议（MAC）和红外数据协会（IrDA）提出的高级红外媒质访问控制层协议（AIr MAC）;研究了两种协议性能估计模型并利用OPNET仿真工具对IEEE 802.11 MAC与高级红外AIr MAC接入性能进行了仿真验证.通过对两种MAC协议接入方式、吞吐量性能估计模型以及吞吐量性能仿真结果进行比较分析,总结了IEEE 802.11红外局域网媒质接入协议和高级红外媒质接入协议之间的不同之处.     

面向大规模物联网的随机接入:现状、挑战与机遇

在传统通信系统中,随机接入是终端与网络之间建立无线链路的必经过程,只有在随机接入完成之后,终端与网络之间才能正常进行数据传输.聚焦大规模节点物联网,首先阐述了大规模物联网随机接入的基本特征,分析了传统授权随机接入(RA)方法对于大规模物联网应用的局限性;然后从系统模型、协议框架、算法流程、系统性能等多个角度,讨论免授权...     

移动无线传感器网络中MAC性能分析及改进

以往无线传感器网络中的媒体接入控制协议主要针对静止网络。当存在移动节点时。协议性能会大幅度降低。对存在移动节点的无线传感器网络中的媒体接入控制协议进行了性能分析，提出了改进算法。仿真结果验证了算法的有效性。最后给出了一种适合移动节点较多的场景的无线传感器网络媒体接入控制协议。     

定向接收低冲突率水声网络媒体接入控制协议

在全向水声通信网络场景中,较大的传播时延和较高的数据包碰撞率严重影响了网络性能。相比全向接收技术,声矢量传感器的声压和振速通过线性加权组合可以形成单边指向性,实现定向接收某个方向上的信号,进而提高网络的空间复用率。该文首先分析了声矢量传感器定向接收模式下的网络中断概率,验证定向接收技术网络应用的可行性。然后,提出了定向接收低冲突概率媒体接入控制协议(DRLCP-MAC)。该协议利用指向性接收波束握手机制建立稳定的数据传输链路,通过状态转移策略构建多对并行通信链路,缩小虚拟载波监听范围,提高网络的空间复用度。仿真结果表明,与水下冲突避免多址接入协议(MACA-U)和时隙地面多址接入协议(Slotted-FAMA)相比,DRLCP-MAC协议使信道接入成本降低了约50%和60%,网络吞吐量提升了约60%和400%,端到端时延降低了约50%和85%。     

依据用户妥善安排的多址接入协议在分布式无线网络中的性能研究

本文基于有效竞争预约接入、无冲突轮询传输的思想提出了在多跳分布式无线网络中支持节点移动性和多跳网络结构的依据用户妥善安排的多址接入(UPMA)协议.该协议能够保证发送节点快速接入信道,从而大大提高信道的使用效率.用仿真方法研究了多跳分布式无线网络中采用该协议时的网络性能.结果表明,UPMA协议可以提供较高的通过量、较低的平均分组时延和较小的平均分组丢失率.     

移动Ad Hoc网络中一种分布式QoS保证的多址接入协议

基于随机竞争和冲突解决的思想,本文为多跳移动Ad Hoc网络提出了一种分布式服务质量(QoS)保证的多址接入(QMA)协议.该协议中,节点在发送业务分组前利用预报突发进行竞争接入,节点根据业务分组时延情况和最早失效优先原则确定预报突发的长度,所发预报突发能持续到最后的节点优先获得接入.同时,具有实时业务的节点可以按照其优先级在更早的竞争微时隙中开始发送预报突发,而有非实时业务的节点只能在前面竞争微时隙空闲的情况下,才能在后面的微时隙开始发送预报突发,因此发送实时业务的节点可以比发送非实时业务的节点更优先接入信道,从而在移动Ad Hoc网络中实现了对多媒体业务的QoS保证.最后利用OPNET仿真评估了QMA协议的多址性能,并与IEEE 802.11e协议的性能做了比较,结果表明QMA协议可以提供较高的吞吐量和较低的实时业务时延.     

一种带有负载监听的多信道Ad hoc网络MAC协议

针对Ad hoc网络提出了一种新的媒体接入控制（MAC）协议——带有负载监听的多信道协议。它能够有效地解决多跳的Ad hoc网络中暴露节点的问题。在该协议中,每个节点都可以根据当前的信道负载来决定是否接入信道,并进行信道预留。在信道预留成功后,多速率的数据包就可以在指定的信道上不受干扰地进行同步传输。该机制允许一个节点同时占用多个空闲信道,不同节点间可以同时传递数据包。仿真结果显示,该机制要优于单信道的RTS／CTS模型,它提高了Ad hoc网络的吞吐量和抗干扰能力。     

Fair MAC protocol for optical ring network of wavelength-shared access nodes

In this paper, a WDM optical ring consisting of access nodes with fixed transmitter-n fixed receivers (FT—FR ⁿ ) is considered. As access nodes share a wavelength channel there is trade-off between node throughput and fairness among them. In order to abbreviate the transmission unfairness and to increase the throughput, we propose p-persistent medium access control (MAC) protocol. Each node uses the carrier sense multiple access with collision avoidance (CSMA/CA) protocol to transmit packets, and decides whether to use a local empty slot with probability p when a transferred packet based on source-stripping is dropped and emptied. Numerical prediction for the proposed MAC protocol is introduced to compute the maximum node throughput under uniform traffic condition. For more detail results, we use network simulation with self-similar traffic and introduce various results. The proposed MAC protocol gives better node throughput than non-persistent protocol and shows an improved fairness factor than 1-persistent protocol. Through simulation, we also find the reasonable probability of p-persistent protocol for a given architecture.     

无线Ad Hoc网络中基于业务感知的多信道MAC协议(英文)

Existing multi-channel Medium Access Control (MAC) protocols have been demonstrated to significantly increase wireless network performance compared to single channel MAC protocols. Traditionally, the channelization structure in IEEE 802.11 based wireless networks is pre-configured, and the entire available spectrum is divided into subchannels and equal channel widths. In contrast, this paper presents a Traffic-Aware Channelization MAC (TAC-MAC) protocol for wireless ad hoc networks, where each node is equipped with a single half duplex transceiver. TAC-MAC works in a distributed, fine-grai-ned manner, which dynamically divides variable-width subchannels and allocates subchannel width based on the Orthogonal Frequency Division Multiplexing (OFDM) technique according to the traffic demands of nodes. Simulations show that the TAC-MAC can significantly improve network throughput and reduce packet delay compared with both fixed-width multi-channel MAC and single channel 802.11 protocols, which illustrates a new paradigm for high-efficient multi-channel MAC design in wireless ad hoc networks.     

Relay-based cooperative MAC protocol with rate adaptation

The existing wireless cooperative MAC protocols rarely consider the impact of channel condition and node energy consumption.To this issue,a new wireless cooperative MAC protocol was proposed,which used the random linear network coding,and introduced a mechanism of request relay frame to solve the hidden terminal problem.Specifically,the proposed method adaptively adjusted the node rate according to RSSI,and determined the relay node based on the requirements of cooperative transmission.The simulation results show that the network performance can be improved through deploying the proposed protocol.     

基于SMAC的无线传感器网络MAC协议的分析与优化

首先对MAC协议进行了相关介绍。然后重点介绍了一种基于竞争的无线传感器网络MAC层协议S-MAC协议。其核心是提出了一种新的无线传感器网络的MAC协议设计方案。基于动态调整占空比的思想,提出了ATC-SMAC协议。该协议在S-MAC协议的基础上改进了固定占空比的劣势,根据每个节点上的数据包的平均延迟调整占空比。通过动态地调整每个节点的占空比,使不同流量的节点拥有不同的工作时间,协议根据不同节点的流量情况自适应地对其占空比进行调整。经过仿真试验,得到ATC-MAC在网络端对端延迟、能量消耗以及吞吐量方面较S-MAC协议都有比较明显的提高。     

On combining network coding with duty-cycling in flood-based wireless sensor networks

Network coding and duty-cycling are two major techniques for saving energy in wireless sensor networks. To the best of our knowledge, the idea to combine these two techniques for even more aggressive energy savings, has not been explored. This is not unusual, since these two techniques achieve energy efficiency through conflicting means, e.g., network coding saves energy by exploiting overhearing (i.e., nodes are awake), whereas duty-cycling saves energy by reducing idle listening (i.e., nodes sleep). In this article, we thoroughly investigate if network coding and duty cycling can be used together for more aggressive energy savings in flood-based wireless sensor networks.Our main idea is to exploit the redundancy sometimes present in flooding applications that use network coding, and put a node to sleep (i.e., duty cycle) when a redundant transmission takes place (i.e., the node has already received and successfully decoded a sequence of network-coded packets). We propose a scheme, called DutyCode, in which a multiple access control (MAC) protocol implements packet streaming and allows the network coding-aware application to decide when a node can sleep. We also present an algorithm for deciding the optimal coding scheme for a node to further reduce energy consumption by minimizing redundant packet transmissions. Finally, we propose an adaptive switching technique between DutyCode and an existing duty-cycling MAC protocol. We investigate our proposed solutions analytically and implement them on mote hardware. Our performance evaluation results, obtained from a 42-node indoor testbed, show that our scheme saves 30–46% more energy than network coding-based solutions.     

Efficient protocols for multimedia streams on WDMA networks

This paper introduces a new approach to integrate different types of medium access control (MAC) protocols into a single wavelength-division-multiplexing (WDM) network system. The WDM network is based on a passive star coupler, and the purpose of integrating different MAC protocols is to efficiently accommodate various types of multimedia traffic streams with different characteristics and quality of service demands. Our integrated MAC protocol is termed multimedia wavelength-division multiple-access (M-WDMA). Three types of multimedia traffic streams are considered in this paper: constant-bit-rate traffic and two classes of variable-bit-rate traffic. Accordingly, three tunable transmitters and one fixed home channel receiver are used in the design of each WDM node. The transmitters transmit the three types of multimedia traffic streams in a pipeline fashion so as to overcome the tuning time overhead and to support parallel transmissions of traffic streams that emerge simultaneously. We further incorporate a dynamic bandwidth allocation scheme that dynamically adjusts the portions of bandwidth occupied by the three types of traffic streams according to their demands. Consequently the M-WDMA protocol achieves high utilization and efficiently adapts to the demands of the multimedia streams so as to guarantee their QoS. The performance of the M-WDMA is evaluated through a simple analytical model and extensive discrete-event simulations. It is shown that the M-WDMA can satisfy the QoS requirements of various mixes of multimedia traffic streams even under very stringent requirements. Moreover, we show that the M-WDMA outperforms conventional MAC protocols for WDM networks. As a result, we expect M-WDMA to be a good multimedia MAC candidate protocol for future-generation WDM networks.     

Scheduling in Optical WDM Networks Using Hidden Markov Chain Based Traffic Prediction

This paper presents the design and performance analysis of a predictor-based scheduling algorithm for optical wavelength division multiplexed (WDM) networks. WDM technology provides multiple, simultaneous and independent gigabit-per-second channels on a single fiber. A reservation-based multiple access control (MAC) protocol is considered here for a local area WDM network based on the passive star topology. The MAC protocol schedules reservation requests from the network nodes on the multiple channels. In previous work, we have presented an on-line scheduling algorithm for such a network. We have shown earlier that schedule computation time can significantly affect performance and the scheduling algorithms should be simple for better performance. In this work, we further improve system performance by using a hidden Markov chain based prediction algorithm. The objective here is to reduce the amount of time spent in computing the schedule by predicting traffic requests. Performance analysis based on discrete-event simulation, varying parameters such as number of nodes and channels is presented. The results show that the error of prediction is reasonable for most cases: more than 70% of the time, the error between actual request and predicted request is less than 20%. Network throughput is higher with the proposed prediction algorithm due to pipelining of schedule computation.     

Experimental demonstration of an access point for HORNET-Apacket-over-WDM multiple-access MAN

Hybrid opto-electronic ring network (HORNET) is a novel packet-over-WDM multiple-access network designed by the Stanford Optical Communications Research Laboratory (OCRL) to provide efficient bandwidth sharing among a large number of access points (APs) in a metropolitan area. The HORNET network eliminates the cost and complexity of SONET equipment by transmitting IP/ATM packets directly over the wavelength division multiplexing (WDM) layer. To improve performance above that of a conventional ring network, HORNET employs a multiple-access architecture using fast tunable transmitters and a novel carrier-sense multiple-access with collision avoidance (CSMA/CA) media access control (MAC) protocol. The OCRL has constructed a testbed to demonstrate the ability of a HORNET AP to transmit packets using a fast-tunable transmitter and a novel MAC protocol and to asynchronously receive packets in the packet-over-WDM architecture. The experimental results confirm that HORNET successfully achieves the following functions: 1) fast (low overhead) wavelength tuning using a fast-tunable transmitter; 2) collision-free packet transmission over a multiple-access network via the CSMA/CA MAC protocol; and 3) fast clock and data recovery using the embedded clock tone (ECT) technique     

Multi-channel access technology based on wavelength division multiplexing in wireless UV communication mesh network

In this paper, the multi-channel access technology of wavelength division multiplexing (WDM) in the wireless ultraviolet (UV) scattering communication is studied. A multi-interface and multi-channel device is deployed in each UV transceiver node. The band-pass filter is configured in the receiving node so as to realize the multi-channel access by use of the UV WDM technology. Both the UV communication node model and the UV channel model are established. Three types of UV no-line-of-sight (NLOS) multi-channel communications are simulated in the mesh topologies with NS2. The results show that the UV multi-channel access technology can increase network throughput effectively with using WDM.     

Analysis of delay mean and variance of collision-free WDM rings with segment recirculation of blocked traffic

In Tunable-Transmitter Fixed-Receiver (TT-FR)-based Wavelength Division Multiplexed (WDM) ring topologies, each node is provided with a dedicated wavelength (home channel) for reception, which must be shared by the upstream nodes willing to communicate with it. Thus, to avoid channel collisions, it is necessary to define a Medium Access Control (MAC) mechanism that arbitrates access to a given destination wavelength. This work proposes and analyses a simple MAC mechanism that avoids channel collisions by recirculating traffic on the upstream ring segment where congestion was detected. Essentially, whenever a given node has got any traffic to transmit, it must first block access to in-transit traffic, which is reflected back to the upstream node over a second optical fibre. Such blocked traffic is given a second chance to pass through the congested node after a round segment delay, thus making use of the ring topology as buffering units. This work analyses the performance operation of such a MAC protocol under two policies applied to recirculated traffic: (1) recirculation bypass and (2) recirculation store-and-forward.