电视传送技术的无线传感器网络

为了适应未来市场的需求，新一代有线数字电视传送网络必须具有多传感器信息访问及设备互联能力。因此，无线传感器网络技术的引进势在必行。为了实现新一代有线数字电视网络延伸，进一步涵盖更多的区域，增加额外价值效益，通过集成新一代有线数字电视传输网络为骨干传输，搭建用户端无线传感器网络，其中网络架构设计包括物理网络构建和协议体系、无线及有线数字电视网络互联方案以及业务类别设计等内容。     

无线局域网帧数据流量研究

无线局域网中的信道要比有线局域网信道复杂的多,运载其上的流量研究成为评估和了解无线局域网行为模式的关键。比较了有线和无线局域网在体系结构和协议机制上的差异,进而分析了由于这种差异所导致的IP层数据包流量和MAC层帧数据流量不同之处,提出了无线局域网流量研究中存在的问题,探讨了无线局域网帧数据流量的研究内容和方向。     

无线局域网技术

无线局域网是计算机网络与无线通信技术相结合的产物。它是在不采用传统缆线的同时,以无线多址信道作为传输媒介,利用电磁波完成数据交互,从而为移动化、个性化和多媒体应用提供了可能,并实现了传统有线局域网的功能,解决了一些有线网络无法解决的难题。     

通信信道的建模与仿真

借助MATLAB软件详细阐述了有线信道、无线信道的类型及信道中的传输损耗;以曼彻斯特码作为数字基带传输的码型,建立传输线的等效电路模型,通过MATLAB软件仿真信号在有线信道中的传输过程,以及从四进制键控数字调制方式(QPSK)仿真入手,建立了多径信道、瑞利信道等无线信道模型,借助MATLAB软件仿真信号在无线信道中的传输过程。     

ATXOP：一种传输机会自适应分配算法

在无线局域网(W LAN)中,由于各个站点竞争信道引起的数据帧冲突严重损害了整个网络的性能。首先分析了目前提高无线局域网性能的算法及存在的问题,在此基础上提出了一种自适应分配传输机会(TXOP)的算法ATXOP。该算法根据当前信道隙利用率,动态地调整连续传输数据帧的数目。不仅减少了由传统竞争算法引起的网络拥塞,而且避免了固定分配传输机会带来的不公平性。算法简单易行。仿真结果表明,在保证公平性的同时,该算法能够有效地提高网络的吞吐量和降低数据帧传输平均延时。     

适用于AMI的有线无线融合数据传输方法

针对AMI的需求和有线/无线系统各自的不足,提出了一种适用于AMI的有线无线融合的数据传输系统及方法.该系统将有线传输和无线传输有机地结合起来,实现了系统与环境和信道特性相适应的传输方案的灵活选择;采用OFDM技术,增强了系统的抗干扰性能,提高了数据传输率;通过多种调制模式的设计,使系统在可靠稳定的前提下拥有尽可能高的速率;通过有线无线的基带复用,简化了系统设计,节约了系统成本.     

无线数据采集模块设计

在工业控制领域,常常需要采集大量的数据,然后传输给主机进行处理。这些网络多基于有线传输,在使用中有很多缺点,而无线传输具有成本低、效率高、维护方便等优势。这里介绍一种以555定时器组成的电路为主体的多参数无线数据采集模块,可对温度、压力等多种参数进行采集,并分时地用同一无线信道进行传输,有着广泛的应用前景。     

中兴通讯无线局域网解决方案

无线局域网（WLAN）是计算机网络与无线通信技术相结合的产物，它以无线信道作为传输媒介，提供了传统有线局域网的功能，并具备有线网络无法相比的移动、漫游等特性，能够使用户真正实现随时、随地、随意的宽带网络接入。除此之外，无线局域网还具备安装简单、易扩展、易管理等特点，因而具备极大的应用前景。无线局域网广泛地适用于各种场所，为用户提供高速内部网络互联或无线宽带Internet接入。目前无线局域网仍处于众多标准共存的时期。从目前的技术标准来分析，IEEE８０２．１１系列是WLAN的主流发展方向；蓝牙技术主要用于近距…     

无线局域网--宽带接入新选择

一、从局域网的延伸到宽带接入方式 无线局域网(WLAN)是计算机网络与无线通信技术相结合的产物,它以无线信道作为传输媒介,提供传统有线局域网的功能.虽然无线局域网已出现较长的时间(IEEE早在1997年就已经制定了无线局域网标准802.11),但其应用范围却主要局限于办公室或企业内部网络的互联,作为有线网络的延伸和补充而存在.早期制约无线局域网应用的原因主要是其带宽和价格.一方面,早期无线局域网所提供的带宽有限,只能提供最高2 Mbit/s的速率;另一方面,其高昂的价格使广大用户望而却步.     

一种改善TCP性能的cdma2000链路层RLP重传方案

在无线数据传输网络中,物理层帧差错率(FER)是影响网络性能的一个主要因素。无线链路层重传技术是改善网络性能因无线信道误码率较高而下降的一项重要措施。本文主要研究cdma2000无线网络中链路层重传技术对无线TCP数据传输的影响,提出一种cdma2000链路层重传方案,并通过OPNET仿真技术对该重传方案进行仿真,验证了该方案能改善TCP数据在cdma2000无线网络中的传输性能。     

QoS Routing for Mesh-Based Wireless LANs

Wireless LANs with their increased data rate become an attractive technology for connecting mobile users to the Internet. Efficient deployment of wireless LANs will require the ability to extend the wireless LANs coverage without the need to deploy a very large number of access points. Mesh-based wireless LANs are an attractive solution to this problem. These networks extend wireless LAN coverage by using each node in the network as a router, resulting in a multihop topology. In this paper we introduce a novel routing algorithm, wireless mesh routing (WMR), that provides quality-of-service (QoS) support and accounts for the characteristics of both infrastructure-based wireless LANs and ad hoc networks. The algorithm is validated using the OPNET modeler. The simulation results show that the mesh network using WMR protocol can provide QoS support and react dynamically to the network status changes with low control overheads. Using the proposed software architecture the proposed routing protocol can be implemented with any MAC protocol, resulting in easy implementation in existing wireless nodes.     

Cross-Layer Architecture for Adaptive Video Multicast Streaming Over Multirate Wireless LANs

Multicast video streaming over multirate wireless LANs imposes strong demands on video codecs and the underlying network. It is not sufficient that only the video codec or only the underlying protocols adapt to changes in the wireless link quality. Research efforts should be applied in both and in a synchronized way. Cross layer design is a new paradigm that addresses this challenge by optimizing communication network architectures across traditional layer boundaries. This paper presents cross-layer architecture for adaptive video multicast streaming over multirate wireless LANs where layer-specific information is passed in both directions, top-down and bottom-up. The authors jointly consider three layers of the protocol stack: the application, data link and physical layers. The authors analyze the performance of the proposed architecture and extensively evaluate it via simulations. The results show that the real-time video quality of the overall system can be greatly improved by cross-layer signaling.     

Software testing for wireless mobile computing

4G wireless networks make it increasingly difficult to develop and test application software for mobile terminals in comparison with 3G or earlier generations. These 4G networks incorporate wireless LAN technologies, and mobile terminals can access the services provided by LANs as well as global network services. Therefore, software running on mobile terminals may depend on not only its application logic but also on services within the LANs to which the terminals are connected. To construct correct software to run in mobile terminals for 4G wireless networks and wireless LANs, it must be tested in all the networks to which the terminal could be moved and be connected. This article presents a new approach, called flying emulator, to testing software designed to run on mobile terminals. Like existing approaches, the approach provides software-based emulators of its mobile terminals for software designed to run the terminals. It is unique because it constructs emulators as mobile agents that can travel between computers. These emulators can carry the target software to the networks to which the terminals are connected and allow it to access services provided by the networks in the same way as if it was moved with and executed on the terminals connected to the networks. This article describes the idea of the approach, its implementation, and our experience with a typical application.     

一种基于网络编码的重传算法研究

无线网络中,节点发送的数据分组传输失败后,执行重传机制。传统的重传机制ARQ由于在一次重传中只能发送一个丢失的数据分组,因此传输效率比较低。利用网络编码技术和AQR重传机制,我们可以在重传中使用网络编码,广播发送由多个丢失数据分组编码得到的编码分组,从而提高重传效率。本文中我们提出一种将网络编码应用于多个发送方多个接收方(MSMR)无线网络中的算法RMBNC。理论推导和仿真分析验证了我们提出的算法的有效性。     

Local-area networks go wireless

As standards emerge, data rates rise, and laptops seek connectivity, wireless LANs are finding a market niche as extensions to wired networks. Wireless LANs have found homes in buildings where installing wires would expose asbestos or destroy historic architecture. They have also proved valuable to companies that often relocate and want networks they can take with them. Another common use is for connecting wired LANs that are physically separated. The growth has been fueled by the desire to add wireless adjuncts to wired LANs, so that mobile workers can keep in constant contact with corporate networks over short distances. The author discusses the befits of wireless LANs. The radio based wireless LAN is discussed including multipath interference and data bottlenecks. The infrared based wireless LAN is also discussed and an inset discusses standards for wireless LANs     

Approach for voice quality and throughput estimation in wireless convergent networks

A common communications convergence scenario which is being adopted in personal communications relates to the combination of wireless and cellular networks by the use of multimode terminals. Since most of the wireless networks were initially dimensioned only for data communications, this paper shows how voice over wireless LAN dimensioning could be addressed under the optimal network throughput and the perspective of voice quality, using a simple approach. The maximum number of simultaneous users resulting from throughput is limited by the collisions taking place in the shared medium with the statistical contention protocol. The voice quality is conditioned by the delay and the packet loss in the contention protocol. Both approaches are analyzed within the scope of the voice codecs commonly used in voice over wireless LANs, to conclude that voice dimensioning based on network throughput and voice quality show complementary results. Additionally the use of low rate codecs in voice over wireless LANs is advantageous for the network performance point of view but may produce poor voice quality results. Mid range codecs like G729 could represent a trade-off for quality throughput. For these reasons, voice quality and wireless network throughput have to be taken into account in the network admission control, design and deployment to ensure a satisfactory user experience. The impact of handoff interval of wireless convergent networks on the conversation quality need also be assessed for a proper network design.     

An Asymmetric Access Point for Solving the Unfairness Problem in WLANs

In a typical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as a bridge between the wireless and the wired part of the network. Under the current IEEE 802.11 DCF access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay all the frames it receives on the downlink. This causes significant unfairness between uplink and downlink flows, long delays, and frame losses. The main problem is that the access point requires more transmission attempt probability than wireless stations for correct operation at the transport layer. In this paper, we propose to solve the unfairness problem in a simple and elegant way at the MAC layer. We define the operation of an Asymmetric Access Point that benefits from a sufficient transmission capacity with respect to wireless stations so that the overall performance improves. The proposed method of operation is intrinsically adaptive so that when the access point does not need the increased capacity, it is used by wireless stations. We validate the proposed access method by simulation to compare it with other solutions based on IEEE 802.11e. Moreover, we provide measurement data gathered on an experimental prototype that uses wireless cards implementing the proposed method.     

桥梁索力测量无线组网系统

设计实现了一种基于Zig Bee无线组网的桥梁索力测量系统。该系统采用TI公司的CC2530芯片组建无线数据传输网络,采用MEMS传感器对桥梁多个拉索进行布点,用STM32芯片组成控制处理模块,实现一次性同步得到桥梁多拉索的索力数据,解决了桥梁监测数据采集麻烦问题。该系统具有节点功耗小、传输距离远、组网容易、成本低、网络容量大等优势,现场应用实验效果较好。     

Does the IEEE 802.11 MAC protocol work well in multihop wireless adhoc networks?

The IEEE 802.11 MAC protocol is the standard for wireless LANs; it is widely used in testbeds and simulations for wireless multihop ad hoc networks. However, this protocol was not designed for multihop networks. Although it can support some ad hoc network architecture, it is not intended to support the wireless mobile ad hoc network, in which multihop connectivity is one of the most prominent features. In this article we focus on the following question: can the IEEE 802.11 MAC protocol function well in multihop networks? By presenting several serious problems encountered in an IEEE 802.11-based multihop network and revealing the in-depth cause of these problems, we conclude that the current version of this wireless LAN protocol does not function well in multihop ad hoc networks. We thus doubt whether the WaveLAN-based system is workable as a mobile ad hoc testbed     

Standardization efforts for wireless LANs

The Digital European Cordless Telecommunications (DECT) draft standard, which is the only wireless local area network (LAN) standard close to the 1-Mb/s data rate is briefly described. Active standards groups and their activities are reviewed. The work of the IEEE working groups for wireless LANs is examined