基于IEEE802.15.4的无线VoIP话机系统

随着网络的普及,基于分组交换的VoIP技术得到迅猛发展。如何将VoIP技术与无线通信技术相结合,实现无线VoIP话机是当前嵌入式VoIP话机设计的一个新方向。本文提出了一种适用于家庭办公室小范围内的无线VoIP话机系统设计方案,并且将该方案在具体的硬件平台上付诸实现。本文重点介绍了该系统的设计特点,无线MAC层的设计,以及手持设备端的硬件结构和软件结构。     

Distributed Borrowing Addressing Scheme for ZigBee/IEEE 802.15.4 Wireless Sensor Networks

This paper proposes a distributed borrowing addressing (DIBA) scheme to solve problems of failure in address assignments resulting from limited tree depth and width when the distributed address assignment mechanism is used in a ZigBee/IEEE 802.15.4 wireless sensor network. DIBA is a method of borrowing addresses from neighbor nodes for newly entering nodes and assigning the borrowed addresses. Its network or sensing coverage can increase with almost the same overhead as the existing method. DIBA is a simple and lightweight means of addressing and routing, making it suitable for wireless sensor networks. Simulations showed that DIBA is a distributed addressing scheme with consistently excellent performance.     

On the Capacity of IEEE 802.11 DCF with Capture in Multipath-Faded Channels

In this paper, we estimated the influence of capture effect over the capacity of IEEE 802.11b DCF within a single picocell. The channel utilization is examined analytically by introducing two capture models based on Rayleigh-distributed envelopes of the captured and the interfering frames divided into two local-mean power classes. Simulations in a pure Rician-faded channel depict the conditions under which both Rayleigh-faded capture models can be used to accurately predict the peak network capacity. Unlike the RTS/CTS handshake access mode, Basic access mode is significantly sensitive to the capture ratio, i.e., the receiver design. The packet size threshold over which it is convenient to switch from Basic to RTS/CTS handshake access scheme is also sensitive to the capture effect.     

An enhancement to the IEEE 802.11e EDCA providing QoS guarantees

One of the challenges that must be overcome to realize the practical benefits of ad hoc networks is quality of service (QoS). However, the IEEE 802.11 standard, which undeniably is the most widespread wireless technology of choice for WLANs and ad hoc networks, does not address this issue. In order to support applications with QoS requirements, the upcoming IEEE 802.11e standard enhances the original IEEE 802.11 MAC protocol by introducing a new coordination function which has both contention-based and contention-free medium access methods. In this paper, we consider the contention-based medium access method, the EDCA, and propose an extension to it such that it can be used to provide QoS guarantees in WLANs operating in ad hoc mode. Our solution is fully distributed, uses admission control to regulate the usage of resources and gives stations with high-priority traffic streams an opportunity to reserve time for collision-free access to the medium.     

The 802.11n MIMO-OFDM Standard for Wireless LAN and Beyond

An overview is given of the new IEEE 802.11n standard. This is the first wireless LAN standard based on MIMO-OFDM, a technique pioneered by Airgo Networks to give a significant performance increase in both range and rate relative to conventional wireless LAN. Performance results show that net user throughputs over 100 Mbps are achievable, which is about four times larger than the maximum achievable throughput using IEEE 802.11a/g. For the same throughput, MIMO-OFDM achieves a range that is about 3 times larger than non-MIMO systems. This significant improvement in range-rate performance makes MIMO-OFDM the ideal solution not only for wireless LAN, but also for home entertainment networks and 4G networks. Richard van Nee received the M.Sc. degree in Electrical Engineering from Twente University in Enschede, the Netherlands, in 1990. In May 1995, he received the PhD degree from Delft University of Technology. From 1995 to 2000, he worked for Lucent Technologies Bell Labs on wireless LAN transmission techniques. He was one of the original proposers of the CCK and OFDM modulation techniques which were adopted by the IEEE 802.11b and IEEE802.11a wireless LAN standards. In 2001, he cofounded Airgo Networks that developed the first MIMO-OFDM modem for wireless LAN and which techniques form the basis of the IEEE 802.11n standard. Together with Ramjee Prasad, he wrote a book on OFDM, entitled ‘OFDM for Mobile Multimedia Communications.’ In 2002 he received the Dutch Veder award for his contributions to standardization of wireless communications.     

差错信道下IEEE 802.11 DCF最优帧长分析及信道自适应策略

分析了差错信道下IEEE 802.11 DCF在饱和状态下的吞吐量以及帧长度对吞吐量的影响.研究表明在一定的误码率（BER）下存在最优的帧长使得系统吞吐量最大,并且该最优值与发送节点的数目无关.在此基础上,提出了一种简单的基于BER区间划分的帧长控制的信道自适应发送策略.仿真表明,与固定帧长的发送策略相比较,使用该策略在差错信道下可以有效地提高吞吐量.     

无线城域网中中心调度的竞争解决方案

针对无线城域网PMP模式下的竞争问题，提出了一种中心调度的竞争解决方案CSCR（centralized scheduling contention resolution）。通过对每一时间帧内活动用户站（subscriber stations）数目的预测，基站（basestation）给所有用户站提供了一个优化的竞争窗口，所有用户站都采用该窗口独立地参与竞争。理论分析和模拟结果表明，与IEEE802．16推荐的基于二进制指数回退BEB（binary exponential backoff）算法的方案相比，CSCR方案不但易于实现，而且能更加有效地利用无线资源，同时减少请求接入延时。     

WiMAX标准最新进展

概述了WiMAX的发展现状.从固定无线接入空中接口、移动无线接入空中接口以及管理平面相关的标准等方面介绍了IEEE 802.16标准的最新进展情况.进一步阐明了WiMAX的工作重点,包括认证规范与网络规范.     

基于IEEE802.16e移动宽带无线接入网的切换过程分析与实现

随着WiMAX组织的发展壮大加快了IEEE802.16标准的发展,移动WiMAX ——IEEE802.16e标准的提出更加引人注目.该标准对IEEE802.16标准进行了补充和拓展,定义了一个结合固定和移动宽带无线接入的系统,填补了高速无线局域网和高移动性蜂窝系统之间的空白.对IEEE802.16e标准中规定的移动宽带无线接入系统的切换过程进行了分析,并提出了该过程的软件实现方案.     

基于802.16e协议的指挥所无线局域网

文章介绍了基于IEEE802.16e协议的野战指挥所无线局域网的框架设计。首先简要介绍了802.16e协议,其次提出了基于802.16e协议的野战指挥所无线局域网的设计方法。对于野战条件下,快速、高效组建野战指挥所无线局域网,提供保密、实时、可靠、高速、大容量、多类型的业务具有一定的借鉴意义。