Capacity enhancement by terminal originated beamforming for wireless local area networks

In dense traffic areas, wireless local area networks (WLANs) suffer from interference problems due to the usage of the crowded unlicensed ISM band and the lack of available spectrum. To mitigate these problems, a terminal side beamforming framework is proposed—this beamforming is capable of focusing the transmission and the reception in the relevant direction of the access point to exploit the directivity of the indoor propagation channel. It provides network transparency to achieve the backwards compatibility to the existing WLAN networks, and vendor transparency to ease the system design process and thereby achieve low complexity and costs. The beamforming enabled terminal benefits in terms of capacity, energy efficiency, and security while it does not require any change on the network side costing network providers new investments. It will be an attractive value-added feature as well as low-cost solution for the future WLAN terminal design opening the door for WLAN terminal manufacturers to include the proposed solution into their product line. In this work, a WLAN terminal beamforming demonstrator has been developed to demonstrate the capacity enhancement in real environments. Signal to interference ratio (SIR) improvement as well as array gain were investigated by simulations with IEEE 802.11n cluster channel models and by experiments with the demonstrator in a typical office environment. The comparable results of simulations and experiments show significant array gain and SIR improvement. The significant capacity increase has been demonstrated in the experiments in both an interference free scenario and an interference limited scenario.     

一种基于软件无线电技术的中频数字接收机的实现

本文主要讨论了一种基于软件无线电技术的中频数字接收机的实现.在系统具体实现中,提出了利用信号的镜像频谱来实现信号数字正交解调的新方法,从而使得数字正交解调的关键部分--数字NCO只需用同采样时钟一样的参考时钟就可以对中频信号实现正交解调.实验结果表明,系统性能优良,可以满足实际需要.     

无线局域网技术及应用

无线局域网技术是目前发展迅速的技术，相对于有线局域网有许多优点。随着无线网络产品性能的提高和价格的不断下降，无线局域网技术有着广泛的应用前景。据此对无线局域网的基本概念、特点及其技术作了简单的介绍，提出了无线局域网面向应用的几种解决方案，并对发展前景作了预测。     

蓝牙技术将主导未来的WLAN通信

对目前研究热门的无线局域网的重要技术之一－－蓝牙技术作了简要介绍与报道,并将它和目前WLAN中的其他技术进行了比较。     

5G时代广播电视无线发射技术研究

文中探讨了5G时代背景下的无线电传输技术、无线网络策略和广播网络设计的最新发展。通过详细分析5G 技术的特点、广播传输技术的现状和面临的挑战以及实际案例,希望能促进各种优化策略和制造解决方案的推广应用。     

WPAN/WLAN应用环境下的一类混合链路自适应算法

该文分析了基于包错误率(PER)测量及基于我干比(C/I)估计的链路自适应算法的优缺点,在此基础上提出了两种WPAN/WLAN应用环境下的混合算法,即同时考虑PER与C/I的混合算法和选择性考虑PER与C/I的混合算法,并对它们进行了理论分析和数值仿真。结果表明,在理想的单用户接入情况下,同时考虑PER与C/I的混合算法的吞吐量要大于其它算法。在实际的多用户接入情况下,分配给每个用户的资源相对较少,此时,选择性考虑PER与C/I的混合算法能够减小接收包数目较少或C/I估计误差大大以及信道误判等因素造成的吞吐量损失,达到比其它算法更大的网络吞吐量。     

Double-polysilicon SiGe HBT architecture with lateral base link

We present an analysis of a modified double-polysilicon SiGe:C HBT module showing a CML ring oscillator gate delay τ_D of 2.5 ps, and f_T/f_max/BV_CEo values of 300 GHz/350 GHz/1.85 V (Fox et al., 2008) [1]. A key feature of the HBT module is a connection of the extrinsic and intrinsic base regions by lateral epitaxial overgrowth, which aims to overcome the limits of the conventional double-polysilicon architecture in simultaneously reducing R_B and C_BC. Potential benefits and barriers of the proposed device structure on the way to higher performance are reviewed with regard to the recently demonstrated performance gain of the classical double-polysilicon approach. The paper addresses technological challenges one is faced when the here presented device structure is scaled to minimum device dimensions.     

Robust channel estimation for the OFDM-based WLAN systems with imperfect synchronization

As an effective technique for combating multipath fading and for high data rate transmission over wireless channels, orthogonal frequ- ency division multiplexing (OFDM) is extensively used in wireless local area network (WLAN) systems to support high-performance bandwidth- efficient multimedia services. In this paper, a robust channel estimation scheme is proposed for the OFDM-based WLAN systems with imperfect synchronization. The frame structure information, the preamble information, the pilot information are efficiently utilized in the proposed channel estimation scheme. Simulation results are used to illustrate the performance of the proposed scheme.     

VPN技术在局域网中的应用

在信息技术迅速发展的今天,用户对网络服务、网络安全及其网络应用的要求也正越来越高,一种组网更加灵活、成本更低的虚拟专网（VPN）也由此应运而生。VPN技术是一种建立在互联网公共网络架构之上,以取代原有连接方式的标准广域网,并通过一定的技术手段以达到类似私有专网的数据安全传输。     

光无线通信技术的应用

说明红外光无线通信系统设计的要点,并简略介绍数字信号脉冲位置调制与时段调制比通断键控的优点、角度分集接收和空分多路复用技术,以及红外光无线局域网的应用     

无线市话校园网建设方案

通过一个工程实例，介绍了无线市话校园网的系统结构、系统配置及中继数量的计算。     

信息化智能小区构建方案初探

简述了信息化智能小区的基础是通信网络。在这一观点的基础上,给出了一种综合利用LonWorks和ATM技术共同构建的信息化智能小区的方案。     

认知无线电技术在广电中的应用

介绍了认知无线电技术的发展背景和当前的研究状况,论述了发展认知无线电的重要性,讨论了认知无线电领域的几种关键技术,论述了认知无线电在广电领域的应用范围和发展前景。举例说明了广电运营商可通过认知无线电系统接入除传统电视业务之外的多种业务。     

Citizen participation and the uses of mobile technology in radio broadcasting

This paper discussed the different ways radio stations in North America engage listeners and provide immersive experiences via the use of mobile technology. The paper described several uses of mobile technology in radio and talked about ways broadcasters can improve engagement and, as a consequence, increase the number of listeners by deploying participatory or citizen journalism type of experiences on the part of the audience. A discussion on the best practices and utilization of convergent technology on radio is also included. Furthermore, the paper analyzed some of the pitfalls and challenges of using social media and mobile technology in today’s radio broadcasting.     

LMDS——本地环路的“第三方力量”

基于本地多点分配系统（ＬＭＤＳ）技术的宽带无线网络方案使交换网在接入技术容量方面产生了飞跃,并在本地环路中引入了具有竞争实力的“第三方力量”本了网垄断无疑是ＬＭＤＳ发展的最后障碍,政策和管制是该技术发展面临的最严峻挑战。     

Calibration study of dual-band Weaver–Hartley receiver architecture

This paper presents a calibration study of dual-band image rejection receiver based on combined Weaver–Hartley architecture, with improved image rejection of first and second image signals. The system implementation is based on dual-band WLAN 802.11 a/g. When the desired signal is at 5.7-GHz band, the 2.4-GHz band becomes the first image signal and vice versa. The output IF frequency is at 30-MHz. The detection of the gain and phase mismatches is based on modeling, extraction of related error signals and correcting them in closed loop. Moreover, we demonstrate an open loop technique to reach the phase and gain correction signals. The correction signals can be digitally stored and applied as digital trimming control on the LO signals. Simulation showed close to 60 dB of image rejection ratio for the first image signal. Second image signal is rejected by a 4-section poly-phase filter.     

宽带便携式接收机的研究

随着无线电技术的发展需要,传统接收机体积庞大、不易携带的缺点越来越突出。本文选择了某小型宽带手持接收机进行研究,该接收机能够提供IQ数据输出及计算机软件控制选件,本文首先对该接收机的参数控制进行了介绍,并对比了三款SDR(Software Defined Radio)软件的功能与特点,最后说明了正确获取IQ数据的方法。     

高层建筑的快速识别方法研究

利用卫星图像对高层建筑进行分类和定位,相比市售数据具有成本更节省、更新更及时的优势,在无线网络规划的环境调查工作中具有重要的意义。本文通过不同方法在高层建筑识别上进行对比测试,发现在高层建筑的识别上,使用VGG16网络具有最好的召回率。在算法和预训练网络的挑选上,需要根据数据集的特点进行仔细甄别。Faster R-CNN配以VGG16骨干网络是效果相对较好的一种方法。不同算法架构和预训练网络在不同的数据集上表现相差较大。     

路由交换技术在构建高性能校园网的应用

本文以肇庆电大校园网为例,描述了构建高性能校园网的目标和方案,应用关键的路由交换技术极大提高了建设高性能校园网的效能性,整体提升了校园网的安全性,增大了网络运维、服务和集中管理的灵活性.