浅析3G／WLAN交互网络

3G／WLAN是人类跨入新一代无线移动网络时代的关键因素，3G／WLAN交互网络通过无线局域网的接入控制功能增加新的功能，如实时对等IP通信等。本文对3G网络、WLAN技术的特点、应用，两者之间的技术特性、功能应用区别，两者的融合方式以及3G／WLAN终端与业务做了详细分析。     

无线局域网存在的安全威胁分析及防范

无线局域网为用户提供了更大的方便,同时也带来了一定的安全隐患,其安全威胁主要有非授权接入、数据窃取和协议漏洞,针对此类威胁,要保障无线局域网的安全防,可提升无线网络的加密级别、不使用弱密码、采用静态IP和MAC地址过滤,此外,还可隐藏无线SSID、定期更换密匙、关闭无线WPS/QSS功能、严控个人无线AP和使用企业防火墙和无线入侵检测系统等。     

McWiLL多媒体集群系统高效语音实现机制

本文介绍了一种基于McWiLL(Multi-carrier Wireless information Local Loop,SCDMA无线接入技术的宽带演进版本)技术的可提供通用、高效语音业务的实现机制,解决目前基于无线IP的语音系统移动性受限、空中资源利用率低下的问题。本机制在无线接入侧通过业务汇聚网关,提供标准的SIP/RTP接口,保证此架构与其它网络互联互通的简单;通过无线接入侧的用户数据库,配合用户标识符,保证本机制的网络移动性管理在无线接入网内部完成,可以方便的支持移动应用场景;通过无线接入侧的空口语音传输机制、宽带基站和业务汇聚网关之间的数据复用技术,提高了空口和无线带宽资源的利用率,实现了用户数据的高效传输。     

宽带无线通信技术研究

近年来,互联网行业和计算机技术蓬勃发展,世界正在迈入大数据时代。随着4G+慢慢走入人们的视野,用户需求越来越广泛。5G、物联网以及云计算的融合终将推动智能网络的无限发展。而无线局域网作为现代无线通信技术中的重要组成部分以及智能网络中不可或缺的部分,在智能网络的未来发展中,必须保证其服务能够满足越来越"挑剔"的服务需求,包括高接入、高速率、高带宽等。本文对之前无线局域网的相关研究进行了分析并提出了对无线局域网发展的想法和研究。     

基于ARM平台的3G无线传输系统的设计与实现

提出一种基于ARM平台的3G无线数据传输系统。在硬件设计电路中,选用ARM9微处理器S3C2440作为主控器,选用内嵌TCP/IP协议栈的中兴WCDMA 3G模块,使用TCP/IP协议连接Internet,用以实现基于ARM平台的3G无线数据传输系统。在软件设计中,采用Visual Studio2005的Visual C++开发嵌入式WinCE应用程序,使用TCP编程实现TCP客户端与服务器端的相互访问。     

无线局域网的优化方式

目前无线局域网（Wireless LAN）技术发展迅速,但无线局域网的性能与传统以太网相比还有一定距离,因此如何提高和优化网络性能显得十分重要。为使无线局域网提供的吞吐量、误码率、传输时延、抗干扰能力满足通信要求,本文分析和讨论移动IP、IEEE80211e与双频多模WLAN等多种方式结合以达到对无线局域网的性能最大的优化。     

无线局域网的概况

无线局域网的覆盖范围为几百米,在这样一个范围内,无线设备可以自由移动,其适合于低移动性的应用环境。而且无线局域网的载频为公用频段,无需另外付费,因而使用无线局域网的成本很低。无线局域网带宽更会发展到上百兆的带宽,能够满足绝大多数用户的带宽要求。基于以上原因,无线局域网在市场赢得热烈的反响,并迅速发展成为一种重要的无线接入互联网的技术。但由于无线局域网应用具有很大的开放性,数据传播范围很难控制,因此无线局域网将面临着更严峻的安个问题。本文在阐述无线局域网安全发展概况的基础上,分析了无线局域网的安全必要性,并从不同方面总结了无线局域网遇到的安全风险,同时重点分析了IEEES02．1Ib标准的安全性、影响因素及其解决方案,最后对无线局域网的安全技术发展趋势进行了展望。     

无线局域网的应用与发展

无线局域网的覆盖范围为几百米,在这样一个范围内,无线设备可以自由移动,其适合于低移动性的应用环境。而且无线局域网的载频为公用频段,无需另外付费,因而使用无线局域网的成本很低。无线局域网带宽更会发展到上百兆的带宽,能够满足绝大多数用户的带宽要求。基于以上原因,无线局域网在市场赢得热烈的反响,并迅速发展成为一种重要的无线接入互联网的技术。但由于无线局域网应用具有很大的开放性,数据传播范围很难控制,因此无线局域网将面临着更严峻的安个问题。本文在阐述无线局域网安全发展概况的基础上,分析了无线局域网的安全必要性,并从不同方面总结了无线局域网遇到的安全风险,同时重点分析了IEEE802．11b标准的安全性、影响因素及其解决方案,最后对无线局域网的安全技术发展趋势进行了展望。     

WAPI技术在3G时代增强MID用户使用体验上的应用

WAPI是中国唯一具有自主知识产权的无线局域网安全标准,由无线局域网鉴别基础结构和无线局域网保密基础结构两大部分构成。在三网合一的大背景下,WAPI技术和第三代移动网络的深度融合和有效补充,通过松散布网,热点补充等方法可以有效的降低建网成本同时提高网络速率进而增强MID用户的使用体验。     

宽带无线IP实验系统

给出了一个宽带无线IP实验系统。该系统由4－6个移动终端、2个无线接入点和2个无线接入服务器组成，可提供2－11Mbps的高速无线传输，支持IEEE802．11b协议和移动IP协议，具有可靠的信息安全机制，可支持在移动环境下的WWW浏览、FTP、VOD等业务。提出了高效的UMPA的多址协议，该协议利用自组织算法来确定网络中的用户数，从而可以无冲突地安排各节点的传输。     

Statistical validation of WLAN range calculated with propagation models for industrial environments by chipset-level received signal strength measurements

The wireless range of an IEEE 802.11b/g system as predicted by an empirical model for path loss and temporal fading is validated statistically by measurements of the received signal strength or RSS reported by WLAN monitoring software. This validation is made for indoor industrial environments. In this work, a comparison between a link budget based on industrial propagation models and site surveys executed with WLAN monitoring software is made for two types of industrial environments, namely production centres and warehouses, and for three practically important 802.11b/g data rates of 2, 11 and 18 Mbps. In general, wireless ranges calculated with the link budget and extracted from the site survey measurements are in good agreement. An important finding is that in production centres, the site survey measurements show severe attenuation of the 802.11b/g signal in the presence of large obstacles with approximately the same height as the access point. This phenomenon can cause a noticeable overestimation of the real wireless range by the link budget. Furthermore, it is shown that changing the receiving antenna?s height between 0.5, 1.5 and 2 m has only very limited effect on the wireless range.     

Survey and Analysis of VoIP Frame Aggregation Methods over A-MSDU IEEE 802.11n Wireless Networks

The IEEE 802.11n standard has provided prominent features that greatly contribute to ubiquitous wireless networks. Over the last ten years, voice over IP (VoIP) has become widespread around the globe owing to its low-cost or even free call rate. The combination of these technologies (VoIP and wireless) has become desirable and inevitable for organizations. However, VoIP faces a bandwidth utilization issue when working with 802.11 wireless networks. The bandwidth utilization is inefficient on the grounds that (i) 80 bytes of 802.11/RTP/UDP/IP header is appended to 10–730 bytes of VoIP payload and (ii) 765 µs waiting intervals follow each 802.11 VoIP frame. Without considering the quality requirements of a VoIP call, be including frame aggregation in the IEEE 802.11n standard has been suggested as a solution for the bandwidth utilization issue. Consequently, several aggregation methods have been proposed to handle the quality requirements of VoIP calls when carried over an IEEE 802.11n wireless network. In this survey, we analyze the existing aggregation methods of VoIP over the A-MSDU IEEE 802.11n wireless standard. The survey provides researchers with a detailed analysis of the bandwidth utilization issue concerning the A-MSDU 802.11n standard, discussion of the main approaches of frame aggregation methods and existing aggregation methods, elaboration of the impact of frame aggregation methods on network performance and VoIP call quality, and suggestion of new areas to be investigated in conjunction with frame aggregation. The survey contributes by offering guidelines to design an appropriate, reliable, and robust aggregation method of VoIP over 802.11n standard.     

IEEE 802.11b based ad hoc networking and its performance in mobile channels

It is widely believed that IEEE 802.11 standard is aimed mainly for fixed indoor wireless local area networks and is not suited for mobile applications, even though the IEEE 802.11b systems may work in either infrastructure mode or ad hoc mode. The impact of node mobility on ad hoc network performance has already been studied intensively, but these studies mostly do not consider temporal fluctuations of the mobile wireless channel due to the Doppler shift. An investigation of the mobility impact on the performance of IEEE 802.11b ad hoc systems with Rician/Rayleigh fading under different node velocities is presented. A comprehensive and in-depth analysis of the impacts of a multitude of different signal distortions on an IEEE 802.11b system performance is also presented. Specifically, the authors study the bit-error rate performances with respect to node velocities for different modulation schemes. The simulation results show that, owing to its extremely low implementation and deployment cost, the current IEEE 802.11b standard has its potential to be deployed in a mobile ad hoc environment if the line-of-sight path between transmitter and receiver exists.     

Traffic scheduling for multimedia transmission over IEEE 802.11e wireless LAN

As the demand for broadband multimedia wireless is increasing, improving the quality of service (QoS) of the widely deployed IEEE 802.11 wireless LAN has become crucial. In order to attain the QoS required by a wide range of applications, the IEEE 802.11 working group has denned a new standard - the IEEE 802.lie. However, very limited work has been performed to address the QoS transmission problem of real-time video over IEEE 802.11e. A novel measurement-based dynamic transmission opportunity (MBDTXOP) scheme is proposed, which adaptively allocates resources to a variable bit rate (VBR) video on the basis of the estimation of future traffic demand to support efficient QoS transmission of VBR video. The novelty of the proposed scheme, when compared with existing methods, lies in estimating the required network resources by exploiting the characteristics of digital video; this capability enables the MBDTXOP scheme to substantially increase network utilisation while preserving the required QoS for the transmission of VBR video. Simulations comparing the proposed scheme with other mechanisms clearly demonstrate the outstanding performance of the former.     

Experimental 1-V flexible-IF CMOS analoguebaseband chain for IEEE 802.11a/b/g WLAN receivers

A low-voltage low-power analogue-baseband chain designed for IEEE 802.11a/b/g wireless local-area network (WLAN) receivers is described. It features architecturally a 'two-step channel selection' to complement the radio front-end, and a flexible intermediate frequency (IF) reception capability to alleviate the cancellation of frequency and DC-offset. In circuit implementation, a double-quadrature downconverter based on a 'series-switching' mixer- quad realises a wideband-accurate I/Q demodulation. A 'switched-current-resistor' programmable-gain amplifier (PGA) minimises the bandwidth variation and transient in gain tuning by stabilising, concurrently, the PGA's feedback factor and quiescent-operating point. An 'inside-OpAmp' DC-offset canceller creates area-efficiently a very low cut-off frequency high-pass pole at DC while providing a fast settling of DC-offset transients. Fabricated in a 0.35 mum complementary metal-oxide semiconductor (CMOS) process without resorting to any specialised device, the prototype consumes 14 mW per channel at 1 V. The transient time in a 52-dB gain step is < 1 mus and the stopband rejection ratio at 20/40 MHz is 32/90 dB. The error vector magnitudes are -27 and -17 dB for 802.11a/g and b modes, respectively.     

Adaptive bandwidth sharing mechanism for quality of service administration in infrastructure wireless networks

In infrastructure wireless networks, the wireless hop can be considered as another hop of the transmission path. With the rapid growth of wireless traffics, the future wireless network is expected to provide services for heterogeneous data traffics with different quality of service (QoS) requirements. Most proposed schemes do not have adaptive mechanisms to deal with the environment changes. In real situation, bandwidths, error rates and loss rates of wireless links vary frequently. We will base on the differentiated service model and propose a wireless differentiation (WD) scheme for user datagram protocol (UDP) flows and a wireless differentiation with prioritised ACK scheme for connections with transmission control protocol (TCP) flows. Both schemes provide QoS support for IEEE 802.11b and do not change the basic access mechanism of IEEE 802.11b.     

Performance measurement of IEEE 802.11b-based networks affected by narrowband interference through cross-layer measurements

Researches and development efforts in wireless networking and systems are progressing at an incredible rate. Among them, measurement and analysis of performance achieved at network layer and perceived by end users is an important task. In particular, recent advances concerning IEEE 802.11b-based networks seem to be focused on the measurement of key parameters at different protocol levels in a cross-layered fashion, because of their inherent vulnerability to in-channel interference. By adopting a cross-layer approach on a real network set-up operating in a suitable experimental testbed, packet loss against signal-to-interference ratio in IEEE 802.11b-based networks is hereinafter assessed. Results of several measurements aimed at establishing the sensitivity of IEEE 802.11b carrier sensing mechanisms to continuous interfering signals and evaluating the effects of triggered interference on packet transmission.     

Experimental Study of Coexistence Issues Between IEEE 802.11b and IEEE 802.15.4 Wireless Networks

Coexistence issues between IEEE 802.11b wireless communication networks and IEEE 802.15.4 wireless sensor networks, operating over the 2.4-GHz industrial, scientific, and medical band, are assessed. In particular, meaningful experiments that are performed through a suitable testbed are presented. Such experiments involve both the physical layer, through measurements of channel power and the SIR, and the network/transport layer, by means of packet loss ratio estimations. Different configurations of the testbed are considered; major characteristics, such as the packet rate, the packet size, the SIR, and the network topology, are varied. The purpose of this paper is to gain helpful information and hints to efficiently face coexistence problems between such networks and optimize their setup in some real-life conditions. Details concerning the testbed, the measurement procedure, and the performed experiments are provided.      

基于最小加代数理论求解无线Mesh网络端到端延迟上界的方法

为分析无线Mesh网络(WMNs)的QoS性能,根据最小加代数理论中的随机性网络演算的知识,提出了基于缓存队列共享的WMNs节点框架,然后利用最小加代数理论中的随机性演算理论求解了基于缓存队列共享的WMNs随机性端到端延迟理想上界和近似上界。对推导出的WMNs端到端延迟上界计算公式进行的实例数值分析证实了统计算方法的有效性。数值分析结果表明,端到端延迟上界随着权重的增加而减少,所得结果对WMNs的QoS控制具有参考意义。     

Improved power-saving medium-access protocol for IEEE 802.11e QoS-enabled wireless networks

The performance of a new pointer-based medium-access control protocol that was designed to significantly improve the energy efficiency of user terminals in quality-of-service-enabled wireless local area networks was analysed. The new protocol, pointer- controlled slot allocation and resynchronisation protocol (PCSARe), is based on the hybrid coordination function-controlled channel access mode of the IEEE 802.11e standard. PCSARe reduces energy consumption by removing the need for power-saving stations to remain awake for channel listening. Discrete event network simulations were performed to compare the performance of PCSARe with the non-automatic power save delivery (APSD) and scheduled-APSD power- saving modes of IEEE 802.11e. The simulation results show a demonstrable improvement in energy efficiency without significant reduction in performance when using PCSARe. For a wireless network consisting of an access point and eight stations in power-saving mode, the energy saving was up to 39% when using PCSARe instead of IEEE 802.11e non-APSD. The results also show that PCSARe offers significantly reduced uplink access delay over IEEE 802.11e non-APSD, while modestly improving the uplink throughput. Furthermore, although both had the same energy consumption, PCSARe gave a 25% reduction in downlink access delay compared with IEEE 802.11e S-APSD.