IEEE 802.11s wireless mesh networks: Framework and challenges

Wireless mesh networking based on 802.11 wireless local area network (WLAN) has been actively explored for a few years. To improve the performance of WLAN mesh networks, a few new communication protocols have been developed in recent years. However, these solutions are usually proprietary and prevent WLAN mesh networks from interworking with each other. Thus, a standard becomes indispensable for WLAN mesh networks. To meet this need, an IEEE 802.11 task group, i.e., 802.11s, is specifying a standard for WLAN mesh networks. Although several standard drafts have been released by 802.11s, many issues still remain to be resolved. In order to understand what performance can be expected from the existing framework of 802.11s standard and what functionalities shall be added to 802.11s standard to improve performance, a detailed study on the existing 802.11s standard is given in this paper. The existing framework of 802.11s standard is first presented, followed by pointing out the challenging research issues that still exist in the current 802.11 standard. The purpose of this paper is to motivate other researchers to develop new scalable protocols for 802.11 wireless mesh networks.     

IEEE802.11无线局域网标准的网络性能比较与分析

本文基于IEEE802．11标准,分析了802．11ab、g三大标准的特点及其实现的关键技术,并在频道数、传播范围、吞吐量、兼容性、传输速度和同频干扰等几方面,对不同标准网络进行了比较与分析,得出IEEE802．11网络在不同环境下使用的优缺点。最后,本文介绍了一种新的无线局域网应用方式：双频多模无线局域网。     

EFT: a high throughput routing metric for IEEE 802.11s wireless mesh networks

In this paper, we present a throughput-maximizing routing metric, referred to as expected forwarding time (EFT), for IEEE 802.11s-based wireless mesh networks. Our study reveals that most of the existing routing metrics select the paths with minimum aggregate transmission time of a packet. However, we show by analyses that, due to the shared nature of the wireless medium, other factors, such as transmission time of the contending nodes and their densities and loads, also affect the performance of routing metrics. We therefore first identify the factors that hinder the forwarding time of a packet. Furthermore, we add a new dimension to our metric by introducing traffic priority into our routing metric design, which, to the best of our knowledge, is completely unaddressed by existing studies. We also show how EFT can be incorporated into the hybrid wireless mesh protocol (HWMP), the path selection protocol used in the IEEE 802.11s draft standard. Finally, we study the performance of EFT through simulations under different network scenarios. Simulation results show that EFT outperforms other routing metrics in terms of average network throughput, end-to-end delay, and packet loss rate.     

Indoor deployment of IEEE 802.11s mesh networks: Lessons and guidelines

Emerging wireless mesh networks (WMNs) are known for their fast and low cost deployment. Conventional mesh deployment focuses on the outdoor environment, which regards the WMNs as backbone networks. This study deploys and measures indoor IEEE 802.11s mesh networks to extend WLAN capabilities with extensive experiment configurations. The testbed is constructed in a laboratory and a field crossing three floors of a building. Disagreeing with previous research, the results of this study indicate that RTS/CTS can improve throughput by up to 87.5%. Moreover, compared with the IEEE 802.11b/g, 802.11n achieves better fairness for multi-stream or multi-hop communications. Experimental results also suggest that a longer beacon interval, e.g. 500 ms, can improve channel efficiency for a denser deployment. On the other hand, sparser deployments should use a shorter beacon interval, e.g. 100 ms, to enhance link stability.     

IEEE802.11无线局域网中的Qos机制

无线局域网（WLAN）是对目前无线接入系统的补充，可以使网络用户摆脱网线的束缚，实现真正意义上的移动互联。与蜂窝系统相比，它的户外移动性虽然受到限制，但适用面广，可在典型的应用环境如办公室、家庭、展览厅、机场、火车站等热点地区，向终端用户提供高速数据传输。WLA     

IEEE802.11g研究综述

全面介绍了IEEE802.11g标准的WLAN，详细讲述了IEEE802.11g草案标准的概念、特点、构件及体系结构、发展前景等，并探讨了实现IEEE802.11g WLAN所需的几项关键技术，同时分析了IEEE802.11g标准的网络性能。其关键技术包括直序列扩频调制技术及补码键控技术，包二进制卷积，正交频分复用技术等。有关IEEE802.11g的兼容性，同频共存性，自身的OFDM问题分析将成为研究的热点。     

IEEE802.11i无线局域网安全技术

介绍了当前无线局域网中的安全缺陷，分析了常见的无线局域网攻击手段，并在研究无线局域早期802．11标准安全缺陷的基础上重点分析了IEEE802．11i标准中的安全机制和关键技术。     

IEEE802.11n:无线局域网标准的又一次飞跃

IEEE802．11n标准是一种高速无线局域网标准。可以和百兆有线网无缝结合IEEE802．11n标准采用了一些4G的关键技术。如MIMOOFDM技术等。IEEE802．11n标准的推出将加快全球无线局域网的发展进程     

An implementation of IEEE 1588 protocol for IEEE 802.11 WLAN

Wireless Networks - Clock synchronization is one of the enabling technologies for Wireless Local Area Networks (WLAN). It is crucial to perform applications such as data fusion, location detection...     

Broadband WLAN Channel Sounder for IEEE 802.11b

Because of the proliferation of indoor wireless local area network (WLAN) communication systems, portable radio measurement devices are becoming quite advantageous. This paper reports on the development of an advanced portable and compact broadband WLAN IEEE 802.11b channel sounder, which directly exploits the physical layer characteristics of the WLAN system. The measurement system and experimental procedures have been presented with the measurement results. The channel sounder provides very good results compared to a vector network analyzer (VNA). Moreover, the measured and reconstructed cross-correlation functions from the estimated power taps are in excellent agreement with a root mean square error (RMSE) of 3%. Hence, this system has been developed to be used in conjunction with a WLAN modeling system to calibrate indoor empirical and deterministic models.      

Enhancement of QoS differentiation over IEEE 802.11 WLAN

IQD, a distributed coordination function (DCF) with integrated quality of service (QoS) differentiation, is proposed in this letter to enhance QoS over IEEE 802.11 WLAN. DCF does not support any QoS differentiation. Enhanced DCF (EDCF) only supports delay differentiation. IQD can achieve both delay and packet-loss-rate differentiation by differentiating the initial window size and the retry limit. Simulation results show that IQD performs better than DCF and EDCF in enhancing QoS, and the proposed analytical model is valid.     

Multi-radio multi-channel routing metrics in IEEE 802.11s based wireless mesh networks

IEEE 802.11s is one of the emerging standards designed to build wireless mesh networks which may serve to extend the coverage of access networks. The default IEEE 802.11s path selection protocol Hybrid Wireless Mesh Protocol (HWMP) is based on the radio-aware airtime link metric (ALM) that outperforms the hop-count metric in single channel multi-hop wireless networks. However, this metric may lead to capacity degradation when multiple channels and/or multi-radio are used. To fully exploit the capacity gain of multiple channels use, new routing metrics have been proposed such as weighted cumulative expected transmission time, metric of interference and channel switching, interference aware routing metric, exclusive expected transmission time, and normalized bottleneck link capacity. These metrics distribute the data traffic load among channels and/or radios to reach the final destination. In this paper, we provide a qualitative comparison study that considers the characteristics of these metrics. Indeed, we substitute ALM by these different metrics, and we evaluate the performance of HWMP through simulation. Obtained results allow us to identify the appropriate use case of each metric.     

IEEE 802.11无线局域网标准发展历程及其发展方向

本详细介绍了IEEE802．11标准组成，标准发展历程和发展方向。     

Transmission and Reception Concepts for WLAN IEEE 802.11b

State-of-the-art wireless local area network (WLAN) IEEE 802.11b terminals employ complementary code keying (CCK) as modulation format. In this paper, receiver concepts tailored for CCK transmission over frequency-selective fading channels are presented in a unified and systematic framework. First, optimum maximum-likelihood (ML) detection for CCK signaling is considered. Second, for complexity reduction, minimum mean-squared error block decision-feedback equalization (MMSE-DFE) is investigated and reduced-state sequence estimation (RSSE) is considered on the basis of an Ungerbock-like set partitioning of the multidimensional CCK code wordset. In order to improve the reliability of CCK transmission over fading channels, time-reversal space-time block codes (TR-STBCs) combined with receive diversity are applied. Simulation results of the considered suboptimum receivers are compared with a performance approximation for optimum detection. Our results demonstrate the excellent performance of the advocated equalization schemes and the significant gains that can be achieved with TR-STBCs and receive diversity in typical WLAN environments     

UWB对IEEE802.11a WLAN的电磁干扰分析

在FCC模板和ECC模板的基础上,分析了室内环境下UWB设备对IEEE802.11a WLAN系统的电磁干扰。在IEEE802.11a系统性能恶化1dB的情况下,使用双线模型分别计算出室内环境下单个UWB设备和多个UWB设备的发射功率限制。分析结果表明,对于IEEE802.11a WLAN来说,距离最近的UWB干扰是最主要的干扰,建议以36cm的最小隔离距离为基础来限制5GHz频段处的UWB发射功率。因此ECC模板更能满足IEEE802.11a的电磁兼容要求,而FCC模板能否保证有待进一步研究。     

无线局域网标准 IEEE802.11g的技术优势

本文详细介绍了无线局域网标准IEEE802.11g的发展历程及其技术优势。     

IEEE802.11无线局域网安全漏洞研究

WLAN主要协议IEEE802.11的安全系统存在重大的漏洞,本文对IEEE802.11的安全系统进行了一定分析,并着重分析了其安全漏洞和容易受到的一些攻击,并针对漏洞和攻击提出了一定的解决方案。     

无线局域网标准IEEE 802.11与HiperLAN-2简介

本文详细介绍了无线局域网的IEEE 802.11标准与HiperLAN-2标准的相关内容,并对这两个标准进行了比较.     

WLAN中IEEE802.11n标准及关键技术研究

对WLAN中最新的802.11n标准进行探讨,从MIMO-OFDM结合的相容性及技术原理分析IEEE802.11n标准中的关键技术MIMO-OFDM,分析MIMO-OFDM中同步,信道估计、MIMO检测等关键技术,从IEEE802.11g/a产品的实践应用及对IEEE802.11n传输速率实验,指出该标准能有效解决WLAN应用中的传榆瓶颈问题,在未来WLAN的应用中将会起到主导作用.     

Evaluation of IEEE 802.11 coexistence in WLAN deployments

Wi-Fi has become a successful technology since the publication of its first WLAN standard due to continuous advances and updates while remaining always backwards compatible. Backwards compatibility among subsequent standards is an important feature in order to take advantage of previous equipment when publishing a new amendment. At present, IEEE 802.11b support is still mandatory to obtain the Wi-Fi certification. However, there are several harmful effects of allowing old legacy IEEE 802.11b transmissions in modern WLAN deployments. Lower throughput per device is obtained at slow rates, but also the effect known as performance anomaly, which nearly leads to starvation of fast stations, has to be taken into account. Finally, backwards compatibility mechanisms pose an important penalty in throughput performance for newer specifications. This paper presents a thorough analysis of the current state of IEEE 802.11, comparing coverage range and throughput performance among subsequent amendments, and focusing on the drawbacks and benefits of including protection mechanisms.