QoS enhancement in IEEE 802.11 wireless local area networks

A distributed medium access scheme called EDCF, which is adopted in an upcoming standard IEEE 802.11e to allow prioritized medium access for applications with QoS requirements, is described and discussed. Its performance is also evaluated via simulations.     

下一代WLAN标准IEEE 802.11ac物理层研究

无线本地接入网络支撑了移动业务的飞速增长,IEEE 802.11系列标准为WLAN的发展提供巨大的支持,文章简要阐述正在开发的新WLAN标准IEEE 802.11ac的物理层,如何使用更多带宽,更高阶调制和更多MIMO流来实现超过1 Gbps限制的高可靠数据速率,同时比较了802.11ac,802.11n和11a标准。     

Polling-based protocols for packet voice transport over IEEE 802.11 wireless local area networks

In this article we present a survey of different polling-based protocols for supporting voice over IEEE 802.11 wireless local area networks (WLANs). In particular, three key issues are discussed: managing a polling list, determining the polling sequence, and reducing polling overhead. These discussions motivate the proposal of an isochronous coordination function (ICF) for transporting voice packets over IEEE 802.11 WLANs, which combines the advantages of some of the previous protocols. Emulating a dynamic TDMA-like service, ICF can greatly reduce polling overhead and provide fair polling for both uplink and downlink voice traffic by means of a cyclic polling queue. Some simulation results are presented to illustrate the advantages of ICF.     

On the fast BSS transition algorithms in the IEEE 802.11r local area wireless networks

Handover performance is critical to support multimedia services that are becoming increasingly available over the wireless devices. The high transition delay can be unaccepted for such services or can be a source of disruption on the session. On the other side, IEEE 802.11 standard is being extended with new functionalities. Security and QoS features, included in recent IEEE 802.11-2007 standard, add management frames that are exchanged during the transition process. In consequence the handover delay is increased. IEEE 802.11r-2008 amendment introduces Fast BSS Transition (FT) that simplifies the handover process. The authors propose the new handover algorithms based on FT protocol and compare them with existing solution. Additionally, simulation experiments are conducted to answer the question if multimedia services can be properly supported in IEEE 802.11r networks. The authors prove that handover delay can be reduced to 13 ms in the average case.     

IEEE 802.11系列标准

介绍了无线局域网(WLAN)的802．11系列标准，描述了WLAN的工作频段，除了论述窄带微波(Narrowband Microwave)技术、红外线(Infrared)技术及扩展频谱技术，还讨论了介质访问控制和802．1l的安全机制和发展。     

Security protocol for IEEE 802.11 wireless local area network

As Wireless Local Area Networks (WLANs) are rapidly deployed to expand the field of wireless products, the provision of authentication and privacy of the information transfer will be mandatory. These functions need to take into account the inherent limitations of the WLAN medium such as limited bandwidth, noisy wireless channel and limited computational power. Moreover, some of the IEEE 802.11 WLAN characteristics such as the use of a point coordinator and the polling based Point Coordination Function (PCF) have also to be considered in this design. In this paper, we introduce a security protocol for the IEEE 802.11 PCF that provides privacy and authentication, and is designed to reduce security overheads while taking into account the WLAN characteristics. We prove this protocol using the original and modified BAN logic.     

几种IEEE802.11无线局域网协议的比较

WLAN的出现，充分解决了有线网络先天性缺陷所带来的一系列问题。与有线网络相比，WLAN具备了很多特定优势。作为有线局域网的一种补充和扩展，WALN使计算机具有了可移动性，能快速、方便地解决有线网络不易实现的网络连通问题，成为今后网络发展的主导方向。IEEE802．11标准是IEEE制定的无线局域网标准，各厂商的产品在同一物理层上可以互相操作，这样就使得无线局域网的两种主要用途“多点接入”和“多网段互联”更易于低成本实现，从而为无线局域网的进一步普及打通了道路，文中介绍了几个常用标准的特点。     

无线局域网IEEE802.11n标准分析

802.11n是制定中的最新的无线局域网标准.首先介绍了无线局域网以及802.11标准系列的发展历史.然后介绍了802.11n标准的特点和发展现状.通过对WWiSE和TGnSynch两大技术阵营的对比.对802.11n的核心技术进行了分析介绍.最后对未来的802.11n标准做出了预测.     

基于IEEE802.11无线局域网的安全性研究

随着无线局域网的不断发展，网络安全问题日益突出。这里根据无线局域网信道的特点，首先介绍了无线局域网的安全需求，其次，描述了基于IEEE802．11无线局域网标准的有线等效保密（WEP）协议原理，并对WEP协议存在的安全漏洞及其相应的攻击进行了分析，最后，针对这些安全漏洞和攻击提出了增强无线局域网安全性的改进方案。     

E‐MAC: an elastic MAC layer for IEEE 802.11 networks

We present a system for real‐time traffic support in infrastructure and ad hoc IEEE 802.11 networks. The proposed elastic MAC (E‐MAC) protocol provides a distributed transmission schedule for stations with real‐time traffic requirements, while allowing a seamless coexistence with standard IEEE 802.11 clients, protecting best‐effort 802.11 traffic from starvation by means of admission control policies. Our scheduling decisions are based on an ‘elastic’ transmission opportunity (TXOP) assignment which allows for efficient wireless resource usage: whenever a real‐time station does not use the assigned TXOP, the other real‐time stations can take over the unused access opportunity, thus preventing the well‐known inefficiencies of static time division multiple access (TDMA) schemes. Unlike other TDMA‐based solutions for 802.11, E‐MAC does not require a tight synchronization among the participating clients, thus allowing its implementation on commodity WLAN hardware via minor software changes at the client side, and no changes at the access points (APs). We studied the performance of our mechanism via ns‐2 simulations and a mathematical model, showing that it outperforms IEEE 802.11e in terms of throughput, delay, and jitter. We finally provide a proof of concept through the results obtained in a real testbed where we implemented the E‐MAC protocol. Copyright © 2011 John Wiley & Sons, Ltd.     

The IEEE 802.11g standard for high data rate WLANs

Continuous WLAN public acceptance comes with increasing demand for provision of higher data rates. Building on this context, the IEEE published the IEEE 802.11g standard for providing data rates of up to 54 Mb/s at the 2.4 GHz band. This article presents the new features of IEEE 802.11g and, using an open source C++-based simulation tool, evaluates both the performance and effectiveness of these features compared to the older IEEE 802.11 standard versions.     

A novel scheme to prevent MAC layer misbehavior in IEEE 802.11 ad hoc networks

The characteristics of ad hoc networks, such as the absence of infrastructure, dynamic topology, shared wireless medium and resource-constrained environment pose various security challenges. Most of the previous research focused on the detection of the misbehavior after it occurred. However, in this paper we propose a new way of thinking to evade the occurrence of misbehavior. In our scheme, Local Most Trustworthy node (LMT node) is allowed to assign the backoff values to originator, rather than permitting the originator to choose the backoff values by itself. With this MAC layer misbehavior avoidance mechanism, the misuse of the backoff in MAC layer in 802.11 DCF can be prevented.     

A buffer management algorithm for improving up/down transmission congestion protocol fairness in IEEE 802.11 wireless local area networks

The fair allocation of the resources is an important issue in wireless local area network (WLAN) because all wireless nodes compete for the same wireless radio channel. When uplink and downlink transmission congestion protocol (TCP) flows coexist in WLAN, the network service is biased toward the uplink TCP flows, and the downlink TCP flows tend to starve. In this article, we investigate the special up/down TCP unfairness problem and point out that the direct cause is the uplink acknowledgement (ACK) packets occupy most buffer space of access point. We thus propose a buffer management algorithm to ensure the fairness among uplink and downlink TCP flows. In order to limit the greedy behavior of ACK packets, the proposed algorithm adjusts the maximum size of buffer allocated for the ACK packets. Analysis and simulation results show that the proposed solution not only provides the fairness but also achieves 10–20% lower queue delay and higher network goodput than the other solutions. Copyright © 2012 John Wiley & Sons, Ltd.     

IEEE802.11无线网络中一种新的切换技术

作为当前无线局域网的主流标准,IEEE802.11网络提供了种类繁多的服务.然而,由于无线网络的移动性本质,切换技术成为IEEES02.11网络的关键技术.对IEEE802.11无线网络中现有的切换技术进行了研究,分析了可行的改进方向,并实现了一种改进的切换方案.     

Optimal frequency assignment for IEEE 802.11 wireless networks

The performance of wireless local area networks (WLANs) is based on the performance of the corresponding access points (APs). Nowadays, network engineers tend to manually assign data channels (frequencies) for each AP. They only use channels 1, 6, and 11 because no interference exists between these channels. But it will be far more efficient if all 11 channels are used. Therefore, the channel allocation problem becomes a major challenge when deploying WLANs. In this paper, we assume that the location of each AP is known. Our objective is to optimally assign a frequency for each AP such that the throughput is maximized and the interference between the various APs is minimized. We also consider a realistic scenario where the APs are not in line of sight of each other, but on the other hand there are different barriers that separate them. We formulate the problem using integer linear programming (ILP) in order to obtain the optimal frequency assignment (OFA). Then, we propose two efficient heuristic algorithms to achieve the same results. Finally, we evaluate the performance of all techniques and make a comparison between them. Copyright © 2008 John Wiley & Sons, Ltd.     

Propagation delay influence in IEEE 802.11 outdoor networks

Originally, Wireless Local Area Networks served only small indoor areas. Nevertheless, the idea of employing IEEE 802.11 networks in large outdoor environments is a very attractive possibility. IEEE 802.11 technology offers several advantages: the low cost of equipment, its operation in the unlicensed spectrum and its higher data rates. Since the advent of the first IEEE 802.11 standard, a great deal of research has been carried out. So-called Wifi-based Long Distance networks are currently being deployed. In this paper, we study the suitability of employing IEEE 802.11 networks in large outdoor environments without modifying the standard working procedure. In such scenarios, IEEE 802.11 networks should offer coverage ranges of several kilometer, which leads to high propagation delay values. Thus, we analyze the influence of increasing propagation delay in the IEEE 802.11 MAC protocol. To carry out our analysis we present a mathematical model and simulation results. We provide an operating range in which IEEE 802.11 performance is feasible and establish a throughput threshold according to the propagation delay.     

Spare node cooperative method for IEEE 802.11 networks

Most of the existing cooperation methods select relay node(s) mainly based on the channel state information, but do not consider whether the selected relay nodes work or not. If the selected relays are invalidated, the performance of cooperative communication will deteriorate. To resolve the above problem, this paper investigates cooperative communication in IEEE 802.11 networks, and proposes a novel Spare Cooperative Method (SCM). SCM chooses a spare cooperation node to enhance the reliability of communication, and uses an enhanced handshaking mechanism to coordinate the access of source nodes and cooperation nodes to the wireless channel. The performance of SCM is comprehensively analyzed in terms of outage probability and saturated throughput. The analysis shows that SCM improves the performance of IEEE 802.11.     

Route selection in IEEE 802.11 wireless mesh networks

This paper addresses the problem of route selection in IEEE 802.11 based Wireless Mesh Networks (WMNs). Traditional routing protocols choose the shortest path between two routers. However, recent research reveals that there can be enormous differences between links in terms of quality (link loss ratio, interference, noise etc) and therefore selecting the shortest path (hop count metric) is a poor choice. We propose a novel routing metric—Expected Link Performance (ELP) metric for wireless mesh networks which takes into consideration multiple factors pertaining to quality (link loss ratio, link capacity and link interference) to select the best end-to-end route. Simulation based performance evaluation of ELP against contemporary routing metrics shows an improvement in terms of throughput and delay. Moreover, we propose an extension of the metric called ELP-Gateway Selection (ELP-GS) which is an extension meant for traffic specifically oriented towards the gateway nodes in the mesh network. We also propose a gateway discovery protocol which facilitates the dissemination of ELP-GS in the network. Simulation results for ELP-GS show substantial improvement in performance.     

Rate adaptive protocol for multirate IEEE 802.11 networks

In this paper, a rate adaptive protocol AMARF (Adaptive Multirate Auto Rate Fallback) for multirate IEEE 802.11 networks is proposed. In AMARF, each data rate is assigned a unique success threshold, which is a criterion to judge when to switch a rate to the next higher one, and the success thresholds can be adjusted dynamically in an adaptive manner according to the running conditions, such as packet length and channel parameters. Moreover, the proposed protocol can be implemented by software without any change to the current IEEE 802.11 standards. Simulation result shows that AMARF yields significantly higher throughput than other existing schemes including ARF and its variants, in various running conditions.     

Estimating the channel capacity of multi-hop IEEE 802.11 wireless networks

In IEEE 802.11 wireless networks, the residual capacity of the wireless links should be accurately estimated to realize advanced network services such as flow admission control or load balancing. In this paper, we propose an algorithm that estimates the packet delivery failure probability by collecting transmission statistics from nearby nodes, and by using a basic collision detection mechanism. This probability is then used in an analytical model to calculate the maximum allowable traffic needed to reach the saturation condition. We show by simulations that estimation error is within 0.5–5.0%, which is significantly lower than the best performance of prior estimation methods. We also demonstrate that the flow admission control is successfully achieved in a realistic wireless network scenario by the help of accurate link residual bandwidth estimation, where the unsatisfied traffic demand remain bounded at a negligibly low level. A routing algorithm that finds max–min residual bandwidth path between source and destination nodes is also implemented, and simulation results show that the network throughput achieved by this algorithm significantly exceeds that of other popular mesh routing protocols. Finally, we provide test results from the real implementation of our algorithm on 802.11 wireless equipment, which are consistent with the simulations.