A survey of QoS enhancements for IEEE 802.11 wireless LAN

Quality‐of‐service (QoS) is a key problem of today's IP networks. Many frameworks (IntServ, DiffServ, MPLS etc.) have been proposed to provide service differentiation in the Internet. At the same time, the Internet is becoming more and more heterogeneous due to the recent explosion of wireless networks. In wireless environments, bandwidth is scarce and channel conditions are time‐varying and sometimes highly lossy. Many previous research works show that what works well in a wired network cannot be directly applied in the wireless environment. Although IEEE 802.11 wireless LAN (WLAN) is the most widely used IEEE 802.11 wireless LAN (WLAN) standard today, it cannot provide QoS support for the increasing number of multimedia applications. Thus, a large number of 802.11 QoS enhancement schemes have been proposed, each one focusing on a particular mode. This paper summarizes all these schemes and presents a survey of current research activities. First, we analyze the QoS limitations of IEEE 802.11 wireless MAC layers. Then, different QoS enhancement techniques proposed for 802.11 WLAN are described and classified along with their advantages/drawbacks. Finally, the upcoming IEEE 802.11e QoS enhancement standard is introduced and studied in detail. Copyright © 2004 John Wiley & Sons, Ltd.     

A novel performance analysis model for an IEEE 802.11 wireless LAN

This letter presents a novel analytic model that accurately evaluates the performance of a single-hop IEEE 802.11 wireless LAN (WLAN). By using a closed queuing network, we model an IEEE 802.11 WLAN system that consists of a fixed number of stations and derive the saturated throughput of the IEEE 802.11 distributed coordination function (DCF). The ns-2 simulation results show that our new analysis model is very accurate in evaluating the performance of the IEEE 802.11 DCF.     

无线局域网 IEEE802.11 高性能局域网统一信息系统

无线局域网标准 IEEE802.11是第一代无线局域网标准之一。 1990年 IEEE802标准化委员会成立 802.11无线局域网 (WLAN)标准工作组。 802.11无线局域网标准工作组任务为研究 1Mbit/s和 2Mbit/s数据速率、工作在 2.4GHz开放频段的无线设备和网络发展的全球标准,并于 1997年 6月公布了该标准。该标准定义物理层和媒体访问控制 (MAC)规范,允许无线局域网及无线设备制造商建立互操作网络设备。 　　IEEE 802.11标准中物理层定义了数据传输的信号特征和调制。在物理层中,定义了两种 RF传输方法和一种红外线传输方法。在该标准中, RF传输采用扩频方法,即采用了跳频扩频 (FHSS)和直接序列扩频 (DSSS)两种方法,工作在 2.4000GHz～ 2.4835GHz频段。     

A 5-GHz CMOS transceiver for IEEE 802.11a wireless LAN systems

A 5-GHz transceiver comprising the RF and analog circuits of an IEEE 802.11a-compliant WLAN has been integrated in a 0.25-/spl mu/m CMOS technology. The IC has 22-dBm maximum transmitted power, 8-dB overall receive-chain noise figure and -112-dBc/Hz synthesizer phase noise at 1-MHz frequency offset.     

Design and implementation of a MAC controller for the IEEE802.11 wireless LAN

IEEE 802.11 wireless LANs have a tremendous market potential, as they support high data rates, work in the world-wide licence free 2.4 GHz ISM band and have high performance in terms of range and power consumption. Hence, the development of a communication processor that supports the IEEE 802.11 MAC functions has a significant potential, making very important the concept of having an ASIC ‘right from the first time’, in order to minimize development cost and to meet short time-to-market requirements. This paper presents the methodology of developing such a component with emphasis on the rapid prototyping approach. The chip architecture, which is based on an ARM processor core, is described in detail, focusing on the implementation of the protocol functions using custom hardware modules. Finally, the paper presents experimental results on the ASIC implementation.     

Performance analysis of MAC layer protocols in the IEEE 802.11 wireless LAN

In recent years, WLANs (Wireless Local Area Networks) based on the IEEE 802.11 standard have been taken a growing interest and developed widely all over the world. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocols are the most popular MAC (Medium Access Control) protocols for WLANs. The performance of CSMA/CA protocols over wireless channels has been investigated over the past years. In this paper, we obtain the probability distribution function of the MAC layer packet service time, and we present the comprehensive performance analysis of IEEE 802.11 MAC protocol by investigating the queue dynamics of a wireless station based on the MAC layer packet service time. We adopt an MMPP(Markov Modulated Poisson Process) as the input traffic model that describes well the bursty nature of Internet traffic. The analysis on the throughput and the delay performance has been carried out by using the MMPP/G/1/K queueing model. We have some numerical results that represent the system throughput and the queue dynamics including the mean packet waiting time and packet blocking probability.     

基于分组到达率的IEEE802.11无线局域网区分服务方法

本文针对IEEE 802.11无线局域网提出了一种基于分组到达率的区分服务实现方法,建立了一种基于二维马尔可夫链的分析模型,结果表明,在控制网络总的负荷的情况下,该方法可有效实现吞吐量的区分并且能够为各个业务流提供统计意义上的吞吐量保证.另外,该方法易于实现而且不需要对IEEE 802.11硬件做任何改动.仿真实验结果表明分析模型相当准确.     

IEEE802.11无线局域网标准

介绍了IEEE802.11无线局域网技术规范.给出了ISM频段、扩频技术的背景及各国相应的标准、规范.描述了允许可证2.4GHzISM频段的直接序列扩频技术及IEEE802.11协议规范。     

Analysis of IEEE 802.11e for QoS support in wireless LANs

The IEEE 802.11e medium access control protocol is an emerging standard for wireless local area networks providing quality of service. An overview of this standard based on the current draft is presented on this article. We analyze the enhancements in 802.11 standard. The new hybrid coordination function of the IEEE 802.11e with its contention-based and contention-free (controlled) medium access control schemes is evaluated. The capability to provide QoS support is discussed by means of simulations.     

IEEE 802.11 roaming and authentication in wireless LAN/cellular mobile networks

A wireless LAN service integration architecture based on current wireless LAN hot spots is proposed so that migration to a new service becomes easier and cost effective. The proposed architecture offers wireless LAN seamless roaming in wireless LAN/cellular mobile networks. In addition, a link-layer-assisted mobile IP handoff mechanism is introduced to improve the network/domain switching quality in terms of handoff delay and packet loss. An application layer end-to-end authentication and key negotiation scheme is proposed to overcome the open-air connection problem existing in wireless LAN deployment. The scheme provides a general solution for Internet applications running on a mobile station under various authentication scenarios and keeps the communications private to other wireless LAN users and foreign network. A functional demonstration of the scheme is given. The research results can contribute to rapid deployment of wireless LANs.     

Quality of service support in IEEE 802.11 wireless ad hoc networks

Supporting Quality of Service (QoS) in wireless networks is a challenging problem. The IEEE 802.11 LAN standard was developed primarily for elastic data applications. In order to support the transmission of real-time data, a polling-based scheme called the point coordination function (PCF) was introduced in IEEE 802.11. However, PCF was not able to meet the desired and practical service differentiation requirements to fulfill the need of real-time data. Therefore, Task Group E of the IEEE 802.11 working group released several IEEE 802.11e drafts, whose main task is to support QoS in IEEE 802.11 LANs. The polling scheme of PCF is extended in IEEE 802.11e into the more complex hybrid coordination function (HCF). We found that HCF has several performance issues that may affect its anticipated performance. In this paper, we address these issues and propose a QoS enhancement over PCF, called enhanced PCF (EPCF) that enables Wireless LAN to send a combination of voice, data and isochronous data packets using the current IEEE 802.11 PCF. First, we compare the performance of the proposed model (EPCF) with the HCF function of the IEEE 802.11e through simulation. Second, we extend the proposed model (EPCF) to work in a multihop wireless ad hoc mode and present the advantages and limitations in this case. Simulation results demonstrate an enhanced performance of our scheme over the legacy PCF and a comparable performance to the IEEE 802.11e HCF in terms of the average delay and system throughput. However, EPCF is much simpler than HCF, provides flow differentiation, and is easy to implement in the current IEEE 802.11 standard.     

Wireless LAN security and IEEE 802.11i

This article reviews wireless LAN security with a focus on the evolving new IEEE 802.11i standard. The major security enhancements in encryption and authentication defined by 802.11i are illustrated. In addition, the newly introduced key management in 802.11i is discussed. Because 802.11i incorporates IEEE 802.1X as its authentication enhancement, 802.1X with consideration of roaming users is depicted. Both intrasubnet and intersubnet roaming are illustrated.     

A novel link adaptation scheme to enhance performance of IEEE 802.11g wireless LAN

A novel link adaptation scheme using linear Auto Regressive （AR） model channel estimation algorithm to enhance the performance of auto rate selection mechanism in IEEE 802.11g is proposed. This scheme can overcome the low efficiency caused by time interval between the time when Received Signal Strength （RSS） is measured and the time when rate is selected. The best rate is selected based on data payload length, frame retry count and the estimated RSS, which is estimated from recorded RSSs. Simulation results show that the proposed scheme enhances mean throughput performance up to 7%, in saturation state, and up to 24% in finite load state compared with those non-estimation schemes, performance enhancements in average drop rate and average number of transmission attempts per data frame delivery also validate the effectiveness of the proposed schelne.     

A single-chip dual-band tri-mode CMOS transceiver for IEEE 802.11a/b/g wireless LAN

A single-chip dual-band tri-mode CMOS transceiver that implements the RF and analog front-end for an IEEE 802.11a/b/g wireless LAN is described. The chip is implemented in a 0.25-/spl mu/m CMOS technology and occupies a total silicon area of 23 mm/sup 2/. The IC transmits 9 dBm/8 dBm error vector magnitude (EVM)-compliant output power for a 64-QAM OFDM signal. The overall receiver noise figure is 5.5/4.5 dB at 5 GHz/2.4 GHz. The phase noise is -105 dBc/Hz at a 10-kHz offset and the spurs are below -64 dBc when measured at the 5-GHz transmitter output.     

Packet Delay Metrics for IEEE 802.11 Distributed Coordination Function

In this paper, we introduce a comprehensive packet delay analysis for wireless networks based on IEEE 802.11 Distributed Coordination Function (DCF). We develop mathematical models that calculate a set of packet delay metrics, namely a) the average packet delay for successfully transmitted packets, b) the average packet delay of successfully transmitted packets experiencing a specific number of collisions, c) the average packet drop time, d) the delay jitter and e) the delay distribution by computing the probability of a packet to be successfully transmitted experiencing delay time lower than a given value. All the developed models are based on calculating station’s delay time at the transmission slot(s) plus the average time that station defers at backoff slots before successful transmission. The mathematical models are simple, computationally fast and can be used to build admission control algorithms. Simulation results show that our proposed mathematical analysis is highly accurate.     

A delay-based admission control mechanism for multimedia support in IEEE 802.11e wireless LANs

Multimedia over IEEE 802.11 wireless local area networks (WLANs) has recently been the focus of many researchers due to its rapidly increasing popularity. Unlike their best-effort counterparts, multimedia applications have quality of service (QoS) needs typically expressed in terms of the maximum allowed delay and/or the minimum required throughput. Therefore, prior to accepting a multimedia application, the network must assure the satisfaction of its QoS requirements. In this paper, we develop a mechanism that can be used to control the admissibility of multimedia applications into WLANs. To develop the proposed mechanism, we first derive an analytical approximation of the delay experienced by packets when travelled through these networks. The analytical approximation of the delay is then used to propose an admission control mechanism for the enhanced distributed channel access (EDCA) method used by the hybrid coordination function (HCF) of IEEE 802.11e. The proposed delay-based admission control mechanism is validated via simulations of voice traffic.     

A 5-GHz direct-conversion CMOS transceiver utilizing automatic frequency control for the IEEE 802.11a wireless LAN standard

A fully integrated CMOS direct-conversion 5-GHz transceiver with automatic frequency control is implemented in a 0.18-/spl mu/m digital CMOS process and housed in an LPCC-48 package. This chip, along with a companion baseband chip, provides a complete 802.11a solution The transceiver consumes 150 mW in receive mode and 380 mW in transmit mode while transmitting +15-dBm output power. The receiver achieves a sensitivity of better than -93.7dBm and -73.9dBm for 6 Mb/s and 54 Mb/s, respectively (even using hard-decision decoding). The transceiver achieves a 4-dB receive noise figure and a +23-dBm transmitter saturated output power. The transmitter also achieves a transmit error vector magnitude of -33 dB. The IC occupies a total die area of 11.7 mm/sup 2/ and is packaged in a 48-pin LPCC package. The chip passes better than /spl plusmn/2.5-kV ESD performance. Various integrated self-contained or system-level calibration capabilities allow for high performance and high yield.     

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.     

QoS provided by the IEEE 802.11 wireless LAN to advanced data applications: a simulation analysis

IEEE 802.11 is a Media Access Control (MAC) protocol which has been standardized by IEEE for Wireless Local Area Networks (WLANs). The IEEE 802.11 MAC protocol offers two types of services to its users: synchronous and asynchronous. This paper presents an in‐depth analysis, by simulation, of the asynchronous part alone. The analysis is performed by considering station data traffic patterns (hereafter advanced data traffic) which have a very similar shape to traffic generated by WWW applications. We carried out the simulation by taking into consideration two classes of scenarios: balanced and unbalanced. In the former class each station has the same offered load while in the latter class a specific station is more loaded than the others. Our conclusion is that the IEEE 802.11 MAC protocol performs satisfactorily for both classes of scenarios, although performance measures with advanced traffic are worse than the corresponding performance measures with Poissonian traffic. Furthermore, we broadened our analysis to include higher medium capacities than those planned (i.e., 1 and 2 Mbit/sec) up to 10 Mbit/sec. This part of the analysis shows that the IEEE 802.11 MAC protocol is not adequate to work at speeds planned for the forthcoming ATM Wireless LAN. This revised version was published online in August 2006 with corrections to the Cover Date.