Efficient MAC strategies for the IEEE 802.11n wireless LANs

Current IEEE 802.11 wireless local area network (WLAN) standard products can provide up to 54 Mbps raw transmission rate, while non‐standard WLAN products with 108 Mbps have already appeared in the market, and the next generation WLAN will provide much higher transmission rates. However, the medium access control (MAC) was designed for lower data rates, such as 1–2 Mbps, and it is not an efficient MAC. Furthermore, a theoretical throughput limit exists due to overhead and limitations of physical implementations, and therefore increasing transmission rate cannot help a lot. Designing efficient MAC strategies becomes critical and important. In this paper, we introduce and propose a series of efficient MAC strategies to overcome the fundamental overhead, and to improve performance. The protocols and mechanisms include Direct Link Protocol, Without Acknowledgement, Without Retransmissions, Block Acknowledgement Protocol, Concatenation, Packing, Multiple Frame Transmission (versions 1 and 2) and Piggyback. The aim of this paper is to introduce and propose these efficient new MACs not only for current IEEE 802.11 standards (.11a/.11b/.11g), but also for the next generation WLAN with higher speed and higher throughput, especially for IEEE 802.11n. Copyright © 2006 John Wiley & Sons, Ltd.     

Proportional fair throughput allocation in multirate IEEE 802.11e wireless LANs

Under heterogeneous radio conditions, Wireless LAN stations may use different modulation schemes, leading to a heterogeneity of bit rates. In such a situation, 802.11 DCF allocates the same throughput to all stations independently of their transmitting bit rate; as a result, the channel is used by low bit rate stations most of the time, and efficiency is low. In this paper, we propose a more efficient throughput allocation criterion based on proportional fairness. We find out that, in a proportional fair allocation, the same share of channel time is given to high and low bit rate stations, and, as a result, high bit rate stations obtain more throughput. We propose two schemes of the upcoming 802.11e standard to achieve this allocation, and compare their delay and throughput performance. Albert Banchs received his M.Sc. and Ph.D. degrees in Telecommunications from the Technical University of Catalonia in 1997 and 2002, respectively. His Ph.D. received the national award for best thesis on Broadband Networks granted by the Professional Association of Telecommunication Engineers. He worked for the International Computer Science Institute, Berkeley, in 1997, for Telefonica I+D, Madrid, in 1998 and for NEC Network Laboratories, Heidelberg, from 1998 to 2003. Since 2003 he is with the University Carlos III of Madrid. Dr. Banchs is Associate Editor of IEEE Communications Letters and has been TPC member of several conferences and workshops including INFOCOM, ICC, GLOBECOM and QoS-IP. His current research interests include resource allocation, QoS and performance evaluation of wireless and wired networks. Pablo Serrano was born in Tarifa, Spain, on May 17, 1979. He received a M.Sc. degree in Telecommunications from the University Carlos III of Madrid in 2002. Since that date he is a Ph.D. candidate and a lecturer at the Telematics Department of the same university. His current research interests are performance evaluation and resource allocation of WLAN networks. Huw Edward Oliver received his MA degree in Mathematics at Cambridge University (1980), and his MSc (1985) and PhD (1988) in Computer Science at the University College of Wales, Aberystwyth. He joined Hewlett-Packard Laboratories, Bristol in 1989 to work on Software Development Environments. Following a period at HP’s Software Engineering Systems, Colorado in 1992 he returned to HP Labs in 1993 as Senior Member of Technical Staff and worked on real-time fault tolerant telecommunication systems. From 1997 to 2000 he was appointed Manager of Hewlett-Packard’s Internet Research Institute. He worked as Technical Director of the European MMAPPS Project from 2000 to 2002, as Senior Research Fellow at Lancaster University from 2002 to 2004, and as Visiting Professor at University Carlos III of Madrid from 2004 to 2005. Since 2005 he has been Senior Researcher with Ericsson R&D Ireland, Athlone where he is responsible for the next-generation network management architecture.     

Saturation throughput analysis of IEEE 802.11 wireless LANs for a lossy channel

We present a way to estimate the saturation throughput of IEEE 802.11 for a lossy channel. The analysis is based on a new concept of virtual slot, which is used to model the dependence of a station's MAC state on the channel. Simulation results show that the analysis accurately predicts the saturation throughput in DCF mode.     

Adaptive coordination function for IEEE 802.11 wireless LANs

Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF) to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay, and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive throughput and delay performance evaluation of both DCF and PCF.     

Admission control in IEEE 802.11e wireless LANs

Although IEEE 802.11 based wireless local area networks have become more and more popular due to low cost and easy deployment, they can only provide best effort services and do not have quality of service supports for multimedia applications. Recently, a new standard, IEEE 802.11e, has been proposed, which introduces a so-called hybrid coordination function containing two medium access mechanisms: contention-based channel access and controlled channel access. In this article we first give a brief tutorial on the various MAC-layer QoS mechanisms provided by 802.11e. We show that the 802.11e standard provides a very powerful platform for QoS supports in WLANs. Then we provide an extensive survey of recent advances in admission control algorithms/protocols in IEEE 802.11e WLANs. Our survey covers the research work in admission control for both EDCA and HCCA. We show that the new MAC-layer QoS schemes and parameters provided in EDCA and HCCA can be well utilized to fulfill the requirements of admission control so that QoS for multimedia applications can be provided in WLANs. Last, we give a summary of the design of admission control in EDCA and HCCA, and point out the remaining challenges.     

无线局域网IEEE 802.11的一种高效调度方案

深入分析了无线局域网IEEE 802.11系列标准的现有调度方案,提出了一种基于IEEE 802.11e标准中HCF接入模式的高效调度方案SA-Multipoll.设计了调度帧结构和调度时序,推导了满足时延和带宽要求的准入协商和调度效率公式.通过数值计算和仿真结果证实了SA-Multipoll的调度效率高于singlepoll,也高于现有multipoll方案中效率较高的CP-Multipoll方案.     

A 2.4-GHz CMOS receiver for IEEE 802.11 wireless LANs

This paper describes a radio-frequency receiver targeting spread-spectrum wireless local-area-network applications in the 2.4-GHz band. Based on a direct-conversion architecture, the receiver employs partial channel selection filtering, dc offset removal, and baseband amplification. Fabricated in a 0.6-μm CMOS technology, the receiver achieves a noise figure of 8.3 dB, IP₃ of -9 dBm, IP₂ of +22 dBm, and voltage gain of 34 dB while dissipating 80 mW from a 3-V supply     

Designing a fair scheduling mechanism for IEEE 802.11 wireless LANs

A fair scheduling mechanism called distributed elastic round robin (DERR) is proposed in this letter for IEEE 802.11 wireless LANs operated in a distributed manner. To quantify the fairness, we not only derive its fairness bound, but also observe the fairness through ratios of throughput and weight using a simulation approach. By numerical comparisons among DERR, distributed deficit round robin (DDRR), and IEEE 802.11e, we demonstrate that DERR outperforms the other two mechanisms in performance and fairness.     

Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs

IEEE 802.11, the standard of wireless local area networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the distributed coordination function (DCF) and point coordination function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic, as well as user mobility. To expand support for applications with quality-of-service (QoS) requirements, the 802.11E task group was formed to enhance the original IEEE 802.11 medium access control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks remains unsolved. In this paper, we propose a polling with nonpreemptive priority-based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff calls can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period, while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLAN's environment, and can be easily incorporated into the hybrid coordination function (HCF) access scheme in the IEEE 802.11e standard.     

A multichannel relay MAC protocol for IEEE 802.11 wireless LANs

One of the challenging issues in wireless LANs (WLANs) is improving the network throughput. One of the possible solutions for the issue is maximizing the number of concurrent transmissions. Although some protocols have been proposed to exploit transmission concurrency in WLANs, their performance depends on the degree of the interference among links. Also, it is hard to obtain interference information because of their dynamics. In this paper, we propose an enhanced medium access control (MAC) protocol for WLANs, named multichannel relay MAC (MRMAC), which is able to transmit multiple frames simultaneously without considering interference. To enable concurrent transmissions, MRMAC adopts the concept of frame relaying. Furthermore, MRMAC utilizes several nonoverlapping channels to eliminate interferences. Through extensive simulations, we found that MRMAC shows better performance than existing well‐known MAC protocols. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

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.     

Performance analysis and enhancements for IEEE 802.11e wireless networks

The IEEE 802.11 WLAN legacy standard cannot provide QoS support for multimedia applications. Thus, considerable research efforts have been carried out to enhance QoS support for 802.11. Among them, 802.11e is the upcoming QoS-enhanced standard proposed by the IEEE working group. This article describes in detail the new QoS features of 802.11e based on the latest version of the standard draft. We investigate the performance of 802.11e through computer simulations. Using simple examples, we show the effectiveness of adaptive schemes under the 802.11e framework.     

Analysis of flow transfer times in IEEE 802.11 wireless LANs

In this paper we present an integrated packet/flow level modelling approach for analysing flow throughputs and transfer times inieee 802.11wlans. It captures the statistical characteristics of the transmission of individual packets at themac layer and takes into account the system dynamics due to the initiation and completion of data flow transfers. In particular, at the flow level the system is modelled by a processor sharing type of queue, reflecting theieee 802.11mac design principle of distributing the transmission capacity fairly among the active flows. The integrated packet/flow level model is analytically tractable and yields a simple approximation for the throughput and flow transfer time. Extensive simulations show that the approximation is very accurate for a wide range of parameter settings. In addition, the simulation study confirms the attractive property following from our approximation that the expected flow transfer delay is insensitive to the flow size distribution (apart from its mean).     

Goodput analysis and link adaptation for IEEE 802.11a wireless LANs

Link adaptation to dynamically select the data transmission rate at a given time has been recognized as an effective way to improve the goodput performance of the IEEE 802.11 wireless local-area networks (WLANs). Recently, with the introduction of the new high-speed 802.11a physical layer (PHY), it is even more important to have a well-designed link adaptation scheme work with the 802.11a PHY such that its multiple transmission rates can be exploited. In this paper, we first present a generic method to analyze the goodput performance of an 802.11a system under the distributed coordination function (DCF) and express the expected effective goodput as a closed-form function of the data payload length, the frame retry count, the wireless channel condition, and the selected data transmission rate. Then, based on the theoretical analysis, we propose a novel MPDU (MAC protocol data unit)-based link adaptation scheme for the 802.11a systems. It is a simple table-driven approach and the basic idea is to preestablish a best PHY mode table by applying the dynamic programming technique. The best PHY mode table is indexed by the system status triplet that consists of the data payload length, the wireless channel condition, and the frame retry count. At runtime, a wireless station determines the most appropriate PHY mode for the next transmission attempt by a simple table lookup, using the most up-to-date system status as the index. Our in-depth simulation shows that the proposed MPDU-based link adaptation scheme outperforms the single-mode schemes and the autorate fallback (ARF) scheme-which is used in Lucent Technologies' WaveLAN-II networking devices-significantly in terms of the average goodput, the frame drop rate, and the average number of transmission attempts per data frame delivery.     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Adaptive polling algorithm for PCF mode of IEEE 802.11 wireless LANs

An adaptive PCF polling algorithm based on recent polling feedback is proposed to improve the medium utilisation rate of IEEE 802.11 wireless LANs. It is compatible with the IEEE 802.11 standard and requires a simple extension. Simulation studies show that the PCF performance can be improved in terms of the successful poll rate and the aggregate throughput.     

Variable bit rate VOiP in IEEE 802.11e wireless LANs [medium access control protocols for wireless LANs]

WLANs have become a ubiquitous networking technology deployed everywhere. Meanwhile. VoIP is one popular application and a viable alternative to traditional telephony systems due to its cost efficiency. VoIP over WLAN (VoWLAN) has been emerging as an infrastructure to provide low-cost wireless voice services. However, VoWLAN poses significant challenges due to the characteristics of contention-based protocols and wireless networks. In this article we propose two mechanisms to provide quality of service for variable bit rate VoIP in IEEE 802.11e contention-based channel access WLANs: access time-based admission control and access point dynamic access. Simulation results are conducted to study these schemes.     

Timing-synchronization analysis for IEEE 802.11a wireless LANs in frequency-nonselective Rician fading environments

This paper derives and computes the probability of synchronization failure P/sub fail/ for IEEE 802.11a wireless LANs on frequency-flat Rician fading channels. For a frequency offset within /spl plusmn/232 kHz, it is shown that its effect on the synchronization performance is minor. The E/sub ds//N/sub 0/ ratios required to achieve P/sub fail/=10/sup -3/ and 10/sup -4/ are computed, where E/sub ds/ is the data-symbol energy. We find that E/sub ds//N/sub 0/ ratios over 20 dB are generally required for channels with Rician factors K/spl les/6 dB. In particular, E/sub ds//N/sub 0/ ratios that yield P/sub fail/=10/sup -4/ exceed 30 dB for K/spl les/4 dB.     

Performance evaluation of IEEE 802.11-based wireless LANs under finite-load conditions

Since its release in 1999, IEEE 802.11 became the defacto standard for Wireless Local Area Networks (WLANs). Despite its widespread deployment, analytical modeling efforts of the IEEE 802.11 standard have been focusing on the performance under saturated load conditions. This paper aims at analytically modeling and analyzing the performance of the IEEE 802.11-based networks. The model proposed in this paper follows exactly the real implementation of the DCF method. Extensive NS2 simulations are conducted to verify the results of the analytical model. Our model gives a new interpretation for the saturation behavior reported in the literature, relates the critical point (inflection point) to the various system and traffic parameters and analytically explains why the RTS/CTS mechanism is favorable for certain offered loads.