QoS guarantee and provisioning at the contention-based wireless MAC layer in the IEEE 802.11e wireless LANs

This article investigates and provides novel solutions for a new research avenue to support QoS in contention-based distributed WLANs. Although QoS is easier to manage in centrally controlled and reservation-based MAC protocols, they are hardly implemented in today's products due to several reasons, such as their higher complexity and their inefficiency for normal data transmissions, lack of robustness, and the strong assumption of global synchronizations. Additionally, end users like contention-based protocols because they plug and play. Almost all end-user networks need a MAC layer, and the IEEE 802.11 WLAN and Ethernet have become widely deployed since these contention-based MAC protocols are simple, robust, and allow fast installation with minimal management and maintenance costs. There is a clear need to support QoS guarantees and provisioning at the contention-based MAC layer. QoS guarantee and bandwidth allocation schemes have been well studied for mobile cellular networks, in which bandwidth is deterministic in terms of number of channels by frequency division, time division, or code division. On the other hand, bandwidth allocation in contention-based distributed WLANs is extremely challenging due to the contention constraint, the packet-based network, and, most important, an unknown number of stations competing for access to the only channel available. As a consequence, both guaranteeing QoS and efficiently allocating bandwidth are challenging issues.     

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.     

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.     

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.     

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.     

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.     

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     

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.     

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.     

IEEE 802.11n: enhancements for higher throughput in wireless LANs

This article introduces a new standardization effort, IEEE 802.11n, an amendment to IEEE 802.11 standards that is capable of much higher throughputs, with a maximum throughput of at least 100 Mb/s, as measured at the medium access control data services access point. The IEEE 802.11n will provide both physical layer and MAC enhancements. In this article we introduce some PHY proposals and study the fundamental issue of MAC inefficiency. We propose several MAC enhancements via various frame aggregation mechanisms that overcome the theoretical throughput limit and reach higher throughput. We classify frame aggregation mechanisms into many different and orthogonal aspects, such as distributed vs. centrally controlled, ad hoc vs. infrastructure, uplink vs. downlink, single-destination vs. multi-destination, PHY-level vs. MAC-level, single-rate vs. multirate, immediate ACK vs. delayed ACK, and no spacing vs. SIFS spacing.     

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).     

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.     

A call admission and rate control scheme for multimedia support over IEEE 802.11 wireless LANs

Quality of service (QoS) support for multimedia services in the IEEE 802.11 wireless LAN is an important issue for such WLANs to become a viable wireless access to the Internet. In this paper, we endeavor to propose a practical scheme to achieve this goal without changing the channel access mechanism. To this end, a novel call admission and rate control (CARC) scheme is proposed. The key idea of this scheme is to regulate the arriving traffic of the WLAN such that the network can work at an optimal point. We first show that the channel busyness ratio is a good indicator of the network status in the sense that it is easy to obtain and can accurately and timely represent channel utilization. Then we propose two algorithms based on the channel busyness ratio. The call admission control algorithm is used to regulate the admission of real-time or streaming traffic and the rate control algorithm to control the transmission rate of best effort traffic. As a result, the real-time or streaming traffic is supported with statistical QoS guarantees and the best effort traffic can fully utilize the residual channel capacity left by the real-time and streaming traffic. In addition, the rate control algorithm itself provides a solution that could be used above the media access mechanism to approach the maximal theoretical channel utilization. A comprehensive simulation study in ns-2 has verified the performance of our proposed CARC scheme, showing that the original 802.11 DCF protocol can statically support strict QoS requirements, such as those required by voice over IP or streaming video, and at the same time, achieve a high channel utilization. Hongqiang Zhai received the B.E. and M.E. degrees in electrical engineering from Tsinghua University, Beijing, China, in July 1999 and January 2002 respectively. He worked as a research intern in Bell Labs Research China from June 2001 to December 2001, and in Microsoft Research Asia from January 2002 to July 2002. Currently he is pursuing the PhD degree in the Department of Electrical and Computer Engineering, University of Florida. He is a student member of IEEE. Xiang Chen received the B.E. and M.E. degrees in electrical engineering from Shanghai Jiao Tong University, Shanghai, China, in 1997 and 2000, respectively, and the Ph.D. degree in electrical and computer engineering from the University of Florida, Gainesville, in 2005. He is currently a Senior Research Engineer at Motorola Labs, Arlington Heights, IL. His research interests include resource management, medium access control, and quality of service (QoS) in wireless networks. He is a Member of Tau Beta Pi and a student member of IEEE. Yuguang Fang received a Ph.D degree in Systems and Control Engineering from Case Western Reserve University in January 1994, and a Ph.D degree in Electrical Engineering from Boston University in May 1997. From June 1997 to July 1998, he was a Visiting Assistant Professor in Department of Electrical Engineering at the University of Texas at Dallas. From July 1998 to May 2000, he was an Assistant Professor in the Department of Electrical and Computer Engineering at New Jersey Institute of Technology. In May 2000, he joined the Department of Electrical and Computer Engineering at University of Florida where he got the early promotion with tenure in August 2003 and has been an Associate Professor since then. He has published over one hundred (100) papers in refereed professional journals and conferences. He received the National Science Foundation Faculty Early Career Award in 2001 and the Office of Naval Research Young Investigator Award in 2002. He is currently serving as an Editor for many journals including IEEE Transactions on Communications, IEEE Transactions on Wireless Communications, IEEE Transactions on Mobile Computing, and ACM Wireless Networks. He is also actively participating in conference organization such as the Program Vice-Chair for IEEE INFOCOM’2005, Program Co-Chair for the Global Internet and Next Generation Networks Symposium in IEEE Globecom’2004 and the Program Vice Chair for 2000 IEEE Wireless Communications and Networking Conference (WCNC’2000).     

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.     

A practical QoS solution to voice over IP in IEEE 802.11 WLANs - [topics in design & implentation]

In this article we study the behavior of voice over IP traffic in IEEE 802.11 wireless networks. Specifically, we design a QoS provisioning mechanism for VoIP traffic, and propose a practical solution of configuring the 802.11e enhanced distributed control access parameter sets for different types of traffic. We show that media access control layer only methods may be insufficient, but the demonstrated cross-layer (layers 2, 3, and 4) method works simply and efficiently. We find that the EDCA parameter sets of the access point are not always necessarily set more aggressively than those of wireless stations even though the traffic load of AP is much heavier than the stations. With our mechanism, the EDCA parameter sets can be easily configured via software interface for off-theshelf WiFi phone products, and there is no need to modify the operations of APs or 802.11 MAC layer protocols. The performance of our mechanism is evaluated via ns-2 simulations and via laboratory experiments over Quanta?s O2 dual mode handsets. The results show our mechanism can provide effective and efficient QoS provisioning for VoIP traffic in IEEE 802.11 WLANs. Since the configuration may be readily configured in the field and the performance is robust across a wide range of environments, we believe that organizations deploying and operating WiFi networks for VoIP may benefit from our work and reduce or eliminate post-deployment tuning and debugging.     

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.     

The Performance Evaluation of IEEE 802.11e for QoS Support in Wireless LANs

During the past few years the widespread use of the wireless local area networks (WLANs) communication technique is one of the most popular technologies in data telecommunications and networking. With the increasing variety of multimedia applications, it is needed to develop a mechanism for the quality of service (QoS) to support different types of traffic. The IEEE 802.11 protocol has achieved worldwide acceptance with WLANs with minimum management and maintenance costs. However, IEEE 802.11 can only provide a best effort service and does not support the QoS. In this paper, we pay attention to the enhanced distributed coordination function (EDCF) of WLANs. First, we modify the Ziouva and Antonakopoulous’s (ZA’s) model and then extend the model to support EDCF. We study the behavior of the station within a Markov chain model, and present a more accurate analysis of the EDCF and also study the saturation throughput when the maximum load that the system can support is reached. The numerical results show that the modified model has a better performance than the ZA’s model under an ideal channel scenario.     

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.