Performance analysis of ONOE protocol—an IEEE 802.11 link adaptation algorithm

Link adaptation (LA) plays an important role in adapting an IEEE 802.11 network to wireless link conditions and maximizing its capacity. However, there is a lack of theoretic analysis of IEEE 802.11 LA algorithms. In this article, we propose a Markov chain model for an 802.11 LA algorithm (ONOE algorithm), aiming to identify the problems and finding the space of improvement for LA algorithms. We systematically model the impacts of frame corruption and collision on IEEE 802.11 network performance. The proposed analytic model was verified by computer simulations. With the analytic model, it can be observed that ONOE algorithm performance is highly dependent on the initial bit rate and parameter configurations. The algorithm may perform badly even under light channel congestion, and thus, ONOE algorithm parameters should be configured carefully to ensure a satisfactory system performance. Copyright © 2011 John Wiley & Sons, Ltd.     

Video transmission strategy in multi-rate and multi-node IEEE 802.11 networks

The video transmission strategy VQCW (video queue contention window) was proposed for video transmission fair problem in multi-rate and multi-node IEEE 802.11 networks.The strategy was based on node queue selective packet drop and contention window dynamic adjustment.It deduced a maximum throughput model according to initial contention window size because of the relation between throughput and initial contention window size.This model can provide theoretical upper limit for improving throughput.The theoretical modeling and NS simulation show that the proposed strategy can maintain both video transmission quality and high network overall throughput.     

基于IEEE 802.11高速无线局域网的速率自适应MAC协议研究

目前的IEEE 802.11标准在物理层提供了对多种发送速率的支持,然而在MAC层却没有规定速率自适应的方法。该文研究了高速IEEE 802.11 无线局域网中的速率自适应方案。首先,提出了EACK协议,EACK使用基本速率发送MAC头,并在ACK帧中携带信道信息,因而能够较快速地响应信道的变化,同时具有少的开销;其次,在EACK基础上,提出了一种恒定发送时间(CEACK)的策略,CEACK能够克服传统IEEE 802.11 DCF MAC协议的理论吞吐量上限,并且具有更好的时间公平性能,能够应用于高速的无线局域网。     

IEEE 802.11中多速率多节点公平的数据分组长度调整策略

在深入剖析多速率机制导致不公平性根源的基础上,提出了基于传输速率的数据分组长度调整(TRPSA)策略,该策略保证了传输速率不同的节点能公平地占用无线信道。理论证明和仿真验证了该策略能有效实现多速率多节点情况下的公平性,显著提高网络性能。该策略只需对IEEE 802.11做细小修改,易于在实际网络中实现和推广。     

基于IEEE802.11r的无线局域网快速切换研究

在IEEE802.11网络中高效地切换是多媒体实时应用的一个关键要求。IEEE802.11r快速切换协议使切换时延得到了有效限制。但整个切换过程仍无法满足实时应用的需求。文中综述了无线局域网快速切换的研究,分析了IEEE802.11r对整个切换过程的影响,并介绍了快速切换研究工作。     

一种IEEE 802.11中慢启动递减的竞争窗口控制算法

本文在研究现有的无线局域网802.11 MAC层拥塞控制的基础上,提出了一种增强的拥塞控制性能的算法,称为"慢启动递减算法"(SSDS:Slow-Start Decrease Scheme).该算法通过修改802.11的MAC层中的DCF(Distributed Coordination Function)子协议,改善了IEEE802.11无线局域网在拥塞情况下的性能,提高了网络吞吐量.文中通过仿真对算法进行了分析和研究.     

一种基于IEEE 802.11的多速率自适应MAC协议

提出了一种新颖的基于连续ACK帧统计信息的IEEE 802.11多速率自适应MAC协议EARF(EnhancedARF),其主要思想是:每一个速率有各自的成功阈值——速率升高的门限值,并且该值根据信道状况(用延时因子量化)动态地变化。协议不需对现有的IEEE 802.11标准做任何修改,因此易于通过编写驱动程序实现。仿真表明在大多数信道条件下,该协议性能较现有的基于ACK帧统计的速率自适应协议如ARF,ARF3-10都有较大的提高。     

Rate adaptation with loss diagnosis on IEEE 802.11 networks

Rate adaptation in wireless networking aims to seek the optimal data transmission rate most appropriate for current wireless channel conditions to make full use of the channel potentials. It is important in wireless networks because (1) most of them support multiple data rates, and (2) wireless channel is unstable with fast changes on which a single rate thereby may not be proper for long. Based on a comprehensive survey of the rate adaptation for IEEE 802.1 networks in literature, this work proposes a rate adaptation scheme, dubbed effective rate adaptation (ERA), for IEEE 802.11 networks. ERA takes advantage of the fragmentation technique in IEEE 802.11 standard and utilizes the lowest rate retransmission in diagnosing frame loss cause (collision or channel degradation), diffusing collision, and promptly recovering frame losses. It also adopts an adaptive rate increase threshold concept to exploit channel potentials. Different from other rate adaptation schemes, ERA effectively addresses two challenges in rate adaptation on IEEE 802.11 networks: (1) it does not require RTS/CTS for loss diagnosis purpose; the use of RTS/CTS that are optional in IEEE standard results in inefficiency on channel utilization; (2) it promptly responds to frame failure due to channel degradation, unlike others waiting till the end of a transmission window or cycle. With extensive simulation, ERA shows its unique strength in different lossy environments, especially in collision‐prone environments. Copyright © 2011 John Wiley & Sons, Ltd.     

Adaptive backoff scheme for ad hoc networks based on IEEE 802.11

The performance of backoff scheme plays an important role in designing efficient Medium Access Protocols for ad hoc networks. In this paper, we propose an adaptive backoff scheme and evaluate the performance of the proposed scheme for ad hoc networks. The backoff mechanism devised by us grants a node access to the channel based on its probability of collision for a transmitted frame in comparison to the nodes in the two‐hop contention area. We use both an analytical model and simulation experiments to evaluate the performance of our adaptive backoff mechanism in an ad hoc network. The results show that our protocol exhibits a significant improvement in power saving, end‐to‐end goodput, packet delivery ratio, and hop‐put, compared with the existing IEEE 802.11 DCF. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance Evaluation,System Design and Network Deployment of IEEE 802.11

This paper presents a system design technique for the IEEE 802.11 Wireless Local Area Network (WLAN) considering the significant parameters namely coverage, cell/frequency planning, interference, power management and data rate. The effect of the parameters on the performance of IEEE 802.11 in terms of throughput has been discussed using measurement and numerical results.These results and concepts are extremely important not only for the system design and deployment of IEEE 802.11 WLANs but also for other indoor wireless communications systems.     

A Distributed Mechanism for Power Saving in IEEE 802.11 Wireless LANs

The finite battery power of mobile computers represents one of the greatest limitations to the utility of portable computers. Furthermore, portable computers often need to perform power consuming activities, such as transmitting and receiving data by means of a random-access, wireless channel. The amount of power consumed to transfer the data on the wireless channel is negatively affected by the channel congestion level, and significantly depends on the MAC protocol adopted. This paper illustrates the design and the performance evaluation of a new mechanism that, by controlling the accesses to the shared transmission channel of a wireless LAN, leads each station to an optimal Power Consumption level. Specifically, we considered the Standard IEEE 802.11 Distributed Coordination Function (DCF) access scheme for WLANs. For this protocol we analytically derived the optimal average Power Consumption levels required for a frame transmission. By exploiting these analytical results, we define a Power Save, Distributed Contention Control (PS-DCC) mechanism that can be adopted to enhance the performance of the Standard IEEE 802.11 DCF protocol from a power saving standpoint. The performance of an IEEE 802.11 network enhanced with the PS-DCC mechanism has been investigated by simulation. Results show that the enhanced protocol closely approximates the optimal power consumption level, and provides a channel utilization close to the theoretical upper bound for the IEEE 802.11 protocol capacity. In addition, even in low load situations, the enhanced protocol does not introduce additional overheads with respect to the standard protocol.     

基于IEEE802.11b的支持QoS的循环偏移轮寻算法

这里提出了一种基于IEEE802.11b无线局域网(WLANs)的支持Qos的循环偏移轮寻算法.和以往的算法相比,该算法通过对连接接入点AP(Access Point)的所有活动终端进行循环偏移轮寻,增加了在CFPR间隔内对语音终端的数量,同时非常有效减少轮寻过程中发生的分组延时和分组丢失率,从而提高了语音数据通信质量QoS.而且算法只在接入点的点协调功能(PCF)上执行,因此不需要对当前的IEEE802.11MAC层的协议做任何修改.仿真结果表明了本算法对WLANs语音服务质量的有效支持.     

基于802．11协议的无线局域网快速切换研究

快速切换是移动管理研究中的重要问题之一,对实现移动终端上的多媒体等实时应用具有重要的意义.综述了基于802.11协议的无线局域网快速切换的研究进展,分析了切换的过程和快速切换的影响因素,并对快速切换研究工作进行了介绍,最后总结了研究现状中存在的问题以及需要进一步研究的工作.     

Throughput Analysis and Admission Control for IEEE 802.11a

We propose a new Markov model for the distributed coordination function (DCF) of IEEE 802.11. The model incorporates carrier sense, non-saturated traffic and SNR, for both basic and RTS/CTS access mechanisms. Analysis of the model shows that the throughput first increases, and then decreases with the number of active stations, suggesting the need for an admission control mechanism.We introduce such a mechanism, which tries to maximize the throughput while maintaining a fair allocation. The maximum achievable throughput is tracked by the mechanism as the number of active stations increases. An extensive performance analysis shows that the mechanism provides significant improvements.Mustafa Ergen received the B.S. degree in electrical engineering from Middle East Technical University (METU) and was the METU Valedictorian in 2000. He received the M.S. and Ph.D. degrees in electrical engineering in 2002 and 2004, the MOT certificate of HAAS Business School in 2003, and the M.A. degree in International and Area Studies in 2004 from the University of California, Berkeley.Dr. Ergen has been conducting research in wireless communication networks with an emphasis on sensor networks, wireless LAN and OFDM systems and is the author of many works in the field, including the book (with A.R.S. Bahai and B.R. Saltzberg) Multi-Carrier Digital Communications: Theory and Applications of OFDM (New York: Springer, 2004).He is National Semiconductor Post Doctoral Fellow and was awarded eight times Bulent Kerim Altay Award by department of electrical engineering in METU and received Best Student Paper Award in IEEE ISCC 2003 and has an invited paper in IEEE GLOBECOM CAMAD 200.Pravin Varaiya is Nortel Networks Distinguished Professor in the Department of Electrical Engineering and Computer Sciences at the University of California, Berkeley. From 1975 to 1992, he was also Professor of Economics at Berkeley. His research is concerned with communication networks, transportation, and hybrid systems. He has taught at MIT and the Federal University of Rio de Janeiro, Varaiya has held a Guggenheim Fellowship and a Miller Research Professorship. He received an Honorary Doctorate from L’Institut National Polytechnique de Toulouse, and the Field Medal of the IEEE Control Systems Society. He is a Fellow of IEEE and a member of the National Academy of Engineering. He is on the editorial board of several journals, including “Discrete Event Dynamical Systems” and “Transportation Research-C.” He has co-authored three books and more than 250 technical papers. The second edition of “High-Performance Communication Networks” (with Jean Walrand) was published by Morgan-Kaufmann in 2000. “Structure and interpretation of signals and systems” (with Edward Lee) was published in 2002 by Addison-Wesley.     

Adaptive QoS Management for IEEE 802.11 Future Wireless ISPs

Wireless Internet Service Providers (WISPs) are expected to be the new generation of access providers using the emerging IEEE 802.11 technology. Face to the high competition of providing network services, the WISP have to offer the best service to the users. For this purpose, the WISP networks' managers need to provide Quality of Service (QoS) with a minimum cost in their wireless networks. The current link layer IEEE 802.11b provides fair sharing of the radio resource with no service differentiation mechanism; similarly to the Internet best effort service. However, the ongoing standard IEEE 802.11e should implement a priority mechanism at the link layer to differentiate the users' traffic. In order to overcome the lack of differentiated mechanism in the current link layer IEEE 802.11b, hence controlling the utilization of the scarce radio resource, we propose in this article to deploy Diffserv architecture coupled with an adaptive provisioning of QoS to provide better services to the users with minimum WISP cost and improve the utilization of the radio resource. Compliant with the current and future IEEE 802.11 link layer, the proposed adaptive QoS provisioning mechanism reacts to the radio resource fluctuation and improves the number of accepted clients in the IEEE 802.11 wireless cells based on the WISP business policies. The network layer differentiation provided by the Diffserv architecture intends to control the concurrent access of the traffic to the scarce radio resources at the IP layer of the mobile hosts for the uplink traffic on one hand, and at the IP layer of the base stations for the downlink traffic on the other hand.     

On Improving the Performance of IEEE 802.11 with Relay-Enabled PCF

Integrating wireless LAN (WLAN) techniques with the third generation cellular networks has become a promising way to improve the performance of wireless systems. As WLANs play an important role in such heterogeneous systems, the performance of WLANs becomes important to the whole system. It is well known that WLANs provide a physical layer multi-rate capability, and hence MAC layer mechanisms are needed to exploit this capability. In this paper, we propose a novel MAC layer relay-enabled point coordination function (PCF) protocol, called rPCF, to exploit the physical layer multi-rate capability. Since WLAN supports multiple data rates in response to different channel conditions, data packets may be delivered faster through a relay node than through the direct link if the direct link has low quality and low rate. To enable MAC layer relay, the access point needs to collect information about the channel conditions, and notify the mobile nodes which data rate to use and whether to transmit the data through a relay station. We design protocols to achieve this goal and refine these protocols to minimize the control overhead. Simulation results show that rPCF can significantly improve the system performance in terms of system throughput and transmission delay by adding only a negligible control overhead.     

IEEE 802.11中MAC子层切换过程分析

IEEE 802．11中MAC运行的关键是其切换功能，即当一个移动节点将它的联结从一个接入点转移到另一个接入点的过程。介绍了关于链接层中这种切换过程的实验方法，对延迟的多种原因进行分析，指出了MAC子层的功能探测是全部切换延迟的主要原因。     

IEEE802.11 DCF中基于能耗最小的RTS门限自适应调整算法

该文通过数学模型分析IEEE 802.11网络中,终端采用分布式协调功能(DCF)方式发送一个数据包消耗的平均能量。研究发现,存在一个使终端发送的平均能耗最小的最佳RTS门限,它与终端的平均重传次数直接相关。在此基础上,该文提出了一个RTS门限调整算法。计算机仿真结果证明该算法能使终端根据网络环境自适应地调整RTS门限到最佳值,从而减少发送过程中的能量消耗。     

Analytical Study of TCP Performance over IEEE 802.11e WLANs

IEEE 802.11 Wireless LAN (WLAN) has become a prevailing solution for broadband wireless Internet access while the Transport Control Protocol (TCP) is the dominant transport-layer protocol in the Internet. Therefore, it is critical to have a good understanding of the TCP dynamics over WLANs. In this paper, we conduct rigorous and comprehensive modeling and analysis of the TCP performance over the emerging 802.11e WLANs, or more specifically, the 802.11e Enhanced Distributed Channel Access (EDCA) WLANs. We investigate the effects of minimum contention window sizes and transmission opportunity (TXOP) limits (of both the AP and stations) on the aggregate TCP throughput via analytical and simulation studies. We show that the best aggregate TCP throughput performance can be achieved via AP’s contention-free access for downlink packet transmissions and the TXOP mechanism. We also study the effects of some simplifying assumptions used in our analytical model, and simulation results show that our model is reasonably accurate, particularly, when the wireline delay is small and/or the packet loss rate is low.

A survey and comparison of multichannel protocols for performance anomaly mitigation in IEEE 802.11wireless networks

Providing multichannel functionality can improve the performance of wireless networks. Although off‐the‐shelf IEEE 802.11 physical layer and medium access control specifications support multiple channels and multiple data rates, one of the major challenges is how to efficiently utilize available channels and data rates to improve network performance. In multirate networks, low‐rate links severely degrade the capacity of high‐rate links, which is known as performance anomaly. To overcome the performance anomaly problem, different data rate links can get equal air‐time by exploiting time diversity and frequency diversity, or they can be separated over nonoverlapping channels. In this paper, we study existing multichannel protocols proposed to mitigate the performance anomaly problem by classifying them into single‐radio protocols, multiradio single‐hop protocols, and multiradio multihop protocols. To investigate the effectiveness of multichannel solutions for performance anomaly, we compare these protocols with well‐known multichannel protocols that do not consider performance anomaly. In addition, this paper gives insightful research issues to design multichannel protocols that mitigate performance anomaly in IEEE 802.11 wireless networks. Copyright © 2012 John Wiley & Sons, Ltd.