IEEE802.11无线局域网中一种支持业务区分的回退算法

支持QoS的MAC机制是WLAN支持QoS的关键所在.我们已经给出了一种低分组碰撞概率的MAC层回退机制——RWBO+BEB.该文进一步讨论如何让RWBO+BEB支持业务区分的问题.首先提出了一个Markov链模型,分析如何根据无线终端的带宽比率设置最小竞争窗口,然后给出了一种新的支持业务区分的回退算法——DS-RWBO,仿真结果表明,DS-RWBO能根据局域网中每个终端的带宽比率分配无线信道的带宽资源.     

Defining and maximizing PPT—a novel performance parameter for IEEE 802.11 DCF

Much research has been conducted on saturation throughput of IEEE802.11 DCF, and has led to some improvement. But increasing the successful transmission probability of packet is also important for saving stations' battery energy and decreasing the packet delay. In this paper, we define a new performance parameter, named Product of successful transmission Probability and saturation Throughput (PPT), for 802.11 DCF, which binds successful transmission probability and saturation throughput together. An analysis is given to maximize PPT. An expression of optimal minimum contention windows (CW_min) is obtained analytically for maximizing PPT. For simplicity, we give a name DCF‐PPT to the 802.11 DCF that sets its CW_min according to this expression. The performance of DCF‐PPT is simulated with different stations in terms of saturation throughput, successful transmission probability and PPT. The simulation results indicate that, compared to 802.11 DCF, DCF‐PPT can significantly increase the PPT and successful transmission probability (about 0.95) on condition that the saturation throughput is not decreased. Copyright © 2006 John Wiley & Sons, Ltd.     

A smart exponential‐threshold‐linear backoff mechanism for IEEE 802.11 WLANs

Based on the standardized IEEE 802.11 Distributed Coordination Function (DCF) protocol, this paper proposes a new backoff mechanism, called Smart Exponential‐Threshold‐Linear (SETL) Backoff Mechanism, to enhance the system performance of contention‐based wireless networks. In the IEEE 802.11 DCF scheme, the smaller contention window (CW) will increase the collision probability, but the larger CW will delay the transmission. Hence, in the proposed SETL scheme, a threshold is set to determine the behavior of CW after each transmission. When the CW is smaller than the threshold, the CW of a competing station is exponentially adjusted to lower collision probability. Conversely, if the CW is larger than the threshold, the CW size is tuned linearly to prevent large transmission delay. Through extensive simulations, the results show that the proposed SETL scheme provides a better system throughput and lower collision rate in both light and heavy network loads than the related backoff algorithm schemes, including Binary Exponential Backoff (BEB), Exponential Increase Exponential Decrease (EIED) and Linear Increase Linear Decrease (LILD). Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative Study of 802.11 DCF and its Modification in the Presence of Noise

IEEE 802.11 specifies a technology for wireless local area networks (LANs) and mobile networking. In this paper, we present an analytical method of estimating the saturation throughput of a 802.11 wireless LAN in the presence of noise, which distorts transmitted frames. With the Distributed Coordination Function (DCF) being the fundamental access mechanism in the IEEE 802.11 MAC protocol, sequential attempts to transfer by every station are separated by backoff intervals. Besides the standard backoff rule of the DCF, according to which the mean backoff interval is doubled after each failure in order to avoid collisions, we propose and study a modification of the backoff rule. This modification relies on the optional 802.11 tools to recognize a reason of a failure (collision or noise-induced distortion) and does not increase the mean backoff interval if a failure happens due to distortion by noise. In addition to the throughput, our method allows estimating a probability of a packet rejection occurring when the number of packet transmission retries attains its limit. The obtained numerical results of investigating 802.11 LANs by the developed method are validated by simulation and show high estimation accuracy for any values of protocol parameters and bit error rates. We adopt this method to tune the protocol parameters and to compare the proposed modification with the standard backoff rule. This work was partially supported by NATO Science Programme in the Collaborative Linkage Grant PST.CLG.977405 “Wireless Access to Internet exploiting the IEEE 802.11 technology”. Andrey I. Lyakhov is a leading researcher of the Institute for Information Transmission Problems of Russian Academy of Sciences, Moscow, Russia. Since 1982, his research interests have been in performance evaluation of parallel and distributed computer and communication systems, including multiprocessors and local area cable networks, using both queuing theory methods and asymptotic analysis of large scale queuing networks. His recent interest is in estimating the performance indices of local and metropolitan area wireless networks. Dr. Lyakhov received a M.S. degree in computer science from Moscow Engineering and Physics Institute in 1983, and Candidate and Doctoral Degrees in computer science from the Institute of Control Sciences of Russian Academy of Sciences (Moscow, Russia) in 1989 and 1996, respectively. He has written a textbook in multiprocessor study and published more than 50 papers in refereed journals and conferences. Vladimir M. Vishnevsky is a full professor, and a deputy director and a head of department of the Institute for Information Transmission Problems of Russian Academy of Sciences, Moscow, Russia. Since 1971, his principal research interests have been in developing mathematical methods based on the queuing theory for performance analysis and structure optimization of computer and communication systems and networks. His current interests include topological design of large-scale communication networks and performance evaluation of wireless networks. Prof. Vishnevsky received a M.S. degree in computer science from Moscow Institute of Electronic and Mathematics in 1971, and Candidate and Doctoral Degrees in computer science from the Institute of Control Sciences of Russian Academy of Sciences (Moscow, Russia) in 1974 and 1989, respectively. He has written three textbooks in communication network study and design and published more than 100 papers in refereed journals and conferences. He is an associate member of the IEEE and an active member of the New York Academy of Sciences. In addition to serving as a program committee member of various conferences, Prof. Vishnevsky serves as a member of editorial boards of such journals as Automation and Remote Control and Electronica (in Russian).     

IEEE 802.11 DCF性能分析及改进

本文通过对IEEE 802.11 DCF的性能分析,发现其在时隙选择概率分布上具有明显的不均匀性,这导致了很高的包碰撞概率.本文给出了一种简单的改进方案——A-DCF.通过理论与仿真比较,证明了A-DCF能有效改进DCF时隙选择概率分布的不均匀性,同时,在不降低系统饱和吞吐量的情况下,A-DCF能明显降低包的碰撞概率,且对网络负荷具有自适应能力.     

Analysis and Optimization of the Energy Efficiency in the 802.11 DCF

This paper introduces an analytical model to investigate the energy efficiency of the IEEE 802.11 distributed coordinated function (DCF). This model not only accounts for the number of contending nodes, the contention window, but also the packet size, and the channel condition. Based on this model, we identify the tradeoff in choosing optimum parameters to optimize the energy efficiency of DCF in the error-prone environment. The effects of contention window and packet size on the energy efficiency are examined and compared for both DCF basic scheme and DCF with four-way handshaking. The maximum energy efficiency can be obtained by combining both the optimal packet size and optimal contention window. To validate our analysis, we have done extensive simulations in ns-2, and simulation results seem to match well with the presented analytical results. The Ohio Board of Regents Doctoral Enhancements Funds and the National Science Foundation under Grant CCR 0113361 have supported this work. Xiaodong Wang received his B.S. degree in communication engineering from Beijing Information Technical Institute of China in 1995, and his M.S. degree in electric engineering from Beijing University of Aeronautics and Astronautics of China in 1998. He joined China Telecom in 1998 where he worked on communication protocols for telecommunication. From June 2000 to July 2002, he worked on GSM base station software development at Bell-labs China, Beijing, China. Currently he is a Ph.D. student in Computer Engineering at University of Cincinnati. His research activities include wireless MAC protocols, energy saving for wireless sensor networks. He is a student member of the IEEE. Jun Yin received the BS degree in automatic control from Dalian Railway Institute of China in 1997, and the MS degree in flight control from Beijing University of Aeronautics and Astronautics of China in 2001. Since 2001 she has been a Ph.D. student in the OBR Research Center for Distributed and Mobile Computing at the University of Cincinnati. Her research interests include performance evaluation of 802.11 MAC protocol, wireless ad hoc networks and sensor networks. She is a student member of the IEEE. Dharma P.Agrawal IEEE Fellow, 1987; ACM Fellow, 1998; AAAS Fellow, 2003 Dr. Agrawal is the Ohio Board of Regents Distinguished Professor of Computer Science and Computer Engineering in the department of Electrical and Computer Engineering and Computer Science, University of Cincinnati, OH. He has been a faculty member at Wayne State University, (1977–1982) and North Carolina State University (1982–1998). He has been a consultant to the General Dynamics Land Systems Division, Battelle, Inc., and the U. S. Army. He has held visiting appointment at AIRMICS, Atlanta, GA, and the AT&T Advanced Communications Laboratory, Whippany, NJ. He has published a number of papers in the areas of Parallel System Architecture, Multi computer Networks, Routing Techniques, Parallelism Detection and Scheduling Techniques, Reliability of Real-Time Distributed Systems, Modeling of C-MOS Circuits, and Computer Arithmetic. His recent research interest includes energy efficient routing, information retrieval, and secured communication in ad hoc and sensor networks, effective handoff handling and multicasting in integrated wireless networks, interference analysis in piconets and routing in scatternet, use of smart directional antennas (multibeam) for enhanced QoS, Scheduling of periodic real-time applications and automatic load balancing in heterogeneous workstation environment. He has four approved patents and three patent filings in the area of wireless cellular networks.     

Maximizing Transmission Time (MTT): A Distributed MAC Scheme for Enhancing Wireless LAN Performance

Distributed contention-based Medium Access Control (MAC) protocols are the fundamental components for IEEE 802.11 type Wireless LANs (WLAN). The deficiency of these types of MAC protocols mainly comes from the idle slots used to contend the channel and from the transmission collisions due to the same backoff slot value being generated. Assigning the same transmission opportunity to various length packets also degrades the system performance. This study takes account of the above issues and presents a new MAC scheme called Maximizing Transmission Time (MTT) to enhance the wireless LAN performance. This scheme allows each station to transmit a burst of packets after winning a transmission opportunity instead of just one packet. This idea can reduce the average number of waiting slots and collision probability in each transmission cycle. Moreover, in order to ensure fairness among stations, a maximum transmission period is assigned to each station for controlling the length of the bursty transmission. An analytical performance model is derived for computing the throughput of the MTT scheme. The extensive simulation experiments reveal that the proposed method can enhance the wireless LANs performance significantly with high throughput, low delay and high degree of fairness.Xin Gang Wang received his 1st B.Sc. degree in Computer Science from the Heilongjiang University, P.R.China, in 2001. He is currently a Ph.D. student in the computing department, University of Bradford. His research interests include performance modeling of the mobile networks.Geyong Min received the PhD degree in computing science from the University of Glasgow, United Kingdom, in 2003, and the BSc degree in computer science from Huazhong University of Science and Technology, China, in 1995. He is currently a lecturer in the Department of Computing at the University of Bradford, United Kingdom. His research interests include Performance Modelling/Evaluation, Parallel and Distributed Systems, Mobile Computing, Computer Networks, Multimedia Systems.Dr. Min is the founding co-chair of the International Workshop on Performance Modelling, Evaluation, and Optimisation of Parallel and Distributed Systems (PMEO-PDS) held in conjunction with IEEE/ACM-IPDPS. He is the guest editor of the journals Computation and Concurrency: Practice and Experience, Future Generation Computer Systems, and Supercomputing. He has served on the program committees of a number of international conferences. He is a member of the IEEE Computer Society.John Mellor has worked in the modelling and simulation of communication networks for 25 years. Early work included dynamic alternate routing and the application of learning automata to routing strategies in circuit and packet switched networks. Collaboration with a Cambridge UK company led to the development of a LAN protocol which consistently outperformed Ethernet. He was sent as a government expert to study the Manufacturing Messaging protocol in the USA and Japan. He later became a technical expert consultant on the application of European Directives within manufacturing industry. A forray into radio frequency identification tags resulted in the development of a novel protocol that was exploited by a major vehicle component manufacturer. He now finds himself involved in wireless protocols with researchers working on WiFi (802.11) and on security aspects of mobile commerce. John is leader of the Mobile Computing and Networks Resaerch Group at the University of Bradford and course tutor to three innovative advanced MSc. courses in mobile computing, applications and security.Lin Guan received the B.Sc degree in computer science from Heilongjiang University, Heilongjiang, China, in 2001. She is currently a PhD student in University of Bradford. Her research interests focus on developing cost effective analytical models for the performance evaluation of congestion control algorithms for Internet traffic.     

Improving IEEE 802.11 power saving mechanism

This paper presents an optimization of the power saving mechanism in the Distributed Coordination Function (DCF) in an Independent Basic Service Set (IBSS) of the IEEE 802.11 standard. In the power saving mode specified for DCF, time is divided into so-called beacon intervals. At the start of each beacon interval, each node in the power saving mode periodically wakes up for a duration called the ATIM Window. Nodes are required to be synchronized to ensure that all nodes wake up at the same time. During the ATIM window, the nodes exchange control packets to determine whether they need to stay awake for the rest of the beacon interval. The size of the ATIM window has a significant impact on energy saving and throughput achieved by the nodes. This paper proposes an adaptive mechanism to dynamically choose a suitable ATIM window size. We also allow the nodes to stay awake for only a fraction of the beacon interval following the ATIM window. On the other hand, the IEEE 802.11 DCF mode requires nodes to stay awake either for the entire beacon interval following the ATIM window or not at all. Simulation results show that the proposed approach outperforms the IEEE 802.11 power saving mechanism in terms of throughput and the amount of energy consumed. This research is supported in part by National Science Foundation grant 01-25859. Eun-Sun Jung received a Ph.D. degree in Computer Science from Texas A&M University, USA, an M.S. degree in Information Security from University of London, UK, and a B.S degree in Computer Science and Statistics from Dankook University, Seoul, Korea. From 1995 to 1996 she was a member of technical staff in Hanwha Corporation, Seoul, Korea. In 1999, she was employed by Korea Information Security Agency as a research scientist. Since 2005, she has been with Samsung Advanced Institute of Technology, Korea, as a senior researcher. Her research interests include Wireless Networks, Mobile Computing, and Network Security. Nitin Vaidya received the Ph.D. from the University of Massachusetts at Amherst. He is presently an Associate Professor of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign (UIUC). He has held visiting positions at Microsoft Research, Sun Microsystems and the Indian Institute of Technology-Bombay, as well as a faculty position at the Texas A&M University. His current research is in wireless networking and mobile computing. He co-authored papers that received awards at the ACM MobiCom and Personal Wireless Communications (PWC) conferences. Nitin’s research has been funded by various agencies, including the National Science Foundation, DARPA, Motorola, Microsoft Research and Sun Microsystems. Nitin Vaidya is a recipient of a CAREER award from the National Science Foundation. Nitin has served on the committees of several conferences, including as program co-chair for 2003 ACM MobiCom and General Chair for 2001 ACM MobiHoc. He has served as an editor for several journals, and presently serves as the Editor-in-Chief for the IEEE Transactions on Mobile Computing. He is a senior member of the IEEE and a member of the ACM. For more information, please visit .     

Enhanced binary exponential backoff algorithm for fair channel access in the ieee 802.11 medium access control protocol

The medium access control protocol determines system throughput in wireless mobile ad hoc networks following the ieee 802.11 standard. Under this standard, asynchronous data transmissions have a defined distributed coordination function that allows stations to contend for channel usage in a distributed manner via the carrier sensing multiple access with collision avoidance protocol. In distributed coordination function, a slotted binary exponential backoff (BEB) algorithm resolves collisions of packets transmitted simultaneously by different stations. The BEB algorithm prevents packet collisions during simultaneous access by randomizing moments at stations attempting to access the wireless channels. However, this randomization does not eliminate packet collisions entirely, leading to reduced system throughput and increased packet delay and drop. In addition, the BEB algorithm results in unfair channel access among stations. In this paper, we propose an enhanced binary exponential backoff algorithm to improve channel access fairness by adjusting the manner of increasing or decreasing the contention window based on the number of the successfully sent frames. We propose several configurations and use the NS2 simulator to analyze network performance. The enhanced binary exponential backoff algorithm improves channel access fairness, significantly increases network throughput capacity, and reduces packet delay and drop. Copyright © 2013 John Wiley & Sons, Ltd.     

Achieving performance enhancement in IEEE 802.11 WLANs by using the DIDD backoff mechanism

Wireless local area networks (WLANs) based on the IEEE 802.11 standards have been widely implemented mainly because of their easy deployment and low cost. The IEEE 802.11 collision avoidance procedures utilize the binary exponential backoff (BEB) scheme that reduces the collision probability by doubling the contention window after a packet collision. In this paper, we propose an easy‐to‐implement and effective contention window‐resetting scheme, called double increment double decrement (DIDD), in order to enhance the performance of IEEE 802.11 WLANs. DIDD is simple, fully compatible with IEEE 802.11 and does not require any estimation of the number of contending wireless stations. We develop an alternative mathematical analysis for the proposed DIDD scheme that is based on elementary conditional probability arguments rather than bi‐dimensional Markov chains that have been extensively utilized in the literature. We carry out a detailed performance study and we identify the improvement of DIDD comparing to the legacy BEB for both basic access and request‐to‐send/clear‐to‐send (RTS/CTS) medium access mechanisms. Copyright © 2006 John Wiley & Sons, Ltd.     

Comprehensive Analysis of the IEEE 802.11

Wireless Local Area Networks (WLANs) have attracted significant research interest over the past few years. The IEEE 802.11 standard is the most mature technology for WLANs and has been widely adopted for wireless networks. This paper outlines a new performance analysis for IEEE 802.11 Distributed Coordinated Function (DCF) using Direct Sequence Spread Spectrum (DSSS) in terms of the channel throughput, packet processing rate, packet loss probability and average packet delay using a perfect channel as well as a slow Rayleigh fading channel. The theoretical results are subsequently compared with the simulation results. It is shown that there is a good match between these two results, which validates the analytical model.Peter P. Pham received the B.E. in computer system engineering (honour) from the University of Adelaide, Australia in December 2000. After graduation, he worked as a software engineer for Motorola for 6 months in Singapore. Since August 2001, he received a President scholarship and started as a Ph.D. candidate at Institute for Telecommunications Research, the University of South Australia. His area of interests are performance analysis and coding techniques for ad hoc networks.     

a high-throughput path metric for multi-hop wireless routing

This paper presents the expected transmission count metric (ETX), which finds high-throughput paths on multi-hop wireless networks. ETX minimizes the expected total number of packet transmissions (including retransmissions) required to successfully deliver a packet to the ultimate destination. The ETX metric incorporates the effects of link loss ratios, asymmetry in the loss ratios between the two directions of each link, and interference among the successive links of a path. In contrast, the minimum hop-count metric chooses arbitrarily among the different paths of the same minimum length, regardless of the often large differences in throughput among those paths, and ignoring the possibility that a longer path might offer higher throughput.This paper describes the design and implementation of ETX as a metric for the DSDV and DSR routing protocols, as well as modifications to DSDV and DSR which allow them to use ETX. Measurements taken from a 29-node 802.11b test-bed demonstrate the poor performance of minimum hop-count, illustrate the causes of that poor performance, and confirm that ETX improves performance. For long paths the throughput improvement is often a factor of two or more, suggesting that ETX will become more useful as networks grow larger and paths become longer.This research was supported by grants from NTT Corporation under the NTT-MIT collaboration, and by MIT’s Project Oxygen.Douglas De Couto received his Ph.D. in Computer Science from MIT in June 2004 for work in multi-hop wireless routing. He was a member of MIT’s Computer Science and Artificial Laboratory. He also received his S.B. and M.Eng. degrees in Computer Science and Electrical Engineering from MIT, in 1998. His research interests include multi-hop wireless networks, sensor and embedded networks, and applications of GPS. E-mail: decouto@csail.mit.eduDaniel Aguayo is a graduate student in MIT’s EECS department and a member of MIT’s Computer Science and Artificial Intelligence Laboratory. He received an S.B. in Computer Science and Electrical Engineering from MIT in 2001, and an M.Eng. in 2002. His research interests are focused on multi-hop wireless networks. E-mail: aguayo@csail.mit.eduJohn Bicket is a graduate student in MIT’s EECS department and a member of MIT’s Computer Science and Artificial Intelligence Laboratory. He received a B.S. from Cornell University. His research interests include multi-hop rooftop 802.11 networks and device drivers. E-mail: jbicket@csail.mit.eduRobert Morris is an associate professor in MIT’s EECS department and a member of MIT’s Computer Science and Artificial Intelligence Laboratory. He received a Ph.D. from Harvard University for work on modeling and controlling data networks with large numbers of competing connections. He co-founded Viaweb, an e-commerce hosting service. His current interests include routing in multi-hop rooftop 802.11 networks, modular software-based routers, distributed hash tables, and peer-to-peer file storage. He has received a Sloan Fellowship, an NSF Career award, and the ITT Career Development Chair at MIT. E-mail: rtm@csail.mit.edu     

High Performance Wireless Switch Protocol for IEEE 802.11 Wireless Networks

All mobile stations (STAs) in IEEE 802.11 infrastructure wireless local area networks (IWLAN) are coordinated by an access point (AP). Within the 2.4 GHz unlicensed industry, science, and medicine (ISM) band defined in the IEEE 802.11 2.4 GHz physical layer (PHY) specifications, three channels are available for concurrently transferring data packets at the coverage area of an AP. In most of small/medium enterprises or home environments, an AP with one selected channel is sufficient for covering whole service area, but this implies that the radio resources for the remaining two channels are wasted. In order to overcome the drawback, we propose a new and simple media access control (MAC) protocol, named wireless switch protocol (WSP), for increasing the throughput of IEEE 802.11 IWLAN network to support high quality multimedia traffic. This is achieved by allowing any pair of STAs in IWLAN to exchange data packets in one of other idle channels after their handshake with each other in the common channel controlled by AP. Simulation results show that the total network throughput of WSP depends on the time taken by channel switching, and on the ‘Intranet’ and ‘Internet’ traffic distribution, where the Intranet and Internet mean data transmission between STAs in IWLAN and between the STA and wired host, respectively. When all data packets are Intranet traffic and the traffic load is heavy, the ratio of Goodput for the proposed WSP to that of IEEE 802.11 standard approximates 400%. In the worse case of all Internet traffic, the proposed WSP still obtains the similar throughput as that of IEEE 802.11 standard.Jenhui Chen was born on October 12, 1971 in Taipei, Taiwan, Republic of China. He received the Bachelor’s and Ph.D. degree in Computer Science and Information Engineering (CSIE) from Tamkang University in 1998 and 2003, respectively. In the Spring of 2003, he joined the faculty of Computer Science and Information Engineering Department at Chang Gung University and served as the Assistant Professor. He occupies the supervisor of Network Department in the Information Center, Chang Gung University. Dr. Chen once served the reviewer of IEEE Transactions on Wireless Communications, ACM/Kluwer Mobile Networks and Applications (MONET), and Journal of Information Science and Engineering. His main research interests include design, analysis, and implementation of communication and network protocols, wireless networks, milibots, and artificial intelligence. He is a member of ACM and IEEE.Ai-Chun Pang was born in Hsinchu, Taiwan, R.O.C., in 1973. She received the B.S., M.S. and Ph.D. degrees in Computer Science and Information Engineering from National Chiao Tung University (NCTU) in 1996, 1998 and 2002, respectively. She joined the Department of Computer Science and Information Engineering, National Taiwan University (NTU), Taipei, Taiwan, as an Assistant Professor in 2002. Her research interests include design and analysis of personal communications services network, mobile computing, voice over IP, and performance modeling.Shiann-Tsong Sheu received his B.S. degree in Applied Mathematics from National Chung Hsing University in 1990, and obtained his Ph.D. degree in Computer Science from National Tsing Hua University in May of 1995. From 1995 to 2002, he was an Associate Professor at the Department of Electrical Engineering, Tamkang University. Since Feb. 2002, he has become a Professor at the Department of Electrical Engineering, Tamkang University. Dr. Sheu received the outstanding young researcher award by the IEEE Communication Society Asia Pacific Board in 2002. His research interests include next-generation wireless communication, WDM networks and intelligent control algorithms.Hsueh-Wen Tseng received his B.S. degree in electrical engineering from Tamkang University, Taipei country, Taiwan, in 2001 and M.S. degree in electrical engineering from National Taiwan University of Science and Technology, Taipei, Taiwan, in 2003. He is currently pursuing the Ph. D. degree at the Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan. His research interests include design, analysis and implementation of network protocols and wireless communications.     

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.     

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.     

Theoretical Analysis and Performance of NC-PRMA Protocol for Multichannel Wireless Networks

In this paper, we analyze the effect of duplexing schemes on the throughput and the average packet dropping probability of a new multichannel wireless access protocol which allows for non-collision packet reservation multiple access with multiple channel (NC-PRMA/MC). N _C equal-capacity, orthogonal, traffic channels are shared by M mobile users on the uplink. Transmission attempts on the uplink are made by using time-frequency signaling in every frame, which enables transmission attempts of mobile users to be conveyed to the base station without collisions. Two kinds of duplexing schemes, frequency division duplexing and shared time division duplexing, are considered in the performance analysis. Using a discrete-time Markov chain analysis, we derive the analytic expressions for the average per channel throughput and the average packet dropping probability. Computer simulation results verify the analysis. Analytical evaluation and computer simulation show that NC-PRMA/MC with shared time division duplexing improves the channel capacity, which approaches the theoretical upper bound. Jenn-Kaie Lain born in Taiwan, R.O.C., in 1973. He received the B.E. degree in engineering science from the National Cheng Kung University, Tainan, Taiwan, R.O.C., and the Ph.D. degree in electrical engineering from the National Chung Cheng University, Chiayi, R.O.C., in 1995 and 2001, respectively. Since August 2001, he joined the faculty of Department of Computer Science and Information Engineering at Shu-Te University, Kaohsiung, Taiwan, R.O.C., as an Assistant Professor. He has been on the Faculty at National Yunlin University of Science and Technology, Yunlin, Taiwan, R.O.C., since August 2002 and currently holds the position of Assistant Professor in the Institute of Electronic and Information Engineering. His current research interest is in the field of coding and modulation as well as efficient receiver designs for broadband wireless communications. Jyh-HorngWen received his B.S. degree in Electronic Engineering from the National Chiao Tung University, Hsing-Chu, Taiwan, in 1979 and the Ph.D. degree in Electrical Engineering from the National Taiwan University, Taipei, in 1990. From 1981 to 1983, he was a Research Assistant with the Telecommunication Laboratory, Ministry of Transportation and Communications, Chung-Li, Taiwan. From 1983 to 1991, he was a Research Assistant with the Institute of Nuclear Energy Research, Taoyun, Taiwan. Since February 1991, he has been with the Institute of Electrical Engineering, National Chung Cheng University, Chia-Yi, Taiwan, first as an Associate Professor and, since 2000, as a Professor. He was also the Managing Director of the Center for Telecommunication Research, National Chung Cheng University, from Aug. 2000 to July 2004. Currently, he is also the Dean of General Affairs, National Chi Nan University. He is an Associate Editor of the Journal of the Chinese Grey System Association. His current research interests include computer communication networks, cellular mobile communications, personal communications, spread-spectrum techniques, wireless broadband systems, and gray theory. Prof.Wen is a member of the IEEE Communication Society, the IEEE Vehicular Technology Society, the International Association of Science and Technology for Development,the Chinese Grey System Association, and the Chinese Institute of Electrical Engineering.     

Performance Evaluation of Directional Adaptive Range Control in Mobile Ad Hoc Networks

This paper presents DARC (Directional Adaptive Range Control), a range control mechanism using directional antennas to be implemented across multiple layers. DARC uses directional reception for range control rather than directional transmission in order to achieve both range extension and high spatial reuse. It adaptively controls the communication range by estimating dynamically changing local network density based on the transmission activities around each network node. The experimental results using simulation with detailed physical layer, IEEE 802.11 DCF MAC, and AODV protocol models have shown the successful adaptation of communication range with DARC for varied network densities and traffic loads. DARC improves the packet delivery ratio by a factor of 9 at the maximum for sparse networks while it maintains the increased network capacity for dense networks. Further, as each node adaptively changes the communication range, the network delivers up to 20% more packets with DARC compared to any fixed range configurations.Mineo Takai is a Principal Development Engineer in the Computer Science Department at University of California, Los Angeles. He received his B.S., M.S. and Ph.D. degrees, all in electrical engineering, from Waseda University, Tokyo, Japan, in 1992, 1994 and 1997 respectively.Dr. Takai’s research interests include parallel and distributed computing, mobile computing and networking, and modeling and simulation of networked systems. He is a member of the ACM, the IEEE and the IEICE.Junlan Zhou received her B.S in Computer Science from Huazhong University of Science and Technology in 1998, her M.Eng in Computer Engineering from Nanyang Technological University in 2001 and her M.S in Computer Science from University of California, Los Angeles in 2003. She is currently a Ph.D candidate in the Computer Science Department at University of California, Los Angeles. Her research interests include modeling and simulation of wireless networks, protocol design and analysis of wireless networks, and broad areas of distributed computing.Rajive Bagrodia is a Professor of Computer Science at UCLA. He obtained a Bachelor of Technology in electrical engineering from the Indian Institute of Technology, Bombay and a Ph.D. in Computer Science from the University of Texas at Austin. Professor Bagrodia’s research interests include~wireless networks, performance modeling and~simulation, and nomadic computing. He has published over a hundred research papers on the preceding topics. The research has been funded by a variety of government and industrial sponsors including the National Science Foundation, Office of Naval Research, and the Defense Advanced Research Projects Agency. He is an associate editor of the ACM Transactions on Modeling and Computer Systems (TOMACS).     

A backoff algorithm based on self-adaptive contention window update factor for IEEE 802.11 DCF

The binary exponential backoff (BEB) mechanism is applied to the packet retransmission in lots of wireless network protocols including IEEE 802.11 and 802.15.4. In distributed dynamic network environments, the fixed contention window (CW) updating factor of BEB mechanism can’t adapt to the variety of network size properly, resulting in serious collisions. To solve this problem, this paper proposes a backoff algorithm based on self-adaptive contention window update factor for IEEE 802.11 DCF. In WLANs, this proposed backoff algorithm can greatly enhance the throughput by setting the optimal CW updating factor according to the theoretical analysis. When the number of active nodes varies, an intelligent scheme can adaptively adjust the CW updating factor to achieve the maximal throughput during run time. As a result, it effectively reduces the number of collisions, improves the channel utilization and retains the advantages of the binary exponential back-off algorithm, such as simplicity and zero cost. In IEEE 802.11 distributed coordination function (DCF) protocol, the numerical analysis of physical layer parameters show that the new backoff algorithm performance is much better than BEB, MIMD and MMS algorithm.     

一种提高IEEE 802.11吞吐量和公平性的自适应优化算法

该文提出了一种针对IEEE 802.11 DCF网络增强其吞吐量和公平性性能的自适应优化算法,算法基于网络节点侦听信道得到的网络状态信息进行竞争发送的自适应调整以获得最优的网络性能,称之为CSCC(Channel Sensing Contention Control)算法。算法采用了对节点的信道接入请求以概率参数P_T进行过滤的方法控制节点竞争接入信道的激烈程度,其主要特点在于在优化调整过程中不需要进行计算复杂的网络节点数量估计,并且可以在不同网络状态下围绕始终确定的优化目标进行参数优化调整。仿真实验结果表明,算法能够适应不同节点数量和不同数据大小的网络进行自适应的网络优化调整,并获得了系统吞吐量、碰撞概率、延迟、延迟抖动、公平性等多方面的性能改善。     

A k-Round Elimination Contention Scheme for WLANs

The contention resolution scheme is a key component in carrier-sense-based wireless MAC protocols. It has a major impact on MAC'S performance metrics such as throughput, delay, and jitter. The IEEE 802.11 DCF adopts a simple contention resolution scheme, namely, the binary exponential backoff (BEB) scheme. The BEB scheme achieves a reasonable performance for transmitting best-effort packets in small-sized wireless networks. However, as the network size increases, it suffers from inefficiency because of the medium contention, which leads to reduced performance. The main reason is that the BEB mechanism incurs an ever- increasing collision rate as the number of contending nodes increases. We devise a novel contention resolution scheme, a k-round elimination contention (k-EC) scheme. The k-EC scheme exhibits high efficiency and robustness during the collision resolution. More importantly, it is insensitive to the number of contending nodes. This feature makes it feasible for use in networks of different sizes. Simulation results show that the k-EC scheme offers a powerful remedy to medium contention resolution. It significantly outperforms the IEEE 802.11 DCF scheme in all the MAC'S performance metrics and also exhibits better fairness.