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1.
A scheduling algorithm for QoS support in IEEE802.11 networks 总被引:2,自引:0,他引:2
This article presents a scheduling algorithm for the IEEE 802.11e hybrid coordination function under definition by the IEEE 802.11e task group. HCF can be used to provide IP quality of service guarantees in IEEE802.11e infrastructure WLANs. The enhanced distributed coordination function is mainly used for data transmission without QoS guarantees, but can also be used to decrease the transmission delay of QoS-sensitive traffic. Scheduling of queued packets follows a delay-earliest-due-date algorithm. The proposed algorithm is compatible with the link adaptation mechanisms implemented in commercial WLANs, as it limits the amount of time during which the stations control the wireless medium. The performance of the algorithm is evaluated through computer simulation and compared with the reference scheduler presented by the IEEE 802.11e task group. 相似文献
2.
In wireless multicast, some users may fail to receive data as a result of bad channel conditions. The throughput of traditional
multicast strategy is constrained by the node with the worst channel condition. In this paper, we propose a distributed cooperative
multicast scheduling strategy, in which, every user which has successfully received data can decide whether to retransmit
data by sensing MNACK packets. The proposed scheme can achieve good throughput by exploiting multi-channel diversity across
multiple users’ cooperation. In addition, the constraint of power consumption is also considered. Simulation results show
that our scheme can provide good throughput and fairness performance with the constraint of average system power consumption. 相似文献
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4.
根据IEEE 802.11ac的标准需求以及IEEE 802.11ac基本原理的理解,全面介绍了罗德与施瓦茨公司对无线局域网IEEE 802.11ac完整而成熟的测试解决方案。 相似文献
5.
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 . 相似文献
6.
Originally, Wireless Local Area Networks served only small indoor areas. Nevertheless, the idea of employing IEEE 802.11 networks in large outdoor environments is
a very attractive possibility. IEEE 802.11 technology offers several advantages: the low cost of equipment, its operation
in the unlicensed spectrum and its higher data rates. Since the advent of the first IEEE 802.11 standard, a great deal of
research has been carried out. So-called Wifi-based Long Distance networks are currently being deployed. In this paper, we study the suitability of employing IEEE 802.11 networks in large
outdoor environments without modifying the standard working procedure. In such scenarios, IEEE 802.11 networks should offer
coverage ranges of several kilometer, which leads to high propagation delay values. Thus, we analyze the influence of increasing
propagation delay in the IEEE 802.11 MAC protocol. To carry out our analysis we present a mathematical model and simulation
results. We provide an operating range in which IEEE 802.11 performance is feasible and establish a throughput threshold according
to the propagation delay. 相似文献
7.
This paper addresses the problem of route selection in IEEE 802.11 based Wireless Mesh Networks (WMNs). Traditional routing protocols choose the shortest path between two routers. However, recent research reveals that there can be enormous differences between links in terms of quality (link loss ratio, interference, noise etc) and therefore selecting the shortest path (hop count metric) is a poor choice. We propose a novel routing metric—Expected Link Performance (ELP) metric for wireless mesh networks which takes into consideration multiple factors pertaining to quality (link loss ratio, link capacity and link interference) to select the best end-to-end route. Simulation based performance evaluation of ELP against contemporary routing metrics shows an improvement in terms of throughput and delay. Moreover, we propose an extension of the metric called ELP-Gateway Selection (ELP-GS) which is an extension meant for traffic specifically oriented towards the gateway nodes in the mesh network. We also propose a gateway discovery protocol which facilitates the dissemination of ELP-GS in the network. Simulation results for ELP-GS show substantial improvement in performance. 相似文献
8.
Fengji Ye Haiming Yang Hua Yang Sikdar B. 《Communications, IEEE Transactions on》2009,57(10):2903-2908
This paper investigates the performance of IEEE 802.11 in multi-hop scenarios and shows how its aggressive behavior can throttle the spatial reuse and reduce bandwidth efficiency. An adaptive, layer-2, distributed coordination scheme for 802.11 using explicit medium access control (MAC) feedback is then proposed to pace the transmissions on adjacent nodes, thereby assisting the MAC protocol to operate around its saturation state while minimizing resource contention. Simulation results show that the proposed scheme outperforms the original 802.11 MAC. 相似文献
9.
Mona Aghababaeetafreshi Lasse K. Lehtonen Toni Levanen Mikko Valkama Jarmo Takala 《Journal of Signal Processing Systems》2016,85(1):167-182
Wireless standards are evolving rapidly due to the exponential growth in the number of portable devices along with the applications with high data rate requirements. Adaptable software based signal processing implementations for these devices can make the deployment of the constantly evolving standards faster and less expensive. The flagship technology from the IEEE WLAN family, the IEEE 802.11ac, aims at achieving very high throughputs in local area connectivity scenarios. This article presents a software based implementation for the Multiple Input and Multiple Output (MIMO) transmitter and receiver baseband processing conforming to the IEEE 802.11ac standard which can achieve transmission bit rates beyond 1Gbps. This work focuses on the Physical layer frequency domain processing. Various configurations, including 2×2 and 4×4 MIMO are considered for the implementation. To utilize the available data and instruction level parallelism, a DSP core with vector extensions is selected as the implementation platform. Then, the feasibility of the presented software-based solution is assessed by studying the number of clock cycles and power consumption of the different scenarios implemented on this core. Such Software Defined Radio based approaches can potentially offer more flexibility, high energy efficiency, reduced design efforts and thus shorter time-to-market cycles in comparison with the conventional fixed-function hardware methods. 相似文献
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11.
基于TSMC RF 0.18 μm CMOS工艺,设计了一种可应用于IEEE 802.11ac标准的5 GHz宽带LC压控振荡器。该振荡器采用了NMOS交叉耦合结构,同时采用了5位开关电容阵列以扩展调谐范围。开关电容阵列使压控振荡器的增益KVCO保持在一个较小的值,有效地降低了压控振荡器的相位噪声。后仿真结果表明,该压控振荡器在1.8 V电源电压下,功耗为9 mW,频率调谐范围为4.52~5.56 GHz,在偏离中心频率1 MHz处仿真得到的相位噪声为-124 dBc/Hz。该LC 压控振荡器的版图尺寸为320 μm×466 μm。 相似文献
12.
In this paper, we develop a model-based frame scheduling scheme, called MFS, to enhance the capacity of IEEE 802.11-operated wireless local area networks (WLANs) for both transmission control protocol (TCP) and user datagram protocol (UDP) traffic. In MFS each node estimates the current network status by keeping track of the number of collisions it encounters between its two consecutive successful frame transmissions, and computes accordingly the current network utilization. The result is then used to determine a scheduling delay to be introduced before a node attempts to transmit its pending frame. MFS does not require any change in IEEE 802.11, but instead lays a thin layer between the LL and medium access control (MAC) layers. In order to accurately calculate the current utilization in WLANs, we develop an analytical model that characterizes data transmission activities in IEEE 802.11-operated WLANs with/without the request to send/clear to send (RTS/CTS) mechanism, and validate the model with ns-2 simulation. All the control overhead incurred in the physical and MAC layers, as well as system parameters specified in IEEE 802.11, are figured in. We conduct a comprehensive simulation study to evaluate MFS in perspective of the number of collisions, achievable throughput, intertransmission delay, and fairness in the cases of TCP and UDP traffic. The simulation results indicate that the performance improvement with respect to the protocol capacity in a WLAN of up to 300 nodes is 1) as high as 20% with the RTS/CTS and 70% without the RTS/CTS in the case of UDP traffic and 2) as high as 10% with the RTS/CTS and 40% without the RTS/CTS in the case of TCP traffic. Moreover, the intertransmission delay in MFS is smaller and exhibits less variation than that in IEEE 802.11; the fairness among wireless nodes in MFS is better than, or equal to, that in IEEE 802.11. 相似文献
13.
Waleed Alasmary Author VitaeWeihua ZhuangAuthor Vitae 《Ad hoc Networks》2012,10(2):222-230
Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. In this paper, we provide a comprehensive evaluation of mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay. An unfairness problem due to the relative speed is identified for both broadcast and unicast scenarios. We propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. The first scheme provides dynamic level of service priority via adaptation to the number of neighboring nodes, while the second scheme provides service priority based on node relative speed. Extensive simulation results demonstrate a significant impact of mobility on the IEEE 802.11p MAC performance, the unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes. 相似文献
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The performance of wireless local area networks (WLANs) is based on the performance of the corresponding access points (APs). Nowadays, network engineers tend to manually assign data channels (frequencies) for each AP. They only use channels 1, 6, and 11 because no interference exists between these channels. But it will be far more efficient if all 11 channels are used. Therefore, the channel allocation problem becomes a major challenge when deploying WLANs. In this paper, we assume that the location of each AP is known. Our objective is to optimally assign a frequency for each AP such that the throughput is maximized and the interference between the various APs is minimized. We also consider a realistic scenario where the APs are not in line of sight of each other, but on the other hand there are different barriers that separate them. We formulate the problem using integer linear programming (ILP) in order to obtain the optimal frequency assignment (OFA). Then, we propose two efficient heuristic algorithms to achieve the same results. Finally, we evaluate the performance of all techniques and make a comparison between them. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
16.
QoS enhancement in IEEE 802.11 wireless local area networks 总被引:7,自引:0,他引:7
Daqing Gu Jinyun Zhang 《Communications Magazine, IEEE》2003,41(6):120-124
A distributed medium access scheme called EDCF, which is adopted in an upcoming standard IEEE 802.11e to allow prioritized medium access for applications with QoS requirements, is described and discussed. Its performance is also evaluated via simulations. 相似文献
17.
《AEUE-International Journal of Electronics and Communications》2014,68(7):667-675
The multi-rate transmission mechanism in IEEE 802.11 can improve its reliability and robustness. However, it causes a performance anomaly. After analyzing the reasons for the performance anomaly in multi-rate mechanism, we propose a new scheme to solve the performance anomaly. By adjusting packet size according to the transmission rate, this scheme guarantees that these nodes with different transmit rates can access wireless channel fairly. Theoretical analysis and performance evaluation show that the proposed scheme can well solve the performance anomaly problem. 相似文献
18.
Most of the existing cooperation methods select relay node(s) mainly based on the channel state information, but do not consider
whether the selected relay nodes work or not. If the selected relays are invalidated, the performance of cooperative communication
will deteriorate. To resolve the above problem, this paper investigates cooperative communication in IEEE 802.11 networks,
and proposes a novel Spare Cooperative Method (SCM). SCM chooses a spare cooperation node to enhance the reliability of communication,
and uses an enhanced handshaking mechanism to coordinate the access of source nodes and cooperation nodes to the wireless
channel. The performance of SCM is comprehensively analyzed in terms of outage probability and saturated throughput. The analysis
shows that SCM improves the performance of IEEE 802.11. 相似文献
19.
Xi Yong Huang Qingyan Wei Jibo Zhao Haitao 《电子科学学刊(英文版)》2007,24(3):289-295
In this paper, a rate adaptive protocol AMARF (Adaptive Multirate Auto Rate Fallback) for multirate IEEE 802.11 networks is proposed. In AMARF, each data rate is assigned a unique success threshold, which is a criterion to judge when to switch a rate to the next higher one, and the success thresholds can be adjusted dynamically in an adaptive manner according to the running conditions, such as packet length and channel parameters. Moreover, the proposed protocol can be implemented by software without any change to the current IEEE 802.11 standards. Simulation result shows that AMARF yields significantly higher throughput than other existing schemes including ARF and its variants, in various running conditions. 相似文献