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该文基于有效竞争接入、高效无冲突轮询传输的思想改进了根据用户数目妥善安排传输的多址接入(UPMA) 协议,根据业务需求对上下带宽资源实行动态分配,使用有效的冲突解决策略保证节点尽快接入信道,采用高效的无冲突轮询传输避免了传输开销。该文还给出了协议的理论分析模型,并通过计算机仿真验证了理论模型的正确性。理论值和仿真结果表明提出的协议可以提供高的通过量、较低的平均消息时延和较小的平均消息丢弃率。最后通过理论计算给出了在给定无竞争服务周期长度的情况下竞争接入周期的最佳长度。 相似文献
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基于IEEE802.11b无线局域网支持QoS的盲检测算法 总被引:1,自引:0,他引:1
这里提出了一种基于IEEE802.11b无线局域网(WLANs)的MAC层的终端盲检测算法.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盲检测,可以非常有效的增加每个AP点所支持的语音通信终端数量,从而增加了信道的带宽,提高语音服务质量QoS.而且算法只执行在接入点的点协调功能上(PCF),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. 相似文献
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针对通信系统中不同编码模式的网络实时音频传输时延、抖动和丢包率等性能指标的检测精度及效率问题,提出了一种网络实时音频服务质量(QoS)性能分析的新方法。该新方法基于音频(声码)识别技术,精确得到语音延迟和抖动;基于信令辅助技术,检查数据包的转换情况,得到精确丢包率。该方法改进了现有的不同编码模式下传输时延的测量方法,提高了传输时延及抖动的测量精度,并实现了音频数据丢包率的有效度量,能有效地支持语音QoS性能分析;并且可提供可视化分析及直观地展示统计结果,支持多种网络协议和测试场景,具备可重用性,可在其他网络实时音频测试环境中推广和部署。 相似文献
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阐述了IP实时传真协议需求,基于T.38协议,针对传输协议的选择、网络丢包、 时延、抖动等问题所需求的解决方案加以讨论,并给出了相应的参数计算过程。 相似文献
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基于快速、有效竞争预约接入、无冲突轮询传输的思想和带冲突预防的冲突分解策略,本文提出了适于移动Ad Hoc网络的公平按需多址接入(FODA)协议.该协议在分群结构的基础上,利用公平冲突预防算法预约信道资源获得轮询服务,从而完全消除了载波侦听方式下多跳无线网络业务传输中的隐藏终端和暴露终端问题.另外,公平冲突预防算法解决了节点竞争接入时的冲突问题和不公平现象.最后,仿真结果表明,与带冲突避免的载波侦听多址接入(CSMA/CA)和轮询协议相比,FODA协议可以提供较高的信道吞吐量、较低的平均消息丢弃率和平均消息时延. 相似文献
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The IEEE 802.11 wireless local area network (WLAN) media access control (MAC) specification is a hybrid protocol of random access and polling when both distributed coordination function (DCF) and point coordination function (PCF) are used. Data traffic is transmitted with the DCF, while voice transmission is carried out with the PCF. Based on the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self‐adaptive transmission scheme to support multi‐service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self‐adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, voice traffic is sensitive to delay jitter, and the self‐adaptive scheme can effectively decrease it. Finally, it is worth noting that the adaptive scheme is easy to be realized, whereas no change in the MAC protocol is needed. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Robust SuperPoll with Chaining Protocol for IEEE 802.11 Wireless LANs in Support of Multimedia Applications 总被引:3,自引:0,他引:3
Design of Wireless Local Area Networks (WLANs) needs to take into consideration the limited bandwidth available in the ISM band along with the noisy characteristics of the wireless environment and hidden terminal effects. In this paper we propose an enhancement for IEEE 802.11 standard that improves the WLAN support for multimedia applications. In the IEEE 802.11 PCF polling based protocol designed for multimedia applications support, the Point Coordinator (PC) polls each station in the Basic Service Area (BSA) individually. In the proposed SuperPoll approach the PC broadcasts at the beginning of the contention free period a SuperPoll, i.e., a message that includes the list of stations that will be polled during the current period. To improve the reliability of the polling based approach in a noisy environment, we propose to use a chaining mechanism in which each packet resends in its turn the SuperPoll message appended to its packet. We provide performance measurements of the proposed method in terms of channel efficiency and channel access time for multimedia applications that use the contention free period of IEEE 802.11 PCF. We notice that for noisy channels, the proposed method provides a dramatic throughput increase and delay decrease when compared with the Single Poll mechanism used in IEEE 802.11 PCF, thus providing better support for multimedia applications. 相似文献
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Byung-Seo Kim Sung Won Kim Yuguang Fang Wong T.F. 《Selected Areas in Communications, IEEE Journal on》2005,23(6):1276-1286
The IEEE 802.11 standard defines two coordination functions: distributed coordination function (DCF) and point coordination function (PCF). These coordination functions coordinate the shared wireless medium. The PCF uses a centralized polling-based channel access method to support time-bounded services. To design an efficient polling scheme, the point coordinator (PC) needs to obtain information about the current transmission status and channel condition for each station. To reduce overhead caused by polling frames, it is better to poll all stations using one polling frame containing the transmission schedule. In this paper, we propose an efficient polling scheme, referred to as two-step multipolling (TS-MP), for the PCF in wireless local area networks (WLANs). In this new scheme, we propose to use two multipolling frames with different purposes. The first frame is broadcast to collect information such as the numbers of pending frames and the physical-layer transmission rates for the communication links among all stations. The second frame contains a polling sequence for data transmissions designed based on the collected information. This frame is broadcast to all stations. Extensive simulation studies show that TS-MP not only overcomes the aforementioned deficiencies, but also help to implement rate adaptation over time-varying wireless channel. 相似文献
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Zhao Liqiang Zhang Jie Zhang Hailin 《Wireless Communications and Mobile Computing》2009,9(9):1220-1230
IEEE 802.11 is one of the most influential wireless LAN (WLAN) standards. Point coordination function (PCF) is its medium access control (MAC) protocol with real‐time traffic (rt‐traffic) quality‐of‐service (QoS) guarantees. In PCF, it is very likely that non‐real‐time traffic (nrt‐traffic) will use the contention free period (CFP) that should be dedicated to traffic having higher priority such as rt‐traffic. Therefore, a modified PCF protocol called MPCF, which is based on hub polling and an integrated QoS differentiation, is presented in this paper. With the integrated QoS differentiation, MPCF can prioritize bandwidth requests according to service classes and QoS requirements. With hub polling, MPCF can reduce the bandwidth for control frames and improve the network throughput. A simple and accurate analytical model is derived and presented in this paper to calculate the system throughput of MPCF. Simulation results show that MPCF protocol is much better than PCF in terms of system capacity and rt‐traffic QoS guarantees. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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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. 相似文献
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Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs 总被引:2,自引:0,他引:2
Der-Jiunn Deng Hsu-Chun Yen 《Selected Areas in Communications, IEEE Journal on》2005,23(6):1240-1252
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. 相似文献
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With the pervasive growth in the popularity of IEEE 802.11‐based wireless local area networks (WLANs) worldwide, the demand to support delay‐sensitive services such as voice has increased very rapidly. This paper provides a comprehensive survey on the medium access control (MAC) architectures and quality of service (QoS) provisioning issues for WLANs. The major challenges in providing QoS to voice services through WLAN MAC protocols are outlined and the solution approaches proposed in the literature are reviewed. To this end, a novel QoS‐aware wireless MAC protocol, called hybrid contention‐free access (H‐CFA) protocol and a call admission control technique, called traffic stream admission control (TS‐AC) algorithm, are presented. The H‐CFA protocol is based on a novel idea that combines two contention‐free wireless medium access approaches, that is, round‐robin polling and time‐division multiple access (TDMA)‐like time slot assignment, and it increases the capacity of WLANs through efficient silence suppression. The TS‐AC algorithm ensures efficient admission control for consistent delay‐bound guarantees and further maximizes the capacity through exploiting the voice characteristic that it can tolerate some level of inconsecutive packet loss. The benefits of the proposed schemes are demonstrated in the simulations results. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Rony Ohayon 《International Journal of Communication Systems》2012,25(5):571-584
Carrier sense multiple access and its variants have been widely used in mobile ad hoc networks. However, most existing access mechanisms cannot guarantee quality of service for real‐time traffic. In this paper, we present a novel approach to guarantee the performance of real‐time applications such as voice and video that require periodic access to the wireless local area network (WLAN) channel. Our approach can work either with distributed coordination function or enhanced distributed coordination function, and includes distributed reservations of time slots between the stations sharing the WLAN without the need to send any signaling or control messages. Stations can access the wireless medium only if they are able to complete the frame transmission without interruption to the reserved slots of existing real‐time sessions. Simulation results indicate that the proposed mechanism provides high channel utilization, and bounded delays and jitter for real‐time traffic. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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In‐Taek Lim 《ETRI Journal》2001,23(2):52-60
In this paper, a medium access control protocol is proposed for integrated voice and data services in wireless local networks. Uplink channels for the proposed protocol are composed of time slots with multiple spreading codes per slot based on slotted code division multiple access (CDMA) systems. The proposed protocol uses spreading code sensing and reservation schemes. This protocol gives higher access priority to delay‐sensitive voice traffic than to data traffic. The voice terminal reserves an available spreading code to transmit multiple voice packets during a talkspurt. On the other hand, the data terminal transmits a packet without making a reservation over one of the available spreading codes that are not used by voice terminals. In this protocol, voice packets do not come into collision with data packets. The numerical results show that this protocol can increase the system capacity for voice service by applying the reservation scheme. The performance for data traffic will decrease in the case of high voice traffic load because of its low access priority. But it shows that the data traffic performance can be increased in proportion to the number of spreading codes. 相似文献