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介绍了一种提高802.11a无线局域网系统的频偏估计的准确度的方法。介绍了无线局域网的概念和特点及其应用,给出了802.11a接收机的结构,并介绍了频偏估计的问题和解决方法,给出了仿真结果。 相似文献
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对无线局域网的两种标准IEEE 802.11b和IEEE 802.11g的差异进行了研究,后者在前者的基础上采用了正交频分复用(OFDM)技术,通过设计一个针对这两种标准的无线局域网上的VoIP性能测试的试验,使用Chariot网络工具进行仿真,对延迟、抖动、丢包率进行对比分析,结果表明IEEE 802.11g标准比IEEE 802.11b标准具有明显的性能优势. 相似文献
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随着高速无线局域网产品的推出,无线局域网开始在企业应用环境中占有一席之地。目前,无线局域网产品的带宽可以达到11Mbps(执行IEEE 802.11b 标准)或 22Mbps(执行 IEEE 802.11a 标准)。企业在网络建设方面,除了建立独立的无线局域网之外,还可以把无线局域网技术用于现有的企业网络之中,以提高企业网的性能。本文将针对这方面的应用探讨相关的解决方案。 相似文献
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量化因子在IEEE 802. 11 b/e无线局域网视频流传输中的图像质量性能仿真研究 总被引:2,自引:0,他引:2
在NS2-MyEvalvid模型基础上分析了量化因子对传输图像质量性能的影响,并在NS2平台上通过仿真实现了基于Evalvid机制的视频流在无线局域网环境下的传输,总结归纳了编码相关参数仿真视频流在无线网络图像传输过程中的一般方法,通过改变编码的量化因子,得到了在多速率无线局域网环境(802.11b/e)下视频流传输的图像平均延迟和平均PSNR值.分析表明,802.11e在视频流传输性能上比802.11b具有更好的表现. 相似文献
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以IEEE 802.11无线局域网标准发展的无线局域网产品最早出现在市场上大约在1990年。 1997年完成制订IEEE802.11无线局域网标准是无线网络技术发展的一个里程碑。 802.11标准除了介绍无线局域网的优点及各种不同性能外,还使得各种不同厂商的无线产品得以互联,802.11标准不久将修订,以引入更高的传输速率。因802.11标准的颁布,使得无 相似文献
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在分析了IEEE 802.11协议的基础上,提出了一种应用于低速率无线局域网环境下的信道接入方法,对其性能进行了分析,通过对仿真结果的比较,得到了该协议在窄信道环境下性能要优于IEEE 802.11的结论,同时验证了理论分析的正确性。 相似文献
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无线mesh网络是从移动Ad hoc网络中分离出来的新型宽带无线多跳网络架构,能够灵活地提高网络覆盖率和增加网络容量,适合作为宽带无线接入骨干网。IEEE成立的802.11s任务组负责802.11 ESS架构的mesh扩展,由于许多关键技术的研究尚未成熟,严重影响了802.11s标准的制定进度。为便于了解802.11s标准,全面地论述802.11s涉及的关键技术,并且从网络性能的角度指出802.11s mesh的不足以及面临的挑战。 相似文献
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席奇 《计算机光盘软件与应用》2011,(20)
无线网络技术的发展已经深入应用到许多领域,如何确定无线网络的解决方案。通过具体阐述无线网络802.11的基本标准和扩展标准,通过对网络接入方式的分析,通过设计一个无线网,采用OPNETModeler的建模层次和建模方法,实现对IEEE802.11协议的模拟,给出了使用OPNET进行网络仿真的步骤,对网络的性能指标进行了有效的测量。 相似文献
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《IT Professional》2001,3(3):17-23
Although the IEEE 802.11 standard has been around since 1997, work continues to make it more adaptable to the demand for higher data rates and true wireless flexibility. Until recently, few organizations used wireless LANs because they cost too much, their data rates were too low, they posed occupational safety problems because of concerns about the health effects of electromagnetic radiation, and the spectrum used required a license. Today, these problems have largely diminished, and wireless LAN popularity is skyrocketing. Wireless LANs must meet requirements typical of any LAN. They must also meet requirements specific to their intended environment. IEEE 802.11 defines several services that the wireless LAN must provide if its usefulness is to match the functionality inherent in wired LANs. IEEE 802.11 is poised to have a significant impact on the LAN marketplace. As the demand for mobility and freedom from wiring requirements increases, the standard offers a comprehensive yet flexible approach to wireless LAN products 相似文献
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Runtime optimization of IEEE 802.11 wireless LANs performance 总被引:2,自引:0,他引:2
Bononi L. Conti M. Gregori E. 《Parallel and Distributed Systems, IEEE Transactions on》2004,15(1):66-80
IEEE 802.11 is the standard for wireless local area networks (WLANs) promoted by the Institute of Electrical and Electronics Engineers. Wireless technologies in the LAN environment are becoming increasingly important and the IEEE 802.11 is the most mature technology to date. Previous works have pointed out that the standard protocol can be very inefficient and that an appropriate tuning of its congestion control mechanism (i.e., the backoff algorithm) can drive the IEEE 802.11 protocol close to its optimal behavior. To perform this tuning, a station must have exact knowledge of the network contention level; unfortunately, in a real case, a station cannot have exact knowledge of the network contention level (i.e., number of active stations and length of the message transmitted on the channel), but it, at most, can estimate it. We present and evaluate a distributed mechanism for contention control in IEEE 802.11 wireless LANs. Our mechanism, named asymptotically optimal backoff (AOB), dynamically adapts the backoff window size to the current network contention level and guarantees that an IEEE 802.11 WLAN asymptotically achieves its optimal channel utilization. The AOB mechanism measures the network contention level by using two simple estimates: the slot utilization and the average size of transmitted frames. These estimates are simple and can be obtained by exploiting information that is already available in the standard protocol. AOB can be used to extend the standard 802.11 access mechanism without requiring any additional hardware. The performance of the IEEE 802.11 protocol, with and without the AOB mechanism, is investigated through simulation. Simulation results indicate that our mechanism is very effective, robust, and has traffic differentiation potentialities. 相似文献
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《Computer》2006,39(10):16-18
Since the approval of the original IEEE 802.11 standard and the increased use of the resulting Wi-Fi technology over the years, interest in wireless networking has grown rapidly. As is the case with other networking technologies, Wi-Fi users have sought faster IEEE 802.11 versions with longer transmission ranges. Because of this, users have eagerly awaited IEEE 802.11n, which promises higher speeds and longer ranges than earlier Wi-Fi versions. However, the technology has had a rocky standardization process. As is so often the case, two groups of vendors squared off over whose 802.11n approach would become the standard and thereby yield revenue and potential market dominance to the winner. Recently, though, the two sides have moved toward a compromise. However, there are still some unresolved issues, and the IEEE 802.11 Wireless Local Area Networks (WLAN) Working Group still hasn't approved the new technology as a standard 相似文献
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The IEEE 802.11e standard has been introduced recently for providing Quality of Service (QoS) capabilities in the emerging wireless local area networks. This standard introduces a contention window based Enhanced Distributed Channel Access (EDCA) technique that provides a prioritized traffic to guarantee the minimum bandwidth needed for time critical applications. However, the EDCA technique resets the Contention Window (CW) of the mobile station statically after each successful transmission. This static behavior does not adapt to the network state since it reduces the network usage and results in bad performance and poor link utilization whenever the demand for link utilization increases. This paper proposes a new adaptive differentiation technique for IEEE 802.11e Wireless Local Area Networks that takes into account the network state before resetting the contention window. In the new technique, the congestion level of the network is sensed by using previous CW values. Three other enhancement techniques that focus on network adaptation are also discussed. Their main limitations are the high complexity of the implemented algorithms and their slow adaptation to the network state when the channel experiences bursty traffic. The proposed technique is compared to the original differentiation techniques of IEEE 802.11a and IEEE 802.11e standards, as well as to the enhancement schemes. Results show that the proposed adaptive technique outperforms IEEE 802.11e and is comparable to the other enhancement schemes while maintaining relatively low complexity requirements. 相似文献
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《Computer Networks》2007,51(11):3013-3046
Wireless broadband technologies provide ubiquitous broadband access to wireless users, enabling services that were available only to wireline users. In this paper, we summarize emerging wireless broadband access technologies, ranging from WLANs to satellite communications. We explain the latest standards in the IEEE 802.11 and IEEE 802.16 families in detail. The MAC layer mechanisms of IEEE 802.11e, 802.11n, and 802.11s standards are explained as well as the point-to-multipoint and Mesh modes of IEEE 802.16. The recent mobility amendment to the WiMAX family, IEEE 802.16e, is also described. Though the earliest versions of some of these technologies date back to 1996 (such as IEEE 802.11) and some are obsolete (such as HiperLAN), they have been included in this survey for the sake of completeness.Wireless technologies can be categorized based on their coverage areas. IEEE 802.11 and ETSI HiperLAN standards are considered for wireless access in local areas. IEEE 802.16 and 802.22, ETSI HiperACCESS and HiperMAN, WiBro, and HAP technologies can be used to provide service in metropolitan areas. Lastly, IEEE 802.20 and satellite systems provide service as wide area networks. Since the aim of this survey is to summarize wireless broadband technologies for data services, technologies such as Wireless USB are excluded. 3G and 4G systems have also been excluded since they are covered in detail in [C. Smith, D. Collins, 3G Wireless Networks, second ed., McGraw-Hill Osborne Media, 2006; S.G. Glisic, Advanced Wireless Networks: 4G Technologies, Wiley Publishing, 2005]. 相似文献
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Wireless security is different 总被引:1,自引:0,他引:1
Wireless security requires slightly different thinking from wired security because it gives potential attackers easy transport medium access. This access significantly increases the threat that any security architecture must address. Wireless networking broadcast nature makes traditional link-layer attacks readily available to anyone. Wireless network security based on the IEEE 802.11 standard has received a lot of negative attention, since it is coupled with several design errors and security problems. IEEE 802.11 uses spread-spectrum signaling technology, which the military depends on for secure communications. Newer architectures are becoming available to dramatically increase the security of 802.11-based networks. 相似文献
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IEEE 802.11n MAC性能优化策略分析 总被引:1,自引:0,他引:1
伴随着各类无线产品的快速发展,传统的无线局域网已越来越不能适应这些产品的要求。IEEE 802.11n是新一代无线局域网标准。它不仅在物理层使用了如MI MO-OFDM、40 MHz信道等先进的技术,而且在MAC层也做了很大的改进,大大提高了网络的传输性能。本文将以IEEE 802.11n草案2.0协议为背景,在全面分析该协议的基础之上重点研究MAC层的帧聚合、TXOP、Block ACK、PSMP等优化策略。 相似文献