共查询到20条相似文献,搜索用时 109 毫秒
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红外数据协会(IrDA)最近公布的先进红外协议(AIr)为红外无线局域网的发展奠定了基础。AIr协议在媒体访问控制(MAC)、链接控制和链接管理上选择了无包级确认协议(No PLACK)、包级确认协议(PLACK)、停-等自动重传请求协议(SW-ARQ)等协议。NoPLACK协议提供窗口中帧确认和重传机制,保证不同误码率下的传输,但链路参数选取的不匹配导致吞吐量性能与其数学模型给出的吞吐量公式相悖,实验表明链路参数的优化对链路传输的质量和稳定有重要的影响。本文对其中的主要参数——窗口大小进行优化,并给出协议改进的方法和建议。 相似文献
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针对RMAC(Routing-enhanced Medium Access Control)协议丢包处理机制的缺陷,采用重传机制,提出了一种高效多跳传输的MAC协议(Efficiency-RMAC,E-RMAC)。根据在规定时间T内的接收值判断是否传输失败,当控制帧传输失败则采用单次重传机制,并引入睡眠模式,由此减小了网络能量消耗;当数据包传输失败时采用的是多次重传机制,由此保证了数据包实时可靠的单周期多跳传输,提高了信道利用率。仿真结果表明,在传输时延和网络吞吐量上E-RMAC均优于RMAC,实现了协议的高效性,延长了网络生命周期。 相似文献
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提出了一种提供QoS保障的多信道MAC协议,该协议把不同种类业务划分优先级和帧 间隔时间,以保障优先级高的数据较早接入信道,同时把高层数据按目的地址的不同建立发送链表,采用自动重传技术,实现数据信道上连续的帧交换过程.仿真结果表明,该方法大大提高了数据信道利用率,改善了系统性能. 相似文献
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TCP协议应用在3G无线网络中时,其传输性能受到了无线网络物理层帧差错率的严重影响。链路层重传技术可以大大改善TCP数据传输性能因无线信道误码率大而下降的情况。主要研究了CDMA2000中链路层重传技术对无线TCP数据传输的影响,并结合TCP层重传超时机制,提出了一种新的自适应链路层重传算法,提高了TCP在无线链路的数据传输性能。最后对该算法进行仿真,验证了此算法可以显著提高TCP吞吐率。 相似文献
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一种改善无线TCP性能的链路层重传方案 总被引:1,自引:0,他引:1
提出一种提高无线环境中TCP性能的链路层选择性重传的改进方案mARQ.根据每个数据包在链路层被拆分成多个无线帧这一特点,对包中所有帧的重传次数之和进行限定,使其可以根据各帧的需求进行自适应分配.系统仿真表明:与传统方案相比,新设计方案mARQ在高误帧率的环境下以较低的误包率获得了较高的TCP吞吐量,提高了无线环境下TCP的性能. 相似文献
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针对以文字书写教学装置为终端的教室系统的数据传输要求和特性,分析已有协议处于该环境下所面临的局限性,提出一种适合该类教室系统的嵌入式局域网协议CSELP。在以太网帧的基础上扩展8个字节实现确认、超时重传、流量控制等功能,提供面向连接的可靠传输服务,简化数据处理和状态机制;采用改进的带宽预估算法估计可用带宽大小,在拥塞避免阶段根据预测的窗口大小变化调整拥塞窗口;设计重传队列实现面向组的确认机制,从而提高系统的实时性和传输效率。实验结果表明,该协议能满足文字书写教学教室系统的应用需求,并且可推广到非文字书写教学的教室系统。 相似文献
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In this paper, we investigate the relationship of quantum teleportation in quantum information science and the Birman–Murakami–Wenzl (BMW) algebra in low-dimensional topology. For simplicity, we focus on the two spin-1/2 representation of the BMW algebra, which is generated by both the Temperley–Lieb projector and the Yang–Baxter gate. We describe quantum teleportation using the Temperley–Lieb projector and the Yang–Baxter gate, respectively, and study teleportation-based quantum computation using the Yang–Baxter gate. On the other hand, we exploit the extended Temperley–Lieb diagrammatical approach to clearly show that the tangle relations of the BMW algebra have a natural interpretation of quantum teleportation. Inspired by this interpretation, we construct a general representation of the tangle relations of the BMW algebra and obtain interesting representations of the BMW algebra. Therefore, our research sheds a light on a link between quantum information science and low-dimensional topology. 相似文献
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The performance of climate control systems in vehicles becomes more and more important, especially against the background of the important relationship between compartment climate and driver mental condition and, thus, traffic safety. The performance of two different types of climate control systems, an un-air-conditioned heating/cooling device (VW) and an air-conditioning climate control unit (BMW), is compared using modern and practical evaluation techniques quantifying both the dynamic 3-D temperature distribution and the local air refreshment rate. Both systems suffer from considerable temperature gradients: temperature gradients in the U-AC (VW) car up to 8-9 degrees C are encountered, while the AC (BMW) delivers clear improvement resulting in temperature gradients of 5-6 degrees C. The experiments clearly demonstrate the effect of the presence of even a single passenger on the thermal regime, increasing the existing thermal discrepancies in the compartment with 15% independent of ventilation rate. Furthermore, in terms of air refreshment rates in the vehicle compartment, an air-conditioning unit halves the air refreshment time at all positions in the vehicle cabin, delivering a significant improvement in terms of human comfort. Similarly, extra air inlets in the back compartment of a car deliver progress in terms of cabin refreshment rate (93 s down to 50 s). 相似文献
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Haeryong Park Seongan Lim Ikkwon Yie Kitae Kim Junghwan Song 《Computer Standards & Interfaces》2009,31(4):856-862
A signature scheme is strongly unforgeable if no adversary can produce a new valid signature σ on a message M even after seeing some signatures on M. We define strong unforgeability of group signature schemes and explain why the strong unforgeability of a group signature scheme is necessary. This relatively new security concept was not considered when Bellare–Micciancio–Warinschi established their security model, what we call the BMW security model, of group signature schemes. We show that a scheme proposed at Eurocrypt'06 that was proven secure in the BMW security model is not strongly unforgeable. We also present a method to convert this scheme into a strongly unforgeable group signature scheme preserving the security in the BMW security model. 相似文献
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《Ergonomics》2012,55(3):364-378
The performance of climate control systems in vehicles becomes more and more important, especially against the background of the important relationship between compartment climate and driver mental condition and, thus, traffic safety. The performance of two different types of climate control systems, an un-air-conditioned heating/cooling device (VW) and an air-conditioning climate control unit (BMW), is compared using modern and practical evaluation techniques quantifying both the dynamic 3-D temperature distribution and the local air refreshment rate. Both systems suffer from considerable temperature gradients: temperature gradients in the U-AC (VW) car up to 8–9°C are encountered, while the AC (BMW) delivers clear improvement resulting in temperature gradients of 5–6°C. The experiments clearly demonstrate the effect of the presence of even a single passenger on the thermal regime, increasing the existing thermal discrepancies in the compartment with 15% independent of ventilation rate. Furthermore, in terms of air refreshment rates in the vehicle compartment, an air-conditioning unit halves the air refreshment time at all positions in the vehicle cabin, delivering a significant improvement in terms of human comfort. Similarly, extra air inlets in the back compartment of a car deliver progress in terms of cabin refreshment rate (93 s down to 50 s). 相似文献
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现已上天的微波辐射计大都采用100GHz以下频率,其观测资料应用的最大限制就是它们的空间分辨率不够高。随着高频微波元器件研制技术的不断发展,我们对使用毫米波、亚毫米波及更高频段进行地气系统遥感的可行性及重要性都已有了相当充分的认识。这里试图给出一个有关使用微波110GHz以上高频在进行大气参量被动遥感方面研究的简要综述,包括大气温度和湿度廓线的反演、卷云遥感以及云和降水的探测 相似文献
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在图像被大噪声污染或具有较低分辨率时,传统的偏微分方程(PDE)模型的稳态解会产生明显的阶梯效应,恢复图像质量较差。针对此缺点,提出了一种新的基于K-奇异值分解(K-SVD)的PDE图像恢复方法,并应用于毫米波(MMW)图像的恢复。K-SVD是一种图像稀疏表示方法,对图像进行稀疏估计的同时实现去噪,对噪声方差较大的图像具有较好的去噪鲁棒性。首先采用K-SVD对MMW图像进行去噪,对去噪图像再应用全变分(TV)模型的PDE方法进行恢复。对所提出的算法分别使用模拟的MMW图像和真实的MMW图像进行测试,并进一步和K-SVD、PDE方法比较,同时使用峰值信噪比(PSNR)对恢复图像进行评价。根据不同噪声方差下的PSNR数据和恢复图像的视觉效果,实验结果证明了所提方法能够有效地恢复MMW图像。 相似文献
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针对毫米波(MMW)图像包含大量未知噪声、图像分辨率较低的问题,考虑模糊径向基函数神经网络(F-RBFNN)的非线性滤波特性和基于K-奇异值分解(K-SVD)稀疏表示(SR)的自适应消噪特性,提出了一种级联消噪的毫米波图像恢复方法。F-RBFNN将模糊逻辑的知识表达和推理能力与RBFNN的快速学习能力和泛化能力结合起来,可根据实际问题调整网络结构参数,对MMW图像达到非线性滤波的目的。进一步利用K-SVD稀疏表示具有人眼视觉特性,在保持目标特征的同时可有效消噪的优点,对FRBFNN的训练结果再次进行局部图像降噪,得到分辨率较高的MMW图像。采用相对信噪比(RSNR)作为消噪图像的评价标准,实验结果表明,与F-RBFNN、K-SVD消噪、小波消噪等方法相比,基于F-RBFNN和SR的降噪方法能够获得较好的MMW图像恢复质量。 相似文献
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毫米波穿透力强且具有全天时、全天候工作能力,在反恐安检方面具有广阔的应用前景。针对藏匿物品的安全检查获取的毫米波辐射图像,与小波软硬阈值预处理滤除噪声算法相比,提出一种复合结构形态学自适应滤波算法对毫米波辐射图像进行了滤波处理,然后对处理后图像进行边缘检测与特征分析。实验结果表明,复合结构形态学自适应滤波算法能有效地去除毫米波辐射图像中的噪声,提取的图像边缘特征符合藏匿物品的几何特征。 相似文献
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基于马氏距离的一维距离像识别算法仿真 总被引:5,自引:0,他引:5
针对欧氏距离受模式特征量纲影响的缺点,且影响制导精度和抗干扰的能力,采用一种基于马氏的一维距离像目标识别方法。通过对毫米波雷达目标回波进行IFFT变换得到一维距离像,用主分量分析算法对距离像进行降噪和特征提取,取最小马氏距离判别目标类别。马氏距离考虑了模式特征参数的大小以及特征间的相关性,克服了欧氏距离受量纲影响的缺点。与欧氏距离的分类算法仿真结果比较,马氏距离算法具有较好的识别性能;在不同信噪比下的仿真结果表明,方法适用于毫米波雷达一维距离像目标识别。 相似文献