指数对的k阶自适应窗口表示算法

给出了一种新的计算指数对g^ah^b的Straus-Shamir类算法,该算法基于整数对的一个新表示,即k阶自适应窗口表示(k-AWE).证明了k-AWE的平均联合Hamming密度为3／(3k+1),与同类算法相比,本文算法更为有效.明确分析了在512到2048比特密钥长度的密码学应用中,窗口宽度的最佳取值为k=3.     

互联网传输协议的性能优化

文章分析了移动无线网络中传输控制协议的改进算法和传输控制协议的友好控制机制,并对新型传输层协议——流控制传输协议及其移动性支持功能进行了研究,进而分析了流控制传输协议在移动互联网中的性能优化方案。     

改善卫星Internet上TCP性能的措施

首先对卫星信道的特点及其对TCP性能的影响进行了分析,然后介绍了几种提高卫星链路上TCP性能的解决方案。     

Modeling TCP Incast Issue in Data Center Networks and an Adaptive Application-Layer Solution

In data centers, the transmission control protocol (TCP) incast causes catastrophic goodput degradation to applications with a many-to-one traffic pattern. In this paper, we intend to tame incast at the receiver-side application. Towards this goal, we first develop an analytical model that formulates the incast probability as a function of connection variables and network environment settings. We combine the model with the optimization theory and derive some insights into minimizing the incast probability through tuning connection variables related to applications. Then, enlightened by the analytical results, we propose an adaptive application-layer solution to the TCP incast. The solution equally allocates advertised windows to concurrent connections, and dynamically adapts the number of concurrent connections to the varying conditions. Simulation results show that our solution consistently eludes incast and achieves high goodput in various scenarios including the ones with multiple bottleneck links and background TCP traffic.     

基于×字形窗口的自适应中值滤波算法

传统的中值滤波方法在去除脉冲噪声的同时会损失部分图像细节,且运行速度也不能很好地满足实时性要求。在此对Matlab工具箱中的中值滤波算法进行改进,提出一种基于×字形滤波窗口的自适应中值滤波算法。该方法具有根据3×3的×字形窗口中噪声点个数自适应调整滤波窗口大小及根据矩阵的对称性及基本的逻辑运算实现×字形窗口的特点。实验结果表明,与传统的方形窗口中值滤波算法相比,该方法在有效去除椒盐噪声和脉冲噪声的同时,较好地保持了图像细节,缩短了运行时间。     

基于自适应滑动窗的模糊场景行人快速检测

智能场景监控是公共安全领域研究的热点.然而当前公共场所监控视频大都比较模糊,如何能够在模糊场景下快速检测行人目标是一个亟待解决的问题.通过引入一个自适应尺寸的行人检测窗,以特定策略滑动扫描前景二值图像,并根据一系列行人轮廓判别条件获取行人目标,实现了对模糊监控场景的实时行人检测与人数统计.实验结果表明,与传统算法相比,该算法可以有效快速地检测出指定区域内的行人目标.     

Detecting spurious timeouts in wireless cellular networks using DS‐Agent

Large and sudden variations in packet transmission delays are often unavoidable in wireless networks. Such large delays, refer to as delay spikes (DSs), are likely to exceed several times the typical network round‐trip‐time figures, which can cause TCP spurious timeouts. The spurious timeouts lead to unnecessary retransmissions and reduction of the TCP sender's transmission rate, and degradation of TCP throughput. In this paper we propose a new scheme called DS‐Agent. The spurious timeout is detected by a DS‐Agent and thus TCP sender can response to this spurious timeout accordingly. The simulation results show the better performance of DS‐Agent scheme compared with F‐RTO and TCP Reno in the presence of DSs which is caused by mobility. Copyright © 2006 John Wiley & Sons, Ltd.     

空时自适应处理的滑窗递推QR算法

在局部平稳的杂波环境下,滑窗样本选取方法可以比较准确地估计检测单元的杂波统计特性。该文提出基于滑窗选取样本的递推QR算法,它采用双曲Householder变换实现QR分解的递推,能有效地抑制局部平稳杂波,且具有数值稳定性好,计算量小的优点。仿真数据处理和实测数据处理验证了该方法的有效性。     

A study on a receiver‐based management scheme of access link resources for QoS‐controllable TCP connections

Although the bandwidth of access networks is rapidly increasing with the latest techniques such as DSL and FTTH, the access link bandwidth remains a bottleneck, especially when users activate multiple network applications simultaneously. Furthermore, since the throughput of a standard TCP connection is dependent on various network parameters, including round‐trip time and packet loss ratio, the access link bandwidth is not shared among the network applications according to the user's demands. In this thesis, we present a new management scheme of access link resources for effective utilization of the access link bandwidth and control of the TCP connection's throughput. Our proposed scheme adjusts the total amount of the receive socket buffer assigned to TCP connections to avoid congestion at the access network, and assigns it to each TCP connection according to characteristics in consideration of QoS. The control objectives of our scheme are (1) to protect short‐lived TCP connections from the bandwidth occupation by long‐lived TCP connections, and (2) to differentiate the throughput of the long‐lived TCP connections according to the upper‐layer application's demands. One of the results obtained from the simulation experiments is that our proposed scheme can reduce the delay of short‐lived document transfer perceived by the receiver host by up to about 90%, while a high utilization of access link bandwidth is maintained. Copyright © 2006 John Wiley & Sons, Ltd.     

TCP拥塞控制慢启动策略的研究

分析了现有的慢启动策略,针对现有策略中拥塞窗口增长不够平滑的问题,提出了一种新的慢启动方式。用NS2进行了仿真,比较了慢启动策略和传统策略的性能。结果表明,和传统策略相比,采用的慢启动策略时,拥塞窗口值的增长更趋平滑,丢包率明显减小,瓶颈链路的利用率也有所提高。     

液压伺服系统自适应模糊变结构控制

结合变结构控制、自适应控制和模糊技术等特点,提出一种自适应模糊变结构控制方法.首先,设计一个带积分开关平面函数的变结构控制器,并构造一个二维模糊边界层宽度调节器以削弱抖振.其次,基于Lyapunov稳定性理论,引入一自适应算法,自适应调节变结构控制参数.应用于液压伺服系统的控制实验结果表明,所提出的控制方法能削弱抖振,改善液压伺服系统稳态控制精度,具有较强的鲁棒自适应综合性能.     

无线传感器网络MAC协议研究

无线传感器网络因其巨大的应用前景,已成为计算机与通信领域一个活跃的研究分支。随着对无线传感器网络MAC(media access control)层的研究的深入,出现了许多为无线传感器网络设计的具有低能耗特征的MAC协议。对其中的典型协议进行了分析比较,给出了进一步的研究方向。     

自由旋气动窗口设计原理及其工作性能的初步实验研究

论述了自由旋气动窗口（ＦＡＤＷ ）的基本工作原理,并对为万瓦级ＣＯ２ 气动激光器配置的３０ ｍ ｍ ×３０ ｍ ｍ 大口径自由旋气动窗口的工作性能进行了实验研究。研究表明,此气动窗口在其工作范围内,密封压比ＰＲ（环境大气压ＰＡＭＢ／密封腔压ＰＣ）＞ ２０, 最大可达到２８;而且该气动窗口具有良好的启动性能和对光束质量影响小的特点。因此对于大口径、低腔压的大功率气体激光器来说,自由旋气动窗口是替代输出镜最有效的手段之一。     

基于预测控制的自适应PID控制器设计与仿真

从数学上建立了预测控制与PID控制的广义联系,并结合某火电厂300MW锅炉机组,针对烟气氧含量控制回路,在不改变原有控制系统框架的基础上,采用基于GPC的PID控制方法,很好地解决了在锅炉负荷和氧含量设定值同时变化的情况下系统的动态响应不理想的问题。通过MATLAB仿真,验证了该控制系统具有较好的控制品质,适合具有一定延迟的复杂控制系统。     

Comparative analysis of cumulative distribution function for TCP congestion window size and triple‐duplicate period

Various version of Transmission Control Protocol (TCP) congestion window model are available in the literature. TCP congestion control is handled in two phases: (a) slow start and (b) congestion avoidance. This paper deals with congestion avoidance phase that is based on additive increase multiplicative decrease (AIMD) mechanism in which window size either increase by one or cuts to half of the previous window size. For distribution of window sizes, a model developed by Yan et al has been presented for two loss indications: (a) triple duplicate (TD) and (b) time‐outs (TOs) only while it does not deal with the window size limitation. It does not allow to cap over the TCP congestion window size if the buffer size is restricted to a fixed value though window size could not move beyond that. The unconstrained window size moves on in the presence of low loss probability. In this paper, we propose a model for the case where the window size is bounded by a maximum value that makes applicable to window size limitation as well. Further, the work has been extended to develop a new model that obtains a cumulative distribution function for TD periods (TDPs). The proposed model is validated on ns‐2, and we conclude that observed results for distribution function are very closed to our proposed model.     

基于自适应窗口固定及传播的 多尺度纹理图像分割

 本文提出一种基于自适应窗口固定及传播的多尺度纹理图像分割方法,在小波域隐马尔科夫树模型(WHMT)的初始分割基础上,根据分割粗尺度上的区域一致性好,细尺度上的边缘准确的特点,利用上下尺度像素之间以及本层邻域像素的马尔科夫性,标记出图像的一致性区域和边缘区域,将一致性区域固定,类标直接下传到下一尺度,边缘区域则利用邻域信息确定出上文权值背景传播到下一尺度,与下尺度一起共同指导图像分割,从而很好的保持了区域均匀性和边缘准确性.同时根据纹理图像区域聚集性的特性,利用基于多项式展开和置信区间交叉(LPA_-ICI)方法找出各类区域聚集的物理位置中心,融入上下文权值背景中,使得指导分割策略能够更好的进行.实验表明,对于合成纹理图像来说,本文提出的多尺度融合算法在均匀区域内部及区域边界都大为改善,而且无须进行参数的训练,使算法快速的完成.     

Ad Hoc网络中具有QoS保障的同步MAC协议

介绍了Ad Hoc网络中保障实时业务QoS要求的时间同步多址接入协议。该类协议以时分多址为基础,通过资源预留为实时业务预约固定的时隙,赋予实时业务接入信道的优先权,保证了实时业务的接入延时,延时抖动以及吞吐量等QoS指标,为Ad Hoc网络支持多媒体业务的接入奠定了基础。     

Adaptive smooth multicast protocol for multimedia transmission: Implementation details and performance evaluation

In this paper we propose a new single‐rate multicast congestion control scheme named Adaptive Smooth Multicast Protocol (ASMP), for multimedia transmission over best‐effort networks. The smoothness lays in the calculation and adaptation of the transmission rate, which is based on dynamic estimations of protocols' parameters and dynamic adjustment of the ‘smoothness factor’, as well. ASMP key attributes are: (a) TCP‐friendly behavior, (b) adaptive scalability to large sets of receivers, (c) high bandwidth utilization, and finally (d) smooth transmission rates, which are suitable for multimedia applications. We evaluate the performance of ASMP and investigate its behavior under various network conditions through extensive simulations conducted with the network simulator software (ns2). Simulation results show that ASMP can be regarded as a serious competitor of TFMCC and PGMCC. In many cases, ASMP outperforms TFMCC in terms of TCP‐friendliness and smooth transmission rates, while PGMCC presents lower scalability than ASMP. We have implemented ASMP on top of RTP/RTCP protocols in ns2 by adding all the RTP/RTCP protocol's attributes that are defined in RFC 3550 and related to quality of service metrics. Copyright © 2009 John Wiley & Sons, Ltd.     

Steady state and transient state behaviours analyses of TCP connections considering interactions between TCP connections and network

The Internet uses a window‐based congestion control mechanism in transmission control protocol (TCP). In the literature, there have been a great number of analytical studies on TCP. Most of those studies have focused on the statistical behaviour of TCP by assuming a constant packet loss probability in the network. However, the packet loss probability, in reality, changes according to the packet transmission rates from TCP connections. Conversely, the window size of a TCP connection is dependent on the packet loss probability in the network. In this paper, we explicitly model the interaction between the congestion control mechanism of TCP and the network as a feedback system. By using this model, we analyse the steady state and the transient state behaviours of TCP. We derive the throughput and the packet loss probability of TCP, and the number of packets queued in the bottleneck router. We then analyse the transient state behaviour using a control theoretic approach, showing the influence of the number of TCP connections and the propagation delay on the transient state behaviour of TCP. Copyright © 2005 John Wiley & Sons, Ltd.     

基于改进自适应IMM算法的高速列车组合定位

针对列车高精度定位问题,该文提出基于改进自适应交互多模型(IMM)的高速列车高精度组合定位方法。首先,根据列车定位需求和各传感器特点,设计了卫星接收器、轮轴测速传感器、测速雷达以及单轴陀螺仪4种传感器的组合定位方案。然后,针对IMM融合滤波算法因先验信息不准导致固定参数设置不当的问题,引入Sage-Husa自适应滤波和转移概率矩阵(TPM)自适应更新集成为自适应IMM算法。针对多模型切换的滞后问题,利用子模型似然函数值能快速反映模型变化趋势的特点,将似然函数值设为判定标志,并引入判定窗对TPM矩阵元素进行修正,有效提升了模型的切换速度。最后,基于改进自适应IMM算法对4种传感器定位信息进行融合滤波,实现高速列车的高精度组合定位。仿真结果表明：改进后的算法相比其他自适应IMM算法提升定位精度1.6%～14.7%,并且能通过提高模型间切换速度来有效降低位置误差峰值,同时具备较好的抗噪性能。