变结构拥塞控制协议(Variable-structure Congestion control Protocol,VCP)是一种专门针对TCP在高带宽时延积网络下存在不稳定性而提出的新型拥塞控制协议,并具有保持稳定的低队列,高带宽利用率,公平性的优点.但在网络突发业务流的情况下,VCP存在收敛于稳定吞吐量速率过慢的问题.针对这个问题,本文分析了导致VCP收敛速率慢的原因,并提出了一种可以提高VCP协议收敛速率的自适应算法,同时给出了稳定性分析.NS2仿真结果表明,该方案可以提高收敛速率,并且保留了VCP原有的优点.
According to the delay property, linear time-delay （LTD） systems can be classified as LTD systems with depen- dent delays （LTD_DD） and LTD systems with independent delays （LTD_ID）. This paper reveals that the stability condition for LTD_ID systems can be applied to LTD_DD systems, a sufficient stability condition for LTD_DD systems is derived from it, while only fewer of the LTD_DD systems can satisfy the stability condition due to the very strict limitation for the delays of the LTD_DD systems. To solve the problem, based on two-dimensional （2-D） hybrid polynomials, some sufficient conditions for stability of LTD_DD systems are pro- posed. Examples show that the proposed stability test algorithms are simple and valid.
该文通过分析SAR图像的噪声成因以及其斑点噪声模型,结合图像的稀疏表示理论提出一种基于稀疏表示的Shearlet域SAR图像去噪算法。算法从整体上对SAR图像进行去噪:首先对SAR图像进行Shearlet变换,然后利用稀疏表示模型构造出去噪的最优化模型,在此基础上进行迭代去噪,然后重构SAR图像得到去噪后的图像。实验结果表明:该文所提出的算法不仅可以显著去除相干斑噪声,提高去噪图像的峰值信噪比(Peak Signal toNoise Ratio,PSNR),还明显地改善了图像的视觉效果,更好地保留了图像纹理信息。
It is difficult to determine the stability of linear systems with interval delays （LID systems） because the roots of the characteristic polynomials of the systems are continuous and vary in a complex plane with the delay. To solve the problem, this paper develops a stability test of LID systems by resorting to 2-D hybrid polynomials and 2-D Hurwitz-Schur stability. Comparing with the existing test approaches for LID systems, the proposed 2-D Hurwitz-Schur stability test is easy to apply, and can obtain closed form constraint conditions for system parameters. This paper proposes some theorems as sufficient conditions for the stability of LID systems, and also reveals that recent results about the stability test of linear systems with any delays （LAD systems） are not suitable for LID systems because they are very conservative for the stability of LID systems.
An active queue management（AQM） algorithm called MCHOKeM is presented,which is borrowed from CHOKeW that draws multi-packets at random from the buffer,the multi-packets are compared with an arriving packet and abandoned if they are from the same flow.But MCHOKeM uses multiple virtual queues for different priority packets and enhances the drawing function by adjusting the maximum number of draws based on the current status of virtual queue length.The number of parameters that MCHOKeM needs to maintain is determined by the number of priority levels being supported by the router,which usually has a small limited value.In order to explain the features of MCHOKeM,an analytical model is used.A series of simulation tests to evaluate the performance are given.
