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.
The existing active queue management （AQM） algorithm acts on subscribers and edge routers only, it does not support differentiate-serve （Diffserv） quality of service （QoS）, while the existing diffserv QoS has not considered the link capacities between edge routers and connected core routers. When a core router in a two layers’ network experiences congestion, the connected edge routers have no ability to adjust their access data rates. Thus, it is difficult to achieve the congestion control for the large scale network with many edge routers and core routers. To solve these problems, two difffserve AQM algorithms are proposed for the congestion control of multilayer network. One diffserv AQM algorithm implements fair link capacities of edge routers, and the other one implements unequal link capacities of edge routers, but it requires the core routers to have multi-queues buffers and Diffserv AQM to support. The proposed algorithms achieve the network congestion control by operating AQM parameters on the conditions of proposed three theorems for core and edge routers. The dynamic simulation results demonstrate the proposed control algorithms for core and edge routers to be valid.
The application of protograph low density parity check （LDPC） codes involves the encoding complexity problem. Since the generator matrices are dense, and if the positions of ＂1＂ s are irregularity, the encoder needs to store every ＂1＂ of the generator matrices by using huge chip area. In order to solve this problem, we need to design the protograph LDPC codes with circular generator matrices. A theorem concerning the circulating property of generator matrices of nonsingular protograph LDPC codes is proposed. The circulating property of generator matrix of nonsingular protograph LDPC codes can be obtained from the corresponding quasi-cyclic parity check matrix. This paper gives a scheme of constructing protograph LDPC codes with circulating generator matrices, and it reveals that the fast encoding algorithm of protograph LDPC codes has lower encoding complexity under the condition of the proposed theorem. Simulation results in ad- ditive white Gaussian noise （AWGN） channels show that the bit error rate （BER） performance of the designed codes based on the proposed theorem is much better than that of GB20600 LDPC codes and Tanner LDPC codes.
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。
