TCP over OBS边缘节点重传机制的研究

使用传输控制协议(TCP)的拥塞控制机制在传统互联网技术中是解决问题的很好方法.然而在面对新型的光网络技术OBS网络,简单地采用TCP技术因受到OBS自身特性的影响,性能表现不佳,吞吐量低下.为此,通过对OBS技术和TCP拥塞控制机制深入的研究,提出一种基于OBS边缘节点的ACK重传机制来提升TCP over OBS性能的方法,提高OBS网络吞吐量.     

卫星网中的TCP慢启动机制的研究

摘要：TCP连接中的慢启动在卫星网的环境下对TCP性能有着非常重要的影响，讨论了动的相关的因素以及针对卫星网的特点做出的改进。在文章的最后，分析了一个实际操作系统中TCP／IP协议的滑动窗口实现。     

On the use of EMD based adaptive filtering for OFDM channel estimation

Hilbert Huang transform (HHT) based data driven empirical mode decomposition (EMD) in conjunction with adaptive filter (AF) is proposed for estimation of communication channel in OFDM system. EMD can be viewed as alike of wavelet decomposition which decomposes the signal of interest to intrinsic mode functions (IMF), whose basis function is derived from signal itself. In this method, the length of channel impulse response (CIR), is approximated using Akaike information criterion (AIC). Then the estimation of CIR is performed using adaptive filter with EMD decomposed IMF of the received OFDM symbol. Conventional AF uses random initial weight vector. The novelty of the proposed method lies in the fact that it uses decimated version of one of the decomposed IMFs of received OFDM symbol as initial weight vector. The selection of useful IMF component is done based on correlation and kurtosis measures. This makes the proposed EMD based AF method converge to minimum mean square error (MMSE) in less number of iterations resulting in almost 50% saving of computations. Bit error rate (BER), mean square error (MSE) and normalized root mean square error (NRMSE) are computed. The simulation studies established the efficacy of proposed method; and comparative studies under different modulation schemes and fading conditions revealed improved performance. Simulations have shown an average improvement of 3 dB in BER performance for proposed EMD based AF as compared to conventional AF.     

基于CS的Kalman滤波OFDM信道估计

在OFDM系统信道估计中,准确的时域卡尔曼滤波（TDKF）估计需要信道多径时延作为先验条件,而且具有较低的频谱效率.考虑到大多数无线信道具有稀疏和时变的特性,提出一种改进的卡尔曼滤波与压缩感知联合信道估计方法,采用稀疏度自适应匹配追踪（SAMP）算法,并对信道响应变化量进行重建.仿真结果表明,相较于已有算法,提出的算法不需要知道信道的稀疏度,而且信道估计结果更加准确.     

基于混合结构导频和FFT低通滤波的OFDM信道估计

精确的估计精度、良好的跟踪能力,以及实现简单是信道估计的三个基本要求.本文提出一种混合结构导频的信道估计新方法,采用块状导频和基于FFT低通滤波的LS算法捕捉准确的信道频域响应,利用少数梳状导频和改进的LS算法跟踪信道变化和修正相位噪声.通过仿真证明,该方法估计精度高,频谱利用高,信道跟踪能力强,实现简单,满足了慢衰落信道环境下的应用要求.     

基于暗原色和加权形态学滤波的图像去雾算法

针对雾天图像能见度低、对比度差的特点,提出一种自动消除雾的方法：基于暗原色和加权形态滤波的增强算法。首先引入暗原色先验信息,然后利用形态学滤波方法估计雾浓度图。该方法既能平滑雾浓度图,又能很好地保留场景的边缘,使估计出的雾浓度图更加精确。最后恢复去雾图像。实验结果表明,该方法简单快速有效,能够很好地达到去雾目的,并且较好地保留图像边缘细节。     

基于三维滤波的视频去噪算法研究

视频去噪的目的是将原始视频从观测到的含噪视频中还原出来。对基于三维滤波的视频去噪算法进行了研究。首先利用贝叶斯阈值对视频序列的各帧在小波域中滤波,之后对帧间连续三帧图像进行帧间滤波。仿真结果表明该算法的有效性。     

光子晶体线缺陷波导中的慢光研究

研究了线缺陷光子晶体波导中的慢光现象。运用平面波展开法对线缺陷光子晶体波导结构进行了模拟计算,分析了填充因子作为敏感结构参量,其变化对色散性质和群速度的影响。发现光子晶体的填充因子决定了光子晶体带隙中导模的传输特性。随着填充因子的增加,光子晶体波导中的群速度先增大再减小。可以证明,通过改变光子晶体的填充因子,群速度可以达到0.01c以下。     

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.     

分子束外延GaAs／AlGaAs超晶格缓冲层量子阱材料的研究

采用分子束外延技术生长了ＧａＡｓ／ＡｌＧａＡｓ单量子阱得多量子阱材料。采用ＧａＡｓ／ＡｌＧａＡｓ超晶格缓冲层掩埋衬底缺陷，获得的量子阱结构材料被成功地用于制作量子阱激光器。波长为７７８ｎｍ的激光器，最低阈值电流为３０ｍＡ，室温下线性光功率大于２０ｍＷ。     

基于数字滤波的半导体激光器温控系统设计

为了使光收发模块发射光波长稳定,突破现有半导体激光器温控系统大都采用模拟器件实现的常规设计,提出了一种基于数字滤波方式的控制方案,采用数字信号处理方式,以固件形式实现了半导体激光器温度控制。通过理论分析和实验验证,取得了采用该方案的光收发模块在应用温度范围内的发射波长变化数据。结果表明,该系统性能稳定,温度控制精度达0.053℃。     

基于线阵图像传感器的新型空间滤波测速仪

为了实现对固体表面运动速度的高精度测量,建立了一套基于线阵图像传感器的新型空间滤波测速仪系统,提出了一种确定系统误差来源的新方法。图像传感器在系统中既作为探测器又作为空间滤波器使用,系统结构得到了很大的简化。在理论上对线阵图像传感器的空间滤波特性进行了分析,并设计了图像传感器的驱动电路、信号采集和预处理电路。测量了由高精度转台作为主动轮的传送带速度和日光灯的发光频率。实验结果表明,传送带速度测量精度在0.77%以内,11 min 内的测量不确定度为0.66%;而在不使用成像系统的条件下直接测量日光灯的发光频率时,测量不确定度在0.056%以内,提高了一个数量级。总之,该测速仪能够基本满足传送带表面运动速度测量的实时、非接触、稳定和高精度等要求。     

平面超材料对曲折线慢波结构行波管效率改善和杂模抑制的影响

针对U型曲折线慢波结构带状注行波管杂模抑制和互作用效率提高等面临的挑战,提出了一种开口菱形超材料结构。在综合考虑电路单元谐振性能、与U型曲折线慢波结构之间的协调配合以及电路实现可行性和结构简单等因素,通过电路设计和数值模拟优化等具体措施相结合,探讨这种超材料对增强注波互作用表面电场和抑制电路振荡的效果。在Ka波段优化的结果表明,这种超材料在抑制杂波和改善注波互作用效率方面效果明显,对此类行波管稳定性提高具有重要意义。     

Potential friendship discovery in social networks based on hybrid ensemble multiple collaborative filtering models in a 5G network environment

At present, 5G network technology is being applied to various social network modes, and it can provide technical and traffic support for social networks. Potential friendship discovery technology in 5G-enabled social networks is beneficial for users to make potential friends and expand their range of activities and social hierarchy, which is highly sought after in today's social networks and has great economic and application value. However, the sparsity of the dominant user association dataset in 5G-enabled social networks and the limitations of traditional collaborative filtering algorithms are two major challenges for the friend recommendation problem. Therefore, in order to overcome these problems regarding previous models, we propose a Hybrid Ensemble Multiple Collaborative Filtering Model (HEMCF) for discovering potential buddy relationships. The HEMCF model draws on a special autoencoder method that can effectively exploit the association matrix between friends and additional information to extract a hidden representation of users containing global structural information. Then, it uses the random walk-based graph embedding algorithm DeepWalk to extract another hidden representation of users in the buddy network containing local structural information. Finally, in the output module, the HEMCF model stacks and multiplies the two types of hidden representations of users to ensure that the information mentioned above is concentrated in the final output to generate the final prediction value. The magnitude of the prediction value represents the probability of the users being friends, with larger values representing a high probability of the two users being friends, and vice versa. Experimental results show that the proposed method boosts the accuracy of the relationship prediction over baselines on 3 real-world public datasets dramatically.     

Adaptive AQM controllers for IP routers with a heuristic monitor on TCP flows

We propose adaptive proportional (P) and proportional‐integral (PI) controllers for Active Queue Management (AQM) in the Internet. We apply the classical control theory in the controller design and choose a proper phase margin to achieve good performance of AQM. We have identified a simple heuristic parameter that can monitor the changes of network environment. Our adaptive controllers would self‐tune only when the dramatic change in the network parameters drift the monitoring parameter outside its specified interval. When compared to P controller, a PI controller has the advantage of regulating the TCP source window size by adjusting the packet drop probability based on the knowledge of instantaneous queue size, thus steadying the queue size around a target buffer occupancy. We have verified our controllers by OPNET simulation, and shown that with an adaptive PI controller applied, the network is asymptotically stable with good robustness. Copyright © 2005 John Wiley & Sons, Ltd.