一种TDD-MIMO系统混合预编码传输机制

针对TDD-MIMO系统中,天线之间存在相关性时会影响系统性能的问题,提出一种混合预编码传输机制.在该机制中,基站首先采用一种低复杂度的信道估计算法来计算信道矩阵,然后计算信道矩阵的相关度来判断相关性的高低并选择相应的预编码方式.当相关度大于等于转换系数时,采用基于协方差矩阵的预编码;反之,则利用基于LR的预编码.仿真结果表明,该机制充分利用了2种预编码分别适用于不同相关性范围的特点,在降低了系统的误码率的同时保持了低复杂度,提高了系统在天线之间存在相关性时的容量.仿真验证了该机制的有效性.     

Deterministic convergence of conjugate gradient method for feedforward neural networks

Conjugate gradient methods have many advantages in real numerical experiments, such as fast convergence and low memory requirements. This paper considers a class of conjugate gradient learning methods for backpropagation neural networks with three layers. We propose a new learning algorithm for almost cyclic learning of neural networks based on PRP conjugate gradient method. We then establish the deterministic convergence properties for three different learning modes, i.e., batch mode, cyclic and almost cyclic learning. The two deterministic convergence properties are weak and strong convergence that indicate that the gradient of the error function goes to zero and the weight sequence goes to a fixed point, respectively. It is shown that the deterministic convergence results are based on different learning modes and dependent on different selection strategies of learning rate. Illustrative numerical examples are given to support the theoretical analysis.     

Joint relay selection and resource allocation in cooperative device-to-device communications

Device-to-device (D2D) communications allow proximate cellular user equipments (UEs) to communicate with each other directly under the control of base station (BS). In this paper, considering the selection relaying (SR) rule which allows a subset of potential relays to forward the source’s data to the corresponding destination, we first establish a multi-relay system model where a D2D UE can act as not only a source but also a potential relay for another D2D link, and then analyze the cooperation behaviors among selfish UEs. Next a simple strategy is proposed to deal with the relay selection problem, and then the fair and efficient resource sharing problem among cooperating D2D UEs is formulated as a bargaining game. Since the game function is non-convex, we turn to an iterative method by introducing an auxiliary function to get the proportional fair resource allocation results. The system efficiency and fairness are proved by numeral simulation results.     

基于概论图灵机的无阈下信道的密码系统定义

文中通过对具有无阈下信道密码系统定义的研究,指出阻止闽下信道使用的唯一方式是修改密码系统使其具有无阈下性,而且一个参与密码系统运行的主动看守是不可或缺的。在分析了Burmester—Desmedt定义缺点的基础上,基于概论图灵机模型给出了一个新的定义,最后简要讨论了具有无阈下信道密码系统的实现代价。     

一种基于IPSec的移动IPv6安全注册技术

目前很多研究都是针对解决切换过程中怎样提高效率,而对切换过程中如何保持注册安全研究得不够。由于缺乏安全措施,节点在切换时容易受到各种安全威胁和攻击。文章提出了一种基于IPSec的安全注册方案,方案结合快速移动IPv6信令,利用IPSec的安全关联保护切换过程中各种信令的交互,能够在不降低切换效率的前提下最大程度的保护注册安全。     

Content adaptive video denoising based on human visual perception

In this paper, we propose content adaptive denoising in highly corrupted videos based on human visual perception. We introduce the human visual perception in video denoising to achieve good performance. In general, smooth regions corrupted by noise are much more annoying to human observers than complex regions. Moreover, human eyes are more interested in complex regions with image details and more sensitive to luminance than chrominance. Based on the human visual perception, we perform perceptual video denoising to effectively preserve image details and remove annoying noise. To successfully remove noise and recover the image details, we extend nonlocal mean filtering to the spatiotemporal domain. With the guidance of content adaptive segmentation and motion detection, we conduct content adaptive filtering in the YUV color space to consider context in images and obtain perceptually pleasant results. Extensive experiments on various video sequences demonstrate that the proposed method reconstructs natural-looking results even in highly corrupted images and achieves good performance in terms of both visual quality and quantitative measures.     

Optimal-correlation-based reconstruction for distributed compressed video sensing

Distributed compressed video sensing (DCVS) is a framework that integrates both compressed sensing and distributed video coding characteristics to achieve a low-complexity video coding. However, how to design an efficient joint reconstruction by leveraging more realistic signal models is still an open challenge. In this paper, we present a novel optimal-correlation-based reconstruction method for compressively sampled videos from multiple measurement vectors. In our method, the sparsity is mainly exploited through inter-signal correlations rather than the traditional frequency transform, wherein the optimization is not only over the signal space to satisfy data consistency but also over all possible linear correlation models to achieve minimum-l₁-norm correlation noise. Additionally, a two-phase Bregman iterative based algorithm is outlined for solving the optimization problem. Simulation results show that our proposal can achieve an improved reconstruction performance in comparison to the conventional approaches, and especially, offer a 0.7–9.9 dB gain in the average PSNR for DCVS.     

应用小波变换的认知无线电频谱检测

频谱检测是认知无线电的核心问题之一,利用小波变换对接收信号的功率谱密度（PSD）进行奇异点检测,为了在低信噪比条件下有效地检测空闲频谱,分两步去除噪声在检测中的影响。首先利用噪声与信号奇异点的小波变换模极大值在不同尺度上具有不同的传播特性,可以去除噪声;再通过小波变换模极大值的衰减计算Lipschitz指数,去掉与信号奇异点具有不同Lipschitz指数的噪声。最后依据剩下的奇异点将PSD划分为多个子带,利用带通滤波器估计每个子带的PSD水平,最终确定出空闲频谱。仿真结果证明了该方法的可行性。     

基于FPGA的部分并行QC-LDPC译码器高效存储方法

针对部分并行结构的准循环低密度校验(QC-LDPC)码译码器,提出了一种将译码准码字存储在信道信息和外信息存储块中的高效存储方法,该方法不需要额外的存储块来存储译码准码字,能够减少译码器实验所需的存储资源数量,并且有效降低了译码电路的布线复杂度.在Xilinx XC2V6000-5ff1152 FPGA上的实验结果表明,提出的QC-LDPC码译码器设计方法能够在降低系统的BRAM资源需求量的同时有效地提高系统的运行频率和译码吞吐量.     

认知网络中的多用户MIMO线性协作频谱感知问题研究

研究了多用户MIMO的线性协作频谱感知问题以提高频谱检测的可靠性,推导了多用户MIMO线性协作感知系统的局部检测和全局检测策略,建立了在给定误警概率的情况下控制中心通过优化给各个用户的信号所分配的权值来最大化全局检测概率的优化模型。进一步,引入了遗传算法来求解上述全局检测优化问题的最优权值,期望能够有效降低算法在频谱感知过程中检测时间。仿真结果表明,多入多出能够明显提高协作频谱感知系统频谱检测可靠性,而遗传算法高效且稳定,相比较其他算法能够有效改善系统的检测性能。