Optimization of LDPC-coded turbo CDMA systems

We consider the analysis and design of low-density parity-check (LDPC) codes for turbo multiuser detection in multipath code division multiple access (CDMA) channels. We develop techniques for computing the probability density function (pdf) of the extrinsic messages at the output of the soft-input soft-output (SISO) multiuser detectors as a function of the pdf of input extrinsic messages, user spreading codes, channel impulse responses, and signal-to-noise ratios. Of particular interest is the soft interference cancellation plus minimum mean square error (SIC-MMSE) multiuser detector, for which the pdf of the extrinsic messages can be characterized analytically. For the case of additive white Gaussian noise (AWGN) channels, the extrinsic messages can be well approximated as symmetric Gaussian distributed. For the case of asynchronous multipath fading channels, the extrinsic messages can be approximated by a mixture of symmetric Gaussian distributions. We show that the expectation-maximization (EM) algorithm can be used to compute the parameters of this mixture. Using these techniques, we are able to accurately compute the thresholds for LDPC codes and design good irregular LDPC codes. Simulation results are in good agreement with the computed thresholds, and the designed irregular LDPC codes outperform regular ones significantly.     

基于改进SBR算法的人脸特征点稳定检测

基于图像的特征点检测器在静态图像上取得了卓越的性能,然而这些方法应用于视频或序列图像时其精度和稳定性显著降低。配准监督(Supervision-by-Registration, SBR)算法利用光流算法(Lucas-Kanade, LK)追踪,可通过无标注视频训练针对视频的特征点检测器,已取得较好的结果,但LK算法仍存在一定局限性,导致检测的特征点序列在时空上的连贯性不强。为获得精准、稳定、连贯的人脸特征点序列检测效果,提出了平滑一致性损失函数、权重掩码函数对传统SBR网络模型进行改进。网络中添加长短期记忆网络(Long Short-Term Memory, LSTM)提高模型训练鲁棒性,在模型训练中使用平滑一致性损失函数提供稳定性约束,获得准确且稳定的人脸视频特征点检测器。在300VW、Youtube Celebrities数据集上的验证显示,SBR改进模型将人脸视频特征点检测的标准化平均误差(Normalized Mean Error, NME)从4.74降低至4.56,且视觉上人脸特征点检测的抖动显著减少。     

Blind signal separation based on ME and statistical estimation

There are two major approaches for Blind Signal Separation (BSS) problem: Maximum Entropy (ME) and Minimum Mutual Information (MMI) algorithms. Based on the recursive architecture and the relationship between the ME and MMI algorithms, an Extended ME(EME) algorithm is proposed by using probability density function (pdf) estimation of the outputs to deduce the corresponding iterative formulas in BSS. Based on the simulation results, it can be concluded that the proposed algorithm has better performances than the traditional ME algorithm in convolute mixture BSS problems.     

基于人工蜂群算法的支持向量机参数优化及应用

为了解决常用的支持向量机(SVM)参数优化方法在寻优过程不同程度的陷入局部最优解的问题,提出一种基于人工蜂群(ABC)算法的SVM参数优化方法。将SVM的惩罚因子和核函数参数作为食物源位置,分类正确率作为适应度,利用ABC算法寻找适应度最高的食物源位置。利用4个标准数据集,将其与遗传(GA)算法、蚁群(ACO)算法、标准粒子群(PSO)算法优化的SVM进行性能比较,结果表明,本文方法能克服局部最优解,获得更高的分类正确率,并在小数目分类问题上有效降低运行时间。将本文方法运用到计算机笔迹鉴别,对提取的笔迹特征进行分类,与GA算法、ACO算法、PSO算法优化的SVM相比,得到了更高的分类正确率。     

采用自适应归一化实数编码遗传算法优化鱼眼镜头系统

针对遗传算法(GA)优化超多参量光学系统时鲁棒性 较差的问题,在混入逃逸函数实数编码GA(MERCGA)的基础上,进一步结合参量归一化和自适 应变异概率的措施,提出了自适应归一化 实数编码GA(ANRCGA)。用ANRCGA对鱼眼镜头光学系统案例进行优化设计,并应用 评价函 数和Zemax光线追迹方法对MERCGA和ANRCGA的优化结果作比较。结果表明,应用本文的ANRCG A 比引自专利的参考设计及MERCGA优化得到光学系统的成像质量有明显提高,算法的鲁棒 性和计算效率也到了改善。     

基于复数因子分析模型的步进频数据压缩感知

认知雷达发射高距离分辨率步进频信号通常需要较长的观测时间。为了节省时间资源,该文提出一种贝叶斯重构算法,用较少的步进频信号脉冲得到的频点缺失频域数据,重构出相应的全带宽频域数据。首先利用复数贝塔过程因子分析(Complex Beta Process Factor Analysis, CBPFA)模型对一组全带宽频域数据进行统计建模,求解得到其概率密度函数;然后在目标被跟踪且姿态变化不大的情况下,只发射步进频信号的部分脉冲,根据先前CBPFA模型得到的概率密度函数,对频点缺失的频域数据利用压缩感知理论和贝叶斯准则解析地重构出相应的全带宽频域数据。基于实测1维高分辨距离(High Range Resolution, HRR)数据的重构实验,证明了该文提出方法的性能。     

核空间自适应非局部均值鲁棒分割算法

为改善传统模糊C均值(FCM)算 法对噪声干扰下图像的分割效果,提出了一种基于核空间邻域信息和自适应非局部均值相结 合的图像鲁棒分割算法。首先,利用传统FCM聚类算法进行初始聚类分割,将 所得聚类中心作为改进算法的初始聚类中心; 其次通过自适应非局部均值算法对图像进行平滑处理,避免图像过度分割;然后对引入核空 间邻域信息的目标函数进行最优化求解, 获取聚类中心和隶属度的迭代表达式;最后对像素进行分类时,利用邻域像素隶属度对像素 进行进一步滤波处理。实验结果表明:本文的 改进算法与传统FCM聚类算法、核空间FCM(KFCM)算法、基于邻域信息的FCM(FCM S)算法和基 于邻域信息KFCM(KFCM-S)算法相比,改进算法对强噪声干扰下的图像具有较好 的鲁棒性,并且能够有效分割图像的目标信 息和背景信息。从几种算法进行聚类分割结果所对应的峰值信噪比(PSNR)也可以看出,本文 改进算法的PSNR更高。     

LDPC编码调制系统中基于反馈LLR均值的迭代解调/译码算法

该文针对LDPC码编码的BICM系统,提出一种对LDPC码译码器输出外附信息的计算方法进行改进的迭代解调/译码算法。与传统的解调/译码算法不同在于,该算法对每次BP迭代中译码器输出的各编码比特的外附LLR分别求均值后,再将其作为先验信息反馈给软解调器开始下次的迭代解调/译码。采用该方法可有效地减轻LDPC码在BP迭代过程中某些比特LLR值的振荡现象,从而使得传递给软解调器的外附信息更准确。仿真结果表明,和传统的两种迭代解调/译码算法相比,该算法能进一步提高LDPC编码BICM迭代系统的译码性能,而复杂度并无明显增加。     

Parameter estimation for autoregressive Gaussian-mixture processes:the EMAX algorithm

The problem of estimating parameters of discrete-time non-Gaussian autoregressive (AR) processes is addressed. The subclass of such processes considered is restricted to those whose driving noise samples are statistically independent and identically distributed according to a Gaussian-mixture probability density function (pdf). Because the likelihood function for this problem is typically unbounded in the vicinity of undesirable, degenerate parameter estimates, the maximum likelihood approach is not fruitful. Hence, an alternative approach is taken whereby a finite local maximum of the likelihood surface is sought. This approach, which is termed the quasimaximum likelihood (QML) approach, is used to obtain estimates of the AR parameters as well as the means, variances, and weighting coefficients that define the Gaussian-mixture pdf. A technique for generating solutions to the QML problem is derived using a generalized version of the expectation-maximization principle. This technique, which is referred to as the EMAX algorithm, is applied in four illustrative examples; its performance is compared directly with that of previously proposed algorithms based on the same data model and that of conventional least-squares techniques     

一种改进的完全搜索块匹配算法

完全搜索块匹配算法是图像序列稳定中常用的运动估计方法,在传统的完全搜索块匹配算法中,在搜索区域中图像序列的当前帧和参考帧对应的像素对对匹配结果的贡献是完全一样的,这样使得算法的性能容易受到待稳定的图像序列中各种噪声的影响。针对这个不足,提出了一种改进的完全搜索块匹配算法。在新的匹配准则中,搜索区域中图像序列的当前帧和参考帧对应的像素对对匹配结果是否有贡献取决于它们灰度值之差的绝对值与预先设定的门限值进行大小比较的结果,对应的灰度值之差的绝对值不超过该门限值的像素对对匹配结果有贡献,而且贡献大小受到与像素对位置相关的加权处理,否则该像素对对匹配结果无贡献。实验结果证明了该算法的优越性。     

基于梯度积分投影和最大期望算法的人眼定位

针对传统积分投影方法易受眉毛、睫毛、阴影、遮挡及噪声等干扰的问题,提出了一种梯度积分投影与最大期望(EM)算法相结合的人眼精确定位方法,可以在人脸图像中分割出人眼区域,并精确定位人眼位置。首先,采用一种新的梯度算子计算人脸图像的行梯度积分投影粗略定位人眼区域;然后计算人眼区域的列梯度积分投影函数,用EM算法将所得列梯度积分投影函数曲线拟合成两个高斯曲线,并根据高斯曲线精确分割出人眼窗口;最后,利用我们提出的加权质心法在所得人眼窗口中精确定位双眼位置。在YaleB人脸数据库及自采数据库上的实验结果表明,本文方法不易受眉毛及噪声干扰,并能有效克服眼睑和睫毛的遮挡,对不同光照条件及头部姿态都有很好的鲁棒性。     

一种适用于强脉冲噪声下的对数型恒模盲均衡算法

针对脉冲噪声下恒模算法(Constant Modulus Algorithm,CMA)失败的问题,通过分析脉冲噪声的影响,提出了一种基于最小均方（Least Mean Square,LMS）准则的对数型恒模算法（Logarithmic-type CMA,LT-CMA）。LT-CMA利用对数函数的非线性变换特性自适应地抑制强脉冲噪声对误差函数的影响,并且利用l2-范数进行信号归一化处理以增强算法的稳健性。仿真结果表明,所提出的LT-CMA可以适应于高斯噪声环境和脉冲噪声环境;与经典自适应均衡算法相比,在收敛速度和稳健性两方面上,所提出的LT-CMA都有显著的提升。     

A new approach to analysis of residue probability density function in pipelined ADCs

This paper presents a new approach to analysis of residue probability density function (pdf) in pipelined ADCs. This work was performed based on the fundamental theorem for function of a random variable to map stage input pdf to its output density. It will be shown that residue pdf converges to uniformity. For the stages with half-bit redundancy, this uniformity is accompanied with an extra bit of resolution. Also, the minimum number of stages required to achieve a given value of resolution improvement are studied. Investigating the impact of backend stage on this extra resolution, the appropriate backend to maintain the most extra resolution is proposed. Examining the allowable comparator offsets in different stages, we can see that with decreasing the offset errors in final stages, offset errors impact of the first stages on the final residue pdf and the total converter resolution can be eliminated.     

A ROBUST PHASE-ONLY DIRECT DATA DOMAIN ALGORITHM BASED ON GENERALIZED RAYLEIGH QUOTIENT OPTIMIZATION USING HYBRID GENETIC ALGORITHM

A robust phase-only Direct Data Domain Least Squares （D3LS） algorithm based on generalized Rayleigh quotient optimization using hybrid Genetic Algorithm （GA） is presented in this letter. The optimization efficiency and computational speed are improved via the hybrid GA composed of standard GA and Nelder-Mead simplex algorithms. First, the objective function, with a form of generalized Rayleigh quotient, is derived via the standard D3LS algorithm. It is then taken as a fitness function and the unknown phases of all adaptive weights are taken as decision variables Then, the nonlinear optimization is performed via the hybrid GA to obtain the optimized solution of phase-only adaptive weights. As a phase-only adaptive algorithm, the proposed algorithm is simpler than conventional algorithms when it comes to hardware implementation. Moreover, it proc- esses only a single snapshot data as opposed to forming sample covariance matrix and operating matrix inversion. Simulation results show that the proposed algorithm has a good signal recovery and interferences nulling performance, which are superior to that of the phase-only D3LS algorithm based on standard GA.     

薛定谔方程中包络孤子运动及相互作用的辛算法模拟

给出并证明了薛定谔方程中高斯包络孤子的表达式.针对该高斯包络孤子进一步提出了薛定谔方程中存在高斯包络孤子相互作用的情况;针对薛定谔方程提出其辛算法.通过分离波函数实部和虚部把薛定谔方程变换成标准的哈密顿正则方程组,对正则方程进行欧拉中心差分离散实现辛算法.给出了辛算法的守恒量,并证明了其稳定性.对薛定谔方程中的高斯包络孤子运动及多孤子相互作用过程进行了数值仿真,实验结果证明了所提观点的正确性及辛算法的有效性.     

一种改进的低复杂度OFDM峰均比抑制PTS算法

针对正交频分复用系统中的信号峰值平均功率比问题,提出了一种基于时域采样点幅度筛选的低复杂度部分传输序列算法。算法通过设置信号经过逆向傅里叶变换后时域采样点的幅度之和为判别函数,并设置适当的幅度门限,筛选出幅度大于门限的信号采样点集合,利用该集合来搜索信号峰均比抑制相位因子,从而降低算法复杂度。仿真表明,与传统峰均比抑制算法相比,改进算法在保持峰均比抑制性能的同时降低了算法复杂度。     

利用ACE值构造QC-LDPC码

为进一步提升中短码长下准循环低密度奇偶校验(Quasi-cyclic Low-density Parity-check,QC-LDPC) 码的纠错性能,提出了一种综合短环数目和环连通性的QC-LDPC码构造方法。首先,采用Golomb规则构造QC-LDPC码,对基矩阵中的部分元素进行替换预处理,初步降低短环数目;其次,采用所提的利用近似环外信息度（Approximate Cycle Extrinsic message degree,ACE）的消环掩模算法来优化QC-LDPC码,使得掩模后的校验矩阵具有较大的ACE平均值,最终完成QC-LDPC码的构造。该构造方法简单、通用性强,在短环数目和连通性间进行了平衡。与只考虑减少短环数目、增大围长等方法相比,该方法构造的QC-LDPC码有更加优异的纠错性能。     

基于YOLOv5的轻量级火焰视频流实时检测算法

针对火焰检测模型小目标检测能力差、模型体积大、计算复杂、难以部署到移动端设备的问题,提出了一种轻量化的DGC＿YOLOv5 (you only look once v5)算法。本文首先调用k-means计算函数,计算出适合本文数据集的锚框尺寸;其次引入卷积块注意力机制(convolutional block attention module, CBAM),提高算法对小目标的检测能力;然后利用轻量型的Ghost模块对主干网络中的C3模块进行改进;最后利用深度可分离卷积(depthwise separable convolution, DS＿Conv),用简单的线性计算代替复杂计算,降低模型复杂度,减小模型体积。实验表明,相比原始的YOLOv5算法,本文算法在测试集上的平均精度均值(mean average precision,mAP)可达到94.4%,比原始算法提高1.7个百分点,在视频测试集上平均检测速度可达到71 FPS,可以满足实时检测的要求,参数量和计算量分别减少为原来的41.2%和34.8%,模型大小减少8.4 M,便于后续移动设备端的部署。     

矩形窗正交时频空检测算法

针对正交时频空(Orthogonal Time Frequency Space, OTFS)调制系统采用矩形窗函数时,信道矩阵结构复杂导致的鲁棒性差的问题,提出了一种基于时域处理和酉近似消息传递的检测算法。该算法首先添加循环前缀,将时域信道转换为分块对角矩阵;然后应用酉变换和近似消息传递建立迭代检测算法。仿真结果表明,所提检测算法能够在不增加复杂度的条件下有效提升检测精度和鲁棒性,特别是存在信道编码的条件下表现出2 dB的性能增益,使得该算法更适用于杂散多径、高速移动等环境,具有较高的应用价值。     

TSR: algorithm of image hole-filling based on three-step repairing

In order to solve the hole-filling mismatch problem in virtual view synthesis, a three-step repairing (TSR) algorithm was proposed. Firstly, the image with marked holes is decomposed by the non-subsampled shear wave transform ( NSST), which will generate high-/ low-frequency sub-images with different resolutions. Then the improved Criminisi algorithm was used to repair the texture information in the high-frequency sub-images, while the improved curvature driven diffusion (CDD) algorithm was used to repair the low-frequency sub-images with the image structure information. Finally, the repaired parts of high-frequency and low-frequency sub-images are synthesized to obtain the final image through inverse NSST. Experiments show that the peak signal-to-noise ratio (PSNR) of the TSR algorithm is improved by an average of 2 - 3 dB and 1 - 2 dB compared with the Criminisi algorithm and the nearest neighbor interpolation (NNI) algorithm, respectively.