Research on Time Reversal Spread Spectrum Underwater Acoustic Communication in Time-varying Channels

随着海洋开发、海洋环境监测和海洋国防安全等领域信息化建设的快速发展，利用海洋信道进行信息传输的需求大大增加，水声通信越来越受到人们的重视。但是，水声环境的复杂性、时变性和不可确定性导致信号多普勒频移、多径效应、幅度和频率选择性衰落等问题，给高性能水声通信带来了极大的挑战。 时间反转技术近年来成为水下通信的热点研究技术，其最大的优点是可在没有任何环境先验知识的情况下实现多径聚焦，提高检测信噪比。直接序列扩频技术具有抗干扰、抗多径衰落、可提高扩频增益等优点已经在水声通信中广泛应用。 考虑到时变信道下时间反转性能的下降，结合时间反转和扩频通信的优点，本文提出可适应时变信道的时间反转扩频通信方案，...With the rapid development of marine exploitation, marine environment monitoring, marine national defense and security, the requirement of transmitting information through underwater channel is increasing in recent years, so underwater acoustic communication has drawn significant attention. However, the complexity, time-varying and uncertainty of underwater acoustic channel character lead to Doppl...学位：理学硕士院系专业：海洋与环境学院_海洋物理学号：3112010115129

Measurements and Study based on Distributed MIMO Small Scale Fading Characteristics

随着宽带移动通信的快速发展，人们希望有高速率和高质量的多媒体通信，然而移动通信系统的性能主要受到无线信道的制约，因此无线信道的分析与建模是显得非常重要和必要。无线信道模型的研究，主要集中在大尺度衰落模型和小尺度衰落模型，同时无线信道的建模是以实际信道测量为基础的。本文以针对目前研究热点场景如高铁或机舱等下的小尺度衰落（莱斯K因子和均方根时延扩展）为主线，分析信道小尺度衰落特性，主要用于传输技术的选择和接收机的设计。 本文首先阐述了小尺度衰落参数及小尺度衰落模型，重点研究了莱斯K因子以及均方根时延扩展的计算方法。然后对清华自主开发的MIMO信道测量平台的构架及工作原理研究并进行改进与完善，为实...In recent years, with the rapid development of wireless communication,people demand high communication quality. However, the property of wireless and mobile communication systems is subject to the constraints of the mobile radio channel. Therefore, it becomes very necessary in the wireless channel analysis and modeling. The fading analysis mainly includes Large-scale fading and Small-scale fading....学位：工程硕士院系专业：信息科学与技术学院通信工程系_电子与通信工程学号：2332009115278

Compressed Sensing Estimation of Underwater Acoustic MIMO Channels Based on Temporal Joint Sparse Recovery

多输入多输出(MIMO)水声通信技术可以在极其有限的水声信道频带资源内提高信道容量,但多径和同道干扰的同时存在,使传统信道估计算法如最小二乘算法、压缩感知估计算法的性能急剧下降。考虑到通信数据块间水声信道多径结构存在一定的相关性,该文利用这种数据块间多径结构的时间域相关性建立水声MIMO信道的时域联合稀疏模型,并利用同步正交匹配追踪算法进行多个数据块联合稀疏恢复信道估计,提高MIMO信道多径稀疏位置的检测增益并抑制同道干扰,提高水声MIMO信道的估计性能。仿真和MIMO水声通信海试实验表明了所提方法的有效性。Multiple-Input-Multiple-Output(MIMO) under water acoustic communication is capable of improving the channel capacity in extremely limited bandwidth. However, the performance of traditional channel estimation algorithms, such as Least Squares(LS) method, Compressed Sensing(CS) method decreases rapidly because of the simultaneous presence of the Co-channel Interference(Co I) and multipath. As the sparse multipath structures between adjacent data blocks exhibit temporal correlation features, in this paper, the temporal correlation of sparse multipath structures is exploited to establish temporal joint sparse MIMO channel estimation model, and the Simultaneous Orthogonal Matching Pursuit(SOMP) algorithm is utilized for compressed sensing estimation of MIMO channels. Simulation and sea trial results validate the effectiveness of the proposed method.国家自然科学基金(11274259;11574258);; 福建省自然科学基金(2015J01172)~

Jointing sparse recovery estimation algorithm of underwater acoustic channels with long time delay spread

对具有长时延扩展的水声信道,传统的信道估计算法如最小二乘法将在大量零值抽头产生严重的估计噪声,导致估计性能下降,同时信道估计时所需的较高估计器阶数大大提高了运算复杂度。压缩感知信道估计方法可有效利用多径稀疏特性改善性能,但需采用较大的训练序列长度以保证稀疏恢复精度,由此导致额外的系统开销。利用水声信道多径稀疏结构在数据块间存在的相关性,建立基于分布式压缩感知的长时延水声信道联合稀疏模型,从而可利用同步正交匹配追踪算法进行联合重构,以进一步减小系统的训练序列开销,提高估计性能。最后通过仿真和海上实验验证了所提方法的有效性。Efficient estimation of underwater acoustic channels with a large time delay spread was addressed. For the conventional channel estimation methods such as LS, this type of channel estimation would produce serious estimation noise in zero-value taps which lead to poor performance of channel estimation. At the same time, a large time delay spread posed significant difficulties such as large channel order and the corresponding huge computation complexity. Compressed sensing(CS) channel estimation algorithm offered a solution to this problem by exploiting the sparsity of channel to improve the estimation performance. However, to ensure acceptable estimation performance, a long training sequence was needed, which unfortunately would cause additional overhead. A method was proposed which exploiting the joint correlation of sparse multipath structure between adjacent data blocks to deal with the estimation of long time delay channels under the framework of distributed compressed sensing(DCS).Thus the large time delay underwater acoustic channels can be jointly reconstructed by the simultaneous orthogonal matching pursuit(SOMP) algorithm to facilitate the system overhead reduction and estimation performance improvement. Simulation as well as the sea trial results indicate the effectiveness of the proposed method.国家自然科学基金资助项目(No.11274259,No.11574258)~

我国基金市场发展的现状与趋势

我国基金市场发展的现状与趋势魏丽，林兴评，周跃投资基金作为一种可供投资者选择的新型投资工具，在我国起步于1991年，经过几年发展到目前已经有了一定的规模，并初步形成了全国性的基金市场。投资基金的发展对于推动我国的投用资体制改革，健全和完善金融市场尤其..

Estimation algorithm for sparse channels with gradient guided p-norm like constraints

为克服l0和l1范数约束的最小均方算法在不同信道稀疏程度下对稀疏信道估计中出现的收敛性能起伏较大等缺点,提出一种新的似P范数约束的最小均方算法,通过在最小均方算法代价函数中引入P值可变的似P范数约束以适应信道的不同稀疏程度,并在验证代价函数凸性的基础上导出P值的梯度导引寻优。最后给出仿真实验及其讨论,实验结果表明了新算法的优越性。The l0 and l1 norm constrained least mean square(LMS) algorithm can effectively improve the performance of the sparse channel estimation, but the convergence performance of such algorithms will considerably vary when the channel exhibits different sparisity.A novel p-norm like constraint LMS algorithm to accommodate the various sparisity of the channels through the introducing of the variable p-value was presented.Furthermore, the gradient guided optimization of the p-value was derived.Numerical simulation results are given to demonstrate the superiority of the new algorithm.国家自然科学基金资助项目(11274259); 教育部高等学校博士点专项基金资助项目(20120121110030)~

A Fast Sparse Signal Recovery Algorithm Based on Approximate l_0 Norm and Hybrid Optimization

欠定系统(又称超完备系统)的稀疏信号恢复在压缩感知、源信号分离和信号采集等领域中被广泛研究.目前这类问题主要采用l1范数约束结合线性规划优化或贪婪算法进行求解,但这些方法存在收敛速度慢、恢复精度不高等缺陷.提出一种快速恢复稀疏信号的算法,该算法采用一种新的近似l0范数代替l1范数构造代价函数,并融合牛顿法和最陡梯度法推导出寻优迭代式,以获得似零范数代价函数的最优解.仿真实验和真实数据实验结果表明,与经典算法相比,该算法在能提供相同精度、甚至更好精度的条件下,收敛速度更快.Obtaining sparse solutions of under-determined, or over-complete, linear systems of equations has found extensive applications in signal processing of compressive sensing, source separation and signal acquisition.However, the previous approaches to this problem, which generally minimize the l1 norm using linear programming(LP) techniques or greedy methods, are subject to drawbacks such as low accuracy and slow convergence.This paper proposes to replace the l1 norm with a newly defined approximate l0norm(AL0), the optimization of which leads to the derivation of a hybrid approach by incorporating the steepest descent method with the Newton iteration.Numerical simulations and real data experiment show that the proposed algorithm is about two to three orders of magnitude faster than the state-of-the-art interior-point LP solvers, while providing the same(or better) accuracy.国家自然科学基金(11274259); 教育部高等学校博士点专项基金(20120121110030)资助~

The Role of PI3K/Akt/HIF-1α Signaling Pathway in Bleomycin-Induced Pulmonary Fibrosis in Mice

目的探讨PI3K/Akt/HIF-1α信号通路在博来霉素(BLM)诱导的小鼠肺纤维化中的作用机制。方法 56只C57BL/6小鼠随机分为对照组和实验组,实验组通过气管内滴注BLM(2.5 mg/kg)建立肺纤维化模型,对照组在相同条件下气管内滴注等量0.9%氯化钠溶液。在造模第21 d取小鼠肺组织标本行HE和Masson染色分析肺组织形态学变化;运用Ashcroft评分以及检测羟脯氨酸含量评估肺纤维化程度;Western blot方法检测PI3K/Akt/HIF-1α信号通路的变化以及肺泡表面活性物质(Pro-SPC)蛋白含量;实时定量PCR(RT-PCR)法检测胶原蛋白3(Collagen3)mRNA表达水平;免疫组织化学法检测肺组织内Collagen3蛋白和细胞凋亡数的变化。结果实验组与对照组相比,肺泡炎和肺纤维化程度明显加重,肺组织内充填大量炎细胞及纤维病灶。试验组Ashcroft评分和羟脯氨酸含量均较对照组显著升高(P<0.05)。同时,PI3K/Akt/HIF-1α信号通路在实验组肺内明显活化,并伴有Pro-SPC蛋白生成减少,Collagen3蛋白含量及mRNA水平增加,以及肺内细胞凋亡数明显增加。结论 PI3K/Akt/HIF-1α信号通路的异常活化促进了肺纤维化形成。Objective To investigate the role of PI3K/Akt/HIF-1α signaling pathway in bleomycininduced pulmonary fibrosis in mice.Methods Fifty-six C57 BL/6 mice were randomly divided into a control group and a bleomycin(BLM)group.The pulmonary fibrosis model was induced by single intratracheal instillation of BLM(2.5 mg/kg)in the BLM group.Similarly,0.9% saline was instilled directly into the trachea in the control group.Then all mice were sacrificed on 21 stday.The lungs were collected for morphometric analysis with HE and Masson staining.The degree of pulmonary fibrosis was evaluated with Ashcroft score and content of hydroxyproline.The activity of PI3 K/Akt/HIF-1α signaling pathway and prosurfactant protein C(Pro-SPC)were measured by Western blot.The level of collagen3 mRNA was assessed with quantitative real time PCR analysis.Collagen3 protein and numbers of apoptosis cells were observed with immuno-histochemistry.Results It was exhibited that the thickening alveolar septa,accumulation of inflammatory cells,and fibrous obliteration in the BLM group but not in the control group.There was a significant difference in Ashcroft score and hydryoproline content in the BLM group.Meanwhile,the activity of PI3 K/Akt/HIF-1α signaling pathway was up-regulated and the protein of Pro-SPC was decreased in the BLM group.It was revealed that the numbers of apoptosis cells,expressions of Collagen3 protein and mRNA were increased in the BLM group.Conclusion Aberrant activity of PI3 K/Akt/HIF-1α signaling pathway may aggravate the pulmonary fibrogenesis.福建省科技局课题(编号:J00162

Two-parameter Adjustable Underwater Acoustic Channel Equalization Algorithm

针对浅海水声信道固有的随机时-空-频变、高噪、强多径等特性及变化的多径时延扩展,在变步长最小均方(lMS)平行滤波器组(Pfb-lMS)算法的基础上提出了一种新的水声通信自适应均衡算法。该算法将变阶数和变步长的调整结合起来,降低了算法对迭代步长和均衡器阶数的敏感度。仿真结果表明,新算法在参数适应性方面优于传统lMS及Pfb-lMS算法。The shallow water acoustic channel is characterized as a complex time,space and frequency-variant channel with several negative factors,e.g.narrow band,high ambient noise,multipath distortion and polytropic multipath time delay which pose serious difficulty for the underwater acoustic communication.A novel two-parameter adjustable least mean square(LMS) equalization algorithm is presented based on the classic parallel filter banks LMS(PFB-LMS) algorithm.The new algorithm enables hybrid adjustment of step-size and tap-length so that the sensitivity of step-size and tap-length parameter selections is alleviated.Simulation results show that the new algorithm outperforms the traditional LMS and PFB-LMS algorithms in parameter robustness under time varying channels.国家自然科学基金项目(11274259); 教育部高等学校博士学科点专项基金项目(20120121110030

Noninvasive transcranial magnetic techniques of the neural engineering and the clinical application

介绍了神经工程研究中的透颅磁刺激、脑磁图、电相关磁共振成像三项新技术的原理、作用和优缺点