两种OFDM多普勒估计算法在水声信道中的比较

为了消除多普勒频偏影响,通过水上实验对两种OFDM（Orthogonal Frequency-Division Multiplexing）水声通信多普勒估计算法进行对比。基于拷贝相关时延差估计的多普勒估计算法结构简单、易于实现;基于空载波的算法较复杂,但精度较高。利用两种方法对相同的实验数据进行多普勒估计和补偿,并对其通信误码率进行对比。研究结果表明,在慢变的信道中两者的误码率基本相同,但在快变的信道中基于空载波的算法更稳定。     

EXPERIMENTAL ESTIMATION OF A SCALING EXPONENT FOR TIP VORTEX CAVITATION VIA ITS INCEPTION TEST IN FULL- ANDMODEL-SHIP

Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.     

Research on the improved frequency-domain equalization algorithm for OFDM underwater acoustic communication

The traditional OFDM frequency-domain equalization algorithm depends on the long circular prefix to overcome the bad influences caused by multi-path effects in the underwater acoustic channel. But the redundant long prefix is actually a serious waste of energy and bandwidth in underwater systems, which restrains the OFDM signal's advantages of high channel utilization greatly. Aiming at the defects of the traditional equalization algorithm, this paper brings forward a new frequency-domain equalization algorithm based on the analysis of the influences caused by multi-path effects and the equalization theory and structure. The results of simulation show that the new algorithm can compensate the multi-path effects efficiently with few circular prefixes and make sure the high-speed and reliability of the underwater acoustic communication system. Finally, based on the amount of computing, a simple algorithm is given.     

基于姿态定位算法的水下电缆监测系统

针对海洋科学考察中连接设备的水下电缆无法观测的现状,该文提出了一种基于姿态定位算法的水下电缆监测系统。系统采用两片V,11SCA60单轴倾角传感器对电缆不同位置处的双轴倾角数据进行采集,并通过CAN总线传送到水下主控CPU,数据经打包后由同轴电缆或光电复合缆传送至甲板上位机,通过姿态定位算法在上位机中完成电缆姿态监测。实验证明该系统可准确地定位电缆姿态并能够对危险操作和异常状态及时做出预警,为设备水下投放提供保障。     

码率可调节的高质量语音编码算法

中远距离水声语音通信时,由于水声信道可利用带宽窄的原因,通信速率较之无线电信道低.在高质量通话的前提下,语音编码码率也在一定范围内受到制约.在众多低速率语音编码标准中,美国联邦标准MELP(mixed excitation lin-ear prediction)是最佳选择,其编码码率2.4 kbit/s对于水声信道来说仍然偏高.考虑到水声信道的特点,结合语音信息不均匀分布、MELP编码参数分析和简化、码本冗余度降低等几个方面,从语音生成和听觉感知角度深入研究了MELP编码标准,采用不定帧数联合编码的方式,提出一种码率可调节的高保真语音编码算法.正常语速下,平均码率约800 bit/s.合成语音清晰可懂,保持了说话人的个性特征,其PESQ MOS(perceptual evaluation of speech quality mean opinion score)评分不低于2.7,语音质量接近2.4 kbit/s MELP标准水平,满足了中远距离(>10 km)水声高质量语音通信的要求.同时,本算法也可用于其他对实时性要求不高的场合.     

有限封闭环境中基于PCA的水声测距方法

有限空间中多途效应严重影响测距的准确性,针对该问题,提出一种基于主成分分析的水声信号测距方法,对信号协方差矩阵进行降维和特征抽取,在保留协方差矩阵信息量的同时抑制多途干扰信号的影响。实验结果表明,该方法能够提高有限封闭液态场环境中水声测距的准确性和稳健性。     

自主式水下航行器三维路径跟踪的神经网络H∞鲁棒自适应控制方法

本文研究了存在模型不确定以及外界未知扰动情况下的自主式水下航行器(AUV)的三维路径跟踪控制问题. 针对此问题, 首先利用时标分离原理及正交投影Serret-Frenet坐标系建立了描述AUV质心运动及姿态运动的的仿射非线性数学模型. 其次, 在控制器设计中运用神经网络H∞鲁棒自适应算法克服了模型的不确定性及扰动, 同时在控制器设计中利用了主导输入的思想, 降低了闭环系统的复杂度, 减少了实时计算工作量, 便于工程应用. 基于Lyapunov理论的分析保证了系统的稳定性. 仿真结果表明, 路径跟踪控制律可以保证AUV沿期望路径运动, 并且具有良好的动态性能.     

具有PID反馈增益的自主水下航行器反步法变深控制

本文针对海底地形测绘时自主水下航行器(autonomous underwater vehicle,AUV)的变深控制问题,提出具有PID增益调节的AUV深度控制方法,基于反馈增益的反步法设计控制器,避免了采用传统反步法导致控制器中存在虚拟控制量的高阶导数问题;基于李雅普诺夫稳定性理论设计控制器参数消除了部分非线性项,得到的控制器的线性部分为状态变量的线性组合,具有PID控制器参数调节的形式;针对存在建模不精确、外界干扰和测量噪声时的闭环系统鲁棒性进行分析,保证了误差系统在扰动作用时的一致最终有界性.最后通过仿真实验验证了本文设计的控制器的有效性.     

基于权值范围设置的多模型稳定切换控制研究

针对线性加权多模型切换过程中权值难以确定问题,提出了具有Lyapunov函数的多模型稳定切换的充分条件,依据该充分条件可以确定加权多模型的权值范围和快速获取加权因子的取值,实现多模型的平滑切换.所提出的充分条件克服了多模型子系统必须稳定的苛刻条件,通过对自主水下机器人多运动模型切换过程的仿真实验表明,依据权值范围所给定的加权因子能够保证加权多模型切换过程中的渐近稳定性.