Adaptive RAKE receiver in chaos based pilot-added DS-CDMA system

This paper presents the theoretical analysis of adaptive multiuser RAKE receiver scheme in frequency selective fading channel for direct-sequence code division multiple access (DS-CDMA) system. Least mean square (LMS) algorithm is used to estimate the channel coefficients. Chaotic sequences are used as spreading sequence and corresponding bit error rate (BER) in closed form is derived for imperfect channel estimation conditions. Performances of chaotic sequences are compared with pseudorandom noise (PN) sequences. Under perfect synchronization assumption, various simulation results are shown to investigate the performance of the proposed system.     

多尺度变步长最小均方自适应算法在光纤陀螺数据处理中的应用

为有效抑制光纤陀螺(FOG)随机噪声,提出将一种多尺度变步长最小均方(MVSLMS)自适应算法应用于FOG数据处理中。根据FOG输出数据的特点,构建了MVSLMS自适应滤波器,提出了FOG信号滤波算法的实现步骤。对FOG实测静态数据、振动数据和速率测试数据进行了滤波实验,结果表明所提算法对FOG随机噪声的抑制效果明显,相比LMS滤波,MVSLMS自适应滤波后的静态数据零偏稳定性数值减小了72.0%,振动数据在振前、振中、振后零偏稳定性数值分别减小91.5%,77.4%和96.5%,速率测试数据标准差减小了54.4%。摇摆测试滤波实验结果表明所用算法对FOG真值信号具有较好的跟踪能力。     

A LUT-based scheme for LNA linearization in direct RF sampling receivers

Direct RF sampling receiver – a fully digital receiver architecture – undoubtedly becomes a favored choice for HF/VHF as this approach inherently bypasses the legacy nonlinearities caused by analog components. In DRF-RF and wideband multichannel in general, LNA is still an indispensable component to ensure the receiver’s sensitivity. However, with the presence of multiple channels, the total RF power often surpasses the linear threshold that LNA and the amplified signal become severely distorted. This paper proposed a method for mitigating the LNA distortion using the look-up table (LUT) approach. Specifically, our receiver is designed with two modes of operation. In training mode, a built-in signal circuit generates a training signal for extracting the LNA characteristic and eventually reconstructs the inverse LNA nonlinear model in the form of a LUT memory. During the receiving mode, a linearization circuit reverses the distortion impact by matching the RF power level with the inverse nonlinear model pre-stored in the LUT. The effectiveness of the proposed distortion compensation method first is evaluated by a MATLAB simulation with a multi-channel DRF-RF model. The simulation results show that the proposed approach significantly improved the SNDR for the channel of interest. Furthermore, the model has been practically verified, where the actual distorted signals are sampled from a commercial LNA (ZFL-500LN+) by a customized FPGA board. Results from measurements show an improvement of $\sim$7 dB for SNDR and 27% for EVM in a strong distortion scenario of QPSK modulation signal.     

直接扩频系统自适应抗干扰技术仿真

近年由于扩频技术具有强的抗干扰能力、隐蔽性、抗多径干扰能力、精确定时和测距，并具有多址能力，所以无论在军事还是在民用方面都受到很大的关注，并且有了很大的发展。为了进一步提高扩频系统的抗干扰能力，将自适应抗干扰技术应用于扩频系统，通过计算机仿真研究了LMS算法的抗干扰性能．结果表明，LMS算法简单，可以应用于扩频系统的前端，对窄带干扰有良好的抑制．     

基于RBF网络信道均衡器

在数字通信系统中为了克服信道畸变引起的码间干扰，在接收端必须采用信道均衡技术。在本文中，我们将RBF网络用作均衡器。采用最近邻聚类和直接判决算法来调整隐藏层中心，然后再用LMS算法调整输出层的系数。该算法可以实现在线学习，根据相应的准则增加，删除隐藏层节点。算法事先不必确定隐藏层的节点个数。模拟结果显示，RBF网络均衡器能够正确地将信号从有噪信道中恢复出来，在计算机模拟仿真中其性能与理想贝叶斯均衡器相当。     

一种采用脉冲串的自适应有源干扰抵消器

在许多应用中，周期性干扰是由旋转的机械设备所产生的。一个周期性信号可以与一个特殊形式的周期性的脉冲串完全相干。本文提出了一种采用脉冲串的自适应有源噪声抵消器(AANC)来抵消周期性干扰，这种抵消器产生一个与干扰信号相同步的周期性的单位脉冲串作为参考输入。将这种有源噪声抵消器和Delayed-X LMS算法相结合，可以大大地减小运算量，并且也可以保证良好的收敛特性。理论分析和计算机仿真验证了本文的结果。     

无次级通道建模有源噪声控制算法的实验研究

以管道中有源噪声控制为实验平台,基于ADSP21161N数字信号处理评估板实现了本文作者早先提出的不需要次级通道建模的基于LMS方法的四方向搜索型有源控制算法,并给出了该算法在实际应用中收敛系数的选取原则。针对单频和多频噪声的实验结果表明,前人两方向搜索型有源控制算法在大部分频率上都能收敛,但在次级通道相位为±90°的频率不能收敛,而本文作者所提出的四方向变收敛系数搜索型算法,在所有频率都能快速收敛。     

一种改进的视觉传感器与激光测距雷达特征匹配点提取算法

激光测距雷达与视觉传感器的配准是视觉图像与激光距离信息融合的前提。激光测距雷达与视觉传感器的配准可分为点匹配与平面匹配。由于混合像素和非结构空间特征激光点丢失现象,使得基于点匹配的视觉传感器与激光测距雷达配准算法精度难以提高。通过对混合像素和非结构空间特征激光点丢失问题的分析,提出了一种结合平面建模思想,利用假想激光光束与平面模型相交提取匹配特征点的方法。验证了实验结果并进行了算法精度比较。实验结果表明,这种改进的特征匹配点提取算法解决了特征点缺失,并且提高了点匹配的精度,使匹配性能大大地改善。     

基于小波变换的LMSV模型对人民币汇率波动的研究

将小波引入到LMSV模型波动长记忆性的估计与检验中,提出了基于小波变换的LMSV模型波动长记忆性的伪极大似然估计法和波动长记忆性的检验方法,并对各汇率波动序列长记忆效应的大小程度进行了验证．结果表明各汇率波动序列存在长记忆效应．人民币对美元的汇率波动序列受历史信息的影响程度最高．     

Enhancement of noise reduction efficiency based on compensation in the ANC headset using fixed-point DSP

In this paper, we have proposed a new algorithm considering commutation error and feedback effect to enhance the convergence rate and noise reduction efficiency of ANC controller. In order to improve noise reduction performance of the ANC headset with fixed-point DSP, we have proposed a new FxLMS algorithm, FxLMS CF, which considers the commutation error and feedback. Also, using a non-real-time simulation, we have decided the phase and amplitude compensation factors of anti-noise signal considering round-off and quantization error, nonlinear distortion and delay of analog device. We estimated the phase and amplitude compensation factors by simulation without using any special measuring devices or analysis devices, and reduced the broadband noise by 24 dB.