Bistable Stochastic Resonance Enhanced 4-ary PAM Signal Detection under Low SNR

To boost the performance of 4-ary pulse amplitude modulated(PAM) at low signal-to-noise ratio(SNR), bistable stochastic resonance(BSR) system is introduced into digital communications system and get a reliable signal detection scheme. In this paper, we first analyse BSR system for different amplitudes of 4-ary PAM signals. The steadystate of the bistable system will be statistically distinct, and the feasibility of the proposed detection scheme is confirmed. On this basis, we present a detailed study on steady-state transitions of the BSR system, and an explicit expression of the bistable system parameters is derived. By setting the bistable system parameters, bistable system, 4-ary PAM signal, and noise reach the resonance state, and the BSR-based detection scheme is implemented. Moreover, we derive an analytical expression to calculate the symbol error rate(SER) of 4-ary PAM signals with the BSR-based detection under additive white Gaussian noise(AWGN). Finally, the simulation results validate that BSR-based detection scheme can improve the detection performance while efficiently reducing the symbol error rate.

Blind parameter estimation of pseudo-random binary code-linear frequency modulation signal based on Duffing oscillator at low SNR

Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation(PRBC-LFM)signals require prior knowledge,are computationally complex,and exhibit poor performance at low signal-to-noise ratios(SNRs).To overcome these problems,a blind parameter estimation method based on a Duffing oscillator array is proposed.A new relationship formula among the state of the Duffing oscillator,the pseudo-random sequence of the PRBC-LFM signal,and the frequency difference between the PRBC-LFM signal and the periodic driving force signal of the Duffing oscillator is derived,providing the theoretical basis for blind parameter estimation.Methods based on amplitude method,short-time Fourier transform method,and power spectrum entropy method are used to binarize the output of the Duffing oscillator array,and their performance is compared.The pseudo-random sequence is estimated using Duffing oscillator array synchronization,and the carrier frequency parameters are obtained by the relational expressions and characteristics of the difference frequency.Simulation results show that this blind estimation method overcomes limitations in prior knowledge and maintains good parameter estimation performance up to an SNR of-35 dB.

Novel Frame Shift and Integral Technique for Enhancing Low-Light-Level Moving Images

A novel frame shift and integral technique for the enhancement of low light level moving image sequence is introduced. According to the technique, motion parameters of target are measured by algorithm based on difference processing. To obtain spatial relativity, images are shifted according to the motion parameters. As a result, the processing of integral and average can be applied to images that have been shifted. The technique of frame shift and integral that includes the algorithm of motion parameter determination is discussed, experiments with low light level moving image sequences are also described. The experiment results show the effectiveness and the robustness of the parameter determination algorithm, and the improvement in the signal-to-noise ratio （SNR） of low light level moving images.

Optimizing Optical Attocells Positioning of Indoor Visible Light Communication System

Visible light communication(VLC),which is a prominent emerging solution that complements the radio frequency(RF)technology,exhibits the potential to meet the demands of fifth-generation(5G)and beyond technologies.The random movement of mobile terminals in the indoor environment is a challenge in the VLC system.The model of optical attocells has a critical role in the uniform distribution and the quality of communication links in terms of received power and signal-to-noise ratio(SNR).As such,the optical attocells positions were optimized in this study with a developed try and error(TE)algorithm.The optimized optical attocells were examined and compared with previous models.This novel approach had successfully increased minimum received power from−1.29 to−0.225 dBm,along with enhanced SNR performance by 2.06 dB.The bit error rate(BER)was reduced to 4.42×10−8 and 6.63×10−14 by utilizing OOK-NRZ and BPSK modulation techniques,respectively.The optimized attocells positions displayed better uniform distribution,as both received power and SNR performances improved by 0.45 and 0.026,respectively.As the results of the proposed model are optimal,it is suitable for standard office and room model applications.

一种新型变步长自适应滤波算法

为改进目前谐波电流检测方法,针对有源滤波器谐波检测,提出了一种新型变步长自适应算法,取得了比较好的效果。由于谐波检测属于适应噪声抵消技术低信噪比条件下的一种应用,因而在该算法中,没有以误差信号e(n)作为改变步长的自适应回馈量,而是将误差信号和上个工频周期的误差信号的差值△e(n)作为自适应回馈量,从而避免了误差信号e(n)一直较大,导致的自适应算法的稳态误差比较大的缺点;同时通过相干平均估计来避免测试计算过程中随机噪声的影响,调节算法的步长,其优越性在于:谐波检测过程能保证既具有较快的动态响应速度,又保证稳定后步长稳定很小,有较高的检测精度。理论分析和仿真试验证明了该算法的正确性和有效性。

激光多普勒测速系统自适应阈值检测算法

信号检测是激光多普勒测速(LDV)系统实现高精度的关键技术,针对LDV中微弱多普勒信号的检测,本文从噪声在频域中的统计特性出发,对多普勒信号进行带阻滤波,结合雷达的恒虚警(CFAR)检测技术,设计了基于频域的单元平方和自适应阈值检测算法以解决在低信噪比(SNR)的环境中LDV的信号检测问题,提高LDV的信号探测能力,同时降低其虚警概率。仿真与实验的结果表明:该算法与固定阈值相比可以在SNR为-12 d B时实现信号的完全检测,保持低虚警概率,运算简单,工程适用性强。

基于最大似然估计和Kalman滤波的BPSK载波同步方法

针对低信噪比及大多普勒频率变化率情况下的载波同步问题,提出一种基于最大似然估计和Kalman滤波相结合的跟踪环结构.利用最大似然估计在低信噪比环境下准确估计载波频率和相位,并结合Kalman滤波对载波变化进行稳定跟踪.其中利用二分法搜索保证低计算复杂度的同时提高了估计精度.仿真结果表明了此载波跟踪环路良好的跟踪性能.

低信噪比环境下基于PR的音频分割

针对当前不同的非白噪声背景研究很少,根据噪音、语音和音乐的性质并且结合统计学理论,提出一种在不同噪声背景下低信噪比的语音/音乐分割算法。以往的检测算法很少考虑低信噪比的环境,首先从音频数据中提取新的特征参数概率密度比(probability density ratio,PR)和概率密度比过零率(probability density ratio crossing rate,PRCR),特征参数在低信噪比环境下亦能明显表征语音和音乐的不同特性,然后根据音频的特性对PRCR进行修正,再基于此修正的特征参数对语音和音乐进行改变点检测,最后得到分割结果。实验结果显示,在信噪比达到5dB时分割点准确率达到85%以上,具有良好的鲁棒性。

BICM-ID中一种新的8PSK星座映射

在比特交织编码调制及迭代译码(BICM-ID)系统基础上,设计一种8PSK调制星座映射方法。该方法以映射符号之间的平均近邻汉明距离为设计准则,将8PSK调制的符号分为2组半径和相位不同的QPSK调制的映射符号,通过调整半径减小星座映射符号之间的平均近邻汉明距离。性能分析和仿真结果表明,与其他BICM-ID中的8PSK星座映射相比,在低信噪比下,该方法的误比特率更低。

非理想信道状态信息下权值可调干扰对齐算法

针对多输入多输出(MIMO)系统获取信道信息过程中存在估计误差、反馈延迟等问题,为了提高低信噪比(SNR)时的系统性能,提出了一种基于权值可调的稳健干扰对齐算法。首先,在理想信道的基础上考虑信道误差的影响重新构建系统模型;然后,采用矩阵投影技术对接收端的信号空间进行分解,分成期望信号子空间与干扰信号子空间两部分;其次,考虑期望信号和干扰信号之间的相互影响,把两者泄漏到相应的子空间的功率加权和作为目标函数运用迭代思想计算出预编码和干扰抑制矩阵;最后,利用计算出的预编码和干扰抑制矩阵推导出存在信道误差的和速率表达式。仿真结果表明与稳健最小干扰泄漏算法相比,在信噪比为10 d B、信道误差方差取值0.05时,系统的频谱效率提升了25%,能量效率提升了38%,因此所提算法在低信噪比时可以有效地提升系统性能。

Long term integration of radar signals with unknown Doppler shift for ubiquitous radar

Ubiquitous radar is a new radar system that provides continuous and uninterrupted multifunction capability within a coverage volume. Continuous coverage from close-in ＂pop-up＂ targets in clutter to long-range targets impacts selection of waveform parameters. The coherent processing interval （CPI） must be long enough to achieve a certain signal-to-noise ratio （SNR） that ensures the efficiency of detection. The condition of detection in the case of low SNR is analyzed, and three different cases that would occur during integration are discussed and a method to determine the CPI is presented. The simulation results show that targets detection with SNR as low as -26 dB in the experimental system can possibly determine the CPI.

基于中继的低延时无线协作视频传输系统

针对无线视频传输系统中数据帧长度变化较大、信源数据速率不断变动的特点,提出一种基于中继的低延时协作视频传输系统。给出传输延时的表达式,分析协作中继系统降低传输延时的原因。设计系统的中继策略和调制编码方案,以提高系统的传输质量。仿真结果表明,该传输系统可以有效地降低视频传输的延时,并获得误码率性能增益。

DOA estimation based on multi-frequency joint sparse Bayesian learning for passive radar

This paper considers multi-frequency passive radar and develops a multi-frequency joint direction of arrival(DOA)estimation algorithm to improve estimation accuracy and resolution.The developed algorithm exploits the sparsity of targets in the spatial domain.Specifically,we first extract the required frequency channel data and acquire the snapshot data through a series of preprocessing such as clutter suppression,coherent integration,beamforming,and constant false alarm rate(CFAR)detection.Then,based on the framework of sparse Bayesian learning,the target’s DOA is estimated by jointly extracting the multi-frequency data via evidence maximization.Simulation results show that the developed algorithm has better estimation accuracy and resolution than other existing multi-frequency DOA estimation algorithms,especially under the scenarios of low signalto-noise ratio(SNR)and small snapshots.Furthermore,the effectiveness is verified by the field experimental data of a multi-frequency FM-based passive radar.

基于正交基函数-编辑距离的低信噪比下磁异常信号相似性度量方法

针对低信噪比下磁异常信号相似性难以度量的问题,该文提出基于正交基函数(OBF)分解和编辑距离法(EDR)相结合的OBF-EDR磁异常信号相似性度量方法。该方法通过对磁异常信号进行正交基函数分解得到离散基函数系数,根据背景噪声与基函数不相关的特性提高离散基函数系数信噪比,利用编辑距离法对离散基函数系数进行相似性计算从而间接实现对磁异常信号的相似性度量。仿真测试表明OBF-EDR方法相较于EDR算法可在更低信噪比情况下对磁异常信号进行相似性度量。

符号速率采样条件下的新型复合载波跟踪环

针对低信噪比和符号速率采样条件下的载波同步问题,提出了一种新型的复合载波跟踪环,同时也给出了一种较直观的环路参数确定方法。该载波同步环改进了原有的符号硬判决算法,并通过引入采样速率变换模块使得数字锁频环(frequency-locked loop,FLL)和数字锁相环(phase-locked loop,PLL)工作在不同采样速率条件下,来提高在低信噪比环境中载波频偏和相偏的估计精度。该参数确定方法是在z域中,直接根据闭环系统的稳定性和单位阶跃响应特性来选择最优的参数。仿真结果表明,该参数确定方法具有很好的可行性,且所提出的载波跟踪环在较低信噪比条件下能获得良好的同步性能。

自适应抗噪的清/浊/静音判决算法

清/浊/静音判决(UVS)是语音压缩、合成以及识别中的一个重要参数。为了解决传统判决方法训练过程复杂,导致语音编码效率低的问题,给出一种无训练过程的判决方法。提取基于循环平均幅度差的特征参量,利用判决参数间的相关性,自适应调整阈值,实现清/浊/静音判决。该判决方法具有很好的抗噪声干扰能力,有效提高判决的准确率。测试结果表明:该算法简化了清/浊/静音判决的计算量,清音误判率降低了10%,浊音误判率保持在4%以内;将该算法应用于低速率语音编码方案MELP(mixed excitation linear prediction)0.6 kbps的清浊音判决中,解码后的合成语音质量优于原始MELP编码方案,PESQ分数提高0.3,具有较好的可懂度和自然度。

基于改进型双门限语音端点检测算法的研究

语音端点检测是语音信号处理过程中的一个重要步骤,其检测准确性直接影响语音信号处理的速度和效果。传统的基于双门限法语言检测技术,在语音处于纯语音情况下判断语音端点较准确,但在语音处于噪声情况下,尤其是低信噪比的情况下,端点识别率很低,出错率很高。基于提高此方法识别率的目的,采用调整阈值个数,平滑滤波,引入语音结束最小长度的方法对其进行改进,通过了Matlab仿真实验,得出了较好的语音端点检测准确率。

400 Gbit/s光通信用超低损耗超大有效面积光纤的研究

从电磁场基本理论出发,采用标量波动方程进行分析与计算,设计出一种超低损耗超大有效面积单模光纤(SMF)的折射率剖面结构,纤芯折射率为1.461 16,纤芯直径为13.99μm,内包层引入低折射率下凹环,其折射率为1.455 62,宽为6.95μm;采用连续化学气相沉积(CCVD)工艺,制造出包层直径为125μm的SMF。测试表明,研发的光纤具备超低损耗与超大有效面积特性,其在1 550nm波长的衰减为0.165dB/km,在1 625nm波长的衰减为0.179dB/km;在1 550nm波长的模场直径为13.96μm,有效面积为153μm2;光纤具备优良的抗弯曲性能,在弯曲半径为30 mm的芯轴上弯曲100圈的条件下,其在1 550nm的弯曲附加损耗为0.032dB,在1 625nm波长的弯曲附加损耗为0.093dB。实验结果表明,本文研发的SMF能够满足400Gbit/s高速光通信的应用需求,可为下一代高速光纤通信提供关键基础材料支撑。

深空通信中极低码率编码技术研究

针对深空通信极低信噪比环境下,通信距离大,信号衰减大等特点,阐述了深空通信对低码率码字的需求。介绍低码率码字的发展情况后,引入GLDPC码,分析了LDPC码和Hadamard码进行级联时存在的度为1的节点问题。将LDPC-Hadamard级联码进行优化,对优化后的LDPC-Hadamard码进行仿真。结果表明,极低信噪比下,低码率LDPC-Hadamard码性能较好,一定程度上能够满足深空通信等恶劣信噪环境下的需求。