波长调制光谱检测下限计算方法的研究

在基于波长调制光谱技术的大气痕量气体检测下限计算方法的研究中,全面准确地描述吸收信号及噪声的大小极为重要。为了探讨半导体二极管激光器在进行波长直接调制时伴随产生的残余振幅调制噪声对检测下限的影响,在理论推导中采用了一种同时考虑波长和振幅调制的二次谐波信号分析及提取方法,以二次谐波信号峰谷差值作为系统的检测信号,对可调谐二极管激光器吸收光谱检测系统的信噪比和检测下限进行了理论分析,取得了洛伦兹吸收线型条件下残余振幅调制噪声对系统信噪比和检测下限的影响的精确计算数据。结果表明,在吸收线的线宽较大的检测条件下,残余振幅调制噪声是影响检测下限的重要因素。     

光学谐振腔增强碘分子调制转移光谱

提出了一种新的高灵敏激光光谱技术——激光双频相位调制环形腔增强调制转移光谱技术。该技术采用单一晶体实现激光双频相位调制，在满足环形腔高精度锁定的同时，又结合了调制转移光谱技术的高灵敏度、高分辨率、无多普勒背景的优点和环形谐振腔增强技术在提高谱线信噪比方面的优势；由此，实验观察到^127I2分子在532nm波段高信噪比的超精细结构光谱。与传统调制转移光谱技术相比，该技术在提高微弱吸收光谱信号的探测灵敏度方面具有明显的优势，在高灵敏、高分辨光谱检测和激光稳频方面将有很好的应用前景。     

基于光弹调制的原子磁强计中光信号检测方法

在无自旋交换弛豫原子磁强计中,需要检测极小的旋光角度。基于光弹调制器的偏振调制技术由于其较低的噪声和长时间的稳定性在各种检测方法中是优选的。但光弹调制器的输出信号里包含有大量噪声和高次谐波,严重影响了原子磁强计的性能。针对以上问题分析了基于光弹调制器的偏振调制技术的原理和待检测信号的特性,并提出一种基于双通道数字锁相放大器的原子磁强计微弱信号检测方法。该方法简化锁相放大算法,减小电路复杂度,并能准确地同时检测一次谐波和二次谐波的幅值。理论分析和仿真结果表明,该检测系统工作良好,可以准确地检测微弱信号,误差在0.1%以内。     

Information, error, and imaging in deadtime-perturbed doubly stochastic Poisson counting systems

The detection of a fluctuating signal in the presence of noise is considered for a doubly stochastic Poisson counting system that is subject to fixed nonparalyzable detector deadtime. Explicit expressions are obtained for the likelihood-ratio detection of a modulated source of arbitrary statistics in the presence of Poisson noise counts. Receiver operating characteristics (ROC curves) are presented for an unmodulated (amplitude-stabilized) source with detector dead-time as a parameter; increasing deadtime causes a decrease in the probability of detection for a fixed false-alarm rate. Probability of error curves are presented for an amplitude-stabilized source, both in the absence of modulation and in the presence of triangular modulation, illustrating the deleterious effects of modulation, noise, and deadtime on receiver performance. Expressions for the average mutual information and channel capacity of the system are obtained and graphically presented for the simple counting receiver and for the maximum-likelihood counting receiver; the channel capacity decreases with decreasing signal level and with increasing deadtime and modulation depth. Representative examples of the appropriate counting distributions are provided. Finally, a maximum-likelihood estimate of the mean signal level is obtained for a simple image detection system with a deadtime-perturbed counting array. An expression for the statistical confidence level of the estimate is also obtained. The results are valid for an arbitrary deadtime-perturbed doubly stochastic Poisson counting system and as such are expected to find application in a broad variety of disciplines including photon counting and lightwave communications, operations research, nuclear particle counting, and neural counting and psychophysics.     

二进制调制信号Duffing振子检测方法及其抗噪声机理分析

根据二进制调制信号的特点及Duffing振子微弱信号检测技术,研究了二进制调制信号的Duffing振子检测原理,给出了2ASK、2FSK及BPSK调制信号的Duffing振子检测的方法和流程.从Dufiing振子与匹配滤波器处理待测信号的不同原理出发,研究了Duffing振子输入前端信号信噪比提升的现象.指出二元通信信...     

Wavelet-denoising technique in near-infrared methane detection based on tunable diode laser absorption spectroscopy

A novel wavelet denoising （WD） assisted wavelength modulation technique is proposed for improving near-infrared de- tection performance on methane concentration based on tunable diode laser absorption spectroscopy （TDLAS）. Due to the ability of multi-level analytical resolutions both in time- and frequency-domains, the noise contained in the differen- tial signal is greatly suppressed. Sensor mechanical part, optical part and electrical part are integrated, and a portable detection device is finally developed. Theory and formulations of the WD-assisted wavelength modulation technique are presented, and experiments are carried out to prove the normal function on the extraction of the second harmonic （2j） signal from severely polluted differential signal by using the technique. By virtue of WD＇s suppression on noises, the sensing characteristics on CH4 concentration are improved, and the limit of detection （LOD） is decreased from 4× 10-6 （without WD processing） to 10-6. The proposed technique can also be used for the measurement on the concentration of other gases with corresponding near-infrared distributed feedback lasers.     

Analysis of FM Systems with Co-Channel Interference Using a Click Model

Rice's click model for ideal FM detection is applied to systems with co-channel interference. Output noise terms consist of a high signal-to-noise ratio (SNR) term due to noise alone, a term due to the desired signal beating with the interferer, and a term due to the clicks. Click rates are determined with and without modulation and it is shown that in the computation of noise due to clicks the interferer can be treated as a simple sinusoid [i.e., an unmodulated carrier] Plots are given for detected SNR versus carrier-to-noise (CNR) with signal-to-interferer ratio (SIR) and modulation index as parameters. The effect of signal suppression is analyzed and for the range of parameters used in this paper it is found to be negligible.     

All-digital reverse modulation architecture based carrier recoveryimplementation for GMSK and compatible FQPSK

A carrier recovery circuit implementation with an all-digital reverse modulation approach for coherent detection in the GSM/GMSK system as well as the GMSK compatible improved efficiency cross-correlated FQPSK system is presented. The proposed carrier recovery implementation utilizes all-digital reverse modulation circuit in a feedback loop to remove the modulated signal from the received intermediate frequency (IF) signal and to estimate the phase error of this carrier signal using a phase-locked loop (PLL). The digital reverse modulation approach avoids the multipliers required in an analog reverse modulation design, so that it can be implemented in a single chip FPGA. Hardware implementation of the coherent detection demonstrates that cross-correlated FQPSK is completely compatible with GMSK in the system performance and the receiver structure for GSM. Experimental performance evaluations show that the proposed carrier recovery circuit provides a Bit Error Rate (BER) performance within 0.3 dB in a non-linearly amplified channel corrupted by additive white Gaussian noise (AWCN) as compared with the simulated performance of the GSM/GMSK system     

基于能量统计的噪声调频干扰信号检测方法

简述了噪声调频信号的基本性质,并给出了基于能量统计的噪声调频信号检测方法的基本原理。利用QuartusⅡ对此方法进行了硬件电路的设计,对电路进行了仿真,验证了此方法对连续波的噪声调频信号检测的有效性。     

Improved ADPCM voice signal transmission employing click-noisedetection scheme for TDMA-TDD personal communication systems

In personal communication systems, better voice quality and lower terminal price are essential requirements, and adaptive differential pulse-code modulation (ADPCM) codecs are one of the voice codec candidates that have good voice quality and reasonable cost. However, in slow fading environments, burst errors induce click noise in ADPCM voice signal transmission. This paper proposes a novel error-concealment scheme to improve the ADPCM voice signal transmission quality of time division multiple access time division duplex (TDMA-TDD) personal communication systems in slow fading environments. The proposed scheme employs an improved error-detection technique with PCM differential detection and overflow detection coupled with a cyclic redundancy check (CRC) code. To compensate for residual click noise, an expanded CRC error-detection signal is used. Erroneous PCM signals are adaptively suppressed according to the click-noise detection information. Hardware simulation results show that these techniques significantly improve ADPCM voice signal transmission quality by 0.5 points and 1.0 compared to that of the conventional ADPCM muting scheme and no processing, respectively, with the mean opinion scoring (MOS) test in the slow fading environments typical of personal communication systems     

基于PWHT的LFM-PRBC雷达信号截获与特征提取

线性调频-伪随机二相编码调相复合调制雷达信号(LFM-PRBC)融合了两者的优点,弥补了单一信号的不足,是一种性能较好的低截获概率雷达信号,给传统雷达截获接收机带来挑战。提出了将周期Wigner Hough变换(PWHT)与相关检测相结合的方法,通过在信号的周期WignerHough域搜索峰值,检测复合调制雷达信号并实现其特征提取。通过理论分析和计算机仿真验证,该方法能实现高斯白噪声背景下低信噪比复合调制信号的截获与特征提取。     

基于高频微波技术的分布式光纤传感器布里渊散射信号检测

分析了布里渊分布式光纤传感技术原理,采用自行研制的光纤单纵模分布反馈(DFB)激光器结合电光调制技术,利用相干检测技术,对布里渊微弱后向散射信号进行检测。通过改进滤波放大技术,对微弱后向散射光信号进行有效放大,再用扰偏技术及信号采样平均处理,实现对光纤传感器后向布里渊散射信号在11 GHz高频段直接采集显示。结果表明,探测所得布里渊散射信号峰值功率可达50 mV,能有效降低解调系统信号检测难度,改善了系统信噪比(SNR)。初步实验结果证明了该方案的可行性。     

Fractional Multi‐bit Differential Detection Technique for Continuous Phase Modulation

A new low‐complexity differential detection technique, fractional multi‐bit differential detection (FMDD), is proposed in order to improve the performance of continuous phase modulation (CPM) signals such as Gaussian minimum shift keying (GMSK) and Gaussian frequency shift keying (GFSK). In comparison to conventional one‐bit differential detected (1DD) GFSK, the FMDD‐employed GFSK provides a signal‐to‐noise ratio advantage of up to 1.8 dB in an AWGN channel. Thus, the bit‐error rate performance of the proposed FMDD is brought close to that of an ideal coherent detection while avoiding the implementation complexity associated with the carrier recovery. In the adjacent channel interference environment, FMDD achieves an even larger SNR advantage compared to 1DD.     

Low‐Noise MEMS Microphone Readout Integrated Circuit Using Positive Feedback Signal Amplification

A low‐noise readout integrated circuit (ROIC) for a microelectromechanical systems (MEMS) microphone is presented in this paper. A positive feedback signal amplification technique is applied at the front‐end of the ROIC to minimize the effect of the output buffer noise. A feedback scheme in the source follower prevents degradation of the noise performance caused by both the noise of the input reference current and the noise of the power supply. A voltage booster adopts noise filters to cut out the noise of the sensor bias voltage. The prototype ROIC achieves an input referred noise (A‐weighted) of ?114.2 dBV over an audio bandwidth of 20 Hz to 20 kHz with a 136 μA current consumption. The chip is occupied with an active area of 0.35 mm² and a chip area of 0.54 mm².     

微弱信号检测系统设计

针对压力传感器输出信号微弱并带有较大噪声干扰的情况,设计了一种基于互相关检测技术的微弱信号检测系统。系统以变压器式压力传感器为压力信号检测器件,采用单片集成函数信号发生器ICL8038产生正弦波信号,再经功率放大器TDA7294放大后,作为传感器信号的调制信号和互相关检测的解调参考信号,采用平衡调制解调芯片AD630设计锁相放大器电路,通过放大、滤波、整流得到直流信号。仿真和实验验证证明了系统对微弱信号的检测效果理想,适用于强背景噪声下对微弱信号的检测。     

船舶航行辐射噪声信号仿真方法研究

船舶航行辐射噪声是被动声纳探测、声纳目标识别、听音判型等工作的重要信息源,其信号仿真是解决上述研究工作中噪声样本类型少或数量不足的有效方法,前提是所仿真信号必须满足逼真度要求。提出了一种基于实测信号重构的船舶航行辐射噪声信号仿真方法。通过谱估计提取信号的连续谱、线谱、调制谱特征,根据谱估计数据合成满足信号谱特征要求的船舶航行辐射噪声,并通过听觉感受调整调制谱参数。仿真结果显示所合成船舶航行辐射噪声信号能够从谱估计和听觉感受两方面逼近实测辐射噪声信号。      

低信噪比下缓变线性调频信号的图像流法检测

研究了低信噪比下缓变线性调频信号(LFM)的检测。信号的频率缓慢变化，微弱且淹没在强的白噪声之中，信噪比在-10dB以下。利用LFM信号在wigner—hough变换(WHT)平面上聚集成一尖峰值点的性质和其峰值点在多帧WHT平面缓慢连续运动的特征，提出了WHT与图像流法相结合检测缓变线性调频信号的新方法。计算机仿真证明了其有效性。     

Signal mappings of 8-ary constellations for bit interleaved coded modulation with iterative decoding

Bit interleaved coded modulation with iterative decoding (BICM-ID) is a spectral efficiency coded modulation technique. This technique is therefore very attractive for many broadcasting services where transmission bandwidth is a primary concern. It has been shown that when signal constellation, interleaver and error-control code are fixed, signal mapping has a critical influence to the error performance of a BICM-ID system. Based on the technique of mutual information, good mappings of different 8-ary constellations are presented for BICM-ID systems over an additive white Gaussian noise (AWGN) channel. It is also shown that, compared to free Euclidean distances, mutual information is a more useful technique to find the good signal mappings for BICM-ID systems.     

调制相位差对TDLAS信噪比的影响

用可调谐二极管激光吸收光谱技术检测气体时,不同的调制相位差结果不同。为了提高谐波检测灵敏度,采用同时考虑频率调制与振幅调制的方法分析和提取二次谐波信号,推导了相位差与二次谐波信号光电流和残余幅度调制噪声光电流的函数关系表达式,通过模拟实验分别取得了二次谐波信号和残余幅度调制噪声随相位差的变化趋势,并重点分析了相位差对信噪比的影响。结果表明,振幅调整和频率调制之间的相位差对信噪比的影响很大,与典型值/2时相比,最大降幅为59.18%;调制相位差是继残余幅度调制之外,影响信噪比的一个重要因素。     

A nonlinear optimum-detection problem. I. Theory

An approximate log-likelihood ratio for detecting a deterministic signal in linear and nonlinear Gaussian noise is derived. The new aspect of this detection problem is the inclusion of a nonlinear form of Gaussian noise and a certain interaction between the signal and the linear noise, such as modulation of the signal by the noise. The derived log-likelihood ratio consists of a modified version of the classical correlation detector and a new processor where the latter is an order of magnitude smaller than the former. In the absence of the signal-noise interaction, the modification consists of subtracting the estimate of the nonlinear noise from the input (to the correlation detector); the nonlinear processor is a quadratic correlation processor where the correlation is not against the (transformed) signal but against the difference of two estimates of the nonlinear noise under the two hypotheses (signal-presence and signal-absence). Presence of the signal-noise interaction introduces further modification and complication on both processors