Noise immunity of a planar array of combined receivers

The far-field noise immunity of a passive direction-finding planar array consisting of combined receivers is considered for different signal processing algorithms. It is shown that there is no point in using combined receivers in arrays with an acoustic baffle.     

Noise immunity of a combined hydroacoustic receiver

A statistical analysis of the noise immunity of a combined receiver is performed for the observation of a fluctuating tone signal against the background of underwater dynamic noise. The analysis is based on the experimental data obtained in deep ocean with the use of two four-component combined hydroacoustic receivers positioned at depths of 150 and 300 m. Theoretical expressions are obtained for the signal-to-noise ratio of a combined receiver, for reciprocal spectral levels of the signal and noise in both narrow and wide frequency bands. The definition of the combined receiver gain is introduced in terms of the functions of a common single-point coherence for the acoustic pressure and the particle velocity in an acoustic wave. According to the experimental data obtained, in the case of multiplicative processing, the maximal gain in the signal-to-noise ratio of a combined receiver, as compared to a hydrophone-based square-law detector, can reach 15–16 dB for the horizontal channel and 30 dB for the vertical channel of the combined receiver in the case of the compensation of opposing flows of the signal and noise energy.     

A Kalman filter based synchronization scheme for telescope array receivers in deep-space optical communication links

In this paper, the impact of random synchronization errors on the performance of ground-based telescope array receivers for an inter-planetary optical deep-space communication (ODSC) link is investigated. An adaptive method based on Kalman filters is developed for the synchronization and combination of different telescope signals in the array. An end-to-end simulation platform for ODSC link between Earth and planet Mars is implemented that incorporates pulse-position modulation (PPM), direct-detection array receivers, and photon-counting detectors. The effects of atmospheric turbulence and background noise are also modeled. The performance of array receivers is evaluated in terms of probability of symbol error and achievable data rates. The simulation results show that the Kalman filter-based synchronization scheme keeps the synchronization induced power losses to less than 1 dB. The analysis also shows that in the worst-case operational scenario and presence of random synchronization errors, an array consisting of hundred, 1 m telescopes performs almost similar to a single 10 m telescope. Hence, the degradation in the combined signal due to synchronization errors places a minor limitation on the number of telescopes in a telescope array receiver consisting of up to 100 telescope elements.     

Analysis of interference cancellation techniques in OFDMA systems employing adaptive antenna arrays

We analyze the problem of interference cancellation in OFDMA cellular communication systems employing adaptive antenna arrays at the receiver and operating in the channels with frequency-selective fading and interference from the neighboring base stations. This problem is very important for modern broadband cellular systems operating with a low coefficient of multiple use of frequencies. Under such conditions of the network deployment, the system efficiency is restricted by the level of intrachannel interference from the neighboring base stations transmitting in the same frequency channel. In this work, we analyze different methods for measuring the interference characteristics and using them for spatial processing of received signals. Five different methods for signal processing in an adaptive antenna array of the receiver are discussed. Each approach (reception method) has its own interference immunity and complexity degree. Comparative analysis of the interference immunity of the considered receivers has been performed for different frequency-channel loads and different numbers of interfering stations. Recommendations for using the considered receivers are given.     

Coherent aperture synthesis for incoherent source

We propose a refinement of the method for aperture synthesis for an incoherent source, imparting selectivity and noise immunity to the method. Instead of measuring the phase difference between the signals of the array receivers, we measure the array-averaged phase difference between neighboring receivers by searching for the maximum of the magnitude of the moving array’s response to the source signal during its direction-of-arrival-scanning (phasing). This procedure is carried out after incoherent accumulation. The gain in noise immunity is determined by the gain in the array with the addition of the gain in incoherent accumulation. The size of this gain in the experiment was on the order of 20 dB. The method retains applicability to wideband signals and the possibility of observing other incoherent signals. We demonstrate the possibility of high angular resolution with the synthesized antenna of the source, which does not possess the perfect time coherency of the source and other sources coherent with it. Owing to phase averaging over the array aperture, we obtain an increase in the method’s stability to reverberation. We present results of simulation and applicability of the method in full-scale experiments.     

Analysis of noise immunity of OFDMA communication systems operated in the presence of interfering stations

We analyze noise immunity of high-speed data transmission systems operated in a complex communication channel with frequency-selective fadings and interference from the neighboring base stations. This problem is very topical for modern orthogonal frequency-division multiple-access (OFDMA) data transmission standards. Such digital communication systems allow one to measure the noise parameters on individual subcarriers simultaneously with reception useful signals. We perform comparative analysis of different methods for measuring the noise characteristics and using them for demodulating the coded signal. Four processing methods with different complexity and noise immunity degree are proposed for receiver signals. Characteristics of the considered receivers are compared for different channel loadings and algorithms of power control by interfering stations. Practical recommendations for using the considered receivers are given. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 533–543, June 2007.     

利用海浪噪声自相关实现散射体无源探测

提出了一种利用海浪噪声自相关实现散射体无源探测的新方法.将各接收器记录噪声信号的自相关减去所有接收器记录噪声信号自相关的平均值,得到散射信号的到达结构,然后结合基尔霍夫移位算法实现对散射体的探测.与利用背景噪声互相关提取格林函数从而实现散射体探测的方法不同,自相关无需考虑各个接收器之间的大量数据传输及时间同步问题,这为相距较远的多接收器和移动平台目标探测提供了极大的方便.将所提出的方法应用于实验数据中,最终探测结果与实际测量结果相比差别不大,验证了方法的有效性.     

Interferometric Direction Finding by a Vector-Scalar Receiver

A method for interferometric direction finding of a broadband sound source in an oceanic waveguide by a single vector-scalar receiver is presented. The method is based on the double Fourier transform of the interference pattern formed during motion. The efficiencies of the proposed direction finding method and the method based on measuring the delay times of signals arriving at spaced scalar receivers are compared based on the natural experiment results. The noise immunity of the interferometric direction finding method is considered.     

基于云计算的嵌入式人脸识别系统建构与研究

在捕获北斗信号的过程中,接收机根据预先设定好的信号搜捕策略和门限值来捕获信号。欺骗干扰源通过产生虚假的相关峰和增加噪声基底,可以有效地干扰普通型北斗接收机正常的捕获工作。欺骗信号会增加噪声基底使得真实的卫星信号埋没,同时欺骗信号相关峰可以诱导接收机捕获到欺骗信号。针对欺骗信号检测问题,在分析欺骗信号入侵对接收机噪声基底影响的基础上,提出了在捕获阶段利用信噪比(SNR)检测技术识别欺骗干扰信号的方法,并对其有效性进行了分析。仿真结果表明,采用该方法的接收机具有一定程度的欺骗干扰识别能力,为提高GNSS接收机抗干扰能力提供了有益的参考 。     

MRI射频接收机多路噪声均衡改善图像质量的实现

磁共振成像(MRI）是一种多通道接收的成像系统. 接收机各通道的噪声差异影响图像的均匀性. 本文提出了一种多路噪声均衡改善图像质量的方法：利用系统特性改进Y因子法用于噪声测量,并依此为依据修正各通道的比例因子进行图像重建,实现各通道的噪声均衡,提高了图像的均匀性.     

Guided wave phase velocity measurement using multi-emitter and multi-receiver arrays in the axial transmission configuration

This paper is devoted to a method of extraction of guided waves phase velocities from experimental signals. Measurements are performed using an axial transmission device consisting of a linear arrangement of emitters and receivers placed on the surface of the inspected specimen. The technique takes benefit of using both multiple emitters and receivers and is validated on a reference wave guide. The guided mode phase velocities are obtained using a projection in the singular vectors basis. The singular vectors are determined by the singular values decomposition (SVD) of the response matrix between the two arrays in the frequency domain. This technique enables to recover accurately guided wave phase velocity dispersion curves. The SVD based approach was designed to overcome limitations of spatio-temporal Fourier transform for receiver array of limited spatial extent as in the case of clinical assessment of cortical bone in axial transmission.     

A sixteen-channel multiplexing upgrade for single channel receivers

With the increasing interest in phased arrays in magnetic resonance imaging, imaging system receivers capable of acquiring larger number of parallel signals are needed. Suggested techniques for rapid imaging propose the use of arrays with as many as 128 elements. While simply duplicating the number of receiver chains as needed is a viable technique, it quickly becomes both cumbersome and expensive.Time domain multiplexing offers an alternative solution to this problem. By using RF multiplexing switches, a single receiver can be upgraded to an array receiver capable of multi-channel data acquisition giving users array capability. Additionally, it can be used to dramatically increase acquisition capability of multiple receiver systems.This paper reports results from a multiplexing system upgrade, which converts a single channel standard clinical imaging system to a 16-channel array system. The upgrade includes both the RF multiplexing front-end and an external data acquisition system with image processing capability. Issues concerning the implementation of high channel-count multiplexers are also discussed.     

非完整阵列接收下的虚拟接收目标定位技术

在浅海近似绝热环境中,利用虚拟接收方法对声源测距的目标定位方法相比于传统的匹配场定位方法可以避免对环境参数和声场模型的依赖,同时省去生成拷贝场时的大量计算·利用虚拟接收方法对声源测距主要是通过估计虚拟声场干涉条纹的斜率进行定位,而非完整阵列接收相当于引入了干扰项,破坏了虚拟声场干涉结构。引入了一种基于图像Hessian矩阵特征值分析的多尺度线性滤波器,通过数值模拟和实验数据处理,结果表明,该滤波器可以有效地增强干涉结构、检测和提取干涉图案中的条纹信息,提高非完整阵列接收条件下的虚拟接收目标定位技术的测距性能。      

Acoustic mapping of the ocean bottom and requirements of the initial data

The amount and degree of detail of the initial information are analyzed as applied to the new method of ocean bottom mapping on the basis of the fine structure of the bottom-reflected sound field at normal incidence. For the mapping data obtained with a planar multielement receiving array, the distortions caused by insufficiently detailed information derived from discrete measurements of the bottom-reflected amplitude are considered. The relations between the number of receivers, the receiver spacing, the array aperture, and the horizontal correlation length of the sound field are determined. The problem is solved by computer simulation with the use of generalized quantitative data obtained in deep-water ocean experiments.     

Influence of low intensity noise on assemblies of diffusively coupled chaotic cells

The effect of time-correlated and white Gaussian noises of low intensity on one-dimensional arrays consisting of diffusively coupled chaotic cells is analyzed. An improvement or worsening of the synchronization between cells of the array driven by low-intensity colored noise is observed for a resonant interval of time correlation values. A comparison between colored and white noise and additive and multiplicative contribution has been carried out investigating the nonlinear cooperative effects of noise strength, correlation time, and coupling strength to control spatiotemporal chaos in coupled arrays of chaotic cells. The possibility to distinguish highly correlated areas of a diffusively coupled network of cells by using low-intensity time correlated noise is discussed. (c) 2001 American Institute of Physics.     

Imaging using air-coupled polymer-membrane capacitive ultrasonic arrays

Polymer-membrane capacitive ultrasonic linear and 2-D arrays have been fabricated for use in air-coupled imaging. By using arrays as receivers, there is a possibility of much faster imaging as the need for physically moving the receiver to scan a sample can be replaced by electronic multiplexing. In order to utilise this, a through-thickness air-coupled image of a composite plate has been made using a 2-D array as a receiver and a comparatively large planar source in air. This was made possible by the use of a chirp drive signal and cross-correlation on the measured waveform. Larger 2-D arrays with an increased number of elements have been simulated using a small scanned single receiver, and excellent imaging potential demonstrated. In addition two array receivers have been used in conjunction with two methods of post-processing, SAFT and ellipse crossing, to locate objects accurately.     

Active light noise filter by a differential operation

A method for an active light noise filter is proposed by using two identical light receivers. They work as a differential electrometer by a common mode connection. Therefore, only an output of a laser light incident upon one receiver can be obtained as a signal. It was found from the experiment that the light noise was reduced to about 0.6% in the usual light room and further the signal to noise ratio was improved up to 30 times at least as compared to a usual light shielding method. The method can then be effectively used under a well-lighted room such as a factory without noise light shielding cover.     

Probability density function of noise statistics for optically pre-amplified DPSK receivers with optical Mach-Zehnder interferometer demodulation

We present explicitly semi-analytical probability density functions (pdf’s) of noise statistics in DPSK receivers with Mach-Zehnder interferometer (MZI) demodulation with considering the phase noise for the first time. Error performance of DPSK receivers with MZI demodulation is evaluated by using the calculated pdf’s. It is found that DPSK receivers with MZI demodulation and balanced detection are less sensitive to phase noise impact than those with the single-port detection to some extent. Moreover, it is found that ASE-ASE beat noise induced pdf difference in balanced detection compared to single-port detection may result in ∼3 dB improvement in receiver sensitivity mainly depending on optical filtering, ASE-amplified spontaneous emission. Therefore, the measured receiver sensitivity improvement by using balanced detection consist of the improvements due to signal energy difference and ASE-ASE beat noise induced pdf difference compared to single-port detection.     

复杂地层声波测井时差处理方法研究

在复杂地层(如砂-泥岩薄互层)的声波测井中,由于地层声速变化及界面反射波叠加干扰,导致不同接收器的地层纵波波形幅度差异明显,且相关性很差,使得提取的时差误差较大。这一声场特征可从薄互层声波测井的有限差分数值模拟中看到。针对这一现象,本文利用频率-波数域相关滤波处理技术来消除薄互层声波测井的界面反射干扰,以改善地层纵波波形的相关性。本文给出了砂-泥岩薄互层数字声波测井的现场资料处理实例,处理结果证明了该方法有效地消除了界面反射波的干扰,明显改善了地层纵波的相关性,提高了地层纵波时差曲线的分辨率,清晰地刻画出了薄互层特征。     

Suppression of acoustic noise in the measurements of wall pressure fluctuations

It is shown that, in hydrodynamic noise measurements in the presence of acoustic noise acting upon the pressure fluctuation receiver, spatial filtering methods should provide the best results. Active methods are developed for suppressing the acoustic noise that affects a miniature receiver in the course of turbulent pressure fluctuation measurements. The methods are based on complicating the structure of the measuring transducer by introducing an extra compensating sensing element whose characteristics are identical with those of the main sensing element. The spatial filtering of small-scale turbulent pressure fluctuations by a finite-size electroacoustic transducer is used as the basis for the development of noise-compensated measuring systems, as well as methods of measuring the turbulent pressure fluctuations by receivers with noise compensation. A numerical study of the wave-number filtering of acoustic noise in wall pressure measurements by a noise-compensated receiver is performed.