Analysis of the operation of adaptive antenna arrays of communication systems maximizing the output signal-to-noise ratio

The statistical characteristics of adaptive antenna arrays of communication systems with amplitude and phase modulated signals are investigated theoretically and by means of computer simulation for Gaussian interference and noise. An adaptive array antenna is considered, in which the host signal is formed by a nonlinear noninertial transformation of the output array signal. It is shown that the optimum vector of weight coefficients, minimizing the mean square deviation between the output and host signals, leads at the same time to a maximum output signal-to-noise ratio.Nizhegorod State University. Translated from Izvestiya Vyssikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 3, pp. 340–350, March, 1994.     

Weight vector fluctuations in adaptive antenna arrays with nonlinear function in a feedback loop

We present the results of statistical analysis of adaptive antenna arrays with nonlinear function in the feedback loop, which are adjusted by an algorithm for recurrent inversion of a sample estimate of the input-signal correlation matrix with allowance for the weight-coefficient fluctuations. Using the perturbation-theory methods in the first (Born) approximation, we obtain expressions for the correlation function and power of the output signal of an adaptive antenna array and a formula for the covariance matrix of the weight-coefficient vector. The weight-coefficient fluctuations are shown to result in signal distortions at the antenna-array output and appearance of additional terms in the statistical characteristics of the antenna array. These terms are second-order infinitesimals with respect to adaptation coefficient. Fluctuations are first-order infinitesimals and, thus, are much greater in an antenna array without nonlinear function in the feedback loop. It is also shown that the weight-vector fluctuations are anisotropic, i.e., they are absent in the constraint direction, minimal in the interference direction, and maximal in all other directions. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 2, pp. 164–172, February 2006.     

Pattern classification using optical Mellin transform and circular photodiode array

Scale-invariant pattern classification using a hybrid system combining the optical Mellin transform and a digital signal processing technique is discussed. We accomplish the optical Mellin transform by a logarithmic coordinate transformation using a computer-generated hologram, followed by an optical Fourier transform. Mellin transform patterns are detected with a circular photodiode array, whose output signals are processed by a micro-computer. A new criterion is discussed, in which circular or periodic correlation is employed. Experimental examples are presented.     

On the Similarity of the Statistical Characteristics of Spontaneous Radiation of a Quantum Amplifier at Different Gain Factors

The transformation laws governing the statistical properties of the quantum noise of an optical amplifier when its gain factor and spectral line profile are varied are considered. The correlation functions of quantum noise both at the amplifier output and after nonlinear transformation normalized to the correlation time of quantum noise at the amplifier output were found to be independent of the amplifier gain provided that it exceeds 10 for the Gaussian spectral line profile and 10³ for the Lorentzian profile. The spectral density of quantum noise transformed in a nonlinear system was shown to possess the same similarity property. It was found that the statistical characteristics possess a similarity property even in the case of variation of the spectral line profile from Gaussian to Lorentzian. It was concluded that such a characteristic of quantum noise of an optical amplifier as the correlation time bears virtually all information on the above-mentioned statistical properties at a reasonably large amplifier gain. The similarity property revealed has an important application. It allows finding the matching condition between the optical signal spectrum and the gain profile of the optical quantum amplifier to achieve the highest sensitivity of signal detection by the amplifier.     

Dynamics of simple computer networks

We consider a simple two-dimensional layered automaton. Each processor in the automaton performs the same nonlinear, thresholdlike operation (so that the row-to-row evolution of the array can also be seen as the time development of a one-dimensional automaton). One row of the machine is reserved for input, another is singled out as output. We study the output space in detail, as restricted by the very wiring of the array, enumerating the output configurations, and characterizing them statistically. We demonstrate that input configurations flow to a set of zero measure in output space. The variations in output that are to be expected when input is subjected to perturbations are also examined.     

Use of the application of heterodyne laser interferometer in power ultrasonics

We are particularly interested in the measurement of nonlinear acoustic waves in air, within the range of the Raman-Nath diffraction regime. We used a heterodyne laser interferometric system with a Bragg cell frequency of 80 MHz. A harmonic power acoustic wave with a frequency in the range of 20 kHz was generated, but higher harmonics appear when nonlinear propagation occurs in restricted volumes or waveguides. This topic raises a number of interesting questions. The most complex problem arises when processing an extremely wide-band output signal from a photo-detector, where the signal contains a huge number of high amplitude harmonics in a measured acoustic signal. The wide-band output signal from nonlinear wave measurement was simulated by means of similar wide-band output signals obtained by measuring known dynamic mechanical displacements. Because the frequency band of common analog circuits used for signal processing is too narrow, the output signal from the interferometer was digitalized and processed. This paper discusses the results of these tests and provides estimates of the frequency restrictions of signal processing.     

Spectral correlation characteristics of an adaptive Antenna array tuned by the Hebb algorithm with allowance for the weight-vector fluctuations

In this paper, we present the results of statistical analysis of the characteristics of an adaptive antenna array tuned by the Hebb algorithm with allowance for the weight-vector fluctuations in the case where signals with different levels of autocorrelatedness of the input-signal readouts arrive at the antenna array. Expressions for the correlation function of the output signal and the power spectral density at the antenna-array output are obtained. It is shown that fluctuations lead to distortions of the output signal of the adaptive antenna array and appearance of additional terms in the formulas for these characteristics.     

相控阵多普勒计程仪声基阵输出信号模型

相控阵多普勒计程仪具有基阵体积小，无需进行声速补偿等优点。本文在讨论相控阵多普勒计程仪原理的基础上，推导了速度解算公式，验证出公式与声速无关，进而推导出声基阵的输出信号模型，利用此模型便可模拟相控阵的输出信号。     

Input-output gain of collective response in an uncoupled parallel array of saturating dynamical subsystems

We explore the collective response of an uncoupled parallel array of saturating dynamical subsystems to a noisy periodic or random signal. Numerical simulation results show that a parallel array of nonlinear saturating subsystems can enhance the signal transmission via tuning the internal noise intensity and increasing the array size. The input-output gain larger than unity, described by the signal-to-noise ratio for a periodic signal or the correlation coefficient for a random signal, is observed in a form of array stochastic resonance. This stochastic resonance phenomenon can be useful for practical information-processing systems.     

Signal amplification based on the local nonlinear Mach–Zehnder interferometer

Using the phase modulation of spatial solitons, a new scheme for all-optical signal amplification has been proposed in this paper. The considered structure is composed of the nonlinear Mach–Zehnder interferometer (NMZI) with the straight control waveguide (CWG), the uniform nonlinear medium (NLM) and the linear output waveguide. The local NMZI functions like a phase shifter. The light-induced index changes in the local nonlinear MZI are responsible for the input beam routing in the uniform nonlinear medium. The coupling of the input beam to the output waveguide depends on its propagation direction in the NLM. It is shown that the signal launched at CWG can deflect the beam launched at the NMZI (input beam) and a modulated (amplified) output could be obtained at the output waveguide. Further, signal pulse may be reshaped by appropriately increasing the NLM length. In addition, amplification factor may be enhanced by increasing the NLM length and injecting an appropriate continuous wave beam along with the signal beam at CWG.     

海洋环境噪声场对称性分析及噪声消除方法

实际的海洋环境是非常复杂的,存在着海洋自噪声、舰船噪声、生物发声等,阵元接收到的噪声信号存在一定的相关性,此时基于传统阵列信号处理的目标方位估计方法的性能将变差,针对这一问题,提出了一种实部消除方法.首先从阵元接收环境噪声的物理机理出发,将圆环阵接收的噪声场分解为对称噪声场和非对称噪声场,并且研究发现对称噪声场只影响数据协方差矩阵的实部.然后通过消除协方差矩阵实部,达到消除对称噪声场的目的,提高信噪比,但是同时产生了虚假声源.针对虚假声源的问题,提出了基于优化算法重构协方差矩阵实部的方法,消除了虚假声源的影响.仿真分析与海试数据处理结果表明:该方法明显消除了对称噪声,提高了信噪比,改善了阵列信号处理算法的性能.实部消除方法易于实现,有一定的工程应用价值.     

Multibeam second-harmonic generation by spatiotemporal shaping of femtosecond pulses

We present a technique for efficient generation of the second-harmonic signal at several points of a nonlinear crystal simultaneously. Multispot operation is performed by using a diffractive optical element that splits the near-infrared light of a mode-locked Ti:sapphire laser into an arbitrary array of beams that are transformed into an array of foci at the nonlinear crystal. We show that, for pulse temporal durations under 100 fs, spatiotemporal shaping of the pulse is mandatory to overcome chromatic dispersion effects that spread both in space and time the foci showing a reduced peak intensity that prevents nonlinear phenomena. We experimentally demonstrate arbitrary irradiance patterns for the second-harmonic signal consisting of more than 100 spots with a multipass amplifier delivering 28 fs, 0.8 mJ pulses at 1 kHz repetition rate.     

The statistical characteristics of adaptive antenna arrays when processing discrete signals with correlated readouts

The most important statistical characteristics of adaptive antenna arrays are determined. These are the mean value and covariance matrix of the vector of the weighting factors, and the powers of the fluctuations of the weighting factors and of the output signal of the array. It is found that under steady-state operating conditions the fluctuations of the vector of the weighting factors lead to a bias of its mean value for an adaptive antenna array without constraints, but the mean value of the weighting vector of an array with constraints and of an array operating using the criterion of the minimum root mean square error is not biased. It is shown that the effect of fluctuations of the weighting vector on the output signal of an adaptive antenna array may be different and is determined by the value of the correlation coefficient between the input-signal read-outs.Nizhegorod State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 12, pp. 1532–1545, December, 1994.     

Controlled supercontinuum generation for optimal pulse compression: a time-warp analysis of nonlinear propagation of ultra-broad-band pulses

We describe the virtues of the pump–probe approach for controlled supercontinuum generation in nonlinear media, using the example of pulse compression by cross-phase modulation in dielectrics. Optimization of a strong (pump) pulse and a weak (probe) pulse at the input into the medium opens the route to effective control of the supercontinuum phases at the output. We present an approximate semi-analytical approach which describes nonlinear transformation of the input pulse into the output pulse. It shows how the input and the output chirps are connected via a time-warp transformation which is almost independent of the shape of the probe pulse. We then show how this transformation can be used to optimize the supercontinuum generation to produce nearly single-cycle pulses tunable from mid-infrared to ultraviolet. PACS 42.65.Re; 42.65.Ky     

Antenna array in the sound field of an arctic waveguide

An antenna array placed in an arctic-type acoustic waveguide is considered. The guided sound field consists of a signal generated by a point source and an isotropic interfering noise produced by the ice cover. The array is operated in a specific regime: the output signals correspond to individual modes of the sound field. The signal received by the array is subjected to correlation processing with a finite averaging time. It is shown that, depending on the processing method, the signal-to-noise ratio can reach 40–60 dB for a realization duration of 1 min, and the quality of the signal detection is increased.     

Proposed solar energy conversion and storage system using a nano-ring in an array waveguide

We propose the new solar energy conversion and storage system using the array waveguide. It can be used to generate and store solar energy within the nano-array waveguide system. The system consists of micro- and nano-ring resonators incorporating a Mach Zhender Interferometer (MZI) that can be integrated into a single system. The large bandwidth signal, i.e. white light, is generated using a soliton pulse in a Kerr-type nonlinear medium propagating within a micro-ring resonator system. The control light concept is applied using a nano-waveguide incorporating an MZI, whereas the incoherent light is filtered being coherence, which is amplified and stored within the system. The white light can be re-generated using the stored coherent light pulse. Furthermore, the combination of signals is formed by the array waveguide, which is allowed to generate the huge amount of solar energy output.     

Ultra-wideband radio tomographic imaging with resolution near the diffraction limit

The experimental ultra-wideband radio tomographic imagings inside and behind dielectric barriers with resolution near the diffraction limit are described. The problem is solved by the method of radio wave tomosynthesis using the theory of spatial spectra of the received signals. The ultra-wideband pulse sensing of the air—building structure medium, developed in Tomsk State University, are described. It has been shown that for the case of sensing with ultra-wideband pulses of 0.2 ns duration, the resolution is about 2 cm. The paper also shows the possibility of accelerating scanning of the investigated space through the use of the MIMO (timed or switched) antenna array technology. As in the timed mode the distance between the receiving and transmitting antennas varies from time step to time step, the algorithm of processing the data obtained from the array is to be modified. The modification itself is a nonlinear stretching of the received UWB signal in time. The signal transformation allows preparation of data for the above algorithm to receive three-dimensional images of the tested space. The paper presents the results of the processed experimental data which confirm the efficiency of the proposed method for MIMO arrays. The resulting image resolution is about 2 cm.     

利用随机共振在强噪声下提取信息信号

已有利用随机共振在强噪声下提取单一频率信号的若干报道，但单一频率信号所携带的信息量为零.本实验研究表明：在调幅波和白噪声的协同作用下，非线性双稳系统的输出不仅可以呈现随机共振现象，而且经检波、滤波后能提取出调制信号(信息信号)；与直接经电子学系统检波、线性滤波后所提取的调制信号相比，前者所获调制信号的信噪比更高.给出了绝热近似条件下，调制信号信噪比的解析表达式. 关键词： 随机共振 信噪比 调制信号 噪声     

Enhancement of Information Transmission by Array Induced Stochastic Resonance in the Processes of Amplitude and Frequency Modulations

Information transmission is studied in the cases of amplitude and frequency modulations where there is an impulsive jamming in the signal. By using the array approach of nonlinear elements, we find that for both the periodic and aperiodic modulations, the information transmission can be enhanced by adding independent external noise on every element of the array. The dependence of information transmission on the size of array and the impulsive interval of the jamming are also studied.     

两级式光伏并网逆变器建模与非线性动力学行为研究

本文首先建立了两级式光伏并网逆变器严格的分段光滑状态方程, 分析级联情况下光伏阵列电压对光伏并网逆变器非线性动力学行为的影响, 然后探讨拓展两级式光伏并网逆变器输入电压范围的策略, 并研究前后级电路内部参数变化引起并网逆变器输出电流的快变尺度分岔和慢变尺度分岔现象. 研究发现: 若对光伏阵列电压进行分段控制, 可以有效展宽两级式光伏并网逆变器的输入电压范围; 适当增加前级输出电容值、电感量, 可以避免系统产生混沌运动, 而后级参数的取值需避开多个不连续的混沌区域. 研究结果对提高光伏发电系统的效率与稳定性有较重要的参考价值.