Invertibility of 2-D linear systems

The concept ofL-delay invertibility is extended for generalized 2-D linear systems. A method based on the left inverse of the transfer function matrix of the model and the realization theory for finding a whole class of generalized or regular inverse systems is presented. Necessary and sufficient conditions for the (d ₁,d ₂)-delay invertibility of the regular 2-D linear systems are established.     

Stability analysis of linear 2-D systems

The present paper is concerned with stability analysis of linear two-dimensional systems described by Fornasini–Marchesini state-space model. Necessary and sufficient conditions for asymptotic stability of the systems are obtained first. Several simple stability criteria are derived via the nonnegative matrix theory, which are sharper than those in literature. When all the parameter matrices are nonnegative, the criteria are necessary and sufficient for stability of the system. Illustrative examples are provided.     

2-D direction finding of coherent signals VIA Temporo-Spatial processing

In most wireless communication systems, two-dimensional Directions-Of-Arrival (DOA) of multipath signals need to be found for spatial selective transmission. However, it is quite difficult to find their DOAs due to the coherent nature of multipath signals and considerable computations when performing 2-D searches. In this paper, a new algorithm to estimate 2-D DOA of multiple narrow-band signals is proposed. A DOA cyclic matrix is constructed whose eigenvalues and eigenvectors can be simultaneously used to extract 2-D DOA without 2-D searches. By exploiting the temporal property of cyclostationarity, the signal detection capability is significantly improved. Besides, based on the decorrelation model for mobile terminal signals, the algorithm can be effectively extended to the coherent case without spatial smoothing and the loss of array aperture. Simulation results are given to illustrate the performance of the new algorithm.     

稳定分布噪声下基于粒子滤波的多径时变信道盲均衡算法

提出了一种基于粒子滤波的多径时变信道盲均衡算法,并在此基础上进行扩展,提出了一种基于延迟抽样的盲均衡算法。新算法的贡献可总结为：推导出对称α稳定分布（SαS）噪声下对传输码元进行最大后验估计的盲贯序算法;对SαS分布噪声进行高斯近似并递推出信道及噪声未知参数的联合后验分布。仿真结果表明,所提出的算法是有效的,特别是在较强脉冲噪声情况下要优于其他算法。     

Localized function method for modeling defect modes in 2-D photoniccrystals

We present a novel, general, and numerically efficient treatment of electromagnetic modes localized at defects in two-dimensional (2-D) photonic crystals. The method represents the fields in terms of orthogonal functions localized at the defect and is a fully vector treatment     

Calculation of coherent attenuation at millimetre-wave frequencies

A formula is presented which enables the coherent attenuation due to rain to be calculated at any millimetre-wave frequency for any drop-size distribution. A method of scaling amplitudes for spherical drops to obtain amplitudes for horizontal polarisation incident on spheroidal drops is also presented.     

High-resolution radar imaging using 2-D linear prediction

An algorithm for radar imaging is described. The algorithm is based on two-dimensional (2-D) linear prediction of 2-D Cartesian frequency spectra. It is shown that the algorithm provides much better resolution than the ISAR image obtained using a 2-D inverse Fourier transform. The algorithm is especially useful for imaging targets using small-bandwidth RCS data over limited aspect angle regions     

Partial realization of 2-D discrete linear system and 2-D Padeapproximation and reduction of 2-D rational transfer function

A method is presented for determining the unknown degree and system function of any 2-D discrete linear shift-invariant system characterized by a 2-D impulse response array, i.e., the coefficients of the formal double power series that are obtained by expanding a rational transfer function. Problems of 2-D Pade approximation and 2-D system reduction can be solved by the same method by making a reasonable assumption in the context of 2-D linear systems theory. The method is based on a 2-D extension of the Berlekamp-Massey algorithm for synthesis of linear feedback shift registers. It gives a novel approach to identification and approximation of 2-D linear systems and is comparable in efficiency with other methods for 2-D rational approximation based on the block Toeplitz and block Hankel matrices     

六角形阵列相干信号二维DOA估计

提出了一种基于扩展重构相关矩阵去相干的二维DOA估计算法。针对六角形阵列的结构特点,首先对各个阵元的接收数据求其共轭矩阵来扩展阵列,扩展后的阵列分为3个六角形子阵列,以此为基础,求得各子阵列的自相关矩阵及互相关矩阵来扩展重构相关矩阵,从而实现解相干的目的,最后利用二维MUSIC算法进行DOA估计。该算法在不减少阵列有效孔径的前提下,增加了可估计相干源数目,并且能够得到较好的估计性能。最后,通过计算机仿真证实了该算法的有效性。      

3-D SPECT simulations of a complex 3-D mathematical brain model: effects of 3-D geometric detector response, attenuation, scatter, and statistical noise

The quantitative imaging characteristics of ultrahigh-resolution parallel-hole SPECT, including 3-D geometric detector response, attenuation, scatter, and statistical noise, were investigated by simulations based on a complex digitized 3-D brain model of the gray and white matter distributions. The projection data resulting from a uniform distribution of gray and white matter radioactivity, in a ratio of 5:1, were simulated. The results demonstrate significant qualitative and quantitative artifacts in reconstructed human brain images. In the absence of attenuation, scatter, and noise, artifactual variation caused inaccuracies in regional radioactivity quantification. Inclusion of attenuation scatter, and noise in the simulation caused additional artifacts, and resulted in reconstructed images which qualitatively and quantitatively corresponded very closely to reconstructed images of the actual 3-D brain phantom which was constructed from the same set of data as the mathematical 3-D brain model. It is concluded that the major degrading factor in SPECT neuroimaging is the 3-D geometric detector response function.     

Intensity noise in ASK coherent lightwave receivers

The effect of local oscillator intensity noise on the performance of two and three-branch ASK homodyne receivers and single-branch ASK heterodyne receivers is investigated and an optimum local oscillator power is found. At optimum local oscillator power, both the three-branch and heterodyne receivers are found to have a somewhat better sensitivity than the two-branch receiver. If the local oscillator power is high than the optimum value, the three-branch receiver is significantly less sensitive to intensity noise than the other two receivers     

Thermal phase noise in coherent optical-fibre systems

Coherent optical-fibre systems are sensitive to optical phase changes along the length of the fibre link. Thermal energy in the optical fibre can give rise to acoustic waves propagating along it and these result in optical phase changes. Thus, there is the possibility of a noise signal induced by thermal acoustic energy propagating along the fibre. This letter postulates a theoretical model for this interaction and estimates the magnitude of the effect. Conditions under which it may be a significant noise source are discussed.     

预测混合交叉有效平滑法去噪声

本文研究了左预测和右预测及交叉有效（ＣＶ）平滑法，并证明了ＣＶ平滑中的两个限制条件。提出了预测混合ＣＶ平滑法去噪，能同时达到以上目的。分析了该方法的统计特性。并通过模拟试验了该方法，并与有限混合中值滤波（ＦＭＨ）法和自适应小波收缩法（ＷＳＡ）作了比较，试验结果说明了该方法是切实可行的，并优于ＦＭＨ和ＷＳＡ。     

Image detail-preserving filter for impulsive noise attenuation

A new nonlinear filter is proposed for attenuating impulsive noise while preserving image details. The filter truncates the grey value of a pixel to the maximal or minimal value of its enclosed surrounding band. Impulsive noise inside the band is thus attenuated while image details are preserved as long as they stretch to the band. The recursive form of the proposed filter leads to a simple architecture for fast implementation. Theoretical analysis and experimental results demonstrate the effectiveness of this new filter for both noise attenuation and detail preservation. For moderately contaminated images, as shown in the experiments, the proposed filter outperforms the standard median filter, the centre-weighted median filter and the unidirectional multistage median filter in terms of mean absolute error and filtering speed.     

2-D FDTD method for exact attenuation constant extraction of lossy transmission lines

The two-dimensional finite-difference time-domain (2-D FDTD) method is undeniably efficient for full-wave analysis of uniform transmission lines. However, conventional 2-D FDTD method ignores the spatial attenuation along the propagation direction and yields approximate results. We propose a new 2-D FDTD method for extracting exact attenuation constants of lossy transmission lines. In the proposed method, we take the variation of field components with the propagation direction into consideration and describe an iterative process for finding exact attenuation constants. Numerical experiments show that, compared with the conventional 2-D FDTD method, results given by the iterative process agree much better with analytical solutions or measured data.     

Analytical modeling methodology for ultrawideband low noise amplifiers with generalized filter-based impedance matching

In this paper, we present a modeling methodology for fully integrated inductively degenerated cascode ultrawideband low noise amplifiers (LNA) with generalized filter-based impedance matching networks. Our accurate analytical models capture the impact of device and passive component parasitics and transistor short channel effects to generate accurate designs. Utilizing our methodology, we are able to accurately generate an ultrawideband LNA in the 3.1–10.6 GHz frequency band using third and fifth order Chebyshev filters as input impedance matching networks. The speed and accuracy of the proposed analytical model will facilitate rapid design space exploration for ultrawideband LNAs.     

Determination of the noise parameters of a linear 2-port

A new algorithm is given for the calculation of the four noise parameters of a linear 2-port from experimental measurements of its noise figure as a function of source admittance. A computer program for performing this calculation is briefly described (more detailed documentation is available).     

A combined multi-channel Wiener filter-based noise reduction and dynamic range compression in hearing aids

Noise reduction (NR) and dynamic range compression (DRC) are basic components in hearing aids, but generally these components are developed and evaluated independently of each other. Hearing aids typically use a serial concatenation of NR and DRC. However, the DRC in such a concatenation negatively affects the performance of the NR stage: the residual noise after NR receives more amplification compared to the speech, resulting in a signal-to-noise-ratio (SNR) degradation. The integration of NR and DRC has not received a lot of attention so far. In this paper, a multi-channel Wiener filter (MWF)-based approach is presented for speech and noise scenarios, where an MWF-based NR algorithm is combined with DRC. The proposed solution is based on modifying the MWF and the DRC to incorporate the conditional speech presence probability in order to avoid residual noise amplification. The goal is then to analyse any undesired interaction effects by means of objective measures. Experimental results indeed confirm that a serial concatenation of NR and DRC degrades the SNR improvement provided by the NR, whereas the combined approach proposed here shows less degradation of the SNR improvement at a low increase in distortion compared to a serial concatenation.     

Generalized linear processors for coherent optical computers

Generalized optical processors are examined from the point-of-view of developing a systematic method for determining which linear processing operations may be performed in a coherent optical system. In this paper a procedure is presented for examining a general n-plane processor and expressing the resulting system in terms of a conventional linear processing model. The generalized kernel of the resulting integral equation is used to describe currently well understood coherent linear processors as simple examples of a more general n-plane processor. A 2-plane processor is shown to correspond to the Fourier transform operation with a simple lens, and the 3-plane processor is associated with convolution or correlation. The kernel of a 4-plane system is shown to resemble the ambiguity function, and to represent an oblique to rectangular plane inverter, when an appropriate assumption is made about the complex amplitude-transmittance function of one optical plane. The more general n-plane kernels have integral representations for which simple physical realizations remain to be developed.