Amplitude-based height-reconstruction techniques for synthetic aperture ladar systems

We examine the performance of amplitude-based height-estimation techniques for use with airborne synthetic aperture ladar (SAL) sensors in generating three-dimensional reconstructions of ground targets. Such techniques lend themselves to implementation more readily than phase-based techniques and are also more tolerant to phase instabilities that might be associated with SAL systems. For pairwise amplitude-comparison monopulse processing, we present analyses of the expected height sensitivity and bias of SAL systems in terms of the system parameters. We verify this analysis with simulations, and we also provide an overview of other SAL phenomena that affect height-estimation accuracy. We then propose an array-based joint-processing approach that can be applied instead of pairwise monopulse processing. We show that the joint-processing approach represents the maximum-likelihood estimator for obtaining the target height, and we demonstrate that the proposed approach significantly reduces bias-induced errors.     

Resolution limits in imaging ladar systems

We introduce a new design concept of laser radar systems that combines both phase comparison and time-of-flight methods. We show from signal-to-noise ratio considerations that there is a fundamental limit to the overall resolution in three-dimensional imaging range laser radar (ladar). We introduce a new metric, volume of resolution, and we show from quantum noise considerations that there is a maximum resolution volume that can be achieved for a given set of system parameters. Consequently, there is a direct trade-offbetween range resolution and spatial resolution. Thus, in a ladar system, range resolution may be maximized at the expense of spatial image resolution and vice versa. We introduce resolution efficiency eta(r) as a new figure of merit for ladar that describes system resolution under the constraints of a specific design, compared with its optimal resolution performance derived from quantum noise considerations. We analyze how the resolution efficiency could be utilized to improve the resolution performance of a ladar system. Our analysis could be extended to all ladars, regardless of whether they are     

Structure design for precision temperaturemeasurement systems

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 6–8, June, 1990.     

Interpolation-based precoding with limited feedback for MIMO-OFDM systems

The channel state information (CSI) at the transmitter can significantly improve the performance of multiple-antenna systems. However, providing full knowledge of CSI at the transmitter may not be affordable in many practical cases. Thus, exploiting the partial channel knowledge to improve system performance seems to be attractive. An interpolation based limited feedback precoding scheme (ILFP) for MIMO-OFDM systems is proposed. In this scheme, both the transmitter and the receiver store the codebook of precoding matrices constructed offline using two-variable joint vector quantisation. Considering the correlation between OFDM subcarriers, they are divided into subcarrier clusters. At the receiver, precoding is carried out on the clusters, and then the precoding information is conveyed to the transmitter by limited bits of feedback. At the transmitter, the precoding matrices for each subcarrier are obtained by interpolation according to the feedback. Simulation results show that the proposed scheme outperforms the existing schemes.     

滤波器组多载波系统的高精度符号定时估计

针对滤波器组多载波(FBMC)系统的传统定时同步算法精度较低的问题,研究了其发送信号统计特性,从理论上量化分析了受数据符号重叠影响部分和非重叠部分的同步训练数据的特性,在此基础上提出了一种适用的高精度符号定时估计算法.该算法通过传输一串长度大于滤波器重叠因子的连续相同的训练符号,使得时域合成信号具有多重延迟冗余特性.仿...     

Production planning for flexible flow systems with limited machine flexibility

A flexible manufacturing system (FMS) is highly capital-intensive and FMS users are concerned with achieving high system utilization. The production planning function for setting up an FMS prior to production should be developed in order to make the most of the potential benefits of FMSs. We consider two production planning problems of grouping and loading a flexible flow system, which is an important subset of FMSs where the routing of parts is unidirectional. We show that considering this routing restriction as well as limited machine flexibility strongly affects both the solution techniques and the quality of the solutions. Because of the complexity of the problem, we present a heuristic approach that decomposes the original problem into three interrelated subproblems. We show that the proposed approach usually finds a near-optimum solution and is superior to an approach that exists in the literature of FMS production planning. We also introduce effective heuristic methods for two new subproblems that arise because of the unidirectional flow precedence and flexibility constraints. Computational results are reported and future research issues are discussed.     

Dielectric losses in materials with limited range of relaxation times

Features of the spectra of dielectric materials with the range of relaxation times limited from below have been studied. It is established that the dielectric losses (and conductivity) exhibit relaxation at an average frequency that is significantly (up to several orders of magnitude) greater than the permittivity relaxation frequency. These effects are characteristic of both homogeneous materials with non-Debye spectra and inhomogeneous materials of the statistical mixture type near the percolation threshold. A giant enhancement of the permittivity and conductivity in these statistical mixtures takes place at various concentrations of components corresponding to the dielectric-conductor and conductor-dielectric phase transitions.     

Improvement in metrological provision for processing technology of precision components in the nanometer range

Studies are carried out for contact and contactless methods of measurement and monitoring plane-parallel gauge blocks and precision components in the nanometer range in order to provide uniformity of linear parameter measurements. __________ Translated from Izmeritel’naya Tekhnika, No. 8, pp. 22–27, August, 2007.     

Reliability of dynamic systems under limited information

A method is developed for reliability analysis of dynamic systems under limited information. The available information includes one or more samples of the system output; any known information on features of the output can be used if available. The method is based on the theory of non-Gaussian translation processes and is shown to be particularly suitable for problems of practical interest. For illustration, we apply the proposed method to a series of relevant examples and compare with results given by traditional statistical estimators. It is demonstrated that the method delivers accurate results for the case of linear and nonlinear dynamic systems, and can be applied to analyze experimental data and/or mathematical model outputs.     

Effects of spatial modes on ladar vibration signature estimation

Ladar-based vibrometry has been shown to be a powerful technique in enabling the plant identification of machines. Rather than sensing the geometric shape of a target laser vibrometers sense motions of the target induced by moving parts within the system. Since the target need not be spatially resolved, vibration can be sensed reliably and provide positive identification at ranges beyond the imaging limits of the aperture. However, as the range of observation increases, the diffraction-limited beam size on the target increases as well, and may encompass multiple vibrational modes on the target's surface. As a result, vibration estimates formed from large laser footprints illuminating multiple modes on a vibrating target will experience a degradation. This degradation is manifest as a spatial low-pass filtering effect: high-order mode shapes, associated with high-frequency vibrations, will be averaged out while low-frequency vibrations will be affected less. A model to predict this phenomenology is proposed for both pulse-pair and cw vibrometry systems. The cw model is compared to results obtained using an off-the-shelf laser vibrometry system.     

The thermal field of an oil layer for phase transformations within a limited temperature range

The dependence of thermal fields on the parameters of petroleum bitumens and oil skimmer were analyzed on the basis of the modified Stefan problem solution as a kinematic wave, taking into account the melting zone is formed in a limited range of temperatures.     

有限反馈SDMA系统中信道矩阵的逐列量化算法

针对多天线广播信道(MIMO BC)块对角化(BD)预编码空分多址接入(SDMA)系统对角化预编码时,直接量化信道矩阵的有限反馈方法复杂度过高的问题,利用系统中用户配置多个天线的特点,提出了基于天线合并逐列量化(PCQ)信道矩阵的有限反馈方法.该方法对接收信号做多次天线合并,将传统算法中直接量化信道矩阵转变为多次量化等效信道矢量,仿真结果表明,在总的反馈比特数相同的情况下,该方法以较少的和容量损失换来了复杂度的大幅降低.