Space-based radar signal processing baselines for air, land and seaapplications

Space-based radar can provide wide-area surveillance and theatre defence against targets in the air, on land, and at sea. This paper describes the airborne and ground-moving target indication problems, and examines environmental and system issues that impact space-based radar design. Radar design and signal processing techniques are presented that help target detection in the presence of clutter, jamming, and noise. Cost-performance trade-offs are used to derive radar signal processing baselines (configurations) that are proposed as candidate solutions     

A novel joint technique for PAPR reduction in CO-OFDM systems

For the high peak-to-average power ratio （PAPR） of coherent optical orthogonal frequency division multiplexing （CO-OFDM） system, a novel joint technique which is the combination of iterative partial transmit sequence （IPTS） and clipping technique is proposed. Simulation results demonstrate that the PAPR and bit error rate （BER） performance of the proposed technique both outperform those of the single techniques. Under the same conditions, the threshold value and peak power of IPTS clipping joint technique are optimized by 3.44 dB and 0.86 dBm compared with those of IPTS techinque, respectively. At the BER of 103, the optical signal to noise ratios （OSNRs） of the novel joint technique after 320 km and 400 km single-mode fiber （SMF） transmission are 0.68 dB and 1.18 dB smaller than those of clipping technique, respectively.     

一种经验模式分解下的海杂波小目标检测方法

利用海杂波有效探测海上小目标是目前雷达探测领域的热点问题,具有重要的应用价值。鉴于海杂波是一种非线性非平稳性的雷达回波信号,充分发挥整体平均经验模式分解的优势,将海杂波分解为若干个不同尺度的独立分量。通过研究发现有目标时,分解出的前5个分量与未分解前信号的相关系数明显减小,因此提出了一种新的海杂波背景下的目标检测方法。通过实测和模拟的海杂波数据进行训练和测试,研究结果表明,该方法能有效地实现海杂波下目标的探测,性能优于经典时域下、分数阶傅里叶变换域下以及平均经验模式分解后的广义Hurst指数的目标检测方法。     

Grid coding: A novel technique for image processing

The encoding of information as the modulation of a grid is explored as the means for allowing the extraction of relevant details or features from images. A major aspect of this approach is the replacement of the heuristics in certain image processing tasks by simple Fourier filtering. Specific examples and particular implementations of coding schemes are described in order to show the wide applicability of the concept. The examples chosen fall in the domains of scene analysis, difference extraction from successive images, automatic extraction of range, extraction of features such as planes, recording of three-dimentional imagery, and the processing of a single coded view to give a set of stereo related pairs.     

Optical processing technique for spot-size measurements in single-mode fibres

A new, simple and very promising technique for spot-size measurements in single-mode fibres is proposed, based on a spatial filter which modulates the optical beam at the output of the fibre. Its inherent simplicity, accuracy and high efficiency make it attractive for laboratory and factory measurements.     

A novel selected mapping technique for PAPR reduction in OFDM systems

Selected mapping (SLM) is a well-known method for reducing the peak-to-average power ratio (PAPR) in orthogonal frequency-division multiplexing (OFDM) systems. The main drawback of this technique is that, for each data block, it requires the transmission of several side information bits, which results in some data rate loss. These redundant bits are so critical to the error performance of the system that they need in practice to be protected by a powerful channel code. This increases the system complexity and transmission delay, and decreases the data rate even further. In this paper, we propose a novel SLM method for which no side information needs to be sent. By considering the example of an OFDM system using 16-QAM modulation, it is shown that the proposed method performs very well both in terms of PAPR reduction and bit error rate at the receiver output.     

A new signal processing technique for ISAR ranging: the Vernierranging method

A new technique for inversed synthetic aperture radar (ISAR) ranging, which resembles the principle of the Vernier measuring system, is presented. In this technique, the transmitted ISAR pulse comprises a train of chirp subpulses with uniformly stepped up center frequencies. The return ISAR echo is first processed, using hardware, to determine a coarse estimate of the target range. Further refinements of the range estimate are achieved through software processing, consisting of two stages of discrete Fourier transform operation. The ranging accuracy can be increased without the need for increased bandwidth, but at the expense of a slight increase in computational complexity. Numerical evaluation shows that a noiseless system is capable of achieving high-ranging accuracy, of the order of millimeters, even in the presence of dispersion and target motion. From computer simulations, the proposed system is also found to be robust against additive system noise and frequency jitter under practical conditions     

A new error reduction technique for reflection coefficient measurements for use in quick laboratory tests

ABSTRACT

Reflection coefficient measurement is one of those fundamental methods for determining the performance of radar absorber materials, and reflections due to these measurements are originated from the discontinuities in the measurement system and they result in error. In this paper, a new technique for the calibration of the scalar reflection coefficient measurements in the frequency range of 3–18 GHz in a portable two-sectioned metallic chamber is being proposed for use in quick laboratory tests with reasonable error (redacted error). Calibration measurements are performed by two calibration standards in frequency domain and transformed to time domain for further calculation. Proposed technique exhibits a good agreement with the theoretical values for especially in compact chambers where plane-wave conditions are not fully satisfied, and it is not in need of any complex time gating process. Furthermore, it does not require considering the phase differences which occurs at the measurement plane, providing a cheap and faster solution, reducing time and complexity in characterization of radar absorber materials. This technique with the mentioned test set-up could supply scalar reflection coefficient measurements with overall 0.55 dB error level and useful for practical applications where high level of accuracy is not required.     

Modified selected mapping technique for PAPR reduction of coded OFDM signal

High peak-to-average power ratio (PAPR) of the transmitted signal is a major drawback of orthogonal frequency division multiplexing (OFDM). In this paper, we propose a modified selective mapping (SLM) technique for PAPR reduction of coded OFDM signal. In this technique, we embed the phase sequence, which is used to lower the PAPR of the data block, in the check symbols of the coded OFDM data block. It is shown that we can achieve both PAPR reduction from the SLM technique as well as error performance improvement from the channel coding with no loss in data rate from the transmission of side information. In addition, approximate expression for the complementary cumulative distribution function (CCDF) of the PAPR of the modified SLM technique is derived and compared with the simulation results.     

A novel phase noise reduction technique in oscillators usingdefected ground structure

A new technique to reduce the phase noise in microwave oscillators is developed using the resonant characteristic of the defected ground structure (DGS). Two kinds of oscillators have been designed and measured for the examination of the reduction of phase noise by the DGS. The first adopts the DGS section under the microstrip line at the gate circuit, while the second has only the conventional microstrip line. Measurement shows reduced phase noise by 10-15 dB in the oscillator with the DGS compared to the conventional one     

A noise reduction technique of speech signal using ICA and spectral analysis

This paper discusses the new method on noise reduction exploiting the combined effects of wavelet decomposition, ICA and spectral analysis on noisy speech. The input noisy speech is wavelet decomposed into two signals. Wavelet entropy is computed based on the modified probability density function for the signal derived from the approximation coefficients during wavelet decomposition. By proper entropy comparison, the starting frame is detected. Between the two signals obtained from the wavelet decomposition, one is speech combined with noise and another one is noise alone. These two signals are analysed in independent component analysis (ICA) domain, in order to generate an enhanced speech. Zero-crossing rate is computed and used to discriminate between speech and noise. Then, spectral analysis is performed on the noise prior to starting frame and noisy speech. Elimination of noise frequencies in the noisy speech leads to noise reduced speech. Subjective analysis and experimental results show the considerable noise reduction capability of the proposed algorithm.     

Robust radar detection of CA, GO and SO CFAR in Pearson measurements based on a non linear compression procedure for clutter reduction

This paper deals with the constant false alarm rate (CFAR) radar detection of targets embedded in Pearson distributed clutter. We develop new CFAR detection algorithms-notably cell averaging (CA), greatest of selection (GO) and smallest of selection SO-CFAR operating in Pearson measurements based on a non-linear compression method for spiky clutter reduction. The technique is similar to that used in non uniform quantization where a different law is used. It consists of compressing the output square law detector noisy signal with respect to a non-linear law in order to reduce the effect of impulsive noise level. Thus, it can be used as a pre-processing step to improve the performance of automatic target detection especially in lower generalised signal-to-noise ratio (GSNR). The performance characteristics of the proposed CFAR detectors are presented for different values of the compression parameter. We demonstrate, via simulation results, that the pre-processed compression procedure is computationally efficient and can significantly enhance detection performance.     

A conceptual framework for consistency, conditioning, and stabilityissues in signal processing

The techniques employed for analyzing algorithms in numerical linear algebra have evolved significantly since the 1940s. Significant in this evolution is the partitioning of the terminology into categories in which analyses involving infinite precision effects are distinguished from analyses involving finite precision effects. Although the structure of algorithms in signal processing prevents the direct application of typical analysis techniques employed in numerical linear algebra, much can be gained in signal processing from an assimilation of the terminology found there. This paper addresses the need for a conceptual framework for discussing the computed solution from an algorithm by focusing on the distinction between a perturbation analysis of a problem or a method of solution and the stability analysis of an algorithm. A consistent approach to defining these concepts facilitates the task of assessing the numerical quality of a computed solution. This paper discusses numerical analysis techniques for signal processing algorithms and suggests terminology that is supportive of a centralized framework for distinguishing between errors propagated by the nature of the problem and errors propagated through the use of finite-precision arithmetic. By this, we mean that the numerical stability analysis of a signal processing algorithm can be simplified and the meaning of such an analysis made unequivocal     

A complete electromagnetic simulation of the separated-aperturesensor for detecting buried land mines

The detection of buried land mines is a problem of military and humanitarian importance. Electromagnetic (EM) sensors (ground-penetrating radars) use signals at radio and microwave frequencies for this purpose. In the past, EM sensors for land-mine detection have been empirically developed and optimized. This has involved experimental tests that are complicated, time consuming, and expensive. An alternative is to carry out initial development and optimization using accurate numerical simulations. One objective of this paper is to show, for the first time, that such simulations can be done using the finite-difference time-domain (FDTD) method. The separated-aperture sensor has been under investigation by the United States Army for land-mine detection for many years. It consists of two parallel dipole antennas housed in corner reflectors that are separated by a metallic septum. It is a continuous-wave sensor tuned to a particular frequency (typically 790 MHz). When the sensor is over empty ground, the coupling between the antennas is very small. As the sensor is moved over a buried mine, the coupling between the antennas increases indicating the presence of the mine. In this paper, the complete EM system composed of the separated-aperture sensor, air and soil, and buried land mine is modeled using the FDTD method. The finite computational volume is truncated with an absorbing boundary condition: the generalized perfectly matched layer. Detailed studies made with the simulation increase the understanding of this sensor. Results computed from the simulation are in good agreement with experimental measurements     

A technique for a substantial reduction of the quantization noise in the direct processing of delta-modulated signals

The quantization noise introduced by the direct arithmetic operations on delta modulated signals can be considerably reduced by a proposed technique. According to this technique, the arithmetic network of a digital filter is clocked at a rate higher than that of the delta modulation encoder. Thus, as it is proved, a considerable reduction of the maximum quantization error can be achieved. A simple network is properly used to restore the filter output rate to that of the delta modulation encoder. The experimental results prove that the output sequence quantization noise can be reduced so much that the remaining noise is very close to that of the input delta modulated signal of the filter.     

A system representation for control, digital signal processing, and estimation

In a recent review article, Willsky describes certain limitations of state-space models for relating digital signal processing research to control research. Here generalized system representations of current interest in algebraic control and estimation research are outlined. These representations also have potential as models of signal processing algorithms.     

用于光学相位检测的数字信号处理系统

介绍了一种利用数字信号处理技术和虚拟仪器技术实现对微弱光学相位信号进行高精度频率、幅度测量的方法。该方法实现了反馈式数据采样率的设定、自适应数字带通带阻滤波器和全数字相敏检波等功能,并且可以对信号相位和强度以及谐波进行精确测量     

A figure of merit for signal processing reflector antennas

In recent years a new class of reflector antennas utilizing array feeds has been receiving attention. An example of this type of antenna is a reflector utilizing a moveable array feed for beam steering. Due to the circuitry required to adjust the weights for the various feed array elements, an appreciable amount of loss can be introduced into the antenna system. One technique to overcome this possible deficiency is to place low noise amplifiers with sufficient gain to overcome the weighting function losses just after each of the feed elements. In the evaluation of signal processing antennas that employ amplifiers the standard antenna gain measurement will not be indicative of the antenna system's performance. In fact, by making only a signal measurement, the antenna gain can be made any arbitrary value by changing the gains of the amplifiers used. In addition, the IEEE Standard Test Procedures for Antennas does not cover the class of antennas where the amplifier becomes part of the antenna system. There exists a need to establish a standard of merit or worth for multi-element antenna systems that involve the use of amplifiers. A proposed figure of merit for evaluating such antenna systems is presented.     

A compensation technique for positioning errors in planarnear-field measurements

Probe positioning errors are among the major sources of inaccuracy in the planar near-field-far-field transformation technique, as their presence destroys the Fourier-transform relationship between the tangential components of the near field and those of the plane-wave spectrum of the test antenna. An optical systematic correction technique is developed which requires only the knowledge of the true probe positions. The `corrected' values are computed by an iterative procedure which turns out to be rapidly convergent and fairly accurate even in the presence of rather high displacement errors. It is concluded that the developed correction technique either includes or compares favorably with alternative methods. It is an optimal generalization of the Z -correction method, being exact in principle and allowing simple control of the attainable precision     

An algebraic technique for designing active filters in the frequency domain for control and signal processing

This paper presents a straightforward algebraic method for designing feedback loops in the frequency domain. The emphasis here is on control system design, but the technique is applicable to active filter design as well. The object is to produce a practical analog filter with a minimum of design effort. The algebraic solution to the design problem is presented, and several examples are explored.