Nonlinear companding transform for reducing peak-to-average power ratio of OFDM signals

A new nonlinear companding transform scheme is proposed to reduce the peak-to-average ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) signals. By exploiting statistical distribution of transmitted OFDM signals, the proposed scheme effectively reduces the PAPR by compressing the peak signals and expanding the small signals, while maintaining the average power unchanged by properly choosing transform parameters. The fact that the proposed companding scheme is described by a single-valued function allows to be transformed before amplification and to be restored the signals at the receiver. The proposed scheme can be applicable with any modulation format and subcarriers. Our simulations results confirm that the suggested scheme exhibits a good ability to reduce PAPR and a good BER performance with a solid state power amplifier (SSPA) in an additive white Gaussian noise (AWGN) channel.     

降低OFDM信号峰均功率比的分段线性压扩变换

为了降低OFDM信号的峰均功率比(PAPR),设计了一种分段线性压扩变换.对小幅度通过数乘变换进行线性放大,而对大幅度先利用数乘变换进行线性缩小,再对缩小后的幅度进行等量放大.得到的压扩变换是分段线性且连续的,用低复杂度的线性运算抑制峰均比,同时用分段的方法减小压扩对系统性能的影响.理论分析和仿真表明,通过数乘因子和增...     

一种远程系统对象的观察和控制方法研究与实现

针对传统的远程系统对象观察和控制方法,存在结构层次混乱、界面响应慢、视图观感差、难以扩展和维护等问题,提出一种新的远程系统对象的观察和控制方法。该方法基于Eclipse平台,使用RSE(Remote System Explore)框架进行总体设计,通过建立服务于RSE的数据存储层(Data Store Layer),实现远程系统对象的观察和控制。经过实际使用,该方法实现数据与视图的分离,结构层次清晰,易于扩展,界面响应速度快。     

适用于低频率生理信号片上谱分析的低功耗数字芯片设计

本文针对人体传感网络的应用定制设计了一款基于片上处理技术的低功耗的数字芯片。该数字芯片主要包括一个用于生物医学信号谱分析的可扩展FFT处理模块,一个授权的ARM7TDMI内核和其他外围IP模块。该FFT采用了一种新的混合结构,存储器优化,减少乘法器,高效率的地址产生技术来降低功耗。芯片经过流片,并实际测试后表明,性能方面能满足生物医学信号处理要求,功耗方面,在1.8v输入下,功耗仅0.69mW @ 1MHz,该芯片计算256点FFT的能量是基于ARM7嵌入式平台计算所耗功耗的0.9%,同时,与业界主流ASIC实现的FFT相比,也具有低功耗优势。     

集中监控遥控遥调常见故障分析

文章主要根据遥控遥调的基本原理,对于变电站遥控遥调的具体操作过程进行了分析,对于常见的故障进行了总结,并且提出了非常有针对性的解决办法.     

Statistics of companding noise for QAM transmission

In modern voiceband data communication, the received signal is subject to nonlinear quantization noise due to companding. Under certain conditions, this quantization noise may become dominant and cause serious degradation in performance. In order to design better signal constellations for this environment, it is of interest to characterize this noise. We study the conditional probability density function (PDF) for the quantization noise found on a PCM companding channel. We obtain an analytical expression for the conditional PDF of the nonlinear quantization noise and an algorithm to compute the conditional PDF of the filtered noise, which is the actual noise at the slicer input of the linear receiver. We compare the results to a Gaussian PDF (with second-order moments that depend on the signal point) and conclude that a Gaussian approximation, although not entirely accurate, is not unreasonable     

Classification of shadow signals created by moving objects

A possibility of classifying signals created by objects with different shape that move in the range of shadow bi-static radar (R) [1] is studied. The efficiency of the main components method [2–4] is demonstrated when forming databases that contain the most informative classifying indicators. A classification algorithm for shadow signals is developed based on fuzzy logic theory.     

Efficient low-frequency inversion of 3-D buried objects with large contrasts

An efficient inversion method is proposed using Cui et al.'s high-order extended Born approximations to reconstruct the conductivity object function of three-dimensional dielectric objects buried in a lossy Earth. High-order solutions of the object function are obtained, which have closed-form relations to the linear inverse-scattering solution. Because such relations can be evaluated quickly using the fast Fourier transform, the high-order solutions have similar simplicity as the linear inversion. When the contrasts of buried objects are large, the high-order solutions are much more accurate due to the approximate consideration of multiple-scattering effects within the objects. Hence, good-resolution images can be obtained for large-contrast objects using the new method by only solving a linear inverse problem. Numerical experiments have shown the validity and efficiency of the proposed method.     

Acquirement and enhancement of remote speech signals

To address the challenges of non-cooperative and remote acoustic detection, an all-fiber laser Doppler vibrometer (LDV) is established. The all-fiber LDV system can offer the advantages of smaller size, lightweight design and robust structure, hence it is a better fit for remote speech detection. In order to improve the performance and the efficiency of LDV for long-range hearing, the speech enhancement technology based on optimally modified log-spectral amplitude (OM-LSA) algorithm is used. The experimental results show that the comprehensible speech signals within the range of 150 m can be obtained by the proposed LDV. The signal-to-noise ratio (SNR) and mean opinion score (MOS) of the LDV speech signal can be increased by 100% and 27%, respectively, by using the speech enhancement technology. This all-fiber LDV, which combines the speech enhancement technology, can meet the practical demand in engineering.     

Simplified technique for syllabic companding in log-domain filters

It is shown that when syllabic companding is applied to log-domain filters using dynamic biasing, their large signal linearity can be exploited to eliminate the state variable compensation circuit. Owing to its simplicity, the proposed technique has several advantages over previous approaches     

DORT method as applied to ultrawideband signals for detection of buried objects

The decomposition of the time reversal operator (DORT) method, originally developed in acoustics, allows detection of scatterers embedded in the probed domain and provides some very robust means for focusing an incident wave onto a given scatterer. Hence, this method is very helpful for clutter reduction. Here, it is applied to the detection of buried cylindrical objects with the help of electromagnetic ultrawideband signals. It is shown that when the set of antennas is located on a piece of line above an interface, the use of the DORT method remains simple, whatever the polarization, provided the contribution from the target can be separated from that of the interface. Using wideband signals also permits one to excite natural resonances of the buried scatterer, which can easily be extracted from the eigenvalues of the time reversal operator. Numerical examples based on a finite-difference time-domain algorithm are given.     

Convergence analysis of finite alphabet beamformers for digital cochannel signals

In this paper, we examine the convergence behavior of finite alphabet (FA) beamformers. The two most popular implementations of FA beamformers for digital communication signals are the iterative least-squares with projection (ILSP) and the minimum mean-square error (MMSE) beamformer. To facilitate the analysis, for the binary communications case, we derive closed-form expressions for the mean weight vector, signal-to-noise ratio, and signal-to-interference ratio for both the ILSP and MMSE beamformers in terms of the bit-error rate (BER) performance at each iteration. Next, we generalize the analysis for the M-ary pulse-amplitude modulation and M-ary phase-shift keying cases. We show that both ILSP and MMSE beamformers have previously unreported bias terms in the array response vectors which are functions of the BER for each iteration. Furthermore, as the BER becomes arbitrarily small, we show that our solutions converge to the well-known asymptotic expressions widely published in the literature. Next, we provide a geometric interpretation of the effects of the noise bias vector in terms of angles between subspaces. Based on our analysis, we were able to develop necessary and sufficient conditions for convergence in the mean. We conclude with Monte-Carlo simulations to validate our analysis.     

Sampling signals with finite rate of innovation

The authors consider classes of signals that have a finite number of degrees of freedom per unit of time and call this number the rate of innovation. Examples of signals with a finite rate of innovation include streams of Diracs (e.g., the Poisson process), nonuniform splines, and piecewise polynomials. Even though these signals are not bandlimited, we show that they can be sampled uniformly at (or above) the rate of innovation using an appropriate kernel and then be perfectly reconstructed. Thus, we prove sampling theorems for classes of signals and kernels that generalize the classic "bandlimited and sinc kernel" case. In particular, we show how to sample and reconstruct periodic and finite-length streams of Diracs, nonuniform splines, and piecewise polynomials using sinc and Gaussian kernels. For infinite-length signals with finite local rate of innovation, we show local sampling and reconstruction based on spline kernels. The key in all constructions is to identify the innovative part of a signal (e.g., time instants and weights of Diracs) using an annihilating or locator filter: a device well known in spectral analysis and error-correction coding. This leads to standard computational procedures for solving the sampling problem, which we show through experimental results. Applications of these new sampling results can be found in signal processing, communications systems, and biological systems     

Coupling of finite element and moment methods for electromagneticscattering from inhomogeneous objects

A hybrid formulation which combines the method of moments (MM) with the finite element method (FEM) to solve electromagnetic scattering and/or absorption problems involving inhomogeneous media is discussed. The basic technique is to apply the equivalence principle and transform the original problem into interior and exterior problems, which are coupled on the exterior dielectric body surface through the continuities of the tangential electric field and magnetic field. The interior problem involving inhomogeneous medium is solved by the FEM, and the exterior problem is solved by the MM. The coupling of the interior and exterior problems on their common surface results in a matrix equation for the equivalent current sources for the interior and exterior problems. Combining advantages of both methods allows complicated inhomogeneous problems with arbitrary geometry to be treated in a straightforward manner. The validity and accuracy of the formulation are checked by two-dimensional numerical results, which are compared with the exact eigenfunction solution, the unimoment solution, and Richmond's pure moment solution     

Optimum design of finite duration nyquist signals

This paper presents a theoretical consideration of the optimal design of Nyquist type signals of M < ∞ baud time duration, which maximizes spectral energy inside a given bandqidth ω and which generates no intersymbol interference. The constraint for intersymbol interference is shown to be easily included into the problem. The optimum signal is a solution of a homogeneous linear equation with constraint. The computation is straightforward and involves the determination of eigenvectors of a symmetric matrix. Because of the fast converging nature of the prolate spheroidal wave functions used in the orthogonal expansion, the number of coefficients to determine the optimum signal is very small.     

High-resolution source coding for non-difference distortionmeasures: multidimensional companding

Entropy-coded vector quantization is studied using high-resolution multidimensional companding over a class of nondifference distortion measures. For distortion measures which are “locally quadratic” a rigorous derivation of the asymptotic distortion and entropy-coded rate of multidimensional companders is given along with conditions for the optimal choice of the compressor function. This optimum compressor, when it exists, depends on the distortion measure but not on the source distribution. The rate-distortion performance of the companding scheme is studied using an asymptotic expression for the rate-distortion function which parallels the Shannon lower bound for difference distortion measures. It is proved that the high-resolution performance of the scheme is arbitrarily close to the rate-distortion limit for large quantizer dimensions if the compressor function and the lattice quantizer used in the companding scheme are optimal, extending an analogous statement for entropy-coded lattice quantization and MSE distortion. The companding approach is applied to obtain a high-resolution quantizing scheme for noisy sources     

Realization of companding filters with large time-constants for biomedical applications

Configurations of companding filters with large time-constants are presented in this paper. For this purpose, novel Log-Domain and Sinh-Domain integrators are introduced, where the realization of time-constants is achieved through a capacitor multiplication. The same concept has been followed in the case of realization of the Log-Domain and Sinh-Domain equivalents of passive elements. The performance of the derived filters has been evaluated through simulation and comparison results using the Analog Design Environment of the Cadence software and MOS transistors parameters provided by the TSMC 180 nm CMOS process. As a design example, a fourth-order bandpass filter has been realized for extracting the alpha, beta, gamma, and theta waves of an electroencephalogram.     

Optimisation of a device for pick-up of low-frequency radio signals and transmission over polymer optical fibres

The development of passive (without RF amplifier) and optimised VHF-detector/optical-modulator circuit module as a device for operation in the 88–108 MHz band will be described in this paper. It uses illumination-type light-emitting diodes (LEDs) emitting at 650 nm as the light source, coupled with poly(methyl methacrylate) polymer optical fibre. Reactive impedance matching is performed between the optoelectronic light source and the antenna by taking into account the some capacitance variation with the frequency of the antenna and of the biased LED, not resolved with the packaging parasitic effects. The relatively simple device presented here and named wireless-over-polymer optical fibre may be useful in many low-frequency radio-over-fibre applications and may contribute to energy savings.     

Mobile agents for remote control of distributed systems

A modern distributed industrial system, such as a power transmission system, consists of many sites distributed throughout a wide area. Each site contains a number of monitoring and control devices, also known as intelligent electronic devices, which perform various tasks including condition monitoring, control, and protection. However, apart from dedicated links to the control center for control purposes, substations are often connected by networks with relatively low bandwidth, which makes remote access to these devices for control or monitoring relatively difficult. Therefore, we propose the use of mobile agents for remote access to devices. In this paper, the advantages and disadvantages of the use of mobile agents are evaluated by means of a theoretical model and a series of experiments. The results suggest that for networks with high latency mobile agents may provide performance improvements over more conventional client-server systems.     

抑制LOFDM系统PAPR非线性压扩变换算法

针对网格正交频分复用(LOFDM,lattice OFDM)系统具有较传统OFDM系统更高峰均功率比(PAPR,peak-to-average power ratio)的问题,在将传统非线性压扩变换应用于LOFDM系统的同时研究并分析了一种新的基于原信号统计分布特性的连续可导非线性压扩算法。该算法从原信号的渐进高斯分布特性出发并对原信号的幅度分布函数进行截断逼近,在保持平均功率不变的条件下,将压扩后的信号限制在与原信号分布特性一致的特定范围内,使压扩后的信号在保持其原有分布特性的同时,能更大程度改善系统PAPR和误比特(BER,biterror ratio)性能。理论分析和仿真实验表明,所提出的算法性能要显著优于传统非线性压扩算法。