A new approach for evaluating clipping distortion in multicarriersystems

Multicarrier signals are known to suffer from a high peak-to-average power ratio, caused by the addition of a large number of independently modulated subcarriers in parallel at the transmitter. When subjected to a peak-limiting channel, such as a nonlinear power amplifier, these signals may undergo significant spectral distortion, leading to both in-band and out-of-band interference, and an associated degradation in system performance. This paper characterizes the distortion caused by the clipping of multicarrier signals in a peak-limiting (nonlinear) channel. Rather than modeling the effects of distortion as additive noise, as is widespread in the literature, we identify clipping as a rare event and focus on evaluating system performance based on the conditional probability of bit error given the occurrence of such an event. Our analysis is based on the asymptotic properties of the large excursions of a stationary Gaussian process, and offers important insights into both the true nature of clipping distortion, as well as the consequent design of schemes to alleviate this problem     

A general approach for the performance assessment of nanoscale silicon FETs

Various nonplanar, multigate field-effect transistors (FET) structures have been reported that offer better gate control than planar MOSFETs. In the nanometer regime, however, multigate (nanowire) structures also suffer strong quantum confinement, which causes deleterious effects such as large threshold voltage variation. In this paper, we propose a general approach to compare planar versus nonplanar FETs with the consideration of both electrostatic integrity (gate control) and quantum confinement (the so-called "EQ approach"). With this EQ approach, we show that the cylindrical wire FET and the planar double-gate MOSFET have approximately equal scaling capability for a [001]-oriented wafer, while the nonplanar wire structures are significantly better for other wafer orientations [e.g., (011)] where the effective mass in the confinement direction of the planar MOSFET is relatively small.     

A novel approach for evaluating the performance of SPC productcodes under erasure decoding

Product codes are powerful codes that can be used to correct errors or recover erasures. The simplest form of a product code is that where every row and every column is terminated by a single parity bit, referred to as single parity check (SPC) product code. This code has a minimum distance of four and is thus guaranteed to recover all single, double, and triple erasure patterns. Judging the code performance based on its minimum distance is very pessimistic because the code is actually capable of recovering many higher erasure patterns. This paper develops a novel approach for deriving an upper bound on the post-decoding erasure rate for the SPC product code with iterative decoding. Simulation shows that the derived bound is very tight     

A new formula for MDPSK symbol error probability

This article presents an extremely compact new formula for the symbol error probability in M-ary differential phase shift keying (MDPSK) that is extraordinarily similar to its counterpart for M-ary phase shift keying (MPSK). This result follows from a new form for a generic error probability associated with the phase angle between two vectors perturbed by Gaussian noise. The new form also leads to a new expression for the Marcum Q-function. As special cases, the generic error probability is noted to also contain MPSK, CPFSK, and digital FM. Finally, it is pointed out that the generic error probability simplifies the error probability expressions in other situations such as nonorthogonal signaling, maximum-likelihood differential detection of DPSK with block-by-block detection, and Gray coding of MDPSK     

A new approach to system reliability

Calculating system-reliability via the knowledge of structure function is not new. However, such attempts have had to compromise with the increasing complexity of a system. This paper overcomes this problem through a new representation of the structure function, and demonstrates that the well-known systems considered in the state-of-art follow this new representation. With this new representation, the important reliability calculations, such as Birnbaum reliability-importance, become simple. The Chaudhuri, et al. (1991) bounds which exploit the knowledge of structure function were implemented by our simple and easy-to-use algorithm for some s-coherent structures, viz, s-series, s-parallel, 2-out-of-3:G, bridge structure, and a fire-detector system. The Chaudhuri bounds are superior to the min-max and Barlow-Proschan bounds. This representation is useful in implementing the Chaudhuri bounds. With this representation of the structure function, the computation of important reliability measures such as the Birnbaum structural and reliability importance are easy. The use of Chaudhuri bounds is recommended for general use, especially when cost and/or time are critical. The C-H-A algorithm (in this paper) is simple and easy to use. It depends on the knowledge of the path sets of a given structure. Standard software packages are available to provide the minimal path sets of any s-coherent system. The C-H-A algorithm has been programmed in SAS, S-PLUS, and MATLAB     

A new general approach to optical waveguide path design

This paper introduces a new general approach to waveguide path design. We propose an alternative approach to the usual concatenation of offset line segments and arc of circles that is geometrically less constrictive and more versatile. We also propose an adapted pure bend loss reduction mechanism that relies on a continuous widening of the waveguide together with the reduction of transition loss through curvature adaptation. The numerical results presented here show that this method can improve the loss figures and ease the burden of waveguide path design. Moreover, because of its continuous nature, the proposed approach is intrinsically less dependent on wavelength than the usual concatenation technique     

A general approach to the evaluation and characterization of packet radio networks performance

In this work a general exact methodology for capture effect and performance evaluation of packet radio networks is presented. Both narrow-band and spread-spectrum systems are investigated and compared. Several network performance quality indexes are considered: throughput, outage probability, packet error probability, average delay time. Two particular capture effect models are investigated. It can be seen that one of the two models can be considered as a good approximation of the other if a appropriate parameter definition is made. By using this methodology various operating conditions given by fading (Rice, Rayleigh, Nakagami), shadowing, different traffic models, different modulation, and coding schemes are investigated. Comparison is performed by means of spectral efficiency parity.     

A parallel algorithm for evaluating general linear recurrence equations

A block parallel partitioning method for evaluating general linearmth order recurrence equations is presented and applied to solve the eigenvalues of symmetric tridiagonal matrices. The algorithm is based on partitioning, in a way that ensures load balance during computation. This method is applicable to both shared memory and distributed memory MIMD systems. The algorithm achieves a speedup ofO(p) on a parallel computer withp-fold parallelism, which is linear and is greater than the existing results, and the data communication between processors is less than that required for other methods. For solving symmetric tridiagonal eigenvalue problems, our method is faster than the best previous results. The results were tested and evaluated on an MIMD machine, and were within 79% to 96% of the predicted performance for the second order linear recurrence problem.Supported by the Texas Advanced Technology Program under Grant No. 999903-165 and the National Science Foundation under Grant No. MIP8809328.     

High-frequency FET noise performance: a new approach

A formulation is proposed for calculating the FET noise performance in the high-frequency range (EHF). In the first step, the concept of a local small-signal equivalent circuit is introduced, and a novel method for calculating the FET admittance parameters is proposed. In the second step, a novel formulation of the impedance field is given. It is shown that this approach reflects better the frequency evolution of the noise source values and consequently gives a better noise figure     

A performance lower bound for quadratic timing recovery accounting for the symbol transition density

The symbol transition density in a digitally modulated signal affects the performance of practical synchronization schemes designed for timing recovery. This paper focuses on the derivation of simple performance limits for the estimation of the time delay of a noisy linearly modulated signal in the presence of various degrees of symbol correlation produced by the various transition densities in the symbol streams. The paper develops high- and low-signal-to-noise ratio (SNR) approximations of the so-called (Gaussian) unconditional Crame/spl acute/r-Rao bound (UCRB), as well as general expressions that are applicable in all ranges of SNR. The derived bounds are valid only for the class of quadratic, non-data-aided (NDA) timing recovery schemes. To illustrate the validity of the derived bounds, they are compared with the actual performance achieved by some well-known quadratic NDA timing recovery schemes. The impact of the symbol transition density on the classical threshold effect present in NDA timing recovery schemes is also analyzed. Previous work on performance bounds for timing recovery from various authors is generalized and unified in this contribution.     

一种提高哼唱匹配效果的新算法

在基于改进离散余弦变换的哼唱检索系统中，采用音高轮廓表示旋律，取原始歌曲中的一段为哼唱片段，使用字符串匹配法，分别在采样率为8kHz和44．1kHz的情况下进行匹配，分析了分帧起始位置对匹配效果的影响，并就此问题提出新算法。实验结果表明了该算法的有效性。     

A new type of traveling-wave deflection system

The analysis of the meander-line type of traveling-wave deflection system shows that the deficiency in the dispersion characteristics is due to the interaction of the electromagnetic field on a section of a finger with that on other fingers. Insertion of a shielding plate between two neighboring sections of the fingers reduces mutual interactions. The meander line with the shielding plate is called the trough-type traveling-wave deflection system. The analysis shows that uniform characteristics of the dispersion and the admittance with respect to the frequency are expected in the trough-type traveling-wave deflection system. Loading by the dielectric material of the space among electrodes serves to decrease the phase velocity and to increase the deflection sensitivity. In the experimental CRT in which the trough-type traveling-wave deflection system is used, a uniform sensitivity is confirmed experimentally in the frequency range from dc to above 4 GHz and the deflection of 6 mm by 10-mW input is measured.     

Unified analysis of a class of blind feedforward symbol timing estimators employing second-order statistics

In this letter, all the previously proposed digital blind feedforward symbol timing estimators employing second-order statistics are casted into a unified framework. The finite sample mean-square error (MSE) expression for this class of estimators is established. Simulation results are also presented to corroborate the analytical results. It is found that the feedforward conditional maximum likelihood (CML) estimator and the square law nonlinearity (SLN) estimator with a properly designed prefilter perform the best and their performances coincide with the asymptotic conditional Cramer-Rao bound (CCRB), which is the performance lower bound for the class of estimators under consideration.     

A general framework for developing and evaluating band-limitedfunction extrapolation methods

It is shown that the bandlimited function extrapolation can be considered as an approximation problem in operator space. Within this framework, the Papoulis-Gerchberg method and two other methods for extrapolation are analyzed. Particular attention is given to approximation using Taylor and Chebyschev series, and to approximation using the Lagrange interpolation method     

一种基于训练序列的OFDM联合同步新算法

OFDM是一种多载波调制技术,为保证oFDM信号的正确传输,必须保持其子载波之间的完全同步,否则将造成子载波问干扰和符号问干扰,严重影响oFDM系统的性能。本文提出一种新的训练序列同步算法,通过仿真,对新算法和传统Schmidl＆cox时频联合同步算法进行了比较。结果表明,采用新算法具有较高的频偏估计精度和较大的估计范围,同时使符号定时非常精确。     

基于CPLD的新型场发射平板显示器的控制驱动系统

介绍一种新型场发射平板显示器件FAHED,利用CPLD作为核心,设计了器件的控制驱动系统,并采用计算机模拟的方法对系统的性能进行了检测,验证了设计的正确性和可行性.     

A pulse compression system employing a linear FM Gaussian signal

Some of the factors involved in the design of a radar pulse compression system are discussed. These include the compression ratio, the detailed characteristics of the signal, the sidelobe level of the receiver output waveform (signal autocorrelation function), the sensitivity of the sidelobe level to Doppler frequency shift in the signal, and the relative complexity of the equipment required to generate and receive the signal. A signal of Gaussian envelope and linear frequency modulation is shown to have an autocorrelation function of Gaussian shape. When the receiver is designed to autocorrelate the linear FM Gaussian signal, it is shown that the shape of the receiver output waveform does not change when the input signal has a Doppler frequency shift. The design and construction of equipment used to generate and receive the signal are discussed. In operating equipment with a compression ratio of about 50 to one, sidelobe levels 40 db below the peak amplitude of the receiver output waveform are achieved, and the shape of the receiver output wave-form does not change appreciably until the Doppler frequency shift exceeds 25 per cent of the 3-db signal bandwidth.     

基于新型前导符号的OFDM同步算法

在多径信道中,循环前缀最大似然估计盲OFDM同步算法的性能较差,循环前缀集相关同步算法增强了对抗多径的能力,获得了较好的同步性能,但同步时延非常大.为了缩短集相关同步算法的同步时延,设计了一种前导符号,基于此前导符号,提出了一种快速集相关运算同步算法.蒙特卡洛仿真结果表明,在多径信道下,该算法比循环前缀集相关同步算法具有更好的同步性能.进一步的分析还证明本文算法的同步时延也大大缩短.