Drift correction in periodic crosscorrelation schemes

In the evaluation of a periodic crosscorrelation for a time-invariant system, a simple-to-instrument method is described for eliminating error terms due to polynomial drift disturbances. The method is based on the periodic input perturbation signal being of inverse repeat form, and leads to the result that polynomial drift up to the rth degree may be eliminated by crosscorrelating over r + 2 half periods with appropriate constant weights associated with each half period.     

Fourier-series drift correction in periodic crosscorrelation schemes

It has recently been shown that polynomial-type output drift may be exactly compensated, up to the rth order, by crosscorrelating over r + 2 half periods of a periodic sequence of inverse-repeat form, where binomially distributed weights are associated with each half period. It is pointed out that the a.c. components of a Fourier-series expansion of output drift may be exactly compensated up to the qth harmonic by crosscorrelating over q + 1 periods of a periodic sequence (not necessarily of inverse-repeat form), where uniformly distributed weights are associated with each period. If the sequence is of inverse-repeat form, the d.c. component is also compensated.     

Aperiodic autocorrelation and crosscorrelation of polyphasesequences

A detailed analysis of the maximum aperiodic autocorrelation of the original Chu sequences (equivalently, P3/P4 pulse compression codes) is presented. The result implies the best known upper bound on the minimax aperiodic autocorrelation for polyphase sequences except when the length is very small or a perfect square. It is well known that determining the minimax aperiodic correlation for polyphase sequence sets is an intractable task. The simplest nontrivial cases for Barker and general polyphase sequences are solved for the first time     

Some new three-valued crosscorrelation functions for binarym-sequences

In 1972 Niho gave various conjectures about the crosscorrelation between a binary maximum-length linear shift register sequence and a decimation of that sequence by an integer d. We prove that the crosscorrelation function for two new values of d takes on precisely three values and thereby confirm two of Niho's conjectures     

Complex gain and fixed-point digital predistorters for CDMA power amplifiers

Two digital baseband predistortion techniques, one based on the complex gain digital predistorter (CGDP) approach and the other based on the fixed-point predistorter (FPPD) approach, are used to compensate a nonlinear high-power amplifier (HPA) in an IS-2000 system. Forward-link performance for a perfectly linear HPA, nonlinear HPA, and compensated HPA using both a CGDP and an FPPD are compared using an IS-2000 forward-link simulator. Both predistortion techniques are shown to provide similar forward-link performance and reduction in spectral regrowth of the sidebands for the wide-band compensated HPAs utilized by IS-2000 systems.     

Bandpass nonlinear systems identification by higher order crosscorrelation

Nonlinear systems constituted by a zero-memory nonlinearity cascaded with linear filters can be identified by input-output cross correlation using a Gaussian input signal. The method is extended to complex systems through a pair of complex invariance theorems. The stated properties allow identifying the linear parts of systems characterized by magnitude/phase nonlinearities with the joint use of second- and third-order input-output moments. The method can be employed for a wide class of communication bandpass circuits when signals are represented by complex envelopes     

Review and comparison of drift-correction schemes for periodic crosscorrelation

The presently available drift-correction schemes are unified and extended. As a means of comparing various schemes quantitatively, the variance of the estimate in the presence of wideband noise is proposed as a performance criterion.     

Influence of clipping during signal detection by crosscorrelation method

The crosscorrelation of a harmonic signal buried in severe noise with another of the same frequency decreases by a constant factor when clipping occurs. Calculation of this factor for a Gaussian noise shows that signal detection may be enhanced by a factor of 2.3 by overdriving the measuring channel.     

Binary m-sequences with three-valued crosscorrelation: a proof ofWelch's conjecture

We prove the long-standing conjecture of Welch stating that for odd n=2m+1, the power function x^d with d=2^m+3 is maximally nonlinear on GF(2ⁿ) or, in other terms, that the crosscorrelation function between a binary maximum-length linear shift register sequence of degree n and a decimation of that sequence by 2^m+3 takes on precisely the three values -1, -1±2^m+1     

Performance in waveform quantization

The quantization noise and dynamic range of commonly known analog/digital converters or modulators are computed from the equations derived by analyzing the generalized quantizer which deploys integer coefficient transversal filters. The results show that signal-to-noise ratio (S/N) curves for high sampling frequency do not have a constant slope of one. At a low signal level, the S/N curve has a slope of 1.5. From the results, equations to approximate S/N curves in the linear region are derived. They can be used to plot a S/N curve for any sampling frequency and any number of quantization steps     

Probability distribution of the crosscorrelation function of finite-duration single-bit random waveforms

The detection errors of a digital crosscorrelator, utilising severely clipped, bandlimited Gaussian waveforms are investigated, and the probability distribution of the correlator output due to finite-duration waveforms and distortion by wideband Gaussian noise is derived and compared with experimental results.     

The effect of quadrature modulator and demodulator errors onadaptive digital predistorters for amplifier linearization

With the increasing importance of spectral efficiency in mobile communications, the power amplifier linearity has become a critical design issue for nonconstant envelope modulation. Imperfections in quadrature modulators and demodulators-gain and phase imbalance and DC offset-have a crippling effect on amplifier linearization circuits, a fact that has previously been noted experimentally. This paper is the first analysis of these effects on an adaptive predistorter. The primary result is an expression that provides an explicit tradeoff among intermodulation power, accuracy of the quadrature modulator and demodulator, and speed of adaptation. Another useful result is a simple and easily measured error figure for quadrature modulators and demodulators     

二维网格编码矢量量化及其在静止图像量化中的应用

该文提出了在二维码书空间中，在矢量量化（VQ）的基础上，应用网格编码量化（TCQ）的思想来实现量化的新方法－－二维网格编码矢量量化（2D－TCVQ）。该方法首先把小码书扩展成大的虚码书，然后用网格编码矢量量化（TCVQ）的方法在扩大的二维码书空间中用维物比算法来寻找最佳量化路径。码书扩大造成第一子集最小失真减小从提高了量化性能。由于二维TCVQ采用的码书尺寸较小，因而可以应用到低存贮、低功耗的编解码环境。仿真结果表明，同一码书尺寸下，二维TCVQ比TCVQ好0．5dB左右。同时，该方法具有计算量适中，解码简单以及对误差扩散不敏感的优点。     

Determination of system frequency response direct from crosscorrelation functions of sinusoidal signals

At the present time, two forms of dynamic-analysis instrumentation are available, each based on the principle of crossorrelation, but with applications so far divided into the time domain and the frequency domain. The letter contains an illustration of how the time-domain instrument can be used to provide frequency-response information, and identifies the advantages of doing so.     

Families of polyphase sequences with near-optimal two-valued auto- and crosscorrelation functions

A construction method is proposed for new families of uniform polyphase sequences with near-optimal correlation. These families consist each of N sequences of length N and energy N with the following unique properties: (a) the sidelobes of the periodic autocorrelation functions have constant, nearly perfect magnitude 1; (b) the sequences are orthogonal; (c) all sidelobes of the periodic crosscorrelation functions have the constant magnitude square root (N+1); and (d) the correlation values asymptotically reach the Sarwate bound.<>     

Single trial evoked potential analysis by means of crosscorrelation and dynamic time-warping

A new approach to obtain evoked potential (EP) estimates is described. EPs are minute voltage fluctuations in the electrical activity of the brain in response to an external stimulus. EPs are often buried in the spontaneous brain activity and special techniques are required to improve the signal-to-noise ratio. The method presented here uses a dynamic time-warping (DTW) algorithm to maximize the crosscorrelation between a template and the recorded block. The algorithm was evaluated using simulated data consisting of triangular shapes superimposed on white noise and a rhythm resembling alpha activity (8–12 Hz).It was found that warping increased the crosscorrelation between the template and single trial, however, the template occasionally converged to the background noise especially for low signal-to-noise ratios. For SNRs larger than 2, the time-warping approach obtained better latency estimates than the conventional averaging method. Amplitude estimates were consistently inferior for DTW.     

Vector quantization in speech coding

Quantization, the process of approximating continuous-amplitude signals by digital (discrete-amplitude) signals, is an important aspect of data compression or coding, the field concerned with the reduction of the number of bits necessary to transmit or store analog data, subject to a distortion or fidelity criterion. The independent quantization of each signal value or parameter is termed scalar quantization, while the joint quantization of a block of parameters is termed block or vector quantization. This tutorial review presents the basic concepts employed in vector quantization and gives a realistic assessment of its benefits and costs when compared to scalar quantization. Vector quantization is presented as a process of redundancy removal that makes effective use of four interrelated properties of vector parameters: linear dependency (correlation), nonlinear dependency, shape of the probability density function (pdf), and vector dimensionality itself. In contrast, scalar quantization can utilize effectively only linear dependency and pdf shape. The basic concepts are illustrated by means of simple examples and the theoretical limits of vector quantizer performance are reviewed, based on results from rate-distortion theory. Practical issues relating to quantizer design, implementation, and performance in actual applications are explored. While many of the methods presented are quite general and can be used for the coding of arbitrary signals, this paper focuses primarily on the coding of speech signals and parameters.     

基于自适应量化矩阵的硬判决量化算法

在视频编码中,视频量化一般分为硬判决量化(HDQ)和软判决量化(SDQ),HDQ与SDQ相比,编码性能虽有所损失,但其编码复杂度低,易于硬件实现的优点依旧是主流编码器所主要采用的量化算法.人眼具有对图像中的高频细节不敏感的特性.因此,基于Bayes最小误判概率约束,离线构建基于视频内容自适应的量化矩阵,在模拟感知SDQ算法机理下,对高频低频分量采用不同的量化步长,提高视频的主观质量和HDQ算法性能.仿真实验表明,相比于传统的HDQ算法,该文算法能达到平均5.048％的码率节省,其中WVGA和WQVGA格式平均达到10.65％的码率节省.相比于感知SDQ算法,平均码率增加仅有1.464％;算法复杂度方面,编码一帧的时间相比于感知SDQ节省了32.956％.