The source coding theorem via Sanov's theorem (Corresp.)

A proof of Shannon's source coding theorem is given using results from large deviation theory. In particular Sanov's theorem on convergence rates for empirical distributions is invoked to obtain the key large deviation result. This result is used directly to prove the source coding theorem for discrete memoryless sources. It is then shown how this theorem can be extended to ergodic Polish space valued sources and continuous distortion measures.     

Block source coding theory for asymptotically mean stationary sources

Several properties of operational and information theoretic distortion rate functions and of mutual information rate are developed for asymptotically mean stationary (ams) processes with standard alphabets and used to prove a block source coding theorem for ergodic ams sources. In the development we prove an ergodic decomposition of the mutual information rate of ams sources, we show that the operational distortion rate function of an ams source equals that of its stationary mean, and we provide a new and direct proof of the equality of the ergodic and stationary process distortion rate functions. The latter result yields a proof of the block source coding theorem not requiring the Nedoma decomposition and complicated code construction used by Gallager and Berger.     

Corrections to "Low PMEPR Code Based on Star-16-QAM Constellations for OFDM"

Although the result of Part II of Theorem 1 in Z. Q. Taha and X. Liu (2007) is correct, the proof is incorrect. A corrected proof is given in this letter.     

星载光机扫描仪像移模型及补偿方法

针对地球自转运动形成的星载光机扫描式成像仪的图像畸变问题,详细描述了畸变量与地球纬度及仪器工作参数之间的关系,给出了太阳同步轨道扫描成像仪的畸变量计算公式。针对传统地面畸变校正算法的不足,提出了基于光学补偿扫描和星上软件补偿采样的两种像移补偿方法。详细分析两种方法的特点与可行性,并给出仿真结果。该研究工作对于提高星载光机扫描式成像系统的图像质量具有参考意义。     

Convergence of the Multidimensional Minimum Variance Spectral Estimator for Continuous and Mixed Spectra

A proof of the pointwise convergence of the multidimensional minimum variance spectral estimator as the region of data support becomes infinite is given. It is shown that an octant is sufficient to ensure that the minimum variance spectral estimator will converge to the true power spectral density. The proof is valid for 1-D, multidimensional, continuous, and mixed spectra. Another useful result is that a normalized minimum variance spectral estimator can be defined to indicate sinusoidal power for processes with a mixed spectrum. Finally, upper and lower bounds on the continuous portion of the spectral estimate are given.     

A Note on “Global Robust Stability Criteria for Interval Delayed Neural Networks Via an LMI Approach”

A recently reported result concerning the global exponential robust stability of delayed neural networks is revisited. It is shown by a counter example that the result is invalid because the proof is incorrect, and then a modified version is given. The paper also presents an improved sufficient condition for global exponential robust stability of the neural networks with unbounded activation functions and time-varying delays. Finally, a numerical simulation is given to show the effectiveness of the obtained result.      

Electron optical properties of a postdeflection acceleration lens in cathode-ray tubes for oscilloscopes of high-bandwidth capability

A postdeflection acceleration lens (PDAL) for use in high-sensitive fast-writing CRTs is described. The lens achieves a vertical scan magnification of about 2.8 and a horizontal of about 2.2. After a discussion of the principle of operation a detailed investigation of defection linearity and distortion is given. A computer was used to calculate deflection linearity and distortion whereas experimental CRTs were evaluated to establish tube parameters which result in a vertical deflection sensitivity of 3 V/cm and a writing speed of 3 cm/ns.     

Intermodulation and harmonic distortion in InGaAsP lasers

A theoretical and experimental study is presented of intermodulation and harmonic distortion in high-speed 1.3 and 1.5 ?m InGaAsP lasers modulated at frequencies up to 8 GHz. It is found that all lasers measured, including Fabry-Perot and distributed feedback lasers, generate approximately the same distortion levels for a given modulation depth and relaxation resonance frequency. There are minor differences between lasers, which result from differences in the damping of the small-signal resonance peak.     

An upper bound for codes in a two-access binary erasure channel (Corresp.)

A method for determining an upper bound for the size of a code for a two-access binary erasure channel is presented. For uniquely decodable codes, this bound gives a combinatorial proof of a result by Liao. Examples of the bound are given for codes with minimum distance 4.     

Transistor input distortion and emitter degeneration

In the design of class A transistor amplifiers it is desirable to be able to predict and control the amount of distortion produced by the nonlinearity of the transistor input characteristic. This note presents an extension of a previously published method, to include the effects of emitter degeneration. The result provides a convenient means of determining the degenerations required to reduce the second-harmonic distortion to a given level.     

Simple universal lossy data compression schemes derived from theLempel-Ziv algorithm

Two universal lossy data compression schemes, one with fixed rate and the other with fixed distortion, are presented, based on the well-known Lempel-Ziv algorithm. In the case of fixed rate R, the universal lossy data compression scheme works as follows: first pick a codebook B_n consisting of all reproduction sequences of length n whose Lempel-Ziv codeword length is ⩽nR, and then use B_n to encode the entire source sequence n-block by n-block. This fixed-rate data compression scheme is universal in the sense that for any stationary, ergodic source or for any individual sequence, the sample distortion performance as n→∞ is given almost surely by the distortion rate function. A similar result is shown in the context of fixed distortion lossy source coding     

Tree coding of image subbands

The authors consider the encoding of image subbands with a tree code that is asymptotically optimal for Gaussian sources and the mean squared error (MSE) distortion measure. They first prove that optimal encoding of ideally filtered subbands of a Gaussian image source achieves the rate distortion bound for the MSE distortion measure. The optimal rate and distortion allocation among the subbands is a by-product of this proof. A bound is derived which shows that subband coding is closer than full-band coding to the rate distortion bound for a finite length sequence. The tree codes are then applied to encode the image subbands, both nonadaptively and adaptively. Since the tree codes are stochastic and the search of the code tree is selective, a relatively few reproduction symbols may have an associated squared error a hundred times larger than the target for the subband. Correcting these symbols through a postcoding procedure improves the signal-to-noise ratio and visual quality significantly, with a marginal increase in total rate.     

Minimax partial distortion competitive learning for optimalcodebook design

The design of the optimal codebook for a given codebook size and input source is a challenging puzzle that remains to be solved. The key problem in optimal codebook design is how to construct a set of codevectors efficiently to minimize the average distortion. A minimax criterion of minimizing the maximum partial distortion is introduced in this paper. Based on the partial distortion theorem, it is shown that minimizing the maximum partial distortion and minimizing the average distortion will asymptotically have the same optimal solution corresponding to equal and minimal partial distortion. Motivated by the result, we incorporate the alternative minimax criterion into the on-line learning mechanism, and develop a new algorithm called minimax partial distortion competitive learning (MMPDCL) for optimal codebook design. A computation acceleration scheme for the MMPDCL algorithm is implemented using the partial distance search technique, thus significantly increasing its computational efficiency. Extensive experiments have demonstrated that compared with some well-known codebook design algorithms, the MMPDCL algorithm consistently produces the best codebooks with the smallest average distortions. As the codebook size increases, the performance gain becomes more significant using the MMPDCL algorithm. The robustness and computational efficiency of this new algorithm further highlight its advantages.     

Convergence of polynomial least squares end-point and mid-point estimators

In a recent corcespondence, Leskiw and Miller [1] obtained the variance of a least squares polynomial estimator, as function of the polynomial order, for a large number of equally spaced data points, when the estimate is for the end-point. A simpler proof is given, and the result is extended to the mid-point. A mid-point estimator may be of special interest since it exhibits the lowest variance.     

Addendum to: Computing Failure Frequency via Mixed Products of Availabilities and Unavailabilities

In a recent paper I forgot to consider situations in which the (fault tree) structure function, when transformed to a multilinear polynomial (of usual algebra), or in which system unavailability, given as a polynomial of component availabilities and/or unavailabilities, contains a constant term. It is shown that constant terms need not be considered since they do not influence failure frequency. A new proof is given for the main result of my above paper.     

Kron's link-at-a-time formula

A short proof of Kron's link-at-a-time formula is given and the applicability and computational effectiveness of the formula are noted. The formula leads to 1st-order sensitivity result that are comparable in efficiency to the adjoint-network methods.     

A note on perfect predictability and analytic processes (Corresp.)

It is well known that perfect reconstruction of an analytic random process can be accomplished given any finite length continuous sample. A proof is given here that sampling infinitely often over any finite interval also leads to perfect reconstruction. Applications of the result to problems in detection theory, particularly concerning optimum array processing, are discussed.     

On a lower bound for the redundancy of reliable networks with noisy gates

A proof is provided that a logarithmic redundancy factor is necessary for the reliable computation of the parity function by means of a network with noisy gates. This result was first stated by R.L. Dobrushin and S.I. Ortyukov (1977). However, the authors believe that the analysis given by Dobrushin and Ortyukov is not entirely correct. The authors establish the result by following the same steps and by replacing the questionable part of their analysis with entirely new arguments.<>     

基于激光钠导星的星载自适应光学系统

用于对地观测的星载光学系统受空间环境及相机内环境的影响而存在波前畸变问题,从而导致成像质量变差。为获得分辨率达到近衍射极限水平的图像,需要利用自适应光学技术对波前畸变进行自适应光学校正。提出了一种基于星外信标的自适应光学系统实现畸变波前校正的方案,并给出仿真实验,从而为星载自适应光学的进一步研究提供了依据。     

On the prediction of a band-limited signal from past samples

An alternate proof is given of a recent result due to A. Papoulis on predicting the current value of a wide-sense stationary band-limited random process in terms of its past samples. The possibility of such prediction is shown to be equivalent to the completeness of a certain set of complex exponentials on an interval, a property that also allows extension to the prediction of deterministic band-limited signals.