The redundancy of source coding with a fidelity criterion. 1. Knownstatistics

The problem of redundancy of source coding with respect to a fidelity criterion is considered. For any fixed rate R>0 and any memoryless source with finite source and reproduction alphabets and a common distribution p, the nth-order distortion redundancy D_n(R) of fixed-rate coding is defined as the minimum of the difference between the expected distortion per symbol of any block code with length n and rate R and the distortion rate function d(p,R) of the source p. It is demonstrated that for sufficiently large n, D_n(R) is equal to -(∂/∂R)d(p,R) ln n/2n+o(ln n/n), where (∂/∂R)d(p,R) is the partial derivative of d(p,R) evaluated at R and assumed to exist. For any fixed distortion level d>0 and any memoryless source p, the nth-order rate redundancy R_n(d) of coding at fixed distortion level d (or by using d-semifaithful codes) is defined as the minimum of the difference between the expected rate per symbol of any d-semifaithful code of length n and the rate-distortion function R(p,d) of p evaluated at d. It is proved that for sufficiently large n, R_n(d) is upper-bounded by ln n/n+o(ln n/n) and lower-bounded by In n/2n+o(In n/n). As a by-product, the lower bound of R_n(d) derived in this paper gives a positive answer to a conjecture proposed by Yu and Speed (1993)     

Detection and partial correction of isolated errors from the received data in a 1st-order d.p.c.m. codec

A detection and partial-correction (d.p.c.) system located at the receiver in a 1st-order d.p.c.m. system enables isolated transmission errors that would cause gross distortion in the recovered signal of a conventional d.p.c.m. decoder to be corrected from the received data, providing that the input signal does not exhibit a rapid change in its slope during a sampling period. The d.p.c. system is disabled when this occurs.     

Performance of a d.p.s.k. detector when presented with a distorted signal plus filtered Gaussian noise

A new approach to the problem of analysing differential phase-shift-keyed (d.p.s.k.) systems, in the presence of distortion and filtered noise is described. The result is presented in a form suitable for fast computation, and is shown to agree with previous workers' results for more idealised systems.     

The redundancy of source coding with a fidelity criterion .II.Coding at a fixed rate level with unknown statistics

The redundancy problem of universal lossy source coding at a fixed rate level is considered. Under some condition on the single-letter distortion measure, which implies that the cardinality K of the reproduction alphabet is not greater than the cardinality J of the source alphabet, it is shown that the redundancy of universally coding memoryless sources p by nth-order block codes of rate R goes like |(∂/∂R)d(p,R)|Kln n/2n+o(ln n/n) for all memoryless sources p except a set whose volume goes to 0 as the block length n goes to infinity, where d(p,R) denotes the distortion rate function of p. Specifically, for any sequence {C_n}_n=1^∞ of block codes, where C_n is an nth-order block code at the fixed rate R, and any ϵ>0, the redundancy D_n(C _n,p) of C_n for p is greater than or equal to |(∂/∂R)d(p,R)|(K-ϵ)ln n/2n for all p satisfying some regular conditions except a set whose volume goes to 0 as n→∞. On the other hand, there exists a sequence {C_n}_n=1^∞ of block codes at the rate R such that for any p satisfying some regular conditions, the super limit of D_n(C_n,p)|(ln n/n) is less than or equal to |(∂/∂R)d(p,R)|K/2     

Nonlinearity of d.h. GaAlAs lasers

Experimental investigation of the relative second- and third-harmonic distortion in d.h. semiconductor lasers is presented. The results are compared to the harmonic distortion predicted from simple rate equations. It is suggested that nearfield instabilities limit the minimum distortion level.     

Elimination of input current in a differential d.c. amplifier

An economical circuit is described in which p?n?p transistors are used to compensate for the input base current of a long-tailed-pair differential d.c. amplifier using n?p?n dual transistors.     

On the redundancy of lossy source coding with abstract alphabets

The redundancy problem of lossy source coding with abstract source and reproduction alphabets is considered. For coding at a fixed rate level, it is shown that for any fixed rate R>0 and any memoryless abstract alphabet source P satisfying some mild conditions, there exists a sequence {C_n}_n=1^∞ of block codes at the rate R such that the distortion redundancy of C_n (defined as the difference between the performance of C_n and the distortion rate function d(P, R) of P) is upper-bounded by |(∂d(P,R))/(∂R)| ln n/2n+o(ln n/n). For coding at a fixed distortion level, it is demonstrated that for any d>0 and any memoryless abstract alphabet source P satisfying some mild conditions, there exists a sequence {C_n}_n=1^∞ of block codes at the fixed distortion d such that the rate redundancy of C_n (defined as the difference between the performance of C _n and the rate distortion function R(P,d) of P) is upper-bounded by (7ln n)/(6n)+o(ln n/n). These results strengthen the traditional Berger's (1968, 1971) abstract alphabet source coding theorem, and extend the positive redundancy results of Zhang, Yang, and Wei (see ibid., vol.43, no.1, p.71-91, 1997, and ibid., vol.42, p.803-21, 1996) on lossy source coding with finite alphabets and the redundancy result of Wyner (see ibid., vol.43, p.1452-64, 1997) on block coding of memoryless Gaussian sources     

High efficiency GaAs Schottky-barrier gate f.e.t. oscillator

A high efficiency high p.p.d. GaAs f.e.t. oscillator was developed. An output power of 63 mW with an efficiency of 39.7% and a p.p.d. of 0.21 mW/?m was easily produced at 9.3 GHz using a HP FET 1101 A-HPAC 100 A. The design of this oscillator was effected using a large signal method by means of a time-domain analysis program IMAG III, which computes the transient response of a nonlinear f.e.t. network.     

High peripheral power density GaAs f.e.t. oscillator

Peripheral power density (p.p.d.), i.e. the output power per Unit gate width is defined as a figure of merit for GaAs f.e.t. oscillators. An X-band oscillator circuit using series and shunt feedback is described and its performance characteristies indicated. It is shown that this GaAs f.e.t. oscillator circuit configuration has the highest peripheral power density.     

An SVD-based grayscale image quality measure for local and global assessment.

The important criteria used in subjective evaluation of distorted images include the amount of distortion, the type of distortion, and the distribution of error. An ideal image quality measure should, therefore, be able to mimic the human observer. We present a new grayscale image quality measure that can be used as a graphical or a scalar measure to predict the distortion introduced by a wide range of noise sources. Based on singular value decomposition, it reliably measures the distortion not only within a distortion type at different distortion levels, but also across different distortion types. The measure was applied to five test images (airplane, boat, goldhill, Lena, and peppers) using six types of distortion (JPEG, JPEG 2000, Gaussian blur, Gaussian noise, sharpening, and DC-shifting), each with five distortion levels. Its performance is compared with PSNR and two recent measures.     

Performance of a multilevel d.c.p.s.k. system in the presence of interference and Gaussian noise

Study of a multilevel d.c.p.s.k. system leads to the consideration of pairs of adjacent symbol vectors which depend on instantaneous levels. An analytic evaluation is made of symbol error probability for a general pair of such vectors in the presence of Gaussian noise.     

On the continuity of the error distortion function for multiple-hypothesis decisions (Corresp.)

Analogously to the rate distortion function, the error distortion function is defined for a multiple-hypothesis decision problem. The error distortion functione(d)is defined as the supremum of the Bayes' error probability for transformed observations for which the average distortion is less thand (d geq O)The main result is that the functione(d)is continuous at O.     

The steady-state performance of a controlled current active filter

An active filter that uses a high-frequency D-class asynchronous switching inverter for power system current distortion compensation is described. The distortion compensation technique involves deriving a signal corresponding to the distortion component of load current, inverting and amplifying this signal, and adding it to the supply current to cancel the load current distortion. A synthetic sinusoid is used to determine the distortion component in the time domain. Extensive computed and experimental results, illustrating the system's steady-state performance and ability to reduce the current harmonic distortion components are presented. An intelligent controller is proposed to maintain the active filter's performance at the optimal operating point under varying load conditions     

Objective distortion measure for binary text image based on edge line segment similarity.

This paper proposes a new approach to measure the distortion introduced by changing individual edge pixels in binary text images. The approach considers not only how many pixels are changed but also where the pixels are changed and how the flipping affects the overall shape formed by the edge line. Similarities between the edge line segments in the original and distorted image are compared to measure the distortion. Subjective testing shows that the new distortion measure correlates well with human visual perception.     

Mechanical fibre optic switching using p.v.d.f. bimorph

An optical fibre switching element has been constructed, based on the electromechanical deformation of a bimorph of piezoclectric polymer, p.v.d.f. (polyvinylidene fluoride). Light transmitted through a fibre was switched between two other fibres situated next to each other by the application of the voltage of 3.5 V r.m.s. at 10 Hz. The insertion loss of this element was 0.7 dB.     

Quantiser selection for interframe differential pulse code modulation of television pictures

A procedure based on subjective and objective assessments has been used to design an 8-level quantiser for an interframe d.p.c.m. digital television coding system handling monochrome 5.5 MHz 625-line pidura The quantiser reduces noise in a static picture over its 8-bit source and attempts to minimise the distortion of movement.     

Hole traps in n-InP by d.l.t.s. and transient capacitance techniques

The parameter of a single hole trap frequently observed in bulk and v.p.e. n-InP have been determined for the first time by both transient-capacitance and d.l.t.s. techniques. An activation energy of 270 meV and capture cross-section of 1.4=10?13 cm2 have been measured.     

Possible use of pilot signals to indicate delay distortion in operating f.m.-f.d.m. radio systems

Pilot tones normally used in f.m.-f.d.m. transmission allow propagation distortion to be estimated on each path of an operating system. The phases of the 1st-order sidebands relative to the carrier provide a finite-difference approximation to the gradient of group delay with frequency.     

基于梯度投影的OFDM峰值功率控制算法研究

OFDM系统中的高峰值功率会引起系统误码率性能恶化和非线性失真.文中研究了一种基于星座扩展的梯度投影算法,能有效地对OFDM系统中的高峰值功率进行控制.该算法采用一个在数据上呈现多零的预限幅向量,大大减小系统进行傅里叶变换时的计算量.仿真结果证明,梯度投影算法在保持峰值功率控制性能的同时,有效地加快了收敛速度,显著地降低算法的计算复杂度.     

An on-line universal lossy data compression algorithm viacontinuous codebook refinement. II. Optimality for phi-mixing sourcemodels

For pt.I see ibid., vol.42, no.3, p.803-21 (1996). Two versions of the gold-washing data compression algorithm, one with codebook innovation interval and the other with finitely many codebook innovations, are considered. The version of the gold-washing algorithm with codebook innovation interval k is a variant of the gold-washing algorithm such that the codebook is innovated once every k+1 source words during the process of encoding the entire source. It is demonstrated that when this version of the gold-washing algorithm is applied to encode a stationary, φ-mixing source, the expected distortion performance converges to the distortion rate function of the source as the codebook length goes to infinity. Furthermore, if the source to be encoded is a Markov source or a finite-state source, then the corresponding sample distortion performance converges almost surely to the distortion rate function. The version of the gold-washing algorithm with finitely many codebook innovations is a variant of the gold-washing algorithm in which after finitely many codebook innovations, the codebook is held fixed and reused to encode the forthcoming source sequence block by block. Similar results are shown for this version of the gold-washing algorithm. In addition, the convergence speed of the algorithm is discussed