Robustness of mean E{X} and R charts

The effect of nonnormality on E{X} and R charts is reported. The effect of departure from normality can be examined by comparing the probabilities that E{X} and R lie outside their three-standard-deviation and two-standard-deviation control limits. Tukey's λ-family of symmetric distributions is used because it contains a wide spectrum of distributions with a variety of tail areas. The constants required to construct E{X} and R charts for the λ-family are computed. Control charts based on the assumption of normality give inaccurate results when the tails of the underlying distribution are thin or thick. The validity of the normality assumption is examined by using a numerical example     

Closest coset decoding of |u|u+v| codes

The general concept of closest coset decoding (CCD) is presented, and a soft-decoding technique for block codes that is based on partitioning a code into a subcode and its cosets is described. The computational complexity of the CCD algorithm is significantly less than that required if a maximum-likelihood detector (MLD) is used. A set-partitioning procedure and details of the CCD algorithm for soft decoding of |u|u+v| codes are presented. Upper bounds on the bit-error-rate (BER) performance of the proposed algorithm are combined, and numerical results and computer simulation tests for the BER performance of second-order Reed-Muller codes of length 16 and 32 are presented. The algorithm is a suboptimum decoding scheme and, in the range of signal-to-noise-power-density ratios of interest, its BER performance is only a few tenths of a dB inferior to the performance of the MLD for the codes examined     

FDTD for Nth-order dispersive media

Previously, a method for applying the finite-difference time domain (FDTD) method to dispersive media with complex permittivity described by a function with a single first-order pole was presented. This method involved the recursive evaluation of a discrete convolution, and was therefore relatively efficient. In this work, the recursive convolution approach is extended to media with dispersions described by multiple second-order poles. The significant change from the first-order implementation is that the single backstore variable for each second-order pole is complex. The approach is demonstrated for a pulsed plane wave incident on a medium with a complex permittivity described by two second-order poles, and excellent agreement is obtained with the exact solution     

Two chi-square statistics for determining the orders p andq of an ARMA (p, q) process

The &thetas;, λ, and η functions have been previously proposed for use in choosing the autoregressive and moving-average orders of an ARMA (q, p) process visually. Two chi-square statistics associated with these three functions are presented and used here to determine the orders of an ARMA process statistically. It is shown that the two statistics are asymptotically equivalent to the Quenouille-Walker's goodness-of-fit test statistic, which is a Lagrange multiplier test statistic. Some numerical examples are presented to illustrate the usefulness of the two chi-square statistics as well as the three functions in ARMA modeling     

Gain measurements on the KrF(B→X), XeF(B→X), and XeF(C→A) lasertransitions in an XeF(C→A) laser gas mixture

Optimum energy extraction from an electron-beam-pumped XeF(C →A) laser is achieved with a five-component rare gas halide mixture. The characterization and modeling of laser action in such a gas mixture requires a knowledge of small-signal gain and absorption coefficients not only on the blue-green XeF(C→ A) transition, but also in the ultraviolet (UV) region for the competing XeF(B→X) and KrF(B→X ) transitions. The authors report gain measurements on the XeF(C→A) transition and small-signal gain and absorption coefficients at or near both the XeF(B→X ) (351 and 353 nm) and KrF(B→X) (248 nm) transitions. A study of the gain for the UV and visible transitions as a function of Kr and Xe partial pressure is reported, and its impact on the XeF(C→A) kinetics is discussed     

G/T and noise figure of active array antennas

A figure of merit, G/T, for a multichannel active array antenna was derived, and the effects of the beamforming network on the overall noise figure of the system were studied. Also examined are the dependence of the noise figure on various losses, and the difference between a resistive and nonresistive taper in the combining network. When the amplifier gain is sufficiently large, the losses following the LNA can usually be ignored. For a photonic array with lossy time shift elements, however, the downstream losses become significant. Also, if resistive tapering is employed, not only the array gain but also the noise figure will be degraded by the collective effect of the feed network     

On (k, t)-subnormal covering codes

The concept of a (k, t)-subnormal covering code is defined. It is discussed how an amalgamated-direct-sumlike construction can be used to combine such codes. The existence of optimal (q, n, M) 1 codes C is discussed such that by puncturing the first coordinate of C one obtains a code with (q, 1)-subnorm 2     

I and Q decomposition of self-noise in square-lawclock regenerators

A method for obtaining power spectra for the self-noise components in phase and in quadrature to the desired generated clock signal for PAM systems is described. A previously recognized cross spectrum is also discussed. Results can be expressed either in a closed form or as the sum of rapidly convergent series, depending on the signalling waveform used. A computation of the in-phase and quadrature spectra for Nyquist pulses for excess bandwidth factors ranging from 0.1-0.9 is included, along with demonstration showing that for signalling waveforms with even or odd symmetry, cross power spectrum is zero at all frequencies. It is also shown that if the cross power spectrum is not zero due to asymmetry in the signalling waveform, sampling keyed to other than zero-crossing of the timing wave can give a lower timing jitter     

An O(kn) algorithm for a circularconsecutive-k-out-of-n:F system

An O(k×n) algorithm is described for evaluating the reliability of a circular consecutive-k-out- n:F system     

The performance of depressed-cladding single-mode fibers withdifferent b/a ratios

Depressed-cladding single-mode fibers with a first cladding-to-core ratio (b/a) ranging from seven to one and relative refractive-index differences of the core from 0.25 to 0.35% and of the cladding from 0 to -0.2% are investigated experimentally with respect to the LP₁₁ mode cutoff properties, the mode-field diameter, the dispersion, and the bending attenuation. Numerical calculations based on actual profile parameters of the bend loss and the mode-field diameter agree well with experiment. It is demonstrated that low attenuation and bend losses independent of b/a can be obtained if the cutoff wavelength is kept constant by adjusting the core radius, the core index or the index of the first cladding     

Modeling the gate I/V characteristic of a GaAsMESFET for Volterra-series analysis

The authors show that the Taylor-series coefficients of a FET's gate/drain I/V characteristic, which is used to model this nonlinearity for Volterra-series analysis, can be derived from low-frequency RF measurements of harmonic output levels. The method circumvents many of the problems encountered in using DC measurements to characterize this nonlinearity. This method was used to determine the incremental gate I/V characteristic of a packaged Aventek AT10650-5 MESFET biased at a drain voltage of 3 V and drain current of 20 mA. The FET's transconductance was measured at DC, and its small-signal equivalent circuit (including the package parasitics) was determined by adjusting its circuit element values until good agreement between calculated and measured S parameters was obtained. The FET was then installed in a low-frequency test fixture. Excellent results were obtained     

Adaptive set-membership identification in O(m)time for linear-in-parameters models

Some fundamental contributions to the theory and applicability of optimal bounding ellipsoid (OBE) algorithms for signal processing are described. All reported OBE algorithms are placed in a general framework that demonstrates the relationship between the set-membership principles and least square error identification. Within this framework, flexible measures for adding explicit adaptation capability are formulated and demonstrated through simulation. Computational complexity analysis of OBE algorithms reveals that they are of O(m²) complexity per data sample with m the number of parameters identified. Two very different approaches are described for rendering a specific OBE algorithm, the set-membership weighted recursive least squares algorithm, of O(m) complexity. The first approach involves an algorithmic solution in which a suboptimal test for innovation is employed. The performance is demonstrated through simulation. The second method is an architectural approach in which complexity is reduced through parallel competition     

Order N log2 N WHT/DHT algorithm

An efficient algorithm is proposed which computes the coefficients of the higher order discrete Hartley transform (DHT) directly from the coefficients of lower-order DHTs. With this new development, the two-stage Walsh-Hadamard transform/discrete Hartley transform (WHT/DHT) is comparable to the existing fast algorithms. The same approach can also be used for the computation of DCT coefficients     

Overshoot-controlled RLC interconnections

How overshoot in the step response of a circuit involving an RLC line can be controlled using a combination of driver and line resistance that depends on the load capacitance is shown. The no-peak condition or its equivalent is used to relate line parameters to the driver and load impedances. This no-peak condition generalizes the impedance matching customarily used for lossless lines, i.e. it provides an alternative to the traditional choice R_D=√ L/C. The results allow improved circuit response without risk of overshoot, for example, by reduction of driver resistance below √L/C for cases where line resistance is unavoidable and/or where load capacitance is not negligible compared to line capacitance. The algebraic formulas derived are more effective than case-by-case numerical simulations for analyzing scaling and technology issues, whether on-chip, or at the packaging, board, or system levels     

A nonsorting VLSI structure for implementing the (M, L) algorithm

A nonsorting structure for implementing the (M, L) algorithm is presented. The processing is based on a survivor selection operation that incorporates parallelism and has an execution time proportional to the product of the logarithm of bM (the number of contender paths), and k (the number of bits used for path metrics). Aside from the path extender(s), the processor area is only a small fraction of the total chip area; most is simply for required storage of path histories and metrics. This means that the structure can support a large M on a single chip. In addition, the structure can be extended to larger M by stacking rows of a few different types of custom chips     

Binary cyclic [n,k] codes used for simultaneoustEC and SBD

In a hybrid forward-error-correction-automatic-repeat-request system one may wish to use an [n,k] cyclic code because its decoding algorithm is well known. An analytic formula is given for determining the fraction of undetectable single bursts of different lengths when a cyclic code is used for simultaneous single-burst-error detection and t-random error correction     

The importance of the n-base in p-n-p-n-like structures subjectedto dV/dt ramps

A simple yet thorough analysis of physical effects induced in p-n-p-n-like silicon structures by the high rate of the OFF-state forward anode voltage rise (dV/dt) is discussed. The importance of n-base parameters in shaping the faulty triggering of thyristors subjected to dV/dt ramps is clearly demonstrated. The main implications of the findings for thyristor physics and design are also outlined     

An O(kn)-time algorithm for computing thereliability of a circular consecutive-k-out-of-n:Fsystem

I. Antonopoulou and S. Papastavridis (1987) published an algorithm for computing the reliability of a circular consecutive-k-out-of-n:F system which claimed O (kn) time. J.S. Wu and R.J. Chen (1993) correctly pointed out that the algorithm achieved only O(kn²) time. The present study shows that the algorithm can be implemented for O(kn) time     

The (d,k) subcode of a linear block code

A simple technique employing linear block codes to construct (d,k) error-correcting block codes is considered. This scheme allows asymptotically reliable transmission at rate R over a BSC channel with capacity C_BSC provided R ⩽C_d,k-(1+C_BSC), where C_d,k is the maximum entropy of a (d,k ) source. For the same error-correcting capability, the loss in code rate incurred by a multiple-error correcting (d,k) code resulting from this scheme is no greater than that incurred by the parent linear block code. The single-error correcting code is asymptotically optimal. A modification allows the correction of single bit-shaft errors as well. Decoding can be accomplished using off-the-shelf decoders. A systematic (but suboptimal) encoding scheme and detailed case studies are provided     

Block-coded M-PSK modulation over GF(M)

Channel codes where the redundancy is obtained not from parity symbols, but from expanding the channel signal-set, are addressed. They were initially proposed by G. Ungerboeck (1982) using a convolutional code. Here, a block coding approach is given. Rate m/(m+1) coded 2^m+1-ary phase-shift keying (PSK) is considered. The expanded signal-set is given the structure of a finite field. The code is defined by a square nonsingular circulant generator matrix over the field. Binary data are mapped on a dataword, of the same length as the codewords, over an additive subgroup of the field. The codes using trellises are described, and then the Viterbi algorithm for decoding is applied. The asymptotic coding gain ranges from 1.8 to 6.0 dB for QPSK going from blocklength 3 to 12. For 8-PSK, the gain is from 0.7 to 3.0 dB with blocklength 4 to 8. With only four states in the trellis, codes of any length for QPSK and 8-PSK are constructed, each having an asymptotic coding gain of 3.0 dB. Simulation results are presented. It is found that the bit-error rate performance at moderate signal-to-noise ratios is sensitive to the number of nearest and next-nearest neighbors