Sort-and-match algorithm for soft-decision decoding

Let a q-ary linear (n, k) code C be used over a memoryless channel. We design a decoding algorithm Ψ_N that splits the received block into two halves in n different ways. First, about √N error patterns are found on either half. Then the left- and right-hand lists are sorted out and matched to form codewords. Finally, the most probable codeword is chosen among at most n√N codewords obtained in all n trials. The algorithm can be applied to any linear code C and has complexity order of n³√N. For any N⩾q^n-k, the decoding error probability P_N exceeds at most 1+q^n-k/N times the probability P_Ψ (C) of maximum-likelihood decoding. For code rates R⩾1/2, the complexity order q^n-k/2 grows as square root of general trellis complexity q^min{n-k,k}. When used on quantized additive white Gaussian noise (AWGN) channels, the algorithm Ψ_N can provide maximum-likelihood decoding for most binary linear codes even when N has an exponential order of q^n-k     

Adaptive recovery of a chirped sinusoid in noise. I. Performance ofthe RLS algorithm

The authors study the ability of the exponentially weighted recursive least square (RLS) algorithm to track a complex chirped exponential signal buried in additive white Gaussian noise (power P _n). The signal is a sinusoid whose frequency is drifting at a constant rate Ψ. lt is recovered using an M-tap adaptive predictor. Five principal aspects of the study are presented: the methodology of the analysis; proof of the quasi-deterministic nature of the data-covariance estimate R(k); a new analysis of RLS for an inverse system modeling problem; a new analysis of RLS for a deterministic time-varying model for the optimum filter; and an evaluation of the residual output mean-square error (MSE) resulting from the nonoptimality of the adaptive predictor (the misadjustment) in terms of the forgetting rate (β) of the RLS algorithm. It is shown that the misadjustment is dominated by a lag term of order β^-2 and a noise term of order β. Thus, a value β_opt exists which yields a minimum misadjustment. It is proved that β_opt={(M+1)ρΨ²} ^1/3, and the minimum misadjustment is equal to (3/4)P_n(M+1)β_opt, where ρ is the input signal-to-noise ratio (SNR)     

Most-vital edge of a graph with respect to spanning trees

A most-vital edge of a connected graph with respect to spanning trees is an edge whose removal most reduces the number of spanning trees. Tsen et al. (1984) proposed a solution to the problem, based on determining the adjoint of a matrix of order n (n=number of nodes of the graph). This paper presents a solution based on determining the adjoint of Ψ≡A×A^t (A=reduced incidence-matrix of the graph); the order of Ψ is (n-1). This procedure leads to a resistance-analog method to determine the vital edge of a graph with respect to the spanning trees     

The third annual special session on image reconstruction using realdata. 2. The application of back-propagation algorithms to the Ipswichdata: preliminary results

For pt.1 see ibid., vol.41, no.1, p.34-51 (1999). The Ipswich data provide a unique opportunity for the validation of the approximate back-propagation (ABP) methods, which were originally developed to identify the shape of acoustic scatterers in the resonance region. These methods rely on a heuristic relationship, i.e., ABP, between the expansion coefficients that represent the scattered wave in the far zone and those on the obstacle boundary, Γ. The unknown is the shape-parameter vector, ψ&oarr;∈Ψ_ad, the admissible set. The objective function to be minimized is the L² (Γ)-norm of the boundary defect. In the vertical-polarization case, ABP consists of an affine map, which is easy to derive. Its ingredients are arrays of inner products in L²(Γ), where outgoing cylindrical wave functions are involved. The corresponding numerical results, based on the IPS001VV data, are satisfactory. The attraction domain of the expected solution, the reference obstacle (a disk), is numerically determined by varying the initial conditions in a wide subset of Ψ_ad. Reconstruction seems to be unique, although no uniqueness condition is known for the obstacle. In the horizontal-polarization case, ABP relies on vector harmonic functions in a cylindrical geometry. The complexity of the algorithm is higher. Results based on the TPS001HH set are summarized. Although the numerical solution does not show any focal minimum other than the reference obstacle, the corresponding attraction domain is smaller than in the vertical-polarization case     

Designing better adaptive sampling algorithms for ECG Holtersystems

Let Ψ be any adaptive sampling algorithm that can run in real time on a tapeless multichannel electrocardiogram (ECG) Holter system. Simple methods which can significantly improve Ψ's fidelity are described and their results are compared in this paper. It is shown that by adding some simple tests to Ψ, the signals reconstructed by Ψ can be improved as much as 5.45 dB. It is also shown that under the same data rate, a good data compressor with slowly sampled input ECG is preferable to a bad data compressor with highly sampled input ECG     

Characteristics of siliconn+-n--n+ diode with sub-micrometer n- region

In this paper, the I-V characteristics of silicon n⁺-n ^--n⁺ diode are investigated as a parameter of the length of the n^- region. This diode with shorter n^- region than 1 μm has the ohmic characteristics until reaching high electric field in spite of the existence of numerous space-charges in the n^- region, for the first time in this report. This conductance of the diode is inversely proportional to the third power of the length of the n^- region. The experimental results are in good agreement with an analytical calculation including the diffusion term of carriers injected from the n+ regions to the n^- region. However, the diode with longer n^- region than 2 μm shows the space-charge-limited conduction which is the same as earlier reports     

Ultra-high differential gain in GaInAs-AlGaInAs quantum wells:experiment and modeling

A high differential gain of 9.3×10^-16 cm² is obtained in GaInAs-AlGaInAs 1.55-μm multiquantum-well lasers with 1% compressive strain grown by molecular-beam epitaxy. This is the highest ever achieved in this material system. The model-solid theory and an approximate k.p method are incorporated in the theoretical gain calculation that provides a detailed understanding of the experimental results and guidance to further improvement     

AM-FM energy detection and separation in noise using multibandenergy operators

This paper develops a multiband or wavelet approach for capturing the AM-FM components of modulated signals immersed in noise. The technique utilizes the recently-popularized nonlinear energy operator Ψ(s)=(s˙)²-ss¨ to isolate the AM-FM energy, and an energy separation algorithm (ESA) to extract the instantaneous amplitudes and frequencies. It is demonstrated that the performance of the energy operator/ESA approach is vastly improved if the signal is first filtered through a bank of bandpass filters, and at each instant analyzed (via Ψ and the ESA) using the dominant local channel response. Moreover, it is found that uniform (worst-case) performance across the frequency spectrum is attained by using a constant-Q, or multiscale wavelet-like filter bank. The elementary stochastic properties of Ψ and of the ESA are developed first. The performance of Ψ and the ESA when applied to bandpass filtered versions of an AM-FM signal-plus-noise combination is then analyzed. The predicted performance is greatly improved by filtering, if the local signal frequencies occur in-band. These observations motivate the multiband energy operator and ESA approach, ensuring the in-band analysis of local AM-PM energy. In particular, the multi-bands must have the constant-Q or wavelet scaling property to ensure uniform performance across bands. The theoretical predictions and the simulation results indicate that improved practical strategies are feasible for tracking and identifying AM-FM components in signals possessing pattern coherencies manifested as local concentrations of frequencies     

Interferometric chromatic dispersion measurements on short lengthsof monomode optical fiber

Chromatic dispersion measurements on short lengths of monomode optical fiber by the technique of `white light' interferometry are presented. Improved optoelectronic signal processing and rigorous data reduction techniques have resulted in a temporal resolution of ⩾7×10^-5 ps·nm^-1 in a 1-m length of fiber, equivalent to 0.06% resolution in the measurement technique. This is equivalent to a first-order chromatic dispersion coefficient ( D(λ)) resolution of 0.07 ps·nm^-1·^-1. The second-order chromatic dispersion coefficient (S(λ)) resolution was 0.02 ps·nm^-2·nm^-1. Experimental results of D(λ) and S(λ) for three different fibers are compared to theoretical calculation of material and waveguide dispersion     

A multidimensional isomorphic operator and its properties-aproposal of finite-extent multidimensional cepstrum

We propose a new multidimensional homomorphic operator that replaces the conventional complex cepstrum transformation. We treat multidimensional signals of finite support since any signal we can actually observe and deal with is of finite support. We first show that for any sequence of finite support there exists a coordinate transformation that transforms the support of a given sequence into the first quadrant in the multidimensional signal space. We then propose a new multidimensional homomorphic operator Ψ which transforms a sequence of finite support into another sequence of finite support in the first quadrant. It is proved that the operator Ψ is an isomorphism between two multidimensional signal spaces of finite support where finite convolution and usual addition, respectively, are defined as binomial operations. It is also shown that unlike the conventional complex cepstrum, the proposed operator Ψ is quite simple to compute and requires no complicated procedure like phase unwrapping, while it maintains the special features of the conventional complex cepstrum transformation that are useful in homomorphic signal processing. Moreover we clarify some algebraic structure of the multidimensional signal space with the finite convolution as a binomial operation. Finally it is shown by a numerical example that the deconvolution system using the proposed operator Ψ gives a much better result than the conventional complex cepstrum method     

Adaptive nulling in monopulse antennas

Theoretical and experimental results are presented for phase-only nulling in low-sidelobe monopulse antennas. Both results are based on a gradient search algorithm that simultaneously searches for a minimum in the sum and difference channel output powers. The array's beam steering phase shifters double as the adaptive weights. Each element in the gradient is found by changing phase shifter setting by ΔΨ (the phase shifter stepsize) and measuring the change in output power. Then the phase shifter is restored to its original value, and the process repeated for all the remaining array phase shifters. The algorithm iterates as long as each new adaptive weight setting reduces the total output power. If the output does not go down, then ΔΨ is decremented by one setting and the iteration is started again. The algorithm stops when ΔΨ=0. The adaptive weights act as random perturbations to the phase taper of the array. Consequently, the sidelobe level is proportional to the size of the phase perturbations and inversely related to the number of elements. By keeping the adaptive phase shifts small, the average sidelobe level and the main beam gain do not drastically change     

The N-dimensional complex delta distribution

The notion of a 1-D complex delta distribution of the form Ψ _δ(t)=δ(t)+j/πt is used in quantum physics from which it has since then proliferated into the theory of signals and systems. This correspondence recalls the definition of the 1-D complex delta distribution using the Gabor's notion of the analytic signal and presents the consequences of its polar notation. The notions of 2-D and 3-D complex delta distributions are illustrated with approximating functions and written in the polar notation. Examples of periodic complex delta distributions are given     

A review of the pseudo-MOS transistor in SOI wafers: operation,parameter extraction, and applications

The pseudo-MOS transistor (Ψ-MOSFET) is a surprising and useful technique for the rapid evaluation of SOI wafers, prior to any CMOS processing. We review the static and dynamic modes of operation as well as the main models and methods for electrical parameter extraction. Selected numerical simulations are presented in order to clarify the optimal conditions of operation. Finally, practical applications are exemplified which illustrate the efficiency of the Ψ-MOSFET technique for in situ characterization of SOI technologies and processes     

Negacyclic convolution using polynomial transforms on hypercubes

A polynomial-transform-based algorithm for calculating products modulo Zⁿ+1 on a hypercube is presented. All interprocessor communication in this algorithm occurs over a Hamming distance of one; that is processors communicate only with their immediate neighbors. This algorithm has been implemented on a Connection Machine, and the performance results are discussed. Current figures show a time of 358 ms for negacyclic convolution of 1 K 16 bit samples, up to about 8 s for a 64 K data set. The authors discuss the use of this algorithm in the calculation of convolution, compare communication costs with the FFT, and discuss directions for future work     

New approach to the frequency response analysis of an InGaAsavalanche photodiode

The frequency response of an avalanche photodiode has been calculated by solving the transport equations, taking the electric field profile into account. The relationship between the carrier concentration (Nb) in the multiplication layer and the frequency response has been obtained for the first time. This calculation has been carried out for a conventional In_0.53Ga_0.47As avalanche photodiode. The results explain well present experimental data. The saturation velocity of holes in InP is estimated to be 2×10⁶ cm/s. The upper limitation of the gain-bandwidth product is estimated to be 140 GHz at Nb=2×10¹⁷ cm^-3      

Design and characterization of a mode-splitting Ψ-junction

It will he shown In this paper, that the mode conversion factor (MCF) as defined for Y-junctions, can be profitably applied for the design of three branch junctions for splitting the three lowest-order modes of a channel waveguide. Accordingly, these so-called mode-splitting Ψ-junctions were designed for implementation in PECVD SiON-technology. Propagation calculations point to crosstalk levels well below -20 dB at 10-20 mm junction length. The produced Ψ-junctions show crosstalk of less than -17 dB, mainly originating from the nonhomogeneity of the refractive indexes of the SiON layers     

Optimum composition of CaO, SrO dielectric materials in AC plasma display panels

The firing voltage Vfof ac operated plasma display panels can be reduced by coating the dielectric materials with (Ca, Sr)oxides. The reasons for the reduction of Vfare explained in this paper. The secondary electron emission yield, γi(Ar⁺), resulting from Ar ion bombardment, was directly measured for the compound oxides having various ratios of Ca to Sr. Also, the work function was obtained from the measurement of thermionic emission. The results show that γi(Ar⁺) reaches a maximum for a weight ratio of CaO to SrO of 1:3 while the work function reaches a minimum. From the results of Auger analysis and the measurement of optical absorption, it was confirmed that the most anion vacancies of SrO (F⁺s(H) color centers and F⁺scolor centers) were found in the sample of the preceding composition. (F⁺s(H) and F⁺scolor center are considered as a direct source of emission. As a result of the increase of (F⁺s(H) and F⁺scolor centers, reduction of the work function and increase of γi(Ar⁺) occur. The theoretical calculation of γi(Ar⁺), using the theory of Parilis et al., was carried out to clarify the influence of the work function upon γi(Ar⁺). The theoretical results are in good agreement with the measurement of γi(Ar⁺). From the discussion based on the potential ejection process in ae-plasma display panels, it is shown that the reduction mechanism of Vfis caused by the increase of F⁺scolor centers.     

A high-speed buried channel MOSFET isolated by an implanted silicon dioxide layer

This paper describes a high-speed buried channel MOSFET dielectrically isolated from the substrate through the use of oxygen implantation technology. An implanted silicon dioxide layer is formed just beneath the surface. An n-type epitaxial layer is grown on the remaining thin single-crystal layer at the surface. Then, buried channel MOSFET's are formed on the n-type layer. The interface between the implanted SiO2and the upper silicon is abrupt, and the interface charge density is 6.9 × 10¹⁰cm^-2. The effective carrier mobility calculated from the drain conductance is 750 cm²/V . s. Leakage current which should be inherent in this device structure can not be observed. Submicron MOSFET's show much smaller threshold voltage shifts than conventional ones, and this agrees with the results of two-dimensional numerical calculation. A ring oscillator composed of MOSFET's with 1-µm channel length shows a minimum delay time of 95 ps and a power delay product of 310 fJ at VDDof 15 V.     

InGaAsP channel HFET's on InP for OEIC applications

A model for the calculation of the input noise of a high impedance photoreceiver is proposed, taking into account the contributions of low-frequency characteristics of the FET. Simulations based on this approach show that excess gate leakage current and low-frequency excess noise, usually observed in InGaAs channel FET's, strongly penalize the photoreceiver sensitivity for low to medium data rates. New InGaAsP channel HFET's have been developed and fabricated to solve those problems, dc measurements on 1×100 μm² gate HFET's show good I_ds-V_ds characteristics with associated gate leakage currents lower than 200 nA. Promising ft of 18 GHz and f _max of 40 GHz have been recorded on 0.5×200 μm² gate transistors. Low-frequency gate and channel noise measurements demonstrate the suitability of InGaAsP channel HFET structure and technology for low noise applications. A hybrid pin-HFET high impedance photoreceiver has been assembled with a 1×150 μm ² gate transistor. A very close agreement is found between photoreceiver input noise predicted by our model and experimental results. Record sensitivities of 34.8 dBm at 622 Mbit/s and -28.7 dBm at 2.5 Gbit/s are inferred from noise measurements, confirming the strong potential of InGaAsP channel HFET's for the fabrication of high sensitivity photoreceivers operating at moderate data rates     

Quantum effects in Si n-MOS inversion layer at high substrate concentration

The charge distribution at the semiconductgor-insulator interface is calculated for electrons by solving Schrödinger's and Poisson's equations self-consistently for particles obeying Fermi-Dirac statistics at 300 K. The results are applied to carriers in the channel of a crystalline MOSFET with the (100) axis perpendicular to the gate oxide. The inversion charge density calculated quantum mechanically is smaller than that calculated classically. This affects the shift of the subthreshold curves. The shift is larger at higher substrate impurity concentrations, and is especially pronounced at more than 10¹⁷ cm⁻³, which is the concentration used in recent MOS devices. The shift is as large as 0.18 V when the substrate impurity concentration is 8.5 × 10¹⁷ cm⁻³. Comparisons with measurement are also shown and it agrees well with quantum mechanical calculations. The inversion layer depth is compared, and a new efficient method is derived by transferring the quantum mechanical effect into the classical calculation. The results of this new method agree well with the quantum mechanical calculations and with the measurements.