Subjective quality tests have proven that embedded adaptive differential PCM (ADPCM), known to tolerate information loss through bit dropping, does not maintain sufficient speech quality when directly applied to asynchronous transfer mode (ATM) due to the fixed-length cell transmission scheme unique to ATM. We propose a coding and transmission scheme which enhances the performance by adjusting the embedded ADPCM coding rate according to input speech characteristics, thereby taking advantage of the ATM environment, where the transmission of variable rate sources is feasible. By varying the number of code bits of an embedded ADPCM coder from 6bits per sample, or 48kbps, for blocks of speech with a high prediction gain, to 2bits, or 16kbps, for silent blocks, a good compromise between coding bit rate and speech quality with gradual degradation due to information loss is achieved. The results of subjective evaluation tests showed the speech quality of the proposed scheme to be over 3.5 mean opinion score (MOS) on a scale of 1 to 5 at a cell loss rate of 10%. A prototype of the codec and the ATM cell assembly/disassembly functions were also fabricated using 3 conventional digital signal processors (DSPs) for real-time conversation tests.

The path diversity improvement inherent in direct sequence spread spectrum (DS/SS) signalling under multi-path propagation environments is investigated for mobile/personal radio communications systems that employ DPSK modulation. The bit error rate (BER) performance of post-demodulation selection diversity reception is theoretically analyzed in the presence of noise-only-paths in the time window for diversity combining. Results of laboratory experiments conducted to evaluate the BER performance are also presented. It is shown that the experimental results agree well with the theoretical BER.

The minimum transferable linewidth by X-ray is derived using waveguide analysis. The minimum width is determined by the refractive index of the absorber and does not depend on the X-ray wavelength. Therefore there is an optimum mask aperture size which provides the minimum linewidth. By using Au as the absorber, 8 nm linewidth is attainable.

A new redundancy technique especially suitable for ultra-high-speed static RAMs (SRAMs) has been developed. This technique is based on a decoding-method that uses two kinds of fuses without introducing any additional delay time. One fuse is initially ON and can be turned OFF afterwards, if necessary, by a cutting process using a focused ion beam (FIB). The other is initially OFF and can be turned ON afterwards by a connecting process using laser chemical vapor deposition (L-CVD). This technique is applied to a 64 kbit SRAM having a 1.5-ns access time. The experimental results obtained through an SRAM chip repaired using this redundancy technique show that this technique does not introduce any increase in the access time and does not reduce the operational margin of the SRAM.

This paper deals with the theory and design method of an efficient radix-4 divider using carry-propagation-free adders based on redundant binary {-1,0,+1} representation. The usual method of normalizing the divisor in the range [1/2,1) eliminates the advantages of using a higher radix than two, bacause many digits of the partial remainder are required to select the quotient digits. In the radix-4 case, it is shown that it is possible to select the quotient digits to refer to only the four (in the usual normalizing method it is seven) most significant digits of the partial remainder, by scaling the divisor in the range [12/8,13/8). This leads to radix-4 dividers more effective than radix-2 ones. We use the hyperstring graph representation proposed in Ref.(18) for redundant binary adders.

This paper describes the novel relaxation-based algorithm for the harmonic analysis of nonlinear circuits. First, we present Iterated Spectrum Analysis based on harmonic balance method, where the harmonic balance method is applied to every node independently. As a result, we can avoid dealing with large scale Jacobian matrices and reduce the total simulation time, compared with the conventional method based on Galerkin's procedure or the harmonic balance method. Next, we define the frequency domain latency. Furthermore, we refer to the possibility for exploitation of three types of latency, i.e., relaxation iteration latency, frequency domain latency and Newton iteration latency. And we propose the multirate-sampling technique based on the consideration of the frequency domain latency. Finally, we apply the present technique to the simple analog circuit simulation and verify its availability for the harmonic analysis.

The Hilbert curve is one of the simplest curves which pass through all points in a space. Many researchers have worked on this curve from the engineering point of view, such as for an expression of two-dimensional patterns, for data compression in an image or in color space, for pseudo color image displays, etc. A computation algorithm of this curve is usually based on a look-up table instead of a recursive algorithm. In such algorithm, a large memory is required for the path look-up table, and the memory size becomes proportional to the image size. In this paper, we present an implementation of a fast sequential algorithm that requires little memory for two and three dimensional Hilbert curves. Our method is based on some rules of quad-tree traversal in two dimensional space, and octtree traversal in three dimensional space. The two dimensional Hilbert curve is similar to the scanning of a DF (Depth First) expression, which is a quad-tree expression of an image. The important feature is that it scans continuously from one quadrant, which is obtained by quad tree splitting, to the next adjacent one in two dimensional space. From this point, if we consider run-lengths of black and white pixels during the scan, the run-lengths of the Hilbert scan tend to be longer than those of the raster scan and the DF expression scanning. We discuss the application to data compression using binary images and three dimensional data.

This paper studies multidimensional linear periodically shift-variant digital filters (LPSV filters). The notion of a generalized multidimensional transfer function is presented for LPSV filters. The frequency characteristic of the filters is discussed in terms of this transfer function. Since LPSV filters can decompose the spectrum of an input signal into some spectral partitions and rearrange the spectrum, LPSV filters can serve as a frequency scrambler. To show the effect of multidimensional frequency scramble, 2-D LPSV filters are designed based on the 1-D Parks-McClellan algorithm. The resultant LPSV filters divide the input spectrum into some components that are permuted and possibly inverted with keeping the symmetric of the spectrum. Experimental results are presented to illustrate the effectiveness of frequency scramble for real images.

An accurate numerical solution is presented for the electromagnetic scattering from a double strip grating, where the strip planes are each supported by a dielectric slab. This structure is a model of polarization diplexers. The direction of propagation and the polarization of the incident plane wave are arbitrary. We derive a set of singular integral equations and solve it by the moment method, where the Chebyshev polynomials are successfully used as the basis and the testing functions. By numerical computations we examine the dependence of the diplexing properties on grating parameters in detail. The cross-polarization characteristics at skew incidence are also referred. From these results we construct an algorithm for the design of polarization diplexers.

This paper describes operating characteristics of a new device named multi-step function MOS transistor (MSF MOSFET) which has stair-shaped I-V curve caused by a stairshaped gap between drain and gate. A quantizing inverter is obtained by using only a single MSF MOSFET as a coupling element of an emitter common amplifier. A pair of the quantizing inverters whose input and output are cross-coupled to each other has multi-stable states. This multiple-valued (MV) flip-flop is available for MV registers and MV memories whose states are changeable by an analog input voltage.

Responses in the Nagumo neural circuit to pulse-train stimulation are studied using the time sequence, phase diagram, Poincare section, return map, firing rate, Lyapunov number and bifurcation diagram. For the mono-stable neuron with an equilibrium point deeper than the maximal point of a tunnel diode curve, main responses are periodic or all-or-none and chaotic responses are rarely observed. For the neuron with an equilibrium point located near the maximal point, the response to one input pulse oscillates after the undershoot and responses to pulse-trains make complex bifurcation structure in the threshold diagram. The ranges of periodic responses are stratified in the diagram. There exist broad regions of chaotic responses and chaos is not a special response of the Nagumo circuit, but it often comes out. The results are different from those obtained from Hodgkin-Huxley equations and the BVP model.

Asynchronous Transfer Mode (ATM) is an information transport technique that well supports Broadband ISDN (B-ISDN). One unsolved problem to the perfection of ATM networks is to provide a testing environment that conforms to some standardized network management scheme. From this point of view, remotely controlled virtual path testing is considered in this paper. Remotely controlled virtual path testing should be executed through the standardized Telecommunications Management Network (TMN) model, which employs the OSI systems management concept as the basis of information exchange. Thus, this paper addresses the two issues that arise when OSI systems management standards are applied to virtual path testing. One issue is to define relevant information models. The other issue is to provide test resources with a concurrency control mechanism that guarantees a consistent test environment without causing deadlocks. To resolve these issues, technical requirements are clarified for the remote control of test resources. Next, alternatives to the concurrency control mechanism are shown and compared through computer simulations. A method of defining information models is then proposed. The proposed method ensures the easy storage and retrieval of intermediate test results as well as permitting the effective provision of concurrency control for test resources. An application scenario is also derived. The scenario shows that tests can be executed by using standardized communication services. These results confirm that virtual path testing can be successfully achieved in conformance with the OSI systems management standards.

The problem of two-dimensional scattering of electromagnetic waves by a grating with several strips arbitrarily oriented in one period is analyzed by means of the Wiener-Hopf technique together with the formulation using the concept of the mutual field. A formulation for the analysis of multiple scattering from the grating is based on the representation of the scattered field by a grating composed of one strip in one period. The Wiener-Hopf equations and a representation of the scattered wave are obtained. The characteristic of the sampling function is used to expand the unknown function associated with the field on the strip into a series, and then the Wiener-Hopf equations are reduced to a set of simultaneous equations. For evaluation of the convergence and the errors in the numerical results, the relative error with respect to the extrapolated value and the square error for satisfaction of the boundary condition are computed. From numerical comparison of the present method with other various methods, it is found that the present method provides us accurate results. Some numerical examples of the reflection coefficients are presented for the reflection grating and transmission gratings.

Compared to multi-level signature file techniques, PSF (Partitioned Signature File) technique has less processing overhead by its characteristics of a simple file organization. In a multi-processor environment, the PSF technique also has an advantage that queries can be processed in parallel effectively by allocating one or more partitions to each processor. Main point of the PSF technique is a partitioning scheme based on a key selection. In this paper, an n-BFK (n-Bounded Floating Key) partitioning scheme is proposed, in which the number of segments for a key selection is bounded by n. The cost model is developed for the performance evaluation of the proposed scheme. By performance comparison with the existing schemes, the efficiencies of the proposed scheme are shown with respect to a disk access cost, a signature reduction ratio, and an uniformity of workload.

Several research institutions in Europe have developed set-ups for wide-band mobile radio communication measurements. The performance and evaluation has been coordinated in the framework of the cooperation in the field of scientific and technical research within the committees COST 207 COST 231. New parameters have been defined to improve the insight into performance limits of digital radio communication systems which are caused by propagation phenomena. The definitions of these new parameters are presented in the paper. Channel sounders developed in Norway, Denmark, the United Kingdom, Switzerland, France and Germany are described. They are based on considerably different technical principles for evaluation and recording of the measured results. A few results gained in European measurement campaigns are also presented.

This paper analyzes the performance of the capacity controlled radio system under a frequency selective fading environment. This system controls the number of modulation levels according to the number of active subscribers. In the analysis, we consider the capacity controlled system either with or without adaptive equalizer. As the results of analysis, it is clarified that the system is superior to the conventional fixed capacity system, and can be considered as a good countermeasure for multi-path fading. And it is found that there exists a synergistic effect due to capacity controlling and adaptive equalizing.

A Decision Feedback Equalizer (DFE) structure with a varying number of tap lengths was used with a recursive least squares (RLS) algorithm to determine tradeoffs between equalizer size and performance in mobile and portable digital radio systems. A mobile channel simulator, SMRCIM, was used to demonstrate how much an equalizer can improve the BER in real world urban channels. The results show that at 850MHz, the DFE is unable to improve the BER when the mobile terminal exceeds speeds of 115km/h for U.S. Digital Cellular systems. The performance of adaptive equalization for indoor high data rate systems was evaluated using the indoor channel simulator SIRCIM, and we found that DFEs have excellent performance for indoor radio channels. For simple structures, the BER is less than 10-3 at 15dB Eb/NO using coherent QPSK modulation. Finally, an equalizer structure for non-coherent π/4 DQPSK modulation was developed and simulation results are presented.

This paper describes a fiber-optic microcell radio system with a spectral delivery switch to meet traffic demands. Optical link performance is discussed from the view points of link loss and noise figure aimed at system design. The theoretical carrier-to-noise ratio (CNR) performance is shown as a function of the input electrical power of the laser and the received optical power. Improvement of dynamic range defined by both CNR and intermodulation distortion is proposed by using the frequency modulation (FM) technique. The experimental results using the proposed technique indicate that the performance is much better than that of conventional methods. Moreover, economical diversity planning delivery methods over fibers are presented. This strategy will provide more cost effective and flexible networks.

We analyze the average bit error probability (BER) performances of BPSK with pilot tone in the frequency-selective Rayleigh fading channel, which can be characterized by the delay power spectrum due to multipath fading. The analysis is based on the error probability conditioned on the receiver input envelope in order to investigate the diversity effects. With taking into consideration of predetection receiving filter characteristic, the average BER is evaluated by treating the normalized standard deviation (rms delay spread), τ0/T (T: digital symbol period), of the delay power spectrum, BT product of predetection filter and power distribution between BPSK signal and pilot tone as parameters. The results show that the optimum power distribution (kopt) can be determined mainly according to the ratio (α) of tone extracting filter bandwidth to predetection filter bandwidth provided that α is small. For fixed α, τ0/T and kopt corresponding to α, optimum BT product, which minimizes the error rate, exists and the value is dependent on signal energy per bit to noise power spectral density ratio (SNR), and is affected slightly by the delay power spectrum shapes. In this paper, one-sided exponential, Gaussian and double spike shapes are treated as delay power spectrum shapes. On the average BER characteristics due to delay spread with fixed α, BT and kopt corresponding to α, the delay power spectrum shape is of no importance for τ0/T0.06. For τ0/T0.06, in the case of double spike delay power spectrum, BER is less than that for the other two spectral shapes. By making use of the selection diversity with 2-branch and predetection filter with optimum BT product, SNR can be improved by 16dB at the average BER of 10-4.

This paper proposes and investigates an adaptive equalizer with diversity-combining over a multipath fading channel. It consists of two space-diversity antennas and a Ts/2-spaced decision-feedback-equalizer (DFE). Received signals from the two antennas are alternatively switched and fed into the feed forward-filter of DFE. We call this structure a Switched Input Combining Equalizer with diversity-combining (SICE). By using an SICE, the receiver structure for combining diversity equalization can be simplified, because it needs only two receiver sections up to IF BPF. The bit error rate (BER) performance of SICE was evaluated by both computer simulation and experiment over a multipath fading channel. We experimentally confirmed the excellent BER performance, around 1% of BER over a multipath fading channel at 160Hz of maximum doppler fading frequency. Therefore, the proposed SICE is applicable to highly reliable transmission in the 1.5-GHz-band mobile radio.