Showing papers in "Electronics and Communications in Japan Part Iii-fundamental Electronic Science in 1993"

Algebraic geometric codes on certain plane curves

Abstract: Necessary and sufficient conditions are given for projective plane curves to have cusps isomorphic to the origin of an affine plane curve xa + yb. Based on them, a family of curves Cab having only one such cusp as a singular point and a family of curves rCab having only two such cusps as singular points are formulated. Also, the structures of algebraic geometric codes generated on curves contained in these families are shown, where a and b are relatively prime. Then the genus is (a − 1)/(b − 1)/2 and the basis of linear space L(m · P) is given by rational functions xiyi only. Second, by giving concrete examples, it is shown that families of curves Cab and rCab contain many curves which attain Hasse-Weil upper bound.

Spectral estimation of speech by mel‐generalized cepstral analysis

Abstract: This paper proposes a spectral estimation method of speech based on mel-generalized cepstral representation. The spectral estimation based on generalized cepstral representation is a method that unifies the cepstral method and the linear prediction method. By this method, the spectral model can be varied continuously from the all-pole model to the exponential model. This paper also discusses the following: the method of spectral estimation, where the mel-generalized cepstrum is used instead of the generalized cepstrum; the uniqueness of the solution for the minimization problem; the solution method; and the convergence of the solution. The proposed method has the same features as those of the method based on the generalized cepstrum where the spectral model can be varied continuously and the stability of the obtained transfer function is guaranteed. Another feature is that characteristics similar to the human auditory sensation, i.e., the high resolution in the low-frequency range and the coarse resolution in the high-frequency range, are obtained since the mel-generalized cepstrum is used as the parameter, which is the generalized cepstrum defined on the mel-frequency axis. Finally, the features and the effectiveness of the proposed method is demonstrated by analysis examples of the synthesized signals and natural speech.

Coupled‐mode theory of SAW periodic structures

Abstract: The coupled-mode theory is extremely useful for analysis of such periodic structures as grating reflector, resonator, and unidirectional transducer making use of electrode reflection as important constituent elements for the SAW devices. Here, the coupled-mode equations describing the transduction characteristics of the inter-digital electrode transducer (IDT) are derived directly by the perturbation theory. In addition, the parameters for the coupled-mode equations are presented for quartz, LiTaO3 and LiNbO3 substrates. Next, based on the coupled-mode equations, the relationship among the quantities of the electrical port and two acoustic ports of the IDT is derived. The entire periodic structure was represented by a simple distributed equivalent circuit. The equivalent circuit analysis method is described for the analysis of the device characteristics. To show the usefulness of the present method, a backward-wave type trapped-energy SAW resonator and the resonator coupled filter are analyzed.

Branch-and-Bound Placement for Building Block Layout

Abstract: This paper proposes a placement technique based on the branch-and-bound method for the block placement problem in building block layout. In contrast to a traditional method of finding an approximate solution by a heuristic approach, the proposed method seeks a solution from all possible placements. To find the solution efficiently, the branch-and-bound operation suited to the placement problem is devised. The proposed method positively considers the constraints imposed on routing length and placement configuration since they could be utilized for restricting the solution space. When the constraints are stronger, the solution space is more restricted, which helps to complete the search of the solution in a short time. By an experimental investigation concerning the number of blocks that can be handled at a time, it is seen that almost six blocks can be handled if there is no constraint. When the number of blocks exceeds this limit, the circuit is decomposed in a hierarchical way and the branch-and-bound placement is applied to each subproblem until the layout of the whole circuit is determined. The proposed placement method is applied to the standard benchmark circuit for building block layout, and it is seen that the result by the proposed method is better than or very close to the best result reported so far.

Fast stabilized adaptive algorithm for IIR bandpass/notch filters for a single sinusoid detection

Abstract: In this paper, a new algorithm for the detection of a single sinusoid corrupted by Gaussian noise using IIR adaptive bandpass/notch filter is presented. As the first step, the relation between the convergence speed and the filter Q-factor in IIR adaptive bandpass filter is analyzed. Based on the result of analysis, an algorithm is derived in which the filter Q-factor and the adaptive control signal generator Q-factor are made continuously variable so that they are inversely proportional to the distance between the filter center frequency f0 and the frequency f of the sinusoid to be detected. This makes both the convergence speed of f0 and f and the resolution high. Then it is found that limiting the maximum amplitude response of the adaptive control signal generator to a value proportional to sin 2πf can suppress the coefficient fluctuation after convergence effectively. By this approach, an IIR adaptive filter with a high Q can easily be realized. As the next step, an additional high-speed and highly stable adaptive algorithm is proposed in which the step size of the filter coefficient update is made to vary inversely with the filter Q-factor. A realization of the IIR adaptive notch filter is also presented. Finally, the usefulness of the proposed adaptive algorithm is verified by a computer simulation.

Digital filters with hypercomplex coefficients

Abstract: This paper considers digital filters with hyper-complex coefficients. Filters of this type can reduce the order of filters to one-fourth the one with real coefficients. It is reported that the first-order digital filter with hypercomplex coefficients can realize the fourth-order digital filter with real coefficients which can be expressed by a second-order all-pass filter with complex coefficients. This paper considers also generalization including the foregoing special case and shows that the first-order digital filter with hypercomplex coefficients can realize an arbitrary-order digital filter with real coefficients less than 4. Arbitrary higher-order digital filter with real coefficients can be realized by parallel connection or cascade connection of first-order digital filters with hypercomplex coefficients. This paper considers the following three different realizations: (a) realization by parallel connection; (b) realization by cascade connection of real part; and (c) realization by cascade connection. We find that case (b) is the most low sensitive. Finally, stability criteria of hypercomplex digital filters of first-order are suggested.

Proposal of median‐type fuzzy filter and its optimum design

Abstract: This paper proposes a median-type fuzzy filter, aiming at the signal estimation in the case where the impulse and white Gaussian noise are superposed on the signal with sudden changes, such as the image signal. The filter is realized by generalizing the fuzzy filter previously proposed by the authors. In the previously proposed fuzzy filter, the signal point to be estimated is taken as the reference point and the signal is estimated by determining the input signals relatively close to the reference point, using the fuzzy clustering; whereas the filter proposed in this paper uses the median value of the input signal sequence as the reference point and the signal is estimated by determining the input signals close to that reference point using the fuzzy clustering. The signal is estimated by determining the center of gravity of the cluster of the points close to the median. Furthermore, in the proposed filter, the optimum design is realized by learning with respect to appropriate training signals. It is in general not possible to decide definitely whether or not the input signal is close to the median, and thus the fuzzy clustering is effective since it takes into consideration the ambiguity of the signal. By introducing the fuzzy clustering, it is shown in particular that an effective signal estimation is realized for the signal with subtle changes.

Two‐route flows in an undirected flow network

Abstract: This paper defines anew the maximum two-route flow as a measure to represent the relation between two vertices in the flow network. The maximum two-route flow corresponds to the maximum number of communication channels that are composed of two-route paths between two terminals in a communication network. The ℱ-rings that can be composed simultaneously, containing the considered two vertices, is defined as the maximum two-route flow between those two vertices. It is shown in this paper that a theorem exists for the maximum two-route flow similar to the max-flow min-cut theorem for the ordinary flow.

A method for synthesizing animation to transmit sign language by intelligent communication

Abstract: The following intelligent communication system is considered for the transmission of the animation image information. The structural models are prepared both at the transmitter and the receiver. Only the information concerning the motion of the object is transmitted to provide the model with the motion parameters, and the animation image is synthesized. In such a system, the real-time image synthesis based on the motion parameters is required. This paper aims at the intelligent communication of the sign language image using a personal computer. A method of real-time synthesis is discussed which is based on the parameter representation of the hand motion and the computer graphics (CG) of the animation image. When the animation image for the human body is to be generated in real-time, using the three-dimensional shape model, the real-time system is difficult to realize at the present stage by a personal computer from the viewpoint of the computation time. An idea is to use the key-frame figure interpolation (which is a two-dimensional figure processing) instead of the three-dimensional shape model to reduce the computation time in generating the animation. However, it is difficult in this method to derive the rotational image of a three-dimensional object such as the human hand. From such a viewpoint, the stick-figure model for the upper limb is adopted in this study, aiming at the intelligent transmission of the sign language image. The state of connection of the three-dimensional segments, which are obtained by the segmentation at the joints, is represented by a vector. The skeleton represented by the vector is shaped appropriately into a geometrical shape. Then, using the three-dimensional vector representing the skeleton motion, the shapes of the figure, etc., are constructed and the result is projected on the two-dimensional plane.

Learning rules of neural networks for inverse systems

Abstract: This paper considers on-line learning of neural networks for an inverse problem. A neural network must learn an inverse system of a static unknown system on the basis of an evaluation function that is a squared error between an output of the unknown system and its desired value. Usual learning methods need information about the sign of the sensitivity of the unknown system. This paper proposes learning rules that do not require the information about that sign. These rules utilize a perturbation signal. Rules with the perturbation on an input of the unknown system and a rule with it on each weight of the neural network are presented. The usefulness of these learning rules is confirmed via some numerical simulations.

Oscillations in negative resistance oscillatory circuit containing periodically operating analog switch

Abstract: Some examples of the electronic circuit containing periodically operating switches are the switched-capacitor circuit, which also are circuits switching the passive elements. This paper considers the nonlinear circuit containing a switch as an example of the circuit containing the periodically switched active element. The circuit containing a nonlinear negative resistor with N-shaped voltage-current characteristic and a resonant circuit is considered. In this type of circuit, even if an oscillation is not self-excited, there arises an extraordinary phenomenon that an oscillation is produced for a certain range of the clock frequency when a switch is inserted between the nonlinear resistor and the resonant circuit and is operated periodically. This paper analyzes this phenomenon. It is verified experimentally that there arises a hard oscillation in the low- and high-frequency range of the clock. A theoretical analysis is attempted for this phenomenon. It is seen that even if a self-oscillation is not produced in the circuit containing a negative resistance, there can arise an oscillation by periodically operating a switch. This is interesting since it may lead to the effective use of the negative resistance.

A discrete logarithm problem over composite modulus

Abstract: Recently, many applications of integer theory to cryptographic techniques have been observed. The discrete logarithm problem is one such case. Usually, the discrete logarithm problem is the determination of the logarithm for the given arbitrary element with a prime number as the modulus. However, the discrete logarithm problem can also be considered with a composite number as the modulus. It is anticipated that the discrete logarithm problem with a composite number as the modulus is a difficult problem if the prime factors of the composite number, which is used as the modulus, are unknown. Then the problem can be applied to the cryptography. In the general discrete logarithm problem with a composite number as the modulus, it is not always true that an arbitrary element has a logarithm. From such a viewpoint, this paper shows that the exponent of an arbitrary element belonging to the irreducible residue class with a composite number as the modulus has a logarithm. Then the necessary condition in the application to the cryptographic technique is presented. Finally, as an application example of the technique proposed in this paper, a cryptographic technique based on the discrete logarithm problem with the composite number as the modulus is shown.

Error control technique for parallel combinatory spread spectrum communication system

Abstract: This paper discusses the application of the error control technique for parallel combinatory spread spectrum (PC-SS) communication system proposed previously by the authors. This paper considers the case where &-bit information is transmitted in the spreading sequences and considers the following two coding methods as suited to PC-SS systems: 1) to use 2k-ary Reed-Solomon code; and 2) to use the constant-weight code by Chung et al. in the transmitter, converting the data into the combinatory spreading sequences, and to suppress the error in the receiver by taking the double correlation. The bit-error rate performance is examined for the two methods and the effectiveness is discussed. It is shown as a result that both methods are useful in improving the bit-error rate of the PC-SS system. In the latter method, the number of spreading sequences needed per user is reduced to approximately one-fourth compared to the conventional PC-SS system with nearly the same bit-error rate.

A realization of real filters using complex resonators

Abstract: The synthesis of real filters using the complex coefficient filters is considered interesting in digital signal processing, since one can expect that the freedom in the design will be increased and the coefficient sensitivity will be decreased. In analog signal processing, on the other hand, there are few reports on the design of the filter from a similar viewpoint. This paper discusses the complex coefficient filter on the analog domain, which is obtained by shifting the frequency response of the lower-order real filter on the frequency axis, together with its application to synthesize real filters. First, the complex analog transfer function is introduced, which is obtained by shifting the frequency response of the real filter on the frequency axis. The elements for the complex analog signal processing are defined. Then, using those elements, the complex resonator is proposed. The proposed circuit can be considered as a special class of the biquad circuit, where the complex conjugate poles of the second-order section are specified. As a result of sensitivity analysis, the proposed circuit is shown to have the same or lower sensitivity as that of the biquad circuit. Another feature is that the circuit can be realized using the lossy integrators and can be used as the functional unit in the active filter to be operated at higher frequencies. Design examples using the operational amplifier and their experimental results are shown to verify the effectiveness of the proposed method.

A new cut for torsional mode quartz crystal resonators of tuning fork type

Abstract: This paper proposes and describes a new cut torsional quartz resonator which is designated “TT-Cut,” and clarifies its frequency characteristics, frequency temperature behavior, and electrical equivalent circuit parameters. First, in the analysis procedure, an equation of motion is derived from an energy method. Next, by solving the equation of motion under the boundary conditions of “free-free bar” or “clamped-free bar,” the frequency equations are derived as a function of thickness z0, width x0, and length y0. Furthermore, from the frequency equation a relationship of frequency constant (f. y0) versus thickness-to-width ratio Rzx (= z0/x0) and a relationship between thickness-to-width ratio Rzx and cut angles (ϕ, θ) where the first-order temperature coefficient α reaches zero are derived theoretically. As a result, numerous relationships where α reaches zero are found to exist between thickness-to-width ratio Rzx and cut angles (ϕ, θ). Especially, the second-order temperature coefficient β has a small value of -1.16 × 10−8/°C2 whose absolute value is approximately one-third of the well-known flexural mode quartz crystal resonator. The value of β then is-compared with the measured data of -1.29 × 10−8/°C2, so that both results are found to agree sufficiently well. Finally, series resistance R1 and a quality factor Q of a tuning-fork-type resonator are examined. Consequently, it is shown that a tuning-fork-type torsional quartz crystal resonator is obtained with a small R1 of 2.2 to 14.4 k° and a large Q value of 276, 000 to 378, 000 in frequency range of 385 to 444 kHz.

Floating‐electrode‐type SAW unidirectional transducers using leaky surface waves and their application to low‐loss filters

Abstract: To realize surface acoustic wave (SAW) filters with low-loss and wide bandwidth for mobile communications, a floating-electrode-type unidirectional transducer (FEUDT) using internal reflection is discussed. The proposed structure for FEUDT has an advantage of manufacturability and also for high-frequency performance exhibiting a second harmonic operation better than a fundamental mode. This paper describes both a theoretical and experimental result. A leaky surface acoustic wave (LSAW) of SH-wave type using 41 °YX LiNbO3 substrate, the velocity of which is much faster than that for a usual Rayleigh wave and has a large K2 is used. A second harmonic FEUDT suitable for this wave is obtained theoretically by using the Green function method. The result is in good agreement with experiment. An SH-type LSAW is more sensitive to a surface boundary condition of a substrate compared to the usual Rayleigh wave and thus the boundary condition for a low-loss filter is very important. This is discussed both theoretically and experimentally. It is found that an open grating is the best for a propagation path if one considers the mode conversion of LSAW excited by a transducer. A prototype filter has been fabricated. The insertion losses of 2.6 dB and 2.8 dB at the center frequency of 360 and 700 MHz, respectively, are obtained successfully.

Synchronized quasi-periodic oscillations in a ring of coupled oscillators with hard characteristics

Abstract: This paper considers properties of quasi-periodic oscillations in a ring of mutually coupled oscillators and investigates phenomena such that envelopes of wave-forms observed in the oscillators are synchronized dynamically. Several properties derived from analysis using a perturbation method are discussed, and the following results are obtained: It is necessary for the stability of double-mode oscillations that oscillators have hard characteristic nonlinearity; phase relations among envelopes depend on oscillatory mode combinations; and so on. It is shown that all quasi-periodic oscillations, whose stability is suggested by the theoretical analysis, are observed numerically in up to four-coupled oscillators. Moreover, the system parameter regions in which quasi-periodic oscillations exist are given for two-coupled oscillators and it is shown that an out-of-phase synchronization of envelopes can be explained by using the bifurcation theory of periodic oscillations.

Design of Two-Channel Perfect Reconstruction QMF

Abstract: This paper proposes a design method for the FIR two-channel perfect quadrature mirror filter (QMF) with the linear phase. The two-channel perfect QMF can be designed by Vetterli's method, where a system of equations representing the condition for the perfect reconstruction of the signal is solved. The filter designed by this method, however, does not, in general, have good frequency characteristics. This paper presents the design for the two-channel QMF with a perfect reconstruction and a good amplitude characteristic. The method is based on Vetterli's method, and a constraint to approximate the amplitude characteristic in the frequency domain is added to the condition of perfect reconstruction in time domain. Then Remez' algorithm is applied to the derived system of equations. The construction of the two-channel perfect QMF, when the coefficient is quantized, also is discussed. Furthermore, a method is shown in which the two-dimensional (2-D) perfect QMF is designed by applying the McClellan transformation to the obtained 1-D QMF. The condition for the McClellan transformation for the perfect reconstruction is derived.

A class of fixed‐point problems on graphs and iterative solution algorithms

Abstract: A family of well-known problems on graphs including the shortest-path problem and the data flow analysis problem can be formulated as a fixed-point problem. The lattice is used to represent the algebraic structure of information and the problem is formulated with fixed-point equations where unknown variables that label vertices of the graph take values over the lattice. Then a practical solution algorithm based on the iterative approach that solves the unified problem is given. When applied to the shortest-path problem, the algorithm is equivalent to the well-known potential method but its validity for the generally formulated problem is not trivial. The correctness and termination of the algorithm within a general framework is proved. Finally, the formulation is compared to other formulations and the most fundamental structure of the problem is discussed. The relation between the general algorithm and various existing methods for each specific domain are analyzed and it is shown that for the data flow problem, the general algorithm practically is improving existing iterative methods such as Kildall's and that of Hecht and Ullman.

Bifurcations of equilibria and periodic solutions in a nonlinear autonomous system with symmetry

Abstract: In the engineering and physical systems described by a lumped-constant system, sometimes a certain kind of symmetry is observed in the structure of the system or the nonlinear characteristics of the element. In such a system the symmetry is reflected on the state equation and the equation becomes invariant under the symmetrical transformation of the state variable. It may happen in the state equation with a symmetry that there exists an equilibrium point or a periodic solution, and the solution bifurcates into the solution without a symmetry when the system parameter changes. This phenomenon is called symmetry-breaking bifurcation. This paper discusses the symmetry concerning the equilibrium point and the periodic solution of the autonomous system and presents the condition for the symmetry-breaking bifurcation and the method to calculate the bifurcation parameters. It is pointed out that the symmetry-breaking bifurcation is, in general, a degenerate bifurcation and the bifurcation parameters cannot be determined by the ordinary method. It is shown that, by considering the symmetry, the calculation is made possible and is simplified.

Analysis and synthesis of continuous‐time hysteretic neural networks

Abstract: In this article the authors propose a continuous-time neural network which includes bipolar hysteretic elements. They then consider the problem of synthesis in order to satisfy the following conditions: I) the system has no oscillating solutions; II) any desired patterns are stored as stable output vectors; and III) the total number of false stable output vectors is made as small as possible. The authors then prove a sufficient condition for I) and the necessary and sufficient conditions for II). Based on these results, they propose a synthesis procedure which is also effective for III). The domain of attraction of stable outputs may be easily calculated using a fast algorithm using exact solutions. The efficiency of the procedure is confirmed through experimental results.

Nonlinear equivalent circuits of acoustic devices

Abstract: Mason's equivalent circuit is well known as a linear equivalent circuit for acoustic devices. By combining Mason's equivalent circuit with Smith's equivalent circuit of surface acoustic wave devices, it becomes a very effective tool for the physical interpretation of acoustic devices. If such equivalent circuit analysis can also be performed for the nonlinear problem, then comparatively simpler and accurate analysis can be obtained for almost all types of nonlinear problems. In this paper, equations are formulated to analyze the equivalent circuit of nonlinear-type acoustic devices. At first, Mason's equivalent circuit is extended to the nonlinear region for the basic circuits of a thin bar of length-extensional vibration and a broad plate of thickness-extensional vibrations. Next, this equivalent circuit is used to analyze the thickness-extensional vibration of Z-cut LiNbO3 and second harmonic generation at the resonance point is clarified. Finally, these nonlinear equivalent circuits of length-extensional vibration are applied to determine the nonlinear constants of PZT ceramics and the nonlinear constants of the equivalent circuit are clarified.

A method for two‐dimensional layout of semantic structure graphs

Abstract: A questionnaire containing multiple-choice questions is a representative method to investigate human behavior. Previously, Takeya proposed the semantic structure analysis (SS analysis) as an analytical means for data obtained by the forementioned method. A structural graph of the SS analysis is called an SS graph, and it is conceived that the SS graph is of the hierarchical structure when items are laid out taking the ordinate for the measurement as the statistic such as mean evaluation values. However, no argument has been made with the layout of the abscissa. With this in mind, an observation concerning the unsolved problem, i.e., a method for two-dimensional layout of the semantic structure graph, is given in this paper. To solve this problem, a concept of a zone is introduced from a relationship between the ordering coefficient and the factor load by means of the centroid method. Then a measure to compose the abscissa by means of the zone determination values is proposed. It is shown that not only can the relationship among the individual items be comprehended but also the meanings grasped as item groups together with the meanings among the item groups. Furthermore, by observing the linkage of the amount of information possessed by the individual items, especially of the effective category numbers and mean evaluation values, by means of a model and examples, the size of scattering of the evaluation values is explained explicitly by composing the abscissa by means of this effective category number. Thus, the relationship of items including the response pattern can be grasped.

Two‐dimensional adaptive state‐space filters using LMS method

Abstract: This paper considers the construction of two-dimensional (2-D) adaptive state-space filters using the least mean squares (LMS) method. The approach is based on the Roesser local state-space model. First, the relation between the coefficient sensitivities and the intermediate transfer functions is investigated. Then, after introducing new systems for generating the gradient vectors, an adaptive algorithm is developed using the LMS method. Next, a 2-D adaptive state-space filter with separable denominator is introduced to reduce the amount of computation in the adaptive process. Finally, a numerical example is given in which the 2-D adaptive state-space filters are used to design 2-D digital filters in the spatial domain.

A bayesian approach to an optimal ARQ number in data transmission

Abstract: The automatic repeat request (ARQ) system is one of the means to achieve a high reliability in the data transmission system. In this system the data are retransmitted for a certain number of times when an error is produced due to the disconnection, noise, or distortion in the data communication channel; thus, the correct transmission is achieved. However, when a correct transmission cannot be achieved due to the incorrect data format or a fault of the channel, it is necessary that the retransmission be terminated as soon as possible, examine the data format or channel state, or switch the channel to another. In such a case, the behavior of the system depends greatly on the upper-limit set for the number of repeat requests. At the present state, however, the upper limit for the number of repeat requests is determined empirically with little theoretical basis. This paper introduces the subjective probability from the viewpoint of the Bayesian theory for the probability that the data transmission is made physically impossible due to the fault of the channel or other factors. To set a reasonable value for the number of repeat requests, the expected cost for the data transmission is formulated and the optimal number of repeat requests to minimize the cost is investigated. By numerical examples, the features of the proposed method are discussed.

SAW resonators using epitaxially grown Al electrodes

Abstract: Stress migration (SM) has become a serious issue with the development of surface acoustic wave (SAW) devices for high-frequency application. For the first time, this paper discusses epitaxially grown Al electrode films as a countermeasure to SM. It also discusses a method of epitaxial growth of Al electrode films for an SAW resonator deposited onto quartz substrates. It is found that an epitaxially grown film has been fabricated under relatively moderate deposition conditions in vacuum evaporation. The orientation relation for this epitaxial growth is (311) «233»Al//(032)«100»SiO2. The SM lifetime for the SAW resonator thus obtained is found to be more than 2000 times longer and the allowable power value is improved by one order of magnitude more than that usually obtained for polycrystalline Al films with Cu. A discussion of the epitaxial growth mode and lifetime of electromigration also is presented.

Mobile communication systems and surface acoustic wave devices

Abstract: With the advent of a highly intelligent society, the role of mobile communication represented by the key words “anytime, anywhere, and with anybody” has become increasingly important. This paper describes mainly the mobile stations of the digital communication system in which the frequency-use efficiency is improved significantly, as well as of analog mobile communication system. Also described are the surface acoustic wave devices, especially the low insertion loss filters, which are expected to be the key devices of mobile communication for small and lightweight equipment.

Characteristics and the present status of SAW materials in Japanese industries

Abstract: Surface acoustic wave (SAW) devices have been used for filters, delay lines, resonators and oscillators. Since the characteristics of SAW devices are determined by the piezoelectric substrate, SAW devices must be selected for appropriate material. This paper examines first the characteristics of SAW propagating through several kinds of piezoelectric substrates. Next, using the reports from companies involved with SAW devices, the application and development of piezoelectric materials and the present status of SAW devices will be summarized. The future of SAW materials will also be described.

Performance evaluation of a minimum bit error decoding algorithm of convolutional codes and its application

Abstract: Basic decoding characteristics of a minimum bit error decoding (MBED), originally proposed by Bahl et al., is investigated. It is shown that MBED can predict the bit error rate of each decoded bit with good precision. Then MBED is applied to the convolutional/Reed-Solomon (RS) concatenated coding scheme. The outer RS codes are decoded by an erasure decoding using the symbol erasure information provided from the MBED results of inner convolutional codes. Simulation results show that the overall bit error rate is reduced one-half to one-third more than the conventional nonerasure decoding.

Delta function model analysis of SSBW spurious responses in SAW devices

Abstract: This paper considers the characterization of surface skimming waves (SSBW) by two newly defined parameters, i.e., effective electromechanical coupling factor and critical length. The parameters are estimated easily by the effective permittivity and are directly applicable to the delta function model analysis. Experiments on a TV-IF SAW filter agreed well with the analysis. In addition, these parameters for SO2/36° KY-LiTaO3 structure were estimated. It is shown both theoretically and experimentally that the SSBW responses can be suppressed by depositing SiO2 with appropriate thickness.