Error correcting codes are divided into two types, i.e., block codes and convolutional codes. In this paper, the error correcting codes of both types for improving the reliabilities on random-error channels, burst-error channels and compound-error channels are briefly surveyed and then some aspects of the wide applicabilities of error correcting codes are discussed.

The TAT system is an efficient analog bandwidth compression scheme for the HDTV. It compresses the bandwidth by reducing the pixels selectively from the non-detailed portions of the picture. The bandwidth can be reduced to half or less, while keeping high resolution in the detailed portions. In this paper, the basic concept, key techniques and some recent results of the TAT system are presented. First, it must be emphasized that the TAT system is a hybrid system of fixed subsampling and variable subsampling. The basic pixels obtained by the fixed subsampling transmit the basic structure of the picture. The additional pixels obtained by the variable subsampling transmit the details of the picture necessary for the HDTV. The concept of complementary subsampling is proposed and a restoration scheme of the removed high frequency component of the subsampled pixels is derived. Applying the concept to the TAT system, simultaneous transmission of an HDTV picture and an aliasing-free subsampled picture compatible with the current TV becomes possible. An efficient mode decision algorithm which determines the location of the additional pixels is developed. Time-varying fluctuation and partial degradation of resolution were observed in pictures having rich details. They are suppressed by introducing the control of mode transition and the interframe interpolation mode into the mode decision.

In the photon communication system, it is known that the communication channel can be modeled by an asymmetric channel (Z-channel) in which symbol 0" does not change to symbol 1", but 1" changes to 0". As a typical error correcting code for Z-channel, there is a Constantin-Rao (CR) code which can correct a 10 type transition error (an asymmetric error). In order to derive the maximum error correcting capability from the code, it is desirable to devise an efficient maximum likelihood decoding (MLD) algorithm for CR codes. This paper presents an implementation of MLD for the CR code in Z-channel. Moreover, some methods to reduce the decoding complexity are proposed. Computer simulation reveals that the proposed decoding algorithm gives better performance than the conventional decoding.

This paper proposes a lossless coding method for the compression of computer files of floating-point or fixed-precision numbers. The method is adaptive in the sense that it requires no prior knowledge about input data. Although it is quite simple and all that needed is the incremental parsing technique by Ziv and Lempel, the proposed method compresses well any i.i.d. sequence of numerical data generated from a source with a smooth distribution. In order to evaluate the performance and the convergence property, a bitwise equivalent model is introduced, which combines the Ziv-Lemple-type data compression methods with the probabilistic framework. The model shows that, for any sufficiently long i.i.d. sequence, the proposed method attains the entropy with only a loss of 0.36 bits per word or so. Computer-simulation results are also presented in support of this evaluation.

In this paper, the criterion for evaluating inductive inference is considered from the information theoretical concept, especially from the view points of source coding and decision theory. Although the finite behavior of the inductive inference methods is important in the application field, there is no theoretical criterion for evaluating hypotheses at a finite stage of process. In the previous paper, we have defined an amount of semantic information included in well-formed formulas (wff) and denoted an analogy between inference and source coding. Inductive inference is regarded as source encoding, assuming that observed facts are compressed into a hypothesis similar to the way a source sequence is compressed into a codeword. By using the above definition, we can apply the criterion of source coding especially Minimum Description Length (MDL) to inductive inference. Therefore, the description length for representing a hypothesis is suitable for the criterion for evaluating a hypothesis inference at the finite stage of the inductive inference process. Moreover, by using the relation between the MDL criterion and Bayes risk, inductive inference can be interpreted with Bayes decision theory. The algorithm for the inductive inference of Horn clause is shown as an application of the proposed criterion. In the algorithm, the search space of hypotheses is restricted by using a refinement relation for increasing efficiency.

All distributions in the sense of Schwartz are considered as signals and their Fourier transforms defined by Gel'fand and Shilov as frequency spectra. The necessary and sufficient condition for a signal to be bandlimited is that it is an entire function of exponential type. This follows from the Gel'fand and Shilov's theorem which states that any distribution whose Fourier transform has a compact support reduces to an entire function of exponential type and vice verse. But their original proof was incomplete; their definition of 'compact support' was insufficient. Here, a reasonable definition of 'compact support' is introduced and a rigorous proof of their theorem is presented. Once the theorem is established, many applications in various fields will be possible. Above all the so-called sampling theorem for bandlimited signal becomes the interpolation/extrapolation for entire function of exponential type. As it is shown from the Gel'fand and Shilov's theorem with the completion presented in this paper that the frequency hand of a bandlimited signal is a point set on the complex plane congruent with the complement of the existence domain of its Borel transform, an explicit interpolation/extrapolation formula with sampling points on the negative time axis can be constructed.

It is well-known that the bit error rate (BER) of digital transmission through a mobile/portable communication channel is strongly dependent on the multipath delay spread. In this paper, we propose an antenna pattern diversity reception system with a new selection strategy based on the measurement of cross-channel-interference which has been confirmed to be a linear function of the multipath rms delay spread assuming BPSK as an example. The coherence bandwidth and BER performances using such a system are studied theoretically and considerable improvement is observed. In addition, the field experiment using a four-direction antenna in 400 MHz band was made to measure error patterns for an individual antenna pattern, and the proposed system was shown to work well even in a real urban area based on the measured data by computer simulation.

Recording and reproducing of quadrature amplitude-modulated (QAM) signals on magnetic recording channel of VCR is studied. While the frequency characteristics of QAM signal is nearly matched to that of the magnetic recording channel, the linearization of magnetic transmission channel associated with odd-order nonlinear transfer function is considered to be essential to record QAM signals, and the employment of bias recording method is experimented for this purpose. Simple 16 QAM and coded 32 QAM signals are recorded on an experimental VCR. It is found that the SNR required by coded 32 QAM signal is lower than that by 16 QAM signal for the channel SNR higher than 14 dB. Coded 32 QAM signals of 20 Mbps data rate are recorded and reproduced at a scanning speed of 3.5 m/s using a head of 50 µm track width, and the word error rate less than 10^-5 is successfully accomplished.

In this paper, a new restoration method for the X-ray images with optical blurs and quantum mottles is proposed by considering the physical formation process of X-ray images. More specifically, the optical blurs are first deterministically cleared away by using the transfer characteristic of the laser scanning, the characteristic of the radiographic screen-film system, the logarithmic transformation of the optical density and a digital inverse filter based on the point spread function. Next, as a restoration method for remaining quantum mottles, a wide sense digital filter of a stochastic type using the statistical properties of quantum mottles is newly derived on the basis of a Bayes' theorem matched to the recursive image processing. Finally, in order to confirm the effectiveness of the proposed method, it is applied to one of the actual medical images.

The linearity of the drain-current versus drain-to-source voltage characteristics of MOSFETs used in switched resistor (SR) circuits is improved by adding a drain-to-gate feedback. When a feedback factor is larger than 0.5, an equivalent resistor with low distortion and wide voltage range is realized.

A new type of wide beamwidth antenna is proposed for mobile satellite communication systems. The microstrip crossed slot antenna consisting of four shorted quarter wave elements is one of the antenna elements of wide beamwidth. To widen the beamwidth still further, the antenna installed on a pyramidal ground plane is presented in this letter. The radiation pattern of this antenna is also measured and discussed.

Fatigue measurement of structural materials under dynamic stress allows the prediction and early detection of potential problems, but under actual working conditions a signal by an instrumentation with a strain-gage is inaccurate because of noise. If the signal and the noise are separated in the frequency domain, the noise can be reduced. Kalman has presented a method with an accurate mathematical model and noise properties for the countermeasure of random noise. By acquiring of the reference noise, the noise is canceled even if the signal and noise can not be separated in the frequency domain. We have developed a method of noise cancellation in an instrumentation; using a sensor, a sensordummy and a simple circuit with an analog switch. This method does not need the acquiring of the reference noise for noise canceling even if the signal and noise can not be separated in the frequency domain. An analog switch, alternative switching between a sensor and a sensordummy, provided two signals to the transmission line. One signal had the signal with noise, and the other signal only had the noise. And we have subtracted the signal which had only noise from the signal which had noise plus the signal. Data processing of the two signals, based on Eqs. (3) and (4) makes a reliable signal without noise on the transmission line. In this case, the noise" which is canceled using this method is the frequency which is a quarter frequency under the frequency of the switching frequency. The accuracy of this new method has been verified by experiments of a signal not only with sinusoidal noises but also with other noises.

This paper describes the postdetection diversity effects on 2-bit differentially detected GMSK with cochannel interference in the slow and fast Rayleigh fading channel. In the analysis, both the intersymbol interference of the baseband waveform and the cochannel interference are taken into consideration. It is shown that the BER performance of GMSK can be improved by making use of the selection diversity and the maximal ratio combining diversity.

Isolation properties of mono-sectional optical isolators consisting of magnetooptic guide layers and substrates have been theoretically investigated by using hybrid modes. The magnetization of its mode converter uniformly tilts by an elevation angle θ from the film plane in the plane transverse to the light propagation direction. The guide layer thickness is chosen to be near the cut-off so that the longitudinal electric field should be large and the mode conversions through the first and second order magnetooptic effects should be the same each other. Since these mode conversions cancel and add up each other in the forward and backward directions, respectively, the unidirectional mode conversion can be realized. By using the substrate which has the opposite first order magnetooptic effect to that of the guide layer, the propagation length of the mode converter can be reduced. When the refractive index, optical birefringence, the first and the second order magnetooptic effects of the guide layer are 2.18, 2.510^-3, -2.7910^-3 and -5.5810^-4, and those of the substrate are 2.137, 2.510^-3, 3.8510^-4 and -7.7010^-5 at the wavelength of 1.152µm, the isolation ratio of 30 dB can be achieved at the propagation length of 4.68 mm and the film thickness of W=0.975µm by tilting the magnetization by the elevation angle of θ=79.5 for the refractive index of the top layer of 1.50.

This paper proposes a new type of evanescent-mode waveguide filters consisting of two parallel cutoff waveguide paths, in which a number of swelled portions are provided as resonators. One of two paths (the subsidiary path), mechanically connected to the main path in parallel, achieves the negative coupling to exhibit an elliptic-like feature. This type of filters includes a number of complicated waveguide-junction discontinuities. They are analized accurately by the full-wave analytical method based on the mode-matching method. After deriving the generalized equivalent network, the main-path structure is designed to exhibit the specified passband response by using its approximated network. The specified overall characteristic is then synthesized by a computer-aided design method by using an equivalent network without approximations. Measurements on the filters modeled in both X- and U-bands show excellent agreement with the designed characteristics, and prove the feasibility of two-path cutoff-waveguides for filter applications in the microwave and millimeter-wave regions.

A new 90-mm magneto-optical disk subsystem has been developed. It features a rewritable 100-Mbyte disk, a half-height drive and a highly reliable controller. Its effective data transfer rate is 330 kbytes/second, its average access time is 100 ms, and its data error rate is less than 10^-12 events/bit. This subsystem uses a novel design method based on the media's physical characteristics. This method employs a statistical model to describe error occurrences. It considers the dimensional characteristics of media defects by analyzing the reproduced signal. Using this design method, the error control strategy, which consists of a defect management scheme and an error-correcting procedure, is determined. Furthermore, this subsystem uses a new physical media format called Discrete Block Format. Optical read-only madia compatibility can be obtained quite easily with this format. The subsystem can be used with personal computers, communication terminals and measuring instruments.

A term-rewriting system (for short, TRS) is said to be a right-ground system if no variable occurs on the right-hand side of a rewrite rule, and a left-linear system if no variable occurs more than once on the left-hand side of a rewrite rule. This paper shows that the word or equivalence problem is undecidable for right-ground TRS's even if they are finite-terminating (i.e., noetherian). Next, we show that the word problem is decidable for left-linear and right-ground TRS's and there exists an efficient algorithm solving this problem. These results show a gap between right-ground TRS's and left-linear and right-ground TRS's.

Using number theoretic properties we show the following results: For any k2, the language family generated by {a^kn|n in N}{ε} with trio and intersection operations contains {aⁿbⁿ|n in N}. If k is a multiple of 3 or 4, then the language family generated by {a^nk|n in N} with trio and intersection operations contains {aⁿbⁿ|n in N}. These language families are commutative.

In recent years, various formal specification languages have been proposed for validity check of specifications and automatic program generation. However, they are rigorously constructed to be processed by machines and difficult to use. On the other hand, informal languages of conventional notations have been widely used in practice for program specifications but inconvenient to automatic processing by machines. This paper presents a method of transforming between informal specifications and formal specifications. A kind of limited English is introduced as an informal description language of specifications. Specifications written in the limited English are parsed based on a case grammar and transformed into the formal specifications. The formal specifications are also used for various automatic processing such as refinement and program generation. The refined formal specifications can be transformed into the limited English expressions which can be used as comments by the reverse process of the above transformation.