This paper proposes an intrasystem interference cancellation technique for spread spectrum multiple access (SSMA) systems to improve the simultaneous operation performance. Theoretical analysis of its performance and experimental results are described. Although thermal noise and interference from other communication systems can not be recovered at the receiver, it is possible to reproduce interchannel interference signals within an SSMA system, because the spreading codes are known to the receiver. The reproduced interference signals are subtracted from the received signal to cancel the interference signals. An interference signal recovery circuit comprises a conventional SSMA demodulator and a re-spread modulator. The interchannel interference power is reduced by a factor of (n-1)/G as compared with a conventional SSMA demodulator where, G is the process gain and n is the number of simultaneously operating channels. Factors degrading interference cancellation performance are carrier phase error, SS code phase error, delay time error, amplitude variation and waveform degradation due to bandwidth limitation. Theoretical considerations and experimental results on the quantitative effect of these factors are presented.

An optical fiber-coupled type laser has been optimized by taking account of field disturbance on a coupling aperture mirror, and this has been examined by using conventional CO2 laser. Solving the eigen equations for a quasi-hemispherical resonator with a coupling aperture to find the field distribution on the plane mirror with an aperture, its effective transmittance is analytically evaluated as a function of normalized aperture ξ by the mirror size and is well approximated by the power series expansion up to the fourth order for various mirror Fresnel numbers N and the g parameter of resonator. Using this obtained and typical laser parameters for the experimental set to be used, the coupling aperture is optimized to yield the maximum power. As a result, the optimum aperture becomes a minimum at a specific g2 parameter of the concave mirror, i.e. g20.73, implying that the optimum configuration corresponds to be slightly off from a pure hemispherical setting. These theoretical estimates of the output power vs aperture have been compared with the experimental results obtained for a CO2 laser, being in qualitative agreements with each other in overall characteristics. By this optimization the maximum output power 6.0 W was extracted from the aperture of 2.4 mm.

This paper presents the derivation of the detection performance of a receiver with square-law postdetection integrator for a Rayleigh correlated fluctuating target in a correlated Gaussian clutter plus white noise environment. The analytic expressions describing the detectability as function of signal-to-noise power ratio (SNR), clutter-to-noise power ratio (CNR), number of pulses integrated and the correlation matrices of both clutter plus noise and signal fluctuation are obtained. The numerical results for a first order Markov exponentially correlation model of clutter under fully correlated and partially correlated as well as independent fluctuating target assumptions are given in a set of plots.

An algorithm is proposed to obtain minimum tree representation of a chordal graph on an algorithm obtained in Ref.(5), and we prove that any tree obtained by this algorithm is optimal for two kinds of optimization problems, that is 1) to obtain a clique tree with the minimum sum of weights on edges and 2) to obtain a clique tree with the minimum sum of weights of subtrees corresponding to vertices.

Centering effect in single mode multi-fiber connectors in investigated precisely by measuring connector loss with various clearances. By comparing the measured loss with the theoretical estimate, the range of clearance over which the centering effect holds is determined.

A short birefringent launching fiber is proposed to reduce the fluctuation of backscattering from single-mode fibers. The fluctuation is due to polarization-sensitive measurements. It is analyzed that the polarization direction of linearly polarized inputted light is required to make an angle of 27.4 with respect to the principal axes of the birefringent launching fiber. It is also clarified that degree of coherence should vanish at the group delay of τ and 2 τ where τ is the group delay difference of the orthogonal polarization modes in the birefringent launching fiber. Experiments reveal that the birefringent launching fiber of only 3-m length makes it possible to reduce the backscattered power fluctuation to less than 0.05 dB. Required properties of laser diodes are discussed by considering the coherency of the laser diodes with multi-longitudinal modes.

This paper presents the realization of a X.25 software which can be used in three different contexts: DTE/DTE interface, DTE/DCE interface and local area networks (LAN). The software is implemented according to a hierarchical environment-dependent scheme, in order to increase its portability. The combination of the three interfaces into the same software permits to optimize the code size and to use it in designing a X.25 gateway.

An asynchronous version is proposed for the waveform relaxation-Newton method. A sufficient condition is given for the proposed algorithm to converge.

A general analysis of the combined effects of an arbitrary nonlinearity followed by a coherent detector and an envelope detector on SNR is performed. Our analysis leads to the expression of the improvement factor which is applicable to noise with an arbitrary amplitude distribution. It is found that output SNR can be improved by combining these two detectors appropriately.

The oscillating linewidth of the semiconductor injection lasers is broadened by the mode competition effect which tends to be induced by the optical feedback. The broadening phenomena are theoretically analyzed by taking into account both interactions among lasing modes and fluctuations caused by the spontaneous emission. Operating conditions to avoid these phenomena are also given. For example in case of BH type AlGaAs laser, the re-injection ratio of going into the laser cavity to the emitted light should be less than 10-7 to keep the stable single mode operation without the hopping phenomena.

The influence of impurities in performs and of the drawing condition on the hydrogen-induced loss increase in the OH absorption band and the radiation-induced loss increase is investigated. The loss increase is much larger in fibers contaminated by sodium. Moreover, the loss increase in fibers with natural SiO2 clad, which is contaminated by alkali ions, increases with increasing maximum temperature in the drawing furnace and with decreasing drawing speed. By thermodynamically analyzing these results, the origin of the loss increase is identified as follows:(1) The OH loss increase and the radiation-induced loss increase are ascribed to the same origin.(2) The structural reorientation from GeO4 tetrahedrons to GeO6 groups thermally occurs in the drawing process, when the perform is contaminated by alkali ions.(3) The loss increase is induced through the reaction of H2 and radiation with GeO6 groups.

Nonreciprocal mode conversion properties and isolation ratios have been experimentally investigated for a mono-sectional optical isolator. The unidirectional mode converter of the mono-sectional optical isolator consists of a Bi-substituted YIG single crystal film sputtered on a GGG substrate. The mode converter is uniformly magnetized at angles with respect to both the film normal and the light propagation direction so that the Faraday and the Cotton-Mouton effects simultaneously occur in one mode converter. At the propagation length of 2.4 mm, the maximum isolation ratio of 13.0 dB has been obtained for the magnetic field of 100.2 Oe which tilts by 6.4and 38.8from the film normal and the plane transverse to the light propagation direction, respectively. In order to achieve large isolation, it is important to control the longitudinal magnetic field component. The insertion loss of the mode converter has been estimated to be 5.5 dB.

The literature on codes for write-once memories (WOM) has been growing steadily in recent years. In this paper, a new method for constructing womcodes is presented. On the basis of the numerical analysis and the computer simulations related to the performance of the proposed womcodes, we show that the codes have the rates higher than any other known womcodes. The upper bounds on the rates of the codes are obtained as well. We also show that, by combining the proposed womcodes with other womcodes known previously, we can significantly improve the utilization efficiency of WOM.

Mode excitation of multimode optical fibers by using a computer generated hologram (CGH) is studied. The excellent field pattern of the multiplex mode, which is transmitted through the fiber, is observed in the experiment.

A parallel sorting is actually executed on the multiprocessor system to estimate the real performance. The sorting algorithm consists of merging and exchanging data between the nearest neighbors. The system performance of parallel sorting is measured experimentally. It is proved that the parallel sorting algorithm is really effective for a multiprocessor system with the limited number of processors.

A zero-knowledge proof system for the discrete logarithm problem is proposed. The idea can be applied to homomorphic one-way functions in general. This is a method to prove that one really knows a discrete logarithm without revealing any information about the logarithm itself. The algorithms are probabilistic ones, performed by two users: the prover and the verifier. The prover proves to the verifier that it knows a discrete logarithm. The prover may cheat the verifier with the probability at most 1/2, but this probability can be decreased by repeating the procedure several times.

A 12-GHz-band GaAs monolithic dual-gate FET mixer using a novel circuit configuration has been demonstrated. Adoption of a negative feedback circuit has reduced the output impedance of the mixing dual-gate FET down to 330 Ω, which is approximately one fourth that of conventional dual-gate FET mixers, resulting in good matching to the next state. An experimental MMIC mixer, which included an IF buffer amplifier, exhibited a 3.4-4.2-dB conversion gain with a 11.3-11.6-dB SSB noise figure in the 11.7-12.2-GHz RF band.

This paper describes a newly-developed 4 GHz 135 Mbps 256 QAM system with a rolloff factor of 20%, which can attain a spectrum efficiency of 6.75 bps/Hz. The key techniques are theoretically investigated to realize this system. It was predicted theoretically that the simultaneous incorporation of 7-tap transversal equalizers (TEQL) and a recursive slope equalizer (SEQL) would be required as countermeasure for multipath fading. The 256 QAM system was designed considering the results of the theoretical investigation. Excellent BER performance was obtained with the aid of forward error correction and pilot carrier injection. Since remarkable improvement in the signature was obtained by the simultaneous user of TEQL and SEQL, the 256 QAM system with a very low rolloff factor is promising.

In this paper, a new method for radical extraction of handritten Chinese characters is proposed. This method, called Background Thinning (BT) method consists of three processing steps: dividing by projection, dividing by background thinning and dividing by window extraction. The BT method is considered to help solving the problems of the radical extraction in our OCR (Optical Character Reader) system, which can find an optimum cursive dividing-path to divide a character into radicals. If there is no joinning strokes between two radicals, a continuous dividing-path can be found, and the character can be divided into radicals by means of this cursive dividing-path. If there is some joinning strokes between two radicals, the dividing-path is discontinuous and a window is designed to point them out. By analyzing the joinning strokes in this window (natural or unnatural connection), a divisible character with unnatural connecting strokes can be divided into radicals by connecting the discontinuous dividing-path in this window. The experiment was conducted on the database ETL8 (produced by Electrotechnical laboratory in Japan), which consists of 881 Chinese characters and 160 variations for each character. We have used 351 Chinese characters in the ETL8 as test data and the experimental results prove that the method is useful.

Sea clutter was measured using an X-band shipboard radar of horizontal polarization, pulse with 250 ns, azimuth beamwidth with 1.0 and grazing angles between 4.2 and 13.4. It is shown that sea clutter amplitude statistics obey a log-normal distribution or a Weibull distribution for different azimuth sectors.