Abstract: The network and each user i share an encryption algorithm EK.sub.i () using his authentication key K.sub.i as a cipher key, its inverse function EK.sub.i.sup.-1 (), a specific function F() and its inverse function F.sup.-1 (), and a function G(). The network calculates C.sub.1 =EK.sub.i (F(r.sub.n, r.sub.u)), using a random number r.sub.n generated by the user and a random number by the network, and sends it to the user. The user calculates (d.sub.1, d.sub.2)=F.sup.-1 (EK.sub.i.sup.-1 (C.sub.1)) and, if d.sub.1 =r.sub.n, judges the network to be an authorized one. The user generates a random number r.sub.c and sends C.sub.2 =EK.sub.i (F(d.sub.2, r.sub.c)) to the network. The network calculates (d.sub.3, d.sub.4)=F.sup.-1 (EK.sub.i.sup.-1 (C.sub.2)) and, if d.sub.3 =r.sub.u, judges the user to be an authorized one.

Abstract: The non-geosynchronous orbiting satellites each transmit identification information given to each of spot beams irradiated from them. A mobile terminal, when registering its location, receives the spot beam identification information at some moments in time with the predetermined time interval. Then, the mobile terminal transmits the received spot beam identification information and each of their reception time together with the terminal identification information assigned to the mobile terminal. On the basis of an overlapped area of spot beam coverage areas at time when each of identification information is received by the terminal, a terrestrial network estimates and registers the latest location of the mobile terminal.

Abstract: At the time of receiving a repeater supervisory signal superimposed on or combined by wavelength multiplexing with a main optical signal in an optical amplifier repeater system, the received optical signal is subjected to a photoelectric conversion by a photodetector and then branched into two electric signals, the one of which is subjected to equalizing amplification, timing extraction and discrimination and regeneration to extract only the main signal component. The main signal component thus extracted and the main signal contained in the other electric signal, which is not regenerated, are respectively subjected to required equalization, delay adjustment and amplitude adjustment so that they match with one another in waveform, phase and amplitude. In addition, the amplitude adjustment of the main signal is automatically controlled. By differentially combining these signals to remove only the main signal component to minimize its residual value, thereby extracting the supervisory signal to be obtained.

Abstract: Through utilization of a transportable earth station capable of communicating with both of a mobile satellite communication system and a terrestrial based mobile communication system and a portable terminal which is capable of radio communication with the transportable earth station and used in the terrestrial based mobile communication system, it is possible to communicate with both of the terrestrial based mobile communication system and the mobile satellite communication system by only one portable terminal in a wide variety of communication environments.

Abstract: An optical transmission system is disclosed, in which the transmission of the optical soliton pulses is controlled by controlling the wavelength dispersion of the optical fiber transmission line for each long section including a plurality of optical amplifier repeaters. In this case,the first sections having an average value of the wavelength dispersion larger than the dispersion value meeting with the soliton condition and the second sections having an average value of the wavelength dispersion smaller than the dispersion value meeting with the soliton condition are alternatively allocated in the optical fiber transmission line, so that the average value of the wavelength dispersion of the entire length of the optical fiber transmission line assumes a positive value.

Abstract: A demodulator receiving as input signal a sum of a plurality of spread spectrum signals is disclosed. The demodulator comprises means for obtaining a correlation between a spreading code assigned to each of spread spectrum signals contained in the input signal and the input signal for each spread spectrum signal symbol and making the correlation thus obtained to be a 0-th detected correlation, a 1-st interference canceller stage for receiving as inputs the input signal and the 0-th detected correlation and outputting 1-st residual error signal, 1-st detected correlation and sum of the 0-th and 1-st detected correlations, and a plurality of interference canceller stages operable similarly to the 1-st interference canceller stage by receiving as input the output signal of the preceding interference canceller stage.

Abstract: A selection diversity system using a decision feedback equalizer which has excellent tracking ability performance and equalization ability performance for frequency selective fading and a diversity effect against Rayleight fading. In a selection diversity system using a decision feedback equalizer, a decision data symbol of the equalizer output of a branch in which an average estimation error over a plurality of symbols is minimum is selected and combined, and the selected decision data symbol is used to recalculate the estimation error of every decision feedback equalizer and the tap gain coefficient of the decision feedback equalizer is updated using the recalculated estimation error, thereby overcoming the step out by the integration of the estimation error and the random selection error which is caused by the selective combined diversity system.

Abstract: An optical short pulse generating device is disclosed, in which semiconductor laser light of a fixed intensity is launched into a first semiconductor electroabsorption optical modulator which is driven by a 0V or forward bias voltage and a sinusoidal voltage, and the output light from the first optical modulator is launched into a second electroabsorption optical modulator to which is applied a bias voltage and a sinusoidal voltage having delayed from the said sinusoidal voltage for a period of time corresponding to the phase reversal thereof, whereby it is possible to generate optical short pulses of a repetition frequency twice higher than the oscillation frequency of a sinusoidal voltage generator.

Abstract: A method which permits the growth of high-quality crystals of n-type II-VI compound semiconductors containing sulfur, by suppressing the reaction of a group III or VII element as a dopant with a group II material at low temperature. A raw material gas containing an organometallic material of the group III or organic material of the group VII is premixed with a raw material gas containing organic sulfur material, then the premixture is mixed with a raw material gas containing an organometallic material of the group II, and the mixture is used to grow a crystal of an n-type II-VI compound semiconductor on a semiconductor substrate by a metal organic vapor phase epitaxial growth method.

Abstract: A coder with a motion estimation system, which comprises a same parity field motion estimator, a near field motion estimator, an inter-field interpolated motion estimator, a comparator for selecting the smallest one of prediction errors E1 to E3 output from the respective motion estimators, and a selector for selectively outputting a motion vector from the motion estimator providing the smallest prediction error.

Abstract: A chromatic dispersion measuring method and apparatus are disclosed which permit highly accurate measurements of the wavelength dispersion characteristic of an optical transmission such as an optical fiber or an optical amplifier repeater system. Measurements are made on the propagation time of a first optical signal of a fixed wavelength through an optical transmission line to be measured and the propagation time through the same optical transmission line of a second optical signal whose wavelength can be arbitrarily set over the measuring wavelength band. By obtaining a difference between the both propagation times, it is possible to obtain only a change in the propagation time of each signal which is caused by a change in the wavelength of the second optical signal. That is, the elongation or shrinkage of the optical fiber has an equal influence on both of the first optical signal and the second optical signal, and hence does not induce an error in the detection of the above-said time difference.

Abstract: To perform waveform shaping, retiming and amplification of the transmitted pulse signal of a binary PCM fiber optic communication employing an optical pulse signal which has a pulse duty factor within 1 with respect to a time slot, an optical waveform shaping device is proposed in which the optical pulse signal is branched by an optical branch circuit into two optical signals. The one transmitted optical signal passes through a photodetector, a band-pass filter for extracting the fundamental frequency component of the signal, an amplifier and a delay circuit, so that the signal is converted to a sinusoidal voltage synchronized with the optical pulse signal. The other optical signal passes through a semiconductor electrical absorption type optical modulator which is driven by the sinusoidal voltage and a DC voltage, so that the width of a gate waveform is changed by controlling the amplitude of the sinusoidal voltage and the DC voltage.

Abstract: The short optical pulse generator is provided with a semiconductor laser which oscillates continuously at a single wavelength, a semiconductor electro-absorption type optical modulator which performs the intensity modulation of the output light from the laser, and a sinusoidal voltage generator and a DC voltage generator for driving the electro-absorption type optical modulator. A DC voltage is applied to the electro-absorption type optical modulator so that the output light from the laser is sufficiently extinguished. By applying a sinusoidal voltage to the optical modulator, short optical pulses are generated.

Abstract: A multiple quantum well structure which permits substantially uniform injection of carriers from the outside into respective quantum well layers of the multiple quantum well and a semiconductor device employing such a multiple quantum well structure. A multiple quantum well structure is formed by laminating at least two pairs of quantum well layers each having a thickness substantially equal to the de Broglie's wave-length of electrons and barrier layers of an energy gap greater than that of the quantum well layers, and the multiple quantum well structure is doped with at least one of p-type and n-type impurities in a manner to slope the energy band of the entire multiple quantum well structure so that carriers injected thereinto are distributed uniformly throughout it.

Abstract: An optical frequency multiplex carrier control system which permits high-accuracy, high-speed stabilization control of the frequency of an optical signal. Based on the fact that the time waveform of the output signal from scanning type Fabry-Perot which receives the output optical signal from an optical frequency multiplexer is composed of pulse signals corresponding to an optical frequency standard and spectrum multiplex carriers of the output optical signal, the time intervals between the pulse corresponding to the optical frequency standard and pulses corresponding to the spectra of a scanning signal and each multiplexed carrier are measured by a counter having a high-accuracy clock, and variations in the optical frequency scanning region of the scanning type Fabry-Perot and in each carrier frequency with respect to the optical frequency standard are detected by hardware, with high accuracy, as variations in the pulse intervals, thereby stabilizing the frequencies of the multiplexed optical carriers.

Abstract: For decoding compressed digital image data of source image, end-of-block (EOB) codes appearing in entropy coded data are utilized to detect a portion of "0" elements in a frequency range coefficient matrix. An inverse orthogonal transform process is fully or partly omitted according to the "0" coefficient distribution.

Abstract: An optical modulator in which waveguide regions are disposed at opposite ends of a modulation region to reduce the capacitance of the device and prevent pn junctions from exposure to air. On an n-side electrode there are laminated a substrate, an n-type clad layer and an optical modulation waveguide layer. A modulation region lies at the center of the optical modulation waveguide layer along the direction of travel of light, and two waveguide regions are disposed at opposite ends of the modulation region, respectively. On the optical modulation waveguide layer which constitutes the modulation region there are laminated a non-doped layer, a p-type clad layer and a p-side electrode, and a semi-insulating semiconductor is formed on the optical modulation waveguide layer which forms the two waveguide regions.

Abstract: A high-output, single fundamental transverse mode solid state laser is disclosed which uses a semiconductor laser array as an excitation light source. The solid state laser comprises: a laser element which includes a core containing an element added as a laser medium, a cladding containing no such laser medium element, and reflecting mirrors coated over the cladding surface for repeatedly reflecting incident excitation light so that it may repeatedly pass through the core; an excitation light source formed by semi-conductor laser or light emitting diode array; means for guiding the excitation light from the excitation light source to one side of the laser element for incidence thereto; and a resonator for the oscillation of the solid state laser.

Abstract: An original grayscale image or color image to be coded is processed by a bi-level image mingled still image coding system to produce a differential image. The original image and the differential image are compared for each pixel block. Only those of the pixel blocks for which the bi-level image mingled still image coding system will be more efficient than a natural image coding system are encoded by the bi-level image mingled still image coding system, and the other pixel blocks are encoded by the natural image coding system. The coding method of the present invention is directed to a grayscale or color image containing an area where pixel values undergo an abrupt change, such as an edge of a letter, or a document with multi-color and natural color images intermingled therein. The method of the present invention obtains a less deteriorated coded image even from an image in which the edge area is very blunt, and moreover, the invention permits high efficiency coding.

Abstract: A communication network and its user i has a device for implementing a common key cryptosystem, an identifier of the user i represented by ID.sub.i which is made public in the network, an authentication key of a user i represented by S.sub.i is known only to the network and the user i and these identifiers and authentication keys of all the users are stored in a database of the network. Data for authentication and encrypted data of a cipher key for the subsequent privacy communication are sent from the network to the user, the user presents his identifier (ID) to the network, after which up to three interactions take place between the network and the user to perform the required authentications and distribution of the cipher key.