Abstract: A semiconductor optical element comprises a semiconductor substrate, a waveguide, an active layer and a clad layer mounted on said substrate; said active layer comprising first region and second region coupled optically with each other, and having opposite signs of .alpha. parameters with each other, where said parameter is ratio of change of refractive index to change of gain following change of carrier density; a first electrode common to all regions attached on one side of said substrate; and second electrodes for each region attached on the other side of said substrate. The invention is used for an AM modulation laser, or an FM modulation laser.

Abstract: An X.25 protocol apparatus can communicate with another X.25 apparatus or a X.32 apparatus through a telephone network, an ISDN network, or a PBX network, by attaching protocol conversion system to the X.25 apparatus. The conversion system has a pair of signal identification portions (1, 6) for separating a receive packet to a data packet and a control packet, a call process portion (3, 12) for dial signal process, and an address table (4) and a packet edition portion (5) for address conversion of a control packet. A data packet is forwarded from one signal identification portion to another signal identification portion through direct path (53). A control packet is forwarded to a control packet identification portion (2) for control process which includes dial signal process, address conversion, and protocol sequences. This system is applicable to couple a data communication network which has a X.32 correspondence portion to another data communication network.

Abstract: A quadrifilar helix antenna according to the present invention incorporates four helix conductors wound around an axis in the same winding direction. Each of the helix conductors has a linear conductor which is parallel to its axis at either end or both ends of the helix conductor. The present antenna reduces the effect of multipath fading due to sea-surface reflection in mobile satellite communications.

Abstract: An image reduction system which reduces binary level images is disclosed. In the system, a reduction pixel value is determined by using, as reference pixels for a filter operation: a plurality of surrounding pixels including an object pixel to be reduced; and reduced pixels, from among pixels which have already been reduced, said reduced pixels being at least a reduced pixel located before the pixel to be determined: a reduced pixel, located on the preceding line, which lies directly above the pixel to be determined; and a reduced pixel before said reduced pixel located on the preceding line.When a pixel referenced during the filter operation is included in a specific pattern, an exception process for correcting binary level results is provided.

Abstract: A phase lock loop for a digital input signal has a phase detector, a loop filter, a digital voltage controlled oscillator (VCO), an initial phase difference calculator, a center frequency difference calculator and an input buffer memory. In an initial training mode prepared in the PLL operation, an optimum initial phase and an optimum center frequency of the VCO to complete a lock-in state is searched for the input signal stored in the buffer memmory. By estimating the initial phase difference and the center frequency difference between the input signal and the VCO output with repetative kick-offs in calculators, optimum values mentioned above are obtained.

Abstract: An input speech signal is encoded by an adaptive quantizer which quantizes the predicted residual signal between the digital input speech signal, and prediction signals provided by predictors and a shaped quantization noise provided by a noise shaping filter. An inverse quantizer, to which the encoded speech signal is supplied, is provided for noise shaping and local decoding. A noise shaping filter makes the spectrum of the quantization noise similar to that of the original digital input speech signal by using the shaping factors. The shaping factors are changed depending upon the prediction gain (ex. ratio of input speech signal to predicted residual signal or the prediction coefficients). On a decoding side of the system there are an inverse quantizer, predictors, and a post noise shaping filter. The shaping factors for the post noise shaping filter are similarly changed depending upon the prediction gain.

Abstract: A moving image is coded through a waveform coding predictor (2), and a model-based coding predictor (3) which is mainly applicable to a head portion of a person, the coded outputs of said two predictors are compared (5) with an input current image for each block element which has for instance 8.times.8 or 16.times.16 pixels. A block element coded for the smaller difference from an input current image is taken, and is transmitted to a receiving side through differential coding (6,7). As the information compression ratio is high, a moving image can be transmitted through conventional telephone line, or a narrow band circuit.

Abstract: An input speech signal is encoded by an adaptive quantizer device (16). The adaptive quantizer device quantizes the predicted residual signal produced by removing correlations from the digital input signal by predictors devices (6, 10). A coefficient or weighting factor, called a leakage, at the predictor device (6) is adaptively adjusted by a leakage selector device (47) depending upon a prediction gain. The prediction gain indicates the accuracy of the prediction. The value of leakage is in the range between 0 and 1, depending upon whether the speech signal is voiced sound or unvoiced sound.

Abstract: A plurality of processor units (6a . . .6n), and a single host processor (4) coupled with the processor units (6a . . .6n) through transparent memories (10a . . . 10n) are provided for reading out results of parallel processing by the processor units. Each of the transparent memories (10a . . .10n) has a first bus (11a, 11b) for coupling processors (1a . . .1n) with memories (2a . . .2n) in the processor units (6a . . .6n), a second bus 12a, 12b) for coupling adjacent processor units, a first switch (13a, 13b, 14a, 14b) for switching the first bus, and the second bus, and a second switch (16) for switching direction of the second bus. The host processor (4) switches the first switch and the second switch, and accesses all the memories (2a . . .2n) simultaneously, and reads out those memories (2a . . .2n) simultaneously.

Abstract: A PSK signal which is subject to frequency fluctuation and noise is demodulated through a quasi-coherent detection process with a fixed local frequency oscillator (5) noise elimination process using a low pass filter (17,18) after frequency adjustment, and a frequency and phase regeneration process using a PLL circuit (20). The PLL circuit (20) is updated by the estimated center frequency of a received signal by using an FFT (fast Fourier transform) circuit (11), a power spectrum means (12,13,14), and a frequency estimation circuit (15) estimating the center frequency based upon the fact that the modulated signal component exists only on a high level portion of the frequency spectrum.

Abstract: In a satellite communication system including a plural small earth stations (3-8), a relay earth station (2) and a satellite (1), information transmission is undertaken by primary modulation of carrier wave, and transmission of operation status of each small earth station (3-8) is carried out by secondary modulation of said carrier wave. Primary modulation may be BPSK or multiphase PSK (MPSK), and secondary modulation may be PSK, ASK or FSK. Said operation status may be receive signal quality in each small earth station, and the relay earth station (2) may adjust transmit power to said small earth station such that the receive signal quality at small earth stations satisfies desired criteria irrespective of rain attenuation.

Abstract: An ATM (asynchronous transfer mode) exchange system for high speed packet exchange with a fixed length packet is implemented by a plurality of cell handlers (10-1 through 10-n) each related to each ATM channel, and a plurality of buses coupled with the cell handlers. An input user cell is subject to add routing information including an output cell handler number (403) and an output virtual channel identifier (404) by a virtual channel converter (12) and a routing header adder (13). The user cell which has routing information is forwarded to the bus. The cell on the bus is read out by all the cell handlers, and the particular cell handler in which the number of cell handlers coincide with the cell handler number in routing information takes the cell on the bus. In the cell handler, the cell itself read out of the bus is stored in the cell buffer memory (16), and the address of the cell buffer memory (16) of the cell is stored in the queue buffer (18).

Abstract: A unique word in a digital communication system is detected on a receiving side by using an acoustic surface wave matched filter (4) having a piezoelectric substrate, an input interdigital electrode (4c) and and output interdigital electrode (4a, 4b) on the substrate. An input signal is applied to the input interdigital electrode in the form of a phase modulated IF band signal. A pattern of the output interdigital electrode is designed depending upon a unique word to be detected where data 1 corresponds to an upper finger (4a) followed by a lower finger (4b), data 0 corresponds to a lower finger (4b) followed by an upper finger (4a) or vice versa, and progagation time of the surface acoustic wave over the spacing (d) between each pairs of fingers (4a, 4b) is equal to a bit time duration of the unique word.

Abstract: A unique word and/or a recovered phase in the demodulator in a multi-phase modulation system and/or a multi-level modulation system is detected by obtaining a plurality of correlation values, performing linear calculations for those correlation values to provide a correlation pattern, and looking at a table if this pattern coincides with one of the predetermined patterns. The invention is useful even when a received signal quality is poor and/or the length of the unique words is short. A plurality of unique word, together with a recovered phase are also recognized by the present invention.

Abstract: A light emitting semiconductor device which emits blue and/or green light has an active layer and a pair of clad layers which sandwich the active layer (3), deposited on a substrate (1). The substrate (1) is made of GaAs, InP, GaAsP or Ge. Said active layer (3) and said clad layers (2, 4) are made of II-VI group compound semiconductor which is lattice-matched with the substrate at both room temperature and growing temperature, for instance 500.degree. C. Said II-VI group compound semiconductor has the same linear thermal expansion coefficient as that of the substrate. The linear thermal expansion coefficient of the II-IV group compound semiconductor is adjusted by additive of Cd, Mg or Hg.

Abstract: A syndrome sequential decoding system for error correction of a convolutional code has a syndrome former for providing a syndrome sequence from a received sequence, a syndrome buffer memory for storing the syndrome sequence, an estimated error buffer memory for storing an estimated error sequence, a syndrome register for representing a syndrome state under searching, a comparator for testing if content of the syndrome register is all zero, and an algorithm controller. The algorithm controller controls the syndrome register, calculates a path metric and raises a flag in the estimated error buffer memory for showing an estimated error bit position. The syndrome sequential decoding system also includes an exclusive-OR circuit for correcting an information bit error according to the output of the estimated error buffer memory. When the content of the syndrome register is all zero, it shows that a currently searching path merges with the maximum likelihood path.

Abstract: A light emitting semiconductor device which emits blue and/or green light has an active layer and a pair of clad layers which sandwich the active layer, and which are deposited on a semiconductor substrate. The substrate is made of one of GaAs, GaP, InP, Si, Ge, ZnSe and mixed crystals of GaAsP. The active layer is made of at least one of II-VI group compound semiconductor, I-III-VI.sub.2 group compound semiconductor, and II-IV-V.sub.2 group compound semiconductor. The clad layer is made of II-transition metal-VI group compound semiconductor, which is lattice-matched to the active layer.

Abstract: A variable length code is converted to a new code in order to improve synchronization recovery capability without changing the length of each codeword. A short codeword with high occurrence probability is first selected as a seed. An object codeword, which is longer than the seed located at a leaf of a tree structure of the code, is exchanged with another node or leaf, which at the same is located depth as that of the object codeword in the tree structure, when a rear portion, called a suffix of said object codeword, coincides with the seed. The seed is also exchanged with another node or leaf on the same level as that of the seed, and the exchange of the object codewords is effected for the fresh seed in a similar manner as above. The final seed and the object codewords are determined so that the number of the codewords which coincide with the suffixes of seeds becomes maximum.

Abstract: In a moving picture transmission in which each picture frame is inter-frame coded for information suppression, and coded data is divided into blocks for transmission, any changes resulting from the loss of transmission blocks in order reproduce a picture on a receiver side is automatically corrected. A receiver side calculates an area in a picture frame affected by the loss of the transmission blocks, conceals the affected picture area by using information from a former picture frame, and affected picture area.

Abstract: In measurement method of dispersion characteristics of an optical fiber, a laser for measurement connected to one end of the fiber and variable in output light wavelength and an oscillation for modulating a measurement light signal sent out from the laser are provided. The modulation frequency of the output from the oscillator is used as an reference electric signal. A measuring light signal obtained through the modulator 8 and transmitted through the fiber is converted into an measuring electric signal. And the characteristics is measured from the phase difference between the reference electric signal and the measuring electric signal, wherein an external modulator, an optical divider and a monitoring section are provided. The modulator modulates the measuring light signal sent out from the laser and having a narrow spectral linewidth. The divider divides the output light signal from the modulator, at a prescribed ratio.