Abstract: A public telephone system includes a plurality of public telephone sets and a center apparatus.

Abstract: A cell delay addition circuit can easily feed any desired delay to each of input cells in a communication apparatus or the like for asynchronous transfer mode operation. A time stamp is obtained for an inputted cell based on a sum of a delay amount from a delay amount producing circuit and the current time produced by a clock circuit. The time stamp and the input cell are written in a cell buffer. On the reading side, a comparator reads out a time stamp from the cell buffer and when the comparator detects that the current time tm is equal to or greater than the time stamp, the comparator produces a cell output enable signal ce so that the cell buffer produces the cell.

Abstract: In a synchronization system for use in a digital transmission system in which an encoded digital transmission signal at least part of bits of which have specific statistic characteristics is transmitted, a digital transmission signal received by a decoder within a digital transmission apparatus at a receiving end is subjected to a decoding processing in units of samples on the basis of a synchronous input signal.

Abstract: A coded video signal encoded into a variable length code is packed into a frame called a cell having a predetermined number of fixed bits for transmission through ATM (Asynchronous Transfer Mode) which is subject to cell loss due to the congestion of network nodes or bit errors in cell headers, causing burst errors or synchronization slips in a received video signal. In order to avoid such errors, one idea for a variable length transmission unit is introduced. A transmission unit has a plurality of cells and any coded video signal terminates in the transmission unit; in other words, a coded video signal is not shared by two transmission units. A transmission unit is closed or terminated during packing operation when the number of available bits in a cell under packing operation becomes less than a predetermined first threshold value and when a cell number in the transmission unit reaches a predetermined second threshold value, so that transmission efficiency is improved.

Abstract: A CDMA communication system using a spreading code has a plurality of mobile stations and at least one base station. The mobile stations and the base station are provided with respective receiving sections, each of which has a path diversity function for reducing multipath fading. The base station includes an array antenna having a plurality of integrated antenna elements spaced by a distance substantially equal to one to several wavelengths from each other so as to produce a space diversity effect. A plurality of delay devices are coupled with the respective antenna elements, for applying time delays to signals which pass through the respective antenna elements. The time delay are different from each other by a one symbol period of the spreading code or more.

Abstract: A spread spectrum communication system has a plurality of transmit ends capable of simultaneous communications and at least one receive end. Each of the transmit ends modulates digital information by a PN code to provide a spread signal, modulates a carrier by the spread signal to provide modulated signal, and then transmits the modulated signal to the receive end. These transmit ends use the same PN code for spreading the respective digital information and use carriers having different frequencies from each other so that spectrums of at least two of the modulated signals overlap each other. The receive end receives signals transmitted from the transmit ends to provide a received signal, frequency-converts the received signal to provide a converted signal, and calculates a correlation between the converted signal and the PN code to recover the digital information transmitted from the desired transmit end.

Abstract: In an echo canceller having PCM interfaces used in a PCM telephone circuit, an echo estimator (6) is coupled with a receive path through a linear code converter (13) for obtaining a linear receive input signal, and a first subtractor (7) is inserted after a linear code converter (13) in a transmit path for cancelling an echo component in a linear transmit input signal and for transmitting a first residual echo to the far-end talker. A non-linear quantization processor (24) is inserted between the first subtracter (7) and the echo estimator (6), and produces a new echo estimate containing quantization noise, based on an echo estimate which is derived from the echo estimator (6). The filter coefficients in the echo estimator (6) are updated by using the second residual echo obtained by the second subtracter (23) separately prepared from the first subtracter (7).

Abstract: A frame of a picture is first divided into a plurality of blocks, each of which is subject to orthogonal transform to provide picture pels in the form of matrixes, which have a coefficient of DC component, and coefficients of AC components. AC components in said matrix are subject to a pre-quantization for each frame evaluate total code length (L') in the encoding. A number (N') of significant coefficients which are not zero in each block or each macro block is counted. A step size in quantization is determined according to said values L' and N' and coefficient position. The quantized block is subject to effective baseband selection for further reduction of information amount so that a zero coefficient after EOB in the block along the selected scanning line defined by the selected effective baseband is eliminated.

Abstract: A cell transfer method and a cell receiving apparatus in which cells of an asynchronous transfer mode are used to transfer information for a plurality of channels regardless of the number of channels and without reduction of the utilization rate of cell in the same cell configuration and the information for the channels can be reproduced while maintaining synchronization between the channels in a receiving side. The cell has an identifier for each channel and is exclusively used for each channel. Cells to be reproduced at the same time are given the same sequence number to be transferred. On the receiving side, when a cell is inputted in a cell disassembling circuit, the cell is disassembled into a sequence number, a channel identifier and channel data and channel information is written or stored in a buffer together with the sequence number by a distributing circuit in accordance with contents of the channel identifier.

Abstract: In radio communication with non-modulated signal at head of receive signal, the non-modulated signal or the head of the receive signal is detected in spite of rather large frequency error of receive signal, and frequency acquisition for coherent detection in a receiver is established during detection operation of the non-modulated signal Discrete Fourier Transform (1) is carried out for an input signal in digital form in every receive sample to provide frequency spectrum of an input signal. Then, the maximum component is selected (2) in the frequency spectrum. Next, a peak detector (3) detects peak value of the selected maximum components on time axis, and recognizes the detection of the non-modulated signal. The frequency (f.sub.e) of the non-modulated signal is estimated through interpolation of the selected component having the peak value and the adjacent component. The receive frequency is adjusted by using said estimated frequency (f.sub.e), and the adjusted frequency is subject to coherent detection.

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 service processing system has a plurality of service processing nodes each having a single local data base, and a plurality of exchanges each of which is coupled user terminals. Said service processing nodes are coupled with one another through communication lines. A query by a user terminal is transferred to a local data base through an exchange to which the user terminal belongs. When a response to the query is stored in that data base, said response is directly given to the exchange from said local data base. On the other hand, when the local data base does not store the response the query of the user terminal is transferred to another service processing node which is designated by the local data base through the communication line between the service processing nodes. The response obtained in said other service processing node returns to the first local service processing node.

Abstract: In an echo canceller used in a four-wire digital telephone circuit, a main echo estimator (21) and a sub echo estimator (22) are coupled with a receive path for measuring a receive signal, and subtracters (25, 26) are inserted in a transmit path for cancelling an echo component in a transmit signal. Filter coefficients in said estimators (21, 22) are adaptively controlled by a convergence control processor (24). The main echo estimator has a small step gain for updating filter coefficients so that the response to an echo is slow, while the sub echo estimator (22) has a large step gain and quick response for an echo. An register accumulator (23) is provided so that the filter coefficients by the sub echo estimator (22) are selectively accumulated on the related filter coefficients in the main echo estimator (21) according to operation modes, ordinary mode, accumulating mode, and reset mode.

Abstract: The optical amplification gain of an optical amplifier consisting of an optical amplifier unit and a single-mode erbium-doped fiber can be optimized when the length of the fiber L in meters and the optical absorption in dB/meter of the fiber per unit length at a wavelength of 1.53 .mu.m satisfy the relationship that L.times.y is in the range from 70 to 170 dB by appropriately selecting the doping level of the glass with erbium and the length of the fiber.

Abstract: A shaped beam antenna system which provides a desired shape of beam, comprises a reflector and at least one primary radiator located essentially at focus of said reflector. Reflection surface of the reflector is a dense set of parabolas in which vertexes of said parabola shift on a predetermined locus which is preferably a three dimensional space curve, but not a plane curve. A second feature of the shaped beam antenna system is the primary radiator which is composed of a plurality of primary radiators positioned closely to each other.

Abstract: In an optical fiber coupler there is provided, in an optical coupling portion between cores of two partly fused together and extended optical fiber, an optical coupling control portion which has a refractive index different from those of claddings covering the cores.

Abstract: A multi-level image is encoded through dither conversion and hierarchy encoding with high image compression ratio and satisfactory image quality for low resolution images. An original multi-level image is first reduced so that a plurality of reduced images are obtained. Each reduced multi-layer image is then dithered to bi-level image, and finally each dithered bi-level image is encoded starting the smallest and the lowest resolution image to the largest and the highest resolution image. No temporary memory for reduced multi-level image is necessary, as a common multi-level line memory (LM2, LM3, LM4) doubles for storing a reduced multi-level image and a temporary memory for effecting dither conversion.

Abstract: In an echo canceller having PCM interfaces used in a PCM telephone circuit, an echo estimator (65) is coupled with a receive path through a linear code converter (632) for measuring a linear receive input signal, and a subtracter (7) is inserted after a linear code converter (631) in a transmit path for cancelling an echo component in a linear transmit input signal. The same procedure as that in a conventional echo canceller is performed in a divergent situation in the echo estimator (65) in which a large step gain is assigned, and in a convergent situation in the echo estimator (65) in which a relatively small step gain is assigned, a non-linear quantization processor (27,271) is inserted between the subtracter (7) and the echo estimator (65). The non-linear quantization processor (27,271) produces a new echo estimate containing a quantization noise, based on an echo estimate which is derived from the echo estimator (65).

Abstract: A novel method is proposed for the preparation of a transparent fused silica glass body co-doped with a rare earth element and aluminum each in a high uniformity of the dopant distribution. The method comprises the steps of: (a) flame-hydrolyzing a silicon compound and an aluminum compound in an oxyhydrogen flame to form a porous silicon oxide body containing aluminum; (b) soaking the porous body having a specified bulk density with a solution of a rare earth compound; (c) drying the solution-soaked porous body; and (d) sintering and vitrifying the dried porous body into a transparent glass body.

Abstract: An adaptive array antenna having a plurality of antenna elements (1-1 through 1-N), related weight circuits (4-1 through 4-N) for weighting amplitude and phase of receive signal by each antenna element, and a combiner (5) for combining weighed signals, has a plurality of antenna beams at the same time by determining weights of said weight circuits, so that a plurality of receive signals due to multipath transmission are received for obtaining high receive level while avoiding multipath interference.