Abstract: A picture coder decodes P frames without having to wait for the next I frame even if a data loss occurs, and ensures quick recovery from degraded picture quality. The picture coder, which controls updating of a reference picture based on a decoding status signal and a frame number sent from a picture decoder, uses an acknowledgment signal (ACK signal) as a decoding status signal. The picture coder has a decoding status determination module 109 which determines that a decoding error has occurred if the acknowledgment signal is not received within a specified time. The picture coder also has a reference frame updating module 110 for use when it is determined that a decoding error has occurred. The reference frame updating module 110 selects from pictures, which were received correctly before the decoding error occurred, one picture for use as the reference picture. This makes it possible for the picture coder to decode P frames without having to wait for the next I frame.

Abstract: A moving picture transmission system enhances the quality of a demand-refreshed image without increasing the amount of code to be transmitted. When a picture data error has been detected, a reception side coder transmits to a transmission side decoder information concerning the location of the error detected in a picture frame. Upon receipt of this information, for several frames, beginning with the picture frame that is distorted by the error and continuing up until the picture frame preceding the frame to be transmitted, the transmission side determines a portion that may be distorted by the occurrence of the error or by the transmission of the error, and a picture portion that may be affected by distortion when picture data are to be coded in the inter-frame coding mode.

Abstract: A coded moving-picture signal consists of segments, each having a start code, header information, and coded picture data. The picture data are coded according to a self-resynchronizing variable-length coding rule. During decoding, if an error is recognized, this coding rule is applied in order to resynchronize; the coded data from the resynchronization point up to the next start code are stored in a memory; then the memory contents are decoded. According to a first aspect of the invention, the header information is coded according to the same variable-length coding rule, except for group header information appearing immediately after the start code. According to a second aspect of the invention, the start code is followed by all the header information in the segment, then by all the coded picture data in the segment.

Abstract: An automatic equalizer for a data transmission channel capable of removing intersymbol interference and phase fluctuations accurately without lowering the convergence rate even when the frequency characteristic of the channel sharply changes. A summation output to be fed to a decision unit has the phase thereof so rotated as to compensate for an amount of phase fluctuation. The output of the decision unit to be applied to a feedback filter, which follows the decision unit, and an error to be applied to a tap coefficient control section each has the phase thereof rotated in such a manner as to add phase rotation in matching relation to the amount of phase rotation. Even when the tap coefficient control section is implemented with an RLS (Recursive Least Square) alogorithm, it can update tap coefficients by the same procedure with no regard to phase fluctuations.

Abstract: An adaptive equalizer is provided with an equalizing assembly for equalizing an input signal having a transmission frame which includes a first training field and a second training field. The input signal is temporarily stored in a storage unit and simultaneously subjected to equalization by the equalizing assembly. An equalization error in the second training field is calculated and compared with a predetermined value. When the equalization error exceeds the predetermined value, the equalizing assembly is reset to do the equalizing operations over again from the head of the second training field, using the input signal stored temporarily in the storage unit.

Abstract: An adaptive equalizer in a digital receiver filters differentially encoded data bursts containing known data preceded and followed by user data. A storage means saves and restores filter coefficients and other values so that the known data can be filtered repeatedly. As the known data are repeatedly filtered, a known-data generating means generates different differential encodings of the known data as desired data which are compared with the filtered values to obtain error values for use in updating the filter coefficients. A comparator means selects the encoding that produces the smallest cumulative error. The known data are then filtered once more, using the selected encoding as desired data, after which adaptive filtering of user data continues.

Abstract: In a cipher system used in transmission or storage of digital data, the encipherment section comprises a first modulo-2 adder for adding, bit by bit, the k-bit contents of a first shift register storing latest k bits of ciphertext information and the k-bit contents of a first register. The k-bit output of the first modulo-2 adder is expanded into m.times.n bits, which are stored in a second register, and extracted in sequence, a set of n bits at a time. Each set of n bits is converted into a single bit. A second modulo-2 adder adds the 1 bit output to the contents of a third register, which stores the output of the second adder. A fifth register stores plaintext information input through the input terminal. A third modulo-2 adder adds the output of the second adder to the contents of a register storing plain text information to ciphertext information. A sixth register stores the output of the third adder.