Hitachi, Ltd.

Hitachi Denshi Kabushiki Kaisha

Hitachi-kokusai Electric Inc.

Other

Hitachi Denshi Kabushiki

Yoshiro Kokuryo

Nobuo Tsukamoto

Makoto Ohnishi

Yasuhiro Kita

Naoya Kobayashi

Kohei Ishizuka

Narimichi Maeda

Masahiro Koya

Kazuhiko Takaoka

Kunihiko Kondo

Nobuo Hirose

Tetsuomi Ikeda

Hiroyuki Hamazumi

Kenji Terada

Atsushi Mizuno

Yasushi Kudo

Takao Koyama

Hiroyuki Ando

Yoshio Iwasaki

A demodulation method, and apparatus, for reproducing data from a received signal. The demodulation method includes the steps of: receiving a signal including a series of frames each containing a training signal for automatic equalization processing and a data signal; controlling an amplitude of the received signal by AGC processing so as to make the amplitude a predetermined level; conducting demodulation processing on the signal subjected to the AGC processing; periodically conducting automatic equalization processing so as to adapt the modulated signal to characteristics of the signal transmission path based on each training signal of the frame; and setting values of a time constant of the AGC processing and an update repetition period of the automatic equalization processing so as to satisfy a predetermined relation.

Signal demodulation method and apparatus for reproducing data from received signal

A demodulation circuit for demodulating a multilevel digital modulation signal. Only an in-phase or quadrature component of the training signal generated in the demodulation circuit is used for equalization convergence. Tap coefficients of an equalizing training equalizer are updated by supplying either the in-phase or quadrature component so that the calculation amount can be reduced. When the equalization convergence is established, the obtained tap coefficients are rotated in phase and set to a data reproduction equalizer.

Automatic equalization circuit and receiver circuit using the same

An encoder and a decoder each having an error correcting operation, and a data transmission apparatus using them for data transmission in a multilevel modulation system. In transmission data is converted into parallel data. One bit thereof is inputted to a convolutional encoder to output two bits. Two bit data and another signal of the parallel data not inputted to the convolutional encoder are respectively separated into real part and imaginary part to independently decide signal points for the parallel data. In reception an area is similarly decided independently for real and imaginary parts and metric is assigned for the data. Real and imaginary parts are combined with each other for Viterbi decoding. Result thereof is fed to a convolutional encoder similar in constitution to that on transmission side. Using convolutional encoding output and decided area, transmission data is decoded.

Coder with error correction, decoder with error correction and data transmission apparatus using the coder and decoder

A transmission data sequence including a plurality of continuous data portions each formed on a byte unit basis and including predetermined code data is transmitted from a transmission station to a receiving station as serial data. At the receiving station, the transmission data sequence is received and converted to parallel data, and the parallel data is processed byte by byte. At the transmission station, out-of-synchronization detection code data sequence derived by shifting the first predetermined code data by from one bit to a predetermined number of bits at one bit pitch is inserted into the transmission data sequence and it is transmitted. At the receiving station, when a part of the out-of-synchronization detection code data sequence in the transmission data sequence is detected during processing on a byte unit basis of the transmission data sequence received and converted to the parallel data, it is determined that the processing on a byte unit basis of the transmission data sequence is in the out-of-synchronization state between the transmission station and the receiving station and an operation to recover the processing on a byte unit basis of the transmission data sequence to a synchronization state is conducted.

Out-of-synchronization recovery method and apparatus of data

A speech signal bandwidth compression and expansion apparatus and its method. On the transmitting side, system parameters are extracted from a speech signal by a linear prediction analyzer. A prediction residual signal is obtained by inverse filtering processing by using the system parameters. The prediction residual signal is lowered in sampling rate by a down-sampler and converted to a baseband signal. From the baseband signal, a time series signal is derived by a linear prediction synthesizer. Thereafter, the time series signal is converted to an analog signal and transmitted. On the receiving side, a received signal is subjected to inverse filtering processing to reproduce a baseband signal. The sampling rate of the reproduced baseband signal is raised to derive a time series signal. From the time series signal, a high frequency band component is generated. The high frequency band component is added to the baseband signal to generate an excitation signal. From the excitation signal, the original speech signal is reproduced by a linear prediction synthesizer.

Speech signal bandwidth compression and expansion apparatus, and

A simplified carrier phase control apparatus used in a modem for demodulating a quadrature amplitude modulated data signal, to correct phase jitters of a carrier signal due to a 50 Hz or a 60 Hz frequency of the commercial power supply, and its harmonic wave frequency components. The carrier phase control apparatus has a predictive filter for predicting a carrier phase jitter, the predictive filter composed of band-pass filters with center frequencies of 50 Hz and 60 Hz, and a circuit where the output signals of the band-pass filters are multiplied by the coefficients and added linearly.

Carrier phase controller for a receiver of phase modulated signals

A maximum likelihood decoder for decoding a code from a signal transmitted through quadrature amplitude modulation of a code including a convolutional code can decode at high speed and high accuracy with a simple hardware configuration. In the maximum likelihood decoding of the convolutional code, the metric processing is not carried out for all of the possible paths and states but a smaller number of path(s) (metric(s)) and state(s) (metric(s)) are selected in a descending order to determine survival paths.

Maximum likelihood decoder

Disclosed is a phase control system for providing by digital processing a timing signal having a certain phase relationship with a timing signal detected in a received, modulated signal, wherein the detected timing signal is delayed by a predetermined time period and the detected timing signal and the delayed timing signal are multiplied by respective constants so that the zero-cross point of the composite signal of the two timing signals matches the sampling point of the timing signal.

Method and device for controlling the phase of timing signal

In a gain control circuit, an electric power calculating circuit is connected to a variable gain amplifier and a gain setting circuit for generating a gain control signal applied to the variable gain amplifier to control the gain thereof.

Electric power detecting circuit and gain control circuit using the same

An equalizer apparatus suitable for use in a MODEM for receiving a signal having passed through a number of carrier-band lines is disclosed in which the number of carrier-band lines is detected from a training signal, and electrical connection of a fixed equalizer to a variable equalizer is controlled on the basis of the number of carrier-band lines, in order to form a precise, simple automatic equalizer apparatus.

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Tachikawa, Japan

Yoshiro Kokuryo