Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: An automatic equalization method, automatic equalization circuit, demodulation circuit or receiver circuit for automatically updating an equalization characteristic required to demodulate a received signal including a training signal of a predetermined pattern transmitted from a transmission side apparatus. First, tap coefficients of an automatic equalizer for data reproduction are initial-set on the basis of received training signal. After the initial-setting, the tap coefficients are updated once every N symbols (where N is an integer of at least unity) of the received signal by using the received signal. The received signal is equalized in the automatic equalizer for data reproduction based the updated tap coefficients. The equalized received signal is demodulated.

Abstract: A transmission system for transmitting information codes by using a multi-level modulation scheme has a transmitter and a receiver. The transmitter has a divider circuit for dividing inputted N-bit information data stream into M (M is integer not less than 2) data stream; an error correction coding circuit for individually converting the M streams into error correcting code streams so as to deliver M error correcting code streams; a multi-level modulation circuit for making the correspondence between data streams of N bits constituted by the M error correcting code streams and a plurality of signal points arranged on a signal constellation and modulating two carriers with coordinate values of signal points on the signal constellation corresponding to the N-bit code stream; and a high frequency circuit unit for outputting a modulated signal in a radio frequency to a transmission antenna.

Abstract: A digital multilevel signal receiver circuit which can sufficiently improve transmission efficiency while suppressing a data transmission error, and an automatic equalization circuit for use in the digital multilevel signal receiver circuit. An equalization training automatic equalizer is provided separately from a data reproducing equalizer having equalization characteristics which can be set up. A received training signal is once stored in a memory, read out from the memory and supplied to the equalization training automatic equalizer so as to update tap coefficients of the equalizer. The updated tap coefficients are given to the data reproducing equalizer so as to update equalization characteristics of the equalizer. A received data signal is equalized with the updated equalization characteristics.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.