Abstract: A modulator-demodulator device includes a transmitter side having an error control coding circuit for adding redundancy to a bit sequence to be transmitted from a bit processing circuit and coding the bit sequence. A data sequence to coordinate transforming circuit transforms the bit sequence from the error control circuit into a signal point coordinate on a complex plane. A coordinate rotating circuit rotates the transformed signal point coordinates based on frame phase information from a frame phase generating circuit. In the receiver side, a coordinate rotating circuit applies rotation in a direction reverse that of the transmitter coordinate rotating circuit based on the frame phase information from the frame phase generating circuit. A second decision circuit decides the maximum likelihood signal point by utilizing the redundancy added by the error control coding circuit of the transmitter side and correcting the coordinate error of the received signal point.

Abstract: In a timing generation device coupled to a transmission line having a main channel and a secondary channel, the main channel having a transmission speed higher than that of the secondary channel, a first unit extracts a timing signal component transmitted via the secondary channel. A second unit generates an internal timing signal in synchronism with the timing signal component, the internal timing signal being used to reproduce data transmitted via the main channel.

Abstract: The invention provides a modulator and demodulator apparatus (modem) which modulates and demodulates a signal in a main channel, for main data, and a secondary channel, for secondary data obtained by frequency division, and which includes a carrier detection unit for detecting a carrier from a demodulation signal and executes a data processing sequence for the demodulation signal in accordance with a result of detection by the carrier detection unit. This apparatus can detect a carrier of a low roll-off ratio accurately and stably without a dispersion in detection time and, consequently, data of a demodulation signal can be processed with certainty. The modulator and demodulator apparatus comprises a filter having a characteristic wherein the time axis response is slow and it is provided at a stage preceding the carrier detection unit so that a demodulation signal which has passed through the filter is input to the carrier detection unit.

Abstract: A modulator and demodulator apparatus for use with a network is provided. The modulator and demodulator apparatus comprises a modulation section which includes a timing phase discrimination section for receiving, as an input signal thereto, a demodulation vector signal sampled into a digital value and discriminating to which one of a plurality of regions of a discrimination plane the phase of the input signal belongs. The timing phase discrimination section supplies, as an input to a next processing stage, a rotation vector obtained by rotating an input vector, moves the rotation vector to a quadrant which includes a reference discrimination region of the discrimination plane and performs, when the vector after the movement is not in the reference discrimination region, a predetermined calculation. When the vector after the movement comes to the reference discrimination region, another calculation is performed. This discriminates a timing phase of the input vector from the result of the calculation.

Abstract: A demodulation and roll-off filter apparatus comprises a demodulation portion, a decimation portion, a demodulation and roll-off filter portion, and a modulation portion. The demodulation portion converts a pass-band signal received from an A/D converter into a base-band signal. The decimation filter portion lowers the sampling frequency of the base-band signal into a frequency four times higher than the frequency of a demodulation carrier used for the demodulation and roll-off filter portion. The modulation portion converts a base-band signal received from the decimation filter portion into a pass-band signal. The demodulation and roll-off filter portion performs a simplified demodulation and roll-off filter process for the pass-band signal.

Abstract: A modulation and demodulation system suitable for use with a modem (modulator and demodulator apparatus) of a first polling type. The system allows reproduction of a signal necessary for initialization of a reception section of a modulator and demodulator apparatus with certainty in a short training time. The modulation and demodulation system is constructed such that, upon transmission of data, training data of a particular pattern are modulated and transmitted prior to transmission of the data, and such training data are demodulated by demodulation means and initialization of a reception section of the modulation and demodulation system is performed using the demodulation training data. The pattern of the training data to be transmitted includes an arrangement of signals wherein signals having phases different by 180.degree. from each other are arranged alternately, and a signal having the same phase as the last signal is arranged intermediately.

Abstract: An automatic gain control circuit which is provided in a demodulation section of a modem to adjust the loop gain so that the level of a band-limited receive signal may have a predetermined reference value and to output the receive signal to an automatic equalization section of the modem. The automatic gain control circuit is improved in that, even when a disturbance of the circuit such as a gain hit or a drop-out occurs, regular communication can be continued without requiring a data mode leading-in operation.

Abstract: In a timing extraction device coupled to a demodulator which derives a real signal component and an imaginary signal component from a signal received via a transmission line, a band-pass filter extracts a 1/2-Nyquist frequency from either the real signal component or the imaginary signal component. The 1/2-Nyquist frequency includes two symmetrical frequency components. A vector conversion unit processes the 1/2-Nyquist frequency so that a vector signal corresponding to one of the two symmetrical frequency components of the 1/2-Nyquist frequency is output from the vector conversion unit. A square multiplier squares the vector signal received from the vector conversion unit and thereby generates a phase error signal indicating timing information concerning the analog signal. The phase error signal has an angle which is double an angle of the vector signal.

Abstract: The invention provides a frequency offset dealing modulator and demodulator apparatus which modulates and demodulates transmission/reception data and is improved in that it can reproduce an accurate impulse when data are transmitted. The modulator and demodulator apparatus includes a modulator for modulating data, and a demodulator for demodulating a receive signal to reproduce such data. The demodulator includes a demodulation processing unit, a roll-off filter, a receive level adjustment unit, an equalizer, a carrier frequency offset removing correction signal generation unit, a normalizer, a multiplier and a sum calculation unit.

Abstract: In a modulator-demodulator device, in the transmitter side an error control coding unit is provided for adding redundancy according to a predetermined procedure to a bit sequence to be transmitted from bit processing unit to code the bit sequence. A data sequence-to-coordinate transforming unit transforms the bit sequence from the error control coding unit into a coordinate of a signal point on a complex plane. A coordinate rotating unit rotates the transformed signal point coordinates based on the frame phase information from a frame phase generating unit. In the receiver side, a coordinate rotating unit applies the rotation in the reverse direction of that of the coordinate rotating unit of the transmitter side based on the frame phase information from the frame phase generating unit. A the second unit determines the maximum likelihood signal point by utilizing the redundancy added by the error control coding unit of the transmitter side and corrects the coordinate error of the received signal point.

Abstract: A system for removing line deterioration elements such as intersymbol interference, carrier frequency offset and phase jitter, etc. from the receiving signal. An automatic equalizing unit compensates for signal deterioration by intersymbol interference. Next, a carrier phase control unit compensates for signal deterioration by carrier frequency offset. Thereafter, a phase jitter interference removing units allows increase of only phase jitter element by utilizing line characteristic to easily extract phase jitter element. Since the signal including phase jitter is a low frequency signal, a phase jitter removing unit further removes phase jitter by shifting the frequency range to a higher frequency range on the frequency axis and then shifting it to the bandwidth for each processing.

Abstract: A system of the transversal type automatic equalizer with a tap coefficient protection in which an inter-symbol interference is prevented. The system includes a summing unit for summing all of the tap powers detected by tap power detecting unit, and a determination unit for comparing the sum produced by the summing unit with a predetermined threshold value, and for producing the output determination of normal when the sum is not more than the threshold value and producing the output determination of abnormal tap coefficient growth when the sum is more than the threshold value.

Abstract: A reception signal processing system in a communication system transmitting a data under a predetermined baud-rate, including: a first unit operated by a first frequency for inputting the reception signal and for recovering loss components in the reception signal; a second unit operatively connected to the first unit and for responding to an output of the first unit, for determining a first ideal reception signal corresponding to the output of the first unit based on a second frequency corresponding to the baud-rate, and the first frequency being higher than the second frequency; and a third unit operatively connected to the first unit and second unit for responding to the first ideal reception signal from the second unit based on the frequency and for generating and providing a second ideal reception signal based on the first frequency to the first unit; the second ideal reception signal being derived by processing the first ideal reception signal based on the first frequency, and the first ideal reception s

Abstract: A multipoint type MODEM communication system having a training device for adapting receiving parameters in a receiving MODEM to a characteristic of a telephone line connected to a sending MODEM in response to a training signal sent from the sending MODEM prior to the reception of data. The training signal includes a tone for gain control, a timing signal for pull-in synchronization, and at least two impulses for equalization and carrier phase control, which are superimposed on each other. A time between the first and the last impulses defines the characteristic of the telephone line which should be adjusted in the receiving MODEM.Additional guard impulses may be added prior to and/or after the impulses. A scramble signal also may be added after the impulses.In addition, a method for training the receiving MODEM is disclosed.

Abstract: A two-wire full duplex frequency division multiplex (FDM) modem system having a unit for cancelling a transmission signal, taking into consideration the line distortion characteristics. The FDM modem system includes two modem units connected through the two-wire full duplex transmission line.Each modem unit includes a unit for modulating a transmission data, a unit for synthesizing the modulated transmission signal and a reception signal, a unit for adding the signal from the synthesizing unit and a signal, a unit for demodulating the reception signal, and a unit for generating the signal supplied to the adding unit cancelling a transmission echo signal included in the signal from the synthesizing unit, from the signal modulated at the modulating unit and the signal from the adding unit. The adding unit subtracts the signal generated at the echo cancellation signal generation unit from the signal from the synthesizer unit.

Abstract: A receiving equipment comprises a modulator, a timing extraction unit, a PLL unit, an impulse recovery unit, a fix-equalizer, and an automatic-equalizer. A timing pull-in operation is performed, in one way, by phase-rotating a timing signal of the timing extraction unit and sends the signal to the PLL unit, and in another way, by introducing an input signal of the timing extraction unit from the equalized output of the fix-equalizer.

Abstract: Data receiving equipment is trained by training signal of optimum length through the steps that the sending equipment sends data signal after sending the training signal having a length corresponding to the characteristics of a line connected thereto and containing information indicating the length and the receiving equipment trains itself with the received training signal and detects, using the information indicating the length, the timing when the training signal changes to a data signal.

Abstract: A method for transmitting a signal with a signal transmission rate selected from a plurality of signal transmission rates applicable to a facsimile transmission system. The distortion amount of a distortion measurement signal transmitted from a transmitting equipment is measured at a receiving equipment on the basis of the variation in the received distortion measurement signal. The distortion allowance range to which the measured distortion amount belongs is decided on the basis of the result of the measurement of the distortion amount. The transmission of the working signals is carried out with a transmission rate corresponding to the result of the decision of the distortion allowance range.

Abstract: In a receiver unit, a synchronous pull-in circuit is formed. The synchronous pull-in circuit is comprised of a transversal filter having a roll-off characteristic (roll-off filter), a timing discriminator for extracting a timing signal contained in a received signal and a decision part for detecting a phase deviation between the thus extracted timing signal and an internal clock by which the receiver unit itself is synchronized. The roll-off filter is provided with a plurality of taps, the tap coefficients of which are varied in accordance with the phase deviation, so that said timing signal is synchronized with the internal clock.

Abstract: An automatic equalization device used in a data communication system includes a unit for extracting a single pulse from a training signal sent from a transmitter and initializing a tap coefficient using the extracted single pulse. The automatic equalization device also includes a first equalization circuit and a second equalization circuit. In the first equalization circuit, an auto-correlation series of the signal corresponding to the single pulse is calculated to provide a symmetric single pulse. In the second equalization circuit, an inverse matrix is calculated from the symmetric single pulse using the auto-correlational series of single pulses. By these calculations, the speed of the initial setting of the tap coefficient is increased.