Fujitsu Corporation

Noboru Kawada

Takashi Kaku

Hideo Miyazawa

Yuri Nigaki

Ryoji Okita

Hiroyasu Murata

Kyoko Hirao

Takeshi Asahina

Tohru Ogawa

Michiko Narita

A limiter is connected with the output of a PLL to limit the amplitude of the output from the PLL. The output from limiter is supplied to a voltage-controlled oscillator (VCXO). The limiter determines the difference between the input signal and the output signal. If the difference exceeds a predetermined value, the change in the output from the limiter is limited to the predetermined value. If the difference does not exceed the predetermined value, the change in the output is considered to be a difference value.

PLL controller, method of PLL control, and limiter

A PLL circuit that causes an internal oscillation signal to lock to an external input clock signal, and is capable of suppressing jitter. The PLL circuit includes a frequency dividing circuit for frequency-dividing an input clock signal; a voltage-controlled oscillator; a missing-pulse clock signal creation circuit for creating, based on an output signal of the voltage-controlled oscillator, a missing-pulse clock signal having a higher speed than that of an output signal of the frequency dividing circuit and having a periodic missing-pulse portion; a phase comparator circuit for sampling the output signal of the frequency dividing circuit by using the missing-pulse clock signal; a shift register for storing a change in the output signal of the phase comparator circuit; and a digital signal processing circuit for converting a value stored in the shift register into a phase difference, and for controlling the input voltage to the voltage-controlled oscillator based on the phase difference.

PLL circuit

A transmission system for transmitting a data signal with an analog passband signal through a analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. In a receiver, the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed bass band signal is extracted by subtracting the decided result from the signal representing the superimposed data signal point. The base band signal is transformed to the analog passband signal. A portion of information carried by the analog passband signal may be converted to a digital signal, and the digital signal is multiplexed with the data signal. Further, a portion of information of each of a plurality of analog passband signals may be converted to a digital signal, and the digital signal is multiplexed with each other, and the other portion of the information is transformed to a base band signal, and the base band signal is superimposed on a signal representing a data signal point generated from a signal generated by the multiplexing.

Multiplex transmission system wherein analog signal is transformed to base band, random-transformed and superimposed on dispersed signal points in vector signal space

A transmission system for transmitting a data signal with an analog passband signal through a analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. In a receiver, the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed base band signal is extracted by subtracting the decided result from the signal representing the superimposed data signal point. The base band signal is transformed to the analog passband signal. A portion of information carried by the analog passband signal may be converted to a digital signal, and the digital signal is multiplexed with the data signal. Further, a portion of information of each of a plurality of analog passband signals may be converted to a digital signal, and the digital signal is multiplexed with each other, and the other portion of the information is transformed to a base band signal, and the base band signal is superimposed on a signal representing a data signal point generated from a signal generated by the multiplexing.

Multiple transmission system wherein analog signal is transformed to base band, random-transformed and superimposed on dispersed signal points in vector signal space

A transmitter has a power calculation unit for calculating the power of a signal. A maximum value detection circuit determines a maximum value of an output of the power calculation unit, and a floating point transformation circuit changes an output of the maximum value detection circuit into a floating point representation. A significant bit extracting circuit extracts significant bits from an output of the floating point transformation circuit and outputs the significant bits as the transmitting signal.

A preceding apparatus for calculating a difference between an inputted signal point and an output signal obtained one timing before and outputting the difference has a position information judging unit for judging which position on a vector plane the output signal obtained one timing before is located in, and a signal point selecting storage for outputting any signal point among a plurality of signal points generated correspondingly to a signal point inputted from the outside with a result of the judgement fed form the position information judging unit nd the signal point inputted from the outside as an address, thereby decreasing the number of cycles required by a DSP process and realizing a precoder process in a degree achieved hitherto.

Judging method and a precoding apparatus

The invention provides a training method for a non-Nyquist transmission system and a training data transmission apparatus for a non-Nyquist transmission system by which initialization processing of a reception section can be performed with certainty even where a non-Nyquist transmission system is employed. Prior to transmission of data in accordance with a non-Nyquist transmission system, training data having a first repeat signal portion formed from a group of signals including components of a lower rate than a Nyquist interval, a first multi-value random signal portion formed from multi-value random signals, a second repeat signal portion formed from a group of signals including components of a lower rate than the Nyquist interval, a third repeat signal portion formed from a group of signals which include components lower in rate than the Nyquist interval and wherein a first signal point is different by 180 degrees in phase from a first signal which forms the second repeat signal portion, and a second multi-value random signal portion formed from multi-value random signals, are transmitted from a transmission section. The training data are received by a reception section, and initialization processing of the reception section is performed using the received training data.

Training method for non-nyquist transmission system and training data

The present invention discloses a timing phase control apparatus which is particularly suitable for use in a modem used for very high speed data transmission employing a metallic line. The timing phase control apparatus includes a timing phase extracting portion to extract timing phase information from an input signal, a timing phase control filter portion to make a timing phase control to the input signal depending upon the timing phase information from the timing phase extracting portion through filter processing using a coefficient operation having a preset impulse response characteristic, and a filter processing coefficient determining portion to determine a coefficient used for the filter processing in the timing phase control filter portion depending upon the timing phase information and information about an approximate expression of the impulse response characteristic. An accuracy of a tap coefficient can be improved while reducing an amount of information about the tap coefficient, which should be stored.

Timing phase control apparatus and timing phase control method

A method of controlling a line equalizer such as a modem includes an extracting step of extracting plural tone signals each superimposed on a transmission signal and having a specific frequency component; a judging step of judging levels of the extracted tone signals; and a controlling step of controlling characteristic of a line equalizer which equalizes a receive signal, based on the levels of the judged tone signals. A line equalizer is controlled without performing an exchange of a training signal prior to starting a data transmission and without increasing the amount of hardware of a modem or the like.

Line equalizer control method, and integrating circuit, frequency shift

The invention provides a carrier phase control circuit which can eliminate a phase intercept fluctuation so that, when the carrier phase control circuit is applied to a very high speed modem having a communication speed of, for example, 28.8 kbps, occurrence of a communication error can be suppressed and the modem has an improved characteristic. The carrier phase control circuit is provided on a reception side of a communication apparatus and interposed between an automatic equalizer and a signal decision section. The carrier phase control circuit includes a frequency offset removal section for predicting and removing an offset of a frequency of a transmission signal based on an output of the automatic equalizer, and a phase intercept variation removal section for predicting and removing a phase intercept variation of the transmission signal based on an output of the frequency offset removal section and inputting a resulted signal as an output thereof to the signal decision section.

Carrier phase control circuit

A transmission system includes a transmitter and a receiver and transmits a data signal with an analog passband signal through an analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The transmitter includes a data signal point generation unit and a vector signal superimposing unit. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. The receiver includes a demodulator unit and a decision unit, wherein the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed base band signal is extracted in a subtracter unit by subtracting the decided result from the signal representing the superimposed data signal point. The base band signal is transformed to the analog passband signal. A portion of information carried by the analog passband signal may be converted to a digital signal, and the digital signal is multiplexed in a multiplexer unit with the data signal. The base band signal is superimposed on a signal representing a data signal point generated from a signal generated by the multiplexing.

Multiplex transmission system wherein analog signal is transformed to

A transmission synchronizing apparatus and method of a modem, in which a phase difference from a change point of an internal timing signal to a change point of a transmission timing signal is detected as a reference phase difference at the time of pull-in, based on a request to transmit from an external device. After pull-in, in a stationary communicating state, a phase difference is obtained from a change point of the internal timing signal to a change point of the transmission timing signal as a measured phase difference. The measured phase difference is controlled to coincide with the reference phase difference.

Method and apparatus for synchronizing modem transmission by controlling

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 of the carrier detection unit. This apparatus improved in that it 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.

Modulator and demodulator apparatus

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. The modulator and demodulator apparatus includes a modulation unit for modulating and transmitting data having a turnoff sequence with a last end and a demodulation unit for receiving and demodulating a receive signal to reproduce data. The modulation unit includes a tone signal generation unit for adding a tone signal to the last end of the turnoff sequence of the data to be transmitted.

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.

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Kawasaki, Japan

Noboru Kawada