Hitachi Denshi Kabushiki Kaisha

Hitachi-kokusai Electric Inc.

Hitachi, Ltd.

Seiichi Sano

Atsushi Miyashita

Nobuo Tsukamoto

Toshiyuki Akiyama

Tatuhiro Nakada

Hiroyuki Takesue

Takayuki Tanaka

Tatsuhiro Nakada

Kenichi Tsuchida

Nobuo Hirose

Yuuichi Oonami

Yoshikatsu Wagatsuma

Shigeki Moriyama

Ryu Watanabe

Shuji Usui

Itsuo Ishida

Hisao Koda

Fumihito Tomaru

An apparatus for receiving digital data includes a memory unit for temporarily storing therein a plurality of data streams, each of which includes data and clock obtained by demodulating plural redundant signals received in each receiver in response to a signal generated based on each clock; a writing control unit for controlling a writing of the plurality of the data streams into the memory unit; a data reading control unit for reading the data streams stored temporarily in the memory unit in a synchronized manner; and a selection unit for selecting one of the read data streams to output the selected data stream. The writing control unit detects a synchronization packet included in the plurality of data streams to control the writing of the plurality of data streams into the memory unit based on the synchronization packet.

Apparatus for receiving digital data

A received, same signal is distributed to two channels, the received signals on the two channels are demodulated to produce a plurality of data streams on each of the two channels, and the plurality of data streams of one channel is selected to produce from the pluralities of data streams on the two channels.

Digital data receiving apparatus and method with system changeover function

A distortion compensating circuit for a power amplifier attains raised compensating accuracy with shorter convergence time by accurately and quickly generating a distortion compensation signal for pre-distortion. An error signal representing the difference between the input and output signals of the power amplifier is generated. From the error signal and the input signal, the coefficients of the third-order intermodulation distortion, fifth-order intermodulation distortion and seventh-order intermodulation distortion are calculated. According to these coefficients, a distortion compensating signal which is characteristically opposite in phase and gain to the intermodulation distortions is generated.

Distortion compensation circuit, distortion compensation signal generating method, and power amplifier

A data transmission system and method utilizing orthogonal frequency division multiplexing, wherein in a receiver apparatus of the data transmission system, synchronization is obtained by the following steps. A correlation value of a reception signal which was orthogonal frequency division multiplexed and a predetermined sync symbol pattern or a signal obtained by delaying one effective symbol period is arithmetically calculated a predetermined times in a predetermined arithmetic calculation window. The correlation values obtained after a predetermined number of arithmetic calculations from an intermediate of a total number of the arithmetic calculations are reduced so as to not exceed a predetermined value. The maximum value is detected from the correlation values and a reference signal for demodulating the reception signal is formed based on information of a time based position of a signal at the time when the maximum value is obtained.

Synchronization control method for receiver apparatus of data transmission system utilizing orthogonal frequency division multiplex, and data transmission system

A data transmission system for transmitting data from a transmitter to a receiver located away therefrom. The transmitter includes circuitry for transmitting together a main signal having a carrier modulated with main data to be transmitted and as well as a sub-signal to be used in frequency conversion and generated by modulating a carrier of a predetermined frequency out of a frequency band of the main signal. The receiver includes circuitry for receiving a receive signal from the transmitter and extracting the sub-signal therefrom and also includes circuitry for generating a signal to be used as a reference at the time of converting the receive signal to a signal having a predetermined frequency on the basis of the extracted sub-signal.

Data transmission system, data transmission communication station, and data transmission method

A communication method in an orthogonal frequency division multiplexing modulation communication system includes a transmission apparatus in which a frequency bandwidth of a signal modulated in accordance with an orthogonal frequency division multiplexing modulation system is changed and the modulated signal is transmitted and a receiving apparatus in which the modulated signal is received and a frequency bandwidth for demodulation of the received signal is changed to follow the change of the frequency bandwidth of the modulated signal.

Communication, transmission and receiving method and apparatus using orthogonal frequency division multiplexing modulation system

A data transmitting apparatus in which in an antenna switching of the data transmitting apparatus, a sudden change of transmission path characteristics is prevented and a state where an automatic equalizing function on the reception side can follow can be held. The apparatus has a processing circuit for gradually switching antennas of the data transmitting apparatus with respect to the time and for continuously switching one antenna from the rated level to the 0 level and for continuously switching the other antenna from the 0 level to the rated level. The apparatus operates so as to always keep the optimum constellation state in which the automatic equalizing process follows.

Data transmitting method and data transmitting apparatus accompanied with a plurality of transmitting of receiving antennas

A data transmission apparatus of an orthogonal frequency multiplex modulation system wherein data is transmitted using a plurality of carriers which are in a mutually orthogonal relationship with one another. The apparatus includes a transmitter which previously inserts a group of predetermined synchronization symbols into an OFDM modulated transmission signal every fixed period and a receiver which demodulates a received OFDM modulated transmission signal to a baseband OFDM signal. In the receiver, an absolute value of an A/D converted digital signal is taken and the signal is bandwidth-limited to a predetermined band width. Then, it is decided whether an amplitude of the signal is larger than or smaller than a predetermined value and a decision result thereof is produced. A null section in the synchronization symbol group is detected on the basis of the decision result and a start point of another synchronization symbol subsequent to the null section is further detected. The time when both of the presence of the null section and the start point of another synchronization symbol are detected is regarded as a synchronization timing and the operation timing of a demodulator for the receiver is set to the synchronization timing.

Data transmission apparatus and receiving apparatus using orthogonal frequency division multiplex modulation system

An orthogonal frequency division multiplex (OFDM) modulator of such a system as to add guard intervals to a temporal waveform generated by modulating an input data train into a large number of (sub)carriers, conducting quadrature modulation, and outputting an OFDM signal. The OFDM modulator includes an IFFT circuit for conducting inverse fast Fourier transform processing to modulate the input data train into a large number of (sub)carriers, a guard interval adder for adding a guard interval to each effective symbol duration of a composite carrier signal supplied from the IFFT circuit and outputting a resultant signal, a control signal generator for generating, in synchronism with each guard interval of the composite carrier signal having the guard intervals added thereto, such a control signal as to attenuate signal amplitude of the composite carrier signal over an interval substantially equal in length to each guard interval; and an amplitude controller, responsive to the control signal, to attenuate the amplitude of the composite carrier signal supplied from the guard interval adder and output a resultant signal, only over an interval substantially equal in length to each guard interval. The amplitude controller outputting, in remaining intervals, the composite carrier signal supplied from the guard interval adder as it is.

OFDM modulator and OFDM modulation method for digital modulated wave having guard interval

A data transmission apparatus using a digital modulation system wherein a transmitting side inserts a group of predetermined synchronization symbols into a transmission signal at predetermined intervals to be transmitted. A receiving side calculates an electric power value of a received transmission signal. When a no-signal period (null section) in the synchronization symbol group is to be detected and decided from a magnitude of the received signal electric power value, a threshold for reference of decision for detecting the null section is calculated on the basis of an average electric power value for a predetermined period in the received signal electric power value and the threshold calculated in accordance with the received signal level of the transmission signal is used to detect synchronization stably.

Synchronization detection method for data transmission apparatus and data transmission apparatus using the same

In a demodulating method of demodulating amplitude-demodulated signals in an amplitude phase shift keying system for conducting an amplitude modulation by setting signal points as information codes on a complex plane representing a signal space of transmission signals onto circumferences of two concentric circles including a first circle having a first diameter and a second circle having a second diameter smaller than the first diameter on the complex plane, there are obtained, in accordance with an amplitude value of an amplitude component of each symbol of a received amplitude-modulated signal, a first threshold value and a second threshold value having a predetermined relationship with the amplitude value. Next, the amplitude value the an amplitude component of each symbol of the successively received amplitude-modulated signal is compared with the first and second first threshold values to determine an amplitude variation in the amplitude component of each symbol in accordance with a result from the comparison so as to output therefrom a signal representing the determination result as a code obtained by demodulating the amplitude component.

Method of an apparatus for demodulating amplitude-modulated signals in

An image signal compression transmission system for transmitting and receiving a compressed image signal, having a transmitter section which entropy codes digitized image data for transmission, a transmission channel through which entropy-coded codes sent from said transmitter section are transmitted, and a receiver section which decodes said entropy-coded codes received from said transmission channel and derives an original digital image signal. In the transmitter section, digital image data is entropy coded. The entropy-coded codes are transmitted to the receiver section through the transmission channel. In the receiver section, the received codes are entropy code decoded at a decoding speed corresponding to a transmission rate on the transmission channel. Coefficient codes derived by the decoding are stored into a memory at the same speed as the decoding speed. Then, the coefficient codes are read from the memory at a speed different from the decoding speed, but at the same speed as a signal processing rate in a signal processing system subsequent to the memory.

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Higashiyamato, Japan

Seiichi Sano