Hitachi, Ltd.

Hitachi Denshi Kabushiki Kaisha

Hitachi-kokusai Electric Inc.

Nippon Hoso' Kyokai

Toshiyuki Akiyama

Kenji Takahashi

Naoki Ozawa

Nobuo Tsukamoto

Kazuhiro Sato

Atsushi Miyashita

Morishi Izumita

Shusaku Nagahara

Itaru Mimura

Seiichi Sano

Iwao Takemoto

Shinya Ohba

Norio Koike

Masuo Umemoto

Haruhisa Ando

Toshifumi Ozaki

Masaaki Nakai

Takahiro Matsumoto

Takashi Nakamura

Yoshizumi Eto

Shuusaku Nagahara

Tatuhiro Nakada

Koji Kudo

Takuya Imaide

Masaharu Kubo

Hiroyuki Takesue

Tetsuomi Ikeda

Takeshi Ogino

Takahiro Nakano

Seiichi Mita

Akira Shibata

Toshihisa Tsukada

Koichi Seki

Hisashi Nakamura

Toru Baji

Shigeru Shimada

Masatada Horiuchi

Haruo Matsumaru

Shigeki Nishizawa

Tatsuhiro Nakada

Chushirou Kusano

Akihide Okuda

Kenichi Tsuchida

Kazuhiro Satoh

Hideyuki Ono

Masanori Sato

Shigeki Moriyama

Kenji Itoh

Yoichi Tokunaga

Satoshi Okabe

Syusaku Nagahara

Kenji Ito

Itsuo Ishida

Shinya Oba

Hisao Koda

A transmission apparatus of orthogonal frequency division multiplexing for multiplexing a plurality of carriers orthogonal to one another to transmit a modulated signal. The transmission apparatus includes a first modulator for outputting a code modulated in accordance a modulation scheme which can be applied with a synchronous detection for demodulation, a second modulator for outputting a code modulated in accordance with a modulation scheme different from the modulation scheme associated with the first modulator, and a distributing circuit for distributing the codes modulated by the first and second modulators to a plurality of carriers. The distributing circuit distributes the code modulated by the second modulator to all or some of carriers existing within a predetermined number of columns from at least one of both end regions of a signal transmission frequency band, and the code modulated by the first modulator to the remaining carriers.

Signal transmission/reception system of orthogonal frequency division multiplexing

A signal transmission apparatus for a digital modulation type, wherein each of information codes is assigned to any one of a plurality of signal points arranged on an I-Q complex plane, a pilot signal used for demodulating said information codes and an auxiliary signal are assigned to be arranged on signals points on the I-Q complex plane, a signal modulated based on coordinates corresponding to the assigned signal points is transmitted, the transmitted signal is received, and the received signal is demodulated to reproduce the information codes, and wherein the signal points of said auxiliary signal and said pilot signal are arranged on different positions on said I-Q complex plane.

Digital modulation type signal transmission apparatus and method of displaying received signal in the signal transmission apparatus

A signal transmission system of an OFDM using a plurality of carriers to transmit signal comprises a transmitting apparatus and a receiving apparatus. The receiving apparatus comprises an input unit for applying the OFDM signal from the transmitting apparatus; a fast Fourier transforming unit for separating the OFDM signal from the input unit into base-band signals including pilot signals; an interpolation unit for interpolating the pilot signals in a time-axis direction and a frequency-axis direction to calculate reference signal vectors of the carriers in which the pilot signals are not included; a demodulation unit for decoding to be produced as information codes; a delay a unit for adjusting a delay time of said base-band signals passing the delay unit; and a control unit coupled with the interpolation unit, for changing frequency band characteristics of the interpolation unit.

Receiving apparatus for signal transmission system of orthogonal frequency division multiplexing type

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 digital signal communication system includes a transmission circuit or a receiving circuit for digitally transmitting two types of signals by orthogonal modulation. The transmission circuit includes an orthogonal modulator and a nonrecursive digital low-pass filter having the same frequency characteristic as a predetermined frequency characteristic of the output signal of the orthogonal modulator. The receiving circuit includes an orthogonal demodulator and a nonrecursive digital low-pass filter having the same frequency characteristic as a predetermined frequency characteristic of the output signal of the orthogonal demodulator. The total number of taps required for determining the frequency characteristic of the nonrecursive digital low-pass filter is set to H, and the series of tap coefficients is set as C , C , C , . . . , C , where H is an arbitrary positive integer of not less than 2. The nonrecursive digital low-pass filters include a first low-pass filter for filtering one of the two types of signal and a second low-pass filter for filtering the other type of the signal. The first low-pass filter has taps about one half of H including a tap coefficient series C , C , C , . . . , C , and the second low-pass filter has taps about one half of H including a tap coefficient series C , C , C , . . . , C .

Digital communication system of orthogonal modulation type

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 bi-directional digital transmission method, and system, for sending and receiving digital transmission signals having a frame configuration modulated by an orthogonal frequency division multiplex modulation scheme. A first sending unit in a first transmission station converts first continuous data to a up-direction intermittent transmission signal, and sends it from a first antenna via a first switchover unit. The up-direction intermittent transmission signal is received by a second antenna of a second transmission station, and supplied to a second receiving unit of the second transmission station via a second switchover unit of the second transmission station. The second receiving unit determines whether receiving operation of the up-direction intermittent transmission signal has been established, and if so, restores the original first continuous data. A second sending unit in the second transmission station converts second continuous data to a down-direction intermittent transmission signal, and sends it from a second antenna via a second switchover unit. In the first transmission station, the down-direction intermittent sending transmission signal is received by the first antenna, and supplied to a first receiving unit via the first switchover unit to restore the original second continuous data.

Bi-directional digital transmission system and bi-directional digital transmission method

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

Transmission method and apparatus allow two channel simultaneous transmission of information codes having a transmission rate of 1.5 Mbps necessary for the transmission of motion pictures or semi-motion pictures through a 2.4 GHz small power communication band (ISM band). Carrier frequencies f.sub.fa and f.sub.hb of the two channels are set to different values from each other, QPSK modulation is demodulated in a receiver and then inverse-spread of the spectrum spread is conducted, and a low pass filter having a root roll-off characteristic is inserted to a succeeding stage of a spectrum spread circuit of a transmitter and a preceding stage of the spectrum inverse-spread circuit of the receiver.

Spectrum spread transmission method and apparatus

An image pickup apparatus for a television and a depth-of-field control apparatus used in the same. Image signals corresponding to a plurality of picture images different in focal point or length position are obtained by a mechanism for changing a focal point or length position to produce a new image signal by composing these image signals through a composition circuit, and motion information of an object is obtained by a circuit for detecting a moving portion in the object to control the image composition by the motion information. The focal point or length position is moved in synchronism with an integer multiple of a vertical scanning period of the television. The image signals corresponding to the plurality of picture images different in focal point or length position are obtained within one vertical scanning period determined by the system of the television. The amount of movement of the focal point or length position is controlled in conjunction with a value of a lens aperture of the camera lens. The image composition is controlled by a composition control circuit made up of a circuit for detecting individual powers of image signals corresponding to a plurality of different picture images, a circuit for comparing the detected powers with each other, and a circuit for detecting the position of an edge included in one of the image signals, wherein a control signal for the image composition produced by the power comparison circuit is compensated by the edge position information obtained by the edge detection circuit.

Depth-of-field control apparatus and image pickup apparatus having the

A signal for a first scanning line including a picture element whose signal does not exist and a signal for a second scanning line adjacent to the first scanning line in the same field are obtained in the same period. Then, a coefficient representing the ratio of the level of the signal for the first scanning line to the level of the signal for the second scanning line is calculated. Multiplying by the coefficient the level of the signal for the second scanning line to thereby provide an interpolation signal. The interpolation signal is added to the signal for the first canning line.

Method and apparatus for interpolating a video signal of a picture

Growing community of inventors

Tokorozawa, Japan

Toshiyuki Akiyama