Hitachi Denshi Kabushiki Kaisha

Tatuhiro Nakada

Toshiyuki Akiyama

Nobuo Tsukamoto

Atsushi Miyashita

Seiichi Sano

Hiroyuki Takesue

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

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.

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Kodaira, Japan

Tatuhiro Nakada