Hitachi, Ltd.

Atsushi Ogane

Junichi Tatezaki

Yasuhiro Sagesaka

Hideo Wada

Yoshifumi Kawamura

Isao Kodama

A base station (5) comprises a base transmitter (6) for transmitting information optically to a plurality of portable stations (1 to 4) at such a predetermined time interval as is designated by portable station designating information. Each of the portable stations (1 to 4) comprises a potable transmitter (7) for transmitting information optically to the base station (5) in response to the transmission, which is designated by the portable station designating information coming from said base station (5), and within the range of the aforementioned time interval immediately after said transmission. Transmissions (ACK1 to ACK4) from the mating portable stations to the base station are individually inserted between the interval periods of the transmissions (REQ1 to REQ4) from the base station (5) to the portable stations (1 to 4) so that the single base station performs optical communications with the plurality of portable stations in a half-duplex time sharing manner.

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Chiba, Japan

Atsushi Ogane