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Spread-spectrum-communication-system-and-transmission-power-control-method-therefor

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Spread spectrum communication system and transmission power control method therefor

Details

Inventors: Yano, Takashi; Doi, Nobukazu;
Assignee: Hitachi, Ltd. (Tokyo, JP)
Primary Examiner: Safourek; Benedict V.
Assistant Examiner:
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus

In a spread spectrum communication system, one (W.sub.n) of a series of orthogonal codes for spectrum spreading is assigned to signal-to-noise ratio measurement in a terminal. On the basis of a noise signal detected by de-spreading a signal received from an antenna with the above described orthogonal code W.sub.n and a pilot signal, each terminal derives a signal-to-noise ratio. Each terminal transmits the signal-to-noise ratio to the base station as a power control signal. On the basis of signal-to-noise information received from each terminal as the power control signal, the base station controls signal transmission power for each terminal.

DETAILED DESCRIPTION An object of the present invention is to provide a spread spectrum communication system and a power control method whereby each terminal can communicate with the base station with a high signal-to-noise ratio.
Another object of the present invention is to provide a spread spectrum communication system and a power control method whereby the number of possible active channels can be increased in each cell.
Another object of the present invention is to provide a mobile terminal capable of rapidly calculating control information for power control to be transmitted to the base station.
In order to achieve the above described objects, in a spread spectrum communication system according to the present invention, the base station assigns at least one orthogonal code included in an orthogonal code sequence for spectrum spreading as "orthogonal code W.
sub.
N for control (for measuring noise)" which is not applied to modulation of the pilot signal and transmission signals addressed to each terminal.
Furthermore, in accordance with present invention, the signal-to-noise ratio of a received signal is derived on the basis of received power of the noise signal obtained by de-spreading the signal received from an antenna with the orthogonal code W.
sub.
N assigned to noise measurement and received power of a pilot signal obtained by de-spreading with the orthogonal code W.
sub.
0 .
In a spread spectrum communication system according to the present invention, each terminal transmits power control information depending upon the value of the above described signal-to-noise ratio to the base station, and the base station controls transmission power of a transmission signal (a data signal) for each terminal according to the power control information received from the terminal.
All signals transmitted from one base station are orthogonal to the orthogonal code used exclusively for control.
If in each terminal as described above the signal received from the antenna is de-spreaded by using the orthogonal code W

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