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Multiplexer-related

CDMA-communications-method-and-system

Method of detecting reference symbols for a digital data receiver

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Method for adaptively filtering doppler signals using a complex time domain filter

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Spatial diversity processing for underwater acoustic telemetry

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Developing a channel impulse response by using distortion

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Method for receiving multicarrier digital signals

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Peak to average power ratio reduction

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Compensation method for I/Q channel imbalance errors

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CDMA communications method and system

Details

Inventors: Adachi, Fumiyuki; Sawahashi, Mamoru;
Assignee: NTT Mobile Communications Network, Inc. (JP)
Primary Examiner: Ton; Dang
Assistant Examiner:
Attorney, Agent or Firm: Johnson; John T. Rogers & Wells

A CDMA communications method capable of multiplex transmission of data over a wide range from a low rate to high rate, such as image data, without a considerable increase in a circuit scale. A fundamental transmission rate is determined, for example, at 32 kbps, a rate higher than 8 kbps conventionally used. The data whose transmission rate is equal to the fundamental transmission rate is transmitted in frames including no vacant portion. Data whose transmission rate is lower than the fundamental transmission rate (16 kbps, for example) are transmitted in frames including vacant portions. The vacant portions are not transmitted. This makes it possible to receive data through other channels during a time period associated with the vacant portions. Data of a higher transmission rate, 128 kbps, for example, can be multiplexed and transmitted through four channels using different spreading codes.

DETAILED DESCRIPTION It is therefore an object of the present invention to provide a CDMA communications method and system which can implement variable rate data transmission from a high-rate to low-rate with a small amount of increase in circuitry of transceivers.
Another object of the present invention is to provide a CDMA communications method and system which can detect a base station, to which a mobile station is to be newly connected, at the mobile station side during the communication.
Still another object of the present invention is to provide a CDMA communications method and system wherein a mobile station can receive various channel data transmitted from base stations while the mobile station is communicating.
In a first aspect of the present invention, there is provided a CDMA (Code Division Multiple Access) communications method for transmitting transmission data through one or mote channels between base stations and a mobile station, the method comprising the steps of: generating a frame including at least a part of the transmission data and a vacant portion when a transmission rate of the transmission data is lower than a predetermined rate, the vacant portion having no data to be transmitted; performing a primary modulation of the frame to produce a primary modulation signal; performing a secondary modulation of the primary modulation signal using a spreading code to produce a secondary modulated wideband signal, the spreading code being different for each of the channels; and transmitting the wideband signal using a carrier.
Here, the step of generating a frame may comprise the steps of: predetermining a transmission rate higher than a minimum transmission rate as a fundamental transmission rate; and determining a frame length such that the frame includes no vacant portion when data is transmitted at the fundamental transmission rate.
The minimum transmission rate may be a rate of transmitting a voice signal.
The CDMA communications method may further comprise the step of generating a plurality of frames to be assigned to a plurality of the channels when data is transmitted at a rate higher than the fundamental transmission rate

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