Pulse or digital communications – Synchronizers
Reexamination Certificate
1999-06-02
2003-04-08
Chin, Stephen (Department: 2734)
Pulse or digital communications
Synchronizers
C375S142000, C375S150000
Reexamination Certificate
active
06546064
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a synchronization acquiring method for matching the phase of a spreading code, which is used to spread data at a base station so as to enable the mobile station to communicate by radio with the base station, with the phase of a spreading code, which is used at the mobile station to de-spread input data that is used to de-spread the input data input from the base station, and a synchronization acquiring apparatus for carrying out the synchronization acquiring method. The act of matching the phase of the spreading code used at the base station with the phase of the spreading code used at the mobile station is called synchronization.
2. Description of Related Art
Two types of operations for performing a synchronization at the mobile station are known. One of them is a synchronization acquiring operation and the other is a synchronization tracking operation.
When a power source is turned on at the mobile station, the mobile station performs a synchronization acquiring operation. Conventionally, the sliding correlating system has been used for the synchronization operation. In the sliding correlating, the phases of a spreading code to be multiplied with the input data are slid so as to be de-spread the input data supplied from the base station, a de-spread result is obtained for each of the phases, and a phase that maximizes the correlation value is obtained from the de-spread result. When the power source is turned on at the mobile station, the mobile station slides the phases of the spreading code by entire bits of the spreading code in the sliding correlating system so as to perform the above-described synchronization acquiring operation. In such a synchronization acquiring operation, the number of phases of the spreading code to be slid by the sliding correlating system is large. Therefore, it requires a long time to perform the synchronization acquiring operation.
The mobile station performs a synchronization tracking operation after the synchronization acquiring operation. In the synchronization tracking operation, the mobile station maintains the state of synchronization between the phases of the spreading code, on which the synchronization acquiring operation has been performed, and the input data that is serially input to the mobile station. For example, a conventional synchronization tracking apparatus in which a PLL circuit (Phase Locked Loop Circuit) is used is able to realize such a synchronization tracking operation.
In general, the mobile station shifts to a sleep state when the mobile station is put into a waiting state while performing a synchronization tracking operation in order to reduce power consumption. While the mobile station is in the sleep state, the mobile station periodically monitors for any input data supplied from the base station while maintaining the state of inactivity. When no data is supplied from the base station, the mobile station remains in the sleep state. If any input data is received during the sleep state, the mobile station shifts from the sleep state to an active state. The mobile station performs a synchronization acquiring operation again to shift to the active state. The same sliding correlating system is used in the synchronization acquiring operation. When the mobile station shifts from the sleep state to the active state, the mobile station repeats exactly the same operation that the mobile station performed when the mobile station last shifted to the active state. Therefore, the mobile station requires a long length of time to perform the synchronization acquiring operation.
SUMMARY OF THE INVENTION
Given these problems, it is an object of the present invention to provide a synchronization acquiring method capable of reducing the length of time required to perform in wireless communication a synchronization acquiring operation when the mobile station shifts from a sleep state to an active state and a synchronization acquiring apparatus capable of performing such a synchronization acquiring method.
In order to achieve the above-stated objective, a synchronization acquiring method according to the embodiments of present invention has the following three steps. In, the first step multiple correlation values are obtained between the input data supplied from a base station to the mobile station and multiple phases of a spreading code multiplied with the input data in the mobile station before the mobile station transits from the active state to the sleep state, multiple phases of the spreading code that correspond to the correlation values are determined, and the multiple phases are stored. In the second step, phases of the spreading code multiplied with the input data are determined using the phases obtained when the mobile station transits from the sleep state to the active state. In the third step, correlation values between the input data and the phases of the spreading code multiplied with the input data are obtained using the phases of the spreading code determining in the second step.
Preferably in the second step, it is judged whether the mobile station has been moved or not while the mobile station was in the sleep state when the mobile station transits from the sleep state to the active state. If the mobile station has remained at rest, the phases of the spreading code are determined using the multiple phases stored in the first step. If the mobile station has been moved, the size of a range, over which the phases of the spreading code are slid, are determined to be equal to the entire range that corresponds to the length of the spreading code.
In order to achieve the above-stated objective, a synchronization acquiring apparatus according to embodiments of the present invention has a correlation storing unit which obtains correlation values between the input data supplied from the base station and the spreading code multiplied with the input data and stores the correlation values and the phases of the spreading code that correspond to the correlation values, and an operation control unit which judges whether a synchronization acquiring operation has been completed or not based on the correlation value stored in the correlation storing unit, sends the phases to synchronization tracking apparatus when the operation control unit judges that the synchronization acquiring operation has been completed, performs a control so as to repeat the synchronization acquiring operation when the operation control unit judges that the synchronization acquiring operation has not been completed, and receives the multiple phases stored in the synchronization tracking apparatus to control the correlation storing unit using the phase stored in the synchronization tracking apparatus and the phase differences between the phases stored in the synchronization tracking apparatus when the mobile station transits from the sleep state to the active state.
Preferably, the correlation storing unit of the synchronization acquiring apparatus according to the present invention has a first spreading code generating unit which, when a first starting phase is input from a phase control unit, generates a spreading code sliding a phase from the first starting phase over a prescribed range and generates the spreading code sliding a phase over a prescribed range that corresponds to the length of the spreading code when a control signal is input from a control unit, a first de-spreading unit which multiplies the spreading code generated by the first spreading code generating unit to the input data and outputs first demodulated data, a second spreading code generating unit which, when a second starting phase is input from the phase control unit, generates a spreading code sliding a phase from the second starting phase over a prescribed range and generates the spreading code sliding a phase over a prescribed range that corresponds to the length of the spreading code when a control signal is input from the control unit, a second de-spreading unit which multiplies the spreading code g
Chin Stephen
Frank Robert
Kaminski Jeffri
Kim Kevin
Oki Electric Industry Co. Ltd.
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