Abstract:
A synchronization acquiring method capable of reducing the length of time required to perform in wireless communication a synchronization acquiring operation is provided when the mobile station transits from a sleep state to an active state. A synchronization acquiring apparatus capable of performing such a synchronization acquiring method is also provided. The method 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 to 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 to the input data are determined using the phase 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 to the input data are obtained using the phases of the spreading code determined in the second step.

Description:
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 generated by the second spreading code generating unit to the input data and outputs second demodulated data, a correlation generating unit which outputs correlation values between the input data and the spreading code based on the first demodulated data and the second demodulated data, and a first memory which receives phases of the spreading code that generates the peaks of the correlation values based on the correlation values from the first de-spreading unit and stores the correlation values and the phases of the spreading code. Also preferably, the operation control unit has a control unit which receives the correlation values stored in the first memory, judges whether the synchronization acquiring operation has been completed or not based on the correlation values, sends the phases stored in the first memory to a second memory installed inside the synchronization tracking apparatus when the operation control unit judges that the synchronization acquiring operation has been completed sends a reset signal for repeating the synchronization acquiring operation to the first de-spreading unit and the second de-spreading unit when the operation control unit judges that the synchronization acquiring operation has not been completed, and reads at least two phases stored in the second memory of the synchronization tracking apparatus to output the phases and a phase difference between the phases when the mobile station transits from the sleep state to the active state, and a phase control unit which outputs the first starting phase and the second starting phase using the phases and the phase difference output from the control unit. 
     More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, an adder which calculates the sum of the first cumulative data and the second cumulative data, and an amplitude calculating unit which calculates the amplitude of the sum and outputs the amplitude as the correlation value. 
     More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has an adder which calculates the sum of the first demodulated data and the second demodulated data, an accumulating unit which accumulates the sum calculated by the adder to produce a cumulative sum and outputs the cumulative sum as cumulative data, and an amplitude calculating unit which calculates the amplitude of the cumulative data and outputs the amplitude as the correlation value. 
     More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, a first amplitude calculating unit which calculates the amplitude of the first cumulative data and outputs the first cumulative data as a first correlation value, a second amplitude calculating unit which calculates the amplitude of the second cumulative data and outputs the second cumulative data as a second correlation value, and an adder which calculates the sum of the first correlation value and the second correlation value. The correlation generating unit then outputs the sum obtained by the adder as the correlation value. 
     More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, a first amplitude calculating unit which calculates the amplitude of the first cumulative data and outputs the first cumulative data as a first correlation value, a second amplitude calculating unit which calculates the amplitude of the second cumulative data and outputs the second cumulative data as a second correlation value, a first square calculating unit which calculates the square of the first correlation value and outputs the square of the first correlation value as a first squared correlation value, a second square calculating unit which calculates the square of the second correlation value and outputs the square of the second correlation value as a second squared correlation value, and an adder which calculates the sum of the first squared correlation value and the second squared correlation value. The correlation generating unit then outputs the sum obtained by the adder as the correlation value. 
     More preferably, the correlation generating unit of the synchronization acquiring apparatus according to the present invention has a first accumulating unit which outputs the cumulative value of the first demodulated data as first cumulative data, a second accumulating unit which outputs the cumulative value of the second demodulated data as second cumulative data, a first amplitude calculating unit which calculates the amplitude of the first cumulative data and outputs the first cumulative data as a first correlation value, a second amplitude calculating unit which calculates the amplitude of the second cumulative data and outputs the second cumulative data as a second correlation value, a first square calculating unit which calculates the square of the first correlation value and outputs the square of the first correlation value as a first squared correlation value, a second square calculating unit which calculates the square of the second correlation value and outputs the square of the second correlation value as a second squared correlation value, and an adder which calculates the sum of the first squared correlation value and the second squared correlation value. The synchronization acquiring apparatus further has a first additional memory which receives the phase of the spreading code that generates the peak of the first squared correlation value based on the first squared correlation value from the first de-spreading unit and stores the phase, and a second additional memory which receives the phase of the spreading code that generates the peak of the second squared correlation value based on the second squared correlation value from the second de-spreading unit and stores the phase. Moreover, the operation control unit has a control unit which receives the phase stored in the first additional memory and said phase stored in the second additional memory, sends the phase stored in the first additional memory and the phase stored in the second additional memory to the second memory installed inside the synchronization tracking apparatus when the operation control unit judges that the synchronization acquiring operation has been completed, sends a reset signal for repeating the synchronization acquiring operation to the first de-spreading unit and the second de-spreading unit when the operation control unit judges that the synchronization acquiring operation has not been completed, and reads at least two phases stored in the second memory of the synchronization tracking apparatus to output the phases and a phase difference between the phases when the mobile station transits from the sleep state to the active state, and a phase control unit which outputs the first starting phase and the second starting phase using the phases and the phase difference output from the control unit. 
     More preferably, the first additional memory of the synchronization acquiring apparatus according to the present invention receives the phase of the spreading code that generates the peak of the first squared correlation value based on the first correlation value from the first de-spreading unit and stores the phase, and the second additional memory receives the phase of the spreading code that generates the peak of the second squared correlation value based on the second correlation value from the second de-spreading unit and stores the phase. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a synchronization acquiring apparatus according to the first embodiment of the present invention. 
     FIG. 2 shows a relation between the phases of the spreading code and the cumulative correlation values for explaining an operation of the synchronization acquiring apparatus according to the first embodiment of the present invention. 
     FIG. 3 shows another relation between the phases of the spreading code and the cumulative correlation values for explaining another operation of the synchronization acquiring apparatus according to the first embodiment of the present invention. 
     FIG. 4 is a block diagram of a synchronization acquiring apparatus according to the second embodiment of the present invention. 
     FIG. 5 is a block diagram of a synchronization acquiring apparatus according to the third embodiment of the present invention. 
     FIG. 6 is a block diagram of a synchronization acquiring apparatus according to the fourth embodiment of the present invention. 
     FIG. 7 is a block diagram of a synchronization acquiring apparatus according to the fifth embodiment of the present invention. 
     FIG. 8 is a block diagram of a synchronization acquiring apparatus according to the sixth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Normally, a synchronization acquiring apparatus installed in a mobile station outputs multiple correlation values for a signal of the same channel received from the base station. It is inferred that the electromagnetic wave carrying the input data transmitted from the base station is caused to travel multiple distinct paths due to the influence of the surrounding environment, and is received by the mobile station. It is inferred that, as a result, these multiple distinct correlation values are generated by the difference between the lengths of the multiple paths. Each of the correlation values that the synchronization acquiring apparatus outputs and the phases of the spreading code that correspond to the correlation values are held constant as long as the operator of the mobile station remains at rest at the same position. This invention is focused on the phases of the spreading code that correspond to the multiple correlation values output by the synchronization acquiring apparatus and the difference between the phases. In what follows, the term “phases” will refer to the phases of spreading code that multiply input data supplied to the mobile station. 
     When the mobile station transits from the sleep state to the active state, the synchronization acquiring apparatus of embodiments of the present invention performs a synchronization acquiring operation by first sliding the phases over a prescribed range using a reference one of the multiple correlation values obtained by the synchronization tracking apparatus before the mobile station was shifted into the sleep state and then uses the sliding correlating system. 
     The synchronization acquiring apparatus stores the phases of the other correlation values that had been obtained by the synchronization tracking apparatus before the mobile station was put to the sleep state. 
     In what follows, preferred embodiments of the present invention will be explained with reference to the attached drawings. However, the range of technical applications of the present invention is not restricted to the following embodiments. 
     (First Embodiment) 
     First, the first embodiment of the present invention will be explained. 
     FIG. 1 shows a block diagram of a synchronization acquiring apparatus according to the first embodiment of the present invention. In FIG. 1, the synchronization acquiring apparatus is installed inside the mobile station. The synchronization acquiring apparatus has a first de-spreading unit  1  and a second de-spreading unit  2 . A first accumulating unit  3  is connected to the first de-spreading unit  1 . A second accumulating unit  4  is connected to the second de-spreading unit  2 . An adder  5  is connected to the first accumulating unit  3  and the second accumulating unit  4 . An amplitude calculating unit  6  is connected to the adder  5 . A first memory  7  is connected to the amplitude calculating unit  6 . The first de-spreading unit  1 , a control unit  8 , and the amplitude calculating unit  6  are connected to the first memory  7 . A phase control unit  9 , a first spreading code generator  10   a , and a second spreading code generator  10   b  are connected to the phase control unit  9 . 
     A second memory  12  installed inside a synchronization tracking apparatus  11  of the mobile station is connected to the control unit  8 . 
     The first de-spreading unit  1  performs a spreading demodulation on the input data Din input from the input unit using the sliding correlating system. The first accumulating unit  3  accumulates demodulated data that has been spread and demodulated by the first de-spreading unit  1 . The second de-spreading unit  2  has the same structure as the first de-spreading unit  1 , and the second accumulating unit  4  has the same structure as the first accumulating unit  3 . The first de-spreading unit  1 , the second de-spreading unit  2 , the first accumulating unit  3 , and the second accumulating unit  4  can be conventional apparatuses. 
     The adder  5  adds up the cumulative data output from the first accumulating unit  3  and the second accumulating unit  4 . 
     The amplitude calculating unit  6  calculates the amplitude of the cumulative data. The cumulative data output from the first accumulating unit  3  and the second accumulating unit  4  is normally represented by a complex number having an imaginary part. The amplitude calculating unit  6  outputs the absolute value of the complex number as a correlation value. 
     The first memory  7  selects the largest and second largest correlation values from the correlation values supplied from the amplitude calculating unit  6 , and stores these selected correlation values and the phases of the spreading code that correspond to these two selected correlation values. Here, the phase of the spreading code that corresponds to a correlation value refers to the spreading code that is multiplied with the input data Din in the first de-spreading unit  1  or second de-spreading unit  2  so as to generate the correlation value. The first memory  7  then compares the two stored correlation values with the correlation values that are sequentially supplied to the first memory  7 . If any of the correlation values that are sequentially supplied to the first memory  7  is larger than the smaller of the two stored correlation values, then the first memory  7  replaces the smaller of the two stored correlation values with the correlation value newly supplied to the first memory  7 , and then stores the phase of the spreading code that corresponds to the newly supplied correlation value. The phase of the spreading code stored in the first memory  7  is supplied from the first de-spreading unit  1 . 
     The control unit  8  receives the two correlation values and the corresponding two phases from the first memory  7  at a prescribed timing. The control unit  8  then compares the larger of the two correlation values with a threshold value preset in the control unit  8 . If the correlation value is smaller than the threshold value, the control unit  8  judges that the synchronization acquiring operation is not completed yet. When the synchronization acquiring operation is not completed yet, the control unit  8  outputs to the spreading code generating units  10   a  and  10   b  a reset signal for repeating the synchronization acquiring operation. The spreading code generating units  10   a  and  10   b  receive the reset signal from the control unit  8 . When the spreading code generating units  10   a  and  10   b  output a spreading code to the first de-spreading unit  1  and the second de-spreading unit  2 , respectively, the spreading code generating units  10   a  and  10   b  slide the phases of the spreading code by the total bits of the spreading code, and then output the resultant spreading code to the first de-spreading unit  1  and the second de-spreading unit  2 , respectively. 
     If the correlation value is larger than the threshold value, the control unit  8  judges that the synchronization acquiring operation is completed. In this case, the control unit  8  sends to the first memory  7  an instruction to output outside the apparatus the phase that corresponds to the maximum correlation value stored in the first memory  7  as output data Dout. The control unit  8  outputs to the second memory  12  inside the synchronization tracking apparatus  11  the two correlation values and the two phases received from the first memory  7 . The synchronization tracking apparatus  11  starts a synchronization tracking operation based on the two correlation values and the two phases supplied to the second memory  2 . The synchronization tracking apparatus  11  obtains correlation values during the synchronization tracking operation, and selects the largest and second largest correlation values, and acquires the phases of the spreading code that correspond to these correlation values. These two correlation values and two phases are stored in the second memory  12 . The synchronization tracking apparatus  11  is a conventional apparatus, and can be realized using, for example, a PLL circuit. 
     When the mobile station transits from the sleeping state to the active state, the control unit  8  receives the two correlation values and two phases from the second memory  12 , and outputs the two phases to the phase control unit  9 . The two correlation values and two phases in the second memory  12  have been stored before the mobile station was put into the sleep state. The phase control unit  9  supplies the phases input from the control unit  8  to the spreading code generating units  10   a  and  10   b . The first spreading code generating unit  10   a  uses the phase input from the phase control unit  9  as the phase of the spread code that starts to be output to the first de-spreading unit  1  (hereafter this phase will be called the first starting phase), generates a spreading code, and slides the phases of the generated spreading code within the range of ±Δ centered about the first starting phase (**Note: ±Δ are shown in FIG.  3 . As will be explained later, the magnitude of Δ is a controllable parameter.**). The second spreading code generating unit  10   b  uses the phase input from the phase control unit  9  as the phase of the spreading code that starts to be output to the second de-spreading unit  2  (hereafter this phase will be called the second starting phase). 
     The control unit  8  calculates the phase differences of the phases received from the second memory  12 . Moreover, the control unit  8  controls the first and second spreading code generating units  10   a  and  10   b , respectively, so that the phase differences of the spreading codes output from the first and second spreading code generating units  10   a  and  10   b , respectively, will be equal to the phase differences calculated by the control unit  8 . 
     The first de-spreading unit  1  multiplies the spreading code input from the first spreading code generating unit  10   a  with the input data and performs a spreading demodulation operation. Similarly, the second de-spreading unit  2  multiplies the spreading code input from the second spreading code generating unit  10   b  with the input data and performs a spreading demodulation operation. 
     Next, operations in the first embodiment will be explained. 
     In FIG. 2, the horizontal axis represents the phases of the spreading code, and the vertical axis represents cumulative correlation values. The two solid line arrows a 1  and b 1  represent the two phases stored in the first memory  7  and the values that correspond to the two phases. 
     (When the Mobile Station Transits to the Active State for the First Time) 
     Here, it is assumed that the operator of the mobile station at rest has turned on the power source of the mobile station and started to operate the mobile station. In this case, a CPU installed in the mobile station detects that the power source of the mobile station has been turned on. Once it is detected that the power source of the mobile station has been turned on, the mobile station transits to the active state for the first time, and a synchronization acquiring operation is started as follows. 
     In FIG. 1, the synchronization acquiring apparatus performs a synchronization acquiring operation on the input data Din using the sliding correlating system. The control unit  8  sends a reset signal to the first and second spreading code generating units  10   a  and  10   b , respectively. The first and second spreading code generating units  10   a  and  10   b  slide the phases by the front bit of the spreading code and output the spreading code of each of the phases. The first de-spreading unit  1  multiplies the spreading code with the input data Din and performs a spreading demodulation operation. Similarly, the second de-spreading unit  2  multiplies the spreading code with the input data Din and performs a spreading demodulation operation. The second spreading code generating unit  10   b  outputs to the second de-spreading unit  2  spreading code having the same phases as the spreading code of the first spreading code generating unit  10   a.    
     The control unit  8  then judges that the synchronization acquiring operation has been completed. 
     In FIG. 2, it is assumed that two distinct correlation values a 1  and b 1  and two distinct phases S 1  and S 2  have been stored in the first memory  7  as a result of the synchronization acquiring operation. It is inferred that the electromagnetic wave carrying the input data transmitted from the base station that was caused to travel two distinct paths due to the influence of the surrounding environment was received by the mobile station, and as a result, these two distinct correlation values were generated by the difference between the lengths of the two paths. The two phases of the spreading code that correspond to the two distinct correlation values, respectively, are held constant as long as the operator remains at rest. 
     The control unit  8  receives the two distinct correlation values and two phases from the first memory  7  and outputs them to the second memory  12  inside the synchronization tracking apparatus  11 . 
     (When the Mobile Station Transits from the Sleep State to the Active State) 
     Next, it is assumed that the mobile station was put to the sleep state and the operator has reset the mobile station to the active state while remaining at rest. 
     In FIG. 3, the horizontal axis represents the phases of the spreading code, and the vertical axis represents cumulative correlation values. The two broken line arrows a 1  and b 1  represent two correlation values that the synchronization tracking apparatus  11  stored in the second memory  12  before the mobile station was put to the sleep state. The two solid line arrows a 2  and b 2  represent two correlation values that the synchronization acquiring apparatus acquired when the mobile station transited from the sleep state to the active state. 
     In FIG. 1, the synchronization acquiring apparatus performs a synchronization acquiring operation on the input data Din in the following manner. The control unit  8  receives the two correlation values and two phases S 1  and S 2  (S 1 &lt;S 2 ) from the second memory  12 , and outputs the two phases S 1  and S 2  to the phase control unit  9 . The phase control unit  9  sends the phases S 1  and S 2  to the first spreading code generating unit  10   a  and the second spreading code generating unit  10   b , respectively. The first spreading code generating unit  10   a  uses the phase S 1  as the first starting phase, generates a spreading code, slides the phases of the generated spreading code within the range of ±Δ centered about the first starting phase S 1 , and sends the spreading code to the first de-spreading unit  1 . The first de-spreading unit  1  performs a spreading demodulation operation on the input data Din using the spreading code received from the first spreading code generating unit  10   a.    
     The second spreading code generating unit  10   b  uses the phase S 2  as the second starting phase, generates a spreading code, slides the phases of the generated spreading code within the range of ±Δ centered about the second starting phase S 2 , and sends the generated spreading code to the second de-spreading unit  2 . The second de-spreading unit  2  performs a spreading demodulation operation on the input data Din using the spreading code received from the second spreading code generating unit  10   b.  It is to be noted that the range ±Δ in which the phases of the spreading code generated by the second spreading code generating unit  10   b  are slid is the same as the range ±Δ in which the phases of the spreading code generated by the first spreading code generating unit  10   a  are slid. The remainder of the operation in this case is the same as in the case in which the mobile station transits to the active state for the first time. 
     In the case in which the mobile station was put to the sleep state and the operator has reset the mobile station to the active state while remaining at rest, the phase T 1  that corresponds to the phase S 1  in FIG. 3 is acquired. When the second de-spreading unit  2  performs the spreading demodulation operation on the input data Din using the phase T 2  as the second starting phase, the second de-spreading unit  2  slides the phases while holding constant the phase difference α (=S 2 −S 1 ) with respect to the phases slid by the first spreading code generating unit  10   a . As a result, the correlation value b 2  that corresponds to the phase T 2  is acquired. 
     In the first embodiment, when the mobile station transits from the sleep state to the active state, the size of the range ±Δ in which the phases of the spreading code to be spread on the input data are slid can be made smaller, that is, the size of Δ can be reduced. Therefore, the length of time required to perform the synchronization acquiring operation can be greatly reduced. 
     (Second Embodiment) 
     Next, a synchronization acquiring apparatus according to the second embodiment of the present invention will be explained. 
     FIG. 4 is a block diagram of a synchronization acquiring apparatus according to the second embodiment of the present invention. 
     In the second embodiment of the present invention, the same reference numerals are given to the same components that are already used in the first embodiment. Such components will not be explained here. The synchronization acquiring apparatus of the second embodiment is identical to that of the first embodiment except in the following respects. 
     First, in the second embodiment shown in FIG. 4, the first accumulating unit  3  and the second accumulating unit shown in FIG. 1 are replaced with an accumulating unit  16  that is connected to the output side of the adder  5 . 
     Second, in the second embodiment, the adder  5  calculates the sum of the output signal of the first de-spreading unit  1  and the output signal of the second de-spreading unit  2 , and sends the sum to the accumulating unit  16 . Since only one accumulating unit is used in the second embodiment in comparison with the first embodiment in which two accumulating units are used, the manufacturing cost of the apparatus can be reduced. Besides these two respects, the synchronization acquiring apparatus of the second embodiment can achieve the same advantages as that of the first embodiment. 
     (Third Embodiment) 
     FIG. 5 is a block diagram of a synchronization acquiring apparatus according to the third embodiment of the present invention. 
     In the third embodiment of the present invention, the same reference numerals are given to the same components that are already used in the first embodiment. Such components will not be explained here. The synchronization acquiring apparatus of the third embodiment is identical to that of the first embodiment except in the following respects. 
     First, in the third embodiment shown in FIG. 5, the amplitude calculating unit  6  shown in FIG. 1 is replaced with a first amplitude calculating unit  21  connected to the output side of the first accumulating unit  3  and a second amplitude calculating unit  22  connected to the output side of the second accumulating unit  4 . Both the first amplitude calculating unit  21  and the second amplitude calculating unit  22  are identically structured as the amplitude calculating unit  6 . The adder  25  calculates the sum of the output signal of the first unit amplitude calculating  21  and the output signal of the second amplitude calculating unit  22 , and sends the sum to the first memory  7 . 
     The synchronization acquiring apparatus of the third embodiment functionally differs from that of the first embodiment in the following respect. 
     In the first embodiment, the signals input to the adder  5  are normally complex-valued signals, that is, they are vector-valued signals having imaginary parts. In the third embodiment, the signals input to the adder  25  are the absolute values of complex-valued signals, that is, they are scalar-valued signals. 
     In the synchronization acquiring apparatus of the third embodiment, the adder  25  calculates the sum of scalar-valued signals. Therefore, the synchronization acquiring apparatus of the third embodiment is able to obtain cumulative correlation values that are more stable than those obtained by the synchronization acquiring apparatus of the first embodiment. Besides this respect, the synchronization acquiring apparatus of the third embodiment can achieve the same advantages as that of the first embodiment. 
     (Fourth Embodiment) 
     FIG. 6 is a block diagram of a synchronization acquiring apparatus according to the fourth embodiment of the present invention. 
     In the fourth embodiment of the present invention, the same reference numerals are given to the same components that are already used in the third embodiment. Such components will not be explained here. The synchronization acquiring apparatus of the fourth embodiment is identical to that of the third embodiment except in the following respect. 
     In the synchronization acquiring apparatus of the fourth embodiment shown in FIG. 6, a first square calculating unit  31  is installed between the first amplitude calculating unit  21  and the adder  25 , and a second square calculating unit  32  is installed between the second amplitude calculating unit  22  and the adder  25 . 
     In FIG. 6, the correlation values output from the first amplitude calculating unit  21  are input to the first square calculating unit  31 . The first square calculating unit  31  then calculates the squares of the correlation values. The calculation results (hereafter they will be referred to as squared correlation values) correspond to the electric energy of the input data Din. The second square calculating unit  32  is identically structured as the first square calculating unit  31 . 
     In the fourth embodiment, the adder  25  calculates the sum of the squared correlation values. Therefore, the signal-to-noise ratio achieved by the synchronization acquiring apparatus of the fourth embodiment is better than that achieved by the synchronization acquiring apparatus of the third embodiment. Besides this respect, the synchronization acquiring apparatus of the fourth embodiment can achieve the same advantages as that of the third embodiment. 
     (Fifth Embodiment) 
     FIG. 7 is a block diagram of a synchronization acquiring apparatus according to the fifth embodiment of the present invention. 
     In the fifth embodiment of the present invention, the same reference numerals are given to the same components that are already used in the fourth embodiment. Such components will not be explained here. The synchronization acquiring apparatus of the fifth embodiment is identical to that of the fourth embodiment except in the following respect. 
     In the synchronization acquiring apparatus of the fifth embodiment shown in FIG. 7, a first additional memory  41  and a second additional memory  42  are installed in addition to all the components shown in FIG.  6 . 
     The first additional memory  41  stores squared correlation values input from the first square calculating unit  31  and the two phases of the two spread codes that correspond to the largest and second largest correlation values. The second additional memory  42  stores squared correlation values input from the second square calculating unit  32  and the two phases of the two spreading codes that correspond to the largest and second largest correlation values. The two phases of the two spreading codes stored in the first additional memory  41  are supplied from the first de-spreading unit  1 . The two phases of the two spreading codes stored in the second additional memory  42  are supplied from the second de-spreading unit  2 . 
     The control unit  8  receives the correlation values and phases stored in the first additional memory  41  and the correlation values and phases stored in the second additional memory  42  at prescribed timings. The control unit  8  then compares the largest of these correlation values with a threshold value that is pre-set in the control unit  8 . 
     If the largest of these correlation values is smaller than the threshold value, the control unit  8  judges that the synchronization acquiring operation is not completed yet. 
     If the largest of these correlation values is larger than the threshold value, the control unit  8  judges that the synchronization acquiring operation is completed. In this case, the control unit  8  outputs outside the apparatus the phase that corresponds to the largest of all the correlation values received from the first additional memory  41  and second additional memory  42  as output data Dout. Moreover, the control unit  8  outputs the largest and second largest correlation values of all the correlation values received from the first additional memory  41  and second additional memory  42  and the phases that correspond to these correlation values to the second memory  12  inside the synchronization tracking apparatus  11 . 
     Next, the operation of the synchronization acquiring apparatus of the fifth embodiment will be explained. 
     (When the Mobile Station Transits to the Active State for the First Time) 
     In FIG. 7, the synchronization acquiring apparatus performs a synchronization acquiring operation on the input data Din using the sliding correlating system. The first spreading code generating unit  10   a  performs a spreading demodulation operation on the first de-spreading unit  1  sliding the spreading code from the phase of the leading spreading code by the number times that corresponds to half the spreading code length. The second spreading code generating unit  10   b  performs a spreading demodulation operation on the second de-spreading unit  2  sliding the spreading code from the phase of the midpoint of the spreading code length by the number times that corresponds to half the spreading code length. 
     The control unit  8  then judges that the synchronization acquiring operation has been completed. 
     In FIG. 2, it is assumed that the control unit  8  has obtained two correlation values a 1  and b 1  and two phases S 1  and S 2  as a result of the above-described synchronization acquiring operation. The control unit  8  outputs the two correlation values a 1  and b 1  and two phases S 1  and S 2  to the second memory  12 . 
     (When the Mobile Station Transits from the Sleep State to the Active State) 
     Next, it is assumed that the mobile station was put to the sleep state and the operator has reset the mobile station to the active state while remaining at rest. 
     The control unit  8  receives the two correlation values a 1  and b 1  and two phases S 1  and S 2  (S 1 &lt;S 2 ) from the second memory  12 . The control unit  8  then outputs the two phases S 1  and S 2  to the phase control unit  9 . The phase control unit  9  sends the phases S 1  and S 2  to the first spreading code generating unit  10   a  and second spreading code generating unit  10   b , respectively. The first spreading code generating unit  10   a  uses the phase S 1  as the first starting phase, generates a spreading code, slides the phases of the generated spreading code within the range of ±Δ centered about the first starting phase S 1 , and sends the spreading code to the first de-spreading unit  1 . The first de-spreading unit  1  performs a spreading demodulation operation on the input data Din using the spreading code received from the first spreading code generating unit  10   a.    
     The second spreading code generating unit  10   b  uses the phase S 2  as the second starting phase, generates a spreading code, slides the phases of the generated spreading code within the range of ±Δ centered about the second starting phase S 2 , and sends the generated spreading code to the second de-spreading unit  2 . The second de-spreading unit  2  performs a spreading demodulation operation on the input data Din using the spreading code received from the second spreading code generating unit  10   b . It is to be noted that the range ±Δ in which the phases of the spreading code generated by the second spreading code generating unit  10   b  are slid is the same as the range ±Δ in which the phases of the spreading code generated by the first spreading code generating unit  10   a  are slid. The remainder of the operation in this case is the same as in the case in which the mobile station transits to the active state for the first time. 
     The control unit  8  receives the two correlation values and two phases stored in the first additional memory  41  and the two correlation values and two phases stored in the second additional memory  42 . The control unit  8  the selects then largest and second largest of the four correlation values, and calculates the difference between the phases that correspond to these two correlation values. This phase difference is denoted by T 2 −T 1 . On the other hand, the control unit  8  also calculates the difference S 26 −S 1  between the two phases S 1  and S 2  stored in the second memory  12 . If the phase difference T 26 −T 1  is equal to the phase difference S 2 −S 1 , the control unit  8  judges that the mobile station was not moved while the mobile station was in the sleep state. In this case, the control unit  8  outputs outside the apparatus the phases stored in the first memory  7  as output data Dout. 
     If the phase difference T 2 −T 1  is not equal to the phase difference S 2 −S 1 , the control unit  8  judges that the mobile station has been moved while the mobile station was in the sleep state. In this case, the control unit  8  supplies a reset signal to the first spreading code generating unit  10   a  and second spreading code generating unit  10   b . Once the first spreading code generating unit  10   a  and second spreading code generating unit  10   b  receive the reset signal, they perform the same operation as in the case in which the power source of the mobile station has been turned on. 
     The synchronization acquiring apparatus according to the fifth embodiment is able to detect whether the mobile station has been moved or not when the mobile station transits from the sleep state to the active state. Moreover, regardless of whether the mobile station is moved while the mobile station is in the sleep state, the synchronization acquiring apparatus according to the fifth embodiment is able to detect the correlation values within a short length of time. Besides these features, the synchronization acquiring apparatus according to the fifth embodiment achieves the same advantages as the synchronization acquiring apparatus according to the fourth embodiment. 
     (Sixth Embodiment) 
     Next, a synchronization acquiring apparatus according to the sixth embodiment of the present invention will be explained. 
     FIG. 8 is a block diagram of a synchronization acquiring apparatus according to the sixth embodiment of the present invention. 
     In the sixth embodiment of the present invention, the same reference numerals are given to the same components that are already used in the fifth embodiment. Such components will not be explained here. The synchronization acquiring apparatus of the sixth embodiment is identical to that of the fifth embodiment except in the following respect. 
     In the synchronization acquiring apparatus of the sixth embodiment shown in FIG. 8, the output signal of the first amplitude calculating unit  21  is input to the first additional memory  41 , and the output signal of the second amplitude calculating unit  22  is input to the second additional memory  42 . Besides these features, the synchronization acquiring apparatus according to the sixth embodiment achieves the same advantages as the synchronization acquiring apparatus according to the fifth embodiment.