Abstract:
A rake receiver is provided with a first decimating unit for extracting received signals in order to perform synchronous acquisition, and a second decimating unit for extracting received signals from a synchronously acquired clock. A despreading unit is used to despread the received signals extracted by the second decimating unit with a PN code and also for supplying the resulting data to a time tracking unit. A second despreading unit is used to despread received signals extracted by the second decimating unit. Selectors are used for switchingly outputting a PN code and the wideband PN code to the second despreading unit. The data to be supplied to the pilot carrier tracking unit and the data path demodulating unit are despread by using the second despreading unit common to those units. The number of despreading units can thus be reduced to two.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a rake receiver which rakes reception results of multipaths, and a mobile unit and a base station for a portable telephone system which use such a rake receiver, and more particularly to a reduction of a circuit scale. 
     In recent years, a portable telephone of the CDMA system in which different PN (pseudo-noise) codes are allocated to users is rapidly developed. Recently, a system in which a PNW code consisting of a combination of short and long codes is used as the PN code has been studied. A short code is defined for each cell. A spread code is generated by multiplying the short code with a long code which is allocated to each user. When a short code has four chips, the chip number of a PNW code is four times that of a PN code constituting a long code. 
     In the case where such a code is used, even when any short code is selected in a base station, the communication channel of a cell never coincides with that of another cell. 
     In the CDMA system, multipaths can be separated from each other in processes of spread and despread. The reception quality can be enhanced by raking reception results of the separated paths. When a PNW code is used, chips are spread in a higher degree, and hence the performance of the rake reception is further improved. 
     A CDMA portable telephone which performs a rake reception has a plurality of finger circuits which perform demodulation. The finger circuits demodulate received data of different paths, and the demodulated data are raked. 
     In the CDMA system, furthermore, a pilot symbol is periodically inserted into a transmitted frame. On the reception side, the pilot symbol is detected so as to acquire synchronization, and the acquired synchronization is tracked. 
     As shown in FIG. 5, a finger circuit of a conventional CDMA portable telephone comprises: a decimating unit  40  which decimates received signals RxI and RxQ in accordance with the acquired synchronization; a despreading unit  42  which despreads OnTimeI and OnTimeQ that are decimated in the decimating unit  40 , by using PNW to demodulate the received data; a data path demodulating unit  45  which receives demodulated data DataOnTimeI and DataOnTimeQ that are obtained as a result of the despread, and which decodes the data; a despreading unit  43  which despreads OnTimeI and OnTimeQ by using a long code PN and demodulates pilot data; a pilot carrier tracking unit  46  which receives pilot data PilotOnTimeI and PilotOnTimeQ that are obtained as a result of the despread, and which performs synchronous tracking; a decimating unit  41  which decimates the received signals RxI and RxQ at various timings in order to perform synchronous acquisition; a despreading unit  44  which despreads ELI and ELQ that are decimated in the decimating unit  41 , by using a long code PN; and a time tracking unit  47  which acquires synchronization by using PilotELI and PilotELQ that are obtained as a result of the despread. 
     In the finger circuit, as shown in FIG. 10, the decimating unit  41  decimates the received signals RxI and RxQ after the timing of ELCLK, and outputs ELI and ELQ, and the despreading unit  44  despreads the PN codes of PnI and PnQ into the ELI and ELQ. 
     In the time tracking unit  47 , when a pilot data cannot be detected from the outputs PilotELI and PilotELQ of the despreading unit  44 , ELCLK is shifted by one clock. When ELCLK is sequentially shifted by one clock in this way, it is possible to acquire a synchronized clock which enables a pilot data to be detected. 
     When synchronous acquisition is attained, the clock is input as OnTimeCLK into the decimating unit  40 , and the decimating unit  40  decimates the received signals RxI and RxQ from OnTimeCLK to output OnTimeI and OnTimeQ. 
     The despreading unit  42  despreads OnTimeI and OnTimeQ by using PNW codes of PnWI and PnWQ, and demodulates the received data DATaOnTimeI and DataOnTimeQ. The demodulated data are supplied to the data path demodulating unit  45 . 
     The despreading unit  43  despreads OnTimeI and OnTimeQ with the PN codes of PnI and PnQ and demodulates pilot data PilotOnTimeI and PilotOnTimeQ. The demodulated data are supplied to the pilot carrier tracking unit  46 . The pilot carrier tracking unit  46  performs synchronous tracking while adjusting OnTimeCLK supplied to the decimating unit  40 , so that the pilot data can be always detected from the outputs PilotOnTimeI and PilotOnTimeQ of the despreading unit  43 . 
     In order to enhance the performance of rake reception, it is required to increase the number of finger circuits and that of paths which are to be subjected to demodulation in the finger circuits. Each finger circuit employed in a rake receiver of the prior art has despreading units which are respectively used for a data path demodulating unit, a pilot carrier tracking unit, and a time tracking unit. As the number of finger circuits is larger, therefore, the number of despreading units is increased, thereby producing a problem in that the circuit scale of the whole of a rake receiver is extremely enlarged. 
     SUMMARY OF THE INVENTION 
     The invention has been conducted in order to solve the problem of the prior art. It is an object of the invention to provide a rake receiver in which the number of despreading units is reduced so as to suppress expansion of the circuit scale, and also to provide a mobile unit and a base station for a portable telephone system which use such a receiver. 
     In the rake receiver of the invention, selecting means for switching a spread code which is to be supplied to despreading means, and/or selecting means for switching received signals which are to be supplied to despreading means are disposed, whereby despreading means for supplying data to a data path demodulating unit, a pilot carrier tracking unit, and a time tracking unit can be commonly used, so that the number of the despreading means is reduced to two or one. 
     Consequently, the circuit scale of the rake receiver can be reduced. 
     When the configuration of the rake receiver is applied to a mobile unit or a base station for a portable telephone system, the circuit scale of the mobile unit or the base station can be reduced. 
     According to the first aspect of the present invention, a rake receiver comprises: first decimating means for extracting received signals in order to perform synchronous acquisition; and second decimating means for extracting received signals from a synchronously acquired clock, and in which the received signals extracted by the first decimating means are despread with a PN code and then supplied to time tracking means, the received signals extracted by the second decimating means are despread with a PN code, obtained pilot data are supplied to pilot carrier tracking means, the received signals extracted by the second decimating means are despread with a wideband PN code, and obtained data are supplied to data path demodulating means, and the rake receiver further comprises: despreading means for despreading the received signals extracted by the second decimating means; and selecting means for switchingly outputting the PN code and the wideband PN code to the despreading means, the data which are to be supplied to the pilot carrier tracking means and the data path demodulating means are despread by using the despreading means which is common to these means. The number of the despreading means can be reduced to two. 
     According to the second aspect of the present invention, a rake receiver comprises: selecting means for switchingly outputting the received signals extracted by the first decimating means and the received signals extracted by the second decimating means; and despreading means for despreading an output of the selecting means with a PN code, and the data which are to be supplied to the pilot carrier tracking means and the time tracking means are despread by using the despreading means which is common to these means. The number of the despreading means can be reduced to two. 
     Further, according to the third aspect of the present invention, a rake receiver comprises: selecting means for switchingly outputting the received signals extracted by the first decimating means and the received signals extracted by the second decimating means; despreading means for despreading an output of the selecting means; and selecting means for switchingly outputting the PN code and the wideband PN code to the despreading means, and the data which are to be supplied to the data path demodulating means and the time tracking means are despread by using the despreading means which is common to these means. The number of the despreading means can be reduced to two. 
     Furthermore, according to the fourth aspect of the present invention, a rake receiver comprises: selecting means for switchingly outputting the received signals extracted by the first decimating means and the received signals extracted by the second decimating means; despreading means for despreading an output of the selecting means; and selecting means for switchingly outputting the PN code and the wideband PN code to the despreading means, and the data which are to be supplied to the data path demodulating means, the time tracking means, and the pilot carrier tracking means are despread by using the despreading means which is common to these means. The number of the despreading means can be reduced to one. 
     Still further, according to the fifth aspect of the present, the configuration of the rake receiver as mentioned above is disposed in a mobile unit for a portable telephone system. The circuit scale of the mobile unit can be made smaller. 
     Still furthermore, according to the sixth aspect of the present invention, the configuration of the rake receiver as mentioned-above is disposed in a base station for a portable telephone system. The circuit scale of the base station can be made smaller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing the configuration of a rake receiver of a first embodiment of the invention; 
     FIG. 2 is a view showing the configuration of a rake receiver of a second embodiment of the invention; 
     FIG. 3 is a view showing the configuration of a rake receiver of a third embodiment of the invention; 
     FIG. 4 is a view showing the configuration of a rake receiver of a fourth embodiment of the invention; 
     FIG. 5 is a view showing the configuration of a rake receiver of the prior art; 
     FIG. 6 is a timing chart showing the operation of the rake receiver of the first embodiment of the invention; 
     FIG. 7 is a timing chart showing the operation of the rake receiver of the second embodiment of the invention; 
     FIG. 8 is a timing chart showing the operation of the rake receiver of the third embodiment of the invention; 
     FIG. 9 is a timing chart showing the operation of the rake receiver of the fourth embodiment of the invention; and 
     FIG. 10 is a timing chart showing the operation of the rake receiver of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. 
     First Embodiment 
     As shown in FIG. 1, a finger circuit of a rake receiver of a first embodiment comprises: a decimating unit  1  which decimates received signals RxI and RxQ with OnTimeCLK; a selector  5  which switchingly outputs PnI and PnWI in accordance with a selection signal Selectl; a selector  6  which switchingly outputs PnQ and PnWQ in accordance with the selection signal Selectl; a despreading unit  3  which despreads OnTimeI and OnTimeQ that are supplied from the decimating unit  1 , by using codes that are output from the selectors  5  and  6 ; a data path demodulating unit  7  which receives outputs DataOnTimeI and DataOnTimeQ that are obtained when despread is performed by using PnWI and PnWQ in the despreading unit  3 ; a pilot carrier tracking unit  8  which receives outputs PilotOnTimeI and PilotOnTimeQ that are obtained when despread is performed by using PnI and PnQ in the despreading unit  3 ; a decimating unit  2  which decimates the received signals RxI and RxQ at a timing of ELCLK; a despreading unit  4  which despreads ELI and ELQ that are supplied from the decimating unit  2 , by using PnI and PnQ; and a time tracking unit  9  which acquires synchronization by using PilotELI and PilotELQ that are obtained as a result of the despread. 
     In the finger circuit, as shown in FIG. 6, the decimating unit  2  decimates the received signals RxI and RxQ after the timing of ELCLK, and outputs ELI and ELQ, and the despreading unit  4  despreads PnI and PnQ into the ELI and ELQ, and supplies outputs PilotELI and PilotELQ to the time tracking unit  9 . The time tracking unit  9  performs synchronous acquisition on the basis of the outputs of the despreading unit  4 . 
     The clock OnTimeCLK which is synchronously acquired is input into the decimating unit  1 . The decimating unit  1  outputs the received signals OnTimeI and OnTimeQ after OnTimeCLK. 
     In accordance with Select 1 , the selectors  5  and  6  switchingly output PnI and PnWI, and PnQ and PnWQ, respectively. When the selectors  5  and  6  respectively output PnWI and PnWQ, the despreading unit  3  despreads OnTimeI and OnTimeQ supplied from the decimating unit  1 , with the PnWI and PnWQ, and demodulates the received data DataOnTimeI and DataOnTimeQ. The demodulated data are supplied to the data path demodulating unit  7 . 
     When the selectors  5  and  6  respectively output PnI and PnQ, the despreading unit  3  despreads OnTimeI and OnTimeQ supplied from the decimating unit  1 , with the PnI and PnQ, and demodulates the pilot data PilotOnTimeI and PilotOnTimeQ. The demodulated data are supplied to the pilot carrier tracking unit  8 . The pilot carrier tracking unit  8  performs synchronous tracking on the basis of the outputs PilotOnTimeI and PilotOnTimeQ. 
     As described above, the finger circuit of the rake receiver of the embodiment can perform demodulation by using the two despreading units. 
     Second Embodiment 
     Also a finger circuit of a rake receiver of a second embodiment can perform demodulation by using two despreading units. 
     As shown in FIG. 2, the finger circuit comprises: a decimating unit  10  which decimates received signals RxI and RxQ with OnTimeCLK; a despreading unit  12  which despreads OnTimeI and OnTimeQ that are supplied from the decimating unit  10 , by using PnWI and PnWQ; a data path demodulating unit  16  which receives outputs DataOnTimeI and DataOnTimeQ of the despreading unit  12 ; a decimating unit  11  which decimates the received signals RxI and RxQ at a timing of ELCLK; a selector  13  which switchingly outputs the output OnTimeI of the decimating unit  10  and an output ELI of the decimating unit  11  in accordance with a selection signal Select 2 ; a selector  14  which switchingly outputs the output OnTimeQ of the decimating unit  10  and an output ELQ of the decimating unit  11  in accordance with the selection signal Select 2 ; a despreading unit  15  which despreads outputs of the selectors  13  and  14  by using PnI and PnQ; a pilot carrier tracking unit  17  which receives outputs PilotOnTimeI and PilotOnTimeQ that are obtained when despread is performed on OnTimeI and OnTimeQ in the despreading unit  15 ; and a time tracking unit  18  which receives outputs PilotELI and PilotELQ that are obtained when despread is performed on ELI and ELQ in the despreading unit  15 . 
     In the finger circuit, as shown in FIG. 7, the decimating unit  11  decimates the received signals RxI and RxQ after the timing of ELCLK, and outputs ELI and ELQ. The selectors  13  and  14  supply the outputs to the despreading unit  15  in accordance with Select 2 . The despreading unit  14  despreads PnI and PnQ into the ELI and ELQ, and supplies PilotELI and PilotELQ to the time tracking unit  18 . The time tracking unit  18  performs synchronous acquisition on the basis of the outputs of the despreading unit  15 . 
     The clock OnTimeCLK which is synchronously acquired is input into the decimating unit  10 . The decimating unit  10  outputs the received signals OnTimeI and OnTimeQ after OnTimeCLK. 
     The despreading unit  12  despreads OnTimeI and OnTimeQ with PnWI and PnWQ, and demodulates the received data DataOnTimeI and DataOnTimeQ. The demodulated data are supplied to the data path demodulating unit  16 . 
     The selectors  13  and  14  supplies OnTimeI and OnTimeQ to the despreading unit  15  in accordance with Select  2 . The despreading unit  15  despreads PnI and PnQ into OnTimeI and OnTimeQ, and demodulates the pilot data PilotOnTimeI and PilotOnTimeQ. The demodulated data are supplied to the pilot carrier tracking unit  17 . The pilot carrier tracking unit  17  performs synchronous tracking on the basis of the outputs PilotOnTimeI and PilotOnTimeQ. 
     As described above, the finger circuit of the rake receiver of the embodiment can perform demodulation by using the two despreading units. 
     Third Embodiment 
     Also a finger circuit of a rake receiver of a third embodiment can perform demodulation by using two despreading units. 
     As shown in FIG. 3, the finger circuit comprises: a decimating unit  19  which decimates received signals RxI and RxQ with OnTimeCLK; a despreading unit  21  which despreads OnTimeI and OnTimeQ that are output from the decimating unit  19 , by using PnI and PnQ; a pilot carrier tracking unit  27  which receives outputs PilotOnTimeI and PilotOnTimeQ of the despreading unit  21 ; a decimating unit  20  which decimates the received signals RxI and RxQ at a timing of ELCLK; a selector  24  which switchingly outputs the output OnTimeI of the decimating unit  19  and an output ELI of the decimating unit  20  in accordance with a selection signal Select 4 ; a selector  25  which switchingly outputs the output OnTimeQ of the decimating unit  19  and an output ELQ of the decimating unit  20  in accordance with the selection signal Select 4 ; a selector  22  which switchingly outputs PnI and PnWI in accordance with a selection signal Select 3 ; a selector  23  which switchingly outputs PnQ and PnWQ in accordance with the selection signal Select 3 ; a despreading unit  26  which despreads outputs of the selectors  24  and  25  by using the codes output from the selectors  22  and  23 ; a data path demodulating unit  28  which receives DataOnTimeI and DataOnTimeQ output from the despreading unit  26 ; and a time tracking unit  29  which receives PilotELI and PilotELQ output from the despreading unit  26 . 
     In the finger circuit, as shown in FIG. 8, the decimating unit  20  decimates the received signals RxI and RxQ after the timing of ELCLK, and outputs ELI and ELQ. The selectors  24  and  25  supply the outputs to the despreading unit  26  in accordance with Select 4 . 
     The selectors  22  and  23  supply PnI and PnQ to the despreading unit  26  in accordance with Select 3 . 
     The despreading unit  26  despreads PnI and PnQ into the ELI and ELQ, and supplies PilotELI and PilotELQ to the time tracking unit  29 . The time tracking unit  29  performs synchronous acquisition on the basis of the outputs PilotELI and PilotELQ of the despreading unit  26 . 
     The clock OnTimeCLK which is synchronously acquired is input into the decimating unit  19 . The decimating unit  19  outputs the received signals OnTimeI and OnTimeQ after OnTimeCLK. 
     The despreading unit  21  despreads OnTimeI and OnTimeQ with PnI and PnQ, and demodulates the pilot data PilotOnTimeI and PilotOnTimeQ. The demodulated data are supplied to the pilot carrier tracking unit  27 . The pilot carrier tracking unit  27  performs synchronous tracking on the basis of the outputs PilotOnTimeI and PilotOnTimeQ. 
     The selectors  24  and  25  supply OnTimeI and OnTimeQ to the despreading unit  26  in accordance with Select 4 , and the selectors  22  and  23  supply PnWI and PnWQ to the despreading unit  26  in accordance with Select 3 . 
     The despreading unit  26  despreads PnWI and PnWQ into OnTimeI and OnTimeQ, and demodulates the received data DataOnTimeI and DataOnTimeQ. The demodulated data are supplied to the data path demodulating unit  28 . 
     As described above, the finger circuit of the rake receiver of the embodiment can perform demodulation by using the two despreading units. 
     Fourth Embodiment 
     A finger circuit of a rake receiver of a fourth embodiment can perform demodulation by using one despreading unit. 
     As shown in FIG. 4, the finger circuit comprises: a decimating unit  30  which decimates received signals RxI and RxQ with OnTimeCLK; a decimating unit  31  which decimates the received signals RxI and RxQ at a timing of ELCLK; a selector  34  which switchingly outputs the output OnTimeI of the decimating unit  30  and an output ELI of the decimating unit  31  in accordance with a selection signal Select 6 ; a selector  35  which switchingly outputs the output OnTimeQ of the decimating unit  30  and an output ELQ of the decimating unit  31  in accordance with the selection signal Select 6 ; a selector  32  which switchingly outputs PnI and PnWI in accordance with a selection signal Select 5 ; a selector  33  which switchingly outputs PnQ and PnWQ in accordance with the selection signal Select 5 ; a despreading unit  36  which despreads outputs of the selectors  34  and  35  by using codes output from the selectors  32  and  33 ; a data path demodulating unit  37  which receives DataOnTimeI and DataOnTimeQ output from the despreading unit  36 ; a pilot carrier tracking unit  38  which receives PilotOnTimeI and PilotOnTimeQ output from the despreading unit  36 ; and a time tracking unit  39  which receives PilotELI and PilotELQ output from the despreading unit  36 . 
     In the finger circuit, as shown in FIG. 9, the decimating unit  31  decimates the received signals RxI and RxQ after the timing of ELCLK, and outputs ELI and ELQ. The selectors  34  and  35  supply the outputs to the despreading unit  36  in accordance with Select 6 . 
     The selectors  32  and  33  supply PnI and PnQ to the despreading unit  36  in accordance with Select 5 . 
     The despreading unit  36  despreads PnI and PnQ into the ELI and ELQ, and supplies outputs PilotELI and PilotELQ to the time tracking unit  39 . The time tracking unit  39  performs synchronous acquisition on the basis of the outputs PilotELI and PilotELQ. 
     The clock OnTimeCLK which is synchronously acquired is input into the decimating unit  30 . The decimating unit  30  outputs the received signals OnTimeI and OnTimeQ after OnTimeCLK. The selectors  34  and  35  supply the outputs to the despreading unit  36  in accordance with Select 6 . 
     In accordance with Select 5 , the selectors  32  and  33  switchingly supply PnI and PnQ, and PnWI and PnWQ to the despreading unit  36 , respectively. 
     When the selectors  32  and  33  respectively output PnWI and PnWQ, the despreading unit  36  despreads OnTimeI and OnTimeQ supplied from the selectors  34  and  35 , with the PnWI and PnWQ, and demodulates the received data DataOnTimeI and DataOnTimeQ. The demodulated data are supplied to the data path demodulating unit  37 . 
     When the selectors  32  and  33  respectively output PnI and PnQ, the despreading unit  36  despreads OnTimeI and OnTimeQ supplied from the selectors  34  and  35 , with the PnI and PnQ, and demodulates the pilot data PilotOnTimeI and PilotOnTimeQ. The demodulated data are supplied to the pilot carrier tracking unit  38 . The pilot carrier tracking unit  38  performs synchronous tracking on the basis of the outputs PilotOnTimeI and PilotOnTimeQ. 
     As described above, the finger circuit of the rake receiver of the embodiment can perform demodulation by using the one despreading unit. 
     As apparent from the above description, in the rake receiver of the invention, the number of despreading units in a finger circuit can be reduced and hence the circuit scale can be made smaller. 
     Furthermore, a mobile unit and a base station for a portable telephone system into which the configuration of the receiver is incorporated can be miniaturized by reducing the circuit scale.