Abstract:
A mobile communication device with positioning capability is provided, including: a global navigation satellite system (GNSS) receiver; a communication circuit for generating a control signal; an oscillator shared between the communication circuit and the GNSS receiver, for providing a clock signal having a frequency value corresponding to the control signal; and a decision unit, coupled to the communication circuit and the GNSS receiver, for recording the control signal; wherein the GNSS receiver obtains the frequency value of the clock signal according to the control signal recorded in the decision unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims the benefit of U.S. provisional application No. 60/806,619, filed on Jul. 5, 2006 and incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of a mobile communication device, and more particularly, to a mobile communication device with a positioning capability. 
     2. Description of the Prior Art 
     Mobile communication devices (such as mobile phones) and global navigation satellite system (GNSS) receivers (such as GPS receivers) are both widely used electronic devices. For many, both of these devices are necessary in daily life. In order to satisfy the users&#39; requirement, integrating GNSS receiver and mobile communication device functions together is becoming a trend. However, when integrating these functions together, many problems must be considered, such as power consumption, hardware cost, circuit board area, etc. 
     It is well known that both GNSS receivers and mobile communication devices need an oscillator to be a reference frequency source during operation. In prior art, the oscillator utilized by the GNSS receiver is usually an oscillator with high precision, such as a Temperature Compensated Crystal Oscillator (TCXO), which is calibrated to a specific frequency (such as 16.368 MHz). Most oscillators utilized in the mobile communication devices, however, are oscillators with lower precision, such as a Voltage-Controlled Temperature Compensated Crystal Oscillator (VCTCXO). 
     In order to reduce the hardware cost of integrating GNSS receiver and mobile communication functions together, a U.S. Pat. No. 6,724,342 provides a mobile communication device with a positioning capability, wherein the communication circuit and the positioning signal receiver share the same oscillator. However, the positioning signal receiver is quite sensitive to the precision and frequency drift of the reference frequency output by the oscillator. In the mobile communication device disclosed by the U.S. Pat. No. 6,724,342, if the communication circuit adjusts the output frequency of the shared oscillator while the positioning signal receiver extracts the satellite signals, the positioning signal receiver will not be immediately aware of the change in the oscillator&#39;s output frequency, thus resulting in occurrences of positioning errors (such as a positioning location suddenly diverging from a previous positioning location by a wide margin), or even not being able to detect the satellite signals. 
     One solution for the above problem is to control the shared oscillator to maintain a constant output frequency when the positioning signal receiver is extracting the satellite positioning signals. Unfortunately, this solution will result in a largely increased call drop rate for the mobile communication device, and thus will bring down the whole communication quality. 
     SUMMARY OF THE INVENTION 
     It is therefore one of the objectives of the present invention to provide a mobile communication device with a positioning capability so as to solve the above problem. 
     According to an embodiment of the present invention, a mobile communication device with positioning functionality is provided. The mobile communication device includes: a global navigation satellite system (GNSS) receiver; a communication circuit for generating a control signal; an oscillator shared between the communication circuit and the GNSS receiver, for providing a clock signal having a frequency value corresponding to the control signal; and a decision unit, coupled to the communication circuit and the GNSS receiver, for recording the control signal; wherein the GNSS receiver obtains the frequency value of the clock signal according to the control signal recorded in the decision unit. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a simplified diagram of a mobile communication device with positioning capability according to a first embodiment of the present invention. 
         FIG. 2  shows a flowchart illustrating an operational embodiment of the mobile communication device in the initial cell search mode. 
         FIG. 3  shows a simplified diagram of the GNSS receiver according to an embodiment of the present invention. 
         FIG. 4  shows a flowchart illustrating an operational embodiment of the mobile communication device in out-of-service mode. 
         FIG. 5  shows a flowchart illustrating an operational embodiment of the mobile communication device in idle mode. 
         FIG. 6  shows a flowchart illustrating an operational embodiment of the mobile communication device in active mode. 
         FIG. 7  shows a simplified diagram of a mobile communication device with positioning capability according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 .  FIG. 1  shows a simplified diagram of a mobile communication device  100  with positioning capability according to a first embodiment of the present invention. In a practical application, the applications of the mobile communication device  100  can include various portable user end equipment such as 2G/3G mobile phones or smart phones, etc. As shown in  FIG. 1 , the mobile communication device  100  includes a communication circuit  102 , a global navigation satellite system (GNSS) receiver  104 , an oscillator  106 , and a decision unit  108 , wherein the oscillator  106  is shared between the communication circuit  102  and the GNSS receiver  104 . 
     The communication circuit  102  in mobile communication device  100  is utilized for communicating with the base station(s) in a mobile communication network so as to provide the audio or data transmission services required by the user. As shown in  FIG. 1 , the communication circuit  102  includes a mixer  112 , an analog-to-digital converter (ADC)  114 , a control unit  116 , a non-volatile storage medium (such as FLASH or ROM)  118 , and a digital-to-analog converter (DAC)  120 , wherein an initial control value Di corresponding to a predetermined oscillating frequency of the oscillator  106  manufactured in a product line is stored in the non-volatile storage medium  118 . For the sake of brevity, an antenna module and transmitting end circuit is not shown in  FIG. 1 . 
     The GNSS receiver  104  is utilized for receiving and analyzing satellite signals transmitted from a plurality of navigation satellites such as longitude, latitude, and altitude data, etc. so as to calculate a location position of the mobile communication device  100 . For example, the above navigation satellites can be the GPS satellites of the United States of America, the Galileo satellites of the European Union, GLONASS satellites of the Russia, or any other satellites of the global navigation satellite system. 
     For convenience in the following illustration, it is presumed that the communication circuit  102  is a Wideband Code Division Multiple Access (W-CDMA) communication circuit complying with the 3GPP specification, and the GNSS receiver  104  is a GPS receiver. In other words, the mobile communication device  100  is a 3G mobile phone with the GPS positioning capability in this embodiment. Please note that this is only an exemplary embodiment, and does not limit the actual capabilities of the communication circuit  102  and the GNSS receiver  104 . 
     The mobile communication device  100  with the GPS positioning capability has four different operation modes: an initial cell search mode, an out-of-service mode, an idle mode, and an active mode during communication. Unlike the CDMA2000 system, the base stations (also called the Node B) in the W-CDMA system need not be synchronized with each other. Thus, each base station in the W-CDMA system uses a unique Primary Scrambling Code (PSC) for identification, and a process of the user end-equipment searching for the base station and becoming synchronized with the PSC thereof is called the cell search. The cell search of the base station can be divided into five phases: slot synchronization, frame synchronization and scrambling code group identification, scrambling code identification, frequency acquisition, and cell identification. The mobile communication device  100  will perform the cell search operation in its initial cell search mode, idle mode, and active mode mentioned above. 
     In a comparison with an oscillator utilized in the base station, the oscillator  106  utilized in the mobile communication device  100  usually has a lower cost and relatively lower precision. In practice, the oscillator  106  can be realized by a voltage-controlled oscillator (VCO), such as a VCTCXO. Since the precision of the oscillator  106  is not as ideal as the oscillator utilized in the base station, the clock signal output from the oscillator  106  will have an offset. If such an offset is not calibrated, it will possibly result in reduced receiving efficiency of the communication circuit  102 , and the communication between the mobile communication device  100  and the base stations will not be successful. Thus, during the above cell search process, the communication circuit  102  of the mobile communication device  100  will calibrate the oscillator  106  to synchronize the oscillator  106  output frequency with the oscillator utilized by the base station. 
     Please refer to  FIG. 2 .  FIG. 2  shows a flowchart  200  illustrating an operational embodiment of the mobile communication device  100  in the initial cell search mode. When the mobile communication device  100  is turned on, the mobile communication device  100  will enter the initial cell search mode (step  210 ). At this time, the control unit  116  of the communication circuit  102  will load the initial control value Di from the non-volatile storage medium  118  (step  220 ), and set the initial control value Di as the digital control value DW for the DAC  120 . The DAC  120  will generate a control voltage Vc according to the digital control value DW, to control the oscillator  106  to generate a clock signal CLK with a predetermined frequency according to the control voltage Vc (step  230 ). When the communication circuit  102  receives a signal Rx transmitted from the base station (step  240 ), the mixer will mix the signal Rx with the clock signal CLK from the oscillator  106  to generate a mixed signal Mx, and the ADC will convert the mixed signal Mx into a digital signal Ds. 
     Next, the control unit  116  will carry out step  250  to deduce a frequency offset of the clock signal CLK outputted by the oscillator  106  according to the digital signal Ds, and the control unit  116  will adjust the digital control value DW according to the frequency offset. In this way, the DAC  120  will adjust the control voltage Vc to calibrate the frequency of the clock signal CLK outputted by the oscillator  106 , in order to synchronize it with the high-precision oscillator utilized by the base station (step  260 ). By utilizing the above calibration method, the present invention can improve the precision of the frequency output by the oscillator  106 , to approach the high precision of the oscillator utilized by the base station, thus allowing the mobile communication device  100  to utilize the lower-cost oscillator  106  as a reference frequency source without decreasing the communication efficiency. In practice, the function of control unit  116  can be realized by utilizing a microprocessor or a digital signal processor (DSP) to execute a program with a proper scheme. 
     It should be noted that the clock signal CLK output from the oscillator  106  might have a greater frequency fluctuation during the above frequency calibration process. Thus, even when the mobile communication device  100  receives an indication (from the user or the communication network) requesting the GNSS receiver  104  to perform the position locating operation, the GNSS receiver  104  of this embodiment will still be in an off or disabled state, to avoid a positioning error or a failure to detect the satellite signals from exceedingly high frequency variation in the clock signal CLK outputted by the oscillator  106 . Only after the communication circuit  102  calibrates the frequency of the clock signal CLK output by the oscillator  106  to synchronize it with the oscillator in the base station will the GNSS receiver  104  will start to perform the positioning operation (step  270 ). 
     In practice, after the above frequency calibration process is finished (i.e. the oscillator  106  is with the oscillator in the base station), there is still a chance for frequency shift to occur between oscillator  106  and the oscillator of the base station. The frequency shift condition is likely caused by factors such as temperature variation of the oscillator  106 , circuit aging of the oscillator  106 , or the Doppler effect induced when the mobile communication device  100  moves, etc. The communication circuit  102  can continuously tune the oscillator  106  to maintain its output frequency within the frequency error range required by the 3GPP specification, thus ensuring good communication quality. 
     Please note that the control unit  116  of the communication circuit  102  will transmit the digital control value DW of the DAC  120  to the decision unit  108  in the first embodiment of  FIG. 1 . The decision unit  108  can be realized by utilizing various storage units such as a memory or register. It is well known from the above illustration that the digital control value DW of the DAC  120  and the frequency value of the clock signal CLK output from the oscillator  106  correspond to each other. Thus, the GNSS receiver  104  can deduce the frequency value of the clock signal CLK outputted by the oscillator  106  according to the digital control value DW stored in the decision unit  108 , and the frequency value of the clock signal CLK is utilized as a reference for the GNSS receiver  104  when it performs the positioning operation. For example, the GNSS receiver  104  can utilize a predetermined transition function or look into a lookup table to get the frequency value of the clock signal CLK output by the oscillator  106  according to the digital control value DW. 
       FIG. 3  shows a simplified diagram of the GNSS receiver  104  according to an embodiment of the present invention. In this embodiment, the GNSS receiver  104  includes a surface audio wave (SAW) filter  310 , a low noise amplifier (LNA)  320 , a radio frequency (RF) circuit  330 , and a baseband circuit  340 . After the GNSS receiver  104  receives a GPS RF signal, the GPS RF signal will be processed via the SAW filter  310  and the LNA  320  and then will be input to the RF circuit  330 . After the RF circuit  330  converts the GPS RF signal into a baseband signal, the baseband signal will be input to the baseband circuit  340 . The RF circuit  330  and the baseband circuit  340  both need to refer to a clock signal when they process the signals. In this embodiment, the clock signal required by the RF circuit  330  and the baseband circuit  340  is provided by the oscillator  106  outside of the GNSS receiver  104 , and since the baseband circuit  340  requires a higher frequency value of the clock signal CLK, the baseband circuit  340  can deduce the frequency value of the clock signal CLK outputted by the oscillator  106  according to the digital control value DW stored in the decision unit  108 . This allows the frequency value of the clock signal CLK output by the oscillator  106  to be utilized as the reference for the GNSS receiver  104  when the GNSS receiver  104  performs the positioning operation. 
     Under this scheme, when the communication circuit  102  intends to adjust the frequency value of the clock signal CLK outputted by the oscillator  106 , the GNSS receiver  104  can be made aware of the new frequency value of the clock signal CLK in advance, according to the digital control value DW received by the decision unit  108 . In this manner, the GNSS receiver  104  will be aware of the upcoming clock signal CLK frequency variation, and does not need to utilize any other circuits to continuously detect the clock signal CLK. In this way, when the frequency value of the clock signal CLK changes, the GNSS receiver  104  can perform a compensation operation on the positioning operation according to the frequency variation of the clock signal CLK at the moment, in order to get a correct positioning result. When the GNSS receiver  104  performs the above compensation operation, the GNSS receiver  104  can refer to a frequency record throughout the history of the clock signal CLK, and the frequency record can be stored in the storage unit or the decision unit  108  inside the GNSS receiver  104 . It is also practical to store all or the last plurality of digital control values output by the control unit  116  into the decision unit  108  so that the GNSS receiver  104  can retrieve the plurality of corresponding frequency values according to the plurality of digital control values. 
     In another embodiment, if the GNSS receiver  104  discovers that the upcoming frequency change in the clock signal CLK is too large (such as exceeding a predetermined variation value), then the GNSS receiver  104  will suspend the positioning operation. This course of action will prevent a wide discrepancy between the positioning point calculated before and after the frequency adjustment in the clock signal CLK. 
     Please refer to  FIG. 4 .  FIG. 4  shows a flowchart  400  illustrating an operational embodiment of the mobile communication device  100  in out-of-service mode. If the mobile communication device  100  is out of a service range of the mobile communication network of the communication circuit  102  (for example, when the user brings the mobile communication device  100  to a remote rural district), or the communication circuit  102  is not able to find a base station after a predetermined time in the initial cell search mode, then the mobile communication device  100  will enter the out-of-service mode (step  410 ). The control unit  116  of the communication circuit  102  will perform a time counting operation when the mobile communication device  100  enters the out-of-service mode (step  420 ). If the mobile communication device  100  receives an indication requesting the GNSS receiver  104  to perform the positioning operation (step  430 ), then the control unit  116  will load the initial control value Di from the non-volatile storage medium  118  as a digital control value DW (step  440 ). The DAC  120  will generate a control voltage Vc according to the digital control value DW to control the oscillator  106  to generate a clock signal CLK with a predetermined frequency according to the control voltage Vc (step  450 ). 
     The GNSS receiver  104  will get the frequency value of the clock signal CLK output by the oscillator  106  according to the digital control value DW stored in the decision unit  108 , and perform the positioning operation according to the frequency value of the clock signal CLK (step  460 ). As shown in the flowchart  400 , before the time counting operation expires or times out (step  470 ), the GNSS receiver  104  will continuously perform the positioning operation to update the locating position of the mobile communication device  100 . When the time counting operation times out (step  470 ), the mobile communication device  100  will switch to the initial cell search mode, and the positioning operation of the GNSS receiver  104  will be suspended (step  480 ), so as to prevent position calculation errors from occurring. In practice, the control unit  116  can send a timeout signal to notify the GNSS receiver  104  to suspend the positioning operation thereof when the timeout of the time counting operation happens. 
     If after switching to initial cell search mode the communication circuit  102  still cannot find any base stations within a predetermined time, then the mobile communication device  100  will enter the out-of-service mode again. Please note that the timeout length setting of the time counting operation in the step  420  can be varied with time. For example, the mobile communication device  100  can increase the timeout length setting of the time counting operation in Step  420  each time when the mobile communication device  100  switches from the initial cell search mode back to out-of-service mode. Doing so will reduce the switching frequency between the out-of-service mode and the initial cell search mode of the mobile communication device  100 . The scheme of adjusting the timeout length setting of the time counting operation mentioned above is only an embodiment for the illustration, and it is a limit of the practical scheme of the present invention. In addition, since certain elements of the communication circuit  102  do not have to operate during most time of the out-of-service mode, it is practical to turn off those certain elements when they are not required to operate, reducing power consumption of the whole system. 
     Please refer to  FIG. 5 .  FIG. 5  shows a flowchart  500  illustrating an operational embodiment of the mobile communication device  100  in idle mode. After the mobile communication device  100  finishes the initial cell search operation, it can enter the idle mode (step  510 ) so communication circuit  102  can enter a discontinuous reception (DRX) scheme to save the electric power consumption. When the mobile communication device  100  enters idle mode, the control unit  116  will perform a DRX time counting operation (step  520 ), wherein the timeout length setting of the DRX time counting operation is usually assigned by the base station. In addition, the control unit  116  will maintain the digital control value DW of the DAC  120  at its last-used value during the previous cell search operation, so the clock signal CLK frequency can remain synchronized with the oscillator of the base station. 
     In idle mode, if the mobile communication device  100  receives an indication requesting the GNSS receiver  104  to perform the positioning operation (step  530 ), then the mobile communication device  100  will obtain the clock signal CLK outputted by the oscillator  106  frequency value according to the last digital control value DW received by the decision unit  108  during the last cell search operation (step  540 ), and will perform the positioning operation according to the obtained frequency value (step  550 ). As shown in the flowchart  500 , before the DRX time counting operation times out (step  560 ), the GNSS receiver  104  will continuously perform the positioning operation to update the position of the mobile communication device  100 . 
     When the DRX time counting operation times out (step  560 ), the mobile communication device  100  will turn on the communication circuit  102  to perform the cell search operation (step  570 ). At this time, the control unit  116  of the communication circuit  102  will control the frequency value of the clock signal CLK to allow synchronization between the communication circuit  102  and the base station. If the control unit  116  does not adjust the frequency value of the clock signal CLK (step  580 ), then GNSS receiver  104  will continue to perform the operation of step  550 . If the control unit  116  adjusts the frequency value of the clock signal CLK outputted by the oscillator  106  (step  580 ), then the GNSS receiver  104  will be aware of the upcoming frequency variation of the clock signal CLK outputted by the oscillator  106  according to the digital control value DW received by the decision unit  108 , and will perform a compensation operation on the positioning operation (step  590 ) to arrive at a correct positioning calculation result. 
     Please refer to  FIG. 6 .  FIG. 6  shows a flowchart  600  illustrating an operational embodiment of the mobile communication device  100  in active mode. When the mobile communication device  100  is communicating, the mobile communication device  100  can enter active mode (step  610 ). Before the mobile communication device  100  receives an indication requesting the GNSS receiver  104  to perform a positioning operation, the control unit  116  of the communication circuit  102  will continuously adjust and control the frequency value of the clock signal CLK output by the oscillator  106 , maintaining synchronization with the base station. When the mobile communication device  100  receives the indication requesting the GNSS receiver  104  to perform a positioning operation (step  620 ), the GNSS receiver  104  will obtain the frequency value of the clock signal CLK output by the oscillator  106  according to the last digital control value DW received by the decision unit  108  (step  630 ), and the mobile communication device  100  will perform the positioning operation according to the obtained frequency value (step  640 ). 
     In active mode, if the frequency offset of the oscillator  106  deduced by the control unit  116  is not greater than a predetermined threshold value TH 1  (step  650 ), then the control unit  116  will not adjust the digital control value DW (i.e. the frequency of the oscillator  106  will not be adjusted) to avoid frequently calibrating the output frequency of the oscillator  106 . At this time, the GNSS receiver  104  will continue to perform the operation in step  640 . 
     If the control unit  116  determines the frequency offset of the oscillator  106  to be greater than the predetermined threshold value TH 1  in the step  650 , then the control unit  116  will decide whether to adjust the frequency of the oscillator  106  or not, according to the communication quality of the communication circuit  102 . For example, the control unit  116  can judge a current communication quality of the communication circuit  102  according to a bit error rate (BER) of the digital signal Ds (step  660 ). In an embodiment, if the BER of the digital signal Ds is higher than a predetermined value TH_BER, then the control unit  116  will determine that the current communication quality of the communication circuit  102  does not achieve a predetermined level (i.e. the current communication quality is not good); otherwise, the control unit  116  will determine that the current communication quality of the communication circuit  102  achieves the predetermined level (i.e. the current communication quality is good). Please note that the scheme of determining the current communication quality of the communication circuit  102  mentioned above is only an embodiment for illustrative purposes, and it should not be used to limit the practical scheme of the present invention. 
     If the control unit  116  determines that the current communication quality of the communication circuit  102  does not achieve the predetermined quality level, then the control unit  116  will adjust the digital control value DW to calibrate the output frequency of the oscillator  106  (step  670 ), in order to improve the communication quality. At this time, the GNSS receiver  104  will obtain a new frequency value of the oscillator  106  according to the digital control value DW received by the decision unit  108  (step  630 ), and the mobile communication device  100  will perform the positioning operation according to the newly obtained frequency value (step  640 ). 
     If the control unit  116  determines that the current communication quality of the communication circuit  102  already achieve the predetermined level, then the control unit  116  will not adjust the digital control value DW; that is, the control unit  116  will not change the frequency value of the clock signal CLK output by the oscillator  106 . However, the control unit  116  will estimate a future communication quality of the communication circuit  102  (step  680 ), and the control unit  116  will adjust the predetermined threshold value TH 1  used in step  650  according to the estimating result (step  690 ). In practice, the control unit  116  can estimate a future communication quality of the communication circuit  102  according to a current power control command of the communication circuit  102 . For example, if a current inner loop power control command of the communication circuit  102  is a power-down command, then the control unit  116  can estimate that the future communication quality of the communication circuit  102  is good, and thus increase the predetermined threshold value TH 1  used in step  650 . On the other hand, if the current inner loop power control command of the communication circuit  102  is a power-up command, then the control unit  116  can estimate that the future communication quality of the communication circuit  102  is not good, and thus decrease the predetermined threshold value TH 1  used in step  650 . Please note that the scheme of estimating the future communication quality of the communication circuit  102  mentioned above is only an embodiment for illustration, and is not to limit the practical scheme of the present invention. 
     It is well known from the above description that the control unit  116  will determine whether to adjust the frequency of the oscillator  106  or not according to the communication quality of the communication circuit  102 , and the control unit  116  will adjust the predetermined threshold value TH 1  used in the step  650  adaptively while GNSS receiver  104  performs its positioning operation. 
     In the embodiment mentioned above, since the digital control value DW output by the control unit  116  and the frequency value of the clock signal CLK output by the oscillator  106  correspond to each other, the GNSS receiver  104  can obtain the frequency value of the clock signal CLK output by the oscillator  106  and the frequency variation thereof according to the digital control value DW. In practice, since the control voltage Vc output by the DAC  120  and the frequency value of the clock signal CLK output by the oscillator  106  also correspond to each other, thus the GNSS receiver  104  also can obtain the frequency value of the clock signal CLK output by the oscillator  106  and the frequency variation thereof according to the control voltage Vc. 
     Please refer to  FIG. 7 .  FIG. 7  shows a simplified diagram of a mobile communication device  700  with positioning capability according to a second embodiment of the present invention. The mobile communication device  700  is very similar with the mobile communication device  100  shown in  FIG. 1 , and thus the elements that are substantially the same in operation in the two mobile communication devices are labeled with the same number for convenience. As in mobile communication device  100 , the oscillator  106  in the mobile communication device  700  is also shared between the communication circuit  102  and the GNSS receiver  704 . 
     One of the differences between mobile communication devices  100  and  700  is that the practical scheme of the decision unit  708  in mobile communication device  700  differs from the decision unit  108  mentioned above. As shown in  FIG. 7 , the decision unit  708  of the second embodiment includes a detecting unit  712  and a storage unit  714 . The detecting unit  712  is utilized for detecting the voltage value of the control voltage Vc output by the DAC  120 , and the storage unit  714  is utilized for storing the detecting result of the detecting unit  712  (that is, the voltage value of the control voltage Vc). 
     Another difference between the mobile communication devices  100  and  700  is that the GNSS receiver  704  in the mobile communication device  700  deduces the frequency value of the clock signal CLK output by the oscillator  106  according to the voltage value of the control voltage Vc stored in the storage unit  714 , allowing the frequency value of the clock signal CLK to be the reference for the GNSS receiver  704  when the GNSS receiver  704  performs the positioning operation. For example, the GNSS receiver  704  can utilize a predetermined transition function or a lookup table to retrieve the frequency value of the clock signal CLK output by the oscillator  106  according to the voltage value of the control voltage Vc. 
     In the scheme of the mobile communication device  700 , when the control unit  116  of the communication circuit  102  intends to adjust the frequency value of the clock signal CLK, the GNSS receiver  704  can be made aware of the new frequency value of the clock signal CLK in advance, according to the control voltage Vc received by the decision unit  708 . In this manner, the GNSS receiver  704  will be aware of the upcoming clock signal CLK frequency variation, and does not need to utilize any other circuits to continuously detect the clock signal CLK. In this way, when the frequency value of the clock signal CLK changes, the GNSS receiver  704  can perform a compensation operation on the positioning operation according to the frequency variation of the clock signal CLK at the moment, in order to get a correct positioning calculation result. When the GNSS receiver  704  performs the above compensation operation, the GNSS receiver  704  can refer to a frequency record throughout the history of the clock signal CLK, and the frequency record can be stored in the storage unit or the storage unit  714  of the decision unit  708  inside the GNSS receiver  704 . It is also practical to store all or the last plurality of control voltages Vc output by the DAC  120  into the storage unit  714  so that the GNSS receiver  704  can retrieve the plurality of corresponding frequency values according to the plurality of voltage values. In practice, both the digital control value DW generated by the control unit  116  and the control voltage Vc generated by the DAC  120  can be viewed as control signals output by the communication circuit  102 . In other words, both of the GNSS receiver  104  and the GNSS receiver  704  in the embodiments mentioned above obtain the frequency value of the clock signal CLK output by the oscillator  106  and are aware of the frequency variation of the oscillator  106  in advance according to the control signals output by the communication circuit  102 . 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.