Abstract:
Output power modification methods and apparatuses for mobile communication devices. The inventive apparatus comprises a receiver, a memory device, a calculation unit, and a translator. The receiver receives transmission channels and transmission power levels from a base station. The memory device stores scaling factors and delta scaling factors corresponding to reference channels and reference power levels. The calculation unit calculates digital control values according to scaling factors and delta scaling factors from the memory device, and the transmission channels and transmission power levels. The translator translates the digital control values to voltage values for controlling transmission power of the mobile communication devices.

Description:
BACKGROUND  
       [0001]     The invention relates to output power modification methods and apparatuses for mobile communication devices, and in particular to adjusting output power of a mobile communication device by estimating a required output power using an interpolation method.  
         [0002]     Output power is critical for transmitters, and changes according to communication range. ETSI (European Telecommunication Standard Institution) Specification GSM 05:05 section 4.1.1 details the requirements for the absolute output power of a class 4 mobile communication device at different power control levels. GSM systems use dynamic power control to ensure that each communication connection is maintained using minimum power.  
         [0003]     To achieve a PCL (Power Control Level), a calibration is done during the cellular phone manufacturing process to map a measured output RF power level to a digital control value, which is typically stored in the Digital Signal Processor (DSP) memory of the handset. The DSP drives a digital-to-analog converter (DAC), which creates an analog voltage waveform that ultimately shapes power amplifier RF ramping. The calibration involves the construction of table of calibration factors for power levels and communication frequency.  
       SUMMARY  
       [0004]     The present invention provides an output power modification method for a mobile communication system. The mobile communication system comprises a mobile communication device and a base station. The base station selects a transmission channel from a plurality of transmission channels. The base station further establishes a connection with the mobile communication device using a transmission power level at the selected transmission channel. The transmission channels comprise a reference channel. The selected transmission channel and the transmission power level are received from the base station. A digital control value is determined using a plurality of scaling factors corresponding to a plurality of power levels at the reference channel. A delta scaling factor corresponding to the reference channel and the transmission channel is used in a reference power level according to the transmission channel and the transmission power level. The digital control value is converted to a voltage value. The transmission power for the mobile communication device is determined according to the voltage value.  
         [0005]     Also provided is a mobile communication device capable of calibrating output power. The mobile communication device connects with a base station using any of a plurality of transmission channels and transmits data thereby. The mobile communication device comprises a receiver, a memory, a calculation unit, and a translator. The receiver receives a transmission channel and a transmission power level from the base station. The memory stores a plurality of scaling factors and delta scaling factors, wherein the scaling factors correspond to a plurality of power levels used when transmitting at the reference channel, and the delta scaling factors correspond to difference between the scaling factors of the reference channel and the transmission channels at a reference power level. The calculation unit determines a digital control value according to the transmission channel and transmission power level received from the receiver and the delta scaling factor and scaling factor retrieved from the memory. The translator converts the digital control value to a voltage value for controlling the transmission power used by the mobile communication device. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0006]     The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
         [0007]      FIG. 1  is a schematic view of an embodiment of a mobile communication device;  
         [0008]      FIGS. 2   a  and  2   b  illustrate an embodiment of a coordinate system used for determining a digital control value for calibrating output power; and  
         [0009]      FIG. 3  illustrates an embodiment of the relationship between the slope and the voltage value.  
     
    
     DETAILED DESCRIPTION  
       [0010]     The invention will now be described with reference to  FIGS. 1 through 3 , which generally relate to mobile communication.  
         [0011]     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration of specific embodiments. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The leading digit(s) of reference numbers appearing in the figures corresponds to the Figure number, with the exception that the same reference number is used throughout to refer to an identical component which appears in multiple figures.  
         [0012]      FIG. 1  is a schematic view of an embodiment of a mobile communication device. A mobile communication device  1  comprises a receiver  12 , a calculation unit  14 , memory  16 , and a converter  18 . The receiver  12  receives signals  101  at an antenna, receives a transmission channel  102  and a transmission power level  103  from a base station, and transmits transmission channel  102  and transmission power level  103  to calculation unit  14 . The memory  16  stores tables  161  and  162 . Table  161  stores a plurality of scaling factors corresponding to a plurality of power levels when transmitting at the reference channel. Table  162  stores scaling factor differences corresponding to the reference channel and the other transmission channels at a reference power level. Typically, the described reference channel is a middle channel of all usable transmission channels, and the scaling factor is a digital counting unit. After receiving transmission channel  102  and transmission power level  103 , the calculation unit  14  retrieves corresponding scaling factor  104  and scaling factor difference  105  from memory  16 , and determines a digital control value  106  accordingly. The converter  18  converts the digital control value  106  to a voltage value  107  for controlling the transmission power used by the mobile communication device  1 .  
         [0013]      FIGS. 2   a  and  2   b  illustrate an embodiment of a coordinate system used for determining a digital control value for calibrating output power. The coordinate system comprises an X-axis and a Y-axis. The X-axis comprises X-coordinates specifying scaling factor differences stored in table  162 . The Y-axis comprises Y-coordinates specifying scaling factors stored in table  161 . According to the invention, scaling factors corresponding to coordinates in the coordinate system may be determined thereby. The coordinates of the coordinate system are determined according to measurements obtained from 38 transmission channels (C 0 ˜C 37 ) at about 1800 MHz in GSM system. In the GSM system, each transmission channel has a bandwidth about 200 KHz, and each channel provides voice transmission services to at most 8 clients. Referring to  FIGS. 2   a  and  2   b,  the Y-axis comprises power levels L 15 ˜L 0 , the difference between two adjacent power levels is 2 dB. Scaling factors corresponding to the power levels are measured during manufacture of a mobile communication device, wherein signals are transmitted at a preset reference channel  22  (channel C 18 ) corresponding to each of the power levels. Referring to  FIGS. 2   a  and  2   b,  the X-axis comprises transmission channels C 0 ˜C 37 . Scaling factor differences corresponding to the transmission channels are measured when transmitting signals at a preset reference power level  24  (power level L 9 ) corresponding to each of the transmission channels.  
         [0014]     The calculation unit  14  receives transmission channel  102  and transmission power level  103 , retrieves corresponding scaling factor  104  and scaling factor difference  105 , and determines a digital control value  106  accordingly. The digital control value is determined according to the following equation:  
               S     cL   ⁡     (   n   )         =       S     RL   ⁡     (   n   )         +       Df   RLf     ⁡     [         S     RL   ⁡     (     n   -   1     )         -     S     RL   ⁡     (   n   )               S     RL   ⁡     (     R   -   1     )         -     S     RL   ⁡     (   R   )             ]                 (     equation   ⁢           ⁢   1     )             
 
         [0015]     S cL(n)  is a digital control value, specifying a scaling factor corresponding to a transmission power level (level n) at a transmission channel. S RL(n)  is a scaling factor (a first scaling factor) corresponding to a transmission power level n at the reference transmission channel. S RL(n−1)  is a scaling factor (a second scaling factor) corresponding to a transmission power level n−1, which is adjacent to the power level of S RL(n) . Similarly, S RL(R)  is a scaling factor (a third scaling factor) corresponding to reference transmission power level R at reference transmission channel. Similarly, S RL(R−1)  is a scaling factor (a fourth scaling factor) corresponding to transmission power level R−1, which is adjacent to the power level of S RL(R) . Df RLf  is a scaling factor difference between the reference transmission channel and a transmission channel at the reference power level.  
         [0016]     Using  FIGS. 2   a  and  2   b  as an example, a channel C 18  is used as a reference transmission channel  22 , and power level L 9  is used as a reference power level  24 . When a mobile communication device sends a request to a base station for establishing a voice communication, the base station assigns a transmission channel thereto. According to this embodiment, a channel C 0  is assigned by the base station. Additionally, the base station assigns a transmission power level to the mobile communication device according to the signal strength amd diminution level from the mobile communication device. In this embodiment, power level L 15  is assigned to the mobile communication device. The mobile communication device determines a digital control value  26  according to the assigned transmission channel C 0  and power level L 15 , and accordingly transmits signals at a proper power level. The mobile communication device retrieves a scaling factor difference corresponding to transmission channel C 0 , and retrieves a scaling factor corresponding to power level L 15 , and determines a digital control value S cL(15)  as the following equation 2.  
               S     cL   ⁡     (   15   )         =       S     RL   ⁡     (   15   )         +       Df   RLf     ⁡     [         S     RL   ⁡     (   14   )         -     S     RL   ⁡     (   15   )               S     RL   ⁡     (   8   )         -     S     RL   ⁡     (   9   )             ]                 (     equation   ⁢           ⁢   2     )             
 
         [0017]     Accordingly,  
         S     cL   ⁡     (   15   )         =       159   +     39   ⁡     [       165   -   159       222   -   207       ]         =   174.6         
 
         [0018]     The digital control value 174.6 is then converted to a voltage value by a converter of the mobile communication device. The voltage value is then used for controlling transmission power of the mobile communication device.  
         [0019]     According to this embodiment, the mobile communication device uses a 10-bit digital control value for calibrating a 2.2-voltage range. The conversion from the digital control value to the voltage ΔV apc  is performed according to the following equation:  
               Δ   ⁢           ⁢     V   apc       =         S     cL   ⁡     (   n   )         ⁡     (     2.2     2   10       )       =       S     cL   ⁡     (   n   )         ⁡     (     2.2   1024     )                 (     equation   ⁢           ⁢   3     )             
 
         [0020]     The voltage value converted from the digital control value (174.6) is 0.375.  
         [0021]     According to equation 1, the ratio of (S RL(n−1) -S RL(n) ) to (S RL(n−1) -S RL(n) ) is determined according to a ratio of scaling factor variations thereof, which can be specified as follows:  
                   S     RL   ⁡     (     n   -   1     )         -     S     RL   ⁡     (   n   )               S     RL   ⁡     (     R   -   1     )         -     S     RL   ⁡     (   R   )             =       Δ   ⁢           ⁢     sf   ⁡     (       L   ⁡     (     n   -   1     )       -     L   ⁡     (   n   )         )           Δ   ⁢           ⁢     sf   ⁡     (       L   ⁡     (     R   -   1     )       -     L   ⁡     (   R   )         )                   (     equation   ⁢           ⁢   4     )             
 
         [0022]     Ratio of a variation of power levels (ΔdBm) to a variation of voltage values (ΔV apc ) is referred to as a slope of these two parameters, which can be specified as follows:  
             slope   =           Δ   ⁢           ⁢   dBm       Δ   ⁢           ⁢     V   apc         ⇒     Δ   ⁢           ⁢     V   apc         =       Δ   ⁢           ⁢   dBm     slope               (     equation   ⁢           ⁢   5     )             
 
         [0023]     The scaling factor is a digital control value, and can be converted to a voltage value according to the equation 3.  
               Δ   ⁢           ⁢   sf     =     Δ   ⁢           ⁢     V   apc     ⁢     1024   2.2               (     equation   ⁢           ⁢   6     )             
 
         [0024]     According to equations 5 and 6, the scaling factor can be determined as follows:  
               Δ   ⁢           ⁢   sf     =         Δ   ⁢           ⁢   dBm     slope     ×     1024   2.2               (     equation   ⁢           ⁢   7     )             
 
         [0025]     Combining equations 7 and 4, an equation 8 can be further determined:  
                   S     RL   ⁡     (     n   -   1     )         -     S     RL   ⁡     (   n   )               S     RL   ⁡     (     R   -   1     )         -     S     RL   ⁡     (   R   )             =           Δ   ⁢           ⁢     dBm   ⁡     (       L   ⁢     (     n   -   1     )       -     L   ⁡     (   n   )         )           slope   ⁡     (       L   ⁢     (     n   -   1     )       -     L   ⁡     (   n   )         )             Δ   ⁢           ⁢     dBm   ⁡     (       L   ⁡     (     R   -   1     )       -     L   ⁡     (   R   )         )           slope   ⁡     (       L   ⁡     (     R   -   1     )       -     L   ⁡     (   R   )         )           =         Δ   ⁢           ⁢     dBm   ⁡     (       L   ⁢     (     n   -   1     )       -     L   ⁡     (   n   )         )           Δ   ⁢           ⁢     dBm   ⁡     (       L   ⁡     (     R   -   1     )       -     L   ⁡     (   R   )         )           ×       slope   ⁡     (       L   ⁡     (     R   -   1     )       -     L   ⁡     (   R   )         )         slope   ⁡     (       L   ⁡     (     n   -   1     )       -     L   ⁡     (   n   )         )                     (     equation   ⁢           ⁢   8     )             
 
         [0026]     According to equation 8, if the slope curves for different transmission channels are similar for a power amplifier of a mobile communication device, an accurate scaling factor can be obtained using the described equations.  FIG. 3  illustrates an embodiment of relationship between the slope and the voltage value.  
         [0027]     Referring to  FIG. 3 , slope curves for transmission channels  31 ˜ 35  are illustrated, wherein Y-coordinates comprise slopes (ΔdBm/ΔV apc ), and X-coordinates comprise voltage values. The channel  33  is reference channel. The slope curves of channels  31 ˜ 35  are similar between 0.35V˜0.4V. The accuracy of scaling factors determined according to the described method depends on the similarity of the slope curves of different transmission channels. At a particular power level, the slopes of scaling factors are preferably similar.  
         [0028]     When determining a reference power level, the difference between scaling factors of a reference channel and other channels at the reference power level is considered. It is preferred that the variation of scaling factor differences (Df RLf ) is the lowest, thus a lowest error ratio of the scaling factor differences may be obtained. The scaling factor differences (Df RLf ) can be determined according to an equation similar to equation 7, which is as follows:  
               Δ   ⁢           ⁢     Df   RLf       =         Δ   ⁢           ⁢   dBm     slope     ×     1024   2.2               (     equation   ⁢           ⁢   9     )             
 
         [0029]     ΔdBm specifies a difference between power multiples of a reference channel and a transmission channel at a reference power level, and the slope is the slope of the reference power level at the reference channel. According to equation 9, when a more proper reference power level is selected, a lower variation of scaling factor difference (Df RLf ) can be obtained. In other words, a power level which results in the lowest variation of scaling factor difference (ΔDf RLf ) is a most proper power level. There are two ways to obtain a lower scaling factor differences variation (ΔDf RLf ). One method is to lower ΔdBm, which is the differences of power multiples between reference power level and the standard power level, so that an accurate digital control value may be obtained. Another method comprises increasing the slope of a reference power level. Typically, a power level corresponding to larger slopes at every transmission channels may be selected as a reference power level.  
         [0030]     While the invention has been described by way of example and in terms of several embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.