Abstract:
A transmission power control apparatus includes a transmission power control signal extracting section, transmission power control signal storage section, transmission power control determination section, and transmission power changing section. The transmission power control signal extracting section extracts a transmission power control signal from a reception signal containing a transmission power control signal. The transmission power control signal storage section sequentially stores transmission power control signals output from the transmission power control signal extracting section. The transmission power control determination section determines whether an instruction to increase/decrease transmission power based on a plurality of transmission power control signals stored in the transmission power control signal storage section is repeatedly generated. The transmission power changing section stops transmission power updating operation if the determination result from the transmission power control determination section indicates that the transmission power is repeatedly increased/decreased. A transmission power control method is also disclosed.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to transmission power control on a mobile terminal and, more particularly, to a transmission power control method and apparatus used for a CDMA (Code Division Multiple Access) mobile terminal. 
   Transmission power control used for a conventional CDMA mobile terminal communication apparatus is performed by generating an instruction to increase/decrease transmission power by using a transmission power control bit sent from a base station for each slot. In a CDMA communication system, in order to provide stable communication, a base station must thoroughly control the transmission power of each mobile communication apparatus in accordance with the service to be provided and the like. 
   In the conventional CDMA communication system, however, the following problems are posed. First, transmission power control must be performed for each slot in accordance with a transmission power control bit updated for each slot, wastefully consuming power. Second, a transmission power control error in an apparatus under a relatively stable reception/transmission environment may affect the communication state of the system. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a transmission power control method and apparatus which suppress consumption of power. 
   It is another object of the present invention to provide a transmission power control method and apparatus which reduce the influence of a decoding error in a transmission power control bit on a system. 
   In order to achieve the above objects, according to the present invention, there is provided a transmission power control apparatus comprising extraction means for extracting a transmission power control signal from a reception signal containing a transmission power control signal, storage means for sequentially storing transmission power control signals output from the extraction means, first determination means for determining whether an instruction to increase/decrease transmission power based on a plurality of transmission power control signals stored in the storage means is repeatedly generated, and update stopping means for stopping transmission power updating operation if the determination result from the first determination means indicates that the transmission power is repeatedly increased/decreased. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a CDMA mobile terminal according to the first embodiment of the present invention; 
       FIG. 2  is a flow chart showing the operation of the transmission power control determination section in  FIG. 1 ; 
       FIG. 3  is a flow chart showing the operation of the transmission power control determination section in  FIG. 1  in detail; 
       FIG. 4  is a block diagram showing a CDMA mobile terminal according to the second embodiment of the present invention; 
       FIG. 5  is a flow chart showing the operation of a transmission power control determination section in  FIG. 4 ; and 
       FIG. 6  is a flow chart showing the operation of the transmission power control determination section in  FIG. 4  in detail. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will be described below in detail with reference to the accompanying drawings. 
     FIG. 1  shows a CDMA mobile terminal according to the first embodiment of the present invention. The CDMA mobile terminal shown in  FIG. 1  includes an antenna  101  for transmitting/receiving radio waves, a circulator  102  connected to the antenna  101 , a receiving section  11  for receiving a signal through the antenna  101 , a transmitting section  12  for transmitting a signal through the antenna  101 , a transmission power control section  13  for controlling transmission power from the transmitting section  12  on the basis of a reception signal in the receiving section  11 , an input/output section  14  for performing input/output operation with an operator, and a control section  111  for controlling the overall terminal. The circulator  102  supplies a reception wave from the antenna  101  to only the receiving section  11 , and supplies a transmission wave from the transmitting section  12  to only the antenna  101 . 
   The receiving section  11  includes a reception-side radio section  103  for obtaining a reception intermediate frequency signal from a reception signal obtained through the antenna  101 , a despreading signal generating section  104  for generating a despreading signal identical or complex conjugate to a spreading signal on the transmission side, a despreading section  105  for extracting a baseband signal of a desired wave (to be referred to as a reception baseband signal hereinafter) by multiplying a reception intermediate frequency signal and a despreading signal from the despreading signal generating section  104 , and a reception-side baseband signal processing section  106  for receiving a reception baseband signal from the despreading section  105  and performing predetermined processing for the signal. 
   The transmitting section  12  includes a transmission-side baseband signal processing section  107  for performing predetermined processing for a transmission baseband signal, a spreading signal generating section  108  for generating a spreading signal unique to each CDMA mobile terminal, a spreading section  109  for obtaining a transmission intermediate frequency signal by multiplying a transmission baseband signal from the transmission-side baseband signal processing section  107  and a spreading signal from the spreading signal generating section  108 , and a transmission-side radio section  110  for generating a transmission wave from a transmission intermediate frequency signal from the spreading section  109 . 
   The input/output section  14  includes a microphone  112  for receiving speech or the like, a speech input section  113  for processing a speech signal input from the microphone  112 , a plurality of keys  114  for allowing an operator to input a telephone number, command, or the like, an operation input section  115  for processing a telephone number, command, or the like input from the keys  114 , a speaker  116  for outputting speech, a speech output section  117  for processing a signal to be output to the speaker  116 , a display device  118  for displaying characters and the like, a display control section  119  for processing characters and the like to be displayed on the display device  118 , and an interface section  120  for interfacing with other devices. 
   The transmission power control section  13  includes a transmission power control signal extracting section  121 , transmission power control signal storage section  122 , transmission power control determination section  123 , and transmission power changing section  124 . 
   The transmission power control signal extracting section  121  extracts a transmission power control signal from a reception baseband signal from the despreading section  105 . The base station determines, on the basis of the result obtained by measuring the base station reception level of the like of a signal sent from a CDMA mobile terminal, whether to increase or decrease the transmission power of the CDMA mobile terminal. The base station then inserts a transmission power control signal for instructing to increase/decrease the transmission power in a downstream signal. The transmission power control signal generally contains information instructing to increase or decrease transmission power by a specific dB. 
   The transmission power control signal is updated once for every one or five slots according to the specifications of a W-CDMA (Wideband-CDMA) system depending on the condition. When the signal is to be updated for every five slots, the same transmission power control signal may be repeatedly inserted in five slots. Alternatively, a valid transmission power control signal is inserted in only one slot, while invalid signals may be inserted in the four remaining slots. According to the specifications of the W-CDMA system, the period of one frame is 10 ms, and one frame is constituted by 15 slots. Therefore, the period of one slot is 0.625 ms. In addition, 64 frames constitute one superframe having a period of 64 ms. 
   The insertion period is an m-slot period, and one or two different periods are used in the system. 
   The transmission power control signal storage section  122  stores a predetermined number of transmission power control signals extracted by the transmission power control signal extracting section  121  in the FIFO (First-In First-Out) scheme. That is, upon reception of a new transmission power control signal from the transmission power control signal extracting section  121 , the transmission power control signal storage section  122  erases the oldest transmission power control signal and stores the newest transmission power control signal. 
   The transmission power control determination section  123  determines, on the basis of a predetermined number of transmission power control signals stored in the transmission power control signal storage section  122 , whether to control the transmission power. The transmission power control determination section  123  outputs a transmission power change instruction with a transmission power increase/decrease value to the transmission power changing section  124  only when determining that the transmission power should be controlled. 
   Upon reception of a transmission power change instruction from the transmission power control determination section  123 , the transmission power changing section  124  controls a variable gain amplifier  151  of the transmission-side radio section  110  in order to change the transmission power by the transmission power increase/decrease value accompanying the transmission power change instruction. 
   The transmission power control operation of the transmission power control determination section  123  will be described next with reference to  FIG. 2 . 
   When a new transmission power control signal is stored in the transmission power control signal storage section  122 , the transmission power control determination section  123  reads out N transmission power control signals X( 0 ) to X(N−1) from the transmission power control signal storage section  122  (step S 201 ). The signal X( 0 ) is the newest transmission power control signal, and the signal X(N−1) is the oldest transmission power control signal. 
   The transmission power control determination section  123  checks the transmission power control signals X( 0 ) to X(N−1) to determine whether the power is kept repeatedly increased/decreased (step S 202 ). If “NO” in step S 202 , the transmission power control determination section  123  sets a transmission power increase/decrease value Y to an increase/decrease value X( 0 ) indicated by the newest transmission power control signal (step S 203 ), and then outputs a transmission power change instruction with the transmission power increase/decrease value Y to the transmission power changing section  124  (step S 204 ). 
   If “YES” in step S 202 , steps S 203  and S 204  are skipped. That is, the transmission power control section  13  does not update the transmission power by the newest transmission power control signal. 
   A specific example of transmission power control operation will be described next with reference to  FIG. 3 . 
   When a new transmission power control signal is stored in the transmission power control signal storage section  122 , the transmission power control determination section  123  reads out N transmission power control signals X( 0 ) to X(N−1) from the transmission power control signal storage section  122  (step S 301 ). The signal X( 0 ) is the newest transmission power control signal, and the signal X(N−1) is the oldest transmission power control signal. 
   The transmission power control signals X( 0 ) to X(N−1) are Fourier-transformed to obtain frequency components S( 0 ) to S(N−1) (step S 302 ). The component S( 0 ) is a DC component. The components S( 1 ) to S(N−1) are AC components and represented by complex numbers. 
   The transmission power control determination section  123  checks whether a predetermined frequency component of frequency components |S( 1 )| to |S(N−1)| is equal to or less than a predetermined value (step S 303 ). When a transmission power control signal is to be updated for every slot, the predetermined frequency component is |S( 1 )|. When a transmission power control signal is to be updated for every five slots and the same transmission power control signal is inserted in five slots, the predetermined frequency component is |S( 5 )|. When a transmission power control signal is updated for every five slots and the same transmission power control signal is to be inserted in every fifth slot, since the transmission power control signal extracting section  121  extracts a transmission power control signal in every fifth slot, the predetermined frequency component is |S( 1 )|. 
   If “NO” in step S 303 , the transmission power increase/decrease value Y is set to the increase/decrease value X( 0 ) indicated by the transmission power control signal (step S 304 ), and a transmission power change instruction with the transmission power increase/decrease value Y is output to the transmission power changing section  124  (step S 305 ). 
   If “YES” in step S 303 , the steps S 304  and S 305  are skipped. That is, the transmission power control determination section  123  and transmission power changing section  124  do not update the transmission power by using the newest transmission power control signal. 
     FIG. 4  shows a CDMA mobile terminal according to the second embodiment of the present invention. 
   The CDMA mobile terminal of this embodiment differs from the CDMA mobile terminal of the first embodiment in that a Doppler effect measuring section  125  is added, and a transmission power control determination section  223  is used in place of the transmission power control determination section  123 . The transmission power control determination section  223  includes a first determination section  223   a  having the same function as that of the transmission power control determination section  123  in  FIG. 1 , and a second determination section  223   b  having a determination function unique to the second embodiment. Other constituent elements are the same as those in the first embodiment, and hence a description thereof will be omitted. 
   The Doppler effect measuring section  125  compares the actual slot period of a reception baseband signal from a despreading section  105  with a reference slot period to measure a slot period deviation due to the Doppler effect on a reception wave which is produced when the CDMA mobile terminal moves, and outputs the deviation to the transmission power control determination section  223 . 
   The transmission power control operation of the transmission power control determination section  223  will be described next with reference to  FIG. 5 . 
   When a new transmission power control signal is stored in a transmission power control signal storage section  122 , the transmission power control determination section  223  reads out N transmission power control signals X( 0 ) to X(N−1) from the transmission power control signal storage section  122  (step S 501 ). In this case, the signal (X 0 ) is the newest transmission power control signal, and the signal X(N−1) is the oldest transmission power control signal. 
   By checking the transmission power control signals X( 0 ) to X(N−1), the first determination section  223   a  of the transmission power control determination section  223  determines whether the power is kept repeatedly increased/decreased (step S 502 ). If “NO” in step S 202 , the transmission power control determination section  223  sets a transmission power increase/decrease value Y to an increase/decrease value X( 0 ) indicated by the newest transmission power control signal (step S 503 ), and then outputs a transmission power control signal with the transmission power increase/decrease value Y to the transmission power changing section  124  (step S 504 ). 
   If “YES” in step S 502 , the second determination section  223   b  of the transmission power control determination section  223  checks whether the frequency deviation of the reception wave due to the Doppler effect is equal to or less than a predetermined value (step S 505 ). If “NO” in step S 505 , the flow advances to step S 203 . If “YES” in step S 505 , steps S 203  and S 204  are skipped. 
   A specific example of transmission power control operation will be described next with reference to  FIG. 6 . Steps S 601  to S 605  are the same as steps S 301  to S 305  in  FIG. 3 , and hence a description thereof will be omitted. 
   If “YES” in step S 603 , the second determination section  223   b  of the transmission power control determination section  223  checks whether the slot period deviation is equal to or less than a predetermined value (step S 606 ). If “NO” in step S 603 , the flow advances to step S 604 . If “YES” in step S 606 , steps S 604  and S 605  are skipped. 
   As has been described above, according to the present invention, unnecessary transmission power changes can be omitted, and low power consumption and stable communication can be realized. In addition, the present invention can decrease the possibility of wrong transmission power control due to a decoding error in a transmission power control signal and determination error.