Abstract:
A transmission power controller includes a transmission amplifier located in a first station and having an adjustable gain. The transmission amplifier controls the power transmitted from the first station to a second station in accordance with a power control information signal transmitted from the second station. The transmission power controller comprises a power control information extracting circuit, and up/down decision circuit, and a filter interposed between the up/down decision circuit and the transmission amplifier. The filter extracts low frequency band components from sequential output signals of the up/down decision circuit, generates command signals, and applies the command signals to the transmission amplifier to control the gain of the transmission amplifier.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a transmission power controller for controlling the transmission power of a mobile station comprising part of a radio communication system. More specifically, it relates to a transmission power controller for use with a code division multiple access (CDMA) communication system. 
     2. Description of the Background Art 
     The CDMA communication system has been standardized by the Telecommunications Industry Association TIA) for use in North America and has adapted spread spectrum communication technology. In this system, since a plurality of mobile stations share the same frequency band, signals transmitted by several such stations tend to interfere with each other resulting in degradation of the quality of the signal transmitted by each of the mobile stations. To overcome this problem, a closed-loop power control operation is employed which adjusts the transmission power of each mobile station. Specifically, power control information is transmitted from a base station to each mobile station to minimize interference between the mobile stations. 
     Referring to the block diagram of FIG. 2, the following is an explanation of the power control operation of a conventional CDMA communication system comprising a base station  100 , a mobile station  200 , and a base station controller  300 . 
     The base station  100  includes a demodulator  101 , a signal-to-noise (S/N) power measuring circuit  102 , a power up/down discriminator  103 , a power control information multiplexer  104  and a modulator  105 . The demodulator  101  demodulates a received signal transmitted from the mobile station  200  via a receiving amplifier  106 , and the S/N power measuring circuit  102  measures the received power level of the received signal provided by the demodulator  101 . 
     The power up/down discriminator  103  determines whether the received power level is in a proper or improper status by comparing the received power level with a threshold level provided by a threshold set-up circuit  303  of the base station controller  300  and outputs a power control signal. The threshold level is determined by calculating an error rate of the received signal. For example, when the received power level exceeds the threshold level, the power up/down discriminator  103  outputs a power control bit having a logical value such as “−1”, which commands a decrease in the transmission power of the mobile station  200 . In contrast, when the received power level does not exceed the threshold level, the power up/down discriminator  103  outputs a power control bit having a logical value such as “+1”, which commands an increase in the transmission power of the mobile station  200 . The power control information multiplexer  104  inserts the power control bit into the transmission signal to be transmitted, the transmission signal is modulated to a spread-spectrum signal for the CDMA communication system by the modulator  105 , and the signal is transmitted to an antenna (not shown) via an amplifier  107 . 
     Each mobile station  200  comprises an amplifier  200   a , a demodulator  201 , a power control information extracting circuit  202 , a decoder  203 , an up/down decision circuit  204 , a transmission amplifier  205 , and a transmission circuit  206 . 
     The demodulator  201  demodulates the spread-spectrum signal transmitted from the base station  100  via the receiving amplifier  200   a  to a baseband signal. The power control information extracting circuit  202  extracts the power control bit from the demodulated received signal. The decoder  203  decodes the demodulated received signal to a voice or data signal. The transmission amplifier  205  is a variable gain amplifier which change its gain as a function of the command signal provided by the up/down decision circuit  204 . 
     The up/down decision circuit  204  is an accumulator which sums the signals received from the power control information extracting circuit  202  during a series of signals received from the base station  100 . For example, if five signals, +1, +1, −1, +1, +1 are received from the poser control information extracting circuit  202 , the up/down decision circuit  204  outputs these command signals, + 1 , + 2 , + 1 , + 2 , + 3 , sequentially to the transmission amplifier  205 . In response, the transmission amplifier  205  would increase the transmission power by 3dB. In the conventional CDMA communication system, the power control operation is periodically performed every 1.25 micro-seconds. As a result, the mobile station  200  frequently controls the transmission power in accordance with the power control bit. 
     The base station controller  300  comprises a decoder  301 , an error rate measuring circuit  302 , a threshold set-up circuit  303  and a coder  304 . The decoder  301  decodes the received demodulated signal, provided by the demodulated  101  of the base station  100 , to a voice or data signal. The voice or data signal is supplied to the error rate measuring circuit  302  which measures the error rate of the voice or data signal. The threshold set-up circuit  303  determines a threshold level, based on the error rate, which is the transmission power of the mobile station  200  to satisfy the predetermined quality of speech or data signal. The signal threshold level is supplied to the power up/down discriminator  103  of the base station  100 . The coder  304  codes a voice or data signal to be transmitted to the mobile station  200 . 
     FIG. 3 is a graph having an abscissa divided into  73  divisions each designating an instant T(n), defined as a sample time, at which the base station  100  transmits a “1” or a “+1” signal to the mobile station  200  where it is received by the power control information extracting circuit  202  and inputted to the up/down decision circuit  204 . The ordinate of FIG. 3 shows variations in the power transmitted by the mobile station  200  to the base station  201 , in decibels, at each instant of time T(n). The graph of FIG. 3 illustrates the operation of a typical CDMA communication system in which the power transmitted by the mobile station  200  changes in 1 dB increments at the following sample times: (1) At sample times T( 1 - 10 ), the transmission power alternates between 1 dB and 0 dB (2) At sample times T( 20 - 53 ), the transmission power alternates between 10 dB and 11 dB; and (3) At sample times T( 60 - 73 ), the transmission power alternates between 4dB and 5dB. 
     During the sample times T( 11 - 21 ), the base station  100  transmits a series of only “+1” signals and therefore the power transmitted by the mobile station  200  gradually increases to 11dB, and during the sample times T( 53 - 60 ), the base station  100  transmits a series of only “−1” signals and therefore the power transmitted by the mobile station  200  gradually decreases to 4dB. 
     It is desirable to keep a fixed transmission power level at the mobile station  200  if the transmission power level matches the threshold level. However, in the conventional CDMA communication system, as shown in FIG. 3, even when the transmission power level matches the threshold level, the mobile station is forced to change transmission power because the base station  100  always sends a transmission power control bit that commands either an increase or a decrease in the transmission power. That is, the power being transmitted by the mobile station  200  is always being changed. As a result, the signal received by the base station  100  does not have a constant received power level. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a transmission power controller that is capable of suppressing deviation in the transmission power at the mobile station. It is an another object of the invention to provide a transmission power controller that is capable of not only suppressing such deviations but also capable of providing a quick response to change in the transmission power when the transmission power level does not match the threshold level. 
     To accomplish these objectives, a transmission power controller having a transmission amplifier for adjusting transmission power based on power control information signal transmitted from a base station is provided which comprises; 
     a power control information extracting means for extracting said power control information signal, 
     an up/down decision means for producing a command signal to control a gain of said transmission amplifier in response to said power control information signal, and 
     a filtering means for extracting a row frequency band signal from said command signal and for controlling a gain of said transmission amplifier based on said extracted row frequency band signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will become more apparent from consideration of the following detailed description taken in conjunction with the accompanying drawing in which: 
     FIG. 1 is a block diagram showing a CDMA communication system according to a first embodiment of the invention. 
     FIG. 2 is a block diagram showing a conventional CDMA communication system. 
     FIG. 3 is a graph showing variations in the transmission power of a mobile station. 
     FIG. 4 is a block diagram showing a filter  207  used in first, second and third embodiments of the invention. 
     FIG. 5 is a block diagram showing a CDMA communication system according to the second embodiment of the invention. 
     FIG. 6 is a block diagram showing a switching circuit  208  used in the second embodiment of the invention. 
     FIG. 7 is a block diagram showing a CDMA communication system according to the third embodiment of the invention. 
     FIG. 8 is a block diagram showing a filter coefficient renewal circuit  209  used in the third embodiment of the invention. 
     FIG. 9 is a block diagram showing a CDMA communication system according to a fourth embodiment of the invention. 
     FIG. 10 is a block diagram showing a soft-decision circuit  210  used in the fourth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of the invention comprising a CDMA communication system having a base station  100 , a mobile station  200 A, and a base station controller  300 . The first embodiment of the invention differs from the conventional CDMA system in that the mobile station  200 A has an infinite-impulse-response (IIR) filter  207 . The mobile station  200 A includes an amplifier  200   a , a demodulator  201 , a power control information extracting circuit  202 , a decoder  203 , an updown decision circuit  204 , a transmission amplifier  205 , a transmission circuit  206  and the filter  207 . The gain of the transmission amplifier  205  is controlled by a command signal from the filter  207 . Filter  207  is a low pass filter which extracts a direct current signal from a signal provided by the up/down decision circuit  204  and outputs the command signal to the transmission amplifier  205 . 
     The filter output Y[n] is given by the equation 
     
       
           Y[n]= (1− A ) X[n]+A Y[n− 1], 
       
     
     where A is the coefficient of filter  207  having a value in the range 0 to 1, X[n] is an output of the up/down decision circuit  204 , and n is the number of the sample being input to the filter. As shown by the schematic diagram of FIG. 4, the filter  207  comprises a gain control element  40  having a transfer function (1−A), an adder  41  and a delay circuit  42  having a transfer function (Z −1 ). The delay circuit  42  delays the output signal of the adder  41  by the time interval before samples and inputs it to a gain control circuit  43  having a transfer function A. As a result, the output signal X[n] of the up/down decision circuit  204  is input to the gain control element  40  which multiplies the coefficient (1−A) by the output (X[n]) and outputs the signal ((1−A) X[n]) to a first input of adder  41 . The output signal Y[n] of the adder  41  is input to the delay circuit  42  and the signal Y(n−1) is then input to the gain control element  43  which multiplies it by A and inputs a second input signal A Y[n−1] to the adder  41  . The adder  41  adds the signal ((1−A) X[n]) to the signal (A Y[n−1]) to generate the output signal Y[n]. 
     The characteristic of the IIR filter is a function of the filter coefficient (1−A). Accordingly, the larger the filter coefficient, the slower the response time and the smaller the deviation in the power transmitted by the mobile station  200 A. Similarly, the smaller the filter coefficient, the more rapid the response time and the larger the deviation of power transmitted by the mobile station. Interference between traffic channels used by a plurality of mobile stations  200 A, each having a filter  207 , is reduced by the CDMA system of FIG. 1 in which each mobile station  200 A operates as follows. 
     The transmission amplifier  205  of the mobile station  200 A transmits a signal to the threshold set-up circuit  303  in the base station controller  300  via the amplifier  106 , demodulator  101 , decoder  301  and error rate measuring circuit  302 . The threshold set-up circuit  303  provides a predetermined threshold level to the power up/down decision circuit  103  which compares the threshold level with the power level received from the S/N power measuring circuit  102  of the base station  100 . Thus, the base station  100  compares the received power level with the predetermined threshold level. 
     When the received power level exceeds the threshold level, the base station  100  sends a logical value [−1] from the power up/down decision circuit  103  to the mobile station  200 A via the power control information multiplexer  104 , modulator  105  and amplifier  107 . The logical value [−1] commands a decrease in the transmission power of the mobile station  200 A. Similarly, when the received power level does not exceed the threshold level, the base station  100  sends a logical value [+1], from the power up(down decision circuit  103  to the mobile station  200 A which commands an increase in the transmission power of the mobile station  200 A. Thus, the mobile station  200 A performs a power control operation based on the power control information. 
     In the mobile station  200 A, the power control information extracting circuit  202  receives the signal transmitted by the base station  100  via amplifier  200   a  and demodulator  201 , extracts power control information from the transmission signal and inputs it to the up/down decision circuit  204 . The up/down decision circuit  204  generates a command signal which commands a decrease of 1 dB in the transmission power transmitted by the transmission amplifier  205  of mobile station  200 A when the power control information has logical value “−1”. Similarly, the up/down decision circuit  204  provides a command signal which commands an increase of 1 dB in the transmission power of 1 dB from transmission amplifier  205  when power control information has a logical value “+1”. 
     The command signal is supplied to the transmission amplifier  205  via the filter  207 . As a result, the power control operation enables the mobile station  200 A to control the transmission power. 
     Ideally, the power control operation should be complete when the received power level at the base station  100  matches the threshold level input to the power up/down circuit  103  by the base station controller  300 . However, in actuality, the operation is not completed when the received power level at the base station  100  matches the threshold level. This is because the base station repeatedly transmits to the mobile station  200 A the two types of power control information (+1 and −1). As a result, the mobile station  200 A repeatedly increases and decreases its transmission power to adjust the received power level to match the threshold level. 
     In the power control operation, according to the first embodiment of the invention, the filter  207  extracts a direct current signal X[n] from the command signal of the up/down decision circuit  204  and provides a controlled command signal Y[n] to the transmission amplifier  205 . The amplitude of the controlled command signal is approximately zero when the mobile station  200 A receives alternating “−1” and “+1” signals. Accordingly, the gain of the transmission amplifier  205  is fixed to a target power level that the base station  100  requires. On the other hand, if the received power level at the base station  100  does not match the threshold level, the filter  207  provides a controlled command signal with a particular value other than zero to the transmission amplifier  205 . The transmission amplifier  205  increases or decreases the transmission power based on the controlled command signal. 
     The first embodiment of the invention provides an improved transmission power controller in that it reduces the transmission power deviation of the mobile station  200 A when the received power level at the base station  100  matches the threshold level. Accordingly, the signal received at the base station  100  from the mobile station  200 A has a fixed power level. Further, a CDMA communication system using the power control operation according to the first embodiment increases the number of subscribers who can communicate at the same time. 
     A second embodiment of the invention is shown in FIG.  5  and comprises a CDMA communication system having the base station  100 , a mobile station  200 B, and the base station controller  300 . The second embodiment of the invention differs from the first embodiment in that the mobile station  200 B further includes a switching circuit  208 . Accordingly, the mobile station  200 B includes the amplifier  200   a , the demodulator  201 , the power control information extracting circuit  202 , the decoder  203 , the up/down decision circuit  204 , the transmission amplifier  205 , the transmission circuit  206 , the filter  207  and the switching circuit  208 . 
     The switching circuit  208  has a basic sequence which consist of a binary bit pattern such as (+1, −1, +1, −1, +1, −1), and compares the basic sequence with the received sequence of power control information. The switching circuit  208  switches the command signal provided bag the up;down decision circuit  204  to the filter  207  when the basic sequence matches the received sequence, and switches the command signal directly to the transmission amplifier  205  when the basic sequence does not match the received sequence. 
     The power control operation of the mobile station  200 B including the switching circuit  208  is as follows. The power control information extracting circuit  202  receives a transmission signal transmitted by the base station  100  and extracts power control information from the transmission signal. Power control information is supplied to the up/down decision circuit  204 . The up/down decision circuit  204  provides a negative command signal, which commands a decrease of 1 dB in the transmission power transmitted by the transmission amplifier  205  when the power control information is a logical value “−1”. Similarly, the up/down decision circuit  204  provides a positive command signal, which commands an increase of 1 dB in the transmission power transmitted by the transmission amplifier  205 , when the power control information is a logical value “+1”. The command signal is supplied to the switching circuit  208 . 
     FIG. 6, shows a preferred embodiment of the switching circuit  208  which comprises a switching element  60 , a received sequence register  61 , a correlator  62 , and a basic sequence register  63 . The switching element  60  switches the output signal X[n] of the up/down decision circuit  204  to either the filter  207  or to the transmission amplifier  205  in accordance with the correlation result provided by the correlator  62 . 
     The received sequence register  61  stores the received sequences of power control information within a predetermined period. The correlator  62  estimates the correlation between the received sequences of power control information stored by the received sequence register  61  and the basic sequence stored by the basic sequence register  63 . If the correlation value exceeds a predetermined threshold value, that is the received sequences match the basic sequences, the switching element  60  switches the command signal X[n] provided by the up/down decision  204  to filter  207 . The filter  207  performs the same operation as described in the first embodiment. In this case, since the output, signal of filter  207  is approximately zero, the gain of the transmission amplifier  205  is fixed at the target power level that the base station  100  requires. 
     On the other hand, if the correlation value does not exceed the predetermined threshold value, that is, the received sequence does not match the basic sequence, the switching clement  60  switches the command signal directly to the transmission amplifier  205 . In this case, since the command signal has a maximum value in response to the power control information “+1” and “−1”, the gain of the transmission amplifier  205  can be changed faster than with the circuit of the first embodiment shown in FIG.  1 . 
     Summarizing, the second embodiment of the present invention provides an improved transmission power controller in which it is possible to reduce the transmission power deviation of the mobile station  200 B when the received sequence of power control information matches the basic sequence. Further, when the received sequence of power control information does not match the basic sequence, the transmission power of the mobile station  200 B can be changed more quickly than with first embodiment CDMA system. 
     A third embodiment of the invention is shown in FIG.  7  and comprises a CDMA communication system having the base station  100 , a mobile station  200 C, and the base station controller  300 . The third embodiment of the invention differ from the first embodiment in that the mobile station  200 C further include a filter coefficient renewal circuit  209 . Accordingly, the mobile station  200 C includes the amplifier  200   a , demodulator  201 , power control information extracting circuit  202 , decoder  203 , up/down decision circuit  204 , transmission circuit  206 , filter  207  and the filter coefficient renewal circuit  209 . 
     The filter coefficient renewal circuit  209  is connected to the up/down decision circuit  204  and has a basic sequence, which consists of a binary bit pattern such as (+1, −1, +1, −1, −1, −1) The filter coefficient renewal circuit  209  changes the filter coefficient A of the filter  207  based on the correlation value between a received sequence of power control information and the basic sequence. That is, when the correlation value is at a maximum. the filter coefficient renewal circuit  209  selects a filter coefficient that will pass a command signal having the maximum bandwidth. When the correlation value is at a minimum, the filter coefficient renewal circuit selects a different filter coefficient that will pass a command signal having the minimum bandwidth. 
     FIG. 8 shoals a preferred embodiment of the filter coefficient renewal circuit  209 . Circuit  209  has a received sequence register  80 , a basic sequence register  81 , a correlator  82 , and a filter coefficient set-up circuit  83 . The received sequence register  80  stores a received sequence of power control information within a predetermined period and the basic sequence register  81  stores a basic sequence such as (+1, −1, +1, −1, +1, −1). 
     The power control operation of the mobile station  200 C including the filter coefficient renewal circuit  209  as illustrated in FIGS. 7 and 8 will now be explained. The correlator  82  estimates the correlation value between the received sequence of power control information and the basic sequence, and supplies this value to the filter coefficient set-up circuit  83 . When the received sequence of power control information completely matches the basic sequence (+1, −1, +1, −1, +1, −1), the filter coefficient set-up circuit  83  selects a filter coefficient that will pass a command signal having the narrowest bandwidth. Hence, the amplitude of the command signal is approximately zero, and the gain of the transmission amplifier  205  is fixed to a target power level that the base station  100  requires. When the received sequence of power control information is similar to the basic sequence, the filter coefficient set-up circuit  83  selects a filter coefficient that will pass a command signal having a comparatively narrow bandwidth. Hence, the amplitude of the command signal is a relatively small value, and the transmission amplifier  205  is slowly controlled within a range having a low value. 
     When the received sequence of power control information is different from the basic sequence, the filter coefficient set-up circuit  83  selects a filter coefficient that will pass the command signal having the broadest bandwidth. Hence, the amplitude of the command signal is similar to the output signal of the up/down decision circuit  204 , and the output of the transmission amplifier  205  is controlled rapidly to the target power level that the base station  100  requires. 
     Summarizing, the third embodiment of the invention provides an improved transmission power controller in which it is possible to reduce the transmission power deviation of the mobile station  200 C when the received sequence matches the basic sequence. Further, when the received sequence of power control information does not match the basic sequence, the transmission power of the mobile station  200 C can be changed more quickly than with the first embodiment. That is, the transmission power of the mobile station  200 C matches what the base station  100  requires. Further, since the filter coefficient renewal circuit  209  selects one of the filter coefficients based on the correlation between the received sequence and the basic sequence, the transmission power control of the mobile station  200 C is carried out in smaller increments than occurs with the first and second embodiments. 
     FIG. 9 shows a CDMA communication system comprising the base station  100 , mobile station  200 D, and the base station controller  300  with regard to a fourth embodiment of the present invention. The difference between the fourth embodiment and the first embodiment is that the mobile station  200 D has a soft-decision output circuit  210  instead of the filter  207 . Accordingly, the mobile station  200 D includes the demodulator  201 , power control information extracting circuit  202 , the decoder  203 , the up/down decision circuit  204 , the transmission amplifier  205 , the transmission circuit  206  and the soft-decision circuit  210 . 
     FIG. 10 shows a preferred embodiment of the soft-decision circuit  210 . The soft-decision circuit  210  comprises a received sequence register  90 , a basic sequence register  91 , a correlator  92 , a confidence level discriminator  93 , and a weighted signal generator  94 . The received sequence a register  90  stores a received sequence of power control information within a predetermined period and the basic sequence register  91  stores a basic sequence such as (+1, −1, +1, −1, +1, −1). 
     The power control operation of the mobile station  200 D including the soft-decision circuit  210  as illustrated in FIGS. 9 and 10 will now be explained. The correlator  92  estimates the correlation value between the received sequence of power control information provided by the up/down decision circuit  204  and the basic sequence and supplies it to the confidence level discriminator  93 . The confidence level discriminator  93  calculates a confidence level based on the correlation value and a high correlation period defined by the period during which a high correlation value is maintained over a predetermined value period. The weighted signal generator  94  produces a weighted command signal based on the confidence level. 
     When the received sequence of past power control information matches the basic sequence, the weighted signal generator  94  changes the filter coefficient to a smaller value in order to suppress the amplitude of the command signal of the up/down decision circuit  204 . Further, when the next received sequence matches the basic sequence, the weighted signal generator  94  reduces further the filter coefficient thereby further suppressing the amplitude of the command signal. As a result, during a high confidence level period, the weighted signal generator  94  reduces gradually the amplitude of the command signal. 
     For example, in a normal mode, the range through which the power output of the transmission amplifier  205  changes is “ 521  1 dB” in response to a power control information signal of “ 521  1”. However, when the received information signal continues to match the basic sequence, the range through which the power output of the amplifier  205  may change is from “ 521  1.00 dB” to “ 521  0.75 dB” and then from “ 521  0.75 dB” to “ 521  0.50 dB” in response to sequential power control information signals of “521 1”. That is, when two sequential power control information signals of “ 521  1” are received which match the basic sequence, the weighted signal generator  94  suppresses the amplitude of the first command signal causing a change in the power output of the transmission amplifier  205  from “ 521  1.00 dB” to “ 521  0.75 dB”, and suppresses the amplitude of the second command signal from “ 521  0.75 dB” to “ 521  0.50 dB”, as mentioned above. Also, if the following received sequence continues to match the basic sequence, the weighted signal generator  94  suppresses the amplitude of the command signal. For example, the output of amplifier  205  may be changed from “ 521  0.50 dB” to “ 521  0.25 dB” in response to a power control information signal of “ 521  1”. However, when the subsequent received sequence does not match the basic sequence, the weighted signal generator  94  returns gradually the amplitude of the control signal to its value in the normal mode. 
     As set forth above, the fourth embodiment of the present invention provides an improved transmission power controller whereby it is possible to reduce gradually the deviation in the power output of the transmission amplifier  205  of the mobile station  200 D when the received power level at the base station  100  matches the threshold thereof Further, the transmission power control of the mobile station  200 D is carried out with smaller changes than is the case with the first and second embodiment. 
     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by those embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope thereof. For example, in the second and third embodiments, it has been described host to estimate the correlation value between the received sequence provided by the up/down decision circuit  204  and the basic sequence. However it is possible to estimate the correlation value based on counting the number of reverses between the plus signs and minus signs of the power control information signal instead of the above mentioned correlation. The third embodiment describes how to alter the filter coefficient and change the gain of the transmission amplifier  205  based on the correlation value. However, if there are a plurality of filters having independent filter characteristics, it is possible to select a filter based on the correlation value. 
     In the fourth embodiment, it has been described how to suppress/expand the amplitude of the command signal from the up/down decision circuit  204  gradually. That is, change in the amplitude is increments of “0.75 dB”, “0.50 dB”, or “0.25 dB” in response to changes in the power control information signal of “+1” and “−1”. It is also possible to adapt another fixed increment in the rate of adaptive change in response to the confidence level. 
     In the embodiments described above, the power control operation occurs in the mobile station. However, it is possible to adapt the operation to a base station having a radio transmission function. Also, it has been described that power control information is transmitted from a base station to a mobile station in the form of a binary signal (+1, −1). However, it is possible to employ multiple power control information signals instead of the binary signal.