JP2002290325A - Mobile wireless system and base station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the availability of frequency bands to be used for communication from lowering by transmitting a broadcast signal at an optimum transmission power level a independently of the distribution state of mobile stations. SOLUTION: A reception section 60 extracts transmission power control information respectively sent from mobile stations PS1-PSm from a received signal, a detection section 71 discriminates whether the transmission power control information requests increased transmission power of the multiple access signal or decreased transmission power, obtains number of requests requesting the increased transmission power of the multiple access signal and informs a control section 101 about the number as number of increased requests D. The control section 101 totally controls each section of the base station and controls a multiple access signal transmission section 20 in response to the number of increased requests D informed from the detection section 71 to increase/decrease the transmission power level of the multiple access signal in addition to the communication control with the mobile stations PS1-PSm and the control of connecting the mobile stations PS1-PSm to the network of the mobile communication system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a mobile radio system that employs a communication method such as a (Code Division Multiple Access) communication method and controls a transmission power level of a base station according to information received from a mobile station.

[0002]

2. Description of the Related Art In a mobile radio system employing a CDMA communication system, signals in the same frequency band are used for radio communication between a base station and a plurality of mobile stations. The base station spreads a code having a random pattern called a spreading code assigned to each communication channel over a signal of the channel, spreads the code into a wideband signal, and transmits the spread signal.

On the other hand, a mobile station receives a wideband signal in which a plurality of channels are mixed, and applies the same spreading code to the received signal as a code used for spreading on a base station side to obtain a desired channel. Can be extracted.

As described above, in a mobile radio system adopting the CDMA communication system, signals of a plurality of channels are spread and multiplexed in the same frequency band. Therefore, in order to increase the number of channels, transmission per channel is performed. The power level needs to be as low as possible.

[0005] However, the distance between the base station and each mobile station is not constant, and the propagation environment of radio waves differs from mobile station to mobile station. Therefore, the transmission power of the base station required to obtain a constant reception quality in each mobile station is considered. The level is different for each mobile station.

For this reason, in the current system, the reception quality of the channel received by each mobile station is determined, and if the desired quality is satisfied, the base station is made to reduce the transmission power level of the channel. If the desired quality is not satisfied, the base station is requested to increase the transmission power level of the channel. Then, the base station performs transmission at a transmission power level according to the request for each mobile station, thereby transmitting each channel at a necessary and sufficient transmission power level, and achieving a certain reception quality at each mobile station. Obtainable.

[0007] CDMA is also used for wireless communication such as broadcast transmission for transmitting the same information to a plurality of mobile stations.
A mobile radio system employing a communication method can be used. In this case, the broadcast data is spread and transmitted by the base station using a common spreading code among a plurality of mobile stations, and the plurality of mobile stations perform despreading with the common spreading code to obtain a plurality of data. The mobile station can receive the same broadcast signal.

[0008] In this case as well, the reception quality differs for each mobile station depending on the positional relationship between the base station and the mobile station. However, in order to enable reception even by a mobile station some distance from the base station, it is somewhat excessive. Transmission must be performed at an appropriate transmission power level.

However, as described above, when the base station transmits a broadcast signal at a certain transmission power level,
For a mobile station relatively close to the base station, the reception quality is too high, and for a mobile station relatively far from the base station, the reception quality is too low.

[0010] For this reason, even if there is no mobile station receiving the broadcast signal, or even if most mobile stations are near the base station, the transmission is performed at the same transmission power level. There has been a problem that the ratio of the power level of the broadcast signal to the total transmission power level of the station becomes unnecessarily large, and as a result, the utilization efficiency of the frequency band is reduced.

[0011]

In a conventional mobile radio system, a base station transmits a broadcast signal at a constant transmission power level regardless of a distribution state of mobile stations. There has been a problem that the ratio of the power level of the broadcast signal to the total transmission power level becomes unnecessarily large, and as a result, the use efficiency of the frequency band is reduced.

The present invention has been made to solve the above-mentioned problem, and it is possible to transmit a broadcast signal at an optimum transmission power level irrespective of a distribution state of mobile stations, and to use a frequency band used for communication. It is an object of the present invention to provide a mobile radio system and a base station capable of preventing a decrease in the radio frequency.

[0013]

To achieve the above object, according to the present invention, a base station and a mobile station connectable to a network are connected to CDMA wireless communication, and the base station is connected to a base station. In a mobile radio system in which a common radio signal is transmitted to a plurality of mobile stations, the mobile station receives a common radio signal, and detects reception quality of the common radio signal. Depending on the detection result,
Transmitting means for transmitting control information for increasing / decreasing transmission power of a common radio signal to the base station, wherein the base station receives control information from a plurality of mobile stations; and A control unit for controlling the transmission power of the common radio signal based on the received control information is provided.

In the mobile radio system having the above-described configuration, the mobile station receives a radio signal transmitted from the base station to a plurality of mobile stations in common, obtains the quality of the radio signal, and transmits the quality to the base station according to the quality. The base station controls the transmission power of the common radio signal based on the control information by transmitting control information for requesting increase or decrease of the transmission power of the radio signal.

Therefore, according to the mobile radio system having the above configuration, even if the distribution of mobile stations located in the radio zone of the base station changes, the common radio signal is optimally transmitted according to the request of the mobile station. Since transmission can be performed with the power level controlled, it is possible to prevent a reduction in the use efficiency of the frequency band used for communication.

According to another aspect of the present invention, there is provided a base station which is connected to a mobile station by CDMA radio communication and transmits a common radio signal to a plurality of mobile stations. Receiving means for receiving, from a plurality of mobile stations, control information for increasing or decreasing the transmission power of a common radio signal, and increasing the transmission power of the common radio signal based on the control information received by the reception means. Request ratio detecting means for detecting a ratio of mobile stations requesting transmission, and a transmission for increasing transmission power of a common radio signal when a ratio detected by the increasing request ratio detecting means is larger than a preset threshold value. And a power control means.

The base station having the above configuration receives control information for increasing or decreasing the transmission power of a radio signal to be commonly transmitted to a plurality of mobile stations, and based on the control information, transmits the transmission power of the common radio signal. To control.

Therefore, according to the base station having the above configuration,
Even if the distribution of mobile stations located in the radio zone of the base station changes, the common radio signal can be controlled and transmitted to the optimum transmission power level according to the request of the mobile station, so that the frequency used for communication can be controlled. It is possible to prevent a reduction in band use efficiency.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a base station according to the first embodiment of the present invention. In the following description, only a configuration related to the present invention will be described.
In addition, description of a configuration related to connection with a mobile communication network is omitted.

The base station includes communication signal transmitting units 11 to 1m
(M> 3), broadcast signal transmitting section 20, multiplexing section 30, antenna sharing section 40, antenna 50, receiving section 60, detecting section 7
1 and a control unit 101.

The communication signal transmitting unit 11 performs communication based on communication data transmitted to the mobile station PS1 as a communication partner.
A multiplexing unit 3 generates a communication signal of a radio frequency of the DMA system.
Output to 0.

Similarly, the communication signal transmission units 12 to 1m generate CDMA radio frequency communication signals based on communication data transmitted to the mobile stations PS2 to PSm to be communication partners, respectively, and multiplex the communication signals. Output to the unit 30.

Broadcast signal transmitting section 20 transmits a CDMA radio frequency broadcast signal based on broadcast data transmitted to all mobile stations PS1 to PSm located in the radio zone of the base station. Generate and output to the multiplexing unit 30.
Further, the broadcast signal transmitting unit 20 sets the transmission power level of the broadcast signal in accordance with an instruction from the control unit 101 described later,
It is increased or decreased stepwise by a certain level (hereinafter referred to as one power unit).

The multiplexing unit 30 includes communication signal transmitting units 11 to 1
m, and multiplexes the communication signal generated at m and the broadcast signal generated at the broadcast signal transmitting unit 20 by RF combining, and outputs the multiplexed signal to the antenna sharing unit 40.

The antenna sharing unit 40 is for sharing the antenna 50 for transmission and reception, and
The RF signal multiplexed at 0 is radiated into the space through the antenna 50, and the RF signal received from the space at the antenna 50 is output to the receiving unit 60.

The receiving section 60 converts the frequency of the received radio frequency signal input through the antenna sharing section 40 into a baseband signal, performs despreading processing on the converted signal, and performs mobile station PS1.
To extract data sent from .PSm.

The receiving section 60 extracts transmission power control information from the data and outputs the information to the detecting section 71. This transmission power control information is transmitted from each of the mobile stations PS1 to PSm.

Each of the mobile stations PS1 to PSm detects the reception quality of the broadcast signal received from the base station, and if the detected reception quality is lower than a predetermined reference level, the mobile station PS1 to PSm reduces the transmission power of the broadcast signal. The transmission power control information including the request for increase is generated and transmitted.

On the other hand, each of the mobile stations PS1 to PSm detects the reception quality of the broadcast signal received from the base station,
If the detected reception quality is equal to or higher than a predetermined reference level, the transmission power control information including a request to reduce the transmission power of the broadcast signal is generated and transmitted.

Further, the mobile stations PS1 to PSm each receive a signal according to the reception quality of the communication signal received from the base station.
The transmission power control information including the request to increase or decrease the transmission power of the communication signal is generated and transmitted, but this point is the same as the conventional one.

The detecting section 71 determines whether the transmission power control information transmitted from each of the mobile stations PS1 to PSm requests the increase or decrease of the transmission power of the broadcast signal. The control unit 101 detects the ratio of requests for an increase in signal transmission power, and notifies the control unit 101 of this ratio as an increase request ratio Rd.

The control section 101 controls the respective sections of the base station in an integrated manner, and controls the base station and the mobile stations PS1 to PS1.
m and the mobile station P communicating with the base station.
In addition to a normal control function such as control for connecting S1 to PSm to the network of the mobile communication system, the broadcast signal transmitting unit 2 according to the increase request ratio Rd notified from the detecting unit 71.
It is newly provided with a control function of controlling 0 to increase or decrease the transmission power level of the broadcast signal.

Next, the operation of the base station having the above configuration will be described. In the following description, ordinary control operations such as communication control between the mobile stations PS1 to PSm and control for connecting the mobile stations PS1 to PSm to a network of a mobile communication system are omitted.

Here, the operation of controlling the transmission power level of the broadcast signal according to the present invention will be described. FIG.
5 is a flowchart for explaining the above control, and this process is executed by the control unit 101 each time a predetermined control cycle Tc arrives.

When the predetermined control cycle Tc arrives, first, in step 2a, the increase request ratio Rd
And the process proceeds to step 2b. In step 2b, it is determined whether the increase request ratio Rd is higher than a threshold thD. Here, when the increase request ratio Rd is higher than the threshold thD, the process proceeds to step 2c. On the other hand, when the increase request ratio Rd is equal to or less than the threshold thD, the process proceeds to step 2d.

In step 2c, the broadcast signal transmission unit 20 is instructed to increase the transmission power level of the broadcast signal by one power unit, and the process ends. Thereby, the broadcast signal transmitting unit 20 increases the transmission power level of the broadcast signal by one power unit.

On the other hand, in step 2d, the broadcast signal transmitting unit 20 is instructed to reduce the transmission power level of the broadcast signal by one power unit, and the process is terminated. Thereby, the broadcast signal transmitting unit 20 reduces the transmission power level of the broadcast signal by one power unit.

As described above, in the base station having the above-described configuration, when the ratio Rd of the mobile stations PS1 to PSm that requires an increase in the transmission power of the broadcast signal is higher than the threshold thD, the broadcast is performed. The transmission power level of the signal is increased by one power unit, while when the ratio Rd is equal to or smaller than the threshold thD, the transmission power level of the broadcast signal is decreased by one power unit.

Therefore, according to the base station having the above configuration,
For example, if the increase request ratio Rd changes as shown in FIG. 3A, the transmission power level of the broadcast signal increases or decreases as shown in FIG. 3B.

Therefore, even if the distribution of mobile stations changes, the broadcast signal can be controlled and transmitted to the optimum transmission power level in accordance with the ratio Rd of mobile stations requesting an increase in transmission power. It is possible to prevent a decrease in the use efficiency of the frequency band to be used.

FIG. 4 shows the configuration of a base station according to the second embodiment of the present invention. In the following description, only the configuration relating to the present invention will be described, and in addition, connection to a mobile communication network will be described. The description of the related configuration will be omitted.

This base station includes communication signal transmitting units 11 to 1 m
(M> 3), broadcast signal transmitting section 20, multiplexing section 30, antenna sharing section 40, antenna 50, receiving section 60, detecting section 7
1, a power detection unit 80 and a control unit 102 are provided.

The communication signal transmitting section 11 transmits a C signal based on communication data transmitted to the mobile station PS1 as a communication partner.
A multiplexing unit 3 generates a communication signal of a radio frequency of the DMA system.
0 and output to the power detection unit 80.

Similarly, the communication signal transmitting units 12 to 1m generate CDMA radio frequency communication signals based on communication data transmitted to the mobile stations PS2 to PSm, which are communication partners, and multiplex the communication signals. It outputs to the unit 30 and the power detection unit 80.

Broadcast signal transmitting section 20 transmits a CDMA radio frequency broadcast signal based on broadcast data transmitted to all mobile stations PS1 to PSm located in the radio zone of the base station. Generated and output to the multiplexing unit 30 and the power detection unit 80. Further, the broadcast signal transmitting unit 20 increases or decreases the transmission power level of the broadcast signal stepwise by a fixed level (hereinafter, referred to as one power unit) according to an instruction from the control unit 102 described later. .

The multiplexing unit 30 includes communication signal transmitting units 11 to 1
m, and multiplexes the communication signal generated at m and the broadcast signal generated at the broadcast signal transmitting unit 20 by RF combining, and outputs the multiplexed signal to the antenna sharing unit 40.

The antenna sharing unit 40 is for sharing the antenna 50 for transmission and reception, and
The RF signal multiplexed at 0 is radiated into the space through the antenna 50, and the RF signal received from the space at the antenna 50 is output to the receiving unit 60.

Receiving section 60 converts the frequency of the received radio frequency signal input through antenna sharing section 40 into a baseband signal, performs despreading processing, and performs mobile station PS1.
To extract data sent from .PSm.

The receiving unit 60 extracts transmission power control information from the data and outputs it to the detecting unit 71. This transmission power control information is transmitted from each of the mobile stations PS1 to PSm.

Each of the mobile stations PS1 to PSm detects the reception quality of the broadcast signal received from the base station, and if the detected reception quality is lower than a predetermined reference level, the transmission power of the broadcast signal is reduced. The transmission power control information including the request for increase is generated and transmitted.

On the other hand, each of the mobile stations PS1 to PSm detects the reception quality of the broadcast signal received from the base station,
If the detected reception quality is equal to or higher than a predetermined reference level, the transmission power control information including a request to reduce the transmission power of the broadcast signal is generated and transmitted.

Further, the mobile stations PS1 to PSm each receive the communication signal received from the base station in accordance with the reception quality of the communication signal.
The transmission power control information including the request to increase or decrease the transmission power of the communication signal is generated and transmitted, but this point is the same as the conventional one.

The detecting section 71 determines whether the transmission power control information transmitted from each of the mobile stations PS1 to PSm requests an increase or a decrease in the transmission power of the broadcast signal. The control unit 102 detects the ratio of requests for an increase in signal transmission power, and notifies the control unit 102 of this ratio as an increase request ratio Rd.

The power detection unit 80 includes communication signal transmission units 11 to
Communication signal and broadcast signal transmission unit 20 generated at 1 m
, The power level of the broadcast signal generated is detected, and the power ratio Rp of the power level of the broadcast signal to the combined power level of these radio frequency signals is determined. This power ratio Rp is notified to the control unit 102.

The control section 102 controls the respective sections of the base station in an integrated manner. The base station and the mobile stations PS1 to PS
m and the mobile station P communicating with the base station.
In addition to normal control functions such as control for connecting S1 to PSm to the network of the mobile communication system, the same is performed according to the increase request ratio Rd notified from the detection unit 71 and the power ratio Rp notified from the power detection unit 80. It has a new control function of controlling the broadcast signal transmission unit 20 to increase or decrease the transmission power level of the broadcast signal.

Next, the operation of the base station having the above configuration will be described. In the following description, ordinary control operations such as communication control between the mobile stations PS1 to PSm and control for connecting the mobile stations PS1 to PSm to a network of a mobile communication system are omitted.

Here, the operation of the transmission power level control of the broadcast signal according to the present invention will be described. FIG.
5 is a flowchart for explaining the above control, and this process is executed by the control unit 101 each time a predetermined control cycle Tc arrives.

When the predetermined control cycle Tc has arrived, first, in step 5a, the power ratio Rp is fetched from the power detector 80, and the process proceeds to step 5b. In step 5b, it is determined whether or not the power ratio Rp is greater than a threshold thP. Here, if the power ratio Rp is larger than the threshold value thP, the process proceeds to step 5c, while the power ratio Rp is set to the threshold value tP.
If hP or less, the process proceeds to step 5d.

In step 5c, the threshold value thD is set to th
1 is set, and the routine goes to Step 5e. On the other hand, in step 5d, th2 (<th1) is set as the threshold thD, and the process proceeds to step 5e.

At step 5e, the increase request ratio Rd is fetched from the detecting section 71, and the routine goes to step 5f. In step 5f, it is determined whether the increase request ratio Rd is higher than a threshold thD. Here, the increase request ratio Rd is equal to the threshold value t.
If higher than hD, go to step 5g, while
If the increase request ratio Rd is equal to or smaller than the threshold thD, the process proceeds to step 5h.

In step 5g, the broadcast signal transmission unit 20 is instructed to increase the transmission power level of the broadcast signal by one power unit, and the process is terminated. Thereby, the broadcast signal transmitting unit 20 increases the transmission power level of the broadcast signal by one power unit.

On the other hand, in step 5h, the broadcast signal transmission unit 20 is instructed to reduce the transmission power level of the broadcast signal by one power unit, and the process is terminated. Thereby, the broadcast signal transmitting unit 20 reduces the transmission power level of the broadcast signal by one power unit.

As described above, in the base station having the above configuration, when the power ratio Rp of the broadcast signal power level to the combined power level of all radio frequency signals to be transmitted is larger than the threshold thD, the threshold thD Is set to th1. On the other hand, when the power ratio Rp is equal to or smaller than the threshold thR, the threshold t
hD is set to th2 which is smaller than th1.

Then, among mobile stations PS1 to PSm, the ratio Rd of those requesting an increase in broadcast signal transmission power is as follows:
If the transmission power level of the broadcast signal is higher than the threshold thD, the transmission power level of the broadcast signal is increased by one power unit. I try to reduce it.

Therefore, according to the base station having the above configuration,
By increasing the transmission power of the broadcast signal, for example, when the power ratio Rp becomes larger than the threshold thP as shown in FIG. 6B, the value of the threshold thD is increased to th1 as shown in FIG. 6A. The transmission power level of the broadcast signal is increased or decreased by setting the value to a value so as to suppress an increase in the power ratio Rp.

As described above, since the threshold value thD for increasing or decreasing the transmission power level of the broadcast signal is made to vary according to the power ratio Rp, it occupies the total power level of the radio signal transmitted from the base station. When the ratio Rp of the broadcast signal transmission power level is small, the value of the threshold thD is reduced to increase the number of mobile stations that satisfy the reception quality of the broadcast signal. Conversely, when the ratio Rp is large, By increasing the value of the threshold thD, lowering the transmission power level of the broadcast signal,
The ratio Rp can be reduced to reduce the influence on other channels.

The present invention is not limited to the above embodiment. For example, in the second embodiment, the threshold for increasing or decreasing the transmission power level of the broadcast signal is determined by the power ratio R
p, but instead of this, for example, as a third embodiment, a base station having a configuration as shown in FIG. 7 is used to transmit a broadcast signal transmitted by the base station. The number may be detected and varied according to this number.

In the base station shown in FIG. 7, the detecting section 72 detects the increase request rate Rd in the same manner as the detecting section 71, and transmits from the base station based on the transmission power control information. Number of mobile stations receiving broadcast signal M
Is detected.

Then, the control unit 103 sets the value of the threshold value thD for determining the increase or decrease of the broadcast signal in accordance with the number M of mobile stations, and compares the threshold value thD with the increase request ratio Rd. The broadcast signal transmitting unit 20 is controlled according to the result to increase or decrease the transmission power level of the broadcast signal.

In such control, when the number M of the mobile stations becomes equal to or more than a certain value, the threshold value thD is set low so as to increase the power ratio Rp. So that the quality is at the desired level,
For mobile stations whose reception quality does not reach the desired level,
By moving to a wireless zone of another base station, the reception quality is adjusted to a desired level. This makes it possible to balance the entire system.

In addition, the threshold value may be varied by combining the number M of mobile stations receiving the broadcast signal and the power ratio Rp. It goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0072]

As described above, according to the present invention, a mobile station receives a radio signal transmitted in common from a base station to a plurality of mobile stations, obtains the quality of the radio signal, and determines the quality of the base station according to the quality. Control information for requesting the station to increase or decrease the transmission power of the radio signal is transmitted to the station, and the base station controls the transmission power of the common radio signal based on the control information.

Therefore, according to the present invention, even if the distribution of mobile stations located in the radio zone of the base station changes, the common radio signal is controlled to the optimum transmission power level in accordance with the request of the mobile station. Therefore, it is possible to provide a mobile radio system capable of preventing a decrease in the use efficiency of a frequency band used for communication.

Further, according to the present invention, control information for requesting an increase or decrease in transmission power of a radio signal to be commonly transmitted to a plurality of mobile stations is received, and the transmission power of the common radio signal is reduced based on the control information. I try to control.

Therefore, according to the present invention, even if the distribution of mobile stations located in the radio zone of the base station changes, the common radio signal is controlled to the optimum transmission power level in accordance with the request of the mobile station. Therefore, it is possible to provide a base station capable of preventing a reduction in the use efficiency of a frequency band used for communication.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a configuration of a first embodiment of a base station according to the present invention.

FIG. 2 is a flowchart for explaining a broadcast signal transmission power control operation of the base station shown in FIG. 1;

FIG. 3 is a diagram for explaining a broadcast signal transmission power control operation of the base station shown in FIG. 1;

FIG. 4 is a circuit block diagram showing a configuration of a second embodiment of the base station according to the present invention.

FIG. 5 is a flowchart for explaining a broadcast signal transmission power control operation of the base station shown in FIG. 4;

FIG. 6 is a diagram for explaining a broadcast signal transmission power control operation of the base station shown in FIG. 4;

FIG. 7 is a circuit block diagram showing a configuration of a third embodiment of the base station according to the present invention.

[Explanation of symbols]

 11 to 1 m: communication signal transmitting unit 20: broadcast signal transmitting unit 30: multiplexing unit 40: antenna sharing unit 50: antenna 60: receiving unit 71, 72 ... detecting unit 80: power detecting unit 101, 102, 103 ... control Unit PS1 to PSm ... mobile station

Claims (8)

[Claims] 1. A base station and a mobile station connectable to a network are connected to CDMA (Code Division Multiple Access) wireless communication, and the base station transmits a common wireless signal to a plurality of mobile stations. In the mobile radio system, the mobile station receives the common radio signal, and detects reception quality of the reception quality.Depending on a detection result of the reception quality detection means, the mobile station transmits the radio signal to the base station. Transmitting means for transmitting control information for increasing or decreasing transmission power of a common radio signal, the base station receiving means for receiving the control information from the plurality of mobile stations, and receiving at the receiving means Control means for controlling transmission power of the common radio signal based on control information. 2. An increase request ratio detecting unit that detects a ratio of mobile stations requesting an increase in transmission power of the common radio signal, based on control information received by the receiving unit, The transmission power control means for increasing the transmission power of the common radio signal when the ratio detected by the increase request ratio detection means is larger than a preset threshold value, is provided. Mobile radio system. 3. The power ratio detecting means for calculating a ratio of the transmission power of the common radio signal to the total transmission power of the radio signals transmitted from the base station; The mobile radio system according to claim 2, further comprising a threshold control unit that sets the threshold according to the ratio. 4. The mobile station number detecting means for detecting the number of mobile stations receiving the common radio signal based on the control information received by the receiving means; 3. The mobile radio system according to claim 2, further comprising: threshold control means for setting the threshold value according to the number of mobile stations detected by the number detection means. 5. A mobile station and a CDMA (Code Division Multi).
In a base station connected by wireless communication of an iple Access) method and transmitting a common radio signal to a plurality of mobile stations, control information for requesting an increase or decrease in transmission power of the common radio signal from the plurality of mobile stations And a control unit for controlling transmission power of the common radio signal based on control information received by the receiving unit. 6. An increase request ratio detecting unit that detects a ratio of mobile stations that request an increase in transmission power of the common radio signal, based on control information received by the receiving unit, The transmission power control means for increasing the transmission power of the common radio signal when the ratio detected by the increase request ratio detection means is larger than a preset threshold value, is provided. Base station. 7. A power ratio detecting means for calculating a ratio of a transmission power of the common radio signal to a total transmission power of a radio signal transmitted from the base station, and according to the ratio detected by the power ratio detecting device. 7. The base station according to claim 6, further comprising: threshold control means for setting the threshold. 8. A mobile station number detecting means for detecting the number of mobile stations receiving the common radio signal based on control information received by the receiving means, The base station according to claim 6, further comprising: a threshold control unit that sets the threshold according to the number of detected mobile stations.