Patent Publication Number: US-2007117582-A1

Title: Radio communication system, communication terminal apparatus, base station apparatus, and transmission power control method

Description:
TECHNICAL FIELD  
      The present invention relates generally to transmission power control in a radio communication system adapted for the Code Division Multiple Access (CDMA) method (hereinafter referred to merely as a “CDMA radio communication system”), and more particularly to a method and apparatus for controlling the transmission power in which a mobile station uses a code sequence assigned separately for each multi-point transmission group to provide a base station of its transmission power control request in the CDMA radio communication system adapted for multi-point transmission where the base station transmits the same signal to a plurality of mobile stations.  
     BACKGROUND ART  
      As known widely, in the CDMA radio communication system, it is indispensable to perform the transmission power control (especially in uplinks) in order to reduce interference.  
      In a conventional CDMA radio communication system, the mobile station determines whether to request the base station to increase or decrease the transmission power on the basis of receiving quality of signals from the base station, and then transmits a transmission power control signal representing an increase request or a decrease request to the base station.  
      An example of such processing is shown in  FIG. 1 . Each mobile station determines whether the receiving quality is good or not by comparing it with a predetermined threshold, and then transmits the transmission power control signal representing the decrease request when the receiving quality exceeds the threshold, while it transmits one that represents the increase request when the receiving quality is lower.  
      The base station, which receives such transmission power control signal, controls its transmission power used for the sending mobile station of that transmission power control signal in accordance with the increase or decrease request that is represented in the received signal.  
      In the conventional CDMA radio communication system, a spreading code is assigned separately for each mobile station. For example, in the example shown in  FIG. 1 , signals transmitted from Mobile Station # 1  are spread by Code # 1 , while ones from Mobile Station # 2  are spread by Code # 2 .  
      In such case where a separate spreading code is assigned for each mobile station, orthogonality among the spreading codes becomes weak and the interference increases in the uplink when the number of the mobile stations increases and hence the number of the spreading codes required increases.  
     DISCLOSURE OF THE INVENTION  
      It is an object of the present invention to provide the method and apparatus for controlling the transmission power that solve the above-mentioned problem when the CDMA radio communication system performs multi-point transmission.  
      Here, multi-point transmission means a transmission method for transmitting the same signal from a single base station to a plurality of the mobile stations at a time, and is considered to be employed in, for example, a multicast information distribution service that has recently become widely watched.  
      The above object is achieved by a radio communication system comprising base stations and mobile stations where the base station is able to perform multi-point transmission for transmitting the same signal to the plurality of the mobile stations, wherein the mobile station targeted for the multi-point transmission provides the base station with the increase or decrease request of the transmission power by transmitting or not transmitting a predetermined signal to the base station.  
      Here, the above-mentioned predetermined signal may be an arbitrary bit sequence, for example.  
      Other objects, features, and advantages of the present invention are elucidated in the following detailed description with reference to the accompanied figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram showing a state of the conventional transmission power control;  
       FIG. 2  is a schematic of a base station according to a first embodiment of the present invention;  
       FIG. 3  is a schematic of a mobile station according to the first embodiment of the present invention;  
       FIG. 4  is a diagram showing a state of transmission power control according to the first embodiment of the present invention;  
       FIG. 5  is a schematic of a base station according to a second embodiment of the present invention;  
       FIG. 6  is a schematic of a mobile station according to the second embodiment of the present invention;  
       FIG. 7  is a diagram showing a state of transmission power control according to the second embodiment of the present invention;  
       FIG. 8  is a schematic of a mobile station according to a third embodiment of the present invention;  
       FIG. 9  is a schematic of a base station according to the third embodiment of the present invention;  
       FIG. 10  is a schematic of a correlation detecting part of the base station according to the third embodiment of the present invention;  
       FIG. 11  is a diagram showing an example of the relationship between PN code sequences and amounts of control of the transmission power;  
       FIG. 12  is a diagram showing an example of the amount of control requested from a mobile station belonging to the multi-point transmission group;  
       FIG. 13  is a schematic of a mobile station according to a fourth embodiment of the present invention;  
       FIG. 14  is a schematic of a mobile station according to a fifth embodiment of the present invention;  
       FIG. 15  is a schematic of a correlation detecting part of a base station according to the fifth embodiment of the present invention;  
       FIG. 16  is a flowchart showing a flow of a correlation detecting process according to the sixth embodiment of the present invention; and  
       FIG. 17  is a flowchart showing a flow of a correlation detecting process according to the seventh embodiment of the present invention.  
    
    
     PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION  
      The embodiments of the present invention are described hereinafter with reference to the accompanying drawings.  
      The method for controlling the transmission power according to the first embodiment of the present invention is now described with reference to  FIGS. 2 through 4 . In this embodiment, the spreading code assigned separately for each multi-point transmission group is used as the request signal transmitted from the mobile station to the base station in the transmission power control, and the increase or decrease request is identified by transmitting or not transmitting the request signal.  
      First, the configuration and operation of the mobile station and the base station according to this embodiment are described with reference to  FIGS. 2 and 3 .  FIG. 2  is the schematic of the multi-point transmitting base station in the CDMA radio communication system according to this embodiment, and  FIG. 3  is the schematic of the mobile station targeted for the multi-point transmission in the CDMA radio communication system according to this embodiment. In both figures, only portions that are necessary for illustrating the present invention are outlined, and showing and detailing known configurations or functions are omitted.  
      In the base station  200 , a multi-point transmitted signal is input from a signal input terminal  201  and modulated at a modulating part  202 . This modulation is a so-called narrow-band modulation such as QPSK and 16QAM. A modulated signal to be transmitted, of which the transmission power is controlled by a variable transmission power amplifier  203 , is then transmitted via an antenna  204  to the plurality of target mobile stations  300  of the multi-point transmission at a time. The transmission power control by the variable transmission power amplifier  203  is performed as directed by a later-mentioned transmission power controlling part  207 .  
      In each mobile station  300 , the multi-point transmitted signal from the base station  200 , which is received by an antenna  301 , is demodulated by a demodulating part  302 , and then output to a signal output terminal  303  and a receiving quality measuring part  304 .  
      A demodulated signal, of which the receiving quality is measured by the receiving quality measuring part  304 , is then determined whether to represent the increase or decrease request of the transmission power to the base station by comparing the result of such measurement with a predetermined threshold.  
      Here, the receiving quality may be determined using any parameters. For example, receiving power, carrier power to noise power ratio (C/N), signal power to noise power ratio (S/N), carrier power to sum of interference power and noise power (C/(I+N) ), signal power to sum of interference power and noise power (S/(I+N)), bit error rate (BER) likelihood obtained in error correction decoding, and any combination of these may be used.  
      The receiving quality measuring part  304  outputs a transmission power control signal representing the increase or decrease request to a switch  305  on the basis of the above determination. The switch  305  is closed when the transmission power control signal input represents the increase request, while it is opened when it represents the decrease request.  
      A code generating part  306  keeps generating a predetermined single code sequence. Therefore, only when the transmission power control signal representing the increase request is input to the switch  305 , the predetermined code sequence is then output to the modulating part  307 . Here, the predetermined single code sequence is the code sequence that is assigned separately for each multi-point transmission group and hence that is unique to the group.  
      The request signal, which is the predetermined single code sequence and is input to the modulating part  307 , is moderated, and then transmitted to the base station  200  via the antenna  301 . This modulation is also narrow-band modulation.  
      An example of the request signal is shown in  FIG. 4 . FIG. 4  is based on the same transmission path condition as one shown in  FIG. 1 . As shown, in each mobile station, the request signal is transmitted only when the receiving quality is lower than the predetermined threshold and hence the mobile station requests the base station to increase the transmission power.  
      On the other hand, in the base station  200 , the request signal in the transmission power control from the multi-point transmission target mobile station  300 , which is received by the antenna  204 , is demodulated by a demodulation part  205  and is output to a request signal detecting part  206 .  
      The request signal detecting part  206  compares a value of the received electric power of the demodulated signal with a predetermined threshold. Since the request signal from the multi-point transmission target mobile station  300  is, as described above, transmitted to the base station only when the mobile station requests to increase the transmission power, it is determined that there are some mobile stations that transmit the request signal when the value exceeds the above threshold and that there is no mobile station that transmits the request signal when it does not exceed.  
      A result of the determination whether the request signal is detected in the request signal detecting part  206  is output to the transmission power controlling part  207 . When the request signal is detected, the transmission power controlling part  207  directs the variable transmission power amplifier  203  to increase the transmission power of a multi-point transmission signal for the benefit of the mobile station that is one of the multi-point transmission target mobile stations and of which the receiving quality is not good. When the request signal is not detected, it is considered that all multi-point transmission target mobile stations receive the multi-point transmission signal with good enough receiving quality, and the transmission power controlling part  207  directs the variable transmission power amplifier  203  to decrease the transmission power. Here, the amount of control to decrease or increase one time may be any value.  
      Thus, according to this embodiment, in the transmission power control in the multi-point transmission, the increase or decrease request is provided from the mobile station to the base station by transmitting or not transmitting the predetermined code sequence assigned separately for each multi-point transmission group. Therefore, when there are some mobile stations in the multi-point transmission group of which the receiving quality is not good, the transmission power of the multi-point transmission signal can be controlled, and the increase of interference in the uplink can be prevented when the number of the mobile stations increases.  
      Here, in this embodiment, assuming that the code sequence output from the code generating part  306  is a code sequence that consists of sequential “1”s, a detection method that uses electric power measurement with unmodulated signals can be utilized in the base station  300 . In other words, the above-mentioned code sequence is not limited to the spreading code, and may be a signal that consists of a predetermined bit sequences.  
      Also, in this embodiment, the above-mentioned code sequence, which is transmitted as the request signal, may be transmitted after it is spread with another spreading code, as well as in the usual CDMA communication. In other words, this embodiment can be directly applied to the existing CDMA communication system.  
      Furthermore, since it is not required for this embodiment to perform the spreading process, this embodiment can be also applied to communication systems adapted for TDMA and FDMA methods.  
      The transmission power controlling method according to the second embodiment of the present invention is now described with reference to  FIGS. 5 through 7 . In this embodiment, the increase or decrease request for transmission power to the base station is identified by spreading or not spreading the transmission power control signal transmitted to the base station from the mobile station in the transmission power control with the spreading code assigned separately for each multi-point transmission group.  
      First, the configuration and operation of the base station and the mobile station according to this embodiment are described with reference to  FIGS. 5 and 6 , respectively.  FIG. 5  is the schematic of the multi-point transmitting base station in the CDMA radio communication system according to this embodiment, and  FIG. 6  is the schematic of the multi-point transmission target mobile station in the CDMA radio communication system according to this embodiment. In both figures, only portions that are necessary for illustrating the present invention are outlined, and showing and detailing known configurations or functions are omitted. Also, the same component as one in the already described embodiment has a consistent reference number, and the detailed description of it is omitted.  
      In the base station  500 , a spreading part  501  spreads a modulated multi-point transmission signal with the spreading code assigned separately for each multi-point transmission group.  
      In each mobile station  600 , a despreading part  601  despreads the received multi-point transmission signal. And, the transmission power control signal modulated by the modulating part  307  is input to a spreading part  602 , while the code sequence output by the code generating part  306  is also input thereto only when that transmission power control signal represents the increase request of the transmission power.  
      If the code sequence is input, the spreading part  602  transmits the transmission power control signal to the base station  500  after spreading it, while, if the code sequence is not input, the spreading part  602  transmits the transmission power control signal to the base station  500  without spreading.  
      An example of the above-mentioned transmission power control signal is shown in  FIG. 7 . FIG. 7  is based on the same transmission path condition as one shown in  FIG. 1 . As shown, in each mobile station, the transmission power control signal is spread with the code sequence assigned separately for each multi-point transmission group only when the receiving quality is lower than the predetermined threshold and hence the mobile station requests the base station to increase the transmission power.  
      In the base station  500 , the transmission power control signal received from the multi-point transmission target mobile station  600  is despread by the despreading part  502  and is correlated with the code sequence assigned for that multi-point transmission group.  
      In the conventional CDMA radio communication system, a transmitting mobile station is identified by the spreading code. However, in this embodiment, since the mobile stations belonging to the same multi-point transmission group use the same code sequence for the sreading process of the transmission power control signal, the transmission power control signals for one group are received in a combined form.  
      Since the despreading process in the despreading part  502  is to perform a correlation process on the combined signal, a peak is detected in the despreading process to the combined signal if there is even one mobile station that requests to increase the transmission power in that multi-point transmission group.  
      A result of the determination whether the peak is detected or not in the despreading part  502  is output to the transmission power controlling part  503 . When the peak is detected, the transmission power controlling part  207  directs the variable transmission power amplifier  203  to increase the transmission power of the multi-point transmission signal for the benefit of the mobile station that is one of the multi-point transmission target mobile stations and of which the receiving quality is not good. When the peak is not detected, it is considered that all multi-point transmission target mobile stations receive a multi-point transmission signal with good enough receiving quality, and directs the variable transmission power amplifier  203  to decrease the transmission power. Here, the amount of control to decrease or increase one time may be any value.  
      Thus, according to this embodiment, in the transmission power control in the multi-point transmission, the increase or decrease request is provided from the mobile station to the base station by spreading or not spreading with the predetermined code sequence assigned separately for each multi-point transmission group. Therefore, when there are some mobile stations in the multi-point transmission group of which the receiving quality is not good, the transmission power of the multi-point transmission signal can be controlled, and the increase of interferences in the uplink can be prevented when the number of the mobile stations increases.  
      The transmission power controlling method according to the third embodiment of the present invention is now described with reference to  FIGS. 8 through 13 . This embodiment utilizes basically the same configuration and operation as ones according to the first embodiment, and provides not only the increase or decrease request of the transmission power but also the request amount of control from each mobile station to the base station by assigning a plurality of predetermined code sequences separately for each multi-point transmission group and utilizing the distinctiveness among the set of code sequences.  
      First, the configuration and operation of the mobile station and the base station according to this embodiment are described with reference to  FIGS. 8 through 10 .  FIG. 8  is the schematic of the multi-point transmission target mobile station  800  in the CDMA radio communication system according to this embodiment,  FIG. 9  is the schematic of the multi-point transmitting base station  900  in the CDMA radio communication system according to this embodiment, and  FIG. 10  is the schematic of the correlation detecting part  901  of the base station according to this embodiment. In each figure, only portions that are necessary for illustrating the present invention are outlined, and showing and detailing known configurations or functions are omitted. Also, the same component as one in the already described embodiments has a consistent reference number, and the detailed description of it is omitted.  
      As shown, the mobile station  800  according to this embodiment has a plurality of (here, N individual) code generating parts  801 , where each of the code generating parts  801  always keeps outputting differentiable PN codes (PN# 1  to PN#N) Each of the N individual PN codes is associated with a different value of control of the transmission power in advance.  
      The set of PN codes is here assigned for different multi-point transmission groups. For example, in the case that the number of available PN codes is 256 and that there are four multi-point transmission groups, the 1st through 64th PN codes are assigned to the 1st group, the 65th through 128th PN codes are assigned to the 2nd group, the 129th through 192nd PN codes are assigned to the 3rd group, and the 193rd through 256th PN codes are assigned to the 4th group.  
      A switch  803  is an (N+1) selector. The switch  803  has N individual input terminals, one for each code generating part  801 , and one connection-less terminal  802 . The terminals of the switch  803  are selected in accordance with the value of control that is represented by the transmission power control signal input from the receiving quality measuring part  304 .  
      An example of the operation standard of the switch  803  is shown in  FIG. 11 . It is here assumed that eight kinds of transmission power control signals (000 to 111) are input to the switch  803  from the receiving quality measuring part  304  and that five code generating parts  801  are provided.  
      As shown, a different transmission power control signal is output from the receiving quality measuring part  304  in accordance with the value of control (dB unit) requested to the base station on the basis of the receiving quality. It is here assumed that the request value of control is, as shown, −2 dB to +5 dB.  
      When the transmission power control signal is input, the switch  803  performs one of operations, which are in advance associated with the transmission power control signals, in accordance with that input signal. In this example, when the request value of control is equal to or lower than ±0 dB (that is, when it is not an increase request), the connection-less terminal  802  is connected (meaning connection-off) and hence the request signal is not output, when +1 dB is requested, the code sequence PN# 1  is used for the request signal, subsequently, in turn, PN# 2  for +2 dB, PN# 3  for +3 dB, PN# 4  for +4 dB, and PN# 5  for +5 dB are respectively output to the modulating part  307  and used for the request signal to the base station.  
      On the other hand, the base station  900  receives the request signal that is any one code sequence in the predetermined set of the code sequences transmitted from each multi-point transmission target mobile station  800 , and calculates correlation between the receiving signal and the above-mentioned predetermined set of the code sequences in the correlation detecting part  901 .  
      The configuration and operation of the above-mentioned correlation detecting part  901  is now described with reference to  FIG. 10 .  FIG. 10  is the schematic of the correlation detecting part  901  according to this embodiment. N individual code generating parts  1001 , each of which employs the same configuration as the code generating part  801  of the mobile station side, are provided and output PN codes PN#1 to PN#N, respectively. Each multiplier  1002  calculates complex multiplication between the received signal and complex conjugate of each PN code sequence.  
      The real part of the complex vector signal obtained by the multiplier  1002  is integrated by each integrator  1003 . The resultant value of the integration is determined whether to be equal to or higher than a predetermined threshold or not by the threshold deciding part  1004 , and the result of this decision is recorded in a memory  1005 . A result of determination whether there are any mobile stations that request to increase the transmission power for each amount of control associated with the code sequence is thus accumulated in the memory  1005 .  
      A retrieving part  1006  makes reference to the determination result accumulated in the memory  1005  to retrieve the largest amount of control among the amounts of control requested by the mobile stations and then to output a PN code number associated with the maximum amount of control to the transmission power controlling part  902 .  
      The transmission power controlling part  902  makes reference to a pre-stored relationship (an example of which is shown in  FIG. 11 ) between the PN code and the amount of control (increase) of the transmission power with input PN code number, and then directs the variable transmission power amplifier  203  to increase the transmission power in accordance with the amount of control of the transmission power of that PN code.  
      Also, when no PN code sequence number is input from the correlation detecting part  901 , the transmission power controlling part  902  considers that all multi-point transmission target mobile stations belonging to that multi-point transmission group receive the multi-point transmission signal with good enough receiving quality, and directs the variable transmission power amplifier  203  to decrease the transmission power.  
      This is now described more specifically with reference to an example of the multi-point transmission group shown in  FIG. 12 . As shown, it is assumed that there is the multi-point transmission group consisting of six mobile stations: MS 1  through MS 6 , and that contents of the transmission power control requested to the base station determined in each mobile station are MS 1 :+3 dB, MS 2 :+2 dB, MS 3 :+1 dB, MS 4 :−1 dB, MS 5 :+2 dB, and MS 6 :±0 dB, respectively.  
      In the case of the above example, assuming that the PN code sequences transmitted from each mobile station to the base station is based on the relationship shown in  FIG. 11 , PN# 3  is transmitted from MS 1 , PN# 2  is transmitted from MS 2  and MS 5 , PN# 1  is transmitted from MS 3 , and no PN code sequence is transmitted from MS 4  or MS 6 .  
      Then, since, in the example shown in  FIG. 12 , +3 dB from MS 1  is the largest request value of control in the amounts of control requested from each mobile station and accumulated in the memory  1005 , the transmission power controlling part  902  directs the variable transmission power amplifier  203  to increase the transmission power of the that multi-point transmission signal by 3 dB.  
      Thus, according to this embodiment, in the transmission power control in the multi-point transmission, the increase or decrease request is provided from the mobile station to the base station by transmitting or not transmitting the predetermined code sequence assigned separately for each multi-point transmission group, and also the request amount of control is provided as well utilizing the distinctiveness among the code sequences used. Therefore, increase of interferences in the uplink can be prevented when the number of the mobile stations increases, and the transmission power can be quickly and flexibly controlled in accordance with the transmission path condition.  
      Here, in the above description, the case is described that the code sequence is transmitted only when the contents of control requested from the mobile station to the base station indicates the increase request. This results so that, when the request to keep or decrease the transmission power is desired, processing can be advantageously simplified, in a view that all mobile stations already receive with good enough receiving quality. However, of course, the code sequences can be assigned separately for each amount of control in the request to keep or decrease to provide the base station of it. In this case, since quick control can be also achieved for decreasing, resource efficiency can improve.  
      Also, in the description of this embodiment, the PN code is just an example of the code sequence having distinctiveness, and other spreading code having the distinctiveness such as orthogonal Gold code, or error correcting codes such as BCH code, RS code, or M-array code may be used.  
      Furthermore, in this embodiment, the code sequence, which is transmitted as the request signal, may be spread with another spreading code, as well as in the usual CDMA communication.  
      The transmission power controlling method according to the fourth embodiment of the present invention is now described with reference to  FIG. 13 . This embodiment utilizes basically the same configuration and operation as ones according to the second embodiment, and provides not only the increase or decrease request of the transmission power but also the request amount of control from each mobile station to the base station by assigning a plurality of predetermined code sequences separately for each multi-point transmission group and utilizing the distinctiveness among the set of the code sequences as well as the third embodiment.  
      Here, since the base station according to this embodiment is identical to the base station  900  ( FIG. 9 ) according to the third embodiment, showing and detailing of it are omitted.  
       FIG. 13  is the schematic of the multi-point transmission target mobile station  1300  in the CDMA radio communication system according to this embodiment. In this figure, only portions that are necessary for illustrating the present invention are outlined, and showing and detailing known configurations or functions are omitted. Also, the same component as one in the already described embodiments has a consistent reference number, and the detailed description of it is omitted.  
      In the mobile station  1300 , as well as the third embodiment, the PN code sequence in accordance with the request value of control is input from the switch  803  to a spreading part  1301 . The spreading part  1301  spreads the transmission power control signal modulated by the modulating part  307  with the code sequence output from the switch  803 . When the transmission power control requested to the base station is not the increase request, the switch  803  turns its input terminal to the connection-less terminal  802 , and hence no code sequence is input to the spreading part  1301 , therefore, the transmission power control signal is then transmitted to the base station without spreading.  
      In the base station, the same processing as one in the base station  900  according to the third embodiment is performed. It is then determined whether there are any mobile stations transmitting the increase request and how large the request amount of control is, and the transmission power is increased in accordance with the request amount of control from the mobile station having the worst receiving condition.  
      Thus, according to this embodiment, in the transmission power control in the multi-point transmission, the increase or decrease request is provided from the mobile station to the base station by spreading or not spreading with the predetermined code sequence assigned separately for each multi-point transmission group, and also the request amount of control is provided as well utilizing the distinctiveness among the code sequences used. Therefore, increase of interferences in the uplink can be prevented when the number of the mobile stations increases, and the transmission power can be quickly and flexibly controlled in accordance with the transmission path condition.  
      Here, in the above description, the case is described that the transmission power control signal spread with the code sequence is transmitted only when the contents of control requested from the mobile station to the base station indicates the increase request. This results so that, when the request to keep or decrease the transmission power is desired, processing can be advantageously simplified, in a view that all mobile stations already receive with good enough receiving quality. However, of course, the code sequences can be assigned separately for each amount of control in the request to keep or decrease to provide the base station of it. In this case, since quick control can be also achieved for decreasing, resource efficiency can improve.  
      Also, in the description of this embodiment, the PN code is just an example of the code sequence having the distinctiveness, and other spreading code having the distinctiveness such as orthogonal Gold code, or error correcting codes such as BCH code, RS code, or M-array code may be used.  
      The transmission power controlling method according to the fifth embodiment of the present invention is now described with reference to  FIGS. 14 and 15 . This embodiment utilizes approximately the same configuration and operation as ones according to the fourth embodiment, however, the mobile station transmits a predetermined signal, instead of the transmission power control signal, to the base station after spreading it with a selected code sequence. Here, only portions that are necessary for illustrating the present invention are outlined, and showing and detailing known configurations or functions are omitted. Also, the same component as one in the already described embodiments has a consistent reference number, and the detailed description of it is omitted.  
       FIG. 14  is the schematic of the mobile station  1400  according to this embodiment. A signal generating part  1401  always keeps outputting a predetermined bit sequence. This bit sequence is spread with the code sequence output from the switch  803  by the spreading part  1301 , and is then transmitted to the base station  1500 .  
       FIG. 15  is the schematic of a correlation detecting part  1501  of the base station  1500  according to this embodiment. Each of deciding parts  1502  decides whether the received signal that is despread with each code sequence is the above predetermined bit sequence output from the signal generating part  1401 . This decision process is similar to a usual data demodulation. Then, this decision result is recorded in the memory  1005 .  
      Detailed description of the transmission power control processes other than those above is omitted since they are similar to the processes according to the fourth embodiment. Here, any bit sequence may be used for the above predetermined bit sequence.  
      Thus, according to this embodiment, the predetermined single bit sequence is used for the request signal from the mobile station, and the base station can utilize the decision using the data demodulation instead of the decision using the predetermined threshold where its detection capability significantly depends on the setting of the threshold, and thereby it is determined whether that code sequence is used for spreading in the mobile station by double examination consisting of the correlation process and the bit decision. Therefore, more reliable and stable correlation detection can be achieved.  
      The transmission power controlling method according to the sixth embodiment of the present invention is now described with reference to  FIG. 16 . This embodiment utilizes basically similar configuration and operation to ones according to the third or fourth embodiment, however, the correlation detector in the base station is implemented by software.  
      The program processing to implement the correlation detector is now described with reference to the flow chart shown in  FIG. 16 . Here, the block diagram showing the configuration of the base station and the mobile station is omitted.  
      First, 0 is assigned to a variable n in S 1601  where n is a variable representing the PN code number. In other words, in S 1601 , the 0th PN code is set as the initialized state. It is here assumed that the value of n is, like the example shown in  FIG. 11 , set such that it corresponds to the request value of control (dB unit).  
      A correlation value between the received signal and the 0th PN code is then calculated in S 1602 , where X (t) is time-series data of the received signal, Xn* (t) is a complex conjugate of the time-series data of the n th  PN code, T is the length of the time-series data, and Γn is the correlation value between the received signal and the n th  PN code.  
      It is then decided in S 1603  whether the correlation value calculated in S 1602  is equal to or higher than a predetermined threshold or not. If it is equal to or higher than the threshold, 1 is then assigned to a variable Sn, while, if it does not reach to the threshold, 0 is then assigned to Sn (S 1605 ), where the variable Sn is a flag that becomes on when the correlation value Γn between the received signal and the nth PN code exceeds the predetermined threshold.  
      The variable n is then incremented by one (S 1606 ), and it is decided whether n reaches N (S 1607 ). If it reaches, the process then proceeds to S 1608 , while, if it does not, the process then returns to S 1602 .  
      In S 1608 , (N−1) is assigned to the variable n, and the (N−1)th PN code is set. It is then decided whether the variable n is 1 or not (S 1609 ). If Sn is not equal to 1 (“No” at S 1609 ) n is then decremented one by one until it becomes 0 (S 1610  and S 1611 ) to find the value of n when Sn=1.  
      If it is decided that Sn=1 in S 1609 , the process then proceeds to S 1613  and the transmission power is increased by n [dB] on the basis of the value of n at that time. Also, if n becomes 0 before it is decided that Sn=1 in S 1609  (“Yes” at S 1611 ), it is decided that the correlation value that exceeded the predetermined threshold is not obtained. In other words, it is determined that th re is no mobile station that requests to increase the transmission power in that multi-point transmission group. Therefore, the transmission power of the multi-point transmission signal is decreased in S 1612 .  
      Thus, according to this embodiment, since the correlation detector can be implemented by software, the base station according to the present invention can have a simplified configuration.  
      The transmission power controlling method according to the seventh embodiment of the present invention is now described with reference to  FIG. 17 . This embodiment also has the correlation detector in the base station implemented by software like the sixth embodiment, however utilizes a different algorithm from one used in the processes of the sixth embodiment.  
      In the correlation detecting process according to the sixth embodiment, the transmission power of the multi-point transmission signal is controlled in accordance with the mobile station requesting the largest amount of increase of the transmission power, i.e. the transmission power is controlled such that the mobile station having the worse receiving quality can have good receiving quality.  
      On the other hand, in this embodiment, putting importance on the efficiency of the whole system, the transmission power is controlled in accordance with the amount of control that is requested by the most mobile stations in the amounts of control requested from the mobile stations. By the way, such control is not performed in the conventional system, since the conventional base station individually controls the transmission power for each mobile station.  
      The program processing to implement the correlation detector is now described with reference to the flow chart shown in  FIG. 17 . Here, detailed description of the variables and the processes used also in the process in  FIG. 16  is omitted. Also, the block diagram showing the configuration of the base station and the mobile station is omitted.  
      First, S 1701  and S 1702  are identical to S 1601  and S 1602  in  FIG. 16 . Γn is then assigned to the variable Sn in S 1703 .  
      Similarly, S 1704  and S 1705  are identical to S 1604  and S 1605  of  FIG. 16 . If n reaches N, the process proceeds to S 1706 .  
      Then, (N−1) and S N−1  are assigned to n max  and Sn max  respectively in S 1706 , where Sn max  represents the largest correlation value obtained by that time, and n max  represents the value of n (i.e. the PN code number) when the largest correlation value is obtained.  
      It is then decided whether Sn at that time is larger than Sn max  or not in S 1707 . If Sn at that time does not exceed the largest value Sn max  obtained by that time (“No” at S 1707 ), n is then decremented one by one until it becomes 0 (S 1710  and S 1711 ) to find the value of n when Sn&gt;Sn max .  
      If Sn is larger than Sn max  (“Yes” at S 1707 ), n and Sn at that time are assigned respectively to n max  and Sn max  as a new maximum value (S 1708 ). Here, since the request signal or the transmission power control signal from the mobile stations that request the same amount of increase consists of the same PN code sequence or is spread with the same PN code sequence, the request signals from all the mobile stations that request the same amount of control are detected in a combined form upon being despread. Therefore, the more the mobile stations that request the same amount of control are, the larger correlation value is obtained. That is, the above comparison of magnitude of the correlation value means the comparison of count for each amount of control requested.  
      Then, if n becomes 0 (“Yes” at S 1710 ) and it is determined that the comparison on Sn is completed for all n, it is decided whether Sn max  at that time exceeds the predetermined threshold or not (S 1711 ).  
      If Sn max  exceeds the predetermined threshold (“Yes” at S 1711 ), the transmission power is increased by n [dB] on the basis of the value of n at that time. For example, in the example shown in  FIG. 12 , since the mobile stations that request +2 dB of increase of the transmission power are the most, the correlation value on the second PN code sequence PN# 2  becomes the largest and the transmission power is increased by +2 dB.  
      Also, if the maximum correlation value Sn max  does not exceed the predetermined threshold in S 1711  (“NO” at S 1711 ), it is then determined that there is no mobile station that requests increase of the transmission power in that multi-point transmission group. Therefore, the transmission power of the multi-point transmission signal is decreased in S 1712 .  
      Thus, according to this embodiment, since the transmission power of the multi-point transmission signal is increased on the basis of the amount of control requested by the most mobile stations in the mobile stations belonging to the multi-point transmission group, the transmission power is not excessively increased in consequence of the reduced receiving quality of a particular mobile station, and the transmission power of the multi-point transmission signal can be controlled in view of the efficiency in the whole system.  
      As described above, according to the above first through seventh embodiments, in the transmission power control in the radio communication system adapted for the CDMA method, as for the target mobile station of the multi-point transmission, since the code sequence is not assigned separately for each mobile station but separately for each request signal or separately for each request amount of control, the possibility of increase of the interference in the uplink by increasing the number of the mobile stations can be reduced.