1. A communications system relating to a multimedia broadcast multicast service (MBMS) of multicasting or broadcasting a multimedia data to a plurality of mobile stations (6) therein, said communications system characterized by comprising: a power ratio transmitting unit for transmitting information about a power ratio between a power of a common control physical channel used for multicasting or broadcasting said multimedia data in each of given cells and a power of a common pilot channel used for transmitting an information on reference of timing in each of the given cells; a service information transmitting unit for transmitting service information indicating a state of an MBMS service in each of the given cells; a power ratio information receiving unit for receiving the information about the power ratio transmitted by said power ratio transmitting unit; a service information receiving unit for receiving the service information transmitted by said service information transmitting unit; and a ranking unit (15) for ranking a plurality of cells on the basis of the information about said power ratio of the given cells, which is received by said power ratio receiving unit, and the power of said common pilot charmel; a cell selecting unit for acquiring a set including a plurality of cells from which a mobile station can receive an MBMS on the basis of the information about the ranking determined by said ranking unit, a predetermined threshold, and said service information received by said service information receiving unit; a decoding vmit for receiving a signal transmitted using said common control physical channel in each of the plurality of cells included in the set acquired by said cell selecting unit, and for decoding said signal to acquire a plurality of decoded signals; and a selectively-combining unit for selecting a signal from the plurality of decoded signals acquired by said decoding unit, and thereby obtaining an output signal.

Field of the Invention The present invention relates to a mobile communications terminal and a radio communijcations system which, when receiving multimedia data transmitted from a base station using a CDMA (Code Division Multiple Access) method, can improve the reception quality of the multiiiaedia data. Background of the Invention Related art radio communic^ations systems are based on the premise that there is a one-to-one correspondence between base stations and mobile communications terminals (e.g., mobile phones and mobile PCs), and therefore do not support services of transmitting data to two c^r more mobile communications terminals simultaneously usin^ a base station. There is a previously known method of notif]^ing broadcast information from control area of the base stati|on all at once using a common channel. However, this meihod is aimed at notifying information about control tcL all mobile communications terminals in the control area a^l at once, but is not aimed at transmitting data, such as audjlo data and image data, to all mobile communications terminal^ in the control area all at once. In recent years, expectat'ions have been running high for the use of multimedia services as mobile communications services. Particularly, the ^potlight has been turned on a technology of simultaneously delivering multimedia data about sports live broadcasting, weadher report, and radio, etc. to two cr TTiore mobile corpjnunicatioi|is terminals. There has been proposed a technology of, in addition uo a first common channel (P-CCPCH: Primary-Common Control Physical Channel) which a base station uses when notifying broadcast information to two or more mobile communications terminals, providing a second common channel (S-CCPCH: Secondary-Common Control Physical Channel) which the base station uses when delivering signaling or multimedia data to I two or more mobile communications terminals, and delivering multimedia data from the base station to two or more mobile communications terminals using the S-CCPCH (see patent reference 1 and nonpatent reference 1). By thus delivering multiirledia data using an S-CCPCH, a base station can simultaneously provide multimedia data to two or more mobile communications terminals. However, when a mobile communications terminal]is located in the vicinity of the periphery of the control s^rea of the base station, the electric wave transmitted from tihe base station may become weak and hence the reception quality Lht elcctr jlo wavc may dcgradj even if the mobile communications terminal is staying in the control area of the base station. To solve this problem, tjie base station has a function of controlling its transmission power so that the mobile communications terminal which has the smallest reception power in all the mobile communications terminals which are staying in the control area thereof will have reception power exceeding reference power. On the other hand, each mobile communications terminal has a function of, when receiviiig the same multimedia data from two or more base stations, improving the reception quality by maximur.-ratio-corribining the two lor more nultimedia data. However, since the propaglation paths of two or more multimedia data from two or more ibase stations to each mobile communications terminal differ f|rom one another, the receipt times when each mobile communications terminal receives the two or more multimedia data transmitted from the two or more base stations differ from one anothep, and therefore each mobile communications terminal cannolp carry out maximum ratio combining of the two or more multimedia data if the receipt time ) difference becomes beyond a predetermined time period. I [Patent reference 1] JP, 2i003-188818, A [Nonpatent reference 1] i^GPP Standardization Document Rl-031103 Selective Combining ^or MBMS A problem with related artj: radio communications systems constructed as mentioned above is that while a base station can secure the reception quality Of each mobile communications terminal staying in the conrrol krea theieuf by contiiollliig its transmission power so that the ihobile communications terminal which has the smallest reception power in all the mobile communications terminals which Jare staying in the control area thereof will have reception po|;er exceeding reference power, an increasing of the transmissipn power assigned to the S-CCPCH may degrade the reception quality of information transmitted to a mobile communications terminal using another channel since the transmission power assigned to the other channel becomes ■ low relatively. Another problem is that while if each mobile communications terminal max'imum-ratio-combines the same multimedia data transmitted from tjvo or more base stations, each mobile commiunications terminal J can improve the recepticr. quality of the multimedia data' vjithout each base station controlling its transmission powet, since the propagation paths of two or more multimedia data froiTi the two or more base stations to each mobile communications terminal differ from one another, the receipt times when each mohpile communications terminal receives the two or more multimefiia data transmitted from the two or more base stations differ fjrom one another, and therefore each mobile communications terminal cannot carry out maximum ratio combining of the two or morejmultimedia data if the receipt time difference becomes beyond |a predetermined time period. The present invention is' made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a ntobile communications terminal I and a radio communications system which can improve the reception quality of multimedia data without controlling the power required for transmission Jof the multimedia data by means of a base station. Disclosure of the Invention In accordance with the ' present invention, there is provided a mobile communications terminal including: a maximum-ratio-combining meansi for dividing a plurality of multipath signals associated ^ith radio signals transmitted I from a plurality of base statipns using a common channel into groups by base station, i.e.^ by transmit source, and for maximum-ratio-combining a pljurality of multipath signals associated with each same ba^e station which is a transmit source into a composite sigAal; and a decoding means for decoding the composite signal qutputted from the maximum- ratio-coiTibining means, the mobile communications terminal selecting a composite signal having a good decoded result from among composite signals decoded by th^ decoding 5 means. Therefore, the present inventiqn offers an advantage of being able to iirprove the reception quality ot the radio signals without each base station controlling its transmissi^on power. Brief Description of the Figures Fig. 1 is a block diagram showing ^ radio communications system in accordance with embodiment 1 of |the present invention; Fig. 2 is a block diagram showing d mobile conmunications terminal in accordance with embodiment 1 of the present invention; Fig. 3 is a block diagram I showing a base station in accordance with embodiment 1 of the present invention; Fig. 4 is a block diagram showing a base station control apparatus in accordance with embodiment 1 of th^ present invention; Fig. 5 is an explanatory diagram showing the configuration of channels between a mobile communications terminal and a base station; i-'iy . cdatcd in the active set, the search unit 15 determines that it will carry out a process of replacing a base station of the current active set with another base station as will be mentioned below. In this case, the search unit 15 shifts to processing of a terminal B of Fig. 11. When there is no reception level which continues to exceed the addition threshold Tadd throughout the predetermined time period T in the reception levels of the CPICHs of the base stations 5 which are not included in the current active set, the search unit 15 calculates a deletion threshold Tdelete from both the lowest one X of the reception levels of the CPICHs of the base stations 5 included in the active set, and the hysteresis parar.eLer K (in step ST26; . As an alternative, the search unin 15 can receive the deletion thresholc .delete from an upper layer instead of calculating the deletion threshold Tdelete. Tdelete = X - H/2 The search unit 15 then checks to see whether or not there is a reception level which continues to be lower than the above-mentioned deletion threshold Tdelete throughout the predetermined time period T in the reception levels of the CPICHs of the base stations 5 which are included in the current active set (in step ST24). When there is a reception level which continues to be lower than the deletion threshold Tdelete throughout the predetermined time period T in the reception levels of the CPICHs of the base stations 5 which are included in the current active set, the search unit 15 determines that it will carry out a process of deleLlny a correspuiiding base station from the active set as will be mentioned below. In this case, the search unit 15 shifts to processing of a terminal C of Fig. 11. On the other hand, when there is no reception level which continues to be lower than the deletion threshold Tdelete throughout the predetermined time period T in the reception levels of the CPICHs of the base stations 5 which are included in the current active set, the search unit 15 ends the processing without carrying out the process of updating the active set. •The process of adding a base station into the active set When the search unit 15 determines implementation of the process of addir.5 a base SLation to the active sei:, rne protocol processing uni:: 26 transmits addition request signaling indicating a request to add a base station to the active set to a base station 5 (in step ST31) . In other words, the protocol processing unit 26 outputs the addition request signaling indicating a request to add a base station to the active set to the uplink dedicated channel transmitting unit 29, and the uplink dedicated channel transmitting unit 29 carries out dedicated channel processing to outputs the addition request signaling to the modulating unit 31. The modulating unit 31 performs spread modulation on the addition request signaling outputted from the uplink dedicated channel transmitting unit 29 using a spread code generated by the code generator 30. The D/A converter 32 converts the modulated signal outputted from the modulating unit 31, which is a digital signal, into an analog signal, the frequency converting unit 33 converts the rrequency of Lhe modulaLeu signal on v.'hich the digital-to-analog conversion is performed by the D/A converter 32 to generate and output an RF signal, and the power amplifying unit 34 amplifies the power of the RF signal and outputs it to the antenna 11. Thus, the addition request signaling indicating the request to add a base station to the active set is transmitted to a base station 5, and the base station 5 transmits the addition request signaling to a corresponding base station control apparatus 4. When the base station control apparatus 4 permits the addition of a base station to the active set, the base station 5 transmits addition permission signaling indicating permission to aad a base station to the active sez 'including the S-CCPCH parameters of the base station 5 which is permitted to be newly added to the active set) to the mobile communications terminal 6 using a DPCH which is a dedicated channel. When the antenna 11 receives the addition permission signaling which is transmitted from the base station 5, and the protocol processing unit 26 of the mobile communications terminal 6 then receives the addition permission signaling from the downlink dedicated channel receiving unit 25 in the same way as previously mentioned in embodiment 1 (in step ST32) , the protocol processing unit 26 determines whether or not the addition of a base station to the active set has been permitted by analyzing the addition permission signaling (in step ST33). When determining that the addition of a base station to the active set has been permitted, the protocol processing unit 26 refers to the S-CCPCH parameters included in the addition permission signaling indicating permission to add a base station to the active set, and identifies tne oase SLauion 5 which is to be added to the active set and then adds the base station 5 to the active set (in step ST34). The protocol processing unit 26 then notifies the S-CCPCH parameters to the search unit 15, finger assignment control unit 17, and RAKE combining unit 18. After that, the mobile communications terminal starts a process of receiving data associated with the S-CCPCH of the base stations 5 of the active set including the added base station 5 (in step ST35). ■The process of replacing a base station of the active set with another base staiion When the search unit 15 determines impieiTienta-ion of the process of replacing a base station of the active set with another base station, the protocol processing unit 26 transmits replacement request signaling indicating a request to replace a base station of the active set with another base station to a base station 5 in the same way that it transmits addition request signaling indicating a request to add a base station to the active set (in step ST41). Thus, the replacement request signaling indicating a request to replace a base station of the active set with another base station is transmitted to a base station 5, and the base station 5 transmits the replacement request signaling to a corresponding base station control apparatus 4. When the base station control apparatus 4 permits the replacement of a base station of the active set with another base station, the base station 5 transmits replacement permission signaling indicating permission to replace a base station of the active set with another Joase sracion (.incluuiny the S-CCPCH parameters of the other base station 5 which is permitted to be newly added to the active set) to the mobile communications terminal 6 using a DPCH. When the antenna 11 receives the replacement request signaling indicating a request to replace a base station of the active set with another base station which is transmitted from the base station 5, and the protocol processing unit 26 of the mobile communications terminal 6 then receives the replacement request signaling from the downlink dedicated channel receiving unit 25 in the same way as previously mentioned in embodiment 1 (in step ST42), the protocol processing unit 26 determines whether or not the replacement of a base station of the active set with another case station has been permitted by analyzing the replacement permission signaling (in step ST43) . When determining that the replacement of a base station of the active set with another base station has been permitted, the protocol processing unit 26 excludes a base station 5 having the lowest reception level from the base stations 5 included in the current active set (in step ST44). The protocol processing unit 26 further refers to the S-CCPCH parameters included in the replacement permission signaling indicating permission to replace a base station of the active set with another base station, and identifies the other base station 5 which is to be added to the active set and then adds the other base station 5 to the active set (in step ST45). The protocol processing unit 26 then notifies the S-CCPCH parameters to the search unit 15, finger assignment control unit 17, and RAKE combining unit 18. After tnat, tne mobile cuiiuuunicciLj-ons terminal starts a process of receiving data associated with the S-CCPCH of the base stations 5 of the active set including the other base station 5 which is added to the active set in place of the excluded base station (in step ST46). ■The process of deleting a base station from the active set When the search unit 15 determines that it will carry out implementation of the process of deleting a base station from the active set, the protocol processing unit 26 transmits deletion request signaling indicating a request to delete a base station from the active set to a base station 5 in the same way that it -crans-jLts addition request signaling indicating a request to add a base station to the active set {in step ST51). Thus, the deletion request signaling indicating a request to delete a base station from the active set is transmitted to 5 a base station 5, and the base station 5 transmits the deletion request signaling to a corresponding base station control apparatus 4 . When the base station control apparatus 4 permits the deletion of a base station from the active set, the base station 10 5 transmits deletion permission signaling indicating pennission to delete a base station from the active set to the mobile communications terminal 6 using a DPCH. When the antenna 11 receives the deletion permission signaling indicating a permission to delete a base station from 15 the active set which is transmitted from the base station 5, and the protocol processing unit 26 of the mobile ccrrmunications terminal 6 then receives the deletion permission signaling from the downlink dedicated channel receiving unit 25 in the same way as previously mentioned in embodiment 1 (in step ST52) , the protocol processing unit 26 determines whether or not the deletion of a base station from the active set has been permitted by analyzing the deletion permission signaling (in step ST4-3"). When determining that the deletion of a base station frcm the active set has been permitted, the protocol processing unit 25 26 stops the process of receiving data associated with the S- CCPCH of a base station 5 having the lowest reception level which is included in the base stations 5 of the current active set (in step ST54) , and excludes the base station 5 having the lowest reception level from the current active set (in step ST55). Fig. 12 is a sequence diagram showing signaling indicating upda-ing of the active set in tr.e radio coinmunications system. Hereafter, exchange of information among a mobile communications terminal 6, a base station 5, and a base station control apparatus 4 will be explained with reference to Fig. 12. When updating the active set in the above-mentioned way (in step ST61), the mobile communications terminal 6 transmits active set update information indicating that the active set has been updated to the base station 5 using a RACH which is a common channel (in step ST62). When receiving the active set update information from the mobile communications terminal 6, the base station 5 transmits the active set update information to the base station control apparatus 4 (in step ST63) . When receiving the active set update information from the base station 5, the base station control apparatus 4 refers to the state of the S-CCPCH of a base station 5 which has been newly included in the active sec (in sLep 5T54) . In ^^thci words, the base station control apparatus checks to see whether the base station 5 newly included in the active set is currently carrying out a multimedia service. When determining that the base station 5 newly included in the active set is not currently carrying out any multimedia service, the base station control apparatus instructs the base station 5 to start performing a multimedia service (in step ST66) . The base station control apparatus 4 then acquires S-CCPCH parameters (e.g., timing, a code, etc.) and information about the state of the service being started, and starts RRC (Radio Resource Control) signaling (in step ST67). The base sraiiion 5 receives the S-CCPCH parare^ers from the base station control apparatus 4, and carries out signaling transmission of the S-CCPCH parameters using, for example, a CPICH which is a common channel (in step ST68). When carrying out signaling reception of the S-CCPCH parameters from the base station 5 (in step ST69), the mobile communications terminal 6 sets the S-CCPCH parameters so as to carry out a process of receiving data (in step ST70). As can be seen from the above description, each mobile communications terminal in accordance with this embodiment 3 includes an update request means for comparing the reception levels of radio signal transmitted from a plurality of base stations 5, and for transmitting a request to update the active set according to the result of the comparison. Therefore, the present embodiment offers an advantage of being able to secure the reception quality of radio signals even if each mobile communications terminal 6 moves. in accoraance wich chis einbouimeiiL 5, eacii uiubile communications terminal 6 transmits a request to update the active set to a base station 5, as previously mentioned. When a dedicated channel has been established with the base station 5, each mobile communications terminal 6 can apply an active set of dedicated channels to common channels, and, in this case, does not need to transmit a request to update the active set to any base station 5. Embodiment 4. In accordance with above-mentioned embodiment 3, each mobile communications terminal 6 compares the reception levels of radio signals transmitted from a plurality of base stations 5, and transmits a request to update the active set to a base station 5 according to the result of the comparison, as previously explained. Each mobile communications terminal 6 can alternatively include a monitor target updating means for, when updating the active set, receiving required broadcast information from a base station 5, and for referring to the broadcast information to update the active set, thereby eliminating the participation of base stations 5 in the updating of the active set. The search unit 15 and protocol control unit 26 of Fig. 2 constitute the monitor target updating means. Fig. 13 is a sequence diagram showing parameter information when the radio communications system of this embodiment updates the active set. First, a base station control apparatus 4 transmits, as broadcast information, information (e.g., a threshold) required for the updating of the active set to corresponding base stations 5 (in step ST71). wrien xecexvxiiy the bi-uadcast mformatron frcrri a base station control apparatus 4, the base station 5 transmits the broadcast information to mobile communications terminals 6 (in step ST72). When receiving the broadcast information from the base station 5 (in step ST73), the mobile communications terminal 6 refers to the broadcast information and then sets the information (e.g., the threshold) required for the updating of the active set (in step ST73). The base station control apparatus 4 refers to the states of the S-CCPCHs (e.g., service conditions and timing) of neighboring base stations after transmitting the broadcast information to base stations 5 (in step ST75) . The base station control apparatus 4 then asseriles, as information elements, S-CCFCH parameters (in step ST'^6) , and transmits, as broadcast information, the S-CCPCH information elements to base stations 5 (in step ST77). When receiving the broadcast information from the base station control apparatus 4, the base station 5 transmits the broadcast information to mobile communications terminals 6 (in step ST78) . When receiving the broadcast information from the base station 5 (in step ST79), each mobile communications terminal 6 refers to the broadcast information to set the S-CCPCH parameters and starts reception of data (in step ST80). Fig. 14 is a flow chart showing a process of updating the active set carried out by each mobile communications terminal 6. However, since a process of adding a base station into the active set, a process of replacing a base station of the active set with another base station, and a process of deleting a base station from che active seu ui each mwLxlc couuTiunications terminal 6 are the same as those of Fig. 11, the explanation of them will be omitted hereafter. ■The process of adding a base station into the active set The protocol processing unit 26 of each mobile communications terminal 6 receives the S-CCPCH parameters (including the state of services using the S-CCPCH) as broadcast information from a base station 5 (in step ST81). The protocol processing unit 26 then refers to the state of services using the S-CCPCH included in the S-CCPCH parameters to check to see whether the base station 5 corresponding to the S-CCPCH para~eters is currently performing a service :in step ST82) . 'When the base station 5 corresponding to the S-CCPCH parameters is currently performing a service, the protocol processing unit 26 adds the base station 5 to the active set (in step ST83). The protocol processing unit 26 also notifies the S-CCPCH parameters to the search unit 15, finger assignment control unit 17, and RAKE combining unit 18. After that, each mobile communications terminal starts a process of receiving data associated with the S-CCPCHs of the base stations 5 included in the active set including the added base station 5 (in step ST84). ■The process of replacing a base station of the active set with another base station The protocol processing unit 26 receives, as broadcast information, the S-CCPCH parameters (including the state of services using cne b-CCPCH) Iruiu d base ouaLion 5 (in step STG5) . The protocol processing unit 26 then refers to the state of services using the S-CCPCH included in the S-CCPCH parameters to check to see whether the base station 5 corresponding to the S-CCPCH parameters is currently performing a service (in step ST86). When the base station 5 corresponding to the S-CCPCH parameters is currently performing a service, the protocol processing unit 26 excludes a base station 5 having the lowest reception level from the base stations 5 included in the current active set (in step ST87) . The protocol processing unit 26 then adds the base station 5 corresponding to the S-CCPCH parameters to the active set (in step ST88). The protocol processing unit 26 also notifies the S-CCPCH parameters to the search unit 15, finger assignment control unit 17, and RAKE combining unit 18. After that, each mobile communications terminal starts a process of receiving data associated with the S-CCPCHs of the base stations 5 included in the active set including the base station 5 which is added to the active set in place of the excluded base station (in step ST89). ■The process of deleting a base station from the active set The protocol processing unit 26 stops the process of receiving data associated with the S-CCPCH of a base station 5 having the lowest reception level which is included in the base s tations 5 of the current active set (in step ST90), and excludes the base station 5 from the active set (in step ST91) . As can be seen from the above description, in accordance w±Lh this eiubuuxiiicnt 4, each mobilc corrjTLunicatrLons terminal 5 is so constructed as to, when updating the active set, receive required broadcast information from a base station 5 and refer to the broadcast information to update the active set. Therefore, the present embodiment offers an advantage of being able to secure the reception quality of radio signals even if each mobile communications terminal 6 moves. In accordance with this embodiment 4, each mobile communications terminal 6 does not need to transmit a request to update the active set to a base station 5, unlike that of above-mentioned embodiment 3. Therefore, the present embodiment offers another advantage of making it possible for each mobile coirjr.unlcations terminal to carry out the process of updating the active set m.ore promptly than -na- of above-mentioned embodiment 3. While the radio communications system of this embodiment can broadcast information about S-CCPCHs to a plurality of mobile communications terminals 6 at a time, each mobile communications terminal does not need to notify information including information about the process of adding a base station to the active set to base stations 5. Therefore, the present embodiment offers a further advantage of being able to reduce the number of times that signaling is performed when a large number of mobile communications terminals 6 are staying in the coverage area of each base station. Embodiment 5. In accordance with above-mentioned embodim.ent 3, each mobile communications terminal 6 compares the reception levels of radio signals transmitted from a plurality of base stations o, and craiisiulLa ct requesL Lo update the activc set tc a bass station 5 according to the result of the comparison, as previously explained. When comparing the reception levels of radio signals transmitted from a plurality of base stations 5, each mobile cominunications terminal 6 can estimate the reception levels of the radio signals as follows. In other words, in order to check reception power as the reception level of a radio signal transmitted using an S-CCPCH, each mobile communications terminal needs to set a code and timing for the S-CCPCH and demodulate the signal to determine power RSCP assigned to the code. However, in order to acquire the S-CCPCH parameters in advance and to cari:^- a„t set the ccde for the S-CCPCH, each mobile communications terminal needs to carry out complicated processing. In accordance with this embodiment 5, a base 'station 5 5 notifies a ratio betv;een the power of a CPICH (i.e., a pilot channel) and that of an S-CCPCH (i.e., a common channel) to a mobile communications terminal 6 in advance, and the mobile communications terminal 6 measures the power of the CPICH and practices the method of estimating the power of the S-CCPCH from 10 the measured power of the CPICH and the above-mentioned ratio between the power of the CPICH and that of the S-CCPCH. To be more specific, the processing is carried out as follows. Fig. 15 is a sequence diagram showing the notification 15 of the ratio between the power of the CPICH and that of the S-CCPCH. First, a base station control apparatus 4 acquires the ratio between the power of the CPICH of each base station 5 and that of the S-CCPCH (in step STIOI). (The base station control apparatus 4 then transmits, as broadcast information, the ratio between the power of the CPICH and that of the S-OCPCH to each base station 5. I When receiving the broadcast information from the base station control apparatus 4, each base station 5 transmits the broadcast information to mobile ccmnunications terminals 6 (in step ST102). Each mobile ccmmunications terminal 6 measures the power of the CPICH of each base station 5, and, when receiving the broadcast information from a base station 5 (in step ST103), refers to the broadcast information, and calculates the power of the S-CCPCH by nulciplying the power of the CPICH cf each base station 5 by the ratio between the power of the CPICH and that of the S-CCPCH (in step ST104). Fig. 16 is a flow chart showing the process of updating the active set of each mobile communications terminal. The search unit 15 of each mobile communications terminal 6 receives, as broadcast information, the ratio between the power of the CPICH of each base station 5 and that of the S-CCPCH from a base station 5 (in step STlll). The search unit 15 measures, as the power of the CPICH of each base station 5, the reception level of the CPICH of each base station 5 which is not included in the current active set, as well as the reception level of the CPICH of each base station 5 included in the current active set (in step ST112) . The search unit 15 then calculates the power of the S-CCPCH of each base station 5 by multiplying the power of the CPICH of each base station 5 by the ratio between the power of the L-tiCri and uhaL of the 5-CCPCH (iii oLep 3T113) . The search unit 15 compares the reception levels of the S-CCPCH of the base stations 5 with one another, and ranks them in order (in step ST114). The search unit 15 sets the lowest one of the reception levels of the S-CCPCHs of the base stations 5 included in the active set to X, and calculates an addition threshold Tadd from the lowest S-CCPCH reception level X and a hysteresis parameter H for preventing variations in the active set. Tadd = X + H/2 In this case, the search unit 15 can receive the addirion -hreshold Tadd from c^n upper layer instead of calculating "he addition threshold Tadd. When calculating the addition threshold Tadd in the above-mentioned way, the search unit 15 shifts to the process of step ST24 of Fig. 10. Since subsequent processes are the same as those of above-mentioned embodiment 1, the explanation of the processes will be omitted hereafter. As can be seen from the above description, in accordance with this embodiment 5, each mobile communications terminal is so constructed as to receive information indicating the ratio between the power of the CPICH and that of the S-CCPCH from each of a plurality of base stations 6 in advance, and estimates the reception levels of radio signals transmitted from the plurality of base stations 5 using the S-CCPCHs from the reception levels of radio signals transmitted from the plurality of base stations 5 using the CPICHs and the ratio between the power of the CPICH of each base station and that of the S-CCPCHs. Tneretore, une present embodimenL orieib an advantage of being able to acquire the reception levels of radio signals transmitted from the plurality of base stations 5 using the S-CCPCHs without carrying out complicated processing, such as a process of acquiring the S-CCPCH parameters to carry out code setting. The present embodiment is useful especially for a case where the transmission levels of the S-CCPCHs vary among the plurality of base stations 5 since a number of code setting processes can be eliminated. Industrial Applicability As mentioned above, the radio communications system in accordance wit:h the present invention is suitable for a case where when a plurality of base stations broadcast multirr.edia data to mobile communications terminals using S-CCPCHs, each mobile communications terminal needs to select a base station from which it can receive the multimedia data optimally to improve the reception quality of the multimedia data. WE CLAIM: 1. A communications system relating to a multimedia broadcast multicast service (MBMS) of multicasting or broadcasting a multimedia data to a plurality of mobile stations (6) therein, said communications system characterized by comprising: a power ratio transmitting unit for transmitting information about a power ratio between a power of a common control physical channel used for multicasting or broadcasting said multimedia data in each of given cells and a power of a common pilot channel used for transmitting an information on reference of timing in each of the given cells; a service information transmitting unit for transmitting service information indicating a state of an MBMS service in each of the given cells; a power ratio information receiving unit for receiving the information about the power ratio transmitted by said power ratio transmitting unit; a service information receiving unit for receiving the service information transmitted by said service information transmitting unit; and a ranking unit (15) for ranking a plurality of cells on the basis of the information about said power ratio of the given cells, which is received by said power ratio receiving unit, and the power of said common pilot charmel; a cell selecting unit for acquiring a set including a plurality of cells from which a mobile station can receive an MBMS on the basis of the information about the ranking determined by said ranking unit, a predetermined threshold, and said service information received by said service information receiving unit; a decoding vmit for receiving a signal transmitted using said common control physical channel in each of the plurality of cells included in the set acquired by said cell selecting unit, and for decoding said signal to acquire a plurality of decoded signals; and a selectively-combining unit for selecting a signal from the plurality of decoded signals acquired by said decoding unit, and thereby obtaining an output signal.