Abstract:
Provided is a base station comprising a multiplexer so constituted as to frequency-divide/multiplex a first channel for transmitting first data to be transmitted to a plurality of mobile stations, and a second channel for transmitting second data to be transmitted to one mobile station.

Description:
This application is a national stage application of PCT/JP2009/057654 filed Apr. 16, 2009, which claims priority to Japanese Priority Application No. 2008-117877 filed on Apr. 28, 2008, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a base station, a mobile station and a frequency division multiplexing communication method. 
     BACKGROUND ART 
     Data communication between a base station and a mobile station is typically conducted in one-to-one communication, so-called unicast communication. On the other hand, there is multimedia broadcast/multicast service (MBMS) for transmitting the same data from a base station to multiple mobile stations simultaneously, which attracts attention due to support for broadcast message service and fast video streaming service. 
     In the MBMS, if the same MBMS data pieces are transmitted from multiple base stations, a mobile station can receive the MBMS data with a high quality by soft-combining the same MBMS data pieces from the multiple base stations (so-called MBSFN (MBMS with Single Frequency Network). In this case, the mobile station has to receive the MBMS data from the multiple base stations with a delay time period less than or equal to a cyclic prefix (CP), and a longer CP would be required in consideration of delay of the MBMS data from a far base station. For example, the CP for unicast communication corresponds to 69μ seconds in LTE (3.9 generation (3.9G)) while the CP corresponds to 16.67μ seconds in the MBMS. In this manner, if the unicast channel and the MBMS channel (shared data channel (SDCH)), which have different CP lengths, are frequency-multiplexed and transmitted, orthogonality between the respective channels cannot be ensured. For this reason, the unicast channel and the MBMS channel are time-multiplexed per subframe unit in the LTE. 
     RELATED ART DOCUMENT 
     Non-Patent Document 
     
         
         Non-patent document 1: 3GPP, TS 36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8). 
       
    
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     However, it is being discussed to use an extremely wide frequency band such as 100 MHz in IMT-Advanced (the fourth generation (4G)) to realize extremely high peak rates and throughputs, and it is inefficient and unreasonable that the unicast channel and the MBMS channel are multiplexed in accordance with only the time division multiplexing (TDM). Also, there is a need that a transmission manner of a L1/L2 control channel for the MBMS channel is reconsidered from the viewpoint of efficient utilization of radio resources. 
     The present invention addresses the above-mentioned problems and intends to provide a base station, a mobile station and a frequency division multiplexing communication method for the MBMS subframes and the unicast frames that realize efficient utilization of radio resources in MBMS and unicast communications. 
     Means for Solving the Problem 
     In order to realize the above objects, a first aspect of the present invention provides a base station comprising: a multiplexing unit configured to multiplex a first channel and a second channel in accordance with frequency division multiplexing, wherein the first channel is for transmitting first data to be transmitted to multiple mobile stations, and the second channel is for transmitting second data to be transmitted to one mobile station. 
     A second aspect of the present invention provides the base station of the first aspect, further comprising: a first signal generation unit configured to generate the first channel, the first signal generation unit inserting a first cyclic prefix to the first channel including the first data; and a second signal generation unit configured to generate the second channel, the second signal generation unit inserting a second cyclic prefix to the second channel including the second data, the second cyclic prefix having a same length as the first cyclic prefix. 
     A third aspect of the present invention provides the base station of the first aspect, further comprising: a third signal generation unit configured to generate the second channel, the third signal generation unit inserting a guard band between the second channel and the first channel. 
     A fourth aspect of the present invention provides the base station of any of the first through third aspects, wherein a L1/L2 control channel to be multiplexed in a frequency band for transmitting the first channel is multiplexed in a frequency band for transmitting the second channel. 
     A fifth aspect of the present invention provides a mobile station for communicating to the base station as claimed in any of the first through fourth aspects, comprising: a demultiplexing unit configured to demultiplex the first channel and the second channel multiplexed in accordance with the frequency division multiplexing. 
     A sixth aspect of the present invention provides a frequency division multiplexing communication method, comprising the steps of: generating a first channel for transmitting first data to be transmitted to multiple mobile stations; generating a second channel for transmitting second data to be transmitted to one mobile station; and multiplexing the first channel and the second channel in accordance with frequency division multiplexing. 
     A seventh aspect of the present invention provides the frequency division multiplexing communication method of the sixth aspect, wherein the step of generating the first channel comprises inserting a first cyclic prefix to the first channel, and the step of generating the second channel comprises inserting a second cyclic prefix to the second channel, the second cyclic prefix having a same length as the first cyclic prefix. 
     An eighth aspect of the present invention provides the frequency division multiplexing communication method of the sixth aspect, wherein the step of generating the second channel comprises inserting a guard band between the second channel and the first channel. 
     A ninth aspect of the present invention provides a base station for transmitting data to multiple mobile stations in N frequency bands, comprising: a control signal generation unit configured to generate a control signal for indicating one or less than N frequency bands for multiplexing a L1/L2 control channel among the N frequency bands used to transmit the data; and a signal generation unit configured to generate a channel including the data depending on the control signal. 
     A tenth aspect of the present invention provides a mobile station for communicating to the base station of the ninth aspect, comprising: a receiving unit configured to receive a signal from the base station; a demultiplexing unit configured to demultiplex the signal received from the receiving unit to extract identification information for identifying one or less than N frequency bands; and a data demodulation and decoding unit configured to obtain information in the L1/L2 control channel based on the identification information supplied from the demultiplexing unit. 
     An eleventh aspect of the present invention provides a frequency division multiplexing communication method for transmitting data to multiple mobile stations in N frequency bands, comprising the steps of: indicating one or less than N frequency bands for multiplexing a L1/L2 control channel among the N frequency bands used to transmit the data; and generating a subframe including the data depending on a control signal. 
     Advantage of the Invention 
     According to the aspects of the present invention, it is possible to provide a base station, a mobile station and a frequency division multiplexing communication method for the MBMS subframes and the unicast frames that realize efficient utilization of radio resources in MBMS and unicast communications. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view illustrating an arrangement of a base station according to a first embodiment of the present invention; 
         FIG. 2  illustrates MBMS channels and unicast channels that are frequency-division-multiplexed at a base station according to the first embodiment of the present invention; 
         FIG. 3  is a schematic view illustrating an arrangement of a mobile station according to the first embodiment of the present invention; 
         FIG. 4  is a flowchart illustrating a frequency division multiplexing communication method according to the first embodiment of the present invention; 
         FIG. 5  is a schematic view illustrating an arrangement of a base station according to a second embodiment of the present invention; 
         FIG. 6  illustrates MBMS channels and unicast channels that are frequency-division-multiplexed at a base station according to the second embodiment of the present invention; 
         FIG. 7  is a flowchart illustrating a frequency division multiplexing communication method according to the second embodiment of the present invention; 
         FIG. 8  is a schematic view illustrating an arrangement of a base station according to a third embodiment of the present invention; 
         FIG. 9  is a schematic view illustrating an exemplary arrangement of the MBMS channels generated at a base station according to the third embodiment of the present invention; 
         FIG. 10  illustrates the MBMS channels and the unicast channels that are frequency-division-multiplexed at a base station according to a third embodiment of the present invention; 
         FIG. 11  is a schematic view illustrating an arrangement of a base station according to the fourth embodiment of the present invention; 
         FIG. 12  is a schematic view illustrating exemplary arrangement of the MBMS channels generated at a base station according to the fourth embodiment of the present invention; and 
         FIG. 13  is a schematic view illustrating an arrangement of a mobile station according to the fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are described with reference to the drawings below. In the following descriptions, the same or similar reference symbols are attached to the same or similar arrangements, and descriptions thereof are omitted. 
     First Embodiment 
     The first embodiment of the present invention is described with reference to  FIGS. 1-4 . 
     [Base Station] 
       FIG. 1  is a schematic view illustrating an arrangement of a base station according to the first embodiment of the present invention. As illustrated, a base station  10  includes a MBMS signal generation unit  12 , a unicast signal generation unit  14 , a frequency division multiplexing (FDM) unit  16  and a transmitting unit  18 . 
     The MBMS signal generation unit  12  fetches data to be transmitted to multiple mobile stations (MBMS data) from a non-illustrated buffer, modulates the fetched MBMS data and L1/L2 control information in accordance with an orthogonal frequency division multiplexing (OFDM) scheme and attaches a cyclic prefix (referred to as a CP hereinafter) OFDM symbol-by-OFDM symbol to generate a MBMS channel. Here a relatively long CP is attached to a MBMS data symbol. This is because delay from the multiple base stations  10  can be accommodated within the CP under the case where the multiple base stations  10  transmit the same data and a mobile station receives the same data from the multiple base stations  10 . Specifically, the CP may have the length of, but not limited to, 16.67μ second, for example. On the other hand, the attached CP corresponding to the L1/L2 control information may be shorter than the CP attached to the MBMS data symbol (e.g., 4.69μ second). In the following description, the CP attached to the L1/L2 control information symbol is referred to as “shorter CP” while the CP attached to the MBMS data symbol is referred to as “longer CP”. Note that the L1/L2 control channel may include scheduling information, uplink feedback information for uplink transmission from the mobile station to the base station  10  (information such as frequency bands to be utilized for the uplink transmissions), information on a modulation coding set (MCS) and information indicative of a reception result of the uplink transmission (ACK, NACK). 
     Also, the MBMS signal generation unit  12  supplies the MBMS channel as generated in the above manner to the FDM unit  16 . 
     The unicast signal generation unit  14  fetches data to be transmitted to any mobile station (unicast data) from a non-illustrated buffer, modulates the fetched data and the L1/L2 control information in accordance with the OFDM and attaches the CP OFDM symbol-by-OFDM symbol to generate the unicast channel. Here, a longer CP is attached to the unicast data symbol similar to the above-mentioned MBMS data. The unicast communication is one-to-one communication between the base station  10  and any mobile station, and due to no need of considering signal delay from multiple base stations, it can be said that it may be sufficient to attach a shorter CP to the unicast data symbol. In the base station  10  according to the first embodiment, however, a longer CP is also attached to the unicast data symbol. Also, a shorter CP is attached to the L1/L2 control information symbol. Also, the unicast signal generation unit  14  supplies the unicast channel as generated in the above manner to the FDM unit  16 . 
     The FDM unit  16  receives the MBMS channel from the MBMS signal generation unit  12  and the unicast channel from the unicast signal generation unit  14 . The FDM unit  16  multiplexes the received MBMS channel and unicast channel in the frequency division multiplexing manner to generate a transmission signal.  FIG. 2  illustrates an exemplary transmission signal. Referring to  FIG. 2 , the MBMS channels and the unicast channels, which have a mutually equal fundamental frequency width (for example, but not limited to, 50 MHz), are arranged in the frequency axis direction. Also, as illustrated, shorter CPs are attached to the L1/L2 control information symbols (consisting of two symbols in the illustrated example) for both frequency bands for transmitting the MBMS channels and the unicast channels, and the resulting data is transmitted. On the other hand, longer CPs are attached to the MBMS channel symbols and the unicast channel symbols. 
     Although  FIG. 2  illustrates the case where the MBMS channel and the unicast channel have the mutually equal frequency bandwidth, different frequency bandwidths may be utilized. 
     Referring to  FIG. 1  again, the FDM unit  16  provides the transmitting unit  18  with a transmission signal resulting from frequency division multiplexing of the MBMS channels and the unicast channels. Upon receiving the transmission signal, the transmitting unit  18  performs predefined operations on the transmission signal and transmits the resulting transmission signal via a non-illustrated antenna. 
     [Mobile Station] 
       FIG. 3  is a schematic view illustrating an arrangement of a base station according to the first embodiment of the present invention. As illustrated, a mobile station  30  includes a receiving unit  32 , a demultiplexing unit  34 , a MBMS signal demodulation and decoding unit  36  and a unicast signal demultiplexing and decoding unit  38 . 
     The receiving unit  32  receives a transmission signal from the base station  10 , performs predefined operations on the received signal and supplies the resulting signal to the demultiplexing unit  34 . 
     The demultiplexing unit  34  demultiplexes the signal received from the receiving unit  32  into the MBMS channels and the unicast channels. For demultiplexing into the MBMS channels and the unicast channels, the mobile station  30  has to comprehend a frequency band used to transmit the MBMS channel and a frequency band used to transmit the unicast channel. To this end, information on the frequency bands is indicated from the base station  10  to the mobile station  30 . The indication may be conducted through upper layer (L3) signaling in connection to the base station  10 , through a broadcast channel to all the mobile stations  30  residing within a cell of the base station  10  or by transmitting the L1/L2 control channel having the multiplexed frequency band information to a certain one or some of the base stations  30 . The indication through the upper layer signaling is preferred under the case where the used frequency bands are changed relatively infrequently (for example, the case where the frequency bands are unchanged after initiation of communication), and the indication through the broadcast channel is preferred under the case where the used frequency bands are changed relatively frequently. Also, the indication by multiplexing into the L1/L2 control channel is preferred under the case where the used frequency bands may be changed for each transmission, for example. 
     Also, the demultiplexing unit  34  supplies the demultiplexed MBMS channels and unicast channels to the MBMS signal demodulation and decoding unit  36  and the unicast signal demodulation and decoding unit  38 , respectively. The MBMS signal demodulation and decoding unit  36  performs predefined operations on the MBMS channels received from the demultiplexing unit  34  to demodulate and decode the MBMS channels. The unicast signal demodulation and decoding unit  38  performs predefined operations on the unicast channels received from the demultiplexing unit  34  to demodulate and decode the unicast channels. 
     [Frequency Division Multiplexing Communication Method] 
     A frequency division multiplexing communication method for the MBMS channels and the unicast channels according to the first embodiment of the present invention is described with reference to  FIG. 4 .  FIG. 4  is a flowchart illustrating the frequency division multiplexing communication method according to the first embodiment. Referring to  FIG. 4 , the MBMS data and the L1/L2 control information are modulated in accordance with the OFDM at step S 402 . At step S 404 , in order to generate the MBMS channel, longer CPs are attached to the MBMS data symbols, and shorter CPs are attached to the L1/L2 control information symbols. 
     Next, the unicast data and the L1/L2 control information are modulated in accordance with the OFDM at step S 406 . At step S 408 , in order to generate the unicast channel, longer CPs are attached to the unicast data symbols, and shorter CPs are attached to the L1/L2 control information symbols. Then, the MBMS channel generated at step S 404  and the unicast channel generated at step S 408  are multiplexed in the frequency division multiplexing manner at step S 410 , and the resulting transmission signal is transmitted at step S 412 . 
     In the above-mentioned embodiment, steps S 402  and S 404  precede steps S 406  and S 408 , but steps S 406  and S 408  may be conducted earlier than steps S 402  and S 404 . Alternatively, steps S 402  and S 404  may be performed approximately in synchronous with steps S 406  and S 408 . 
     In this manner, according to the first embodiment, the CP having the same length as the CP inserted to the MBMS channel is inserted to the unicast channel, and the unicast channel and the MBMS channel are multiplexed in the frequency division multiplexing manner. As a result, it is possible to maintain the orthogonality between the channels. In other words, the insertion of the longer CP into the unicast channel can realize the unicast communication and the MBMS communication in accordance with the frequency division multiplexing. For this reason, radio resources can be efficiently utilized compared with the case where the unicast communication and the MBMS communication are made in accordance with the time division multiplexing. Particularly, the IMT-Advanced allows for utilization of a wide frequency band, and accordingly by using the wide frequency band, the MBMS communication and the unicast communication are conducted in different frequency bands, which can provide smooth services such as fast video streaming. 
     Second Embodiment 
     The second embodiment of the present invention is described with reference to  FIGS. 5-7 . 
     [Base Station] 
       FIG. 5  is a schematic view illustrating an arrangement of a base station according to the second embodiment of the present invention. As illustrated, a base station  50  includes a MBMS signal generation unit  12 , a unicast signal generation unit  54 , a FDM unit  56  and a transmitting unit  18 . 
     The MBMS signal generation unit  12  generates a MBMS channel in the same manner as the MBMS signal generation unit  12  of the base station  10  according to the first embodiment and supplies the generated MBMS channel to the FDM unit  56 . 
     The unicast signal generation unit  54  fetches unicast data to be transmitted to any mobile station from a non-illustrated buffer, modulates the fetched data and L1/L2 control information in accordance with the OFDM and appends a CP to each OFDM symbol to generate a unicast channel. Unlike the first embodiment, in the second embodiment, the CP inserted by the unicast signal generation unit  54  to the unicast channel is a shorter CP. The unicast communication is one-to-one communication between the base station  10  and any mobile station, and due to unnecessary consideration of data delay from multiple base stations, it is sufficient to append the shorter CP to the unicast data symbol. Also, the shorter CP is appended to the L1/L2 control information symbol. This is the same as the first embodiment. 
     Also, the unicast signal generation unit  54  supplies the generated unicast channel to the FDM unit  56 . 
     The FDM unit  56  receives the MBMS channel from the MBMS signal generation unit  12  and the unicast channel from the unicast signal generation unit  54 . In the case where the unicast channel having the shorter CPs appended to the symbols corresponding to the unicast data and the MBMS channel having the appended longer CPs are directly multiplexed in accordance with the frequency division multiplexing manner, there may be a risk that the orthogonality cannot be maintained. For this reason, the FDM unit  56  provides a guard band between the unicast channel and the MBMS channel and multiplexes the unicast channel and the MBMS channel in accordance with the frequency division multiplexing manner to generate a transmission signal.  FIG. 6  illustrates an exemplary transmission signal. Referring to  FIG. 6 , the MBMS channel and the unicast channel are aligned in the frequency axis direction. Also as illustrated, shorter CPs are appended to L1/L2 control symbols (consisting of two symbols in the illustrated example) in both the MBMS channel and the unicast channel, and the longer CPs are appended to the MBMS channel symbols while the shorter CPs are appended to the unicast channel symbols. Furthermore, a guard band is inserted between the unicast channel and the MBMS channel. Due to this guard band, the MBMS channel and the unicast channel will have the same frequency bandwidth. 
     However, the guard band may be inserted between the MBMS channel and the unicast channel such that the MBMS channel and the unicast channel can have different frequency bandwidths. 
     Referring to  FIG. 5  again, the FDM unit  56  supplies the transmission signal generated in accordance with the frequency division multiplexing to the transmitting unit  18 . Upon receiving the transmission signal, the transmitting unit  18  performs predefined operations on the transmission signal and transmits the resulting signal via a not-illustrated antenna. 
     [Mobile Station] 
     The mobile station communicating to the base station  50  according to the second embodiment of the present invention may have the same arrangement as the mobile station  30  according to the first embodiment. Also, without modification of the method for indicating information on frequency bands for use in transmissions of the MBMS channel and the unicast channel, which is necessary to separate the MBMS channel from the unicast channel, the frequency band information may be indicated through upper layer (L3) signaling in connection of the mobile station to the base station  50 . Alternatively, the frequency band information may be indicated to all mobile stations residing within a cell of the base station  50  in a broadcast channel. Alternatively, the frequency band information may be multiplexed into a L1/L2 control channel, and the L1/L2 control channel may be transmitted to a certain one or all of the mobile stations. 
     The demultiplexing unit  34  of the mobile station according to the second embodiment can separate the unicast channel based on the indicated frequency band information for use in the unicast channel transmission. Accordingly, the FDM unit  56  of the base station  50  does not have to comprehend the width of the guard band between the unicast channel and the MBMS channel. 
     [Frequency Division Multiplexing Communication Method] 
     A frequency division multiplexing communication method for the MBMS channel and the unicast channel according to the second embodiment of the present invention is described with reference to  FIG. 7 .  FIG. 7  is a flowchart illustrating the frequency division multiplexing communication method according to the second embodiment. Referring to  FIG. 7 , MBMS data and L1/L2 control information are modulated in accordance with the OFDM at step S 702 . At step S 704 , longer CPs are appended to the MBMS data symbols, and shorter CPs are appended to the L1/L2 control information symbols to generate the MBMS channel. 
     Then, the unicast data and the L1/L2 control information are modulated in accordance with the OFDM at step S 706 . At step S 708 , shorter CPs are appended to the unicast data symbols, and shorter CPs are appended to the L1/L2 control information symbols to generate the unicast channel. Then, at step S 710 , a guard band is provided between the unicast channel and the MBMS channel, and these channels and the guard band are multiplexed in the frequency division multiplexing manner to generate a transmission signal. The transmission signal is transmitted at step S 714 . 
     According to the second embodiment, the guard band is provided between the unicast channel and the MBMS channel, and the unicast channel and the MBMS channel are multiplexed in accordance with the frequency division multiplexing manner. Accordingly, it is possible to maintain the orthogonality between the channels. In other words, the unicast communication and the MBMS communication can be realized with the frequency division multiplexing through the appended guard band. As a result, radio resources can be efficiently utilized compared to the case where the unicast communication and the MBMS communication are based on only time division multiplexing. Particularly, a wide frequency band is available in the IMT-Advanced, and thus services such as fast video streaming can be smoothly provided by using the wide frequency band to perform the MBMS communication and the unicast communication in different frequency bands. Furthermore, the insertion of the guard band makes it possible to use optimum CPs in the unicast channel, and accordingly the optimum CPs can be used for both the MBMS channel and the unicast channel. 
     Third Embodiment 
     The third embodiment of the present invention is described with reference to  FIGS. 8-10 . 
     [Base Station] 
       FIG. 8  is a schematic view illustrating an arrangement of a base station according to the third embodiment of the present invention. As illustrated, a base station  80  includes a MBMS signal generation unit  82 , a unicast signal generation unit  84 , a L1/L2 control signal generation unit  85 , a signal multiplexing unit  86  and a transmitting unit  88 . 
     The MBMS signal generation unit  82  fetches MBMS data from a non-illustrated buffer, modulates the fetched MBMS data in accordance with the OFDM, and appends a longer CP to each OFDM symbol to generate a MBMS channel. Also, the MBMS signal generation unit  82  supplies the generated MBMS channel to the signal multiplexing unit  86 . 
     The unicast signal generation unit  84  fetches unicast data from a non-illustrated buffer, modulates the fetched data in accordance with the OFDM, and appends a CP to each OFDM symbol to generate a unicast channel. Here, the longer CPs are appended to the unicast data symbols as in the above-mentioned MBMS data. Also, the above L1/L2 control information includes not only information necessary for feedback for uplink transmission for reply to reception of the unicast channel from a mobile station at the base station but also reception acknowledgement information (ACK/NACK) transmitted from the base station  80  to the mobile station. 
     The unicast signal generation unit  84  supplies the generated unicast channel to the signal multiplexing unit  86 . 
     The L1/L2 control signal generation unit  85  generates a L1/L2 control signal such as feedback information on the uplink transmission (ACK/NACK, scheduling information, MCS information and so on) and control information for downlink unicast transmission (MCS information, transmission assigned user information and so on) and supplies the generated L1/L2 control signal to the signal multiplexing unit  86 . 
     The signal multiplexing unit  86  receives the MBMS channel from the MBMS signal generation unit  82 , the unicast channel from the unicast signal generation unit  84  and the control signal regarding the L1/L2 control information from the L1/L2 control signal generation unit  85 . The signal multiplexing unit  86  performs mapping on the received channels and signal to generate a transmission signal.  FIG. 9  illustrates an exemplary transmission signal. Referring to  FIG. 9 , the MBMS channel and the unicast channel having the same fundamental frequency bandwidth are aligned in the frequency axis direction. Also as illustrated, the portion corresponding to the L1/L2 control channel in the MBMS channel has no information (unused). As described in conjunction with the first and second embodiments, the MBMS channel and the unicast channel do not have to have the same frequency bandwidth and may have different frequency bandwidths. 
     Referring to  FIG. 8  again, the signal multiplexing unit  86  supplies the generated transmission signal to the transmitting unit  88 . Upon receipt of the transmission signal, the transmitting unit  88  performs predefined operations on the transmission signal and transmits the resulting signal via a non-illustrated antenna. 
     [Mobile Station] 
       FIG. 10  is a schematic view illustrating an arrangement of a mobile station according to the third embodiment of the present invention. As illustrated, a mobile station  100  includes a receiving unit  102 , a demultiplexing unit  104 , a MBMS signal demodulation and decoding unit  106 , a unicast signal demodulation and decoding unit  108  and a control signal demodulation and decoding unit  109 . 
     The receiving unit  102  receives a transmission signal transmitted from the base station  100 , performs predefined operations on the received signal and supplies the resulting signal to the demultiplexing unit  104 . 
     The demultiplexing unit  104  demultiplexes the signal received from the receiving unit  102  into a MBMS signal, a unicast signal and a L1/L2 control signal. Also, the demultiplexing unit  104  supplies the MBMS signal to the MBMS signal demodulation and decoding unit  106 , the unicast signal to the unicast signal demodulation and decoding unit  108  and the L1/L2 control signal to the control signal demodulation and decoding unit  109 . 
     The control signal demodulation and decoding unit  109  obtains a control signal regarding the L1/L2 control information (control information for downlink unicast transmission (MCS information, transmission assigned user information and so on), feedback information for uplink transmission and so on) from the control signal supplied from the demultiplexing unit  104  and supplies the control information for downlink unicast transmission in the obtained control signal to the unicast signal demodulation and decoding unit  108 . 
     The MBMS signal demodulation and decoding unit  106  performs predefined operations on the MBMS channel received from the demultiplexing unit  104  to demodulate and decode the MBMS channel. 
     The unicast signal demodulation and decoding unit  108  uses the L1/L2 control information associated with downlink unicast transmission from the control signal demodulation and decoding unit  109  to perform predefined operations on the unicast signal received from the demultiplexing unit  104  for demodulation and decoding the unicast signal. 
     [Frequency Division Multiplexing Communication Method] 
     Next, a frequency division multiplexing communication method for the MBMS channel and the unicast channel according to the third embodiment of the present invention is described. Initially, in the MBMS signal generation unit  82 , MBMS data is modulated in the OFDM, and longer CPs are appended to the modulated OFDM symbols to generate a MBMS channel. 
     Then, in the unicast signal generation unit  84 , unicast data is modulated in the OFDM, and longer CPs are appended to the OFDM symbols to generate a unicast channel. 
     Then, in the L1/L2 control signal generation unit  85 , a L1/L2 control signal such as feedback information for uplink transmission (ACK/NACK, scheduling information, MCS information and so on) and control information for downlink unicast transmission (MCS information, transmission assigned user information and so on) is generated. 
     Then, the MBMS channel, the unicast channel and the L1/L2 control signal are mapped to generate a transmission signal. Then, predefined operations are performed on the transmission signal, and the resulting signal is transmitted. 
     According to the third embodiment, the L1/L2 control channel transmitted in a frequency band for transmitting the MBMS channel is transmitted in a frequency band for transmitting the unicast channel. For this reason, symbols for transmitting the L1/L2 control channel in the frequency band for transmitting the MBMS channel can be used to transmit other information, which can utilize radio resources efficiently. 
     Fourth Embodiment 
     The fourth embodiment of the present invention is described with reference to  FIGS. 11-13 . 
     [Base Station] 
       FIG. 11  is a schematic view illustrating an arrangement of a base station according to the fourth embodiment of the present invention. As illustrated, a base station  110  includes a MBMS signal generation unit  112 , a L1/L2 control signal generation unit  115 , a signal multiplexing unit  116  and a transmitting unit  118 . 
     The L1/L2 control signal generation unit  115  generates a L1/L2 control signal such as feedback information for uplink transmission (ACK/NACK, scheduling information, MCS information and so on) and supplies the resulting signal to the signal multiplexing unit  116 . 
     The MBMS signal generation unit  112  modulates MBMS data incoming from a non-illustrated buffer in accordance with the OFDM and generates a MBMS channel by appending CPs to OFDM symbols. Here, the longer CPs are inserted to the MBMS channel. 
     Also, the MBMS signal generation unit  112  supplies the generated MBMS channel to the signal multiplexing unit  116 . 
     The signal multiplexing unit  116  receives the MBMS channel from the MBMS signal generation unit  112  and a control signal regarding the L1/L2 control information from the L1/L2 control signal generation unit  115 . The signal multiplexing unit  116  maps the received channels and signals to generate a transmission signal.  FIG. 12  illustrates an exemplary transmission signal. Referring to  FIG. 12 , a frequency band for transmitting the MBMS channel has the L1/L2 control channel while a portion of the frequency band for transmitting the MBMS channel corresponding to the L1/L2 control channel has no information to be transmitted. 
     Referring to  FIG. 11  again, the signal multiplexing unit  116  supplies the generated transmission signal to the transmitting unit  118 . Upon receipt of the transmission signal, the transmitting unit  118  performs predefined operations on the transmission signal and transmits the resulting signal via a non-illustrated antenna. 
     [Mobile Station] 
       FIG. 13  is a schematic view illustrating an arrangement of a base station according to the fourth embodiment of the present invention. As illustrated, a mobile station  130  includes a receiving unit  132 , a demultiplexing unit  134 , a MBMS signal demodulation and decoding unit  136  and a control signal demodulation and decoding unit  139 . 
     The receiving unit  132  receives a transmission signal transmitted from the base station  110 , performs predefined operations on the received signal and supplies the resulting signal to the demultiplexing unit  134 . 
     The demultiplexing unit  134  demultiplexes the signal incoming from the receiving unit  132  into a MBMS channel and a control signal. Also, the demultiplexing unit  134  supplies the MBMS channel to the MBMS signal demodulation and decoding unit  136  and the control signal to the control signal demodulation and decoding unit  139 . 
     The control signal demodulation and decoding unit  139  obtains information regarding L1/L2 control information from the control signal received from the demultiplexing unit  134 . 
     The MBMS signal demodulation and decoding unit  136  performs predefined operations on the MBMS channel received from the demultiplexing unit  134  to demodulate and decode the MBMS channel. 
     [Transmission Method] 
     A MBMS channel transmission method according to the fourth embodiment of the present invention is described. 
     Initially, it is determined whether a frequency band is for transmitting the L1/L2 control information. If the frequency band is for transmitting the L1/L2 control information, MBMS data and a L1/L2 control channel are modulated in accordance with the OFDM, and CPs are appended to OFDM symbols to generate a MBMS channel. Here, longer CPs are inserted to the MBMS channel, and shorter CPs are inserted to the L1/L2 control channel. On the other hand, if the frequency band is not for transmitting the L1/L2 control information, the MBMS data is modulated in accordance with the OFDM, and longer CPs are appended to OFDM symbols to generate the MBMS channel. 
     Subsequently, if the MBMS channel and the L1/L2 control channel are present, the mapping is performed on the channels including the L1/L2 control channel to generate a transmission signal. Then, predefined operations are performed on the generated transmission signal, and the resulting signal is transmitted. 
     The IMT-Advanced allows for utilization of a frequency bandwidth of 100 MHz, but there is a likelihood that this frequency bandwidth of 100 MHz may be the total bandwidth of several frequency bands rather than a continuous frequency bandwidth (so-called frequency aggregation). In this case, the MBMS channel may be transmitted in a 2 GHz band and 3 GHz band, for example. In the base station  110  according to the fourth embodiment, the L1/L2 control signal generation unit  115  specifies frequency bands for transmitting the L1/L2 control channel and accordingly can cause the L1/L2 control channel to be transmitted in the 2 GHz band and not to be transmitted in the 3 GHz band. In this case, a portion in the 3 GHz band corresponding to the L1/L2 control channel can be used to transmit the MBMS data. 
     Also, there is a case that the MBMS signal is transmitted in two frequency bands in a continuous frequency band of 100 MHz instead of the frequency aggregation. Also in this case, the frequency band for transmitting the L1/L2 control channel is specified, and accordingly a certain frequency band may not be used to transmit the L1/L2 control channel. For this reason, a portion of the current subframe corresponding to the L1/L2 control channel can be instead used to transmit the MBMS data. 
     In this manner, it is possible to utilize radio resources efficiently and provide services such as fast video streaming smoothly. 
     Although the present invention has been described with reference some embodiments, the present invention is not limited to the above embodiments, and various modifications and applications can be made in light of the attached claims. For example, in the third embodiment, the longer CPs are inserted to the unicast channel as in the first embodiment. However, as in the second embodiment, shorter CPs may be inserted, and the guard band may be appended in the signal multiplexing unit  86  between the unicast channel and the MBMS channel. 
     Also, the fourth embodiment may be applied to the third embodiment. In other words, in the third embodiment, the L1/L2 control channel to be transmitted in a frequency band for transmitting the MBMS channel is transmitted in a frequency band for transmitting the unicast channel. However, the L1/L2 control channel may be transmitted not in the frequency band for transmitting the unicast channel but by using one or less than N frequency bands of N frequency bands for transmitting the MBMS channel. As a result, there arises a frequency band for the L1/L2 control channel that does not include information, and the frequency band can be utilized to transmit other information (e.g., MBMS data). 
     Furthermore, although several frequency division multiplexing communication methods according to embodiments of the present invention have been illustrated, the steps (or procedures) do not have to be conducted in the above-mentioned order. It will be apparently appreciated by those skilled in the art that some of the steps may be conducted in a different order or simultaneously. 
     Also, it has been described above that the base station, the mobile station and the frequency division multiplexing communication method of the present invention are particularly effective to the IMT-Advanced. However, radio resources can be efficiently utilized not only in the IMT-Advanced but also in the LTE, and accordingly it goes without saying that the embodiments of the present invention may be applied to the LTE system. Furthermore, the so-called MBSFN has been intensively described as the MBMS communication, but even in the case of single cell MBMS, the present invention may be applicable if several channels having inserted CPs of different lengths are multiplexed in the frequency division multiplexing. 
     LIST OF REFERENCE SYMBOLS 
     
         
         
           
               10 ,  50 ,  80 ,  110 : base station 
               12 ,  112 : MBMS signal generation unit 
               14 ,  54 ,  84 : unicast signal generation unit 
               16 ,  56 : FDM multiplexing unit 
               18 ,  88 ,  118 : transmitting unit 
               85 ,  115 : control signal generation unit 
               30 ,  100 ,  130 : mobile station 
               32 ,  102 ,  132 : receiving unit 
               34 ,  104 ,  134 : demultiplexing unit 
               36 ,  106 ,  136 : MBMS signal demodulation and decoding unit 
               38 ,  108 : unicast signal demodulation and decoding unit 
               109 ,  139 : control signal demodulation and decoding unit