Abstract:
A base station, a terminal, a band allocation method, and a downlink data communication method are disclosed, with which bands can be efficiently allocated. In a base station in which a plurality of unit bands can be allocated to a single communication, when a data receiver acquires terminal capability information transmitted by a terminal in the initial access unit band and the bandwidth available for communication indicated by the terminal capability information can accommodate a plurality of unit bands, a unit band group which includes the initial access unit band as well as the unit bands adjacent thereto is allocated to the terminal, and a communication band movement indication, which indicates the movement of the center frequency in the communication band of the terminal toward the center frequency in the unit band group, is transmitted to the terminal using the initial access unit band.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a base station, terminal, band assignment method and downlink data communication method 
         [0003]    2. Description of the Related Art 
         [0004]    In 3GPP LTE, OFDMA (Orthogonal Frequency Division Multiple Access) is adopted as a downlink communication scheme. In a radio communication system adopting 3GPP LTE, a radio communication base station apparatus (which may be simply referred to as “base station” below) transmits a synchronization channel (“SCH”) or broadcast channel (“BCH”) using predetermined communication resources. Then, first, a radio communication terminal apparatus (which may be simply referred to as “terminal” below) secures synchronization with the base station by capturing the SCH. That is, first, the terminal performs a cell search. After that, the terminal obtains parameters unique to the base station (such as a frequency bandwidth) by reading the BCH information (see Non-Patent Literatures 1, 2 and 3). 
         [0005]    Also, standardization of 3GPP LTE-advanced, which realizes faster communication than 3GPP LTE, has been started. The 3GPP LTE-advanced system (which may be referred to as “LTE+ system” below) follows the 3GPP LTE system (which may be referred to as “LTE system” below). In 3GPP LTE-advanced, to realize downlink transmission speed equal to or greater than maximum 1 Gbps, it is expected to adopt a base station and terminal that can perform communication in a wideband frequency equal to or greater than 20 MHz. Here, to prevent unnecessary complication of the terminal, the terminal side is expected to define the terminal capability related to frequency band support. The terminal capability defines that, for example, the minimum value of support bandwidth is 20 MHz. 
         [0006]    That is, a base station supporting the LTE+ system (which may be referred to as “LTE+ base station” below) is formed to be able to perform communication in a frequency band including a plurality of “unit bands.” Here, a “unit band” is a band of a 20-MHz range, including SCH (Synchronization CHannel) near the center, and is defined as a base unit of a communication band. Also, a “unit band” may be expressed as “component carrier(s)” in English in 3GPP LTE. 
         [0007]    Also, terminals supporting the LTE+ system (which may be referred to as “LTE+ terminal” below) include a terminal in which a communication-capable bandwidth can contain only one unit band (which may be referred to as “type-1 LTE+ terminal” below) and a terminal in which a communication-capable bandwidth can contain a plurality of unit bands (which may be referred to as “type-2 LTE+ terminal” below). 
       CITATION LIST 
     Non-Patent Literature 
       [0008]    NPL 1 
         [0009]    3GPP TS 36.211 V8.3.0, “Physical Channels and Modulation (Release 8),” May 2008 
         [0010]    NPL 2 
         [0011]    3GPP TS 36.212 V8.3.0, “Multiplexing and channel coding (Release 8),” May 2008 
         [0012]    NPL 3 
         [0013]    3GPP TS 36.213 V8.3.0, “Physical layer procedures (Release 8),” May 2008 
       BRIEF SUMMARY 
     Technical Problem 
       [0014]    Here, a case is assumed where an LTE+ base station supports an LTE+ terminal.  FIG. 1  shows an example of mapping SCH and BCH in the LTE+ system support base station. 
         [0015]    In  FIG. 1 , a communication bandwidth of the LTE+ base station is 40 MHz and includes two unit bands. Also, SCH and BCH are placed at 20 MHz intervals near the center frequency of each unit band. Here, a null carrier for DC offset compensation in a terminal is inserted in the center of each frequency band in which SCH and BCH are placed. Also, SCH and BCH are placed in 36 subcarriers each in the higher and lower frequency (i.e. a total of 72 subcarriers) from the center of the null carrier. Also, physical downlink control channels (“PDCCH&#39; s”) are placed in a distributed manner in the whole unit bands. 
         [0016]    Similar to a case of the above-noted LTE system, when powered on, the LTE+ terminal first tries capturing an SCH transmitted from the LTE+ base station by performing correlation synchronization processing while moving the center frequency of the communication band. Upon capturing the SCH transmitted from the LTE+ base station by peak detection in the correlation result, the LTE+ terminal captures a BCH transmitted from the LTE+ base station and reads the frequency band of the uplink pair band. Then, the LTE+ terminal starts communicating with the LTE+ base station by transmitting a signal in PRACH (Physical Random Access CHannel). Also, a unit band synchronized between the terminal and the base station may be referred to as “initial access unit band.” 
         [0017]      FIG. 2  illustrates an access condition of an LTE+ terminal (i.e. type-2 LTE+ terminal) that can perform communication in a communication bandwidth of 40 MHz, with respect to an LTE+ base station that transmits SCH and BCH by the mapping method shown in  FIG. 1 . 
         [0018]    As shown in  FIG. 2 , the type-2 LTE+ terminal adjusts the center frequency of that terminal to the SCH frequency position in the initial access unit band and receives data signals transmitted from the LTE+ base station. Therefore, in spite of being able to receive data signals in 40 MHz continuous bands, the type-2 LTE+ terminal cannot cover the whole unit band adjacent to the initial access unit band. That is, actually, communication is performed only in the initial access unit band, and the capability of the LTE+ terminal is not utilized. Therefore, there is a problem that the LTE+ base station cannot assign a band to the type-2 LTE+ terminal efficiently. 
         [0019]      FIG. 3  shows another example of mapping SCH and BCH in the LTE+ system support base station. 
         [0020]    In  FIG. 3 , a communication bandwidth of the LTE+ base station is 40 MHz and includes two unit bands. Also, SCH and BCH are placed near the center frequency of the communication band. 
         [0021]    According to the mapping method in  FIG. 3 , the LTE+ terminal adjusts the center frequency of that terminal to the SCH frequency position, so that it is possible to cover the whole communication band of the LTE+ base station by the communication band of that LTE+ terminal. 
         [0022]    However, with the mapping method in  FIG. 3 , SCH and BCH are not mapped on 10 MHz bands at both ends, and, consequently, the LTE+ terminal, which has only 20 MHz terminal capability (i.e. type-1 LTE+ terminal), cannot use the 10 MHz bands at both ends. That is, with the mapping method in  FIG. 3 , frequency is wasted. Therefore, there is a problem that the LTE+ base station cannot assign a band to the type-1 LTE+ terminal efficiently. 
         [0023]      FIG. 4  shows another example of mapping SCH and BCH in the LTE+ system support base station. 
         [0024]    In  FIG. 4 , a communication bandwidth of the LTE+ base station is 40 MHz and includes two unit bands. Then, SCH and BACH are placed near the center frequency of the communication band and placed near the center frequencies of bands of 10 MHz bandwidth from the both ends. 
         [0025]    According to the mapping method shown in  FIG. 4 , the type-1 LTE+ terminal can use bands of 10 MHz bandwidth from both ends. However, in the case where the type-2 LTE+ terminal uses 10 MHz bands at both ends as initial access unit bands, communication is possible only in a narrower band than the case of the mapping method shown in  FIG. 2 . That is, with the mapping method of  FIG. 4 , there is a problem that the LTE+ base station cannot assign a band to the type-2 LTE+ terminal efficiently, 
         [0026]    It is therefore an object of the present invention to provide a base station, terminal, band assignment method and downlink data communication method that enable efficient band assignment. 
       Solution to Problem 
       [0027]    The base station of the present invention that can assign a plurality of unit bands to single communication, employs a configuration having: an obtaining section that obtains terminal capability information which is transmitted by a terminal in an initial access unit band and which indicates a communication-capable bandwidth of the terminal; and a control section that, when the terminal can have the plurality of unit bands in the communication-capable bandwidth indicated by the obtained terminal capability information, assigns a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to the terminal transmitting the obtained terminal capacity information, and transmits a communication band moving instruction to instruct for a reference frequency in a communication band of the terminal to be moved to a reference frequency in the unit band group, to the terminal using the initial access unit band. 
         [0028]    The terminal of the present invention that receives a data signal transmitted from the above base station in the unit band group assigned from the base station, employs a configuration having: a reception section that receives the data signal; and a control section that makes the reception section start receiving the data signal in the initial access unit band before a moving process based on the communication band moving instruction starts, and continue the reception during a period of the moving process and after the period. 
         [0029]    The band assignment method of the present invention for assigning a band used for data communication from a base station to a second terminal in a communication system including the base station that can assign a plurality of unit bands to single communication, a first terminal that can have only one unit band in a communication-capable bandwidth and the second terminal that can have the plurality of unit bands in a communication-capable bandwidth, includes: in a terminal, transmitting terminal capability information indicating a communication-capable bandwidth of the terminal in an initial access unit band for the base station; and, in the base station, when the terminal can have the plurality of unit bands in the communication-capable bandwidth indicated by the transmitted terminal capability information, assigning a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to the terminal, and transmitting a communication band moving instruction to instruct for a reference frequency in a communication band of the assignment target terminal to be moved to a reference frequency in the unit band group, to the assignment target terminal using the initial access unit band. 
         [0030]    The downlink data communication method of the present invention including the steps of the above band assignment method, includes: starting downlink data communication between the base station and the terminal in the initial access unit band; and in the terminal, moving the reference frequency in the communication band of the terminal based on the communication band moving instruction, where the downlink data communication starts before a moving process of the reference frequency starts, and continues during a period of the moving process and after the period. 
       Advantageous Effects of Invention 
       [0031]    According to the present invention, it is possible to provide a base station, terminal, band assignment method and downlink data communication method that enable efficient band assignment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  shows an example of mapping SCH and BCH in an LTE+ system support base station; 
           [0033]      FIG. 2  illustrates an access condition of an LTE+ terminal that can perform communication in a 40 MHz communication bandwidth, with respect to an LTE+ base station that transmits SCH and BCH by the mapping method shown in  FIG. 1 ; 
           [0034]      FIG. 3  shows another example of mapping SCH and BCH in an LTE+ system support base station; 
           [0035]      FIG. 4  shows another example of mapping SCH and BCH in an LTE+ system support base station; 
           [0036]      FIG. 5  is a block diagram showing a configuration of a terminal according to Embodiment 1 of the present invention; 
           [0037]      FIG. 6  is a block diagram showing a configuration of a base station according to Embodiment 1 of the present invention; 
           [0038]      FIG. 7  is a sequence diagram showing signal transmission and reception between a terminal and a base station according to Embodiment 1 of the present invention; 
           [0039]      FIG. 8  illustrates a communication band moved by a terminal according to Embodiment 1 of the present invention; 
           [0040]      FIG. 9  is a block diagram showing a configuration of a terminal according to Embodiment 2 of the present invention; 
           [0041]      FIG. 10  is a block diagram showing a configuration of a base station according to Embodiment 2 of the present invention; 
           [0042]      FIG. 11  is a sequence diagram showing signal transmission and reception between a terminal and a base station according to Embodiment 2 of the present invention; and 
           [0043]      FIG. 12  illustrates RB formation. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    Now, embodiments of the present invention will be explained in detail with reference to the accompanying drawings. Also, in embodiments, the same components will be assigned the same reference numerals and overlapping explanation will be omitted. 
       Embodiment 1 
       [0045]    [Terminal configuration]  FIG. 5  is a block diagram showing a configuration of terminal  100  according to Embodiment  1  of the present invention. Terminal  100  is an LTE+ terminal in which the communication-capable bandwidth includes a plurality of unit bands. In  FIG. 5 , terminal  100  is provided with RF receiving section  105 , OFDM signal demodulating section  110 , frame synchronization section  115 , demultiplexing section  120 , broadcast information receiving section  125 , PDCCH receiving section  130 , PDSCH (Physical Downlink Shared CHannel) receiving section  135 , control section  140 , RACH (Random Access CHannel) preamble section  145 , modulating section  150 , SC-FDMA (Single-Carrier Frequency Division Multiple Access) signal forming section  155  and RF transmitting section  160 . 
         [0046]    RF receiving section  105  is formed to be able to change a reception band. RF receiving section  105  receives a center frequency directive from control section  140  and, by moving the center frequency based on this center frequency directive, moves the reception band. RF receiving section  105  performs radio reception processing (such as down-conversion and analog-to-digital (A/D) conversion) on a radio reception signal received in the reception band via an antenna, and outputs the resulting reception signal to OFDM signal demodulating section  110 . Also, here, although the center frequency of the reception band is used as a reference frequency, it is equally possible to use an arbitrary frequency included in the reception band as the reference frequency. OFDM signal demodulating section  110  has CP (Cyclic Prefix) removing section  111  and fast Fourier Transform (FFT) section  112 . OFDM signal demodulating section  110  receives the reception OFDM signal from RF receiving section  105 . In OFDM signal demodulating section  110 , CP removing section  111  removes a CP from the reception OFDM signal and FFT section  112  transforms the reception OFDM signal without a CP into a frequency domain signal. This frequency domain signal is outputted to frame synchronization section  115 . 
         [0047]    Frame synchronization section  115  searches for a synchronization signal (SCH) included in the signal received from OFDM signal demodulating section  110  and finds synchronization with base station  200  (described later). A unit band included in the found synchronization signal (SCH) is used as the initial access unit band. The synchronization signal includes a P-SCH (Primary SCH) and S-SCH (Secondary SCH). To be more specific, frame synchronization section  115  searches for the P-SCH and finds synchronization with base station  200  (described later). 
         [0048]    After finding the P-SCH, frame synchronization section  115  performs blind detection of the S-SCH placed in resources having a predetermined relationship with resources in which the P-SCH is placed. By this means, it is possible to find more precise synchronization and obtain the cell ID associated with the S-SCH sequence. That is, frame synchronization section  115  performs the same processing as in a normal cell search. 
         [0049]    Frame synchronization section  115  outputs frame synchronization timing information related to the synchronization establishment timing, to demultiplexing section  120 . 
         [0050]    Demultiplexing section  120  demultiplexes the reception signal received from OFDM signal demodulating section  110  into the broadcast signal, control signal (i.e. PDCCH signal) and data signal (i.e. PDSCH signal) included in this reception signal, based on the frame synchronization timing information. The broadcast signal is outputted to broadcast information receiving section  125 , the PDCCH signal is outputted to PDCCH receiving section  130 , and the PDSCH signal is outputted to PDSCH receiving section  135 . Here, the PDSCH includes individual information for a given terminal. 
         [0051]    Broadcast information receiving section  125  reads the content of the input P-BCH (Primary BCH) and obtains information related to the number of antennas of base station  200  (described later) and downlink system bandwidth. This information is outputted to control section  140 . 
         [0052]    Broadcast information receiving section  125  receives a D-BCH signal placed in resources indicated by D-BCH (Dynamic BCH) resource position information (D-BCH frequency position information in this case) included in the PDCCH signal and extracted in PDCCH receiving section  130 , and obtains information included in this received D-BCH signal (e.g. information about the frequency and frequency band of uplink pair band or PRACH (Physical Random Access CHannel)). This information is outputted to control section  140 . Also, in this specification, an example case will be explained using frequency as resources. 
         [0053]    Based on the decoding directive from control section  140 , PDCCH receiving section  130  extracts information (including the frequency position in which the 
         [0054]    D-BCH is placed, the frequency position in which the PDSCH is placed, and uplink frequency allocation information (PDSCH frequency position information in this case)), included in the PDCCH signal received from demultiplexing section  120 . Out of this extracted information, information about the frequency position in which the D-BCH is placed is outputted to broadcast information receiving section  125 , information about the frequency position in which the PDSCH is placed is outputted to PDSCH receiving section  135 , and the uplink frequency allocation information is outputted to SC-FDMA signal forming section  155 . 
         [0055]    PDSCH receiving section  135  extracts a communication band moving instruction from the PDSCH signal received from demultiplexing section  120 , based on the information about the frequency position in which the PDSCH is placed, received from PDCCH receiving section  130 . Then, the extracted communication band moving instruction is outputted to control section  140 . 
         [0056]    Here, the communication band moving instruction is a directive for moving the center frequency in the communication band of terminal  100  to the center frequency in the whole unit band group assigned from base station  200  (described later) to terminal  100  (hereinafter “assignment unit band group”). Here, in order to reduce the signaling amount required for the communication band moving instruction, the center frequency of the whole assignment unit band group to adjust in RF receiving section  105  of terminal  100  is reported as a multiple of 300 KHz, which is the lowest common multiple of the downlink subcarrier bandwidth (15 KHz) and the minimum resolution of frequency that can be set by RF receiving section  105  of terminal  100  (100 KHz). This is because, when an LTE+ base station transmits a plurality of SCH&#39;s using one IFFT circuit, the interval between SCH&#39;s is nothing but an integral multiple of 15 KHz, and, furthermore, needs to be a multiple of 100 KHz to adjust the center frequency of a reception band for any SCH on the terminal side. 
         [0057]    Control section  140  sequentially changes the reception band of RF receiving section  105  before synchronization is established. Also, after synchronization is established and before an RACH preamble is transmitted, control section  140  prepares RACH preamble transmission in the initial access unit band based on the broadcast signal (P-BCH), control channel (PDCCH) and dynamic broadcast signal (D-BCH) transmitted from base station  200  (described later) in the initial access unit band including the frequency position of a synchronization channel. Also, after RACH preamble transmission in the initial access unit band, control section  140  obtains report resource assignment information reported by the control channel from base station  200  (described later), and transmits terminal capability information of that terminal using resources indicated by that report resource allocation information. At this stage, data communication is possible between base station  200  and terminal  100  in the initial access unit band. Then, control section  140  obtains the communication band moving instruction transmitted by base station  200  according to the terminal capability information, and, first, cuts off downlink data communication and then moves the center frequency in the communication band of terminal  100  to the center frequency in the whole assignment unit band group based on the communication band moving instruction. 
         [0058]    Also, after cutting off downlink data communication in the initial access unit band, based on a broadcast signal, control channel and LTE dynamic broadcast signal transmitted in a unit band different from the initial access unit band in the assignment unit band group (hereinafter “additional assignment unit band”), control section  140  prepares RACH preamble transmission in the additional assignment unit band. Also, upon completing the preparation of RACH preamble transmission in the additional assignment unit band, first, control section  140  cuts off uplink communication between terminal  100  and base station  200  (described later) and then transmits the RACH preamble in the additional assignment unit band. Also, after transmitting the RACH preamble in the additional assignment unit band, control section  140  obtains the report resource assignment information reported by the control channel from base station  200 , and using resources indicated by this report resource assignment information, transmits a communication starting request (aggregation communication starting request) for the whole unit band group assigned by base station  200 , to base station  200 . 
         [0059]    To be more specific, control section  140  identifies PDCCH placement information based on the information obtained in broadcast information receiving section  125 . This PDCCH placement information is uniquely determined by the number of antennas of base station  200  (described later) and downlink system bandwidth. Control section  140  outputs the PDCCH placement information to PDCCH receiving section  130  and commands decoding of a signal placed in the frequency position according to that information. 
         [0060]    Also, control section  140  commands RACH preamble section  145  to transmit an RACH preamble according to information included in the D-BCH signal received from broadcast information receiving section  125 , that is, according to the uplink frequency band and PRACH frequency position. 
         [0061]    Also, upon receiving the uplink frequency allocation information from PDCCH receiving section  130 , control section  140  outputs terminal capability information (i.e. capability information) of that terminal to modulating section  150  and outputs the uplink frequency allocation information to SC-FDMA signal forming section  155 . By this means, the terminal capability information is mapped on frequency corresponding to the uplink frequency allocation information and then transmitted. 
         [0062]    Also, based on the communication band moving instruction received from PDSCH receiving section  135 , control section  140  outputs a center frequency directive to RF receiving section  105  such that the center frequency of the reception band of RF receiving section  105  matches the center frequency in the assignment unit band group. Here, control section  140  cuts off downlink data communication if the reception band is subjected to move control based on that communication band moving instruction. 
         [0063]    According to the directive from control section  140 , RACH preamble section  145  outputs an RACH preamble sequence and information related to the uplink frequency band and PRACH frequency position included in that directive, to SC-FDMA signal forming section  155 . 
         [0064]    Modulating section  150  modulates the terminal capability information received from control section  140  and outputs the resulting modulation signal to SC-FDMA signal forming section  155 . 
         [0065]    SC-FDMA signal forming section  155  forms an SC-FDMA signal from the modulation signal received from modulating section  150  and the RACH preamble sequence received from RACH preamble section  145 . In SC-FDMA signal forming section  155 , discrete Fourier transform (DFT) section  156  transforms the input modulation signal on the frequency axis and outputs a plurality of resulting frequency components to frequency mapping section  157 . These plurality of frequency components are mapped on frequency based on the uplink frequency allocation information in frequency mapping section  157  and transformed into a time domain waveform in IFFT section  158 . The RACH preamble sequence is also mapped on frequency based on the uplink frequency allocation information in frequency mapping section  157  and transformed into a time domain waveform in IFFT section  158 . CP attaching section  159  attaches a CP to the time domain waveform and provides an SC-FDMA signal. 
         [0066]    RF transmitting section  160  performs radio transmission processing on the SC-FDMA signal formed in SC-FDMA signal forming section  155  and transmits the result via an antenna. 
         [0067]    Base Station Configuration 
         [0068]      FIG. 6  is a block diagram showing a configuration of base station  200  according to Embodiment 1 of the present invention. Base station  200  is an LTE+ base station. In each unit band, base station  200  always continues to transmit a P-SCH, S-SCH, P-BCH, D-BCH and PDCCH representing frequency scheduling information of D-BCH, in an OFDM scheme. The BCH includes frequency band information, which divides a communication band every unit band. Therefore, a unit band is also defined as a band divided using frequency band information in BCH or a band defined by a distribution width upon placing PDCCH in a distributed manner. 
         [0069]    In  FIG. 6 , base station  200  is provided with PDCCH generating section  205 , PDSCH generating section  210 , broadcast signal generating section  215 , modulating section  220 , OFDM signal forming section  225 , RF transmitting section  230 , RF receiving section  235 , CP removing section  240 , FFT section  245 , extracting section  250 , RACH preamble receiving section  255 , data receiving section  260  and control section  265 . CP removing section  240 , FFT section  245 , extracting section  250 , RACH preamble receiving section  255  and data receiving section  260  form an SC-FDMA signal demodulating section. 
         [0070]    PDSCH generating section  205  receives uplink frequency allocation information for terminal  100  and generates a PDCCH signal including this uplink frequency allocation information. PDCCH generating section  205  masks the uplink frequency allocation information by CRC based on an RACH preamble sequence transmitted from terminal  100 , and then includes the result in the PDCCH signal. The generated PDCCH signal is outputted to modulating section  220 . Here, a sufficient number of RACH preamble sequences are prepared, and the terminal selects an arbitrary sequence from these RACH preamble sequences and accesses the base station. That is, there is an extremely low possibility that a plurality of terminals access base station  200  at the same time using the same RACH preamble sequence, so that, by receiving a PDCCH subjected to CRC masking based on that RACH preamble sequence, terminal  100  can detect uplink frequency allocation information for that terminal without problems. 
         [0071]    PDSCH generating section  210  receives a communication band moving instruction from control section  265  and generates a PDSCH signal including this communication band moving instruction. Also, PDSCH generating section  210  receives as input transmission data after transmission of the communication band moving instruction. Then, PDSCH generating section  210  generates a PDSCH signal including the input transmission data. The PDSCH signal generated in PDSCH generating section  210  is received as input in modulating section  220 . 
         [0072]    Broadcast signal generating section  215  generates and outputs a broadcast signal to modulating section  220 . This broadcast signal includes P-BCH and D-BCH. 
         [0073]    Modulating section  220  forms modulation signals by modulating input signals. These input signals include the PDCCH signal, PDSCH signal and broadcast signal. The formed modulation signals are received as input in OFDM signal forming section  225 . 
         [0074]    OFDM signal forming section  225  receives as input the modulation signals and synchronization signals (P-SCH and S-SCH) and forms an OFDM signal in which those signals are mapped on predetermined resources, respectively. In OFDM signal forming section  225 , multiplexing section  226  multiplexes the modulation signals and the synchronization signals, and IFFT section  227  obtains a time domain waveform by performing serial-to-parallel conversion and then performing an IFFT of the multiplex signal. By attaching a CP to this time domain waveform in CP attaching section  228 , the OFDM signal is provided. 
         [0075]    RF transmitting section  230  performs radio transmission processing on the OFDM signal formed in OFDM signal forming section  225  and transmits the result via an antenna. 
         [0076]    RF receiving section  235  performs radio reception processing (such as down-conversion and analog-to-digital (A/D) conversion) on a radio reception signal received in a reception band via the antenna, and outputs the resulting reception signal to CP removing section  240 . 
         [0077]    CP removing section  240  removes a CP from the reception SC-FDMA signal and FFT section  245  transforms the reception SC-FDMA signal without a CP into a frequency domain signal. 
         [0078]    Extracting section  250  extracts a signal mapped on resources corresponding to RACH, from the frequency domain signal received from FFT section  245 , and outputs the extracted signal to RACH preamble receiving section  255 . This extraction of a signal mapped on resources corresponding to RACH is always performed so that an LTE+ terminal transmits an RACH preamble to base station  200  at any timing. 
         [0079]    Also, extracting section  250  extracts a signal corresponding to uplink frequency allocation information received from control section  265 , and outputs this signal to data receiving section  260 . This extracted signal includes, for example, terminal capability information transmitted by terminal  100  in PUSCH. 
         [0080]    First, RACH preamble receiving section  255  transforms the extracted signal received from extracting section  250  into a single carrier signal. That is, RACH preamble receiving section  255  includes an inverse discrete Fourier transform (IDFT) circuit. Then, 
         [0081]    RACH preamble receiving section  255  finds correlation between the resulting single carrier signal and an RACH preamble pattern, and, if the correlation value is equal to or greater than a certain level, decides that an RACH preamble is detected. Then, RACH preamble receiving section  255  outputs an RACH detection report including pattern information of the detected RACH preamble (e.g. the sequence number of the RACH preamble) to control section  265 . 
         [0082]    Data receiving section  260  transforms the extracted signal received from extracting section  250  into a single carrier signal on the time axis and outputs terminal capability information included in the resulting single carrier signal to control section  265 . Also, after transmission of the communication band moving instruction, data receiving section  260  outputs the resulting single carrier signal to a higher layer as reception data. 
         [0083]    Upon receiving the RACH detection report from RACH preamble receiving section  255 , control section  265  allocates uplink frequency to terminal  100  having transmitted the detected RACH preamble. This allocated uplink frequency is used to, for example, transmit terminal capability information in terminal  100 . Then, the uplink frequency allocation information is outputted to PDCCH generating section  205 . Also, upon receiving the terminal capability information from data receiving section  260 , control section  265  decides the communication-capable bandwidth of the LTE+ terminal based on the terminal capability information. As a result of decision, if the communication-capable bandwidth indicated by the terminal capability information can contain a plurality of unit bands, control section  265  allocates a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to the transmission source terminal of the terminal capacity information (terminal  100  in this case), forms a communication band moving instruction to instruct for the center frequency in the communication band of the transmission source terminal to be moved to the center frequency in the whole unit band group, and outputs the communication band moving instruction to PDSCH generating section  210 . Here, as described above, this communication band moving instruction includes information about the difference from the center frequency position in the RF receiving section of the RF receiving section of the terminal. This difference information has the value that is an integral multiple of 300 KHz. Similar to normal downlink data, the communication bend moving instruction is prepared for each terminal in PDSCH generating section  210  and then received as input in the modulating section. 
         [0084]    Also, after outputting the communication band moving instruction, control section  265  cuts off downlink data communication with terminal  100 . Then, upon receiving, from RACH preamble receiving section  255 , the detection report of an RACH preamble transmitted in an additional assignment unit band from terminal  100 , control section  265  allocates uplink frequency to terminal  100 . This allocated uplink frequency is used to, for example, transmit terminal capability information in terminal  100 . Then, the uplink frequency allocation information is outputted to PDCCH generating section  205 . 
         [0085]    Also, upon receiving an aggregation communication starting request from terminal  100 , control section  265  starts communicating using the whole assignment unit band. 
         [0086]    Operations of Terminal  100  and Base Station  200   
         [0087]      FIG. 7  is a sequence diagram showing signal transmission and reception between terminal  100  and base station  200 . 
         [0088]    In step S 1001 , a synchronization signal is transmitted, and cell search processing is performed using this synchronization signal. That is, in step S 1001 , the reception band of RF receiving section  105  is sequentially shifted by control of control section  140 , and frame synchronization section  115  searches for a P-SCH. By this means, the initial synchronization is established. Then, frame synchronization section  115  performs blind detection of an S-SCH placed in resources having a predetermined relationship with resources in which the P-SCH is placed. By this means, it is possible to find more precise synchronization and obtain the cell ID associated with the S-SCH sequence. 
         [0089]    In step S 1002  to step S 1004 , a broadcast signal and control channel are transmitted and used to prepare RACH preamble transmission in the initial access unit band. 
         [0090]    That is, in step S 1002 , control section  140  identifies PDCCH placement information based on information included in a received D-BCH signal and obtained in broadcast information receiving section  125  (e.g. information about frequency and frequency band of uplink pair band or PRACH (Physical Random Access CHannel)). Then, control section  140  outputs the PDCCH placement information to PDCCH receiving section  130  and commands decoding of a signal placed in the frequency position based on the information. 
         [0091]    In step S 1003 , according to the decoding directive from control section  140 , frequency position information of the D-BCH is extracted in PDCCH receiving section  130 . 
         [0092]    In step S 1004 , based on the D-BCH frequency position information, information included in the received D-BCH signal (e.g. information about frequency and frequency band of uplink pair band or PRACH (Physical Random Access CHannel)) is extracted in broadcast information receiving section  125 . 
         [0093]    In step S 1005 , under control of control section  140 , RACH preamble section  145  transmits an RACH preamble using the uplink frequency band and PRACH frequency position obtained in step S 1002 . 
         [0094]    In step S 1006 , control section  265  of base station  200  having received the RACH preamble allocates uplink frequency to terminal  100  having transmitted the RACH preamble, and transmits uplink frequency allocation information to that terminal  100 . 
         [0095]    In step S 1007 , control section  140  of terminal  100  having received the uplink frequency allocation information transmits terminal capability information of that terminal, using the uplink frequency. 
         [0096]    At this stage, base station  200  and terminal  100  are in conditions where communication is possible, and, in step S 1008 , data communication starts between base station  200  and terminal  100 . 
         [0097]    In step S 1009 , if the communication-capable bandwidth indicated by the received terminal capability information can contain a plurality of unit bands, control section  265  of base station  200  allocates a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to terminal  100  of the terminal capacity information, and transmits a communication band moving instruction to instruct for the center frequency in the communication band of terminal  100  to be moved to the center frequency in the whole unit band group. 
         [0098]    First, in step S 1010 , terminal  100  having received this communication band moving instruction cuts off downlink data communication and then moves the center frequency in the communication band to the center frequency in the whole assignment unit band group based on the communication band moving instruction. 
         [0099]      FIG. 8  illustrates the communication band moved in terminal  100 . 
         [0100]    As shown in the left side of  FIG. 8 , in step S 1001  to step S 1009 , the center frequency of the communication band of terminal  100  matches the SCH frequency position in unit band A of the initial access unit band. In this condition, as explained using  FIG. 2 , the capability of terminal  100  is not utilized. 
         [0101]    By contrast with this, by moving the center frequency of the communication band of terminal  100  in step S 1010 , as shown in the right side of  FIG. 8 , it is possible to contain the whole assignment unit band group in the communication band of terminal  100 . Also, the width of each unit band is the same in  FIG. 8 , and therefore the center frequency of the communication band of terminal  100  matches the boundary frequency between unit band A and unit band B. 
         [0102]    Referring back to the flow of  FIG. 7 , in step S 1011  to step S 1013 , a broadcast signal and control channel are transmitted and used to prepare RACH preamble transmission in an additional assignment unit band. 
         [0103]    Upon completing the preparation of the RACH preamble in the additional assignment unit band, control section  140  cuts off uplink communication between terminal  100  and base station  200  in step S 1014 , and transmits the RACH preamble in the additional assignment unit band in step S 1015 . 
         [0104]    In step S 1016 , control section  265  of base station  200  having received the RACH preamble allocates uplink frequency to terminal  100  having transmitted the RACH preamble in the additional assignment unit band, and transmits uplink frequency allocation information to that terminal  100 . 
         [0105]    In step S 1017 , control section  140  of terminal  100  transmits an aggregation communication starting request using resources indicated by the uplink frequency allocation information transmitted from base station  200  in step S 1016 . 
         [0106]    Upon receiving this aggregation communication starting request, control section  265  of base station  200  starts communicating using the whole assignment unit band group. 
         [0107]    As described above, according to the present embodiment, in base station  200  in which a plurality of unit bands can be assigned in single communication, data receiving section  260  obtains terminal capability information transmitted by terminal  100  in the initial access unit band, and, when the communication-capable bandwidth indicated by that terminal capability information can contain a plurality of unit bands, assigns a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to terminal  100 , and transmits a communication band moving instruction to instruct for the center frequency in the communication band of terminal  100  to be moved to the center frequency in that unit band group, to terminal  100  using the initial access unit band. 
         [0108]    By this means, it is possible to contain the whole assignment unit band group in the communication band of terminal  100 . That is, base station  200  that allows efficient band assignment for terminal  100  is realized. 
         [0109]    Also, in the above explanation, the reference frequency of the reception band of terminal  100 , the reference frequency of a unit band (i.e. SCH frequency position) and the reference frequency of an assignment unit band group have been explained as respective center frequencies. However, the present invention is not limited to this, and it is equally possible to use other frequency positions as the reference frequency. An essential requirement is that each reference frequency is determined such that the whole unit band is contained in the reception band of terminal  100  by adjusting the reference frequency of the reception band of terminal  100  to the reference frequency of the unit band and the whole assignment unit band group is contained in the reception band of terminal  100  by adjusting the reference frequency of the reception band of terminal  100  to the reference frequency of the assignment unit band group. 
       Embodiment 2 
       [0110]    In Embodiment 1, when a terminal transmits an RACH preamble in an additional assignment unit band, RF frequency has to be switched to an uplink pair band corresponding to the additional assignment unit band, and, consequently, communication is momentarily cut off (i.e. condition in which an ACK to uplink data and downlink data cannot be transmitted) in the communication system. By contrast with this, in Embodiment 2, it is possible to realize a communication system in which efficient band assignment is possible without cutting off communication momentarily. Now, a terminal and base station forming this communication system will be explained. 
         [0111]      FIG. 9  is a block diagram showing a configuration of terminal  300  according to Embodiment 2. In  FIG. 9 , terminal  300  has control section  310 . 
         [0112]    In control section  310 , control processing from synchronization establishment to data communication between base station  200  and terminal  100  in the initial access unit band, is the same as the control processing in control section  140  of terminal  100  according to Embodiment 1. 
         [0113]    Control section  310  obtains a communication band moving instruction transmitted according to terminal capability information from base station  400  (described later), and, based on this communication band moving instruction, moves the center frequency in the communication band of terminal  300  to the center frequency in the whole assignment unit band group. At this time, data communication between base station  400  and terminal  300  started in the initial access unit band before the center frequency moving process, is not cut off. 
         [0114]    Here, base station  400  (described later) transmits the communication band moving instruction and all of the content of P-BCH transmitted in an additional assignment unit band (i.e. the content of MIB (Master Information Block)). To be more specific, the MIB includes the extension of PDCCH in the frequency axis direction (downlink frequency bandwidth), the number of antennas of the base station in the move destination band (i.e. the number of antennas to transmit a reference signal) and the number of OFDM resources used for others than PDCCH (e.g. a response signal to an uplink data signal). Further, base station  400  transmits the communication band moving instruction and information related to the SCH position and null carrier position in the additional assignment unit band. 
         [0115]    Therefore, based on the obtained MIB, control section  310  obtains a control channel and LTE dynamic broadcast signal in the additional assignment unit band. Here, although terminal  100  according to Embodiment 1 performs, for example, RACH preamble transmission in the additional assignment unit band, terminal  300  does not perform that processing. 
         [0116]    Upon obtaining the control channel and D-BCH (i.e. SIB (System Information Block)) in the additional assignment unit band, control section  310  transmits a read completion report of the SIB to base station  400  using an uplink pair band of the initial access unit band. This SIB read completion report is used as an aggregation communication starting request. 
         [0117]      FIG. 10  is a block diagram showing a configuration of base station  400  according to Embodiment 2 of the present invention. 
         [0118]    In  FIG. 10 , base station  400  has control section  410 . 
         [0119]    When the communication-capable bandwidth indicated by terminal capability information can contain a plurality of unit bands, control section  410  assigns a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to the transmission source terminal of the terminal capability information (terminal  300  in this case), forms a communication band moving instruction to indicate the center frequency in the communication band of the transmission source terminal to be moved to the center frequency in the whole unit band group, and outputs the communication band moving instruction to PDSCH generating section  210 . Also, control section  410  outputs the communication band moving instruction, the content of MIB and information related to the SCH position and null carrier position, to PDSCH generating section  210 . 
         [0120]      FIG. 11  is a sequence diagram showing signal transmission and reception between terminal  300  and base station  400 . 
         [0121]    The sequence diagram of  FIG. 11  and the sequence in  FIG. 7  are the same in step S 1001  to step S 1008 . 
         [0122]    In step S 2001 , when the communication-capable bandwidth indicated by received terminal capability information can contain a plurality of unit bands, control section  410  of base station  400  assigns a unit band group including a unit band adjacent to the initial access unit band in addition to the initial access unit band, to terminal  300  of the terminal capacity information, and transmits a communication band moving instruction to instruct for the center frequency in the communication band of terminal  300  to be moved to the center frequency in the whole unit band group. Further, control section  410  transmits the communication band moving instruction, the content of MIB and information related to the SCH position and null carrier position in the additional assignment unit band. 
         [0123]    Terminal  300  having received the communication band moving instruction moves the center frequency in the communication band to the center frequency in the whole assignment unit band group, based on the communication band moving instruction. At this time, data communication between base station  200  and terminal  100  started before the center frequency moving process in the initial access unit band, is not cut off. That is, reception of a downlink data signal in the initial access unit band starts before a moving process based on the communication band moving instruction starts, and this reception continues during the moving process period and after the end of this period. 
         [0124]    After that, upon obtaining the control channel and D-BCH (i.e. SIB (System Information Block)) in the additional assignment unit band based on the MIB, control section  310  of terminal  300  transmits an aggregation communication starting request to base station  400  using an uplink pair band of the initial access unit band (step S 2002 ). 
         [0125]    As described above, according to the present embodiment, terminal  300  starts receiving a data signal in the initial access unit band before a moving process based on a communication band moving instruction starts, and continues the reception during the moving process period and after the end of this period. That is, communication in the initial access unit band is not cut off momentarily. 
         [0126]    Also, according to the present embodiment, in base station  400 , control section  410  transmits information used to identify a control channel transmitted in an additional assignment unit band, together with a communication band moving instruction in the initial access unit band. 
         [0127]    By this means, terminal  300  needs not receive a P-BCH in the additional assignment unit band, so that it is possible to start aggregation communication earlier than in the case of Embodiment 1. 
         [0128]    Also, in the above explanation, the reference frequency of the reception band of terminal  300 , the reference frequency of a unit band (i.e. SCH frequency position) and the reference frequency of an assignment unit band group have been explained as respective center frequencies. However, the present invention is not limited to this, and it is equally possible to use other frequency positions as the reference frequency. An essential requirement is that each reference frequency is determined such that the whole unit band is contained in the reception band of terminal  300  by adjusting the reference frequency of the reception band of terminal  300  to the reference frequency of the unit band and the whole assignment unit band group is contained in the reception band of terminal  300  by adjusting the reference frequency of the reception band of terminal  300  to the reference frequency of the assignment unit band group. 
         [0129]    Also, in the above explanation, MIB information of an additional assignment band is reported from base station  400  to terminal  300 . However, the present invention is not limited to this, and base station  400  may report only the difference between MIB in the initial access unit band and MIB in the additional assignment unit band. By this means, it is possible to reduce the signaling amount. 
         [0130]    Also, in the above explanation, MIB information is transmitted with a communication band moving instruction. However, the present invention is not limited to this, and it is equally possible to perform broadcasting to all terminals using, for example, the D-BCH of each unit band. By this means, at the stage of step S 1004 , terminal  300  can obtain MIB information in an additional assignment unit band. 
         [0131]    Also, an aggregation communication starting request is not always transmitted by a PUCCH in the initial access unit band. For example, base station  400  may transmit the aggregation communication starting request by a certain specific RACH preamble in the initial access unit band. 
       Other Embodiment 
       [0132]    (1) Here, an index attached to a resource block (RB) used as a base unit in scheduling and so on, will be explained. 
         [0133]    In Embodiment 2, terminal  300  receives a communication band moving instruction, SCH position, null carrier position and the MIB content in each unit band, from base station  400 . 
         [0134]    Here, as described above, the center frequency of the communication band of terminal  300  is moved to a position different from the position of SCH placed near the center of each unit band. That is, it follows that a null carrier is present in a position different from the center position of a frequency band in which an SCH is placed. 
         [0135]    Each RB is formed with a certain number of carriers without null carriers. Therefore, terminal  300  needs to redefine RB&#39;s using information obtained from base station  400 . 
         [0136]    Therefore, first, with the system frequency bandwidth read from the SCH position and MIB content in a certain unit band, terminal  300  virtually calculates the extension of PDCCH in the unit band. 
         [0137]    Next, terminal  300  checks whether or not a null carrier is present in other positions than the SCH center in the unit band. As a result, if there is a null carrier in a position apart from the SCH center, terminal  300  forms an RB using twelve subcarriers excluding the null carrier in the same way as other null carriers. 
         [0138]      FIG. 12  illustrates an RB form. NC 1  in  FIG. 12  represents a null carrier that is present in a position different from the SCH center. As shown in  FIG. 12 , similar to other null carriers, the null carrier that is present in a position different from the SCH center is removed from the RB-forming subcarriers to form RB&#39;s. 
         [0139]    Here, the extension of PDCCH is set in RB units. Then, the number of RB&#39;s included in the PDCCH corresponds to the system frequency bandwidth on a one-to-one basis. 
         [0140]    Therefore, terminal  300  recalculates the PDCCH extension calculated virtually (in RB units), taking into account the null carrier that is present in the position different from the SCH center, and determines the frequency band in which a PDCCH is finally placed. 
         [0141]    (2) Although example cases have been described above with Embodiments 1 to 4 where the present invention is implemented with hardware, the present invention can be implemented with software. 
         [0142]    Furthermore, each function block employed in the description of each of 
         [0143]    Embodiments 1 to 4 may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. “LSI” is adopted here but this may also be referred to as “IC,” “system LSI,” “super LSI,” or “ultra LSI” depending on differing extents of integration. 
         [0144]    Further, the method of circuit integration is not limited to LSI&#39;s, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells in an LSI can be regenerated is also possible. 
         [0145]    Further, if integrated circuit technology comes out to replace LSI&#39;s as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application of biotechnology is also possible. 
         [0146]    The disclosure of Japanese Patent Application No. 2008-201006, filed on Aug. 4, 2008, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
       INDUSTRIAL APPLICABILITY 
       [0147]    The base station, terminal, band assignment method and downlink data communication method of the present invention are effective to allow efficient band assignment.