Abstract:
A base station performs wireless communication with a terminal using a first frequency band which needs a license to use for wireless communication and a second frequency band which does not need the license to use for the wireless communication. The base station includes: a generator that generates a request signal for requesting data transmission of the terminal in the second frequency band and specifying a first transmission timing of the terminal; and a transmitter that transmits the request signal to the terminal, wherein the request signal includes information specifying a second transmission timing, which is a next transmission timing when the terminal does not perform data transmission at the first transmission timing and is specified by an offset from a reference timing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of International Application No. PCT/JP2015/061036, filed on Apr. 8, 2015 and designating the U.S., the entire contents of which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present invention relates to a base station, a terminal, a wireless communication system, a control method of the base station, and a control method of the terminal. 
       BACKGROUND 
       [0003]    In recent years, in a wireless communication system such as a mobile phone system, discussion is being conducted on the next generation wireless communication technology in order to further increase the speed and increase the capacity, etc. of wireless communication. For example, in a communication standard called LTE (Long Term Evolution), a technique of performing communication using a carrier wave in a frequency band that requires a license (LC: Licensed band Carrier) and a carrier wave in a frequency band that does not require a license (UC: Unlicensed band Carrier) is being studied. The technique is called LAA (Licensed Assisted Access). 
         [0004]    In LAA, when a terminal performs UL (Up Link) transmission to a base station in the unlicensed band, the base station transmits a UL grant for requiring data transmission to the terminal via a licensed band. The base station then executes LBT (Listen Before Talk) in the unlicensed band, for example, before the terminal performs transmission in UL. When the unlicensed band is detected idle, the base station examines whether to transmit a reservation signal to the unlicensed band until a transmission timing of the terminal, for example, in order that the terminal ensures the unlicensed band used for UL data transmission. Thus, the terminal can perform UL data transmission using the unlicensed band after a predetermined period of time from the UL grant. 
         [0005]    Non Patent Literature 1: 3GPP RANI Contribution R1-50186 
         [0006]    Incidentally, in the technique of the non patent literature, when a busy state of the unlicensed band continues and the terminal does not receive the reservation signal in the unlicensed band by the time of timing of the UL data transmission, the terminal cancels, for example, the UL data transmission. As a result, the transmission opportunity of data scheduled to be transmitted by the terminal is postponed until a predetermined period of time passes since the next UL grant transmitted from the terminal. Therefore, the throughput of data transmission in UL from the terminal to the base station may decrease. 
       SUMMARY 
       [0007]    According to an aspect of an embodiment of the invention, a base station performs wireless communication with a terminal using a first frequency band which needs a license to use for wireless communication and a second frequency band which does not need the license to use for the wireless communication. The base station includes: a generator that generates a request signal for requesting data transmission of the terminal in the second frequency band and specifying a first transmission timing of the terminal; and a transmitter that transmits the request signal to the terminal, wherein the request signal includes information specifying a second transmission timing, which is a next transmission timing when the terminal does not perform data transmission at the first transmission timing and is specified by an offset from a reference timing. 
         [0008]    The object and advantages of the embodiment will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0009]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the embodiment, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a diagram illustrating an example of a wireless communication system; 
           [0011]      FIG. 2  is a diagram illustrating an example of an operation of a wireless communication system according to a first embodiment; 
           [0012]      FIG. 3  is a diagram illustrating an example of the operation of the wireless communication system according to the first embodiment; 
           [0013]      FIG. 4  is a block diagram illustrating an example of a base station according to the first embodiment; 
           [0014]      FIG. 5  is a block diagram illustrating an example of a terminal according to the first embodiment; 
           [0015]      FIG. 6  is a flowchart illustrating an example of an operation of the base station according to the first embodiment; 
           [0016]      FIG. 7  is a flowchart illustrating an example of an operation of the terminal according to the first embodiment; 
           [0017]      FIG. 8  is a flowchart illustrating an example of an operation of a base station according to a second embodiment; 
           [0018]      FIG. 9  is a flowchart illustrating an example of an operation of a terminal according to the second embodiment; 
           [0019]      FIG. 10  is a diagram illustrating an example of an operation of a wireless communication system according to a third embodiment; 
           [0020]      FIG. 11  is a block diagram illustrating an example of a terminal according to the third embodiment; 
           [0021]      FIG. 12  is a flowchart illustrating an example of an operation of a base station according to the third embodiment; 
           [0022]      FIG. 13  is a flowchart illustrating an example of an operation of the terminal according to the third embodiment; 
           [0023]      FIG. 14  is a flowchart illustrating an example of the operation of the terminal according to the third embodiment; and 
           [0024]      FIG. 15  is a diagram illustrating an example of a wireless communication device that implements a function of the base station or of the terminal. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Exemplary embodiments of the base station, the terminal, the wireless communication system, the control method of the base station, and the control method of the terminal disclosed in the present application will be explained in detail below with reference to the accompanying drawings. It is to be noted that the embodiments below are not intended to limit the disclosed technology. Moreover, the embodiments can be combined appropriately without inconsistencies in processing contents. 
       [a] First Embodiment 
       [0026]    Wireless Communication System  10   
         [0027]      FIG. 1  is a diagram illustrating an example of a wireless communication system  10 . The wireless communication system  10  includes a base station  20 , a base station  22 , and terminals  30   a  to  30   f . Hereinafter, when the terminals  30   a  to  30   f  are generically referred to without discrimination, they are referred to as terminal  30 . The base station  20  performs wireless communication based on, for example, LTE. The base station  20  is, for example, eNB (evolved Node B) in the LTE. The terminal  30  is, for example, UE (User Equipment) in the LTE. The terminal  30  belongs to a cell managed by the base station  20 , and performs communication with the base station  20  in the cell. In the following explanation, the base station  20  and the terminal  30  may be described as an LTE system. 
         [0028]    The base station  22  is, for example, a base station that belongs to a system different from the LTE system to which the base station  20  belongs. The base station  22  is, for example, a base station that belongs to an LTE system of a business operator different from the LTE system to which the base station  20  belongs, or a base station that belongs to other communication system such as a wireless LAN system. 
         [0029]    The base station  20  performs wireless communication with the terminal  30  in the cell by using a first band dedicated to the LTE system to which the base station  20  belongs and a second band shared between the LTE system to which the base station  20  belongs and the other communication system. The first band is, for example, an LC in 2 GHz band. The second band is, for example, a UC in 5 GHz band. Hereinafter, the first band is called a licensed band, and the second band is called an unlicensed band. 
         [0030]    In the LTE system to which the base station  20  belongs, the first band is allocated to, for example, PCC (Primary Component Carrier), and the second band is allocated to, for example, SCC (Secondary Component Carrier). In the present embodiment, the first band is a band dedicated to the LTE system to which the base station  20  belongs, and the second band is a shared band shared between the LTE system to which the base station  20  belongs and other communication system to which the base station  22  belongs. 
         [0031]    Reference sign  21  in  FIG. 1  indicates a range in which a radio wave transmitted from an arbitrary device reaches the base station  20  at an intensity determined to be busy by a carrier sense of the base station  20 . Reference sign  23  indicates a range in which a radio wave transmitted from an arbitrary device reaches the base station  22  at an intensity determined to be busy by a carrier sense of the base station  22 . 
         [0032]    When UL data transmission using the unlicensed band is to be requested to the terminal  30 , the base station  20  transmits the UL grant including resource information used for the UL data transmission to the terminal  30  in the licensed band. The UL grant is an example of a request signal for requesting the terminal  30  to transmit data to the base station  20 . The base station  20  then executes LBT in the unlicensed band at a timing earlier than the timing of UL data transmission by the terminal  30 . When the unlicensed band is detected idle, the base station  20  transmits a permission signal to the unlicensed band. In the present embodiment, the permission signal is, for example, a CTS (Clear to Send) signal. When detecting the permission signal in the unlicensed band, the terminal  30  having received the UL grant performs UL data transmission using the resource of the unlicensed band specified by the UL grant. 
         [0033]    Operation of Wireless Communication System  10   
         [0034]    An example of the operation when the terminal  30  performs data transmission to the base station  20  in the unlicensed band according to an instruction from the base station  20  will be explained next with reference to  FIG. 2  and  FIG. 3 .  FIG. 2  and  FIG. 3  are diagrams illustrating an example of the operation of the wireless communication system  10  according to the first embodiment.  FIG. 2  represents a case where the unlicensed band is detected idle upon execution of LBT by the base station  20 , and  FIG. 3  represents a case where the unlicensed band is detected busy upon execution of LBT by the base station  20 . 
         [0035]    As illustrated in  FIG. 2  and  FIG. 3 , the upper part represents the operation of the base station  20 , and the lower part represents the operations of the terminals  30   a  to  30   f . The horizontal axis in  FIG. 2  and  FIG. 3  indicates the flow of time, and each of t 1  to t 8  indicates, for example, a period (for example, 1 millisecond) of each subframe in LTE. The unlicensed band (UC) is divided into a plurality of subbands, for example, as illustrated in the lower parts of  FIG. 2  and  FIG. 3 . In the present embodiment, the unlicensed band is, for example, 20 MHz, and is divided into, for example, four subbands for each 5 MHz. 
         [0036]    For example, as illustrated in  FIG. 2 , when a data transmission request to the terminal  30   a  and the terminal  30   b  occurs, the base station  20  creates a UL grant  40 - 1  for requesting data transmission in UL. The base station  20  then transmits the created UL grant  40 - 1  to the terminal  30   a  and the terminal  30   b  in the licensed band (LC). Likewise, when a data transmission request to the terminal  30   c  and the terminal  30   d  occurs, the base station  20  transmits a UL grant  40 - 2  to the terminal  30   c  and the terminal  30   d  in the licensed band. Similarly, when a data transmission request to the terminal  30   e  and the terminal  30   f  occurs, the base station  20  transmits a UL grant  40 - 3  to the terminal  30   e  and the terminal  30   f  in the licensed band. 
         [0037]    In the example illustrated in  FIG. 2 , the base station  20  transmits, for example, the UL grant  40 - 1  in a subframe period t 1 , transmits the UL grant  40 - 2  in a subframe period t 2 , and transmits the UL grant  40 - 3  in a subframe period t 3 . When receiving the permission signal in the unlicensed band by the time of a first transmission timing after a predetermined time since the reception of the UL grant  40 , the terminal  30  transmits data to the base station  20  in the unlicensed band at the first timing. In the present embodiment, the first transmission timing is a timing after, for example, four subframes from the subframe in which the terminal  30  receives the UL grant  40 . 
         [0038]    In the present embodiment, each of UL grants  40  includes subband information, offset, and time limit information. The subband information included in the UL grant  40  indicates a subband of the unlicensed band used when the terminal  30  having received the UL grant  40  performs UL data transmission. The offset is information for specifying a second transmission timing at which the terminal  30  performs next data transmission when the terminal  30  does not receive the permission signal by the time of the first transmission timing after the reception of the UL grant  40  and receives the permission signal after the first transmission timing. In the offset, the second transmission timing is specified, for example, as a relative time from the first transmission timing. In the present embodiment, the second transmission timing is specified, for example, in units of subframes. 
         [0039]    The time limit information included in the UL grant  40  indicates a time limit for the terminal  30  having received the UL grant  40  to wait for a permission signal. In the present embodiment, the time limit information is specified in units of subframes based on, for example, the subframe in which the UL grant  40  is transmitted. In the present embodiment, the time limit specified by the time limit information is, for example, a timing after 10 subframes from the subframe in which the UL grant  40  is transmitted. The time limit information may be specified by the number of times that the trial of UL retransmission is permitted. 
         [0040]    In the present embodiment, the base station  20  allocates the period of data transmission in UL to each of the terminals  30  in units of subframes. When allocating the same subband to the UL data transmission performed by a plurality of terminals  30 , the base station  20  performs scheduling so that data is transmitted from each of the terminals  30  in continuous subframes. However, the unlicensed band is also used in a communication system different from the LTE system to which the base station  20  belongs. Therefore, there are cases where the period that can be continuously occupied for data transmission is limited. In this case, the base station  20  performs scheduling so that data is transmitted from each of the terminals  30  in continuous subframes within the limits. 
         [0041]    The base station  20  then transmits the UL grant  40 , in the respective continuous subframes, to each of the terminals  30  that perform data transmission using the same subband. In the example of  FIG. 2 , for example, the base station  20  allocates same subband  1  to the UL data transmission performed by the terminals  30   a ,  30   c , and  30   e , and allocates same subband  2  to the UL data transmission performed by the terminals  30   b ,  30   d , and  30   f . The base station  20  then transmits the UL grants  40 - 1  to  40 - 3  in continuous subframe periods t 1  to t 3 , respectively. 
         [0042]    After the UL grant  40  is transmitted, the base station  20  executes LBT in the unlicensed band after a predetermined time (for example, after three subframes) has passed since the transmission of the UL grant  40 . In the LBT, when it is confirmed that an idle state of the unlicensed band continues for a predetermined back-off period  41 , the base station  20  transmits a permission signal  42  to all the subbands in the unlicensed band. For example, the permission signal  42  is transmitted to the unlicensed band with a length so that an end timing of a period  43  of SIFS (Short Inter Frame Space) after transmission of the permission signal  42  is ended is a timing of the boundary between the subframe in which the permission signal  42  is transmitted and the next subframe. 
         [0043]    When receiving the UL grant  40 , the terminal  30  acquires subband information, offset, and time limit information of the unlicensed band used for UL data transmission from the UL grant  40 . Then, when receiving the permission signal  42  in the unlicensed band for a period before the first transmission timing after the reception of the UL grant  40 , the terminal  30  transmits data in the subband specified by the UL grant  40  at the first transmission timing. 
         [0044]    In the example illustrated in  FIG. 2 , the terminals  30   a  and  30   b  receive the permission signal  42  in a subframe period t 4  for a period before a subframe period t 5  which is the first transmission timing after the predetermined period since the reception of the UL grant  40 - 1 . Then, the terminal  30   a  transmits UL data  44 - 1  in the subframe period t 5 , and the terminal  30   b  transmits UL data  45 - 1  in the subframe period t 5 . Likewise, the terminals  30   c  and  30   d  receive the permission signal  42  for a period before a subframe period t 6  after the predetermined period since the reception of the UL grant  40 - 2 . Then, the terminal  30   c  transmits UL data  44 - 2  in the subframe period t 6 , and the terminal  30   d  transmits UL data  45 - 2  in the subframe period t 6 . Similarly, the terminals  30   e  and  30   f  receive the permission signal  42  for a period before a subframe period t 7  after the predetermined period since the reception of the UL grant  40 - 3 . Then, the terminal  30   e  transmits UL data  44 - 3  in the subframe period t 7 , and the terminal  30   f  transmits UL data  45 - 3  in the subframe period t 7 . 
         [0045]    On the other hand, for example, as illustrated in  FIG. 3 , when other signal  46  is transmitted to the unlicensed band in the subframe period t 4  after a predetermined time from the transmission of the UL grant  40 , the base station  20  detects that the unlicensed band is busy by the LBT. The base station  20  then continues the LBT in the unlicensed band. For example, as illustrated in  FIG. 3 , when the unlicensed band is detected idle in the subframe period t 5 , the base station  20  transmits the permission signal  42  to the unlicensed band after confirming continuation of the idle state for the predetermined back-off period  41 . 
         [0046]    In the example of  FIG. 3 , the terminals  30   a  and  30   b  do not receive the permission signal  42  for a period before the subframe period t 5  including the first transmission timing after the predetermined period since the reception of the UL grant  40 - 1 . Then, the terminals  30   a  and  30   b  receive the permission signal  42  in the subframe period t 5  including the first transmission timing after the predetermined period since the reception of the UL grant  40 - 1 . 
         [0047]    Therefore, the terminal  30  transmits data to the base station  20  at the second timing at which the time specified by the offset acquired from the UL grant  40 - 1  passes based on the first transmission timing after the predetermined period since the reception of the UL grant  40 - 1 . In the example of  FIG. 3 , each of the UL grants  40  includes offset for specifying a period of three subframes. Therefore, the terminals  30   a  and  30   b  specify a subframe period t 8 , as the second transmission timing, after the period of the three subframes from the subframe period t 5  based on the subframe period t 5  after the predetermined period since the reception of the UL grant  40 - 1 . Then, the terminal  30   a  transmits the UL data  44 - 1  in the subframe period t 8 , and the terminal  30   b  transmits the UL data  45 - 1  in the subframe period t 8 . 
         [0048]    Here, in the present embodiment, the value of the offset is set to the same value as the number of subframes continuously allocated as UL data transmission timing in the same subband. In the example of  FIG. 3 , the number of subframes continuously allocated as the UL data transmission timing in the same subband is 3. Therefore, in the example of  FIG. 3 , the value of the offset is set to, for example, 3. In the example of  FIG. 3 , although the subframe continuously allocated as the UL data transmission timing in the same subband is allocated to each separate terminal  30 , the continuous subframes may be allocated to one terminal  30 . 
         [0049]    In the example of  FIG. 3 , the terminals  30   c  to  30   f  receive the permission signal  42  for a period before the subframe period after the predetermined period since the reception of the UL grant  40 . Therefore, the terminals  30   c  to  30   f  do not postpone the transmission timing and transmit the UL data  44  and  45  in the subframe period after the predetermined period since the reception of the UL grant  40 . 
         [0050]    In this way, when not receiving the permission signal  42  by the time of the first transmission timing after the reception of the UL grant  40 , each terminal  30  transmits data at the second transmission timing in which the period specified by the offset in the UL grant  40  has passed from the first transmission timing. As a result, when the terminal  30  does not receive the permission signal  42  by the time of the first transmission timing after the predetermined time since the reception of the UL grant  40 , the terminal  30  can perform UL data transmission even if the transmission opportunity of the terminal  30  is not specified again by retransmission of the UL grant  40 . Therefore, the terminal  30  can obtain the opportunity of UL data transmission earlier than the timing after the predetermined time from the retransmission of the UL grant  40 . This makes it possible to improve the throughput in UL. 
         [0051]    In the present embodiment, the value of the offset is set to the same value as the number of subframes continuously allocated as UL data transmission timing in the same subband. As a result, it is possible to avoid the data transmission timing from overlapping with the transmission timing of other terminal  30  even if data transmission is performed at the second transmission timing after the elapse of the period specified by the offset since the first transmission timing after the reception of the UL grant  40 . Therefore, the base station  20  can more reliably receive the data transmitted from the terminal  30 . 
         [0052]    Moreover, in the present embodiment, the value of the offset is set to the same value as the number of subframes continuously allocated as UL data transmission timing in the same subband. As a result, the timing of data transmission of the terminal  30  that does not receive the permission signal by the time of the first transmission timing after the reception of the UL grant  40  is the timing of the next subframe of the continuously allocated subframes. As a result, when the timing of data transmission is postponed, respective data transmission timings are allocated to the continuous subframes. Accordingly, it is possible to prevent the start of data transmission by other communication device before the start of transmission of the postponed data in the unlicensed band. 
         [0053]    Base Station  20   
         [0054]      FIG. 4  is a block diagram illustrating an example of the base station  20  according to the first embodiment. The base station  20  includes a packet generating unit  200 , a MAC (Media Access Control) scheduling unit  201 , an uplink managing unit  202 , and an RRC (Radio Resource Control) control unit  203 . The base station  20  also includes a MAC•RLC (Radio Link Control) processing unit  204  and a carrier sense unit  205 . Furthermore, the base station  20  includes a licensed band transmitting unit  210 , an unlicensed band transmitting unit  220 , an unlicensed band receiving unit  230 , a licensed band receiving unit  240 , an antenna  216 , an antenna  226 , an antenna  235 , and an antenna  245 . In the present embodiment, although the antenna  216 , the antenna  226 , the antenna  235 , and the antenna  245  are implemented by separate antennas, these antennas may be implemented by a single antenna as other example. 
         [0055]    The licensed band receiving unit  240  performs processing of decoding data from the signal received in the licensed band. The licensed band receiving unit  240  includes a decoding unit  241 , a demodulating unit  242 , an FFT processing unit  243 , and a wireless processing unit  244 . 
         [0056]    The wireless processing unit  244  performs wireless processing on the signal received via the antenna  245 . The wireless processing performed by the wireless processing unit  244  includes, for example, processing of converting the frequency of the reception signal from the frequency of the licensed band to the frequency of baseband. The wireless processing unit  244  outputs the reception signal subjected to the wireless processing to the FFT processing unit  243 . 
         [0057]    The FFT processing unit  243  performs FFT (Fast Fourier Transform) processing on the reception signal output from the wireless processing unit  244 . As a result, the reception signal whose frequency is converted from the licensed band to the baseband is converted from a time domain to a frequency domain. The FFT processing unit  243  outputs the reception signal subjected to the FFT processing to the demodulating unit  242 . 
         [0058]    The demodulating unit  242  demodulates the reception signal output from the FFT processing unit  243 . The demodulating unit  242  then outputs the demodulated reception signal to the decoding unit  241 . The decoding unit  241  decodes the reception signal output from the demodulating unit  242 . The decoding unit  241  then outputs the decoded data to the MAC•RLC processing unit  204 . 
         [0059]    The unlicensed band receiving unit  230  performs processing of decoding data from the signal received in the unlicensed band. The unlicensed band receiving unit  230  includes a decoding unit  231 , a demodulating unit  232 , an FFT processing unit  233 , and a wireless processing unit  234 . 
         [0060]    The wireless processing unit  234  performs wireless processing on the signal received via the antenna  235 . The wireless processing performed by the wireless processing unit  234  includes, for example, processing of converting the frequency of the reception signal from the frequency of the unlicensed band to the frequency of baseband. The wireless processing unit  234  outputs the reception signal subjected to the wireless processing to the FFT processing unit  233  and the carrier sense unit  205 . 
         [0061]    The FFT processing unit  233  performs FFT processing on the reception signal output from the wireless processing unit  234 . As a result, the reception signal whose frequency is converted from the unlicensed band to the baseband is converted from the time domain to the frequency domain. The FFT processing unit  233  outputs the reception signal subjected to the FFT processing to the demodulating unit  232 . 
         [0062]    The demodulating unit  232  demodulates the reception signal output from the FFT processing unit  233 . The demodulating unit  232  then outputs the demodulated reception signal to the decoding unit  231 . The decoding unit  231  decodes the reception signal output from the demodulating unit  232 . The decoding unit  241  then outputs the decoded data to the MAC•RLC processing unit  204 . 
         [0063]    The carrier sense unit  205  measures interference power in the unlicensed band based on the reception signal output from the wireless processing unit  234 , and determines whether the unlicensed band is idle or busy based on the measurement result. The carrier sense unit  205  then outputs the determination result to the uplink managing unit  202 . The carrier sense unit  205  receives, for example, timing information on the start and the end of the carrier sense and information on a predetermined idle period or the like from the uplink managing unit  202 , and sends back information as to whether it can be determined as idle by the time of delimiter timing to the uplink managing unit  202 . 
         [0064]    The MAC•RLC processing unit  204  performs processing in a MAC layer and processing in an RLC layer based on the data output from the decoding unit  231  and the decoding unit  241 . The MAC•RLC processing unit  204  outputs the data obtained through the processing in the layers to, for example, a higher-level device of the base station  20 . Moreover, the MAC•RLC processing unit  204  outputs the control information included in the data obtained through the processing of the layers to the RRC control unit  203 . 
         [0065]    The RRC control unit  203  performs wireless resource control based on the control information output from the MAC•RLC processing unit  204 . The RRC control unit  203  generates control information based on the wireless resource control and outputs the generated control information to the uplink managing unit  202 . 
         [0066]    The uplink managing unit  202  controls the MAC layer based on the control information output from the RRC control unit  203 . When a data transmission request to the terminal  30  occurs, the uplink managing unit  202  creates a UL grant to request data transmission in UL. The uplink managing unit  202  then transmits the UL grant to the terminal  30  by outputting the control signal including the created UL grant to a multiplexing unit  213  which is explained later. 
         [0067]    The UL grant includes subband information, offset, and time limit information which are used for data transmission by the terminal  30 . In the present embodiment, the offset specifies a second transmission timing as a relative time from the first transmission timing using, for example, a value of 2 bits. For example, when the value of 2 bits is “01”, the offset indicates that the second transmission timing is a timing after one subframe from the first transmission timing. For example, when the value of 2 bits is “10”, the offset indicates that the second transmission timing is a timing after two subframes from the first transmission timing. For example, when the value of 2 bits is “11”, the offset indicates that the second transmission timing is a timing after three subframes from the first transmission timing. In addition, for example, when the value of 2 bits is “00”, the offset indicates that the terminal  30  cancels data transmission when the terminal  30  does not receive the permission signal by the time of the first transmission timing after the reception of the UL grant  40 . 
         [0068]    For example, a case is considered in which the terminal  30  receives the UL grant  40  in which “11” is set as the offset, does not receive the permission signal by the time of the first transmission timing after the reception of the UL grant  40 , and receives the permission signal after seven subframes from the first transmission timing. In this case, the terminal  30  calculates a remainder obtained by dividing, for example, 7 by 3 as the value of the offset, and subtracts the obtained value from 3 as the value of the offset. The terminal  30  then specifies a period of subframe after the remaining number of subframe periods as the second transmission timing. Then, the terminal  30  performs the UL data transmission at the specified second transmission timing. Because the remainder obtained by dividing 7 by 3 being the offset value is 1, the terminal  30  performs UL data transmission in, for example, the period of the subframe after two subframes from the subframe in which the permission signal is received. 
         [0069]    In the present embodiment, either one of two periods is specified in the time limit information according to, for example, the value of 1 bit. For example, when the value of 1 bit is “0”, the time limit information indicates that the timing after five subframes from the first transmission timing is a time limit. For example, when the value of 1 bit is “1”, the time limit information indicates that the timing after 10 subframes from the first transmission timing is a time limit. In the present embodiment, the time limit information is valid when a value other than “00” is set in the offset. It may be configured that an arbitrary value can be specified using 3 bits or more as the offset and the time limit information. 
         [0070]    The uplink managing unit  202  transmits the UL grant to the terminal  30 , thereafter generates the permission signal, and outputs the generated permission signal to a multiplexing unit  223  which is explained later. The uplink managing unit  202  then causes the carrier sense unit  205  to execute LBT of the unlicensed band before UL data transmission timing by the terminal  30 . Then, when the unlicensed band is detected idle, the carrier sense unit  205  instructs an IFFT processing unit  224 , explained later, to transmit the transmission signal. Accordingly, the permission signal is transmitted to the unlicensed band. 
         [0071]    The packet generating unit  200  generates a packet including user data output from a higher-level device. The packet generating unit  200  then outputs the generated packet to the MAC scheduling unit  201 . 
         [0072]    The MAC scheduling unit  201  performs scheduling in the MAC layer on the packet output from the packet generating unit  200 . The MAC scheduling unit  201  then controls the output of the packet generated by the packet generating unit  200  to the licensed band transmitting unit  210  or to the unlicensed band transmitting unit  220  based on the result of the scheduling. 
         [0073]    The licensed band transmitting unit  210  performs processing of data transmission in the licensed band. The licensed band transmitting unit  210  includes an encoding unit  211 , a modulating unit  212 , the multiplexing unit  213 , an IFFT (Inverse FFT) processing unit  214 , and a wireless processing unit  215 . 
         [0074]    The encoding unit  211  encodes the data of the packet output from the MAC scheduling unit  201 . The encoding unit  211  then outputs the encoded data of the packet to the modulating unit  212 . The modulating unit  212  modulates the data output from the encoding unit  211 . The modulating unit  212  then outputs the modulated signal to the multiplexing unit  213 . 
         [0075]    The multiplexing unit  213  multiplexes the control signal including the UL grant etc. output from the uplink managing unit  202  and the signal output from the modulating unit  212 . The multiplexing unit  213  then outputs the multiplexed transmission signal to the IFFT processing unit  214 . 
         [0076]    The IFFT processing unit  214  performs IFFT processing on the transmission signal output from the multiplexing unit  213 . As a result, the transmission signal output from the multiplexing unit  213  is converted from the frequency domain to the time domain. The IFFT processing unit  214  outputs the transmission signal subjected to the IFFT processing to the wireless processing unit  215 . 
         [0077]    The wireless processing unit  215  performs wireless processing on the transmission signal output from the IFFT processing unit  214 . The wireless processing performed by the wireless processing unit  215  includes, for example, processing of converting the frequency of the transmission signal from the frequency of the baseband to the frequency of the licensed band. The wireless processing unit  215  transmits the transmission signal subjected to the wireless processing from the antenna  216 . 
         [0078]    The unlicensed band transmitting unit  220  performs processing of transmitting data in the unlicensed band. The unlicensed band transmitting unit  220  includes an encoding unit  221 , a modulating unit  222 , the multiplexing unit  223 , the IFFT processing unit  224 , and a wireless processing unit  225 . 
         [0079]    The encoding unit  221  encodes the data of the packet output from the MAC scheduling unit  201 . The encoding unit  221  then outputs the encoded data of the packet to the modulating unit  222 . The modulating unit  222  modulates the data of the packet output from the encoding unit  221 . The modulating unit  222  then outputs the modulated signal to the multiplexing unit  223 . 
         [0080]    The multiplexing unit  223  multiplexes the control signal including the permission signal etc. output from the uplink managing unit  202  and the signal output from the modulating unit  222 . The multiplexing unit  223  then outputs the multiplexed transmission signal to the IFFT processing unit  224 . 
         [0081]    The IFFT processing unit  224  performs IFFT processing on the transmission signal output from the multiplexing unit  223 . As a result, the transmission signal output from the multiplexing unit  223  is converted from the frequency domain to the time domain. When transmission of the transmission signal is instructed from the carrier sense unit  205 , the IFFT processing unit  224  outputs the transmission signal subjected to the IFFT processing to the wireless processing unit  225 . 
         [0082]    The wireless processing unit  225  performs wireless processing on the transmission signal output from the IFFT processing unit  224 . The wireless processing performed by the wireless processing unit  225  includes, for example, processing of converting the frequency of the transmission signal from the frequency of the baseband to the frequency of the unlicensed band. The wireless processing unit  225  transmits the transmission signal subjected to the wireless processing from the antenna  226 . 
         [0083]    Terminal  30   
         [0084]      FIG. 5  is a block diagram illustrating an example of the terminal  30  according to the first embodiment. The terminal  30  includes an antenna  300 , a decoding unit  301 , an RRC processing unit  304 , an uplink managing unit  305 , an encoding/modulating unit  306 , and a packet generating unit  307 . The terminal  30  also includes a licensed band receiving unit  310 , an unlicensed band receiving unit  320 , an unlicensed band transmitting unit  330 , and a licensed band transmitting unit  340 . 
         [0085]    The antenna  300  may be separately provided in each of the licensed band receiving unit  310 , the unlicensed band receiving unit  320 , the unlicensed band transmitting unit  330 , and the licensed band transmitting unit  340 . 
         [0086]    The licensed band receiving unit  310  performs processing of decoding data from the signal received in the licensed band. The licensed band receiving unit  310  includes a wireless processing unit  311 , an FFT processing unit  312 , and a demodulating unit  315 . 
         [0087]    The wireless processing unit  311  performs wireless processing on the signal received via the antenna  300 . The wireless processing performed by the wireless processing unit  311  includes, for example, processing of converting the frequency of the reception signal from the frequency of the licensed band to the frequency of baseband. The wireless processing unit  311  outputs the reception signal subjected to the wireless processing to the FFT processing unit  312 . 
         [0088]    The FFT processing unit  312  performs FFT processing on the reception signal output from the wireless processing unit  311 . As a result, the reception signal output from the wireless processing unit  311  is converted from the time domain to the frequency domain. The FFT processing unit  312  outputs the reception signal subjected to the FFT processing to the demodulating unit  315 . 
         [0089]    The demodulating unit  315  demodulates the reception signal by performing equalization processing on the signal output from the FFT processing unit  312 . The demodulating unit  315  then outputs the demodulated reception signal to the decoding unit  301 . The data decoded from the reception signal demodulated by the licensed band receiving unit  310  includes the control signal including the UL grant etc. 
         [0090]    The unlicensed band receiving unit  320  performs processing of demodulating data from the signal received in the unlicensed band. The unlicensed band receiving unit  320  includes a wireless processing unit  321 , an FFT processing unit  322 , and a demodulating unit  325 . 
         [0091]    The wireless processing unit  321  performs wireless processing on the signal received via the antenna  300 . The wireless processing performed by the wireless processing unit  321  includes, for example, processing of converting the frequency of the reception signal from the frequency of the unlicensed band to the frequency of the baseband. The wireless processing unit  321  outputs the reception signal subjected to the wireless processing to the FFT processing unit  322 . 
         [0092]    The FFT processing unit  322  performs FFT processing on the reception signal output from the wireless processing unit  321 . As a result, the reception signal output from the wireless processing unit  321  is converted from the time domain to the frequency domain. The FFT processing unit  322  then outputs the reception signal subjected to the FFT processing to the demodulating unit  325 . 
         [0093]    The demodulating unit  325  demodulates the reception signal by performing equalization processing on the signal output from the FFT processing unit  322 . The demodulating unit  325  then outputs the demodulated reception signal to the decoding unit  301 . The data decoded from the reception signal demodulated by the unlicensed band receiving unit  320  includes the control signal including the permission signal etc. 
         [0094]    The decoding unit  301  decodes the user data and the control signal from the reception signals output from the licensed band receiving unit  310  and the unlicensed band receiving unit  320 . The decoding unit  301  then outputs the decoded user data to an application processor (not illustrated) that performs processing based on, for example, the received data. In addition, the decoding unit  301  outputs the decoded control signal to the RRC processing unit  304  and the uplink managing unit  305 . The control signal output to the uplink managing unit  305  includes the UL grant and the permission signal etc. 
         [0095]    The RRC processing unit  304  performs wireless resource control based on the control information output from the decoding unit  301 . The RRC processing unit  304  generates control information based on the wireless resource control and outputs the generated control information to the uplink managing unit  305 . 
         [0096]    The uplink managing unit  305  controls UL based on the control information output from the RRC processing unit  304  and the control signal output from the decoding unit  301 . For example, when a UL grant is output from the decoding unit  301 , the uplink managing unit  305  acquires subband information, offset, and time limit information of the unlicensed band allocated to UL data transmission from the UL grant. 
         [0097]    The uplink managing unit  305  determines whether the permission signal is output from the decoding unit  301  for a period before the first transmission timing after the predetermined period since the output of the UL grant from the decoding unit  301 . When the permission signal is output from the decoding unit  301  for a period before the first transmission timing after the predetermined period since the output of the UL grant from the decoding unit  301 , the uplink managing unit  305  instructs the encoding/modulating unit  306  to perform data transmission at the first transmission timing. 
         [0098]    On the other hand, when the permission signal is not output from the decoding unit  301  for a period before the first transmission timing after the output of the UL grant from the decoding unit  301 , the uplink managing unit  305  determines whether the permission signal is output from the decoding unit  301  before the time limit indicated by the time limit information. When the permission signal is output from the decoding unit  301  before the time limit indicated by the time limit information, the uplink managing unit  305  specifies the second transmission timing at which UL data transmission is performed based on the first transmission timing after the reception of the UL grant. The uplink managing unit  305  then instructs the encoding/modulating unit  306  to perform data transmission at the specified second transmission timing. 
         [0099]    For example, a case is considered in which the UL grant  40  including the offset for specifying the period of three subframes is received and the permission signal is received after seven subframes from the first transmission timing. In this case, for example, the uplink managing unit  305  specifies the timing after nine subframes from the first transmission timing as the second transmission timing. 
         [0100]    The uplink managing unit  305  outputs resource allocation information used for the UL data transmission to a frequency mapping unit  333  and a frequency mapping unit  343 , which are explained later. 
         [0101]    The packet generating unit  307  generates a packet including the user data output from, for example, the application processor (not illustrated). The packet generating unit  307  then outputs the generated packet to the encoding/modulating unit  306 . The encoding/modulating unit  306  performs encoding and modulation processing on the packet output from the packet generating unit  307 . The encoding/modulating unit  306  then outputs the transmission signal subjected to the encoding and modulation processing to the unlicensed band transmitting unit  330  or to the licensed band transmitting unit  340  according to the instruction from the uplink managing unit  305 . 
         [0102]    The licensed band transmitting unit  340  performs processing of transmitting data in the licensed band. The licensed band transmitting unit  340  includes a wireless processing unit  341 , an IFFT processing unit  342 , a frequency mapping unit  343 , an FFT processing unit  344 , and a multiplexing unit  345 . 
         [0103]    The multiplexing unit  345  multiplexes the control signal output from the uplink managing unit  305  and the transmission signal output from the encoding/modulating unit  306 . The multiplexing unit  345  then outputs the multiplexed transmission signal to the FFT processing unit  344 . The FFT processing unit  344  performs FFT processing on the transmission signal output from the multiplexing unit  345 . As a result, the transmission signal output from the multiplexing unit  345  is converted from the time domain to the frequency domain. The FFT processing unit  344  outputs the transmission signal subjected to the FFT processing to the frequency mapping unit  343 . 
         [0104]    The frequency mapping unit  343  performs frequency mapping on the transmission signal output from the FFT processing unit  344  based on the UL resource allocation information output from the uplink managing unit  305 . The frequency mapping unit  343  then outputs the transmission signal subjected to the frequency mapping to the IFFT processing unit  342 . 
         [0105]    The IFFT processing unit  342  performs IFFT processing on the transmission signal output from the frequency mapping unit  343 . As a result, the transmission signal output from the frequency mapping unit  343  is converted from the frequency domain to the time domain. The IFFT processing unit  342  outputs the transmission signal subjected to the IFFT processing to the wireless processing unit  341 . 
         [0106]    The wireless processing unit  341  performs wireless processing on the transmission signal output from the IFFT processing unit  342 . The wireless processing performed by the wireless processing unit  341  includes, for example, processing of converting the frequency of the transmission signal from the frequency of the baseband to the frequency of the licensed band. The wireless processing unit  341  transmits the transmission signal subjected to the wireless processing via the antenna  300 . 
         [0107]    The unlicensed band transmitting unit  330  performs processing of transmitting data in the unlicensed band. The unlicensed band transmitting unit  330  includes a wireless processing unit  331 , an IFFT processing unit  332 , the frequency mapping unit  333 , an FFT processing unit  334 , and a multiplexing unit  335 . 
         [0108]    The multiplexing unit  335  multiplexes the control signal output from the uplink managing unit  305  and the signal output from the encoding/modulating unit  306 . The multiplexing unit  335  then outputs the multiplexed transmission signal to the FFT processing unit  334 . The FFT processing unit  334  performs FFT processing on the transmission signal output from the multiplexing unit  335 . As a result, the transmission signal output from the multiplexing unit  335  is converted from the time domain to the frequency domain. The FFT processing unit  334  outputs the transmission signal subjected to the FFT processing to the frequency mapping unit  333 . 
         [0109]    The frequency mapping unit  333  performs frequency mapping on the transmission signal output from the FFT processing unit  334  based on the UL resource allocation information output from the uplink managing unit  305 . The frequency mapping unit  333  then outputs the transmission signal subjected to the frequency mapping to the IFFT processing unit  332 . 
         [0110]    The IFFT processing unit  332  performs IFFT processing on the transmission signal output from the frequency mapping unit  333 . As a result, the transmission signal output from the frequency mapping unit  333  is converted from the frequency domain to the time domain. The IFFT processing unit  332  outputs the transmission signal subjected to the IFFT processing to the wireless processing unit  331 . 
         [0111]    The wireless processing unit  331  performs wireless processing on the transmission signal output from the IFFT processing unit  332 . The wireless processing performed by the wireless processing unit  331  includes, for example, processing of converting the frequency of the transmission signal from the frequency of the baseband to the frequency of the unlicensed band. The wireless processing unit  331  transmits the transmission signal subjected to the wireless processing via the antenna  300 . 
         [0112]    Operation of Base Station  20   
         [0113]    The operation of the base station  20  will be explained next.  FIG. 6  is a flowchart illustrating an example of the operation of the base station  20  according to the first embodiment. 
         [0114]    First of all, the uplink managing unit  202  determines whether a data transmission request to the terminal  30  has occurred (S 100 ). When a data transmission request to the terminal  30  has occurred (Yes at S 100 ), the uplink managing unit  202  determines the value of the offset (S 101 ). The uplink managing unit  202  determines, for example, the number of continuous subframes to be allocated to data transmission in the same subband as the value of offset. 
         [0115]    Then, the uplink managing unit  202  creates time limit information (S 102 ). The uplink managing unit  202  then creates a UL grant that includes the determined offset and the created time limit information and also includes subband information of the unlicensed band allocated to the UL data transmission. Then, the uplink managing unit  202  determines whether it is a transmission timing of the UL grant (S 103 ). When the continuous subframes are to be allocated to the data transmission, the uplink managing unit  202  transmits the UL grant at each timing of the continuous subframes. 
         [0116]    When it is not a transmission timing of the UL grant (No at S 103 ), the uplink managing unit  202  executes the process illustrated at Step S 105 . Meanwhile, when it is a transmission timing of the UL grant (Yes at S 103 ), the uplink managing unit  202  transmits the UL grant to the terminal  30  via the licensed band transmitting unit  210  (S 104 ). The uplink managing unit  202  then determines whether it is a transmission timing of the permission signal (S 105 ). When a period of, for example, three subframes has passed from the subframe in which the UL grant is transmitted at Step S 104 , the uplink managing unit  202  determines that it is a transmission timing of the permission signal. 
         [0117]    When it is not a transmission timing of the permission signal (No at S 105 ), the uplink managing unit  202  again executes the process illustrated at Step S 103 . Meanwhile, when it is a transmission timing of the UL grant (Yes at S 105 ), the uplink managing unit  202  outputs the permission signal to the multiplexing unit  223  and instructs the carrier sense unit  205  to perform carrier sense. The carrier sense unit  205  executes the carrier sense and determines whether the unlicensed band is idle (S 106 ). When the unlicensed band is idle (Yes at S 106 ), the carrier sense unit  205  instructs the IFFT processing unit  224  to transmit the transmission signal. As a result, the permission signal is transmitted to the unlicensed band (S 107 ). The uplink managing unit  202  then again executes the process illustrated at Step S 100 . 
         [0118]    Meanwhile, when the unlicensed band is busy (No at S 106 ), the uplink managing unit  202  refers to the time limit information including the UL grant to determine whether the time limit has passed (S 108 ). When the time limit has not passed (No at S 108 ), the uplink managing unit  202  again executes the process illustrated at Step S 106 . Meanwhile, when the time limit has passed (Yes at S 108 ), the uplink managing unit  202  cancels the transmission of the permission signal (S 109 ). The uplink managing unit  202  then again executes the process illustrated at Step S 100 . 
         [0119]    Operation of Terminal  30   
         [0120]    The operation of the terminal  30  will be explained next.  FIG. 7  is a flowchart illustrating an example of the operation of the terminal  30  according to the first embodiment. 
         [0121]    First of all, the uplink managing unit  305  determines whether the UL grant has been received in the licensed band (S 200 ). When the UL grant has been received (Yes at S 200 ), the uplink managing unit  305  acquires the offset and the time limit information from the received UL grant (S 201 ). 
         [0122]    Then, the uplink managing unit  305  determines whether the permission signal has been received (S 202 ). When the permission signal has not been received (No at S 202 ), the uplink managing unit  305  determines whether the time limit indicated by the time limit information acquired from the UL grant has passed (S 206 ). When the time limit has not passed (No at S 206 ), the uplink managing unit  305  again executes the process illustrated at Step S 202 . Meanwhile, when the time limit has passed (Yes at S 206 ), the uplink managing unit  305  cancels the UL data transmission instructed by the UL grant, and again executes the process illustrated at Step S 200 . 
         [0123]    When the permission signal has been received (Yes at S 202 ), the uplink managing unit  305  determines whether the reception timing of the permission signal is a timing earlier than the first transmission timing after the reception of the UL grant (S 203 ). When the reception timing of the permission signal is the timing earlier than the first transmission timing (Yes at S 203 ), the uplink managing unit  305  transmits the data in UL in the subframe of the first transmission timing (S 204 ). The uplink managing unit  305  then again executes the process illustrated at Step S 200 . 
         [0124]    When the reception timing of the permission signal is the timing later than the first transmission timing (No at S 203 ), the uplink managing unit  305  specifies the second transmission timing after the time specified by the offset from the first transmission timing. The uplink managing unit  305  then transmits the data in UL in the subframe of the specified second transmission timing (S 205 ). Then, the uplink managing unit  305  again executes the process illustrated at Step S 200 . 
         [0125]    Advantageous Effects of First Embodiment 
         [0126]    The first embodiment has been explained above. As is apparent from the explanation, according to the wireless communication system  10  of the present embodiment, the throughput of UL in the unlicensed band can be improved. 
       [b] Second Embodiment 
       [0127]    In the first embodiment, the offset is included in the UL grant, however, the present embodiment is different from the first embodiment in that the offset is included in the permission signal. Except for the points explained below, the functional blocks of the base station  20  and the terminal  30  are the same as the respective functional blocks explained with reference to  FIG. 4  and  FIG. 5 , and therefore detailed explanation thereof is omitted. 
         [0128]    Operation of Base Station  20   
         [0129]      FIG. 8  is a flowchart illustrating an example of an operation of the base station  20  according to a second embodiment. 
         [0130]    First of all, the uplink managing unit  202  initializes a variable T indicating an offset to 0 (S 300 ). The uplink managing unit  202  then determines whether a data transmission request to the terminal  30  has occurred (S 301 ). When a data transmission request to the terminal  30  has occurred (Yes at S 301 ), the uplink managing unit  202  increases the variable T by 1 (S 302 ), and creates time limit information (S 303 ). 
         [0131]    Then, the uplink managing unit  202  creates a UL grant including the created time limit information and the subband information of the unlicensed band allocated to UL data transmission. The uplink managing unit  202  then transmits the created UL grant to the terminal  30  via the licensed band transmitting unit  210  (S 304 ). Then, the uplink managing unit  202  again executes the process illustrated at Step S 301 . 
         [0132]    When a data transmission request to the terminal  30  has not occurred (No at S 301 ), the uplink managing unit  202  determines whether it is a transmission timing of the permission signal (S 305 ). When it is not a transmission timing of the permission signal (No at S 305 ), the uplink managing unit  202  again executes the process illustrated at Step S 301 . 
         [0133]    Meanwhile, when it is a transmission timing of the permission signal (Yes at S 305 ), the uplink managing unit  202  determines the value of the variable T as the value of the offset (S 306 ). The uplink managing unit  202  then creates the permission signal including the value of the determined offset and outputs the created permission signal to the multiplexing unit  223 . Then the uplink managing unit  202  instructs the carrier sense unit  205  to perform carrier sense. The carrier sense unit  205  executes carrier sense and determines whether the unlicensed band is idle (S 307 ). 
         [0134]    When the unlicensed band is idle (Yes at S 307 ), the carrier sense unit  205  instructs the IFFT processing unit  224  to transmit the transmission signal. As a result, the permission signal is transmitted to the unlicensed band (S 308 ). Then the uplink managing unit  202  initializes the value of the variable T to 0 (S 311 ), and again executes the process illustrated at Step S 301 . 
         [0135]    Meanwhile, when the unlicensed band is busy (No at S 307 ), the uplink managing unit  202  refers to the time limit information including the UL grant to determine whether the time limit has passed (S 309 ). When the time limit has not passed (No at S 309 ), the uplink managing unit  202  again executes the process illustrated at Step S 307 . Meanwhile, when the time limit has passed (Yes at S 309 ), the uplink managing unit  202  cancels the transmission of the permission signal (S 310 ). The uplink managing unit  202  then again executes the process illustrated at Step S 311 . 
         [0136]    Operation of Terminal  30   
         [0137]      FIG. 9  is a flowchart illustrating an example of an operation of the terminal  30  according to the second embodiment. 
         [0138]    First of all, the uplink managing unit  305  determines whether the UL grant has been received in the licensed band (S 400 ). When the UL grant has been received (Yes at S 400 ), the uplink managing unit  305  acquires the time limit information from the received UL grant (S 401 ). 
         [0139]    Then, the uplink managing unit  305  determines whether the permission signal has been received (S 402 ). When the permission signal has not been received (No at S 402 ), the uplink managing unit  305  determines whether the time limit indicated by the time limit information acquired from the UL grant has passed (S 407 ). When the time limit has not passed (No at S 407 ), the uplink managing unit  305  again executes the process illustrated at Step S 402 . Meanwhile, when the time limit has passed (Yes at S 407 ), the uplink managing unit  305  cancels the UL data transmission instructed by the UL grant, and again executes the process illustrated at Step S 400 . 
         [0140]    When the permission signal has been received (Yes at S 402 ), the uplink managing unit  305  acquires an offset from the permission signal (S 403 ). The uplink managing unit  305  then determines whether the reception timing of the permission signal is a timing earlier than the first transmission timing after the reception of the UL grant (S 404 ). When the reception timing of the permission signal is the timing earlier than the first transmission timing (Yes at S 404 ), the uplink managing unit  305  transmits the data in the subframe of the first transmission timing (S 405 ). The uplink managing unit  305  then again executes the process illustrated at Step S 400 . 
         [0141]    Meanwhile, when the reception timing of the permission signal is the timing later than the first transmission timing (No at S 404 ), the uplink managing unit  305  specifies the second transmission timing after the time specified by the offset from the first transmission timing. The uplink managing unit  305  then transmits the data in UL in the subframe of the specified second transmission timing (S 406 ). Then, the uplink managing unit  305  again executes the process illustrated at Step S 400 . 
         [0142]    Advantageous Effects of Second Embodiment 
         [0143]    The second embodiment has been explained above. As is apparent from the explanation, according to the wireless communication system  10  of the present embodiment, the throughput of UL in the unlicensed band can be improved. Moreover, in the present embodiment, because it is sufficient that the value of the offset is determined by the time of transmission of the permission signal, the value of the offset can be determined more flexibly according to the data transmission timing of UL allocated to the terminal  30 . 
       [c] Third Embodiment 
       [0144]    In the first embodiment, the base station  20  performs LBT of the unlicensed band before the terminal  30  performs UL data transmission, however, the present embodiment is different from the first embodiment in that the terminal  30  itself performs LBT of the unlicensed band before the terminal  30  performs UL data transmission. 
         [0145]    Operation of Wireless Communication System  10   
         [0146]      FIG. 10  is a diagram illustrating an example of an operation of the wireless communication system  10  according to a third embodiment. Except for the points explained below, the elements in  FIG. 10  assigned with the same reference signs as these in  FIG. 2  or  FIG. 3  are the same as the elements illustrated in  FIG. 2  or  FIG. 3 , and therefore explanation thereof is omitted. 
         [0147]    In the present embodiment, when receiving the UL grant  40  from the base station  20 , each terminal  30  executes LBT in the unlicensed band before a predetermined time (for example, before one subframe) than the first transmission timing after the reception of the UL grant  40 . Each terminal  30  performs UL data transmission at the first transmission timing after it is checked that the unlicensed band is continuously idle for a predetermined back-off period. 
         [0148]    Meanwhile, when the unlicensed band is not detected idle earlier than the first transmission timing after the reception of the UL grant  40 , the terminal  30  postpones the LBT up to the timing before the predetermined time than the second transmission timing specified by the offset. When the unlicensed band is detected idle in restarted LBT, the terminal  30  performs the UL data transmission at the second transmission timing after the period specified by the offset included in the UL grant  40  from the first transmission timing. 
         [0149]    As illustrated in  FIG. 10 , when other signal  47  is transmitted to the unlicensed band in the subframe period t 4  after the predetermined time from the subframe in which the UL grant  40 - 1  is transmitted, the terminals  30   a  and  30   b  detect that the unlicensed band is busy. Then, the terminals  30   a  and  30   b  wait for the LBT from the subframe period t 4  until the subframe period t 7  before the subframe period t 8  at the second transmission timing in which the period (period of three subframes in the example of  FIG. 10 ) specified by the offset has passed. 
         [0150]    The terminals  30   a  and  30   b  then restart the LBT in the subframe period t 7 . Then, when the unlicensed band is detected idle in the subframe period t 7 , the terminal  30   a  transmits the UL data  44 - 1  in the unlicensed band after it is checked that the idle state continues for a predetermined back-off period  48 - 1 . Similarly, when the unlicensed band is detected idle in the subframe period t 7 , the terminal  30   b  also transmits the UL data  45 - 1  in the unlicensed band after it is checked that the idle state continues for a predetermined back-off period  49 - 1 . 
         [0151]    In this way, in the present embodiment, when the unlicensed band is not detected idle by the time of the first transmission timing after the reception of the UL grant, the terminal  30  waits from the first transmission timing until a predetermined time before the second transmission timing after the period specified by the offset. Then, the terminal  30  restarts the LBT at a timing before the predetermined time than the second transmission timing, and performs the UL data transmission at the second transmission timing when the unlicensed band is detected idle. As a result, when the unlicensed band is busy at the first transmission timing, the terminal  30  performs the UL data transmission after the unlicensed band is detected idle even if the UL grant is not retransmitted from the base station  20 . This makes it possible to improve the throughput of UL. Moreover, because retransmission of the UL grant can be reduced, it is possible to reduce the processing load of the base station  20  and suppress an increase in traffic of the licensed band. 
         [0152]    Base Station  20   
         [0153]    Because the base station  20  according to the present embodiment is the same as the base station  20  according to the first embodiment explained with reference to  FIG. 4  except for the points explained below, detailed explanation thereof is omitted. The base station  20  in the present embodiment is different from the base station  20  in the first embodiment in that it does not include the carrier sense unit  205 . The uplink managing unit  202  in the present embodiment is different from the uplink managing unit  202  in the first embodiment in that if the UL grant is transmitted, the permission signal is not transmitted. 
         [0154]    Terminal  30   
         [0155]      FIG. 11  is a block diagram illustrating an example of the terminal  30  according to the third embodiment. Except for the points explained below, the elements in  FIG. 11  assigned with the same reference signs as these in  FIG. 5  are the same as the elements explained with reference to  FIG. 5 , and therefore detailed explanation thereof is omitted. The terminal  30  in the present embodiment is different from the terminal  30  in the first embodiment in that it includes a carrier sense unit  302 . 
         [0156]    The carrier sense unit  302  measures interference power in the unlicensed band based on the reception signal output from the wireless processing unit  321  of the unlicensed band receiving unit  320 . Then, the carrier sense unit  302  determines whether the unlicensed band is idle or busy based on the measurement result. The carrier sense unit  302  then outputs the determination result to the uplink managing unit  305 . The carrier sense unit  302  receives, for example, timing information on the start and the end of the carrier sense and information on a predetermined idle period or the like from the uplink managing unit  305 , and sends back information as to whether it can be determined as idle by the time of delimiter timing to the uplink managing unit  305 . 
         [0157]    When receiving the UL grant from the base station  20 , the uplink managing unit  305  acquires the offset and the time limit information from the UL grant. In the present embodiment, the time limit information indicates a time limit that can postpone the data transmission of the terminal  30 . The uplink managing unit  305  instructs the carrier sense unit  302  to perform carrier sense and execute LBT in the unlicensed band. When the unlicensed band is detected idle for a period before the first transmission timing after the reception of the UL grant, the uplink managing unit  305  checks that idle continues for a predetermined length of back-off period. When idle continues for the back-off period, the uplink managing unit  305  instructs the encoding/modulating unit  306  to perform UL data transmission at the first transmission timing. The carrier sense unit  302  instructs the IFFT processing unit  332  to transmit the transmission signal at the first transmission timing. As a result, the transmission signal is transmitted to the unlicensed band at the first transmission timing. 
         [0158]    Meanwhile, when the unlicensed band is not detected idle until the first transmission timing, the uplink managing unit  305  specifies the second transmission timing after the period specified by the offset from the first transmission timing. The uplink managing unit  305  then instructs the carrier sense unit  302  to perform carrier sense at a timing before a predetermined time than the specified second transmission timing and again execute LBT in the unlicensed band. Then, when the unlicensed band is detected idle, the uplink managing unit  305  instructs the encoding/modulating unit  306  to perform data transmission at the second transmission timing. The carrier sense unit  302  instructs the IFFT processing unit  332  to transmit the transmission signal at the second transmission timing. As a result, the transmission signal is transmitted to the unlicensed band at the second transmission timing. 
         [0159]    Operation of Base Station  20   
         [0160]      FIG. 12  is a flowchart illustrating an example of an operation of the base station  20  according to the third embodiment. 
         [0161]    First of all, the uplink managing unit  202  determines whether a data transmission request to the terminal  30  has occurred (S 500 ). When a data transmission request to the terminal  30  has occurred (Yes at S 500 ), the uplink managing unit  202  determines the value of the offset (S 501 ). The uplink managing unit  202  determines, for example, the number of continuous subframes to be allocated to data transmission in the same subband as the value of offset. 
         [0162]    Then, the uplink managing unit  202  creates time limit information (S 502 ). The uplink managing unit  202  then creates a UL grant that includes the determined offset and the created time limit information and also includes subband information of the unlicensed band allocated to the UL data transmission. Then, the uplink managing unit  202  transmits the created UL grant to the terminal  30  via the licensed band transmitting unit  210  (S 503 ). The uplink managing unit  202  then again executes the process illustrated at Step S 500 . 
         [0163]    Operation of Terminal  30   
         [0164]      FIG. 13  and  FIG. 14  are flowcharts illustrating an example of an operation of the terminal  30  according to the third embodiment. 
         [0165]    First of all, the uplink managing unit  305  determines whether the UL grant has been received in the licensed band (S 600 ). When the UL grant has been received (Yes at S 600 ), the uplink managing unit  305  acquires the offset and the time limit information from the UL grant (S 601 ). The uplink managing unit  305  then initializes a variable k to 0 (S 602 ). Then, the uplink managing unit  305  waits from the first transmission timing after the reception of the UL grant until a timing before a predetermined time (S 603 ). 
         [0166]    Then, the uplink managing unit  305  instructs the carrier sense unit  302  to perform carrier sense. The carrier sense unit  302  executes carrier sense and determines whether the unlicensed band is idle (S 604 ). When the unlicensed band is idle (Yes at S 604 ), the uplink managing unit  305  determines whether the unlicensed band has been detected idle earlier than the first transmission timing (S 605 ). When the unlicensed band has been detected idle earlier than the first transmission timing (Yes at S 605 ), the uplink managing unit  305  instructs the encoding/modulating unit  306  to perform UL data transmission at the first transmission timing. The carrier sense unit  302  instructs the IFFT processing unit  332  to transmit the transmission signal at the first transmission timing. As a result, the transmission signal is transmitted to the unlicensed band at the first transmission timing (S 606 ). Then, the uplink managing unit  305  again executes the process illustrated at Step S 600 . 
         [0167]    Meanwhile, when the unlicensed band has been detected idle later than the first transmission timing (No at S 605 ), the uplink managing unit  305  instructs the encoding/modulating unit  306  to perform UL data transmission at the second transmission timing. The second transmission timing is specified at Step S 609  explained later. The carrier sense unit  302  instructs the IFFT processing unit  332  to transmit the transmission signal at the second transmission timing. As a result, the transmission signal is transmitted to the unlicensed band at the second transmission timing (S 607 ). Then, the uplink managing unit  305  again executes the process illustrated at Step S 600 . 
         [0168]    When the unlicensed band is busy (No at S 604 ), the uplink managing unit  305  increases the variable k by 1 (S 608  in  FIG. 14 ). Then, the uplink managing unit  305  specifies the timing at which the time k-times the offset has passed from the first transmission timing as the second transmission timing (S 609 ). The uplink managing unit  305  then determines whether the time limit indicated by the time limit information acquired from the UL grant has passed (S 610 ). When the time limit has passed (Yes at S 610 ), the uplink managing unit  305  cancels the UL data transmission indicated by the UL grant (S 611 ), and again executes the process at Step S 600  illustrated in  FIG. 13 . 
         [0169]    Meanwhile, when the time limit has not passed (No at S 610 ), the uplink managing unit  305  determines whether it reaches the timing before a predetermined time from the second transmission timing specified at Step S 609  (S 612 ). When it does not reach the timing before a predetermined time from the second transmission timing (No at S 612 ), the uplink managing unit  305  again executes the process illustrated at Step S 610 . Meanwhile, when it reaches the timing before a predetermined time from the second transmission timing (Yes at S 612 ), the uplink managing unit  305  again executes the process at Step S 604  illustrated in  FIG. 13 . 
         [0170]    Advantageous Effects of Third Embodiment 
         [0171]    The third embodiment has been explained above. As is apparent from the explanation, according to the wireless communication system  10  of the present embodiment, when the unlicensed band is not detected idle by the time of the first transmission timing after the reception of the UL grant, the terminal  30  waits from the second transmission timing until a timing before a predetermined time. Then, the terminal  30  again executes the LBT at the timing before the predetermined time from the second transmission timing, and performs UL data transmission at the second transmission timing when the unlicensed band is detected idle. As a result, when the unlicensed band is busy at the first transmission timing, the terminal  30  autonomously performs UL data transmission after the unlicensed band is detected idle even if the UL grant is not retransmitted from the base station  20 . This makes it possible to improve the throughput of UL. Moreover, because the retransmission of the UL grant can be reduced, it is possible to reduce the processing load of the base station  20  and suppress an increase in traffic of the licensed band. 
         [0172]    Hardware 
         [0173]    The base station  20  and the terminal  30  according to the embodiments can be implemented by, for example, a wireless communication device  70  illustrated in  FIG. 15 .  FIG. 15  is a diagram illustrating an example of the wireless communication device  70  that implements the function of the base station  20  or of the terminal  30 . The wireless communication device  70  includes, for example, a memory  71 , a processor  72 , an analog-to-digital converter (A/D)  73 , a multiplier  74 , an amplifier  75 , an oscillator  76 , a digital-to-analog converter (D/A)  77 , a multiplier  78 , an amplifier  79 , and an antenna  80 . Beside this, the wireless communication device  70  may include an interface for performing wired communication with an external communication device. 
         [0174]    The antenna  80  receives a radio signal and outputs the received signal to the amplifier  75 . The antenna  80  transmits the signal output from the amplifier  79  to the outside. The amplifier  75  amplifies the signal received by the antenna  80  and outputs the amplified signal to the multiplier  74 . The multiplier  74  multiplies the signal output from the amplifier  75  and a clock signal output from the oscillator  76  to convert the frequency of the reception signal from the high frequency band to the baseband. Then, the multiplier  74  outputs the frequency-converted signal to the analog-to-digital converter  73 . The analog-to-digital converter  73  converts the analog reception signal output from the multiplier  74  to a digital reception signal, and outputs the converted reception signal to the processor  72 . 
         [0175]    The processor  72  controls the entire wireless communication device  70 . The processor  72  can be implemented by, for example, CPU (Central Processing Unit) or DSP (Digital Signal Processor). The processor  72  performs reception processing of the signal output from the analog-to-digital converter  73 . In addition, the processor  72  generates a transmission signal and outputs the generated transmission signal to the digital-to-analog converter  77 . 
         [0176]    The memory  71  includes, for example, a main memory and an auxiliary memory. The main memory is, for example, RAM (Random Access Memory). The main memory is used as a work area of the processor  72 . The auxiliary memory is a nonvolatile memory such as a magnetic disk and a flash memory. The auxiliary memory stores various types of programs that operate the processor  72 . The program stored in the auxiliary memory is loaded to the main memory and executed by the processor  72 . 
         [0177]    The digital-to-analog converter  77  converts a digital transmission signal output from the processor  72  into an analog transmission signal and outputs the converted transmission signal to the multiplier  78 . The multiplier  78  multiplies the transmission signal converted by the digital-to-analog converter  77  by a clock signal output from the oscillator  76 , thereby converting the frequency of the transmission signal from the baseband to the high frequency band. The multiplier  78  then outputs the frequency-converted transmission signal to the amplifier  79 . The amplifier  79  amplifies the signal output from the multiplier  78  and transmits the amplified transmission signal to the outside via the antenna  80 . 
         [0178]    The oscillator  76  generates a clock signal (continuous wave alternating signal) of a predetermined frequency. The oscillator  76  then outputs the generated clock signal to the multiplier  74  and the multiplier  78 . 
         [0179]    When the wireless communication device  70  functions as the base station  20  illustrated in  FIG. 4 , the antennas  216 ,  226 ,  235 , and  245  illustrated in  FIG. 4  can be implemented by, for example, the antenna  80 . The wireless processing units  215 ,  225 ,  234 , and  244  illustrated in  FIG. 4  can be implemented by, for example, the analog-to-digital converter  73 , the multiplier  74 , the amplifier  75 , the oscillator  76 , the digital-to-analog converter  77 , the multiplier  78 , and the amplifier  79 . The other components illustrated in  FIG. 4  can be implemented by, for example, the processor  72  and the memory  71 . 
         [0180]    When the wireless communication device  70  functions as the terminal  30  illustrated in  FIG. 5  or  FIG. 11 , the antenna  300  illustrated in  FIG. 5  or  FIG. 11  can be implemented by, for example, the antenna  80 . The wireless processing units  311 ,  321 ,  331 , and  341  illustrated in  FIG. 5  or  FIG. 11  can be implemented by, for example, the analog-to-digital converter  73 , the multiplier  74 , the amplifier  75 , the oscillator  76 , the digital-to-analog converter  77 , the multiplier  78 , and the amplifier  79 . The other components illustrated in  FIG. 5  or  FIG. 11  can be implemented by, for example, the processor  72  and the memory  71 . 
         [0181]    Others 
         [0182]    In each of the embodiments, although the base station  20  transmits the UL grant to the terminal  30  in the licensed band, the disclosed technology is not limited thereto. For example, the base station  20  may transmit the UL grant to the terminal  30  in the unlicensed band. However, in the unlicensed band, transmission is preformed after each communication device detects the availability of the band. Therefore, when a data transmission request to the terminal  30  occurs, the base station  20  performs LBT in the unlicensed band, checks the availability of the band, and then transmits the UL grant  40  to the terminal  30 . In addition, the base station  20  may transmit the permission signal in the licensed band. 
         [0183]    The terminal  30  with poor reception quality of radio waves transmitted from the base station  20  may possibly fail in reception of the UL grant and the permission signal transmitted from the base station  20 . For example, when the UL grant including the offset indicating any value other than 0 is transmitted to a terminal  30 , the terminal  30  does not perform UL data transmission when failing in reception of the UL grant or the permission signal. The base station  20  waits for data transmission from the terminal  30  until the time limit specified by the time limit information included in the UL grant has passed. Therefore, when there is unreceived data for the UL grant, transmission of the UL grant to other terminal  30  is postponed. As a result, the throughput of UL may be decreased as the entire system. 
         [0184]    In order to avoid this, information indicating that retransmission is not performed may be included in the UL grant to be transmitted to the terminal  30  with poor reception quality of radio waves transmitted from the base station  20 . As the information indicating that retransmission is not performed, for example, an offset indicating the value of 0 may be used. As a result, it is possible to avoid the decrease in the throughput of UL due to securing of the retransmission period for UL data transmission with a low success rate. 
         [0185]    As a method for identifying the terminal  30  with poor reception quality of radio waves transmitted from the base station  20 , for example, the uplink managing unit  202  counts the number of times UL data transmission is not performed even if the UL grant and the permission signal are transmitted as the number of failures for each terminal  30 . Then, it is conceivable that the uplink managing unit  202  identifies the terminal  30  having the number of failures that is more than a predetermined number of times as the terminal  30  with poor reception quality of radio waves transmitted from the base station  20 . Even if the terminal  30  is identified as the terminal  30  with poor reception quality, thereafter, when the number of times the UL data transmission is performed for the transmission of the UL grant and the permission signal is continuously above the predetermined number of times, identification of the terminal as the terminal  30  with poor reception quality may be released. 
         [0186]    The components illustrated in the embodiments are functionally divided according to main processing content in order to facilitate understanding of each device. Therefore, the disclosed technology is not limited by a method of dividing the components and their names. Each device illustrated in the embodiments can be configured to be divided into further more components according to the processing content or to be divided so that one component execute more processes. Moreover, each of the processes may be implemented as a process by software or may be implemented by dedicated hardware such as ASIC (Application Specific Integrated Circuit). 
         [0187]    According to one aspect of the present invention, it is possible to improve UL throughput in the unlicensed band. 
         [0188]    All examples and conditional language recited herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.