Patent Publication Number: US-10771217-B2

Title: Wireless base station apparatus, wireless terminal apparatus, frequency resource allocation method, and method of forming transmission signal

Description:
TECHNICAL FIELD 
     The present invention relates to a radio base station apparatus, a radio terminal apparatus, a method of assigning frequency resources, and a method of forming transmission signals. 
     BACKGROUND ART 
     For an uplink channel of LTE-A (LTE-Advanced), which is an evolved version of 3rd generation partnership project long-term evolution (3GPP LTE), using “non-contiguous frequency transmission” in addition to contiguous frequency transmission is under consideration to improve sector throughput performance (see Non-Patent Literature 1). 
     Non-contiguous frequency transmission is a method of transmitting a data signal and a reference signal by assigning such signals to non-contiguous frequency bands, which are dispersed in a wide range of band. As shown in  FIG. 1 , in non-contiguous frequency transmission, it is possible to assign a data signal and a reference signal to discrete frequency bands. Therefore, in non-contiguous frequency transmission, compared to contiguous frequency transmission, the flexibility in assigning a data signal and a reference signal to frequency bands in each terminal increases. By this means, it is possible to gain greater frequency scheduling effects. 
     As a method of reporting frequency resource assignment information for non-contiguous frequency transmission from a base station to a terminal, there is a method of reporting whether or not to perform assignment for each resource block group (RBG) in the system band, using a bitmap (see Non-Patent Literature 2). As shown in  FIG. 2 , a base station reports to a terminal subject to frequency assignment using one bit whether or not to assign frequency resources per predetermined RBG (per four [RBs] in  FIG. 2 ). That is, in a plurality of RBGs formed by dividing the system band per predetermined RB, including an RBG that is assigned to a terminal subject to frequency assignment (hereinafter referred to as “assigned RBG”) and an RBG that is not subject to assignment (hereinafter referred to as “RBG not assigned”), a base station reports to a terminal subject to frequency assignment, a frequency assignment bit sequence that is obtained by assigning the bit value of 1 to one of the above RBGs and assigning the bit value of 0 to the other. In  FIG. 2 , the RBG to which bit “1” is assigned is frequency area assigned to a terminal subject to assignment while the RBG to which bit “0” is assigned is frequency area that is not subject to assignment to the terminal subject to assignment. Therefore, the number of signaling bits required for frequency resource assignment information matches the number of RBGs in the system bandwidth. 
     In LTE, as shown in  FIG. 3 , the size of an RBG (=P) varies depending on the system bandwidth (see Non-Patent Literature 3). As shown in  FIG. 3 , a greater size of an RBG is used for the broader system bandwidth, reducing the number of signaling bits. 
     Further, in LTE, a sounding reference signal (SRS) of an uplink channel is used. Here, “sounding” means estimation of channel quality. An SRS is transmitted by time-multiplexing data on a specific symbol, mainly to perform estimation of the channel quality indicator (CQI) of an uplink channel data channel. 
     Further, among the methods of transmitting SRSs are a method of transmitting SRSs in the transmission bandwidth as broad as the system bandwidth (i.e. method of transmitting SRSs in a broad band), and a method of transmitting SRSs in which SRSs are transmitted in a narrow band at each transmission timing by changing transmission frequency bands in time sequence (that is, by performing frequency hopping) (i.e. method of transmitting SRSs in a narrow band). When the broad-band SRS transmission method is used, CQIs are estimated over a broad band at one time. Further, when the narrow-band SRS transmission method is used, CQIs are estimated over a broad band by using several SRSs transmitted in a narrow band. 
     Generally, path loss for a signal that is transmitted from a terminal near the cell border and is received by a base station, is significant. Further, because the maximum transmission power of a terminal is limited, in the case of the broad-band SRS transmission, reception power of a base station per unit frequency lowers and the reception SINR lowers. As a result of this, the accuracy of CQI estimation deteriorates. Therefore, for a terminal near the cell border, the narrow-band SRS transmission method for performing transmission so as to focus limited power on a predetermined frequency band, is employed. In contrast, path loss for a signal that is transmitted from a terminal near the cell center and is received by a base station, is small. For this reason, even when the broad-band SRS transmission method is employed, is possible to fully secure reception power of a base station per unit frequency. As a result of this, the broad-band SRS transmission method is employed for a terminal near the cell center. 
     Further, in LTE, the transmission bandwidth of the broad-band SRS transmission method is set N times (N is an integer) as broad as the transmission bandwidth of the narrow-band SRS transmission method, so as to use the same frequency band in which SRSs can be transmitted (i.e. sounding band, or frequency band with which CQI estimation can be performed), regardless of the broad-band SRS transmission method or the narrow-band SRS transmission method. That is, when the narrow-band SRS transmission method is employed, CQIs of the same frequency band as the frequency band in the broad-band SRS transmission method are estimated by applying frequency hopping N times. Specifically, in LTE, the minimum bandwidth for transmitting SRSs is four RBs, and all of the transmission bandwidths of SRSs are formed with RBs of multiples of four (see Non-Patent Literature 4). 
     CITATION LIST 
     Non-Patent Literature 
     
         
         NPL 1 
         3GPP R1-090257, Panasonic, “System performance of uplink non-contiguous resource allocation” 
         NPL 2 
         3GPP TS36.212 V8.5.0. 5.3.3.1.2 Format 1, “E-UTRA Multiplexing and channel coding (Release 8)” 
         NPL 3 
         3GPP TS36.213 V8.5.0. 7.1.6.1 Resource allocation type 0, “Physical layer procedures (Release 8)” 
         NPL 4 
         3GPP TS36.211 V8.5.0. 5.5.3.2 Mapping to physical resources, “Physical Channels and Modulation (Release 8)” 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     By the way, when the above-described conventional method of reporting frequency resource assignment information for non-contiguous frequency transmission and the SRS transmission method are simply combined, there is a possibility that the borders of SRS transmission bands and RBGs do not match. For example, when the system bandwidth is fifty RBs, as shown in  FIG. 3 , while the size of an RBG is three RBs, the transmission bandwidth of SRSs are formed with RBs of multiples of four regardless of the system bandwidth. At this time, because the accuracy of CQI estimation for some RBGs deteriorates, frequency scheduling gain lowers and, consequently, system throughput deteriorates. 
     More specifically, when the broad-band SRS transmission method is employed, as shown in  FIG. 4 , for the RBGs located at the ends of the SRS transmission band, SRSs are transmitted only in part of the bands of those RBGs. For this reason, it is not possible to perform accurate calculation for estimating the average CQI in the RBG, deteriorating the accuracy of CQI estimation. 
     On the other hand, when the narrow-band SRS transmission method is employed, as shown in  FIG. 5 , for the RBGs located at the ends of the sounding band for SRSs (the whole band in which SRSs are transmitted), in the same way as the broad-band SRS transmission method, SRSs are transmitted only in part of the bands of those RBGs. Besides this, for the RBG located on the border of SRSs in the narrow band, all SRSs in the band of that RBG are transmitted only after a plurality of SRSs are transmitted. Because there is a time interval between the timings in which that plurality of SRSs are transmitted, in the environment where there is time fading, for example, it is not possible to perform accurate calculation for estimating the average CQI in an RBG, deteriorating the accuracy of CQI estimation. 
     In view of the above, it is therefore an object of the present invention to provide a radio base station apparatus, a radio terminal apparatus, a method of assigning frequency resources, and a method of forming transmission signals for making it possible to prevent the accuracy of channel estimation from lowering when non-contiguous frequency transmission and SRS transmission are employed in an uplink channel. 
     Solution to Problem 
     One aspect of a radio base station apparatus according to the present invention employs a configuration to comprise: an extraction section that extracts a reference signal contained in a reception signal based on a set reception band; a channel estimation section that estimates channel quality per frequency assignment unit based on the extracted reference signal; an assignment section that assigns frequency resources to a terminal per frequency assignment unit based on a result of the estimation of the channel quality; and an assignment unit setting section that is a section of setting the reception band of the reference signal in the extraction section and setting frequency assignment units in the channel estimation section and the assignment section; makes a frequency position of an end of the reception band match a frequency position of an end of either frequency assignment unit; and sets a width of the reception band of the reference signal as a natural number multiple of a bandwidth of the frequency assignment unit. 
     One aspect of a radio terminal apparatus according to the present invention employs a configuration to comprise: a formation section that forms a transmission signal by mapping a reference signal to a set transmission band and mapping transmission data based on assignment information per frequency assignment unit; and a band setting section that is a section of setting the transmission band and the frequency assignment units; makes a frequency position of an end of the transmission band match a frequency position of an end of either frequency assignment unit; and sets a width of the transmission band of the reference signal as a natural number multiple of a bandwidth of the frequency assignment unit. 
     One aspect of a method of assigning frequency resources according to the present invention employs a configuration to comprise steps of: setting a reception band and frequency assignment units of a reference signal; extracting the reference signal contained in a reception signal based on the set reception band; estimating channel quality per set frequency assignment unit based on the extracted reference signal; assigning frequency resources to a terminal per frequency assignment unit based on a result of the estimation of the channel quality; wherein a frequency position of an end of the reception band is made match a frequency position of an end of either frequency assignment unit, and a width of the reception band of the reference signal is a natural number multiple of a bandwidth of the frequency assignment unit. 
     One aspect of a method of forming transmission signals according to the present invention employs a configuration to comprise steps of: setting a transmission band and frequency assignment units; and forming a transmission signal by mapping a reference signal to the set transmission band and mapping transmission data based on assignment information per set frequency assignment unit; wherein a frequency position of an end of the transmission band is made match a frequency position of an end of either frequency assignment unit, and a width of the transmission band of the reference signal is a natural number multiple of a bandwidth of the frequency assignment unit. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide a radio base station apparatus, a radio terminal apparatus, a method of assigning frequency resources, and a method of forming transmission signals for making it possible to prevent the accuracy of channel estimation from lowering when non-contiguous frequency transmission and SRS transmission are employed in an uplink channel. 
    
    
     
         FIG. 1  shows non-contiguous frequency transmission; 
         FIG. 2  shows a method of reporting frequency resource assignment information for non-contiguous frequency transmission; 
         FIG. 3  shows dependency of the size of RBG on the system bandwidth; 
         FIG. 4  shows a case where non-contiguous frequency transmission and broad-band SRS transmission are employed in an uplink channel; 
         FIG. 5  shows a case where non-contiguous frequency transmission and narrow-band SRS transmission are employed in an uplink channel; 
         FIG. 6  is a block diagram showing a configuration of a base station apparatus according to Embodiment 1 of the present invention; 
         FIG. 7  is a block diagram showing a configuration of a terminal apparatus according to Embodiment 1 of the present invention; 
         FIG. 8  shows the basic size of an RBG when the transmission bandwidth of an SRS is set as four RBs; 
         FIG. 9  shows an operation of a base station apparatus; 
         FIGS. 10A and 10B  show RBG groups defined in the system bandwidth according to where the sounding band is positioned in the system band; 
         FIG. 11  shows an operation of a base station apparatus; 
         FIG. 12  shows an operation of a base station apparatus; 
         FIG. 13  shows an operation of a base station apparatus; 
         FIG. 14  is a block diagram showing a configuration of a base station apparatus according to Embodiment 2 of the present invention; 
         FIG. 15  is a block diagram showing a configuration of a terminal apparatus according to Embodiment 2 of the present invention; and 
         FIG. 16  shows an operation of a base station apparatus. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In embodiments, the same parts will be assigned the same reference numerals and overlapping explanations will be omitted. 
     Embodiment 1 
       FIG. 6  is a block diagram showing a configuration of a base station apparatus  100  according to Embodiment 1 of the present invention. In  FIG. 6 , base station apparatus  100  includes radio reception section  101 , demodulation section  102 , SRS extraction section  103 , CQI estimation section  104 , assignment section  105 , assignment unit setting section  106 , control signal generation section  107 , modulation section  108 , and radio transmission section  109 . 
     Radio reception section  101  performs reception processing, such as down-conversion and A/D conversion, on a signal received from terminal apparatus  200  (described later) via an antenna, and outputs the reception-processed signal to demodulation section  102 . 
     Demodulation section  102  demodulates the signal received from radio reception section  101  and outputs the demodulated signal to SRS extraction section  103 . 
     SRS extraction section  103  extracts an SRS transmitted from terminal apparatus  200  based on SRS information received from assignment unit setting section  106 . SRS information includes information about the transmission bandwidth, the position of the transmission band, and the frequency hopping pattern with which terminal apparatus  200  transmits an SRS. When viewed from base station apparatus  100 , SRS information contains information about the reception bandwidth and the position of the reception band in which an SRS is received at one timing, and the hopping pattern of that position of the reception band. The extracted SRS is output to CQI estimation section  104 . 
     CQI estimation section  104  estimates channel quality (CQI) between base station apparatus  100  and terminal apparatus  200  by performing correlation calculation between the reception SRS extracted from SRS extraction section  103  and an SRS replica known between base station apparatus  100  and terminal apparatus  200 . This correlation calculation is performed per RBG based on the RBG information received from assignment unit setting section  106 . RBG information contains the basic size and the position of an RBG. 
     The result of the channel quality estimation is output to assignment section  105 . Here, in the same way as in the above-described conventional technique, when the broad-band SRS transmission method is employed, the estimation result of channel quality for the whole sounding band can be obtained at one timing, while, when the narrow-band SRS transmission method is employed, SRSs are transmitted only in part of the transmission band of the sounding band at one timing, so that it is possible to obtain the estimation result of channel quality for the whole sounding band by performing correlation calculation on the reception SRS a plurality of times. 
     Assignment section  105  assigns frequency resources to terminal  200  subject to frequency assignment, per RBG unit that is determined by the RBG information received from assignment unit setting section  106 . This assignment of frequency resources is performed based on the result of channel estimation obtained in CQI estimation section  104  for each RBG. Assignment section  105  generates a frequency resource assignment bit sequence corresponding to the arrangement pattern of the RBG subject to assignment in the system band and the RBG that is not subject to assignment, and outputs the generated frequency resource assignment bit sequence to control signal generation section  107 . 
     Assignment unit setting section  106  outputs SRS information containing information about the transmission bandwidth, the position of the transmission band, and the frequency hopping pattern with which terminal apparatus  200  transmits an SRS at one timing, to SRS extraction section  103 , and outputs the RBG information containing the basic size and the frequency position of an RBG to assignment section  105 . Here, the frequency position of an end of an arbitrary SRS transmission band that is determined by SRS information matches the frequency position of an end of either RBG that is determined by RBG information. Further, the basic size of an RBG contained in RBG information (i.e. standard bandwidth of an RBG) is a divisor of the transmission bandwidth contained in SRS information. That is, the transmission bandwidth contained in SRS information is a natural number multiple of the basic size of an RBG contained in RBG information. 
     Specifically, assignment unit setting section  106  includes SRS information setting section  111  and RBG information setting section  112 . 
     SRS information setting section  111  outputs SRS information to SRS extraction section  103 . Further, SRS information setting section  111  outputs the minimum bandwidth of an SRS (represented by the number of RBs) and information about the border of the transmission band of an SRS, to RBG information setting section  112 . Information about the border of the transmission band of an SRS refers to the start position of the sounding band, for example. 
     RBG information setting section  112  determines the basic size of an RBG depending on the system bandwidth. This basic size of an RBG is a divisor of the transmission bandwidth with which terminal apparatus  200  transmits an SRS at one timing. Further, RBG information setting section  112  determines the frequency position of an RBG so that the frequency position of an end of the transmission band indicated by information about the border of the transmission band of an SRS received from SRS information setting section  111  matches the frequency position of an end of an RBG. 
     Information about the basic size of an RBG and the frequency position of the RBG thus determined is output as RBG information to CQI estimation section  104  and assignment section  105 . 
     Control signal generation section  107  generates a control signal containing the frequency resource assignment bit sequence received from assignment section  105 , and outputs the generated control signal to modulation section  108 . 
     Modulation section  108  modulates the control signal and outputs the modulated signal to radio transmission section  109 . 
     Radio transmission section  109  performs transmission processing, such as D/A conversion, up-conversion, and amplification, on the modulated signal, and transmits by radio the transmission-processed signal via the antenna. 
       FIG. 7  is a block diagram showing a configuration of terminal apparatus  200  according to Embodiment 1 of the present invention. In  FIG. 7 , terminal apparatus  200  includes radio reception section  201 , demodulation section  202 , decoding section  203 , band information setting section  204 , transmission band setting section  205 , encoding section  206 , modulation section  207 , DFT section  208 , SRS generation section  209 , mapping sections  210  and  211 , IDFT sections  212  and  213 , multiplexing section  214 , and radio transmission section  215 . 
     Radio reception section  201  performs reception processing, such as down-conversion and A/D conversion, on a signal received via the antenna, and outputs the reception-processed signal to demodulation section  202 . 
     Demodulation section  202  demodulates the reception signal and outputs the demodulated signal to decoding section  203 . 
     Decoding section  203  performs decoding processing on the signal received from demodulation section  202  and, from the result of the decoding, extracts a control signal containing the frequency resource assignment bit sequence transmitted from base station apparatus  100 . 
     Band information setting section  204  outputs SRS information containing the information about the transmission bandwidth, the position of the transmission band, and the frequency hopping pattern with which terminal apparatus  200  transmits an SRS at one timing, to mapping section  211 , and outputs RBG information containing the basic size and the frequency position of an RBG to transmission band setting section  205 . Here, the frequency position of an end of an arbitrary SRS transmission band that is determined by SRS information matches the frequency position of an end of either RBG that is determined by RBG information. Further, the basic size of an RBG contained in RBG information (i.e. standard bandwidth of an RBG) is a divisor of the transmission bandwidth contained in SRS information. That is, the transmission bandwidth contained in SRS information is a natural number multiple of the basic size of an RBG contained in RBG information. 
     Specifically, band information setting section  204  includes SRS information setting section  221  and RBG information setting section  222 . 
     SRS information setting section  221  outputs SRS information to mapping section  211 . Further, SRS information setting section  221  outputs the minimum bandwidth of an SRS (represented by the number of RBs) and information about the border of the transmission band of an SRS, to RBG information setting section  222 . Information about the border of the transmission band of an SRS refers to the start position of the sounding band, for example. 
     RBG information setting section  222  determines the basic size of an RBG depending on the system bandwidth. This basic size of an RBG is a divisor of the transmission bandwidth with which terminal apparatus  200  transmits an SRS at one timing. Further, RBG information setting section  222  determines the frequency position of an RBG so that the frequency position of an end of the transmission band indicated by information about the border of the transmission band of an SRS received from SRS information setting section  221  matches the frequency position of an end of an RBG. Information about the basic size of the RBG and the frequency position of the RBG thus determined is output as RBG information to transmission band setting section  205 . 
     Transmission band setting section  205  designates the assigned RBG based on a bit value of a constituent bit of the frequency resource assignment bit sequence contained in control information received from decoding section  203 , out of the RBG groups in which the basic size and the frequency position are detected based on the RBG information received from band information setting section  204 , and outputs the basic size and the frequency position of the designated assigned RBG as transmission band information to mapping section  210 . That is, the band designated from the basic size and the frequency position of the assigned RBG is the transmission band. 
     Encoding section  206  encodes transmission data and outputs the obtained encoded data to modulation section  207 . 
     Modulation section  207  modulates the encoded data received from encoding section  206  and outputs the data-modulated signal to DFT section  208 . 
     DFT section  208  performs DFT processing on the data-modulated signal received from modulation section  207  and outputs the obtained frequency domain data signal to mapping section  210 . 
     Mapping section  210  maps the data signal received from DFT section  208  to the frequency resources indicated by transmission band information received from transmission band setting section  205 , and outputs the obtained signal to IDFT section  212 . 
     IDFT section  212  performs IDFT processing on the signal received from mapping section  210 , and outputs the obtained signal to multiplexing section  214 . 
     SRS generation section  209  generates an SRS to measure channel quality of an uplink channel data channel, and outputs the generated SRS to mapping section  211 . 
     Mapping section  211  arranges an SRS on the frequency/time resources designated by SRS information received from band information setting section  204 , and outputs the obtained signal to IDFT section  213 . 
     IDFT section  213  performs IDFT processing on the signal received from mapping section  211 , and outputs the obtained signal to multiplexing section  214 . 
     Multiplexing section  214  multiplexes the data signal received from IDFT section  213  with the SRS, and outputs the obtained multiplexed signal to radio transmission section  215 . 
     Radio transmission section  215  performs transmission processing, such as D/A conversion, up-conversion, and amplification, on the multiplexed signal received from multiplexing section  214 , and transmits the obtained radio signal to base station apparatus  100  from the antenna. 
     Operations of base station apparatus  100  and terminal apparatus  200  having the above configuration will be described below. 
     Base station apparatus  100  assigns frequency resources to terminal  200  subject to frequency assignment, per RBG unit, based on the result of the channel estimation obtained for each RBG, and generates a frequency resource assignment bit sequence corresponding to an arrangement pattern of RBGs subject to assignment in the system band and RBGs that are not subject to assignment. Then, base station apparatus  100  transmits the frequency resource assignment bit sequence to terminal apparatus  200 . Terminal apparatus  200  performs data transmission using the frequency resources designated based on the received frequency resource assignment bit sequence. 
     Specifically, in base station apparatus  100 , SRS extraction section  103  extracts an SRS in the SRS reception band designated from the reception signal received via radio reception section  101  and demodulation section  102 , based on the SRS information received from assignment unit setting section  106 . SRS information includes information about the reception bandwidth and the position of the reception band of an SRS at one timing, and the frequency hopping pattern of that position of the reception band. As described above, among the methods of transmitting SRSs are a method of transmitting SRSs in a broad band and a method of transmitting SRSs in a narrow band. In the broad-band SRS transmission method, SRSs are transmitted in one transmission band (i.e. sounding band) at all timings of SRS transmission. Therefore, when the broad-band SRS transmission method is employed, SRS information contains information indicating that the position of the reception band is not subject to hopping. 
     CQI estimation section  104  obtains the result of channel estimation per RBG by performing correlation calculation between the reception SRS extracted from SRS extraction section  103  and the SRS replica, based on the RBG information received from assignment unit setting section  106 . RBG information contains the basic size and the position of an RBG. 
     Assignment section  105  assigns frequency resources to terminal  200  subject to frequency assignment, per RBG unit determined by the RBG information received from assignment unit setting section  106 , based on the result of channel estimation obtained by CQI estimation section  104 , and generates a frequency resource assignment bit sequence corresponding to an arrangement pattern of RBGs subject to assignment in the system band and RBGs that are not subject to assignment. 
     Here, the frequency position of an end of an arbitrary SRS transmission band that is determined by SRS information matches the frequency position of an end of either RBG that is determined by RBG information. Further, the basic size of an RBG contained in RBG information (i.e. standard bandwidth of an RBG) is a divisor of the transmission bandwidth contained in SRS information. That is, the transmission bandwidth contained in SRS information is a natural number multiple of the basic size of the RBG contained in RBG information. For example, because the minimum bandwidth of an SRS for LTE is four RBs, the basic size of an RBG determined by assignment unit setting section  106  is limited to one, two, or four RBs, which are divisors of four RBs, as shown in  FIG. 8 . 
     By this means, as shown in  FIG. 9 , one SRS is transmitted across RBGs located in the sounding band, without any dead space in each RBG. Therefore, because it is possible to obtain the result of channel estimation using the SRS transmitted at one timing in each RBG, it is possible to prevent the accuracy of CQI estimation from deteriorating. As a result of this, base station apparatus  100  can assign frequency resources to terminal apparatus  200 , using a CQI without deterioration of the accuracy, so that it is possible to prevent system throughput performance from deteriorating. Further, the SRS transmission method is the same as the method for LTE, it is possible to multiplex SRSs of a plurality of terminals in the same cell, without differentiating terminals supporting only the LTE system from terminals that can also be applied to the LTE-A system. 
     Here, as is the case with the present embodiment, when setting the sounding band as the standard and an end of an RBG is made match an end of the sounding band, there is a possibility that RBGs that are smaller than the basic size appear at the both ends of the system band, depending on where the sounding band is positioned in the system band. 
       FIGS. 10A and 10B  show RBG groups defined in the system bandwidth according to where the sounding band is positioned in the system band. In  FIG. 10A , the frequency position of an end of the sounding band matches the frequency position of an end of an RBG, under the condition that RBGs are arranged in series from the end of the system band. On the other hand, in  FIG. 10B , because the frequency position of an end of the sounding band does not match the frequency position of an end of an RBG, under the condition that RBGs are arranged in series from the end of the system band, the frequency positions of RBGs are shifted to make the frequency position of an end of the sounding band match the frequency position of an end of an RBG. 
     Between  FIG. 10A  and  FIG. 10B , the positions of the sounding band are different while the system bandwidth and the sounding bandwidth are the same. With this difference, the number of constituent bits of the frequency resource assignment bit sequence is eight in  FIG. 10A  while the number of constituent bits is nine in  FIG. 10B . This is because, in  FIG. 10B , each of the RBGs that are smaller than the basic size and are located at the both ends of the system band is counted as one RBG. 
     As described above, when the number of constituent bits of the frequency resource assignment bit sequence transmitted from base station apparatus  100  to terminal apparatus  200  changes, the transmission format for control signals changes, so that decoding processing for detecting the transmission format increases in terminal apparatus  200 . 
     To resolve this inconvenience, there are the following three methods. 
     The first method is that assignment section  105  assigns two RBGs that are smaller than the basic size and are located at the ends of the system band, as one congregation (see  FIG. 11 ). By this means, it is possible to report whether or not two RBGs located at the both ends of the system band are assigned, using one bit, to a terminal subject to frequency assignment. As a result of this, even in the condition of  FIG. 10B , assignment section  105  can generate a frequency resource assignment bit sequence using the same number of bits as the number of constituent bits in the condition of  FIG. 10A . 
     The second method is that assignment section  105  sets only one of two RBGs that are smaller than the basic size and are located at both ends of the system band as an RBG subject to assignment, and sets the other as an RBG that is not subject to assignment (see  FIG. 12 ). However, “not subject to assignment” here means being not reported whether or not assignment will be performed using a frequency resource assignment bit sequence. Therefore, it is possible to assign this RBG that is not subject to assignment to a terminal subject to frequency assignment, by other signaling methods (for example, a frequency resource assignment bit sequence for contiguous frequency transmission). By this means, even in either condition of  FIG. 10A  or  FIG. 10B , it is possible to use one signaling format. As a result of this, because it is possible to omit decoding processing for detecting the signaling format in terminal apparatus  200 , it is possible to prevent the amount of processing in terminal apparatus  200  from increasing. 
     The third method is that assignment section  105  sets both of two RBGs that are smaller than the basic size and are located at both ends of the system band as RBGs that are not subject to assignment. That is, assignment section  105  makes the band that can be assigned match the sounding band (see  FIG. 13 ). By this means, both of two RBGs that are smaller than the basic size and are located at the ends of the system band are set as the RBGs that are not subject to assignment, it is possible to reduce the number of signaling bits. However, here again, it is possible to assign these RBGs that are not subject to assignment to a terminal subject to frequency assignment, by other signaling methods (for example, by using a frequency resource assignment bit sequence for contiguous frequency transmission). Further, by setting the sounding bandwidth as the maximum value that can be set in the cell, the same number of signaling bits is used in the cell, so that it is possible to use the same signaling format in the cell. 
     As described above, according to the present embodiment, in base station apparatus  100 , assignment unit setting section  106 , which sets the reception band of an SRS in SRS extraction section  103  and sets the frequency assignment units (RBGs) in CQI estimation section  104  and assignment section  105 , makes the frequency position of an end of the SRS reception band match the frequency position of an end of either frequency assignment unit, and sets the reception bandwidth of a reference signal as a natural number multiple of the bandwidth of the frequency assignment unit. 
     Further, in terminal apparatus  200 , band information setting section  204 , which sets the transmission band and the frequency assignment units (RBGs), makes the frequency position of an end of the transmission band match the frequency position of an end of either frequency assignment unit, and sets the transmission bandwidth of an SRS as a natural number multiple of the bandwidth of the frequency assignment unit. 
     By this means, one SRS is transmitted across RBGs without any dead space in each RBG. Therefore, it is possible to obtain the result of channel estimation using the SRS transmitted at the same timing in each RBG, making it possible to prevent the accuracy of CQI estimation from deteriorating. As a result of this, base station apparatus  100  can assign frequency resources to terminal apparatus  200 , using the CQI without deterioration of the accuracy, so that it is possible to prevent system throughput performance from deteriorating. 
     Embodiment 2 
     A case has been described with Embodiment 1 where the basic size of an RBG is determined by setting the sounding band as the standard, and an end of the RBG is made match an end of the sounding band. A case will be described with Embodiment 2 where by setting the basic size and the position of an RBG as the standard, the transmission bandwidth with which terminal apparatus  200  transmits an SRS at one timing is determined, and an end of the transmission band of that SRS is made match an end of an RBG. 
       FIG. 14  is a block diagram showing a configuration of base station apparatus  300  according to Embodiment 2 of the present invention. Base station apparatus  300  includes assignment unit setting section  301 . 
     Assignment unit setting section  301  outputs SRS information containing information about the transmission bandwidth, the position of the transmission band, and the frequency hopping pattern with which terminal apparatus  400  (described later) transmits an SRS at one timing, to SRS extraction section  103 , and outputs RBG information containing the basic size and the frequency position of an RBG to assignment section  105 . Here, the frequency position of an end of an arbitrary SRS transmission band that is determined by SRS information matches the frequency position of an end of either RBG that is determined by RBG information. Further, the trans mission bandwidth contained in the SRS information is a natural number multiple of the basic size of the RBG contained in the RBG information. 
     Specifically, assignment unit setting section  301  includes RBG information setting section  311  and SRS information setting section  312 . 
     RBG information setting section  311  determines the basic size of an RBG depending on the system bandwidth, and determines the frequency position of the RBG. Information about the basic size and the frequency position of the RBG thus determined is output as RBG information to assignment section  105 , CQI estimation section  104 , and SRS information setting section  312 . When following this RBG information, it is possible to arrange RBGs thoroughly in the whole system band from the end of the system band. 
     SRS information setting section  312  determines the transmission bandwidth with which terminal apparatus  400  transmits an SRS at one timing, depending on the basic size contained in the RBG information received from RBG information setting section  311 . Further, SRS information setting section  312  determines the frequency position of an SRS so that the frequency position of an end of the RBG detected by the basic size and the frequency position contained in the RBG information received from RBG information setting section  311  matches the frequency position of an end of the SRS. 
     Information about the SRS transmission bandwidth, the frequency position of each SRS transmission band, and the hopping pattern of that frequency position thus determined are output as SRS information to SRS extraction section  103 . 
       FIG. 15  is a block diagram showing a configuration of terminal apparatus  400  according to Embodiment 2 of the present invention. In  FIG. 15 , terminal apparatus  400  includes band information setting section  401 . 
     Band information setting section  401  outputs SRS information containing information about the transmission bandwidth, the position of the transmission band, and the frequency hopping pattern, with which terminal apparatus  400  transmits an SRS at one timing, to mapping section  211 , and outputs RBG information containing the basic size and the frequency position of an RBG to transmission band setting section  205 . Here, the frequency position of an end of an arbitrary SRS transmission band that is determined by SRS information matches the frequency position of an end of either RBG that is determined by RBG information. Further, the transmission bandwidth contained in SRS information is a natural number multiple of the basic size of the RBG contained in RBG information. 
     Specifically, band information setting section  401  includes RBG information setting section  411  and SRS information setting section  412 . 
     RBG information setting section  411  determines the basic size of an RBG depending on the system bandwidth, and determines the frequency position of the RBG. Information about the basic size and the frequency position of the RBG thus determined is output as RBG information to transmission band setting section  205  and SRS information setting section  412 . When following this RBG information, it is possible to arrange RBGs thoroughly in the whole system band from the end of the system band. 
     SRS information setting section  412  determines the transmission bandwidth with which terminal apparatus  400  transmits an SRS at one timing, depending on the basic size contained in the RBG information received from RBG information setting section  411 . Further, SRS information setting section  412  determines the frequency position of an SRS so that the frequency position of an end of the RBG detected by the basic size and the frequency position contained in the RBG information received from RBG information setting section  411  matches the frequency position of an end of the transmission band of the SRS. 
     Information about the SRS transmission bandwidth, the frequency position of each SRS transmission band, and the hopping pattern of that frequency position thus determined are output as SRS information to mapping section  211 . 
     Operations of base station apparatus  300  and terminal apparatus  400  having the above configuration will be described below. 
     Base station apparatus  300  assigns the frequency resources to terminal  400  subject to frequency assignment, per RBG unit, based on the result of the channel estimation obtained for each RBG, and generates a frequency resource assignment bit sequence corresponding to an arrangement pattern of RBGs subject to assignment in the system band and RBGs that are not subject to assignment. Then, base station apparatus  300  transmits the frequency resource assignment bit sequence to terminal apparatus  400 . Terminal apparatus  400  performs data transmission using the frequency resources designated based on the received frequency resource assignment bit sequence. 
     Specifically, in base station apparatus  300 , assignment section  105  assigns frequency resources to terminal  400  subject to frequency assignment, per RBG unit determined by the RBG information received from assignment unit setting section  301 , based on the result of the channel estimation obtained in CQI estimation section  104 , and generates a frequency resource assignment bit sequence corresponding to the arrangement pattern of the RBGs subject to assignment in the system band and the RBGs that are not subject to assignment. 
     Here, the frequency position of an end of an arbitrary SRS transmission band that is determined by SRS information matches the frequency position of an end of either RBG that is determined by RBG information. Further, the transmission bandwidth contained in SRS information is a natural number multiple of the basic size of the RBG contained in RBG information. 
     By this means, as shown in  FIG. 16 , one SRS is transmitted across RBGs located in the sounding band, without any dead space in each RBG. Therefore, it is possible to obtain the result of channel estimation using the SRS transmitted at one timing in each RBG, making it possible to prevent the accuracy of CQI estimation from deteriorating. As a result of this, base station apparatus  300  can assign frequency resources to terminal apparatus  400 , using the CQI without deterioration of the accuracy, so that it is possible to prevent system throughput performance from deteriorating. 
     It is possible to set the transmission bandwidth of an SRS as multiples of the least common multiple of all sizes of RBGs that can be employed in the system. By this means, in addition to the above-described effects, the transmission bandwidth of an SRS that does not depend on changes of the size of an RBG is set, so that processing in terminal apparatus  400  becomes easy. For example, when the size of an RBG used in the system changes in the range of one, two, three and four RBs, the transmission bandwidth of an SRS is set as integral multiples of twelve RBs, which is the least common multiple of the sizes of those RBGs (for example, twelve, twenty four, or thirty six RBs). By this means, it becomes unnecessary to change the transmission bandwidth of an SRS depending on the change of the size of an RBG. 
     As described above, according to the present embodiment, in base station apparatus  300 , assignment unit setting section  301 , which sets the reception band of an SRS in SRS extraction section  103  and sets frequency assignment units (RBGs) in CQI estimation section  104  and assignment section  105 , makes the frequency position of an end of the SRS reception band match the frequency position of an end of either frequency assignment unit, and sets the reception bandwidth of a reference signal as a natural number multiple of the bandwidth of the frequency assignment unit. 
     Further, in terminal apparatus  400 , band information setting section  401 , which sets the transmission band and the frequency assignment units (RBGs), makes the frequency position of an end of the transmission band match the frequency position of an end of either frequency assignment unit, and sets the transmission bandwidth of an SRS as a natural number multiple of the bandwidth of the frequency assignment unit. 
     By this means, one SRS is transmitted across RBGs without any dead space in each RBG. Therefore, it is possible to obtain the result of channel estimation using the SRS transmitted at one timing in each RBG, making it possible to prevent the accuracy of CQI estimation from deteriorating. As a result of this, base station apparatus  300  can assign frequency resources to terminal apparatus  400 , using the CQI without deterioration of the accuracy, so that it is possible to prevent system throughput performance from deteriorating. 
     Also, although cases have been described with the above embodiments as examples where the present invention is configured by hardware, the present invention can also be realized by software. 
     Each function block employed in the description of each of the aforementioned embodiments 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. 
     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 a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible. 
     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. 
     The disclosure of Japanese Patent Application No. 2009-096221, filed on Apr. 10, 2009, including the specification, drawings and abstract, is incorporated herein by reference in its entirety. 
     INDUSTRIAL APPLICABILITY 
     A radio base station apparatus, a radio terminal apparatus, a method of assigning frequency resources, and a method of forming transmission signals according to the present invention are useful for making it possible to prevent the accuracy of channel estimation from lowering when non-contiguous frequency transmission and SRS transmission are employed in an uplink channel. 
     REFERENCE SIGNS LIST 
     
         
           100 ,  300  Base station apparatus 
           101 ,  201  Radio reception section 
           102 ,  202  Demodulation section 
           103  SRS extraction section 
           104  CQI estimation section 
           105  Assignment section 
           106 ,  301  Assignment unit setting section 
           107  Control signal generation section 
           108 ,  207  Modulation section 
           109 ,  215  Radio transmission section 
           111 ,  221 ,  312 ,  412  SRS information setting section 
           112 ,  222 ,  311 ,  411  RBG information setting section 
           200 ,  400  Terminal apparatus 
           203  Decoding section 
           204 ,  401  Band information setting section 
           205  Transmission band setting section 
           206  Encoding section 
           208  DFT section 
           209  SRS generation section 
           210 ,  211  Mapping section 
           212 ,  213  IDFT section 
           214  Multiplexing section