Patent Publication Number: US-2021195575-A1

Title: Radio communication apparatus, method, program, and recording medium

Description:
BACKGROUND 
     Technical Field 
     The present invention relates to a radio communication apparatus, a method, a program, and a recording medium. 
     Background Art 
     Currently, in 3rd Generation Partnership Project (3GPP), standardization of New Radio (NR), which supports even wider frequency band than that supported by Long Term Evolution (LTE), is in progress. 
     For LTE, specifications have been drafted on the assumption that all terminal apparatuses have the capability of performing transmission/reception in a bandwidth of 20 MHz, which is the maximum system bandwidth. In contrast, for NR, it is agreed to define a different maximum communication bandwidth for each user type, by taking account of the possibility of the maximum system bandwidth ranging several hundred MHz to several GHz otherwise (refer to, for example, NPL 1). 
     When a different maximum communication bandwidth is defined for each user type as described above, transmission/reception in the entire system band is not possible for some user types in some cases. To address this, specifications have been drafted in 3GPP that a bandwidth part (BWP) consisting of frequency resources of a system band, is allocated to each user for communication (refer to, for example, NPL 2). A plurality of bandwidth parts may be allocated to each user. Each allocated bandwidth part is switched to active or inactive according to a control signal from a base station. 
     PTL 1, 2, 3, and 4 include disclosures related to a technique for determining resources, such as carriers or the number of carriers allocated for each user, in a technique such as carrier aggregation for aggregating a plurality of carriers, for example. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] JP 2017-050633 A 
         [PTL 2] JP 2015-149566 A 
         [PTL 3] WO 2010/137259 
         [PTL 4] WO 2010/016596 
       
    
     Non Patent Literature 
     
         
         [NPL 1] 3GPP R1-1613663 RAN WG1, “LS on UE RF Bandwidth Adaptation in NR,” November 2016. 
         [NPL 2] 3GPP TR 38.211 V1.0.0, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 15)”, September 2017. 
       
    
     SUMMARY 
     Technical Problem 
     In technologies such as LTE, the center of a communication band used by a terminal apparatus is fixed at the center frequency of a system band or a component carrier, or the like, for example. In contrast, in communication systems, such as NR described above, that use bandwidth parts, it is desired to be able to flexibly determine a communication band in consideration of a bandwidth part(s) configured for each terminal apparatus within a system band. 
     An example object of the present invention is to provide a radio communication apparatus, a method, a program, and a recording medium that make it possible to flexibly determine a communication band in consideration of a bandwidth part(s) configured for a terminal apparatus. 
     Solution to Problem 
     According to an example aspect of the present invention, a radio communication apparatus includes an obtaining unit configured to obtain information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus, and a determining unit configured to determine a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     According to an example aspect of the present invention, a method includes obtaining information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus, and determining a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     According to an example aspect of the present invention, a program is a program that causes a processor to obtain information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus, and determine a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     According to an example aspect of the present invention, a recording medium is a readable non-transitory recording medium having recorded thereon a program that causes a processor to obtain information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus, and determine a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to flexibly determine a communication band in consideration of a bandwidth part(s) configured for a terminal apparatus. Note that, according to the present invention, instead of or together with the above effect, other effects may be exerted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory diagram for illustrating a concrete example of bandwidth parts configured for a terminal apparatus and a communication band used by the terminal apparatus; 
         FIG. 2  is an explanatory diagram illustrating an example of a schematic configuration of a system  1  according to example embodiments of the present invention; 
         FIG. 3  is a block diagram illustrating an example of a schematic configuration of a base station  100  according to a first example embodiment; 
         FIG. 4  is a block diagram illustrating an example of a schematic configuration of a terminal apparatus  300  according to the first example embodiment; 
         FIG. 5  is an explanatory diagram for illustrating an example of a communication band according to a first concrete example; 
         FIG. 6  is an explanatory diagram for illustrating an example of a communication band according to a second concrete example; 
         FIG. 7  is an explanatory diagram for illustrating an example of a communication band according to a third concrete example; 
         FIG. 8  is an explanatory diagram for illustrating an example of a plurality of candidate communication bands; 
         FIG. 9  is an explanatory diagram for illustrating an example of bandwidth parts configured in the same candidate communication band; 
         FIG. 10  is a block diagram illustrating an example of a schematic configuration of a base station  100  according to an example alteration; 
         FIG. 11  is a block diagram illustrating an example of a schematic configuration of a terminal apparatus  200  according to the example alteration; and 
         FIG. 12  is a block diagram illustrating an example of a schematic configuration of a radio communication apparatus  500  according to a second example embodiment. 
     
    
    
     DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     Hereinafter, example embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, in the Specification and drawings, elements to which similar descriptions are applicable are denoted by the same reference signs, and overlapping descriptions may hence be omitted. 
     Descriptions will be given in the following order. 
     1. Overview of Example Embodiments of the Present Invention 
     2. Configuration of System 
     3. First Example Embodiment
         3.1. Configuration of Base Station   3.2. Configuration of Terminal Apparatus   3.3. Technical Features   3.4. Example Alteration       

     4. Second Example Embodiment
         4.1. Configuration of Radio Communication Apparatus   4.2. Technical Features       

     5. Other Example Aspects 
     1. Overview of Example Embodiments of the Present Invention 
     First, an overview of example embodiments of the present invention will be described. 
     (1) Technical Issues 
     Currently, in 3rd Generation Partnership Project (3GPP), standardization of New Radio (NR), which supports even wider frequency band than that supported by Long Term Evolution (LTE), is in progress. 
     For LTE, specifications have been drafted on the assumption that all terminal apparatuses have the capability of performing transmission/reception in a bandwidth of 20 MHz, which is the maximum system bandwidth. In contrast, for NR, it is agreed to define a different maximum communication bandwidth for each user type, by taking account of the possibility of the maximum system bandwidth ranging several hundred MHz to several GHz otherwise (refer to, for example, Reference Literature 1 below). 
     Reference Literature 1: 3GPP R1-1613663 RAN WG1, “LS on UE RF Bandwidth Adaptation in NR,” November 2016. 
     When a different maximum communication bandwidth is defined for each user type as described above, transmission/reception in the entire system band is not possible for some user types in some cases. To address this, specifications have been drafted in 3GPP that a bandwidth part (BWP) consisting of part of frequency resources of a system band, is allocated for each user, to perform communication in the bandwidth part (refer to, for example, Reference Literature 2 below). A plurality of bandwidth parts may be allocated to each user. The allocated bandwidth part(s) is switched to active or inactive according to a control signal from a base station. 
     Reference Literature 2: 3GPP TR 38.211 V1.0.0, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Physical channels and modulation (Release 15)”, September 2017. 
     Reference Literature 3, 4, 5, and 6 below include disclosures related to a technique for determining resources, such as carriers and/or the number of carriers assigned for each user, in a technique such as carrier aggregation for aggregating a plurality of carriers, for example. 
     Reference Literature 3: JP 2017-050633 A 
     Reference Literature 4: JP 2015-149566 A 
     Reference Literature 5: WO 2010/137259 
     Reference Literature 6: WO 2010/016596 
     In technologies such as LTE, the center of a communication band used by a terminal apparatus is fixed at the center frequency of a system band or a component carrier, or the like, for example. In contrast, in communication systems, such as NR described above, that use bandwidth parts, it is desired to be able to flexibly determine a communication band in consideration of a bandwidth part(s) configured for each terminal apparatus within a system band. This is because, for example, if a communication band used by a terminal apparatus is determined without any consideration of a bandwidth part(s) configured for the terminal apparatus, switching of the communication band may occur frequently, for example, as in the following example. 
       FIG. 1  is an explanatory diagram for illustrating a concrete example of bandwidth parts configured for a terminal apparatus and a communication band used by the terminal apparatus. As illustrated in  FIG. 1 , it is assumed that two bandwidth parts BWP #1 and BWP #2 are allocated to the terminal apparatus in a system band. It is also assumed that a communication band used by the terminal apparatus is determined to be a communication band including the bandwidth part BWP #1 but not including the bandwidth part BWP #2 as illustrated in  FIG. 1 , without any consideration of the bandwidth parts BWP #1 and BWP #2. 
     In the example illustrated in  FIG. 1  described above, for example, when the bandwidth part BWP #2 is active, or when the bandwidth part BWP #2 is changed from inactive to active, the terminal apparatus needs to switch the communication band to include the bandwidth part BWP #2, in order to perform reception in the bandwidth part BWP #2. Such switching of the communication bands may cause a time lag in communication, an increase in power consumption by the terminal apparatus, and the like, for example. 
     In view of these, an example object of the example embodiments of the present invention is to flexibly determine a communication band in consideration of a bandwidth part(s) configured for a terminal apparatus. 
     (2) Technical Features 
     In the example embodiments of the present invention, for example, information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus are obtained, and a communication band used by the terminal apparatus is determined based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     With this, it is possible, for example, to flexibly determine a communication band in consideration of a bandwidth part(s) configured for a terminal apparatus. 
     Note that the above-described technical features are concrete examples of the example embodiments of the present invention, and the example embodiments of the present invention are, of course, not limited to the above-described technical features. 
     2. Configuration of System 
     With reference to  FIG. 2 , an example of a configuration of a system  1  according to the example embodiments of the present invention will be described.  FIG. 2  is an explanatory diagram illustrating an example of a schematic configuration of the system  1  according to the example embodiments of the present invention. With reference to  FIG. 2 , the system  1  includes a base station  100  and terminal apparatuses  200 . 
     Although two terminal apparatuses  200  (a terminal apparatus  200 A and a terminal apparatus  200 B) are illustrated in  FIG. 2 , the system  1  may include three or more terminal apparatuses  200 . Here, when the two terminal apparatuses  200  need to be distinguished from each other, the terminal apparatuses  200  are described as the terminal apparatus  200 A and the terminal apparatus  200 B. However, when the two terminal apparatuses  200  need not be distinguished from each other, the terminal apparatuses  200  are simply described as the terminal apparatus(es)  200 . 
     The system  1  is, for example, a system conforming to Third Generation Partnership Project (3GPP) standards/specifications. More specifically, for example, the system  1  may be a system conforming to LTE/LTE-Advanced and/or System Architecture Evolution (SAE) standards/specifications. Alternatively, the system  1  may be a system conforming to fifth-generation (5G)/New Radio (NR) standards/specifications. The system  1  is, of course, not limited to these examples. 
     (1) Base Station  100   
     The base station  100  is a radio access network (RAN) node and is configured to perform radio communication with terminal apparatuses (e.g., the terminal apparatuses  200 ) located in a coverage area  10 . 
     For example, the base station  100  may be an evolved Node B (eNB) or a generation Node B (gNB) in 5G. The base station  100  may include a plurality of units (or a plurality of nodes). The plurality of units (or the plurality of nodes) may include a first unit (or a first node) configured to perform higher protocol layer processing and a second unit (or a second node) configured to perform lower protocol layer processing. As an example, the first unit may be referred to as a center/central unit (CU), and the second unit may be referred to as a distributed unit (DU) or an access unit (AU). As another example, the first unit may be referred to as a digital unit (DU), and the second unit may be referred to as a radio unit (RU) or a remote unit (RU). The digital unit (DU) may be a base band unit (BBU), and the RU may be a remote radio head (RRH) or a remote radio unit (RRU). The terms for the first unit (or the first node) and the second unit (or the second node) are, of course, not limited to these examples. Alternatively, the base station  100  may be a single unit (or a single node). In this case, the base station  100  may be one of the plurality of units (e.g., either one of the first unit and the second unit) or may be connected to another unit of the plurality of units (e.g., the other one of the first unit and the second unit). 
     (2) Terminal Apparatus  200   
     Each terminal apparatus  200  performs radio communication with a base station. For example, the terminal apparatus  200  performs radio communication with the base station  100  in a case of being located in the coverage area  10  of the base station  100 . For example, the terminal apparatus  200  is a user equipment (UE). 
     3. First Example Embodiment 
     Next, a description will be given of a first example embodiment of the present invention with reference to  FIGS. 3 to 11 . 
     3.1. Configuration of Base Station 
     Next, with reference to  FIG. 3 , a description will be given of an example of a configuration of the base station  100  according to the first example embodiment.  FIG. 3  is a block diagram illustrating an example of a schematic configuration of the base station  100  according to the first example embodiment. With reference to  FIG. 3 , the base station  100  includes a radio communication unit  110 , a network communication unit  120 , a storage unit  130 , and a processing unit  140 . 
     (1) Radio Communication Unit  110   
     The radio communication unit  110  wirelessly transmits and/or receives a signal. For example, the radio communication unit  110  receives a signal from a terminal apparatus and transmits a signal to the terminal apparatus. 
     (2) Network Communication Unit  120   
     The network communication unit  120  receives a signal from a network and transmits a signal to the network. 
     (3) Storage Unit  130   
     The storage unit  130  temporarily or permanently stores programs (instructions) and parameters for operations of the base station  100  as well as various data. The program includes one or more instructions for operations of the base station  100 . 
     (4) Processing Unit  140   
     The processing unit  140  provides various functions of the base station  100 . The processing unit  140  includes a communication processing unit  141 , an obtaining unit  143 , a determining unit  145 , a measurement unit  147 , and a configuring unit  149 . Note that the processing unit  140  may further include constituent elements other than these constituent elements. In other words, the processing unit  140  may also perform operations other than the operations of these constituent elements. Concrete operations of the communication processing unit  141 , the obtaining unit  143 , the determining unit  145 , the measurement unit  147 , and the configuring unit  149  will be described later in detail. 
     For example, the processing unit  140  (the communication processing unit  141 ) communicates with a terminal apparatus (e.g., the terminal apparatus  200 ) via the radio communication unit  110 . 
     (5) Implementation Example 
     The radio communication unit  110  may be implemented with an antenna, a radio frequency (RF) circuit, and the like, and the antenna may be a directional antenna. The network communication unit  120  may be implemented with a network adapter and/or a network interface card, and the like. The storage unit  130  may be implemented with a memory (e.g., a nonvolatile memory and/or a volatile memory) and/or a hard disk, and the like. The processing unit  140  may be implemented with one or more processors, such as a baseband (BB) processor and/or a different kind of processor. The communication processing unit  141 , the obtaining unit  143 , the determining unit  145 , the measurement unit  147 , and the configuring unit  149  may be implemented with the same processor or may be implemented with separate processors. The memory (storage unit  130 ) may be included in the one or more processors or may be provided outside the one or more processors. 
     The base station  100  may include a memory configured to store a program (instructions) and one or more processors that can execute the program (instructions). The one or more processors may execute the program and thereby perform operations of the processing unit  140  (operations of the communication processing unit  141 , the obtaining unit  143 , the determining unit  145 , the measurement unit  147 , and/or the configuring unit  149 ). The program may be a program for causing the processor(s) to perform operations of the processing unit  140  (operations of the communication processing unit  141 , the obtaining unit  143 , the determining unit  145 , the measurement unit  147 , and/or the configuring unit  149 ). 
     Note that the base station  100  may be virtual. In other words, the base station  100  may be implemented as a virtual machine. In this case, the base station  100  (the virtual machine) may operate as a physical machine (hardware) including a processor, a memory, and the like, and a virtual machine on a hypervisor. 
     3.2. Configuration of Terminal Apparatus 
     Next, with reference to  FIG. 4 , an example of a configuration of the terminal apparatus  300  of the first example embodiment will be described.  FIG. 4  is a block diagram illustrating an example of a schematic configuration of the terminal apparatus  300  of the first example embodiment. With reference to  FIG. 4 , the terminal apparatus  300  includes a radio communication unit  310 , a storage unit  320 , and a processing unit  330 . 
     (1) Radio Communication Unit  310   
     The radio communication unit  310  wirelessly transmits and/or receives a signal. For example, the radio communication unit  310  receives a signal from a base station and transmits a signal to the base station. 
     (2) Storage Unit  320   
     The storage unit  320  temporarily or permanently stores programs and parameters for operations of the terminal apparatus  300  as well as various data. 
     (3) Processing Unit  330   
     The processing unit  330  provides various functions of the terminal apparatus  300 . The processing unit  330  includes a communication processing unit  331 . Note that the processing unit  330  may further include constituent elements other than these constituent elements. In other words, the processing unit  330  may also perform operations other than the operations of these constituent elements. Concrete operations of the communication processing unit  331  will be described later in detail. 
     For example, the processing unit  330  (for example, the communication processing unit  331 ) communicates with a base station (e.g., the base station  100 ) via the radio communication unit  310 . 
     (4) Implementation Example 
     The radio communication unit  310  may be implemented with an antenna, a radio frequency (RF) circuit, and the like. The storage unit  320  may be implemented with a memory (e.g., a nonvolatile memory and/or a volatile memory) and/or a hard disk, and the like. The processing unit  330  may be implemented with a baseband (BB) processor and/or a different kind of processor, or the like. The memory (the storage unit  320 ) may be included in such a processor (a chip) or may be provided outside the one or more processors. As an example, the processing unit  330  may be implemented in a system on chip (SoC). 
     The terminal apparatus  300  may include a memory configured to store a program (instructions) and one or more processors that can execute the program (instructions). The one or more processors may execute the program and thereby perform operations of the processing unit  330  (operations of the communication processing unit  331 ). The program may be a program for causing the processor(s) to perform operations of the processing unit  330  (operations of the communication processing unit  331 ). 
     3.3. Technical Features 
     Next, technical features of the first example embodiment will be described with reference to  FIGS. 5 to 9 . 
     In the first example embodiment, the base station  100  (the obtaining unit  143 ) obtains information related to a maximum communication bandwidth for the terminal apparatus  200  and information related to one or more bandwidth parts configured for the terminal apparatus  200 . The base station  100  (the determining unit  145 ) then determines a communication band used by the terminal apparatus  200 , based on the information related to the maximum communication bandwidth for the terminal apparatus  200  and the information related to the one or more bandwidth parts configured for the terminal apparatus  200 . 
     The base station  100  (the communication processing unit  141 ) also notifies, to the terminal apparatus  200 , information related to the communication band used by the terminal apparatus  200 . In contrast, the terminal apparatus  200  (the communication processing unit  231 ) communicates with the base station  100  by using the information related to the communication band notified from the base station  100 . 
     (1) Bandwidth Parts 
     For example, each of the bandwidth parts has a bandwidth of two or more resource blocks in a system band (or a component carrier) of a cellular system (or a mobile communication system). In other words, the bandwidth part includes two or more contiguous resource blocks. 
     For example, the base station  100  (the configuring unit  149 ) configures one or more bandwidth parts for the terminal apparatus  200  within the system band (or the component carrier) in consideration of radio transmission path characteristics between the terminal apparatus  200  and the base station  100 , the maximum communication bandwidth for the terminal apparatus  200 , and the like. 
     The one or more bandwidth parts configured for the terminal apparatus  200  is switched to active or inactive by the base station  100 , for example. Only when the bandwidth part is active, data is mapped to the resource blocks in the bandwidth part. Specifically, the bandwidth part is switched to active or inactive according to the amount of data communicated between the base station  100  and the terminal apparatus  200 , and the like. 
     (2) Communication Band Used by Terminal Apparatus 
     The communication band used by the terminal apparatus  200  is, for example, a reception band used by the terminal apparatus  200  or a transmission band used by the terminal apparatus  200 . Alternatively, the communication band used by the terminal apparatus  200  corresponds to both a reception band and a transmission band. 
     (2-1) Determination of Communication Band 
     The bandwidth of the communication band used by the terminal apparatus  200  is determined based on the maximum communication bandwidth for the terminal apparatus  200  within a range not exceeding the maximum communication bandwidth. The communication band used by the terminal apparatus  200  is determined based on the information related to the bandwidth part(s) configured for the terminal apparatus  200 , as in first to third concrete examples below, for example. 
     First Concrete Example 
     For example, as a first concrete example, the communication band used by the terminal apparatus  200  may include all bandwidth parts configured for the terminal apparatus  200 . 
       FIG. 5  is an explanatory diagram for illustrating an example of a communication band according to the first concrete example. Specifically,  FIG. 5  illustrates an example of a case where two bandwidth parts BWP #1 and BWP #2 are configured for the terminal apparatus  200 . In this case, the base station  100  (the determining unit  145 ) determines the communication band used by the terminal apparatus  200 , to include all the bandwidth parts BWP #1 and BWP #2. 
     By thus determining the communication band, it is possible, for example, even when the bandwidth part BWP #1 or the bandwidth part BWP #2 as that illustrated in  FIG. 5  is switched to active, to perform communication using the bandwidth parts BWP #1 and BWP #2 without switching the communication band for the terminal apparatus  200 . 
     Second Concrete Example 
     For example, as a second concrete example, the communication band used by the terminal apparatus  200  may include all active bandwidth part(s) among one or more bandwidth parts configured for the terminal apparatus  200 . 
       FIG. 6  is an explanatory diagram for illustrating an example of a communication band according to the second concrete example. Specifically,  FIG. 6  illustrates an example of a case where three bandwidth parts BWP #1, BWP #2, and BWP #3 aligned in the frequency direction are configured for the terminal apparatus  200 . Here, the two bandwidth parts BWP #1 and BWP #2 are active, while the one bandwidth part BWP #3 is inactive. 
     In the example illustrated in  FIG. 6 , the base station  100  (the determining unit  145 ) determines the communication band used by the terminal apparatus  200 , to include all the active bandwidth parts BWP #1 and BWP #2 among the configured bandwidth parts BWP #1, BWP #2, and BWP #3. 
     By thus determining the communication band, switching of the communication band for the terminal apparatus  200  occurs only when the bandwidth part BWP #3 is switched from inactive to active. Hence, it is possible to suppress the frequency of switching of the communication band for the terminal apparatus  200 . 
     Third Concrete Example 
     For example, as a third concrete example, the communication band used by the terminal apparatus  200  may include all active bandwidth parts and one or more inactive bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus  200 . 
       FIG. 7  is an explanatory diagram for illustrating an example of a communication band according to the third concrete example. Specifically,  FIG. 7  illustrates an example of a case where four bandwidth parts BWP #1, BWP #2, BWP #3, and BWP #4 aligned in the frequency direction are configured for the terminal apparatus  200 . Here, the one bandwidth part BWP #2 is active, while the other three bandwidth parts BWP #1, BWP #3, and BWP #4 are inactive. 
     In this case, the base station  100  (the determining unit  145 ) determines the communication band used by the terminal apparatus  200 , to include at least one of the inactive bandwidth parts BWP #1, BWP #3, and BWP #4 in addition to all the active bandwidth part BWP #1 among the configured bandwidth parts BWP #1, BWP #2, BWP #3, and BWP #4. 
     In particular, the base station  100  (the determining unit  145 ) preferably determines the communication band used by the terminal apparatus  200 , to include all the active bandwidth parts and the maximum number of inactive bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus  200 . 
     For example, in the example illustrated in  FIG. 7 , a gap between the bandwidth part BWP #2 and the bandwidth part BWP #3 and a gap between the bandwidth part BWP #3 and the bandwidth part BWP #4 are shorter than a gap between the bandwidth part BWP #1 and the bandwidth part BWP #2. Hence, the communication band can include the total of three bandwidth parts BWP #2, BWP #3, and BWP #4 as illustrated in  FIG. 7 . In other words, the base station  100  (the determining unit  145 ) determining the communication band used by the terminal apparatus  200 , to include the bandwidth parts BWP #2, BWP #3, and BWP #4, allows more inactive bandwidth parts to be included. 
     By thus determining the communication band as illustrated in  FIG. 7 , switching of the communication band for the terminal apparatus  200  occurs only when the bandwidth part BWP #1 among the inactive bandwidth parts BWP #1, BWP #3, and BWP #4 is switched to active. Hence, it is possible to suppress the frequency of switching of the communication band for the terminal apparatus  200 . 
     (2-2) Measurement Based on Communication Band 
     For example, the base station  100  (the measurement unit  147 ) may measures radio transmission path characteristics between the terminal apparatus  200  and the base station  100 , within the communication band used by the terminal apparatus  200 . Concretely, the base station  100  (the measurement unit  147 ) may measure radio transmission path characteristics with reference to an uplink reference signal transmitted from the terminal apparatus  200  within the communication band, for example. Then, based on a result of the measurement, the base station  100  (the configuring unit  149 ) may update the configuration of the bandwidth part(s) with a priority given to the bandwidth(s) included in the communication band in the system band. 
     As described above, for example, by giving a priority to measurement within the communication band at the time of updating the configuration of the bandwidth part(s), it is possible to suppress frequency of switching of the communication band for the terminal apparatus  200 . 
     (2-3) Plurality of Candidate Communication Bands 
     For example, the communication band used by the terminal apparatus  200  may be determined from among candidate communication bands the number of which is equal to or smaller than a predetermined number. Specifically, the base station  100  (the determining unit  145 ) may determine a communication band used by the terminal apparatus  200  from among a plurality of candidate communication bands, based on the information related to the maximum communication bandwidth for the terminal apparatus  200  and the information related to the one or more bandwidth parts configured for the terminal apparatus  200 . 
     In this case, the information related to the communication band used by the terminal apparatus  200  may be information related to a candidate corresponding to the communication band used by the terminal apparatus  200  among the plurality of candidate communication bands. In other words, the base station  100  (the communication processing unit  141 ) may notify, to the terminal apparatus  200 , information related to the candidate corresponding to the communication band used by the terminal apparatus  200 . 
       FIG. 8  is an explanatory diagram for illustrating an example of a plurality of candidate communication bands. In the example illustrated in  FIG. 8 , three candidate communication bands (candidate communication bands #1, #2, and #3) are configured within a system band. In the example illustrated in  FIG. 8 , the communication band used by the terminal apparatus  200  is determined from among the candidate communication bands #1, #2, and #3. Information indicating the determined candidate communication band is then notified from the base station  100  to the terminal apparatus  200 . 
     By thus determining the communication band used by the terminal apparatus  200  from among the three candidate communication bands #1, #2, and #3, information related to the communication band notified from the base station  100  to the terminal apparatus  200  can be expressed by 2-bit information. In other words, it is possible to suppress overhead of control information for notifying the information related to the communication band used by the terminal apparatus  200 . 
     Note that information related to a plurality of candidate communication bands may be included in control information notified from the base station  100  to the terminal apparatus  200  before determination of the communication band. With this, it is possible for the base station  100  and the terminal apparatus  200  to have common understanding about the type of communication band of each candidate. 
     Configuration of Bandwidth Part(s), Based on Plurality of Candidate Communication Bands 
     For example, the one or more bandwidth parts may be configured in the same candidate communication band among the plurality of candidate communication bands. In other words, the base station  100  (the configuring unit  149 ) may configure all bandwidth parts used by the terminal apparatus  200  within one candidate communication band. 
       FIG. 9  is an explanatory diagram for illustrating an example of bandwidth parts configured in the same candidate communication band. In the example illustrated in  FIG. 9 , all the bandwidth parts BWP #1 and BWP #2 are configured within the candidate communication band #1. In other words, the base station  100  (the configuring unit  149 ) configures all the bandwidth parts BWP #1 and BWP #2 within the candidate communication band #1. The base station  100  (the determining unit  145 ) only needs to determine the candidate communication band #1 as the communication band used by the terminal apparatus  200 , with reference to the above-described configuration of the bandwidth parts BWP #1 and BWP #2. 
     By thus configuring all the bandwidth parts used by the terminal apparatus  200  within the same communication band, it is possible, for example, even when the bandwidth part BWP #1 or BWP #2 is switched to active as illustrated in  FIG. 9 , to perform communication using the bandwidth parts BWP #1 and BWP #2 without switching the communication band for the terminal apparatus  200 . 
     3.4. Example Alteration 
     Various alterations are possible in the first example embodiment without being limited to the above-described configurations. For example, determination of the communication band used by the terminal apparatus  200  may be performed by the terminal apparatus  200 . The information related to the communication band used by the terminal apparatus  200  may be notified from the terminal apparatus  200  to the base station  100 . 
     (1) Configuration of Base Station  100   
       FIG. 10  is a block diagram illustrating an example of a schematic configuration of the base station  100  according to an example alteration. As illustrated in  FIG. 10 , the base station  100  includes the radio communication unit  110 , the network communication unit  120 , the storage unit  130 , and the processing unit  140 . The processing unit  140  includes the communication processing unit  141  and the configuring unit  149 . Note that the processing unit  140  may further include constituent elements other than these constituent elements. 
     (2) Configuration of Terminal Apparatus  200   
       FIG. 11  is a block diagram illustrating an example of a schematic configuration of a terminal apparatus  200  according to the example alteration. As illustrated in  FIG. 11 , the terminal apparatus  200  includes the radio communication unit  210 , the storage unit  220 , and the processing unit  230 . The processing unit  230  includes the communication processing unit  231 , the obtaining unit  233 , the determining unit  235 , and the measurement unit  237 . Note that the processing unit  230  may further include constituent elements other than these constituent elements. 
     (3) Technical Features 
     Next, technical features of the example alteration will be described. 
     In the example alteration, the terminal apparatus  200  (the obtaining unit  233 ) obtains information related to a maximum communication bandwidth for the terminal apparatus  200  and information related to one or more bandwidth parts configured for the terminal apparatus  200 . The terminal apparatus  200  (the determining unit  235 ) then determines a communication band used by the terminal apparatus  200 , based on the information related to the maximum communication bandwidth for the terminal apparatus  200  and the information related to the one or more bandwidth parts configured for the terminal apparatus  200 . 
     The terminal apparatus  200  (the communication processing unit  231 ) also notifies, to the base station  100 , information related to the communication band used by the terminal apparatus  200 . In contrast, the base station  100  (the configuring unit  149 ) updates a configuration of bandwidth part(s) used by the terminal apparatus  200 , based on the information related to the communication band notified from the terminal apparatus  200 . 
     Determination of Communication Band 
     The bandwidth of the communication band used by the terminal apparatus  200  is determined based on the maximum communication bandwidth for the terminal apparatus  200  within a range not exceeding the maximum communication bandwidth. The communication band used by the terminal apparatus  200  is determined based on the information related to the bandwidth part configured for the terminal apparatus  200 , as follows, for example. 
     For example, the communication band used by the terminal apparatus  200  may include all bandwidth parts configured for the terminal apparatus  200 . 
     As another example, the communication band used by the terminal apparatus  200  may include all active bandwidth part(s) among one or more bandwidth parts configured for the terminal apparatus  200 . 
     As a still another example, the communication band used by the terminal apparatus  200  may include all active bandwidth part(s) and one or more inactive bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus  200 . In particular, the terminal apparatus  200  (the determining unit  235 ) may determine the communication band used by the terminal apparatus  200 , to include all active bandwidth parts and the maximum number of inactive bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus  200 . 
     Measurement Based on Communication Band 
     For example, the terminal apparatus  200  (measurement unit  237 ) may perform measurement of radio transmission path characteristics between the terminal apparatus  200  and the base station  100 , within the communication band used by the terminal apparatus  200 . 
     For example, for update of a configuration of a bandwidth part(s), the terminal apparatus  200  (the measurement unit  237 ) performs, in response to request of measurement of radio transmission path characteristics from the base station  100 , measurement of radio transmission path characteristics within the determined communication band with a higher priority than that for other band within the system band. Concretely, the terminal apparatus  200  (the measurement unit  237 ) measures radio transmission path characteristics with reference to a downlink reference signal transmitted from the base station  100  within the communication band, for example. 
     By notifying a result of the measurement from the terminal apparatus  200  to the base station  100 , a bandwidth part(s) within the communication band can be configured with a higher priority. Consequently, it is possible to suppress the frequency of switching of the communication band for the terminal apparatus  200 . 
     Plurality of Candidate Communication Bands 
     For example, the communication band used by the terminal apparatus  200  may be determined from among candidate communication bands the number of which is equal to or smaller than a predetermined number. Specifically, the terminal apparatus  200  (determining unit  235 ) may determine a communication band used by the terminal apparatus  200  from among a plurality of candidate communication bands, based on the information related to the maximum communication bandwidth for the terminal apparatus  200  and the information related to the one or more bandwidth parts configured for the terminal apparatus  200 . 
     4. Second Example Embodiment 
     Next, a description will be given of a second example embodiment of the present invention with reference to  FIG. 12 . The above-described first example embodiment is a concrete example embodiment, whereas the second example embodiment is a more generalized example embodiment. 
     4.1. Configuration of Radio Communication Apparatus 
     With reference to  FIG. 12 , an example of a configuration of a radio communication apparatus  500  according to the second example embodiment will be described.  FIG. 12  is a block diagram illustrating an example of a schematic configuration of the radio communication apparatus  500  according to the second example embodiment. With reference to  FIG. 12 , the radio communication apparatus  500  includes an obtaining unit  510  and a determining unit  520 . Concrete operations of the obtaining unit  510  and the determining unit  520  will be described later in detail. 
     The obtaining unit  510  and the determining unit  520  may be implemented with one or more processors (such as a BB processor and/or a different kind of processor) and a memory. The memory may be included in the one or more processors or may be provided outside the one or more processors. 
     The obtaining unit  510  and the determining unit  520  may include a memory configured to store a program (instructions) and one or more processors that can execute the program (instructions). The one or more processors may execute the program and thereby perform operations of the obtaining unit  510  and the determining unit  520 . The program may be a program for causing the processor(s) to execute the operations of the obtaining unit  510  and the determining unit  520 . 
     Note that the radio communication apparatus  500  may, of course, further include constituent elements other than the obtaining unit  510  and the determining unit  520 . For example, the radio communication apparatus  500 , as in the first example embodiment, may further include the radio communication unit  110 , the network communication unit  120 , and/or the storage unit  130 , and/or may further include other constituent elements. 
     4.2. Technical Features 
     Technical features of the second example embodiment will be described. 
     In the second example embodiment, the radio communication apparatus  500  (the obtaining unit  510 ) obtains information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus. The radio communication apparatus  500  (the determining unit  520 ) then determines a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     With this, it is possible, for example, to flexibly determine a communication band in consideration of a bandwidth part(s) configured for the terminal apparatus. 
     As an example, descriptions of a bandwidth part(s) and/or a communication band used by the terminal apparatus may be the same as those in the first example embodiment. Hence, overlapping descriptions are omitted here. Note that, in this case, the obtaining unit  510  may operate similarly to the obtaining unit  143  or the obtaining unit  233  of the first example embodiment, and the determining unit  520  may operate similarly to the determining unit  145  or the determining unit  235  of the first example embodiment. 
     The second example embodiment is, of course, not limited to this example. 
     5. Other Example Aspects 
     Descriptions have been given above of the example embodiments of the present invention. However, the present invention is not limited to these example embodiments. It should be understood by those of ordinary skill in the art that these example embodiments are merely examples and that various alterations are possible without departing from the scope and the spirit of the present invention. 
     An apparatus including constituent elements (e.g., the communication processing unit, the obtaining unit, the determining unit, the measurement unit, and/or the configuring unit) of the base station described in the Specification (e.g., one or more apparatuses (or units) among a plurality of apparatuses (or units) constituting the base station or a module for one of the plurality of apparatuses (or units)) may be provided. An apparatus including the constituent elements (e.g., the communication processing unit, the obtaining unit, the determining unit, and/or the measurement unit) of the terminal apparatus described in the Specification (e.g., a module for the terminal apparatus) may be provided. Moreover, methods including processing of the constituent elements may be provided, and programs for causing a processor to execute processing of the constituent elements may be provided. Moreover, non-transitory computer-readable recording media (non-transitory computer readable media) having recorded thereon the programs may be provided. It is apparent that such apparatuses, modules, methods, programs, and non-transitory computer-readable recording media are also included in the present invention. 
     The whole or part of the example embodiments disclosed above can be described as, but not limited to, the following supplementary notes. 
     (Supplementary Note 1) 
     A radio communication apparatus comprising: 
     an obtaining unit configured to obtain information related to a maximum communication band for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus; and 
     a determining unit configured to determine a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 2) 
     The radio communication apparatus according to Supplementary Note 1, wherein the radio communication apparatus is a base station which performs radio communication with the terminal apparatus. 
     (Supplementary Note 3) 
     The radio communication apparatus according to Supplementary Note 2, further comprising a communication processing unit configured to notify, to the terminal apparatus, information related to the communication band used by the terminal apparatus. 
     (Supplementary Note 4) 
     The radio communication apparatus according to Supplementary Note 1, wherein the radio communication apparatus is the terminal apparatus. 
     (Supplementary Note 5) 
     The radio communication apparatus according to Supplementary Note 4, further comprising a communication processing unit configured to notify, to a base station which performs radio communication with the terminal apparatus, information related to the communication band used by the terminal apparatus. 
     (Supplementary Note 6) 
     The radio communication apparatus according to Supplementary Note 3 or 5, wherein 
     the determining unit is configured to determine the communication band used by the terminal apparatus among a plurality of candidate communication bands, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus, and 
     the information related to the communication band used by the terminal apparatus is information related to a candidate corresponding to the communication band used by the terminal apparatus among the plurality of candidate communication bands. 
     (Supplementary Note 7) 
     The radio communication apparatus according to Supplementary Note 6, wherein the one or more bandwidth parts are configured in the same candidate communication band among the plurality of candidate communication bands. 
     (Supplementary Note 8) 
     The radio communication apparatus according to any one of Supplementary Notes 1 to 7, wherein the communication band used by the terminal apparatus includes all bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 9) 
     The radio communication apparatus according to any one of Supplementary Notes 1 to 7, wherein the communication band used by the terminal apparatus includes all active bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 10) 
     The radio communication apparatus according to any one of Supplementary Notes 1 to 7, wherein the communication band used by the terminal apparatus includes all active bandwidth parts and one or more inactive bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 11) 
     The radio communication apparatus according to Supplementary Note 10, wherein the determining unit is configured to determine the communication band used by the terminal apparatus to include all active bandwidth parts and a maximum number of inactive bandwidth parts among the one or more bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 12) 
     The radio communication apparatus according to any one of Supplementary Notes 1 to 11, further comprising a measurement unit configured to perform measurement of a radio transmission path characteristic between the terminal apparatus and a base station, within the communication band used by the terminal apparatus. 
     (Supplementary Note 13) 
     A method comprising: 
     obtaining information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus; and 
     determining a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 14) 
     A program that causes a processor to: 
     obtain information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus; and 
     determine a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     (Supplementary Note 15) 
     A readable non-transitory recording medium having recorded thereon a program that causes a processor to: 
     obtain information related to a maximum communication bandwidth for a terminal apparatus and information related to one or more bandwidth parts configured for the terminal apparatus; and 
     determine a communication band used by the terminal apparatus, based on the information related to the maximum communication bandwidth for the terminal apparatus and the information related to the one or more bandwidth parts configured for the terminal apparatus. 
     This application claims priority based on JP 2017-218768 filed on Nov. 14, 2017, the entire disclosure of which is incorporated herein. 
     INDUSTRIAL APPLICABILITY 
     It is possible to flexibly determine a communication band in consideration of a bandwidth part configured for a terminal apparatus, in a mobile communication system. 
     REFERENCE SIGNS LIST 
     
         
           1  System 
           100  Base Station 
           141 ,  231  Communication Processing Unit 
           143 ,  233 ,  510  Obtaining Unit 
           145 ,  235 ,  520  Determining Unit 
           147 ,  237  Measurement Unit 
           149  Configuring Unit 
           200  Terminal Apparatus 
           500  Radio Communication Apparatus