Radio base station, wireless terminal, radio communication system, transmission power controlling method, control circuit and program storage medium

The present invention includes: a plurality of antenna sections, each of which to generate base station reception beams and to receive, by using the base station reception beams, one or more signals transmitted from a wireless terminal using one or more terminal transmission beams; a measurement unit that measures reception quality of each of the signals for each of the base station reception beams; and a control unit that groups the base station reception beams into groups in units of the antenna sections, and perform transmission power control on the terminal transmission beams of the wireless terminal in units of the groups, on the basis of a result of measurement of the measurement unit in units of the groups.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio base station, a wireless terminal, a radio communication system, and a transmission power controlling method for controlling transmission power of the wireless terminal.

2. Description of the Related Art

A wireless terminal that communicates with a radio base station typically controls transmission power of a signal transmitted therefrom to the radio base station. This is to allow a signal transmitted by the wireless terminal to be received by the radio base station without any error, and to prevent unnecessary interference with other radio base stations.

The New Radio (NR) standard defined in the 3rd Generation Partnership Project (3GPP) specifies two control methods, which are open-loop power control and closed-loop power control, as transmission power control methods for wireless terminals, for application to the 5th Generation Mobile Communications Systems (Non Patent Literature 1).

The open-loop power control is a control method performed when a wireless terminal starts communicating with a radio base station, or when a wireless terminal connects with another radio base station by handover and starts communicating with the radio base station. In the open-loop power control, the radio base station notifies the wireless terminal of, a target reception power value of a preamble to be transmitted by the wireless terminal using a physical random access channel (PRACH) when starting communication as notification information. The wireless terminal calculates a path loss of downlink transmission (in the direction from the radio base station to the wireless terminal) from a reception power value of a signal transmitted periodically from the radio base station and a transmission power value of the radio base station of which the wireless terminal is separately notified by the radio base station. Then, the wireless terminal determines transmission power of an uplink signal by adding a power value corresponding to the calculated path loss to the target reception power value of the preamble, of which the wireless terminal is notified by the radio base station.

In contrast, the closed-loop power control is a control method for controlling transmission power of a wireless terminal by transmitting a transmission power control (TPC) command explicitly identifying an increase or decrease in the transmission power by a radio base station to the wireless terminal after communication is started. While communicating with the radio base station, the wireless terminal once determines the transmission power value by the open-loop power control, adjusts the transmission power in accordance with the closed-loop power control from the radio base station, and determines a final transmission power value (See, for example, Non Patent Literature 1: 3GPP TS 38.213 V15.0.0 (2017-12)).

According to the NR standard, a configuration in which one radio base station transmits signals from a plurality of antennas installed at different locations, that is, a configuration in which one radio base station includes a plurality of transmission reception points (TRPs) can be considered. A TRP is a location at which the radio base station actually transmits and receives signals, that is a location at which an antenna is installed. In a case where a wireless terminal transmits signals by setting the same transmission power for all transmission beams, the reception powers of the signals from the wireless terminal may be different among TRPs of a radio base station that includes a plurality of TRPs. In addition, interference powers from other wireless terminals may also be different among the TRPs of the radio base station. Moreover, the signal to interference plus noise power ratios (SINRs) of the signals from the wireless terminal may be different among the TRPs, and some TRPs may satisfy proper SINR values while other TRPs may not.

With the technology described in Non Patent Literature 1, however, different transmission power control commands cannot be used for each of the TRPs. Thus, in a case where the SINRs of signals from a wireless terminal are different among different TRPs and some TRPs satisfy proper SINR values while the other TRPs do not, the transmission powers of the transmission beams from the wireless terminal toward the TRPs can only be performed such that the transmission powers are increased or decreased for all the TRPs according to the technology described in Non Patent Literature 1. There is thus a problem in that control for making the individual SINRs at the TRPs included in the radio base station closer to proper SINR values, cannot be performed.

The present invention has been made in view of the above, and an object thereof is to provide a radio base station capable of controlling transmission powers of signals transmitted by a wireless terminal in units of locations at which the signals are received in a case where signals from a wireless terminal can be received at a plurality of locations.

SUMMARY OF THE INVENTION

A radio base station according to the present invention includes: a plurality of base station antenna sections, each of which generates base station reception beams, and receives, by using the base station reception beams, one or more signals transmitted from a wireless terminal using one or more terminal transmission beams. The radio base station also includes a measurement unit that measures reception quality of each of the signals for each of the base station reception beams. The radio base station also includes a control unit that groups the base station reception beams into groups in units of the base station antenna sections, and performs transmission power control on the terminal transmission beams of the wireless terminal in units of the groups on the basis of a result of measurement of the measurement unit in units of the groups.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A radio base station, a wireless terminal, a radio communication system, and a transmission power controlling method according to certain embodiments of the present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments.

First Embodiment

In the present embodiment, assume a radio communication system, in which the wireless terminal generates a transmission beam and the radio base station generates a reception beam to perform radio communication therebetween when a radio base station receives a signal transmitted from a wireless terminal. While a case where the radio base station includes two TRPs will be described in the present embodiment, the number of TRPs of the radio base station is not limited to two. Hereinafter, one or more beams associated with one TRP will be referred to as a TRP group. Specifically, a reception beam generated by one TRP in the radio base station belongs to one TRP group, and one or more transmission beams generated to be directed toward one TRP by the wireless terminal also belongs to one TRP group. The radio base station applies a transmission power control command in units of TRP groups, that is, controls transmission power of transmission beams of the wireless terminal in units of TRP groups. In the description below, a transmission beam generated by the wireless terminal will be referred to as a terminal transmission beam, and a reception beam generated by the radio base station will be referred to as a base station reception beam.

First, a method for determining association between a plurality of terminal transmission beams generated by the wireless terminal and a TRP will be explained.FIG. 1is a diagram illustrating an example of a configuration of a radio communication system50according to the first embodiment of the present invention. The radio communication system50includes a radio base station10, and a wireless terminal20. The radio base station10includes a signal processing unit17, and antenna sections14aand14b. Hereinafter, the locations at which the antenna sections14aand14bare installed will be referred to as TRP #1and TRP #2, respectively. The radio base station10performs radio communication with the wireless terminal20by using the antenna sections14aand14b. The antenna sections14aand14beach generate four base station reception beams, and receive signals transmitted from the wireless terminal20by using the base station reception beams. In the example ofFIG. 1, the base station reception beams generated by the antenna section14awill be referred to as base station reception beams101to104, and the base station reception beams generated by the antenna section14bwill be referred to as base station reception beams105to108. The wireless terminal20generates six terminal transmission beams201to206, and transmits signals to the radio base station10by using the terminal transmission beams201to206. While the number of wireless terminals20in the radio communication system50is one inFIG. 1, this is one example, and the number of wireless terminals20may be two or more.

In the radio communication system50illustrated inFIG. 1, the wireless terminal20first transmits sounding signals by using the terminal transmission beams201to206that are all the beams which can be generated. A sounding signal is a measurement signal used for measuring the reception quality of a signal received by the radio base station10. The sounding signals are used for associating a plurality of terminal transmission beams with a TRP. The radio base station10receives the sounding signals by using the base station reception beams101to108, and measures the reception quality of each sounding signal for each base station reception beam. Note that, in a case where the wireless terminal20cannot generate all of the terminal transmission beams201to206at the same time, the wireless terminal20may generate the terminal transmission beams at different timings. In other words, the wireless terminal20may generate the terminal transmission beams201to206separately at multiple timings. In a similar manner, in a case where the radio base station10cannot generate all of the base station reception beams101to108at the same time, the radio base station10may generate the base station reception beams at different timings. In other words, the radio base station10may generate the base station reception beams101to108separately at multiple timings. In the present embodiment, an example in which the wireless terminal20is capable of generating all of the terminal transmission beams201to206at the same time, and the radio base station10is capable of generating all of the base station reception beams101to108at the same time will be described.

The radio base station10selects a terminal transmission beam from the wireless terminal20with which base station reception beams can achieve good reception quality on the basis of the results of measurement of the reception quality of the sounding signals. Good reception quality indicates a level in which the result of measurement of the reception quality, such as the SINR, is equal to or higher than a preset threshold. Note that, in order to select a terminal transmission beam with which good reception quality can be achieved, the radio base station10needs to distinguish a plurality of terminal transmission beams from the wireless terminal20from each other. Examples of methods for distinguishing a plurality of terminal transmission beams from the wireless terminal20at the radio base station10include a method of associating, by the wireless terminal20, a sequence pattern on a sounding signal to be transmitted by each terminal transmission beam with a terminal transmission beam identifier (ID). The examples also include a method of associating, by the wireless terminal20, the time at which a sounding signal to be transmitted by each terminal transmission beam with a terminal transmission beam ID. The examples also include a method of associating, by the wireless terminal20, a frequency domain in which a sounding signal to be transmitted by each terminal transmission beam is placed with a terminal transmission beam ID. A terminal transmission beam ID is identification information for identifying each terminal transmission beam, that is, information capable of identifying each of the terminal transmission beams201to206in the example ofFIG. 1. Note that, a method for generating a sequence to be put on a sounding signal is described in 6.4.1.4.2 of 3GPP specification TS 38.211 V15.0.0.

FIG. 2is a diagram illustrating an example of frequency mapping of a sounding signal transmitted by the wireless terminal20according to the first embodiment. Information on the frequency mapping illustrated inFIG. 2shows association between frequency domains f1to f6in each of which a sounding signal transmitted by the wireless terminal20is placed and terminal transmission beam IDs. InFIG. 2, the terminal transmission beam IDs are represented by201to206. The wireless terminal20transmits a sounding signal by each terminal transmission beam by using only the frequency domain assigned to the terminal transmission beam. For example, the wireless terminal20transmits a sounding signal by the terminal transmission beam201within the frequency domain f1. The radio base station10is capable of determining terminal transmission beams from the wireless terminal20with which base station reception beams can achieve good reception quality by specifying information on frequency mapping illustrated inFIG. 2to the wireless terminal20in advance.

FIG. 3is a table illustrating an example of a result of selecting, for each base station reception beam, a terminal transmission beam from the wireless terminal20achieving good reception quality at the radio base station10according to the first embodiment. As illustrated inFIG. 3, at the radio base station10, regarding the base station reception beam102, the sounding signal transmitted from the wireless terminal20by the terminal transmission beam202has good reception quality. In addition, at the radio base station10, regarding the base station reception beam103, the sounding signal transmitted from the wireless terminal20by the terminal transmission beam201has good reception quality. In addition, at the radio base station10, regarding the base station reception beam106, the sounding signal transmitted from the wireless terminal20by the terminal transmission beam205has good reception quality. In addition, at the radio base station10, regarding the base station reception beam107, the sounding signal transmitted from the wireless terminal20by the terminal transmission beam206has good reception quality.FIG. 3also illustrates that, at the radio base station10, good reception quality of the sounding signal transmitted from the wireless terminal20is not achieved regarding the base station reception beams101,104,105, and108.

FIG. 3further illustrates the association between each base station reception beam at the radio base station10and a TRP group ID. A TRP group ID is information identifying each TRP group. In the example illustrated inFIG. 3, the TRP group ID of the TRP group associated with the TRP #1is represented by #1, and the TRP group ID of the TRP group associated with the TRP #2is represented by #2. In the example illustrated inFIG. 3, the base station reception beams101to104belong to TRP group ID #1, and the base station reception beams105to108belong to TRP group ID #2.

The radio base station10notifies the wireless terminal20of the association between the terminal transmission beams from the wireless terminal20achieving good reception quality and the TRP group IDs as illustrated inFIG. 3. For a method for the notification from the radio base station10to the wireless terminal20, layer1signaling using a physical downlink control channel (PDCCH) defined in the NR standard, MAC signaling by a medium access control (MAC) layer, or the like is used. A specific example of the notification information contains: TRP group ID #1={terminal transmission beam201, terminal transmission beam202}; and TRP group ID #2={terminal transmission beam205, terminal transmission beam206}. This means that the radio base station10grouped the terminal transmission beams201and202into the TRP group ID #1, and the terminal transmission beams205and206into the TRP group ID #2. The groups represented by the TRP group IDs #1and #2are groups into which a plurality of terminal transmission beams from the wireless terminal20are grouped in units of TRPs #1and #2, of the radio base station10at which signals transmitted by the terminal transmission beams are received.

Next, a method by which the radio base station10controls the transmission power of the wireless terminal20by using a transmission power control command will be explained.FIG. 4is a diagram illustrating an example of a state in which the radio base station10according to the first embodiment causes the wireless terminal20to transmit signals such as data by using the specified terminal transmission beams201,202,205, and206. The radio base station10specifies the terminal transmission beams of the wireless terminal20by using UL grant defined in the NR standard. Format 0_1 of downlink control information (DCI) defined in 3GPP specification TS 38.212 V15.0.0 is used for transmission of a message permitting the wireless terminal20to perform PUSCH transmission, that is, the aforementioned UL grant. An “SRS resource indicator” is defined in a message of Format 0_1, which specifies a beam of a sounding signal (sounding reference signal: SRS) or a beam of a PUSCH signal using the same beam as the sounding signal. In addition, “TPC command for scheduled PUSCH” is defined in the message of Format 0_1, which is a transmission power control command. Note that, in the present embodiment, elements of the transmission power control command are extended to correspond to the number of TRP groups. Specifically, when the number of TRP groups is n, the transmission power control command is defined as “TPC command for scheduled PUSCH #1”, “TPC command for scheduled PUSCH #2”, . . . , “TPC command for scheduled PUSCH #n”. In the present embodiment, the extended format will be referred to as Format 0_1E.

A case where the extended format of Format 0_1E is applied to the example ofFIG. 4will be explained.FIG. 5is a diagram illustrating an example of a result of measurement of reception quality at each TRP of the radio base station10according to the first embodiment. As described above, assume that the reception quality indicates an SINR. In the example ofFIG. 5, the SINR satisfies a proper SINR value at the TRP #1while the SINR does not satisfy the proper SINR value at the TRP #2. In such a case, the radio base station10notifies the wireless terminal20of a message containing content of the transmission power control command. The content included in the message is: “TPC command for scheduled PUSCH #1=−1 [dB]”, “TPC command for scheduled PUSCH #2=+1 [dB]”, and “SRS resource indicator={201,202,205,206}”.

Upon receiving the message including the aforementioned content, the wireless terminal20controls the transmission powers of the terminal transmission beams in accordance with the content in the message. As described above, the wireless terminal20has separately received the information of TRP group ID #1={terminal transmission beam201, terminal transmission beam202} and TRP group ID #2={terminal transmission beam205, terminal transmission beam206}. The wireless terminal20uses the obtained information, and accumulates the transmission power by −1 [dB] from the value at the previous transmission for the TRP group ID #1that is, the group of the terminal transmission beams201and202and accumulates the transmission power by +1 [dB] from the value at the previous transmission for the TRP group ID #2, that is, the group of the terminal transmission beams205and206.

Regarding the SINRs at the TRPs illustrated inFIG. 5, the radio base station10is capable of lowering the SINR at the TRP #1and increasing the SINR at the TRP #2by lowering the transmission power of the terminal transmission beams201and202of the wireless terminal20and increasing the transmission power of the terminal transmission beams205and206of the wireless terminal20. In this manner, the radio base station10is capable of making the SINR closer to the proper SINR value in units of TRPs by controlling the transmission power of signals transmitted by the wireless terminal20in units of TRPs, or more specifically, the transmission power of the terminal transmission beams.

Next, a configuration of the radio base station10will be described.FIG. 6is a diagram illustrating an example of a configuration of the radio base station10according to the first embodiment. The radio base station10includes a signal processing unit17, and antenna sections14aand14b. The signal processing unit17includes a control unit11, a modulation/demodulation unit12, a transmission/reception unit13, and a measurement unit15.

The control unit11instructs the wireless terminal20to transmit a sounding signal, and associates the TRP group IDs, the base station reception beams, and the terminal transmission beams with each other, that is, groups the TRP group IDs, the base station reception beams, and the terminal transmission beams as illustrated inFIG. 3on the basis of the reception quality of each sounding signal. In addition, the control unit11selects a wireless terminal20to which a PUSCH is to be assigned, selects a terminal transmission beam of the wireless terminal20with which good reception quality is achieved at each base station reception beam, calculates a transmission power control value to be instructed using a transmission power control command, controls the directions of the base station reception beams, transmits and receives data to and from a core network, which is not illustrated, and the like.

The modulation/demodulation unit12modulates a signal, such as data and control information, acquired from the control unit11, and outputs the modulated signal to the transmission/reception unit13. The modulation/demodulation unit12also demodulates a signal acquired from the transmission/reception unit13, and outputs the demodulated signal to the control unit11.

The transmission/reception unit13converts a signal acquired from the modulation/demodulation unit12from a digital signal into an analog signal, and up-converts the frequency thereof. The transmission/reception unit13outputs the analog signal obtained by the up-conversion to each of the antenna sections14aand14b. The transmission/reception unit13also down-converts the frequencies of signals acquired from the antenna sections14aand14b, and converts the signals from analog signals into digital signals. The transmission/reception unit13outputs the digital signals obtained by the conversion to the modulation/demodulation unit12.

The antenna sections14aand14bare base station antenna sections that each generate a plurality of base station reception beams, and receive, by using the base station reception beams, signals transmitted from the wireless terminal20using a plurality of terminal transmission beams. Specifically, the antenna sections14aand14beach transmit signals acquired from the transmission/reception unit13in corresponding beam directions as instructed by the control unit11. The antenna sections14aand14balso receive signals from the wireless terminal20in beam directions as instructed by the control unit11. The antenna sections14aand14beach generate a plurality of base station reception beams at the same time.

The measurement unit15measures the reception quality, the reception power, or the like of signals acquired from the antenna sections14aand14b. Specifically, the measurement unit15measures the reception quality, the reception power, or the like of a signal for each of the base station reception beams generated by the antenna sections14aand14b. The measurement unit15outputs results of measurements such as the reception quality, the reception power, or the like to the control unit11. The signals whose reception quality, reception power, or the like is measured by the measurement unit15include the aforementioned sounding signal.

Operation of the radio base station10will be explained.FIG. 7is a flowchart illustrating an operation of grouping the terminal transmission beams of the wireless terminal20, at the radio base station10according to the first embodiment. For causing the wireless terminal20to transmit a sounding signal and causing the measurement unit15to measure the reception quality of the sounding signal for each of the base station reception beams101to108at the antenna sections14aand14b, the control unit11generates frequency mapping as illustrated inFIG. 2. The control unit11generates control information containing information on the frequency mapping and instructing to transmit a sounding signal, and transmits the control information to the wireless terminal20via the modulation/demodulation unit12, the transmission/reception unit13, and the antenna section14a. In this manner, the control unit11instructs the wireless terminal20to transmit a sounding signal (step S11). Upon receiving the control information from the radio base station10, the wireless terminal20transmits a sounding signal in accordance with the control information.

For measurement of the reception quality of the sounding signal, the control unit11indicates the directions of the base station reception beams to each of the antenna sections14aand14band causes the antenna sections14aand14bto receive the sounding signal from the wireless terminal20(step S12). The measurement unit15receives the received signals from the antenna sections14aand14b, and measures the reception quality, that is specifically, the SINR for each of the received signals as described above (step S13). The measurement unit15notifies the control unit11of the result of measurements of the reception quality. The control unit11groups the terminal transmission beams of the wireless terminal20on the basis of the result of measurements from the measurement unit15(step S14). Specifically, the control unit11generates a map indicating the relation of the TRP group IDs, the base station reception beams, and terminal transmission beams that achieve good reception quality as illustrated inFIG. 3. The control unit11associates a TRP group ID with each terminal transmission beam that achieves good reception quality from the generated map, and groups the terminal transmission beams of the wireless terminal20in units of TRPs of the radio base station10. Specifically, the control unit11selects, for each base station reception beam that has achieved preset reception quality, a terminal transmission beam from the wireless terminal20used for transmission of the sounding signal received using the base station reception beam. The control unit11groups a plurality of terminal transmission beams of the wireless terminal20into groups in units of base station antenna sections in such a manner that terminal transmission beams selected for base station reception beams generated by one base station antenna section are grouped into the same group. The control unit11generates control information containing group information on the grouping of the terminal transmission beams of the wireless terminal20, and transmits the control information to the wireless terminal20via the modulation/demodulation unit12, the transmission/reception unit13, and the antenna section14a. In this manner, the control unit11notifies the wireless terminal20of the group information of the terminal transmission beams of the wireless terminal20(step S15). Note that, for transmitting the control information to the wireless terminal20, that is, for notifying the wireless terminal20of the group information, the radio base station10can transmit the control information by using base station transmission beams generated by one TRP that is monitored as a main TRP by the wireless terminal20, for example.

FIG. 8is a flowchart illustrating an operation when a wireless terminal20to which a PUSCH is to be assigned is selected in the radio base station10according to the first embodiment. Upon selecting a wireless terminal20to which a PUSCH is to be assigned (step S21), the control unit11calculates a transmission power control value for each TRP group (step S22). The control unit11compares the SINRs of base station reception beams at each TRP measured by the measurement unit15when the PUSCH has previously been received from the same wireless terminal20with the proper SINR value, for example. The control unit11calculates a transmission power control value for each TRP group on the basis of the result of comparison. The control unit11notifies the wireless terminal20of the transmission power control value for the terminal transmission beams of the wireless terminal20for each TRP group (step S23). Specifically, the control unit11generates DCI Format 0_1E in which the transmission power control value for TRP group is a TPC command for scheduled PUSCH #1to #2, and transmits the DCI Format 0_1E to the wireless terminal20via the modulation/demodulation unit12, the transmission/reception unit13, and the antenna section14a.

Next, a configuration of the wireless terminal20will be described.FIG. 9is a diagram illustrating an example of a configuration of the wireless terminal20according to the first embodiment. The wireless terminal20includes a control unit21, a modulation/demodulation unit22, a transmission/reception unit23, an antenna section24, and a sounding signal generating unit25.

The control unit21analyzes the control information of which the wireless terminal20is notified from the radio base station10, and instructs transmission of a sounding signal, instructs transmission of a PUSCH, controls the transmission power for each group of terminal transmission beams, controls the directions of the terminal transmission beams, and the like.

The modulation/demodulation unit22modulates a signal, such as data and control information, acquired from the control unit21, and outputs the modulated signal to the transmission/reception unit23. The modulation/demodulation unit22also demodulates a signal acquired from the transmission/reception unit23, and outputs the demodulated signal to the control unit21.

The transmission/reception unit23converts a signal acquired from the modulation/demodulation unit22from a digital signal into an analog signal, and up-converts the frequency thereof. The transmission/reception unit23outputs the analog signal obtained by the up-conversion to the antenna section24. The transmission/reception unit23also down-converts the frequency of a signal acquired from the antenna section24, and converts the signal from an analog signal into a digital signal. The transmission/reception unit23outputs the digital signal obtained by the conversion to the modulation/demodulation unit22.

The antenna section24is a terminal antenna section that generates a plurality of terminal transmission beams, and transmits signals to the radio base station10by using the plurality of terminal transmission beams. The antenna section24transmits a signal acquired from the transmission/reception unit23in a beam direction as instructed by the control unit21. The antenna section24also receives a signal from the radio base station10in a beam direction as instructed by the control unit21. The antenna section24generates a plurality of terminal transmission beams at the same time.

The sounding signal generating unit25is a measurement signal generating unit that generates a sounding signal on the basis of an instruction from the control unit21.

Operation of the wireless terminal20will be explained.FIG. 10is a flowchart illustrating an operation until the wireless terminal20according to the first embodiment acquires the group information of the terminal transmission beams of the wireless terminal20from the radio base station10. Upon acquiring control information instructing to transmit a sounding signal from the radio base station10via the antenna section24, the transmission/reception unit23, and the modulation/demodulation unit22(step S31), the control unit21instructs the sounding signal generating unit25to generate a sounding signal. In this process, the control unit21notifies the sounding signal generating unit25of information of frequency mapping contained in the control information. The sounding signal generating unit25generates a sounding signal for each terminal transmission beam on the basis of the information of frequency mapping (step S32). In addition, the control unit21determines the directions of the terminal transmission beams on the basis of the information of frequency mapping, and indicates the directions of the terminal transmission beams to the antenna section24. The antenna section24generates terminal transmission beams on the basis of the instruction from the control unit21, and transmits a sounding signal acquire from the sounding signal generating unit25via the transmission/reception unit23, in each of the directions of the terminal transmission beam that are instructed by the control unit21(step S33). As described above, the radio base station10groups the terminal transmission beams of the wireless terminal20on the basis of the reception quality of each of the base station reception beams by which the sounding signal is received, and notifies the wireless terminal20of a control signal including the group information. The control unit21acquires the control information containing the group information from the radio base station10via the antenna section24, the transmission/reception unit23, and the modulation/demodulation unit22. In this manner, the wireless terminal20is capable of acquiring the group information generated by the radio base station10(step S34).

FIG. 11is a flowchart illustrating an operation of the wireless terminal20according to the first embodiment when a PUSCH is assigned to the wireless terminal20by the radio base station10. Upon acquiring DCI Format 0_1E from the radio base station10via the antenna section24, the transmission/reception unit23, and the modulation/demodulation unit22, the control unit21detects that a PUSCH is assigned to the wireless terminal20(step S41). The control unit21generates a signal to be transmitted to the radio base station10, and outputs the signal to the modulation/demodulation unit22. In addition, the control unit21accumulates the transmission power control values for each group of terminal transmission beams on the basis of “TPC command for scheduled PUSCH #1to #2” and “SRS resource indicator” for each TRP group contained in the DCI Format 0_1E. Specifically, the control unit21accumulates the transmission power control values for each group of terminal transmission beams and determines the transmission power on the basis of the information of TRP group ID #1={terminal transmission beam201, terminal transmission beam202} and TRP group ID #2={terminal transmission beam205, terminal transmission beam206}, which are acquired group information (step S42), and notifies the antenna section24of the determined transmission power. The antenna section24transmits signals to the radio base station10by using the terminal transmission beams in accordance with the transmission power of which the antenna section24has been notified by the control unit21(step S43).

Next, a hardware configuration for implementing the radio base station10and the wireless terminal20will be described.FIG. 12is a diagram illustrating an example of a hardware configuration for implementing the radio base station10and the wireless terminal20according to the first embodiment. The radio base station10is implemented by a processor31, a memory32, a transmitter33, a receiver34, and antenna device35, for example.

The processor31is a central processing unit (CPU; also referred to as a central processing device, a processing device, a computing device, a microprocessor, a microcomputer, a processor or a digital signal processor (DSP)), a system large scale integration (LSI), or the like. The memory32is a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, and an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM: registered trademark), a magnetic disk, a flexible disk, an optical disk, a compact disc, a mini disc, a digital versatile disc (DVD), or the like.

The control unit11and the modulation/demodulation unit12of the base station are implemented by the processor31and programs stored in the memory32. Specifically, the control unit11and the modulation/demodulation unit12are implemented by the processor31by reading programs for performing operations of the units from the memory32and executing the programs. The transmission/reception unit13is implemented by the transmitter33and the receiver34. Specifically, transmission processes of the transmission/reception unit13are performed by the transmitter33, and reception processes of the transmission/reception unit13are performed by the receiver34. The measurement unit15is also implemented by the receiver34. The antenna sections14aand14bare each implemented by the antenna device35.

The wireless terminal20has a similar configuration. The control unit21, the modulation/demodulation unit22, and the sounding signal generating unit25are implemented by the processor31and programs store in the memory32. Specifically, the control unit11and the modulation/demodulation unit12are implemented by the processor31by reading programs for performing operations of the units from the memory32and executing the programs. The transmission/reception unit23is implemented by the transmitter33and the receiver34. Specifically, transmission processes of the transmission/reception unit23are performed by the transmitter33, and reception processes of the transmission/reception unit23are performed by the receiver34. The antenna section24is implemented by the antenna device35.

While Format 0_1E, which is an extension based on Format 0_1 defined in the NR standard, is defined for transmission of the transmission power control command for each TRP from the radio base station10to the wireless terminal20in the present embodiment, the format is not limited to Format 0_1E. Any other format may be used as long as a transmission power control command corresponding to TPC command for scheduled PUSCH #1to #n for each TRP group can be defined.

As described above, according to the present embodiment, in the case where the radio base station10includes a plurality of TRPs that are installed at different locations from each other, the radio base station10performs transmission power control of the wireless terminal20on the basis of the signal reception quality, such as the SINR, at each TRP. Specifically, the radio base station10measures the reception quality of a sounding signal transmitted from the wireless terminal20for each base station reception beam at each TRP, groups a plurality of terminal transmission beams directed toward one TRP, among a plurality of terminal transmission beams generate by one wireless terminal20, into one TRP group on the basis of the result of measurements, and performs transmission power control in units of TRP groups. Thus, in the case where signals from the wireless terminal20can be received at a plurality of TRPs, the radio base station10is capable of performing control to make the SINR at each of the TRPs close to the proper SINR value by controlling the transmission power of the signals transmitted by the wireless terminal20in units of TRPs at which the signals are to be received. In addition, because the radio base station10does not perform transmission power control in units of terminal transmission beams, transmission power control can be performed without unnecessarily increasing the number of transmission power control commands, which reduces the increase in the overhead of control during communication.

Second Embodiment

In the first embodiment, the radio base station10groups the terminal transmission beams of the wireless terminal20. In a second embodiment, a case where the wireless terminal groups the terminal transmission beams will be described. In the second embodiment, assume that so-called beam correspondence, which means that base station transmission beams and base station reception beams form the same gain patterns as each other, is satisfied at each of the TRPs of the radio base station. The base station transmission beams are transmission beams generated at the respective TRPs of the radio base station of the second embodiment for transmission of signals to the wireless terminal. In addition, assume that the so-called beam correspondence, which means that terminal transmission beams and terminal reception beams form the same gain patterns as each other, is satisfied in the wireless terminal as well. The terminal reception beams are reception beams generated in the wireless terminal of the second embodiment for reception of signals from the radio base station.

FIG. 13is a diagram illustrating an example of a configuration of a radio communication system50aaccording to the second embodiment. The radio communication system50aincludes a radio base station10a, and a wireless terminal20a. The radio base station10aincludes a signal processing unit17a, and antenna sections14aand14b. The radio base station10aperforms radio communication with the wireless terminal20aby using the antenna sections14aand14b. The antenna sections14aand14bgenerate base station reception beams101to104and base station reception beams105to108, respectively, and receive signals transmitted from the wireless terminal20aby using the base station reception beams101to104and the base station reception beams105to108, respectively, in a manner similar to the first embodiment illustrated inFIG. 1. In addition, in the present embodiment, the antenna sections14aand14bgenerate base station transmission beams111to114and base station transmission beams115to118, respectively, and transmit signals to the wireless terminal20aby using the base station transmission beams111to114and the base station transmission beams115to118, respectively, as illustrated inFIG. 13. The wireless terminal20agenerates six terminal transmission beams201to206, and transmits signals to the radio base station10aby using the terminal transmission beams201to206, in a manner similar to the wireless terminal20illustrated inFIG. 1. In addition, in the present embodiment, the wireless terminal20agenerates terminal reception beams211to216, and receives signals transmitted from the radio base station10aby using the terminal reception beams211to216as illustrated inFIG. 13. While the number of wireless terminals20ain the radio communication system50ais one inFIG. 13, the number of wireless terminals20amay be two or more.

Specifically, in the present embodiment, assume that base station reception beams101to108correspond to base station transmission beams111to118, respectively, the base station reception beams101to108and the base station transmission beams111to118form the same gain patterns as each other, and thus beam correspondence is satisfied in the radio base station10a. In addition, assume that terminal transmission beams201to206correspond to terminal reception beams211to216, respectively, the terminal transmission beams201to206and the terminal reception beams211to216form the same gain patterns as each other, and thus beam correspondence is satisfied in the wireless terminal20a.

When beam correspondence is satisfied, the radio base station10anotifies the wireless terminal20aof information as illustrated inFIG. 14.FIG. 14is a table illustrating an example of information on the relation of TRP group IDs and base station transmission beams which is notified by the radio base station10ato the wireless terminal20ain the second embodiment. In this manner, the radio base station10anotifies the wireless terminal20aof the information on base station transmission beams to be used for transmission at each TRP. The radio base station10amay notify all the wireless terminals20ain common of the information illustrated inFIG. 14as notification information, or may individually notify the wireless terminals20aof the information.

A wireless terminal20athat has acquired the information on the association between the TRP group IDs and the base station transmission beams, associates a base station transmission beam with a terminal reception beam. As illustrated inFIG. 13, the wireless terminal20ameasures the reception quality of each of the terminal reception beams211to216to select which of the terminal reception beams211to216to use to receive signals transmitted using the base station transmission beams111to118from the radio base station10a.FIG. 15is a table illustrating the association between the base station transmission beams111to118selected from the result of measurements of the reception quality for each of the terminal reception beams211to216and the terminal reception beams211to216of the wireless terminal20aaccording to the second embodiment.

As illustrated inFIG. 15, the wireless terminal20aachieves the best reception quality when receiving, by using the terminal reception beam213, a signal transmitted from the radio base station10ausing the base station transmission beam111. In addition, the wireless terminal20aachieves the best reception quality when receiving, by using the terminal reception beam212, a signal transmitted from the radio base station10ausing the base station transmission beam112. In addition, the wireless terminal20aachieves the best reception quality when receiving, by using the terminal reception beam211, a signal transmitted from the radio base station10ausing the base station transmission beam113. In addition, the wireless terminal20aachieves the best reception quality when receiving, by using the terminal reception beam214, a signal transmitted from the radio base station10ausing the base station transmission beam115. In addition, the wireless terminal20aachieves the best reception quality when receiving, by using the terminal reception beam215, a signal transmitted from the radio base station10ausing the base station transmission beam116. In addition, the wireless terminal20aachieves the best reception quality when receiving, by using the terminal reception beam216, a signal transmitted from the radio base station10ausing the base station transmission beam117.FIG. 15also illustrates that, at the wireless terminal20a, there are no terminal reception beams that achieved good reception quality concerning signals transmitted from the radio base station10ausing the base station transmission beams114and118.

A signal transmitted from the radio base station10aand used for measurement of the reception quality at the wireless terminal20a, is a synchronization signal (SS) or a channel state information-reference signal (CSI-RS) defined in the NR standard. Either of the signals is a signal that is periodically transmitted from the radio base station10a. An SS is added with an index that identifies each base station transmission beam. A CSI-RS uses a different time-frequency resource for different base station transmission beam. Thus, in both cases of receiving either of an SS and a CSI-RS, the wireless terminal20ais capable of distinguishing which base station transmission beam was used for transmission of the signal.

The wireless terminal20athat has associated the base station transmission beams with the terminal reception beams is capable of associating a TRP group ID with a terminal transmission beam by using the information illustrated inFIGS. 14 and 15because beam correspondence is satisfied in both of the radio base station10aand the wireless terminal20a. In this manner, the wireless terminal20ais capable of generating groups of terminal transmission beams in units of TRPs of the radio base station10a. Specifically, the wireless terminal20ais capable of determining that terminal transmission beams201,202, and203associated with the terminal reception beams211,212, and213are grouped into the same group of TRP group #1, and that terminal transmission beams204,205, and206associated with terminal reception beams214,215, and216are grouped into the same group of TRP group #2. Note that the operations of the radio base station10aand the wireless terminal20aother than the grouping are similar to those of the radio base station10and the wireless terminal20, respectively, in the first embodiment.

Next, a configuration of the radio base station10awill be described.FIG. 16is a diagram illustrating an example of a configuration of the radio base station10aaccording to the second embodiment. The radio base station10aincludes a signal processing unit17a, and antenna sections14aand14b. The signal processing unit17acorresponds to the signal processing unit17of the first embodiment illustrated inFIG. 6but additionally includes a measurement signal generating unit16. The measurement signal generating unit16generates a measurement signal, that is specifically, an SS or a CSI-RS as described above, in accordance with an instruction from the control unit11. In the radio base station10a, the control unit11further causes the measurement signal generating unit16to generate an SS or a CSI-RS to enable grouping of a plurality of terminal transmission beams at the wireless terminal20ain units of base station antenna sections by which the signals are to be received in the radio base station10a, in addition to the operation explained in the first embodiment. The control unit11indicates the directions of the base station transmission beams to the antenna sections14aand14bfor transmission of the SS or the CSI-RS. The control unit11also generates control information containing the information on the association between the TRP group IDs and the base station transmission beams illustrated inFIG. 14, and notifies the wireless terminal20aof the control information via the modulation/demodulation unit12, the transmission/reception unit13, and the antenna section14a.

Operation of the radio base station10awill be explained.FIG. 17is a flowchart illustrating an operation of transmitting a measurement signal and control information to the wireless terminal20athat groups terminal reception beams, in the radio base station10aaccording to the second embodiment. The control unit11causes the measurement signal generating unit16to generate a measurement signal, that is specifically, an SS or a CSI-RS as described above. The measurement signal generating unit16generates a measurement signal (step S51). The measurement signal generating unit16outputs the measurement signal to each of the antenna sections14aand14bvia the transmission/reception unit13. The control unit11also determines the directions of base station transmission beams, and indicates the directions of the base station transmission beams to the antenna sections14aand14b. The antenna sections14aand14bgenerate a plurality of base station transmission beams on the basis of the instruction from the control unit11, and transmit the measurement signal, which is acquired from the measurement signal generating unit16via the transmission/reception unit13, by using each of the base station transmission beams in the directions of the base station transmission beams as indicated by the control unit11(step S52). The control unit11also generates control information containing the information on the association between the TRP group IDs and the base station transmission beams (step S53). The control unit11notifies the wireless terminal20aof the control information via the modulation/demodulation unit12, the transmission/reception unit13, and the antenna section14a(step S54). Note that the operations of the radio base station10awhen a wireless terminal20ato which a PUSCH is to be assigned is selected, are similar to those of the radio base station10in the first embodiment illustrated inFIG. 8.

Next, a configuration of the wireless terminal20awill be described.FIG. 18is a diagram illustrating an example of a configuration of the wireless terminal20aaccording to the second embodiment. The wireless terminal20acorresponds to the wireless terminal20of the first embodiment illustrated inFIG. 9but additionally includes a measurement unit26. The measurement unit26measures the reception quality, the reception power, or the like of a measurement signal received using each terminal reception beam acquired from the antenna section24to generate the association between the base station transmission beams and the terminal reception beams as illustrated inFIG. 15. Specifically, the measurement unit26measures, for each of the terminal reception beams, the reception quality, the reception power, or the like when measurement signals transmitted from the radio base station10aare received by using the terminal reception beams generated by the antenna section24. The measurement unit26notifies the control unit21of the result of measurements. Upon receiving the result of measurements, the control unit21generates the map illustrated inFIG. 15. The control unit21acquires control information on the association between the TRP group IDs and the base station transmission beams as illustrated inFIG. 14separately from the radio base station10a, and finally determines the association between the TRP group IDs and the terminal transmission beams.

Operation of the wireless terminal20awill be explained.FIG. 19is a flowchart illustrating an operating of grouping terminal transmission beams of the wireless terminal20aat the wireless terminal20aaccording to the second embodiment. For measurement of the reception quality of measurement signals transmitted from the radio base station10a, the control unit21instructs the directions of the terminal reception beams to the antenna section24and causes the antenna section24to receive the measurement signals from the radio base station10a(step S61). The measurement unit26receives the received signals from the antenna section24, and measures the reception quality, that is specifically, the SINR as described above (step S62). The measurement unit26reports the reception quality, that is, the result of measurements of the SINR to the control unit21. In addition, the antenna section24receives control information containing the information on the association between the TRP group IDs and the base station transmission beams from the radio base station10a(step S63). The antenna section24outputs the received control information to the control unit21via the transmission/reception unit23and the modulation/demodulation unit22. The control unit21groups the terminal transmission beams of the wireless terminal20aon the basis of the acquired result of measurements and the control information (step S64). In this manner, the control unit21selects, for each terminal reception beam, a base station transmission beam of the radio base station10aused for transmission of the measurement signal received by the terminal reception beam on the basis of the reception quality. The control unit21groups the terminal transmission beams associated with the terminal reception beams in units of base station antenna sections of the radio base station on the basis of the terminal reception beams, for which base station transmission beams generated by the same base station antenna section of the radio base station10aare selected. Note that the operations of the wireless terminal20awhen a PUSCH is assigned to the wireless terminal20aby the radio base station10a, are similar to those of the wireless terminal20in the first embodiment illustrated inFIG. 11.

Regarding the hardware configuration of the radio base station10a, the measurement signal generating unit16included in addition to the radio base station10of the first embodiment is implemented by the processor31illustrated inFIG. 12and programs stored in the memory32illustrated inFIG. 12. In addition, regarding the hardware configuration of the wireless terminal20a, the measurement unit26included in addition to the wireless terminal20of the first embodiment is implemented by the receiver34illustrated inFIG. 12.

As described above, according to the present embodiment, in the case where beam correspondence is satisfied in both of the radio base station10aand the wireless terminal20a, the wireless terminal20agroups the terminal transmission beams. In this case as well, the same effects as those in the first embodiment are produced.

Third Embodiment

While the radio base station10transmits transmission power control commands correspondingly associated with TRP groups at the same time to the wireless terminal20in the first embodiment, the transmission power control commands need not necessarily be transmitted at the same time. In a third embodiment, a case where the radio base station10transmits transmission power control commands one by one, each command being associated with one TRP group at timings different from each other will be explained. Although this case is also applicable to the radio base station10aof the second embodiment, an example of application to the radio base station10of the first embodiment will be explained because the operations in the second embodiment are similar to those in the first embodiment.

In the third embodiment, only one definition of a transmission power control command “TPC command for scheduled PUSCH” is sufficient, and the radio base station10alternatively notifies the wireless terminal20of the TRP group ID, to which the TPC command for scheduled PUSCH is to be applied. Specifically, information on a TRP group ID is added to any region defined in a message of the aforementioned Format 0_1. The format to which the information of the TRP group ID is added will be referred to as Format 0_1EE, for example. The radio base station10generates a message containing “TRP group ID=#1” and “TPC command for scheduled PUSCH=−1 [dB]” by using the Format 0_1EE, and notifies the wireless terminal20of the message at a first timing, for example. In addition, the radio base station10generates a message containing “TRP group ID=#2” and “TPC command for scheduled PUSCH=+1 [dB]” by using the Format 0_1EE, and notifies the wireless terminal20of the message at a second timing, for example. Specifically, in the radio base station10, the control unit11performs an operation of notifying the wireless terminal20of a transmission power control value in units of TRP groups at different transmission timings for different TRP groups. Note that the operations such as determination on the association between the TRP group IDs and the terminal transmission beams in the radio base station10are similar to those in the first embodiment.

Upon acquiring “TRP group ID” and “transmission power control command” through the message of the Format 0_1EE, the wireless terminal20accumulates the transmission power control command values for each group of terminal transmission beams. Although the difference from the first embodiment lies in that the wireless terminal20acquires a message for each TRP group ID, the operation of accumulating the transmission power control command values after acquisition of the message of the Format 0_1EE is similar to that in the first embodiment.

Note that the radio base station10can perform transmission power control only on TRP groups the SINR, which is reception quality, of which has not reached the proper SINR value, instead of controlling transmission power for all the TRP groups. In a case where TRP #1and TRP #2are present and the SINR of TRP #1has not reached the proper SINR value while that of TRP #2has reached the proper SINR value, for example, the radio base station10notifies the wireless terminal20of a transmission power control command for TRP #1only. Specifically, in the radio base station10, the control unit11performs an operation of notifying the wireless terminal20of a transmission power control value for the TRP group for which the transmission power needs to be changed.

In addition, in a case where control for increasing the transmission power is needed for all of a plurality of TRP groups but it is determined that the increase in the transmission power for all the TRP groups will result in an excess of the transmission power of the wireless terminal20over maximum transmission power, the radio base station10can select one or more TRP groups that are more important, and increase the transmission power for the selected TRP group(s). In this case, the radio base station10notifies the wireless terminal20of a transmission power control command for the selected TRP group only. The method for selecting a more important TRP group in the radio base station10may be selecting a TRP associated with a base station reception beam with the lowest SINR, for example. Note that a mechanism for the wireless terminal20to periodically notify the radio base station10of a difference between the maximum transmission power and the current transmission power is already defined in the NR standard. Thus, the radio base station10is capable of easily determining whether the transmission power of the wireless terminal20exceeds the maximum transmission power. The radio base station10may change the number of TRP groups to be selected on the basis of the difference between the maximum transmission power and the current transmission power of the wireless terminal20. Specifically, in the radio base station10, in a case where the transmission power of the wireless terminal20exceeds the maximum transmission power if the transmission power is increased for a plurality of TRP groups, the control unit11performs an operation of notifying the wireless terminal20of a transmission power control value for some TRP group(s) selected from a plurality of TRP groups.

As described above, according to the present embodiment, the radio base station10notifies the wireless terminal20of a plurality of transmission power control commands one by one, the commands being associated with a plurality of TRP groups, at a timing different from each other. Thus, in a case where the number of TRP groups is large, the radio base station10is capable of reducing the increase in the number of control bits necessary for one transmission of a transmission power control command.

In addition, the radio base station10notifies the wireless terminal20of a transmission power control command only for one or more TRP groups the SINR of each of which has not reached the proper SINR value. This enables the radio base station10to reduce the overhead of control for TRP groups on which the control need not be performed.

In addition, in a case where the transmission power of the wireless terminal20exceeds the maximum transmission power if the transmission power is increased for a plurality of TRP groups, the radio base station10selects one or more important TRP groups, and performs control of increasing the transmission power for the selected TRP group(s) only. Thus, the radio base station10is capable of preventing the transmission power of the wireless terminal20from exceeding the maximum transmission power and making the SINR for a TRP on which control is needed closer to the proper value.

Fourth Embodiment

In the first to third embodiments, the radio base station controls the transmission power of the wireless terminal always in units of TRP groups. In a fourth embodiment, a case where the radio base station10performs transmission power control in units of TRP groups or transmission power control in common for all the TRP groups depending on conditions, will be explained. Although this case is also applicable to the radio base station10aof the second embodiment and to the radio base station10and the radio base station10aof the third embodiment, an example of application to the radio base station10of the first embodiment will be explained because the operations in the second and third embodiments are similar to those in the first embodiment.

For example, in the wireless terminal20, when a data unit that is a section in transmitting or retransmitting a signal is a codeword, there are a method of mapping one codeword to all the terminal transmission beams used for transmission and a method of mapping in units of terminal transmission beams or beam groups.FIG. 20is a diagram illustrating an example of a mapping pattern in which the wireless terminal20according to the fourth embodiment maps one codeword in all the terminal transmission beams to be used for transmission. In addition,FIG. 21is a diagram illustrating an example of a mapping pattern in which the wireless terminal20according to the fourth embodiment maps one codeword in units of terminal transmission beams. The pattern illustrated inFIG. 20will be referred to as a mapping pattern A, and the pattern illustrated inFIG. 21will be referred to as a mapping pattern B. The wireless terminal20maps one codeword into a plurality of layers in accordance with a mapping pattern defined in the NR standard. Furthermore, for mapping from each of the layers to beams, the wireless terminal20uses a technology called precoding. In the NR standard, beams are called antenna ports. Beams illustrated inFIGS. 20 and 21correspond to the terminal transmission beams in the first to third embodiments. The wireless terminal20performs a matrix operation on a signal of each layer, and maps the operation result to the beams. Note that examples of a matrix used for the matrix operation of precoding are described in Chapter 6.3.1.5 of 3GPP specification TS 38.211 V15.0.0.

Note that, the mapping pattern A is selected or the mapping pattern B is selected depending on the matrix used in the wireless terminal20. First, assume a case where the mapping pattern A illustrated inFIG. 20is selected in the wireless terminal20, a signal is transmitted by beams a and b toward the TRP #1, and a signal is transmitted by beams e and f toward the TRP #2. Even when a condition as illustrated inFIG. 5, for example, occurs at the TRPs #1and #2in the radio base station10that receives the signal, there is no problem just as long as the SINR at the TRP #1and the TRP #2have reached the proper SINR value if interference with other radio base stations need not be considered. In such a case, it is sufficient that the radio base station10controls the wireless terminal20with one transmission power control command as in the related art. For example, such a case where no other radio base station using the same frequency is present around the radio base station10can be assumed. In contrast, in a case where interference with another radio base station needs to be considered, when the condition as illustrated inFIG. 5occurs at the TRPs #1and #2, the radio base station10preferably performs transmission power control on the wireless terminal20in units of TRP groups. In such a case, the radio base station10selects the mapping pattern B as the pattern to be used by the wireless terminal20, and performs transmission power control in units of TRP groups if the wireless terminal20has transmitted a signal toward the TRP #1by using beam group1and a signal toward the TRP #2by using beam group2.

The radio base station10determines whether to use the mapping pattern A or the mapping pattern B, that is, whether to perform transmission power control in units of groups or in common for all the groups on the basis of whether interference with another radio base station is present. The NR standard states that the radio base station10notifies the wireless terminal20of the result of determination on which of the mapping patterns A and B is selected by using “precoding information” in the Format 0_1. In this manner, when the transmission power control of the wireless terminal20is to be performed for each TRP group in view of the condition of communication with the wireless terminal20, the radio base station10uses the Format 0_1E described in the first embodiment or the Format 0_1EE described in the second embodiment. When the transmission power control of the wireless terminal20is to be performed in common for all the TRP groups, the radio base station10uses the existing Format 0_1. In this manner, the radio base station10is capable of using two modes. In addition, a method in which the radio base station10determines either one mode to be always used, and notifies the wireless terminal20, with which the radio base station10is to communicate, of the mode only once when starting the communication can be considered.

FIG. 22is a flowchart illustrating an operation of determining a transmission power controlling method for the wireless terminal20in the radio base station10according to the fourth embodiment. In a case where transmission power control of the wireless terminal20is needed, when interference with another radio base station needs to be considered (step S71: Yes), the control unit11determines that transmission power control in units of TRP groups is effective, and determines to control the transmission power of the terminal transmission beams of the wireless terminal20in units of TRP groups (step S72). When interference with another radio base station need not be considered (step S71: No), the control unit11determines that the transmission power control in units of TRP groups is not necessary, and determines to control the transmission power of the terminal transmission beams of the wireless terminal20in common for the TRP groups (step S73).

As described above, according to the present embodiment, the radio base station10performs transmission power control in common for the TRP groups when interference with another radio base station need not be considered, and performs transmission power control in units of TRP groups when interference with another radio base station needs to be considered. This enables the radio base station10to appropriately control the reception quality such as the SINR for each TRP group by performing the transmission power control in units of TRP groups where necessary, and to reduce the overhead of control of the entire system when the transmission power control in common for the TRP groups is sufficient.

While the terminal transmission beams are grouped in units of TRPs in the first to third embodiments, the grouping method is not limited to that in units of TRPs. For example, when signals transmitted by the terminal transmission beams are received, the radio base station may group the terminal transmission beams of the wireless terminal in view of similarity in reception quality or difference in reception quality.

The configurations presented in the embodiments above are examples of the present invention, and can be combined with other known technologies or can be partly omitted or modified without departing from the scope of the present invention.

A radio base station according to the present invention produces an effect of controlling transmission powers of signals transmitted by a wireless terminal in units of locations at which the signals are received in a case where signals from a wireless terminal can be received at a plurality of locations.