Patent Publication Number: US-2019199411-A1

Title: Effective scheduling of terminals in a wireless communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2017-251481, filed on Dec. 27, 2017, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to effective scheduling of terminals in a wireless communication system. 
     BACKGROUND 
     As a technology for implementing ultra wideband transmission in high frequency bands, there is the Massive multi-input multi-output (MIMO) technology. In Massive MIMO, a base station apparatus may perform wireless communication simultaneously with a plurality of terminal apparatuses by spatially multiplexing wireless signals. 
     However, in Massive MIMO, the number of antenna elements increases from hundreds to thousands in comparison with MIMO. Therefore, in the case where a base station apparatus performs a precoding process (or a digital precoding process), the arithmetic operation amount becomes very great by performing matrix operation of dimensions that increase in proportion to the number of antenna elements. 
     Therefore, by IEEE (the Institute of Electrical and Electronics Engineers, Inc.), hybrid beam forming (BF) is examined. The hybrid BF is a technology that combines, for example, analog BF and a digital precoding process. The analog BF is a technology that controls, for example, the phase of analog signals to be individually inputted to a plurality of antenna elements to control the directionality of beams. Meanwhile, the digital precoding process is a technology that performs weighting, for example, for each of transmission streams of a baseband. 
     By combining the analog BF and the digital precoding process, for example, it becomes possible to optimize weighting of the analog BF and a precoding matrix or to optimize also the number of converters or baseband processing circuits. 
     However, for example, in terms of a certain beam formed by analog BF, the number of terminals that perform wireless communication with a base station apparatus utilizing the beam is sometimes smaller than a given number. In such a case, in comparison with an alternative case in which the number of terminals is greater than the given number, the utilization ratio of wireless resources sometimes decreases, resulting in decrease of the throughput. 
     Thus, there is an analog beam forming technology that utilizes a mini-slot. The mini-slot is a technology that performs scheduling, for example, in a unit of a symbol. For example, in the case where the number of terminals smaller than such a given number as described above are scheduled, since, in long term evolution (LTE), scheduling is performed in a unit of a sub-frame, such a state as described above continues at least for a sub-frame time period (14 symbols). However, in the case of an analog beam forming technology that utilizes the mini-slot, since scheduling is performed in a unit of a symbol, even in the case where the number of terminals smaller than the given number are scheduled, such a state as described above continues only for a period of time of one to several symbols. By performing scheduling in a unit of a symbol in this manner, for example, it is possible to improve the utilization ratio of wireless resources and suppress decrease of the throughput. 
     Examples of the related art include “Joint Fixed Beamforming and Eigenmode Precoding for Super High Bit Rate Massive MIMO Systems Using Higher Frequency Bands,” T. Obara, S. Suyama, J. Shen, and Y. Okumura, NTT DOCOMO, INC., Proc. 2014 IEEE 25th Annual International Symposium on Personal, Indoor, and Mobile Radio Communication, September 2014, and R1-1700629, “Mini-slot for analog beam-forming,” NTT DOCOMO, INC., 16th-20th Jan. 2017. 
     SUMMARY 
     According to an aspect of the embodiments, a base station apparatus includes a processor and a plurality of antennas that transmit, to each of terminals, first and second wireless signals to form first and second beams, respectively, and receives, from each terminal, a third wireless signal including feedback information of the terminal in response to the second wireless signal. The processor selects, from among the terminals, based on the feedback information and a correlation value between the first beam and the second beam, a terminal to which the second beam is optimum, as a first terminal that performs communication via the first beam, or selects a terminal as a second terminal that performs communication via the second beam while communication via the first beam is performed in parallel. The plurality of antennas transmit a fourth wireless signal including data to each terminal apparatus to form the first beam or the second beam. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view depicting an example of a configuration of a wireless communication system; 
         FIG. 2  is a view depicting an example of a configuration of a base station apparatus; 
         FIG. 3  is a view depicting an example of a configuration of a terminal apparatus; 
         FIGS. 4A and 4B  are views depicting an example of a configuration of a base station apparatus and a terminal apparatus, respectively; 
         FIG. 5  is a flow chart depicting an example of operation of a base station apparatus; 
         FIG. 6  is a flow chart depicting an example of operation of a base station apparatus; 
         FIG. 7  is a view depicting an example of a relationship between an analog beam and a terminal; 
         FIGS. 8A and 8B  are views depicting an example of coefficients W NUE,m  and W CQIu , respectively; 
         FIG. 9A  is a view depicting an example of a relationship between analog beams #m and #n and a threshold value ┌ A,u , and  FIG. 9B  is a view depicting an example of a result of scheduling; 
         FIGS. 10A to 10C  are views depicting examples of a digital beam; 
         FIGS. 11A and 11B  illustrate a flow chart depicting an example of operation of a base station apparatus; 
         FIG. 12  is a flow chart depicting an example of operation of a base station apparatus; 
         FIGS. 13A to 13C  are views depicting examples of a digital beam; 
         FIGS. 14A and 14B  are views depicting an example of digital beams #m and #n; 
         FIG. 15A and 15B  are views depicting an example of coefficients w k  and w DSu , respectively; 
         FIG. 16  is a view depicting an example of a relationship between digital beams #m and #n and a threshold value ┌ D,u ; 
         FIG. 17  is a view depicting an example of a coefficient w ant ; and 
         FIG. 18  is a view depicting an example of a configuration of a wireless communication system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the case of the analog beam forming technology that utilizes the mini-slot, a base station apparatus performs allocation to terminal apparatus (users) in a unit of a symbol. Therefore, the base station apparatus inserts a demodulation reference signal (DMRS) in a unit of a symbol. Accordingly, in comparison with an alternative case in which a DMRS signal is inserted in a unit of a slot, according to the analog beam-forming technology that utilizes the mini-slot, a region to which wireless resources for data are to be allocated sometimes decreases, resulting in deterioration of the throughput because a DMRS is inserted in a unit of a symbol. 
     Therefore, it is desirable to provide a base station apparatus, a scheduling method and a wireless communication system that improve the throughput. 
     In the following, embodiments are described in detail with reference to the drawings. The subject and the embodiments are exemplary and does not restrict the scope of the right of the present application. Further, the individual embodiments may be combined suitably to the extent that the processing range does not conflict. Further, as the terms used herein and the technical contents described herein, terms described in specifications or technical contents specified by IEEE, third generation partnership project (3GPP) or the like may be used suitably. 
     First Embodiment 
     &lt;Example of Configuration of Wireless Communication System&gt; 
       FIG. 1  is a view depicting an example of a configuration of a wireless communication system according to a first embodiment. 
     A wireless communication system  10  depicted in  FIG. 1  includes a base station apparatus  100  (hereinafter referred to sometimes as “base station”), and a plurality of terminal apparatuses (each hereinafter referred to sometimes as “terminal”)  200 - 1  to  200 -N UE . 
     The base station  100  is a wireless communication apparatus that performs wireless communication, for example, with the plurality of terminals  200 - 1  to  200 -N UE . The base station  100  provides various services to the plurality of terminals  200 - 1  to  200 -N UE  located in a cover area (or a range within which a service may be provided) by performing wireless communication with the terminals  200 - 1  to  200 -N UE . Along with this, the base station  100  transmits a wireless signal to the terminals  200 - 1  to  200 -N UE  to form a plurality of analog beams # 1  to #N beam  to transmit user data and so forth. As services to be provided, for example, there are a communication service, a Web browsing service and so forth. 
     The terminals  200 - 1  to  200 -N UE  are wireless communication apparatuses capable of performing wireless communication, such as a smartphone, a feature phone, a tablet terminal, a personal computer, or a game apparatus. The terminals  200 - 1  and  200 - 2  may perform wireless communication with the base station  100  to enjoy various services provided through the base station  100 . 
     It is to be noted that, while, in the example of  FIG. 1 , one base station  100  performs wireless communication with N UE  terminals  200 - 1  to  200 -N UE , a plurality of terminals will suffice. For example, N UE  may be N UE =2. Also the analog beams # 1  to #N beam  may be a plurality of analog beams, and for example, N beam  may be N beam =2. 
     In the following, for example, each of the terminals  200 - 1  to  200 -N UE  is sometimes referred to as terminal  200 . 
     &lt;Example of Configuration of Base Station Apparatus&gt; 
       FIG. 2  is a view depicting an example of a configuration of a base station. 
     The base station  100  depicted in  FIG. 1  includes antennas (or antenna elements; each of them is sometimes referred to as “antenna”)  101 - 1  to  101 -N ANT  (ANT is an integer equal to or greater than  2 ), an analog BF unit  102 , radio frequency (RF) units  103 - 1  to  103 -N RF , and a channel estimation unit  104 . The base station  100  further includes a scheduling unit  105 , an interface (IF) unit  106 , a user data generation unit  107 , a digital precoding unit  108 , a reference signal generation unit  109 , a channel multiplexing unit  110 , and RF units  111 - 1  to  111 -N RF . 
     The antennas  101 - 1  to  101 -N ANT  receive wireless signals outputted from the analog BF unit  102  and transmit the received wireless signals to the terminals  200 . Further, the antennas  101 - 1  to  101 -N ANT  receive wireless signals transmitted from the terminals  200  and output the received wireless signals to the analog BF unit  102 . 
     The analog BF unit  102  performs weighting for a wireless signal outputted from each of the RF units  111 - 1  to  111 -N RF , based on a weighting value (or weighting factor) received from the scheduling unit  105 . The analog BF unit  102  outputs the weighted wireless signals to the antennas  101 - 1  to  101 -N ANT . The weighting value may be represented, for example, by a complex function or the like with fixing a (main axis) direction of a beam. Accordingly, when the wireless signals weighted by the analog BF unit  102  are transmitted from the antennas  101 - 1  to  101 -N ANT , it becomes possible to form (transmission) analog beams # 1  to #N beam  directed to a certain fixed direction. 
     Further, the analog BF unit  102  outputs wireless signals outputted from the antennas  101 - 1  to  101 -N ANT  to the RF units  103 - 1  to  103 -N RF , respectively. The analog BF unit  102  performs weighting of the received wireless signals, based on weighting values received from the scheduling unit  105 . Also in this case, the wireless signals received by the antennas  101 - 1  to  101 -N ANT  may form (reception) analog beams # 1  to #N beam  directed toward a certain fixed direction by the weighting. 
     In order to perform such weighting as described above, the analog BF unit  102  may include a phase controlling circuit, for example, for each antenna  101 - 1  to  101 -N ANT . The phase controlling circuit controls the phase of a wireless signal outputted from each of the RF units  111 - 1  to  111 -N RF  or a wireless signal received from each of the antennas  101 - 1  to  101 -N ANT  in accordance with weighting values outputted, for example, from the scheduling unit  105 . 
     It is to be noted that each of the analog beams # 1  to #N beam  is a flux of one or more wireless signals. By the analog BF unit  102 , wireless signals having phases different from each other are transmitted from the plurality of antennas  101 - 1  to  101 -N ANT . The base station  100  may form one or more analog beams # 1  to #N beam  having phases controlled to a certain direction by transmitting wireless signals having phases different from each other from the plurality of antennas  101 - 1  to  101 -N ANT . 
     In the following, to form analog beams # 1  to #N beam  by transmission of wireless signals and to transmit wireless signals utilizing such analog beams # 1  to #N beam  are sometimes used without distinguishing them from each other. 
     Further, the analog beams # 1  to #N beam  are beams formed by wireless signals that are obtained, for example, by weighting wireless signals after frequency conversion. 
     Each of the RF units  103 - 1  to  103 -N RF  performs a frequency conversion process and so forth for a wireless signal received from the analog BF unit  102  to convert (or down convert) the wireless signal into a baseband signal of a baseband. Each of the RF units  103 - 1  to  103 -N RF  outputs the baseband signal after the conversion to the channel estimation unit  104 . 
     The channel estimation unit  104  calculates a channel estimation value, for example, based on an uplink reference signal from among baseband signals and performs a reception process according to channel compensation, on the other baseband signals, by utilizing the calculated channel estimation value. The channel estimation unit  104  may extract, by the reception process or the like, a feedback signal transmitted from the terminal  200  from among the baseband signals. The channel estimation unit  104  outputs the extracted feedback signal to the scheduling unit  105 . 
     It is to be noted that the channel estimation unit  104  may extract, by a reception process or the like, user data and so forth transmitted from the terminal  200 , and in this case, the channel estimation unit  104  may output the extracted user data and so forth to the IF unit  106 . 
     The scheduling unit  105  extracts feedback information and candidate beam information from the feedback signal. Then, the scheduling unit  105  determines, for example, based on a correlation value of a second beam to a first beam and a feedback signal of the terminal  200  to the first or second beam, whether or not a terminal  200  to which the second beam is optimum is to be selected as a terminal with which communication is to be performed using the first beam. For example, the scheduling unit  105  determines, based on the correlation value and the feedback information, whether or not a terminal to which the second beam is optimum is to be selected as a terminal with which communication is to be performed using the first beam. Details are hereinafter described in the description of an example of operation. The scheduling unit  105  outputs a signal indicative of a result of scheduling to the user data generation unit  107 , digital precoding unit  108 , channel multiplexing unit  110 , and analog BF unit  102 . 
     For example, the scheduling unit  105  outputs information relating to a terminal  200  (or a user) that has been allocated by scheduling, to the user data generation unit  107 . Further, the scheduling unit  105  outputs, for example, a precoding matrix indicator (PMI) included in channel state information (CSI), from among feedback information, to the digital precoding unit  108 . Further, the scheduling unit  105  outputs a result of scheduling to the channel multiplexing unit  110 . Furthermore, the scheduling unit  105  outputs, for example, a weighting value relating to an analog beam to the analog BF unit  102 . 
     The IF unit  106  receives, for example, packet data transmitted from the another station or a node apparatus, extracts user data and so forth destined for the terminal  200  from the received packet data, and outputs the extracted user data to the user data generation unit  107 . Further, the IF unit  106  receives, for example, user data and so forth from the channel estimation unit  104 , generates packet data for the received user data and so forth, and transmits the packet data to another base station or another node apparatus. 
     The user data generation unit  107  outputs, for example, in accordance with information relating to the user outputted from the scheduling unit  105 , from among user data outputted from the IF unit  106 , the user data corresponding to the user to the digital precoding unit  108 . The user data generation unit  107  outputs one or more pieces of user data to the digital precoding unit  108 . 
     The digital precoding unit  108  performs weighting on the user data, for example, in accordance with a PMI outputted from the scheduling unit  105 . To perform a weighting process on user data (or a data stream) in a baseband in this manner is sometimes referred to, for example, as digital precoding (process). The digital precoding unit  108  outputs the weighted user data to the channel multiplexing unit  110 . 
     The reference signal generation unit  109  generates a reference signal and outputs the generated reference signal to the channel multiplexing unit  110 . As the reference signal, for example, there are a channel state information-reference signal (CSI-RS), a DMRS and so forth. 
     The channel multiplexing unit  110  multiplexes user data outputted from the digital precoding unit  108  and the reference signal outputted from the reference signal generation unit  109  into each channel, for example, in accordance with a scheduling result outputted from the scheduling unit  105 . The channel multiplexing unit  110  outputs the multiplexed signals to the RF units  111 - 1  to  111 -N RF . 
     The RF units  111 - 1  to  111 -N RF  convert (or up convert) the multiplexed signals of the baseband into wireless signals of a wireless band, for example, by a frequency conversion process or the like. The RF units  111 - 1  to  111 -N RF  output the wireless signals after conversion to the analog BF unit  102 . 
     &lt;Example of Configuration of Terminal Apparatus&gt; 
       FIG. 3  is a view depicting an example of a configuration of a terminal. 
     The terminal  200  depicted in  FIG. 3  includes an antenna  201 , RF units  202  and  205 , a channel estimation unit  203 , and a feedback signal generation unit  204 . 
     The antenna  201  receives a wireless signal transmitted from the base station  100 , and outputs the received wireless signal to the RF unit  202 . Further, the antenna  201  transmits a wireless signal outputted from the RF unit  205  to the base station  100 . 
     The RF unit  202  performs, for example, a frequency conversion process and so forth on a wireless signal received from the antenna  201  to convert (or down convert) the wireless signal into a baseband signal of the baseband. The RF unit  202  outputs the baseband signal after the conversion to the channel estimation unit  203 . 
     The channel estimation unit  203  calculates a channel estimation value, based on a reference signal from among baseband signals, and measures the communication quality between the base station  100  and the terminal  200  by using the calculated channel estimation value. The communication quality may be represented, for example, as channel quality indicator (CQI) or may be represented as a received power value with respect to the reference signal, a signal to noise ratio (SNR), or a signal to interference plus noise ratio (SINR). In the following description, the CQI is taken as an example of the communication quality. 
     Further, the channel estimation unit  203  calculates a PMI indicative of a desired precoding matrix or a rank indicator (RI) indicative of a desired stream number, for example, based on the measured communication quality. The channel estimation unit  203  outputs channel state information (CSI) including the RI, the CQI, and the PMI, as feedback signal, to the feedback signal generation unit  204 . 
     Furthermore, the channel estimation unit  203  calculates candidate beam information indicative of an optimum beam from among a plurality of beams formed by the base station  100 . The channel estimation unit  203  may measure, for example, for each of the beams formed by the base station  100 , the communication quality based on a reference signal transmitted using the beam, and select an optimum beam, based on the measured communication quality. As a range of the transmission frequency via which the reference signal is transmitted, for example, a range, within which the base station  100  may perform scheduling, may be applied. For example, while  FIG. 9B  depicts an example of a scheduling result, the reference signal may be included in a frequency range to which the terminals  200 - 1  to  200 - 8  are allocated. An optimum beam selected by the channel estimation unit  203  is sometimes referred to, for example, candidate beam. For example, in the example of  FIG. 1 , the candidate beam for the terminal  200 - 1  is the analog beam # 1 , and the candidate beam for the terminal  200 - 2  is the analog beam # 2 . Referring back to  FIG. 2 , the channel estimation unit  203  outputs the selected (or calculated) candidate beam information to the feedback signal generation unit  204 . 
     The feedback signal generation unit  204  generates a feedback signal including feedback information and candidate beam information, and outputs the generated feedback signal to the RF unit  205 . 
     The RF unit  205  performs, for example, a frequency conversion process and so forth on the feedback signal to convert (up convert) the feedback signal in the baseband to a wireless signal in the wireless band. The RF unit  205  outputs the wireless signal after the conversion to the antenna  201 . It is to be noted that the RF unit  205  transmits, for example, a wireless signal corresponding to the feedback signal, by utilizing a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH) determined in advance. 
     &lt;Example of Hardware Configuration of Base Station and Terminal&gt; 
       FIG. 4A  is a view depicting an example of a hardware configuration of a base station. 
     The base station  100  depicted in  FIG. 4A  further includes a processor  120 , a wireless processing circuit  121 , a large-scale integration (LSI)  122 , a network interface (NIF) circuit  123 , and a storage apparatus  124 . 
     The processor  120  may read out, for example, a program stored in the storage apparatus  124 , and execute the read out program to implement functions of the scheduling unit  105 , user data generation unit  107 , and digital precoding unit  108 . The processor  120  corresponds, for example, to the scheduling unit  105 , user data generation unit  107 , and digital precoding unit  108 . 
     The LSI  122  may implement functions of the channel estimation unit  104 , reference signal generation unit  109 , and channel multiplexing unit  110 , for example, in accordance with an instruction from the processor  120 . The LSI  122  corresponds, for example, to the channel estimation unit  104 , reference signal generation unit  109 , and channel multiplexing unit  110 . 
     Further, the wireless processing circuit  121  corresponds, for example, to the analog BF unit  102 , RF units  103 - 1  to  103 -N RF , and RF units  111 - 1  to  111 -N RF . Furthermore, the NIF circuit  123  corresponds, for example, to the IF unit  106 . 
       FIG. 4B  is a view depicting an example of a hardware configuration of a terminal. 
     The terminal  200  depicted in  FIG. 4B  further includes a processor  220 , a wireless processing circuit  221 , an LSI  222 , and a storage apparatus  224 . 
     The processor  220  reads out, for example, a program stored in the storage apparatus  224  and executes the read out program to implement the function of the feedback signal generation unit  204 . The processor  220  corresponds, for example, to the feedback signal generation unit  204 . 
     Meanwhile, the LSI  222  implements the function of the channel estimation unit  203 , for example, in accordance with an instruction from the processor  220 . The LSI  222  corresponds, for example, to the channel estimation unit  203 . 
     Further, the wireless processing circuit  221  corresponds, for example, to the RF units  202  and  205 . 
     It is to be noted that each of the processors  120  and  220  may be a control unit or a controller, such as a central processing unit (CPU), a micro processing unit (MPU), a digital processing unit (DSP), or a field programmable gate array (FPGA). 
     Further, each of the storage apparatuses  124  and  224  may be a read only memory (ROM), a random access memory (RAM), a hard disk drive (HDD), or a combination thereof. 
     &lt;Example of Operation&gt; 
       FIG. 5  is a flowchart depicting an example of operation of the base station  100 .  FIG. 7  is a view depicting an example of a relationship between analog beams # 1  to # 5  (N beam =5) and the terminals  200 - 1  to  200 - 9  (N UE =9). The example of operation of  FIG. 5  is described with additional reference to  FIG. 7 . 
     It is assumed here that, before the operation depicted in  FIG. 5 , the base station  100  has acquired candidate beam information and feedback information from the terminals  200 - 1  to  200 - 9 . In the example of  FIG. 7 , the candidate beam for the terminals  200 - 1  and  200 - 2  is the analog beam # 2 , and the candidate beam for the terminals  200 - 3  to  200 - 5  is the analog beam # 1 . Further, the candidate beam for the terminals  200 - 6  and  200 - 7  is the analog beam # 3 , and the candidate beam for the terminals  200 - 8  and  200 - 9  is the analog beam # 4 . 
     Further, it is assumed that the base station  100  receives data destined for the terminals  200 - 1  to  200 - 9  from a node apparatus. 
     Referring back to  FIG. 5 , after the base station  100  starts its processing (S 10 ), it sets the number of terminals g (hereinafter referred to sometimes as “frequency multiplexing terminal number”) whose frequency is able to be multiplexed, to g=1 (S 11 ). The frequency multiplexing terminal number g indicates, for example, the number of terminals that may be allocated to one analog beam by a single time of scheduling. Meanwhile, G indicates, for example, a maximum value of the frequency multiplexing terminal number g. In the following process, the scheduling unit  105  selects G terminals  200  in the maximum from among, for example, the N UE  terminals  200 . 
       FIG. 9B  is a view depicting a final result of scheduling for the analog beam # 2  in the present example of operation. In  FIG. 9B , an example is depicted in which the maximum value G of the frequency multiplexing terminal number g is G=4. The base station  100  starts the process by setting the frequency multiplexing terminal number g at “1”, and successively increments the frequency multiplexing terminal number g to perform scheduling for the terminals  200 - 1  to  200 - 9 . In the present process (S 10 ), for example, the scheduling unit  105  sets the frequency multiplexing terminal number g to g=1. 
     It is to be noted that the base station  100  may calculate the maximum value G in the process of S 11 . For example, the scheduling unit  105  may calculate the maximum value G, for each of the analog beams # 1  to # 4 , based on the wireless resource amount that may be allocated by a single time of scheduling, and the amount of data destined for each of the terminals  200 - 1  to  200 - 9 . 
     Referring back to  FIG. 5 , the base station  100  subsequently notices an unallocated terminal  200  (S 12 ). For example, in the example of  FIG. 7 , the scheduling unit  105  notices the terminal  200 - 1 . In the following description, the terminal on which attention has been focused at S 12  is sometimes referred to as noticed terminal  200 . The noticed terminal  200  is, for example, a terminal other than the terminals selected by a process at S 18  hereinafter described. 
     Referring back to  FIG. 5 , the base station  100  subsequently decides whether or not the scheduling target slot is a slot that does not include a synchronization signal block (SSB) and a CSI-RS or the like but includes a DMRS and data (S 13 ). 
     As types of slot, for example, there is a slot that includes an SSB and a CSI-RS, and a slot that does not include any of an SSB and a CSI-RS but includes a DMRS and data. The former type is sometimes referred to as pattern (1) and the latter type is sometimes referred to as pattern (2). Further, the former is sometimes referred to as “slot including an SSB” and the latter is sometimes referred to as “slot that does not include an SSB.” 
     For example, when the scheduling target slot is the pattern (1), the scheduling unit  105  makes a decision of “No” at S 13 , but when the scheduling target slot is the pattern (2), the scheduling unit  105  makes a decision of “Yes” at S 13 . 
     The base station  100  decides, when the scheduling target slot is the pattern (2) (Yes at S 13 ), whether or not the frequency multiplexing terminal number g is g=1 (S 14 ). 
     When the frequency multiplexing terminal number g is g=1 (Yes at S 14 ), the base station  100  calculates a selection metric value (S 16 ). 
     The selection metric represents, for example, a norm for selecting a terminal to be made a scheduling target from among a plurality of terminals  200 . As an example of the selection metric, for example, there is a proportional fair (PF) norm (hereinafter referred to sometimes as “PF norm”). For example, the scheduling unit  105  may calculate a selection metric value, based on feedback information (for example, a CQI) fed back from each of the terminals  200 - 1  to  200 - 9 . For example, the scheduling unit  105  may calculate instant received power from the received CQI and calculate the ratio between the instant received power and average received power as the selection metric value. 
     As the selection metric, there is also a round robin norm. The round robin norm is a norm that allocates wireless resources to the terminals  200  in order, for example, beginning with “1.” In this case, the scheduling unit  105  successively selects the terminals  200 - 1  to  200 - 9  in the process of S 16 . 
     For example, the scheduling unit  105  calculates a selection metric value for the noticed terminal  200 - 1  by using the PF norm or the like. 
     Then, the base station  100  decides whether or not there remains a terminal for which the processes at S 12  to S 16  are not completed (S 17 ). The processes at S 12  to S 16  are hereinafter referred to sometimes as “first process.” The base station  100  decides, in the case where the processes at S 12  to S 16  are completed for all terminals  200 - 1  to  200 - 9  that become a scheduling target when g=1, that the first process is completed (No at S 17 ), but in any other case, the base station  100  decides that the first process is not completed (Yes at S 17 ). 
     In the example of  FIG. 7 , for example, the scheduling unit  105  makes a decision of Yes at S 17  because the selection metric value is calculated for the terminal  200 - 1  and the first process is not performed for the other terminals  200 - 2  to  200 - 9 . In this case, the base station  100  selects a terminal  200  from among the terminals  200 - 2  to  200 - 9  as a noticed terminal (S 12 ). Here, the base station  100  selects, for example, the terminal  200 - 2  as a noticed terminal. Thereafter, the base station  100  performs, for example, the following processes. 
     For example, the base station  100  does not change the scheduling target slot from that in the case where the terminal  200 - 1  is made a noticed terminal in the pattern (2) (Yes at S 13 ) and there is no change also in g=1 (Yes at S 14 ), and the base station  100  calculates the selection metric value of the terminal  200 - 2  (S 16 ). The base station  100  checks again whether or not the first process is completed, and since the terminals  200 - 3  to  200 - 9  remain as terminals for which the first process is not completed (Yes at S 17 ), the base station  100  notices, for example, the terminal  200 - 3  and calculates the selection metric value (Yes at S 13 , Yes at S 14 , and S 16 ). Thereafter, the base station  100  calculates the selection metric value for the terminals  200 - 4  to  200 - 9  (Yes at S 13 , Yes at S 14 , and S 16 ). 
     When the base station  100  decides that there remains no terminal for which the first process is not completed (No at S 17 ), the base station  100  selects a terminal  200  based on the selection metric value (S 18 ). For example, when the scheduling unit  105  completes the first process for all terminals  200 - 1  to  200 - 9  with g=1, the scheduling unit  105  decides that there remains no terminal for which the first process is not completed, and selects a terminal  200 , based on the selection metric value. In the example of  FIG. 7 , the scheduling unit  105  selects the terminal  200 - 1 . 
     By this selection, the scheduling unit  105  allocates a wireless resource for the analog beam # 1  to the terminal  200 - 1 . Accordingly, as depicted in  FIG. 9B , to the terminal  200 - 1  as the terminal  200  of g=1, a wireless resource for the analog beam # 2  is allocated. 
     Referring back to  FIG. 5 , the base station  100  subsequently decides whether or not there exists a terminal  200  of a scheduling target (S 19 ). For example, the scheduling unit  105  may make the decision depending upon whether or not there exists some remaining amount of wireless resources available for terminals, whose number is represented as a scheduling target terminal number, when a wireless resource is allocated to the terminal  200  selected at S 18 . 
     When a terminal  200  of a scheduling target exists, or the scheduling target terminal number is greater than  0  (Yes at S 19 ), the base station  100  increments the frequency multiplexing terminal number g and decides whether or not the incremented frequency multiplexing terminal number g exceeds the maximum value G (S 20 ). For example, the scheduling unit  105  compares the incremented frequency multiplexing terminal number g and the maximum value G calculated at S 11  to decide whether or not the former exceeds the latter. In the example of  FIG. 7 , the scheduling unit  105  increments g to g=2, and since g does not exceed the maximum value G=4, the scheduling unit  105  makes a decision of “No” at S 20  and advances the processing to S 12 . 
     The following description is given with reference to  FIG. 5  in the example in which g=2. 
     At S 12 , for example, the scheduling unit  105  notices the terminal  200 - 2  as an unallocated terminal (S 12 ), and decides whether or not the scheduling target slot is the pattern (2) (S 13 ). In the case after g=2, irrespective of whether the scheduling target slot is the pattern (1) (No at S 13 ) or the pattern (2) (No at S 14 ), the processing advances to S 15 , at which the scheduling unit  105  performs a decision of whether or not the noticed terminal  200 - 2  is a scheduling target terminal. 
     In the example, it is assumed that, when the scheduling target slot is the pattern (1) (No at S 13 ), the analog beam formed using the slot is referred to as analog beam #a. On the other hand, it is assumed that, when the scheduling target slot is the pattern (2) (Yes at S 13 ), the analog beam selected with g=1 is referred to as analog beam #b. The base station  100  uses the analog beam #a or #b to perform a decision process (S 15 ). 
     It is to be noted that the decision process (S 15 ) is described taking, as an example, the analog beam #b selected with g=1 when the scheduling target slot is the pattern (2) (Yes at S 13 ). The decision process in the case of the analog beam #a is described after an example of the analog beam #b is described. 
     In the example of  FIG. 7 , as an example in which g=1, the base station  100  has selected the terminal  200 - 1  as a terminal  200  of a scheduling target (S 18 ). In the example of  FIG. 7 , the candidate beam of the terminal  200 - 1  is the analog beam # 2 . Accordingly, the base station  100  performs a decision process by using the analog beam # 2  as the analog beam #b. In the decision process, for example, the base station  100  decides whether or not each of the unallocated terminals  200 - 2  to  200 - 9  may be selected as a target for communication using the analog beam #b (here, the analog beam # 2 ). 
       FIG. 6  is a flowchart depicting an example of a decision process (S 15 ). 
     The base station  100  calculates a correlation value ρ A,m,n  in the decision process (S 151 ). Here, the base station  100  determines an analog beam #m and another analog beam #n, and calculates a correlation value ρ A,m,n  between the two analog beams #m and #n. 
     The analog beam #m is, for example, an analog beam to be used for a scheduling target slot, and the analog beam #a or #b corresponds to the analog beam #m. For example, in the example of  FIG. 7 , since the candidate beam for the terminal  200 - 1  selected with g=1 is the analog beam # 2 , the analog beam # 2  becomes the analog beam #m. 
     On the other hand, the analog beam #n is an analog beam corresponding to the candidate beam, for example, for an unallocated terminal  200  (or noticed terminal  200 ). For example, in the example of  FIG. 7 , the analog beams # 1 , # 2 , # 3  and # 4  that are candidate beams for the noticed terminals  200 - 2  to  200 - 9  may become the analog beam #n. 
     In the example of  FIG. 7 , since, in the case of the noticed terminal  200 - 2 , the analog beam #m=analog beam # 2  and the candidate beam for the noticed terminal  200 - 2  is the analog beam # 2 , in the case of the noticed terminal  200 - 2 , the analog beam #n=analog beam # 2 . 
     Then, the base station  100  calculates the correlation value ρ A,m,n  of the analog beam #n to the analog beam #m, for example, using the following expression: 
     
       
         
           
             
               
                 
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     In the expression (1), w m  is a weight vector that is outputted from the scheduling unit  105  to the analog BF unit  102  when the analog beam #m is formed by the antennas  101 - 1  to  101 -N ANT , and is to be applied to a wireless signal. Further, w n  is a weight vector that is outputted from the scheduling unit  105  to the analog BF unit  102  when the analog beam #n is to be formed by the antenna  101 - 1  to  101 -N ANT , and is to be applied to a wireless signal. 
     The second term of the numerator on the right side of the expression (1) represents an Hermitian transposed matrix of the weight vector w n , and may be represented as the weight vector w n  itself. Accordingly, by performing calculation of the inner product, the right side of the expression (1) becomes |cosθ| 2 . Here, θ represents an angle, for example, defined by the two weight vectors w m  and w n . It is to be noted that the two weight vectors w m  and w n  may be represented using a complex vector. 
     Accordingly, the correlation value ρ A,m,n  may be regarded as representing, for example, an index indicating a degree of the angle between the analog beam #m and the analog beam #n that is a candidate beam for the noticed terminal  200 , in other words, an index indicating to what degree the analog beams #m and #n are close to or apart from each other. 
     When the scheduling target slot is the pattern (2) (Yes at S 13  of  FIG. 5 ), the scheduling unit  105  sets the analog beam selected with g=1 as the analog beam #b=analog beam #m (or m=b). In the example of  FIG. 7 , the analog beam #m is the analog beam # 2 . Therefore, the scheduling unit  105  calculates the correlation value ρ A,m,n  between the analog beam # 2  and the analog beam # 2  (=analog beam #n) that is the candidate beam for the noticed terminal  200 - 2 . 
     On the other hand, when the scheduling target slot is the pattern (1) (No at S 13  of  FIG. 5 ), the scheduling unit  105  sets the analog beam formed in the pattern (1) as the analog beam #a and determines m as m=a, and then calculates the correlation value ρ A,m,n . Details in this case are hereinafter described. 
     The scheduling unit  105  retains the expression (1), for example, in an internal memory or the like, reads out the weight vector w m  corresponding to the analog beam #m and the weight vector w n  corresponding to the analog beam #n from the internal memory, and substitutes the weight vector w m  and the weight vector w n  into the expression (1) to obtain a correlation value  92   A,m, n . Alternatively, the scheduling unit  105  may retain, for example, correlation values ρ A,m,n  corresponding to combinations of arbitrary weight vectors w m  and w n  in the internal memory in advance so that, in the present process, it reads out a correlation value ρ A,m,n  corresponding to a combination (m, n) of arbitrary weight vectors from the internal memory. 
     Referring back to  FIG. 6 , the base station  100  subsequently calculates a threshold value ┌ A,u  (S 152 ). For example, the base station  100  calculates the threshold value ┌ A,u  by using the following expression (2): 
       [Expression 2] 
       Γ A,u   =pw   N     UE,m     +qw   CQI     u      (2)
 
     In the expression (2), w NUE,m  represents a coefficient determined, for example, by the number of terminals N UE,m  corresponding to the analog beam #m. The number of terminals N UE,m  corresponding to the analog beam #m represents, for example, the number of terminals  200  that utilizes the analog beam #m. 
     For example, in the example of  FIG. 7 , since the terminal  200 - 1  is scheduled for the analog beam # 2  (=analog beam #m) and the terminal  200 - 2  is a noticed terminal, the number of terminals N UE,m  corresponding to the analog beam #m is N UE,m =2. 
       FIG. 8A  depicts an example of the coefficient W NUE,m . The coefficient w NUE,m  is set such that, for example, it has a numerical value that decreases as the number of terminals N UE,m  decreases (or comes closer to “0”) and has a numerical value that increases as the number of terminals N UE,m  increases (or comes closer to the maximum value G). Alternatively, the scheduling unit  105  sets the coefficient w NUE,m  (or the threshold value ┌ A,u ) such that, for example, it has a value that comes closer to “0” (or “0.1”) as the number of terminals N UE,m  comes closer to “0” and has a value that comes closer to “1” as the number of terminals N UE,m  comes closer to the maximum value G. 
     Further, in the expression (2), w CQIu  represents a coefficient determined by an index CQI u  representative of the reception quality, for example, in the noticed terminal  200 - u . In the example of  FIG. 7 , CQI u  of the noticed terminal  200 - 2  is a CQI for the analog beam # 2  (=candidate beam=analog beam #m). Further, in the case where the terminal  200 - 3  becomes a noticed terminal, CQI u  of the same may be the CQI of the analog beam # 1  (candidate beam) or the CQI of the analog beam # 2  (analog beam #m). 
       FIG. 8B  represents an example of the coefficient w CQIu . The coefficient w CQIu  is set such that, for example, it has a value that increases as CQI u  decreases and decreases as CQI u  increases. Alternatively, the scheduling unit  105  may set the coefficient w CQIu  (or the threshold value ┌ A,u ) such that the value comes closer to “1” as the CQI comes closer to “0” and comes closer to “0” (or “0.1”) as the CQI comes closer to the requested CQI (CQI req ) requested by the terminal  200 . 
     The coefficients w NUE,m  and w CQIu  indicated in  FIGS. 8A and 8B  are an example and may have some other numerical values if they have such a relationship in magnitude as described hereinabove. 
     Further, in the expression (2), p and q are weighting coefficients for the coefficients w NUE,m  and w CQIu , and may be set at arbitrary values by the user. For example, the base station  100  may set one of p and q at “0” to use one of the coefficients w NUE,m  and w CQIu  as the threshold value ┌ A,u . 
     For example, the scheduling unit  105  reads out the expression (2) stored in the internal memory, and substitutes the CQI extracted from feedback information and the number of terminals N UE,m  allocated to the analog beam #m into the expression (2) to calculate the threshold value ┌ A,u . 
     In this manner, the base station  100  may control (or change) the threshold value ┌ A,u  for each terminal  200 . 
     Referring back to  FIG. 6 , the base station  100  subsequently decides whether or not the correlation value ρ A,m,n  is equal to or greater than the threshold value ┌ A,u  (S 153 ). Then, when the correlation value ρ A,m,n  is equal to or greater than the threshold value ┌ A,u  (Yes at S 153 ), the base station  100  determines the noticed terminal  200 - u  as a scheduling target. On the other hand, when the correlation value ρ A,m,n  is smaller than the threshold value ┌ A,u  (No at S 153 ), the base station  100  does not determine the noticed terminal  200 - u  as a scheduling target. 
     For example, in the example of  FIG. 7 , when the correlation value ρ A,m,n  between the analog beam # 2  (m=2) and the analog beam # 2  (n=2) is equal to or greater than the threshold value ┌ A,u  (Yes at S 153 ), the scheduling unit  105  determines the noticed terminal  200 - 2  as a terminal of a scheduling target. On the other hand, when the correlation value ρ A,2,1  is smaller than the threshold value ┌ A,3  (No at S 153 ), scheduling unit  105  does not determine the noticed terminal  200 - 2  as a terminal of a scheduling target of the analog beam # 1   
       FIG. 9A  is a view depicting an example of a relationship between the correlation value ρ A,m,n  and the threshold value ┌ A,u . 
     The threshold value ┌ A,u  includes coefficients w NUE,m  and w CQIu  as indicated by the expression (2). Accordingly, the threshold value ┌ A,u  transits such that the angle θ 1  defined by the threshold value ┌ A,u  and the analog beam #m increases as the number of terminals N UE,m  corresponding to the analog beam #m decreases and as CQIu for the analog beam #m increases. 
     On the other hand, the threshold value ┌ A,u  transits such that the angle θ 1  defined between the threshold value ┌ A,u  and the analog beam #m decreases as the number of terminals N UE,m  corresponding to the analog beam #m increases and as the index CQI u  for the analog beam #m decreases. 
     For example, the threshold value ┌ A,u  is adjusted such that, for example, the number of terminals N UE,m  corresponding to the analog beam #m is appropriate, and such that a terminal, whose communication quality is equal to or higher than a fixed level even if the analog beam #m is utilized, is scheduled. 
     Then, when the correlation value ┌ A,m,n  becomes equal to or greater than the threshold value ┌ A,u  adjusted in this manner (Yes at S 153 ), the base station  100  selects the aimed noticed terminal  200 - u  as a terminal of a scheduling target of the analog beam #m. 
     For example, as depicted in  FIG. 9A , the analog beam #n sometimes exists such that the angle θ defined by the analog beam #m and the analog beam #n remains within a range of the angle θ 1  defined by the threshold value ┌ A,u  with reference to the analog beam #m. In such a case as just described, the base station  100  selects the noticed terminal  200 - u , for which such an analog beam #n as described above is the candidate beam, as a terminal  200  of a scheduling target. 
     In this case, the analog beam #n exists within a range narrower than the threshold value ┌ A,u  or more with respect to the analog beam #m. Therefore, even if the terminal  200  for which the analog beam #n is the candidate beam receives data transmitted thereto by utilizing the analog beam #m, the analog beam #n becomes an analog beam that is guaranteed sufficiently in terms of the number of terminals or the communication quality. 
     On the other hand, when the correlation value ρ A,m,n  is smaller than the threshold value ┌ A,u  adjusted in such a manner as described above (No at S 153 ), the base station  100  does not select the noticed terminal  200 - u  as a terminal of a scheduling target of the analog beam #m. 
     For example, the angle θ defined by the analog beam #m and the analog beam #n sometimes exists which exceeds a range of the angle θ 1  defined by the threshold value ┌ A,u  with respect to the analog beam #m as depicted in  FIG. 9A . 
     In this case, the analog beam #n exists at an angle spaced from the threshold value ┌ A,u  with respect to the analog beam #m. Therefore, even if data is transmitted toward the terminal  200 , for which the analog beam #n is the candidate beam, by utilizing the analog beam #m, the analog beam #m is not guaranteed in terms of the number of terminals or the communication quality. In this case, the base station  100  does not determine the noticed terminal  200 - u , for which the analog beam #n is the candidate beam, as a scheduling target for the analog beam #m. 
     For example, the scheduling unit  105  decides whether or not the noticed terminal  200 - u  is to be made a scheduling target depending upon whether or not the correlation value ρ A,m,n  calculated at S 151  is equal to or greater than the threshold value ┌ A,u  calculated at S 152  (S 153 ). 
     Referring back to  FIG. 5 , when the noticed terminal  200  is made a scheduling target (Yes at S 15 ), the base station  100  calculates the selection metric of the noticed terminal  200  (S 16 ). For example, the scheduling unit  105  calculates the selection metric of the noticed terminal  200  that is made a scheduling target. 
     On the other hand, when the noticed terminal  200  is not made a scheduling target (No at S 15 ), the base station  100  advances its processing to S 17  without calculating the selection metric of the noticed terminal  200 . 
     In the example of  FIG. 7 , the scheduling unit  105  decides that the noticed terminal  200 - 2  is a terminal of a scheduling target (Yes at S 15 ) and calculates the selection metric of the noticed terminal  200 - 2  (S 16 ). 
     Since, in the case where g=2, the scheduling unit  105  has not performed the first process for the terminals  200 - 3  to  200 - 9  (Yes at S 17 ), it preforms the processes at S 13  to S 16 , for example, by setting the terminal  200 - 3  as a noticed terminal. The base station  100  performs, for example, the following processes. 
     For example, the scheduling unit  105  sets, for example, the terminal  200 - 3  as a noticed terminal and decides whether or not the noticed terminal is a scheduling target terminal (S 15 ). In this case, the scheduling unit  105  calculates, using m=2, n=1 and u=3, the correlation value ρ A,2,1  and the threshold value ┌ A,3  and compares them with each other to make a decision (S 153 ). In this case, the scheduling unit  105  decides, for example, that the correlation value ρ A,2,1  is greater (Yes at S 153  of  FIG. 6 ). Then, the scheduling unit  105  calculates the selection metric of the terminal  200 - 3 . The scheduling unit  105  repeats such processes as described above to perform the decision process for the noticed terminal  200  (S 15 ). Then, after the scheduling unit  105  performs the processes at steps S 13  to S 16  for the terminals  200 - 2  to  200 - 9 , it makes a decision of No at S 17  and selects a terminal  200  from the calculated selection metric values (S 18 ). In this case, the scheduling unit  105  here selects the terminal  200 - 4  as a terminal for which scheduling is to be performed (S 18 ). As depicted in  FIG. 19B , in the case of g=2, a wireless resource is allocated to the terminal  200 - 4 . 
     Thereafter, the base station  100  repeats S 12  to S 20  until G=4 is reached. Then, when the frequency multiplexing terminal number g exceeds the maximum value G (Yes at S 20 ), the base station  100  ends the scheduling (S 21 ). Even in the case where the frequency multiplexing terminal number g does not exceed the maximum value G, in the case where a wireless resource amount that may be allocated once is exceeded (No at S 19 ), the base station  100  ends the scheduling (S 21 ). 
       FIG. 9B  is a view depicting an example of allocation by scheduling. To the analog beam #m, the four terminals  200 - 1 ,  200 - 4 ,  200 - 6  and  200 - 8  are allocated. In this case, for example, the base station  100  performs the following processes. 
     For example, the scheduling unit  105  instructs the user data generation unit  107  to output user data destined for the terminals  200 - 1 ,  200 - 4 ,  200 - 6  and  200 - 8 . Further, the scheduling unit  105  outputs weighting values indicative of a result of allocation to the analog BF unit  102 . The analog BF unit  102  performs weighting for wireless signals including data destined for the terminals  200 - 1 ,  200 - 4 ,  200 - 6  and  200 - 8  in accordance with the weighting values, and outputs the resulting wireless signals to the antennas  101 - 1  to  101 -N ANT . From the antennas  101 - 1  to  101 -N ANT , the weighted wireless signals are transmitted to form an analog beam # 2 , and wireless signals including the data are transmitted to the terminals  200 - 1 ,  200 - 4 ,  200 - 6  and  200 - 8 . 
     Here, operation when the scheduling target slot is the pattern (1) (No at S 13 ) after the base station  100  sets g to g=1 (S 12 ) is described. 
     In the example of  FIG. 7 , an analog beam formed from a slot including an SSB may become one of the analog beams # 1  to # 5 . Such an analog beam as just described is determined in advance by the scheduling unit  105 . Here, it is assumed that the analog beam # 1  is an analog beam formed from a slot including an SSB. In this case, the scheduling unit  105  performs the decision process (S 15 ) by setting the analog beam # 1  as the analog beam #a and setting this analog beam #a as the analog beam #m. For example, in the case where the terminal  200 - 1  is made a noticed terminal (S 12 ), the scheduling unit  105  calculates the correlation value ρ A,m,n  from the analog beam # 1  (=analog beam #a=analog beam #m) and the analog beam # 2  (=analog beam #n) that is a candidate beam for the terminal  200 - 1  (S 151 ) and further calculates the threshold value ┌ A,u  (S 152 ), and then decides from a relationship in magnitude between the correlation value ρ A,m,n  and the threshold value ┌ A,u  whether or not the terminal  200 - 1  is a scheduling target (S 153 ). On the other hand, when the terminal  200 - 3  is made a noticed terminal (S 12 ), the scheduling unit  105  performs calculation of the correlation value ρ A,m,n  and so forth from the analog beam # 1  (=analog beam #a=analog beam #m) and the analog beam # 2  (=analog beam #n) that is a candidate beam for the terminal  200 - 3  (S 151  and S 152 ). Then, the scheduling unit  105  decides whether or not the terminal  200 - 3  is a scheduling target (S 153 ). Thereafter, the scheduling unit  105  performs the decision process also for the unallocated terminals  200 - 4  to  200 - 9  and selects a terminal  200  based on the selection metric values. 
     The scheduling unit  105  performs the decision process (S 15 ) and so forth by setting the analog beam #m, which is to be made a target of the decision process, to the analog beam #a or the analog beam #b depending upon whether the scheduling target slot is the pattern (1) or the pattern (2). 
     As described above, in the first embodiment, the base station  100  may allocate the terminal  200 - 1 , and besides, the terminals  200 - 4 ,  200 - 6  and  200 - 8  to the analog beam # 2 . 
     Therefore, for example, in comparison with an alternative case in which the base station  100  allocates only the terminals  200 - 1  and  200 - 2  to the analog beam # 2 , it is possible to allocate terminals  200  to a full frequency band that is utilized for transmission of the analog beam # 2  as depicted in  FIG. 9B . 
     Accordingly, in the first embodiment, since a wireless resource for an analog beam is utilized effectively, improvement in throughput may be achieved. 
     Further, in the first embodiment, allocation of wireless resources is performed in a unit of a slot. On the other hand, in the mini-slot technology, allocation of wireless resources is performed in a unit of a symbol and a DMRS is transmitted in a unit of a symbol. Accordingly, in the first embodiment, since transmission opportunities of a DMRS are reduced in terms of a unit of a slot in comparison with that in the case of a mini-slot, improvement of the throughput may be achieved. 
     Second Embodiment 
     A second embodiment is an example in which spatial multiplexing is applied to scheduling. 
       FIGS. 10A to 10C  are views depicting examples of spatial multiplexing. In MIMO, for example, it is possible to allocate one stream to one antenna by digital precoding so as to perform communication with a plurality of terminals  200 , in parallel, using a plurality of antennas. Where the number of terminals that may perform spatial multiplexing (hereinafter referred to sometimes as spatial multiplexing terminal number) is represented by k, in the case where k=1, the base station  100  forms one digital beam # 1  using at least one antenna  101  to perform communication with one terminal  200 - 1 . Meanwhile, in the case where k=2, the base station  100  may form two digital beams # 1  and # 2  simultaneously by two antennas  101 - 1  and  101 - 2  to communicate simultaneously with two terminals  200 - 1  and  200 - 2 . Then, in the case where spatial multiplexing may be performed with a multiplicity of K that is the maximum value for the spatial multiplexing terminal number k, the base station  100  may form K digital beams # 1  to #K simultaneously using K antennas  101 - 1  to  101 -K to communicate simultaneously with K terminals  200 - 1  to  200 -K. Also it is possible to consider the spatial multiplexing terminal number as the number of terminals that perform communication by using, for example, digital beams that are formed simultaneously with the digital beam # 1 . 
     It is to be noted that the digital beams # 1  to #K are beams formed, by the antennas  101 , using digital precoding. 
       FIGS. 11A and 11B  illustrate a flowchart depicting an example of operation of the second embodiment. In the present operation example, the base station  100  selects, as terminals that may perform spatial multiplexing, a plurality of (K in the maximum) terminals  200  by processes at S 31  to S 40 . On the other hand, the base station  100  selects, as the number of terminals that may perform frequency multiplexing, a plurality of (G in the maximum) terminals  200  by the first embodiment (S 10  to S 21 ) (S 45 ). Then, the base station  100  calculates a total throughput of the terminals  200  selected as the terminals that may perform spatial multiplexing and a total throughput of the terminals  200  selected as the terminals that may perform frequency multiplexing, and adopts the selection result that has a higher (or greater) throughput value (S 41 ). 
     Note that it is assumed that, also in the present operation example, the base station  100  acquires candidate beam information and feedback information from the terminals  200  and receives also user data destined for the terminals  200  from a node apparatus. 
     After the base station  100  starts its processing (S 30 ), it sets the spatial multiplexing terminal number k to k=1 (S 31 ). For example, the scheduling unit  105  sets the spatial multiplexing terminal number k to k=1. In this case, the scheduling unit  105  calculates the maximum value K for the spatial multiplexing terminal number k, for example, based on the number N ANT  of the antennas  101 - 1  to  101 -N ANT  and the number of terminals  200 . For example, the scheduling unit  105  may determine the number of pieces of acquired feedback information as the maximum value K. 
     Then, the base station  100  notices an unallocated terminal (S 32 ) and decides whether or not a scheduling target slot is a slot that does not include an SSB or the like (or a slot of the pattern (2)) (S 33 ). Also in the second embodiment, the base station  100  decides whether the scheduling target slot is the pattern (2) or the pattern (1) similarly as in the first embodiment. In the following, description is given using examples of  FIGS. 13A to 13C , and it is assumed that the scheduling unit  105  in this case determines the terminal  200 - 1  as an unallocated noticed terminal and the scheduling target slot is the pattern (2). Operation in the case where the scheduling target slot is the pattern (1) is described after the description of the pattern (2). 
     When the scheduling target slot is a slot that does not include an SSB (Yes at S 33 ), the base station  100  decides whether or not k=1 (S 34 ), and calculates, when k=1 (Yes at S 34 ), the selection metric (S 36 ). 
       FIGS. 13A to 13C  are views depicting examples of a digital beam in the case where k=1. As depicted in  FIGS. 13A to 13C , the base station  100  may form digital beams # 1  to #K individually for the terminals  200 - 1  to  200 -K. For example, the digital beam # 1  is a digital beam that corresponds to PMI fed back to the base station  100  by the terminal  200 - 1 , and the digital beam # 2  is a digital beam corresponding to PMI fed back by the terminal  200 - 2 . 
     In the examples of  FIGS. 13A to 13C , in the case where k=1, the scheduling unit  105  calculates the selection metric value for the noticed terminal  200 - 1 . The selection metric may be, for example, the PF norm or the round robin norm similarly as in the first embodiment. 
     Then, the base station  100  decides whether or not there remains a terminal for which the processes at S 33  to S 36  (S 37 ) are not completed. The processes at S 33  to S 36  are hereinafter referred to sometimes as “second process.” When k=1, in the case where the processes at S 32  to S 36  are completed for all terminals  200  that are a scheduling target, the base station  100  decides that the second process is completed (No at S 37 ), but in any other case, the base station  100  decides that the second process is not completed (Yes at S 37 ). 
     In the examples of  FIGS. 13A to 13C , since the processes at S 32  to S 36  are not completed for the terminals  200 - 2  to  200 -K, the scheduling unit  105  makes a decision of Yes at S 37 . In this case, the base station  100  performs the processes at S 32  to S 36  by setting each of the other terminals  200 - 2  to  200 -K as a noticed terminal. For example, when the terminal  200 - 2  is set as a noticed terminal, since the target slot remains the pattern (2) (Yes at S 33 ) and also k remains k=1 without a change (Yes at S 34 ), the scheduling unit  105  calculates the selection metric value for the terminal  200 - 2  (S 36 ). Thereafter, the scheduling unit  105  repeats the processes up to S 37  to calculate the selection metric value for the terminals  200 - 1  to  200 -K. 
     Then, when there remains no terminal for which the processes at S 33  to S 36  are not completed (No at S 37 ), the base station  100  selects a terminal  200 , based on the selection metric values. For example, the scheduling unit  105  selects the terminal  200 - 1 . 
     Then, when a scheduling target terminal exists, or a scheduling target terminal number representative of the number of terminals available for a scheduling target is greater than 0 (Yes at S 39 ), the base station  100  increments the spatial multiplexing terminal number k and decides whether or not k after incremented is greater than the maximum value K (S 40 ). When k is not greater than the maximum value K (No at S 40 ), the base station  100  advances the processing to S 32  to repeat the processes described above. 
     On the other hand, when a scheduling target terminal does not exist (No at S 39 ), the base station  100  advances the processing to S 41  even in the case where the spatial multiplexing terminal number k does not exceed the maximum value K. 
     The following description is given assuming that k=2. The base station  100  notices, for example, the terminal  200 - 2  as an unallocated terminal  200  (S 32 ). It is to be noted that, since k=1 does not occur after k=2 (No at S 34 ), the base station  100  performs a decision process for the noticed terminal  200  (S 35 ). 
       FIG. 12  is a flowchart depicting an example of the decision process (S 35 ) for deciding whether or not the noticed terminal  200  is a scheduling target terminal. 
     The base station  100  first decides whether or not the noticed terminal  200  is to be subjected to the decision process (S 15 ) applied in the first embodiment, for example, whether or not the noticed terminals  200  is a scheduling target of an analog beam (S 350 ). For example, the base station  100  performs the following processes. 
     For example, the scheduling unit  105  notices the noticed terminal  200 - 2  in regard to the analog beam # 1  (=analog beam #b=analog beam #m) that is a candidate beam for the terminal  200 - 1  selected with k=1. The scheduling unit  105  calculates the correlation value ρ A,m,n  and the threshold value ┐ A,u  between the analog beam #m and the analog beam # 2  (=analog beam #n) that is a candidate beam for the noticed terminal  200 - 2  (S 151  and S 152 ), and decides whether or not the correlation value ρ A,m,n  is equal to or greater than the threshold value ┌ A,u  (S 153 ). When the correlation value ρ A,m,n  is equal to or greater than the threshold value ┌ A,u , the scheduling unit  105  selects the noticed terminal  200 - 2  as a scheduling target terminal (Yes at S 350 ), and performs the processes at S 351  to S 353  for the selected terminal  200 - 2 . On the other hand, when the correlation value ρ A,m,n  is smaller than the threshold value ┌ A,u , the scheduling unit  105  decides that the noticed terminal  200 - 2  is not a scheduling target (No at S 350 ), and thereafter advances the processing to S 37 . 
     For example, the scheduling unit  105  performs, for example, the following process at S 350 . For example, the scheduling unit  105  sets the selection priority degree of a terminal  200  selected when the correlation value ρ A,m,n  is equal to or greater than the threshold value ┌ A,u  to a value equal to or higher than the selection priority degree threshold value, but sets the selection priority degree of a terminal  200  when the correlation value ρ A,m,n  is smaller than the threshold value ┌ A,u  to a value lower than the selection priority degree threshold value. Then, the scheduling unit  105  performs the decision processes beginning with step S 351  for the terminal  200  whose selection priority degree is equal to or higher than the selection priority degree threshold value. 
     When the base station  100  decides that the noticed terminal  200 - 2  is a scheduling target terminal (Yes at S 350 ), it calculates the correlation value ρ D,m,n  (S 351 ). For example, the scheduling unit  105  calculates the correlation value ρ D,m,n  by using the following expression: 
     
       
         
           
             
               
                 
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     In the expression (3), v m  is a weight vector of the digital beam #m applied, for example, by the digital precoding unit  108 . Meanwhile, v n  is a weight vector of the digital beam #n applied by the digital precoding unit  108 . 
     In the second embodiment, the digital beam #m is a digital beam, for example, corresponding to PMI fed back by a terminal  200  selected as a scheduling target terminal when g=1. On the other hand, the digital beam #n is a digital beam, for example, corresponding to PMI fed back by an unallocated terminal  200  (or the noticed terminal  200 ). 
       FIG. 14A  is a view depicting an example of the digital beam #n when the digital beam # 1  is the digital beam #m in the case where k=2. In the example of  FIG. 14A , the digital beam # 1  is a digital beam corresponding to PMI fed back by the terminal  200 - 1  selected as a scheduling target terminal and is the digital beam #m. On the other hand, the digital beam # 2  corresponding to PMI fed back by an unallocated terminal  200 - 2  (noticed terminal  200 - 2 ) may be the digital beam #n. 
     In the following description, the digital beam corresponding to PMI fed back by a terminal  200  is referred to sometimes as “digital beam corresponding to the terminal  200 ,” and a terminal  200  having such a digital beam as just described is referred to sometimes as “terminal  200  corresponding to the digital beam.” 
     It is to be noted that, although, in  FIG. 14A . the digital beam # 2  is indicated as an example of the digital beam #n, a plurality of digital beams #n from the digital beam # 2  to the digital beam #K exist. 
     For example, the scheduling unit  105  calculates the correlation value ρ D,m,n  of the digital beam #m (digital beam # 1 ) to each digital beam #n (digital beam # 2  to digital beam #K) by utilizing the expression (3). The expression (3) is retained, for example, in an internal memory of the scheduling unit  105  or the like, and the scheduling unit  105  may suitably read out and use the expression (3) for calculation. Alternatively, the scheduling unit  105  may store correlation values ρ D,m,n  for arbitrary combinations (m, n) into the internal memory in advance and suitably read out a correlation value ρ D,m,n  upon processing. 
     Also in the expression (3), the second term of the numerator of the right side represents an Hermitian transposed matrix of the weight vector v n  and may be represented as the weight vector v n  itself similarly as in the expression (1). Accordingly, the right side of the expression (3) becomes |cosθ 2 | 2  by performing calculation of the inner product. Here, θ 2  represents, for example, an angle defined by two weight vectors v m  and v n . It is to be noted that the two weight vectors v m  and v n  may be represented using a complex vector. 
     Referring back to  FIG. 12 , the base station  100  subsequently calculates the threshold value ┌ D,u  (S 352 ). For example, the base station  100  calculates the threshold value ┌ D,u  by using the following expression: 
       [Expression 4] 
       ┌ D,u   =rw   k   +sw   Ds     u      (4)
 
     In the expression (4), w k  represents, for example, a coefficient determined by the spatial multiplexing terminal number k.  FIG. 15A  is a view depicting an example of the coefficient w k . The coefficient w k  is set such that it increases as the spatial multiplexing terminal number k decreases but decreases as the spatial multiplexing terminal number k increases. Alternatively, the scheduling unit  105  sets the coefficient w k  (or the threshold value ┌ A,u ) to a value that comes closer to “1” as the spatial multiplexing terminal number k comes closer to “1” but to a value that comes closer to “0” as the spatial multiplexing terminal number k comes closer to the maximum value K. 
     In the expression (4), w DSu  represents, for example, a coefficient determined by an index (hereinafter referred to sometimes as “delay spread”) DS u  representative of a delay spread of the noticed terminal  200 - u .  FIG. 15B  is a view depicting an example of the coefficient w Dsu . The coefficient w Dsu  is set such that it increases as the delay spread DS u  decreases but decreases as the delay spread DS u  increases. Alternatively, the scheduling unit  105  sets the coefficient w Dsu  (or the threshold value ┌ D,u ) to a value closer to “1” as the delay spread DS u  comes closer to “0” but to a value closer to “0” as the delay spread DS u  comes closer to the maximum value. 
     Further, in the expression (4), r and s are numerical values settable by the user, and by setting one of r and s at “0,” the base station  100  may calculate the threshold value ┌ D,u  by using one of the coefficients w k  and w DSu  similarly to p and q in the first embodiment. 
     It is to be noted that the scheduling unit  105  may calculate the delay spread DS u , for example, based on feedback information. For example, the scheduling unit  105  calculates the delay spread DS u  by determining a reception power value from the acquired CQI and substituting the reception power value into a specific calculation expression. 
     In this manner, the base station  100  may control (or change) the threshold value ┌ D,u  for each terminal  200 . 
     Referring back to  FIG. 12 , the base station  100  subsequently decides, in regard to all digital beams #m, whether or not the correlation value ρ D,m,n  is equal to or smaller than the threshold value ┌ D,u  (S 353 ). Then, when the correlation value ρ D,m,n  is equal to or smaller than the threshold value ┌ D,u  (when the correlation value ρ D,m,n  threshold value ┌ D,u ) in regard to all digital beam #m (Yes at S 353 ), the base station  100  determines the noticed terminal  200 - u  as a terminal  200  of a scheduling target. On the other hand, when the correlation value ρ D,m,n  is greater than the threshold value ┌ D,u  (when the correlation value ρ D,m,n &gt;threshold value ┌ D,u ) in regard to some of the digital beams #m (No at S 35 ), the base station  100  does not determine the noticed terminal  200 - u  as a terminal  200  of a scheduling target. 
       FIG. 16  is a view depicting an example of a relationship between the digital beams #m and #n and the threshold value ┌ d,u . 
     For example, when the delay spread DS u  is small and the spatial multiplexing terminal number k is small, the angle θ 3  defined by the digital beam #m and the threshold value ┌ D,u  gradually decreases, and in the reverse case, the angle θ 3  gradually increases. 
     When the correlation value ρ D,m,n  becomes equal to or smaller than the threshold value ┌ D,u , the scheduling unit  105  of the base station  100  selects the noticed terminal  200 - u  as a terminal  200  of a scheduling target. 
     For example, when the digital beam #n indicates, with reference to the digital beam #m, an angle θ 2  that is apart in angle from a threshold value as depicted in  FIG. 16 , the scheduling unit  105  selects the noticed terminal  200 - u  corresponding to the digital beam #n as a terminal  200  of a scheduling target. In this case, the scheduling unit  105  may, for example, spatially multiplex the digital beam #n, which is appropriate in terms of the delay spread DS u  and appropriate also in terms of the spatial multiplexing terminal number k, with the digital beam #m. 
     On the other hand, when the correlation value ρ D,m,n  is greater than the threshold value ┌ D,u , in other words, when the digital beam #n exists within a range of an angle that is smaller in angle than the threshold value ┌ D,u  with reference to the digital beam #m, the base station  100  does not determine the noticed terminal  200 - u  corresponding to the digital beam #n as a scheduling target. 
     In this case, the noticed terminal  200 - u  corresponding to the digital beam #n exists within an angular range that is so close to the digital beam #m that neither the delay spread DS u  is appropriate nor the spatial multiplexing terminal number k is appropriate. In such a case as just described, for example, the scheduling unit  105  does not select the noticed terminal  200 - u  so that the digital beam #n is not spatially multiplexed with the digital beam #m. 
     Referring back to  FIG. 12 , for example, the scheduling unit  105  determines the noticed terminal  200 - u  as a scheduling target when the correlation value ρ D,m,n  calculated at S 351  is equal to or smaller than the threshold value ┌ D,u  calculated at S 352  (Yes at S 353 ). On the other hand, in any other case (No at S 353 ), the scheduling unit  105  does not determine the noticed terminal  200 - u  as a scheduling target. 
     Referring back to  FIG. 11B , the base station  100  calculates the selection metric value for a terminal  200  determined as a scheduling target (S 38 ), and repeats the processes at S 32  to S 36  until an unallocated terminal  200  exists no more (No at S 37 ). On the other hand, the base station  100  does not calculate, for a terminal  200  that is not made a scheduling target, the selection metric value and repeats the processes until an unallocated terminal  200  does not exist any more (No at S 37 ). 
     When an unallocated terminal  200  does not exist any more (No at S 37 ), the base station  100  selects a terminal  200 , based on the selection metric values (S 38 ). For example, as depicted in  FIG. 14A , the base station  100  sets k to k=2, and determines the terminal  200 - 2  corresponding to the digital beam # 2  as a scheduling target. 
     Thereafter, the base station  100  increments the spatial multiplexing terminal number k, and repeats the processes at S 32  to S 40 . It is to be noted that  FIG. 14B  is a view depicting an example in the case where k=3 and the terminal  200 - 3  is selected as a scheduling target. 
     Referring back to  FIG. 11B , when the spatial multiplexing terminal number k exceeds the maximum value K (Yes at S 40 ) or a scheduling target terminal exists no more (Yes at S 39 ), the base station  100  calculates all throughputs and compares the throughputs. For example, the base station  100  performs the following processes. 
     For example, the scheduling unit  105  calculates all throughputs of the terminal  200  selected at S 38 . As such throughput, the selection metric value (S 36 ) may be utilized. Further, the scheduling unit  105  executes the processes at S 10  to S 21  to calculate all throughputs of the selected frequency multiplexing target terminals  200  (S 18 ). Also in this case, for each throughput, the selection metric value (S 16 ) may be used. Then, the scheduling unit  105  selects a terminal  200  having a higher throughput (either the terminal  200  selected for frequency multiplexing or the terminal  200  selected for spatial multiplexing). 
     When the terminal  200  selected for frequency multiplexing is selected, the scheduling unit  105  outputs the weighting value to the analog BF unit  102  to perform analog BF. 
     On the other hand, in the case where the terminal  200  selected for spatial multiplexing is selected, the scheduling unit  105  outputs a PMI representative of a result of the weighting to the digital precoding unit  108 . In the example of  FIG. 14B , the scheduling unit  105  outputs a PMI representative of the digital beam # 1  to the antenna  101 - 1  and outputs a PMI representative of the digital beam # 2  to the antenna  101 - 2 . In this case, the scheduling unit  105  outputs, for example, the weighting value indicative of the digital beam #m to the analog BF unit  102  similarly as in the first embodiment. The base station  100  may perform hybrid BF by analog BF and digital precoding. 
     Then, the base station  100  ends the series of processes (S 42 ). 
     Here, a case is described in which the base station  100  sets k to k=1 (S 31 ) and notices the noticed terminal  200 - 1  and the scheduling target slot is the pattern (1) (No at S 33 ) is described. 
     Also in this case, the base station  100  makes a decision of No at S 33  and decides whether or not the noticed terminal  200 - 1  is a scheduling target terminal (S 35 ). The base station  100  performs, for example, the following processes. 
     For example, the scheduling unit  105  may perform S 350  by setting an analog beam formed from a slot including an SSB as the analog beam #a=analog beam #m and setting an analog beam that is a candidate beam for the terminal  200 - 1  as the analog beam #n. The scheduling unit  105  calculates the correlation value ρ A,m,n  and the threshold value ┌ A,u  for the analog beam #m and the analog beam #n that corresponds to the noticed terminal  200 - 1  (S 151  and S 152 ), and decides whether or not the correlation value ρ A,m,n  is equal to or greater than the threshold value ┌ A,u  (S 153 ). When the correlation value ρ A, m,n  is equal to or greater than the threshold value ┐ A,u , the scheduling unit  105  selects the noticed terminal  200 - 1  as a scheduling target terminal (Yes at S 350 ) and performs the processes at S 351  to S 353  for the selected terminal  200 - 1 . On the other hand, when the correlation value ρ A,m,n  is smaller than the threshold value ┌ A,u , the scheduling unit  105  decides that the noticed terminal  200 - 1  is not a scheduling target (No at S 350 ), and advances the processing to S 37 . Then, in the case where k=1, the scheduling unit  105  notices each of the other unallocated terminals  200 - 2  to  200 -K to calculate the correlation value ρ A,m,n  and so forth from the analog beam #a=analog beam #m and the analog beam #n that is a candidate beam (S 151  and S 152 ). The scheduling unit  105  calculates the correlation value ρ D,m,n  and the threshold value ┌ D,u  for each of the terminals  200 - 2  to  200 -K with regard to which a decision of Yes has been made at S 350  (S 351  and S 352 ), and decides whether or not the terminal is a scheduling target (S 353 ). 
     In this manner, also in the second embodiment, the base station  100  selects a terminal  200  as a terminal, with which the base station  100  is to communicate by using the digital beam #n simultaneously with the digital beam #m, based on feedback information and the correlation value of the digital beam #n to the digital beam #m. Consequently, for example, the number of digital beams #n to be spatially multiplexed with the digital beam #m becomes an appropriate number, and improvement of the throughput may be achieved in comparison with that in an alternative case in which the number is equal to or smaller than the threshold value. 
     It is to be noted that the foregoing description of the second embodiment is described taking the delay spread DS u  as a numerical value to be used for calculation of the threshold value ┌ D,u . Alternatively, for example, CQI u  may be used similarly as in the first embodiment. The numerical values to be used for calculation of the threshold value ┌ D,u  may be those capable of being calculated, for example, from numerical values and so forth included in feedback information. 
     Third Embodiment 
     In the first embodiment, the base station  100  calculates the threshold value ┐ A,u  by using the expression (2). Meanwhile, in the second embodiment, the base station  100  calculates the threshold value ┌ D,u  by using the expression (4). In the third embodiment described below, an example is described in which antenna configuration information is used for calculation of the threshold values ┌ A,u  and ┐ D,u . 
     The base station  100  may calculate the threshold value ┌ A,u  by using the following expression (5) in place of the expression (2): 
       [Expression 5] 
       ┌ A,u   =pw   N     UE,m     +qw   CQI     u     +tw   ant    (5)
 
     w ant  is a coefficient determined from antenna configuration information of an antenna to be utilized to form the analog beam #m applied, for example, in a scheduling target slot. The antenna configuration information is information, for example, relating to the antennas  101 - 1  to  101 -N ANT . As the information relating to the antennas  101 - 1  to  101 -N ANT , for example, there are an antenna number indicating the number of antennas, a distance between antennas, a combination of them and so forth. In the case where an antenna number and a distance between antennas are used in combination as the antenna configuration information, for example, numerical values obtained by rounding two values including a value indicative of the number of antennas and a numerical value indicative of a distance between antennas may be used. 
       FIG. 17  is a view depicting examples of the coefficient w ant .  FIG. 17  depicts examples in which an antenna number is used as the antenna configuration information. As the antenna number N ant  increases, also the coefficient w ant  increases, and as the antenna number N ant  decreases, the coefficient w ant  decreases. 
     Similarly as in the first embodiment, the base station  100  uses the expression (5) such that, when the correlation value ρ A,m,n  threshold value ┌ A,u  is satisfied, the base station  100  determines the noticed terminal  200 - u  as a scheduling target, but in any other case, the base station  100  does not determine the noticed terminal  200  as a scheduling target (S 153  of  FIG. 6 ). 
     It is to be noted that t is, for example, a weight coefficient of the coefficient w ant  and may be set at an arbitrary value by the user similarly to p and q. 
     Alternatively, the base station  100  may calculate the threshold value ┌ D,u  by using the following expression (6) in place of the expression (4): 
       [Expression 6] 
       ┌ D,u   =rw   k   +sw   DS     u     +xw   ant    (6)
 
     Also in this case, similarly as in the second embodiment, the base station  100  uses the expression (6) such that, when the correlation value ρ D,m,n ≤threshold value ┌ D,u  is satisfied, the noticed terminal  200 - u  may be determined as a scheduling target, but in any other case, the noticed terminal  200 - u  is not determined a scheduling target (S 353  of  FIG. 12 ). 
     The two threshold values ┌ A,u  and ┌ D,u  are changeable (or controllable) for each terminal  200  to be made a target similarly as in the first and second embodiments (S 152  and S 352 ). 
     It is to be noted that x is, for example, a weight coefficient of the coefficient w ant  and may be set at an arbitrary value by the user. 
     In this manner, in the third embodiment, since antenna configuration information is further included as a factor into the threshold values ┌ A,u  and ┌ D,u , appropriate threshold values ┌ A,u  and ┌ D,u  may be set for each terminal  200  in response to the number of antennas  101 - 1  to  101 -N ANT  or the distance between the antennas  101 - 1  to  101 -N ANT . 
     Other Embodiments 
       FIG. 18  is a view depicting an example of a configuration of a wireless communication system. 
     The wireless communication system  10  depicted in  FIG. 18  includes a base station apparatus  100 , and a terminal apparatus  200 . The base station apparatus  100  includes a plurality of antennas  101 - 1  to  101 -N ANT , and a scheduling unit  105 . 
     The plurality of antennas  101 - 1  to  101 -N ANT  transmit first and second wireless signals to the terminal apparatus  200 , and individually form first and second beams. Further, the plurality of antennas  101 - 1  to  101 -N ANT  receive a third wireless signal including feedback information of the terminals  200  to the second wireless signal, from the terminal apparatus  200 . 
     The scheduling unit  105  selects a terminal apparatus  200 , to which the second beam is optimum, as a terminal that is to perform communication via the first beam, based on the feedback information and a correlation value between the first beam and the second beam. Further, the scheduling unit  105  selects, based on the feedback information and the correlation value, a terminal apparatus that is to perform communication via the second beam simultaneously via the first beam. 
     The plurality of antennas  101 - 1  to  101 -N ANT  transmit a fourth wireless signal including data to the terminal apparatus  200 , and form first and second beams. 
     By selecting a terminal apparatus  200  to which the second beam is optimum, as a terminal apparatus that is to perform communication via the first beam in this manner, the number of terminal apparatuses that perform communication via the first beam may be increased appropriately. Therefore, in comparison with an alternative case in which communication is performed only by a terminal apparatus to which the first beam is optimum, the base station apparatus  100  may communicate also with other terminals  200  via the first beam, and may improve the throughput. 
     Further, by selecting a terminal apparatus  200  as a terminal apparatus that is to perform communication via a second beam simultaneously via a first beam, the base station apparatus  100  may increase also the spatial multiplexing number appropriately. Therefore, in comparing with an alternative case in which communication is performed only via the first beam, the base station apparatus  100  may increase the number of terminal apparatuses  200  with which the base station apparatus  100  communicate simultaneously via the first beam, and may improve the throughput. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.