Patent Publication Number: US-2020287677-A1

Title: User equipment and transmission and reception point

Description:
TECHNICAL FIELD 
     The present invention generally relates to a method of beam management in a wireless communication system including a transmission and reception point (TRP) and a user equipment (UE). 
     BACKGROUND 
     In Third Generation Partnership Project (3GPP), beam management and Channel State Information (CSI) acquisition schemes for New Radio (NR; fifth generation (5G) radio access technology) are being studied to achieve efficient precoding with massive antenna array. For a massive array system using narrow beams, it is fundamental that the beams at a transmission and reception point (TRP) and/or a user equipment (UE) are fully adjusted, which can be also called as beam management. For a massive array system using narrow beams, it is fundamental that the beams at a transmission and reception point (TRP) and a user equipment (UE) are fully aligned to each other, which can be also called as beam pair link control. 
     In NR technologies, the UE performs beam management and CSI acquisition using Resource setting, CSI reporting setting, and Link. 
     Some of the contents for each parameters on CSI acquisition are listed as follows.
         (1) Resource setting (Number of Resource setting: M)
           RS information (e.g., CSI-RS resource, the number of antenna ports)   Interference measurement resource (IMR) information   Time-domain behavior (periodic, aperiodic or semi-persistent), etc.
               Periodicity and timing offset for periodic and aperiodic   
               
           (2) CSI reporting setting (Number of CSI reporting setting: N)
           Time-domain behavior (periodic, aperiodic or semi-persistent)   Frequency granularity (subband, partial band or wideband)   CSI parameters (RI, PMI, CRI, CQI)
               Each CSI parameters are configured on/off   
               CSI types (e.g., type I or II)   Codebook information, etc.   
           (3) Link (Number of Links: 1)       

     The conventional technologies under legacy Long Term Evolution (LTE) (e.g., Rel. 13 LTE) do not support the aforementioned beam management and CSI acquisition schemes using beam pair link control. Furthermore, the beam pair link control is not defined and UE procedures using the beam pair control is not determined in the 3GPP standard. 
     CITATION LIST 
     Non-Patent Reference 
     
         
         [Non-Patent Reference 1] 3GPP, TS 36.211 V 14.1.0 
         [Non-Patent Reference 2] 3GPP, TS 36.213 V14.1.0 
       
    
     SUMMARY 
     One or more embodiments of the present invention relate to a user equipment (UE) that includes a receiver that receives one or more RSs transmitted using a first beam from a transmission and reception point (TRP), using at least a second beam, and a processor that determines the first beam paired with the second beam based on reception quality of the RSs. 
     One or more embodiments of the present invention relate to a TRP a receiver that receives at least a RS transmitted using a first beam from a UE, using at least a second beam; and a processor that determines the first beam paired with the second beam based on reception quality of the RSs. 
     One or more embodiments of the present invention relate to a UE that includes a processor that performs beam management using a beam pair link. The beam pair link is configured as association of a downlink reference signal (RS) and an uplink RS. 
     One or more embodiments of the present invention can perform efficient UE procedures using the beam pair control, which are further enhanced to accommodate much narrower beams compared to legacy systems. 
     Other embodiments and advantages of the present invention will be recognized from the description and figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a wireless communication system according to one or more embodiments of the present invention. 
         FIG. 2  is a diagram showing an example of a configuration of a beam pair link according to one or more embodiments of the present invention. 
         FIG. 3  is a diagram showing an example of a configuration of a beam pair link according to one or more embodiments of the present invention. 
         FIG. 4  is a flowchart showing an example of a beam management operation according to one or more embodiments of the present invention. 
         FIG. 5  is a schematic diagram showing an example of a beam management operation according to one or more embodiments of a first example of the present invention. 
         FIG. 6  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the first example of the present invention. 
         FIG. 7  is a schematic diagram showing an example of a beam management operation according to one or more embodiments of a second example of the present invention. 
         FIG. 8  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the second example of the present invention. 
         FIG. 9  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of a second modified example of the present invention. 
         FIG. 10  is a schematic diagram showing an example of a beam management operation according to one or more embodiments of a third example of the present invention. 
         FIG. 11  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the third example of the present invention. 
         FIG. 12  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of a third modified example of the present invention. 
         FIG. 13  is a schematic diagram showing an example of a beam management operation according to one or more embodiments of a fourth example of the present invention. 
         FIG. 14  is a schematic diagram showing an example of a beam management operation according to one or more embodiments of a fourth modified example of the present invention. 
         FIG. 15  is a schematic diagram showing an example of a beam sweeping operation according to one or more embodiments of a fifth example of the present invention. 
         FIG. 16  is a schematic diagram showing an example of a beam sweeping operation according to one or more embodiments of a fifth example of the present invention. 
         FIG. 17  is a schematic diagram showing an example of a beam sweeping operation according to one or more embodiments of a fifth example of the present invention. 
         FIG. 18  is a flowchart showing an example of a method to determine UE Tx according to one or more embodiments of a sixth example of the present invention. 
         FIG. 19  is a schematic diagram showing an example of a method to determine TRP Tx according to one or more embodiments of a seventh example of the present invention. 
         FIG. 20  is a schematic diagram showing an example of a beam sweeping operation according to one or more embodiments of an eighth example of the present invention. 
         FIG. 21  is a schematic diagram showing an example of a beam sweeping operation according to one or more embodiments of an eighth example of the present invention. 
         FIG. 22  is a schematic diagram showing an example of a beam sweeping operation according to one or more embodiments of an eighth example of the present invention. 
         FIG. 23  is a diagram showing a schematic configuration of the TRP according to one or more embodiments of the present invention. 
         FIG. 24  is a diagram showing a schematic configuration of the UE according to one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described in detail below, with reference to the drawings. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. 
       FIG. 1  is a wireless communications system  1  according to one or more embodiments of the present invention. The wireless communication system  1  includes a user equipment (UE)  10 , a transmission and reception point (TRP)  20 , and a core network  30 . The wireless communication system  1  may be a New Radio (NR) system. The wireless communication system  1  is not limited to the specific configurations described herein and may be any type of wireless communication system such as an LTE/LTE-Advanced (LTE-A) system. 
     The TRP  20  may communicate uplink (UL) and downlink (DL) signals with the UE  10  in a cell of the TRP  20 . The DL and UL signals may include control information and user data. The TRP  20  may communicate DL and UL signals with the core network  30  through backhaul links  31 . The TRP  20  may be referred to as a base station (BS). The TRP  20  may be gNodeB (gNB). 
     The TRP  20  includes antennas, a communication interface to communicate with an adjacent TRP  20  (for example, X2 interface), a communication interface to communicate with the core network  30  (for example, S1 interface), and a CPU (Central Processing Unit) such as a processor or a circuit to process transmitted and received signals with the UE  10 . Operations of the TRP  20  may be implemented by the processor processing or executing data and programs stored in a memory. However, the TRP  20  is not limited to the hardware configuration set forth above and may be realized by other appropriate hardware configurations as understood by those of ordinary skill in the art. Numerous TRPs  20  may be disposed so as to cover a broader service area of the wireless communication system  1 . 
     The UE  10  may communicate DL and UL signals that include control information and user data with the TRP  20  using Multi Input Multi Output (MIMO) technology. The UE  10  may be a mobile station, a smartphone, a cellular phone, a tablet, a mobile router, or information processing apparatus having a radio communication function such as a wearable device. The wireless communication system  1  may include one or more UEs  10 . 
     The UE  10  includes a CPU such as a processor, a RAM (Random Access Memory), a flash memory, and a radio communication device to transmit/receive radio signals to/from the TRP  20  and the UE  10 . For example, operations of the UE  10  described below may be implemented by the CPU processing or executing data and programs stored in a memory. However, the UE  10  is not limited to the hardware configuration set forth above and may be configured with, e.g., a circuit to achieve the processing described below. 
     (Indication of Beam Pair Link) 
     A beam pair link (BPL) is a combination of a TRP beam and a UE beam. The combination of the TRP beam and the UE beam includes a combination of a TRP transmission (Tx) beam and a UE reception (Rx) beam in downlink transmission and a combination of a TRP Rx beam and a UE Tx beam in uplink transmission. According to one or more embodiments of the present invention, the BPL may be indicated by association of Channel State Information Reference Signal (CSI-RS) resource and Sounding Reference Signal (SRS) resource. In other words, the BPL may be indicated by a combination of downlink and uplink reference signals (RSs). 
       FIGS. 2 and 3  show configurations of BPLs according to one or more embodiments of the present invention. As shown in  FIGS. 2 and 3 , the TRP  20  uses four beams, TRP beams #1-#4, for signal transmission/reception. The UE  10  uses two beams, UE beams #1-#2, for signal transmission/reception. 
     In  FIG. 2 , the number of BPLs may be indicated as the number of TRP beams paired with the UE beam. Thus, in  FIG. 2 , the number of BPLs (N TRP ) is four (BPLs #1-4). 
     In  FIG. 3 , the number of BPLs may be indicated as the number of UE beams paired with the TRP beam. Thus, in  FIG. 3 , the number of BPLs (N UE ) is two (BPLs #1-2). 
     According to one or more embodiments of another example of the present invention, the number of BPLs may be indicated as a minimum value of the N TRP  and N UE  (min (N TRP , N UE )). 
     According to one or more embodiments of another example of the present invention, the number of BPLs may be indicated as a maximum value of the N TRP  and N UE  (max (N TRP , N UE )). 
     According to one or more embodiments of another example of the present invention, the number of BPLs may include the N TRP  and N UE  (N TRP +N UE ). 
     According to one or more embodiments of another example of the present invention, the number of BPLs may be indicated as at least one of the N TRP , N UE , min (N TRP , N UE ), max (N TRP , N UE ), and N TRP +N UE . 
     (Beam Management for Beam Pair Link Determination) 
     A method to determine the BPL for the beam management will be described below. 
     (Method to Determine TRP Tx Beam) 
       FIG. 4  is a flowchart showing an example of a beam management operation according to one or more embodiments of a first example of the present invention. 
     As shown in step S 11 , the TRP  20  may transmit CSI-RS resource information and/or beam selection information to the UE  10 . The CSI-RS resource information includes information explicitly or implicitly indicating the number of CSI-RS resources transmitted from the TRP  20  (the number of TRP Tx beam N TRP ). For example, the beam selection information includes information indicating UE assumption for beam selection such as the number of selected beams. 
     For example, the TRP  20  may explicitly notify the UE  10  of the number of TRP Tx beam N TRP  used for the CSI-RS transmission. 
     For example, the TRP  20  may implicitly notify the UE  10  of the number of TRP Tx beam N TRP . For example, the TRP  20  may transmit the number of CSI-RS resources, the number of CSI-RS resource sets, a Beam ID that identifies each TRP Tx beam, or a virtual cell ID to notify the UE  10  of the number of TRP Tx beam N TRP . 
     Furthermore, information indicating the number of TRP Tx beam N TRP  may be set commonly or independently between transmission and reception. If N TRP  is used for reception, it may mean the number of candidate Rx beams (or the number of Rx beams capable to be generated) at a TRP side. 
     At the step S 11 , the CSI-RS resource information includes information of the beam applied to the CSI-RS resource. For example, the TRP  20  may notify the UE  10  of precoding information as Quasi Co-Location (QCL). For example, the TRP  20  may notify the UE  10  of information indicating whether different precoding is applied to multiple CSI-RS resources (e.g., 1 bit information). For example, the TRP  20  may notify the UE  10  of information indicating whether the same precoding is applied to multiple CSI-RS resources (e.g., 1 bit information). 
     At step S 12  in  FIG. 4 , the TRP  20  may transmit one or more TRP Tx beams (CSI-RS(s)) to the UE  10 . The UE  10  may receive the TRP Tx beam(s) using the UE Rx beams. 
     At step S 13 , the UE  10  may determine the TRP Tx beam and/or UE Rx beam for the BPL. 
     At step S 14 , the UE  10  may transmit feedback information including information indicating the determined TRP Tx beam and/or UE Rx beam at the step S 13 . 
     Thus, according to one or more embodiments of the present invention, the TRP Tx beam used for the BPL can be determined. The methods to determine the BPL will be described in detail below. 
     First Example 
     According to one or more embodiments of a first example of the present invention, in a TRP Tx beam determination operation, the UE  10  may receive the CSI-RSs using an omni-directional beam (omni-directional antenna). For example, the UE Rx beam may be determined at an antenna connector of the UE  10 . As shown in  FIG. 5 , the TRP  20  may transmit the CSI-RSs using the TRP Tx beams #1-#4 by beam sweeping. The UE  10  may receive the CSI-RSs from the TRP  20  using the omni-directional beam. 
       FIG. 6  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the first example of the present invention. 
     As shown in  FIG. 6 , at step S 101 , the TRP  20  may transmit the CSI-RS resource information and/or beam selection information. The CSI-RS resource information includes information indicating the number of TRP Tx beam N TRP  and UE Rx beam designation information to designate the UE Rx beam. one or more embodiments of the first example of the present invention, the UE Rx beam designation information may be indicated as the omni-directional beam. For example, the UE Rx beam designation information may be informed as the QCL to designate the UE Rx beam as the omni-directional beam. For example, the UE Rx beam designation information may be informed that there is no QCL between the CSI-RS resource and SS/RS, to designate the UE Rx beam as the omni-directional beam. For example, the UE Rx beam designation information may be informed as a special case of Sounding Reference Signal (SRS) Resource Indicator (SRI). 
     At step S 102 , the TRP  20  may transmit the CSI-RS #1-#4 using the TRP Tx beam #1-#4, respectively, by beam sweeping. 
     At step S 103 , the UE  10  may receive the CSI-RSs using the omni-directional antenna (omni-directional beam) based on the UE Rx beam designation information. The UE  10  may determine the TRP Tx beam based on reception quality of the CSI-RSs. 
     At step S 104 , the UE  10  may transmit feedback information to the TRP  20 . 
     For example, the feedback information includes information indicating the determined TRP Tx beam (e.g., CSI-RS Resource Indicator (CRI)), the applied UE Rx beam (e.g., SRI), and beam reception quality (e.g., CSI, Reference Signal Received Power (RSRP), and Received Signal Strength Indicator (RSSI)). The applied UE Rx beam is a UE Rx beam corresponding to the determined TRP Tx beam. The information indicating the applied UE Rx beam (e.g., Rx beam index) may be included in CSI parameters. The RSRP and RSSI may be included in the CSI parameters. 
     Furthermore, the configuration information includes information indicating the number of the selected beam pairs (the number of paired information for feedback). 
     For example, the number of the selected beam pairs may be determined to be single. 
     For example, the number of the selected beam pairs may be determined based on the number of TRP Tx beams. For example, the feedback information includes the best UE Rx beam and/or the beam reception quality for each TRP Tx beam. 
     For example, the number of the selected beam pairs may be determined based on the number of UE Rx beams. For example, the feedback information includes the best TRP Tx beam and/or the beam reception quality for each UE Rx beam. 
     For example, the number of the selected beam pairs may be designated by the TRP  20 . For example, when the beam pair is selected based on a best-M scheme, the TRP  20  may designate a value “M”. 
     For example, the number of the selected beam pairs may be determined by the UE  10 . 
     Second Example 
     According to one or more embodiments of a second example of the present invention, in a TRP Tx beam determination operation, the UE  10  may receive the CSI-RSs using a predetermined UE Rx beam (Rx antenna panel or Rx antenna group). The predetermined UE Rx beam may be designated by the TRP  20  or determined by the UE  10 . The predetermined UE Rx beam may be at least one. As shown in  FIG. 7 , the TRP  20  may transmit the CSI-RSs using the TRP Tx beams #1-#4 by beam sweeping. The UE  10  may receive the CSI-RSs from the TRP  20  using the UE Rx beam #1. 
       FIG. 8  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the second example of the present invention. 
     As shown in  FIG. 8 , at step S 201 , the UE  10  may transmit UE capability information including UE Rx beam information. For example, the UE Rx beam information includes the number of UE Rx beams and/or the maximum number of UE Rx beams. For example, the UE Rx beam information includes information indicating candidates of the UE Rx beams associated with candidates of the TRP Rx beams. For example, all or part of TRP Tx beams may be common to the UE Rx beams. 
     For example, the number of UE Rx beams of the UE capability information may be common to Tx/Rx or different between Tx and Rx. 
     For example, the number of UE Rx beams of the UE capability information may be indicated as the number of UE Rx digital beams (N UE, D ) and the number of UE Rx analogue beams (N UE, A ) separately. For example, the number of UE Rx beams may be acknowledged as N UE  (=N UE, D ×N UE, A ) by the TRP  20 . 
     Furthermore, the number of UE Rx beams may be included in other signals other than the UE capability information, e.g., implicitly signaled as the number of RS resources for mobility. 
     At step S 202 , the TRP  20  may transmit the CSI-RS resource information and/or beam selection information. The CSI-RS resource information includes information indicating the number of TRP Tx beam N TRP  and UE Rx beam information to designate the UE Rx beam. 
     At step S 203 , the TRP  20  may transmit UE Rx beam designation information to designate the UE Rx beam (e.g., UE Rx beam #1). 
     For example, the designated UE Rx beam may be indicated as a Beam index or SRS resource index. 
     For example, the designated UE Rx beam may be notified to the UE  10  as a Precoding Matrix Indicator (PMI) such as an uplink PMI. 
     For example, the designated UE Rx beam may be indicated as an antenna panel index, an antenna group index, or a TXRU index. 
     For example, the UE Rx beam designation information includes information to instruct a fallback to the omni-directional beam. 
     For example, the designated UE Rx beam may be commonly or independently used to receive the multiple TRP Tx beams. 
     At step S 204 , the TRP  20  may transmit the CSI-RS #1-#4 using the TRP Tx beam #1-#4, respectively, by beam sweeping. 
     At step S 205 , the UE  10  may receive the CSI-RSs using the designated UE Rx beam (e.g., UE Rx beam #1) based on the UE Rx beam designation information. The UE  10  may determine the TRP Tx beam based on reception quality of the CSI-RSs. 
     At step S 206 , the UE  10  may transmit the feedback information to the TRP  20 . The operation in the step S 206  is the same as that in the step S 104  in  FIG. 6 . 
     Second Modified Example 
     According to one or more embodiments of a second modified example of the present invention, the UE  10  may determine the UE Rx beam used to receive the CSI-RSs.  FIG. 9  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the second modified example of the present invention. Similar steps in  FIG. 9  to steps in  FIG. 8  may have the same reference labels. 
     As shown in  FIG. 9 , at step S 203   a , the UE  10  may determine the UE Rx beam used to receive the CSI-RSs (e.g., UE Rx beam #1). Thus, according to one or more embodiments of the second modified example of the present invention, the UE Rx beam used to receive the CSI-RSs may be common to multiple TRP Tx beams. 
     For example, the UE  10  may not be allowed to switch the UE Rx beam for each TRP Tx beam. 
     For example, the UE Rx beam used to receive the CSI-RSs may be the same as the UE Rx beam used to receive predetermined physical channels and signals. Furthermore, association of the UE Rx beam used to receive predetermined physical channels and signals with the UE Rx beam used to receive the CSI-RSs may be signaled from the UE  10  to the TRP  20 . 
     For example, the UE  10  may determine a fallback to the omni-directional beam. 
     For example, the UE  10  may determine the UE Rx beam used to receive the CSI-RSs based on QCL information from the TRP  20  and information on beam pair link. For example, the QCL information may be transmitted from the TRP  20  to the UE  10  for each TRP Tx beam or TRP Tx beam group. For example, the QCL information may be common to the TRP Tx beams. 
     For example, the UE  10  may determine the UE Rx beam used to receive the CSI-RSs based on Beam Index, e.g., CRI, from the TRP  20  and information on beam pair link. For example, the Beam index may be transmitted from the TRP  20  to the UE  10  for each TRP Tx beam or TRP Tx beam group. For example, the Beam Index may be common to the TRP Tx beams. 
     For example, all or part of the above methods to determine the UE Rx beam used to receive the CSI-RSs may be switched based on instructions from the TRP  20  or a core network. For example, when the determined UE Rx beam used to receive the CSI-RSs is not proper, the determined UE Rx beam may be changed to the omni-directional beam as a fallback because the proper TRP Tx beam may not be determined. 
     Third Example 
     According to one or more embodiments of a third example of the present invention, in a TRP Tx beam determination operation, the UE  10  may receive the CSI-RSs using UE Rx beams switched for each TRP Tx beam. As shown in  FIG. 10 , the TRP  20  may transmit the CSI-RSs using the TRP Tx beams #1-#4 by beam sweeping. The UE  10  may receive the CSI-RSs from the TRP  20  using the UE Rx beams #1 and #2 by switching the UE Rx beams. 
       FIG. 11  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the third example of the present invention. 
     As shown in  FIG. 11 , at step S 301 , the UE  10  may transmit UE capability information including UE Rx beam information. For example, the UE Rx beam information includes the number of UE Rx beams and/or the maximum number of UE Rx beams. For example, the UE Rx beam information includes information indicating candidates of the UE Rx beams associated with candidates of the TRP Rx beams. For example, all or part of TRP Tx beams may be associated with the UE Rx beams. 
     Operations at steps S 301  and S 302  are the same as the operations at the steps S 201  and S 202 , respectively. 
     At step S 303 , the TRP  20  may transmit information to determine the UE Rx beams for each TRP Tx beam. 
     At steps S 304   a - 304   d , the TRP  20  may transmit the CSI-RS #1-#4 using the TRP Tx beam #1-#4, respectively, by beam sweeping. 
     At steps S 305   a - 305   d , the UE  10  may receive the CSI-RSs using TRP Tx beams #1-#4, using UE Rx beam #1-#4, respectively, by switching the UE Rx beams. The UE  10  may determine the TRP Tx beam based on reception quality of the CSI-RSs. 
     An operation at step S 306  is the same as the operations at the step S 104  and at the step S 206 . 
     Third Modified Example 
     According to one or more embodiments of a third modified example of the present invention, the UE  10  may determine to switch the UE Rx beam used to receive the CSI-RSs.  FIG. 12  is a sequence diagram showing an operation example of the beam management operation according to one or more embodiments of the third modified example of the present invention. Similar steps in  FIG. 12  to steps in  FIG. 11  may have the same reference labels. 
     As shown in  FIG. 12 , at step S 303   a , the UE  10  may determine to switch the UE Rx beam used to receive the CSI-RSs. 
     (Method to Determine UE Rx Beam) 
     Fourth Example 
     According to one or more embodiments of a fourth example of the present invention, to determine the UE Rx beam, the TRP  20  may transmit multiple CSI-RSs and the UE  10  may apply different UE Rx beam to each of the multiple CSI-RSs and select the best UE Rx beam. 
     As shown in  FIG. 13 , the TRP  20  may transmit multiple CSI-RS using the omni-directional beam. Thus, the same beam may be applied to the multiple CSI-RSs. 
     Furthermore, when the UE  10  may perform digital sweeping, the multiple CSI-RS resources may not be necessary. 
     Furthermore, for example, the TRP  20  may transmit information of the beam applied to the CSI-RSs to the UE  10 . The information of the applied beam may be notified to the UE  10  as the CRI or QCL. 
     Turning to  FIG. 13 , the UE  10  may receive the CSI-RSs using different UE Rx beam. Thus, the UE Rx beam applied to each CSI-RS may be different from each other. The UE  10  may determine the best UE Rx beam based on the reception quality of the received CSI-RSs. 
     For example, when the UE  10  may apply a digital beam, the number of CSI-RSs may be one. 
     For example, when the UE  10  may apply an analogue beam and a hybrid beam, the number of CSI-RSs may be the number of UE Rx analogue beams (N UE, A ). 
     For example, when the number of candidates of the UE Rx beams is large, the number of CSI-RSs used to determine the UE Rx beam may increase. Furthermore, when a plurality of UEs  10  use different UE Rx beams, the number of CSI-RSs may be different for each UE  10 . As a result, the UE Rx beam may not be efficiently determined. 
     According to one or more embodiments of the fourth example of the present invention, the TRP  20  may limit candidates of the UE Rx beams. For example, the TRP  20  may designate the number of UE Rx beams. 
     For example, if the TRP  20  is able to designate the predetermined number of the UE Rx beams, operational flexibility is improved, but implementation of the UE  10  is complicated. According to one or more embodiments of the fourth example of the present invention, the predetermined number of the UE Rx beams may be limited. For example, the predetermined number of the UE Rx beams may be {1, 2, 4, 8, 16, 32}. For example, the predetermined number of the UE Rx beams may be the number of antenna panels and antennas of the UE  10 . The TRP  20  may notify the UE  10  of the predetermined number of the UE Rx beams as an over sampling factor of the number of antenna panels and/or antennas of the UE  10 . The TRP  20  may notify the UE  10  of the predetermined number of the UE Rx beams as an over sampling factor on the number which is derived by multiplying the number of antenna panels and antennas per panel of the UE  10 . 
     Similarly, the TRP  20  may limit candidates of the UE Tx beams similar to the limitation of UE Rx beam candidates. The TRP  20  may designate the number of the UE Tx beams. 
     According to one or more embodiments of the fourth example of the present invention, the UE  10  may transmit feedback information including the UE Rx beam information and beam reception quality (e.g., CSI, RSRP, and RSSI). 
     The aforementioned technologies (e.g., notification of the number of Tx beams from the TRP  20  and the method to select multiple beams) in the method to determine the TRP Tx beam may be applied to technologies in the method to determine the UE Rx beam. At step S 12 , the TRP  20  may transmit, to the UE  10 , periodic, aperiodic, and/or semi-persistent CSI-RS(s) in accordance with the information element designated in the RS setting. 
     Fourth Modified Example 
     As shown in  FIG. 14 , according to one or more embodiments of a fourth modified example of the present invention, to determine the UE Rx beam, the TRP  20  may transmit multiple CSI-RSs using a single TRP Tx beam (TRP Tx beam #1). The UE  10  may receive the CSI-RSs using different UE Rx beam. 
     (Method to Determine TRP-UE Beam Pair) 
     In an initial access procedure, it is required to determine proper Tx/Rx beams without prior information. The beams to be determined are at most four patterns such as the TRP Tx beam, TRP Rx beam, UE Tx beam, and UE Rx beam. Depending on calibration accuracy of the UE  10 , the common beam to Tx/Rx may be applied. 
     Fifth Example 
       FIGS. 15-17  are schematic diagrams showing an example of a beam sweeping operation according to one or more embodiments of a fifth example of the present invention. Operation examples in  FIGS. 15-17  uses downlink reference signals, but similar operations may be applied to uplink reference signals. 
     According to one or more embodiments of the fifth example of the present invention, as shown  FIGS. 15-17 , to determine the TRP-UE beam pair, the TRP  20  may transmit TRP Tx beam information to the UE  10 . 
     For example, the TRP Tx beam information includes the number of CSI-RS resources (Nall) transmitted from the TRP  20 . In examples of  FIGS. 15 and 16 , Nall is 8. 
     For example, the TRP Tx beam information includes the number of TRP Tx beams (Nb) used for the CSI-RS transmission. In examples of  FIGS. 15 and 16 , Nb is 4. 
     For example, the TRP Tx beam information includes the number of repetition of CSI-RS transmission (Nr). In examples of  FIGS. 15 and 16 , Nr is 2. 
     According to one or more embodiments of the fifth example of the present invention, the TRP Tx beam information includes at least two of the number of CSI-RS resources (Nall), the number of TRP Tx beams (Nb), and the number of repetition of CSI-RS transmission (Nr) to configure sweeping information. 
     As shown in  FIGS. 15-17 , there are a plurality orders of beam transmission from the TRP  20 . According to one or more embodiments of the fifth example of the present invention, the TRP  20  may transmit information of orders of beam sweeping to the UE  10 . For example, the information of orders of beam sweeping indicates which of the TRP beam and the UE beam is the beam sweeping performed on first. For example, the information of orders of beam sweeping may be notified as the Beam index (CRI) or QCL information. Furthermore, the orders of beam sweeping may be defined in the specification such as 3GPP specification. 
     According to one or more embodiments of the fifth example of the present invention, as shown  FIGS. 15-17 , the UE  10  may transmit feedback information of the beam pair to the TRP  20 . 
     For example, the feedback information of the beam pair includes a beam pair having the best reception quality. For example, the feedback information of the beam pair includes beam pairs having the best-M reception quality. 
     For example, the feedback information of the beam pair includes the best UE Rx beam for each TRP Tx beam. 
     For example, the feedback information of the beam pair includes the best TRP Tx beam for each UE Rx beam. 
     For example, the UE  10  may assume the different UE Rx beam for each TRP Tx beam. The feedback information of the beam pair includes the different UE Rx beam. 
     For example, the UE  10  may assume an omni-directional beam and a directional beam for each TRP Tx beam. The feedback information of the beam pair includes the assumed omni-directional beam and directional beam. 
     For example, the feedback information of the beam pair includes reception quality (e.g., CSI, RSRP, and/or RSSI) of the beam pair. 
     For example, the beam pair for feedback may be determined based on the CSI. 
     For example, the beam pair for feedback may be determined based on the RSRP and/or RSSI. 
     (Method to Determine Uplink Beam) 
     Although the technologies of the above examples are related to the methods to determine the downlink beam pair, the technologies may be applied to methods to determine an uplink beam pair. 
     (Method to Determine UE Tx Beam) 
     Sixth Example 
       FIG. 18  is a flowchart showing an example of a method to determine UE Tx according to one or more embodiments of a sixth example of the present invention. 
     As shown  FIG. 18 , at step S 21 , the UE  10  may transmit SRS resource information to the TRP  200 . 
     At step S 22 , the UE  10  may transmit one or more UE Tx beams (SRS(s)) to the TRP  20 . The TPR  20  may receive the UE Tx beam(s) using the TPR Rx beams. 
     At step S 23 , the TRP  20  may determine the UE Tx beam and/or TRP Rx beam for the BPL. 
     At step S 24 , the TRP  20  may transmit feedback information including information indicating the determined UE Tx beam and/or TRP Rx beam at the step S 23 . For example, the information indicating the determined UE Tx beam may be SRS Resource Indicator (SRI). 
     Thus, according to one or more embodiments of the present invention, the UE Tx beam used for the BPL can be determined by the UE Tx beam sweeping and the TRP Rx beam switching. 
     (Method to Determine TRP Rx Beam) 
     Seventh Example 
     According to one or more embodiments of a seventh example of the present invention, to determine the TRP Rx beam, the UE  10  may transmit multiple SRSs and the TRP  20  may apply different TRP Rx beam to each of the multiple SRSs and select the best TRP Rx beam. 
     As shown in  FIG. 19 , the UE  10  may transmit multiple SRSs (SRS resources) using a predetermine UE Tx beam (e.g., UE Tx beam #1). The same precoding may be applied to the multiple SRS resources. The UE Tx beam applied to the SRSs may be designated by the TRP  20  using the SRI. Furthermore, in  FIG. 19 , for example, the predetermine UE Tx beam the omni-directional beam. 
     The TRP  20  may switch the TRP Rx beams and receive the SRSs using the switched TRP Rx beam. The TRP  20  may determine the best TRP Rx beam based on the reception quality of the received SRSs. 
     Then, the TRP  20  may transmit feedback information to the UE  10 . The feedback information includes information indicating the determined UE Tx beam and the TRP Tx beam corresponding to the determined UE Tx beam. Furthermore, the feedback information includes information indicating quality information of the determined UE Tx beam and the TRP Tx beam corresponding to the determined UE Tx beam. 
     (Method to Determine TRP-UE Beam Pair) 
     Eighth Example 
       FIGS. 20-22  are schematic diagrams showing an example of a beam sweeping operation according to one or more embodiments of an eighth example of the present invention. According to one or more embodiments of the fifth example of the present invention, as shown  FIGS. 20-22 , to determine the TRP-UE beam pair, the UE  20  may perform the UE Tx beam sweeping and transmit SRSs and the TRP  20  may perform the TRP Rx beam switching. For example, in  FIG. 20-22 , the TRP  20  may designate the UE Tx beam used for the SRS transmission. 
     Another Example 
     When there is no reciprocity of the uplink/downlink, a determined BPL in the downlink may be different from a determined BPL in the uplink. According to one or more embodiments of the present invention, the UE  10  may notify the TRP  20  of the determined BPL in the downlink and the UE  10  may notify the TRP  20  of the determined BPL in the uplink. 
     For example, when there are a lot of candidates of the TRP beams and the UE beams, the beam sweeping of all of the TRP beams and the UE beams may cause increase of a signaling overhead. According to one or more embodiments of the present invention, oversampling may be applied to the candidates of the TRP and/or UE beams. For example, oversampling may be applied to the candidates of the TRP and UE beams having odd (or even) numbers (Beam index). According to one or more embodiments of the present invention, a beam group for the TRP and/or UE beams used for the beam sweeping may be set. 
     (Configuration of TRP) 
     The TRP  20  according to one or more embodiments of the present invention will be described below with reference to  FIG. 23 .  FIG. 23  is a diagram illustrating a schematic configuration of the TRP  20  according to one or more embodiments of the present invention. The TRP  20  may include a plurality of antennas (antenna element group)  201 , amplifier  202 , transceiver (transmitter/receiver)  203 , a baseband signal processor  204 , a call processor  205  and a transmission path interface  206 . 
     User data that is transmitted on the DL from the TRP  20  to the UE  20  is input from the core network  30 , through the transmission path interface  206 , into the baseband signal processor  204 . 
     In the baseband signal processor  204 , signals are subjected to Packet Data Convergence Protocol (PDCP) layer processing, Radio Link Control (RLC) layer transmission processing such as division and coupling of user data and RLC retransmission control transmission processing, Medium Access Control (MAC) retransmission control, including, for example, HARQ transmission processing, scheduling, transport format selection, channel coding, inverse fast Fourier transform (IFFT) processing, and precoding processing. Then, the resultant signals are transferred to each transceiver  203 . As for signals of the DL control channel, transmission processing is performed, including channel coding and inverse fast Fourier transform, and the resultant signals are transmitted to each transceiver  203 . 
     The baseband signal processor  204  notifies each UE  10  of control information (system information) for communication in the cell by higher layer signaling (e.g., RRC signaling and broadcast channel). Information for communication in the cell includes, for example, UL or DL system bandwidth. 
     In each transceiver  203 , baseband signals that are precoded per antenna and output from the baseband signal processor  204  are subjected to frequency conversion processing into a radio frequency band. The amplifier  202  amplifies the radio frequency signals having been subjected to frequency conversion, and the resultant signals are transmitted from the antennas  201 . 
     As for data to be transmitted on the UL from the UE  10  to the TRP  20 , radio frequency signals are received in each antennas  201 , amplified in the amplifier  202 , subjected to frequency conversion and converted into baseband signals in the transceiver  203 , and are input to the baseband signal processor  204 . 
     The baseband signal processor  204  performs FFT processing, IDFT processing, error correction decoding, MAC retransmission control reception processing, and RLC layer and PDCP layer reception processing on the user data included in the received baseband signals. Then, the resultant signals are transferred to the core network  30  through the transmission path interface  206 . The call processor  205  performs call processing such as setting up and releasing a communication channel, manages the state of the TRP  20 , and manages the radio resources. 
     (Configuration of UE) 
     The UE  10  according to one or more embodiments of the present invention will be described below with reference to  FIG. 24 .  FIG. 24  is a schematic configuration of the UE  10  according to one or more embodiments of the present invention. The UE  10  has a plurality of UE antennas  101 , amplifiers  102 , the circuit  103  comprising transceiver (transmitter/receiver)  1031 , the controller  104 , and an application  105 . 
     As for DL, radio frequency signals received in the UE antennas  101  are amplified in the respective amplifiers  102 , and subjected to frequency conversion into baseband signals in the transceiver  1031 . These baseband signals are subjected to reception processing such as FFT processing, error correction decoding and retransmission control and so on, in the controller  104 . The DL user data is transferred to the application  105 . The application  105  performs processing related to higher layers above the physical layer and the MAC layer. In the downlink data, broadcast information is also transferred to the application  105 . 
     On the other hand, UL user data is input from the application  105  to the controller  104 . In the controller  104 , retransmission control (Hybrid ARQ) transmission processing, channel coding, precoding, DFT processing, IFFT processing and so on are performed, and the resultant signals are transferred to each transceiver  1031 . In the transceiver  1031 , the baseband signals output from the controller  104  are converted into a radio frequency band. After that, the frequency-converted radio frequency signals are amplified in the amplifier  102 , and then, transmitted from the antenna  101 . 
     One or more embodiments of the present invention may be used for each of the uplink and the downlink independently. One or more embodiments of the present invention may be also used for both of the uplink and the downlink in common. 
     Although the present disclosure individually described the technology targeting for TRP Tx beam selection, TRP Rx beam selection, UE Tx beam selection, UE Rx beam selection, Joint TRP Tx and UE Rx selection, Joint UE Tx and TRP Rx beam selection, applicability of the technologies are not limited to each of the beam selection technology but open to other types of beam selection. 
     Although the present disclosure mainly described examples of a channel and signaling scheme based on NR, the present invention is not limited thereto. One or more embodiments of the present invention may apply to another channel and signaling scheme having the same functions as NR such as LTE/LTE-A and a newly defined channel and signaling scheme. 
     Although the present disclosure mainly described examples of channel estimation and CSI feedback scheme based on the CSI-RS, the present invention is not limited thereto. One or more embodiments of the present invention may apply to another synchronization signal, reference signal, and physical channel such as synchronization signal (SS), measurement RS (MRS), mobility RS (MRS), and beam RS (BRS). 
     Although the present disclosure mainly described examples of an uplink channel estimation method based on the SRS, the present invention is not limited thereto. One or more embodiments of the present invention may apply to another synchronization signal, reference signal, and physical channel. 
     Although the present disclosure mainly described examples of various signaling methods, the signaling according to one or more embodiments of the present invention may be explicitly or implicitly performed. 
     Although the present disclosure mainly described examples of various signaling methods, the signaling according to one or more embodiments of the present invention may be the higher layer signaling such as the RRC signaling and/or the lower layer signaling such as the DCI and the MAC CE. Furthermore, the signaling according to one or more embodiments of the present invention may use a Master Information Block (MIB) and/or a System Information Block (SIB). For example, at least two of the RRC, the DCI, and the MAC CE may be used in combination as the signaling according to one or more embodiments of the present invention. 
     Although the present disclosure described examples of the beamformed RS (RS transmission using the beam), whether the physical signal/channel is beamformed may be transparent for the UE. The beamformed RS and the beamformed signal may be called the RS and the signal, respectively. Furthermore, the beamformed RS may be referred to as a RS resource. Furthermore, the beam selection may be referred to as resource selection. Furthermore, the Beam Index may be referred to as a resource index (indicator) or an antenna port index. 
     One or more embodiments of the present invention may apply to CSI measurement, channel sounding, beam management, and other beam control scheme such as beam management using the SS. 
     In one or more embodiments of the present invention, the RB and a subcarrier in the present disclosure may be replaced with each other. A subframe, a symbol, and a slot may be replaced with each other. 
     The above examples and modified examples may be combined with each other, and various features of these examples can be combined with each other in various combinations. The invention is not limited to the specific combinations disclosed herein. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.