WIRELESS COMMUNICATION METHOD, USER EQUIPMENT, BASE STATION, AND SYSTEM

Abstract

A wireless communication method includes transmitting, from a base station (BS) to a user equipment (UE), a configuration information indicating a resource used in transmission of a Channel State Information-Reference Signal (CSI-RS) by higher layer signaling; and receiving, with the UE, the CSI-RS from the BS based on the configuration information. The configuration information indicates a mapping for CSI-RS transmission using a single antenna port (AP) to a single resource element per a resource block. In other aspects, a UE, a BS, and a system are also disclosed.

Claims

1. A wireless communication method comprising: transmitting, from a base station (BS) to a user equipment (UE), a configuration information indicating a resource used in transmission of a Channel State Information-Reference Signal (CSI-RS) by higher layer signaling; and receiving, with the UE, the CSI-RS from the BS based on the configuration information, wherein the configuration information indicates a mapping for CSI-RS transmission using a single antenna port (AP) to a single resource element per a resource block.

2. A user equipment (UE) comprising: a controller that controls to receive a Channel State Information-Reference Signal (CSI-RS) based on a configuration information, transmitted by higher layer signaling from a base station (BS), indicating a resource used in transmission of the CSI-RS; and a receiver that receives, from the BS, the CSI-RS, wherein the configuration information indicates a mapping for CSI-RS transmission using a single antenna port (AP) to a single resource element per a resource block.

3. A base station (BS) comprising: a transmitter that transmits, to the UE, a configuration information indicating a resource used in transmission of a Channel State Information-Reference Signal (CSI-RS) by higher layer signaling; and a controller that controls to transmit, to the UE, the CSI-RS based on the configuration information, wherein the configuration information indicates a mapping for CSI-RS transmission using a single antenna port (AP) to a single resource element per a resource block.

4. A system comprising a base station (BS) and a user equipment (UE), wherein: the BS comprises: a transmitter that transmits, to the UE, a configuration information indicating a resource used in transmission of a Channel State Information-Reference Signal (CSI-RS) by higher layer signaling; and a first controller that controls to transmit, to the UE, the CSI-RS based on the configuration information; and the UE comprises: a second controller that controls to receive, from the BS, the CSI-RS based on the configuration information; and a receiver that receives, from the BS, the CSI-RS, wherein the configuration information indicates a mapping for CSI-RS transmission using a single antenna port (AP) to a single resource element per a resource block.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIGS. 1A, 1B, 1C, and 1D are diagrams showing REs mapped to 2, 4, 8, and 1-port CSI-RS, respectively, according to conventional LTE standard.

[0015] FIGS. 2A and 2B are diagrams showing the REs mapped to each AP for 2 and 1-port CSI-RS transmission, respectively, according to the conventional LTE standard.

[0016] FIG. 3 is a diagram showing an example operation of beamformed CSI-RSs and CSI feedback according to the conventional LTE standard.

[0017] FIG. 4 is a diagram showing a configuration of a wireless communication system according to one or more embodiments of the present invention.

[0018] FIG. 5 is a diagram showing a resource configuration for 1-port CSI-RS transmission according to one or more embodiments of a first example of the present invention.

[0019] FIG. 6 is a sequence diagram showing an example operation for the 1-port CSI-RS transmission according to one or more embodiments of the first example of the present invention.

[0020] FIG. 7 is a diagram showing a resource configuration for 1-port CSI-RS transmission according to one or more embodiments of a modified first example of the present invention.

[0021] FIG. 8 is a diagram showing the REs mapped to the 1-port CSI-RS AP according to one or more embodiments of a second example of the present invention.

[0022] FIG. 9 is a sequence diagram showing an example operation for the 1-port CSI-RS transmission according to one or more embodiments of the second example of the present invention.

[0023] FIG. 10 is a diagram showing the REs mapped to the CSI-RS AP according to one or more embodiments of a third example of the present invention.

[0024] FIG. 11 is a sequence diagram showing an example operation for the CSI-RS transmission with low resource density according to one or more embodiments of the third example of the present invention.

[0025] FIG. 12 is a sequence diagram showing an example operation for the CSI-RS transmission with low resource density according to one or more embodiments of a fourth example of the present invention.

[0026] FIG. 13 is a sequence diagram showing an example operation for the CSI-RS transmission with low resource density according to one or more embodiments of a modified fourth example of the present invention.

[0027] FIG. 14 is a diagram showing a resource configuration for ZP CSI-RS resource according to one or more embodiments of a fifth example of the present invention.

[0028] FIG. 15 is a sequence diagram showing an example operation for notifying the UE of the ZP CSI-RS resource according to one or more embodiments of the fifth example of the present invention.

[0029] FIG. 16 is a block diagram showing a schematic configuration of a base station according to one or more embodiments of the present invention.

[0030] FIG. 17 is a block diagram showing a schematic configuration of a user equipment according to one or more embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0031] 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.

[0032] FIG. 4 illustrates 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 base stations (BS) 20, and a core network 30. The wireless communication system 1 may be an LTE/LTE-Advanced (LTE-A) system, New Radio (NR), or other systems. The wireless communication system 1 is not limited to the specific configurations described herein and may be any type of wireless communication system.

[0033] The BS 20 may communicate uplink (UL) and downlink (DL) signals with the UE 10 in a cell 21. The DL and UL signals may include control information and user data. The BS 20 may communicate DL and UL signals with the core network 30 through backhaul links 31. The BS 20 may be Evolved NodeB (eNB).

[0034] The BS 20 includes one or more antennas, a communication interface to communicate with an adjacent BS 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 BS 20 may be implemented by the processor processing or executing data and programs stored in a memory. However, the BS 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 BSs 20 may be disposed so as to cover a broader service area of the wireless communication system 1.

[0035] The UE 10 may communicate DL and UL signals that include control information and user data with the BS 20. 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.

[0036] 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 BS 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.

[0037] According to one or more embodiments of the present invention, the BS 20 may transmit a Channel State Information-Reference Signal (CSI-RS) (or CSI-RSs) using 1, 2, 4, 8, 12, or 16- antenna ports (APs). The number of APs is not limited to 1, 2, 4, 8, 12, and 16-port and may be more than 16-port such as 32-port. When the UE 10 receives the CSI-RS(s) from the BS 20, the UE 10 may transmit CSI feedback to the BS 20 in response to the CSI-RS(s).

[0038] In one or more embodiments of the present invention, a resource element (RE) may be an example of a resource.

[0039] In one or more embodiments of the present invention, the CSI-RS may be an example of a Reference Signal (RS).

FIRST EXAMPLE

[0040] Embodiments of a first example of the present invention will be described below in detail with reference to FIGS. 5 and 6.

[0041] In the 2, 4, 8, 12, and 16-port CSI-RS under the conventional LTE-A standard, resource density of the CSI-RS resource is one RE per AP for each resource block (RB) (1RE/AP/RB). On the other hand, in the 1-port CSI-RS, density of the CSI-RS resource is two REs per AP for each RB (2RE/AP/RB). As a result, the 1-port CSI-RS transmission efficiency under the conventional LTE-A standard may be lower than the 2, 4, 8, 12, and 16-port CSI-RS transmission efficiency.

[0042] According to one or more embodiments of the first example of the present invention, in the 1-port CSI-RS transmission, a single RE may be used to the 1-port CSI-RS AP. As shown in FIG. 5, in one or more embodiments of the first example of the present invention, the resource density of the 1-port CSI-RS transmission may be one RE per AP for each RB (1RE/AP/RB) which is the same resource density as the 2, 4, 8, 12, and 16-port CSI-RS transmission. Thus, the BS 20 may designate one RE from 40 REs available for the CSI-RS transmission in the conventional LTE-A standard as the RE mapped to the 1-port CSI-RS AP.

[0043] As shown in FIG. 6, the BS 20 may designate one RE from 40 REs for the 1-port CSI-RS transmission and transmit CSI-RS configuration information indicating the designated RE to the UE 10 via Radio Resource Control (RRC) signaling or lower layer signaling (step S101). Then, the BS 20 may transmit the CSI-RS using the RE mapped to the 1-port CSI-RS AP (step S102). The UE 10 may receive the 1-port CSI-RS with the CSI-RS configuration size of one RE.

[0044] Thus, according to one or more embodiments of the first example of the present invention, the resource density of the 1-port CSI-RS transmission may be lower than the resource density in the conventional LTE-A standard. This makes it possible to decrease CSI-RS overhead. As a result, the 1-port CSI-RS transmission efficiency may be improved.

MODIFIED FIRST EXAMPLE

[0045] In a CSI-RS configuration under the conventional LTE-A standard, two REs mapped to the 1-port CSI-RS AP can be designated. According to one or more embodiments of a modified first example of the present invention, as shown in FIG. 7, the BS 20 may designate either one of the two REs mapped to the 1-port CSI-RS AP in the conventional CSI-RS configuration. The BS 20 may transmit information indicating the RE designated from the two REs which can be designated in the conventional CSI-RS configuration.

SECOND EXAMPLE

[0046] Embodiments of a second example of the present invention will be described below in detail with reference to FIGS. 8 and 9. In the conventional LTE-A standard, Code Division Multiplexing (CDM) is not applied to the REs for the 1-port CSI-RS transmission. According to one or more embodiments of a second example of the present invention, in the 1-port CSI-RS transmission, the CDM (Orthogonal Cover Code (OCC)) may be applied to the REs for the 1-port CSI-RS transmission.

[0047] In one or more embodiments of a second example of the present invention, as shown in FIG. 8, when the CDM is applied to the REs for the 1-port CSI-RS transmission, sequence length of the CDM (CDM length) may be two. For example, a set of “[a, a] ([1, 1])” or “[b, −b] ([1, −1])” may be applied to the two REs mapped to the 1-port CSI-RS transmission as the CDM.

[0048] As shown in FIG. 9, the BS 20 may apply the CDM to the REs mapped to the 1-port CSI-RS AP and transmit, to the UE 10, a CSI-RS configuration including information indicating which parameter is applied as the CDM, [1, 1] or [1, −1] (step S201). Then, the BS 20 may transmit the CSI-RS to which the CDM is applied, using the 1-port (step S202).

THIRD EXAMPLE

[0049] Embodiments of a third example of the present invention will be described below in detail with reference to FIGS. 10 and 11. According to one or more embodiments of the third example of the present invention, the CSI-RS resource for the 1-port CSI-RS transmission may be frequency-multiplexed (Frequency Division Multiplexing (FDM). For example, the RE(s) mapped to the 1-port CSI-RS AP, of which the RB number is either even or odd, may be frequency-multiplexed. In an example of FIG. 10, the RE mapped to the 1-port CSI-RS AP of each of the RBs of which the RB number is odd such as RB#1, #3, and #5 may be frequency-multiplexed. Furthermore, the RE of each of the RBs of which the RB number is even may be frequency-multiplexed.

[0050] As shown in FIG. 11, the BS 20 may transmit the CSI-RS configuration including frequency-multiplexing information indicating which REs are multiplexed via the RRC signaling (step S301). Then, the BS 20 may transmit the CSI-RS frequency-multiplexed to the UE 10 (step S302). The UE 10 may receive the 1-port CSI-RS with FDM in the unit of RB.

[0051] According to one or more embodiments of the third example of the present invention, the resource density for the CSI-RS transmission may decrease because the REs in the specific RB of which the RB number is either even or odd are frequency-multiplexed. This makes it possible to be the CSI-RS transmission efficiency can be improved.

[0052] Furthermore, the RE mapping method (CSI-RS transmission with the low frequency resource density) using the frequency multiplexing scheme according to one or more embodiments of the third example of the present invention may be applied to not only the 1-port CSI-RS transmission but also the CSI-RS transmission other than the 1-port CSI-RS transmission.

[0053] Furthermore, the RE mapping method using the frequency multiplexing scheme according to one or more embodiments of the third example of the present invention and the conventional RE mapping method may switched in the BS 20. For example, the BS 20 may notify the UE 10 of information indicating a switch of the CSI-RS transmission with the low resource density and the CSI-RS transmission under the conventional LTE-A standard using the RRC signaling.

FOURTH EXAMPLE

[0054] Embodiments of a fourth example of the present invention will be described below in detail with reference to FIG. 12. According to one or more embodiments of the fourth example of the present invention, a single CSI-RS resource defined in the conventional LTE-A standard may be assumed as multiple CSI-RS resources.

[0055] For example, in one or more embodiments of the fourth example of the present invention, when the BS 20 may transmit the CSI-RS using the 8-ports, the 8-port CSI-RS resource may be assumed as the four 2-port CSI-RS resources. In this case, as shown in FIG. 12, the BS 20 may notify the UE 10 of the single CSI-RS resource (e.g., 8-port CSI-RS resource) and the number of groups (e.g., “4”) via the RRC signaling (step S401). The number of groups is the number of the multiple CSI-RS resources constituting the single CSI-RS resource. Then, the BS 20 may transmit the CSI-RS (step S402).

[0056] The UE 10 may receive the CSI-RS based on the CSI-RS configuration including information indicating the single CSI-RS resource and the number of groups (step S403). For example, when the single CSI-RS resource is the 8-port CSI-RS resource and the number of groups is four, the UE 10 may assume the single CSI-RS resource consists of four 2-port CSI-RS resources. Thus, the multiple CSI-RS resources constituting the single CSI-RS resource may be reserved using the number of groups.

[0057] Furthermore, the RE mapping method using the frequency multiplexing scheme according to one or more embodiments of the fourth example of the present invention and the conventional RE mapping method may switched in the BS 20. For example, the BS 20 may notify the UE 10 of information indicating a switch of the CSI-RS transmission with the low resource density and the CSI-RS transmission under the conventional LTE-A standard using the RRC signaling.

[0058] According to one or more embodiments of a modified fourth example of the present invention, the multiple CSI-RS resources may be reserved based on information indicating the single CSI-RS resource and the number of APs for each of the groups.

[0059] For example, in one or more embodiments of the modified fourth example of the present invention, when the BS 20 may transmit the CSI-RS using the 8-APs, the 8-port CSI-RS resource may be assumed as the four 2-port CSI-RS resources. In this case, as shown in FIG. 13, the BS 20 may notify the UE 10 of the single CSI-RS resource (e.g., 8-port CSI-RS resource) and the number of APs per group (e.g., “2”) via the RRC signaling (step S401a). Then, the BS 20 may transmit the CSI-RS (step S402a).

[0060] The UE 10 may receive the CSI-RS based on the CSI-RS configuration including information indicating the single CSI-RS resource and the number of APs per group (step S403a). For example, when the single CSI-RS resource is the 8-port CSI-RS resource and the number of APs per group is two, the UE 10 may assume the single CSI-RS resource consists of four 2-port CSI-RS resources. Thus, the multiple CSI-RS resources constituting the single CSI-RS resource may be reserved using the number of APs per group.

FIFTH EXAMPLE

[0061] Embodiments of a fifth example of the present invention will be described below in detail with reference to FIGS. 14 and 15.

[0062] The LTE-A standard supports a zero-power (ZP) CSI-RS scheme for high accurate CSI estimation. However, the conventional ZP CSI-RS may be notified using the REs mapped to the 4-port CSI-RS configurations. That is, the ZP CSI-RS resources can be designated only in a unit of four REs. As a result, Physical Downlink Shared Channel (PDSCH) transmission efficiency may decrease by designating the excessive ZP CSI-RS resources.

[0063] According to one or more embodiments of the fifth example of the present invention, the BS 20 may transmit, to the UE 10, information indicating a resource designated as a ZP CSI-RS (ZP RS) or an Interference Measurement Resource (IMR) dynamically. The UE 10 may receive the ZP RS or the IMR from the BS 10 using the information. In one or more embodiments of the fifth example of the present invention, the ZP CSI-RS resource may be designated in a unit of one RE. For example, the ZP CSI-RS resource in the unit of one RE may be notified based on a configuration of the REs mapped to the 1-port CSI-RS (low resource density like embodiments of the first example of the present invention). For example, as shown in FIG. 14, the ZP CSI-RS resource in each RE may be notified as bitmaps (bit-map format) based on the configuration of the RE mapped to the 1-port CSI-RS. In FIG. 14, the number of REs available for 1-port CSI-RS transmission is 40.

[0064] As shown in FIG. 15, the BS 20 may notify the UE 10 of the ZP CSI-RS resource in each RE based on the configuration of the RE mapped to the 1-port CSI-RS via the higher layer signaling such as the RRC signaling and/or the lower layer signaling using Downlink Control Information (DCI) or Media Access Control (MAC) Control Element (CE) (step S501). Then, the BS 20 may transmit the CSI-RS (step S502). For example, the RE used for the ZP CSI-RS may be switched using the higher layer signaling such as the RRC signaling and/or the lower layer signaling using DCI format.

[0065] As a result, according to one or more embodiments of the fifth example of the present invention, it may be advantageous to improve transmission efficiency of the PDSCH even if more ZP CSI-RSs are designated.

MODIFIED FIFTH EXAMPLE

[0066] According to one or more embodiments of a modified fifth example of the present invention, the ZP CIS-RS resource in a unit of two REs may be notified based on the REs mapped to the 2-port CSI-RS configurations. That is, ZP CSI-RS resource may be designated in a unit of two REs. The ZP CSI-RS resource may be indicated as a bit-map format. The ZP CSI-RS resource may be designated from 40 resources used in a 2-port CSI-RS mapping configuration where multiple CSI-RS resources are mapped to 2-antenna ports of the BS.

[0067] According to one or more embodiments of a modified fifth example of the present invention, a method for notifying the UE 10 of the conventional ZP CSI-RS resource (in a unit of four REs) and a method according to embodiments of the fifth example of the present invention may be switched using the higher layer signaling such as the RRC signaling and/or the lower layer signaling using DCI format.

[0068] According to one or more embodiments of a modified fifth example of the present invention, the ZP CSI-RS resource may be frequency-multiplexed. For example, in an example of FIG. 10, when the RE “a” is designated as the ZP CSI-RS (or the IMR), part of a plurality of RBs (RBs #1, #3, and #5) may be frequency-multiplexed. The RE “a” designated as the ZP CSI-RS may be the ZP CSI-RS resource. For example, the RB number of the part of a plurality of RBs including the ZP CSI-RS resources may be either even or odd. Furthermore, the frequency-multiplexing information indicating the part of a plurality of RBs including the ZP CSI-RS resources may be notified from the BS to the UE via the RRC signaling.

[0069] As another example, the ZP CSI-RS resource according to embodiments of the fifth example of the present invention may be used as an interference measurement resource (IMR).

(Configuration of Base Station)

[0070] The BS 20 according to one or more embodiments of the present invention will be described below with reference to FIG. 16. FIG. 16 is a diagram illustrating a schematic configuration of the BS 20 according to one or more embodiments of the present invention. The BS 20 may include a plurality of antennas 201, amplifier 202, transceiver (transmitter/receiver) 203, a baseband signal processor 204, a call processor 205 and a transmission path interface 206.

[0071] User data that is transmitted on the DL from the BS 20 to the UE 20 is input from the core network 30, through the transmission path interface 206, into the baseband signal processor 204.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] As for data to be transmitted on the UL from the UE 10 to the BS 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.

[0076] 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 BS 20, and manages the radio resources.

(Configuration of User Equipment)

[0077] The UE 10 according to one or more embodiments of the present invention will be described below with reference to FIG. 17. FIG. 17 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.

[0078] 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.

[0079] 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.

ANOTHER EXAMPLE

[0080] 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.

[0081] Although the present disclosure mainly described examples of a channel and signaling scheme based on LTE/LTE-A, 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 LTE/LTE-A, New Radio (NR), and a newly defined channel and signaling scheme.

[0082] 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.

[0083] 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. Furthermore, the signaling according to one or more embodiments of the present invention may use the MAC-CE.

[0084] 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.

[0085] Although the present disclosure mainly described examples of the UE including planer antennas, the present invention is not limited thereto. One or more embodiments of the present invention may also apply to the UE including one dimensional antennas and predetermined three dimensional antennas.

[0086] In one or more embodiments of the present invention, the resource block (RB) and a subcarrier in the present disclosure may be replaced with each other. A subframe and a symbol may be replaced with each other.

[0087] In one or more embodiments of the present invention, beamforming may be applied to the CSI-RS or may not be applied.

[0088] 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.

[0089] 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.

EXPLANATION OF REFERENCES

[0090] 1 Wireless communication system [0091] 10 User equipment (UE) [0092] 101 Antenna [0093] 102 Amplifier [0094] 103 Circuit [0095] 1031 Transceiver (transmitter/receiver) [0096] 104 Controller [0097] 105 Application [0098] 106 Switch [0099] 20 Base station (BS) [0100] 201 Antenna [0101] 202 Amplifier [0102] 203 Transceiver (transmitter/receiver) [0103] 204 Baseband signal processor [0104] 205 Call processor [0105] 206 Transmission path interface