阅读说明：本技术 无线通信系统中用于传输数据的设备和方法 (Apparatus and method for transmitting data in wireless communication system ) 是由 卢智焕 金泰莹 柳铉逸 于 2018-03-22 设计创作，主要内容包括：公开了一种用于支持比诸如长期演进(LTE)的第四代(4G)通信系统更高的数据传输速率的第五代(5G)或预5G通信系统。根据本公开的各种实施例,终端的设备可以包括：至少一个处理器和至少一个收发器,该终端从基站接收根据与基站的信道互易性是否被满足而确定的并且用于控制终端的波束形成操作的指示信号；并且从基站接收参考信号；并且基于指示信息和参考信号向基站传输上行链路数据。(A fifth generation (5G) or pre-5G communication system for supporting higher data transmission rates than fourth generation (4G) communication systems such as Long Term Evolution (LTE) is disclosed. According to various embodiments of the present disclosure, a device of a terminal may include: at least one processor and at least one transceiver, the terminal receiving an indication signal, which is determined according to whether channel reciprocity with a base station is satisfied or not and is used to control a beamforming operation of the terminal, from the base station; and receiving a reference signal from a base station; and transmitting uplink data to the base station based on the indication information and the reference signal.)

1. A method for operation in a terminal, the method comprising:

receiving indication information from a base station, the indication information being determined according to whether channel reciprocity with the base station is satisfied and being used to control a beamforming operation of the terminal;

receiving a reference signal from the base station; and

transmitting uplink data to the base station based on the indication information and the reference signal.

2. The method of claim 1, further comprising:

performing an uplink beam search and a downlink beam search with the base station; and

determining a first beam corresponding to a downlink transmission beam of the base station, a second beam corresponding to an uplink reception beam of the base station, a third beam corresponding to a downlink reception beam of the terminal, and a fourth beam corresponding to an uplink transmission beam of the terminal.

3. The method of claim 2, wherein transmitting the uplink data comprises transmitting the uplink data through the fourth beam,

the indication information includes the following information: the information is for controlling a receive beam of the terminal for receiving the reference signal by the fourth beam in response to the channel reciprocity not being satisfied and the purpose of the reference signal being for uplink transmission, and

the reference signal is transmitted through the second beam.

4. The method of claim 2, wherein transmitting the uplink data comprises transmitting the uplink data through one of the third beam or the fourth beam according to the indication information,

the indication information represents which beam among the third beam and the fourth beam is used for transmission of uplink data of the terminal according to satisfaction or non-satisfaction of the channel reciprocity, and

the reference signal is received through the third beam.

5. The method of claim 2, wherein transmitting the uplink data comprises:

applying a precoder of a precoding matrix indicator, PMI, transmitted from the base station to the terminal to the uplink data in response to the precoding scheme of the terminal being based on uplink measurements; and

applying a precoder calculated based on the measurement results of the reference signals to the uplink data in response to the precoding scheme being based on downlink measurements, and

wherein the indication information indicates whether the precoding scheme is based on the uplink measurement or the downlink measurement according to satisfaction or non-satisfaction of the channel reciprocity.

6. The method of claim 2, further comprising receiving a precoding matrix indicator, PMI, from the base station, and

wherein transmitting the uplink data comprises:

applying a precoder calculated based on a measurement result of the reference signal to the uplink data in response to the PMI indicating a precoder for reflecting uplink interference; and

applying the uplink precoder to the uplink data in response to the PMI indicating an uplink precoder, an

Wherein the indication information indicates whether the PMI indicates a precoder for reflecting the uplink interference or indicates the uplink precoder according to satisfaction or non-satisfaction of the channel reciprocity.

7. The method of claim 2, wherein transmitting the uplink data comprises applying a precoder determined according to a transmission scheme indicated by the indication information to the uplink data, and

the indication information indicates whether the transmission scheme of the uplink data is a codebook-based transmission scheme according to satisfaction or non-satisfaction of the channel reciprocity.

8. The method of claim 1, wherein the beamforming operation of the terminal comprises:

an analog beamforming operation of forming a reception beam of the terminal for receiving the reference signal and a transmission beam of the terminal for transmitting the uplink data; and

a digital beamforming operation of a precoder to be applied to uplink data is determined.

9. The method of claim 1, wherein the indication information is received from the base station through downlink control information, DCI, media access control, MAC, control element, CE, or higher layer signaling.

10. A method for operation in a base station, the method comprising:

transmitting indication information to a terminal, the indication information being determined according to whether channel reciprocity with the terminal is satisfied and being used to control a beamforming operation of the terminal;

receiving a reference signal from the terminal; and

transmitting downlink data to the terminal based on the indication information and the reference signal.

11. The method of claim 10, further comprising:

performing an uplink beam search and a downlink beam search with the terminal; and

determining, based on the uplink beam search and the downlink beam search, a first beam corresponding to a downlink transmission beam of the base station, a second beam corresponding to an uplink reception beam of the base station, a third beam corresponding to a downlink reception beam of the terminal, and a fourth beam corresponding to an uplink transmission beam of the terminal.

12. The method of claim 11, wherein transmitting the indication information comprises: transmitting, to the terminal, indication information for controlling a transmission beam of the terminal for transmitting the reference signal by the third beam in response to the channel reciprocity not being satisfied and the purpose of the reference signal being a purpose for downlink transmission,

receiving the reference signal comprises receiving the reference signal through the first beam, an

Transmitting the downlink data includes transmitting the downlink data through the first beam.

13. The method of claim 11, wherein transmitting the indication information comprises transmitting indication information indicating which of the first beam and the second beam is used for transmission of the downlink data of the base station according to satisfaction or non-satisfaction of the channel reciprocity,

transmitting the downlink data includes transmitting the downlink data to the terminal through the first beam or the second beam according to the indication information, and

the reference signal is received through the first beam.

14. An apparatus of a terminal, comprising:

at least one transceiver; and

at least one processor operatively coupled with the at least one transceiver,

wherein the at least one processor is configured to perform one of the methods of claims 1-9.

15. An apparatus of a base station, comprising:

at least one transceiver; and

at least one processor operatively coupled with the at least one transceiver,

wherein the at least one processor is configured to perform one of the methods of claim 10 to claim 13.

Background

The present disclosure relates generally to wireless communication systems. In more detail, the present disclosure relates to an apparatus and method for transmitting data in a wireless communication system.

In order to meet the demand for wireless data services, which are on the increase after commercialization of the fourth generation (4G) communication system, efforts are being made to develop an improved fifth generation (5th-generation, 5G) communication system or a pre-5G communication system. Accordingly, the 5G communication system or the pre-5G communication system is referred to as a super 4G network communication system or a Long Term Evolution (LTE) system.

In order to achieve high data transmission rates, 5G communication systems are considering implementation in an ultra-high frequency (millimeter wave) band, for example, a 60 gigahertz (GHz) band. In order to mitigate path loss of radio waves in the uhf band and increase propagation distance of radio waves, the 5G communication system is discussing beamforming, massive Multiple Input Multiple Output (MIMO), full-dimensional multiple input multiple output (FD-MIMO), array antenna, analog beamforming, and massive antenna technologies.

Further, for the purpose of improvement of a system network, the 5G communication system is implementing development of technologies such as evolved small cells, advanced small cells, cloud radio access networks (cloud RANs), ultra-dense networks, device to device communication (D2D), wireless backhaul, mobile networks, cooperative communication, coordinated multi-point (CoMP), reception interference cancellation, and the like.

In addition, the 5G system is developing Advanced Coding Modulation (ACM) schemes such as hybrid frequency shift keying and quadrature amplitude modulation (FQAM) and Sliding Window Superposition Coding (SWSC), and advanced connection technologies such as filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), Sparse Code Multiple Access (SCMA), and the like.

To overcome the path loss problem caused by the characteristics of the ultra-high frequency (e.g., millimeter wave) band, the 5G communication system is increasing the signal gain by using a beamforming technique. Therefore, there is a need for a way to manage reciprocity (reciprocity) -based precoding in an environment where systems employing beamforming are considered.

Disclosure of Invention

Technical problem

Based on the above discussion, the present disclosure provides an apparatus and method for efficiently determining a precoder in a wireless communication system.

Further, the present disclosure provides an apparatus and method for transmitting data based on a procedure determined according to beam correspondence and channel reciprocity in a wireless communication system.

Further, the present disclosure provides an apparatus and method for transmitting indication information representing satisfaction or non-satisfaction of beam correspondence or channel reciprocity in a wireless communication system.

Further, the present disclosure provides an apparatus and method for transmitting an uplink reference signal through a previously determined downlink reception beam or transmitting a downlink reference signal through a previously determined uplink reception beam in a wireless communication system.

Further, the present disclosure provides an apparatus and method for transmitting uplink data through a previously determined downlink reception beam or transmitting downlink data through a previously determined uplink transmission beam in a wireless communication system.

Further, the present disclosure provides an apparatus and method for determining a measurement scheme for transmitting data in a wireless communication system.

In addition, the present disclosure provides an apparatus and method for representing a function of a Precoding Matrix Indicator (PMI) in a wireless communication system.

Further, the present disclosure provides an apparatus and method for indicating an uplink transmission scheme in a wireless communication system.

According to various embodiments of the present disclosure, a device of a terminal may include at least one processor and at least one transceiver to: receiving indication information from the base station, the indication information being determined according to whether channel reciprocity with the base station is satisfied and being used to control a beamforming operation of the terminal; and receiving a reference signal from a base station; and transmitting uplink data to the base station based on the indication information and the reference signal.

According to various embodiments of the present disclosure, an apparatus of a base station may include at least one processor and at least one transceiver to: transmitting indication information to the terminal, the indication information being determined according to whether channel reciprocity with the terminal is satisfied and being used to control a beamforming operation of the terminal; and receiving a reference signal from the terminal; and transmitting downlink data to the terminal based on the indication information and the reference signal.

According to various embodiments of the present disclosure, a method for operating in a terminal may include: receiving indication information from the base station, the indication information being determined according to whether channel reciprocity with the base station is satisfied and being used to control a beamforming operation of the terminal; receiving a reference signal from a base station; and transmitting uplink data to the base station based on the indication information and the reference signal.

According to various embodiments of the present disclosure, a method for operating in a base station may comprise: transmitting indication information to the terminal, the indication information being determined according to whether channel reciprocity with the terminal is satisfied and being used to control a beamforming operation of the terminal; receiving a reference signal from a terminal; and transmitting downlink data to the terminal based on the indication information and the reference signal.

The apparatus and methods of various embodiments of the present disclosure may determine or identify precoders and perform beamforming communication by using beam correspondence or channel reciprocity.

Effects that the present disclosure can obtain are not limited to the above-described effects, and other effects that are not mentioned may be clearly understood by those skilled in the art from the following description.

Drawings

Fig. 1 illustrates a wireless communication system in accordance with various embodiments of the present disclosure.

Fig. 2 illustrates a structure of a base station in a wireless communication system according to various embodiments of the present disclosure.

Fig. 3 illustrates a structure of a terminal in a wireless communication system according to various embodiments of the present disclosure.

Fig. 4a to 4c illustrate the structure of a communication unit in a wireless communication system according to various embodiments of the present disclosure.

Fig. 5 illustrates a wireless environment in accordance with various embodiments of the present disclosure.

Fig. 6 illustrates an uplink transmission process according to various embodiments of the present disclosure.

Fig. 7 illustrates an example of determining beams for reference signals for uplink transmission, in accordance with various embodiments of the present disclosure.

Fig. 8 illustrates an operational flow of a base station for determining beams of reference signals for uplink transmission according to various embodiments of the present disclosure.

Fig. 9 illustrates an operational flow of a terminal for determining a reference signal beam for uplink transmission according to various embodiments of the present disclosure.

Fig. 10 illustrates an example of determining a beam for uplink transmission according to various embodiments of the present disclosure.

Fig. 11 illustrates an operational flow of a base station for determining a beam for uplink transmission, in accordance with various embodiments of the present disclosure.

Fig. 12 illustrates an operational flow of a terminal for determining a beam for uplink transmission according to various embodiments of the present disclosure.

Fig. 13 shows an example of indicating a precoder determination scheme, according to various embodiments of the present disclosure.

Fig. 14 illustrates an operational flow of a base station for indicating a precoder determination scheme, according to various embodiments of the present disclosure.

Fig. 15 illustrates an operational flow of a terminal for indicating a precoder determination scheme according to various embodiments of the present disclosure.

Fig. 16 illustrates an example of a function of indicating a Precoding Matrix Indicator (PMI) according to various embodiments of the present disclosure.

Fig. 17 illustrates an operational flow of a base station for indicating PMI functionality according to various embodiments of the present disclosure.

Fig. 18 illustrates an operational flow of a terminal for indicating a PMI function according to various embodiments of the present disclosure.

Fig. 19 shows an example of indicating an uplink transmission scheme in accordance with various embodiments of the present disclosure.

Fig. 20 illustrates an operational flow of a base station for indicating an uplink transmission scheme according to various embodiments of the present disclosure.

Fig. 21 illustrates an operational flow of a terminal for indicating an uplink transmission scheme according to various embodiments of the present disclosure.

Fig. 22 illustrates a downlink transmission process according to various embodiments of the present disclosure.

Fig. 23 illustrates an example of determining beams for reference signals for downlink transmission in accordance with various embodiments of the present disclosure.

Fig. 24 illustrates an operational flow of a base station for determining beams for reference signals for downlink transmission, in accordance with various embodiments of the present disclosure.

Fig. 25 illustrates an operational flow of a terminal for determining a reference signal beam for downlink transmission according to various embodiments of the present disclosure.

Fig. 26 illustrates an example of determining a beam for downlink transmission in accordance with various embodiments of the present disclosure.

Fig. 27 illustrates an operational flow of a base station for determining a beam for downlink transmission, in accordance with various embodiments of the present disclosure.

Fig. 28 illustrates an operational flow of a terminal for determining a beam for downlink transmission according to various embodiments of the present disclosure.

Detailed Description

The terminology used in the present disclosure is for the purpose of describing particular embodiments only and may not be intended to limit the scope of other embodiments. Expressions in the singular may include expressions in the plural unless the context clearly dictates otherwise. Terms used herein, including technical or scientific terms, may have the same meaning as terms commonly understood by one of ordinary skill in the art to which this disclosure pertains. Among the terms used in the present disclosure, terms defined in a general dictionary may be interpreted as meanings identical or similar to the contextual meanings of the related art, and are not interpreted as ideal or excessively formal meanings unless explicitly defined in the present disclosure. According to circumstances, even terms defined in the present disclosure should not be construed to exclude embodiments of the present disclosure.

In the various embodiments of the present disclosure described below, the hardware access method is explained as an example. However, various embodiments of the present disclosure include techniques that use all hardware and software, and thus, various embodiments of the present disclosure do not preclude software-based access methods.

Various embodiments of this document are referred to below with reference to the figures. It is to be understood that the embodiments and terms used therein are not intended to limit the techniques set forth therein to the particular forms of embodiments, but rather to include various modifications, equivalents, and/or alternatives to the corresponding embodiments. Similar reference characters may be used for similar components with respect to the description of the figures. Expressions in the singular may include expressions in the plural unless the context clearly dictates otherwise.

In this document, the expression "a or B", "at least one of a and/or B", etc. may include all available combinations of the words listed together. The expressions "first", "second", "the first", "the second", and the like may use the respective constituent elements regardless of order and/or importance, and are used to distinguish the constituent elements from another constituent element without limiting the respective constituent elements. When it is stated that any (e.g., a first) component is coupled/coupled … "with …" (operatively or communicatively) or is "connected" to another (e.g., a second) component, that any component may be directly coupled to the other component or coupled via the other component (e.g., a third component).

In this document, the expression "configured (or set) to" can be used interchangeably with, for example, "suitable for", "having a capability of", "suitable for", "made to" or "capable of" or "designed to" in hardware or software, depending on the case. In some contexts, the expression "a device configured as a-" may mean that the device is "capable of" with other devices or components. For example, the phrase "a processor configured (or arranged) to perform A, B and C" may refer to a dedicated processor (e.g., an embedded processor) for performing the respective operations, or a general-purpose processor (e.g., a Central Processing Unit (CPU) or an application processor) capable of performing the respective operations by executing one or more software programs stored in a memory device.

Hereinafter, the present disclosure relates to an apparatus and method for performing precoding in a non-codebook based precoding scheme in a wireless communication system. In detail, the present disclosure explains a technique for performing precoding by using channel reciprocity in a beamforming-based wireless communication system.

In the following description, terms representing signals, terms representing channels, terms representing control information, terms representing network entities, terms representing components of devices, and the like are illustrated for convenience of description. Accordingly, the present disclosure is not limited to the terms described later, and other terms having equivalent technical meanings may be used.

In addition, the present disclosure explains various embodiments by using terms used in some communication standards, for example, 3rd generation partnership project (3 GPP), but this is only an example for explanation.

Fig. 1 illustrates a wireless communication system in accordance with various embodiments of the present disclosure. Fig. 1 illustrates a base station 110, a terminal 120, and a terminal 130 as some nodes using wireless channels in a wireless communication system. Fig. 1 shows only one base station, but may further include another base station that is the same as or similar to base station 110.

Base station 110 is the network infrastructure that provides wireless connectivity to terminals 120 and 130. The base station 110 has a coverage area defined as a specific geographical area based on a distance over which signals can be transmitted. In addition to the base station, the base station 110 may also be denoted as "Access Point (AP)", "enodeb (enb)", "fifth generation node", "wireless point", "transmission/reception point (TRP)", or other terms having technical meanings equivalent to these.

Each of the terminal 120 and the terminal 130 (devices used by the user) performs communication with the base station 110 through a wireless channel. According to circumstances, at least one of the terminal 120 and the terminal 130 may be managed without user participation. That is, at least one of the terminal 120 and the terminal 130, a device performing Machine Type Communication (MTC) may not be carried by a user. In addition to the terminals, each of the terminals 120 and 130 may be denoted as "User Equipment (UE)", "mobile station", "subscriber station", "remote terminal", "wireless terminal", or "user equipment" or other terms having technical meanings equivalent to these.

Base station 110, terminal 120, and terminal 130 may transmit and receive wireless signals in the millimeter wave frequency bands (e.g., 28GHz, 30GHz, 38GHz, and 60 GHz). At this time, in order to improve channel gain, the base station 110, the terminal 120, and the terminal 130 may perform beamforming. Here, the beamforming includes transmission beamforming and reception beamforming. That is, the base station 110, the terminal 120, and the terminal 130 may impart directivity to a transmission signal or a reception signal. To this end, the base station or the terminal may select a serving beam through a beam search or a beam management procedure. After the serving beam is selected, subsequent communications may be performed over resources that are in a quasi co-located (QCL) relationship with the resources transmitting the serving beam. Base station 110 and terminals 120 and 130 may select serving beams 112, 113, 121, and 131 through a beam search process.

When a large-scale (large-scale) characteristic of a channel forwarding symbols on the first antenna port is inferred from a channel forwarding symbols on the second antenna port, it may be evaluated that the first antenna port and the second antenna port are in a QCL relationship. For example, the large-scale characteristics may include at least one of delay spread, doppler shift, average gain, average delay, and spatial receiver parameters.

Fig. 2 illustrates a structure of a base station in a wireless communication system according to various embodiments of the present disclosure. The structure illustrated in fig. 2 can be understood as the structure of the base station 110. The terms "… cell," "… device," and the like, as used below, denote a cell that handles at least one function or operation. These terms may be implemented by hardware, software, or a combination of hardware and software.

Referring to fig. 2, the base station 110 includes a wireless communication unit 210, a backhaul communication unit 220, a storage unit 230, and a control unit 240.

The wireless communication unit 210 performs a function for transceiving signals through a wireless channel. For example, the wireless communication unit 210 performs a conversion function between a baseband signal and a bit stream according to a physical layer standard of the system. For example, at the time of data transmission, the wireless communication unit 210 generates a complex symbol by encoding and modulating a transmission bit stream. Also, at the time of data reception, the wireless communication unit 210 restores the received bit stream by demodulating and decoding the baseband signal. Also, the wireless communication unit 210 up-converts a baseband signal into a Radio Frequency (RF) band signal, and then transmits the RF band signal through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal.

To this end, the wireless communication unit 210 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a digital to analog converter (DAC), an analog to digital converter (ADC), and the like. In addition, the wireless communication unit 210 may include a plurality of transceiving paths. Further, the wireless communication unit 210 may comprise at least one antenna array comprising a plurality of antenna elements. In terms of hardware, the wireless communication unit 210 may include a digital unit and an analog unit, and the analog unit may include a plurality of sub-units according to an operation power, an operation frequency, and the like.

As described above, the wireless communication unit 210 transmits and receives signals. Accordingly, the whole or part of the wireless communication unit 210 may be denoted as a "transmitting unit", a "receiving unit", or a "transceiving unit". Further, in the following description, transmission and reception performed through a wireless channel are used as meaning including the aforementioned processing performed by the wireless communication unit 210.

The backhaul communication unit 220 provides an interface for performing communication with other nodes in the network. That is, the backhaul communication unit 220 converts a bitstream transmitted from the base station 110 to another node (e.g., another connection node, another base station, an upper node, a core network, etc.) into a physical signal and converts a physical signal received from another node into a bitstream.

The storage unit 230 stores data such as basic programs, application programs, setting information, and the like for the operation of the base station 110. The storage unit 230 may be composed of a volatile memory, a non-volatile memory, or a combination of a volatile memory and a non-volatile memory. And, the storage unit 230 provides the stored data in response to a request of the control unit 240.

The control unit 240 controls the general operation of the base station 110. For example, the control unit 240 may transmit and receive signals through the wireless communication unit 210 or the backhaul communication unit 220. Further, the control unit 240 records and reads data in the storage unit 230. Also, the control unit 240 may perform functions of a protocol stack required in a communication standard. To this end, the control unit 240 may include at least one processor. According to various embodiments, the control unit 240 may comprise a precoder calculation unit. Here, the precoder calculation unit, the set of instructions or code stored in the storage unit 230 may be instructions/code residing at least temporarily in the control unit 240 or in a memory space where the instructions/code are stored, or part of the circuitry configuring the control unit 240. For example, the control unit 240 may control the base station 110 to perform operations of various embodiments described later.

Fig. 3 illustrates a structure of a terminal in a wireless communication system according to various embodiments of the present disclosure. The structure illustrated in fig. 3 can be understood as the structure of the terminal 120. The terms "… element," "… device," and the like as used below refer to an element that handles at least one function or operation. These terms may be implemented by hardware, software, or a combination of hardware and software.

Referring to fig. 3, the terminal 120 includes a communication unit 310, a storage unit 320, and a control unit 330.

The communication unit 310 performs a function for transceiving signals through a wireless channel. For example, the communication unit 310 performs a conversion function between a baseband signal and a bit stream according to a physical layer standard of the system. For example, at the time of data transmission, the communication unit 310 generates complex symbols by encoding and modulating a transmission bit stream. Also, at the time of data reception, the communication unit 310 restores the received bit stream by demodulating and decoding the baseband signal. Also, the communication unit 310 up-converts a baseband signal into an RF band signal and then transmits the RF band signal through an antenna, and down-converts the RF band signal received through the antenna into a baseband signal. For example, the communication unit 310 may include a transmission filter, a reception filter, an amplifier, a mixer, an oscillator, a DAC, an ADC, and the like.

Further, the communication unit 310 may include a plurality of transceiving paths. Furthermore, the communication unit 310 may comprise at least one antenna array comprising a plurality of antenna elements. In terms of hardware, the communication unit 310 may include digital circuitry and analog circuitry (e.g., a Radio Frequency Integrated Circuit (RFIC) — here, the digital circuitry and analog circuitry may be implemented as one package.

Further, the communication unit 310 may include communication modules different from each other in order to process frequency band signals different from each other. Further, the communication unit 310 may include a plurality of communication modules in order to support a plurality of wireless connection technologies different from each other. For example, mutually different wireless connection technologies may include Bluetooth Low Energy (BLE), Wireless fidelity (Wi-Fi), WiFi gigabyte (WiGig), cellular networks (e.g., Long Term Evolution (LTE), etc. furthermore, mutually different frequency bands may include ultra high frequency (SHF) (e.g., 2.5GHz and 5GHz) frequency bands and/or millimeter wave (e.g., 60GHz) frequency bands.

As described above, the communication unit 310 transmits and receives signals. Accordingly, all or part of the communication unit 310 may be denoted as a "transmitting unit", a "receiving unit", or a "transceiving unit". Further, in the following description, transmission and reception performed through a wireless channel are used as meaning including the aforementioned processing performed by the communication unit 310.

The storage unit 320 stores data such as basic programs, application programs, setting information, and the like for the operation of the terminal 120. The storage unit 320 may be composed of a volatile memory, a non-volatile memory, or a combination of a volatile memory and a non-volatile memory. And, the storage unit 320 provides the stored data in response to a request of the control unit 330.

The control unit 330 controls the general operation of the terminal 120. For example, the control unit 330 transmits and receives signals through the communication unit 310. Further, the control unit 330 records and reads data in the storage unit 320. Also, the control unit 330 may perform functions of a protocol stack required in a communication standard. To this end, the control unit 330 may comprise or be part of at least one processor or microprocessor. Further, the communication unit 310 and a part of the control unit 330 may be represented as a Communication Processor (CP). Specifically, according to various embodiments, the control unit 330 controls the terminal 120 to calculate a precoder and generate uplink data symbols by applying the precoder. For example, the control unit 330 may control the terminal 120 to perform operations of various embodiments described later.

Fig. 4a to 4c illustrate the structure of a communication unit in a wireless communication system according to various embodiments of the present disclosure. Fig. 4a to 4c illustrate an example of a detailed structure of the wireless communication unit 210 of fig. 2 or the wireless communication unit 210 of fig. 3. Specifically, fig. 4a to 4c illustrate constituent elements for performing beamforming as part of the wireless communication unit 210 of fig. 2 or the communication unit 310 of fig. 3.

Referring to fig. 4a, the wireless communication unit 210 or the communication unit 310 includes a coding and modulation unit 402, a digital beam forming unit 404, a plurality of transmission paths 406-1 to 406-N, and an analog beam forming unit 408.

The coding and modulation unit 402 performs channel coding. For the channel coding, at least one of a Low Density Parity Check (LDPC) code, a convolutional code, and a polar code may be used. By performing constellation mapping, the coding and modulation unit 402 generates modulation symbols.

The digital beamforming unit 404 performs beamforming on the digital signals (e.g., modulation symbols). To this end, the digital beamforming unit 404 multiplies the modulation symbols by beamforming weights. Here, the beamforming weights are used to change the amplitude and phase of the signals, and may be represented as a "precoding matrix", "precoder", or the like. The digital beam forming unit 404 outputs the digitally beamformed modulation symbols to a plurality of transmission paths 406-1 to 406-N. At this time, modulation symbols may be multiplexed or the same modulation symbol may be provided to a plurality of transmission paths 406-1 to 406-N according to a Multiple Input Multiple Output (MIMO) transmission technique.

The plurality of transmission paths 406-1 to 406-N convert the digital beamformed digital signals to analog signals. To this end, each of the plurality of transmission paths 406-1 to 406-N may include an Inverse Fast Fourier Transform (IFFT) operation unit, a Cyclic Prefix (CP) insertion unit, a DAC, and an up-conversion unit. The plurality of transmission paths 406-1 to 406-N provide independent signal processing procedures for the plurality of streams generated by digital beamforming, however, some constituent elements of the plurality of transmission paths 406-1 to 406-N may be commonly used according to an embodiment.

The analog beamforming unit 408 performs beamforming on the analog signal. To this end, the digital beamforming unit 404 multiplies the analog signal by beamforming weights. Here, the beamforming weights are used to change the amplitude and phase of the signals. In detail, the analog beamforming unit 408 may be configured as in fig. 4b or 4c according to a coupling structure between the plurality of transmission paths 406-1 to 406-N and the antenna.

Referring to fig. 4b, the signal input to the analog beam forming unit 408 is subjected to phase/amplitude conversion and/or amplification and transmitted through an antenna. At this time, the signals of each path are transmitted through mutually different antenna groups (i.e., antenna arrays). In the description of the processing of the signal input through the first path, the signal is converted into a signal sequence having mutually different or same phase/amplitude by the phase/amplitude conversion units 412-1-1 to 412-1-M, and amplified by the amplifiers 414-1-1 to 414-1-M, and then transmitted through the antenna.

Referring to fig. 4c, the signal input to the analog beam forming unit 408 is subjected to phase/amplitude conversion and/or amplification and then transmitted through the antenna. At this time, the signal of each path is transmitted through the same antenna group (i.e., antenna array). In the description of the processing of the signal input through the first path, the signal is converted into a signal sequence having mutually different or same phases/amplitudes by the phase/amplitude conversion units 412-1-1 to 412-1-M, and amplified by the amplifiers 414-1-1 to 414-1-M. And, the amplified signals are summed by the summing units 416-1-1 to 416-1-M with the standard of the antenna elements, where the signals are transmitted through an antenna array and then through the antennas.

Fig. 4b shows an example where each transmission path uses an independent antenna array, i.e. the transmission paths of fig. 4c share one antenna array. However, according to another embodiment, some transmission paths may use separate antenna arrays and the remaining transmission paths may share one antenna array. Furthermore, according to a further embodiment, a structure that adaptively changes according to situations by applying a switchable structure between the transmission path and the antenna array may be used. Hereinafter, a beam refers to a signal formed by analog beamforming, and a precoder refers to processing of a signal controlled by digital beamforming. That is, the beamforming operation may include an analog beamforming operation for forming a beam (a transmission beam or a reception beam) of the base station or the terminal, and a digital beamforming operation for determining a precoder used for data transmission.

Fig. 5 illustrates a wireless environment in accordance with various embodiments of the present disclosure. Base station 510 may correspond to base station 110 of fig. 1. Terminal 520 may correspond to terminal 120 of fig. 1.

Referring to fig. 5, a wireless network environment 500 may include a base station 510 and a terminal 520. The wireless network environment 500 includes a Downlink (DL), i.e., a link from the base station 510 to the terminal 520, and an Uplink (UL), i.e., a link from the terminal 520 to the base station 510.

Base station 510 and terminal 520 may exchange signals to determine a beam to be used for downlink or uplink transmissions. The handshake process may be denoted as a beam training process, a beam searching process, or a beam management process. The terminal 520 may measure each of the received reference signals to determine a channel quality of each of the reference signals. Hereinafter, in the present disclosure, the channel quality may be, for example, at least one of Beam Reference Signal Received Power (BRSRP), Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), received signal strength indicator (RSRI), signal to interference and noise ratio (SINR), carrier to interference and noise ratio (CINR), signal to noise ratio (SNR), Error Vector Magnitude (EVM), bit error rate (bit error rate, BER), and/or block error rate (BLER). It goes without saying that other terms having technical meanings equivalent thereto or other metrics representing channel quality may be used in addition to the foregoing examples. In the following, in the present disclosure, channel quality is high meaning that a signal amplitude-dependent channel quality value is high or an error rate-dependent channel quality value is small. This means that when the channel quality is high, a smooth wireless communication environment is guaranteed. Further, the best beam may mean a beam of the highest channel quality among the beams.

Uplink transmission may mean transmission of uplink data. Downlink transmission may mean transmission of downlink data. The base station 510 and the terminal 520 may each determine a downlink beam or an uplink beam from the handshake process. For example, base station 510 may determine a downlink transmission beam and terminal 520 may determine a downlink reception beam. For another example, base station 510 may determine an uplink receive beam and terminal 520 may determine an uplink transmit beam.

Hereinafter, for convenience of description, the determined beam is denoted as a downlink transmission beam, a downlink reception beam, an uplink reception beam, and an uplink transmission beam, but the denoted term only denotes the determined beam itself and does not limit the use thereof. For example, base station 510 may use a downlink transmission beam for uplink reception. This means that the beam determined as the downlink transmission beam is used as a reception beam for receiving the uplink signal.

After each of the base station 510 and the terminal 520 determines a beam to be used, each of the base station 510 and the terminal 520 may perform a process for determining a precoder (or precoding matrix) to be applied to data transmission. For example, in uplink transmission, base station 510 may transmit a reference signal to terminal 520. The terminal 520 may determine the precoder according to the received reference signal. The reference signal transmitted by the base station 510 is for downlink transmission, but may be used to determine a precoder for uplink transmission when channel reciprocity is guaranteed. In the following description, channel reciprocity means the following properties: the uplink channel and the downlink channel have similar characteristics, in other words, mean the following channel properties: the uplink channel response can be treated the same as the downlink channel response. When channel reciprocity is used, a downlink channel response may be obtained by using an uplink channel response, or an uplink channel response may be obtained by using a downlink channel response. The terminal 520 may transmit uplink data to the base station 510 by applying the determined precoder. Of course, in response to the channel reciprocity being guaranteed, the precoder to be applied by the base station 510 to downlink transmission (downlink data transmission) can be determined from the uplink reference signal transmitted by the terminal 520.

On the other hand, the downlink transmission beam and the uplink reception beam of the base station 510 may be different from each other. In response to the downlink beam and the uplink beam of the base station 510 being different from each other, the base station 510 may be represented as not satisfying beam correspondence or beam reciprocity. Here, the beam correspondence means the following properties: the uplink and downlink beams have similar characteristics, in other words, mean the following beam properties: the uplink beam direction can be treated the same as the downlink beam direction. When the beam correspondence is used, a beam used in uplink may be used in downlink or a beam used in downlink may be used in uplink. Similar to the base station 510, the downlink reception beam and the uplink transmission beam of the terminal 520 may be different from each other. That is, terminal 520 may not be able to satisfy beam reciprocity.

In response to the beams used in the downlink and uplink being different (e.g., the downlink transmission beam and the uplink reception beam of the base station 510 are different, and the downlink reception beam and the uplink transmission beam of the terminal 520 are different), it is difficult to ensure channel reciprocity. This is because the state of the wireless channel experienced by the signal becomes different due to the directional characteristics of the beam.

Further, when an uplink beam and a downlink beam are different in one base station, channel reciprocity may not be satisfied even when a base station coupled for uplink and a base station coupled for downlink are different with one terminal as in the wireless network environment 550. Wireless network environment 550 may include base station 510, base station 515, and terminal 520. Base station 510 may be a base station coupled for downlink transmissions to terminal 520 and base station 515 may be a base station for uplink transmissions for terminal 520. For example, terminal 520 is located near base station 515 and is therefore coupled to base station 515 for uplink transmissions, but coupled to base station 510 for downlink transmissions because the transmission power of the downlink transmissions of base station 510 is high.

Unlike that shown in fig. 5, the base station 510 or the terminal 520 may also satisfy the beam correspondence. In this case, the base station 510 may determine a downlink precoder from an uplink reference signal (e.g., Sounding Reference Signal (SRS)) by using channel reciprocity, and the terminal 520 may determine an uplink precoder from a downlink reference signal (e.g., CSI-RS) by using channel reciprocity.

As described above, in determining a precoder by using channel reciprocity, it is necessary to consider the relationship between an uplink beam and a downlink beam used in a base station or a terminal. Further, the terminal may recognize that a downlink reception beam and an uplink transmission beam of the terminal obtained through the beam management procedure are different, but may not be able to determine whether a base station (e.g., base station 510 of wireless network environment 500) satisfies the beam correspondence, and may not even be able to determine whether the base stations coupled with the terminal for downlink/uplink transmission are the same or different (e.g., base stations 510 and 515 of wireless network environment 500). A problem of failing to accurately reflect the state of the channel may also occur in response to the terminal determining the uplink precoder according to the received downlink reference signal.

In the following, in order to solve the aforementioned problems, precoder determination and uplink/downlink transmission procedures considering uplink beams and downlink beams are described. In particular, indication information for notifying a terminal of a channel state is required, wherein the terminal accurately reflects the channel state. Hereinafter, for convenience of description, the precoder determining operation may be denoted as "reciprocity-based precoding", and uplink/downlink transmission may be denoted as "reciprocity-based uplink/downlink transmission". Fig. 6 to 21 depict uplink transmission methods according to various embodiments of the present disclosure, and fig. 22 to 28 depict downlink transmission methods according to various embodiments of the present disclosure. On the other hand, the present disclosure may assume an environment that satisfies channel reciprocity when beam correspondence is satisfied (e.g., a TDD system).

Reciprocity-based uplink transmission

Fig. 6 illustrates an uplink transmission process according to various embodiments of the present disclosure.

Referring to fig. 6, a base station 510 and a terminal 520 may determine a beam to be used in uplink and/or downlink in step 610. Step 610 may be represented as a beam management process, a beam search process, or a beam training process. For example, the base station 510 may transmit a reference signal to the terminal 520 through each of the plurality of beams and receive feedback information from the terminal 520, thereby determining a downlink transmission beam. The terminal 520 may receive a reference signal from the base station 510 through each of the plurality of beams to determine a downlink receive beam. Here, an operation of transmitting/receiving a reference signal through each of the plurality of beams may be denoted as a beam scanning operation. Similarly, the terminal 520 may transmit a reference signal to the base station 510 through a beam scanning operation and receive feedback information from the base station 510, thereby determining an uplink transmission beam. The base station 510 may receive a reference signal from the terminal 520 through a beam scanning operation to determine an uplink reception beam. Next, fig. 7 to 21 assume a case where a reception beam to be used in uplink and a transmission beam to be used in downlink by the base station 510, and a transmission beam to be used in uplink and a reception beam to be used in downlink by the terminal 520 are determined. In other words, a case where beams to be used for uplink transmission or downlink transmission in each of the base station 510 and the terminal 520 are determined in advance is described.

In step 620, the base station 510 may transmit indication information for reciprocity-based precoding to the terminal 520. The indication information may indicate an operation required for uplink transmission. The required operations may include: a beamforming operation of setting a reception beam for receiving a reference signal, a transmission beamforming operation for data transmission, an operation of measuring a reference signal, an operation of transmitting an uplink reference signal, an operation of setting a codebook, or a digital beamforming operation of calculating a precoder.

In some embodiments, the indication information may include information representing a use of a reference signal transmitted to determine the precoder. The precoder may be a precoder to be applied to uplink transmission from the terminal 520 to the base station 510 (hereinafter, uplink precoder). The reference signal may be a downlink reference signal transmitted from the base station 510 in step 630 described later. The indication information may indicate whether the downlink reference signal is used for downlink transmission, uplink transmission, or all of the downlink transmission and the uplink transmission. Here, as a usage for all downlink transmission and uplink transmission may mean that channel reciprocity is satisfied. Not only the beam on which the base station 510 transmits the reference signal but also the beam on which the terminal 520 receives the reference signal may become different according to the usage of the downlink reference signal.

In some other embodiments, the indication information may include information indicative of a beam to be used for uplink transmission. The beam may be the beam determined in step 610. The terminal 520 may determine the uplink transmission beam or the downlink reception beam determined in step 610 as a beam to be used for uplink transmission according to the indication information.

In some other embodiments, the indication information may include information indicative of a precoding scheme. Here, the precoding scheme may mean a scheme of determining an uplink precoder. The precoding scheme may include a scheme of calculating a precoder by using a reference signal received from the base station 510 (downlink measurement-based scheme), or a scheme of obtaining a precoder according to a Precoding Matrix Indicator (PMI) received from the base station 510 (uplink measurement-based scheme). The precoding scheme may be determined according to satisfaction or non-satisfaction of channel reciprocity between the base station 510 and the terminal 520.

In still other embodiments, the indication information may include information representing the function of the PMI. Here, the PMI function may mean a role (role) of PMI when the base station 510 feeds back the PMI to the terminal 520. The PMI functionality may include the following functions: denotes a function of a precoder to be applied to uplink transmission, or a function for reflecting the influence of uplink interference when a precoder is calculated based on a downlink reference signal.

In some other embodiments, the indication information may include information indicative of an uplink transmission scheme. The uplink transmission scheme may include a codebook-based UL transmission scheme, a non-codebook based UL transmission scheme (codebook-not-based uplink transmission), or a diversity-based UL transmission scheme. Here, the codebook-based uplink transmission scheme means a scheme in which a precoder feeding back a PMI is applied to perform uplink transmission, and the non-codebook-based UL transmission scheme means a scheme in which a precoder is autonomously (not limited to codebook use or non-use) selected and applied to perform uplink transmission at a transmission end. In other words, in the operation scheme, the non-codebook based uplink transmission scheme has a higher degree of freedom than the codebook based uplink transmission scheme.

On the other hand, in some embodiments, the partial information included in the indication information of the foregoing embodiments may be included together in the indicated information. For example, the indication information may include both information indicating a beam to be used for uplink transmission and information indicating an uplink transmission scheme. Furthermore, in other embodiments, one information (or field) may also indicate some of the aforementioned embodiments at the same time. For example, the at least one specific bit may indicate the use of a reference signal and also indicate the use of an uplink PMI.

Also, in step 620 of fig. 6, it is illustrated that the indication information is transmitted once, but the embodiment is not limited thereto. Each of the indication information including other information may also be transmitted at different timing. For example, the base station 510 may transmit information indicating the PMI function after transmitting information indicating the use of the reference signal.

The indication information may be transmitted from the base station 510 to the terminal 520 through various schemes. In some embodiments, the indication information may be transmitted through Downlink Control Information (DCI). In other embodiments, the indication information may be transmitted via a Media Access Control (MAC) Control Element (CE). In other embodiments, the indication information may also be transmitted by higher layer signaling.

In step 630, base station 510 may transmit a reference signal to terminal 520. Each of the base station 510 and the terminal 520 may perform step 630 through the beam determined in step 610. In some embodiments, base station 510 may transmit the reference signal through the downlink transmission beam determined in step 610. The terminal 520 may receive the reference signal through the downlink reception beam determined in step 610. The reference signal may be used to measure a downlink channel formed through downlink beamforming. In other embodiments, base station 510 may transmit the reference signal by using the uplink receive beam determined in step 610 as the transmit beam. The terminal 520 may receive the reference signal by using the uplink transmission beam determined in step 610 as a reception beam. The reference signal may be used to measure an uplink channel formed by uplink beamforming.

Hereinafter, in the present disclosure, the reference signal may be a reference signal for estimating a channel. For example, the reference signal may be a channel state information-reference signal (CSI-RS). For another example, the reference signal may be a cell-specific reference signal (CRS). For yet another example, the reference signal may be a demodulation-RS (DM-RS). To support non-codebook based precoding in the uplink, the DM-RS may be defined as a separate uplink reference signal. Further, for yet another example, the reference signal may be a Beam Reference Signal (BRS). Further, for yet another example, the reference signal may be a Beam Refinement Reference Signal (BRRS).

Hereinafter, in the present disclosure, a signal transmitted or received using a beam is described by taking a reference signal as an example, but not only the reference signal but also a synchronization signal may be used. For example, the synchronization signal may include at least one of a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), an Extended Synchronization Signal (ESS), and an SS block.

In fig. 6, the transmission of the indication information of step 620 is shown to be earlier than the transmission of the reference signal of step 630, but the embodiment is not limited thereto. From the information included in the indication information, the timing of the transmission of the indication information may be determined. For example, in response to the indication information including information about the reference signal transmitted in step 630, step 620 may be performed first, as shown in fig. 6. However, step 630 may also be performed first, in response to the indication information including information on beams to be used for uplink transmission, which is different from that shown in fig. 6.

In step 640, the terminal 520 may determine a precoder to be used for uplink transmission. The terminal 520 may determine the precoder according to a codebook-based precoding scheme, which is determined according to a codebook including the PMI and precoder information received from the base station 510, or identify the precoder according to a non-codebook-based coding scheme, which is calculated according to the PMI or a reference signal.

The terminal 520 may determine the precoder based on information included in the indication information. In some embodiments, terminal 520 may calculate a precoder based on a reference signal received from base station 510. The terminal 520 may measure the received reference signal according to the indication information indication and calculate the precoder based on the measurement result. This is because the base station 510 can determine that the channel reciprocity is or is not satisfied and generate the indication information accordingly. The reference signal is transmitted over the downlink but may be used for uplink precoder determination.

In other embodiments, although not shown in fig. 6, terminal 520 may determine the precoder according to the PMI received from base station 510. The base station 510 may determine whether to determine the precoder indicated by the PMI according to the indication information indication. For example, the terminal 520 may identify a precoder corresponding to an index indicated by a PMI in a codebook included in the terminal 520. For another example, the terminal 520 may also calculate a precoder from a PMI that represents interference of uplink transmissions and a reference signal.

In step 650, the terminal 520 may perform uplink transmission. Terminal 520 may transmit uplink data to base station 510. Terminal 520 may transmit uplink data to base station 510 by applying the precoder determined (or calculated) in step 640 to the data symbols intended for transmission.

According to various embodiments of the present disclosure, a device of a terminal may include at least one processor and at least one transceiver to: receiving indication information from the base station, the indication information being determined according to whether channel reciprocity with the base station is satisfied and being used to control a beamforming operation of the terminal; and receiving a reference signal from a base station; and transmitting uplink data to the base station based on the indication information and the reference signal.

Fig. 6 shows a schematic flow of a reciprocity-based precoding uplink transmission procedure through various embodiments of the present disclosure. Next, fig. 7 to 21 depict a detailed procedure of reciprocity-based precoding in a beamforming communication system.

Reference signals for uplink precoding

Next, in fig. 7 to 9, transmission of reference signals for uplink precoding is supported. Here, the reference signal may be CSI-RS. General reference signals for downlink transmission are supported as such. In addition, transmission of reference signals for uplink precoding may be supported in response to uplink or downlink beams being different (e.g., wireless network environment 500), or in response to a base station coupled to a terminal over an uplink and a base station coupled over a downlink being different (i.e., in response to not satisfying channel reciprocity). Here, in response to the reference signal for uplink precoding being transmitted, in order to satisfy channel reciprocity, the corresponding reference signal may be transmitted by the base station by using an uplink reception beam and may be received by the terminal by using an uplink transmission beam. The uplink reception beam and the uplink transmission beam may be beams determined by a beam search procedure (e.g., step 610 of fig. 6) between the terminal and the base station.

Fig. 7 illustrates an example of determining beams for reference signals for uplink transmission, in accordance with various embodiments of the present disclosure. Fig. 7 shows that the uplink reception beam 731, the uplink transmission beam 732, the downlink transmission beam 741, and the downlink reception beam 742 are each distinguished, but the embodiment is not limited thereto. That is, unlike what is shown in fig. 7, the beam correspondence is satisfied, and thus, an uplink reception beam of the base station 510 may correspond to a downlink transmission beam, and a downlink reception beam of the terminal 520 may also correspond to an uplink transmission beam. Needless to say, the above-described example is applied not only to fig. 7 but also to conceptual diagrams (fig. 10, fig. 13, fig. 16, fig. 19, fig. 23, and fig. 26) of embodiments described later.

Referring to fig. 7, a base station 510 may transmit a reference signal (e.g., CSI-RS) to a terminal 520 through an uplink beam (710). In detail, the base station 510 may use the uplink reception beam 731 as a beam to be used for transmission of a reference signal. This operation means that the base station 510 uses a beam indicated by the same index as the index corresponding to the uplink reception beam 731 as a transmission beam. Here, it is assumed that the uplink reception beam 731 and the uplink transmission beam 732 are predetermined by the base station 510 and the terminal 520 through a beam management process.

Although not shown in fig. 7, it is needless to say that the reference signal for downlink transmission may be transmitted through a downlink beam (e.g., beam 741 or beam 742). Further, when the reference signal is available for all uplinks and downlinks, such as when channel reciprocity is satisfied, the reference signal may be transmitted through either a downlink beam or an uplink beam.

The base station 510 may determine through which beam the reference signal is transmitted. On the other hand, the terminal 520 may receive separate indication information in order to determine whether the reference signal to be received is transmitted using the uplink reception beam 731 or through the downlink transmission beam 741. This is because the beams to be used for uplink transmission may become different depending on which beam the reference signal is transmitted through. Base station 510 may transmit indication information to terminal 520. In detail, according to the procedure illustrated in fig. 8, the base station 510 may determine a beam on which a reference signal for uplink transmission will be transmitted. Fig. 8 illustrates an operational flow of a base station 510 for determining beams of reference signals for uplink transmission, in accordance with various embodiments of the present disclosure.

In step 810, base station 510 may determine whether uplink beams (e.g., beam 731 and beam 732) and downlink beams (e.g., beam 741 and beam 742) are the same as each other and whether a base station coupled to terminal 520 via uplink and a base station coupled via downlink are the same as each other. Hereinafter, for convenience of description, whether an uplink beam and a downlink beam are identical to each other is represented as a first condition of reciprocity-based precoding, and whether a base station coupled through an uplink and a base station coupled through a downlink are identical to each other is represented as a second condition of reciprocity-based precoding.

Base station 510 may determine whether a first condition is satisfied. The base station 510 may determine whether the uplink reception beam and the downlink transmission beam of the base station 510 are identical to each other and the uplink transmission beam and the downlink reception beam of the terminal 520 are identical to each other. In response to both base station 510 and terminal 520 satisfying the beam correspondence, base station 510 may determine that a first condition is satisfied.

Base station 510 may determine whether the second condition is satisfied. Base station 510 may determine whether the base station coupled for the downlink with terminal 520 and the base station coupled for the uplink with terminal 520 are the same. For example, base station 510 may determine whether both uplink and downlink are coupled with terminal 520. When base station 510 and terminal 520 are in an RRC connected state for downlink transmissions, but the base station coupled for uplink transmissions for terminal 520 is base station 515 rather than base station 510, base station 510 may determine that the second condition is not satisfied.

In response to all of the first and second conditions being met, the base station 510 may perform step 820. However, in response to even one of the first condition or the second condition not being satisfied, the base station 510 may perform step 840. In the present disclosure, the first condition and the second condition are described for convenience of description, but satisfaction or non-satisfaction of the first condition and the second condition means satisfaction or non-satisfaction of channel reciprocity. That is, in response to the base station 510 determining that channel reciprocity is satisfied, the base station 510 may perform step 820, otherwise the base station 510 may perform step 840.

In step 820, base station 510 can transmit indication information to terminal 520. The indication information may indicate that the measurement results of the transmitted reference signals are available for all uplink and downlink transmissions. This is because all of the first and second conditions are satisfied and thus channel reciprocity (and beam correspondence) can be used.

In step 830, the base station 510 may transmit a reference signal to the terminal 520 through a downlink transmission beam. In response to step 830 performed after step 820, the beam correspondence is satisfied, and thus the index of the downlink transmission beam and the index of the uplink reception beam may be identical to each other.

In step 840, the base station 510 may determine whether the reference signal is for downlink transmission. In response to the need for downlink transmission, base station 510 may determine the reference signal as a purpose for downlink transmission and perform step 850. Conversely, in response to a need for uplink transmission, the base station 510 may determine the reference signal as a use for uplink transmission and perform step 860.

In step 850, base station 510 may transmit indication information to terminal 520. The indication information may indicate a use for downlink transmission.

In step 860, the base station 510 may transmit indication information to the terminal 520. The indication information may indicate a use for uplink transmission.

In step 870, base station 510 may transmit a reference signal to terminal 520 by using uplink receive beam 731. The base station 510 may transmit a reference signal to the terminal 520 by using a beam having the same index as the uplink reception beam 731 as a transmission beam.

As described above, the base station 510 may transmit indication information to the terminal 520 in step 820, step 850, and step 860. Here, the indication information may be configured in various schemes. The terminal 520 may obtain the use of the reference signal in various schemes according to the structure of the indication information. In detail, the terminal 520 may obtain through which beam the reference signal is transmitted based on signaling (embodiment 1) or a predetermined pattern (embodiment 2) of the base station 510.