HK40001603B - Uplink transmission/reception method in wireless communication system and device therefor - Google Patents

Description

Uplink transmission/reception method and apparatus in wireless communication system

Technical Field

The present invention relates to a wireless communication system, and more particularly, to a method for uplink Multiple Input Multiple Output (MIMO) transmission and an apparatus supporting the same.

Background Art

Mobile communication systems have evolved to provide voice services while ensuring user mobility. However, their service coverage has expanded to include data services as well as voice services. Today, the explosive growth of services has led to resource shortages and user demand for high-speed services, necessitating the need for more advanced mobile communication systems.

The requirements for next-generation mobile communication systems may include supporting huge data traffic, a significant increase in the transmission rate per user, accommodating a significantly increased number of connected devices, very low end-to-end latency, and high energy efficiency. To this end, various technologies have been studied, such as small cell enhancement, dual connectivity, massive multiple-input multiple-output (MIMO), in-band full-duplex, non-orthogonal multiple access (NOMA), support for ultra-wideband, and device networking.

Summary of the Invention

Technical issues

The object of the present invention is to propose a method for uplink Multiple Input Multiple Output (MIMO) transmission.

In addition, an object of the present invention is to propose a method for configuring downlink control information (DCI) for multiple-input multiple-output (MIMO) transmission.

Another object of the present invention is to propose a method for transmitting an uplink reference signal serving as a basis for uplink multiple-input multiple-output (MIMO) transmission and a control method thereof.

The technical objectives to be achieved by the present invention are not limited to the aforementioned technical purposes, and a person skilled in the art in the art to which the present invention pertains can obviously understand other technical purposes not described above from the following description.

Technical Solution

In one aspect of the present invention, a method for performing uplink transmission by a user equipment (UE) in a wireless communication system may include: receiving downlink control information (DCI) including a sounding reference signal (SRS) resource indication (SRI) and a precoding indication from a base station; and sending an uplink to the base station by applying precoding indicated by the precoding indication on the antenna port of the SRS transmitted in the SRS resource selected by the SRI.

In another aspect of the present invention, a user equipment (UE) performing uplink transmission in a wireless communication system may include: a radio frequency (RF) unit for sending and receiving radio signals; and a processor that controls the RF unit, and the processor may be configured to: receive downlink control information (DCI) including a sounding reference signal (SRS) resource indication (SRI) and a precoding indication from a base station, and send an uplink to the base station by applying the precoding indicated by the precoding indication on the antenna port of the SRS transmitted in the SRS resource selected by the SRI.

Preferably, the method may further include: transmitting, to the base station, a precoded SRS for each of the one or more SRS resources configured for the UE.

Preferably, the beamforming vector and/or beamforming coefficient applied to transmit the precoded SRS may be configured by the base station through control channel signaling or arbitrarily determined by the UE.

Preferably, the beamforming vector and/or beamforming coefficient applied to the precoded SRS transmission in the SRS resource may be determined based on the beamforming vector and/or beamforming coefficient used to receive a downlink reference signal (DL RS).

Preferably, the DL RS may be a channel state information reference signal (CSI-RS), and the base station may indicate a CSI-RS resource for determining a beamforming vector and/or beamforming coefficient applied to precoded SRS transmission.

Preferably, an independent beamforming vector and/or beamforming coefficient is applied to each subband used for precoded SRS transmission in the SRS resource.

Preferably, the beamforming vector and/or beamforming coefficient applied to the precoded SRS transmission of each subband may be determined based on the beamforming vector and/or beamforming coefficient used to receive a downlink reference signal (DL RS).

Preferably, the DL RS may be a channel state information reference signal (CSI-RS), and the base station may indicate a CSI-RS resource for determining a beamforming vector and/or beamforming coefficient applied to precoded SRS transmission.

Preferably, the DCI may also include a rank indication for uplink transmission.

Preferably, the number of ranks used for uplink transmission may be determined as the number of antenna ports of SRS transmitted in the SRS resources selected by the SRI.

Preferably, the precoding indicator may be divided into a first precoding indicator and a second precoding indicator, and the second precoding indicator may be jointly encoded together with uplink resource allocation information scheduled to the UE.

Beneficial effects

According to an embodiment of the present invention, frequency selective optimized precoding can even be supported in the uplink.

In addition, according to the embodiments of the present invention, uplink transmission throughput can be enhanced by applying optimized precoding for each uplink subband (resource block group).

In addition, according to the embodiments of the present invention, it is possible to minimize the overhead of downlink control information related to an uplink to which uplink subband (resource block group) precoding is applied.

Effects obtainable by the present invention are not limited to the above-described effects, and other effects not described above may be apparently understood from the following description by those having ordinary skill in the art to which the present invention pertains.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included as part of the specification to help understand the present invention, provide embodiments of the present invention, and describe the technical features of the present invention with the help of the following description.

FIG1 illustrates the structure of a radio frame in a wireless communication system to which the present invention can be applied.

FIG2 is a diagram illustrating a resource grid for a downlink slot in a wireless communication system to which the present invention can be applied.

FIG3 illustrates the structure of a downlink subframe in a wireless communication system to which the present invention may be applied.

FIG4 illustrates a structure of an uplink subframe in a wireless communication system to which the present invention is applicable.

FIG5 shows the configuration of a known MIMO communication system.

FIG6 is a diagram illustrating channels from multiple transmit antennas to a single receive antenna.

FIG7 illustrates reference signal patterns mapped to downlink resource block pairs in a wireless communication system to which the present invention may be applied.

FIG8 is a diagram illustrating resources to which reference signals are mapped in a wireless communication system to which the present invention can be applied.

FIG9 illustrates an uplink subframe including a sounding reference signal symbol in a wireless communication system to which the present invention may be applied.

FIG10 is a diagram illustrating a self-contained subframe structure in a wireless communication system to which the present invention may be applied.

FIG11 illustrates a transceiver unit model in a wireless communication system to which the present invention can be applied.

FIG. 12 is a diagram illustrating a service area of each transceiver unit in a wireless communication system to which the present invention can be applied.

FIG13 is a diagram illustrating a method for transmitting and receiving uplink according to an embodiment of the present invention.

FIG14 is a block diagram of a wireless communication apparatus according to an embodiment of the present invention.

DETAILED DESCRIPTION

Some embodiments of the present invention are described in detail with reference to the accompanying drawings. The detailed description to be disclosed in conjunction with the accompanying drawings is intended to describe some embodiments of the present invention and is not intended to describe the only embodiment of the present invention. The following detailed description includes further details to provide a complete understanding of the present invention. However, those skilled in the art will understand that the present invention can be practiced without such further details.

In some cases, in order to avoid obscuring the concept of the present invention, known structures and devices may be omitted or may be shown in a block diagram format based on the core functions of each structure and device.

In this specification, a base station has the meaning of a terminal node of a network that communicates directly with a device through its base station. In this document, specific operations described as being performed by a base station may be performed by an upper node of the base station according to the circumstances. That is, it is obvious that in a network consisting of multiple network nodes including a base station, various operations performed for communication with a device may be performed by a base station or other network nodes other than the base station. Base station (BS) may be replaced by another term such as a fixed station, Node B, eNB (evolved Node B), base transceiver system (BTS), access point (AP), g-NodeB (gNB), new RAT (NR) or 5G-NodeB. In addition, a device may be fixed or may have mobility and may be replaced by other terms such as user equipment (UE), mobile station (MS), user terminal (UT), mobile subscriber station (MSS), subscriber station (SS), advanced mobile station (AMS), wireless terminal (WT), machine type communication (MTC) device, machine to machine (M2M) device or device to device (D2D) device.

Hereinafter, downlink (DL) refers to communication from an eNB to a UE, and uplink (UL) refers to communication from a UE to an eNB. In the DL, the transmitter may be part of the eNB and the receiver may be part of the UE. In the UL, the transmitter may be part of the UE and the receiver may be part of the eNB.

Specific terms used in the following description have been provided to help understanding of the present invention, and the use of such specific terms may be changed in various forms without departing from the technical spirit of the present invention.

The following technologies can be used in various wireless access systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and non-orthogonal multiple access (NOMA). CDMA can be implemented using radio technologies such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can be implemented using radio technologies such as Global System for Mobile Communications (GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA can be implemented using radio technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, or Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is a part of Evolved UMTS (E-UMTS) that uses Evolved UMTS Terrestrial Radio Access (E-UTRA) and adopts OFDMA in the downlink and SC-FDMA in the uplink. LTE-Advanced (LTE-AA) is an evolution of 3GPP LTE.

The embodiments of the present invention may be supported by standard documents disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, i.e., wireless access systems. In other words, steps or parts that fall within the embodiments of the present invention and are not described to clearly reveal the technical spirit of the present invention may be supported by these documents. Furthermore, all terms disclosed in this document may be described in standard documents.

For a clearer description, 3GPP LTE/LTE-A or new RAT (RAT in a 5G (5th generation) system) is briefly described, but technical characteristics of the present invention are not limited thereto.

General systems to which the present invention can be applied

FIG1 shows a structure of a radio frame in a wireless communication system to which embodiments of the present invention may be applied.

3GPP LTE/LTE-A supports a radio frame structure type 1, which may be applied to frequency division duplex (FDD), and a radio frame structure type 2, which may be applied to time division duplex (TDD).

The size of a radio frame in the time domain is expressed as a multiple of a time unit of T_s = 1/(15000*2048). UL and DL transmissions comprise a radio frame of duration T_f = 307200*T_s = 10 ms.

1( a ) illustrates a radio frame structure type 1. The type 1 radio frame may be applied to both full-duplex FDD and half-duplex FDD.

A radio frame consists of 10 subframes. A radio frame consists of 20 time slots of length T_slot = 15360 * T_s = 0.5 ms, and each time slot is indexed from 0 to 19. A subframe consists of two consecutive time slots in the time domain, and subframe i consists of time slot 2i and time slot 2i+1. The time required to transmit a subframe is called a transmission time interval (TTI). For example, the length of subframe i can be 1 ms, and the length of a time slot can be 0.5 ms.

In FDD, UL and DL transmissions are separated in the frequency domain. While there is no restriction in full-duplex FDD, a UE cannot transmit and receive simultaneously in half-duplex FDD operation.

A slot includes multiple orthogonal frequency division multiplexing (OFDM) symbols in the time domain and multiple resource blocks (RBs) in the frequency domain. In 3GPP LTE, because OFDMA is used in the downlink, an OFDM symbol is used to represent one symbol period. An OFDM symbol may be referred to as an SC-FDMA symbol or symbol period. An RB is a resource allocation unit and includes multiple consecutive subcarriers in a slot.

FIG1(b) shows a frame structure type 2. ...

A type 2 radio frame includes two half-frames each having a length of 153600*T_s=5 ms, and each half-frame includes five subframes each having a length of 30720*T_s=1 ms.

In the frame structure type 2 of the TDD system, uplink-downlink configuration is a rule indicating whether uplink and downlink are allocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

[Table 1]

Referring to Table 1, in each subframe of a radio frame, 'D' represents a subframe for DL transmission, 'U' represents a subframe for UL transmission, and 'S' represents a special subframe including three types of fields: a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS).

DwPTS is used for initial cell search, synchronization, or channel estimation in the UE. UpPTS is used for channel estimation in the eNB and for synchronizing the UE's UL transmission. GP is the duration used to remove interference that occurs in the UL due to multipath delay of DL signals between the UL and DL.

Each subframe i includes a time slot 2i and a time slot 2i+1 of T_slot=15360*T_s=0.5 ms.

UL-DL configurations may be classified into 7 types, and for each configuration, the positions and/or numbers of DL subframes, special subframes, and UL subframes are different.

The point in time when a change from downlink to uplink is made, or the point in time when a change from uplink to downlink is made, is called a switching point. The periodicity of the switching point means that the cycle in which the uplink subframe and downlink subframe are changed is repeated identically. The periodicity of the switching point supports both 5 ms and 10 ms. If the periodicity of the switching point has a downlink-uplink switching point period of 5 ms, the special subframe S exists in every half-frame. If the periodicity of the switching point has a downlink-uplink switching point period of 5 ms, the special subframe S exists only in the first half-frame.

In all configurations, subframes 0 and 5 and DwPTS are used only for downlink transmission. UpPTS and the subframes following it are always used for uplink transmission.

Such uplink-downlink configurations are known to both the eNB and the UE as system information. Whenever the uplink-downlink configuration information changes, the eNB can notify the UE of the change in the uplink-downlink allocation state of the radio frame by simply sending the UE the index of the uplink-downlink configuration information. Furthermore, the configuration information is a type of downlink control information and can be sent via the Physical Downlink Control Channel (PDCCH) like other scheduling information. The configuration information can be sent as broadcast information to all UEs within a cell via a broadcast channel.

Table 2 shows the configuration of the special subframe (length of DwPTS/GP/UpPTS).

[Table 2]

The structure of the radio frame according to the example of FIG. 1 is just one example, and the number of subcarriers included in the radio frame, the number of slots included in the subframe, and the number of OFDM symbols included in the slot may be changed in various ways.

FIG2 is a diagram illustrating a resource grid of one downlink slot in a wireless communication system to which an embodiment of the present invention may be applied.

2 , one downlink slot includes a plurality of OFDM symbols in the time domain. For exemplary purposes only, it is described herein that one downlink slot includes 7 OFDM symbols and one resource block includes 12 subcarriers in the frequency domain, and the present invention is not limited thereto.

Each element on the resource grid is called a resource element, and one resource block includes 12×7 resource elements.The number N ^DL of resource blocks included in a downlink slot depends on a downlink transmission bandwidth.

The structure of the uplink timeslot may be the same as that of the downlink timeslot.

FIG3 shows a structure of a downlink subframe in a wireless communication system to which an embodiment of the present invention may be applied.

3, up to three OFDM symbols located in the first portion of the subframe's first slot correspond to a control region in which control channels are allocated, and the remaining OFDM symbols correspond to a data region in which a physical downlink shared channel (PDSCH) is allocated. Downlink control channels used in 3GPP LTE include, for example, the Physical Control Format Indicator Channel (PCFICH), the Physical Downlink Control Channel (PDCCH), and the Physical Hybrid ARQ Indicator Channel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe and carries information about the number of OFDM symbols used to transmit control channels in the subframe (i.e., the size of the control region). The PHICH is a response channel for the uplink and carries positive acknowledgement (ACK)/negative acknowledgement (NACK) signals for hybrid automatic repeat request (HARQ). The control information transmitted in the PDCCH is called downlink control information (DCI). DCI includes uplink resource allocation information, downlink resource allocation information, or uplink transmit (Tx) power control commands for a specific UE group.

The PDCCH can carry information on the resource allocation and transmission format of the downlink shared channel (DL-SCH) (also known as "downlink grant"), resource allocation information on the uplink shared channel (UL-SCH) (also known as "uplink grant"), paging information on the PCH, system information on the DL-SCH, resource allocation for upper layer control messages such as random access responses sent on the PDSCH, a set of transmit power control commands for a single UE in a specific UE group, and activation of the Internet Voice Protocol (VoIP), etc. Multiple PDCCHs can be sent within the control region, and the UE can monitor multiple PDCCHs. The PDCCH is sent on a single control channel element (CCE) or an aggregation of some consecutive CCEs. The CCE is a logical allocation unit used to provide a coding rate to the PDCCH according to the state of the radio channel. The CCE corresponds to multiple resource element groups. The format of the PDCCH and the number of available bits of the PDCCH are determined by the association between the number of CCEs and the coding rate provided by the CCEs.

The eNB determines the format of the PDCCH based on the DCI to be sent to the UE and attaches a cyclic redundancy check (CRC) to the control information. Depending on the owner or use of the PDCCH, a unique identifier (radio network temporary identifier (RNTI)) is masked to the CRC. If the PDCCH is a PDCCH for a specific UE, an identifier unique to the UE, for example, a cell-RNTI (C-RNTI) can be masked to the CRC. If the PDCCH is a PDCCH for a paging message, a paging indication identifier, for example, a paging-RNTI (P-RNTI) can be masked to the CRC. If the PDCCH is a PDCCH for system information (more specifically, a system information block (SIB)), a system information identifier, for example, a system information-RNTI (SI-RNTI) can be masked to the CRC. The random access-RNTI (RA-RNTI) can be masked to the CRC to facilitate the indication of a random access response by the UE as a response to the transmission of the random access preamble.

FIG4 shows a structure of an uplink subframe in a wireless communication system to which an embodiment of the present invention may be applied.

Referring to Figure 4, the uplink subframe can be divided into a control region and a data region in the frequency domain. The physical uplink control channel (PUCCH) carrying uplink control information is allocated to the control region. The physical uplink shared channel (PUSCH) carrying user data is allocated to the data region. To maintain the single-carrier characteristic, a UE does not transmit both the PUCCH and the PUSCH simultaneously.

Within a subframe, a resource block (RB) pair is allocated to the PUCCH for one UE. The RBs belonging to the RB pair occupy different subcarriers in each of the two time slots. This is called frequency hopping of the RB pair allocated to the PUCCH at the time slot boundary.

Multiple Input Multiple Output (MIMO)

MIMO technology uses multiple transmit (Tx) and receive (Rx) antennas, rather than the single transmit and receive antennas typically used to date. In other words, MIMO technology uses multiple input/output antennas at the transmit or receive end of a wireless communication system to increase capacity or enhance performance. Hereinafter, MIMO is referred to as "multiple input/output antennas."

More specifically, MIMO antenna technology does not rely on a single antenna path to receive a single overall message, but rather completes the overall data by combining multiple data blocks received via multiple antennas. Therefore, MIMO antenna technology can increase the data transfer rate within a specific system range, and can also increase the system range at a specific data transfer rate.

It is expected that efficient multiple-input/output antenna technology will be used because next-generation mobile communications require higher data transmission rates than existing mobile communications. Under such circumstances, MIMO communication technology is a next-generation mobile communication technology that can be widely used in mobile communication terminals and relay nodes, and has attracted public attention as a technology that can overcome the limitations of mobile communication transmission rates caused by the expansion of data communications.

Meanwhile, multiple input/output (MIMO) technology, among various transmission efficiency improvement technologies being developed, has attracted widespread attention as a method that can significantly improve communication capacity and transmission/reception performance even without additional frequency allocation or power increase.

FIG5 shows the configuration of a known MIMO communication system.

Referring to Figure 5, if the number of transmit (Tx) antennas is increased to N_T and the number of receive (Rx) antennas is simultaneously increased to N_R, then, unlike the case where multiple antennas are used only in the transmitter or receiver, the theoretical channel transmission capacity increases in proportion to the number of antennas. Therefore, the transmission rate can be increased and the frequency efficiency can be significantly improved. In this case, the transmission rate according to the increase in channel transmission capacity can theoretically increase the value obtained by multiplying the following rate increment R_i by the maximum transmission rate R_o when using one antenna.

[Equation 1]

R _i = min( _NT , _NR )

That is, for example, in a MIMO communication system using four transmission antennas and four reception antennas, a transfer rate four times higher can theoretically be obtained compared to a single antenna system.

Such multi-input/output antenna technologies can be divided into spatial diversity, which uses symbols that have passed through various channel paths to increase transmission reliability, and spatial multiplexing, which uses multiple transmit antennas to simultaneously transmit multiple data symbols to increase the transmission rate. Furthermore, research is currently underway into combining these two methods to optimally leverage their respective advantages.

Each of these methods will be described in more detail below.

First, spatial diversity methods include space-time block code families and space-time Trelis code families, which utilize both diversity gain and coding gain. Generally, Trelis code families offer superior bit error rate improvement performance and code generation freedom, while space-time block code families offer lower computational complexity. Such spatial diversity gain can correspond to an amount corresponding to the product (N_T × N_R) of the number of transmit antennas (N_T) and the number of receive antennas (N_R).

Secondly, the spatial multiplexing scheme is a method of sending different data streams in the transmitting antenna. In this case, in the receiver, mutual interference occurs between the data sent simultaneously by the transmitter. The receiver removes the interference using an appropriate signal processing scheme and receives the data. The noise removal method used in this case may include a maximum likelihood detection (MLD) receiver, a zero forcing (ZF) receiver, a minimum mean square error (MMSE) receiver, a diagonal Bell Labs layered space-time code (D-BLAST) and a vertical Bell Labs layered space-time code (V-BLAST). In particular, if the transmitting end is able to know the channel information, a singular value decomposition (SVD) method can be used.

Third, there are methods that use a combination of spatial diversity and spatial multiplexing. If only spatial diversity gain is to be obtained, the performance improvement gain due to the increase in diversity difference gradually saturates. If only spatial multiplexing gain is used, the transmission reliability in the radio channel is degraded. Methods for solving this problem and obtaining both gains have been studied and may include dual space-time transmit diversity (dual STTD) methods and space-time bit-interleaved coded modulation (STBICM).

In order to describe the communication method in the multiple-input/output antenna system, as described above, in more detail, the communication method can be expressed as follows via mathematical modeling.

First, as shown in FIG5 , it is assumed that there are N_T transmit antennas and N_R receive antennas.

First, a transmission signal is described below: If there are N_T transmitting antennas as described above, the maximum number of items of information that can be transmitted is N_T, which can be represented using the following vector.

[Equation 2]

Meanwhile, the transmission power may be different in each piece of transmission information s_1, s_2, ..., s_NT. In this case, if the respective transmission powers are P_1, P_2, ..., P_NT, the transmission information with the controlled transmission power may be represented using the following vector.

[Equation 3]

In addition, the transmission information with controlled transmission power in Equation 3 can be expressed as follows using a diagonal matrix P of transmission power.

[Equation 4]

Meanwhile, the information vector with controlled transmit power in Equation 4 is multiplied by the weighting matrix W, thereby forming N_T transmission signals x_1, x_2, ..., x_NT that are actually transmitted. In this case, the weighting matrix is used to appropriately distribute the transmission information to the antennas according to the transmission channel conditions. The following equation can be expressed using the transmission signals x_1, x_2, ..., x_NT.

[Equation 5]

In this case, w_ij represents the weight between the i-th transmit antenna and the j-th transmission information, and W is an expression of the matrix of weights. Such a matrix W is called a weighting matrix or a precoding matrix.

Meanwhile, the transmission signal x such as described above may be considered for use in a case where spatial diversity is used and in a case where spatial multiplexing is used.

If spatial multiplexing is used, all elements of the information vector s have different values because different signals are multiplexed and transmitted. In contrast, if spatial diversity is used, all elements of the information vector s have the same value because the same signal is transmitted through several channel paths.

A method of mixing spatial multiplexing and spatial diversity can be considered. In other words, for example, the same signal can be transmitted through three transmit antennas using spatial diversity, and the remaining different signals can be spatially multiplexed and transmitted.

If there are N_R receiving antennas, the received signals y_1, y_2, ..., y_NR of the respective antennas are expressed using a vector y as follows.

[Equation 6]

Meanwhile, if the channels in a multi-input/output antenna communication system are modeled, the channels can be classified by transmit/receive antenna index. The channel from transmit antenna j through receive antenna i is represented as h_ij. In this case, it should be noted that in the order of the index of h_ij, the index of the receive antenna appears first, and the index of the transmit antenna appears later.

Several channels can be grouped and expressed in vector and matrix form. For example, the vector expression is described below.

FIG6 is a diagram illustrating channels from multiple transmit antennas to a single receive antenna.

As shown in FIG6 , the channel from a total of N_T transmitting antennas to receiving antenna i can be represented as follows.

[Equation 7]

Furthermore, if all channels from N_T transmit antennas to N_R receive antennas are expressed by a matrix, such as Equation 7, they can be expressed as follows.

[Equation 8]

Meanwhile, additive white Gaussian noise (AWGN) is added to the actual channel after the actual channel undergoes the channel matrix H. Therefore, AWGN n_1, n_2, ..., n_NR respectively added to N_R receiving antennas are expressed as follows using vectors.

[Equation 9]

A transmission signal, a reception signal, a channel, and AWGN in a multiple-input/output antenna communication system can be expressed as having the following relationship through modeling of the transmission signal, reception signal, channel, and AWGN such as described above.

[Equation 10]

Meanwhile, the number of rows and columns of the channel matrix H, which indicates the state of the channel, is determined by the number of transmit/receive antennas. In the channel matrix H, as described above, the number of rows becomes equal to the number of receive antennas N_R, and the number of columns becomes equal to the number of transmit antennas N_T. That is, the channel matrix H becomes an N_R×N_T matrix.

Typically, the rank of a matrix is defined as the minimum number of independent rows or columns. Therefore, the rank of a matrix is no greater than the number of rows or columns. In terms of representation, for example, the rank of the channel matrix H is limited as follows.

[Equation 11]

rank(H)≤min( _NT , _NR )

Furthermore, if the matrix undergoes eigenvalue decomposition, the rank can be defined as the number of eigenvalues that belong to the eigenvalue and are not 0. Similarly, if the rank undergoes singular value decomposition (SVD), it can be defined as the number of singular values other than 0. Therefore, the physical meaning of the rank in the channel matrix can be said to be the maximum number of different information that can be transmitted in a given channel.

In this specification, the term "rank" used for MIMO transmission refers to the number of paths through which signals can be independently transmitted at a specific time point and on specific frequency resources. The term "number of layers" refers to the number of signal streams transmitted through each path. Generally, unless otherwise specified, the term "rank" has the same meaning as the number of layers, as the transmitting end transmits the number of layers corresponding to the number of ranks used in signal transmission.

Reference Signal (RS)

In wireless communication systems, because data is transmitted over a radio channel, signals may be distorted during transmission. In order for the receiving end to accurately receive distorted signals, it is necessary to use channel information to correct the distortion of the received signal. To detect channel information, a method is typically used that utilizes the degree of distortion of the signal transmission method when transmitting a signal known to both the transmitting and receiving sides over a channel, as well as a signal known to both the transmitting and receiving sides. This signal is called a pilot signal or reference signal (RS).

Furthermore, most mobile communication systems recently use methods that improve data transmission and reception efficiency by employing multiple transmit and receive antennas, rather than the single transmit and receive antennas typically used. When using multiple input and output antennas to transmit and receive data, it is necessary to monitor the channel conditions between the transmit and receive antennas in order to accurately receive signals. Therefore, each transmit antenna must have a separate reference signal.

In a mobile communication system, RSs can be basically divided into two types according to their purpose. There are RSs with the purpose of obtaining channel state information and RSs for data demodulation. The former has the purpose of obtaining channel state information in the downlink by the UE. Therefore, the corresponding RS must be sent in a wideband, and the UE must be able to receive and measure the RS, although the UE does not receive downlink data in a specific subframe. In addition, the former is also used for radio resource management (RRM) measurements such as handover. The latter is an RS sent together with the corresponding resources when the eNB sends a downlink. The UE can perform channel estimation by receiving the corresponding RS and can therefore demodulate the data. The corresponding RS must be sent in the area where the data is transmitted.

The downlink RS includes a common RS (CRS) for acquiring and measuring information about channel states shared by all UEs in a cell (such as handover) and a dedicated RS (DRS) for data demodulation only for a specific UE. Such RSs can be used to provide information for demodulation and channel measurement. In other words, the DRS is only used for data demodulation, while the CRS is used for both channel information acquisition and data demodulation.

The receiving side (i.e., the UE) measures the channel state based on the CRS and feeds back indicators related to the channel quality, such as the channel quality indicator (CQI), precoding matrix index (PMI), and/or rank indicator (RI), to the transmitting side (i.e., the eNB). CRS is also called cell-specific RS. In contrast, a reference signal related to the feedback of channel state information (CSI) can be defined as CSI-RS.

If the data on the PDSCH needs to be demodulated, a DRS can be sent through a resource element. The UE can receive information about whether a DRS exists through a higher layer, and the DRS is only valid when the corresponding PDSCH has been mapped. DRS can also be called UE-specific RS or demodulation RS (DMRS).

FIG7 illustrates a reference signal pattern mapped to a downlink resource block pair in a wireless communication system to which the present invention can be applied.

7 , a downlink resource block pair (i.e., a unit mapped with a reference signal) can be represented in the form of one subframe in the time domain × 12 subcarriers in the frequency domain. That is, on the time axis (x-axis), one resource block pair has a length of 14 OFDM symbols in the case of a normal cyclic prefix (CP) ( FIG. 7 a), and has a length of 12 OFDM symbols in the case of an extended cyclic prefix (CP) ( FIG. 7 b). In the resource block grid, the resource elements (REs) indicated by “0,” “1,” “2,” and “3” respectively mean the positions of the CRSs of the antenna port indices “0,” “1,” “2,” and “3,” and the RE indicated by “D” means the position of the DRS.

The CRS is described in more detail below. CRS is a reference signal used to estimate the channel of the physical antenna and can be received by all UEs located in the cell. CRS is allocated to the full frequency bandwidth. In other words, CRS is a cell-specific signal and is transmitted every subframe in the broadband. In addition, CRS can be used to obtain channel quality information (CSI) and data demodulation.

CRS is defined in various formats according to the antenna array on the transmitting side (eNB). In the 3GPP LTE system (e.g., Release 8), RSs for up to four antenna ports are transmitted according to the number of transmit antennas of the eNB. The side that transmits the downlink signal has three types of antenna arrays, such as a single transmit antenna, two transmit antennas, and four transmit antennas. For example, if the number of transmit antennas of the eNB is two, CRSs for antenna ports 0 and 1 are transmitted. If the number of transmit antennas of the eNB is four, CRSs for antenna ports 0 to 3 are transmitted. If the number of transmit antennas of the eNB is four, the CRS pattern in one RB is shown in FIG7 .

If the eNB uses a single transmit antenna, the reference signal for the single antenna port is arranged.

If the eNB uses two transmit antennas, the reference signals for the two transmit antenna ports are arranged using a time division multiplexing (TDM) scheme and/or a frequency division multiplexing (FDM) scheme. That is, to distinguish the reference signals for the two antenna ports, different time resources and/or different frequency resources are allocated.

In addition, if the eNB uses four transmit antennas, the reference signals for the four transmit antenna ports are arranged using a TDM and/or FDM scheme. The channel information measured by the receiving side of the downlink signal (i.e., the UE) can be used to demodulate data sent using transmission schemes such as single transmit antenna transmission, transmit diversity, closed-loop spatial multiplexing, open-loop spatial multiplexing, or multi-user multiple input/output (MIMO) antennas.

If multiple-input multiple-output antennas are supported, when RSs are transmitted through a specific antenna port, the RSs are transmitted in the positions of resource elements specified according to the RS pattern, and not in the positions of resource elements specified for other antenna ports. In other words, RSs between different antennas do not overlap.

The DRS is described in more detail below. The DRS is used to demodulate data. In multiple-input multiple-output antenna transmission, when a UE receives the RS, the precoding weights for the specific UE are combined with the transmission channel sent by each transmit antenna and used to estimate the corresponding channel without any changes.

The 3GPP LTE system (eg, Release 8) supports a maximum of four transmit antennas and defines a DRS for rank 1 beamforming. The DRS for rank 1 beamforming also indicates an RS for antenna port index 5.

In the LTE-A system (i.e., an advanced and developed form of the LTE system), it is necessary to design the eNB to support up to eight transmit antennas in the downlink. Therefore, RSs for up to eight transmit antennas must also be supported. In the LTE system, downlink RSs are defined only for up to four antenna ports. Therefore, if the eNB has four to a maximum of eight downlink transmit antennas in the LTE-A system, RSs for these antenna ports must be additionally defined and designed. Regarding the RSs for up to eight transmit antenna ports, the aforementioned RSs for channel measurement and the aforementioned RSs for data demodulation must be designed.

An important factor that must be considered when designing LTE-A systems is backward compatibility. This means that LTE UEs must operate well even in LTE-A systems, which the system must support. From the perspective of RS transmission, in the time-frequency domain, where the CRS defined in LTE is transmitted across the full frequency band every subframe, RSs for up to eight transmit antenna ports must also be defined. In LTE-A systems, if the same method as existing LTE CRS is used to add RS patterns for up to eight transmit antennas across the full frequency band every subframe, RS overhead would increase excessively.

Therefore, the RS redesigned in the LTE-A system is basically divided into two types, which include an RS with a channel measurement purpose for selecting MCS or PMI (Channel State Information-RS or Channel State Indication-RS (CSI-RS)) and an RS for demodulation of data transmitted through eight transmit antennas (Data Demodulation-RS (DM-RS)).

The characteristic of the CSI-RS for channel measurement is that, unlike the existing CRS used for measurement (such as channel measurement and handover) and for data demodulation, it is designed to focus on the purpose of channel measurement. In addition, the CSI-RS can also be used for measurement purposes such as handover. Unlike the CRS, it is not necessary to transmit the CSI-RS every subframe because it is transmitted for the purpose of obtaining information about the channel state. In order to reduce the overhead of the CSI-RS, the CSI-RS is transmitted intermittently on the time axis.

For data demodulation, DM-RS is transmitted exclusively to the UE scheduled in the corresponding time-frequency domain. That is, the DM-RS for a specific UE is transmitted only in the area where the corresponding UE is scheduled (i.e., in the time-frequency domain where data is received).

In the LTE-A system, a maximum of eight transmit antennas are supported in the downlink of the eNB. In the LTE-A system, if the RS for up to eight transmit antennas is transmitted in the full band per subframe using the same method as the CRS in the existing LTE, the RS overhead will increase excessively. Therefore, in the LTE-A system, the RS has been divided into CSI-RS for CSI measurement purposes for selecting MCS or PMI and DM-RS for data demodulation, and thus two RSs have been added. CSI-RS can also be used for purposes such as RRM measurement, but has been designed for the main purpose of obtaining CSI. There is no need to transmit CSI-RS in every subframe because it is not used for data demodulation. Therefore, in order to reduce the overhead of CSI-RS, CSI-RS is transmitted intermittently on the time axis. That is, CSI-RS has a period corresponding to an integer multiple of one subframe and can be transmitted periodically or in a specific transmission pattern. In this case, the period or pattern of transmitting CSI-RS can be set by the eNB.

For data demodulation, the DM-RS is transmitted exclusively to the UE scheduled in the corresponding time-frequency domain. That is, the DM-RS for a specific UE is transmitted only in the area where the scheduling is performed for the corresponding UE (i.e., only in the time-frequency domain where data is received).

In order to measure CSI-RS, the UE must know information about the CSI-RS transmission subframe index, the time-frequency position of the CSI-RS resource element (RE) within the transmission subframe, and the CSI-RS sequence for each CSI-RS antenna port of the cell to which the UE belongs.

In the LTE-A system, the eNB must transmit CSI-RS for each of up to eight antenna ports. The resources used for CSI-RS transmission for different antenna ports must be orthogonal. When an eNB transmits CSI-RS for different antenna ports, it can allocate resources orthogonally using an FDM/TDM scheme by mapping the CSI-RS for each antenna port to different REs. Alternatively, the CSI-RS for different antenna ports can be transmitted using a CDM scheme that maps the CSI-RS to orthogonal codes.

When an eNB notifies a UE belonging to the eNB of CSI-RS information, it must first inform the UE of the time-frequency information to which the CSI-RS for each antenna port is mapped. Specifically, this information includes the subframe number or period for transmitting the CSI-RS, the subframe offset for transmitting the CSI-RS, the OFDM symbol number of the RE transmitting the CSI-RS for a specific antenna, the frequency spacing, and the offset or shift value of the RE on the frequency axis.

The CSI-RS is transmitted through one, two, four or eight antenna ports. The antenna ports used in this case are p=15, p=15, 16, p=15, ..., 18 and p=15, ..., 22, respectively. The CSI-RS can be defined for a subcarrier spacing Δf=15 kHz.

In a subframe configured for CSI-RS transmission, the CSI-RS sequence is mapped to a complex-valued modulation symbol a_k,l^(p) used as a reference symbol on each antenna port p as in Equation 12.

[Equation 12]

l″＝0，1

In Equation 12, the conditions of (k', l') (where k' is the subcarrier index within the resource block and l' indicates the OFDM symbol index within the time slot) and n_s are determined according to the CSI-RS configuration, such as Table 3 or Table 4.

Table 3 illustrates mapping of (k', l') from CSI-RS configuration in normal CP.

[Table 3]

Table 4 illustrates mapping of (k', l') from CSI-RS configuration in extended CP.

[Table 4]

Referring to Tables 3 and 4, in the transmission of CSI-RS, in order to reduce inter-cell interference (ICI) in a multi-cell environment including a heterogeneous network (HetNet) environment, up to 32 different configurations (in the case of normal CP) or up to 28 different configurations (in the case of extended CP) are defined.

The CSI-RS configuration varies depending on the number of antenna ports and the CP within a cell, and adjacent cells may have the most different configurations. In addition, the CSI-RS configuration can be divided into the case where it is applied to both FDD and TDD frames and the case where it is applied to only TDD frames according to the frame structure.

(k', l') and n_s are determined according to the CSI-RS configuration based on Table 3 and Table 4, and the time-frequency resources used for CSI-RS transmission are determined according to each CSI-RS antenna port.

FIG8 is a diagram illustrating resources to which reference signals are mapped in a wireless communication system to which the present invention can be applied.

Figure 8(a) shows twenty types of CSI-RS configurations that can be used for CSI-RS transmission by one or two CSI-RS antenna ports, Figure 8(b) shows ten types of CSI-RS configurations that can be used for four CSI-RS antenna ports, and Figure 8(c) shows five types of CSI-RS configurations that can be used for eight CSI-RS antenna ports.

As described above, the radio resources (ie, RE pairs) for transmitting the CSI-RS are determined according to each CSI-RS configuration.

If one or two antenna ports are configured for CSI-RS transmission for a specific cell, the CSI-RS is transmitted on radio resources of the configured CSI-RS configuration among the twenty types of CSI-RS configurations shown in FIG. 8( a ).

Similarly, when four antenna ports are configured for CSI-RS transmission for a specific cell, the CSI-RS is transmitted on radio resources configured with the CSI-RS configurations of the ten types of CSI-RS configurations shown in FIG8(b). In addition, when eight antenna ports are configured for CSI-RS transmission for a specific cell, the CSI-RS is transmitted on radio resources configured with the CSI-RS configurations of the five types of CSI-RS configurations shown in FIG8(c).

The CSI-RS for each antenna port is CDMed and transmitted on the same radio resource for every two antenna ports (i.e., {15, 16}, {17, 18}, {19, 20}, and {21, 22}). For example, in the case of antenna ports 15 and 16, the CSI-RS replica symbols for the corresponding antenna ports 15 and 16 are the same, but are multiplied by different types of orthogonal codes (e.g., Walsh codes) and mapped to the same radio resource. The replica symbol of the CSI-RS for antenna port 15 is multiplied by [1, 1], and the replica symbol of the CSI-RS for antenna port 16 is multiplied by [1-1] and mapped to the same radio resource. The same is true for antenna ports {17, 18}, {19, 20}, and {21, 22}.

The UE can detect the CSI-RS for a specific antenna port by multiplying the transmitted symbol by the code by which it has been multiplied. That is, to detect the CSI-RS for antenna port 15, the transmitted symbol is multiplied by the multiplied code [1 1], and to detect the CSI-RS for antenna port 16, the transmitted symbol is multiplied by the multiplied code [1-1].

8(a) to 8(c), for the same CSI-RS configuration index, radio resources for a CSI-RS configuration with a large number of antenna ports include radio resources for a small number of CSI-RS antenna ports. For example, in the case of CSI-RS configuration 0, radio resources for eight antenna ports include radio resources for four antenna ports and radio resources for one or two antenna ports.

Multiple CSI-RS configurations can be used in one cell. 0 or one CSI-RS configuration can be used for non-zero power (NZP) CSI-RS, and 0 or more CSI-RS configurations can be used for zero power (ZP) CSI-RS.

For each bit set to 1 in the zero power (ZP) CSI-RS ("ZeroPowerCSI-RS"), which is a 16-bit bitmap configured by higher layers, the UE assumes zero transmit power in the REs corresponding to the four CSI-RS columns of Tables 3 and 4 (except when the REs overlap with REs assuming NZP CSI-RS configured by higher layers). The most significant bit (MSB) corresponds to the lowest CSI-RS configuration index, and the next bit in the bitmap corresponds sequentially to the next CSI-RS configuration index.

The CSI-RS is transmitted only in downlink slots satisfying the conditions of (n_s mod 2) in Tables 3 and 4 and subframes satisfying the CSI-RS subframe configuration.

In the case of frame structure type 2 (TDD), CSI-RS is not transmitted in special subframes, synchronization signals (SS), subframes that conflict with PBCH or System Information Block Type 1 (SIB1) message transmissions, or subframes configured for paging message transmissions.

In addition, the RS for transmitting the CSI-RS for any antenna port belonging to the antenna port set S (S = {15}, S = {15, 16}, S = {17, 18}, S = {19, 20} or S = {21, 22}) is not used for PDSCH transmission or CSI-RS transmission for another antenna port.

The time-frequency resources used for CSI-RS transmission cannot be used for data transmission. Therefore, data throughput decreases as CSI-RS overhead increases. Taking this into account, the CSI-RS is not configured to be transmitted every subframe, but rather to be transmitted in each transmission period corresponding to multiple subframes. In this case, the CSI-RS transmission overhead can be significantly reduced compared to the case where the CSI-RS is transmitted every subframe.

Table 5 shows a subframe period (hereinafter referred to as a 'CSI transmission period') T_CSI-RS and a subframe offset Δ_CSI-RS for CSI-RS transmission.

Table 5 illustrates the CSI-RS subframe configuration.

[Table 5]

Referring to Table 5, the CSI-RS transmission period T_CSI-RS and the subframe offset Δ_CSI-RS are determined according to the CSI-RS subframe configuration I_CSI-RS.

The CSI-RS subframe configuration of Table 5 may be configured as one of the aforementioned 'SubframeConfig' field and the 'zeroTxPowerSubframeConfig' field. The CSI-RS subframe configuration may be configured separately for the NZP CSI-RS and the ZP CSI-RS.

A subframe including a CSI-RS satisfies Equation 13.

[Equation 13]

In Equation 13, T_CSI-RS means a CSI-RS transmission period, Δ_CSI-RS means a subframe offset value, n_f means a system frame number, and n_s means a slot number.

If the UE has been configured with transmission mode 9 for the serving cell, one CSI-RS resource configuration may be configured for the UE. If the UE has been configured with transmission mode 10 for the serving cell, one or more CSI-RS resource configurations may be configured for the UE.

In the current LTE standard, the CSI-RS configuration includes the number of antenna ports (antennaPortsCount), the subframe configuration (subframeConfig), and the resource configuration (resourceConfig). Therefore, the CSI-RS configuration provides a notification of how many antenna ports transmit CSI-RS, a notification of the period and offset of the subframe in which the CSI-RS will be transmitted, and a notification of which RE position (i.e., frequency and OFDM symbol index) in the corresponding subframe the CSI-RS is transmitted.

Specifically, the following parameters for each CSI-RS (resource) configuration are configured through higher layer signaling.

- If transmission mode 10 has been configured, configure the CSI-RS resource configuration identifier

- Number of CSI-RS ports (antennaPortsCount): A parameter indicating the number of antenna ports used for CSI-RS transmission (e.g., one CSI-RS port, two CSI-RS ports, four CSI-RS ports, or eight CSI-RS ports)

-CSI-RS configuration (resourceConfig) (see Table 3 and Table 4): Parameters related to the CSI-RS allocation resource location

-CSI-RS subframe configuration (subframeConfig, i.e., I_CSI-RS) (see Table 5): Parameters regarding the period and/or offset of the subframe in which the CSI-RS will be transmitted

- If transmission mode 9 has been configured, configure the transmit power P_C for CSI feedback: Regarding the assumption of the reference PDSCH transmit power used by the UE for feedback, P-C is assumed to be the ratio of the energy per resource element (EPRE) per PDSCH RE to the CSI-RS EPRE when the UE derives CSI feedback and takes values in the range [8,15] dB with a 1-dB step size.

- If transmission mode 10 is configured, configure the transmit power P_C for CSI feedback for each CSI process. If the CSI subframe sets C_CSI,0 and C_CSI,1 are configured by higher layers for the CSI process, configure P_C for each CSI subframe set in the CSI process.

- Pseudo-random sequence generator parameter n_ID

- If transmission mode 10 has been configured, the higher layer parameter "qcl-CRS-Info-r11" including the QCL scrambling identifier (qcl-ScramblingIdentity-r11), CRS port count (crs-PortsCount-r11) and MBSFN subframe configuration list (mbsfn-SubframeConfigList-r11) parameters assumed for quasi-co-located (QCL) type BUE is configured.

When the CSI feedback value derived by the UE has a value in the range of [-8, 15] dB, P_C is assumed to be the ratio of PDSCH EPRE to CSI-RS EPRE. In this case, PDSCH EPRE corresponds to the sign of the ratio of PDSCH EPRE to CRS EPRE being ρ_A.

CSI-RS and PMCH are not configured in the same subframe of the serving cell at the same time.

In frame structure type 2, if four CRS antenna ports have been configured, the CSI-RS configuration index belonging to the [20-31] set (refer to Table 3) in the case of normal CP or the CSI-RS configuration index belonging to the [16-27] set (refer to Table 4) in the case of extended CP is not configured in the UE.

The UE may assume that the CSI-RS antenna port of the CSI-RS resource configuration has a QCL relationship with the delay spread, Doppler spread, Doppler shift, average gain, and average delay.

A UE that has configured transmission mode 10 and QCL type B may assume that antenna ports 0-3 corresponding to the CSI-RS resource configuration and antenna ports 15-22 corresponding to the CSI-RS resource configuration have a QCL relationship with Doppler spread and Doppler shift.

In the case of a UE configured with transmission modes 1-9, one ZP CSI-RS resource configuration may be configured in the UE for the serving cell. In the case of a UE configured with transmission mode 10, one or more ZP CSI-RS resource configurations may be configured in the UE for the serving cell.

The following parameters for ZP CSI-RS resource configuration may be configured through higher layer signaling.

-ZP CSI-RS configuration list (zeroTxPowerResourceConfigList) (see Table 3 and Table 4): Parameters related to zero power CSI-RS configuration

-ZP CSI-RS subframe configuration (eroTxPowerSubframeConfig, i.e., I_CSI-RS) (see Table 5): Parameters regarding the period and/or offset of the subframe in which zero-power CSI-RS is transmitted

The ZP CSI-RS and PMCH are not configured in the same subframe of the serving cell at the same time.

In the case of a UE that has been configured with transmission mode 10, one or more channel state information-interference measurement (CSI-IM) resource configurations may be configured in the UE for the serving cell.

The following parameters for each CSI-IM resource configuration may be configured through higher layer signaling.

-ZP CSI-RS configuration (see Table 3 and Table 4)

-ZP CSI RS subframe configuration I_CSI-RS (see Table 5)

The CSI-IM resource configuration is the same as any of the configured ZP CSI-RS resource configurations.

CSI-IM resources and PMCH are not configured in the same subframe of the serving cell at the same time.

Sounding Reference Signal (SRS)

SRS is mainly used for channel quality measurement to perform uplink frequency selective scheduling and is not related to the transmission of uplink data and/or control information. However, the present invention is not limited to this and SRS can be used for various other purposes to enhance power control or to support various startup functions of recently unscheduled terminals. As examples of startup functions, initial modulation and coding scheme (MCS), initial power control for data transmission, timing advance and frequency semi-selective scheduling can be included. In this case, frequency semi-selective scheduling refers to scheduling in which frequency resources are selectively allocated to the first time slot of a subframe and frequency resources are allocated by pseudo-randomly jumping to another frequency in the second time slot.

In addition, SRS can be used to measure downlink channel quality under the assumption that the radio channel is reciprocal between uplink and downlink. This assumption is particularly valid in time division duplex (TDD) systems, in which uplink and downlink share the same spectrum and are separated in the time domain.

The SRS subframes transmitted by a particular UE in a cell can be indicated by a cell-specific broadcast signal. The 4-bit cell-specific 'srsSubframeConfiguration' parameter indicates an array of 15 available subframes that can be used to transmit SRS in each radio frame. These arrays provide flexibility in adjusting SRS overhead based on deployment scenarios.

The 16th array completely turns off the switch of SRS in the cell, and is mainly suitable for serving cells serving high-speed terminals.

FIG9 illustrates an uplink subframe including a sounding reference signal symbol in a wireless communication system to which the present invention may be applied.

9 , the SRS is continuously transmitted on the last SC-FDMA symbol on the arranged subframe. Therefore, the SRS and the DMRS are located in different SC-FDMA symbols.

PUSCH data transmission is not allowed in specific SC-FDMA symbols used for SRS transmission, and as a result, when sounding overhead is highest, that is, even if SRS symbols are included in all subframes, the sounding overhead does not exceed about 7%.

Each SRS symbol is generated for a given time unit and frequency band using a base sequence (either a random sequence or a Zadoff-Ch (ZC)-based sequence set), and all terminals in the same cell use the same base sequence. In this case, SRS transmissions from multiple UEs in the same cell simultaneously in the same frequency band are orthogonal and distinguishable from each other by different cyclic shifts of the base sequence.

By assigning different base sequences to each cell, SRS sequences from different cells can be distinguished, but the orthogonality between different base sequences is not guaranteed.

As more and more communication devices demand greater communication capacity, there is a need for improved mobile broadband communications compared to existing radio access technologies (RATs). Large-scale machine-type communications (MTC), which connects numerous devices and objects to provide a variety of services anytime and anywhere, is one of the major issues to be considered in next-generation communications. Furthermore, communication system designs that take into account services and users that are sensitive to reliability and latency are under discussion.

The introduction of a next generation radio access technology considering enhanced mobile broadband communication, massive MTC, ultra-reliable and low latency communication (URLLC) is discussed, and in the present invention, for convenience, the technology is referred to as a new RAT.

Self-contained subframe structure

FIG10 is a diagram illustrating a self-contained subframe structure in a wireless communication system to which the present invention may be applied.

In a TDD system, in order to minimize the delay of data transmission, the 5th generation (5G) new RAT considers a self-contained subframe structure as shown in FIG10 .

In Figure 10, the dotted area (symbol index 0) indicates the downlink (DL) control region and the black area (symbol index 13) indicates the uplink (UL) control region. The unmarked area can also be used for DL data transmission or for UL data transmission. This structure is characterized by sequentially performing DL transmission and UL transmission in one subframe, sending DL data in the subframe, and also receiving UL ACK/NACK. As a result, it takes less time to retransmit data when a data transmission error occurs, thereby minimizing the delay of the final data transmission.

In this self-contained subframe structure, a time gap is required between the base station and the UE for the switching process from transmit mode to receive mode or vice versa. To this end, some OFDM symbols when switching from DL to UL in the self-contained subframe structure are allocated to a guard period (GP).

Analog beamforming

In millimeter waves (mmW), the wavelength is shortened, allowing multiple antenna units to be installed in the same area. That is, a total of 64 (8×8) antenna units can be installed in a 2D array with a 1cm wavelength on a 4×4 (4 by 4) cm panel at 0.5λ (i.e., wavelength) intervals in the 30GHz band. Therefore, in mmW, beamforming (BF) gain can be increased by using multiple antenna units to increase coverage or throughput.

In this case, if a transceiver unit (TXRU) is provided so that the transmit power and phase can be adjusted for each antenna unit, independent beamforming is possible for each frequency resource. However, when the TXRU is installed on all 100 antenna units, there is a problem that effectiveness deteriorates in terms of cost. Therefore, a method of mapping multiple antenna units to one TXRU and using an analog phase shifter to adjust the direction of the beam is considered. This analog BF method has a disadvantage that, by forming only one beam direction in all frequency bands, frequency selective BF may not be performed.

As an intermediate form between digital BF and analog BF, a hybrid BF with B TXRUs and fewer than Q antenna elements can be considered. In this case, although there are differences in the connection method between the B TXRUs and the Q antenna elements, the number of directions of beams that can be transmitted simultaneously is limited to B or less.

Hereinafter, a representative example of a connection method of the TXRU and the antenna unit will be described with reference to the accompanying drawings.

FIG. 11 shows a transceiver unit model in a radio communication system to which the present invention is applicable.

The TXRU virtualization model shows the relationship between the TXRU output signal and the antenna unit output signal. Based on the correlation between the antenna unit and the TXRU, the TXRU virtualization model can be divided into TXRU virtualization model option 1 and the subarray partition model as shown in Figure 11(a) and TXRU virtualization model option 2 and the fully connected model as shown in Figure 11(b).

Referring to Figure 11(a), in the case of the subarray partitioning model, the antenna elements are divided into multiple antenna element groups and each TXRU is connected to one of these groups. In this case, the antenna element is connected to only one TXRU.

Referring to Figure 11(b), in the fully connected model, signals from multiple TXRUs are combined and sent to a single antenna unit (or array of antenna units). In other words, the diagram illustrates a scenario where the TXRUs are connected to all antenna units. In this case, the antenna units are connected to all TXRUs.

In Figure 11, q represents the transmitted signal vector for a column of M co-polarized antenna elements. w represents the wideband TXRU virtualization weight vector, and W represents the phase vector multiplied by the analog phase shifter. In other words, the direction of the analog beamforming is determined by W. x represents the signal vector for each of the M_TXRU TXRUs.

In this document, the mapping between antenna ports and TXRUs can be 1-to-1 or 1-to-many.

In Figure 11, the mapping between the TXRU and the antenna unit (TXRU-to-unit mapping) is merely an example, and the present invention is not limited thereto. The present invention can also be similarly applied to the mapping between the TXRU and the antenna unit, and the mapping can be implemented in various other forms in terms of hardware.

Channel State Information (CSI) feedback

In the 3GPP LTE/LTE-A system, a user equipment (UE) is defined to report channel state information (CSI) to a base station (BS or eNB).

CSI refers to information that can indicate the quality of a radio channel (or link) formed between a UE and an antenna port. For example, rank indicator (RI), precoding matrix indicator (PMI), channel quality indicator (CQI), etc. correspond to this information.

Here, RI represents channel rank information, which means the number of streams received by a UE using the same time-frequency resources. Because this value is determined based on long-term channel fading, it is fed back from the UE to the BS at a period that is generally longer than that of PMI and CQI. PMI is a value that reflects the spatial characteristics of the channel and indicates the preferred precoding index selected by the UE based on metrics such as the signal-to-interference-plus-noise ratio (SINR). CQI is a value that indicates the strength of the channel and generally refers to the received SINR that can be obtained when the BS uses PMI.

In 3GPP LTE/LTE-A systems, a base station (BS) configures multiple CSI processes for a UE and can receive CSI for each process. A CSI process consists of a CSI-RS for signal quality measurement from the BS and a CSI-Interference Measurement (CSI-IM) resource for interference measurement.

Reference Signal (RS) Virtualization

In mmW, analog beamforming can be used to transmit the PDSCH in only one analog beam direction at a time. In this case, data transmission from the base station is only possible for a small number of UEs in that direction. Therefore, if necessary, the analog beam direction is configured differently for each antenna port, allowing simultaneous data transmission to multiple UEs in several analog beam directions.

FIG. 12 is a diagram illustrating a service area of each transceiver unit in a wireless communication system to which the present invention can be applied.

In FIG12 , 256 antenna elements are divided into 4 parts to form 4 subarrays, and the structure of connecting the TXRU to the subarrays will be described as an example as shown in FIG11 above.

When each subarray is composed of a total of 64 (8×8) antenna elements in the form of a 2D array, a specific analog beamforming can cover an area corresponding to a 15-degree horizontal angle area and a 15-degree vertical angle area. In other words, the area that the BS should serve is divided into multiple areas and serviced one at a time.

In the following description, it is assumed that the CSI-RS antenna port and the TXRU are mapped 1 to 1. Therefore, the antenna port and the TXRU have the same meaning as in the following description.

As shown in Figure 12(a), if all TXRUs (antenna ports, subarrays) (i.e., TXRUs 0, 1, 2, and 3) have the same analog beamforming direction (i.e., region 1), the throughput of the corresponding region can be increased by forming digital beams with higher resolution. In addition, the throughput of the corresponding region can be increased by increasing the rank of the data transmitted to the corresponding region.

As shown in Figures 12(b) and 12(c), if each TXRU (antenna port, subarray) (i.e., TXRU 0, 1, 2, 3) has a different analog beamforming direction (i.e., area 1 or area 2), data can be simultaneously sent to UEs distributed in a wider area in a subframe (SF).

As an example shown in FIGS. 12( b ) and 12 ( c ), two of four antenna ports are used for PDSCH transmission to UE1 in region 1 , and the remaining two antenna ports are used for PDSCH transmission to UE2 in region 2 .

In particular, in Figure 12(b), PDSCH1 transmitted to UE1 and PDSCH2 transmitted to UE2 represent an example of spatial division multiplexing (SDM). Different from this, as shown in Figure 12(c), PDSCH1 transmitted to UE1 and PDSCH2 transmitted to UE2 may also be transmitted by frequency division multiplexing (FDM).

The preferred method for maximizing cell throughput varies depending on the rank and modulation and coding scheme (MCS) of the UE being served, between using all antenna ports to serve one area and dividing the antenna ports to serve multiple areas simultaneously. Furthermore, the preferred method varies depending on the amount of data to be transmitted to each UE.

The base station calculates the cell throughput or scheduling metric that can be achieved when using all antenna ports to serve one area, and also calculates the cell throughput or scheduling metric that can be achieved when dividing the antenna ports to serve two areas. The base station compares the cell throughput or scheduling metric that can be achieved using each scheme to select the final transmission scheme. As a result, the number of antenna ports participating in PDSCH transmission changes on a SF-by-SF basis. In order for the base station to calculate the PDSCH transmission MCS based on the number of antenna ports and reflect this calculated transmission MCS in the scheduling algorithm, CSI feedback from appropriate UEs is required.

Beam Reference Signal (BRS)

The beam reference signal is transmitted on one or more antenna ports (p={0, 1, ..., 7}).

The reference signal sequence ‘r_1(m)’ can be defined by the following equation 14.

[Equation 14]

Where l = 0, 1, ..., 13 is the OFDM symbol number. represents the maximum downlink frequency band configuration and is expressed by a multiple. represents the size of a resource block in the frequency domain and is expressed by the number of subcarriers.

In Equation 14, c(i) may be predefined as a pseudo-random sequence. A pseudo-random sequence generator may be initialized at the beginning of each OFDM symbol by using Equation 15 below.

[Equation 15]

wherein represents a physical layer cell identifier. _{n s} =floor(1/7) and floor(x) represents a floor function for deriving the largest integer x or less than x. l'=1 mod 7 and mod represents a modular operation.

Beam Steering Reference Signal (BRRS)

Beam Steering Reference Signals (BRRS) may be transmitted on up to eight antenna ports (p=600, ..., 607). Transmission and reception of BRRS are dynamically scheduled in the downlink resource allocation on the xPDCCH.

The reference signal sequence ‘r_l,ns(m)’ can be defined by the following equation 16.

[Equation 16]

Where n _s represents the slot number in the radio frame. l represents the OFDM symbol number in the slot. c(i) can be predefined as a pseudo-random sequence. The pseudo-random sequence generator can be initialized at the beginning of each OFDM symbol using the following equation 17.

[Equation 17]

In this document, it is configured to the UE through RRC signaling.

DL phase noise compensation reference signal

The phase noise compensation reference signal associated with xPDSCH can be sent on antenna ports p=60 and/or p=61 according to the signaling in the DCI. In addition, the phase noise compensation reference signal associated with xPDSCH can exist as a valid reference for phase noise compensation only when the xPDSCH transmission is associated with the corresponding antenna port. In addition, the phase noise compensation reference signal associated with xPDSCH can be sent only on the physical resource blocks and symbols of the xPDSCH corresponding to the mapping above. In addition, the phase noise compensation reference signal associated with xPDSCH can be the same in all symbols with xPDSCH allocation.

For any antenna port p∈{60,61}, the reference signal sequence ‘r(m)’ is defined by the following Equation 18.

[Equation 18]

Herein, c(i) may be predefined as a pseudo-random sequence. A pseudo-random sequence generator may be initialized at the beginning of each subframe by using the following equation 19.

[Equation 19]

Where n _DCID is 0 unless otherwise specified. In an xPDSCH transmission, n _SCID is given in the DCI format associated with the xPDSCH transmission.

(where i = 0, 1) is given as follows. When the value of is not provided by a higher layer, i is not provided by a higher layer, equal to If not, then equal to

The following techniques are discussed for New RAT (NR) uplink (UL) multiple-input multiple-output (MIMO).

i) Uplink transmission/reception scheme for data channel

- Non-reciprocal UL MIMO (e.g., PMI-based)

- Reciprocity-based UL MIMO (e.g., UE derives precoder based on downlink RS measurements (including partial reciprocity))

-Supports Multi-User (MU)-MIMO

-Open-loop/closed-loop single/multipoint spatial multiplexing (SM)

For example, for multi-point SM, multiple layers are received jointly or independently by different transmit receive points (TRPs).

For multipoint SM, multiple points can be coordinated.

-Single/multi-panel spatial diversity

- Uplink antenna/panel switching (UE side)

-UL beamforming management for simulated implementations

- A combination of the above technologies

ii) UL RS design considering the following functions

-Detection

-demodulation

-Phase noise compensation

iii) UL Transmit Power/Timing Advance Control in the Context of UL MIMO

iv) Transmission scheme for carrying UL control information

v) Other UL MIMO and related technologies are not restricted.

The following aspects shall be supported for UL MIMO transmission:

i) Transmission schemes/methods for reciprocity-calibrated UEs, reciprocity-non-calibrated UEs, and non-reciprocity/partial reciprocity cases

- If necessary, introduce signaling associated with UL reciprocity based operations. For example, UE capability indicating calibration accuracy

- It will be discussed whether to distinguish reciprocal non-calibrated UEs from non-reciprocal ones.

- The number of transmission schemes/methods can be discussed further.

ii) At least one of the following candidate solutions/methods will be supported.

-Candidate 1: Codebook-based transmission

Frequency selective precoding and frequency non-selective precoding in the digital domain can be considered for wide system bandwidth. Support for frequency selective precoding is determined based on the decision of the NR waveform. The value of wide system bandwidth will be discussed later.

For example, similar to LTE based on base stations (BS).

For example, UE-assisted and BS-centric mechanisms: the UE recommends candidate UL precoders from a predefined codebook to the BS based on DL RS measurements. In addition, the BS determines the final precoder taken from the codebook.

For example, UE-centric and BS-assisted mechanisms: the BS provides CSI (e.g., channel response, interference-related information) to the UE. In addition, the UE determines the final precoder based on the information from the BS.

-Candidate 1: Non-codebook based transmission

Frequency selective precoding and frequency non-selective precoding in the digital domain can be considered for wide system bandwidth. Support for frequency selective precoding is determined based on the decision of the NR waveform. The value of wide system bandwidth will be discussed later.

For example, reciprocity-based (DL RS-based) transmission only for calibrated UEs

For example, UE-assisted and BS-centric mechanisms: UE recommends candidate UL precoders to BS based on DL RS measurements. In addition, BS determines the final precoder.

For example, UE-centric and BS-assisted mechanisms: the BS provides CSI (e.g., channel response, interference-related information) to the UE. In addition, the UE determines the final precoder based on the information from the BS.

- Other transmission schemes/methods are not restricted.

i) Discussion on UL precoder signaling for frequency selective/non-selective precoding

- Example 1: Signaling single or multiple PMIs via DL control and/or data channels

Multiple PMIs may be signaled via a single DCI or multi-level DCI (the first level DCI contains an indication of the location of the second level DCI).

- Example 2: For TDD, precoder calculation based on DL RS at UE

The implementation of frequency selective precoding is determined by RAN1 decisions (e.g., NR frame structure, waveform).

The impact on other system design aspects (eg, DL control channel decoding performance/complexity) should be considered.

ii) Discussion on using UL frequency selective precoding for precoded transmission including precoder cycling

iii) For frequency selective precoding, the UL precoding granularity (i.e., UL subband size) is discussed considering the following aspects:

- Implicit (defined by the specification) or explicit (determined by eNB/UE) signaling support

-Whether it is aligned with DL

iv) The evaluation should include UL specific aspects such as cubic metric (CM) analysis based on UL waveforms.

v) Discussion on frequency non-selective precoding has a higher priority.

In the existing LTE standard, when a base station sends an uplink (UL) grant for UL-MIMO transmission to a UE (e.g., via DCI format 4), the base station also sends precoding information (e.g., included in the DCI format). The UE then performs UL transmission by applying the indicated (single wideband) precoder to the scheduled physical resource blocks (PRBs).

As described above, a method for indicating a frequency selective precoder even in UL is also considered. As a result, transmission yield performance can be improved by applying a more optimized UL precoder for each subband.

However, unlike DL, UL needs to directly indicate a subband precoder upon UL grant of the base station, which may cause excessive control channel overhead in proportion to the number of subbands.

Therefore, the present invention proposes a scheme for applying UL subband precoding while minimizing UL-related DCI overhead.

In the present invention, a specific UL precoder 'P' is basically described as being divided into types such as P = U1 * U2, etc. Here, it can be divided into U1 as a relative wideband (and/or long-term) precoder property and U2 as a relative subband (and/or short-term) precoder property.

However, the present invention is not limited thereto, and operations of the present invention to be described below may be performed based on a single PMI (eg, TPMI) and a precoder.

A method is provided in which UI information is indicated as being common in the entire subband and only U2 information is indicated for each subband to be indicated to a UE at the time of UL scheduling (or in association with UL scheduling).

For example, assuming that the full P is 6 bits, U1 is 4 bits, and U2 is 2 bits, 6 bits are allocated to each subband without applying the hierarchical structure proposed in the present invention. If the total number is N, a total of 6N bits are consumed in the corresponding UL precoder instructions. On the other hand, according to the proposed method of the present invention, because 6+2N bits are consumed, the number of subbands N increases, resulting in a reduction in control channel overhead.

In this specification, for the convenience of description, a specific frequency axis resource unit is referred to as a "subband", but the present invention is not limited thereto, and it should be understood that a "subband" is generally referred to as a specific frequency axis resource unit. For example, the term "subband" may be changed/mixed with each other in all/some descriptions of the present invention, such as RB, PRB, PRB group (e.g., PRG (PRB group)).

U1 Information Relationship

The U1 codebook may also be configured for widely spaced beams in environments where widely spaced beams are selectively indicated for each subband (e.g., similar to the open-loop approach, where the terminal velocity is high, etc.), rather than where closely spaced beams are selectively indicated for each subband due to channel characteristics.

In the above example, a 4-bit U1 means that a total of 16 different U1 information can be indicated. Each U1 information may include a specific beam vector to be selected in U2. As an example, each U1 may be composed of a set of discrete Fourier transform (DFT) vectors as many as the number of UL transmission antenna ports of the UE (for example, the number of ports may be signaled in advance by the UE in the form of an SRS).

In this case, each U1 index can be designed in the form of a closely spaced beam group. As a result, it is advantageous for the base station to indicate UL scheduling by configuring the UI with surrounding candidate beam vectors including the final specific beam direction intended to indicate the corresponding UE during UL scheduling. That is, because U1 is a relatively wideband (and/or long-term) precoder property, it is advantageous to store the beam used to select/indicate the final beam optimized for each subband in U1, and each U1 information should be designed so that the effect can be appropriately demonstrated.

In the present invention, at least one different codebook can be defined/configured, such as a "closely spaced beam group," a "widely spaced beam group," and/or a "beam group consisting of a specific form (e.g., configurable by the eNB)." Furthermore, the base station can configure/instruct the UE via separate signaling which U1 and/or U2 codebook to apply during UL scheduling (e.g., via DCI) or before UL scheduling. As a result, although the U1 codebook itself can be fixed to one, like the present invention, there is an advantage in that a more flexible codebook can be operated by supporting a function that can be changed/activated/reactivated by configuring/instructing the base station.

U2 Information Relationship

In the above example, the 2-bit U1 means that a total of 4 different U2 information can be indicated. Each U2 information can be configured in such a way that the beam group corresponding to the U1 index indicated above can include four specific beam vectors, and the 2-bit U2 selection index indicates which beam among the beams will be ultimately applied for each subband.

In addition, in the above example, when U1 is 4 bits, U2 can exceed 2 bits. For example, if U2 is 4 bits, 2 bits are allocated as a "beam selector" so that a total of four different U2 information can be indicated. In order to connect the corresponding beams in the form of a common phase (for example, QPSK (quadrature phase shift keying) "common phase"), 2 bits can be allocated and thus the total U2 can be configured as 4 bits. The common phase is configured between the specific (two) transmit antenna port groups of the UE in the form of cross-polarized antennas, and the same beam can be applied so that the precoder can be configured in the form of a common phase by applying the group phase between the same group of ports.

Alternatively, it is apparent that “co-phasing” can allocate only 1 bit to apply, for example, BPSK co-phasing and the bit width of “beam selector” can be modified/changed according to the UE's transmit antenna port configuration and U1/U2 codebook structure.

The U2 information is mapped/indicated for each sub-band and may be configured/indicated together by being interlocked with a UL Resource Allocation (RA) field scheduled for a corresponding UE.

For example, if the resource allocation information of the corresponding UL grant message is in the form of a specific PRB bitmap (for example, if each bit is '1', the corresponding PRB is included in the scheduled PRB, and if each bit is '0', the corresponding PRB is not included), then the structure can be expanded to store K bits of information for each PRB index instead of using a bitmap of '1' or '0'. That is, the information can correspond to one PRB for each K bits in the bitmap. Therefore, in one embodiment of the present invention, a structure for transmitting U2 information through a corresponding 2^K state for each PRB is proposed.

For example, if K=2, a specific default state may be defined/configured for each PRB as follows.

- '00' indicates "the corresponding PRB is not included in the scheduled PRBs"

- '01' indicates "the corresponding PRB is included in the scheduled PRBs and the first precoder in U1 is applied"

- '10' indicates "the corresponding PRB is included in the scheduled PRBs and the second precoder in U1 is applied"

- '11' indicates "the corresponding PRB is included in the scheduled PRBs and the third precoder in U1 is applied"

This encoding method is only an example, and the description of the state such as '01', '10', and '11' can be defined in different forms or can be changed/configured by the base station through a higher layer signal such as RRC signaling. As described above, when the description of the state is defined/supported in the form of a parameter configurable by the base station (for example, through RRC signaling), it is advantageous to increase the configuration flexibility of the base station.

Therefore, when the scheduling information and the U2 information are jointly encoded in one bitmap, signaling overhead can be reduced compared to a case where a bitmap for transmitting the scheduling information and a bitmap for transmitting the U2 information are separately configured.

In addition, the RA field is maintained as a 1-bit unit bitmap, and the RA field can be applied in the form of a bitmap of K bits for transmitting U2 information per subband (per PRB/PRG) provided as a separate field (or provided separately as a separate DCI (at a separate time). That is, a separate field indicating K bits of (U2) precoder information for each subband corresponding to a specific PRB in the scheduled PRB region indicated in the RA field can be defined/configured.

Operations associated with a specific uplink reference signal (UL RS) (e.g., SRS) (used for link adaptation (LA)) Work relationship

- In association with some operations proposed in the present invention, specific RS (eg, SRS) transmission may be configured/implemented by the UE in order to determine the UL precoder at the base station.

Hereinafter, for convenience of description, the uplink RS is referred to as an SRS, but the present invention is not limited thereto.

1) Type 1 UL-LA UE (UL-LA process operation initiated by starting precoded SRS transmission):

Such an SRS may be first defined/configured to send a specific precoded SRS. In this case, the base station measures the precoded SRS of a specific port to determine the proposed U1 and/or U2 information. Thereafter, the base station sends an UL scheduling grant (e.g., in the case of U1, a separate DCI (field) or a separate message container for specific control information delivery (via L1 and/or L2 signaling) including the determined U1 and/or U2 information) to the UE separately. Thus, the frequency selective UL-MIMO scheduling considered in the present invention is disclosed.

A type of initiating a UL link adaptation (UL-LA) process by starting precoded SRS transmission without (ie, omitting) a specific non-precoded SRS transmission process may be referred to as a Type 1 UL-LA operation (or UE).

That is, the UE can transmit an SRS port with precoding/beamforming, such as analog beamforming, applied in a specific direction using a corresponding specific precoded SRS. Furthermore, the base station measures the (analog) beamformed SRS port to derive appropriate U1 and/or U2, and then notifies the UE of the derived U1 and/or U2 using the aforementioned method for UL transmission.

More specifically, the corresponding beamforming vector/coefficient to be applied by the UE to the precoded/beamformed SRS can be determined as follows. First, the UE can measure the DL specific RS (e.g., radio resource management-RS (RRM-RS), BRS, BRRS, etc.) sent by the base station. In addition, the UE finds (and also reports) the best "serving beam" to determine the (paired) best "Rx receiving beam" of the UE itself. Then, by using the DL/UL channel reciprocity characteristics to invert the best "Rx receiving beam" (e.g., take the Hermitian conjugate), the UE can send the SRS by applying the corresponding beamforming vector/coefficient when sending the precoded/beamformed SRS. That is, SRS transmission can be performed using the same spatial filtering as that used to receive a specific DL RS (e.g., the best "serving beam"). The operation of the UE can be defined in advance or configured in the UE.

Alternatively, it is not necessary to limit the application of only the "Rx receive beam" corresponding to the best "serving beam." For example, operations can be supported so that the base station can instruct/trigger the transmission of SRS using precoding/beamforming of the "Rx receive beam" corresponding to the second best "serving beam."

This method is generalized, and thus, in the same manner as for the third best "serving beam," the fourth best "serving beam," ..., a specific identifier (e.g., beam state information (BSI)) may be indicated from the base station to identify the corresponding nth "serving beam." In this manner, the beamforming vector/coefficient to be applied by the UE when transmitting a precoded/beamformed SRS may be configured/indicated.

In other words, when transmitting the SRS, the UE can use the same spatial filtering as that used to receive the specific DL RS to transmit the beamforming vector/coefficient. That is, the UE can implement the optimal spatial filtering for DL RS reception for each DL RS, and the base station can instruct the UE to use the same spatial filtering as that used by the UE to receive the specific DL RS to perform transmission of the specific SRS resource.

Alternatively, a method in which the base station directly configures/indicates the beamforming vector/coefficient to be applied by the UE when transmitting the precoded SRS to the UE (for example, a case where the base station can obtain information based on channel reciprocity (for example, according to another specific method) or the like) may be applied. The base station may directly notify the UE of the beamforming vector/coefficient through a control channel such as a specific DCI that triggers the transmission of the corresponding precoded SRS, or through separate specific Layer 1 (L1), Layer 2 (L2), and/or Layer 3 (L3) (for example, through RRC semi-static) signaling.

As a result, the type 1 UL-LA UEs to which the operation can be applied may be limited to i) "channel reciprocity calibrated UEs (e.g., NR (or 5G) UEs, 3GPP Release 15 and subsequent UEs, etc.)", ii) "UEs that do not perform full digital beamforming in their transmitter (TX) (and/or transmitter and receiver (TRX)) antennas/ports", iii) "UEs that apply analog beamforming to UL TX ports" and/or iv) "UEs operating in TDD".

Additionally/alternatively, the UE provides its own specific capabilities associated therewith (eg, whether Type 1 related support is available, etc.) to the base station in advance, and thus, the above-mentioned operation/process may be configured/initiated.

2) Type 2 UL-LA UE (UL-LA process operation initiated by starting precoded SRS transmission)

Regarding this SRS, the UE may be defined/configured to send a non-precoded SRS. In this case, the base station measures the non-precoded SRS of a specific port to determine the proposed U1 and/or U2 information. Thereafter, the base station sends an UL scheduling grant (e.g., in the case of U1, a separate DCI (field) or a separate message container for specific control information delivery (via L1 and/or L2 signaling) including the determined U1 and/or U2 information) to the UE separately. Thus, the frequency selective UL-MIMO scheduling considered in the present invention is disclosed.

Therefore, the type in which the UL link adaptation (UL-LA) process is initiated only by sending a specific non-precoded SRS and the base station notifies the UE of the final UL precoder such as U1 and/or U2 determined by measuring the non-precoded SRS of a specific port during UL scheduling is called Type 2 UL-LA operation (or UE).

More specifically, this Type 2 UE may mean a UE whose TX (and/or TRX) antenna/port is fully digital beamforming.

As a result, the type 2 UL-LA UEs to which the operation can be applied can be limited to i) "channel reciprocity non-calibrated UEs" (e.g., LTE/LTE-A UEs, UEs up to 3GPP Release 14), ii) "full digital beamforming capable UEs" and/or iii) "UEs operating in FDD (and/or TDD)", etc.

Additionally/alternatively, the UE provides the base station with its own specific capabilities associated therewith (eg, whether type 2 related support is available, etc.) in advance, and thus, the above-mentioned operation/process may be configured/initiated.

3) Type 3 UL-LA UE (UL-LA process operation initiated by receiving specific beamforming information from the base station via starting (S1 port) non-precoded SRS transmission and initiating (S2 (<= S1) port precoded SRS transmission) by applying the received information)

Alternatively, with respect to such SRS, the UE may be configured/instructed to primarily (per long-term periodically) transmit a specific (S1 port) non-precoded SRS by the UE, so that the base station derives the main beamforming vector/coefficient. In addition, the base station indicates the beamforming vector/coefficient to the UE to transmit an auxiliary specific (S2 (<= S1) port) precoded SRS. In this case, the only difference is the addition of a coarse beam estimation operation utilizing the primary non-precoded SRS. In other words, the base station measures the (S2 (<= S1) port) precoded SRS to determine the proposed U1 and/or U2 information. Thereafter, the base station sends an UL scheduling grant (for example, in the case of U1, a separate message container may be sent separately to the UE via a separate DCI (field) or for specific control information delivery (via L1 and/or L2 signaling) including the determined U1 and/or U2 information). Therefore, the frequency selective UL-MIMO scheduling considered in the present invention is disclosed.

At this time, as a method for configuring/instructing the UE to apply the beamforming vector/coefficient derived (by receiving the non-precoded SRS in the base station) to the corresponding precoded SRS, the base station can directly notify the UE of the beamforming vector/coefficient through a control channel such as a specific DCI that triggers the transmission of the corresponding precoded SRS or separately through specific L1, L2 and/or L3 (for example, through RRC semi-static) signaling.

Therefore, the type that includes the transmission of a specific non-precoded SRS and initiating the transmission of a specific precoded SRS by receiving information related to the application of beamforming from the base station and applying the received information, and the base station notifying the UE of the final UL precoder such as U1 and/or U2 determined by measuring the precoded SRS at the time of UL scheduling is called Type 3 UL-LA operation (or UE).

More specifically, this Type 3 UE may mean a UE whose TX (and/or TRX) antenna/port is fully digital beamforming.

As a result, the type 2 UL-LA UEs to which the operation can be applied may be limited to i) “channel reciprocity non-calibrated UEs”, ii) “UEs that do not perform full digital beamforming in their TX (and/or TRX) antennas/ports”, iii) “UEs that apply analog beamforming to UL TX ports” and/or iv) “UEs operating in FDD (and/or TDD)”.

Additionally/alternatively, the UE provides the base station with its own specific capabilities associated therewith (eg, whether type 3 related support is available, etc.) in advance, and thus, the above-mentioned operation/process may be configured/initiated.

- Additionally/alternatively, specific SRS resources are configured in advance in the UE, and the UE may be configured to transmit a separate precoded SRS based on each SRS resource configuration. In this case, the number of SRS ports per SRS resource may be one or more.

That is, the UE may perform SRS transmission based on the number of SRS ports corresponding to each SRS resource and the corresponding configuration.

At this time, the beamforming vector/coefficient to be applied at this time is selected arbitrarily (transparently and randomly by the eNB) or according to the instruction of the base station, and the UE can transmit a precoded SRS for each SRS resource. In this case, the base station first selects the SRS resource with the highest reception quality through SRS measurement for each SRS resource, derives U1 and/or U2 for the SRS port in the SRS resource, and indicates U1 and/or U2 to the UE. In other words, the base station derives U1 and/or U2 to be applied to the SRS port in the corresponding SRS resource and indicates the derived U1 and/or U2 to the UE.

In this case, an UL scheduling grant (e.g., U1 and/or SRI) including not only the proposed U1 and/or U2 information but also the optimal SRS resource indicator is transmitted (e.g., U1 and/or SRI can be separately transmitted to the UE via a separate DCI (field) or a separate message container for transmitting specific control information (via L1, L2, and/or L3 (e.g., via RRC semi-static) signaling). Thus, the frequency-selective UL-MIMO scheduling considered in the present invention is disclosed.

In other words, the base station configures multiple SRS resources to the UE, and the UE can send a precoded SRS with a different beam direction for each SRS resource to the base station. In addition, the base station notifies the UE of an uplink scheduling grant (DCI) including the SRI and precoding indication (e.g., U1 and/or U2, or Transmitted Precoding Matrix Indicator (TPMI)) sent by the UE at the previous time instance. In this case, the precoding indication can be used to indicate the preferred precoder on the SRS port in the SRS resource selected by the SRI.

For example, if a specific SRS resource is configured to transmit a 1-port SRS, then when the UE implements X transmit antennas/ports, the UE may be defined/configured to transmit a type of "rank 1 precoded SRS" by applying a specific X times 1 beamforming vector/coefficient.

Similarly, if a specific SRS resource is configured to transmit v (>1) port SRS, then when the UE implements X (>=v) transmit antennas/ports, the UE can be defined/configured to transmit a type of "rank v precoded SRS" by applying a specific X times v beamforming vector/coefficient.

That is, there may be a corresponding "SRS port number = number of (target) ranks" property configured for each SRS resource.

Therefore, when the base station configures/indicates SRI to the UE, it can recognize that SRI includes a meaning of rank indication. In addition, SRI can be defined/configured to be applied when interpreting other fields within the corresponding UL grant based on the indicated rank.

In other words, the number of SRS antenna ports can be predefined or configured for each SRS resource (e.g., through higher layer signaling such as RRC), and when the base station sends a UL grant including an SRI to the UE, the number of ranks used to send uplink data (e.g., PUSCH) for the UE can be determined as the number of antenna ports corresponding to the SRS resources indicated by the SRI.

As another example, the information indication of SRI can be omitted and which SRS resource index is indicated can be automatically indicated by the rank indication (field) indicated by the UL grant, etc., and the operation can be defined/configured/indicated so that the precoder applied to the corresponding implicitly indicated SRS resource index is applied when the UE's UL is transmitted (however, it is preferred that only one SRS resource associated with a specific rank is limited to a one-to-one link).

Alternatively, as more flexible UL scheduling-related signaling, the base station can be defined/configured to indicate the rank indication and the SRI independently to the UE. This is a case where one or more SRS resources can be configured for a specific target rank. The reason why the base station configures multiple SRS resources for a certain rank is that the UE applies different beamforming vectors/coefficients for the same rank and attempts to send SRS several times. That is, the base station measures the precoded SRS with different beam coefficients for the same rank to provide the following flexibility, that is, even when the corresponding rank is finally selected, it determines and indicates which UL precoder is more advantageous (in terms of performance).

Additionally/alternatively, when the UE applies a specific "beamforming vector/coefficient" to the corresponding precoded SRS, the UE may be configured to apply the "beamforming vector/coefficient" as a beamforming vector/coefficient that is common across a transmission band as a wideband property.

In addition, an operation may be defined or configured for the UE to frequency-selectively transmit a subband-precoded SRS for a corresponding SRS resource by applying different/independent beamforming vectors/coefficients in units of specific subbands (or PRB (groups)) on a transmission frequency band.

In addition, that is, the base station can specify to the UE whether the precoded SRS applies wideband precoding or subband precoding through L1 (through DCI), L2 (through MAC control element (CE)) and/or L3 (through RRC) signaling.

Even when a specific "frequency selective (subband) beamforming vector/coefficient" is applied when transmitting a specific precoded SRS, the following operation may be defined or configured to the UE.

i) The base station informs the UE of the corresponding “frequency selective (subband) beamforming vector/coefficient” (either individually or when indicating/triggering the corresponding SRS transmission), so that the UE follows this information.

ii) The UE may arbitrarily (eNB transparently, randomly) choose to send (frequency selective) precoded SRS for each SRS resource.

iii) The UE can find (or alternatively, find and report) the best "serving beam" by measuring Y (e.g., Y=1) DL-specific RS (e.g., RRM-RS, BRS, BRRS, etc.) ports transmitted by the base station. In addition, the UE can selectively determine an X-by-Y precoder/beamformer vector/coefficient (with the number X of the UE's TRX antennas/ports as the dimension) for each subband frequency when the UE determines its own (paired) best "Rx receive beam" to apply the determined X-by-Y precoder/beamformer vector/coefficient inversely (e.g., taking Hermitian conjugation) when transmitting the corresponding precoded SRS.

When using this RRM-RS type (eg, BRS, BRRS, etc.), it is limited to Y=1, so that the UE's transmission SRS can be limited to only rank-1 precoded SRS.

In addition, it is possible to explicitly indicate whether the X-by-Y precoder is calculated for a specific RRM-RS (e.g., BRS, BRRS, etc.) signaling type. In addition, a specific RRM-RS (e.g., BRS, BRRS, etc.) (port) can be indicated as a quasi-co-located (QCL) signaling type.

iv) The UE can determine its own (paired) best "Rx receive beam" by measuring Z (>= 1) DL-specific (for CSI measurement) RS (e.g., CSI-RS) ports transmitted from the base station. In this case, the UE selectively determines an X-by-Z precoder/beamformer vector/coefficient for each subband frequency (with the number X of the UE's TRX antennas/ports as the dimension) and applies the determined X-by-Z precoder/beamformer vector/coefficient inversely (e.g., taking Hermitian conjugation) when transmitting the corresponding precoded SRS. The operation can be defined or configured for the UE.

In other words, when transmitting SRS in a specific subband, the UE can use the same spatial filtering as that used to receive the specific DL RS to transmit the SRS. That is, the UE can implement the optimal spatial filtering for DL RS reception for each DL RS, and the base station can instruct the UE to use the same spatial filtering as that used by the UE to receive the specific DL RS to perform SRS resource transmission in the specific subband.

When using CSI-RS like this, it can be limited to Z>1, or can be flexibly defined or configured to the UE as Z>=1. The reason for not using the above-mentioned RRM-RS (e.g., BRS, BRRS) is that it can be limited to rank 1. Since it can be limited to a single port, it is effective to use CSI-RS to support rank>1.

In addition, the UE can be explicitly instructed to calculate the X times Z precoder for a specific CSI-RS (port). In addition, a specific CSI-RS (port) can be indicated as a QCL signaling type. In addition or alternatively, the UE can be defined or configured so that the corresponding CSI-RS (port) has a QCL link with the RRM-RS (e.g., BRS, BRRS) together or separately.

It will be apparent that all (or some) of the proposed operations associated with SRS can be applied to schemes that do not follow the U1 and/or U2 structure (e.g., single PMI (TPMI), precoder-based schemes). For example, in order to determine a specific single UL precoder U, the operations can be modified/applied to, for example, send a specific UL precoder indication for non-precoded/precoded SRS (based on the configuration of SRS resources).

- The expression "SRS resource" is a name given for convenience, and therefore, the SRS resource can be signaled/indicated to the UE in the form of a specific index actually given for each SRS resource unit. Alternatively, the operation of the present invention can be applied by another name/parameter that replaces the concept of "SRS resource" by binding specific/some/virtualized SRS ports grouped by a specific grouping for (all) SRS ports that can be transmitted by the UE.

Additional proposals

In such an operation, semi-open loop (OL) UL transmission may be configured/indicated to the UE in the form of deleting all U2 information for each subband.

For example, the base station may send a type of UL grant without U2 information to the UE through specific (separate) signaling (or using one of the U1 indexes) as described above, and this may operate as an instruction to the UE to perform specific (semi)OL UL transmission.

When the UE is configured/instructed as described above, even if U2 information is present in the UL Grant, the UE may ignore the information.

Alternatively, when the UE is configured/directed as described above, the payload where U2 information may be present may be deleted from the (UL-related) DCI. In this case, the UE may be defined or configured to perform blind detection (BD) for different payload sizes in a manner such that the total payload size of the corresponding DCI is reduced compared to the case where U2 information is present.

Additionally, (half)OL UL transmission may be indicated in the form of deleting only precoder information in the direction of a specific (spatial) dimension of U1 and/or U2.

For example, when the UE determines that the channel variation is not significant in the vertical direction and the channel variation is relatively severe in the horizontal direction, the U1 and/or U2 information may be indicated in conjunction with UL scheduling in a form in which specific precoder information for the horizontal component is deleted (or ignored or replaced with other information). In this case, the UE can UL transmit the corresponding portion by applying an OL scheme such as a precoder cycle according to a specific predefined/indicated OL precoding scheme. In addition, the UE can perform UL transmission by applying the precoder portion as indicated for the specific (spatial) dimension for which the U1 and/or U2 information is provided.

As described above, when specific (spatial) dimension precoder information is deleted and indicated, the payload portion can be deleted. In this case, the UE can be defined or configured to perform BD for different payload sizes in the form of a total payload reduction of the corresponding DCI compared to the normal payload.

The mapping of payload sizes of U1 and U2 and corresponding information as above may be defined to correspond to the number of UL (link adaptation) specific RS (eg, SRS) ports of the corresponding UE that is transmitted in advance (linked with mapping) or configured/indicated to the UE.

UL MIMO Design Framework

In LTE UL MIMO, the network indicates the precoder to the UE, which then transmits DMRS and data using the indicated precoder. In NR UL MIMO, the same precoder is applied to both DMRS and physical data channels. Precoded RS transmission is still desirable in terms of DMRS overhead because the transmission rank will be less than the number of TXRUs in most cases due to the lack of scatterers.

Therefore, it is preferred that the same precoder be applied to both DMRS and physical data channel, and precoded RS-based transmission becomes the baseline in NR UL MIMO.

Regarding transmission technology, it is agreed to support UL DMRS-based spatial multiplexing (Single User (SU)-MIMO/MU-MIMO). UL coordinated multi-point (CoMP) transmission can also be supported. In other words, the UL reception point can be transparent to the UE.

For UL SU-MIMO, in addition to conventional closed-loop techniques in which the network signals the complete precoder information (i.e., PMI and RI) to the UE, open-loop (OL) techniques in which the network does not signal the precoder information to the UE and semi-open-loop (OL) techniques in which a portion of the precoder information is signaled to the UE can also be considered. OL and semi-OL MIMO can be useful when full or partial DL/UL reciprocity is effective in TDD. UL MU-MIMO can be based on closed-loop operation, but is not limited thereto.

UL MIMO transmission techniques can be categorized with respect to the presence and completeness of precoder information signaled from the network to the UE:

- Closed loop: complete precoder information is signaled to the UE

- Open loop: no precoder information is signaled to the UE

- Semi-open loop: Part of the precoder information is signaled to the UE

In addition, it is agreed to support at least 8 orthogonal DL DMRS ports for both DL SU-MIMO and DL MU-MIMO. Similar to DL, the reference for UL can be LTE, so we propose to support at least 4 orthogonal DMRS ports for both UL SU-MIMO and UL MU-MIMO as a baseline. From the SU-MIMO perspective, by considering the possibility of higher ranks in practical environments (i.e., a limited number of main rays at high frequency bands and a limited number of TXRUs at the UE), there is no clear motivation to support a higher number of layers than LTE. However, when considering forward compatibility, it is possible to consider increasing the maximum number of layers from the beginning (e.g., by considering 8 layers for UL SU-MIMO for large UE types). From the MU-MMO perspective, NR has a clear motivation to implement higher-order MU-MIMO to achieve the target spectral efficiency. However, it will be expected to support more than a certain number (e.g., 4 or 8) of MU multiplexing layers by utilizing non-orthogonal DMRS ports (e.g., scrambling sequences) in order to manage DMRS overhead within a reasonable range.

Therefore, it is preferred to support at least 4 orthogonal UL DMRS ports for both SU-MIMO and MU-MIMO.

Regarding the number of codewords used for spatial multiplexing, it may be reasonable to support up to two codewords like LTE by considering the trade-off between link adaptation flexibility and control signaling overhead.

Therefore, it is preferred that for NR UL MIMO, basically up to two codes are supported.

Frequency Selective Precoding for UL MIMO

There is a consensus that cyclic prefix (CP)-OFDM without specified low peak-to-average power ratio (PAPR)/cubic metric (CM) techniques is recommended to support uplink NR waveforms at least up to 40 GHz for enhanced mobile broadband (eMBB) and ultra-reliable low latency communication (URLLC) services.

Considering the CP-OFDM waveform and the increased supportable system bandwidth in NR, the introduction of frequency selective precoding for UL MIMO may be considered. However, the increased control channel overhead due to the indicated sub-band PMI may be a key issue in applying such frequency selective UL-MIMO precoding. Although it may be considered to signal multiple PMIs separately from the UL-related DCI and include a pointer field in the DCI used to indicate such signaling, such a two-step approach may not be desirable due to the latency of providing the complete information of the multiple PMIs per sub-band in the first step. In other words, the motivation for introducing such a frequency selective UL precoder is to also achieve fast UL link adaptation utilizing the frequency domain, so that the complete precoder information set is expected to be delivered to the UE instantly when the precoder information set is scheduled for UL transmission.

In order to solve the control channel overhead problem of frequency-selective UL-MIMO scheduling, it is necessary to study the application of a dual codebook structure as in the DL, similar to the UL case (e.g., 4-Tx case). Considering the consensus CP-OFDM structure for UL, the final UL precoder W for each subband can be decomposed into a wideband PMI component W_1 and a corresponding subband PMI component W_2. Then, in the UL scheduling DCI, the W_1 information is sufficient to be included once, and multiple W_2s need to be included according to the scheduled RB area given by the resource allocation field in the same DCI. How to define the codebooks for W_1 and W_2 is for further study, but the baseline should reuse the Release 12 DL 4-Tx codebook. The existing LTE 2-Tx DL codebook can be reused as is for the 2-Tx UL case and the entire per-subband PMI needs to be provided in the UL scheduling grant. It should also be studied whether to support UL-MIMO precoder based on DFT-spread OFDM (DFT-S-OFDM), and in that case, study how to configure the UE by using CP-OFDM based UL precoder as discussed above or by using DFT-S-OFDM based precoder.

That is, the base station may configure the UE with at least one of codebook 1 based on CP-OFDM (e.g., a dual codebook structure) and codebook 2 based on DFS-S-OFDM (e.g., a cubic metric-preserving codebook, etc.). Furthermore, the base station may configure the UE via L1 (e.g., DCI), L2 (e.g., MAC CE), and L3 (e.g., RRC) which codebook to use for codebook-based UL precoding.

In particular, when CP-OFDM-based UL transmission is configured/instructed, the UE may be configured/instructed (and/or exchanged) with one of codebook 1 and codebook 2 by the base station and may apply the configured/instructed codebook. Conversely, when DFS-OFDM-based UL transmission is configured/instructed, the UE may be restricted to continuously applying only codebook 2. This is because, under the DFS-S-OFDM scheme, the application of codebook 1 may be inappropriate because, for example, the application of codebook 1 significantly amplifies the PAPR.

More specifically, which codebook is applied in conjunction with a specific rank value may be defined or configured to the UE. For example, in the case of rank X (e.g., X = 1) transmission, codebook 2 may be defined to be applied or may be configured to the UE in terms of transmit power (such as PAPR issues). Conversely, in the case of rank Y (e.g., Y = 2) or greater, codebook 1 is configured (e.g., generally speaking, for UEs other than the cell edge region) to be applied as defined or configured to the UE to apply a precoder that maximizes throughput rather than transmit power.

When such an operation is applied, when the rank is indicated by a UL grant or the like, the UE may automatically analyze/apply the indicated PMI/precoder while applying different codebooks in conjunction with the indicated rank as above.

In the above description, as an example, an operation is described in which a specific codebook (eg, codebook 1 or codebook 2, . . . ) is employed in conjunction with configuration based on a specific waveform (eg, based on CP-OFDM or DFS-S-OFDM).

However, the present invention is not limited thereto, and such an operation may be defined or configured/indicated to the UE so that the UE can initiate UL transmission by applying a specific codebook among specific candidate codebook 1 (e.g., a DFT-based codebook), codebook 2 (e.g., a Grassmannian codebook), and codebook 3 (e.g., a Householder codebook) under the instruction of the base station regardless of the specific waveform when the UE performs UL transmission.

As a more specific embodiment, candidate codebook 1 can be defined or configured for the UE in a specific DFT-based codebook using DFT vectors or the like (e.g., a dual codebook structure including an LTE-A codebook). This candidate codebook 1 is more suitable when the arrangement/spacing between antennas according to the UE antenna configuration is relatively uniform and/or closely spaced. Furthermore, candidate codebook 2 can be defined or configured in the form of a codebook optimized to maximize the maintenance of equal distances between internal vectors (such as a Grassmann codebook). This candidate codebook 2 is more suitable when the arrangement/spacing between antennas according to the UE antenna configuration is relatively irregular or widely spaced. Furthermore, candidate codebook 3 can be defined or configured for the UE in the form of a specific hybrid codebook (e.g., a Householder codebook formed by extracting some code vectors from different codebooks with different properties and purposes (including codebook 1 and codebook 2 according to the UE antenna configuration)).

As a result, when the UE accesses a specific base station in advance, the UE can be defined or configured to perform capability signaling through UE capability signaling, as at least one codebook among (the) specific candidate codebooks that can be applied during UL transmission is implemented or supported. In addition, or alternatively, when the number of codebooks implemented/supported in this way is two or more, the UE can inform the base station which of the two codebooks the UE prefers (subdivided preference information can be provided in such a way as to give a weight). In this case, it can be determined which codebook is more suitable based on the antenna configuration characteristics of the corresponding UE implemented, and there is the following effect: information about the codebook that shows a more favorable effect in terms of the performance of the codebook implemented/supported in this way is provided to the base station.

In addition, based on this information, the base station allows the UE to configure/indicate the codebook to be applied when transmitting in UL. In this case, among the codebooks that the UE performs capability signaling to implement/support, there may also be codebooks that are not implemented/supported by the corresponding base station. In this case, the base station can configure the UE to use only the codebooks implemented/supported thereby (regardless of the codebook-to-codebook preference information reported by the UE). Alternatively, even if the base station is able to configure/indicate multiple codebooks to the UE (that is, even if all codebooks are implemented), the base station can configure/indicate the specific codebook to be generally applied as cell-specific or UE group-specific (for example, to facilitate UL MU-MIMO transmission, etc.) by comprehensively considering the codebook implementation/support status and/or codebook preference status of multiple UEs accessing the corresponding cell.

In the method where the base station configures/instructs the corresponding UE to apply a specific codebook during UL transmission, a relatively semi-static configuration method through RRC signaling (and/or MAC CE signaling) is also applicable. As described above, the specific codebook to be applied to the UE can be dynamically indicated through relatively more dynamic signaling/indication in conjunction with a specific UL scheduling grant. This dynamic indication can be implicitly and/or explicitly indicated (in conjunction with characteristic field information) via a specific field in control signaling (such as a corresponding UL grant).

More specifically, as mentioned above, which codebook is to be applied in conjunction with a specific rank can be predefined or configured to the UE. For example, when a UL grant scheduling rank 1 UL transmission is transmitted, the UE can be continuously defined or configured to initiate UL transmission by applying a specific codebook associated therewith (e.g., codebook 2). In addition, when a UL grant scheduling rank X (e.g., X>1) UL transmission is transmitted, the UE can be continuously defined or configured to initiate UL transmission by applying a specific codebook associated therewith (e.g., codebook 1).

Therefore, if supported, all sub-band UL-MIMO precoders are preferably provided to the UE on-the-fly within the UL scheduling grant, and in this case, the wideband component may be included only once to reduce control channel overhead.

Precoding-based SRS transmission for UL MIMO

For UL Link Adaptation (LA), LTE can configure the UE to transmit SRS with multiple different sets of SRS-related parameters, where the UE can apply specific precoding/selection on the SRS ports, especially when the number of configured SRS ports is less than the total transmit (Tx) antenna ports of the UE. Compared with the operation of the beamformed CSI-RS based on Release 13/14 enhanced (e) FD-MIMO, it is necessary to thoroughly study the precoded/beamformed SRS transmission for UL LA in NR. For the convenience of description, there can be three UE types in terms of the UL LA process as follows:

1) Type 1 UE (UL-LA initiated when sending precoded SRS)

- A UE may be configured with one or more SRS resources and beamforming indicated by a transmit and receive point (TRP) or TRP transparent beamforming is applied to SRS transmission on each SRS resource.

-Based on measuring the UE's transmit precoded SRS resources, the TRP determines the SRS resource indicator (SRI) (in case of multiple configured SRS resources), and the MCS and/or precoder across the SRS ports in the SRI are determined and the SRI, MCS and precoder are indicated to the UE when the UL scheduling grant is delivered to the UE.

2) Type 2 UE (UL-LA initiated when sending non-precoded SRS)

- The UE may be configured with one SRS resource and the UE transmits non-precoded SRS.

- Based on measuring the UE's transmitting non-precoded SRS resources, the TRP determines the MCS and/or precoder across the SRS ports in the SRS and indicates the MCS and precoder to the UE when the UL scheduling grant is delivered to the UE.

In the case of 4-Tx UE and CP-OFDM, the above-mentioned dual codebook structure is used for the frequency selective UL-MIMO precoder.

3) Type 3 UE (UL-LA initiated when transmitting non-precoded SRS and precoded SRS according to TRP instructions)

- Based on measuring the UE's non-precoded _SRSK1 port, the TRP determines the coarse beamformer and indicates it to the UE to be applied when transmitting the following precoded _SRSK2 ( _≤K1 ) port. Then, based on measuring the UE's transmit precoded SRS port, the TRP determines the MCS and/or precoder and indicates them to the UE when the UL scheduling grant is delivered.

Based on the above classified types that can be reported by the UE, different UL-LA processes can be configured as UE-specific, including which types of SRS transmissions are performed by the UE. With respect to precoded SRS transmission cases (e.g., type 1 and/or type 3), multiple SRS resources can be configured to the UE, where the UE transmits differently beamformed SRS ports on each configured SRS resource. The TRP can indicate such beamformer information to the UE, or the UE is allowed to apply a beamformer that is transparent to the TRP for SRS transmission. Then, when an UL scheduling grant is given to the UE, for the scheduled UL transmission, the TRP can indicate an SRS resource indicator to which the UE should apply the same beamformer used on the SRS transmission corresponding to the indicated SRS resource. In addition, on the selected SRS resource, the TRP can also indicate digital precoding information (e.g., UL PMI) on the SRS port within the indicated SRS resource. It should be noted that the number of configured SRS ports for each SRS resource can be interpreted as the target rank in the UE's UL transmission. Therefore, the TRP can configure multiple SRS resources, each corresponding to a different rank to cover ranks 1 to 4 (for example, v-port SRS configured for the vth SRS resource (where v=1, 2, 3)).

Therefore, the procedures related to non-precoded and/or precoded SRS transmission based on different UE types should be further studied in terms of UL link adaptation process.

FIG13 is a diagram illustrating a method of transmitting and receiving an uplink according to an embodiment of the present invention.

In FIG. 13 , the operation of the present invention is simply illustrated, and a more detailed description thereof may follow the aforementioned operation.

13 , the UE receives downlink control information (DCI) from the base station ( S1303 ).

The DCI may include an SRS resource indication (SRI), a precoding indication (eg, U1 and/or U2 or TPMI), and/or a rank indication (eg, TRI).

For example, the precoding indicator can be divided into a first precoding indicator (i.e., U1) with a wideband attribute and a second precoding indicator (U2) indicated for each subband. In this case, the second precoding indicator U2 can be transmitted while being jointly encoded with the uplink resource allocation information scheduled for the UE. In other words, the second precoding indicator U2 can be configured/indicated in association with the UL RA field.

The UE transmits uplink to the base station by applying precoding indicated by the precoding indication on the antenna port of the SRS transmitted in the SRS resource selected according to the SRI (S1304).

The number of ranks used for uplink transmission may be explicitly indicated by DCI or implicitly determined as the number of antenna ports of SRS transmitted in SRS resources selected according to SRI in DCI.

Meanwhile, before step S1303 , the UE may receive a downlink reference signal (DL RS) (eg, CSI-RS, etc.) from a base station ( S1301 ).

In addition, the UE may transmit a precoded SRS for each of one or more SRS resources configured for the UE to the base station ( S1302 ).

In this case, the base station may select the SRS resource with the highest reception quality through SRS measurement for each SRS resource and instruct the UE by deriving a precoding indication (eg, U1 and/or U2 or TPMI) for an SRS port in the selected SRS resource.

In addition, the beamforming vector and/or beamforming coefficient applied to transmit the precoded SRS may be configured by the base station through control channel signaling or arbitrarily determined by the UE.

In addition, the beamforming vector and/or beamforming coefficient applied to the precoded SRS transmission in the SRS resource may be determined based on the beamforming vector and/or beamforming coefficient used to receive the DL RS (eg, CSI-RS, etc.).

More specifically, the UE measures the DL RS transmitted by the base station to find (and also report) the best "serving beam". In addition, the UE can determine its paired best "Rx receiving beam" for the best "serving beam". In addition, by inverting the best "Rx receiving beam" (e.g., taking the Hermitian conjugate) by using the DL/UL channel reciprocity property (or beam pair link), the UE can transmit the precoded SRS by applying the corresponding beamforming vector/coefficient when transmitting the precoded/beamformed SRS. That is, the precoded SRS transmission can be performed using the same spatial filtering as that used to receive a specific DL RS (e.g., the best "serving beam").

When the DL-RS is a CSI-RS, CSI-RS resources used to determine a beamforming vector and/or a beamforming coefficient applied to precoded SRS transmission are indicated by the base station.

Furthermore, precoded SRS transmission performed by the UE in the SRS resource may be performed independently for each subband.

For example, for precoded SRS transmission in an SRS resource, an independent beamforming vector and/or beamforming coefficient may be applied for each subband.

In addition, the beamforming vector and/or beamforming coefficient applied to the SRS transmission precoded for each subband in the SRS resource may be determined based on the beamforming vector and/or beamforming coefficient used to receive the DL RS (eg, CSI-RS, etc.).

More specifically, the UE measures the DL RS transmitted by the base station to find (and also report) the best "serving beam". In addition, the UE can determine its paired best "Rx receiving beam" for the best "serving beam". In addition, by inverting the best "Rx receiving beam" (e.g., taking the Hermitian conjugate) by using the DL/UL channel reciprocity property (or beam pair link), the UE can transmit the precoded SRS for each subband by applying the corresponding beamforming vector/coefficient when transmitting the precoded/beamformed SRS. That is, the precoded SRS transmission can be performed using the same spatial filtering as that used to receive a specific DL RS (e.g., the best "serving beam") in a specific subband.

In this case, when the DL-RS is a CSI-RS, CSI-RS resources used to determine a beamforming vector and/or a beamforming coefficient applied to precoded SRS transmission are indicated by the base station.

General devices to which the present invention can be applied

FIG14 illustrates a block diagram of a wireless communication device according to an embodiment of the present invention.

14 , the wireless communication system includes a base station (eNB) 1410 and a plurality of user equipments (UEs) 1420 located within an area of the eNB 1410 .

The eNB 1410 includes a processor 1411, a memory 1412, and a radio frequency unit 1413. The processor 1411 performs the functions, processes, and/or methods described in Figures 1 to 13 above. The layers of the radio interface protocol can be executed by the processor 1411. The memory 1412 is connected to the processor 1411 and stores various types of information for driving the processor 1411. The radio frequency unit 1413 is connected to the processor 1411 and transmits and/or receives radio signals.

The UE 1420 includes a processor 1421, a memory 1422, and a radio frequency unit 1423. The processor 1421 performs the functions, processes, and/or methods described in Figures 1 to 13. The layers of the radio interface protocol may be executed by the processor 1421. The memory 1422 is connected to the processor 1421 and stores various types of information for driving the processor 1421. The radio frequency unit 1423 is connected to the processor 1421 and transmits and/or receives radio signals.

The memories 1412 and 1422 may be located inside or outside the processors 1411 and 1421 and may be connected to the processors 1411 and 1421 through well-known means. In addition, the eNB 1410 and/or the UE 1420 may have a single antenna or multiple antennas.

The embodiments described so far are embodiments of elements and technical features coupled in a predetermined form. Although there has been no obvious mention so far, each of the elements or technical features should be considered to be optional. Each of the elements or features can be implemented without being coupled with other elements or technical features. In addition, it is also possible to construct embodiments of the present invention by coupling a part of the elements and/or technical features. The order of the operations described in the embodiments of the present invention can be changed. A part of the elements or technical features of the embodiment can be included in another embodiment, or can be replaced with elements or technical features corresponding to other embodiments. Obviously, an embodiment can be constructed by combining claims that do not have a clear reference relationship in the following claims, or it can be included in a new claim set by amendment after submitting the application.

The embodiments of the present invention may be implemented by various means, such as hardware, firmware, software, and combinations thereof. In the case of hardware implementation, the embodiments of the present invention may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of being implemented by firmware or software, the embodiments of the present invention may be implemented in the form of modules, procedures, or functions that perform the functions or operations described so far. The software code may be stored in a memory and driven by a processor. The memory may be located inside or outside the processor and may exchange data with the processor via various well-known means.

It will be understood by those skilled in the art that various modifications and variations can be made without departing from the essential features of the present invention. Therefore, the detailed description is not limited to the above-mentioned embodiments, but should be regarded as examples. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the scope of equivalents should be included within the scope of the present invention.

Industrial Applicability

The present invention has been described based on an example in which the present invention is applied to a 3GPP LTE/LTE-A system or a 5G system, but the present invention can be applied to various wireless communication systems in addition to the 3GPP LTE/LTE-A system or the 5G system.

Claims (16)

1. A method for uplink transmission performed by a user equipment (UE) in a wireless communication system, the method comprising: Send the SRS of each of the multiple detection reference signal SRS resources configured for the UE to the base station; The base station receives downlink control information (DCI) including: (i) an SRS resource indication (SRI) indicating an SRS resource among a plurality of SRS resources; and (ii) a precoding indication indicating a precoder for uplink transmission corresponding to the SRS resource indicated by the SRI; and The uplink transmission to the base station is performed by applying the precoder, which is indicated by the precoder indication and corresponds to the SRS resource indicated by the SRI. 2. The method according to claim 1, wherein, for the uplink transmission, at least one of (i) the uplink beamforming vector or (ii) the uplink beamforming coefficient is configured by the base station via control channel signaling or determined by the UE. 3. The method according to claim 1, wherein at least one of the uplink beamforming vector or uplink beamforming coefficient is determined based on at least one of the downlink beamforming vector or downlink beamforming coefficient for receiving downlink reference signal DL RS from the base station. 4. The method according to claim 3, wherein the DL RS is a Channel State Information Reference Signal (CSI-RS), and The base station indicates CSI-RS resources used to determine at least one of the uplink beamforming vector or the uplink beamforming coefficient. 5. The method of claim 1, wherein at least one of an uplink beamforming vector or an uplink beamforming coefficient is applied independently for each subband used for the uplink. 6. The method of claim 5, wherein at least one of the uplink beamforming vector or the uplink beamforming coefficient applied to the uplink transmission for each subband is determined based on at least one of the downlink beamforming vector or the downlink beamforming coefficient for receiving the downlink reference signal DL RS from the base station. 7. The method according to claim 6, wherein the DL RS is a Channel State Information Reference Signal (CSI-RS), and The base station indicates CSI-RS resources used to determine at least one of the uplink beamforming vector or the uplink beamforming coefficient. 8. The method of claim 1, wherein the DCI further includes a rank indication for the uplink transmission. 9. The method of claim 1, wherein the number of ranks for the uplink transmission is determined as the number of antenna ports of the SRS transmitted in the SRS resource indicated by the SRI. 10. The method of claim 1, wherein the precoding indication comprises a first precoding indication and a second precoding indication, and The second precoding indication is jointly encoded together with the uplink resource allocation information scheduled to the UE. 11. The method of claim 1, wherein the precoding indication is configured to indicate the precoder corresponding to the antenna port of the SRS resource indicated by the SRI. 12. The method of claim 1, wherein applying the precoder indicated by the precoding indication and corresponding to the SRS resource indicated by the SRI comprises: The pre-encoder is used to encode the information to be transmitted to the base station. 13. The method of claim 1, wherein receiving the precoding indication corresponding to the precoder of the SRS resource indicated by the SRI comprises: Receive the precoding matrix indicator TPMI transmitted from the base station. 14. A user equipment (UE) configured to perform uplink transmission in a wireless communication system, the UE comprising: At least one radio frequency (RF) unit; At least one processor operatively connected to the at least one RF unit; and At least one computer memory, operatively connected to the at least one processor and storing computer instructions, which, when executed, cause the at least one processor to perform operations including the following steps: Send the SRS of each of the multiple detection reference signal SRS resources configured for the UE to the base station; The base station receives downlink control information (DCI) including: (i) an SRS resource indication (SRI) indicating an SRS resource among a plurality of SRS resources; and (ii) a precoding indication indicating a precoder for uplink transmission corresponding to the SRS resource indicated by the SRI; and The uplink transmission to the base station is performed by applying the precoder, which is indicated by the precoder indication and corresponds to the SRS resource indicated by the SRI. 15. A method for a base station to receive uplink transmissions from a user equipment (UE) in a wireless communication system, the method comprising: Receive from the UE the SRS of each of the plurality of probe reference signal SRS resources configured for the UE; The UE is sent downlink control information (DCI) including: (i) an SRS resource indication (SRI) indicating an SRS resource among the plurality of SRS resources; and (ii) a precoding indication indicating a precoder for uplink transmission corresponding to the SRS resource indicated by the SRI; and The UE receives the uplink transmission that has been precoded by the UE using the precoder, the precoder being indicated by the precoding indication and corresponding to the SRS resource indicated by the SRI. 16. A base station configured to receive uplink transmissions from a user equipment (UE) in a wireless communication system, the base station comprising: At least one radio frequency (RF) unit; At least one processor operatively connected to the RF unit; and At least one computer memory, operatively connected to the at least one processor and storing computer instructions, which, when executed, cause the at least one processor to perform operations including the following steps: Receive from the UE the SRS of each of the plurality of probe reference signal SRS resources configured for the UE; The UE is sent downlink control information (DCI) including: (i) an SRS resource indication (SRI) indicating an SRS resource among the plurality of SRS resources; and (ii) a precoding indication indicating a precoder for uplink transmission corresponding to the SRS resource indicated by the SRI; and The UE receives the uplink transmission that has been precoded by the UE using the precoder, the precoder being indicated by the precoding indication and corresponding to the SRS resource indicated by the SRI.