Multi-antenna based precoding method and device in a wireless communication system

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting higher data transmission rates than 4G communication systems such as LTE. According to one embodiment of the present disclosure, a method of a network entity in a communication system is provided. The method of the network entity comprises: a step of determining whether to perform scheduling to adjust the ratio between a plurality of first transmission points (TPs) included in a first group serving at least one terminal and a plurality of second TPs included in a second group; a step of determining whether to switch at least one of the plurality of second TPs to the first TP based on information associated with the at least one terminal when it is determined to perform the scheduling; and a step of transmitting an indicator to the at least one second TP instructing it to operate as the first TP when it is determined to switch the at least one second TP to the first TP, wherein when it operates as the first TP, precoding of a signal is performed in the network entity, and when it operates as the second TP, precoding of a signal is performed in the second TP. According to this, it is possible to provide a more enhanced service in an environment where the computational complexity and front-haul capacity that a CPU controlling multiple TPs can allow are limited.

Description

Technology Field

[0001] The present disclosure relates to a wireless communication system, and more specifically, to a communication system that considers a function split into a central unit (CU) and a distributed unit (DU), a precoding method that considers the load of a fronthaul, which is a data transmission and reception path between a CU and a DU, and the computational complexity of a CU that controls a DU, and an apparatus capable of performing the same. Background Technology

[0002] Looking back at the evolution of wireless communication through successive generations, technologies have been developed primarily for human-oriented services such as voice, multimedia, and data. 5G (5 th Connected devices, which have been increasing explosively since the commercialization of -generation) communication systems, are expected to be connected to communication networks. Examples of networked objects include vehicles, robots, drones, home appliances, displays, smart sensors installed in various infrastructures, construction machinery, and factory equipment. Mobile devices are expected to evolve into various form factors, such as augmented reality glasses, virtual reality headsets, and holographic devices. 6G (6 th In the era of generation, efforts are being made to develop an improved 6G communication system to connect hundreds of billions of devices and objects and provide various services. For this reason, the 6G communication system is referred to as a "Beyond 5G" system.

[0003] In the 6G communication system predicted to be realized around 2030, the maximum transmission speed is tera (i.e., 1,000 gigabit) bps, and the wireless latency is 100 microseconds (μsec). In other words, compared to the 5G communication system, the transmission speed in the 6G communication system is 50 times faster, and the wireless latency is reduced to one-tenth.

[0004] To achieve such high data transmission speeds and ultra-low latency, 6G communication systems are being considered for implementation in the terahertz band (e.g., the 95 GHz to 3 terahertz (3 THz) band). In the terahertz band, due to more severe path loss and atmospheric absorption compared to the millimeter wave (mmWave) band introduced in 5G, the importance of technology capable of guaranteeing signal reach, or coverage, is expected to increase. As key technologies to ensure coverage, radio frequency (RF) devices, antennas, new waveforms that offer better coverage than orthogonal frequency division multiplexing (OFDM), beamforming, and multi-antenna transmission technologies such as massive multiple-input and multiple-output (MIMO), full-dimensional MIMO (FD-MIMO), array antennas, and large-scale antennas must be developed. In addition, new technologies are being discussed to improve coverage of terahertz band signals, including metamaterial-based lenses and antennas, high-dimensional spatial multiplexing technology using orbital angular momentum (OAM), and reconfigurable intelligent surface (RIS).

[0005] In addition, to improve frequency efficiency and system network, development is underway in 6G communication systems for full duplex technology, in which uplink and downlink simultaneously utilize the same frequency resources at the same time; network technology that integrates satellites and HAPS (high-altitude platform stations); network structure innovation technology that supports mobile base stations and enables network operation optimization and automation; dynamic spectrum sharing technology through collision avoidance based on spectrum usage prediction; AI-based communication technology that utilizes AI from the design stage and internalizes end-to-end AI support functions to realize system optimization; and next-generation distributed computing technology that realizes services of complexity exceeding the limits of terminal computing capabilities by utilizing ultra-high performance communication and computing resources (mobile edge computing (MEC), cloud, etc.). In addition, attempts are continuing to further strengthen connectivity between devices, further optimize networks, promote the softwareization of network entities, and increase the openness of wireless communication through the design of new protocols to be used in 6G communication systems, the implementation of hardware-based security environments, the development of mechanisms for the safe utilization of data, and the development of technologies regarding privacy maintenance methods.

[0006] Due to the research and development of such 6G communication systems, it is expected that a new dimension of hyper-connected experience will become possible through the hyper-connectivity of 6G communication systems, which encompasses not only connections between objects but also connections between people and objects. Specifically, it is projected that 6G communication systems will enable the provision of services such as truly immersive extended reality (XR), high-fidelity mobile holograms, and digital replicas. Furthermore, services such as remote surgery, industrial automation, and emergency response, which are provided through 6G communication systems with enhanced security and reliability, will be applied in various fields including industry, healthcare, automotive, and home appliances.

[0007] In line with the advancement of communication systems as described above, there is an increasing demand for technology that provides improved transmission and reception performance to UEs (user equipment). As a solution to this demand, a structure for a communication system capable of transmitting and receiving data according to the CoMP (coordinated multi-point) method, a multi-cell cooperative communication technology, has been proposed. The CoMP method is a method in which multiple TPs (transmission points) cooperate to perform data transmission and reception with at least one UE. Through this, a UE located relatively far from the TP can have improved data transmission and reception performance, thereby supporting efficient communication services. However, there is a problem in that as the number of TPs cooperating to perform data transmission to the UE increases, the computational complexity of the CPU (central processing unit) (or network entity) controlling the TPs increases significantly, and the load on the fronthaul, which is the signal transmission and reception channel between the CPU and the TPs, increases. The problem to be solved

[0008] In a communication system composed of multiple TPs (for example, a cell-free massive MIMO (multi-input multi-output) system where data transmission and reception by multiple TPs is possible and cell boundaries are blurred), when uplink or downlink data is transmitted and received between the UE and multiple TPs according to the CoMP method, problems such as increased computational complexity of the CPU and increased load on the front haul, which is the data transmission and reception channel between the CPU and TPs, may occur. Therefore, it is necessary to devise a precoding method that can solve these problems and a system structure to which said method can be applied. means of solving the problem

[0009] In order to solve the aforementioned problems, according to one embodiment of the present disclosure, a method of a network entity in a communication system is provided. The method of the network entity comprises: a step of determining whether to perform scheduling to adjust the ratio between a plurality of first transmission points (TPs) included in a first group serving at least one terminal and a plurality of second TPs included in a second group; a step of determining whether to switch at least one second TP among the plurality of second TPs in the second group to the first TP based on information associated with the at least one terminal when it is determined to perform the scheduling; and a step of transmitting an indicator to the at least one second TP instructing it to operate as the first TP when it is determined to switch the at least one second TP to the first TP, wherein when it operates as the first TP, precoding of the signal is performed in the network entity, and when it operates as the second TP, precoding of the signal is performed in the second TP.

[0010] Additionally, according to one embodiment of the present disclosure, a network entity of a communication system is provided. The network entity determines whether to perform scheduling to adjust the ratio between a plurality of first TPs included in a first group serving a transceiver and at least one terminal and a plurality of second TPs included in a second group; if it is determined to perform the scheduling, it determines whether to convert at least one second TP among the plurality of second TPs in the second group into a first TP based on information associated with the at least one terminal; and if it is determined to convert the at least one second TP into the first TP, it includes a control unit that transmits an indicator to the at least one second TP through the transceiver instructing it to operate as the first TP, wherein when operating as the first TP, precoding of the signal is performed in the network entity, and when operating as the second TP, precoding of the signal is performed in the second TP. Effects of the invention

[0011] According to various embodiments of the present disclosure, a precoding method is provided for a communication system composed of a plurality of TPs, taking into account the computational complexity allowed to a CPU controlling the plurality of TPs and the capacity of a front hole, which is a signal transmission and reception channel between the CPU and the TPs. According to this, when transmitting and receiving uplink data or downlink data between a UE and a plurality of TPs according to the CoMP method, the UE can be enabled to have optimal data transmission and reception performance.

[0012] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below.

[0013] The effects obtainable from the present disclosure are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which the present disclosure belongs from the description below. Brief explanation of the drawing

[0014] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure with reference to the accompanying drawings. FIG. 1 is a diagram illustrating the structure of a cellular mobile communication system to which the present disclosure can be applied. FIG. 2 is a diagram illustrating the structure of an LTE (long term evolution) system according to 3GPP standards to which the present disclosure can be applied. FIG. 3 is a diagram illustrating the wireless protocol structure of an LTE system of 3GPP standards to which the present disclosure can be applied. FIG. 4 is a diagram illustrating the system structure of a next-generation mobile communication according to 3GPP standards to which the present disclosure can be applied. FIG. 5 is a diagram illustrating the structure of a wireless protocol in a next-generation mobile communication system of 3GPP standards to which the present disclosure can be applied. FIG. 6 is a diagram illustrating the structure of a system to which a non-CoMP (non-coordinated multi-point) method is applied according to one embodiment of the present disclosure. FIG. 7 is a diagram illustrating the structure of a system to which a CoMP (coordinated multi-point) method is applied according to one embodiment of the present disclosure. FIG. 8 is a diagram illustrating the classification of CoMP methods in an LTE system or next-generation mobile communication system to which the present disclosure can be applied. FIG. 9 is a diagram illustrating coherent joint transmission (CJT) and non-coherent joint transmission (NCJT) methods in an LTE system or next-generation mobile communication system to which the present disclosure can be applied. FIG. 10 is a diagram illustrating a distributed antenna system in which the CJT method of a CoMP according to one embodiment of the present disclosure can be implemented. FIG. 11 is a diagram illustrating an example of a CPRI (common public radio interface) between a RRH (remote radio header) (or, RU (radio unit)) and a BBU (base band unit) according to one embodiment of the present disclosure. FIG. 12 is a diagram illustrating a model of a cell-free massive MIMO-based system to which the present disclosure can be applied. FIG. 13 is a diagram illustrating the sequence in which a CPU performs complexity-shared scheduling (CSS) according to one embodiment of the present disclosure. FIG. 14 is a drawing illustrating the location of a functional separation point according to one embodiment of the present disclosure. FIG. 15a is a diagram illustrating a system structure in which a terminal and a TP instructed to operate as a Central TP or Local TP according to the result of CSS execution according to one embodiment of the present disclosure transmit and receive uplink data. FIG. 15b is a diagram illustrating a system structure in which a terminal and a TP instructed to operate as a Central TP or Local TP according to the CSS execution result according to one embodiment of the present disclosure transmit and receive downlink data. FIG. 16 is a diagram illustrating a downlink data transmission and reception procedure when multiple DM-RS (demodulation-reference signals) are assigned to Central TP and Local TP determined according to the CSS execution result according to one embodiment of the present disclosure. FIG. 17 is a diagram illustrating the sequence of operations of a UE according to one embodiment of the present disclosure based on whether it receives a CJRI (coherent joint reception indicator). FIG. 18 is a diagram illustrating an example of a CSS algorithm that can be performed on a CPU according to one embodiment of the present disclosure. FIG. 19 is a drawing illustrating a CSS framework based on a TP that incorporates eCPRI (enhanced CPRI) according to one embodiment of the present disclosure. FIG. 20 is a diagram illustrating the results of evaluating the average user yield while increasing the ratio of Central TPs when supporting 2 UEs per TP when applying one embodiment of the present disclosure. FIG. 21 is a diagram illustrating the results of evaluating the average user yield while increasing the ratio of Central TPs when supporting 4 UEs per TP when applying one embodiment of the present disclosure. FIG. 22 is a diagram illustrating the results of evaluating the lower 10% performance user yield while increasing the ratio of Central TPs when supporting 2 UEs per TP when applying one embodiment of the present disclosure. FIG. 23 is a diagram illustrating the results of evaluating the lower 10% performance user yield while increasing the ratio of Central TPs when supporting 4 UEs per TP when applying one embodiment of the present disclosure. FIG. 24 is a diagram illustrating the results of evaluating the yield of the lower 10% performance users while increasing the ratio of Central TPs when supporting 2 UEs per TP when applying one embodiment of the present disclosure. FIG. 25 is a diagram illustrating the results of evaluating the yield of the lower 10% performance users while increasing the ratio of Central TPs when supporting 4 UEs per TP when applying one embodiment of the present disclosure. FIG. 26 is a figure illustrating the results of comparing the user's bit error performance according to the presence or absence of inter-group channel correlation determined by CSS execution when one or two DM-RSs are used when applying one embodiment of the present disclosure. FIG. 27 is a drawing illustrating the structure of a UE to which an embodiment of the present disclosure can be applied. FIG. 28 is a drawing illustrating the structure of a TP to which an embodiment of the present disclosure can be applied. FIG. 29 is a diagram illustrating the structure of a network entity to which an embodiment of the present disclosure can be applied. Specific details for implementing the invention

[0015] Embodiments of the present disclosure will be described in detail below with reference to the attached drawings.

[0016] In describing the embodiments, descriptions of technical details that are well known in the technical field to which this disclosure belongs and are not directly related to this disclosure are omitted.

[0017] This is intended to convey the gist of the present disclosure more clearly without obscuring it by omitting unnecessary explanations.

[0018] For the same reason, some components in the attached drawings have been exaggerated, omitted, or schematically depicted. Additionally, the dimensions of each component do not entirely reflect their actual dimensions. Identical or corresponding components in each drawing have been assigned the same reference number.

[0019] The advantages and features of the present disclosure and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings.

[0020] However, the present disclosure is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to complete the configuration of the present disclosure and to fully inform those skilled in the art of the scope of the invention, and the present disclosure is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0021] At this point, it will be understood that each block of the process flow diagrams and combinations of the flow diagrams can be executed by computer program instructions. Since these computer program instructions can be loaded into the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing equipment, the instructions executed through the processor of the computer or other programmable data processing equipment create means to perform the functions described in the flow diagram block(s). Since these computer program instructions can also be stored in computer-available or computer-readable memory that can be directed toward the computer or other programmable data processing equipment to implement the function in a specific way, the instructions stored in computer-available or computer-readable memory can also produce a manufactured item containing instruction means to perform the function described in the flow diagram block(s). Since computer program instructions can be loaded onto a computer or other programmable data processing equipment, instructions that perform a series of operation steps on the computer or other programmable data processing equipment to create a process executed by the computer can also provide steps for executing the functions described in the flowchart block(s).

[0022] Additionally, each block may represent a module, segment, or part of code containing one or more executable instructions for executing a specified logical function(s). It should also be noted that in some alternative execution examples, the functions mentioned in the blocks may occur out of order. For instance, two blocks described in succession may actually be executed substantially simultaneously, or the blocks may be executed in reverse order according to their corresponding functions.

[0023] In this disclosure, the term “part” as used refers to a software or hardware component, such as an FPGA or ASIC, and the “part” performs certain roles. However, the “part” is not limited to software or hardware. The “part” may be configured to reside in an addressable storage medium or may be configured to operate one or more processors. Thus, by example, the “part” includes components such as software components, object-oriented software components, class components, and task components, as well as processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables. The functions provided within the components and “parts” may be combined into a smaller number of components and “parts” or further separated into additional components and “parts.” Furthermore, the components and “parts” may be implemented to operate one or more CPUs within a device or secure multimedia card.

[0024] For convenience of explanation, some terms and names defined in 3GPP (3rd generation partnership project) standards (specifications for 5G, NR, LTE, or similar systems) may be used below. The use of such terms is not limited to the terms and names of this disclosure and may be applied equally to systems conforming to other standards and may be modified in other forms within the scope of the technical concept of this disclosure.

[0025] Additionally, in this disclosure, expressions such as "greater than" or "less than" have been used to determine whether specific conditions are satisfied or fulfilled; however, this is merely for illustrative purposes and does not exclude descriptions of "greater than" or "less than." Conditions described as "greater than" may be replaced with "greater than," conditions described as "less than" with "less than," and conditions described as "greater than and less than" with "greater than and less than."

[0026] In the present disclosure, the UE may be referred to as a terminal, mobile station, or WTRU (wireless transmit / receive unit), but is not limited thereto, and may be referred to by terms having the same or similar meaning.

[0027] In addition, in the present disclosure, TP (transmission point) refers to a point capable of transmitting and receiving wireless signals by having one or more antennas, and various types of base stations may be referred to as TP regardless of their names. Additionally, TP may be referred to as TRP (transmission reception point), AP (access point), distributed antenna, RU (radio unit), or DU (distributed unit) according to one embodiment of the present disclosure, but is not limited thereto, and may be referred to by terms having the same or similar meaning.

[0028] Additionally, in this disclosure, the CPU (central processing unit) may be referred to as a separate entity or network entity that performs the operation proposed in this disclosure. Alternatively, various types of base stations may be referred to as CPUs regardless of their names. Furthermore, the CPU may be referred to as a CU (central unit) according to one embodiment of this disclosure, but is not limited thereto, and may be referred to by a term having the same or similar meaning.

[0029] Additionally, the data described in this disclosure may be referred to as a data stream or a signal, and may also be referred to as a signal transmitting control information, but is not limited thereto, and may be referred to by terms having the same or similar meaning.

[0030] Additionally, in the present disclosure, precoding may refer to the operation of multiplying a precoder (or precoding vector, beamforming weight) by a modulated transmission signal. For example, in the present disclosure, precoding may refer to the operation of changing the amplitude and phase of a complex symbol by multiplying a complex symbol by a precoder after layer mapping. FIG. 1 is a diagram illustrating the structure of a cellular mobile communication system to which the present disclosure can be applied.

[0031] Referring to FIG. 1, the mobile communication system illustrated in FIG. 1 includes a first cell (100), a second cell (110), and a third cell (120), and a TP (which may mean a base station) that performs (or provides) mobile communication within each cell may be positioned in the center of each cell (100, 110, 120). The first cell (100) includes a TP (130), a first UE (140), and a second UE (150). The TP (130) may provide mobile communication services to the two UEs (140, 150) located in the first cell (100). The first UE (140), which receives mobile communication services through the TP (130), is relatively far from the TP (130) compared to the second UE (150). Therefore, the data transmission and reception performance that can be supported in the first UE (140) may be relatively lower than the data transmission and reception performance that can be supported in the second UE (150).

[0032] Meanwhile, in a mobile communication system such as that shown in FIG. 1, a reference signal (RS) may be transmitted to measure the downlink channel status of each cell or to estimate the downlink channel. The reference signal may also be referred to as a pilot. According to 3GPP standards, reference signals transmitted by the TP to the UE include CSI-RS (channel status information-reference signal) and DM-RS (demodulation-reference signal). The UE can use CSI-RS to measure the channel status between the TP and the UE and provide feedback on the channel status information. Additionally, the UE can use DM-RS to estimate the downlink channel and demodulate the resources allocated to it based on the estimated channel.

[0033] FIG. 2 is a diagram illustrating an LTE system structure of 3GPP standards to which an embodiment of the present disclosure can be applied.

[0034] Referring to FIG. 2, as illustrated, the wireless access network of an LTE system consists of a next-generation base station (eNB, hereinafter eNB, Node B, or base station, where eNB may refer to a TP according to the present disclosure) (2-05, 2-10, 2-15, 2-20), an MME (2-25, mobility management entity), and an S-GW (2-30, serving-gateway). A UE (2-35) connects to an external network through the eNB (2-05 - 2-20) and the S-GW (2-30).

[0035] In FIG. 2, the eNB (2-05 - 2-20) corresponds to the existing Node B of the UMTS system. The eNB is connected to the UE (2-35) via a wireless channel and performs a more complex role than the existing Node B. In an LTE system, since all user traffic, including real-time services such as VoIP (voice over IP) via the Internet Protocol, is serviced through a shared channel, a device is required to collect status information such as the buffer status, available transmission power status, and channel status of the UEs to perform scheduling, and this is handled by the eNB (2-05 - 2-20). A single eNB typically controls multiple cells. For example, to achieve a transmission speed of 100 Mbps, the LTE system uses Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM) as a wireless access technology, for instance, in a 20 MHz bandwidth. In addition, an Adaptive mouldation & coding (hereinafter referred to as AMC) method is applied to determine the modulation scheme and channel coding rate according to the channel conditions of the terminal. The S-GW (2-30) is a device that provides data bearers and creates or removes data bearers according to the control of the MME (2-25). The MME is a device that is responsible for various control functions as well as mobility management functions for the terminal and is connected to multiple base stations.

[0036] FIG. 3 is a diagram illustrating the wireless protocol structure of an LTE system of 3GPP standards to which the present disclosure can be applied.

[0037] Referring to Fig. 3, the wireless protocol of the LTE system consists of PDCP (packet data convergence protocol 3-05, 3-40), RLC (radio link control 3-10, 3-35), and MAC (medium access control 3-15, 3-30) at the terminal and eNB, respectively.

[0038] PDCP (3-05, 3-40) is responsible for operations such as IP header compression / recovery. The main functions of PDCP are summarized as follows.

[0039] - Header compression and decompression (ROHC only)

[0040] - User data transfer function

[0041] - Sequential delivery function (in-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM)

[0042] - Order reordering function (for split beareres in DC (only supprt for RLC AM): PDCP PDU routing for transmission and PDCP PDU reordering for reception)

[0043] - Duplicate detection function (duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM)

[0044] - Retransmission function (retransmission of PDCP SDUs at handover and, for split bearers in DC, of ​​PDCP PDUs at PDCP data-recovery procedure, for RLC AM)

[0045] - Encryption and decryption functions (ciphering and deciphering)

[0046] - Timer-based SDU discard in uplink

[0047] Radio link control (hereinafter referred to as RLC) (3-10, 3-35) reconstructs PDCP PDUs (packet data units) into appropriate sizes to perform ARQ operations, etc. The main functions of RLC are summarized as follows.

[0048] - Data transfer function (transfer of upper layer PDUs)

[0049] - ARQ function (error correction through ARQ (only for AM data transfer))

[0050] - Concatenation, segmentation, and reassembly functions (concatenation, segmentation, and reassembly of RLC SDUs (only for UM and AM data transfer))

[0051] - Re-segmentation function (re-segmentation of RLC data PDUs (only for AM data transfer))

[0052] - Reordering function (reordering of RLC data PDUs (only for UM and AM data transfer)

[0053] - Duplicate detection function (only for UM and AM data transfer)

[0054] - Error detection function (protocol error detection (only for AM data transfer))

[0055] - RLC SDU deletion function (RLC SDU discard (only for UM and AM data transfer))

[0056] RLC re-establishment function

[0057] MAC (3-15, 3-30) is connected to multiple RLC layer devices configured in a terminal and performs the operation of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC are summarized as follows.

[0058] - Mapping function (Mapping between logical channels and transport channels)

[0059] - Multiplexing and demultiplexing function (Multiplexing / demultiplexing of MAC SDUs belonging to one or different logical channels into / from transport blocks (TB) delivered to / from the physical layer on transport channels)

[0060] - Scheduling information reporting function

[0061] - HARQ function (Error correction through HARQ)

[0062] - Priority handling between logical channels of one UE

[0063] - Priority handling between UEs by means of dynamic scheduling

[0064] - MBMS service identification function

[0065] - Transport format selection function

[0066] - Padding

[0067] The physical layer (3-20, 3-25) performs the operation of channel coding and modulating upper layer data, creating OFDM symbols and transmitting them to the wireless channel, or demodulating OFDM symbols received through the wireless channel and channel decoding them to transmit them to the upper layer.

[0068] FIG. 4 is a diagram illustrating the structure of a next-generation mobile communication system according to 3GPP standards to which the present disclosure can be applied.

[0069] Referring to FIG. 4, as illustrated, the wireless access network of a next-generation mobile communication system may be composed of a next-generation base station (New Radio Node B, hereinafter referred to as NR gNB or NR base station, wherein NR gNB may refer to a TP according to the present disclosure) (4-10) and an NR CN (4-05, New Radio Core Network). A UE (New Radio User Equipment, hereinafter referred to as NR UE or terminal) (4-15) connects to an external network through the NR gNB (4-10) and the NR CN (4-05).

[0070] In FIG. 4, the NR gNB (4-10) corresponds to the eNB (Evolved Node B) of the existing LTE system. The NR gNB is connected to the NR UE (4-15) via a wireless channel and can provide superior service compared to the existing Node B. In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device is required to collect status information such as the buffer status, available transmission power status, and channel status of the UEs and perform scheduling, and this is handled by the NR NB (4-10). A single NR gNB typically controls multiple cells. To achieve ultra-high-speed data transmission compared to current LTE, it can have a bandwidth greater than the existing maximum bandwidth, and orthogonal frequency division multiplexing (hereinafter referred to as OFDM) can be used as a wireless access technology, and additional beamforming technology can be incorporated. In addition, an adaptive modulation & coding (hereinafter referred to as AMC) method is applied to determine the modulation scheme and channel coding rate according to the channel conditions of the terminal. The NR CN (4-05) performs functions such as mobility support, bearer configuration, and QoS configuration. The NR CN is a device responsible for various control functions as well as mobility management functions for the terminal, and is connected to multiple base stations. Furthermore, the next-generation mobile communication system can be interoperable with the existing LTE system, and the NR CN is connected to the MME (4-25) via a network interface. The MME is connected to the existing base station eNB (4-30).

[0071] FIG. 5 is a diagram illustrating the structure of a wireless protocol in a next-generation mobile communication system of 3GPP standards to which the present disclosure can be applied.

[0072] Referring to FIG. 5, the wireless protocol of the next-generation mobile communication system consists of NR SDAP (5-01, 5-45), NR PDCP (5-05, 5-40), NR RLC (5-10, 5-35), and NR MAC (5-15, 5-30) at the terminal and the NR base station, respectively.

[0073] The main functions of NR SDAP (5-01, 5-45) may include some of the following functions.

[0074] - User data transfer function (transfer of user plane data)

[0075] - Mapping function between a QoS flow and a DRB for both DL and UL for uplink and downlink

[0076] - Marking QoS flow ID in both DL and UL packets for uplink and downlink

[0077] - A function to map reflective QoS flow to the data bearer for the uplink SDAP PDUs.

[0078] Regarding the above SDAP layer device, the terminal may receive a setting via an RRC message indicating whether to use the header of the SDAP layer device or the functions of the SDAP layer device for each PDCP layer device, bearer, or logical channel. If the SDAP header is configured, the terminal may be instructed to update or reset the mapping information for the uplink and downlink QoS flows and data bearers using the NAS reflective QoS and AS reflective QoS 1-bit indicators of the SDAP header. The above SDAP header may include QoS flow ID information indicating QoS. The above QoS information may be used for data processing priority, scheduling information, etc., to support smooth service.

[0079] The main functions of NR PDCP(5-05, 5-40) may include some of the following functions.

[0080] - Header compression and decompression (ROHC only)

[0081] - User data transfer function (Transfer of user data)

[0082] - Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0083] - Out-of-sequence delivery of upper layer PDUs

[0084] - Reordering function (PDCP PDU reordering for reception)

[0085] - Duplicate detection function (Duplicate detection of lower layer SDUs)

[0086] - Retransmission of PDCP SDUs

[0087] - Encryption and decryption functions (Ciphering and deciphering)

[0088] - Timer-based SDU discard in uplink.

[0089] In the above, the reordering function of the NR PDCP device refers to a function of reordering PDCP PDUs received from a lower layer in order based on the PDCP SN (sequence number), and may include a function of transmitting data to an upper layer in the reordered order, or a function of transmitting immediately without considering the order, may include a function of recording lost PDCP PDUs by reordering, may include a function of reporting the status of lost PDCP PDUs to the transmitting side, and may include a function of requesting retransmission of lost PDCP PDUs.

[0090] The main functions of NR RLC(5-10, 5-35) may include some of the following functions.

[0091] - Data transfer function (Transfer of upper layer PDUs)

[0092] - Sequential delivery function (In-sequence delivery of upper layer PDUs)

[0093] - Out-of-sequence delivery of upper layer PDUs

[0094] - ARQ function (Error Correction through ARQ)

[0095] - Concatenation, segmentation, and reassembly functions of RLC SDUs

[0096] - Re-segmentation function (Re-segmentation of RLC data PDUs)

[0097] - Reordering function (Reordering of RLC data PDUs)

[0098] - Duplicate detection

[0099] - Error detection function (Protocol error detection)

[0100] - RLC SDU discard function

[0101] RLC re-establishment function

[0102] In the above, the in-sequence delivery function of the NR RLC device refers to the function of delivering RLC SDUs received from a lower layer to an upper layer in sequence; it may include a function to reassemble and deliver them if a single RLC SDU is received divided into multiple RLC SDUs; it may include a function to rearrange received RLC PDUs based on an RLC SN (sequence number) or PDCP SN (sequence number); it may include a function to record lost RLC PDUs after rearranging the order; it may include a function to report the status of lost RLC PDUs to the transmitting side; it may include a function to request retransmission of lost RLC PDUs; if there are lost RLC SDUs, it may include a function to deliver only the RLC SDUs prior to the lost RLC SDU to the upper layer in sequence; or if a predetermined timer has expired even if there are lost RLC SDUs, it may include a function to deliver all RLC SDUs received before the timer started to the upper layer in sequence; or It may include a function that delivers all RLC SDUs received up to the present to the upper layer in order once a predetermined timer has expired, even if there are lost RLC SDUs. Additionally, the RLC PDUs mentioned above may be processed in the order of receipt (regardless of the order of sequence numbers, but in the order of arrival) and delivered to the PDCP device out of order (out-of-sequence delivery). In the case of segments, segments stored in a buffer or to be received later may be received, reconstructed into a single complete RLC PDU, processed, and then delivered to the PDCP device.The above NR RLC layer may not include a concatenation function, and the function may be performed in the NR MAC layer or replaced with the multiplexing function of the NR MAC layer.

[0103] In the above, the out-of-sequence delivery function of the NR RLC device refers to a function of delivering RLC SDUs received from a lower layer directly to an upper layer regardless of order. It may include a function of reassembling and delivering them when a single RLC SDU is received divided into multiple RLC SDUs, and may include a function of storing the RLC SN or PDCP SN of the received RLC PDUs and sorting the order to record the lost RLC PDUs.

[0104] The NR MAC (5-15, 5-30) can be connected to multiple NR RLC layer devices configured in a terminal, and the main functions of the NR MAC may include some of the following functions.

[0105] - Mapping function (Mapping between logical channels and transport channels)

[0106] - Multiplexing and demultiplexing functions (Multiplexing / demultiplexing of MAC SDUs)

[0107] - Scheduling information reporting function

[0108] - HARQ function (Error correction through HARQ)

[0109] - Priority handling between logical channels of one UE

[0110] - Priority handling between UEs by means of dynamic scheduling

[0111] - MBMS service identification function

[0112] - Transport format selection function

[0113] - Padding

[0114] The NR PHY layer (5-20, 5-25) can perform the operation of channel coding and modulating upper layer data, creating OFDM symbols and transmitting them to the wireless channel, or demodulating OFDM symbols received through the wireless channel and channel decoding them to transmit them to the upper layer.

[0115] Meanwhile, the LTE system and next-generation mobile communication system of the 3GPP standard described in FIGS. 2 and FIGS. 4 above can generally be implemented through a non-coordinated multi-point (non-CoMP) data transmission and reception method in which multiple cells are established in a limited area and one UE within the cell receives data from one TP serving it. A more specific explanation of the non-CoMP method will be provided with reference to FIG. 6.

[0116] FIG. 6 is a diagram illustrating the structure of a system to which a non-CoMP (non-coordinated multi-point) method is applied according to one embodiment of the present disclosure.

[0117] Referring to FIG. 6, FIG. 6 shows an example of a mobile communication system that includes three cells, with a TP placed in the center of each cell.

[0118] The TP of each cell can perform data transmission to the UE present in the cell. That is, the TP of Cell 0 can transmit data (600) to UE0 present in the service area of ​​Cell 0. Additionally, by using time and frequency resources different from those used in Cell 0, the TP of Cell 1 can transmit data (610) to UE1 present in the service area of ​​Cell 1, and the TP of Cell 2 can transmit data (620) to UE2 present in the service area of ​​Cell 2. By referring to the wireless resources (630) used in Cell 0, the wireless resources (650) used in Cell 1, and the wireless resources (640) used in Cell 2, it can be seen that data can be transmitted using different time and frequency resources in Cells 0 to 2. In this way, a transmission method in which the TP of each cell transmits data only to the UE within the cell using different time and frequency resources, and there is no cooperation between the TPs, can be referred to as a non-CoMP method.

[0119] Meanwhile, the above-mentioned non-CoMP data transmission and reception method has a limitation in that it cannot support high data transmission and reception performance for UEs located far from the center of the cell (i.e., at the boundary of the cell), as the transmitting and receiving antennas of each TP are concentrated in the center of the cell. Accordingly, various system structures have been proposed to which the CoMP method, a multi-cell cooperative communication technology, can be applied. A detailed explanation of the above-mentioned CoMP method will be provided with reference to Fig. 7.

[0120] FIG. 7 is a diagram illustrating the structure of a system to which a CoMP (coordinated multi-point) method is applied according to one embodiment of the present disclosure.

[0121] Unlike the non-CoMP method, which performs data transmission and reception without cooperation between each TP as seen in Fig. 6, Fig. 7 illustrates a system structure in which the CoMP method, which performs data transmission and reception with cooperation between each TP, is applied.

[0122] Referring to FIG. 7, an example is given in which a UE receives data transmitted via a PDSCH (physical downlink shared channel) from Cell 0 and Cell 2. That is, the UE receives data (700) (710) transmitted from two TPs simultaneously. In a mobile communication system where multiple TPs exist, one or more TPs cooperate to perform the same data transmission for a single UE, thereby enabling a UE located relatively far from the TP (e.g., at the boundary of a cell) to have improved data transmission and reception performance.

[0123] Meanwhile, the above CoMP method, which enables the provision of improved services to users at the cell boundary, can be implemented in various ways in a communication system and will be explained below through Fig. 8.

[0124] FIG. 8 is a diagram illustrating the classification of CoMP methods in an LTE system or next-generation mobile communication system to which an embodiment of the present disclosure can be applied.

[0125] Referring to FIG. 8, the CoMP method can be classified into an uplink CoMP method for improving uplink data transmission and reception performance, which is a wireless connection from the UE to the TP, and a downlink CoMP method for improving downlink data transmission and reception performance, which is a wireless connection from the TP to the UE.

[0126] First, the uplink CoMP method can be implemented using JR (joint reception), CS (coordinated scheduling), or a combination of the above methods.

[0127] JR is a method in which data transmitted from a terminal is received by multiple TPs together. CS is a method in which multiple TPs cooperate with each other to perform scheduling and precoding.

[0128] The downlink CoMP method can be implemented using JP (joint processing), CS / CB (coordinated scheduling / coordinated beamforming), or a combination of the above methods.

[0129] CS / CB is a method in which a single TP transmits data to a UE, but multiple TPs cooperate to perform scheduling and beamforming. This reduces interference to UEs located at the boundaries of the TPs.

[0130] JP is a method in which multiple TPs share data to be transmitted to the UE, and it can be further classified into DPS (dynamic point selection) and JT (joint transmission). The above DPS may refer to DCS (dynamic cell selection), which is a method in which one of the multiple TPs transmits downlink data to the UE, but the TP transmitting data to the UE changes dynamically. In other words, it refers to a method in which downlink data is transmitted through a TP selected according to a specific rule among multiple TPs.

[0131] JT is a method in which multiple TPs cooperate to transmit the same data to the UE.

[0132] Meanwhile, JT can be further classified into CJT (coherent JT) and NCJT (non-coherent JT) depending on whether the TPs synchronize and transmit a data stream, and a detailed explanation thereof will be provided in Fig. 9.

[0133] FIG. 9 is a diagram illustrating coherent joint transmission (CJT) and non-coherent joint transmission (NCJT) methods in an LTE system or next-generation mobile communication system to which the present disclosure can be applied.

[0134] Figure 9A illustrates a system for transmitting data to a UE according to the CJT method, and Figure 9B illustrates a system for transmitting data to a UE according to the NCJT method.

[0135] In FIG. 9A, according to the CJT method, the CPU (central processing unit) performs central scheduling (which can be referred to as central scheduling), and the TPs controlled by the CPU synchronize according to the scheduling and transmit data to the UE (coherent transmission).

[0136] In Fig. 9B, according to the NCJT method, each TP schedules independently (which can be referred to as local scheduling) and transmits data to the UE independently without synchronizing with other TPs (non-coherent transmission).

[0137] Meanwhile, coherent transmission involves multiple TPs each transmitting a data stream that is time-synced by compensating for delay to the UE, and the UE receives the sum of the data streams transmitted from multiple TPs, thereby improving the UE's reception performance.

[0138] According to the CJT method, through cooperation among multiple TPs, interference from cells to which other users belong can be reduced in a system with multiple users, and the throughput and data reception performance of the UE at the cell boundary can be improved.

[0139] Meanwhile, the CJT method of the CoMP considered in the present disclosure can be implemented in a communication system based on a distributed antenna system composed of a plurality of TPs and a CPU connected to the plurality of TPs through a front hole. The CPU can transmit and receive data with the plurality of TPs through the front hole and can control the TPs. A more detailed explanation will be provided with reference to FIG. 10.

[0140] FIG. 10 is a diagram illustrating a distributed antenna system in which a CJT method of a CoMP according to one embodiment of the present disclosure can be implemented. However, the embodiments of the present disclosure are not limited thereto, and a JR method may be implemented in the distributed antenna system of FIG. 10.

[0141] Referring to FIG. 10, FIG. 10 illustrates a distributed antenna system including a cell (1000) as an example. A CU (1030) (1030), connected to a DU (as described above, the DU of the present disclosure may refer to the TP of the above disclosure) via a front hole, is positioned in the center of the cell (1000), and DUs (1060, 1070, 1080, 1090) within each cell may be positioned at different locations. The CU (1030) controls the DUs (1060, 1070, 1080, 1090) within the cell, and each DU can transmit a downlink signal (JT) to a UE located in the cell (1000) under the control of the CU (1030). In this case, the DU (1060, 1070, 1080, 1090) may each include one or multiple antennas. Meanwhile, in such a distributed antenna system, downlink data can be coherently transmitted to the UE via beamforming using antennas located at the TP, similar to the distributed MIMO method (CJT). To this end, the CPU can generate a centralized precoder (or refer to the operation of acquiring or verifying the precoder) and apply it to the data to be transmitted to the UE. Then, the CPU transmits the data with the applied precoder to each TP connected to the CPU via fronthall, and each TP synchronizes to transmit the data stream to the UE (coherent transmission).

[0142] Meanwhile, the CJT method of the CoMP, which can be implemented through the distributed antenna system structure described above, may have the problem that the amount of data transmitted and received through the front hole between each TP and the CPU is excessive, and the computational complexity of the CPU increases significantly as the number of TPs controlled by the CPU increases. Specific details are explained through Fig. 11.

[0143] FIG. 11 is a diagram illustrating an example of a CPRI (common public radio interface) between a RRH (remote radio header) (or, RU (radio unit), DU) and a BBU (base band unit) (or, CU) according to one embodiment of the present disclosure.

[0144] Referring to FIG. 11, when using a distributed antenna system in a 4G (or LTE) system, the CPRI standard (hereinafter referred to as CPRI) may be used. For example, based on option 8 shown in FIG. 11, functions can be separated into a CU and a DU, and CPRI can be used as a communication interface between the CU and the DU. In this case, if functions are separated based on option 8 as described above, only the RF stage exists in the DU, and the remaining signal processing operations can be performed in the CU. Meanwhile, when transmitting downlink data, the CU must sample the RF signal and transmit it to the DU through the fronthall, so a heavy load is placed on the fronthall. Furthermore, in the case of the uplink, where the RF signal sampled from the DU must be transmitted to the CU, the load on the fronthall becomes even greater. In addition, in the case of the aforementioned CJT method, accurate channel information for generating not only user data but also a precoder (or precoding vector) must be transmitted to the CPU (CU) through the front hole, so there are limitations in implementing the aforementioned CJT method when the transmission capacity of the front hole is limited.

[0145] In next-generation mobile communication systems, to overcome the limitations of the aforementioned front-haul, the eCPRI (enhanced common public radio interface) standard was defined to allow for the separation of functions by selecting other options. For example, functions can be separated into a CU and a DU based on option 2 or option 7 shown in Fig. 11. If functions are separated at an upper layer as in option 2, precoding must be performed in a distributed manner at the DU, which may reduce the improvement in data transmission and reception performance obtainable through the CJT method. Conversely, if functions are separated at a lower layer as in option 7, the transmission volume of the front-haul may still be excessive compared to the existing method. In other words, a trade-off between CJT performance and front-haul transmission volume may occur depending on the point of functional separation. In this regard, there are limitations to implementing the CJT method through eCPRI.

[0146] Meanwhile, in addition to the problems mentioned above, generating a precoder matrix for CJT in the CPU requires knowing the channels accurately, and there is also the problem that significant overhead can occur depending on the operation required for this.

[0147] In addition, there are limitations in implementing the above CJT method when the number of UEs is greater than the number of TPs. For example, in a cellular network as shown in Fig. 1, downlink channel estimation was possible based on the downlink pilot of each TP. When the number of TPs is not greater than the number of UEs, the overhead due to channel estimation is not significant; however, in an ultra-dense network (UDN) environment where the number of UEs is greater than the number of TPs, channel estimation must be performed using a separate downlink pilot for each TP, which can lead to a problem where the overhead due to channel estimation increases significantly.

[0148] In addition, due to uplink overhead, each UE cannot accurately provide feedback on channel information, or generally, it provides feedback in the form of CQI (channel quality information), PMI (precoding matrix indicator), RI (rank indicator), etc. by quantizing the channel information; however, due to limitations caused by the quantization of channel information, accurate channel information may not be reflected in the feedback. Therefore, there are various limitations in implementing the CJT method of CoMP in existing communication systems.

[0149] Meanwhile, as a method to eliminate cell boundaries of terminals in a UDN environment, a cell-free massive MIMO-based system (which can be referred to as distributed MIMO or a distributed antenna system) with a system structure in which the number of TPs supporting a single terminal is large has recently been proposed. A detailed description of the cell-free massive MIMO-based system will be provided with reference to Fig. 12.

[0150] FIG. 12 is a diagram illustrating a model of a cell-free massive MIMO-based system to which the present disclosure can be applied.

[0151] Referring to FIG. 12, a cell-free massive MIMO-based system can estimate a downlink channel based on an uplink pilot by operating with time division duplexing (TDD). That is, unlike the downlink channel being estimated based on a downlink pilot transmitted from the TP to the UE, the downlink channel can be estimated based on an uplink pilot transmitted from the UE to the TP. The TP (1210) can generate channel information for the terminal based on the uplink pilot received from the UE (1220) and transmit the channel information to the CPU (1200). Through this, the limitations caused by the quantization of channel information and the overhead problems caused by channel estimation as described above can be overcome.

[0152] Subsequently, the CPU (1200) can perform precoding to control multi-user interference based on the channel information. Accordingly, the TP (1210) can coherently transmit data to the UE (1220), thereby enabling the implementation of the CJT method of the CoMP considered in this disclosure.

[0153] On the other hand, since the number of TPs that must cooperate in cell-free massive MIMO systems increases significantly compared to existing systems, a problem may arise where the computational complexity required to control numerous TPs on the CPU increases significantly when implementing the CJT method in cell-free massive MIMO systems. For example, the CPU of a cell-free massive MIMO-based system must accurately synchronize data transmission and reception among numerous TPs, and since numerous TPs cooperate dynamically, the computational complexity of the CPU regarding the precoder generation process (or precoding execution process) considering these cooperating TPs can become very high. In addition, there is a limitation in that the load of data or channel information transmitted through the fronthaul remains high. Therefore, problems may arise in implementing the CJT method of CoMP even in cell-free massive MIMO-based systems.

[0154] Accordingly, the present disclosure proposes a method to solve the problems of fronthaul load and high computational complexity of the CPU that may occur when implementing the CoMP CJT method in a cell-free massive MIMO-based wireless communication system. Specifically, the present disclosure proposes a precoding method in which a plurality of TPs controlled by a CPU are divided into a Central TP group in which precoding is performed centrally by the CPU and a Local TP group in which precoding is performed distributedly at each TP, and each TP is enabled to operate as either a Central TP or a Local TP. Furthermore, according to the precoding method proposed in the present disclosure, a system structure is proposed in which uplink data or downlink data transmission and reception between a plurality of TPs and UEs can be performed.

[0155] According to the present disclosure, scheduling may be performed to determine whether a TP will operate as a Central TP or a Local TP based on a given front-haul capacity and computational complexity according to UE and network performance. At this time, since the computational complexity is distributed and shared among the TPs according to the scheduling result based on the constraints on computational complexity, the scheduling that determines the operation method of such TPs may be referred to as Complexity-Shared Scheduling (CSS). Additionally, CSS may mean distinguishing (determining, or classifying) multiple TPs to perform either the operation performed by the Central TP group or the operation performed by the Local TP group. Furthermore, CSS may mean a process of classifying all TPs into a Central TP group and a Local TP group, or a process of determining the ratio of the Central TP group to the Local TP group among all TPs. Additionally, since it is determined whether precoding will be performed on the CPU (Central TP) or on the TP (Local TP) according to the result of performing CSS, CSS may also mean a precoding method. Meanwhile, for convenience of explanation in the present disclosure, the Central TP group may be referred to as the first group and the Local TP group as the second group.

[0156] In the cell-free massive MIMO system described above, in order to obtain optimal data transmission and reception performance, front-haul capacity (e.g., It can be said that) and computational complexity (for example, We can consider the objective function of [Mathematical Equation 1] as follows, in which (it can be said that) is taken into account.

[0157]

[0158] In the above [Mathematical Formula 1], Is throughput is the amount of computation to be performed for each TP unit, and represents the amount of information to be transmitted over the fronthall link. To solve the optimization problem for the above objective function, two situations can be assumed: when all TPs operate centrally (i.e., Central TPs) or when they operate distributedly (i.e., Local TPs). If all TPs operate as Central TPs, the amount of information to be transmitted over the fronthall link ( ) and total calculation amount( It becomes subject to the limitations of ). In contrast, if all TPs are Local TPs, reception performance may degrade due to high interference between TPs. Considering these characteristics, the CPU, through CSS TP groups that support (e.g., It can be said that) the Central TP group (for example, It can be said that) and Local TP groups (for example, It can be classified (or divided, distinguished) as follows.

[0159] More specifically, the objective function of CSS considering the trade-off between transmission and reception performance and constraints on front-haul capacity and computational complexity can be expressed by the following [Equation 2].

[0160]

[0161] In the above [Equation 2], the amount of information to be transmitted via the front haul link ( ) is the number of antennas (e.g., It can be said that) and symbol size (for example, It can be said that), and quantization level( Q)It can be determined based on [this]. At this time, the CPU determines whether each TP will operate as a Central TP or a Local TP so as to optimize the performance given by the objective function under the given constraints. Specific details regarding the execution of the CSS by the CPU will be explained with reference to Fig. 13.

[0162] FIG. 13 is a diagram illustrating the sequence in which a CPU performs CSS according to one embodiment of the present disclosure.

[0163] Referring to FIG. 13, in step 13-100, the CPU can determine whether to perform a CSS that determines whether TPs controlled by the CPU will operate as Central TPs or Local TPs. The CPU can determine whether to perform the CSS based on at least one of several criteria. For example, the CPU receives channel information regarding a channel between a TP and a UE, and can determine whether to perform the CSS based on said channel information and various criteria. For example, the CPU can initiate the CSS in the following cases. However, the following conditions are merely examples of the present disclosure and the scope of the present disclosure is not limited thereto.

[0164] - When the CPU periodically executes CSS

[0165] - When the CPU executes CSS based on certain criteria (threshold values, etc.)

[0166] - When the UE requests the CPU to perform CSS

[0167] First, when the CPU performs CSS periodically, CSS may be performed for the first time when clustering (which may mean determining the set of TPs to serve the UE) is performed, or CSS may be performed at arbitrary intervals. For example, CSS may be performed at intervals shorter than the large-scale coherence time. Specifically, clustering is performed at large-scale coherence time intervals, which is longer than CSS, or when a terminal handover occurs; however, if channel information changes rapidly, such as when the UE's mobility increases, the CPU may perform CSS at intervals shorter than the clustering interval (for example, T_CSS = T_Clustering / 2). In this case, although CSS is performed more frequently than clustering, since CSS is a procedure that consumes less cost than clustering, which requires performing complex procedures, there is an advantage in that network performance can be optimized at a lower cost by operating CSS than a network that performs only clustering without CSS.

[0168] Secondly, in cases where the CPU performs CSS based on a certain standard (threshold), the UE reports its downlink throughput information or its channel reception status (RSRP), etc., to the CPU via the uplink, and the CPU can determine the uplink and / or downlink throughput of the UE through this. At this time, if the throughput of a specific UE falls below a certain threshold, or if the difference in throughput between the UE with the highest throughput and the UE with the lowest throughput becomes greater than a certain threshold, or if the variance of the UE's throughput distribution becomes greater than a certain threshold, the CPU may perform CSS.

[0169] Additionally, the UE may request the CPU to perform CSS. In this case, the UE may check its downlink throughput or channel status and, if the UE's throughput or channel status falls below a certain threshold, request the CPU to perform CSS so that more Central TPs can be allocated to the UE.

[0170] In step 13-100 above, if the CPU determines that it will perform CSS, in step 13-200, the CPU may determine whether to operate the TPs as Central TPs or Local TPs based on at least one of the front-haul capacity and the computational complexity that the CPU can allow. For example, to maximize performance for cell-bound users through CSS, the CPU may preferentially have TPs supporting UEs with low yield (which may refer to throughput) operate as Central TPs. That is, the CPU may group at least one TP supporting a UE as a group of Local TPs ( ), Central TP's group( When divided by ), the set of the above Central TP ( CSS can be performed to ensure that more TPs belong to ). If the number of UEs that can be supported by TPs in the clustering matrix decreases due to limitations such as the number of pilots, and the number of TPs is fixed, the CPU can increase the proportion of Central TPs among the TPs supporting UEs. On the other hand, if the proportion of Central TPs cannot be increased due to limitations such as complexity, the CPU can allocate computational resources of UEs with already sufficiently good reception performance to lower-tier users (i.e., the CPU can make the Central TPs of UEs with sufficient reception performance operate as Local TPs, and make the Local TPs of UEs with lower performance operate as Central TPs). On the other hand, if a UE requests the CPU to allocate more Central TPs, CSS can be performed to reflect this.

[0171] In addition, the embodiments of the present disclosure are not limited to the examples described above, and the CPU may perform CSS based on various criteria to maximize the reception performance of the UE.

[0172] When CSS execution is completed, in step 13-300, the CPU may transmit the CSS execution result (e.g., an indicator instructing to act as a Central TP or Local TP) to the TPs that were the targets of the CSS execution. The TPs that receive the CSS execution result may act as a Central TP or Local TP depending on the CSS result.

[0173] Meanwhile, the CSS according to one embodiment of the present disclosure may be implemented through TPs containing the eCPRI shown in FIG. 14. In this case, since a TP that was instructed to operate as a Local TP may be instructed by the CPU to operate as a Central TP depending on the result of the CSS execution, or a TP that was instructed to operate as a Central TP may be instructed to operate as a Local TP depending on the result of the CSS execution, the TPs subject to CSS execution must be able to freely select split 1 or split 2 shown in FIG. 14. That is, if layer splitting occurs in split 1 or split 2, all procedures for said split 1 or split 2 may be embedded in the TP so that the TP can perform all necessary procedures according to the selected split. If the precoding procedure is performed in a DU (distributed unit), layer splitting occurs in split 1, and in this case, the DU can be referred to as a Local TP. In contrast, if the precoding procedure is performed in the CU (central unit), layer splitting takes place in split 2, and in this case, the DU can be called the Central TP.

[0174] The present disclosure may be applied to a communication system utilizing eCPRI in which a Local TP that performs precoding in a distributed manner at a DU (or RU) and a Central TP that performs precoding centrally at a CU coexist, depending on the eCPRI function separation point. As described above, a TP corresponding to a Central TP or a Local TP may be changed to operate as a Local TP or a Central TP as needed. That is, according to one embodiment of the present disclosure, for each TP, it may be determined whether precoding is performed in a distributed manner at the corresponding TP or centrally at a CU controlling the corresponding TP.

[0175] As shown in FIG. 13, a data transmission and reception system of the CoMP method can be implemented based on TPs that are instructed to operate as a Central TP or Local TP depending on the result of the CSS execution, and whereby the CPU performs CSS. For a more detailed explanation, refer to FIG. 15a and FIG. 15b.

[0176] FIGS. 15a and FIGS. 15b are drawings illustrating a system structure in which a TP instructed to operate as a Central TP or a Local TP according to the CSS execution result according to one embodiment of the present disclosure transmits and receives uplink data and downlink data.

[0177] First, in FIGS. 15a and FIGS. 15b, for the convenience of explanation, the following assumptions may be applied.

[0178] - L TPs are distributed, and each TP is It is equipped with several antennas, and the above TPs are connected to the CPU through the front hole.

[0179] - Based on the basic premise of a cell-free massive MIMO system that there are UEs and the number of TPs is greater than the number of UEs, the number of the above TPs ( L) is the number of UEs ( K) There are more than that.

[0180] - Each UE is equipped with one antenna, and the channel between the UE and TP has a Rayleigh fading distribution.

[0181] - At this time, The th TP and The channel between the nth terminals is a vector , the spatial correlation between TP antennas for each UE is the correlation matrix , large-scale fading coefficients representing the channel's path loss and shadowing It was defined as.

[0182] Meanwhile, the assumptions described above are merely for convenience of explanation and the present disclosure is not limited thereto. That is, the assumptions described above are merely one embodiment for carrying out the present disclosure, and some of the assumptions may not apply.

[0183] FIG. 15a illustrates a system structure in which, as a result of CSS being performed according to an embodiment of the present disclosure, a UE transmits and receives uplink data to and from a CPU through a Central TP and a Local TP serving it. The Central TP estimates the channel based on the uplink pilot received from the UE and transmits information regarding the estimated channel to the CPU. Subsequently, the CPU calculates a central combining vector based on the estimated channel and estimates the signal by applying the combining vector to the signal transmitted from the UE. In contrast, the Local TP estimates the channel based on the uplink pilot received from the UE and calculates a local combining vector based on the estimated channel. Subsequently, the Local TP estimates the symbol by applying the combining vector to the signal transmitted from the UE and sends the estimated symbol to the CPU, whereupon the CPU combines them to estimate the signal transmitted from the UE. According to the method described above, since the signal transmitted by the UE can be received through a plurality of TPs composed of a Central TP and a Local TP, the JR method considered in the present disclosure can be implemented.

[0184] More specifically, referring to FIG. 15a, the terminals have any number of mutually orthogonal numbers (e.g.,) during the coherence time interval. (There may be several) uplink pilots can be transmitted, and the uplink pilots can be represented by the following [Equation 3].

[0185]

[0186] In mathematical equation 3, each uplink pilot is of arbitrary length (e.g., It can have a length of ). In this case, An uplink pilot is assigned to each UE, and since the number of UEs is generally greater than the number of uplink pilots, a single pilot can be assigned to multiple UEs. The Central TP or Local TP that receives an uplink pilot from a UE establishes a channel between the UE and the TP ( ) can be estimated. In this case, channel estimation can be performed based on, for example, MMSE (minimum mean square error), ZF (zero-forcing), or LS Square (least square).

[0187] Channel estimate values ​​between UE and TP In this case, the estimate of the channel between the UE and all TPs can be expressed by [Equation 4] as follows.

[0188]

[0189] At this time, is, The signal of the th UE If you say that, The data reception signal of the uplink at the nth TP can be represented by the following [Equation 5].

[0190]

[0191] Here, Is It is independent received noise from each antenna of the th TP.

[0192] In the CPU To detect the symbol of the th UE L Combines uplink signals received from TPs, wherein a combination vector (e.g., at each TP) at each TP Uplink data is estimated by combining the (which can be represented as) with weights for all TPs, and this can be expressed as [Equation 6] as follows.

[0193]

[0194] Here, is the result of integrating the combination vectors for each TP, as It can be expressed as, This represents the noise for each TP.

[0195] Meanwhile, the combination vector for each TP It can be calculated based on MR or MMSE. When calculating the combination vector for each TP based on MR, It can be expressed as such, and can also be applied to estimate symbols at each TP. Meanwhile, the central combining vector can be expressed as shown in [Equation 7] below.

[0196]

[0197] Here, is, am.

[0198] The method described above is a method that estimates by centrally combining received signals at the CPU. On the other hand, unlike this, at each TP We can consider a method to estimate the symbols of the i-th UE and collect and combine them in the CPU. At this time The symbols estimated at the nth TP If so, this can be estimated by combining the received signals based on the following [Equation 8].

[0199]

[0200] In this case, if the combination vector is calculated based on MR, And when calculated based on MMSE, it can be expressed as [Equation 9] as follows.

[0201]

[0202] Estimated at each TP in the CPU It is combined in the form of, and this can be called large-scale fading decoding (LSFD).

[0203] Meanwhile, according to one embodiment of the present disclosure, clustering can be assumed in which the TP supports (or serves) only some of the UEs belonging to the system, rather than the TP supporting all UEs within the system. For example, UE index and TP index Regarding , the number of TP antennas When By defining a diagonal matrix consisting of the set of, it is possible to indicate which TP's antenna supports which UE. diagonal matrix( ) can be expressed by the following [Mathematical Formula 10].

[0204]

[0205] In [Mathematical Formula 10], The th TP A set of TPs that supports If it belongs to TP's Assign an identity matrix to each antenna, and The th TP If it does not belong to, a matrix of the same size with all entries being 0 is assigned. Accordingly, A clustering matrix that supports can be represented by the following [Equation 11].

[0206]

[0207] of [Mathematical Formula 11] Using, Uplink transmission data consisting only of clustered TPs serving can be represented by the following [Equation 12].

[0208]

[0209] At this time, is a combination vector for estimating uplink data, and Is Represents the uplink transmission symbol.

[0210] Unlike this The set of UEs supported by the nth TP If so, the above clustering may also be defined by the following [Equation 13].

[0211]

[0212] Meanwhile, in the above clustering situation, in order to consider interference affecting the calculation of the combination vector, the UE can determine the interfering UE that strongly interferes with it. For example, A set of UEs that interfere with If defined as such, the set of such UEs is A TP serving (or supporting) may include all UEs serving, and can be represented by the following [Equation 14].

[0213]

[0214] When considering interfering UEs in such a clustering situation, the existing centralized MMSE coupling vector (Equation 7) or distributed MMSE coupling vector (Equation 9) can be represented by the following [Equation 15] and [Equation 16], respectively.

[0215]

[0216]

[0217] At this time, [Equation 15] can be referred to as the P-MMSE (partial MMSE) combined vector and [Equation 16] as the LP-MMSE (local partial MMSE), in the sense that it is an MMSE combined vector that considers interference from some of the UEs among the entire UE. The CPU can estimate the uplink data transmitted by the UE as described above based on the combined vectors according to [Equation 15] and [Equation 16].

[0218] Hereinafter, with reference to FIG. 15b, a system structure for transmitting and receiving downlink data according to one embodiment of the present disclosure will be described.

[0219] In FIG. 15b, when transmitting and receiving downlink data, the Central TP receives data precoded by the CPU from the CPU, processes the data, and transmits it to the UE, and the Local TP performs precoding on the data to be transmitted to the UE, processes the precoded data, and transmits it to the UE. According to this, since multiple TPs composed of the Central TP and the Local TP can transmit downlink data to the UE, the CJT method considered in the present disclosure can be implemented.

[0220] More specifically, for the convenience of explanation, applying the assumption made in FIG. 15a above, the k-th received signal of the UE in the downlink of FIG. 15b can be expressed by the following [Equation 17].

[0221]

[0222] At this time, Is It is a downlink data signal to be transmitted to the nth UE ( ), represents a precoding vector considering L TPs respectively. Meanwhile, regarding the above precoding vector The allocated power of the th UE When this happens, MR precoding can be applied in each TP as shown in [Equation 18] below.

[0223]

[0224] If channel compatibility (which may be referred to as reciprocity or duality) between the uplink and downlink is assumed, the power of the combination vector for uplink data may be normalized and used as a precoding vector for downlink transmission. In this case, the precoding vector may be used as a central precoder applied by the CPU or a local precoder applied by the TP. Meanwhile, in determining the precoding vector, a vector with the normalized power of the combination vector may be used, or the combination vector may be used, and the present embodiment is not limited thereto.

[0225] Meanwhile, when transmitting and receiving downlink data, clustering can be assumed such that the TP supports only some of the UEs belonging to the system, rather than supporting all UEs within the system as described in FIG. 15a. When the above clustering is assumed, the downlink transmission data can be represented by the following [Equation 19].

[0226]

[0227] At this time, is a precoding vector for downlink data, represents the downlink transmission symbol.

[0228] Meanwhile, as explained in FIG. 15a, the clustering A set of UEs that interfere with It can be defined as. Such a set of UEs is The TP serving can include all UEs serving, and can be represented by the following [Equation 20].

[0229]

[0230] When considering interfering UEs in a cluster situation, central precoders and distributed MMSE precoders can be used as heuristic solutions by normalizing the power of uplink data combination vectors and using them as normalized precoding vectors for downlink transmission, provided that channel compatibility (which can be called reciprocity or duality) between uplink and downlink is assumed.

[0231]

[0232] Meanwhile, in the downlink of a cell-free massive MIMO-based system to which an embodiment of the present disclosure may be applied, a unique downlink DM-RS for the UE ( ) can be assigned. The UE can accurately estimate the downlink channel based on DM-RS and obtain a gain in reception performance accordingly. To this end, assuming a situation where a TP and a UE, each having a single antenna, transmit and receive downlink signals through conjugate beamforming (CB), is the normalized SNR, and go and When the power control coefficient is, conjugate beamforming( through ) The signal being transmitted can be represented by the following [Equation 22].

[0233]

[0234] At this time, via the downlink The signal received by can be represented by the following [Equation 23].

[0235]

[0236] In [Equation 23], represents noise, and in this case, the combined beamformed effective channel gain, ) can be expressed as [Mathematical Formula 24] as follows.

[0237]

[0238] The nth UE is an effective channel ( In order to know ), one must have sufficient information, and the UE If you know, Downlink data through ( ) can be reliably estimated. To estimate, it can be divided into cases where a downlink pilot (which may be referred to as a downlink reference signal, DM-RS, etc.) is transmitted through beamforming and cases where it is not transmitted.

[0239] If DM-RS is not transmitted, perfect channel estimation via uplink files in a massive MIMO environment with a very large number of antennas, and perfect transmit precoding in an ideal environment without mobility, would allow reception based solely on the statistical characteristics of the channel without a downlink pilot due to the channel hardening effect. However, in real-world environments, the number of antennas is insufficient to achieve sufficient channel hardening due to various reasons such as channel estimation errors, interference, and mobility, so the UE cannot decode based solely on the statistical characteristics of the channel. Therefore, in real-world environments, DM-RS is required to estimate the downlink channel through which the data is transmitted in order to receive downlink data coherently.

[0240] Accordingly, the reception procedure for a UE using a single DM-RS, the existing method, is as follows. First, the network provides a unique downlink DM-RS for the UE ( Allocates ), and TP uses the same single DM-RS resource to UE-specific DM-RS( It transmits ), and accordingly, the signal received by the UE can be represented by the following [Equation 25].

[0241]

[0242] In [Mathematical Formula 25], This represents the receiver noise. After that, second If projected, it can be represented by the following [Equation 26].

[0243]

[0244] At the receiving end, the above Effective channels based on MMSE through ( ) is estimated. At this time, the estimated effective channel ( ) can be expressed as [Mathematical Formula 27] as follows.

[0245]

[0246] At this time, in the Rayleigh fading channel performing combined beamforming, the values ​​of [Equation 27] can be expressed by the following mathematical formulas, respectively.

[0247]

[0248]

[0249]

[0250] The effective channel estimated in this way ( through ) is a downlink signal It can receive coherently.

[0251] Meanwhile, the effective channel estimation error (estimation error, )cast In this case, the capacity of the downlink can be calculated based on [Equation 31] as follows.

[0252]

[0253] Referring to [Equation 31], the accurate effective channel ( By estimating ) the estimation error of the effective channel ( It can be derived that reception performance can be improved as ) decreases.

[0254] The situation described above assumes that the TP and the UE each use a single antenna, and the UE receives downlink data through a single DM-RS. Meanwhile, this A multi-antenna TP having multiple antennas Multiple antennas having two antennas It can also be extended to the situation.

[0255] class The channel between ( Each downlink pilot transmitted via ) Defined as such, and the same precoder for each downlink pilot ( Assuming that ) applies, a specific time (e.g., Signals received by the UE during time ( ) can be expressed as [Mathematical Formula 32] as follows.

[0256]

[0257] In [Equation 32], indicates interference caused by another user's DM-RS transmitted from the same DM-RS resource.

[0258] The above received signal ( From ) each effective channel ( ) can be estimated. Then, based on the estimated effective channel, the UE ( ) can generate. The UE receives the downlink signal ( Symbols can be coherently estimated by applying a downlink combination vector to ) and combining them. (e.g., , here can mean the presumed symbol.)

[0259] Meanwhile, according to one embodiment of the present disclosure, multiple DM-RS may be used to obtain a receive diversity gain. In this case, different DM-RS resources may be allocated to the Central TP and Local TP determined as a result of CSS execution, respectively. For example, one DM-RS may be allocated to the Central TP, and the remaining DM-RS may be allocated to the Local TPs. Meanwhile, when using multiple DM-RS, since the diversity gain can be secured only when the correlation between the effective channels of the group is low when grouping the TPs, the CPU may select (or schedule) the Central TPs during CSS execution so that the diversity gain can be secured.

[0260] More specifically, in existing cellular networks, multiple TPs are clustered in one place, and because of this class Inter-effective channel ( Since a high correlation exists between them, as explained earlier, when multiple TPs allocate the same DM-RS resource to transmit pilots to the UE (i.e., transmit pilots using a single DM-RS), there is no significant difference in reception performance compared to perfect CSIR (channel state information reception) even if the UE estimates the effective channel, which is the sum of the channels transmitted by multiple TPs. However, each class Inter-effective channel ( If the correlation between the distributions of ) is very low (e.g., when precoding independently or distributedly in a distributed antenna), allocating DM-RS resources separately for each TP to estimate the effective channels individually can estimate more accurate channels closer to perfect CSIR, and if the receiver is configured using these more accurately estimated channels, a higher diversity gain can be obtained.

[0261] Accordingly, the present disclosure proposes a structure that estimates a channel close to perfect CSIR by using multiple DM-RSs to improve receive diversity performance through accurate estimation of the user's effective channel.

[0262] According to the present disclosure, the CPU allocates different DM-RS resources to the Central TP and Local TP, respectively, and each TP transmits data to the UE based on the allocated DM-RS resources. The reason for allocating DM-RS resources by distinguishing between the Central TP and Local TP in this way is that, in the case of the Central TP, the channel correlation of the Central TPs is reflected in the effective channel through centralized precoding, so DM-RS capable of channel estimation are allocated separately to them. The remaining DM-RS can be allocated to the Local TP, and as the number of DM-RS increases, the UE can accurately estimate the effective channel and improve reception performance.

[0263] Meanwhile, as the overhead increases as the number of DM-RS increases, the number of DM-RS must be limited. In this disclosure, for the convenience of explanation, the case of applying two DM-RS was considered, but it is not limited to this, and more DM-RS may be used.

[0264] To examine the performance gain when using two DM-RSs, we can extend the MIMO pilot allocation structure described above and assume a case where one DM-RS resource is allocated to each of the Central TP group and the Local TP group. In this case, Multi-antenna TP having two antennas and Multiple antennas having two antennas Assuming, class Liver channel ( The two downward link pilots transmitted via ) are, for example, each and It can be represented as follows. Each of the above pilots has the same precorder (e.g., (It can be expressed as.) is applied. At this time, a specific time (e.g., It can be said.) Signals received by the UE (e.g., , (It can be expressed as follows.) can be expressed as [Equation 33] and [Equation 34] respectively as follows.

[0265]

[0266]

[0267] In [Equation 33] and [Equation 34], and represents interference caused by DM-RS of other UEs transmitted from the DM-RS resources of Local TP and Central TP, respectively. is the received signal and From each effective channel class is estimated. Subsequently, the UE estimates the combination vector based on each of the two estimated effective channels. and Generates, and through coherent combining of the generated combination vector, the received signal ( ) can be estimated (or, detected).

[0268] At this time, in order to obtain sufficient receive diversity gain through two DM-RSs, the two effective channels to be estimated class There may be low correlation between them. If the distributions of two effective channels are similar and thus highly correlated, the diversity gain obtained from accurate channel estimation based on multiple DM-RS is smaller than that obtained from estimating effective channels based on a single DM-RS. Conversely, if the distributions of the two effective channels differ and the correlation between channels is low, the performance gain obtained from accurately estimating each channel based on two DM-RSs is significant.

[0269] Accordingly, in order to obtain diversity gain as described above, a CPU according to one embodiment of the present disclosure may determine whether each TP will operate as a Central TP or a Local TP through a CSS, and then assign multiple DM-RSs to the Central TP and Local TP.

[0270] Meanwhile, as described above, when multiple DM-RSs are assigned to the Central TP and Local TP, it is necessary to instruct the UE to perform coherent reception coupling, and for this purpose, a separate indicator (e.g., coherent joint reception indicator, CJRI) may be included in the message and transmitted to the UE. A specific procedure considering such CSS and multiple DM-RS assignments will be explained with reference to FIG. 16.

[0271] FIG. 16 is a diagram illustrating a downlink data transmission and reception procedure when multiple DM-RS are assigned to Central TP and Local TP determined according to the CSS execution result according to one embodiment of the present disclosure.

[0272] Meanwhile, some of the steps 16-100, 16-110, 16-120, 16-130, 16-140, 16-150, 16-160, 16-170, 16-180, 16-190, 16-200, 16-210, 16-220, and 16-230 illustrated in FIG. 16 may be omitted, performed sequentially, or performed simultaneously. This will be explained in detail below.

[0273] In steps 16-100, the UE (1220) may transmit an uplink pilot (which may be referred to as an uplink reference signal or SRS (sounding reference signal)) to the TPs (which may be referred to as a TP group or a set of TPs) (1210) serving it for channel estimation.

[0274] A TP (1210) that has received an uplink pilot from a UE can generate channel information (or, may be channel status information) between the UE (1220) and the TP (1210) based on the uplink pilot in steps 16-110. Then, the TP (1210) can transmit the channel information to the CPU (1200) in steps 16-120. At this time, the channel information may refer to channel information for performing clustering or CSS (large-scale channel information), rather than information about the entire channel for performing precoding.

[0275] A CPU (1200) that receives channel information from each TP (which may be a TP group or a set of TPs) (1210) may determine whether to perform CSS based on at least one of several criteria in steps 16-130. In FIG. 16, an example is given in which the CPU (1200) receives channel information from the TP (1210) and determines whether to perform CSS based on the channel information and several criteria, but the present disclosure is not limited thereto. For example, as described in FIG. 13, CSS may also be initiated by a predetermined period, a specific threshold value, or a request to perform CSS by the UE (1220), in which case steps 16-100 to 16-120 may be omitted.

[0276] If the CPU (1200) decides to perform CSS, the CPU (1200) may perform CSS based on a pre-set standard in steps 16-140 (e.g., a standard set by a network operator). Meanwhile, in steps 16-130, the CPU (1200) may decide whether to perform clustering based on channel information (or channel status information) received in steps 16-120. If the CPU (1200) decides to perform clustering in steps 16-130, the CPU (1200) may perform clustering in steps 16-140. In this case, if the CPU (1200) decides to perform clustering, the CSS may not be performed, but is not limited thereto, the clustering and CSS may be performed simultaneously or sequentially.

[0277] Meanwhile, in step 16-140, it is decided to perform CSS, and when the CSS performance is completed, in step 16-150, the CPU (1200) transmits the result of the CSS performance to each TP (1210). Meanwhile, the result of the CSS performance is whether each TP (1210) will operate as a Central TP or as a Local TP. According to one embodiment of the present disclosure, in order to inform each TP (1210) of the result of the CSS performance, the CPU may transmit a central / local indicator to each TP (1210) indicating whether to operate as a Central TP or a Local TP, and said indicator may consist of 1 bit. For example, if said indicator indicates a value of '0', it may mean that it will operate as a Local TP, and if it indicates a value of '1', it may mean that it will operate as a Central TP. Meanwhile, each Central TP or Local TP may be included in a Central TP group (or set of Central TPs) composed of multiple Central TPs or a Local TP group (or set of Local TPs) composed of multiple Local TPs, and in this case, the CPU (1200) may instruct any one of the TPs included in the Central TP group or Local TP group to operate as a Central TP or Local TP. At this time, the TPs in the group to which the TP instructed by the CPU (1200) to operate as a Central TP or Local TP belongs may operate as a Central TP or Local TP as instructed (i.e., the CPU may instruct them to operate as a Central TP or Local TP on a TP group basis).

[0278] In steps 16-150, the TP (1210) that receives the indicator transmitted from the CPU (1200) can determine whether it will operate as a Central TP or a Local TP based on the indicator. After determining which TP it will operate as, it can generate a central precoder or a local precoder by performing the processing of the Central TP (steps 16-160) or the processing of the Local TP (steps 16-170) as described above. Since the specific details of the processing of each TP have been described above, they will be omitted here.

[0279] Meanwhile, in order to obtain reception diversity gain through the central precoder and local precoder generated as described above, the CPU (1200) may allocate multiple DM-RS resources to the Central TP and Local TP, and allow the UE (1220) to receive signals received from each TP (1210) by coherently combining them based on the effective channels estimated through the multiple DM-RS.

[0280] Accordingly, in steps 16-180, the CPU (1200) determines which TPs will share multiple DM-RS resources to be transmitted to the UE (1220), and in steps 16-190, the CPU (1200) can transmit information regarding the allocation of the DM-RS to the Central TP (or a set or group of Central TPs) and the Local TP (or a set or group of Local TPs) (1210), respectively. Meanwhile, in steps 16-180, the CPU (1200) can allocate DM-RS resources so that the Central TPs share one DM-RS resource. That is, in this case, the Central TPs may be characterized by sharing the same DM-RS resource. A TP (which may be either a Central TP or a Local TP, or both) (1210) that has received information about the allocation of DM-RS from the CPU (1200) can transmit information about the allocation of DM-RS to a UE (1220) that will receive data in steps 16-200.

[0281] Since the UE (1220) does not know whether to coherently receive signals transmitted based on multiple DM-RSs, it is necessary to instruct the UE (1220) to coherently receive combined signals before transmitting downlink data. To this end, a TP (which may be either a Central TP or a Local TP) (1210) may, in steps 16-210, transmit a coherent joint reception indicator (CJRI) (or may be referred to as a coherent reception indicator, CRI) to the UE (1220) to coherently receive data streams transmitted corresponding to multiple DM-RSs. In other words, when a data stream precoded with the same precoder as the DM-RS assigned to each of the multiple TPs is transmitted from each of the multiple TPs (1210) to the UE (1220), the UE (1220) may receive an indicator (e.g., the CJRI described above) that instructs to receive the data stream coherently prior to or simultaneously.

[0282] Meanwhile, generally, in the JT of a CoMP, the Local TP operates in a non-coherent joint transmission (NCJT) manner. That is, it is common for Local TPs to transmit data by independently scheduling (local scheduling) without synchronizing transmission with cooperative TPs. Meanwhile, in steps 16-220, the Local TP according to the present disclosure can transmit data coherently by synchronizing with cooperative TPs such as the Central TP. In other words, the Local TP can choose to transmit data non-coherently or coherently, and can instruct the UE (1220) to do so via CJRI. In steps 16-230, the UE (1220) can receive data coherently or non-coherently depending on the method in which the TP (1210) transmitted the data (coherent transmission or non-coherent transmission). Accordingly, the operation of the UE (1220) may vary depending on whether the UE (1220) receives CJRI from the TP, and this will be explained with reference to FIG. 17.

[0283] FIG. 17 is a diagram illustrating the sequence of operations of a UE according to one embodiment of the present disclosure depending on whether it receives a CJRI.

[0284] Referring to FIG. 17, if the UE receives a CJRI from a TP in step 17-100 of FIG. 17, this means that the cooperating TPs synchronize and transmit a data stream to the UE, so the UE can coherently receive data streams transmitted from the Central TP and the Local TP, respectively, in step 16-230. In this case, since the resource allocation information of the Local TP can be verified through the resource allocation information of the Central TP, the Local TP does not need to inform the UE of separate resource allocation instructions through DCI (downlink control information).

[0285] Meanwhile, when the UE receives CJRI, the operation may be performed differently depending on whether the Local TP and Central TP share DM-RS.

[0286] In steps 17-110, if the Local TP shares a DM-RS with the Central TP (which may mean sharing DM-RS ports or the UE being assigned only one DM-RS port), in step 17-130, the UE performs channel estimation through the single DM-RS and creates a receive filter through the estimated channel. Then, it receives a single DCI (which may mean a DCI transmitted from the Central TP), identifies the resource location assigned to it through the said DCI, and can receive data.

[0287] In contrast, in step 17-110, if the Local TP does not share the DM-RS with the Central TP (which may mean that they each use DM-RS ports independently, or that the UE is assigned two or more DM-RS ports), in step 17-140, the UE estimates one channel based on the multiple DM-RSs assigned to it and creates a receive filter through the estimated channel. Then, it receives one of the DCIs transmitted from the multiple TPs, identifies the resource location assigned to it based on the received DCI, and can receive data.

[0288] Meanwhile, if the UE does not receive the CJRI in step 17-100, this means that the Local TP is transmitting the data stream to the UE without synchronizing with other cooperating TPs. Therefore, the Local TP operates as NCJT, and each Local TP transmits an independent DM-RS and allocates resources to the UE, and transmits a DCI indicating the resource allocation location. Accordingly, the UE receives and combines the non-coherently transmitted data stream in a non-coherent manner. That is, in step 17-120, the UE estimates the channel based on the DM-RS transmitted from each TP for demodulation, identifies the resource locations independently transmitted by each TP to the UE based on the DCI sent independently by each TP, and can demodulate the location based on the channel estimated through the DM-RS of the corresponding TP.

[0289] Meanwhile, some of steps 17-100, 17-110, 17-120, 17-130, and 17-140 of FIG. 17 may be omitted, performed sequentially, or performed simultaneously.

[0290] Meanwhile, as described above, CSS performed to obtain optimal data transmission and reception performance can be implemented in the form of various algorithms, which will be explained with reference to Fig. 18.

[0291] FIG. 18 is a diagram illustrating an example of a CSS algorithm that can be performed on a CPU according to one embodiment of the present disclosure.

[0292] Referring to Fig. 18, as an example of a CSS algorithm implementation, (At this time, A set of TPs that supports (e.g., which can be specified according to predetermined conditions or arbitrarily specified by the CPU) (It can be said that) a procedure was illustrated to check and change all (or some) of the TPs belonging to this into Central TPs.

[0293] First, in step 18-100, the CPU determines whether to perform CSS based on at least one of several criteria. For example, as described above, if a CSS period is set, the CPU may perform CSS periodically based on said period, or determine whether to perform CSS based on certain criteria such as a threshold value, or determine whether to perform CSS when receiving a request to perform CSS from the UE. In step 18-100, if the CPU decides not to perform CSS, data transmission and reception can be performed based on the existing Central TP or Local TP. On the other hand, if it decides to perform CSS, the operation of step 18-110 is performed. At this time, the CPU [determines] the available front-haul capacity (e.g., ) and computational complexity (e.g., Considering ), the total number of Central TPs supported by the above CPU (e.g., ) can be calculated.

[0294] In steps 18-110, the CPU can identify UEs that satisfy predetermined conditions based on throughput information for each of at least one UE. Additionally, the CPU can serve the identified UEs using a set of TPs ( You can check ). For example, based on throughput information, the CPU with the lowest yield (throughput value) Check , and the TP set serving the UE( ...can verify ). Alternatively, the CPU can identify UEs corresponding to a predetermined number, a number determined according to predetermined conditions, or a number calculated by the CPU, starting from the UE with the lowest yield in order of lowest yield, and identify a set of TPs serving the identified UEs. In this case, the number calculated by the CPU is, for example, the number calculated in steps 18-100 It can mean.

[0295] Subsequently, in steps 18-120, the CPU identifies the set of TPs ( All TPs corresponding to Local TPs among the TPs belonging to ) can be converted to Central TPs. Meanwhile, although the description of FIG. 18 states that all TPs corresponding to Local TPs can be converted to Central TPs, it is not limited to this, and at least one of the Local TPs can be converted to a Central TP. In this case, converting a TP corresponding to a Local TP to a Central TP may mean that the Local TP is changed to the group to which the Central TP belongs. Alternatively, converting a TP that was formerly a Local TP to a Central TP may mean that the Local TP is instructed to perform the operation performed by the Central TP. Furthermore, although the description of FIG. 18 gave the conversion of a Local TP to a Central TP as an example, it is not limited to this, and the CPU [identifies] a set of TPs ( It is also possible to switch a TP corresponding to a Central TP among them to a Local TP. Meanwhile, steps 18-120 may refer to an operation in which the CPU adjusts the ratio of Central TPs and Local TPs in the set of TPs identified in steps 18-110. That is, based on a predetermined ratio between Central TPs and Local TPs, the CPU may adjust the ratio between Central TPs and Local TPs in the set of TPs in steps 18-120 by instructing or switching an existing Central TP to operate as a Local TP, or instructing or switching an existing Local TP to operate as a Central TP, as described above. At this time, the ratio between Central TPs and Local TPs may be characterized by being determined based on at least one of computational complexity and fronthaul capacity.

[0296] Subsequently, in steps 18-130, the CPU can check whether CSS has ended. The CPU can check whether CSS has ended based on various criteria. For example, if the number of Central TPs is the total number of supported Central TPs calculated in steps 18-110 ( If it is smaller than ), you can return to steps 18-110. Conversely, if the number of Central TPs is If it is equal to or greater than, the CPU may terminate CSS execution.

[0297] Meanwhile, some of the steps 18-100, 18-110, 18-120, and 18-130 of FIG. 18 may be omitted, performed sequentially, or performed simultaneously.

[0298] As described above, by performing CSS according to an algorithm that considers the given fronthole capacity and computational complexity, a communication system that provides enhanced services can be implemented.

[0299] FIG. 19 is a drawing illustrating a CSS framework based on a TP that incorporates eCPRI according to one embodiment of the present disclosure.

[0300] Referring to Fig. 19, as a result of performing CSS, it is determined where to perform layer splitting for each TP (split 1 or split 2 shown in Fig. 14), and accordingly, the procedures for CU and DU differ. Since the processing of the TP after it is determined to be Central TP or Local TP as a result of performing the CSS has been described above, a detailed explanation will be omitted.

[0301] Meanwhile, each TP can perform all procedures corresponding to different layer splitting, and by performing different procedures according to the results of the CSS execution, optimal data transmission and reception performance can be obtained under constraints on CPU computation amount and front-hole usage.

[0302] FIGS. 20 and FIGS. 21 are drawings showing the yield of the entire user when one embodiment of the present disclosure is applied.

[0303] Figures 20 and 21 show the yield of all users as a CDF in a system with 100 TPs and 20 UEs, supporting 2 UEs or 4 UEs per TP, respectively. The solid line represents the case where MMSE is performed considering interference from all users, while the dotted lines represent the method of generating and transmitting a precoder that considers only the interference of UEs belonging to their own cluster (or the set of TPs to which they belong) using TP clustering. In this case, the leftmost dotted line graph represents the L-MMSE performance using a distributed scalable MMSE precoder, and the rightmost dotted line graph represents the performance of the P-MMSE method using a centralized scalable MMSE precoder. The middle graph shows the CDF plotted while randomly modifying TP generation to be centralized. In both Figures 20 and 21, it can be observed that performance trades off as the percentage of centralized TPs changes from 0% to 100%. Therefore, it is necessary to select a precorder generation method to maximize the performance of the TP depending on the complexity and front haul load.

[0304] FIGS. 22 and FIGS. 23 are drawings showing the performance of the bottom 10% of users when one embodiment of the present disclosure is applied.

[0305] Figures 22 and 23 show the performance of the bottom 10% of users when supporting 2 UEs or 4 UEs per TP, respectively, in a system with 100 TPs and 20 UEs, as in Figures 20 and 21.

[0306] At this time, it can be confirmed that the performance of the bottom 10% of users can be improved by up to 2 or 2.5 times in each embodiment through the control of the centralized or distributed precoder generation method of the TP. In the existing method, all TPs must operate using only distributed precoders considering the constraints due to the load of the front hole, whereas by applying the CSS structure of the present disclosure to control the TP precoder generation method according to the capacity constraints of the front hole, the performance of the bottom 10% of users is improved by up to 2 to 2.5 times.

[0307] FIGS. 24 and 25 are drawings showing the performance of the bottom 10% of users when one embodiment of the present disclosure is applied.

[0308] FIGS. 24 and 25 illustrate the results of evaluating the yield of the bottom 10% of users when supporting 2 UEs and 4 UEs per TP, respectively, in a system with 100 TPs and 20 UEs. In FIG. 24, the average number of TPs servicing the UE is 10, and in FIG. 25, the average number of TPs servicing the UE is 20.

[0309] In Figures 24 and 25, the Distributed-MMSE: Clustering graph represents the performance of the L-MMSE method, where all TPs are Local TPs and use a distributed scalable MMSE precoder for the UEs they serve. The Partial_MMSE: Clustering graph represents the performance of the P-MMSE method, where all TPs are Central TPs that have performed clustering and use a centralized scalable MMSE precoder. The Multicell-MMSE: Full Clustering graph represents the theoretical maximum performance that can be obtained when all TPs are Central TPs and serve all UEs.

[0310] The Hybrid-MMSE: Clustering+Random CSS graph in Figures 24 and 25 shows the yield of the bottom 10% of users as TPs are randomly changed to Central TPs (Random CSS). According to the Hybrid-MMSE: Clustering+Random CSS graph in Figures 24 and 25, it can be seen that performance is traded off as the percentage of Central TPs changes from 0% to 100%.

[0311] The Hybrid-MMSE: Clustering+Greedy CSS graph in Figures 24 and 25 represents the performance when using a method (Greedy CSS) that preemptively switches TPs serving low-performance UEs to Central TPs, unlike the aforementioned Random CSS. According to the Hybrid-MMSE: Clustering+Greedy CSS graph in Figures 24 and 25, as the percentage of Central TPs changes from 0% to 100%, it can be seen that the performance of the bottom 10% of UEs improves faster than in the case according to the Random CSS method.

[0312] Therefore, referring to the graphs shown in Figures 24 and 25, it can be seen that it is necessary to select an optimal precoder generation method to obtain maximum performance depending on the CPU computational complexity and front haul load.

[0313] FIG. 26 is a diagram illustrating the results of comparing the user's bit error performance based on the presence or absence of channel correlation between TP groups determined by CSS execution when one or two DM-RSs are used when applying one embodiment of the present disclosure.

[0314] Figure 26 assumes a single antenna situation where the total number of antennas for the Central TP and Local TP is 100 each. The effective channel vectors coming from each TP group When so, transmission correlation between effective channels It can be expressed by the following mathematical formula.

[0315]

[0316] At this time, is the correlation coefficient, If this value is 0.9, there is no correlation between the Central TP and the Local TP, and if it is 0.9, it is an environment with high correlation. Therefore, the effective channel vector of the group reflecting the transmission correlation can be expressed by [Equation 36] as follows.

[0317]

[0318] Assuming that the effective channel was accurately estimated through DM-RS, when one DM-RS is used, one effective channel is generated ( ) is estimated, and when two DM-RS are used and are estimated separately. Consequently, when there is only one effective channel, the sum of each channel is estimated and received, and when there are two effective channels, the values ​​received through them are combined. In this case, while sufficient diversity gain through the antenna cannot be obtained when using one DM-RS, when using two DM-RS and Maximum diversity can be obtained when they are independent and have the same distribution. According to Fig. 26, It can be confirmed that bit error performance improves as the correlation between Central TP and Local TP decreases.

[0319] FIG. 27 is a drawing illustrating the structure of a UE to which an embodiment of the present disclosure can be applied.

[0320] Referring to FIG. 27, the UE may include a transceiver (2710), a control unit (2720), and a memory (2730). In the present disclosure, the control unit may be defined as a circuit or an application-specific integrated circuit or at least one processor.

[0321] The transmitting and receiving unit (2710) can transmit and receive signals. The transmitting and receiving unit (2710) can receive data streams (or data, signals) transmitted from, for example, Central TP and Local TP.

[0322] The control unit (2720) can control the overall operation of the UE according to one embodiment proposed in the present disclosure. For example, the control unit (2720) can control the signal flow between each block to perform operations according to the diagram (or flowchart, flowchart) described above.

[0323] The memory (2730) can store at least one of the information transmitted and received through the transmission and reception unit (2710) and the information generated through the control unit (2720).

[0324] FIG. 28 is a drawing illustrating the structure of a TP to which an embodiment of the present disclosure can be applied.

[0325] Referring to FIG. 28, the TP may include a transceiver (2810), a control unit (2820), and a memory (2830). In the present disclosure, the control unit may be defined as a circuit or an application-specific integrated circuit or a processor.

[0326] The transceiver (2810) may include a communication unit or a network interfacing unit, and according to one embodiment of the present disclosure, the transceiver (2810) may be connected to the CPU through a front hole to transmit and receive signals. Additionally, the TP may transmit and receive signals with the UE through the transceiver (2810).

[0327] The control unit (2820) can control the overall operation of the TP according to the embodiment proposed in the present disclosure. For example, the control unit (2820) can control the signal flow between each block to perform operations according to the diagram (or flowchart, flowchart) described above. For example, if the CPU instructs the TP to operate as a Central TP or a Local TP, the TP can be controlled to perform operations according to the instruction.

[0328] The memory (2830) can store at least one of the information transmitted and received through the transmission and reception unit (2810) and the information generated through the control unit (2820).

[0329] FIG. 29 is a diagram illustrating the structure of a network entity to which an embodiment of the present disclosure can be applied.

[0330] Referring to FIG. 29, a network entity (CPU, which may refer to a central unit (CU) according to one embodiment of the present disclosure) may include a transceiver (2910), a control unit (2920), and a memory (2930). In the present disclosure, the control unit may be defined as a circuit or an application-specific integrated circuit or a single processor.

[0331] The transceiver (2910) may include a communication unit or a network interfacing unit, and the transceiver (2910) according to one embodiment of the present disclosure may be connected to a TP through a front hole to transmit and receive signals. Additionally, signals may be transmitted and received with other network entities (e.g., may refer to an MME, gateway of an LTE system, or an AMF, SMF, etc. of a 5G (NR) system) through the transceiver (2910).

[0332] The control unit (2920) can control the overall operation of a network entity according to an embodiment proposed in the present disclosure. For example, the control unit (2920) can control the signal flow between each block to perform operations according to the diagram (or flowchart, flowchart) described above. For example, according to one embodiment of the present disclosure, it can determine whether to perform CSS to control the ratio between Central TP and Local TP, and can control the network entity so that CSS is performed.

[0333] The memory (2930) can store at least one of the information transmitted and received through the transmission and reception unit (2910) and the information generated through the control unit (2920).

[0334] Meanwhile, in the present disclosure, a network entity may refer to an external server or an external network entity configured to control at least one TP.

[0335] According to various embodiments of the present disclosure as described above, in a communication system composed of a plurality of TPs (or DUs) and a CPU (or CU) controlling them, a precoding method is provided that takes into account the computational complexity allowed to the CPU controlling the plurality of TPs and the capacity of the front hole, which is a signal transmission and reception channel between the CPU and the TPs. According to this, when transmitting and receiving uplink data or downlink data between a UE and a plurality of TPs according to the CoMP method, the UE can be enabled to have optimal data transmission and reception performance.

[0336] Although the present disclosure describes a communication system based on a star topology in which at least one TP (or DU) is directly connected to one CPU (or CU) in a 1-hop manner, the present disclosure is not limited thereto. The embodiments proposed in the present disclosure may also be applied to various communication systems, such as a communication system with multiple CUs, a multi-hop communication system in which a DU is connected to another DU, or a communication system based on various topologies such as a bus or a mesh.

[0337] In the drawings illustrating the method of the present disclosure, the order of description does not necessarily correspond to the order of execution, and the order of execution may be changed or executed in parallel.

[0338] Alternatively, the drawings describing the method of the present disclosure may omit some components and include only some components to the extent that the essence of the present invention is not impaired.

[0339] Meanwhile, the present specification and drawings disclose preferred embodiments of the present disclosure. Although specific terms have been used, they are used merely in a general sense to facilitate the explanation of the technical content of the present disclosure and to aid in understanding the invention, and are not intended to limit the scope of the present disclosure. It is obvious to those skilled in the art that, in addition to the embodiments disclosed herein, other variations based on the technical concept of the present disclosure are possible.

[0340] That is, although specific embodiments have been described in the detailed description of the present disclosure, it is understood that various modifications are possible without departing from the scope of the present disclosure, and the scope of the present disclosure should not be limited to the described embodiments but should be defined by the claims set forth below as well as equivalents thereof.

Claims

Claim 1 A method for a network entity in a communication system, comprising: a step of determining whether to perform scheduling to adjust the ratio between a plurality of first transmission points (TPs) included in a first group serving at least one terminal and a plurality of second TPs included in a second group; a step of determining whether to switch at least one of the plurality of second TPs to the first TP based on information associated with the at least one terminal when it is determined to perform the scheduling; and a step of transmitting an indicator to the at least one second TP instructing it to operate as the first TP when it is determined to switch the at least one second TP to the first TP, wherein when operating as the first TP, precoding for a signal is performed in the network entity, and when operating as the second TP, precoding for a signal is performed in the second TP. Claim 2 ◈Claim 2 was abandoned upon payment of the setup registration fee.◈ The method of Claim 1, further comprising: a step of determining whether to switch at least one of the plurality of first TPs to a second TP based on information associated with at least one terminal when it is determined to perform the scheduling; and a step of transmitting an indicator to the at least one first TP instructing it to operate as the second TP when it is determined to switch the at least one first TP to the second TP. Claim 3 A method according to claim 1, further comprising: a step of assigning a plurality of DM-RS (demodulation-reference signal) ports to each of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group; and a step of transmitting information about the DM-RS ports to the plurality of first TPs included in the first group and the plurality of second TPs included in the second group, wherein the plurality of first TPs included in the first group share the same DM-RS port. Claim 4 A method according to claim 3, wherein when the plurality of DM-RS ports are assigned to each of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group, a coherent joint reception indicator (CJRI) indicating to receive data to be transmitted from the plurality of first TPs included in the first group and the plurality of second TPs included in the second group in synchronization is transmitted to the at least one terminal. Claim 5 ◈Claim 5 was abandoned upon payment of the registration fee.◈ A method according to Claim 1, characterized in that whether the scheduling is performed is determined based on at least one of channel status information for each of the at least one terminal, a predefined period, or whether a message requesting the scheduling to be performed is received from the at least one terminal. Claim 6 ◈Claim 6 was abandoned upon payment of the registration fee.◈ The method according to Claim 1, wherein the step of determining whether to convert the at least one second TP to the first TP comprises: a step of identifying the first terminal with the lowest throughput value among the at least one terminals based on throughput information corresponding to each of the at least one terminals; a step of identifying a third TP serving the first terminal among the at least one second TPs; and a step of determining whether to convert the third TP to the first TP. Claim 7 ◈Claim 7 was abandoned upon payment of the registration fee.◈ A method according to Claim 1, wherein the number of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group is greater than the number of the at least one terminal, and the maximum number of TPs that can be included in the first group is determined based on at least one of the computational complexity and fronthaul capacity that the network entity can allow. Claim 8 In a network entity of a communication system, the network entity comprises: a transceiver that transmits and receives signals with a plurality of TPs through a fronthaul; A network entity comprising a control unit that determines whether to perform scheduling to adjust the ratio between a plurality of first TPs (transmission points) included in a first group serving at least one terminal and a plurality of second TPs included in a second group, and when it is determined to perform said scheduling, determines whether to convert at least one of the plurality of second TPs into a first TP based on information associated with the at least one terminal, and when it is determined to convert the at least one second TP into the first TP, transmits an indicator to the at least one second TP through the transceiver unit instructing it to operate as the first TP, wherein when operating as the first TP, precoding of a signal is performed in the network entity, and when operating as the second TP, precoding of a signal is performed in the second TP. Claim 9 A network entity according to claim 8, wherein the control unit, when deciding to perform the scheduling, determines whether to switch at least one of the plurality of first TPs to a second TP based on information associated with at least one terminal, and when it is determined to switch at least one first TP to the second TP, transmits an indicator instructing the at least one first TP to operate as the second TP through the transceiver. Claim 10 A network entity according to claim 8, wherein the control unit assigns a plurality of DM-RS (demodulation-reference signal) ports to each of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group, transmits information regarding the DM-RS ports to the plurality of first TPs included in the first group and the plurality of second TPs included in the second group through the transceiver, and wherein the plurality of first TPs included in the first group share the same DM-RS ports. Claim 11 A network entity according to claim 10, wherein, when the plurality of DM-RS ports are assigned to each of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group, a CJRI (coherent joint reception indicator) indicating to receive data to be transmitted from the plurality of first TPs included in the first group and the plurality of second TPs included in the second group in synchronization is transmitted to the at least one terminal. Claim 12 A network entity according to claim 8, characterized in that whether the scheduling is performed is determined based on at least one of channel state information for each of the at least one terminal, a predefined period, or whether a message requesting the scheduling to be performed is received from the at least one terminal. Claim 13 A network entity according to claim 8, wherein the control unit identifies a first terminal with the lowest throughput value among the at least one terminal based on throughput information corresponding to each of the at least one terminal, identifies a third TP serving the first terminal among the at least one second TP, and determines whether to switch the third TP to the first TP. Claim 14 A network entity according to claim 8, wherein the communication system has more than the number of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group than the number of the at least one terminal, and the maximum number of TPs that can be included in the first group is determined based on at least one of the computational complexity and fronthaul capacity that the network entity can allow.

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