WO2022055196A1

WO2022055196A1 - Multi-antenna-based precoding method and device in wireless communication system

Info

Publication number: WO2022055196A1
Application number: PCT/KR2021/012013
Authority: WO
Inventors: 이승현; 한민식; 강충구; 이재원; 이효진
Original assignee: 삼성전자 주식회사; 고려대학교 산학협력단
Priority date: 2020-09-11
Filing date: 2021-09-06
Publication date: 2022-03-17
Also published as: KR20230066275A

Abstract

The present disclosure relates to a 5G or 6G communication system for supporting a data transmission rate higher than that of a 4G communication system, 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 a network entity comprises steps of: determining whether to perform scheduling for adjusting 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; determining whether to convert at least one from among the plurality of second TPs into a first TP on the basis of information associated with the at least one terminal, if performance of the scheduling has been determined; and transmitting, to the at least one second TP, an indicator indicating an operation with the first TP, if conversion of the at least one second TP into the first TP has been determined, wherein, if operating occurs with the first TP, signals are precoded in the network entity, and if operating occurs with the second TP, signals are precoded in the second TP. Therefore, an improved service can be provided in an environment where computational complexity, which can be permitted by a CPU controlling multiple TPs, and the fronthaul capacity are limited.

Description

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

The present disclosure relates to a wireless communication system, and more particularly, in a communication system considering function split into a central unit (CU) and a distributed unit (DU), a data transmission/reception path between the CU and the DU The present invention relates to a precoding method in consideration of a load of a fronthaul and a computational complexity of a CU for controlling a DU, and an apparatus capable of performing the same.

Looking back on the progress of wireless communication generations, technologies for mainly human services such as voice, multimedia, and data have been developed. After the commercialization of 5G ( ^5th -generation) communication system, it is expected that connected devices, which are on an explosive increase, will be connected to the communication network. Examples of things connected to the network include vehicles, robots, drones, home appliances, displays, smart sensors installed in various infrastructures, construction machines, and factory equipment. Mobile devices are expected to evolve into various form factors such as augmented reality glasses, virtual reality headsets, and hologram devices. In the 6G (6th ^-gerneration ) era, efforts are being made to develop an improved 6G communication system to provide various services by connecting hundreds of billions of devices and things. For this reason, the 6G communication system is called a system after 5G communication (Beyond 5G).

In a 6G communication system predicted to be realized around 2030, the maximum transmission speed is tera (ie, 1,000 gigabytes) bps, and the wireless latency is 100 microseconds (μsec). That is, the transmission speed in the 6G communication system is 50 times faster than in the 5G communication system, and the wireless delay time is reduced by one-tenth.

In order to achieve such high data rates and ultra low latency, 6G communication systems use terahertz bands (such as the 95 gigahertz (95 GHz) to 3 terahertz (3 THz) bands). implementation is being considered. In the terahertz band, compared to the millimeter wave (mmWave) band introduced in 5G, the importance of technology that can guarantee the signal reach, that is, the coverage, is expected to increase due to more severe path loss and atmospheric absorption. As major technologies to ensure coverage, new waveforms, beamforming, and massive arrays that are superior in terms of coverage than radio frequency (RF) devices, antennas, orthogonal frequency division multiplexing (OFDM) Multi-antenna transmission technologies such as input and multiple-output (MIMO)), full dimensional MIMO (FD-MIMO), array antennas, and large scale antennas should be developed. In addition, new technologies such as metamaterial-based lenses and antennas, high-dimensional spatial multiplexing technology using orbital angular momentum (OAM), and reconfigurable intelligent surface (RIS) are being discussed to improve the coverage of terahertz band signals.

In addition, in order to improve frequency efficiency and system network, in a 6G communication system, a full duplex technology in which an uplink and a downlink simultaneously use the same frequency resource at the same time, satellite and HAPS (high-altitude platform stations); AI-based communication technology that realizes system optimization by utilizing dynamic spectrum sharing technology and artificial intelligence (AI) from the design stage and internalizing end-to-end AI support functions, limiting the limitations of terminal computing power The development of next-generation distributed computing technology that realizes services of exceeding complexity by utilizing ultra-high-performance communication and computing resources (mobile edge computing (MEC), cloud, etc.) is being developed. In addition, through the design of a new protocol to be used in the 6G communication system, the implementation of a hardware-based security environment, the development of mechanisms for the safe use of data, and the development of technologies for maintaining privacy, the connectivity between devices is further strengthened and the network is further enhanced. Attempts to optimize, promote the softwareization of network entities, and increase the openness of wireless communication continue.

Due to the research and development of this 6G communication system, the next hyper-connected experience (the next hyper-connected) through the hyper-connectivity of the 6G communication system, which includes not only the connection between objects but also the connection between people and objects. experience) is expected to become possible. Specifically, the 6G communication system is expected to provide services such as true immersive extended reality (XR), high-fidelity mobile hologram, and digital replica. In addition, services such as remote surgery, industrial automation, and emergency response through security and reliability enhancement are provided through the 6G communication system, so it is applied in various fields such as industry, medical care, automobiles, and home appliances. will be

In keeping with the development of the communication system as described above, there is an increasing demand for a technology that provides improved transmission/reception performance to user equipment (UE). As a method in response to this request, a structure of a communication system capable of transmitting and receiving data according to a coordinated multi-point (CoMP) method, which is a multi-cell cooperative communication technology, has been proposed. The CoMP method is a method in which a plurality of TPs (transmission points) cooperate to transmit and receive data with at least one UE. Through this, a UE located relatively far from the TP can have improved data transmission/reception performance, and thus It can support efficient communication service. On the other hand, as the number of TPs that cooperate to perform data transmission to the UE increases, the computational complexity of a central processing unit (CPU) (or network entity) controlling the TPs greatly increases, and the signal between the CPU and the TPs increases. There is a problem in that the load of the fronthaul, which is a transmission/reception passage, increases.

In a communication system composed of multiple TPs (for example, a cell-free massive MIMO (multi-input multi-output) system in which data transmission and reception is possible by multiple TPs and the boundary between cells is broken), the CoMP method Accordingly, when uplink data or downlink data is transmitted/received between the UE and a plurality of TPs, problems such as an increase in computational complexity of the CPU and an increase in the load on the front haul, which is a data transmission/reception path between the CPU and the TPs, may occur. Therefore, it is necessary to devise a precoding method capable of solving such a problem and a system structure to which the method can be applied.

In order to solve the above problems, according to an embodiment of the present disclosure, a method of a network entity in a communication system is provided. The method of the network entity is for adjusting a 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. determining whether to perform scheduling; When it is determined to perform the scheduling, it is determined whether to convert at least one second TP among the plurality of second TPs in the second group to a first TP based on information associated with the at least one terminal to do; transmitting an indicator instructing to operate as the first TP to the at least one second TP when it is determined to switch the at least one second TP to the first TP; In the case of operating as , precoding of the signal is performed by the network entity, and when operating as a second TP, precoding of the signal is performed by the second TP.

Also, according to an embodiment of the present disclosure, a network entity of a communication system is provided. The network entity determines whether to perform scheduling for adjusting a ratio between a plurality of first TPs included in a first group and a plurality of second TPs included in a second group serving the transceiver and at least one terminal, , whether to convert at least one second TP among the plurality of second TPs in the second group to a first TP based on information associated with the at least one terminal when determining to perform the scheduling and, when it is determined to switch the at least one second TP to the first TP, a control unit configured to transmit an indicator instructing the at least one second TP to operate as the first TP through the transceiver and, when operating as a first TP, precoding is performed on the signal in the network entity, and when operating as a second TP, precoding is performed on the signal in the second TP. .

According to various embodiments of the present disclosure, in a communication system configured with a plurality of TPs, a precoding method is provided in consideration of the computational complexity allowed for the CPU controlling the plurality of TPs and the capacity of the front haul, which is a signal transmission/reception path between the CPU and the TPs. . According to this, when it is desired to transmit/receive uplink data or downlink data between the UE and a plurality of TPs according to the CoMP scheme, the UE may have optimal data transmission/reception performance.

Effects obtainable in the present disclosure are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those of ordinary skill in the art to which the present disclosure belongs from the description below. will be.

The above and other objects, features and advantages of the present disclosure will become clearer through the following description of embodiments of the present disclosure with reference to the accompanying drawings.

1 is a diagram illustrating a structure of a cellular mobile communication system to which the present disclosure can be applied.

2 is a diagram illustrating a long term evolution (LTE) system structure of a 3GPP standard to which the present disclosure can be applied.

3 is a diagram illustrating a radio protocol structure in a 3GPP standard LTE system to which the present disclosure can be applied.

4 is a diagram illustrating a system structure of a 3GPP standard next-generation mobile communication to which the present disclosure can be applied.

5 is a diagram illustrating a radio protocol structure in a 3GPP standard next-generation mobile communication system to which the present disclosure can be applied.

6 is a diagram illustrating a structure of a system to which a non-coordinated multi point (non-CoMP) scheme is applied according to an embodiment of the present disclosure.

7 is a diagram illustrating a structure of a system to which a coordinated multi point (CoMP) scheme is applied according to an embodiment of the present disclosure.

8 is a diagram illustrating the classification of CoMP schemes in an LTE system or a next-generation mobile communication system to which the present disclosure can be applied.

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

10 is a diagram illustrating a distributed antenna system in which the CJT scheme of CoMP according to an embodiment of the present disclosure can be implemented.

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

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

13 is a diagram illustrating an order in which a CPU performs complexity-shared scheduling (CSS) according to an embodiment of the present disclosure.

14 is a diagram illustrating a location of a function separation point according to an embodiment of the present disclosure.

15A is a diagram illustrating a system structure in which uplink data is transmitted/received between a TP instructed to operate as a Central TP or a Local TP and a UE according to a CSS execution result according to an embodiment of the present disclosure.

FIG. 15B is a diagram illustrating a system structure in which a TP instructed to operate as a Central TP or a Local TP and a UE transmit and receive downlink data according to a CSS execution result according to an embodiment of the present disclosure.

16 is a diagram illustrating a downlink data transmission/reception procedure when multiple demodulation-reference signals (DM-RSs) are allocated to a Central TP and a Local TP determined according to a CSS execution result according to an embodiment of the present disclosure.

17 is a diagram illustrating a sequence in which a UE operates depending on whether a coherent joint reception indicator (CJRI) is received according to an embodiment of the present disclosure.

18 is a diagram illustrating an example of a CSS algorithm that may be executed in a CPU according to an embodiment of the present disclosure.

19 is a diagram illustrating a CSS framework based on a TP embedding enhanced CPRI (eCPRI) according to an embodiment of the present disclosure.

20 is a diagram illustrating a result of evaluating a user average yield while increasing a ratio of a central TP when supporting two UEs per TP when an embodiment of the present disclosure is applied.

21 is a diagram illustrating a result of evaluating a user average yield while increasing a ratio of a central TP when four UEs per TP are supported when an embodiment of the present disclosure is applied.

22 is a diagram illustrating a result of evaluating a lower performance 10% user yield while increasing a central TP ratio when supporting two UEs per TP when an embodiment of the present disclosure is applied.

23 is a diagram illustrating a result of evaluating a lower performance 10% user yield while increasing a ratio of a central TP when supporting 4 UEs per TP when an embodiment of the present disclosure is applied.

24 is a diagram illustrating a result of evaluating a yield of 10% lower performance users while increasing a ratio of a central TP when supporting two UEs per TP when an embodiment of the present disclosure is applied.

25 is a diagram illustrating a result of evaluating a yield of 10% lower performance users while increasing a ratio of a central TP when supporting 4 UEs per TP when an embodiment of the present disclosure is applied.

26 is a diagram illustrating a result of comparing the bit error performance of a user according to the presence or absence of channel correlation between groups determined by performing CSS when one or two DM-RSs are used when an embodiment of the present disclosure is applied. .

27 is a diagram illustrating a structure of a UE to which an embodiment of the present disclosure can be applied.

28 is a diagram illustrating a structure of a TP to which an embodiment of the present disclosure can be applied.

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

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

In describing the embodiments, descriptions of technical contents that are well known in the technical field to which the present disclosure pertains and are not directly related to the present disclosure will be omitted.

This is to more clearly convey the gist of the present disclosure without obscuring the gist of the present disclosure by omitting unnecessary description.

For the same reason, some components are exaggerated, omitted, or schematically illustrated in the accompanying drawings. In addition, the size of each component does not fully reflect the actual size. In each figure, the same or corresponding elements are assigned the same reference numerals.

Advantages and features of the present disclosure, and a method for achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings.

However, the present disclosure is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only the present embodiments complete the configuration of the present disclosure, and common knowledge in the art to which the present disclosure pertains It is provided to fully inform those who have the scope of the invention, and the present disclosure is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

At this time, it will be understood that each block of the flowchart diagrams and combinations of the flowchart diagrams may be performed by computer program instructions. These computer program instructions may be embodied in a processor of a general purpose computer, special purpose computer, or other programmable data processing equipment, such that the instructions performed by the processor of the computer or other programmable data processing equipment are not described in the flowchart block(s). It creates a means to perform functions. These computer program instructions may also be stored in a computer-usable or computer-readable memory that may direct a computer or other programmable data processing equipment to implement a function in a particular manner, and thus the computer-usable or computer-readable memory. It is also possible that the instructions stored in the flow chart block(s) produce an article of manufacture containing instruction means for performing the function described in the flowchart block(s). The computer program instructions may also be mounted on a computer or other programmable data processing equipment, such that a series of operational steps are performed on the computer or other programmable data processing equipment to create a computer-executed process to create a computer or other programmable data processing equipment. It is also possible that instructions for performing the processing equipment provide steps for performing the functions described in the flowchart block(s).

Additionally, each block may represent a module, segment, or portion of code that includes one or more executable instructions for executing specified logical function(s). It should also be noted that in some alternative implementations it is also possible for the functions recited in blocks to occur out of order. For example, two blocks shown one after another may be performed substantially simultaneously, or the blocks may sometimes be performed in the reverse order according to a corresponding function.

In this case, the term '~ unit' used in the present disclosure means software or hardware components such as FPGA or ASIC, and '~ unit' performs certain roles. However, '-part' is not limited to software or hardware. '~' may be configured to reside on an addressable storage medium or may be configured to refresh one or more processors. Accordingly, as an example, '~' indicates components such as software components, object-oriented software components, class components, and task components, and processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functions provided in the components and '~ units' may be combined into a smaller number of components and '~ units' or further separated into additional components and '~ units'. In addition, components and '~ units' may be implemented to play one or more CPUs in a device or secure multimedia card.

For convenience of description, some terms and names defined in the 3rd generation partnership project (3GPP) standard (standards of 5G, NR, LTE, or similar systems) may be used below. The use of these terms is not limited by the terms and names of the present disclosure, and may be equally applied to systems conforming to other standards, and may be changed into other forms without departing from the technical spirit of the present disclosure.

In addition, in the present disclosure, in order to determine whether a specific condition is satisfied (satisfied) or satisfied (fulfilled), an expression of more than or less than is used, but this is only a description to express an example, and more or less description is excluded not to do Conditions described as 'more than' may be replaced with 'more than', conditions described as 'less than', and conditions described as 'more than and less than' may be replaced with 'more than and less than'.

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

In addition, in the present disclosure, a TP (transmission point) means a point at which wireless signals can be transmitted and received with one or more antennas, and various types of base stations may be referred to as TPs regardless of their names. can In addition, the TP may be referred to as a transmission reception point (TRP), an access point (AP), a distributed antenna, a radio unit (RU), or a distributed unit (DU) according to an embodiment of the present disclosure, It is not limited thereto, and may be referred to by terms having the same or similar meaning.

Also, in the present disclosure, a central processing unit (CPU) may be referred to as a separate entity or a network entity that performs an operation proposed in the present disclosure. Alternatively, various types of base stations may be referred to as CPUs regardless of their names. In addition, the CPU may be referred to as a central unit (CU) according to an embodiment of the present disclosure, and is not limited thereto, and may be referred to by terms having the same or similar meaning.

In addition, data described in the present disclosure may be referred to as a data stream or a signal, may also be referred to as a signal transferring control information, but is not limited thereto, and terms having the same or similar meaning may be referred to by

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

Referring to FIG. 1 , the mobile communication system shown in FIG. 1 includes a first cell 100 , a second cell 110 , and a third cell 120 , and A TP (herein, it may mean a base station) for performing (or providing) mobile communication within each cell may be disposed in the center. Among them, the first cell 100 includes a TP 130 , a first UE 140 , and a second UE 150 . The TP 130 may provide a mobile communication service to the two

UEs

140 and 150 located in the first cell 100 . The first UE 140 receiving the mobile communication service through the TP 130 has a relatively long distance to the TP 130 compared to the second UE 150 . Accordingly, the data transmission/reception performance that may be supported by the first UE 140 may be relatively lower than the data transmission/reception performance that may be supported by the second UE 150 .

Meanwhile, in the mobile communication system shown in FIG. 1 , a reference signal (RS) may be transmitted to measure a downlink channel state of each cell or to estimate a downlink channel. The reference signal may also be referred to as a pilot. According to the standard of 3GPP, the reference signal transmitted by the TP to the UE includes a CSI-RS channel status information-reference signal and a demodulation-reference signal (DM-RS). The UE may measure the channel state between the TP and the UE by using the CSI-RS, and may feed back channel state information. In addition, the UE may estimate a downlink channel by using the DM-RS and perform demodulation of resources allocated to it based on the estimated channel.

2 is a diagram illustrating a structure of an LTE system of the 3GPP standard to which an embodiment of the present disclosure can be applied.

Referring to FIG. 2, as shown, the radio access network of the LTE system is a next-generation base station (evloved node B, 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), MME (2-25, mobility management entity) and S-GW (2-30, serving-gateway). The UE 2-35 connects to an external network through the eNB 2-05 - 2-20 and the S-GW 2-30.

In FIG. 2 , the eNBs 2-05 - 2-20 correspond to the existing Node B of the UMTS system. The eNB is connected to the UE 2-35 through a radio channel, and performs a more complex role than the existing Node B. In the LTE system, all user traffic, including real-time services such as voice over IP (VoIP) through the Internet protocol, are serviced through a shared channel, so status information such as buffer status, available transmission power status, and channel status of UEs A device for scheduling is required, and the eNB (2-05 - 2-20) is responsible for this. One eNB typically controls multiple cells. For example, in order to implement a transmission rate of 100Mps, the LTE system uses, for example, orthogonal frequency division multiplexing (OFDM) in a 20Mhz bandwidth as a radio access technology. In addition, an adaptive modulation & coding (AMC) method that determines a modulation scheme and a channel coding rate according to the channel state of the terminal is applied. The S-GW (2-30) is a device that provides a data bearer, and creates or removes a data bearer under the control of the MME (2-25). The MME is a device in charge of various control functions as well as the mobility management function for the UE, and is connected to a number of base stations.

Referring to FIG. 3 , the radio protocols of the LTE system are packet data convergence protocols 3-05 and 3-40 (PDCP), radio link control 3-10, 3-35 (RLC), and medium access (MAC) in the UE and the eNB, respectively. control 3-15, 3-30).

The PDCPs 3-05 and 3-40 are in charge of operations such as IP header compression/restore. The main functions of PDCP are summarized below.

- Header compression and decompression (ROHC only)

- Transfer of user data

- in-sequence delivery of upper layer PDUs at PDCP re-establishment procedure for RLC AM

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

- Duplicate detection of lower layer SDUs at PDCP re-establishment procedure for RLC AM

- 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)

- Encryption and decryption function (ciphering and deciphering)

- Timer-based SDU discard function (timer-based SDU discard in uplink)

The radio link control (hereinafter referred to as RLC) 3-10 and 3-35 reconfigures a PDCP packet data unit (PDU) to an appropriate size to perform ARQ operation and the like. The main functions of RLC are summarized below.

- Data transfer function (transfer of upper layer PDUs)

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

- Concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer)

- Re-segmentation of RLC data PDUs (only for AM data transfer)

- Reordering of RLC data PDUs (only for UM and AM data transfer)

- Duplicate detection (only for UM and AM data transfer)

- Protocol error detection (only for AM data transfer)

- RLC SDU discard function (RLC SDU discard (only for UM and AM data transfer))

- RLC re-establishment function (RLC re-establishment)

The MACs 3-15 and 3-30 are connected to several RLC layer devices configured in one terminal, and perform operations of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The main functions of MAC are summarized below.

- Mapping function (Mapping between logical channels and transport channels)

- 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)

- Scheduling information reporting function (Scheduling information reporting)

- HARQ function (Error correction through HARQ)

- Priority handling between logical channels of one UE

- Priority handling between UEs by means of dynamic scheduling

- MBMS service identification

- Transport format selection

- Padding function

The physical layer (3-20, 3-25) channel-codes and modulates upper layer data, creates an OFDM symbol and transmits it over a radio channel, or demodulates and channel-decodes an OFDM symbol received through the radio channel and transmits it to a higher layer do the action

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

4, as shown, the radio access network of the next-generation mobile communication system is a next-generation base station (New Radio Node B, hereinafter NR gNB or NR base station, where NR gNB may refer to a TP according to the present disclosure). (4-10) and NR CN (4-05, New Radio Core Network). UE (New Radio User Equipment, hereinafter NR UE or terminal) 4-15 accesses an external network through NR gNB 4-10 and NR CN 4-05.

In FIG. 4 , the NR gNBs 4-10 correspond to an Evolved Node B (eNB) of the existing LTE system. The NR gNB is connected to the NR UE 4-15 through a radio channel and can provide a service superior to that of the existing Node B. In the next-generation mobile communication system, since all user traffic is serviced through a shared channel, a device for scheduling by collecting status information such as buffer status, available transmission power status, and channel status of UEs is required. (4-10) is in charge. One NR gNB typically controls multiple cells. In order to implement ultra-high-speed data transmission compared to current LTE, it can have more than the existing maximum bandwidth, and additional beamforming technology can be grafted using orthogonal frequency division multiplexing (OFDM) as a radio access technology. . In addition, an adaptive modulation & coding (AMC) method that determines a modulation scheme and a channel coding rate according to the channel state of the terminal is applied. The NR CN (4-05) performs functions such as mobility support, bearer setup, QoS setup, and the like. NR CN is a device in charge of various control functions as well as mobility management functions for the terminal and is connected to a number of base stations. In addition, the next-generation mobile communication system can be linked with the existing LTE system, and the NR CN is connected to the MME (4-25) through a network interface. The MME is connected to the existing base station eNB (4-30).

Referring to FIG. 5 , the radio protocols of the next-generation mobile communication system are NR SDAP (5-01, 5-45), NR PDCP (5-05, 5-40), and NR RLC (5-10) in the terminal and the NR base station, respectively. , 5-35), and NR MAC (5-15, 5-30).

The main functions of the NR SDAPs 5-01 and 5-45 may include some of the following functions.

- Transfer of user plane data

- Mapping between a QoS flow and a DRB for both DL and UL for uplink and downlink

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

- A function of mapping a relective QoS flow to a data bearer for uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL SDAP PDUs).

With respect to the SDAP layer device, the UE can receive a configuration of whether to use the SDAP layer device header or the function of the SDAP layer device for each PDCP layer device, for each bearer, or for each logical channel in an RRC message, and the SDAP header If is set, the UE uses the uplink and downlink QoS flow and data bearer mapping information with the NAS QoS reflection setting 1-bit indicator (NAS reflective QoS) and the AS QoS reflection setting 1-bit indicator (AS reflective QoS) of the SDAP header. can be instructed to update or reset The SDAP header may include QoS flow ID information indicating QoS. The QoS information may be used as data processing priority and scheduling information to support a smooth service.

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

-Header compression and decompression (ROHC only)

- Transfer of user data

- In-sequence delivery of upper layer PDUs

- Out-of-sequence delivery of upper layer PDUs

- Order reordering function (PDCP PDU reordering for reception)

- Duplicate detection of lower layer SDUs

- Retransmission of PDCP SDUs

- Ciphering and deciphering

- Timer-based SDU discard in uplink.

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 a PDCP sequence number (SN), and a function of delivering data to the upper layer in the reordered order may include, or may include a function of directly delivering without considering the order, may include a function of reordering the order to record the lost PDCP PDUs, and report the status of the lost PDCP PDUs It may include a function for the transmitting side, and may include a function for requesting retransmission for lost PDCP PDUs.

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

- Data transfer function (Transfer of upper layer PDUs)

- In-sequence delivery of upper layer PDUs

- Out-of-sequence delivery of upper layer PDUs

- ARQ function (Error Correction through ARQ)

- Concatenation, segmentation and reassembly of RLC SDUs

- Re-segmentation of RLC data PDUs

- Reordering of RLC data PDUs

- Duplicate detection

- Protocol error detection

- RLC SDU discard function (RLC SDU discard)

- RLC re-establishment function (RLC re-establishment)

In the above, in-sequence delivery of the NR RLC device refers to a function of sequentially delivering RLC SDUs received from a lower layer to an upper layer, and one RLC SDU is originally divided into several RLC SDUs and received , it may include a function of reassembling and delivering it, and may include a function of rearranging the received RLC PDUs based on an RLC sequence number (SN) or PDCP SN (sequence number), and rearranging the order May include a function of recording the lost RLC PDUs, may include a function of reporting a status on the lost RLC PDUs to the transmitting side, and may include a function of requesting retransmission of the lost RLC PDUs. and, if there is a lost RLC SDU, it may include a function of sequentially delivering only RLC SDUs before the lost RLC SDU to the upper layer, or even if there is a lost RLC SDU, if a predetermined timer has expired, the timer It may include a function of sequentially delivering all RLC SDUs received before the start of RLC to the upper layer, or if a predetermined timer expires even if there are lost RLC SDUs, all RLC SDUs received so far are sequentially transferred to the upper layer. It may include a function to transmit. In addition, the RLC PDUs may be processed in the order in which they are received (in the order of arrival regardless of the sequence number and sequence number) and delivered to the PDCP device out of sequence (out-of sequence delivery). Segments stored in the buffer or to be received later are received, reconstructed into one complete RLC PDU, processed and delivered to the PDCP device. The NR RLC layer may not include a concatenation function, and the function may be performed by the NR MAC layer or replaced with a multiplexing function of the NR MAC layer.

In the above, the out-of-sequence delivery function of the NR RLC device refers to a function of directly delivering RLC SDUs received from a lower layer to a higher layer regardless of order, and one RLC SDU originally has several RLCs. When it is received after being divided into SDUs, it may include a function of reassembling it and delivering it, and it may include a function of storing the RLC SN or PDCP SN of the received RLC PDUs, arranging the order, and recording the lost RLC PDUs. can

The NR MACs 5-15 and 5-30 may be connected to several NR RLC layer devices configured in one terminal, and the main function of the NR MAC may include some of the following functions.

- Mapping function (Mapping between logical channels and transport channels)

- Multiplexing/demultiplexing of MAC SDUs

- Scheduling information reporting function (Scheduling information reporting)

- HARQ function (Error correction through HARQ)

- Priority handling between logical channels of one UE

- Priority handling between UEs by means of dynamic scheduling

- MBMS service identification

- Transport format selection

- Padding function

The NR PHY layer (5-20, 5-25) channel-codes and modulates upper layer data, creates an OFDM symbol and transmits it over a radio channel, or demodulates and channel-decodes an OFDM symbol received through the radio channel to an upper layer. You can perform a forwarding action.

On the other hand, in the LTE system and the next-generation mobile communication system of the 3GPP standard described in FIGS. 2 and 4, a plurality of cells are generally built in a limited area, and one UE in the cell serves itself. It may be implemented through a non-coordinated multi point (non-CoMP) data transmission/reception method for receiving data from one TP. A more detailed description of the non-CoMP scheme will be described with reference to FIG. 6 .

Referring to FIG. 6 , a mobile communication system including three cells and a TP disposed in the center of each cell is exemplified as an example.

The TP of each cell may transmit data to the UE existing in the cell. That is, the TP of Cell 0 may transmit data 600 to UE0 existing in the service area of Cell 0. In addition, by using a time and frequency resource different from the time and frequency resource used for Cell 0, the TP of Cell 1 transmits data 610 to UE1 existing in the service area of Cell 1, and the TP of Cell 2 is the Cell Data 620 may be transmitted to UE2 existing in the service area of 2. Referring to the radio resource 630 used in Cell 0, the radio resource 650 used in Cell 1, and the radio resource 640 used in Cell 2, Cell 0 to Cell 2 use different time and frequency resources. This indicates that data can be transmitted. In this way, a transmission scheme in which the TPs of each cell transmit data only to the UE in the corresponding cell using different time and frequency resources, and there is no cooperation between the TPs may be referred to as a non-CoMP scheme.

Meanwhile, in the non-CoMP data transmission/reception method, since the transmission/reception antennas of each TP are intensively disposed in the center of the cell, high data transmission/reception performance is provided to the UE located far from the center of the cell (ie, the cell boundary). There is a limit that cannot be supported to have it. Accordingly, various system structures to which the CoMP scheme, which is a multi-cell cooperative communication technology, can be applied have been proposed. A detailed description of the CoMP scheme will be described with reference to FIG. 7 .

Unlike the non-CoMP method in which data transmission/reception is performed in the absence of cooperation between TPs as shown in FIG. 6, in FIG. 7, the system structure to which the CoMP method in which data transmission/reception is performed in the presence of cooperation between TPs is applied. shown.

Referring to FIG. 7 , it is exemplified that the UE receives data transmitted through a physical downlink shared channel (PDSCH) in Cell 0 and Cell 2 . That is, the UE simultaneously receives

data

700 and 710 transmitted from two TPs. In a mobile communication system in which a plurality of TPs exist, one or more TPs cooperate to perform the same data transmission for one UE, so that a UE located relatively far from the TP (eg, a cell boundary) is more improved It is now possible to support data transmission/reception performance.

On the other hand, the CoMP scheme for providing a more improved service to a user at a cell boundary may be implemented in various ways in a communication system, and will be described below with reference to FIG. 8 .

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

Referring to FIG. 8 , the CoMP scheme is an uplink CoMP scheme for improving uplink data transmission/reception performance, which is a wireless connection from a UE to a TP, and a downlink method for improving downlink data transmission/reception performance, which is a wireless connection from a TP to the UE. It can be classified according to the CoMP method.

First, the uplink CoMP scheme may be implemented as joint reception (JR), coordinated scheduling (CS), or a combination of the above schemes.

JR is a method of receiving data transmitted from a terminal together at multiple TPs. CS is a method in which a plurality of TPs cooperate with each other to perform scheduling and precoding.

The downlink CoMP scheme may be implemented by joint processing (JP) and coordinated scheduling/coordinated beamforming (CS/CB), or a combination of the above schemes.

In CS/CB, one TP transmits data to the UE, but a plurality of TPs cooperate to perform scheduling and beamforming. Through this, interference to the UE located at the boundary of the TP can be reduced.

The JP is in which a plurality of TPs share data to be transmitted to the UE, and may be further classified into dynamic point selection (DPS) and joint transmission (JT). The DPS may refer to dynamic cell selection (DCS), in which one TP among a plurality of TPs transmits downlink data to the UE, but the TP transmitting data to the UE is dynamically changed. That is, it means a method in which downlink data is transmitted through a TP selected according to a specific rule among a plurality of TPs.

JT is a method in which several TPs cooperate to transmit the same data to the UE.

On the other hand, JT can be divided into CJT (coherent JT) and NCJT (non-coherent JT) again depending on whether TPs transmit data streams in synchronization. For a detailed description of this, refer to FIG. 9 do it with

9A shows a system for transmitting data to the UE according to the CJT scheme, and FIG. 9B shows a system for transmitting data to the UE according to the NCJT scheme.

In FIG. 9A , according to the CJT scheme, a central processing unit (CPU) performs centralized scheduling (which may be referred to as central scheduling), and the TPs controlled by the CPU are synchronized according to the scheduling, and the UE to transmit data (coherent transmission).

In B of FIG. 9 , according to the NCJT scheme, each TP independently schedules (which may be referred to as local scheduling), does not synchronize with other TPs, and independently transmits data to the UE (non-coherent transmission) .

On the other hand, in coherent transmission, a plurality of TPs transmit a data stream that is time synchronized by compensating for a delay to the UE, respectively, and the UE transmits from the plurality of TPs. By receiving the sum of the data streams, the reception performance of the UE can be improved accordingly.

According to the CJT method, interference by cells belonging to other users can be reduced in a system where multiple users exist through cooperation between a plurality of TPs, and the throughput and data reception performance of the UE at the cell boundary can be increased. .

Meanwhile, the CJT method of CoMP considered by the present disclosure may be implemented in a communication system based on a distributed antenna system including a plurality of TPs and a CPU connected to the plurality of TPs through a front hole. The CPU may transmit/receive data to and from a plurality of TPs through the front hall, and may control the TPs. A more detailed description will be given with reference to FIG. 10 .

10 is a diagram illustrating a distributed antenna system in which the CJT scheme of CoMP according to an embodiment of the present disclosure can be implemented. However, the embodiment of the present disclosure is not limited thereto, and the JR scheme may be implemented in the distributed antenna system of FIG. 10 .

Referring to FIG. 10 , a distributed antenna system including one cell 1000 is illustrated as an example. A DU (as described above, a DU of the present disclosure may refer to the above-described TP) and a CU connected through a front hole (as described above, a CU of the present disclosure may refer to the above-described CPU) (1030) ) may be disposed in the center of the cell 1000 , and the

DUs

1060 , 1070 , 1080 , and 1090 may be disposed at different positions within each cell. The CU 1030 controls the

DUs

1060, 1070, 1080, and 1090 in the cell, and each DU may transmit a downlink signal to the UE located in the cell 1000 under the control of the CU 1030 ( JT). In this case, each of the

DUs

1060 , 1070 , 1080 and 1090 may include one or a plurality of antennas. Meanwhile, in such a distributed antenna system, as in the distributed MIMO scheme, downlink data can be coherently transmitted to the UE through beamforming using an antenna located in the TP (CJT). To this end, the CPU may generate a centralized precoder (or may refer to an operation of acquiring or confirming the precoder), and may apply it to data to be transmitted to the UE. In addition, the CPU transmits the precoder-applied data to each TP connected to the CPU through a front haul, and each TP may synchronize and transmit a data stream to the UE (coherent transmission).

Meanwhile, in the CJT method of CoMP, which can be implemented through the distributed antenna system structure as described above, the amount of data transmitted and received through the fronthaul between each TP and CPU is excessive, and as the number of TPs controlled by the CPU increases, the There may be a problem in that the computational complexity of the CPU greatly increases. Specific details will be described with reference to FIG. 11 .

11 illustrates a common public radio interface (CPRI) between a remote radio header (RRH) (or radio unit (RU), DU) and a base band unit (BBU) (or CU) according to an embodiment of the present disclosure. It is a drawing showing an example.

Referring to FIG. 11 , when a distributed antenna system is used in a 4G (or LTE) system, the CPRI standard (hereinafter, may be referred to as CPRI) may be used. For example, a function may be separated into a CU and a DU based on option 8 shown in FIG. 11 , and CPRI may be used as a communication interface between the CU and the DU. In this case, if the functions are separated based on option 8 as described above, only the RF stage exists in the DU, and the remaining signal processing-related operations can be performed by the CU. On the other hand, when transmitting downlink data, the CU must sample an RF signal and transmit it to the DU through the front haul, which causes a large load on the front haul. In addition, in the case of uplink in which the RF signal sampled from the DU needs to be transmitted to the CU, the load of the front haul becomes larger. In addition, in the case of the above-described CJT method, not only user data but also accurate channel information for generating a precoder (or a precoding vector) must be transmitted to the CPU (CU) through the front haul. In a situation where the transmission capacity is limited, there is a limit to implementing the above-described CJT method.

In the next-generation mobile communication system, an enhanced common public radio interface (eCPRI) standard was defined in order to solve the aforementioned fronthaul limitation, so that functions can be separated by selecting another option. For example, functions may be divided into CUs and DUs based on option 2 or option 7 shown in FIG. 11 . If the function is separated in the upper layer as in option 2, since precoding must be performed distributedly in the DU, the effect of improving data transmission/reception performance obtained through the CJT method may be reduced. On the other hand, if the function is separated from the lower layer as in option 7, the transmission amount of the front haul may still be excessive compared to the existing one. That is, a trade-off between CJT performance and fronthaul transmission may occur depending on the function separation point. In this regard, there is a limit to implementing the CJT method through eCPRI.

Meanwhile, in addition to the above problems, the CPU needs to know exactly the channel to generate the precoder matrix for CJT.

In addition, when the number of UEs is greater than the number of TPs, there is a limitation in implementing the CJT scheme. For example, in the cellular network shown in FIG. 1 , it is possible to estimate a downlink channel based on a downlink pilot of each TP. If the number of TPs is not greater than the number of UEs, the overhead due to channel estimation is not large, but in an ultra-dense network (UDN) environment in which the number of UEs is greater than the number of TPs, a separate downlink pilot is provided for each TP. Since channel estimation must be performed using the method, there may be a problem in that overhead due to channel estimation may greatly increase.

In addition, due to the overhead of the uplink, each UE cannot accurately feed back channel information, or, in general, quantizes channel information to perform channel quality information (CQI), precoding matrix indicator (PMI), Feedback is provided in the form of a rank indicator (RI) or the like. In this case, due to a limitation due to quantization of channel information, accurate channel information may not be reflected in the feedback. Therefore, there are several limitations in implementing the CJT method of CoMP in the existing communication system.

On the other hand, in recent UDN environment, as a method of removing the cell boundary of a terminal, a cell-free massive MIMO-based system (distributed MIMO, or distributed antenna system, etc.), which is a system structure with a large number of TPs supporting one terminal. This has been suggested. A detailed description of the cell-free massive MIMO-based system will be described with reference to FIG. 12 .

Referring to FIG. 12 , the cell-free massive MIMO-based system may estimate a downlink channel based on an uplink pilot by operating with time division duplexing (TDD). That is, unlike the downlink channel estimated based on the downlink pilot transmitted from the TP to the UE, the downlink channel may be estimated based on the uplink pilot transmitted from the UE to the TP. The TP 1210 may 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, it is possible to overcome the above-described limitations due to quantization of channel information and overhead problems due to channel estimation.

Thereafter, the CPU 1200 may perform precoding for controlling multi-user interference based on the channel information. Accordingly, the TP 1210 coherently transmits data to the UE 1220, so that the CJT method of CoMP considered by the present disclosure can be implemented.

On the other hand, in the cell-free massive MIMO system, the number of TPs that need to cooperate with each other increases significantly compared to the existing system. Therefore, in implementing the CJT method in the cell-free massive MIMO system, the computational complexity required to control numerous TPs in the CPU A problem may arise in that it increases significantly. For example, the CPU of a cell-free massive MIMO-based system must precisely synchronize data transmission and reception between numerous TPs, and since many TPs cooperate dynamically, the precoder generation process (or precoding process) taking these cooperative TPs into consideration The computational complexity of the CPU can be very high. In addition, there is a limitation in that the load of data or channel information transmitted through the front hole is still large. Therefore, even in a cell-free massive MIMO-based system, there may be problems in implementing the CJT method of CoMP.

Accordingly, the present disclosure proposes a method to solve the problem of high computational complexity of the CPU and the load of the front hall that may occur in implementing the CoMP CJT method in a cell-free massive MIMO-based wireless communication system. Specifically, through the present disclosure, a plurality of TPs controlled by the CPU are divided into a Central TP group in which precoding is centrally performed in the CPU and a Local TP group in which precoding is performed in each TP distributedly, and the Central TP or We propose a precoding method that enables each TP to operate as a local TP. In addition, according to the precoding method proposed in the present disclosure, a system structure in which uplink data or downlink data transmission/reception can be performed between a plurality of TPs and a UE is proposed.

According to the present disclosure, scheduling may be performed to determine whether a TP operates as a Central TP or a Local TP based on a given fronthaul capacity and computational complexity according to UE and network performance. At this time, according to the scheduling result based on the constraint of the computational complexity, since the computational complexity is distributed and shared among TPs, the scheduling that determines the operation method of the TP may be referred to as CSS (complexity-shared scheduling). Also, CSS may mean dividing (determining or classifying) a plurality of TPs to perform either an operation performed by the Central TP group or an operation performed by the Local TP group. Also, CSS may refer to a process of classifying all TPs into a Central TP group and a Local TP group or a process of determining a ratio of the Central TP group and the Local TP group among all TPs. Also, since it is determined whether precoding is performed in the CPU (Central TP) or the TP (Local TP) according to the CSS execution result, CSS may refer to a precoding method. Meanwhile, in the present disclosure, for convenience of description, the Central TP group may be referred to as a first group and the Local TP group may be referred to as a second group.

In the cell-free massive MIMO system described above, in order to obtain optimal data transmission/reception performance, the fronthaul capacity (eg,

) and computational complexity (e.g.,

The objective function of [Equation 1] as follows in consideration of ) can be considered.

In the above [Equation 1],

Is

The yield (throughput) of

is the amount of calculation to be performed in each TP unit,

denotes the amount of information to be transmitted on the front haul link. In order to solve the optimization problem for the objective function, two situations can be assumed: when all TPs operate centrally (ie, Central TP) or when they operate distributedly (ie, Local TP). If all TPs operate as Central TPs, the amount of information to be transmitted through the front haul link (

) and total computation (

) will be limited. On the other hand, when all TPs are local TPs, reception performance may be deteriorated due to high interference between TPs. Considering these characteristics, the CPU is

TP groups that support (eg,

) to the Central TP group (for example,

) and the Local TP group (eg,

) can be classified (or divided, divided).

More specifically, the objective function of CSS in consideration of a trade-off between transmission/reception performance and constraints according to fronthaul capacity and computational complexity can be expressed by the following [Equation 2].

In [Equation 2], the amount of information to be transmitted through the front haul link (

) is the number of antennas (eg,

) and symbol size (e.g.,

), and it can be determined based on the quantization level ( Q) . At this time, the CPU determines whether each TP operates as a Central TP or a Local TP so as to optimize the performance given by the objective function in the given constraint. Specific details of performing the CSS in the CPU will be described with reference to FIG. 13 .

13 is a diagram illustrating a sequence in which a CPU performs CSS according to an embodiment of the present disclosure.

Referring to FIG. 13 , in steps 13 - 100 , the CPU may check whether CSS for determining whether TPs controlled by the CPU operate as a Central TP or a Local TP is performed. The CPU may check whether CSS is executed based on at least one of several criteria. For example, the CPU may receive a report of channel information for a channel between the TP and the UE, and may check whether to perform CSS based on the channel information and various criteria. For example, the CPU may initiate CSS in the following cases. However, the following conditions are only an example of the present disclosure, and the scope of the present disclosure is not limited thereto.

- If the CPU periodically performs CSS

- When the CPU performs CSS based on certain criteria (threshold values, etc.)

- When the UE requests the CPU to perform CSS

First, when the CPU periodically performs CSS, CSS is first performed when clustering (which may mean determining a set of TPs to serve the UE) is performed, or CSS is performed at every arbitrary cycle can be For example, CSS may be performed with a shorter cycle than the large-scale coherence time. Specifically, clustering is performed every large-scale coherence time period, which is a longer period than CSS, or is performed when a handover of the terminal occurs. CSS may be performed at a shorter cycle than the clustering cycle (eg, T_CSS = T_Clustering/2 may be set). In this case, CSS is performed more frequently than clustering, but CSS is a procedure that consumes less cost than clustering that requires complex procedures. It has the advantage of optimizing the performance of

Second, when the CPU performs CSS based on a certain criterion (threshold value), the UE reports its downlink throughput information or its own channel reception status (RSRP) to the CPU through uplink, and the CPU can know the uplink and/or downlink throughput of the UE through this. In this case, when the throughput of a specific UE falls below a certain threshold, the difference in throughput between the UE with the highest throughput and the lowest UE exceeds a certain threshold, or the distribution of the throughput of the UE becomes greater than or equal to a certain threshold. , the CPU may perform CSS.

Also, the UE may request the CPU to perform CSS. In this case, the UE checks its downlink throughput or channel status, and when the UE's throughput or channel status falls below a certain threshold, it can request the CPU to perform CSS so that the UE can further allocate a Central TP. there is.

When it is determined in step 13-100 that the CPU is to perform CSS, in step 13-200, the CPU converts the TPs to a Central TP based on at least one of a front hall capacity and a computational complexity allowable by the CPU. Alternatively, it may be determined to operate as a Local TP. For example, the CPU preferentially operates as a Central TP for TPs supporting a UE with low yield (it may refer to throughput) in order to maximize performance for cell-edge users through CSS. can do it That is, the CPU assigns at least one TP group supporting the UE to a group of Local TPs (

), the Central TP's group (

), the set of Central TPs (

), you can perform CSS so that more TPs belong to it. If the number of UEs that a TP can support in the clustering matrix decreases due to a limitation in the number of pilots, etc., and the number of TPs is fixed, the CPU may increase the ratio of Central TPs among TPs supporting UEs. On the other hand, if the ratio of the Central TP cannot be increased due to a complexity limitation or the like, the CPU can allocate the computational resources of the UE already having good enough reception performance to lower users (that is, the CPU is the Central TP of the UE having sufficiently good reception performance). The TP can be operated as a Local TP, and the Local TP of the UE, which is a lower performance, can be operated as a Central TP). On the other hand, when the UE requests the CPU to allocate more Central TPs, CSS may be performed by reflecting this.

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

When CSS execution is completed, the CPU may transmit a CSS execution result (eg, an indicator instructing to operate as a Central TP or a Local TP) to TPs that have been CSS execution targets in steps 13 to 300 . TPs receiving the CSS execution result may operate as a Central TP or a Local TP according to the CSS result.

Meanwhile, CSS according to an embodiment of the present disclosure may be implemented through TPs having eCPRI embedded in FIG. 14 . At this time, the TP that was instructed to operate as a Local TP is instructed by the CPU to operate as a Central TP according to the CSS execution result, or the TP that was instructed to operate as an existing Central TP is expected to act as a Local TP according to the CSS execution result. Since it can be instructed, CSS execution target TPs should be able to freely select split 1 or split 2 shown in FIG. 14 . That is, when layer splitting occurs in split 1 or split 2, all procedures for split 1 or split 2 may be embedded in TP so that the TP can perform all necessary procedures according to the T-selected split. If the precoding procedure is performed in a distributed unit (DU), layer splitting is performed in split 1, and in this case, the DU may be referred to as a local TP. On the other hand, if the precoding procedure is performed in a central unit (CU), layer splitting is performed in split 2, in which case the DU may be referred to as a Central TP.

According to the eCPRI function separation point among communication systems utilizing eCPRI, the present disclosure provides a system in which a Local TP that distributes precoding in DUs (or RUs) and a Central TP that centrally performs precoding in CUs coexist can be applied to As described above, the Central TP or the TP corresponding to the Local TP may be changed to operate as the Local TP or the Central TP as needed. That is, according to an embodiment of the present disclosure, for each TP, it may be determined whether precoding is performed in the TP distributedly or in a CU that centrally controls the TP.

As shown in FIG. 13 , the CoMP data transmission/reception system may be implemented based on TPs in which the CPU is instructed to operate as a Central TP or a Local TP according to a CSS execution result. For a more detailed description, reference will be made to FIGS. 15A and 15B .

15A and 15B are diagrams illustrating a system structure in which a TP instructed to operate as a Central TP or a Local TP transmits/receives uplink data and downlink data according to a CSS execution result according to an embodiment of the present disclosure; .

First, in FIGS. 15A and 15B , the following assumptions may be applied for convenience of description.

- L TPs are distributed, and each TP is

antennas are mounted, and the TPs are connected to the CPU through a front hole.

-

There are UEs, and in accordance with the basic premise of the cell-free massive MIMO system that the number of TPs is greater than the number of UEs, the number of TPs ( L) is greater than the number of UEs ( K) .

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

- At this time,

with the second TP

The channel between the second terminals is a vector

, the spatial correlation between the antennas of the TP for each UE is the correlation matrix

, a large-scale fading coefficient representing the path loss and shadowing of the channel.

was defined as

On the other hand, the above-mentioned assumption is only for convenience of description, and the present disclosure is not limited thereto. That is, the above-mentioned assumptions are only an example for carrying out the present disclosure, and some of the assumptions may not be applied.

15A illustrates a system structure in which the UE transmits/receives uplink data to/from the CPU through a Central TP and a Local TP serving the UE as a result of performing CSS according to an embodiment of the present disclosure. The Central TP estimates the channel based on the uplink pilot received from the UE, and transmits information on the estimated channel to the CPU. Thereafter, the CPU calculates a central combining vector based on the estimated channel, and estimates the signal by applying the combining vector to a signal transmitted from the UE. In contrast, the local TP estimates a channel based on an uplink pilot received from the UE, and calculates a local combining vector based on the estimated channel. Thereafter, the Local TP estimates a symbol by applying a joint vector to the signal transmitted from the UE, and sends the estimated symbol to the CPU, and the CPU combines them to estimate the signal transmitted from the UE. According to the above-described method, since a 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 by the present disclosure can be implemented.

More specifically, referring to FIG. 15A , the terminal has an arbitrary number (eg, orthogonality) with each other during the coherence time period.

) can be transmitted, and the uplink pilot can be expressed by the following [Equation 3].

In Equation 3, each uplink pilot has an arbitrary length (eg,

) can have any length. At this time,

am. Uplink pilots are allocated to each UE, and since the number of UEs is generally greater than the number of uplink pilots, one pilot may be allocated to multiple UEs. After receiving the uplink pilot from the UE, the Central TP or Local TP sends a channel between the UE and the TP (

) can be estimated. In this case, the channel estimation may be performed based on, for example, minimum mean square error (MMSE) zero-forcing (ZF) or least square (LS Square).

Channel estimation value between UE and TP

, the estimate of the channel between the UE and all TPs can be expressed by the following [Equation 4].

At this time,

is,

signal from the second UE

If you say

In the th TP, the uplink data reception signal may be expressed by the following [Equation 5].

here,

Is

Independent reception noise at each antenna of the th TP.

in the CPU

In order to detect the symbol of the th UE, the received uplink signal is combined with L TPs, in which case the combining vector (eg,

) is multiplied by a weight and combined for all TPs to estimate uplink data, which can be expressed by [Equation 6] as follows.

here,

is an integrated binding vector for each TP.

can be expressed as,

is the noise for each TP.

On the other hand, the binding vector for each TP

may be calculated based on MR or MMSE. When calculating the binding vector for each TP based on the MR,

It can be expressed as , and may be applied to estimating a symbol in each TP. On the other hand, the centralized MMSE combining vector (central combining vector) can be expressed as in [Equation 7].

here,

is,

am.

The above-described method is a method for estimating by centrally combining received signals in the CPU. On the other hand, on the other hand, in each TP

A method of estimating the symbols of the second UE, collecting them in the CPU and combining them may be considered. At this time

The symbol estimated at the th TP

, it can be estimated by combining the received signals based on the following [Equation 8].

In this case, when the binding vector is calculated based on MR,

, and when it is calculated based on the MMSE, it can be expressed by [Equation 9] as follows.

Estimated from each TP

is on the CPU

is combined in the form of , and this can be called large-scale fading decoding (LSFD).

Meanwhile, according to an embodiment of the present disclosure, clustering may be assumed such that the TP does not support all UEs in the system, but only supports (or serves) some UEs belonging to the system. For example, UE index

and TP index

For , the number of antennas in the TP is

when

By defining a diagonal matrix consisting of a set of , it is possible to indicate which TP antenna supports which UE. diagonal matrix(

) can be expressed by the following [Equation 10].

In [Equation 10],

the second TP

is a set of TPs that support

If you belong to the TP

An identity matrix is given to each antenna,

the second TP

If it does not belong to , a matrix is given in which all entries of the same size are 0. Accordingly,

The clustering matrix supporting

of [Equation 11]

using ,

Uplink transmission data in the case where only TPs clustered by serving

At this time,

is a joint vector for estimating uplink data,

Is

represents an uplink transmission symbol of

Contrary to this

The set of UEs supported by the second TP

, the clustering may be defined by the following [Equation 13].

Meanwhile, in the clustering situation, in order to consider interference affecting the calculation of the joint vector, the UE may determine an interfering UE that strongly interferes with itself. E.g,

A set of UEs that interfere with

If defined as , the set of such UEs is

A TP serving (or supporting) may include all UEs served, and may be expressed by the following [Equation 14].

When considering the interfering UE in this clustering situation, the conventional centralized MMSE combination vector (Equation 7) or the distributed MMSE combination vector (Equation 9) is represented by the following [Equation 15] and [Equation 16], respectively. can

At this time, as an MMSE combining vector in consideration of interference of some UEs among all UEs, [Equation 15] is called a P-MMSE (partial MMSE) combined vector, and [Equation 16] is LP-MMSE (local partial MMSE) can be referred to as The CPU may estimate the uplink data transmitted by the UE as described above based on the joint vectors according to Equations 15 and 16.

Hereinafter, a system structure for transmitting and receiving downlink data according to an embodiment of the present disclosure will be described with reference to FIG. 15B.

In FIG. 15b, in 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. and processes the precoded data and transmits it to the UE. Accordingly, a plurality of TPs composed of a Central TP and a Local TP can transmit downlink data to the UE, so that the CJT scheme considered by the present disclosure can be implemented.

More specifically, for convenience of explanation, applying the assumption in FIG. 15A , the k-th reception signal of the UE in the downlink of FIG. 15B may be expressed by the following [Equation 17].

At this time,

Is

It is a downlink data signal to be transmitted to the second UE (

),

denotes a precoding vector in consideration of L TPs, respectively. On the other hand, for the precoding vector

The allocated power of the second UE is

, MR precoding may be applied to each TP as shown in Equation 18 below.

If channel compatibility between uplink and downlink (which may be referred to as reciprocity or duality) is assumed, the power of a joint vector for uplink data may be normalized and used as a precoding vector for downlink transmission. there is. In this case, the precoding vector may be used as a centralized precoder applied by the CPU or a distributed precoder applied by the TP. Meanwhile, in determining the precoding vector, a vector obtained by normalizing the power of the combined vector may be used, or the combined vector may be used, and the present embodiment is not limited thereto.

Meanwhile, even when transmitting and receiving downlink data, clustering may be assumed such that the TP supports only some UEs belonging to the system, rather than supporting all UEs in the system as described with reference to FIG. 15A . When the clustering is assumed, downlink transmission data can be expressed by the following [Equation 19].

At this time,

is a precoding vector for downlink data,

denotes a downlink transmission symbol.

On the other hand, as described in FIG. 15A, the clustering

A set of UEs that interfere with

can be defined as The set of such UEs is

The TP that serves may include all UEs served, and may be expressed by the following [Equation 20].

In this way, when interfering UE is considered in a cluster situation, a centralized MMSE precoder and a distributed MMSE precoder are a heuristic solution, and channel compatibility between uplink and downlink (reciprocity, or duality) can be called. .), the power of the uplink data combining vector may be normalized and used as a normalized precoding vector for downlink transmission.

On the other hand, in the downlink of the cell-free massive MIMO-based system to which an embodiment of the present disclosure can be applied, a unique downlink DM-RS (

) can be assigned. The UE can accurately estimate the downlink channel based on the DM-RS, and thus obtain a gain in reception performance. To this end, assuming a situation in which a TP and a UE each having one antenna transmit and receive a downlink signal through conjugate beamforming (CB),

is the normalized SNR,

go

and

When the power control coefficient of , conjugate beamforming (

)Through the

This transmitted signal can be expressed by [Equation 22] as follows.

In this case, downlink

The signal received by is can be expressed by [Equation 23] as follows.

In [Equation 23],

is the noise, in this case the combined beamformed effective channel gain (effective channel gain,

) can be expressed by [Equation 24] as follows.

The th UE is an effective channel (

), it is necessary to have sufficient information to know

If you know

downlink data (

) can be reliably estimated.

A case in which a downlink pilot (a downlink reference signal, a DM-RS, etc. may be referred to) is transmitted through beamforming in order to estimate .

If DM-RS is not transmitted, the channel is perfectly estimated through the uplink file in a massive MIMO environment with a very large number of antennas, and transmission precoding is perfect in an ideal environment such as no mobility due to the channel hardening effect. It can be received only by the statistical characteristics of the channel without a link pilot. However, in an actual environment, since the number of antennas is insufficient to achieve sufficient channel hardening due to various reasons such as channel estimation error, interference, and mobility, the UE cannot decode only the statistical characteristics of the channel. Therefore, in a real environment, in coherently receiving downlink data, a DM-RS for estimating a downlink channel through which data is transmitted is required.

Accordingly, the reception procedure of the UE through one DM-RS, which is the existing method, is as follows. First, in the network, a unique downlink DM-RS (

), and the TP is UE-specific DM-RS (

), and thus a signal received by the UE may be expressed by the following [Equation 25].

In [Equation 25],

is the noise of the receiver. After that,

second

It can be expressed by the following [Equation 26] if it is projected as .

At the receiving end, the

Based on the MMSE through the effective channel (

) is estimated. At this time, the estimated effective channel (

) can be expressed by [Equation 27] as follows.

In this case, the values of [Equation 27] in a Rayleigh fading channel performing combined beamforming may be respectively expressed by the following equations.

The estimated effective channel (

)Through

is the downlink signal

can be received coherently.

On the other hand, effective channel estimation error (estimation error,

)cast

, the downlink capacity may be calculated based on [Equation 31] as follows.

Referring to [Equation 31], the correct effective channel (

) by estimating the estimation error of the effective channel (

It can be derived that the reception performance can be improved as ) decreases.

The situation described above assumes that the TP and the UE each use one antenna, and the UE receives downlink data through one DM-RS. On the other hand, this

A multi-antenna TP with two antennas

multiple antennas with two antennas

It can be extended to the situation of

class

channel between

) for each downlink pilot transmitted through

, and the same precoder (

) applies, a certain time (e.g.,

time) the signal the UE receives (

) can be expressed by [Equation 32] as follows.

In [Equation 32],

indicates interference by another user's DM-RS transmitted from the same DM-RS resource.

is the received signal (

) from each effective channel (

) can be estimated. Then, based on the estimated effective channel, the UE determines the downlink combining vector (

) can be created. The UE receives a downlink reception signal (

), it is possible to coherently estimate a symbol by applying a downlink combining vector and combining it. (For example,

, here

may mean the estimated symbol.)

Meanwhile, according to an embodiment of the present disclosure, multiple DM-RSs may be used to obtain a reception diversity gain. In this case, different DM-RS resources may be allocated to the Central TP and the Local TP determined as a result of performing CSS. For example, one DM-RS may be allocated to a Central TP, and the remaining DM-RSs may be allocated to Local TPs. On the other hand, when using multiple DM-RSs, the diversity gain can be secured only when the correlation between the effective channels of the group is low when TPs are grouped. You can select (or schedule) them.

More specifically, in the existing cellular network (cellular network), several TPs are gathered in one place, so

class

Live channel (

), when multiple TPs allocate the same DM-RS resource to transmit a pilot to the UE as described above (that is, transmit a pilot using one DM-RS) Even if an effective channel, which is the sum of transmitted channels, is estimated, there is no significant difference in reception performance compared to perfect channel state information reception (CSIR). However, each

class

Live channel (

), it is more perfect to estimate each effective channel by allocating DM-RS resources to each TP separately (for example, when precoding is performed independently or distributedly in a distributed antenna, etc.) An accurate channel close to CSIR can be estimated, and a higher diversity gain can be obtained by configuring the receiving end through the more accurately estimated channel.

Accordingly, the present disclosure proposes a structure for estimating a channel close to perfect CSIR by using a plurality of DM-RSs in order to increase receive diversity performance through accurate effective channel estimation of a user.

According to the present disclosure, the CPU allocates different DM-RS resources to the Central TP and the Local TP, respectively, and each TP transmits data to the UE based on the allocated DM-RS resource. The reason for allocating DM-RS resources by dividing Central TP and Local TP in this way is that, in the case of Central TP, the channel correlation of Central TPs is reflected in the effective channel through centralized precoding. It is to allocate DM-RS that can be estimated. The remaining DM-RSs may be allocated to the Local TP, and as the number of DM-RSs increases, the UE may accurately estimate an effective channel to improve reception performance.

On the other hand, since the overhead increases as the number of DM-RSs increases, the number of DM-RSs should be limited, and the present disclosure considers a case of applying two DM-RSs for convenience of explanation, but is not limited thereto, More DM-RSs can be used.

In order to examine the performance gain in the case of using two DM-RSs, it can be assumed that one DM-RS resource is allocated to each of the Central TP group and the Local TP group by extending the MIMO pilot allocation structure described above. there is. At this time,

multi-antenna TP with two antennas and

multiple antennas with two antennas

Assuming ,

class

liver channel (

), the two downlink pilots transmitted through

Wow

can be expressed as Each pilot has the same precoder (e.g.,

can be expressed as .) is applied. At this time, a specific time (eg,

Signals received by the UE (eg,

,

It can be expressed as.) can be represented by [Equation 33] and [Equation 34] as follows, respectively.

In [Equation 33] and [Equation 34],

Wow

denotes interference by DM-RS of another UE transmitted from DM-RS resources of Local TP and Central TP, respectively.

is the received signal

Wow

each effective channel from

class

to estimate Then, the UE performs a joint vector based on each of the estimated two effective channels.

Wow

, and through coherent combining of the generated joint vector, the received signal (

) can be estimated (or detected).

At this time, in order to obtain sufficient receive diversity gain through two DM-RSs, two effective channels to be estimated

class

There may be a low correlation between If the distributions of two effective channels are similar and thus highly correlated, the diversity gain obtained through accurate channel estimation based on multiple DM-RSs is less than when effective channels are estimated based on one DM-RS. On the other hand, if the distribution of two effective channels is different and the correlation between channels is low, the performance gain obtained by accurately estimating each channel based on two DM-RSs is large.

Therefore, the CPU according to an embodiment of the present disclosure determines whether each of the TPs operates as a Central TP or a Local TP through CSS in order to obtain the diversity gain as described above, and then the Central TP and the Local TP Multiple DM-RSs can be assigned to a TP.

On the other hand, as described above, when a plurality of DM-RSs are allocated to the Central TP and the Local TP, it is necessary to instruct the UE to perform coherent reception coupling, and for this, a separate indicator (eg, coherent joint reception indicator (CJRI) may be included in the message and transmitted to the UE. A detailed procedure in consideration of such CSS and multiple DM-RS assignment will be described with reference to FIG. 16 .

16 is a diagram illustrating a downlink data transmission/reception procedure when multiple DM-RSs are allocated to a Central TP and a Local TP determined according to a CSS execution result according to an embodiment of the present disclosure.

Meanwhile, steps 16-100, steps 16-110, steps 16-120, steps 16-130, steps 16-140, steps 16-150, steps 16-160, steps 16-170, and steps 16-180 shown in FIG. Some of steps, steps 16-190, steps 16-200, steps 16-210, steps 16-220, and steps 16-230 may be omitted, may be performed sequentially, or may be performed simultaneously. Hereinafter, it will be described in detail.

In steps 16-100, the UE 1220 sends an uplink pilot (uplink reference signal or SRS (sounding) reference signal) can be transmitted.

Upon receiving the uplink pilot from the UE, the TP 1210 generates channel information (or may be channel state information) between the UE 1220 and the TP 1210 based on the uplink pilot in steps 16-110. can do. In addition, the TP 1210 may transmit the channel information to the CPU 1200 in steps 16-120. In this case, the channel information may mean channel information (large-scale channel information) for performing clustering or CSS, rather than information on all channels to perform precoding.

Upon receiving the channel information from each TP (which may be a TP group or a TP set) 1210 , the CPU 1200 may check whether CSS is performed based on at least one of various criteria in steps 16 to 130 . In FIG. 16 , the CPU 1200 receives channel information from the TP 1210 and performs CSS based on the channel information and various criteria as an example, but the present disclosure is not limited thereto. For example, as described in FIG. 13 , the CSS may be initiated by a predetermined period, a specific threshold, and a CSS execution request of the UE 1220, in this case, steps 16-100 to 16-120 may be omitted.

If the CPU 1200 decides to perform the CSS, the CPU 1200 executes the CSS based on a preset standard (eg, it may mean a standard set by a network operator) in steps 16-140. can be done Meanwhile, in steps 16-130, the CPU 1200 may determine whether to cluster based on the channel information (or channel state information) received in steps 16-120. If it is determined to perform clustering in steps 16-130, the CPU 1200 may perform clustering in steps 16-140. At this time, when the CPU 1200 determines to perform clustering, CSS may not be performed, and the present invention is not limited thereto, and the clustering and CSS may be performed simultaneously or sequentially.

Meanwhile, when it is determined to perform CSS in steps 16-140 and the CSS execution is completed, the CPU 1200 transmits the CSS execution result to each TP 1210 in steps 16-150. On the other hand, the CSS execution result relates to whether each TP 1210 operates as a Central TP or as a Local TP. According to an embodiment of the present disclosure, the CPU provides the CSS execution result to each TP 1210 . In order to notify the TP, an indicator (central/local indicator) indicating to operate as a Central TP or a Local TP may be transmitted to each TP 1210, and the indicator may consist of 1 bit. For example, when the indicator indicates a value of '0', it may mean indicating to operate as a Local TP, and when indicating a value of '1', indicating to operate as a Central TP can mean Meanwhile, each Central TP or Local TP may be included in a Central TP group (or Central TP set) consisting of a plurality of Central TPs or a Local TP group (or a Local TP set) consisting of a plurality of Local TPs, and in this case, the CPU 1200 may instruct any one of the TPs included in the Central TP group or the Local TP group to operate as a Central TP or a Local TP. At this time, the TPs of the group to which the TP instructed to operate as the Central TP or the Local TP by the CPU 1200 may operate as the Central TP or the Local TP according to the instruction (that is, the CPU is the Central TP in the TP group unit). It can also be instructed to operate as a TP or Local TP).

Upon receiving the indicator transmitted from the CPU 1200 in steps 16-150, the TP 1210 may determine whether it will operate as either a Central TP or a Local TP based on the indicator. After confirming which TP it will operate with in this way, the central TP processing process (steps 16-160) or the local TP processing process (steps 16-170) as described above is performed to create a centralized precoder (central precoder). precoder) or a distributed precoder (local precoder). Since the detailed description of the processing process of each TP has been described above, it will be omitted here.

On the other hand, in order to obtain a receive diversity gain through the central precoder and local precoder generated as described above, the CPU 1200 allocates several DM-RS resources to the Central TP and the Local TP, and the UE 1220 Signals received from each TP 1210 may be coherently combined and received based on an effective channel estimated through DM-RS.

Accordingly, in steps 16-180, the CPU 1200 determines which TPs will share a plurality of DM-RS resources to be transmitted to the UE 1220, and in steps 16-190, the CPU 1200 determines the DM-RS of the DM-RS. Allocation information may be transmitted to a Central TP (or may be a set or a group made of Central TPs) and a Local TP (or may be a set or a group made of Local TPs) 1210 , respectively. Meanwhile, in steps 16-180, the CPU 1200 may allocate a DM-RS resource so that the Central TP shares one DM-RS resource. That is, in this case, the Central TP may be characterized in sharing the same DM-RS resource. The TP (which may be any one of a Central TP, a Local TP, or both), which has received the information on the DM-RS assignment from the

CPU

1200 , 1210 receives data in steps 16-200 Information on allocation of DM-RS may be transmitted to the UE 1220 to be used.

Since the UE 1220 does not know whether to coherently receive a signal transmitted based on a plurality of DM-RSs, it is necessary to instruct the UE 1220 to receive coherent reception combination before transmitting downlink data to the UE 1220 . To this end, the TP (which may be either a Central TP or a Local TP) 1210 coherently receives a data stream transmitted to the UE 1220 corresponding to a plurality of DM-RSs in steps 16-210. It may transmit an indicator (coherent joint reception indicator, CJRI) (or coherent reception indicator, may be referred to as CRI) indicating that. In other words, when a data stream precoded with the same precoder as the DM-RS each allocated to a plurality of TPs is transmitted from each of the plurality of TPs 1210 to the UE 1220, the UE 1220 may be configured prior to or at the same time. An indicator (eg, CJRI described above) instructing to coherently receive the data stream may be received.

Meanwhile, in general, in JT of CoMP, Local TP operates in a non-coherent joint transmission (NCJT) method for non-coherent transmission. That is, it is common for local TPs to transmit data by performing independent scheduling (local scheduling) without synchronizing transmission with the cooperative TPs. Meanwhile, the Local TP according to the present disclosure may transmit data coherently in synchronization with cooperative TPs such as the Central TP in steps 16-220. In other words, the Local TP may select either non-coherent data transmission or coherent data transmission, and may indicate this to the UE 1220 through CJRI. In steps 16 to 230 , the UE 1220 may receive data coherent or non-coherent according to a method in which the TP 1210 transmits data (coherent transmission or non-coherent transmission). Accordingly, the operation of the UE 1220 may vary depending on whether the UE 1220 has received the CJRI from the TP, which will be described with reference to FIG. 17 .

17 is a diagram illustrating a sequence in which a UE operates depending on whether CJRI is received according to an embodiment of the present disclosure.

Referring to FIG. 17 , in steps 17-100 of FIG. 17, if the UE receives CJRI from the TP, this means that the cooperative TPs synchronize and transmit a data stream to the UE, so that the UE transmits a data stream to the UE in steps 16-230 The data stream transmitted from each of the TP and the local TP can be coherently received. In this case, since the resource allocation information of the Local TP can be checked through the resource allocation information of the Central TP, the Local TP does not need to inform the UE of additional resource allocation indication information through downlink control information (DCI).

On the other hand, when the UE receives the CJRI, an operation may be performed differently depending on whether the DM-RS is shared between the Local TP and the Central TP.

In steps 17-110, if the Local TP shares DM-RS with the Central TP (this may mean that the DM-RS port is shared or the UE is allocated only one DM-RS port), In steps 17-130, the UE estimates a channel through one DM-RS, and generates a reception filter through the estimated channel. Thereafter, by receiving one DCI (which may mean DCI transmitted from a central TP), the location of a resource allocated to the DCI is confirmed through the DCI, and data can be received.

On the other hand, in steps 17-110, if the Local TP does not share the DM-RS with the Central TP (when the DM-RS ports are used independently, or the UE is assigned two or more DM-RS ports, case), in steps 17-140, the UE estimates one channel based on a plurality of DM-RSs allocated to it, and generates a reception filter through the estimated channels. Thereafter, one DCI among DCIs transmitted from multiple TPs may be received, a location of a resource allocated to itself may be confirmed based on the received DCI, and data may be received.

On the other hand, if the UE does not receive CJRI at 17-100, this means that the Local TP transmits the data stream to the UE without synchronizing with other cooperative TPs, so the Local TP operates as an NCJT, and each Local TP , allocates independent DM-RS transmission and resources to the UE, and transmits DCI indicating the resource allocation location. Accordingly, the UE performs non-coherent reception-combination with respect to the non-coherent transmitted data stream. That is, the UE estimates a channel based on the DM-RS transmitted from each TP for demodulation in steps 17-120, and each TP is independently transmitted to the UE based on DCI transmitted independently by each TP. After identifying one's own resource locations, the corresponding location may be demodulated based on a channel estimated through the DM-RS of the corresponding TP.

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

Meanwhile, as described above, CSS performed to obtain optimal data transmission/reception performance may be implemented in the form of various algorithms, which will be described with reference to FIG. 18 .

Referring to Figure 18, as an example of CSS algorithm implementation,

(At this time,

may be designated according to a predetermined condition, or may be arbitrarily designated by the CPU.) A set of TPs (for example,

), and the procedure for changing all (or some) Central TPs of the TPs belonging to it is shown.

First, in steps 18-100, the CPU determines whether to perform CSS based on at least one of several criteria. For example, as described above, when a CSS cycle is set, the CPU may periodically perform CSS based on the cycle, or may determine whether to perform CSS based on a certain criterion such as a threshold, Alternatively, when receiving a request to perform CSS from the UE, it may be determined whether to perform CSS. In step 18-100, when the CPU determines not to perform CSS, data transmission/reception may be performed based on the existing Central TP or Local TP. Meanwhile, if it is decided to perform CSS, steps 18-110 are performed. At this time, the CPU has the available front hall capacity (eg,

) and computational complexity (e.g.,

), taking into account the total number of Central TPs supported by the CPU (for example,

) can be calculated.

In steps 18-110, the CPU may identify a UE that satisfies a predetermined condition based on throughput information for each of the at least one UE. In addition, the CPU is a set of TPs serving the identified UE (

)can confirm. For example, the CPU has the lowest yield (throughput value) based on the throughput information.

Check the TP set that serves the UE (

)can confirm. Alternatively, the CPU identifies UEs corresponding to a predetermined number or a number determined according to a predetermined condition or a number calculated by the CPU in order from the lowest UE to the lowest yield, and a set of TPs serving the identified UEs. can confirm. At this time, the number calculated by the CPU is, for example, the number calculated in steps 18-100.

can mean

Subsequently, in steps 18-120, the CPU determines the set of TPs (

), all TPs belonging to Local TPs can be converted to Central TPs. Meanwhile, in the description of FIG. 18 , all of the TPs corresponding to the Local TPs may be converted to the Central TPs, but the present invention is not limited thereto, and at least one of the Local TPs may be converted into the Central TPs. In this case, the conversion of the TP corresponding to the Local TP to the Central TP may mean that the Local TP is changed to a group to which the Central TP belongs. Alternatively, the conversion of a TP corresponding to the Local TP to the Central TP may mean instructing the Local TP to perform an operation performed by the Central TP. In addition, in the description of FIG. 18, the example of converting a Local TP to a Central TP is exemplified, but the present invention is not limited thereto, and the CPU uses a set of TPs (

), it is also possible to convert the TP corresponding to the Central TP to the Local TP. Meanwhile, steps 18-120 may mean an operation in which the CPU adjusts the ratio of the Central TP and the Local TP in the TP set identified in steps 18-110. That is, based on the predetermined ratio between the Central TP and the Local TP, the CPU instructs or converts the existing Central TP to operate as a Local TP as described above in steps 18-120, or converts the existing Local TP to a Central TP By instructing or switching to operate, the ratio between the Central TP and the Local TP in the TP set can be adjusted. In this case, the ratio between the Central TP and the Local TP may be determined based on at least one of calculation complexity and fronthaul capacity.

Thereafter, in steps 18-130, the CPU may check whether the CSS is terminated. The CPU can check whether CSS is terminated based on various criteria. For example, if the number of Central TPs is the total number of supportable Central TPs calculated in steps 18-110 (

), it is possible to return to steps 18-110 again. On the other hand, if the number of Central TPs

If equal to or greater than , the CPU may terminate CSS execution.

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

As described above, by performing CSS according to an algorithm in consideration of a given fronthaul capacity and computational complexity, a communication system that provides a more improved service can be implemented.

19 is a diagram illustrating a CSS framework based on a TP embedding eCPRI according to an embodiment of the present disclosure.

Referring to FIG. 19 , as a result of CSS execution, it is determined where layer splitting is to be performed for each TP (split 1 or split 2 shown in FIG. 14 ), and accordingly, CU and DU procedures are changed. After the CSS execution result is determined as Central TP or Local TP, the processing of the TP has been described above, and thus a detailed description thereof will be omitted.

On the other hand, each TP can perform all procedures corresponding to different layer splitting, and by performing different procedures according to the CSS execution result, optimal data transmission/reception performance is achieved in the constraint of CPU calculation amount and fronthaul usage. can be obtained

20 and 21 are diagrams illustrating the yield of all users when an embodiment of the present disclosure is applied.

20 and 21 show the total user yield in CDF when 2 UEs or 4 UEs are supported per TP in a system having 100 TPs and 20 UEs, respectively. The solid line is the case when MMSE considering interference from all users is performed, and the dotted lines are the precoder that only considers the interference of UEs belonging to its own cluster (or the TP set to which it belongs) using TP clustering. How to create and send. In this case, the leftmost dotted line graph is the L-MMSE performance using a distributed scalable MMSE precoder, and the right dotted line graph is the P-MMSE performance using the centralized scalable MMSE precoder. The middle graph shows the CDF by centrally transforming the random TP generation. In both FIGS. 20 and 21 , it can be seen that the performance is traded off as the percentage of the central TP (Central TP) varies from 0% to 100%. Therefore, it is necessary to select a precoder generation method so as to have the maximum performance of the TP according to the complexity and the fronthaul load.

22 and 23 are diagrams illustrating the performance of the lower 10% of users when an embodiment of the present disclosure is applied.

22 and 23 show the performance of the lower 10% users when supporting 2 UEs or 4 UEs per TP in a system having 100 TPs and 20 UEs, respectively, as shown in FIGS. 20 and 21 .

In this case, it can be confirmed that the performance of the lower 10% users can be improved by 2 times 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 have to operate only with distributed precoders in consideration of the constraints according to the load of the front hall, 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 hall, the lower 10 % Users' performance has been improved by up to 2x to 2.5x.

24 and 25 are diagrams illustrating the performance of the lower 10% of users when an embodiment of the present disclosure is applied.

24 and 25 are diagrams illustrating results of evaluating the yield of the lower 10% users when supporting 2 UEs and 4 UEs per TP, respectively, in a system having 100 TPs and 20 UEs. In FIG. 24 , the average number of TPs serving the UE is 10 , and in FIG. 25 , the average number of TPs serving the UE is 20 .

24 and 25 , the Distributed-MMSE: Clustering graph shows the performance of the L-MMSE scheme in which all TPs are local TPs, and a distributed scalable MMSE precoder is used for the UE it serves. The Partial_MMSE:Clustering graph shows the performance of the P-MMSE method using a centralized scalable MMSE precoder as a Central TP where all TPs have performed clustering. The Multicell-MMSE: Full Clustering graph shows the theoretical maximum performance when all TPs are Central TPs and service all UEs.

The Hybrid-MMSE: Clustering+Random CSS graph in FIGS. 24 and 25 shows the yield of the lower 10% users while arbitrarily changing the TP to the Central TP (Random CSS). According to the Hybrid-MMSE: Clustering+Random CSS graph in FIGS. 24 and 25, it can be seen that the performance is traded off as the percentage of the Central TP varies from 0% to 100%.

Hybrid-MMSE: Clustering+Greedy CSS graph in FIGS. 24 and 25, unlike the above-described Random CSS, preemptively converts a TP serving a UE of lower performance to a Central TP (Greedy CSS) When using shows the performance of According to the Hybrid-MMSE: Clustering+Greedy CSS graph in FIGS. 24 and 25, the performance of the lower 10% UE is faster than that according to the Random CSS method while the percentage of Central TP is changed from 0% to 100% it can be confirmed that

Therefore, referring to the graphs shown in FIGS. 24 and 25 , it can be confirmed that it is necessary to select an optimal precoder generation method to obtain maximum performance according to CPU calculation complexity and fronthaul load.

26 is a diagram illustrating a result of comparing a user's bit error performance according to the presence or absence of channel correlation between TP groups determined by performing CSS when one or two DM-RSs are used when an embodiment of the present disclosure is applied; am.

26 shows that the total number of antennas of the Central TP and the Local TP is 100, respectively, and a single antenna situation is assumed.

The effective channel vector from each TP group of

When , the effective channel-to-channel transmission correlation

can be expressed by the following equation.

At this time,

is a correlation coefficient,

, then there is no correlation between the Central TP and the Local TP, and in the case of 0.9, the correlation is high. Therefore, the effective channel vector of the group to which the transmission correlation is reflected can be expressed by [Equation 36] as follows.

Assuming that the effective channel is accurately estimated through the DM-RS, when one DM-RS is used, one effective channel is created (

) is estimated, and when two DM-RSs are used,

Wow

are estimated for each. As a result, when there is 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, when one DM-RS is used, the diversity gain through the antenna cannot be sufficiently obtained, whereas when two DM-RSs are used,

Wow

Maximum diversity can be obtained when is independent and has the same distribution. According to Figure 26,

It can be seen that the bit error performance is improved as the number increases, that is, there is no correlation between the Central TP and the Local TP.

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

The transceiver 2710 may transmit/receive a signal. The transceiver 2710 may receive, for example, a data stream (or data, signal) transmitted from a Central TP and a Local TP.

The controller 2720 may control the overall operation of the UE according to an embodiment proposed in the present disclosure. For example, the controller 2720 may control the signal flow between blocks to perform an operation according to the above-described drawing (or flowchart, flowchart).

The memory 2730 may store at least one of information transmitted/received through the transceiver 2710 and information generated through the control unit 2720 .

Referring to FIG. 28 , the TP may include a transceiver 2810 , a controller 2820 , and a memory 2830 . In the present disclosure, the controller may be defined as a circuit or an application-specific integrated circuit or one processor.

The transceiver 2810 may include a communication unit or a network interfacing unit, and the transceiver 2810 according to an embodiment of the present disclosure is connected to the CPU through a front hall. Signals can be sent and received. In addition, the TP may transmit/receive a signal to/from the UE through the transceiver 2810 .

The controller 2820 may control the overall operation of the TP according to the embodiment proposed in the present disclosure. For example, the controller 2820 may control a signal flow between blocks to perform an operation according to the above-described drawing (or flowchart, flowchart). For example, when an instruction to operate as a Central TP or a Local TP is received from the CPU, the TP may be controlled to perform an operation according to the instruction.

The memory 2830 may store at least one of information transmitted and received through the transceiver 2810 and information generated through the control unit 2820 .

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

The transceiver 2910 may include a communication unit or a network interfacing unit, and the transceiver 2910 according to an embodiment of the present disclosure is connected to a TP through a front hole. Signals can be sent and received. In addition, it is possible to transmit and receive a signal with another network entity (eg, MME of an LTE system, a gateway, or AMF of a 5G (NR) system, SMF, etc.) through the transceiver 2910 . .

The controller 2920 may control the overall operation of the network entity according to the embodiment proposed in the present disclosure. For example, the controller 2920 may control the signal flow between blocks to perform an operation according to the above-described drawing (or flowchart, flowchart). For example, according to an embodiment of the present disclosure, whether to perform CSS for controlling a ratio between a Central TP and a Local TP may be determined, and the network entity may be controlled so that the CSS is performed.

The memory 2930 may store at least one of information transmitted and received through the transceiver 2910 and information generated through the control unit 2920 .

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.

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, the computational complexity allowed for the CPUs controlling the plurality of TPs and A precoding method is provided in consideration of the capacity of a front haul, which is a signal transmission/reception path between a CPU and a TP. According to this, when it is desired to transmit/receive uplink data or downlink data between the UE and a plurality of TPs according to the CoMP scheme, the UE may have optimal data transmission/reception performance.

Although the present disclosure has been described with reference to a communication system according to a star topology in which at least one TP (or DU) is directly connected to one CPU (or CU) through 1-hop, the present disclosure is not limited thereto. The embodiments proposed in the present disclosure are also applicable to various communication systems such as a communication system in which a plurality of CUs exist, a multi-hop communication system in which DUs are connected to DUs again, or communication systems according to various topologies such as bus or mesh. can

In the drawings for explaining the method of the present disclosure, the order of description does not necessarily correspond to the order of execution, and the precedence relationship may be changed or may be executed in parallel.

Alternatively, some components may be omitted and only some components may be included in the drawings for explaining the method of the present disclosure without impairing the essence of the present invention.

On the other hand, in the present specification and drawings, a preferred embodiment of the present disclosure has been disclosed, and although specific terms are used, it is only used in a general sense to easily explain the technical content of the present disclosure and to help the understanding of the present disclosure, It is not intended to limit the scope of the present disclosure. It will be apparent to those of ordinary skill in the art to which the present disclosure pertains that other modifications based on the technical spirit of the present disclosure may be implemented in addition to the embodiments disclosed herein.

That is, in the detailed description of the present disclosure, specific embodiments have been described, but various modifications are possible without departing from the scope of the present disclosure, and the scope of the present disclosure is not limited to the described embodiments. and should be defined not only by the claims described below, but also by the claims and equivalents.

Claims

A method of a network entity in a communication system, comprising:

determining whether to perform scheduling for adjusting a 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;

determining whether to convert at least one second TP among the plurality of second TPs to a first TP based on information associated with the at least one terminal when it is determined to perform the scheduling; and

transmitting an indicator instructing to operate as the first TP to the at least one second TP when it is determined to switch the at least one second TP to the first TP;

When operating as the first TP, precoding is performed on the signal in the network entity,

When operating as the second TP, the method characterized in that the precoding is performed on the signal in the second TP.
According to claim 1,

determining whether to convert at least one first TP among the plurality of first TPs to a second TP based on information associated with the at least one terminal when it is determined to perform the scheduling; and

When it is determined to switch the at least one first TP to the second TP, the method further comprising the step of transmitting an indicator instructing to operate as the second TP to the at least one first TP How to.
According to claim 1,

allocating a plurality of demodulation-reference signal (DM-RS) 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

Further comprising the step of transmitting the information on the DM-RS port to the plurality of first TPs included in the first group and the plurality of second TPs included in the second group,

The plurality of first TPs included in the first group share the same DM-RS port.
4. The method of claim 3,

When the plurality of DM-RS ports are allocated to each of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group, the plurality of DM-RS ports included in the first group A coherent joint reception indicator (CJRI) instructing to receive data to be transmitted from the first TP and the plurality of second TPs included in the second group in synchronization is transmitted to the at least one terminal How to.
The method of claim 1,

Whether the scheduling is performed depends on at least one of channel state information for each of the at least one terminal, a predefined period, or whether a message requesting to perform the scheduling is received from the at least one terminal. A method characterized in that it is determined based on
The method of claim 1 , wherein determining whether to convert the at least one second TP to the first TP comprises:

identifying a first UE having the lowest throughput value among the at least one UE based on throughput information corresponding to each of the at least one UE;

identifying a third TP serving the first terminal among the at least one second TP; and

and determining whether to convert the third TP to the first TP.
The method of claim 1,

In the communication system, 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,

The method of claim 1, wherein the maximum number of TPs that can be included in the first group is determined based on at least one of computational complexity and fronthaul capacity that the network entity can tolerate.
A network entity in a communication system, the network entity comprising:

a transceiver for transmitting and receiving signals to and from a plurality of TPs through a fronthaul; and

determining whether to perform scheduling for adjusting a 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;

When it is determined to perform the scheduling, determining whether to convert at least one second TP among the plurality of second TPs to a first TP based on information associated with the at least one terminal;

and a control unit transmitting, through the transceiver, an indicator instructing the at least one second TP to operate as the first TP to the at least one second TP when it is determined to switch the at least one second TP to the first TP, ,

When operating as the first TP, precoding is performed on the signal in the network entity,

When operating as the second TP, the network entity characterized in that precoding is performed on the signal in the second TP.
9. The method of claim 8,

The control unit is

When it is determined to perform the scheduling, determining whether to convert at least one first TP among the plurality of first TPs to a second TP based on information associated with the at least one terminal;

When it is determined to switch the at least one first TP to the second TP, an indicator instructing the at least one first TP to operate as the second TP is transmitted through the transceiver. network entity.
9. The method of claim 8,

The control unit is

Allocating a plurality of demodulation-reference signal (DM-RS) 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,

transmitting information on the DM-RS port 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;

The plurality of first TPs included in the first group share the same DM-RS port.
11. The method of claim 10,

When the plurality of DM-RS ports are allocated to each of the plurality of first TPs included in the first group and the plurality of second TPs included in the second group, the plurality of DM-RS ports included in the first group A coherent joint reception indicator (CJRI) instructing to receive data to be transmitted from the first TP and the plurality of second TPs included in the second group in synchronization is transmitted to the at least one terminal network entity that does.
9. The method of claim 8,

Whether the scheduling is performed depends on at least one of channel state information for each of the at least one terminal, a predefined period, or whether a message requesting to perform the scheduling is received from the at least one terminal. Network entity, characterized in that determined based on.
9. The method of claim 8,

The control unit is

Based on the throughput information corresponding to each of the at least one UE, a first UE having the lowest throughput value among the at least one UE is identified,

identifying a third TP serving the first terminal among the at least one second TP;

and determining whether to convert the third TP to the first TP.
9. The method of claim 8,

In the communication system, 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,

The maximum number of TPs that can be included in the first group is determined based on at least one of a computational complexity and a fronthaul capacity that the network entity can tolerate.