KR20230028239A - Method and apparatus for clustering in wireless communication system - Google Patents

Abstract

This disclosure relates to a method in wireless communication. The method includes transmitting, by a plurality of first access points, a plurality of synchronization signals to a terminal; transmitting, by a terminal, a plurality of preamble signals to the plurality of first access points, respectively; determining channel state information and timing advance (TA) information for the terminal and each of the plurality of first access points, by means of a plurality of first access points; Transmitting channel state information and TA information to a central processing unit (CPU) by a plurality of first access points; performing, by a CPU, an operation of allocating a pilot related to a terminal and an operation of determining a cluster; Transmitting, by the CPU, pilot allocation information and cluster information to the terminal; and transmitting, by a terminal, pilot signals to the second access points.

Description

Method and apparatus for clustering in wireless communication system

This disclosure relates generally to wireless communication systems. Specifically, the present disclosure relates to clustering in a wireless communication system.

Efforts are being made to develop an improved 5th generation (5G) communication system or a pre-5G communication system in order to meet the growing demand for wireless data traffic after the commercialization of a 4G (4th generation) communication system. For this reason, the 5G communication system or pre-5G communication system is being called a system after a 4G network (Beyond 4G Network) communication system or an LTE system (Post LTE). In order to achieve a high data rate, the 5G communication system is being considered for implementation in a mmWave band (eg, a 60 gigabyte (60 GHz) band). In order to mitigate the path loss of radio waves and increase the propagation distance of radio waves in the ultra-high frequency band, beamforming, massive MIMO, and Full Dimensional MIMO (FD-MIMO) are used in 5G communication systems. ), array antenna, analog beam-forming, and large scale antenna technologies are being discussed. In addition, to improve the network of the system, in the 5G communication system, an evolved small cell, an advanced small cell, a cloud radio access network (cloud RAN), and an ultra-dense network , Device to Device communication (D2D), wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation etc. are being developed. In addition, in the 5G system, advanced coding modulation (Advanced Coding Modulation: ACM) methods FQAM (Hybrid FSK and QAM Modulation) and SWSC (Sliding Window Superposition Coding), advanced access technologies FBMC (Filter Bank Multi Carrier), NOMA (non-orthogonal multiple access), SCMA (sparse code multiple access), and the like are being developed.

On the other hand, the Internet is evolving from a human-centered connection network in which humans create and consume information to an Internet of Things (IoT) network in which information is exchanged and processed between distributed components such as things. IoE (Internet of Everything) technology, which combines IoT technology with big data processing technology through connection with a cloud server, etc., is also emerging. In order to implement IoT, technical elements such as sensing technology, wired/wireless communication and network infrastructure, service interface technology, and security technology are required, and recently, sensor networks for connection between objects and machine to machine , M2M), and MTC (Machine Type Communication) technologies are being studied. In an IoT environment, intelligent IT (Information Technology) services that create new values in human life by collecting and analyzing data generated from connected objects can be provided. IoT can be applied to fields such as smart home, smart building, smart city, smart car or connected car, smart grid, health care, smart home appliances, and advanced medical service through convergence and combination of existing IT technology and various industries. there is.

Accordingly, various attempts are being made to apply the 5G communication system to the IoT network. For example, technologies such as sensor network, machine to machine (M2M), and machine type communication (MTC) are implemented by techniques such as beamforming, MIMO, and array antenna, which are 5G communication technologies. . The application of the cloud radio access network (cloud RAN) as the big data processing technology described above can be said to be an example of convergence of 5G technology and IoT technology.

As various services can be provided according to the development of the wireless communication system as described above, a method for smoothly providing these services is required.

The 5G communication system defined by 3GPP follows the New Radio (NR) standard. In the 5G communication system, a wider bandwidth is used to achieve a high data rate, and for this purpose, mmWave bands such as the 60GHz band as well as the 3.5GHz band are used. In particular, in order to mitigate the path loss of radio waves and increase the transmission distance of radio waves in the ultra-high frequency band, beamforming, massive MIMO, and full dimensional multiple input/output (FD-MIMO) are used in 5G communication systems. ), array antenna, analog beam-forming, and large scale antenna technologies have been discussed and applied to NR systems.

Existing technology methods create many inefficiencies. For example, in a standard such as LTE, after a plurality of base stations are bundled to form a cluster, the same cell identification number must be assigned to the base stations in order for the terminal to identify the base stations included in the cluster as the same cell. For this purpose, which base stations will be identified as the same cell must be determined in advance, but it is possible to determine base stations to be identified as the same cell only after clustering. That is, it is inefficient to assign the same cell identification number to the base stations included in the cluster only after the clustering procedure has been performed in this way to form a single cell.

Based on the above discussion, the present disclosure provides an apparatus and method capable of effectively providing clustering and pilot allocation in a wireless communication system.

1 is a block diagram of a wireless communication system according to an embodiment of the present disclosure.
2 is a diagram for explaining a frame structure in a wireless communication system according to an embodiment of the present disclosure.
3A is a diagram for explaining clustering in initial positions of a first terminal, a second terminal, and a third terminal.
3B is a diagram illustrating re-clustering according to movement of a terminal.
4A is a diagram for explaining an operation in which access points transmit downlink synchronization signals to a terminal according to the first embodiment of the present disclosure.
4B is a diagram for explaining a method of determining a master access point according to the first embodiment of the present disclosure.
4C is a diagram for explaining an operation in which a terminal transmits pilot signals to neighboring access points according to the first embodiment of the present disclosure.
4D is a diagram for explaining a method of performing clustering according to the first embodiment of the present disclosure.
5A is a diagram for explaining an operation of transmitting information on a pilot assigned to a CPU from a master access point according to a second embodiment of the present disclosure.
5B is a diagram for explaining an operation in which a terminal transmits pilot signals to neighboring access points according to a second embodiment of the present disclosure.
5C is a diagram for explaining a method of performing clustering according to a second embodiment of the present disclosure.
6A is a diagram for explaining an operation of transmitting downlink synchronization signals from neighboring access points to a terminal according to a third embodiment of the present disclosure.
6B is a diagram for explaining an operation in which a terminal broadcasts preamble signals according to a third embodiment of the present disclosure.
6C is a diagram for explaining an operation in which neighbor access points transmit information on a channel state to a CPU according to a third embodiment of the present disclosure.
6D is a diagram for explaining a method of performing clustering according to a third embodiment of the present disclosure.
6E is a diagram for explaining an operation in which a terminal transmits pilot signals to neighboring access points based on pilots allocated according to a third embodiment of the present disclosure.
7 is a sequence diagram illustrating pilot allocation and clustering according to the third embodiment.
8 is a flowchart illustrating a method of operating a wireless communication system according to a third embodiment.
9 is a flowchart illustrating a method of operating a terminal according to a third embodiment.
10 is a flowchart illustrating a method of operating a CPU according to a third embodiment.
11 is a flowchart illustrating a method of operating a wireless communication system according to a second embodiment.
12 is a diagram illustrating a detailed configuration of a terminal in a wireless communication system according to an embodiment.
13 is a diagram illustrating a detailed configuration of an AP in a wireless communication system according to an embodiment.
14 is a diagram illustrating a detailed configuration of a CPU in a wireless communication system according to an embodiment.
15 is a diagram illustrating a method of measuring signal strength and timing advance (TA) using random access based on non-contention in a handover process.
16 is a simulation result of pilot allocation and clustering according to the first embodiment and pilot allocation and clustering according to the third embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In addition, in describing the present disclosure, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the present disclosure, which may vary according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout this specification.

Advantages and features of the present disclosure, and methods for achieving them, will become clear with reference to embodiments described below in detail in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed below and may be implemented in various different forms, only the present embodiments make the disclosure of the present disclosure complete, and the common knowledge in the art to which the present disclosure belongs It is provided to fully inform the holder of the scope of the invention, and the present disclosure is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification.

At this time, it will be understood that each block of the process flow chart diagrams and combinations of the flow chart diagrams can 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, so that the instructions executed by the processor of the computer or other programmable data processing equipment are described in the flowchart block(s). It creates means to perform functions. These computer program instructions may also be stored in a computer usable or computer readable memory that can be directed to a computer or other programmable data processing equipment to implement functionality in a particular way, such that the computer usable or computer readable memory The instructions stored in are also capable of producing an article of manufacture containing instruction means that perform the functions described in the flowchart block(s). The computer program instructions can also be loaded on a computer or other programmable data processing equipment, so that a series of operational steps are performed on the computer or other programmable data processing equipment to create a computer-executed process to generate computer or other programmable data processing equipment. Instructions for performing processing equipment may also 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 possible for the functions mentioned in the blocks to occur out of order. For example, it is possible that two blocks shown in succession may in fact be performed substantially concurrently, or that the blocks may sometimes be performed in reverse order depending on their function.

At this time, the term '~unit' used in this embodiment means software or hardware components such as FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuit), and '~unit' performs certain roles. do. However, '~ part' is not limited to software or hardware. '~bu' may be configured to be in an addressable storage medium and may be configured to reproduce one or more processors. Therefore, as an example, '~unit' refers to components such as software components, object-oriented software components, class components, and task components, processes, functions, properties, and procedures. , subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Functions provided within components and '~units' may be combined into smaller numbers 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 a secure multimedia card. Also, in an embodiment, '~ unit' may include one or more processors.

In the following description of the present disclosure, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present disclosure, the detailed description will be omitted. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

A term used in the following description to identify a connection node, a term referring to network entities, a term referring to messages, a term referring to an interface between network objects, and various types of identification information. Referring terms and the like are illustrated for convenience of description. Accordingly, the present disclosure is not limited to the terms described below, and other terms referring to objects having equivalent technical meanings may be used.

In the following description, physical channels and signals may be used interchangeably with data or control signals. For example, a physical downlink shared channel (PDSCH) is a term that refers to a physical channel through which data is transmitted, but PDSCH may also be used to refer to data. That is, in the present disclosure, the expression 'transmitting a physical channel' may be interpreted as equivalent to the expression 'transmitting data or signals through a physical channel'.

Hereinafter, in the present disclosure, higher-order signaling refers to a method of transmitting a signal from a base station to a terminal using a downlink data channel of a physical layer or from a terminal to a base station using an uplink data channel of a physical layer. Higher signaling may be understood as radio resource control (RRC) signaling or media access control (MAC) control element (CE).

For convenience of description below, the present disclosure uses terms and names defined in the 3rd Generation Partnership Project NR (New Radio) (3GPP NR) standard. However, the present disclosure is not limited by the above terms and names, and may be equally applied to systems conforming to other standards. In the present disclosure, gNB may be used interchangeably with eNB for convenience of description. That is, a base station described as an eNB may indicate a gNB. In addition, the term terminal may represent other wireless communication devices as well as mobile phones, MTC devices, NB-IoT devices, and sensors.

Hereinafter, a base station is a subject that performs resource allocation of a terminal, and is at least one of a gNode B (gNB), an eNode B (eNB), a Node B, a base station (BS), a radio access unit, a base station controller, or a node on a network. can The terminal may include a user equipment (UE), a mobile station (MS), a cellular phone, a smart phone, a computer, or a multimedia system capable of performing communication functions. Of course, it is not limited to the above example.

While using mmWave bands in next-generation mobile communication after 5G, the number of access points serving terminals in cooperation may increase in order to support exponentially increasing terminals. As the number of access points included in a wireless communication system far exceeds the number of terminals, a plurality of access points may cooperate to serve a single terminal. A wireless communication system capable of such user-centered access may be referred to as a cell-free wireless communication system or a large-scale multiple-input and multiple-output (MIMO) without a cell boundary.

According to an embodiment of the present disclosure, a cluster means a set of a plurality of access points serving a terminal, and the terminal sends a pilot signal used for channel estimation between the terminal and each of the access points to the access points included in the cluster. can transmit them. Accordingly, in one embodiment of the present disclosure, clustering may mean that a set of a plurality of points serving a terminal is formed.

In a cell-free wireless communication system, as a plurality of access points serve a terminal, potential interference issues can be resolved.

Meanwhile, in a cell-free wireless communication system, it is necessary to effectively allocate pilots and determine clusters.

In a method in wireless communication according to an embodiment of the present disclosure, the method includes a plurality of first access points located within a predetermined distance from a terminal, and a plurality of synchronization signals shared by the plurality of first access points. transmitting them to the terminal; broadcasting, by the terminal, a plurality of preamble signals; determining channel state information and timing advance (TA) information for the terminal and each of the plurality of first access points by receiving the plurality of preamble signals, by the plurality of first access points; transmitting, by the plurality of first access points, the channel state information to a central processing unit (CPU) connected to the plurality of first access points; performing, by the CPU, an operation of allocating a pilot related to the terminal and an operation of determining a cluster that is a set of second access points serving the terminal, based on the channel state information; and transmitting, by the terminal, pilot signals generated based on the pilot allocation information to the second access points.

In a method for a terminal in wireless communication according to an embodiment of the present disclosure, the method comprises a plurality of first access points shared by the plurality of first access points from a plurality of first access points located within a predetermined distance from the terminal. receiving synchronization signals; broadcasting a plurality of preamble signals based on the plurality of synchronization signals; performing random access to the first access points based on the plurality of preamble signals; Receiving information on pilot allocation and information on a cluster from a representative access point included in a cluster that is a set of second access points serving the terminal; and transmitting a pilot signal generated based on the pilot allocation information to the second access points.

In a method for a Central Processing Unit (CPU) in wireless communication according to an embodiment of the present disclosure, the method includes channel state information and timing for each of a terminal and a plurality of first access points located within a predetermined distance from the terminal Receiving Advance (TA) information from the first access points; Based on the channel state information, performing an operation of allocating a pilot related to the terminal and an operation of determining a cluster that is a set of second access points serving the terminal; selecting a representative access point transmitting a response to the random access to the terminal from among the first access points; and transmitting information on the allocated pilot and the determined cluster to the terminal through the representative access point.

In a method in wireless communication according to an embodiment of the present disclosure, the method transmits, by a master access point, pilot allocation information related to a terminal to the terminal and a plurality of first access points located within a predetermined distance from the terminal. Transmitting to a Central Processing Unit (CPU) associated with the; transmitting, by the CPU, information on the pilot assignment to a plurality of second access points located within a predetermined distance from the master access point; transmitting, by the terminal, pilot signals generated based on the pilot allocation information to the plurality of second access points and the master access point; determining, by the plurality of second access points and the master access point, channel state information based on the pilot signals; transmitting the channel state information to the CPU by the second access points; determining, by the CPU, a cluster that is a set of third access points serving the terminal based on the channel state information; transmitting, by the CPU, information on the determined cluster to the terminal; and transmitting, by the terminal, the pilot signals to the third access points.

In a terminal in wireless communication according to an embodiment of the present disclosure, the terminal includes a transceiver; and at least one processor, wherein the at least one processor receives a plurality of synchronization signals from a plurality of first access points located within a predetermined distance from the terminal through the transceiver, and through the transceiver, the plurality of synchronization signals. broadcasts a plurality of preamble signals based on synchronization signals of, performs random access to the first access points based on the plurality of preamble signals through the transceiver, and through the transceiver, the terminal Receives information on pilot allocation and information on a cluster from a representative access point included in a cluster, which is a set of second access points serving, and generates information on the pilot allocation through the transceiver based on the information on the pilot allocation. The pilot signal may be transmitted to the second access points.

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

1 is a block diagram of a wireless communication system according to an embodiment of the present disclosure.

Referring to FIG. 1, a wireless communication system 100 includes a central processing unit (CPU) 120, a plurality of access points (APs) 140-1 to 140-M, and a plurality of terminals 160-1 to 140-M. 160-K).

The CPU 120 may be connected to a plurality of APs 140-1 to 140-M through a front-haul. The CPU 120 may coordinate and process signals of the terminals 160-1 to 160-K served by the plurality of APs 140-1 to 140-M. .

The CPU 120 is not necessarily limited to a physical unit, and the CPU 120 may be a set of centralized processing tasks to be performed in a network. For example, for centralized processing, each of the plurality of APs 140-1 to 140-M may be connected to an edge-cloud processor through a front hall, and CPU tasks may be performed by a plurality of edge-cloud processors. can be distributed among In this case, the CPU 120 may correspond to a physical unit called an edge-cloud processor.

As another example, when a plurality of APs 140-1 to 140-M each including local processors are connected to a core network through a back-haul, a physical CPU may not exist. However, in this case, tasks of the CPU may be distributed to a plurality of APs 140-1 to 140-M. For example, when information is transmitted to/from the CPU 120, the information may in fact be transmitted to/from the AP performing the CPU task.

Each of the plurality of APs 140-1 to 140-M may include a plurality of antennas, and a case in which each of the plurality of APs 140-1 to 140-M includes N antennas will be described below. . The plurality of APs 140-1 to 140-M may be connected to the CPU 120 through a high-capacity front hole. The plurality of APs 140-1 to 140-M may perform baseband processing or radio-band processing. A plurality of APs 140-1 to 140-M may serve a plurality of terminals 160-1 to 160-K. Although FIG. 1 illustrates a plurality of APs 140-1 to 140-M located close to each other for convenience of description, the plurality of APs 140-1 to 140-M may not be located at the same location. Not-colocated.

The wireless communication system 100 shown in FIG. 1 may have an ultra-dense environment in which a large number of APs serve a relatively small number of terminals. The wireless communication system 100 may include M APs 140-1 to 140-M and K terminals 160-1 to 160-K, and the value of 'M' is 'N' value can be much greater than As such, in the wireless communication system 100 in which the number of APs 140-1 to 140-M is much greater than the number of terminals 160-1 to 160-K, an autonomous cell does not need to be created. , A plurality of APs can cooperate to serve the terminal at the same time. Such a wireless communication system 100 may be referred to as a cell-free massive MIMO system.

In a cell-free massive MIMO system, user-centric clustering may be performed to determine a set of APs that simultaneously transmit data to a terminal for each terminal. For example, in the wireless communication system 100, a cluster including APs simultaneously serving the k-th terminal 160-k must be determined, and in order for the APs to simultaneously transmit data to the k-th terminal 160-k, APs can be synchronized with each other.

Clustering may be necessary for scalability of the wireless communication system 100 . For example, when clustering is not performed, when the number of terminals included in the wireless communication system 100 increases exponentially, the CPU 120 performs power control, pilot detection, data processing, etc. for each terminal. Complexity may increase excessively. Conversely, when a plurality of APs serve multiple terminals on a one-to-one basis, scalability may be improved, but since there is only one AP serving a single terminal, cell boundaries exist, resulting in overall transmission performance deterioration. Both scalability and average performance can be guaranteed by configuring a cluster with APs capable of serving the UE among APs neighboring the UE.

Each of the plurality of terminals 160-1 to 160-K may be served by APs included in corresponding clusters. The plurality of terminals 160-1 to 160-K may share entire time/frequency radio resources without separating time/frequency radio resources into channels for user multiplexing. The plurality of terminals 160-1 to 160-K may transmit pilot signals for channel state estimation to the plurality of APs 140-1 to 140-M. For example, the k-th terminal 160-k may transmit pilot signals to a plurality of APs included in the cluster for the k-th terminal 160-k, and the plurality of APs, based on the pilot signals, A channel state between each of the plurality of APs and the kth terminal 160-k may be estimated.

)는 아래 수학식 1과 같이 표현될 수 있다.A channel vector indicating channel state information between the kth terminal 160-k and the mth AP 140-m (

) can be expressed as in Equation 1 below.

[Equation 1]

)는 라지-스케일(large-scale) 채널 계수(coefficient)(

)와 스몰-스케일(small-scale) 채널 계수(

)에 기초하여 결정될 수 있다. 스몰-스케일 채널 벡터(

)는 라지-스케일 채널 계수(

)에 비해 보다 빈번히 변하며, 스몰-스케일 채널 벡터(

)가 일정한 값으로 유지되는 시간을 채널 코히런스 시구간이라고 하고, 그 주기를 정의할 수 있다. 예를 들어, 복수의 채널 코히런스 시구간들 동안 라지-스케일 채널 계수(

)는 일정한 값으로 유지될 수 있다. 복수의 AP들(140-1 내지 140-M)은 주기적으로 다운 링크 동기화 신호들을 복수의 단말들(160-1 내지 160-K)에게 전송할 수 있으며, 설명의 편의를 위해, 다운 링크 동기화 신호들이 전송되는 주기 동안 라지-스케일 채널 계수(

)가 일정한 값으로 유지되는 경우로 이하 설명한다. Referring to Equation 1, the channel vector (

) is a large-scale channel coefficient (

) and small-scale channel coefficients (

) can be determined based on The small-scale channel vector (

) is the large-scale channel coefficient (

) and changes more frequently than the small-scale channel vector (

) is maintained at a constant value is called a channel coherence time period, and its period can be defined. For example, a large-scale channel coefficient (

) can be maintained at a constant value. The plurality of APs 140-1 to 140-M may periodically transmit downlink synchronization signals to the plurality of terminals 160-1 to 160-K, and for convenience of description, the downlink synchronization signals Large-scale channel coefficient during the transmitted period (

) will be described below as a case where it is maintained at a constant value.

The independent correlated Rayleigh fading realization in the channel coherence time period can be expressed as Equation 2 below.

[Equation 2]

)는 컴플랙스 가우시안 분포(complex Gaussian distribution)를 갖는 램덤 변수로 나타낼 수 있으며, 이때 컴플랙스 가우시안 분포의 평균 값은 '0'의 값을 갖는다고 가정한다. 컴플랙스 가우시안 분포의 공분산(covariance)는 행렬로 나타낼 수 있으며, 공분산 행렬(

)의 구성 요소(element)들의 값은 AP들로부터 전송된 다운 링크 동기화 신호의 세기이다. 공분산 행렬(

)의 모든 구성 요소들의 합은 라지-스케일 채널 계수(

)이다.channel vector (

) can be represented as a random variable having a complex Gaussian distribution, and it is assumed that the average value of the complex Gaussian distribution has a value of '0'. The covariance of the complex Gaussian distribution can be represented by a matrix, the covariance matrix (

) is the strength of the downlink synchronization signal transmitted from the APs. covariance matrix (

) is the large-scale channel coefficient (

)am.

)는 아래 수학식 3과 같이 나타낼 수 있다.A channel vector indicating a channel state between the kth terminal 160-k and each of the plurality of APs 140-1 to 140-M (

) can be expressed as in Equation 3 below.

[Equation 3]

)는 제1 채널 벡터(

)내지 제M 채널 벡터(

)를 포함할 수 있으며, 채널 벡터(

)의 구성 요소들은 각각 복소수로 나타낼 수 있다. 제1 채널 백터(

) 및 제M 채널 벡터(

)는 각각 제k 단말(160-k)와 제1 AP(140-1) 간의 채널 상태 및 제k 단말(160-k)와 제M AP(140-M) 간의 채널 상태를 나타낼 수 있다.channel vector (

) is the first channel vector (

) to the Mth channel vector (

), and the channel vector (

) can be expressed as a complex number. The first channel vector (

) and the Mth channel vector (

) may indicate a channel state between the k th terminal 160-k and the first AP 140-1 and a channel state between the k th terminal 160-k and the M th AP 140-M, respectively.

)를 결정할 수 있다. 선택적으로, 파일럿 신호들은 단말의 송신 파워, 처리 이득 및 열 잡음(thermal noise) 등에 의해 결정될 수 있다. 제m AP(140-m)는 파일럿 신호들에 기초하여, 채널 벡터(

)에 대한 mean-squared-error(MMSE)를 사용하여 추정한 결과를 추정된 채널 벡터(

)로 결정할 수 있다.The plurality of APs 140-1 to 140-M are connected to the plurality of APs 140-1 to 140-M based on pilot signals transmitted from the plurality of terminals 160-1 to 160-K. A channel state between the terminal 160-1 and the plurality of terminals 160-1 to 160-K may be estimated. For example, the m-th AP 140-m connects the m-th AP 140-m and the k-th terminal 160 based on pilot signals transmitted from terminals served by the m-th AP 140-m. -k) by estimating the inter-channel state, the estimated channel vector (

) can be determined. Optionally, the pilot signals may be determined by transmit power, processing gain, and thermal noise of the terminal. Based on the pilot signals, the mth AP 140-m is a channel vector (

) using the mean-squared-error (MMSE) for the estimated channel vector (

) can be determined.

2 is a diagram for explaining a frame structure in a wireless communication system according to an embodiment of the present disclosure.

개의 파일럿 전송 심볼들,

개의 업링크 데이터 전송 심볼들 및

개의 다운링크 데이터 전송 심볼들을 포함할 수 있다. 전송 프레임(FRAME)은 스몰-스케일 채널 벡터(

)가 일정한 값으로 유지되는 시간인 제1 채널 코히런스 시구간보다 작거나 같은 값을 가질 수 있다. 선택적으로, 제1 채널 코히런스 시구간은

개의 심볼들을 포함할 수 있다. 전송 프레임(FRAME)에 포함된 심볼들의 개수는

,

및

를 모두 합한 결과일 수 있다. 도 2는 전송 프레임(FRAME)에 포함된 심볼들의 개수(

)와 제1 채널 코히런스 시간에 포함된 심볼들의 개수(

)가 같은 경우를 나타내고 있다.The transmission frame (FRAME) is

pilot transmission symbols,

uplink data transmission symbols and

downlink data transmission symbols. The transmission frame (FRAME) is a small-scale channel vector (

) may have a value equal to or smaller than the first channel coherence time period, which is a time period in which ) is maintained at a constant value. Optionally, the first channel coherence time period is

It can contain up to 10 symbols. The number of symbols included in the transmission frame (FRAME) is

,

and

may be the result of the sum of all 2 shows the number of symbols included in the transmission frame (FRAME) (

) and the number of symbols included in the first channel coherence time (

) represents the same case.

)가 일정한 값으로 유지되는 시간인 제2 채널 코히런스 시구간은

개의 심볼들을 포함할 수 있으며, 복수의 제1 채널 코히런스 시구간들을 포함할 수 있다. 파일럿 전송을 위해 할당된 파일럿 전송 심볼들의 개수(

)가 간섭하는 사용자들의 수보다 작으면, 파일럿 오염(contamination) 및 채널 추정에서 후속 에러가 발생할 수 있다. 동일한 라디오 자원들을 공유하는 사용자들의 수가 소정의 임계치보다 높으면, 파일럿 오염으로 인한 채널 추정 에러는 가우시안 랜덤 백터로 모델링될 수 있다.The large-scale channel coefficients (

) is maintained at a constant value, the second channel coherence time period is

symbols, and may include a plurality of first channel coherence time periods. The number of pilot transmission symbols allocated for pilot transmission (

) is less than the number of interfering users, pilot contamination and subsequent errors in channel estimation may occur. If the number of users sharing the same radio resources is higher than a predetermined threshold, a channel estimation error due to pilot contamination may be modeled as a Gaussian random vector.

The arrangement order of the pilot transmission symbols, uplink data transmission symbols, and downlink data transmission symbols shown in FIG. 2 is only an example, and the pilot transmission symbols may be interlaced with the uplink data transmission symbols. may be In this case, pilot transmission symbols may be mapped to different subcarriers in OFDM symbols of an Orthogonal Frequency Division Multiplexing (OFDM) system.

)의 개수가 단일 AP가 서빙하는 단말들의 개수보다 작은 경우에, 복수의 단말들이 동일한 파일럿 전송 심볼을 공유하거나, 복수의 단말들에게 직교하지 않는 파일럿 전송 심볼들이 할당되는 파일럿 오염(contamination) 발생할 수 있다. 파일럿이 오염되어 복수의 단말들이 동일한 파일럿을 공유할 경우에, AP는 동일한 파일럿을 공유하는 단말들을 구분하기 어렵기 때문에 채널 추정에서 에러가 발생할 수 있다. 따라서, 상관관계(correlated)가 있거나 동일한 파일럿을 최소한의 간섭을 야기하는 단말들간에 할당할 필요가 있다. For example, the number of interfering terminals may be the number of terminals served by a single AP, and if the pilot transmission symbols (

) is smaller than the number of terminals served by a single AP, pilot contamination may occur in which a plurality of terminals share the same pilot transmission symbol or non-orthogonal pilot transmission symbols are allocated to a plurality of terminals. there is. When a pilot is contaminated and a plurality of terminals share the same pilot, an error may occur in channel estimation because it is difficult for the AP to distinguish between terminals sharing the same pilot. Therefore, it is necessary to allocate a correlated or identical pilot between terminals causing minimal interference.

3A and 3B are diagrams illustrating re-clustering according to movement of a terminal.

3A shows the initial positions of the first terminal 310, the second terminal 320, and the third terminal 330. Referring to FIG.

Referring to FIG. 3A , a plurality of APs 311 , 312 , 313 , 314 , 316 , and 318 included in a first cluster 340 for a first terminal 310 may serve the first terminal 310 . In addition, the plurality of APs 311 , 313 , 321 , 322 , and 324 included in the second cluster 350 for the second terminal 320 may serve the second terminal 320 . In addition, the plurality of APs 321 , 332 , 334 , 336 , and 338 included in the third cluster 360 for the third terminal 330 may serve the third terminal 330 .

The first terminal 310 and the second terminal 320 may be located at a relatively close distance compared to the first terminal 310 and the third terminal 330 .

Since the first terminal 310 and the second terminal 320 are physically located at a relatively close distance, the first cluster 340 and the second cluster 350 can share two APs 311 and 313. . In addition, since the second terminal 320 and the third terminal 330 are physically located at a relatively close distance, the second cluster 350 and the third cluster 360 may share one AP 321 . On the other hand, since the first terminal 310 and the third terminal 330 are physically located far apart, the first cluster 340 and the third cluster 360 may not share an AP. That is, since there is no AP that simultaneously serves the first terminal 310 and the third terminal 330, there is a problem in channel estimation even when the same pilot is allocated to the first terminal 310 and the third terminal 330. does not occur

3B shows positions of the first terminal 310, the second terminal 320, and the third terminal 330 after the first terminal 310 and the third terminal 330 move.

Referring to FIG. 3B , when the first terminal 310 moves, the APs 311 , 312 , 313 , 314 , 316 , and 318 that have previously served the first terminal 310 are farther away from the first terminal 310 and are no longer the first terminal 310 . (310) cannot be served. Accordingly, re-clustering needs to be performed so that APs located within a predetermined distance from the first terminal 310 can serve the first terminal 310 .

The plurality of APs 341 , 343 , 348 , 352 , and 354 included in the first cluster 380 re-clustered for the moved first terminal 310 may serve the first terminal 310 . In addition, the plurality of APs 341 , 343 , 344 , and 346 included in the third cluster 370 re-clustered for the moved third terminal 330 may serve the third terminal 330 .

Since the first terminal 310 and the third terminal 330 are physically located at a relatively close distance, the first cluster 380 and the third cluster 370 can share two APs 341 and 343. . On the other hand, since the second terminal 320 is located at a physically long distance from the first terminal 310 and the third terminal 330, the second cluster 350 is the first cluster 380 and the third cluster 370. ) and may not share the AP.

As a result of re-clustering by moving the first terminal 310 and the third terminal 330, there are APs 341 and 343 serving the first terminal 310 and the third terminal 330 at the same time. , If the same pilot is allocated to the first terminal 310 and the third terminal 330, a problem may occur in channel estimation. Therefore, it is necessary to allocate different pilots to the first terminal 310 and the third terminal 330. As such, since re-clustering and pilot allocation must be performed as the terminal moves, a method capable of simultaneously and effectively performing re-clustering and pilot allocation is required.

4A to 4D are diagrams for explaining pilot allocation and clustering according to the first embodiment.

4A is a diagram for explaining an operation in which access points transmit downlink synchronization signals to a terminal according to the first embodiment of the present disclosure.

Referring to FIG. 4A , first neighbor APs 414 , 424 , 434 , 444 , 454 , and 464 located within a predetermined distance from a terminal 406 transmit a first downlink synchronization signal SIGNAL_DL1 to a sixth downlink synchronization signal SIGNAL_DL6 to the terminal 406 , respectively. can transmit The first downlink synchronization signal SIGNAL_DL1 to the sixth downlink synchronization signal SIGNAL_DL6 may each include identification information, and the terminal 406 transmits the first downlink synchronization signal SIGNAL_DL1 to the sixth downlink synchronization signal SIGNAL_DL1 to the sixth downlink synchronization signal SIGNAL_DL6 based on the identification information. 6 It is possible to determine from which AP the downlink synchronization signal (SIGNAL_DL6) is transmitted.

The UE 406 can determine a point in time at which data can be transmitted to the first neighboring APs 414, 424, 434, 444, 454, and 464 based on the first downlink synchronization signal SIGNAL_DL1 to the sixth downlink synchronization signal SIGNAL_DL5.

Also, the UE 406 may determine a master AP for pilot allocation among the first neighbor APs 414 , 424 , 434 , 444 , 454 , and 464 based on the strength of the downlink synchronization signal. For example, the terminal 406 may measure the strengths of the first downlink synchronization signal SIGNAL_DL1 to the sixth downlink synchronization signal SIGNAL_DL6. The terminal 406 may determine the maximum value of the intensities of the first downlink synchronization signal SIGNAL_DL1 to the sixth downlink synchronization signal SIGNAL_DL6. The terminal 406 may determine the AP 424 that has transmitted the downlink synchronization signal having the maximum value as the master AP (MASTER_AP).

4B is a diagram for explaining a method of determining a master access point according to the first embodiment of the present disclosure.

Referring to FIG. 4B , the terminal 406 attempts to access the master AP 424 by transmitting a random access signal (RA) to the master AP 424 . Optionally, the random access signal (RA) may include a preamble signal. The master AP 424 may determine a timing advance (TA) according to a propagation delay based on a preamble signal while performing random access.

In addition, the master AP 424 may allocate pilots for channel estimation based on terminals served by the master AP 424 . For example, the master AP 424 may allocate a pilot for the terminal 406 based on a correlation matrix for pilot signals transmitted from the terminals served by the master AP 424. . Optionally, the master AP 424 may allocate a pilot for the terminal 406 by selecting the most available pilot or the least polluted pilot. The master AP 424 may transmit information on the allocated pilot (INFO_PA) to the terminal 406 .

4C is a diagram for explaining an operation in which a terminal transmits pilot signals to neighboring access points according to the first embodiment of the present disclosure.

Referring to FIG. 4C , the master AP 424 may transmit connection request messages (RQ_CONNECT) to second neighbor APs 414, 434, and 444 located within a predetermined distance from the master AP 424. The connection request message (RQ_CONNECT) may include information indicating that the master AP 424 is serving the terminal 406 and information about a pilot assigned to the terminal 406.

The terminal 406 may transmit pilot signals SIG_PILOT to the second neighboring APs 414 , 434 , and 444 . The second neighbor APs 414 , 434 , and 444 may determine information about a channel state between each of the second neighbor APs 414 , 434 , and 444 and the terminal 406 based on the received pilot signals SIG_PILOT. For example, the second neighboring APs 414 , 434 , and 444 may determine channel state information by measuring the strength of pilot signals SIG_PILOT received from the terminal 406 . Optionally, the information on the channel state may include a large-scale channel coefficient representing channel statistical information.

4D is a diagram for explaining a method of performing clustering according to the first embodiment of the present disclosure.

Referring to FIG. 4D, the second neighboring APs 414, 434, and 444 independently establish a terminal 406 based on channel state information and pilot information of other terminals served by the second neighboring APs 414, 434, and 444. You can decide whether or not to serve. For example, the second neighboring APs 414 , 434 , and 444 have weak pilot signals transmitted from the terminal 406 , or the second neighboring APs 414 , 434 , and 444 are serving pilots of other terminals and the terminal 406 . When the pilot correlation is high, it may be determined that the terminal 406 is not served. As a result of determining whether the second neighboring APs 414, 434, and 444 independently serve the terminal 406, some of the second neighboring APs 414, 434, and 444 that have determined to serve the terminal 406 include some APs 414 and 434. A cluster 410 that does may be determined.

Clustering and pilot allocation according to the first embodiment described with reference to FIGS. 4A to 4D do not use a centralized method. Clustering according to the first embodiment is highly scalable because only channel state information estimated by APs located around the master AP is required to perform clustering and pilot allocation, but the CPU centrally allocates pilots and allocates pilots. There is a disadvantage of not taking advantage of the performance gains that can be obtained by performing clustering.

For example, since the master AP 424 independently allocates pilots without considering pilots of other terminals connected to the second neighbor APs 414, 434, and 444, the pilot allocated by the master AP 424 is the second neighbor AP 424. A situation in which it cannot be used by the APs 414 , 434 , and 444 may occur. Alternatively, the pilot allocated by the master AP 424 may not be used by all of the second neighbor APs 414 , 434 , and 444 , in which case only the master AP 424 may serve the terminal 406 . . Since the data rate of the terminal 406 increases as the number of APs serving the terminal 406 increases, when the only AP included in the cluster is the master AP 424, the data rate of the terminal 406 is Significantly lowering may occur.

5A to 5C are diagrams for explaining pilot allocation and clustering according to the second embodiment.

Pilot allocation according to the second embodiment may be performed in the same manner as described above with reference to FIGS. 4A and 4B. For example, the terminal 506 may receive a first downlink synchronization signal to a sixth downlink synchronization signal from first neighboring APs 514, 524, 534, 544, 554, and 564 located within a predetermined distance from the terminal 506. The terminal 506 may determine the master AP 524 based on the strengths of the first downlink synchronization signal to the sixth downlink synchronization signal. For example, the terminal 506 may determine the AP 524 having the best channel condition as the master AP (MASTER_AP).

The terminal 506 may perform random access with the master AP 524 . The terminal 506 may start random access by transmitting a preamble signal to the master AP 524 . Master AP 524 may allocate a pilot for UE 506 based on the preamble signal and the pilots of other UEs served by master AP 524 . In the process of performing random access, the master AP 524 may determine a TA for synchronizing. The master AP 524 may transmit information on the allocated pilot (INFO_PA) to the terminal 506 . The terminal 506 may generate a pilot signal (SIG_PILOT) based on information (INFO_PA) on allocated pilots.

Referring to FIG. 5A , the master AP 524 may transmit information on allocated pilots (INFO_PA) to the CPU 502 . The CPU 502 may transmit information (INFO_PA) on pilots allocated to second neighbor APs 514 , 534 , and 544 located within a predetermined distance from the master AP 524 .

Referring to FIG. 5B , the terminal 506 may transmit pilot signals (SIG_PILOT) to the second neighbor APs 514 , 534 , and 544 and the master AP 524 . The second neighboring APs 514 , 534 , and 544 may determine information (INFO_CH) on a channel state between each of the second neighboring APs 514 , 534 , and 544 and the terminal 506 based on the received pilot signals SIG_PILOT. In addition, the master AP 524 may determine information on a channel state between the master AP 524 and the terminal 506 (INFO_CH) based on the received pilot signal (SIG_PILOT). For example, the second neighbor APs 514 , 534 , and 544 and the master AP 524 may determine channel state information (INFO_CH) by measuring the strength of pilot signals (SIG_PILOT) received from the terminal 506. . Optionally, the channel state information (INFO_CH) may include a large-scale channel coefficient indicating channel statistical information. The second neighbor APs 514 , 534 , and 544 and the master AP 524 may transmit channel state information (INFO_CH) to the CPU 502 .

Referring to FIG. 5C , the CPU 502 may perform clustering based on received channel state information (INFO_CH). For example, the cluster 510 for the terminal 506 may include only some APs 514 , 524 , and 534 among the second neighbor APs 514 , 534 , and 544 and the master AP 524 .

According to an embodiment, the CPU 502 may reassign APs serving other existing terminals to serve a new terminal by centrally performing clustering based on a minimum rate requirement. there is. By centrally performing clustering by the CPU 502 according to the second embodiment, compared to the case where clustering is performed by the master AP according to the first embodiment, the wireless communication system can provide a more uniform user experience. can

The CPU 502 may control the access rate of the terminal through clustering. The CPU 502 may perform clustering by allocating radio resources to ensure a data transmission rate of a terminal having the lowest data transmission rate among terminals included in the wireless communication system. According to an embodiment, the CPU 502 may perform clustering by maximizing a minimum transmission rate for uplink transmission according to Equation 4 below.

[Equation 4]

)은 제k 단말에 대한 클러스터에 포함된 AP들의 집합(

)및 제k 단말에 할당된 전송 파워(

)에 의해 결정될 수 있다. 예를 들어, 제k 단말에 대한 클러스터에 포함된 AP들의 집합(

)이 더 많은 개수의 AP들을 포함할수록 제k 단말의 데이터 전송률(

)은 증가할 수 있다. 또한, 제k 단말에 할당된 전송 파워(

)가 증가할수록 제k 단말의 데이터 전송률(

)은 증가할 수 있다.In Equation 4, the data rate of the kth terminal for uplink transmission (

) is a set of APs included in the cluster for the kth terminal (

) and transmission power allocated to the kth terminal (

) can be determined by For example, a set of APs included in a cluster for the kth terminal (

) includes a larger number of APs, the data transmission rate of the kth terminal (

) can increase. In addition, the transmission power allocated to the kth terminal (

) increases, the data transmission rate of the kth terminal (

) can increase.

)는 단말에 대해 허용되는 최대 전송 파워(P)를 초과할 수 없다. In order to provide consistent performance to the terminals, the CPU 502 may maximize the data transmission rate of the terminal having the lowest data transmission rate among the terminals included in the wireless communication system. However, the transmission power allocated to the kth terminal (

) cannot exceed the maximum transmission power (P) allowed for the terminal.

For example, in uplink data transmission, precoding based on Minimum Mean-Squared-Error (MMSE) and the combined Signal-To-Noise Ratio (SINR) for a signal received from the kth user are It can be expressed as 5.

[Equation 5]

는 제k 단말의 채널 추정 에러 및 부가 잡음(additive noise)를 나타낸다.

는 채널 백터들의 추정에 대한 연결(concatenation)을 나타내며,

는 제m 블록(

)과의 블록 대각 클러스터링 행렬을 나타낸다.

는 N행 N열의 행렬이며, 제k 단말에 대한 클러스터에 포함된 AP들의 집합(

)에 제m AP가 포함되어 있는지 여부를 식별하도록 설정되며, 제k 단말에 대한 클러스터에 포함된 AP들의 집합(

)에 제m AP가 포함되어 있지 않은 경우에,

는 영행렬이다. 클러스터 사이즈가 증가하면 수학식 4의 파라미터들이 증가할 수 있다. 달리 말하면, 클러스터 사이즈가 증가하면 라지-스캐일 채널 계수가 작은 AP들이 클러스터에 포함될 수 있다. 클러스터 사이즈의 증가가 전송 파워의 증가와 결합되면, 단말 각각의 데이터 전송률은 효과적으로 증가될 수 있다.The set P _k represents a set of terminals sharing at least one AP with the kth terminal.

represents the channel estimation error and additive noise of the kth terminal.

Represents the concatenation of the estimation of channel vectors,

is the mth block (

) represents the block diagonal clustering matrix with

Is a matrix of N rows and N columns, and a set of APs included in the cluster for the k th terminal (

) is set to identify whether the m-th AP is included, and a set of APs included in the cluster for the k-th terminal (

) does not include the m AP,

is a zero matrix. As the cluster size increases, the parameters of Equation 4 may increase. In other words, when the cluster size increases, APs having small large-scale channel coefficients may be included in the cluster. When an increase in cluster size is combined with an increase in transmission power, the data transmission rate of each terminal can be effectively increased.

Similarly, the CPU 502 may perform clustering by maximizing the minimum transmission rate for downlink transmission according to Equation 6 below.

[Equation 6]

)는 제k 단말에 대한 클러스터에 포함된 AP들의 집합(

) 및 제k 단말에 할당된 전송 파워(

)를 변수로 한 함수로 나타낼 수 있다. 단말들 중에서 일관된 성능을 제공하기 위해서, CPU(502)는 무선 통신 시스템에 포함된 단말들 중 데이터 전송률이 최소인 단말의 데이터 전송률을 최대화할 수 있다. The data rate of the kth terminal for downlink transmission (

) is a set of APs included in the cluster for the kth terminal (

) and transmission power allocated to the kth terminal (

) as a variable can be expressed as a function. In order to provide consistent performance among terminals, the CPU 502 may maximize the data transmission rate of a terminal having the lowest data transmission rate among terminals included in the wireless communication system.

)를 제m AP에 의해 서빙되는 단말들의 집합(D_m)에 대해 모두 합한 값은 제m AP에 대해 할당된 최대 가능한 전송 전력(P_m)을 초과할 수 없다. However, a portion of the power allocated to the k-th terminal by the m-th AP (

) for the set of terminals (D _m ) served by the m-th AP cannot exceed the maximum possible transmit power (P _m ) allocated to the m-th AP.

)를 제k 단말에 대한 클러스터에 포함된 AP들의 집합(

)에 대해 모두 합한 값은 제k 단말에 할당된 전송 전력(p_k)을 초과할 수 없다. In addition, some of the power allocated to the k-th terminal by the m-th AP (

) to a set of APs included in the cluster for the kth terminal (

) cannot exceed the transmit power (p _k ) allocated to the k th terminal.

The CPU 502 may allocate a new pilot based on channel state information (INFO_CH). For example, the CPU 502 determines whether the pilot assigned by the master AP 524 has the same or high correlation with the pilots of other terminals connected to the second neighboring APs 514, 534, and 544. Channel conditions between (514,534,544) and the terminal 506 may be poor. In this case, the CPU 502 may allocate a new pilot based on pilot information of other terminals connected to the second neighboring APs 514 , 534 , and 544 .

After the new pilot is allocated, the CPU 502 may transmit information about the newly allocated pilot to the terminal 506 , second neighbor APs 514 , 534 , and 544 , and the master AP 524 . The terminal 506 may generate pilot signals based on pilot information, and may transmit the generated pilot signals to the second neighbor APs 514 , 534 , and 544 and the master AP 524 . The second neighbor APs 514 , 534 , and 544 and the master AP 524 may determine channel state information based on the pilot signals and transmit the channel state information to the CPU 502 . The CPU 502 may maximize the data transmission rate of a terminal having the lowest data transmission rate among terminals included in the wireless communication system 100 by performing clustering based on the channel state information.

6A to 6E are diagrams for explaining a method of performing pilot allocation and clustering according to a third embodiment.

Referring to FIG. 6A , a terminal 606 may receive downlink synchronization signals SIGNAL_DL from first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 located within a predetermined distance from the terminal 606 . The terminal 606 can be synchronized through a downlink synchronization signal allocated to an arbitrary time/frequency resource. According to an embodiment, the first neighbor APs 614 , 624 , 634 , 644 , 654 , and 664 may share downlink synchronization signals SIGNAL_DL. Unlike the first and second embodiments described above, in the third embodiment, since the terminal 606 does not designate a separate master AP, the downlink synchronization signals SIGNAL_DL do not include identification information. can Thus, overhead due to identification information can be reduced.

Referring to FIG. 6B, the terminal 606 may broadcast a random access signal (RA). The terminal 606 may transmit a random access signal (RA) to the first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 . Optionally, the random access signal RA may include a preamble signal. The UE 606 may initiate random access with the first neighbor APs 614 , 624 , 634 , 644 , 654 , and 664 by transmitting preamble signals to the first neighbor APs 614 , 624 , 634 , 644 , 654 , and 664 . During random access, the first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 may determine TAs for synchronizing with each other. Unlike the first and second embodiments, since the UE 606 transmits preamble signals to all first neighbor APs (614, 624, 634, 644, 654, and 664) instead of transmitting the preamble signal only to a specific AP, the first neighbor APs (614, 624, 634, 644, 654, 664) may determine a TA in advance before a cluster is determined using preamble signals.

Referring to FIG. 6C , the first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 may transmit TA information (INFO_TA) generated according to the determined TA to the CPU 602 .

Also, the first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 may determine channel state information (INFO_CH) based on the preamble signals. For example, the channel state information (INFO_CH) may include a large-scale channel coefficient. The first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 may determine the channel state information (INFO_CH) by measuring strengths of preamble signals and determining a large-scale channel coefficient. The first neighboring APs 614 , 624 , 634 , 644 , 654 , and 664 may transmit channel state information (INFO_CH) to the CPU 602 .

Referring to FIG. 6D , the CPU 602 may allocate pilots in one-shot based on channel state information (INFO_CH) and perform clustering. According to an embodiment, the CPU 602 simultaneously performs clustering and pilot allocation based on the minimum rate requirement described above with reference to FIG. 5C in order to increase the performance of a terminal having the worst performance in a wireless communication system. can be done For example, the CPU 602 allocates pilots so that the number of APs serving the terminal 606 is increased when the data transmission rate of the terminal 606 has a minimum value among the data transmission rates of terminals included in the wireless communication system. and clustering. Specifically, the CPU 602 may allocate a pilot to the terminal 606 that has a low correlation with pilots of other terminals served by the first neighboring APs 614, 624, 634, 644, 654, and 664, and the AP included in the cluster for the other terminal. may be included in the cluster for terminal 606.

Conversely, when the data rate of the terminal 606 does not have the minimum among the data rates of the terminals included in the wireless communication system, the CPU 602 configures the pilot so that the number of APs serving the terminal with the minimum data rate is increased. Assignment and clustering can be performed.

The CPU 602 may transmit cluster information (INFO_CLUSTER) and pilot allocation information (INFO_PA) to the APs 614, 624, and 634 included in the cluster 620. The CPU 602 may determine a representative AP (DELEGATE_AP) among the APs 614 , 624 , and 634 included in the cluster 620 . For example, the CPU 602 may determine a representative AP (DELEGATE_AP) based on channel state information (INFO_CH). The CPU 602 may determine the AP 614 having the largest large-scale channel coefficient as the representative AP (DELEGATE_AP).

The CPU 602 may perform timing adjustment based on the TA information (INFO_TA). The CPU 602 may transmit information about the adjusted timing (INFO_AT) to the APs 614 , 624 , and 634 included in the cluster 620 .

Referring to FIG. 6E , the representative AP 614 may transmit pilot allocation information (INFO_PA) and cluster information (INFOR_CLUSTER) to the terminal 606. In addition, the representative AP 614 may transmit a random access response (RP_RA) to the terminal 606 . The terminal 606 may generate a pilot signal (SIG_PILOT) based on pilot allocation information (INFO_PA). The terminal 606 may transmit uplink data together with pilot signals SIG_PILOT to the APs 614 , 624 , and 634 included in the cluster 620 based on the cluster information INFOR_CLUSTER.

7 is a transaction flow illustrating pilot allocation and clustering according to the third embodiment.

In step S702, the terminal 710 may transmit random access signals (RA) to the APs 720. For example, the terminal 710 may broadcast random access signals RA, and first neighbor APs located within a predetermined distance from the terminal 710 may receive the broadcast random access signals RA. can Optionally, the random access signal may include a preamble signal. The terminal 710 may match synchronization for transmitting random access signals based on downlink synchronization signals received from first neighboring APs. According to one embodiment, the first neighbor APs may share downlink synchronization signals. Since the shared downlink synchronization signals do not separately include identification information, overhead for the downlink synchronization signal can be reduced.

In step S704, the APs 720 may transmit first channel state information (INFO_CH1) and TA information (INFO_TA) to the CPU 730. The first neighboring APs may determine first channel state information (INFO_CH1) indicating a channel state between the terminal 710 and the first neighboring APs based on the received preamble signals. Specifically, the first channel state information (INFO_CH1) may include a large-scale channel coefficient, and first neighboring APs may determine a large-scale channel variable by measuring strengths of preamble signals.

The first neighboring APs may determine a TA for synchronization based on the received preamble signals. According to an embodiment, the first neighboring APs transmit downlink synchronization signals shared by the first neighboring APs to the terminal 710, and the terminal 710 transmits random access signals (RA) that do not include identification information. ) can be broadcast. The first neighbor APs receiving the broadcast random access signals (RAs) may determine TAs in advance before clustering is performed. The first neighboring APs may determine TA information (INFO_TA) based on the determined TA.

In step S706, the CPU 730 may transmit cluster information (INFO_CLUSTER), assigned pilot information (INFO_PA), and adjusted timing information (INFO_AT) to APs included in the cluster. The CPU 730 may perform clustering and pilot allocation based on the first channel state information (INFO_CH1). According to an embodiment, the CPU 730 may determine the relative data rate of the terminal 710 based on the first channel state information (INFO_CH1). The CPU 730 may perform pilot assignment and clustering based on the data transmission rate of the terminal 710 compared to the data transmission rate of the plurality of terminals included in the wireless communication system. The CPU 730 may transmit cluster information (INFO_CLUSTER) and assigned pilot information (INFO_PA) to APs included in the cluster.

For example, when the relative data rate of the terminal 710 is low, the CPU 730 may perform clustering so that a larger number of APs can serve the terminal 710, and pilot for other terminals. It is possible to allocate a pilot having a low correlation with . Uniform performance of the terminals included in the wireless communication system can be guaranteed by performing clustering and pilot allocation based on the relative data rates of the terminals 710 .

Also, the CPU 730 may perform timing adjustment based on the received TA information (INFO_TA). The CPU 730 can synchronize a plurality of APs simultaneously serving the terminal 710, that is, APs included in the cluster, through timing adjustment, and transmits information on the adjusted timing (INFO_AT) to the APs included in the cluster. can be sent to

In step S708, the APs 720 may transmit a random access response (RP_RA), assigned pilot information (INFO_PA), and cluster information (INFO_CLUSTER) to the terminal 710. The CPU 730 may determine a representative AP among a plurality of APs included in the cluster. For example, the CPU 730 may determine a representative AP based on the first channel state information (INFO_CH1). The CPU 730 may determine an AP having the largest large-scale channel coefficient among APs included in the cluster as a representative AP. The representative AP may transmit a random access response (RP_RA), assigned pilot information (INFO_PA), and cluster information (INFO_CLUSTER) to the terminal 710 .

In step S710, the terminal 710 may transmit pilot signals SIG_PILOT and uplink data DATA_UL to the APs 720. The terminal 710 may generate pilot signals SIG_PILOT based on information on allocated pilots (INFO_PA). The terminal 710 may transmit pilot signals (SIG_PILOT) to APs included in the cluster based on cluster information (INFO_CLUSTER).

In step S712, the APs 720 may transmit second channel state information (INFO_CH2) to the CPU 730. APs included in the cluster may determine the second channel state information (IFNO_CH2) based on the pilot signals (SIG_PILOT).

In step S714, the APs 720 may transmit downlink data DATA_DL to the terminal 710.

8 is a flowchart illustrating a method of operating a wireless communication system according to a third embodiment.

In step S802, a plurality of first access points located within a predetermined distance from the terminal may transmit a plurality of synchronization signals shared by the plurality of first access points to the terminal. Since the plurality of synchronization signals do not include identification information, overhead of synchronization signals may be reduced.

In step S804, the terminal may broadcast a plurality of preamble signals based on the plurality of synchronization signals received. For example, the terminal may broadcast random access signals including merged preambles. The terminal may perform random access to the first access points based on a plurality of preamble signals.

In step S806, a plurality of first access points may receive a plurality of preamble signals. The plurality of first access points may determine channel state information and timing advance (TA) information for the terminal and each of the plurality of first access points. For example, the plurality of first access points may determine channel state information by measuring strengths of preamble signals.

In step S808, the plurality of first access points may transmit channel state information to the CPU connected to the plurality of first access points.

In step S810, the CPU may determine an operation of allocating a pilot related to the terminal and a cluster, which is a set of second access points serving the terminal, based on the channel state information. The CPU may select a representative access point from among the first access points. The CPU may transmit a response to random access, information on pilot allocation, and information on clusters to the terminal through the representative access point.

In step S812, the terminal may generate pilot signals based on pilot allocation information. The terminal may transmit the generated pilot signals to the second access points.

9 is a flowchart illustrating a method of operating a terminal according to a third embodiment.

In step S902, the terminal may receive a plurality of synchronization signals shared by the plurality of first access points from the plurality of first access points located within a predetermined distance from the terminal.

In step S904, the terminal may broadcast a plurality of preamble signals based on a plurality of synchronization signals.

In step S906, the terminal may perform random access to the first access points based on a plurality of preamble signals.

In step S908, the terminal may receive pilot allocation information and cluster information from a representative access point included in a cluster that is a set of second access points serving the terminal. According to an embodiment, the first access points may determine channel state information based on preamble signals received from the terminal, and the CPU may perform pilot allocation and clustering based on the channel state information. The terminal may receive a response to random access from the representative access point.

In step S910, the terminal may transmit a pilot signal generated based on the pilot allocation information to the second access points.

10 is a flowchart illustrating a method of operating a CPU according to a third embodiment.

In step S1002, the CPU may receive channel state information and Timing Advance (TA) information for each of the terminal and a plurality of first access points located within a predetermined distance from the terminal from the first access points. The channel state information may be determined by the first access points based on random access signals broadcast from the terminal. Also, TA information may be determined by the first access points based on random access signals broadcast from the terminal. Random access signals may be broadcast by a terminal based on downlink synchronization signals transmitted from first access points.

In step S1004, the CPU may perform an operation of allocating a pilot related to the terminal and an operation of determining a cluster, which is a set of second access points serving the terminal, in one-shot based on the channel state information. According to an embodiment, since the CPU centrally performs clustering and pilot assignment in one-shot, the performance of terminals included in the wireless communication system can be maintained uniformly. The CPU may perform timing adjustment based on the TA information.

In step S1006, the CPU may select a representative access point that transmits a response to the random access to the terminal from among the first access points. For example, the CPU may select an access point having the largest large-scale coefficient among access points included in the cluster as a representative access point based on the channel state information.

In step S1008, the CPU may transmit cluster information and pilot allocation information to the terminal through the representative access point. Also, the CPU may transmit timing adjustment information to the terminal through the representative access point.

11 is a flowchart illustrating a method of operating a wireless communication system according to a second embodiment.

In step S1102, the master access point may transmit information on pilot allocation related to the terminal to the terminal and a CPU connected to a plurality of first access points located within a predetermined distance from the terminal. The plurality of first access points may transmit a plurality of synchronization signals to the terminal, and the terminal may determine a master access point among the plurality of first access points based on the plurality of synchronization signals. A master access point may allocate a pilot associated with a terminal based on the terminals served by the master access point.

In step S1104, the CPU may transmit pilot allocation information to a plurality of second access points located within a predetermined distance from the master access point.

In step S1106, the terminal may transmit pilot signals generated based on the pilot allocation information to the plurality of second access points and the master access point.

In step S1108, the plurality of second access points and the master access point may determine channel state information based on the pilot signals. For example, a plurality of second access points may determine information about a channel state between a terminal and each of a plurality of second access points, and a master access point may determine information about a channel state between a terminal and a master access point. there is. A plurality of second access points may determine channel state information based on strengths of a plurality of pilot signals.

In step S1110, the second access points may transmit channel state information to the CPU.

In step S1112, the CPU may determine a cluster, which is a set of third access points serving the terminal, based on the channel state information. According to one embodiment, the CPU may transmit a request for allocating a new pilot to the master access point based on the channel state information. For example, when a pilot allocated by the master access point has a high degree of contamination, the CPU may request the master access point to allocate a new pilot.

In step S1114, the CPU may transmit information on the determined cluster to the terminal.

In step S1116, the terminal may transmit pilot signals to the third access points.

12 is a diagram illustrating a detailed configuration of a terminal in a wireless communication system according to an embodiment.

Referring to FIG. 12 , a terminal 1200 may include a transceiver 1220, a processor 1240, and a memory 1260. However, not all components shown in FIG. 12 are essential components of the terminal 1200 . The terminal 1200 may be implemented with more components than those shown in FIG. 12 , or the terminal 1200 may be implemented with fewer components than those shown in FIG. 12 . In addition, the transceiver 1220, the processor 1240, and the memory 1260 may be implemented as a single chip.

In one embodiment, the transceiver 1220 may transmit and receive signals with APs or other electronic devices connected to the terminal 1200 by wire or wirelessly. Here, the signal may include control information and data. The transceiver 1220 may receive a signal through a wireless channel, output the signal to the processor 1240, and transmit the signal output from the processor 1240 through the wireless channel. For example, the transceiver 1220 may receive downlink synchronization signals from APs to synchronize. The transceiver 1220 may transmit preamble signals to APs for random access. The transceiver 1220 may receive pilot allocation information from an AP and may transmit a pilot signal to the APs for channel estimation.

In one embodiment, the processor 1240 controls the overall operation of the terminal 1200, and may include at least one processor such as a CPU or GPU. The processor 1240 may control other components included in the terminal 1200 to perform an operation for operating the terminal 1200 . For example, the processor 1240 may execute a program stored in the memory 1260, read a stored file, or store a new file. In one embodiment, the processor 1240 may perform an operation for operating the terminal 1200 by executing a program stored in the memory 1260 . For example, the processor 1240 may generate a pilot signal based on pilot allocation information received from the AP.

In one embodiment, various types of data such as programs and files, such as applications, may be installed and stored in the memory 1260 . The processor 1240 may access and use data stored in the memory 1260 or may store new data in the memory 1260 . That is, the memory 1260 may store programs and data necessary for the operation of the UE 1200 . Also, the memory may store control information or data included in a signal acquired by the UE 1200 . The memory may include a storage medium such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

13 is a diagram illustrating a detailed configuration of an AP in a wireless communication system according to an embodiment.

Referring to FIG. 13 , an AP 1300 may include a transceiver 1320, a processor 1340, and a memory 1360. However, not all components shown in FIG. 13 are essential components of the AP 1300 . The AP 1300 may be implemented with more components than those shown in FIG. 13 , or the AP 1300 may be implemented with fewer components than those shown in FIG. 13 . In addition, the transceiver 1320, the processor 1340, and the memory 1360 may be implemented as a single chip.

In one embodiment, the transceiver 1320 may transmit and receive signals to and from a terminal or CPU or other electronic device connected to the AP 1300 by wire or wirelessly. Here, the signal may include control information and data. For example, the transceiver 1320 may transmit a downlink synchronization signal to the terminal and receive a preamble signal from the terminal. In addition, the transceiver 1320 may transmit channel state information and TA information to the CPU, and may receive pilot allocation information, clustering information, and timing adjustment information from the CPU. The transceiver 1320 may receive a pilot signal and uplink data from a terminal. The transceiver 1320 may transmit downlink data to the terminal.

In one embodiment, the processor 1340 controls the overall operation of the AP 1300 and may include at least one processor such as a CPU or GPU. The processor 1340 may control other elements included in the AP 1300 to perform an operation for operating the AP 1300 . For example, the processor 1340 may execute a program stored in the memory 1360, read a stored file, or store a new file. In one embodiment, the processor 1340 may perform an operation for operating the AP 1300 by executing a program stored in the memory 1360 . For example, the processor 1340 may estimate a channel state based on a preamble signal and may estimate a channel state based on a pilot signal. The processor 1340 may determine the TA based on the preamble signal or the pilot signal.

In one embodiment, various types of data such as programs and files, such as applications, may be installed and stored in the memory 1360 . The processor 1340 may access and use data stored in the memory 1360 or may store new data in the memory 1360 . In one embodiment, memory 1360 may store a threshold for determining the offset.

14 is a diagram illustrating a detailed configuration of a CPU in a wireless communication system according to an embodiment.

Referring to FIG. 14 , a CPU 1400 may include a transceiver 1420, a processor 1440, and a memory 1460. However, not all components shown in FIG. 14 are essential components of the CPU 1400 . The CPU 1400 may be implemented with more components than those shown in FIG. 14, or the CPU 1400 may be implemented with fewer components than those shown in FIG. In addition, the transceiver 1420, the processor 1440, and the memory 1460 may be implemented as a single chip.

In one embodiment, the transceiver 1420 may transmit/receive signals with APs or other electronic devices connected to the CPU 1400 by wire or wirelessly. Here, the signal may include control information and data. For example, the transceiver 1420 may receive channel state information from APs and may receive TA information. The transceiver 1420 may receive pilot allocation information from the AP when the pilot is allocated by the AP, and transmit information on the pilot allocated to the APs when the pilot is allocated by the CPU 1400. can be sent The transceiver 1420 may transmit clustering information and adjusted timing information to APs.

In one embodiment, the processor 1440 may control the overall operation of the CPU 1400. The processor 1340 may control other components included in the CPU 1400 to perform an operation for operating the CPU 1400 . For example, the processor 1440 may execute a program stored in the memory 1460, read a stored file, or store a new file. In one embodiment, the processor 1440 may perform an operation for operating the CPU 1400 by executing a program stored in the memory 1460 . For example, the processor 1440 may perform pilot allocation and clustering based on channel state information, and may perform timing adjustment based on TA information.

In one embodiment, various types of data such as programs and files, such as applications, may be installed and stored in the memory 1460 . The processor 1440 may access and use data stored in the memory 1460 or may store new data in the memory 1360 . In one embodiment, memory 1460 may store a threshold for determining the offset.

15 is a diagram illustrating a method of measuring signal strength and timing advance using random access based on a non-contention scheme in a handover process.

)는 복수의 코히런스 시구간들 동안 일정한 값으로 유지될 수 있다. 라지-스캐일 채널 계수(

)가 변하는 시점에 새로운 클러스터링이 수행될 수 있으며, 이때 핸드오버 상황이 발생할 수 있다.As described above with reference to FIG. 2, the small-scale channel coefficient may be maintained at a constant value during the coherence time period, and the large-scale channel coefficient (

) may be maintained at a constant value for a plurality of coherence time intervals. Large-scale channel coefficients (

), new clustering may be performed, and at this time, a handover situation may occur.

According to an embodiment, the terminal may initially perform contention-based random access to neighboring APs, and at this time, a set of preambles is reserved for random access based on non-contention. can be reserved. The CPU may perform clustering and pilot allocation for UEs. Then, when a handover situation occurs, the CPU may allocate a preamble sequence from a set of preambles reserved for the terminal. Accordingly, the UE can perform random access based on a contention-free method using the allocated preamble sequence. Neighboring APs located within a predetermined distance from the terminal may measure signal strength and determine a TA for synchronization based on a random access signal based on a non-contention scheme.

16 is a simulation result of pilot allocation and clustering according to the first embodiment and pilot allocation and clustering according to the third embodiment.

The proposed method is implemented according to the LTE / NR standard specifications to examine performance, and simulation parameters for an example implementation are shown in Table 1 below.

[Table 1]

는 길이가

인 Zadoff-Chu (ZC) sequence를 사용하고, 이때 루트(root)는 다음 수학식 7과 같다.Preamble

is the length

A Zadoff-Chu (ZC) sequence is used, and the root at this time is as shown in Equation 7 below.

[Equation 7]

The index of the preamble sequence is shown in Equation 8 below.

[Equation 8]

One root is assigned to each AP, and the correlation between preambles having the same root becomes 0 so that no interference occurs. Meanwhile, inter-cell interference occurs due to a preamble of an adjacent cell. The preamble signal received from the m-th AP can be modeled by Equation 9 as follows.

[Equation 9]

을 전송했을 때 1로 되는 지시자이며,

는 convolution 연산자이다.

이면

이고, 그렇지 않으면 제로 벡터(zero vector)이다.In Equation 9, 1(u,l) is the preamble of the kth terminal

is an indicator that becomes 1 when sending

is the convolution operator.

the other side

, otherwise it is a zero vector.

이면, 마스터 AP는 수학식 9의 두 번째 항을 다른 셀 간섭으로 간주하게 된다.In the clustering according to the first embodiment, if the k-th terminal selects the m-th AP as the master AP, the terminal uses one of the preambles allocated to the m-th AP. For example, if the preamble of root u* is allocated to the mth AP, that is, the preamble is

, the master AP regards the second term of Equation 9 as interference with other cells.

In clustering according to the third embodiment, since all APs share preambles generated from multiple roots, all APs can estimate a gain of a corresponding channel while detecting a preamble transmitted by a terminal for random access. Using the channel gain estimated in this way, the CPU may combine signals by maximal-ratio combination.

16 illustrates performance when implementing a method according to an embodiment of the present disclosure.

16 shows performance of a preamble detection failure rate in a master AP-based random access method in clustering according to the first embodiment and in clustering according to the third embodiment. In FIG. 16, the master TP-based RA corresponds to clustering according to the first embodiment, and the broadcast RA corresponds to clustering according to the third embodiment.

In the clustering according to the third embodiment, it can be seen that a preamble detection failure rate performance is improved because a plurality of APs receive a preamble transmitted and broadcasted by a UE to obtain a diversity gain. Meanwhile, it can be seen that clustering according to the first embodiment suffers from very serious performance degradation due to transmission of preambles from other users. Preambles are selected from a set exclusively designated for each AP, but since they are not orthogonal to each other, if another terminal selects another AP as the master AP, these preambles cause interference with each other.

It can be seen that the clustering according to the first embodiment and the clustering according to the third embodiment have the same collision probability in the random access process. Therefore, the clustering according to the third embodiment has the same collision probability as the clustering according to the first embodiment and has better preamble transmission success probability performance.

The disclosed embodiments may be implemented as a S/W program including instructions stored in computer-readable storage media.

A computer is a device capable of calling instructions stored in a storage medium and performing operations according to the disclosed embodiments according to the called instructions, and may include electronic devices according to the disclosed embodiments.

A computer-readable storage medium may be provided in the form of a non-transitory storage medium. Here, 'non-temporary' only means that the storage medium does not contain a signal and is tangible, but does not distinguish whether data is stored semi-permanently or temporarily in the storage medium.

In addition, the control method according to the disclosed embodiments may be provided by being included in a computer program product. Computer program products may be traded between sellers and buyers as commodities.

A computer program product may include a S/W program and a computer-readable storage medium in which the S/W program is stored. For example, the computer program product may include a product (eg, downloadable app) in the form of a S/W program that is distributed electronically through a device manufacturer or an electronic market (eg, Google Play Store, App Store). . For electronic distribution, at least a part of the S/W program may be stored in a storage medium or temporarily generated. In this case, the storage medium may be a storage medium of a manufacturer's server, an electronic market server, or a relay server temporarily storing SW programs.

A computer program product may include a storage medium of a server or a storage medium of a device in a system composed of a server and a device. Alternatively, if there is a third device (eg, a smart phone) that is communicatively connected to the server or device, the computer program product may include a storage medium of the third device. Alternatively, the computer program product may include a S/W program itself transmitted from the server to the device or the third device or from the third device to the device.

In this case, one of the server, the device and the third apparatus may execute the computer program product to perform the method according to the disclosed embodiments. Alternatively, two or more of the server, the device, and the third device may execute the computer program product to implement the method according to the disclosed embodiments in a distributed manner.

For example, a server (eg, a cloud server or an artificial intelligence server) may execute a computer program product stored in the server to control a device communicatively connected to the server to perform a method according to the disclosed embodiments.

As another example, the third apparatus may execute a computer program product to control a device communicatively connected to the third apparatus to perform a method according to the disclosed embodiment. When the third device executes the computer program product, the third device may download the computer program product from the server and execute the downloaded computer program product. Alternatively, the third device may perform the method according to the disclosed embodiments by executing a computer program product provided in a preloaded state.

Various embodiments of the present disclosure have been described above. The foregoing description of the present disclosure is for illustrative purposes, and the embodiments of the present disclosure are not limited to the disclosed embodiments. Those of ordinary skill in the art to which the present disclosure belongs will be able to understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present disclosure. The scope of the present disclosure is indicated by the following claims rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be interpreted as being included in the scope of the present disclosure. do.

Claims (15)

A method in wireless communication, the method comprising:
transmitting, by a plurality of first access points located within a predetermined distance from the terminal, a plurality of synchronization signals shared by the plurality of first access points to the terminal;
broadcasting, by the terminal, a plurality of preamble signals;
determining channel state information and timing advance (TA) information for the terminal and each of the plurality of first access points by receiving the plurality of preamble signals, by the plurality of first access points;
transmitting, by the plurality of first access points, the channel state information to a central processing unit (CPU) connected to the plurality of first access points;
performing, by the CPU, an operation of allocating a pilot related to the terminal and an operation of determining a cluster that is a set of second access points serving the terminal, based on the channel state information; and
Transmitting, by the terminal, pilot signals generated based on the pilot allocation information to the second access points.
How to include. The method of claim 1, wherein the method
performing, by the terminal, random access to the first access points based on the plurality of preamble signals;
selecting, by the CPU, a representative access point from among the first access points; and
Transmitting, by the representative access point, a response to the random access to the terminal
How to include more. According to claim 1,
Transmitting, by the CPU, pilot allocation information and information about the determined cluster to the terminal through a representative access point.
How to include more. According to claim 1,
Determining the channel state information and the TA information
Determining, by the plurality of first access points, the channel state information based on strengths of the plurality of preamble signals.
How to include. A method for a terminal in wireless communication, the method comprising:
receiving a plurality of synchronization signals shared by the plurality of first access points from a plurality of first access points located within a predetermined distance from the terminal;
broadcasting a plurality of preamble signals based on the plurality of synchronization signals;
performing random access to the first access points based on the plurality of preamble signals;
Receiving information on pilot allocation and information on a cluster from a representative access point included in a cluster that is a set of second access points serving the terminal; and
Transmitting a pilot signal generated based on the pilot allocation information to the second access points
How to include. 6. The method of claim 5, wherein the method
Receiving a response to the random access from the representative access point selected from among the second access points
How to include more. According to claim 5,
The cluster is determined based on channel state information for each of the terminal and the plurality of first access points by a CPU connected to the plurality of first access points
method. A method for a central processing unit (CPU) in wireless communication, the method comprising:
Receiving channel state information and TA (Timing Advance) information for each of a terminal and a plurality of first access points located within a predetermined distance from the terminal from the first access points;
Based on the channel state information, performing an operation of allocating a pilot related to the terminal and an operation of determining a cluster that is a set of second access points serving the terminal;
selecting a representative access point that transmits a response to the random access to the terminal from among the first access points; and
Transmitting information on the allocated pilot and the determined cluster to the terminal through the representative access point
How to include. The method of claim 1, wherein the method
performing timing adjustment based on the TA information; and
Transmitting information about the adjusted timing to the first access points
How to include more. A method in wireless communication, the method comprising:
Transmitting, by a master access point, pilot allocation information related to a terminal to a central processing unit (CPU) connected to the terminal and a plurality of first access points located within a predetermined distance from the terminal;
transmitting, by the CPU, information on the pilot assignment to a plurality of second access points located within a predetermined distance from the master access point;
transmitting, by the terminal, pilot signals generated based on the pilot allocation information to the plurality of second access points and the master access point;
determining, by the plurality of second access points and the master access point, channel state information based on the pilot signals;
transmitting the channel state information to the CPU by the second access points;
determining, by the CPU, a cluster that is a set of third access points serving the terminal based on the channel state information;
transmitting, by the CPU, information on the determined cluster to the terminal; and
Transmitting, by the terminal, the pilot signals to the third access points.
How to include. 11. The method of claim 10, wherein the method
sending, by the CPU, a request to allocate a new pilot to the master access point based on the channel state information;
How to include more. 11. The method of claim 10, wherein the method
transmitting a plurality of synchronization signals to the terminal by the plurality of first access points;
determining, by the terminal, the master access point from among the plurality of first access points based on a plurality of synchronization signals; and
Allocating, by the master access point, a pilot related to the terminal based on the terminals served by the master access point.
How to include more. According to claim 10,
Determining the master access point
determining strengths of the plurality of synchronization signals; and
Determining a first access point transmitting a synchronization signal having the greatest strength among the plurality of synchronization signals as the master access point
How to include. According to claim 10,
Determining the channel state information
determining the channel state information based on the strengths of the plurality of pilot signals;
How to include. In a terminal in wireless communication, the terminal
transceiver; and
at least one processor
Including,
the at least one processor
Through the transceiver, a plurality of synchronization signals are received from a plurality of first access points located within a predetermined distance from the terminal;
broadcasting, through the transceiver, a plurality of preamble signals based on the plurality of synchronization signals;
performing random access to the first access points based on the plurality of preamble signals through the transceiver;
Through the transceiver, information on pilot allocation and information on a cluster are received from a representative access point included in a cluster, which is a set of second access points serving the terminal,
Transmitting a pilot signal generated based on the pilot allocation information to the second access points through the transceiver
Terminal.

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