KR102429756B1 - Hybrid beamforming method for beam-based cooperative transmission, and apparatus for the same - Google Patents

Abstract

A system for hybrid beamforming-based cooperative transmission includes a centralized processor (CP), access nodes (ANs) connected to the CP, and fronthaul links connecting the CP and the ANs. , the CP provides an external precoding matrix for the first AN among the ANs derived from the global statistical CSI generated from the regional statistical CSI collected from the ANs through the fronthaul link to the first AN and, the first AN sets the RF precoder of the first AN based on the external precoding matrix, and the first AN and the first AN provide a local instantaneous local instantaneous between the first terminals to which the service is to be provided. The digital precoder of the first AN may be configured based on the effective CSI.

Description

Hierarchical hybrid beamforming method for beam-based cooperative transmission, and apparatus therefor

The present invention relates to beam-based cooperative transmission in a mobile communication system, and more particularly, interference management and cooperation in a mobile communication network in which base stations using high frequencies that require beamforming to increase traffic capacity are densely deployed. It relates to a hierarchical hybrid beamforming method for transmission and an apparatus therefor.

In order to accommodate the explosively increasing mobile traffic in a mobile communication network, the need to use a high-frequency (eg, millimeter wave, terahertz) band capable of securing a wider bandwidth has increased. In the high frequency band, there is a problem that the reception signal-to-noise ratio (SNR) is lowered due to severe propagation loss (path loss, object penetration loss, etc.). application is essential.

Since analog beamforming steers a signal only with a phase shifter, an RF chain is not required for each antenna element, so cost-effective implementation is possible. However, analog beamforming has a disadvantage in that angular resolution is inaccurate. On the other hand, digital beamforming can have high accuracy because the direction of the beam is controlled by digitally adjusting the phase and amplitude of the signal. However, since an RF chain including an analog-to-digital converter (ADC)/digital-to-analog converter (DAC) is required for each antenna, implementation is difficult due to hardware complexity and increased power consumption when using a large-scale antenna. The downside is that it is difficult.

Therefore, in order to reduce the complexity of digital beamforming and increase the accuracy of analog beamforming, a hybrid beamforming technology that uses analog beamforming in the RF domain and digital beamforming in baseband is essential.

An object of the present invention for solving the above problems is to provide a method of operating a centralized processor (CP) for cooperative transmission based on hierarchical hybrid beamforming.

Another object of the present invention for solving the above problems is to provide a method of operating an access node (AN) for cooperative transmission based on hierarchical hybrid beamforming.

Another object of the present invention for solving the above problems is to provide a system for cooperative transmission based on hierarchical hybrid beamforming.

An embodiment of the present invention for achieving the above object is a method of operating a centralized processor (CP) for hybrid beamforming-based cooperative transmission, from each of the access nodes (ANs) connected to the CP. generating global statistical CSI by collecting regional statistical channel state information (CSI); configuring a set of first terminals to which a first AN of the ANs will provide a service based on the global statistical CSI; Construct a transmit signal space and an interfering signal space for the first AN, and derive an external precoding matrix defining an interference-controlled transmit signal space for the first AN based on the transmit signal space and the interfering signal space to do; and transmitting the derived external precoding matrix to the first AN.

The regional statistical CSI may be a spatial channel covariance matrix between each of the ANs and terminals.

The CP provides configuration information for a synchronized random access channel (RACH) interval through the AN, and the first terminal transmits a RACH signal to the first AN through the RACH interval, and An uplink pilot may be allocated from 1 AN.

The regional statistical CSI between the first terminal and the first AN may be measured based on the uplink pilot.

A radio frequency (RF) precoder of the first AN is set based on the derived external precoding matrix, and the digital precoder of the first AN is instantaneous locally between the first AN and the first terminals. It can be configured using valid CSI.

The method of operating the CP includes performing performance monitoring; adjusting a size of an interference-controlled transmission signal space for the first AN according to a result of the performance monitoring; and transmitting an external precoding matrix modified according to the size of the adjusted interference-controlled transmission signal space to the first AN.

The method of operating the CP further includes transmitting data to the first AN, wherein the data is transmitted through cooperative transmission of the first AN with at least one AN other than the first AN among the ANs. may be transmitted to the first terminals.

An embodiment of the present invention for achieving the above other object is an operating method of a first access node (AN) for hybrid beamforming-based cooperative transmission, regional statistical channel state information for neighboring terminals measuring (channel state information, CSI) and reporting the measured regional statistical CSI to a centralized processor (CP); receiving, from a CP, an external precoding matrix derived from the global statistical CSI generated from the regional statistical CSI and information on a set of first terminals to which the first AN will provide a service; and setting a radio frequency (RF) precoder of the first AN based on the external precoding matrix.

The regional statistical CSI may be a spatial channel covariance matrix between the first AN and the neighboring terminals.

The regional statistical CSI may be reported periodically or may be reported when the regional statistical CSI is changed.

The neighboring terminals for which the regional statistical CSI is measured may be limited to terminals that transmit a signal received from the first AN with an intensity greater than or equal to a predetermined value.

When the RF precoder includes only phase shifters, the size of each element of the external precoding matrix is set to be constant, and the phase of each of the phase shifters is the value of each element of the external precoding matrix. phase can be set.

The method of operating the first AN further includes providing configuration information for a synchronized random access channel (RACH) interval provided from the CP to the neighboring UEs, and the neighboring UEs are configured with the RACH. The RACH signal may be transmitted to the first AN through the interval, and an uplink pilot may be allocated from the first AN.

Regional statistical CSI between the peripheral terminals and the first AN may be measured based on the uplink pilots.

The digital precoder of the first AN may be configured using a local instantaneous effective CSI between the first AN and the first terminals.

The method of operating the first AN may further include receiving data from the CP, and the data may be transmitted to the first terminals through cooperative transmission of the first AN and the second AN.

A system for cooperative transmission based on hybrid beamforming according to an embodiment of the present invention for achieving the another object includes: a centralized processor (CP); access nodes (ANs) connected to the CP; and fronthaul links connecting the CP and the ANs, wherein the CP is an external free for a first AN of the ANs derived from global statistical CSI generated from local statistical CSI collected from the ANs. provide a coding matrix to the first AN through the fronthaul link, the first AN configures an RF precoder of the first AN based on the external precoding matrix, and the first AN and the first AN The digital precoder of the first AN may be configured based on the local instantaneous effective CSI between the first terminals to which the AN will provide a service.

The regional statistical CSI may be a spatial channel covariance matrix between each of the ANs and terminals.

The CP and the ANs may be nodes in which a function of a base station is functionally divided in a physical layer.

The first AN converts the data transmitted from the CP into a precoded signal using the RF precoder and the digital precoder of the first AN, and converts the precoded signal to the first AN among the ANs. It may be transmitted to the first terminals through cooperative transmission with at least one other AN except for the AN.

According to embodiments of the present invention, distributed ANs and CPs can be connected with a relatively low fronthaul capacity compared to a low-level (RF level or Low-PHY) functional division through functional division in the PHY layer. have. Accordingly, a C-RAN system including high-density distributed ANs can be constructed cost-effectively. In embodiments of the present invention, the CP collects regional statistical CSI reported by distributed ANs to calculate global statistical CSI, and allocates an interference-controlled transmission space for each AN derived based on the global statistical CSI to each AN can do. Meanwhile, distributed ANs can control interference between terminals they service by performing detailed hybrid beamforming again within each interference-controlled transmission space defined by the CP. Therefore, according to embodiments of the present invention, overhead required for cooperative transmission can be minimized through user-centered beam management and clustering, and the effect of reducing the construction cost of a mobile communication network and increasing the traffic capacity can be obtained. .

1 is a conceptual diagram for explaining the structures of a transmitter and a receiver to which hybrid beamforming is applied.
2 is a conceptual diagram for explaining cell arrangement of a 5G NR-based system in a high-density urban environment.
3 is a conceptual diagram for explaining the architecture of a cloud radio access network (C-RAN).
4 is a conceptual diagram for explaining the concept of user-centric clustering in a high-density C-RAN to which embodiments of the present invention are applied.
5 is a conceptual diagram for explaining the concept of user-centered beam management in high-density C-RAN to which embodiments of the present invention are applied.
6 is a conceptual diagram for explaining a method of allocating RACH slots within a synchronized RACH interval.
7 is a conceptual diagram for explaining a beam sweeping operation in an RACH slot.
8 is a conceptual diagram illustrating a method in which mini-slots are allocated within a synchronized RACH interval.
9 is a conceptual diagram illustrating a user-centered beam management procedure according to an embodiment of the present invention.
10 is a block diagram illustrating a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.
11 is a flowchart illustrating an operation of a CP belonging to a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.
12 is a flowchart illustrating an operation of an AN belonging to a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.
13 is a flowchart illustrating an operation procedure of a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.
14 is a block diagram for explaining the configuration of an apparatus for performing methods according to embodiments of the present invention.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention. In describing each figure, like reference numerals have been used for like elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being “connected” or “connected” to another component, it may be directly connected or connected to the other component, but it is understood that other components may exist in between. it should be On the other hand, when it is said that a certain element is "directly connected" or "directly connected" to another element, it should be understood that the other element does not exist in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present application, terms such as “comprise” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It is to be understood that this does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related art, and should not be interpreted in an ideal or excessively formal meaning unless explicitly defined in the present application. does not

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a conceptual diagram for explaining the structures of a transmitter and a receiver to which hybrid beamforming is applied.

Referring to FIG. 1 , digital beamforming may be performed by changing the phase and amplitude of a baseband signal by the digital precoder 110 belonging to the baseband portion of the transmitter. Meanwhile, analog beamforming may be performed by changing a phase of an RF signal obtained through RF conversion of a signal output from the baseband portion using phase shifters of the analog precoder 120 .

That is, as mentioned above, in order to reduce the complexity of digital beamforming and increase the accuracy of analog beamforming, analog beamforming is used in the RF domain and digital beamforming is used in baseband. A hybrid beamforming technology that uses a beamforming method together is essential. Meanwhile, hereinafter, the analog precoder may also be referred to as a radio frequency (RF) precoder.

2 is a conceptual diagram for explaining cell arrangement of a 5G NR-based system in a high-density urban environment.

2 shows a cell deployment based on a 5G NR system in a high-density urban environment that is being considered for 5G system evaluation in ITU and 3GPP. Referring to FIG. 2 , three micro base stations 211 , 212 , and 213 are disposed in one macro sector cell 210 operated by the macro base station 200 to operate three micro cells. In addition, a plurality of mobile stations may be located in each cell.

To accommodate the explosion of mobile traffic, both macro base stations and micro base stations can use millimeter waves. In the 3GPP 5G NR-based system, beam management centered on the base station is performed. Considering that one base station accommodates a plurality of terminals, base station-centered beam management may be appropriate. However, in an ultra-dense network (UDN) where the number of distributed base stations may be greater than the number of terminals, user-centered beam management may be more efficient.

3 is a conceptual diagram for explaining the architecture of a cloud radio access network (C-RAN).

In the C-RAN architecture shown in FIG. 3 , baseband processing performed locally in conventional base stations may be aggregated into one cloud computing center and performed centrally.

Unlike conventional base stations, a Remote Radio Head (RRH) in the C-RAN architecture may have only RF and antenna functions. Each of the RRHs and the cloud 310 may be connected by fronthaul links. The fronthaul link should have a low signal propagation delay and have a characteristic capable of smoothly transmitting large-capacity signals. In general, it is known that a capacity of 20 times the transmission speed of a radio link is required for a fronthaul link. Meanwhile, as the 5G mobile communication system is introduced and the transmission speed of the wireless section is increased to 20 Gbps, the required fronthaul capacity is difficult to provide realistically in terms of cost and the like. In order to lower the required fronthaul capacity, a functional split in which a part of the baseband function is moved back to the RRH site is being studied. Although functional division can lower the capacity of the fronthaul, it is necessary to carefully examine the point where the function is divided because it redistributes functions such as centralized signal processing.

In order to solve the above problems of the prior art, the embodiments of the present invention allow the maximum utilization of centralized signal and resource processing while limiting the use of fronthaul in a C-RAN architecture to which high frequency is applied and functional division is applied. Accordingly, an object of the present invention is to provide an apparatus and method for providing a high-capacity service to a user terminal through cooperative transmission of dense access nodes (ANs).

In a centralized or cloud radio access network (C-RAN) architecture, a remote radio unit (RRU) performs RF-to-baseband conversion at a location close to the antenna, and a centralized baseband unit ( The baseband unit (BBU) performs baseband (ie, higher layers on the PHY, MAC, and radio protocol stack) processing. Such an architecture can reduce the total-cost of ownership (TCO) by pooling the baseband resources of the BBU while improving the network capacity and applying advanced radio coordination functions to improve the user experience. In this case, the connection between the RRU and the centralized BBU is referred to as a fronthaul compared to the backhaul from the BBU to the core network. In the current C-RAN architecture, since digitized time-domain sample signals of each antenna device are transmitted through the fronthaul link between the RRU and the BBU, the fronthaul capacity increases in proportion to the number of antennas. In advanced 5G networks and next-generation networks, large-scale MIMO and UDN technologies will be more widely used and will be highlighted as major wireless functions that significantly improve spectrum efficiency and network capacity. Therefore, it is important to reduce fronthaul network cost and increase system scalability for antennas and wireless edge nodes.

To solve this problem, various functional partitioning options for the wireless protocol stack are being discussed. Separation of functions determines how many base station functions are left geographically close to users while relaxing fronthaul network capacity and latency requirements, and how many functions are centralized for the potential to gain more processing benefits. will do Embodiments of the present invention deal with 'intra-PHY Functional Split (iPFS)' in order to reduce the fronthaul load while maintaining the cooperative transmission function of the high-density C-RAN.

According to functional division, one base station may be divided into an 'Access Node (AN)' and a 'Base Node (BN)'. ANs are distributed close to a 'mobile station (MS)', and BNs are centralized to form a pool at one site, which will be referred to as a 'Centralized Processor (CP)'. can

4 is a conceptual diagram for explaining the concept of user-centric clustering in a high-density C-RAN to which embodiments of the present invention are applied.

Referring to FIG. 4 , a C-RAN system in which distributed n (>>2) ANs (AN1, AN2, AN3, ..., ANn) is connected to a CP through wired capacity-limited fronthaul links is shown. has been In FIG. 4A, for convenience of description, a case in which the C-RAN system provides a service to two terminals is illustrated. In this case, cooperative transmission in which distributed ANs participate can be facilitated while minimizing the use of beam control overhead and fronthaul through user-centered beam management.

5 is a conceptual diagram for explaining the concept of user-centered beam management in high-density C-RAN to which embodiments of the present invention are applied.

4 and 5, the operation of nodes through user-centered beam management, synchronized RACH resource allocation and signaling through system information broadcasting by ANs, and beam-sweeping of the terminal in the synchronized RACH interval (sweeping), user-centered clustering, training using an uplink (UL) pilot and channel information acquisition, and downlink (DL) cooperative transmission may be performed.

The CP may broadcast system information. Here, the system information may include parameters necessary for system operation defined in standards such as LTE, LTE-A, and 5G NR. Specifically, the system information may include downlink/uplink configuration information, random access-related detailed parameter information, and the like. Terminals must obtain this information to perform a cell-free high-density cloud RAN operation. In addition, the CP may provide a physical synchronization signal for obtaining frame synchronization between the distributed ANs and the terminals through the ANs. When broadcasting system information, the CP must secure coverage and minimize broadcasting overhead. In order to secure the coverage of the millimeter wave frequency signal, the CP may transmit system information while sweeping the directional beam through the AN.

Referring to FIG. 5 , the CP controls the distributed ANs AN1, AN2, AN3, ..., ANn to sequentially transmit system information, thereby reducing the overhead of system information broadcasting. For example, AN1 is controlled to transmit system information in frame #1 (501), AN2 is controlled to transmit system information in frame #2 (502), and ANn is controlled to transmit system information in frame #n (503). can be controlled to transmit.

Here, the overhead of system information broadcasting includes time, frequency, and power resources used to transmit system information. Here, there is a trade-off relationship between the overhead of system information broadcasting and the time required for the terminal to acquire the system information. That is, if each AN individually broadcasts system information in every frame, the overhead increases, but the terminal can quickly acquire the system information. Meanwhile, system information may be transmitted through a macro base station using a centimeter wave (cmWave) frequency band having wide coverage.

Meanwhile, the CP may provide a synchronized RACH duration to the distributed ANs. By allocating the synchronized RACH period to the distributed ANs, interference between the ANs caused by the overlapping of the RACH period and the data transmission period can be eliminated. A specific operation for this will be described later as a random access operation of terminals. As an example of allocating the synchronized RACH interval, as shown in FIG. 5 , the CP may provide the ANs with the synchronized RACH interval for every frame. Meanwhile, each synchronized RACH interval may include at least one RACH slot. The CP may allocate at least one RACH slot within the synchronized RACH interval in various ways.

6 is a conceptual diagram for explaining a method of allocating RACH slots within a synchronized RACH interval.

Referring to FIG. 6 , within the synchronized RACH interval, RACH slots may be arranged on the time axis (case (a)) or on the frequency axis (case (b)). 6 illustrates an example in which a total of L RACH slots are arranged in one synchronized RACH interval.

On the other hand, the RACH slot may mean a time unit in which the corresponding terminal can complete the beam-sweeping operation. For example, when the UE supports the beam sweeping operation for M beams, the beam sweeping operation from beam #1 to beam #M may be completed in one RACH slot.

7 is a conceptual diagram for explaining a beam sweeping operation in an RACH slot.

Referring to FIG. 7 , if it is assumed that the maximum number of beams used for beam-sweeping of the UE is M, the UE may sequentially transmit a total of M beams within one RACH slot. The number of beams used for beam sweeping may be different for each terminal.

In another embodiment, instead of defining the RACH slot within the RACH interval, the RACH interval may be configured with a plurality of mini-slots. That is, in the above-described embodiments, the RACH slot is defined as a time unit in which the UE can complete the beam-sweeping operation, but the time unit in which the UE can transmit one beam is a mini-slot (ie, RACH mini-slot). can be defined as

8 is a conceptual diagram illustrating a method in which mini-slots are allocated within a synchronized RACH interval.

개의 RACH 미니-슬롯들로 구성될 수 있다.Referring to FIG. 8, the synchronized RACH interval does not distinguish between RACH slots.

RACH mini-slots.

As in the case of the aforementioned system information broadcasting, a trade-off relationship may exist between the number of configured RACH intervals and the network entry time of the terminal. For example, in order to reduce overhead according to the RACH intervals, the interval of the RACH intervals may be increased. For example, although the RACH interval exists for each frame in FIG. 5, the RACH interval may exist for every two or more frames. On the other hand, two or more RACH sections may exist in one frame in order to reduce the network entry time of the UE.

On the other hand, when distributed terminals perform random access in one RACH interval, collision may occur. CPs and ANs should provide a mechanism to minimize the collision of random access by UEs.

User-Centered Beam Management Procedures

Hereinafter, a user-centered beam management procedure according to an embodiment of the present invention will be described.

9 is a conceptual diagram illustrating a user-centered beam management procedure according to an embodiment of the present invention.

In step S910, the CP configures a synchronized RACH resource (ie, RACH intervals (and RACH slots)) and includes information on the configured RACH resource in system information to transmit it to the terminals through the ANs. UEs may receive system information broadcast by a CP through ANs and check information on configured RACH intervals.

In step S920, the UE may perform beam-sweeping based on information on the configured RACH intervals. In this case, as described in FIG. 6 , when a plurality of RACH slots are given within the RACH interval, the UE may select one RACH slot. By selecting a RACH slot to be used by the UE, random access collisions between UEs may be resolved temporally or in frequency. Meanwhile, assuming beam-based access, spatial separation is possible even if two or more terminals select the same RACH slot to perform random access. Alternatively, code separation in which different terminals use orthogonal RACH codes as in LTE/NR is also possible. When the RACH interval consists of mini-slots without distinction of RACH slots as illustrated in FIG. 8, the UE uses virtual RACHs into M mini-slots according to the number M of beams used for its own beam-sweeping. A slot may be configured, and a beam-sweeping operation may be performed through a virtually created RACH slot.

In step S930, the CP may select candidate terminals to be serviced for each AN based on the strength of signals received in the RACH section through cooperation with distributed ANs. Through the cooperation of the CP and ANs, the reception strength (eg, received signal strength indicator (RSSI), etc.) of the RACH signal received for each AN is measured, and the transmitters of the RACH signal may be sorted in the order of reception strength. For example, RACH signal transmitters up to N ranks of reception strength are arranged for each AN. In this case, the best beam information of the corresponding RACH signal transmitter may also be recorded. The CP and the ANs may allocate different uplink pilots to RACH signal transmitters (ie, terminals) through mutual cooperation. The CP may generate a list of target terminals to which each AN provides a service, and based on this, a list of ANs capable of providing a service to a specific terminal (ie, clustering information) may be generated. That is, a cluster of ANs providing a service for each terminal may be configured. Meanwhile, clustering by an uplink pilot, which will be described later, may be referred to as fine clustering, and clustering based on RACH performed by step S930 may be referred to as coarse clustering. The clustering information may include information on the best beam received by each AN and information on an uplink pilot allocated to terminals (pilot sequence, resource information to be used for pilot transmission, etc.). The CP may transmit the clustering information to the terminals through ANs. Based on the clustering information received through the CP and AN, the terminal provides information on the cluster of ANs that will provide the service to the terminal, information on the best beam received by each AN, and an uplink pilot allocated to the terminal. information can be checked. Accordingly, the terminal can periodically transmit the allocated uplink pilot through beams that it can form simultaneously.

In step S940 , the ANs belonging to the cluster for the terminal may perform cooperative reception of an uplink pilot transmitted by the terminal, and may obtain channel information between the terminal and the ANs based on the received uplink pilot. Finally, in step S950 , the ANs belonging to the cluster for the terminal may perform cooperative transmission for the terminal based on the obtained channel information.

The cell-apartment high-density cloud-based RAN facilitates centralized resource and interference management by the CP, but the limitation of the fronthaul connecting the distributed ANs with the CP should be considered. In particular, when densely distributed ANs are connected to a CP, the fronthaul cost and power consumption increase by the number of ANs. In order to enable smooth cooperative transmission between distributed ANs and to minimize the required fronthaul capacity, the present invention considers functional division of the PHY layer. Functional division in the PHY layer can be roughly divided into two types.

In the first PHY layer function division, a digital beamforming function (eg, a digital precoder) may be deployed in the CP. In this case, in order to acquire instantaneous CSI for the digital precoder, instantaneous CSI measured using an uplink pilot must be transmitted to the CP, and thus a significant load may be generated in the fronthaul. However, interference between ANs can be minimized through the instantaneous CSI information.

In the second PHY layer function partitioning, the digital precoder and modulation block may be deployed in the local AN, and only the higher PHY functions may be deployed in the CP. In this case, instantaneous CSI for the digital precoder is required only in the local AN, so there is no need to transmit it to the CP through the fronthaul. However, the function of performing interference control between ANs may be additionally required in the CP.

On the other hand, the carrier frequency of the radio section is a millimeter wave band capable of providing a large-capacity service by securing a bandwidth of 1 GHz or more. The millimeter wave system is a directional beam based system. As described above, a cost-effective hybrid beamforming technique is essential in a millimeter wave system. In a directional beam-based system, interference may be limited if correct beamforming is performed.

Accordingly, embodiments of the present invention provide a method and apparatus for providing a service to terminals through cooperative transmission of ANs in a cell-free high-density cloud-based RAN in which the second PHY layer function division is reflected, and an apparatus thereof. Embodiments of the present invention are based on hierarchical hybrid beamforming. In embodiments of the present invention, since hybrid beamforming is performed in distributed AN, embodiments of the present invention may also be applied to cooperative transmission in a cloud-based RAN in which functional division in a layer higher than the PHY layer is reflected.

Hierarchical hybrid beamforming-based cooperative transmission system

10 is a block diagram illustrating a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.

Referring to FIG. 10, as described above, one base station function is divided into AN and BN. Each of the distributed ANs may be equipped with a large-scale array antenna and may have a smaller number of RF chains than the number of antenna elements of the array antenna. Analog beams may be formed through an RF precoder consisting of phase shifters that adjust the phases of signals transmitted to a plurality of antenna elements connected to each RF chain. In addition, each AN may include a digital precoder that controls interference between the beams by utilizing the formed analog beams. The upper PHY functions, MAC layer functions, and upper layer functions of the radio protocol stack other than the lower PHY functions of the AN are performed in the BN, and these BNs may be centralized and configured as a BN pool. Such a BN pool may be referred to as a centralized processor (CP). Distributed ANs and centralized BNs are connected by a fronthaul. Compared to the case of using the conventional RRH function partitioned at the RF level, since the PHY layer function partitioning considered in the embodiments of the present invention requires only a relatively small fronthaul transmission capacity, the compression of the fronthaul transmission signal is Fronthaul transmission is possible with only unnecessary or light compression.

)의 안테나 개수는

로 가정되며, RF 체인 수는

개로 가정된다. 동시에 서비스되는 단말들의 개수는

로 표기되며

로 가정된다. 또한, 단말

가 동시에 형성할 수 있는 수신 빔들의 개수는

로 표시되며,

는 단말

에 동시에 서비스를 제공할 수 있는 AN들의 최대 숫자로도 이해될 수 있다. 만약 단말

가 큰 빔폭을 갖는 하나의 omni 또는 quasi-omni 수신 빔을 사용하는 경우라면, 이 역시 단말

를 동시에 서비스하는 AN의 최대 숫자를 제한하기 위해 특정한

값을 가정한다.For a detailed description of embodiments of the present invention, AN l (

) is the number of antennas

is assumed, and the number of RF chains is

assumed to be a dog. The number of terminals serviced at the same time is

is marked with

is assumed to be Also, the terminal

The number of receive beams that can be formed simultaneously is

is displayed as

is the terminal

It can also be understood as the maximum number of ANs that can simultaneously provide services to . if the terminal

In the case of using one omni or quasi-omni receive beam having a large beam width, this is also

to limit the maximum number of ANs serving simultaneously

assume a value

An object to be achieved in the present invention is to provide a service to terminals through cooperative transmission that uses less fronthaul and minimizes interference between ANs distributed in a high-density form. The fronthaul is used for sharing channel state information and data to be transmitted between distributed ANs and CPs. In order to minimize interference between distributed ANs, global perfect CSI must be secured by sharing local CSI (ie, local CSI) measured by individual ANs with other ANs. That is, in order to secure accurate global CSI, local CSI must be frequently shared through the fronthaul. In addition, for smooth cooperative transmission in which distributed ANs participate, data to be transmitted to the terminal should be shared with more ANs, and for this purpose, more fronthaul consumption may occur.

과 모든 단말들의 공간적 채널 공분산(spatial channel covariance) 행렬(즉,

)과 같이, 장기적인(long-term) 채널 통계 정보이다. 따라서, 통계적 CSI는 순시적인 채널에 비해 긴 시간 척도에 따라 변하기 때문에 추정하기가 용이하다. 또한, 통계적 CSI는 모든 부반송파들에 걸쳐 균일하기 때문에 모든 부반송파들에 대해 하나의 아날로그 프리코더를 설계하기 위해 활용될 수 있다. In order to solve the above-described CSI sharing problem, distributed ANs according to an embodiment of the present invention may measure/estimate local statistical CSI and notify the CP (). This statistical CSI is,

and the spatial channel covariance matrix of all terminals (i.e.,

), long-term channel statistics information. Therefore, statistical CSI is easy to estimate because it varies over a long time scale compared to an instantaneous channel. In addition, since statistical CSI is uniform across all subcarriers, it can be utilized to design one analog precoder for all subcarriers.

)은 주기적으로 또는 통계적 CSI가 변경될 때마다 CP에게 통계적 CSI(즉,

)를 통보함으로써, CSI 공유에 사용되는 프론트홀 소비를 최소화할 수 있다. 추가적으로, AN

에 의한 통계적 CSI의 측정 대상이 되는 단말들의 범위를 제한함으로써, 전체 단말들 대신 제한된 범위의 단말들에 대해서만 통계적 CSI를 측정하고 통보함으로써 프론트홀 소비를 보다 감소시킬 수 있다. 이를 위해, 도 9의 단계(S930)에서 설명한 정보들이 활용될 수 있다.In embodiments of the present invention, it is assumed that each AN can measure/estimate a spatial channel covariance matrix. AN l(

) is the statistical CSI (i.e., ) to the CP periodically or whenever the statistical CSI is changed.

), it is possible to minimize the fronthaul consumption used for CSI sharing. Additionally, AN

By limiting the range of UEs to be measured for statistical CSI by , fronthaul consumption can be further reduced by measuring and reporting statistical CSI only for UEs in a limited range instead of all UEs. To this end, the information described in step S930 of FIG. 9 may be utilized.

How the central controller (CP) works

11 is a flowchart illustrating an operation of a CP belonging to a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.

As described in FIG. 9 , the CP is a central controller of the cloud RAN. Each of the distributed ANs simultaneously receives information about the number of RF chains that determine the number of terminals that can provide a service, and each terminal at the same time. It also has information on the maximum number of beams that can be used. Hereinafter, the operation procedure of the CP in a state in which the above-described information is already secured will be described.

)를 수집하여 전역적인 통계적 CSI를 생성할 수 있다(S1110). CP는 AN l(

)의 단말 별 통계적 CSI들(

)을 내림차순으로 정렬하고, 해당 AN

이 제공하는 RF 체인의 숫자(

)만큼 가장 높은

을 가지는 단말들을 선택하여

집합을 구성할 수 있다(S1120). 또한, CP는 동시에 단말

에게 서비스를 제공하는 AN들의 집합

를 구성할 수 있다. CP가 구성한 집합들은

과

를 만족해야 한다. 만약

인 경우가 발생하면, CP는 낮은

값을 가진 단말의

로부터 해당 AN을 제거할 수 있고, 이에 따라 관련된

에

이 그 다음으로 높은 다른 단말을 추가할 수 있다. 만약

인 경우가 발생하면, CP는 해당 단말

의 높은

값을 갖는 AN들을

에 추가할 수 있고, 이에 따라 관련된

에 해당 단말을 추가할 수 있다. 여기서, 후술될 계층적 하이브리드 빔형성을 통해 단말의 위치에 무관하게 단말들 간의 간섭을 해소될 수 있다. 사실, AN의 안테나 개수와 RF 체인들이 충분히 많은 경우, 무선 주파수의 반파장 이상만 이격 되는 단말들의 간섭도 제어될 수 있다. AN의 안테나 및 RF 체인 수가 제한되는 경우, CP는

의 유사성에 따라 단말들을 그룹핑하고 동일 그룹에 속한 단말들은 서로 다른 AN이 서비스하도록 할 수 있다. 상기 기능을 통해, CP는 단말

를 서비스하는 복수의 AN l (

)을 선택할 수 있고, 단말

를 위한 데이터를

에 속한 AN들에게만 공유할 수 있다. Referring to FIG. 11, the CP is the regional statistical CSI (

) to generate global statistical CSI (S1110). CP is AN l(

) of statistical CSIs for each UE (

) in descending order, and the corresponding AN

The number of RF chains it provides (

) as the highest

By selecting terminals with

A set can be configured (S1120). In addition, the CP is the terminal at the same time

A set of ANs that provide services to

can be configured. The sets formed by the CP are

class

must be satisfied what if

If this happens, the CP is low

terminal with a value

may remove the AN from the

to

It is possible to add another terminal with the next highest rank. what if

When the case of , the CP is the corresponding terminal

high of

ANs with values

can be added to, and thus related

The corresponding terminal can be added to . Here, interference between terminals can be resolved regardless of the location of the terminal through hierarchical hybrid beamforming, which will be described later. In fact, when the number of antennas and RF chains of the AN are sufficiently large, the interference of terminals spaced apart by more than half a wavelength of the radio frequency can also be controlled. If the number of antennas and RF chains in the AN is limited, the CP is

UEs are grouped according to the similarity of , and UEs belonging to the same group can be serviced by different ANs. Through the above function, the CP is the terminal

Multiple ANs serving l (

) can be selected, and the terminal

data for

It can be shared only with ANs belonging to

정보를 수집하여 전역적인 통계적 CSI

정보를 구축하고, AN 별 전송 공간을 이웃 AN들과의 간섭을 최소화할 수 있도록 설정하기 위해, 전역적인 통계적 CSI

정보 을 활용한 AN 별 외부 프리코딩 행렬(outer precoding matrix)를 계산할 수 있다. 실제로 AN 별 상기한 외부 프리코딩 행렬은 해당 AN의 RF 프리코더의 설정을 위한 정보이며, 해당 AN에서 자신의 RF 프리코더 하드웨어 제약을 반영하여 수정하게 된다.Interference control between ANs densely deployed in the PHY function split cloud RAN according to an embodiment of the present invention may be performed in the CP while consuming a limited fronthaul as described above. CP is local statistical CSI notified from distributed ANs.

Gather information to get global statistical CSI

In order to construct information and set the transmission space for each AN to minimize interference with neighboring ANs, global statistical CSI

An outer precoding matrix for each AN can be calculated using the information. In fact, the above-described external precoding matrix for each AN is information for setting the RF precoder of the corresponding AN, and the AN is modified by reflecting the limitations of its RF precoder hardware.

에 속한 단말

들에 대하여

의 고유 분해(eigen decomposition)를 통해

를 획득할 수 있다. 이를 통해, CP는 AN l을 위한 전송 신호 공간

과 간섭 공간

을 구성할 수 있다(S1130).As an example of deriving the outer precoding matrix for each AN, the outer precoding matrix may be derived through low-complexity non-repetitive block diagonalization. First, the CP is a set of terminals serviced by AN i.

terminal belonging to

about the field

through the eigen decomposition of

can be obtained. Through this, CP is the transmit signal space for AN l

over-interfering space

can be configured (S1130).

은 하기 수학식1과 같이 구성될 수 있다.Transmission signal space for AN l

may be configured as in Equation 1 below.

은

집합의

번째 원소인 단말의 식별자이며,

은

의 랭크

보다 작은 개수

개의 주요 고유 벡터들로 구성된 행렬이다. 다음으로, AN l을 위한 간섭 신호 공간 간섭 공간

은 하기 수학식 2와 같이 구성될 수 있다.here

silver

collective

The second element is the identifier of the terminal,

silver

rank of

smaller number

It is a matrix of principal eigenvectors. Next, the interfering signal space for AN l

may be configured as in Equation 2 below.

의 특이 분해(singular decomposition)를 통해 획득되는

개의 가장 약한 고유 모드(eigen mode)들로 구성되는 왼쪽 고유 공간(eigenspace)은

로 표기될 수 있다. 즉,

는

의 가장 약한

개의 좌측 고유 벡터(eigenvector)들로 구성된다. 다음으로, AN l의 신호 채널

를

공간 상으로 투영(projection)하여

이 도출되고,

의 가장 강한 좌측 고유 벡터들로 구성되는

이 도출될 수 있다. 최종적으로, AN l의 단말

를 위한 외부 프리코딩 벡터

는 하기 수학식 3과 같이 표현될 수 있다.Next, the UE may derive an external precoding matrix defining an interference-controlled transmission signal space for each AN (S1140). Specifically,

obtained through singular decomposition of

The left eigenspace, consisting of the weakest eigen modes, is

can be denoted as in other words,

Is

the weakest of

It consists of the left eigenvectors. Next, the signal channel of AN l

cast

by projecting it into space

is derived,

consisting of the strongest left eigenvectors of

this can be derived. Finally, the terminal of AN l

External precoding vector for

can be expressed as in Equation 3 below.

에 속한 다른 단말

에 대해서도 상기와 같은 절차를 통해

가 계산될 수 있다. 상기 프리코딩 벡터들 각각이 열(column)로서 설정된 행렬을 생성하면, AN l을 위한 외부 프리코딩 행렬

이 도출될 수 있다. 여기서 고려해야 할 점은 AN l의 전송 공간의 차원 크기 및 프론트홀 용량이다. 상술된 바와 같이, CP는 AN l의 RF 체인 개수

만큼의 전송 공간들을 설정하게 되는데, 그 차원 크기를 줄이면 주변 간섭 공간과의 겹침이 줄어들 수 있고 또한 프론트홀 용량을 줄이는 효과도 함께 발생한다. 따라서, 본 발명의 일 실시예에 따르는 CP는 AN l에 연결된 프론트홀의 용량을 초과하지 않도록 AN l의 전송 공간 크기, 즉

의 열 벡터들의 개수를 조절할 수 있다(S1150). 또한, CP는 성능 모니터링을 통해 직/간접적으로 간섭이 강하다고 판단되는 경우, 전송 공간 크기를 추가로 줄일 수 있다. 상기 조정에 따라

도 수정될 수 있다.

other terminals belonging to

Through the same procedure as above for

can be calculated. If each of the precoding vectors generates a matrix set as a column, the outer precoding matrix for AN l

this can be derived. The considerations here are the dimensional size of the transmission space of AN l and the fronthaul capacity. As described above, CP is the number of RF chains in AN l

As many transmission spaces are set, if the dimension size is reduced, overlap with the surrounding interference space can be reduced, and also the effect of reducing the fronthaul capacity occurs. Therefore, the CP according to an embodiment of the present invention does not exceed the capacity of the fronthaul connected to AN 1, that is, the size of the transmission space of AN 1, that is,

It is possible to adjust the number of column vectors of (S1150). In addition, when it is determined that the interference is directly/indirectly strong through performance monitoring, the CP may further reduce the size of the transmission space. according to the above adjustment

can also be modified.

를 계산함으로써, AN l 의 전송 부공간을 간섭 신호 공간에 가급적 직교가 되도록 하면서 AN l 의 신호 채널에 맞춰지도록 한다. CP는 전역적인 통계적 CSI 정보에 기반하여 계산된 외부 프리코딩 벡터

를

정보와 함께 해당 AN들에게 전달할 수 있다(S1160). 이후, CP는 단말

에게 서비스를 제공하는 AN들의 집합

에 속한 AN들에게 프론트홀로 통하여 단말

에게 전송될 데이터를 공유할 수 있다(S1170).As described above, CP is the outer precoding matrix for AN l.

By calculating , the transmission subspace of AN 1 is made to fit the signal channel of AN 1 while making it as orthogonal as possible to the interfering signal space. CP is an external precoding vector calculated based on global statistical CSI information

cast

It can be delivered to the corresponding ANs together with the information (S1160). After that, the CP is the terminal

A set of ANs that provide services to

terminal through fronthaul to ANs belonging to

It is possible to share data to be transmitted to (S1170).

Meanwhile, in FIG. 11 , it has been described that the step (S1150) of adjusting the size of the transmission space of the AN1 is performed after the steps (S1160) and (S1170). However, as described above, when it is determined that the interference is directly/indirectly strong through performance monitoring even while performing step S1170, the CP can further adjust the size of the transmission space and provide related information to the ANs. can That is, even during the execution of step S1170, if necessary, steps S1150 and S1160 may be re-executed.

On the other hand, when statistical CSI is periodically reported to the CP or reported to the CP according to a change in the statistical CSI, it may start again from step S1110. That is, the outer precoding matrix may be changed by the new global statistical CSI.

How an Access Node (AN) Works

12 is a flowchart illustrating an operation of an AN belonging to a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.

In FIG. 12, the operation procedure of the AN for performing hierarchical hybrid beamforming-based cooperative transmission in conjunction with the CP operating according to the procedure shown in FIG. 11 is shown.

)의 통계적 CSI 정보

를 측정/추정하고 이를 CP에게 보고할 수 있다(S1210). AN l은 프론트홀 소비를 고려하여 통계적 CSI 정보를 주기적으로 또는 통계적 CSI 정보가 변경되는 시점에 보고할 수 있다. 또한, 통계적 CSI 정보가 보고되는 대상 단말들은 수신 신호 세기 등과 같은 정보에 기반하여 제한할 수도 있다. 즉, 일정 값이상의 세기로 수신된 신호를 가진 단말들로 통계적 CSI 정보가 보고되는 대상 단말들이 제한될 수 있다.12, AN l is all terminals k (

) of statistical CSI information

may be measured/estimated and reported to the CP (S1210). AN l may report statistical CSI information periodically or at a time when statistical CSI information is changed in consideration of fronthaul consumption. In addition, target UEs to which statistical CSI information is reported may be limited based on information such as received signal strength. That is, target UEs to which statistical CSI information is reported may be limited to UEs having a signal received with an intensity greater than or equal to a predetermined value.

와

에 대한 정보를 수신할 수 있다(S1220). 단계(S1220)는 앞서 도 11을 참조하여 설명된 CP의 동작 단계(S1160)에 대응되는 AN l의 동작 단계이다.AN l is the outer precoding matrix from CP

Wow

It is possible to receive information on (S1220). Step S1220 is an operation step of AN 1 corresponding to operation step S1160 of the CP described above with reference to FIG. 11 .

의 차원 수만큼의 RF 체인들을 활성화시키고 해당 RF 체인들에 연결된 위상 천이기들로 구성된 RF 프리코더를 설정할 수 있다(S1230). 위상 천이기들만으로 구성되는 RF 프리코더에 상기

을 적용하기 위해서는, CP는

의 각 원소의 크기를 각각

로 일정하게 설정하고, 각 위상 천이기의 위상은

의 각 원소의 위상인

으로 설정할 수 있다. 위상 천이기만으로 구성되는 RF 프리코더의 제약을 '일정 진폭(constant modulus: CM)'이라 할 수 있다. 따라서, AN l은 CP로부터 전달받은

를 하기 수학식 4에 따라 RF 프리코딩 행렬

으로 변경해야 한다.AN l is now

It is possible to activate RF chains as many as the number of dimensions of , and set an RF precoder composed of phase shifters connected to the corresponding RF chains (S1230). The RF precoder, which consists only of phase shifters,

To apply , CP is

the size of each element in

is set constant, and the phase of each phase shifter is

is the phase of each element in

can be set to The constraint of the RF precoder consisting of only a phase shifter can be called 'constant modulus (CM)'. Therefore, AN l received from CP

RF precoding matrix according to Equation 4 below

should be changed to

에 따라 각 RF 체인의 개별 위상천이기들의 위상들을 설정할 수 있다. AN l is derived based on Equation 4

The phases of individual phase shifters of each RF chain can be set according to

AN l can acquire local instantaneous effective CSI reduced from the antenna dimension to the RF chain dimension through the RF precoder, and based on this, conjugate (maximum-ratio transmission), zero forcing, regularized zero forcing It is possible to set a linear digital precoder of the method (S1240).

에 속한 단말들에게 전달할 데이터를 CP로부터 수신하고, 수신된 데이터를 상기한 디지털 프리코더 및 RF 프리코더를 이용하여 계층적으로 하이브리드 빔포밍된 신호로 변환하여 송신할 수 있다(S1250). 이후, AN l은 지속적인 채널 측정 모니터링을 통해 CP에게 관측 가능한 모든 단말들의 지역적인 통계적 CSI 및 서비스 중에 있는 단말들의 간섭 성능을 보고할 수 있다(S1260). 이를 통해, AN l은 자신의 활성화된 RF 체인 수와 그에 따른

를 CP에 제어에 따라 조정하게 된다. As described above, AN 1 may set the interference control RF precoder generated from the global statistical CSI by the CP, and may set the digital precoder generated from the locally instantaneous effective CSI acquired by it. After that, AN l is

Data to be transmitted to terminals belonging to the CP may be received from the CP, and the received data may be converted into a hierarchically hybrid beamformed signal using the digital precoder and the RF precoder and transmitted (S1250). Thereafter, AN l may report regional statistical CSI of all observable UEs and interference performance of UEs in service to the CP through continuous channel measurement monitoring (S1260). Through this, AN l determines the number of its active RF chains and the corresponding

is adjusted according to the control of the CP.

On the other hand, when AN l reports regional statistical CSI to the CP periodically or according to a change in regional statistical CSI to the CP, it may start again from step S1210. That is, the outer precoding matrix may be changed by the new global statistical CSI.

The entire operating procedure of the system

Hereinafter, a procedure in which distributed ANs (eg, AN i and AN j) in which the hierarchical hybrid beamforming is implemented and one CP perform cooperative transmission for terminal k will be described.

13 is a flowchart illustrating an operation procedure of a hierarchical hybrid beamforming-based cooperative transmission system according to an embodiment of the present invention.

First, as described with reference to FIGS. 5 to 9 , UE k may transmit a random access channel in a beam sweeping manner in the synchronized RACH period set by the CP (S1310). Each AN and CP receiving the random access channel of terminal k determines whether the corresponding AN can provide a service to terminal k based on the signal strength of the received random access channel, and provides terminal k with a terminal-specific uplink A pilot is assigned (S1320). 13 illustrates a case in which terminal k establishes a connection simultaneously with AN i and AN j. That is, FIG. 13 illustrates a case in which AN i and AN j are determined as clusters providing a service to UE k.

,

및

에 대한 정보도 AN i, AN j, 및 단말 k에게 제공될 수 있다. 한편, CP는 단말 k에게 전송할 데이터를 AN i 및 AN j에게 전달할 수 있다(S1370). 도 13에서 단계(S1370)는 단계(S1360) 이후에 수행되는 것처럼 도시되어 있으나, 단계(S1370)의 수행 순서는 단계(S1360)과는 무관하다. 즉, 단계(S1370)는 단계(S1350) 이전에 수행될 수도 있고, 단계(S1350) 또는 단계(S1350)과 동시에 수행될 수도 있다. Thereafter, terminal k periodically transmits the allocated uplink pilot (S1330), and the neighboring ANs including AN i and AN j measure/estimate regional statistical CSI based on the uplink pilot of terminal k to receive the CP. It can be reported (S1340). The CP collects regional statistical CSI reported from ANs to generate global statistical CSI, and based on the global statistical CSI, derives an external precoding matrix for each AN that can control interference between ANs to each of the ABs. It can be transmitted (S1350). At this time, set

,

and

Information on AN i, AN j, and terminal k may also be provided. Meanwhile, the CP may transmit data to be transmitted to terminal k to AN i and AN j (S1370). In FIG. 13 , step S1370 is illustrated as being performed after step S1360 , but the execution order of step S1370 is independent of step S1360 . That is, step S1370 may be performed before step S1350 or may be performed simultaneously with step S1350 or S1350.

Each of AN i and AN j converts the received external precoding matrix into an RF precoding matrix having a constant amplitude based on Equation 4 to set the RF precoder, and uses the local instantaneous CSI obtained by itself A digital precoder may be set (S1360). This is to minimize the interference between terminals serviced by AN i and AN j by calculating the internal RF and digital hybrid precoding matrix again on each interference-controlled transmission space defined by the external precoding matrix received from the CP. It is the same as redefining the available transmission space. Each of AN i and AN j may convert data received from the CP into a precoded signal using the above-described digital precoder and RF precoder and transmit the data to terminal k ( S1380 ). Terminal k simultaneously receives interference-controlled data from AN i and AN j.

Additionally, UE k feeds back HARQ information to AN i and AN j in the data reception process, and AN i and AN j may transmit interference-related performance monitoring information to the CP ( S1380 ). The CP may redefine the transmission space for each AN based on the interference-related performance monitoring information transmitted from AN i and AN j ( S1385 ).

Terminal/device configuration

14 is a block diagram for explaining the configuration of an apparatus for performing methods according to embodiments of the present invention.

The apparatus illustrated in FIG. 14 may be a communication node (eg, CP, AN, or terminal) for performing a method according to embodiments of the present invention.

Referring to FIG. 14 , the communication node 1400 may include at least one processor 1410 , a memory 1420 , and a transceiver 1430 connected to a network to perform communication. Also, the communication node 1400 may further include an input interface device 1440 , an output interface device 1450 , a storage device 1460 , and the like. Each component included in the communication node 1400 may be connected by a bus 1470 to communicate with each other.

The processor 1410 may execute a program command stored in at least one of the memory 1420 and the storage device 1460 . The processor 1410 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which methods according to embodiments of the present invention are performed. Each of the memory 1420 and the storage device 1460 may be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 1420 may be configured as at least one of a read only memory (ROM) and a random access memory (RAM).

The methods according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the computer readable medium may be specially designed and configured for the present invention, or may be known and available to those skilled in the art of computer software.

Examples of computer-readable media include hardware devices specially configured to store and carry out program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine language codes such as those generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as at least one software module to perform the operations of the present invention, and vice versa.

Although it has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. will be able

Claims (20)

As a method of operating a centralized processor (CP) for hybrid beamforming-based cooperative transmission,
generating global statistical CSI by collecting local statistical channel state information (CSI) from each of the access nodes (ANs) connected to the CP;
configuring a set of first terminals to which a first AN of the ANs will provide a service based on the global statistical CSI;
Construct a transmit signal space and an interfering signal space for the first AN, and derive an external precoding matrix defining an interference-controlled transmit signal space for the first AN based on the transmit signal space and the interfering signal space to do; and
transmitting the derived outer precoding matrix to the first AN;
A radio frequency (RF) precoder of the first AN is set based on the derived external precoding matrix, and the digital precoder of the first AN is instantaneous locally between the first AN and the first terminals. Set using valid CSI,
How the central controller (CP) works. The method according to claim 1,
The regional statistical CSI is a spatial channel covariance matrix between each of the ANs and terminals,
How the central controller (CP) works. The method according to claim 1,
The CP provides configuration information for a synchronized random access channel (RACH) interval through the AN, and the first terminal transmits a RACH signal to the first AN through the RACH interval, and 1 Receive an uplink pilot (pilot) from the AN,
How the central controller (CP) works. 4. The method of claim 3,
The regional statistical CSI between the first terminal and the first AN is measured based on the uplink pilot,
How the central controller (CP) works. delete The method according to claim 1,
performing performance monitoring;
adjusting a size of an interference-controlled transmission signal space for the first AN according to a result of the performance monitoring; and
Further comprising the step of transmitting an external precoding matrix modified according to the size of the adjusted interference-controlled transmission signal space to the first AN,
How the central controller (CP) works. The method according to claim 1,
Further comprising the step of forwarding data to the first AN,
The data is transmitted to the first terminals through the cooperative transmission of at least one AN other than the first AN among the ANs and the first AN,
How the central controller (CP) works. As a method of operation of a first access node (access node, AN) for hybrid beamforming-based cooperative transmission,
measuring regional statistical channel state information (CSI) for neighboring terminals and reporting the measured regional statistical CSI to a centralized processor (CP);
receiving, from a CP, an external precoding matrix derived from the global statistical CSI generated from the regional statistical CSI and information on a set of first terminals to which the first AN will provide a service; and
Setting a radio frequency (RF) precoder of the first AN based on the external precoding matrix,
The digital precoder of the first AN is configured using the locally instantaneous effective CSI between the first AN and the first terminals,
A method of operation of a first access node. 9. The method of claim 8,
The regional statistical CSI is a spatial channel covariance matrix between the first AN and the neighboring terminals,
A method of operation of a first access node. 9. The method of claim 8,
The regional statistical CSI is reported periodically or reported when the regional statistical CSI is changed,
A method of operation of a first access node. 9. The method of claim 8,
The neighboring terminals for which the regional statistical CSI is measured are limited to terminals transmitting a signal received from the first AN with an intensity greater than or equal to a certain value,
A method of operation of a first access node. 9. The method of claim 8,
When the RF precoder includes only phase shifters, the size of each element of the external precoding matrix is set to be constant, and the phase of each of the phase shifters is the value of each element of the external precoding matrix. set in phase,
A method of operation of a first access node. 9. The method of claim 8,
Further comprising the step of providing configuration information for a synchronized random access channel (RACH) interval provided from the CP to the neighboring terminals,
The neighboring terminals transmit a RACH signal to the first AN through the RACH interval, and receive an uplink pilot assigned from the first AN;
A method of operation of a first access node. 14. The method of claim 13,
The regional statistical CSI between the peripheral terminals and the first AN is measured based on the uplink pilots,
A method of operation of a first access node. delete 9. The method of claim 8,
Further comprising the step of receiving data from the CP,
The data is transmitted to the first terminals through the cooperative transmission of the first AN and the second AN,
A method of operation of a first access node. a centralized processor (CP);
access nodes (ANs) connected to the CP; and
and fronthaul links connecting the CP and the ANs;
The CP provides an external precoding matrix for the first AN among the ANs derived from the global statistical CSI generated from the local statistical CSI collected from the ANs to the first AN through the fronthaul link, , the first AN sets the RF precoder of the first AN based on the external precoding matrix, and the local instantaneous validity between the first AN and the first terminals to which the first AN will provide a service Set the digital precoder of the first AN based on the CSI,
The CP and the ANs are nodes in which the function of the base station is functionally divided in a physical layer,
A system for cooperative transmission based on hybrid beamforming. 18. The method of claim 17,
The regional statistical CSI is a spatial channel covariance matrix between each of the ANs and terminals,
A system for cooperative transmission based on hybrid beamforming. delete 18. The method of claim 17,
The first AN converts the data transmitted from the CP into a precoded signal using the RF precoder and the digital precoder of the first AN, and converts the precoded signal to the first AN among the ANs. Transmitted to the first terminals through cooperative transmission with at least one other AN except for,
A system for cooperative transmission based on hybrid beamforming.

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