KR20200061291A - Hybrid beamforming method for beam-based cooperative transmission, and apparatus for the same - Google Patents

Abstract

The present invention relates to a hierarchical hybrid beamforming method for beam-based cooperative transmission, to minimize overhead required for the cooperative transmission, and an apparatus for the same. According to the present invention, a system for hybrid beamforming-based cooperative transmission comprises: a centralized processor (CP); access nodes (ANs) connected to the CP; and fronthaul links connecting the CP and the ANs. The CP provides, through the fronthaul link, a first AN with an external precoding matrix for the first AN, among the ANs, extracted from global statistical channel state information (CSI) generated from local statistical CSI collected from the ANs. The first AN can set an RF precoder of the first AN based on the external precoding matrix and can set a digital precoder of the first AN based on local instantaneous valid CSI between the first AN and first terminals to receive a service from the first AN.

Description

A hierarchical hybrid beamforming method for beam-based cooperative transmission and an apparatus therefor {Hybrid beamforming method for beam-based cooperative transmission, and apparatus for the same}

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

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

Since analog beamforming steers signals using only 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 by adjusting the phase and amplitude of the signal digitally to adjust the direction of the beam. However, an RF chain including an analog-to-digital converter (ADC)/digital-to-analog converter (DAC) is required for each antenna, and when a large-scale antenna is used, it is implemented by increasing hardware complexity and power consumption. It has the disadvantage of becoming difficult.

Therefore, in order to lower the complexity of digital beamforming and increase the accuracy of analog beamforming, hybrid beamforming technology using analog beamforming in the RF region and digital beamforming in the 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 hierarchical hybrid beamforming based cooperative transmission.

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

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 access nodes (ANs) connected to the CP Collecting local statistical channel state information (CSI) to generate global statistical CSI; Configuring a set of first terminals to be provided by a first AN among the ANs based on the global statistical CSI; Constructs a transmission signal space and an interference signal space for the first AN, and derives an external precoding matrix defining an interference-controlled transmission signal space for the first AN based on the transmission signal space and the interference 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 random access channel (RACH) section synchronized through the AN, and the first terminal transmits a RACH signal to the first AN through the RACH section, and the first 1 An uplink pilot may be allocated from the AN.

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

The 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 a local instantaneous between the first AN and the first terminals. It can be set using the effective CSI.

The CP operating method may include performing performance monitoring; Adjusting a size of an interference-controlled transmission signal space for the first AN according to the performance monitoring result; And transmitting the modified external precoding matrix 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, and the data is transmitted through a cooperative transmission of at least one AN other than the first AN among the ANs and the first AN. It can be transmitted to the first terminal.

An embodiment of the present invention for achieving the other object, as a method of operating a first access node (access node, AN) for a hybrid beamforming-based cooperative transmission, local statistical channel state information for the neighboring terminals measuring (channel state information, CSI) and reporting the measured local statistical CSI to a centralized processor (CP); Receiving information on an external precoding matrix derived from the global statistical CSI generated from the local statistical CSI and a set of first terminals to be provided by the first AN from the CP; 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 when the regional statistical CSI is changed.

The peripheral terminals for which the regional statistical CSI is measured may be limited to a terminal transmitting a signal received from the first AN with an intensity of a predetermined value or more.

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

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

The 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 set using a local instantaneous effective CSI between the first AN and the first terminals.

The operation method of 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 above another object includes a centralized processor (CP); Access nodes (ANs) connected to the CP; And front hole links connecting the CP and the ANs, wherein the CP is an external free of the first AN among the ANs derived from the global statistical CSI generated from the local statistical CSI collected from the ANs. A coding matrix is provided to the first AN through the front hole link, 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 The digital precoder of the first AN may be set based on a local instantaneous effective CSI between the first terminals to which the AN will provide the service.

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

The CP and the AN may be nodes that have functionally divided a function of a base station in a physical layer.

The first AN converts data transmitted from the CP into a precoded signal using an RF precoder and a 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.

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

1 is a conceptual diagram illustrating the structure of a transmitter and a receiver to which hybrid beamforming is applied.
2 is a conceptual diagram for explaining a cell arrangement of a 5G NR based system in a dense urban environment.
3 is a conceptual diagram for explaining the architecture of a cloud radio access network (C-RAN).
4 is a conceptual diagram illustrating a user-centric clustering concept in a high-density C-RAN to which embodiments of the present invention are applied.
5 is a conceptual diagram illustrating the concept of user-centered beam management in a high-density C-RAN to which embodiments of the present invention are applied.
6 is a conceptual diagram illustrating a method of allocating RACH slots within a synchronized RACH section.
7 is a conceptual diagram illustrating a beam sweeping operation in an RACH slot.
8 is a conceptual diagram illustrating a method of assigning mini-slots within a synchronized RACH interval.
9 is a conceptual diagram illustrating a user-oriented 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 illustrating a configuration of an apparatus for performing methods according to embodiments of the present invention.

The present invention can be applied to various changes and can have various embodiments, and specific embodiments will be 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 drawing, similar reference numerals are used for similar components.

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

When an element is said to be "connected" to or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but may exist in the middle. It should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

The terms used in this application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “include” or “have” are intended to indicate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

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

1 is a conceptual diagram illustrating the structure 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 the baseband signal by the digital precoder 110 belonging to the baseband portion of the transmitter. Meanwhile, the analog beamforming may be performed by changing the phase of the RF signal obtained through RF conversion on the signal output from the baseband part using phase shifters of the analog precoder 120.

That is, as mentioned above, to reduce the complexity of digital beamforming and increase the accuracy of analog beamforming, analog beamforming is used in the RF region, and digital beamforming is used in the baseband. Hybrid beamforming technology using a beamforming method 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 a cell arrangement of a 5G NR based system in a dense urban environment.

FIG. 2 shows a cell arrangement based on 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 may be arranged 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.

Both macro base stations and micro base stations can use millimeter waves to accommodate explosive mobile traffic. In the 3GPP 5G NR based system, beam management centered on the base station is performed. Considering that one base station accommodates multiple terminals, beam management centered at the base station may be feasible. However, in an ultra dense network (UDN), where the number of distributed base stations may be more than the number of terminals, user-oriented 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 can be performed centrally and aggregated into one cloud computing center.

Unlike conventional base stations, in a C-RAN architecture, a remote radio head (RRH) may have only RF and antenna functions. Each of the RRHs and the cloud 310 may be connected to front hole links. The front-hole link should have a characteristic that can smoothly transmit a large amount of signals with a low signal transmission delay. In general, it is known that a capacity of up to 20 times the transmission speed of a radio link is required for a front-hole link. On the other hand, as the 5G mobile communication system is introduced, the transmission speed of the wireless section increases to 20 Gbps, and the required capacity of the front hole is difficult to be realistically provided in terms of cost. In order to lower the required front hole capacity, a functional split that moves a part of the baseband function back to the RRH site has been studied. Function division can lower the capacity of the front hole, but there is a side to redistribute functions such as centralized signal processing, so it is necessary to carefully select the point where the function is divided.

In order to solve the above-mentioned problems of the prior art, embodiments of the present invention use the high frequency and limit the use of the front hole in the C-RAN architecture to which the function division is applied, so as to make the most of centralized signal and resource processing. Through this, embodiments of the present invention have an object 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 central-centralized or cloud radio access network (C-RAN) architecture, a remote radio unit (RRU) performs RF-baseband conversion at a location proximate to the antenna, and the centralized centralized baseband unit ( The baseband unit (BBU) performs baseband (ie, upper layer 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 network capacity and applying advanced radio coordination to enhance the user experience. At this time, 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 the digitized time domain sample signals of each antenna device are transmitted through the front hole link between the RRU and the BBU, the capacity of the front hole 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 spotlighted as major wireless functions that significantly improve spectral efficiency and network capacity. Therefore, it is important to reduce the cost of the front-hole network and increase the system scalability for the antenna and radio edge nodes.

To solve this, various function partitioning options for the radio protocol stack are being discussed. Functional partitioning determines how many base station functions remain locally close to the user and how many functions are centralized for the possibility of gaining more processing benefits while alleviating fronthaul network capacity and latency requirements. Is done. Embodiments of the present invention deal with'intra-PHY functional split (iPFS)' to reduce the front-hole load while maintaining the cooperative transmission function of the high-density C-RAN.

According to the function division, one base station may be divided into an'Access Node (AN)' and a'Base Node (BN)'. ANs are distributed in close proximity to'Mobile Station (MS)', BNs are centralized and configured as a pool at one site, which is referred to as'Centralized Processor (CP)'. Can be.

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

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

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

4 and 5, the operations of nodes through user-centered beam management include synchronized RACH resource allocation and signaling through system information broadcast by ANs, and beam-sweeping of a terminal in a synchronized RACH section. It can be performed through (sweeping), user-centric clustering, training using uplink (UL) pilots, acquiring channel information, and downlink (DL) cooperative transmission.

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

Referring to FIG. 5, the CP may control the distributed ANs AN1, AN2, AN3, ?, ANn to sequentially transmit system information, thereby reducing the overhead of system information broadcast. 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 configured to transmit system information in frame #n 503. It can be controlled to transmit.

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

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

6 is a conceptual diagram illustrating a method of allocating RACH slots within a synchronized RACH section.

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

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

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

Referring to FIG. 7, when 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 an RACH slot within the RACH interval, the RACH interval may be set as a plurality of mini-slots. That is, in the above-described embodiments, the RACH slot is defined as a time unit in which the terminal can complete the beam-sweeping operation, but the time unit in which the terminal can transmit one beam is a mini-slot (ie, RACH mini slot). Can be defined as

8 is a conceptual diagram illustrating a method of assigning mini-slots within a synchronized RACH interval.

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

RACH mini-slots.

As in the case of the above-mentioned system information broadcasting, a trade-off relationship may exist between the number of set RACH periods and the network entry time of the terminal. For example, in order to reduce the overhead according to the RACH intervals, the intervals of the RACH intervals can be increased. For example, in FIG. 5, an RACH interval exists for each frame, but an RACH interval may exist for two or more frames. On the other hand, two or more RACH intervals may exist in one frame in order to reduce the network entry time of the terminal.

Meanwhile, when terminals distributed in one RACH section perform random access, a collision may occur. CP and AN should provide a mechanism to minimize collision of random access by terminals.

User-oriented beam management procedure

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

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

In step S910, the CP may set the synchronized RACH resource (that is, RACH intervals (and RACH slots)) and transmit information on the configured RACH resource to the terminals through ANs by including system information. The terminals can receive system information broadcast by the CP through the ANs and check information on the set RACH intervals.

In step S920, the terminal may perform beam-sweeping based on the information on the set RACH intervals. At this time, as described in FIG. 6, when a plurality of RACH slots are provided in the RACH section, the UE may select one RACH slot. By selecting the RACH slot to be used by the terminal, random access collisions between the terminals can be resolved in time or frequency. Meanwhile, assuming beam-based access, spatial separation is possible even when two or more UEs perform the random access by selecting the same RACH slot. Alternatively, code separation in which different terminals use orthogonal RACH codes as in LTE/NR is possible. When the RACH section is composed of mini-slots without distinguishing the RACH slot, as illustrated in FIG. 8, the UE virtually performs RACH with M mini-slots according to the number M of beams used for its beam-sweeping. A slot can be configured, and a beam-sweeping operation can be performed through a virtually generated 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 CP and AN, the reception strength (eg, a received signal strength indicator (RSSI)) of the RACH signal received for each AN is measured, and the transmitters of the RACH signal can be sorted in the order of reception strength. For example, RACH signal transmitters up to a reception power N rank are sorted by AN. At this time, the best beam information of the corresponding RACH signal sender can also be recorded. CPs and ANs can allocate uplink pilots that are distinct from each other to RACH signal senders (ie, UEs) through mutual cooperation. The CP may generate a list of target terminals for which each AN will provide a service, and based on this, may generate a list of ANs (that is, clustering information) capable of providing a service to a specific terminal. That is, clusters of ANs providing services for each terminal may be configured. On the other hand, clustering by 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 uplink pilots allocated to terminals (pilot sequence, resource information to be used for pilot transmission, etc.). The CP may transmit the clustering information to terminals through ANs. The terminal, based on the clustering information received through the CP and AN, provides information on a cluster of ANs to provide services to itself, information on the best beam received by each AN, and an uplink pilot allocated to itself. Information. Accordingly, the terminal can periodically transmit the uplink pilot allocated through beams that it can simultaneously form.

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

The cell-shedding high-density cloud-based RAN is easy to manage centralized resources and interference by the CP, but the limitation of the front hole connecting the distributed ANs to the CP should be considered. In particular, when densely distributed ANs are connected to the CP, front hole cost and power consumption are increased by the number of ANs. In order to enable smooth cooperative transmission between distributed ANs and to minimize the required capacity of the front hole, the present invention considers the functional division of the PHY layer. Function division in the PHY layer can be roughly divided into two types.

In the first PHY layer function segmentation, a digital beamforming function (eg, digital precoder) may be placed in the CP. In this case, in order to obtain an instantaneous CSI for the digital precoder, since the instantaneous CSI measured using the uplink pilot must be transmitted to the CP, a significant load may be generated in the front hole. However, interference between ANs can be minimized through instantaneous CSI information.

In the second PHY layer function division, the digital precoder and modulation block are placed in the local AN, and only the upper PHY functions can be placed in the CP. In this case, the instantaneous CSI for the digital precoder is required only at the local AN, so there is no need to transmit it to the CP through the front hole. However, a function of performing interference control between ANs may be additionally required in the CP.

Meanwhile, the carrier frequency of the wireless 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, in the millimeter wave system, a cost effective hybrid beamforming technique is essential. In a directional beam-based system, interference can be limited if correct beamforming is performed.

Accordingly, embodiments of the present invention provide a method and apparatus for providing services to terminals through cooperative transmission of ANs in a cell-shedding dense cloud-based RAN in which the second PHY layer function division is reflected. Embodiments of the present invention are based on hierarchical hybrid beamforming. In the embodiments of the present invention, since hybrid beamforming is performed in a distributed AN, the embodiments of the present invention can 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 functionally divided into AN and BN. Each of the distributed ANs is equipped with a large-scale array antenna and may have fewer RF chains than the number of antenna elements of the array antenna. Analog beams may be formed through an RF precoder composed of phase shifters that adjust phases of signals transmitted to a plurality of antenna elements connected to each RF chain. Further, each AN may include a digital precoder that controls interference between beams by using the formed analog beams. Except for the lower PHY functions of the AN, the upper PHY functions, the MAC layer functions, and the upper layer functions of the radio protocol stack are performed in the BN, and these BNs can be centralized and configured as a BN pool. Such a BN pool may be referred to as a centralized processor (CP). The distributed ANs and the centralized BNs are connected to the front hole. Compared to the case of using the existing RRH functionally divided at the RF level, since the PHY layer functional division considered in the embodiments of the present invention requires only relatively small fronthaul transmission capacity, compression of the fronthaul transmission signal is reduced. Fronthole transmission becomes possible only with 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 detailed description of embodiments of the present invention, AN l(

) The number of antennas

Is assumed, and the number of RF chains is

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

Is written as

Is assumed to be. Also, the terminal

The number of beams that can be simultaneously formed is

Is indicated by,

The terminal

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

If using a single omni or quasi-omni receiving beam having a large beam width, this is also the terminal

To limit the maximum number of ANs serving simultaneously

Assume the value.

The object to be achieved in the present invention is to provide services to terminals through cooperative transmission that minimizes interference between ANs distributed in a high-density form while using less front holes. The front hole 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, a global perfect CSI must be secured by sharing the local CSI (ie, local CSI) measured by individual ANs with other ANs. That is, in order to secure an accurate global CSI, the local CSI must be frequently shared through the front hole. In addition, for smooth cooperative transmission in which distributed ANs participate, data to be transmitted to the terminal must be shared with more ANs, and for this, consumption of more front holes 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 (). These statistical CSI, specific AN

And spatial channel covariance matrices of all terminals (ie,

), long-term channel statistics. Therefore, it is easy to estimate because the statistical CSI changes according to a long time scale compared to an instantaneous channel. In addition, since the 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., the CP) periodically or whenever the statistical CSI changes.

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

By limiting the range of terminals to be measured by the statistical CSI by, it is possible to further reduce front-hole consumption by measuring and reporting statistical CSI only for a limited range of terminals instead of all terminals. To this end, the information described in step S930 of FIG. 9 may be used.

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 illustrated in FIG. 9, CP is a central controller of the cloud RAN, and information on the number of RF chains that determine the number of terminals that can provide services to each of the distributed ANs at the same time, and each terminal simultaneously receives It also has information on the maximum number of beams that can be done. Hereinafter, an operation procedure of the CP in a state where 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, CP is a regional statistical CSI (notified from each of the ANs)

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

Statistical CSIs for each terminal of)

) In descending order, corresponding AN

The number of RF chains it provides (

Highest)

By selecting the terminal having

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

Of ANs providing services to customers

Can be configured. The set composed by CP

and

Should be satisfied. if

If is, CP is low

Terminal of value

Can remove the corresponding AN from the

on

Other next higher terminals can be added. if

If occurs, CP is the corresponding terminal

High

ANs with values

Can be added to and related accordingly

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

According to the similarity of the UEs, UEs belonging to the same group may be serviced by different ANs. Through the above function, CP is the terminal

A plurality of AN l (

) Can be selected, terminal

Data for

It can only be shared 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 the front hole as described above. CP is a regional statistical CSI notified by distributed ANs.

Collecting information to provide global statistical CSI

To build information and to set the transmission space for each AN to minimize interference with neighboring ANs, the global statistical CSI

The outer precoding matrix for each AN using the information can be calculated. Actually, the above-described external precoding matrix for each AN is information for setting the RF precoder of the corresponding AN, and is modified by reflecting the RF constraint of the RF precoder in the corresponding AN.

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 an external precoding matrix for each AN, an external precoding matrix may be derived through low-complexity non-repetitive block diagonalization. First, CP is a set of terminals served by AN i

Terminals belonging to

Against

Through eigen decomposition of

Can be obtained. Through this, CP can transmit space for AN l

And interfering space

It 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

It is the identifier of the terminal, the first element,

silver

Rank

Less than

A matrix of four major eigenvectors. Next, the interference 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 the singular decomposition of

The left eigenspace, consisting of the dog's weakest eigen modes,

It can be written as. In other words,

The

Weakest

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

To

Projection 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 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

Can be calculated. When each of the precoding vectors generates a matrix set as a column, an external precoding matrix for AN l

This can be derived. The points to be considered here are the dimension size of the transmission space of AN l and the front hole capacity. As described above, CP is the number of RF chains of AN l

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

The number of column vectors of can be adjusted (S1150). In addition, when it is determined that the interference is strong directly or indirectly through the 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 an external precoding matrix for AN l

By calculating, the transmission subspace of AN l is made to be matched to the signal channel of AN l while being orthogonal to the interfering signal space. CP is an external precoding vector calculated based on global statistical CSI information.

To

The information may be transmitted to the corresponding ANs (S1160). Thereafter, the CP terminal

Of ANs providing services to customers

Terminal through the front hall to the ANs belonging to

Data to be transmitted to the user (S1170).

Meanwhile, in FIG. 11, it has been described that the step of adjusting the transmission space size of AN 1 (S1150) is performed after steps S1160 and S1170. However, as described above, if it is determined that the interference is strong directly or indirectly through performance monitoring while performing step S1170, the CP can further adjust the transmission space size and provide relevant information to the ANs. Can be. That is, even during the execution of step S1170, if necessary, steps S1150 and S1160 may be re-executed.

Meanwhile, when the statistical CSI is periodically reported to the CP or the CP according to the change of the statistical CSI, it may be restarted from step S1110. That is, the external precoding matrix can be changed by the new global statistical CSI.

How the 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, an operation procedure of an AN performing hierarchical hybrid beamforming-based cooperative transmission in conjunction with a CP operating according to the procedure illustrated in FIG. 11 is illustrated.

)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.Referring to FIG. 12, AN l is all terminals k (

) Of statistical CSI information

Can be measured/estimated and reported to CP (S1210). AN l may report statistical CSI information periodically or at a time when statistical CSI information is changed in consideration of front-hole consumption. In addition, target terminals for which statistical CSI information is reported may be limited based on information such as received signal strength. That is, target terminals for which statistical CSI information is reported may be limited to terminals having a signal received with an intensity higher than a certain 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

Information about the may be received (S1220). Step S1220 is an operation step of AN 1 corresponding to the operation step S1160 of the CP described with reference to FIG. 11 above.

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 as many RF chains as the number of dimensions and configure an RF precoder composed of phase shifters connected to the RF chains (S1230). Recall the RF precoder that consists of only phase shifters.

In order to apply, CP

The size of each element of each

Set to constant, and the phase of each phase shifter

Phase of each element of

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

RF precoding matrix according to the following equation (4)

Should be changed to

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

Depending on the phase of each phase shifter of each RF chain can be set.

AN l can acquire a local instantaneous effective CSI that is dimensionally reduced from the antenna dimension to the RF chain dimension through the RF precoder, and based on this, conjugate (maximum-ratio transmission), zero forcing, and regularized zero forcing A linear digital precoder can be set (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 the digital precoder generated from the local instantaneous effective CSI obtained by the CP. After that, AN l

The data to be delivered to the terminals belonging to may be received from the CP, and the received data may be converted into a hierarchically hybrid beamformed signal and transmitted using the digital precoder and RF precoder (S1250). Subsequently, the AN l can report the local statistical CSI of all the terminals observable to the CP through the continuous channel measurement monitoring and the interference performance of the terminals in service (S1260). Through this, AN l has the number of active RF chains and accordingly

The CP is adjusted according to the control.

On the other hand, if AN l is periodically reported to the CP, the local statistical CSI, or is reported to the CP according to the change of the local statistical CSI, it may be restarted from step S1210. That is, the external precoding matrix can be changed by the new global statistical CSI.

The whole operating procedure of the system

Hereinafter, a procedure in which the distributed ANs (for example, AN i and AN j) and hierarchical hybrid beamforming in which the hierarchical hybrid beamforming is implemented and one CP perform cooperative transmission for the UE 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, the terminal k may transmit a random access channel through a beam sweeping method in a synchronized RACH interval set by the CP (S1310). Each AN and CP that have received the random access channel of the terminal k determines whether the corresponding AN can provide the service to the terminal k based on the signal strength of the received random access channel, and the terminal-specific uplink to the terminal k The pilot is allocated (S1320). In FIG. 13, a case is illustrated in which terminal k establishes a connection with AN i and AN j simultaneously. That is, FIG. 13 shows a case in which AN i and AN j are determined as a cluster providing a service to terminal 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, the terminal k periodically transmits the allocated uplink pilot (S1330; channel measurement is erased in the drawing step), and neighboring ANs including AN i and AN j are local based on the uplink pilot of the terminal k. Statistical CSI may be measured/estimated and reported to the CP (S1340). CP collects regional statistical CSIs reported from ANs to generate global statistical CSIs, and derives external precoding matrices for each AN that can control interference between ANs based on the global statistical CSIs to each of the ABs. It can be transmitted (S1350). At this time, set

,

And

Information about 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 step 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, sets the RF precoder, and uses the local instantaneous CSI obtained by itself. A digital precoder can be set (S1360). This is to minimize the interference between the terminals that they service by calculating the internal RF and digital hybrid precoding matrix again on each interference controlled transmission space defined by the external precoding matrix that AN i and AN j receive from the CP. It's like redefining the available transport space. Each of AN i and AN j may convert the data received from the CP into a precoded signal using the above-described digital precoder and RF precoder and transmit it to the terminal k (S1380). The terminal k receives interference-controlled data from AN i and AN j simultaneously.

Additionally, the terminal k feeds back HARQ information to AN i and AN j in the data reception process, and AN i and AN j can transmit interference-related performance monitoring information to the CP (S1380). 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 illustrating a 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. In addition, 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 mean 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 read only memory (ROM) and random access memory (RAM).

The methods according to the present invention may be implemented in the form of program instructions that can be executed through various computer means and recorded on a computer readable medium. Computer-readable media may include program instructions, data files, data structures, or 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 usable by those skilled in computer software.

Examples of computer-readable media include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include high-level language code that can be executed by a computer using an interpreter, etc., as well as machine code such as that produced by a compiler. The hardware device described above may be configured to operate with at least one software module to perform the operation of the present invention, and vice versa.

Although described with reference to the above embodiments, those skilled in the art understand 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 to.

Claims (20)

A method of operating a centralized processor (CP) for cooperative transmission based on hybrid beamforming,
Generating local statistical CSI by collecting local statistical channel state information (CSI) from each of access nodes (ANs) connected to the CP;
Configuring a set of first terminals to be provided by a first AN among the ANs based on the global statistical CSI;
Constructing a transmission signal space and an interference signal space for the first AN, and deriving an external precoding matrix defining an interference-controlled transmission signal space for the first AN based on the transmission signal space and the interference signal space To do; And
And transmitting the derived external precoding matrix to the first AN,
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 random access channel (RACH) section synchronized through the AN, and the first terminal transmits an RACH signal to the first AN through the RACH section, and the first 1 is allocated an uplink pilot from the AN,
How the central controller (CP) works. The method according to 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. The method according to claim 1,
The 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 a local instantaneous between the first AN and the first terminals. Set using the effective CSI,
How the central controller (CP) works. 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 the performance monitoring result; And
The method further includes transmitting an external precoding matrix corrected 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 transmitting data to the first AN,
The data is transmitted to the first terminals through 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. A method of operating a first access node (AN) for cooperative transmission based on hybrid beamforming,
Measuring local statistical channel state information (CSI) for neighboring terminals and reporting the measured local statistical CSI to a centralized processor (CP);
Receiving information on an external precoding matrix derived from the global statistical CSI generated from the local statistical CSI and a set of first terminals to be provided by the first AN from the CP; And
And setting a radio frequency (RF) precoder of the first AN based on the external precoding matrix,
Method of operation of the first access node. The method according to claim 8,
The regional statistical CSI is a spatial channel covariance matrix between the first AN and the neighboring terminals,
Method of operation of the first access node. The method according to claim 8,
The regional statistical CSI is periodically reported, or when the regional statistical CSI is changed,
Method of operation of the first access node. The method according to claim 8,
The neighboring UEs on which the regional statistical CSI is measured are limited to UEs that transmit signals received from the first AN with an intensity greater than a certain value.
Method of operation of the first access node. The method according to claim 8,
When the RF precoder includes only phase shifters, the size of each element of the external precoding matrix is set constant, and the phase of each of the phase shifters is the value of each element of the external precoding matrix. Set to phase,
Method of operation of the first access node. The method according to claim 8,
Further comprising the step of providing the configuration information for the synchronized random access channel (RACH) interval provided from the CP to the peripheral terminals,
The peripheral terminals transmit the RACH signal to the first AN through the RACH section, and are allocated an uplink pilot from the first AN,
Method of operation of the first access node. The method according to claim 13,
The regional statistical CSI between the peripheral terminals and the first AN is measured based on the uplink pilots,
Method of operation of the first access node. The method according to claim 8,
The digital precoder of the first AN is set using a local instantaneous effective CSI between the first AN and the first terminals,
Method of operation of the first access node. The method according to 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,
Method of operation of the first access node. A centralized processor (CP);
Access nodes (ANs) connected to the CP; And
Includes front hole links connecting the CP and the AN,
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 front hole link. , The first AN sets the RF precoder of the first AN based on the external precoding matrix, and the regional instantaneous validity between the first AN and the first terminals to which the first AN will provide service. Setting the digital precoder of the first AN based on the CSI,
System for cooperative transmission based on hybrid beamforming. The method according to claim 17,
The regional statistical CSI is a spatial channel covariance matrix between each of the ANs and terminals,
System for cooperative transmission based on hybrid beamforming. The method according to claim 17,
The CP and the AN are nodes that functionally divide the function of the base station in a physical layer,
System for cooperative transmission based on hybrid beamforming. The method according to claim 17,
The first AN converts data transmitted from the CP into a precoded signal using an RF precoder and a digital precoder of the first AN, and converts the precoded signal to the first AN among the ANs. Transmitting to the first terminal through cooperative transmission with at least one other AN,
System for cooperative transmission based on hybrid beamforming.

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