KR20220061907A - Method and apparatus for calibration of channel reciprocity in wireless communication system - Google Patents

Abstract

The present invention relates to a method and apparatus for calibrating channel reciprocity in a wireless communication system to easily perform calibration to secure or guarantee uplink/downlink channel reciprocity. According to one embodiment of the present invention, a channel reciprocity calibration method performed by a control node of a communication system comprises the following steps of: receiving channel measurement result information from a plurality of APs connected to a control node through a fronthaul; selecting one reference AP based on the information of the received channel measurement result; receiving, from the reference AP, information on a reference calibration coefficient for calibrating channel reciprocity for a channel with a UE; calculating a relative calibration coefficient for calibrating channel reciprocity with respect to a channel with the UE of each of the APs except for the reference AP among the plurality of APs on the basis of reference calibration coefficient information; and transmitting information on the calculated relative calibration coefficient to each of the APs except for the reference AP.

Description

Method and apparatus for correcting channel reciprocity in a wireless communication system

The present invention relates to a channel reciprocity correction technique in a wireless communication system, and more particularly, to a correction (reciprocity) for wireless channel reciprocity between wireless access points (APs) and terminals in a cell-free wireless network environment It relates to a channel reciprocity correction technique for efficiently performing calibration).

Recently, mobile data traffic has been increasing explosively. As a technology that can accommodate the increase in mobile traffic, a massive multiple input multiple output (MIMO) technology and an ultra-dense network (UDN) are being discussed. Massive MIMO may refer to a technology for providing a service to many users at the same time through a plurality of access nodes (APs) or base stations. Massive MIMO technology may have relatively high traffic throughput and reliability. On the other hand, in the large-scale MIMO technology, there may be some limitations in the transceiver due to the use of a large number of antennas in a plurality of APs or base stations, and the complexity of signal processing is high due to the multiplexing of communication with a plurality of UEs. There is a limiting factor that can.

The UDN may refer to a wireless environment in which a plurality of APs may exist in a location close to the terminal by increasing the density of APs with miniaturized cells. In UDN, as the distance between the APs providing services to the UEs and the UEs increases, pathloss may be greatly reduced, link performance may be improved, and network capacity may be increased. On the other hand, in UDN, there is a limiting factor that interference between adjacent cells may increase due to an increase in the distance between cells.

As a technology to overcome the limitations of large-scale MIMO and UDN, a cell-free massive MIMO (Cell-Free massive MIMO, CFmMIMO) system is being studied. The CFmMIMO system may have a characteristic of a distributed MIMO system in which an individual AP configured with one or more antennas provides a service to a small number of users distributed over a wide area. APs constituting the CFmMIMO system may provide services to terminals through cooperative communication using a centralized processor (CP).

In order to improve the performance of the CFmMIMO system, channel state information at each transmitter (Channel State Information at Transmitter, CSIT) may need to be accurately collected. For accurate CSIT collection, channel reciprocity of uplink/downlink may need to be secured or guaranteed. However, there is a problem that correction for channel reciprocity may not be easy in a large-scale MIMO system such as CFmMIMO.

Matters described in this background section are prepared to enhance understanding of the background of the invention, and may include matters that are not already known to those of ordinary skill in the art to which this technology belongs.

It is an object of the present invention to solve the above problems, and in a communication system to which CFmMIMO is applied, channel complementarity correction for easily performing correction to secure or guarantee channel reciprocity of uplink/downlink between wireless APs and terminals. To provide a method and apparatus.

A channel reciprocity correction method performed by a control node of a communication system according to an embodiment of the present invention for achieving the above object, from a plurality of access points (APs) connected to the control node by a fronthaul, Receiving information of a channel measurement result, selecting one reference AP based on the information of the received channel measurement result, From the reference AP, a channel with a user equipment (UE) of the reference AP Receiving information on a reference correction coefficient for correction of channel reciprocity with respect to, based on the information of the reference correction coefficient, each of the other APs except the reference AP among the plurality of APs for a channel with the UE The method may include calculating a relative correction coefficient for correction of channel reciprocity, and transmitting information on the calculated relative correction coefficient to each of APs other than the reference AP.

According to an embodiment of the present invention, in a communication system to which large-scale MIMO such as CFmMIMO is applied, one reference AP having high communication quality or reliability with the UE may be selected. The reference AP may calculate a reference correction coefficient for correction of channel reciprocity for a channel with the UE. The CP may receive information on the reference correction coefficient from the reference AP. The CP may calculate relative correction coefficients for the UEs of APs other than the reference AP based on the received reference correction coefficient information. If there is an AP having difficulty communicating with the reference AP among other APs other than the reference AP, a relative correction coefficient may be calculated based on an additionally selected auxiliary AP. Through this, all APs that are connected to the CP through the fronthaul and provide services to the UE can easily obtain a relative correction coefficient for correcting channel reciprocity with respect to a channel with the UE.

1 is a conceptual diagram illustrating an embodiment of a communication system.
2 is a block diagram illustrating an embodiment of a communication node constituting a communication system.
3 is a conceptual diagram for explaining an embodiment of a communication system to which CFmMIMO (Cell-Free massive multiple input multiple output) is applied.
4 is a conceptual diagram illustrating a first embodiment of a method for correcting channel reciprocity in a communication system.
5 is a conceptual diagram for explaining a second embodiment of a method for correcting channel reciprocity in a communication system.
6 is a conceptual diagram for explaining a third embodiment of a method for correcting channel reciprocity in a communication system.
7 is a flowchart illustrating a fourth embodiment of a method for correcting channel reciprocity in a communication system.

Since the present invention can have various changes and can have various embodiments, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Terms such as first, second, etc. 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.

In embodiments of the present application, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B”. Also, in the embodiments of the present application, “at least one of A and B” may mean “at least one of A or B” or “at least one of combinations of one or more of A and B”.

When an element is referred to as being “connected” or “connected” to another element, it is understood that it may be directly connected or connected to the other element, but other elements 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 should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical and 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

A communication system to which embodiments according to the present invention are applied will be described. The communication system to which the embodiments according to the present invention are applied is not limited to the content described below, and the embodiments according to the present invention can be applied to various communication systems. Here, a communication system may be used in the same sense as a communication network (network).

Throughout the specification, a network is, for example, a wireless Internet such as WiFi (wireless fidelity), a wireless broadband internet (WiBro) or a mobile Internet such as a world interoperability for microwave access (WiMax), a global system for mobile communication (GSM). ) or 2G mobile communication network such as CDMA (code division multiple access), WCDMA (wideband code division multiple access) or 3G mobile communication network such as CDMA2000, high speed downlink packet access (HSDPA) or high speed uplink packet access (HSUPA) such as It may include a 3.5G mobile communication network, a 4G mobile communication network such as a long term evolution (LTE) network or an LTE-Advanced network, and a 5G mobile communication network.

Throughout the specification, a terminal refers to a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, and an access terminal. and the like, and may include all or some functions of a terminal, a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, an access terminal, and the like.

Here, a desktop computer that can communicate with a terminal, a laptop computer, a tablet PC, a wireless phone, a mobile phone, a smart phone, a smart watch (smart watch), smart glass, e-book reader, PMP (portable multimedia player), portable game console, navigation device, digital camera, DMB (digital multimedia broadcasting) player, digital voice Digital audio recorder, digital audio player, digital picture recorder, digital picture player, digital video recorder, digital video player ) can be used.

Throughout the specification, a base station is an access point, a radio access station, a Node B, an advanced nodeB, a base transceiver station, MMR ( It may refer to mobile multihop relay)-BS, etc., and may include all or some functions of a base station, an access point, a radio access station, a Node B, an eNodeB, a transceiver base station, and an MMR-BS.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, in order to facilitate the overall understanding, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

1 is a conceptual diagram illustrating an embodiment of a communication system.

1, the communication system 100 is a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130-4, 130-5, 130-6). A plurality of communication nodes 4G communication (eg, long term evolution (LTE), LTE-A (advanced)), 5G communication (eg, NR (new radio)) defined in the 3rd generation partnership project (3GPP) standard ) can be supported. 4G communication may be performed in a frequency band of 6 GHz or less, and 5G communication may be performed in a frequency band of 6 GHz or more as well as a frequency band of 6 GHz or less.

For example, a plurality of communication nodes for 4G communication and 5G communication is a CDMA (code division multiple access) based communication protocol, WCDMA (wideband CDMA) based communication protocol, TDMA (time division multiple access) based communication protocol, FDMA (frequency division multiple access) based communication protocol, OFDM (orthogonal frequency division multiplexing) based communication protocol, Filtered OFDM based communication protocol, CP (cyclic prefix)-OFDM based communication protocol, DFT-s-OFDM (discrete) Fourier transform-spread-OFDM) based communication protocol, OFDMA (orthogonal frequency division multiple access) based communication protocol, SC (single carrier)-FDMA based communication protocol, NOMA (Non-orthogonal multiple access), GFDM (generalized frequency) Division multiplexing)-based communication protocol, FBMC (filter bank multi-carrier)-based communication protocol, UFMC (universal filtered multi-carrier)-based communication protocol, SDMA (Space Division Multiple Access)-based communication protocol, etc. can be supported. .

Also, the communication system 100 may further include a core network. When the communication system 100 supports 4G communication, the core network may include a serving-gateway (S-GW), a packet data network (PDN)-gateway (P-GW), and a mobility management entity (MME). there is. When the communication system 100 supports 5G communication, the core network may include a user plane function (UPF), a session management function (SMF), an access and mobility management function (AMF), and the like.

On the other hand, a plurality of communication nodes (110-1, 110-2, 110-3, 120-1, 120-2, 130-1, 130-2, 130-3, 130- 4, 130-5, 130-6) may each have the following structure.

2 is a block diagram illustrating an embodiment of a communication node constituting a communication system.

Referring to FIG. 2 , the communication node 200 may include at least one processor 210 , a memory 220 , and a transceiver 230 connected to a network to perform communication. In addition, the communication node 200 may further include an input interface device 240 , an output interface device 250 , a storage device 260 , and the like. Each of the components included in the communication node 200 may be connected by a bus 270 to communicate with each other.

However, each of the components included in the communication node 200 may not be connected to the common bus 270 but to the processor 210 through an individual interface or an individual bus. For example, the processor 210 may be connected to at least one of the memory 220 , the transceiver 230 , the input interface device 240 , the output interface device 250 , and the storage device 260 through a dedicated interface. .

The processor 210 may execute a program command stored in at least one of the memory 220 and the storage device 260 . The processor 210 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 220 and the storage device 260 may be configured as at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 220 may be configured as at least one of a read only memory (ROM) and a random access memory (RAM).

Referring back to FIG. 1 , the communication system 100 includes a plurality of base stations 110 - 1 , 110 - 2 , 110 - 3 , 120 - 1 and 120 - 2 , and a plurality of terminals 130 - 1, 130-2, 130-3, 130-4, 130-5, 130-6). Base stations 110-1, 110-2, 110-3, 120-1, 120-2 and terminals 130-1, 130-2, 130-3, 130-4, 130-5, 130-6 The comprising communication system 100 may be referred to as an “access network”. Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may form a macro cell. Each of the fourth base station 120-1 and the fifth base station 120-2 may form a small cell. The fourth base station 120-1, the third terminal 130-3, and the fourth terminal 130-4 may belong to the cell coverage of the first base station 110-1. The second terminal 130-2, the fourth terminal 130-4, and the fifth terminal 130-5 may belong to the cell coverage of the second base station 110-2. The fifth base station 120-2, the fourth terminal 130-4, the fifth terminal 130-5, and the sixth terminal 130-6 may belong to the cell coverage of the third base station 110-3. there is. The first terminal 130-1 may belong to the cell coverage of the fourth base station 120-1. The sixth terminal 130-6 may belong to the cell coverage of the fifth base station 120-2.

Here, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, 120-2 is a NodeB (NodeB), an advanced NodeB (evolved NodeB), a BTS (base transceiver station), Radio base station (radio base station), radio transceiver (radio transceiver), access point (access point), access node (node), RSU (road side unit), RRH (radio remote head), TP (transmission point), TRP ( transmission and reception ooint), eNB, gNB, and the like.

Each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, 130-6 is a user equipment (UE), a terminal, an access terminal, and a mobile Terminal (mobile terminal), station (station), subscriber station (subscriber station), mobile station (mobile station), portable subscriber station (portable subscriber station), node (node), device (device), Internet of Things (IoT) It may be referred to as a device, a mounted device (such as a mounted module/device/terminal or on board device/terminal).

Meanwhile, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may operate in different frequency bands or may operate in the same frequency band. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to each other through an ideal backhaul link or a non-ideal backhaul link. , information can be exchanged with each other through an ideal backhaul link or a non-ideal backhaul link. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be connected to the core network through an ideal backhaul link or a non-ideal backhaul link. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits a signal received from the core network to the corresponding terminals 130-1, 130-2, 130-3, 130 -4, 130-5, 130-6), and a signal received from the corresponding terminal (130-1, 130-2, 130-3, 130-4, 130-5, 130-6) is transmitted to the core network can be sent to

In addition, each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 transmits MIMO (eg, single user (SU)-MIMO, multi user (MU)- MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) transmission, carrier aggregation (CA) transmission, transmission in an unlicensed band, device to device communication (D2D) (or, ProSe ( proximity services)), and the like. Here, each of the plurality of terminals 130-1, 130-2, 130-3, 130-4, 130-5, 130-6 is the base station 110-1, 110-2, 110-3, and 120-1. , 120-2) and corresponding operations, and operations supported by the base stations 110-1, 110-2, 110-3, 120-1, and 120-2 may be performed. For example, the second base station 110-2 may transmit a signal to the fourth terminal 130-4 based on the SU-MIMO method, and the fourth terminal 130-4 may transmit a signal based on the SU-MIMO method. A signal may be received from the second base station 110 - 2 . Alternatively, the second base station 110 - 2 may transmit a signal to the fourth terminal 130 - 4 and the fifth terminal 130 - 5 based on the MU-MIMO scheme, and the fourth terminal 130 - 4 . and each of the fifth terminals 130 - 5 may receive a signal from the second base station 110 - 2 by the MU-MIMO method.

Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 may transmit a signal to the fourth terminal 130-4 based on the CoMP scheme, and the fourth The terminal 130-4 may receive signals from the first base station 110-1, the second base station 110-2, and the third base station 110-3 by the CoMP method. Each of the plurality of base stations 110-1, 110-2, 110-3, 120-1, and 120-2 is a terminal 130-1, 130-2, 130-3, 130-4 belonging to its own cell coverage. , 130-5, 130-6) and the CA method can transmit and receive signals. Each of the first base station 110-1, the second base station 110-2, and the third base station 110-3 controls D2D between the fourth terminal 130-4 and the fifth terminal 130-5. and each of the fourth terminal 130-4 and the fifth terminal 130-5 may perform D2D under the control of the second base station 110-2 and the third base station 110-3, respectively. .

Next, methods for correcting channel reciprocity in a wireless communication system will be described. Here, even when a method (eg, transmission or reception of a signal) performed in a first communication node among communication nodes is described, a second communication node corresponding thereto is a method corresponding to the method performed in the first communication node (eg, receiving or transmitting a signal). For example, when the operation of the reception node is described, the corresponding transmission node may perform the operation corresponding to the operation of the reception node. Conversely, when the operation of the transmitting node is described, the corresponding receiving node may perform the operation corresponding to the operation of the transmitting node.

3 is a conceptual diagram for explaining an embodiment of a communication system to which CFmMIMO (Cell-Free massive multiple input multiple output) is applied.

Referring to FIG. 3 , the communication system 300 may include a plurality of communication nodes. The communication system 300 may be a communication system to which CFmMIMO (Cell-Free massive multiple input multiple output) is applied. The communication system 300 may include one or more centralized processors (CPs), one or more access points (APs), and one or more user equipments (UEs). In FIG. 3 , the communication system 300 includes one CP, M APs (AP 1, ..., AP m, ..., AP M), and K UEs (UE 1, ..., UE). k, ..., UE K) can be seen as illustrated. However, this is only an example for convenience of description, and the embodiment of the present invention is not limited thereto.

은

일 수 있고, UE들의 집합

는

일 수 있다. 채널 측정을 통하여, AP들 각각과 UE들 각각 간의 통신 품질에 대한 정보가 획득될 수 있다. 이를테면, AP m 및 UE k 간의 통신 품질에 대한 정보는 g_mk와 같이 표현될 수 있다.In the communication system 300 to which CFmMIMO is applied, the base station is equipped with one CP and one or more antennas instead of having a large-scale antenna at one point, and M number of APs (AP 1, ..., AP) connected to the CP m, ..., AP M) may be configured in a geographically distributed form. M APs (AP 1, ..., AP m, ..., AP M) cooperate with K UEs (UE 1, ..., UE k, ..., UE K) that are distributed communication can be performed. set of APs

silver

may be, a set of UEs

Is

can be Through channel measurement, information on communication quality between each of the APs and each of the UEs may be obtained. For example, information on communication quality between AP m and UE k may be expressed as g _mk .

Specifically, the CP is a plurality of distributed APs (AP 1, ..., AP m, ..., AP M) through a plurality of distributed terminals or UEs (UE 1, ... , UE k, ..., UE K) may support or control the operation of providing a service. The CP may be connected to distributed APs (AP 1, ..., AP m, ..., AP M) through a wired or wireless fronthaul. CP is through distributed APs (AP 1, ..., AP m, ..., AP M) connected by fronthaul, UEs (UE 1, ..., UE k, ..., UE K) can provide services to For example, the CP transmits data to be transmitted to the UEs (UE 1, ..., UE k, ..., UE K) to the distributed APs (AP 1, ..., AP m, ... , AP M). On the other hand, the CP is connected to the APs (AP 1, ..., AP m, ..., AP M) from the distributed APs (AP 1, ..., AP m, ..., AP M). Channel statistics information for all UEs (UE 1, ..., UE k, ..., UE K) may be transmitted. The CP is based on the channel statistics information received from the distributed APs (AP 1, ..., AP m, ..., AP M), the APs (AP 1, ..., AP m, ... , AP M) may control the transmit power used by each of the UEs (UE 1, ..., UE k, ..., UE K) to provide a service.

일 수 있다.Each of the APs (AP 1, ..., AP m, ..., AP M) may be connected to the CP by a fronthaul. Each of the APs (AP 1, ..., AP m, ..., AP M) may include one or more antennas and/or one or more radio frequency (RF) devices. Each of the APs (AP 1, ..., AP m, ..., AP M) is each of the UEs (UE 1, ..., UE k, ..., UE K) through cooperation with one or more other APs. can provide services to APs (AP 1, ..., AP m, ..., AP M) UEs (UE 1, ..., UE k, ..., UE K) capable of providing a service through cooperative communication ) may be smaller than the number of APs. in other words,

can be

Each of the UEs (UE 1, ..., UE k, ..., UE K) transmits a predetermined pilot signal to the APs (AP 1, ..., AP m, ..., AP M) through an uplink. ) can be sent to Based on the pilot signal transmitted by each of the UEs (UE 1, ..., UE k, ..., UE K), APs (AP 1, ..., AP m, ..., AP M) may obtain channel information for each of the UEs (UE 1, ..., UE k, ..., UE K) based on the channel reciprocity. Each of the UEs (UE 1, ..., UE k, ..., UE K) is a signal including downlink data from the APs (AP 1, ..., AP m, ..., AP M). can receive

In order to improve the performance of the CFmMIMO system, channel state information at each transmitter (Channel State Information at Transmitter, CSIT) may need to be accurately collected. For accurate CSIT collection, channel reciprocity of uplink/downlink may need to be secured or guaranteed. However, there is a problem that correction for channel reciprocity may not be easy in a large-scale MIMO system such as CFmMIMO.

Specifically, in an embodiment of the CSIT measurement method, a 'pilot signal', which is a predetermined pattern known to each other by the transmitting node and the receiving node, may be transmitted for each antenna. For example, in the case of downlink communication, when all antennas on the side of the base station or APs sequentially transmit downlink pilot signals, UEs may perform channel measurement based on the received pilot signal. CSIT may be measured by the UEs transmitting the channel measurement result in uplink. However, such a CSIT measurement method may not be easy to operate or realize in a large-scale MIMO system.

An embodiment of a communication system to which large-scale MIMO is applied may operate in a Time Division Duplex (TDD) mode. In the TDD mode, it can be expected that the channel state measured in the uplink is applied to the downlink by channel reciprocity or channel duality. In the TDD mode, channel reciprocity may be assumed on the premise that an over-the-air (OTA) radio channel of an uplink and an OTA radio channel of a downlink are the same within a channel coherence time.

Under the assumption of channel reciprocity, the base station or APs may obtain channel state information (CSI) based on an uplink pilot signal transmitted from the UE, and may recover uplink data transmitted from the UE based on the obtained CSI. there is. Meanwhile, the base station or APs may transmit downlink data by preprocessing or precoding the downlink data by using CSI obtained based on the uplink pilot signal as the CSIT.

On the other hand, in wireless communication, in the channel experienced by the communication node or the digital baseband processor of the communication node, not only the OTA channel, but also analog devices such as DAC (Digital-Analogue Converter) and ADC (Analog-Digital Converter), RF frequency processing The characteristics of hardware such as a modem, a power amplifier (PA), and a low-noise amplifier (LNA) may all be reflected. However, in general, the transceiver analog element or RF hardware of each communication node may not be the same. That is, from the viewpoint of digital signal processing, it may be difficult to expect channel reciprocity even in TDD mode. In other words, if hardware-related asymmetry between the transmitting node/receiving node is not taken into account, inaccuracy may occur in CSIT estimation, and as a result, downlink communication performance may be deteriorated.

4 is a conceptual diagram illustrating a first embodiment of a method for correcting channel reciprocity in a communication system.

Referring to FIG. 4 , the communication system 400 may include a plurality of communication nodes. The communication system 400 may include one or more access points (APs) and one or more user equipments (UEs). The communication system 400 may be the same as or similar to the communication system 300 to which the CFmMIMO described with reference to FIG. 3 is applied. The one or more APs may be the same as or similar to the APs (AP 1, ..., AP m, ..., AP M) described with reference to FIG. 3 . One or more UEs may be the same as or similar to the UEs (UE 1, ..., UE k, ..., UE K) described with reference to FIG. 3 . In FIG. 4 , the communication system 400 can be seen as showing an embodiment including three APs ( B ₁ , B ₂ , B ₃ ), and one UE (M ₁ ). However, this is only an example for convenience of description, and the embodiment of the present invention is not limited thereto. Hereinafter, in describing the first embodiment of the method for correcting channel reciprocity with reference to FIG. 4 , content overlapping with those described with reference to FIGS. 1 to 3 may be omitted.

In the communication system 400 to which CFmMIMO is applied, the base station may provide a service to the UE (M ₁ ) through the first to third APs (B ₁ , B ₂ , B ₃ ). APs ( B ₁ , B ₂ , B ₃ ) may provide a service to UE ( M ₁ ) based on cooperative communication. The communication system 400 may further include a CP (not shown) for controlling or supporting the operation of the APs B ₁ , B ₂ , and B ₃ . In order to improve communication performance between the APs (B ₁ , B ₂ , B ₃ ) and the UE (M ₁ ), channel reciprocity of uplink/downlink may need to be secured or guaranteed. In order to secure channel reciprocity of uplink/downlink, it may be required to correct not only reciprocity of OTA channels but also channel characteristics in which hardware characteristics are reflected.

일 수 있다. 하지만, 통신 노드 A 및 통신 노드 B 각각의 송신기 특성(t_A, t_B)과 수신기 특성(r_A, r_B)이 서로 동일하지 않을 수 있기 때문에, OTA 채널에 송신기 특성 및 수신기 특성이 부가된 기저대역 관점에서의 채널은 서로 달라지게 될 수 있다. 이를테면, 통신 노드 A가 송신 노드이고 통신 노드 B가 수신 노드일 때의 기저대역 관점에서의 채널은 수학식 1과 같이 표현될 수 있다.Specifically, the physical OTA channel between the communication node A and the communication node B may be expressed as h _AB and h _BA . The OTA channels h _AB and h _BA can be expected to be equal or approximate. in other words,

can be However, since the transmitter characteristics (t _A , t _B ) and receiver characteristics (r _A , r _B ) of communication node A and communication node B may not be identical to each other, the transmitter characteristics and receiver characteristics are added to the OTA channel. Channels from a baseband point of view may be different from each other. For example, when the communication node A is a transmission node and the communication node B is a reception node, a channel in the baseband perspective can be expressed as Equation (1).

Meanwhile, when the communication node B is the transmission node and the communication node A is the reception node, the channel in the baseband point of view can be expressed as Equation (2).

, 및 수학식 2와 같이 표현된

는 서로 동일 또는 근사하지 않을 수 있다. 여기서, 따라서, 채널 상호성을 달성 또는 복원하기 위하여는

및

간의 차이를 보상하기 위한 보정(Calibration) 기술이 필요할 수 있다. 한편,

및

에는 노이즈의 영향을 반영하는 성분이 더 추가될 수 있다.expressed as Equation 1

, and expressed as Equation 2

may not be equal to or approximate to each other. Here, thus, in order to achieve or restore channel reciprocity,

and

A calibration technique may be required to compensate for the difference between the two. Meanwhile,

and

A component that reflects the influence of noise may be further added.

As a method for securing channel reciprocity between the first to third APs (B ₁ , B ₂ , B ₃ ) and the UE (M ₁ ) in an embodiment of the communication system 400 shown in FIG. 4 , the first AP (B ₁ ) Channel reciprocity between the UE (M ₁ ), the channel reciprocity between the second AP (B ₂ ) and the UE (M ₁ ), and the channel reciprocity between the third AP (B ₃ ) and the UE (M ₁ ) are corrected, respectively method can be used.

For example, the UE (M ₁ ) may transmit a predetermined uplink pilot signal to the first to third APs ( B ₁ , B ₂ , B ₃ ). The first to third APs (B ₁ , B ₂ , B ₃ ) may estimate or measure an uplink channel based on an uplink pilot signal transmitted from the UE ( M ₁ ). For example, the uplink channel information estimated by the first to third APs (B ₁ , B ₂ , B ₃ ) may be the same as or similar to Equation (3).

In the uplink channel estimate expressed as in Equation 3, it can be seen that the effect of noise is omitted for convenience of description. The first to third APs (B ₁ , B ₂ , B ₃ ) may sequentially transmit a downlink pilot signal to the UE (M ₁ ). The uplink channel can be estimated as in Equation (3). The UE (M ₁ ) is the first to third APs (B ₁ , B ₂ , B ₃ ) based on the downlink pilot signals sequentially received from each of the first to third APs (B ₁ , B ₂ , B ) ₃ ) It is possible to estimate or measure a downlink channel with each. The UE (M ₁ ) feeds back information on the downlink channel estimation results for the first to third APs (B ₁ , B ₂ , B ₃ ) to the first to third APs (B ₁ , B ₂ , B ₃ ). can do. The first to third APs (B ₁ , B ₂ , B ₃ ) may obtain a downlink channel estimate with the UE ( M ₁ ) based on the information fed back from the UE ( M ₁ ). For example, the downlink channel estimate values obtained by the first to third APs (B ₁ , B ₂ , B ₃ ) may be the same as or similar to Equation (4).

), 제1 내지 제3 AP(B₁, B₂, B₃)는 채널 상호성의 보정을 위한 보정 계수를 수학식 5와 동일 또는 유사하게 계산할 수 있다.In the downlink channel estimate expressed as in Equation 4, it can be seen that the effect of noise is omitted for convenience of description. The first to third APs (B ₁ , B ₂ , B ₃ ) may calculate a correction coefficient for correcting channel reciprocity based on the same or similar uplink/downlink channel estimation values as in Equations 3 and 4 . For example, assuming that there is channel reciprocity in the OTA channel (i.e.,

), and the first to third APs ( B ₁ , B ₂ , B ₃ ) may calculate a correction coefficient for correction of channel reciprocity in the same way as in Equation 5 or similarly.

Thereafter, the first to third APs ( B ₁ , B ₂ , B ₃ ) may obtain an estimated value of a downlink channel based on the estimated value of the uplink channel without a separate downlink channel estimation operation. This may be the same as or similar to Equation (6).

However, in a system to which large-scale MIMO having a large total number of antennas of base stations or APs, such as CFmMIMO, is applied, overhead and computational resources required for a signal transmission/reception procedure for operations such as Equations 3 to 6 may become excessively large. . Accordingly, the efficiency of the communication system 400 may be reduced.

In another embodiment of the communication system 400, one reference AP or reference antenna may be selected for channel reciprocity correction. First, a correction coefficient (hereinafter, a 'reference correction coefficient') for correction of channel reciprocity may be calculated based on a reference AP or a reference antenna, and the remaining correction coefficients may be calculated or estimated based on the reference correction coefficient.

와 동일 또는 유사할 수 있다. 제1 AP(B₁)는 획득된 보정 계수

에 기초하여, UE(M₁)와의 채널 상호성의 보정을 수행할 수 있다. 기준 AP인 제1 AP(B₁)가 획득한 보정 계수

는 '기준 보정 계수'와 같이 칭할 수 있다. For example, a first AP (B ₁ ) from among the first to third APs (B ₁ , B ₂ , B ₃ ) may be selected as the reference AP. The first AP(B ₁ ) may obtain a correction coefficient for correcting channel reciprocity based on a pilot signal transmission/reception operation with the UE(M ₁ ). Referring to Equation 5, the correction coefficient obtained by the first AP (B ₁ ) is

may be the same as or similar to The first AP (B ₁ ) is the obtained correction coefficient

Based on , correction of channel reciprocity with the UE (M ₁ ) may be performed. A correction factor obtained by the first AP (B ₁ ), which is the reference AP

may be referred to as a 'reference correction coefficient'.

에 기초하여, 채널 상호성 보정을 위한 보정 계수를 상대적으로 계산할 수 있다. 기준 보정 계수에 기초하여 상대적으로 계산되는 보정 계수를, '상대 보정 계수'와 같이 칭할 수 있다. 상대 보정 계수의 계산을 위하여, 먼저 제2 및 제3 AP(B₂, B₃)는 제1 AP(B₁)와의 채널에서의 채널 상대성의 보정을 위한 보정 계수를 계산할 수 있다. 이를 위하여, 제2 및 제3 AP(B₂, B₃)는 제1 AP(B₁)와의 파일럿 신호 송수신을 수행할 수 있다. 제2 및 제3 AP(B₂, B₃)는 제1 AP(B₁) 간의 파일럿 신호 송수신은, 데이터 통신과 무관하게 백그라운드로 수행될 수 있다. 제2 및 제3 AP(B₂, B₃)와 제1 AP(B₁) 간의 파일럿 신호 송수신 동작에 기초하여, 제2 및 제3 AP(B₂, B₃)와 제1 AP(B₁) 간의 채널 상대성의 보정을 위한 보정 계수가 수학식 7과 동일 또는 유사하게 계산될 수 있다.The second and third APs (B ₂ , B ₃ ) are the reference correction factors

Based on , a correction coefficient for channel reciprocity correction may be relatively calculated. A correction coefficient that is relatively calculated based on the reference correction coefficient may be referred to as a 'relative correction coefficient'. In order to calculate the relative correction coefficient, first, the second and third APs (B ₂ , B ₃ ) may calculate a correction coefficient for correction of channel relativity in a channel with the first AP(B ₁ ). To this end, the second and third APs (B ₂ , B ₃ ) may perform pilot signal transmission/reception with the first AP (B ₁ ). The second and third APs (B ₂ , B ₃ ) transmit and receive pilot signals between the first APs ( B ₁ ), and may be performed in the background regardless of data communication. Based on the pilot signal transmission/reception operation between the second and third APs (B ₂ , B ₃ ) and the first AP(B ₁ ), the second and third APs (B ₂ , B ₃ ) and the first AP (B ₁ ) ) A correction coefficient for correcting the channel relativity between

에 기초하여, 수학식 8과 동일 또는 유사하게 계산될 수 있다.The relative correction factor is Equation 7 and the reference correction factor

Based on Equation (8), it can be calculated in the same way or similarly to Equation (8).

Based on the relative correction coefficient calculated as in Equation 8, the second and third APs (B ₂ , B ₃ ) may perform channel reciprocity correction with the UE(M ₁ ).

5 is a conceptual diagram for explaining a second embodiment of a method for correcting channel reciprocity in a communication system.

Referring to FIG. 5 , a communication system 500 may include a plurality of communication nodes. The communication system 500 may include one or more access points (APs) and one or more user equipment (UEs). The communication system 500 may be the same as or similar to the communication system 400 described with reference to FIG. 4 . The one or more APs may be the same as or similar to the APs B ₁ , B ₂ , and B ₃ described with reference to FIG. 4 . One or more UEs may be the same as or similar to the UE (M ₁ ) described with reference to FIG. 4 . In FIG. 5 , it can be seen that an embodiment in which the communication system 500 includes 12 APs (B ₁ , ..., B ₁₂ ), and one UE (M ₀ ) is illustrated. However, this is only an example for convenience of description, and the embodiment of the present invention is not limited thereto. Hereinafter, in describing the second embodiment of the method for correcting channel reciprocity with reference to FIG. 5 , content overlapping with those described with reference to FIGS. 1 to 4 may be omitted.

In the communication system 500 to which CFmMIMO is applied, the base station may provide a service to the UE (M ₀ ) through at least some of the 12 APs (B ₁ , ..., B ₁₂ ). APs (B ₁ , ..., B ₁₂ ) may provide a service to UE (M ₀ ) based on cooperative communication. The communication system 500 may further include a CP (not shown) for controlling or supporting the operation of the APs B ₁ , ..., B ₁₂ . The CP and/or APs (B ₁ , ..., B ₁₂ ) may perform operations for correction of channel reciprocity between the APs (B ₁ , ..., B ₁₂ ) and the UE (M ₀ ). there is.

At least one AP among the 12 APs (B ₁ , ..., B ₁₂ ) may periodically or aperiodically transmit a pilot signal so that other APs may perform channel measurement. To this end, the CP is selected from among the 12 APs connected through the fronthaul. At least one AP (hereinafter, referred to as a pilot AP) to transmit a pilot signal to other APs may be selected. The CP may set information such as a time point or period when at least one pilot AP transmits a pilot signal to other APs. The CP may transmit a signal including information on the selected pilot AP to the pilot AP and/or APs other than the pilot AP.

The pilot AP may recognize that it has been selected as the pilot AP based on a signal transmitted from the CP. The pilot AP may check information such as a time point or period for transmitting a pilot signal to other APs based on a signal transmitted from the CP. The pilot AP may transmit a pilot signal to other APs based on the identified information. APs other than the pilot AP may receive a signal transmitted from the pilot AP. APs other than the pilot AP may perform channel estimation based on a signal transmitted from the pilot AP. Each of the APs other than the pilot AP may transmit or report information on the channel estimation result to the CP.

In an embodiment of the communication system, the CP may control all APs connected through the fronthaul to sequentially operate as pilot APs. Alternatively, in another embodiment of the communication system, the CP may control only some of the APs connected through the fronthaul to sequentially operate as pilot APs.

CP is based on information transmitted from APs other than the pilot AP. At least one table can be configured and managed. For example, when the total number of APs is M, the CP may configure and manage a table identical to or similar to Table 1 based on information transmitted from APs other than the pilot AP.

Table 1 may correspond to a table recording instantaneous values for channel states of respective channels between APs. When a specific AP transmits a pilot signal as a pilot AP at a specific time, other APs may transmit channel state information to the CP based on the received pilot signal, and accordingly, components in a corresponding row in Table 1 are newly measured. It can be updated with information of the channel state. For example, when the second AP(B ₂ ) transmits a pilot signal as a pilot AP at a specific time, the remaining APs except for the second AP(B ₂ ) are channel measurement results based on the pilot signal from the second AP(B ₂ ) By reporting to the CP, the components of the second row from the top of Table 1 ('From B ₂ ' row) can be updated with information on the newly measured channel state.

Meanwhile, the CP may configure and manage a table identical to or similar to Table 2 based on information transmitted from APs other than the pilot AP.

Table 2 may correspond to a table recording an average value of instantaneous values for each channel state of channels between APs. When a specific AP transmits a pilot signal as a pilot AP at a specific time, other APs may transmit channel state information to the CP based on the received pilot signal. Accordingly, in Table 2, components in a corresponding row are newly measured. It may be updated as an average value of instantaneous values up to a corresponding point in time including information on the channel state. For example, when the second AP(B ₂ ) transmits a pilot signal as a pilot AP at a specific time, the remaining APs except for the second AP(B ₂ ) are channel measurement results based on the pilot signal from the second AP(B ₂ ) By reporting to the CP, the components of the second row from the top of Table 2 ('From B ₂ ' row) may be updated with an average value of instantaneous values up to a corresponding point in time including the newly measured channel state information.

The UE (M ₀ ) may periodically or aperiodically transmit the uplink pilot signal a plurality of times. The uplink pilot signal may be transmitted in a broadcast manner. Each of the APs (B ₁ , ..., B ₁₂ ) performs channel measurement on a wireless communication channel with the UE (M ₀ ) based on an uplink pilot signal received from the UE (M ₀ ). can do. APs (B ₁ , ..., B ₁₂ ) may report a channel measurement result for a channel with the UE (M ₀ ) to the CP. The CP may select one AP having the best channel state with the UE (M ₀ ) based on the channel measurement results reported from the APs (B ₁ , ..., B ₁₂ ). For example, the CP may select the second AP ( _{B 2} ) having the best channel state with the UE (M ₀ ) among the APs (B ₁ , ..., B ₁₂ ) as the reference AP (BR ) (that is, , B ₂ =B _R ). The CP may transmit a signal including information indicating that the second AP (B ₂ ) is selected as the reference AP. Alternatively, the CP may transmit a signal including information indicating that the second AP (B ₂ ) is selected as the reference AP to the second AP (B ₂ ). Alternatively, the CP may transmit a signal including information indicating that the second AP (B ₂ ) is selected as the reference AP to all the APs (B ₁ , ..., B ₁₂ ). Alternatively, the CP may transmit a signal including information indicating that the second AP( _{B 2} ) is selected as the reference AP(BR) in a broadcast manner.

을 획득할 수 있다. 기준 AP(B_R)는 UE(M₀)로 하향링크 파일럿 신호를 전송할 수 있다. UE(M₀)는 기준 AP(B_R)로부터 전송된 하향링크 파일럿 신호에 기초하여, 기준 AP(B_R)와의 하향링크 채널에 대한 채널 측정을 수행할 수 있다. UE(M₀)는 채널 측정의 결과를 기준 AP(B_R)로 피드백할 수 있다. 기준 AP(B_R)는 UE(M₀)로부터 피드백된 채널 측정의 결과에 기초하여, 하향링크 채널의 추정값

을 획득할 수 있다. 기준 AP(B_R)는 획득된 상향링크 채널의 추정값

및 하향링크 채널의 추정값

에 기초하여, UE(M₀)와의 채널에 대한 채널 상호성의 보정을 위한 기준 보정 계수

를 계산할 수 있다. 이를테면, 기준 보정 계수

는 수학식 9와 동일 또는 유사하게 계산될 수 있다.The reference AP(BR) may receive an uplink pilot signal transmitted from the UE( _{M 0} ). The reference AP(BR) may perform channel measurement for an uplink channel with the UE( _{M 0} ) based on an uplink pilot signal transmitted from the UE(M ₀ ). The reference AP( _BR ) is an estimate of the uplink channel based on the channel measurement result.

can be obtained. The reference AP(BR) may transmit a downlink pilot signal to the UE( _{M 0} ). The UE( _{M 0} ) may perform channel measurement for a downlink channel with the reference AP( _BR ) based on a downlink pilot signal transmitted from the reference AP(BR). The UE( _{M 0} ) may feed back the result of the channel measurement to the reference AP(BR ). The reference AP(BR) is an estimate of the downlink channel based on the result of the channel measurement fed back from the UE( _{M 0} ).

can be obtained. Reference AP( _BR ) is an estimate of the acquired uplink channel

and an estimate of the downlink channel.

Based on , the reference correction coefficient for the correction of the channel reciprocity for the channel with the UE (M ₀ )

can be calculated. For example, the reference correction factor

may be calculated the same as or similar to Equation (9).

의 정보를 CP로 전송할 수 있다. CP는 기준 AP(B_R)를 제외한 다른 AP들(B₁, B₃, ..., B₁₂)의, UE(M₀)에 대한 상대 보정 계수 계산 절차를 수행할 수 있다. 통신 시스템(500)의 일 실시예에서, CP는 표 1에서와 같이 구성 및 관리된 AP들 간의 채널 상태의 정보에 기초하여, 상대 보정 계수 계산 절차를 수행할 수 있다. CP는 기준 AP(B_R)를 제외한 다른 AP들(B₁, B₃, ..., B₁₂)로부터 보고된 기준 AP(B_R)와의 채널 상태의 정보에 기초하여, 기준 AP(B_R)를 제외한 다른 AP들(B₁, B₃, ..., B₁₂)의 기준 AP(B_R)에 대한 상대 보정 계수를 계산할 수 있다. 이를테면, CP는 기준 AP(B_R)를 제외한 다른 AP들(B₁, B₃, ..., B₁₂)의 기준 AP(B_R)에 대한 상대 보정 계수를 수학식 10과 같이 계산할 수 있다.Reference AP(B _R ) is the calculated correction factor

of information can be transmitted to the CP. The CP may perform a relative correction coefficient calculation procedure for the UE(M ₀ ) of the other APs ( _{B 1} , B ₃ , ..., B ₁₂ ) except for the reference AP(BR ). In an embodiment of the communication system 500 , the CP may perform a relative correction factor calculation procedure based on the information on the channel state between the configured and managed APs as shown in Table 1. CP is based on the information of the channel state with the reference AP (BR) reported from other APs ( _{B 1} , B ₃ , ..., _{B 12} ) except the reference AP ( _BR ), the reference AP (BR ) A relative correction coefficient with respect to the reference AP(BR) of the other APs ( _{B 1} , B ₃ , ..., B ₁₂ ) except for ) may be calculated. For example, the CP may calculate the relative correction coefficient for the reference AP(BR) of the other APs ( _{B 1} , B ₃ , ..., _{B 12} ) except the reference AP(BR ) as in Equation 10. .

CP is relative to the UE(M ₀ ) of other APs (B ₁ , B ₃ , ..., _{B 12} ) except for the reference AP(BR ), based on the relative correction coefficient calculated as in Equation 10. A correction factor can be calculated. For example, the CP may calculate the relative correction coefficient for the UE(M ₀ ) of the other APs ( _{B 1} , B ₃ , ..., B ₁₂ ) except for the reference AP(BR ) as in Equation 11.

의 정보를, 각각의 대응되는 AP들(B₁, B₃, ..., B₁₂)에 전송할 수 있다. AP들(B₁, B₃, ..., B₁₂) 각각은 CP로부터 전달된 UE(M₀)에 대한 상대 보정 계수의 정보에 기초하여, UE(M₀)와의 채널에 대한 채널 상호성의 보정을 수행할 수 있다.CP is the relative correction coefficient calculated as in Equation 11

Information of may be transmitted to each of the corresponding APs (B ₁ , B ₃ , ..., B ₁₂ ). Each of the APs (B ₁ , B ₃ , ..., B ₁₂ ) is based on the information of the relative correction factor for the UE (M ₀ ) transmitted from the CP, the channel reciprocity for the channel with the UE (M ₀ ) Calibration can be performed.

6 is a conceptual diagram for explaining a third embodiment of a method for correcting channel reciprocity in a communication system.

Referring to FIG. 6 , a communication system 600 may include a plurality of communication nodes. The communication system 600 may include one or more access points (APs) and one or more user equipment (UEs). The communication system 600 may be the same as or similar to the communication system 500 described with reference to FIG. 5 . One or more APs may be the same as or similar to the APs B ₁ , B ₃ , ..., B ₁₂ described with reference to FIG. 5 . One or more UEs may be the same as or similar to the UE (M ₀ ) described with reference to FIG. 5 . In FIG. 6 , it can be seen that an embodiment in which the communication system 600 includes 12 APs B ₁ , ..., B ₁₂ , and one UE M ₀ is shown. However, this is only an example for convenience of description, and the embodiment of the present invention is not limited thereto. Hereinafter, in the description of the third embodiment of the method for correcting channel reciprocity with reference to FIG. 6 , content overlapping with those described with reference to FIGS. 1 to 5 may be omitted.

In the communication system 600 to which CFmMIMO is applied, the base station may provide a service to the UE (M ₀ ) through at least some of the 12 APs (B ₁ , ..., B ₁₂ ). APs (B ₁ , ..., B ₁₂ ) may provide a service to UE (M ₀ ) based on cooperative communication. Communication system 600 may further include a CP (not shown) for controlling or supporting the operation of the APs (B ₁ , ..., B ₁₂ ). The CP and/or APs (B ₁ , ..., B ₁₂ ) may perform operations for correction of channel reciprocity between the APs (B ₁ , ..., B ₁₂ ) and the UE (M ₀ ). there is.

를 계산할 수 있다. CP는 기준 AP(B_R)를 제외한 다른 AP들(B₁, B₃, ..., B₁₂)의 UE(M₀)에 대한 상대 보정 계수 계산 절차를 수행할 수 있다. CP는 계산된 상대 보정 계수

의 정보를, 각각의 대응되는 AP들(B₁, B₃, ..., B₁₂)에 전송할 수 있다. 기준 AP(B_R)를 제외한 AP들(B₁, B₃, ..., B₁₂) 각각은 CP로부터 전달된 UE(M₀)에 대한 상대 보정 계수의 정보에 기초하여, UE(M₀)와의 채널에 대한 채널 상호성의 보정을 수행할 수 있다. 이는 도 5를 참조하여 설명한 통신 시스템에서 채널 상호성 보정 방법의 제3 실시예와 동일 또는 유사할 수 있다.The CP may select a reference AP(BR) based on a channel state with the UE( _{M 0} ). Reference AP(BR) is a reference correction factor for correction of channel reciprocity for a channel with UE( _{M 0} )

can be calculated. The CP may perform a relative correction coefficient calculation procedure for the UE(M ₀ ) of the other APs ( _{B 1} , B ₃ , ..., B ₁₂ ) except for the reference AP(BR ). CP is the calculated relative correction factor

Information of may be transmitted to each of the corresponding APs (B ₁ , B ₃ , ..., B ₁₂ ). Each of the APs (B ₁ , B ₃ , ..., _{B 12} ) except the reference AP(BR) is based on the information of the relative correction factor for the UE (M ₀ ) transmitted from the CP, the UE (M ₀ ) ) and channel reciprocity can be corrected. This may be the same as or similar to the third embodiment of the method for correcting channel reciprocity in the communication system described with reference to FIG. 5 .

Meanwhile, in another embodiment of the communication system 600 , some of the APs ( B ₁ , B ₃ , ..., _{B 12} ) other than the reference AP ( BR ) are the UE ( M ₀ ) and/or the reference AP. ( _BR ) The communication quality may not be excellent. For example, some of the APs (B ₁ , B ₃ , ..., _{B 12} ) other than the reference AP (BR ) (B ₃ , B ₄ , etc.) of the obstacle (Ob) existing in the communication environment Due to its existence, communication with the reference AP( _BR ) may not be easy. The evaluation of communication quality or channel state between APs may be performed based on comparison of average values of instantaneous values of channel state information between APs shown in Table 2 with a preset reference value.

The CP is one or more APs whose communication status with the reference AP(BR) is worse than the preset standard among the APs ( _{B 1} , B ₃ , ..., _{B 12} ) except the reference AP(BR). A set of one or more confirmed APs, 'A set of APs with poor communication status', can be set S _Bad . For example, the poor communication state AP set S _Bad may have as elements the APs (B ₃ , _{B 4} , etc.) that are not easy to communicate with the reference AP ( BR ) due to the presence of an obstacle (Ob).

를 계산할 수 있다. 이를테면, 상대 보정 계수

는 수학식 12와 같이 계산될 수 있다.The CP may select one or more APs having a communication state with the poor communication state AP set S _Bad and a communication state with the reference AP superior to a preset criterion as an 'Auxiliary AP' (B _A ). Based on the selected 'Auxiliary AP' (B _A ), the CP may calculate a relative correction coefficient for APs of the AP set S _Bad with poor communication state. Specifically, the CP is the relative correction coefficient for the channel with the secondary AP (B _A ) of the APs of the poor communication state AP set S _Bad .

can be calculated. For example, the relative correction factor

can be calculated as in Equation 12.

를 계산할 수 있다. 이를테면, 상대 보정 계수

는 수학식 13과 같이 계산될 수 있다.CP is the secondary AP(B _A )'s relative correction factor for the channel with the reference AP( _BR )

can be calculated. For example, the relative correction factor

can be calculated as in Equation 13.

를 계산할 수 있다. 이를테면, 상대 보정 계수

는 수학식 14와 같이 계산될 수 있다.CP is a relative correction coefficient for the channel with the reference AP (BR ) of the APs of the poor communication state AP set _{S Bad} based on Equations 12 and 13.

can be calculated. For example, the relative correction factor

can be calculated as in Equation 14.

The CP may calculate a relative correction coefficient for the UE (M ₀ ) of APs in the poor communication state AP set S _Bad based on the relative correction coefficient calculated as in Equation 14. For example, the CP may calculate the relative correction coefficient for the UE (M ₀ ) of the APs of the poor communication state AP set S _Bad as in Equation 15.

의 정보를, 통신 상태 불량 AP 집합 S_Bad의 AP들에 전송할 수 있다. 통신 상태 불량 AP 집합 S_Bad의 AP들 각각은 CP로부터 전달된 UE(M₀)에 대한 상대 보정 계수의 정보에 기초하여, UE(M₀)와의 채널에 대한 채널 상호성의 보정을 수행할 수 있다.CP is the relative correction coefficient calculated as in Equation 15

The information of may be transmitted to APs of the poor communication state AP set S _Bad . Each of the APs of the poor communication state AP set S _Bad may perform channel reciprocity correction with respect to the channel with the UE (M ₀ ) based on the information on the relative correction coefficient for the UE (M ₀ ) transmitted from the CP. .

7 is a conceptual diagram for explaining a fourth embodiment of a method for correcting channel reciprocity in a communication system.

Referring to FIG. 7 , a communication system may include a plurality of communication nodes. A communication system may include one or more access points (APs) and one or more user equipment (UEs). The communication system may be the same as or similar to the communication system described with reference to FIG. 5 or FIG. 6 . The one or more APs may be the same as or similar to the APs B ₁ , B ₃ , ..., B ₁₂ described with reference to FIG. 5 or 6 . One or more UEs may be the same as or similar to the UE (M ₀ ) described with reference to FIG. 5 or FIG. 6 . Hereinafter, in describing the fourth embodiment of the method for correcting channel reciprocity with reference to FIG. 7 , content overlapping with those described with reference to FIGS. 1 to 6 may be omitted.

In an embodiment of the communication system, the CP may receive information on the result of channel measurement from APs connected through the fronthaul (S710). The CP may receive, from the APs, the result of the channel measurement performed between the APs. The CP may receive, from the APs, the result of the channel measurement performed between the UE and the UE. The CP may select one reference AP from among the APs based on a channel measurement result with the UE (S720). The CP may transmit information indicating that the reference AP has been selected.

The CP may check whether one or more APs whose communication status with the reference AP is worse than a preset standard exist, based on a result of channel measurement between APs other than the reference AP and the reference AP. When one or more APs whose communication status with the reference AP is worse than the preset standard among APs other than the reference AP is identified, the CP may set a set of APs with poor communication status having one or more identified APs as an element (S730). Specifically, the AP set with poor communication state may be defined as in Equation (16).

The CP may select one or more APs in the set of APs with poor communication state and one or more APs in which communication states with the reference AP are superior to a preset reference as the secondary AP (S740). One or more secondary APs are selected from among APs having excellent average communication quality with the reference AP shown in Table 2 by the first criterion or higher, and having many APs with average communication quality equal to or higher than the second criterion among APs in the set of APs with poor communication state. can When there are many candidates for the corrected AP, the AP having the highest average communication quality with the APs in the set of APs with poor communication state shown in Table 2 may be selected as the corrected AP.

A plurality of secondary APs may be selected. For example, if there are APs for which a reliable relative correction coefficient cannot be obtained even through one secondary AP (primary secondary AP) among APs in the poor communication state AP set, the CP has excellent communication state with the primary secondary AP. APs may be determined as secondary or tertiary secondary APs and calculated in conjunction with a correction coefficient. Steps S730 and S740 may be optionally performed according to an embodiment of the communication system.

The CP may receive information on the reference correction coefficient from the reference AP (S750). The CP may calculate relative correction coefficients of the APs other than the reference AP to the UE based on the information on the reference correction coefficient (S760). This may be the same as or similar to that described with reference to FIG. 5 and Equation 8. If the AP set with poor communication state is set according to step S730 and the secondary AP is selected according to step S740, the relative correction coefficients for the UEs of the APs included in the AP set with poor communication state for the UE are calculated based on the relationship with the secondary AP. can This may be the same as or similar to that described with reference to FIG. 6 and Equation 15.

The CP may transmit information on the relative correction coefficient calculated in step S760 to the corresponding APs (S770). Each of the APs except for the reference AP may perform channel reciprocity correction with respect to the channel with the UE based on the information on the relative correction coefficient for the UE transmitted from the CP.

According to an embodiment of the present invention, in a communication system to which large-scale MIMO such as CFmMIMO is applied, one reference AP having high communication quality or reliability with the UE may be selected. The reference AP may calculate a reference correction coefficient for correction of channel reciprocity for a channel with the UE. The CP may receive information on the reference correction coefficient from the reference AP. The CP may calculate relative correction coefficients for the UEs of APs other than the reference AP based on the received reference correction coefficient information. If there is an AP having difficulty communicating with the reference AP among other APs other than the reference AP, a relative correction coefficient may be calculated based on an additionally selected auxiliary AP. Through this, all APs that are connected to the CP through the fronthaul and provide services to the UE can easily obtain a relative correction coefficient for correcting channel reciprocity with respect to a channel with the UE.

However, effects that can be achieved by the method and apparatus for correcting channel reciprocity in a wireless communication system according to embodiments of the present invention are not limited to those mentioned above, and other effects not mentioned are described in the specification of the present application. From the configurations described in the present invention will be clearly understood by those of ordinary skill in the art.

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, etc. 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 setting 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 (1)

A method for correcting channel reciprocity performed by a control node of a communication system, the method comprising:
receiving information on a channel measurement result from a plurality of access points (APs) connected to the control node through a fronthaul;
selecting one reference AP based on the received channel measurement result information;
receiving, from the reference AP, information on a reference correction coefficient for correction of channel reciprocity for a channel of the reference AP with a user equipment (UE);
calculating a relative correction coefficient for correcting channel reciprocity with respect to a channel with the UE of each of the APs other than the reference AP among the plurality of APs, based on the information on the reference correction coefficient; and
and transmitting information on the calculated relative correction coefficient to each of APs other than the reference AP.

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