KR102571051B1 - Calibration method for cooperative transmission of cell-free wireless network, and apparatus therefor - Google Patents

Abstract

at least one calibration device; and A calibration method in a series fronthaul in which two AN(s) are connected in series is: the calibration device transmitting a calibration command message instructing calibration of transmission paths to at least some of the AN(s); determining, by the calibration device and the at least some AN(s), time delay values and phase characteristic values of transmission paths of the at least some AN(s); and a calibration adjustment message instructing the calibration device to calibrate transmission paths of the at least some AN(s) based on time delay values and phase characteristic values of the transmission paths of the at least some AN(s). It may include sending.

Description

Calibration method for cooperative transmission of cell-free wireless network and apparatus therefor

The present invention relates to a cooperative communication method of distributed base station devices in a radio access network (RAN), and more particularly, to an uplink in a cell-free massive MIMO (CFmMIMO) radio system. A method and apparatus for RF calibration of cooperative base station devices necessary for calculation of precoding (beamforming) matrices for accurate downlink cooperative transmission based on channel estimation.

In a cellular wireless communication system, each user terminal is generally served by one serving base station. However, in order to provide constant communication quality to all user terminals while accommodating the explosively increasing mobile traffic, all base stations around the user terminals need to provide services to the user terminals without cell boundaries. The above-described method may be defined as cell-free wireless communication.

In cell-breaking wireless communication, user terminals can synchronously and simultaneously transmit their own pilot signals to all base stations according to a time division duplex (TDD) protocol. Each base station estimates uplink channel coefficients between itself and each user terminal through the pilot signal, and uses TDD channel reciprocity to estimate downlink channel coefficients between itself and each user terminal. there is. Each base station can estimate downlink channel information based on uplink channel information without channel state information feedback from the terminal through the above-described TDD channel reciprocity. All base stations around the terminal acquire downlink channel information with the corresponding terminal in the above-described method, and based on the downlink channel information, precode and transmit a signal for the corresponding terminal. Therefore, regardless of location, the terminal can simultaneously receive signals precoded based on the downlink channel information from all nearby base stations, so that it can receive signals of good quality without interference with other terminals. A scheme in which base stations cooperate to perform transmission for a specific terminal is referred to as 'coherent joint transmission (hereinafter referred to as 'C-JT')'. In cell-breaking wireless communication, the C-JT cooperative transmission scheme may be basically used.

As described above, in order to efficiently perform the C-JT cooperative transmission scheme in cell-breaking wireless communication, bidirectional (ie, uplink and downlink) channels are obtained from unidirectional (in particular, uplink) channel information by utilizing TDD channel reversibility. Information must be obtained, and a characteristic difference (mismatch) between RF transmission/reception paths must be corrected (calibrated) in order for TDD channel reciprocity to be applied.

An object of the present invention to solve the above problem is, at least one calibration controller and dog( is a natural number of 1 or more) to provide a method for performing correction (calibration) for a mismatch of transmission paths in a serial fronthaul in which access node (AN) (s) are serially connected .

Another object of the present invention for solving the above problem is, at least one calibration controller and dog( is a natural number of 1 or more) to provide a method for calibrating mismatches of receive paths in a serial fronthaul in which AN(s) are connected in series.

Another object of the present invention for solving the above problem is, at least one calibration controller and dog( is to provide a method of performing calibration for time division duplex (TDD) channel reciprocity of each AN in a serial fronthaul in which AN(s) of natural numbers of 1 or more are serially connected.

One embodiment of the present invention for achieving the above object, at least one calibration device and dog( is a natural number of 1 or more) is a calibration method in a serial fronthaul in which access node (AN) (s) are connected in series, wherein the calibration device Transmitting a calibration command message instructing calibration of transmission paths to at least some AN(s) among the AN(s) (a); (b) determining, by the calibration device and the at least some AN(s), time delay values and phase characteristic values of transmission paths of the at least some AN(s); and a calibration adjustment message instructing the calibration device to calibrate transmission paths of the at least some AN(s) based on time delay values and phase characteristic values of the transmission paths of the at least some AN(s). It may include the step (c) of transmitting.

Step (b) includes: of the at least some AN(s) The th AN recalls the transmission path calibration signal th AN contains transmitting to the calibration device through each of the transmission paths (b-1); The calibration device is of the transmission paths The time delay value of the th transmission path is determined as the value of the transmission path calibration signal. determining based on a difference between a transmission time in the AN-th and a reception time in the calibration device (b-2); and the calibration device of the transmission paths and determining a phase characteristic value of the th transmission path based on a difference between a phase of the transmission path calibration signal at the transmission time point and a phase at the reception time point (b-3).

The step (b) is: th AN above reporting time delay values and phase characteristic values of the number of transmission paths to the calibration device (b-4); and (b-5) the calibration device determining time delay values and phase characteristic values of the transmission paths of the at least some AN(s) through the steps (b-1) to (b-4). can include

The transmission path calibration signals are transmitted at the time of transmission of the calibration command message ( ) from a predetermined time ( ) after elapsed, the time interval ( ) can be transmitted sequentially.

The step (c): the calibration device determines the maximum time delay value among time delay values of the transmission paths of the at least some AN(s) and the Recall of the second AN Recall the difference between the time delay values of the th transmission path Determining a time delay calibration value of a th transmission path (c-1); The calibration device determines the maximum phase characteristic value among the phase characteristic values of the transmission paths of the at least some AN(s) and the Recall of the second AN Recall the difference between the phase characteristic values of the th transmission path determining a phase characteristic calibration value of a th transmission path (c-2); and the calibration device The time delay calibration value and the phase characteristic calibration value of the th transmission path are and transmitting the calibration adjustment message to the th AN (c-3).

The serial front hall is: the calibration device and the a timing clock signal line for clock synchronization between the number of AN(s); The calibration device and the a calibration signal line for transferring a calibration signal between the two AN(s); and the calibration device and the It may include data and control signal lines for transferring data and control signals for calibration between the two AN(s).

The calibration device exists as a separate hardware device, or One of the AN(s) serves as the calibration device, or A central processor (CP) connected to the number of AN(s) through the serial fronthaul may serve as the calibration device.

One embodiment of the present invention for achieving the above other object is, at least one calibration device and dog( is a calibration method in a serial front hall in which AN(s) of (is a natural number of 1 or more) are connected in series, and the calibration device Transmitting a calibration command message instructing calibration for reception paths to at least some of the AN(s) (a); (b) determining, by the calibration device and the at least some AN(s), time delay values and phase characteristic characteristic values of receive paths of the at least some AN(s); Transmitting, by the calibration device, a calibration adjustment message instructing calibration of reception paths to the at least some AN(s) based on time delay values and phase characteristic values of the reception paths of the at least some AN(s) ( c) can be included.

The step (b) is: the calibration device transmits a received path calibration signal among the at least some AN(s). th AN contains through each of the two receive paths. Transmitting to the th AN (b-1); remind th AN above of the receiving paths Recall the time delay value of the th receive path A transmission time in the calibration device of the reception path calibration signal received through the th reception path and the Step (b-2) of determining based on the difference between reception points in the th AN; remind th AN above of the receiving paths determining a phase characteristic value of a th transmission path based on a difference between a phase of the reception path calibration signal at the transmission time point and a phase at the reception time point (b-3); and above th AN through the steps (b-1) to (b-3) A step (b-4) of determining delay characteristic values and phase characteristic values of the number of reception paths and reporting them to the calibration device may be further included.

When the calibration command message indicates the number of repetitions R of the reception path calibration signal, the reception path calibration signal It is repeatedly transmitted R times in the th reception path, A time delay value and a phase characteristic value for the th reception path may be determined based on R repeated transmissions of the reception path calibration signal.

The received path calibration signals are transmitted at the time of transmission of the calibration command message ( ) from a predetermined time ( ) after elapsed, the time interval ( ) can be transmitted sequentially.

The step (c) is: the calibration device determines the maximum time delay value among the time delay values of the receive paths of the at least some AN(s) and the maximum phase among the phase characteristic values of the receive paths of the at least some AN(s) determining a characteristic value (c-1); The calibration device determines the maximum time delay value and the The difference between the maximum time delay values of the reception paths of the th AN is determining the time delay calibration value of the th AN (c-2); The calibration device determines the maximum phase characteristic value and the The difference between the maximum phase characteristic values of the reception paths of the th AN is determining a phase characteristic calibration value of the th AN (c-3); And the calibration device determines the time delay calibration value and the phase characteristic calibration value. A step (c-4) of transmitting the calibration adjustment message to the th AN may be further included.

The serial front hall is: the calibration device and the a timing clock signal line for clock synchronization between the number of AN(s); The calibration device and the a calibration signal line for transferring a calibration signal between the two AN(s); and the calibration device and the It may include data and control signal lines for transferring data and control signals for calibration between the two AN(s).

The calibration device exists as a separate hardware device, or One of the AN(s) serves as the calibration device, or A central processor (CP) connected to the number of AN(s) through the serial fronthaul may serve as the calibration device.

An embodiment of the present invention for achieving the above another object is, at least one calibration device and dog( is a calibration method in a serial front hall in which AN(s) of (is a natural number of 1 or more) are connected in series, and the calibration device of the AN(s) Transmitting a calibration command message instructing calibration for TDD channel reciprocity to a th AN (a); The calibration device and the th AN above included in the second AN Gain characteristic values of the N receive paths and measuring gain characteristic values of the N transmission paths (b); and the calibration device gain characteristic values of the N receive paths and the Based on the gain characteristic values of the transmission paths Determines a gain calibration value of each of the N receive paths and sends a calibration adjustment message including the gain calibration value to the It may include step (c) of transmitting to the th AN.

The step (b) is: the calibration device Remind with the second AN included in the second AN transmitting a TDD channel reciprocity calibration signal through the N receive paths; remind th an measuring a received signal gain of the TDD channel reciprocity calibration signal for each of the N receive paths and reporting the result to the calibration device; remind th AN above included in the second AN transmitting a TDD channel reversibility calibration signal to the calibration device through the TDD transmission paths; and the calibration device The method may further include measuring a received signal gain of the TDD channel reciprocity calibration signal for each of the N transmission paths.

The TDD channel reversibility calibration signals are transmitted at the time of transmission of the calibration command message ( ) or a predetermined time from the time of reporting the measured value of the received signal gain ( ) after elapsed, the time interval ( ) can be transmitted sequentially.

The serial front hall is: the calibration device and the a timing clock signal line for clock synchronization between the number of AN(s); The calibration device and the a calibration signal line for transferring a calibration signal between the two AN(s); and the calibration device and the It may include data and control signal lines for transferring data and control signals for calibration between the two AN(s).

The calibration device exists as a separate hardware device, or One of the AN(s) serves as the calibration device, or A central processor (CP) connected to the number of AN(s) through the serial fronthaul may serve as the calibration device.

Downlink channel information for the ANs can be estimated from uplink channel information for the ANs using the TDD channel reciprocity.

According to embodiments of the present invention, in a serial fronthaul environment in which distributed ANs are connected with a single cable, mismatches between multiple RF transmission/reception paths can be corrected (calibrated) without wasting radio resources. In particular, more accurate mismatch calibration can be performed while maintaining the simple cabling advantages of serial fronthaul. Through this, bidirectional (uplink and downlink) channels can be estimated through unidirectional (in particular, uplink) channel measurement, and services can be provided to terminals through cooperative transmission between ANs, resulting in higher quality data transmission. it could be possible

1 is a conceptual diagram for explaining the configuration of a cell-leaving massive MIMO (CFmMIMO) system to which embodiments of the present invention are applied.
2 is a conceptual diagram illustrating the configuration of a cell-breaking massive MIMO system using serial fronthaul to which embodiments of the present invention are applied.
3 is a conceptual diagram illustrating the configuration of a serial fronthaul system to which a serial fronthaul calibration method according to an embodiment of the present invention is applied.
4 is a conceptual diagram illustrating a mismatch adjustment block according to an embodiment of the present invention.
5A and 5B are flowcharts illustrating a method of calibrating mismatches of transmit paths and/or receive paths in serial fronthaul according to an embodiment of the present invention.
FIG. 6A is a flowchart illustrating an operation of a calibration controller in the method of calibrating a mismatch of transmission paths according to FIG. 5A.
FIG. 6B is a flowchart illustrating an operation of a calibration block in the method of calibrating a mismatch of transmission paths according to FIG. 5A.
FIG. 7A is a flowchart illustrating an operation of a calibration controller in the method of calibrating mismatching of receive paths according to FIG. 5B.
FIG. 7A is a flowchart illustrating an operation of a calibration block in the method of calibrating a mismatch of receive paths according to FIG. 5B.
8A is a flowchart illustrating a method of performing calibration for TDD channel reversibility in serial fronthaul according to an embodiment of the present invention.
9 is a conceptual diagram for explaining a connection structure of a serial front hall according to an embodiment of the present invention.
10 is a conceptual diagram for explaining a hierarchical calibration method according to an embodiment of the present invention in a system composed of a plurality of serial fronthauls.
11 is a conceptual diagram for explaining a hierarchical calibration method according to another embodiment of the present invention in a system composed of a plurality of serial fronthauls.
12 is a conceptual diagram for explaining the configuration of a communication node according to an embodiment of the present invention.

본 발명은 다양한 변경을 가할 수 있고 여러 가지 실시예를 가질 수 있는 바, 특정 실시예들을 도면에 예시하고 상세한 설명에 상세하게 설명하고자 한다. 그러나, 이는 본 발명을 특정한 실시 형태에 대해 한정하려는 것이 아니며, 본 발명의 사상 및 기술 범위에 포함되는 모든 변경, 균등물 내지 대체물을 포함하는 것으로 이해되어야 한다. 각 도면을 설명하면서 유사한 참조부호를 유사한 구성요소에 대해 사용하였다.

Since the present invention can make various changes and have various embodiments, 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. Like reference numerals have been used for like elements throughout the description of each figure.

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. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. The terms and/or include any combination of a plurality of related recited items or any of a plurality of related recited items.

It is understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may exist in the middle. It should be. On the other hand, when an element is referred to as “directly connected” or “directly connected” to another element, it should be understood that no other element exists in the middle.

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 dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

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

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

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

1 is a conceptual diagram for explaining the configuration of a cell-leaving massive MIMO (CFmMIMO) system to which embodiments of the present invention are applied.

Referring to FIG. 1, a cell-leaving massive MIMO system 100 includes one central processor (CP) 110, a plurality of distributed access nodes (AN) 120, and a distributed It is composed of a plurality of user equipment (UE) 130. Functions of the devices may be described as follows in terms of downlink cooperative transmission.

One CP 110 is connected to the distributed ANs 120 through a fronthaul, and can transfer data of all terminals 130 to the ANs 120 through the fronthaul. In addition, the CP 110 may receive channel statistical information of all terminals 130 from the distributed ANs and control transmission power used by a specific AN to provide a service to a specific terminal. Each AN is connected to the CP 110 through a fronthaul, and each AN includes one or more antennas and RF devices, and may include part or all of a baseband function. Each AN may cooperate with other ANs to provide services to UEs. The terminal transmits a pilot signal allocated to the terminal to all ANs through uplink, so that the ANs can acquire downlink channel information through channel reciprocity. In addition, the terminal may receive a C-JT signal including downlink data from all ANs.

In order for C-JT cooperative transmission used in cell-breaking wireless communication to provide a high-quality signal to the terminal, accurate synchronization must be maintained between the distributed ANs, and an array antenna of a specific AN and a plurality of transmit / receive RFs connected to it Paths must have the same time delay and phase shift values. In addition, for C-JT cooperative transmission, transmit/receive RF paths between ANs must have the same time delay and phase shift values. Meanwhile, in C-JT cooperative transmission used in cell-breaking wireless communication, downlink channel information may be obtained from uplink channel information by utilizing TDD channel reciprocity. The uplink channel information may include TX RF path characteristic information of the terminal, uplink radio channel information, and RX RF path characteristic information of the base station. Downlink channel information applied to downlink data transmission may include TX RF path characteristic information of a base station, downlink radio channel information, and RX RF path characteristic information of a terminal. Accordingly, in order to apply the TDD channel reciprocity, a characteristic difference (mismatch) between RF transmission/reception paths must be corrected (calibrated).

A function of correcting a characteristic difference between the aforementioned RF transmission/reception paths is called 'calibration'. As the use of multiple antennas and the MIMO transmission method have been standardized, calibration functions have also been developed. The RF transmit path includes a digital-to-analog converter (DAC), up converter, power amplifier, and filter, and the RF receive path includes a duplexer. ), a low-noise amplifier (LNA), a down converter, a filter, and an analog-to-digital converter (ADC). The RF transmit path and the RF receive path is generally connected to one antenna through a switch, and according to the TDD operation, the transmission function and the reception function are performed separately in time Since each path includes different components, each path has different delay characteristics , phase characteristics and gain characteristics Existing calibration techniques are limited to calibration that adjusts mismatches of a plurality of transmit/receive paths according to the use of multiple antennas within one base station. Therefore, the cell In order to cost-effectively support C-JT cooperative transmission in breakaway wireless communication, a technology for calibrating mismatches of transmission/reception paths between a plurality of ANs is required.

Existing cell-breaking MIMO systems require a dedicated fronthaul link for each of the ANs as shown in FIG. 1 . Each AN preprocesses a signal (e.g., a pilot signal) received on the uplink, calculates a channel estimate, and forwards the calculated channel estimate to the CP over the fronthaul link, which is based on the received channel estimates. to generate a precoded signal and deliver it to each AN. The above-described architecture is desirable from a communication performance point of view, but has a problem from a cost point of view because a large number of long cables are required.

2 is a conceptual diagram illustrating the configuration of a cell-breaking massive MIMO system using serial fronthaul to which embodiments of the present invention are applied.

Referring to FIG. 2, in order to enable a more practical architecture and distributed processing, one fronthaul connects multiple ANs in series in a daisy-chain manner to reduce cabling (serial fronthaul) A cell-leaving massive MIMO system 200 using serial fronthaul is shown.

However, for cell-breaking C-JT cooperative transmission, 1) mismatch between transmit/receive paths within the same AN and between distributed ANs, and 2) between transmit/receive paths of the same transceiver. A calibration function that solves the irreversible TDD channel problem due to mismatch has not been considered.

Configuration of a serial fronthaul calibration system

3 is a conceptual diagram illustrating the configuration of a serial fronthaul system to which a serial fronthaul calibration method according to an embodiment of the present invention is applied.

Referring to FIG. 3, the serial front hole 310 is ( is a natural number of 1 or more) number of AN(s) (eg, 320 and 330) may be connected in series. Each AN # connected to serial fronthaul (310) (Hereinafter, AN #1 (320) is referred to as AN # exemplified by) is plural ( ) antennas, a switch for switching the antennas between a transmit path and a receive path according to the TDD protocol (hereinafter 'TDD switch (S _TDD )'; 321), transceivers (TX) connected to the corresponding antennas through the switch and RX , =1,..., ; 322), mismatch adjustment blocks 323 that adjust mismatch between transceivers, and a signal processing module 324 that interfaces with the CP 340 and performs a signal processing function.

The signal processing module 324 is AN # A local clock (324-1) providing timing for the internal operation of, a calibration block (hereinafter referred to as 'calibration block', 324-2) to be described later, and a baseband function block functionally divided with the CP (340) ( 324-3). Also, AN# is a switch that connects the calibration signal line 311 of the front hall 310 to the transmission path and the reception path of the transceiver 322 in conjunction with the TDD switch 321 (hereinafter 'CAL switch (S _CAL )'; 325) may additionally include. Further describing the interworking between the TDD switch 321 and the CAL switch 325, when antennas are used for transmission according to the TDD protocol, the TDD switch 321 connects the antennas to the TX parts of the transceivers 322 And, the CAL switch 325 may connect the calibration signal line 311 to the RX parts of the transceivers 322. Conversely, when the TDD switch 321 connects the antennas to the RX parts of the transceivers 322, the CAL switch 325 may connect the calibration signal line 311 to the TX parts of the corresponding transceivers 322. .

As shown in FIG. 3 , a plurality of ANs each including the above components include a data and control signal line 312, a timing clock signal line 313, and a calibration signal line 311 included in a serial front hall 310. can be interconnected through In addition, the plurality of ANs are also connected to the CP 340 through the serial front hole 310 . In the following embodiments relating to calibration in serial fronthaul, data and control signal lines 312 are connected to CP 340, calibration controller 355 in calibration device 350, and calibration block 324-2 in an individual AN. ) can be used to exchange information necessary for calibration between them. The timing clock signal line 313 may support synchronization between the master clock 341 of the CP providing the reference clock and internal local clocks 324-1 of the distributed ANs. In the case of the calibration signal line 311, in the CAL switch 351 within the calibration device 350 Circuit length to contact, from CAL switch (325) on individual antenna within AN #1 (320) Circuit Length to Contact, and AN # ( =2,..., ) at the CAL switch of the individual antenna within The length of the circuit to the contact can all be designed to have an exact fixed length. In the following embodiments, it is assumed that the above circuit lengths are all the same. Although not separately mentioned below, an additional correction circuit may be used for the assumption of the same circuit length.

As mentioned above, the serial fronthaul according to an embodiment of the present invention may include a calibration device (hereinafter referred to as 'calibration device'; 350) to adjust the RF mismatch of a series of ANs connected to the serial fronthaul. . Although an embodiment in which the calibration device 350 exists as an independent device is shown in FIG. 3 , embodiments in which a specific AN serves as the calibration device or the CP 340 serves as the calibration device are also possible. The following description considers an embodiment in which one independent calibration device 350 is included in the serial fronthaul.

The calibration device 350 includes a CAL switch 351 for connecting the calibration transceiver 352 to the calibration signal line 311 of the serial fronthaul 310 according to the TDD protocol, and a calibration transmission for transmitting a calibration waveform signal ( A transceiver 352 composed of a CAL TX) part and a calibration reception (CAL RX) part that receives a calibration signal, a mismatch adjustment block 353 that adjusts mismatch between the transmission/reception parts of the calibration transceiver, components of the calibration device It may include a local clock 354 that provides timing to , and a calibration controller (hereinafter referred to as 'calibration controller'; 355) to be described later.

4 is a conceptual diagram illustrating a mismatch adjustment block according to an embodiment of the present invention.

Referring to Figure 4, AN# with two antennas ( =1,..., )undergarment A configuration diagram of the mismatch adjustment block 323 for adjusting the mismatch of the th transceiver is shown. in other words, Transceivers and mismatching adjustment blocks may have a one-to-one correspondence.

Each mismatch adjustment block is a transmission delay adjuster that corrects the time delay and phase of the transmission path of the corresponding transceiver ( ) and a transmit phase adjuster ( ), a reception delay adjuster for calibrating the time delay and phase of the reception path of the transceiver ( ) and receive phase adjuster ( ), and a gain adjuster for calibrating the channel irreversibility of the transmit path and the receive path of the transceiver ( ) may be included.

Calibration values for the transceiver mismatch adjustment blocks may be provided from the calibration block 324-2 of the corresponding AN through cooperation with the calibration device 350. The mismatch adjustment block 323 may be implemented as an additional HW block as an example. However, embodiments in which the mismatch adjustment block 323 is implemented in a SW manner within the baseband function block 324-3 are also possible.

Hereinafter, with reference to FIGS. 3 and 4, time delay and phase mismatch of transmit/receive paths of a plurality of transceivers in an AN and transmit/receive paths of multiple transceivers in ANs, and TDD channel irreversible mismatch of the same transceiver Calibration How to do this is explained. In the following description, the local clocks of the calibration device 350 and all ANs 320, 330, .. connected to the serial fronthaul and the master clock 341 of the CP 340 are precisely synchronized at the baseband operating level. It is assumed that In addition, message delivery through the data and control signal lines 312 is assumed to be error-free. The calibration controller 355 of the calibration device 350 designates a specific transceiver of a specific AN connected to the serial fronthaul through the data and control signal line 312 of the serial fronthaul at an arbitrary point in time to instruct the execution of calibration, or all ANs It is possible to collectively instruct calibration to be performed on all transceivers of the .

Send/receive path calibration

5A and 5B are flowcharts illustrating a method of calibrating mismatches of transmit paths and/or receive paths in serial fronthaul according to an embodiment of the present invention.

In Figure 5a, the calibration controller 355 of the calibration device 350 and the AN # A procedure for exchanging a message and a calibration signal for calibrating the mismatch of the transmission paths between the calibration blocks 324-2 of . In addition, in FIG. 5B, the calibration controller 355 of the calibration device 350 and the AN # A procedure for exchanging a message and a calibration signal for calibrating the mismatch of the receive paths between the calibration blocks 324-2 of the is shown.

Referring to Figure 5a, the calibration controller 355 AN # of To initiate measurements of the time delay and phase characteristics of the transmission paths, AN # A calibration command message (AID= , DIR=Tx) can be transmitted through the data and control signal line 312 of the serial fronthaul 310 (S510). Here, AID may indicate an identifier (AN ID) of an AN, and DIR may indicate a target path (transmission path or reception path) for measuring mismatch. In the embodiment of FIG. 5A , DIR is set to 'Tx', which means that the target of mismatch correction is a transmission path. AN# The calibration block 324-2 of the time point when the calibration command message is transmitted from After the elapse of time, a transmission path calibration signal (TX CAL waveform) may be transmitted (S521). Since the clocks of the calibration block 324-2, which is the transmitter of the transmission path calibration signal, and the calibration controller 355, which is the receiver of the transmission path calibration signal, are synchronized, the calibration controller 355 generates the point of transmission can be transmitted by including in the form of a timestamp in the calibration command message, and the calibration block 324-2 At this point, a transmission path calibration signal may be transmitted on transmission path 1 (TX 1) (S521). The calibration block 324-2 is total at intervals transmit path calibration signals TX 1, TX 2, ..., TX It is sequentially transmitted on the path (S521 to S524). After transmitting the last transmission path calibration signal (S524), the calibration block 324-2 transmits a calibration completion report (CAL report (complete)) message to the calibration controller 355 through the data and control signal line 312 to , it is notified that transmission of the transmission path calibration signal has been completed (S530). On the other hand, the calibration controller 355 from the point The time interval to the time point is AN # according to the TDD protocol of the radio reception operation period. AN# tx Time delay value of the transmit path calibration signal transmitted through the path is the transmission time (in the calibration block 324-2) of the corresponding transmission path calibration signal It is defined as the difference between the transmission path calibration signal and the reception time (in the calibration controller 355) of the corresponding transmission path calibration signal, and can be expressed as Equation 1 below by the transmission path of the transmission path calibration signal.

in Equation 1 is the AN# to be calibrated tx is the time delay value of the route, AN# at the S _CAL branch of is the time delay value to the point, Is at the branch is the time delay value to the point, At the S _CAL point of the calibration device 350 is the time delay value to the point, Is the time delay value of the RX path of the calibration device 350. above , , The values are well-known fixed values, value is It is the component value of the common pathway in the measurement. thus, value is the measurement can be derived from

That is, AN# tx The phase characteristic value of the path is It may be determined based on a difference between a phase at the time of transmission and a phase at the time of reception of the transmission path calibration signal transmitted through the th transmission path. Also, AN# tx Phase measurements of the transmit path calibration signal transmitted through the path. Can be expressed as Equation 2 below by the transmission path of the corresponding transmission path calibration signal.

in Equation 2 is the AN# to be calibrated tx is the phase characteristic value of the path, AN# at the S _CAL branch of is the phase characteristic value up to the point, Is at the branch is the phase characteristic value up to the point, At the S _CAL point of the calibration device 350 is the phase characteristic value up to the point, represents the phase characteristic value of the RX path of the calibration device 350. above , , The values are well-known fixed values, value is It is the component value of the common pathway in the measurement. thus, value is the measurement can be derived from Calibration controller 355 is AN # By receiving the CAL report (report (complete)) message from the calibration block 324-2 of AN # of Time delay value of transmission paths and phase characteristic values measurement can be completed.

The calibration controller 355 of the calibration device 350 performs the above-described procedure with each of the other ANs (S540). Total included in serial fronthaul Total transmit path for ANs The maximum value of the time delay after completing mismatch measurements for dogs and phase characteristic maximum this can be derived. Calibration controller 355 is AN # of Calibration values of time delay and phase characteristics of each transmission path Calibration adjustment (including ) message AN# It can be transmitted to the calibration block 324-2 of (S550). AN# of Time delay and phase characteristic calibration values for the -th transmission path Can be expressed as in Equation 3 below.

Referring to Figure 5b, the calibration controller 355 AN # of To initiate measurements of the time delay and phase characteristics of the AN # Calibration command (AID = , DIR=Rx, REP=n) message can be transmitted through the data and control signal line 312 of the serial fronthaul 310 (S550). Here, AID may indicate an identifier (AN ID) of an AN, and DIR may indicate a target path (transmission path or reception path) for measuring mismatch. In the embodiment of FIG. 5B , DIR is set to 'Rx', which means that the target of mismatch adjustment is the receive path. Also, REP means the number of transmissions of a reception path calibration signal (RX CAL waveform) for mismatch measurement. The calibration controller 355 determines when the calibration command message is transmitted. from After the elapse of time, the reception path calibration signal may be transmitted (S561). Since the clocks of the calibration block 324-2, which is the receiver of the receive path calibration signal, and the calibration controller 355, which is the transmitter of the receive path calibration signal, are synchronized, the calibration controller 355 generates the point of transmission is transmitted in the form of a timestamp in the calibration command message, At this point, a receive path calibration signal may be transmitted on the calibration TX path. Calibration controller 355 At intervals, a total of REP=n received path calibration signals are sequentially transmitted on the same calibration TX path (S561, S562). On the other hand, the calibration controller 355 transmits the repeatedly transmitted reception path calibration signal to AN # according to the TDD protocol. AN # described above in the radio transmission operation period of It must be able to be received on the receive path of AN# rx received through Time delay value of -th received path calibration signal is the transmission time point (in the calibration controller 355) of the corresponding received path calibration signal and a difference in reception time (in the calibration block 325-4) of the corresponding reception path calibration signal, and can be expressed as Equation 4 below by the transmission path of the reception path calibration signal.

in Equation 4 is the AN# to be calibrated rx is the time delay value of the route, AN# at the S _CAL branch of is the time delay value to the point, Is at the branch is the time delay value to the point, At the S _CAL point of the calibration device 350 is the time delay value to the point, Is the TX path time delay value of the calibration device 350. above , , The values are well-known fixed values, value is It is the component value of the common pathway in the measurement. thus, value is the measurement can be derived from

Also, AN# rx Phase measurement of the receive path calibration signal received through the path Can be expressed as in Equation 5 below by the transmission path of the corresponding reception path calibration signal.

in Equation 4 is the AN# to be calibrated receive path of (RX ) is the phase characteristic value of AN# at the S _CAL branch of is the phase characteristic value up to the point, Is at the branch the phase characteristic value up to the point, At the S _CAL point of the calibration device 350 is the phase characteristic value up to the point, Is a TX path phase characteristic value of the calibration device 350. above , , The values are well-known fixed values, value is It is the component value of the common pathway in the measurement. thus, value is the measurement can be derived from

According to one embodiment of the present invention, AN # through one receive path calibration signal transmitted by calibration controller 355. of for all receive paths and Can be measured in parallel, in the case of such an embodiment AN # The calibration block 324-2 of is derived by the repeatedly received receive path calibration signals and The average value of can be taken, through which the measurement error can be minimized.

In another embodiment of the present invention, through one receive path calibration signal transmitted by the calibration controller It is possible to measure some of the receive paths, and in this case, the measurement can be completed for the entire receive path through the repeated receive path calibration signal. AN# of The calibration block 324-2, which has completed measurement for all of the two receive paths, has the largest time delay measurement value and phase characteristic values It can be determined as in Equation 6 below.

AN# Is the two measurement maximum values determined as described above in a calibration report message ( ) through which it can be reported to the calibration controller 355 (S570).

The calibration controller 355 of the calibration device 350 may perform the above-described reception path mismatch measurement procedure with other ANs (S580). Total included in serial fronthaul ANs (or total All receive paths for at least some AN(s) of the ANs After completing the mismatch measurement for the dog, the calibration controller 355 determines the maximum time delay value and the maximum phase characteristic value can be derived. Calibration controller 355 is AN # The largest time delay measurement among the receive paths of and phase characteristic measurements Time delay calibration value and phase characteristic calibration value based on Can be calculated as in Equation 7 below.

After this, the calibration controller sends a calibration adjustment message ( ) to AN# It can be transmitted to the calibration block 324-2 of (S580). AN# The calibration block 324-2 of Time delay calibration value and phase characteristic calibration value for the -th receive path ( ) can be calculated as in Equation 8 below, respectively.

Hereinafter, with respect to the procedures described with reference to FIGS. 5A and 5B, the operation procedure and AN # of the calibration controller 355 side of the calibration device 350 Operation procedures in terms of the calibration block 324-2 of are described respectively.

FIG. 6A is a flowchart illustrating an operation of a calibration controller in the method of calibrating a mismatch of transmission paths according to FIG. 5A.

Referring to FIG. 6A, the calibration controller 355 determines whether clock synchronization with ANs, which are targets of transmission path mismatch calibration, has been completed (S611), ANs and included in each AN Sets of antennas/transceivers may be identified (S612).

Calibration controller 355 AN # of ANs A CAL command message (AID= , DIR=Tx) can be transmitted (S613). That is, step S613 may correspond to step S510 in FIG. 5A.

Next, the calibration controller 355 AN # of ANs Receives transmission path calibration signals (TX CAL waveforms) sequentially transmitted from the calibration block 324-2 of AN # using them Time delay values and phase characteristic values of transmission paths of can be measured (S614). That is, step S614 may correspond to steps S521 to S524 in FIG. 5A.

Next, the calibration controller 355 AN # of ANs Receives a calibration completion report message from the calibration block 324-2 of (S615), It may be determined whether the measurement of time delay values and phase characteristic values of transmission paths for all ANs has been completed (S616). As a result of the determination, when there are remaining AN(s) to be measured, steps S613 to S615 are repeated for the next AN, and when the measurement of all AN(s) is completed, the measured time delay value and Calibration values determined based on the phase characteristic values may be transmitted through a calibration adjustment message (S617).

FIG. 6B is a flowchart illustrating an operation of a calibration block in the method of calibrating a mismatch of transmission paths according to FIG. 5A.

Referring to FIG. 6B, the calibration block 324-2 receives a CAL command message (AID= , Dir = Tx) can be received (S621). That is, step S621 may correspond to step S510 in FIG. 5A.

Next, the calibration block 324-2 through the TX blocks The TX CAL waveform signal may be sequentially transmitted to the calibration controller 355 at intervals (S622, S623). That is, steps S622 and 623 may correspond to steps S521 to S524 in FIG. 5A.

Next, the calibration block 324-2 transmits a CAL completion report message to the calibration controller 355 (S624), and the AN # from the calibration controller 355. Calibration values according to time delay and phase characteristics of the transmission paths may be received through a CAL adjustment message (S625).

Finally, the calibration block 324-2 may complete the calibration of the transmission paths by setting the mismatch adjustment blocks of the transmission paths corresponding to the received calibration values (S627).

FIG. 7A is a flowchart illustrating an operation of a calibration controller in the method of calibrating mismatching of receive paths according to FIG. 5B.

Referring to FIG. 7A, the calibration controller 355 is the target of the receive path mismatch calibration. ANs and included in each AN Sets of antennas/transceivers may be identified (S711).

Calibration controller 355 A calibration command message (AID=all, DIR=rx, REP=R) may be transmitted to the calibration blocks 324-2 of the ANs (S712). That is, in the calibration command message (AID=all, Dir=rx, REP=R), the calibration target is all ANs, the calibration target path is the reception path, and the reception path calibration signal (RX CAL waveform) is repeated. It may be indicated that the number of transmissions is set to R.

Next, the calibration controller 355 may transmit a received path calibration signal to all ANs (S713). The calibration controller 355 may determine whether the reception path calibration signal has been transmitted as many times as the repeated transmission count R set by the calibration command message (S714). When the reception path calibration signal is not transmitted as many times as the set number of repeated transmissions R, the calibration controller 355 may additionally transmit the reception path calibration signal by performing steps S712 to S713 again.

When the reception path calibration signal is transmitted as many times as the number of repeated transmissions (R) set for the ANs, the calibration controller 355 A CAL completion report message including time delay values and phase characteristic values of reception paths may be received from the ANs (S715).

Finally, the calibration controller 355 A calibration adjustment message including a calibration value in which the measured time delay value and the phase characteristic value are reflected may be transmitted to the ANs (S716).

FIG. 7B is a flowchart illustrating an operation of a calibration block in the method of calibrating mismatching of receive paths according to FIG. 5B.

Referring to FIG. 7B , the calibration block 324-2 may receive a calibration command message (AID=all, DIR=Rx, REP=R) from the calibration controller 355 (S721). That is, step S721 may correspond to step S550 in FIG. 5B.

Next, the calibration block 324-2 A reception path calibration signal (RX CAL waveform) for the number of reception paths may be received from the calibration controller 355 (S722). That is, step S722 may correspond to step S561 in FIG. 5A. The calibration block 324-2 determines whether the received path calibration signal is received for the set number of repeated transmissions (R) (S723), and if the received path calibration signal is not received for the set number of repeated transmissions (R), the calibration block (324-2) may additionally receive the receive path calibration signal by performing step S722 again.

Next, the calibration block 324-2 determines a time delay value and a phase characteristic value for each receive path, and determines the maximum value of the time delay values. and the maximum value of the phase characteristic values can be derived (S724).

The calibration block 324-2 provides the maximum value of the time delay to the calibration controller 355. and phase characteristic maximum Sends a calibration completion report message including (S725), and AN # from the calibration controller 355 Calibration values according to time delay values and phase characteristic values of the transmission paths may be received through a calibration adjustment message (S726).

Finally, the calibration block 324-2 may complete calibration of the reception paths by setting mismatch adjustment blocks of the reception paths corresponding to the received calibration values (S727).

Channel reversibility calibration

When the calibration of the distributed transmit paths and receive paths is completed according to the procedures described with reference to FIGS. 5A to 7B, the calibration controller 355 will calibrate the transmit/receive mismatch of transceivers of a specific AN. can Such mismatch calibration is referred to as TDD channel reversible calibration. Hereinafter, a TDD channel reversibility calibration operation of a specific AN through a calibration controller will be described with reference to FIGS. 8A and 8B.

8A is a flowchart illustrating a method of performing calibration for TDD channel reversibility in serial fronthaul according to an embodiment of the present invention.

Referring to FIG. 8A, a calibration controller 355 and AN # for measuring and calibrating TDD channel reversible mismatch The interaction between the calibration blocks 324-2 of is shown.

Calibration controller 355 is AN # A calibration command (AID=l, DIR=Tx/Rx) message may be transmitted to the calibration block 324-2 of the data and control signal line 312 to indicate mismatch measurement for TDD channel reversibility (S811). . Here, DIR may be set to 'Tx/Rx' to indicate that the calibration command is a TDD channel reversible mismatch measurement command.

The calibration controller 355 transmits a TDD channel reversible calibration signal (TDD Ch. Rec. CAL waveform) through a calibration transmission (CAL TX) path (S812), which transmits the calibration signal line 311 of the serial fronthaul 310 via AN# included in It can be distributed to 2 receive paths and detected in the calibration block 324-2. AN# receive path of (RX ) Received signal gain of the TDD channel reversible calibration signal received through may be expressed as in Equation 9 below according to the delivery path.

In Equation 9, Is a gain characteristic value of the calibration transmission (CAL TX) path of the calibration device 350, At the S _CAL point of the calibration device 350 is the gain characteristic value up to the point, Is at the branch is the gain characteristic value up to the point, AN# at the S _CAL branch of is the gain characteristic value up to the point, AN# receive path of is the gain characteristic value of above , , and is a well-known gain characteristic value, is also the gain characteristic value of the common path. AN# The calibration block 324-2 of Gain characteristic values of the TDD channel reciprocity calibration signal received through the i receive paths ( ) may be measured, and the measured values may be included in the calibration report message and reported to the calibration controller 355 through the serial fronthaul data and control signal line 312 (S813).

AN# The calibration block 324-2 of TDD channel reversible calibration signals are sequentially transmitted through the transmission paths (S814 to S817), and each transmission signal is detected by the calibration controller 355 through the calibration reception (CAL RX) path of the calibration device 350. AN# tx Received signal gain of the TDD channel reciprocity calibration signal transmitted through a path and received through a calibration reception (CAL RX) path of the calibration controller 350 may be expressed as in Equation 10 below according to the delivery path.

In Equation 10, Is a gain characteristic value of the calibration receiving (CAL RX) path of the calibration device 350, At the S _CAL point of the calibration device 350 is the gain characteristic value up to the point, Is at the branch is the gain characteristic value up to the point, AN# at the S _CAL branch of is the gain characteristic value up to the point, AN# tx is the value of the gain characteristic of the path. above , , and is a well-known gain characteristic value, is also the gain characteristic value of the common path. The calibration block 324-2 is After transmitting the TDD channel reversibility calibration signal on the -th TX path, the completion of transmission of the TDD channel reversibility calibration signal may be reported by transmitting a calibration completion report message to the calibration controller 355 (S818). Calibration controller 355 received through the calibration completion report message determined through values and measurements Using the values, AN # included in Gain calibration values of the dog transceivers It can be calculated as in Equation 11 below.

remind The gain calibration values of the transceivers are transmitted to the calibration block 324-2 through a calibration adjust message (S819), and the calibration block 324-2 converts the corresponding calibration values to the corresponding gain adjustment value of the mismatch adjustment block. will be set to

8B is a flowchart illustrating an operation of a calibration controller in a method of performing calibration for TDD channel reversibility in serial fronthaul according to an embodiment of the present invention.

Referring to FIG. 8B , operations of a calibration controller for calibrating TDD channel reversible mismatch of all ANs connected to a serial fronthaul based on the procedure of measuring TDD channel reversible mismatch of a specific AN and calculating calibration values described with reference to FIG. 8A The procedure is shown.

Referring to FIG. 8B, the calibration controller 355 first connects AN # to the serial fronthaul. It may be determined whether calibration of the transmission paths and the reception paths of is completed (S821).

AN# connected to serial fronthaul When the calibration of the transmission paths and reception paths of AN is completed, the calibration controller 355 AN # Calibration command message (ADI = , DIR=tx/rx) is transmitted (S822), and AN # A TDD channel reciprocity calibration signal (TDD Ch. Rec. CAL waveform) may be transmitted through a calibration transmission (CAL TX) path to the calibration block 324-2 of (S823).

Calibration controller 355 is AN # Receives a calibration report message from the calibration block 324-2 of AN # Gain of receive paths of can be checked (S824).

Calibration controller 355 is AN # of A TDD channel reciprocity calibration signal may be received through the th transmission path, and a gain of the transmission path may be measured (S825). The above step (S825) is AN # of It can be repeated for the number of transmission paths.

Calibration controller 355 is AN # Receives a calibration completion report message from the calibration block 324-2 of AN # of Gain calibration values of the dog transceivers can be calculated (S727), and a calibration adjustment message including the calculated gain calibration values is sent to AN # It can be delivered to (S728).

Hierarchical Calibration

9 is a conceptual diagram for explaining a connection structure of a serial front hall according to an embodiment of the present invention.

Referring to FIG. 9, each serial fronthaul link connects one CAL device and a plurality of ANs, the plurality of serial fronthaul links connects to a CP, and the plurality of serial fronthaul links connects to a connector. ) An embodiment connected by ) is shown. That is, one CP includes a serial fronthaul including a first calibration device (CAL device 1), a serial fronthaul including a second calibration device (CAL device 2), and a third calibration device (CAL device 3) serial fronthaul is connected. In particular, the serial fronthaul including the third calibration device (CAL device 3) includes the serial fronthaul including the fourth calibration device (CAL device 4) and the serial fronthaul including the fifth calibration device (CAL device 5) through the connector. It is connected to the front hall. As such, calibration must be performed for all distributed ANs connected to the CP through a plurality of serial frontholes. Hereinafter, a procedure for calibrating distributed ANs by collaborating with a plurality of calibration devices will be described.

As one of the calibration methods for a system composed of a plurality of serial fronthauls as shown in FIG. Mismatches between all included RF paths can be directly corrected by the method proposed in FIGS. 3 to 8B. This method has the highest accuracy and reliability, but may lack scalability as the time required for mismatch calibration increases.

Therefore, to maximize scalability, a hierarchical calibration scheme may be considered. For example, after the mismatch calibration between the CP and the calibration devices (CAL devices 1 to 5) is first completed, the calibration devices perform mismatch calibration with ANs of the local fronthaul (ie, ANs connected to the fronthaul including the corresponding calibration device). can be performed in parallel. A calibration method considering the scalability described above will be described with reference to FIGS. 10 and 11 .

10 is a conceptual diagram for explaining a hierarchical calibration method according to an embodiment of the present invention in a system composed of a plurality of serial fronthauls.

Referring to FIG. 10, the CP can check the topology of the serial fronthaul (s) included in the system through communication with all ANs and calibration devices (CAL 1 to 5) connected through the serial fronthaul ( S1001). The CP may determine the occurrence of an event indicating the need for mismatch calibration through an event such as expiration of a timer having a predetermined cycle or topology change (S1002). When a mismatch calibration event occurs, the CP may set itself as a single calibration controller and perform a mismatch calibration procedure targeting calibration devices (CALs 1 to 5) included in a plurality of serial fronthauls (S1003). Through this, after the mismatch between all calibration devices is calibrated, each of the calibration devices (CALs 1 to 5) may perform mismatch calibration with the local ANs of the serial fronthaul including the calibration devices (S1004). Mismatch calibration between the aforementioned calibration devices and local ANs can be performed in parallel, so that the calibration procedure can be quickly completed.

11 is a conceptual diagram for explaining a hierarchical calibration method according to another embodiment of the present invention in a system composed of a plurality of serial fronthauls.

As shown in FIG. 9, the third calibration device (CAL device 3), the fourth calibration device (CAL device 4), and the fifth calibration device (CAL device 5) are connected to each other through a connector, and the third It can be connected to the CP through a serial fronthaul that includes a calibration device (CAL device 3).

Referring to FIG. 11, the CP can check the topology of the serial fronthaul (s) included in the system through communication with all ANs and calibration devices (CALs 1 to 5) connected through the serial fronthaul (S1101). The CP may determine the occurrence of an event indicating the need for mismatch calibration through an event such as expiration of a timer having a predetermined cycle or topology change (S1102). When a mismatch calibration event occurs, the CP may set itself as a single calibration controller and first perform mismatch calibration with the calibration devices (CALs 1 to 3) of serial front holes directly connected to the CP (S1103). After that, the third calibration device (CAL 3) directly connected to the CP serves as a calibration controller and performs mismatch calibration with the fourth calibration device (CAL 4) and the fifth calibration device (CAL 5) connected through the connector. It can (S1104).

Meanwhile, the first to third calibration devices that have completed the mismatch calibration directly with the CP may perform calibration with the ANs of each local serial fronthaul (S1105), and via the third calibration device, the CP and the mismatch calibration are completed The fourth and fifth calibration devices may also perform calibration with the ANs of each local serial fronthaul (S1106).

12 is a conceptual diagram for explaining the configuration of a communication node according to an embodiment of the present invention.

A communication node according to an embodiment of the present invention illustrated in FIG. 12 may be the previously described calibration controller, an access node (AN), or a central processing unit (CP).

Referring to FIG. 12 , a communication node 1200 may include at least one processor 1210, a memory 1220, and a transceiver 1230 connected to a network to perform communication. In addition, the communication node 1200 may further include an input interface device 1240, an output interface device 1250, a storage device 1260, and the like. Respective elements included in the communication node 1200 may be connected by a bus 1270 to communicate with each other.

However, each component included in the communication node 1200 may be connected through an individual interface or an individual bus centered on the processor 1210 instead of the common bus 1270 . For example, the processor 1210 may be connected to at least one of the memory 1220, the transmission/reception device 1230, the input interface device 1240, the output interface device 1250, and the storage device 1260 through a dedicated interface. .

The processor 1210 may execute a program command stored in at least one of the memory 1220 and the storage device 1260 . The processor 1210 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 1220 and the storage device 1260 may include at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 1220 may include at least one of a read only memory (ROM) and a random access memory (RAM).

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

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

Although described with reference to the above embodiments, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the present invention described in the claims below. You will be able to.

Claims (20)

at least one calibration device; and dog( is a natural number of 1 or more) as a calibration method in a serial fronthaul in which access node (AN)(s) are connected in series,
The calibration device is Transmitting, to at least some of the AN(s), a calibration command message instructing calibration of transmission paths of transceivers of the at least some AN(s) (a);
(b) determining, by the calibration device and the at least some AN(s), time delay values and phase characteristic values of transmission paths of transceivers of the at least some AN(s); and
The calibration device determines the transmission path of the transceivers of the at least some AN(s) to the at least some AN(s) based on the time delay values and phase characteristic values of the transmission paths of the transceivers of the at least some AN(s). (c) transmitting a calibration adjustment message indicating calibration of
The in-line fronthaul is:
The calibration device and the a timing clock signal line for clock synchronization between the number of AN(s);
The calibration device and the a calibration signal line for transferring a calibration signal between the two AN(s); and
The calibration device and the Including data and control signal lines for transferring data and control signals for calibration between the two AN(s),
Calibration method. The method of claim 1,
The step (b) is:
of said at least some AN(s) The th AN recalls the transmission path calibration signal th AN contains transmitting to the calibration device through each of the transmission paths of the transceivers (b-1);
The calibration device is of the transmission paths of the transceivers The time delay value of the transmission path of the th transceiver is defined as the value of the transmission path calibration signal. determining based on a difference between a transmission time in the AN-th and a reception time in the calibration device (b-2); and
The calibration device is of the transmission paths of the transceivers Determining a phase characteristic value of a transmission path of a th transceiver based on a difference between a phase at the transmission time point and a phase at the reception time point of the transmission path calibration signal (b-3).
Calibration method. The method of claim 2,
The step (b) is:
remind th AN above reporting time delay values and phase characteristic values of transmission paths of the N transceivers to the calibration device (b-4); and
Step (b-5) of the calibration device determining time delay values and phase characteristic values of transmission paths of the transceivers of the at least some AN(s) through the steps (b-1) to (b-4) Including with,
Calibration method. The method of claim 2,
The transmission path calibration signals are transmitted at the time of transmission of the calibration command message ( ) from a predetermined time ( ) after elapsed, the time interval ( ), which are sequentially transmitted,
Calibration method. The method of claim 1,
The step (c) is:
The calibration device calculates a maximum time delay value among time delay values of transmission paths of transceivers of the at least some AN(s) and the Recall of the second AN The difference between the time delay values of the transmission path of the th transceiver determining a time delay calibration value of a transmission path of a th transceiver (c-1);
The calibration device determines the maximum phase characteristic value among the phase characteristic values of the transmission paths of the transceivers of the at least some AN(s) and the Recall of the second AN The difference between the phase characteristic values of the transmission path of the th transceiver determining a phase characteristic calibration value of a transmission path of a th transceiver (c-2); and
The calibration device is The time delay calibration value and the phase characteristic calibration value of the transmission path of the th transceiver are Including step (c-3) of transmitting a calibration adjustment message to the th AN,
Calibration method. delete The method of claim 1,
The calibration device exists as a separate hardware device, or One of the AN(s) serves as the calibration device, or A central processor (CP) connected to the number of AN(s) through the serial fronthaul serves as the calibration device,
Calibration method. at least one calibration device; and dog( is a natural number of 1 or more) as a calibration method in a serial fronthaul in which access node (AN)(s) are connected in series,
The calibration device Transmitting, to at least some AN(s) of the AN(s), a calibration command message instructing calibration of reception paths of transceivers of the at least some AN(s) (a);
(b) determining, by the calibration device and the at least some AN(s), time delay values and phase characteristic characteristic values of receive paths of transceivers of the at least some AN(s);
Transceivers of the at least some AN(s) to the at least some AN(s) based on time delay values and phase characteristic values of receive paths of the transceivers of the at least some AN(s) (c) transmitting a calibration adjustment message indicating calibration of receive paths of
The in-line fronthaul is:
The calibration device and the a timing clock signal line for clock synchronization between the number of AN(s);
The calibration device and the a calibration signal line for transferring a calibration signal between the two AN(s); and
The calibration device and the Including data and control signal lines for transferring data and control signals for calibration between the two AN(s),
Calibration method. The method of claim 8,
The step (b) is:
The calibration device transmits a received path calibration signal to one of the at least some AN(s). th AN contains Through each of the receive paths of the transceivers Transmitting to the th AN (b-1);
remind th AN above of the receive paths of the transceivers Recall the time delay value of the receive path of the th transceiver A transmission time in the calibration device of the reception path calibration signal received through the reception path of the th transceiver and the Step (b-2) of determining based on a difference between reception points in the th AN;
remind th AN above of the receive paths of the transceivers determining a phase characteristic value of a transmission path of a th transceiver based on a difference between a phase of the reception path calibration signal at the transmission time point and a phase at the reception time point (b-3); and
remind th AN through the steps (b-1) to (b-3) Further comprising the step (b-4) of determining delay characteristic values and phase characteristic values of the receive paths of the transceivers and reporting them to the calibration device.
Calibration method. The method of claim 9,
When the calibration command message indicates the number of repetitions R of the reception path calibration signal, the reception path calibration signal It is repeatedly transmitted R times in the reception path of the th transceiver, The time delay value and phase characteristic value for the receive path of the th transceiver are determined based on R repeated transmissions of the receive path calibration signal,
Calibration method. The method of claim 9,
The received path calibration signals are transmitted at the time of transmission of the calibration command message ( ) from a predetermined time ( ) after elapsed, the time interval ( ), which are sequentially transmitted,
Calibration method. The method of claim 8,
The step (c) is:
The calibration device determines the maximum time delay value among the time delay values of the receive paths of the transceivers of the at least some AN(s) and the maximum phase characteristic value among the phase characteristic values of the receive paths of the transceivers of the at least some AN(s). Step of determining (c-1);
The calibration device determines the maximum time delay value and the The difference between the maximum time delay values of the receive paths of the transceivers of the th AN determining the time delay calibration values of the transceivers of the th AN (c-2);
The calibration device determines the maximum phase characteristic value and the The difference between the maximum phase characteristic values of the reception paths of the transceivers of the th AN determining a phase characteristic calibration value of the th AN (c-3); and
The calibration device recalls the time delay calibration value and the phase characteristic calibration value Further comprising the step (c-4) of transmitting a calibration adjustment message to the th AN,
Calibration method. delete The method of claim 8,
The calibration device exists as a separate hardware device, or One of the AN(s) serves as the calibration device, or A central processor (CP) connected to the number of AN(s) through the serial fronthaul serves as the calibration device,
Calibration method. at least one calibration device; and dog( is a natural number of 1 or more) as a calibration method in a serial fronthaul in which access node (AN)(s) are connected in series,
The calibration device is of the AN(s) Transmitting a calibration command message indicating calibration for time division duplexing (TDD) channel reciprocity to a th AN (a);
The calibration device and the th AN above included in the second AN Gain characteristic values of the receive paths of the transceivers and measuring gain characteristic values of transmission paths of the N transceivers (b); and
The calibration device is Gain characteristic values of the receive paths of the N transceivers and the Based on the gain characteristic values of the transmission paths of the transceivers Determines a gain calibration value of each of the receive paths of the transceivers and sends a calibration adjustment message including the gain calibration value Including the step (c) of transmitting to the th AN,
The in-line fronthaul is:
The calibration device and the a timing clock signal line for clock synchronization between the number of AN(s);
The calibration device and the a calibration signal line for transferring a calibration signal between the two AN(s); and
The calibration device and the Including data and control signal lines for transferring data and control signals for calibration between the two AN(s),
Calibration method. The method of claim 15
The step (b) is:
The calibration device Remind with the second AN included in the second AN transmitting a TDD channel reciprocity calibration signal through receive paths of the N transceivers;
remind th an reporting a received signal gain measurement value of the TDD channel reciprocity calibration signal for each of the receive paths of the N transceivers to the calibration device;
remind th AN above included in the second AN transmitting a TDD channel reversibility calibration signal to the calibration device through transmission paths of the transceivers; and
The calibration device Further comprising measuring a received signal gain of the TDD channel reciprocity calibration signal for each of the transmit paths of the transceivers.
Calibration method. The method of claim 16
The TDD channel reversibility calibration signals are transmitted at the time of transmission of the calibration command message ( ) or a predetermined time from the time of reporting the measured value of the received signal gain ( ) after elapsed, the time interval ( ), which are sequentially transmitted,
Calibration method. delete The method of claim 15
The calibration device exists as a separate hardware device, or One of the AN(s) serves as the calibration device, or A central processor (CP) connected to the number of AN(s) through the serial fronthaul serves as the calibration device,
Calibration method. The method of claim 15
Downlink channel information for the ANs is estimated from uplink channel information for the ANs using the TDD channel reciprocity,
Calibration method.

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