KR20180105895A - Communication node and operation method of the communication node - Google Patents

Abstract

Disclosed are a first communication node capable of variably adjusting a TDD transmission/reception switching time and an operation method thereof. The operation method comprises the steps of: receiving a signal from a second communication node; estimating a starting point of a frame from a preamble included in the signal; setting a TDD reception period and a TDD transmission period based on the starting point of the estimated frame; and performing switching between a transmission mode and a reception mode based on the set TDD transmission period and the TDD reception period.

Description

TECHNICAL FIELD [0001] The present invention relates to a communication node and a communication node,

The present invention relates to a method of operating a communication node and a communication node, and more particularly, to a method for compensating for a signal delay effect between a first communication node and a second communication node in a time division duplex scheme.

The communication system may be a core network (e.g., a mobility management entity (MME), a serving gateway (SGW), a packet data network (PDW) A small base station, a relay, etc.), a terminal, and the like. Communication between a base station and a terminal may be performed using various radio access technologies (e.g., 4G communication technology, 5G communication technology, WiBro (wireless broadband) technology, wireless local area network (WLAN) Etc.). ≪ / RTI >

Many methods have been discussed to increase data throughput. A frequency division duplex (FDD) scheme and a time division duplex scheme (TDD) scheme have been proposed as a multiplexing scheme. TDD is a system designing system in which signal flows of a down link and an up link are temporally distinguished and is superior in frequency use efficiency to FDD.

In a communication system, a base station can be divided into a digital unit (DU) and a radio unit (RU) according to a supporting function. Alternatively, the base station may be divided into a cloud digital unit (CDU) and a remote radio head (RRH). In such a distributed base station, the function of the base station can be performed by devices physically different. In the case of a distributed base station, a time delay may occur in a signal transmission process between communication nodes serving as a base station. And, this time delay can be an obstacle to the TDD system in which synchronization is important.

The present invention proposes an operation method of a communication node and a communication node capable of variably adjusting a TDD transmission / reception switching time in consideration of a time delay occurring in a distributed base station.

According to an aspect of the present invention, there is provided an operation method performed at a first communication node of a communication network, the method comprising: receiving a signal from a second communication node; Estimating a starting point of a frame from a preamble included in the signal; Setting a TDD reception period of the TDD transmission period based on the starting point of the estimated frame; And switching between the transmission mode and the reception mode based on the set TDD transmission period and the TDD reception period.

Here, the first communication node may be a radio unit device, and the second communication node may be a digital unit device.

Here, the method of operating the first communication node may further include transmitting the preamble in the TDD transmission interval.

Here, the setting of the TDD transmission period and the TDD reception period may include:

It is possible to change at least one of the start point of the TDD transmission interval and the start point of the TDD reception interval without changing the size of the preset TDD transmission interval and the size of the TDD reception interval.

Here, the method of operating the first communication node may further include generating a TDD switching signal based on the TDD reception period and the TDD transmission period,

The performing of the switching may switch between the transmission mode and the reception mode by the TDD switching signal.

The generating of the TDD switching signal may determine a time at which the intensity of the TDD switching signal is changed based on the TDD reception period and the TDD transmission period.

Wherein the generating of the TDD switching signal includes changing a frame start point of the TDD switching signal based on the TDD reception period and the TDD transmission period, The pattern of the signal may not be changed.

The signal may be an optical signal received via an optical cable.

The optical signal may be an analog optical signal.

A first communication node of a communication network, according to an embodiment of the present invention,

A processor; And a memory in which at least one instruction executed via the processor is stored,

Wherein the at least one instruction comprises:

Estimates a start point of a frame from a preamble included in the signal, sets a TDD reception period of the TDD transmission period based on the starting point of the estimated frame, May be performed to switch between the transmission mode and the reception mode based on the TDD reception period.

The first communication node may be a radio unit device, and the second communication node may be a digital unit device.

Wherein the at least one instruction comprises:

And to transmit the preamble using a downlink signal.

Wherein the at least one instruction comprises:

The size of the TDD transmission interval and the size of the TDD reception interval may be changed without changing the size of the TDD transmission interval and the starting point of the TDD transmission interval.

Wherein the at least one instruction comprises:

Generating a TDD switching signal based on the TDD reception period and the TDD transmission period, and switching the transmission mode and the reception mode by the TDD switching signal.

Wherein the at least one instruction comprises:

And may be performed to determine a time point at which the strength of the TDD switching signal is changed based on the TDD reception period and the TDD transmission period.

Wherein the at least one instruction comprises:

The frame start timing of the TDD switching signal is changed based on the TDD reception period and the TDD transmission period and the pattern of the TDD switching signal after the frame start point of the predetermined TDD switching signal is not changed have.

The signal may be an optical signal received via an optical cable.

The optical signal may be an analog optical signal.

According to the present invention, the starting point of a signal frame is estimated from the preamble of the signal received from the second communication node by the first communication node, and the TDD transmission period and the TDD reception period are set by utilizing the starting point of the signal frame, It is possible to prevent a distortion or a ripple phenomenon. Further, by generating the TDD switching signal based on the TDD transmission period and the TDD reception period set by the first communication node, the switching point between the transmission mode and the reception mode can be appropriately changed. Further, even when the first communication node and the second communication node communicate using the analog optical signal, it is possible to prevent signal jamming or signal distortion that may occur due to the transmission delay time between the first communication node and the second communication node can do.

1 is a block diagram illustrating a communication node performing a method of operating a communication node in a communication network according to an embodiment of the present invention.
2 is a conceptual diagram illustrating an example of a distributed base station.
3 is a conceptual diagram illustrating a problem caused by a transmission delay time between the first communication nodes and the second communication node.
4 is a flow diagram illustrating a method of operating one of the first communication nodes in accordance with an exemplary embodiment of the present invention.
5 is a conceptual diagram illustrating an example of switching between a transmission mode and a reception mode based on a TDD transmission period and a TDD reception period in which the first communication node is set.
6 is a flowchart illustrating a method of operating a first communication node in accordance with another exemplary embodiment of the present invention.
7 is a conceptual diagram illustrating an example of a TDD switching signal generated by the first communication node in step S135.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

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

It is to be 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, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

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

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the present invention, the same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.

Throughout the specification, the network can be, for example, a wireless Internet such as WiFi (wireless fidelity), a wireless broadband internet (WiBro) or a portable internet such as world interoperability for microwave access (WiMax) A 3G mobile communication network such as a Wideband Code Division Multiple Access (WCDMA) or CDMA2000, a high speed downlink packet access (HSDPA), or a high speed uplink packet access (HSUPA) A 3.5G mobile communication network, a 4G mobile communication network such as an LTE (Long Term Evolution) network or an LTE-Advanced network, a 5G mobile communication network, and a C-RAN (Cloud Radio Access Network).

Throughout the specification, a terminal is referred to as a mobile station, a mobile terminal, a subscriber station, a portable subscriber station, a user equipment, an access terminal, A terminal, a mobile station, a mobile station, a subscriber station, a mobile subscriber station, a user equipment, an access terminal, and the like.

Throughout the specification, a base station is referred to as an access point, a radio access station, a node B, an evolved node B, a base transceiver station, an MMR mobile multihop relay) -BS, and may include all or some of the functions of a base station, an access point, a radio access station, a Node B, an eNodeB, a base transceiver station, and a MMR-BS.

Throughout the specification, a decentralized base station means a base station in which the function of the base station is divided into a digital unit and a wireless unit.

Hereinafter, a method of operating a communication node in a communication network according to an embodiment of the present invention and a communication node performing the same will be described.

1 is a block diagram illustrating a communication node performing a method of operating a communication node in a communication network according to an embodiment of the present invention.

Referring to FIG. 1, a communication node 100 may include at least one processor 110, a memory 120, and a network interface device 130 for communicating with a network. The communication node 100 may further include an input interface device 140, an output interface device 150, a storage device 160, and the like. Each component included in the communication node 100 may be connected by a bus 170 and communicate with each other.

The processor 110 may execute a program command stored in the memory 120 and / or the storage device 160. The processor 110 may refer to a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the methods of the present invention are performed. The memory 120 and the storage device 160 may be composed of a volatile storage medium and / or a non-volatile storage medium. For example, the memory 120 may be comprised of read only memory (ROM) and / or random access memory (RAM). Here, a program instruction executed through the processor 310 may include a plurality of steps for performing a method of operating a communication node in the communication network proposed by the present invention.

2 is a conceptual diagram illustrating an example of a distributed base station.

Referring to FIG. 2, a distributed base station may include first communication nodes 202, 204, 206 and a second communication node 300. The first communication nodes 202, 204, 206 and the second communication node 300 may be spatially separated. The first communication nodes 202, 204, and 206 may be installed at different locations to provide services to different areas. The second communication node 300 may process signals in the baseband and intermediate frequency bands and the first communication nodes 202, 204, 206 may process signals in the radio frequency band. The first communication nodes 202, 204, and 206 may be radio unit (RU) devices. The second communication node 300 may be a digital unit (DU) device.

Communication between the first communication nodes 202, 204, 206 and the second communication node 300 may be via the optical cables 402, 404, 406. The second communication node 300 may convert the analog type intermediate frequency signal into an optical signal and transmit it to the first communication nodes 202, 204, and 206 through the optical cables 402, 404, and 406. Optical cables 402,404 and 406 may couple between the first communication nodes 202,204 and 206 and the second communication node 300, respectively. The location of each of the first communication nodes 202, 204, 206 may be different. Therefore, the lengths of the first optical cable 402, the second optical cable 404, and the third optical cable 406 may be different from each other. In addition, the length of the optical cables 402, 404, 406 may be non-fixed and variable.

Communication through the optical cables 402, 404, 406 may be an analog optical signal or a digital optical signal. The intensity of the analog optical signal can be continuously changed. On the other hand, the intensity of a digital optical signal may be discontinuously changed. Since a digital optical signal carries each sample signal in a digital form, a relatively large transmission capacity may be required. On the other hand, since the analog optical signal transmits an analog type signal intact, a relatively small transmission capacity may be required.

Because the propagation speed of the optical signal in the optical cables 402, 404 and 406 is finite, the signal transmission between the second communication node 300 and the first communication nodes 202, 204 and 206, respectively, This can be. The transmission delay time may vary depending on the length of the optical cables 402, 404, 406. The transmission delay time in each of the optical cables 402, 404, 406 may be variable. When using a digital optical signal, the transmission delay time can be measured using the clock counters across the first communication nodes 202, 204, 206 and the second communication node 300. However, when an analog optical signal is used, it may be difficult to measure the transmission delay time.

The first communication nodes 202, 204, and 206 may use Time Division Duplex (TDD) when providing services to the UE. The first communication nodes 202, 204, and 206 may temporally distinguish the downlink signal transmitted to the UEs from the uplink signal received from the UEs.

The first communication nodes 202, 204, and 206 can maintain the transmission mode in the time interval for transmitting the downlink signals to the terminals and can switch to the reception mode in the time interval in which the uplink signals are received from the terminals . Since the time division duplex scheme does not have to separate the downlink frequency and the uplink frequency, the frequency efficiency can be increased. In the time division duplex scheme, it is important that the base station and the UE accurately share the start point of the uplink time interval and the start point of the downlink time interval.

In the case of the distributed base station as described above, the second communication node 300 for generating a control command for the UEs, and a second communication node 300 for transmitting a downlink signal to the actual UEs, The nodes 202, 204, and 206 may be located in different spaces. Because of the transmission delay time between the first communication nodes 202, 204, 206 and the second communication node 300, the first communication nodes 202, 204, 206 and the first communication nodes 202 , 204, and 206 may not be accurate in time synchronization between the terminals providing the service.

FIG. 3 is a conceptual diagram illustrating a problem caused by a transmission delay time between the first communication nodes 202, 204, and 206 and the second communication node 300. FIG.

3, the first communication nodes 202, 204, and 206 are located at the start of the frame (e.g., the first communication node 202, 204, 206), due to the transmission time delay between the first communication nodes 202, Can be set incorrectly. The starting point of the frame may be the start point of the downlink signal frame or the start point of the uplink signal frame. For example, when the first communication nodes 202, 204, and 206 switch to the reception mode before the transmission of the downlink signal is completed, a part of the downlink signal may be missed. Likewise, if the transmission mode is switched before the reception of the uplink signal is completed, a part of the uplink signal may not be received. As a result, the service quality of the communication network may be deteriorated.

4 is a flow diagram illustrating a method of operating one of the first communication nodes 202, 204, 206 in accordance with an exemplary embodiment of the present invention. For convenience, 202 nodes among the first communication nodes 202, 204, and 206 will be described as an example.

Referring to FIG. 4, in step S110, the first communication node 202 may receive a signal from the second communication node 300. FIG. The first communication node 202 can check the preamble included in the signal received from the second communication node 300. The second communication node 300 may attach a preamble to the head of the frame to be transmitted to the first communication node 200. [ The preamble can be utilized for time synchronization between the terminal and the base station.

In step S120, the first communication node 202 can estimate the starting point of the signal frame received from the second communication node 300 from the preamble of the signal. For example, the first communication node 202 can estimate the start time of a signal frame by checking the time when the preamble signal is received from the second communication node 300.

In step S130, the first communication node 202 may set the TDD transmission period and the TDD reception period from the start point of the signal frame.

 In the TDD transmission period, the first communication node 202 may transmit the downlink signal. In the TDD reception period, the first communication node 202 may transmit an uplink signal. The first communication node 202 may change at least one of a starting point of the TDD transmission period and a starting point of the TDD reception period based on the starting point of the estimated frame. For example, the first communication node 202 may delay the start time of the TDD transmission interval shown in FIG. 3, thereby preventing the downlink transmission signal from being missed.

The first communication node 202 may not change the size of the TDD transmission interval and the size of the TDD reception interval when setting the TDD transmission interval and the TDD reception interval. The first communication node 202 may not change the size of the duration of the TDD transmission interval from the start of the changed TDD transmission interval. The first communication node 202 may not change the duration of the duration of the TDD reception interval from the start time of the TDD reception interval. The size of the TDD transmission interval and the size of the TDD reception interval can be determined according to the LTE standard. As another example, the TDD transmission period and the TDD reception period may be set in advance according to the amount of transmission data and the amount of reception data. The first communication node 202 may change the starting point of the TDD transmission interval and the starting point of the TDD reception interval so that the duration of each of the intervals may be the same as the predetermined interval.

In step S140, the first communication node 202 may perform switching between the transmission mode and the reception mode based on the set TDD transmission period and the TDD reception period.

5 is a conceptual diagram illustrating an example in which switching between the transmission mode and the reception mode is performed based on the TDD transmission period and the TDD reception period in which the first communication node 202 is set.

Referring to FIG. 5, the first communication node 202 may change the switching time between the transmission mode and the reception mode based on the TDD transmission period and the TDD reception period. For example, as shown in FIG. 3, if the TDD transmission period ends before all the downlink signals are transmitted or the TDD reception period ends before all the uplink signals are received, the first communication node 202 transmits The starting point of the TDD transmission period and the starting point of the TDD reception period may be delayed in consideration of the starting point.

 The first communication node 202 may delay the switching time from the transmission mode to the reception mode according to the delayed TDD transmission period and the TDD reception period. Also, the first communication node 202 may delay the time point of switching from the reception mode to the transmission mode again. The first communication node 202 may delay the start time of the TDD transmission interval and the start time of the TDD reception interval. The first communication node 202 can maintain the duration of the TDD transmission interval after the start time of the TDD transmission interval and the duration of the TDD reception interval after the start time of the TDD reception interval as before. The first communication node 202 can prevent the trimming of the downlink signal and the uplink signal by changing the switching point between the transmission mode and the reception mode.

In step S150, the first communication node 202 may transmit the preamble received from the second communication node 300 through the downlink signal. The first communication node 202 may transmit a preamble using a downlink signal in a TDD transmission period. The UEs in the cell coverage in which the first communication node 202 provides service can receive the downlink signal including the preamble. The UEs can check the preamble and use it to time synchronize with the first communication node 202. The UEs can synchronize with the first communication node 202 by adjusting the TDD transmission period and the TDD reception period by checking the preamble.

6 is a flow diagram illustrating a method of operating a first communications node 202 in accordance with another exemplary embodiment of the present invention. In the description of the embodiment of Fig. 6, the description of the contents overlapping with those of Fig. 4 is omitted.

Referring to FIG. 6, in step S135, the first communication node 202 may generate a TDD switching signal based on the set TDD transmission period and the TDD reception period. In step S140, the first communication node 202 may perform switching between the transmission mode and the reception mode by the TDD switching signal. The first communication node 202 can determine the switching time between the transmission mode and the reception mode by sensing a change in the TDD switching signal.

7 is a conceptual diagram illustrating an example of a TDD switching signal generated by the first communication node 202 in step S135.

Referring to FIG. 7, the first communication node 202 may generate a TDD switching signal based on a TDD transmission period and a TDD reception period. The first communication node 202 may perform switching from the transmission mode to the reception mode or from the reception mode to the transmission mode in accordance with the TDD switching signal. For example, the first communication node 202 can maintain the transmission mode when the strength of the TDD switching signal is equal to or greater than the reference value. In the transmission mode, the first communication node 202 may transmit the downlink signal. Further, the first communication node 202 can maintain the reception mode when the intensity of the TDD switching signal is lower than the reference value. In the receive mode, the first communication nodes 202, 204, and 206 may receive the uplink signals. The above description is merely illustrative, and the embodiment is not limited thereto. For example, the first communication node 202 may be in a receive mode when the strength of the TDD switching signal is above a reference value, and may be in a transmit mode when the strength of the TDD switching signal is below a reference value.

The first communication node 202 may determine a time point at which the intensity of the TDD switching signal is changed based on the TDD reception period and the TDD transmission period. For example, when the start time of the TDD transmission interval and the start time of the TDD reception interval shown in FIG. 3 are delayed, the first communication node 202 starts the start time of the delayed TDD transmission interval and the start time of the TDD reception interval , It is possible to delay the time point at which the intensity of the TDD switching signal is changed.

The first communication node 202 may change the starting point of the TDD switching signal frame. A TDD switching signal frame may refer to a pattern of a TDD switching signal. The size of the time interval of the frame indicating the transmission interval in the TDD switching signal frame and the size of the time interval of the frame indicating the reception interval can be determined according to the LTE communication standard or the amount of transmission data and the amount of reception data.

The first communication node 202 may delay the start time of the TDD switching signal frame when the start time of the TDD transmission period and the TDD reception period is delayed. The first communication node 202 may change the starting point of the TDD switching signal frame but not the pattern of the TDD switching signal after the starting point of the TDD switching signal frame. That is, after the starting point of the TDD switching signal frame, the first communication node 202 can keep the size of the time interval in which the TDD switching signal is the transmission mode signal and the time interval in which the TDD switching signal is the reception mode signal, have. The size of the time interval in which the TDD switching signal is the transmission mode signal and the size of the time interval in which the TDD switching signal is the reception mode signal can be predetermined according to the LTE standard. As another example, the size of the time interval in which the TDD switching signal is the transmission mode signal and the size of the time interval in which the TDD switching signal is the reception mode signal can be predetermined according to the amount of uplink data and the amount of downlink data.

The first communication node 202 can prevent the ripple of the downlink transmission signal and the uplink reception signal by changing the start point of the TDD switching signal frame.

[0043] The operation of the communication node and the communication node according to the exemplary embodiments of the present invention has been described above with reference to Figs. According to the above-described embodiments, the first communication node estimates the start time point of a signal frame from the preamble of the signal received from the second communication node, sets the TDD transmission period and the TDD reception period by utilizing the start point of the signal frame, It is possible to prevent the occurrence of signal distortion and jerkiness. Further, by generating the TDD switching signal based on the TDD transmission period and the TDD reception period set by the first communication node, the switching point between the transmission mode and the reception mode can be appropriately changed. Further, even when the first communication node and the second communication node communicate using the analog optical signal, it is possible to prevent signal jamming or signal distortion that may occur due to the transmission delay time between the first communication node and the second communication node can do.

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

Examples of computer readable media include hardware devices that are specially configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by the compiler 1, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (18)

A method of operation performed at a first communication node of a communication network,
Receiving a signal from a second communication node;
Estimating a starting point of a frame from a preamble included in the signal;
Setting a TDD reception period of the TDD transmission period based on the starting point of the estimated frame;
And performing switching between a transmission mode and a reception mode based on the set TDD transmission period and the TDD reception period. The method according to claim 1,
Wherein the first communication node is a radio unit device and the second communication node is a digital unit device. The method according to claim 1,
And transmitting the preamble in the TDD transmission interval. The method according to claim 1,
Wherein the setting of the TDD transmission period and the TDD reception period comprises:
Wherein at least one of a start time of a TDD transmission period and a start time of a TDD reception period is changed without changing a size of a predetermined TDD transmission period and a size of a TDD reception period. The method according to claim 1,
Generating a TDD switching signal based on the TDD reception period and the TDD transmission period,
Wherein performing the switching comprises switching between the transmission mode and the reception mode by the TDD switching signal. The method of claim 5,
Wherein the generating of the TDD switching signal determines a time when the strength of the TDD switching signal is changed based on the TDD reception period and the TDD transmission period. The method of claim 5,
Wherein the generating of the TDD switching signal comprises changing a frame start point of the TDD switching signal based on the TDD reception period and the TDD transmission period, And does not change the pattern of the signal. The method according to claim 1,
Wherein the signal is an optical signal received over an optical cable. The method of claim 8,
Wherein the optical signal is an analog optical signal. A first communication node of a communication network,
A processor; And
Wherein at least one instruction executed through the processor includes a memory,
Wherein the at least one instruction comprises:
Estimates a start point of a frame from a preamble included in the signal, sets a TDD reception period of the TDD transmission period based on the starting point of the estimated frame, A first communication node is configured to switch between a transmission mode and a reception mode based on a TDD reception interval. The method of claim 10,
Wherein the first communication node is a radio unit device and the second communication node is a digital unit device. The method of claim 10,
Wherein the at least one instruction comprises:
And transmitting the preamble using a downlink signal. The method of claim 10,
Wherein the at least one instruction comprises:
Wherein the first communication node is configured to change at least one of a start point of a TDD transmission period and a start point of a TDD reception period without changing a size of a predetermined TDD transmission period and a size of a TDD reception period. The method of claim 10,
Wherein the at least one instruction comprises:
And generating a TDD switching signal based on the TDD reception period and the TDD transmission period, and switching between the transmission mode and the reception mode by the TDD switching signal. 15. The method of claim 14,
Wherein the at least one instruction comprises:
Wherein the first communication node is configured to determine when the strength of the TDD switching signal changes based on the TDD reception period and the TDD transmission period. 15. The method of claim 14,
Wherein the at least one instruction comprises:
A TDD switching signal generation unit that changes a frame start point of the TDD switching signal based on the TDD reception period and the TDD transmission period so as to not change a pattern of the TDD switching signal after a frame start point of a predetermined TDD switching signal, 1 communication node. The method of claim 10,
Wherein the signal is an optical signal received via an optical cable. 18. The method of claim 17,
Wherein the optical signal is an analog optical signal.

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