KR100770883B1 - Radio over fiber system of tdd type and method for controlling transmission time - Google Patents

Abstract

A TDD(Time Division Duplex) ROF(Radio Over Fiber) system and a method for controlling transmission time are provided to control the temporal synchronization of uplink/downlink RF signals, transmitted and received through a base station and the antenna of a remote, in a TDD wireless communication system consisting of the donor of the base station and the remote by adding transmission time delays to the RF signals. A TDD ROF system consists of a base station and a remote(300). The base station comprises a modem(110) and a donor(100). The modem(110) creates a switch control signal for the routing of uplink/downlink signals between the base station and the remote(300), and executes TDD data communication. The donor(100) creates a delay request pattern to measure the delay time based on the distance of an optical line and transmits it to the remote together with the switch control signal. Also the donor(100) measures RTT(Round Trip Time) according to the distance of the optical line and controls the transmission time of the uplink/downlink signals. The remote(300) receives the delay request pattern from the donor(100) and transmits a delay response pattern and a delay response follow up message to the donor(100). Also, the remote(300) executes the routing of the uplink/downlink signals, based on the switch control signal transmitted from the donor(100).

Description

Radio Over Fiber System of TDD Type and Method for Controlling Transmission Time} ＴＤＤ Ｒａｄｉｏ Ｏｖｅｒ Ｆｉｂｅｒ

1 is a configuration diagram schematically showing a wireless communication system using a TDD scheme

2 is a configuration diagram of a Radio Over Fiber system for wireless communication in a TDD scheme according to an exemplary embodiment of the present invention.

3 is a flowchart illustrating a transmission time synchronization control method in a Radio Over Fiber system for a TDD wireless communication according to an exemplary embodiment of the present invention.

* Description of the main drawing codes *

100: donor 110: modem

115: variable time delay module 120, 320: first and second receiving amplifier

130, 240, 330, 380: all-optical converter 140, 340: wavelength division multiplexing / demultiplexing

150, 260, 350, 370: photoelectric converter 160, 360: first and second transmission amplifier

170: time delay measuring instrument 220: time delay compensator

230: signal combiner 250, 345: first and second optical circulator

270: first signal separator 300: remote

310: RF switch 385: time transmission module

390: switch controller

The present invention is a TDD (Time Division Duplex) method of wireless communication consisting of a donor and a remote of a base station connected through an optical line, the up and down RF transmitted and received through the antenna of the base station and the remote (Remote) The present invention relates to a TDD radio over fiber system and a transmission time control method for controlling a time synchronization by adding a delay of a transmission time to a signal.

As computer, electronic, and communication technologies have made rapid progress, various wireless communication services using wireless networks have been provided. The most basic wireless communication service is a wireless voice call service that provides a voice call to a mobile terminal user wirelessly, which can provide a service regardless of time and place. In addition, while providing a text message service to complement the voice call service, a wireless Internet service has recently emerged to provide an Internet communication service to a user of a mobile communication terminal through a wireless communication network.

Recently, with the development of information and communication, IMT-2000 (International Mobile Telecommunication 2000), a third generation mobile communication system established by ITU-R as a standard, for example, CDMA (Code Division Multiple Access), EV-DO, WCDMA (WideBand) CDMA) and the like are commercially available. IMT-2000 is a mobile communication system that aims to implement various application services by combining global direct roaming including personal mobility and service mobility, same call quality as wired telephone, high speed packet data service and wired / wireless network. As a result, as well as improving existing voice and WAP service quality, various multimedia services (AOD, VOD, etc.) may be provided at a higher speed.

However, the existing mobile communication system has a limitation in providing high-speed wireless Internet due to high base station construction cost and high usage rate of the wireless Internet, and a small screen size of the mobile communication terminal, thus limiting the available contents. Wireless Local Area Network (WLAN) technology has limitations in providing public services due to problems such as radio wave interference and a narrow convergence area. Accordingly, 4G wireless mobile communication has emerged with WiBro (Wireless Broadband Internet), a high-speed portable Internet service that guarantees portability and mobility and can use high-speed wireless Internet service at a low price.

The WiBro (WiBro) and 4G wireless mobile communication uses a time division duplex (TDD) method as a duplex method, unlike code division multiple access (CDMA) and wide band CDMA (WCDMA), and a modulation method. A portable Internet technology using an Orthogonal Frequency Division Multiplexing (OFDM) scheme is used.

Here, the TDD scheme is a bidirectional transmission scheme in which uplinks and downlinks are alternately assigned in time in the same frequency band. The TDD scheme has higher transmission efficiency than the frequency division duplex (FDD) scheme, which allocates two different frequencies, uplink and downlink, and is suitable for asymmetric or bursty application transmission due to dynamic allocation of timeslots. There is this. The OFDMA / TDMA scheme is a multiple access scheme similar to TDMA, in which all subcarriers spread over the entire bandwidth are allocated to one user for a predetermined time period and then assigned to another user for the next predetermined time period. Multipath) has the property to prevent interference.

In general, a mobile communication system divides a mobile communication service area into a plurality of cells by using a frequency reuse concept and the like to expand coverage of a mobile communication network, and moves near a center of each cell. A wireless base station (BS) is being installed to handle communication services. Here, the radius of the cell is determined according to the signal strength of the region or the traffic amount of data. In other words, the cell radius is reduced in urban areas with high traffic volume, and the cell radius is increased in non-city areas with relatively low traffic, so that the traffic generated from each cell is handled by the wireless base station that is responsible for the corresponding mobile communication service. Do not exceed the.

Despite efforts to support better mobile communication services by appropriately adjusting the cell radius according to the frequency reuse concept and traffic volume, radio shadowing areas such as underground, inside buildings, tunnels, etc. are difficult to reach in urban areas. This exists. Installing a number of new wireless base stations to address radio shadows in radio shadow areas is not only economically inferior due to facility costs, installation costs, and maintenance costs, but can also have undesirable consequences for cell design. will be. As a solution to this, it is possible to provide a mobile communication service in the radio shadow area using an optical repeater system. The optical relay system solves the problem of radio shading by transmitting a call channel allocated to a mortgage station to a radio shadow area through an optical transmission method using an optical repeater.

In particular, the third generation mobile communication system and the WiBro system use higher frequencies than the second generation mobile communication system, so the propagation path loss is large, the diffraction effect is small, and the building transmission loss is large. Preference is given to using.

In addition, in order to relay the radio signal between the base station and the terminal in the optical repeater it should be able to distinguish the down signal and the up signal. In the case of using the FDD scheme in the optical repeater of the mobile communication system, the duplexer is used to distinguish the downlink signal from the uplink signal. In the case of the TDD scheme, the same frequency is used for the transmission of the downlink and uplink signals. Since the downlink signal and the uplink signal are distinguished, the duplexer cannot be used to distinguish the downlink signal and the uplink signal. Accordingly, the optical repeater using the TDD scheme may use a switch to distinguish the downlink signal and the uplink signal, and selectively provide a path for each signal. To this end, a control signal for accurately determining the start point of the downlink signal and the start point of the uplink signal and changing the movement path of the signal by controlling the opening and closing of the switch according to each signal is needed. Can be sent over an optical cable.

The TDD optical repeater should have a function of analyzing a transmission signal frame and generating a switch control signal for controlling a switch so that a switching operation occurs between a down signal section and an up signal section. On the other hand, since the optical repeater transmits a signal through the optical communication cable, a time delay may occur in the transmission process. If the time delay of the optical communication cable is not corrected to the switch control signal, an incorrect switch control signal is generated, which causes a problem in that the down signal and the up signal cannot be accurately distinguished.

As a solution to this, for example, Korean Patent Application Publication No. 2006-0010963 (name: T Timing Method and System for Generating Switching Signal for Separating Transmission Signal in Optical Repeater of Mobile Communication Network Using OFDM Modulation Method) For example, as shown in FIG. 1, the terminal MS multi-passes a signal received directly from a base station and a signal received through a donor 100 and a remote 300. -Path) signal to receive. At this time, if the time delay difference between the two signals exceeds the cyclic prefix time of the OFDMA symbol, an intersymbol interference phenomenon occurs between the two signals. Therefore, when demodulating the OFDMA symbol, the data error rate is increased as well as the base station (Base). There was a problem that it is difficult to synchronize the time synchronization of the radio signals transmitted and received by the station and the remote (Remote, 300).

SUMMARY OF THE INVENTION An object of the present invention is an uplink and a transmission and reception through an antenna of a base station and a remote in a TDD (Time Division Duplex) type wireless communication including a donor and a remote of a base station connected through an optical line. It is to control the time synchronization by adding a delay of transmission time to the downlink RF signal.

The present invention for achieving the above object is a wireless communication system consisting of a donor and a remote of a base station connected via an optical line, generating a switch control signal for routing the up and down signals between the base station and the remote, the TDD A modem for performing data communication of the method, a delay request pattern is generated and transmitted to the remote to measure a delay time according to the distance between the switch control signal generated from the modem and the optical line, and according to the distance of the optical line A donor controlling the transmission time of the uplink and downlink signals by measuring an RTT, a delay request pattern transmitted from the donor, and transmitting a delay response pattern and a delay response estimation message to the donor, and controlling a switch transmitted from the donor. And a remote for setting up and down paths of signals by signals. It is done.

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

2 is a configuration diagram of a Radio Over Fiber system for wireless communication in a TDD scheme according to an embodiment of the present invention.

Since the Radio Over Fiber system of the present invention uses a time division duplex mode (TDD), two-way communication is possible by time-dividing the same frequency into a downlink signal and an uplink signal, as shown in FIG. 2. The Radio Over Fiber system includes a base station and a remote 300 including a modem 110 and a donor 100.

First, the modem 110 is a switch for controlling the RF switch (not shown) and the RF switch 310 of the remote 300 to selectively set the path for the downlink signal and the uplink signal of the TDD scheme transmitted and received from the antenna. Generate and transmit control signals.

When the donor 100 receives the downlink signal from the modem 110, the donor 100 converts the light signal into an optical signal, transmits the optical signal to the remote 300 through the optical line, and transmits the optical signal received from the remote 300. The signal is converted to an uplink signal and transmitted to the modem 110.

When the remote 300 receives the optical signal from the donor 100, the remote 300 converts the photoelectric signal into a downlink signal and transmits the signal to the air through the antenna 315. The uplink signal transmitted from the air through the antenna 315 is converted into an all-optical signal and converted into an optical signal, and transmitted to the donor 100 through an optical line.

The donor 100 has internal components such as a first receiving amplifier 120, a second all-optical converter (E / O, 130), a first wavelength division multiplexer (Wavelength Division Multiplexer) 140, and a second photoelectric converter. O / E, 150, a first transmission amplifier 160, a first photoelectric converter 240, a first optical circulator 250, a first photoelectric converter 260 and a variable time delay module 115 can do. In addition, the variable time delay module 115 is a type of a programmable logic chip (Field Programmable Gate Array) as an internal component of the time delay measuring unit 170, time delay compensator 220, signal combiner 230 and One signal separator 270 may be included.

The remote 300 is an internal component of the RF switch 310, the second receiving amplifier 320, the third optical converter 330, the second wavelength division multiplexer / demultiplexer 340, and the fourth. Photoelectric converter 350, second transmit amplifier 360, second optical circulator 345, third photoelectric converter 370, third photoelectric converter 380, time transfer module 385 and switch controller 390 ) May be included. In addition, the time transfer module 385 may be implemented as a form of a programmable logic chip (Field Programmable Gate Array).

Here, the donor 100 of the Radio Over Fiber system may be connected to a plurality of remotes 300 through an optical line to extend coverage of the base station.

First, the first and second wavelength division multiplexers / demultiplexers (140, 340) is a device that divides the optical fiber channel into a plurality of channels by the wavelength of light to be used as a plurality of communication paths, and transmits an optical signal In this case, it operates as a wavelength division multiplexer for carrying signals of several wavelengths in one optical fiber and transmitting them, and acts as a wavelength division demultiplexer for demultiplexing signals of several wavelengths. In addition, the all-optical converter used in the base station may be implemented using a laser diode, and the photoelectric converter may be implemented using a photo diode.

The transmission of signals in the forward and reverse channels using the above-described components of the Radio Over Fiber system will be described in detail as follows.

In the case of the forward channel, the downlink signal transmitted from the antenna via the modem 110 is transmitted to the first receiving amplifier 120 of the donor 100. The first receiving amplifier 120 reduces the noise component of the downlink signal, amplifies the signal component and transmits the signal to the second optoelectric converter 130, and converts the downlink signal from the second optoelectric converter 130 into an optical signal. The signal is transmitted to the one wavelength division multiplexer / demultiplexer 140. The first wavelength division multiplexer / demultiplexer 140 transmits the optical signal received from the second all-optical converter 130 to the remote 300 through the optical line.

The optical signal transmitted from the donor 100 through the second photoelectric converter 130 is transferred to the fourth photoelectric converter 350 through the second wavelength division multiplexer / demultiplexer 340 of the remote 300 and the fourth photoelectric converter 350. The photoelectric converter 350 converts the downlink signal to the second transmission amplifier 360 of the remote 300. The second transmit amplifier 360 of the remote 300 is amplified to an effective output for transmitting through the antenna 315 is transmitted to the switch 310, the switch 310 to the switch control signal from the modem 110 By setting the path of the downlink signal is radiated to the air through the antenna 315.

In the case of the reverse channel, the TDD type uplink signal received from the antenna 315 of the remote 300 is transmitted through a path for the uplink signal set by the switch control signal from the modem 110 in the switch 310. Transmitted to receive amplifier 320. Thereafter, the noise is removed through the second receiving amplifier 320, and signal components are amplified and transferred to the fourth all-optical converter 330. The fourth optical converter 330 converts an uplink signal into an optical signal and transmits the optical signal to the second wavelength division multiplexer / demultiplexer 340. The second wavelength division multiplexer / demultiplexer 340 transmits the fourth signal through an optical line. The optical signal received from the all-optical converter 330 is transmitted to the donor 100.

The optical signal transmitted from the remote 300 is transmitted to the second photoelectric converter 150 through the first wavelength division multiplexer / demultiplexer 140 of the donor 100, and the uplink signal from the second photoelectric converter 150. Is converted and delivered to the first transmit amplifier 160.

The uplink signal converted from the second photoelectric converter 150 is amplified to an effective output for transmission from the first transmission amplifier 160 to the modem 110 and transmitted to the modem 110. In the modem 110, when the uplink signal of the TDD scheme transmitted from the first transmit amplifier 160 is transmitted to a switch (not shown) separately from the downlink signal, the uplink signal is transmitted by the switch control signal from the modem 110 in the switch. It sets the path of and radiates to the air through the antenna.

On the other hand, the variable time delay module 115 is delayed as shown in Table 1 showing the characteristics of the variable time delay module to measure the delay time according to the distance of the optical path between the donor 100 and the remote 300 of the base station Generate a request request pattern and encode 8b / 10b. Here, the delay request pattern may be a pulse, a packet, or the like. For example, it is composed of a pulse 40ns that lasts high for 5 clocks, and the pulses have 8b / 10b encoding because the DC component is very large and may not be suitable for optical transmission.

The remote 300 transmits the optical signals transmitted from the first and second wavelength division multiplexing / demultiplexers 140 and 340 to the third photoelectric converter 380 in a desired transmission direction in the second optical circulator 345. Also isolate them from propagating in other directions.

The third photoelectric converter 380 converts the electrical signal through photoelectric conversion, and the time transmission module 385 detects the electrical signal converted by the third photoelectric converter 380 as shown in Table 2, which shows the characteristics thereof. / 10b Decode

Thereafter, it is determined whether it is a delay request pattern or a switch control signal generated to set a path for uplink and downlink signals of the TDD scheme transmitted and received from the modem 110 to the remote 300. delay request pattern), check the counter number. For example, in the case of a 5 clock delay request pattern, since the switch control signal has a relatively long period, it can be determined as the length of the continuous high signal. In addition, if High continues for a longer time than a relatively short delay request pattern, it is regarded as a switch control signal of the TDD scheme.

In addition, in the case of a switch control signal generated to set a path for the uplink and downlink signals of the TDD scheme transmitted and received from the modem 110 to the remote 300, the switch controller 390 transmits the remote control to the switch controller 390. The switch 310 of 300 is controlled.

Meanwhile, the time transmission module 385 generates a delay response pattern in the same form as the delay request pattern. The generated delay response pattern is again 8b / 10b encoded and converted into an optical signal by the third all-optical converter 380. Thereafter, the first and second wavelength division multiplexers 140 and 340 transmit to the donor 100 in the reverse direction of the direction transmitted from the second optical circulator 345.

The time transmission module 385 transmits a delay response follow up message, which includes a delay request pattern at a counter value checked at the moment the previously transmitted delay response pattern is transmitted. The difference in the counter number at the time of receiving the pattern is stored in a delay response follow up message, subjected to 8B / 10B encoding, and then converted into an optical signal by the third all-optical converter 380. Thereafter, the first and second wavelength division multiplexers 140 and 340 transmit to the donor 100 in the reverse direction of the direction transmitted from the second optical circulator 345.

The donor 100 converts the optical signal transmitted from the remote 300 into an electrical signal through the first photoelectric converter 260, and the variable time delay module 115 converts the electrical signal converted from the first photoelectric converter 260 into Delay response pattern is detected from the conventional signal. If a delay response pattern is detected within 5 clocks, an error or warning is reported.

Afterwards, the variable time delay module 115 calculates a round trip time (RTT) for the delay request and response between the donor 100 and the remote 300 from the counter number of the delay response follow up message. If the measured value of the RTT is within a predetermined error range (+/- 8ns), the variable delay control signal (VDCS) is calculated. In addition, if the value is out of the error range (+/- 8ns), an error or warning is reported.

The variable time control module 115 calculates a variable delay control signal (VDCS) value and transmits it to the time delay compensator 220. The time delay compensator 220 then connects the donor 100 and the remote 300 to the optical path. The variable delay control signal value is added to the up and down signals between the two signals to control the temporal synchronization of the transmitted and received signals.

3 is a flowchart illustrating a transmission time synchronization control method in a Radio Over Fiber system for a TDD wireless communication according to an exemplary embodiment of the present invention.

As shown in FIG. 3, in step 300, the modem 110 generates a switch control signal for routing up and down signals in the TDD scheme, and transmits the control signal to the time delay compensator 220 of the donor 100. Thereafter, in step 310, the time delay measuring unit 170 generates a delay request pattern to encode an 8b / 10b to measure the delay time of the optical line, and transmits the delay request pattern to the signal combiner 230. At this time, the time delay measuring unit 170 checks the counter number for the delay request pattern.

Step 320 combines the switch control signal of the TDD scheme transmitted from the time delay compensator 220 and the delay request pattern generated by the time delay measuring unit 170 in the signal combiner 230, and in step 330 The first optical circulator 250 separates the optical signal from a desired transmission direction in the first optical circulator 250 and converts the optical signal into a optical signal through the first optical converter 240, and the first and second wavelength division multiplexers / demultiplexers 140 and 340 To be transmitted to the remote (300). At this time, the time delay measuring unit 170 of the donor 100 checks the counter number for the delay request pattern.

The remote 300 transmits the optical signals transmitted from the first and second wavelength division multiplexing / demultiplexers 140 and 340 from the second optical circulator 345 to the third photoelectric converter 380 in a desired transmission direction. At this time, the optical signal is isolated so as not to transmit in the other direction.

The third photoelectric converter 370 converts the electrical down signal through photoelectric conversion, and the time transmission module 385 detects the converted electrical signal through the third photoelectric converter 370, which is again 8b / 10b. After decoding, step 340 determines whether a delay request pattern is a delay control pattern or a switch control signal generated for routing TDD-type up and down signals transmitted and received from the modem 110 to the remote 300. In the case of a delay request pattern, the counter number is checked in step 350.

Thereafter, in step 360, when the time control module 385 is a TDD-type switch control signal generated to set up and down a path of up and down signals transmitted and received from the modem 110 to the remote 300, the controller 110 transmits the switch to the switch controller 390. The switch controller 390 controls the switch 310 of the remote 300. Here, the RF switch 310 is shorted in accordance with the switch control signal from the switch controller 390 to selectively set the path for each of the up and down signals. Therefore, the RF switch 310 is set to radiate to the air through the antenna 315 when a downward signal is input from the second transmit amplifier 360 of the remote 300, and the uplink signal is transmitted through the antenna 315. If the input is set to be input to the second receiving amplifier 320 of the remote 300, it operates in the TDD mode between the base station and the remote (300).

In operation 370, the time transmission module 385 generates a delay response pattern having the same form as the delay request pattern transmitted from the donor 100. The generated delay response pattern is again 8d / 10d encoded and converted into an optical signal by the third all-optical converter 380. Thereafter, the first and second wavelength division multiplexers 140 and 340 transmit to the donor 100 in the reverse direction of the direction transmitted from the second optical circulator 345. At this time, the time transmission module 385 checks the counter value when receiving the delay request pattern.

Thereafter, in step 380, the time transmission module 385 transmits a delay response follow up message, which includes a delay request at a counter value checked at the moment when the delay response pattern previously transmitted is transmitted. The difference in the counter number at the time of receiving the delay request pattern is stored in a delay response follow up message, subjected to 8b / 10b encoding, and then converted into an optical signal by the third electro-optical converter 380. do.

Thereafter, the second optical circulator 345 transmits to the donor 100 through the reverse direction of the transmission direction. In other words, the donor's processing time is stored and transmitted.

In operation 390, the optical signal transmitted from the remote 300 is transmitted to the first photoelectric converter 260 through the reverse direction of the transmission direction of the first optical circulator 250.

The optical signal transmitted to the first photoelectric converter 260 is converted into an electrical signal and a delay response pattern from the electrical signal transmitted through the first signal separator 270 in the time delay measuring unit 170. Is detected.

In addition, a round trip time (RTT) between the donor 100 and the remote 300 is measured by Equation 1 from the counter number of the delay response follow up message transmitted from the remote 300.

[Equation 1]

Round Trip Time = [(Counter Num. Of delay_response @Donor)-(Counter Num. Of Delay_Request @Donor)]-[(Counter Num. Of delay_response @Remote)-(Counter Num. Of Delay_Request @Remote)]

In step 400, the measurement is repeated at least once at a predetermined cycle to determine whether the measured value is within an error range. Thereafter, in step 410, if the value is within the error range, the variable delay control signal VDCS value is calculated as in Equation 2 and transmitted to the time delay compensator 220.

[Equation 2]

VDCS = fixed delay (@Donor)-[(Round Trip Time) / 2]

On the other hand, in step 420, when the measured value is not within a certain error range, an error (Error) or warning (Report) is reported.

Thereafter, in step 430, the variable delay control signal (VDCS) is applied to the up and down signals between the donor 100 and the remote 300 passing through the optical path by the time delay compensator 220 receiving the calculated variable delay control signal (VDCS). By adding a value, in step 440, the time synchronization of up and down signals transmitted and received between the base station and the remote 300 is controlled.

As described above, a TDD radio over fiber system and a transmission time control method according to a preferred embodiment of the present invention can be made. Meanwhile, in the above description of the present invention, specific embodiments have been described. There may be various embodiments without departing from the gist. Therefore, the scope of the present invention should not be defined by the described embodiments, but by the claims and equivalents of the claims.

The present invention is a TDD (Time Division Duplex) wireless communication consisting of a donor and a remote of a base station connected through an optical line, the up and down signals transmitted and received through the antenna of the base station and the remote (Remote) By adding a delay to the transmission time, the TDD Radio Over Fiber system provides reliable and excellent performance by controlling the time synchronization of up and down RF signals transmitted and received between the base station and the remote. can do.

Claims (16)

In a wireless communication system consisting of a donor and a remote of the base station connected via an optical line, A modem for generating a switch control signal for routing uplink and downlink signals between the base station and the remote and performing data communication according to the TDD scheme; In order to measure the delay time according to the distance between the switch control signal generated from the modem and the optical line, the delay request pattern is generated and transmitted to the remote, A donor for controlling a transmission time of the uplink and downlink signals by measuring an RTT according to the distance of the optical line; Detect a delay request pattern transmitted from the donor and transmit a delay response pattern and a delay response estimation message to the donor, And a remote for setting up and down paths of the uplink and downlink signals by the switch control signal transmitted from the donor. The radio over fiber system according to claim 1, wherein the donor comprises a variable time delay module for measuring the RTT from the delay response estimation message and calculating a variable delay control signal value. The method of claim 2, wherein the variable time delay module generates a delay request pattern and transmits the delay request pattern to the remote to measure the delay time of the optical line, and the measured value of the RTT measured from the delay response estimation message is a constant error. A time delay measuring unit for calculating a variable delay control signal value if the value is within a range; A signal combiner for combining the delay request pattern with a switch control signal generated from a modem; A first signal separator separating the delay response pattern and the switch control signal generated from the modem; And And a time delay compensator for adding a variable time delay to the upstream and the downlink signals according to the variable delay control signal value. The TDD radio over fiber system of claim 3, wherein the time delay measuring instrument repeats the measurement of the RTT at least once in a predetermined period. 3. The apparatus of claim 2, wherein the donor comprises: a first receiving amplifier for removing noise of a downlink signal transmitted from the time delay compensator and amplifying a signal component; A second all-optical converter for converting the downlink signal amplified from the transmission amplifier into an optical signal; A second photoelectric converter converting the optical signal received from the remote into an uplink signal; A first transmitting amplifier for amplifying the uplink signal converted from the second photoelectric converter to an effective output; And A first wavelength division multiplexing / demultiplexing for multiplexing a plurality of optical wavelengths in one optical line to an optical signal converted from the second all-optical converter, and demultiplexing a plurality of optical wavelengths to an optical signal received from the remote, respectively TDD radio Over Fiber system, characterized in that it comprises a group. 6. The TDD radio over fiber system according to claim 5, wherein the donor is connected to a plurality of remotes through an optical line. The method of claim 1, wherein the remote determines whether a signal transmitted from a donor is a delay request pattern or a switch control signal generated to route the upstream and downstream signals, and the delay response having the same form as the delay request pattern. And a time transmission module configured to generate a pattern and transmit the pattern to the donor. 8. The donor of claim 7, wherein the time transmission module uses the donor as a delay response estimation message containing a difference between the counter number at the time when the delay request pattern is received and the counter value checked at the moment when the delay response pattern is transmitted to the donor. TDD radio over fiber system, characterized in that for transmitting. 9. The apparatus of claim 8, wherein the remote unit comprises: a second optical circulator for isolating an optical signal transmitted from the donor in a direction different from a desired transmission direction; A third photoelectric converter converting the optical signal transmitted from the second optical circulator into an electrical signal; A third electro-optical converter for converting an electrical signal transmitted from the time transmission module into an optical signal; And And a switch detector for detecting the switch control signal from the electrical signal converted from the third photoelectric converter. 10. The apparatus of claim 8, wherein the remote unit comprises: an RF switch for setting up and down paths of up and down signals transmitted and received from an antenna by the switch control signal; A second receiving amplifier for removing noise of an uplink signal and amplifying a signal component according to a path set from the second RF switch; A fourth all-optical converter for converting an uplink signal amplified from the second receiving amplifier into an optical signal; A fourth photoelectric converter converting the optical signal received from the donor into a downlink signal; A second transmission amplifier for amplifying the downlink signal converted from the fourth photoelectric converter to an effective output; And A second wavelength division multiplexer / reverse that multiplexes a plurality of optical wavelengths on one optical line to the optical signal converted from the second all-optical converter, and demultiplexes the plurality of optical wavelengths onto the optical signal received from the donor, respectively TDD radio over fiber system comprising a multiplexer. In a wireless communication system consisting of a donor and a remote of the base station connected via an optical line, Generating and transmitting a switch control signal for routing up and down signals transmitted and received from the donor to a remote; Generating a delay request pattern to measure a delay time of the optical line; Combining the delay request pattern with the switch control signal and transmitting the combined request to the remote; Detecting a signal transmitted from the donor to determine whether a delay request pattern or the switch control signal is performed; Checking a counter number in the case of the delay request pattern; Generating a delay response pattern having the same form as the delay request pattern and transmitting the same to the donor; Storing a difference between the counter numbers and transmitting a delay response estimation message to the donor; Measuring an RTT between the donor and a remote from the delay response estimation message; Determining whether the measured value of the RTT is within an error range; Calculating a variable delay control signal value when the value is within the error range; And controlling the time synchronization of the uplink and downlink RF signals transmitted and received between the base station and the remote by adding the variable delay control signal values to the uplink and downlink signals. Transmission time control method. The method of claim 11, wherein the signal transmitted from the donor is detected and transmitted to the switch controller in the case of the switch control signal, and controlled by the switch controller to selectively set the paths for the up and down signals in the switch. The transmission time control method further comprising the step of operating in the TDD mode. 12. The method of claim 11, wherein the transmitting of the delay request pattern and the switch control signal by combining includes checking a counter number for the delay request pattern. 12. The method of claim 11, wherein the transmitting of the delay response pattern comprises checking a counter value when receiving a delay request pattern at the remote. 12. The method of claim 11, wherein the measuring of the RTT is repeated at least once in a predetermined period. 12. The method of claim 11, further comprising reporting an error or a warning when the value is not within the error range.

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