WO2014106981A1

WO2014106981A1 - Master unit for distributed antenna system, distributed antenna system having the same, and communication signal relay method of distributed antenna system

Info

Publication number: WO2014106981A1
Application number: PCT/KR2013/008569
Authority: WO
Inventors: Tae-Hoon Lee
Original assignee: Ls Cable & System Ltd.
Priority date: 2013-01-02
Filing date: 2013-09-25
Publication date: 2014-07-10
Also published as: KR20140089054A

Abstract

Disclosed are a master unit for a distributed antenna system, the distributed antenna system having the master unit and a communication signal relay method of the distributed antenna system. The master unit of a distributed antenna system for relaying a communication signal between a base station and a user equipment includes: an A/D conversion unit for generating a signal sample by converting a signal flowing in from the base station into a digital signal; a signal detection unit for determining whether or not a communication signal is received, based on the signal sample; and a mode control unit for setting an operation mode based on a result of determining whether or not a communication signal is received.

Description

MASTER UNIT FOR DISTRIBUTED ANTENNA SYSTEM, DISTRIBUTED ANTENNA SYSTEM HAVING THE SAME, AND COMMUNICATION SIGNAL RELAY METHOD OF DISTRIBUTED ANTENNA SYSTEM

One or more aspects of embodiments according to the present invention relate to a master unit for a distributed antenna system (DAS), the distributed antenna system having the master unit and a communication signal relay method of the distributed antenna system.

Radio communication is a communication method using radio waves and is generally referred to as radio frequency (RF) communication. The radio communication using radio waves modulates information desired to be transmitted into a radio wave and transmits the radio wave through a power amplifier (PA), and a receiving side demodulates the radio wave and receives the information.

In the case of bi-directional radio communication such as communication of a cellular phone, a transmit frequency is separated from a receive frequency so that transmission and reception may be performed concurrently. In addition, a bi-directional radio communication system allocates communication channels so that a plurality of users may use communication channels different from one another.

Such a radio communication system should take into account such problems as a limit in the capacity of accommodating subscribers and restrictions on service areas. To this end, an actually implemented radio communication system performs communication by dividing a service area into a plurality of cells.

Meanwhile, although the radio communication system adjusts cell coverage so that a shadow area may not be generated, shadow areas are generated in a building, an underground space or the like in an actual environment. In this case, a relay system is installed in the shadow area so as to relay a signal transmitted from a base station to a user equipment.

In such a relay system, a distributed antenna system is an apparatus having a plurality of distributed antennas installed within existing cell coverage in order to provide service to a shadow area by amplifying a signal of a base station so as to arrive at the shadow area and relaying a signal of a user equipment in the shadow area so as to arrive at the base station, targeting a radio wave blocking area where radio waves are blocked by a mountain, a building or other terrain features or a shadow area such as a tunnel, an underground parking lot or an underground shopping center at which a radio wave is difficult to arrive.

The distributed antenna system may be configured of a master hub unit (MU), a hub unit (HU), a remote unit (RU) and the like in order to relay a communication signal between the base station and the user equipment. In the conventional 2G/3G radio communication environment, the distributed antenna system does not change a service frequency. However, in the current 4G radio communication environment, service frequencies of an upper base station system are frequently changed. In this case, the operation mode of the MU connected to the upper base station system needs to be changed to a manual mode, and accordingly, a worker should visit a site and set the operation mode to be appropriate to a previously grasped output frequency pattern of an antenna of the base station, and thus the work is troublesome, and services may be unnecessarily delayed.

In relation to this, a technique of “Remote relay monitoring system and method thereof” is disclosed in Korean Laid-open Patent No. 2008-0101019. The invention of Korean Laid-open Patent No. 2008-0101019 relates to a relay installed on a path between a base station and a user equipment to re-amplify and provide a signal of the base station to the user equipment, which is configured to include a sensing unit for detecting and coupling the signal of the base station and measuring a signal level based on the coupled signal and an operation unit for determining whether or not the relay provides a normal service, by comparing the signal level measured by the sensing unit with a predetermined signal level.

However, the invention of Korean Laid-open Patent No. 2008-0101019 has a problem in that only existence of a signal or whether or not a relay provides a normal service can be determined using the measured signal level, and an operation mode of the relay cannot be automatically set.

In addition, a technique of “Mobile communication system, base station, mobile station and communication control method” is disclosed in Korean Laid-open Patent No. 2009-0074257. The invention of Korean Laid-open Patent No. 2009-0074257 relates to a mobile communication system configured of a base station and a mobile station, which is configured to include an adjacent system notification unit for possessing and notifying information on a frequency-adjacent system and an uplink (UL) transmission power control unit for controlling a transmission power level of an uplink based on the type of the frequency-adjacent system.

However, the invention of Korean Laid-open Patent No. 2009-0074257 has a problem in that only the transmission power level can be controlled based on the type of the frequency-adjacent system, and an operation mode of a relay cannot be automatically set.

In addition, in the prior art, the hub unit is connected to the remote unit through an optical cable, and the remote unit has a separate power supply unit. In this case, since an electrical wiring work should be separately performed in order to install the remote unit, additional installation cost is required, and a UPS for the remote unit should be separately installed in order to maintain services in the case of power failure.

In order to solve this problem, the hub unit is connected to the remote unit through a UTP cable. Since the UTP cable has a power line inside thereof and may supply power from the hub unit to the remote unit, a separate power supply unit is not required for the remote unit. However, in the case of the UTP cable, there is a limit in the distance of transmitting a signal without a loss since the signal is transmitted using a conductive wire, and there is also a limit in the power that can be transmitted using the UTP cable, and thus there is also a limit in the output signal of the remote unit.

Therefore, according to one or more aspects of embodiments of the present invention have been made in view of the above problems, and it is an object of the present invention to provide a master unit for a distributed antenna system and the distributed antenna system, which can automatically detect an output frequency pattern of an upper base station system and automatically set an operation mode.

Another object of an embodiment of the present invention is to provide a master unit for a distributed antenna system and the distributed antenna system, which can save maintenance cost incurred when a worker is dispatched to a site in order to change a frequency pattern of the master unit for a distributed antenna system and prevent damage to equipment resulting from a mistake made in a work.

In addition, still another object of an embodiment of the present invention is to provide a distributed antenna system, which is easy to install and maintain and has an increased distance for transmitting a communication signal.

The objects of the present invention are not limited to objects described above, and unmentioned other objects can be clearly understood from the following descriptions.

According to one of more aspects of embodiments of the present invention, a master unit for a distributed antenna system, for relaying a communication signal between a base station and a user equipment, comprises: an A/D conversion unit to generate a signal sample by converting a signal flowing in from the base station into a digital signal; a signal detection unit to determine whether or not a communication signal is received, based on the signal sample; and a mode control unit to set an operation mode based on a result of determining whether or not a communication signal is received.

The master unit may further comprise a communication mode determination unit to determine a communication mode of the flow-in signal.

The mode control unit may set the operation mode based on a result of determining whether or not a communication signal is received and a result of determining a communication mode.

The communication mode determination unit may determine a communication mode of the flow-in signal for each service frequency band.

The signal detection unit may determine whether or not a communication signal is received for each service frequency band.

The mode control unit may operate only when the signal detection unit determines that the communication signal is received.

The master unit may further comprise a signal input and output unit wiredly or wirelessly connected to the base station, to transmit and receive the communication signal.

The master unit may further comprise an optical/electrical conversion unit to convert the communication signal from an optical signal into an electrical signal; and an optical transmission unit to transmit the electrical signal converted into an optical signal, in the set operation mode.

The signal detection unit may determine that the communication signal is received when a magnitude of the signal sample is larger than a previously set reference value.

According to another embodiment of the present invention, a communication signal relay method of a master unit for a distributed antenna system, comprises converting a flow-in signal received from a base station into a digital signal and creating a signal sample, determining whether or not a communication signal is received, based on the signal sample, setting an operation mode based on a result of determining whether or not a communication signal is received, and relaying the communication signal in the set operation mode.

The communication signal relay method may further comprise determining a communication mode of the flow-in signal.

Setting an operation mode is a step of setting an operation mode based on a result of determining whether or not a communication signal is received and a result of determining a communication mode.

Determining a communication mode is a step of determining a communication mode of the flow-in signal for each service frequency band.

Creating a signal sample is a step of converting the flow-in signal into a digital signal and creating the signal sample for each service frequency band.

Determining whether or not a communication signal is received is a step of dividing the signal sample into service frequency bands and determining whether or not a communication signal is received on each of the service frequency bands.

Setting an operation mode is performed only when the communication signal is received.

The method may further comprise wiredly or wirelessly connecting to the base station and transmitting and receiving the communication signal.

Relaying the communication signal may include converting the communication signal from an electrical signal into an optical signal, and transmitting the converted optical signal in the set operation mode.

Determining whether or not a communication signal is received is a step of determining that the communication signal is received if a magnitude of the signal sample is larger than a previously set reference value.

According to another embodiment of the present invention, a distributed antenna system comprise a master unit to transmit and receive a communication signal to and from a base station, a hub unit to receive the communication signal processed by the master unit or transmit the communication signal to the master unit, a remote unit to transmit and receive a communication signal to and from the hub unit, and an optical/electrical composite cable to connect the hub unit and the remote unit, wherein the remote unit receives power from the hub unit through the optical/electrical composite cable.

The remote unit may not have a separate power source and operates by the power supplied from the hub unit.

The hub unit may have a power supply unit to supply power to the remote unit.

The remote unit may receive an optical signal from the hub unit through the optical/electrical composite cable and convert the optical signal into an electrical signal.

The communication signal may be transmitted and received between the hub unit and the remote unit through the optical/electrical composite cable.

The optical/electrical composite cable may include an optical cable disposed at a center of the optical/electrical composite cable, one or more first power line units and one or more second power line units surrounding and contacting with an outer surface of the optical cable, and an outer shell layer wrapping around the first power line units and the second power line units, wherein the optical cable may include a tube disposed at the center of the optical cable, one or more optical fiber units collected around the tube in a lengthwise direction, respectively containing a plastic tube and optical fiber core lines installed inside the plastic tube, and a sheath layer wrapping around the optical fiber units, wherein one of the first power line units, one of the second power line units and one of the optical fiber units may be branched and connected to the remote unit.

The tube may have a diameter as large as to contact with outer surfaces of the one or more optical fiber units and stably support the one or more optical fiber units.

The plastic tube may be formed of polypropylene (PP), polybutylene terephthalate (PBT), polycarbonate (PC), polyamide (PA) or a mixture of these.

The tube may be formed of a foamed plastic resin having a strength lower than that of the plastic tube.

A waterproof material may include a jelly compound, waterproof powder, waterproof yarn and a combination of these is installed in the plastic tube together with the optical fiber core lines.

The power may be supplied to the remote unit through the power line units.

The communication signal may be transmitted and received between the hub unit and the remote unit through the optical cable.

The optical/electrical composite cable may include a first power line unit, a second power line unit and a ground line externally contacting with each other, an outer shell layer surrounding and contacting with outer surfaces of the first and second power line units and the ground line, and optical fiber units contacting with the outer surface of the first power line unit, the second power line unit or the ground line and contacting with an inner surface of the outer shell layer.

The master unit may include an A/D conversion unit to generate a signal sample by converting a signal flowing in from the base station into a digital signal, a signal detection unit to determine whether or not the communication signal is received, based on the signal sample, and a mode control unit to set an operation mode based on a result of determining whether or not the communication signal is received.

The system may comprise a communication mode determination unit to determine a communication mode of the flow-in signal.

The mode control unit may set the operation mode based on a result of determining whether or not the communication signal is received and a result of determining a communication mode.

The system may further comprise a signal input and output unit wiredly connected to the base station, for transmitting and receiving the communication signal.

The system may further comprise an optical/electrical conversion unit for converting the communication signal from an electrical signal into an optical signal, and an optical transmission unit to transmit the converted optical signal, in the set operation mode.

According to one of the technical solutions of embodiments of the present invention described above, an output frequency pattern of an upper base station system can be automatically sensed, and an operation mode can be automatically set.

In addition, maintenance cost which incurs when a worker is dispatched to a site in order to change a frequency pattern of a master unit for a distributed antenna system can be saved, and damage to equipment resulting from a mistake made in a work can be prevented.

In addition, a separate power supply unit is not required for a remote unit, and accordingly, system installation cost may be saved, and it is easy to install and maintain the system. In addition, since a high power can be supplied, a flexible network can be designed.

FIG. 1 is an overall conceptual view showing a distributed antenna system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the detailed configuration of a communication relay apparatus which configures a distributed antenna system according to an embodiment of the present invention.

FIG. 3 is a table showing an example of operation modes of a communication relay apparatus according to an embodiment of the present invention.

FIG. 4 is a view illustrating an operation mode of a communication relay apparatus according to an embodiment of the present invention.

FIG. 5 is a view schematically showing the configuration of a hub unit of a distributed antenna system according to an embodiment of the present invention.

FIG. 6 is a view schematically showing the configuration of a remote unit of a distributed antenna system according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view schematically showing an optical/electrical composite cable of a distributed antenna system according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view schematically showing the optical cable shown in FIG. 7.

FIG. 9 is a cross-sectional view schematically showing an optical/electrical composite cable according to another embodiment of the present invention.

FIG. 10 is a cross-sectional view schematically showing an optical/electrical composite cable according to still another embodiment of the present invention.

FIG. 11 is a flowchart illustrating a communication signal relay method using a master unit for a distributed antenna system according to an embodiment of the present invention.

Since some exemplary embodiments of the present invention may be modified in a variety of ways and may have various embodiments, specific embodiments are shown in the figures and described in detail with reference to the figures. However, the described embodiments is not limited to the specific embodiments, but should be understood to include all the modifications, equivalents and substitutions contained within the spirit and scope of the present invention.

In describing some embodiments of the present invention, if already known functions related to the present invention may unnecessarily make the spirit of the present invention unclear, detailed description thereof will be omitted. In addition, the numerals (e.g., a first, a second or the like) used in describing the specification are merely identification symbols for distinguishing an element from the other elements.

It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion.

In this specification, a user equipment is a device which transmits and receives voices or data with other user equipments via a base station or a relay, which can be, for example, a cellular phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigator or the like.

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

FIG. 1 is a conceptual view schematically showing a distributed antenna system according to an embodiment of the present invention.

The distributed antenna system may amplify a downlink signal flowing in from an upper base station 100 system and relays the downlink signal to a user equipment (UE). An example of an in-building distributed antenna system for providing radio communication coverage within a building is shown in FIG. 1, and BS 100 denotes a base station (eNodeB or eNB), MU 200 denotes a master unit, HU 300 denotes a hub unit, and RU 400 denotes a remote unit.

Communication signal streams may be transmitted and received between the base station 100 and the MU 200. At this point, the base station 100 and the MU 200 may be connected wirelessly or through a wired cable such as a coaxial cable or the like, and the communication signal streams may be transmitted and received in the form of an RF signal or an electrical signal.

The MU 200 may convert the communication signal received from the base station 100 into a digital signal and transmits the digital signal to the HU 300 or convert the communication signal transmitted from the HU 300 into an analog signal and transmits the analog signal to the base station 100. The MU 200 and the HU 300 may be connected through an optical cable, and a plurality of HUs 300 may be connected to one MU 200. The HU 300 may be connected to one or more RUs 400, convert an optical signal received from the MU 200 into an Ethernet signal or the like and transmit the Ethernet signal or the like to the RUs 400. At this point, in the case of the in-building distributed antenna system, each of the RUs 400-1 to 400-n is installed in each floor to secure communication coverage. In addition, the present invention is not limited to this, and a plurality of RUs may be installed in each floor, and one RU may be installed for a plurality of floors.

The HU 300 and the RU 400 may be connected through an optical/electrical composite cable 700. Through the optical/electrical composite cable 700, optical signals are transmitted and received between the HU 300 and the RU 400, and power can be supplied from the HU 300 to the RU 400. This will be described below.

The communication signal transmitted to the MU 200 may be transmitted to the RUs 400 via the HU 300, and the RUs 400 may transmit the communication signal transmitted through one or more antennas 500-1 to 500-n to user equipments.

Meanwhile, the radio communication system may provide one of service modes including Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA) or Long Term Evolution (LTE), and the base station 100 transmits a communication signal in a predetermined service mode. The MU 200 detects a type of the communication signal received from the base station 100 and changes an operation mode setting to an operation mode corresponding to the communication signal type.

Hereinafter, the detailed configuration of the MU 200 and a function of automatically setting the operation mode will be described.

FIG. 2 is a view showing the detailed configuration of the MU 200 according to an embodiment of the present invention.

As shown in FIG. 2, the MU 200 may include a signal input and output unit 210, an analog/digital (A/D) converter 220, a Field Programmable Gate Array (FPGA) unit, a communication mode determination unit 240, an optical/electrical (O/E) conversion unit 260, an optical transmission unit 270 and a digital/analog (D/A) converter 280. In addition, the FPGA unit may include a signal detection unit 230 and a mode control unit 250 therein.

The signal input and output unit 210 may provide an interface connected to the base station 100, be wiredly or wirelessly connected to the base station 100 and transmit and receive a communication signal. The communication signal transmitted and received through the signal input and output unit 210 may be an analog signal such as an RF signal or an electrical signal. A downlink signal flowed in from the base station 100 is converted into a digital signal by the A/D converter 220, and contrarily, an uplink signal received from the user equipment is converted into an analog signal by the D/A converter 280 and transmitted to the base station 100 through the signal input and output unit 210.

The A/D converter 220 may convert the flow-in signal received through the signal input and output unit 210 into a digital signal and create a signal sample by sampling the digital signal at regular intervals. The created signal sample may be a data created from a magnitude value of the flow-in signal at a specific time point, sequentially at predetermined time intervals, such as 00011, 00100 or the like.

The created signal sample may be used as a base data for determining existence of a communication signal by the signal detection unit 230. Specifically, the signal detection unit 230 determines whether or not the flow-in signal is a meaningful communication signal by comparing the created signal sample with a threshold value. To this end, the signal detection unit 230 may store and manage one or more threshold values set in a separate table at regular time intervals. If the data of the signal sample compared with the threshold value at a specific time exceeds the threshold value, the signal detection unit 230 may determine that a communication signal is flowed in.

On the other hand, the signal detection unit 230 may determine whether or not a communication signal is received on each service frequency band. The radio communication system may provide a radio communication service using a predetermined frequency band, divide an allocated frequency band into one or more service frequency bands and allocate the service frequency band to different communication services.

FIGs. 3 and 4 show an example of such service frequency bands and corresponding operation modes. In FIG. 3, a service frequency band that may be used in the radio communication system is divided into four sub-frequency bands of F0 to F3, and the operation mode can be divided into a plurality of operation modes according to combinations of services for which the respective sub-frequency bands are used. For example, in the case of operation mode 5, sub-frequency band F0 is not used, and both the MAIN port and the MIMO port operate as LTE in F1, and only the MAIN port operates as WCDMA in F2 and F3.

FIG. 4(a) shows a receive frequency pattern of a service frequency band in operation mode 5. If a frequency band that may be used in the radio communication system is between 1749.9MHz to 1784.9MHz, sub-frequency band F0 is not used, and a signal received through frequency band F1 is an LTE signal, and a WCDMA signal is received through frequency bands F2 and F3.

In this case, the MU 200 grasps existence of a flow-in signal and a communication mode of each sub-frequency band and sets the operation mode to mode 5 based on the grasped information. Specifically, the signal detection unit 230 compares a magnitude value of a signal sample of the flow-in signal created by the A/D converter 220 with a threshold value (e.g., -50dB) stored in a previously set table, and if the magnitude value of the signal sample is larger than the threshold value, the signal detection unit 230 determines that the flow-in signal is a communication signal containing a meaningful data. The mode control unit 250 re-sets the operation mode of the MU 200 based on a result of the determination on the existence of a communication signal performed by the signal detection unit 230.

At this point, if the signal detection unit 230 determines that a communication signal is not received, the mode control unit 250 and other modules in the following stage do not operate, and the modules may operate in an active mode only when a communication signal flows in.

The communication mode determination unit 240 may analyze packets of the communication signal flowed in through the downlink and determines whether the corresponding signal is a WCDMA signal or an LTE signal. Such a determination on the communication mode may be performed for each sub-frequency band, and a result of the determination may be transferred to the mode control unit 250.

The mode control unit 250 may determine a communication mode of each sub-frequency bandwidth based on the existence of a communication signal and the result of the determination on the communication mode of the received communication signal, respectively acquired by the signal detection unit 230 and the communication mode determination unit 240, and sets an operation mode of the MU 200 based on the determined communication mode. Then, the communication signal received from the base station may be transmitted to the UE through the HU 300 and the RU 400 on the downlink path in the set operation mode. The RU 400 controls output frequencies of the MAIN antenna port and the MIMO antenna port depending on the operation mode, and as shown in FIG. 4(b), in the case of mode 5, the MAIN antenna radiates radio waves on the frequency bands of F1, F2 and F3, and the MIMO antenna radiates radio waves on the frequency band of F1.

At this point, the communication signal transmitted to the HU 300 and the RU 400 may be converted into an optical signal by the O/E conversion unit 260 and transmitted through the optical transmission unit 270.

On the other hand, the communication signal received from the UE through the uplink path may be received by the MU 200 through the optical transmission unit 270, converted into a digital signal through the O/E conversion unit 260 and input into the FPGA unit, and thereafter, the converted digital signal may be converted into an analog signal by the D/A converter 280 to be transmitted to the base station.

Through the configuration as described above, the MU 200 may determine existence of a communication signal and the communication mode of the communication signal received from the base station 100 and automatically set an operation mode based on the determination, and thus it is possible to solve a problem such as a device or communication failure resulting from a mistake or the like that can be made in manually setting the operation mode.

Hereinafter, a communication signal relay method using the MU 200 of the above configuration will be described.

Referring to FIG. 5, a HU 300 may include

optical transmission units

310 and 340, optical/

electrical conversion units

320 and 330, a signal coupling/splitting unit 360 and a power supply unit 350.

An optical signal transmitted from the MU 200 is received by the optical transmission unit 310 of the HU 300 and may be converted into an electrical signal through the optical/electrical conversion unit 320. The electrical signal may be transmitted to the signal coupling/splitting unit 360. The signal coupling/splitting unit 360 may split the signal transmitted from the optical/electrical conversion unit 320 into a plurality of signals. That is, since the HU 300 is connected to a plurality of RUs 400, the signal coupling/splitting unit 360 may split the electrical signal so that the electrical signal may be transmitted to each of the RUs 400 connected to the HU 300.

Each of the electrical signals split by the signal coupling/splitting unit 360 may be transmitted to the optical/electrical conversion unit 330 and converted into an optical signal, and the optical signal may be transmitted from the optical transmission unit 340 to the RU 400 through the optical/electrical composite cable 700. The optical/electrical conversion unit 330 and the optical transmission unit 340 may be disposed in the HU 300 as many as the number of the RUs 400 connected to the HU 300.

An optical signal transmitted from the RU 400 may be transmitted to the optical transmission unit 340 of the HU 300 through the optical/electrical composite cable 700 and transmitted to the MU 200 by way of the optical/electrical conversion unit 330, the signal coupling/splitting unit 360, the optical/electrical conversion unit 320 and the optical transmission unit 310.

The HU 300 may further include the power supply unit 350. The power supply unit 350 may supply power to the RU 400. That is, the RU 400 itself does not have a separate power source and may operate by the power supplied from the power supply unit 350 of the HU 300. The power of the power supply unit 350 may be transmitted through the optical/electrical composite cable 700 which connects the HU 300 and the RU 400. The optical/electrical composite cable 700 includes an optical fiber and a conductive wire, and the power may be supplied from the HU 300 to the RU 400 through the conductive wire. The optical/electrical composite cable 700 will be described below in detail.

A plurality of RUs 400 may be connected to the HU 300, and all the RUs 400 connected to the HU 300 may be supplied with power from the HU 300. Like this, since a separate power supply unit does not need to be installed in each of the plurality of the RUs 400, the RUs 400 are easy to install, and since the RU 400 can be miniaturized into a small size, the RU 400 can be easily installed in a narrow installation space. In addition, since the RU 400 itself does not have a power supply unit, a UPS for maintaining power of the RU 400 does not need to be installed, and since a work for installing a power supply unit does not need to be separately performed in order to install the RU 400, installation cost of the distributed antenna system can be saved. In addition, a network of a distributed antenna system can be flexibly designed using a small number of RUs 400, compared with a case of using the optical/electrical composite cable 700 which can transmit a power of 1,200W or higher.

Referring to FIG. 6, an RU 400 may include an optical transmission unit 410, an optical/electrical conversion unit 420, a digital signal processing unit 430, a digital/analog (D/A) converter 440, an analog/digital (A/D) converter 450, a signal input and output unit 460 and an antenna 470.

An optical signal transmitted through the optical/electrical composite cable 700 may be received by the optical transmission unit 410 of the RU 400 and converted into an electrical signal through the optical/electrical conversion unit 420, and the electrical signal may be digitally signal-processed by the digital signal processing unit 430 and converted into an analog signal by the D/A converter 440. The analog signal may be amplified by the signal input and output unit 460 and transmitted to the user equipment through the antenna 470.

A signal output from the user equipment may be transmitted to the HU 300 through the optical/electrical composite cable 700 by way of the antenna 470, the signal input and output unit 460, the A/D converter 450, the digital signal processing unit 430, the optical/electrical conversion unit 420 and the optical transmission unit 410 of the RU 400.

As described above, since the RU 400 is connected to the HU 300 through the optical fiber in the optical/electrical composite cable 700, it may receive a signal from the HU 300 placed at a far distance without loss of signal. In the case of a conventional Unshielded Twisted Pair (UTP) cable, a distance capable of transmitting a signal within an allowed signal loss range is merely 100m in maximum, and thus there is limitation in designing a system. However, according to an embodiment of the present invention, since a signal is transmitted through the optical fiber in the optical/electrical composite cable 700, the signal can be transmitted over a long distance without loss of signal, and accordingly, a flexible distributed antenna system can be designed.

In addition, since the RU 400 does not have a separate power supply unit and receives power from the HU 300 through the optical/electrical composite cable 700, installation cost can be saved in installing the RU 400, and since the RU 400 can be manufactured into a relatively small size, it can be installed in a relatively narrow space. Since power of 1,200W or higher can be supplied through the optical/electrical composite cable 700, the RU 400 may transmit an RF signal of high power, and thus an optimum network can be designed with a relatively small number of RUs 400.

Referring to FIG. 7, the optical/electrical composite cable 700 of the present invention may include an optical cable 20 disposed at the center of the optical/electrical composite cable 700, one or more first power line units 30 and one or more second power line units 50 contacting with the outer surface of the optical cable 20, and an outer shell layer 70 surrounding and contacting with the outer surfaces of the first and second

power line units

30 and 50.

The outer shell layer 70 may be a part forming an outer appearance of the optical/electrical composite cable 700 and may protect the optical cable and the power line units contained in the optical/electrical composite cable 700.

Preferably, the outer shell layer 70 may include a metal layer 71 surrounding the first and second

power line units

30 and 50 in a circular form so that the first and second

power line units

30 and 50 may simultaneously contact with the inner surface of the outer shell layer and protecting the first and second

power line units

30 and 50 and the optical cable 20 from an external shock, and an outer cladding layer 73 surrounding the metal layer 71.

The metal layer 71 may be formed of a wrinkled steel tape.

The outer cladding layer 73 may have a fireproof characteristic and may be preferably an environmentally friendly resin. For example, the outer cladding layer 73 may be formed of polyethylene, polypropylene, polyvinyl chloride (PVC) or the like.

The outer shell layer 70 may further include a waterproof tape 75, instead of the metal layer 71, surrounding the first and second

power line units

30 and 50 in a circular form on the inner surface of the metal layer 71 so that the first and second

power line units

30 and 50 may simultaneously contact with the inner surface of the metal layer. The waterproof tape 75 may be disposed in the form of wrapping the power line units with a non-woven fabric processed with a waterproof material. The waterproof cladding layer 75 is formed to cross wind or laminate a material formed in the shape of a tape. Since such a waterproof tape is provided, damage of the optical fiber and cable caused by penetration of moisture can be prevented.

A ripcord string (not shown) may be provided in the outer shell layer 70 (e.g., the metal layer 71 or the waterproof tape 75) so that the outer shell layer 70 may be easily stripped.

The first power line unit 30 and the second

power line unit

30 and 50 may respectively include one or more

unit power lines

31 or 51 formed of a conductor and an

insulation cladding layer

33 or 53 formed of an insulator wrapping the one or more

unit power lines

31 or 51. Preferably, the power line unit may conform to a specification used for general electric power. The plurality of

unit power lines

31 or 51 may be formed to be twisted with each other. The

insulation cladding layer

33 or 53 may be manufactured to have a variety of colors according to its usage. The

unit power line

31 or 51 is formed of copper, and the

insulation cladding layer

33 or 53 is preferably formed of a resin material including polyethylene, polypropylene and polyvinyl chloride.

The first power line unit 30 may correspond to a + terminal, and the second power line unit 50 may correspond to a - terminal. One of the first power line units 30, one of the second power line units 50 and one of the optical fiber units (21 of FIG. 8) may be branched from the optical/electrical composite cable 700 to form a set, and the one set may be connected to one RU 500 and transmit signals and power.

Referring to FIG. 8, the optical cable has a structure including one or more optical fiber units 21 collected in the lengthwise direction around a tube 22 positioned at the center of the cable 20, respectively having a predetermined number of optical fiber core lines 21a inside a plastic tube 21b formed of plastic resin, and a sheath layer 24 wrapping around the one or more optical fiber units 21.

The plastic tube 21b configuring the optical fiber unit 21 may be formed of plastic resin including polypropylene (PP), polybutylene terephthalate (PBT), polycarbonate (PC), polyamide (PA) such as nylon-12 and the like and may be preferably formed of polybutylene terephthalate (PBT). Since the polybutylene terephthalate (PBT) resin is flexible and has excellent mechanical strength and fast crystallization speed, it does not excessively contract in the lengthwise direction after the tube 21b is manufactured.

The plastic tube 21b is formed in a shape of a cylinder as a whole and structured to have a penetration hole for installing the optical fiber core lines 21a, a waterproof material 21c and the like inside thereof. Here, specifications of the inner/outer diameters of the plastic tube 21b are determined in advance according to the usage of the cable 20, and the specifications are determined depending on the number of optical fiber core lines 21a installed inside the plastic tube 21b, the amount of the waterproof material 21c contained in the plastic tube 21b, a bending characteristic required by the cable 20, and the like.

That is, if the inner diameter of the plastic tube 21b is less than the specification, efficiency of transmitting data per unit time can be lowered since the amount of the waterproof material 21c contained in the plastic tube 21b is insufficient and the number of the optical fiber core lines 21a is also reduced, whereas if the inner diameter of the plastic tube 21b exceeds the specification, the diameter of the cable 20 is unnecessarily increased, and flexibility of the cable 20 is lowered so as to make it difficult to wind the cable.

In addition, thickness of the plastic tube 21b may be determined considering the mechanical strength, flexibility and the like required for the plastic tube 21b, and, for example, the thickness of the plastic tube 21b may be larger than the outer diameter of the plastic tube 21b by 10%, preferably 15%.

Preferably, the plastic tube 21b may be configured to form a color coating layer of various colors outside thereof so as to easily distinguish the optical fiber units 21 according to a function or an action and easily identify an optical fiber unit 21 when a work for repairing disconnection is performed.

A predetermined number of optical fiber core lines 21a may be installed in the plastic tube 21b configuring the optical fiber unit 21. The number of optical fiber core lines 21a installed in the plastic tube 21b may be one, two or three or more as needed. That is, the number of optical fiber core lines 21a may vary according to data transmission efficiency per unit time of the optical cable containing the optical fiber core lines, flexibility of the optical cable, and the like.

Each of the optical fiber core lines 21a is formed as a dual cylindrical structure in which a part called as cladding wraps around a part at the center called as a core. Here, a glass optical fiber of a silica material having a high refractive index is used as the core, and a glass, a synthetic resin or the like of a silica material having a refractive index relatively lower than that of the core is used as the cladding, and thus the optical fiber core lines may be implemented to transmit a signal by generating total reflection of light passing through the center. A core having a diameter of a few μm is referred to as a single mode optical fiber, and a core having a diameter of a few tens of μm is referred to as a multi-mode optical fiber, and the optical fiber is classified as a step index optical fiber or a graded index optical fiber depending on distribution of the refractive index of the core.

In addition, a waterproof material 21c such as a jelly compound, water proof powder, waterproof yarn or a combination of these may be filled in the plastic tube 21b together with the optical fiber core lines 21a. If moisture penetrates into the optical cable 20, mechanical reliability of the optical cable 20 may be lowered, or hydrogen gas may be generated due to the chemical reaction of the moisture with the metal in the optical cable 20, and there may be some cases in which a connection device and a termination device of the cable are corroded since the moisture moves into the optical cable 20.

Accordingly, the waterproof material performs a function of preventing moisture from penetrating into the plastic tube 21b, and preferably, it guarantees the optical fiber core lines 21a to fluidly move inside the plastic tube 21b.

The jelly compound as the waterproof material 21c may be formed of a resin having excellent thermal stability, waterproof property and electrical insulation, and preferably, it may be a thixotropic jelly compound of high viscosity to have excellent adhesiveness to the optical fiber core lines 21a and an excellent function of preventing penetration of moisture.

In addition, the waterproof powder as the waterproof material 21c is super absorbent polymer (SAP), which is appropriate to be used for the purpose of waterproofing for preventing penetration of moisture into the plastic tube 21b since it has a characteristic of absorbing water as much as a few tens or hundreds times of its weight. The waterproof powder may be a polyacrylate series, a PVA maleate reactant, an isobutylene maleate copolymer, a polyacrylonitrile copolymer, a polyethylene oxide crosslink, a starch acrylonitrile copolymer, a starch acrylic graft copolymer or the like.

In addition, the waterproof yarn as the waterproof material 21c may be inserted into the penetration hole of the plastic tube 21b in the lengthwise direction, and a waterproof yarn manufactured by attaching waterproof powder to a continuous fiber or a waterproof yarn manufactured by twisting waterproof powder processed in the form of a string with a continuous fiber or attaching the processed waterproof powder to the continuous fiber may be used.

The waterproof yarn may have a thickness of 300 to 3,000 deniers, a swelling capacity of 20g/g or higher in distilled water, and a tensile strength of 3 to 150N. If the thickness of the waterproof yarn is 300 deniers or less, an excessively large amount of waterproof yarn is needed to accomplish waterproof performance, and thus it is difficult to handle the cable, and price of the cable will increase. In addition, if the swelling capacity of the waterproof yarn in distilled water is less than 20g/g, desired waterproof performance may not be attained, and if the tensile strength is less than 3N, a disconnection may occur due to the tensile stress generated in the process of inserting the waterproof yarn into the plastic tube 21b in the lengthwise direction or bending the cable.

As described above, in the optical cable 20 according to an embodiment of the present invention, one or more of the optical fiber units 21 having a predetermined number of the optical fiber core lines 21a and the waterproof material 21c installed in the plastic tube 21b are collected in the lengthwise direction around the tube 22 positioned at the center of the cable 20. The number of the optical fiber units 21 may vary according to the usage of the cable, and preferably, it may be six so that the optical cable 20 may easily maintain its cross section in a circular form.

Meanwhile, a stress is applied to the optical fiber core line 21a of the optical fiber unit 21 contained in the optical cable 20 due to the bending of the optical cable 20 generated when the optical cable 20 is wound around a reel, a drum or the like, and disconnection, characteristic degradation or the like of optical fiber core lines 21a may be induced.

In order to solve such a problem, strain of the optical cable 20 caused by bending stress generated by bending the optical cable 20 may be compensated by the length extended by stretching the twisted optical fiber unit 21. That is, the optical fiber unit 21 may be collected around the tube 22 at the center in the form of helical twist or S-Z twist in order to allow a margin in the length of the optical fiber unit 21 and the optical fiber core line 21a contained therein so as to compensate the strain of the optical cable 20 caused by winding the optical cable 20 around a reel or the like.

In this case, the optical fiber units 21 may maintain a state of being twisted at a predetermined pitch, and the pitch may be appropriately selected considering a diameter, a bending radius and the like of the optical cable 20 so that the strain of the optical cable 20 may be compensated when the optical fiber unit 21 twisted at the pitch is stretched by bending or the like of the optical cable 20.

Meanwhile, the shape of the tube 22 may be strained when a shock, a load or the like is applied to the optical cable 20 so that the tube 22 may protect the plastic tube 21b of the optical fiber unit 21 contacting with the tube and the optical fiber core lines 21a installed inside the plastic tube and perform a function of giving tensile strength to the optical cable 20 by absorbing the shock or the like.

The tube 22 may be formed of a plastic resin the same as that of the plastic tube 21b and preferably formed of a foamed plastic resin having a strength lower than that of the plastic tube 21b, such as foamed polyethylene, foamed polyvinyl chloride (PVC) or the like. Since the shape of the tube 22 is strained when a load is applied in the lateral direction of the optical cable 20 in the case where the strength of the tube 22 is lower than that of the plastic tube 21b, it is easy to maintain the shape of the plastic tube 21b and protect the optical cable core lines 21a installed in the plastic tube 21b.

The shape of the tube 22 is not specially limited if the tube 22 may stably support one or more optical fiber units 21 collected around the tube 22. Preferably, the tube 22 has a cross section of a circular form, and the diameter of the circular form may be appropriately selected according to the diameter of the optical fiber unit 21 so as to stably contact with the outer surfaces of all the optical fiber units 21 collected around the tube 22.

On the other hand, an internal strength wire for preventing excessive bending and stretching of the optical cable 20 may substitute for the tube 22 of the present invention. Preferably, the internal strength wire may be formed of Fiber Reinforced Plastic (FRP). As the internal strength wire is provided like this, mechanical strength of the optical cable 20 may be reinforced, and durability of the optical cable 20 may be improved furthermore by preventing excessive bending and snapping of the optical fiber unit.

In the optical cable 20 according to an embodiment of the present invention, preferably, a tensile strength wire (not shown) contacting with the outer surface of the optical fiber units 21, the tube 22 or all of these may be additionally included in the empty space of the sheath layer 24. Here, the tensile strength wire performs a function of protecting the optical fiber core lines 21a inside the optical cable 20 by reinforcing tensile strength of the optical cable 20 and may be formed of Kevlar aramid yarn, a fiber glass epoxy rod, Fiber Reinforced Polyethylene (FRP), a high strength fiber, a galvanized steel wire, a steel wire or the like.

The optical cable 20 according to an embodiment of the present invention may have a structure of wrapping one or more optical fiber units 21 collected around the tube 22 with the sheath layer 24. Thickness of the sheath layer 24 may be appropriately selected according to the usage of the optical cable 20, specifically, the entire diameter of the optical cable, required flexibility, bending characteristics or the like.

Meanwhile, the optical cable 20 according to an embodiment of the present invention may additionally include a reinforcement layer 25, a waterproof layer 26 or both of these between the sheath layer 24 and the one or more optical fiber units 21.

If the sheath layer 24 is formed directly outside of the optical fiber units 21, the entire outer surface of the optical cable 20 is formed uneven, or the material of the sheath layer 24 may be adhered to the material of the plastic tube 21b of the optical fiber unit 21, and this may be undesirable since it may spoil the appearance of the optical cable 20 and unnecessary shock and friction resistance may be easily applied when the optical cable is wound. Accordingly, the sheath layer 24 may be formed by cross-winding a metallic reinforcement tape such as aluminum foil around the optical fiber units 21, or the sheath layer 24 may be formed when an outer appearance further close to the original shape of the optical cable is formed by wrapping the optical fiber units 21 with the reinforcement layer 25 formed of a transparent film of a synthetic resin, a non-woven fabric or the like.

In addition, the waterproof layer 26 may be formed inside, outside or both inside and outside of the reinforcement layer 25. The waterproof layer 26 may be formed by cross-winding a waterproof tape, such as a paper swellable tape, around the optical fiber units 21 or the reinforcement layer 25 and may perform a function of suppressing moisture penetrated through a damaged part of the sheath layer 24 from penetrating into the optical cable 20. Particularly, when the waterproof layer 26 is disposed outside of the reinforcement layer 25, the waterproof layer may accomplish tight adhesion to fluoride resin forming the sheath layer 24.

In the optical cable 20 according to an embodiment of the present invention, a bedding material made of a waterproof material such as a jelly compound, waterproof powder, waterproof yarn or the like may be filled in the empty space between the sheath layer 24 and the optical fiber units 21. The waterproof material such as a jelly compound, waterproof powder, waterproof yarn or the like may be the same as or different from the waterproof material 21c filled in the plastic tube 21b described above.

Referring to FIG. 9, the optical/electrical composite cable 800 is the same as the optical/electrical composite cable 700 of FIG. 7 in that it includes an optical cable 20’ disposed at the center of the optical/electrical composite cable 800, a plurality of first power line units 30 and a plurality of second power line units 50 disposed to contact with the outer surface of the optical cable 20’, and an outer shell layer 70 contacting with the outer surfaces of the first and second

power line units

30 and 50, and the difference is only in the configuration of the optical cable 20’. That is, in the optical cable 20’, a tube 22 is disposed at the center of the optical cable 20’, and optical fiber units 21’ may be disposed to contact with the outer surface of the tube 22. The optical/electrical composite cable 800 is different from the optical/electrical composite cable 700 of FIG. 7 using a loose tube in that the optical fiber configuring the optical fiber unit 21’ is a tight buffer type optical fiber 21a’.

Referring to FIG. 10, the optical/electrical composite cable 900 may include a first power line unit 30, a second power line unit 50 and a ground line 40 externally contacting with each other, an outer shell layer 70 surrounding and contacting with the outer surfaces of the first and second

power line units

30 and 50 and the ground line 40, and optical fiber units 21’’ contacting with the outer surface of the first power line unit 30, the second power line unit 50 or the ground line 40 and contacting with the inner surface of the outer shell layer 70. The optical fiber unit 21’’ may have a configuration the same as that of the optical fiber unit 21 of FIG. 8 or the optical fiber unit 21’ of FIG. 9.

Such an optical/electrical composite cable 900 is not separately branched, but directly connects the HU 300 and each of the RUs 400 to transmit and receive optical signals between the HU 300 and the RU 400 and, at the same time, supply power from the HU 300 to the RU 400.

The optical/electrical composite cable used in the distributed antenna system according to an embodiment of the present invention is not limited to those shown in FIGs. 7 to 10, and any one which combines a power line and an optical cable can be used.

FIG. 11 shows flow of a communication signal relay method according to an embodiment of the present invention.

First, the MU 200 receives a signal flowing in from the base station through the signal input and output unit 210, and the A/D converter 220 converts the received signal into a digital signal and extracts a signal sample S100. The extracted signal sample is transferred to the FPGA unit, and the signal detection unit 230 of the FPGA unit compares the signal sample with a threshold value set in advance for each service frequency band S102, and if the magnitude of the signal sample is larger than the threshold value, the signal detection unit 230 determines that a communication signal using a corresponding service frequency band is received from the base station S104, and if the magnitude of the signal sample is smaller than the threshold value, the signal detection unit 230 determines that a communication signal using a corresponding service frequency band is not received from the base station S108. When the communication signal is received, the communication mode determination unit 240 may determine a service mode of the corresponding communication signal and provide the mode control unit 250 with a result of the determination S106.

Next, the mode control unit 250 determines existence of a communication signal in each service frequency band using a result of detecting a communication signal by the signal detection unit 230 and sets an operation mode of the MU 200 according to the determination S110. At this point, the operation mode may be set based on a result of determining a communication mode by the communication mode determination unit 240. Then, the O/E conversion unit 260 converts the received communication signal into an optical signal and transmits the optical signal through the optical transmission unit 270 in the set operation mode.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

A master unit for a distributed antenna system, for relaying a communication signal between a base station and a user equipment, the master unit comprising:

an A/D conversion unit to generate a signal sample by converting a signal flowing in from the base station into a digital signal;

a signal detection unit to determine whether or not a communication signal is received, based on the signal sample; and

a mode control unit to set an operation mode based on a result of determining whether or not a communication signal is received.
The master unit according to claim 1, further comprising a communication mode determination unit to determine a communication mode of the flow-in signal.
The master unit according to claim 2, wherein the mode control unit sets the operation mode based on a result of determining whether or not a communication signal is received and a result of determining a communication mode.
The master unit according to claim 2, wherein the communication mode determination unit determines a communication mode of the flow-in signal for each service frequency band.
The master unit according to claim 1, wherein the signal detection unit determines whether or not a communication signal is received for each service frequency band.
The master unit according to claim 1, wherein the mode control unit operates only when the signal detection unit determines that the communication signal is received.
The master unit according to claim 1, further comprising a signal input and output unit wiredly or wirelessly connected to the base station, to transmit and receive the communication signal.
The master unit according to claim 1, further comprising:

an optical/electrical conversion unit to convert the communication signal from an electrical signal into an optical signal; and

an optical transmission unit to transmit the converted optical signal, in the set operation mode.
The master unit according to claim 1, wherein the signal detection unit determines that the communication signal is received when a magnitude of the signal sample is larger than a previously set reference value.
A communication signal relay method of a master unit for a distributed antenna system, the method comprising the steps of:

converting a flow-in signal received from a base station into a digital signal and creating a signal sample;

determining whether or not a communication signal is received, based on the signal sample;

setting an operation mode based on a result of determining whether or not a communication signal is received; and

relaying the communication signal in the set operation mode.
The communication signal relay method according to claim 10, further comprising the step of determining a communication mode of the flow-in signal.
The communication signal relay method according to claim 11, wherein the step of setting an operation mode is a step of setting an operation mode based on a result of determining whether or not a communication signal is received and a result of determining a communication mode.
The communication signal relay method according to claim 11, wherein the step of determining a communication mode is a step of determining a communication mode of the flow-in signal for each service frequency band.
The communication signal relay method according to claim 10, wherein the step of creating a signal sample is a step of converting the flow-in signal into a digital signal and creating the signal sample for each service frequency band.
The communication signal relay method according to claim 10, wherein the step of determining whether or not a communication signal is received is a step of dividing the signal sample into service frequency bands and determining whether or not a communication signal is received on each of the service frequency bands.
The communication signal relay method according to claim 10, wherein the step of setting an operation mode is performed only when the communication signal is received.
The communication signal relay method according to claim 10, further comprising the step of wiredly or wirelessly connecting to the base station and transmitting and receiving the communication signal.
The communication signal relay method according to claim 10, wherein the step of relaying the communication signal includes the steps of:

converting the communication signal from an electrical signal into an optical signal; and

transmitting the converted optical signal in the set operation mode.
The communication signal relay method according to claim 10, wherein the step of determining whether or not a communication signal is received is a step of determining that the communication signal is received if a magnitude of the signal sample is larger than a previously set reference value.
A distributed antenna system comprising:

a master unit to transmit and receive a communication signal to and from a base station;

a hub unit to receive the communication signal processed by the master unit or transmit a communication signal to the master unit;

a remote unit to transmit and receive a communication signal to and from the hub unit; and

an optical/electrical composite cable to connect the hub unit and the remote unit, wherein

the remote unit receives power from the hub unit through the optical/electrical composite cable.
The distributed antenna system according to claim 20, wherein the remote unit does not have a separate power source and operates by the power supplied from the hub unit.
The distributed antenna system according to claim 20, wherein the hub unit has a power supply unit to supply power to the remote unit.
The distributed antenna system according to claim 20, wherein the remote unit receives an optical signal from the hub unit through the optical/electrical composite cable and converts the optical signal into an electrical signal.
The distributed antenna system according to claim 20, wherein the communication signal is transmitted and received between the hub unit and the remote unit through the optical/electrical composite cable
The distributed antenna system according to claim 20, wherein the optical/electrical composite cable includes:

an optical cable disposed at a center of the optical/electrical composite cable;

one or more first power line units and one or more second power line units surrounding and contacting with an outer surface of the optical cable; and

an outer shell layer wrapping around the first power line units and the second power line units, wherein

the optical cable includes:

a tube disposed at the center of the optical cable;

one or more optical fiber units collected around the tube in a lengthwise direction, respectively containing a plastic tube and optical fiber core lines installed inside the plastic tube; and

a sheath layer wrapping around the optical fiber units, wherein

one of the first power line units, one of the second power line units and one of the optical fiber units are branched and connected to the remote unit.
The distributed antenna system according to claim 25, wherein the tube has a diameter as large as to contact with outer surfaces of the one or more optical fiber units and stably support the one or more optical fiber units.
The distributed antenna system according to claim 25, wherein the plastic tube is formed of polypropylene (PP), polybutylene terephthalate (PBT), polycarbonate (PC), polyamide (PA) or a mixture of these.
The distributed antenna system according to claim 27, wherein the tube is formed of a foamed plastic resin having a strength lower than that of the plastic tube.
The distributed antenna system according to claim 25, wherein a waterproof material including a jelly compound, waterproof powder, waterproof yarn and a combination of these is installed in the plastic tube together with the optical fiber core lines.
The distributed antenna system according to claim 25, wherein the power is supplied to the remote unit through the power line units.
The distributed antenna system according to claim 25, wherein the communication signal is transmitted and received between the hub unit and the remote unit through the optical cable.
The distributed antenna system according to claim 20, wherein the optical/electrical composite cable includes a first power line unit, a second power line unit and a ground line externally contacting with each other, an outer shell layer surrounding and contacting with outer surfaces of the first and second power line units and the ground line, and optical fiber units contacting with the outer surface of the first power line unit, the second power line unit or the ground line and contacting with an inner surface of the outer shell layer.
The distributed antenna system according to claim 20, wherein the master unit includes

an A/D conversion unit to generate a signal sample by converting a signal flowing in from the base station into a digital signal;

a signal detection unit to determine whether or not the communication signal is received, based on the signal sample; and

a mode control unit to set an operation mode based on a result of determining whether or not the communication signal is received.
The distributed antenna system according to claim 33, further comprising a communication mode determination unit to determine a communication mode of the flow-in signal.
The distributed antenna system according to claim 34, wherein the mode control unit sets the operation mode based on a result of determining whether or not the communication signal is received and a result of determining a communication mode.
The distributed antenna system according to claim 34, wherein the communication mode determination unit determines a communication mode of the flow-in signal for each service frequency band.
The distributed antenna system according to claim 33, wherein the signal detection unit determines whether or not a communication signal is received for each service frequency band.
The distributed antenna system according to claim 33, wherein the mode control unit operates only when the signal detection unit determines that the communication signal is received.
The distributed antenna system according to claim 33, further comprising a signal input and output unit wiredly connected to the base station, for transmitting and receiving the communication signal.
The distributed antenna system according to claim 33, further comprising:

an optical/electrical conversion unit to convert the communication signal from an electrical signal into an optical signal; and

an optical transmission unit to transmit the converted optical signal, in the set operation mode.
The distributed antenna system according to claim 33, wherein the signal detection unit determines that the communication signal is received when a magnitude of the signal sample is larger than a previously set reference value.