JPH11239091A - Radio base station and antenna unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a means which economically expands a practical communication area and eliminates a blind zone by making it possible to install only an antenna at an appropriate place when communication by radio is difficult even through the actual distance to a base station is relatively short. SOLUTION: A mobile communication device that communicates between a radio base station 1 and a mobile radio terminal 3 through a radio channel is provided with an antenna unit 2 which is arranged in the neighborhood of the radio communicable area 9 of the station 1 or outside the radio communicable area. The unit 2 is connected to the station 1 through a wire circuit 8 and the terminal 3 can communicate with the station 1 through the unit 2. The station 1 and the unit 2 are connected with an RF signal coaxial cable 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication method, a mobile communication apparatus, and an antenna unit for economically expanding a communicable area in a mobile communication system.

[0002]

2. Description of the Related Art In a mobile communication system using a high frequency represented by a PHS system, a communication radio wave has a strong straight-line property and remarkably low wrap-around capability. turn into.

[0003] For this reason, it is considered that the inside of the area is considered to be due to the physical distance from the radio base station, but the view of the house is poor, so that it cannot enter the talkable area, or a conference room or factory having a highly shielded structure. Although it is necessary to have a communicable area, it is expected that communication traffic will be relatively small, so that there are many places where there is no cost merit to add wireless base stations.

[0004]

According to the conventional method,
In such a case, add a base station or install a device that operates in the same way as a generally known repeater device that receives weak radio waves from the base station, converts the frequency, and transmits the boosted output Although there is a method for eliminating a dead zone of radio waves, a device equipped with a wireless device is relatively expensive, so that a user who installs a base station has a large economic burden.

[0005] The present invention has been made in view of the above points, and when the wireless communication is difficult despite the fact that the actual distance from the base station is relatively short, only the antenna is appropriately used. It is an object of the present invention to provide a technology that economically realizes expansion of a practical communication area and elimination of a dead zone by enabling installation at an appropriate position.

[0006]

According to the present invention, there is provided a mobile communication method for communicating between a wireless base station and a mobile wireless terminal via a wireless line. An antenna unit for expanding the wireless communication area of the wireless base station is arranged near the area or outside the wireless communication area, and communication is performed between the wireless base station and the mobile wireless terminal via the antenna unit. In that case, communication can also be performed by connecting the wireless base station and the antenna unit via a wired line. In addition, the mobile radio terminal can communicate with the radio base station via the antenna of the radio base station or the antenna of the antenna unit. Further, according to the present invention, in a mobile communication device for communicating between a wireless base station and a mobile wireless terminal via a wireless line, an antenna unit disposed near or outside the wireless communicable area of the wireless base station is provided. The mobile radio terminal is configured to be able to communicate with the radio base station via the antenna unit. here,
The wireless base station and the antenna unit may be connected by an RF signal coaxial cable. Also, the radio base station includes a radio unit including a plurality of antennas for radio communication with the mobile radio terminal, an antenna switching unit for switching to one of the antennas or the antenna unit, and a connection to the antenna unit. A connection determining unit that determines an unconnected state and outputs the determination result to the antenna switching unit; a control unit that controls the wireless unit and controls data communication between the wireless unit and the mobile wireless terminal via a wireless line. And a configuration including: Further, the antenna unit may be configured to include a cable attenuation compensation circuit for amplifying a signal of the wired line and compensating a signal attenuation amount based on the length of the wired line. Further, in the present invention, an antenna unit connected to a wireless base station via a wired line and arranged to expand the wireless communicable area of the wireless base station near or outside the wireless communicable area of the wireless base station. The antenna unit includes a power supply circuit and a cable attenuation compensation circuit for amplifying a signal on a wired line and compensating for a signal attenuation based on the length of the wired line.

According to the present invention, a communicable area can be economically expanded in a radio base station used for communicating with a mobile radio terminal in a mobile communication system via a radio line.

Further, the radio base station and the antenna unit are R
They are connected by an F signal coaxial cable and exchange radio frequency band signals. By installing the antenna unit near or outside the wireless communication area of the wireless base station, the effective communication area of the wireless base station is expanded.

Since the antenna unit is composed of only the antenna, the cable attenuation compensating circuit and the power supply circuit, it can be realized at relatively low cost. Therefore, it is possible to expand the communicable area relatively inexpensively, compared to newly installing a wireless base station equivalent to the wireless base station.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of one embodiment of the present invention. The embodiment shown in FIG. 1 is an example applied to a business-use PHS system of the mobile communication system, in which a radio base station 1 and a main unit 4 are connected by a communication data line 6 for exchanging communication data, 1
The power supply to the power supply is performed by a method such as phantom power supply.

The main unit 4 and the private branch exchange 5 are connected to a communication data line 7.
And exchanges communication data. Home switch 5
Is connected to the subscriber network. The radio base station 1 and the antenna unit 2 are connected by an RF signal coaxial cable 8 and exchange radio frequency band signals. The mobile radio terminal 3 is connected to the radio base station 1 or the antenna unit 2 via a radio line.
And transmission and reception of communication data. The radio base station communicable area 9 indicates a range in which the radio base station 1 can communicate with the mobile radio terminal 3, and the antenna unit communicable area 10 indicates a range in which the antenna unit can communicate with the mobile radio terminal 3.

FIG. 2 shows an embodiment of the internal configuration of the radio base station 1 of FIG. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. The control unit 102 is the main unit 4 of FIG.
And receives power from the main unit 4 by a method such as phantom power supply, and distributes power to each unit in the wireless base station 1.

The radio unit 101 has two antenna terminals, and a first antenna 107 is fixedly connected to the first antenna terminal, and an antenna switching unit 103 is connected to the second antenna terminal. Radio section 101 selects an antenna system having a better reception state by a generally known reception diversity system, and sequentially switches the antenna system.

The control unit 102 controls the radio unit 101 and controls the radio unit 101 via the radio channel by the secondary antenna 108 (or the antenna 204 of the antenna unit 2 in FIG. 3) connected via the primary antenna 107 and the antenna switching unit 103. The communication data is exchanged with the mobile radio terminal 3 of FIG.

The antenna switching unit 103 receives the connection determination signal 10
5 and the RF signal 106 are connected to the connection determination unit 104. The connection determination unit 104 is provided at a connection end with the antenna unit 2, determines whether or not the antenna unit 2 is connected by the physical switch 501 (see FIG. 5), and sends a connection determination signal 105 to the antenna switching unit 103. Notify by

When the antenna switching unit 103 is notified that the antenna unit 2 is not connected, the radio unit 1
01, and the connection between the radio unit 101 and the connection determination unit 104 (R
F signal 106) is disconnected. Conversely, when it is notified that the antenna unit 2 is in the connected state, the connection between the second system antenna terminal of the wireless unit 101 and the antenna 108 is disconnected, and the second system antenna terminal of the wireless unit 101 is connected to the connection determination unit 10.
4 is valid (RF signal 106).

FIG. 3 shows an embodiment of the internal configuration of the antenna unit 2. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. When the antenna unit 2 in FIG. 1 of the present invention is used, the antenna unit 2 is transmitted from the wireless base station 1 in FIG.
The RF signal connected to the cable attenuation compensator 20 shown in FIG.
Connected to 1.

The cable attenuation compensating unit 201 compensates for the attenuation of the RF signal caused by passing through the RF signal coaxial cable 8 by an amplifier circuit. The amount of compensation in the cable attenuation compensating unit 201 can be calculated from the amount of attenuation of the RF signal caused by passing through the RF signal coaxial cable 8 and the amount of attenuation per unit length of the cable used, and the amount of attenuation. Is adjusted by the compensation amount adjustment unit 202 so as to obtain a compensation amount equivalent to The power supply unit 203 supplies power to the internal circuit of the antenna unit 2, and external power supply from a battery or an AC power adapter is conceivable.

FIG. 4 shows an embodiment of the internal configuration of the antenna switching section 103 of FIG. 2, the same components as those in FIG. 2 are denoted by the same reference numerals. The antenna switching unit 103 mainly includes a switch 401 using a high-frequency switch IC using a generally known GaAs (gallium arsenide) field effect transistor.

The common terminal of the switch 401 is connected to the second system antenna terminal of the radio unit 101 of FIG. 2, and the signal of the connection determination signal 105 from the connection determination unit 104 of FIG. Either side of the connection determination unit 104 is selected and electrically connected. The connection on the non-selected side is electrically open. In this embodiment, when the signal logic of the connection determination signal 105 is correct, the connection to the antenna 108 in FIG. 2 is selected, and when the signal logic is negative, the connection determination unit 104 in FIG. Connection is selected.

FIG. 5 shows an embodiment of the internal configuration of the connection judging section 104 shown in FIG. In the figure, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals. The connection end for connecting the RF signal coaxial cable 8 of FIG.
It comprises a signal terminal 502. Physical switch 50
2 is pulled up to the power supply voltage via the current limiting resistor 503 and input to the antenna switching unit 103 in FIG.

On the other hand, the terminal b is connected to the ground. The RF signal terminal 502 is connected as the RF signal 106 to the antenna switching unit 103 in FIG. Now, when the RF signal coaxial cable 8 of FIG. 1 is not connected to the connection determination unit 104, the a-side terminal and the b-side terminal are in a non-contact state, and the connection determination signal 105 indicates the power supply voltage level, that is, the positive logic. Output. Conversely, the RF signal coaxial cable 8 of FIG.
Are connected, the a-side terminal and the b-side terminal come into contact with each other.
At this time, the connection determination signal 105 outputs a ground level, that is, negative logic, due to a voltage drop of the current limiting resistor 503.

Next, the operation of this embodiment shown in FIG. 1 will be described with reference to FIGS. Now, it is assumed that all the system elements in FIG. 1, that is, the wireless base station 1, the main unit 4, the private branch exchange 5, and the wireless base station 1 and the antenna unit 2 are connected via the RF signal coaxial cable 8. In this case, the connection determination unit 104 inside the wireless base station 1 in FIG. 2 determines that the RF signal coaxial cable 8 is connected, and the connection determination unit 104 sends the connection determination signal 105 to the antenna switching unit 103. Output with negative logic.

The antenna switching unit 103 that has received the negative logic connection determination signal 105 switches the switch 401 inside the antenna switching unit 103 in FIG. 4 so that the RF signal 106 is connected. Thereby, the antenna 204 inside the antenna unit 2 of FIG.
The signal is connected to the second system antenna terminal of the wireless unit 101 via the signal coaxial cable 8, the connection determination unit 104, and the antenna switching unit.

Therefore, the radio base station 1 uses two antenna systems, one for the antenna 107 and the other for the antenna 204 of the antenna unit 2, and sequentially selects the antenna system judged to be better in the reception state. Communication is performed with the mobile radio terminal 3 by a generally known reception diversity method for switching.

The communicable area at this time is the radio base station 1
And the base unit communicable area 9 by the antenna unit 2 and the communicable area 10 by the antenna unit 2, and the communicable area is almost doubled as compared with the case where the antenna unit 2 is not used. Become.

Since the RF signal is attenuated by passing through the RF signal coaxial cable 8, the compensation amount adjusting unit 202 determines beforehand the communication before starting communication so that a compensation amount corresponding to the attenuation amount can be obtained. Adjust the compensation amount. The amount of attenuation of the RF signal caused by passing through the RF signal coaxial cable 8 can be calculated from the amount of attenuation per unit length of the cable used and the cable length.

For example, in the 1.9 GHz frequency band used by the PHS, the attenuation per unit length (1 m) is 0.1 d.
When a cable of B / m is used and the cable length is 100 m, the total attenuation is 10 dB. Therefore, the compensation amount adjusting unit 202 adjusts so that a compensation amount of 10 dB can be obtained.

Next, the radio base station 1 and the antenna unit 2
The following three cases in which the difference in the communication state and the usage form depending on the installation location of the server are described. (Case 1) The communicable areas of the wireless base station 1 and the antenna unit 2 partially overlap, and the mobile wireless terminal 3
If used. (Case 2) A case where the mobile radio terminal 3 is used in a non-overlapping area where the communicable areas of the radio base station 1 and the antenna unit 2 partially overlap. (Case 3) When the communicable areas of the wireless base station 1 and the antenna unit 2 do not overlap at all.

First, the case 1 is the same as when the system is used only by the radio base station 1, and selects an antenna system having a better reception state from the two antenna systems of the first system and the second system. Communication is performed by switching sequentially. When the mobile wireless terminal 3 moves during communication and comes out of the overlapping area, the mode shifts to the same mode as the case 2.

In case 2, when a terminal is used in the radio base station communicable area 9, only one antenna system is used. The reason is that the electric field strength of the transmission radio wave emitted from the mobile radio terminal 3 is absolutely stronger when the radio wave is received by the radio base station 1 having the first antenna, so that the first antenna is always selected by the reception diversity function. That is because If the mobile wireless terminal 3 moves during communication and enters an overlapping area, the mode shifts to the same as in the case 1.

In case 2, when a terminal is used in the antenna unit communicable area 10, only two antenna systems are used. The reason is that the electric field intensity of the transmission radio wave emitted from the mobile wireless terminal 3 is absolutely stronger when the electric field intensity is received by the antenna unit 2 having the second system antenna. Therefore, the second system antenna is always selected by the reception diversity function. That's because. If the mobile wireless terminal 3 moves during communication and enters the overlapping area, case 1
Shift to the same form as.

In case 3, when a terminal is used in the communication area 9 of the radio base station, only one antenna system is used. The reason is the same as when the terminal is used in the radio base station communicable area 9 in case 2. In case 3, when a terminal is used in the antenna unit talkable area 10, only two antenna systems are used. The reason is the same as when the terminal is used in the antenna unit communicable area 10 in case 2. If the mobile wireless terminal 3 moves out of the area during communication in the present case 3, the mobile terminal 3 does not shift to the case 1 or case 2 but communicates as in all wireless communication systems. It cannot be continued.

As described above, the spread of the communicable area depending on the installation location of the wireless base station 1 and the antenna unit 2 in the case 1 and the case 2 is a continuous planar spread on the same floor such as a business office. While it is possible to move between the base station communicable area 9 and the antenna unit communicable area 10, the spread of the communicable area depending on the installation location in Case 3 is a discontinuous planar spread between different floors. Therefore, it is impossible to move between areas in the radio base station communicable area 9 and the antenna unit communicable area 10.

However, the location where the antenna unit 2 of the present invention is installed is most effective when the area is discontinuous as in the case 3, and depending on the situation of the house to be installed and the purpose of use, the cases 1 and As shown in 2, the installation location is more convenient than simply expanding the communicable area, and is more cost-effective than adding wireless base stations.

For example, according to the physical distance from the wireless base station 1, it is considered to be within the area, but the view of the house is poor, so that it is not possible to enter the wireless base station communicable area 9 or a conference having a highly shielded structure. It is necessary to have a communicable area such as a room or a factory, but it is expected that communication traffic will be relatively small, so there is no cost advantage to add a wireless base station.

As described above, according to the present invention, an antenna unit which can be realized at a relatively low cost by adopting a simple configuration, and a radio base having an interface which can suppress an increase in cost by a simple configuration By connecting the stations, it is possible to expand the communicable area of one wireless base station. Therefore, it has a feature that it greatly contributes to the reduction of the economic burden accompanying the expansion of the communicable area.

On the other hand, it is assumed that only the wireless base station 1, the main unit 4, and the private branch exchange 5 in FIG. 1 are connected, and the RF signal coaxial cable 8 and the antenna unit 2 are not connected. In this case, the operation of the connection determination unit 104 in the wireless base station 1 shown in FIG.
Is determined not to be connected, and connection determination signal 105 is output from connection determination section 104 to antenna switching section 103 in positive logic.

The antenna switching unit 103 that has received the positive logic connection determination signal 105 switches the switch 401 inside the antenna switching unit 103 in FIG. 4 so that the antenna 108 is connected. Thereby, the antenna 108 of FIG. 2 is connected to the second system antenna terminal of the wireless unit 101.

Accordingly, the radio base station 1 generally uses two antenna systems, one for the antenna 107 and the other for the antenna 108, to sequentially select and switch the antenna system judged to be better in the reception state. Communication with the mobile radio terminal 3 is performed according to the received diversity scheme. However, the communicable area at this time is only the wireless base station communicable area 9 of the wireless base station 1.

According to the present invention, when the antenna unit 2 is not connected as described above, high-quality wireless communication using reception diversity can be realized between the wireless base station 1 and the mobile wireless terminal 3 without any change. is there. This is radio base station 1
Are the connection determination unit 104 and the antenna switching unit 1 in FIG.
This is because it is possible to automatically determine whether the RF signal coaxial cable 8 is connected or not and to perform antenna switching.

The present invention is not limited to the application of the mobile communication system shown in the above embodiment to a business PHS system, for example, a home PHS home station (digital cordless telephone base station) or a public PHS system. For example, the present invention can be applied to all wireless base stations using a diversity scheme in which a plurality of antenna systems are provided and the antenna system that can maintain the best communication quality is sequentially selected from the antenna systems.

The power supply in the power supply unit 203 inside the antenna unit 2 in FIG.
The power supply is not limited to the external power supply by the C power adapter. For example, the RF signal coaxial cable 8 is not a cable dedicated to the RF signal, but is used as a common cable with the power supply line. It is possible to supply power to

[0044]

As described above, according to the present invention,
In cases where wireless communication is difficult despite the fact that the distance to the base station is relatively short, the antenna can be installed at an appropriate position to expand the effective communication area and reduce the dead zone. Elimination can be realized economically.

[Brief description of the drawings]

FIG. 1 is a block diagram of a mobile communication device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of an internal configuration of a radio base station according to the embodiment of the present invention.

FIG. 3 is a block diagram illustrating an example of an internal configuration of the antenna unit according to the embodiment of the present invention.

FIG. 4 is a block diagram showing an example of an internal configuration of an antenna switching unit of the wireless base station according to the embodiment of the present invention.

FIG. 5 is a block diagram showing an example of an internal configuration of a connection determination unit of the radio base station according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 radio base station 2 antenna unit 3 mobile radio terminal 4 main unit 5 private branch exchange 6 communication data line 7 communication data line 8 RF signal coaxial cable 9 radio base station communicable area 10 antenna unit communicable area 101 radio unit 102 control unit 103 Antenna switching unit 104 Connection determination unit 105 Connection determination signal 106 RF signal 107 1st system antenna 108 2nd system antenna 201 Cable connection compensation unit 202 Compensation amount adjustment unit 203 Power supply unit (power supply circuit) 204 Antenna 401 Switch 501 Switch 502 RF signal terminal 503 Current limiting resistor

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[Procedure amendment]

[Submission date] February 5, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Wireless base station and antenna unit

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

The present invention relates to a technology of a radio base station and an antenna unit for economically expanding a communicable area in a mobile communication system.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

According to a first aspect of the present invention, there is provided a radio unit (101), a control unit (102), an antenna switching unit (103), and a connection determining unit (104). A wireless base station (1) for a PHS or other mobile communication device to which an antenna unit (2) can be connected or disconnected by a wire, wherein the wireless unit (101)
Has two antenna terminals and one antenna terminal
The system antenna (107) is fixedly connected, the antenna switching unit (103) is connected to the system antenna terminal, and the radio unit (101) selects a better antenna system in a reception state by a reception diversity system. Sequentially switching, the control unit (102) controls the wireless unit (101),
The first system antenna (107) and the second system antenna (108) connected via the antenna switching unit (103).
Alternatively, the antenna (204) of the antenna unit (2)
To exchange communication data with the mobile wireless terminal (3) of FIG.
03) is a connection determination signal (105) and an RF signal (10
6) is connected to the connection determination unit (104), and the connection determination unit (104) is connected to the antenna unit (2).
And a physical switch (50) for determining whether the antenna unit (2) is connected or not.
1), and notifies the antenna switching unit (103) with a connection determination signal (105). The antenna switching unit (103) is notified that the antenna unit (2) is not connected. In this case, the radio unit (10
1) The 2 system antenna terminal and the antenna (108)
Connection is enabled, the connection between the wireless unit (101) and the connection determination unit (104) is disconnected, and when it is notified that the antenna unit (2) is in the connected state, the wireless unit Disconnecting the connection between the second system antenna terminal of (101) and the antenna (108) and enabling the connection between the second system antenna terminal of the radio unit (101) and the connection determination unit (104). A radio base station (1) characterized by: The gist of the invention described in claim 2 is that of claim 1
An antenna unit connectable to or disconnectable from the wireless base station (1) according to claim 1, wherein the antenna unit is connected to the antenna (204) by wire and connected to the wireless base station (1) to attenuate a signal caused by the connection. And a cable attenuation compensator (201) for compensating for
A compensation amount adjustment unit (202) for adjusting so that 1) obtains a compensation amount corresponding to the attenuation amount, and a power supply unit (203)
An antenna unit comprising:

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] Explanation of sign

[Correction method] Change

[Correction contents]

[Description of Signs] 1 Radio base station 2 Antenna unit 3 Mobile radio terminal 4 Main unit 5 Private branch exchange 6 Communication data line 7 Communication data line 8 RF signal coaxial cable 9 Radio base station communicable area 10 Antenna unit communicable area 101 Radio Unit 102 control unit 103 antenna switching unit 104 connection determination unit 105 connection determination signal 106 RF signal 107 system 1 antenna 108 system 2 antenna 201 cable attenuation compensation unit 202 compensation amount adjustment unit 203 power supply unit (power supply circuit) 204 antenna 401 switch 501 switch 502 RF signal terminal 503 Current limiting resistor

Claims (8)

[Claims] 1. A mobile communication method for communicating between a wireless base station and a mobile wireless terminal via a wireless line, wherein the wireless base station is located near or outside the wireless communicable area of the wireless base station. A mobile communication method, comprising: arranging an antenna unit for expanding a wireless communicable area, and performing communication between the wireless base station and the mobile wireless terminal via the antenna unit. 2. The mobile communication method according to claim 1, wherein the communication is performed by connecting the wireless base station and the antenna unit via a wired line. 3. The mobile communication according to claim 1, wherein the mobile radio terminal can communicate with a radio base station via an antenna of the radio base station or an antenna of the antenna unit. Method. 4. A mobile communication device for communicating between a wireless base station and a mobile wireless terminal via a wireless line, comprising: an antenna unit disposed near or outside the wireless communicable area of the wireless base station. A mobile communication device, comprising: an antenna unit connected to the radio base station by a wire line; and the mobile radio terminal capable of communicating with the radio base station via the antenna unit. 5. The radio base station and the antenna unit,
The mobile communication device according to claim 4, wherein the mobile communication device is connected by an RF signal coaxial cable. 6. The radio base station, comprising: a radio unit including a plurality of antennas for radio communication with the mobile radio terminal; an antenna switching unit for switching to one of the antennas or the antenna unit; A connection determination unit that determines the connection and non-connection state to the antenna unit and outputs the determination result to the antenna switching unit, controls the wireless unit, and controls the wireless unit and the mobile wireless terminal via a wireless line. The mobile communication device according to claim 4, further comprising: a control unit that controls the data communication. 7. The antenna unit according to claim 4, wherein the antenna unit includes a cable attenuation compensation circuit for amplifying a signal of the wired line and compensating a signal attenuation amount based on a length of the wired line. 6. The mobile communication device according to 5. 8. An antenna unit which is connected to a wireless base station via a wired line and arranged to extend the wireless communicable area of the wireless base station near or outside the wireless communicable area of the wireless base station. Wherein the antenna unit includes: a cable attenuation compensation circuit for amplifying a signal of the wired line and compensating a signal attenuation amount based on a length of the wired line; and a power supply circuit. .