JPH06189364A - Toll base station system and its equipment - Google Patents

Abstract

PURPOSE:To realize the system in which a radio base station is made small and line connection and changeover with a mobile station are executed flexibly with simple control with respect to a toll base station system in a mobile communication system. CONSTITUTION:A toll base station 21 is provided with a means using a distribute switch to connect optionally a radio modulation signal to each radio base station and a means switching radio zones through the use of the distribution switch of the toll base station based on the detection of transfer of a mobile station 27 between radio zones by the detection of a reception level or an error in the toll base station 21 or a radio base station 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system in which a centralized base station and a plurality of radio base stations are connected by a transmission line to communicate with a mobile station.

[0002]

2. Description of the Related Art In a mobile communication system using a microcell, many radio base stations form a small zone, and each radio base station has a modulator / demodulator, a frequency converter, a high frequency amplifier, an antenna,
A wireless device such as a control circuit is provided to connect between a mobile station located in a wireless zone and a switching center, and the wireless base station and the switching center are connected by a telephone line. When a call originates from a mobile station in the wireless zone, the wireless base station connects to the wireless line and connects to the telephone line.

FIG. 7 is a diagram showing an example of the configuration of a conventional mobile communication system. In the figure, each base station 30 has the same configuration, but in order to simplify the figure, the detailed configuration is omitted except for the base station shown in the uppermost stage.

The exchange 20 and each radio base station 30 are connected by a telephone line 10. In the downlink, a telephone signal is inputted to a modulator 2 of the radio base station through an interface circuit 1 and is radio-modulated to be intermediate. It becomes a modulated signal in the frequency band. The modulated signal is converted to a radio frequency band (controlled by the control circuit 9) by the frequency converter 3, amplified to the required transmission power by the transmission amplifier 4, passes through the transmission / reception separator 5, and is emitted from the antenna 6 as a radio wave. Then, the wireless connection is established with the mobile station.

In the uplink, the radio wave transmitted from the mobile station is received by the antenna 6 of the radio base station, the received signal is amplified by the receiving amplifier 7, and the frequency converter 3'converts the signal into an intermediate frequency band signal. It is input to the demodulator 8. The demodulated output signal is connected as a telephone signal to the telephone line 10 through the interface circuit 1.

As described above, the radio base station is provided with the modulator 2 and the demodulator 8 and the like, and each radio zone can be connected to a mobile station having the number of radio communication channels of the radio base station apparatus. For this reason, it is necessary to install the number of wireless devices in anticipation of the peak call volume even in the wireless zone where the call volume during the steady state is small.

Further, when the mobile station moves out of the wireless zone and the received power becomes small and it becomes necessary to switch to the transfer destination wireless zone, a wireless base station whose received power exceeds a specified level value is searched for and connected. At the exchange, it was necessary to switch telephone lines and set up new wireless lines.

[0008] Such a small zone mobile communication system can reduce the transmission power of the base station and the mobile station, and can improve the frequency utilization efficiency by repeatedly using the same frequency. However, it is necessary to reduce the size and weight of the wireless base station because many wireless base stations are installed in various places due to the small zone. Therefore, for the purpose of downsizing the wireless base station, for example, a device such as a modulator / demodulator, an optical / electrical converter, or an electrical / optical converter is installed in the centralized base station, and an optical / electrical converter or an electrical converter is installed in the wireless base station. / Optical converter,
There is a system in which only a device such as an amplifier and an antenna is provided and an optical fiber transmission line is used for signal transmission between a centralized base station and a wireless base station.

FIG. 8 shows an example of the configuration of a mobile communication system in which such a radio base station and a centralized base station are connected by an optical fiber. In FIG. 1, reference numeral 21 is a toll base station, 30 is a radio base station, and the toll base station 21 is connected to a public network via an interface circuit 1.

The signal modulated to the radio frequency by the modulator 2 of the centralized base station 21 is converted to an optical signal by the electric / optical converter 25. Further, the optical output signal of the electrical / optical converter 25 is transmitted to the wireless base station 30 via the optical transmission line 24.
The optical signal transmitted to the radio base station is converted into an electric signal again by the optical / electrical converter 35, power-amplified to the required power by the transmission amplifier 4, and then passed through the transmission / reception separator 18 and radiated into space by the antenna 6. And received by the mobile station. on the other hand,
A transmission signal from a mobile station located in the radio zone of the radio base station is received by the antenna 6 of the radio base station, and input to the reception amplifier 7 on the uplink side by the transmission / reception separator 18.
The reception signal amplified by the reception amplifier 7 is optically converted by the electric / optical converter 34 and then transmitted to the toll base station 21 through the optical transmission line 24. The signal transmitted to the centralized base station 21 is converted again into an electric signal by the optical / electrical converter 23, and demodulated by the demodulator 8 fixedly connected to each radio base station.

[0011]

In the conventional radio base station, the number of mobile stations that can be connected by each radio base station is limited by the number of radio communication channels of the installed modulator / demodulator. If it occurs, there is a problem that the call is lost. Also, when switching between wireless zones when a mobile station moves between wireless zones, it is necessary to set new wireless lines and telephone lines in the destination wireless zone and switch the telephone lines to connect to a new wireless base station. Therefore, there are unfavorable problems such as occurrence of code error and loss of synchronization due to the switching time, and necessity of transfer of control information with the switching center, and complicated switching control.

Also, in the conventional toll base station apparatus configured to connect the radio base station and the toll base station by the optical fiber as shown in FIG. 8, the modulator / demodulator of the toll base station and the toll base station are also provided. The number of modulators / demodulators that can be connected to a mobile station in one radio base station is fixed because the fixed number of mobile stations in the radio zone is Even if it exceeds the limit, there is a disadvantage that a call is lost because the idle call channel of the modulator / demodulator connected to another wireless zone cannot be used. In addition, when the mobile station moves out of the wireless zone, it is necessary to set up a new line to connect to the wireless base station in the transfer destination wireless zone in order to continue the call. There was a problem that it occurred.

According to the present invention, when the number of mobile stations in the wireless zone increases and more calls are generated than the number of connectable communication channels, and when the mobile station moves between the wireless zones,
An object of the present invention is to provide a centralized base station system having a function of flexibly switching to a connection destination zone without causing a code error or loss of synchronization of a modulator / demodulator arranged in the centralized base station, and an apparatus therefor.

[0014]

According to the present invention, the above-mentioned problems can be solved by the means described in the "Claims".

That is, according to the first aspect of the present invention, the modulator / demodulator and the transceiver are centrally arranged in the centralized base station, and a transmission line such as an optical fiber is provided between the centralized base station and the wireless base stations arranged in each wireless zone. A method for transmitting a radio modulated signal between base stations, which comprises a means for arbitrarily connecting the radio modulated signal to each radio base station using a distribution switch, and a receiving level or error detection at the centralized base station or the radio base station. In this way, the centralized base station system has means for detecting a shift between the wireless zones of the mobile station and switching between the wireless zones by using the distribution switch of the centralized base station.

Further, the inventions of claims 2 and 3 define a more practical configuration for realizing the above invention. The difference in structure between the invention of claim 2 and the invention of claim 3 lies in that the invention of claim 2 transmits a radio frequency signal transmitted from a toll base station to a mobile station as it is. On the other hand, the invention of claim 3 is
The transmission frequency between the toll base station and the radio base station is different from the radio frequency at which the radio base station communicates with the mobile station.

Further, the invention of claim 4 is a centralized base station device of a mobile communication system for connecting a centralized base station and a plurality of radio base stations through a transmission line to communicate with a mobile station. A modulator and a demodulator fixedly connected to a radio base station, a modulator and a demodulator arbitrarily switched and connected to a plurality of radio base stations, and a modulator output and a demodulator input connected to the plurality of radio base stations. The centralized base station device includes a switch for switching to an arbitrary wireless base station.

[0018]

According to the inventions of claims 1 to 3, in the inter-base station communication of the mobile communication in which the modulator / demodulator and the frequency converter are centrally arranged in the centralized base station, the radio modulation signal is switched by the distribution switch to call each radio zone. Since there is a method of flexibly connecting lines according to the amount and a method of switching between wireless zones of a mobile station that shifts between wireless zones by switching a wireless modulated signal in a centralized base station, By using the distribution switch to switch the modulation signal, it is possible to flexibly set the line according to the call volume generated in each wireless zone and absorb the increase or decrease in the call volume between wireless zones. Can be improved.

Further, the switching control between the radio zones of the mobile station which shifts between the radio zones can be performed by switching the route of the modulation signal by the distribution switch in the centralized base station, which shortens the switching time and It is possible to simplify the control.

Further, in the invention of claim 4, in the toll base station, the modulator / demodulator fixedly connected to the radio base station can communicate with the mobile station in the radio zone fixedly connected. On the other hand, a modulator / demodulator that arbitrarily switches and connects to a plurality of radio base stations can connect to a mobile station in any radio zone by switching its modulator output and demodulator input to any radio base station. Therefore, when the call volume in the wireless zone increases and there is a mobile station that cannot be connected with the number of fixedly connected modulators / demodulators, a call loss can be caused by connecting a modulator / demodulator that can be arbitrarily switched using the switch. Can be reduced. That is, the present invention enables flexible line connection according to the call volume of the wireless zone.

[0021]

FIG. 1 is a diagram showing a first embodiment of the present invention. In the figure, the centralized base station 21 includes an interface circuit 1, a modulator 2, a demodulator 8, frequency converters 3 and 3 ', a transmission distribution switch 50, and a reception distribution switch 51.
The wireless base station 31 includes a transmission amplifier 4, a reception amplifier 7, a transmission / reception separator 5, and an antenna 6.

The transmission distribution switch 50 in the centralized base station 21
Further, 12 in the reception distribution switch 51 is a distributor composed of a 1-input n-output switch, 13 is a combiner, 14 is a branch circuit, and 15 is an n-input 1-output switch. Toll base station 2
1 and the radio base station 31 are connected by a transmission line 19 such as an optical fiber.
Connected by.

In the downlink (centralized base station → base station), the telephone signal from the exchange 20 is connected to the modulator 2 through the interface circuit 1, and the modulated signal is converted into the radio frequency band by the frequency converter 3. It is output to the radio base station selected by the transmission distribution switch 50. The output signal of the toll base station is transmitted to each radio base station 31 through the transmission line 19.
Be transmitted to. The signal sent to the radio base station is amplified to the required transmission power by the transmission amplifier 4, emitted from the antenna 6 through the transmission / reception separator 5 to the space, and received by the mobile station.

In the uplink (base station → centralized base station), the radio signal transmitted from the mobile station is received by the antenna 6 of each radio zone, the received signal is amplified by the reception amplifier 7, and concentrated through the transmission line 19. It is transmitted to the base station 21. The reception signal of the wireless base station 31 is input to the branch circuit 14 of the reception distribution switch 51 and selected by the demodulator 8
And the level detector 16 detects the reception level. The received signal is converted into a telephone signal and connected to the exchange 20 through the interface circuit 1.

The above-mentioned distribution switch control is performed by the distribution switch control circuit 17 according to the call generation status of each radio zone and the reception level of the mobile station detected by the reception level detector 16. Further, since the distribution switch control circuit performs the connection between the mobile station and the toll base station, the switching between the wireless zones of the mobile station that shifts between the wireless zones is performed by the transmission distribution switch 50 and the reception distribution switch 51 of the toll base station 21. By switching. Therefore, switching can be performed at high speed and without loss of synchronization. The switching control can be performed in the same manner by detecting a reception error instead of detecting the reception level.

FIG. 2 shows T of the toll base station apparatus of the first embodiment.
It is a figure explaining operation | movement of the transmission distribution switch 50 at the time of using a DMA communication system (3 channels). The reception distribution switch 51 in FIG. 1 is the same as the transmission distribution switch 50 in circuit operation, except that the reception distribution switch 51 is an uplink and the signal path is in the opposite direction.

The modulator output signal has TDMA bursts of three channels, is an intermediate frequency of fIF, and is converted by the frequency converter 3 to a radio frequency set for each burst. The distributor 12 of the transmission switch 50 is configured to switch the output signal of the frequency converter 3 for each burst, and combine it with the combiner 13 to connect it to an arbitrary wireless base station. FIG. 2 shows that the frequency of the modulation burst output from the nth frequency converter is represented by fn, fn ′, and fn ″ so that when the call volume increases in the second radio base station, the first distribution switch The second slot of the port input signal and the third slot input signal of the third port (frequency f1 ', f
3 ″) to the input signal (frequency f2, f
2 ', f2 ") are frequency-multiplexed and output.

In the uplink, the received signal from the mobile station is input to the branch circuit 14 of the reception distribution switch 51, switched by the n-input 1-output switch 15 for each TDMA burst and input to the demodulator 3.

FIG. 3 is a diagram showing a second embodiment of the present invention. In the centralized base station 21, the output of the frequency converter 11 is set to an intermediate frequency in the downlink, and the transmission distribution switch 50 is used.
Is switched in the intermediate frequency stage, and the transmission of the wireless carrier between the base stations is transmitted using the intermediate frequency band.
In 2, the frequency converter 3 converts the frequency to a radio frequency band, the transmission amplifier 4 amplifies it to the required transmission power, and transmits it from the antenna 6 through the transmission / reception separation circuit 5. In the uplink, the transmission signal from the mobile station is transmitted by the antenna 6. The point of receiving, amplifying by the receiving amplifier 4 through the transmission / reception separating circuit 5, converting to the intermediate frequency by the frequency converter 3 and transmitting to the centralized base station through the transmission line 19, and switching of the receiving distribution switch 51 is performed at the intermediate frequency stage. Is different from the first embodiment.

FIG. 4 is a diagram showing a third embodiment of the present invention. Reference numeral 21 is a centralized base station, and 33 is a wireless base station. The toll base station apparatus of the present invention includes a modulator 2 and a demodulator 8 that are fixedly connected to a radio base station 33, a modulator 45 and a demodulator 44 that are arbitrarily switched and connected to a plurality of radio base stations, and their modulation. A transmitter switch 52 for switching the output of the device 45 to an arbitrary wireless base station and a reception switch 53 for switching the input of the demodulator 44 to an arbitrary wireless base station.

FIG. 4 shows an example in which four modulators 2 and four demodulators 8 are installed, and one modulator 45 and one demodulator 44 are installed. In the downlink (centralized base station 21 → wireless base station 33), the telephone signal sent from the public network to the centralized base station 21 through the interface circuit 1 is
The modulator / demodulator 40 is connected to the modulators 2 and 45 and the demodulators 8 and 44. The telephone signal is modulated into a radio frequency band by the modulator 2, passes through the combiner 13 of the transmission distribution switch 52, and is transmitted to the centralized base station 21. When the call volume in the wireless zone increases and the number of call channels becomes insufficient, the modulated signal of the modulator 45 is line-connected to the wireless zone having insufficient call channels using the transmission distribution switch 52 and can be used in the wireless zone. Increase the number of call channels.

The control circuit 22 detects the number of communication channels used in the wireless zone, switches the connection destination of the 1-input n-output switch 26 to the wireless zone in which the number of channels is insufficient, and the synthesizer 13 of the modulator 2 switches the connection destination. Combine with signal.

The signal from the centralized base station 21 to the radio base station 33 is connected using the electrical / optical converter 25, the optical / electrical converter 23 and the optical transmission line 24. The optical signal transmitted to the radio base station 33 is converted into an electric signal again by the optical / electrical converter 35, amplified by the transmission amplifier 4 to the required power, transmitted to the space by the antenna 6, and connected to the mobile station through a line. It

Uplink (radio base station 33 → centralized base station 2
In 1), the transmission signal from the mobile station is the radio base station 33.
Is received by the antenna 6 and is transmitted and amplified by the transmission / reception separator 5 to the reception amplifier 7 connected to the reception side. The electric / optical converter 34 and the optical / electric converter are provided between the centralized base station 21 and the wireless base station 33. 35 and the optical transmission line 24 are used for optical transmission connection.

The upstream optical signal transmitted from the radio base station 33 is converted into an electric signal again by using the optical / electrical converter 35 of the centralized base station 21, and then the reception distribution switch 53.
Entered in. The reception distribution switch 53 branches the uplink signal into the connection path between the demodulator 8 and the demodulator 44 by the branch circuit 14, inputs one branch output to the demodulator 8 of the modulator / demodulator 40, and outputs the other branch output to n. The input 1 output switch is used to select the input of the demodulator 44 so that the demodulator 44 demodulates any of the received signals of the radio base station. When the uplink signal from the mobile station is connected to the demodulator 44, in the reception switch 53, the switch 15 is switched at the reception timing for the target reception signal and connected to the demodulator 44.

FIG. 5 is a diagram for explaining the line connection of the toll base station apparatus of the third embodiment in more detail, and shows the operation of the transmission switch 52 when the TDMA communication system is used. Since the receiving switch 53 switches the uplink, the signal path is in the opposite direction, but the operation is similar to that of the transmitting switch.

In the downlink, the combiner 13 of the transmission switch 52 has a signal (frequency f1, f1 ', f1 "to f4, f) of the modulator 2 fixedly connected to the radio base station 33.
4 ', f4 ") is input to establish a line connection with the radio base station 33. When the call volume in the radio zone covered by the radio base station 33 increases, the signal of the modulator 45 (frequency fa, frequency fa, fa ′, fa ″) are connected for each time slot to the wireless zone where the communication channel is insufficient.
At this time, the control circuit 22 controls switching of the connection path. Therefore, at the downlink output port of the toll base station 21, the signal (frequency f1, f2
1 ′, f1 ″ to f4, f4 ′, f4 ″) and the signal of the modulator 45 (frequency fa, fa ′, fa ″) are frequency-multiplexed by the combiner 13 and output.

In the uplink, the received signal from the mobile station is input to the branch circuit of the reception distribution switch 53, and the demodulator 8
And to the input of the demodulator 44. That is, frequencies f1, f1 ', f1 "to f4 used in the wireless zone.
The received signals of f4 ′ and f4 ″ are fixedly connected to each demodulator 8, and the received signals of frequencies fa, fa ′ and fa ″ are connected to the demodulator 44 and demodulated. The control circuit 22 drives the n-input 1-output switch 15 of the reception switch 53, selectively outputs the reception signal branched to the connection path of the demodulator 44, and connects it to the demodulator 44. Since the received signals of a plurality of frequencies are input to the demodulators 8 and 44, the demodulators 8 and 44 select the frequency to be received among the input signals and demodulate.

In the example of FIG. 5, the modulator / demodulator frequencies (f1, f1 ', f1 "to f4, f of each of the ports 1, 2, 3, 4).
4 ', f4 ") are fixedly assigned to the ports 1', 2 ', 3', 4'connected to the radio base station 33, and the added modulator / demodulator frequencies (fa, fa ', fa") are It is connected to a radio base station having a shortage of communication channels (a mobile station requesting line connection of the radio base station connected to port 2 ').

When a new line connection request is issued from the mobile station as shown in FIG. 5, the modulator / demodulator (frequency fa, f
By connecting a ', fa ") to the port 2', up to 6 channels can be used. Therefore, at the port 2 ', signals of frequencies f2, f2', f2" and fa, fa ', fa "are frequency-multiplexed. This switching control is performed by the control circuit 22.
Is performed by switching the connection paths of the transmission / reception switches 52 and 53. Further, when the shortage of the communication channels of the wireless base station 33 connected to the port 2'is resolved, it is possible to switch to another wireless base station 33 and connect.

FIG. 6 is a diagram showing a fourth embodiment of the present invention. In this embodiment, the centralized base station 21 is provided with modulators / demodulators 44, 4
5 are provided for each of the two units, so that the transmission / reception switches 52,
53 includes two modulator / demodulators 44 and 45, respectively, in the radio base station 33.
Is different from the first embodiment in that it can be connected to. In the centralized base station, the modulator / demodulators 44 and 45 can be installed according to the variation in the number of mobile stations connected to the wireless base station,
Each of the installed modulator / demodulators 44 and 45 is composed of a transmission / reception switch that can be connected to an arbitrary wireless base station.

The modulators / demodulators 44, 45 may be constructed so that the number thereof is further increased as required.

[0043]

As described above, according to the present invention,
The centralized modulators / demodulators can be flexibly connected to each wireless base station in response to fluctuations in call volume in each wireless zone, and the call loss rate can be reduced due to the large grouping effect. Further, since the switching between the wireless zones of the mobile station which shifts between the wireless zones can be performed by switching the centralized base station or the transmission distribution switch and the reception distribution switch, it is possible to perform the switching between the wireless zones without any code error and loss of synchronization. .

Further, the centralized base station device configuration of the present invention enables flexible line connection with respect to traffic fluctuations in the wireless zone. Therefore, there is an advantage that the call loss rate can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of a transmission distribution switch of the centralized base station device of the first embodiment.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a third embodiment of the present invention.

FIG. 5 is a diagram illustrating line connection of a toll base station apparatus according to a third embodiment.

FIG. 6 is a diagram showing a fourth embodiment of the present invention.

FIG. 7 is a diagram showing an example of a configuration of a conventional mobile communication system.

FIG. 8 is a diagram showing an example of a mobile communication system in which a line base station and a toll base station are connected by an optical fiber.

[Explanation of symbols]

 1 interface circuit 2,45 modulator 3,3 'frequency converter 4 transmission amplifier 5 transmission / reception separator 6 antenna 7 reception amplifier 8,44 demodulator 9 control circuit 10 telephone line 11 frequency converter 12 distributor 13 combiner 14 branching Circuit 15 n-input 1-output switch 16 Reception level detector 17 Distribution switch control circuit 18 Transmission / reception separator 19 Transmission line 20 Switching station 21 Centralized base station 22 Control circuit 23,35 Optical / electrical converter 24 Optical transmission line 25,34 Electric / Optical converter 26 1 input n output switch 27 Mobile station 30-33 Radio base station 40 Modulator / demodulator 50,52 Transmission distribution switch 51,53 Reception distribution switch

Claims (4)

[Claims] 1. A modulator / demodulator and a transmitter / receiver are centrally arranged in a centralized base station, and a radio modulation signal is transmitted between base stations by a transmission line such as an optical fiber between the centralized base station and the radio base stations arranged in each radio zone. A method of transmitting, a method of arbitrarily connecting a radio modulated signal to each radio base station using a distribution switch, and a radio zone of a mobile station by detecting a reception level or an error in the centralized base station or radio base station. Means for detecting a shift between the wireless zones and switching between the wireless zones by using the distribution switch of the centralized base station. 2. The downlink from the toll base station to the radio base station is for connecting a modulator for modulating a telephone signal to a radio signal and a frequency converter for converting the telephone signal to a radio frequency and the radio modulated signal to the radio base station. A transmission distribution switch that switches a connection path, a toll base station device that includes a distribution switch control circuit that controls the transmission distribution switch, a transmission path for transmitting a wireless modulated signal from the toll base station, and an toll base station And a radio base station device having a transmission amplifier for amplifying a radio modulation signal transmitted from the radio base station device, and an uplink from the radio base station to the toll base station, the transmission signal from the mobile station side. A radio base station equipped with an antenna for receiving a signal and a reception amplifier for high-frequency amplification of the received signal, and the radio signal transmitted from the mobile station to the toll base station by the radio base station. A transmission path, a reception distribution switch for switching the reception radio signal and inputting it to a demodulator, a frequency converter, a means for detecting a reception level or a reception error, a control circuit for controlling the reception distribution switch, and a reception radio The toll base station system according to claim 1, further comprising a toll base station device including a demodulator for demodulating a signal. 3. The downlink from the centralized base station to the radio base station is for connecting a modulator for modulating a telephone signal to a radio signal and a frequency converter for converting the telephone signal to an intermediate frequency and the radio modulated signal to the radio base station. A transmission distribution switch for switching a connection path, a centralized base station device equipped with a distribution switch control circuit for controlling the transmission distribution switch, and a transmission line for transmitting a radio modulated signal from the centralized base station to the radio base station. , A radio base station device provided with a frequency converter for converting a radio signal of an intermediate frequency transmitted from the toll base station to a radio frequency, a transmission amplifier and an antenna for transmitting, and the radio base station to the toll base station The uplink to is an antenna that receives the transmission signal from the mobile station, a reception amplifier that amplifies the reception signal at high frequency, and a radio frequency reception signal that is converted to an intermediate frequency. A radio base station equipped with a frequency converter, a transmission path between the base stations for transmitting the received radio signal to the centralized base station, a reception distribution switch for switching the reception radio signal and inputting the demodulator, and a frequency conversion The centralized base station according to claim 1, further comprising: a receiver, a means for detecting a reception level or a reception error, a control circuit for controlling the reception distribution switch, and a centralized base station device equipped with a demodulator for demodulating a received radio signal. Bureau system. 4. A centralized base station device of a mobile communication system for connecting a centralized base station and a plurality of radio base stations via a transmission line to communicate with a mobile station, the fixed base station device being fixed to one radio base station. A modulator and a demodulator connected to, and a modulator and a demodulator arbitrarily switched and connected to a plurality of radio base stations; a modulator output and a demodulator input connected to the plurality of radio base stations; A centralized base station device comprising a switch for switching to a station.