JP2000197091A - Channel changeover device in mobile communication system and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a mobile communication system to continue a speech service using a speech channel where a failure has taken place, even if a radio output is decreased on the occurrence of the failure in one of a plurality of parallelly connected amplifiers shared by a plurality of speech channels. SOLUTION: When the range of a service area is reduced to an area 5 on the occurrence of a failure in part of common radio amplifiers used for digital speech channels of a radio base station 1, the speech service is continued by changing over from the digital speech channel where the failure has occurred place to another channel keeping a service in a usual state through the setting of a channel switching level on the occurrence of a failure at the border of the area 5, when a mobile terminal 3 that receives the service by the digital speech channel, where the failure has taken place and is resident in the area 5 moves in a direction of an area 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for switching between an analog communication channel and a digital communication channel in a mobile communication system, and more particularly to a switching apparatus in a radio base station when a failure occurs in a radio amplifier shared by a plurality of digital communication channels. The present invention relates to a channel switching device that controls channel switching between radio base stations and between an analog communication channel and a digital communication channel in a base station to avoid disconnection of a call.

[0002]

2. Description of the Related Art A channel switching method in a conventional mobile communication system will be described. Radio base station 1 shown in FIG.
A plurality of digital communication channel devices 18 to 19
Share the digital communication channel transmission common amplifier 24. When a part of the radio amplifier 26 or 27 constituting the digital communication channel transmission common amplifier 24 becomes a failure and the radio transmission output decreases, the digital communication channel device 18 or 19 connected to the digital communication channel transmission sharing amplifier 24 is turned off. The mobile communication terminal in use is instructed to disconnect, and the digital communication channel device 1
8 and 19 are closed. Due to the blocking of the digital communication channel devices 18 and 19, the area 4 served by the radio base station 1 shown in FIG. 1 can be continued to be serviced only by the analog communication channel devices 16 to 17 shown in FIG.

[0003]

The channel switching method of the conventional mobile communication system is such that when a failure occurs in a part of the radio amplifiers constituting the digital communication channel transmission common device, all the channels connected to the digital communication channel transmission common device are failed. There is a problem that the digital communication channel device becomes blocked and the digital communication channel service cannot be performed. Further, if the service of the digital communication channel becomes impossible due to the failure of the digital communication channel transmission common device, the traffic concentrates on the analog communication channel that can be serviced, and the channel switching of the mobile terminal moving from the adjacent radio base station. However, there is a problem that the analog communication channel or the digital communication channel to be allocated to the system is lost. SUMMARY OF THE INVENTION The present invention has been made to solve these problems. Even if a failure occurs in a digital communication channel transmission common device, the digital communication channel connected to the digital communication channel transmission common device can be stopped without stopping the service. The purpose of this service is to maintain the service of the above and to enhance the reliability of the system.

[0004]

SUMMARY OF THE INVENTION A channel switching device according to the present invention comprises an analog communication channel device for transmitting and receiving voice and data during a communication by analog transmission, and an analog communication channel individual transmission for amplifying a radio transmission signal of the analog communication channel device. An amplifier and a digital communication channel device for transmitting and receiving voice and data during communication by digital transmission, a digital communication channel transmission common amplifier for accommodating a plurality of the digital communication channel devices and amplifying a radio signal, controlling an analog communication channel device and a digital communication channel device. A mobile base station having a plurality of wireless base stations, a mobile switching center accommodating a plurality of wireless base stations, and a service of both an analog communication channel and a digital communication channel. Analog call A digital communication channel transmission comprising a plurality of transmission amplifiers in a mobile communication system comprising a mobile terminal having means for measuring a reception electric field level of a channel and a digital communication channel radio signal and reporting the measurement result to a radio base station. When a failure occurs in some of the transmission amplifiers in the common amplifier and the radio output of the digital communication channel transmission common device decreases, the output decreases without blocking the digital communication channel accommodated in the failed digital communication channel transmission common amplifier. A failure channel switching level (11 in FIG. 1) is provided at the boundary of the area (5 in FIG. 1) where the service area is reduced, and the digital communication channel whose service area is reduced due to the failure of the digital communication channel transmission common amplifier is provided. Uninterrupted digital calls Characterized in that it continues the call service to Yaneru or analog communication channel to the movement of the mobile terminal performs channel switching processing. A wireless base station having an analog communication channel for transmitting and receiving voice and data during communication by analog transmission and a digital communication channel for transmitting and receiving voice and data during communication by digital transmission; In a channel switching method of a mobile communication system comprising a mobile switching center for controlling a station and providing a call service to a mobile terminal and a mobile terminal having means for receiving services of both an analog call channel and a digital call channel. Means for amplifying a radio transmission output of a plurality of digital communication channels provided in the radio base station by a digital communication channel transmission common amplifier configured by connecting a plurality of radio amplifiers in parallel to obtain a rated radio transmission output; Means for monitoring and detecting faults in the wireless amplifier; Means for continuing the call service of the failed digital communication channel without stopping even if the radio transmission output decreases due to the occurrence of the line amplifier failure and the service area served by the wireless base station decreases. It is characterized by having. According to a second aspect of the present invention, in the channel switching method according to the first aspect, the means for responding to a failure occurring in the wireless amplifier constituting the digital communication channel common amplifier is configured to reduce the failure due to the failure occurring in the wireless amplifier. Electric field strength at the boundary of the service area, ie, the electric field strength at the level of switching to an analog communication channel or a digital communication channel accommodated in the same radio base station as the digital communication channel and having no failure (channel at the time of failure) (Switching level) can be stored and set, and means for performing a channel switching process from the failed digital communication channel to an analog communication channel or a digital communication channel in which no failure has occurred. According to a third aspect of the present invention, there is provided a radio base station having an analog communication channel for transmitting and receiving voice and data by analog transmission and a digital communication channel for transmitting and receiving voice and data during digital transmission, and a plurality of radio base stations. Channel switching method for a mobile communication system comprising: a mobile switching center for centrally controlling a station to provide a speech service to a mobile terminal; and a mobile terminal having means for receiving services of both an analog speech channel and a digital speech channel. In the step of constantly monitoring and detecting the failure of the radio amplifier of the digital communication channel, and when a failure occurs in the digital communication channel transmission amplifier, the failure is detected and the normal channel switching level is changed to the failure channel switching level. The process of performing the change process and the A step of determining whether the digital communication channel device connected to the digital communication channel transmission common amplifier is busy, and, when the digital communication channel is busy, the mobile terminal or the wireless terminal of the busy digital communication channel; A step of determining whether or not the measured electric field level is lower than the area switching level at the time of the failure at the base station; and, if the electric field level of the measurement is lower than the area switching level at the time of the failure, the radio base station accommodating the digital communication channel. A step of determining whether or not there is a vacant analog call channel in the station, a step of performing channel switching processing to the vacant analog call channel, and a mobile terminal continuing to move to an adjacent service area, and the analog call channel measures. When the received electric field level becomes lower than the normal area switching level, Is characterized by having a process of performing channel switching to a free analog communication channel or a digital traffic channel are accommodated in a radio base station that, the.

[0005]

Next, embodiments of the present invention will be described in detail with reference to the drawings. The upper diagram of FIG. 1 is a diagram illustrating a wireless base station service area. That is, the areas 4 and 6 where the radio base station 1 and the radio base station 2 provide service, and the digital traffic channel transmission amplifier (FIG. 2) constituting the digital traffic channel transmission common amplifier (24 in FIG. 2) in the radio base station 1. 26, 27) shows a configuration of an area 5 which is a service area of a digital communication channel using a common amplifier (24 in FIG. 2) for transmitting a digital communication channel in which a failure has occurred when a failure occurs in a part of 26, 27). The graph in the lower diagram of FIG. 1 shows the distance between the radio base station 1 and the radio base station 2 and the radio transmission output 7 to 7 during normal operation.
FIG. 8 is a diagram showing a relationship between the digital communication channel transmission common amplifier (24 in FIG. 2) and a radio transmission output 9 when a failure occurs in a part of the radio amplifier constituting the digital communication channel transmission common amplifier (24 in FIG. 2). The lower part of FIG. 1 also shows a normally used channel switching level 10 and a failed channel switching level 11 used when a failure occurs in the digital communication channel transmission common amplifier.

Next, with reference to FIG. 2, a description will be given of an apparatus configuration of a mobile communication system that implements the channel switching method of the present invention. The mobile switching center 12 and the radio base station 1 shown in FIG. 2 are connected by a control signal line 29, and control signals are transmitted and received between the mobile switching center 12 and the radio base station main controller 14. A plurality of wireless base stations 1 and 2 are connected to the mobile switching center 12. The radio base station main controller 14 that controls the radio base station 1 controls the control channel device 15 and the analog communication channel devices 16 to 1 via a control signal line 35.
7. Connected to digital communication channel devices 18 to 19 to transmit and receive control signals. The control channel device 15 is connected to the control channel individual transmission amplifier 20 via a signal line 37 and transmits a transmission signal. Analog communication channel devices 16 to 17 are connected to analog communication channel individual transmission amplifiers 22 to 23 via signal lines 38 to 39 to transmit signals. The digital communication channel devices 18 to 19 are connected to the digital communication channel transmission common amplifier 24 via a signal line 40.
The signal line 40 is connected in parallel to the digital communication channel transmission amplifiers 26 and 27 in the digital communication channel transmission common amplifier 24 to transmit signals. The reception common amplifier 21 is connected to the control channel device 15, the analog communication channel devices 16 to 17, and the digital communication channel devices 18 to 19 via a signal line 36, and amplifies and distributes a reception signal. The duplexer 25 is connected to the signal line 4
The control channel individual transmission amplifier 20, the reception common amplifier 21, the analog communication channel individual transmission amplifiers 22 to 23 and the digital communication channel transmission common amplifier 24 are connected via 1 to 45. The duplexer 25 supplies a reception signal to the reception common amplifier 21, and receives signals transmitted from the control channel individual transmission amplifier 20, the analog communication channel individual transmission amplifiers 22 to 23, and the digital communication channel transmission common amplifier 24. Do. Further, the duplexer 25 is connected to the antenna line 28,
It distributes and combines transmission and reception radio signals with mobile terminals. The mobile switching center 12 is connected to analog communication channel devices 16 to 17 and digital communication channel devices 18 to 19 via voice signal lines 30 to 33, and performs transmission and reception of voice signals. The radio base station main controller 14 controls the digital communication channel transmission amplifier 26 via a control signal line 34.
27 to monitor the status of the digital communication channel transmission amplifier. When a failure occurs in the digital communication channel transmission amplifier 26 or 27, the digital communication channel transmission amplifiers 26 to 27 autonomously report the status to the radio base station main controller 14.

Next, an operation example of the channel switching method will be described with reference to FIGS. 1 and 2 and a flowchart shown in FIG. FIG. 3 shows a control flow of the mobile switching center 12, the radio base station 1, and the mobile terminal 3 in the mobile communication system of the present embodiment. The radio base station main controller 14 shown in FIG. 2 constantly performs a digital communication channel transmission amplifier monitoring process (steps S2 to S
4). The mobile terminal 3 located in the service area 4 and the area 5 of the radio base station 1 shown in FIG.
It is assumed that the user is moving in the direction of the service area 6 of the wireless base station 2 while talking via the digital communication channel device 18 accommodated in the wireless base station 2. If a failure has occurred in one of the digital communication channel transmission amplifiers 26 and 27 shown in FIG. 2 (step S2 Yes, step S4 No, or step S2 No, step S3 Yes), the radio base station main controller 14 sets the digital communication channel transmission amplifier 26 or 27 27, and reports a failure occurrence to the mobile switching center 12 via the control signal line 29. When the mobile switching center 12 receives the report of the failure of the digital communication channel transmission amplifier 26 or 27, the mobile switching center 12 transmits the digital communication channel device 18
, Ie, a process of changing from the normal channel switching level (10 in FIG. 1) to the failure channel switching level (11 in FIG. 1) (step S5).
The mobile switching center 12 that has performed the process of changing from the normal channel switching level (10 in FIG. 1) to the failure channel switching level (11 in FIG. 1) is connected to the failed digital communication channel transmission common amplifier 24. It is determined whether the digital communication channel device 18 or 19 is busy (step S6). Since the digital communication channel 18 connected to the failed digital communication channel transmission common amplifier 24 is busy (step S6, Yes), the mobile switching center 12 can communicate with the mobile terminal or the wireless terminal of the busy digital communication channel 18. The base station determines whether or not the measured electric field level is lower than the failure area switching level (step S7). The reception electric field level of the radio signal transmitted and received by the digital communication channel device 18 via the antenna 28 of FIG. 2 is reported to the mobile switching center 12 via the radio base station main controller 14. That is, the digital communication channel device 18 measures the electric field from the mobile terminal 3 to the radio base station, and the measured level is reported to the mobile switching center 12 via the radio base station main controller 14, and the mobile terminal 3 An electric field measurement from the station to the mobile terminal is performed, and the measured level is reported to the mobile switching center 12 via the digital communication channel device 18 and the radio base station main controller 14.

The mobile terminal 3 shown in FIG. 1 is moving to the service area 6 of the radio base station 2, so that the reception electric field level measured by the digital communication channel device 18 or the mobile terminal 3 is lower than the area switching level when a failure occurs. Become
The mobile switching center 12 determines whether there is a vacant analog communication channel in the radio base station 1 in which the digital communication channel 18 is accommodated (step S8). The radio base station 1
If there is an available analog call channel 16 at
A channel switching process is performed on the analog communication channel device 16 (step S9). After the channel is switched to the analog communication channel device 16, when the mobile terminal 3 that continues the communication continues to move to the service area 6 of the radio base station 2, the analog communication channel 16 of the radio base station 1 is finally reached.
Reduces the received electric field level measured by. At this time, the mobile switching center 12 receives a report that the reception electric field level measured on the analog communication channel 16 has become lower than the normal area switching level (10 in FIG. 1) (step S10), and is accommodated in the adjacent radio base station 2. The channel is switched to an analog communication channel or a digital communication channel that is idle (step S11). As described above, when a failure occurs in a part of the transmission amplifier to which the digital communication channel used for communication is connected, the transmission output of the radio base station is reduced, and the service area is reduced, the mobile terminal is adjacent. Even if the user moves toward the base station, the call service can be continued. When a failure occurs in both the digital communication channel transmission amplifiers 26 and 27 shown in FIG. 2 (step S2 Yes, step S4 Ye
s) Although the digital communication channel device 18 is closed (step S12), the probability that a failure will occur in both amplifiers at the same time is small and is a subject outside the scope of the present invention.

[0009]

As described above, in the present invention according to the first to third aspects, a part of the transmission amplifier to which the digital communication channel used for communication is connected has a fault and the transmission of the radio base station is performed. In the state where the output power is reduced and the service area is reduced, as a means for continuing the speech service even if the mobile terminal moves to the adjacent base station, the channel switching level at the time of failure is set as a means to continue the speech service and the process of switching to the speech channel capable of speech service By doing so, the call service can be continued.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a radio base station service area and a channel switching level in the present invention.

FIG. 2 is a diagram showing a connection between a mobile switching center and a radio base station and a device configuration in the radio base station according to the present invention.

FIG. 3 is a diagram showing a flowchart of a channel switching process in the present invention.

[Explanation of symbols]

1, 2 ... Radio base station 3 ... Mobile terminal 4, 5, 6 ... Area 7, 8 ... Normal radio transmission output of radio base station 9 ... Digital communication channel radio transmission output when common amplifier fails 10: Normal Channel switching level 11: Failure channel switching level 12: Mobile switching center 13: Signal line 14: Radio base station main controller 15: Control channel device 16, 17, Analog communication channel device 18, 19 Digital communication channel device 20 ... Control channel individual transmission amplifier 21 ... Reception common amplifier 22,23 ... Analog communication channel individual transmission amplifier 24 ... Digital communication channel transmission common amplifier 25 ... Duplexer 26,27 ... Digital communication channel transmission amplifier 28 ... Antenna line 29 ... Control signal line 30, 31 ... analog audio signal line 32, 33 ... digital audio signal lines 34, 35 ... control signal lines 36 to 45 ...
Signal line

[Procedure amendment]

[Submission date] November 8, 1999 (1999.11.
8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

2. A radio base station having an analog communication channel for transmitting and receiving voice and data during communication by analog transmission, a digital communication channel for transmitting and receiving voice and data during communication by digital transmission, and integrally controlling a plurality of radio base stations. A mobile switching center for providing a call service to the mobile terminal; and a mobile terminal having means for receiving services of both an analog call channel and a digital call channel. The process of constantly monitoring and detecting the failure of the radio amplifier in the digital communication channel, and the process of detecting the failure and changing the normal channel switching level to the channel switching level in the event of a failure when a failure occurs in the digital communication channel transmission amplifier. And the failed digit A step of determining whether a digital communication channel device connected to the communication channel transmission common amplifier is busy, and, when the digital communication channel is busy, a mobile terminal or a radio base station of the busy digital communication channel. A step of determining whether or not the electric field level of the measurement is lower than the area switching level at the time of the failure; and, if the electric field level of the measurement is lower than the area switching level at the time of the failure, the radio base station accommodating the digital communication channel. Determining whether or not there is a vacant analog communication channel, performing a channel switching process on the vacant analog communication channel, and receiving the mobile terminal continues to move to an adjacent service area and measuring the analog communication channel. When the electric field level falls below the normal area switching level, Channel switching method of a mobile communication system, comprising the steps of performing a channel switching to a free analog communication channel or a digital traffic channel is accommodated in the earth station.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0004

[Correction method] Change

[Correction contents]

[0004]

SUMMARY OF THE INVENTION A channel switching device according to the present invention comprises an analog communication channel device for transmitting and receiving voice and data during a communication by analog transmission, and an analog communication channel individual transmission for amplifying a radio transmission signal of the analog communication channel device. An amplifier and a digital communication channel device for transmitting and receiving voice and data during communication by digital transmission, a digital communication channel transmission common amplifier for accommodating a plurality of the digital communication channel devices and amplifying a radio signal, controlling an analog communication channel device and a digital communication channel device. A mobile base station having a plurality of wireless base stations, a mobile switching center accommodating a plurality of wireless base stations, and a service of both an analog communication channel and a digital communication channel. Analog call A digital communication channel transmission comprising a plurality of transmission amplifiers in a mobile communication system comprising a mobile terminal having means for measuring a reception electric field level of a channel and a digital communication channel radio signal and reporting the measurement result to a radio base station. When a failure occurs in some of the transmission amplifiers in the common amplifier and the radio output of the digital communication channel transmission common device decreases, the output decreases without blocking the digital communication channel accommodated in the failed digital communication channel transmission common amplifier. A failure channel switching level (11 in FIG. 1) is provided at the boundary of the area (5 in FIG. 1) where the service area is reduced, and the digital communication channel whose service area is reduced due to the failure of the digital communication channel transmission common amplifier is provided. Uninterrupted digital calls Characterized in that it continues the call service to Yaneru or analog communication channel to the movement of the mobile terminal performs channel switching processing. A wireless base station having an analog communication channel for transmitting and receiving voice and data during communication by analog transmission and a digital communication channel for transmitting and receiving voice and data during communication by digital transmission; In a mobile communication system comprising: a mobile switching center for controlling a station to provide a communication service to a mobile terminal; and a mobile terminal having means for receiving services of both an analog communication channel and a digital communication channel. Means for amplifying a radio transmission output of a plurality of digital communication channels provided in a station by a digital communication channel transmission common amplifier configured by connecting a plurality of radio amplifiers in parallel to obtain a rated radio transmission output; means for monitoring and fault detection, the occurrence of failure of the radio amplifier Service area is reduced more wireless transmission output is service reduced the radio base station
At the border of this reduced service area
Accommodated in the same radio base station as the above digital communication channel
Analog communication channels that are
Or switch to a digital communication channel.
The channel switching level at the time of failure, which is the electric field level, is recorded.
Means for setting and setting, and channel switching at the time of the failure
The failed digital call channel is
Analog call channel with no fault from channel
Or, switch to digital communication channel
And means for performing processing . Claim
Item 2 is a radio base station having an analog communication channel for transmitting and receiving voice and data by analog transmission and a digital communication channel for transmitting and receiving voice and data during digital transmission, and a plurality of radio base stations. And a mobile switching center for providing a call service to the mobile terminal and a mobile terminal having means for receiving both the analog call channel and the digital call channel. A process for constantly monitoring and detecting a failure in the radio amplifier of the digital communication channel, and, when a failure occurs in the digital communication channel transmission amplifier, detecting the failure and changing the normal channel switching level to the failure channel switching level. Process and the failed data Determining whether the digital communication channel device connected to the digital communication channel transmission common amplifier is busy, and, when the digital communication channel is busy, the mobile terminal or wireless terminal of the busy digital communication channel. A step of determining whether or not the measured electric field level is lower than the area switching level at the time of the failure at the base station; and, if the electric field level of the measurement is lower than the area switching level at the time of the failure, the radio base station which accommodates the digital communication channel. A step of determining whether or not there is a vacant analog call channel in the station, a step of performing channel switching processing to the vacant analog call channel, and a mobile terminal continuing to move to an adjacent service area, and the analog call channel measures. When the reception electric field level becomes lower than the normal area switching level, It is characterized by having the steps of performing a channel switching to a free analog communication channel or a digital traffic channel is accommodated in the line base station.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

[0009]

[Effect of the Invention] As described above, the transmission of some failure occurs in the radio base station of the transmission amplifier digital speech channel used for the call is connected in the present invention according to claim 1, 2 output As a means for continuing the speech service even when the mobile terminal moves to the adjacent base station in a state where the service area is reduced due to a decrease in the service area, a failure channel switching level is set and the speech channel is switched to a speech channel capable of the speech service. This enables the call service to be continued.

Claims (3)

[Claims] 1. A radio base station having an analog communication channel for transmitting and receiving voice and data during communication by analog transmission and a digital communication channel for transmitting and receiving voice and data during communication by digital transmission, and integrally controlling a plurality of radio base stations. A mobile switching center for providing a call service to the mobile terminal, and a mobile terminal having means for receiving services of both an analog call channel and a digital call channel. Means for amplifying wireless transmission outputs of a plurality of digital communication channels by a digital communication channel transmission common amplifier configured by connecting a plurality of wireless amplifiers in parallel to obtain a rated wireless transmission output; Means for detecting, and the Means for continuing the call service of the failed digital call channel without stopping even if the service area served by the radio base station is reduced due to a decrease in the signal output. A channel switching device in a wireless system. The means for responding to a failure occurring in the radio amplifier constituting the digital communication channel common amplifier comprises: an electric field strength at a boundary of a service area in which a failure has occurred in the radio amplifier, ie, the digital communication channel and Means for storing and setting a channel switching level at the time of failure as an electric field strength of a level for switching a channel to an analog communication channel or a digital communication channel accommodated in the same radio base station and having no failure, and 2. The channel switching device according to claim 1, further comprising means for performing a channel switching process from the generated digital communication channel to an analog communication channel or a digital communication channel in which no failure has occurred. 3. A radio base station having an analog communication channel for transmitting and receiving voice and data during communication by analog transmission and a digital communication channel for transmitting and receiving voice and data during communication by digital transmission, and integrally controlling a plurality of radio base stations. A mobile switching center for providing a call service to the mobile terminal; and a mobile terminal having means for receiving services of both an analog call channel and a digital call channel. A process of constantly monitoring and detecting a failure of the wireless amplifier of the digital communication channel, and when a failure occurs in the transmission amplifier of the digital communication channel, detecting the failure and performing a process of changing from the normal channel switching level to the failure channel switching level. The process and the failed digit A step of determining whether a digital communication channel device connected to the communication channel transmission common amplifier is busy, and, when the digital communication channel is busy, a mobile terminal or a radio base station of the busy digital communication channel. A step of determining whether or not the electric field level of the measurement is lower than the area switching level at the time of the failure; and, if the electric field level of the measurement is lower than the area switching level at the time of the failure, the radio base station accommodating the digital communication channel. Determining whether or not there is a vacant analog communication channel, performing a channel switching process on the vacant analog communication channel, and receiving the mobile terminal continues to move to an adjacent service area and measuring the analog communication channel. When the electric field level falls below the normal area switching level, Channel switching method of a mobile communication system, comprising the steps of performing a channel switching to a free analog communication channel or a digital traffic channel is accommodated in the earth station.