Radio relay device

Abstract

[PROBLEM] The purpose of the present invention is to solve the problem of a size increase by integrating two systems of system configuration into one system with an intermediate frequency band. [SOLUTION] A first unit, a second unit, and one cable connecting the first unit and the second unit are provided. The first unit comprises: a first connection part connected to an analog cable and N donor antennas which are from among a first donor antenna to an N-th donor antenna and which communicate with a base station, where N is an integer of 2 or greater; and N donor-side frequency conversion units from among a donor-side first frequency conversion unit to a donor-side N-th frequency conversion unit. Each of the N donor-side frequency conversion units from the donor-side first frequency conversion unit to the donor-side N-th frequency conversion unit converts a signal with a frequency fRF received by a corresponding donor antenna, among the N donor antennas from the first donor antenna to the N-th donor antenna, into an intermediate signal according to the respective local signal. The local signal and the intermediate signal have different frequencies for each donor-side frequency conversion unit. The second unit is provided with: a second connection part connected to an analog cable and N service antennas, from a first service antenna to an N-th service antenna, which communicate with a communication terminal; and N service-side frequency conversion units from a service-side first frequency conversion unit to a service-side N-th frequency conversion unit. Each of the N service-side frequency conversion units from the service-side first frequency conversion unit to the service-side Nth frequency conversion unit converts a signal with a frequency fRF received by a corresponding service antenna, among the N service antennas from the first service antenna to the N-th service antenna, into an intermediate signal which is an analog signal, according to the respective local signal. The local signal and the intermediate signal have different frequencies for each service-side frequency conversion unit.　The intermediate signals from a first intermediate signal to an N-th intermediate signal are transmitted multiplexed on one cable.

Description

wireless repeater

[0001] The present invention relates to a wireless repeater, and in particular to a simple configuration of a wireless repeater for a millimeter wave band mobile communication system, such as the 28 GHz band used in the 5G standard.

[0002] As the frequency used for communication increases in standards such as 5G, the directionality of radio waves increases, making radio communication difficult when buildings or other structures exist between a base station and a communication terminal. For this reason, wireless repeaters are often used. Wireless repeaters consist of a donor unit that transmits and receives signals to and from a base station (BS) and a service unit that transmits and receives signals to and from a terminal (UE). They are used when a direct wireless link between a base station and a terminal cannot be established due to obstacles or other factors (see Patent Document 1). Figure 4 in Cited Document 1 shows an example of the configuration of a wireless repeater. In the case of analog wiring, a wireless repeater uses frequency conversion to reduce the feeder loss of the coaxial cable and connects the signal to an intermediate frequency band lower than the radio frequency (see Patent Document 1). A wireless repeater includes a donor unit, a service unit, and a coaxial cable connecting the two. Wireless repeaters for 5G millimeter wave mobile communication systems, for example, support MIMO. In such wireless repeaters, both the BS and UEs use two antennas for MIMO communication, forming two-path wireless links in the same frequency band (fRF). For MIMO communications, each wireless repeater requires two antennas, i.e., two fRF paths. This configuration, particularly when using analog cables such as coaxial cables, requires two cables, making installation difficult. While digital systems can combine the cables into a single cable, the donor unit and service unit each require digital processing, making the wireless repeater larger and again complicating installation. Wireless repeaters for 5G millimeter-wave mobile communication systems also utilize synchronization functions. 5G and millimeter-wave bands use TDD (Time Division Duplex) for transmit / receive switching. Therefore, the BS / UEs use a synchronization signal specified in 5G communications to synchronize the transmit / receive switching timing. For synchronization, the wireless repeater also requires a synchronization module capable of demodulating the 5G signal and extracting the synchronization signal. This synchronization function is performed in the intermediate frequency band, but if two systems are wired separately, a synchronization module is required for each system, resulting in a larger device. Here, the synchronization signal can be confirmed in either or both of the two systems using the transmission wave from the BS.In these wireless repeaters, two systems are wired separately. For example, wireless repeaters in the 5G standard support MIMO, so a two-system configuration is used as shown in Figures 1 and 2.

[0003] Japanese Patent Application Laid-Open No. 2022-67016

[0004] In a two-system system configuration, only one local signal and intermediate frequency are required, but two coaxial cables and two synchronization modules are required, resulting in higher costs and larger equipment size, including the demodulator. In particular, analog wiring between the donor and service unit is advantageous for minimizing equipment size, but two coaxial cables are required, which reduces installation ease. Furthermore, TDD synchronization of the wireless repeater is performed by demodulating the 5G synchronization signal from the base station. However, since the repeater does not know which system the synchronization signal can be obtained from, two synchronization modules are required, resulting in larger equipment size. For example, even when a 5G wireless repeater supports MIMO, the goal is to solve the problem of larger equipment size by combining two system configurations into one system using the intermediate frequency band. For example, even when a 5G wireless repeater supports MIMO, the goal is to solve the problem of larger equipment size by enabling the local signal to be switched using a synchronization signal. Furthermore, even in a configuration where a synchronization signal is used to synchronize the timing of transmission and reception switching, such as when switching between transmission and reception using TDD in the millimeter wave band of the 5G standard, if two systems are individually wired, a synchronization module is required for each system, but this object is to solve this problem by providing a configuration where a single synchronization module fulfills the above functions. Other objects of the present invention will be described in the description of the embodiment of the invention.

[0005] a first connection section connected to the cable; and N donor-side frequency conversion sections from a first donor antenna to an Nth donor antenna, where N is an integer equal to or greater than 2, each converting a signal of frequency fRF received by a corresponding donor antenna among the N donor antennas from the first donor antenna to the Nth donor antenna into an intermediate signal, which is an analog signal, from a first intermediate signal to an Nth intermediate signal, using a corresponding local signal; and the local signal and the intermediate signal have different frequencies for each donor-side frequency conversion section; and the second unit comprises N service antennas from a first service antenna to an Nth service antenna, each communicating with a communication terminal; a second connection unit connected to an analog cable, and N service-side frequency conversion units from a first service-side frequency conversion unit to a N-th service-side frequency conversion unit, wherein each of the N service-side frequency conversion units from the first service antenna to the N-th service antenna converts a signal of frequency fRF received by a corresponding one of the N service antennas from the first service antenna to the N-th service antenna using a local signal, into analog intermediate signals from a first intermediate signal to a N-th intermediate signal, wherein the local signals and the intermediate signals have different frequencies for each service-side frequency conversion unit, the cable passes the analog intermediate signals, and the first intermediate signal to the N-th intermediate signal are superimposed and transmitted via a single cable. In one embodiment of the present invention, the wireless repeater is any of the above wireless repeaters, comprising: a donor-side combining / dividing unit connected between the donor antenna and the cable, and a service-side combining / dividing unit connected between the service antenna and the cable.In one embodiment of the present invention, the wireless repeater is any of the above wireless repeaters, comprising: a donor-side filter connected between the donor antenna and the cable, and a service-side filter connected between the service antenna and the cable. In another embodiment of the present invention, the wireless repeater is any of the above wireless repeaters, comprising: a donor-side combiner / divider connected between the donor antenna and the cable, a service-side combiner / divider connected between the service antenna and the cable, a donor-side filter connected between the donor antenna and the cable, and a service-side filter connected between the service antenna and the cable. In another embodiment of the present invention, the wireless repeater is any of the above wireless repeaters, wherein the donor-side combiner / divider and the donor-side filter are integrally configured as a donor-side multiplexer, and the service-side combiner / divider and the service-side filter are integrally configured as a service-side multiplexer. In another embodiment of the present invention, the wireless repeater is any of the above wireless repeaters, wherein the first to Nth intermediate signals each have a predetermined bandwidth, and the bands of the first to Nth intermediate signals are separated from adjacent bands by a predetermined band width. In one embodiment of the present invention, the wireless repeater further comprises a synchronization signal acquisition unit, a donor-side local signal switching unit, and a service-side local signal switching unit, wherein the first unit comprises a first demodulator and a first synchronization module connected to the first connection unit, and the second unit comprises a second demodulator and a second synchronization module connected to the second connection unit, and the synchronization signal acquisition unit is any of the above wireless repeaters, wherein the donor-side local signal switching unit switches the donor-side local signal based on the demodulation result in the first demodulator to obtain a synchronization signal, or the service-side local signal switching unit switches the service-side local signal based on the demodulation result in the second demodulator to obtain a synchronization signal.In one embodiment of the present invention, the wireless repeater is any of the wireless repeaters described above, wherein the donor-side local signal switching unit and the service-side local signal switching unit further include a donor-side switching transceiver unit and a service-side switching transceiver unit, respectively, and when one of the donor-side local signal switching unit and the service-side local signal switching unit switches the local signal, it transmits a local signal switching signal to the other via the donor-side switching transceiver unit and the service-side switching transceiver unit, and the other of the donor-side local signal switching unit and the service-side local signal switching unit selects the frequency of the local signal.

[0006] With the above configuration, the present invention allows two systems to be transmitted over a single coaxial cable by sharing a transmission path in the intermediate frequency band, simplifying the layout. Furthermore, with the above configuration, the present invention allows 5G synchronization to be achieved with a single synchronization module, resulting in a smaller device size compared to conventional devices. Furthermore, by appropriately switching the local signal, the signal-to-noise ratio during demodulation can be improved, achieving stable and efficient synchronization. Furthermore, with the above configuration, the present invention not only reduces costs by reducing the number of parts, but also achieves miniaturization and improved performance. Other advantages of the present invention are also described in the detailed description of the invention.

[0007] 1 shows an example of the configuration of a conventional wireless repeater. 2 shows an example of the configuration of a conventional wireless repeater. 3 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 4 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 5 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 6 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 7 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 8 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 9 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 10 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 11 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 12 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention. 13 shows a frequency allocation of a wireless repeater according to an embodiment of the present invention. 14 shows an example of the configuration of a wireless repeater according to an embodiment of the present invention.

[0008] 3, 4, and 5 show an example of the configuration of a wireless repeater 1 according to an embodiment of the present invention. In the following example, for ease of understanding, an example will be described in which there are two donor antennas 101, 102, ..., 10N and two service antennas 201, 202, ..., 20N, i.e., two systems. However, the same applies when N is 2 or greater. The wireless repeater 1 includes a first unit 100, a second unit, and one cable 300 connecting the first unit 100 and the second unit. The first unit 100 includes N donor antennas 101, 102, ..., 10N, a first connection unit 110 connected to the analog cable 300, and N donor-side frequency conversion units 111, 112, ..., 11N from the first donor-side frequency conversion unit to the Nth donor-side frequency conversion unit, where N is an integer greater than or equal to 2. In this embodiment, N is 2.

[0009] The N donor antennas 101, 102, ..., 10N are donor antennas 101, 102, ..., 10N from the first donor antenna 101, 102, ..., 10N to the Nth donor antenna 101, 102, ..., 10N that communicate with the base station. The N donor-side frequency conversion units 111, 112, ..., 11N from the donor-side first frequency conversion unit to the donor-side Nth frequency conversion unit respectively convert signals of frequency fRF received by corresponding donor antennas 101, 102, ..., 10N among the N donor antennas 101, 102, ..., 10N from the first donor antenna 101, 102, ..., 10N to the Nth donor antenna 101, 102, ..., 10N into intermediate signals, which are analog signals, from the first intermediate signal to the Nth intermediate signal, using the respective local signals. Here, the local signals and intermediate signals have different frequencies for each of the donor-side frequency converters 111, 112, . . . , 11N.

[0010] The second unit includes N service antennas 201, 202, ..., 20N, a second connection unit connected to analog cable 300, and N service-side frequency conversion units 211, 212, ..., 21N from the first service-side frequency conversion unit to the Nth service-side frequency conversion unit. The N service antennas 201, 202, ..., 20N are service antennas 201, 202, ..., 20N from the first service antennas 201, 202, ..., 20N to the Nth service antennas 201, 202, ..., 20N that communicate with the communication terminal.

[0011] The N service-side frequency converters 211, 212, ..., 21N from the first service-side frequency converter to the Nth service-side frequency converter each converts a signal of frequency fRF received by a corresponding service antenna 201, 202, ..., 20N among the N service antennas 201, 202, ..., 20N from the first service antenna 201, 202, ..., 20N to the Nth service antenna 201, 202, ..., 20N, using the respective local signals, into analog intermediate signals from the first intermediate signal to the Nth intermediate signal, respectively. The local signals and intermediate signals have different frequencies for each service-side frequency converter 211, 212, ..., 21N.

[0012] The cable 300 is a cable that transmits analog intermediate signals and is capable of properly transmitting analog signals. As in the present embodiment, the cable 300 does not have a digital processing unit for the intermediate signals, making the digital processing unit unnecessary. The first to Nth intermediate signals are superimposed and transmitted on a single cable 300.

[0013] The meaning of "transmitted superimposed" in the claims and this description includes a configuration in which there are time periods when the signals are not superimposed depending on the timing of the signals, and means that the signals can be processed without any problems even if they are transmitted superimposed. The local signal and intermediate signal do not have to be fixed. In other words, they can be configured as an integrated signal, and each superimposed signal may have a different frequency.

[0014] In this embodiment, high-frequency band fRF signals from two antenna systems, donor antennas 101, 102, ..., 10N and service antennas 201, 202, ..., 20N, are frequency-converted to separate intermediate frequency bands with frequencies fIF1 and fIF2 using local signals with frequencies fLO1 and fLO2, respectively. Here, fIF1 is smaller than fIF2. The intermediate frequency band signals with frequencies fIF1 and fIF2 are superimposed onto a single transmission path by an intermediate frequency band diplexer, enabling wiring between the donor and service units using a single coaxial cable 300. Cable 300 may be a digital cable 300 or a wireless communication cable, but it may also be an analog cable 300 such as a coaxial cable 300 as in this embodiment. Using an analog cable 300 eliminates the need for an analog-to-digital converter, simplifying the circuit configuration and allowing the overall device to be more compact.

[0015] 6 shows an example of the configuration of a wireless repeater 1 according to an embodiment of the present invention. In this embodiment, the wireless repeater 1 includes a donor-side combiner / divider 121 connected between donor antennas 101, 102, ..., 10N and cable 300, and a service-side combiner / divider 221 connected between service antennas 201, 202, ..., 20N and cable 300.

[0016] 7 shows an example of the configuration of a wireless repeater 1 according to an embodiment of the present invention. In this embodiment, the wireless repeater 1 includes a donor-side filter 122 connected between donor antennas 101, 102, ..., 10N and the cable 300, and a service-side filter 222 connected between service antennas 201, 202, ..., 20N and the cable 300.

[0017] 8 shows an example of the configuration of a wireless repeater 1 according to an embodiment of the present invention. In this embodiment, the wireless repeater 1 includes a donor-side combiner / divider 121 connected between donor antennas 101, 102, ..., 10N and cable 300, a service-side combiner / divider 221 connected between service antennas 201, 202, ..., 20N and cable 300, a donor-side filter 122 connected between donor antennas 101, 102, ..., 10N and cable 300, and a service-side filter 222 connected between service antennas 201, 202, ..., 20N and cable 300.

[0018] 9 shows an example of the configuration of a wireless repeater 1 in one embodiment of the present invention. In this embodiment, the wireless repeater 1 includes a donor-side combiner / divider 121 and a donor-side filter 122 integrated into a donor-side multiplexer 120. A service-side combiner / divider 221 and a service-side filter 222 integrated into a service-side multiplexer 220. When there are two antennas, this embodiment uses a diplexer. The term "multiplexer" in the claims and this description includes a diplexer.

[0019] In one embodiment of the present invention, the first unit 100 includes a first demodulator 131 and a first synchronization module 132 connected to the first connection part 110 side, and the first synchronization module 132 switches between the donor-side frequency converters 111, 112 and the local signal based on the demodulation result in the first demodulator 131. In one embodiment of the present invention, the second unit includes a second demodulator 231 and a second synchronization module 232 connected to the second connection part side, and the second synchronization module 232 switches between the service-side frequency converters 211, 212 and the local signal based on the demodulation result in the second demodulator 231.

[0020] 10 shows an example of the configuration of a wireless repeater 1 according to an embodiment of the present invention. In this embodiment, the first unit 100 includes a first demodulator 131 and a first synchronization module 132 connected to the first connection unit 110. The second unit includes a second demodulator 231 and a second synchronization module 232 connected to the second connection unit. The wireless repeater 1 according to this embodiment further includes synchronization signal acquisition units 133 and 233, a donor-side local signal switching unit 134, and a service-side local signal switching unit 234.

[0021] The first unit 100 includes a first demodulator 131 and a first synchronization module 132 connected to the first connection unit 110. The second unit includes a second demodulator 231 and a second synchronization module 232 connected to the second connection unit. The synchronization signal acquisition unit 133 obtains a synchronization signal by switching the donor-side local signal using the donor-side local signal switching unit 134 based on the demodulation result in the first demodulator 131, or by switching the service-side local signal using the service-side local signal switching unit 234 based on the demodulation result in the second demodulator 231.

[0022] 11 shows an example of the configuration of a wireless repeater 1 in one embodiment of the present invention. In this embodiment, the donor-side local signal switching unit 134 and the service-side local signal switching unit 234 further include a donor-side switching transceiver unit 135 and a service-side switching transceiver unit 235, respectively. When one of the donor-side local signal switching unit 134 and the service-side local signal switching unit 234 switches the local signal, it transmits a local signal switching signal to the other via the donor-side switching transceiver unit 135 and the service-side switching transceiver unit 235, and the other of the donor-side local signal switching unit 134 and the service-side local signal switching unit 234 selects the frequency of the local signal.

[0023] In this way, a unit other than the unit that performed local signal switching control receives the frequency information of the local signal from the unit that performed switching control and adjusts the frequency of the local signal. The synchronization module obtains the synchronization signal by demodulating fIF1. Since only one synchronization module is required, the system is small and low cost.

[0024] In one embodiment of the present invention, when there is an intermediate signal from which a synchronization signal cannot be obtained, the first synchronization module 132 and the second synchronization module 232 of the wireless repeater 1 perform local signal switching control to search for an intermediate frequency signal containing a synchronization signal. That is, in this embodiment, when a synchronization signal can be obtained from both of the two systems, no special ingenuity is required, and when a synchronization signal can be obtained from only one of the antennas 1 and 2, the two local signals of frequency fLO1 and frequency fLO2 are switched, and the one from which a synchronization signal can be obtained is set as fIF1.

[0025] 12 shows a frequency allocation of the wireless repeater 1 in one embodiment of the present invention. In this embodiment, the first to Nth intermediate signals each have a predetermined bandwidth D1. The bands of the first to Nth intermediate signals are separated from adjacent bands by a predetermined bandwidth D2.

[0026] In this embodiment, fRF = 28.0 GHz ± 200 MHz (400 MHz width), fIF1 = 3.0 GHz ± 200 MHz (400 MHz width), and fIF2 = 3.6 GHz ± 200 MHz (400 MHz width). The values ​​of fLO1 and fLO2 are determined according to the specifications of the mixer. For example, the signals received by donor antennas 101 and 102 and the signals received by donor antennas 101 and 102 have different paths but the same frequency in the RF band, i.e., the high frequency band in which the antennas transmit and receive signals to and from the outside. On the other hand, in the IF band, i.e., the intermediate frequency band in which signals are transmitted and received via cable 300, the paths are the same but the frequencies are different.

[0027] 13 shows a generalized configuration of N systems, where N is an integer equal to or greater than 2. The local signal can be switched so that the system from which the synchronization signal can be obtained has the lowest frequency, and also so that the band of the intermediate frequency band extracted by the synchronization module has the lowest frequency, thereby achieving the same effect as in the case of two systems with N systems.

[0028] The present invention is not limited to the above-described embodiments, and it goes without saying that various embodiments are included within the scope of the present invention.

[0029] 1 Wireless repeater 100 First unit 101, 102, 10N Donor antenna 110 First connection unit 111, 112, 11N Donor side frequency conversion unit 120 Donor side multiplexer 121 Donor side combining / dividing unit 122 Donor side filter 131 First demodulator 132 First synchronization module 133 Synchronization signal acquisition unit 134 Donor side local signal switching unit 135 Donor side switching / transmitting unit 200 Second unit 201, 202, 20N Service antenna 210 Second connection unit 211, 212, 21N Service side frequency conversion unit 220 Service side multiplexer 221 Service side combining / dividing unit 222 Service side filter 231 Second demodulator 232 Second synchronization module 233 Synchronization signal acquisition unit 234 Service side local signal switching unit 235 Service side switching transmitting / receiving unit 300 Cable 401 Transmission front end 402 Reception front end 403 Multiplier 404 Band pass filter BS Base station UE Terminal DU Donor unit SU Service unit D1 Predetermined bandwidth D2 Predetermined band portion

Claims

1. A radio communication system comprising: a first unit, a second unit, and one cable connecting the first unit and the second unit, wherein the first unit comprises: N donor antennas from a first donor antenna to an Nth donor antenna, where N is an integer equal to or greater than 2, for communicating with a base station; a first connection unit connected to the cable; and N donor-side frequency conversion units from a donor-side first frequency conversion unit to a donor-side Nth frequency conversion unit, wherein the N donor-side frequency conversion units from the donor-side first frequency conversion unit to the donor-side Nth frequency conversion unit each converts a signal of frequency fRF received by a corresponding one of the N donor antennas from the first donor antenna to the Nth donor antenna into an intermediate signal which is an analog signal from a first intermediate signal to an Nth intermediate signal using a respective local signal, wherein the local signal and the intermediate signal have mutually different frequencies for each donor-side frequency conversion unit, and the second unit comprises: N service antennas from a first service antenna to an Nth service antenna for communicating with a communication terminal, a second connection unit connected to the cable, and N service side frequency conversion units from a service side first frequency conversion unit to a service side Nth frequency conversion unit, wherein the N service side frequency conversion units from the service side first frequency conversion unit to the service side Nth frequency conversion unit each converts a signal of frequency fRF received by a corresponding service antenna among the N service antennas from the first service antenna to the Nth service antenna into an intermediate signal which is an analog signal from a first intermediate signal to an Nth intermediate signal using a respective local signal, wherein the local signal and the intermediate signal have different frequencies for each service side frequency conversion unit, the cable passes an intermediate signal which is an analog signal, and the intermediate signals from the first intermediate signal to the Nth intermediate signal are superimposed and transmitted on the one cable.

2. The wireless repeater according to claim 1, comprising: a donor-side combiner / divider connected between the donor antenna and the cable; and a service-side combiner / divider connected between the service antenna and the cable.

3. The wireless repeater according to claim 1, further comprising: a donor-side filter connected between the donor antenna and the cable; and a service-side filter connected between the service antenna and the cable.

4. A wireless repeater as described in claim 1, comprising: a donor-side combiner / distributor connected between the donor antenna and the cable; a service-side combiner / distributor connected between the service antenna and the cable; a donor-side filter connected between the donor antenna and the cable; and a service-side filter connected between the service antenna and the cable.

5. The wireless repeater according to claim 4, wherein the donor side combining / distributing unit and the donor side filter are integrally configured as a donor side multiplexer, and the service side combining / distributing unit and the service side filter are integrally configured as a service side multiplexer.

6. A wireless repeater as described in claim 1, wherein the first intermediate signal to the Nth intermediate signal each have a predetermined bandwidth, and the band of the first intermediate signal to the band of the Nth intermediate signal are separated from adjacent bands by a predetermined band width.

7. A wireless repeater as described in any one of claims 1 to 6, further comprising a synchronization signal acquisition unit, a donor side local signal switching unit, and a service side local signal switching unit, wherein the first unit comprises a first demodulator and a first synchronization module connected to the first connection unit, and the second unit comprises a second demodulator and a second synchronization module connected to the second connection unit, and the synchronization signal acquisition unit: based on the result of demodulation in the first demodulator, switches the donor side local signal by the donor side local signal switching unit to obtain a synchronization signal, or based on the result of demodulation in the second demodulator, switches the service side local signal by the service side local signal switching unit to obtain a synchronization signal.

8. A wireless repeater as described in claim 7, wherein the donor side local signal switching unit and the service side local signal switching unit further have a donor side switching transceiver unit and a service side switching transceiver unit, respectively, and when one of the donor side local signal switching unit and the service side local signal switching unit switches the local signal, a local signal switching signal is transmitted to the other via the donor side switching transceiver unit and the service side switching transceiver unit, and the other of the donor side local signal switching unit and the service side local signal switching unit selects the frequency of the local signal.

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