JP7690141B2 - Wireless communication system and relay device - Google Patents

Description

The present disclosure relates to a wireless communication system that communicates with a mobile station and a relay device in the wireless communication system.

Patent Document 1 discloses a train communication system for communicating between a base station and a train.
The train communication method disclosed in Patent Document 1 has a relay amplifier arranged in the middle of a leaky coaxial transmission line connecting a base station and a receiving station, in which an intermediate frequency signal transmitted from a base station is amplified by the amplifier, then converted to a high frequency by a frequency converter and transmitted to the leaky coaxial transmission line and sent to the train, and the high frequency signal transmitted from the train is down-converted to an intermediate frequency by the frequency converter, amplified by the amplifier, transmitted to the leaky coaxial transmission line and sent to the receiving station.

Special Publication No. 48-028569

Patent Document 1 does not describe a local oscillation signal used in a frequency converter that down-converts a high-frequency signal to an intermediate frequency, nor a local oscillation signal used in a frequency converter that converts an intermediate-frequency signal to a high-frequency signal.
Moreover, only one relay amplifier is shown, and no example of a cascade connection of a plurality of relay amplifiers is shown.
When long-distance transmission is performed using multiple relay amplifiers connected in cascade, if a low frequency with small transmission loss is attempted, a problem arises as to how to generate the local oscillation signal used in the frequency converter in each of the multiple relay amplifiers in order to obtain high frequency stability for the frequency-converted signal.

The present disclosure has been made in consideration of the above-mentioned points, and aims to obtain a wireless communication system having a base station and multiple relay devices cascade-connected to the base station, in which high frequency stability can be obtained for frequency-converted signals.

A wireless communication system according to the present disclosure includes a base station and a plurality of relay devices connected in cascade to the base station , each of which receives a transmission wave from a mobile station as a received wave . The base station includes a receiver, a local oscillator that outputs a local oscillation signal, and a duplexer that transmits the local oscillation signal from the local oscillator to a transmission path and transmits the received signal from the transmission path to the receiver. Of the plurality of relay devices, a relay device adjacent to the base station includes a received signal generation path that receives a local oscillation signal from the base station and uses the local oscillation signal to frequency - convert a received wave signal based on an input received wave into a received signal having a frequency lower than that of the received wave signal and transmits the received signal to a transmission path connected to the base station, and a local oscillation signal transmission path that transmits the local oscillation signal from the base station to a transmission path connected to a relay device at a next stage. and a received signal transmission path that transmits a received signal from the next stage relay device to a transmission path connected to the base station, and among the multiple relay devices, each relay device other than the relay device adjacent to the base station is equipped with a received signal generation path that receives a local oscillation signal from the local oscillation signal transmission path in the previous stage relay device, frequency converts a received wave signal based on a received wave input using the local oscillation signal to a received signal having a frequency lower than that of the received wave signal, and transmits the received signal to the transmission path connected to the previous stage relay device, a local oscillation signal transmission path that transmits the local oscillation signal from the local oscillation signal transmission path in the previous stage relay device to the transmission path connected to the next stage relay device, and a received signal transmission path that transmits the received signal from the next stage relay device to the transmission path connected to the previous stage relay device.

According to the present disclosure, a local oscillator that outputs a local oscillation signal is provided in the base station, and the local oscillation signal from the local oscillator in the base station is used for frequency conversion in multiple relay devices that are cascade-connected, thereby achieving high frequency stability for the frequency-converted signal.

1 is a block diagram showing a wireless communication system according to a first embodiment; 2 is a schematic diagram illustrating signal distribution in a signal transmission path of a base station in a wireless communication system according to the first embodiment. FIG. 4 is a schematic diagram illustrating signal distribution in a first duplexer of a relay device in the wireless communication system according to the first embodiment. FIG. 4 is a schematic diagram illustrating signal distribution in a second duplexer of a relay device in the wireless communication system according to the first embodiment. FIG. FIG. 11 is a block diagram showing a wireless communication system according to a second embodiment. FIG. 11 is a block diagram showing a wireless communication system according to a third embodiment. A block diagram showing a wireless communication system according to a fourth embodiment.

Embodiment 1.
A wireless communication system according to a first embodiment will be described with reference to FIGS.
The wireless communication system according to the first embodiment includes a base station 10 and a plurality of relay devices 20 ₁ , 20 _k cascade-connected to the base station 10, where k is an integer of 2 or more.
Relay device ₂₀₁ indicates a first-stage relay device adjacent to a base station, and relay device _20k indicates a second-stage or subsequent relay device.

The base station 10 comprises a receiver 11 , a local oscillator 12 and a duplexer 13 .
A local oscillator 12 outputs a local oscillation signal LO having a frequency f _LO .
In this example, the frequency f _LO is in the band of several MHz to 100 MHz. Note that the high frequency at which loss in the transmitted signal increases or the frequency at which loss can be suppressed varies depending on the transmission path connecting the base station 10 and the first-stage relay device _20-1 and the transmission path connecting the adjacent relay devices 20, so the frequency f _LO is selected appropriately depending on the transmission path.

The duplexer 13 transmits the local oscillation signal LO from the local oscillator 12 to the transmission line connected to the first-stage repeater _20-1 , and transmits the reception signal RX- _IF of intermediate frequency f- _IF from the transmission line connected to the first-stage repeater _20-1 to the receiver 11.
The duplexer 13 has an input terminal, an output terminal, and an input/output terminal. The input terminal is connected to the output terminal of the local oscillator 12, the output terminal is connected to the input terminal of the receiver 11, and the input/output terminal is connected to a transmission path connected to the first-stage repeater device ₂₀₁ .

In the duplexer 13, as shown in FIG. 2, a local oscillation signal LO having a frequency f _LO input to an input terminal is transmitted to an input/output terminal, and a received signal RX _IF1 having an intermediate frequency f _IF based on a received wave RX ₁ received by the first-stage repeater device _20-1 input to the input/output terminal and a received signal RX _IF2 having an intermediate frequency f _IF from the next-stage repeater device _20-2 input to the input/output terminal via the first-stage repeater device _20-1 are transmitted to an output terminal.
The duplexer 13 is a frequency duplexer that appropriately distributes frequencies, that is, has the function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing the frequency f _LO and the intermediate frequency f _IF1 .

The transmission line connecting the base station 10 and the first-stage repeater ₂₀₁ is a coaxial cable or an antenna.
When the transmission line is a coaxial cable, the input/output terminals of the duplexer 13 are connected to the coaxial cable by a connector.
When the transmission line is an antenna, the input/output terminals of the duplexer 13 are connected to an antenna that transmits the local oscillation signal LO and an antenna that receives the reception signals RX _IF1 and RX _IFk from the first-stage repeater _20-1 .
The input/output terminals of the duplexer 13 may be divided into an input terminal and an output terminal, which may be connected to different transmission paths.

The plurality of repeater devices 20 ₁ , 20 _k each have basically the same configuration, and include a first duplexer 21, a second duplexer 22, a frequency converter 23, a distributor 24, and first to third amplifiers 25 to 27, as shown in FIG.
The first to third amplifiers 25 to 27 are provided to supplement the signal strength of the signal to be transmitted, that is, to increase the signal strength.
The relay devices 20 ₁ , 20 _k are installed in a direction that progressively moves away from the base station 10 .

Each of the relay devices 20 ₁ , 20 _k has a reception area for receiving a transmission wave from a mobile station and a reception wave for the relay device, and receives a transmission wave from a mobile station present within the corresponding reception area as a reception wave.
The mobile stations are in this example transmitters mounted on, for example, rail vehicles or automobiles.

Each of the plurality of relay devices 20 ₁ , 20 _k includes a reception signal generation path, a local oscillation signal transmission path, and a reception signal transmission path.
Among the multiple relay devices 20 ₁ , 20 _k , the reception signal generation path in the first-stage relay device 20 ₁ connected to the base station 10 via a transmission path receives a local oscillation signal LO of frequency f _LO from the base station 10, and converts the input reception wave RX ₁ using the local oscillation signal into an electrical signal to obtain a reception wave signal with frequency f _RX . The frequency of the reception wave signal is converted to a reception signal RX _IF1 with an intermediate frequency f _IF lower than the frequency f _RX of the reception wave signal, and the resulting signal is transmitted to the transmission path connected to the base station 10.
In this example, the frequency f _RX is in the UHF band, such as 300 MHz to 500 MHz, and the intermediate frequency f _IF is a value lower than the frequency f _RX by the frequency f _LO .

As shown in FIG. 1, the reception signal generation path in the first-stage repeater _20-1 has a first duplexer 21, a second duplexer 22, a frequency converter 23, and a first amplifier 25. The second duplexer 22 receives and transmits a reception wave signal of frequency f _RX from the reception wave RX _-1. The frequency converter 23 uses one local oscillation signal LO of the frequency f _LO distributed from the distributor 24 to convert the frequency of the reception signal RX- _IF1 of intermediate frequency f _IF , which is a frequency lower than the frequency f _RX. The frequency-converted reception signal RX- _IF1 of intermediate frequency f _IF is amplified by the first amplifier 25 and then output to the transmission path via the first duplexer 21.
The relationship between the frequency f _RX and the intermediate frequency f _IF is f _IF =f _RX -f _LO .

The local oscillation signal transmission path in the first-stage repeater _20-1 transmits the local oscillation signal LO of frequency f _LO from the base station 10 to a transmission path connected to the next-stage repeater _20-2 .
As shown in FIG. 1 , the local oscillation signal transmission path in the first-stage repeater _20-1 has a first duplexer 21, a second duplexer 22, a distributor 24, and a second amplifier 26. The first duplexer 21 distributes the local oscillation signal LO of frequency f _LO received and transmitted, outputs one of the distributed local oscillation signals LO of frequency f _LO to frequency converter 23, and the other distributed local oscillation signal LO of frequency f _LO is amplified by second amplifier 26 and then output to a transmission path connected to the next-stage repeater _20-2 via second duplexer 22.

The reception signal transmission path in the first-stage repeater 20 ₁ transmits the reception signal RX _{IF 2} of the intermediate frequency f _{IF 2} from the next-stage repeater 20 ₂ to a transmission path connected to the base station 10 .
As shown in FIG. 1, the reception signal transmission path in the first-stage repeater _20-1 has a first duplexer 21, a second duplexer 22, and a third amplifier 27. The reception signal RX- _IF2 of intermediate frequency f- _IF from the next-stage repeater _20-2 , which is received and transmitted by the second duplexer 22, is amplified by the third amplifier 27 and then output to the transmission path via the first duplexer 21.

The first duplexer 21 is a frequency duplexer that receives a local oscillation signal LO of frequency f _LO output from the local oscillator 12 of the base station 10, outputs the local oscillation signal LO to the distributor 24, outputs a reception signal RX IF1 of intermediate frequency f _IF obtained by frequency conversion of a reception wave signal from a frequency converter 23 and amplified by a first amplifier 25 to the base station 10, and outputs a reception signal RX _IF2 of intermediate frequency f _IF from the next stage relay device _20-2 transmitted from the second duplexer 22 and amplified by a third amplifier ₂₇ to the base station 10.

As shown in FIG. 3, the first duplexer 21 has an input/output terminal, a first input terminal, a second input terminal and an output terminal, and the input/output terminals are connected to a transmission path connected to the base station 10, the first input terminal is connected to the output terminal of a first amplifier 25 constituting a received signal generation path, the second input terminal is connected to the output terminal of a third amplifier 27 in the received signal transmission path, and the output terminal is connected to the input terminal of a distributor 24 constituting a local oscillation signal transmission path.

In the first duplexer 21, as shown in FIG. 3, a local oscillation signal LO having a frequency f _LO input to an input/output terminal is transmitted to an output terminal, a reception wave signal RX IF1 having an intermediate frequency f IF obtained by frequency conversion of a reception wave signal due to a reception wave RX ₁ input to a first input terminal by a frequency converter 23 is transmitted to an input/output terminal, and a reception signal RX _IF2 having an intermediate frequency f _IF from the next-stage repeater device 20 ₂ input to a _second input _terminal is transmitted to an input/output terminal.
The first duplexer 21 has a function of appropriately distributing frequencies, that is, a function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing the frequency f _LO and the intermediate frequency f _IF .

When the transmission line connected to the base station 10 is a coaxial cable, the input/output terminal of the first duplexer 21 is connected to the coaxial cable by a connector.
When the transmission line is an antenna, the input/output terminals of the first duplexer 21 are connected to an antenna for receiving the local oscillation signal LO and an antenna for transmitting the reception signals RX _{IF1 and} RX _IFk .
The input/output terminals of the first duplexer 21 may be divided into an input terminal and an output terminal in correspondence with the input/output terminals of the duplexer 13 in the base station 10 and connected to different transmission paths.

The second duplexer 22 is a frequency duplexer that outputs a received wave signal based on the received wave to the frequency converter 23, outputs the other local oscillation signal LO of frequency f _LO to which the local oscillation signal LO is distributed by the distributor 24 to the next-stage repeater device _20-2 , and outputs a received signal RX _IF2 of intermediate frequency f _IF from the next-stage repeater device _20-2 to the first duplexer 21 via the third amplifier 27.

As shown in FIG. 4 , the second duplexer 22 has an input/output terminal, an input terminal, a first output terminal and a second output terminal, and the input/output terminal is connected to a transmission path connected to the next-stage repeater device ₂₀₂ , the input terminal is connected to the output terminal of a second amplifier 26 constituting a local oscillation signal transmission path, the first output terminal is connected to an input terminal of a frequency converter 23 constituting a received signal generation path, and the second output terminal is connected to an input terminal of a third amplifier 27 in the received signal transmission path.

In the second duplexer 22, as shown in FIG. 4, a received wave signal of frequency f _RX due to a received wave _RX1 input to an input/output terminal is transmitted to a first output terminal, a received signal RX _IF2 of intermediate frequency f _IF from the next stage repeater device _20-2 input to an input/output terminal is transmitted to a second output terminal, and a local oscillation signal LO of frequency f _LO input to an input terminal is transmitted to an input/output terminal.
The second duplexer 22 has a function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing frequencies, that is, for appropriately distributing the frequency f _LO , the frequency f _RX , and the intermediate frequency f _IF .

The input/output terminal of the second duplexer 22 is connected to an antenna for receiving a transmission wave from a mobile station present within the reception area of the first-stage relay device ₂₀₁ .
When the transmission line connected to the next stage repeater ₂₀₂ is a coaxial cable, the input/output terminals of the second duplexer 22 are connected to the coaxial cable by a connector.
When the transmission path is an antenna, the input/output terminals of the second duplexer 22 are connected to an antenna that transmits the local oscillation signal LO and an antenna that receives the reception signal RX _IFk .
The input/output terminals of the second duplexer 22 may be divided into an input terminal and an output terminal in correspondence with the input/output terminals of the second duplexer 22 in the next stage repeater ₂₀₂ , and may be connected to different transmission paths.

1 to 4, signals are expressed by frequency, a subscript indicating the stage in the relay device 20 is added to the received wave RX input to the relay device 20 of each stage, and a subscript indicating the stage in the next stage relay device 20 is added to the received signal RX _IF from the next stage relay device 20. Although subscripts are added, the frequencies are the same.
In the following description, except in special cases, the subscripts indicating stages will be omitted to avoid complicating the explanation.

Among the multiple relay devices 20 ₁ and 20 _k , the second-stage and subsequent relay devices 20 _k other than the first-stage relay device 20 ₁ adjacent to the base station 10 have the same configuration as the first-stage relay device 20 ₁ , and as shown in FIG. 1, have a first duplexer 21, a second duplexer 22, a frequency converter 23, a distributor 24, and a first amplifier 25 to a third amplifier 27.

The transmission lines connecting adjacent repeaters 20 are each a coaxial cable or an antenna, similar to the transmission line connecting the base station 10 and the first-stage repeater ₂₀₁ .
Each of the multiple relay devices 20 has an antenna that receives transmitted waves from mobile stations located within the corresponding receiving area as received waves RX, and the received waves RX received by the receiving antenna are input to the input/output terminal of the second duplexer 22.

Similarly to the repeater device _20-1 in the first stage, the repeater device 20 _- k in the second stage or later also includes a received signal generation path that receives a local oscillation signal LO of frequency f _LO from the local oscillation signal transmission path in the repeater device 20 in the previous stage, frequency-converts the frequency f _RX of a received wave signal due to a received wave RX input using the local oscillation signal LO to a received signal RX _IF of an intermediate frequency f _IF lower than the frequency f _RX , and transmits the converted signal to a transmission path connected to the repeater device 20 in the previous stage, a local oscillation signal transmission path that transmits the local oscillation signal LO of frequency f _LO from the local oscillation signal transmission path in the repeater device 20 in the previous stage to a transmission path connected to the repeater device 20 in the next stage, and a received signal transmission path that transmits the received signal RX _IF of intermediate frequency f _IF from the repeater device 20 in the next stage to a transmission path connected to the repeater device 20 in the previous stage.

The reception signal generation path in the repeater device _20k at the second stage or later has a first duplexer 21, a second duplexer 22, a frequency converter 23, and a first amplifier 25, similar to the reception signal generation path in the repeater device ₂₀₁ at the first stage. The second duplexer 22 receives and transmits a reception wave signal of frequency fRX from the reception wave _RX , which is converted by the frequency converter 23 into a reception signal _RXIF of intermediate frequency _fIF using one local oscillation signal LO of frequency _fLO distributed from the distributor 24. The converted reception signal _RXIF1 of intermediate frequency _fIF is amplified by the first amplifier 25 and then output to the transmission path via the first duplexer 21.

The local oscillation signal transmission path in repeater device _20k at the second stage or later, like the local oscillation signal transmission path in repeater device _20-1 at the first stage, has a first duplexer 21, a second duplexer 22, a distributor 24, and a second amplifier 26, in which the first duplexer 21 distributes the local oscillation signal LO of frequency _fLO received and transmitted, outputs one of the distributed local oscillation signals LO of frequency _fLO to frequency converter 23, and amplifies the other local oscillation signal LO of frequency _fLO by second amplifier 26 and then outputs it to the transmission path connected to repeater device 20 at the next stage via second duplexer 22.

The reception signal transmission path in the repeater device 20 _k at the second stage or later has a first duplexer 21, a second duplexer 22, and a third amplifier 27, similar to the reception signal transmission path in the repeater device 20 ₁ at the first stage. The reception signal RX _IF at intermediate frequency f _IF from the repeater device 20 ₂ at the next stage, which is received and transmitted by the second duplexer 22, is amplified by the third amplifier 27 and then output to the transmission path via the first duplexer 21.
It should be noted that the final stage repeater device 20 may not have a received signal transmission path, and the local oscillation signal transmission path may not have a path beyond the second amplifier 26 .

Next, the operation of the wireless communication system according to the first embodiment will be described.
A local oscillation signal LO of frequency f _LO from a local oscillator 12 in the base station 10 is distributed by a duplexer 13 and transmitted to the first-stage repeater _20-1 via a transmission line.
In the first-stage repeater _20-1 , a local oscillation signal LO of frequency f _LO is distributed by a distributor 24, one of the local oscillation signals LO of frequency f _LO is output to a frequency converter 23 constituting a received signal generation path, and the other local oscillation signal LO of frequency f _LO is amplified by a second amplifier 26 constituting a local oscillation signal transmission path, and then output from a second duplexer 22 to a next-stage repeater _20-2 via a transmission path.

In repeater device 20 _k at the second or subsequent stage, the local oscillation signal LO of frequency f _LO from repeater device 20 at the previous stage is distributed by distributor 24, and one local oscillation signal LO of frequency f _LO is output to frequency converter 23, and the other local oscillation signal LO of frequency f _LO is output to repeater device 20 at the next stage.

That is, the local oscillation signal LO having a frequency f _LO from the local oscillator 12 in the base station 10 is transmitted in sequence in each relay device 20 to the next relay device 20 via the local oscillation signal transmission path, and is used by the frequency converter 23 constituting the received signal generation path.
Each relay device 20 does not have a local oscillator, and the local oscillation signal LO of frequency f _LO used in each relay device 20 is concentrated in the local oscillator 12 in the base station 10. Therefore, by ensuring the frequency stability of the local oscillator 12 in the base station 10, the frequency stability in each relay device 20 can also be ensured, and high frequency stability can be obtained for the wireless communication system as a whole.

In this embodiment, the frequency f _LO of the local oscillation signal LO can be, for example, a frequency in the range of several MHz to 100 MHz, whereas the frequency f _RX of the received wave signal by the received wave _RX1 is in the UHF range of 300 MHz to 500 MHz. This makes it possible to suppress transmission loss in the local oscillation signal LO through the transmission line connecting the base station 10 and the first-stage repeater _20-1 and the transmission line connecting adjacent repeaters 20, and enables the local oscillation signal LO to be transmitted over longer distances with little transmission loss.

In each relay device 20, when a transmission wave from a mobile station present within the corresponding receiving area is received as a received wave, the received wave signal of frequency f _RX due to the received received wave RX is distributed by the second duplexer 22 and input to the frequency converter 23 that constitutes the received signal generation path.
The frequency converter 23 converts the received wave signal of frequency f _RX from the received wave RX into a received signal RX IF of intermediate frequency f _IF (=f _RX -f _LO ), which is a frequency lower than frequency f _RX , using one of the local oscillation signals _LO of frequency f _LO distributed by the distributor 24.
A received signal RX _IF of intermediate frequency f _IF is amplified by a first amplifier 25 constituting a received signal generating path, and is then output from a first duplexer 21 to a preceding repeater 20 via a transmission line.

On the other hand, in each relay device 20 that receives a reception signal RX _IF of intermediate frequency f _IF from the next-stage relay device 20, the reception signal RX _IF of intermediate frequency f _IF is distributed by the second duplexer 22 and amplified by the third amplifier 27 constituting the reception signal transmission path, and then output from the first duplexer 21 through the transmission path to the previous-stage relay device 20, and is finally transmitted to the base station 10.
In the base station 10 , a received signal RX _IF with an intermediate frequency f _IF is distributed by a duplexer 13 and input to a receiver 11 .

That is, the received wave signal of frequency f _RX by the received wave RX at each relay device 20 is frequency-converted to a received signal _{RX IF of intermediate frequency f IF (} = f _RX - f _LO ) lower than frequency f RX at each relay device 20, and the received signal RX _{IF of intermediate frequency f IF is} amplified at the preceding relay device 20 while remaining at the low intermediate frequency f _IF , and is sequentially relayed to the relay device 20 to reach the base station 10.

The received wave signal of frequency f _RX by the received wave RX is frequency-converted to a received signal RX _IF of a low intermediate frequency f _IF and then relayed to the relay devices 20 in sequence to reach the base station 10. This makes it possible to suppress transmission loss in the received signal RX _IF by the transmission paths connecting adjacent relay devices 20 and the transmission path connecting the base station 10 and the first-stage relay device _20-1 , and therefore makes it possible to transmit the received signal RX _IF over a longer distance with less transmission loss.

As described above, the wireless communication system according to the first embodiment includes the base station 10 having the local oscillator 12 that outputs the local oscillation signal LO of the frequency f _LO , and the plurality of relay devices 20 that are cascade-connected to the base station 10. Each relay device 20 is provided with a received signal generation path that frequency-converts a received wave signal by a received wave RX input using the local oscillation signal LO of the frequency f _LO from the base station 10 to a received signal RX _IF of an intermediate frequency f _IF (=f _RX -f _LO ) lower than the frequency f _RX of the received wave signal and transmits the converted signal to a transmission path, a local oscillation signal transmission path that transmits the local oscillation signal LO of the frequency f _LO from the base station 10 to a transmission path connected to the relay device 20 of the next stage, and a received signal transmission path that transmits the received signal RX _IF of the intermediate frequency f _IF from the relay device 20 of the next stage to the transmission path. Therefore, the local oscillation signal transmission path transmits the frequency f LO from the local oscillator 12 in the base station 10 to the transmission path connected to the relay device 20 of the next stage. Since _{the LO} local oscillation signal LO is transmitted sequentially to the next relay device 20, by ensuring the frequency stability of the local oscillator 12 in the base station 10, the frequency stability in each relay device 20 can also be ensured, resulting in high frequency stability for the wireless communication system as a whole.

Moreover, in the wireless communication system according to the first embodiment, the frequency f _LO of the locally oscillated signal LO is set to a low frequency. This makes it possible to suppress transmission loss in the locally oscillated signal LO due to the transmission line connecting the base station 10 and the first-stage relay device _20-1 and the transmission line connecting adjacent relay devices 20. As a result, the locally oscillated signal LO can be transmitted over a longer distance with less transmission loss.

Furthermore, in the wireless communication system according to the first embodiment, the received wave signal by the received wave RX received at each relay device 20 is frequency-converted by the received signal generation path to a frequency lower than the frequency f _RX of the received wave signal to generate a received signal RX _IF of an intermediate frequency f _IF . This is then transmitted to the previous relay device 20 by the received signal transmission path in the previous relay device 20 in sequence, and transmitted to the base station 10. Therefore, it is possible to suppress transmission loss in the received signal RX _IF by the transmission path connecting the base station 10 and the first relay device _20-1 and the transmission path connecting adjacent relay devices 20, and it is possible to transmit the received signal RX _IF over a longer distance with little transmission loss.

Embodiment 2.
A wireless communication system according to the second embodiment will be described with reference to FIG.
The wireless communication system according to the first embodiment includes a receiving system that frequency-converts a received wave signal by a received wave RX, and transmits the received signal to a base station 10 via a relay device 20 at a previous stage.

In contrast, the wireless communication system of embodiment 2 differs from the wireless communication system of embodiment 1 in that, in addition to the receiving system, it also has a transmitting system that transmits a transmission signal to multiple relay devices 20A that are cascade-connected from a transmitter 14 in a base station 10A.
Therefore, since the receiving system in the wireless communication system according to the second embodiment is the same as the receiving system in the wireless communication system according to the first embodiment, the following description will be centered on the transmitting system.
In FIG. 5, the same reference numerals as those in FIGS. 1 to 4 denote the same or corresponding parts.

The wireless communication system according to the second embodiment includes a base station 10A and a plurality of relay devices 20A ₁ , 20A _k cascade-connected to the base station 10A, where k is an integer of 2 or more.
The base station 10A includes a receiver 11, a local oscillator 12, a duplexer 13A, and a transmitter .
The receiver 11 and the local oscillator 12 are the same as the receiver 11 and the local oscillator 12 in the first embodiment.

The transmitter 14 outputs a transmission signal TX _IFT having an intermediate frequency f _IFT .
The intermediate frequency f _IFT of the transmission signal TX _IFT is in the same frequency band as the intermediate frequency f _IF of the reception signal RX _IF , and in duplex transmission where transmission and reception are simultaneous, the intermediate frequency f IFT is several MHz to several tens of MHz higher or lower than the intermediate frequency f _IF of the reception signal RX _IF .
In semi-duplex communication in which transmission and reception are alternately performed, the intermediate frequency f _IFT of the transmission signal TX _IFT and the intermediate frequency f _IF of the reception signal RX _IF may be the same frequency.

The duplexer 13A transmits the local oscillation signal LO from the local oscillator 12 and the transmission signal TX _IFT having an intermediate frequency f _IFT from the transmitter 14 to a transmission line connected to the first-stage repeater device _20A1 , and transmits the reception signal RX _IF having an intermediate frequency f _IF from the transmission line connected to the _first -stage repeater device 20A1 to the receiver 11.
The duplexer 13A has a first input terminal, a second input terminal, an output terminal and an input/output terminal, the first input terminal being connected to the output terminal of the local oscillator 12, the second input terminal being connected to the output terminal of the transmitter 14, the output terminal being connected to the input terminal of the receiver 11, and the input/output terminal being connected to a transmission path connected to the first-stage repeater device _20A1 .

Similar to the duplexer 13 in the first embodiment, the duplexer 13A has the function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing the frequency f _LO , the intermediate frequency f _IF , and the intermediate frequency f _IFT .
Also, similarly to the duplexer 13 in the first embodiment, when the transmission path is a coaxial cable, the input/output terminals of the duplexer 13A are connected to the coaxial cable via a connector, and when the transmission path is an antenna, the input/output terminals of the duplexer 13A are connected to an antenna for transmitting a local oscillation signal LO, an antenna for transmitting a transmission signal TX _IFT , and an antenna for receiving reception signals RX _IF1 and RX _IFk from the first-stage repeater device _20A1 .

The plurality of relay devices 20A ₁ , 20A _k basically have the same configuration, and include a receiving system, a transmitting system, a fifth duplexer 41 and a sixth duplexer 42 .
Each of the multiple relay devices _20A1 , _20Ak receives a transmission wave from a mobile station located within the corresponding receiving area as a received wave, and transmits a transmission wave based on a transmission signal from the transmitter 14 of the base station 10A to a mobile station located within a transmission area that is the same as the corresponding receiving area.

The receiving system is the same as that in the first embodiment, and includes a first duplexer 21, a second duplexer 22, a frequency converter 23, a distributor 24A, and first to third amplifiers 25 to 27, as shown in FIG.
The receiving system includes a receiving signal generating path, a local oscillation signal transmitting path, and a receiving signal transmitting path, similar to the receiving system in the first embodiment.
Therefore, in the following description, a detailed description of the receiving system will be omitted.

As shown in FIG. 5, the transmission system includes a third duplexer 31, a fourth duplexer 32, a frequency converter 33, a distributor 24A, a fourth amplifier 35, and a fifth amplifier 37.
The fourth amplifier 35 and the fifth amplifier 37 are provided to supplement the signal strength of the signal to be transmitted, that is, to increase the signal strength.
The transmission system includes a transmission wave signal generating path, a transmission signal transmission path, and a local oscillation signal transmission path.
The local oscillation signal transmission path in the transmission system is also used as the local oscillation signal transmission path in the reception system.

In the first stage repeater 20A- ₁ , the fifth duplexer 41 is a frequency duplexer, which receives a local oscillation signal LO of frequency f _LO from the local oscillator 12 of the base station 10A and outputs the local oscillation signal LO to the distributor 24A, receives a transmission signal TX _IFT of intermediate frequency f _IFT output from the transmitter 14 of the base station 10A and outputs it to the third duplexer 31, outputs a reception signal RX IF1 of intermediate frequency f _IF obtained by frequency conversion of a reception wave signal due to a reception wave from the first duplexer 21 by the frequency converter 23 and amplified by the first amplifier 25 to the base station 10, and outputs a reception signal RX _IF2 of intermediate frequency f _IF from the next stage repeater 20A- ₂ transmitted from the second duplexer 22 and amplified by the third amplifier ₂₇ to the base station 10A .

The fifth duplexer 41 has an input/output terminal, an input terminal, a first output terminal and a second output terminal, and the input/output terminal is connected to a transmission path connected to the base station 10A , the input terminal is connected to the output terminal of the first duplexer 21, the first output terminal is connected to the input terminal of the distributor 24A , and the second output terminal is connected to the input terminal of the third duplexer 31.

In the fifth duplexer 41, the local oscillation signal LO of frequency f _LO input to the input/output terminal is transmitted to the first output terminal, a received signal RX IF1 of intermediate frequency f IF obtained by frequency conversion of the received wave signal RX ₁ input to the input terminal by the frequency converter 23 and a received signal RX _IF2 of intermediate frequency f _IF from the next stage repeater device _{20A 2} are transmitted to the input/output terminal, and a transmission signal TX _{IFT of intermediate frequency f IFT input} to the input _/ output terminal is transmitted to the second output terminal.
The fifth duplexer 41 appropriately distributes frequencies, that is, has a function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing the frequency f _LO , the intermediate frequency f _IF , and the intermediate frequency f _IFT .

When the transmission line connected to the base station 10A is a coaxial cable, the input/output terminal of the fifth duplexer 41 is connected to the coaxial cable by a connector.
When the transmission path is an antenna, the input/output terminals of the fifth duplexer 41 are connected to an antenna for receiving a local oscillation signal LO, an antenna for transmitting reception signals RX _IF1, RX _IFk , and an antenna for transmitting a transmission signal TX _IFT .
The input/output terminals of the fifth duplexer 41 may be divided into an input terminal and an output terminal in correspondence with the input/output terminals of the duplexer 13A in the base station 10A , and may be connected to different transmission paths.

The sixth duplexer 42 outputs a reception wave signal based on the received reception wave to the second duplexer 22, the local oscillation signal LO is distributed by the distributor 24A, the second local oscillation signal LO with frequency f _LO amplified by the second amplifier 26 is output to the next-stage relay device _20A2 , the reception signal RX _IF2 with intermediate frequency f _IF from the next-stage relay device _20A2 is output to the second duplexer 22, the transmission signal TX _IFT with intermediate frequency f _IFT from the fourth duplexer 32 is frequency-converted by the frequency converter 33 and output to the antenna a transmission wave signal with frequency f _TX amplified by the fourth amplifier 35, and the transmission signal TX _IFT with intermediate frequency f _IFT transmitted from the third duplexer 31 and amplified by the fifth amplifier 37 is output to the next-stage relay device _20A2 .

The sixth duplexer 42 has an input/output terminal, a first input terminal, a second input terminal and an output terminal, and the input/output terminals are connected to a transmission path connected to the next stage repeater device _20A2 , the first input terminal is connected to the output terminal of the second amplifier 26 constituting the local oscillation signal transmission path, the output terminal is connected to the input terminal of the second duplexer 22, and the second input terminal is connected to the output terminal of the fourth duplexer 32 .

In the sixth duplexer 42, a received wave signal of frequency f _RX due to the received received wave _RX1 input to the input/output terminal and a received signal RX _IF2 of intermediate frequency f _IF from the next stage repeater _20A2 are transmitted to the output terminal, a local oscillation signal LO of frequency f _LO input to the first input terminal is transmitted to the input/output terminal, and a transmitted wave signal of frequency f _TX and a transmitted signal TX _IFT of intermediate frequency f _IFT input to the second input terminal are transmitted to the input/output terminal.
The sixth duplexer 42 appropriately distributes frequencies, that is, has a function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing the frequency f _LO , the intermediate frequency f _IF , the intermediate frequency f _IFT , and the frequency f _TX .

The input/output terminal of the sixth duplexer 42 is connected to an antenna for receiving a transmission wave from a mobile station present within the receiving area of the first-stage relay device _20A1 .
The input/output terminal of the sixth duplexer 42 is connected to an antenna that transmits a transmission wave to a mobile station present within the transmission area of the first-stage relay device _20A1 .

When the transmission line connected to the next stage repeater _20A2 is a coaxial cable, the input/output terminal of the sixth duplexer 42 is connected to the coaxial cable by a connector.
When the transmission path is an antenna, the input/output terminals of the sixth duplexer 42 are connected to an antenna that transmits a local oscillation signal LO, an antenna that receives a reception signal RX _IFk , and an antenna that transmits a transmission signal TX _IFT .
The input/output terminals of the sixth duplexer 42 may be divided into an input terminal and an output terminal in correspondence with the input/output terminals of the second duplexer 22 in the next stage repeater _20A2 , and may be connected to different transmission paths.

The transmission wave signal generation path in the first-stage repeater device _20A1 frequency-converts a transmission signal TX _IFT of intermediate frequency f _IFT from the transmitter 14 of the base station 10A using a local oscillation signal LO of frequency f _LO from the base station 10 to a transmission wave signal of frequency f _TX which is higher than the local oscillation signal LO, and transmits the transmission wave TX to an antenna that transmits the transmission wave TX.

As shown in FIG. 5, the transmission wave signal generation path in the first-stage repeater _20A1 has a third duplexer 31, a fourth duplexer 32, a second frequency converter 33, and a fourth amplifier 35. The third duplexer 31 frequency-converts the transmission signal TX _IFT of intermediate frequency f _IFT from the fifth duplexer 41 into a transmission wave signal of frequency f _TX , which is higher than the intermediate frequency f _IFT , using the third local oscillation signal LO of frequency f _LO distributed by the distributor 24A by the second frequency converter 33. The frequency-converted transmission wave signal of frequency f _TX is amplified by the fourth amplifier 35 and then transmitted to the sixth duplexer 42 via the fourth duplexer 32.

The sixth duplexer 42 to which the transmission wave signal of frequency f _TX is input outputs the transmission wave signal of frequency f _TX to the antenna, which transmits the signal as a transmission wave TX of frequency f _TX to the corresponding transmission area.
The relationship between the frequency f _TX and the intermediate frequency f _IFT is f _TX =f _IFT +f _LO .

The transmission signal transmission path in the first-stage repeater _20A1 transmits a transmission signal TX _IFT of intermediate frequency f _IFT from the transmitter 14 of the base station 10A to a transmission path connected to the next-stage repeater _20A2 .
As shown in FIG. 5 , the transmission signal transmission path in the first-stage repeater 20A- ₁ has a third duplexer 31, a fourth duplexer 32, and a fifth amplifier 37. The third duplexer 31 amplifies a transmission signal TX _IFT of intermediate frequency f _IFT from a fifth duplexer 41 by the fifth amplifier 37, and then transmits the amplified signal to a sixth duplexer 42 via the fourth duplexer 32.
The sixth duplexer 42 transmits a transmission signal TX _IFT of an intermediate frequency f _IFT to a transmission line connected to the relay device 20A ₂ at the next stage.

The third duplexer 31 is a frequency duplexer that receives a transmission signal TX _IFT of an intermediate frequency f _IFT from the fifth duplexer 41 and transmits the transmission signal TX _IFT to both the second frequency converter 33 and the fifth amplifier 37 .
The third duplexer 31 has a function of distributing the transmission signal TX _IFT of the intermediate frequency f _IFT to the second frequency converter 33 and the fifth amplifier 37 .

The third duplexer 31 has an input terminal, a first output terminal and a second output terminal, and the input terminal is connected to the second output terminal of the fifth duplexer 41, the first output terminal is connected to the input terminal of the second frequency converter 33, and the second output terminal is connected to the input terminal of the fifth amplifier 37.
A transmission signal TX _IFT of intermediate frequency f _IFT input to an input terminal of the third duplexer 31 is transmitted to the first output terminal and the second output terminal.
The third duplexer 31 has the function of a band-pass filter, a low-pass filter, or a high-pass filter.

The fourth duplexer 32 is a frequency duplexer, in which the second frequency converter 33 frequency converts the transmission signal TX _IFT having the intermediate frequency f _IFT , and transmits the transmission wave signal having the intermediate frequency f _TX amplified by the fourth amplifier 35 and the transmission signal TX _IFT having the intermediate frequency f _IFT from the fifth amplifier 37 to the sixth duplexer 42.
The fourth duplexer 32 has a first input terminal, a second input terminal and an output terminal, the first input terminal being connected to the output terminal of the fourth amplifier 35, the second input terminal being connected to the output terminal of the fifth amplifier 37, and the output terminal being connected to the input terminal of the sixth duplexer 42.

In the fourth duplexer 32, the transmission wave signal having the frequency f _TX input to the first input terminal is transmitted to the output terminal, and the transmission signal TX _IFT having the intermediate frequency f _IFT input to the second input terminal is transmitted to the output terminal.
The fourth duplexer 32 appropriately distributes frequencies, that is, has a function of a band-pass filter, a low-pass filter, or a high-pass filter for appropriately distributing the intermediate frequency f _IFT and the frequency f _TX .

5, signals are expressed by frequency, a subscript indicating the stage in the relay device 20A is added to the received wave RX input to the relay device 20A of each stage, and a subscript indicating the stage in the next stage relay device 20A is added to the received signal RX _IF from the next stage relay device 20A. Note that although subscripts are added, the frequency is the same.
In the following description, except in special cases, the subscripts indicating stages will be omitted to avoid complicating the explanation.

The repeater devices _20Ak from the second stage onwards have the same configuration as the repeater device _20A1 in the first stage, and as shown in FIG. 5, have a first duplexer 21, a second duplexer 22, a first frequency converter 23, a distributor 24A, and a first amplifier 25 to a third amplifier 27 as a receiving system, and a third duplexer 31, a fourth duplexer 32, a frequency converter 33, a distributor 24A, a fourth amplifier 35, a fifth amplifier 37, a fifth duplexer 41 and a sixth duplexer 42 as a transmitting system.

The transmission lines connecting adjacent repeater devices 20A are each a coaxial cable or an antenna, similar to the transmission line connecting the base station 10A and the first-stage repeater device _20A1 .
Each of the multiple relay devices 20A has an antenna that receives transmitted waves from mobile stations located within the corresponding receiving area as received waves RX, and the received waves RX received by the receiving antenna are input to the input/output terminal of the sixth duplexer 42.
In addition, each of the multiple relay devices 20A has an antenna that transmits a transmission wave to a mobile station located within the corresponding transmission area, and a transmission wave signal obtained by frequency-converting the transmission signal from the transmitter 14 in the base station 10A for the transmission wave transmitted by the transmission antenna is input to the input/output terminal of the sixth duplexer 42.

The fifth duplexer 41 of the repeater device 20A _k at the second or subsequent stage, like the fifth duplexer 41 of the repeater device 20A ₁ at the first stage, transmits the local oscillation signal LO of frequency f _LO input to the input/output terminal from the local oscillation signal transmission path in the repeater device 20A at the previous stage to the first output terminal, transmits the received wave signal RX IF of intermediate frequency f _IF obtained by frequency conversion by the frequency converter 23 of the received wave signal RX ₁ input to the input terminal and the received signal RX _IF of intermediate frequency f _IF from the repeater device 20A at the next stage to the input/output terminal, _and transmits the transmitted signal input to the input/output terminal from the transmission signal transmission path in the repeater device 20A at the previous stage to the second output terminal.

The sixth duplexer 42 of the repeater device 20A _k at the second or subsequent stages, like the sixth duplexer 42 of the repeater device 20A ₁ at the first stage, transmits to its output terminal a received wave signal of frequency f _RX resulting from the received received wave RX ₁ input to its input/output terminal and a received signal RX _IF of intermediate frequency f _IF from the repeater device 20A at the next stage, transmits to its input/output terminal a local oscillation signal LO of frequency f _LO input to its first input terminal, and transmits to its input/output terminal a transmitted wave signal of frequency f _TX and a transmitted signal TX _IFT of intermediate frequency f _IFT input to its second input terminal.

Like the first-stage repeater _20A1 , the repeater device 20Ak at the second stage _or later also includes a transmission wave signal generation path that receives a local oscillation signal LO of frequency f _LO from the local oscillation signal transmission path in the repeater device 20A at the previous stage and a transmission signal TX _IFT of intermediate frequency f _IFT from the transmission signal transmission path in the repeater device 20A at the previous stage, and frequency-converts the transmission signal TX _IFT using the local oscillation signal LO into a transmission wave signal of frequency f _TX higher than the intermediate frequency f _IFT and transmits the transmission wave to an antenna that transmits the transmission wave, and a transmission signal transmission path that transmits the transmission signal TX _IFT of intermediate frequency f _IFT from the transmission signal transmission path in the repeater device 20A at the previous stage to a transmission path connected to the repeater device 20A at the next stage.

The transmission wave signal generation path in the repeater device _20Ak at the second stage or later has a third duplexer 31, a fourth duplexer 32, a second frequency converter 33, and a fourth amplifier 35, similar to the transmission wave signal generation path in _the repeater device 20A1 at the first stage. The third duplexer 31 frequency-converts the transmission signal TX _IFT at intermediate frequency f _IFT from the fifth duplexer 41 into a transmission wave signal at frequency f _TX , which is a frequency higher than the intermediate frequency f _IFT , by using the third local oscillation signal LO at frequency f _LO distributed by the distributor 24A by the second frequency converter 33. The frequency-converted transmission wave signal at frequency f _TX is amplified by the fourth amplifier 35 and then transmitted to the sixth duplexer 42 via the fourth duplexer 32.

The transmission signal transmission path in the repeater device 20A _k at the second stage or later has a third duplexer 31, a fourth duplexer 32, and a fifth amplifier 37, similar to the transmission signal transmission path in the repeater device 20A ₁ at the first stage. The third duplexer 31 amplifies a transmission signal TX _IFT having an intermediate frequency f _IFT from the fifth duplexer 41 by the fifth amplifier 37, and then transmits the amplified signal to the sixth duplexer 42 via the fourth duplexer 32.
The final stage relay device 20A may not have a reception signal transmission path, may not have a path beyond the second amplifier 26 in the local oscillation signal transmission path, and may not have a transmission signal transmission path.

Next, the operation of the wireless communication system according to the second embodiment will be described.
The operation of the receiving system is the same as that of the wireless communication system according to the first embodiment, and therefore a description thereof will be omitted.
The local oscillation signal LO of frequency f _LO from the base station 10 is distributed to the fifth duplexer 41 in each relay device 20A and distributed by the distributor 24A into first to third local oscillation signals LO. The first local oscillation signal LO of frequency f _LO is output to the first frequency converter 23 constituting the received signal generation path. The second local oscillation signal LO of frequency f _LO is amplified by the second amplifier 26 constituting the local oscillation signal transmission path and then output from the sixth duplexer 42 via the transmission path to the next relay device 20A. The third local oscillation signal LO of frequency f _LO is output to the second frequency converter 33 constituting the transmission wave signal generation path.

That is, the local oscillation signal LO having the frequency f _LO from the local oscillator 12 in the base station 10A is transmitted in sequence in each relay device 20A through a local oscillation signal transmission path to the next relay device 20A, and is used in the first frequency converter 23 constituting the received signal generation path and the second frequency converter 33 constituting the transmitted wave signal generation path.
A local oscillator is not provided in each relay device 20A, and even in the transmission system, the local oscillation signal LO of frequency f _LO used in each relay device 20A is concentrated in the local oscillator 12 in the base station 10A . Therefore, by ensuring the frequency stability of the local oscillator 12 in the base station 10, the frequency stability in each relay device 20A can also be ensured, and high frequency stability can be obtained for the wireless communication system as a whole.

In each relay device 20 A, the transmission signal TX _IFT of the intermediate frequency f _IFT that is distributed to the fifth duplexer 41 and then to the third duplexer 31 is input to the second frequency converter 33 .
The second frequency converter 33 frequency-converts the transmission signal TX _IFT having the intermediate frequency f _IFT into a transmission wave signal having a frequency _{f TX (} =f _IFT +f _LO ), which is higher than the intermediate frequency f _IFT , using the third local oscillation signal LO having the frequency f LO distributed by the distributor 24A.
The transmission wave signal of frequency f _TX is amplified by the first amplifier 25 constituting the transmission wave signal generation path, and then passed through the fourth duplexer 32 and input to the antenna from the sixth duplexer 42, and is then transmitted from the antenna as a transmission wave to mobile stations present within the corresponding transmission area.

On the other hand, in each relay device 20A, a transmission signal TX IFT of intermediate frequency f IFT that is input to the input _terminal of the fifth amplifier 37 constituting the _transmission signal transmission path, distributed to the fifth duplexer 41, and further distributed to the third duplexer 31 is amplified by the fifth amplifier 37, passes through the fourth duplexer 32, and is output from the sixth duplexer 42 via the transmission path to the next-stage relay device 20A, and is finally transmitted to the final-stage relay device 20A.

That is, in each relay device 20A, the input transmission signal TX _IFT of the intermediate frequency f _IFT is frequency converted into a transmission wave signal of frequency f _TX in each relay device 20A and the transmission wave is transmitted from each relay device 20A. Therefore, the transmission signal TX _IFT input to each relay device _20A is transmitted through the transmission line connecting adjacent relay devices 20A and the transmission line connecting the base station 10A and the first-stage relay device 20A- ₁ while maintaining the low intermediate frequency f IFT. Therefore, the transmission loss in the transmission signal TX _IFT can be suppressed, and the transmission signal TX _IFT can be transmitted over a longer distance with small transmission loss.

The wireless communication system according to the second embodiment has the same effects as the wireless communication system according to the first embodiment in the receiving system, and further includes a transmission system including a transmission wave signal generation path for converting the transmission signal TX _IFT to a transmission wave signal of a frequency f _TX (=f _IFT +f _LO ) that is higher than the intermediate frequency f _IFT using the local oscillation signal LO of frequency f _LO from the local oscillator 12 in the base station 10A and the transmission signal TX _IFT of intermediate frequency f _IFT from the transmitter 14 in the base station 10A, and transmitting the converted transmission signal to an antenna that transmits the transmission wave, and a transmission signal transmission path for transmitting the transmission signal TX _IFT of intermediate frequency f _IFT from the _transmitter 14 to a transmission path connected to the relay device _20A in the next stage. Since _{the IFT} is transmitted sequentially to the next relay device 20A, by ensuring the frequency stability of the local oscillator 12 in the base station 10A, frequency stability can also be ensured in the transmission system in each relay device 20A, thereby obtaining high frequency stability for the entire wireless communication system.

Furthermore, since the transmission signal transmission path in the relay device 20A sequentially transmits the transmission signal TX _IFT of the intermediate frequency f _IFT to the relay device 20A of the next stage and then to the relay device 20A of the final stage, it is possible to suppress the transmission loss in the transmission signal TX _IFT , and the transmission signal TX _IFT can be transmitted over a longer distance with small transmission loss.

In the wireless communication system according to the second embodiment, a local oscillator _LO having a frequency fLO from the local oscillator 12 is used for both the receiving system and the transmitting system. However, a local oscillator for generating a local oscillator signal _LOT having a frequency _fLOT different from the frequency _fLOT of the receiving system for the transmitting system may be provided in the base station 10A, and in each relay device 20A, the second frequency converter 33 may use the local oscillator signal _LOT having a frequency _fLOT from the local oscillator in the base station 10A to frequency convert the transmission signal _TXIFT having an intermediate frequency _fIFT into a transmission wave signal having a frequency ( _fIFT + _fLOT ).

In this case, in each repeater device 20A, similar to the receiving system, a distributor may be provided that distributes the local oscillation signal _LOT of _frequency f to output one local oscillation signal _LOT of _frequency f to the second frequency converter 33 and output the other local oscillation signal LOT of _{frequency f} to the repeater device 20A of the next stage.

In this way, the frequencies f _LO and f _LOT of the local oscillation signals LO and _LOT in the receiving system and the transmitting system are different, so that the degree of freedom in frequency selection can be increased.
Furthermore, by ensuring frequency stability of the local oscillator for the transmission system in the base station 10A , frequency stability can also be ensured in the transmission system in each relay device 20A, and high frequency stability can be obtained for the entire wireless communication system.

Embodiment 3.
A wireless communication system according to the third embodiment will be described with reference to FIG.
The wireless communication system of embodiment 3 differs from the wireless communication system of embodiment 1 in that each relay device 20B is provided with a frequency multiplier 28 that multiplies one of the local oscillation signals LO from the distributor 24 and outputs it to the frequency converter 23, but is otherwise the same.
6, the same reference numerals as those in FIGS. 1 to 4 denote the same or corresponding parts.

The following description will focus on the differences from the wireless communication system according to the first embodiment.
The wireless communication system according to the second embodiment includes a base station 10 and a plurality of relay devices 20B ₁ , 20B _k cascade-connected to the base station 10, where k is an integer of 2 or more.
Relay device _20B1 indicates a first-stage relay device adjacent to the base station, and relay device _20Bk indicates a second-stage or subsequent relay device.

The base station 10 is the same as the wireless communication system according to the first embodiment, and includes a receiver 11, a local oscillator 12, and a duplexer 13, as shown in FIG.
A local oscillator 12 outputs a local oscillation signal LO having a frequency f _LO .
Each of the multiple relay devices _20B1 , _20Bk basically has the same configuration, and includes a first duplexer 21, a second duplexer 22, a frequency converter 23, a distributor 24, a frequency multiplier 28, and first to third amplifiers 25 to 27, as shown in FIG.

The frequency multiplier 28 multiplies the frequency of one of the local oscillation signals LO having a frequency _{f_LO} distributed from the distributor 24, and outputs it to the frequency converter as a local oscillation signal _{LO_H} having a frequency _{f_LOH} .
The relationship between the frequency _fLO and the frequency _fLOH is _fLOH = _mfLOH , where m is a number greater than 1, and _fLOH > _fLOH .

The frequency converter 23 frequency-converts the received wave signal of frequency f _RX due to the received wave RX received and transmitted by the second duplexer 22, into a received signal RX _IFL of intermediate frequency f _IFL , which is a frequency lower than the frequency f _RX , using a local oscillation signal LO _H of frequency f _LOH from the frequency multiplier 28.
The relationship between the frequency f _RX and the intermediate frequency f _IFL is f _IFL = f _RX - f _LOH = f _RX - mf _LO < f _RX - f _LO .

Therefore, the received wave signal by the received wave RX received at each relay device 20 is frequency-converted by the received signal generation path to a frequency lower than the frequency f _RX of the received _wave signal, and the received signal RX _IFL is transmitted to the previous relay device 20B in sequence by the received signal transmission path in the previous relay device 20B and transmitted to the base station 10. Therefore, the transmission loss in the received signal RX _IFL by the transmission path connecting the base station ₁₀ and the first relay device 20B1 and the transmission path connecting the adjacent relay devices 20B can be further reduced, and the received signal RX _IFL can be transmitted over a longer distance with less transmission loss.

Next, the operation of the wireless communication system according to the third embodiment will be described.
As described above, the wireless communication system of embodiment 3 differs from the wireless communication system of embodiment 1 in that each relay device 20B is provided with a frequency multiplier 28 that multiplies one of the local oscillation signals LO from the distributor 24 and outputs it to the frequency converter 23. All other points are the same, so the operation of the wireless communication system of embodiment 2 is basically the same as that of the wireless communication system of embodiment 1, and will only be briefly described.

A local oscillation signal LO of frequency f _LO from a local oscillator 12 in the base station 10 is distributed by a duplexer 13 and transmitted to the first stage repeater _20B1 via a transmission line.
The local oscillation signal LO of frequency f _LO input to the first-stage relay device 20B ₁ is transmitted in sequence to the next-stage relay device 20B via the local oscillation signal transmission path in each relay device 20B, similar to the wireless communication system according to the first embodiment.

In each relay device 20B, the input local oscillation signal LO of frequency f _LO is distributed by distributor 24, and one of the distributed local oscillation signals LO of frequency f _LO is multiplied by frequency multiplier 28 and input to frequency converter 23 as a local oscillation signal LO _H of frequency f _LOH .
On the other hand, in each relay device 20B, when a transmission wave from a mobile station present within the corresponding receiving area is received as a received wave, the received wave signal of frequency f _RX due to the received received wave _RX is frequency converted by the frequency converter 23 into a received signal RX _IFL of intermediate frequency f _IFL (= f _RX - f _LOH ) using a local oscillation signal LO _H of frequency f LOH.

In addition, in each relay device 20 that receives a reception signal RX _IFL of intermediate frequency f _IFL from the next-stage relay device 20B, the reception signal RX _IFL of intermediate frequency f _IFL is transmitted in sequence to the previous-stage relay device 20B via a reception signal transmission path, and is finally transmitted to the base station 10.
In the base station 10 , a received signal RX _IFL of an intermediate frequency f _IFL is distributed by a duplexer 13 and input to a receiver 11 .

As described above, the wireless communication system according to the third embodiment has the same effects as the wireless communication system according to the first embodiment. In addition, the frequency multiplier 28 multiplies the frequency of the local oscillation signal _LO having a frequency fLO and inputs the multiplied signal to the frequency converter 23. The frequency converter 23 converts the received wave signal having a frequency _fRX received by the received wave _RX using the local oscillation signal _LOH having a frequency fLOH into a received signal _RXIFL having an intermediate frequency _fIFL (= _fRX - _fLOH ). The received signal is then relayed to the relay device 20B in sequence at the low intermediate frequency _fIFL to reach the base station 10. This makes it possible to further reduce transmission loss in the received signal _RXIFL through the transmission path connecting the base station ₁₀ and the first relay device 20B1 and the transmission path connecting the adjacent relay devices 20B. This makes it possible to transmit the received signal _RXIFL over a longer distance with less transmission loss.

In the wireless communication system according to the third embodiment, the frequency of the local oscillation signal LO from the local oscillator 12 is set to f _LO . However, by setting the frequency of the local oscillation signal LO from the local oscillator 12 to a frequency lower than f _LO and increasing the multiplication by the frequency multiplier 28, the local oscillation signal LO and the received signal RX _IFL transmitted through the transmission path connecting the base station 10 and the first-stage relay device 20B- ₁ and the transmission path connecting the adjacent relay devices 20 can be set to a lower frequency, and the local oscillation signal LO and the received signal RX _IFL can be transmitted over a longer distance with less transmission loss.

In addition, in the wireless communication system of embodiment 3, the idea of providing a frequency multiplier 28 in relay device 20B that multiplies one of the local oscillation signals LO from distributor 24 and outputs it to frequency converter 23 may be applied not only to the receiving system in the wireless communication system of embodiment 2, but also to the transmitting system.

That is, in the wireless communication system according to the second embodiment, the received signal generation path may have a first frequency multiplier that multiplies the second local oscillation signal LO of frequency _fLO distributed from distributor 24 and outputs the local oscillation signal _LOH of frequency _fLOH (= _mfLO ) to the first frequency converter 23, and the transmitted wave signal generation path may be provided with a second frequency multiplier that multiplies the third local oscillation signal LO of frequency _fLOH distributed from distributor 24A and outputs the local oscillation signal _LOH of frequency _fLOH (= _mfLO ) to the second frequency converter 33.
Although the first frequency multiplier and the second frequency multiplier perform the same multiplication, they may perform different multiplications.

Embodiment 4.
A wireless communication system according to a fourth embodiment will be described with reference to FIG.
The wireless communication system according to the fourth embodiment is different from the wireless communication system according to the first embodiment in that a leaky coaxial cable (LCX: Leaky Coaxial Cable) 100 is used as a transmission line connecting the base station 10 and the first-stage relay device _20-1 and as a transmission line connecting adjacent relay devices 20, but is the same in other respects.
6, the same reference numerals as those in FIGS. 1 to 4 denote the same or corresponding parts.

The following description will focus on the differences from the wireless communication system according to the first embodiment.
The input/output terminals of the duplexer 13 are connected to the leaky coaxial cable 100 by connectors.
In each repeater 20, the input/output terminals of the first duplexer 21 are connected to the leaky coaxial cable 100 via a connector, and the input/output terminals of the second duplexer 22 are connected to the leaky coaxial cable 100 via a connector.

Since the input/output terminals of the second duplexer 22 are connected to the leaky coaxial cable 100, each relay device 20 does not require an antenna to receive the transmitted waves from the mobile station located within the corresponding receiving area as received waves RX, and receives the transmitted waves from the mobile station located within the corresponding receiving area as received waves RX via the leaky coaxial cable 100 connected to the input/output terminals of the second duplexer 22.

The leaky coaxial cable 100 has a characteristic that the lower the frequency, the less the signal passing through it leaks, and the smaller the transmission loss.
Therefore, a low frequency that is unlikely to leak from the leaky coaxial cable 100 is selected as the frequency f _LO of the local oscillation signal LO from the local oscillator 12 in the base station 10 and the intermediate frequency f _IF of the reception signal RX _IF obtained by frequency-converting the reception wave signal from the reception wave RX ₁ in each relay device.

The configuration and operation of the base station 10 and each relay device 20 in the wireless communication system of embodiment 4 are substantially the same as the configuration and operation of the base station 10 and each relay device 20 in the wireless communication system of embodiment 1, so description thereof is omitted.

The wireless communication system according to the fourth embodiment has the same effects as the wireless communication system according to the first embodiment, and also has the following effects.
That is, since the local oscillation signal LO from the local oscillator 12 in the base station 10 is transmitted to the first-stage repeater _20-1 via the leaky coaxial cable 100, a lower frequency f _LO can be selected in accordance with the leaky coaxial cable 100, and longer-distance transmission can be performed with less transmission loss. Furthermore, since leakage of the local oscillation signal LO from the leaky coaxial cable 100 is suppressed and radiation into space can be substantially prevented, the frequency utilization efficiency does not decrease.

In each repeater, the local oscillation signal LO of frequency f _LO transmitted to the next repeater 20 via the local oscillation signal transmission path is also selected to a lower frequency f _LO in accordance with the leaky coaxial cable 100, and since the signal is transmitted through the leaky coaxial cable 100 connecting adjacent repeaters 20, longer distance transmission can be achieved with less transmission loss.

In addition, the intermediate frequency f _IF of the received signal RX _IF , which is obtained by frequency-converting the received wave signal by the received wave RX ₁ in each repeater, can also be set to a lower frequency f _LO in accordance with the leaky coaxial cable 100. Since the signal is transmitted through the leaky coaxial cable 100 at the low intermediate frequency f _IF and then relayed to the repeater 20 to reach the base station 10, a longer distance transmission can be achieved with less transmission loss.

In addition, in the wireless communication system according to the fourth embodiment, compared to the wireless communication system according to the first embodiment, the idea of using the leaky coaxial cable 100 as the transmission path connecting the base station 10 and the first-stage relay device _20-1 and the transmission path connecting between adjacent relay devices 20 may be applied to the wireless communication system according to the second embodiment and the wireless communication system according to the third embodiment.
That is, in the wireless communication system according to the second embodiment, the leaky coaxial cable 100 may be used as a transmission line connecting the base station 10 and the first-stage relay device _20A1 and as a transmission line connecting adjacent relay devices 20A.
In addition, in the wireless communication system according to the third embodiment, the leaky coaxial cable 100 may be used as a transmission line connecting the base station 10 and the first-stage relay device _20B1 and as a transmission line connecting between adjacent relay devices 20B.

In addition, any combination of the embodiments may be used, or any component of each embodiment may be modified, or any component of each embodiment may be omitted.

The wireless communication system disclosed herein is suitable for use as a wireless communication system in which a transmitter mounted on a railway vehicle or automobile serves as a mobile station and relays wireless communication signals for trains or road traffic.

10 base station, 11 receiver, 12 local oscillator, 13, 13A duplexer, 14 transmitter, ₂₀ , _201, 20k, _{20A ,} 20A1, 20Ak, 20B, _20B1 , _20Bk relay device, 21 first duplexer, 22 second duplexer, 23 frequency converter, 24, 24A distributor, 25-27 first amplifier to third amplifier, 28 frequency multiplier, 31 third duplexer, 32 fourth duplexer, 33 frequency converter, 35 fourth amplifier, 37 fifth amplifier, 41 fifth duplexer, 42 sixth duplexer, 100 leaky coaxial cable.

Claims (13)

The present invention comprises a base station and a plurality of relay devices connected in series to the base station , each of which receives a transmission wave from a mobile station as a received wave ,
The base station includes a receiver, a local oscillator that outputs a local oscillation signal, and a duplexer that transmits the local oscillation signal from the local oscillator to a transmission line and transmits a received signal from the transmission line to the receiver. Among the plurality of relay devices, a relay device adjacent to the base station includes:
a reception signal generation path that receives a local oscillation signal from the base station, and uses the local oscillation signal to frequency-convert a reception wave signal based on an input reception wave into a reception signal having a frequency lower than that of the reception wave signal, and transmits the reception signal to a transmission path connected to the base station;
a local oscillation signal transmission path for transmitting a local oscillation signal from the base station to a transmission path connected to a relay device at a next stage;
a reception signal transmission path for transmitting a reception signal from a next-stage relay device to a transmission path connected to the base station,
Among the plurality of relay devices, a relay device other than the relay device adjacent to the base station,
a reception signal generation path that receives a local oscillation signal from a local oscillation signal transmission path in a previous stage relay device , and uses the local oscillation signal to frequency-convert a reception wave signal based on an input reception wave into a reception signal having a frequency lower than that of the reception wave signal, and transmits the reception signal to a transmission path connected to the previous stage relay device;
a local oscillation signal transmission path that transmits a local oscillation signal from the local oscillation signal transmission path in the relay device at a previous stage to a transmission path connected to the relay device at a next stage;
a reception signal transmission path that transmits a reception signal from a next-stage relay device to a transmission path connected to a previous-stage relay device,
Wireless communication system. each of the plurality of relay devices includes a first duplexer, a second duplexer, a frequency converter, and a distributor;
the received signal generation path has the first duplexer, the second duplexer, and the frequency converter, a received wave signal due to a received wave received as a received wave from a transmission wave from a mobile station is received by the second duplexer, and the frequency converter converts the frequency of the received wave signal due to the received wave received and transmitted into a received signal using one of the local oscillation signals distributed from the distributor, and outputs the frequency-converted received signal via the first duplexer;
the local oscillation signal transmission path has the first duplexer, the second duplexer, and the distributor, the distributor distributes the local oscillation signal received and transmitted by the first duplexer, and outputs the other distributed local oscillation signal via the second duplexer;
the reception signal transmission path has the first duplexer and the second duplexer, and outputs a reception signal from a next-stage relay device, which is received and transmitted by the second duplexer, via the first duplexer;
2. The wireless communication system according to claim 1. The wireless communication system according to claim 2, wherein the received signal generation path includes a frequency multiplier that multiplies one of the local oscillation signals distributed from the distributor and outputs the multiplied signal to the frequency converter. the base station comprises a transmitter;
Each of the plurality of relay devices includes an antenna for transmitting a transmission wave,
A relay device adjacent to the base station
a transmission wave signal generating path that converts a transmission signal from the transmitter into a transmission wave signal having a higher frequency than the local oscillation signal from the base station by using the local oscillation signal from the base station, and transmits the converted signal to an antenna that transmits the transmission wave;
a transmission signal transmission path for transmitting a transmission signal from the transmitter to a transmission path connected to a relay device at a next stage,
A relay device other than the relay device adjacent to the base station,
a transmission wave signal generation path that converts a transmission signal from a transmission signal transmission path in a previous stage relay device into a transmission wave signal having a higher frequency than the transmission signal by using a local oscillation signal from a local oscillation signal transmission path in the previous stage relay device, and transmits the converted transmission wave to an antenna that transmits the transmission wave;
A transmission signal transmission path that transmits a transmission signal from a transmission signal transmission path in a previous stage relay device to a transmission path connected to a next stage relay device,
2. The wireless communication system according to claim 1. each of the plurality of relay devices includes a first duplexer, a second duplexer, a first frequency converter, a distributor, a third duplexer, a fourth duplexer, a second frequency converter, a fifth duplexer, and a sixth duplexer;
the received signal generation path has the first duplexer, the second duplexer, and the first frequency converter, a received wave signal due to a received wave received as a received wave from a transmission wave from a mobile station is received by the sixth duplexer, the received wave signal due to a received wave transmitted via the second duplexer is frequency-converted into a received signal by the first frequency converter using a first local oscillation signal distributed from the distributor, and the frequency-converted received signal is output via the first duplexer and the fifth duplexer;
the local oscillation signal transmission path has the first duplexer, the second duplexer, and the distributor, the distributor distributes the local oscillation signal received and transmitted by the first duplexer via the fifth duplexer, and outputs the distributed second local oscillation signal via the second duplexer and the sixth duplexer;
the received signal transmission path has the first duplexer and the second duplexer, and outputs a received signal from a next-stage relay device, the received signal being received by the second duplexer via the sixth duplexer and transmitted by the second duplexer, via the first duplexer and the fifth duplexer;
the transmission wave signal generation path has the third duplexer, the fourth duplexer, and the second frequency converter, and the second frequency converter converts the frequency of a transmission signal received by the third duplexer via the fifth duplexer into a transmission wave signal using a third local oscillation signal distributed from the distributor, and outputs the transmission wave signal via the fourth duplexer and the sixth duplexer;
the transmission signal transmission path has the third duplexer and the fourth duplexer, and outputs a transmission signal received by the third duplexer via the fifth duplexer via the fourth duplexer and the sixth duplexer;
5. The wireless communication system according to claim 4. the reception signal generation path includes a first frequency multiplier that multiplies the second local oscillation signal distributed from the distributor and outputs the multiplied signal to the first frequency converter;
6. The wireless communication system according to claim 5, wherein the transmission wave signal generating path has a second frequency multiplier that multiplies the third local oscillation signal distributed from the distributor and outputs the multiplied signal to the second frequency converter. 7. The wireless communication system according to claim 1, wherein the transmission line connecting the base station and a receiving signal generation path in a relay device adjacent to the base station, the transmission line connecting a previous stage local oscillation signal transmission path in an adjacent relay device among the plurality of relay devices and a receiving signal generation path in a next stage relay device, the transmission line connecting the receiving signal transmission path in a relay device adjacent to the base station and the base station, and the transmission line connecting the receiving signal transmission paths in adjacent relay devices among the plurality of relay devices are each a coaxial cable. 7. The wireless communication system according to claim 1, wherein the transmission path connecting the base station and a receiving signal generation path in a relay device adjacent to the base station, the transmission path connecting a previous stage local oscillation signal transmission path in an adjacent relay device among the plurality of relay devices and a receiving signal generation path in a next stage relay device, the transmission path connecting the receiving signal transmission path in a relay device adjacent to the base station and the base station, and the transmission path connecting the receiving signal transmission paths in adjacent relay devices among the plurality of relay devices are each an antenna. The wireless communication system according to any one of claims 1 to 6, wherein the transmission line connecting the base station and the reception signal generation path in the relay device adjacent to the base station, the transmission line connecting the local oscillation signal transmission path of the previous stage in the adjacent relay device among the plurality of relay devices and the reception signal generation path in the next stage relay device, the transmission line connecting the reception signal transmission path in the relay device adjacent to the base station and the base station, and the transmission line connecting the reception signal transmission paths of the adjacent relay devices among the plurality of relay devices are each a leaky coaxial cable. A relay device of a wireless communication system that receives a transmission wave from a mobile station as a received wave,
The present invention has a first duplexer, a second duplexer, a frequency converter, and a distributor,
the first duplexer receives a local oscillation signal output from a local oscillator of a base station, outputs the local oscillation signal to the distributor, outputs a reception signal obtained by frequency-converting a reception wave signal based on a reception wave from the frequency converter, and outputs a reception signal from a next-stage relay device from the second duplexer;
the second duplexer receives a received wave signal based on a received wave received as a received wave from a transmission wave from a mobile station, outputs the received wave signal based on the received wave to the frequency converter, outputs the other locally oscillated signal obtained by distributing the locally oscillated signal by the distributor to a next-stage relay device, and outputs a received signal from the next-stage relay device to the first duplexer;
the frequency converter converts the frequency of the received wave signal from the second duplexer into a received signal having a frequency lower than the frequency of the received wave signal from the received wave , using one of the local oscillation signals to which the local oscillation signal is distributed by the distributor, and outputs the converted received signal to the first duplexer.
A repeater for wireless communication systems. The relay device of the wireless communication system according to claim 10, further comprising a frequency multiplier that multiplies one of the local oscillation signals distributed from the distributor and outputs the multiplied signal to the frequency converter. A relay device of a wireless communication system that receives a transmission wave from a mobile station as a received wave,
a first duplexer, a second duplexer, a first frequency converter, a distributor, a third duplexer, a fourth duplexer, a second frequency converter, a fifth duplexer and a sixth duplexer;
the fifth duplexer receives a local oscillation signal output from a local oscillator of a base station and a transmission signal output from a transmitter of the base station, outputs the local oscillation signal to the distributor, outputs the transmission signal to the third duplexer, and outputs the reception signal from the first duplexer;
the sixth duplexer receives a received wave signal due to a received wave received as a received wave from a transmission wave from a mobile station , outputs the received wave signal due to the received wave to the second duplexer, outputs a received signal from a next-stage relay device to the second duplexer, outputs a second locally oscillated signal obtained by distributing the locally oscillated signal by the distributor to the next-stage relay device, outputs a transmission signal from the fourth duplexer to the next-stage relay device, and outputs a transmission wave signal from the fourth duplexer;
the first duplexer outputs to the fifth duplexer a reception signal obtained by frequency-converting a reception wave signal based on a reception wave from the frequency converter, and outputs to the fifth duplexer a reception signal from a next-stage relay device from the second duplexer;
the second duplexer outputs a reception wave signal based on the reception wave from the sixth duplexer to the frequency converter, and outputs a reception signal from a next-stage relay device from the sixth duplexer to the first duplexer;
the first frequency converter converts the frequency of the received wave signal from the second duplexer into a received signal having a frequency lower than the frequency of the received wave signal from the received wave, using a first local oscillation signal obtained by distributing the local oscillation signal by the distributor, and outputs the converted signal to the first duplexer;
the second frequency converter frequency-converts the transmission signal from the third duplexer to a transmission wave signal having a higher frequency than the frequency of the transmission signal by using a third local oscillation signal obtained by distributing the local oscillation signal by the distributor, and outputs the converted transmission wave signal to the sixth duplexer.
A repeater for wireless communication systems. a first frequency multiplier that multiplies the second local oscillation signal distributed from the distributor and outputs the multiplied signal to the first frequency converter;
13. The relay device of a wireless communication system according to claim 12, further comprising a second frequency multiplier that multiplies the third local oscillation signal distributed from said distributor and outputs the multiplied signal to said second frequency converter.

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