Wireless apparatus and wireless communication method

Abstract

This wireless apparatus is provided between a carrier wave generator that generates a carrier wave and a master wireless device that communicates with a wireless base station, and is connected to each of the carrier wave generator and the master wireless device via an optical fiber. The wireless apparatus comprises: a first conversion unit that converts an optical signal including the carrier wave transmitted from the carrier wave generator via the optical fiber into an electric signal to acquire the carrier wave; a frequency modulator that uses the carrier wave to frequency-modulate a wireless signal transmitted from a wireless terminal; and a second conversion unit that converts the frequency-modulated wireless signal into an optical signal and outputs the optical signal to the master wireless device via the optical fiber.　

Description

Wireless devices and wireless communication methods

[0001] The present invention relates to a wireless device and a wireless communication method.

[0002] Structures such as tunnels and buildings have properties that shield radio waves, which can interfere with the transmission and reception of radio waves between wireless terminals and base stations located inside and outside these structures. Areas where radio waves are difficult to reach, i.e., areas where it is difficult to transmit and receive radio waves with base stations, are called dead zones. The process of enabling wireless terminals in areas that were originally dead zones to transmit and receive radio waves with base stations is called dead zone countermeasures. One method of dead zone countermeasures is to relay radio waves from base stations into dead zones and also relay radio waves from within dead zones to base stations (see, for example, Non-Patent Document 1).

[0003] Figure 5 shows an example of a system configuration for addressing dead zones. The system shown in Figure 5 comprises a master device (also referred to as a master radio device in this document), optical fibers, and one or more slave devices (one or more slave devices are referred to as one slave radio device or radio device in this document). The master device and each slave device are connected via optical fibers. Radio Over Fiber (RoF) transmission technology is used between the master device and each slave device. The master device is installed outside the dead zone (a tunnel in Figure 5), and each slave device is installed inside the dead zone. The direction from a slave device to the master device is considered the upstream direction, and the direction from the master device to a slave device is considered the downstream direction.

[0004] Here, the flow of a signal path in the downlink direction will be described. A radio wave (downlink signal) transmitted from a radio base station is received by an antenna provided in a master device installed outside the dead zone. After converting the radio wave received via the antenna into an electrical signal, the master device converts it into an optical signal by an E / O (E / O converter). Then, the master device sends the optical signal to each slave device via an optical fiber. Each slave device converts the optical signal sent from the master device into an electrical signal by an O / E (O / E converter), and then radiates a radio wave into the dead zone via an antenna installed in the dead zone. This allows a radio terminal located in the dead zone to receive the radio wave transmitted from the radio base station located outside the dead zone.

[0005] Next, the flow of a signal path in the uplink direction will be described. A radio wave (uplink signal) transmitted from a radio terminal is received by an antenna provided in a slave device installed in the dead zone. After converting the radio wave received via the antenna into an electrical signal, the slave device converts it into an optical signal by E / O. Then, the slave device sends the optical signal to the master device via an optical fiber. After converting the optical signal sent from the slave device into an electrical signal by O / E, the master device radiates a radio wave to the outside of the dead zone via an antenna installed outside the dead zone. This allows a radio base station located outside the dead zone to receive the radio wave transmitted from the radio terminal located in the dead zone.

[0006] Here, optical fibers, slave devices, and antennas equipped on the slave devices may be required in multiple quantities depending on the shape of the structure, such as in long tunnels or multi-story buildings. When multiple quantities are required, as shown in Figure 6, it is conceivable to use a single-frequency network (SFN) that constitutes one area by having the antennas equipped on each slave device use the same frequency and transmit and receive the same signal (see, for example, Non-Patent Document 2). Wireless terminals belonging to a single-frequency network are controlled by the wireless base station so that they do not use the same subcarrier simultaneously (see, for example, Non-Patent Document 3). Here, Figure 7 is a conceptual diagram representing the allocation of wireless subcarriers and transmission times, and each of the white rectangular sections (sections without hatching) shown in Figure 7 is called a resource block. Here, wireless terminals belonging to a single-frequency network are assigned different resource blocks so that they do not use the same subcarrier simultaneously.

[0007] Suganuma, et al., "Tunnel Booster for 1.5GHz Digital Mobile Communication System," NTT DOCOMO Technical Journal, Vol. 2, No. 2. Takada, et al., "Technology for Improving Characteristics in High-Speed ​​Mobile Environments in LTE-Advanced Release 14," NTT DOCOMO Technical Journal, Vol. 25, No. 3. Okubo, et al., "Overview of LTE Wireless System for Achieving High Speed, High Capacity, and Low Latency," NTT DOCOMO Technical Journal, Vol. 19, No. 1.

[0008] As shown in Figure 5, in conventional dead zone countermeasures, when the dead zone is long (wide), such as in long tunnels, many sub-devices are required. Furthermore, the parent device must be connected to each sub-device individually via optical fiber. As a result, the longer the dead zone, the longer the optical fiber needed to connect to the sub-device located furthest from the parent device becomes. In addition, as the number of sub-devices increases with the length of the dead zone, the total number of optical fibers required for individual connections also increases, which presents a problem.

[0009] In view of the above circumstances, the present invention aims to provide a technology that can implement measures to address dead zones in uplink communication while suppressing the total number and length of optical fibers.

[0010] One aspect of the present invention is a wireless device provided between a carrier wave generator that generates a carrier wave and a master wireless device that communicates with a wireless base station, and connected to the carrier wave generator and the master wireless device by optical fiber, the wireless device comprising: a first conversion unit that converts an optical signal including a carrier wave transmitted from the carrier wave generator via the optical fiber into an electrical signal to acquire the carrier wave; a frequency modulator that frequency modulates a wireless signal transmitted from a wireless terminal using the carrier wave; and a second conversion unit that converts the frequency modulated wireless signal into an optical signal and outputs it to the master wireless device via the optical fiber.

[0011] One aspect of the present invention is a wireless communication method performed by a wireless device provided between a carrier wave generator that generates a carrier wave and a master wireless device that communicates with a wireless base station, and connected to the carrier wave generator and the master wireless device by optical fiber, the method comprising: converting an optical signal including a carrier wave transmitted from the carrier wave generator via the optical fiber into an electrical signal to obtain the carrier wave; frequency modulating a wireless signal transmitted from a wireless terminal using the carrier wave; converting the frequency modulated wireless signal into an optical signal and outputting it to the master wireless device via the optical fiber.

[0012] This invention makes it possible to implement measures to address dead zones while suppressing the total number and length of optical fibers.

[0013] This figure shows an example configuration of the wireless communication system 100 in the first embodiment. This is a flowchart showing the processing flow performed by the slave device 20 in the first embodiment. This figure shows an example configuration of the wireless communication system 100a in the second embodiment. This figure shows an example configuration of the wireless communication system 100b in the third embodiment. This figure shows an example system configuration for dead zone countermeasures. This figure illustrates a conventional single-frequency network. This is a conceptual diagram showing the allocation of wireless subcarriers and transmission times.

[0014] One embodiment of the present invention will be described below with reference to the drawings.

[0015] (First Embodiment) Figure 1 shows an example of the configuration of a wireless communication system 100 in the first embodiment. The wireless communication system 100 is a system for dealing with dead zones. The wireless communication system 100 comprises a carrier generator 10, a slave device 20, and a master device 30. The carrier generator 10 and the slave device 20, and the slave device 20 and the master device 30 are connected by optical fiber. In addition, optical fiber wireless (RoF) transmission technology is used between the carrier generator 10 and the slave device 20, and between the slave device 20 and the master device 30. Here, the carrier generator 10 is installed either inside or outside a dead zone (for example, a tunnel or a building), the slave device 20 is installed inside a dead zone, and the master device 30 is installed outside a dead zone. In the following description, the direction from the carrier generator 10 to the master device 30 is referred to as the upward direction, and the direction from the master device 30 to the carrier generator 10 is referred to as the downward direction.

[0016] The carrier wave generator 10 generates a carrier wave. The slave device 20 performs wireless communication with a terminal device located within a dead zone. The slave device 20 sends an optical signal containing the radio wave (radio signal) transmitted from the terminal device to the master device 30. The master device 30 transmits the optical signal sent from the slave device 20 wirelessly to a wireless base station (not shown).

[0017] [Configuration of Carrier Wave Generator 10] The carrier wave generator 10 comprises an oscillator 11 and an E / O unit 12. The oscillator 11 generates a carrier wave. The E / O unit 12 converts the carrier wave generated by the oscillator 11 into an optical signal. That is, the E / O unit 12 superimposes the carrier wave onto the optical signal.

[0018] [Configuration of the sub-device 20] The sub-device 20 comprises an O / E unit 21, an Armstrong-type frequency modulator 22, an E / O unit 23, and an antenna 24. The O / E unit 21 converts the optical signal transmitted from the carrier wave generator 10 into an electrical signal. As a result, the O / E unit 21 obtains the carrier wave required by the Armstrong-type frequency modulator 22. The Armstrong-type frequency modulator 22 performs frequency modulation using the carrier wave on the radio signal (modulated signal) received by the antenna 24. As a result, the Armstrong-type frequency modulator 22 generates a frequency-modulated wave (FM-modulated wave). The E / O unit 23 converts the frequency-modulated wave generated by the Armstrong-type frequency modulator 22 into an optical signal. That is, the E / O unit 23 superimposes the frequency-modulated wave onto the optical signal. The antenna 24 receives radio waves transmitted from a wireless terminal (not shown). The O / E unit 21 is one embodiment of the first conversion unit. The E / O unit 23 is one embodiment of the second conversion unit.

[0019] Next, the configuration of the Armstrong frequency modulator 22 will be described. The Armstrong frequency modulator 22 comprises a distribution unit 221, a phase adjustment unit 222, an attenuator 223, an integrator 224, a multiplication unit 225, and an addition unit 226. The distribution unit 221 divides the carrier wave acquired by the O / E unit 21 into two. As a result, the distribution unit 221 outputs the carrier wave to the phase adjustment unit 222 and the addition unit 226. The phase adjustment unit 222 rotates the input carrier wave by 90 degrees in phase and then outputs it to the attenuator 223. The attenuator 223 attenuates the signal level (amplitude) of the input carrier wave to an appropriate level. The integrator 224 integrates the input modulated signal and outputs the integrated modulated signal to the multiplication unit 225. The multiplier 225 multiplies the carrier wave output from the attenuator 223 with the modulated signal integrated by the integrator 224, and outputs the multiplied signal to the adder 226. The adder 226 combines the signal output from the multiplier 225 with the carrier wave distributed by the distributor 221. As a result, the adder 226 obtains a frequency-modulated wave (FM modulated wave).

[0020] [Configuration of the Master Device 30] The master device 30 comprises an O / E unit 31 and a frequency detector (FM detector) 32. The O / E unit 31 converts the optical signal transmitted from the slave device 20 into an electrical signal. The FM detector 32 extracts the radio signal received by the slave device 20 by FM detection of the electrical signal. The radio signal extracted by the FM detector 32 is output as a radio wave from an antenna (not shown) connected to the master device 30 to a radio base station (not shown).

[0021] Figure 2 is a flowchart showing the processing flow of the sub-device 20 in the first embodiment. The antenna 24 receives radio waves transmitted from a wireless terminal (not shown) (step S101). The antenna 24 converts the received radio waves into an electrical signal (modulated signal) and outputs it to the integrator 224. The integrator 224 performs integration processing on the electrical signal (modulated signal) output from the antenna 24 (step S102). The integrator 224 outputs the integrated electrical signal (modulated signal) to the multiplier 225.

[0022] The O / E unit 21 converts the optical signal sent from the carrier wave generator 10 into an electrical signal (step S103). As a result, the O / E unit 21 acquires the carrier wave. The O / E unit 21 outputs the acquired carrier wave to the distribution unit 221. The distribution unit 221 divides the carrier wave output from the O / E unit 21 into two (step S104). The carrier waves divided by the distribution unit 221 are input to the phase adjustment unit 222 and the adder unit 226. The phase adjustment unit 222 rotates the input carrier wave by 90 degrees and then outputs it to the attenuator 223 (step S105). The attenuator 223 attenuates the signal level (amplitude) of the input carrier wave to an appropriate level (step S106). The attenuator 223 outputs the carrier wave with the attenuated signal level (amplitude) to the multiplier unit 225.

[0023] The multiplier 225 multiplies the carrier wave, whose signal level (amplitude) output from the attenuator 223 has been attenuated, with the modulated signal, which has been integrated by the integrator 224, and outputs the multiplied signal to the adder 226 (step S107). The adder 226 combines (adds) the signal output from the multiplier 225 with the carrier wave distributed by the distributor 221 (step S108). As a result, the adder 226 obtains a frequency modulated wave. The adder 226 outputs the obtained frequency modulated wave to the E / O unit 23. The E / O unit 23 converts the frequency modulated wave output from the adder 226 into an optical signal (step S109). The E / O unit 23 sends the optical signal to the master device 30 via an optical fiber.

[0024] According to the wireless communication system 100 configured as described above, the slave device 20 includes an O / E unit 21 that converts an optical signal including a carrier wave transmitted from the carrier wave generator 10 via an optical fiber into an electrical signal to acquire the carrier wave, an Armstrong type frequency modulator 22 that frequency modulates a wireless signal transmitted from a wireless terminal (not shown) using the carrier wave, and an E / O unit 23 that converts the frequency-modulated wireless signal into an optical signal and outputs it to the master device 30 via an optical fiber.

[0025] This allows for a separate configuration of the carrier generator 10, which requires a large-scale equipment setup due to the need for high frequency precision in uplink communication and therefore requires focused monitoring and control, and the sub-device 20, which needs to be installed in a dead zone. This configuration allows for flexibility in the placement of each component while also enabling dead zone countermeasures.

[0026] Furthermore, as long as the uplink and downlink (not shown in Figure 1) are configured so that their signals do not interfere with each other, the above effects can be obtained regardless of the configuration of the downlink wireless communication system (not shown in Figure 1), including conventional configurations.

[0027] (Second Embodiment) In the second embodiment, a configuration in which two slave devices are connected in series will be described. Figure 3 is a diagram showing an example of the configuration of the wireless communication system 100a in the second embodiment. The wireless communication system 100a is a system for dealing with dead zones. The wireless communication system 100a comprises a carrier generator 10, two slave devices 20-1 to 20-2, and a master device 30. Optical fibers are connected between the carrier generator 10 and slave device 20-1, between slave device 20-1 and slave device 20-2, and between slave device 20-2 and master device 30. As shown in Figure 3, the carrier generator 10, slave devices 20-1 to 20-2, and master device 30 are connected in series with optical fibers.

[0028] Furthermore, optical fiber wireless (RoF) transmission technology is used between the carrier generator 10 and the sub-device 20, between sub-device 20-1 and sub-device 20-2, and between sub-device 20-2 and the parent device 30. Here, the carrier generator 10 is installed either inside or outside a dead zone (for example, a tunnel or a building), sub-devices 20-1 and 20-2 are installed inside the dead zone, and the parent device 30 is installed outside the dead zone.

[0029] The wireless communication system 100a in the second embodiment differs from the wireless communication system 100 in that it includes two slave devices 20. The slave devices 20-1 to 20-2 have the same configuration as the slave device 20 in the first embodiment. In addition, in the wireless communication system 100a in the second embodiment, the wireless terminal (not shown) that communicates with each slave device 20 is a wireless terminal belonging to a single-frequency network. The slave devices 20-1 to 20-2 are one form of wireless device.

[0030] In the second embodiment, the signal output from the sub-device 20-1 includes not only the carrier wave but also the radio wave received by the antenna 24 of the sub-device 20-1. The signal output from the sub-device 20-1 is distributed in the distribution unit 221 of the sub-device 20-2 into a component that is mixed with the radio wave received by the antenna 24 of the sub-device 20-2 and a component that is not mixed. Of these, the component that is mixed with the radio wave passes through the attenuator 223 of the sub-device 20-2 and is therefore attenuated compared to the component that is not mixed. As a result, even when the sub-devices 20 are connected in series, it is possible to suppress signal quality degradation such as radio waves from different wireless terminals being mixed in the multiplication unit 225.

[0031] In the wireless communication system 100a configured as described above, the carrier generator 10, the slave devices 20-1 and 20-2, and the master device 30 are connected in series. This eliminates the need to individually connect the master device 30 to each slave device 20 when multiple slave devices 20 are present, as was the case in conventional systems. Therefore, the length of the optical fiber can be reduced.

[0032] Furthermore, as long as the uplink and downlink (not shown in Figure 3) are configured so that their signals do not interfere with each other, the above effects can be obtained regardless of the configuration of the downlink wireless communication system (not shown in Figure 3), including conventional configurations.

[0033] (Third Embodiment) In the third embodiment, a configuration in which three or more slave devices are connected in series will be described. Figure 4 is a diagram showing an example of the configuration of the wireless communication system 100b in the third embodiment. The wireless communication system 100b is a system for dealing with dead zones. The wireless communication system 100b comprises a carrier generator 10, three slave devices 20-1 to 20-3, and a master device 30. The wireless communication system 100b may also comprise four or more slave devices 20. Slave devices 20-1 to 20-3 are one form of wireless device.

[0034] Optical fibers connect the carrier generator 10 to the sub-device 20-1, to sub-device 20-2, to sub-device 20-2 and sub-device 20-3, and to sub-device 20-3 and the parent device 30. As shown in Figure 4, the carrier generator 10, sub-devices 20-1 to 20-3, and the parent device 30 are connected in series by optical fibers.

[0035] Furthermore, optical fiber wireless (RoF) transmission technology is used between the carrier generator 10 and the sub-device 20-1, between sub-device 20-1 and sub-device 20-2, between sub-device 20-2 and sub-device 20-3, and between sub-device 20-3 and the parent device 30. Here, the carrier generator 10 is installed either inside or outside a dead zone (for example, a tunnel or a building), the sub-devices 20-1 to 20-3 are installed inside the dead zone, and the parent device 30 is installed outside the dead zone. Figure 4 shows, as an example, a case where the carrier generator 10 and sub-devices 20-1 to 20-3 are installed inside a tunnel T.

[0036] The wireless communication system 100b in the third embodiment differs from the wireless communication system 100 in that it includes three slave devices 20. The slave devices 20-1 to 20-3 have the same configuration as the slave device 20 in the first embodiment. In addition, in the wireless communication system 100b in the third embodiment, the wireless terminal (not shown) that communicates with each slave device 20 is a wireless terminal belonging to a single-frequency network.

[0037] In the wireless communication system 100b, as in the second embodiment, even when the slave devices 20 are connected in series, it is possible to suppress signal quality degradation such as the mixing of radio waves from different wireless terminals in the multiplication unit 225.

[0038] Furthermore, in the wireless communication system 100b, the carrier generator 10, the slave devices 20-1 and 20-3, and the master device 30 are connected in series. This eliminates the need to individually connect the master device 30 to each slave device 20 when multiple slave devices 20 are installed, as is the case in conventional systems. Therefore, the length of the optical fiber can be reduced.

[0039] Furthermore, as long as the uplink and downlink (not shown in Figure 4) are configured so that their signals do not interfere with each other, the above effects can be obtained regardless of the configuration of the downlink wireless communication system (not shown in Figure 4), including the conventional configuration.

[0040] (Modification 1 in the First to Third Embodiments) In each of the embodiments described above, the phase adjustment unit 222 uses a phase shifter to rotate the phase of the input signal by 90 degrees (for example, changing the carrier wave from cosine to sine). However, it does not have to be a phase shifter as long as it is a device capable of adjusting the phase. For example, a delay device may be used, or the wiring path length may be adjusted to change the phase by 90 degrees.

[0041] (Modification 2 of the first to third embodiments) The integral process in each of the embodiments described above may be replaced with other processes such as addition, if mathematically equivalent results can be obtained instead of integration.

[0042] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0043] This invention can be applied to countermeasures against dead ground.

[0044] 10...Carrier generator, 20, 20-1 to 20-3...Slave devices, 30...Master device, 11...Oscillator, 12, 23...E / O section, 21...O / E section, 22...Armstrong frequency modulator, 24...Antenna, 221...Distributor, 222...Phase adjustment section, 223...Attenuator, 224...Integrator, 225...Multiplier, 226...Adder, 100, 100a, 100b...Wireless communication system

Claims

1. A wireless device provided between a carrier wave generator that generates a carrier wave and a master wireless device that communicates with a wireless base station, and connected to the carrier wave generator and the master wireless device by optical fiber, comprising: a first conversion unit that converts an optical signal including a carrier wave transmitted from the carrier wave generator via the optical fiber into an electrical signal to acquire the carrier wave; a frequency modulator that frequency modulates a wireless signal transmitted from a wireless terminal using the carrier wave; and a second conversion unit that converts the frequency modulated wireless signal into an optical signal and outputs it to the master wireless device via the optical fiber.

2. The wireless device according to claim 1, comprising two or more sub-devices each comprising the first conversion unit, the frequency modulator, and the second conversion unit.

3. The wireless device according to claim 2, wherein two or more of the aforementioned sub-devices are connected in series by an optical fiber.

4. The wireless device according to claim 1, wherein the frequency modulator comprises: a distribution unit that distributes the carrier wave to a first path and a second path; a phase adjustment unit that adjusts the phase of the carrier wave distributed to the second path by the distribution unit; an attenuator that reduces the signal level of the carrier wave whose phase has been adjusted; and an adder that generates a frequency modulated wave by adding the result of multiplying the wireless signal, which has been integrated or has an approximate integral operation performed on it, with the carrier wave whose signal level has been attenuated, and the carrier wave distributed to the first path by the distribution unit.

5. A wireless communication method performed by a wireless device provided between a carrier wave generator that generates a carrier wave and a master wireless device that communicates with a wireless base station, and connected to the carrier wave generator and the master wireless device by optical fiber, comprising: converting an optical signal including a carrier wave transmitted from the carrier wave generator via the optical fiber into an electrical signal to obtain the carrier wave; frequency modulating a wireless signal transmitted from a wireless terminal using the carrier wave; and converting the frequency modulated wireless signal into an optical signal and outputting it to the master wireless device via the optical fiber.

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