Wireless communication system and wireless communication method

Abstract

To provide a wireless communication system capable of suppressing characteristic degradation of an RF signal and improving communication quality in a DAS using analog RoF.SOLUTION: A wireless communication system multiplexes a TDD signal, an RF signal synchronized with timing of the TDD signal, and a DL control signal and a UL control signal synchronized with the timing of the TDD signal, between an A-RoF master unit 2 and an A-RoF slave unit 30, a frequency of the DL control signal and a frequency of the UL control signal are made the same, and a control signal of downlink is synchronized with the RF signal of uplink, and the control signal of uplink is synchronized with the RF signal of downlink.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wireless communication system and a wireless communication method using a distributed antenna system (DAS) by analog Radio on Fiber (RoF), and more particularly to a wireless communication system and a wireless communication method capable of improving communication performance. [Background technology]

[0002] [Prior Art] Mobile communication systems are currently transitioning to the fifth generation (5G) in order to achieve high speed, large capacity, low latency, and multiple simultaneous connections, and are expected to transition further to the sixth generation (6G) ten years later. In particular, in order to achieve high speeds, large capacity, and multiple simultaneous connections for 5G and 6G, there is a demand for efficient communications using technologies such as high utilization of radio frequency bands, Massive MIMO, which uses large-scale array antennas for beamforming, and distributed antennas.

[0003] 5G has a Distributed Antenna System (DAS) as a countermeasure for indoor and dead zones. In DAS, an optical communication master unit is connected to the base station of the mobile communication system, and the master unit and multiple slave units equipped with antennas are connected by optical fiber, allowing many distributed antennas to be installed and expanding the communication area. However, 6G uses higher frequency bands than 5G, which makes it more susceptible to attenuation and shortens the transmission distance, necessitating the installation of more distributed antennas.

[0004] In the distributed antenna systems using digital RoF (Radio on Fiber) that have been used until now, it was necessary to implement high-performance circuits (D / A conversion circuits, modulation / demodulation circuits, RF (Radio Frequency) conversion circuits, etc.) in the radio section (RF section) of the slave unit. Therefore, if a large number of slave units are installed in a distributed antenna system using digital RoF, the system becomes expensive.

[0005] Therefore, in order to save power and reduce costs, a distributed antenna system using analog RoF, which can reduce the cost of the slave unit, is being considered. When analog RoF is used, it is possible to simply configure the high-frequency circuit in the slave unit. However, it is necessary to individually control specific slave units among the multiple connected slave units, such as to change the beam direction of some of the slave units or to control the device.

[0006] [Configuration of a conventional wireless communication system: Figure 6] The configuration of a conventional wireless communication system will be described with reference to Fig. 6. Fig. 6 is a schematic diagram of a conventional wireless communication system. The conventional wireless communication system is a distributed antenna system using analog RoF, and as shown in FIG. 6, the conventional wireless communication system includes an RU (Radio Unit) section 61, an analog RoF master (hereinafter referred to as an A-RoF master and written as A-RoF master in the figure) 62, and an analog RoF slave (hereinafter referred to as an A-RoF slave and written as A-RoF slave in the figure) 60, and the A-RoF master 62 and the A-RoF slave 63 are connected by optical fiber. Furthermore, the A-RoF slave device 60 includes an optical / electrical conversion unit 63 and an RF (Radio Frequency) unit 64.

[0007] The RU unit 61 is provided between a base station of a mobile communication system such as 5G or 6G and the A-RoF base station 62, and transmits and receives four types of signals: an RF signal which is communication data, a TDD (Time Division Duplex) signal for timing control, a downlink (DL) control signal from the base station to the RF unit 64, and an uplink (UL) control signal from the RF unit 64 to the base station. The RU unit 61 also includes a modulation / demodulation unit 65, which performs signal processing such as modulation / demodulation associated with RF signal communication.

[0008] The A-RoF base station 62 includes an E / O·O / E conversion unit 66 that performs electrical / optical (E / O) conversion and optical / electrical (O / E) conversion, and communicates with the RU unit 61 via electrical signals and with the A-RoF slave station 60 via optical signals. The A-RoF base station 62 multiplexes the downlink signals, converts them into optical signals, and transmits them to the A-RoF slave station 60. It also converts the uplink optical signals from the A-RoF slave station 60 into electrical signals, separates the RF signals and UL control signals, and outputs them to the RU unit 61.

[0009] The optical / electrical conversion unit 63 of the A-RoF slave device 60 includes an O / E·E / O conversion unit 67 that performs optical / electrical (O / E) conversion and electrical / optical (E / O) conversion, and communicates with the A-RoF master device 62 via optical signals and with the RF unit 64 via electrical signals. The optical / electrical conversion unit 63 of the A-RoF slave device 60 receives a downlink optical signal and converts it into an electrical signal, separates the RF signal and DL control signal and outputs them to the RF unit 64, and multiplexes the uplink RF signal and UL control signal, converts them into an optical signal, and transmits it to the A-RoF master device 62.

[0010] The RF unit 64 is a wireless communication unit and includes an information control unit 68, a communication control unit 69, and an antenna 70. It is connected to the optical / electrical conversion unit 63 via a wired connection and communicates wirelessly with terminals such as a mobile station (not shown). The information control unit 68 outputs the received TDD signal to the communication control unit 69, controls the inside of the own device based on the DL control information, and outputs UL control information from the own device to the optical / electrical conversion unit 63. The communication control unit 69 switches the timing of transmission and reception based on the TDD signal, controls the antenna 70 according to control information from the information control unit 68, and transmits and receives RF signals.

[0011] Then, the RF unit 64 radiates the DL RF signal from the antenna 70 into space via the communication control unit 69 , and outputs the RF signal captured by the antenna 70 to the optical / electrical conversion unit 63 via the communication control unit 69 .

[0012] In conventional wireless communication systems, WDM (Wavelength Division Multiplexing) technology is used to multiplex TDD signals, DL control signals, and UL control signals in addition to RF signals, for two-way communication over optical fibers. As shown in FIG. 6, in a conventional wireless communication system, a TDD signal is multiplexed at a frequency f1, a DL control signal is multiplexed at a frequency f2, and a UL control signal is multiplexed at a frequency f3.

[0013] [Transmission and reception timing in a conventional wireless communication system: Figure 7] Next, transmission and reception in a wireless communication system using a conventional analog RoF will be described with reference to Fig. 7. Fig. 7 is a time chart of conventional transmission and reception. Here, the operation of the A-RoF master device 62 will be described. As shown in Fig. 7, in a conventional wireless communication system, an A-RoF master device 62 switches between transmitting and receiving an RF signal based on a TDD signal. Here, when the TDD signal is at H (High) level, the A-RoF master device 62 transmits a DL RF signal, and when the TDD signal is at L (Low) level, the A-RoF master device 62 receives a UL RF signal. On the other hand, DL control signals and UL control signals are transmitted and received at timings different from those of RF signals.

[0014] [Signal levels in a conventional wireless communication system: Figure 8] Next, the signal levels of transmission signals in a conventional wireless communication system will be described with reference to Fig. 8. Fig. 8 is an explanatory diagram showing the signal levels of conventional transmission signals. In FIG. 8, the horizontal axis represents frequency and the vertical axis represents signal level. As shown in FIG. 8, in a conventional wireless communication system, a DL control signal with frequency f2, a UL control signal with frequency f3, a TDD signal with frequency f1, and an RF signal as a main signal are multiplexed and transmitted over an optical fiber.

[0015] Here, if the number of frequency signals (wave numbers) that are superimposed / have been superimposed during electrical-to-optical conversion / optical-to-electrical conversion is large, IM distortion (Intermodulation distortion) is likely to occur, resulting in more distortion around the RF signal. In addition, since the upper limit of the total power of the transmission signals is determined by the allowable power of the components of the E / O·O / E conversion unit 66 and the O / E·E / O conversion unit 67, the more signals are superimposed, the more pressure is placed on the signal level of the RF signal. For these reasons, when many signals are multiplexed, the characteristics of the RF signal deteriorate.

[0016] [Related Technology] As a related prior art, there is JP 2014-187450 A, “Optical Transmission Device” (Patent Document 1). Patent Document 1 discloses an optical transmission device that can reduce the optical transmission capacity while satisfying the signal standards when transmitting optically with multiple shared frequencies. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] JP 2014-187450 A Summary of the Invention [Problem to be solved by the invention]

[0018] As described above, in wireless communication systems using conventional analog RoF, a large number of frequency signals are multiplexed onto the main RF signal, which causes degradation of the RF signal characteristics due to IM distortion and signal level reduction.

[0019] Incidentally, Patent Document 1 does not disclose a configuration in which a downlink control signal and an uplink control signal are transmitted at the same frequency in a DAS using an analog RoF.

[0020] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a wireless communication system and a wireless communication method that can suppress degradation of RF signal characteristics and improve communication quality in a DAS using analog RoF. [Means for solving the problem]

[0021] The present invention, which solves the problems of the above-mentioned conventional examples, is a wireless communication system that uses analog radio on optical fiber, in which a parent unit and a child unit are connected by optical fiber and radio signals and control signals are communicated bidirectionally via the optical fiber, and is characterized in that communication between the parent unit and the child unit is performed by multiplexing a time division duplex signal, a radio signal synchronized with the timing of the time division duplex signal, and a downlink control signal and an uplink control signal synchronized with the timing of the time division duplex signal, and the frequency of the downlink control signal and the frequency of the uplink control signal are made the same.

[0022] Furthermore, the present invention is characterized in that in the above-mentioned wireless communication system, communication between the parent unit and the child unit is performed by multiplexing an uplink wireless signal and a downlink wireless signal synchronized with the timing of the time division duplex signal, a downlink control signal synchronized with the uplink wireless signal, and an uplink control signal synchronized with the downlink wireless signal.

[0023] In the wireless communication system according to the present invention, the frequency of the wireless signal and the frequency of the control signal are set to be the same in communication between the master unit and the slave unit.

[0024] Furthermore, the present invention is characterized in that in the above-mentioned wireless communication system, a control distribution device using analog optical fiber radio is provided between a parent unit and a plurality of child units, and the control distribution device receives a plurality of downlink control signals from the parent unit and distributes them to the child units, and if a downlink control signal is addressed to the control distribution device, it is not transmitted to the child units, and if a downlink control signal is addressed to a specific child unit, it is not transmitted to any unit other than the specific child unit.

[0025] The present invention is also a wireless communication method using analog optical fiber radio in which a parent unit and a child unit are connected by optical fiber and radio signals and control signals are communicated bidirectionally via the optical fiber, and is characterized in that the communication between the parent unit and the child unit multiplexes a time division duplex signal, a radio signal synchronized with the timing of the time division duplex signal, and a downlink control signal and an uplink control signal synchronized with the timing of the time division duplex signal and using the same frequency. Effect of the Invention

[0026] According to the present invention, a parent unit and a child unit are connected by an optical fiber, and a wireless communication system using an analog optical fiber radio is used for two-way communication of wireless signals and control signals via the optical fiber. The communication between the parent unit and the child unit is a wireless communication system in which a time division duplex signal, a wireless signal synchronized with the timing of the time division duplex signal, and a downlink control signal and an uplink control signal synchronized with the timing of the time division duplex signal are multiplexed, and the frequency of the downlink control signal and the frequency of the uplink control signal are made the same. This reduces the number of multiplexed frequency signals, suppresses distortion around the wireless signal, and increases the level of the wireless signal, resulting in an effect of improving the communication quality of the wireless signal with an inexpensive configuration.

[0027] Furthermore, according to the present invention, communication between the parent unit and the child unit is performed using the above-mentioned wireless communication system in which an uplink radio signal and a downlink radio signal synchronized with the timing of a time division duplex signal, a downlink control signal synchronized with the uplink radio signal, and an uplink control signal synchronized with the downlink radio signal, are multiplexed. This eliminates the need to superimpose a control signal on the radio signal during electrical-to-optical conversion and optical-to-electrical conversion, and has the effect of further improving the quality of the radio signal.

[0028] Furthermore, according to the present invention, a control distribution device using analog optical fiber radio is provided between a parent unit and a plurality of child units, and the control distribution device receives a plurality of downlink control signals from the parent unit and distributes them to the child units. If a downlink control signal is addressed to the control distribution device, it is not transmitted to the child units, and if a downlink control signal is addressed to a specific child unit, the control signal is not transmitted to any unit other than the specific child unit. As a result, by not transmitting a control signal to a child unit that is not the destination of the control signal, the number of multiplexed signals is reduced, thereby reducing distortion of the radio signals and reducing the cost of the entire system.

[0029] Furthermore, according to the present invention, a parent unit and a child unit are connected by an optical fiber, and a wireless communication method using analog optical fiber radio is used for two-way communication of wireless signals and control signals via the optical fiber. The communication between the parent unit and the child unit is a wireless communication method in which a time division duplex signal, a wireless signal synchronized with the timing of the time division duplex signal, and a downlink control signal and an uplink control signal synchronized with the timing of the time division duplex signal and using the same frequency are multiplexed. This reduces the number of multiplexed frequency signals, suppresses distortion around the wireless signal, and increases the level of the wireless signal, resulting in an effect of improving the communication quality of the wireless signal with an inexpensive configuration. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic diagram of a wireless communication system. [Diagram 2] 3 is a time chart of the present system. [Diagram 3] FIG. 2 is an explanatory diagram showing signal levels of the present system. [Figure 4] FIG. 13 is a schematic diagram of another system. [Diagram 5] FIG. 11 is an explanatory diagram showing an example of DL control information in another system. [Figure 6] FIG. 1 is a schematic diagram of a conventional wireless communication system. [Figure 7] 1 is a time chart of conventional transmission and reception. [Figure 8]FIG. 1 is an explanatory diagram showing conventional signal levels. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. [Outline of the embodiment] A wireless communication system (this system) according to an embodiment of the present invention is a DAS using analog RoF, and communication between an analog RoF parent device (A-RoF parent device) and an analog RoF child device (A-RoF child device) is performed by multiplexing a TDD signal, an RF signal synchronized with the timing of the TDD signal, and a DL control signal and a UL control signal synchronized with the timing of the TDD signal, with the frequency of the DL control signal and the frequency of the UL control signal being the same. This reduces the number of frequencies used for transmitting and receiving control signals, reduces the number of multiplexed frequency signals, reduces IM distortion, and increases the signal level of the RF signal, making it possible to prevent deterioration of the characteristics of the RF signal and improve communication quality while suppressing equipment costs. Moreover, a wireless communication method according to an embodiment of the present invention is a wireless communication method in this system.

[0032] [System configuration: Figure 1] This system will be described with reference to Figure 1. Figure 1 is a schematic diagram of the system. The basic configuration of this system is almost the same as the conventional wireless communication system shown in Fig. 6, and basically comprises an RU unit 1, an A-RoF base station 2, and an A-RoF slave station 30 as shown in Fig. 1. However, the method of communication between the A-RoF base station 2 and the A-RoF slave station 30 is different from the conventional method.

[0033] The RU unit 1 includes a modulation / demodulation unit 11, and performs signal processing such as modulation / demodulation associated with RF signal communication. In this system, as in the past, four types of signals are transmitted and received: RF signals, TDD signals, DL control signals, and UL control signals, but the frequencies used for the control signals are the same for the downlink and uplink.

[0034] Specifically, the TDD signal is multiplexed with the RF signal at frequency f1, and the DL control signal and the UL control signal are multiplexed with frequency f2. Conventionally, a different frequency was assigned to each of the four types of signals to be multiplexed, and four waves were multiplexed. However, in this system, the number of frequencies to be multiplexed is reduced to three, thereby reducing the number of superimposed signals and reducing IM distortion while also increasing the signal level of the RF signal, thereby improving communications quality. The frequencies and timing of transmission and reception in this system will be described later.

[0035] The A-RoF base station 2 includes a control signal switching unit (a control signal switching unit in the figure) 21 and an E / O·O / E conversion unit 22, and communicates with the RU unit 1 by electrical signals and with the A-RoF slave station 30 by optical signals via optical fiber. The control signal switching unit 21 performs processing for switching the connection between the DL control signal and the UL control signal and the E / O·O / E conversion unit 22 .

[0036] Specifically, based on the timing of the TDD signal, the control signal switching unit 21 controls whether to switch the connection with the E / O·O / E conversion unit 22 to the DL control signal side and transmit the DL control signal to the A-RoF slave device 30, or to switch the connection with the E / O·O / E conversion unit 22 to the UL control signal side and transmit the UL control signal to the RU unit 1.

[0037] The A-RoF slave device 30 includes an optical / electrical conversion unit 3 and an RF unit 4 . The optical / electrical conversion unit 3 performs mutual conversion between optical and electrical signals (optical / electrical, electrical / optical) and is equipped with an O / E·E / O conversion unit 31 and a TDD switch (written as TDD SW in the figure) 32. It receives downlink optical signals and converts them into electrical signals, separates the RF signals, TDD signals, and DL control signals and outputs them to the RF unit 4, and superimposes the UL control signal on the uplink RF signal, converts it to an optical signal, and transmits it to the A-RoF base station 2.

[0038] One of the UL control signals is switched so as to be connected to the O / EE / O conversion unit 31. The timing of the switching will be described later.

[0039] The RF unit 4 includes an information control unit 41, a communication control unit 42, and an antenna 43, and wirelessly connects to and communicates with terminals such as mobile stations. The communication control unit 42 and the antenna 43 are the same as in the past, and the description thereof will be omitted. The information control unit 41 outputs the TDD signal received from the optical / electrical conversion unit 3 to the communication control unit 42 based on the timing of the TDD signal, controls its own device based on DL control information, and outputs UL control information from its own device to the optical / electrical conversion unit 3.

[0040] [Transmission and reception timing in this wireless communication system: Figure 2] Next, transmission and reception in this wireless communication system will be described with reference to Fig. 2. Fig. 2 is a time chart of this wireless communication system. Also, the operation of the A-RoF master device 2 will be described here. As shown in Fig. 2, in this wireless communication system, RF signals are switched between transmission and reception in synchronization with the TDD signal, similar to the conventional wireless communication system shown in Fig. 7. Specifically, the A-RoF master unit 2 transmits DL RF signals when the TDD signal is at H level, and receives UL RF signals when the TDD signal is at L level.

[0041] A feature of this wireless communication system is that DL control signals and UL control signals are transmitted using the same frequency f2, and switching between DL control signals and UL control signals is performed in synchronization with the TDD signal. Specifically, the control signal switching unit 21 of the A-RoF base station 2 receives a UL control signal in synchronization with the transmission of a DL RF signal (here, when the TDD signal is at H level), and transmits a DL control signal in synchronization with the reception of a UL RF signal (here, when the TDD signal is at L level).

[0042] In this way, by reversing the timing of the UL control signal and the DL control signal and controlling so that transmission and reception do not overlap, it becomes possible to transmit and receive using the same frequency. Furthermore, by reversing the transmission and reception of the RF signal and the control signal, it is not necessary to superimpose the RF signal and the control signal in the E / O·O / E conversion unit 22 and the O / E·E / O conversion unit 31, thereby reducing distortion and ensuring the level of the RF signal.

[0043] [Signal levels in this wireless communication system: Figure 3] Next, the signal levels of transmission signals in this wireless communication system will be described with reference to Fig. 3. Fig. 3 is an explanatory diagram showing the signal levels of transmission signals in this wireless communication system. As shown in FIG. 3, in this wireless communication system, three waves, namely, an RF signal, a TDD signal of frequency f1, and a UL control signal and a DL control signal of frequency f2, are multiplexed and transmitted over an optical fiber.

[0044] Compared to the conventional method in which four waves were multiplexed, the number of waves multiplexed is reduced, which suppresses IM distortion and allows the transmission power of the RF signal to be increased compared to the conventional method, even if there is an upper limit on the transmission power, thereby improving the characteristics of the RF signal and enhancing communication quality.

[0045] In addition, by making the frequency of the RF signal the same as that of the control signal (f2), the number of multiplexed waves is reduced to two, reducing the distortion components of the RF signal and further improving communication quality. Even if the frequencies of the RF signal and the control signal are the same, the RF signal and the control signal are synchronized for downlink and uplink, so there is no problem with processing in the E / O·O / E conversion unit 22 and the O / E·E / O conversion unit 31.

[0046] Furthermore, in the above example, the TDD signal sent from the base station is transmitted to the A-RoF master 2 and the A-RoF slave 30, but it is also possible to generate the TDD signal from an RF signal in the A-RoF master 2 and the A-RoF slave 30. In that case, it is not necessary to multiplex and transmit the TDD signal, so that it is possible to further reduce the number of multiplexed waves and improve communication quality.

[0047] [Another embodiment] In the above example, an example in which one A-RoF slave device 30 is connected has been described, but in another embodiment of the present invention, a system in which a plurality of A-RoF slave devices 30 are connected is provided by providing a control distribution device that distributes a signal from the A-RoF master device 2. A system according to another embodiment of the present invention will be referred to as another system.

[0048] In another system, a control distribution device transmits DL RF signals and DL control signals addressed to each A-RoF slave device 30 only to that A-RoF slave device 30, and when a DL control signal is addressed to the control distribution device, the control device controls the transmission of the control signal to no A-RoF slave device 30. This makes it possible to avoid multiplexing unnecessary control signals and maintain good RF signal characteristics. The control distribution device will be described later.

[0049] [Another system configuration: Figure 4] The configuration of the other system will be described with reference to Fig. 4. Fig. 4 is a schematic diagram of the other system. As shown in FIG. 4, in another system, the configuration on the slave side includes A-RoF slaves 30a and 30b (sometimes referred to as A-RoF slaves 30 when no distinction is made) similar to those in FIG. 1, and the configuration on the master side includes an RU section 10 and an A-RoF master 20, and a control distribution device (referred to as A-RoF control distribution device in the figure) 5 between the A-RoF master 20 and the A-RoF slaves 30a and 30b. The A-RoF slave device 30 has the same configuration and operates as in FIG. 1, and therefore a description thereof will be omitted.

[0050] The RU unit 10 includes multiple modulation / demodulation units 11a and 11b corresponding to the RF signals transmitted and received by the RF units 4 of each A-RoF slave device 30, and each modulates and demodulates the corresponding RF signal. Here, the RF unit 4a transmits and receives an RF signal (1) (referred to as RF signal 1 in the figure), and the RF unit 4b transmits and receives an RF signal (2) (referred to as RF signal 2 in the figure).

[0051] The A-RoF master unit 20 includes a control signal switching unit 21 and a multiplexing / demultiplexing unit (denoted as MUX / DEMUX in the figure) 23, similar to those in the present system shown in FIG. The demultiplexing unit 23 converts the downlink signals, that is, the RF signal (1), the RF signal (2), the TDD signal of frequency f1, and the DL control signal and the UL control signal of frequency f2, into optical signals, multiplexes them, and outputs them to the control distributor 5 via the optical fiber. It also separates the multiplexed uplink optical signal input from the optical fiber into each signal, converts them into electrical signals, and sends them to the base station.

[0052] The control distribution device 5 includes a multiplexing / demultiplexing unit 51, an RF switch 52, a TDD switch 53, a control signal determination unit 54, and E / O·O / E conversion units 55a, 55b (sometimes referred to as E / O·O / E conversion unit 55). The demultiplexing unit 51 converts the multiplexed downlink optical signals input from the optical fiber into electrical signals and separates them into each signal, outputs the downlink RF signal (1) and RF signal (2) to the RF switch 52, and outputs the TDD signal and DL control signal to the E / O·O / E conversion unit 55. Furthermore, the demultiplexer 51 multiplexes the uplink signals, converts them into optical signals, and outputs them to the A-RoF master unit 20 via optical fiber.

[0053] The RF switch 52 outputs the downlink RF signal to the E / O·O / E conversion unit 55 corresponding to the optical / electrical conversion unit 3 connected to the destination RF unit 4, and switches on / off so as not to output the signal to other E / O·O / E conversion units 55. Specifically, when a downlink RF signal (1) is input from the demultiplexer 51, the RF switch 52 turns on the connection to the E / O·O / E converter 55a and turns off the connection to the E / O·O / E converter 55b. Conversely, when a downlink RF signal (2) is input from the demultiplexer 51, the connection to the E / O·O / E converter 55b is turned on, and the connection to the E / O·O / E converter 55a is turned off.

[0054] Furthermore, the RF switch 52 switches the output of the RF signal off in accordance with an instruction from the control signal determination unit 54 accompanying the input of a DL control signal addressed to the control distribution device 5, and switches it on again in accordance with the instruction. The switching regarding DL control signals will be described later.

[0055] The TDD switch 53 switches between the DL control signal and the UL control signal in synchronization with the TDD signal, outputs the DL control signal from the demultiplexing unit 51 to the control signal determination unit 54, and outputs the UL control signal from the E / O·O / E conversion unit 55 to the demultiplexing unit 51.

[0056] The control signal determination unit 54 controls the output destination according to the destination of the DL control signal. In another system, information on the destination (a specific RU 4 or control distribution device 5) is included at a specific position in the DL control signal, and the control distribution device 5 switches the output destination based on this information.

[0057] Specifically, the control signal determination unit 54 determines the destination of the DL control signal, and if the input DL control signal is addressed to a specific RF unit 4, it outputs it to the E / O·O / E conversion unit 55 corresponding to that RF unit 4, and if the control signal is addressed to the control distribution device 5, it controls its own device based on the control signal and terminates the DL control signal. At that time, it also controls the RF switch 52 to turn off the output of the RF signal. This makes it possible to eliminate the transmission of unnecessary DL control signals, reduce distortion, and increase the transmission level of the RF signal to improve characteristics. When the RF switch 52 is turned off, the control signal determination unit 54 controls the RF switch 52 to be turned on at the timing of the UL control signal, for example, in accordance with the timing of the TDD signal.

[0058] In another system, it is also possible to reduce the amount of control information transmitted to the RF unit 4 by having the control distribution device 5 perform part of the control of the RF unit 4. In other words, the DL control signal addressed to the control distribution device 5 includes, in addition to a signal for controlling the control distribution device 5, a signal for controlling the RF units of the A-RoF slave devices 30 connected under it on a control distribution device 5 basis. The control of the RF unit 4 performed on a control distribution device 5 basis includes, for example, resetting an individual RF unit or a specific group.

[0059] In another system, the one wave saved by making the control signals the same frequency is used to allocate one wavelength to each RF unit 4 or to a specific group of RF units 4 that transmit and receive the same control signal, thereby making it possible to effectively use the optical wavelengths. This makes it possible to increase the number of RF units 4 to be connected depending on the performance of the multiplexing / demultiplexing unit 51. In the example of FIG. 4, by converting the RF signal into individual optical wavelengths (λ1, λ2), even if a control signal is multiplexed in transmission between the A-RoF master device 20 and the control distribution device 5, no distortion occurs. Distortion occurs in the E / O·O / E conversion unit 55 of the control distribution device 5, but since the control signal is superimposed on the RF signal only in some of the RF units 4, it is possible to reduce distortion components overall.

[0060] [DL control information: Figure 5] DL control information in another system will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram showing an example of DL control information in another system. As shown in Fig. 5, in another system, a specific section of a DL control signal section synchronized with a TDD signal is allocated as control information for a control distribution device, and another specific section is allocated as control information for the RF unit 4. In the example of Fig. 5, the first half is used as DL control information for the control distribution device 5, and the latter half is used as DL control information for the RF unit 4.

[0061] Then, the control signal determination unit 54 of the control distribution device 5 determines whether the DL control signal is included in the first half section, identifies that the DL control signal is addressed to the control distribution device 5, and performs control. If it is for the RF unit 4, the destination is further identified, and the output destination of the DL control signal is specified accordingly.

[0062] [Effects of the embodiment] According to this system, in communication between the A-RoF parent device 2 and the A-RoF child device 30, a TDD signal, an RF signal synchronized with the timing of the TDD signal, and a DL control signal and a UL control signal synchronized with the timing of the TDD signal are multiplexed, and the frequency of the DL control signal and the frequency of the UL control signal are made the same. This reduces the number of frequencies used for transmitting and receiving control signals, reduces the number of multiplexed frequency signals, reduces IM distortion, and increases the signal level of the RF signal. This has the effect of preventing degradation of the characteristics of the RF signal and improving communication quality while suppressing equipment costs. [Industrial Applicability]

[0063] INDUSTRIAL APPLICABILITY The present invention is suitable for a wireless communication system and a wireless communication method capable of suppressing degradation of RF signal characteristics and improving communication quality in a DAS using analog RoF. [Explanation of symbols]

[0064] 1,10,61...RU section, 2,20,62...A-RoF parent device, 3,63...optical / electrical conversion section, 30,60...A-RoF child device, 4,64...RF section, 5...control distribution device, 11,65...modulation / demodulation section, 21...control signal switching section, 22,55,66...E / O·O / E conversion section, 23,51...multiplexing / demultiplexing section, 31,67...O / E·E / O conversion section, 32,53...TDD switch, 41,68...information control section, 42,69...communication control section, 43,70...antenna, 52...RF switch, 54...control signal determination section

Claims

1. A wireless communication system using analog radio-on-fiber in which a parent device and a child device are connected by an optical fiber and radio signals and control signals are bidirectionally communicated through the optical fiber, A wireless communication system characterized in that communication between the parent unit and the child unit is performed by multiplexing a time division duplex signal, a radio signal synchronized with the timing of the time division duplex signal, and a downlink control signal and an uplink control signal synchronized with the timing of the time division duplex signal, and the frequency of the downlink control signal is made the same as the frequency of the uplink control signal.

2. 2. The wireless communication system according to claim 1, characterized in that communication between the parent unit and the child unit multiplexes an uplink radio signal and a downlink radio signal synchronized with the timing of the time division duplex signal, a downlink control signal synchronized with the uplink radio signal, and an uplink control signal synchronized with the downlink radio signal.

3. 3. The wireless communication system according to claim 2, wherein the communication between said master unit and said slave unit is performed using the same frequency for the wireless signal and the control signal.

4. a control distribution device using analog radio optical fiber between the master unit and the plurality of slave units; The wireless communication system according to claim 1 or 2, characterized in that the control distribution device inputs a plurality of downlink control signals from the parent unit and distributes them to the child units, and if a downlink control signal is addressed to the control distribution device, it does not transmit it to the child unit, and if the downlink control signal is addressed to a specific child unit, it does not transmit the control signal to any unit other than the specific child unit.

5. A wireless communication method using analog radio-on-fiber in which a master unit and a slave unit are connected by an optical fiber and radio signals and control signals are bidirectionally communicated through the optical fiber, comprising: A wireless communication method characterized in that communication between the parent unit and the child unit multiplexes a time division duplex signal, a radio signal synchronized with the timing of the time division duplex signal, and a downlink control signal and an uplink control signal synchronized with the timing of the time division duplex signal and using the same frequency.

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