Wireless communication methods, base station equipment, and wireless communication systems

Abstract

This wireless communication method is for a wireless communication system comprising an aggregation station and an extension station that performs beamforming in accordance with aggregation station control, wherein: the aggregation station performs extension station beamforming control by transmitting, to the extension station via an optical transmission path, an optical signal including a beam control signal for at least controlling beamforming at the extension station and a transmission signal which is data to be transmitted; and the extension station transmits the transmission signal by setting a phase shifter, or configuring a setting by means of a switch change, to a phase difference for forming a beam in a specific direction on the basis of the beam control signal included in the optical signal.　

Description

[Technical Field]

[0001] The present invention relates to a wireless communication method, a base station device, and a wireless communication system. [Background technology]

[0002] Conventionally, wireless communication using the millimeter-wave band, which enables high-speed transmission, has attracted attention. However, when using the millimeter-wave band, there is a problem in that propagation loss is large and long-distance transmission is difficult. Radio over Fiber (RoF) systems enable long-distance transmission of millimeter-wave RF signals (Radio Frequency signals), but the coverage area of ​​the antenna remains a challenge. One solution to this is beamforming using an array antenna. As a beamforming technology using RoF systems or optical technology, the technology described in Patent Document 1 is known. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-120252 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, conventional beamforming technology involves phase-controlling the same transmitted signal at the receiving station and transmitting signals with different phase controls at different wavelengths. Therefore, controlling one beam requires a fixed optical wavelength equal to the number of antenna elements at the extension station, occupying a wide optical bandwidth. This leads to a problem of reduced wavelength utilization efficiency. For example, if the number of antenna elements is 64, even when using a commercially available 1.55 μm band (c-band) DWDM optical multiplexer / demultiplexer, only 48 wavelengths can be accommodated with a frequency spacing of 100 GHz, which is a limitation.

[0005] In view of the above circumstances, the present invention aims to provide a technology that enables beamforming control while suppressing a decrease in wavelength utilization efficiency. [Means for solving the problem]

[0006] One aspect of the present invention is a wireless communication method in a wireless communication system comprising a central station and an extension station that performs beamforming according to the control of the central station, wherein the central station transmits an optical signal to the extension station via an optical transmission path, which includes at least a beam control signal for controlling beamforming at the extension station and a transmission signal which is data to be transmitted, to perform beamforming control at the extension station, and the extension station transmits the transmission signal by setting a phase difference for beamforming in a specific direction based on the beam control signal included in the optical signal, by setting it in a phase shifter or by switching a switch.

[0007] One aspect of the present invention is a base station device in a wireless communication system comprising an aggregation station and an extension station that performs beamforming according to the control of the aggregation station, wherein the aggregation station transmits an optical signal including at least a beam control signal for controlling beamforming at the extension station and a transmission signal which is data to be transmitted to the extension station via an optical transmission path to perform beamforming control of the extension station, and the extension station transmits the transmission signal by setting a phase difference for beamforming in a specific direction based on the beam control signal included in the optical signal, either by setting it in a phase shifter or by switching a switch.

[0008] One aspect of the present invention is a wireless communication system comprising a central station and an extension station that performs beamforming according to the control of the central station, wherein the central station transmits an optical signal including at least a beam control signal for controlling beamforming at the extension station and a transmission signal which is data to be transmitted to the extension station via an optical transmission path to perform beamforming control of the extension station, and the extension station transmits the transmission signal by setting a phase difference for beamforming in a specific direction based on the beam control signal included in the optical signal, either by setting it in a phase shifter or by switching a switch. [Effects of the Invention]

[0009] This invention makes it possible to perform beamforming control while suppressing a decrease in wavelength utilization efficiency. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the configuration of a wireless communication system in the first embodiment. [Figure 2] This figure shows a first example of the configuration of the beam forming section. [Figure 3] This figure shows a second example of the beamforming section configuration. [Figure 4] This is a sequence diagram showing the processing flow of the wireless communication system in the first embodiment. [Figure 5] This figure shows an example of the configuration of a wireless communication system in the second embodiment. [Figure 6] This is a sequence diagram showing the processing flow of the wireless communication system in the second embodiment. [Figure 7] This figure shows an example of the configuration of a wireless communication system in the third embodiment. [Figure 8] This is a sequence diagram showing the processing flow of the wireless communication system in the third embodiment. [Figure 9] This figure shows an example configuration of a wireless communication system in the fourth embodiment. [Figure 10]This is a sequence diagram showing the processing flow of the wireless communication system in the fourth embodiment. [Figure 11] This figure shows an example configuration of a wireless communication system in the fifth embodiment. [Figure 12] This is a sequence diagram showing the processing flow of the wireless communication system in the fifth embodiment. [Figure 13] This figure shows an example configuration of a wireless communication system in the sixth embodiment. [Modes for carrying out the invention]

[0011] One embodiment of the present invention will be described below with reference to the drawings. (First embodiment) Figure 1 shows an example configuration of a wireless communication system 1 in the first embodiment. The wireless communication system 1 comprises a central station 10 and an extension station 20. The central station 10 and the extension station 20 are configured as a single base station device. The central station 10 and the extension station 20 are connected via an optical transmission path 40. The optical transmission path 40 is, for example, an optical fiber. The optical transmission path 40 may be one or more single-core fibers or a multi-core fiber having two or more cores. In the following description, the direction from the central station 10 to the extension station 20 is referred to as the downstream direction, and the direction from the extension station 20 to the central station 10 is referred to as the upstream direction.

[0012] Figure 1 shows the case where there is one extension station 20, but the wireless communication system 1 may have multiple extension stations 20. In this case, the aggregation station 10 and the multiple extension stations 20 may be connected by a passive optical network (PON). When the aggregation station 10 and the multiple extension stations 20 are connected by a PON, an optical splitter (branching unit) is provided between the aggregation station 10 and the multiple extension stations 20. The optical splitter branches the optical signal output from the aggregation station 10 and outputs it to the extension stations 20. The passive optical network is, for example, WDM-PON (Wavelength Division Multiplexing - Passive Optical Network) or TDM-PON (Time Division Multiplexing - Passive Optical Network).

[0013] The aggregation station 10 remotely controls the beamforming of the extension station 20. For example, the aggregation station 10 converts the transmission signal and the control signal into optical signals of different wavelengths, and remotely controls the beamforming of the extension station 20 using a wavelength division multiplexed signal generated by wavelength division multiplexing (WDM) of the optical signals of different wavelengths. For example, the aggregation station 10 remotely controls the beamforming of the extension station 20 using analog RoF technology.

[0014] The transmit signal is the main signal containing the data to be transmitted. The transmit signal may be an IF signal (Intermediate Frequency signal) or an RF signal.

[0015] The control signal is a signal used to control the operation of the extension station 20. The control signal includes at least a beam control signal to control beamforming at the extension station 20. The beam control signal includes phase indication information for radiating the transmission signal in the direction in which beamforming is desired. In addition to the beam control signal, the control signal may also include a clock signal, a level adjustment signal, or a TDD (Time Division Duplex) signal. Here, the clock signal is the reference signal used when generating the LO (Local Oscillator) signal for frequency conversion of the transmission signal from IF to RF at the extension station 20. The level adjustment signal is the LO signal. Note that if the transmission signal is an RF signal, frequency conversion is not necessary, so the control signal does not include either the clock signal or the level adjustment signal. The TDD signal is a signal that indicates the timing for switching between transmission and reception at the extension station 20. The TDD signal is a signal required when realizing bidirectional communication using the time division duplex (TDD) method. Therefore, when bidirectional communication is realized at the extension station 20 using the frequency division duplex (FDD) method, the control signal does not need to include the TDD signal. The following descriptions of each embodiment assume that the extension station 20 performs bidirectional communication using the time-division duplex (TDD) method.

[0016] The projecting station 20 is installed at a location separate from where the aggregation station 10 is located. The projecting station 20 performs beamforming based on control signals transmitted from the aggregation station 10 and radiates a transmission signal wirelessly. This allows the projecting station 20 to communicate with wireless devices located in the vicinity of its installation location. Furthermore, when the projecting station 20 performs bidirectional communication using the time-division duplex (TDD) method, it switches between transmitting and receiving at the timing indicated by the TDD signal.

[0017] Next, we will describe the specific configuration of the aggregation station 10 and the extension station 20. Figure 1 shows the configuration of the aggregation station 10 and the extension station 20 for realizing downlink communication.

[0018] The aggregation station 10 comprises multiple E / O 11-1 to 11-2 and an optical multiplexing unit 12.

[0019] The E / O11-1 receives the transmission signal. The E / O11-1 uses the input transmission signal to measure the wavelength λ TX1 The optical signal is intensity-modulated. As a result, E / O11-1 has a wavelength λ TX1 This generates an optically modulated signal. The power level of the transmission signal input to E / O11-1 may be adjusted as needed.

[0020] Control signals are input to E / O11-2. For example, if the transmit signal is an IF signal, E / O11-2 receives control signals including the beam control signal, the clock signal, and the TDD signal. For example, if the transmit signal is an RF signal, E / O11-2 receives control signals including the beam control signal and the TDD signal.

[0021] The beam control signal is information S for forming a beam in one of m (where m is an integer greater than or equal to 1) directions. T1 ,…,S Tm It includes at least one of the following. The m beam control signals correspond one-to-one with the m transmit beams, and the user can switch the transmit beam in the desired direction by switching the beam control signals. E / O11-2 uses the input control signal to transmit the wavelength λ TX2 The optical signal is intensity-modulated. As a result, E / O11-2 has a wavelength λ TX2Generate an optical modulation signal. As the intensity modulation method, a direct modulation method (DML: Directly Modulated Laser) may be used, or an external modulation method (MAZ: Mach Zehnder Modulator, EAM: Electro Absorption Modulator) may be used. The modulation signal propagating through the optical transmission path 40 may be ODSB (Optical Double Sideband), OSSB (Optical Single Sideband), or OCS (Optical Carrier Suppression). The control signal input to E / O11-2 may be adjusted in power level as needed.

[0022] The optical multiplexer 12 multiplexes the optical modulation signal with wavelength λ TX1 generated by E / O11-1 and the optical modulation signal with wavelength λ TX2 generated by E / O11-2. Specifically, the optical multiplexer 12 generates a wavelength multiplexed signal by wavelength division multiplexing the optical modulation signal with wavelength λ TX1 generated by E / O11-1 and the optical modulation signal with wavelength λ TX2 generated by E / O11-2. The optical multiplexer 12 outputs the generated wavelength multiplexed signal to the remote station 20 via the optical transmission path 40.

[0023] The remote station 20 includes an optical demultiplexer 21, a plurality of O / E22-1 to 22-2, a demultiplexing unit 23, a frequency conversion unit 24, a beam forming unit 25, and a transmit / receive switching unit 33. When the aggregation station 10 transmits an RF signal as a transmission signal, the remote station 20 may not include the frequency conversion unit 24. Here, the case where the remote station 20 includes the frequency conversion unit 24 will be described assuming that the aggregation station 10 transmits an IF signal as a transmission signal. The transmit / receive switching unit 33 may be integrated with the frequency conversion unit 24 or may be provided in the beam forming unit 25.

[0024] The optical demultiplexer 21 demultiplexes the wavelength multiplexed signal transmitted through the optical transmission path 40. Thereby, the optical demultiplexer 21 demultiplexes the wavelength multiplexed signal into wavelengths λ TX1The optical modulation signal and the wavelength λ TX2 The optical modulation signal is separated into two wavelengths. The optical demultiplexer 21 separates the wavelength λ. TX1 The optically modulated signal is output to O / E22-1, with wavelength λ TX2 The optically modulated signal is output to O / E22-2.

[0025] O / E22-1 has a wavelength λ TX1 This is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. Wavelength λ TX1 The optically modulated signal includes the transmission signal. Therefore, O / E22-1 outputs an electrical signal including the transmission signal to the frequency conversion unit 24. If the extension station 20 is not equipped with a frequency conversion unit 24, O / E22-1 will output the electrical signal to the beamforming unit 25.

[0026] O / E22-2 has a wavelength λ TX2 This is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. Wavelength λ TX2 The optical modulation signal includes a control signal. Therefore, O / E22-2 outputs an electrical signal including the control signal to the demultiplexer 23.

[0027] The demultiplexer 23 demultiplexes the electrical signal output by O / E22-2 according to its frequency. This allows the demultiplexer 23 to separate the electrical signal into a clock signal (CLK in Figure 1) and a beam control signal (S in Figure 1). Ti The demultiplexer 23 separates the clock signal from the TDD signal. The demultiplexer 23 outputs the clock signal to the frequency conversion unit 24, the beam control signal to the beam forming unit 25, and the TDD signal to the transmit / receive switching unit 33.

[0028] The frequency conversion unit 24 converts the frequency of the transmission signal (IF signal) contained in the electrical signal output from O / E22-1 into an RF band frequency signal (RF signal) using the LO signal generated based on the clock signal.

[0029] The transmit / receive switching unit 33 is a switch for switching between transmit and receive based on the input TDD signal. Specifically, the transmit / receive switching unit 33 switches the connection to electrically connect the frequency conversion unit 24 and the beamforming unit 25 at the transmit timing indicated by the TDD signal. When the frequency conversion unit 24 and the beamforming unit 25 are electrically connected, the RF band frequency signal (RF signal) output from the frequency conversion unit 24 is output to the beamforming unit 25. At the receive timing indicated by the TDD signal, the transmit / receive switching unit 33 switches the connection to electrically connect the beamforming unit 25 and the frequency conversion unit used for reception.

[0030] The beamforming unit 25 performs beamforming based on the input beam control signal and emits a radio signal corresponding to the transmission signal. The beamforming unit 25 is a functional unit equipped with a control unit that can control the direction of beamforming at the extension station 20.

[0031] Figure 2 shows a first configuration example of the beamforming unit 25. The beamforming unit 25 shown in Figure 2 comprises a control unit 251, n (where n is an integer of 2 or more) phase shifters 252-1 to 252-n, and n antennas 253 to 253-n. One antenna 253 is attached to each phase shifter 252.

[0032] The control unit 251 receives the input beam control signal S Ti Accordingly, the phase shifters 252-1 to 252-n are electrically controlled. This allows the phase of the transmission signal input to each phase shifter 252-1 to 252-n to be adjusted.

[0033] The phase shifters 252-1 to 252-n adjust the phase of the input transmission signal according to the control of the control unit 251.

[0034] Antennas 253 to 253-n convert the transmitted signal, whose phase has been adjusted by phase shifters 252-1 to 252-n, into a radio signal and radiate it.

[0035] In the beamforming unit 25 shown in Figure 2, when a transmission signal is input in phase, each phase shifter 252-1 to 252-n adjusts the phase to correspond to the beam control signal, and reinforces the signal in phase in a specific direction, thereby forming the transmission beam. Beam control signal S Ti Depending on the direction of reinforcement in the same phase, the direction of reinforcement differs. The beamforming unit 25 shown in Figure 2 has reversibility of input and output, and when an RF signal arrives from the beam direction corresponding to a certain beam control signal, it reinforces in the same phase. When an RF signal arrives from any other direction, it destructively cancels out the signal. Because the beamforming unit 25 shown in Figure 2 has these properties, the beam control signal S Ti Depending on the selection, the direction of the received beam can also be selected. The configuration of the first example of the beamforming unit 25 is described, for example, in Reference 1.

[0036] (Reference 1: Keith Benson, “Beamforming ICs for Phased Arrays Simplifying Antenna Design”, Analog Dialogue 53-01, January 2019)

[0037] Figure 3 shows a second example configuration of the beamforming unit 25. The beamforming unit 25 shown in Figure 3 comprises a control switch 254, a passive beamforming unit 255, and N (where N is an integer of 2 or more) antennas 253 to 253-N.

[0038] The control switch 254 receives the input beam control signal S Ti This is a switch that can switch the connection between the input port and the output port accordingly. The transmission signal is input to the input port. Each port of the passive beam forming unit 255 is connected to the output port. The control switch 254 has one input port and m output ports SW-1 to SW-m. The output ports SW-1 to SW-m of the control switch 254 and the beam control signal S T1 ~S Tm There is a one-to-one correspondence between them. For example, the control switch 254 is a beam control signal S. T1If this is input, connect the input port and output port SW-1. This will cause the transmission signal to be output from output port SW-1 of the control switch 254.

[0039] The passive beamforming unit 255 is a functional unit capable of beamforming by applying a specific phase difference to the output beams from each antenna 256-1 to 256-N according to the input port. The passive beamforming unit 255 has m input ports and N (where N is an integer greater than or equal to 1) output ports. The passive beamforming unit 255 is, for example, a beamforming circuit, a reflector, or a lens.

[0040] The beamforming circuit has m first ports and N second ports. The m output ports SW-1 to SW-m of the control switch 254 are connected to the m first ports of the beamforming circuit. The antennas 256-1 to 256-N are connected to the second ports of the beamforming circuit.

[0041] A beamforming circuit, when a signal is input to one first port, outputs signals from N second ports that have the same amplitude and a linear phase slope. The phase slope differs depending on the first port. The beamforming circuit can form a beam in a direction corresponding to the first port to which the transmitted signal was input.

[0042] A beamforming circuit has reversibility of input and output, so that when a signal arrives from the beam direction corresponding to a certain first port, the signal is output only from that first port. Examples of beamforming circuits include Butler matrices, Brass matrices, Nolan matrices, and Rottman lenses (see, for example, Reference 2).

[0043] (Reference 2: Wei Hong, Zhi Hao Jiang, Chao Yu, Jianyi Zhou, Peng Chen, Zhiqiang Yu, Hui Zhang, Binqi Yang, Xingdong Pang, Mei Jiang, Yujian Cheng, Mustafa K. Taher Al-Nuaimi, Yan Zhang, Jixin Chen, and Shiwen He, “Multibeam antenna technologies for 5G wireless communications”, IEEE Transactions on Antennas and Propagation, 65(12), 6231-6249 (2017).)

[0044] Figure 4 is a sequence diagram showing the processing flow of the wireless communication system 1 in the first embodiment. In Figure 4, the case in which an IF signal is input as a transmission signal to the aggregation station 10 is explained as an example.

[0045] E / O11-1 of aggregation station 10 takes the IF signal (transmit signal) as input. E / O11-1 uses the input IF signal (transmit signal) to determine the wavelength λ TX1 The optical signal is intensity-modulated (step S101). This modulates the wavelength λ. TX1 A light-modulated signal is generated. E / O11-1 is the generated wavelength λ TX1 The optically modulated signal is output to the optical multiplexer 12.

[0046] E / O11-2 of aggregation station 10 receives a control signal as input. E / O11-2 uses the input control signal to measure wavelength λ TX2 The optical signal is intensity-modulated (step S102). This modulates the wavelength λ. TX2 A light-modulated signal is generated. E / O11-2 is the generated wavelength λ TX2The optical modulation signal is output to the optical multiplexer 12. The control signals input to E / O11-2 include a beam control signal corresponding to the direction in which beam formation is desired at the extension station 20, a clock signal, and a TDD signal. The beam control signal corresponding to the direction in which beam formation is desired at the extension station 20 is selected by the user.

[0047] The optical multiplexer 12 receives the wavelength λ output from E / O11-1. TX1 The optically modulated signal and the wavelength λ output from E / O11-2 TX2 The optical modulation signal is wavelength-division multiplexed (step S103). This generates a wavelength-division multiplexed signal. The optical multiplexing unit 12 sends the generated wavelength-division multiplexed signal to the optical transmission line 40 (step S104). The wavelength-division multiplexed signal sent to the optical transmission line 40 is input to the extension station 20.

[0048] The optical demultiplexer 21 of the extension station 20 demultiplexes the input wavelength-multiplexed signal (step S105). As a result, the wavelength-multiplexed signal is divided into wavelength λ TX1 The optical modulation signal and the wavelength λ TX2 The optical modulation signal is separated into the optical demultiplexing unit 21, with wavelength λ. TX1 The output port of is connected to O / E22-1, with wavelength λ TX2 The output port is connected to O / E22-2. Therefore, the wavelength λ TX1 The optically modulated signal is output to O / E22-1, with wavelength λ TX2 The optically modulated signal is output to O / E22-2.

[0049] O / E22-1 has a wavelength λ TX1 The optically modulated signal is directly detected to extract the electrical signal. O / E22-1 outputs the electrical signal, including the extracted IF signal (transmission signal), to the frequency conversion unit 24. O / E22-2 outputs the wavelength λ TX2 The optically modulated signal is directly detected to extract the electrical signal (step S106). O / E22-2 outputs the electrical signal, including the extracted control signal, to the demultiplexer 23.

[0050] The demultiplexer 23 demultiplexes the electrical signal output from the O / E22-2 according to its frequency (step S107). Specifically, the demultiplexer 23 separates the clock signal, beam control signal, and TDD signal contained in the electrical signal output from the O / E22-2 according to their frequency. This separates the clock signal, beam control signal, and TDD signal from the electrical signal. The demultiplexer 23 outputs the clock signal to the frequency conversion unit 24, the beam control signal to the beam forming unit 25, and the TDD signal to the transmit / receive switching unit 33.

[0051] The frequency conversion unit 24 generates an LO signal based on the clock signal output from the demultiplexer unit 23. Using the generated LO signal, the frequency conversion unit 24 converts the frequency of the IF signal (transmit signal) contained in the electrical signal output from O / E22-1 to an RF band frequency (step S108). In other words, the frequency conversion unit 24 converts the frequency of the transmit signal. The frequency conversion unit 24 outputs the frequency-converted transmit signal to the transmit / receive switching unit 33.

[0052] The transmit / receive switching unit 33 switches the connection so that the frequency conversion unit 24 and the beamforming unit 25 are electrically connected at the transmission timing indicated by the TDD signal. As a result, the frequency-converted transmission signal output from the frequency conversion unit 24 is output to the beamforming unit 25.

[0053] The beamforming unit 25 forms a beam based on the beam control signal output from the demultiplexing unit 23 and radiates the frequency-converted transmission signal wirelessly (step S108). Here, the specific operation of the beamforming unit 25 will be explained using the beamforming unit 25 shown in Figure 2 as an example. The control unit 251 controls the amount of phase rotation adjusted by each phase shifter 252-1 to 252-n according to the input beam control signal.

[0054] Phase shifters 252-1 to 252-n adjust the phase of the input transmission signal. In this process, phase shifters 252-1 to 252-n adjust the phase of the transmission signal so that the beam is formed in a direction corresponding to the beam control signal input to the control unit 251, under the control of the control unit 251. The transmission signal whose phase has been adjusted by phase shifters 252-1 to 252-n is output to antennas 253-1 to 253-n. Antennas 253-1 to 253-n convert the input transmission signal into a radio signal and radiate it.

[0055] As described above, the wireless communication system 1 makes it possible to perform beamforming control while suppressing a decrease in wavelength utilization efficiency. Specifically, in the wireless communication system 1, the aggregation station 10 transmits a control signal including a beam control signal (a signal for phase control) for controlling beam formation, and a main signal, to the extension station 20 at different wavelengths, and the extension station 20 performs beamforming based on the beam control signal. This makes it possible to achieve remote beamforming using only two wavelengths. Therefore, as in the conventional method, it does not require a fixed optical wavelength equal to the number of antenna elements in the extension station for controlling one beam. In this way, the wireless communication system 1 can significantly reduce the number of wavelengths required for controlling one beam. As a result, it becomes possible to perform beamforming control while suppressing a decrease in wavelength utilization efficiency.

[0056] Conventionally, it was necessary to prepare a direct detection unit for the optical modulation signal at the extension station for each antenna element, which limited the simplification and cost reduction of the extension station. In contrast, in wireless communication system 1, the configuration required for single-beam control at the extension station 20 can be significantly reduced compared to conventional systems. Therefore, it becomes possible to suppress the high cost of the equipment.

[0057] (Second embodiment) In the first embodiment, a configuration was described in which the aggregation station converts the transmission signal and control signal into optical signals of different wavelengths and then wavelength division multiplexing is performed. In the second embodiment, the difference from the first embodiment is that the aggregation station frequency multiplexes the transmission signal and control signal and transmits them through the optical transmission path using the subcarrier multiplexing (SCM) method. The second embodiment will be described mainly in terms of the differences from the first embodiment.

[0058] Figure 5 shows an example configuration of the wireless communication system 1a in the second embodiment. The wireless communication system 1a comprises a central station 10a and an extended station 20a. The central station 10a and the extended station 20a are connected via an optical transmission path 40.

[0059] The aggregation station 10a remotely controls the beamforming of the extension station 20a using a multiplexed signal generated by frequency multiplexing the transmission signal and the control signal. For example, the aggregation station 10a remotely controls the beamforming of the extension station 20a using analog RoF technology.

[0060] The aggregation station 10a comprises an E / O 11a and a multiplexing unit 13.

[0061] The multiplexer 13 receives the transmission signal and the control signal as inputs. For example, the control signal input to the multiplexer 13 includes a beam control signal, a clock signal, and a TDD signal. The multiplexer 13 generates a multiplexed signal by frequency multiplexing the input transmission signal and control signal. The multiplexer 13 outputs the generated multiplexed signal to E / O 11a. The power levels of the transmission signal and control signal input to the multiplexer 13 may be adjusted as needed.

[0062] E / O11a uses the input multiplexed signal to determine the wavelength λ TX The optical signal is intensity-modulated. As a result, E / O11a has a wavelength λ TX It generates an optically modulated signal. E / O11a generates the generated wavelength λ TX The optically modulated signal is sent to the optical transmission line 40.

[0063] The projecting station 20a comprises an O / E 22a, a demultiplexer 23, a frequency conversion unit 24, a beamforming unit 25, a demultiplexer 26, and a transmit / receive switching unit 33. Note that the projecting station 20a does not need to include the frequency conversion unit 24 if the aggregation station 10a transmits an RF signal as the transmit signal. Here, we will describe the case where the aggregation station 10a transmits an IF signal and the projecting station 20a includes the frequency conversion unit 24.

[0064] O / E22a is the wavelength λ transmitted from aggregation station 10a. TX This is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. Wavelength λ TX The optically modulated signal includes the transmission signal and the control signal. Therefore, O / E22a outputs an electrical signal including the transmission signal and the control signal to the demultiplexer 26.

[0065] The demultiplexer 26 demultiplexes the electrical signal output from O / E 22a according to its frequency. This separates the transmitted signal from the control signal. The demultiplexer 26 outputs the transmitted signal to the frequency converter 24 and the control signal to the demultiplexer 23. If the extension station 20a is not equipped with a frequency converter 24, the demultiplexer 26 will output the transmitted signal to the beamforming unit 25.

[0066] The processing of the wave demultiplexing unit 23, the frequency conversion unit 24, and the beamforming unit 25 is the same as in the first embodiment, so a description will be omitted.

[0067] Figure 6 is a sequence diagram showing the processing flow of the wireless communication system 1a in the second embodiment. In Figure 6, the case in which an IF signal is input as a transmission signal to the aggregation station 10a is explained as an example. In Figure 6, the same reference numerals as in Figure 4 are used for processes similar to those in Figure 4, and their explanation is omitted.

[0068] The multiplexer 13 of the aggregation station 10a receives the IF signal (transmission signal) and the control signal as inputs. The multiplexer 13 frequency multiplexes the input IF signal (transmission signal) and the control signal (step S201). This generates a multiplexed signal. The control signal input to the multiplexer 13 includes a beam control signal corresponding to the direction in which beam formation is desired at the extension station 20a, and a clock signal. The beam control signal corresponding to the direction in which beam formation is desired at the extension station 20a is selected by the user. The multiplexer 13 outputs the generated multiplexed signal to the E / O 11a.

[0069] E / O11a uses the multiplexed signal output from the multiplexer 13 to determine the wavelength λ TX The optical signal is intensity-modulated (step S202). This modulates the wavelength λ. TX A light-modulated signal is generated. E / O11a is the generated wavelength λ TX The optically modulated signal is sent to the optical transmission line 40 (step S203). The optically modulated signal sent to the optical transmission line 40 is input to the extension station 20a.

[0070] The O / E22a of the extension station 20a directly detects the input optically modulated signal and extracts an electrical signal (step S204). The O / E22a outputs the extracted electrical signal to the demultiplexer 26. The demultiplexer 26 demultiplexes the electrical signal output from the O / E22a according to frequency (step S205). Specifically, the demultiplexer 26 separates the transmission signal and control signal contained in the electrical signal output from the O / E22a according to frequency. This separates the transmission signal and the control signal. The demultiplexer 26 outputs the transmission signal to the frequency conversion unit 24 and the control signal to the demultiplexer 23. After that, processing from step S107 onwards is carried out.

[0071] With the wireless communication system 1a configured as described above, even when the transmission signal and control signal are frequency multiplexed, beamforming can be performed at the extension station 20a based on the beam control signal. This enables remote beamforming using only one wavelength. Therefore, unlike conventional systems, it does not require a fixed optical wavelength equal to the number of antenna elements at the extension station for single-beam control. In this way, the number of wavelengths required for single-beam control can be significantly reduced with wireless communication system 1a. As a result, beamforming control can be performed while suppressing a decrease in wavelength utilization efficiency.

[0072] (Third embodiment) In the second embodiment, a configuration was shown in which the outbound station generates the LO signal in the frequency conversion unit based on the clock signal. In contrast, the difference in the third embodiment from the second embodiment is that the LO signal is transmitted from the aggregation station. The third embodiment will be explained mainly in terms of the differences from the second embodiment.

[0073] Figure 7 shows an example configuration of the wireless communication system 1b in the third embodiment. The wireless communication system 1b comprises a central station 10b and an extended station 20b. The central station 10b and the extended station 20b are connected via an optical transmission path 40.

[0074] The aggregation station 10b remotely controls the beamforming of the extension station 20b using a multiplexed signal generated by frequency multiplexing the transmission signal, control signal, and LO signal. For example, the aggregation station 10b remotely controls the beamforming of the extension station 20b using analog RoF technology.

[0075] The aggregation station 10b comprises an E / O 11a and a multiplexing unit 13b.

[0076] The multiplexer 13b receives the transmission signal, control signal, and LO signal as inputs. For example, the control signal input to the multiplexer 13b includes the beam control signal and the TDD signal. In this third embodiment, it is assumed that the frequency conversion of the transmission signal is performed at the extension station 20b. Therefore, the transmission signal input to the multiplexer 13b is the IF signal. The multiplexer 13b generates a multiplexed signal by frequency multiplexing the input transmission signal, control signal, and LO signal. The multiplexer 13b outputs the generated multiplexed signal to the E / O 11a. The power levels of the transmission signal, control signal, and LO signal input to the multiplexer 13 may be adjusted as needed.

[0077] The projecting station 20b comprises an O / E 22b, a demultiplexer 23b, a frequency conversion unit 24b, a beamforming unit 25, a demultiplexer 26b, and a transmit / receive switching unit 33.

[0078] O / E22b is transmitted from aggregation station 10b at wavelength λ TX This is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. The wavelength λ transmitted from the aggregation station 10b TX The optically modulated signal includes a transmission signal, a control signal, and an LO signal. Therefore, O / E22b outputs an electrical signal containing the transmission signal, control signal, and LO signal to the demultiplexer 26b.

[0079] The demultiplexer 26b demultiplexes the electrical signal extracted by the O / E 22b according to its frequency. Specifically, the demultiplexer 26b separates the transmission signal, control signal, and LO signal contained in the electrical signal extracted by the O / E 22b according to their frequencies. This separates the transmission signal, control signal, and LO signal. The demultiplexer 26b outputs the transmission signal and LO signal to the frequency conversion unit 24b, and outputs the control signal to the demultiplexer 23b.

[0080] The demultiplexer 23b demultiplexes the control signal output by the demultiplexer 26b according to its frequency. As a result, the demultiplexer 23b demultiplexes the control signal into beam control signals (S in Figure 7). TiThe beam control signal is separated from the TDD signal. The demultiplexer 23b outputs the beam control signal to the beamforming unit 25 and the TDD signal to the transmit / receive switching unit 33.

[0081] The frequency conversion unit 24b converts the frequency of the transmission signal (IF signal) output from the demultiplexer unit 26b into an RF band frequency signal (RF signal) using the LO signal output from the demultiplexer unit 26b.

[0082] The processing of the beamforming unit 25 and the transmit / receive switching unit 33 is the same as in the second embodiment, so a description will be omitted.

[0083] Figure 8 is a sequence diagram showing the processing flow of the wireless communication system 1b in the third embodiment. In Figure 8, processes similar to those in Figure 6 are denoted by the same reference numerals as in Figure 6, and their explanation is omitted.

[0084] The multiplexer 13b of the aggregation station 10b receives the IF signal (transmission signal), control signal, and LO signal as inputs. The multiplexer 13b frequency multiplexes the input IF signal (transmission signal), control signal, and LO signal (step S301). This generates a multiplexed signal. The control signals input to the multiplexer 13b include a beam control signal and a TDD signal corresponding to the direction in which beam formation is desired at the extension station 20b. Unlike the second embodiment, the control signals do not include a clock signal. The beam control signal corresponding to the direction in which beam formation is desired at the extension station 20b is selected by the user. The multiplexer 13b outputs the generated multiplexed signal to the E / O 11a.

[0085] E / O11a uses the multiplexed signal output from the multiplexer 13b to determine the wavelength λ TX The optical signal is intensity-modulated (step S302). This modulates the wavelength λ. TX A light-modulated signal is generated. E / O11a is the generated wavelength λ TX The optically modulated signal is sent to the optical transmission line 40 (step S303). The optically modulated signal sent to the optical transmission line 40 is input to the extension station 20b.

[0086] The O / E 22b of the extension station 20b directly detects the input optical modulation signal and extracts an electrical signal (step S304). The O / E 22b outputs the electrical signal, which includes the IF signal (transmission signal), control signal, and LO signal, to the demultiplexer 26b. The demultiplexer 26b demultiplexes the electrical signal output from the O / E 22b according to frequency (step S305). Specifically, the demultiplexer 26b separates the transmission signal, clock signal, and LO signal contained in the electrical signal output from the O / E 22b according to frequency. The demultiplexer 26b outputs the transmission signal and LO signal to the frequency conversion unit 24b and outputs the control signal to the demultiplexer 23b. The demultiplexer 23b separates the beam control signal and the TDD signal from the control signal output from the demultiplexer 26b. The demultiplexer 23b outputs the beam control signal to the beamforming unit 25 and outputs the TDD signal to the transmit / receive switching unit 33.

[0087] The frequency conversion unit 24b uses the LO signal output from the demultiplexer 26b to convert the frequency of the IF signal (transmit signal) output from the demultiplexer 26b to an RF band frequency (step S306). In other words, the frequency conversion unit 24b converts the frequency of the transmit signal. The frequency conversion unit 24b outputs the frequency-converted transmit signal to the transmit / receive switching unit 33. The transmit / receive switching unit 33 switches the connection so that the frequency conversion unit 24b and the beamforming unit 25 are electrically connected at the transmission timing indicated by the TDD signal. As a result, the frequency-converted transmit signal output from the frequency conversion unit 24b is output to the beamforming unit 25. After that, the process in step S109 is performed.

[0088] In the wireless communication system 1b configured as described above, the aggregation station 10b transmits an optical signal, including the LO signal which is a frequency conversion signal, to the extension station 20b. This eliminates the need for the extension station 20b to generate the LO signal. Thus, the configuration of the extension station 20b can be simplified compared to the second embodiment. Many extension stations 20b are installed compared to the aggregation station 10b. Therefore, by simplifying the extension station 20b and reducing its cost, a significant cost reduction can be expected. As a result, the same effects as the second embodiment can be obtained, while the cost of realizing the system can be reduced compared to the second embodiment.

[0089] (Fourth embodiment) The first to third embodiments described the configuration for signal transmission in the downlink direction. The fourth embodiment describes the configuration for signal transmission in the uplink direction.

[0090] Figure 9 shows an example configuration of the wireless communication system 1c in the fourth embodiment. The wireless communication system 1c comprises a central station 10c and an extended station 20c. The central station 10c and the extended station 20c are connected via an optical transmission path 40.

[0091] Similar to the first embodiment, the aggregation station 10c remotely controls the beamforming of the extension station 20c by transmitting control signals to the extension station 20c. For example, the aggregation station 10c remotely controls the beamforming of the extension station 20c using analog RoF technology. Furthermore, the aggregation station 10c receives the received signals received by the extension station 20c.

[0092] The extension station 20c performs beamforming based on a control signal transmitted from the aggregation station 10c, similar to the first embodiment. The extension station 20c receives a radio signal transmitted from an external device located in the direction in which the beam was formed. The external device is, for example, a radio device with which the extension station 20c communicates. The radio signal received by the extension station 20c is an RF band signal. The extension station 20c may transmit the received RF band signal to the aggregation station 10c, or it may convert the frequency of the received RF band signal to an IF band frequency and transmit it to the aggregation station 10c.

[0093] For example, the projection station 20c converts the received signal in the RF band or IF band and the response signal into optical signals of different wavelengths, respectively, and transmits the wavelength-division multiplexed signal generated by wavelength division multiplexing of the optical signals of different wavelengths to the aggregation station 10c. Here, the response signal is a signal used to notify information about the beamforming unit 27. For example, the response signal may include status information indicating the current settings of the antenna 253 or antenna 256 provided in the beamforming unit 27.

[0094] The projecting station 20c comprises an O / E 22, a demultiplexer 23, a beamforming unit 27, a frequency conversion unit 28, a plurality of E / O 29-1 to 29-2, an optical combining and demultiplexing unit 30, and a transmit / receive switching unit 33. The processing of the O / E 22 and the demultiplexer 23 is the same as that of the O / E 22-2 and the demultiplexer 23 in the first embodiment. Note that the projecting station 20c does not need to have a frequency conversion unit 28 when transmitting an RF signal as a received signal to the aggregation station 10c. Here, we will describe the case where the projecting station 20c transmits an IF signal as a received signal to the aggregation station 10c and is equipped with a frequency conversion unit 28. The transmit / receive switching unit 33 may be integrated with the frequency conversion unit 28 or may be provided within the beamforming unit 27.

[0095] The beamforming unit 27 has the same configuration as the beamforming unit 25. That is, the beamforming unit 27 forms a beam in accordance with the beam control signal included in the control signal transmitted from the aggregation station 10c. The beamforming unit 27 receives a radio signal transmitted from an external device located in the direction in which the beam was formed. The beamforming unit 27 converts the received radio signal into an electrical signal and outputs it to the transmit / receive switching unit 33.

[0096] The beamforming unit 27 may also output a response signal. If the beamforming unit 27 outputs a response signal, the response signal output from the beamforming unit 27 is input to E / O29-2.

[0097] In the fourth embodiment, the transmit / receive switching unit 33 switches the connection to electrically connect the frequency conversion unit 28 and the beamforming unit 27 at the reception timing indicated by the TDD signal. When the frequency conversion unit 28 and the beamforming unit 27 are electrically connected, the received signal output from the beamforming unit 27 is output to the frequency conversion unit 28. At the transmission timing indicated by the TDD signal, the transmit / receive switching unit 33 switches the connection to electrically connect the beamforming unit 27 and the frequency conversion unit used for transmission.

[0098] The frequency conversion unit 28 converts the frequency of the received signal (RF signal) output via the transmit / receive switching unit 33 into an IF band frequency signal (IF signal) using an LO signal generated based on the clock signal output from the demultiplexing unit 23.

[0099] The E / O29-1 receives the received signal. For example, if the aggregation station 10c is equipped with a frequency conversion unit 28, the E / O29-1 receives the received signal (IF signal) after frequency conversion. If the aggregation station 10c is not equipped with a frequency conversion unit 28, the E / O29-1 receives the received signal (RF signal). The E / O29-1 uses the received signal to convert the wavelength λ RX1 The optical signal is intensity-modulated. As a result, E / O29-1 has a wavelength λ RX1This generates an optically modulated signal. The power level of the received signal input to E / O29-1 may be adjusted as needed.

[0100] The response signal is input to E / O29-2. E / O29-2 uses the input response signal to measure the wavelength λ RX2 The optical signal is intensity-modulated. As a result, E / O29-2 has a wavelength λ RX2 This generates an optically modulated signal. The response signal input to E / O29-2 may have its power level adjusted as needed.

[0101] The optical combining / demultiplying unit 30 combines or demultiplies the input optical signal. Specifically, the optical combining / demultiplying unit 30 demultiplies the optical signal transmitted via the optical transmission path 40. For example, in this embodiment, the optical combining / demultiplying unit 30 receives the wavelength λ transmitted from the aggregation station 10c. TX2 A light-modulated signal of wavelength λ is input. TX2 The optical modulation signal includes, for example, a beam control signal and a clock signal. The photomultiplier / demultiplier unit 30 uses a wavelength λ TX2 The optically modulated signal is output to O / E22.

[0102] Furthermore, the photomultiplier / demultiplier section 30 uses the wavelength λ generated by E / O29-1. RX1 The optically modulated signal and the wavelength λ generated by E / O29-2 RX2 The optical modulation signal is combined with the optical modulation signal. Specifically, the optical combining / demultiplying unit 30 combines the wavelength λ generated by E / O29-1. RX1 The optically modulated signal and the wavelength λ generated by E / O29-2 RX2 A wavelength-multiplexed signal is generated by wavelength division multiplexing with the optically modulated signal. The optical multiplexing and demultiplexing unit 30 outputs the generated wavelength-multiplexed signal to the aggregation station 10c via the optical transmission line 40.

[0103] The aggregation station 10c comprises an E / O 11, an optical multiplexer / demultiplexer 14, and a plurality of O / E 15-1 to 15-2. The processing of E / O 11 is the same as that of E / O 11-2 in the first embodiment.

[0104] The optical combining / demultiplying unit 14 combines or demultiplies the input optical signal. Specifically, the optical combining / demultiplying unit 14 combines or demultiplies the wavelength λ generated by E / O 11. TX2 The optically modulated signals are combined. In the example shown in Figure 9, the optical multiplexer / demultiplexer 14 contains the wavelength λ as the signal transmitted by the aggregation station 10c. TX2 Only the optically modulated signal of wavelength λ is input. Therefore, the photomultiplier / demultiplier unit 14 receives the input wavelength λ. TX2 The optically modulated signal is output to the extension station 20c via the optical transmission line 40.

[0105] Furthermore, the optical multiplexer / demultiplexer unit 14 demultiplexes the optical signal transmitted via the optical transmission path 40. For example, in this embodiment, the optical multiplexer / demultiplexer unit 14 receives a wavelength multiplexed signal transmitted from the extension station 20c. As a result, the optical multiplexer / demultiplexer unit 14 divides the wavelength multiplexed signal into wavelength λ RX1 The optical modulation signal and the wavelength λ RX2 The optical modulation signal is separated into two. The optical combining and demultiplexing unit 14 uses a wavelength λ RX1 The optically modulated signal is output to O / E15-1, with wavelength λ RX2 The optically modulated signal is output to O / E15-2.

[0106] O / E15-1 has a wavelength λ RX1 This is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. Wavelength λ RX1 The optically modulated signal includes the received signal.

[0107] O / E15-2 has a wavelength λ RX2 This is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. Wavelength λ RX2 The optical modulation signal includes a response signal.

[0108] Figure 10 is a sequence diagram showing the processing flow of the wireless communication system 1c in the fourth embodiment. It is assumed that at the start of processing in Figure 10, beamforming control is performed by the aggregation station 10c to the extension station 20c. For example, in the processing of Figure 10, the beam control signal S Ti Assume that the beam is formed in the direction corresponding to [the specified direction].

[0109] The beamforming unit 27 of the extension station 20c controls the beam control signal S Ti The beamforming unit 27 receives a radio signal transmitted from an external device located in the corresponding direction via antenna 253-i or 256-i (step S401). The beamforming unit 27 converts the received radio signal into an electrical signal and outputs it to the transmit / receive switching unit 33. For example, the beamforming unit 27 outputs the electrical signal from the port corresponding to the port that received the radio signal (for example, the port to which antenna 253-i or 256-i is directly or indirectly connected).

[0110] The transmit / receive switching unit 33 switches the connection so that the frequency conversion unit 28 and the beamforming unit 27 are electrically connected at the reception timing indicated by the TDD signal. As a result, the electrical signal output from the beamforming unit 27 is output to the frequency conversion unit 28.

[0111] The frequency conversion unit 28 generates an LO signal based on the clock signal output from the demultiplexer unit 23. The frequency conversion unit 28 uses the generated LO signal to convert the frequency of the electrical signal (received signal) output via the transmit / receive switching unit 33 to the frequency of the IF band (step S402). In other words, the frequency conversion unit 28 converts the frequency of the received signal. The frequency conversion unit 28 outputs the frequency-converted received signal to E / O29-1.

[0112] E / O29-1 takes the frequency-converted received signal output from the frequency conversion unit 28 as input. E / O29-1 uses the input frequency-converted received signal to calculate the wavelength λ RX1 The optical signal is intensity-modulated (step S403). This modulates the wavelength λ. RX1 A light-modulated signal is generated. E / O29-1 is the generated wavelength λ RX1 The optically modulated signal is output to the optical multiplexer / demultiplexer 30.

[0113] When a response signal is output from the beamforming unit 27, E / O29-2 takes the response signal output from the beamforming unit 27 as input. Using the input response signal, E / O29-2 calculates the wavelength λ RX2Modulate the optical signal in intensity (step S404). As a result, an optical modulation signal with wavelength λ RX2 is generated. E / O29-2 outputs the generated optical modulation signal with wavelength λ RX2 to the optical multiplexer / demultiplexer 30.

[0114] The optical multiplexer / demultiplexer 30 wavelength-division multiplexes the optical modulation signal with wavelength λR X1 output from E / O29-1 and the optical modulation signal with wavelength λR X2 output from E / O29-2 (step S405). As a result, a wavelength-multiplexed signal is generated. The optical multiplexer / demultiplexer 30 sends the generated wavelength-multiplexed signal to the optical transmission line 40 (step S406). The wavelength-multiplexed signal sent to the optical transmission line 40 is input to the concentration station 10c.

[0115] The optical multiplexer / demultiplexer 14 of the concentration station 10c demultiplexes the input wavelength-multiplexed signal (step S407). As a result, the wavelength-multiplexed signal is demultiplexed into the optical modulation signal with wavelength λ RX1 and the optical modulation signal with wavelength λ RX2 . At the output port with wavelength λ RX1 in the optical multiplexer / demultiplexer 14, O / E15-1 is connected, and at the output port with wavelength λ RX2 , O / E15-2 is connected. Therefore, the optical modulation signal with wavelength λ RX1 is output to O / E15-1, and the optical modulation signal with wavelength λ RX2 is output to O / E15-2.

[0116] O / E15-1 directly detects the optical modulation signal with wavelength λ RX1 and extracts an electrical signal. As a result, O / E15-1 extracts an IF signal (received signal). O / E15-2 directly detects the optical modulation signal with wavelength λ RX2 and extracts an electrical signal (step S408). As a result, O / E15-2 extracts a response signal.

[0117] According to the wireless communication system 1c configured as described above, the same effects as in the first embodiment can be obtained in the uplink direction.

[0118] (Modification of the fourth embodiment) The wireless communication system 1c may incorporate the technology of the wireless communication system 1 in the first embodiment for downlink communication. In this case, the aggregation station 10c is equipped with a configuration for downlink communication (for example, multiple E / O11-1 to 11-2 instead of E / O11). The extension station 20c is equipped with a configuration for downlink communication (for example, multiple O / E22-1 to 22-2 instead of O / E22). The frequency conversion unit 28 performs the same processing as the frequency conversion unit 24 during downlink communication. The beamforming unit 27 performs the same processing as the beamforming unit 25 during downlink communication. When the technology of wireless communication system 1 and the technology of wireless communication system 1c are combined, bidirectional communication becomes possible using the time-division duplexing (TDD) method.

[0119] When combining the technologies of wireless communication system 1 and wireless communication system 1c to perform bidirectional communication using frequency division duplex (FDD), different frequencies are used for the uplink and downlink directions, and the extension station 20c does not have a transmit / receive switching unit 33. With this configuration, bidirectional communication in both the uplink and downlink directions becomes possible even with frequency division duplex (FDD).

[0120] (Fifth embodiment) In the fourth embodiment, a configuration was described in which the extended station converts the received signal and the response signal into optical signals of different wavelengths, and then wavelength division multiplexing is performed. In the fifth embodiment, the difference from the fourth embodiment is that the extended station frequency multiplexes the received signal and the response signal. The fifth embodiment will be described mainly in terms of the differences from the fourth embodiment.

[0121] Figure 11 shows an example configuration of the wireless communication system 1d in the fifth embodiment. The wireless communication system 1d comprises a central station 10d and an extended station 20d. The central station 10d and the extended station 20d are connected via an optical transmission path 40.

[0122] Similar to the second embodiment, the aggregation station 10d remotely controls the beamforming of the remote station 20d by transmitting a control signal to the remote station 20d. For example, the aggregation station 10d remotely controls the beamforming of the remote station 20d using analog RoF technology. Further, the aggregation station 10d receives the received signal received at the remote station 20d.

[0123] Similar to the second embodiment, the remote station 20d performs beamforming based on the control signal transmitted from the aggregation station 10d. The remote station 20d receives a wireless signal transmitted from an external device located in the direction in which the beam is formed. The wireless signal received by the remote station 20d is a signal in the RF band. The remote station 20d may transmit the RF band received signal to the aggregation station 10d, or may convert the frequency of the RF band received signal to the IF band frequency and transmit it to the aggregation station 10d. For example, the remote station 20d converts a multiplexed signal generated by frequency multiplexing the received signal in the RF band or IF band and the response signal into an optical signal and transmits it to the aggregation station 10d.

[0124] The remote station 20d includes an O / E 22d, a demultiplexing unit 23, a beamforming unit 27, a frequency conversion unit 28, an E / O 29d, an optical multiplexer / demultiplexer 30d, a multiplexing unit 31, a demultiplexing unit 32, and a transmit / receive switching unit 33. Note that when the remote station 20d transmits an RF signal to the aggregation station 10d as a received signal, it may not include the frequency conversion unit 28. Here, the case where the remote station 20d includes the frequency conversion unit 28 will be described assuming that the remote station 20d transmits an IF signal to the aggregation station 10d as a received signal.

[0125] The O / E 22d is a direct detection unit that directly detects an optical modulation signal with a wavelength λ TX and extracts an electrical signal. Thereby, the O / E 22d extracts at least the control signal. The O / E 22d outputs the control signal to the demultiplexing unit 32.

[0126] The demultiplexer 32 demultiplexes the signal extracted by the O / E 22d according to its frequency. For example, the demultiplexer 32 separates the control signal from other signals from the signal extracted by the O / E 22d. The demultiplexer 32 outputs the control signal to the demultiplexer 23. At the aggregation station 10d, the control signal and other signals may have been combined by the combiner 16. Therefore, it is necessary to separate the control signal from other signals at the extension station 20d. In this embodiment, the demultiplexer 32 is provided with the function of separating the control signal from other signals.

[0127] The combined wave unit 31 receives the received signal and the response signal as inputs. The received signal input to the combined wave unit 31 is either the RF band received signal received by the beamforming unit 27, or the received signal that has been frequency-converted to the IF band frequency by the frequency conversion unit 28. The combined wave unit 31 generates a multiplexed signal by frequency multiplexing the input received signal and the response signal. The combined wave unit 31 outputs the generated multiplexed signal to E / O 29d. The power levels of the received signal and the response signal input to the combined wave unit 31 may be adjusted as needed.

[0128] E / O29d uses the input multiplexed signal to determine the wavelength λ RX The optical signal is intensity-modulated. As a result, E / O29d has a wavelength λ RX It generates an optically modulated signal. E / O29d is the generated wavelength λ RX The optically modulated signal is sent to the optical multiplexer / demultiplexer 30d.

[0129] The optical multiplexer / demultiplexer 30d combines or demultiplexes the input optical signal. Specifically, the optical multiplexer / demultiplexer 30d demultiplexes the optical signal transmitted via the optical transmission path 40. For example, in this embodiment, the optical multiplexer / demultiplexer 30d receives the wavelength λ transmitted from the aggregation station 10d. TX A light-modulated signal of wavelength λ is input. TX The optical modulation signal includes, for example, a beam control signal and a clock signal. The optical multiplexing and demultiplexing unit 30d uses a wavelength λ TX The optically modulated signal is output to O / E22d.

[0130] Furthermore, the photomultiplier / demultiplier section 30d is the wavelength λ generated by E / O29d. RX The optically modulated signals are combined. In the example shown in Figure 11, the optical multiplexer / demultiplexer 30d contains the wavelength λ as the signal transmitted by the extension station 20d. RX Only the optically modulated signal is input. Therefore, the photomultiplier / demultiplier unit 30d receives the input wavelength λ. RX The optically modulated signal is output to the aggregation station 10d via the optical transmission line 40.

[0131] The aggregation station 10d comprises an E / O 11a, an optical multiplexing / demultiplexing unit 14d, an O / E 15d, a multiplexing unit 16, and a demultiplexing unit 17.

[0132] At least control signals are input to the multiplexer 16. For example, the control signals input to the multiplexer 16 include a beam control signal, a clock signal, and a TDD signal. The multiplexer 16 generates a multiplexed signal by frequency multiplexing the input control signals. In the same case as in the second embodiment, when a transmission signal and control signals are input to the multiplexer 16, the multiplexer 16 generates a multiplexed signal by frequency multiplexing the input transmission signal and control signals. The multiplexer 16 outputs the generated multiplexed signal to E / O 11a. The power level of the control signals input to the multiplexer 16 may be adjusted as needed.

[0133] The optical multiplexer / demultiplexer 14d combines or demultiplexes the input optical signal. Specifically, the optical multiplexer / demultiplexer 14d combines or demultiplexes the wavelength λ generated by E / O 11a. TX The optically modulated signals are combined. In the example shown in Figure 11, the optical multiplexer / demultiplexer 14d contains the wavelength λ as the signal transmitted by the aggregation station 10d. TX Only the optically modulated signal is input. Therefore, the photomultiplier / demultiplier unit 14d receives the input wavelength λ. TX The optically modulated signal is output to the extension station 20d via the optical transmission line 40.

[0134] Furthermore, the optical multiplexer / demultiplexer 14d demultiplexes the optical signal transmitted via the optical transmission path 40. For example, in this embodiment, the optical multiplexer / demultiplexer 14d receives the wavelength λ transmitted from the extension station 20d. RXA light-modulated signal is input. The photomultiplier / demultiplier unit 14d is at wavelength λ RX The optically modulated signal is output to O / E15d.

[0135] O / E15d has a wavelength λ RX This is a direct detection unit that directly detects the optically modulated signal and extracts the electrical signal. As a result, O / E15-1d extracts the received signal and the response signal.

[0136] The demultiplexer 17 demultiplexes the received signal and response signal output from O / E15d according to their frequencies. This separates the received signal from the response signal.

[0137] Figure 12 is a sequence diagram showing the processing flow of the wireless communication system 1d in the fifth embodiment. It is assumed that at the start of processing in Figure 12, beamforming control is performed by the aggregation station 10d to the extension station 20d. For example, in the processing in Figure 12, the beam control signal S Ti Assume that the beam is formed in the direction corresponding to [the specified direction].

[0138] The beamforming unit 27 of the extension station 20d controls the beam control signal S Ti The beamforming unit 27 receives a radio signal transmitted from an external device located in the corresponding direction via antenna 253-i or 256-i (step S501). The beamforming unit 27 converts the received radio signal into an electrical signal and outputs it to the transmit / receive switching unit 33. For example, the beamforming unit 27 outputs an electrical signal from the port corresponding to the port that received the radio signal (for example, the port to which antenna 253-i or 256-i is directly or indirectly connected). Furthermore, the beamforming unit 27 outputs a response signal to the multiplexing unit 31 as needed.

[0139] The transmit / receive switching unit 33 switches the connection so that the frequency conversion unit 28 and the beamforming unit 27 are electrically connected at the reception timing indicated by the TDD signal. As a result, the electrical signal output from the beamforming unit 27 is output to the frequency conversion unit 28.

[0140] The frequency conversion unit 28 generates an LO signal based on the clock signal output from the demultiplexer unit 23. The frequency conversion unit 28 uses the generated LO signal to convert the frequency of the electrical signal (received signal) output via the transmit / receive switching unit 33 to the frequency of the IF band (step S502). In other words, the frequency conversion unit 28 converts the frequency of the received signal. The frequency conversion unit 28 outputs the frequency-converted received signal to the combiner unit 31.

[0141] The multiplexer 31 frequency multiplexes the received signal after frequency conversion and the response signal (step S503). This generates a multiplexed signal. The multiplexer 31 outputs the generated multiplexed signal to the E / O29d. The E / O29d takes the multiplexed signal output from the multiplexer 31 as input. The E / O29d uses the input multiplexed signal to calculate the wavelength λ RX The optical signal is intensity-modulated (step S504). This modulates the wavelength λ. RX A light-modulated signal is generated. E / O29d is the generated wavelength λ RX The optically modulated signal is output to the optical multiplexer / demultiplexer 30d.

[0142] The photomultiplier / demultiplier section 30d receives the wavelength λ output from E / O29. RX The optical modulation signal is taken as input. The optical multiplexer / demultiplexer 30d takes the input wavelength λ as input. RX The optically modulated signal is sent to the optical transmission line 40 (step S505). The wavelength λ sent to the optical transmission line 40 RX The optically modulated signal is input to the aggregation station 10d.

[0143] The photomultiplier / demultiplier section 14d of the aggregation station 10d receives the input wavelength λ. RX The optically modulated signal is demultiplexed (step S506). This results in wavelength λ RX The optically modulated signal is output to O / E15d. O / E15d has a wavelength λ RXThe optically modulated signal is directly detected to extract an electrical signal. As a result, O / E15d extracts the IF signal (received signal) and the response signal (step S507). O / E15d outputs the IF signal (received signal) and the response signal to the demultiplexer 17. The demultiplexer 17 demultiplexes the IF signal (received signal) and the response signal output from O / E15d according to their frequencies (step S508). As a result, the demultiplexer 17 separates the IF signal (received signal) and the response signal.

[0144] With the wireless communication system 1d configured as described above, the same effects as in the second embodiment can be obtained in the uplink direction as well.

[0145] (Modified version of the fifth embodiment) The wireless communication system 1d may incorporate the technology of the wireless communication system 1a in the second embodiment for downlink communication. In this case, the multiplexer 16 of the aggregation station 10d receives the transmission signal and the control signal as input, and the input transmission signal and control signal are frequency multiplexed. The demultiplexer 32 of the extension station 20d receives the electrical signal, which is the output from the O / E 22d, and the input electrical signal is separated into the control signal and other signals (e.g., the transmission signal). The demultiplexer 32 outputs the control signal to the demultiplexer 23 and the other signals to the frequency converter 28. The frequency converter 28 performs the same processing as the frequency converter 24 during downlink communication. The beamforming unit 27 performs the same processing as the beamforming unit 25 during downlink communication. When the technology of wireless communication system 1a and the technology of wireless communication system 1d are combined, bidirectional communication becomes possible using the time-division duplexing (TDD) method.

[0146] When combining the technologies of wireless communication system 1a and wireless communication system 1d to perform bidirectional communication using frequency division duplexing (FDD), different frequencies are used for the uplink and downlink directions, and the extension station 20d does not have a transmit / receive switching unit 33. With this configuration, bidirectional communication in both the uplink and downlink directions becomes possible even with frequency division duplexing (FDD).

[0147] (Sixth embodiment) In the fifth embodiment, a configuration was shown in which the extension station generates the LO signal in the frequency conversion unit based on the clock signal. In contrast, the sixth embodiment differs from the fifth embodiment in that the LO signal is transmitted from the aggregation station. The sixth embodiment will be explained focusing on the differences from the fifth embodiment.

[0148] Figure 13 shows an example configuration of the wireless communication system 1e in the sixth embodiment. The wireless communication system 1e comprises a central station 10e and an extended station 20e. The central station 10e and the extended station 20e are connected via an optical transmission path 40.

[0149] The aggregation station 10e remotely controls the beamforming of the extension station 20e using a multiplexed signal generated by frequency multiplexing at least the control signal and the LO signal. For example, the aggregation station 10e remotely controls the beamforming of the extension station 20e using analog RoF technology. Furthermore, the aggregation station 10e receives the received signal received by the extension station 20e.

[0150] The extension station 20e performs beamforming based on control signals included in the multiplexed signal transmitted from the aggregation station 10e, similar to the third embodiment. The extension station 20e receives radio signals transmitted from external devices located in the direction in which the beam was formed. The radio signals received by the extension station 20e are RF band signals. The extension station 20d may transmit the received RF band signal to the aggregation station 10e, or it may convert the frequency of the received RF band signal to an IF band frequency and transmit it to the aggregation station 10e. For example, the extension station 20e converts the multiplexed signal generated by frequency multiplexing the received RF band or IF band signal with the response signal into an optical signal and transmits it to the aggregation station 10e.

[0151] The projecting station 20e includes an O / E 22e, a demultiplexer 23e, a beamforming unit 27, a frequency conversion unit 28e, an E / O 29d, an optical combining / demultiplexing unit 30, a combining unit 31, a demultiplexer 32e, and a transmit / receive switching unit 33.

[0152] O / E22e has a wavelength λ TXThis is a direct detection unit that directly detects the optically modulated signal and extracts an electrical signal. As a result, O / E22e extracts at least the control signal and the LO signal. O / E22d outputs the control signal and the LO signal to the demultiplexer 32e.

[0153] The demultiplexer 32e demultiplexes the electrical signal extracted by the O / E 22e according to its frequency. Specifically, the demultiplexer 32e separates the control signal and the LO signal contained in the electrical signal extracted by the O / E 22e according to their frequencies. This separates the control signal from the LO signal. The demultiplexer 32e outputs the LO signal to the frequency conversion unit 28e and the control signal to the demultiplexer 23e.

[0154] The demultiplexer 23e receives the control signal separated by the demultiplexer 32e. The demultiplexer 23e demultiplexes the input control signal according to its frequency. As a result, the demultiplexer 23e separates the control signal from the beam control signal (S in Figure 13). Ti The beam control signal is separated from the TDD signal. The demultiplexer 23e outputs the beam control signal to the beamforming unit 27 and the TDD signal to the transmit / receive switching unit 33.

[0155] The frequency conversion unit 28e converts the frequency of the received signal (RF signal) output via the transmit / receive switching unit 33 into an IF band frequency signal (IF signal) using the LO signal output from the demultiplexer unit 32e.

[0156] The aggregation station 10e comprises an E / O 11a, an optical multiplexing / demultiplexing unit 14d, an O / E 15d, a multiplexing unit 16e, and a demultiplexing unit 17.

[0157] At least a control signal and an LO signal are input to the multiplexer 16e. For example, the control signals input to the multiplexer 16e include a beam control signal and a TDD signal. The multiplexer 16e generates a multiplexed signal by frequency multiplexing the input control signal and LO signal. In the same case as in the third embodiment, when a transmission signal, a control signal, and an LO signal are input to the multiplexer 16e, the multiplexer 16e generates a multiplexed signal by frequency multiplexing the input transmission signal, control signal, and LO signal. The multiplexer 16e outputs the generated multiplexed signal to E / O 11a. The power levels of the control signal and LO signal input to the multiplexer 16 may be adjusted as needed.

[0158] With the wireless communication system 1e configured as described above, the same effects as those of the third embodiment can be obtained in the uplink direction as well.

[0159] (Modified version of the sixth embodiment) The wireless communication system 1e may incorporate the technology of the wireless communication system 1b in the third embodiment for downlink communication. In this case, the multiplexer 16e of the aggregation station 10e receives the transmit signal, control signal, and LO signal as in the third embodiment, and the input transmit signal, control signal, and LO signal are frequency multiplexed. The demultiplexer 32e of the extension station 20e receives the electrical signal extracted by the O / E 22e, and the input electrical signal is separated into a control signal and other signals (e.g., the transmit signal and the LO signal). The demultiplexer 32e outputs the control signal to the demultiplexer 23e and the other signals to the frequency converter 28e. The frequency converter 28e performs the same processing as the frequency converter 24e during downlink communication. The beamforming unit 27 performs the same processing as the beamforming unit 25 during downlink communication. When the technology of wireless communication system 1b and the technology of wireless communication system 1e are combined, bidirectional communication becomes possible using the time-division duplexing (TDD) method.

[0160] When combining the technologies of wireless communication system 1b and wireless communication system 1e to perform bidirectional communication using frequency division duplexing (FDD), different frequencies are used for the uplink and downlink directions, and the extension station 20e does not have a transmit / receive switching unit 33. This configuration enables bidirectional communication in both the uplink and downlink directions.

[0161] In the above-described embodiment, some of the functional parts of the aggregation stations 10, 10a, 10b, 10c, 10d, 10e and the extension stations 20, 20a, 20b, 20c, 20d, 20e may be implemented by a computer. In that case, the program for implementing this function may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be loaded into a computer system and executed. The term "computer system" as used herein includes hardware such as an operating system and peripheral devices.

[0162] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. In addition, "computer-readable recording media" may also include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs over networks such as the Internet or communication lines such as telephone lines, and those that hold programs for a certain period of time, such as volatile memory inside computer systems that act as servers or clients in such cases. Moreover, the above-mentioned programs may be for the purpose of realizing some of the functions described above, or they may be able to realize the above-mentioned functions in combination with programs already recorded in the computer system, or they may be realized using programmable logic devices such as FPGAs.

[0163] 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. [Industrial applicability]

[0164] This invention is applicable to wireless communication systems that perform RoF transmission. [Explanation of Symbols]

[0165] 10, 10a, 10b, 10c, 10d, 10e...Aggregation station, 20, 20a, 20b, 20c, 20d, 20e...Outgoing station, 11-1, 11-2, 11a, 29, 29d, 29-1, 29-2...E / O, 12...Optical multiplexing section, 13, 16, 16e, 31...combining section, 14, 14d, 30, 30d...optical multiplexing / demultiplexing section, 15, 15d, 15-1, 15-2, 22-1, 22-2, 22a...O / E, 17, 23, 23e, 26...demultiplexing section, 21...optical demultiplexing section, 24, 28, 28e...frequency conversion section, 25, 27...beam forming section, 33, 33e...transmission / reception switching section, 251...Control unit, 252-1~252-n...Phase shifter, 253-1~253-n, 256-1~256-N...Antenna, 254...Control switch, 255...Passive beam forming unit

Claims

1. A wireless communication method in a wireless communication system comprising a aggregation station and an extension station that performs beamforming according to the control of the aggregation station, The aggregation station transmits an optical signal to the extension station via an optical transmission path, which includes at least a beam control signal for controlling beamforming at the extension station, a TDD (Time Division Duplex) signal indicating the timing for switching between transmission and reception at the extension station, and a transmission signal which is the data to be transmitted, thereby performing beamforming control at the extension station. A wireless communication method in which the extended station transmits the transmission signal by setting a phase difference for beamforming in a specific direction in a phase shifter or by switching a switch, based on the beam control signal included in the optical signal, at the transmission timing indicated by the TDD signal included in the optical signal.

2. The aggregation station generates the optical signal by intensity modulating the beam control signal and the transmission signal to different wavelengths and performing wavelength division multiplexing. The aforementioned extension station decouples the optical signal according to its wavelength and acquires the beam control signal contained in the optical signal, thereby setting a phase difference for beamforming in the specific direction in a phase shifter or by switching a switch. The wireless communication method according to claim 1.

3. The aggregation station generates the optical signal by frequency multiplexing the beam control signal and the transmission signal and then intensity modulating them to a specific wavelength. The aforementioned projection station directly detects the optical signal to extract an electrical signal, and then acquires the beam control signal contained in the extracted electrical signal to set a phase difference for beamforming in the specific direction, either by setting it in a phase shifter or by switching a switch. The wireless communication method according to claim 1.

4. If the transmitted signal is in the intermediate frequency band, The aggregation station generates the optical signal by frequency multiplexing the beam control signal, the transmission signal, and the frequency conversion signal, and then intensity modulating them to a specific wavelength. The aforementioned extension station, after directly detecting the optical signal and extracting an electrical signal, frequency-converts the frequency of the transmission signal included in the extracted electrical signal based on the frequency conversion signal, and obtains the beam control signal included in the electrical signal to set the phase difference for beamforming in the specific direction in a phase shifter or by switching a switch. The wireless communication method according to claim 3.

5. The extension station performs beamforming in the specific direction by controlling the amount of phase rotation in a plurality of phase shifters in accordance with the beam control signal, or performs beamforming in the specific direction by switching the connection of a switch so that the transmission signal is input to a port capable of beamforming in the specific direction in accordance with the beam control signal. The wireless communication method according to any one of claims 1 to 4.

6. The extension station converts a radio signal transmitted from an external device into an electrical signal and inputs it to the second port of the beamforming unit, outputs the electrical signal from the first port of the beamforming unit corresponding to the second port, and sends an optical signal obtained by intensity modulating an optical signal using the electrical signal to the aggregation station. The aggregation station acquires at least a received signal from the optical signal transmitted from the extension station. The wireless communication method according to any one of claims 1 to 4.

7. The aggregation station further includes a clock signal, which is a reference signal used when the extension station generates an LO signal for frequency conversion of the transmission signal from an intermediate frequency to a radio frequency, into the optical signal, and transmits it to the extension station via the optical transmission path, thereby causing the extension station to perform frequency conversion processing based on the clock signal, and then performs beamforming control of the extension station. The aforementioned broadcasting station converts the frequency band of the transmission signal to a radio frequency band signal using the LO signal generated based on the clock signal included in the optical signal, and then transmits the frequency-converted transmission signal by setting the phase difference in the phase shifter or by switching a switch. The wireless communication method according to any one of claims 1 to 3.

8. The extension station outputs the electrical signal input to the second port of the beamforming unit from the first port of the beamforming unit at the reception timing indicated by the TDD signal included in the optical signal, and transmits the optical signal obtained by intensity modulating the optical signal using the electrical signal to the aggregation station. The wireless communication method according to claim 6.

9. The extension station further includes a response signal, which is a signal for notifying information relating to the beamforming unit, in the optical signal and transmits it to the aggregation station. The wireless communication method according to claim 6.

10. A base station device in a wireless communication system comprising a aggregation station and an extension station that performs beamforming according to the control of the aggregation station, An aggregation station that performs beamforming control of the extension station by transmitting an optical signal to the extension station via an optical transmission path, the optical signal including at least a beam control signal for controlling beamforming at the extension station, a TDD (Time Division Duplex) signal which is a signal indicating the timing for switching between transmission and reception at the extension station, and a transmission signal which is the data to be transmitted, An extension station that transmits the transmission signal by setting a phase difference for beamforming in a specific direction based on the beam control signal included in the optical signal, at the transmission timing indicated by the TDD signal included in the optical signal, by setting it in a phase shifter or by switching a switch, A base station device equipped with the following features.

11. A wireless communication system comprising a aggregation station and an extension station that performs beamforming according to the control of the aggregation station, The aforementioned aggregation station is An optical signal including at least a beam control signal for controlling beamforming at the extension station, a TDD (Time Division Duplex) signal which indicates the timing for switching between transmission and reception at the extension station, and a transmission signal which is the data to be transmitted, is transmitted to the extension station via an optical transmission path to perform beamforming control of the extension station. The aforementioned branch office, A beamforming unit transmits the transmission signal by setting a phase difference for beamforming in a specific direction based on the beam control signal included in the optical signal, at the transmission timing indicated by the TDD signal included in the optical signal, by setting it in a phase shifter or by switching a switch. A wireless communication system equipped with [the necessary components].

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