WIRELESS TRANSMITTING SYSTEM, WIRELESS RECEIVING SYSTEM, BASE STATION APPARATUS, WIRELESS COMMUNICATION SYSTEM, WIRELESS TRANSMITTING METHOD, AND WIRELESS RECEIVING METHOD

Abstract

An accommodation station transmission unit modulates light to generate an optical signal based on an RF signal and outputs the generated optical signal, a base station transmission unit obtains the optical signal from an input port, demultiplexes the obtained optical signal for each wavelength, outputs the demultiplexed optical signals from output ports of corresponding wavelengths from among a plurality of output ports allocated to each of the wavelengths of the light, and demodulates the RF signal by converting the optical signals output by the output ports into electrical signals, a plurality of transmission antennas emit the demodulated RF signal, and a reflect array or a transmit array receives the RF signal emitted by each of the transmission antennas and forms a transmission beam in a different direction for each position of the transmission antenna that is a transmission source of the RF signal for each RF signal.

Claims

1. A wireless transmission system, comprising: an accommodation station transmission unit configured to modulate light based on a plurality of RF signals to generate a plurality of optical signals and output the plurality of generated optical signals; and a base station transmission unit configured to obtain the plurality of optical signals output by the accommodation station transmission unit, wherein the base station transmission unit includes: an optical demultiplexer including a plurality of output ports each assigned to a wavelength of the light, the optical demultiplexer being configured to obtain, from an input port, the plurality of optical signals output by the accommodation station transmission unit, demultiplex the plurality of obtained optical signals for each wavelength, and output the plurality of demultiplexed optical signals from the output ports corresponding to each wavelength, a plurality of photoelectric converters each connected to each of the plurality of output ports of the optical demultiplexer, the plurality of photoelectric converters being configured to convert the optical signal output by the optical demultiplexer into an electrical signal to demodulate the RF signal, and output the demodulated RF signal, a plurality of transmission antennas each connected to each of the plurality of photoelectric converters and configured to emit the plurality of RF signals output by the photoelectric converters, and a transmission beam formation unit including a reflect array or a transmit array, the reflect array or the transmit array being configured to receive a plurality of the RF signals emitted by the plurality of transmission antennas and form, for each of the plurality of received RF signals, a plurality of transmission beams in different directions depending on positions of the plurality of transmission antennas that are transmission sources of the plurality of RF signals.

2. The wireless transmission system according to claim 1, wherein the accommodation station transmission unit includes one optical modulator, and the optical modulator modulates light of a single wavelength to generate the optical signal based on the RF signal, or the accommodation station transmission unit includes a plurality of optical modulators and an optical multiplexer, light of different wavelengths is given to each of the plurality of optical modulators, the light given to each of the optical modulators is modulated to generate the optical signal based on the RF signal, and the optical multiplexer multiplexes and outputs a plurality of the optical signals generated by the plurality of optical modulators.

3. A wireless reception system, comprising: a base station reception unit; and an accommodation station reception unit, wherein the base station reception unit includes: a reception beam formation unit including a reflect array or a transmit array, the reflect array or the transmit array being configured to receive a plurality of arriving RF signals and converge the plurality of RF signals at a plurality of convergence positions that differ depending on arriving directions of the plurality of received RF signals to form a plurality of reception beams; a plurality of reception antennas disposed at each of the plurality of convergence positions and configured to receive the RF signals that have converged at the plurality of convergence positions; a plurality of optical modulators connected to the plurality of reception antennas, the plurality of optical modulators being configured to obtain light of different wavelengths and modulate the obtained light to generate a plurality of optical signals based on the plurality of RF signals received by the plurality of connected reception antennas, and an optical multiplexer configured to multiplex the plurality of optical signals of different wavelengths generated by the plurality of optical modulators and output the plurality of multiplexed optical signals; and the accommodation station reception unit is configured to obtain the plurality of optical signals output by the base station reception unit, and includes: an optical demultiplexer configured to obtain the plurality of optical signals output by the optical multiplexer of the base station reception unit and demultiplex the plurality of optical signals for each wavelength, and an output unit configured to convert the plurality of optical signals demultiplexed by the optical demultiplexer into a plurality of electrical signals to demodulate the plurality of RF signals and output the plurality of demodulated RF signals.

4. The wireless reception system according to claim 3, wherein the output unit includes a plurality of photoelectric converters, the plurality of photoelectric converters convert, into an electrical signal, the optical signal of any one of the wavelengths included in the optical signals output by the optical demultiplexer to demodulate the RF signal and outputs the demodulated RF signal, or the plurality of photoelectric converters is each connected to an output of the optical demultiplexer, each of the plurality of photoelectric converters obtains the optical signals of the mutually different wavelengths demultiplexed by the optical demultiplexer, converts the obtained optical signals into electrical signals to demodulate the plurality of RF signals, and outputs the plurality of demodulated RF signals.

5. (canceled)

6. (canceled)

7. A wireless transmission method performed by a wireless transmission system including an accommodation station transmission unit and a base station transmission unit, the method comprising: by the accommodation station transmission unit, modulating light based on a plurality of RF signals to generate a plurality of optical signals and outputting the plurality of generated optical signals; by an optical demultiplexer of the base station transmission unit, obtaining, from an input port, the plurality of optical signals output by the accommodation station transmission unit, demultiplexing the plurality of obtained optical signals for respective wavelengths, and outputting the plurality of demultiplexed optical signals from a plurality of output ports corresponding to the wavelengths from among the plurality of output ports each assigned to each of the wavelengths of the light; by a plurality of photoelectric converters of the base station transmission unit, each of which is connected to the plurality of output ports of the optical demultiplexer, converting the plurality of optical signals output by the optical demultiplexer into electrical signals to demodulate the plurality of RF signals and outputting the plurality of demodulated RF signal; by a plurality of transmission antennas of the base station transmission unit, emitting the plurality of RF signals output by each of the photoelectric converters; and by a transmission beam formation unit of the base station transmission unit, which includes a reflect array or a transmit array, receiving the plurality of RF signals emitted by each of the plurality of transmission antennas and forming a plurality of transmission beams, for each of the plurality of RF signals, in different directions for positions of the plurality of transmission antennas that are transmission sources of the plurality of RF signals.

8. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] FIG. 1 is a block diagram illustrating a configuration of a basic embodiment.

[0040] FIG. 2 is a block diagram illustrating the basic embodiment in a separated manner for a wireless transmission system and a wireless reception system.

[0041] FIG. 3 is a block diagram illustrating a configuration of a wireless transmission system according to a first embodiment.

[0042] FIG. 4 is a block diagram illustrating an internal configuration of an accommodation station transmission unit according to the first embodiment.

[0043] FIG. 5 is a flowchart illustrating a flow of processing performed by the wireless transmission system according to the first embodiment.

[0044] FIG. 6 is a block diagram illustrating an internal configuration of another configuration example of the accommodation station transmission unit according to the first embodiment.

[0045] FIG. 7 is a block diagram illustrating another configuration example of the wireless transmission system according to the first embodiment.

[0046] FIG. 8 is a block diagram illustrating a configuration of a wireless reception system according to a second embodiment.

[0047] FIG. 9 is a block diagram illustrating an internal configuration of an optical modulation unit according to the second embodiment.

[0048] FIG. 10 is a block diagram illustrating an internal configuration of an accommodation station reception unit according to the second embodiment.

[0049] FIG. 11 is a flowchart illustrating a flow of processing performed by the wireless reception system according to the second embodiment.

[0050] FIG. 12 is a block diagram illustrating an internal configuration of another configuration example of the accommodation station reception unit according to the second embodiment.

[0051] FIG. 13 is a block diagram illustrating another configuration example of the wireless reception system according to the second embodiment.

[0052] FIG. 14 is a block diagram illustrating a configuration of a wireless transmission system according to a third embodiment.

[0053] FIG. 15 is a block diagram illustrating an internal configuration of an accommodation station transmission unit according to the third embodiment.

[0054] FIG. 16 is a flowchart illustrating a flow of processing performed by the wireless transmission system according to the third embodiment.

[0055] FIG. 17 is a block diagram illustrating another configuration example of the wireless transmission system according to the third embodiment.

[0056] FIG. 18 is a block diagram illustrating a configuration of a wireless reception system according to a fourth embodiment.

[0057] FIG. 19 is a flowchart illustrating a flow of processing performed by the wireless reception system according to the fourth embodiment.

[0058] FIG. 20 is a block diagram illustrating another configuration example of the wireless reception system according to the fourth embodiment.

[0059] FIG. 21 is a diagram (No. 1) illustrating an example of a connection configuration between a base station apparatus and an accommodation station apparatus according to the first to fourth embodiments.

[0060] FIG. 22 is a diagram (No. 2) illustrating an example of a connection configuration between the base station apparatus and the accommodation station apparatus according to the first to fourth embodiments.

[0061] FIG. 23 is a block diagram illustrating a technique disclosed in PTL 1.

[0062] FIG. 24 is a block diagram (No. 1) illustrating a technique disclosed in NPL 1.

[0063] FIG. 25 is a block diagram (No. 2) illustrating a technique disclosed in NPL 1.

[0064] FIG. 26 is a diagram illustrating a beamforming method using a reflect array.

[0065] FIG. 27 is a diagram illustrating a beamforming method using a transmit array.

DESCRIPTION OF EMBODIMENTS

Basic Embodiment

[0066] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a wireless communication system 90 according to an embodiment of the present invention. The wireless communication system 90 includes an accommodation station apparatus 2, a base station apparatus 1, a terminal apparatus 9, and an optical fiber 3 connecting the accommodation station apparatus 2 to the base station apparatus 1.

[0067] The accommodation station apparatus 2 includes an accommodation station transmission unit 10 and an accommodation station reception unit 40. The base station apparatus 1 includes a base station transmission unit 20 and a base station reception unit 30. The accommodation station transmission unit 10 transmits an optical signal modulated with an RF signal to the base station transmission unit 20 through the optical fiber 3. The base station transmission unit 20 receives the optical signal, demodulates the RF signal, and transmits the RF signal to the terminal apparatus 9 through wireless communication. The terminal apparatus 9 transmits the RF signal to the base station reception unit 30 through wireless communication. The base station reception unit 30 receives the RF signal transmitted by the terminal apparatus 9 and transmits the optical signal modulated with the received RF signal to the accommodation station reception unit 40 through the optical fiber 3.

[0068] FIG. 2 is a block diagram illustrating the wireless communication system 90 in a separated manner for a transmission side and a reception side. FIG. 2 illustrates the terminal apparatus 9 in FIG. 1 in a separated manner for a reception terminal apparatus 9-1 configured to perform only reception of the RF signal and a transmission terminal apparatus 9-2 configured to perform only transmission of the RF signal for convenience of explanation. Further, the optical fiber 3 is assumed to have two cores, and a downstream optical fiber 3-1 configured to transmit the RF signal to the reception terminal apparatus 9-1 and an upstream optical fiber 3-2 configured to transmit the RF signal from the transmission terminal apparatus 9-2 are illustrated in a separated manner for convenience of explanation.

[0069] If the wireless communication system 90 is separated into a transmission side and a reception side, the wireless communication system 90 can be represented as a wireless transmission system 90t and a wireless reception system 90r. The wireless transmission system 90t includes an accommodation station transmission unit 10, a downstream optical fiber 3-1, a base station transmission unit 20, and a reception terminal apparatus 9-1. The wireless reception system 90r includes a transmission terminal apparatus 9-2, a base station reception unit 30, an upstream optical fiber 3-2, and an accommodation station reception unit 40.

[0070] Hereinafter, wireless transmission systems 90t on the transmission side in a single mode, that is, with a configuration of transmitting and receiving a beam of a single RF signal will be described as wireless transmission systems 90t1a and 90t1b in a first embodiment. Further, wireless reception systems 90r on the reception side in a single mode will be described as wireless reception systems 90r1a and 90r1b in a second embodiment.

[0071] In addition, wireless transmission systems 90t on the transmission side in a multi mode, that is, with a configuration of transmitting and receiving beams of a plurality of RF signals will be described as wireless transmission systems 90t2a and 90t2b in a third embodiment. Moreover, wireless reception systems 90r on the reception side in multi mode will be described as wireless reception systems 90r2a and 90r2b in a fourth embodiment.

First Embodiment: Transmission Side in Single Mode “Application Example of Reflect Array”

[0072] FIG. 3 is a block diagram illustrating a configuration of the wireless transmission system 90t1a according to the first embodiment. The wireless transmission system 90t1a includes an accommodation station transmission unit 10s, a base station transmission unit 20a, a downstream optical fiber 3-1, and a reception terminal apparatus 9-1 which is illustrated not in FIG. 3 but in FIG. 2.

[0073] The accommodation station transmission unit 10s includes an optical modulator 11. The optical modulator 11 obtains light of a single wavelength λ.sub.Ti arbitrary selected from light of n wavelengths λ.sub.T1 to λ.sub.Tn, performs intensity modulation with an RF signal to be transmitted using the light of the wavelength λ.sub.Ti as an optical carrier, and generates an optical signal of the wavelength λ.sub.Ti. Here, the wavelengths λ.sub.T1 to λ.sub.Tn are mutually different wavelengths, n is an integer that is equal to or greater than two, and i is any value from 1 to n. The optical modulator 11 outputs the generated optical signal with the wavelength λ.sub.T1 to the downstream optical fiber 3-1.

[0074] FIG. 4 is a block diagram illustrating an internal configuration of an accommodation station transmission unit 10sa, which is an example of a specific configuration of an accommodation station transmission unit 10s configured to generate light of a single wavelength λ.sub.Ti. Note that the optical modulator 11 illustrated in FIG. 4 has the same configuration as that of the optical modulator 11 in FIG. 3. The accommodation station transmission unit 10sa illustrated in FIG. 4 includes an optical modulator 11, a transmission wavelength control unit 12a, and a wavelength variable light source 13.

[0075] The transmission wavelength control unit 12a outputs a control signal for designating a wavelength of light to be generated to the wavelength variable light source 13. The wavelength variable light source 13 generates light of any one arbitrary wavelength λ.sub.Ti from among the wavelengths λ.sub.T1 to λ.sub.Tn. Once the wavelength variable light source 13 receives the control signal output by the transmission wavelength control unit 12a, the wavelength variable light source 13 generates and outputs the light of the wavelength λ.sub.Ti, designated by the control signal. In other words, the wavelength λ.sub.T1 of the optical signal generated and output by the optical modulator 11 is switched by the transmission wavelength control unit 12a switching the wavelength designated by the control signal.

[0076] Returning to FIG. 3, the downstream optical fiber 3-1 delivers the optical signal of the wavelength λ.sub.Ti output by the optical modulator 11 to the base station transmission unit 20a. The base station transmission unit 20a includes an optical demultiplexer 21, n O/E converters (in the specification, the “O/E converters” may also be referred to as “photoelectric converters”) 22-1 to 22-n, n transmission antennas 23-1 to 23-n, and a reflect array 24-1 which is a transmission beam formation unit configured to form a transmission beam.

[0077] The optical demultiplexer 21 includes one input port and n output ports, and the one input port is connected to the downstream optical fiber 3-1. Each of then output ports of the optical demultiplexer 21 is assigned to each of the n wavelengths λ.sub.T1 to λ.sub.Tn in a fixed manner. The O/E converters 22-1 to 22-n are connected to the n output ports, respectively, and for example, the wavelengths λ.sub.T1, λ.sub.T2, . . . , λ.sub.Ti, . . . , λ.sub.Tn are assigned in a fixed manner in the order from the output port to which the O/E converter 22-1 is connected.

[0078] The optical demultiplexer 21 obtains the optical signal transmitted through the downstream optical fiber 3-1, demultiplexes the obtained optical signal for each wavelength, and each of the demultiplexed optical signals is branched and output to the output port corresponding to each wavelength. Each of the O/E converters 22-1 to 22-n obtains the optical signals output by the optical demultiplexer 21 from the n output ports and converts the obtained optical signals into electrical signals, thereby demodulating and outputting the RF signals superimposed on the optical signals.

[0079] Each of the transmission antennas 23-1 to 23-n is connected to the O/E converters 22-1 to 22-n and emits radio waves of the RF signals output by the O/E converters 22-1 to 22-n.

[0080] The reflect array 24-1 has a plane for receiving the radio waves of the RF signals. The reflect array 24-1 is disposed at a position at which the radio waves of the RF signals emitted by the transmission antennas 23-1 to 23-n can be received by the plane.

[0081] An element configured to reflect the radio waves of the RF signals is formed on the plane of the reflect array 24-1, and if the element receives the RF signals, the element changes phases of the RF signals to strengthen each other in phase in a specific direction and reflects the RF signals (hereinafter, the action of the element on the RF signals will be represented with an expression that “the reflect array reflects the RF signals”).

[0082] If a radio wave of an RF signal emitted by a certain transmission antenna, for example, the transmission antenna 23-i is reflected by the reflect array 24-1, then the reflected radio wave of the RF signal is strengthened in the same phase in a specific direction, and a transmission beam 5-i is formed in the specific direction. The amount of change in phase of the radio wave of the RF signal is different in accordance with each of the positions of the transmission antennas 23-1 to 23-n that emit the radio waves of the RF signals. Thus, because the n RF signals emitted by the transmission antennas 23-1 to 23-n are reflected by the reflect array 24-1 and strengthen each other in phase in different directions, and transmission beams 5-1 to 5-n are formed in the different directions.

[0083] Processing Performed by Wireless Transmission System According to First Embodiment

[0084] FIG. 5 is a flowchart illustrating a flow of processing performed by the wireless transmission system 90t1a according to the first embodiment. The following description will be given on the assumption that the accommodation station transmission unit 10sa illustrated in FIG. 4, for example, is provided as the accommodation station transmission unit 10s.

[0085] The transmission wavelength control unit 12a of the accommodation station transmission unit 10sa outputs, to the wavelength variable light source 13, a control signal for designating the wavelength λ.sub.Ti as any one of the wavelengths. The wavelength variable light source 13 generates light of the wavelength λ.sub.Ti designated by the control signal and outputs the light to the optical modulator 11. The optical modulator 11 performs intensity modulation with the RF signal to be transmitted and generates an optical signal using the light of the wavelength λ.sub.Ti output by the wavelength variable light source 13 as an optical carrier. The optical modulator 11 outputs the generated optical signal to the downstream optical fiber 3-1 (Step Sa1).

[0086] The downstream optical fiber 3-1 delivers the optical signal output by the optical modulator 11 to the optical demultiplexer 21 of the base station transmission unit 20a. The optical demultiplexer 21 demultiplexes the optical signal obtained from the downstream optical fiber 3-1 into the n wavelengths λ.sub.T1 to λ.sub.Tn. By the optical demultiplexer 21, each of the demultiplexed optical signals is branched to the output port corresponding to the wavelength and output to the O/E converters 22-1 to 22-n connected to the output ports (Step Sa2).

[0087] Here, the optical signal output by the optical modulator 11 is only the optical signal of the wavelength λ.sub.Ti. Thus, the optical demultiplexer 21 demultiplexes only the optical signal of the wavelength λ.sub.Ti, and only the O/E converter 22-i connected to the output port corresponding to the wavelength λ.sub.Ti obtains the optical signal. The O/E converter 22-i converts the optical signal of the wavelength λ.sub.Ti branched and output by the optical demultiplexer 21 into an electrical signal and demodulates the RF signal (Step Sa3).

[0088] The O/E converter 22-i outputs the demodulated RF signal to the transmission antenna 23-i. The transmission antenna 23-i emits the radio wave of the RF signal output by the O/E converter 22-i (Step Sa4). If the radio wave of the RF signal emitted by the transmission antenna 23-i is reflected by the reflect array 24-1, the transmission beam 5-i is formed in a specific direction depending on the position of the transmission antenna 23-i (Step Sa5). The reception terminal apparatus 9-1 receives and obtains the RF signal transmitted by the transmission beam 5-i.

[0089] Another Configuration Example of Accommodation Station Transmission Unit According to First Embodiment

[0090] Note that an accommodation station transmission unit 10sb illustrated in FIG. 6 may be applied instead of the accommodation station transmission unit 10sa illustrated in FIG. 4 as the accommodation station transmission unit 10s. The accommodation station transmission unit 10sb illustrated in FIG. 6 includes an optical modulator 11, a transmission wavelength control unit 12b, a multiple-wavelength light source 14, an optical demultiplexer 15, and n×1 optical switches 16. Note that the optical modulator 11 illustrated in FIG. 6 has the same configuration as that of the optical modulator 11 in FIG. 3.

[0091] The multiple-wavelength light source 14 generates and outputs light of the wavelengths λ.sub.T1 to λ.sub.Tn. The optical demultiplexer 15 includes one input port and n output ports, and each of the n output ports is assigned to each of the n wavelengths λ.sub.T1 to λ.sub.Tn in a fixed manner. The optical demultiplexer 15 demultiplexes the light of the wavelengths λ.sub.T1 to λ.sub.Tn output by the multiple-wavelength light source 14 for each wavelength, and the demultiplexed light is branched and output to the output port corresponding to the wavelengths of the demultiplexed light.

[0092] The n×1 optical switches 16 include n input ports and one output port, and each of the n input ports is connected to each of then output ports of the optical demultiplexer 15. The n×1 optical switches 16 changes the switches based on a control signal received from the transmission wavelength control unit 12b and connects any one of the n input ports to the output port.

[0093] The transmission wavelength control unit 12b outputs, to the n×1 optical switches 16, a control signal to connect, to the output port, the input port that obtains, from the optical demultiplexer 15, the light of the one wavelength λ.sub.Ti sent to the optical modulator 11. The wavelength of the optical signal generated and output by the optical modulator 11 is switched by the transmission wavelength control unit 12b switching an output port that is a connecting destination of the input port of the n×1 optical switches 16 using the control signal.

[0094] In a case in which the accommodation station transmission unit 10sb is applied and the transmission beam 5-i is formed, in Step Sa1 in FIG. 5, the transmission wavelength control unit 12b of the accommodation station transmission unit 10sb outputs, to the n×1 optical switches 16, a control signal that connects the input port for obtaining the wavelength λ.sub.Ti from the optical demultiplexer 15 to the output port.

[0095] Note that in FIG. 6, n light sources that generate light of the wavelengths λ.sub.T1 to λ.sub.Tn may be applied instead of the multiple-wavelength light source 14 and the optical demultiplexer 15 and each of the n light sources may be connected to each of the input ports of the n×1 optical switches 16.

First Embodiment: Transmission Side in Single Mode “Application Example of Transmit Array”

[0096] FIG. 7 is a block diagram illustrating a configuration of the wireless transmission system 90t1b that is another configuration example of the first embodiment. In FIG. 7, the same reference signs will be applied to the same configurations as those in FIG. 3, and different configurations will be described below. The wireless transmission system 90t1b includes an accommodation station transmission unit 10s, a base station transmission unit 20b, a downstream optical fiber 3-1, and a reception terminal apparatus 9-1 illustrated in FIG. 2 although not illustrated in FIG. 7.

[0097] The base station transmission unit 20b includes an optical demultiplexer 21, n O/E converters 22-1 to 22-n, n transmission antennas 23-1 to 23-n, and a transmit array 24-2 that is a transmission beam formation unit configured to form a transmission beam.

[0098] The transmit array 24-2 has a plane configured to receive radio waves of RF signals. The transmit array 24-2 is disposed at a position at which the radio waves of the RF signals emitted by the transmission antennas 23-1 to 23-n can be received by the plane. Elements are formed on one plane and the other plane of the transmit array 24-2, and when the element on the one plane receives the radio waves of the RF signals, the element on the other plane changes the phases of the RF signals to strengthen in phase in a specific direction and emits the RF signals (hereinafter, the action of the element on the RF signal may be simply represented with an expression that “the RF signal passes through the transmit array”).

[0099] When a radio wave of an RF signal emitted by a certain transmission antenna, for example, the transmission antenna 23-i passes through the transmit array 24-2, the radio wave of the RF signal that has passed through the transmit array 24-2 is strengthened in phase in a specific direction, and the transmission beam 5-i is formed in the specific direction. The amount of phase change of the radio wave of the RF signal is different in accordance with each of the positions of the transmission antennas 23-1 to 23-n that emit the radio waves of the RF signals. Thus, because the n RF signals emitted by the transmission antennas 23-1 to 23-n are strengthened in phase in different directions by passing through the transmit array 24-2, transmission beams 5-1 to 5-n are formed in the different directions.

[0100] Processing in Another Configuration Example of First Embodiment

[0101] In processing performed by the wireless transmission system 90t1b, in Step Sa1 to Sa4, the processing as with the wireless transmission system 90t1a is performed as illustrated in the flowchart of FIG. 5. When the radio wave of the RF signal emitted by the transmission antenna 23-i passes through the transmit array 24-2, then the transmission beam 5-i is formed in the specific direction depending on the position of the transmission antenna 23-i in Step Say. The reception terminal apparatus 9-1 receives and obtains the RF signal transmitted by the transmission beam 5-i.

[0102] Note that the accommodation station transmission unit 10sa illustrated in FIG. 4 may be applied or the accommodation station transmission unit 10sb illustrated in FIG. 6 may be applied as the accommodation station transmission unit 10s included in the wireless transmission system 90t1b similarly to the wireless transmission system 90t1a.

[0103] In the wireless communication systems 90t1a and 90t1b according to the first embodiment, the accommodation station transmission unit 10s includes one optical modulator 11, and based on the RF signal, the optical modulator 11 modulates the light of the single wavelength λ.sub.Ti, generates an optical signal, and outputs the generated optical signal. The base station transmission units 20a and 20b include the optical demultiplexer 21, the transmission antennas 23-1 to 23-n, the O/E converters 22-1 to 22-n, and the reflect array 24-1, or the transmit array 24-2. The optical demultiplexer 21 includes a plurality of output ports associated to each wavelength of light, obtains the optical signal output by the accommodation station transmission unit 10s from the input port, demultiplexes the obtained optical signal for each wavelength, and outputs the demultiplexed optical signals from the output ports of the corresponding wavelengths. Each of the O/E converters 22-1 to 22-n is connected to the plurality of output ports of the optical demultiplexer 21, converts the optical signals output by the optical demultiplexer 21 into electrical signals to demodulate the RF signals, and outputs the demodulated RF signals. The transmission antennas 23-1 to 23-n are connected to the O/E converters 22-1 to 22-n, respectively, and the transmission antenna 23-i emits the RF signal output by the O/E converter 22-i. The reflect array 24-1 or the transmit array 24-2 receives the RF signal emitted by the transmission antenna 23-i and forms the transmission beam 5-i in a direction in accordance with the position of the transmission antenna 23-i that is a transmission source of the received RF signal.

[0104] In a case in which the reception terminal apparatus 9-1 that serves as a transmission destination of an RF signal to be transmitted, for example, is replaced with another reception terminal apparatus 9-1 in the aforementioned wireless transmission systems 90t1a and 90t1b, the transmission wavelength control unit 12a of the accommodation station transmission unit 10sa gives a control signal to designate the wavelength λ.sub.Tj instead of the wavelength λ.sub.Ti to the wavelength variable light source 13 (here, j is any value from 1 to n and it is assumed that i≠j). In this manner, the reflect array 24-1 or the transmit array 24-2 can form the transmission beam 5-j in a direction that is different from the direction of the transmission beam 5-i, and the other reception terminal apparatus 9-1 can receive the RF signal transmitted with the transmission beam 5-j. The same applies to a case in which one reception terminal apparatus 9-1 moves. This is because each of the n wavelengths λ.sub.T1 to λ.sub.Tn is correlated with one of the transmission antennas 23-1 to 23-n in a fixed manner by the optical demultiplexer 21. In other words, it is possible to state that each of the n wavelengths λ.sub.T1 to λ.sub.Tn and each of the n transmission beams 5-1 to 5-n are correlated in a one-to-one relationship. Thus, it is possible to switch the transmission beams 5-1 to 5-n to be formed by the base station transmission units 20a and 20b merely by switching the wavelengths λ.sub.T1 to λ.sub.Tn in the accommodation station transmission unit 10s.

[0105] The aforementioned wireless transmission systems 90t1a an 90t1b perform only control of selecting the wavelength λ.sub.Ti of the optical signal to be modulated with the RF signal transmitted by the accommodation station transmission unit 10s of the accommodation station apparatus 2, and it is not necessary for the base station apparatus 1 to perform any control at all. In addition, information regarding the distance of the downstream optical fiber 3-1 is not needed, and the number of wavelengths used is limited to the number of transmission antennas 23-1 to 23-n.

[0106] In a case in which an RoF transmission configuration is realized using the technique described in NPL 2, a certain feed 501-i is selected from among a plurality of feeds 501-1 to 501-n illustrated in FIGS. 26 and 27 to emit a radio wave of an RF signal. In this case, 1×n switches that perform electrical switching are used, the RF signal is given to one input port of the 1×n switches, for example, and each of the n feeds 501-1 to 501-n is connected to each of n output ports of the 1×n switches. There is a problem that a loss occurs when the RF signal passes through the 1×n switches, and the loss generally increases as the value of n increases.

[0107] On the other hand, no switches are present in the case of the accommodation station transmission unit 10sa illustrated in FIG. 4 in the wireless transmission systems 90t1a and 90t1b. Further, in the case of the accommodation station transmission unit 10sb illustrated in FIG. 6, a configuration in which the transmission antenna 23-i which emits the radio wave of the RF signal is selected through processing of changing switching of the n×1 optical switches 16 configured to optically perform switching is employed.

[0108] Thus, it is possible to perform switching with a lower loss as compared with the processing of electrically switching the transmission antenna 23-i to emit the radio wave of the RF signal. Thus, it is thus possible to perform beamforming for the transmission/reception antennas without using control of the base station apparatus 1 and the information regarding the distance of the optical fiber while curbing degradation of wavelength utilization efficiency and an increase in cost.

Second Embodiment: Reception Side in Single Mode “Application Example of Reflect Array”

[0109] FIG. 8 is a block diagram illustrating a configuration of a wireless reception system 90r1a according to the second embodiment. The wireless reception system 90r1a includes an accommodation station reception unit 40s, a base station reception unit 30a, an upstream optical fiber 3-2, and a transmission terminal apparatus 9-2 which is illustrated not in FIG. 8 but in FIG. 2.

[0110] The base station reception unit 30a includes a reflect array 31-1 that is a reception beam formation unit for converging received RF signals, n reception antennas 32-1 to 32-n, an optical modulation unit 33, and an optical multiplexer 34. The reflect array 31-1 has the same configuration as that of the reflect array 24-1 according to the first embodiment, and these reflect arrays have reversibility.

[0111] As described above with reference to FIG. 3, if a radio wave of an RF signal is emitted from the transmission antenna 23-i, for example, the radio wave of the RF signal is reflected by the reflect array 24-1. When the reflect array 24-1 reflects the radio wave of the RF signal, the radio wave of the RF signal is strengthened in phase in a specific direction in accordance with the position of the transmission antenna 23-i, and the transmission beam 5-i is formed.

[0112] For example, it is assumed that an RF signal of the same frequency as that of the RF signal with which the transmission beam 5-i is formed has arrived from the traveling direction of the transmission beam 5-i. The reversibility of the reflect array means that if the reflect array 24-1 reflects the RF signal arriving in the direction of the transmission beam 5-i, the RF signal converges at the position of the transmission antenna 23-i. Thus, if the reception antenna 32-i is disposed at the position of the transmission antenna 23-i, for example, the reception antenna 32-i can perform same-phase synthesis on the RF signal arriving in the direction of the transmission beam 5-i and receive the RF signal. It is thus possible to form a reception beam 6-i by selecting the RF signal to be received by the reception antenna 32-i. For this reason, the reflect array 31-1 and the n reception antennas 32-1 to 32-n illustrated in FIG. 8 are disposed in a positional relationship in accordance with arriving directions of reception beams 6-1 to 6-n such that the reception beams 6-1 to 6-n arriving in the mutually different directions can be received.

[0113] The reception antennas 32-1 to 32-n receive and output the radio wave of the RF signal that the reflect array 31-1 converges at each of the positions of the reception antennas 32-1 to 32-n.

[0114] The optical modulation unit 33 includes an internal configuration illustrated in FIG. 9. The optical modulation unit 33 includes n optical modulators 33-1 to 33-n, an optical demultiplexer 36, and a multiple-wavelength light source 35. The multiple-wavelength light source 35 generates light of n different wavelengths λ.sub.R1 to λ.sub.Rn and outputs the generated light to the optical demultiplexer 36. Here, each of the wavelengths λ.sub.T1 to λ.sub.Tn may be a wavelength that is different from each of the wavelengths λ.sub.T1 to λ.sub.Tn or may be the same wavelength as each of the wavelengths λ.sub.T1 to λ.sub.Tn.

[0115] The optical demultiplexer 36 includes one input port and n output ports. Each of the n output ports is assigned to each of then wavelengths λ.sub.R1 to λ.sub.Rn in a fixed manner and is connected to each of the optical modulators 33-1 to 33-n. The optical demultiplexer 36 demultiplexes the light output by the multiple-wavelength light source 35 for each wavelength, the demultiplexed light is branched and output to the optical modulators 33-1 to 33-n connected to the output ports of the corresponding wavelengths.

[0116] The optical modulators 33-1 to 33-n obtains RF signals output by the reception antennas 32-1 to 32-n that are connected to the optical modulators 33-1 to 33-n. The optical modulators 33-1 to 33-n performs intensity modulation with the obtained RF signals and generates and outputs optical signals using the light of the wavelengths λ.sub.T1 to λ.sub.Tn sent to each of the optical modulators 33-1 to 33-n from the optical demultiplexer 36 as an optical carrier.

[0117] Note that in FIG. 9, n light sources configured to generate light of the wavelengths λ.sub.R1 to λ.sub.Rn are applied instead of the multiple-wavelength light source 35 and the optical demultiplexer 36 and each of the n light sources may be connected to each of the optical modulators 33-1 to 33-n. Alternatively, m direct optical modulators configured to generate light of the wavelengths λ.sub.R1 to λ.sub.Rn may be used instead of the multiple-wavelength light source 35, the optical demultiplexer 36, and the optical modulators 33-1 to 33-n.

[0118] Returning to FIG. 8, the optical multiplexer 34 multiplexes the n optical signals of the wavelengths λ.sub.T1 to λ.sub.Tn output by each of the optical modulators 33-1 to 33-n and outputs the multiplexed optical signal to the upstream optical fiber 3-2. The upstream optical fiber 3-2 delivers, to the accommodation station reception unit 40s, the optical signal obtained by multiplexing the n wavelengths λ.sub.R1 to λ.sub.Rn output by the optical multiplexer 34.

[0119] The accommodation station reception unit 40s includes an optical demultiplexer 41 and an output unit 42. The optical demultiplexer 41 includes one input port and n output ports, and each of then output ports is assigned to each of then wavelengths λ.sub.R1 to λ.sub.Rn in a fixed manner. The optical demultiplexer 41 obtains the optical signal delivered by the upstream optical fiber 3-2 from the input port and demultiplexes the obtained optical signal for each wavelength. By the optical demultiplexer 41, each of the demultiplexed optical signals is branched and output to the output port corresponding to a wavelength of each of the demultiplexed optical signals.

[0120] The output unit 42 obtains the optical signals output by the optical demultiplexer 41 from the output ports and selects an optical signal corresponding to any one wavelength λ.sub.Ri from among the optical signals obtained from the output ports. The output unit 42 converts the selected optical signal into an electrical signal, demodulates the RF signal, and outputs the demodulated RF signal.

[0121] FIG. 10 is a block diagram illustrating an internal configuration of an accommodation station reception unit 40sa which is an example of a specific configuration of the accommodation station reception unit 40s. Note that the optical demultiplexer 41 illustrated in FIG. 10 has the same configuration as that of the optical demultiplexer 41 in FIG. 8. The accommodation station reception unit 40sa illustrated in FIG. 10 includes an optical demultiplexer 41, an output unit 42a, and a reception wavelength control unit 43. The output unit 42a includes n×1 optical switches 44 and an O/E converter 45.

[0122] The n×1 optical switches 44 include n input ports and one output port, and each of the n input ports is connected to each of then output ports of the optical demultiplexer 41. Based on a control signal received from the reception wavelength control unit 43, the n×1 optical switches 44 switches and connects any one of the n input ports to the output port. The O/E converter 45 converts the optical signal output by the n×1 optical switches 44 from the output port into an electrical signal to demodulate an RF signal, and outputs the demodulated RF signal. The RF signal is an RF signal received with the reception beam 6-i.

[0123] The reception wavelength control unit 43 outputs, to the n×1 optical switches 44, a control signal for connecting, to the output port, the input port that obtains, from the optical demultiplexer 41, the light of the one wavelength λ.sub.Ri on which the RF signal is superimposed. The wavelength λ.sub.Ri of the light on which the RF signal that is an output target is superimposed is switched by the reception wavelength control unit 43 switching the output port that is a connecting destination of the input port of the n×1 optical switches 44 using the control signal.

[0124] Processing Performed by Wireless Reception System According to Second Embodiment

[0125] FIG. 11 is a flowchart illustrating a flow of processing performed by the wireless reception system 90r1a according to the second embodiment. The following description will be given on the assumption that the accommodation station reception unit 40sa illustrated in FIG. 10, for example, is included as the accommodation station reception unit 40s.

[0126] It is assumed that an RF signal transmitted by the transmission terminal apparatus 9-2 has arrived from a direction of the reception beam 6-i. The arriving RF signal is reflected by the reflect array 31-1 and converges at the position of the reception antenna 32-i due to the aforementioned reversibility of the reflect array. The reception antenna 32-i receives the RF signal that has converged at the position of the reception antenna 32-i and outputs the RF signal to the optical modulator 33-i (Step Sb1).

[0127] At this time, the RF signal does not converge at the positions of the other reception antennas 32-1 to 32-(i−1) and 32-(i+1) to 32-n. Thus, the other reception antennas 32-1 to 32-(i−1) and 32-(i+1) to 32-n do not receive anything and thus do not output anything. The optical modulator 33-i performs intensity modulation with the RF signal output by the reception antenna 32-i to generate and output an optical signal, using the light of the wavelength λ.sub.Ri sent from the optical demultiplexer 36 as an optical carrier (Step Sb2).

[0128] The reception antenna 32-1 to 32-(i−1) and 32-(i+1) to 32-n connected thereto do not output anything. The optical modulators 33-1 to 33-(i−1) and 33-(i+1) to 33-n other than the optical modulator 33-i directly output the light of the wavelengths λ.sub.R1 to λ.sub.R(i+1) and λ.sub.R(i+1) to λ.sub.Rn sent from the optical demultiplexer 36 to each of the optical modulators 33-1 to 33-(i−1) and 33-(i+1) to 33-n.

[0129] The optical multiplexer 34 multiplexes the optical signal of the wavelength λ.sub.Ri modulated with the RF signal output by the optical modulator 33-i and light of the wavelengths λ.sub.R1 to λ.sub.R(i−1) and λ.sub.R(i+1) to λ.sub.Rn output by the optical modulators 33-1 to 33-(i−1) and 33-(i+1) to 33-n and output to the upstream optical fiber 3-2 (Step Sb3).

[0130] The upstream optical fiber 3-2 delivers the optical signal multiplexed by the optical multiplexer 34 to the optical demultiplexer 41 of the accommodation station reception unit 40sa. The optical demultiplexer 41 demultiplexes the optical signal obtained from the upstream optical fiber 3-2 into n wavelengths λ.sub.R1 to λ.sub.Rn. By the optical demultiplexer 41, each of the demultiplexed optical signals are branched and output to the output port of the corresponding wavelength (Step Sb4).

[0131] The reception wavelength control unit 43 outputs, to the n×1 optical switches 44, a control signal for connecting an input port of the n×1 optical switches 44 connected to the output port assigned to the wavelength λ.sub.Ri of the optical demultiplexer 41 to the output port of the n×1 optical switches 44. The n×1 optical switches 44 output the optical signal of the wavelength λ.sub.Ti from the output port by the n×1 optical switches 44 receiving the control signal and switching the switch.

[0132] The O/E converter 45 obtains the optical signal of the wavelength λ.sub.Ri output by the n×1 optical switches 44 from the output port, demodulates the RF signal by converting the obtained optical signal into an electrical signal, and outputs the demodulated RF signal (Step Sb5). This means that the RF signals arriving from the direction of the reception beam 6-i is synthesized in-phase, such that the reception beam 6-i is formed.

[0133] Another Configuration Example of Accommodation Station Reception Unit According to Second Embodiment Note that an accommodation station reception unit 40sb illustrated in FIG. 12 may be applied instead of the accommodation station reception unit 40sa illustrated in FIG. 10 as the accommodation station reception unit 40s. The accommodation station reception unit 40sb illustrated in FIG. 12 includes an optical demultiplexer 41, an output unit 42b, and a reception wavelength control unit 43. Note that the optical demultiplexer 41 illustrated in FIG. 12 has the same configuration as that of the optical demultiplexer 41 in FIG. 8, and the reception wavelength control unit 43 has the same configuration as that of the reception wavelength control unit 43 illustrated in FIG. 10.

[0134] The output unit 42b includes n O/E converters 45-1 to 45-n and n×1 electrical switches 46. Each of the n O/E converters 45-1 to 45-n is connected to the n output ports of the optical demultiplexer 41 and converts the optical signals of the wavelengths λ.sub.R1 to λ.sub.Rn output from each of the n output ports of the optical demultiplexer 41 into electrical signals and outputs the electrical signals.

[0135] The n×1 electrical switches 46 include n input ports and one output port, and each of the n input ports is connected to each of the n O/E converters 45-1 to 45-n. The n×1 electrical switches 46 changes switches based on a control signal received from the reception wavelength control unit 43 and connects any one of the n input ports to the output port.

[0136] In other words, the accommodation station reception unit 40sa in FIG. 10 selects the wavelength λ.sub.Ti of the light that is an output target using the n×1 optical switches 44 first, and the O/E converter 45 converts the light into an electrical signal. On the other hand, the accommodation station reception unit 40sb in FIG. 12 has a configuration in which the n O/E converters 45-1 to 45-n convert optical signals into electrical signals first and the wavelength λ.sub.Ri of the light that is an output target is then selected by the n×1 electrical switches 46. Thus, in the accommodation station reception unit 40sb as with the accommodation station reception unit 40sa, when the reception wavelength control unit 43 switches the output port of the connecting destination of the input port of the n×1 electrical switches 46 using the control signal, the wavelength λ.sub.Ti of the light on which the RF signal that is an output target is superimposed is switched.

[0137] In a case in which the accommodation station reception unit 40sb is applied and an RF signal arrives from the direction of the reception beam 6-i, the reception wavelength control unit 43 of the accommodation station reception unit 40sb outputs, to the n×1 electrical switches 46, a control signal for connecting the input port that obtains the electrical signal output by the O/E converter 45-i to the output port in Step Sb5 in FIG. 11.

Second Embodiment: Reception Side in Single Mode “Application Example of Transmit Array”

[0138] FIG. 13 is a block diagram illustrating a configuration of a wireless reception system 90r1b which is another configuration example of the second embodiment. In FIG. 13, the same reference signs will be applied to the same configurations as those in FIG. 8, and different configurations will be described below.

[0139] The wireless reception system 90r1b includes an accommodation station reception unit 40s, a base station reception unit 30b, an upstream optical fiber 3-2, and a transmission terminal apparatus 9-2 illustrated in FIG. 2, although not illustrate in FIG. 13.

[0140] The base station reception unit 30b includes a transmit array 31-2 that is a reception beam formation unit configured to converge received RF signals, n reception antennas 32-1 to 32-n, an optical modulation unit 33, and an optical multiplexer 34. The transmit array 31-2 has the same configuration as that of the transmit array 24-2 according to the first embodiment, and these transmit arrays have reversibility.

[0141] As described above with reference to FIG. 7, if a radio wave of an RF signal is emitted from a transmission antenna 23-i, for example, the radio wave of the RF signal passes through the transmit array 24-2. When the radio wave of the RF signal passes through the transmit array 24-2, the radio wave of the RF signal is strengthened in the same phase in a specific direction in accordance with the position of the transmission antenna 23-i, and the transmission beam 5-i is formed.

[0142] For example, it is assumed that an RF signal of the same frequency as that of the RF signal with which the transmission beam 5-i is formed has arrived from the traveling direction of the transmission beam 5-i. The reversibility of the transmit array means that when the RF signal arriving from the direction of the transmission beam 5-i passes through the transmit array 24-2, the RF signal converges at the position of the transmission antenna 23-i. Thus, for example, when the reception antenna 32-i is placed at the position of the transmission antenna 23-i, the reception antenna 32-i synthesizes the RF signal arriving from the direction of the transmission beam 5-i in phase and receive the RF signal. It is thus possible to form a reception beam 6-i by selecting the RF signal to be received by the reception antenna 32-i. Thus, the transmit array 31-2 and the n reception antennas 32-1 to 32-n illustrated in FIG. 13 are disposed in a positional relationship in accordance with arriving directions of the reception beams 6-1 to 6-n such that the reception beams 6-1 to 6-n arriving from mutually different directions can be received.

[0143] Processing in Another Configuration Example of Second Embodiment

[0144] Processing performed by the wireless reception system 90r1b includes the following processing in Step Sb1 of the flowchart illustrated in FIG. 11. In other words, it is assumed that an RF signal transmitted by the transmission terminal apparatus 9-2 has arrived from the direction of the reception beam 6-i. The arriving RF signal passes through the transmit array 31-2 and converges at the position of the reception antenna 32-i due to the aforementioned reversibility of the transmit array. The reception antenna 32-i receives the RF signal that has converged at the position of the reception antenna 32-i and outputs the RF signal to the optical modulator 33-i. The same processing as that of the wireless reception system 90r1a is performed in Steps Sb2 to Sb5.

[0145] Note that, as the accommodation station reception unit 40s included in the wireless reception system 90r1b. as with the wireless reception system 90r1a, the accommodation station reception unit 40sa illustrated in FIG. 10 may be applied or the accommodation station reception unit 40sb illustrated in FIG. 12 may be applied.

[0146] Note that, in the aforementioned wireless reception systems 90r1a and 90r1b, in a case in which an RF signal arrives from a direction other than the directions of the reception beams 6-1 to 6-m, RF signals with different amplitudes and different phases from those of the original RF signal arrives at the positions of the plurality of reception antennas 32-1 to 32-n. Thus, each of the reception antennas 32-1 to 32-n output an RF signal with a different amplitude and a different phase from those of the original RF signal.

[0147] In this case, the RF signals with the different amplitudes and the different phases are sent the optical modulators 33-1 to 33-n. Each of the optical modulators 33-1 to 33-n generates optical signals of the wavelengths λ.sub.T1 to λ.sub.Tn modulated with the RF signal sent to each of the optical modulators 33-1 to 33-n. From a different viewpoint, a state in which RF signals are separately superimposed on the optical signals of the plurality of wavelengths λ.sub.T1 to λ.sub.Tn is achieved. Thus, the output unit 42 of the accommodation station reception unit 40s is required to perform processing of demodulating the RF signals by targeting the plurality of optical signals output by the optical demultiplexer 41 from the plurality of output ports. For example, the output unit 42 of the accommodation station reception unit 40s performs electrical conversion on each of the optical signals demultiplexed and output by the optical demultiplexer 41 for each wavelength and demodulates the RF signal superimposed on each of the optical signals. The output unit 42 may select and output an RF signal with the highest power from among the demodulated RF signals or may adjust the amplitudes and phases of the plurality of demodulated RF signals, perform maximum ratio synthesis, and output the result, for example.

[0148] In the wireless reception systems 90r1a and 90r2b according to the second embodiment, the base station reception units 30a and 30b include the reflect array 31-1 or the transmit array 31-2, the reception antennas 32-1 to 32-n, the optical modulators 33-1 to 33-n, and the optical multiplexer 34. Further, the reflect array 31-1 or the transmit array 31-2 receives an RF signal with the reception beam 6-i and converges the RF signal at the convergence position in accordance with the reception beam 6-i. The reception antenna 32-i receives the RF signal that has converged at the convergence position. The optical modulators 33-1 to 33-n are connected to the reception antennas 32-1 to 32-n, and light of different wavelengths λ.sub.T1 to λ.sub.Tn is given to each of the optical modulators 33-1 to 33-n. Then, the optical modulator 33-i modulates the light of the given wavelength λ.sub.Ti and generates an optical signal based on the RF signal received by the connected reception antenna 32-i. The optical multiplexer 34 multiplexes the optical signals of the mutually different wavelengths generated by the optical modulators 33-1 to 33-n and outputs the multiplexed optical signal. The accommodation station reception unit 40s includes an optical demultiplexer 41 and an output unit 42, and the optical demultiplexer 41 obtains the optical signals output by the optical multiplexer 34 and demultiplexes the optical signals depending on wavelengths. The output unit 42 demodulates the RF signal by converting the optical signal of the wavelength λ.sub.Ti included in the optical signal output by the optical demultiplexer 41 into an electrical signal and outputs the demodulated RF signal.

[0149] It is assumed that in the aforementioned wireless reception systems 90r1a and 90r1b, the transmission terminal apparatus 9-2 that transmits a radio wave of an RF signal serves as another transmission terminal apparatus 9-2 and a reception beam 6-j arrives from a direction that is different from that of the reception beam 6-i (here, j is any value from 1 to n and it is assumed that i≠j). In this case, the accommodation station reception unit 40s can obtain the RF signal that forms the reception beam 6-j by selecting the wavelength λ.sub.Rj. It is assumed that an RF signal has arrived from a direction of the reception beam 6-j that is different from the reception beam 6-i (here, j is any value from 1 to n, and it is assumed that i≠j). In this case, the accommodation station reception unit 40s can obtain the RF signal with the reception beam 6-j by selecting the wavelength λ.sub.Rj. The desired RF signal can be obtained merely by selecting any of the wavelengths λ.sub.T1 to λ.sub.Tn in this manner. This is because each of the n wavelengths λ.sub.T1 to λ.sub.Tn and each of then reception antennas 32-1 to 32-n are correlated in a fixed manner by the optical multiplexer 34 and the optical demultiplexer 41. In other words, it is possible to state that each of the n wavelengths λ.sub.T1 to λ.sub.Tn and each of the n reception beams 6-1 to 6-n are correlated in a one-to-one relationship. Thus, the accommodation station reception unit 40s can switch the reception beams 6-1 to 6-n merely by switching the wavelengths λ.sub.R1 to λ.sub.Rn.

[0150] The aforementioned wireless reception systems 90r1a and 90r1b perform only control of selecting the wavelength λ.sub.Ti of the optical signal on which the RF signal demodulated by the accommodation station reception unit 40s of the accommodation station apparatus 2 is superimposed, and it is not necessary for the base station apparatus 1 to perform any control at all. Moreover, the information regarding the distance of the upstream optical fiber 3-2 is also not needed, and the number of wavelengths used is limited to the number of reception antennas 32-1 to 32-n.

[0151] In a case in which an RoF reception configuration is realized using the technique described in NPL 2, a certain feed 501-i is selected from a plurality of feeds 501-1 to 501-n illustrated in FIGS. 26 and 27 to receive a radio wave of an RF signal. In this case, 1×n switches configured to perform electrical switching are used, for example, and each of the n feeds 501-1 to 501-n is connected to each of n input ports of the 1×n switches. A loss occurs when the RF signal passes through the 1×n switches, and there is typically a problem that the loss increases as the value of n increases.

[0152] On the other hand, in the wireless reception systems 90r1a and 90r1b, in the case of the accommodation station reception unit 40sa illustrated in FIG. 10, the reception antenna 32-i that receives an RF signal is selected through processing of switching the n×1 optical switches 44 that optically switches. Thus, it is possible to perform the switching with a lower loss as compared with the processing of electrically switching the reception antenna 32-i configured to receive the RF signal.

[0153] Further, in the case of the accommodation station reception unit 40sb illustrated in FIG. 12, the reception antenna 32-i that receives an RF signal is selected through processing of switching the n×1 electrical switches 46.

Third Embodiment: Transmission Side in Multi Mode “Application Example of Reflect Array”

[0154] FIG. 14 is a block diagram illustrating a configuration of a wireless transmission system 90t2a according to a third embodiment. In FIG. 14, the same reference signs will be applied to the same configurations as those in FIG. 3, and different configurations will be described below. The wireless transmission system 90t2a includes an accommodation station transmission unit 10m, a base station transmission unit 20a, a downstream optical fiber 3-1, and a reception terminal apparatus 9-1 illustrated in FIG. 2, although not illustrated in FIG. 14. Here, it is assumed that n reception terminal apparatuses 9-1 are provided and are represented as reception terminal apparatuses 9-1-1 to 9-1-n.

[0155] The accommodation station transmission unit 10m has an internal configuration illustrated in FIG. 15. The accommodation station transmission unit 10m includes a multiple-wavelength light source 18, an optical demultiplexer 19, n optical modulators 11-1 to 11-n, and an optical multiplexer 17. The multiple-wavelength light source 18 generates and outputs light of the wavelengths λ.sub.T1 to λ.sub.Tn. The optical demultiplexer 19 includes one input port and n output ports, and each of the n output ports is assigned to each of the n wavelengths λ.sub.T1 to λ.sub.Tn in a fixed manner. The optical demultiplexer 19 demultiplexes the light of the wavelengths λ.sub.T1 to λ.sub.Tn output by the multiple-wavelength light source 18 for each wavelength, and the demultiplexed light is branched and output to the output ports of the corresponding wavelengths.

[0156] Each of the optical modulators 11-1 to 11-n is connected to n output ports of the optical demultiplexer 19. Each of the optical modulators 11-1 to 11-n obtains an RF signal for a different transmission destination, for example. Each of the optical modulators 11-1 to 11-n obtains the light of the wavelengths λ.sub.T1 to λ.sub.Tn output from the output port of the optical demultiplexer 19 connected to each of the optical modulators 11-1 to 11-n. Each of the optical modulators 11-1 to 11-n performs intensity modulation with the RF signal obtained by each of the optical modulators 11-1 to 11-n using the obtained light as an optical carrier to generate an optical signal and outputs the generated optical signal. The optical multiplexer 17 multiplexes the n optical signals generated by the optical modulators 11-1 to 11-n and outputs the multiplexed optical signal to the downstream optical fiber 3-1.

[0157] Processing Performed by Wireless Transmission System According to Third Embodiment

[0158] FIG. 16 is a flowchart illustrating a flow of processing performed by a wireless transmission system 90t2a according to the third embodiment. The multiple-wavelength light source 18 of the accommodation station transmission unit 10m generates and outputs the light of the wavelengths λ.sub.T1 to λ.sub.Tn. The optical demultiplexer 19 demultiplexes the light of the wavelengths λ.sub.T1 to λ.sub.Tn output by the multiple-wavelength light source 18 for each wavelength and branches and outputs the demultiplexed light to the output ports of the corresponding wavelengths.

[0159] Each of the optical modulators 11-1 to 11-n uses, as an optical carrier, light of the wavelengths λ.sub.T1 to λ.sub.Tn output from the output ports by the optical demultiplexer 19 connected to each of the optical modulators 11-1 to 11-n, and performs intensity modulation with RF signals of different transmission destinations obtained by each of the optical modulators 11-1 to 11-n to generate optical signals. The optical modulators 11-1 to 11-n outputs the generated optical signals to the optical multiplexer 17 (Step Sc1).

[0160] The optical multiplexer 17 multiplexes n optical signals output by the optical modulators 11-1 to 11-n and outputs the multiplexed optical signal to the downstream optical fiber 3-1 (Step Sc2). The downstream optical fiber 3-1 delivers the optical signal output by the optical multiplexer 17 to the optical demultiplexer 21 of the base station transmission unit 20a. The optical demultiplexer 21 demultiplexes the optical signal obtained from the downstream optical fiber 3-1 into the n wavelengths λ.sub.T1 to λ.sub.Tn. Each of the demultiplexed optical signals is branched by the optical demultiplexer 21 to the output port corresponding to each wavelength and outputs to the O/E converters 22-1 to 22-n connected to the output ports (Step Sc3).

[0161] Each of the O/E converters 22-1 to 22-n converts each of the optical signals of the wavelengths λ.sub.T1 to λ.sub.Tn branched and output by the optical demultiplexer 21 into an electrical signal and demodulates the RF signal (Step Sc4). Each of the O/E converters 22-1 to 22-n outputs the demodulated RF signal to the transmission antennas 22-1 to 22-n connected to each of the O/E converters 22-1 to 22-n. Each of the transmission antennas 23-1 to 23-n emits radio waves of the RF signals output by each of the O/E converters 22-1 to 22-n (Step Sc5). When the radio waves of the RF signals emitted by each of the transmission antennas 23-1 to 23-n are reflected by the reflect array 24-1, the transmission beams 5-1 to 5-n are formed in mutually different directions which are directions in accordance with each of the positions of the transmission antennas 23-1 to 23-n. In other words, multi-beams including the n transmission beams 5-1 to 5-n are formed (Step Sc6).

[0162] Each of then reception terminal apparatuses 9-1-1 to 9-1-n receives the RF signals transmitted with the transmission beams 5-1 to 5-n and demodulates and obtains the RF signals.

Third Embodiment: Transmission Side in Multi Mode “Application Example of Transmit Array”

[0163] FIG. 17 is a block diagram illustrating a configuration of a wireless transmission system 90t2b that is another configuration example of the second embodiment. In FIG. 17, the same reference signs will be applied to the same configurations as those in FIGS. 7 and 14, and different configurations will be described below. The wireless transmission system 90t2b includes an accommodation station transmission unit 10m, a base station transmission unit 20b, a downstream optical fiber 3-1, and a reception terminal apparatus 9-1 illustrated in FIG. 2, although not illustrated in FIG. 17. Here, it is assumed that n reception terminal apparatuses 9-1 are provided and are represented as reception terminal apparatuses 9-1-1 to 9-1-n.

[0164] In other words, the wireless transmission system 90t2b has a configuration in which an accommodation station transmission unit 10m of the wireless transmission system 90t2a according to the third embodiment and the base station transmission unit 20b of the wireless transmission system 90t1b, which is another configuration example of the first embodiment, are connected with the downstream optical fiber 3-1.

[0165] Processing in Another Configuration Example of Third Embodiment

[0166] As processing performed by the wireless transmission system 90t2b, the same processing as that of the wireless transmission system 90t2a is performed in Steps Sc1 to Sc 5 in the flowchart illustrated in FIG. 16.

[0167] In Step Sc6, when the radio waves of the RF signals emitted by each of the transmission antennas 23-1 to 23-n passes through the transmit array 24-2, the transmission beams 5-1 to 5-n are formed in specific directions that are different in accordance with each of the positions of the transmission antennas 23-1 to 23-n. In other words, multi-beams including the n transmission beams 5-1 to 5-n are formed. Each of the n reception terminal apparatuses 9-1-1 to 9-1-n receives the RF signal transmitted with the transmission beams 5-1 to 5-n and demodulates and obtains the RF signal.

[0168] In the wireless communication systems 90t2a and 90t2b according to the third embodiment, the accommodation station transmission unit 10m includes the optical modulators 11-1 to 11-n and the optical multiplexer 17, and light of mutually different wavelengths λ.sub.T1 to λ.sub.Tn is given to each of the optical modulators 11-1 to 11-n. Each of the optical modulators 11-1 to 11-n modulates the light given to each of the optical modulators 11-1 to 11-n to generate optical signals based on the RF signal, and the optical multiplexer 17 multiplexes and outputs the optical signals generated by the optical modulators 11-1 to 11-n. The base station transmission units 20a and 20b include an optical demultiplexer 21, O/E converters 22-1 to 22-n, transmission antennas 23-1 to 23-n, and a reflect array 24-1 or a transmit array 24-2. The optical demultiplexer 21 includes a plurality of output ports allocated for each wavelength of the light, obtains the optical signal output by the accommodation station transmission unit 10m from the input port, demultiplexes the obtained optical signal for each wavelength, and outputs the demultiplexed optical signals from the output ports of the corresponding wavelengths. Each of the O/E converters 22-1 to 22-n is connected to the plurality of output ports of the optical demultiplexer 21, converts the optical signals output by the optical demultiplexer 21 into electrical signals to demodulate the RF signals, and outputs the demodulated RF signals. The transmission antennas 23-1 to 23-n are connected to each of the O/E converters 22-1 to 22-n and emit the RF signal output by each of the O/E converters 22-1 to 22-n. The reflect array 24-1 or the transmit array 24-2 receives the RF signal emitted by each of the transmission antennas 23-1 to 23-n and forms, for each of the received RF signals, the transmission beams 5-1 to 5-n in different directions for each of the positions of the transmission antennas 23-1 to 23-n that are transmission sources of the RF signals.

[0169] In the aforementioned wireless transmission systems 90t2a and 90t2b, each of the n wavelengths λ.sub.Ti to λ.sub.Tn and each of the transmission antennas 23-1 to 23-n are correlated in a fixed manner by the optical multiplexer 17 and the optical demultiplexer 21. In other words, it is possible to state that each of the n wavelengths λ.sub.Ti to λ.sub.Tn and each of the n transmission beams 5-1 to 5-n are correlated in a one-to-one relationship. Thus, it is possible to form multi beams, that is, the n transmission beams 5-1 to 5-n by the accommodation station transmission unit 10m performing modulation with the n RF signals using the light of the n wavelengths λ.sub.T1 to λ.sub.Tn as an optical carrier and generating the n optical signals.

[0170] The aforementioned wireless transmission systems 90t2a and 90t2b do not need any control of the base station apparatus 1 at all. Further, information regarding the distance of the downstream optical fiber 3-1 is not needed, and the number of wavelengths used is limited to the number of transmission antennas 23-1 to 23-n. Further, a configuration for electrically switching switches is also not included. It is thus possible to perform beamforming for transmission/reception antennas without using control of the base station apparatus and information regarding the distance of the optical fiber while curbing degradation of wavelength utilization efficiency and an increase in cost.

Fourth Embodiment: Reception Side in Multi Mode “Application Example of Reflect Array”

[0171] FIG. 18 is a block diagram illustrating a configuration of a wireless reception system 90r2a according to the fourth embodiment. In FIG. 18, the same reference signs will be applied to the same configurations as those in FIG. 8, and different configurations will be described below.

[0172] The wireless reception system 90r2a includes an accommodation station reception unit 40m, a base station reception unit 30a, an upstream optical fiber 3-2, and a transmission terminal apparatus 9-2 illustrated in FIG. 2, although not illustrated in FIG. 18. Here, it is assumed that n transmission terminal apparatuses 9-2 are provided and are represented as transmission terminal apparatus 9-2-1 to 9-2-n.

[0173] The accommodation station reception unit 40m includes an optical demultiplexer 41 and an output unit 42c, and the output unit 42c includes n O/E converters 45-1 to 45-n. Each of the n O/E converters 45-1 to 45-n is connected to each of the n output ports of the optical demultiplexer 41. The optical demultiplexer 41 demultiplexes the optical signals of the n wavelengths λ.sub.R1 to λ.sub.Rn delivered through the upstream optical fiber 3-2, and each of the demultiplexed optical signals are branched and output to the output ports of the corresponding wavelengths. Each of the n O/E converters 45-1 to 45-n obtains the optical signal output by the optical demultiplexer 41 from each of the n output ports, converts the obtained optical signal into an electrical signal, and demodulates and outputs the RF signal.

[0174] Processing Performed by Wireless Reception System According to Fourth Embodiment

[0175] FIG. 19 is a flowchart illustrating a flow of processing performed by a wireless reception system 90r2a according to the fourth embodiment.

[0176] It is assumed that the RF signals transmitted by each of the n transmission terminal apparatuses 9-2-1 to 9-2-n have arrived from the directions of the n reception beams 6-1 to 6-n. The arriving RF signals are reflected by the reflect array 31-1 and converge at the positions of the reception antennas 32-1 to 32-n due to the aforementioned reversibility of the reflect array. Each of the reception antennas 32-1 to 32-n receives the RF signals that have converged at each position and outputs the RF signals to the optical modulators 33-1 to 33-n connected to each of the reception antennas 32-1 to 32-n (Step Sd1).

[0177] Each of the optical modulators 33-1 to 33-n performs intensity modulation with the RF signals output by the reception antennas 32-1 to 32-n using the light of the wavelengths λ.sub.R1 to λ.sub.Rn given from the optical demultiplexer 36 to each of the optical modulators 33-1 to 33-n as an optical carrier to generate and output optical signals (Step Sd2).

[0178] The optical multiplexer 34 multiplexes the n optical signals of the wavelengths λ.sub.R1 to λ.sub.Rn output by each of the optical modulators 33-1 to 33-n and outputs the multiplexed optical signal to the upstream optical fiber 3-2 (Step Sd3). The upstream optical fiber 3-2 delivers the optical signal multiplexed by the optical multiplexer 34 to the optical demultiplexer 41 of the accommodation station reception unit 40m.

[0179] The optical demultiplexer 41 demultiplexes the optical signal obtained from the upstream optical fiber 3-2 into n wavelengths λ.sub.R1 to λ.sub.Rn. The optical demultiplexer 41 branches and outputs each of the demultiplexed optical signals to the output ports of the corresponding wavelengths (Step Sd4).

[0180] Each of the n O/E converters 45-1 to 45-n of the output unit 42c obtains the optical signal output by the optical demultiplexer 41 from each of the output ports, converts the obtained optical signal into an electrical signal, and demodulates and outputs the RF signal. This means that the RF signals arriving from directions of the reception beams 6-1 to 6-m are synthesized in-phase, such that the reception beams 6-1 to 6-m are formed (Step Sd5).

Fourth Embodiment: Reception Side in Multi Mode “Application Example of Transmit Array”

[0181] FIG. 20 is a block diagram illustrating a configuration of a wireless reception system 90r2b that is another configuration example of the fourth embodiment. In FIG. 20, the same reference signs will be applied to the same configurations as those in FIGS. 13 and 18, and different configurations will be described below.

[0182] The wireless reception system 90r2b includes an accommodation station reception unit 40m, a base station reception unit 30b, an upstream optical fiber 3-2, and a transmission terminal apparatus 9-2 that is illustrated FIG. 2, although not illustrated in FIG. 20. Here, it is assumed that n transmission terminal apparatuses 9-2 are present and are represented as transmission terminal apparatus 9-2-1 to 9-2-n.

[0183] In other words, the wireless reception system 90r2b has a configuration in which the accommodation station reception unit 40m of the wireless reception system 90r2a according to the fourth embodiment and the base station reception unit 30b of the wireless reception system 90r1b that is another configuration example of the second embodiment are connected with the optical fiber 3-2.

[0184] Processing in Another Configuration Example of Fourth Embodiment

[0185] As processing performed by the wireless reception system 90r2b, the following processing is performed in Step Sd1 of the flowchart illustrated in FIG. 19. In other words, it is assumed that n reception beams 6-1 to 6-n formed by each of the RF signals transmitted by the n transmission terminal apparatuses 9-2-1 to 9-2-n have arrived. The n reception beams 6-1 to 6-n pass through the transmit array 31-2, and the RF signals forming the reception beams 6-1 to 6-n converge at the positions of the reception antennas 32-1 to 32-n due to the aforementioned reversibility of the transmit array. Each of the reception antennas 32-1 to 32-n receives the RF signal that has converged at each position and outputs the RF signal to the optical modulators 33-1 to 33-n connected to each of the reception antennas 32-1 to 32-n. The same processing as that of the wireless reception system 90r2a is performed in Steps Sd2 to Sd5.

[0186] In the wireless reception systems 90r2a and 90r2b according to the aforementioned fourth embodiment, the base station reception units 30a and 30b include a reflect array 31-1 or a transmit array 31-2, reception antennas 32-1 to 32-n, optical modulators 33-1 to 33-n, and an optical multiplexer 34. The reflect array 31-1 or the transmit array 31-2 receives the RF signal arriving from each of the directions of the reception beams 6-1 to 6-n and converges the RF signal at a different convergence position in accordance with the arriving direction of the received RF signal. The reception antennas 32-1 to 32-n are disposed at each of the convergence positions and receive the RF signals that have converged at the convergence positions. The optical modulators 33-1 to 33-n are connected to the reception antennas 32-1 to 32-n, and light of different wavelengths λ.sub.R1 to λ.sub.Rn is given to each of the optical modulators 33-1 to 33-n. Further, the optical modulators 33-1 to 33-n modulate the given light to generate optical signals based on the RF signals received by the connected reception antennas 32-1 to 32-n. The optical multiplexer 34 multiplexes the optical signals of the mutually different wavelengths generated by the optical modulators 33-1 to 33-n and outputs the multiplexed optical signal. The accommodation station reception unit 40m includes an optical demultiplexer 41 and an output unit 42c, and the optical demultiplexer 41 obtains the optical signal output by the optical multiplexer 34 and demultiplexes the optical signal for each wavelength. The output unit 42c includes O/E converters 45-1 to 45-n connected to outputs of the optical demultiplexer 41, and each of the O/E converters 45-1 to 45-n obtains the optical signals with mutually different wavelengths λ.sub.R1 to λ.sub.Rn demultiplexed by the optical demultiplexer 41, converts the obtained optical signals into electrical signals to demodulate the RF signals, and output the demodulated RF signals.

[0187] In the aforementioned wireless reception systems 90r2a and 90r2b, each of the n wavelengths λ.sub.R1 to λ.sub.Rn and each of then reception antennas 32-1 to 32-n are correlated by the optical multiplexer 34 and the optical demultiplexer 41 in a fixed manner. In other words, it is possible to state that each of the n wavelengths λ.sub.R1 to λ.sub.Rn and each of the n reception beams 6-1 to 6-n are correlated in a one-to-one relationship. Thus, the optical modulators 33-1 to 33-n of the base station reception units 30a and 30b perform modulation with the RF signals output by the reception antennas 32-1 to 32-n using the light of the n wavelengths λ.sub.R1 to λ.sub.Rn as an optical carrier to generate n optical signals. It is possible to demodulate and output the RF signal by the optical multiplexer 34 multiplexing the n optical signals and transmitting the multiplexed optical signal to the accommodation station reception unit 40m and by the accommodation station reception unit 40m demultiplexing the optical signal for each wavelength and converting the demultiplexed optical signals into electrical signals. In this manner, the wireless reception systems 90r2a and 90r2b can form the multi beams, that is, the n reception beams 6-1 to 6-n corresponding to each RF signal.

[0188] Note that in a case in which an RF signal has arrived from a direction other than the directions of the reception beams 6-1 to 6-n in the aforementioned wireless reception systems 90r2a and 90r2b, RF signals with different amplitudes and different phases as those of the original RF signal arrive at the positions of the plurality of reception antennas 32-1 to 32-n. Thus, each of the reception antennas 32-1 to 32-n output RF signals with different amplitudes and different phases from those of the original RF signal.

[0189] In this case, the RF signals with different amplitudes and different phases are given to each of the optical modulators 33-1 to 33-m. Each of the optical modulators 33-1 to 33-m generates the optical signals of the wavelengths λ.sub.R1 to λ.sub.Rn modulated with the RF signals given to each of the optical modulators 33-1 to 33-m. From a different viewpoint, a state in which the RF signals are separately superimposed on the optical signals of the plurality of wavelengths λ.sub.R1 to λ.sub.Rn is achieved. Thus, the output unit 42c of the accommodation station reception unit 40m is required to perform processing of demodulating the RF signals while targeting the plurality of optical signals output by the optical demultiplexer 41 from the plurality of output ports. For example, the output unit 42c of the accommodation station reception unit 40m performs electrical conversion on each of the optical signals demultiplexed and output by the optical demultiplexer 41 for each wavelength and demodulates the RF signal superimposed on each of the optical signals. The output unit 42c may select and output the RF signal with the highest power from among the demodulated RF signals or may perform MIMO signal processing on the plurality of demodulated RF signals and output the result.

[0190] The aforementioned wireless reception systems 90r2a and 90r2b do not need any control of the base station apparatus 1 at all. Moreover, the information regarding the distance of the upstream optical fiber 3-2 is also not needed, and the number of wavelengths used is limited to the number of reception antennas 32-1 to 32-n. Further, a configuration for electrically changing switches is also not included. It is thus possible to perform beamforming for transmission/reception antennas without using control of the base station apparatus and information regarding the distance of the optical fiber while curbing degradation of wavelength utilization efficiency and an increase in cost.

[0191] Connection Configuration between Accommodation Station Apparatus and Base Station Apparatus

[0192] Although the optical fiber 3 is separately described as the downstream optical fiber 3-1 and the upstream optical fiber 3-2 on the assumption that the optical fiber 3 has two cores in the aforementioned first to fourth embodiments, a configuration may be employed in which circulators 50 and 60 as illustrated in FIG. 21 are used, for example. FIG. 21 is a block diagram illustrating a configuration in which the accommodation station apparatus 2 and the base station apparatus 1 are connected with a one-core optical fiber 3a. Note that as for the base station apparatus 1, the configuration in a case in which the base station transmission unit 20a including the reflect array 24-1 and the base station reception unit 30a including the reflect array 31-1 are included is illustrated.

[0193] The circulator 50 has three ports. The three ports that the circulator 50 has is a port connected to the accommodation station transmission unit 10, a port connected to the circulator 60 via the optical fiber 3a, and a port connected to the accommodation station reception unit 40. The circulator 50 obtains the optical signal output by the accommodation station transmission unit 10, outputs the optical signal to the optical fiber 3a, obtains the optical signal delivered through the optical fiber 3a, and outputs the optical signal to the accommodation station reception unit 40. The circulator 60, as with the circulator 50, has three ports. The three ports that the circulator 60 has is a port connected to the circulator 50 via the optical fiber 3a, a port connected to the base station transmission unit 20a, and a port connected to the base station reception unit 30a. The circulator 60 obtains the optical signal delivered through the optical fiber 3a, outputs the optical signal to the base station transmission unit 20a, obtains the optical signal output by the base station reception unit 30a, and outputs the optical signal to the optical fiber 3a.

[0194] Further, the base station apparatus 1 may include a base station transmission unit 20b including the transmit array 24-2 and a base station reception unit 30b including the transmit array 31-2, and a configuration in that case is the configuration illustrated in FIG. 22.

[0195] Note that in the case of the single mode, the accommodation station transmission unit 10s is applied to the accommodation station transmission unit 10, and the accommodation station reception unit 40s is applied to the accommodation station reception unit 40 in FIGS. 21 and 22. In the case of the multi mode, the accommodation station transmission unit 10m is applied to the accommodation station transmission unit 10, and the accommodation station reception unit 40m is applied to the accommodation station reception unit 40.

[0196] Although the wavelengths λ.sub.T1 to λ.sub.Tn of the light delivered through the downstream optical fiber 3-1 may be the same as the wavelengths λ.sub.R1 to λ.sub.Rn of the light delivered by through the upstream optical fiber 3-2 in the aforementioned first to fourth embodiments, the optical fiber 3a in the case of the configuration in FIGS. 21 and 22 has one core, and it is thus necessary for the wavelengths λ.sub.T1 to λ.sub.Tn to be different from the wavelengths λ.sub.R1 to λ.sub.Rn.

[0197] The transmission wavelength control units 12a and 12b and the reception wavelength control unit 43 in the aforementioned embodiments may be realized by a computer. In that case, the functions may be realized by recording a program for realizing the functions in a computer readable recording medium and causing a computer system to read and execute the program recorded in the recording medium. Note that the “computer system” described here is assumed to include an OS and hardware such as a peripheral device. Further, the “computer-readable recording medium” means a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM or a storage device such as a hard disk incorporated in the computer system. Moreover, the “computer-readable recording medium” may include a recording medium that dynamically holds the program for a short period of time, such as a communication line in a case in which the program is transmitted via a network such as the Internet or a communication line such as a telephone line, or a recording medium that holds the program for a specific period of time, such as a volatile memory inside a computer system that serves as a server or a client in that case. Further, the aforementioned program may be for realizing some of the aforementioned functions, may be able to realize the aforementioned functions in combination with a program that has already been recorded in the computer system, or may be realized using a programmable logic device such as a field programmable gate array (FPGA).

[0198] Although the embodiment of the present invention has been described in detail with reference to the drawings, a specific configuration is not limited to the embodiment, and a design or the like in a range that does not depart from the gist of the present invention is included.

INDUSTRIAL APPLICABILITY

[0199] The present invention is applicable in a case in which beamforming is performed in a wireless communication system using an RoF.

REFERENCE SIGNS LIST

[0200] 90 Wireless communication system [0201] 1 Base station apparatus [0202] 2 Accommodation station apparatus [0203] 3 Optical fiber [0204] 9 Terminal apparatus [0205] 10 Accommodation station transmission unit [0206] 20 Base station transmission unit [0207] 30 Base station reception unit [0208] 40 Accommodation station reception unit