Communication method, communication device, and communication system

Abstract

This communication method, which is to be executed by any one of a plurality of communication devices connected in multiple stages, comprises: a step of acquiring, from the previous stage, downlink optical signals having one or more wavelengths including a predetermined wavelength for reception and of transmitting, to the previous stage, a communication state signal or assignment requesting signal of the communication device by use of uplink optical signals having one or more wavelengths including a predetermined wavelength for transmission; a step of selecting the downlink optical signals having wavelengths for reception; a step of acquiring, from the selected downlink optical signals having the wavelengths for reception, an assignment control signal representative of the assignment of the wavelength for reception and the wavelength for transmission; a step of updating the wavelength for reception and the wavelength for transmission in accordance with the acquired assignment control signal; and a step of transmitting, to the previous stage, the uplink optical signal having the updated wavelength for transmission.

Description

[Technical Field]

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

[0002] Millimeter wave bands, which enable high-speed transmission, have attracted attention. Because propagation loss is large in millimeter wave bands, wireless base stations must be deployed densely in a communication area. To deploy wireless base stations densely, analog RoF (Radio over Fiber) is sometimes applied to communication systems. With analog RoF, the functions of a wireless base station are divided into an aggregate station and a base station. By deploying base stations with simple configurations in a communication area, a flexible and economical wireless communication environment is realized (see Non-Patent Document 1). Furthermore, to make it easier to deploy base stations, a communication system in which an aggregate station and multiple base stations are connected in a cascade configuration is being studied (see Non-Patent Document 2).

[0003] 6 is a diagram showing an example of the configuration of a communication system 100 disclosed in Non-Patent Document 2. The communication system 100 is a communication system to which analog RoF is applied. The communication system 100 includes a central station 200 and a plurality (N units) of base stations 300. The plurality of base stations 300 are cascade-connected to the central station 200 using a transmission path such as an optical fiber.

[0004] Hereinafter, the configuration closer to the central station will be referred to as the "preceding stage." For example, the base station 300-1 is the preceding stage of the base station 300-2. Hereinafter, the configuration farther from the central station will be referred to as the "rear stage." For example, the base station 300-N is the rear stage of the base station 300-(N-1).

[0005] Hereinafter, the direction from the base station to the aggregation station will be referred to as "upstream." Hereinafter, the direction from the aggregation station to the base station will be referred to as "downstream."

[0006] Different wavelengths are assigned to the upstream (uplink) optical signal and the downstream (downlink) optical signal for each base station 300. The central station 200 transmits the downstream optical signal to each base station 300. The central station 200 receives the upstream optical signal from each base station 300.

[0007] The base station 300 receives an optical signal from the aggregation station 200 via each base station 300 in the previous stage. The base station 300 generates a radio signal based on the optical signal of the wavelength assigned to its own downstream optical signal. The base station 300 uses the generated radio signal to perform downstream wireless communication with a terminal (not shown).

[0008] The base station 300 performs upstream wireless communication with a terminal (not shown). In response to a wireless signal received from the terminal (not shown), the base station 300 generates an optical signal with a wavelength assigned to its own upstream optical signal. The base station 300 transmits the generated optical signal to the aggregation station 200 via each base station 300 in the previous stage.

[0009] 7 is a diagram showing an example of the configuration of the central station 200. The central station 200 includes N converters 201, a multiplexer / demultiplexer 202, and N converters 203. A signal to be transmitted to the base station 300-n is input to the converter 201-n (where "n" is any integer from 1 to "N"). The converter 201-n converts the signal (electrical signal) to be transmitted to the base station 300-n into a signal with a wavelength "λ DLn The N converters 201 convert the wavelengths of the optical signals into DL1 " to wavelength "λ DLN ” are output to the multiplexing / demultiplexing unit 202.

[0010] The multiplexing / demultiplexing unit 202 receives a signal of wavelength “λ DL1 " to wavelength "λ DLN The optical signals of each wavelength from wavelength "λ" to wavelength "λ" are input from N converters 201. DL1 " to wavelength "λ DLN " are transmitted to each base station 300 via a transmission path such as an optical fiber.

[0011] The multiplexing / demultiplexing unit 202 receives a signal of wavelength “λ UL1 " to wavelength "λ ULN Optical signals of wavelengths up to λ are input from a plurality (N units) of base stations 300. The multiplexing / demultiplexing unit 202 multiplexes and demultiplexes the optical signals of wavelengths UL1 " to wavelength "λ ULN The converter 203-n demultiplexes the optical signal of each wavelength from the base station 300-n to the wavelength "λ ULn The N converters 203 convert the optical signals of wavelengths "λ" into received signals (electrical signals). ULn The received signal for each " is output to a predetermined device (not shown).

[0012] 8 is a diagram showing an example of the configuration of the base station 300. The base station 300 includes an optical splitter 301, a multiplexing / demultiplexing unit 302, a converting unit 303, an amplifier 304, a circulator 305, an antenna 306, an amplifier 307, and a converting unit 308.

[0013] The optical splitter 301 may be an equal-branch splitter or an unequal-branch splitter. The performance of the optical splitter 301 provided in all base stations 300 is the same. Furthermore, the performance of the optical splitter 301 is fixed for all base stations 300.

[0014] The optical splitter 301 splits an optical signal input from a base station 300 at a preceding stage to a base station 300 at a succeeding stage and to the multiplexing / demultiplexing unit 302. The optical splitter 301 outputs an optical signal input from a base station 300 at a succeeding stage to the base station 300 at a preceding stage.

[0015] The optical signal split by the optical splitter 301 is input to the multiplexing / demultiplexing unit 302. The multiplexing / demultiplexing unit 302 splits the wavelength of the optical signal split by the optical splitter 301 into a wavelength "λ" assigned to the downstream optical signal of the local station. DLn " optical signal.

[0016] The multiplexer / demultiplexer 302 receives the wavelength “λ 1 ” assigned to the upstream optical signal of the own station. ULn The optical signal of wavelength "λ" is input from the conversion unit 308.ULn ” optical signal to the optical splitter 301.

[0017] The converter 303 converts the wavelength “λ DLn The amplifier 304 amplifies the power of the electrical signal input from the converter 303. The circulator 305 applies a voltage to the antenna 306 in accordance with the electrical signal whose power has been amplified by the amplifier 304. The circulator 305 outputs the electrical signal input from the antenna 306 to the amplifier 307.

[0018] Antenna 306 transmits a radio signal in response to the voltage applied from circulator 305. Antenna 306 receives a radio signal from a terminal (not shown) that performs wireless communication. Antenna 306 outputs an electrical signal in response to the received radio signal to circulator 305.

[0019] The amplifier 307 amplifies the power of the electrical signal input from the circulator 305. The converter 308 converts the electrical signal into a signal having a wavelength of λ ULn The converter 308 converts the wavelength "λ ULn ” optical signal to the multiplexing / demultiplexing unit 302. [Prior art documents] [Non-patent literature]

[0020] [Non-Patent Document 1] Kodai Ito, Mizuki Suga, Hirofumi Shirato, Naoki Kita, and Takeshi Onisawa, "Efficient Accommodation of Diverse High-Frequency Band Wireless Systems Using Analog Radio Fiber," NTT Technical Journal, 32(3), pp. 15-17, 2020. [Non-patent document 2] E.-S. Kim, M. Sung, JH Lee, JK Lee, S.-H. Cho and J. Kim, "Coverage Extension of Indoor 5G Network Using RoF-Based Distributed Antenna System," IEEE Access, vol. 8, pp. 194992-194999, 2020. Summary of the Invention [Problem to be solved by the invention]

[0021] The communication resources allocated to each base station are not changed. For example, the wavelength of the optical signal remains allocated to a base station that is not communicating with a terminal. In addition, because the branching of the optical signal by the optical splitter is fixed, the allocation of optical power to each base station is fixed. This causes a problem in that it is not possible to prevent waste of communication resources allocated to the base station.

[0022] In view of the above circumstances, an object of the present invention is to provide a communication method, a communication device, and a communication system that can prevent communication resources allocated to a base station from being wasted. [Means for solving the problem]

[0023] One aspect of the present invention is a communication method executed by a communication device among a plurality of communication devices connected in multiple stages, the communication method including the steps of: acquiring downstream optical signals of one or more wavelengths including a predetermined receiving wavelength from a previous stage; and transmitting a communication status signal or an allocation request signal of the communication device to the previous stage using upstream optical signals of one or more wavelengths including a predetermined transmitting wavelength; selecting the downstream optical signals of the receiving wavelengths; acquiring an allocation control signal representing allocation of the receiving wavelengths and the transmitting wavelengths from the selected downstream optical signals of the receiving wavelengths; updating the receiving wavelengths and the transmitting wavelengths in accordance with the acquired allocation control signal; and transmitting an upstream optical signal of the updated transmitting wavelength to the previous stage.

[0024] One aspect of the present invention is a communication device comprising: a front-stage transmission unit that acquires downstream optical signals of one or more wavelengths including a predetermined receiving wavelength from a front stage, and transmits a communication status signal or an allocation request signal of the communication device to the front stage using upstream optical signals of one or more wavelengths including a predetermined transmitting wavelength; a selection unit that selects the downstream optical signals of the receiving wavelengths; a receiving unit that acquires an allocation control signal representing the allocation of the receiving wavelength and the transmitting wavelength from the downstream optical signals of the selected receiving wavelengths; a base station control unit that updates the receiving wavelength and the transmitting wavelength in accordance with the acquired allocation control signal; and a transmitting unit that transmits upstream optical signals of one or more wavelengths including the updated transmitting wavelength to the front stage using the front-stage transmission unit.

[0025] One aspect of the present invention is a communication system comprising a central station at a front end and a plurality of base stations connected in multiple stages including a rear end, wherein the central station comprises a central station transmitter that transmits downstream optical signals of one or more wavelengths including a predetermined receiving wavelength to the plurality of base stations, a central station receiver that receives upstream optical signals of one or more wavelengths including a predetermined transmitting wavelength from the plurality of base stations, and a central station controller that generates an allocation control signal representing allocation of the receiving wavelength and the transmitting wavelength based on a communication status signal or an allocation request signal of the base station, and includes the allocation control signal in downstream optical signals of one or more wavelengths including the receiving wavelength, and the base station comprises: a upstream transmission unit that acquires downstream optical signals of one or more wavelengths including the receiving wavelength from a previous stage and transmits a communication status signal or an allocation request signal of the base station to the previous stage using upstream optical signals of one or more wavelengths including the transmitting wavelength; a selection unit that selects downstream optical signals of the receiving wavelength; a base station receiving unit that acquires the allocation control signal from the selected downstream optical signal of the receiving wavelength; a base station control unit that updates the receiving wavelength and the transmitting wavelength in accordance with the acquired allocation control signal; and a base station transmitting unit that transmits upstream optical signals of one or more wavelengths including the updated transmitting wavelength to the previous stage using the upstream transmission unit. [Effects of the Invention]

[0026] According to the present invention, it is possible to prevent communication resources allocated to a base station from being wasted. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of the configuration of a central station in an embodiment. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a base station in an embodiment. [Figure 4] FIG. 2 is a sequence diagram illustrating an example of the operation of a communication system according to an embodiment. [Figure 5]FIG. 2 is a diagram illustrating an example of a hardware configuration of a communication device according to an embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of the configuration of a communication system disclosed in Non-Patent Document 2. [Figure 7] FIG. 2 is a diagram illustrating an example of the configuration of a central station. [Figure 8] FIG. 2 is a diagram illustrating an example of the configuration of a base station. DETAILED DESCRIPTION OF THE INVENTION

[0028] (overview) The communication system includes a plurality of base stations and a central station that are cascade-connected (multi-stage connected) using optical fibers. For example, analog RoF is applied to the communication system. Here, the central station dynamically controls the allocation (distribution) of communication resources to each base station as a centralized control. The communication resources are, for example, the wavelength and optical intensity of an optical signal. Each base station may dynamically control the allocation of communication resources to each base station as an autonomous control.

[0029] At least one of the central station and the base station executes the process according to the following steps (1) to (4).

[0030] (1) Acquisition of communication status (communication status) of the base station The control unit of the base station acquires information about the communication status of at least its own station (own communication device) among multiple base stations in the communication system. The information about the communication status of its own station is, for example, information indicating whether or not there is a terminal communicating with its own station.

[0031] (2) Feedback on communication status of the base station (2-1) When centralized control is performed by the central station, each base station transmits the communication status of each base station to the central station. (2-2) When autonomous control is performed by the base station, the control unit of each base station derives the amount of communication resources (e.g., the number of wavelengths of optical signals) allocated to the base station based at least on the communication status of the base station. For example, the control unit of a base station that is not communicating with a terminal deletes the amount of communication resources allocated to the base station. For example, the control unit of each base station that is communicating with many terminals requests the central station to increase the amount of communication resources allocated to the base station for downstream optical signals. Note that the control unit of each base station may increase the amount of communication resources allocated to the base station for upstream optical signals in accordance with the communication status of the other base stations and the communication status of the base station itself, without requesting the central station to increase the amount of allocation.

[0032] (3) Determining the amount of communication resources allocated (allocation status) The central station determines whether the amount of communication resources allocated to each base station is sufficient. For example, the central station determines whether communication resources are allocated to a base station that is not communicating with a terminal, or whether the amount of communication resources allocated to a base station that is communicating with a large number of terminals is sufficient.

[0033] (4) Reallocation of communication resources The central station reallocates communication resources to each base station based on the communication status of each base station. For example, the central station reduces the amount of communication resources allocated to a base station that is not communicating with a terminal. When autonomous control is performed by the base station, the control unit of each base station may reduce the amount of communication resources allocated to that station without control from the central station. For example, the central station increases the amount of communication resources allocated to a base station that is communicating with a large number of terminals.

[0034] These measures make it possible to prevent communication resources allocated to base stations from being wasted.

[0035] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a communication system 1 according to an embodiment. The communication system 1 is a communication system to which analog RoF is applied. The communication system 1 includes a central station 2 at the front end and multiple (N) base stations 3 connected in multiple stages including the rear end. The multiple base stations 3 are cascade-connected (multistage-connected) to the central station 2 using a transmission path such as optical fiber. The communication system 1 can be applied to, for example, a mobile fronthaul.

[0036] The optical fiber of the transmission path may be one or more. The optical fiber of the transmission path may be a single-core fiber or a multi-core fiber. One or more cascade configurations may branch off midway along the cascade-configured transmission path. Furthermore, in a physical topology in which the base station 3 is a node and the transmission path is an edge, multiple base stations 3 may be connected in a loop using the transmission path. The communication system 1 may include an optical amplifier (not shown) in the cascade configuration including multiple base stations 3 and transmission paths.

[0037] The allocation of communication resources to each base station 3 is dynamically controlled by at least one of the central station 2 and the base station 3 according to the communication conditions required for the communication system 1 and the communication status of the base station 3. This makes it possible to prevent waste of communication resources allocated to the base station 3. The communication resources are, for example, the number of wavelengths of the optical signal and the optical power of the optical signal.

[0038] The aggregation station 2 transmits N1 transmission signals at mutually different wavelengths “λ DL The central station 2 transmits the N2 received signals downstream to one or more base stations 3 using optical signals of different wavelengths "λ UL The upstream signal is received from one or more base stations 3 using the optical signal ".

[0039] The base station 3 can perform wireless communication with one or more terminals 4. The terminals 4 can perform wireless communication with one or more base stations 3. The base station 3-1 performs optical communication with the central station 2 using optical signals. The base stations 3 other than the base station 3-1 perform optical communication with the central station 2 via the base station 3 preceding the base station 3 and the transmission path.

[0040] 2 is a diagram showing an example of the configuration of the central station 2 in the embodiment. The central station 2 includes a central station control unit 21, a sending unit 22, a transmitting unit 23, and a receiving unit 24.

[0041] The central station control unit 21 controls each functional unit of the central station 2. The central station control unit 21 generates an allocation control signal based on predetermined communication conditions. The allocation control signal indicates, for example, the allocation (distribution) of communication resources (each wavelength and optical power) to multiple base stations 3. The central station control unit 21 outputs the allocation control signal to the transmitter 22.

[0042] The central station control unit 21 acquires a communication status signal from the receiving unit 24. The communication status signal includes, for example, a signal indicating the communication status of each base station 3. The communication status is, for example, the number of terminals 4 with which each base station 3 is communicating. The communication status may also be, for example, the status of the communication traffic volume at each base station 3. The communication status signal may also include, for example, temperature information of devices at each base station 3. The device temperature is, for example, proportional to the communication traffic volume.

[0043] The transmitter 22 transmits N1 transmission signals at mutually different wavelengths “λ DL The N1 transmission signals 5 may be main signals transmitted from the base station 3 to the terminal 4, or may be allocation control signals transmitted from the central station 2 to the base station 3. The transmission unit 22 may multiplex the main signals and allocation control signals into the transmission signals 5. The transmission unit 22 may multiplex a plurality of main signals and a plurality of allocation control signals into the transmission signals 5. The transmission unit 22 may multiplex a plurality of main signals and a timing signal into the transmission signals 5.

[0044] The transmission section 23 has a wavelength “λ DL The optical signals of different wavelengths "λ" are input from the transmitting unit 22. DL The transmitter 23 transmits the combined optical signal downstream to one or more base stations 3 via a transmission path.

[0045] The transmission section 23 transmits light having different wavelengths “λ UL The optical signals of different wavelengths "λ" are received from the base station 3-1. UL The optical signal "λ" may be an optical signal transmitted from a plurality of base stations 3 connected in cascade. UL The transmission unit 23 separates the optical signals of different wavelengths "λ UL The optical signal " is transmitted to the receiver 24.

[0046] The receiver 24 receives the N2 received signals 6 at different wavelengths “λ UL The received signal 6 is received upstream from the transmission unit 23 using an optical signal ". The received signal 6 may be multiplexed with a main signal and a communication status signal. The received signal 6 may be multiplexed with multiple main signals and multiple communication status signals.

[0047] 3 is a diagram illustrating an example of the configuration of a base station 3 according to an embodiment. The base station 3 includes a base station control unit 31, a front-end transmission unit 32, a selection unit 33, a reception unit 34, an antenna unit 35, a rear-end transmission unit 36, and a transmission unit 37.

[0048] In Fig. 3, downlink signal lines for the main signal and allocation control signal are represented by solid arrows. Uplink signal lines for the main signal and communication status signal are represented by dashed arrows. Signal lines for base station control signals are represented by dashed arrows. The base station control signals are control signals for the functional units of the base station 3.

[0049] In the base station 3, the downlink signal lines for the main signal and allocation control signal and the uplink signal line for the communication status signal are independent of each other. Therefore, even if the main signal is congested, it is possible to transmit and receive the communication status signal.

[0050] In the base station 3, the downlink signal lines for the main signal and allocation control signal and the signal line for the base station control signal are independent of each other. Therefore, even if the main signal is congested, the base station control unit 31 can transmit and receive the base station control signal.

[0051] At least one of the front-end transmission unit 32 and the rear-end transmission unit 36 may include an optical amplifier. The optical amplifier amplifies the optical intensity of the optical signal transmitted through the transmission path to compensate for optical loss of the optical signal. This makes it possible to increase the number of base stations 3 connected via the transmission path.

[0052] The base station control unit 31 controls the operation of each functional unit of the base station 3. The base station control unit 31 inputs a base station control signal to the receiving unit 34. This base station control signal is, for example, multiplexed information that allows the receiving unit 34 to separate a signal multiplexed into a transmission signal from the central station 2.

[0053] The front-end transmission unit 32 of the base station 3-1 receives the wavelength “λ1 DL " to wavelength "λ N1 DL The front-end transmission unit 32 of the base station 3-n (n≧2) receives optical signals of at least some of the wavelengths from the central station 2 using optical fibers. DL " to wavelength "λ N1 DL 」 from the base station 3-(n-1) using optical fibers.

[0054] The front-end transmission unit 32 transmits the signal of wavelength "λ1 UL " to wavelength "λ N2 UL" from the transmitter 37. The front-end transmission unit 32 of the base station 3-1 transmits the optical signal obtained from the transmitter 37 to the central station 2 using optical fiber. The front-end transmission unit 32 of the base station 3-n (n≧2) transmits the optical signal obtained from the transmitter 37 to the base station 3-(n-1) using optical fiber.

[0055] The selector 33 selects at least some of the wavelengths of the optical signal received by the front-end transmitter 32 by wavelength demultiplexing in accordance with the base station control signal acquired from the base station controller 31. The base station control signal indicates, for example, the wavelength selected by the selector 33 (the wavelength assigned to the downstream optical signal addressed to the base station). The wavelength indicated by the base station control signal is determined, for example, in accordance with the allocation control signal separated by the receiver 34. The selector 33 outputs the optical signal of the selected wavelength (optical power) to the receiver 34. The selector 33 outputs the optical signal of the unselected wavelength (the wavelength other than the receiving wavelength) to the rear-end transmitter 36.

[0056] The receiving unit 34 (base station receiving unit) (acquiring unit) acquires the optical signal of the selected wavelength from the selecting unit 33. The receiving unit 34 converts the optical signal of the selected wavelength into an electrical signal for each wavelength. If multiple main signals and allocation control signals are multiplexed into the converted electrical signal, the receiving unit 34 separates the multiple main signals and allocation control signal from the transmission signal. The receiving unit 34 outputs the separated allocation control signal (the allocation control signal transmitted from the central station 2) to the base station control unit 31. The receiving unit 34 outputs the separated main signal to the antenna unit 35. If optical signals of multiple wavelengths are selected by the selecting unit 33, the receiving unit 34 outputs the multiple main signals to the antenna unit 35. If multiple main signals for each wavelength are multiplexed into the optical signal, the receiving unit 34 outputs the multiple main signals to the antenna unit 35.

[0057] The antenna unit 35 acquires a main signal to be transmitted to the terminal 4 from the receiving unit 34. The antenna unit 35 may perform frequency conversion on the main signal acquired from the receiving unit 34. The antenna unit 35 may generate a local signal required for the frequency conversion. The specifications of the local signal are determined in advance.

[0058] A local signal required for frequency conversion may be supplied to the base station 3 from an aggregate station 2 located remotely from the base station 3. In this case, the local signal is generated by the base station control unit 31 using a timing signal supplied from the aggregate station 2. The local signal generated using the timing signal is input from the base station control unit 31 to the antenna unit 35. If the timing signal is a clock signal, the base station control unit 31 generates the local signal using the timing signal that is the clock signal. The base station control unit 31 inputs the local signal generated in this manner to the antenna unit 35.

[0059] When the frequency of the timing signal and the frequency of the local signal are the same, the timing signal may be input to the antenna unit 35 from the receiving unit 34. When the frequency of the timing signal and the frequency of the local signal are different, the base station control unit 31 may generate the local signal by converting (multiplying) the frequency of the timing signal to a desired frequency. The base station control unit 31 inputs the local signal generated in this manner to the antenna unit 35.

[0060] The antenna unit 35 transmits the main signal to the terminal 4 using a downstream radio signal. The antenna unit 35 may transmit the frequency-converted main signal to the terminal 4. The antenna unit 35 may be an array antenna. The antenna unit 35 may control the beam direction in accordance with a control signal acquired from the base station control unit 31.

[0061] The antenna unit 35 receives the main signal from the terminal 4 using the uplink radio signal. When the receiving unit 34 outputs a plurality of main signals to the antenna unit 35, the antenna unit 35 transmits the plurality of main signals to the terminal 4 using the radio signal. When transmitting a plurality of main signals to the terminal 4, the antenna unit 35 may form a multi-beam. When transmitting a plurality of main signals to the terminal 4, the antenna unit 35 may perform transmission MIMO (Multiple Input Multiple Output) processing.

[0062] The antenna unit 35 acquires the main signal from the terminal 4 using the radio signal. The antenna unit 35 outputs the main signal (electrical signal) received from the terminal 4 to the transmission unit 37. The antenna unit 35 may perform frequency conversion on the main signal acquired from the terminal 4. The antenna unit 35 may output the frequency-converted main signal to the transmission unit 37. When receiving a plurality of main signals from the terminal 4, the antenna unit 35 may form a multi-beam. When receiving a plurality of main signals from the terminal 4, the antenna unit 35 may perform reception MIMO processing.

[0063] The subsequent stage transmission unit 36 acquires at least some of the optical signals of each wavelength from wavelength “λ1” to wavelength “λ”. UL ” to wavelength “λ” N2 UL ” from the selection unit 33. The extension station 3-n (n < N) acquires at least some of the optical signals of the wavelengths from wavelength “λ1” to wavelength “λ” using an optical fiber from the subsequent stage extension station 3-(n + 1). UL ” to wavelength “λ” N2 UL ” using an optical fiber from the subsequent stage extension station 3-(n + 1).

[0064] Optical signals of wavelengths not selected by the selection unit 33 are input to the subsequent stage transmission unit 36. As a result, the subsequent stage transmission unit 36 transmits at least some of the optical signals of the wavelengths from wavelength “λ” to wavelength “λ” to the subsequent stage extension station 3 using an optical fiber. DL1 ” to wavelength “λ” DLN ” using an optical fiber.

[0065] The transmitter 37 (base station transmitter) acquires a base station control signal from the base station control unit 31. The base station control signal indicates, for example, the communication status between the base station and terminals 4 and the internal state of the base station. The communication status indicates, for example, the number of terminals 4 currently communicating with the base station. The internal state of the base station indicates, for example, the operating status and temperature of devices in the base station.

[0066] When the antenna unit 35 receives a plurality of radio signals of the main signal from the terminal 4, the transmitter 37 acquires a plurality of main signals (electrical signals) corresponding to the received radio signals from the antenna unit 35. The transmitter 37 transmits the main signals input from the antenna unit 35 and the communication status signal input from the base station control unit 31 as a signal having a wavelength of "λ1 UL " to wavelength "λ N2 UL The wavelengths are determined in accordance with the base station control signal. This base station control signal indicates, for example, the wavelengths assigned to the upstream optical signals of the base station.

[0067] When a plurality of main signals and communication status signals are input, the transmitter 37 may convert each of the plurality of main signals and communication status signals into optical signals of a plurality of wavelengths.When a plurality of main signals and communication status signals are input, the transmitter 37 may multiplex the plurality of main signals and communication status signals and convert the multiplexed signal into an optical signal of a single wavelength.

[0068] The transmitter 37 multiplexes the optical signal received from the downstream base station 3 by the downstream transmission unit 36 with the optical signal converted from the main signal and the communication status signal. The transmitter 37 outputs the multiplexed optical signal to the upstream transmission unit 32. The upstream transmission unit 32 transmits the multiplexed optical signal to the upstream base station 3 or the central station 2. In this way, the transmitter dynamically controls the wavelength and optical power of the optical signal converted from the main signal and the communication status signal.

[0069] Next, an example of the operation of the communication system 1 will be described. 4 is a sequence diagram showing an example of operation of the communication system 1 in the embodiment. The central station 2 transmits a downstream main signal to a subsequent stage using a downstream optical signal of a predetermined wavelength for reception (step S101). The base station 3-n acquires downstream optical signals of one or more wavelengths from the previous stage (the central station 2 or the base station 3-(n-1)) (step S102). The base station 3-n selects a downstream optical signal of a predetermined wavelength for reception from the downstream optical signals of one or more wavelengths (step S103).

[0070] The base station 3-n acquires a downstream main signal from the selected downstream optical signal (step S104). The base station 3-n performs wireless communication with the terminal 4 based on the downstream main signal. The base station 3-n may acquire an upstream main signal from the terminal 4 (step S105).

[0071] Hereinafter, a signal requesting allocation of an allocation amount of communication resources will be referred to as an "allocation request signal." The base station 3-n transmits a communication status signal to the previous stage using an upstream optical signal of the transmission wavelength. As an execution of autonomous control by the base station 3-n, the base station 3-n derives an allocation amount (allocation) of communication resources for downstream optical signals according to at least the communication status of the base station. The base station 3-n (base station control unit 31) generates an allocation request signal for the downstream optical signal. The base station 3-n may transmit an allocation request signal according to the communication status of the base station to the previous stage using an upstream optical signal of the transmission wavelength (step S106).

[0072] The central station 2 acquires a communication status signal from the base station 3-1 using an upstream optical signal of the transmission wavelength. When autonomous control by each base station 3 is performed, the central station 2 may acquire an allocation request signal for a downstream optical signal from the base station 3-1 using an upstream optical signal of the transmission wavelength (step S107). The central station 2 generates an allocation control signal representing the allocation of communication resources (each wavelength and optical power) to the base station 3-n based on the communication status signal or the allocation request signal (step S108). The central station 2 transmits the allocation control signal to the subsequent stage using a downstream optical signal of the reception wavelength (step S109).

[0073] In addition, as an execution of autonomous control by the base station 3-n, the base station 3-n may derive the allocation amount (allocation) of communication resources for upstream optical signals in accordance with the communication status of the base station 3-n itself. For example, if the communication volume between the base station 3-n and the terminal 4 increases, the base station 3-n increases the allocation amount of communication resources for upstream optical signals of the base station 3-n itself. In this case, as an execution of autonomous control by the base station 3-n, the base station 3-n does not need to request the central station 2 to increase the allocation amount of communication resources for upstream optical signals of the base station 3-n itself. The base station 3-n may collect information on the communication status of other base stations 3. The base station 3-n may derive the allocation amount (allocation) of communication resources for upstream optical signals in accordance with the communication status of the other base stations 3 and the communication status of the base station 3-n itself. For example, if the upstream transmission volume of optical signals between the base station 3 and another base station 3 increases, the base station 3-n increases the allocation amount of communication resources for upstream optical signals of the base station 3-n itself. In this case, the base station 3-n may execute autonomous control without requesting the aggregation station 2 to increase the allocation of communication resources for the upstream optical signal of the base station 3-n. Furthermore, the base station 3-n may notify the aggregation station 2 that the allocation of communication resources for the upstream optical signal of the base station 3-n has been autonomously increased by the base station 3-n. In this way, the base station 3-n autonomously increases the allocation of communication resources for the upstream optical signal of the base station 3-n.

[0074] The base station 3-n acquires downstream optical signals of one or more wavelengths from the previous stage (the aggregation station 2 or the base station 3-(n-1)) (step S110). The base station 3-n selects a downstream optical signal of a predetermined receiving wavelength from the downstream optical signals of one or more wavelengths (step S111). The base station 3-n acquires an allocation control signal from the selected downstream optical signal (step S112).

[0075] The base station 3-n updates its base station control signal based on the allocation control signal, thereby updating at least one of the transmission wavelength and the reception wavelength. Here, updating a wavelength includes not only changing a wavelength but also adding or deleting a wavelength (step S113). The base station 3-n transmits an upstream main signal to the previous stage using an upstream optical signal with the updated transmission wavelength (step S114). The central station 2 acquires an upstream main signal from the base station 3-1 using the upstream optical signal with the updated transmission wavelength (step S115).

[0076] The central station 2 transmits the downstream main signal to the subsequent stage using the downstream optical signal with the updated receiving wavelength. The base station 3-n acquires the downstream main signal using the downstream optical signal with the updated receiving wavelength.

[0077] <Downlink control> As described above, the base station 3-1 can extract, from the optical signal received from the aggregation station 2, an optical signal with a wavelength and optical power selected in accordance with the allocation control signal transmitted from the aggregation station 2. The base station 3-n (n≧2) can extract, from the optical signal received from the previous base station 3-(n-1), an optical signal with a wavelength and optical power selected in accordance with the allocation control signal transmitted from the aggregation station 2.

[0078] The central station control unit 21 can allocate the wavelength and optical power of the downstream optical signal to the base station 3 in accordance with the communication status of each base station 3. The base station control unit 31 may autonomously generate allocation request information in accordance with the communication status of its own station and the terminal 4. The transmitter 37 may upstream transmit the allocation request information to the central station 2. The central station 2 can allocate the wavelength and optical power of the optical signal to the base station 3 in accordance with the allocation request information autonomously generated by each base station 3.

[0079] The central station control unit 21 preferentially allocates a large number of wavelengths and optical power to downstream optical signals of a base station 3 communicating with a threshold number of terminals 4 or more. The central station control unit 21 may lower the priority of wavelength and optical power allocation for a base station 3 communicating with a number of terminals 4 less than the threshold. For example, wavelengths and optical power may not be allocated to a base station 3 communicating with a number of terminals 4 less than the threshold. The central station control unit 21 may preferentially allocate a large number of wavelengths and optical power to a base station 3 in which the quality of communication with the terminals is deteriorating.

[0080] The central station control unit 21 can also dynamically control the main signal and allocation control signal multiplexed into the downstream optical signal of one wavelength. For a base station 3 communicating with a threshold number of terminals 4 or more, the central station control unit 21 preferentially allocates more wavelengths and optical power to the downstream optical signal of one wavelength.

[0081] <Uplink control> As described above, the base station 3-1 can control the wavelength and optical power of an optical signal transmitted to the aggregation station 2. The base station 3-n (n≧2) can control the wavelength and optical power of an optical signal transmitted to the previous base station 3-(n-1).

[0082] The central station control unit 21 can allocate the wavelength and optical power of the upstream optical signal to each central station 3 by using an allocation control signal to each central station 3. The central station control unit 31 may autonomously generate allocation request information according to the communication status of its own station and the terminal 4. The transmitter 37 may upstream transmit the allocation request information (allocation request information) to the central station 2.

[0083] The central station control unit 21 preferentially allocates a large number of wavelengths and optical power to upstream optical signals of a base station 3 communicating with a threshold number of terminals 4 or more. The central station control unit 21 may lower the priority of wavelength and optical power allocation for a base station 3 communicating with a number of terminals 4 less than the threshold. For example, wavelengths and optical power may not be allocated to a base station 3 communicating with a number of terminals 4 less than the threshold. The central station control unit 21 may preferentially allocate a large number of wavelengths and optical power to a base station 3 in which the quality of communication with the terminals is deteriorating.

[0084] The central station control unit 21 can also dynamically control the main signal and allocation control signal multiplexed into the upstream optical signal of one wavelength. For a base station 3 that is communicating with a threshold number of terminals 4 or more, the central station control unit 21 preferentially allocates more wavelengths and optical power to the upstream optical signal of one wavelength.

[0085] As described above, the communication system 1 includes the central station 2 at the frontmost stage and a plurality of base stations 3 connected in multiple stages, including the rearmost stage. DL The receiver 24 (central station receiver) transmits downstream optical signals of one or more wavelengths including a predetermined transmission wavelength "λ UL " is acquired from a plurality of base stations 3. The central station control unit 21 generates an allocation control signal representing the allocation of at least one of the receiving wavelength and the transmitting wavelength based on the communication status signal or the allocation request signal of the base station 3. The central station control unit 21 includes the allocation control signal in downstream optical signals of one or more wavelengths including the receiving wavelength.

[0086] The upstream transmission unit 32 acquires downstream optical signals of one or more wavelengths including a receiving wavelength from the upstream unit. The upstream transmission unit 32 transmits a communication status signal or an allocation request signal of its own station to the upstream unit using upstream optical signals of one or more wavelengths including a transmitting wavelength. The selection unit 33 selects a downstream optical signal of a receiving wavelength. The reception unit 34 (base station reception unit) acquires an allocation control signal from the downstream optical signal of the selected receiving wavelength. The base station control unit 31 updates the receiving wavelength and the transmitting wavelength in accordance with the acquired allocation control signal. The transmission unit 37 (base station transmission unit) transmits upstream optical signals of one or more wavelengths including the updated transmitting wavelength to the upstream unit using the upstream transmission unit 32.

[0087] In this way, the allocation of communication resources to each base station 3 is dynamically controlled by at least one of the central station 2 and the base station 3 according to the communication conditions required for the communication system 1 and the communication status of the base station 3. This makes it possible to prevent communication resources allocated to the base station 3 from being wasted.

[0088] Since appropriate resource allocation is performed for the entire communication system 1, it is possible to improve the communication quality for the entire communication system 1. It is also possible to reduce the power consumption for the entire communication system 1. In addition, it is easy to change the connection configuration of the base stations 3 (for example, to add a base station 3 in the middle or at the end of a cascade configuration).

[0089] (Example of hardware configuration) FIG. 5 is a diagram illustrating an example of a hardware configuration of a communication device 10 according to an embodiment. The communication device 10 corresponds to at least one of a central station 2 and a base station 3. Some or all of the functional units of the communication device 10 are implemented as software by a processor 101, such as a central processing unit (CPU), executing programs stored in a storage device 102 having a non-volatile recording medium (non-transitory recording medium) and a memory 103. The programs may be recorded on a computer-readable non-transitory recording medium. Examples of computer-readable non-transitory recording media include portable media such as flexible disks, magneto-optical disks, read-only memories (ROMs), and compact disc read-only memories (CD-ROMs), and storage devices such as hard disks built into computer systems. A communication unit 104 executes predetermined communication processing. The communication unit 104 may acquire data and programs.

[0090] Some or all of the functional units of the communication device 10 may be realized using hardware including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0091] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0092] For example, the communication system 1 may be applied to a digital RoF such as CPRI (Common Public Radio Interface) or eCPRI (enhanced Common Public Radio Interface) by adding a configuration required for digital processing (for example, a processor) to the communication system 1. For example, the central station control unit 21 may be provided with a configuration required for digital processing.

[0093] For example, the communication system 1 may be applied to digital coherent transmission by adding a configuration required for digital coherent transmission (for example, a laser oscillator) to the communication system 1. For example, at least one of the transmitter 22, the receiver 24, and the transmitter 23 may have a configuration required for digital coherent transmission. [Industrial Applicability]

[0094] The present invention is applicable to communication systems. [Explanation of symbols]

[0095] 1...communication system, 2...aggregator station, 3...base station, 4...terminal, 5...transmitted signal, 6...received signal, 10...communication device, 21...aggregator station control unit, 22...transmitting unit, 23...transmitting unit, 24...receiving unit, 31...base station control unit, 32...pre-stage transmitting unit, 33...selecting unit, 34...receiving unit, 35...antenna unit, 36...post-stage transmitting unit, 37...transmitting unit, 101...processor, 102...storage device, 103...memory, 104...communication unit, 100...communication system, 200...aggregator station, 201...converting unit, 202...multiplexing / demultiplexing unit, 203...converting unit, 300...base station, 301...optical splitter, 302...multiplexing / demultiplexing unit, 303...converting unit, 304...amplifier, 305...circulator, 306...antenna, 307...amplifier, 308...converting unit

Claims

1. A communication method executed by a communication device among a plurality of communication devices connected in a multistage configuration, acquiring downstream optical signals of one or more wavelengths including a predetermined receiving wavelength from a previous stage, and transmitting a communication status signal or an allocation request signal of the communication device to the previous stage using upstream optical signals of one or more wavelengths including a predetermined transmitting wavelength; selecting a downstream optical signal of the receiving wavelength; acquiring an allocation control signal representing allocation of the receiving wavelength and the transmitting wavelength from a downstream optical signal of the selected receiving wavelength; updating the receiving wavelength and the transmitting wavelength in response to the acquired allocation control signal; transmitting an upstream optical signal with the updated transmission wavelength to the previous stage; Including, the updating step includes updating the receiving wavelength and the transmitting wavelength in the communication device via a signal line independent from downstream signal lines for a main signal and for the allocation control signal. Communication method.

2. 2. The communication method according to claim 1, further comprising the step of transmitting downstream optical signals of wavelengths other than said receiving wavelength, among downstream optical signals of one or more wavelengths including said receiving wavelength, to a subsequent stage.

3. a upstream transmission unit that acquires downstream optical signals of one or more wavelengths including a predetermined receiving wavelength from a upstream unit, and transmits a communication status signal or an allocation request signal of the communication device to the upstream unit using upstream optical signals of one or more wavelengths including a predetermined transmitting wavelength; a selector for selecting a downstream optical signal of the receiving wavelength; a receiving unit that acquires an allocation control signal representing allocation of the receiving wavelength and the transmitting wavelength from a downstream optical signal of the selected receiving wavelength; a base station control unit that updates the receiving wavelength and the transmitting wavelength in response to the acquired allocation control signal; a transmitting unit that transmits upstream optical signals of one or more wavelengths including the updated transmission wavelength to the upstream stage using the upstream transmission unit; Equipped with the base station control unit updates the receiving wavelength and the transmitting wavelength in the communication device via a signal line independent from downstream signal lines for the main signal and the allocation control signal. Communication equipment.

4. 4. The communication device according to claim 3, further comprising a downstream transmission section that transmits downstream optical signals of wavelengths other than the receiving wavelength, among downstream optical signals of one or more wavelengths including the receiving wavelength, to a downstream stage.

5. A communication system including a central station at a front end and a plurality of base stations connected in multiple stages including a rear end, The aggregation station a central station transmitter that transmits downstream optical signals of one or more wavelengths including a predetermined receiving wavelength to the plurality of base stations; a central station receiving unit configured to receive upstream optical signals of one or more wavelengths including a predetermined transmission wavelength from the plurality of base stations; a central station control unit that generates an allocation control signal representing allocation of the receiving wavelengths and the transmitting wavelengths based on a communication status signal or an allocation request signal of the base station, and includes the allocation control signal in downstream optical signals of one or more wavelengths including the receiving wavelength, The said station a upstream transmission unit that receives downstream optical signals of one or more wavelengths including the receiving wavelength from a upstream unit, and transmits a communication status signal or an allocation request signal of the base station to the upstream unit using upstream optical signals of one or more wavelengths including the transmitting wavelength; a selector for selecting a downstream optical signal of the receiving wavelength; a base station receiving unit that acquires the allocation control signal from a downstream optical signal of the selected receiving wavelength; a base station control unit that updates the receiving wavelength and the transmitting wavelength in response to the acquired allocation control signal; a base station transmitting unit that transmits upstream optical signals of one or more wavelengths including the updated transmission wavelength to the upstream stage using the upstream stage transmission unit, the base station control unit updates the receiving wavelength and the transmitting wavelength via a signal line independent from downstream signal lines for the main signal and the allocation control signal in the base station. Communication system.

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