JP2013090217A - Radio base station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio base station in which uplink signals from remote base stations are propagated to a centralized base station without losing signal strength.SOLUTION: A radio base station 100 comprises a centralized base station 101 and remote base stations 103a and 103b. A first coupler 107 has a first and a second input/output port composed of N lines of ports, in which a signal for any line of port of the first input/output port is branched from the second input/output port before being output, and a signal for any line of port of the second input/output port is branched from the first input/output port before being output. A second coupler 109 outputs a signal for a first port P5 from a second port P6, and outputs a signal for a third port P7 from the first port P5. The N remote base stations are respectively connected to the first input/output port, and a port P4 of the second input/output port is connected to the first port P5, in which a remaining port P3 of the second input/output port and the second port P6 are connected to an uplink signal processing unit 117.

Description

  The present invention relates to a radio base station.

  In recent years, a central base station (CS: Central Station or BDE: Base station Digital Equipment) and a plurality of remote base stations (BS: Base Station or RRE: Remote Radio Equipment) have been provided. Attention is focused on an optically protruding radio base station connected via a fiber transmission line. The centralized base station has a digital signal processing function, a maintenance monitoring function, and the like, and collectively performs radio resource control between cells of the remote base station. The remote base station has a function of transmitting / receiving radio waves via an antenna. That is, the remote base station corresponds to a radio unit (RE: Radio Equipment) of the independent base station, and the communication area can be expanded by installing only the radio unit.

  Conventionally, various techniques relating to an optical extension radio base station have been proposed (see, for example, Patent Document 1). Patent Document 1 describes an ROF (Radio Over Fiber) system using an SCM (Subcarrier Multiplexing) transmission system. The remote base station (slave station device) has a plurality of antennas and employs MIMO (Multiple Input Multiple Output). The remote base station multiplexes radio signals corresponding to a plurality of antennas and transmits them to a centralized base station (parent base station) using a single optical fiber. There are a plurality of remote base stations, and each is connected to the centralized base station in a star shape by an optical fiber.

JP 2010-87921 A

  However, in the technique described in Patent Document 1, each remote base station is connected to the centralized base station by two optical fibers for uplink and downlink. Therefore, as the number of remote base stations increases, the number of required optical fibers also increases, and it takes time and money to install the optical fibers.

  In order to use one optical fiber for both the uplink and the downlink, for example, it is assumed that a branch coupler such as a 3 dB coupler is provided in the optical fiber transmission line as shown in FIG. The port P41 of the 3 dB coupler 407 is in the CS downlink signal processing unit 419 of the centralized base station (CS) 401, the port P42 is in the CS upstream signal unit 417 of the centralized base station 401, and the port P43 is the BS of the remote base station (BS) 403. The port P44 is connected to the downlink signal processing unit 411 and the BS uplink signal processing unit 413 of the remote base station 403, respectively.

  In uplink signal transmission from the mobile station 410 to the centralized base station 401, the BS uplink signal processing unit 413 inputs a signal (uplink signal) received from the mobile station 410 to the port P44. Then, the upstream signal is divided into two by the 3 dB coupler 407 and output from the port P41 and the port P42. That is, the CS uplink signal processing unit 417 processes an uplink signal whose signal intensity is halved. If the signal intensity is halved, the signal-to-noise ratio (SNR) is reduced, which may make it difficult for the CS upstream signal processing unit 417 to perform processing. In the signal transmission in the downlink direction from the centralized base station 401 to the mobile station 410, the downlink signal generated by the CS downlink signal processing unit 419 is divided into two by the 3 dB coupler 407 and output from the port P43 and the port P44. The That is, the BS downlink signal processing unit 411 processes the downlink signal whose signal strength is halved, like the CS uplink signal processing unit 417. BS downlink signal processing section 411 then transmits a downlink signal whose signal strength is halved to mobile station 410.

  Here, use of CoMP (Coordinated Multi-Point transmission / reception) technology is assumed to prevent a decrease in signal strength in the downlink direction. CoMP means that a plurality of cells (remote base stations) perform transmission / reception in cooperation with a certain mobile station, and the desired signal power can be increased.

  As shown in FIG. 12, it is assumed that the two remote base stations 403a and 403b communicate with the mobile station in cooperation. Similarly to FIG. 11, the port P41 and the port P42 of the 3 dB coupler 407 are connected to the CS downlink signal processing unit 419 and the CS uplink signal processing unit 417, respectively. Further, the port P43 and the port P44 of the 3 dB coupler 407 are connected to the ports P45a and P45b of the WDM (Wavelength Division Multiplexing) couplers 415a and 415b of the remote base stations 403a and 403b, respectively. The port P46a and the port P47a of the WDM coupler 415a are connected to the BS downlink signal processing unit 411a and the BS uplink signal processing unit 413a, respectively. Further, the port P46b and the port P47b of the WDM coupler 415b are connected to the BS downlink signal processing unit 411b and the BS uplink signal processing unit 413b, respectively. The WDM coupler demultiplexes a signal for each wavelength, and does not divide a signal having a single wavelength. Therefore, the signal intensity does not decrease with demultiplexing.

  In the downlink direction, the downlink signal from the CS downlink signal processing unit 419 is divided into two by the 3 dB coupler 407 and transmitted to the BS downlink signal processing units 411a and 411b via the WDM couplers 415a and 415b. Then, BS downlink signal processing sections 411a and 411b transmit downlink signals whose signal strengths are halved to mobile station 410, respectively. That is, the mobile station 410 receives a composite signal of signals from the two remote base stations 403a and 403b. Since the mobile station 410 can process the combined signal from the two remote base stations 403a and 403b, the decrease in the signal strength of the downlink signal due to the 3 dB coupler is eliminated.

  On the other hand, in the uplink direction, the signal from the mobile station 410 is received by the BS uplink signal processing units 413a and 413b. The signals received by the BS uplink signal processing sections 413a and 413b are divided by the 3 dB coupler 407 and transmitted to the CS uplink signal processing section 417. That is, only the half of the combined signal is transmitted to the CS upstream signal processing unit 417, not the combined signal of the signals received by the BS upstream signal processing units 413a and 413b.

  Therefore, an object of the present invention made in view of the above problems is to provide a radio base station in which the signal is transmitted to the central base station without reducing the strength of the uplink signal from the remote base station. There is.

In order to solve the above-described problems, the radio base station according to the first aspect is
N centralized base stations having a downlink signal processing unit and an uplink signal processing unit are connected via an optical fiber transmission line provided with a first coupler and a second coupler, and transmit and receive radio signals with a mobile station. A wireless base station including a remote base station (N is a natural number of 2 or more),
The first coupler has a first input / output port and a second input / output port composed of N ports, and a signal to any one of the first input / output ports is sent to the second input / output port. Branch from the output port and output, branch the signal to any of the second input / output ports from the first input / output port, and output
The second coupler has a first port, a second port, and a third port, outputs a signal to the first port from the second port, and outputs a signal to the third port from the first port;
N remote base stations are respectively connected to the first input / output ports;
One of the second input / output ports is connected to the first port;
The remaining ports of the second input / output port and the second port are radio base stations connected to the uplink signal processing unit.

  The first coupler is preferably a 3 dB coupler in which N is 2.

  The upstream signal processing unit includes N electro-optical conversion units that convert the signals from the remaining ports of the second input / output port and the second port into electrical signals, and the electro-optical conversion unit. It is desirable to include one amplification unit that synthesizes and amplifies N electrical signals.

  The radio signal is preferably a signal in an OFDM (Orthogonal Frequency-Division Multiplexing) communication system or a CDMA (Code Division Multiple Access) communication system.

  The third port is preferably connected to the downlink signal processing unit.

  The second coupler is preferably a wavelength division multiplexing coupler.

  The second coupler is preferably a three-terminal circulator.

In order to solve the above-mentioned problems, the radio base station according to the second aspect is
A centralized base station having a downlink signal processing unit and an uplink signal processing unit is connected via an optical fiber transmission line provided with a first coupler and N second couplers, and transmits and receives radio signals to and from a mobile station. A wireless base station comprising N remote base stations (N is a natural number of 2 or more),
The first coupler has an output port composed of N ports and an input port composed of one port, and a signal to the input port is branched from the output port and output.
The second coupler has a first port, a second port, and a third port, outputs a signal to the first port from the second port, and outputs a signal to the third port from the first port;
N remote base stations are respectively connected to the first ports of the N second couplers,
Second ports of the N second couplers are connected to the upstream signal processing unit, respectively.
A third port of each of the N second couplers is connected to the output port;
The input port is a radio base station connected to the downlink signal processing unit.

  According to the radio base station of the present invention configured as described above, signals from a plurality of remote base stations are input to the first coupler, branched and output. One branched signal is input to the uplink signal processing unit of the centralized base station via the second coupler without being branched. Further, the remaining branched signal is directly input to the uplink signal processing unit of the centralized base station. Therefore, all signals from a plurality of remote base stations are transmitted to the uplink signal processing unit. That is, the strength of signals from a plurality of remote base stations does not decrease. Therefore, the degradation of the signal-to-noise ratio of the signal from the remote base station is suppressed, and stable communication can be realized in the communication system.

FIG. 1 is a schematic configuration diagram of a communication system including an optical extension radio base station according to the first embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic configuration of the optical extension radio base station according to the first embodiment of the present invention. FIG. 3 is a functional block diagram showing a schematic configuration of the BS downlink signal processing unit according to the first embodiment of the present invention. FIG. 4 is a functional block diagram showing a schematic configuration of the BS uplink signal processing unit according to the first embodiment of the present invention. FIG. 5 is a functional block diagram showing a schematic configuration of the CS uplink signal processing unit according to the first embodiment of the present invention. FIG. 6 is a functional block diagram showing a schematic configuration of the CS downlink signal processing unit according to the first embodiment of the present invention. FIG. 7 is a functional block diagram showing a schematic configuration of the BS uplink signal processing unit according to the first embodiment of the present invention. FIG. 8 is a functional block diagram showing a schematic configuration of the BS downlink signal processing unit according to the first embodiment of the present invention. FIG. 9 is a schematic configuration diagram of a communication system including an optical extension radio base station according to the second embodiment of the present invention. FIG. 10 is a functional block diagram showing a schematic configuration of an optical extension radio base station according to the second embodiment of the present invention. FIG. 11 is a functional block diagram illustrating an example of a schematic configuration of the light extension radio base station. FIG. 12 is a functional block diagram illustrating an example of a schematic configuration of the light extension radio base station.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a communication system including an optical extension radio base station according to the first embodiment of the present invention. The communication system 10 includes a light projecting radio base station (radio base station) 100 and a mobile station 110. The communication system 10 is a system that employs, for example, an OFDM (Orthogonal Frequency-Division Multiplexing) communication method or a CDMA (Code Division Multiple Access) communication method. The optical extension radio base station 100 includes a centralized base station 101 and N remote base stations 103 (103a and 103b) connected to the centralized base station 101 via an optical fiber transmission path 105. N is a natural number of 2 or more. In the present embodiment, it is assumed that N is 2. The mobile station 110 performs wireless communication with the light protruding radio base station 100 and is a wireless communication terminal such as a mobile phone.

  The centralized base station 101 has a digital signal processing function, a maintenance monitoring function, and the like, and performs radio resource control between cells of the remote base station 103 at once. The remote base station 103 has a function of transmitting / receiving an RF (Radio Frequency) signal (radio signal) to / from the mobile station 110, a signal modulation / demodulation function, and the like. When the OFDM communication system or CDMA communication system is employed in the communication system 10, the RF signal is a signal of the OFDM communication system or CDMA communication system. In FIG. 1, an area 104a indicates a cell (communication area) of the base station 103a. An area 104b shows a cell of the base station 103b. When the mobile station 110 is located in an area where the two areas overlap as shown in FIG. 1, the mobile station 110 can communicate with both the remote base stations 103a and 103b. Therefore, the light extension radio base station 100 can communicate with the mobile station 110 by CoMP.

  The optical fiber transmission line 105 is provided with a first coupler 107 and a second coupler 109 that couple paths of a plurality of optical fibers.

  The first coupler 107 has a first input / output port composed of N ports and a second input / output port composed of N ports. In this embodiment, N is 2, and the first input / output port is composed of ports P1 and P2. The second input / output port includes ports P3 and P4. The first coupler 107 divides and outputs a signal to any one of the first input / output ports from all the ports of the second input / output port, and also outputs to any one of the second input / output ports. The signal is branched from the first input / output port and output. The first coupler 107 is, for example, an optical branching device. The optical branching device is, for example, a branching coupler generated by fusion drawing of an optical fiber.

  The second coupler 109 has a first port P5 (hereinafter referred to as port P5), a second port P6 (hereinafter referred to as port P6) and a third port P7 (hereinafter referred to as port P7). A signal to P5 is output from port P6, and a signal to port P7 is output from port P5. The second coupler 109 is, for example, a three-terminal circulator or an optical multiplexer / demultiplexer that can determine the light path for each wavelength. The optical multiplexer / demultiplexer is, for example, a WDM coupler generated by fusion drawing.

  FIG. 2 is a functional block diagram showing a schematic configuration of the optical extension radio base station according to the first embodiment of the present invention.

  The remote base station 103 includes a BS downlink signal processing unit 111, a BS uplink signal processing unit 113, and a BS coupler 115. The functional blocks related to the remote base station 103 shown in FIG. 2 are common to the remote base stations 103a and 103b. The reference numeral of the functional block related to the remote base station 103a is a, and the functional block related to the remote base station 103b. In the following description, b is attached to the reference numeral. The downlink signal is a signal transmitted from the centralized base station 101 to the mobile station 110 via the remote base station 103, and the upstream signal is the centralized base station 101 from the mobile station 110 via the remote base station 103. It is a signal transmitted to.

  The BS downlink signal processing unit 111 receives a downlink signal from the centralized base station 101 via the optical fiber transmission line 105 and transmits it to the mobile station 110, and can be configured as shown in FIG. 3, for example. . The photoelectric conversion unit 121 converts an optical signal from the central base station 101 into an electrical signal, and is, for example, a photodiode. The radio unit 123 generates an RF signal by up-converting the electrical signal, and transmits the RF signal to the mobile station 110 via the antenna. The up-conversion of the electric signal is realized by, for example, a local oscillator of the radio unit 123 and a mixer (mixer).

  The BS uplink signal processing unit 113 receives an uplink signal from the mobile station 110 and transmits it to the centralized base station 101 via the optical fiber transmission path 105.

  The BS uplink signal processing unit 113 can be configured as shown in FIG. 4, for example. The radio unit 125 receives an RF signal from the mobile station 110 via an antenna and down-converts it to generate an IF (Intermediate Frequency) signal. The down conversion of the RF signal is realized by, for example, a local oscillator of the radio unit 125 and a mixer. The electro-optical conversion unit 127 converts the IF signal into an optical signal, and is, for example, a laser diode. Note that the wireless unit 125 does not need to be completely independent of the wireless unit 123, and may share, for example, an antenna or a filter that is a component. Hereinafter, in the present embodiment, it is assumed that the signal output from the BS uplink signal processing unit 113 is an optical signal having a wavelength of λu.

  The BS coupler 115 receives the uplink signal from the BS uplink signal processing unit 113 to the centralized base station 101 (first coupler 107) and the signal from the centralized base station 101 (first coupler 107) to the BS downstream signal processing unit. For example, a WDM coupler or a three-terminal circulator. BS couplers 115a and 115b are connected to port P1 and port P2 of first coupler 107, respectively.

  The optical signal from the BS upstream signal processing unit 113a is input to the port P1 of the first coupler 107, branches, and is output from the ports P3 and P4. When the first coupler 107 is a 3 dB coupler, the signal strength of the output signals from the ports P3 and P4 is half of the signal strength of the input signal to the port P1. Similarly, the optical signal from the BS upstream signal processing unit 113b is input to the port P2 of the first coupler 107, branched from the ports P3 and P4, and output.

  The port P4 is connected to the port P5 of the second coupler 109. The remaining ports of the second input / output port, that is, the port P3 are connected to a CS uplink signal processing unit 117 described later of the centralized base station 101. Therefore, the output signal from the port P3 is input to the CS uplink signal processing unit 117, and the output signal from the port P4 is input to the port P5 of the second coupler 109.

  Port P 6 of second coupler 109 is coupled to CS uplink signal processing section 117 of centralized base station 101. Then, the port P7 can be connected to a CS downlink signal processing unit 119 described later of the centralized base station 101. An input signal to the port P5 of the second coupler 109 is output from the port P6 without branching and input to the CS uplink signal processing unit 117. An input signal to the port P7 of the second coupler 109 is output from the port P5 without branching.

  Next, functional blocks of the remote base station 103 will be described. The remote base station 103 includes a CS uplink signal processing unit 117 (uplink signal processing unit in the claims) and a CS downlink signal processing unit 119 (downlink signal processing unit in the claims).

  The CS uplink signal processing unit 117 receives an uplink signal from the remote base station 103 and demodulates it, and can be configured as shown in FIG. 5, for example. The photoelectric conversion unit 131 (131-1 and 131-2) converts an optical signal from the remote base station 103 into an electrical signal (output current), and is, for example, a photodiode. The amplifying unit 133 combines output currents from the plurality of photoelectric conversion units 131-1 and 131-2. The amplifying unit 133 converts the synthesized output current into a voltage and amplifies it. The amplification unit 133 is, for example, a current / voltage converter and a feedback amplification circuit. The two photodiodes are connected in parallel between the two input terminals of the feedback amplifier circuit. By amplifying the signals from both the port P3 of the first coupler 107 and the port P6 of the second coupler 109 by a single amplifying unit 133, it is not necessary to provide a plurality of amplifying units 133. Reduction is possible. Further, the circuit scale of the CS upstream signal processing unit 117 can be reduced with the reduction in the number of components. The baseband unit 135 demodulates the amplified voltage signal by AD conversion and fast Fourier transform (FFT).

  The CS downlink signal processing unit 119 modulates a downlink signal to be sent to the mobile station 110 and transmits it to the remote base station 103. The CS downlink signal processing unit 119 can be configured as shown in FIG. 6, for example. The baseband unit 137 digitally modulates a baseband signal and performs DA conversion. The electro-optical converter 139 converts the DA-converted signal into an optical signal, and is a laser diode, for example. Note that the baseband unit 137 does not need to be completely independent of the baseband unit 135, and may share a CPU (central processing unit) that performs software processing such as fast Fourier transform and digital modulation. Hereinafter, in the present embodiment, it is assumed that the signal output from the CS downlink signal processing unit 119 is an optical signal having a wavelength of λd.

  The signal from the CS downlink signal processing unit 119 is input to the port P7 of the second coupler 109, and is output from the port P5 without branching. When the second coupler 109 is a WDM coupler, the port from which the signal is output is determined by the wavelength of the input signal. Therefore, in order to prevent the signal from the CS downlink signal processing unit 119 from being output to the port P6, the wavelength λd of the signal from the CS downlink signal processing unit 119 is the wavelength of the signal output from the BS uplink signal processing unit 113. Must be different from λu. When the second coupler 109 is a three-terminal circulator, the path between the input port and the output port is determined in advance by the structure of the three-terminal circulator, so that the output destination does not depend on the wavelength. Therefore, λd can be set to the same value as λu.

  The downlink signal output from the port P5 is input to the port P4 of the first coupler 107, branched from the ports P1 and P2, and output. The downlink signals output from the ports P1 and P2 are input to the BS downlink signal processing units 111a and 111b via the BS couplers 115a and 115b and transmitted to the mobile station 110.

  In the above description, the remote base station 103 communicates with the mobile station 110 using one antenna. However, the above-described connection mode between the central base station 101 and the remote base station 103 includes a plurality of remote base stations 103. The same applies to the case with an antenna. When the remote base station 103 has a plurality of antennas, the light-extending radio base station 100 can perform MIMO (Multiple Input Multiple Output) communication with the mobile station 110 having a plurality of antennas. Hereinafter, a case where the remote base station 103 has two antennas will be described.

  First, signal transmission in the uplink direction in MIMO communication will be described. The BS uplink signal processing unit 113 capable of MIMO communication includes radio units 125-1 and 125-2, an addition unit 126, and an electro-optical conversion unit 127 as shown in FIG. In addition to the functions of the wireless unit 125 described above, the wireless units 125-1 and 125-2 generate IF signals of different frequency bands for each antenna when down-converting the RF signal from the mobile station 110. Generation of IF signals in different frequency bands is realized by changing the frequency of the signal of the local oscillator used for down-conversion. IF signals in different frequency bands mean that the frequency bands of the signals do not overlap each other.

  Adder 126 multiplexes the IF signals generated by radio units 125-1 and 125-2 in the frequency domain. Since the IF signals of the radio units 125-1 and 125-2 do not overlap each other in the frequency domain, even if a plurality of IF signals are multiplexed, they can be separated and extracted by FFT. The multiplexed signal is converted into an optical signal of one wavelength by the electro-optical converter 127. The optical signal from the BS upstream signal processing unit 113 is input to the CS upstream signal processing unit 117 via the first coupler 107 and the second coupler 109.

  The functional block diagram of the CS uplink signal processing unit 117 capable of MIMO communication is the same as that in FIG. 5, and is the photoelectric conversion units 131-1 and 131-2, the amplification unit 133, and the baseband unit 135. Since the functions of the photoelectric conversion unit 131 and the amplification unit 133 are the same as the communication using one antenna, the description thereof is omitted.

  The baseband unit 135 first AD converts the electrical signal amplified by the amplification unit 133. Subsequently, the baseband unit 135 performs fast Fourier transform on the AD-converted signal, separates the frequency corresponding to each antenna of the remote base stations 103a and 103b, and demodulates. Since an IF signal of a different frequency band is generated for each antenna of the remote base stations 103a and 103b, the baseband unit 135 can be separated into signals for each antenna by fast Fourier transform. Therefore, the optical extension radio base station 100 can perform MIMO communication with the mobile station 110. The frequency separation by the fast Fourier transform is more accurate than the frequency separation by an analog filter or the like. Therefore, compared with frequency separation using an analog filter or the like, it is possible to narrow the frequency interval between a plurality of IF signals generated for each antenna. Therefore, the frequency resource in the IF signal can be effectively used. The present invention is not limited to performing frequency separation of IF signals by fast Fourier transform. For example, frequency separation of IF signals can be performed by an analog filter such as a bandpass filter. In this case, AD conversion by the baseband unit 135 is not necessary.

  Next, downlink signal transmission in MIMO communication will be described. A functional block diagram of the CS downlink signal processing unit 119 capable of MIMO communication is the same as that in FIG. 6, and is a baseband unit 137 and an electro-optical conversion unit 139. Since the function of the electro-optical conversion unit 139 is the same as that of communication using one antenna, the description thereof is omitted.

  The baseband unit 137 generates transmission signals to the plurality of remote base stations 103a and 103b so that the frequency bands do not overlap each other for each antenna of each remote base station. Then, the baseband unit 137 multiplexes the generated transmission signal and performs DA conversion. The DA-converted signal is converted into an optical signal by the electro-optical conversion unit 139 and input to the BS downlink signal processing unit 111 via the second coupler 109 and the first coupler 107.

  As shown in FIG. 8, the BS downlink signal processing unit 111 capable of MIMO communication includes a photoelectric conversion unit 121, a signal processing unit 122, and radio units 123-1 and 123-2. Since the function of the photoelectric conversion unit 121 is the same as that of communication using one antenna, the description thereof is omitted.

  The signal processing unit 122 AD converts the electrical signal from the photoelectric conversion unit 121. Subsequently, the signal processing unit 122 performs fast Fourier transform on the AD-converted signal, and performs frequency separation corresponding to each antenna. Since the transmission signal frequency bands do not overlap for each antenna of the remote base station 103, the signal processing unit 122 can extract a signal corresponding to each antenna of the remote base station 103.

  Subsequently, the signal processing unit 122 performs IFFT (Inverse Fast Fourier Transform) on each of the signals extracted for each antenna, and performs DA conversion.

  The present invention is not limited to performing frequency separation of signals by fast Fourier transform. For example, frequency separation can be performed by an analog filter such as a bandpass filter. In this case, AD conversion, inverse fast Fourier transform, and DA conversion by the signal processing unit 122 are unnecessary.

  The radio units 123-1 and 123-2 up-convert signals distributed to the radio units by the signal processing unit 122. Then, the radio units 123-1 and 123-2 amplify the upconverted signal and transmit the amplified signal to the mobile station 110 via each antenna.

  As described above, in the present embodiment, the BS uplink signal processing units 113a and 113b that receive the uplink signal are connected to the port P1 or P2 of the first coupler 107 that branches the signal. The port P3 of the first coupler 107 is connected to the CS upstream signal processing unit 117, and the port P4 of the first coupler 107 is connected to the CS upstream signal processing unit 117 via the ports P5 and P6 of the second coupler 109. Has been. Therefore, all the upstream signals branched by the first coupler 107 are collected in the CS upstream signal processing unit 117. That is, by combining the signals collected by the CS uplink signal processing unit 117, the uplink signals are transmitted from the remote base stations 103a and 103b to the centralized base station 101 without reducing the signal strength. Therefore, deterioration of the S / N ratio of the uplink signal is suppressed, and stable communication can be realized in the communication system 10.

  In this embodiment, the CS uplink signal processing unit 117 can include two photoelectric conversion units 131-1 and 131-2 and one amplification unit 133. That is, the electric signals from the two photoelectric conversion units 131-1 and 131-2 are not separately amplified, but the single amplification unit 133 synthesizes the electric signals and amplifies them in a lump. Therefore, it is not necessary to provide a plurality of amplifiers 133, and the number of parts can be reduced. Further, the circuit scale of the CS upstream signal processing unit 117 can be reduced with the reduction in the number of components.

  In this embodiment, the radio signal transmitted and received between the mobile station 110 and the remote base station 103 can be a signal in the OFDM communication system or the CDMA communication system. The remote base stations 103a and 103b may receive not only the desired wave from the mobile station 110 but also the delayed wave of the desired wave. The uplink signal including the delayed wave is synthesized by the CS uplink signal processing unit 117 of the centralized base station 101. The more the delayed wave, the worse the demodulation process in the CS uplink signal processing unit 117. However, when the OFDM communication system is adopted in the communication system 10, a guard interval is added to the radio signal. Even if a delayed wave is synthesized by the CS uplink signal processing unit 117 by the guard interval, the accuracy of demodulation can be improved. When the CDMA communication system is adopted in the communication system 10, the CS uplink signal processing unit 117 combines a plurality of delayed waves by despreading processing using a spreading code by using the rake reception technique. Deterioration can be prevented.

  In the present embodiment, the port P7 of the second coupler 109 is connected to the CS downlink signal processing unit 119. Thereby, the downlink signal from the CS downlink signal processing unit 119 is output from the ports P1 and P2 via the ports P7 and P5 of the second coupler 109 and the port P4 of the first coupler 107. Then, the downlink signal is transmitted to BS downlink signal processing sections 111a and 111b of the remote base station 103a via BS couplers 115a and 115b. Therefore, by connecting the port P7 to the CS downlink signal processing unit 119, light between the port P5 and the port P4, between the port P1 and the BS coupler 115a, and between the port P2 and the BS coupler 115b. The fiber transmission line 105 is shared by the upstream signal and the downstream signal. The shared use of the optical fiber transmission path 105 shortens the installation distance of the optical fiber, and can reduce labor and cost required for the installation of the optical fiber.

  In the present embodiment, the second coupler 109 can be a WDM coupler. Since the WDM coupler can be produced by fusion drawing of an optical fiber, no material other than the optical fiber is required. Therefore, the cost for providing the second coupler 109 can be reduced. Moreover, since the optical fiber itself forms the second coupler 109, the insertion loss can be reduced.

  In the present embodiment, the second coupler 109 can be a three-terminal circulator. In the 3-terminal circulator, the path between each port of the 3-terminal circulator is determined not by the wavelength input to the port but by the structure of the 3-terminal circulator. Therefore, it is not necessary to distinguish the downlink signal and the uplink signal by the wavelength, and the same wavelength can be used for the downlink signal and the uplink signal.

(Second Embodiment)
FIG. 9 is a schematic configuration diagram of a communication system including an optical extension radio base station according to the second embodiment of the present invention. The communication network 20 according to the second embodiment is the same as the communication network 10 according to the first embodiment except for the coupler provided in the optical fiber transmission line. Therefore, the description of the light-extending radio base station 200 (concentrated base station 201 and N remote base stations 203), the mobile station 210, and the cells 204 (204a and 204b) of the remote base stations 203 (203a and 203b) is as follows. Omitted. In this embodiment, N, which is a natural number of 2 or more, is 2.

  The optical fiber transmission line 205 is provided with a first coupler 207 and N second couplers 209 that couple paths of a plurality of optical fibers.

  The first coupler 207 has an output port composed of N ports and an input port composed of one port. In this embodiment, N is 2, and the output port is composed of a port P11 and a port P12. The input port is configured by port P13. The first coupler 207 branches and outputs the signal to the input port, that is, the port P13, from the output ports, that is, the ports P11 and P12. The first coupler 207 is a branch coupler, for example, and is generated by fusion drawing of an optical fiber.

  The second coupler 209 has a first port P14 (hereinafter referred to as port P14), a second port P15 (hereinafter referred to as port P15), and a third port P16 (hereinafter referred to as port P16). A signal to P14 is output from port P15, and a signal to port P16 is output from port P14. The second coupler 209 is, for example, a three-terminal circulator or a WDM coupler that can determine a light path for each wavelength. The WDM coupler is generated by, for example, fusion drawing. In this embodiment, since N is 2, two second couplers 209-1 and 209-2 are provided in the optical fiber transmission line 205. The function of the port related to the second coupler shown in FIG. 9 is common to the second couplers 209-1 and 209-2, and the reference numeral of the port related to the second coupler 209-1 is “−1”. Will be described with “−2” attached to the reference numerals of the ports related to the second coupler 209-2.

  FIG. 10 is a functional block diagram showing a schematic configuration of an optical extension radio base station according to the second embodiment of the present invention. The functional blocks of the centralized base station 201 and the remote base station 203 are the same as those of the centralized base station 101 and the remote base station 103 according to the first embodiment. Therefore, BS downlink signal processing unit 211 (BS downlink signal processing units 211a and 211b), BS uplink signal processing unit 213 (BS uplink signal processing units 213a and 213b), BS coupler 215 (BS couplers 215a and 215b), CS Description of the uplink signal processing unit 217 and the CS downlink signal processing unit 219 is omitted.

  In uplink signal transmission, first, uplink signals received by the BS uplink signal processing sections 213a and 213b of the remote base stations 203a and 203b are transmitted to the ports P14-1 and P14 of the second couplers 209-1 and 209-2. -2, respectively. Then, the uplink signal is output from the port P15-1 and the port P15-2, and is output to the CS uplink signal processing unit (uplink signal processing unit in claims) 217 of the centralized base station 201. Since the uplink signal does not pass through a coupler such as a branch coupler in which the signal strength decreases, the uplink signal is transmitted to the centralized base station 201 without the signal strength decreasing.

  In signal transmission in the downlink direction, a downlink signal from the CS downlink signal processing unit (downlink signal downlink signal processing unit in the claims) 219 of the centralized base station 201 is input to the port P13 of the first coupler 207. Then, the downlink signal is branched and output from the port P11 and the port P12, and transmitted to the remote base stations 203a and 203b.

  As described above, in this embodiment, the BS uplink signal processing units 213a and 213b that receive the uplink signal are connected to the ports P14-1 or P14-2 of the second couplers 209-1 and 209-2. The upstream signal is output from the ports P15-1 and P15-2 without being branched by the second couplers 209-1 and 209-2. Then, the uplink signals output from the second couplers 209-1 and 209-2 are transmitted to the CS uplink signal processing unit 217. Therefore, the uplink signals from the BS uplink signal processing units 213a and 213b are not branched, and are transmitted to the CS uplink signal processing unit 217 without decreasing the signal strength. Therefore, degradation of the S / N ratio of the uplink signal is suppressed, and stable communication can be realized in the communication system 20.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

  For example, functions included in each member, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined or divided into one. Is possible.

10, 20 Communication system 100, 200 Optical overhang base station 101, 201 Centralized base station 103a, 103b, 203a, 203b Remote base station 104a, 104b, 204a, 204b Area 105, 205 Optical fiber transmission path 107, 207 First coupling Unit 109, 209-1, 209-2 Second coupler 110, 210 Mobile station P1-P7, P11-P13, P14-1, P14-2, P15-1, P15-2, P16-1, P16-2 Port 111a, 111b, 211a, 211b BS downlink signal processor 113a, 113b, 213a, 213b BS uplink signal processor 115a, 115b, 215a, 215b BS coupler 117, 217 CS uplink signal processor 119, 219 CS downlink signal processing Part 121, 131-1, 131-2 photoelectric Air conversion unit 122 Signal processing unit 123, 123-1, 123-2, 125, 125-1, 125-2 Radio unit 126 Addition unit 127, 139 Electric light conversion unit 133 Amplification unit 135, 137 Baseband unit

Claims (8)

N centralized base stations having a downlink signal processing unit and an uplink signal processing unit are connected via an optical fiber transmission line provided with a first coupler and a second coupler, and transmit and receive radio signals with a mobile station. A wireless base station including a remote base station (N is a natural number of 2 or more),
The first coupler has a first input / output port and a second input / output port composed of N ports, and a signal to any one of the first input / output ports is sent to the second input / output port. Branch from the output port and output, branch the signal to any of the second input / output ports from the first input / output port, and output
The second coupler has a first port, a second port, and a third port, outputs a signal to the first port from the second port, and outputs a signal to the third port from the first port;
The N remote base stations are respectively connected to the first input / output ports;
One of the second input / output ports is connected to the first port;
The remaining ports of the second input / output port and the second port are radio base stations connected to the uplink signal processing unit.   The radio base station according to claim 1, wherein the first coupler is a 3 dB coupler in which N is two. In the radio base station according to claim 1 or 2,
The upstream signal processing unit includes N electro-optical conversion units that convert signals from the remaining ports of the second input / output port and the second port into electric signals, and N units from the electro-optical conversion unit. A radio base station comprising: an amplification unit that synthesizes and amplifies the electrical signals of In the radio base station according to any one of claims 1 to 3,
The radio base station, wherein the radio signal is a signal in an OFDM (Orthogonal Frequency-Division Multiplexing) communication system or a CDMA (Code Division Multiple Access) communication system.   5. The radio base station according to claim 1, wherein the third port is connected to the downlink signal processing unit. 6.   The radio base station according to claim 1, wherein the second coupler is a wavelength division multiplexing coupler.   The radio base station according to any one of claims 1 to 5, wherein the second coupler is a three-terminal circulator. A centralized base station having a downlink signal processing unit and an uplink signal processing unit is connected via an optical fiber transmission line provided with a first coupler and N second couplers, and transmits and receives radio signals to and from a mobile station. A wireless base station comprising N remote base stations (N is a natural number of 2 or more),
The first coupler has an output port composed of N ports and an input port composed of one port, and a signal to the input port is branched from the output port and output.
The second coupler has a first port, a second port, and a third port, outputs a signal to the first port from the second port, and outputs a signal to the third port from the first port;
The N remote base stations are respectively connected to first ports of the N second couplers;
Second ports of the N second couplers are connected to the upstream signal processing unit, respectively.
A third port of each of the N second couplers is connected to the output port;
The input port is a radio base station connected to the downlink signal processing unit.

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