JP2005086782A - Combined modulation method, method for demultiplexing optical signals subjected to combined modulation and combined modulation type radio base station - Google Patents

Combined modulation method, method for demultiplexing optical signals subjected to combined modulation and combined modulation type radio base station Download PDF

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JP2005086782A
JP2005086782A JP2003320144A JP2003320144A JP2005086782A JP 2005086782 A JP2005086782 A JP 2005086782A JP 2003320144 A JP2003320144 A JP 2003320144A JP 2003320144 A JP2003320144 A JP 2003320144A JP 2005086782 A JP2005086782 A JP 2005086782A
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Mitsufumi Miyashita
充史 宮下
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Central Research Institute of Electric Power Industry
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a combined modulation method by which a millimeter wave band signal and a low frequency band signal can be efficiently multiplexed and which is simpler than a conventional method and reduces costs, and to provide a method for demultiplexing optical signals subjected to combined modulation and combined modulation type radio base station. <P>SOLUTION: The method of for subjecting optical signals to combined modulation is composed of: a central control station 2 provided with radio modulation/demodulation parts 3, 4; a radio base station 1 provided with antenna parts 13, 14; and an optical fiber 6 for connecting both stations 1, 2. When a fiber radio communication system which multiplexes a plurality of radio signals of different frequencies is utilized to optically transmit the multiplexed signal, the intensity of input light to an optical modulator 5 is modulated by using one radio signal in advance, and the intensity of the input light whose intensity is modulated is further modulated by using another radio signal in the optical modulator 5, so that the plurality of signals are multiplexed and then optically transmitted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は複合変調方法、複合変調された光信号の分離方法および複合変調型無線基地局に関する。さらに詳述すると、本発明は光電波融合通信技術における複合変調方法とそれを利用した複合変調型無線基地局等、無線通信技術の改良に関する。   The present invention relates to a composite modulation method, a method of separating a composite modulated optical signal, and a composite modulation type radio base station. More specifically, the present invention relates to an improvement in radio communication technology such as a composite modulation method in an optical radio wave fusion communication technology and a composite modulation type radio base station using the same.

ミリ波（ＥＨＦ）帯つまり３０ＧＨｚ〜３００ＧＨｚ程度の周波数帯域の電波は、その広帯域性からすれば高速通信に適するものであるが、その反面、電波伝搬減衰が大きいという性質も併せ持っている。このため、広域エリアをカバーするためには多数の無線基地局が必要となることからより簡素で低コストな無線基地局構成が望まれている。さらに、ミリ波帯信号と低周波信号とを効率的に多重し、より柔軟で、付加価値の高いアクセス網を構築することが望まれている。   A millimeter wave (EHF) band, that is, a radio wave having a frequency band of about 30 GHz to 300 GHz is suitable for high-speed communication because of its wide band characteristics, but on the other hand, it also has a characteristic that radio wave propagation attenuation is large. For this reason, since a large number of radio base stations are required to cover a wide area, a simpler and lower cost radio base station configuration is desired. Furthermore, it is desired to efficiently multiplex millimeter-wave band signals and low-frequency signals to construct a more flexible and high added value access network.

このような無線基地局の簡素化が可能な技術の一つとしてファイバ無線技術を挙げることができる。ファイバ無線技術を利用したファイバ無線通信システムによれば、ミリ波帯信号と低周波帯信号（ここでいう低周波帯信号とは、マイクロ波（３ＧＨｚ〜３０ＧＨｚ）をはじめ、ミリ波帯信号よりも低周波帯域の信号を指す）とを多重する無線基地局を構成することが期待される。   One of the technologies that can simplify the radio base station is a fiber radio technology. According to the fiber radio communication system using the fiber radio technology, the millimeter wave band signal and the low frequency band signal (here, the low frequency band signal includes a microwave (3 GHz to 30 GHz) and more than a millimeter wave band signal. It is expected to construct a radio base station that multiplexes signals in the low frequency band.

ここでファイバ無線通信システムについて簡単に説明しておくと、ファイバ無線通信システムにおいては、低周波信号とミリ波帯信号とを多重する技術としては、図７に示す副搬送波多重方式（非特許文献１参照）、及び図８に示す波長分割多重方式（非特許文献２参照）がある。副搬送波多重方式（ＳＣＭ）は、低周波信号とミリ波帯信号とを電気信号の段階で多重するものである。すなわち、電気信号の段階で低周波信号とミリ波帯信号を広帯域カプラ（ミリ波帯合波器）１０１を用いて多重し、外部光変調器１０２により光変調を行い、受信側においてはミリ波帯フォトダイオード１０３を用いて検波し、広帯域カプラ（ミリ波帯分波器）１０４により分波した後、ミリ波帯帯域透過フィルタ１０５によりミリ波帯信号を、低域透過フィルタ（または帯域透過フィルタ）１０６により低周波信号をそれぞれ分離する手法である（図７参照）。   Here, the fiber radio communication system will be briefly described. In the fiber radio communication system, as a technique for multiplexing a low frequency signal and a millimeter wave band signal, a subcarrier multiplexing system shown in FIG. 1) and the wavelength division multiplexing system shown in FIG. 8 (see Non-Patent Document 2). The subcarrier multiplexing system (SCM) multiplexes a low frequency signal and a millimeter wave band signal at the stage of an electric signal. That is, a low-frequency signal and a millimeter-wave band signal are multiplexed using a wide-band coupler (millimeter-wave band multiplexer) 101 at an electrical signal stage, optical modulation is performed by an external optical modulator 102, and a millimeter wave is received on the receiving side. After detection using a band-band photodiode 103 and demultiplexing by a wide-band coupler (millimeter-wave band splitter) 104, a millimeter-wave band signal is converted by a millimeter-wave band band-pass filter 105 into a low-pass filter (or band-pass filter). ) 106 to separate the low-frequency signals from each other (see FIG. 7).

また、波長分割多重方式（ＷＤＭ）は、低周波信号とミリ波帯信号にそれぞれ異なる光波長を割当て、ＷＤＭカプラ２０１，２０２により光信号を多重、分離した後、ミリ波帯のフォトダイオード２０３及び低周波帯のフォトダイオード２０４によりミリ波帯信号、低周波信号をそれぞれ検波することで無線信号を分離して受信する手法である（図８参照。図８中の符号２０７はミリ波ＩＦ（Intermediate Frequency：中間周波数）帯信号復調器、２０８は低周波帯信号復調器を指している）。   In the wavelength division multiplexing (WDM), low-frequency signals and millimeter-wave signals are assigned different optical wavelengths, and the optical signals are multiplexed and separated by WDM couplers 201 and 202. This is a technique of separating and receiving a radio signal by detecting a millimeter-wave band signal and a low-frequency signal by a low-frequency photodiode 204 (see FIG. 8. Reference numeral 207 in FIG. 8 denotes a millimeter-wave IF (Intermediate). Frequency: intermediate frequency) band signal demodulator, 208 indicates a low frequency band signal demodulator).

上坂他、「１０Ｇｂ／ｓベースバンド信号と６０ＧＨｚ帯ミリ波信号の単一波長同時光変調ファイバ伝送」、電子情報通信学会通信ソサイエティ大会、B-5-147、2000年9月Uesaka et al., “Single-wavelength simultaneous optical modulation fiber transmission of 10 Gb / s baseband signal and 60 GHz band millimeter wave signal”, IEICE Communication Society, B-5-147, September 2000 久利他、「６０ＧＨｚ帯光トランシーバを用いた光ファイバ無線双方向ＷＤＭ伝送」、電子情報通信学会通信ソサイエティ大会、SB-4-1、1999年9月Kuri et al., “Fiber-optic two-way WDM transmission using 60 GHz optical transceiver”, IEICE Communication Society, SB-4-1, September 1999

しかしながら、副搬送波多重方式（ＳＣＭ）においては、ファイバ無線通信システムを１つの外部光変調器１０２とミリ波帯フォトダイオード１０３で構成するため光系統は簡素である反面、広帯域カプラ（ミリ波帯合波器）１０１、広帯域カプラ（ミリ波帯分波器）１０４、ミリ波帯帯域通過フィルタ１０５など多数のミリ波帯素子が必要であるため電気回路が複雑になるという問題がある。例えば図７においては、ＬＤ（レーザダイオード）、ＥＡＭ（電界吸収型光変調器）、ＰＤ（フォトダイオード）がそれぞれ１つで構成可能であるため光伝送系は非常に簡素である反面、ミリ波帯においても動作する広帯域カプラ１０１，１０４が送受信側において必要であり、さらに受信側においてはミリ波帯帯域通過フィルタ１０５も必要となることから多種の電気信号処理用デバイスを組み合わせる必要があり複雑である。   However, in the subcarrier multiplexing system (SCM), since the fiber radio communication system is composed of one external optical modulator 102 and the millimeter wave band photodiode 103, the optical system is simple, but on the other hand, a broadband coupler (millimeter wave band coupling) is used. A large number of millimeter wave band elements such as a wave filter 101, a wide band coupler (millimeter wave band demultiplexer) 104, a millimeter wave band band pass filter 105, and the like. For example, in FIG. 7, an LD (laser diode), an EAM (electro-absorption optical modulator), and a PD (photodiode) can each be configured, so that the optical transmission system is very simple, but the millimeter wave Wideband couplers 101 and 104 that operate also in the band are required on the transmission / reception side, and the millimeter-wave bandpass filter 105 is also required on the reception side. Therefore, it is necessary to combine various electric signal processing devices, which is complicated. is there.

また、波長分割多重方式（ＷＤＭ）においては、より少ないミリ波帯素子によってファイバ無線通信システムを構成可能である反面、複数個の光変調器、光源、光検波器が必要であるため光系統が複雑になるという問題がある。例えば図８においては、各無線信号にはそれぞれ異なる光変調器２０５，２０６、光検波器（フォトダイオード）２０３，２０４が割り当てられるため、無線信号の周波数帯に依存することなく信号品質を保ちながらの光伝送が可能ではあるが、ＷＤＭカプラの透過波長特性に応じた光源が必要となるなど光系統が複雑になりやすく、またその分だけ高コストとなりやすい。加えて、光信号を分波するＷＤＭカプラ２０２はこの光信号を予め決まった光波長毎に分離するものであるため、送信側においてＷＤＭカプラ２０２の動作波長にあった光波長を選択しなければならないという問題もある。   In the wavelength division multiplexing (WDM), a fiber radio communication system can be configured with fewer millimeter-wave band elements, but a plurality of optical modulators, light sources, and optical detectors are required. There is a problem of complexity. For example, in FIG. 8, since different optical modulators 205 and 206 and optical detectors (photodiodes) 203 and 204 are assigned to the respective radio signals, the signal quality is maintained without depending on the frequency band of the radio signal. However, the optical system is likely to be complicated, such as the need for a light source corresponding to the transmission wavelength characteristics of the WDM coupler, and the cost is likely to be increased accordingly. In addition, since the WDM coupler 202 that demultiplexes the optical signal separates the optical signal for each predetermined optical wavelength, an optical wavelength that matches the operating wavelength of the WDM coupler 202 must be selected on the transmission side. There is also the problem of not becoming.

上述したような理由から、ミリ波帯信号と低周波帯信号とを多重する無線基地局を構成する場合には構成が複雑化してしまうという問題がある。   For the reasons described above, there is a problem that the configuration becomes complicated when configuring a radio base station that multiplexes a millimeter-wave band signal and a low-frequency band signal.

そこで本発明は、ミリ波帯信号と低周波数帯信号とを効率的に多重することができ、尚かつ従来よりも簡素で低コストな複合変調方法、複合変調された光信号の分離方法および複合変調型無線基地局を提供することを目的とする。   Therefore, the present invention can efficiently multiplex a millimeter-wave band signal and a low-frequency band signal, and is simpler and lower cost than the conventional complex modulation method, a method of separating a complex-modulated optical signal, and a complex An object is to provide a modulation type radio base station.

かかる目的を達成するため、本発明者は種々の検討を行った。ミリ波帯の無線信号を光伝送する場合にはＥＡＭなどの外部光変調器、つまり、無線信号の電圧に応じて光信号の強度を変えて出力する装置を必要とする。このような従来の技術を踏まえ、本発明者は、外部光変調器への入力光を低周波帯（例えばマイクロ波帯）の信号で強度変調しておくという技術について着想し、１つの光源を用いてミリ波帯と低周波帯の２つの帯域信号を同時に伝送可能とするシステムについて検討した結果、新しい技術を知見するに至った。   In order to achieve this object, the present inventor has conducted various studies. When optically transmitting a millimeter-wave band radio signal, an external optical modulator such as EAM, that is, a device that changes the intensity of the optical signal according to the voltage of the radio signal and outputs it is required. Based on such conventional techniques, the present inventor has conceived the technique of intensity-modulating input light to an external optical modulator with a signal in a low frequency band (for example, a microwave band), and uses one light source. As a result of investigating a system that can transmit two band signals of millimeter wave band and low frequency band at the same time, it came to know new technology.

すなわち、ミリ波帯ファイバ無線通信システムにおける信号に対し更に低周波信号を多重することによって付加価値の高い無線システムを構築する場合、光信号を低周波信号で予め強度変調しておいてから外部光変調器へ入力し更にそこで強度変調するという複合変調技術が効果的であることを知見するに至った。また、受信側においては図１に示すようにミリ波帯の受光素子（例えばフォトダイオード）の出力を周波数変換することで、低周波電気信号分波器によりミリ波変調信号と低周波変調信号を分離する電気信号分離方式が有効であることを知見するに至った。さらに、受信側において、図２に示すように光分波器により信号を分岐し、ミリ波帯受光素子と低周波数帯受光素子により検波することで信号を分離する光信号分離方式が有効であることも知見するに至った。   In other words, when constructing a radio system with high added value by further multiplexing a low-frequency signal to a signal in a millimeter-wave band wireless communication system, an optical signal is modulated in advance with the low-frequency signal and then external light is transmitted. It came to know that the composite modulation technique of inputting to the modulator and further modulating the intensity there is effective. On the receiving side, as shown in FIG. 1, the output of a millimeter-wave band light receiving element (for example, a photodiode) is frequency-converted so that a low-frequency electric signal demultiplexer converts a millimeter-wave modulation signal and a low-frequency modulation signal. It came to know that the electric signal separation system which isolate | separates is effective. Further, on the receiving side, as shown in FIG. 2, an optical signal separation method is effective in which a signal is branched by an optical demultiplexer and separated by detecting with a millimeter wave band light receiving element and a low frequency band light receiving element. I came to know that.

本発明はかかる知見に基づくものであり、請求項１記載の発明の複合変調方法は、無線変復調部を備えた中央制御局とアンテナ部を備えた無線基地局とこれら両局を接続する光ファイバとで構成され、周波数の異なる複数の無線信号を多重化するファイバ無線通信システムを利用してこの多重化した信号を光伝送する際の光信号の変調方法であって、外部光変調器への入力光を一の無線信号で予め強度変調しておき、この強度変調した入力光を外部光変調器において他の無線信号で更に強度変調することによって複数信号を多重化した後に光伝送するというものである。   The present invention is based on such knowledge, and the composite modulation method according to the first aspect of the present invention includes a central control station having a radio modulation / demodulation unit, a radio base station having an antenna unit, and an optical fiber connecting these two stations. And a method of modulating an optical signal when optically transmitting the multiplexed signal using a fiber radio communication system that multiplexes a plurality of radio signals having different frequencies, The input light is intensity-modulated in advance with one radio signal, and the intensity-modulated input light is further intensity-modulated with another radio signal in an external optical modulator, and a plurality of signals are multiplexed and then optically transmitted. It is.

従来の信号多重方法においては、例えば副搬送波多重方式（ＳＣＭ）であれば電気信号の足し算をし、波長分割多重方式（ＷＤＭ）であれば光信号の足し算をするといった演算を行っていたのに対し、複合変調では、ＥＡＭ（電界吸収型光変調器）において、光信号となった低周波信号と、電気信号であるミリ波信号とを掛け算するという形をとる。ただし、受信側では、掛け算された成分を抽出するのではなく、掛け算をする過程で派生する足し算成分を抽出する。具体的には、
（１＋低周波）×（１＋ミリ波）＝１＋低周波＋ミリ波＋低周波×ミリ波
のうちの右辺中の 低周波＋ミリ波 の部分を指している。このような複合変調を行うことで、信号としては足し算で多重されたものと同様ということになる。 In the conventional signal multiplexing method, for example, an electric signal is added in the case of subcarrier multiplexing (SCM), and an optical signal is added in the case of wavelength division multiplexing (WDM). On the other hand, composite modulation takes the form of multiplying a low frequency signal, which is an optical signal, and a millimeter wave signal, which is an electrical signal, in an EAM (electro-absorption optical modulator). However, the receiving side does not extract the multiplied component, but extracts an addition component derived in the process of multiplication. In particular,
(1 + Low frequency) x (1 + Millimeter wave) = 1 + Low frequency + Millimeter wave + Low frequency x This refers to the low frequency + millimeter wave part in the right side of the millimeter wave. By performing such complex modulation, the signal is the same as that multiplexed by addition.

請求項２記載の発明は、請求項１記載の複合変調方法において、周波数が３０ＧＨｚ以下の低周波帯無線信号により入力光を強度変調しておき、この強度変調された入力光を外部光変調器へ入力し、この入力光をミリ波帯信号により更に強度変調するというものである。   According to a second aspect of the present invention, in the composite modulation method according to the first aspect, the input light is intensity-modulated by a low frequency band radio signal having a frequency of 30 GHz or less, and the intensity-modulated input light is converted into an external optical modulator. The input light is further intensity-modulated by a millimeter waveband signal.

請求項３記載の発明は、請求項２記載の複合変調方法において、外部光変調器へ入力されるミリ波帯信号に加えてミリ波帯ローカル信号も入力無線信号とし、低周波帯無線信号により強度変調された入力光を更に強度変調するというものである。   According to a third aspect of the present invention, in the composite modulation method according to the second aspect, in addition to the millimeter wave band signal input to the external optical modulator, the millimeter wave band local signal is also used as the input radio signal, and the low frequency band radio signal is used. Intensity-modulated input light is further intensity-modulated.

請求項４記載の発明の複合変調された光信号の分離方法は、請求項１から３のいずれかの複合変調方法により複合変調された光信号を光分波器により分離し、ミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波するというものである。   According to a fourth aspect of the present invention, there is provided a method for separating a composite-modulated optical signal, wherein the optical signal modulated by the composite modulation method according to any one of the first to third aspects is separated by an optical demultiplexer. The millimeter wave band modulation signal and the low frequency band modulation signal are detected by the element and the low frequency band light receiving element, respectively.

請求項５記載の発明の複合変調された光信号の分離方法は、請求項１から３のいずれかの複合変調方法により複合変調された光信号をミリ波帯受光素子により検波し、その直後に周波数変換器により低周波数に周波数変換し、ミリ波帯中間周波信号と低周波帯信号とを電気分波器により分離するというものである。   According to a fifth aspect of the present invention, there is provided a method for separating an optical signal that has been subjected to composite modulation, wherein the optical signal modulated by the composite modulation method according to any one of claims 1 to 3 is detected by a millimeter wave band light receiving element. The frequency is converted to a low frequency by a frequency converter, and the millimeter wave band intermediate frequency signal and the low frequency band signal are separated by an electric branching filter.

請求項６記載の発明の複合変調型無線基地局は、無線変復調部を備えた中央制御局と光ファイバで接続されてファイバ無線通信システムを構成し、周波数の異なる複数の無線信号を多重化して光伝送する無線基地局であって、外部光変調器への入力光をこの外部光変調器に入力される前に一の無線信号で予め強度変調しておく変調装置と、この強度変調された入力光を他の無線信号で更に強度変調することによって複数信号を多重化する外部光変調器とを備えるというものである。   According to a sixth aspect of the present invention, a composite modulation type radio base station is connected to a central control station having a radio modulation / demodulation unit through an optical fiber to form a fiber radio communication system, and multiplexes a plurality of radio signals having different frequencies. A radio base station that performs optical transmission, and a modulator that intensity-modulates input light to an external optical modulator with a single radio signal before being input to the external optical modulator, and the intensity modulated And an external optical modulator that multiplexes a plurality of signals by further modulating the intensity of the input light with another radio signal.

請求項７記載の発明は、請求項６記載の複合変調型無線基地局において、周波数が３０ＧＨｚ以下の低周波帯電気信号を光信号に変換する低周波帯発光素子と、この変換された光信号が入力されるとともにミリ波帯無線信号に基づきこの光信号を更に強度変調する外部光変調器とを備え、周波数の異なる複数の無線信号を多重化して中央制御局へ光伝送するというものである。   According to a seventh aspect of the present invention, there is provided a composite modulation type radio base station according to the sixth aspect, wherein a low-frequency band light-emitting element that converts a low-frequency band electrical signal having a frequency of 30 GHz or less into an optical signal, and the converted optical signal And an external optical modulator that further modulates the intensity of the optical signal based on the millimeter-wave band radio signal, and multiplexes a plurality of radio signals having different frequencies and optically transmits them to the central control station. .

請求項８記載の発明は、請求項６または７記載の複合変調型無線基地局において、中央制御局から当該無線基地局への下り回線においては複合変調された光信号を光分波器により分離してミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波する一方、当該無線基地局から中央制御局への上り回線においては複合変調された光信号をミリ波帯受光素子により検波し、その直後に周波数変換器により低周波数に周波数変換し、ミリ波帯中間周波信号と低周波帯信号とを電気分波器により分離するというものである。   According to an eighth aspect of the present invention, in the composite modulation type radio base station according to the sixth or seventh aspect, in the downlink from the central control station to the radio base station, the optical signal subjected to the composite modulation is separated by the optical demultiplexer. Then, the millimeter wave band light receiving element and the low frequency band light receiving element detect the millimeter wave band modulation signal and the low frequency band modulation signal, respectively, while the uplink from the radio base station to the central control station is compositely modulated. The optical signal is detected by a millimeter-wave band light receiving element, and immediately after that, the frequency is converted to a low frequency by a frequency converter, and the millimeter-wave band intermediate frequency signal and the low-frequency band signal are separated by an electric demultiplexer. .

請求項９記載の発明は、請求項６または７記載の複合変調型無線基地局において、当該無線基地局から中央制御局への上り回線およびこの中央制御局から当該無線基地局への下り回線の両回線において、複合変調された光信号を光分波器により分離してミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波するというものである。   The invention according to claim 9 is the composite modulation type radio base station according to claim 6 or 7, wherein the uplink from the radio base station to the central control station and the downlink from the central control station to the radio base station In both lines, the combined modulated optical signal is separated by an optical demultiplexer, and the millimeter wave band modulated signal and the low frequency band modulated signal are detected by the millimeter wave band light receiving element and the low frequency band light receiving element, respectively. is there.

請求項１記載の複合変調方法によると、周波数の異なる複数の無線信号を多重化して光伝送する際、外部光変調器への入力光をその入力前に一の無線信号によって予め強度変調し、このように強度変調した状態で外部光変調器に入力することになる。こうした場合、従来の副搬送波多重方式（ＳＣＭ）において必要であった広帯域カプラ（ミリ波帯カプラ）、波長分割多重方式（ＷＤＭ）において用いられていたＷＤＭカプラ、使用波長の決められた光源などを備えていなくても複数の無線信号を効率的に多重化して光伝送することが可能となる。したがって本願のこの複合変調方法によればきわめて簡易な構造の光系統と電気回路により高周波帯無線基地局と低周波帯無線基地局とを構成することが可能である。また、上述したようにＷＤＭカプラを用いる必要がなくなるため、この複合変調方法によれば従来の波長分割多重方式（ＷＤＭ）におけるようなＷＤＭカプラによる光波長の制限がなくなり、ＷＤＭカプラの動作波長にあった光波長を選択しなければならなかったという問題が解消することになる。   According to the composite modulation method of claim 1, when a plurality of radio signals having different frequencies are multiplexed and optically transmitted, the input light to the external optical modulator is intensity-modulated in advance with one radio signal before the input, The light is input to the external optical modulator in the state of intensity modulation in this way. In such a case, the broadband coupler (millimeter wave band coupler) required in the conventional subcarrier multiplexing system (SCM), the WDM coupler used in the wavelength division multiplexing system (WDM), the light source whose wavelength is determined, etc. Even if it is not provided, a plurality of radio signals can be efficiently multiplexed and optically transmitted. Therefore, according to the composite modulation method of the present application, it is possible to configure a high frequency band radio base station and a low frequency band radio base station by an optical system and an electric circuit having a very simple structure. Further, as described above, since it is not necessary to use a WDM coupler, this composite modulation method eliminates the limitation of the optical wavelength by the WDM coupler as in the conventional wavelength division multiplexing (WDM), so that the operating wavelength of the WDM coupler can be reduced. The problem of having to select a certain light wavelength is solved.

さらに、一の無線信号で光信号を予め強度変調しておき、その後に別の無線信号で更に強度変調するというように複数段階に分けて光信号を強度変調するようにしているため、これら高周波帯無線基地局と低周波帯無線基地局を隔離して設置することができるなど無線基地局の設置自由度が高い。しかも、上述したように従来用いられていた合波器、分波器、フィルタ等を省略することが可能となるためコスト圧縮と装置の小型化を図れる。   Furthermore, since the optical signal is intensity-modulated in advance with one radio signal and then further intensity-modulated with another radio signal, the optical signal is intensity-modulated in multiple stages. The radio base station has a high degree of freedom in installation, such as being able to install the radio base station and the low frequency radio base station separately. In addition, as described above, it is possible to omit a multiplexer, a demultiplexer, a filter, and the like that have been conventionally used, so that the cost can be reduced and the apparatus can be downsized.

また、請求項２記載の複合変調方法によると、周波数が３０ＧＨｚ以下の低周波帯無線信号で入力光を予め強度変調しておき、この強度変調された入力光を外部光変調器へ入力して更に強度変調するという手法により、周波数が３０ＧＨｚ以下の低周波帯無線信号とミリ波帯（周波数３０ＧＨｚ〜３００ＧＨｚ）の無線信号とを多重化して光伝送することができる。   According to the composite modulation method of claim 2, the input light is intensity-modulated in advance with a low frequency band radio signal having a frequency of 30 GHz or less, and the intensity-modulated input light is input to the external optical modulator. Furthermore, by the technique of intensity modulation, it is possible to multiplex a low frequency radio signal having a frequency of 30 GHz or less and a radio signal in the millimeter wave band (frequency 30 GHz to 300 GHz) for optical transmission.

請求項３記載の複合変調方法によると、ミリ波帯無線信号にミリ波帯ローカル信号を加え多重化して伝送することにより、予め変調しておいた一の無線信号をミリ波帯へとアップコンバートすること、つまり低周波帯信号の周波数を上げてミリ波帯信号にすることが可能となる。また受信側においては、アップコンバートされた一の無線信号を抽出する際に、アップコンバートされた低周波帯信号も一緒にダウンコンバートできることから、ミリ波帯信号をＩＦ周波数にまでダウンコンバートするためのダウンコンバータを共有可能となり、光伝送系が簡素になると共に電気回路も簡素となることから低コストな無線基地局を構成することが可能となる。   According to the composite modulation method of claim 3, by converting a millimeter-wave band radio signal to a millimeter-wave band local signal and multiplexing the signal, up-converting one radio signal modulated in advance to the millimeter-wave band In other words, it is possible to increase the frequency of the low frequency band signal to a millimeter wave band signal. On the receiving side, when extracting one up-converted radio signal, the up-converted low-frequency band signal can be down-converted together, so that the millimeter-wave band signal can be down-converted to the IF frequency. The down converter can be shared, the optical transmission system is simplified, and the electric circuit is also simplified, so that a low-cost wireless base station can be configured.

請求項４記載の複合変調された光信号の分離方法によると、上述した複合変調方法により複合変調された光信号を光分波器により分離し、その後でミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波することができる（図２参照）。本発明にかかる複合変調方法においては光波長が単一（光源が１つ）であるため光分波器としてＷＤＭカプラを用いるメリットがなく、例えば３ｄＢ−光カプラにより光を２方向に分離することができ、こうした場合、光波長に関わらず光を半分ずつ２方向に分離することが可能となる。このような分離方法によれば、従来手法である波長分割多重方式（ＷＤＭ）において必要であったＷＤＭカプラによる光波長の制限がなくなり、低コストで柔軟な無線基地局を構成することが可能となる。   According to the separation method of the composite modulated optical signal according to claim 4, the optical signal modulated by the composite modulation method is separated by the optical demultiplexer, and then the millimeter wave band light receiving element and the low frequency light receiving element are separated. The element can detect the millimeter wave band modulation signal and the low frequency band modulation signal, respectively (see FIG. 2). In the composite modulation method according to the present invention, since the optical wavelength is single (one light source), there is no merit of using a WDM coupler as an optical demultiplexer. For example, the light is separated in two directions by a 3 dB optical coupler. In such a case, light can be separated in two directions by half regardless of the light wavelength. According to such a separation method, there is no limitation on the optical wavelength by the WDM coupler, which is necessary in the conventional wavelength division multiplexing (WDM) method, and it is possible to configure a flexible radio base station at a low cost. Become.

また、請求項５記載の複合変調された光信号の分離方法によると、上述した複合変調方法により複合変調された光信号をミリ波帯受光素子により検波し、その直後に周波数変換器により低周波数に周波数変換し、ミリ波帯中間周波信号と低周波帯信号とを電気分波器により分離することができる。この分離方法を採用することにより、多数のミリ波帯素子を必要としていた従来の副搬送波多重方式や光系統が複雑となっていた従来の波長分割多重方式に比べて構成要素が少なくて済み、より低コストで簡素な無線基地局を構成することが可能となる。   Further, according to the separation method of the composite modulated optical signal according to claim 5, the optical signal compositely modulated by the composite modulation method described above is detected by the millimeter wave band light receiving element, and immediately after that, a low frequency is detected by the frequency converter. Thus, the millimeter wave band intermediate frequency signal and the low frequency band signal can be separated by an electric demultiplexer. By adopting this separation method, there are fewer components compared to the conventional subcarrier multiplexing method that required a large number of millimeter waveband devices and the conventional wavelength division multiplexing method in which the optical system was complicated, A simple radio base station can be configured at a lower cost.

請求項６記載の複合変調型無線基地局によると、周波数の異なる複数の無線信号を多重化して光伝送する際、外部光変調器への入力光をその入力前に一の無線信号によって予め強度変調し、このように強度変調した状態で外部光変調器に入力することになる。こうした場合、従来の副搬送波多重方式において必要であったミリ波帯カプラや波長分割多重方式において用いられていたＷＤＭカプラ、使用波長の決められた光源などを備えていなくても複数の無線信号を効率的に多重化して光伝送することが可能となる。したがって本願の複合変調型無線基地局によればきわめて簡易な構造の光系統と電気回路により高周波帯無線基地局と低周波帯無線基地局とを構成することが可能である。また、一の無線信号で光信号を予め強度変調しておき、その後に別の無線信号で更に強度変調するというように複数段階に分けて光信号を強度変調するようにしているため、これら高周波帯無線基地局と低周波帯無線基地局を隔離して設置することができるなど基地局の設置自由度が高い。しかも、上述したように従来用いられていた合波器、分波器、フィルタ等を省略することが可能となるためコスト圧縮と装置の小型化を図れる。   According to the composite modulation type radio base station according to claim 6, when a plurality of radio signals having different frequencies are multiplexed and optically transmitted, the input light to the external optical modulator is previously intensified by one radio signal before the input. Then, the signal is modulated and input to the external optical modulator in the state of intensity modulation. In such a case, a plurality of radio signals can be obtained even without a millimeter-wave band coupler required in the conventional subcarrier multiplexing system, a WDM coupler used in the wavelength division multiplexing system, or a light source having a determined wavelength. It becomes possible to efficiently multiplex and transmit light. Therefore, according to the composite modulation type radio base station of the present application, it is possible to configure a high frequency band radio base station and a low frequency band radio base station with an optical system and an electric circuit having a very simple structure. Further, since the optical signal is intensity-modulated in advance with one radio signal and then further intensity-modulated with another radio signal, the optical signal is intensity-modulated in a plurality of stages. The base station has a high degree of freedom of installation, such as being able to install a radio base station and a low frequency radio base station separately. In addition, as described above, it is possible to omit a multiplexer, a demultiplexer, a filter, and the like that have been conventionally used, so that the cost can be reduced and the apparatus can be downsized.

また請求項７記載の複合変調型無線基地局によると、低周波帯発光素子によって低周波無線装置からの低周波帯電気信号を光信号に変換し、この再変換された光信号を外部光変調器に入力するとともにミリ波帯無線信号に基づき更に強度変調することによって複数の無線信号が多重化される。これにより、周波数が３０ＧＨｚ以下の低周波帯無線信号とミリ波帯（周波数３０ＧＨｚ〜３００ＧＨｚ）の無線信号とを多重化して光伝送することができる。   According to the composite modulation type radio base station of claim 7, the low frequency band electrical signal from the low frequency radio apparatus is converted into an optical signal by the low frequency band light emitting element, and the reconverted optical signal is converted into the external optical modulation. A plurality of radio signals are multiplexed by inputting into the receiver and further modulating the intensity based on the millimeter wave band radio signal. As a result, it is possible to multiplex a low frequency radio signal having a frequency of 30 GHz or less and a radio signal in the millimeter wave band (frequency 30 GHz to 300 GHz) for optical transmission.

請求項８記載の複合変調型無線基地局によると、中央制御局から当該無線基地局への下り回線においては複合変調された光信号を光分波器により分離した後、受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波することができる。また、上り回線においては複合変調された光信号をミリ波帯受光素子により検波し、その直後に周波数変換器により低周波数に周波数変換し、ミリ波帯中間周波信号と低周波帯信号とを電気分波器により分離することができる。   According to the composite modulation type radio base station according to claim 8, after the optical signal subjected to the composite modulation is separated by the optical demultiplexer in the downlink from the central control station to the radio base station, the light receiving element and the low frequency band The millimeter wave band modulation signal and the low frequency band modulation signal can be detected by the light receiving element. In addition, in the uplink, a composite modulated optical signal is detected by a millimeter wave band light receiving element, and immediately after that, it is converted to a low frequency by a frequency converter, and the millimeter wave band intermediate frequency signal and the low frequency band signal are electrically converted. They can be separated by a duplexer.

さらに請求項９記載の複合変調型無線基地局によると、当該無線基地局から中央制御局への上り回線およびこれとは逆の下り回線の両回線において、複合変調された光信号を光分波器により分離してミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波することができる。この場合、ミリ波帯基地局においてバンドパスフィルタ（ＢＰＦ）が一つ、中央制御局の受信装置において低周波帯受光素子（低周波帯フォトダイオード）が一つ必要とはなるが、その反面、不要放射は一切発生しない構成となることから、このように変調信号を検波するための装置を上り回線と下り回線とに対照的に設けることによって不要放射のない柔軟な無線基地局を構成することが可能となる。   Furthermore, according to the composite modulation type radio base station as claimed in claim 9, optical signals that have been subjected to composite modulation are optically demultiplexed on both the uplink from the radio base station to the central control station and the downlink opposite thereto. The millimeter wave band modulated signal and the low frequency band modulated signal can be detected by the millimeter wave band light receiving element and the low frequency band light received element. In this case, one band pass filter (BPF) is required in the millimeter wave band base station, and one low frequency light receiving element (low frequency photodiode) is required in the receiver of the central control station. Since unnecessary radiation is not generated at all, a flexible radio base station without unnecessary radiation is configured by providing a device for detecting a modulated signal in this way in contrast to the uplink and downlink. Is possible.

以下、本発明の構成を図面に示す実施の形態に基づいて詳細に説明する。   Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

図１〜図６に本発明の一実施形態を示す。本発明にかかる複合変調型無線基地局１は、無線変復調部（無線変調部３および無線復調部４からなる）を備えた中央制御局２と光ファイバ６で接続されており、この中央制御局２や光ファイバ６とともにファイバ無線通信システムを構成しているものである。なお図４と図６を除く図中では、太い矢印線で光ファイバ６を表し、細い矢印線で同軸（導線）１５を示している。   1 to 6 show an embodiment of the present invention. A composite modulation type radio base station 1 according to the present invention is connected to a central control station 2 having a radio modulation / demodulation unit (comprising a radio modulation unit 3 and a radio demodulation unit 4) by an optical fiber 6, and this central control station. 2 and the optical fiber 6 constitute a fiber radio communication system. In the drawings excluding FIGS. 4 and 6, the optical fiber 6 is represented by a thick arrow line, and the coaxial (conductive wire) 15 is represented by a thin arrow line.

この複合変調型無線基地局１は、周波数の異なる複数の無線信号を多重化して光伝送するように構成された無線基地局であって、外部光変調器５への入力光をこの外部光変調器５に入力される前の段階で一の無線信号で予め強度変調しておく変調装置７と、この強度変調された入力光を他の無線信号で更に強度変調することによって複数信号を多重化する外部光変調器５とを備えている（図３参照）。なお、この複合変調型無線基地局１は周波数の異なる複数の無線信号を伝送対象としてはいるがこれら無線信号の周波数帯域を厳密に区切っているわけではなく、例示すれば、今後さらなる利用が期待される周波数３０〜３００ＧＨｚのミリ波帯信号と、周波数３０ＧＨｚ以下の帯域（本明細書ではこれを「低周波帯」と表現している）の信号（たとえばマイクロ波）という組合せを対象としている。本実施形態の複合変調型無線基地局１は、低周波帯で使用される装置２６との間で無線信号の送受信を行う低周波帯基地局１Ａと、ミリ波帯で使用される装置２７との間で無線信号の送受信を行うミリ波帯基地局１Ｂとの両無線基地局によって構成されている。各無線基地局１Ａ，１Ｂはそれぞれアンテナ部１３，１４を備えている。符号９は信号の送受を切り換えるサーキュレータである。   The composite modulation type radio base station 1 is a radio base station configured to multiplex and transmit a plurality of radio signals having different frequencies, and the input light to the external optical modulator 5 is modulated by the external optical modulation. Modulator 7 that modulates the intensity with one radio signal in advance before it is input to the device 5 and a plurality of signals are multiplexed by further modulating the intensity of the intensity-modulated input light with another radio signal. And an external optical modulator 5 (see FIG. 3). Although the composite modulation type radio base station 1 is intended for transmission of a plurality of radio signals having different frequencies, the frequency bands of these radio signals are not strictly divided. For example, further use is expected in the future. The target is a combination of a millimeter-wave band signal having a frequency of 30 to 300 GHz and a signal (for example, a microwave) having a frequency band of 30 GHz or less (in this specification, this is expressed as a “low frequency band”). The composite modulation radio base station 1 of the present embodiment includes a low frequency base station 1A that transmits and receives radio signals to and from the device 26 used in the low frequency band, and a device 27 used in the millimeter wave band. The base station 1 is configured by both radio base stations with a millimeter wave band base station 1B that transmits and receives radio signals. Each of the radio base stations 1A and 1B includes antenna units 13 and 14, respectively. Reference numeral 9 denotes a circulator for switching between transmission and reception of signals.

低周波帯基地局１Ａに設けられる変調装置７は上述したとおり外部光変調器５への入力光をその前の段階で予め強度変調しておく装置であり、本実施形態ではこの変調装置７を、低周波帯電気信号を光信号に変換する低周波帯発光素子１０で構成している（図３参照）。受光素子８としては例えば低周波帯フォトダイオードが、低周波帯発光素子１０としては例えばレーザダイオードが使用される。   The modulation device 7 provided in the low frequency band base station 1A is a device that modulates the intensity of the input light to the external optical modulator 5 in advance in the previous stage as described above. The low-frequency band light-emitting element 10 converts a low-frequency band electrical signal into an optical signal (see FIG. 3). As the light receiving element 8, for example, a low frequency band photodiode is used, and as the low frequency band light emitting element 10, for example, a laser diode is used.

ミリ波帯基地局１Ｂには、光分波器２５で分光された光信号を電気信号に変換するミリ波帯発光素子１１が設けられている（図３参照）。ミリ波帯発光素子１１としては例えばフォトダイオード（ＰＤ）が用いられる。また、このミリ波帯基地局１Ｂには上述した外部光変換器５も設けられている。アンテナ部１４で受信されたミリ波帯無線信号はカプラ１２において電気信号に加え合わせられる。光分波器２５は具体的には３ｄＢ‐光カプラであるがこれ以外の分波器が用いられる可能性もある（図３参照）。   The millimeter wave band base station 1B is provided with a millimeter wave band light emitting element 11 that converts an optical signal dispersed by the optical demultiplexer 25 into an electrical signal (see FIG. 3). For example, a photodiode (PD) is used as the millimeter-wave band light emitting element 11. The millimeter-wave band base station 1B is also provided with the external optical converter 5 described above. The millimeter-wave band radio signal received by the antenna unit 14 is added to the electrical signal by the coupler 12. The optical demultiplexer 25 is specifically a 3 dB optical coupler, but other demultiplexers may be used (see FIG. 3).

中央制御局２は光ファイバ６によって複合変調型無線基地局１と接続されており、これら複合変調型無線基地局１や光ファイバ６とともにファイバ無線通信システムを構成している。この中央制御局２は、無線変調部３および無線復調部４を備えている（図３参照）。無線変調部３は、特に図示していないネットワーク（例えばインターネット）等を通じて送信されたベースバンド信号を変調する低周波帯無線信号の変調装置１６、ミリ波帯無線信号の変調装置１７、および低周波帯無線信号を光信号に変換するレーザダイオード１８、この光信号にミリ波帯無線信号を多重化する外部光変調器１９等によって構成されている。外部光変調器１９において強度変調された光信号はその後段に設けられている光カプラ２５によって分岐され、低周波帯フォトダイオード８とミリ波帯フォトダイオード１１とへ伝送される。また無線復調部４は、ミリ波帯受光素子２０、ダウンコンバータ（ＤＣ）２１、ミリ波ＩＦ帯復調器２２、低周波帯復調器２３等によって構成されている。なお、実際にはこの中央制御局２に対し多数の複合変調型無線基地局１（低周波帯基地局１Ａおよびミリ波帯基地局１Ｂ）が接続されることになるが、本実施形態では単一の複合変調型無線基地局１のみ図示している。ミリ波帯受光素子２０としては例えばフォトダイオードが用いられる。   The central control station 2 is connected to the composite modulation type radio base station 1 by an optical fiber 6 and constitutes a fiber radio communication system together with the composite modulation type radio base station 1 and the optical fiber 6. The central control station 2 includes a radio modulation unit 3 and a radio demodulation unit 4 (see FIG. 3). The radio modulation unit 3 includes a low-frequency band radio signal modulation device 16, a millimeter-wave band radio signal modulation device 17, and a low-frequency modulation unit that modulates a baseband signal transmitted through a network (for example, the Internet) not shown. A laser diode 18 that converts a band radio signal into an optical signal, an external optical modulator 19 that multiplexes the millimeter wave band radio signal with the optical signal, and the like are configured. The optical signal intensity-modulated in the external optical modulator 19 is branched by the optical coupler 25 provided in the subsequent stage and transmitted to the low frequency band photodiode 8 and the millimeter wave band photodiode 11. The radio demodulation unit 4 includes a millimeter wave band light receiving element 20, a down converter (DC) 21, a millimeter wave IF band demodulator 22, a low frequency band demodulator 23, and the like. In practice, a large number of composite modulation type radio base stations 1 (low frequency band base station 1A and millimeter wave band base station 1B) are connected to the central control station 2. Only one composite modulation type radio base station 1 is shown. As the millimeter wave band light receiving element 20, for example, a photodiode is used.

また、複合変調型無線基地局１（ミリ波帯基地局１Ｂ）から中央制御局２への上り回線においては、複合変調−電気信号分離方式が採用されている。この方式について説明すると、まず、低周波帯基地局１Ａのアンテナ部１３で受信された低周波数帯無線信号により、低周波帯基地局１Ａ内の低周波帯発光素子（レーザダイオード）１０において信号を強度変調し、強度変調された光信号を発する（図３参照）。低周波帯基地局１Ａとミリ波帯基地局１Ｂとは光ファイバ６により接続されており、低周波帯基地局１Ａにおいて予め強度変調された光信号はミリ波帯基地局１Ｂの外部光変調器５への光入力として用いられ、ミリ波帯基地局１Ｂのアンテナ１４において受信されたミリ波信号によって更に強度変調されることで上り回線における複合変調が行われる。この複合変調−電気信号分離方式では低周波帯信号をミリ波帯にまでアップコンバートするためにミリ波帯ローカル信号が必要となるが、この場合におけるミリ波帯ローカル信号は中央制御局２から複合変調型無線基地局１へと向かう下り回線を通じて供給されるようになっている。これは、装置２７からミリ波帯基地局１Ｂのアンテナ部１４へと到着する信号（電波）は単純なミリ波帯信号であるため上述のミリ波帯ローカル信号を中央制御局２から供給する必要があるからであり、本実施形態ではミリ波帯フォトダイオード１１から出力されるミリ波帯ローカル信号が外部光変調器５の方向にも流れる構成としている（図３参照）。このようにして複合変調された光信号は光ファイバ６を通じて中央制御局２へ伝送される。中央制御局２においては、上述したミリ波帯受光素子（フォトダイオード）２０により光信号が検波され、その直後、ダウンコンバータ（周波数変換器）２１により中間周波数帯に周波数変換される。中間周波数帯に周波数変換された無線信号は中間周波帯域電気信号分波器（電気分波器）２４により分割され、ミリ波ＩＦ帯復調器２２と低周波帯復調器２３によりそれぞれ復調される。   Further, in the uplink from the composite modulation type radio base station 1 (millimeter wave band base station 1B) to the central control station 2, a composite modulation-electric signal separation method is adopted. This method will be described. First, a signal is transmitted from a low frequency band light-emitting element (laser diode) 10 in the low frequency band base station 1A by a low frequency band radio signal received by the antenna unit 13 of the low frequency band base station 1A. Intensity modulation is performed and an intensity-modulated optical signal is emitted (see FIG. 3). The low frequency band base station 1A and the millimeter wave band base station 1B are connected by an optical fiber 6, and an optical signal whose intensity is modulated in advance in the low frequency band base station 1A is an external optical modulator of the millimeter wave band base station 1B. 5 is used as an optical input to 5 and further intensity-modulated by a millimeter wave signal received by the antenna 14 of the millimeter wave band base station 1B, thereby performing composite modulation in the uplink. In this composite modulation / electrical signal separation method, a millimeter wave band local signal is required to up-convert the low frequency band signal to the millimeter wave band. In this case, the millimeter wave band local signal is combined from the central control station 2. It is supplied through a downlink toward the modulation type radio base station 1. This is because the signal (radio wave) arriving from the device 27 to the antenna unit 14 of the millimeter wave band base station 1B is a simple millimeter wave band signal, and the above-mentioned millimeter wave band local signal needs to be supplied from the central control station 2. In this embodiment, the millimeter wave band local signal output from the millimeter wave band photodiode 11 also flows in the direction of the external optical modulator 5 (see FIG. 3). The compositely modulated optical signal is transmitted to the central control station 2 through the optical fiber 6. In the central control station 2, the optical signal is detected by the above-described millimeter-wave band light receiving element (photodiode) 20, and immediately thereafter, the frequency is converted to the intermediate frequency band by the down converter (frequency converter) 21. The radio signal frequency-converted to the intermediate frequency band is divided by the intermediate frequency band electric signal demultiplexer (electric demultiplexer) 24 and demodulated by the millimeter wave IF band demodulator 22 and the low frequency band demodulator 23, respectively.

このローカル信号について更に説明を加えると以下のようになる。すなわち、本実施形態では外部光変調器５への電気信号の入力をミリ波信号としているが、これに加えてミリ波帯ローカル信号（図４中のｆMMWとｆLO参照）も入力することで、低周波信号成分をミリ波領域にアップコンバートさせることを可能としている。受信側においては、ミリ波信号であるｆMMWと、元々低周波信号であるｆLO＋ｆmicroを抽出する。この抽出時において、ミリ波ダウンコンバータ２１を共有することが可能となる。というのも、ミリ波信号というのはミリ波帯ローカル信号と中間周波信号（ＩＦ信号）との乗算（周波数でいうと足し算）により作成され、ｆMMW＝ｆLO＋ｆIFという周波数成分となっているためである。受信側では、ミリ波ダウンコンバータ２１によりｆIF成分を抽出する。また、元々の低周波信号は、受信側においてはｆLO＋ｆmicroとなっているため、ｆmicroを抽出するために元々必要不可欠であるミリ波ダウンコンバータ２１を用いることが可能となっている。 This local signal is further explained as follows. That is, in this embodiment, the input of the electric signal to the external optical modulator 5 is a millimeter wave signal, but in addition to this, a millimeter wave band local signal (see f MMW and f LO in FIG. 4) is also input. Thus, it is possible to up-convert the low frequency signal component to the millimeter wave region. On the receiving side, f MMW that is a millimeter wave signal and f LO + f micro that is originally a low frequency signal are extracted. At the time of this extraction, the millimeter wave down converter 21 can be shared. This is because a millimeter wave signal is created by multiplication (addition in terms of frequency) of a millimeter wave band local signal and an intermediate frequency signal (IF signal) and becomes a frequency component of f MMW = f LO + f IF. Because it is. On the reception side, the f IF component is extracted by the millimeter wave down converter 21. Further, since the original low frequency signal is f LO + f micro on the receiving side, it is possible to use the millimeter wave down converter 21 that is originally essential for extracting f micro .

一方、中央制御局２から複合変調型無線基地局１へと向かう下り回線においては、複合変調−光信号分離方式が採用されている。この方式においては、まず中央制御局２において無線変調された低周波帯無線信号をレーザダイオード１８において光信号に変換し、外部光変調器１９への入力として用いられ、ミリ波信号によってさらに強度変調されることでミリ波信号と低周波信号とが複合変調されることになる。さらにこの光信号を光カプラ２５によって分離し、分離した光信号を低周波帯基地局１Ａとミリ波帯基地局１Ｂとに伝送する（図３参照）。この際、伝送される信号には上り回線において必要であるミリ波帯ローカル信号も加えられるため、図４に示すように、ミリ波ローカル信号（ミリ波信号アップコンバート用ローカル信号）ｆLO、ミリ波ローカル信号ｆLOと低周波信号（マイクロ波信号周波数）ｆmicroとの乗算成分、ミリ波信号ｆMMW、ミリ波信号ｆMMWと低周波信号ｆmicroとの乗算成分および低周波信号ｆmicroが発生する。複合変調された光信号は、光ファイバ６により低周波帯基地局１Ａの方向へ伝送され、光カプラ２５により２つの光信号に分離され、一方は低周波帯基地局１Ａに、他方はミリ波帯基地局１Ｂに伝送される。ミリ波帯無線基地局１Ｂにおいては、光信号はミリ波帯発光素子（ミリ波帯フォトダイオード）１１により検波されて無線信号を検出する。検出される無線信号は、低周波信号ｆmicro、ミリ波ローカル信号ｆLO、ミリ波ローカル信号ｆLOと低周波信号ｆmicroとの乗算成分、ミリ波信号ｆMMW及びミリ波信号ｆMMWと低周波信号ｆmicroとの乗算成分となる。ミリ波帯フォトダイオード１１の出力をカプラ（分波器）１２により分波し、ミリ波ローカル信号ｆLO成分を上り回線における複合変調に用いる。アンテナ部１４は低周波信号によっては励起されないので、このアンテナ部１４からはミリ波ローカル信号ｆLO、ミリ波ローカル信号ｆLOと低周波信号ｆmicroとの乗算成分、ミリ波信号ｆMMWおよびミリ波信号ｆMMWと低周波信号ｆmicroとの乗算成分が放射されるが、ミリ波帯は電波伝搬減衰が大きく、他のシステムへの干渉となりにくいという特徴を持つため他の周波数成分が放射されることを許容する。また、低周波帯基地局１Ａにおいては、低周波帯フォトダイオード８によりミリ波帯信号は検出されないため、低周波信号のみがアンテナ部１３を通じて放射される。 On the other hand, in the downlink from the central control station 2 to the composite modulation type radio base station 1, the composite modulation / optical signal separation method is adopted. In this method, first, a low frequency band radio signal radio-modulated in the central control station 2 is converted into an optical signal in the laser diode 18 and used as an input to the external optical modulator 19 and further intensity-modulated by a millimeter wave signal. As a result, the millimeter wave signal and the low frequency signal are combined and modulated. Further, the optical signal is separated by the optical coupler 25, and the separated optical signal is transmitted to the low frequency band base station 1A and the millimeter wave band base station 1B (see FIG. 3). At this time, since the millimeter wave band local signal necessary for the uplink is also added to the transmitted signal, as shown in FIG. 4, the millimeter wave local signal (millimeter wave signal up-conversion local signal) f LO , millimeter The multiplication component of the wave local signal f LO and the low frequency signal (microwave signal frequency) f micro , the millimeter wave signal f MMW , the multiplication component of the millimeter wave signal f MMW and the low frequency signal f micro , and the low frequency signal f micro Occur. The composite-modulated optical signal is transmitted in the direction of the low-frequency band base station 1A through the optical fiber 6 and separated into two optical signals by the optical coupler 25, one being the low-frequency band base station 1A and the other being the millimeter wave. Is transmitted to the band base station 1B. In the millimeter wave band radio base station 1B, the optical signal is detected by a millimeter wave band light emitting element (millimeter wave photodiode) 11 to detect a radio signal. The detected radio signals are low frequency signal f micro , millimeter wave local signal f LO , multiplication component of millimeter wave local signal f LO and low frequency signal f micro , millimeter wave signal f MMW and millimeter wave signal f MMW and low. It becomes a multiplication component with the frequency signal f micro . The output of the millimeter wave band photodiode 11 is demultiplexed by a coupler (demultiplexer) 12 and the millimeter wave local signal f LO component is used for the composite modulation in the uplink. Since the antenna unit 14 is not excited by the low-frequency signal, the antenna unit 14 generates a millimeter-wave local signal f LO , a multiplication component of the millimeter-wave local signal f LO and the low-frequency signal f micro , a millimeter-wave signal f MMW, and millimeter-wave. Multiplying component of wave signal f MMW and low frequency signal f micro is radiated, but millimeter wave band has a characteristic that radio wave propagation attenuation is large and it is difficult to interfere with other systems, so other frequency components are radiated. Is allowed. Further, in the low frequency band base station 1 </ b> A, since the millimeter wave band signal is not detected by the low frequency band photodiode 8, only the low frequency signal is radiated through the antenna unit 13.

以上、上り回線において複合変調−電気信号分離方式、下り回線において複合変調−光信号分離方式というように上下回線で異なる方式を採用したいわば複合変調非対称型無線基地局１について説明した。このような複合変調型無線基地局１の場合、中央制御局２が必要とするフォトダイオードが１つ（具体的にはミリ波帯フォトダイオード１１）だけで済むという利点がある。   As described above, the so-called composite modulation asymmetric type radio base station 1 has been described in which different systems such as the composite modulation / electrical signal separation system on the uplink and the composite modulation / optical signal separation system on the downlink are adopted. The composite modulation type radio base station 1 has an advantage that only one photodiode (specifically, the millimeter wave band photodiode 11) is required for the central control station 2.

続いて、不要波を放出しない複合変調対称型無線基地局１について説明する（図５〜図６参照）。この複合変調対称型無線基地局１では、上り回線、下り回線の両方に複合変調−光信号分離方式を採用している。複合変調−光信号分離方式においては、ミリ波ローカル信号を複合変調に用いる必要はないため、周波数スペクトルは図６のようになる。すなわち、複合変調−光信号分離方式は光検波器（ミリ波帯受光素子２０および低周波帯受光素子３０）の応答速度の違いを用いて低周波帯信号とミリ波帯信号とを分離する方法であるが、この場合における低周波帯受光素子３０は応答速度が遅すぎるためにミリ波帯信号を出力できず、結果として、低域通過フィルタとして働くため、低周波帯信号をミリ波帯域にアップコンバートする必要がなく、図６に示すような周波数スペクトルとなる。この図６に示す周波数スペクトルにおいては４本の信号が立ち上っており、このうち左から２番目と４番目の信号は不要放射となり得るがこれら両信号はバンドパスフィルタ（ＢＰＦ）２８により切り取ってしまうことが可能である。   Next, the composite modulation symmetrical radio base station 1 that does not emit unnecessary waves will be described (see FIGS. 5 to 6). This composite modulation symmetric radio base station 1 employs a composite modulation / optical signal separation system for both the uplink and the downlink. In the composite modulation / optical signal separation method, it is not necessary to use a millimeter-wave local signal for composite modulation, so the frequency spectrum is as shown in FIG. That is, the composite modulation-optical signal separation method is a method of separating a low frequency band signal and a millimeter wave band signal by using a difference in response speed between optical detectors (millimeter wave band light receiving element 20 and low frequency band light receiving element 30). However, the low frequency band light receiving element 30 in this case cannot output a millimeter wave band signal because the response speed is too slow. As a result, the low frequency band light receiving element 30 functions as a low-pass filter. There is no need to up-convert, resulting in a frequency spectrum as shown in FIG. In the frequency spectrum shown in FIG. 6, four signals rise, and the second and fourth signals from the left can be unwanted radiation, but both these signals are cut out by the bandpass filter (BPF) 28. It is possible.

下り回線では、中央制御局２において複合変調された光信号が光カプラ２５により分波され、それぞれ低周波帯基地局１Ａ、ミリ波帯基地局１Ｂへと伝送される。低周波帯基地局１Ａでは、低周波帯フォトダイオード８により低周波信号のみが出力され、ミリ波帯基地局１Ｂにおいては低周波信号、ミリ波信号およびミリ波信号と低周波信号の乗算成分がミリ波帯フォトダイオード１１より出力されるが、ミリ波信号のみを切り出すバンドパスフィルタ（ＢＰＦ）２８により、低周波信号およびミリ波信号と低周波信号との乗算成分は除去されるため、ミリ波アンテナ部１４からは所望のミリ波信号のみが放射される。上り回線においても同様に、低周波帯基地局１Ａの低周波帯発光素子（レーザダイオード）１０において信号が低周波信号により強度変調され、強度変調された光信号がミリ波帯基地局１Ｂの外部光変調器５への入力光となり、ミリ波信号によりさらに強度変調されることで複合変調される。複合変調された信号は光カプラによって構成された光分波器２９によって分波された後、中央制御局２において低周波帯受光素子３０、ミリ波帯受光素子２０によりそれぞれ検波される。ミリ波帯受光素子２０の出力信号は、低周波信号、ミリ波信号およびミリ波信号と低周波信号の乗算成分となるが、ダウンコンバータ２１および中間周波帯バンドパスフィルタ（ミリ波帯ＩＦ帯復調器２２）により所望の信号のみを抽出することが可能である。なお、ミリ波帯受光素子２０、低周波帯受光素子３０にはフォトダイオードが使用されている。   On the downlink, the optical signal that has undergone complex modulation in the central control station 2 is demultiplexed by the optical coupler 25 and transmitted to the low frequency band base station 1A and the millimeter wave band base station 1B, respectively. In the low frequency band base station 1A, only the low frequency signal is output from the low frequency band photodiode 8, and in the millimeter wave band base station 1B, the low frequency signal, the millimeter wave signal, and the multiplication component of the millimeter wave signal and the low frequency signal are included. Although output from the millimeter-wave band photodiode 11, the band-pass filter (BPF) 28 that cuts out only the millimeter-wave signal removes the low-frequency signal and the multiplication component of the millimeter-wave signal and the low-frequency signal. Only a desired millimeter wave signal is radiated from the antenna unit 14. Similarly, in the uplink, the signal is intensity-modulated by the low-frequency signal in the low-frequency band light emitting element (laser diode) 10 of the low-frequency band base station 1A, and the intensity-modulated optical signal is external to the millimeter-wave band base station 1B. It becomes input light to the optical modulator 5 and is further subjected to complex modulation by further intensity modulation with a millimeter wave signal. The compositely modulated signal is demultiplexed by an optical demultiplexer 29 composed of an optical coupler, and then detected by the low frequency band light receiving element 30 and the millimeter wave band light receiving element 20 in the central control station 2. The output signal of the millimeter-wave band light receiving element 20 is a low-frequency signal, a millimeter-wave signal, and a multiplication component of the millimeter-wave signal and the low-frequency signal, but the down-converter 21 and the intermediate frequency band-pass filter (millimeter-wave band IF band demodulation). It is possible to extract only the desired signal by means of the device 22). Note that photodiodes are used for the millimeter wave band light receiving element 20 and the low frequency band light receiving element 30.

以上説明した本実施形態の複合変調型無線基地局１によれば、多種の電気信号処理用デバイスを組み合わせる必要がなくなるため構成がより簡単になる。例えば図３に示した複合変調型無線基地局１の場合には中央制御局２に設ける受光素子が１つ（ミリ波帯フォトダイオード２０）で済むなど、より低コストで簡素な無線基地局を構成することが可能となる。したがって、ミリ波帯信号と低周波帯信号とを多重する無線基地局を構成する場合に構成が複雑化してしまうという問題が解決する。   According to the composite modulation type radio base station 1 of the present embodiment described above, the configuration becomes simpler because it is not necessary to combine various electric signal processing devices. For example, in the case of the composite modulation type radio base station 1 shown in FIG. 3, a simple radio base station at a lower cost such as one light receiving element (millimeter wave photodiode 20) provided in the central control station 2 is sufficient. It can be configured. Therefore, the problem that the configuration becomes complicated when a radio base station that multiplexes a millimeter-wave band signal and a low-frequency band signal is configured is solved.

また、本実施形態の複合変調型無線基地局１によれば、送受信装置における必要最低限の光デバイス及びミリ波帯デバイスにより、不要放射のない柔軟な無線基地局を構成することが可能となる。ここでいう不要放射とは例えば図４におけるｆmicroとｆMMWの信号以外の不要な信号が放射されることを指し、仮にこれら不要な信号が空間中に放射されると、同じ周波数の信号を用いる無線信号が近傍に存在した場合に、信号同士が干渉し、特性を劣化させる要因となりうる。これに対し、本実施形態で用いられたようなミリ波帯信号（特に６０ＧＨｚ帯）は大気中における伝搬減衰が大きいことから、たとえ不要放射が発生したとしてもそれが他の無線システムに与える影響は小さい。したがって、本実施形態の複合変調型無線基地局１によれば基地局の配置にかかわりなく他の無線システムに悪影響を及ぼさない（及ぼしにくい）ファイバ無線通信システムを構築することができる。 Further, according to the composite modulation type radio base station 1 of the present embodiment, it is possible to configure a flexible radio base station free from unnecessary radiation by using the minimum necessary optical device and millimeter wave band device in the transmission / reception apparatus. . Unnecessary radiation here means, for example, that unnecessary signals other than the f micro and f MMW signals in FIG. 4 are radiated. If these unnecessary signals are radiated into the space, signals of the same frequency are emitted. When a wireless signal to be used is present in the vicinity, the signals interfere with each other, which can be a factor that degrades the characteristics. On the other hand, the millimeter wave band signal (especially 60 GHz band) as used in the present embodiment has a large propagation attenuation in the atmosphere, so even if unnecessary radiation occurs, it has an effect on other wireless systems. Is small. Therefore, according to the composite modulation type radio base station 1 of the present embodiment, a fiber radio communication system that does not adversely affect other radio systems regardless of the arrangement of the base stations can be constructed.

しかも、上述した波長分割多重方式によれば、大容量無線システムを構築でき、かつ効率的に広域エリアをカバーできる。すなわち、ミリ波帯信号を広帯域に用いることでより高速な無線信号を作ることが可能となることから大容量無線システムを構築することができるようになる。また、波長分割多重方式（ＷＤＭ）と複合変調方式とを組み合わせ、ミリ波帯基地局１Ｂを多数配置することで面的なエリアカバーが可能となり、広域エリアをカバーできるようになる。   Moreover, according to the wavelength division multiplexing system described above, a large-capacity wireless system can be constructed and a wide area can be efficiently covered. That is, a high-speed radio signal can be created by using a millimeter-wave band signal in a wide band, so that a large-capacity radio system can be constructed. Further, by combining a wavelength division multiplexing (WDM) and a complex modulation system and arranging a large number of millimeter wave band base stations 1B, a surface area can be covered, and a wide area can be covered.

また、上述したような複合変調型無線基地局１によれば、より柔軟で付加価値の高い基地局が簡易かつ低コストに構築可能となる。具体的な一例を挙げて説明すれば、例えば４００ＭＨｚ帯移動無線通信装置の電波が届かない不感地帯である山間部に、送電線監視映像伝送用のミリ波帯システムがファイバ無線技術により構築されているような場合において、このミリ波帯システムに対して簡易な変更を施し複合変調型無線基地局１を構築することができる。こうした場合、例えば画像信号を６０ＧＨｚの無線信号とし、この無線信号を４００ＭＨｚ帯の無線信号（例えば音声信号）に多重化することによって音声に映像が付加された信号を送受信することが可能となる。このようなシステムによれば、移動無線通信装置の通信圏外である例えば山岳地帯における電線保守作業時に、撮影した画像と音声とを同時に送受信することによって状況を画像で確認しながら的確な指示をリアルタイムで行うことが可能となるなどの利点がある。   Also, according to the composite modulation type radio base station 1 as described above, a more flexible and high added value base station can be constructed easily and at low cost. To explain with a specific example, for example, a millimeter wave band system for transmission line monitoring video transmission is constructed by fiber radio technology in a mountainous area where the radio wave of a 400 MHz band mobile radio communication device does not reach. In such a case, the composite modulation type radio base station 1 can be constructed by making a simple change to the millimeter wave band system. In such a case, for example, an image signal is a radio signal of 60 GHz, and this radio signal is multiplexed with a radio signal of 400 MHz band (for example, an audio signal), so that a signal in which video is added to audio can be transmitted and received. According to such a system, an accurate instruction is confirmed in real time while confirming the situation on the image by simultaneously transmitting and receiving the photographed image and sound during the electric wire maintenance work outside the communication range of the mobile wireless communication device, for example, in a mountainous area. There are advantages such as being able to be performed in.

なお、上述の実施形態は本発明の好適な実施の一例ではあるがこれに限定されるものではなく本発明の要旨を逸脱しない範囲において種々変形実施可能である。例えば本実施形態では装置２７，２８の具体例として携帯電話機やビデオカメラを示したがその他の通信機器に対しても適用可能であることはいうまでもない。   The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, a mobile phone and a video camera are shown as specific examples of the devices 27 and 28, but it is needless to say that the present invention can be applied to other communication devices.

本発明に係る無線信号の複合変調方法（複合変調−電気信号分離方式）の特徴を示す概略図である。It is the schematic which shows the characteristic of the composite modulation method (composite modulation-electric signal separation system) of the radio signal which concerns on this invention. 本発明に係る無線信号の複合変調方法（複合変調−光信号分離方式）の特徴を示す概略図である。It is the schematic which shows the characteristic of the composite modulation method (complex modulation-optical signal separation system) of the radio signal which concerns on this invention. 複合変調型無線基地局（複合変調−電気信号分離方式）の構成を概略的に示す図である。It is a figure which shows roughly the structure of a composite modulation | alteration radio | wireless base station (complex modulation-electric signal separation system). 複合変調型無線基地局（複合変調−電気信号分離方式）における周波数スペクトルを示す図である。It is a figure which shows the frequency spectrum in a composite modulation type | mold radio | wireless base station (complex modulation-electrical signal separation system). 複合変調型無線基地局（複合変調−光信号分離方式）の構成を概略的に示す図である。It is a figure which shows schematically the structure of a composite modulation | alteration radio | wireless base station (complex modulation-optical signal separation system). 複合変調型無線基地局（複合変調−光信号分離方式）における周波数スペクトルを示す図である。It is a figure which shows the frequency spectrum in a composite modulation type | mold radio | wireless base station (complex modulation-optical signal separation system). 従来における無線信号の複合変調方法（副搬送波多重方式）の特徴を示す概略図である。It is the schematic which shows the characteristic of the composite modulation method (subcarrier multiplexing system) of the conventional radio signal. 従来における無線信号の複合変調方法（波長分割多重方式）の特徴を示す概略図である。It is the schematic which shows the characteristic of the composite modulation method (wavelength division multiplexing system) of the radio signal in the past.

符号の説明Explanation of symbols

１ 複合変調型無線基地局
２ 中央制御局
３ 無線変調部
４ 無線復調部
５ 外部光変調器
６ 光ファイバ
７ 変調装置
８ 低周波フォトダイオード（受光素子）
１０ レーザダイオード（低周波帯発光素子）
１１ ミリ波帯フォトダイオード（ミリ波帯発光素子）
１３ アンテナ部
１４ アンテナ部
２０ ミリ波帯フォトダイオード（ミリ波帯受光素子）
２１ ダウンコンバータ（周波数変換器）
２４ 中間周波帯域電気信号分波器（電気分波器）
２５ 光カプラ（光分波器）
２９ 光カプラ（光分波器）
３０ 低周波帯フォトダイオード（低周波帯受光素子） DESCRIPTION OF SYMBOLS 1 Compound modulation type radio base station 2 Central control station 3 Radio modulation part 4 Radio demodulation part 5 External optical modulator 6 Optical fiber 7 Modulator 8 Low frequency photodiode (light receiving element)
10 Laser diode (low frequency light emitting element)
11 mm-wave band photodiode (millimeter-wave band light emitting device)
13 Antenna part 14 Antenna part 20 Millimeter wave band photodiode (millimeter wave band light receiving element)
21 Down converter (frequency converter)
24 Intermediate frequency band electric signal demultiplexer (electric demultiplexer)
25 Optical coupler (optical demultiplexer)
29 Optical coupler (optical demultiplexer)
30 Low frequency band photodiode (low frequency band light receiving element)

Claims (9)

無線変復調部を備えた中央制御局とアンテナ部を備えた無線基地局とこれら両局を接続する光ファイバとで構成され、周波数の異なる複数の無線信号を多重化するファイバ無線通信システムを利用してこの多重化した信号を光伝送する際の光信号の変調方法であって、外部光変調器への入力光を一の無線信号で予め強度変調しておき、この強度変調した入力光を前記外部光変調器において他の無線信号で更に強度変調することによって複数信号を多重化した後に光伝送することを特徴とする複合変調方法。   It consists of a central control station with a radio modulation / demodulation unit, a radio base station with an antenna unit, and an optical fiber that connects these two stations, and uses a fiber radio communication system that multiplexes multiple radio signals with different frequencies. A method of modulating an optical signal when optically transmitting the multiplexed signal, wherein the input light to the external optical modulator is intensity-modulated in advance with one radio signal, and the intensity-modulated input light is A composite modulation method, wherein a plurality of signals are multiplexed by further intensity-modulating with another radio signal in an external optical modulator, and then optical transmission is performed. 周波数が３０ＧＨｚ以下の低周波帯無線信号により前記入力光を強度変調しておき、この強度変調された入力光を前記外部光変調器へ入力し、この入力光をミリ波帯信号により更に強度変調することを特徴とする請求項１記載の複合変調方法。   The input light is intensity-modulated by a low frequency band radio signal having a frequency of 30 GHz or less, the intensity-modulated input light is input to the external optical modulator, and the input light is further intensity-modulated by a millimeter wave band signal. The composite modulation method according to claim 1, wherein: 前記外部光変調器へ入力されるミリ波帯信号に加えてミリ波帯ローカル信号も入力無線信号とし、前記低周波帯無線信号により強度変調された入力光を更に強度変調することを特徴とする請求項２記載の複合変調方法。   In addition to the millimeter-wave band signal input to the external optical modulator, a millimeter-wave band local signal is also used as an input radio signal, and the intensity of the input light that has been intensity-modulated by the low-frequency band radio signal is further modulated. The composite modulation method according to claim 2. 請求項１から３のいずれかの複合変調方法により複合変調された光信号を光分波器により分離し、ミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波することを特徴とする複合変調された光信号の分離方法。   4. An optical signal modulated by the composite modulation method according to claim 1 is separated by an optical demultiplexer, and the millimeter wave band modulated signal and the low frequency band modulated by the millimeter wave band light receiving element and the low frequency band light receiving element. A method for separating a composite-modulated optical signal, wherein each of the signals is detected. 請求項１から３のいずれかの複合変調方法により複合変調された光信号をミリ波帯受光素子により検波し、その直後に周波数変換器により低周波数に周波数変換し、ミリ波帯中間周波信号と低周波帯信号とを電気分波器により分離することを特徴とする複合変調された光信号の分離方法。   An optical signal that has been composite-modulated by the composite modulation method according to any one of claims 1 to 3 is detected by a millimeter-wave band light-receiving element, and immediately after that, frequency-converted to a low frequency by a frequency converter, A method for separating a composite modulated optical signal, wherein the low frequency band signal is separated by an electric demultiplexer. 無線変復調部を備えた中央制御局と光ファイバで接続されてファイバ無線通信システムを構成し、周波数の異なる複数の無線信号を多重化して光伝送する無線基地局であって、外部光変調器への入力光をこの外部光変調器に入力される前に一の無線信号で予め強度変調しておく変調装置と、この強度変調された入力光を他の無線信号で更に強度変調することによって複数信号を多重化する当該外部光変調器とを備えることを特徴とする複合変調型無線基地局。   A wireless base station that is connected to a central control station equipped with a wireless modulation / demodulation unit via an optical fiber to form a fiber wireless communication system, multiplexes a plurality of wireless signals having different frequencies, and transmits the optical signal to an external optical modulator. And a modulation device that modulates the intensity of the input light in advance with one radio signal before being input to the external optical modulator, and a plurality of optical signals by further intensity-modulating the intensity-modulated input light with another radio signal. A composite modulation type radio base station comprising the external optical modulator for multiplexing signals. 周波数が３０ＧＨｚ以下の低周波帯電気信号を光信号に変換する低周波帯発光素子と、この変換された光信号が入力されるとともにミリ波帯無線信号に基づきこの光信号を更に強度変調する前記外部光変調器とを備え、周波数の異なる複数の無線信号を多重化して前記中央制御局へ光伝送することを特徴とする請求項６記載の複合変調型無線基地局。   The low frequency band light emitting element for converting a low frequency band electric signal having a frequency of 30 GHz or less into an optical signal, and the converted optical signal is input and the intensity of the optical signal is further modulated based on a millimeter wave band radio signal. 7. The composite modulation radio base station according to claim 6, further comprising an external optical modulator, wherein a plurality of radio signals having different frequencies are multiplexed and optically transmitted to the central control station. 前記中央制御局から当該無線基地局への下り回線においては複合変調された光信号を光分波器により分離してミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波する一方、当該無線基地局から前記中央制御局への上り回線においては複合変調された光信号をミリ波帯受光素子により検波し、その直後に周波数変換器により低周波数に周波数変換し、ミリ波帯中間周波信号と低周波帯信号とを電気分波器により分離することを特徴とする請求項６または７記載の複合変調型無線基地局。   In the downlink from the central control station to the radio base station, the composite modulated optical signal is separated by an optical demultiplexer and the millimeter wave band modulated signal and the low frequency are separated by the millimeter wave band light receiving element and the low frequency light receiving element. In the uplink from the radio base station to the central control station, the complex modulated optical signal is detected by a millimeter wave band light receiving element, and immediately after that, a low frequency is detected by a frequency converter. 8. The composite modulation type radio base station according to claim 6 or 7, wherein the frequency is converted into an intermediate frequency signal and the millimeter wave band intermediate frequency signal and the low frequency band signal are separated by an electric demultiplexer. 当該無線基地局から前記中央制御局への上り回線およびこの中央制御局から当該無線基地局への下り回線の両回線において、複合変調された光信号を光分波器により分離してミリ波帯受光素子と低周波帯受光素子によりミリ波帯変調信号と低周波帯変調信号とをそれぞれ検波することを特徴とする請求項６または７記載の複合変調型無線基地局。
In both the uplink from the radio base station to the central control station and the downlink from the central control station to the radio base station, the composite modulated optical signal is separated by an optical demultiplexer and the millimeter wave band 8. The composite modulation type radio base station according to claim 6, wherein the millimeter wave band modulation signal and the low frequency band modulation signal are detected by the light receiving element and the low frequency band light receiving element, respectively.
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