WO2009043272A1 - Terminal de ligne optique, réseau optique passif et méthode de transmission d'un signal rf - Google Patents

Terminal de ligne optique, réseau optique passif et méthode de transmission d'un signal rf Download PDF

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Publication number
WO2009043272A1
WO2009043272A1 PCT/CN2008/072466 CN2008072466W WO2009043272A1 WO 2009043272 A1 WO2009043272 A1 WO 2009043272A1 CN 2008072466 W CN2008072466 W CN 2008072466W WO 2009043272 A1 WO2009043272 A1 WO 2009043272A1
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WO
WIPO (PCT)
Prior art keywords
optical
onu
signal
uplink
downlink
Prior art date
Application number
PCT/CN2008/072466
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English (en)
French (fr)
Inventor
Fan Yu
Jun Zhao
Original Assignee
Huawei Technologies Co., Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Huawei Technologies Co., Ltd. filed Critical Huawei Technologies Co., Ltd.
Priority to JP2010524340A priority Critical patent/JP2010539759A/ja
Priority to EP08800955A priority patent/EP2180614B1/en
Publication of WO2009043272A1 publication Critical patent/WO2009043272A1/zh
Priority to US12/707,100 priority patent/US20100142955A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
    • H04J14/0245—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU
    • H04J14/0246—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for downstream transmission, e.g. optical line terminal [OLT] to ONU using one wavelength per ONU
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2575—Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
    • H04B10/25752—Optical arrangements for wireless networks
    • H04B10/25753—Distribution optical network, e.g. between a base station and a plurality of remote units
    • H04B10/25754—Star network topology
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2587—Arrangements specific to fibre transmission using a single light source for multiple stations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
    • H04J14/0249—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU
    • H04J14/025—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON for upstream transmission, e.g. ONU-to-OLT or ONU-to-ONU using one wavelength per ONU, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0254—Optical medium access
    • H04J14/0261—Optical medium access at the optical multiplex section layer
    • H04J14/0265—Multiplex arrangements in bidirectional systems, e.g. interleaved allocation of wavelengths or allocation of wavelength groups
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0278—WDM optical network architectures
    • H04J14/0282—WDM tree architectures
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0298—Wavelength-division multiplex systems with sub-carrier multiplexing [SCM]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • H04J14/0227—Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
    • H04J14/0241—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
    • H04J14/0242—Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths in WDM-PON
    • H04J2014/0253—Allocation of downstream wavelengths for upstream transmission

Definitions

  • the present invention relates to the field of network communication technologies, and in particular, to an optical line terminal, a passive optical network, and a radio frequency signal transmission method. Background of the invention
  • PON Passive Optical Network
  • a Radio Frequency (RF) signal transmission method is: using a same pair of optical carriers for transmission of RF signals between a central office and a plurality of Base stations (base stations, BSs), that is, In the downlink direction, the central office side modulates the RF signals of different frequencies that need to be sent to multiple BSs to the same downlink optical carrier in a subcarrier multiplexing manner, and the modulated optical signals are transmitted to multiple BSs via the optical fiber, BS.
  • base stations base stations
  • the received optical signal is converted into an electrical signal by a Photo Diode (photodiode, PD), which is converted into an RF signal, and the RF signal of the BS is obtained by filtering, and then the obtained RF signal is amplified and filtered, and transmitted by the antenna.
  • PD Photo Diode
  • multiple BSs need to transmit RF signals of different frequencies sent to the central office to the upstream optical carriers of the same wavelength, and the uplink optical carriers of multiple BSs are mixed at the Remote Node (RN). After that, it is transmitted to the central office via fiber optics.
  • RN Remote Node
  • the photoelectrically converted signal is an RF signal, it can be directly transmitted by the base station. Therefore, the base station does not need to perform secondary modulation mixing on the received signal, so that the PON-based network is compared with the conventional wireless transmission network.
  • the base station has been simplified.
  • the optical fiber only transparently transmits the RF signal as a carrier. Therefore, it is not necessary to make full use of the large-capacity bandwidth resource of the optical fiber network, thereby causing the bandwidth of the wireless access network to be low.
  • Summary of the invention provide an optical line terminal, a passive optical network, and a radio frequency signal transmission method, which can fully utilize the large-capacity bandwidth resource of the optical network, improve the bandwidth of the wireless access network, and have a simple ONU design.
  • An embodiment of the present invention provides an optical line terminal, including:
  • At least one transmitting unit is configured to provide a downlink optical carrier and two uplink optical carriers dedicated to the ONU for the optical network unit ONU, where the downlink RF signal that needs to be sent to the ONU is modulated onto the downlink optical carrier dedicated to the ONU, And the modulated downlink optical carrier is mixed with the two uplink optical carriers dedicated to the ONU to output a downlink optical signal; the two uplink optical carriers dedicated to the ONU are used to carry the uplink radio frequency signal of the ONU;
  • the multiplexing/demultiplexing unit is configured to wavelength-multiplex multiplex the downlink optical signals output by the transmitting units, and then transmit them to the ONU through the optical fiber distribution network ODN, and decompose the uplink optical waves after the wavelength division multiplexing of the ONUs transmitted by the ODN. Using, and outputting the demultiplexed uplink optical signal;
  • the at least one receiving unit is configured to obtain an uplink signal from the demultiplexed uplink optical signal.
  • the embodiment of the present invention further provides a passive optical network, including: an optical line terminal OLT, a fiber distribution network ODN, and at least one optical network unit ONU, where the OLT includes:
  • the at least one transmitting unit is configured to provide the ONU with a downlink optical carrier and two uplink optical carriers dedicated to the ONU, and modulate the downlink RF signal that needs to be sent to the ONU to the downlink optical carrier dedicated to the ONU, and modulate the modulated
  • the downlink optical carrier is mixed with the two uplink optical carriers dedicated to the ONU to output a downlink optical signal; the two uplink optical carriers dedicated to the ONU are used to carry the uplink radio frequency signal of the ONU;
  • a multiplexing/demultiplexing unit configured to wavelength-multiplex multiplex the downlink optical signals output by the respective transmitting units, and then transmit them to the ONU through the ODN, and demultiplex and multiplex the uplink optical waves after the wavelength division multiplexing of the ONUs transmitted by the ODN, and Outputting the demultiplexed uplink optical signal;
  • the at least one receiving unit is configured to obtain an uplink signal from the demultiplexed uplink optical signal.
  • An embodiment of the present invention further provides a radio frequency signal transmission method, where the method includes:
  • the OLT modulates the downlink radio frequency signal sent to the ONU to the downlink optical carrier dedicated to the ONU, and mixes the modulated downlink optical carrier of the ONU with two uplink optical carriers dedicated to the ONU, and mixes the ONUs. After the respective downlink optical signals are wavelength division multiplexed, they are transmitted to the ONU through the ODN;
  • Two uplink optical carriers dedicated to the ONU are used to carry ONU uplink RF signals;
  • the OLT receives the uplink light after the wavelength division multiplexing of each ONU transmitted by the ODN, performs wave decomposition and multiplexing, and acquires an uplink signal from each of the demultiplexed uplink optical signals.
  • the downlink optical carrier dedicated to the ONU and the two uplink optical carriers are mixed, and the mixed downlink optical carriers are wavelength-division multiplexed and transmitted, thereby realizing the ONU colorlessness.
  • the optical carrier can carry more signals, and the large-capacity bandwidth resources of the optical network are fully utilized, thereby improving the bandwidth of the wireless access network.
  • the power spectrum of the modulated signal is enhanced, and the ONU process for amplifying the upstream optical signal is avoided, so that the ONU is simple in design.
  • FIG. 1 is a schematic structural diagram 1 of a passive optical network according to an embodiment of the present invention.
  • FIG. 2 is a schematic diagram showing the frequency relationship of three optical carriers according to an embodiment of the present invention.
  • FIG. 3 is a schematic diagram of a signal spectrum in a mixed downlink optical carrier according to an embodiment of the present invention.
  • FIG. 4 is a schematic diagram of a signal spectrum in a downlink optical carrier after wavelength division multiplexing according to an embodiment of the present invention
  • FIG. 5 is a schematic diagram of a signal spectrum in an uplink optical carrier according to an embodiment of the present invention
  • FIG. 6 is a second schematic structural diagram of a passive optical network according to an embodiment of the present invention. Mode for carrying out the invention
  • the passive optical network in the embodiment of the present invention includes: an Optical Line Terminal (OLT), an Optical Distribution Network (ODN), and at least one Optical Network Unit (ONU).
  • the ONU is generally multiple.
  • the ONU here has a dedicated optical carrier, that is, each ONU corresponds to a dedicated optical carrier, and one ONU has two dedicated upstream optical carriers and one dedicated downstream optical carrier.
  • the OLT includes: a transmitting unit, a multiplexing/demultiplexing unit, and a receiving unit.
  • the number of transmitting units may be one or more, and the number of receiving units may also be one or more.
  • One transmitting unit corresponds to one ONU, and one receiving unit corresponds to one ONU.
  • the number of transmitting units and the number of receiving units can be related to the number of ONUs.
  • the process by which the OLT sends downlink radio signals to multiple ONUs is as follows:
  • Each transmitting unit provides a dedicated downlink optical carrier and two dedicated uplink optical carriers for its corresponding ONU.
  • Two uplink optical carriers dedicated to the ONU provided by the transmitting unit are transmitted to the corresponding ONUs.
  • the two uplink optical carriers dedicated to the ONU are used to carry the uplink RF signals sent by the ONUs to the OLT, that is, the ONUs modulate the uplink RF signals to the transmitting units of the OLT.
  • the uplink optical carrier is provided and transmitted to the OLT through the ODN, thereby achieving colorlessness of the ONU.
  • the two dedicated uplink optical carriers provided for one ONU can satisfy certain conditions.
  • the carrier frequencies of two dedicated uplink optical carriers provided by the transmitting unit for the ONU are /c n /c3 respectively , then /ci and /c3 need to be satisfied.
  • the condition can be - Where: ⁇ -" is the RF frequency of the upstream RF signal.
  • the conditions for satisfying the two uplink optical carriers dedicated to the ONU may be other forms, for example, performing minor adjustments on both sides of the above equations, and the like.
  • the transmitting unit modulates the downlink radio frequency signal sent to the ONU to the downlink optical carrier dedicated to the ONU.
  • the modulation method here may be a carrier-suppression double-band modulation method. Of course, other existing modulation methods may also be used, for example, a double-side band modulation method or the like.
  • Embodiments of the present invention do not limit the modulation scheme for modulating a downlink radio frequency signal onto a downlink optical carrier.
  • the RF frequency of the downlink RF signal here may be a millimeter wave band.
  • the multiplexing/demultiplexing unit in the OLT wavelength-multiplexes the mixed downlink optical signals output from the respective transmitting units, and outputs the wavelength-multiplexed downlink light.
  • the downlink light output by the multiplexing/demultiplexing unit is transmitted to the ONU through the ODN.
  • the downlink light output by the multiplexing/demultiplexing unit is transmitted through the optical fiber to the remote node having the wave decomposition multiplexing function in the ODN.
  • the remote node demultiplexes the downlink optical signals in the optical fibers into the plurality of mixed downlink optical signals, and then transmits the demultiplexed downlink optical signals to different ONUs.
  • the ONU receives the mixed downlink optical signal transmitted by the ODN, and divides the mixed downlink optical signal into two parts.
  • the ONU detects a part of the downlink optical signal (ie, performs photoelectric conversion) to obtain a downlink RF signal in the downlink optical signal after the photoelectric conversion. Another part of the downlink optical signal can be used to carry the uplink radio frequency signal.
  • the ONU can process the downlink radio frequency signal in multiple manners, for example, sending the downlink radio frequency signal directly through the antenna; for example, down-converting the downlink radio frequency signal, and down-converting
  • the processed signal is transmitted to the user terminal through a transmission medium such as a copper wire.
  • the embodiment of the present invention does not limit the specific processing manner of the downlink radio frequency signal after the ONU detects the downlink radio frequency signal.
  • the process of sending multiple uplink signals to multiple OLTs to the OLT is as follows:
  • the ONU directly modulates the uplink radio frequency signal to another part of the downlink optical signal obtained above, generates an uplink optical signal, and sends the uplink optical signal to the OLT through the ODN.
  • the uplink optical signal is transmitted through an optical fiber to a remote node having a wavelength division multiplexing function in the ODN, and the remote node performs wavelength division on the uplink optical signal transmitted by each ONU. Multiplexing, and transmitting the wavelength-multiplexed upstream light to the OLT through the optical fiber.
  • the multiplexing/demultiplexing unit in the OLT receives the uplink light transmitted in the optical fiber, and demultiplexes and multiplexes the uplink optical wave to obtain an uplink optical signal of each ONU, and transmits the uplink optical signal to the corresponding receiving unit.
  • the receiving unit in the OLT After receiving the multiplexed/demultiplexed uplink optical signal, the receiving unit in the OLT obtains an uplink signal from the uplink optical signal. For example, the receiving unit detects the uplink optical signal, and down-converts the detected uplink signal to obtain an uplink signal after the down-conversion processing.
  • the receiving unit can detect the uplink optical signal by using optical frequency heterodyne detection. Of course, other existing detection methods can also be used for detection. For example, a photodiode detection method can be used.
  • the embodiment of the present invention does not limit the specific implementation manner in which the receiving unit in the OLT detects the uplink optical signal.
  • the receiving unit may use the optical signal emitted by the receiving unit as the local oscillator optical signal, or may use the partial downlink optical carrier provided by the transmitting unit as the local oscillator signal.
  • the carrier frequency 2 of the downlink optical carrier can satisfy the following conditions:
  • Fci ⁇ ⁇ RF soil flF ' where //F is the intermediate frequency, which is the RF carrier frequency of the upstream RF signal, «the carrier frequency of one of the two dedicated upstream optical carriers of 0 ⁇ 1 .
  • a passive optical network according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 6.
  • FIG. 1 is a schematic structural diagram of a passive optical network according to an embodiment of the present invention.
  • the passive optical network in Figure 1 shows: OLT, multiple ONUs, and RNs (remote nodes) in the ODN; between the OLT and the RN, and between the RN and each ONU are connected by optical fibers.
  • the OLT includes a plurality of transmitting units, a plurality of receiving units, and a multiplexing/demultiplexing unit (a multiplexing/demultiplexing unit, that is, MUX and DEMUX in Fig. 1).
  • One transmitting unit and one receiving unit correspond to one ONU.
  • the transmitting unit includes: a laser group, a mixer, an MZM (Mach-Zehnder Modulator), and a mixer.
  • the laser group here is the laser module
  • the mixer is the up-conversion module
  • the MZM is the external modulation module
  • the mixer is the hybrid module.
  • the receiving unit includes: a detecting module and a down converting module.
  • the detecting module may further include: a local oscillator module that generates the local oscillator optical signal, and an optical frequency signal generated by the local oscillator module. Probe submodule for heterodyne detection.
  • the ONU includes: PD and EAM.
  • PD Photo Diode
  • EAM electro-absorption modulator
  • the downlink RF signal transmission process in Figure 1 is:
  • the laser group in each transmitting unit transmits a downlink optical carrier and two uplink optical carriers dedicated to the ONU for its corresponding ONU.
  • the carrier frequencies of the three optical carriers are set to /ci , /c2 , and /c3 , where: the optical carrier with the carrier frequency of / C2 is used as the downlink optical carrier for carrying the downlink RF signal; the carrier frequency is ⁇ ⁇
  • the optical carrier of the optical carrier 3 is used as an uplink optical carrier, and is sent to the ONU to carry the uplink radio frequency signal.
  • the receiving unit in the OLT uses the downlink optical carrier as the local oscillator signal for optical frequency heterodyne detection, the frequency relationship between the three optical carriers is as shown in FIG. 2 .
  • ⁇ -" is the RF carrier frequency of the uplink RF signal, for example, 60 GHz can be used ;
  • fKF_a is the RF carrier frequency of the downlink RF signal, for example, ⁇ - can be used at 40 GHz;
  • //F is an intermediate frequency, for example, ⁇ ⁇ can be used at 5 GHz.
  • the carrier frequencies of three optical carriers /ci , /c2 , /c3 need to meet the following conditions:
  • Fci ⁇ fc ⁇ soil flF
  • RF carrier frequency of the upstream RF signal which is the intermediate frequency.
  • f C2 - f cl ⁇ — Struktur ⁇ / F can make the downlink optical carrier /c2 spectrum be located on the left/right side of the modulated uplink RF signal spectrum, and the spacing is an intermediate frequency signal, for example, the spacing is 5GHz, so as to make the uplink
  • the optical device When the optical device is transmitted to the OLT, it can be coherently mixed with part of the downlink carrier 2 to perform optical heterodyne detection to obtain an uplink signal.
  • the signal detected by the OLT may be an intermediate frequency signal due to the modulation mode adopted by the ONU. It is no longer a radio frequency signal. Therefore, in the embodiment of the present invention, the signals detected by the OLT are collectively referred to as an uplink signal.
  • the ONU-dedicated downlink optical carriers transmitted by the laser are respectively sent to the MZM and Rx modules (Note: The Rx module is the Optical heterodyne detection in Figure 1), and the Rx module is the detection module.
  • the two upstream optical carriers of the ONU transmitted by the laser are sent to the mixer.
  • the mixer mixes the downlink data of the ONU and the RF carrier whose RF frequency is in the millimeter wave band (for example, the RF frequency can be 40 GHz), obtains the downlink RF signal of the ONU, and transmits the downlink RF signal to the MZM.
  • the MZM modulates the downlink radio frequency signal transmitted by the mixer to the downlink optical carrier with the carrier frequency of /c2 transmitted by the laser, and transmits the modulated downlink optical carrier to the mixer.
  • the modulated downlink optical carrier and the two upstream optical carriers with carrier frequencies of /ci and f , respectively, are mixed at the mixer to generate a downstream optical signal.
  • the mixer transmits the downstream optical signal to the MUX.
  • the signal spectrum in the downstream optical signal after mixing by the mixer is shown in FIG. In Figure 3, the shaded portion is the signal spectrum in the mixed downstream optical signal.
  • the MUX performs wavelength division multiplexing on the mixed downlink optical signals transmitted by the mixers, and then transmits the wavelength-multiplexed downlink optical fibers to the RN through the optical fibers.
  • Different ONU dedicated uplink and downlink optical carriers can adopt different optical wavelengths.
  • the signal spectrum in the downstream light after wavelength division multiplexing is as shown in Fig. 4.
  • the RN has a multiplexing/demultiplexing function.
  • the RN may select a wavelength division device with a channel spacing of 400 GHz.
  • the RN receives the downlink light transmitted by the OLT in the optical fiber, and demultiplexes the uplink optical carrier and the modulated downlink optical carrier belonging to each ONU from the downlink optical, and the RN belongs to each through the distributed optical fiber connected to each ONU.
  • the uplink optical carrier of the ONU and the modulated downlink optical carrier are transmitted to the respective ONUs.
  • the upstream optical carrier and the modulated downstream optical carrier are downlink optical signals.
  • the ONU receives the uplink optical carrier and the modulated downlink optical carrier transmitted by the RN, and the ONU divides the received downlink optical signal into two parts and provides them to the PD and the EAM.
  • the PD can detect a part of the received downlink optical signal to obtain a downlink radio frequency signal that is carried on the downlink optical carrier, and the PD outputs the detected downlink radio frequency signal, and the downlink radio frequency signal can be directly processed through the antenna after being processed by filtering, amplifying, and the like. Launched.
  • the uplink RF signal transmission process in Figure 1 is:
  • the EAM modulates another part of the received downlink optical signal.
  • the OLT adopts a suppression carrier-side modulation method to modulate the downlink RF signal, so that the downlink optical carrier that modulates the downlink RF signal is suppressed. Therefore, the ONU can directly uplink the RF.
  • the signal is modulated into the other part of the downlink optical signal, and the ONU modulates the uplink RF signal onto the mixed two uplink optical carriers.
  • the ONU modulates the uplink RF signal to the downstream optical signal to generate an upstream optical signal, and outputs the uplink optical signal.
  • the signal spectrum in the EAM-modulated upstream optical carrier is shown in Figure 5.
  • the spectrum of the white portion is the signal spectrum in the modulated upstream optical carrier.
  • the EAM-modulated upstream optical carrier that is, the upstream optical signal
  • the RN performs wavelength division multiplexing on the uplink optical signals of the ONUs to obtain uplink light, and transmits the optical signals to the OLT through the optical fibers.
  • the OLT receives the wavelength division multiplexed uplink light transmitted through the optical fiber, and the DEMUX in the OLT transmits the uplink light.
  • Wave demultiplexing processing is performed to obtain an upstream optical signal, which is an uplink optical carrier modulated by each ONU.
  • the DEMUX transmits the modulated uplink optical carriers of the respective ONUs to the receiving units corresponding to the ONUs.
  • the detecting module in the receiving unit performs optical frequency heterodyne detection on the modulated uplink optical carrier by using a part of the downlink optical carrier transmitted by the corresponding transmitting module, that is, the detecting module uses the partial downlink optical carrier whose carrier frequency is /c2 transmitted by the transmitting module as the local
  • the oscillating signal is coherently mixed with the modulated upstream optical carrier transmitted by the DEMUX, and then the optical frequency heterodyne is detected to obtain an uplink signal carried in the intermediate frequency band and output.
  • the local oscillator signal provided for the detecting submodule may be: an optical signal emitted by the local oscillator module.
  • the detecting sub-module in the detecting module performs the optical frequency heterodyne detection on the uplink optical signal transmitted by the DEMUX by using the local oscillator signal provided by the local oscillator module to obtain an uplink signal and output.
  • the down-conversion module down-converts the uplink signal output by the detection module to obtain an uplink baseband signal.
  • the passive optical network in the embodiment of the present invention may be slightly converted into the passive optical network shown in FIG. 6.
  • the passive optical network in FIG. 6 is basically the same as the passive optical network shown in FIG. 1, and the difference includes: at the ONU, the ONU may include: a PD, an EAM, and a down-conversion module. That is to say, the down-conversion module can down-convert the downlink radio frequency signal detected by the PD, and the downlink signal after the down-conversion processing is transmitted to the user terminal in a wired manner such as copper wire.
  • the passive optical network may further include an ONU unit in a Wavelength Division Multiplex (WDM) PON, and the OLT also includes: a transmitting unit and a receiving unit in the WDM PON.
  • WDM Wavelength Division Multiplex
  • the multi-wavelength optical signal in the WDM PON and the optical wave signal in the embodiment of the present invention are transmitted in a shared optical fiber by means of a multiplexing/demultiplexing module in the OLT and a WDM device in the RN node in a wavelength division multiplexing manner. Since these units are existing units, the processing of the uplink signals and the downlink signals is not described in detail herein.
  • the passive optical network in Figure 6 can implement both wireless and wired services.
  • the passive optical network in the embodiment of the present invention may be combined with WDM PON (Wavelength Division Multiplexed Passive Optical Network) and Radio over Fiber (Fiber Over Ethernet).
  • RoF Hybrid passive optical network for networks.
  • the transmitting unit in the OLT of the embodiment of the present invention provides a dedicated optical carrier for each ONU, and mixes the dedicated uplink and downlink optical carriers of the ONU, and the multiplexing/demultiplexing unit in the OLT mixes the downstream light of each ONU.
  • the signal is wavelength division multiplexed, so that the downlink optical after wavelength division multiplexing can carry more signals, so that the large-capacity bandwidth resources of the optical network are fully utilized, and the bandwidth of the wireless access network is improved.
  • the modulation of the uplink RF signal on the two optical carriers enhances the power spectrum of the modulated signal, and improves the detection sensitivity of the receiving unit of the OLT to the uplink signal; the receiving unit of the OLT further improves the pair by using the optical frequency heterodyne technology.
  • the detection sensitivity of the uplink signal therefore, does not require the use of an amplification module at the ONU, thereby making the design of the ONU simple.
  • the hybrid passive optical network in the embodiment of the present invention not only fully utilizes the advantages of the two networks, but also supports the technical features in the two networks, and obtains technical effects that are not available in the two networks. . Therefore, the hybrid optical network in the embodiment of the present invention is a passive optical network with rich access bandwidth and low construction cost.
  • An OLT provided by an embodiment of the present invention includes: a plurality of transmitting units, a plurality of receiving units, and a multiplexing/demultiplexing unit.
  • One transmitting unit and one receiving unit correspond to one ONU.
  • the transmitting unit includes: a laser module, an up-conversion module, an external modulation module, and a hybrid module.
  • the receiving unit includes: a detecting module and a down converting module.
  • the detecting module may further include: a local oscillator module that generates the local oscillator optical signal, and an optical frequency signal generated by the local oscillator module. Probe submodule for heterodyne detection.
  • the radio frequency signal transmission method provided by the embodiment of the present invention will be described below.
  • the transmission process of the downlink RF signal is:
  • the OLT provides one downlink optical carrier and two upstream optical carriers for each ONU.
  • the carrier frequencies of the three optical carriers are respectively set to /en, fc fc where: the optical carrier with the carrier frequency of ⁇ 2 is used as the downlink optical carrier for carrying the downlink radio frequency signal; the optical carrier with the carrier frequency of /ci and /c3 As an uplink optical carrier, it is sent to the ONU to carry the uplink radio frequency signal.
  • ⁇ -" is the RF frequency of the upstream RF signal.
  • the downlink optical carrier is used as the local oscillator signal at the OLT. In the case of optical frequency heterodyne detection, the conditions that ⁇ 2 need to satisfy can be:
  • the radio frequency carrier frequency of the uplink radio frequency signal is an intermediate frequency.
  • the OLT separately mixes the downlink data of each ONU and the RF carrier whose RF frequency is a millimeter wave band (for example, the RF frequency can be 40 GHz), and obtains downlink RF signals of each ONU.
  • the OLT uses the carrier-suppression double-band modulation mode to modulate the downlink radio frequency signals of the ONUs to the downlink optical carriers provided by the OLTs. For example, the OLT modulates the downlink radio frequency signals of the ONUs to the ONUs.
  • On the downstream optical carrier of f On the downstream optical carrier of f .
  • the dedicated uplink and downlink optical carriers of different ONUs can adopt different optical wavelengths.
  • the OLT mixes the modulated downlink optical carrier of each ONU with the corresponding uplink optical carrier to generate a downlink optical signal of each ONU.
  • the OLT performs wavelength division multiplexing on the downlink optical signals of the ONUs to generate downlink opticals, and then the OLT transmits the wavelength-multiplexed downlink optical fibers to the RN through the optical fibers.
  • the RN has a multiplexing/demultiplexing function.
  • the RN may select a wavelength division device with a channel spacing of 400 GHz.
  • the RN receives the downlink light transmitted by the OLT in the optical fiber, and demultiplexes the uplink optical carrier and the modulated downlink optical carrier belonging to each ONU from the downlink optical, and the RN belongs to each through the distributed optical fiber connected to each ONU.
  • the uplink optical carrier of the ONU and the modulated downlink optical carrier are transmitted to the respective ONUs.
  • the upstream optical carrier and the modulated downstream optical carrier are downlink optical signals.
  • the ONU receives the uplink optical carrier and the modulated downlink optical carrier, and the ONU divides the received downlink optical signal into two parts, and a part of the downlink optical signal is used for detecting the downlink RF signal to obtain the downlink optical signal.
  • the downlink RF signal of the carrier and another part of the downlink optical signal are used to modulate the uplink RF signal.
  • the ONU can detect the downlink RF signal by using the detection mode such as photodiode detection. After the ONU detects the downlink radio frequency signal, the downlink radio frequency signal can be processed in various manners.
  • the downlink radio frequency signal can be filtered, amplified, and the like, and then directly transmitted through the antenna; for example, the downlink radio frequency signal is The down conversion processing is performed, and the signal after the down conversion processing is transmitted to the user terminal through a transmission medium such as a copper wire.
  • the embodiment of the present invention does not limit the specific processing manner of the downlink radio frequency signal after the ONU detects the downlink radio frequency signal.
  • the uplink RF signal transmission process is:
  • the ONU modulates the uplink RF signal of another part of the received downlink optical signal.
  • the OLT adopts the suppression carrier-side modulation method to modulate the downlink RF signal
  • the downlink optical carrier is suppressed.
  • the ONU can directly modulate the uplink RF signal to the other part of the downlink optical signal, that is, the ONU will uplink the RF signal. Modulated onto the two mixed upstream optical carriers.
  • the ONU modulates the uplink RF signal to the downstream optical signal, generates an uplink optical signal, and transmits the upstream optical signal to the RN through the optical fiber.
  • the RN performs wavelength division multiplexing on the uplink optical signals of the ONUs to obtain uplink light, and the uplink opticals are transmitted to the OLT through the optical fibers.
  • the OLT receives the wavelength division multiplexed uplink light transmitted by the optical fiber, and the OLT performs wave decomposition multiplexing processing on the uplink light to obtain an uplink optical signal of each ONU. Then, OLT using the downstream optical carrier which provides for each ONU, respectively upstream optical signal of each ONU performs the optical frequency heterodyne detection, i.e., the OLT carrier frequency of each ONU is ⁇ partial downlink optical carrier 2 as a local oscillation optical signal, The local oscillator signals of the ONUs are coherently mixed with the uplink optical signals of the ONUs, and then the optical frequency heterodyne detection obtains the uplink signals of the ONUs carried in the intermediate frequency band. when However, the OLT can also use its own transmitted optical signal as the local oscillator signal to perform optical frequency difference detection on the upstream optical signal.
  • the OLT can down-convert the detected uplink signal to obtain an uplink baseband signal.
  • the OLT of the embodiment of the present invention provides a dedicated optical carrier for each ONU, and mixes the dedicated uplink and downlink optical carriers of the ONU to mix the downlink optical signals of the ONUs.
  • Wavelength division multiplexing is performed to enable the downlink optical after wavelength division multiplexing to carry more signals, so that the large-capacity bandwidth resources of the optical network are fully utilized, and the bandwidth of the wireless access network is improved.
  • the modulation of the uplink RF signal on the two uplink optical carriers enhances the power spectrum of the modulated signal, which improves the detection sensitivity of the OLT to the uplink signal; the OLT further improves the detection sensitivity of the uplink signal by using the optical frequency heterodyne technology. Therefore, there is no need to use an amplification module at the ONU, which makes the design of the ONU simple.

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Description

光线路终端、 无源光网络和射频信号传输方法
本申请要求于 2007年 9月 26日提交中国专利局、 申请号为 200710122523.3、发明 名称为"光线路终端、 无源光网络和射频信号传输方法"的中国专利申请的优先权， 其全 部内容通过引用结合在本申请中。
技术领域
本发明涉及网络通讯技术领域，具体涉及一种光线路终端、无源光网络和射频信号 传输方法。 发明背景
Passive Optical Network (无源光网络， PON)是一种点到多点的树状网络结构。 由 于 PON具有网络结构简单、 光纤资源共享、成本低、 外部不需要安装有源设备等特点， 因此， PON被公认为最有发展前途的光纤接入技术。
目前， 在基于 PON的网络中， Radio Frequency (射频， RF)信号的传输方法为： 中心局端与多个 Base station (基站， BS)之间利用同一对光载波进行 RF信号的传 输， 也就是说， 在下行方向， 中心局端将需要发送至多个 BS的不同频率的 RF信号以副 载波复用的方式调制到同一个下行光载波上， 调制后的光信号经光纤传至多个 BS， BS 通过 Photo Diode (光电二极管， PD)将接收到的光信号转换为电信号， 即转换为 RF信 号， 并通过滤波得到该 BS的 RF信号， 然后， 将得到的 RF信号放大滤波， 并由天线发送 出去； 在上行方向， 多个 BS需要发送至中心局端的不同频率的 RF信号调制到同一个波 长的上行光载波上， 多个 BS的上行光载波在 Remote Node (远端节点， RN) 处混合后， 经过光纤传输至中心局端。
由于光电转换后的信号即为 RF信号， 可以由基站直接发送， 因此， 基站不需要对 接收到的信号进行二次调制混频， 从而相对于传统的无线传输网络而言， 基于 PON的网 络中的基站得到了简化。
但是， 在实现本发明的过程中， 发明人发现上述现有的 RF信号传输至少存在如下 问题：
在上述 RF信号传输过程中， 光纤仅仅是作为载体对 RF信号进行透明传输， 因此， 没用充分利用光纤网络的大容量带宽资源， 从而导致无线接入网络的带宽低。 发明内容 本发明实施方式提供一种光线路终端、无源光网络和射频信号传输方法，可充分利 用光纤网络的大容量带宽资源， 提高了无线接入网络的带宽， 且 ONU设计简单。
本发明实施方式提供一种光线路终端， 包括：
至少一个发射单元， 用于为光网络单元 ONU提供该 ONU专用的一个下行光载波和 两个上行光载波， 其中， 将需要发送给 ONU的下行射频信号调制到该 ONU专用的下行 光载波上，并将调制后的下行光载波与该 ONU专用的两个上行光载波混合后输出下行光 信号； 所述 ONU专用的两个上行光载波用于承载 ONU上行射频信号；
复用 /解复用单元， 用于将各发射单元输出的下行光信号波分复用后通过光纤分配 网 ODN向 ONU传输， 将 ODN传输来的各 ONU波分复用后的上行光波分解复用， 并输出 解复用后的上行光信号；
至少一个接收单元， 用于从解复用后的上行光信号中获取上行信号。
本发明实施方式还提供一种无源光网络，包括：光线路终端 OLT、光纤分配网 ODN 和至少一个光网络单元 ONU， 所述 OLT包括：
至少一个发射单元， 用于为 ONU提供该 ONU专用的一个下行光载波和两个上行光 载波， 将需要发送给 ONU的下行射频信号调制到该 ONU专用的下行光载波上， 并将调 制后的下行光载波与该 ONU专用的两个上行光载波混合后输出下行光信号； 所述 ONU 专用的两个上行光载波用于承载 ONU上行射频信号；
复用 /解复用单元， 用于将各发射单元输出的下行光信号波分复用后通过 ODN向 ONU传输， 将 ODN传输来的各 ONU波分复用后的上行光波分解复用， 并输出解复用后 的上行光信号；
至少一个接收单元， 用于从解复用后的上行光信号中获取上行信号。
本发明实施方式还提供一种射频信号传输方法， 所述方法包括：
在下行方向：
OLT将发送给 ONU的下行射频信号分别调制到该 ONU专用的下行光载波上， 将所 述 ONU的调制后的下行光载波与该 ONU专用的两个上行光载波混合， 并将各 ONU的混 合后的各下行光信号波分复用后通过 ODN向 ONU传输；
所述 ONU专用的两个上行光载波用于承载 ONU上行射频信号；
在上行方向：
OLT接收 ODN传输来的各 ONU波分复用后的上行光， 并波分解复用， 从所述解复 用后的各上行光信号中获取上行信号。 通过上述技术方案的描述可知， 通过将 ONU专用的下行光载波和两个上行光载波 混合， 并将各混合后的下行光载波波分复用后发送， 在实现 ONU无色化的基础上， 使光 载波能够携带更多的信号， 使光纤网络的大容量带宽资源得到了充分利用， 提高了无线 接入网络的带宽。而且， 通过将上行射频信号在两个上行光载波上调制， 增强了调制信 号的功率谱， 避免了 ONU对上行光信号进行放大的处理过程， 使 ONU设计简单。 附图简要说明
图 1是本发明实施方式的无源光网络结构示意图一；
图 2是本发明实施方式的三个光载波的频率关系示意图；
图 3是本发明实施方式的混合后下行光载波中的信号频谱示意图；
图 4是本发明实施方式的波分复用后的下行光载波中的信号频谱示意图； 图 5是本发明实施方式的上行光载波中的信号频谱示意图；
图 6是本发明实施方式的无源光网络结构示意图二。 实施本发明的方式
下面首先对本发明实施方式的无源光网络进行说明。
本发明实施方式的无源光网络包括： Optical Line Terminal (光线路终端， OLT)、 Optical Distribution Network (光纤分配网， ODN)、 以及至少一个 Optical Network Unit (光网络单元， ONU)。 ONU在一般情况下为多个。 这里的 ONU具有专用的光载波， 即每个 ONU都对应有专用的光载波， 一个 ONU具有两个专用的上行光载波和一个专 用的下行光载波。
OLT包括： 发射单元、 复用 /解复用单元和接收单元。 发射单元的数量可以为一个 或多个， 接收单元的数量也可以为一个或多个。 一个发射单元对应一个 ONU， 且一个 接收单元对应一个 ONU。 发射单元的数量和接收单元的数量可以与 ONU的数量相关。
OLT向多个 ONU发送下行射频信号的过程如下：
各发射单元分别为与其对应的 ONU提供一个专用的下行光载波和两个专用的上行 光载波。 发射单元提供的 ONU专用的两个上行光载波传送给对应的 ONU， ONU专用的 两个上行光载波用于承载 ONU向 OLT发送的上行射频信号，即 ONU将上行射频信号调制 到 OLT的发射单元提供的上行光载波上，并通过 ODN向 OLT发送，从而实现 ONU的无色 化。
为保证 OLT能够准确探测到上行光信号， 保证 OLT接收单元的灵敏度， 发射单元 为一个 ONU提供的两个专用上行光载波可以满足一定的条件， 例如，发射单元为 0NU 提供的两个专用上行光载波的载波频率分别为 /c n /c3，则 /ci、 /c3需要满足的条件可 以为-
Figure imgf000006_0001
其中： ^-"为上行射频信号的射频频率。
当然， 上述 ONU专用的两个上行光载波满足的条件也可以为其它形式， 例如， 对 上述等式两边进行微量调整等等。
发射单元将发送至 ONU的下行射频信号调制到该 ONU专用的下行光载波上。 这里 的调制的方式可以为载波抑制双边带调制方式，当然，也可以采用现有的其它调制方式， 例如， 可以为双边带调制方式等等。本发明实施方式不限制将下行射频信号调制到下行 光载波上的调制方式。这里的下行射频信号的射频频率可以为毫米波波段。在调制完成 后，发射单元将调制后的下行光载波与该 ONU专用的两个上行光载波混合，并输出混合 后的下行光信号。
OLT中的复用 /解复用单元将各发射单元输出的混合后的下行光信号波分复用， 并 输出波分复用后的下行光。
复用 /解复用单元输出的下行光通过 ODN向 ONU传输， 例如， 复用 /解复用单元输出 的下行光通过光纤传输至 ODN中的具有波分解复用功能的远端节点，由该远端节点将光 纤中的下行光解复用为上述多个混合后的下行光信号， 然后， 将解复用后的下行光信号 传输至不同的 ONU。
ONU接收 ODN传输来的混合后的下行光信号， 并将混合后的下行光信号分成两部 分。 ONU对其中一部分下行光信号进行探测（即进行光电转换）， 以获得光电转换后的 下行光信号中的下行射频信号。另一部分下行光信号可以用于承载上行射频信号。 ONU 探测到下行射频信号后， 可以采用多种方式来处理该下行射频信号， 例如， 将该下行射 频信号直接通过天线发送出去； 再例如， 将该下行射频信号进行下变频处理， 并将下变 频处理后的信号通过铜线等传输介质发送给用户终端。本发明实施方式不限制 ONU在探 测到下行射频信号后， 对下行射频信号的具体处理方式。
多个 ONU向 OLT发送上行射频信号的过程如下：
ONU将上行射频信号直接调制到上述获得的另一部分下行光信号上， 生成上行光 信号， 并将此上行光信号通过 ODN向 OLT发送。例如，上行光信号通过光纤传输至 ODN 中的具有波分复用功能的远端节点，该远端节点将各 ONU传输来的上行光信号进行波分 复用， 并将波分复用后的上行光通过光纤传输至 OLT。
OLT中的复用 /解复用单元接收光纤中传输的上行光， 并对该上行光波分解复用， 获得各 ONU的上行光信号， 并传输至对应的接收单元。
OLT中的接收单元接收到复用 /解复用传输来的上行光信号后， 从上行光信号中获 得上行信号。例如， 接收单元对上行光信号进行探测， 并对探测到的上行信号进行下变 频， 从而获得下变频处理后的上行信号。接收单元可以采用光频外差探测方式对上行光 信号进行探测， 当然， 也可以使用现有的其它探测方式进行探测， 例如可以采用光电二 极管探测方式。本发明实施方式不限制 OLT中的接收单元对上行光信号进行探测的具体 实现方式。
接收单元在采用光频外差探测方式对上行光信号进行探测过程中，接收单元可以采 用其自身发射的光信号作为本振光信号，也可以采用发射单元提供的部分下行光载波作 为本振信号。在接收单元采用下行光载波作为本振信号的情况下， 下行光载波的载波频 率 2可以满足如下条件：
fci― ~ RF 土 flF ' 其中， //F为中频频率， 为上行射频信号的射频载波频率， «为0^1的两个 专用上行光载波中的一个上行光载波的载波频率。
下面结合附图 1至附图 6对本发明实施方式的无源光网络进行说明。
图 1为本发明实施方式的无源光网络结构示意图。
图 1中的无源光网络示出了： OLT、 多个 ONU、 以及 ODN中的 RN (远端节点） ； OLT与 RN之间、 以及 RN与各 ONU之间均通过光纤连接。 OLT中包括多个发射单元、 多 个接收单元和一个复用 /解复用单元（复用 /解复用单元即图 1中的 MUX和 DEMUX) 。 一 个发射单元、 以及一个接收单元对应一个 ONU。
发射单元包括： 激光器组、 混频器、 MZM (Mach-Zehnder Modulator, 马赫曾德尔 调制器)、 以及混合器。 这里的激光器组即为激光模块， 混频器即为上变频模块， MZM 即为外调制模块， 混合器即为混合模块。
接收单元包括：探测模块和下变频模块。在探测模块不利用下行光载波作为本振信 号进行光频外差探测时， 探测模块可以进一步包括： 产生本振光信号的本振子模块、 以 及利用本振子模块产生的本振光信号进行光频外差探测的探测子模块。
ONU包括： PD和 EAM。 PD (Photo Diode, 光电二极管） 即为接收模块， EAM ( electro-absorption modulator, 电吸收调制器） 即为调制模块。 图 1中的下行射频信号传输过程为：
每个发射单元中的激光器组为其对应的 ONU发射该 ONU专用的一个下行光载波 和两个上行光载波。 设定这三个光载波的载波频率分别为 /ci、 /c2、 /c3， 其中： 载波 频率为 /C2的光载波作为下行光载波， 用于承载下行射频信号； 载波频率为 ^^π Λ3的 光载波作为上行光载波， 用于下发给 ONU， 以承载上行射频信号。 在 OLT中的接收单 元采用下行光载波作为本振信号进行光频外差探测的情况下，上述三个光载波之间的频 率关系如图 2所示。
图 2中， ^-"为上行射频信号的射频载波频率，例如， 可以采用 60GHz; fKF_a 为下行射频信号的射频载波频率， 例如， ^- 可以采用 40GHz; //F为一个中频频率， 例如， · ^可以采用 5GHz。 三个光载波的载波频率 /ci、 /c2、 /c3需要满足的条件可以为：
Figure imgf000008_0001
fci― fc\ = 土 flF 其中， 为上行射频信号的射频载波频率， 为中频频率。 /c3 _ /ci = 2 x/^-"可以使得承载于 的上行信号在 ONU处同时双边带调制到
/C1、 /C3两个上行光载波上后， 的右边带信号频谱和 /C3的左边带信号频谱在两个上 行光载波的中间处叠加， 从而使调制后的上行光信号的功率谱得到了增强； fC2 - fcl = ^—„± /F可以使得下行光载波 /c2频谱位于调制后的上行射频信号频谱左 侧 /右侧， 间距为一个中频信号， 例如间距为 5GHz， 以便使上行光传送到 OLT时， 可与 部分下行载波 2相干混合来进行光频外差探测，从而获得上行信号。由于 ONU采用的 调制方式等原因， 使 OLT探测到的信号可能会是一个中频信号， 而不再是射频信号， 因此， 在本发明实施方式中， 将 OLT探测到的信号统称为上行信号。
激光器发射的 ONU专用的下行光载波分别发送至 MZM和 Rx模块（注： Rx模块 即图 1中的 Optical heterodyne detection), Rx模块即探测模块。 激光器发射的 ONU的 两个上行光载波发送至混合器。
混频器将 ONU 的下行数据和射频频率为毫米波波段 （例如， 射频频率可以为 40GHz)的射频载波混频，获得 ONU的下行射频信号，并将下行射频信号传输至 MZM。 MZM利用载波抑制双边带调制方式， 将混频器传输来的下行射频信号调制到激光 器传输来的载波频率为 /c2的下行光载波上， 并将调制后的下行光载波传输至混合器。 调制后的下行光载波与载波频率分别为 /ci和 f 的两上行光载波在混合器处进行 混合， 生成下行光信号。 混合器将下行光信号传输至 MUX。 混合器混合后的下行光信 号中的信号频谱如图 3所示。 图 3中， 带阴影的部分为混合后的下行光信号中的信号频 谱。
MUX将各混合器传输来的混合后的下行光信号进行波分复用， 然后， 将波分复用 后的下行光通过光纤传输至 RN。 不同 ONU的专用上下行光载波可以采用不同的光波 长。 波分复用后的下行光中的信号频谱如附图 4所示。
RN具有复用 /解复用功能。在本实施方式中，如果载波频率为 /(^和/< 3的两个上行 光载波之间的间距为 120GHz, 则 RN可以选用 400GHz通道间隔的波分设备。
RN接收光纤中 OLT传输来的下行光， 并从该下行光中解复用出属于各个 ONU的 上行光载波及经调制后的下行光载波， RN通过与各 ONU连接的分布光纤， 将属于各 个 ONU的上行光载波及调制后的下行光载波发送给各个 ONU。这里的上行光载波及经 调制后的下行光载波即为下行光信号。
ONU接收 RN传输来的上行光载波及经调制后的下行光载波， ONU将接收到的下 行光信号分为两部分， 分别提供给 PD和 EAM。 PD可以对接收到的一部分下行光信号 进行探测， 以获得承载于下行光载波的下行射频信号， PD输出探测出的下行射频信号， 该下行射频信号可以在经过滤波、 放大等处理后经天线直接发射出去。
图 1中的上行射频信号传输过程为：
EAM对接收到的另一部分下行光信号进行调制， 由于 OLT采用了抑制载波双边调 制方式来调制下行射频信号， 使调制了下行射频信号的下行光载波得到了抑制， 因此， ONU可以直接将上行射频信号调制到上述另一部分下行光信号中， 也就等于， ONU将 上行射频信号调制到混合的两个上行光载波上。 ONU将上行射频信号调制到下行光信 号上生成上行光信号， 并输出。
EAM调制后的上行光载波中的信号频谱如图 5所示。 图 5中， 白色部分的频谱为 调制后的上行光载波中的信号频谱。
EAM调制后的上行光载波即上行光信号通过光纤传输至 RN。 RN将各 ONU的上 行光信号进行波分复用， 获得上行光， 并通过光纤传输至 OLT。
OLT接收通过光纤传输来的波分复用后的上行光， OLT中的 DEMUX将该上行光 进行波分解复用处理， 以获得各 ONU 的调制后的上行光载波即上行光信号。 DEMUX 将各 ONU的调制后的上行光载波分别传输至 ONU对应的接收单元。
接收单元中的探测模块利用对应发射模块发射的部分下行光载波对调制后的上行 光载波进行光频外差探测， 即探测模块将发射模块发射的载波频率为 /c2的部分下行光 载波作为本振光信号，该本振光信号与 DEMUX传输来的调制后的上行光载波进行相干 混合， 然后光频外差探测， 得到承载于中频频带^^的上行信号， 并输出。
当接收单元中的探测模块包括本振子模块及探测子模块时，为探测子模块提供的本 振光信号可以为： 本振子模块发射的光信号。探测模块中的探测子模块利用本振子模块 提供的本振信号对 DEMUX传输来的上行光信号进行光频外差探测， 以获得上行信号， 并输出。
下变频模块对探测模块输出的上行信号进行下变频处理， 从而获得上行基带信号。 本发明实施方式中的无源光网络可以略加变换为图 6所示的无源光网络。
图 6中的无源光网络与图 1所示的无源光网络基本相同，其区别包括：在 ONU处， ONU可以包括： PD、 EAM和下变频模块。 也就是说， 下变频模块可以对 PD探测到的 下行射频信号进行下变频处理，下变频处理后的下行信号以铜线等有线方式传输给用户 终端。另外，无源光网络中还可以包括 Wavelength Division Multiplex (波分复用， WDM ) PON中的 ONU单元，在 OLT处也应包括： WDM PON中的发射单元和接收单元。 WDM PON中的多波长光信号与本发明实施方式中的光波信号以波分复用的方式通过 OLT中 的复用 /解复用模块和 RN节点的 WDM器件实现在共享的光纤中传输。由于这些单元为 现有的单元， 其具体对上行信号、 下行信号的处理过程在此不再详细说明。 图 6中的无 源光网络可以同时实现无线业务和有线业务。
从上述对无源光网络的描述中可以看出，本发明实施方式中的无源光网络可以为结 合了 WDM PON (波分复用无源光网络） 、 Radio over Fiber (光纤传输无线信号， RoF) 网络的混合无源光网络。本发明实施方式的 OLT中的发射单元通过为各 ONU提供专用光 载波， 并对 ONU的专用上、 下行光载波进行混合， OLT中的复用 /解复用单元对各 ONU 混合后的下行光信号进行波分复用， 使波分复用后的下行光能够携带更多的信号， 从而 使光纤网络的大容量带宽资源得到了充分利用， 提高了无线接入网络的带宽。 而且， 上 行射频信号在两个光载波上的调制增强了调制信号的功率谱，提高了 OLT的接收单元对 上行信号的探测灵敏度； OLT的接收单元通过采用光频外差技术， 进一步提高了对上行 信号的探测灵敏度， 因此， 在 ONU处无需采用放大模块， 从而使 ONU的设计简单。 由此可知， 本发明实施方式的混合无源光网络不但充分发挥了两种网络各自的优 势，而且，使两种网络中的技术特征相互支持，并取得了两种网络均不具备的技术效果。 因此， 本发明实施方式中的混合光网络是一种接入带宽丰富、建设成本较低的无源光网 络。
下面对本发明实施方式提供的 OLT进行说明。
本发明实施方式提供的 OLT包括： 多个发射单元、 多个接收单元和一个复用 /解复 用单元。 一个发射单元、 以及一个接收单元对应一个 ONU。
发射单元包括： 激光模块、 上变频模块、 外调制模块和混合模块。 接收单元包括： 探测模块和下变频模块。在探测模块不利用下行光载波作为本振信号进行光频外差探测 时， 探测模块可以进一步包括： 产生本振光信号的本振子模块、 以及利用本振子模块产 生的本振光信号进行光频外差探测的探测子模块。
上述各模块执行的操作如上述无源光网络中的描述， 在此不再重复说明。
下面对本发明实施方式提供的射频信号传输方法进行说明。
下行射频信号的传输过程为：
OLT针对每个 ONU均提供一个下行光载波和两个上行光载波。设定这三个光载波 的载波频率分别为/ en、 fc fc 其中： 载波频率为 ^2的光载波作为下行光载波， 用 于承载下行射频信号； 载波频率为 /ci和 /c3的光载波作为上行光载波， 用于下发给 ONU，以承载上行射频信号。上述 /(^、 3需要满足的条件可以为： /c3 _ /C1 = 2 x /^_M。 其中： ^-"为上行射频信号的射频频率。 在 OLT采用下行光载波作为本振信号进行光频外差探测的情况下， ^2需要满足的 条件可以为：
fci― ~ RF 土 flF。 其中， 为上行射频信号的射频载波频率， 为中频频率。
OLT分别将各 ONU的下行数据和射频频率为毫米波波段（例如， 射频频率可以为 40GHz) 的射频载波混频， 获得各 ONU的下行射频信号。 OLT利用载波抑制双边带调 制方式， 将各 ONU的下行射频信号分别调制到上述 OLT为各 ONU提供的下行光载波 上， 例如， OLT将各 ONU的下行射频信号分别调制到 ONU的上述载波频率为 f 的下 行光载波上。 不同 ONU的专用上下行光载波可以采用不同的光波长。 OLT将各 ONU的调制后的下行光载波与对应上行光载波进行混合， 生成各 ONU 的下行光信号。 OLT将各 ONU的下行光信号进行波分复用， 生成下行光， 然后， OLT 将波分复用后的下行光通过光纤传输至 RN。
RN具有复用 /解复用功能。在本实施方式中，如果载波频率为 /(^和/< 3的两个上行 光载波之间的间距为 120GHz, 则 RN可以选用 400GHz通道间隔的波分设备。
RN接收光纤中 OLT传输来的下行光， 并从该下行光中解复用出属于各个 ONU的 上行光载波及经调制后的下行光载波， RN通过与各 ONU连接的分布光纤， 将属于各 个 ONU的上行光载波及调制后的下行光载波发送给各个 ONU。这里的上行光载波及经 调制后的下行光载波即为下行光信号。
ONU接收 RN传输来的上行光载波及经调制后的下行光载波， ONU将接收到的下 行光信号分为两部分， 其中一部分下行光信号用于下行射频信号的探测， 以获得承载于 下行光载波的下行射频信号， 另一部分下行光信号用于调制上行射频信号。 ONU可以 采用光电二级管探测等探测方式进行下行射频信号的探测。 ONU探测到下行射频信号 后，可以采用多种方式来处理该下行射频信号，例如，可以对该下行射频信号进行滤波、 放大等处理后， 经天线直接发射出去； 再例如， 将该下行射频信号进行下变频处理， 并 将下变频处理后的信号通过铜线等传输介质发送给用户终端。 本发明实施方式不限制 ONU在探测到下行射频信号后， 对下行射频信号的具体处理方式。
上行射频信号传输过程为：
ONU对接收到的另一部分下行光信号进行上行射频信号的调制。在 OLT采用抑制 载波双边调制方式来调制下行射频信号的情况下， 下行光载波得到了抑制， 此时， ONU 可以直接将上行射频信号调制到上述另一部分下行光信号上， 即 ONU将上行射频信号 调制到混合的两个上行光载波上。 ONU将上行射频信号调制到下行光信号上， 生成上 行光信号， 并将上行光信号通过光纤传输至 RN。
RN将各 ONU的上行光信号进行波分复用， 获得上行光， 上行光通过光纤传输至 OLT。
OLT接收通过光纤传输来的波分复用后的上行光， OLT将该上行光进行波分解复 用处理， 以获得各 ONU的上行光信号。 然后， OLT利用其为各 ONU分别提供的下行 光载波对各 ONU的上行光信号进行光频外差探测，即 OLT将各 ONU的载波频率为 ^2 的部分下行光载波作为本振光信号， 各 ONU的本振光信号分别与各 ONU的上行光信 号进行相干混合，然后光频外差探测得到各 ONU的承载于中频频带 的上行信号。当 然， OLT也可以使用其自身发射的光信号作为本振信号，对上行光信号进行光频外差探
OLT可以对探测到的上行信号进行下变频处理， 从而获得上行基带信号。
从上述对射频信号传输的描述中可以看出， 本发明实施方式的 OLT通过为各 ONU 提供专用光载波， 并对 ONU的专用上、 下行光载波进行混合， 对各 ONU混合后的下行 光信号进行波分复用， 使波分复用后的下行光能够携带更多的信号， 从而使光纤网络的 大容量带宽资源得到了充分利用， 提高了无线接入网络的带宽。 另外， 上行射频信号在 两个上行光载波上的调制增强了调制信号的功率谱，提高了 OLT对上行信号的探测灵敏 度； OLT通过采用光频外差技术，进一步提高了对上行信号的探测灵敏度，因此，在 ONU 处无需采用放大模块， 从而使 ONU的设计简单。
虽然通过实施例描绘了本发明，本领域普通技术人员知道，本发明有许多变形和变 化而不脱离本发明的精神， 本发明的申请文件的权利要求包括这些变形和变化。

Claims

权利要求
1、 一种光线路终端， 其特征在于， 包括：
至少一个发射单元， 用于为光网络单元 0NU提供该 0NU专用的一个下行光载波和 两个上行光载波， 其中， 将需要发送给 ONU的下行射频信号调制到该 ONU专用的下行 光载波上，并将调制后的下行光载波与该 ONU专用的两个上行光载波混合后输出下行光 信号； 所述 ONU专用的两个上行光载波用于承载 ONU上行射频信号；
复用 /解复用单元， 用于将各发射单元输出的下行光信号波分复用后通过光纤分配 网 ODN向 ONU传输， 将 ODN传输来的各 ONU波分复用后的上行光波分解复用， 并输出 解复用后的上行光信号；
至少一个接收单元， 用于从解复用后的上行光信号中获取上行信号。
2、 如权利要求 1所述的光线路终端， 其特征在于， 所述发射单元包括： 激光模块， 用于为 ONU提供专用的一个下行光载波和两个上行光载波； 上变频模块， 用于将发送给 ONU的下行数据和射频频率为毫米波波段的射频载波 混频， 获得 ONU的下行射频信号；
外调制模块， 用于将 ONU的下行射频信号通过载波抑制双边带调制到该 ONU专 用的下行光载波上， 并输出；
混合模块， 用于将 ONU的两个上行光载波和外调制模块输出的下行光载波混合， 并输出混合后的下行光信号。
3、 如权利要求 1所述的光线路终端， 其特征在于， 所述接收单元包括： 探测模块， 用于对 ONU的上行光信号进行光频外差探测， 并输出探测到的上行信 号；
下变频模块， 将所述探测到的上行信号下变频， 获得上行基带信号。
4、如权利要求 3所述的光线路终端， 其特征在于， 所述探测模块将发射单元提供的 部分下行光载波作为本振信号，并利用该本振信号对 ONU的上行光信号进行光频外差探 测； 所述下行光载波的载波频率为 /c2， 且 c2满足：
Figure imgf000014_0001
其中， 为中频频率， 为上行射频信号的射频载波频率， (^为0 的两个 专用上行光载波中的一个上行光载波的载波频率；
或者
所述探测模块包括： 本振子模块， 用于产生本振光信号；
探测子模块， 用于利用本振子模块产生的本振光信号对 ONU的上行光信号进行光 频外差探测， 并输出探测到的上行信号。
5、 如权利要求 1所述的光线路终端， 其特征在于， 所述发射单元为 ONU提供的 两个上行光载波的载波频率为 /c^n /c3， 且满足 /c3 _ /ci = 2 x/^-"， 其中， ―"为上 行射频信号的射频频率。
6、 一种无源光网络， 包括： 光线路终端 OLT、 光纤分配网 ODN和至少一个光网 络单元 ONU， 其特征在于， 所述 OLT包括：
至少一个发射单元， 用于为 ONU提供该 ONU专用的一个下行光载波和两个上行光 载波， 将需要发送给 ONU的下行射频信号调制到该 ONU专用的下行光载波上， 并将调 制后的下行光载波与该 ONU专用的两个上行光载波混合后输出下行光信号； 所述 ONU 专用的两个上行光载波用于承载 ONU上行射频信号；
复用 /解复用单元， 用于将各发射单元输出的下行光信号波分复用后通过 ODN向 ONU传输， 将 ODN传输来的各 ONU波分复用后的上行光波分解复用， 并输出解复用后 的上行光信号；
至少一个接收单元， 用于从解复用后的上行光信号中获取上行信号。
7、 如权利要求 6所述的网络， 其特征在于， 所述发射单元包括：
激光模块， 用于为 ONU提供专用的一个下行光载波和两个上行光载波， 所述两个 上行光载波的载波频率为 /c n /c3， 且满足 /c3 _ /ci = 2 x/^ -"， 其中， 为上行射 频信号的射频频率；
上变频模块， 用于将发送给 ONU的下行数据和射频频率为毫米波波段的射频载波 混频， 获得 ONU的下行射频信号；
外调制模块， 用于将 ONU的下行射频信号通过载波抑制双边带调制到该 ONU专 用的下行光载波上， 并输出；
混合模块， 用于将 ONU的两个上行光载波和外调制模块输出的下行光载波混合， 并输出混合后的下行光信号。
8、 如权利要求 6所述的网络， 其特征在于， 所述接收单元包括：
探测模块， 用于对 ONU的上行光信号进行光频外差探测， 并输出探测到的上行信 号；
下变频模块， 将所述探测到的上行信号下变频， 获得上行基带信号。
9、 一种射频信号传输方法， 其特征在于， 所述方法包括：
在下行方向：
OLT将发送给 ONU的下行射频信号分别调制到该 ONU专用的下行光载波上， 将所 述 ONU的调制后的下行光载波与该 ONU专用的两个上行光载波混合， 并将各 ONU的混 合后的各下行光信号波分复用后通过 ODN向 ONU传输；
所述 ONU专用的两个上行光载波用于承载 ONU上行射频信号；
在上行方向：
OLT接收 ODN传输来的各 ONU波分复用后的上行光， 并波分解复用， 从所述解复 用后的各上行光信号中获取上行信号。
10、如权利要求 9所述的方法， 其特征在于， 所述方法中的下行射频信号包括： 将 发送给 ONU的下行数据和射频频率为毫米波波段的射频载波混频而获得 ONU的下行 射频信号。
11、 如权利要求 9所述的方法， 其特征在于， 所述将 ONU的下行射频信号调制到 该 ONU专用的下行光载波上包括：
将 ONU的下行射频信号通过载波抑制双边带调制到该 ONU专用的下行光载波上。
12、 如权利要求 9所述的方法， 其特征在于， 所述获取上行信号包括：
OLT对 ONU通过 ODN传输来的上行光信号进行光频外差探测，以获得上行信号， 并对所述获得的上行信号进行下变频， 获得上行基带信号。
13、 如权利要求 12所述的方法， 其特征在于， 所述 OLT对 ONU通过 ODN传输 来的上行光信号进行光频外差探测包括：
OLT将 ONU专用的部分下行光载波作为本振光信号，并利用该本振光信号对 ONU 的上行光信号进行光频外差探测； 所述下行光载波的载波频率为 /c2， 且 /c2满足/ e2 - /ei = y^—„± /F， 其中， f'F为 中频频率， 为上行射频信号的射频载波频率， /(^为0 的两个专用上行光载波中 的一个上行光载波的载波频率；
或者所述进行光频外差探测包括： OLT产生本振光信号，并利用所述产生的本振光信号对 ONU的上行光信号进行光频 外差探测。
14、 如权利要求 9所述的方法， 其特征在于， 所述 ONU的两个专用的上行光载波的 载波频率为 /ci和 /c3， 且满足 /c3_/ci =2x/^ -"， 其中， 为上行射频信号的射频 频率。
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