CN102158452A - Optical orthogonal frequency division multiplexing system and method based on avalanche photodiode - Google Patents
Optical orthogonal frequency division multiplexing system and method based on avalanche photodiode Download PDFInfo
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Abstract
本发明提供了一个基于雪崩二极管的光正交频分复用系统和方法，该系统中信号源装置包含的离线DSB模块产生一路调制格式为4QAM-OFDM的数字电信号，数模转换器把其转换成模拟电信号；光链路装置把接收到的模拟电信号调制到光载波上传至远方的接收端，并利用高灵敏度的雪崩二极管进行光电检测，实现了光电转换，获得模拟电信号；信号处理装置对接收的模拟电信号进行带通滤波、模数转换和解调，获得包含信息的高速数据比特，实现了光正交频分复用的传输。
The present invention provides an optical orthogonal frequency division multiplexing system and method based on avalanche diodes. The offline DSB module included in the signal source device in the system generates a digital electrical signal whose modulation format is 4QAM-OFDM, and the digital-to-analog converter converts it to Convert it into an analog electrical signal; the optical link device modulates the received analog electrical signal to an optical carrier and uploads it to the remote receiving end, and uses a high-sensitivity avalanche diode for photoelectric detection to realize photoelectric conversion and obtain an analog electrical signal; signal The processing device performs band-pass filtering, analog-to-digital conversion and demodulation on the received analog electrical signal, obtains high-speed data bits containing information, and realizes optical orthogonal frequency division multiplexing transmission.
Description
Technical field
The present invention relates to the communication technology, particularly a kind of system and method for handing over frequency division multiplexing based on the highly sensitive light positive of avalanche photodide.
Background technology
Development communication technologies is divided into two periods of analog-modulated and digital modulation so far in the modulation system aspect.In the digital modulation stage, a plurality of stages such as amplitude modulation(PAM) (ASK), frequency shift keying (FSK), phase-shift keying (PSK) and multi-system modulation have also been experienced.In PSK research and application,, constantly reform, thereby the differentiation to MPSK occurred especially, also comprise (Gaussian Minimum Shift-frequency Keying) GMSK that is most widely used in mobile communications industry now by 2PSK around the lifting of the availability of frequency spectrum and the error rate.Nowadays, a kind of novel modulation format-OFDM (OFDM) is suggested.It comes from the frequency division multiplexing (FDM) in the analog-modulated, but difference mutually with it, its subcarrier is mutually orthogonal, can utilize simple system to realize the coherent reception of its modulation signal at receiving terminal.It has following advantage:
1: the availability of frequency spectrum improves.In ofdm system, each subcarrier is mutually orthogonal, and allow the spectrum overlapping of subchannel and do not cause interference, at bit rate more greatly and comparatively under the appropriate signal transmitted waveform situation, can be so that band efficiency doubles.
2: chip rate reduces, channel is easy to equilibrium.The OFDM technology is to be N cycle T
sSerial data to be converted into N cycle be NT
sParallel bit as message transmission.Under identical bit, the code element transmission rate reduces, and the bandwidth of each subchannel diminishes.In the frequency band of relative narrower, be easy to realize the equilibrium of channel.
3: the very big application of digital processing signalling technique.The signal modulation of OFDM can realize by discrete digital Fourier transform (DFT), in the swift and violent fast Fourier transform (FFT) of integrated circuit connection development, makes OFDM more be widely used in reality in conjunction with undoubtedly.
4: the modulation format of each subchannel is flexible.Can make whole multipling channel performance improve greatly according to the suitable modulation format of its subchannel feature selecting to guarantee the best transmission of its signal for each subcarrier.
The OFDM modulation technique that has so many advantage is used in the widely used optical fiber communication of primary transmission, can greatly improve signal to the GVD (Group Velocity Dispersion) of optical fiber and the tolerance of polarization mode dispersion, and can compensate the chromatic dispersion in the uncertain optical switching network of linkage length, be fit to very much long haul communication.Yet, exist the higher degree of correlation between each subcarrier, when launched power is too high, can cause between each subcarrier from nonlinear effects such as phase modulated, cross-phase modulation and four wave mixings, produce new frequency component, make that each subcarrier is no longer mutually orthogonal and cause crosstalking between the code element, cause the performance of system significantly to worsen.So how we will study under the situation of relatively low launched power, realize that ofdm signal transmits at the optical fiber middle and long distance.
Fig. 1 is the structural representation that existing light positive is handed over frequency division multiplexing (OOFDM) system, and is existing in conjunction with Fig. 1, and the structure of existing OOFDM system is described, specific as follows:
Existing OOFDM system comprises: signal generator module 10, light delivery module 11 and signal receiving module 12.
12 pairs of analog electrical signals that receive of signal receiving module carry out bandpass filtering and D/A switch, and obtaining modulation format is the digital electric signal of OFDM, and demodulates the signal flow that comprises information.Wherein, signal receiving module 12 comprises electric band pass filter 120, digital to analog converter 121 and field programmable gate array (FPGA) chip 122.Wherein, electric band pass filter is used for the analog electrical signal that receives is carried out bandpass filtering, removes the direct current signal, high fdrequency component and the out-of-band noise that are mixed in the signal of telecommunication, obtains purer analog electrical signal, exports it to AWG (Arbitrary Waveform Generator) AWG121; Digital to analog converter 121 is converted into the digital electric signal that modulation format is OFDM to the analog electrical signal that receives by digital-to-analogue conversion, and exports field programmable gate array (FPGA) chip 122 to; It is that the digital electric signal of OFDM carries out the high-speed data signal that demodulation obtains to comprise information that field programmable gate array (FPGA) chip 122 is used for the modulation format that receives.
Above-mentioned is existing OOFDM system, this system can realize tentatively that lower powered modulation format is the transmission of the signal of telecommunication in light of OFDM, but owing to adopted conventional photodetection pipe PIN, can not satisfy the requirement of receiving terminal sensitivity, making modulation format after the transmission is that the error rate of the signal of telecommunication of OFDM is higher, and the modulation format that has limited high bit rate to a great extent is the long-distance transmissions of the OFDM signal of telecommunication on optical fiber.
Summary of the invention
In view of this, the object of the present invention is to provide a kind of light positive based on avalanche diode to hand over frequency division multiplexing OOFDM system, it is the generation of the OFDM signal of telecommunication that this system is used for modulation format, the transmission on optical link and demodulation and to the processing of this ofdm signal.
Another object of the present invention is to provide a kind of light positive based on avalanche diode to hand over frequency division multiplexing OOFDM method, it is the generation of the OFDM signal of telecommunication that this method is used for modulation format, the transmission on optical link and demodulation and to the processing of this ofdm signal.
For achieving the above object, technical scheme of the present invention specifically is achieved in that
A kind of light positive based on avalanche diode is handed over frequency division multiplexing OOFDM system, and this system comprises: signal source device, optical link device and signal processing apparatus;
Described signal source device is used to produce the 4QAM-OFDM digital electric signal, and utilize digital-to-analogue conversion be translated into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal, output analog electrical signal to optical link device; Described 4QAM-OFDM digital electric signal is that modulation format is the digital electric signal of 4QAM-OFDM; Described spectrum efficiency refers to the ratio of baud rate and shared bandwidth; Described digital-to-analogue conversion is that digital signal is converted into analog signal;
Described optical link device is modulated at the analog electrical signal that receives on the light signal that is adapted at transmitting on the optical fiber by the external modulation technology, and modulated light signal is transmitted on optical fiber, and at receiving terminal analog electrical signal is demodulated from light signal, export signal processing apparatus to; Described external modulation technology promptly is not that signal is directly loaded on laser, but realizes the technology of the light modulation of signal on the modulator externally; The described light signal that is adapted at transmitting on the optical fiber for be used for optical fiber communication now, wave band is near the narrow band light the 1550nm; Described receiving terminal is the terminal of optical link transmission;
Described signal processing apparatus is used for the analog electrical signal that receives is carried out bandpass filtering and analog-to-digital conversion, obtains digital electric signal, and demodulates the high-speed data-flow that contains information; Described bandpass filtering is only to allow required sideband signals by the outer signal of, elimination sideband and the process of noise; Described analog-to-digital conversion is that analog signal is converted into digital signal.Described signal processing apparatus is under the jurisdiction of receiving terminal in the communications field of broad sense, but in this invention for introducing convenient event, it is described as an independent module;
In said apparatus, described signal source device comprises:
The DSB module of reaching the standard grade by the parameter of data in the adjusting module, is carried out the OFDM modulation to the high-speed data-flow that comprises information, obtains the OFDM digital electric signal, and the output OFDM digital electric signal is to the signal shaping device;
The signal shaping device, be used for the OFDM digital electric signal that receives be converted into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal; Its optical link device of output analog electrical signal;
In said apparatus, described optical link device comprises:
Laser links to each other with horse pool modulator by optical fiber, and as the light source of optical link transmission, the light signal that output is adapted at transmitting on the optical fiber is to horse pool modulator;
Signal modulator, be used for the analog electrical signal that receives is modulated to light signal, the light signal entering signal modulator that provides by light source, and the signal of telecommunication control end of the analog electrical signal entering signal modulator that provides by signal source device, continuous variation by the signal modulator terminal voltage, realize the modulation of analog signal, and export modulated light signal to image intensifer to light signal;
Image intensifer is used for the light signal that receives is carried out the as far as possible little amplification of distortion, has avoided like this obscuring at noise too greatly in signal long-distance transmission back decay, causes and can't accurately signal be demodulated;
Optical fiber is used for providing long Distance Transmission path to light signal as transmitting medium;
Avalanche photodide, be used for light signal is converted into the associated signal of telecommunication by photoelectric effect, the output signal of telecommunication is to signal processing apparatus, described avalanche diode structurally can bear higher reverse voltage, thereby at high electric field region of the inner formation of PN junction, utilize charge carrier to form the avalanche multiplication effect in the ionization by collision of high field region, compare with traditional photodetection pipe PIN, the sensitivity of its Photoelectric Detection improves greatly; The described associated signal of telecommunication is an analog electrical signal, comprises direct current signal, modulation signal and corresponding frequency-doubled signal;
In the said apparatus, described signal processing apparatus comprises:
Band pass filter is used for filtering band outer direct current signal, frequency-doubled signal and noise, guarantees the pure of handled signal, and the output inband signaling is to the time domain sample device; Described inband signaling still is an analog signal;
The time domain sample device is converted into digital signal to the analog signal that receives by analog-to-digital conversion, obtains the OFDM digital electric signal, exports it to descending DSB module;
The DSB module that rolls off the production line, by the parameter of data in the adjusting module, the demodulation of the digital signal received of achieving a butt joint, and the model of transmission channel estimated, thus obtained to comprise comparatively accurately the high-speed data-flow signal of information;
A kind of light positive based on avalanche diode is handed over frequency division multiplexing OOFDM method, and this method comprises:
A: by input with adjust the parameter generating 4QAM-OFDM digital electric signal of data in the chip, and utilize digital-to-analogue conversion be translated into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal; Described 4QAM-OFDM digital electric signal is that modulation format is the digital electric signal of 4QAM-OFDM; Described spectrum efficiency refers to the ratio of baud rate and shared bandwidth; Described digital-to-analogue conversion is that digital signal is converted into analog signal;
B: utilize the external modulation technology that the analog electrical signal that receives is modulated on the light signal that is adapted at transmitting on the optical fiber, and modulated light signal is transmitted on optical fiber, and at receiving terminal analog electrical signal is demodulated from light signal, export signal processing apparatus to; Described external modulation technology promptly is not that signal is directly loaded on laser, but realizes the technology of the light modulation of signal on the modulator externally; The described light signal that is adapted at transmitting on the optical fiber for be used for optical fiber communication now, wave band is near the narrow band light the 1550nm; Described receiving terminal is the terminal of optical link transmission;
C: the analog electrical signal that receives is carried out bandpass filtering and analog-to-digital conversion, obtain digital electric signal, and from digital electric signal, demodulate the high-speed data-flow that contains information; Described bandpass filtering is only to allow required sideband signals by the outer signal of, elimination sideband and the process of noise; Described analog-to-digital conversion is that analog signal is converted into digital signal;
In the said method, the described parameter generating OFDM digital electric signal by data in input and the adjustment chip of steps A comprises:
A1: in the binary system high-speed data bit of serial input electric modulator, it is carried out the MQAM modulation, realize the modulation mapping, the acquisition spectrum efficiency is log
2The MQAM digital electric signal of M bit/Hz;
A2: the QAM digital electric signal is carried out serial/parallel conversion, obtain the Parallel Digital signal of telecommunication of N road identical data transmission rate; The symbol period of the described Parallel Digital signal of telecommunication is N a times of serial signal before the conversion; N is the positive integer greater than 1;
A3: the N road Parallel Digital signal of telecommunication is carried out inverse Fourier transform (IFFT), realize the OFDM modulation of signal, obtain the Parallel Digital signal of telecommunication after modulate on the N road; Described N is if equal 2
m, can directly carry out IFFT, otherwise add 2
m-N zero so that realize IFFT; M is the positive integer more than or equal to 1;
A4: the Parallel Digital signal of telecommunication after the modulation of N road is carried out parallel/serial conversion, the Parallel Digital signal of telecommunication after the modulation of N road is combined into one tunnel, obtain the MQAM-OFDM digital electric signal; Mutually orthogonal between each subcarrier of described MQAM-OFDM digital electric signal;
A5: in the sequence of symhols of MQAM-OFDM digital electric signal, add Cyclic Prefix (CP), propagate intersymbol interference (ISI) and the inter-carrier interference (ICI) that causes so that reduce signal when after transmission, carrying out signal processing;
In the said method, the analog electrical signal that the described handle of step B receives is modulated on the light signal that is adapted at transmitting on the optical fiber, and modulated light signal is transmitted on optical fiber, and at receiving terminal analog electrical signal is comprised from the method that light signal demodulates:
B1: utilize the external modulation technology that analog electrical signal is modulated on the light signal;
B2: modulated optical signal is carried out the as far as possible little amplification of distortion, and put it and on optical fiber, transmit;
B3: carry out Photoelectric Detection by avalanche photodide, obtain the associated signal of telecommunication; Described Photoelectric Detection is an opto-electronic conversion, is expressed as on mathematics light signal is asked mould; The described associated signal of telecommunication comprises direct current signal, modulation signal and corresponding frequency-doubled signal;
In the said method, the described method that demodulates the high-speed data-flow that contains information from digital electric signal of step C comprises:
C1: remove the Cyclic Prefix (CP) in the digital signal sequence of symhols that receives, obtain the sampled sequence of OFDM modulated signal;
C2: the sampled sequence of the OFDM modulated signal that step C1 is obtained carries out serial/parallel conversion, obtains 2
mThe digital electric signal that the road is parallel;
C3: with described 2 of step C2 acquisition
mThe digital electric signal that the road is parallel; Carry out fast discrete Fourier transform (FFT), realize the demodulation of OFDM modulation format;
C4: the pilot tone of inserting in the digital electric signal that obtains through step C3 is analyzed, estimated the transfer function of whole communication channel, it is carried out inverse transformation, and carry out convolution with the code element that obtains;
C5: carry out parallel/serial conversion, and carry out the MQAM demodulation, obtain binary system high-speed data bit.
By above technical scheme as seen, the invention provides a kind of system and method for handing over frequency division multiplexing based on the light positive of avalanche photodide, utilize avalanche photodide that the light signal that receives is carried out photodetection in this system, with respect to common PIN pipe, its sensitivity promotes greatly, makes the transmission that (light positive friendship frequency division multiplexing) OOFDM signal of high modulation form can farther distance.
Description of drawings
Fig. 1 is the structural representation that existing light positive is handed over Frequency Division Multiplexing system.
Fig. 2 is the structural representation that the present invention is based on the light positive friendship Frequency Division Multiplexing system of avalanche photodide
Fig. 3 is the flow chart that the present invention is based on the light positive friendship frequency-division multiplexing method of avalanche diode.
Embodiment
For the purposes of the present invention, technical scheme, and advantage clearer, below with reference to the accompanying drawing embodiment that develops simultaneously, the present invention is described in more detail.
The invention provides a light positive and hand over Frequency Division Multiplexing system and method based on avalanche diode, the off-line DSB module that signal source device comprises in this system produces the digital electric signal that one road modulation format is 4QAM-OFDM, and digital to analog converter converts it to analog electrical signal; Optical link device is modulated to the receiving terminal that light carrier is uploaded to a distant place to the analog electrical signal that receives, and utilizes highly sensitive avalanche diode to carry out Photoelectric Detection, has realized opto-electronic conversion, obtains analog electrical signal; Signal processing apparatus carries out bandpass filtering, analog-to-digital conversion and demodulation to the analog electrical signal that receives, and obtains to comprise the high-speed data bit of information, has realized the transmission that light positive is handed over frequency division multiplexing.
Fig. 2 is the structural representation that the present invention is based on the light positive friendship Frequency Division Multiplexing system of avalanche diode, and is existing in conjunction with Fig. 2, hands over the structure of Frequency Division Multiplexing system to describe to the light positive that the present invention is based on avalanche diode, specific as follows:
For sake of clarity, hand over Frequency Division Multiplexing system to define to the light positive that the present invention is based on avalanche diode earlier, DSB off-line module of the present invention can produce the digital electric signal that sub-carrier number is the 4QAM-OFDM of N, and wherein, the span of N is the positive integer more than or equal to 1; The sub-carrier number of the OFDM that system of the present invention selects for use is 64, and wherein, 48 are used to transmit useful information, do channel estimating for 16.
The light positive that the present invention is based on avalanche diode hands over Frequency Division Multiplexing system to comprise: signal source device 20., optical link device 21, signal processing apparatus.
Signal source device 20 is used to produce the 4QAM-OFDM digital electric signal, and utilize digital-to-analogue conversion be translated into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal, output analog electrical signal to optical link device 21.Wherein, the 4QAM-OFDM digital electric signal is that modulation format is the digital electric signal of 4QAM-OFDM; Spectrum efficiency refers to the ratio of baud rate and shared bandwidth; Digital-to-analogue conversion is that digital signal is converted into analog signal.
Wherein, signal source device comprises field programmable gate array (FPGA) chip 200, AWG (Arbitrary Waveform Generator) (AWG) 201.
Field programmable gate array (FPGA) chip 200 links to each other with AWG (Arbitrary Waveform Generator) (AWG) 201, and field programmable gate array (FPGA) chip is the digital electric signal of 4QAM-OFDM with the modulation format that produces.The sub-carrier number of the OFDM digital electric signal that system of the present invention produces is 64, and wherein, 48 are used to transmit useful information, and 16 are used for channel estimating.
AWG (Arbitrary Waveform Generator) (AWG) 201 1 ends link to each other with field programmable gate array (FPGA) chip, other end chain is to optical link device 21, the OFDM digital electric signal that receives be converted into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal; The output analog electrical signal is to optical link device 21, and wherein, the sampling frequency of the AWG (Arbitrary Waveform Generator) that adopts in the system of the present invention is 10Gbit/s, and the speed of the signal that soon transmits in optical link is 10Gbit/s.
Horse pool modulator 211 1 ends link to each other with laser 200, receive the light signal of narrow linewidth laser 200 outputs; Other end chain is to the analog electrical signal that has information of Erbium-Doped Fiber Amplifier EDFA212 received signal source apparatus output; Horse pool modulator 211 utilizes direct intensity modulated that analog electrical signal is modulated on the light signal, and the method for concrete modulation is the content of prior art.The method of existing brief description horse pool modulator 211 signals modulation, be specially: horse pool modulator 211 will be divided into two from the light signal that input port receives and restraint respectively two waveguide arms in modulator and propagate, utilize modulation voltage that the information that contains in electro optic effect and the high-speed data-flow signal changes two waveguide arms in the modulator changing the refractive index of waveguide, thereby change the phase difference between the two-beam of two waveguide arms outputs; Wherein, when the information that contains when the high-speed data-flow signal was 1, modulation voltage made that the phase difference of two-beam of two waveguide arms output is the integral multiple of 2 π, and two-beam is relevant to strengthen the light signal that output is strengthened; When the information that contains when the high-speed data-flow signal was 0, modulation voltage made that the phase difference of two-beam of two waveguide arms output is the integral multiple of π, and the two-beam coherent subtraction does not have light signal output, thereby realizes the modulation of analog electrical signal to light signal.
Erbium-Doped Fiber Amplifier 212 and horse pool modulator 211 links to each other, the amplification of the light signal received of being used to achieve a butt joint, and export Transmission Fibers 213 to.Concrete principle and method of amplifying is the content of prior art, and the amplification principle of existing brief description Erbium-Doped Fiber Amplifier 212 is specially: after flashlight enters Erbium-Doped Fiber Amplifier 212, and inner Er
+ 3The light absorbing energy of particle, by ground state
4I
15/2Jump to the pumping attitude that is in high level, for the different energy level of different pumping wavelength electron transitions, wherein, the energy level that the photoconduction of 1550nm wavelength is sent a telegraph sub-transition is
4I
13/2Because the life time of the electronics of pumping attitude has only 1us, electronics is relaxed to metastable state by pumping attitude Henan in non-radiative mode rapidly, charge carrier has the long life-span on metastable state, under pumping endlessly, population accumulation on the metastable state, the counter-rotating that realizes population distributes, and the state that this moment, Erbium-Doped Fiber Amplifier 212 was positioned is called activated state.Under this state, when flashlight was responded to, metastable particle transitted to ground state in the mode of raying, realized the amplification to input signal light.
The light signal that Transmission Fibers 213 is used for receiving reaches the receiving terminal in a distant place, and wherein, what adopted is the G.655 optical fiber of 50km.
The two ends of avalanche photodide 214 link to each other with signal processing apparatus 22 with Transmission Fibers 213 respectively, by photoelectric effect the light signal that receives is converted into associated analog electrical signal, exporting signal processing apparatus 22 concrete amplification principles to is: after light signal enters avalanche diode 214, the energy of light is absorbed by the P-N of inside knot, forms photoelectric current; And the two ends at the P-N knot add reverse voltage, along with reverse voltage increases, can produce snowslide (photoelectric current surge at double) phenomenon, and the photoelectric current of output is bigger.With respect to the common photoelectric diode, its sensitivity is bigger.
The narrow-band amplifier in electricity territory is used to amplify inband signaling, and outer direct current signal, frequency-doubled signal and the noise of filtering band, guarantees the pure of handled signal, and amplifying signal is to time domain sample device TDS 221 in the output band.Wherein, the three dB bandwidth of the narrow-band amplifier device in the electric territory of being adopted is 1GHz.
Time domain sample device TDS 221, its two ends link to each other with field programmable gate array (FPGA) chip 222 with the narrow-band amplifier 220 in electric territory respectively, be used for the analog electrical signal that receives is carried out the high speed sampling, the digital electric signal of the correspondence that output distortion is less, in order to satisfy time domain sampling theorem, its sampling rate is at least 20Gs/s; So-called time domain sampling theorem promptly for frequency band limits in that (0, time-continuous signal f (t) fh) desires not grudge sampled signals and can recover prime information completely, must make the sample time be at least 1/2fh at interval.
Field programmable gate array (FPGA) chip 222, by adjusting the parameter of data in the chip, the demodulation of the digital signal received of achieving a butt joint, and the model of transmission channel estimated, thus obtained to comprise comparatively accurately the high-speed data-flow signal of information; With fpga chip described in the signal source device be with a kind of device, but function difference;
Fig. 3 is the flow chart that the present invention is based on the light positive friendship frequency-division multiplexing method of avalanche diode.Now, hand over frequency-division multiplexing method to describe to the light positive that the present invention is based on avalanche diode in conjunction with Fig. 3, specific as follows:
Step 301: by the parameter generating 4QAM-OFDM digital electric signal of data in input and the adjusting module, and utilize digital-to-analogue conversion be translated into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal;
In this step, the method that produces the 4QAM-OFDM digital electric signal comprises:
Step 3011: in the binary system high-speed data bit of serial input electric modulator, it is carried out the 4QAM modulation, realize the modulation mapping, obtaining spectrum efficiency is the 4QAM digital electric signal of 2bit/Hz;
Step 3012: the 4QAM digital electric signal is carried out serial/parallel conversion, obtain the Parallel Digital signal of telecommunication of 64 road identical data transmission rates;
Step 3013: 64 tunnel Parallel Digital signals of telecommunication are carried out inverse Fourier transform (IFFT), realize the OFDM modulation of signal, obtain the Parallel Digital signal of telecommunication after 64 tunnel modulation;
Step 3014: the Parallel Digital signal of telecommunication after 64 tunnel modulation is carried out parallel/serial conversion, the Parallel Digital signal of telecommunication after 64 tunnel modulation is combined into one tunnel, obtain the 4QAM-OFDM digital electric signal;
Step 3015: in the sequence of symhols of 4QAM-OFDM digital electric signal, add Cyclic Prefix (CP), propagate intersymbol interference (ISI) and the inter-carrier interference (ICI) that causes so that reduce signal when after transmission, carrying out signal processing.
Step 302: utilize the external modulation technology that the analog electrical signal that receives is modulated on the light signal that is adapted at transmitting on the optical fiber, and modulated light signal is transmitted on optical fiber, and at receiving terminal analog electrical signal is demodulated from light signal, export signal processing apparatus to;
In this step, the method for the signal of telecommunication being carried out light modulation, optical transmission and optical modulator comprises:
Step 3021: utilize the external modulation technology that analog electrical signal is modulated on the light signal, modulated optical signal is amplified, and put it and on optical fiber, transmit;
Step 3022: carry out Photoelectric Detection by avalanche photodide, obtain associated analog electrical signal.
Step 303: the analog electrical signal that receives is carried out bandpass filtering and analog-to-digital conversion, obtain digital electric signal, and from digital electric signal, demodulate the high-speed data-flow that contains information;
In this step, the method that demodulates the high-speed data-flow that contains information from digital electric signal comprises:
Step 3031: remove the Cyclic Prefix (CP) in the digital signal sequence of symhols that receives, and the sampled sequence that obtains is carried out serial/parallel conversion, obtain 6 road parallel signals;
Step 3032: described 6 road parallel signals that step 3031 is obtained carry out fast discrete Fourier transform (FFT), realize the demodulation of OFDM modulation format;
Step 3033: pilot tone is analyzed, estimated the transfer function of channel, it is carried out inverse transformation, and carry out convolution with the code element that obtains;
Step 3034: carry out parallel/serial conversion, and carry out the 4QAM demodulation, obtain binary system high-speed data bit.
In the above-mentioned example of the present invention, adopted avalanche photodide that the light signal that receives is carried out photodetection, with respect to common PIN pipe, its sensitivity promotes greatly, make that the distance of digital electric signal transmission of high modulation form is farther, equate that the error rate after the transmission range is lower.
The above only is preferred embodiment of the present invention, and is in order to restriction the present invention, within the spirit and principles in the present invention not all, any modification of being made, is equal to replacement, improvement etc., all should be included within the scope of protection of the invention.
Claims (8)
1. the light positive based on avalanche diode is handed over frequency division multiplexing OOFDM system, to be used for modulation format be the generation of the OFDM signal of telecommunication, the transmission on optical link and demodulation and to the processing of this ofdm signal, it is characterized in that this system comprises: signal source device, optical link device and signal processing apparatus;
Described signal source device is used to produce the 4QAM-OFDM digital electric signal, and utilize digital-to-analogue conversion be translated into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal, output analog electrical signal to optical link device; Described 4QAM-OFDM digital electric signal is that modulation format is the digital electric signal of 4QAM-OFDM; Described spectrum efficiency refers to the ratio of baud rate and shared bandwidth; Described digital-to-analogue conversion is that digital signal is converted into analog signal;
Described optical link device is modulated at the analog electrical signal that receives on the light signal that is adapted at transmitting on the optical fiber by the external modulation technology, and modulated light signal is transmitted on optical fiber, and at receiving terminal analog electrical signal is demodulated from light signal, export signal processing apparatus to; Described external modulation technology promptly is not that signal is directly loaded on laser, but realizes the technology of the light modulation of signal on the modulator externally; The described light signal that is adapted at transmitting on the optical fiber for be used for optical fiber communication now, wave band is near the narrow band light the 1550nm; Described receiving terminal is the terminal of optical link transmission;
Described signal processing apparatus is used for the analog electrical signal that receives is carried out bandpass filtering and analog-to-digital conversion, obtains digital electric signal, and demodulates the high-speed data-flow that contains information; Described bandpass filtering is only to allow required sideband signals by the outer signal of, elimination sideband and the process of noise; Described analog-to-digital conversion is that analog signal is converted into digital signal.Described signal processing apparatus is under the jurisdiction of receiving terminal in the communications field of broad sense, but in this invention for introducing convenient event, it is described as an independent module.
2. the light positive based on avalanche diode according to claim 1 is handed over Frequency Division Multiplexing system, it is characterized in that described signal source device comprises:
The DSB module of reaching the standard grade by the parameter of data in the adjusting module, is carried out the OFDM modulation to the high-speed data-flow that comprises information, obtains the OFDM digital electric signal, and the output OFDM digital electric signal is to the signal shaping device;
The signal shaping device, be used for the OFDM digital electric signal that receives be converted into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal; Its optical link device of output analog electrical signal.
3. the light positive based on avalanche diode according to claim 1 is handed over Frequency Division Multiplexing system, it is characterized in that described optical link device comprises:
Laser links to each other with horse pool modulator by optical fiber, and as the light source of optical link transmission, the light signal that output is adapted at transmitting on the optical fiber is to horse pool modulator;
Signal modulator, be used for the analog electrical signal that receives is modulated to light signal, the light signal entering signal modulator that provides by laser, and the signal of telecommunication control end of the analog electrical signal entering signal modulator that provides by signal source device, continuous variation by the signal modulator terminal voltage, realize the modulation of analog signal, and export modulated light signal to image intensifer to light signal;
Image intensifer is used for the light signal that receives is carried out the as far as possible little amplification of distortion, has avoided like this obscuring at noise too greatly in signal long-distance transmission back decay, causes and can't accurately signal be demodulated;
Optical fiber is used for providing long Distance Transmission path to light signal as transmitting medium;
Avalanche photodide: be used for light signal is converted into the associated signal of telecommunication by photoelectric effect, the output signal of telecommunication is to signal processing apparatus, described avalanche diode structurally can bear higher reverse voltage, thereby at high electric field region of the inner formation of PN junction, utilize charge carrier to form the avalanche multiplication effect in the ionization by collision of high field region, compare with traditional photodetection pipe PIN, the sensitivity of its Photoelectric Detection improves greatly; The described associated signal of telecommunication is an analog electrical signal, comprises direct current signal, modulation signal and corresponding frequency-doubled signal.
4. the light positive based on avalanche diode according to claim 1 is handed over Frequency Division Multiplexing system, it is characterized in that described signal processing apparatus comprises:
Band pass filter is used for filtering band outer direct current signal, frequency-doubled signal and noise, guarantees the pure of handled signal, and the output inband signaling is to the time domain sample device; Described inband signaling still is an analog signal;
The time domain sample device is converted into digital signal to the analog signal that receives by analog-to-digital conversion, obtains the OFDM digital electric signal, exports it to descending DSB module;
The DSB module that rolls off the production line, by the parameter of data in the adjusting module, the demodulation of the digital signal received of achieving a butt joint, and the model of transmission channel estimated, thus obtained to comprise comparatively accurately the high-speed data-flow signal of information.
5. the light positive based on avalanche diode is handed over frequency division multiplexing OOFDM method, it is characterized in that this method comprises:
A, by the parameter generating MQAM-OFDM digital electric signal of data in input and the adjusting module, and utilize digital-to-analogue conversion be translated into spectrum efficiency higher waveform with analog electrical signal suitable modulated light signal; Described MQAM-OFDM digital electric signal is that modulation format is the digital electric signal of MQAM-OFDM; Described spectrum efficiency refers to the ratio of baud rate and shared bandwidth; Described digital-to-analogue conversion is that digital signal is converted into analog signal;
B, the analog electrical signal that utilizes external modulation technology handle to receive are modulated on the light signal that is adapted at transmitting on the optical fiber, and modulated light signal is transmitted on optical fiber, and at receiving terminal analog electrical signal is demodulated from light signal, export signal processing apparatus to; Described external modulation technology promptly is not that signal is directly loaded on laser, but realizes the technology of the light modulation of signal on the modulator externally; The described light signal that is adapted at transmitting on the optical fiber for be used for optical fiber communication now, wave band is near the narrow band light the 1550nm; Described receiving terminal is the terminal of optical link transmission;
C, the analog electrical signal that receives is carried out bandpass filtering and analog-to-digital conversion, obtain digital electric signal, and from digital electric signal, demodulate the high-speed data-flow that contains information; Described bandpass filtering is only to allow required sideband signals by the outer signal of, elimination sideband and the process of noise; Described analog-to-digital conversion is that analog signal is converted into digital signal.
6. method according to claim 5 is characterized in that, the described parameter generating OFDM digital electric signal by data in input and the adjusting module of steps A comprises:
A1, in the binary system high-speed data bit of the serial input electric modulator, it is carried out the MQAM modulation, realize the modulation mapping, the acquisition spectrum efficiency is log
2The MQAM digital electric signal of M bit/Hz;
A2, the MQAM digital electric signal is carried out serial/parallel conversion, obtain the Parallel Digital signal of telecommunication of N road identical data transmission rate; The symbol period of the described Parallel Digital signal of telecommunication is N a times of serial signal before the conversion; N is the positive integer greater than 1;
A3, the N road Parallel Digital signal of telecommunication is carried out inverse Fourier transform (IFFT), realize the OFDM modulation of signal, obtain the Parallel Digital signal of telecommunication after the modulation of N road; Described N is if equal 2
m, can directly carry out IFFT, otherwise add 2
m-N zero so that realize IFFT; M is the positive integer more than or equal to 1;
A4, the Parallel Digital signal of telecommunication after the N road modulation is carried out parallel/serial conversion, the Parallel Digital signal of telecommunication after the modulation of N road is combined into one the tunnel, obtain the MQAM-OFDM digital electric signal; Mutually orthogonal between each subcarrier of described MQAM-OFDM digital electric signal;
A5, in the sequence of symhols of MQAM-OFDM digital electric signal, add Cyclic Prefix (CP), propagate intersymbol interference (ISI) and the inter-carrier interference (ICI) that causes so that reduce signal when after transmission, carrying out signal processing.
7. method according to claim 6, it is characterized in that, the analog electrical signal that the described handle of step B receives is modulated on the light signal that is adapted at transmitting on the optical fiber, and modulated light signal is transmitted on optical fiber, and analog electrical signal is comprised from the method that light signal demodulates at receiving terminal:
B1, utilize the external modulation technology that analog electrical signal is modulated on the light signal;
B2, modulated optical signal is carried out the as far as possible little amplification of distortion, and put it and on optical fiber, transmit; B3, carry out Photoelectric Detection, obtain the associated signal of telecommunication by avalanche diode; It is opto-electronic conversion that described Photoelectric Detection is surveyed, and is expressed as on mathematics light signal is asked mould; The described associated signal of telecommunication comprises direct current signal, modulation signal and corresponding frequency-doubled signal.
8. method according to claim 6 is characterized in that, the described method that demodulates the high-speed data-flow that contains information from digital electric signal of step C comprises:
C1, remove the Cyclic Prefix (CP) in the digital signal sequence of symhols that receives, obtain the sampled sequence of OFDM modulated signal;
The sampled sequence of C2, OFDM modulated signal that step C1 is obtained carries out serial/parallel conversion, obtains 2
mThe digital electric signal that the road is parallel;
C3, with step C2 obtain described 2
mThe digital electric signal that the road is parallel; Carry out fast discrete Fourier transform (FFT), realize the demodulation of OFDM modulation format;
The pilot tone of inserting in C4, the digital electric signal to process step C3 acquisition is analyzed, and estimates the transfer function of whole communication channel, it is carried out inverse transformation, and carry out convolution with the code element that obtains;
C5, carry out parallel/serial conversion, and carry out the MQAM demodulation, obtain binary system high-speed data ratio.
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