CN102427387A - Optical communication method and system - Google Patents
Optical communication method and system Download PDFInfo
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- CN102427387A CN102427387A CN2011103970650A CN201110397065A CN102427387A CN 102427387 A CN102427387 A CN 102427387A CN 2011103970650 A CN2011103970650 A CN 2011103970650A CN 201110397065 A CN201110397065 A CN 201110397065A CN 102427387 A CN102427387 A CN 102427387A
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Abstract
The invention provides an optical communication method which comprises the steps of: modulating obtained bit stream data to obtain a modulating signal; carrying out differential coding on the modulating signal to obtain a differential coding signal; converting the differential coding signal into an electrical signal; mapping the electrical signal on an optical carrier to form an optical signal; and then transmitting the optical signal. By using the method, on the premise that a frequency spectrum utilization rate is not reduced, the system capability of resisting disturbance among carriers is enhanced; thus, the tolerance of the existing optical communication sysem for resisting laser linewidth, quick change PMD (Physical Media Dependent), nonlinear fiber, disturbance among channels and other damage is enhanced; and system performance is greatly enhanced.
Description
Technical field
The present invention relates to technical field of optical fiber communication, more particularly, relate to a kind of optical communication method and system based on differential coding.
Background technology
In order to improve the availability of frequency spectrum of optical transmission system, people have proposed multi-transceiver technology.Up to now, mainly comprise the super channel that utilizes WDM, OFDM and proposed by the AT&T Labs in 2010.
Wherein, WDM is that the English of wavelength division multiplexing is called for short, and the carrier spacing is generally in tens GHz magnitudes.OFDM is that the English of OFDM is called for short, and is incorporated in the optical communication from radio communication, and the branch of traditional OFDM and full light OFDM is arranged at present; The former is loaded into the ofdm signal that electric territory produces on the light carrier, and subcarrier spacing is therefore very little, generally in the MHz magnitude; And the latter produces in the light territory entirely; Be similar to wdm system, but subcarrier spacing is littler, carrier number is less relatively.Super channel is based on the subcarrier of a plurality of phase lockings of a light source generation, and purpose is the availability of frequency spectrum of the system that increases substantially.
Yet the multicarrier optical communication system of having reported at present mainly is phase shift keying (PSK) modulation technique or quadrature amplitude (QAM) modulation technique, does not relate to the differential coded modulation technology, for example differential amplitude phase shift keying (DAPSK) modulation technique.No matter be the multicarrier system that adopts PSK or QAM coding, all can relate to the problem of inter-carrier interference, to concrete system, there is corresponding the whole bag of tricks to compensate again.
In present research focus-optical OFDM system, because the ofdm signal that adopts conventional modulation system to obtain has higher peak power ratio, the influence that nonlinear fiber is introduced just becomes insoluble problem.For traditional P SK or QAM coded OFDM signal; Generally be to use training sequence, pilot sub-carrier; Perhaps insert a radiofrequency signal separately, utilize these given datas to carry out channel estimating, phase noise compensation etc., this has increased data redudancy on the one hand; Reduce the availability of frequency spectrum, caused the digital signal processing of receiving terminal to become complicated on the other hand.
Summary of the invention
In view of the above problems, the purpose of this invention is to provide a kind of optical communication method and system based on differential coding.Utilize this method and system, can be under the prerequisite that does not reduce the availability of frequency spectrum, the ability of enhanced system antagonism inter-carrier interference, thus improve existing optical communication system antagonism laser linewidth, become the tolerance of PMD, nonlinear fiber and other damages soon.
According to an aspect of the present invention, a kind of optical communication method is provided, comprising: the bitstream data to being obtained is modulated, to obtain modulation signal; Said modulation signal is carried out differential coding, to obtain encoded difference signal; Said encoded difference signal is transformed to the signal of telecommunication; And the said signal of telecommunication is mapped on the light carrier sends after forming light signal.
In the example aspect above-mentioned; At the said signal of telecommunication is under the situation of multi-carrier signal; Said modulation signal is carried out differential coding, can comprise with the step that obtains encoded difference signal: if in time domain, carry out said differential coding, then the same subcarrier to the adjacent code element in the said modulation signal carries out differential coding; If perhaps in frequency domain, carry out said differential coding, then the adjacent sub-carrier to the same code element in the said modulation signal carries out differential coding.
In another example aspect above-mentioned, be under the situation of single-carrier signal at the said signal of telecommunication, said modulation signal is carried out differential coding, can comprise with the step that obtains encoded difference signal: the adjacent code element in the said modulation signal is carried out difference.
In another example aspect above-mentioned, said bitstream data adopts amplitude-phase keying (APSK) to modulate.
In the example aspect above-mentioned, when in time domain, carrying out said differential coding, said method can also comprise: before carrying out said differential coding, said modulation signal is carried out serial/parallel conversion, so that said modulation signal is transformed to parallel signal; And after accomplishing said differential coding, said encoded difference signal is carried out Fourier inversion, adds Cyclic Prefix and carries out parallel/serial conversion, to obtain the OFDM data-signal behind the differential coding.
In the example aspect above-mentioned; When in frequency domain, carrying out said differential coding; Said method can also comprise: after accomplishing said differential coding; Said encoded difference signal is carried out serial/parallel conversion, Fourier inversion, interpolation Cyclic Prefix and carries out parallel/serial conversion, to obtain the OFDM data-signal behind the differential coding.
According to a further aspect in the invention, a kind of optical communication method is provided, has comprised: at transmitting terminal, the bitstream data of being obtained has been modulated, to obtain modulation signal; Said modulation signal is carried out differential coding, to obtain encoded difference signal; Said encoded difference signal is transformed to the signal of telecommunication; And the said signal of telecommunication is mapped on the light carrier sends after forming light signal, and at receiving terminal, convert the light signal of said reception into the corresponding signal of telecommunication; The signal of telecommunication after the said opto-electronic conversion is carried out differential decoding; And the signal of telecommunication that will pass through after said differential decoding is handled carries out demodulation, to obtain said bitstream data.
According to an aspect of the present invention, a kind of transmitter is provided, has comprised: modulating unit is used for the bitstream data of being obtained is modulated, to obtain modulation signal; The differential coding unit is used for said modulation signal is carried out differential coding, to obtain encoded difference signal; Converter unit is used for said encoded difference signal is transformed to the signal of telecommunication; Map unit is used for the said signal of telecommunication is mapped to and forms light signal on the light carrier; And transmitting element, be used to send the light signal that is generated.
In the example aspect above-mentioned; At the said signal of telecommunication is under the situation of multi-carrier signal; If in time domain, carry out said differential coding; Then said differential coding unit carries out differential coding to the same subcarrier of the adjacent code element in the said modulation signal, if perhaps in frequency domain, carry out said differential coding, then said differential coding unit carries out differential coding to the adjacent sub-carrier of the same code element in the said modulation signal.
In the example aspect above-mentioned; Said transmitter can also comprise: the first serial/parallel modular converter, and being used at the said signal of telecommunication is multi-carrier signal and when time domain is carried out differential coding, and said modulation signal is carried out serial/parallel conversion; To obtain parallel signal; Be multi-carrier signal and when in time domain, carrying out differential coding perhaps, said encoded difference signal carried out serial/parallel conversion, to obtain parallel signal at the said signal of telecommunication; The IFFT module is used for the encoded difference signal of said differential coding unit output or the parallel signal of said serial/parallel modular converter output are carried out Fourier inversion; Cyclic prefix adding module is used for to adding Cyclic Prefix through the signal after the Fourier inversion; And the first parallel/serial modular converter, be used for the signal that adds after handling through Cyclic Prefix is carried out parallel/serial conversion, to obtain the ofdm signal behind the differential coding.
In the example aspect above-mentioned, said map unit can comprise: first lasing light emitter is used to produce light carrier; And the light signal generation unit, be used for said encoded difference signal is modulated to and convert light signal on the light carrier into.
According to a further aspect in the invention, a kind of receiver is provided, has comprised: receiving element is used to receive the light signal that said transmitter sends; Photoelectric conversion unit is used for converting the light signal of said reception into the corresponding signal of telecommunication; The differential decoding unit is used for the signal of telecommunication after the said opto-electronic conversion is carried out differential decoding; And demodulating unit, be used for to carrying out demodulation, to obtain said bitstream data through the signal of telecommunication after the said differential decoding cell processing.
In the example aspect above-mentioned, said receiver can also comprise: the second serial/parallel modular converter is used for converting the said signal of telecommunication into parallel signal from serial signal; Cyclic Prefix removes module, is used for removing the Cyclic Prefix of said parallel signal; The FFT module is used for the said signal that removes behind the Cyclic Prefix is carried out Fourier transform; And the second parallel/serial modular converter; Be used for passing through parallel signal after the FFT resume module and convert serial signal into and supply said differential decoding cell processing, the parallel signal that perhaps will after said differential decoding unit is handled the signal of said FFT module output, obtain converts serial signal into.
According to a further aspect in the invention, a kind of optical communication system is provided, has comprised: aforesaid transmitter; And aforesaid receiver.
Utilize above-mentioned according to optical communication method and the system based on differential coding of the present invention; Owing to carried out differential coding at transmitting terminal; Can be under the prerequisite that does not reduce the availability of frequency spectrum; Therefore the ability of enhanced system antagonism inter-carrier interference improves existing system antagonism laser linewidth, becomes the tolerance of PMD, nonlinear fiber, interchannel interference and other damages soon, has greatly improved systematic function.In addition, the present invention does not need given datas such as training sequence, pilot sub-carrier the auxiliary backoff algorithm such as channel estimating that carries out can improve systematic function simultaneously, has improved the effective speed and the spectrum efficiency of system greatly.
In order to realize above-mentioned and relevant purpose, one or more aspects of the present invention comprise the characteristic that the back will specify and in claim, particularly point out.Following explanation and accompanying drawing have specified some illustrative aspects of the present invention.Yet, the indication of these aspects only be some modes that can use in the variety of way of principle of the present invention.In addition, the present invention is intended to comprise all these aspects and their equivalent.
Description of drawings
Through with reference to below in conjunction with the explanation of accompanying drawing and the content of claims, and along with to more complete understanding of the present invention, other purpose of the present invention and result will understand more and reach easy to understand.In the accompanying drawings:
Fig. 1 is the block diagram based on the optical communication system of differential coding according to the embodiment of the invention;
Fig. 2 A-2C is the sketch map of the differential coding process in the transmitter among Fig. 1;
Fig. 3 A-3C is the sketch map of the differential decoding process in the receiver among Fig. 1;
Fig. 4 is the sketch map how the present invention produces frequency domain differential demodulation APSK (f-DAPSK) and time-domain difference APSK (t-DAPSK) signal;
Fig. 5 is the generation of f-DAPSK of the present invention and t-DAPSK signal and the principle schematic of demodulating process;
Fig. 6 is that what to produce according to the embodiment of the invention is the planisphere of example with the 16APSK signal;
Fig. 7 is to be the concrete mode of generation APSK signal of example according to the embodiment of the invention with the 16APSK signal;
Fig. 8 is the sketch map that produces the DAPSK signal according to the frequency domain of the embodiment of the invention;
Fig. 9 is the sketch map that produces the DAPSK signal according to the time domain of the embodiment of the invention;
Figure 10 is the sketch map according to the generative process of the light DAPSK signal of the embodiment of the invention;
Figure 11 is the sketch map that produces light DAPSK signal according to the relevant mapping of the embodiment of the invention;
Figure 12 is the structural representation according to the Direct-Detection Optical DAPSK signal of the embodiment of the invention;
Figure 13 is the structural representation according to the coherent detection light DAPSK signal of the embodiment of the invention;
Figure 14 is the flow chart according to the method for carrying out at the transmitter place of the embodiment of the invention;
Figure 15 is the flow chart according to the method for carrying out at the receiver place of the embodiment of the invention;
Figure 16 shows under situation back-to-back the Q value with the change curve of the OSNR of receiver;
Figure 17 shows the change curve of Q value cost under the different accumulated chromatic dispersions;
Figure 18 shows through the change curve of 480km transmission back Q value with incident power;
Figure 19 shows through the spectrogram before and after the 480km transmission;
Figure 20 shows through the change curve of 480km transmission back Q value with incident power.
Identical label is indicated similar or corresponding feature or function in institute's drawings attached.
Embodiment
Below will combine accompanying drawing that embodiments of the invention are described.Obviously, described embodiment only is a part of embodiment of the present invention, rather than whole embodiment.Based on the embodiment among the present invention, the every other embodiment that those of ordinary skills are obtained under the prerequisite of not paying creative work belongs to the scope that the present invention protects.
In order under the prerequisite that does not reduce the availability of frequency spectrum, to strengthen the ability of antagonism inter-carrier interference; Optical communication system according to the present invention uses differential encoding that the bitstream data that will send is encoded at transmitting terminal; And the differential coding signal of telecommunication that is produced is modulated on the light carrier sends as light signal; And the differential decoding technology in that the receiving terminal utilization is corresponding is decoded to the light signal that is received, thereby obtains the bitstream data of being sent.Utilize this method, signal is carried out differential modulation, thereby improve optical communication system antagonism laser linewidth, become the tolerance of PMD, nonlinear fiber and other damages soon, improve the performance of communication system through transmitting terminal at signal.
In the following description, adopt the APSK modulation technique to describe as an example, but should be appreciated that, also can adopt other modulation technique, such as QAM, BPSK, QPSK etc.
Fig. 1 shows the block diagram according to the optical communication system 100 based on difference APSK (DAPSK) of the present invention.
As shown in Figure 1, said optical communication system 100 comprises transmitter 110 and receiver 120, and wherein, said transmitter 110 comprises modulating unit 111, differential coding unit 113, converter unit 115, map unit 117 and transmitting element 119.Said receiver 120 comprises receiving element 121, photoelectric conversion device 122, differential decoding unit 125 and demodulating unit 127.
At the transmitter place, 111 pairs of bitstream data of being obtained of modulating unit are modulated, to obtain modulation signal.Said bitstream data can be imported from the external world, also can be that transmitter 110 inner data signal sources produce.The 113 pairs of said modulation signals in differential coding unit carry out differential coding, obtaining encoded difference signal, and are transported to converter unit 115.Converter unit 115 is the signal of telecommunication with said differential coding data conversion.Here, said converter unit 115 typically refers to the D/A converter unit, and being used for digital signal conversion is analog electrical signal.
Then, map unit 117 is mapped to the said signal of telecommunication and forms light signal on the light carrier, and sends the light signal that is generated through transmitting element 119.
Below the logical construction of coupling system is done further explanation to signal processing of the present invention.
Differential coding signal of telecommunication generative process
Obtain the signal of telecommunication behind the differential coding about how based on bitstream data, will combine Fig. 2 A to specify as follows to 2C.
When the said signal of telecommunication is multi-carrier signal; Shown in Fig. 2 A and 2B; Except modulating unit 111, differential coding unit 113 and converter unit 115, said transmitter also comprises first serial, IFFT unit, Cyclic Prefix adding device and the first parallel/serial converting unit.
In this case, if said differential coding carries out, then when carrying out differential coding, the same subcarrier of the adjacent code element in the said modulation signal is carried out difference in time domain, this mode is also referred to as the time-domain difference coding.In this case, shown in Fig. 2 A, after 111 pairs of bitstream data of being obtained of modulating unit were modulated the acquisition modulation signal, said first serial was carried out serial/parallel conversion to said modulation signal, to obtain parallel signal.The 113 pairs of said parallel signals in said differential coding unit carry out differential coding, and said then IFFT unit carries out Fourier inversion to the encoded difference signal of said differential coding unit 113 outputs, so that said signal is transformed into time domain from frequency domain.Then, the Cyclic Prefix adding device is to adding Cyclic Prefix through the signal after the above-mentioned Fourier inversion.Then, the first parallel/serial converting unit is changed to serial signal (that is, the ofdm signal behind the differential coding) with the parallel signal transformation of adding through Cyclic Prefix after handling, and exports to D/A converter unit 115.
If said differential coding carries out in frequency domain, then when carrying out differential coding, the adjacent sub-carrier of the same code element in the said modulation signal is carried out difference, this mode is also referred to as the frequency domain differential demodulation coding.In this case, shown in Fig. 2 B, after 111 pairs of bitstream data of being obtained of modulating unit were modulated the acquisition modulation signal, the 113 pairs of said modulation signals in said differential coding unit carried out differential coding.Then, said first serial is carried out serial/parallel conversion to said encoded difference signal, to obtain parallel signal.Then, said IFFT unit carries out Fourier inversion to the parallel signal of said first serial output, so that said signal is transformed into time domain from frequency domain.Then, the Cyclic Prefix adding device is to adding Cyclic Prefix through the signal after the above-mentioned Fourier inversion.Then, the first parallel/serial converting unit is changed to serial signal (that is, the ofdm signal behind the differential coding) with the parallel signal transformation of adding through Cyclic Prefix after handling, and exports to D/A converter unit 115.
When the signal of telecommunication behind resulting differential coding was single-carrier signal, shown in Fig. 2 C, 111 pairs of bitstream data of being obtained of modulating unit were modulated, to obtain modulation signal.Then, the adjacent code element in the 113 pairs of said modulation signals in said differential coding unit is carried out differential coding, to obtain encoded difference signal.Then, said D/A converter unit is transformed to the signal of telecommunication with said encoded difference signal.The signal of telecommunication that is generated can send through single light carrier or a plurality of light carrier.
Mapping process
Map unit 117 is used for the signal of telecommunication that obtains behind the differential coding is mapped to and forms light signal on the light carrier.
In said bitstream data is the bitstream data of Direct-Detection Optical ofdm system input when (that is, said transmitter is used for the Direct-Detection Optical ofdm system), and said map unit 117 comprises: first lasing light emitter and light signal generation unit.Said first lasing light emitter is used to produce light carrier; Said light signal generation unit is used for the signal of telecommunication behind the said differential coding is modulated to and converts light signal on the light carrier into, sends for transmitting element.
Said bitstream data be coherent light ofdm system input bitstream data (promptly; Said transmitter is used for the relative photo ofdm system) time; Except first lasing light emitter, light signal generation unit; Said map unit 117 also comprises the one 90 degree light phase biasing device, is used for 90 ° of the phase changes of the light signal after the said conversion.
In receiver 120, receiving element 121 is used to receive the light signal that said transmitter sends.Photoelectric conversion unit 123 is used for converting the light signal of said reception into the corresponding signal of telecommunication.Differential decoding unit 125 is used for the signal of telecommunication after the said opto-electronic conversion is carried out differential decoding.Demodulating unit 127 is used for to carrying out demodulation through the signal of telecommunication after the said differential decoding cell processing, to obtain said bitstream data.
Wherein, adopt directly detection or coherent detection according to receiver 220, photoelectric conversion device 123 is divided into direct checkout gear and coherent detection device.
Directly checkout gear comprises optical filter and photodiode.
Wherein, optical filter is used to extract the light carrier that carries desired signal; Photodiode is used for light signal is converted into the signal of telecommunication.
The coherent detection device comprises optical filter, second lasing light emitter, 90 degree optical mixer unit and photodiodes, can also comprise optical coupler.
Wherein, optical filter is used to extract the DAPSK light signal on the light carrier, and lasing light emitter is used to produce local light carrier; 90 degree optical mixer units carry out mixing with filtered DAPSK light signal and local light carrier; Photodiode is used for the DAPSK light signal after the mixing is converted into the DAPSK signal of telecommunication; Lasing light emitter, 90 degree optical mixer units and photodiode connect.
Equally, similar with the said circumstances in the transmitter, be single-carrier signal or multi-carrier signal according to the resulting DAPSK signal of telecommunication, after obtaining the DAPSK signal of telecommunication, adopt different processing modes.
When the resulting DAPSK signal of telecommunication was multi-carrier signal, shown in Fig. 3 A and 3B, said receiver also comprised second serial, cp removal unit, FFT unit and the second parallel/serial converting unit.
If said differential coding carries out in time domain, when then carrying out the processing of the DAPSK signal of telecommunication at the receiver place, shown in Fig. 3 A, the said second serial/parallel conversion converts the said signal of telecommunication into parallel signal from serial signal.Cyclic Prefix removes the Cyclic Prefix in the said parallel signal of module removal.Then, said FFT module is used for the said signal that removes behind the Cyclic Prefix is carried out Fourier transform.Said differential decoding unit is to carrying out differential decoding through the parallel signal after the Fourier transform.Then, the parallel signal that the second parallel/serial converting unit will be exported in said differential decoding unit converts serial signal into, and this serial signal is exported to demodulating unit carry out demodulation.
If said differential coding carries out in frequency domain, when then carrying out the processing of the DAPSK signal of telecommunication at the receiver place, shown in Fig. 3 B, the said second serial/parallel conversion converts the said signal of telecommunication into parallel signal from serial signal.Cyclic Prefix removes the Cyclic Prefix in the said parallel signal of module removal.Then, said FFT module is used for the said signal that removes behind the Cyclic Prefix is carried out Fourier transform.The parallel signal that the said second parallel/serial converting unit will be passed through after the FFT resume module converts serial signal into.Said differential decoding unit carries out differential decoding to the serial signal after changing, and the signal behind the differential decoding is exported to demodulating unit carry out demodulation.
When the resulting DAPSK signal of telecommunication is single-carrier signal, shown in Fig. 3 C, at first,, the said DAPSK signal of telecommunication is transformed to digital signal from analog signal through the A/D converter unit.Then, said differential decoding unit carries out differential decoding to said digital signal, and said differential decoding mode is corresponding with the differential coding mode in the transmitter.Then, the data behind the differential decoding are outputed to demodulating unit carry out demodulation, to obtain said bitstream data.
In the DAPSK modulation format that the present invention uses, no matter be that signal does not need given datas such as training sequence, pilot sub-carrier, when receiving terminal, does not have extra backoff algorithm consumption such as channel estimating yet at the frequency domain or the DAPSK signal of time domain generation.Depend on the difference relation that transmitting terminal is introduced just; Above-mentioned multicarrier optical communication method and system provided by the invention based on DAPSK; The auxiliary backoff algorithms such as channel estimating that carry out that do not need given datas such as training sequence, pilot sub-carrier; And can effectively reduce inter-carrier interference, the antagonism laser linewidth, become the tolerance of PMD, nonlinear fiber, interchannel interference and other damages soon.
Fig. 4 is the structural representation at frequency domain generation f-DAPSK and t-DAPSK signal according to the embodiment of the invention.This structural representation is drawn signal according to time orientation and frequency direction, wherein 401 represent the longitudinal axis, and promptly frequency axis is spaced apart a number of sub-carrier, 402 expression transverse axis, and promptly time shaft is spaced apart a code element.Data carried by data on the number of sub-carrier in code element of 403 expressions.The direction that frequency domain differential demodulation produces f-DAPSK is carried out in 404 expressions, promptly along the adjacent sub-carrier of same code element.The direction that time-domain difference produces t-DAPSK is carried out in 405 expressions, the adjacent code element of promptly carrying on the same subcarrier.
Fig. 5 is the generation of f-DAPSK of the present invention and t-DAPSK signal and the principle schematic of demodulating process, has specifically introduced how to generate the DAPSK signal and how to realize non-coherent demodulation.As shown in Figure 5; Complex signal on i the code element k number of sub-carrier behind the 501 expression differential codings; Complex signal on i the code element k number of sub-carrier before the 502 expression differential codings, the complex signal on i the code element k-1 number of sub-carrier behind the 503 expression differential codings.Therefore, for the f-DAPSK signal, be to carry out difference to the information of the adjacent sub-carrier of same code element to obtain.
Complex signal on i the code element k number of sub-carrier behind the 504 expression differential codings, the complex signal on i the code element k number of sub-carrier before the 505 expression differential codings, the complex signal on i-1 the code element k number of sub-carrier behind the 506 expression differential codings.Therefore, for the t-DAPSK signal, be to carry out difference to the information of the adjacent code element of carrying on the same subcarrier to obtain.
Signal on i the code element k number of sub-carrier behind the 507 expression receiving terminal differential decodings; Complex signal on i the code element k number of sub-carrier that 508 expressions receive; Complex signal on i the code element k-1 number of sub-carrier that 509 expressions receive, the complex signal on i code element k of the 510 expression transmitting terminals number of sub-carrier.Complex signal on i code element k-1 of the 511 expression transmitting terminals number of sub-carrier; The transfer function factor on i code element k number of sub-carrier of 512 expressions; The transfer function factor on i code element k-1 number of sub-carrier of 513 expressions; Complex signal on i the code element k number of sub-carrier before the 514 expression transmitting terminal differential codings, the transfer function factor on i code element k number of sub-carrier of 515 expressions, the transfer function factor on i code element k-1 number of sub-carrier of 516 expressions; Signal on i the code element k number of sub-carrier behind the 517 expression differential decodings, the complex signal on i the code element k number of sub-carrier that 518 expressions receive.Complex signal on i-1 the code element k number of sub-carrier that 519 expressions receive.Complex signal on i code element k of the 520 expression transmitting terminals number of sub-carrier, the complex signal on i-1 code element k of the 521 expression transmitting terminals number of sub-carrier.The transfer function factor on i code element k number of sub-carrier of 522 expressions.The transfer function factor on i-1 code element k number of sub-carrier of 523 expressions.Complex signal on i the code element k number of sub-carrier before the 524 expression transmitting terminal differential codings.The transfer function factor on i code element k number of sub-carrier of 525 expressions.The transfer function factor on i code element k-1 number of sub-carrier of 526 expressions.
What Fig. 6 was that the present invention produces is the planisphere of example with the 16APSK signal.It should be noted that 16DAPSK is that a code element comprises 4 bit informations, what adopt among Fig. 6 only is a kind of 16APSK planisphere mode, and 8 phase places, 2 amplitudes are arranged.This is the same for f-DAPSK and t-DAPSK.
Fig. 7 is to be the sketch map of the APSK signal generative process of example according to the embodiment of the invention with the 16APSK signal.As shown in Figure 7, corresponding to Fig. 6,701 expressions are used for 3 bit informations of phase modulated, and 8 kinds of compound modes shown in 702, are represented the not phase information of differential coding according to corresponding 8 phase places of Gray code mode.703 expressions are used for 1 bit information of amplitude modulation(PAM), and 2 kinds of modes are corresponding to 2 amplitudes, shown in 704, and the amplitude information when representing differential coding not.
Fig. 8 be of the present invention under the situation of multi-carrier signal the structural representation of DAPSK signal generative process.As shown in Figure 8,801 expression bitstream data.The DAPSK coding is carried out in 802 expressions, and 803 expressions are transformed into parallel bit stream to serial bit stream, and this is to the f-DAPSK signal, for the t-DAPSK signal, carries out 804 serial to parallel conversion earlier and carries out the DAPSK coding again.806 expressions are carried out Fourier inversion to the signal after shining upon.807 expressions are transformed into serial signal to parallel signal.808 expression steering D/A conversions convert digital signal to analog signal.
Fig. 9 is the sketch map of DAPSK signal generative process under the situation of single carrier according to the embodiment of the invention.As shown in Figure 9,901 expression bitstream data.The DAPSK differential coding is carried out in 902 expressions.903 expression steering D/A conversions convert digital signal to analog signal.
Figure 10 is the sketch map that produces light DAPSK signal according to the direct mapping of the embodiment of the invention.Shown in figure 10,1001 expressions, first lasing light emitter, the 1002 expression signals of telecommunication, 1003 expression modulators (that is, the light signal generation unit) are used for the signal of telecommunication is changed into light signal.Different according to required light carrier number, possibly need a plurality of lasing light emitters or other modes to produce light carrier and substitute 1001.
Figure 11 is the sketch map that produces light DAPSK signal according to the relevant mapping of the embodiment of the invention.Shown in figure 11,1101 expression lasing light emitters, 1102,1103 represent the in-phase component and the quadrature component of the signal of telecommunication respectively.Modulator 1104,1105 is transformed into the light territory with signal from electric territory, and quadrature component also needs the light phase-shifter 1106 through 90 °.Different according to required light carrier number, possibly need a plurality of lasing light emitters or other modes to produce light carrier and substitute 1101.
Figure 12 is the sketch map according to the direct detection DAPSK light signal of the embodiment of the invention.Shown in figure 12, the 1201st, optical band pass filter is used to select to carry the light carrier of desired data signal, and 1202 expression photodiodes are converted into the signal of telecommunication with light signal.
Figure 13 is the structural representation according to the coherent detection light DAPSK signal of the embodiment of the invention.Shown in figure 13, the local laser of 1301 expression receivers, 1302 expressions receive the optical mixer unit of one 90 ° of signal 1303 expressions.1306,4 photodiodes of 1307,1308,1309 expressions carry out balance to light signal and receive.Export the in-phase component I and the quadrature component Q of receiving end signal respectively.
As above show optical communication system according to an embodiment of the invention, will the process of carrying out according to the transmitter and receiver place in the optical communication system of the present invention be described with reference to Figure 14 and Figure 15 below referring to figs. 1 through Figure 13.
Figure 14 shows the sketch map of the process of carrying out according to the transmitter place in the optical communication system of the present invention.Shown in figure 14, at the transmitter place, at first,, the bitstream data of being obtained is modulated, to obtain modulation signal at step S1401.Then, at step S1402, said modulation signal is carried out differential coding, to obtain encoded difference signal.Subsequently, in step S1403, be the signal of telecommunication with said differential coding data conversion.After being transformed to the signal of telecommunication, in step S1404, the said signal of telecommunication being mapped on the light carrier sending after forming light signal.To the said signal of telecommunication is multi-carrier signal or single-carrier signal, and with adopting different differential coding modes, detailed process is described in detail to the counterpart of transmitter in the above, repeats no more at this.
Figure 15 shows the sketch map of the process of carrying out at the receiver place in optical communication system according to the present invention.Shown in figure 15, at first at step S1501, the light signal of said reception is converted into the signal of telecommunication of correspondence.Then, at step S1502, the signal of telecommunication after the said opto-electronic conversion is carried out differential decoding.Then, at step S1503, the signal of telecommunication that will pass through after said differential decoding is handled carries out demodulation, to obtain said bitstream data.About how the signal of telecommunication being carried out differential coding, referring to top detailed description of carrying out to receiver.
Communication means provided by the invention and system can be widely used in the various forms of optical communication systems, are not only applicable to the base band optical OFDM system, and are applicable to the rf modulations optical OFDM system; Be not only applicable to Direct-Detection Optical ofdm system (DD-OFDM), and be applicable to coherent light ofdm system (CO-OFDM); Be not only applicable to the optical OFDM system of extra long distance transmission, and be applicable to the other optoelectronic systems that adopts the OFDM technology, comprise the OFDM-PON system.Be not only applicable to also be applicable in the full optical OFDM system in traditional ofdm system.Be applicable to WDM and superchannel in addition.Because this mode does not need given datas such as training sequence, pilot sub-carrier to carry out backoff algorithms such as channel estimating.Depend on the difference relation that transmitting terminal is introduced just, the present invention can effectively reduce inter-carrier interference, improves systematic function.
Particularly, as an example, be that 40Gb/s coherent light ofdm system is an example with the transmission rate, the performance of different ofdm systems under 16DAPSK and the 16QAM modulation case relatively.Wherein, the sub-carrier number of ofdm signal is 165, and the cumulative length of IFFT is 256 when carrying out IFFT, and all signals do not add pilot tone, only 16QAM is added a training symbol, and the length of cyclic prefix CP is 10.Suppose that other conditions are ideal situation, be made as 100dB like the extinction ratio of modulator, inserting loss is 0, and the phase place of laser is 0, only considers to send and the laser linewidth of receiving terminal.At this moment, when the error rate reached 1.2 * 10-3, the tolerable live width of frequency domain differential demodulation 16DAPSK was 110kHz, and the tolerable live width of time-domain difference 16DAPSK is 45kHz, and 16QAM can only tolerate the live width of 22kHz; If the hypothesis laser linewidth is 40kHz, the 16QAM coded OFDM system system Q value of comparing frequency domain differential demodulation 16DAPSK coding has reduced by 6 dB so, compares time-domain difference and has reduced by 4 dB.It is thus clear that the ability of the system tolerant phase noise of DAPSK coding is significantly increased.Consider under the nonlinear situation; Transmit 6 sections of striding, each section of striding 80km, the optical fiber parameter value is abbe number DSSMF=17ps/nm/km; Attenuation alpha SSMF=0.2dB/km; Non linear coefficient γ SSMF=1.3w-1km-1, the EDFA in the section of striding (erbium-doped fiber amplifier) is used for the loss of full remuneration optical fiber, and its noise figure is 6dB.Ignore other factor affecting; Can obtain: the best launched power of 16QAM coded OFDM system is-10dBm; Corresponding Q value is 9.7dB, and the best launched power of time-domain difference 16DAPSK coded OFDM system is-8dBm that corresponding Q value is 12.2dB; The best launched power of frequency domain differential demodulation 16DAPSK coded OFDM system is-8dBm that corresponding Q value is 11.7dB.It is thus clear that the nonlinear ability of system tolerant of DAPSK coding also is improved.
In addition; Do not use the advantage of the optical communication system of differential coding in order to be illustrated more clearly in optical communication system according to the present invention with respect to other; Be that example describes with q-OFDM, t-OFDM, f-OFDM below, wherein q-OFDM, t-OFDM, f-OFDM represent 16QAM coded OFDM system, time-domain difference 16DAPSK coded OFDM system and frequency domain differential demodulation 16DAPSK coded OFDM system respectively.As shown in the figure, they have a little difference when producing ofdm signal.For for simplicity, ignored the influence of D/A and A/D in the actual emulation, just hypothesis is perfect digital-to-analogue conversion.
The baseband OFDM signal is to 2 in Matlab
15-1 pseudo noise code (PRBS) is shone upon successively, serial to parallel conversion (S/P), add training symbol, inversefouriertransform, adding Cyclic Prefix and parallel serial conversion and obtain.Wherein, mapping is chosen as 16QAM, time-domain difference 16DAPSK and frequency domain differential demodulation 16DAPSK; Fourier transform is of a size of 256, useful subcarrier numerical digit 165, and remaining 91 0 empty subcarriers are positioned in the middle of the frequency spectrum.For 16DAPSK coded OFDM system,,, also need training symbol and pilot tone to carry out the estimation and the equilibrium of channel as far as 16QAM coded OFDM system without training symbol and pilot tone; The length of Cyclic Prefix (CP) is 10.
The duration of an OFDM code element is 26.6ns, and the protection shared time of interval is 0.1ns so, and normalization bit rate (promptly all data comprise training symbol and useful data) is 40Gbit/s, and shared bandwidth is less than 6.7GHz.After the baseband OFDM signal comes the elimination distorted portion through a raised cosine filter, be modulated to the light territory through an I/Q modulator (realizing through double-parallel modulator usually).Optical fiber link comprises EDFA and optical fiber loop of a power controlled.Comprise the standard single-mode fiber (SMF) of one section 80km and the EDFA of a gain controlling in the loop.Optical fiber parameter is: abbe number DSSMF=17ps/nm/km, attenuation alpha SSMF=0.2dB/km, non linear coefficient γ SSMF=1.3w-1km-1.The EDFA noise factor of controllable gain is 6dB, and its gain is set to full remuneration SMF decay.Receiving terminal uses a bandwidth to be the outer ASE noise of the second order Gauss type band pass filter filtering band of 20GHz.Coherent receiver is by a local oscillator (LO), and 90 ° of optical mixer units and two balance detection devices constitute.In Matlab, the filtered signal of telecommunication is carried out Digital Signal Processing at last.In signal processing, remove corresponding to outside the corresponding inverse operation of transmitting terminal, for q-OFDM, need to estimate channel transfer functions according to adding training symbol at the ofdm signal initiating terminal, come the compensation of phase deviation according to the pilot tone of periodically inserting.And, only need carry out differential ference spiral for t-OFDM and f-OFDM.Each simulation result all has about 500 OFDM code elements is carried out the Monte Carlo error code testing, and Q value (Q2Factor) is transformed through the error rate (BER):
When carrying out emulation, it should be noted that among t-OFDM and the f-OFDM; Owing to adopted differential modulation; Receiving terminal need be abandoned first code element, therefore, and for the purpose of justice; Q-OFDM does not add pilot tone and only uses a training symbol, obtains and t-OFDM and approaching spectrum efficiency and the useful data speed of f-OFDM.In addition, in order to reach similar performance, q-OFDM need add some pilot tones and training symbol, but will reduce spectrum efficiency and useful data speed like this.Like Figure 20, Figure 21, shown in Figure 22, two numerals representing in the branch are represented the interval and the training symbol load of pilot tone successively.The training symbol load is defined as training symbol number/useful data code element number.Only if particularly point out like this, the q-OFDM that mentions in the emulation is meant the situation that pilot tone has only a training symbol that do not add.
Figure 16 shows under the situation back-to-back the Q value with the change curve of receiving terminal OSNR.In Figure 18, when illustration is OSNR=15dB, the planisphere of corresponding receiving terminal, at this moment three's poor performance is few, and BER is about 1.2 * 10-3.Can see that thus t-OFDM, f-OFDM and q-OFDM have the same OSNR requirement during to resisting ASE noise.
Figure 17 shows the change curve of Q value cost under the different accumulated chromatic dispersions, at this moment OSNR=15dB/0.1nm.Come these three kinds of systems of research separately to resist the ability of chromatic dispersions through one section optical fiber that only comprises CD ofdm signal.The change curve of Q value cost under different accumulated chromatic dispersions when Figure 19 is illustrated in OSNR=15dB/0.1nm.It is the poor of 0 o'clock Q value that Q value cost is defined as than chromatic dispersion.Can see that when being 34000ps/nm through 2000km virtual fiber transmission accumulated chromatic dispersion value, greater than 1.5dB, and the Q value cost of t-OFDM is only than the little 0.3dB of q-OFDM than the Q value cost of q-OFDM for f-OFDM.As far as f-OFDM, its differential modulation is carried out on adjacent sub-carrier, and is therefore relatively responsive to the phase deviation of accumulated chromatic dispersion introducing, the very big phase change of introducing when especially chromatic dispersion is very big.To belong to the constellation of 16QAM at interval big slightly and q-OFDM compares the main merit of the edge of t-OFDM.
Figure 18 shows the change curve of under single-channel situation 480km transmission back Q value with incident power, and wherein q-OFDM has only a training symbol and do not add pilot tone among Figure 18 (a), and the middle existing pilot tone of q-OFDM of Figure 18 (b) has training symbol.
Figure 18 has shown nonlinear tolerance in three kinds of system's antagonism channels.Shown in Figure 18 (a), in the launched power scope from-16dBm to-1dBm, t-OFDM and f-OFDM are good than the q-OFDM performance, and wherein the best launched power of q-OFDM is-10dBm, and corresponding Q value is 9.7dB; The best launched power of t-OFDM and f-OFDM is-8dBm, and corresponding Q value is 11.7dBm and 12.2dBm, has improved 2dB at least than q-OFDM.Even if used pilot tone and training symbol among the q-OFDM, shown in Figure 18 (b), the improvement of performance is also very limited, and especially launched power is higher, and nonlinear effect accounts for leading the time.And at this moment the bands of a spectrum of q-OFDM are wide has increased by 6.6%～9.4%, and bit rate has reduced 1.9%～5.6%.
Figure 19 shows the non-linear effects in the wdm system.Shown in Figure 19 is 5 channels, and channel spacing is that the wdm system of 50GHz is through (left figure) before the 480km Optical Fiber Transmission back spectrum of (right figure).In wdm system, cross-phase modulation can reduce systematic function greatly as a kind of main damage, therefore below simulation analysis three kinds of nonlinear performances of systems' antagonism interchannel.
Figure 20 has shown the simulation result of the channel in the middle of being positioned at.In Figure 20 (a), q-OFDM does not insert pilot tone, has only a training symbol; At this moment, t-OFDM, the best launched power of f-OFDM and q-OFDM is respectively-9dBm;-9dBm and-11dBm, corresponding Q value is 11.4dB, 11.2dB and9.2dB; Show and compare q-OFDM, t-OFDM and f-OFDM have the 2dB advantage at least.Shown in Figure 20 (b); Add the systematic function of improving that pilot tone and training symbol can be suitable, still have and the single carrier similar phenomenon, promptly when non-linear occupying an leading position; Performance improvement is very limited; Simultaneously, bands of a spectrum are wide to have increased by 6.6%～9.4%, and bit rate has reduced 1.9%～5.6%.
In the f-OFDM system, differential modulation is between adjacent sub-carrier, and is therefore more responsive to the phase deviation of chromatic dispersion introducing.But this difference correlation also has the function of similar pilot tone, therefore makes f-OFDM that the function of very strong antagonism nonlinear interaction arranged.As far as t-OFDM, the difference correlation is between adjacent code element, and this has just reduced the influence of chromatic dispersion.Therefore, no matter be amplitude and the phase difference of doing at time domain or frequency domain, be moreover improved nonlinear effect among ofdm signal antagonism single channel and the WDM.As far as q-OFDM; This between the subcarrier, all it doesn't matter between the code element, therefore need Given information such as pilot tone and training symbol to estimate channel matrix, though can well damage by compensated linear; It is just very limited that but the antagonism non-linear behaviour improves; In addition, the outer frequency spectrum of pilot tone meeting occupying volume, the insertion of training symbol can reduce data rate.Therefore, can see that the optical OFDM system of 16DAPSK coding can finely must resist transmission impairment such as ASE noise, chromatic dispersion and nonlinear fiber do not need Given information simultaneously, thereby have reduced the receiver complexity.
Optical communication system based on differential coding provided by the invention can directly be used for various optical transmission systems, and simplified system under the situation that guarantees the availability of frequency spectrum reduces cost.
Statement through above execution mode can find out that optical communication method and system based on differential coding provided by the invention have following advantage:
1) can avoid inserting given datas such as training sequence, pilot sub-carrier and carry out backoff algorithms such as channel estimating,, improve the effective speed and the availability of frequency spectrum of system greatly, reduce system cost in the direct demodulation of receiving terminal, judgement.
2) can improve signal antagonism laser linewidth, become the tolerance of PMD, nonlinear fiber, interchannel interference and other damages soon, improve systematic function.
3) the various elements that adopted all are universal components, and are therefore with low cost, practical.
4) the multicarrier optical communication system of the present invention's description can be applicable in the various optical communication systems.
As above describe according to optical communication method and the system based on differential coding of the present invention with the mode of example with reference to accompanying drawing.But, it will be appreciated by those skilled in the art that optical communication method and the system that propose for the invention described above based on differential coding, can also on the basis that does not break away from content of the present invention, make various improvement.Therefore, protection scope of the present invention should be confirmed by the content of appending claims.
Claims (14)
1. optical communication method comprises:
Bitstream data to being obtained is modulated, to obtain modulation signal;
Said modulation signal is carried out differential coding, to obtain encoded difference signal;
Said encoded difference signal is transformed to the signal of telecommunication; And
The said signal of telecommunication is mapped on the light carrier sends after forming light signal.
2. optical communication method as claimed in claim 1 wherein, is under the situation of multi-carrier signal at the said signal of telecommunication, and said modulation signal is carried out differential coding, comprises with the step that obtains encoded difference signal:
If in time domain, carry out said differential coding, then the same subcarrier to the adjacent code element in the said modulation signal carries out differential coding, perhaps
If in frequency domain, carry out said differential coding, then the adjacent sub-carrier to the same code element in the said modulation signal carries out differential coding.
3. like right 1 described optical communication method, wherein, be under the situation of single-carrier signal, said modulation signal carried out differential coding, comprise with the step that obtains encoded difference signal at the said signal of telecommunication:
Adjacent code element in the said modulation signal is carried out difference.
4. like any one described optical communication method in the claim 1 to 3, wherein, said bitstream data adopts amplitude-phase keying (APSK) to modulate.
5. optical communication method as claimed in claim 2, wherein, when in time domain, carrying out said differential coding, said method also comprises:
Before carrying out said differential coding, said modulation signal is carried out serial/parallel conversion, so that said modulation signal is transformed to parallel signal; And
After accomplishing said differential coding, said encoded difference signal is carried out Fourier inversion, adds Cyclic Prefix and carries out parallel/serial conversion, to obtain the OFDM data-signal behind the differential coding.
6. optical communication method as claimed in claim 2, wherein, when in frequency domain, carrying out said differential coding, said method also comprises:
After accomplishing said differential coding, said encoded difference signal is carried out serial/parallel conversion, Fourier inversion, interpolation Cyclic Prefix and carries out parallel/serial conversion, to obtain the OFDM data-signal behind the differential coding.
7. optical communication method comprises:
At transmitting terminal,
Bitstream data to being obtained is modulated, to obtain modulation signal;
Said modulation signal is carried out differential coding, to obtain encoded difference signal;
Said encoded difference signal is transformed to the signal of telecommunication; And
The said signal of telecommunication is mapped on the light carrier sends after forming light signal, and at receiving terminal,
Convert the light signal of said reception into the corresponding signal of telecommunication;
The signal of telecommunication after the said opto-electronic conversion is carried out differential decoding; And
The signal of telecommunication to after handling through said differential decoding carries out demodulation, to obtain said bitstream data.
8. transmitter comprises:
Modulating unit is used for the bitstream data of being obtained is modulated, to obtain modulation signal;
The differential coding unit is used for said modulation signal is carried out differential coding, to obtain encoded difference signal;
Converter unit is used for said encoded difference signal is transformed to the signal of telecommunication; And
Map unit is used for the said signal of telecommunication is mapped to and forms light signal on the light carrier; And
Transmitting element is used to send the light signal that is generated.
9. transmitter as claimed in claim 8 wherein, is under the situation of multi-carrier signal at the said signal of telecommunication,
If in time domain, carry out said differential coding, then said differential coding unit carries out differential coding to the same subcarrier of the adjacent code element in the said modulation signal, perhaps
If in frequency domain, carry out said differential coding, then said differential coding unit carries out differential coding to the adjacent sub-carrier of the same code element in the said modulation signal.
10. transmitter as claimed in claim 9 also comprises:
The first serial/parallel modular converter; Being used at the said signal of telecommunication is multi-carrier signal and when time domain is carried out differential coding; Said modulation signal is carried out serial/parallel conversion, to obtain parallel signal, is multi-carrier signal and when in time domain, carrying out differential coding at the said signal of telecommunication perhaps; Said encoded difference signal is carried out serial/parallel conversion, to obtain parallel signal;
The IFFT module is used for the encoded difference signal of said differential coding unit output or the parallel signal of said serial/parallel modular converter output are carried out Fourier inversion;
Cyclic prefix adding module is used for to adding Cyclic Prefix through the signal after the Fourier inversion; And
The first parallel/serial modular converter is used for the signal after add handling through Cyclic Prefix is carried out parallel/serial conversion, to obtain the ofdm signal behind the differential coding.
11. transmitter as claimed in claim 8, wherein, said map unit comprises:
First lasing light emitter is used to produce light carrier; And
The light signal generation unit is used for said encoded difference signal is modulated to and converts light signal on the light carrier into.
12. a receiver comprises:
Receiving element is used to receive the light signal that said transmitter sends;
Photoelectric conversion unit is used for converting the light signal of said reception into the corresponding signal of telecommunication;
The differential decoding unit is used for the signal of telecommunication after the said opto-electronic conversion is carried out differential decoding; And
Demodulating unit is used for to carrying out demodulation through the signal of telecommunication after the said differential decoding cell processing, to obtain said bitstream data.
13. receiver as claimed in claim 12 also comprises:
The second serial/parallel modular converter is used for converting the said signal of telecommunication into parallel signal from serial signal;
Cyclic Prefix removes module, is used for removing the Cyclic Prefix of said parallel signal;
The FFT module is used for the said signal that removes behind the Cyclic Prefix is carried out Fourier transform; And
The second parallel/serial modular converter; Be used for passing through parallel signal after the FFT resume module and convert serial signal into and supply said differential decoding cell processing, the parallel signal that perhaps will after said differential decoding unit is handled the signal of said FFT module output, obtain converts serial signal into.
14. an optical communication system comprises:
Like any one described transmitter in the claim 8 to 11; And
Like claim 12 or 13 described receivers.
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Application publication date: 20120425 |