CN101895346A - Transmitter of OOFDM system and method of delay caused by pre-compensated optical fibre dispersion - Google Patents
Transmitter of OOFDM system and method of delay caused by pre-compensated optical fibre dispersion Download PDFInfo
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- CN101895346A CN101895346A CN2009101384737A CN200910138473A CN101895346A CN 101895346 A CN101895346 A CN 101895346A CN 2009101384737 A CN2009101384737 A CN 2009101384737A CN 200910138473 A CN200910138473 A CN 200910138473A CN 101895346 A CN101895346 A CN 101895346A
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Abstract
The invention discloses a transmitter of an OOFDM system and a method of delay caused by pre-compensated optical fibre dispersion. The pre-compensated method comprises the steps of: receiving a plurality of pre-compensated values corresponding to a subcarrier; transmitting the subcarrier after the time for delaying the corresponding pre-compensated value; estimating the delay time among the subcarriers at the receiver end and setting the pre-compensated value of the transmitter based on the delay time. The transmitter delays the pre-compensated value when the subcarrier is transmitted out so that the subcarrier reaches the receiver during the period of time consistent to achieve the purpose of delay caused by the pre-compensated optical fibre dispersion.
Description
Technical field
The invention relates to that (Optical Orthogonal Frequency-division Multiplexing OOFDM) in the system of technology, is able to the conveyer and the method for the caused delay of precompensation optical fiber chromatic dispersion to a kind of employing optical orthogonal frequency-division multitask.
Background technology
Orthogonal frequency division multitask (Orthogonal Frequency-division Multiplexing, OFDM) system is a kind of frequency division multi-task (Frequency-division Multiplexing, FDM) system that adopts digital multi-carrier modulation (Digital multi-carrier modulation) method.A plurality of subcarriers (orthogonal sub-carrier also can be described as sub-band or subcarrier) with orthogonality are used to transmit data.These data are cut into a plurality of parallel data stream (data stream) of corresponding each subcarrier or claim passage (Channel).Each subcarrier is all carried out transfer of data with the low quadrature modulation technology that accords with first speed (low symbol rate) of a kind of tool.Thus, can in identical frequency range (bandwidth), obtain compared to the more total data transfer rate (total data rates) of the single carrier wave of tradition (single-carrier).
Please refer to Figure 1A and Figure 1B is to be respectively to have now directly to transmit with the distribution of orthogonal frequency division multitask transmission frequency spectra to compare schematic diagram.Directly the maximum difference of transmission and OFDM transmission is the distribution of frequency range, and Figure 1A shows that the shared frequency range of direct transmission is f
0If with this frequency range f
0Mode with the orthogonal frequency division multitask is subdivided into five wide five equilibriums with this section frequency range.Each sub-band (being aforesaid subcarrier) mutually orthogonal, then new spectrum distribution will be shown in Figure 1B.In the OFDM transmission, as long as sub-band is more than enough, basically for each sub-band, the frequency response of this section frequency band can roughly be considered as smooth.That is to say the equalizer that only needs a single coefficient at each sub-band, in order to decay and the phase distortion that overcomes each subchannel.In addition, because the data transfer rate that the data transfer rate that each sub-band transmitted all directly transmits far below script, the frequency of operation of this equalizer also descends with equal proportion naturally.
The orthogonal frequency division multi-tasking is applied on the wireless communication field, and the problem that often runs into has multi-path effect (multi-path effect).The multi-path effect can be derived and be disturbed (inter-symbol interference, ISI) problem between time delay expansion (time-spreading) and symbol.This is so-called frequency selectivity (Frequency-selective) passage.This frequency selectivity problem is normally (or to claim the symbol sign indicating number, to add Symbol) that (Guard interval) solves between the guard plot in the symbol unit of each OFDM.This measure will strengthen symbol unit's cycle, take the frequency range in order to the transmission data.
When the orthogonal frequency division multi-tasking is applied to optical communication system, because light transmits in same optical fiber, therefore, the multi-path effect of optical orthogonal frequency-division multitask system is not remarkable, but can make when receiving terminal receives signal because of optical fiber dispersion (Chromatic Dispersion) phenomenon, have the problem of disturbing between the symbol of the problem of inter-channel synchronization and similar multi-path.
Optical fiber dispersion makes when light signal transmits on optical fiber, and the speed that the light signal of high frequency is transmitted is slow than the speed that the light signal of low frequency is transmitted.In the optical orthogonal frequency-division multitask technology, because each subcarrier is to transmit with different frequency, though transmitting terminal sends out each subcarrier simultaneously, each subcarrier received at receiving terminal arrives at different time.This is so-called group delay (Group delay) phenomenon.
About the group delay phenomenon, please refer to Fig. 2 A and Fig. 2 B, it is the schematic diagram that is respectively the transmission end of optical orthogonal frequency-division multitask system and receiving terminal transmission and received signal.Fig. 2 A and Fig. 2 B show the schematic diagram of orthogonal frequency division multi-task signal at frequency domain.Trunnion axis among the figure is the time, and vertical axis is a frequency.Each subcarrier (sub-band) uses a frequency band.With Fig. 2 A is example, and each subcarrier uses the frequency range of df in the diagram, and first subcarrier place frequency band (frequency range) is M*df, and its next one is (M+1) * df, and the rest may be inferred.Shown among the figure for the data of a symbol unit are only arranged on each subcarrier.During actual the transmission is that continuous symbol unit is transmitted and receives.Fig. 2 A is the schematic diagram of the symbol unit that transmits of transmission end.Can see among the figure and know that the zero-time first at each symbol of transmission end is identical.Because the time span of each symbol unit is all identical, so the termination time of each symbol unit of transmission end is also identical.Secondly, please refer to Fig. 2 B, it is received the signal schematic representation that end receives for after the orthogonal frequency division multi-task signal passes through Optical Fiber Transmission.Can see among the figure and know, early be received, the then later arrival of the higher subcarrier of frequency (ascending the throne) at the subcarrier of frequency axis below at the lower subcarrier of frequency (ascending the throne) at the subcarrier of frequency axis above.This is above-mentioned so-called group delay variation (Group Delay ' s Variation/Dispersion).
For solving the group delay variation problem, the dealer is between each symbol unit adding guard plot of subcarrier (Guard Interval), can be cyclic-prefix sign indicating number (Cyclic Prefix) or circulation postamble (Cyclic Postfix) etc. between the guard plot.By the setting between the guard plot, during the interior acquisition data of receiving terminal interval at one time (be the first length of former symbol add between the guard plot when long), the data of each subcarrier all can be complete.After only needing to judge starting point, can Xie Code.
Though can solve the group delay variation problem that optical fiber dispersion brings between the guard plot, the optical fiber dispersion situation is more serious, and the time is longer between required additional guard plot.Yet, longer between this guard plot, its shared frequency range promptly the more, the frequency range that meaning promptly can be used for transmitting data promptly reduces.And the group delay that chromatic dispersion produced is to be proportional to the distance that is transmitted in optical fiber and the frequency difference between subcarrier.That is to say when total frequency range bigger, or transmission range is longer, group delay variation is promptly bigger, it is longer promptly to need between the guard plot, the side is able to head it off.
Communication is usually because of having accounted for 6 percent communication frequency range at least between the guard plot that optical fiber dispersion added.This communication frequency range is if deduct guiding carrier wave (the scatter pilot that is used as channel response (channel response) estimation again, preamble or mid-amble) the shared frequency range and the frequency range of control signal, can will more reduce in order to the frequency range of transmission data.
Summary of the invention
In view of needing to increase because of transmission range increases between aforementioned guard plot, and then taken the phenomenon of communication frequency range, the present invention proposes the conveyer of a kind of OOFDM system and the method for the caused delay of precompensation optical fiber chromatic dispersion thereof, and effectively to shorten between the guard plot, increase can transmit the frequency range of data.
The method of the caused delay of precompensation optical fiber chromatic dispersion that the present invention proposes is applicable to the optical orthogonal frequency-division multitask conveyer.This conveyer is the light signal that transmission one has a plurality of subcarriers.This carrier frequency that each subcarrier has carrier frequency and this subcarrier is different, and this method comprises: receive a plurality of pre-compensation value, this pre-compensation value is to should subcarrier; And this subcarrier is postponed send out after time of this corresponding with it pre-compensation value.
The multi-subcarrier signal generator that the present invention proposes is suitable for the conveyer of an optical orthogonal frequency-division multitask system.A string commentaries on classics of conveyer and element are that conversion and mapping one numerical sequence signal are a plurality of and column signal.Generator comprises add ons between a plurality of time-domain signal modulators, a plurality of guard plot, a plurality of delay cell, reaches a colligator.The time-domain signal modulator with one-one relationship to signal side by side.And respectively this time-domain signal modulator is to produce a time domain signal according to corresponding with it also column signal.Between the guard plot add ons with one-one relationship to should the time-domain signal modulator.Become one by additional signal in corresponding with it this time-domain signal that this time-domain signal modulator produced between the additional respectively guard plot of add ons between each guard plot.Delay cell with one-one relationship to add ons between should the guard plot.This delay cell has a predetermined delay value respectively.And respectively this delay cell be postpone to transmit after this predetermined delay value add ons produced between this corresponding with it guard plot this by additional signal.Colligator is in conjunction with this is exported a combined signal by additional signal by this delay cell transmitted.
The conveyer of the optical orthogonal frequency-division multitask system that the present invention proposes is to send out after a numerical sequence signal is converted to a light signal.Conveyer comprises string changes also element, multi-subcarrier signal generator, digital revolving die plan element and the electric optical element that changes.String changes and element is that conversion and this numerical sequence signal of mapping are a plurality of and column signal.The multi-subcarrier signal generator according to should and column signal and produce corresponding a plurality of time-domain signals, this multi-subcarrier signal generator in addition according to this and the pairing a plurality of predetermined delay values of column signal, postpone behind this time-domain signal this time-domain signal that is delayed to be merged into a combined signal.The numeral revolving die is intended element and is transferred this combined signal to an analog signal.It is this light signal with this analog signal conversion that electricity changes optical element.
The precompensation method that proposes by the invention described above, multi-subcarrier signal generator, with the optical orthogonal frequency-division multitask conveyer, making the caused delay of chromatic dispersion be able at the conveyer end is suitably precompensation of quilt, and each subcarrier can both arrive receiving terminal in the quite consistent time through after the Optical Fiber Transmission.
Describe the present invention below in conjunction with the drawings and specific embodiments, but not as a limitation of the invention.
Description of drawings
Figure 1A and Figure 1B are for having relatively schematic diagram of directly transmission and the distribution of orthogonal frequency division multitask transmission frequency spectra now;
Fig. 2 A and Fig. 2 B are the schematic diagrames that is respectively the transmission end of existing optical orthogonal frequency-division multitask system and receiving terminal transmission and received signal;
Fig. 3 hands over the conveyer of multitask system and the system architecture schematic diagram of receiver according to the light positive of the invention process example;
Fig. 4 is the circuit box schematic diagram according to the multi-subcarrier signal generator of the conveyer of the optical orthogonal frequency-division multitask system of the invention process example;
Fig. 5 A is the frequency domain schematic diagram according to the time-domain signal that is delayed that each delay cell spread out of of the conveyer of the invention process example;
Fig. 5 B is the frequency domain schematic diagram that the time-domain signal that is delayed of Fig. 5 A is received by the receiver;
Fig. 6 is the schematic flow sheet according to the method for the caused delay of precompensation optical fiber chromatic dispersion of the invention process example;
Fig. 7 is the preceding method flow schematic diagram of precompensation method of Fig. 6 the invention process example;
Fig. 8 is the method flow schematic diagram according to the invention process exemplary steps S72;
Fig. 9 is the method flow schematic diagram according to the invention process exemplary steps S722;
Figure 10 A and Figure 10 B be respectively do not adopt the invention process example and adopt the invention process sample method after, at the signal schematic representation of receiving terminal;
Figure 11 is the circuit box schematic diagram according to another embodiment of multi-subcarrier signal generator of the conveyer of the optical orthogonal frequency-division multitask system of the invention process example.
Wherein, Reference numeral
10 conveyers
12 strings change and element
14,24 multi-subcarrier signal generators
138a, 138b, 238a, 238b is by additional signal
139a, 139b, 239a, add ons between the 239b guard plot
140,141,240,241 time-domain signal modulators
142a, 242a real part look-up table
142b, 242b imaginary part look-up table
143,144,243,244 time-domain signals
145,146,245,246 delay cells
147a, 247a first multiplexer
147b, 247b second multiplexer
147c phasing back device
148 colligators
149,249 multiplexer groups
16 digital revolving dies are intended element
18 electricity change optical element
247c the 3rd multiplexer
247d the 4th multiplexer
247e, 247f phasing back device
247g, the 247h signal amplifier
247m second colligator
248 first colligators
60 receivers
62 optical receivers
64 analog-to word elements
66 synchronous elements
68 fast fourier transform elements
69 chromatic dispersions monitor and wait the change element
80 optical fiber
82 image intensifers
84 control channels
90 numerical sequence signals
91 and column signal
910 real parts
912 imaginary parts
92 combined signals
93 analog signals
94 light signals
The signal of telecommunication of 95 simulations
96 first digital signals
97 second digital signals
98 three digital signals
99 decoding back signals
Embodiment
At first, see also Fig. 3, it is to hand over the conveyer 10 of multitask system and the system architecture schematic diagram of receiver 60 according to the light positive of the invention process example.Can see among the figure that knowing conveyer 10 as to send out after a numerical sequence signal 90 is converted to a light signal 94.After the transmission of these light signal 94 process optical fiber 80 and the amplification of image intensifer 82, be received device 60 and receive.
Wherein, this light signal 94 light signal 94 that is an orthogonal frequency division multitask.Aforesaid image intensifer 82 can be but be not limited to erbium-doped fiber amplifier.Aforementioned optical fiber 80 be for but be not limited to monomode fiber (Single mode fiber).
Receiver 60 is estimated and this light signal 94 total delay times because of the group delay that chromatic dispersion produced after having received light signal 94, then this total delay time is passed back this conveyer 10.This total delay time can be given conveyer 10 via control channel 84 (Control channel) passback of the usefulness of communicating by letter between conveyer 10 and the receiver 60.Or otherwise be returned to conveyer 10.Though aforementioned control channel 84 is illustrated in the mode that is different from optical fiber 80 on figure, in fact can be a channel in the optical fiber communication.In addition, also can adopt the mode of artificial setting, for example, measure at receiver 60 places or estimate behind the total delay time of group delay, by manually manually setting this total delay time at conveyer 10 places.
Aforementioned conveyer 10 comprises a string commentaries on classics and element 12, a multi-subcarrier signal generator 14, one digital revolving die intends element 16 and an electricity changes optical element 18.String changes and element 12 is that conversion and this numerical sequence signal 90 of mapping (mapping) are a plurality of and column signal 91.Aforesaid total delay time is to be converted into a plurality of predetermined delay values.Each predetermined delay value is corresponding aforementioned and column signal 91.How to be converted to the predetermined delay value about total delay time, to be detailed later.
Aforementioned string change and element 12 be earlier will be to be transmitted numerical sequence signal 90 cut into a plurality of parallel data flow.The modulation tech of the low first speed of symbol (low symbol rate) is converted to aforementioned and column signal 91 each parallel data flow to have again.Aforesaid modulation tech can be but be not limited to orthogonal amplitude modulating and changing (QAM, Quadrature Amplitude Modulation) or phase deviation modulation (claiming the phase shift key again, PSK, Phase Shift Keying).
As seen know among the figure, multi-subcarrier signal generator 14 comprises a plurality of time-domain signal modulators (time domain modulated waveform generator) 140,141, add ons (Guard Interval Adding Element) 139a between a plurality of guard plots, 139b, a plurality of delay cell 145,146 and a colligator (adder) 148.This time-domain signal modulator 140,141st, with one-one relationship to signal 91 side by side.Time-domain signal modulator 140,141st is converted to the time-domain signal 143,144 that belongs to time domain with the also column signal 91 that belongs to frequency domain.Thereafter, add ons 139a between the guard plot, 139b are with corresponding time-domain signal modulator 140,141 of one-one relationship and delay cell 145,146.Add ons 139a between the guard plot, 139b additional protection interval becomes by additional signal (GI-added signal) 138a 138b in time-domain signal 143,144.Each delay cell 145,146th postpones to transmit after this predetermined delay value attachment element 139a between this corresponding with it guard plot, and 139b produced by additional signal 138a, 138b.Thus, though each and column signal 91 are received simultaneously by multi-subcarrier signal generator 14, after the adjustment of multi-subcarrier signal generator 14, delay cell 145,146 will be by additional signal 138a, and 138b postpones to send out after time of predetermined delay value of a correspondence.Colligator 148 be transmitted in conjunction with this delay cell 145,146 this by additional signal 138a, 138b and export this combined signal 92.
Aforementioned delay cell 145,146 can be a digital delay unit.It can be but be not limited to adjustable digital delay (variable digital delay), the adjustable digit delay device of first in first out formula (FIFO-based first-in-first-out based variable digital delay).
Purpose and calculating about group delay and predetermined delay value refer again to Fig. 2 A.By experiment as can be known, when the frequency-splitting of (group) between each subcarrier is a fixed value, (differ the df frequency range as shown in FIG.), and under the condition that do not change of the transmission environment of light signal 94, it is linear that aforementioned group delay is.Below propose one to be illustrated for example.Suppose that for example one orthogonal frequency division multi-task signal has 8 subcarriers, received first subcarriers of receiver 60 to the total delay time of a last subcarrier (because of chromatic dispersion caused) be 0.7ns (second how, 1x10
-9Second).With this understanding, the group delay between each subcarrier is 700ps (1x10
-12Second) divided by (8-1) (because of always having seven carrier spacings), equal 100ps.That is to say that though each subcarrier (group) is sent out simultaneously, adjacent subcarrier (group) is that the 100ps of being separated by is received in regular turn, shown in Fig. 2 B.
Be head it off, the invention process example promptly before conveyer 10 transmission light signals 94, estimates that according to it time that postpones compensates in advance with each subcarrier.Make each subcarrier (group) when being transmitted, all be delayed transmission according to this scheduled delay.The subcarrier that frequency is adjacent will be transmitted successively.This time interval that transmits successively promptly equals the group delay difference time (for example one of the top of continuing is 100ps) between the above-mentioned subcarrier.By this, receiver 60 promptly can receive and be close to each subcarrier that arrives simultaneously.Solve the problem of group delay.
Because the cause of chromatic dispersion, have light signal 94 that speed that the light signal 94 of upper frequency is transmitted has lower frequency for slow in optical fiber 80, therefore, the subcarrier with upper frequency will be transmitted out earlier.That is to say that the higher subcarrier of frequency is early spread out of.Please refer to Fig. 5 A, it is the frequency domain schematic diagram of the time-domain signal that is delayed 143,144 that spread out of of each delay cell 145,146 according to conveyer 10 of the present invention.Trunnion axis among the figure is the time, and vertical axis is a frequency.Vertical axis is more toward the drawing below, and its frequency is higher.Fig. 5 A is to be example with four subcarriers.As can be seen, more the subcarrier of high frequency more early is sent out among the figure.More the subcarrier of low frequency then more is sent out evening.A unit delay time at interval then between the adjacent subcarrier.
Above-mentioned unit delay time is that the integral multiple with the unit sample time (Sampling time) is good.It is above-mentioned for example one to continue, and supposes that the unit sample time is 40ps (equaling the sampling rate samplingrate of 25GHz).Each sampling point is called one and counts.Be separated by between sampling point and the sampling point the aforementioned unit sample time (40ps).The carrier frequency of first subcarrier is minimum, transfer rate is the fastest.The carrier frequency of the 8th subcarrier is the highest, and transfer rate is the slowest.Bin width between each subcarrier identical (being that aforesaid frequency-splitting is identical).Therefore, according to the delay difference between each subcarrier of receiving before the compensation not in the transmission end 10 carry out time of delay of precompensation such as following table (this for example one unit delay count and equal the unit sample time, be 40ps).The field of " not before the compensation; the time of delay during reception " refers to conveyer 10 and transmits each subcarrier simultaneously in the following table, and receiver 60 is compared the time that each subcarrier is received resulting time of delay when receiving each subcarrier with the subcarrier of receiving at first.With table 1 is example, will receive first subcarrier earlier, and remaining receives in regular turn, so this hurdle (column) compares other subcarrier and first subcarrier and time of delay of obtaining.
Table time of delay of table 1 precompensation
From table 1, can learn, the second, the pre-compensation value of four, six, eight subcarriers promptly is set at the time difference that this subcarrier and the 8th subcarrier (the 8th subcarrier is to have the subcarrier of high carrier frequency) arrive receiver 60, and first and third, five and seven subcarriers,, be with the most for it then near the multiple of the unit sample time of time difference between this subcarrier because its " time difference between subcarrier " fails to be divided exactly sample time by unit.For example, though the time difference of first subcarrier and the 8th subcarrier is 700ps, because of failing to be divided exactly sample time, so with the time of delay of 720ps as delayed delivery by unit.Certainly can also 680ps for it.The rest may be inferred for all the other.
With the example in the table 1, second, four, six and eight subcarriers are received with being received device 60 simultaneously, and first and third, five and seven subcarriers then can be received by late 20ps.Therefore, between the guard plot can from non-700ps with the technology of the present invention reduce to use 40ps of the present invention (because of 20ps less than 1 sampling point, be to carry out during receiver 60 decodings, so 20ps is also in 1 sampling point with sampling point).Significantly reduced frequency range shared between the guard plot.If this for example in one the time span of each symbol unit be 128 points (they being the 128x40ps=5120ps time span), postpone 18 points between then traditional guard plot, account between traditional guard plot between Fu Yuan and guard plot and the frequency range of 12.8% (18/ (18+128)=12.8%).One adopts technology of the present invention if will give an example, and only accounts for 0.8% (1/ (1+128)=0.77%) of total frequency range between guard plot then of the present invention.
Can learn that from the carrier frequency of above-mentioned pre-compensation value and each subcarrier this pre-compensation value with this subcarrier of this higher carrier frequency is this pre-compensation value less than this subcarrier with this lower carrier frequency.
Aforesaid for example in one, the pre-compensation value of each subcarrier is all inequality.But during practical application, not as limit.If the delay time of advent between three subcarriers, then counting of these three required delays of subcarrier will be identical less than a sampling point (time).
In addition, the continue explanation of earlier figures 5A.The time-domain signal 143,144 that Fig. 5 A is delayed is after being merged and being sent out with light signal 94.This light signal 94 arrives receiver 60 through optical fiber 80.The received signals of receiver 60 are through (being detailed later) after the fast fourier transform, and the signal frequency-domain schematic diagram that this is converted please refer to Fig. 5 B.From figure, can see and know,, and not have delay phenomenon before transmission so each subcarrier of the signal that icon receives is promptly almost same up to reaching because the delay that conveyer 10 earlier causes chromatic dispersion compensate in advance.Arriving in the time of herein is not restrictive condition, only represents the small time difference relative system that each subcarrier arrives, and can't cause decoding problem.
The technology of the group delay phenomenon that the precompensation optical fiber chromatic dispersion that proposes about the invention process example is caused, can be when system's construction be finished, promptly set about carrying out the setting of aforementioned pre-compensation value, thereafter, because optical fiber dispersion is in same optical fiber telecommunications system, unless hardware has change or fiber path that replacing is arranged, otherwise the mobility of chromatic dispersion is little, that is to say the way of this precompensation, quite be suitable for the optical orthogonal frequency-division multitask system.
Aforesaid for example is to be example with similar frequency bands and spacing between each subcarrier in, if frequency range spacing difference also can adopt the present invention, needs only and adjusts each subcarrier required time of delay respectively.
About the thin bilge construction example of time-domain signal modulator 140,141, please consult Fig. 4 again.Can know among the figure, each time-domain signal modulator 140,141 comprises a real part look-up table 142a (look up table for real part), an imaginary part look-up table 142b (look up table for imaginary part), reaches a multiplexer group 149.Real part look-up table 142a has a plurality of real part basic waveforms.Imaginary part look-up table 142b has a plurality of phase values.Multiplexer group 149 be according to these time-domain signal modulator 140,141 correspondences should and column signal 91 consult out this time-domain signal 143,144 to this real part look-up table 142a and this imaginary part look-up table 142b.
Aforementioned real part look-up table 142a stores a plurality of basic waveforms, and imaginary part look-up table 142b then stores a plurality of phase places.Aforementioned each and column signal 91 have a real part 910 (real part) and an imaginary part 912 (imaginary part).The real part 910 of multiplexer group 149 foundations and column signal 91 is consulted corresponding basic waveform and phase place at this and column signal 91 pairing real part look-up table 142a with imaginary part look-up table 142b with imaginary part 912.
The time-domain signal modulator 140,141st of Fig. 4, (QPSK, Quadrature PSK) is example with quadrature phase deviation modulation.The signal of quadrature phase deviation modulation comprises four kinds: (0,0), (0,1), (1,1) and (1,0).That is to say in the bracket first digit for and the real part 910 (generally representing) of column signal 91 with I, and second digit for and the imaginary part 912 (generally representing) of column signal 91 with Q.This multiplexer group 149 receives the also real part 910 and imaginary part 912 of column signal 91, and selects corresponding look-up table 142a, 142b according to this.This multiplexer group 149 is this basic waveform of consulting out a correspondence according to this real part 910 of this and column signal 91 to this real part look-up table 142a.Multiplexer group 149 is consulted out the phase value of a correspondence according to this imaginary part 912 of this and column signal 91 to this imaginary part look-up table 142b.Then, multiplexer group 149 is this basic waveform of finding according to this quilt and phase value and export this time-domain signal.
This multiplexer group 149 has one first multiplexer 147a, one second multiplexer 147b and a phasing back device 147c (Inverter).The first multiplexer 147a receives the also real part 910 of column signal 91, and being used for selecting from the real part look-up table still is that the imaginary part look-up table is done output.If also the value of the real part 910 of column signal 91 is 1, then do output by imaginary part look-up table 142b.Otherwise,, then do output by real part look-up table 142a if also the value of the real part 910 of column signal 91 is 0.Then, the output of the first multiplexer 147a is divided into two signals, and one of them signal is through being connected to the input of the representative " 0 " of the second multiplexer 147b behind the aforementioned phasing back device 147c.Another signal then is connected directly to the input of second multiplexer 147b representative " 1 ".
Be with the element of phasing back device 147c in this enforcement example as phase transition, if but be applied in the 16QAM system, then need this phasing back device 147c is replaced by phase converter (Phase Converter) or signal amplifier, other circuit then correspondence is made an amendment.
The second multiplexer 147b receives and the imaginary part 912 of column signal 91, is used for selecting that output as the second multiplexer 147b from two signals that institute's difference of the first multiplexer 147a is come out.If also the value of the imaginary part 912 of column signal 91 is 1, then the output of the first multiplexer 147a directly becomes the output of the second multiplexer 147b.Otherwise if also the value of the imaginary part 912 of column signal 91 is 0, then the output of the second multiplexer 147b is the output signal of phasing back device 147c.Thus, time-domain signal modulator 140,141 can be suitably and column signal 91 be converted to basic waveform according to its real part 910 with imaginary part 912 with phase place.
Aforementioned basic waveform with phase place is output to delay cell 145,146.As aforementioned, each delay cell 145,146 has been set pre-compensation value respectively.The corresponding delay cell 145,146 of pre-compensation value.The setting of this pre-compensation value is an example with the digital delay unit, adopts aforesaid counting to be unit of account.Meaning promptly adopts the mode that postpones N number of sampling to set.Delay cell 145,146 can comprise a plurality of bit shift registers (Shift Register, for example length is the bit shift register of N) and a controller.Count when delay cell 145,146 need be delayed one, setting controller then makes delay cell 145,146 be triggered time a time, and the signal of input delay unit is moved into a bit shift register, is triggered to shift out time a time again again.In like manner, count if need to postpone two, setting controller then, make the signal of input delay unit 145,146 through two bit shift registers after, be moved out of again, promptly reach and postpone two purposes of counting.
Therefore, aforementioned basic waveform with phase place is output to delay cell 145,146, and delay cell 145,146 according to the pre-compensation value that is set will with corresponding " basic waveform " with phase place postpone back output.148 synthetic aforementioned combined signals 92 of signal node that each delay cell 145,146 is exported of colligator.
Above-mentioned time-domain signal modulator 140,141st is an example with quadrature phase deviation modulation (QPSK), but not as limit.If the signal of time-domain signal modulator desire conversion is orthogonal amplitude modulating and changing (QAM), then multiplexer group 149 will comprise the element that amplifies amplitude, and is selected.That is to say time-domain signal modulator 140,141 can according to and column signal 91 and select corresponding basic waveform, phase place and amplitude.
Above-mentionedly be one-one relationship about the corresponding relation between time-domain signal modulator 140,141, multiplexer group 149 and column signal 91, pre-compensation value and the subcarrier.That is each subcarrier corresponding one and column signal 91, multiplexer group 149, a pre-compensation value and a time-domain signal modulator 140.And the real part look-up table 142a of each time-domain signal modulator 140 is the real part 910 and imaginary part 912 of corresponding respectively and column signal 91 with imaginary part look-up table 142b.
Please consult Fig. 3 again.Aforementioned receiver 60 comprises optical receiver 62 (optical sensor), analog-to word element 64 (analog to digital converter), synchronous element 66 (Synchronizer), fast fourier transform element 68 (Fast Fourier Transferring element) and chromatic dispersion monitors and etc. change element 69 (Dispersion monitor and equalizer QAM demodulator).
Optical receiver 62 is the signals of telecommunication 95 that receive aforementioned lights signal 94 and convert it to simulation.The signal of telecommunication 95 of this simulation is converted to first digital signal 96 via analog-to word element 64.Then, synchronous element 66 is promptly estimated and is removed between the Fu Yuan border (Symbol boundary) of first digital signal 96 and the guard plot with first digital signal 96 and form second digital signal 97.Fast fourier transform element 68 is about to second digital signal 97 and carries out fast fourier transform, and becomes the three digital signal 98 arranged side by side that belongs to frequency domain.Chromatic dispersion monitors and waits in the changes element 69 estimation three digital signals 98 whether still have chromatic dispersion to postpone to exist between each subcarrier, if still have chromatic dispersion delay existence, then can be back to conveyer 10 as the graphic control channel 84 of utilizing, to compensate.Then chromatic dispersion monitor and wait changes element 69 promptly three digital signal 98 to be deciphered according to the frequency range of each subcarrier after spread out of decipher after signal 99.Thus, the data decoding that can successfully conveyer 10 be spread out of.
Moreover, see also Fig. 6.It is the schematic flow sheet according to the method for the caused delay of precompensation optical fiber chromatic dispersion of the invention process example.This precompensation method is applicable to an optical orthogonal frequency-division multitask conveyer.Conveyer is the light signal that transmission one has a plurality of subcarriers.This carrier frequency that each subcarrier has a carrier frequency and this subcarrier is different.This precompensation method comprises:
Step S74: receive a plurality of pre-compensation value, this pre-compensation value is to should subcarrier; And
Step S76: this subcarrier is postponed send out after time of this corresponding with it pre-compensation value.
Aforementioned precompensation method is performed by optical orthogonal frequency-division multitask conveyer 10.The carrier frequency of aforementioned subcarrier is the employed frequency range of aforementioned each subcarrier, promptly as the M*df of Fig. 2 A or (M+1) * df or the like.The employed carrier frequency of each subcarrier is all inequality.
The pre-compensation value of step S74 can be the time of delay of each subcarrier of correspondence of being returned through control channel 84 from receiver 60 in real time.Also can by manually through the inquiry receiver 60 after, be set in this conveyer 10.Conveyer 10 has received this pre-compensation value can carry out preceding method.
Step S76 then is the mode of Fig. 5 A as described above, and each subcarrier is postponed its pairing pre-compensation value (compensating the time of its delay).Thus, can receive signal at receiver 60 places as Fig. 5 B.
The precompensation method of the invention process example please refer to Fig. 7, before step S74, can comprise in addition:
Step S71: receive a length of delay that causes by optical fiber dispersion; And
Step S72: calculate a plurality of pre-compensation value that should subcarrier according to this length of delay.
The increase of this two step is that what consider that receiver 60 passed back can be the caused total delay time of optical fiber dispersion.Total delay time between the subcarrier of just high frequency and lowest frequency, but not the time of delay that each subcarrier is received.Therefore, conveyer 10 promptly need be carried out above-mentioned step, total delay time is converted to the pre-compensation value of respectively corresponding each subcarrier.
Step S71 receives the length of delay of being passed back by receiver 60, or behind the length of delay of artificial input, this length of delay is converted to this pre-compensation value of corresponding each subcarrier by step S72.This length of delay is the total delay time between subcarrier that arrives the latest and the subcarrier that arrives the earliest.
See also Fig. 8.Step S72 comprises in addition: step S720: a time of delay of estimating this subcarrier according to this length of delay respectively; And step S722: be this pre-compensation value this time of delay of changing this subcarrier.
The estimation of abovementioned steps S720, if with above-mentioned one be example for example, conveyer 10 received length of delays are 700ps.Because the frequency difference between each subcarrier (claim bin width or claim carrier frequency apart from) identical, so estimate respectively according to length of delay and to be this length of delay time of delay of this subcarrier divided by the subcarrier spacing number.To give an example one, meaning is about to 700ps divided by (8-1), obtains 100ps.Then, the subcarrier of lowest frequency (first subcarrier) arrives the earliest, so be 0ps subcarrier time of delay of lowest frequency.(low to high according to frequency) calculates the time of delay of each subcarrier with arithmetic series successively.Be followed successively by 100,200,300,400,500,600 the time of delay of from second to the 8th subcarrier, 700ps.
Then, execution in step S722: be this pre-compensation value this time of delay of changing this subcarrier.See also Fig. 9.This step S722 comprises: S726: changing this time of delay is a plurality of make-up times; And step S728: respectively should the make-up time and the integral multiple of a sample time compare, be set at this pre-compensation value with the value near the integral multiple of this time of delay.
Step S726 will be converted to the make-up time (i.e. the time that need postpone to send) time of delay.The present invention is that the subcarrier with high frequency transmits earlier, so need not delay with one, the eight subcarrier for example, first subcarrier need postpone 700ps.That is to say that the required make-up time of each subcarrier is that total delay time (700ps) deducts each other time of delay.Therefore, each other make-up time distinctly is 700,600,500,400,300,200 from first subcarrier to the, eight subcarriers, 100ps.
Consider that then this is a digital delay, need synchronous with sample time, so need execution in step S728, with the make-up time consistent with the multiple of sample time, anticipating promptly is set at this pre-compensation value with the value near the integral multiple of this time of delay.Therefore with the 7th subcarrier is example, and its make-up time is 100ps, is not the integral multiple for sample time, can consider with 80ps or 120ps for it.Above Biao example, promptly for it with 120p.
By above-mentioned method, can effectively the caused delay of chromatic dispersion promptly be carried out precompensation at conveyer 10 ends, can make light signal 94 after optical fiber 80 transmission, the subcarrier that receives in receiver 60 places is synchronously approaching, and reduces the necessity that receiver 60 is estimated.
At last, except above-mentioned for example one, below propose for example two now, so as to explanation the present invention compared to the enhancement of prior art on effect.The two CHROMATIC DISPERSION IN FIBER OPTICS constants that adopted are 17ps/nm/km (being the chromatic dispersion delay that whenever how the long transmission of metric wave can produce 17ps of every kilometer length) for example.Use at frequency range to be 25GHz as 25GHz, sampling rate, count (size) of fast fourier transform is 128 points.Transmission range is 1000 kilometers (km).Under this test condition, use conventional method, approximate frequency and differ 125GHz because wavelength differs 1nm, therefore, 25GHz approximates 0.2nm (promptly 25/125).Through after the transmission of 1000km, the highest and group delay time low-limit frequency are 3400ps (17ps/nm/km * 1000km * 0.2nm=3400ps).The sampling rate of 25GHz is the 40ps/ point.To need 85 sampling points (3400ps/40ps=85point) between its guard plot.This will make that each symbol elementary time length was 128 points originally, increase to 213 points (85+128).Thus, shared total transmitting bandwidth is 85/ (85+128)=40% (also can to claim overhead at this) between the guard plot.That is to say in the frequency range of 25GHz have 10GHz transmitting between the guard plot (as cyclic-prefix sign indicating number Cyclic prefix).If be used in 100Gps (10 future
9Bit/second) Ethernet (Ethernet Link), it is between the guard plot that transmission repeats that 40Gps is then arranged.
On the contrary,, can understand, only need one to count and to solve the group delay variation problem between the guard plot from the calculation specifications of last table with above-mentioned for example two methods that adopt the invention process examples.If adopt conservative way, will be set at two points between the guard plot, thus, account for only about 1.5% (2/ (2+128)=1.5%) of total frequency range between the guard plot.Compared to prior art, saved considerable frequency range.
Secondly, please refer to Figure 10 A and Figure 10 B, it is to be respectively not adopt the present invention and adopt the inventive method, at the signal schematic representation of receiving terminal.Both test frequency ranges are 10GHz (10x10
9Hz).Measuring distance is 1000 kilometers monomode fiber transmission.This two figure is the planisphere of the received 16QAM of receiver 60.Trunnion axis is real part (I also can be described as sine), and vertical axis is imaginary part (Q also can be described as cosine).Figure 10 A is not for adopting the planisphere of precompensation method of the present invention.Figure 10 B is for adopting the planisphere of precompensation method of the present invention.As can be seen from Figure 10A, (scattering) quite dispersed in receiving terminal 60 each some district on planisphere, and this will make the error rate (error rate) after the decoding heighten.Relatively, use Figure 10 B of the invention process example, then its each some district is all quite concentrated, and obvious the present invention promotes part compared to the effect of prior art.
Circuit box schematic diagram about another embodiment of multi-subcarrier signal generator of the conveyer of the optical orthogonal frequency-division multitask system of the invention process example sees also Figure 11.This multi-subcarrier signal generator 24 is the time-domain signals 243,244 that are suitable for producing 16QAM.
The multi-subcarrier signal generator 24 of Figure 11 be according to should and column signal 91 and produce a plurality of time-domain signals 243 that correspond respectively to each subcarrier, 244, multi-subcarrier signal generator 24 in addition according to this and column signal 91 pairing a plurality of pre-compensation value, postpone this time-domain signal 243, the time-domain signal 243,244 that after 244 this is delayed is merged into a combined signal 92.
Time-domain signal modulator 240,241 comprises a real part look-up table 242a, an imaginary part look-up table 242b, reaches a multiplexer group 249.Multiplexer group 249 be according to time-domain signal modulator 240,241 correspondences should and column signal 91 consult and change out this time-domain signal 243,244 to this real part look-up table 242a and this imaginary part look-up table 242b.
The first multiplexer 247a of corresponding real part look-up table 242a and the second multiplexer 247b combine phasing back device 247e and signal amplifier 247g, and consult out the output signal corresponding with column signal also 91 according to column signal 91 also from real part look-up table 242a.This output signal may be after consulting out from real part look-up table 242a, has passed through phasing back device 247e and signal amplifier 247g forms, and also may all not pass through phasing back device 247e and signal amplifier 247g.Look closely and column signal 91 is exported to the signal of the first multiplexer 247a and the second multiplexer 247b and decided.Similarly, the 3rd multiplexer 247c of corresponding imaginary part look-up table 242b and the 4th multiplexer 247d combine phasing back device 247f and signal amplifier 247h, and consult out the output signal corresponding with column signal also 91 according to column signal 91 also from imaginary part look-up table 242b.
The second colligator 247m then will combine (action of similar addition) back from the second multiplexer 247b and form aforementioned time-domain signal 243 with the output signal of the 4th multiplexer 247d.
Certainly; the present invention also can have other various embodiments; under the situation that does not deviate from spirit of the present invention and essence thereof; those of ordinary skill in the art work as can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong to the protection range of the appended claim of the present invention.
Claims (13)
1. the method for the caused delay of precompensation optical fiber chromatic dispersion, it is characterized in that, be applicable to an optical orthogonal frequency-division multitask conveyer, this conveyer is the light signal that transmission one has a plurality of subcarriers, this carrier frequency that each subcarrier has a carrier frequency and this subcarrier is different, and this method comprises:
Receive a plurality of pre-compensation value, this pre-compensation value is to should subcarrier;
This subcarrier is postponed send out after time of this corresponding with it pre-compensation value.
2. the method for the caused delay of precompensation optical fiber chromatic dispersion according to claim 1 is characterized in that, wherein comprises before the step that receives a plurality of pre-compensation value:
The length of delay that reception is caused by optical fiber dispersion;
Calculate this pre-compensation value that should subcarrier according to this length of delay.
3. the method for the caused delay of precompensation optical fiber chromatic dispersion according to claim 2 is characterized in that, wherein the step of calculating this pre-compensation value that should subcarrier according to this length of delay comprises:
Estimate a time of delay of this subcarrier respectively according to this length of delay;
Be this pre-compensation value this time of delay of changing this subcarrier.
4. the method for the caused delay of precompensation optical fiber chromatic dispersion according to claim 3 is characterized in that, be that the step of this pre-compensation value comprises this time of delay of wherein changing this subcarrier:
Changing this time of delay is a plurality of make-up times;
Respectively should the make-up time and the integral multiple of a sample time compare, be set at this pre-compensation value with the integral multiple near sample time of this make-up time.
5. the method for the caused delay of precompensation optical fiber chromatic dispersion according to claim 4, it is characterized in that this pre-compensation value that wherein has this subcarrier of this higher carrier frequency is this pre-compensation value less than this subcarrier with this lower carrier frequency.
6. multi-subcarrier signal generator, it is characterized in that, it is the conveyer that is suitable for an optical orthogonal frequency-division multitask system, a string commentaries on classics of this conveyer and element are that conversion and mapping one numerical sequence signal are a plurality of and column signal, respectively this signal arranged side by side comprises a real part and an imaginary part, and this generator comprises:
A plurality of time-domain signal modulators, be with one-one relationship to signal side by side, respectively this time-domain signal modulator be according to it corresponding should and column signal produce a time domain signal;
Add ons between a plurality of guard plots, be with one-one relationship to should the time-domain signal modulator, respectively add ons is to become one by additional signal in corresponding with it this time-domain signal that this time-domain signal modulator produced between an additional respectively guard plot between this guard plot;
A plurality of delay cells, be to add ons between should the guard plot with one-one relationship, this delay cell has a predetermined delay value respectively, respectively this delay cell be postpone to transmit after this predetermined delay value add ons produced between this corresponding with it guard plot this by additional signal;
One colligator is that this that transmit in conjunction with this delay cell exported a combined signal by additional signal.
7. multi-subcarrier signal generator according to claim 6 is characterized in that, wherein respectively this time-domain signal modulator comprises:
One real part look-up table has a plurality of real part basic waveforms;
One imaginary part look-up table has a plurality of phase values;
One multiplexer group is to consult out this time-domain signal according to also column signal to this real part look-up table and this imaginary part look-up table corresponding with this time-domain signal modulator.
8. multi-subcarrier signal generator according to claim 7, it is characterized in that, wherein this multiplexer group is this basic waveform of consulting out a correspondence according to this real part of this and column signal to this real part look-up table, this multiplexer group is consulted out the phase value of a correspondence according to this imaginary part of this and column signal to this imaginary part look-up table, and this multiplexer group is this basic waveform of finding according to this quilt and phase value and export this time-domain signal.
9. the conveyer of an optical orthogonal frequency-division multitask system is characterized in that, this conveyer is to send out after a numerical sequence signal is converted to a light signal, and this conveyer comprises:
A string commentaries on classics and element are that conversion and this numerical sequence signal of mapping are a plurality of and column signal;
One multi-subcarrier signal generator, be according to should and column signal and produce corresponding a plurality of time-domain signals, this multi-subcarrier signal generator in addition according to this and the pairing a plurality of predetermined delay values of column signal, postpone behind this time-domain signal this time-domain signal that is delayed to be merged into a combined signal;
One digital revolving die is intended element, is to transfer this combined signal to an analog signal;
One electricity changes optical element, is this light signal with this analog signal conversion.
10. the conveyer of optical orthogonal frequency-division multitask according to claim 9 system is characterized in that, wherein should electricity changeing optical element be a laser.
11. the conveyer of optical orthogonal frequency-division multitask according to claim 9 system is characterized in that wherein this multi-subcarrier signal generator comprises:
A plurality of time-domain signal modulators, be with one-one relationship to signal side by side, respectively this time-domain signal modulator be according to it corresponding should and column signal produce this time-domain signal;
A plurality of delay cells, be with one-one relationship to should the time-domain signal modulator, respectively this delay cell is to postpone to transmit this time-domain signal that this corresponding with it time-domain signal modulator is produced after this predetermined delay value;
One colligator is this time-domain signal that transmits in conjunction with this delay cell and export this combined signal.
12. the conveyer of optical orthogonal frequency-division multitask according to claim 11 system is characterized in that wherein respectively this time-domain signal modulator comprises:
One real part look-up table has a plurality of real part basic waveforms;
One imaginary part look-up table has a plurality of phase values;
One multiplexer group is to consult out this time-domain signal according to also column signal to this real part look-up table and this imaginary part look-up table corresponding with this time-domain signal modulator.
13. the conveyer of optical orthogonal frequency-division multitask according to claim 12 system, it is characterized in that, wherein respectively this signal arranged side by side comprises a real part and an imaginary part, this multiplexer group is this basic waveform of consulting out a correspondence according to this real part of this and column signal to this real part look-up table, this multiplexer group is consulted out the phase value of a correspondence according to this imaginary part of this and column signal to this imaginary part look-up table, and this multiplexer group is this basic waveform of finding according to this quilt and phase value and export this time-domain signal.
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| TWI382683B (en) * | 2009-05-06 | 2013-01-11 | Ind Tech Res Inst | Method for pre-compensating for time delay incurred by chromatic dispersion, multi-subcarrier waveform generator employed therefor, and transmitter having the multi-subcarrier waveform generator |
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