CN103780519A - Channel equalization and frequency deviation estimation joint parallel method based on LMS - Google Patents
Channel equalization and frequency deviation estimation joint parallel method based on LMS Download PDFInfo
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- CN103780519A CN103780519A CN201410007137.XA CN201410007137A CN103780519A CN 103780519 A CN103780519 A CN 103780519A CN 201410007137 A CN201410007137 A CN 201410007137A CN 103780519 A CN103780519 A CN 103780519A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03178—Arrangements involving sequence estimation techniques
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
- H04L25/03114—Arrangements for removing intersymbol interference operating in the time domain non-adaptive, i.e. not adjustable, manually adjustable, or adjustable only during the reception of special signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L2025/03592—Adaptation methods
- H04L2025/03598—Algorithms
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- H04L2025/03636—Algorithms using least mean square [LMS]
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Abstract
The invention discloses a channel equalization and frequency deviation estimation joint parallel method based on LMS. At the initialization phase of an optical receiver, train sequence signals are converted into parallel signals and are sent into parallel signal processing branches for balance and frequency deviation estimation. The frequency deviation estimation average value of all branches and an error signal of each branch are computed. A unified equalizer tap coefficient is used for each group of parallel signals. When the equalizer tap coefficient is updated, the average value of the branch error signals is used. At a data transmission phase, a transmitting end inserts train symbols into data symbols. The optical receiver converts data signals into parallel signals. The train signals use balance signals and known train symbols to carry out frequency deviation estimation. The data signals use accumulation phase error corresponding to the train signals and the acquired frequency deviation estimation average value to carry out compensation and decision, and uses the balance signals and decision signals to carry out frequency deviation estimation. According to the invention, signal parallel processing is used, which reduces the limitation influence of data signal processing hardware on the system performance.
Description
Technical field
The invention belongs to optical burst receiver technical field, more specifically say, relate to a kind of based on LMS(Least Mean Square, least mean square algorithm) channel equalization and frequency deviation estimate associating parallel method.
Background technology
In current high speed coherent optical communication system, PDM-QPSK(palarization multiplexing-tetra-phase absolute phase shift keying) coherent light transmission system is one of technical scheme of tool potentiality.In PDM-QPSK coherent light transmission system, signal transmission is mainly subject to chromatic dispersion (the Chromatic Dispersion of optical fiber, and polarization mode dispersion (Polarization Mode Dispersion CD), the impact of the frequency shift (FS) that linear damage PMD) and sending and receiving end laser produce, these two problems are having a strong impact on the service behaviour of optical receiver.And adaptive balancing technique can be eliminated the intersymbol interference being brought by dispersion substantially, frequency offset estimation technique can be used to solve the impact that frequency deviation is brought.Owing to can influencing each other between equalizer and frequency offset estimator, the unified algorithm that therefore can use time domain equalization and frequency deviation to estimate.
For light burst transmission system, the feature of light burst requires equalizer in optical burst receiver to want to realize convergence fast.Fig. 1 is the system block diagram of optical burst receiver.As shown in Figure 1, the input signal r (t) of receiver is that the orthogonal smooth PDM-QPSK signal in two-way polarization direction passes through polarization coupled, also passes through the signal of the fibre channel transmission of certain distance.In fibre channel transmission process, light signal can be subject to the impact of the factors such as dispersion, polarization mode dispersion, noise of optical amplifier, causes the Quality Down of signal transmission.PDM-QPSK signal r (t) and FTLO(fast tunable laser) enter 90 degree mixers together with light wave and carry out coherent demodulation.Coherent demodulation Hou tetra-road signals carry out AD sampling and quantification.The 4 road signal Ix that export through sampling with after quantizing, Qx, Iy, Qy represents respectively homophase and the orthogonal demodulation signal of two polarization state x, y, this 4 road signal enters digital signal processing module and carries out channel equalization (Channel Equalization) and frequency deviation estimation (Frequency Offset Estimation, FOE), with compensation, last phase place judgement recovers sent data.
The unified algorithm that channel equalization based on LMS and frequency deviation are estimated is a kind of effective ways that improve coherent optical heterodyne communicatio performance.But in the design of optical burst receiver, use FPGA(Field-Programmable Gate Array, field programmable gate array) or application-specific integrated circuit (ASIC) while realizing digital signal processing algorithm, computational speed and chip area are two subject matters of restriction mutually.Therefore, be necessary in performance and realize between complexity and making a choice.Due to the two-forty feature of optical fiber communication, take the PDM-QPSK fiber optic transmission system of 112Gb/s as example, the character rate on coherent demodulation Hou tetra-each road of signal, road is 28G/s, article 4, first the branch road signal of telecommunication needs carry out the AD sampling of dual-rate and quantize, each tributary signal speed is up to 56G/s, so enter the discrete signal that the symbol is-symbol speed of equalizer is 56G/s.Follow-up digital signal processing unit (DSPU) cannot be realized the processing to this speed on hardware, so must adopt the mode of parallel processing, according to the input speed of data and the processing speed of chip, parallel branch number likely uses larger numerical value, this just requires in the time of application in real time, and algorithm must meet the requirement of parallel processing.The renewal of equalizer tap coefficient simultaneously and the frequency deviation algorithm for estimating based on pre-judgement all need the feedback of signal, and the time delay being caused by feedback in Parallel Implementation is also very large to the performance impact of system.Therefore,, in the specific implementation design of optical burst receiver, also must consider parallel and the impact of delay of feedback on receiver performance.
Summary of the invention
The object of the invention is to overcome the deficiencies in the prior art, provide a kind of channel equalization and frequency deviation based on LMS to estimate associating parallel method, reduce the limitations affect of data-signal processing hardware to systematic function.
For achieving the above object, the channel equalization and the frequency deviation that the present invention is based on LMS are estimated associating parallel method, comprise the following steps:
S1: adopt training sequence to carry out initialization, comprise step:
S1.1: send training sequence to optical burst receiver, carry out serial to parallel conversion through the training sequence signal of coherent demodulation and sample quantization and obtain N road parallel signal; Equalizer tap coefficient corresponding to n=1 group parallel signal is set
S1.2: n group parallel signal enters N parallel signal and processes branch road, and each parallel signal is processed branch road and comprised equalizer and frequency deviation estimating modules, and the equalizer of i branch road obtains equalizing signal
wherein k=(n-1) × N+i, 1≤i≤N;
S1.3: frequency deviation estimating modules is according to known training symbol
to equalizing signal
carry out frequency deviation estimation, obtain accumulated phase error
with frequency deviation estimated value
S1.4: by the frequency deviation estimated value of N branch road
average the frequency deviation estimated mean value that obtains n group parallel signal
S1.5:N branch road calculates respectively its error signal
n,i:
S1.6: upgrade the equalizer tap coefficient that n+1 group parallel signal uses:
Wherein,
represent respectively the equalizer tap coefficient that n+1 group, n group parallel signal use; D represents the delay of error signal; λ is the iteration step length arranging, and is positive number; N
crepresent the error signal quantity of the participation tap coefficient calculating of selecting from N branch road, 1≤N
c≤ N, 1≤i
c≤ N
c;
represent
corresponding observation vector,
represent
conjugation;
S1.7: whether training of judgement sequence is disposed, if untreated complete, return to step S1.2 and continues to process next group parallel signal, if be disposed, enters step S2;
S2: enter data transmission phase data are processed, comprise step:
S2.1: data sending terminal inserts training symbol in data symbol, its insertion method is: send symbol as one group take N, send symbol by N again and be divided into R group, every NR of group transmission comprises a training symbol in symbol, and R training symbol sequence number in parallel symbol is designated as i
r, 1≤r≤R;
S2.2: send data-signal to optical burst receiver, obtain N road parallel signal to carrying out serial to parallel conversion through the data-signal of coherent demodulation and sample quantization, n group parallel signal enters N parallel signal and processes branch road, the parallel signal of data transmission phase is processed branch road and is comprised equalizer, frequency deviation estimating modules and judging module, and the equalizer processes of i branch road obtains equalizing signal
S2.3: N bar branch road is carried out respectively to frequency deviation estimation:
In the time that branch road is training signal, directly according to known training symbol
to equalizing signal
carry out frequency deviation estimation, obtain accumulated phase error
with frequency deviation estimated value
In the time that branch road is data-signal, first to equalizing signal
carry out phase compensation, the signal after phase compensation
for:
Wherein, d represents the delay of frequency deviation estimated mean value,
expression rounds up; Judging module is to signal
adjudicate and obtain decision signal
according to decision signal
to equalizing signal
carry out frequency deviation estimation, obtain frequency deviation estimated value
and accumulated phase error
S2.4: by the frequency deviation estimated value of N branch road
average the frequency deviation estimated mean value that obtains n group parallel signal
S2.5:N branch road calculates respectively its error signal
n,i:
When branch road is training signal, i.e. i=i
rtime, error signal
n,ifor:
In the time that branch road is data-signal, error signal
n,ifor:
S2.6: upgrade the equalizer tap coefficient that n+1 group parallel symbol is used:
Wherein, λ
*the iteration step length that data transmission phase arranges,
the error signal quantity that the participation tap coefficient that expression data transmission phase is selected from N branch road calculates,
S2.7: judge whether data are disposed, if untreated complete, return to step S2.2 and continue to process, if be disposed, finish.
Further, the concrete grammar that frequency deviation is estimated comprises the following steps:
S3.1: calculate equalizing signal
accumulated phase error:
In the time that branch road is training symbol, accumulated phase error
wherein
represent the phase place of known training symbol,
represent equalizing signal
phase place;
In the time that branch road is data-signal, accumulated phase error
wherein
represent data decision signal
phase place;
S3.2: the frequency deviation estimated value of calculating this branch road
wherein
represent the accumulated phase error of k-1 signal.
The channel equalization and the frequency deviation that the present invention is based on LMS are estimated associating parallel method, at the initial phase of optical receiver, after being converted into parallel signal by serial to parallel conversion, the sampled signal of training sequence signal sends into parallel signal processing branch road, every branch road carries out respectively equilibrium and frequency deviation estimation, the frequency deviation estimated value that all branch roads are obtained averages and obtains frequency deviation estimated mean value, every branch road calculates respectively its error signal according to frequency deviation estimated mean value, every group of parallel signal adopts unified equalizer tap coefficient, equalizer tap coefficient adopts the average of branch road error signal to upgrade while renewal, in data transmission phase, transmitting terminal inserts training symbol in data symbol, to obtain parallel signal by serial to parallel conversion through the data-signal of coherent demodulation and sample quantization, training signal adopts equalizing signal and known training symbol to carry out frequency deviation estimation, data-signal uses the accumulated phase error of corresponding training signal and the frequency deviation estimated mean value that obtained reconvicts after compensating, adopt again equalizing signal and decision signal to carry out frequency deviation estimation, then adopt with initial phase same procedure and carry out the renewal of equalizer tap coefficient.
The present invention has following beneficial effect:
(1) the present invention, by parallelization, has reduced signal rate, thereby has reduced the limitations affect of data-signal processing hardware to systematic function;
(2) at initial phase, adopt frequency deviation estimated mean value error signal, can improve the initialized reliability of equalizer;
(3) in data transmission phase, in parallel symbol, insert the training symbol of some, can improve the accuracy of judgement, frequency deviation estimation and error signal feedback;
(4) show through emulation, the present invention has good tolerance to the delay of error signal.
Accompanying drawing explanation
Fig. 1 is the system block diagram of optical burst receiver;
Fig. 2 is initial phase parallel signal branch road algorithm schematic diagram;
Fig. 3 is data transmission phase parallel signal branch road algorithm schematic diagram;
Fig. 4 is the equalizer convergence speed comparison diagram of parallel method of the present invention and serial approach;
Fig. 5 is to having computing relay and the convergence rate comparison diagram without computing relay in parallel method of the present invention;
Fig. 6 is the serial approach error rate comparison diagrams that postpone lower parallel method different from the present invention.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.Requiring particular attention is that, in the following description, in the time that perhaps the detailed description of known function and design can desalinate main contents of the present invention, these are described in here and will be left in the basket.
Embodiment
The present embodiment is still take the PDM-QPSK fiber optic transmission system of 112Gb/s as example, by the signal of 56G/s speed through going here and there and being converted to multi-path parallel signal, Wei256 road herein, makes like this speed on each road effectively reduce, thereby can reduce its physics realization difficulty.Owing to being two samplings, therefore judgement is drawn 128 symbols by each Zu256 road signal, needs as seen the parallel processing branch road quantity N=128 of configuration.
The work of optical burst receiver is divided into two stages: initial phase and data transmission phase.Detecting after optical burst signal arrival, first optical burst receiver enters initial phase, adopts training sequence to upgrade until convergence completes the initialization of equalizer and optical burst receiver equalizer tap coefficient iteration.After optical burst receiver initialization completes, then enter data transmission phase.Below the algorithm in two stages in the present invention is elaborated.
One, initial phase
Fig. 2 is initial phase parallel signal branch road algorithm schematic diagram.As shown in Figure 2, compared with the algorithm of serial, the difference of parallel algorithm of the present invention is, one group of 128 parallel symbol correspondence 128 equalizers (EQ) based on LMS algorithm, each equalizer adopts identical tap coefficient.The renewal of tap coefficient is the initialized key of equalizer, and the renewal of tap coefficient needs use error signal, therefore needs first to obtain the error signal of every branch road.The training sequence that initial phase uses should long enough, to guarantee that the equalizer tap coefficient that initialization obtains can restrain.Initial phase comprises following concrete steps:
S101: send training sequence to optical burst receiver, carry out serial to parallel conversion through the training sequence signal of coherent demodulation and sample quantization and obtain N road parallel signal; Equalizer tap coefficient corresponding to n=1 group parallel signal is set
the present embodiment Zhong Wei 128 tunnels.
S102: n group parallel signal enters N parallel signal and processes branch road, and each parallel signal is processed branch road and comprised equalizer and frequency deviation estimating modules, and the equalizer of i branch road obtains equalizing signal
wherein k=(n-1) × N+i, 1≤i≤N.
S103: frequency deviation estimating modules is according to known training symbol
to equalizing signal
carry out frequency deviation estimation, obtain accumulated phase error
with frequency deviation estimated value
The frequency deviation estimating method adopting in present embodiment is the phase estimation method based on pre-judgement, and algorithm thinking is: equalizing signal
phase place Φ
kcan be expressed as:
Wherein, θ
kthe phase information that is-symbol is carried,
it is accumulated phase error.Phase error
can be expressed as:
Wherein, φ
0, kbeing caused by laser phase noise, is slowly to change for high speed signal, so can think constant, φ concerning one group of parallel symbol
nby ASE(spontaneous radiation) phase fluctuation that causes of noise, k Δ ω
n,it is caused by frequency deviation.Visible, the phase place of Jiang Mei road signal is removed symbol phase θ
kjust remaining afterwards
the accumulated phase error of adjacent-symbol is carried out to calculus of differences, obtain the frequency deviation estimated value of each branch road
average again computing and obtain frequency deviation estimated mean value
just can suppress to a certain extent φ
nimpact.Frequency deviation is slowly to change for the signal of two-forty, so in the present invention, can think that its frequency deviation size is identical for one group of parallel symbol.The concrete steps that frequency deviation is estimated comprise:
S3.1: calculate equalizing signal
accumulated phase error
wherein, Φ
krepresent equalizing signal
phase place.
S3.2: the frequency deviation estimated value of calculating this branch road
wherein
represent the accumulated phase error of k-1 symbol of training sequence.Significantly, when in initial phase, the 1st branch road calculates frequency deviation estimated value, accumulated phase error
initial value
In present embodiment, as shown in Figure 2, step S3.1 and step S3.2 adopt equalizing signal
with training sequence symbols
conjugation (conj ()) obtain after multiplying each other
with
conjugation multiply each other and obtain
right
get angle (arg ()) and can obtain frequency deviation estimated value
S104: by the frequency offset estimation result of N branch road
average the frequency deviation estimated mean value that obtains n group parallel signal
?
S105:N branch road calculates respectively its error signal
n,i:
Be known training sequence due to what adopt at initial phase, therefore in the time of error signal, do not need to use decision signal, but directly adopt known training symbol.
S106: upgrade the equalizer tap coefficient that n+1 group parallel symbol is used:
Wherein,
represent respectively the equalizer tap coefficient that n+1 group, n group parallel signal use.D represents the delay of error signal, and parallel symbol is input to error signal and feeds back to the time of equalizer.Postpone owing to existing, therefore, in the time of 1≤n≤D, cannot upgrade tap coefficient, tap coefficient uses initial value always
λ is the iteration step length arranging, and is positive number, and its selection needs enough little of to guarantee that iterative process can restrain.
The equalizer adopting in the present invention is the equalizer based on LMS algorithm, is not the error signal of single branch road in the time carrying out the renewal of tap coefficient, but adopts the average of branch road error signal,
nc represents the error signal quantity of the participation tap coefficient calculating of selecting from N branch road, 1≤N
c≤ N, 1≤i
c≤ N
c.In the time that branch road quantity is larger, all calculate a grouping error signal and can produce larger delay, therefore can meet under the condition of convergence, can reduce the error signal number that participates in average computation, i.e. N
c< N.
represent
corresponding observation vector, i.e. the signal of input equalizer,
represent
conjugation.
S107: whether reception & disposal is complete for training of judgement sequence signal, if untreated complete, return to step S102 and continues to process next group parallel signal, if be disposed, enters data transmission phase.
Two, data transmission phase
The Main Differences of data transmission phase and initial phase is phase place the unknown of data symbol, need to recover by judgement.Because the phase place judging process of data symbol may be made mistakes, therefore the present invention inserts the reference phase of the training symbol acquisition phase compensation needs of some in the data symbol sending simultaneously.Fig. 3 is data transmission phase parallel signal branch road algorithm schematic diagram.As shown in Figure 3, data transmission phase comprises the following steps:
S201: data sending terminal inserts training symbol in data symbol, its insertion method is: send symbol as one group take N, send symbol by N again and be divided into R group, every NR of group transmission comprises a training symbol in symbol, and R training symbol sequence number in parallel symbol is designated as i
r, 1≤r≤R.
In data transmission phase, because every group of N symbol after parallel need to be adjudicated in advance to N bar branch road simultaneously, if made mistakes when judgement, the error signal of feedback is just probably made mistakes, can be to the performance generation ill effect of system.So in order to obtain a relatively accurate phase compensation in the time adjudicating, the present invention inserts the training symbol of some in the time of transmitting terminal transmitted signal in transmission symbol.The computational methods of every branch road of branch road and training sequence stage that training symbol is corresponding are identical, training signal branch road first calculates accumulated phase accurately as the reference phase using when several data-signal branch decisions before and after this branch road, estimates to carry out frequency deviation more accurately.
For the noise being exaggerated in the time that when judgement makes frequency deviation estimated value reaches minimum, a kind of optimal way is the centre position that insertion symbol is inserted in to this small group, send symbol as example take one group 128, the position of the training symbol at this moment inserting is: 128/ (R × 2)+x × 128/R, x=0,1 ..., R.For example every group is inserted when 4 symbols, and 32 symbols of Ze Mei group are adjudicated based on an identical accumulated phase error, therefore 4 training symbols are inserted in respectively to i
1=16, i
2=48, i
3=80, i
4article=112, on branch road, in judgement, can reduce like this error of phase compensation, use at most 16 times of training signal branch road frequency deviation estimated value.
S202: send data-signal to optical burst receiver, obtain N road parallel signal to carrying out serial to parallel conversion through the data-signal of coherent demodulation and sample quantization, n group parallel signal enters N parallel signal and processes branch road, the parallel signal of data transmission phase is processed branch road and is comprised equalizer, frequency deviation estimating modules and judging module, and the equalizer processes of i branch road obtains equalizing signal
The parallel symbol group sequence number n of data transmission phase continues to arrange from the sequence number of last parallel symbol group of initial phase, and equalizer tap coefficient when first group of parallel symbol of data transmission phase carried out equalizer processes is the equalizer tap coefficient that initial phase finally obtains.
S203: N bar branch road is carried out respectively to frequency deviation estimation.The handling process of training signal and data-signal is distinguished to some extent.
In the time that branch road is training signal, x as shown in Figure 3
n, 16road signal, adopts the algorithm identical with initial phase to obtain error signal, that is: directly according to known training symbol
to equalizing signal
carry out frequency deviation estimation, obtain frequency deviation estimated value
and accumulated phase error
?
with
In the time that branch road is data-signal, x as shown in Figure 3
n, 15and x
n, 17road signal, first to equalizing signal
carry out phase compensation, the signal after phase compensation
for:
Wherein, d represents the delay of frequency deviation estimated mean value,
expression rounds up.Visible, what in data transmission phase n group parallel signal, the phase compensation of data-signal adopted the is frequency deviation estimated mean value that n-d group parallel signal obtains and the accumulated phase error that under it, in group, training signal obtains.
With x
n, 15for example, due to
i
1=16, the therefore signal after its phase compensation
for:
Judging module is to signal
adjudicate and obtain decision signal
according to decision signal
to equalizing signal
carry out frequency deviation estimation, obtain frequency deviation estimated value
and accumulated phase error
as shown in Figure 3
with
S204: by the frequency offset estimation result of N branch road
average the frequency deviation estimated mean value that obtains n group parallel signal
?
S205:N branch road calculates respectively its error signal
n,i.Same, the processing method of training signal and data-signal is distinguished to some extent.
When branch road is training signal, i.e. i=i
rtime, error signal
n,ifor:
In the time that branch road is data-signal, error signal
n,ifor:
S206: upgrade the equalizer tap coefficient that n+1 group parallel symbol is used:
Wherein, λ
*the iteration step length that data transmission phase arranges,
the error signal quantity that the participation tap coefficient that expression data transmission phase is selected from N branch road calculates,
if participate in the error signal quantity N of average computation in initial phase and data transmission phase
cwith
not identical, iteration step length λ and λ that they use
*also need corresponding adjustment.
In data transmission phase, because exceeded error signal delay D the running time of system, therefore can realize the renewal of equalizer tap coefficient at every turn.
S207: judge whether data are disposed, if untreated complete, return to step S202 and continue to process next group parallel signal, if be disposed, finish.
The channel equalization and the frequency deviation that the present invention is based on LMS are estimated to associating parallel method carries out simulating, verifying below.In emulation, parallel branch quantity is 256, uses standard single-mode fiber, and Optical Fiber Transmission distance is about 50km, and equalizer uses 11 taps.
First error signal quantity N in initial phase equalizer tap coefficient being upgraded
csize the impact of systematic function is carried out to emulation.The computation delay Qu Liao10Ge clock-unit of equalizer error signal, the delay Ye Qu10Ge clock-unit that FOE calculates, 20 timers altogether.At initial phase, use the training data of 12 frames, 1024 symbols of every frame, the duration is about 440ns.In data transmission phase, in each group parallel data, insert 4 training symbols.Other parameter using in emulation comprises the frequency deviation of 1G, and Optical Signal To Noise Ratio (OSNR) is fixed as 13dB.Table 1 is the impact of different error signal quantity on systematic function during equalizer tap coefficient upgrades.
| Nc | The error rate | λ/N c |
| 32 | 1.7516×10 -2 | 0.2/32 |
| 64 | 4.6241×10 -4 | 0.2/64 |
| 128 | 4.2286×10 -4 | 0.2/128 |
Table 1
As can be seen from Table 1, in the time that Optical Signal To Noise Ratio is 13dB, only need 64 error signals just can obtain good systematic function.
Then the training symbol amount R of every group of transmission symbol of data transmission phase being inserted is carried out emulation to the impact of systematic function, has carried out twice emulation in the situation that OSNR is respectively 12dB and 13dB, and the simulation parameter that other parameters are used with table 1 is identical.Table 2 is that every group of data transmission phase sends the impact of the training symbol quantity of inserting in symbol on systematic function.
| R | The error rate (OSNR=12dB) | The error rate (OSNR=13dB) |
| 2 | 3.2787×10 -2 | 5.5445×10 -4 |
| 4 | 3.1583×10 -2 | 4.0015×10 -4 |
| 8 | 3.1293×10 -2 | 4.7803×10 -4 |
Table 2
As can be seen from Table 2, in the situation that OSNR is respectively 12dB and 13dB, the number of inserting training symbol is to have obtained enough good performance at 4 o'clock.In the time of specific design burst mode optical receivers, can need to select different insertion training symbol numbers according to different systems.
Fig. 4 is the equalizer convergence speed comparison diagram of parallel method of the present invention and serial approach.The OSNR using in this emulation is 13dB, and MSE represents mean square error (Mean Squared Error).As shown in Figure 4, to the parallelization of serial algorithm, although can reduce to a certain extent the convergence rate of equalizer, can't affect the performance after convergence.
Fig. 5 combines and in parallel method, has computing relay and convergence rate comparison diagram without computing relay the present invention.The total delay size using in this emulation is 20 clock-units.As shown in Figure 5, in the time having computing relay, the convergence of equalizer is the phase delay along with the delay of iterative computation just, does not affect the performance after iteration convergence.And if use other different delay size in emulation, can obtain equally similar effect, the present invention has good tolerance for the size of computing relay as can be seen here.
Fig. 6 is the serial approach error rate comparison diagrams that postpone lower parallel method different from the present invention.As shown in Figure 6, as long as after the correct initialization of optical burst receiver, the error rate (BER) performance of the computing relay size in the present invention on optical burst receiver do not affect.Meanwhile, compared with the performance of desirable serial approach, the performance loss bringing due to parallelization in the present invention also only has general 0.2dB left and right.
Although above the illustrative embodiment of the present invention is described; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various variations appended claim limit and definite the spirit and scope of the present invention in, these variations are apparent, all utilize innovation and creation that the present invention conceives all at the row of protection.
Claims (3)
1. the channel equalization based on LMS and frequency deviation are estimated an associating parallel method, it is characterized in that comprising lower step:
S1: adopt training sequence to carry out initialization, comprise step:
S1.1: send training sequence to optical burst receiver, carry out serial to parallel conversion through the training sequence signal of coherent demodulation and sample quantization and obtain N road parallel signal; Equalizer tap coefficient corresponding to n=1 group parallel signal is set
S1.2: n group parallel signal enters N parallel signal and processes branch road, and each parallel signal is processed branch road and comprised equalizer and frequency deviation estimating modules, and the equalizer of i branch road obtains equalizing signal
wherein k=(n-1) × N+i, 1≤i≤N;
S1.3: frequency deviation estimating modules is according to known training symbol
to equalizing signal
carry out frequency deviation estimation, obtain accumulated phase error
with frequency deviation estimated value
S1.4: the frequency deviation of N branch road is estimated to frequency deviation value
t averages the frequency deviation estimated mean value that obtains n group parallel signal
t;
S1.5:N branch road calculates respectively its error signal
n,i:
S1.6: upgrade the equalizer tap coefficient that n+1 group parallel signal uses:
Wherein,
represent respectively the equalizer tap coefficient that n+1 group, n group parallel signal use; D represents the delay of error signal; λ is the iteration step length arranging, and is positive number; N
crepresent the error signal quantity of the participation tap coefficient calculating of selecting from N branch road, 1≤N
c≤ N, 1≤i
c≤ N
c;
represent
corresponding observation vector,
represent
conjugation;
S1.7: whether training of judgement sequence is disposed, if untreated complete, return to step S1.2 and continues to process next group parallel signal, if be disposed, enters step S2;
S2: enter data transmission phase data are processed, comprise step:
S2.1: data sending terminal inserts training symbol in data symbol, its insertion method is: send symbol as one group take N, send symbol by N again and be divided into R group, every NR of group transmission comprises a training symbol in symbol, and R training symbol sequence number in parallel symbol is designated as i
r, 1≤r≤R;
S2.2: send data-signal to optical burst receiver, obtain N road parallel signal to carrying out serial to parallel conversion through the data-signal of coherent demodulation and sample quantization, n group parallel signal enters N parallel signal and processes branch road, the parallel signal of data transmission phase is processed branch road and is comprised equalizer, frequency deviation estimating modules and judging module, and the equalizer processes of i branch road obtains equalizing signal
S2.3: N bar branch road is carried out respectively to frequency deviation estimation:
In the time that branch road is training signal, directly according to known training symbol
to equalizing signal
carry out frequency deviation estimation, obtain accumulated phase error
with frequency deviation estimated value
In the time that branch road is data-signal, first to equalizing signal
carry out phase compensation, the signal after phase compensation
for:
Wherein, d represents the delay of frequency deviation estimated mean value,
expression rounds up; Judging module is to signal
adjudicate and obtain decision signal
according to decision signal
to equalizing signal
carry out frequency deviation estimation, obtain frequency deviation estimated value
and accumulated phase error
S2.4: by the frequency deviation estimated value of N branch road
average the frequency deviation estimated mean value that obtains n group parallel signal
S2.5:N branch road calculates respectively its error signal
n,i:
When branch road is training signal, i.e. i=i
rtime, error signal
n,ifor:
In the time that branch road is data-signal, error signal
n,ifor:
S2.6: upgrade the equalizer tap coefficient that n+1 group parallel symbol is used:
Wherein, λ
*the iteration step length that data transmission phase arranges,
the error signal quantity that the participation tap coefficient that expression data transmission phase is selected from N branch road calculates,
S2.7: judge whether data-signal is disposed, if untreated complete, return to step S2.2 and continue to process, if be disposed, finish.
2. associating parallel method according to claim 1, is characterized in that, the concrete grammar that described frequency deviation is estimated comprises the following steps:
S3.1: calculate equalizing signal
accumulated phase error:
In the time that branch road is training symbol, accumulated phase error
wherein θ k represents the phase place of known training symbol, Φ
krepresent equalizing signal
phase place;
In the time that branch road is data-signal, accumulated phase error
wherein
represent data decision signal
phase place;
S3.2: the frequency deviation estimated value of calculating this branch road
wherein
represent the accumulated phase error of k-1 signal.
3. parallel method according to claim 1, is characterized in that, in described step S2.1, the insertion position of training symbol is N/ (R × 2)+x × N/R, x=0, and 1 ..., R.
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