CN107769841B - Satellite communication Turbo code iterative demodulation method under high dynamic Arctic ice area - Google Patents
Satellite communication Turbo code iterative demodulation method under high dynamic Arctic ice area Download PDFInfo
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Abstract
The present invention discloses a kind of satellite communication Turbo code iterative demodulation method under high dynamic Arctic ice area, comprising: (10) will receive bandpass signal and be converted to baseband signal；(20) frequency deviation rough estimate evaluation is obtained, and carries out carrier wave frequency deviation compensation using the estimated value；(30) the compensated signal of carrier wave frequency deviation is subjected to matched filtering；(40) timing frequency deviation is estimated, frequency deviation amendment is timed to filtered signal；(50) pre-estimation frequency deviation compensates signal；(60) smart estimation is carried out to frequency deviation skew, and the compensated signal of pre-estimation is compensated；(70) residual timing frequency deviation compensated to carrier deviation, timing offset carry out smart estimation, output decoding court verdict；(80) next code is grouped, introduces frequency deviation counter, improved EM algorithm and complete Doppler shift variation tracking.Turbo code iterative demodulation method of the invention, complexity is low, efficiency is higher, adaptability is good.
Description
Technical field
The invention belongs to technical field of satellite communication, especially a kind of efficiency is higher, adaptability the is good extremely low letter of high dynamic
It makes an uproar than lower satellite communication Turbo code iterative demodulation method.
Background technique
It is answered for the advanced encoding techniques of representative in satellite mobile communication, the extensive of navigation industry with Turbo code, LDPC code etc.
With allowing communication system to work under the conditions of low-down signal-to-noise ratio.But its excellent performance, which is established, correctly to be demodulated
On the basis of.It even if the frequency shift (FS) of very little, can also cause the sharply decline of error performance in receiving end, thus obtain accurately same
It is most important to normal communication to walk information.
Meanwhile in order to sufficiently obtain the high coding gain of channel code bring and transmit system in a manner of close to shannon limit,
It must be using the channel coding method with more low bit- rate.And the every reduction by 1/2 of encoder bit rate, demodulation threshold decline 3dB, this is just
It is to say, although means the promotion that can be provided message capacity under equal-wattage resources supplIes using low bit- rate, but require demodulation
Device works under extremely low demodulation threshold.Arctic ice area mentioned here is referred to using the even lower code rate system of 1/6 code rate
It unites corresponding thresholding.In so low signal-to-noise ratio (Es/N0< -6dB) under the conditions of, it is a bottleneck for existing demodulator.
Either carrier synchronization, Timing Synchronization or frame synchronization, algorithm for estimating are all extremely sensitive to signal-to-noise ratio.Traditional
Unbound nucleus algorithm, although operation is simple, as signal-to-noise ratio descent performance deteriorates, data aided algorithm estimated accuracy
Height, but need largely to use pilot frequency sequence, it is low for the satellite channel spectrum efficiency of Bandwidth-Constrained.
It is proposed in recent years that high-performance code gain assist in synchronization can then be made full use of based on coding aided algorithm, it is pole
One kind of design framework effectively selection under low signal-to-noise ratio.
The basic thought of coding auxiliary is: by the iterative decoding process of the high gain coding such as Turbo code, LDPC code and front end
Parameter estimation procedure combine, estimated with the Soft Inform ation auxiliary parameter of iterative decoding, and enterprising on new parameter Estimation basis
Row decoding, the two is mutually promoted to be restrained jointly eventually, completes the accurate estimation and decoding of parameter.Comprehensive existing literature, coding auxiliary
Algorithm mainly includes three classes scheme: directly carrying out assist in synchronization using symbol accurate after decoding as reference sequences, realizes low SNR
Under iteration it is synchronous, by the maximum a posteriori such as Turbo code (MAP) iterative decoding, by searching for the best good fortune of performance under assigned error
It deposits path and realizes synchronization；Decoding gained Soft Inform ation is fed back into synchronous ring after processing, to judge and compensate synchronism deviation.Its
In, scheme one is only that for information simply instead of reference sequences in synchronized algorithm, program convergence will be slow after decoding, limited performance in
Synchronized algorithm interferes vulnerable to burst signal, is only used for the synchronized tracking stage.Scheme two uses most complicated Turbo code MAP
Decoding, delay and computation complexity are all relatively large, but the performance phase estimated by search survivor path on the basis of the decoding
To preferable.There are two main classes the implementation method of scheme three: first kind method is by need to estimate synchronism deviation parameter greatest hope
(EM) criterion derives the iteration more new formula of the parameter, and the resulting Soft Inform ation of each iterative decoding is used for more new formula and is synchronized
Straggling parameter to reach best estimate as a result, this method the number of iterations is relatively smaller, and can and be decoded while be carried out, but estimate model
Enclose it is very narrow, another kind of method pass through using decoding output Soft Inform ation constructed fuction, obtained by search function maximum value optimal
Estimation.This method estimated accuracy is high, can work in parameter Estimation domain, but due to using search arithmetic, iteration complexity is very high.
In short, problem of the existing technology is: it is multiple that satellite communication receives demodulation under the conditions of high dynamic Arctic ice area
Miscellaneous degree is high, demodulation coding delay is larger.
Summary of the invention
The purpose of the present invention is to provide satellite communication Turbo code iterative demodulation sides under a kind of high dynamic Arctic ice area
Method, complexity is low, efficiency is higher, adaptability is good.
The technical solution for realizing the aim of the invention is as follows:
A kind of high dynamic Arctic ice area satellite communication Turbo code iterative demodulation method, includes the following steps:
(10) it receives signal down coversion: bandpass signal will be received by quadrature frequency conversion, be converted to baseband signal；
(20) the big frequency deviation of signal is eliminated: baseband signal being segmented and carries out Fourier transformation and carries out after adding up, is filtered with matching
The Fourier transform shifting of wave device receptance function is added, and obtains likelihood function；It is thick that frequency deviation is obtained by search likelihood function peak value
Estimated value, and carrier wave frequency deviation compensation is carried out using estimated value docking take-up messenger；
(30) Signal Matching filters: the compensated signal of carrier wave frequency deviation being carried out matched filtering, obtains channel matched signal；
(40) frame synchronization and bit timing Combined estimator: high rate sampling is carried out to the signal after matched filtering, is obtained more
Road sampled signal carries out Frame Synchronization Test to multi-channel sampling signal parallel, searches for related peak maximum, utilizes related peak maximum
And corresponding position, timing frequency deviation is estimated, frequency deviation is timed to filtered signal using the timing frequency deviation and is corrected；
(50) frequency deviation skew pre-estimation: sequence is assisted as the data of Frequency Estimation using the frame head that Frame Synchronization Test captures
Column carry out pre-estimation to frequency deviation using based on trigonometric polynomial interpolated data quenching frequency algorithm for estimating, and repair to timing frequency deviation
Signal after just compensates；
(60) frequency deviation skew essence is estimated: being calculated using the cascade code auxiliary of trigonometric interpolation EM algorithm is searched for and be based on based on M value
Method carries out smart estimation to frequency deviation skew, and compensates to the compensated signal of pre-estimation；
(70) timing offset essence is estimated: compensated to carrier deviation to M value two-dimensional search algorithm of the utilization based on interpolation
Residual timing frequency deviation, timing offset are estimated, and are modified to be sent into revised signal to coding groups data and decode
Device decoding, output decoding court verdict complete initial code grouping iterative demodulation decoding.；
(80) Doppler shift variation tracking: being grouped next code, counts in frequency EM algoritic module pull-in frequency
Device improves EM algorithm, completes Doppler shift variation tracking.
Compared with prior art, the present invention its remarkable advantage are as follows:
1, demodulation threshold is very low: the synchronous links parameter Estimation demand of comprehensive analysis of the present invention proposes a kind of complete
Iterative demodulation method, can be directed to the even lower code rate of 1/6 code rate coded system, under very low demodulation threshold, complete letter
Number synchronous and decoding.
2, efficiency is higher: giving a kind of new Frame Synchronization Test algorithm, detection probability is higher under identical frame head length；
And carrier wave, Timing Synchronization are completed using coding aided algorithm, increase pilot frequency sequence without additional, pilot tone sequence can be greatly decreased
Column, efficiency of transmission are higher.
3, complexity is lower: trigonometric polynomial interpolation being applied to carrier wave, timing coding assist in synchronization algorithm, gives one
The Cascade algorithms of kind EM algorithm and the search of M value reduce decoding iteration while guaranteeing estimation range and estimated accuracy
Number reduces the complexity of algorithm realization.
4, adaptability is good: the present invention is unstable there are timing frequency deviation, move in the presence of most general frequency to star for send-receive clock
The application scenarios such as inclined and Doppler shift change rate give corresponding solution annual reporting law, enhance system and hold under very low signal-to-noise ratio
Bear high dynamic ability.
The present invention is described in further detail with reference to the accompanying drawings and detailed description.
Detailed description of the invention
Fig. 1 is the main flow chart of high dynamic Arctic ice area satellite communication Turbo code iterative demodulation method of the present invention.
Fig. 2 is the flow chart of the big frequency deviation removal process of signal in Fig. 1.
Fig. 3 is the working principle diagram of frame lock bit timing Combined estimator step in Fig. 1.
Fig. 4 is the flow chart of Fig. 1 frequency deviation pre-estimation step step.
Fig. 5 is the flow chart of the carrier wave essence estimating step based on code auxiliary in Fig. 1.
Fig. 6 is the flow chart based on M value-based algorithm frequency rough search step in Fig. 5.
Fig. 7 is the flow chart based on trigonometric interpolation EM algorithm frequency essence estimating step in Fig. 5.
Fig. 8 is the flow chart based on code auxiliary timing deviation essence estimating step in Fig. 1.
Fig. 9 is the working principle diagram of Doppler shift variation tracking step in Fig. 1.
Figure 10 is the Performance Simulation Results of high dynamic Arctic ice area satellite communication Turbo code iterative demodulation method of the present invention
Figure.
Specific embodiment
As shown in Figure 1, high dynamic Arctic ice area satellite communication Turbo code iterative demodulation method of the present invention, including it is as follows
Step:
(10) it receives signal down coversion: bandpass signal will be received by quadrature frequency conversion, be converted to baseband signal；
(20) the big frequency deviation of signal is eliminated: baseband signal being segmented and carries out Fourier transformation and carries out after adding up, is filtered with matching
The Fourier transform shifting of wave device receptance function is added, and obtains likelihood function；It is thick that frequency deviation is obtained by search likelihood function peak value
Estimated value, and carrier wave frequency deviation compensation is carried out using estimated value docking take-up messenger；
As shown in Fig. 2, the big frequency deviation removal process of (20) signal includes:
(21) baseband signal is segmented Fourier transform: being L by observation interval length0Baseband signal be divided into N sections, every segment
Then a length of L converts to obtain R to l sections of progress N point discrete Fouriersl(k), and acquire grouping it is cumulative and,
(22) N point discrete Fourier matched filtering receptance function Fourier transform: is carried out to matched filter receptance function g (t)
Vertical leaf transformation obtains the corresponding Fourier transformation value G (k) of function；
(23) shifter-adder: by G (k) Xiang Zuoyi m withIt adds up after multiplication, obtains likelihood function Λ (m),
(24) offset estimation: by the continuous shifted left of G (k), searching plain Λ (m) function maxima, is maximized and corresponding is
ForSample frequency is fs, then Frequency Estimation are as follows:
(25) big frequency deviation compensation: frequency rough estimated value is utilizedIt docks take-up messenger and carries out carrier wave frequency deviation compensation.
(30) Signal Matching filters: the compensated signal of carrier wave frequency deviation being carried out matched filtering, obtains channel matched signal；
(40) frame synchronization and bit timing Combined estimator: high rate sampling is carried out to the signal after matched filtering, is obtained more
Road sampled signal carries out Frame Synchronization Test to multi-channel sampling signal parallel, searches for related peak maximum, utilizes related peak maximum
And corresponding position, timing frequency deviation is estimated, frequency deviation is timed to filtered signal using the timing frequency deviation and is corrected；
As shown in figure 3, (40) the frame lock bit timing Combined estimator step includes:
(41) signal sampling: high rate sampling is carried out to the signal after wave frequency offset compensation, obtains multi-channel sampling signal；
(42) multi-channel sampling signal multichannel Frame Synchronization Test: is sent to N respectivelypRoad Frame Synchronization Test unit carries out frame synchronization
Detection, search obtain NpA correlation peak maximum, every road Frame Synchronization Test unit use the tolerance frequency deviation of following expression
Frame Detection Algorithm,
Wherein,The detection limit obtained when being set to i for start of frame bits；
rkTo receive signal, a length of L of frame headh, by long LhSequence be divided into LPDISection, every segment length are Lcoh, that is,
Lh=LPDI×Lcoh；
xnIt is L for n-th section of lengthcohSignal is obtained after sequence and frame synchronization head conjugate multiplication；
(43) timing frequency deviation rough estimate: rough estimate timing frequency deviation according to the following formula,
In formula, NpOffset section is timing slip τ where maximum value in a correlation peak0Place section, maximum value place
Position is frame head initial position μ, and the frame head of two continuous frames capture obtainsWithOne frame length is Lf；
(44) timing frequency deviation is corrected: being timed in frequency deviation using timing frequency deviation rough estimate evaluation docking take-up messenger
Insert amendment.
(50) frequency deviation skew pre-estimation: sequence is assisted as the data of Frequency Estimation using the frame head that Frame Synchronization Test captures
Column carry out pre-estimation to frequency deviation using based on trigonometric polynomial interpolated data quenching frequency algorithm for estimating, and repair to timing frequency deviation
Signal after just compensates；
As shown in figure 4, (50) the frequency deviation pre-estimation step includes:
(51) it eliminates modulated signal: receiving signal rkWith corresponding preamble sequence akConjugate multiplication obtains a length of LhSimple signal
zn；
(52) FFT frequency rough estimate: being L to lengthhSequence znMend L in endhA 0, and it is 2LhThe FFT operation of point is searched
The main lobe position l of FFT spectral line " sinc " envelope, the then corresponding position of spectral line of actual frequencyPositioned at spectral line R (l) and R (l+1) it
Between；
(53) trigonometric polynomial interpolation essence is estimated: being calculated using trigonometric polynomial interpolation formula
Further according to the relational expression of following frequency plots and FFT transform, the estimated value about frequency and phase is obtained,
(54) frequency deviation phase offset compensation: the Frequency Estimation obtained is utilizedAnd phase estimationFrequency deviation skew school is carried out to signal
Just.
(60) frequency deviation skew essence is estimated: being calculated using the cascade code auxiliary of trigonometric interpolation EM algorithm is searched for and be based on based on M value
Method carries out smart estimation to frequency deviation skew, and compensates to the compensated signal of pre-estimation；
As shown in figure 5, (60) the frequency deviation skew essence estimating step includes:
(61) be based on M value-based algorithm frequency coarse search: construction M value function determines search rate group by pre-estimation compression zone,
Frequency rough estimated value is determined by searching for M value function maximum value
As shown in fig. 6, described (61) include: based on M value-based algorithm frequency rough search step
(611) it constructs M value function: constructing objective function MSSO (f using decoding output Soft Inform ationn), it is shown below,
Wherein, LdTo encode frame length, Λ (mk) it is the Soft Inform ation that Turbo decoder exports, mkIt is k-th of decoding output
Information bit, fnIndicate n-th of frequency search amount；
(612) frequency deviation skew dynamic range is set: after the completion of frequency deviation skew pre-estimation link, frequency deviation fres, skew θres's
Compression zone determines by MCRB circle of frequency and phase respectively, that is, meet following formula,
Wherein, MCRBfIndicate MCRB circle, MCRB of frequencyθIndicate MCRB circle of phase.
(613) step-size in search is arranged: setting step-size in search Δ f makes it meet following formula,
Wherein θresmaxTo remain skew maximum jitter range；
(614) frequency search value is determined: by step-size in search and the corresponding carrier wave frequency deviation search value { f of frequency deviation dynamic rangen}
Meet
fn=fn-1+Δf；
(615) M value is searched for: utilizing every last set value fn, to reception data rkCarrier wave frequency deviation correction is carried out, is translated by 1 time
After code iteration, according to the Soft Inform ation Λ (m of its outputk) MSSO (f is calculatedn)；Finally by comparing, { MSSO (f is selectedn)}
The corresponding f of middle maximum valuenAs final estimated value, i.e.,
(62) frequency deviation compensates: M value-based algorithm is obtained frequencyTo coding groups data rkCarry out frequency deviation amendment；
(63) estimated based on trigonometric interpolation EM algorithm frequency essence: eliminating modulation intelligence using decoding output Soft Inform ation, pass through
Trigonometric interpolation algorithm obtains the estimation of frequency deviation skew essence, after being then corrected to frequency deviation skew, then carries out successive ignition, completes frequency
Inclined skew essence estimation and compensation.
As shown in fig. 7, described (63) include: based on trigonometric interpolation EM algorithm frequency essence estimating step
(631) by coded data rkIt is sent into decoder and carries out an iteration, obtain soft information value Λ (mk), after symbol
Probability and Soft Inform ation relationship are tested, as shown in formula, obtains symbol posterior probability η (mk)
(632) modulation intelligence is eliminated: by posterior probability η (mk) and data rkConjugate multiplication is carried out, modulation intelligence is eliminated, obtains
To sequence { zk}；
(633) FFT frequency rough estimate: being L to lengthd{ zkSequence end benefit LdA 0, and it is 2LdThe FFT operation of point, is searched
The main lobe position l for seeking FFT spectral line " sinc " envelope determines the somewhere that actual frequency is located between spectral line R (l) and R (l+1)；
(634) trigonometric polynomial Interpolate estimation: the trigonometric polynomial interpolation formula provided in (53) is utilized to obtain about frequency
The accurate estimation of rate and phase；
(635) frequency deviation skew corrects: previous step being obtained frequency and phase estimation value is corrected coding groups signal；
(636) the number of iterations judges: if decoding iteration frequency n is less than maximum number of iterations, step (631) are jumped to, into
Row next iteration, and remember n=n+1, otherwise, iteration is completed；
(637) it exports more new data: after reaching the decoding iteration upper limit, exporting updated packet data.
(70) timing offset essence is estimated: compensated to carrier deviation to M value two-dimensional search algorithm of the utilization based on interpolation
Residual timing frequency deviation, timing offset are estimated, and are modified to be sent into revised signal to coding groups data and decode
Device decoding, output decoding court verdict complete initial code grouping iterative demodulation decoding.；
As shown in figure 8, (70) the timing offset essence estimating step includes:
(71) timing frequency deviation search sequence is determined.If being divided into Δ f between timing frequency deviation estimationτ, Δ fτValue meets formula, by Δ
fτDetermine timing frequency deviation search sequence { fj},
Δfτ·N<0.05；
(72) 4 M values are iteratively solved: giving a timing frequency deviation fj, to the correction for timing interpolation of coding groups data,
It is reference with datum mark, is spaced T/4, select 4 tunnel sampled datas, time interval is-T/4,0, T/4, T/2, is respectively fed to decode
Device carries out an iteration, obtains 4 M values, is denoted as Γ (- T/4), Γ (0), Γ (T/4), Γ (T/2)；
(73) trigonometric interpolation acquires given frequency point maximum value: maximum value position is on this group of Frequency pointAnd on the basis of the estimated value, one group of amendment is obtained by interpolation filter
Data, and be sent into decoder and obtain new Γmax(fj)；
(74) timing offset essence is estimated: comparing Γ one by onemax(fj), by the M value two dimension about timing frequency deviation and timing offset
Function characteristic knows that extreme value is distributed by center both sides of highest point, works as Γmax(fj-1)<Γmax(fj), Γmax(fj+1)<Γmax
(fj), then it can determine whether maximizing, then respective frequencies are the timing frequency deviation essence to be obtained estimation ffine, corresponding initial
Timing offset is the τ of being obtained0；
(75) decoding judgement output: with timing frequency deviation ffine, initial timing deviation τ0Sampled data is corrected, and is sent
Decoding judgement output is completed after entering decoder successive ignition.
(80) Doppler shift variation tracking: being grouped next code, counts in frequency EM algoritic module pull-in frequency
Device improves EM algorithm, completes Doppler shift variation tracking.
As shown in figure 9, (80) the Doppler shift variation tracking step includes:
(81) pre-estimation frequency deviation pre-estimation: is carried out to frequency deviation using known preamble sequence；
(82) be based on the frequency deviation rough estimate of M value-based algorithm: the code aided algorithm based on the search of M value carries out the frequency deviation of first frame thick
Estimation, to eliminate most of frequency deviation；
(83) it frequency-tracking: sets n-th frame and uses the offset estimation value of EM algorithm acquisition as fn, then frequency deviation counter storage value
It is denoted asThen for the (n+1)th frame, phase data aided algorithm estimated initial phases, pressure are used first with frame head
Contracting skew, then uses fncoFrequency offset correction is carried out, decoder is then sent to carry out EM algorithm offset estimation again.
Figure 10 is the Performance Simulation Results of high dynamic Arctic ice area satellite communication Turbo code iterative demodulation method of the present invention
Figure.
As shown in Figure 10, it is emulated 10000 times using the Turbo code (1960,11760) of 1/6 code rate and obtains receiver error code
Performance curve.Wherein, frame length N=256 is sampled using 16 times of character rates.Simulation parameter is provided that
1) modulation system and the characteristic of channel: BPSK modulates lower awgn channel
2) character rate: fs=1Mb/s
3) initial frequency deviation: Δ f=2fs, initial skew: θ ∈ (- 180 °~180 °)
4) frequency deviation change rate: a=1KHz/s
5) timing offset: τ0=0.2Ts, timing frequency deviation: τfr=50ppm
Performance curve in the case of ideal synchronisation it can be seen that, is compared by Figure 10, performance loss about 0.2dB, loss is smaller, tests
The feasibility of the program is demonstrate,proved.
The present invention is directed to satellite communication applications scene under high dynamic Arctic ice area, fully considers satellite channel feature, comprehensive
Analysis synchronization parameter links potential demand is closed, it is auxiliary to existing coding under the premise of guaranteeing estimated accuracy and estimation range
Boostrap algorithm is optimized, provide it is a set of it is steady estimate calculating method, finally devise the receiver entirety side of complete set
Case realizes fast demodulation and decoding function under high dynamic Arctic ice area.
Claims (3)
1. a kind of satellite communication Turbo code iterative demodulation method under high dynamic Arctic ice area, which is characterized in that including walking as follows
It is rapid:
(10) it receives signal down coversion: bandpass signal will be received by quadrature frequency conversion, be converted to baseband signal；
(20) the big frequency deviation of signal is eliminated: baseband signal being segmented and carries out Fourier transformation and carries out after adding up, with matched filter
The Fourier transform shifting of receptance function is added, and obtains likelihood function；Frequency deviation rough estimate is obtained by search likelihood function peak value
Value, and carrier wave frequency deviation compensation is carried out using estimated value docking take-up messenger；
(30) Signal Matching filters: the compensated signal of carrier wave frequency deviation being carried out matched filtering, obtains channel matched signal；
(40) frame synchronization and bit timing Combined estimator: carrying out high rate sampling to the signal after matched filtering, obtains multichannel and adopts
Sample signal carries out Frame Synchronization Test to multi-channel sampling signal parallel, searches for related peak maximum, utilizes related peak maximum and right
The position answered, estimates timing frequency deviation, is timed frequency deviation to filtered signal using the timing frequency deviation and corrects；
(50) frequency deviation skew pre-estimation: the frame head captured using Frame Synchronization Test as the data auxiliary sequencel of Frequency Estimation,
Using based on trigonometric polynomial interpolated data quenching frequency algorithm for estimating to frequency deviation carry out pre-estimation, and to timing frequency deviation amendment after
Signal compensate；
(60) frequency deviation skew essence is estimated: the cascade code aided algorithm of trigonometric interpolation EM algorithm is searched for and is based on using M value is based on, it is right
Frequency deviation skew carries out smart estimation, and compensates to the compensated signal of pre-estimation；
(70) timing offset essence is estimated: to the M value two-dimensional search algorithm based on interpolation is utilized, to the compensated residual of carrier deviation
Timing frequency deviation, timing offset are estimated, and are modified to coding groups data and translate revised signal feeding decoder
Code, output decoding court verdict complete initial code grouping iterative demodulation decoding；
(80) Doppler shift variation tracking: next code is grouped, in frequency EM algoritic module pull-in frequency counter, is changed
Into EM algorithm, Doppler shift variation tracking is completed；
The big frequency deviation removal process of (20) signal includes:
(21) baseband signal is segmented Fourier transform: being L by observation interval length0Baseband signal be divided into N sections, every segment is a length of
Then L converts to obtain R to l sections of progress N point discrete Fouriersl(k), and acquire grouping it is cumulative and,
(22) N point discrete Fourier matched filtering receptance function Fourier transform: is carried out to matched filter receptance function g (t)
Transformation obtains the corresponding Fourier transformation value G (k) of function；
(23) shifter-adder: by G (k) Xiang Zuoyi m withIt adds up after multiplication, obtains likelihood function Λ (m),
(24) offset estimation: by the continuous shifted left of G (k), searching plain Λ (m) function maxima, be maximized it is corresponding for for
Sample frequency is fs, then Frequency Estimation are as follows:
(25) big frequency deviation compensation: frequency rough estimated value is utilizedIt docks take-up messenger and carries out carrier wave frequency deviation compensation；
(40) the frame lock bit timing Combined estimator step includes:
(41) signal sampling: high rate sampling is carried out to the signal after wave frequency offset compensation, obtains multi-channel sampling signal；
(42) multi-channel sampling signal multichannel Frame Synchronization Test: is sent to N respectivelypRoad Frame Synchronization Test unit carries out Frame Synchronization Test,
Search obtains NpA correlation peak maximum, the NpEvery road Frame Synchronization Test unit of road Frame Synchronization Test unit uses such as following table
Up to the Frame Detection Algorithm of the tolerance frequency deviation of formula,
Wherein, liThe detection limit obtained when being set to i for start of frame bits；
rkTo receive signal, a length of L of frame headh, by long LhSequence be divided into LPDISection, every segment length are Lcoh, that is,
Lh=LPDI×Lcoh；
xnIt is L for n-th section of lengthcohSignal is obtained after sequence and frame synchronization head conjugate multiplication；
(43) timing frequency deviation rough estimate: rough estimate timing frequency deviation according to the following formula,
In formula, NpOffset section is timing slip τ where maximum value in a correlation peak0Place section, maximum value position
Frame head for frame head initial position μ, two continuous frames capture obtainsWithOne frame length is Lf；
(44) timing frequency deviation is corrected: being timed frequency deviation interpolation using timing frequency deviation rough estimate evaluation docking take-up messenger and is repaired
Just；
(50) the frequency deviation pre-estimation step includes:
(51) it eliminates modulated signal: receiving signal rkWith corresponding preamble sequence akConjugate multiplication obtains a length of LhSimple signal zn；
(52) FFT frequency rough estimate: being L to lengthhSequence znMend L in endhA 0, and it is 2LhFFT spectrum is searched in the FFT operation of point
The main lobe position l of line " sinc " envelope, the then corresponding position of spectral line of actual frequencyBetween spectral line R (l) and R (l+1)；
(53) trigonometric polynomial interpolation essence is estimated: being calculated using trigonometric polynomial interpolation formula
Further according to the relational expression of following frequency plots and FFT transform, the estimated value about frequency and phase is obtained,
(54) frequency deviation phase offset compensation: the Frequency Estimation obtained is utilizedAnd phase estimationThe correction of frequency deviation skew is carried out to signal；
(60) the frequency deviation skew essence estimating step includes:
(61) be based on M value-based algorithm frequency coarse search: construction M value function determines search rate group by pre-estimation compression zone, passes through
Search M value function maximum value determines frequency rough estimated value
(62) frequency deviation compensates: M value-based algorithm is obtained frequencyTo coding groups data rkCarry out frequency deviation amendment；
(63) estimated based on trigonometric interpolation EM algorithm frequency essence: eliminating modulation intelligence using decoding output Soft Inform ation, pass through triangle
Interpolation algorithm obtains the estimation of frequency deviation skew essence, after being then corrected to frequency deviation skew, then carries out successive ignition, completes frequency deviation phase
Essence estimation and compensation partially；
(70) the timing offset essence estimating step includes:
(71) it determines timing frequency deviation search sequence: setting between timing frequency deviation is estimated and be divided into Δ fτ, Δ fτValue meets following formula, by Δ fτ
Determine timing frequency deviation search sequence { fj},
ΔfτN < 0.05；
(72) 4 M values are iteratively solved: from the timing frequency deviation search sequence { fjIn select a Frequency point fj, to coding groups
Data correction for timing interpolation, with datum mark be reference, be spaced T/4, select 4 tunnel sampled datas, time interval be-T/4,0,
T/4, T/2 are respectively fed to decoder and carry out an iteration, obtain 4 M values, be denoted as Γ (- T/4), Γ (0), Γ (T/4), Γ
(T/2)；
(73) trigonometric interpolation acquires given frequency point maximum value: in the Frequency point fjThe estimated value of upper maximum value present position isAnd on the basis of the estimated value, one group of amendment is obtained by interpolation filter
Data, and be sent into decoder and obtain new Γmax(fj)；
(74) timing offset essence is estimated: comparing Г one by onemax(fj), by the M value two-dimensional function about timing frequency deviation and timing offset
Characteristic knows that extreme value is distributed by center both sides of highest point, works as Γmax(fj-1) < Γmax(fj), Γmax(fj+1) < Γmax(fj),
It then can determine whether maximizing, then respective frequencies are the timing frequency deviation essence to be obtained estimation ffine, corresponding initial timing
Deviation is the τ of being obtained0；
(75) decoding judgement output: with timing frequency deviation ffine, initial timing deviation τ0Sampled data is corrected, and is sent into and translates
Decoding judgement output is completed after code device successive ignition；
(80) Doppler shift changes tracking step
(81) pre-estimation frequency deviation pre-estimation: is carried out to frequency deviation using known preamble sequence；
(82) be based on the frequency deviation rough estimate of M value-based algorithm: the code aided algorithm based on the search of M value carries out rough estimate to the frequency deviation of first frame
Meter, to eliminate most of frequency deviation；
(83) it frequency-tracking: sets n-th frame and uses the offset estimation value of EM algorithm acquisition as fn, then frequency deviation counter storage value is denoted asThen for the (n+1)th frame, phase data aided algorithm estimated initial phases are used first with frame head, compress phase
Partially, f is then usedncoFrequency offset correction is carried out, decoder is then sent to carry out EM algorithm offset estimation again.
2. Turbo code iterative demodulation method according to claim 1, which is characterized in that described (61) are based on M value-based algorithm frequency
Rate coarse search step includes:
(611) it constructs M value function: constructing objective function MSSO (f using decoding output Soft Inform ationn), it is shown below,
Wherein, LdTo encode frame length, Λ (mk) it is the Soft Inform ation that Turbo decoder exports, mkFor k-th of information of decoding output
Bit, fnIndicate n-th of frequency search amount；
(612) frequency deviation skew dynamic range is set: after the completion of frequency deviation skew pre-estimation link, frequency deviation fres, skew θresCompression
Range is determined by MCRB circle of frequency and phase respectively, that is, meets following formula,
Wherein, MCRBfIndicate MCRB circle, MCRB of frequencyθIndicate MCRB circle of phase；
(613) step-size in search is arranged: setting step-size in search Δ f makes it meet following formula,
Wherein θresmaxTo remain skew maximum jitter range；
(614) frequency search value is determined: by step-size in search and the corresponding carrier wave frequency deviation search value { f of frequency deviation dynamic rangenMeet
fn=fn-1+Δf；
(615) M value is searched for: utilizing every last set value fn, to reception data rkCarrier wave frequency deviation correction is carried out, is changed by 1 decoding
Dai Hou, the Soft Inform ation Λ (m exported according to itk) MSSO (f is calculatedn)；Finally by comparing, { MSSO (f is selectedn) in most
It is worth corresponding f greatlynAs final estimated value, i.e.,
3. Turbo code iterative demodulation method according to claim 1, which is characterized in that described (63) are based on trigonometric interpolation
EM algorithm frequency essence estimating step includes:
(631) by coded data rkIt is sent into decoder and carries out an iteration, obtain soft information value Λ (mk), it is general according to symbol posteriority
Rate and Soft Inform ation relationship obtain symbol posterior probability η (m as shown in formulak)
(632) modulation intelligence is eliminated: by posterior probability η (mk) and data rkConjugate multiplication is carried out, modulation intelligence is eliminated, obtains sequence
Arrange { zk}；
(633) FFT frequency rough estimate: being L to lengthd{ zkSequence end benefit LdA 0, and it is 2LdFFT is searched in the FFT operation of point
The main lobe position l of spectral line " sinc " envelope determines the somewhere that actual frequency is located between spectral line R (l) and R (l+1)；
(634) trigonometric polynomial Interpolate estimation: utilize in (53) the trigonometric polynomial interpolation formula that provides obtain about frequency and
The accurate estimation of phase；
(635) frequency deviation skew corrects: previous step being obtained frequency and phase estimation value is corrected coding groups signal；
(636) the number of iterations judges: if decoding iteration frequency n is less than maximum number of iterations, jumping to step (631), carries out down
An iteration, and remember n=n+1, otherwise, iteration is completed；
(637) it exports more new data: after reaching the decoding iteration upper limit, exporting updated packet data.
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