CN103475619A - Carrier synchronizer for demodulating low signal-to-noise ratio burst signals - Google Patents
Carrier synchronizer for demodulating low signal-to-noise ratio burst signals Download PDFInfo
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Abstract
The invention discloses a carrier synchronizer for demodulating low signal-to-noise ratio burst signals. The carrier synchronizer comprises an input cache module, an initial frequency deviation estimation module, a frequency deviation partition preset module, N two-way capture tracking modules, N unwrapping phase ambiguity and soft de-mapping modules, an iterative decoding module and an optimal judgment module. Each two-way capture tracking module corresponds to one unwrapping phase ambiguity and soft de-mapping module. Initial frequency deviation is estimated based on preceding heads of the burst signals, then, after an initial frequency deviation estimation result is preset in a partition mode, two-way capture tracking is utilized to conduct carrier synchronization, the optimal judgment module selects an optimal carrier to conduct synchronous output according to judgment soft information statistical values output by the iterative decoding module, and eventually the iterative decoding module conducts decoding on the carrier and outputs a final result. By the adoption of the carrier synchronizer, optimization design is conducted on burst signal carrier synchronization under the low signal-to-noise ratio, and the problem of low signal-to-noise ratio carrier synchronization of TDMA system communication is solved.
Description
Technical field
The invention discloses a kind of carrier synchronization device for the demodulation of low signal-to-noise ratio burst.
Background technology
In the demodulation of low signal-to-noise ratio burst, key problem is carrier synchronization.Carrier synchronization method can be divided into the open loop carrier synchronization of reaction type closed loop carrier synchronization and feed forward type.For the burst demodulation, there are the problems such as capture time length, " outstanding putting " in the closed loop carrier synchronization of traditional reaction type, can't finely meet application requirements, thereby generally adopt the open loop carrier synchronization method based on parameter Estimation.The signal to noise ratio scope of the adaptation of open loop carrier synchronization mainly is limited to Parameter Estimation Precision, and Parameter Estimation Precision depends on algorithm for estimating and the front top guide length for estimating.But, under Low SNR, will sharply glide for its Parameter Estimation Precision of front top guide of length-specific, thereby affect Carrier Synchronization Algorithm work thresholding.
Recent years, for carrier synchronization under low signal-to-noise ratio, academia has proposed the multiple synchronized algorithm auxiliary based on coding successively.Document [1] has been studied the external information of channel decoding output and the relation between the carrier phase offset distribution, and utilizes the weighting of external information to be estimated phase place; Document [2] is incorporated into auxiliary estimation in the carrier phase maximum likelihood decision by the soft information of channel decoding; Document [3] has provided the carrier phase iterative estimate method based on the EM algorithm; Document [4] has proposed a kind of APPA (APriori Probability Aided) phase estimation algorithm, is the auxiliary iterative phase algorithm for estimating of a kind of coding based on maximum-likelihood criterion.Above-mentioned algorithm can effectively be estimated the carrier phase deviation at low signal-to-noise ratio, but be all that when having residual carrier wave frequency deviation, the performance of these algorithms will sharply descend in the situation that the supposition phase deviation is that constant carries out.Document [5] has proposed a kind of improved APPA algorithm, go for having the carrier phase estimation of certain residual frequency deviation, but its implementation complexity is very high.
List of references:
[1]Oh?W?and?Cheun?K.Joint?decoding?and?carrier?phase?recovery?algorithm?for?turbo?codes.IEEE?Communications?Letters,2001,5(9).
[2]Valles.E?L,Richard?D?W,John?D?V,et?al.Pilotless?carrier?phase-synchronization?via?LDPC?code?feedback.IEEE,2010.
[3]Nods?N,Herzet?C,and?Dejonghe?A.Turbo?synchronization:an?EM?algorithm?interpretation.IEEE?International?Conference?on?Communicatians,Alaska,2003）
[4]Zhang?L?and?Burr?A?G.Iterative?carrier?recovery?suited?to?turbo-coded?systems.IEEE?Transactions?on?Wireless?Communications,2004,3(6).
[5] Xu Junhui, Liu Chaosheng, Zhang Zhongpei. a kind of code subcarrier synchronized algorithm based on APPA. electronics and information journal, 2009,31 (12).
Summary of the invention
Technical problem to be solved by this invention is: overcome the deficiencies in the prior art, a kind of carrier synchronization device for the demodulation of low signal-to-noise ratio burst is provided, can decrease to the length requirement of front top guide, can effectively solve the carrier synchronization problem in the burst demodulation under Low SNR.
Technical scheme of the present invention is:
A kind of carrier synchronization device for the demodulation of low signal-to-noise ratio burst, comprise that input buffer module, initial frequency deviation estimation module, frequency deviation subregion preset module, a N bidirectional acquisition tracking module, N separate phase ambiguity and soft demapping module, iteration decoding module and optimal judgement module; Corresponding one of each bidirectional acquisition tracking module is separated phase ambiguity and soft demapping module;
Input buffer module is carried out buffer memory to I road and Q road input message Data_I, Data_Q;
The initial frequency deviation estimation module obtains carrier wave initial frequency deviation fc according to the front top guide of described burst;
Frequency deviation subregion preset module is with carrier wave initial frequency deviation f
cfor benchmark, the residual frequency departure span possible according to it after initial frequency deviation is estimated evenly is divided into the center frequency point in ，Jiang Ge subinterval, N subinterval as side-play amount, to initial frequency deviation f
ccarry out presetly, obtain N fine frequency offset estimated value, each fine frequency offset estimated value is corresponding inputs to a bidirectional acquisition tracking module;
Each bidirectional acquisition tracking module fine frequency offset estimated value corresponding according to it carried out initially preset to the frequency control word of the carrier synchronization loop in the bidirectional acquisition tracking module, the bidirectional acquisition tracking module utilizes forward direction to catch to make loop to enter lock, then take keyed end as benchmark, employing is recalled and is followed the tracks of and the forward direction tracking realizes respectively the carrier synchronization to information before keyed end, after keyed end, finally obtains the output signal after carrier track;
Each separate phase ambiguity and soft demapping module according to the unique word in burst the output signal after to carrier track separated phase ambiguity, and carry out soft demapping and obtain soft demapping information;
The soft demapping information in iteration decoding module Dui Mei road is respectively carried out l iterative decoding acquisition variable node and is adjudicated soft information; The optimal judgement module is adjudicated soft information according to the variable node of iteration decoding module output, calculates the decision statistic value, and a road of decision statistic value maximum is indicated to iteration decoding module; Finally, iteration decoding module is according to the indication of optimal judgement module, the soft demapping information on a road of decision statistic value maximum carried out to iterative decoding k time, and export final decode results.
Described iterations 2≤l≤5, k >=10.
Described decision statistic value is that variable node is adjudicated soft information absolute value sum.
The present invention compared with prior art has following advantage:
(1) under Low SNR, adopt the carrier synchronization method of conventional phase locked loops, the initial frequency deviation estimated accuracy has been proposed to very high requirement, and this also just requires each burst must have very long front top guide (hundreds of symbols), and this can reduce the effective information efficiency of transmission greatly.By the bidirectional acquisition tracking module in the present invention, at first forward direction is caught and is reached lock-out state, and the keyed end of then take is recalled and followed the tracks of and the forward direction tracking as starting point, thereby reaches the purpose of eliminating the carrier synchronization transition band.Different from traditional burst carrier synchronization method, the method also do not require enter lock-out state in front top guide, thus can decrease to the length requirement of front top guide;
(2) in the present invention by the frequency deviation subregion preset with optimal judgement to combination, first frequency deviation is carried out to subregion preset, then according to the capturing carrier tracking respectively of preset frequency deviation, a road of the soft Information Selection optimum in the optimal utilization iterative decoding process is as the carrier synchronization Output rusults.Under the condition of top guide length, can indirectly improve the Nonlinear Transformation in Frequency Offset Estimation precision before not increasing, thereby be conducive to phase-locked loop under low signal-to-noise ratio, enter fast lock.In fact this expanded the range of application that aforementioned bidirectional acquisition is followed the tracks of carrier synchronization method, makes the method not only can be applied to long bursty data, also can be applied to short bursty data.
The accompanying drawing explanation
Fig. 1 is the structure chart of the carrier synchronization device for the demodulation of low signal-to-noise ratio burst of the present invention.
Fig. 2 is the burst frame structure.
Fig. 3 is carrier synchronization loop (second order digital phase-locked loop) theory diagram in the bidirectional acquisition tracking module.
Fig. 4 is bidirectional acquisition tracing process schematic diagram.
Fig. 5 is normalization residual frequency departure 10
-3loop under low signal-to-noise ratio (Eb/No=0dB) is caught into lock figure.
Fig. 6 is that the bi-directional tracking loop is caught into the lock curve chart.
Embodiment
Below just by reference to the accompanying drawings the present invention is described further.
For iterative decoding (as LDPC decoding, Turbo decoding etc., being decoded as example with LDPC in embodiment describes), the signal I received when the carrierfree frequency difference, Q amplitude maximum, and in the situation that there is carrier beat, receive signal demand and be multiplied by the phase deviation item, make the effective breadth of actual reception signal descend, and cause that relevant likelihood ratio (receiving the soft information of signal) descends.Exist as draw a conclusion: in the situation that there is carrier deviation, it is also more accurate for carrier frequency and the phase deviation of compensation to estimate, iterative decoding export soft information absolute value sum will be larger.Therefore, can be as target function, as the judgment criterion of carrier synchronization quality after the soft information absolute value of all code words is cumulative.In the present invention, export soft information absolute value sum and will, as criterion, with lower complexity, realize that the coding subcarrier is synchronous.
As shown in Figure 1, the carrier synchronization device for the demodulation of low signal-to-noise ratio burst of the present invention comprises that input buffer module, initial frequency deviation estimation module, frequency deviation subregion preset module, a N bidirectional acquisition tracking module, N separate phase ambiguity and soft demapping module, iteration decoding module and optimal judgement module.Corresponding one of each bidirectional acquisition tracking module is separated phase ambiguity and soft demapping module.
Usually the burst frame format as shown in Figure 2.Wherein, front top guide is for input and initial parameter estimation, and unique word is used for separating phase ambiguity, the information that effective information transmits for actual needs.
If carrier synchronization input signal mathematic(al) representation is as follows:
R
n(i)=e
-j (2 π Δ fi+ Δ θ)+ n (i), wherein, Δ θ is initial skew to 0≤i≤L-1 (1), and Δ f is initial frequency difference, and n (i) is white complex gaussian noise, and L is burst data length.Whole carrier synchronization process is as follows:
1) by input buffer module, input message Data_I, Data_Q(are corresponded respectively to real part and the imaginary part of input signal) store, for subsequent module, processed;
2) the leading header of the burst based on buffer memory, the initial frequency deviation estimation module adopts the auxiliary algorithm for estimating of data (as M& M, L& R etc.) obtain carrier wave initial frequency deviation estimated value f
c;
3) with above-mentioned carrier wave initial frequency deviation f
cfor benchmark, possible the span ([df of residual frequency departure after initial frequency deviation is estimated
max, df
max]) evenly being divided into N subinterval, the center frequency point in each subinterval is (Δ f
1, Δ f
2..., Δ f
n), using it as side-play amount, to initial frequency deviation f
ccarry out presetly, obtain N fine frequency offset and estimate f
i=f
c+ Δ f
i(i ∈ [1,2 ..., N]).N is more than or equal to 2.
4) for each fine frequency offset estimated value, using it as original frequency control word F
cw(1) be preset in the carrier synchronization loop of bidirectional acquisition tracking module, then by the bidirectional acquisition tracking module, complete carrier synchronization.Carrier synchronization loop in the bidirectional acquisition tracking module is second order Costas loop as shown in Figure 3, and in figure, PD is that section's Stas phase discriminator, C1 and C2 are that second order loop loop parameter, NCO are digital controlled oscillator.As shown in Figure 4, concrete processing procedure is the acquisition and tracking process:
At first, sense data from input-buffer, utilize the carrier synchronization loop to carry out forward direction and catch, and when detecting after the carrier synchronization loop enters lock, stops.When practical application, can its size of keyed end M(be set according to simulation scenarios relevant with carrier synchronization loop loop bandwidth), when after M symbol, think that loop has entered lock;
Then, take keyed end as datum mark, by the negate of frequency loop control word, even it is-F
cw(M), from input-buffer, backward is read M to the 1st data corresponding to symbol, utilizes carrier synchronization loop (phase-locked loop) to be recalled tracking;
Finally, again by the negate of frequency loop control word, even it is-F
cw(1), read successively the 1st to L the data that symbol is corresponding from input-buffer, utilize carrier synchronization loop (phase-locked loop) to carry out the forward direction tracking, obtain the carrier synchronization output of whole burst.
5) after completing the bidirectional acquisition tracking, utilize unique word to eliminate phase ambiguity, then carry out soft solution and hint obliquely at, the N obtained is organized to soft demapping information and send into iteration decoding module;
6) the soft demapping information in iteration decoding module Dui Mei road is respectively carried out l iterative decoding and is obtained variable node and adjudicate soft information, 2≤l≤5.The optimal judgement module is adjudicated soft information according to the variable node of iteration decoding module output, calculates decision statistic value ψ (f
n), by decision statistic value ψ (f
n) a maximum road indicates to iteration decoding module; Finally, iteration decoding module is according to the indication of optimal judgement module, the road carrier synchronization Output rusults of the best carried out k time to iterative decoding again, and export final decode results.k≥10。
Suppose that the LDPC code check matrix is H, the set of the variable node i be connected with j check-node is M (i)={ j:H
j,i=1}, c
i, x
i, y
ibe respectively i code element, decision signal and reception signal, L (c
i) be channel input message log-likelihood ratio, r
jibe respectively check-node i and pass to the external information probability of variable node j, Q
ifor judgment variables node c
isoft informational probability.The objective definition function:
Wherein, l means iterations, f
nmean n fine frequency offset estimated value, n ∈ [1,2 ..., N],
l(c
i| f
n), L (r
ji| f
n) be illustrated respectively in the variable node obtained under this Nonlinear Transformation in Frequency Offset Estimation value and adjudicate soft information, input log-likelihood ratio, external information etc.As ψ (f
n) when maximum, corresponding frequency deviation is best frequency deviation:
Its corresponding demodulation result is subject to frequency deviation to affect minimum, and accuracy is the highest, after decoding, as final, exports.
Embodiment
Suppose that certain burst communication system information rate is 2Mbps, adopt the LDPC coding that code check is 0.5, the maximum frequency deviation in transmitting procedure is 10KHz.The burst frame structure is 128 front top guides, 32 unique words and 2048 effective informations, and modulation system is QPSK, and requiring work signal to noise ratio Eb/No is 0dB.In order to reduce the cycle-skipping probability, Costas loop normalization loop bandwidth gets 0.004.The concrete steps that employing the present invention carries out carrier synchronization are as follows:
1) input message after sign synchronization is stored in input-buffer;
2) adopt the data aided algorithm to utilize 128 front top guides to estimate normalization initial frequency deviation value fc;
3) when signal to noise ratio Eb/No is 0dB, after initial frequency deviation is estimated, possible normalization residual frequency departure scope is between [0.001,0.001], and it evenly is divided into to 4 subintervals, and each interval normalization center frequency point is f
1, f
2, f
3, f
4, its value is respectively f
c-0.00075, f
c-0.00025, f
c+ 0.00025, f
c+ 0.00075;
4) by f
1as original frequency control word F
cw(1) be preset in loop;
5) at first, read successively the 1st to the 1000th symbol (during the 1000th symbol, loop has entered lock) of whole burst from input-buffer, utilize Costas loop to carry out forward direction and catch; Then, by frequency control word F
cw(1000) obtain-F of negate
cw(1000) be preset in loop, from input-buffer, backward is read the 1000th to the 1st symbol of whole burst, utilizes Costas loop to be recalled tracking; Finally, by frequency control word F
cw(1) obtain-F of negate
cw(1) be preset to loop, read successively the 1st of whole burst and utilize Costas loop to carry out the forward direction tracking to last symbol from input-buffer, thereby obtain the carrier synchronization Output rusults of whole burst;
6) successively by f
2, f
3, f
4control and be preset in loop as original frequency, repeating step 5), obtain other three groups of carrier synchronization Output rusults;
7) utilize unique word to separate phase ambiguity to four groups of carrier synchronization outputs, then soft demapping, send result into the LDPC iteration decoding module;
8), in the LDPC iteration decoding module, at first four groups of carrier synchronization results are carried out respectively to iterative decoding 2 times.Add up the corresponding soft information absolute value of judgement sum by the optimal judgement module, obtain successively ψ (f
1), ψ (f
2), ψ (f
3), ψ (f
4), and compare ψ (f
1), ψ (f
2), ψ (f
3), ψ (f
4), indicate to iteration decoding module on the road that ψ (f) value is maximum; Then, iteration decoding module is according to the indication of optimal judgement module, and iterative decoding is carried out on a road maximum to ψ (f) value 30 times, and the output final result.
For the burst carrier synchronization, usually in above-mentioned steps 2) after, directly utilize Costas loop to carry out acquisition and tracking, simulation result shows, need to be after several thousand symbol, loop could enter lock (as shown in Figure 5) smoothly, and this obviously can't meet the demands.And the carrier synchronization device that the present invention proposes is recalled tracking owing to having adopted, eliminated forward direction and followed the tracks of the impact that intermediate ring road enters to lock transition band, equivalence enter the lock time be 0(as shown in Figure 6), can finely meet burst carrier synchronization demand.
The unspecified part of the present invention belongs to general knowledge as well known to those skilled in the art.
Claims (3)
1. the carrier synchronization device for the demodulation of low signal-to-noise ratio burst, it is characterized in that, comprise input buffer module, initial frequency deviation estimation module, frequency deviation subregion preset module, N road bidirectional acquisition tracking module, N road solution phase ambiguity and soft demapping module, iteration decoding module and optimal judgement module; Phase ambiguity and soft demapping module are separated in bidirectional acquisition tracking module corresponding road in every road,
Input buffer module is carried out buffer memory to I road and Q road input message Data_I, Data_Q;
The initial frequency deviation estimation module obtains carrier wave initial frequency deviation fc according to the front top guide of described burst;
Frequency deviation subregion preset module is with carrier wave initial frequency deviation f
cfor benchmark, the residual frequency departure span possible according to it after initial frequency deviation is estimated evenly is divided into the center frequency point in ，Jiang Ge subinterval, N subinterval as side-play amount, to initial frequency deviation f
ccarry out presetly, obtain N fine frequency offset estimated value, each fine frequency offset estimated value is corresponding inputs to a bidirectional acquisition tracking module;
Each bidirectional acquisition tracking module fine frequency offset estimated value corresponding according to it carried out initially preset to the frequency control word of the carrier synchronization loop in the bidirectional acquisition tracking module, the bidirectional acquisition tracking module utilizes forward direction to catch to make loop to enter lock, then take keyed end as benchmark, employing is recalled and is followed the tracks of and the forward direction tracking realizes respectively the carrier synchronization to information before keyed end, after keyed end, finally obtains the output signal after carrier track;
Each separate phase ambiguity and soft demapping module according to the unique word in burst the output signal after to carrier track separated phase ambiguity, and carry out soft demapping and obtain soft demapping information;
The soft demapping information in iteration decoding module Dui Mei road is respectively carried out l iterative decoding acquisition variable node and is adjudicated soft information; The optimal judgement module is adjudicated soft information according to the variable node of iteration decoding module output and is calculated the decision statistic value, and a road of decision statistic value maximum is indicated to iteration decoding module; Finally, iteration decoding module is according to the indication of optimal judgement module, the soft demapping information on a road of decision statistic value maximum carried out to iterative decoding k time, and export final decode results.
2. a kind of carrier synchronization device for the demodulation of low signal-to-noise ratio burst according to claim 1, is characterized in that 2≤l≤5, k >=10.
3. a kind of carrier synchronization device for the demodulation of low signal-to-noise ratio burst according to claim 1, is characterized in that, described decision statistic value is that variable node is adjudicated soft information absolute value sum.
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| CN110445735B (en) * | 2019-07-24 | 2022-04-01 | 南京理工大学 | Burst short data carrier synchronization method based on signal backtracking |
| US10992450B1 (en) * | 2020-03-05 | 2021-04-27 | Rohde & Schwarz Gmbh & Co. Kg | Signal processing method and signal analysis module |
| CN112073351A (en) * | 2020-11-16 | 2020-12-11 | 湖南国科锐承电子科技有限公司 | Novel carrier frequency offset estimation method for MPSK system |
| CN114039623A (en) * | 2021-10-22 | 2022-02-11 | 中国电子科技集团公司第五十四研究所 | Low-carrier-to-noise-ratio short burst spread spectrum signal tracking method |
| WO2023193518A1 (en) * | 2022-04-06 | 2023-10-12 | 中兴通讯股份有限公司 | Signal processing method, electronic device and computer-readable storage medium |
| CN115037331A (en) * | 2022-08-10 | 2022-09-09 | 中国电子科技集团公司第十研究所 | Asynchronous burst signal timing synchronization method based on reverse extrapolation |
| CN115037331B (en) * | 2022-08-10 | 2022-12-06 | 中国电子科技集团公司第十研究所 | Asynchronous burst signal timing synchronization method based on reverse extrapolation |
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