CN109412644B - Doppler frequency estimation method for direct sequence spread spectrum MSK signal - Google Patents

Doppler frequency estimation method for direct sequence spread spectrum MSK signal Download PDF

Info

Publication number
CN109412644B
CN109412644B CN201811064884.1A CN201811064884A CN109412644B CN 109412644 B CN109412644 B CN 109412644B CN 201811064884 A CN201811064884 A CN 201811064884A CN 109412644 B CN109412644 B CN 109412644B
Authority
CN
China
Prior art keywords
frequency
signal
direct spread
code
doppler frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
CN201811064884.1A
Other languages
Chinese (zh)
Other versions
CN109412644A (en
Inventor
王丙休
仇雯
谢仁宏
芮义斌
李鹏
郭山红
乔帅
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nanjing University of Science and Technology
Original Assignee
Nanjing University of Science and Technology
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nanjing University of Science and Technology filed Critical Nanjing University of Science and Technology
Priority to CN201811064884.1A priority Critical patent/CN109412644B/en
Publication of CN109412644A publication Critical patent/CN109412644A/en
Application granted granted Critical
Publication of CN109412644B publication Critical patent/CN109412644B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/7075—Synchronisation aspects with code phase acquisition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69—Spread spectrum techniques
    • H04B1/707—Spread spectrum techniques using direct sequence modulation
    • H04B1/7073—Synchronisation aspects
    • H04B1/7075—Synchronisation aspects with code phase acquisition
    • H04B1/70754—Setting of search window, i.e. range of code offsets to be searched

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The invention discloses a Doppler frequency estimation method of a direct spread MSK signal, which constructs the direct spread MSK signal into an approximate direct spread BPSK signal form, and then optimizes a Doppler frequency offset value by adopting triangular fitting of a cross fuzzy function under the condition of large Doppler and low signal to noise ratio. The method specifically comprises the following steps: converting the received direct spread MSK signal into an approximate direct spread BPSK signal by using an intermediate frequency matched filter; carrying out code phase search on the approximate direct spread BPSK signal by using a pseudo code parallel acquisition algorithm based on FFT; and optimizing the Doppler frequency offset value by triangular fitting of a cross fuzzy function to obtain an accurate Doppler frequency estimation value, and improving the capture probability by using amplitude and frequency information before and after frequency accurate estimation. The invention can effectively improve the estimation precision of the Doppler frequency offset.

Description

Doppler frequency estimation method for direct sequence spread spectrum MSK signal
Technical Field
The invention belongs to the technical field of direct sequence spread spectrum signal synchronization, and particularly relates to a Doppler frequency estimation method of a direct sequence spread spectrum MSK signal.
Background
At present, BPSK and QPSK modulation modes are mostly adopted in a spread spectrum system, but the two modulation modes cannot be applied to the application fields with serious nonlinear distortion, Doppler frequency shift and multipath fading. The direct spread MSK communication system has the advantages of low interception performance, multi-user random site selection capability, strong anti-interference performance and the like of a spread spectrum system, has the advantages of constant MSK signal envelope, high frequency spectrum utilization rate, energy concentration, fast side lobe attenuation, low out-of-band radiation power, insensitivity to nonlinear distortion and the like, and is widely applied to the fields of tactical data links, civil aviation ground-air data links, missile guidance instruction transmission, satellite communication and the like. Therefore, the direct spread MSK signal still has good application prospect in the field that the direct spread BPSK/QPSK signal can not be applied.
G.j.r.povey et al first propose a capture model based on the combination of a digital partial matched filter and FFT (PMF-FFT), which alleviates the effect of doppler frequency offset on the pseudo code capture performance to a certain extent and realizes two-dimensional capture of pseudo code phase and carrier frequency offset, but which is mainly adapted to MPSK signals and has a small capture range of doppler frequency offset, and is still not applicable in a high dynamic and low signal-to-noise environment.
Disclosure of Invention
The invention aims to provide a Doppler frequency estimation method of a direct spread spectrum (MSK) signal, which solves the problem that the two-dimensional capture of a pseudo code phase and Doppler frequency offset of a spread spectrum signal is inaccurate in a high-dynamic and low signal-to-noise environment.
The technical solution for realizing the purpose of the invention is as follows: a Doppler frequency estimation method of direct spread MSK signals comprises the following steps:
step 1, converting a received direct sequence spread spectrum (MSK) signal into an approximate direct sequence spread spectrum (BPSK) signal by using an intermediate frequency matched filter;
step 2, code phase searching is carried out on the approximate direct spread BPSK signal by using a pseudo code parallel capturing algorithm based on FFT, circumferential correlation operation of local pseudo codes and received pseudo codes is achieved in a frequency domain, and correlation values on all code phases are obtained;
step 3, detecting the non-correlation integral output of the frequency domain, and performing Doppler frequency offset value f on the result of the non-correlation integral exceeding the constant false alarm detection threshold value through triangular fitting of the cross fuzzy functiondAnd optimizing to obtain an accurate Doppler estimated value.
Preferably, in step 1, an intermediate frequency matched filter h (t) is used to receive the direct spread MSK signal, and the impulse response of the filter h (t) is:
Figure GDA0002821067320000021
wherein, Tc＝1/RcFor spreading code period, RcIs the spreading code rate;
Figure GDA0002821067320000022
fcis the carrier frequency.
Preferably, the expression of the approximate direct spread BPSK signal obtained in step 1 is:
Figure GDA0002821067320000023
wherein A is the signal amplitude,
Figure GDA0002821067320000024
to an initial phase, TsFor the sampling interval of the received signal, d (-) is the transmitted symbol, c (-) is the PN code, τ is the code phase error between the received signal and the local pseudo code, fdIs the doppler frequency offset.
Preferably, in step 2, the result of correlating the received signal with the local PN code is:
Figure GDA0002821067320000025
wherein the content of the first and second substances,
Figure GDA0002821067320000026
is a copy of the local PN code and,
Figure GDA0002821067320000027
is an estimate of the code phase difference,
Figure GDA0002821067320000028
is the Doppler frequency estimate of the kth search cell, K is the total number of cells in the frequency search, fspFor frequency search stepping, N is the total number of samples for the correlation process.
Preferably, the result of the non-correlation integration output of the kth frequency search unit in step 3 is:
Figure GDA0002821067320000029
wherein the content of the first and second substances,
Figure GDA00028210673200000210
TN＝NTsl is the length of the incoherent integration, Rc(. cndot.) is the normalized autocorrelation function of the PN code.
Preferably, in step 3, the non-coherent integration result S in the k-th frequency search area is assumedkExceeding the threshold of constant false alarm detection, storing the point exceeding the threshold and two points at the same position in adjacent frequency search, defining the three points as P according to the order of magnitude of amplitudemax，PmidAnd PminThe frequency and amplitude of which are respectively defined as fmax，fmidAnd fminAnd Amax，AmidAnd AminAnd finding the accurate vertex position of the cross fuzzy function by adopting triangular fitting.
Preferably, the accurate doppler estimates are:
Figure GDA0002821067320000031
wherein the content of the first and second substances,
Figure GDA0002821067320000032
and alpha e [ -0.5,0]。
Compared with the prior art, the invention has the following remarkable advantages: 1) the direct sequence spread spectrum MSK signal is converted into the direct sequence spread spectrum BPSK signal through the intermediate frequency matched filter, so that the synchronization difficulty of a receiver is reduced; 2) the method utilizes the triangular fitting of the cross fuzzy function to accurately estimate the Doppler frequency value; 3) the invention effectively improves the acquisition probability of the receiver.
The present invention is described in further detail below with reference to the attached drawing figures.
Drawings
Fig. 1 is a schematic block diagram of FFT-based pseudo code parallel acquisition.
Fig. 2 is a flow chart of a pseudo code parallel acquisition method based on FFT.
Fig. 3 is a schematic diagram of a triangle fitting scheme for correct detection and false alarm of signals, (a) is a schematic diagram of a triangle fitting scheme for correct detection, and (b) is a schematic diagram of a triangle fitting scheme for false alarm.
Fig. 4 is a flow chart of a method of doppler frequency estimation of a direct spread MSK signal.
Detailed Description
As shown in fig. 4, a doppler frequency estimation method for direct spread MSK signal first converts the direct spread MSK signal into an approximate direct spread BPSK signal, i.e. the intermediate frequency direct spread MSK signal is processed by an intermediate frequency matched filter with impulse response h (t):
Figure GDA0002821067320000033
wherein, Tc＝1/RcFor spreading code chip period, RcIs the spreading code rate;
Figure GDA0002821067320000034
fcis the carrier frequency. According to the impulse response, the frequency response of the matched filter can be obtained as follows:
Figure GDA0002821067320000035
and solving the filter coefficient of the matched filter by using a convex optimization algorithm. The intermediate frequency direct spread MSK signal passes through the matched filter, and the output result is as follows:
Figure GDA0002821067320000041
wherein A is the signal amplitude,
Figure GDA0002821067320000042
to an initial phase, TsFor the sampling interval of the received signal, d (-) is the transmitted symbol, c (-) is the PN code, τ is the code phase error between the received signal and the local pseudo code, fdIs the doppler frequency offset.
As shown in fig. 1, the basic idea of the FFT-based parallel acquisition algorithm is that the circular correlation of two discrete signal time domains is equivalent to the conjugate multiplication of the frequency domain signals, so the circular correlation operation of the local pseudo code and the received pseudo code can be realized in the frequency domain by using FFT and IFFT calculation, and the correlation values on all code phases can be calculated by 3 times of FFT calculation. The correlation of the received signal with the local PN code results in
Figure GDA0002821067320000043
Wherein the content of the first and second substances,
Figure GDA0002821067320000044
is a copy of the local PN code and,
Figure GDA0002821067320000045
is an estimate of the code phase difference,
Figure GDA0002821067320000046
is the Doppler frequency estimate of the kth search cell, K is the total number of cells in the frequency search, fspFor frequency search stepping, N is the total number of samples for the correlation process.
And detecting the non-correlation integral output of the frequency domain, wherein the result of the non-correlation integral output of the k frequency searching unit is as follows:
Figure GDA0002821067320000047
wherein the content of the first and second substances,
Figure GDA0002821067320000048
TN＝NTsl is the length of the incoherent integration, Rc(. cndot.) is the normalized autocorrelation function of the PN code.
Suppose a non-coherent integration result S in the k-th frequency search regionk′Exceeding a threshold for Constant False Alarm (CFAR) detection, the point exceeding the threshold and two points at the same position in the adjacent frequency search are saved. Defining these three points as P according to the order of magnitude of the amplitudesmax，PmidAnd PminThe frequency and amplitude of which are respectively defined as fmax，fmidAnd fminAnd Amax，AmidAnd AminTrigonometric fitting is used to find the exact vertex position of the cross-ambiguity function (CAF). The fitting situation is shown in fig. 3. First, P is evaluatedmaxAnd PminIs used as a linear equation of (a). Next, the evaluation is made at PmidThe linear coefficients of the above fitted linear equation are opposite in sign to the coefficients derived in the first step. Finally, according to the characteristics of the isosceles triangle, the vertex of the CAF is obtained as the vertex of the isosceles triangle fitted on the two lines, which is defined as point PvFrequency fvAnd amplitude AvExpressed as:
Figure GDA0002821067320000051
Figure GDA0002821067320000052
if the signal is correctly detected and f, as shown in FIG. 3amin＞fmax＞fmid(fmid＞fmax＞fminSimilarly for the analysis), the amplitude values of the three points can be expressed as:
Figure GDA0002821067320000053
is represented by the formula (8), fvAnd AvIs shown as
Figure GDA0002821067320000054
Av＝Amax+(Amid-Amin)/2 (10)
Comparison Pmax、PvFrequency and amplitude of (2) can be obtained
Figure GDA0002821067320000055
Av≥Amax (12)
The residual frequency difference after the frequency fine estimation is as follows:
Figure GDA0002821067320000056
wherein the content of the first and second substances,
Figure GDA0002821067320000057
is the residual frequency difference before frequency fine estimation and
Figure GDA0002821067320000058
to ensure Pmax、PmidAnd PminAll in the main lobe of the CAF, the amplitudes of the three can be obviously distinguished, and the frequency search step f is setsp＝2/(3TN). The frequency estimation value after accurate estimation is as follows:
Figure GDA0002821067320000061
wherein the content of the first and second substances,
Figure GDA0002821067320000062
and alpha e [ -0.5,0]. Thus, Δ f ranges from
(8×10-5)·fsp≤Δf≤0.5·fsp (15)
As can be seen from equation (15), the doppler frequency estimation accuracy after the triangle fitting is greatly improved.
Conversely, if the signal is not detected correctly, i.e. a false alarm occurs, the frequency versus amplitude relationship of the three points will change as shown in fig. 3 b. Equations (11) (12) no longer apply but can be used to exclude false alarms.
In the frequency search, the false alarm probability of the neighboring correct frequency search unit is higher than that of the other search units. Therefore, the maximum false alarm probability of the triangle fitting in the invention is:
Figure GDA0002821067320000063
wherein, PdThe probability of detection of a non-coherent integration,
Figure GDA0002821067320000064
false alarm probability, V, for non-coherent integrationtIs the detection threshold. Due to Pd＜1，Pfa< 1, available
Figure GDA0002821067320000065
Therefore, under the same false alarm probability requirement, the CFAR detection threshold can be set to be lower, and the detection probability is improved. According to the characteristic, the method can not only improve the estimation precision of the Doppler frequency, but also improve the capture probability.
The range of the residual frequency difference before the fine frequency estimation is [0, fsp/2]The residual frequency difference range after the frequency fine estimation is reduced to [ (8 multiplied by 10 ] range-5)·fsp,0.5·fsp]And the Doppler frequency estimation precision is greatly improved after the triangle fitting.

Claims (3)

1. A Doppler frequency estimation method of direct spread MSK signals is characterized by comprising the following steps:
step 1, converting the received direct spread spectrum MSK signal into an approximate direct spread spectrum BPSK signal by using an intermediate frequency matched filter, wherein the expression of the approximate direct spread spectrum BPSK signal is as follows:
Figure FDA0002821067310000011
wherein A is the signal amplitude,
Figure FDA0002821067310000012
to an initial phase, TsFor the sampling interval of the received signal, d (-) is transmissionThe input symbols, c (-) are PN codes, tau is the code phase error between the received signal and the local pseudo code, fdIs the Doppler frequency offset;
step 2, code phase search is carried out on the approximate direct spread BPSK signal by using a pseudo code parallel acquisition algorithm based on FFT, circumferential correlation operation of local pseudo codes and received pseudo codes is realized in a frequency domain, correlation values on all code phases are obtained, and the correlation result of the received signal and the local PN codes is as follows:
Figure FDA0002821067310000013
wherein the content of the first and second substances,
Figure FDA0002821067310000014
Figure FDA0002821067310000015
is a copy of the local PN code and,
Figure FDA0002821067310000016
is an estimate of the code phase difference,
Figure FDA0002821067310000017
Figure FDA0002821067310000018
is the Doppler frequency estimate of the kth search cell, K is the total number of cells in the frequency search, fspFor frequency search stepping, N is the total number of samples for the correlation process;
step 3, detecting the non-correlation integral output of the frequency domain, and performing Doppler frequency offset value f on the result of the non-correlation integral exceeding the constant false alarm detection threshold value through triangular fitting of the cross fuzzy functiondOptimizing to obtain an accurate Doppler estimated value, wherein the result output by the non-correlation integral of the kth frequency search unit is as follows:
Sk＝A|sinc(Δfd,kTN)|Rc(Δτ)
wherein the content of the first and second substances,
Figure FDA0002821067310000019
TN＝NTs，Rc(. is a normalized autocorrelation function of the PN code;
suppose a non-coherent integration result S in the k-th frequency search regionkExceeding the threshold of constant false alarm detection, storing the point exceeding the threshold and two points at the same position in adjacent frequency search, defining the three points as P according to the order of magnitude of amplitudemax，PmidAnd PminThe frequencies are respectively defined as fmax，fmidAnd fminThe amplitudes of which are respectively defined as Amax，AmidAnd AminAnd finding the accurate vertex position of the cross fuzzy function by adopting triangular fitting.
2. The method according to claim 1, wherein the step 1 employs an intermediate frequency matched filter h (t) to receive the direct spread MSK signal, and the impulse response of the filter h (t) is:
Figure FDA0002821067310000021
wherein, Tc＝1/Rc，TcFor spreading code period, RcIs the spreading code rate;
Figure FDA0002821067310000022
fcis the carrier frequency.
3. The method of claim 1, wherein the accurate doppler estimation value is:
Figure FDA0002821067310000023
wherein the content of the first and second substances,
Figure FDA0002821067310000024
and alpha e [ -0.5,0]，
Figure FDA0002821067310000025
For the residual frequency difference before the frequency fine estimation,
Figure FDA0002821067310000026
the residual frequency difference after the frequency fine estimation is obtained.
CN201811064884.1A 2018-09-13 2018-09-13 Doppler frequency estimation method for direct sequence spread spectrum MSK signal Active CN109412644B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201811064884.1A CN109412644B (en) 2018-09-13 2018-09-13 Doppler frequency estimation method for direct sequence spread spectrum MSK signal

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201811064884.1A CN109412644B (en) 2018-09-13 2018-09-13 Doppler frequency estimation method for direct sequence spread spectrum MSK signal

Publications (2)

Publication Number Publication Date
CN109412644A CN109412644A (en) 2019-03-01
CN109412644B true CN109412644B (en) 2021-02-12

Family

ID=65464745

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201811064884.1A Active CN109412644B (en) 2018-09-13 2018-09-13 Doppler frequency estimation method for direct sequence spread spectrum MSK signal

Country Status (1)

Country Link
CN (1) CN109412644B (en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110113074B (en) * 2019-05-17 2021-02-26 中国电子科技集团公司第五十四研究所 High-speed pseudo code parallel capturing and tracking method based on FPGA
CN110958035A (en) * 2019-11-12 2020-04-03 天津津航计算技术研究所 Frequency secondary capturing device and method based on triangular envelope fitting
CN110912844B (en) * 2019-11-28 2022-03-22 上海瀚讯信息技术股份有限公司 Channel estimation optimization method based on big data analysis
CN113640842B (en) * 2021-08-25 2023-12-05 北京理工大学 Direct-spread signal capturing method based on intelligent Doppler search
CN113890563A (en) * 2021-09-24 2022-01-04 天津津航计算技术研究所 Time-frequency two-dimensional interpolation fine estimation method for direct sequence spread spectrum signal

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6879647B1 (en) * 2000-09-29 2005-04-12 Northrop Grumman Corporation Radio receiver AM-MSK processing techniques
CN105141340A (en) * 2015-07-24 2015-12-09 南京理工大学 Full-digital receiving method of direct spread MSK signal
CN105790788A (en) * 2016-04-28 2016-07-20 南京理工大学 Pseudocode-Doppler combined capturing method of direct sequence spread spectrum MSK signal
CN107493117A (en) * 2016-06-12 2017-12-19 南京理工大学 The two-dimentional joint acquisition method of DS msk signal under a kind of high dynamic

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6879647B1 (en) * 2000-09-29 2005-04-12 Northrop Grumman Corporation Radio receiver AM-MSK processing techniques
CN105141340A (en) * 2015-07-24 2015-12-09 南京理工大学 Full-digital receiving method of direct spread MSK signal
CN105790788A (en) * 2016-04-28 2016-07-20 南京理工大学 Pseudocode-Doppler combined capturing method of direct sequence spread spectrum MSK signal
CN107493117A (en) * 2016-06-12 2017-12-19 南京理工大学 The two-dimentional joint acquisition method of DS msk signal under a kind of high dynamic

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
一种改进的快速频偏捕获算法;朱雯等;《信息化研究》;20170420(第02期);全文 *

Also Published As

Publication number Publication date
CN109412644A (en) 2019-03-01

Similar Documents

Publication Publication Date Title
CN109412644B (en) Doppler frequency estimation method for direct sequence spread spectrum MSK signal
CN101444055B (en) Delay-doppler channel response demodulation method and apparatus
CN110071738B (en) Spread spectrum signal despreading and tracking method based on multi-pseudo code branch receiver
CN107493117B (en) The two-dimentional joint acquisition method of direct expansion msk signal under a kind of high dynamic
CN105162493A (en) Doppler domain and delay domain two-dimension acquiring method and device
CN102662183B (en) Method and system for global position system (GPS) signal capture
CN105790788B (en) A kind of pseudo-code of direct expansion msk signal-Doppler&#39;s joint acquisition method
CN109088838B (en) Pseudo code-Doppler fast capturing method of direct sequence spread spectrum DPSK signal under high dynamic condition
CN101777933A (en) Generation and capture system of encrypted frame hopping spread spectrum signal of air fleet link
CN101969321B (en) FFT (Fast Fourier Transform) based large frequency offset secondary catching method of direct sequence spread spectrum system
CN112910499B (en) Spread spectrum signal accurate acquisition system
CN106879068B (en) Method for estimating arrival time of signal in strong multipath environment
RU2658625C1 (en) Spread spectrum signal generating method, generating apparatus, receiving method and receiving apparatus
CN112187316A (en) Signal processing method, signal processing device, receiver and storage medium
CN109150235A (en) Compressed sensing based multicycle direct expansion msk signal two dimension joint acquisition method
CN108196274A (en) Be applicable in BOC (n, n) signal without fuzziness catching method and device
CN102035770B (en) Method for estimating channel by means of correlation
CN101072045A (en) Short-period spreading code time frequency parallel searching method based on frequency folding
CN107247276A (en) Weak signal catching method based on overlapping polylith zero padding algorithm
CN117270002B (en) Novel system Beidou signal ambiguity-free rapid capturing method, system and equipment
CN104601512A (en) Method and system for detecting carrier frequency offset of phase-modulated signals
CN104779993B (en) Deep space TT＆C system and method based on frequency domain equalization
CN114553656B (en) Weak signal capturing method based on unequal-length double-block zero padding algorithm
CN109104215A (en) A kind of Frequency Hopping Signal chip rate blind estimating method based on wavelet transformation
CN100493052C (en) Method for channel evaluating of weak energy parallel PN sequence

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant