CN109768812B - Underwater acoustic communication Doppler estimation and synchronization method based on chaotic frequency modulation - Google Patents
Underwater acoustic communication Doppler estimation and synchronization method based on chaotic frequency modulation Download PDFInfo
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Abstract
The invention discloses a chaos frequency modulation based underwater acoustic communication Doppler estimation and synchronization method, which comprises the steps of selecting a section of chaos frequency modulation signals, regularly sequencing the section of chaos frequency modulation signals to serve as frame synchronization signals, performing convolution action on received signals and the chaos frequency modulation signals and comparing the convolution action with a threshold, continuously performing copy convolution processing when the convolution action is smaller than the threshold, and increasing the distance and the median of different peak values and simultaneously completing Doppler estimation and signal synchronization when the convolution action is larger than the threshold. The method only uses a section of chaotic signal and convolution processing to complete Doppler estimation and signal synchronization, has small calculated amount and high engineering realization degree, is suitable for working in a large Doppler environment, and provides accurate Doppler and synchronization estimation.
Description
Technical Field
The invention belongs to the field of underwater acoustic communication, and particularly relates to a method for simultaneously completing Doppler estimation and synchronization in underwater acoustic communication based on chaotic frequency modulation.
Background
The underwater acoustic communication is used as a unique underwater communication means, is a key point of research in various countries, is one of high and new technologies urgently needed in various countries, and has the greatest technical challenge from an underwater acoustic channel with the characteristics of random time variation, space variation and frequency variation, wherein the multipath effect causes intersymbol interference and fluctuation effect to cause fluctuation of signals, how to inhibit the multipath, and the realization of stable and reliable detection of the signals is the primary problem to be solved in the underwater acoustic communication. On the other hand, due to the relative motion between the transmitter and the receiver and the action of sea water flow and turbulence, a certain frequency drift, namely Doppler frequency shift, is generated in the process of transmitting sound waves in an ocean channel, and the Doppler interference of the sound waves is far greater than that of road communication because the transmission speed of the sound in water is about 1500 m/s.
The common underwater Doppler estimation is divided into time domain, frequency domain and time-frequency domain methods, wherein the time domain is judged according to step length change among observation signals, the frequency domain is subjected to Doppler estimation by inserting frequency change of single-frequency signals, the frequency domain has advantages and disadvantages, the time domain Doppler generally judges a signal frame as the step length, the frequency domain judging method has requirements on the length of processed data, the longer the length is, the larger the frequency resolution is, and the calculated amount is large. The synchronization comprises an external synchronization method and an automatic synchronization method, and corresponds to different data frame formats and bandwidth requirements. The patent to the adult et al (application No. 200910021976.6) uses chirp as the synchronization frame and additionally uses the acquisition data to set the delay for synchronization and doppler determination. The patent of the bear army et al (application number 200910100598.0) adds single-frequency signals at two ends at a transmitting end, and a receiving end uses Zoom-FFT to reduce the calculated amount to complete Doppler estimation without completing synchronization, and the requirement of the length of a data frame still exists.
The chaotic signal is a random-like process expressed by a nonlinear dynamic system, namely, the chaotic signal has no period and is not converged, and the chaotic signal is sensitive to an initial value.
Disclosure of Invention
In view of the above, the invention provides a method for underwater acoustic communication doppler estimation and synchronization based on chaotic frequency modulation, which overcomes the defects that the calculation steps are large and doppler estimation and synchronization cannot be completed simultaneously.
The mechanism of the invention is as follows: by utilizing the orthogonality of the chaotic sequences, the same chaotic sequence is arranged at intervals, the second chaotic sequence is added with a conjugate flip sequence to form a synchronization head, and the Doppler estimation and synchronization are completed only by copying and convolving the chaotic sequences.
The underwater acoustic communication Doppler estimation and synchronization method based on the chaos frequency modulation comprises the following specific steps:
(1) generating a chaotic signal with the length of D according to a Chebyshev chaotic sequence formula, wherein the time interval of two identical chaotic signals is D, and adding a conjugate turning signal of the existing chaotic signal on the latter chaotic sequence to be used as a frame synchronization signal;
(2) sampling a received signal, wherein the sampling rate is 4-6 times of the highest frequency of a communication signal; copying and convolving the chaotic signal to the received signal r, and calculating an absolute value peak value | C | of a convolution function result;
(3) comparing | C | with a set threshold, if the | C | is smaller than the threshold, returning to the step (2) to continue convolution; if the number of the synchronization signals is larger than the threshold, judging that the synchronization signals arrive, and obtaining coarse synchronization;
(4) doubling the observation time length of convolution processing, respectively performing copy convolution of chaotic signal inversion signal and copy convolution of chaotic signal on the received signal r to respectively obtain C1，C2And C3Three peak points, calculating Doppler factor
Time synchronization point
Drawings
Fig. 1 is a diagram illustrating a data frame structure of a chaotic signal as a frame synchronization signal;
FIG. 2 is a diagram illustrating the convolution result of a conjugate inverted chaotic sequence copy under Doppler and delay conditions;
FIG. 3 is a diagram illustrating the convolution results of a chaotic sequence copy under Doppler and delay conditions;
figure 4 is a flow chart of an implementation of doppler and synchronization estimation of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
In the present invention, the frame synchronization signal uses a chaotic signal s (t), and can be represented by formula (1):
sn+1＝cos(q*arccos(sn))，-1≤Xn≤1 (1)
wherein s (t) is the initial value of chaotic signal, and the length of signal is D, s (t)*The conjugate inverted signal of s (t), combined with signal interval D, forms the frame synchronization signal, which can be expressed as:
due to the relative motion between the underwater acoustic communication transceivers, the signals propagating through the underwater acoustic channel can be expressed as:
r(t)＝p((1+Δ)t+d) (3)
where Δ is the Doppler factor and d is the time taken for the signal to arrive.
Taking the received signal r (t) and the chaos signal conjugate flip s (t)*Copying and convolving according to a formula (4), comparing a peak value | C | with a set threshold, and returning to continue to convolve if the peak value | C | is smaller than the threshold; if the received signal is larger than the threshold, judging that a synchronous signal arrives, obtaining coarse synchronization, and taking a received signal r (t) with the length of 2 times.
The extended observation time length of convolution processing is respectively carried out on the received signal r (t) by copying convolution of the chaotic signal inversion signal and copying convolution of the chaotic signal to respectively obtain C1，C2And C3Three peak points, calculating Doppler factor
Time synchronization starting point
In addition to the above embodiments, any technical solutions formed by equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (2)
1. A Doppler estimation and synchronization method for underwater acoustic communication based on chaos frequency modulation is characterized by comprising the following steps:
(1) generating a chaotic signal with the length of D according to a Chebyshev chaotic sequence formula, wherein the time interval of two identical chaotic signals is D, and adding a conjugate turning signal of the existing chaotic signal on the latter chaotic sequence to be used as a frame synchronization signal;
(2) sampling a received signal, wherein the sampling rate is 4-6 times of the highest frequency of a communication signal; convolving a received signal r (t) with a copy of the chaotic signal, and calculating an absolute value peak value | C | of a convolution function result C (tau);
(3) comparing | C | with a set threshold, if the | C | is smaller than the threshold, returning to the step (2) to continue convolution; if the number of the synchronization signals is larger than the threshold, judging that the synchronization signals arrive, and obtaining coarse synchronization;
(4) doubling the observation time length of convolution processing, respectively performing copy convolution of chaotic signal inversion signal and copy convolution of chaotic signal on received signal r (t), and respectively obtaining C1，C2And C3Three peak points, calculating Doppler factor
Time synchronization point
2. The underwater acoustic communication Doppler estimation and synchronization method based on chaotic frequency modulation according to claim 1, wherein: step (2) taking the received signal r (t) and the chaos signal conjugate flip s (t)*Copying and convolving according to a formula (4);
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Effective date of registration: 20211029 Address after: 310030 Room 302, building 1, Jihong Shidai commercial building, Sandun Town, Xihu District, Hangzhou City, Zhejiang Province Patentee after: Hangzhou Quanxin Technology Co.,Ltd. Address before: 310018 No. 2 street, Xiasha Higher Education Zone, Hangzhou, Zhejiang Patentee before: HANGZHOU DIANZI University |