CN115842567B - Dynamic threshold synchronization method and device based on CHIRP communication - Google Patents
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Abstract
The invention discloses a dynamic threshold synchronization method and a device based on CHIRP communication, which are relatively time-consuming for searching a dynamic threshold calculation method of a wireless communication system to be compatible with all application scenes of the wireless communication system aiming at the fact that the dynamic threshold is relatively complex to realize in the prior art. And when the signal-to-noise ratio is low, the dynamic threshold algorithm still has a certain false alarm rate and false alarm rate. The technical scheme of the invention comprises the following steps: firstly, division operation of receiving baseband IQ signals and baseband signals is completed in a time domain, then the frequency domain is transferred to complete some subsequent columns of demodulation threshold calculation, preamble search, frame synchronization, ID demodulation and the like according to the result of fast Fourier transform. The method has the advantages of simple operation process, easy logic realization, low resource occupancy rate and the like.
Description
Technical Field
The invention belongs to the technical field of communication of the Internet of things, and particularly relates to a dynamic threshold synchronization method and device based on CHIRP communication.
Background
In wireless communication, the most important step for correctly demodulating the received data packet is synchronization, a synchronization algorithm with excellent performance can ensure the accuracy of demodulation and improve the performance, the key of the synchronization algorithm is the determination of a threshold, the false alarm rate and the false alarm rate of synchronization are directly related to the quality of the threshold, and then whether the sensitivity index of the whole wireless communication system meets the requirement is determined. Thus, research on synchronization algorithms has been a long-standing interest.
In the existing synchronization technology, the threshold is mainly divided into two categories: 1. fixed threshold, fixed threshold value of final application is determined by algorithm modeling/simulation and actual test. The fixed threshold has the advantages of simple realization, low resource consumption and easy acquisition, but has larger difference between the false alarm rate and the false alarm rate under different scenes such as large signals, small signals and the like, and cannot achieve optimal performance under the same condition.
2. The dynamic threshold is dynamically calculated in real time through an algorithm, so that the optimal demodulation performance can be achieved under different scenes such as large signals, small signals and the like. The method has the defects that the realization is complex, and the searching of a dynamic threshold calculation method of a wireless communication system which is compatible with all application scenes is time-consuming. And when the signal-to-noise ratio is low, the dynamic threshold algorithm still has a certain false alarm rate and false alarm rate.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a dynamic threshold synchronization method and a device based on CHIRP communication, and the purpose is as follows: the false alarm rate and the false alarm rate are reduced by a dynamic threshold calculation mode, and the sensitivity performance close to an expected value can be realized by flexibly adjusting factors.
The technical scheme adopted by the invention for achieving the purpose is as follows: the dynamic threshold synchronization method based on CHIRP communication comprises the following steps:
s1: the digital-to-analog converter processes the acquired initial data to obtain a baseband IQ signal, and outputs the baseband IQ signal to a baseband filter bank;
s2: the baseband filter bank carries out filtering and downsampling corresponding to the signal bandwidth according to the signal bandwidth of the input baseband IQ signal, and conversion of the sampling rate of the baseband IQ signal is completed to obtain a converted signal;
s3: grouping the converted signals according to the number of points configured by different spread spectrum factors SF, and performing division operation on the different groups and the baseband signals;
s4: performing variable-point fast Fourier transform on the division result according to the spread spectrum factor SF configuration; modulo a result obtained by the fast Fourier transform by using a CORDIC function to obtain modulo data;
s5, finding out the peak-to-peak value position and the value of the modulus data, and calculating a dynamic threshold through the peak-to-peak value position and the value thereof;
s6: and carrying out preliminary matching synchronization by using the dynamic threshold and the peak value numerical value, and further confirming whether synchronization is completed or not through the peak-to-peak value position.
Preferably, in the present invention S2, the baseband filter component is four stages, which are respectively: after the baseband IQ signals are input into the baseband filter bank, the baseband filter bank carries out corresponding filtering and downsampling according to paths of the baseband filter bank passing through different signal bandwidths, and conversion of the sampling rate of the baseband IQ signals is completed.
Preferably, the invention S3 specifically comprises:
s3.1. waveform using chirp symbol in CSS is:
wherein ,
is a quadratic function with respect to time, +.>
A and b are coefficients;
s3.2: the instantaneous frequency of the chirp symbol is defined as:
wherein ,
is->
A linear function after deriving the time t, a and b being coefficients;
therefore, the instantaneous frequency characteristic of the chirp symbol is modeled as f0=at+b, and when b=0, it is a fundamental frequency signal;
s3.3: the matlab reduced model in which chirp symbols are generated is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M-1/2*m))]
wherein, data_css is generated chirp symbol data, M is 2 SF, and the value of M is 0-M-1;
s3.4: the matlab reduced model generated by the fundamental frequency signal is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M))]
wherein M is 2 SF, and the value of M is 0-M-1;
s3.5: the converted signals are grouped by taking 2 SF sampling points as units according to different spreading factors SF, and each group of data is divided with a locally generated base frequency signal.
Preferably, the final threshold calculated in S5 of the present invention is specifically:
s5.1: summing the modular data of the whole packet, resulting in sum:
SF is a spread spectrum factor, dn is a numerical value of each sampling point in n-point modulo data;
s5.2: searching to obtain the value of the peak value, and marking the value as max_value;
s5.3: searching and obtaining the average value of the numerical values of the two points in front of the peak position, and marking the average value as max_p1;
s5.4: searching and obtaining the average value of the numerical values of two points behind the peak value position, and marking the average value as max_p2;
s5.5: calculating and averaging the calculation results in the steps S5.1 to S5.4, wherein the formula is as follows:
Mean_thld=(sum - max_value - max_p1 - max_p2)/2^SF
s5.6: multiplying the average result by a coefficient F1 to obtain a dynamic threshold, wherein the formula is as follows:
Final_thld= Mean_thld * F1。
preferably, in the step S6 of the present invention, the specific steps for performing the preliminary matching synchronization are:
s6.1: calculate the decision value 1, noted as judge1:
judge1= (（max_value + max_p1 + max_p2）/2^SF) * F2
s6.2: calculate decision value 2, noted as judge2:
judge2= (max_value/2^SF) * F2
s6.3: calculate the decision value 3, noted as judge3:
judge3= (max_p1/2^SF )* F2
s6.4: calculate decision value 4, noted as judge4:
judge4= (max_p2/2^SF) * F2
wherein F2 is a coefficient;
the preliminary synchronization conditions are specifically as follows:
s6.5: judging whether the condition I is successfully matched, if the condition1 is greater than the final_thld, the condition I is met and is marked as condition 1=1, otherwise, the condition 1=0;
s6.6: judging whether the condition II is successfully matched, if the condition II is satisfied when the joint 2 is greater than the final_thld, marking the condition II as condition 2=1, otherwise, the condition 2=0;
s6.7: judging whether the condition III is successfully matched, if the joint 3 is greater than the final_thld, the condition III is met and is marked as condition 3=1, otherwise, the condition 3=0;
s6.8: judging whether the condition four is successfully matched, if the condition4 is greater than the final_thld, the condition four is met and is marked as condition 4=1, otherwise, the condition 4=0;
s6.9: judging whether the condition five is successfully matched, if (max_value/2 SF) > K, the condition five is met and is marked as condition 5=1, otherwise, the condition 5=0;
wherein K is a coefficient;
s6.10: judging whether synchronization is generated or not, and if a result of the condition1& (condition 2 condition 3) & condition4& condition5 is 1, completing preliminary matching synchronization.
Preferably, the specific steps for further determining whether to complete synchronization in the step S6 of the present invention by using the peak-to-peak position are as follows:
s6.11: saving the peak-to-peak value position searched after obtaining the module for the first time, and marking the position (1);
s6.12: storing the peak-to-peak position searched after obtaining the module data for the second time, marking as position (2), and returning to S6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
s6.13: storing the peak value position searched after obtaining the module data for the nth time, marking as position (n), wherein n is a natural number, and returning to S6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
s6.14: step S6.11 to S6.13 continuously searches and stores peak-to-peak positions in a flowing water mode; if the peak-to-peak value positions of the continuous m times of searching are all within a range of a point before and after a certain position, judging that the synchronous condition is met, wherein m is a coefficient;
s6.15: if the conditions of step S6.10 and step S6.14 are simultaneously satisfied, it is determined that synchronization is completed, then the subsequent demodulation processing is performed, and if the conditions of step S6.10 and step S6.14 are not simultaneously satisfied, the process returns to step S5, and the peak-to-peak position and the value thereof are continuously searched.
The invention also provides a dynamic threshold synchronization device based on CHIRP communication, which comprises:
a digital-to-analog converter: acquiring initial data, preprocessing the initial data, and outputting a baseband IQ signal;
baseband filter bank: inputting and outputting a baseband IQ signal, filtering and downsampling corresponding to the signal bandwidth are implemented according to the signal bandwidth of the input baseband IQ signal, and conversion of the sampling rate of the baseband IQ signal is completed, so that a converted signal is obtained;
division operation unit: grouping the converted signals according to the number of points configured by different spread spectrum factors SF, and performing division operation on the different groups and the baseband signals;
DFT modulo unit: performing variable-point fast Fourier transform on the division result according to the spread spectrum factor SF configuration; modulo a result obtained by the fast Fourier transform by using a CORDIC function to obtain modulo data;
the dynamic threshold unit is used for finding out the peak-to-peak value position and the value of the modulus data and calculating a dynamic threshold through the peak-to-peak value position and the value thereof;
synchronization unit: and carrying out preliminary matching synchronization by using the dynamic threshold and the peak value numerical value, and further confirming whether synchronization is completed or not through the peak-to-peak value position.
Compared with the prior art, the technical scheme of the invention has the following advantages/beneficial effects:
1. the invention completes the division operation of receiving baseband IQ signals and baseband signals in the time domain, then transfers to the frequency domain to complete the subsequent processing of demodulation threshold calculation, preamble search, frame synchronization, ID demodulation and other columns according to the result of fast Fourier transformation, and the processing has the characteristics of simple operation process, easy realization of logic, low resource occupancy rate and the like.
2. The invention can realize the sensitivity performance close to the expected value by flexibly adjusting the parameter F1, the parameter F2 and the parameter K.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some examples of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic flow chart of embodiment 1 of the present invention.
Fig. 2 is a schematic diagram of a frame structure of embodiment 1 of the present invention.
Fig. 3 is a schematic diagram of dynamic threshold calculation according to embodiment 1 of the present invention.
Detailed Description
To make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, based on the embodiments of the invention, which are apparent to those of ordinary skill in the art without inventive faculty, are intended to be within the scope of the invention. Accordingly, the detailed description of the embodiments of the invention provided below is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention.
Example 1:
as shown in fig. 1-3, this embodiment 1 provides a dynamic threshold synchronization method based on CHIRP communication, where symbols used in the synchronization process are preambles, and fig. 2 shows a frame structure of the system of the present invention. The number of preambles in the frame structure is configured by the upper layer protocol, but is at least 4. The SF is 10, and the following specific implementation steps are as follows:
s1: the digital-to-analog converter processes the acquired initial data to obtain a baseband IQ signal, and outputs the baseband IQ signal to a baseband filter bank;
s2: the baseband filter bank carries out filtering and downsampling corresponding to the signal bandwidth according to the signal bandwidth of the input baseband IQ signal, and conversion of the sampling rate of the baseband IQ signal is completed to obtain a converted signal; the baseband filter component is four stages, which are respectively: after the baseband IQ signals are input into the baseband filter bank, the baseband filter bank carries out corresponding filtering and downsampling according to paths of the baseband filter bank passing through different signal bandwidths, and conversion of the sampling rate of the baseband IQ signals is completed.
S3: grouping the converted signals in 1024 units, and dividing different groups with the baseband signals; s3 specifically comprises the following steps:
s3.1. waveform using chirp symbol in CSS is:
wherein ,
is a quadratic function with respect to time, +.>
；
S3.2: the instantaneous frequency of the chirp symbol is defined as:
thus, the instantaneous frequency characteristic of the chirp symbols is modeled as f0=at+b, and thus the b corresponding to each chirp symbol is demodulated, i.e., found, by dividing the received signal by the locally generated chirp baseband signal, and when b=0, the baseband signal; the result obtained after the division is the superposition result of the single-tone signal with the frequency b and the channel distortion. And then finding out the frequency point of the single-tone signal through DFT calculation, thereby obtaining the value of b.
S3.3: the matlab reduced model in which chirp symbols are generated is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M-1/2*m))]
wherein, data_css is generated chirp symbol data, M is 2 SF, and the value range of M is 0-M-1;
s3.4: the matlab reduced model generated by the fundamental frequency signal is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M))]
wherein M is 2 SF, and the value of M is 0-M-1;
s3.5: the converted signals are grouped in units of 2 SF sample points according to different spreading factors SF, each group of data is conjugate multiplied with a locally generated baseband signal,
data_demod = rec_data*conj(basic_data)。
s4: performing variable-point fast Fourier transform on the division result according to the spread spectrum factor SF configuration; modulo the result obtained by the fast Fourier transform by a CORDIC function, namely performing DFT operation and abs modulo operation on the result obtained by the division operation to obtain modulo data;
s5, finding out the peak-to-peak value position and the value of the modulus data, and calculating a dynamic threshold through the peak-to-peak value position and the value thereof; the final threshold is calculated specifically as:
s5.1: summing the modular data of the whole packet, resulting in sum:
SF is a spread spectrum factor, dn is a numerical value of each sampling point in n-point modulo data;
s5.2: searching to obtain the value of the peak value, and marking the value as max_value;
s5.3: searching and obtaining the average value of the numerical values of the two points in front of the peak position, and marking the average value as max_p1;
s5.4: searching and obtaining the average value of the numerical values of two points behind the peak value position, and marking the average value as max_p2;
s5.5: calculating and averaging the calculation results in the steps S5.1 to S5.4, wherein the formula is as follows:
Mean_thld=(sum - max_value - max_p1 - max_p2)/2^SF
s5.6: multiplying the average result by a coefficient F1 to obtain a dynamic threshold, wherein the formula is as follows:
Final_thld= Mean_thld * F1。
s6: and carrying out preliminary matching synchronization by using the dynamic threshold and the peak value numerical value, and further confirming whether synchronization is completed or not through the peak-to-peak value position. The specific steps of the preliminary matching synchronization are as follows:
s6.1: calculate the decision value 1, noted as judge1:
judge1= (（max_value + max_p1 + max_p2）/2^SF) * F2
s6.2: calculate decision value 2, noted as judge2:
judge2= (max_value/2^SF) * F2
s6.3: calculate the decision value 3, noted as judge3:
judge3= (max_p1/2^SF )* F2
s6.4: calculate decision value 4, noted as judge4:
judge4= (max_p2/2^SF) * F2
wherein F2 is a coefficient;
the preliminary synchronization conditions are specifically as follows:
s6.5: judging whether the condition I is successfully matched, if the condition1 is greater than the final_thld, the condition I is met and is marked as condition 1=1, otherwise, the condition 1=0;
s6.6: judging whether the condition II is successfully matched, if the condition II is satisfied when the joint 2 is greater than the final_thld, marking the condition II as condition 2=1, otherwise, the condition 2=0;
s6.7: judging whether the condition III is successfully matched, if the joint 3 is greater than the final_thld, the condition III is met and is marked as condition 3=1, otherwise, the condition 3=0;
s6.8: judging whether the condition four is successfully matched, if the condition4 is greater than the final_thld, the condition four is met and is marked as condition 4=1, otherwise, the condition 4=0;
s6.9: judging whether the condition five is successfully matched, if (max_value/2 SF) > K, the condition five is met and is marked as condition 5=1, otherwise, the condition 5=0;
wherein K is a coefficient;
s6.10: judging whether synchronization is generated or not, and if a result of the condition1& (condition 2 condition 3) & condition4& condition5 is 1, completing preliminary matching synchronization.
The specific steps of further determining whether to complete synchronization using peak-to-peak positions are:
s6.11: saving the peak-to-peak value position searched after obtaining the module for the first time, and marking the position (1);
s6.12: storing the peak-to-peak position searched after obtaining the module data for the second time, marking as position (2), and returning to S6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
s6.13: storing the peak value position searched after obtaining the module data for the nth time, marking as position (n), wherein n is a natural number, and returning to S6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
s6.14: step S6.11 to S6.13 continuously searches and stores peak-to-peak positions in a flowing water mode; if the peak-to-peak value positions of the continuous m times of searching are all within a range of a point before and after a certain position, judging that the synchronous condition is met, wherein m is a coefficient;
s6.15: if the conditions of step S6.10 and step S6.14 are simultaneously satisfied, it is determined that synchronization is completed, then the subsequent demodulation processing is performed, and if the conditions of step S6.10 and step S6.14 are not simultaneously satisfied, the process returns to step S5, and the peak-to-peak position and the value thereof are continuously searched.
In this embodiment 1, the maximum value and the position of the modulo data are continuously searched in the form of running water, the position is marked as P, the dynamic threshold is continuously calculated, the flow chart of the dynamic threshold calculation is shown in fig. 3, the calculation process is shown in S5.1-S5.6, and the synchronization process is shown in S6.1-S6.15. If the continuous 3 times of maximum values are larger than the dynamic threshold, and the positions of the continuous 3 times of maximum values meet |P1-P2| < =1, and |P2-P3| < =1, the synchronization is completed, and the subsequent demodulation processing is performed.
The embodiment 1 also provides a dynamic threshold synchronization device based on the CHIRP communication, which comprises:
a digital-to-analog converter: acquiring initial data, preprocessing the initial data, and outputting a baseband IQ signal;
baseband filter bank: inputting and outputting a baseband IQ signal, filtering and downsampling corresponding to the signal bandwidth are implemented according to the signal bandwidth of the input baseband IQ signal, and conversion of the sampling rate of the baseband IQ signal is completed, so that a converted signal is obtained;
division operation unit: grouping the converted signals according to the number of points configured by different spread spectrum factors SF, and performing division operation on the different groups and the baseband signals;
DFT modulo unit: performing variable-point fast Fourier transform on the division result according to the spread spectrum factor SF configuration; modulo a result obtained by the fast Fourier transform by using a CORDIC function to obtain modulo data;
the dynamic threshold unit is used for finding out the peak-to-peak value position and the value of the modulus data and calculating a dynamic threshold through the peak-to-peak value position and the value thereof;
synchronization unit: and carrying out preliminary matching synchronization by using the dynamic threshold and the peak value numerical value, and further confirming whether synchronization is completed or not through the peak-to-peak value position.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that the above-mentioned preferred embodiment should not be construed as limiting the invention, and the scope of the invention should be defined by the appended claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (3)
1. A method for dynamic threshold synchronization based on CHIRP communication, comprising:
s1: the digital-to-analog converter processes the acquired initial data to obtain a baseband IQ signal, and outputs the baseband IQ signal to a baseband filter bank;
s2: the baseband filter bank carries out filtering and downsampling corresponding to the signal bandwidth according to the signal bandwidth of the input baseband IQ signal, and conversion of the sampling rate of the baseband IQ signal is completed to obtain a converted signal;
s3: grouping the converted signals according to the number of points configured by different spread spectrum factors SF, and performing division operation on the different groups and the baseband signals; the method comprises the following steps:
s3.1. waveform using chirp symbol in CSS is:
wherein ,
is a quadratic function with respect to time, +.>
A and b are coefficients;
s3.2: the instantaneous frequency of the chirp symbol is defined as:
wherein ,
is->
A linear function after deriving the time t, a and b being coefficients;
thus, the instantaneous frequency characteristic of the chirp symbol is modeled as f0=at+b, and when b=0, is a fundamental frequency signal;
s3.3: the matlab reduced model in which chirp symbols are generated is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M-1/2*m))]
wherein, data_css is generated chirp symbol data, M is 2 SF, and the value of M is 0-M-1;
s3.4: the matlab reduced model generated by the fundamental frequency signal is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M))]
wherein M is 2 SF, and the value range of M is 0-M-1;
s3.5: the converted signals are grouped by taking 2 SF sampling points as units according to different spreading factors SF, and division operation is carried out on each group of data and locally generated fundamental frequency signals;
s4: performing variable-point fast Fourier transform on the division result according to the spread spectrum factor SF configuration; modulo a result obtained by the fast Fourier transform by using a CORDIC function to obtain modulo data;
s5, finding out the peak-to-peak value position and the value of the modulus data, and calculating a dynamic threshold through the peak-to-peak value position and the value thereof; the final threshold is calculated specifically as:
s5.1: summing the modular data of the whole packet, resulting in sum:
SF is a spread spectrum factor, dn is a numerical value of each sampling point in n-point modulo data;
s5.2: searching to obtain the value of the peak value, and marking the value as max_value;
s5.3: searching and obtaining the average value of the numerical values of the two points in front of the peak position, and marking the average value as max_p1;
s5.4: searching and obtaining the average value of the numerical values of two points behind the peak value position, and marking the average value as max_p2;
s5.5: calculating and averaging the calculation results in the steps S5.1 to S5.4, wherein the formula is as follows:
Mean_thld=(sum - max_value - max_p1 - max_p2)/2^SF
s5.6: multiplying the average result by a coefficient F1 to obtain a dynamic threshold, wherein the formula is as follows:
Final_thld= Mean_thld * F1；
s6: preliminary matching synchronization is carried out by utilizing a dynamic threshold and a peak value, and then whether synchronization is completed is further confirmed through the peak-to-peak value position; the specific steps of the preliminary matching synchronization are as follows:
s6.1: calculate the decision value 1, noted as judge1:
judge1= (（max_value + max_p1 + max_p2）/2^SF) * F2
s6.2: calculate decision value 2, noted as judge2:
judge2= (max_value/2^SF) * F2
s6.3: calculate the decision value 3, noted as judge3:
judge3= (max_p1/2^SF )* F2
s6.4: calculate decision value 4, noted as judge4:
judge4= (max_p2/2^SF) * F2
wherein F2 is a coefficient;
the preliminary synchronization conditions are specifically as follows:
s6.5: judging whether the condition I is successfully matched, if the condition1 is greater than the final_thld, the condition I is met and is marked as condition 1=1, otherwise, the condition 1=0;
s6.6: judging whether the condition II is successfully matched, if the condition II is satisfied when the joint 2 is greater than the final_thld, marking the condition II as condition 2=1, otherwise, the condition 2=0;
s6.7: judging whether the condition III is successfully matched, if the joint 3 is greater than the final_thld, the condition III is met and is marked as condition 3=1, otherwise, the condition 3=0;
s6.8: judging whether the condition four is successfully matched, if the condition4 is greater than the final_thld, the condition four is met and is marked as condition 4=1, otherwise, the condition 4=0;
s6.9: judging whether the condition five is successfully matched, if (max_value/2 SF) > K, the condition five is met and is marked as condition 5=1, otherwise, the condition 5=0;
wherein K is a coefficient;
s6.10: judging whether synchronization is generated or not, and if a result of a condition1& (condition 2 condition 3) & condition4& condition5 is 1, completing preliminary matching synchronization;
the specific steps of further determining whether to complete synchronization using peak-to-peak positions are:
s6.11: saving the peak-to-peak value position searched after obtaining the module for the first time, and marking the position (1);
s6.12: storing the peak-to-peak position searched after obtaining the module data for the second time, marking as position (2), and returning to S6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
s6.13: storing the peak value position searched after obtaining the module data for the nth time, marking as position (n), wherein n is a natural number, and returning to S6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
s6.14: step S6.11 to S6.13 continuously searches and stores peak-to-peak positions in a flowing water mode; if the peak-to-peak value positions of the continuous m times of searching are all within a range of a point before and after a certain position, judging that the synchronous condition is met, wherein m is a coefficient;
s6.15: if the conditions of step S6.10 and step S6.14 are simultaneously satisfied, it is determined that synchronization is completed, then the subsequent demodulation processing is performed, and if the conditions of step S6.10 and step S6.14 are not simultaneously satisfied, the process returns to step S5, and the peak-to-peak position and the value thereof are continuously searched.
2. The method for dynamic threshold synchronization based on CHIRP communication according to claim 1, wherein in S2, the baseband filter component is four stages, which are respectively: after the baseband IQ signals are input into the baseband filter bank, the baseband filter bank carries out corresponding filtering and downsampling according to paths of the baseband filter bank passing through different signal bandwidths, and conversion of the sampling rate of the baseband IQ signals is completed.
3. A dynamic threshold synchronization device based on CHIRP communication, comprising:
a digital-to-analog converter: acquiring initial data, preprocessing the initial data, and outputting a baseband IQ signal;
baseband filter bank: inputting and outputting a baseband IQ signal, filtering and downsampling corresponding to the signal bandwidth are implemented according to the signal bandwidth of the input baseband IQ signal, and conversion of the sampling rate of the baseband IQ signal is completed, so that a converted signal is obtained;
division operation unit: grouping the converted signals according to the number of points configured by different spread spectrum factors SF, and performing division operation on the different groups and the baseband signals; the method comprises the following steps:
step 3.1 waveforms using chirp symbols in CSS are:
wherein ,
is a quadratic function with respect to time, +.>
A and b are coefficients;
step 3.2: the instantaneous frequency of the chirp symbol is defined as:
wherein ,
is->
A linear function after deriving the time t, a and b being coefficients;
thus, the instantaneous frequency characteristic of the chirp symbol is modeled as f0=at+b, and when b=0, is a fundamental frequency signal;
step 3.3: the matlab reduced model in which chirp symbols are generated is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M-1/2*m))]
wherein, data_css is generated chirp symbol data, M is 2 SF, and the value of M is 0-M-1;
step 3.4: the matlab reduced model generated by the fundamental frequency signal is:
data_css(m+1) = [exp(j*2*pi*(m^2/2/M))]
wherein M is 2 SF, and the value range of M is 0-M-1;
step 3.5: the converted signals are grouped by taking 2 SF sampling points as units according to different spreading factors SF, and division operation is carried out on each group of data and locally generated fundamental frequency signals;
DFT modulo unit: performing variable-point fast Fourier transform on the division result according to the spread spectrum factor SF configuration; modulo a result obtained by the fast Fourier transform by using a CORDIC function to obtain modulo data;
the dynamic threshold unit is used for finding out the peak-to-peak value position and the value of the modulus data and calculating a dynamic threshold through the peak-to-peak value position and the value thereof; the final threshold is calculated specifically as:
step 5.1: summing the modular data of the whole packet, resulting in sum:
SF is a spread spectrum factor, dn is a numerical value of each sampling point in n-point modulo data;
step 5.2: searching to obtain the value of the peak value, and marking the value as max_value;
step 5.3: searching and obtaining the average value of the numerical values of the two points in front of the peak position, and marking the average value as max_p1;
step 5.4: searching and obtaining the average value of the numerical values of two points behind the peak value position, and marking the average value as max_p2;
step 5.5: calculating and averaging the calculation results in the steps 5.1 to 5.4, wherein the formula is as follows:
Mean_thld=(sum - max_value - max_p1 - max_p2)/2^SF
step 5.6: multiplying the average result by a coefficient F1 to obtain a dynamic threshold, wherein the formula is as follows:
Final_thld= Mean_thld * F1；
synchronization unit: preliminary matching synchronization is carried out by utilizing a dynamic threshold and a peak value, and then whether synchronization is completed is further confirmed through the peak-to-peak value position; the specific steps of the preliminary matching synchronization are as follows:
step 6.1: calculate the decision value 1, noted as judge1:
judge1= (（max_value + max_p1 + max_p2）/2^SF) * F2
step 6.2: calculate decision value 2, noted as judge2:
judge2= (max_value/2^SF) * F2
step 6.3: calculate the decision value 3, noted as judge3:
judge3= (max_p1/2^SF )* F2
step 6.4: calculate decision value 4, noted as judge4:
judge4= (max_p2/2^SF) * F2
wherein F2 is a coefficient;
the preliminary synchronization conditions are specifically as follows:
step 6.5: judging whether the condition I is successfully matched, if the condition1 is greater than the final_thld, the condition I is met and is marked as condition 1=1, otherwise, the condition 1=0;
step 6.6: judging whether the condition II is successfully matched, if the condition II is satisfied when the joint 2 is greater than the final_thld, marking the condition II as condition 2=1, otherwise, the condition 2=0;
step 6.7: judging whether the condition III is successfully matched, if the joint 3 is greater than the final_thld, the condition III is met and is marked as condition 3=1, otherwise, the condition 3=0;
step 6.8: judging whether the condition four is successfully matched, if the condition4 is greater than the final_thld, the condition four is met and is marked as condition 4=1, otherwise, the condition 4=0;
step 6.9: judging whether the condition five is successfully matched, if (max_value/2 SF) > K, the condition five is met and is marked as condition 5=1, otherwise, the condition 5=0;
wherein K is a coefficient;
step 6.10: judging whether synchronization is generated or not, and if a result of a condition1& (condition 2 condition 3) & condition4& condition5 is 1, completing preliminary matching synchronization;
the specific steps of further determining whether to complete synchronization using peak-to-peak positions are:
step 6.11: saving the peak-to-peak value position searched after obtaining the module for the first time, and marking the position (1);
step 6.12: storing the peak-to-peak position searched after obtaining the module data for the second time, marking as position (2), and returning to step 6.11 for searching again if the 2 SF point in the module data is not satisfied with the primary synchronization condition;
step 6.13: saving the peak-to-peak position searched after obtaining the modulus data for the nth time, marking as position (n), wherein n is a natural number, and returning to the step 6.11 for searching again if the 2 SF point in the modulus data is not satisfied with the primary synchronization condition;
step 6.14: step 6.11 to step 6.13, continuously searching and storing peak-to-peak positions in a flowing water mode; if the peak-to-peak value positions of the continuous m times of searching are all within a range of a point before and after a certain position, judging that the synchronous condition is met, wherein m is a coefficient;
step 6.15: if the conditions of step 6.10 and step 6.14 are simultaneously satisfied, the synchronization is judged to be completed, then the subsequent demodulation processing is carried out, and if the conditions of step 6.10 and step 6.14 are not simultaneously satisfied, the dynamic threshold unit is returned to, and the peak-to-peak position and the value thereof are continuously searched.
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