CN116318245A - Folding capturing method for direct sequence spread spectrum long code - Google Patents
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Abstract
The invention discloses a folding capturing method of a direct sequence spread spectrum long code, which comprises the following steps: the high-frequency spread spectrum signal is subjected to preprocessing and mixing processing and then is subjected to partial matching correlation with a local folding code, a correlation result is stored in a two-dimensional register, grouping FFT operation and accumulation are carried out on the correlation result to obtain a power spectrum of the same code phase of the correlation result, the power spectrum of the I/Q path is subjected to modular sum to obtain a maximum peak value which is far larger than the amplitude of other power spectrums, the maximum peak value is compared with a threshold value, if the maximum peak value is larger than the threshold value, the phase offset of the local spread spectrum code corresponding to the peak value is consistent with the code offset of an input signal at the moment, and meanwhile, the Doppler frequency offset estimation value of the input signal can be obtained through the corresponding local spread spectrum code. The local codes are folded, a plurality of code phases can be searched by one-time correlation, and meanwhile, the correlation results are subjected to grouping FFT (fast Fourier transform), so that the operation difficulty and the calculation time can be reduced.
Description
Technical Field
The invention relates to a folding capturing method of a direct sequence spread spectrum long code, belonging to the technical field of spread spectrum communication.
Background
Spread spectrum communication is widely used because of its advantages of good multipath resistance, strong interference resistance, good confidentiality, etc.
For a complete set of spread spectrum communication systems, the system can be divided into a transmitting end and a receiving end. The transmitting end modulates the data information to be transmitted through a spread spectrum code sequence to realize the spectrum spreading of the data information, and transmits the data information after molding and filtering; the receiving end receives the signal after wireless transmission, and performs correlation operation by using the same spread spectrum code sequence as the transmitting end, so as to realize synchronous receiving, despreading and recovering the original data information to be transmitted. The final purpose of the whole wireless transmission system is to make the original data consistent with the data information after despreading and recovering, thus achieving error-free transmission of the data.
However, after the whole signal is transmitted through the wireless channel, the whole signal is inevitably affected by transmission environments such as noise, obstacles, relative movement and the like, so that the signal is subjected to code error in the transmission process, and the effectiveness of the communication system is lowered. The capturing of the spread spectrum communication system is the first processing module that the data arrives after being transmitted through the wireless channel, which directly determines the performance of subsequent synchronization and despreading, so the research on the capturing system is particularly important.
Disclosure of Invention
Synchronization in a direct sequence spread spectrum communication system can generally be divided into two phases: capturing and tracking. The spread spectrum acquisition is also called coarse synchronization, realizes the initial synchronization of data, and determines the code phase of a data symbol to be within a 1/2 symbol interval deviation range. Spread spectrum tracking, also called fine synchronization, is a tracking phase after initial synchronization, in which the phase deviation is controlled within one sampling interval by using the autocorrelation of the PN code.
For DSSS fast acquisition methods, two main categories can be distinguished: time domain acquisition and frequency domain acquisition. The time domain-based acquisition method includes serial/parallel acquisition by using a matched filter, and the frequency domain-based acquisition method includes cyclic correlation by using FFT to realize parallel matched search. The time domain correlation and the frequency domain parallel FFT search are jointly searched, and the combined technology is called partial matched filter PMF-FFT and a series of regenerated optimization algorithms. The time domain capturing method carries out correlation operation on each code phase and the local code by a matched filtering method, the structure is simple to realize, but the required registers and operation units are too many, so that the capturing time is too long. The frequency domain capturing method has fast time for capturing the frequency domain conjugate convolution by the parallel FFT method, but has high implementation complexity. The fast capturing frequency offset correcting capability based on PMF-FFT is limited by the number of FFT points, and the requirements of large frequency offset and limited resources can not be met.
The present invention aims to solve the above-mentioned problems of the prior art, and provides a folded acquisition method for a direct sequence spread spectrum long code.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
in a first aspect, the present invention provides a method for folding acquisition of a direct sequence spread spectrum long code, including:
s1, acquiring a received high-frequency spread spectrum signal transmitted through a wireless channel;
s2, carrying out down-conversion treatment and A/D conversion on the high-frequency spread spectrum signal to obtain a digital intermediate frequency signal;
s3, carrying out energy detection on the digital intermediate frequency signal;
s4, responding to the detected packet signal energy, preprocessing and modulating the digital intermediate frequency signal into data with fixed bit width to obtain preprocessed data; carrying out digital down-conversion processing on the preprocessed data by using orthogonal carriers to obtain I/Q two paths of orthogonal data;
s5, obtaining M-point local spread spectrum code data generated by a local spread spectrum code module; performing local code staggering N-chip superposition on the local spread spectrum code data to obtain M x L folding codes;
s6, performing partial matching correlation operation on the I/Q two-way orthogonal data and the folding code to obtain a partial matching correlation result of the folding code and the I/Q two-way orthogonal data;
s7, grouping the partial matching correlation results to obtain grouped matching correlation results, and performing frequency domain FFT (fast Fourier transform) on each group of the grouped matching correlation results to obtain frequency domain data; accumulating the frequency domain data with the set period to obtain M frequency domain energies K;
s8, comparing the maximum value of the M frequency domain energies K with an adaptive threshold value;
in response to the maximum value of the M frequency domain energies K not exceeding the adaptive threshold value, updating M-point local spread spectrum code data generated by a local spread spectrum code module, and repeating the steps S5 to S8 to acquire the next round;
s9, responding to the fact that the maximum value of M frequency domain energies K exceeds an adaptive threshold value, and indicating that the capturing is successful; and restoring the folding code corresponding to the maximum value in the M frequency domain energy K values into a group of unfolded N sections of local spread spectrum original codes, respectively carrying out correlation operation on the high-frequency spread spectrum signal and the N sections of local spread spectrum original codes, determining the position information of the aligned local spread spectrum code data, and realizing folding capture of the direct sequence spread spectrum long code.
In some embodiments, S3, performing energy detection on the digital intermediate frequency signal includes:
the digital intermediate frequency signal contains noise, and the digital intermediate frequency signal r n ＝s n +w n ，s n To receive the signal, w n Is a noise component, so that the decision component m n Selected as the sum of the received signal energy over the window length L, expressed as
Bringing the decision component to a predetermined threshold T h Judging packet detection condition after comparison:
H 0 :m n ＜T h no grouping occurs
H 1 :m n ≥T h Occurrence of packets
Wherein r is n-k The value after delay k of the digital intermediate frequency signal,
r is n-k N and k are variables from 0 to L-1.
In some embodiments, preprocessing and modulating the digital intermediate frequency signal into data with a fixed bit width to obtain preprocessed data, including:
modulating the digital intermediate frequency signal into data with a fixed bit width, and dividing the data into M data blocks, wherein each data block comprises L-point data and is marked as x i (n), where i=0, 1,..m-1, n=0, 1,..l-1, and sequentially registering the pieces of data with a register.
In some embodiments, performing digital down-conversion processing on the preprocessed data by using orthogonal carriers to obtain I/Q two-way orthogonal data, including:
data x after preprocessing i (n) performing digital down-conversion processing by using orthogonal carriers to obtain:
Ix i (n)＝x i (n)*sin(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1；
Qx i (n)＝x i (n)*cos(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1，
wherein Ix is i (n) is I-path orthogonal data, qx i (n) is Q-way orthogonal data, f I For the intermediate frequency carrier frequency of the transmitting end, t s For sampling time, m is the mth sampling point, and the window length is L.
In some embodiments, S5, obtain m×l local spreading code data generated by a local spreading code module; performing local code staggering N-chip superposition on local spread spectrum code data to obtain m×l folding codes, including:
the local spread spectrum code data is divided into M segments, each segment having a length of L code elements r i (n) is noted as:
r i (n)i＝0,1,...,M-1,n＝0,1,...L-1；
local code staggering N-chip superposition is carried out on the local spread spectrum code data to obtain M x L folded codes r o (n) is noted as: r is (r) o (n)＝r i (n)+r i (n+1)+...+r i (n+N-1)n＝0,1,...,L-1。
In some embodiments, S6, performing a partial matching correlation operation on the I/Q two-way orthogonal data and the folding code to obtain a partial matching correlation result of the folding code and the I/Q two-way orthogonal data, including:
the I path and the Q path are respectively provided with an L-bit matching correlation arithmetic unit, and partial matching correlation results of the folding code and the I/Q path orthogonal data are stored by using a two-dimensional register of M rows and L columns; taking the I-path data as an example, the matching correlation results of all parts are recorded as follows:
…
Ix i (n) is I-path orthogonal data, and the COR (0, 0) correlation value is r with the first segment length L o (n) and a first segment of length L r o (n) incoherent accumulated values for each corresponding phase; and (3) the same principle:
…
the partial match correlation result of the two-dimensional register stores a value of (C i，j ＝COR(i,j))：
In some embodiments, S7, grouping the partial matching correlation results to obtain grouped matching correlation results, and performing frequency domain FFT conversion on each group of grouped matching correlation results to obtain frequency domain data, where the steps include:
the grouping rule is as follows: each column of correlation values is divided into W groups, each group has P=M/W correlation values, and the correlation values of the corresponding bits of each group are different by W intervals; the first packet of a column is: p (P) 0,i :C 0,i ,C w,i ,C 2w,i ,...,C w*(P-1),i ；P 0,i Representing the first packet sequence of column i;
the grouped matching correlation results have M x L data, wherein the phase difference is the same and M data are totally used; i.e. the phase of the correlation value obtained in the ith column is the same;
selecting P data from each column in the first clock cycle to perform FFT, selecting P data from the second clock cycle to perform FFT, …, selecting P data from the W clock cycle to perform FFT; (I) 0 ,I 1 ,...,I w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )、(Q 0 ,Q 1 ,...,Q w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )；
After W clock cycles, incoherent accumulation is carried out on W groups of frequency domain data in each row of two I/Q paths, and the accumulated value of the nth row of the I path is I n The accumulated value of the nth column of the Q path is Q n The accumulated value of the corresponding columns of the I/Q paths is added in a modular manner to obtain frequency domain energy K n Frequency domain energy K n ＝I n 2 +Q n 2 。
In some embodiments, the adaptive threshold value p=p max /P ave Wherein P is max Peak energy, P, for I/Q two-way quadrature data signal ave The energy is averaged for the I/Q two-way quadrature data.
In a second aspect, the present invention provides a folded acquisition device for a direct sequence spread spectrum long code, comprising a processor and a storage medium;
the storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method according to the first aspect.
In a third aspect, the present invention provides a storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the method of the first aspect.
The beneficial effects are that: when the local code is folded and is partially matched and correlated with the received signal, the method is equivalent to one-time correlation and simultaneously detects a plurality of code phases, so that the average acquisition time is greatly reduced, the realization structure is not more complicated, and the contradiction between the acquisition efficiency and the realization complexity is effectively solved. Meanwhile, the grouping FFT operation is carried out aiming at the problem that the calculation time is longer as the calculation amount is larger as the FFT point number is more, the complexity is reduced and the resource consumption is greatly reduced under the condition that the signal envelope characteristic and the FFT spectrum resolution accuracy are not affected. The method has the advantages of high efficiency, short capturing time, large capturing bandwidth and the like, and has better capturing probability under the condition of high dynamic low signal to noise ratio than the traditional capturing algorithm.
Drawings
FIG. 1 is a general block diagram of a capture method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an energy detection module in a capturing method according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating data folding in a capturing method according to an embodiment of the present invention;
FIG. 4 is a diagram showing a sequence of partial matching correlation module correlation operations in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram of FFT performed by partial matching correlation module phase grouping in an embodiment of the present invention;
FIG. 6 is a diagram illustrating an implementation of a capture method according to an embodiment of the present invention;
FIG. 7 is a capturing effect diagram according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
In the description of the present invention, the meaning of a number is one or more, the meaning of a number is two or more, and greater than, less than, exceeding, etc. are understood to exclude the present number, and the meaning of a number is understood to include the present number. The description of the first and second is for the purpose of distinguishing between technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.
In the description of the present invention, the descriptions of the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Example 1:
a method of folded acquisition of a direct sequence spread spectrum long code, comprising:
s1, acquiring a received high-frequency spread spectrum signal transmitted through a wireless channel;
s2, carrying out down-conversion treatment and A/D conversion on the high-frequency spread spectrum signal to obtain a digital intermediate frequency signal;
s3, carrying out energy detection on the digital intermediate frequency signal;
s4, responding to the detected packet signal energy, preprocessing and modulating the digital intermediate frequency signal into data with fixed bit width to obtain preprocessed data; carrying out digital down-conversion processing on the preprocessed data by using orthogonal carriers to obtain I/Q two paths of orthogonal data;
s5, obtaining M-point local spread spectrum code data generated by a local spread spectrum code module; performing local code staggering N-chip superposition on the local spread spectrum code data to obtain M x L folding codes;
s6, performing partial matching correlation operation on the I/Q two-way orthogonal data and the folding code to obtain a partial matching correlation result of the folding code and the I/Q two-way orthogonal data;
s7, grouping the partial matching correlation results to obtain grouped matching correlation results, and performing frequency domain FFT (fast Fourier transform) on each group of the grouped matching correlation results to obtain frequency domain data; accumulating the frequency domain data with the set period to obtain M frequency domain energies K;
s8, comparing the maximum value of the M frequency domain energies K with an adaptive threshold value;
in response to the maximum value of the M frequency domain energies K not exceeding the adaptive threshold value, updating M-point local spread spectrum code data generated by a local spread spectrum code module, and repeating the steps S5 to S8 to acquire the next round;
s9, responding to the fact that the maximum value of M frequency domain energies K exceeds an adaptive threshold value, and indicating that the capturing is successful; and restoring the folding code corresponding to the maximum value in the M frequency domain energy K values into a group of unfolded N sections of local spread spectrum original codes, respectively carrying out correlation operation on the high-frequency spread spectrum signal and the N sections of local spread spectrum original codes, determining the position information of the aligned local spread spectrum code data, and realizing folding capture of the direct sequence spread spectrum long code.
In some embodiments, S3, performing energy detection on the digital intermediate frequency signal includes:
the digital intermediate frequency signal contains noise, and the digital intermediate frequency signal r n ＝s n +w n ，s n To receive the signal, w n Is a noise component, so that the decision component m n Selected as the sum of the received signal energy over the window length L, expressed as
Bringing the decision component to a predetermined threshold T h Judging packet detection condition after comparison:
H 0 :m n ＜T h no grouping occurs
H 1 :m n ≥T h Occurrence of packets
Wherein r is n-k The value after delay k of the digital intermediate frequency signal,
r is n-k N and k are variables from 0 to L-1.
In some embodiments, preprocessing and modulating the digital intermediate frequency signal into data with a fixed bit width to obtain preprocessed data, including:
modulating the digital intermediate frequency signal into data with a fixed bit width, and dividing the data into M data blocks, wherein each data block comprises L-point data and is marked as x i (n), where i=0, 1,..m-1, n=0, 1,..l-1, and sequentially registering the pieces of data with a register.
In some embodiments, performing digital down-conversion processing on the preprocessed data by using orthogonal carriers to obtain I/Q two-way orthogonal data, including:
data x after preprocessing i (n) performing digital down-conversion processing by using orthogonal carriers to obtain:
Ix i (n)＝x i (n)*sin(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1；
Qx i (n)＝x i (n)*cos(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1，
wherein Ix is i (n) is I-path orthogonal data, qx i (n) is Q-way orthogonal data, f I For the intermediate frequency carrier frequency of the transmitting end, t s For sampling time, m is the mth sampling point, and the window length is L.
In some embodiments, S5, obtain m×l local spreading code data generated by a local spreading code module; performing local code staggering N-chip superposition on local spread spectrum code data to obtain m×l folding codes, including:
the local spread spectrum code data is divided into M segments, each segment having a length of L code elements r i (n) is noted as:
r i (n)i＝0,1,...,M-1,n＝0,1,...L-1；
local code staggering N-chip superposition is carried out on the local spread spectrum code data to obtain M x L folded codes r o (n) is noted as: r is (r) o (n)＝r i (n)+r i (n+1)+...+r i (n+N-1)n＝0,1,...,L-1。
In some embodiments, S6, performing a partial matching correlation operation on the I/Q two-way orthogonal data and the folding code to obtain a partial matching correlation result of the folding code and the I/Q two-way orthogonal data, including:
the I path and the Q path are respectively provided with an L-bit matching correlation arithmetic unit, and partial matching correlation results of the folding code and the I/Q path orthogonal data are stored by using a two-dimensional register of M rows and L columns; taking the I-path data as an example, the matching correlation results of all parts are recorded as follows:
…
Ix i (n) is I-path orthogonal data, and the COR (0, 0) correlation value is r with the first segment length L o (n) and a first segment of length L r o (n) incoherent accumulated values for each corresponding phase; and (3) the same principle:
…
the partial match correlation result of the two-dimensional register stores a value of (C i，j ＝COR(i,j))：
In some embodiments, S7, grouping the partial matching correlation results to obtain grouped matching correlation results, and performing frequency domain FFT conversion on each group of grouped matching correlation results to obtain frequency domain data, where the steps include:
the grouping rule is as follows: each column of correlation values is divided into W groups, each group has P=M/W correlation values, and the correlation values of the corresponding bits of each group are different by W intervals; the first packet of a column is: p (P) 0,i :C 0,i ,C w,i ,C 2w,i ,...,C w*(P-1),i ；P 0,i Representing the first packet sequence of column i;
the grouped matching correlation results have M x L data, wherein the phase difference is the same and M data are totally used; i.e. the phase of the correlation value obtained in the ith column is the same;
selecting P data from each column in the first clock cycle to perform FFT, selecting P data from the second clock cycle to perform FFT, …, selecting P data from the W clock cycle to perform FFT; (I) 0 ,I 1 ,...,I w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )、(Q 0 ,Q 1 ,...,Q w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )；
After W clock cycles, incoherent accumulation is carried out on W groups of frequency domain data in each row of two I/Q paths, and the accumulated value of the nth row of the I path is I n The accumulated value of the nth column of the Q path is Q n The accumulated value of the corresponding columns of the I/Q paths is added in a modular manner to obtain frequency domain energy K n Frequency domain energy K n ＝I n 2 +Q n 2 。
In some embodiments, the adaptive threshold value p=p max /P ave Wherein P is max Peak energy, P, for I/Q two-way quadrature data signal ave The energy is averaged for the I/Q two-way quadrature data.
Example 2
In a second aspect, the present embodiment provides a folded acquisition device for a direct sequence spread spectrum long code, including a processor and a storage medium;
the storage medium is used for storing instructions;
the processor is operative according to the instructions to perform the steps of the method according to embodiment 1.
In some embodiments, as shown in fig. 1, a folded acquisition device for a high dynamic direct sequence spread spectrum long code, comprising: the device comprises an A/D analog-to-digital conversion unit, an energy detection module, a data preprocessing module, a mixing module, a sampling clock control module, a local spread spectrum code generation module, a folding control module, a partial matching correlation module, a shift control module, a grouping control module, an FFT operation module, a data accumulation buffer module, a feedback control module, a threshold judgment module and a code position determination module. After the input signal is processed by a module and then is subjected to correlation processing with the local code to obtain a power spectrum, a maximum peak value far larger than the amplitude values of other power spectrums is obtained, the maximum peak value is compared with a threshold value, if the maximum peak value is larger than the threshold value, the received signal corresponding to the peak value is aligned with the local code phase, then the received signal is correlated with the corresponding local code which participates in folding, and then the peak value is obtained, and then the two-dimensional coordinate corresponding to the peak value can determine the input code phase and Doppler frequency offset.
The sampling clock control module comprises a local code and a receiving signal which are sent into a partial matching correlation module control clock and a group extraction correlation data value which is subjected to FFT operation control clock, wherein the group extraction correlation data clock is W times of the partial matching correlation module clock, and W is the number of groups of data.
The code phase determining module determines the accurate code phase of the received signal after the acquisition is successful, and determines that the received signal is aligned with one code phase of a plurality of local codes participating in overlapping due to the fact that the correlation energy between the received signal and the local code obtained after overlapping is the largest, so that the received signal and the local code obtained before non-overlapping addition are respectively subjected to correlation operation, and the code phase with the largest correlation energy is found, namely the code phase of the received signal is determined.
The local spreading code is folded, and when the local spreading code is partially matched and correlated with a received signal, the method is equivalent to one-time correlation and simultaneously detects a plurality of code phases, so that the average acquisition time is greatly reduced, the realization structure is not more complicated, and the contradiction between the acquisition efficiency and the realization complexity is effectively solved. Meanwhile, the grouping FFT operation is carried out aiming at the problem that the calculation time is longer as the calculation amount is larger as the FFT point number is more, the complexity is reduced and the resource consumption is greatly reduced under the condition that the signal envelope characteristic and the FFT spectrum resolution accuracy are not affected.
The spread spectrum signal capturing process in this embodiment includes the following steps:
1) The folding capture method receives a high-frequency spread spectrum signal transmitted through a wireless channel, transmits the received high-frequency spread spectrum signal to a radio frequency unit for down-conversion treatment, and converts the signal into a digital intermediate frequency signal through an A/D conversion unit after the down-conversion treatment.
2) Fig. 2 shows a structure of the energy detection module. The energy detection module comprises a data caching module, a main control module, a delay window energy calculation module, a correlation window energy calculation module and a code element search module. The data caching module is used for caching the input data to be detected and outputting and stopping the cached data when the starting position and the ending position of the data packet are found; the main control module outputs corresponding control instructions (effective packet detection, effective packet detection completion and the like) to the data cache module according to the current state of the system (such as the packet detection processing is completed in the packet detection processing process) and the output result of the code element searching module; the three modules of delay window energy calculation, correlation window energy calculation and code element search form the main body of delay correlation algorithm, and the packet detection is completed and fed back to the main control module.
The digital intermediate frequency signal enters an energy detection module, namely, whether new data arrives on a channel in a burst transmission mode or not is detected. Due to noise contained in the received signal, i.e. r n ＝s n +w n ，s n To receive the signal, w n Is a noise component, so that the decision component m n Selected as the cumulative sum of the received signal energy over the window length L, can be expressed as
Bringing the decision component to a predetermined threshold T h Judging packet detection condition after comparison:
H 0 :m n ＜T h no grouping occurs
H 1 :m n ≥T h A packet occurs.
3) After the packet signal energy is detected, the digital intermediate frequency signal is sent to a data preprocessing module, and the data preprocessing module modulates the digital intermediate frequency signal into data with fixed bit width. Dividing the data into M data blocks, wherein each data block comprises L-point data marked as x i (n), where i=0, 1,..m-1, n=0, 1,..l-1, and sequentially registering the pieces of data with a register.
4) And sending the preprocessed data to a frequency mixing module for digital down conversion, down converting the intermediate frequency signal by using orthogonal carrier waves, and generating I/Q two paths of orthogonal data.
Ix i (n)＝x i (n)*sin(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1；
Qx i (n)＝x i (n)*cos(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1，
Wherein f I For the intermediate frequency carrier frequency of the transmitting end, t s For the sampling time, m is the mth sampling point.
5) The local spreading code module generates M-point data spreading code data and sequentially stores the data into the local spreading code register. The spreading code may be divided into M segments, each segment being L symbols in length, and may be denoted as:
r i (n)i＝0,1,...,M-1,n＝0,1,...L-1；
6) The generated local spread spectrum code data is sent to a folding control module for local code staggering N code chip superposition, and the superposed data can be recorded as: r is (r) o (n)＝r i (n)+r i (n+1)+...+r i (n+n-1) n=0, 1. The local spreading codes can obtain M x L folding codes after passing through the folding control module. Fig. 3 is a schematic diagram of a local spreading code folding operation.
7) And transmitting the I/Q two paths of orthogonal data and the local code to a partial matching correlation module for correlation operation, wherein the I path and the Q path are respectively provided with an L-bit matching correlation operator. The partial matching correlation result of each code bit of the folding code can be stored by a two-dimensional register of M rows and L columns. FIG. 4 is a schematic diagram of a partial match correlation operation. Each of the resulting expressions is noted:
as can be seen from COR (0, 0), the correlation value is r with the first segment length L o (n) and a first segment of length L x i (n) incoherent accumulated values for each corresponding phase. It can be seen from the same principle
…
And then sequentially obtaining other stored values of the two-dimensional register as (C i，j ＝COR(i,j))：
8) And sending the COR register into a grouping control module, wherein each column of correlation values is divided into W groups, each group has P=M/W correlation values, and each group of corresponding bit correlation values are different by W intervals. Taking the first packet of a column as an example: p (P) i,0 :C i,0 ,C i,w ,C i,2w ,...,C i,w*(P-1) 。
9) After the matching correlation there are m×l data, where there are M total of identical phase differences. I.e. the correlation values obtained in column i are in phase. From each column, P data is selected for FFT at the first clock cycle, P data is selected for FFT at the second clock cycle, …, and P data is selected for FFT at the W-th clock cycle. (I) 0 ,I 1 ,...,I w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )、(Q 0 ,Q 1 ,...,Q w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 ). Fig. 5 is a block FFT operation schematic diagram.
10 W clock cycles later, non-coherent accumulation of W groups of frequency domain data of each row of two I/Q paths, wherein the accumulated value of the nth row of the I path is I n The accumulated value of the nth column of the Q path is Q n The accumulated value of the corresponding columns of the I/Q paths is added in a modular manner to obtain frequency domain energy K n Frequency domain energy K n ＝I n 2 +Q n 2 。
11 I/Q two-way orthogonal data pass through a threshold self-adaptive module, and the self-adaptive threshold value is calculated. Comparing the maximum value of the M accumulated K values obtained in the maximum step 9 with a threshold value, if the maximum value is found to exceed the threshold, then the code is successfully captured, otherwise, the local spreading code module is adjusted, the spreading code value of the next round is changed, and the steps (5) to (10) are repeated for carrying out the next round of capturing until the capturing is successful.
12 After the code is successfully captured, the spreading code corresponding to the maximum value is restored to be a local unfolded code and the received signal are respectively subjected to correlation operation, and the exact code element position is found out.
The local folding codes are respectively sent into I, Q paths and are respectively in partial matching correlation with the in-phase receiving signals and the quadrature receiving signals.
The local code generated by the local spread spectrum code generating module is stored in a register, and the register can perform simultaneous reading and writing, reading and writing before reading, reading after writing and the like.
The packet FFT selects a correlation value having a processing clock that is W times faster than the direct FFT processing correlation value clock.
After successful capturing, the highest peak is found out to a corresponding folded local pseudo code sequence, the folded codes are restored to N sections of unfolded local spread spectrum original codes, the received signals and the N sections of local spread spectrum codes are respectively subjected to correlation operation, and the local spread spectrum code corresponding to the highest value is found out, so that the code offset is determined.
The above-described spread spectrum signal acquisition method is described below by way of a specific example.
As shown in fig. 6, a block diagram of an example capture implementation is shown. After the module receiving signal passes through the a/D conversion unit 1001, it is sent to the energy detection unit 1002, and when detecting that new data arrives on the channel in the burst transmission mode, it can be observed that the receiving energy signal will have obvious jump.
The detected signal reception model can be expressed as:
P s for the received signal power, d (t) represents the data modulation, ω 0 Data carrier frequency, omega d The carrier doppler shift, n (t), representing the propagation process is gaussian white noise. Dividing the received signal into I/Q paths, sending the I/Q paths to a mixing module 1003, mixing the signals with the same quadrature signal as the data carrier frequency, and x I (n)＝r I (t)cos(ω 0 t)、x Q (n)＝r Q (t)sin(ω 0 t). The mixed signals are stored in a register, and 2048 signal symbols are sequentially registered. The 2048 signal symbols are divided into 64 sets of 64 data, i.e., 64 bits of received signal length per partial-match correlation 1004.
Local spreading code the local spreading pseudo code period generated by the linear feedback shift register 1005 is l=2 23 -1. Each time, 64×256 local codes are sequentially taken for 4 times of folding, the length of the fold code after accumulation is 64, three code losses exist in 256 segments of fold codes, but the capturing result is sequentially sent to the partial matching correlator 1004 to perform correlation operation on the receiving signal.
The two input ends of the partial match correlator 1004 are respectively from a local folding code and a received signal, the length is 64, when the correlation operation is performed, the first segment x (0), x (1), x (63) receives the signal and r (0), r (1), r (63) the local folding code is input into the partial match correlator at the same time, then the local folding code is sequentially moved by one code element, for example, the second correlation time is x (0), x (1), x (63) and r (1), r (2), r (64) perform the correlation operation, and when the local folding code r (64), r (65), r (127) moves into the partial match correlator, the received signal is input into the x (64), x (127) and the corresponding bit. Each correlation result is stored in a two-dimensional (64, 64) register 1006.
The two-dimensional register has 64 rows and 64 columns in total, and the first column is taken as an example, and is subjected to four-grouping when being fed into the grouping FFT module 1007 for operation, namely (C) 0,0 ,C 0,4 ,...,C 0,60 )、(C 0,1 ,C 0,5 ,...,C 0,61 )、(C 0,2 ,C 0,6 ,...,C 0,62 )、(C 0,3 ,C 0,7 ,...,C 0,63 ) And respectively performing 16-point FFT operation, and accumulating the operated results. The FFT operation method is the same for each column.
One two-dimensional register can calculate 64 energy values, and two paths of I/Q are respectively provided with one two-dimensional register, which can be recorded as: i 0 ,I 1 ,...,I 63 ；Q 0 ,Q 1 ,...,Q 63 。
Order the
Comparing to obtain the maximum peak value K, comparing the peak value K with a judgment threshold value module 1008, if the peak value K is larger than the threshold value, capturing successfully, determining the phase of the pseudo code in the next step, and if the peak value K is smaller than the threshold value, searching the local pseudo code in the next round, and repeating the operation.
The pseudo code phase determining module 1009 finds out the corresponding local spread spectrum folding code through the maximum peak value, restores the local spread spectrum folding code to the local spread spectrum original code, then respectively correlates the local spread spectrum original code with the received signal, finds out the maximum peak value of the correlation, and aligns the received signal with the local spread spectrum code phase at this time, thereby determining the Doppler frequency offset and the code phase value. The determined doppler frequency offset is then tracked with the code phase value for fine synchronization, as shown in fig. 7.
Example 3
In a third aspect, the present embodiment provides a storage medium having stored thereon a computer program which, when executed by a processor, implements the steps of the method described in embodiment 1.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing is only a preferred embodiment of the invention, it being noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the invention.
Claims (10)
1. A method for folding acquisition of a direct sequence spread spectrum long code, comprising:
s1, acquiring a received high-frequency spread spectrum signal transmitted through a wireless channel;
s2, carrying out down-conversion treatment and A/D conversion on the high-frequency spread spectrum signal to obtain a digital intermediate frequency signal;
s3, carrying out energy detection on the digital intermediate frequency signal;
s4, responding to the detected packet signal energy, preprocessing and modulating the digital intermediate frequency signal into data with fixed bit width to obtain preprocessed data; carrying out digital down-conversion processing on the preprocessed data by using orthogonal carriers to obtain I/Q two paths of orthogonal data;
s5, obtaining M-point local spread spectrum code data generated by a local spread spectrum code module; performing local code staggering N-chip superposition on the local spread spectrum code data to obtain M x L folding codes;
s6, performing partial matching correlation operation on the I/Q two-way orthogonal data and the folding code to obtain a partial matching correlation result of the folding code and the I/Q two-way orthogonal data;
s7, grouping the partial matching correlation results to obtain grouped matching correlation results, and performing frequency domain FFT (fast Fourier transform) on each group of the grouped matching correlation results to obtain frequency domain data; accumulating the frequency domain data with the set period to obtain M frequency domain energies K;
s8, comparing the maximum value of the M frequency domain energies K with an adaptive threshold value;
in response to the maximum value of the M frequency domain energies K not exceeding the adaptive threshold value, updating M-point local spread spectrum code data generated by a local spread spectrum code module, and repeating the steps S5 to S8 to acquire the next round;
s9, responding to the fact that the maximum value of M frequency domain energies K exceeds an adaptive threshold value, and indicating that the capturing is successful; and restoring the folding code corresponding to the maximum value in the M frequency domain energy K values into a group of unfolded N sections of local spread spectrum original codes, respectively carrying out correlation operation on the high-frequency spread spectrum signal and the N sections of local spread spectrum original codes, determining the position information of the aligned local spread spectrum code data, and realizing folding capture of the direct sequence spread spectrum long code.
2. The method for folding acquisition of direct sequence spread spectrum long codes according to claim 1, wherein S3, performing energy detection on the digital intermediate frequency signal, comprises:
the digital intermediate frequency signal contains noise, and the digital intermediate frequency signal r n ＝s n +w n ，s n To receive the signal, w n Is a noise component, so that the decision component m n Selected as the sum of the received signal energy over the window length L, expressed as
Bringing the decision component to a predetermined threshold T h Judging packet detection condition after comparison:
H 0 :m n ＜T h no grouping occurs
H 1 :m n ≥T h Occurrence of packets
Wherein r is n-k The value after delay k of the digital intermediate frequency signal,
r is n-k N and k are variables from 0 to L-1.
3. The method for folding and capturing a direct sequence spread spectrum long code according to claim 1, wherein preprocessing and modulating the digital intermediate frequency signal into data with a fixed bit width to obtain preprocessed data comprises:
modulating the digital intermediate frequency signal into data with a fixed bit width, and dividing the data into M data blocks, each data blockIncluding L-point data noted as x i (n), where i=0, 1,..m-1, n=0, 1,..l-1, and sequentially registering the pieces of data with a register.
4. The method for folding and capturing a direct sequence spread spectrum long code according to claim 1, wherein the step of performing digital down-conversion processing on the preprocessed data by using orthogonal carriers to obtain I/Q two-way orthogonal data comprises:
data x after preprocessing i (n) performing digital down-conversion processing by using orthogonal carriers to obtain:
Ix i (n)＝x i (n)*sin(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1；
Qx i (n)＝x i (n)*cos(2π*f I *m*t s ),i＝0,1,...,M-1,n＝0,1,...,L-1，
wherein Ix is i (n) is I-path orthogonal data, qx i (n) is Q-way orthogonal data, f I For the intermediate frequency carrier frequency of the transmitting end, t s For sampling time, m is the mth sampling point, and the window length is L.
5. The method for folding and capturing direct sequence spread spectrum long codes according to claim 1, wherein S5, obtaining m×l point local spread spectrum code data generated by a local spread spectrum code module; performing local code staggering N-chip superposition on local spread spectrum code data to obtain m×l folding codes, including:
the local spread spectrum code data is divided into M segments, each segment having a length of L code elements r i (n) is noted as:
r i (n)i＝0,1,...,M-1,n＝0,1,...L-1；
local code staggering N-chip superposition is carried out on the local spread spectrum code data to obtain M x L folded codes r o (n) is noted as: r is (r) o (n)＝r i (n)+r i (n+1)+...+r i (n+N-1)n＝0,1,...,L-1。
6. The method for folding and capturing the direct sequence spread spectrum long code according to claim 1, wherein the step of S6 of performing a partial matching correlation operation on the I/Q two-way orthogonal data and the folding code to obtain a partial matching correlation result of the folding code and the I/Q two-way orthogonal data includes:
the I path and the Q path are respectively provided with an L-bit matching correlation arithmetic unit, and partial matching correlation results of the folding code and the I/Q path orthogonal data are stored by using a two-dimensional register of M rows and L columns; taking the I-path data as an example, the matching correlation results of all parts are recorded as follows:
…
Ix i (n) is I-path orthogonal data, and the COR (0, 0) correlation value is r with the first segment length L o (n) and a first segment of length L r o (n) incoherent accumulated values for each corresponding phase; and (3) the same principle:
…
the partial match correlation result of the two-dimensional register stores a value of (C i，j ＝COR(i,j))：
7. The method for folding and capturing a direct sequence spread spectrum long code according to claim 1, wherein S7 groups the partial matching correlation results to obtain grouped matching correlation results, and performs frequency domain FFT conversion on each group of grouped matching correlation results to obtain frequency domain data, and the method comprises:
the grouping rule is as follows: each column of correlation values is divided into W groups, each group has P=M/W correlation values, and the correlation values of the corresponding bits of each group are different by W intervals; the first packet of a column is: p (P) 0,i :C 0,i ,C w,i ,C 2w,i ,...,C w*(P-1),i ；P 0,i Representing the first packet sequence of column i;
the grouped matching correlation results have M x L data, wherein the phase difference is the same and M data are totally used; i.e. the phase of the correlation value obtained in the ith column is the same;
selecting P data from each column in the first clock cycle to perform FFT, selecting P data from the second clock cycle to perform FFT, …, selecting P data from the W clock cycle to perform FFT; (I) 0 ,I 1 ,...,I w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )、(Q 0 ,Q 1 ,...,Q w-1 )＝fft(P i,0 ,P i,1 ,...,P i,w-1 )；
After W clock cycles, incoherent accumulation is carried out on W groups of frequency domain data in each row of two I/Q paths, and the accumulated value of the nth row of the I path is I n The accumulated value of the nth column of the Q path is Q n The accumulated value of the corresponding columns of the I/Q paths is added in a modular manner to obtain frequency domain energy K n Frequency domain energy K n ＝I n 2 +Q n 2 。
8. The method of folded acquisition of direct sequence spread spectrum long codes according to claim 1, wherein said method comprisesAdaptive threshold p=p max /P ave Wherein P is max Peak energy, P, for I/Q two-way quadrature data signal ave The energy is averaged for the I/Q two-way quadrature data.
9. A folding acquisition device of a direct sequence spread spectrum long code, which is characterized by comprising a processor and a storage medium;
the storage medium is used for storing instructions;
the processor being operative according to the instructions to perform the steps of the method according to any one of claims 1 to 8.
10. A storage medium having stored thereon a computer program, which when executed by a processor performs the steps of the method according to any of claims 1 to 8.
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