Disclosure of Invention
Synchronization in a direct sequence spread spectrum communication system can generally be divided into two phases, acquisition 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.
The DSSS fast acquisition methods can be largely divided into two categories, 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 x L point local spread spectrum code data generated by a local spread spectrum code module, and carrying out local code staggering and 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;
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 the M frequency domain energy K exceeds the self-adaptive threshold value to indicate successful capture, restoring the folding code corresponding to the maximum value of the M frequency domain energy K 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 codes.
In some embodiments, S3, performing energy detection on the digital intermediate frequency signal includes:
The digital intermediate frequency signal contains noise, the digital intermediate frequency signal rn＝sn+wn,sn is a receiving signal, wn is a noise component, so that the decision component mn is selected as the accumulated sum of the energy of the receiving signal under the window length L, and is expressed asComparing the decision component with a predetermined threshold Th to decide the packet detection situation:
H0:mn＜Th does not appear to be a packet
H1:mn≥Th occurrence of packet
Where rn-k is the value of the digital intermediate frequency signal delayed by k,N and k are 0~L-1 variables, which are conjugate values of rn-k.
In some embodiments, preprocessing and modulating the digital intermediate frequency signal into data with a fixed bit width to obtain preprocessed data, including:
the digital intermediate frequency signal is modulated into fixed bit width data and the data is divided into M data blocks, each data block containing L-point data denoted xi (n), where i=0, 1.
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:
And carrying out digital down-conversion processing on the preprocessed data xi (n) by utilizing orthogonal carriers to obtain:
Ixi(n)＝xi(n)*sin(2π*fI*m*ts),i=0,1,...,M-1,n=0,1,...,L-1;
Qxi(n)＝xi(n)*cos(2π*fI*m*ts),i=0,1,...,M-1,n=0,1,...,L-1,
wherein Ixi (n) is I-path orthogonal data, qxi (n) is Q-path orthogonal data, fI is intermediate frequency carrier frequency of the transmitting end, ts is sampling time, m is the mth sampling point, and window length L.
In some embodiments, S5, obtaining M x L point local spread spectrum code data generated by the local spread spectrum code module, and performing local code staggered N chip superposition on the local spread spectrum code data to obtain M x L folding codes, including:
the local spread code data is divided into M segments, each segment having a length of L symbols ri (n), denoted as:
ri(n)i=0,1,...,M-1,n=0,1,...L-1;
And (3) carrying out local code staggering N-chip superposition on the local spread spectrum code data to obtain M x L folding codes ro (N), wherein the M x L folding codes are denoted as ro(n)＝ri(n)+ri(n+1)+...+ri (n+N-1) n=0, 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, 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, and the I path data are taken as an example, and each partial matching correlation result is recorded as follows:
...
Ixi (n) is I-path orthogonal data, the relevant value of COR (0, 0) is the incoherent accumulated value of the corresponding phases of ro (n) with the length L of the first segment and ro (n) with the length L of the first segment, and the same is true:
...
The partial match correlation result of the two-dimensional register stores a value of (Ci,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 that 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;
M pieces of data are included in the matched correlation results after grouping, wherein M pieces of data are in total, and the phase differences are the same;
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 W clock cycle FFT;(I0,I1,...,Iw-1)＝fft(Pi,0,Pi,1,...,Pi,w-1)、(Q0,Q1,...,Qw-1)＝fft(Pi,0,Pi,1,...,Pi,w-1);
And after W clock cycles, carrying out incoherent accumulation on W groups of frequency domain data of each row of each I/Q, wherein the accumulated value of the nth row of the I way is In, the accumulated value of the nth row of the Q way is Qn, and carrying out modular square addition on the accumulated values of the corresponding rows of the I/Q way to obtain frequency domain energy Kn and frequency domain energy Kn＝In2+Qn2.
In some embodiments, the adaptive threshold p=pmax/Pave, where Pmax is the peak energy of the I/Q two-way orthogonal data signal, and Pave is the average energy of the I/Q two-way orthogonal data signal.
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 method has the advantages 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.
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 x L point local spread spectrum code data generated by a local spread spectrum code module, and carrying out local code staggering and 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;
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 the M frequency domain energy K exceeds the self-adaptive threshold value to indicate successful capture, restoring the folding code corresponding to the maximum value of the M frequency domain energy K 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 codes.
In some embodiments, S3, performing energy detection on the digital intermediate frequency signal includes:
The digital intermediate frequency signal contains noise, the digital intermediate frequency signal rn＝sn+wn,sn is a receiving signal, wn is a noise component, so that the decision component mn is selected as the accumulated sum of the energy of the receiving signal under the window length L, and is expressed asComparing the decision component with a predetermined threshold Th to decide the packet detection situation:
H0:mn＜Th does not appear to be a packet
H1:mn≥Th occurrence of packet
Where rn-k is the value of the digital intermediate frequency signal delayed by k,N and k are 0~L-1 variables, which are conjugate values of rn-k.
In some embodiments, preprocessing and modulating the digital intermediate frequency signal into data with a fixed bit width to obtain preprocessed data, including:
the digital intermediate frequency signal is modulated into fixed bit width data and the data is divided into M data blocks, each data block containing L-point data denoted xi (n), where i=0, 1.
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:
And carrying out digital down-conversion processing on the preprocessed data xi (n) by utilizing orthogonal carriers to obtain:
Ixi(n)＝xi(n)*sin(2π*fI*m*ts),i=0,1,...,M-1,n=0,1,...,L-1;
Qxi(n)＝xi(n)*cos(2π*fI*m*ts),i=0,1,...,M-1,n=0,1,...,L-1,
wherein Ixi (n) is I-path orthogonal data, qxi (n) is Q-path orthogonal data, fI is intermediate frequency carrier frequency of the transmitting end, ts is sampling time, m is the mth sampling point, and window length L.
In some embodiments, S5, obtaining M x L point local spread spectrum code data generated by the local spread spectrum code module, and performing local code staggered N chip superposition on the local spread spectrum code data to obtain M x L folding codes, including:
the local spread code data is divided into M segments, each segment having a length of L symbols ri (n), denoted as:
ri(n)i=0,1,...,M-1,n=0,1,...L-1;
And (3) carrying out local code staggering N-chip superposition on the local spread spectrum code data to obtain M x L folding codes ro (N), wherein the M x L folding codes are denoted as ro(n)＝ri(n)+ri(n+1)+...+ri (n+N-1) n=0, 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, 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, and the I path data are taken as an example, and each partial matching correlation result is recorded as follows:
...
Ixi (n) is I-path orthogonal data, the relevant value of COR (0, 0) is the incoherent accumulated value of the corresponding phases of ro (n) with the length L of the first segment and ro (n) with the length L of the first segment, and the same is true:
...
The partial match correlation result of the two-dimensional register stores a value of (Ci,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 that 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;
M pieces of data are included in the matched correlation results after grouping, wherein M pieces of data are in total, and the phase differences are the same;
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 W clock cycle FFT;(I0,I1,...,Iw-1)＝fft(Pi,0,Pi,1,...,Pi,w-1)、(Q0,Q1,...,Qw-1)＝fft(Pi,0,Pi,1,...,Pi,w-1);
And after W clock cycles, carrying out incoherent accumulation on W groups of frequency domain data of each row of each I/Q, wherein the accumulated value of the nth row of the I way is In, the accumulated value of the nth row of the Q way is Qn, and carrying out modular square addition on the accumulated values of the corresponding rows of the I/Q way to obtain frequency domain energy Kn and frequency domain energy Kn＝In2+Qn2.
In some embodiments, the adaptive threshold p=pmax/Pave, where Pmax is the peak energy of the I/Q two-way orthogonal data signal, and Pave is the average energy of the I/Q two-way orthogonal data signal.
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 folding capture device for a high dynamic direct sequence spread spectrum long code 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 decision 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 buffer module realizes buffer of input data waiting to be detected, and realizes output and stop of buffer data when the start and end positions of data packets are found, the main control module outputs corresponding control instructions (packet detection is effective, etc.) to the data buffer module according to the current state of the system (such as the packet detection is completed in the process of processing the packet detection) and the output result of the code element search module, and three modules of delay window energy calculation, correlation window energy calculation and code element search form the main body of a delay correlation algorithm to complete packet detection and feed 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. Since the received signal contains noise, i.e. rn＝sn+wn,sn is the received signal and wn is the noise component, the decision component mn is selected as the cumulative sum of the received signal energy under the window length L, and can be expressed asComparing the decision component with a predetermined threshold Th to decide the packet detection situation:
H0:mn＜Th does not appear to be a packet
H1:mn≥Th presents a packet.
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. The data is divided into M data blocks simultaneously, each data block containing L-point data denoted as xi (n), where i=0, 1.
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.
Ixi(n)＝xi(n)*sin(2π*fI*m*ts),i=0,1,...,M-1,n=0,1,...,L-1;
Qxi(n)＝xi(n)*cos(2π*fI*m*ts),i=0,1,...,M-1,n=0,1,...,L-1,
Wherein fI is the intermediate frequency carrier frequency of the transmitting end, ts is the sampling time, and m is the m-th 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:
ri(n)i=0,1,...,M-1,n=0,1,...L-1;
6) And sending the generated local spread spectrum code data into a folding control module for local code staggering and N chip superposition, wherein the superposed data can be recorded as ro(n)＝ri(n)+ri(n+1)+...+ri (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 an incoherent accumulated value of ro (n) with the first segment length L and xi (n) with the first segment length L, which correspond to the phases. It can be seen from the same principle
...
Further, this two-dimensional register can be obtained in turn with other stored values (Ci,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, Pi,0:Ci,0,Ci,w,Ci,2w,...,Ci,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. P data is selected for FFT at the first clock cycle, P data is selected for FFT at the second clock cycle, P data is selected for FFT at the W-th clock cycle, FFT.(I0,I1,...,Iw-1)＝fft(Pi,0,Pi,1,...,Pi,w-1)、(Q0,Q1,...,Qw-1)＝fft(Pi,0,Pi,1,...,Pi,w-1). for packet FFT operation is illustrated in fig. 5.
10 W clock cycles later, carrying out incoherent accumulation on W groups of frequency domain data of each row of each I/Q, wherein the accumulated value of the nth row of the I way is In, the accumulated value of the nth row of the Q way is Qn, and carrying out modular square addition on the accumulated values of the corresponding rows of the I/Q way to obtain frequency domain energy Kn and frequency domain energy Kn＝In2+Qn2.
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: Ps is the received signal power, d (t) represents data modulation, ω0 is the data carrier frequency, ωd is the carrier doppler shift of the propagation process, and n (t) is gaussian white noise. The received signal is split into I/Q paths and fed to the mixing module 1003 where it is mixed using quadrature signals of the same data carrier frequency xI(n)＝rI(t)cos(ω0t)、xQ(n)＝rQ(t)sin(ω0 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=223 -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 takes the first column as an example, when the two-dimensional register is sent to the grouping FFT module 1007 for operation, four groupings are carried out, namely (C0,0,C0,4,...,C0,60)、(C0,1,C0,5,...,C0,61)、(C0,2,C0,6,...,C0,62)、(C0,3,C0,7,...,C0,63) respectively carry out 16-point FFT operation, and the results after operation are accumulated. The FFT operation method is the same for each column.
One two-dimensional register can calculate 64 energy values, and each of the two paths of I/Q has one two-dimensional register, which can be recorded as I0,I1,...,I63;Q0,Q1,...,Q63.
Order theComparing 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 merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.