CN117665867A - Optimization method of Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation - Google Patents
Optimization method of Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related
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Abstract
The invention provides an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, and aims to greatly reduce the operation complexity and operation time of the polarity compensation algorithm in a multi-period capturing algorithm under the multi-modulation type on the premise of not affecting capturing accuracy. The invention expands the phase-coherent accumulation time and introduces a rapid polarity compensation technology for the text information, carries out phase-coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to search the phase-coherent accumulation operation result with the maximum peak value, expands the rapid polarity compensation method to other Beidou satellite signals, compares the peak-to-peak ratio of the phase-coherent accumulation operation result of each carrier frequency with a threshold value, and confirms that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal if the peak-to-peak ratio of the phase-coherent accumulation operation result of each carrier frequency is larger than the threshold value. The invention expands the application field of algorithm and improves the accumulation efficiency of multicycle coherent accumulation.
Description
Technical Field
The invention belongs to the technical field of satellite navigation signal processing, and particularly relates to an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation.
Background
The satellite navigation system has extremely wide application, can provide accurate coordinate and time information for users, and along with the development of the Beidou satellite navigation system, the technical research on the receiving part of the Beidou satellite navigation system is more and more valuable. The acquisition is the first part to start in the receiving process, so the acquisition algorithm is the first problem to be solved in the Beidou navigation receiving signal processing.
The essence of the satellite acquisition algorithm is the parameter estimation process of the received signal, which is to estimate and detect the Doppler frequency and code delay of the navigation signal of the satellite. And (3) correlating the sampled intermediate frequency satellite signal with a local signal preset with a parameter estimation value, finding out the maximum correlation peak value according to the correlation operation result, comparing with a threshold value to judge whether a satellite is captured or not, and obtaining the corresponding Doppler frequency and code delay.
Since the navigation signal is obtained by using a navigation satellite in space as an actual radiation source, and the navigation satellite is relatively far away from a ground receiving station, the reflected power of the received navigation signal is low, so in actual capturing, a dual-channel method is generally adopted, that is, a direct wave is received through a reference channel, the parameters such as a received carrier wave of the direct wave, the polarity of a modulation code element and the like are analyzed to assist in capturing the reflected wave in a monitoring channel. In this case, if the direct wave power received in the reference channel is also weak, more ranging code periods are needed to capture the direct wave, and once the ranging code period is increased by one period, the operation complexity of the algorithm for traversing the modulation polarity in the original coherent accumulation is doubled, and the operation time is correspondingly doubled, i.e. if the direct wave capture needs signals of K ranging code periods, the complexity of the algorithm for traversing is 2 K-1 。
D1 navigation messages broadcast by B1I and B3I signals in the Beidou system are subjected to secondary code modulation of NH (New Huffman) codes with the speed of 1 kbps; the ranging codes broadcast by the B1C and B2a signals have the mutual modulation of the subcodes and the main codes, so that different types of code element jump can exist in each ranging code period in different modulation modes, and the jump of the code element can reduce the peak value of a correlation peak, thereby influencing the judgment of a capturing result, so that the influence of different types of code element jump must be eliminated, and the integral time is prolonged.
The prior art scheme is as follows: a Beidou satellite navigation signal capturing method based on NH code element jump detection. The prior art scheme discloses a Beidou satellite navigation signal capturing method based on NH code element jump detection, and belongs to the technical field of satellite navigation receiver baseband signal processing methods. The scheme adopts the ideas of NH code element matching and TONG detector, firstly carries out circular correlation operation on the condition that whether NH code element jump exists in intermediate frequency navigation satellite signals of each 1ms, and applies a parallel code phase searching method to the circular correlation operation, sets pre-detection integration time as Kms, accumulates the circular correlation operation results of each 1ms according to various combinations of NH code element jump assumptions, compares the combination result with a detection threshold value with the maximum value, and judges the signal capturing result and the initial position of navigation information bits according to the processing results of the TONG detector and a bit synchronization detection module.
The prior art is that the complexity and the running time are greatly increased under the condition of long coherent accumulation time in 20ms, namely the coherent accumulation capture of one NH code period length; and the prior art processes in the case of the NH code related signals, B1I and B3I, it is clear that this cannot be achieved for a variety of modulations. In addition, the polarity of the telegram influences greatly in the actual process, so that the capturing precision of the scheme in the prior art is influenced.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation. The technical problems to be solved by the invention are realized by the following technical scheme:
in a first aspect, the invention provides an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, which comprises the following steps:
s100, receiving an intermediate frequency navigation satellite signal;
s200, generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle; performing down-conversion processing on the intermediate frequency navigation satellite signals by using the local complex carrier signals in each ranging code period to obtain baseband signals, and fusing the baseband signals into complex baseband signals according to the ranging code modulation condition of the baseband signals;
s300, respectively generating corresponding local resampling ranging code signals aiming at two conditions of modulation code hopping and no modulation code hopping of the navigation satellite signals; performing matched filtering operation on the complex baseband signal and local resampling ranging codes under two conditions respectively, and performing low-pass filtering processing on an operation result to obtain a matched filtering operation result of each ranging code period under two conditions;
s400, traversing a text code element to generate a local text and circularly shifting an NH code to generate a local NH code sequence, modulating the local text and the local NH code sequence to generate a modulation code, and performing coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to find a coherent accumulation operation result with the maximum peak value;
s500, adjusting the carrier frequency of the local signal, taking the adjusted carrier frequency as the carrier frequency of the current cycle, and repeating S200 to S400 until the carrier frequency traversal times are reached;
s600, comparing the peak-to-peak ratio of the coherent accumulation operation result of each carrier frequency with a threshold value, and if the peak-to-peak ratio is larger than the threshold value, confirming that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal.
In a second aspect, the present invention provides an optimizing device for a beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, including:
the receiving device is used for receiving the intermediate frequency navigation satellite signals;
the fusion device is used for generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle; performing down-conversion processing on the intermediate frequency navigation satellite signals by using the local complex carrier signals in each ranging code period to obtain baseband signals, and fusing the baseband signals into complex baseband signals according to the ranging code modulation condition of the baseband signals;
the operation device is used for respectively generating corresponding local resampling ranging code signals aiming at the two conditions of modulation code element hopping and no modulation code element hopping of the navigation satellite signals; performing matched filtering operation on the complex baseband signal and local resampling ranging codes under two conditions respectively, and performing low-pass filtering processing on an operation result to obtain a matched filtering operation result of each ranging code period under two conditions;
the searching device is used for traversing the text code element to generate a local text and circularly shifting the NH code to generate a local NH code sequence, modulating the local text and the local NH code sequence to generate a modulation code, and performing coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to search the coherent accumulation operation result with the maximum peak value;
the circulating device is used for adjusting the carrier frequency of the local signal, taking the adjusted carrier frequency as the carrier frequency of the current circulating time, and executing the specific processes of the fusion device, the operation device and the search device until the carrier frequency traversal times are reached;
and the confirming device is used for comparing the peak-to-peak ratio of the coherent accumulation operation result of each carrier frequency with a threshold value, and if the peak-to-peak ratio is larger than the threshold value, confirming that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal.
The beneficial effects are that:
the invention provides an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, and aims to greatly reduce the operation complexity and operation time of the polarity compensation algorithm in a multi-period capturing algorithm under the multi-modulation type on the premise of not affecting capturing accuracy. The invention expands the phase-coherent accumulation time and introduces a rapid polarity compensation technology for the text information, carries out phase-coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to search the phase-coherent accumulation operation result with the maximum peak value, expands the rapid polarity compensation method to other Beidou satellite signals, compares the peak-to-peak ratio of the phase-coherent accumulation operation result of each carrier frequency with a threshold value, and confirms that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal if the peak-to-peak ratio of the phase-coherent accumulation operation result of each carrier frequency is larger than the threshold value. The invention expands the application field of algorithm and improves the accumulation efficiency of multicycle coherent accumulation.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
FIG. 1 is a schematic flow chart of an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation;
FIG. 2 is a schematic diagram of matched filtering without polarity hopping provided by the present invention;
FIG. 3 is a schematic diagram of matched filtering with polarity hopping provided by the present invention;
FIGS. 4a-4c are schematic views of hierarchical text traversal provided by the present invention;
FIG. 5 is a schematic diagram of the NH code cyclic shift algorithm provided by the present invention;
FIG. 6 is a schematic diagram of a cyclic shift result sequence of multiple NH code periods provided by the present invention;
fig. 7 is a schematic block diagram of a modulation code related polarity compensation section provided by the present invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
Referring to fig. 1 to 7, the invention provides an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, which comprises the following steps:
s100, receiving an intermediate frequency navigation satellite signal;
before S100, the optimization method of the beidou satellite navigation signal capturing algorithm based on the modulation code polarity compensation further comprises the following steps:
s000, setting a pre-detection integration time Kms, (K)>0, K.epsilon.integer), doppler range of locally capturable signalsSearch frequency step f Δ_1 And a threshold value threshold_1 for judging peak-to-peak ratio;
wherein,representing the lower limit of the range of values of the Doppler frequency offset of the carrier frequency of the local signal compared to the transmission frequency, < >>Representing the upper limit of the range of the Doppler frequency offset of the carrier frequency of the local signal compared with the transmitting frequency, the carrier frequency traversal times are +.>And simultaneously setting a threshold value threshold_1 for judging the peak-to-peak ratio.
S200, generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle; performing down-conversion processing on the intermediate frequency navigation satellite signals by using the local complex carrier signals in each ranging code period to obtain baseband signals, and fusing the baseband signals into complex baseband signals according to the ranging code modulation condition of the baseband signals;
s300, respectively generating corresponding local resampling ranging code signals aiming at two conditions of modulation code hopping and no modulation code hopping of the navigation satellite signals; performing matched filtering operation on the complex baseband signal and local resampling ranging codes under two conditions respectively, and performing low-pass filtering processing on an operation result to obtain a matched filtering operation result of each ranging code period under two conditions;
referring to the two cases of the presence of modulation code hopping and the absence of modulation code hopping in the navigation satellite signal in each ranging code period, as shown in fig. 2 and 3, corresponding local resampling ranging code signals are respectively generated for the two cases, complex baseband signals are respectively subjected to matched filtering operation with the local resampling ranging codes in the two cases, and the operation result is subjected to low-pass filtering processing to obtain matched filtering operation results in the two cases.
S400, traversing a text code element to generate a local text and circularly shifting an NH code to generate a local NH code sequence, modulating the local text and the local NH code sequence to generate a modulation code, and performing coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to find a coherent accumulation operation result with the maximum peak value;
since the message is completely random, the compensation for the message polarity can only be determined by traversing all possible message symbol hopping sequences. The method adopts a hierarchical traversal mode on the compensation of the polarity of the text code element to obtain a final text result sequence, and a specific calculation method is shown in fig. 4a-4c, wherein the hierarchical traversal mode can greatly reduce the operation time of an algorithm compared with the complete traversal mode, such as the complete traversal algorithm needs to circulate 2 if 30 text period data are needed to be accumulated 30-1 The hierarchical traversal mode is that if 10 periods are used as one layer, only 2 loops are needed 3-1 +3*2 10-1 And (5) repeating the process for several times.
For the B1I and B3I signals having NH codes and the B2a and b1c_p signals having subcodes), the NH code of the B1I signal is fixed with respect to the randomness of the message, so that the method divides the compensation process thereof into the compensation of NH codes and the compensation of messages and performs different processes in the compensation of the polarities of the complex codes modulated on the ranging codes. According to the method, cyclic shift matching compensation is adopted on compensation for NH codes, namely, because NH Code related parameters such as a Code rate, a Code length, a single-period Code sequence and the like of the NH codes are determined in advance, the beginning Code element position of a signal can be circularly assumed, namely, code_Begin_location=1 and 2 are set, the number is 20, the cyclic shift result is shown in fig. 5, and at the moment, in a Kms complex baseband signal, the overall arrangement of NH is divided into a beginning NH Code period, a middle NH Code period and an end NH Code period. The overall sequence of NH codes over Kms can be determined from the overall arrangement of NH codes and the monocycle sequence of NH codes, and the overall sequence result is shown in fig. 6, where m=mod (k+code_begin_location-1, 20).
Referring to fig. 7, the sequence of the message and the sequence of the NH symbol at the corresponding position need to be modulated inside each cycle to obtain a local modulation code sequence in the current cycle, a corresponding matched filtering period is extracted in S300 according to whether the polarities between the symbols before and after the local modulation code sequence are the same, and the matched filtering result of each period is subjected to polarity compensation according to the local modulation code, and then coherent accumulation of a plurality of ranging code period signals is performed.
S500, adjusting the carrier frequency of the local signal, taking the adjusted carrier frequency as the carrier frequency of the current cycle, and repeating S200 to S400 until the carrier frequency traversal times are reached;
the invention circularly operates S200 to S400 in a grading way to obtain the final overall sequence of the NH code and the final text result sequence, and the text result sequence and the final overall sequence of the NH code are brought into the modulation of the NH code to generate the coherent accumulation result sequence under the local carrier wave f.
S600, comparing the peak-to-peak ratio of the coherent accumulation operation result of each carrier frequency with a threshold value, and if the peak-to-peak ratio is larger than the threshold value, confirming that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal.
The invention provides an optimization method of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, and aims to greatly reduce the operation complexity and operation time of the polarity compensation algorithm in a multi-period capturing algorithm under the multi-modulation type on the premise of not affecting capturing accuracy. The invention expands the phase-coherent accumulation time and introduces a rapid polarity compensation technology for the text information, carries out phase-coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to search the phase-coherent accumulation operation result with the maximum peak value, expands the rapid polarity compensation method to other Beidou satellite signals, compares the peak-to-peak ratio of the phase-coherent accumulation operation result of each carrier frequency with a threshold value, and confirms that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal if the peak-to-peak ratio of the phase-coherent accumulation operation result of each carrier frequency is larger than the threshold value. The invention expands the application field of algorithm and improves the accumulation efficiency of multicycle coherent accumulation.
As an alternative embodiment of the present invention, S200 includes:
s210, obtaining the carrier frequency of the local signal under the current cycle according to the traversal number n under the current cycle
S220, generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle;
s230, performing down-conversion processing on the intermediate frequency navigation satellite signals with the length of each ranging code period in the pre-detection integration time Kms by using a local complex carrier signal to obtain baseband signals with a plurality of ranging code periods;
s240, according to the ranging code modulation condition of the baseband signal of each ranging code period, the baseband signals of the real part and the imaginary part are fused into complex baseband signals.
The invention records the data of the intermediate frequency navigation satellite signals acquired every 1ms in Kms as r k (N), where K represents Kms, k=1, 2,..k, n=0, 1,..n-1, N represents the nth sampling point in each 1ms, N represents the number of sampling points in each 1ms, down-converting the received intermediate frequency navigation satellite signal of each ranging code period length in Kms by the local complex carrier signal to obtain a baseband signal (real part i_signal+imaginary part q_signal) of a plurality of ranging code periods, and fusing the baseband signals of the real part i_signal and the imaginary part q_signal into a complex baseband signal basic_signal according to the ranging code modulation condition of the baseband signal of each period. The specific classifications are as follows:
(1) Navigation signals such as B1I, b1c_d, B3I, b2a_d, B2B, which are basic_signal=i_signal-j×q_signal since the ranging codes are modulated on the cosine carrier component when transmitted;
(2) Relative navigation signals such as b1c_p, b2a_p, etc. are basic_signal= -1 x (q_signal+j x i_signal) because the ranging codes are modulated on the sinusoidal carrier component during their transmission and the pilot component leads the data component pi/2 phases.
Referring to fig. 5 and 6, as an alternative embodiment of the present invention, S300 includes:
s310, the original signals of the local spreading codes are recorded as the two conditions of whether the hopping of the modulation code elements exists in the ranging code period
S320, if the intermediate frequency navigation satellite signal in the ranging code period does not have modulation code element jump, performing FFT conversion on a local spread spectrum code original signal, and then taking conjugation to obtain a local resampling ranging code signal, wherein the local resampling ranging code signal is expressed as: l (L) 0 ＝(FFT(C)) * ；
S330, if the intermediate frequency navigation satellite signal in the ranging code period has a modulation code symbol jump, the local spreading code is reversely spliced, and the splicing result is expressed as: c (C) new ＝[C,-C]And performing FFT conversion on the continuous binding result, and then taking conjugate to obtain a local resampling ranging code signal, which is expressed as: l (L) 0 ＝(FFT(C new )) * ；
S340, aiming at the condition that the intermediate frequency navigation satellite signal does not have modulation code element jump, the baseband signal and the local resampling ranging code are subjected to dot multiplication, and then IFFT is taken to obtain a corresponding matched filtering result, wherein the corresponding matched filtering result is expressed as: result=ifft (FFT (basic_signal.) L 0 )；
S350, aiming at the condition that the intermediate frequency navigation satellite signal has modulation code element jump, zero padding operation is carried out on the baseband signal, so that the length of the baseband signal is consistent with the length of a local spread spectrum code splicing result;
s360, carrying out FFT conversion on the baseband signal after zero padding and then carrying out local resampling ranging code L 0 After dot multiplication, IFFT is taken to obtain a corresponding matched filtering result, which is expressed as:
result＝IFFT(FFT([Basic_signal,zeros(1,N)]).*L 0 )；
wherein basic_signal represents a baseband signal.
Referring to fig. 7, as an alternative embodiment of the present invention, S400 includes:
s410, traversing all possible message code element hopping sequences in a hierarchical traversal mode to generate a local message;
s420, generating a local NH code sequence by adopting cyclic shift to the NH code;
s430, modulating the local text and the local NH code sequence at the corresponding position to obtain a local modulation code under the current cycle;
s440, performing a coherent accumulation operation on the matched filtering operation result under the current circulation time by using the local modulation code to obtain a coherent accumulation operation result;
s450, judging whether the peak value of the coherent accumulation operation result under the current cycle is larger than a maximum value zone bit, if so, assigning the peak value of the coherent accumulation operation result under the current cycle to the maximum zone bit, and replacing the maximum value sequence by the coherent accumulation operation result under the current cycle; the maximum value sequence is formed by the correlation accumulation operation result with the maximum peak value;
s460, the local modulation code, the carrier frequency and the peak position under the current cycle are saved.
Referring to fig. 4a to 4c, as an alternative embodiment of the present invention, S410 includes:
s411, determining the code element number of the text code element according to the starting code element position of the NH code and the total cycle number of the captured data, and grading the code element number of the text code element;
and determining the Number of periods of the NH Code according to the code_Begin_location, wherein the Number of periods of the NH Code is the Message Number message_number because the Message rate is the reciprocal of the period of the NH Code and the Message Code element is strictly corresponding to the position of the starting Code element in the period of the NH Code. Then, taking the single_layer_type Number (default 10) as the boundary of the hierarchy, the Message Number message_number can be divided into layer_number layers at most, wherein the layer_number satisfies the following conditions:
Single_Lawyer_TypeNumber Lawyer_Number-1 <Message_Number
Message_Number<Single_Lawyer_TypeNumber Lawyer_Number
s412, setting an operation sequence of message traversal, wherein the operation sequence is that a bottom layer is operated firstly and then an upper layer is operated sequentially;
s413, inside each text group, according to 2 f-1 Traversing the bipolar sequence with the first length f once; storing the sequence with the maximum peak value module value;
s414, circulating S413 until the number of the bottommost text groups is reached to obtain the bottommost sequence result;
the operation sequence of the invention is to operate the bottom layer firstly, then operate the upper layer, wherein the Number of the bottom layer text group is basic_number=ceil (message_number/single_layer_typenumber), traverse the bipolar sequence of single_layer_typenumber length in each text group according to times, and store the sequence with the maximum result peak value module value to the corresponding position after S400. And (5) circulating the basic_number for the times to finish the whole text bottom sequence result.
S415, running a second layer, wherein the number of the message groups is 2 f-1 Traversing the bipolar sequence of the first length once;
the invention operates the Second layer, the Number of the Second layer text groups is second_number=ceil (message_number/single_layer_type Number), and the Second layer text groups are 2 in each text group, which is the same as the bottom layer algorithm Single _Lawyer_TypeNumber-1 Traversing the bipolar sequence with the length of single_layer_TypeNumber for a plurality of times, resampling the bipolar sequence with the length of single_layer_TypeNumber for a plurality of times, modulating the bipolar sequence with a bottom layer sequence group, storing a sequence with the maximum peak value module value of the result to a corresponding position after S400, and cycling the second_Number for a plurality of times to obtain the result of the whole Second layer sequence.
S416, circulating S415 until the number of second-layer text groups is reached, and obtaining a second-layer sequence result;
s417, repeating S413 to S416 up layer by layer until each layer is traversed;
this step is repeated layer by layer up the above-described operations layer-Number-3 times.
And S418, finally, running the top layer to generate a local text.
The invention finally runs the top layerAccording to 2 Top_Number-1 Traversing TopBipolar sequence with_number length, S400, and single_Lawyer_TypeNumber sequence with maximum peak value module value Lawyer_Number-1 And (5) modulating with a lower layer sequence group after secondary resampling to obtain a final text result sequence.
As an alternative embodiment of the present invention, S420 includes:
s421, setting a start code element position of a cyclic hypothesis signal according to a code rate, a code length and a single-period code sequence of a subcode of a target signal aiming at the target signal with NH codes; in the complex baseband signal of Kms, the overall arrangement of the subcodes is divided into a start subcode period, a middle subcode period and an end subcode period.
S422, determining the whole sequence of the subcode on Kms according to the whole arrangement of the subcode and the single-period sequence of the subcode;
s423, using the whole sequence of subcodes over Kms, generating a local NH code sequence by cyclic shift for the NH code.
B3I and B1I have the same NH code sequence and the same modulation scheme, then B3I compensates substantially the same as B1I. The signals b1c_p and B2a are not modulated by the NH code sequence, which is modulated by the text- > subcode- > main code, so the polarities of subcodes need to be compensated for in the compensation of the signals b1c_p and B2a, and the specific compensation steps are described below for different signals:
(1) According to the relevant parameters of the sub-codes such as the Code rate, the Code length, the single-period Code sequence and the like of the sub-codes of the B1c_p signal, the starting Code element position of the signal can be circularly assumed, namely the code_begin_location=1, 2 is set, 1800 is set, and at this time, in the complex baseband signal of Kms, the overall arrangement of the sub-codes is divided into a starting sub-Code period, a middle sub-Code period and an end sub-Code period. The overall sequence of the subcodes over Kms can then be determined from the overall arrangement of the subcodes and the monocycle sequence of the subcodes.
(2) According to the Code rate, code length, single-period Code sequence and other related parameters of the sub-codes of the B2a_d signal, the starting symbol position of the signal can be circularly assumed, namely, the code_begin_location=1, 2 is set, and the number is 5, and at this time, in the Kms complex baseband signal, the overall arrangement of the sub-codes is divided into a starting sub-Code period, a middle sub-Code period and an end sub-Code period. The overall sequence of the subcodes over Kms can then be determined from the overall arrangement of the subcodes and the monocycle sequence of the subcodes.
(3) According to the relevant parameters of the sub-codes such as the Code rate, the Code length, the single-period Code sequence and the like of the sub-codes of the B2a_p signal, the starting Code element position of the signal can be circularly assumed, namely the code_begin_location=1, 2 is set, the number is 100, and at the moment, in the complex baseband signal of Kms, the overall arrangement of the sub-codes is divided into a starting sub-Code period, a middle sub-Code period and an end sub-Code period. The overall sequence of the subcodes over Kms can then be determined from the overall arrangement of the subcodes and the monocycle sequence of the subcodes.
As an alternative embodiment of the present invention, S600 includes:
s610, determining the position of a peak value and the peak-to-peak ratio in a frequency slice to which the peak value belongs in the coherent accumulation operation result of each carrier frequency;
s620, if the peak-to-peak ratio is greater than or equal to a threshold value threshold_1, determining that a signal is captured under the search frequency step of the current cycle; if the peak-to-peak ratio is smaller than a threshold value threshold_1, judging that no signal is captured under the search frequency step of the current cycle;
s630, the carrier frequency corresponding to the captured signal is the real carrier frequency of the intermediate frequency navigation satellite signal.
As an optional implementation manner of the present invention, after S630, the optimization method of the beidou satellite navigation signal capturing algorithm based on the modulation code polarity compensation further includes:
if the search frequency step of the current cycle is determined to be lower than the search frequency step, judging whether the search frequency step is larger than an allowable received carrier frequency error; if so, the true carrier frequency f acq_1 Narrowing the range of (f) to a local capturable range [ f ] acq_1 -f Δ_1 ,f acq_1 +f Δ_1 ]；
Resetting search frequency step f Δ_2 Repeating S200 to S600 until searching for the frequency stepAnd outputting the acquisition result and related acquisition parameters when the received carrier frequency error is smaller than the allowable received carrier frequency error.
If the result is that a signal is acquired and the search step is greater than the allowable received carrier frequency error, the frequency f can be determined based on the acquired result acq_1 Narrowing the local capturable range to [ f ] acq_1 -f Δ_1 ,f acq_1 +f Δ_1 ]And resetting the search frequency step by two f Δ_2 . The above operations are repeated until the search frequency step is smaller than the allowable received carrier frequency error, and the acquisition result and the related acquisition parameters are output.
The invention provides an optimization device of a Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation, which comprises the following components:
the receiving device is used for receiving the intermediate frequency navigation satellite signals;
the fusion device is used for generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle; performing down-conversion processing on the intermediate frequency navigation satellite signals by using the local complex carrier signals in each ranging code period to obtain baseband signals, and fusing the baseband signals into complex baseband signals according to the ranging code modulation condition of the baseband signals;
the operation device is used for respectively generating corresponding local resampling ranging code signals aiming at the two conditions of modulation code element hopping and no modulation code element hopping of the navigation satellite signals; performing matched filtering operation on the complex baseband signal and local resampling ranging codes under two conditions respectively, and performing low-pass filtering processing on an operation result to obtain a matched filtering operation result of each ranging code period under two conditions;
the searching device is used for traversing the text code element to generate a local text and circularly shifting the NH code to generate a local NH code sequence, modulating the local text and the local NH code sequence to generate a modulation code, and performing coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to search the coherent accumulation operation result with the maximum peak value;
the circulating device is used for adjusting the carrier frequency of the local signal, taking the adjusted carrier frequency as the carrier frequency of the current circulating time, and executing the specific processes of the fusion device, the operation device and the search device until the carrier frequency traversal times are reached;
and the confirming device is used for comparing the peak-to-peak ratio of the coherent accumulation operation result of each carrier frequency with a threshold value, and if the peak-to-peak ratio is larger than the threshold value, confirming that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal.
The specific details of the device embodiment and the method embodiment of the present invention are consistent, and will not be described herein.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
Although the present application has been described herein in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed application, from a review of the figures, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the "a" or "an" does not exclude a plurality.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (10)
1. The optimization method of the Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation is characterized by comprising the following steps of:
s100, receiving an intermediate frequency navigation satellite signal;
s200, generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle; performing down-conversion processing on the intermediate frequency navigation satellite signals by using the local complex carrier signals in each ranging code period to obtain baseband signals, and fusing the baseband signals into complex baseband signals according to the ranging code modulation condition of the baseband signals;
s300, respectively generating corresponding local resampling ranging code signals aiming at two conditions of modulation code hopping and no modulation code hopping of the navigation satellite signals; performing matched filtering operation on the complex baseband signal and local resampling ranging codes under two conditions respectively, and performing low-pass filtering processing on an operation result to obtain a matched filtering operation result of each ranging code period under two conditions;
s400, traversing a text code element to generate a local text and circularly shifting an NH code to generate a local NH code sequence, modulating the local text and the local NH code sequence to generate a modulation code, and performing coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to find a coherent accumulation operation result with the maximum peak value;
s500, adjusting the carrier frequency of the local signal, taking the adjusted carrier frequency as the carrier frequency of the current cycle, and repeating S200 to S400 until the carrier frequency traversal times are reached;
s600, comparing the peak-to-peak ratio of the coherent accumulation operation result of each carrier frequency with a threshold value, and if the peak-to-peak ratio is larger than the threshold value, confirming that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal.
2. The optimization method of the beidou satellite navigation signal capturing algorithm based on the modulation code polarity compensation according to claim 1, wherein before S100, the optimization method of the beidou satellite navigation signal capturing algorithm based on the modulation code polarity compensation further comprises:
s000, setting a pre-detection integralTime Kms, (K)>0, K.epsilon.integer), doppler range of locally capturable signalsSearch frequency step f Δ_1 And a threshold value threshold_1 for judging peak-to-peak ratio;
wherein the method comprises the steps ofRepresenting the lower limit of the range of values of the Doppler frequency offset of the carrier frequency of the local signal compared to the transmission frequency, < >>Representing the upper limit of the range of the Doppler frequency offset of the carrier frequency of the local signal compared with the transmitting frequency, the carrier frequency traversal times are +.>
3. The optimization method of the beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation according to claim 2, wherein the step S200 includes:
s210, obtaining the carrier frequency of the local signal under the current cycle according to the traversal number n under the current cycle
S220, generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle;
s230, performing down-conversion processing on the intermediate frequency navigation satellite signals with the length of each ranging code period in the pre-detection integration time Kms by using a local complex carrier signal to obtain baseband signals with a plurality of ranging code periods;
s240, according to the ranging code modulation condition of the baseband signal of each ranging code period, the baseband signals of the real part and the imaginary part are fused into complex baseband signals.
4. The optimization method of the beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation according to claim 2, wherein the step S300 includes:
s310, the original signals of the local spreading codes are recorded as the two conditions of whether the hopping of the modulation code elements exists in the ranging code period
S320, if the intermediate frequency navigation satellite signal in the ranging code period does not have modulation code element jump, performing FFT conversion on a local spread spectrum code original signal, and then taking conjugation to obtain a local resampling ranging code signal, wherein the local resampling ranging code signal is expressed as: l (L) 0 ＝(FFT(C)) * ；
S330, if the intermediate frequency navigation satellite signal in the ranging code period has a modulation code symbol jump, the local spreading code is reversely spliced, and the splicing result is expressed as: c (C) new ＝[C,-C]And performing FFT conversion on the continuous binding result, and then taking conjugate to obtain a local resampling ranging code signal, which is expressed as: l (L) 0 ＝(FFT(C new )) * ；
S340, aiming at the condition that the intermediate frequency navigation satellite signal does not have modulation code element jump, the baseband signal and the local resampling ranging code are subjected to dot multiplication, and then IFFT is taken to obtain a corresponding matched filtering result, wherein the corresponding matched filtering result is expressed as: result=ifft (FFT (basic_signal.) L 0 )；
S350, aiming at the condition that the intermediate frequency navigation satellite signal has modulation code element jump, zero padding operation is carried out on the baseband signal, so that the length of the baseband signal is consistent with the length of a local spread spectrum code splicing result;
s360, carrying out FFT conversion on the baseband signal after zero padding and then carrying out local resampling ranging code L 0 After dot multiplication, IFFT is taken to obtain a corresponding matched filtering result, which is expressed as:
result＝IFFT(FFT([Basic_signal,zeros(1,N)]).*L 0 )；
wherein basic_signal represents a baseband signal.
5. The optimization method of the beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation according to claim 2, wherein the step S400 includes:
s410, traversing all possible message code element hopping sequences in a hierarchical traversal mode to generate a local message;
s420, generating a local NH code sequence by adopting cyclic shift to the NH code;
s430, modulating the local text and the local NH code sequence at the corresponding position to obtain a local modulation code under the current cycle;
s440, performing a coherent accumulation operation on the matched filtering operation result under the current circulation time by using the local modulation code to obtain a coherent accumulation operation result;
s450, judging whether the peak value of the coherent accumulation operation result under the current cycle is larger than a maximum value zone bit, if so, assigning the peak value of the coherent accumulation operation result under the current cycle to the maximum value zone bit, and replacing a maximum value sequence by the coherent accumulation operation result under the current cycle; the maximum value sequence is formed by the correlation accumulation operation result with the maximum peak value;
s460, the local modulation code, the carrier frequency and the peak position under the current cycle are saved.
6. The optimization method of the Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation according to claim 5, wherein S410 includes:
s411, determining the code element number of the text code element according to the starting code element position of the NH code and the total cycle number of the captured data, and grading the code element number of the text code element;
s412, setting an operation sequence of message traversal, wherein the operation sequence is that a bottom layer is operated firstly and then an upper layer is operated sequentially;
s413, inside each text group, according to 2 f-1 Traversing the first bipolar of length fA sequence; storing the sequence with the maximum peak value module value;
s414, circulating S413 until the number of the bottommost text groups is reached to obtain the bottommost sequence result;
s415, running a second layer, wherein the number of the message groups is 2 f-1 Traversing the bipolar sequence of the first length once;
s416, circulating S415 until the number of second-layer text groups is reached, resampling the sequence with the maximum peak value module value for the first length times, and modulating the sequence with the bottom-layer sequence group to obtain a second-layer sequence result;
s417, repeating S413 to S416 up layer by layer until each layer is traversed;
and S418, finally, running the top layer to generate a local text.
7. The optimization method of the Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation according to claim 5, wherein S420 comprises:
s421, setting a start code element position of a cyclic hypothesis signal according to a code rate, a code length and a single-period code sequence of a subcode of a target signal aiming at the target signal with NH codes; in the Kms complex baseband signal, the overall arrangement of the subcodes is divided into a start subcode period, a middle subcode period and an end subcode period;
s422, determining the whole sequence of the subcode on Kms according to the whole arrangement of the subcode and the single-period sequence of the subcode;
s423, using the whole sequence of subcodes on Kms, generating a local NH code sequence by cyclic shift on the NH code.
8. The optimization method of the Beidou satellite navigation signal capturing algorithm based on modulation code polarity compensation according to claim 2, wherein the step S600 comprises:
s610, determining the position of a peak value and the peak-to-peak ratio in a frequency slice to which the peak value belongs in the coherent accumulation operation result of each carrier frequency;
s620, if the peak-to-peak ratio is greater than or equal to a threshold value threshold_1, determining that a signal is captured under the search frequency step of the current cycle; if the peak-to-peak ratio is smaller than a threshold value threshold_1, judging that no signal is captured under the search frequency step of the current cycle;
s630, the carrier frequency corresponding to the captured signal is the real carrier frequency of the intermediate frequency navigation satellite signal.
9. The optimization method of the beidou satellite navigation signal capturing algorithm based on the modulation code polarity compensation according to claim 8, wherein after S630, the optimization method of the beidou satellite navigation signal capturing algorithm based on the modulation code polarity compensation further comprises:
if it is determined that a signal is captured at the search frequency step of the current cycle, determining whether the search frequency step is greater than an allowable received carrier frequency error; if so, the true carrier frequency f acq_1 Narrowing the range of (f) to a local capturable range [ f ] acq_1 -f Δ_1 ,f acq_1 +f Δ_1 ]；
Resetting search frequency step f Δ_2 And repeating the repeating of S200 to S600 until the search frequency step is smaller than the allowable received carrier frequency error, outputting the acquisition result and the associated acquisition parameters.
10. The utility model provides an optimizing equipment of big dipper satellite navigation signal acquisition algorithm based on modulation code polarity compensation which characterized in that includes:
the receiving device is used for receiving the intermediate frequency navigation satellite signals;
the fusion device is used for generating a local complex carrier signal with the length of a ranging code period according to the carrier frequency of the local signal under the current cycle; performing down-conversion processing on the intermediate frequency navigation satellite signals by using the local complex carrier signals in each ranging code period to obtain baseband signals, and fusing the baseband signals into complex baseband signals according to the ranging code modulation condition of the baseband signals;
the operation device is used for respectively generating corresponding local resampling ranging code signals aiming at the two conditions of modulation code element hopping and no modulation code element hopping of the navigation satellite signals; performing matched filtering operation on the complex baseband signal and local resampling ranging codes under two conditions respectively, and performing low-pass filtering processing on an operation result to obtain a matched filtering operation result of each ranging code period under two conditions;
the searching device is used for traversing the text code element to generate a local text and circularly shifting the NH code to generate a local NH code sequence, modulating the local text and the local NH code sequence to generate a modulation code, and performing coherent accumulation operation on the matched filtering operation result by utilizing the modulation code to search the coherent accumulation operation result with the maximum peak value;
the circulating device is used for adjusting the carrier frequency of the local signal, taking the adjusted carrier frequency as the carrier frequency of the current circulating time, and executing the specific processes of the fusion device, the operation device and the search device until the carrier frequency traversal times are reached;
and the confirming device is used for comparing the peak-to-peak ratio of the coherent accumulation operation result of each carrier frequency with a threshold value, and if the peak-to-peak ratio is larger than the threshold value, confirming that the corresponding carrier frequency is the real carrier frequency of the intermediate frequency navigation satellite signal.
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