CN114994721A - Universal navigation signal digital intermediate frequency preprocessing method - Google Patents
Universal navigation signal digital intermediate frequency preprocessing method Download PDFInfo
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- CN114994721A CN114994721A CN202210599062.3A CN202210599062A CN114994721A CN 114994721 A CN114994721 A CN 114994721A CN 202210599062 A CN202210599062 A CN 202210599062A CN 114994721 A CN114994721 A CN 114994721A
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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
- G01S19/13—Receivers
- G01S19/35—Constructional details or hardware or software details of the signal processing chain
- G01S19/37—Hardware or software details of the signal processing chain
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention provides a general navigation signal digital intermediate frequency preprocessing method which can realize the down-sampling and the re-quantization processing of the front-end digital intermediate frequency of a satellite navigation signal. Firstly, sampling a received navigation signal, and carrying out digital down-conversion on an obtained digital intermediate frequency signal to obtain a zero intermediate frequency or near-zero intermediate frequency digital baseband signal; then, the digital baseband signal passes through a linear phase FIR anti-aliasing low-pass filter, the bandwidth of the signal is limited before down-sampling, and the frequency spectrum aliasing caused by down-sampling is avoided; then each adjacent filtered digital signalnAccumulating the points to obtain a digital signal after down sampling; and finally, carrying out self-adaptive quantization processing on the down-sampled high-bit-width digital signal to obtain the required low-bit-width intermediate frequency data. The invention can improve the signal-to-noise ratio of the down-sampled signal and greatly reduce the storage capacity and the operation amount of subsequent data.
Description
Technical Field
The invention relates to the field of satellite navigation, in particular to a universal navigation signal digital intermediate frequency preprocessing method.
Background
Current global satellite navigation systems include: the GPS system in the united states, the GLONASS system in russia, the beidou system in china, the Galileo system in europe, japan and india also build respective satellite navigation systems. For the above various satellite navigation systems, the acquisition and tracking processes of the satellite navigation signals are similar, and the digital intermediate frequency signals of the AD samples must be preprocessed before the baseband processing. The sampling rate and data bit width of the AD are generally high, and the requirements on the subsequent navigation signal processing operation amount and data storage amount are particularly high, which greatly increases the signal processing cost.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provides a universal navigation signal digital intermediate frequency preprocessing method which can improve the signal-to-noise ratio of a signal after down sampling compared with the operation of directly extracting every n points. In addition, the self-adaptive quantization processing is carried out on the digital signals with high bit widths after the down sampling, so that the storage capacity and the operation amount of subsequent data can be greatly reduced.
The purpose of the invention is realized by the following technical scheme:
a general navigation signal digital intermediate frequency preprocessing method comprises the following steps:
(1) carrying out down-conversion and AD sampling on spread spectrum navigation signals transmitted by satellites to obtain digital intermediate frequency signals;
(2) carrying out digital down-conversion on the digital intermediate frequency signal to obtain a zero intermediate frequency or near-zero intermediate frequency digital baseband signal;
(3) inputting a digital baseband signal into a linear phase FIR anti-aliasing low-pass filter, wherein the coefficient h (m) adopts an even symmetry form, h (m) is h (K-1-m), K is an even number, and m is a serial number, so as to obtain a filtered digital signal;
(4) for the filtered digital signal d 0 ,d 1 ,d 2 ,d 3 ,d 4 ,d 5 And (c) accumulating each adjacent n points to obtain a new digital signal (d) 0 +d 0 +···+d n-1 ,d n +d n+1 +···+d 2n-1 ,d 2n +d 2n+1 +···+d 3n-1 C, the new digital signal sampling rate becomes the previous digital signal sampling rateIs/are as follows
Namely the digital signal after down sampling;
(5) and performing self-adaptive quantization processing on the down-sampled digital signal to obtain low-bit-width intermediate frequency data, and finishing the navigation signal digital intermediate frequency preprocessing.
Further, in the step (5), the bit width of the obtained low-bit-width intermediate frequency data is 4 bits.
Compared with the prior art, the invention has the following beneficial effects:
1. compared with the operation of directly extracting at n points at intervals, the down-sampling technology of the sampling accumulation processing can improve the signal-to-noise ratio of the down-sampled signal.
2. The invention carries out self-adaptive quantization processing on the digital signal with high bit width after down sampling, and can greatly reduce the storage capacity and the operation amount of subsequent data.
Drawings
FIG. 1 is a schematic diagram of the method of an embodiment of the present invention;
FIG. 2 is a schematic diagram of an NCO numerically controlled oscillator according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a linear phase FIR anti-aliasing low-pass filter according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail below with reference to the accompanying drawings.
As shown in fig. 1, a general navigation signal digital intermediate frequency preprocessing method includes the following steps:
(1) and performing down-conversion and AD sampling on the spread spectrum navigation signal transmitted by the satellite to obtain a digital intermediate frequency signal.
In the embodiment, for the Beidou B3I signals, the carrier center frequency is 1268.52MHz, the AD sampling rate is 75MHz, the bit width of the digital intermediate frequency signal is 16bit, and the center frequency of the sampled digital signal is 15.52 MHz.
(2) And carrying out digital down-conversion on the digital intermediate frequency signal to obtain a zero intermediate frequency or near-zero intermediate frequency digital baseband signal.
In the embodiment, the down-conversion module performs the functions of NCO and mixer, the NCO is aimed at generating a data sample of variable-frequency time-discrete sine wave and cosine wave, as shown in fig. 2, and the frequency f of the sine wave and cosine wave to be generated is obtained according to the input carrier frequency control word D out Is shown as
Wherein N is the bit width of the frequency control word D, and the larger N is, the higher the phase resolution is, and the higher the phase precision is, and the value of N is generally 32. f. of s The NCO system clock is the sampling frequency of sine wave and cosine wave.
If the local needs to generate data samples of sine wave cos and cosine wave sin with output frequency of 15.52MHz and sampling rate of 75MHz, the carrier control word
(3) And (3) passing the digital baseband signal through a linear phase FIR anti-aliasing low-pass filter, wherein the coefficient h (m) is in an even symmetry form, h (m) is h (K-1-m), and K is an even number, so as to obtain a filtered digital signal.
In an embodiment, the linear phase FIR anti-aliasing low pass filter functions to limit the bandwidth of the signal before down-sampling, and to avoid spectral aliasing caused by down-sampling, and the principle is shown in fig. 3.
The order of the local FIR filter is 16 orders, and the total number of the coefficients is 16, because of the symmetry of the filter coefficients, the number of the coefficients is reduced by half to 8, and all the coefficient bit widths are 8 bits and are represented by binary complement codes. The filter coefficients corresponding to the 1 st input data and the 16 th input data are the same, the filter coefficients corresponding to the 2 nd input data and the 15 th input data are the same, and so on, symmetrically adding the data in the shift register to obtain the filtered data:
wherein, K is 16, K is 0,1,2, 15.
In the step, the coefficient of the linear phase FIR anti-aliasing low-pass filter adopts an even symmetry form, so that the number of the stored filter coefficients is reduced by half, and the multiplication times can be reduced by half.
(4) For filtered digital signal d 0 ,d 1 ,d 2 ,d 3 ,d 4 ,d 5 Every adjacent n points are accumulated to obtain new digital signal d 0 +d 0 +···+d n-1 ,d n +d n+1 +···+d 2n-1 ,d 2n +d 2n+1 +···+d 3n-1 C, the new digital signal sample rate becomes that of the previous digital signal sample rate
A down-sampled digital signal is obtained.
In the embodiment, the spreading code rate of the beidou B3I signal is 10.23MHz, and in order to avoid signal loss, the signal rate after down-sampling must be greater than 2 times the spreading code rate, so that every 3 sampling points are accumulated to obtain a down-sampled signal of 75 ÷ 3 ═ 25 MHz.
In the step, accumulation processing is carried out on every adjacent n points of the filtered digital signal, and compared with the operation of directly extracting every n points, the signal-to-noise ratio of the down-sampled signal can be improved.
(5) And carrying out self-adaptive weighting processing on the down-sampled high-bit-width digital signal to obtain the required low-bit-width intermediate frequency data.
In the embodiment, for the navigation signal, in order to reduce the operation amount of subsequent acquisition tracking, the bit width of the digital intermediate frequency data output by preprocessing needs to be reduced, and the high-bit-width digital signal needs to be adaptively weighted to 4 bits. The quantification is based on the statistics of white Gaussian noise, and the average value of a section of data is counted first
Then, quantization is performed according to the following formula:
x is to be o (m) is represented by a two's complement code of 4 bits wide.
In the step, the digital signal with high bit width is subjected to self-adaptive quantization processing to obtain intermediate frequency data with 4bit width, so that the subsequent data storage capacity and the operation amount can be greatly reduced.
In a word, the invention can realize the down-sampling and the re-quantization processing of the front-end digital intermediate frequency of the satellite navigation signal, firstly, the received navigation signal is sampled, and the digital down-conversion is carried out on the obtained digital intermediate frequency signal to obtain a digital baseband signal of zero intermediate frequency or near-zero intermediate frequency; then, the digital baseband signal is subjected to a linear phase FIR anti-aliasing low pass filter, the bandwidth of the signal is limited before down-sampling, and spectrum aliasing caused by down-sampling is avoided; accumulating the adjacent n points of the filtered digital signal to obtain a down-sampled digital signal; and finally, carrying out self-adaptive quantization processing on the down-sampled high-bit-width digital signal to obtain the required low-bit-width intermediate frequency data. Compared with the operation of directly extracting at n points at intervals, the down-sampling technology of the sampling accumulation processing can improve the signal-to-noise ratio of the down-sampled signal; the invention also carries out self-adaptive quantization processing on the digital signals with high bit width after down sampling, and can greatly reduce the storage capacity and the operand of subsequent data.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present application and not for limiting, and although the present application is described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application, and all of them should be covered in the scope of the claims of the present application.
Claims (2)
1. A general navigation signal digital intermediate frequency preprocessing method is characterized by comprising the following steps:
(1) carrying out down-conversion and AD sampling on spread spectrum navigation signals transmitted by satellites to obtain digital intermediate frequency signals;
(2) carrying out digital down-conversion on the digital intermediate frequency signal to obtain a zero intermediate frequency or near-zero intermediate frequency digital baseband signal;
(3) inputting a digital baseband signal into a linear phase FIR anti-aliasing low-pass filter, wherein the coefficient h (m) adopts an even symmetry form, h (m) is h (K-1-m), K is an even number, and m is a serial number, so as to obtain a filtered digital signal;
(4) for the filtered digital signal d 0 ,d 1 ,d 2 ,d 3 ,d 4 ,d 5 Is, every adjacent n points are added to obtain new digital signal d 0 +d 0 +···+d n-1 ,d n +d n+1 +···+d 2n-1 ,d 2n +d 2n+1 +···+d 3n-1 C, the new digital signal sample rate becomes that of the previous digital signal sample rate
Namely the digital signal after down sampling;
(5) and performing self-adaptive quantization processing on the down-sampled digital signal to obtain low-bit-width intermediate frequency data, and completing navigation signal digital intermediate frequency preprocessing.
2. The method as claimed in claim 1, wherein in the step (5), the bit width of the obtained low-bit-width intermediate frequency data is 4 bits.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117471508A (en) * | 2023-12-27 | 2024-01-30 | 中国人民解放军国防科技大学 | Data optimal framing method and device under bandwidth limited condition |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117471508A (en) * | 2023-12-27 | 2024-01-30 | 中国人民解放军国防科技大学 | Data optimal framing method and device under bandwidth limited condition |
| CN117471508B (en) * | 2023-12-27 | 2024-03-26 | 中国人民解放军国防科技大学 | Data optimal framing method and device under bandwidth limited condition |
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