CN116381757B - Iridium opportunistic signal Doppler frequency fine estimation method based on phase difference - Google Patents
Iridium opportunistic signal Doppler frequency fine estimation method based on phase difference Download PDFInfo
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- 229910052741 iridium Inorganic materials 0.000 title claims abstract description 39
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 35
- 238000012545 processing Methods 0.000 claims abstract description 10
- 238000001914 filtration Methods 0.000 claims abstract description 9
- 238000001228 spectrum Methods 0.000 claims description 21
- 238000012937 correction Methods 0.000 claims description 18
- 238000010183 spectrum analysis Methods 0.000 claims description 12
- 238000004364 calculation method Methods 0.000 claims description 4
- 230000011218 segmentation Effects 0.000 claims description 3
- 238000012935 Averaging Methods 0.000 claims description 2
- 230000005540 biological transmission Effects 0.000 claims description 2
- 230000008569 process Effects 0.000 abstract description 2
- 238000007476 Maximum Likelihood Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 150000002503 iridium Chemical class 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
Classifications
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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
- G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
- G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/42—Determining position
- G01S19/43—Determining position using carrier phase measurements, e.g. kinematic positioning; using long or short baseline interferometry
-
- 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
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
- G01S19/254—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS relating to Doppler shift of satellite signals
-
- 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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- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Position Fixing By Use Of Radio Waves (AREA)
- Radio Relay Systems (AREA)
Abstract
The invention provides a phase difference-based iridium opportunistic signal Doppler frequency fine estimation method, which specifically comprises the following steps: step 1, carrying out band-pass filtering and continuous wave signal positioning; step 2, carrying out Doppler frequency shift rough estimation; and step 3, carrying out Doppler frequency shift refined estimation by adopting a phase difference method. The invention has the advantages of small operand, high processing speed and short time consumption, can rapidly and accurately process the satellite opportunity signal, and accurately estimate Doppler frequency shift, thereby calculating the user position information.
Description
Technical Field
The invention belongs to the field of radio navigation communication, and particularly relates to an iridium opportunistic signal Doppler frequency fine estimation method based on phase difference.
Background
The Beidou satellite navigation system is a main navigation system in the current and future period of China, and plays a great role in various fields of economic development. However, similar to the satellite navigation system such as GPS, galileo, GLONASS, the beidou navigation system has some disadvantages. Such as serious attenuation of signals received by a user receiver, low message propagation rate, slow change of space geometric layout of a medium-high orbit satellite, easy attack, deception and the like.
The iridium satellite system in the united states is the only low-orbit satellite system that has achieved global coverage, and the ground terminals receive about 30dB more powerful signals than GPS. The low orbit satellite has a high motion speed relative to the ground user, and the Doppler frequency shift of the opportunistic signals received by the user is about 30kHz, so that the Doppler observability is good. Therefore, the Doppler observed value of the signal is utilized to perform positioning calculation to be very matched with the characteristics of the low-orbit satellite, and the Doppler positioning is very suitable for a low-orbit satellite navigation system.
In the process of Doppler positioning, the accuracy and the speed of the opportunistic signal Doppler frequency estimation directly influence the accuracy and the speed of positioning, and are an important part of the whole positioning system. The conventional method for determining the accurate doppler shift is to use the maximum likelihood estimation (maximum likelihood estimation, MLE) method to make the doppler accurate measurement within the adjacent frequency bandwidth. In order to obtain accurate Doppler shift, the method needs to perform high-resolution search in a wide frequency range, and has very large operation amount and quite time-consuming. Therefore, on the premise of using Doppler positioning, an alternative signal processing method is needed to obtain accurate Doppler frequency shift, so that the positioning accuracy and speed are ensured.
Disclosure of Invention
In order to overcome the defects of non-uniform space-time reference, poor signal/information fusion degree and the like of random/opportunistic signal sources and solve the requirements of local/hot spot emergency navigation positioning services of complex scenes (physical shielding, electromagnetic interference, battle zone striking/countermeasures and the like) under the condition of GNSS refusal, the invention provides a Doppler frequency fine estimation method for iridium opportunistic signals based on phase difference, which adopts a phase difference division method to carry out fine estimation on Doppler frequency.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a method for finely estimating Doppler frequency of an iridium opportunistic signal based on phase difference comprises the following steps:
step 1, carrying out band-pass filtering and continuous wave signal positioning;
step 2, carrying out Doppler frequency shift rough estimation;
and step 3, carrying out Doppler frequency shift refined estimation by adopting a phase difference method.
Further, the step 1 specifically includes: the iridium L-band opportunistic signal structurally comprises three parts of a continuous wave signal unit without modulation, a BPSK-modulated independent word unit and a QPSK-modulated data information unit, wherein the time length of the continuous wave signal unit is about 2.6ms. The iridium opportunistic signal obtains the Doppler frequency shift estimated value required by the position calculation of the receiver by identifying, capturing and processing the continuous wave signal of the continuous wave signal unit of the Ring Alert channel.
The transmission period of the iridium satellite downlink L-band opportunistic signal is 4.32s, and the time frame length is 90ms; in order to ensure the accurate acquisition of continuous wave signals of a channel continuous wave signal unit of Ring Alert, firstly, randomly intercepting and receiving 4.32s long signals, carrying out frame-by-frame band-pass filtering processing on the signals, and positioning the signals to the initial position of the continuous wave signals in a time domain through amplitude comparison; then, calculating the frequency spectrum of continuous wave signals of two continuous frames, and comparing and checking the time of the large amplitude through the frequency spectrum, namely: the time interval of the two frames is integral multiple of 90ms, so that the correctness check of the continuous wave signal and the time position thereof is realized.
The step 2 specifically comprises the following steps:
extracting a continuous wave signal on the time domain based on the time position of the continuous wave signal of the Ring Alert channel after the correctness checking, and equally dividing the continuous wave signal of 2.6ms into two sections of signals of 1.3 ms; and then carrying out Fourier transformation, respectively carrying out spectrum analysis on the two sections of signals of 1.3ms, calculating Doppler frequency shift estimated values of the two sections of signals of 1.3ms through spectrum peak positions, and averaging the Doppler frequency shift estimated values of the two sections of signals of 1.3ms to obtain a Doppler frequency shift rough estimated value of the iridium opportunistic signal.
The step 3 specifically comprises the following steps:
phase difference separation is used. And (3) carrying out carrier stripping on the iridium opportunistic signal by using a Doppler frequency shift rough estimation value obtained by rough capturing, moving a signal to be analyzed to a baseband, namely near 0 intermediate frequency, then carrying out time domain segmentation on a continuous wave signal of 2.6ms, dividing the continuous wave signal into a signal segment of front 1.3ms and a signal segment of rear 1.3ms, respectively carrying out Fourier transform spectrum analysis and searching for spectrum peaks of signals at the front end and the rear end, and obtaining a fine frequency correction quantity by using a phase difference of complex numbers corresponding to the two DFT peaks.
The complex phase corresponding to the peak value is searched after DFT operation is carried out on the front and back signal segments of 1.3ms respectively, and is supposed to be inThe time is: DFT spectrum analysis is carried out on the signal segment of the first 1.3ms, and the corresponding complex number of the spectrum peak value is searched to be +.>，For the frequency component of the input signal, the phase of the corresponding peak is calculated as:
(5)
wherein Im and Re represent the imaginary and real parts, respectively, and the initial phase of the input signal is obtained by the above formula。
At the position ofImmediately after->The time is: DFT spectrum analysis is carried out on the signal segment of the last 1.3ms, and the corresponding complex number of the spectrum peak value is searched to be +.>，/>For the frequency component of the input signal, the phase of the corresponding peak is calculated as:
(6)
iridium satellite opportunity letterThe number continuous wave signal is 2.6ms, and is respectively processed after being intercepted in a front-back equal segment, and then corresponds toTime and->The time difference between the moments is 0.0013s, the fine correction frequency is:
(7)
wherein the unit of the fine correction frequency is Hz. Due to the presence of noise, it is difficult to determine the formula (7)Is a compensation mode of the system. A better method to eliminate this uncertainty is an amplitude comparison method, whose basic principle is: the maximum value of the Fourier transform spectrum X (k), the left and right adjacent amplitudes of the comparison peak X (k-1) and X (k+1), if |X (k-1) | is significantly greater than |X (k+1) |, the frequency of the input signal should be less than +>Corresponding frequency, the refinement correction amount obtained by phase difference +.>Negative compensation is required on the basis of the doppler coarse estimate, namely: doppler coarse estimate minus correction +.>The method comprises the steps of carrying out a first treatment on the surface of the Otherwise, the positive compensation is taken.
Compared with the prior art, the invention has the beneficial effects that:
(1) The treatment speed is high: the present invention uses phase difference division in the step of refining the doppler shift. Compared with the maximum likelihood estimation method, the phase difference method does not need to search in a wide frequency range in a high resolution mode, so that the operation amount is small, the processing speed is high, and the calculated hardware resources are saved.
(2) The structure and parameters of the iridium signals do not need to be known: the invention only uses the non-modulated continuous wave signal part with simple structure, the time length of the part signal is about 2.6ms, and Doppler frequency shift information required for calculating the position of the receiver can be obtained by capturing and processing the continuous wave. The structure and parameters of other partial signals need not be known.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below, and it is apparent that the drawings in the following description are only for the purpose of illustrating the preferred embodiments and are not to be construed as limiting the present invention. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:
FIG. 1 is a flow chart of a method for finely estimating Doppler frequency of an iridium opportunistic signal based on phase difference;
FIG. 2 is a schematic diagram of a time frame structure of an Iridium opportunistic signal;
fig. 3 is a schematic diagram of locating a continuous wave by bandpass filtering.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
As shown in FIG. 1, the iridium opportunistic signal Doppler frequency fine estimation method based on phase difference comprises the following steps:
step 1, band-pass filtering and continuous wave signal positioning are carried out:
the iridium L-band opportunistic signal structurally comprises three parts of a continuous wave signal unit without modulation, a BPSK modulated independent word unit and a QPSK modulated data information unit, wherein the time length of the continuous wave signal unit is about 2.6ms, as shown in fig. 2. The iridium opportunistic signal obtains the Doppler frequency shift estimated value required by the position calculation of the receiver by identifying, capturing and processing the continuous wave signal of the continuous wave signal unit of the Ring Alert channel.
In order to ensure the accurate acquisition of continuous wave signals of a channel continuous wave signal unit of Ring Alert, firstly, randomly intercepting and receiving 4.32s long signals, carrying out frame-by-frame band-pass filtering processing on the signals, and positioning the initial position of the continuous wave signals in a time domain through amplitude comparison after filtering because the power of the continuous wave signals is higher than the environment base low noise, as shown in figure 3. Then, calculating the frequency spectrum of continuous wave signals of two continuous frames, and comparing and checking the time of the large amplitude through the frequency spectrum, namely: the time interval of the two frames is integral multiple of 90ms, so that the correctness check of the continuous wave signal and the time position thereof is realized.
Step 2, carrying out Doppler frequency shift rough estimation:
extracting a continuous wave signal on the time domain based on the time position of the continuous wave signal of the Ring Alert channel after the correctness checking, and equally dividing the continuous wave signal of 2.6ms into two sections of signals of 1.3 ms; then, fourier transformation is performed, spectrum analysis is performed on the two sections of signals of 1.3ms, and the estimated doppler shift value of the two sections of signals of 1.3ms is calculated through the positions of the spectrum peak values. However, since the Doppler frequency shift of the iridium signal changes rapidly, the Doppler frequency shift estimated values of the two sections of signals of 1.3ms are averaged, and only the rough Doppler frequency shift estimated value of the iridium opportunistic signal can be obtained.
Step 3, carrying out Doppler frequency shift refined estimation by adopting a phase difference method:
phase difference separation is used. And (3) carrying out carrier stripping on the iridium opportunistic signal by using a Doppler frequency shift rough estimation value obtained by rough capturing, moving a signal to be analyzed to a baseband, namely near 0 intermediate frequency, then carrying out time domain segmentation on a continuous wave signal of 2.6ms, dividing the continuous wave signal into a signal segment of front 1.3ms and a signal segment of rear 1.3ms, respectively carrying out Fourier transform spectrum analysis and searching for spectrum peaks of signals at the front end and the rear end, and obtaining a fine frequency correction quantity by using a phase difference of complex numbers corresponding to the two DFT peaks.
The complex phase corresponding to the peak value is searched after DFT operation is carried out on the front and back signal segments of 1.3ms respectively, and is supposed to be inThe time is: DFT spectrum analysis is carried out on the signal segment of the first 1.3ms, and the corresponding complex number of the spectrum peak value is searched to be +.>，For the frequency component of the input signal, the phase of the corresponding peak is calculated as:
(5)
wherein Im and Re represent the imaginary and real parts, respectively, and the initial phase of the input signal is obtained by the above formula。
At the position ofImmediately after->The time is: DFT spectrum analysis is carried out on the signal segment of the last 1.3ms, and the corresponding complex number of the spectrum peak value is searched to be +.>，/>For the frequency component of the input signal, the phase of the corresponding peak is calculated as:
(6)
iridium opportunistic signal continuous wave signal of 2.6ms, after the front and rear equal segment interception, respectively processing, then corresponding toTime and->The time difference between the moments is 0.0013s, the fine correction frequency is:
(7)
wherein the unit of the fine correction frequency is Hz. Due to the presence of noise, it is difficult to determine in equation (7)Is a compensation mode of the system. A better method to eliminate this uncertainty is an amplitude comparison method, whose basic principle is: the maximum value of the Fourier transform spectrum X (k), the left and right adjacent amplitudes of the comparison peak X (k-1) and X (k+1), if |X (k-1) | is significantly greater than |X (k+1) |, the frequency of the input signal should be less than +>Corresponding frequency, fine correction amount obtained by phase difference +.>Negative compensation is required on the basis of the doppler coarse estimate, namely: doppler coarse estimate minus correction frequency +.>The method comprises the steps of carrying out a first treatment on the surface of the Otherwise, the positive compensation is taken.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (7)
1. The iridium opportunistic signal Doppler frequency fine estimation method based on phase difference is characterized by comprising the following steps of:
step 1, carrying out band-pass filtering and continuous wave signal positioning;
step 2, carrying out Doppler frequency shift rough estimation;
step 3, carrying out Doppler frequency shift refined estimation by adopting a phase difference method;
the step 2 specifically includes:
extracting a continuous wave signal on the time domain based on the time position of the continuous wave signal of the Ring Alert channel after the correctness checking, and equally dividing the continuous wave signal of 2.6ms into two sections of signals of 1.3 ms; then carrying out Fourier transform, respectively carrying out spectrum analysis on the two sections of signals of 1.3ms, calculating Doppler frequency shift estimated values of the two sections of signals of 1.3ms through spectrum peak positions, and averaging the Doppler frequency shift estimated values of the two sections of signals of 1.3ms to obtain a Doppler frequency shift rough estimated value of the iridium opportunistic signal;
the step 3 specifically includes:
the complex phase corresponding to the peak value is searched after DFT operation is carried out on the front and back signal segments of 1.3ms respectively, and is supposed to be inThe time is: DFT spectrum analysis is carried out on the signal segment of the first 1.3ms, and the corresponding complex number of the spectrum peak value is searched to be +.>，/>For the frequency component of the input signal, the phase of the corresponding peak is calculated as:
(1)
wherein Im and Re represent the imaginary and real parts, respectively, and the initial phase of the input signal is obtained by the above formula；
At the position ofImmediately after->The time is: DFT spectrum analysis is carried out on the signal segment of the last 1.3ms, and the corresponding complex number of the spectrum peak value is searched to be +.>，/>For the frequency component of the input signal, the phase of the corresponding peak is calculated as:
(2)
the fine correction frequency is:
(3)
wherein the unit of the fine correction frequency is Hz;
correction of frequencyThe compensation mode of the Doppler frequency shift rough estimation value is as follows: the positive or negative compensation is determined by an amplitude comparison method.
2. The method for finely estimating the Doppler frequency of the iridium opportunistic signal based on phase difference according to claim 1, wherein the iridium L-band opportunistic signal structurally comprises a continuous wave signal unit without modulation, a BPSK-modulated independent word unit and a QPSK-modulated data information unit from a time frame structure; the iridium opportunistic signal obtains the Doppler frequency shift estimated value required by the position calculation of the receiver by identifying, capturing and processing the continuous wave signal of the continuous wave signal unit of the Ring Alert channel.
3. The method for fine estimation of doppler frequency of iridium opportunistic signals based on phase difference according to claim 1, wherein the step 1 specifically includes:
in order to ensure the accurate acquisition of continuous wave signals of a channel continuous wave signal unit of Ring Alert, firstly, randomly intercepting and receiving 4.32s long signals, carrying out frame-by-frame band-pass filtering processing on the signals, and positioning the signals to the initial position of the continuous wave signals in a time domain through amplitude comparison; then, calculating the frequency spectrum of continuous wave signals of two continuous frames, and comparing and checking the time of the large amplitude through the frequency spectrum, namely: the time interval of the two frames is integral multiple of 90ms, so that the correctness check of the continuous wave signal and the time position thereof is realized.
4. The method for finely estimating the Doppler frequency of the iridium opportunistic signal based on phase difference according to claim 2, wherein,
the time length of the continuous wave part signal unit without modulation is about 2.6ms, the time frame length of each frame of iridium satellite opportunistic signal is 90ms, and the transmission period of the iridium downlink L-band satellite opportunistic signal is 4.32s.
5. The method for fine estimation of doppler frequency of iridium opportunistic signals based on phase difference according to claim 1, wherein the step 3 specifically includes:
and carrying out carrier stripping of iridium opportunistic signals by using a Doppler frequency shift rough estimation value obtained by rough capturing, moving a signal to be analyzed to a baseband, namely near 0 intermediate frequency, then carrying out time domain segmentation on a continuous wave signal of 2.6ms, dividing the continuous wave signal into a signal segment of front 1.3ms and a signal segment of rear 1.3ms, respectively carrying out Fourier transform spectrum analysis and searching for spectrum peaks of signals at the front end and the rear end, and obtaining a fine frequency correction quantity by using a phase difference of complex numbers corresponding to the two DFT peaks.
6. The method for finely estimating Doppler frequency of iridium opportunistic signals based on phase difference as claimed in claim 1, wherein,
the iridium opportunistic signal continuous wave signal is 2.6ms, and is processed after being intercepted in a front-back equal-section mode, and then the iridium opportunistic signal continuous wave signal is corresponding toTime and->The time difference between the moments is 0.0013s, then:
(4)
thus, the Doppler frequency shift fine correction amount of the iridium opportunistic signal is obtained.
7. The method for finely estimating Doppler frequency of iridium opportunistic signal based on phase difference as claimed in claim 1, wherein the correction frequency isThe compensation mode of the Doppler frequency shift rough estimation value is as follows: positive or negative compensation is determined by an amplitude comparison method, specifically:
determination by amplitude comparisonIf the maximum value X (k) of the Fourier transform spectrum is adjacent to the amplitude X (k-1) and X (k+1) around the comparison peak, if |X (k-1) | is significantly larger than |X (k+1) |, the frequency of the input signal should be smaller thanCorresponding frequency, doppler shift refinement correction amount obtained by phase difference>Negative compensation is required on the basis of the doppler coarse estimate, namely: doppler coarse estimate minus correction +.>The method comprises the steps of carrying out a first treatment on the surface of the Otherwise, the positive compensation is taken.
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