A residual frequency offset estimation method based on multi-channel in-track interferometry

Abstract

The application discloses a residual frequency offset estimation method based on multi-channel in-track interference, and belongs to the field of radio reconnaissance. The method comprises the following steps: arranging multiple detection antennas in front of and behind the flight direction; the detection antennas passively receive signals emitted by a radiation source target; and the received signals are processed. Since the multiple antennas pass through the same slant range course in sequence, interference processing is performed after compensating for the phase caused by time delay. In an ideal case, the interference phase between channels is 0. In the case that there is a residual frequency offset, the interference phase between channels is the phase generated by the joint action of time delay and the residual frequency offset. The residual frequency offset can be estimated according to the corresponding relationship between the residual frequency offset and the interference phase. The application can realize accurate estimation of the residual frequency offset in the case of non-cooperative reception, and eliminate the influence of the residual frequency offset on subsequent signal processing.

Description

Technical Field

[0001] The invention belongs to the technical field of radio reconnaissance, and in particular relates to a residual frequency offset estimation method based on multi-channel along-track interference. Background Art

[0002] In non-cooperative reception, such as in radio spectrum monitoring, the received signal, after downconversion, still contains residual frequency offset, known as residual frequency offset. This residual frequency offset can cause signal distortion and error accumulation, impacting system accuracy and reliability. Effective frequency offset estimation and compensation are key to ensuring system performance. Summary of the Invention

[0003] In order to solve the technical problems existing in the background technology, the present invention aims to provide a residual frequency offset estimation method based on multi-channel along-track interference, which can realize the residual frequency offset estimation between transceivers in the case of non-cooperative reception.

[0004] In order to solve the technical problem, the technical solution of the present invention is:

[0005] A residual frequency offset estimation method based on multi-channel along-track interferometry, the method comprising:

[0006] S1: Down-convert and de-modulate the received signals of multiple channels to obtain the corresponding Doppler signals;

[0007] S2: Calculate the time delay between channels for the same slant range based on the platform flight speed and antenna baseline;

[0008] S3: Perform phase compensation on the Doppler signals of different channels based on the calculated time delay to eliminate the phase deviation caused by the distance difference between antennas;

[0009] S4: Perform interference processing on the signals of different channels and obtain the interference phase through conjugate multiplication; preliminarily estimate the short baseline and long baseline frequency deviation values ​​based on the relationship between the interference phase and the residual frequency deviation; defuzzify the long baseline estimation result based on the short baseline estimation result to obtain the final estimation result.

[0010] Furthermore, the step S1 specifically includes:

[0011] A three-channel along-track interferometer is used, with three detection antennas arranged in front and behind along the flight direction. Antenna 1 and antenna 2 form a short baseline, and antenna 1 and antenna 3 form a long baseline. The antenna passively receives the signal emitted by the radiation source target, down-converts the received signal to obtain the baseband signal, and demodulates the baseband signal to obtain the corresponding Doppler signal.

[0012] Let the instantaneous distances between the three-channel antenna of the airplane and the radiation source target be R1, R2 and R3 respectively, the distance between the radiation source target and the flight line of the airplane be R0, and the relationships between R1, R2, R3 and R0 be shown in formulas (1) and (2),

[0013]

[0014] wherein, the flight speed of the airplane be v, the baseline length of the antenna 1 and the antenna 2 be d 12 , the baseline length of the antenna 1 and the antenna 3 be d 13 , and the zero Doppler moment be t p .

[0015] The Doppler signals r1(t), r2(t) and r3(t) obtained after the baseband demodulation processing of the antenna 1, 2 and 3 are expressed as:

[0016]

[0017] wherein, f0 is the carrier frequency of the radiation source, c is the speed of light, and f1 is the residual frequency offset.

[0018] Further, the step S2 specifically comprises:

[0019] The instantaneous distances between the three-channel antenna of the airplane and the radiation source target are respectively R1, R2 and R3, which are respectively expanded to the quadratic terms at t=t p , and by using the Taylor formula, and there are:

[0020]

[0021] wherein, is the time delay corresponding to the baseline length of the antenna 1 and the antenna 2 and the flight speed of the airplane, is the time delay corresponding to the baseline length of the antenna 1 and the antenna 3 and the flight speed of the airplane.

[0022] Further, the step S3 of short baseline compensation specifically comprises:

[0023] According to the flight speed of the airplane and the baseline length of the antenna 1 and the antenna 2, the time delay is calculated, and the phase compensation is performed on r1(t), and the compensated signal is expressed as:

[0024]

[0025] Further, the step S4 specifically comprises:

[0026] Short baseline interference processing: the compensated signal r′1(t) and the signal r2(t) of the antenna 2 are conjugatedly multiplied, the interference result I 12 is calculated, and the interference phase is extracted

[0027] Short baseline frequency offset estimation: using interferometric phase and t 12 The relationship between the short baseline frequency offset f′1 is estimated, and its unambiguous range is:

[0028] Long baseline compensation: Perform long baseline compensation on the signal of antenna 1 to obtain r1″(t);

[0029] Long baseline interferometry processing: multiply the compensated signal r1″(t) by the conjugate of the signal r3(t) from antenna 3 to calculate the interference result I 13 , and extract the interference phase

[0030] Long baseline frequency offset estimation: using interferometric phase and t 13 The relationship between the long baseline frequency offset f1″ is estimated, and its unambiguous range is:

[0031] Frequency offset deambiguation: The long baseline result f1″ is deambiguated using the short baseline result f′ to obtain the final residual frequency offset estimate.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] The present invention discloses a method for measuring residual frequency offset using multi-antenna along-track interferometry, which can accurately estimate residual frequency offset in non-cooperative reception scenarios. By accurately estimating the residual frequency offset in the signal at the receiving end and compensating for it based on the estimated result, the impact of frequency offset on system performance can be reduced or eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 , a flow chart of a residual frequency offset estimation method based on multi-channel along-track interferometry disclosed in the present invention;

[0035] Figure 2 , Geometric model diagram of the residual frequency offset estimation method based on multi-channel along-track interference. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is described below in conjunction with examples:

[0037] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0038] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0039] Example 1:

[0040] The purpose of the present invention is achieved through the following technical solutions:

[0041] A residual frequency offset estimation method based on multi-channel along-track interferometry: multiple detection antennas are arranged in front and behind the flight direction to passively receive signals emitted by the radiation source target, and the received signals are processed. Since multiple antennas pass through the same slant range, interference processing is performed after compensating for the phase caused by time delay.

[0042] Ideally, the inter-channel interference phase is 0. In the presence of residual frequency offset, the inter-channel interference phase is the phase generated by the combined effect of time delay and residual frequency offset. The residual frequency offset can be estimated from the corresponding relationship between the residual frequency offset and the interference phase.

[0043] Since the interference phase range is (-π,π), the frequency offset estimation value is obtained by performing the corresponding deambiguation process through the interference phase of multiple channels.

[0044] Specifically, the following steps are included:

[0045] Step 1: Taking three-channel down-track interferometry as an example, three detection antennas are arranged in front and behind along the flight direction. Antenna 1 and antenna 2 form a short baseline, and antenna 1 and antenna 3 form a long baseline. The antennas passively receive the signal emitted by the radiation source target, down-convert the received signal to obtain the baseband signal, and demodulate the baseband signal to obtain the corresponding Doppler signal.

[0046] Assume that the instantaneous distances between the aircraft's three-channel antenna and the radiation source target are R1, R2, and R3 respectively, and the distance between the radiation source target and the aircraft's flight path is R0. The relationship between R1, R2, R3, and R0 is shown in formulas (1) and (2).

[0047]

[0048] Wherein: the flight speed of the airplane is v, the baseline length of the antenna 1 and the antenna 2 is d 12 , the baseline length of the antenna 1 and the antenna 3 is d 13 , the zero Doppler moment is t p ;

[0049] The Doppler signals r1(t), r2(t) and r3(t) obtained after the baseband demodulation processing of the antenna 1, 2 and 3 in step one are expressed as:

[0050]

[0051] Wherein, f0 is the carrier frequency of the radiation source, c is the speed of light, and f1 is the residual frequency offset;

[0052] The R1, R2 and R3 are respectively expanded to the quadratic term at t=t p , and by using the Taylor formula, and there are

[0053]

[0054] Wherein, is the time delay corresponding to the baseline length of the antenna 1 and the antenna 2 and the flight speed of the airplane, is the time delay corresponding to the baseline length of the antenna 1 and the antenna 3 and the flight speed of the airplane.

[0055] Step two, the time delay is calculated according to the flight speed of the airplane and the baseline length of the antenna 1 and the antenna 2, and the phase compensation is performed on r1(t), and the compensated signal is expressed as

[0056]

[0057] Step three, the interference processing result is obtained by conjugate multiplication of the compensated signal r'1(t) of channel one and the Doppler signal r2(t) of channel two:

[0058]

[0059] Step four, as shown in formula (12), the corresponding relationship between the residual frequency offset and the interference phase is

[0060]

[0061] Wherein, is the interference phase of channel one and channel two after phase compensation.

[0062] Since the range of the interference phase is (-π, π), the unambiguous range of the frequency offset measured in step four is

[0063] Step 5: Calculate the time delay based on the aircraft's flight speed and the baseline lengths of antenna 1 and antenna 3, and perform phase compensation on r1(t). The compensated signal is expressed as

[0064]

[0065] Step 6: Conjugate multiply the compensated signal r1″(t) of channel 1 with the Doppler signal r3(t) of channel 3 to obtain the interference processing result:

[0066]

[0067] Step 7: As shown in formula (15), the corresponding relationship between the residual frequency offset and the interference phase is:

[0068]

[0069] in, is the interference phase between channel 1 and channel 3 after phase compensation.

[0070] Since the range of the interference phase is (-π,π), the unambiguous range of the frequency deviation measurement in step 4 is

[0071] Step 8: Deambiguate the long baseline measurement result f1″ based on the short baseline measurement result f′1 to obtain a frequency offset estimation result.

[0072] Example 2:

[0073] like Figure 1 As shown, the present embodiment discloses a residual frequency offset estimation method based on multi-channel along-track interference, and the specific implementation steps are as follows:

[0074] Assume that the drone is flying in a straight line at a constant speed v of 15m / s and a flight altitude of 500 meters. The carrier frequency f0 of the radiation source is 5GHz, and the distance R0 from the radiation source to the drone's flight path is 10km. Taking three-channel down-track interferometry as an example, three detection antennas are arranged in front and behind along the flight direction. Antenna A1 and antenna A2 form a short baseline with a baseline length d 12 is 0.05m, antenna A1 and antenna A3 form a long baseline, the baseline length d 13 is 0.3m, and the residual frequency deviation is set to 218.64Hz. The geometric model is as follows Figure 2 shown.

[0075] Step 1: The three antennas passively receive the signal emitted by the radiation source target, down-convert the received signal to obtain a baseband signal; and demodulate the baseband signal to obtain a corresponding Doppler signal.

[0076] Assume that the instantaneous distances between the aircraft's three-channel antenna and the radiation source target are R1, R2, and R3 respectively, and the distance between the radiation source target and the aircraft's flight path is R0. The relationship between R1, R2, R3, and R0 is shown in formulas (1) and (2).

[0077]

[0078] Where: the aircraft's flight speed is v, and the baseline length between antenna 1 and antenna 2 is d 12 , the baseline length between antenna 1 and antenna 3 is d 13 , the zero Doppler moment is the azimuth time t p ;

[0079] The Doppler signals r1(t), r2(t), and r3(t) obtained after baseband demodulation processing of antennas 1, 2, and 3 in step 1 are expressed as:

[0080]

[0081]

[0082] Where f0 is the carrier frequency of the radiation source, c is the speed of light, and f1 is the residual frequency deviation;

[0083] Use Taylor's formula to change R1, R2 and R3 at t=t p 、 and Expanding to the quadratic term, we have

[0084]

[0085] in, is the time delay between the baseline length of antenna 1 and antenna 2 and the aircraft speed, is the time delay corresponding to the baseline length of antenna 1 and antenna 3 and the aircraft speed.

[0086] Step 2: Calculate the time delay based on the aircraft's flight speed and the baseline lengths of antenna 1 and antenna 2, and perform phase compensation on r1(t). The compensated signal is expressed as

[0087]

[0088] Step 3: Conjugate multiply the compensated signal r′1(t) of channel 1 with the Doppler signal r2(t) of channel 2 to obtain the interference processing result:

[0089]

[0090] Step 4: As shown in formula (12), the corresponding relationship between the residual frequency offset and the interference phase is:

[0091]

[0092] in, is the interference phase between channel 1 and channel 2 after phase compensation.

[0093] Since the range of the interference phase is (-π,π), the unambiguous range of the frequency offset measurement in step 4 is In this embodiment, the time delay t between antenna A1 and antenna A2 over the same slant distance is 12 The unambiguous range of frequency deviation measurement is (-250, 250) Hz. The mean value is -2.6504rad. According to formula (12), the residual frequency offset estimation result f′1 is 210.9134Hz.

[0094] Step 5: Calculate the time delay based on the aircraft's flight speed and the baseline lengths of antenna 1 and antenna 3, and perform phase compensation on r1(t). The compensated signal is expressed as

[0095]

[0096] Step 6: Conjugate multiply the compensated signal r1″(t) of channel 1 with the Doppler signal r3(t) of channel 3 to obtain the interference processing result:

[0097]

[0098] Step 7: As shown in formula (12), the corresponding relationship between the residual frequency offset and the interference phase is:

[0099]

[0100] in, is the interference phase between channel 1 and channel 3 after phase compensation.

[0101] Since the range of the interference phase is (-π,π), the unambiguous range of the frequency offset measurement in step 4 is In this embodiment, the time delay t between antenna A1 and antenna A3 over the same slant distance is 13 The unambiguous range of frequency deviation measurement is (-41.6667, 41.6667) Hz. The mean value is 2.3604 rad. According to formula (12), the residual frequency offset estimation result f1″ is -31.3052 Hz.

[0102] Step 8: Defuzzify the long baseline measurement result f1″ based on the short baseline measurement result f′1 to obtain a frequency offset estimation result. In this embodiment, the fuzzy number is 6, and the final estimation result is 218.6948 Hz.

[0103] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0104] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0105] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0106] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0107] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

[0108] Many other changes and modifications can be made without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A residual frequency offset estimation method based on multi-channel along-track interferometry, characterized in that: The method comprises: S1: Down-convert and de-modulate the received signals of multiple channels to obtain the corresponding Doppler signals; S2: Calculate the time delay between channels for the same slant range based on the platform flight speed and antenna baseline; S3: Perform phase compensation on the Doppler signals of different channels based on the calculated time delay to eliminate the phase deviation caused by the distance difference between antennas; S4: Interference processing is performed on the signals from different channels, and the interference phase is obtained by conjugate multiplication. Based on the relationship between the interference phase and the residual frequency offset, the short baseline and long baseline frequency offset values ​​are preliminarily estimated. The long baseline estimation result is defuzzified based on the short baseline estimation result to obtain the final estimation result. The step S1 specifically includes: A three-channel along-track interferometer is used, with three detection antennas arranged in front and behind along the flight direction. Antenna 1 and antenna 2 form a short baseline, and antenna 1 and antenna 3 form a long baseline. The antenna passively receives the signal emitted by the radiation source target, down-converts the received signal to obtain the baseband signal, and demodulates the baseband signal to obtain the corresponding Doppler signal. Assume that the instantaneous distances between the aircraft's three-channel antenna and the radiation source target are R1, R2, and R3 respectively, and the distance between the radiation source target and the aircraft's flight path is R0. The relationship between R1, R2, R3, and R0 is shown in formulas (1) and (2). Where: the aircraft's flight speed is v, and the baseline length between antenna 1 and antenna 2 is d 12 , the baseline length between antenna 1 and antenna 3 is d 13 , the zero Doppler moment is the azimuth time t p ; The Doppler signals r1(t), r2(t), and r3(t) obtained after baseband demodulation processing of antennas 1, 2, and 3 are expressed as: Where f0 is the carrier frequency of the radiation source, c is the speed of light, and f1 is the residual frequency deviation; The short baseline compensation step S3 specifically includes: The time delay is calculated based on the aircraft's flight speed and the baseline length between antenna 1 and antenna 2, and phase compensation is performed on r1(t). The compensated signal is expressed as: The step S4 specifically includes: Short baseline interferometry processing: multiply the compensated signal r1′(t) by the conjugate of the signal r2(t) from antenna 2 to calculate the interference result I 12 , and extract the interference phase Short baseline frequency offset estimation: using interferometric phase and t 12 The relationship between the short baseline frequency offset f1′ is estimated, and its unambiguous range is: Long baseline compensation: Perform long baseline compensation on the signal of antenna 1 to obtain r1″(t); Long baseline interferometry processing: multiply the compensated signal r1″(t) by the conjugate of the signal r3(t) from antenna 3 to calculate the interference result I 13 , and extract the interference phase Long baseline frequency offset estimation: using interferometric phase and t 13 The relationship between the long baseline frequency offset f1″ is estimated, and its unambiguous range is: Frequency offset deambiguation: The long baseline result f1″ is deambiguated using the short baseline result f1′ to obtain the final residual frequency offset estimate.

2. The residual frequency offset estimation method based on multi-channel along-track interferometry according to claim 1, characterized in that: The step S2 specifically includes: Taylor’s formula is used to calculate the instantaneous distances between the aircraft’s three-channel antenna and the radiation source target as R1, R2, and R3 at t=t p 、 and Expanding to the quadratic term, we have: in, is the time delay between the baseline length of antenna 1 and antenna 2 and the aircraft speed, is the time delay corresponding to the baseline length of antenna 1 and antenna 3 and the aircraft speed.

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