Interpolation algorithm applied to chirp signal high-dynamic carrier synchronization frequency offset estimation

Abstract

The invention relates to the technical field of remote sensing satellite signals, in particular to an interpolation algorithm applied to chirp signal high-dynamic carrier synchronization frequency offset estimation, which is used for estimating positioning and frequency offset of near-orbit satellite signals by using chirp signals and helping to control the signal frequency offset within a smaller range. Therefore, the situation that the low-orbit satellite cannot be accessed due to abnormal signal sending power of the user terminal is effectively avoided, and the satellite resource utilization rate and the working efficiency are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of remote sensing satellite signals, and in particular to an interpolation algorithm applied to chirp signal high-dynamic carrier synchronization frequency deviation estimation. Background Art

[0002] Satellite navigation systems have the ability to provide high-precision positioning, speed measurement and timing services over a large range, all-weather and all-day, and have been widely used in various fields of national defense and national economy. With the increasing dependence on satellite navigation systems, competition in the field of satellite navigation will inevitably intensify. When the antenna is not aligned with the satellite signal, the satellite signal power received by the satellite will be weakened, which will affect the performance of the receiver.

[0003] Due to the high-speed movement of low-orbit satellites, the communication effect is seriously affected by the Doppler effect caused by the high-dynamic radial movement of the communicating parties. There is a large frequency offset in the received signals of low-orbit satellites and ground users. At the same time, the spatial distance between the satellite and the user is also changing in real time, causing the path loss to change, resulting in the signal power received by the satellite and the user also changing continuously. If the impact of Doppler frequency offset and power change on the signal spectrum quality cannot be effectively and timely reduced, it will cause signal deformation and distortion, resulting in the demodulator being unable to complete carrier synchronization, and users being unable to access the satellite and conduct business communications when the satellite is passing.

[0004] Chirp signal (linear frequency modulation signal) is a special signal with low power consumption, high receiving sensitivity, wide coverage, and support for ranging and positioning. It has the characteristics of linear increase or decrease of frequency over time, no need for time synchronization, and strong ability to resist Doppler frequency shift. In the existing technology, the positioning and frequency offset estimation of near-orbit satellite signals using chirp signals have not been applied.

[0005] Based on the above reasons, the present invention designs an interpolation algorithm for high-dynamic carrier synchronization frequency deviation estimation of chirp signals, which uses chirp signals to estimate the positioning and frequency deviation of low-orbit satellite signals, helping to control the signal frequency deviation within a smaller range, thereby effectively avoiding abnormal signal power sent by user terminals that lead to inability to access low-orbit satellites, thereby improving satellite resource utilization and work efficiency. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an interpolation algorithm for high-dynamic carrier synchronization frequency deviation estimation of chirp signals, which uses chirp signals to estimate the positioning and frequency deviation of low-orbit satellite signals, helping to control the signal frequency deviation within a smaller range, thereby effectively avoiding the user terminal from being unable to access the low-orbit satellite due to abnormal signal power transmission, thereby improving satellite resource utilization and work efficiency.

[0007] In order to achieve the above object, the present invention provides an interpolation algorithm for high dynamic carrier synchronization frequency offset estimation of chirp signal, comprising the following steps: S1, a certain section of the received satellite signal is multiplied by the conjugate of the sweep signal with positive slope and negative slope in the double chirp signal to perform unscanning, and two groups of signals are obtained, namely, positive slope and negative slope ; S2, perform fast Fourier transform (FFT) calculation on the two groups of signals obtained in S1 to obtain their peak values ​​and the corresponding mth group of frequency data and ; S3, receive the signal and extract a certain segment again, then multiply it with the conjugate of the double chirp signal again to unscan and obtain two groups of signals: and ; S4, the two groups of signals obtained in S3 are subjected to fast Fourier transform (FFT) calculation again to obtain their peak values ​​and corresponding frequencies and ; S5, judging whether the mth group obtains the chirp signal, using the characteristics of the chirp signal, that is, whether the frequencies corresponding to the two peaks of the mth group coincide, that is, = Whether it is established, and the constraint condition that the peak value of the mth group is higher than the peak value of the m+1th group is judged; if no signal is obtained, return to step S1; when returning to step S1, take a signal segment after a certain point in the original satellite signal that does not affect the interpolation, and so on; S6: If the peak value is obtained in step S5, the frequency deviation is calculated using the interpolation algorithm. The calculation formula is: ; in and They are the mth fast Fourier transform FFT calculations, that is, the peak corresponding frequency when the chirp signal is captured, and fd is the frequency offset.

[0008] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses chirp signals to estimate the positioning and frequency deviation of low-orbit satellite signals, helping to control the signal frequency deviation within a smaller range, thereby effectively avoiding the inability of user terminals to access low-orbit satellites due to abnormal signal power, thereby improving satellite resource utilization and work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Schematic diagram of the overall steps of the present invention; DETAILED DESCRIPTION

[0010] The present invention will now be further described with reference to the accompanying drawings. See also Figure 1 The present invention provides an interpolation algorithm for high dynamic carrier synchronization frequency offset estimation of chirp signals: The following steps are involved: Satellite signals are received by special equipment. The chirp signal is a signal we determine in advance. It is used to correlate with the chirp signal added to the satellite signal as positioning to identify the frequency offset and to calculate the frequency offset.

[0011] “Dual chirp signal” is an emphasis on the characteristics of the chirp signal, which means that the presence of two frequency change signals constitutes the chirp signal, and the present invention uses both of these signals.

[0012] S1, a certain section of the received satellite signal is multiplied by the conjugate of the sweep signal with positive slope and negative slope in the double chirp signal to perform unscanning, and two groups of signals are obtained, namely, positive slope and negative slope ; The signal obtained in S1 is a transformation of the satellite signal. The chirp signal is only a small segment of the satellite signal. Therefore, when using the chirp signal in the satellite signal for calculation, its position must be found first, which is also the process of solving the offset.

[0013] S2, perform fast Fourier transform (FFT) calculation on the two groups of signals obtained in S1 to obtain their peak values ​​and the corresponding mth group of frequency data and ; When calculating FFT, if you are using MATLAB software, you can directly use the FFT function in it. The number of points is required to be slightly larger than the total length of the chirp signal after sampling.

[0014] S3, receive the signal and extract a certain segment again, then multiply it with the conjugate of the double chirp signal again to unscan and obtain two groups of signals: and ; S4, the two groups of signals obtained in S3 are subjected to fast Fourier transform (FFT) calculation again to obtain their peak values ​​and corresponding frequencies and ; S5, judging whether the mth group obtains the chirp signal, using the characteristics of the chirp signal, that is, whether the frequencies corresponding to the two peaks of the mth group coincide, that is, = Whether it is established, and the constraint condition that the peak value of the mth group is higher than the peak value of the m+1th group is judged; if no signal is obtained, return to step S1; when returning to step S1, take a signal segment after a certain point in the original satellite signal that does not affect the interpolation, and so on; S6: If the peak value is obtained in step S5, the frequency deviation is calculated using the interpolation algorithm. The calculation formula is: ; The interpolation algorithm is mainly as follows: assuming that the peak value is obtained for the mth time, the frequencies of the mth and m+1th signal peaks are used for interpolation, rather than a single result. is an estimate of the approximate frequency deviation, The peak position details are fitted based on the frequency characteristics of the chirp signal.

[0015] in and They are the mth fast Fourier transform FFT calculations, that is, the peak corresponding frequency when the chirp signal is captured, and fd is the frequency offset.

[0016] The key to determining whether the chirp signal in the satellite is found is whether the FFT peak is found. Due to the characteristics of the chirp function, if the chirp signal is obtained and the FFT peak is obvious after the above operation, it can be determined whether the chirp signal is obtained by judging whether the peak value obtained this time is higher than the previous and subsequent peak values.

[0017] The above are only preferred embodiments of the present invention, which are only used to help understand the method and core idea of ​​the present application. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the idea of ​​the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention. The present invention solves the problems in the prior art that the communication effect is seriously affected by the Doppler effect caused by the high dynamic radial motion of the communicating parties, there is a large frequency offset in the received signals of the low-orbit satellite and the ground users, and the low power consumption, high receiving sensitivity, wide coverage and strong anti-Doppler frequency shift capability of the chirp signal are not fully utilized. The chirp signal is used to estimate the positioning and frequency deviation of the near-orbit satellite signal, which helps to control the signal frequency deviation within a smaller range, thereby effectively avoiding the abnormal signal power sent by the user terminal and causing the user terminal to be unable to access the low-orbit satellite, thereby improving the satellite resource utilization and work efficiency.

Claims

1. An interpolation algorithm for high dynamic carrier synchronization frequency offset estimation of chirp signals, characterized in that , including the following steps: S1, a certain section of the received satellite signal is multiplied by the conjugate of the sweep signal with positive slope and negative slope in the double chirp signal to perform unscanning, and two groups of signals are obtained, namely, positive slope and negative slope ; S2, performing fast Fourier transform (FFT) calculation on the two groups of signals obtained in S1 to obtain their peak values ​​and the corresponding mth group of frequency data and ; S3, receive the signal and extract a certain segment again, then multiply it with the conjugate of the double chirp signal again to unscan and obtain two groups of signals respectively and ; S4, performing fast Fourier transform (FFT) calculation on the two groups of signals obtained in S3 again to obtain their peak values ​​and corresponding frequencies and ; S5, judging whether the mth group obtains the chirp signal, using the characteristics of the chirp signal, that is, whether the frequencies corresponding to the two peaks of the mth group coincide, that is, = Whether it is established, and the constraint condition that the peak value of the mth group is higher than the peak value of the m+1th group is judged; if no signal is obtained, return to the step S1; when returning to the step S1, take a signal segment after a certain point in the original satellite signal that does not affect the interpolation, and so on; S6: If the peak value is obtained in step S5, the frequency deviation is calculated using an interpolation algorithm, and the calculation formula is: ;in and They are respectively the mth Fast Fourier Transform FFT calculations, that is, the peak corresponding frequency when the chirp signal is captured, and the fd is the frequency offset.

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