An Active Guidance Carrier Acquisition Method for Low Earth Orbit Constellations with Periodically Varying Power

Abstract

The present invention discloses a method for capturing an active guided carrier of a low-orbit constellation with periodic power changes, which relates to channel transmission technology in the field of low-orbit satellite communications. The low-orbit constellation moves at high speed, generating a Doppler effect and periodic changes in link level, which is reflected in the signal as a large frequency deviation and frequency deviation change rate, as well as a large level change at the receiving end. In particular, in the application scenario where beam hopping is used to expand the coverage of a point beam, the downlink guidance signal appears periodically. The present invention uses a preset power + scanning method to speed up the capture speed, and uses a C / N-based capture algorithm to improve the capture accuracy. The method adopted by the present invention is very effective for capturing a guided carrier that periodically resides in a beam hopping. It is particularly suitable for the design of low-orbit satellites that are resistant to high dynamics.

Description

Technical Field

[0001] The present invention relates to the field of physical layer channel transmission in the field of low-orbit satellite communications, and is particularly suitable for low-orbit satellite processing and anti-high dynamic transmission channel design. Specifically, it is a low-orbit constellation active guidance carrier capture method with periodic power changes. Background Art

[0002] In low-Earth orbit (LEO) satellite communication systems, the high speed of satellites creates a significant Doppler effect during communications. This makes communication extremely difficult, particularly for resource-constrained LEO satellite communication systems, directly leading to reduced system performance. Furthermore, fluctuations in received power can easily cause ground terminals to falsely acquire or even miss signals. To ensure reliable communication, it is necessary to analyze carrier acquisition methods within the visible range of satellites, under the influence of Doppler frequency deviation, its changing patterns, and periodic variations in signal power. This allows for proper demodulation between the satellite and the ground, improving communication quality.

[0003] Currently, various carrier acquisition methods for low-Earth orbit (LEO) satellite communication systems are under investigation, including phase-locked loop (PLL) methods, fast-changing Doppler frequency offset acquisition algorithms based on cyclic shifting of spectral lines, and automatic frequency control (AFC). However, these algorithms struggle with acquisition and tracking when the Doppler frequency offset is large or fluctuates rapidly. Furthermore, they fail to consider the impact of periodic variations in signal power. Furthermore, they increase resource usage and the cost of LEO payloads, making them less suitable for resource-constrained LEO payloads. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems mentioned in the background technology and propose a method for actively guiding carrier capture of a low-orbit constellation with periodic power changes.

[0005] The technical solution adopted in the present invention is:

[0006] A method for actively guiding carrier acquisition of a low-orbit constellation with periodically varying power includes the following implementation processes:

[0007] (1) After the low-orbit satellite communication system is started, it transmits an active pilot signal and a downlink TDM signal at a frequency preset by the system. The active pilot signal is a single-tone signal.

[0008] (2) The ground terminal presets the initial attenuation so that the ground terminal operates within the effective receiving signal level range;

[0009] (3) The ground terminal uses a fixed step search within the initial attenuation setting range;

[0010] (4) The ground terminal uses a C / N-based acquisition algorithm to capture the active guidance signal;

[0011] (5) If the ground terminal has not completed the capture of the active guidance signal, jump to step (2); if the ground terminal has completed the capture of the active guidance signal, recover the Doppler correction carrier and jump to step (6);

[0012] (6) The ground terminal uses the Doppler correction carrier obtained in step (5) to perform digital mixing with the downlink carrier to compensate for the Doppler frequency deviation and change rate in the downlink TDM signal;

[0013] (7) After eliminating the Doppler effect of the downlink TDM signal of the ground terminal, the downlink TDM signal is captured according to the frame structure and the frame sequence number and wave position number are analyzed;

[0014] (8) If the ground terminal has not completed the capture of the downlink TDM signal, it detects whether the active pilot signal has been captured. If the active pilot signal has not been captured, it jumps to step (2). If the active pilot signal has been captured, it adjusts the receiving attenuation value and jumps to step (6) until the downlink TDM signal is captured.

[0015] (9) After the ground terminal completes the capture of the downlink TDM signal, it counts the power value of the received signal;

[0016] (10) The ground terminal calculates the link level attenuation value based on the power value of the statistical signal;

[0017] (11) The ground terminal configures the link level attenuator and then returns to step (7).

[0018] Furthermore, the specific process of step (4) is as follows:

[0019] (401) The ground terminal performs power adjustment;

[0020] (402) digitally down-converting the ground terminal receiving signal to the receiving frequency of the active guidance signal;

[0021] (403) performing low-pass filtering on the received signal after frequency conversion, with the filter bandwidth being BW;

[0022] (404) performing CIC data extraction on the low-pass filtered data;

[0023] (405) storing the data extracted from the CIC;

[0024] (406) Performing N-point FFT on the stored data; N is a set value;

[0025] (407) Find the maximum address and calculate the active pilot signal power [Es] and noise power [En] in decibel units;

[0026] (408) Determine whether [En]-[Es]<A+B+[BW]-[Rb] is true in the decibel unit. If so, the capture of the active guidance signal is completed; if not, the capture of the active guidance signal is not completed; where A is the difference between the power of the active guidance signal transmitted by the low-orbit satellite and the power of the downlink TDM signal, B is the demodulation threshold of the downlink TDM signal, [BW] is the low-pass filter bandwidth, and [Rb] is the downlink TDM signal information rate.

[0027] The advantages of the present invention compared to the prior art are:

[0028] The method of the present invention performs multiple, accurate, and high-frequency measurements on active guidance signals sent from and to the satellite. This method is very effective for capturing periodic resident guidance carriers in beam hopping, and is particularly suitable for low-orbit satellite communication systems.

[0029] The method of the present invention has the characteristics of fast capture speed and high accuracy for the beam-hopping periodic resident guided carrier, thereby improving the high dynamic resistance capability of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the working principle of the present invention.

[0031] Figure 2 This is a flow chart of the active guidance signal capture of the present invention. DETAILED DESCRIPTION

[0032] Reference Figures 1 to 2In the present invention, the low-orbit satellite payload transmits active guidance signals and downlink TDM signals at a preset frequency and level, and the ground terminal receives the downlink TDM signal and measures the active guidance signal. First, the ground terminal scans within the range of ±5dB and 2.5dB step according to the received preset level reception value to capture the active guidance signal. If the capture is not completed, the active guidance signal is continuously scanned within the range of ±5dB and 2.5dB step of the preset level until the capture of the active guidance signal is completed. If the capture of the active guidance signal is completed, it is continuously detected whether the active guidance signal is captured; then, the measurement result of the active guidance signal generates a digital Doppler correction carrier and a Doppler compensation carrier to eliminate the Doppler effect of the downlink; secondly, based on According to the frame structure, the downlink TDM signal is captured, and the frame sequence number, wave position number and other information are parsed. If the downlink TDM signal is not captured, the active pilot signal is detected to see if it has been captured. If not, the receiving level is scanned again to complete the capture of the active pilot signal. If the active pilot signal is captured, the receiving level is fine-tuned to compensate for the downlink TDM signal until the downlink TDM signal is captured. Finally, the receiving levels of different wave positions with the same frame number are counted, and the maximum value is selected as the level value of the current wave position, and the attenuation value of the level attenuation register is calculated. Figure 1 The ground terminal implements the method for capturing active guidance signals as shown in Figure 2 shown.

[0033] The implementation process steps of the present invention are as follows:

[0034] (1) After the low-orbit satellite communication system is started, it transmits an active pilot signal and a downlink TDM signal at a frequency preset by the system. The active pilot signal is a single-tone signal.

[0035] (2) The ground terminal presets the initial attenuation so that the ground terminal operates within the effective receiving signal level range;

[0036] (3) The ground terminal searches within the range of ±5dB of the initial attenuation, with a search step of 2.5dB;

[0037] (4) The ground terminal uses a C / N-based acquisition algorithm to capture the active guidance signal. The specific implementation process is as follows: Figure 2 ;

[0038] ① The ground terminal adjusts the receiving attenuator to make the received signal power appropriate;

[0039] ② Down-convert the ground terminal receiving signal to the receiving frequency of the active guidance signal;

[0040] ③ To prevent spectrum aliasing in the frequency domain from affecting the FFT calculation results, the received signal after frequency conversion is low-pass filtered;

[0041] ④ Perform CIC data extraction on the low-pass filtered data to reduce the sampling rate and improve the FFT resolution;

[0042] ⑤Store and convert the clock of the data extracted by CIC to prepare for FFT;

[0043] ⑥ Perform N-point FFT on the stored data; N is the set value;

[0044] ⑦Find the maximum address and calculate the active pilot signal power Es and noise power En;

[0045] When data is expressed as data = i + j * q, then:

[0046] Active guidance signal power: Es = |i^2 + q^2 |max;

[0047] Noise power: En = ∑(i^2 + q^2) - Es;

[0048] Among them, i represents the real part, j represents the imaginary unit, q represents the imaginary part, and max represents the maximum value;

[0049] ⑧ Determine whether the active guidance signal is successfully captured. Determine the capture threshold based on the C / N algorithm and compare En / Es with the threshold to determine the capture result.

[0050] In the embodiment of the present invention, the measured downlink TDM signal information rate is determined to be Rb, the active pilot signal power is 16 dB lower than the downlink TDM signal power, and the low-pass filter bandwidth before the FFT is BW. When the downlink TDM signal Eb / N0 is required to be greater than 3 dB, then:

[0051] Eb / N0>10^0.3

[0052] Where: Eb is the signal power per bit, and N0 is the noise power spectral density.

[0053] When the active pilot signal power Es and noise power En are used to represent it, then:

[0054] [(Es / Rb)·10^1.6] / (En / BW)>10^0.3, that is:

[0055] En / Es <BW / Rb·10^1.3

[0056] When En / Es is less than the threshold BW / Rb·10^1.3, it is considered that the active guidance signal is captured.

[0057] (5) If the ground terminal has not completed the capture of the active guidance signal, jump to step (2); if the ground terminal has completed the capture of the active guidance signal, recover the Doppler correction carrier and jump to step (6);

[0058] (6) The ground terminal uses the Doppler correction carrier obtained in step (5) to perform digital mixing with the downlink carrier to compensate for the Doppler frequency deviation and change rate in the downlink TDM signal;

[0059] In this embodiment, the downlink TDM signal is subjected to Doppler elimination by digital mixing, and the carrier after elimination is:

[0060] y 消除 (t) = y(t)·x(t)

[0061] Where: x(t) is the Doppler-eliminated carrier, y(t) is the downlink TDM signal, and y 消除 (t) is the signal after Doppler correction.

[0062] (7) After the ground terminal eliminates the Doppler effect of the downlink TDM signal, it completes the downlink signal capture and analyzes the frame sequence number, wave position number and other information according to the frame structure;

[0063] (8) If the ground terminal has not completed the capture of the downlink TDM signal, it detects whether the active pilot signal has been captured. If the active pilot signal has not been captured, it jumps to step (2). If the active pilot signal has been captured, it adjusts the receiving attenuation value and jumps to step (6) until the downlink TDM signal is captured.

[0064] (9) After the ground terminal completes the capture of the downlink TDM signal, it counts the power value of the received signal;

[0065] (10) The ground terminal calculates the link level attenuation value based on the power value of the statistical signal;

[0066] (11) The ground terminal configures the link level attenuator and then returns to step (7).

Claims

1. A method for actively guiding carrier acquisition of a low-orbit constellation with periodic power changes, characterized in that: The implementation process includes the following: (1) After the low-orbit satellite communication system is started, it transmits an active pilot signal and a downlink TDM signal at a frequency preset by the system. The active pilot signal is a single-tone signal. (2) The ground terminal presets the initial attenuation so that the ground terminal operates within the effective receiving signal level range; (3) The ground terminal uses a fixed step search within the initial attenuation setting range; (4) The ground terminal uses a C / N-based acquisition algorithm to capture the active guidance signal; (5) If the ground terminal has not completed the capture of the active guidance signal, jump to step (2); if the ground terminal has completed the capture of the active guidance signal, recover the Doppler correction carrier and jump to step (6); (6) The ground terminal uses the Doppler correction carrier obtained in step (5) to perform digital mixing with the downlink carrier to compensate for the Doppler frequency deviation and change rate in the downlink TDM signal; (7) After eliminating the Doppler effect of the downlink TDM signal of the ground terminal, the downlink TDM signal is captured according to the frame structure and the frame sequence number and wave position number are analyzed; (8) If the ground terminal has not completed the capture of the downlink TDM signal, it detects whether the active pilot signal has been captured. If the active pilot signal has not been captured, it jumps to step (2). If the active pilot signal has been captured, it adjusts the receiving attenuation value and jumps to step (6) until the downlink TDM signal is captured. (9) After the ground terminal completes the capture of the downlink TDM signal, it counts the power value of the received signal; (10) The ground terminal calculates the link level attenuation value based on the power value of the statistical signal; (11) The ground terminal configures the link level attenuator and then returns to step (7).

2. The method for actively guiding carrier acquisition of a low-orbit constellation with periodic power variation according to claim 1, characterized in that: The specific process of step (4) is as follows: (401) The ground terminal performs power adjustment; (402) digitally down-converting the ground terminal receiving signal to the receiving frequency of the active guidance signal; (403) performing low-pass filtering on the received signal after frequency conversion, with the filter bandwidth being BW; (404) performing CIC data extraction on the low-pass filtered data; (405) storing the data extracted from the CIC; (406) Performing N-point FFT on the stored data; N is a set value; (407) Find the maximum address and calculate the active pilot signal power [Es] and noise power [En] in decibel units; (408) Determine whether [En]-[Es]<A+B+[BW]-[Rb] is true in the decibel unit. If so, the capture of the active guidance signal is completed; if not, the capture of the active guidance signal is not completed; where A is the difference between the power of the active guidance signal transmitted by the low-orbit satellite and the power of the downlink TDM signal, B is the demodulation threshold of the downlink TDM signal, [BW] is the low-pass filter bandwidth, and [Rb] is the downlink TDM signal information rate.

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