Satellite communication adaptive coding and modulation method based on link quality estimation

Abstract

This invention provides an adaptive coding and modulation method for satellite communication based on link quality estimation, relating to the field of satellite communication. The method includes the following steps: Step S1: The transmitter generates and transmits a physical layer frame containing a pilot sequence; the receiver receives the physical layer frame and extracts the pilot sequence from it, estimating the mean and variance of the channel signal-to-noise ratio (SNR) based on the extracted and transmitted pilot sequences; Step S2: Based on the mean and variance of the channel SNR estimated in Step S1, the receiver queries a preset joint decision table to determine the coding and modulation scheme and pilot insertion frequency for the next frame, and feeds this information back to the transmitter to adjust the transmission strategy. This invention achieves optimal combined system throughput and reliability performance even when the channel state changes rapidly.

Description

Technical Field

[0001] This invention relates to the field of satellite communications, and in particular to an adaptive coding and modulation method for satellite communications based on link quality estimation. Background Technology

[0002] Satellite communication, as an indispensable supplement and extension to terrestrial communication networks, plays a crucial role in long-distance communication, emergency communication, the Internet of Things (IoT), and global mobile connectivity due to its wide coverage and lack of geographical limitations. However, satellite channels, especially mobile communication channels, exhibit significant time-varying fading characteristics. Their signal transmission quality is severely affected by various factors, including weather conditions (such as rain attenuation), shadowing effects, Doppler shift, and rapid channel changes caused by high-speed satellite movement. These factors lead to drastic fluctuations in channel link quality, posing a serious challenge to the reliability and effectiveness of satellite communication.

[0003] While traditional fixed coding and modulation schemes have lower system complexity, they also have lower efficiency. For example, if the coding and modulation scheme is designed based on the worst channel quality and reserves sufficient link margin, when the channel quality is good, the fixed coding and modulation scheme will not be able to fully utilize the ample link budget, resulting in low spectral efficiency and wasted channel resources, thus affecting the average throughput of the system. Conversely, if the optimal channel quality is used as the benchmark to maximize information transmission, when the channel quality is poor, the fixed coding and modulation scheme will produce a high bit error rate, thus affecting the reliability of the system.

[0004] To address the incomplete adaptability of inherent coding and modulation schemes under different channel environments, adaptive coding and modulation (CCDM) technology has emerged and become a key technology for improving communication system performance. Specifically, this technology measures and estimates the channel link quality at the receiver and feeds the estimated link quality back to the transmitter. The transmitter then selects an appropriate equal-transmission strategy based on the channel link quality information transmitted from the receiver, thereby achieving optimal combined system throughput and reliability. However, traditional adaptive coding and modulation schemes select the coding and modulation scheme only based on the current channel state during the link performance evaluation phase, without fully considering the degree of channel variation. Therefore, their efficiency is low in scenarios with rapid and drastic changes in channel quality. Summary of the Invention

[0005] The main objective of this invention is to propose an adaptive coding and modulation method for satellite communication based on link quality estimation, which can still achieve optimal combined performance of system throughput and reliability when the channel state changes rapidly.

[0006] This invention is achieved through the following technical solution:

[0007] The adaptive coding and modulation method for satellite communication based on link quality estimation includes the following steps:

[0008] Step S1: The transmitting end generates and sends a physical layer frame containing a pilot sequence. The receiving end receives the physical layer frame and extracts the pilot sequence from it. Based on the extracted pilot sequence and the sent pilot sequence, the mean and variance of the channel signal-to-noise ratio are estimated.

[0009] Step S2: Based on the mean and variance of the channel signal-to-noise ratio estimated in step S1, the receiver queries the preset joint decision table to determine the coding and modulation scheme and pilot insertion frequency to be used in the next frame, and feeds it back to the transmitter to adjust the transmission strategy.

[0010] Furthermore, step S1 specifically includes the following steps:

[0011] Step S11: The transmitter performs BCH and LDPC encoding and bit interleaving on the baseband signal, uses MAPSK modulation for constellation mapping, generates an encoded modulation frame, and inserts a pilot sequence and frame header to form a physical layer frame. The pilot sequence uses QPSK modulation.

[0012] Step S12: The receiving end identifies and parses the frame header to extract the pilot sequence;

[0013] Step S13: Calculate the error vector magnitude EVM of each pair of pilot symbols in the extracted pilot sequence and the transmitted pilot sequence, based on the relationship... Determine the channel signal-to-noise ratio (SNR) corresponding to each pair of pilot symbols, and then obtain the mean and variance of the channel SNR within the time period corresponding to the extracted pilot sequence.

[0014] Furthermore, in step S1, the MAPSK modulation specifically includes four modulation orders: QPSK, 8PSK, 16APSK, and 32APSK. Each modulation order is combined with multiple LDPC code rates to form multiple coding modulation schemes formed by the combination of adjustment order and LDPC code rate.

[0015] Furthermore, in step S2, the joint decision table includes pilot insertion modes, which include sparse mode, standard density mode, high density mode, and ultra-high density mode. The pilot insertion mode is determined based on the channel fluctuation level, which is based on the average channel signal-to-noise ratio. with standard deviation Sure.

[0016] Furthermore, in step S2, based on the estimated mean channel signal-to-noise ratio... with standard deviation Calculate the first confidence interval Second confidence interval The channel fluctuation level is determined based on the relationship between the first confidence interval, the second confidence interval, and the mode interval. Each coding and modulation scheme has a corresponding mode interval.

[0017] Furthermore, in step S2, when the second confidence interval... When the channel fluctuation level is within the mode interval, it is at a stable level, and a sparse pilot insertion mode is used; when the second confidence interval... Not located in the pattern interval and first confidence interval When within the mode range, the channel fluctuation level is slight fluctuation, and the standard pilot insertion mode is used; when Less than the lower bound of the mode interval and When the channel fluctuation level is less than the upper limit of the mode interval, the channel fluctuation level is the first moderate fluctuation level, and a high-density pilot insertion mode is adopted; when Greater than the lower bound of the pattern interval and When the channel fluctuation level is less than the upper limit of the mode interval, the channel fluctuation level is the second moderate fluctuation level, and a high-density pilot insertion mode is adopted; when Less than the lower bound of the mode interval and When the channel fluctuation level is greater than the upper limit of the mode range, the channel fluctuation level is classified as severe fluctuation, and an ultra-high density pilot insertion mode is adopted.

[0018] Furthermore, the sparse mode refers to inserting one pilot symbol every 32 time slots, the standard density mode refers to inserting one pilot symbol every 16 time slots, the high density mode refers to inserting one pilot symbol every 8 time slots, and the ultra-high density mode refers to inserting one pilot symbol every 4 time slots.

[0019] Furthermore, for each coding and modulation scheme, the system bit error rate and the number of LDPC decoding iterations are set, and simulations are performed to obtain the corresponding mode ranges.

[0020] Furthermore, the frame header includes a frame start flag, modulation scheme, and LDPC code rate.

[0021] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention generates and transmits physical layer frames containing pilot sequences at the transmitting end, and the receiving end receives the physical layer frames and extracts the pilot sequences from them. Based on the extracted and transmitted pilot sequences, the receiving end estimates the mean and variance of the channel signal-to-noise ratio (SNR). Using the estimated SNR mean and variance, the receiving end queries a preset joint decision table to determine the coding and modulation scheme and pilot insertion method for the next frame, and feeds this information back to the transmitting end to adjust the transmission strategy. This achieves real-time adjustment of the signal transmission method according to the channel state, improving transmission performance. The invention utilizes the mean and variance of the channel ratio to provide a more detailed classification of the coding and modulation scheme, offering a more detailed description of the channel state compared to existing single SNR-adaptive coding and modulation strategy mapping. Dynamically adjusting the pilot insertion frequency reduces pilot overhead and increases information throughput when the channel state is stable. When the channel state changes rapidly, the invention utilizes more pilot sequences to make the satellite communication link quality assessment more accurate, thereby improving the effectiveness of the adaptive coding and modulation strategy and reducing the bit error rate. In summary, the present invention achieves optimal combined system throughput and reliability performance even when the channel state changes rapidly. Attached Figure Description

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 This is a flowchart of the present invention.

[0025] Figure 2 This is a detailed flowchart of the present invention.

[0026] Figure 3 This is a schematic diagram of the FECFRAME frame structure of the present invention.

[0027] Figure 4 This is a schematic diagram of bit interleaving in this invention.

[0028] Figure 5 This is the MAPSK constellation diagram of the present invention.

[0029] Figure 6 This is a schematic diagram of the transmitter frame structure of the present invention.

[0030] Figure 7 This is a comparison chart of the overhead of four pilot insertion modes.

[0031] Figure 8 This is a comparison graph showing the spectral efficiency of the present invention and the comparative method under different channel conditions over time. Detailed Implementation

[0032] The present invention will be further described below through specific embodiments.

[0033] like Figure 1 and Figure 2As shown, the adaptive coding and modulation method for satellite communication based on link quality estimation includes the following steps:

[0034] Step S1: The transmitting end generates and sends a physical layer frame containing a pilot sequence. The receiving end receives the physical layer frame and extracts the pilot sequence from it. Based on the extracted pilot sequence and the sent pilot sequence, the mean and variance of the channel signal-to-noise ratio are estimated.

[0035] Specifically, the steps include the following:

[0036] Step S11: The transmitting end performs BCH and LDPC encoding on the baseband signal (BBFRAME) using the encoding and modulation scheme agreed upon by both the transmitting and receiving parties. The encoded frame is the FECFRAME, and its frame structure is as follows: Figure 3 As shown in Table 1, the FECFRAME parameters are displayed for different LDPC bitrates (taking a FECFRAME length of 64800 as an example):

[0037] Table 1

[0038]

[0039] The FECFRAME encoded by LDPC requires bit interleaving and constellation mapping. For the bit interleaving process, please refer to [link to documentation]. Figure 4 , Figure 4 This diagram illustrates bit interleaving with a FECFRAME length of 64800 bits and an 8PSK modulation scheme. First, the 64800-bit frame sequence is written column-wise and divided into three columns. Next, it is read row-wise, i.e., 3 bits of information are read at a time. The constellation mapping process maps the sequentially read 3 bits of information onto a constellation diagram. The frame after constellation mapping is denoted as XFECFRAME. MAPSK modulation is used for constellation mapping. MAPSK modulation specifically includes four modulation orders: QPSK, 8PSK, 16APSK, and 32APSK, and their respective constellation diagrams are shown below. Figure 5 As shown, each modulation order is combined with multiple LDPC code rates to form various coding and modulation schemes formed by the combination of modulation order and LDPC code rate.

[0040] Taking a FECFRAME length of 64800 as an example, Table 2 shows the structure of the bit interleaver under different constellation mapping methods.

[0041] Table 2

[0042]

[0043] XFECFRAME obtains PLFRAME by adding pilots and a frame header. The pilot sequence is a crucial part of the subsequent channel quality assessment at the receiver. The pilot signal is modulated using QPSK and includes a unique word of length 16 and a fixed symbol of length 20, represented as follows: ,in, This represents a set of pilot signals with a length of 36, arranged cyclically by four constellation points. The frame header contains frame information such as the start-of-frame marker, modulation scheme, and LDPC code rate, used for frame synchronization, demodulation, and other operations at the receiver. Figure 6 The diagram shown is a schematic of the frame structure transmitted by the transmitter.

[0044] Step S12: The receiving end identifies and parses the frame header to extract the pilot sequence;

[0045] Specifically, the receiving end identifies the start position of each frame by recognizing the frame header information, and obtains the corresponding pilot sequence and data sequence;

[0046] Step S13: In addition to demodulating the data signal, the receiving end also needs to calculate the error vector magnitude (EVM) of each pair of pilot symbols in the extracted pilot sequence and the transmitted pilot sequence, based on the relationship... The channel signal-to-noise ratio (SNR) corresponding to each pair of pilot symbols is determined, and then the mean and variance of the channel SNR within the corresponding time period of the extracted pilot sequence are obtained. , This is the extracted pilot signal.

[0047] According to the formula respectively and Calculate the mean of the channel signal-to-noise ratio. With variance , This represents the signal-to-noise ratio measured for each pilot symbol, where n is the number of pilot signals contained in the pilot sequence.

[0048] Step S2: Based on the mean and variance of the channel signal-to-noise ratio estimated in step S1, the receiver queries the preset joint decision table to determine the coding and modulation scheme and pilot insertion frequency to be used in the next frame, and feeds it back to the transmitter to adjust the transmission strategy.

[0049] For each coding and modulation scheme, the system bit error rate is set to 1×10. -4 The number of LDPC decoding iterations (50 times) is used to simulate and obtain the corresponding mode intervals. This process is existing technology. In this embodiment, each coding and modulation scheme (including modulation order and LDPC code rate) and its corresponding mode intervals are shown in Table 3:

[0050] Table 3

[0051]

[0052] For each channel signal-to-noise ratio (SNR), the corresponding mode interval can be found in Table 3. Based on the estimated mean channel SNR... with standard deviation Calculate the first confidence interval Second confidence interval Based on the relationship between the first confidence interval, the second confidence interval, and the mode interval, the channel fluctuation level is determined, and then the pilot insertion mode is determined. Each coding and modulation scheme has a corresponding mode interval. The pilot insertion modes include sparse mode (SM mode), standard density mode (SD mode), high density mode (HD mode), and ultra-high density mode (UHD mode).

[0053] Specifically, as shown in Table 4, the channel condition is divided into five levels according to the interval hierarchy. When the second confidence interval... When the channel fluctuation level is within the mode interval, it is at a stable level, and a sparse pilot insertion mode is used; when the second confidence interval... Not located in the pattern interval and first confidence interval When within the mode range, the channel fluctuation level is slight fluctuation, and the standard pilot insertion mode is used; when Less than the lower bound of the mode interval and When the channel fluctuation level is less than the upper limit of the mode interval, the channel fluctuation level is the first moderate fluctuation level, and a high-density pilot insertion mode is adopted; when Greater than the lower bound of the pattern interval and When the channel fluctuation level is less than the upper limit of the mode interval, the channel fluctuation level is the second moderate fluctuation level, and a high-density pilot insertion mode is adopted; when Less than the lower bound of the mode interval and When the channel fluctuation level is greater than the upper limit of the mode range, the channel fluctuation level is classified as severe fluctuation, and an ultra-high density pilot insertion mode is adopted.

[0054] Sparse mode inserts one pilot symbol every 32 time slots, standard density mode inserts one pilot symbol every 16 time slots, high-density mode inserts one pilot symbol every 8 time slots, and ultra-high-density mode inserts one pilot symbol every 4 time slots. The lower the inserted pilot frequency, the lower the pilot overhead. When sparse mode is used, the pilot overhead is only 1.23%; while when ultra-high-density mode is used, the pilot overhead reaches 9.09%. Figure 7 The diagram shows a comparison of the overhead of four pilot insertion modes.

[0055] Table 4

[0056]

[0057] To make the decision rules in Table 4 more intuitive, several examples are given below. Assume the measurement result is... According to Table 3, the signal strength falls within the mode range corresponding to 8PSK 5 / 6, ranging from 8.63 to 10.02 dB. The range is (8.8, 9.2), which is within 8.63~10.02dB, therefore it belongs to level 1, that is, the channel is relatively stable;

[0058] Assume the measurement result is According to Table 3, it is located at 8PSK 5 / 6 gear, with a range of 8.63~10.02dB. At this time... The range is (8.6, 9.4), not entirely within the range of 8.63~10.02dB; The range is (8.8, 9.2), which is within 8.63~10.02dB, therefore it belongs to level 2, that is, slight channel fluctuation;

[0059] Assume the measurement result is According to Table 3, it is located at 8PSK 5 / 6 gear, with a range of 8.63~10.02dB. At this time... The interval is (8.6, 9.4). Less than the lower bound of the pattern interval, 8.63. The value is less than the upper limit of the mode range of 10.02. In other words, the minimum value exceeds the gear level, so it belongs to level 3, which is the first level of moderate fluctuation. Therefore, it is necessary to reduce the gear level by one level, that is, to use the 8PSK 3 / 4 modulation mode.

[0060] Assume the measurement result is According to Table 3, it is located at 8PSK 5 / 6 gear, with a range of 8.63~10.02dB. At this time... The interval is (9.4, 10.2). Greater than the lower bound of the pattern interval, 8.63. The value is greater than the upper limit of the mode range of 10.02. In other words, the maximum value exceeds the level, so it belongs to level 4, which is the second moderate fluctuation. Therefore, it is necessary to increase the level by one level, that is, to use the 8PSK 8 / 9 modulation mode.

[0061] Assume the measurement result is According to Table 3, it is located at 8PSK 5 / 6 gear, with a range of 8.63~10.02dB. At this time... The interval is (8.2, 10.2). Less than the lower bound of the pattern interval, 8.63. The value is greater than the upper limit of the mode range by 10.02. In other words, both the minimum and maximum values ​​have exceeded the gear level, so it belongs to level 5, which is severe fluctuation. Therefore, it is necessary to keep the gear level unchanged and use the highest density pilot insertion frequency to detect possible sudden changes in the channel.

[0062] In summary, the joint decision table, which includes the coding and modulation scheme and the pilot insertion mode, is shown in Table 5:

[0063] Table 5

[0064]

[0065] Assume the modulated signal data rate transmitted by the transmitter is Pilot overhead is (like Figure 8 , There are four possible values), the selected MAPSK order is M, and the LDPC bit error rate is... LDPC code rate Then the spectral efficiency of the system is... It can be represented as ,

[0066] The following simulation compares the performance differences between the present invention (as shown in Table 5) and the comparative method (as shown in Table 3, the adaptive modulation method that uses only the SNR value decision table) under different channel conditions.

[0067] First, assume that the system's unit time T is the length of one frame, and pre-set two signal-to-noise ratio standard deviation scenarios, namely... (The channel changes are not drastic, represented by case A) and (The channel changes drastically, referred to as case B); two signal-to-noise ratio (SNR) scenarios are preset for the first five time periods: one is that the SNR is 7dB for all five time periods (i.e., the SNR is stable, referred to as case C), and the other is that the SNR decision results for the five time periods are 7, 6, 7, 8, and 7dB respectively (i.e., the SNR fluctuates, referred to as case D).

[0068] Tables 6 and 7 show the modulation scheme selection of the present invention and the comparative method under different signal-to-noise ratios and variances:

[0069] Table 6

[0070]

[0071] Table 7

[0072]

[0073] Based on the simulation results of the bit error rate of the above coding and modulation schemes, the spectral efficiency of these coding and modulation schemes is given in Tables 8 and 9:

[0074] Table 8

[0075]

[0076] Table 9

[0077]

[0078] By combining the signal-to-noise ratio and its variance in pairs, simulations were performed on the four modes to obtain the simulation results as follows: Figure 8 As shown in the figure, this diagram illustrates the improvement in spectral efficiency of the adaptive modulation method employed in this invention compared to the adaptive modulation method utilizing only SNR under four different scenarios, as well as the change in spectral efficiency over time. For modes AC and AD, under relatively stable channel conditions, the adaptive strategy proposed in this invention reduces pilot overhead without changing the coding modulation method, thus theoretically increasing the system spectral efficiency slightly. Simulation results show that these two scenarios can increase spectral efficiency by approximately 1.3%. For modes BC and BD, when channel conditions change drastically, the adaptive strategy proposed in this invention makes a slight correction to the modulation method, keeping the bit error rate within a low range, thereby improving the system spectral efficiency to some extent. Simulation results show that these two scenarios can increase spectral efficiency by approximately 10%. In summary, the adaptive strategy proposed in this invention improves the system's spectral efficiency under different channel conditions, demonstrating the feasibility and effectiveness of the strategy.

[0079] This invention enables the formulation of refined joint adaptive coding and modulation strategies based on a comprehensive assessment of link quality, by evaluating the channel's signal-to-noise ratio (SNR) and variance. This invention innovatively constructs a multi-dimensional dynamic pilot switching strategy. The switching logic selects the modulation mode based on the channel SNR, changes the pilot insertion frequency based on the SNR variance, and fine-tunes the modulation mode. This avoids the shortcomings of most traditional adaptive coding and modulation mechanisms, which rely on overly simplistic link parameters and rigid, fixed pilot overhead, resulting in insufficient estimation accuracy in rapidly changing channels or information transmission efficiency loss in static channels. Therefore, this invention effectively improves the link robustness, spectrum utilization efficiency, and overall throughput of satellite communication systems in complex time-varying channels.

[0080] In this invention, the terms "first," "second," and "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. The use of terms such as "upper," "lower," "left," "right," "front," and "rear" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention, not to indicate or imply that the device referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the scope of protection of this invention. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0081] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0082] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A satellite communication adaptive coding and modulation method based on link quality estimation, characterized in that: Includes the following steps: Step S1: The transmitting end generates and sends a physical layer frame containing a pilot sequence. The receiving end receives the physical layer frame and extracts the pilot sequence from it. Based on the extracted pilot sequence and the sent pilot sequence, the mean and variance of the channel signal-to-noise ratio are estimated. Step S2: Based on the mean and variance of the channel signal-to-noise ratio estimated in step S1, the receiver queries the preset joint decision table to determine the coding and modulation scheme and pilot insertion frequency to be used in the next frame, and feeds it back to the transmitter to adjust the transmission strategy.

2. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 1, characterized in that: Step S1 specifically includes the following steps: Step S11: The transmitter performs BCH and LDPC encoding and bit interleaving on the baseband signal, uses MAPSK modulation for constellation mapping, generates an encoded modulation frame, and inserts a pilot sequence and frame header to form a physical layer frame. The pilot sequence uses QPSK modulation. Step S12: The receiving end identifies and parses the frame header to extract the pilot sequence; Step S13: Calculate the error vector magnitude EVM of each pair of pilot symbols in the extracted pilot sequence and the transmitted pilot sequence, based on the relationship... Determine the channel signal-to-noise ratio (SNR) corresponding to each pair of pilot symbols, and then obtain the mean and variance of the channel SNR within the time period corresponding to the extracted pilot sequence.

3. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 2, characterized in that: In step S1, the MAPSK modulation specifically includes four modulation orders: QPSK, 8PSK, 16APSK, and 32APSK. Each modulation order is combined with multiple LDPC code rates to form multiple coding modulation schemes formed by the combination of adjustment order and LDPC code rate.

4. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 3, characterized in that: In step S2, the joint decision table includes pilot insertion modes, which include sparse mode, standard density mode, high density mode, and ultra-high density mode. The pilot insertion mode is determined based on the channel fluctuation level, which is based on the average channel signal-to-noise ratio. with standard deviation Sure.

5. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 4, characterized in that: In step S2, based on the estimated mean channel signal-to-noise ratio... with standard deviation Calculate the first confidence interval Second confidence interval The channel fluctuation level is determined based on the relationship between the first confidence interval, the second confidence interval, and the mode interval. Each coding and modulation scheme has a corresponding mode interval.

6. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 5, characterized in that: In step S2, when the second confidence interval When the channel fluctuation level is within the mode interval, it is at a stable level, and a sparse pilot insertion mode is used; when the second confidence interval... Not located in the pattern interval and first confidence interval When within the mode range, the channel fluctuation level is slight fluctuation, and the standard pilot insertion mode is used; when Less than the lower bound of the mode interval and When the channel fluctuation level is less than the upper limit of the mode interval, the channel fluctuation level is the first moderate fluctuation level, and a high-density pilot insertion mode is adopted; when Greater than the lower bound of the pattern interval and When the channel fluctuation level is less than the upper limit of the mode interval, the channel fluctuation level is the second moderate fluctuation level, and a high-density pilot insertion mode is adopted; when Less than the lower bound of the mode interval and When the channel fluctuation level is greater than the upper limit of the mode range, the channel fluctuation level is classified as severe fluctuation, and an ultra-high density pilot insertion mode is adopted.

7. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 4, 5, or 6, characterized in that: The sparse mode refers to inserting one pilot symbol every 32 time slots, the standard density mode refers to inserting one pilot symbol every 16 time slots, the high density mode refers to inserting one pilot symbol every 8 time slots, and the ultra-high density mode refers to inserting one pilot symbol every 4 time slots.

8. The satellite communication adaptive coding and modulation method based on link quality estimation according to claim 5 or 6, characterized in that: For each coding and modulation scheme, the system bit error rate and the number of LDPC decoding iterations are set, and simulation is performed to obtain the corresponding mode range.

9. The satellite communication adaptive coding and modulation method based on link quality estimation according to any one of claims 2 to 5, characterized in that: The frame header includes a frame start flag, modulation scheme, and LDPC code rate.

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