A ground terminal decision-based feeder link adaptive transmission method

Abstract

The present application relates to the field of satellite communication, and discloses a kind of based on ground terminal decision's feed link adaptive transmission method, it is related to the adaptive transform modulation coding mode of low-orbit satellite communication process feed link and the technology of adjusting uplink transmission power.The present application proposes to use ground feed terminal as the statistics, storage and decision center of channel state, according to the comparison of the signal-to-noise ratio of uplink and downlink, the receiving power of satellite-borne feed terminal and the set threshold, make uplink and downlink modulation coding mode, uplink transmission power adjustment decision, reduce the implementation difficulty of satellite-borne feed terminal, to adapt to the change of channel state in the process of low-orbit satellite motion, realize the maximization and optimization of channel capacity utilization.The present application is suitable for the transmission design of low-orbit satellite feed link.

Description

Technical Field

[0001] This invention relates to the field of satellite communication, and more particularly to an adaptive transmission method for power supply links based on ground terminal decisions in the field of low-Earth orbit satellite communication technology. Background Technology

[0002] The feeder link is a crucial component of low-Earth orbit (LEO) satellite communication systems. It primarily transmits user data received by the satellite to the ground, while simultaneously transmitting control commands and data from the ground to the satellite. The link's transmission capacity determines the final data transmission volume for the user. However, as the LEO satellite moves, the channel state changes with its trajectory. Clearly, a consistent communication method cannot fully utilize the feeder link's channel resources. Therefore, designing an adaptive transmission method for the feeder link becomes critical in the design of LEO satellite communication systems. Summary of the Invention

[0003] To avoid the problems mentioned in the background art, this invention proposes an adaptive transmission method for power supply links based on ground terminal decision-making.

[0004] The technical solution adopted in this invention is as follows:

[0005] An adaptive transmission method for power supply links based on ground terminal decision-making includes the following steps:

[0006] Uplink power supply link adaptive transmission method flow:

[0007] Step 101: Before the low-orbit satellite enters the station, the user selects the uplink control mode; when the uplink transmission power is controlled independently, the ground feeder terminal initializes the uplink transmission power; when the uplink modulation and coding mode is controlled independently, the ground feeder terminal initializes the uplink modulation and coding mode; when the uplink transmission power and uplink modulation and coding mode are jointly controlled, the ground feeder terminal initializes both the uplink modulation and coding mode and the uplink transmission power; after initialization, the ground feeder terminal sends the uplink feeder link signal.

[0008] Step 102: After the low-orbit satellite enters the station, the onboard power supply baseband platform adaptively demodulates the uplink power supply link signal, estimates the uplink received power and uplink signal-to-noise ratio, and then uses the estimation results to form a signaling frame, performs modulation and coding, and outputs the downlink power supply link signal.

[0009] Step 103: The ground feeder terminal receives the downlink feeder link signal, and after demodulation and decoding, extracts the uplink received power and uplink signal-to-noise ratio estimation results.

[0010] Step 104: The ground power supply terminal generates an uplink control decision based on the uplink control mode selected by the user, through the estimation results of uplink received power and uplink signal-to-noise ratio, and sends uplink power supply link signal; then returns to execute step 102.

[0011] Downlink feeder link adaptive transmission method flow:

[0012] Step 201: Before the low-orbit satellite enters the station, the ground feeder terminal initializes the downlink modulation and coding scheme and then sends the uplink feeder link signal.

[0013] Step 202: After the low-orbit satellite enters the station, the onboard power supply baseband platform receives the uplink power supply link signal, and after adaptive demodulation and decoding, extracts the downlink modulation and coding scheme, controls the downlink modulation and coding scheme, and sends the downlink power supply link signal.

[0014] Step 203: The ground feeder terminal receives the downlink feeder link signal, demodulates it, and estimates the downlink signal-to-noise ratio.

[0015] Step 204: After obtaining the downlink signal-to-noise ratio estimation result, the ground power supply terminal generates a control decision on the downlink modulation and coding scheme, forms a signaling frame, and sends the uplink power supply link signal; then it returns to execute step 202.

[0016] Furthermore, the uplink and downlink modulation and coding schemes are sorted from low to high according to the demodulation threshold to form a 0-N level modulation and coding scheme, and each modulation and coding scheme is set with an admission signal-to-noise ratio and an output signal-to-noise ratio; where N is the type of modulation and coding scheme, and the admission signal-to-noise ratio and output signal-to-noise ratio are set according to the demodulation threshold; during the initialization of steps 101 and 201, both the uplink and downlink modulation and coding schemes are initialized to the 0 level modulation and coding scheme.

[0017] Furthermore, in step 104, when the uplink transmit power is independently controlled, the uplink control decision is as follows:

[0018] 1) If the current uplink signal-to-noise ratio is less than the outgoing signal-to-noise ratio (SNR_OUT) of the current uplink modulation and coding scheme, proceed to step 2); otherwise, proceed to step 4.

[0019] 2) If the current uplink received power is less than the saturation power of the satellite-borne baseband platform, proceed to step 3); otherwise, proceed to step 6.

[0020] 3) Increase uplink transmission power by setting a step size;

[0021] 4) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 6); otherwise, proceed to step 5.

[0022] 5) Reduce uplink transmission power in set steps;

[0023] 6) Keep the uplink transmission power unchanged.

[0024] Furthermore, in step 104, when the uplink modulation and coding scheme is independently controlled, the uplink control decision is as follows:

[0025] 1) If the current uplink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current uplink modulation scheme, proceed to step 2); otherwise proceed to step 3).

[0026] 2) Adjust the uplink modulation and coding scheme to a lower-level modulation and coding scheme;

[0027] 3) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 4); otherwise, proceed to step 5.

[0028] 4) Keep the current uplink modulation and coding scheme unchanged;

[0029] 5) Adjust the uplink modulation and coding scheme to a higher-level modulation and coding scheme.

[0030] Furthermore, in step 104, when the uplink transmit power and uplink modulation and coding scheme are jointly controlled, the uplink control decision is as follows:

[0031] 1) If the current uplink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current uplink modulation mode, proceed to step 2); otherwise proceed to step 5.

[0032] 2) If the current uplink received power is less than the saturation power of the satellite-borne baseband platform, proceed to step 3); otherwise, proceed to step 4.

[0033] 3) Increase uplink transmission power by setting a step size;

[0034] 4) Adjust the uplink modulation and coding scheme to a lower-level modulation and coding scheme;

[0035] 5) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 6); otherwise, proceed to step 7.

[0036] 6) Keep the current uplink transmit power and uplink modulation and coding scheme unchanged;

[0037] 7) Adjust the uplink modulation coding scheme to a higher-level modulation coding scheme.

[0038] Furthermore, in step 204, the control decision for the downlink modulation and coding scheme is specifically as follows:

[0039] 1) If the current downlink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current downlink modulation scheme, proceed to step 2); otherwise, proceed to step 3).

[0040] 2) Adjust the downlink modulation and coding scheme to a lower-level modulation and coding scheme;

[0041] 3) If the current downlink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current downlink modulation and coding scheme, proceed to step 4); otherwise, proceed to step 5.

[0042] 4) Keep the current downlink modulation and coding scheme unchanged;

[0043] 5) Adjust the downlink modulation and coding scheme to a higher-level modulation and coding scheme.

[0044] The advantages of this invention compared to the prior art are:

[0045] This invention proposes using a ground-based power supply terminal as a statistical, storage, and decision-making center for channel status. Based on the comparison between the uplink and downlink signal-to-noise ratio, the received power of the satellite power supply terminal, and a set threshold, it makes decisions to adjust the uplink and downlink modulation and coding schemes and the uplink transmission power. This reduces the implementation difficulty of the satellite power supply baseband platform, adapts to the changes in channel status during the movement of low-Earth orbit satellites, and maximizes and optimizes the utilization of channel capacity. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the independent control of uplink transmission power in a low-orbit satellite-to-ground feeder link according to an embodiment of the present invention.

[0047] Figure 2 This is a flowchart illustrating the independent control of the uplink modulation and coding scheme for the low-orbit satellite-to-ground feeder link in an embodiment of the present invention.

[0048] Figure 3 This is a flowchart illustrating the joint control of uplink transmission power and uplink modulation and coding scheme for the low-orbit satellite-to-ground feeder link in an embodiment of the present invention.

[0049] Figure 4 This is a flowchart illustrating the control process of downlink modulation and coding scheme for the low-orbit satellite-to-ground feeder link according to an embodiment of the present invention. Detailed Implementation

[0050] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0051] This invention is based on a low-Earth orbit (LEO) satellite feed link FDMA mode communication system, which consists of an onboard feed baseband platform and a ground-based feed terminal. The onboard feed baseband platform has an uplink feed link adaptive demodulation function, extracting the uplink modulation and coding scheme from the feed link physical frame structure for uplink demodulation and decoding without additional configuration. It also has uplink received power and signal-to-noise ratio (SNR) estimation functions, and downlink modulation and coding scheme control command extraction functions. Furthermore, the onboard feed baseband platform also has a downlink feed link transmission function, capable of combining the uplink received power estimation and SNR results into a signaling frame, modulating it into a downlink feed link signal using the extracted downlink modulation and coding scheme, and transmitting it.

[0052] The ground-based power supply terminal possesses downlink power supply link adaptive demodulation functionality. It extracts the downlink modulation and coding scheme from the physical frame structure of the downlink power supply link transmission for demodulation and decoding, requiring no additional configuration. It also features downlink signal-to-noise ratio (SNR) estimation and uplink power supply link received power and SNR estimation result extraction. Furthermore, it has uplink power supply link transmission functionality, capable of converting downlink modulation and coding control commands into uplink signals via signaling frames according to user-defined uplink modulation and coding schemes. Finally, it possesses system adaptive transmission decision-making functionality, acting as the decision-making center for the entire system. It is responsible for collecting uplink and downlink power supply link SNR estimation results and uplink received power estimation results, and generating adjustment decisions for uplink transmit power, uplink modulation and coding scheme, and downlink modulation and coding scheme based on the power supply link adaptive transmission method described in this invention, thereby controlling the adaptive transmission of the uplink and downlink power supply links.

[0053] This invention discloses an adaptive transmission method for a feeder link based on ground terminal decision-making, comprising an uplink feeder link control method and a downlink feeder link control method. Uplink and downlink modulation and coding schemes are sorted from low to high (0, 1, 2, ..., N) according to demodulation thresholds (the lowest demodulation signal-to-noise ratio with zero bit error rate). Each modulation and coding scheme has a pre-set entry signal-to-noise ratio (2dB higher than the demodulation threshold) and a pre-set output signal-to-noise ratio (1dB higher than the demodulation threshold), which are stored in a table in the ground feeder terminal as the basis for the ground feeder terminal to make modulation and coding scheme decisions. At the factory, the spaceborne feeder baseband platform provides the ground feeder terminal with an optimal uplink transmit power and a saturation power for the spaceborne feeder baseband platform, which are stored in the ground feeder terminal as the basis for the ground feeder terminal to make uplink transmit power decisions.

[0054] The uplink power supply link adaptive transmission method process includes the following steps:

[0055] The user-selectable uplink control mode includes three types: independent control of uplink transmit power, independent control of uplink modulation and coding scheme, and joint control of uplink transmit power and uplink modulation and coding scheme.

[0056] like Figure 1 As shown, the uplink transmit power independent control includes the following steps:

[0057] Step 101: Before the low-orbit satellite enters the station, the ground feeder terminal initializes the uplink transmission power; after initialization, the ground feeder terminal controls the uplink transmission power to transmit the uplink feeder link signal.

[0058] Step 102: After the low-orbit satellite enters the station, the onboard power supply baseband platform adaptively demodulates the uplink power supply link signal, estimates the uplink received power and uplink signal-to-noise ratio, and then uses the estimation results to form a signaling frame, performs modulation and coding, and outputs the downlink power supply link signal.

[0059] Step 103: The ground feeder terminal receives the downlink feeder link signal, and after demodulation and decoding, extracts the uplink received power and uplink signal-to-noise ratio estimation results.

[0060] Step 104: The ground power supply terminal generates an uplink control decision based on the uplink control mode selected by the user, through the estimation results of uplink received power and uplink signal-to-noise ratio, and sends uplink power supply link signal; then returns to execute step 102.

[0061] The uplink control decision in this embodiment is as follows:

[0062] 1) If the current uplink signal-to-noise ratio is less than the outgoing signal-to-noise ratio (SNR_OUT) of the current uplink modulation and coding scheme, proceed to step 2); otherwise, proceed to step 4.

[0063] 2) If the current uplink received power is less than the saturation power of the satellite-borne baseband platform, proceed to step 3); otherwise, proceed to step 6.

[0064] 3) Increase uplink transmission power by 0.5dB / s (in adjustable steps);

[0065] 4) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 6); otherwise, proceed to step 5.

[0066] 5) Reduce uplink transmission power by 0.5 dB / s (in adjustable steps);

[0067] 6) Keep the uplink transmission power unchanged.

[0068] like Figure 2 As shown, the uplink modulation and coding scheme is independently controlled, including the following steps:

[0069] Step 101: Before the low-orbit satellite enters the station, the ground feeder terminal initializes the uplink modulation and coding scheme; after initialization, the ground feeder terminal controls the uplink transmission power to transmit the uplink feeder link signal.

[0070] Step 102: After the low-orbit satellite enters the station, the onboard power supply baseband platform adaptively demodulates the uplink power supply link signal, estimates the uplink received power and uplink signal-to-noise ratio, and then uses the estimation results to form a signaling frame, performs modulation and coding, and outputs the downlink power supply link signal.

[0071] Step 103: The ground feeder terminal receives the downlink feeder link signal, and after demodulation and decoding, extracts the uplink received power and uplink signal-to-noise ratio estimation results.

[0072] Step 104: The ground power supply terminal generates an uplink control decision based on the uplink control mode selected by the user, through the estimation results of uplink received power and uplink signal-to-noise ratio, and sends uplink power supply link signal; then returns to execute step 102.

[0073] The uplink control decision in this embodiment is as follows:

[0074] 1) If the current uplink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current uplink modulation scheme, proceed to step 2); otherwise proceed to step 3).

[0075] 2) Adjust the uplink modulation and coding scheme to a lower-level modulation and coding scheme;

[0076] 3) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 4); otherwise, proceed to step 5.

[0077] 4) Keep the current uplink modulation and coding scheme unchanged;

[0078] 5) Adjust the uplink modulation and coding scheme to a higher-level modulation and coding scheme.

[0079] like Figure 3 As shown, the joint control of uplink transmit power and uplink modulation and coding scheme includes the following steps:

[0080] Step 101: Before the low-orbit satellite enters the station, the ground feeder terminal initializes the uplink modulation and coding scheme and the uplink transmission power; after initialization, the ground feeder terminal controls the uplink transmission power to transmit the uplink feeder link signal.

[0081] Step 102: After the low-orbit satellite enters the station, the onboard power supply baseband platform adaptively demodulates the uplink power supply link signal, estimates the uplink received power and uplink signal-to-noise ratio, and then uses the estimation results to form a signaling frame, performs modulation and coding, and outputs the downlink power supply link signal.

[0082] Step 103: The ground feeder terminal receives the downlink feeder link signal, and after demodulation and decoding, extracts the uplink received power and uplink signal-to-noise ratio estimation results.

[0083] Step 104: The ground power supply terminal generates an uplink control decision based on the uplink control mode selected by the user, through the estimation results of uplink received power and uplink signal-to-noise ratio, and sends uplink power supply link signal; then returns to execute step 102.

[0084] The uplink control decision in this embodiment is as follows:

[0085] 1) If the current uplink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current uplink modulation mode, proceed to step 2); otherwise proceed to step 5.

[0086] 2) If the current uplink received power is less than the saturation power of the satellite-borne baseband platform, proceed to step 3); otherwise, proceed to step 4.

[0087] 3) Increase uplink transmission power by 0.5dB / s (in adjustable steps);

[0088] 4) Adjust the uplink modulation and coding scheme to a lower-level modulation and coding scheme;

[0089] 5) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 6); otherwise, proceed to step 7.

[0090] 6) Keep the current uplink transmit power and uplink modulation and coding scheme unchanged;

[0091] 7) Adjust the uplink modulation coding scheme to a higher-level modulation coding scheme.

[0092] like Figure 4 As shown, the adaptive transmission method for downlink feeder links includes the following steps:

[0093] Step 201: Before the low-orbit satellite enters the station, the ground feeder terminal initializes the downlink modulation and coding scheme and then sends the uplink feeder link signal.

[0094] Step 202: After the low-orbit satellite enters the station, the onboard power supply baseband platform receives the uplink power supply link signal, and after adaptive demodulation and decoding, extracts the downlink modulation and coding scheme, controls the downlink modulation and coding scheme, and sends the downlink power supply link signal.

[0095] Step 203: The ground feeder terminal receives the downlink feeder link signal, demodulates it, and estimates the downlink signal-to-noise ratio.

[0096] Step 204: After obtaining the downlink signal-to-noise ratio estimation result, the ground power supply terminal generates a control decision on the downlink modulation and coding scheme, forms a signaling frame, and sends the uplink power supply link signal; then it returns to execute step 202.

[0097] The control decisions for downlink modulation and coding schemes are as follows:

[0098] 1) If the current downlink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current downlink modulation scheme, proceed to step 2); otherwise, proceed to step 3).

[0099] 2) Adjust the downlink modulation and coding scheme to a lower-level modulation and coding scheme;

[0100] 3) If the current downlink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current downlink modulation and coding scheme, proceed to step 4); otherwise, proceed to step 5.

[0101] 4) Keep the current downlink modulation and coding scheme unchanged;

[0102] 5) Adjust the downlink modulation and coding scheme to a higher-level modulation and coding scheme.

Claims

1. A power supply link adaptive transmission method based on ground terminal decision-making, characterized in that, Includes the following processes: Uplink power supply link adaptive transmission method flow: Step 101: Before the low-orbit satellite enters the station, the user selects the uplink control mode; when the uplink transmission power is independently controlled, the ground feeder terminal initializes the uplink transmission power. When the uplink modulation and coding scheme is controlled independently, the ground feeder terminal initializes the uplink modulation and coding scheme; when the uplink transmit power and uplink modulation and coding scheme are jointly controlled, the ground feeder terminal initializes the uplink modulation and coding scheme and the uplink transmit power; after initialization, the ground feeder terminal transmits the uplink feeder link signal. Step 102: After the low-orbit satellite enters the station, the onboard power supply baseband platform performs adaptive demodulation on the uplink power supply link signal to estimate the uplink received power and uplink signal-to-noise ratio. The estimation results are then combined into a signaling frame, modulated and coded, and the downlink feed link signal is output. Step 103: The ground feeder terminal receives the downlink feeder link signal, and after demodulation and decoding, extracts the uplink received power and uplink signal-to-noise ratio estimation results. Step 104: The ground power supply terminal generates an uplink control decision based on the uplink control mode selected by the user, through the estimation results of uplink received power and uplink signal-to-noise ratio, and sends uplink power supply link signal. Then return to step 102; Downlink feeder link adaptive transmission method flow: Step 201: Before the low-orbit satellite enters the station, the ground feeder terminal initializes the downlink modulation and coding scheme and then sends the uplink feeder link signal. Step 202: After the low-orbit satellite enters the station, the onboard power supply baseband platform receives the uplink power supply link signal, and after adaptive demodulation and decoding, extracts the downlink modulation and coding scheme, controls the downlink modulation and coding scheme, and sends the downlink power supply link signal. Step 203: The ground feeder terminal receives the downlink feeder link signal, demodulates it, and estimates the downlink signal-to-noise ratio. Step 204: After obtaining the downlink signal-to-noise ratio estimation result, the ground feeder terminal generates a control decision on the downlink modulation and coding scheme, forms a signaling frame, and sends the uplink feeder link signal; then it returns to execute step 202. Specifically, the uplink and downlink modulation and coding schemes are sorted from low to high according to the demodulation threshold to form a 0-N level modulation and coding scheme, and each modulation and coding scheme is set with an admission signal-to-noise ratio and an output signal-to-noise ratio; where N is the type of modulation and coding scheme, and the admission signal-to-noise ratio and output signal-to-noise ratio are set according to the demodulation threshold; during the initialization of steps 101 and 201, both the uplink and downlink modulation and coding schemes are initialized to the 0 level modulation and coding scheme.

2. The adaptive transmission method for power supply links based on ground terminal decision-making according to claim 1, characterized in that, In step 104, when uplink transmit power is independently controlled, the uplink control decision is as follows: 1) If the current uplink signal-to-noise ratio is less than the outgoing signal-to-noise ratio (SNR_OUT) of the current uplink modulation and coding scheme, proceed to step 2); otherwise, proceed to step 4. 2) If the current uplink received power is less than the saturation power of the satellite-borne baseband platform, proceed to step 3); otherwise, proceed to step 6. 3) Increase uplink transmission power by setting a step size; 4) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 6); otherwise, proceed to step 5. 5) Reduce uplink transmission power in set steps; 6) Keep the uplink transmission power unchanged.

3. The adaptive transmission method for power supply links based on ground terminal decision-making according to claim 1, characterized in that, In step 104, when the uplink modulation and coding scheme is controlled independently, the uplink control decision is as follows: 1) If the current uplink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current uplink modulation scheme, proceed to step 2); otherwise, proceed to step 3). 2) Adjust the uplink modulation and coding scheme to a lower-level modulation and coding scheme; 3) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 4); otherwise, proceed to step 5. 4) Keep the current uplink modulation and coding scheme unchanged; 5) Adjust the uplink modulation and coding scheme to a higher-level modulation and coding scheme.

4. The adaptive transmission method for power supply links based on ground terminal decision-making according to claim 1, characterized in that, In step 104, when the uplink transmit power and uplink modulation and coding scheme are jointly controlled, the uplink control decision is as follows: 1) If the current uplink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current uplink modulation mode, proceed to step 2); otherwise proceed to step 5. 2) If the current uplink received power is less than the saturation power of the satellite-borne baseband platform, proceed to step 3); otherwise, proceed to step 4. 3) Increase uplink transmission power by setting a step size; 4) Adjust the uplink modulation and coding scheme to a lower-level modulation and coding scheme; 5) If the current uplink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current uplink modulation and coding scheme, proceed to step 6); otherwise, proceed to step 7. 6) Keep the current uplink transmit power and uplink modulation and coding scheme unchanged; 7) Adjust the uplink modulation coding scheme to a higher-level modulation coding scheme.

5. The adaptive transmission method for power supply links based on ground terminal decision-making according to claim 1, characterized in that, In step 204, the control decision for the downlink modulation and coding scheme is specifically as follows: 1) If the current downlink signal-to-noise ratio is less than the quasi-out signal-to-noise ratio SNR_OUT of the current downlink modulation scheme, proceed to step 2); otherwise, proceed to step 3). 2) Adjust the downlink modulation and coding scheme to a lower-level modulation and coding scheme; 3) If the current downlink signal-to-noise ratio is less than the admission signal-to-noise ratio SNR_IN of the current downlink modulation and coding scheme, proceed to step 4); otherwise, proceed to step 5. 4) Keep the current downlink modulation and coding scheme unchanged; 5) Adjust the downlink modulation and coding scheme to a higher-level modulation and coding scheme.

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