Method for determining variable parameters of satellite Ka-band variable coding modulation data transmission system

Abstract

The present invention proposes a method for determining variable parameters of a satellite Ka-band variable coding modulation data transmission system, comprising: step 1, selecting an available modulation and coding mode (MODCOD) combination from a satellite Ka-band variable modulation and coding mode; step 2, calculating the link unavailability of the MODCOD combination obtained in step 1; step 3, selecting an available MODCOD from the MODCOD combination in step 1 according to the link unavailability to form a set Mi, and selecting a row amplifier input power back-off (IBO) corresponding to the corresponding MODCOD to form a set IBO; step 4, calculating the link unavailability of the MODCOD combination obtained in step 1; step 5, calculating the link unavailability of the MODCOD combination obtained in step 1; step 6, calculating the link unavailability of the MODCOD combination obtained in step 1; step 7, calculating the link unavailability of the MODCOD combination obtained in step 7, and calculating the link unavailability of the MODCOD combination obtained in step 7; step 8, calculating the link unavailability of the MODCOD combination obtained in step 8, and ... i In the step, the modulation coding mode is started with the minimum MODCOD as the minimum elevation angle to form a variable parameter switching elevation angle threshold combination; Step five: assign a unique ground station number to each ground station, and combine its location information with the MODCOD combination, IBO combination, and switching elevation angle threshold combination determined in steps three and four to form variable parameters related to the ground station.

Description

Technical Field

[0001] The present invention relates to a variable parameter determination method for a satellite Ka-band variable coding modulation data transmission system, which is applicable to high-resolution remote sensing satellites using non-geostationary circular orbits such as low orbits or medium orbits. Background Art

[0002] With the continuous development of my country's remote sensing technology, the spatial resolution, spectral resolution and other indicators are rapidly improving, and the remote sensing satellite payload will generate more and more observation data. Within the limited data transmission arc to the ground, these data need to be transmitted back in a timely manner, which puts higher and higher requirements on the effective information rate of the downlink data transmission link.

[0003] The patent "Near Earth Remote Sensing Satellite Adaptive Variable Coding Modulation Data Transmission System and Method" with authorization announcement number "CN109379167B" and authorization announcement date July 2021 provides a variable coding modulation data transmission system and method based on the DVB-S2 protocol, which adopts a variable coding modulation (VCM) system and mainly utilizes the improvement of link resources brought about by the decrease of free space attenuation with increasing elevation angle to effectively improve the efficiency of satellite-to-ground data transmission. The method includes 4 steps: S1, receiving satellite position information, and calculating satellite operation information in combination with ground station position parameter information; S2, calculating the ground reception carrier-to-noise ratio in combination with preset link parameters; S3, switching to the optimal modulation coding method according to the carrier-to-noise ratio to transmit data to the ground; S4, the ground receives and demodulates the data and outputs it to subsequent equipment for processing.

[0004] However, this method is only applicable to the X-band (frequency range 8025-8400MHz, bandwidth 375MHz) which is less affected by the atmosphere, and its atmospheric attenuation value is small, so it cannot be directly applied to the satellite-to-ground data transmission system of the Ka-band (frequency range 25.5-27GHz, bandwidth 1.5GHz) which is more affected by the atmosphere. In addition, step S2 calculates the carrier-to-noise ratio in real time on the satellite, and there are many types of related parameters, and the calculation process is relatively complicated. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a method for determining variable parameters of a satellite Ka-band variable coding modulation data transmission system, which can determine the relevant variable parameters on the ground instead of on the satellite, and can be applied to the Ka-band satellite-to-ground data transmission system of non-geostationary circular orbit remote sensing satellites such as low orbit or medium orbit.

[0006] The present invention is achieved through the following technical solutions.

[0007] A method for determining variable parameters of a satellite Ka-band variable coding modulation data transmission system comprises the following steps:

[0008] Step 1: Select an available modulation and coding mode (MODCOD) combination in the satellite Ka-band variable modulation and coding mode;

[0009] Step 2: Calculate the link unavailability of the MODCOD combination obtained in step 1;

[0010] According to the link unavailability, an available MODCOD is selected from the MODCOD combination in step 1 to form a set M i , and select the row amplifier input power back-off (IBO) corresponding to the corresponding MODCOD to form a set IBO i = {IBO MODCOD ,MODCOD∈M i};

[0011] Step 4: In the set M i In the modulation coding mode, the minimum MODCOD is used as the minimum elevation angle to form a variable parameter switching elevation angle threshold combination;

[0012] Step 5: Assign a unique ground station number to each ground station, and combine its location information with the MODCOD combination, IBO combination, and switching elevation angle threshold combination determined in steps 3 and 4 to form variable parameters related to the ground station.

[0013] Beneficial effects of the present invention:

[0014] 1. The present invention expands the variable coding modulation (VCM) system from the X-band to the Ka-band, and increases the available radio frequency bandwidth from 375MHz to 1.5GHz, an increase of up to 300%, and can use the large bandwidth to achieve higher-speed data transmission;

[0015] 2. The present invention can complete the determination of relevant variable parameters on the ground, and only the elevation angle is used as a criterion on the satellite to determine whether it is necessary to switch the relevant transmission parameter combination, thereby simplifying the system complexity;

[0016] 3. The present invention can be applied to the Ka-band satellite-to-ground data transmission system of non-geostationary circular orbit remote sensing satellites such as low-orbit or medium-orbit;

[0017] 4. Based on the free space loss, the present invention further considers the statistical characteristic that the atmospheric attenuation in the lower elevation angle region decreases rapidly with the increase of the elevation angle. In this region, as the elevation angle increases, it can choose to switch to a modulation coding mode with higher spectrum efficiency to fully utilize the margin of the satellite-to-ground data transmission link and further enhance the transmission capacity of the satellite-to-ground data transmission system of my country's remote sensing satellite. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A method for determining variable parameters of a satellite Ka-band variable coding modulation data transmission system according to the present invention;

[0019] Figure 2 The atmospheric attenuation of the Ka-band radio frequency signal of Miyun Station in the embodiment of the present invention;

[0020] Figure 3 The variation of the satellite-to-ground distance between Miyun Station and the satellite with the elevation angle in the embodiment of the present invention;

[0021] Figure 4 The free space attenuation of Miyun Station varies with elevation angle in the embodiment of the present invention;

[0022] Figure 5 Graph 1 shows the variation of the effective information rate in different elevation angle intervals of the Miyun station in the embodiment of the present invention. DETAILED DESCRIPTION

[0023] The exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the accompanying drawings are only exemplary and are intended to illustrate the principles and spirit of the present invention, rather than to limit the scope of the present invention.

[0024] like Figure 1 As shown, a method for determining variable parameters of a satellite Ka-band variable coding modulation data transmission system of the present invention specifically comprises the following steps:

[0025] Step 1: Select an available modulation and coding mode (MODCOD) combination in the satellite Ka-band variable modulation and coding mode;

[0026] The prior art supports 11 BCH+LDPC channel coding modes with code rates of 1 / 4 to 9 / 10 and 4 modulation modes of QPSK, 8PSK, 16APSK and 32APSK in the DVB-S2 protocol modulation and coding mode, and forms a total of 28 modulation and coding modes through combination. According to the simulation and measured data given in the CCSDS (Consultative Committee for Space Data Systems) green paper CCSDS 130.12-G-1 "CCSDS protocols over DVB-S2——summary of definition, implementation, and performance", the digital transmission link budget is equivalently converted to the saturated power output of the traveling wave tube amplifier;

[0027] In this embodiment, after comprehensively considering the ground demodulation loss and the output power back-off of the onboard traveling wave tube amplifier, the symbol signal-to-noise ratio E is selected. s / N 0 (That is, the average energy E per transmitted symbol s and the noise power spectral density N 0 The demodulation threshold (E s / N 0 ) th The MODCOD combination with increasing spectrum efficiency is used as the available MODCOD combination. The characteristics of the 28 modulation coding modes are shown in Table 1:

[0028] Table 1

[0029]

[0030] In specific implementation, the selection can be made according to the test results of the physical product of the manufacturer, referring to the above method, and other selection criteria can be added. For example, in order to avoid too frequent modulation and coding mode switching, adjacent (E s / N 0 ) th The difference is not less than 1dB or other value combinations.

[0031] Step 2: Calculate the link unavailability of the modulation and coding mode (MODCOD) combination obtained in step 1; the specific steps are as follows:

[0032] S201, calculate the symbol signal-to-noise ratio E actually received by the ground station according to the satellite and ground station data transmission link related parameters s / N 0 ; The specific formula is as follows:

[0033] E S / N 0 =EIRP+Q r -R S -(L space +L point +L polar +L atom )+228.6 (1)

[0034] The EIRP is the equivalent isotropic radiated power (in dBW) emitted by the satellite, and the maximum EIRP that can be emitted by the satellite is EIRP max (unit: dBW) and the output power back-off OBO (unit: dB) of the traveling wave tube amplifier are determined, that is, EIRP = EIRP max -OBO;

[0035] Among them, Q r is the quality factor of the ground station (usually also called G / T value, unit: dB / K); R S is the symbol rate transmitted by the RF channel (the corresponding value in baud is 10lg());

[0036] Among them, L space is the free space loss (in dB), which is determined by the carrier frequency f 0 (unit: GHz), satellite-to-ground distance Dis (unit km) is determined, i.e. L space =92.45+20lg(f 0 ·D is );L point is the antenna pointing loss (in dB); L polar is the polarization loss (in dB);

[0037] Among them, L atom is the atmospheric attenuation (in dB), including rain attenuation A rain (Unit: dB), Cloud attenuation A cloud (unit: dB), atmospheric absorption loss A gaz (unit: dB), atmospheric scintillation A iscint (unit: dB), both related to the carrier frequency f 0 (unit: GHz), ground station location L ocation (including longitude L on (Unit °) / latitude L at (unit: °) / height H (unit: km)), ground station elevation angle E le (unit: °) and the attenuation exceeding probability p are related and calculated using the method recommended by the International Telecommunication Union (ITU). Rain attenuation and atmospheric scintillation refer to ITU-R P.618-13, cloud attenuation refers to ITU-R P.840-8, and atmospheric absorption loss refers to ITU-R P.676-12, where p ranges from 0.001% to 50%. Therefore, for systems operating at frequencies above about 18 GHz, the following formula is used for calculation:

[0038]

[0039] In specific implementation, the Ka-band RF signal is easily affected by the atmosphere, and the link condition is the worst at the minimum elevation angle (typical value 5°, which can be modified as needed). The link availability at this time directly determines the data reliable transmission capability of the full receiving arc. For ground stations with different climate characteristics and different locations, different and appropriate link availability can be considered to avoid over-design and cause a large waste of resources.

[0040] S202, according to the signal-to-noise ratio E s / N 0 Calculate the link margin to determine the unavailability of the link;

[0041] For remote sensing satellites, in order to ensure reliable transmission of the data transmission link, a certain link system margin M is usually reserved. th (Generally 3dB is required, and the setting can be modified as needed). For different MODCODs, the demodulation threshold (E s / N 0 ) thTherefore, in this embodiment, the link margin M MODCOD The calculation is done using the following formula:

[0042] M MODCOD =E S / N 0 -(E S / N 0 ) th

[0043] For a given ground station, when other parameters of the satellite-to-ground data transmission link have been determined, the symbol signal-to-noise ratio E of the ground station received at the minimum elevation angle is s / N 0 Only related to the decay exceeding probability p; when M MODCOD =M th When , the attenuation excess probability p associated with this MODCOD can be calculated in reverse MODCOD . In the average annual proportion of p MODCOD Within a certain period of time, the atmospheric attenuation exceeds a certain threshold value, which makes the data transmission link margin insufficient, the signal cannot be transmitted reliably, and the link bit error rate is difficult to meet the application requirements. Therefore, the attenuation exceeds the probability p MODCOD That is, "link unavailability", which sums with link availability to 100%.

[0044] Step 3: Select available MODCOD from the MODCOD combination in step 1 according to the link unavailability to form a set M i , and select the row amplifier input power back-off (IBO) corresponding to the corresponding MODCOD to form a set IBO i = {IBO MODCOD ,MODCOD∈M i};

[0045] In specific implementation, for the N ground stations commonly used by satellites, different link unavailability requirements can be specified with a maximum value p i , forming a set p avai ={p i , i=1,2,…,N}; For the i-th ground station, the available MODCOD can be selected from the available MODCOD combinations of the system determined in step 1 (where the minimum MODCOD is p MODCOD ≤p i The largest of

[0046] M i ={MODCOD,min(MODCOD)=max{MODCOD,p MODCOD ≤p i}}, the number of MODCODs in this set is recorded as K i, and select the IBO corresponding to the corresponding MODCOD to form a set IBO i = {IBO MODCOD ,MODCOD∈M i}, the number of IBOs in this set is also K i .

[0047] Step 4: In the set M i In the modulation coding mode, the minimum MODCOD is used as the minimum elevation angle to form a variable parameter switching elevation angle threshold combination; the specific method is as follows:

[0048] In the set M i In the modulation coding mode, the minimum MODCOD is used as the minimum elevation angle. As the receiving elevation angle increases, the free space loss L space and atmospheric attenuation L atom (According to the specified link unavailability requirement, the maximum value p i ) gradually decreases, and the symbol signal-to-noise ratio E s / N 0 Gradually increases; when the value reaches the sum of the demodulation threshold of the next smallest MODCOD and the link system margin (E S / N 0 ) th_MODCOD +M th When , switch to the next smallest MODCOD, the corresponding elevation angle is the first switching elevation angle E 1 ; And so on, until the largest MODCOD is used, at which point the corresponding elevation angle is the Kth i -1 Switch Elevation Ki-1 ; These elevation angles form the set The switching elevation angle threshold combination;

[0049] The switching elevation angle threshold in this set The data is gradually increasing (the latter part of the data may be 90). Among them, the MODCOD set M i The minimum MODCOD is applicable to the elevation range of [5,E 1 ), the elevation angle range applicable to the second smallest MODCOD is [E 1 ,E 2 ), and so on, until the maximum MODCOD applicable elevation range is

[0050] Step 5: Assign a unique ground station number to each ground station, and combine its location information (longitude / latitude / elevation) with the MODCOD combination, IBO combination, and switching elevation threshold combination determined in steps 3 and 4 to form variable parameters related to the ground station.

[0051] During specific implementation, all variable parameters related to the ground stations are further combined to form variable parameters of the satellite Ka-band variable coding modulation data transmission system, and stored in the parameter storage module on the satellite.

[0052] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A method for determining variable parameters of a satellite Ka-band variable coding modulation data transmission system, characterized in that: The steps include: Step 1: Select an available modulation and coding mode MODCOD combination from the satellite Ka-band variable modulation and coding modes; Step 2: Calculate the link unavailability of the MODCOD combination obtained in step 1; Step 3: Select available MODCODs from the MODCOD combination in step 1 according to the link unavailability to form a set , and select the row amplifier input power back-off IBO corresponding to the corresponding MODCOD to form a set ; Step 4: In the collection In the modulation coding mode, the minimum MODCOD is used as the minimum elevation angle to form a variable parameter switching elevation angle threshold combination; Step 5: Assign a unique ground station number to each ground station, and combine its location information with the MODCOD combination, IBO combination, and switching elevation angle threshold combination determined in steps 3 and 4 to form variable parameters related to the ground station; The available modulation and coding mode combination is specifically: a MODCOD combination whose spectrum efficiency increases continuously as the demodulation threshold of the symbol signal-to-noise ratio increases, and it is used as an available MODCOD combination; The specific steps of step 2 are as follows: S201, calculating the signal-to-noise ratio of symbols actually received by the ground station according to the satellite and ground station data transmission link related parameters; S202, calculating a link margin according to the signal-to-noise ratio, thereby determining the unavailability of the link; When the step 3 is specifically implemented: for N ground stations commonly used by the satellite, specify different link unavailability requirements for maximum values , forming a set ; for ground stations, select available MODCODs from the available MODCOD combinations of the system determined in step 1 to form a set , the number of MODCODs in this set is recorded as , and select the IBO corresponding to the corresponding MODCOD to form a set , the number of IBOs in this set is also ; The specific method of forming a variable parameter switching elevation angle threshold combination is as follows: In the collection In the modulation coding mode, the minimum MODCOD is used as the minimum elevation angle. As the receiving elevation angle increases, the free space loss and atmospheric attenuation gradually decrease, and the symbol signal-to-noise ratio received by the ground station gradually increases. When the value reaches the sum of the demodulation threshold of the second smallest MODCOD and the link system margin, it switches to the second smallest MODCOD, and the corresponding elevation angle is the first switching elevation angle. This continues until the largest MODCOD is used, and the corresponding elevation angle is the switching elevation angles; these elevation angles form a set of switching elevation angle threshold combinations.

2. The method according to claim 1, characterized in that After step five, the method also includes combining all variable parameters related to the ground stations to form variable parameters of the satellite Ka-band variable coding modulation data transmission system, and storing them in the parameter storage module on the satellite.

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