A system adaptive demodulation and decoding method that can smoothly adapt to satellite elevation angle

Abstract

The present invention discloses a system adaptive demodulation and decoding method that can smoothly adapt to the satellite elevation angle, belonging to the field of information transmission and processing. The method includes the steps of timing recovery, carrier recovery, system judgment, frame header search, channel decoding, data multiplexing, etc. The present invention adopts a system adaptive demodulation and decoding method that can smoothly adapt to the satellite elevation angle, so that when the satellite passes overhead, the modulation and coding mode smoothly adapts to the link power condition, and at the same time, there is no need to add additional leading data and pilot data of the link transmission frame, so that the transmission efficiency of the link transmission frame is greatly improved.

Description

Technical Field

[0001] The invention relates to the field of information transmission and processing, and in particular to a system adaptive demodulation and decoding method capable of smoothly adapting to satellite elevation angles. Background Art

[0002] The feeder link is a link that connects low-orbit communication satellites and ground gateway stations to transmit high-speed broadband information. When a low-orbit satellite flies over a ground gateway station, its flight elevation angle goes from low to high and then to low. Figure 1 As shown in the figure, as the satellite elevation angle changes, the bit signal-to-noise ratio Eb / N0 at the receiving end will also change (Eb is the bit energy, N0 is the noise power spectrum density). The bit signal-to-noise ratio at the receiving end when the satellite just enters is defined as Eb / N0+0dB. As the elevation angle gradually increases, the bit signal-to-noise ratio at the receiving end also gradually increases, experiencing Eb / N0+2dB, Eb / N0+4dB, until the satellite passes the top, the elevation angle is the largest, and the bit signal-to-noise ratio at the receiving end also reaches the maximum value Eb / N0+6dB. Then the satellite begins to leave the country, the elevation angle begins to decrease, and the bit signal-to-noise ratio at the receiving end also gradually decreases, experiencing Eb / N0+4dB, Eb / N0+2dB. When the satellite leaves the country, the elevation angle is the smallest, and the bit signal-to-noise ratio at the receiving end also drops to the lowest, which is Eb / N0+0dB. The change in the satellite elevation angle leads to a change in the power limitation of the satellite-to-ground communication link, and the bit signal-to-noise ratio Eb / N0 at the receiving end changes by at least 6dB.

[0003] The feeder link generally adopts CCSDS or DVB system. When the CCSDS system is adopted, in order to adapt to the lowest signal-to-noise ratio under low elevation conditions during the satellite passing overhead, the link power margin can reach 6dB when the satellite is at the highest elevation, and the corresponding transmission rate can be increased by 3 times, resulting in power waste. When the DVB system is adopted, although the modulation and coding methods can change with the satellite elevation angle, a large amount of preamble data and pilot data are added to the link transmission frame, which reduces the frame efficiency of the link transmission frame. Summary of the invention

[0004] In view of this, the present invention provides a system adaptive demodulation and decoding method that can smoothly adapt to the satellite elevation angle. The present invention does not need to add additional link transmission frame preamble data and pilot data, and can realize the smooth adaptation of the modulation and coding method to the link power condition. While adapting to the link power condition, the modulation and coding method further improves the frame efficiency of the link transmission.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A system adaptive demodulation and decoding method capable of smoothly adapting to satellite elevation angles comprises the following steps:

[0007] Step 1, receiving an intermediate frequency signal, the modulation mode of the intermediate frequency signal is QPSK, 8PSK or 16APSK, the coding system is an LDPC code with efficiency of 1 / 2, 3 / 4 and 7 / 8, and LDPC code groups with different coding efficiencies use different frame headers;

[0008] The Garden timing algorithm is used to perform clock recovery on the received intermediate frequency signal to extract the peak point of each symbol in the signal; the peak point is the value of the middle moment of each transmission code element;

[0009] Step 2, performing carrier recovery according to the peak point of each symbol in the signal to eliminate the carrier frequency difference;

[0010] Step 3, simultaneously judge the signals of QPSK, 8PSK and 16APSK systems, and obtain judgment information of the three systems;

[0011] Step 4, simultaneously searching for frame headers corresponding to LDPC 1 / 2, LDPC 3 / 4, and LDPC 7 / 8 in the decision information of each system;

[0012] Step 5: Determine the encoding mode of the current transmission frame according to the searched frame header, and send it to the corresponding LDPC 1 / 2, LDPC 3 / 4 or LDPC 7 / 8 decoding module for decoding;

[0013] Step 6, outputting the decoded data at different times in sequence to achieve data multiplexing;

[0014] Complete system adaptive demodulation and decoding.

[0015] Furthermore, the specific method of step 2 is:

[0016] For the constellation points of each constellation diagram of QPSK, 8PSK and 16APSK system signals, the constellation points in each quadrant are accumulated multiple times and the average value is calculated. The constellation diagrams of 8PSK and 16APSK signals are converted into QPSK signal constellation diagrams by accumulation; then the carrier recovery method of the QPSK system is uniformly adopted to complete the carrier recovery of QPSK, 8PSK and 16APSK.

[0017] Further, step 4 includes simultaneous searches of nine frame headers, namely, LDPC 1 / 2 frame header search for QPSK system decision information, LDPC 3 / 4 frame header search for QPSK system decision information, LDPC 7 / 8 frame header search for QPSK system decision information, LDPC 1 / 2 frame header search for 8PSK system decision information, LDPC 3 / 4 frame header search for 8PSK system decision information, LDPC 7 / 8 frame header search for 8PSK system decision information, LDPC 1 / 2 frame header search for 16APSK system decision information, LDPC 3 / 4 frame header search for 16APSK system decision information, and LDPC 7 / 8 frame header search for 16APSK system decision information.

[0018] The present invention has the following beneficial effects:

[0019] 1. The demodulation and decoding in the present invention can smoothly adapt to the changes in the received power and signal-to-noise ratio caused by the changes in the satellite elevation angle, and make full use of the link power margin.

[0020] 2. The present invention improves the problem of low transmission efficiency in the prior art that the transmission frame needs to insert leading data and pilot data. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the change of the signal-to-noise ratio of the satellite as it passes over the top of the building with the elevation angle.

[0022] Figure 2 It is a principle block diagram of the adaptive demodulation and decoding system of the present invention.

[0023] Figure 3 This is a schematic diagram of the physical layer transmission frame structure of the DVB system.

[0024] Figure 4 It is a schematic diagram of the physical layer transmission frame structure of the present invention.

[0025] Figure 5-Figure 10 This is a schematic diagram of a carrier recovery algorithm that can smoothly adapt to multiple modulation modes. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0027] A system adaptive demodulation and decoding method that can smoothly adapt to the satellite elevation angle, such as Figure 2 As shown, it includes the steps of timing recovery, carrier recovery, system judgment, frame header search, channel decoding, data multiplexing, etc., as follows:

[0028] Step 1, receiving an intermediate frequency signal, the modulation mode of the intermediate frequency signal is QPSK, 8PSK or 16APSK, the coding system is an LDPC code with efficiency of 1 / 2, 3 / 4 and 7 / 8, and LDPC code groups with different coding efficiencies use different frame headers;

[0029] The Garden timing algorithm is used to perform clock recovery on the received intermediate frequency signal to extract the peak point of each symbol in the signal; the peak point is the value of the middle moment of each transmission code element;

[0030] Step 2, performing carrier recovery according to the peak point of each symbol in the signal to eliminate the carrier frequency difference;

[0031] Step 3, simultaneously judge the signals of QPSK, 8PSK and 16APSK systems, and obtain judgment information of the three systems;

[0032] Step 4, simultaneously searching for frame headers corresponding to LDPC 1 / 2, LDPC 3 / 4, and LDPC 7 / 8 in the decision information of each system;

[0033] Step 5: Determine the encoding mode of the current transmission frame according to the searched frame header, and send it to the corresponding LDPC 1 / 2, LDPC 3 / 4 or LDPC 7 / 8 decoding module for decoding;

[0034] Step 6, outputting the decoded data at different times in sequence to achieve data multiplexing;

[0035] Complete system adaptive demodulation and decoding.

[0036] In step 1, for any of the three modulation modes of QPSK, 8PSK or 16APSK received signals, a clock recovery algorithm that is smoothly adaptable to multiple modulation modes is used to extract the peak point of each symbol in the signal.

[0037] In step 2, according to the peak point of any signal of the three modulation modes, such as QPSK, 8PSK or 16APSK, a carrier recovery algorithm that is smoothly adapted to multiple modulation modes is used to eliminate the carrier frequency difference. Specifically, when calculating the carrier phase error, the constellation points of each constellation diagram of the modulation signals such as QPSK, 8PSK and 16APSK are averaged in each quadrant, that is, the constellation points in each quadrant are accumulated 100 times and then the average value is calculated. After the accumulation, the constellation diagrams of 8PSK and 16APSK signals will become QPSK signal constellations, such as Figure 5-Figure 10 As shown, the carrier recovery method of the QPSK system is uniformly adopted to complete the carrier recovery of QPSK, 8PSK and 16APSK.

[0038] In step 3, the signals of the QPSK, 8PSK and 16APSK systems are judged simultaneously to obtain the judgment information of the three systems.

[0039] In step 4, the transmission code group frame header search is performed on the decision information of QPSK, 8PSK and 16APSK at the same time. The frame header search includes searching the coding system 1 frame header (LDPC 1 / 2) of the decision information of the QPSK system, searching the coding system 2 frame header (LDPC 3 / 4) of the decision information of the QPSK system, searching the coding system 3 frame header (LDPC 7 / 8) of the decision information of the QPSK system, searching the coding system 1 frame header (LDPC 1 / 2) of the decision information of the 8PSK system, searching the coding system 2 frame header (LDPC 3 / 4) of the decision information of the 8PSK system, searching the coding system 3 frame header (LDPC 7 / 8) of the decision information of the 8PSK system, searching the coding system 1 frame header (LDPC 1 / 2) of the decision information of the 16APSK system, searching the coding system 2 frame header (LDPC3 / 4) of the decision information of the 16APSK system, and searching the coding system 3 frame header (LDPC 7 / 8) of the decision information of the 16APSK system.

[0040] In step 5, according to the transmission code group frame header search situation, the LDPC codes with coding efficiencies of 1 / 2, 3 / 4 and 7 / 8 are respectively sent to different decoding modules for decoding.

[0041] In step 6, the LDPC decoded data with coding efficiencies of 1 / 2, 3 / 4 and 7 / 8 are multiplexed, thereby achieving smooth output of the demodulated decoded data.

[0042] Still see Figure 2, the carrier recovery data is divided into three paths, and the three signals are sent to the QPSK system judgment, 8PSK system judgment and 16APSK system judgment in the system judgment one by one. The QPSK system judgment judges the received carrier recovery data in the form of QPSK system signal, and divides the judged data into three paths and sends them to the frame header search module; the 8PSK system judgment judges the received carrier recovery data in the form of 8PSK system signal, and divides the judged data into three paths and sends them to the frame header search module. The 16APSK system judgment judges the received carrier recovery data in the form of 16APSK system signal, and divides the judged data into three paths and sends them to the frame header search module. The frame header search module has a total of 9 sub-modules, among which there are three frame header searches for coding system 1, which are connected to the QPSK system decision, 8PSK system decision and 16APSK system decision respectively, and are used to search for the frame header of coding system 1 (LDPC 1 / 2), and send the searched transmission frame to the coding system 1 in the channel decoding for decoding; there are three frame header searches for coding system 2, which are connected to the QPSK system decision, 8PSK system decision and 16APSK system decision respectively, and are used to search for the frame header of coding system 2 (LDPC 3 / 4), and send the searched transmission frame to the coding system 2 in the channel decoding for decoding; there are three frame header searches for coding system 3, which are connected to the QPSK system decision, 8PSK system decision and 16APSK system decision respectively, and are used to search for the frame header of coding system 3 (LDPC 7 / 8), and send the searched transmission frame to the coding system 3 in the channel decoding for decoding. The channel decoding decodes the transmission frames corresponding to the coding system 1, coding system 2 and coding system 3 from the frame header search, and sends the decoded data to the data multiplexing module; since only one module of the channel decoding coding system 1 decoding, coding system 2 decoding and coding system 3 decoding has output at a certain moment, the data multiplexing module selects one path as input according to the output of the channel decoding coding system 1 decoding, coding system 2 decoding and coding system 3 decoding, thereby realizing the smooth output of demodulation and decoding.

[0043] The timing recovery of the present invention realizes the timing processing of multiple modulation signals and realizes the clock synchronization of the sampling clock and the receiving signal; the carrier recovery realizes the frequency difference between the sending end and the receiving end of the multiple modulation signals, and the signal after the carrier recovery is sent to the system judgment module to judge multiple systems such as QPSK, 8PSK, 16APSK, etc. at the same time; the signal after the multi-system judgment is sent to the frame header search module, and the current modulation system and encoding method are determined by searching the frame header, and the transmission frame with the correctly searched frame header is sent to the channel decoding module for corresponding channel decoding; finally, the data of different channel decoding modules are output in sequence by data multiplexing.

[0044] The traditional physical layer transmission frame structure is as follows Figure 3 As shown, a physical layer transmission frame consists of three parts: a physical layer transmission frame synchronization header, a coding modulation mode indication segment, and a data symbol segment. The physical layer transmission frame synchronization header adopts BPSK modulation; the coding modulation mode indication segment is mainly used to carry coding modulation instruction words, which are represented by WASH codes, and different instruction words correspond to different coding modulation modes; the data symbol segment consists of several data symbol blocks; the data symbol block consists of data symbols and pilot symbols, wherein the pilot symbols adopt BPSK modulation; the data symbol consists of a frame header and a coding block. The physical layer transmission frame structure of the present invention is as follows Figure 4 As shown, it only consists of a frame header and a coding block.

[0045] In summary, the present invention adopts a system adaptive demodulation and decoding method that can smoothly adapt to the satellite elevation angle, so that when the satellite passes overhead, the modulation and coding methods can smoothly adapt to the link power conditions. At the same time, there is no need to add additional leading data and pilot data to the link transmission frame, so that the transmission efficiency of the link transmission frame is greatly improved.

Claims

1. A system adaptive demodulation and decoding method capable of smoothly adapting to satellite elevation angle, characterized in that: The following steps are involved: Step 1, receiving an intermediate frequency signal, the modulation mode of the intermediate frequency signal is QPSK, 8PSK or 16APSK, the coding system is an LDPC code with efficiency of 1 / 2, 3 / 4 and 7 / 8, and LDPC code groups with different coding efficiencies use different frame headers; The Garden timing algorithm is used to perform clock recovery on the received intermediate frequency signal to extract the peak point of each symbol in the signal; the peak point is the value of the middle moment of each transmission code element; Step 2: Carrier recovery is performed based on the peak point of each symbol in the signal to eliminate the carrier frequency difference; the specific method is: For each constellation point of the constellation diagram of the QPSK, 8PSK and 16APSK system signals, the constellation points in each quadrant are accumulated multiple times and then the average value is calculated, so that the constellation diagrams of the 8PSK and 16APSK signals are converted into QPSK signal constellations by accumulation; then the carrier recovery method of the QPSK system is uniformly adopted to complete the carrier recovery of QPSK, 8PSK and 16APSK; Step 3, simultaneously judge the signals of QPSK, 8PSK and 16APSK systems, and obtain judgment information of the three systems; Step 4, simultaneously searching for frame headers corresponding to LDPC 1 / 2, LDPC 3 / 4 and LDPC 7 / 8 in the decision information of each system; step 4 includes simultaneous searching of nine frame headers, namely, LDPC 1 / 2 frame header search of QPSK system decision information, LDPC 3 / 4 frame header search of QPSK system decision information, LDPC 7 / 8 frame header search of QPSK system decision information, LDPC 1 / 2 frame header search of 8PSK system decision information, LDPC 3 / 4 frame header search of 8PSK system decision information, LDPC 7 / 8 frame header search of 8PSK system decision information, LDPC 1 / 2 frame header search of 16APSK system decision information, LDPC 3 / 4 frame header search of 16APSK system decision information, and LDPC 7 / 8 frame header search of 16APSK system decision information; Step 5: Determine the encoding mode of the current transmission frame according to the searched frame header, and send it to the corresponding LDPC 1 / 2, LDPC3 / 4 or LDPC 7 / 8 decoding module for decoding; Step 6, outputting the decoded data at different times in sequence to achieve data multiplexing; Complete system adaptive demodulation and decoding.

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