Signal modulation method and communication method for spaceflight

Abstract

The invention discloses a signal modulation method for spaceflight. Data are modulated based on a direct sequence spread spectrum and Gaussian minimum frequency shift keying modulation technology. Compared with DSSS-BPSK modulation, satellite EMC of multi-frequency-point emission is improved, the frequency spectrum captured by PMF-FFT is more characteristic, the phenomenon of mistaken capturing is not prone to occurring, and due to the fact that the single-path code rate is half of the DSSS-BPSK, the chip migration effect is easy to eliminate.

Description

Technical Field

[0001] The present invention relates to the field of aerospace technology, and in particular to a signal modulation method and a communication method used in aerospace. Background Art

[0002] DSSS-BPSK, a combination of direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation, is commonly used in wireless communication systems, particularly in scenarios requiring interference resistance, low power consumption, or security. For this reason, DSSS-BPSK is currently the most widely used modulation method in satellite communication systems.

[0003] However, DSSS-BPSK signals have distinct spectral characteristics, poor sidelobe suppression, and low bandwidth utilization efficiency. The mainlobe spectrum occupies a range of 2Rc (Rc is the spreading code rate), which is detrimental to EMC performance across multiple frequencies within the same band for the entire satellite. Ground equipment using high-gain antennas and high-GT systems can detect distinct spectral characteristics. Furthermore, in a large Doppler environment, the chip migration effect caused by long integration times is more pronounced. Summary of the Invention

[0004] In order to solve some or all of the problems in the prior art, the first aspect of the present invention provides a signal modulation method for aerospace, which combines direct sequence spread spectrum and Gaussian minimum shift keying (GMSK) modulation technology to modulate data.

[0005] Furthermore, the signal modulation method includes:

[0006] Performing an XOR operation on the data and the pseudo code sequence to obtain a first data sequence;

[0007] Performing serial-to-parallel conversion on the first data sequence to obtain an I bit stream and a Q bit stream;

[0008] The I-channel bit stream is delayed, wherein the delay time is T C ;

[0009] Performing Gaussian pulse shaping on the delayed I bit stream and the Q bit stream to obtain an I baseband signal and a Q baseband signal;

[0010] Multiply the I-channel baseband signal and the Q-channel baseband signal by post-modulation to an intermediate frequency carrier; and

[0011] Combine the two signals modulated to the intermediate frequency carrier.

[0012] Furthermore, the signal modulation method further includes:

[0013] Multiple groups of spreading codes are modulated simultaneously to form the signal to be transmitted.

[0014] Based on the above-mentioned signal modulation method, the second invention of the present invention provides a communication method for aerospace, comprising:

[0015] After receiving a digital intermediate frequency signal, capturing the optimal effective signal and determining a Doppler shift value, wherein the digital intermediate frequency signal is modulated according to the signal modulation method as described above; and

[0016] The digital intermediate frequency signal is demodulated based on the Doppler shift value.

[0017] Furthermore, capturing the optimal effective signal includes:

[0018] multiplying the digital intermediate frequency signal by a plurality of locally generated local carriers, wherein the center frequencies of the local carriers are different and each local carrier includes an I carrier and a Q carrier;

[0019] Down-sampling the I and Q signals obtained by multiplication in each channel and then interleaving them;

[0020] Capturing each interleaved signal separately, and determining the normalized gain of each channel based on the spectrum characteristics; and

[0021] The channel with the largest normalized gain is selected as the optimal effective signal.

[0022] Furthermore, capturing the optimal effective signal also includes:

[0023] Before multiplying the digital intermediate frequency signal with the locally generated multiple local carriers, a DC filter and digital automatic gain control (AGC) are performed on the digital intermediate frequency signal.

[0024] Furthermore, capturing the optimal effective signal also includes:

[0025] Before downsampling, the I-path and Q-path signals obtained by multiplication are low-pass filtered, wherein the passband bandwidth adopted by the low-pass filtering is Rc / 2, where Rc is the spread spectrum code rate.

[0026] Furthermore, each interleaved signal is captured based on the probability mass function (PMF) and the fast Fourier transform (FFT):

[0027] Perform L-point partial correlation on the interleaved signal and the local spread spectrum PN code, and perform K summation operations;

[0028] The calculated K correlator output data are stored in a block random access memory (BRAM), where the length of the BRAM is N, where N is a power of 2. If K is less than N, NK zeros are added to pad the data.

[0029] Performing a fast Fourier transform on the data in the block random access memory to obtain N-point output results; and

[0030] The N-point output results are normalized and calculated. If the result meets the preset requirements, it is considered that a valid signal is captured. Otherwise, the local spread spectrum code is moved by one code phase, and correlation and fast Fourier transform operations are performed again until a valid signal is captured.

[0031] Furthermore, the preset conditions include:

[0032] The ratio of the maximum value to the average value of the modulus values ​​of the N-point output results is greater than a first preset value, and the ratio of the maximum value to the sub-maximum value is less than a second preset value.

[0033] Furthermore, demodulating the digital intermediate frequency signal based on the Doppler shift value includes:

[0034] multiplying the digital intermediate frequency signal by a locally generated local carrier, wherein a center frequency of the local carrier is equal to a center frequency of the local carrier used by the optimal effective signal, and the local carrier includes an I carrier and a Q carrier;

[0035] Downsampling the I and Q signals obtained by multiplication, wherein an initial interval of the downsampling is the same as the downsampling interval used when capturing the optimal valid signal;

[0036] Performing a product operation on the I and Q signals obtained by downsampling and the local spreading code, wherein the local spreading code has been coarsely synchronized;

[0037] Perform phase detection operation on the calculation results of I and Q channels;

[0038] Phase compensation is generated based on the phase detection result and sent to the I and Q local carriers. At the same time, code phase compensation is generated based on the leading and lagging codes and sent to the local spread spectrum code.

[0039] Interweaving signals synchronized with the local carrier and local spreading code;

[0040] Low-pass filtering the interleaved signal;

[0041] Down-sample the low-pass filtered signal;

[0042] performing data bit synchronization on the downsampled signal; and

[0043] The result of data bit synchronization is frame synchronized to complete demodulation.

[0044] Furthermore, demodulating the digital intermediate frequency signal based on the Doppler shift value further includes:

[0045] Before multiplying the digital intermediate frequency signal with the locally generated multiple local carriers, direct current filtering and digital automatic gain control are performed on the digital intermediate frequency signal.

[0046] The present invention provides a signal modulation method and communication method for aerospace, which adopts Gaussian Minimum Shift Keying (GMSK) modulation technology to replace the existing binary phase shift keying (BPSK) modulation technology. It has phase continuity, a spectrum with relatively fast out-of-band attenuation, which can better improve bandwidth utilization and has good EMC characteristics. At the same time, its envelope fluctuation is small, and its performance deteriorates slightly after passing through a nonlinear channel. It can also operate in a region with slightly poor linearity when selecting an amplifier. It can be regarded as consisting of two interleaved I and Q channels, with the rate of a single channel being half the total rate. When there is a large Doppler uncertainty, its impact on chip migration is small, and the number of parallel capture units can be reduced at the capture end. Furthermore, the spectrum characteristics during capture can significantly reduce the probability of false capture. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] To further illustrate the above and other advantages and features of various embodiments of the present invention, a more detailed description of various embodiments of the present invention will be presented with reference to the accompanying drawings. It will be understood that these drawings depict only typical embodiments of the present invention and are not to be considered as limiting the scope thereof. In the drawings, for clarity, identical or corresponding components will be represented by the same or similar reference numerals.

[0048] Figure 1 A schematic flow chart showing a signal modulation method for aerospace according to an embodiment of the present invention;

[0049] Figure 2 A schematic diagram illustrating a process of a signal modulation method for aerospace according to an embodiment of the present invention;

[0050] Figure 3 A schematic flow chart showing a communication method for aerospace according to an embodiment of the present invention;

[0051] Figure 4 A schematic diagram illustrating a process of an effective signal acquisition method according to an embodiment of the present invention;

[0052] Figure 5 A schematic diagram illustrating a process of determining an optimal effective signal according to an embodiment of the present invention is shown;

[0053] Figure 6 A schematic diagram showing the calculation results of PMF-FFT according to an embodiment of the present invention; and

[0054] Figure 7 A schematic diagram showing the process of a signal tracking and demodulation method according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0055] In the following description, the present invention is described with reference to various embodiments. However, those skilled in the art will recognize that the various embodiments can be implemented without one or more of the specific details or with other alternative and / or additional methods or components. In other cases, well-known structures or operations are not shown or described in detail to avoid obscuring the inventive aspects of the present invention. Similarly, for the purpose of explanation, specific numbers and configurations are set forth in order to provide a comprehensive understanding of the embodiments of the present invention. However, the present invention is not limited to these specific details. In addition, it should be understood that the various embodiments shown in the drawings are illustrative representations and are not necessarily drawn to scale.

[0056] In this specification, reference to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. The appearances of the phrase "in one embodiment" in various places in this specification are not necessarily all referring to the same embodiment.

[0057] It should be noted that the embodiments of the present invention describe the method steps in a specific order, but this is only for the purpose of illustrating the specific embodiment and does not limit the order of the steps. On the contrary, in different embodiments of the present invention, the order of the steps can be adjusted according to actual needs.

[0058] In response to the problems of low bandwidth utilization efficiency of DSSS-BPSK, adverse effects on EMC of multiple frequencies in the same frequency band of the entire satellite, and obvious chip migration effect, the present invention provides a signal modulation method and communication method for aerospace, which adopts DSSS-GMSK instead of DSSS-BPSK to make the spectrum captured by PMF-FFT more characteristic and less prone to false capture. In addition, since the single-channel code rate is half that of DSSS-BPSK, the chip migration effect is also easily eliminated.

[0059] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings of the embodiments.

[0060] Figure 1 A schematic flow chart illustrating a signal modulation method for aerospace according to an embodiment of the present invention is shown. Figure 2A schematic diagram illustrating a process of a signal modulation method for aerospace according to an embodiment of the present invention is shown. As shown in the figure, a signal modulation method for aerospace, which combines direct sequence spread spectrum with Gaussian minimum shift keying (GMSK) modulation technology to modulate a signal, includes:

[0061] First, in step 101, an XOR operation is performed with the pseudo code sequence. The signal data to be modulated is XORed with the pseudo code sequence to obtain a first data sequence;

[0062] Next, in step 102, serial-to-parallel conversion is performed on the first data sequence to obtain an I bit stream and a Q bit stream. The serial-to-parallel conversion can be implemented using a common serial-to-parallel conversion circuit in the art, which will not be described in detail again.

[0063] Next, in step 103, data is delayed. The I bit stream is delayed, wherein the delay time is T C , which is equal to the width of one chip;

[0064] Next, in step 104, Gaussian pulse shaping is performed. Gaussian pulse shaping is performed on the delayed I-channel bit stream and the Q-channel bit stream to obtain the I-channel baseband signal a i (t) and Q roadbed signal a q (t);

[0065] Next, in step 105, the baseband signal a is modulated to an intermediate frequency carrier. i (t) and Q roadbed signal a q (t) are multiplied by Then modulate it to the intermediate frequency carrier, that is, a i (t) multiplied by Then multiply it by cos(ω*t) to get a q (t) multiplied by Then multiply by sin(ω*t), where ω is the angular frequency of the RF carrier; and

[0066] Finally, in step 106, the signals are combined. By combining the two signals modulated onto the intermediate frequency carrier, a DSSS-GMSK signal is obtained, which can be up-converted and transmitted to the satellite. The DSSS-GMSK signal is a digital intermediate frequency signal.

[0067] In one embodiment of the present invention, 1 to N groups of spreading codes may be modulated together to form the following final transmitted signal:

[0068]

[0069] in, is the I-channel baseband signal of the k-th group of spreading codes, is the Q-path baseband signal of the k-th group of spreading codes, and f0 is the RF carrier frequency.

[0070] Based on the signal modulation method described above, Figure 3 A flow chart showing a communication method for aerospace according to an embodiment of the present invention is shown as follows: Figure 3 As shown, spacecraft and satellites need to dynamically capture the received DSSS-GMSK signal with low carrier-to-noise ratio and high Doppler, and perform signal tracking and demodulation. Specifically, this includes:

[0071] First, in step 301, a valid signal is captured. After receiving the digital intermediate frequency signal, it is necessary to capture the valid signal. In one embodiment of the present invention, the digital intermediate frequency signal is modulated according to the signal modulation method as described above, that is, a DSSS-GMSK signal. In one embodiment of the present invention, after the digital intermediate frequency signal is input, it is first subjected to DC filtering and digital automatic gain control (AGC), and then multiplied by a locally generated local carrier, wherein the local carrier includes I carrier cos(2πft)cos(R c t / 2) and Q-channel carrier-sin(2πft)sin(R c t / 2), then passes through a low-pass filter and then performs downsampling, wherein the sampling interval of downsampling is related to the Doppler frequency shift, and the result is recorded as I udsam , Q udsam , then I udsam and Q udsam Interweaving is denoted as S rev The result is sent to the PMF-FFT capture module for calculation. In one embodiment of the present invention, the low-pass filter is a high-order CIC filter, and its passband bandwidth is Rc / 2, where Rc is the spread spectrum code rate. Figure 4 A schematic diagram showing the process of an effective signal acquisition method according to an embodiment of the present invention is shown. Figure 4As shown, in one embodiment of the present invention, the PMF-FFT capture module captures a valid signal as follows: performing L-point partial correlation on the interleaved signal and the local spreading PN code, performing K summation operations, and then storing the output data of the K correlators obtained by calculation into a block random access memory (BRAM, Block Random Access Memory), where the length of the block random access memory is N, and N is a power of 2. If K is less than N, then pad N - K zeros. Next, perform a fast Fourier transform on the data in the block random access memory to obtain an N-point output result. After that, perform a normalization calculation on the N-point output result. If the result meets the preset requirements, it is considered that a valid signal has been captured; otherwise, move the local spreading code by one code phase and perform the correlation and fast Fourier transform operations again until a valid signal is captured. In one embodiment of the present invention, using the spectral characteristics, the maximum value of the modulus in the N-point output result is denoted as P i max0 , the second largest value is denoted as P i max1 , and the average value of the modulus is denoted as P i avg , then the preset condition means that the ratio of the maximum value of the modulus in the N-point output result to the average value of the modulus is greater than the first preset value, and the ratio of the maximum value to the second maximum value is less than the second preset value, that is, |P i max0 \P i avg |>X, and |P i max0 \P i max1 |<Y. In one embodiment of the present invention, the value of X is 22, and the value of Y is 1.1. It should be understood that in some other embodiments of the present invention, the values of X and Y can be fine-tuned according to actual needs, or other values can be adopted;

[0072] Next, in step 302, determine the Doppler shift value. In one embodiment of the present invention, as Figure 5 shown, multiply the digital intermediate frequency signal by multiple locally generated local carriers, where the center frequencies of each local carrier are different, and according to the method described in step 301, capture the valid signals of each path in parallel, and then select an optimal valid signal therefrom to determine the Doppler shift value. Except that the center frequencies of the local carriers used by each path of signals are different, the sampling intervals during downsampling are also different, and different sampling intervals correspond to different Doppler translations. In one embodiment of the present invention, the total number of parallel captures is determined based on a comprehensive consideration of the capture time and resources. In one embodiment of the present invention, the one with the maximum normalization gain, that is, |P i max \Pi avg The branch with the largest | value is regarded as the optimal effective signal and used as the reference branch for calculating the Doppler shift. Figure 6 A schematic diagram of the PMF-FFT calculation results of an embodiment of the present invention is shown. The Doppler shift value can be calculated based on the peak and sub-peak numbers of the PMF-FFT calculation results of the optimal effective signal; and

[0073] Finally, in step 303, signal demodulation is performed, wherein the digital intermediate frequency signal is demodulated based on the Doppler shift value. Figure 7 FIG. 1 is a schematic diagram showing a process of a signal tracking and demodulation method according to an embodiment of the present invention. Figure 7 As shown, in one embodiment of the present invention, after determining the Doppler shift value, the digital intermediate frequency signal is first subjected to DC filtering and digital automatic gain control, and then combined with the local carrier cos(2πf acq t)cos(R c t / 2), -sin(2πf acq t)sin(R c t / 2), where f acq The center frequency of the local carrier is equal to the center frequency of the local carrier used by the optimal effective signal. The I and Q signals obtained by multiplication are then downsampled, wherein the initial downsampling interval is provided by the PMF-FFT capture module and is the same as the downsampling interval used when capturing the optimal effective signal. After downsampling, the I and Q signals are multiplied by a local spreading code, wherein the local spreading code is coarsely synchronized. The calculation results of the I and Q signals are then phase-detected. Phase compensation is generated based on the phase-detection results and sent to the I and Q local carriers. Code phase compensation is also generated based on the leading and lagging codes and sent to the local spreading code. In one embodiment of the present invention, the phase compensation is output through a phase-locked loop. The signal synchronized with the local carrier and the local spreading code is then interleaved and input into a low-pass filter for low-pass filtering, wherein the bandwidth of the low-pass filter is determined by the data rate. The low-pass filtered signal is then downsampled, and then bit-looped for data bit synchronization. Finally, the result of the data bit synchronization is frame-synchronized to complete demodulation.

[0074] The aforementioned communication method can improve and replace DSSS-BPSK modulation, enhancing the EMC of satellites transmitting at multiple frequencies while also increasing bandwidth utilization. Specifically, for satellite X-band multi-frequency transmissions, including one spread-spectrum signal and one data transmission signal, with a spread-spectrum signal bit rate of 3.069 Mbps, the DSSS-BPSK communication system occupies a total bilateral bandwidth of approximately 6.138 Mbps. However, using DSSS-GMSK and selecting a Gaussian filter with a BT of 0.3 reduces the bilateral bandwidth to 2.36 Mbps, significantly reducing the impact of the spread-spectrum signal on the data transmission signal's bandwidth.

[0075] Based on the signal modulation method described above, the present invention further provides a signal modulation system, which includes:

[0076] An XOR module, which is used to perform an XOR operation on the data code element and the pseudo code sequence;

[0077] a serial-to-parallel conversion module, communicatively connected to the XOR module, for converting the output data of the XOR module into serial-to-parallel data;

[0078] a data delay module, communicatively connected to the serial-to-parallel conversion module, for performing delay processing on the I-channel bit stream obtained by the serial-to-parallel conversion;

[0079] a Gaussian filter shaping module, communicatively connected to the data delay module and the serial-to-parallel conversion module, for performing Gaussian pulse shaping on the delayed I bit stream and the Q bit stream obtained by the serial-to-parallel conversion, respectively, to obtain an I baseband signal and a Q baseband signal;

[0080] A plurality of first multiplication modules are communicatively connected to the Gaussian filter shaping module, and are used to implement the multiplication operation of the I-way baseband signal and the Q-way baseband signal. Specifically, the I-way baseband signal is multiplied by Then multiply it by cos(ω*t) to multiply the Q-band signal by Then multiply by sin(ω*t), where ω is the angular frequency of the RF carrier; and

[0081] A signal combining module is communicatively connected to the first multiplication module and is used to combine two signals modulated onto an intermediate frequency carrier to obtain a DSSS-GMSK signal.

[0082] Based on the aforementioned communication method, the present invention further provides a communication system for aerospace applications, comprising a capture module and a demodulation module. The capture module is configured to receive a signal and determine a Doppler shift according to the aforementioned method. The demodulation module is communicatively connected to the capture module and is configured to perform signal demodulation based on the Doppler shift according to the aforementioned method. The signal received by the capture module is modulated using the aforementioned signal modulation method, i.e., a DSSS-GMSK signal.

[0083] In one embodiment of the present invention, the capture module includes:

[0084] A DC filtering submodule, which is used to perform DC filtering on the input intermediate frequency digital signal;

[0085] A digital AGC, which is communicatively connected to the DC filtering submodule and is used to perform digital automatic gain control on the DC filtered signal;

[0086] a plurality of second multiplication submodules, communicatively connected to the digital AGC, and configured to multiply the automatically gained signal by a local carrier;

[0087] a plurality of first low-pass filters, communicatively connected to the second multiplication submodules in a one-to-one correspondence, for performing low-pass filtering on the output data of the second multiplication module. In one embodiment of the present invention, the first low-pass filters are high-order CIC low-pass filters;

[0088] a plurality of first downsampling submodules, which are communicatively connected to the first low-pass filters in a one-to-one correspondence and are used to downsample the data after the low-pass filtering;

[0089] a first interleaving submodule, communicatively connected to the first downsampling submodule, and configured to interleave the downsampled I and Q signals;

[0090] a signal capture submodule, communicatively connected to the first interleaving submodule, for performing effective signal capture based on the interleaved signal according to the aforementioned method, i.e., the PMF-FFT technique;

[0091] a threshold decision submodule, which is communicatively connected to the signal capture submodule and is used to perform normalization calculation on the output result of the signal capture submodule and determine whether the signal is a valid signal; and

[0092] The optimal effective signal determination submodule is communicatively connected to each threshold decision submodule, and is used to compare the outputs of each threshold decision submodule and select the one with the largest normalized gain as the optimal effective signal.

[0093] In one embodiment of the present invention, the demodulation module includes:

[0094] A DC filtering submodule, which is used to perform DC filtering on the input intermediate frequency digital signal;

[0095] A digital AGC, which is communicatively connected to the DC filtering submodule and is used to perform digital automatic gain control on the DC filtered signal;

[0096] two third multiplication submodules, communicatively connected to the digital AGC, and configured to multiply the automatically gained signal by a local carrier;

[0097] two second low-pass filters, communicatively connected to the third multiplication submodule in a one-to-one correspondence, for performing low-pass filtering on the output data of the multiplication module. In one embodiment of the present invention, the second low-pass filters are high-order CIC low-pass filters;

[0098] two second downsampling submodules, which are communicatively connected to the second low-pass filters in a one-to-one correspondence and are used to downsample the data after the low-pass filtering;

[0099] two fourth multiplication submodules, which are communicatively connected to the second downsampling submodule in a one-to-one correspondence, and are used to perform a product operation on the downsampled I and Q signals with the local spreading code;

[0100] a second interleaving submodule, communicatively connected to the fourth multiplication submodule, configured to interleave the I and Q signals multiplied by the local spreading code;

[0101] a third low-pass filter, communicatively connected to the second interleaving submodule, and configured to perform low-pass filtering on the interleaved signal;

[0102] a third down-sampling submodule, communicatively connected to the third low-pass filter, and configured to down-sample the low-pass filtered signal;

[0103] a bit ring, communicatively connected to the third downsampling submodule, for performing data bit synchronization on the downsampled signal;

[0104] a frame capture submodule, which is communicatively connected to the bit ring and is used to perform frame synchronization on the result of data bit synchronization to complete demodulation;

[0105] a phase detector, communicatively connected to the fourth multiplication submodule, for performing a phase detection operation on the I and Q signals multiplied by the local spreading code;

[0106] A phase-locked loop is communicatively connected to the phase detector and is used to obtain phase compensation based on the phase detection operation result.

[0107] a spreading code loop, communicatively connected to the fourth multiplication submodule, for generating a code phase compensation based on the leading and lagging codes and sending the generated code phase compensation to the local spreading code module; and

[0108] The local spreading code module is used to generate leading and lagging codes.

[0109] Although various embodiments of the present invention have been described above, it should be understood that they are presented by way of example only and not limitation. It will be apparent to those skilled in the relevant art that various combinations, modifications, and variations may be made thereto without departing from the spirit and scope of the present invention. Therefore, the breadth and scope of the present invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely in accordance with the appended claims and their equivalents.

Claims

1. A signal modulation method for aerospace, characterized in that: The data is modulated based on direct sequence spread spectrum and Gaussian minimum shift keying modulation technology.

2. The signal modulation method according to claim 1, wherein: include: Perform XOR operation on the data and the pseudo code sequence; Performing serial-to-parallel conversion on the data obtained by the XOR operation to obtain an I-path bit stream and a Q-path bit stream; The I-channel bit stream is delayed, wherein the delay time is T C , which is equal to the width of one chip; Performing Gaussian pulse shaping on the delayed I bit stream and the Q bit stream to obtain an I baseband signal and a Q baseband signal; Multiply the I-channel baseband signal and the Q-channel baseband signal by post-modulation to an intermediate frequency carrier; and Combine the two signals modulated to the intermediate frequency carrier.

3. The signal modulation method according to claim 1, wherein: Also includes: N groups of spreading codes are modulated simultaneously to form the signal to be transmitted: in, is the I-channel baseband signal of the k-th group of spreading codes, is the Q-path baseband signal of the k-th group of spreading codes, and f0 is the RF carrier frequency.

4. A communication method for aerospace, characterized in that: include: After receiving a digital intermediate frequency signal, capturing an optimal effective signal and determining a Doppler shift value, wherein the digital intermediate frequency signal is modulated according to the signal modulation method according to any one of claims 1 to 3; as well as The digital intermediate frequency signal is demodulated based on the Doppler shift value.

5. The communication method according to claim 4, wherein: Capturing the best valid signals includes: multiplying the digital intermediate frequency signal by a plurality of locally generated local carriers, wherein the center frequencies of the local carriers are different and each local carrier includes an I carrier and a Q carrier; Down-sampling the I and Q signals obtained by multiplication in each channel and then interleaving them; Capturing each interleaved signal separately, and determining the normalized gain of each channel based on the spectrum characteristics; and The channel with the largest normalized gain is selected as the optimal effective signal.

6. The communication method according to claim 5, wherein: Capturing the best valid signal also includes: Before multiplying the digital intermediate frequency signal with the locally generated multiple local carriers, performing DC filtering and digital automatic gain control on the digital intermediate frequency signal; and / or Before downsampling, the I-channel and Q-channel signals obtained by multiplication are low-pass filtered.

7. The communication method according to claim 5, wherein: Capture each interleaved signal based on the probability mass function and fast Fourier transform: Perform L-point partial correlation on the interleaved signal and the local spread spectrum PN code, and perform K summation operations; The calculated K correlator output data are stored in a block random access memory, where the length of the block random access memory is N, where N is a power of 2, and if K is less than N, NK zeros are padded; Performing a fast Fourier transform on the data in the block random access memory to obtain N-point output results; as well as The N-point output results are normalized and calculated. If the result meets the preset requirements, it is considered that a valid signal is captured. Otherwise, the local spread spectrum code is moved by one code phase, and correlation and fast Fourier transform operations are performed again until a valid signal is captured.

8. The communication method according to claim 7, wherein: The preset conditions include: The ratio of the maximum value to the average value of the modulus values ​​of the N-point output results is greater than a first preset value, and the ratio of the maximum value to the sub-maximum value is less than a second preset value.

9. The communication method according to claim 5, wherein: Demodulating the digital intermediate frequency signal based on the Doppler shift value includes: multiplying the digital intermediate frequency signal by a locally generated local carrier, wherein a center frequency of the local carrier is equal to a center frequency of the local carrier used by the optimal effective signal, and the local carrier includes an I carrier and a Q carrier; Downsampling the I and Q signals obtained by multiplication, wherein an initial interval of the downsampling is the same as the downsampling interval used when capturing the optimal valid signal; Performing a product operation on the I and Q signals obtained by downsampling and the local spreading code, wherein the local spreading code has been coarsely synchronized; Perform phase detection operation on the calculation results of I and Q channels; Phase compensation is generated based on the phase detection result and sent to the I and Q local carriers. At the same time, code phase compensation is generated based on the leading and lagging codes and sent to the local spread spectrum code. Interweaving signals synchronized with the local carrier and local spreading code; Low-pass filtering the interleaved signal; Down-sample the low-pass filtered signal; performing data bit synchronization on the downsampled signal; and The result of data bit synchronization is frame synchronized to complete demodulation.

10. The communication method according to claim 9, wherein: Demodulating the digital intermediate frequency signal based on the Doppler shift value further includes: Before multiplying the digital intermediate frequency signal with the locally generated multiple local carriers, direct current filtering and digital automatic gain control are performed on the digital intermediate frequency signal.

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