Adaptive adaptive link transmission method for airborne missile group network

Abstract

The invention discloses a self-adaptive adaptive link transmission method for an airborne missile group network, and the method comprises the steps: carrying out the digital down-conversion of a received signal, so as to obtain sampling data; enabling the sampling data to pass through a correlator, and obtaining a coherent demodulation data sequence from the sampling data; performing N-point FFT (Fast Fourier Transform) spectrum analysis on the obtained coherent demodulation data sequence to obtain a frequency offset value of a carrier wave; after the FFT spectrum analysis, detecting whether a spectrum peak appears in a spectrum analysis result, and performing capture judgment to finish coarse synchronization; after the signals are captured, peak values of power spectrums corresponding to the captured signals are solved respectively, the maximum value of the peak values is found out, and a sampling point corresponding to the maximum peak value is a fine synchronization point; through the above steps, rapid frame synchronization, accurate symbol synchronization and initial frequency offset estimation are carried out on the signal. According to the invention, by combining a related FFT-based rapid capture synchronization technology and a space diversity reception technology, efficient and reliable communication of the airborne missile group in a complex electromagnetic environment is realized.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to an airborne missile swarm network self-adaptive link transmission method. Background Art

[0002] Airborne missile swarms are a vital aerial strike force, and the stability and efficiency of their communication networks are crucial to the successful completion of combat missions. However, due to the high relative speed and acceleration between the sending and receiving ends of airborne missiles, this highly dynamic environment introduces significant Doppler frequency deviation and frequency deviation variation to the signal. Conventional acquisition and tracking algorithms struggle to achieve timely synchronous despreading, severely impacting the transmission efficiency and reliability of the airborne missile swarm communication link.

[0003] Therefore, a self-adaptive link transmission method for an airborne swarm network is provided. Summary of the Invention

[0004] The purpose of the present invention is to overcome the existing defects and provide an adaptive link transmission method for airborne missile swarm networks, which realizes efficient and reliable communication of airborne missile swarms in complex electromagnetic environments by combining fast capture synchronization technology based on correlation FFT (Fast Fourier Transform) and spatial diversity reception technology.

[0005] The technical solution to achieve the above purpose is: An airborne missile swarm network self-adaptive link transmission method, comprising: Step S1, receiving a signal and performing digital down-conversion to obtain sampled data; Step S2, after the sampled data passes through the correlator, a coherently demodulated data sequence is obtained from the sampled data; Step S3, performing N-point FFT spectrum analysis on the obtained coherently demodulated data sequence to obtain the frequency deviation value of the carrier; Step S4: After FFT spectrum analysis, detect whether there is a spectrum peak in the spectrum analysis result, make a capture decision, and then complete coarse synchronization; Step S5: After the signal is captured, the peak values ​​of the power spectrum corresponding to the captured signal are calculated respectively, and the maximum value of these peak values ​​is found. The sampling point corresponding to the maximum peak value is the precise synchronization point. Step S6: Through the above steps, fast frame synchronization, precise symbol synchronization, and initial frequency offset estimation are performed on the signal.

[0006] Preferably, in step S1, obtaining sampling data includes: Assume receiving signal for: ; ; Where, To transmit the signal, is the code width, is the transmission delay relative to the receiver, is additive white Gaussian noise, For known data, is the number of code elements.

[0007] Preferably, in step S2, for the data-assisted algorithm, the log-likelihood function is: ; ; Where, is the coefficient of the log-likelihood function, is the matched filter output.

[0008] Preferably, in step S3, the peak with the largest amplitude among the N outputs is selected as the output of FFT, and it is determined whether the peak is greater than the capture threshold. If it is greater than the threshold, it means that it has been captured, and the frequency value corresponding to the peak is the frequency deviation value of the carrier.

[0009] Preferably, in step S4, the maximum value of the spectrum analysis result is compared with a threshold value. If the maximum value exceeds the threshold value, it is determined that the pseudo code has been searched.

[0010] Preferably, in step S5, the frequency deviation value is synchronized with the coordinates of the corresponding power spectrum peak. One-to-one correspondence, when When it is less than N / 2, the carrier frequency deviation is positive and its absolute value is ,when When it is greater than N / 2, the carrier frequency deviation is negative, and its absolute value is , under QPSK (quadrature phase shift keying) modulation, the carrier frequency deviation Symbol rate Proportional to the number of FFT points and decimation factor , MF (the size of the range of values ​​of the discrete random variable) length Inversely proportional, that is: ; .

[0011] The beneficial effects of the present invention are as follows: the present invention performs capture judgment through correlator demodulation, N-point FFT output, maximum correlation value selection, and after completing coarse synchronization, further modulates based on this to complete fine synchronization, significantly improving the synchronization speed and accuracy, enhancing the signal-to-noise ratio and transmission reliability of the received signal, and realizing real-time monitoring and dynamic adjustment of the channel status, thereby improving the communication performance of the airborne missile swarm network. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a flow chart of an airborne missile swarm network self-adaptive link transmission method of the present invention; Figure 2 This is a schematic diagram of the capture principle based on correlation FFT in the present invention; Figure 3 is a schematic diagram of a maximum ratio receiver using two receiving antennas in the present invention; Figure 4 1 is a comparison chart of the receiving performance of a single antenna and a dual antenna in an embodiment of the present invention; Figure 5 1 is a performance comparison diagram of maximum ratio combining and equal gain combining in an embodiment of the present invention; Figure 6 3 is a performance comparison diagram of an ideal signal-to-noise ratio and an estimated signal-to-noise ratio in an embodiment of the present invention. DETAILED DESCRIPTION

[0013] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0014] The present invention will be further described below with reference to the accompanying drawings.

[0015] like Figure 1 、 2 As shown, an airborne swarm network adaptive link transmission method includes: Step S1: The received signal is digitally down-converted to obtain sampled data.

[0016] In the embodiment, obtaining the sampled data includes: Assume receiving signal for: ; ; Where, To transmit the signal, is the code width, is the transmission delay relative to the receiver, is additive white Gaussian noise, For known data, is the number of code elements.

[0017] Step S2: After the sampled data passes through a correlator, a coherently demodulated data sequence is obtained from the sampled data.

[0018] In the embodiment, for the data-assisted algorithm, the log-likelihood function is: ; ; Where, is the coefficient of the log-likelihood function, is the matched filter output.

[0019] The above analysis demonstrates that rapid synchronization can be achieved using the correlation acquisition method. Considering the influence of the transceiver's local oscillator frequency offset and Doppler shift, the correlation peak in the traditional correlation acquisition method drops dramatically. To overcome the effects of frequency offset, an FFT-based acquisition method is employed. This method simultaneously estimates the frequency offset while searching for the synchronization code phase, transforming the original two-dimensional frequency offset and phase search process into a one-dimensional phase search.

[0020] Step S3: Perform N-point FFT spectrum analysis on the obtained coherently demodulated data sequence (taking into account the maximum frequency deviation, a partial FFT is sufficient) to obtain the frequency deviation value of the carrier.

[0021] In the embodiment, the peak with the largest amplitude among the N outputs is selected as the FFT output, and it is determined whether the peak is greater than the capture threshold. If it is greater than the threshold, it means that it has been captured, and the frequency value corresponding to the peak is the frequency deviation value of the carrier.

[0022] Step S4: After FFT spectrum analysis, detect whether a spectrum peak appears in the spectrum analysis result, make a capture decision, and then complete coarse synchronization.

[0023] In this embodiment, theoretically, after completing FFT spectrum analysis, it is necessary to detect the presence of a spectral peak in the spectrum analysis results. Specifically, the maximum value of the spectral analysis result is compared with a threshold value. If the maximum value exceeds the threshold value, it is determined that the pseudo code has been found. However, in actual systems, the amplitude of the transmitted signal is unknown, so the peak value alone cannot be used for judgment. Instead, the ratio of the peak value of the power spectrum to the average value after removing the peak value can be used as the basis for judgment. This ratio (peak-to-average ratio) can be compared with the threshold value, which is not affected by the signal amplitude.

[0024] Removing the peak from the power spectrum and averaging the remaining power spectrum values ​​is actually an estimate of the background signal power level, which decreases rapidly with increasing signal-to-noise ratio. That is, at full synchronization, the peak-to-average ratio increases rapidly with increasing signal-to-noise ratio. Therefore, using the lowest operating point as a benchmark, we calculate the average peak-to-average ratio at full synchronization and use this as the basic decision threshold for the peak-to-average ratio. Through simulation observations, we set this value to 32. Furthermore, since the amplitude of the received signal's fluctuations can well reflect the signal-to-noise ratio, we calculate the peak-to-average ratio of the received signal and use it to adjust the peak-to-average ratio threshold of the power spectrum. This ensures that the peak-to-average ratio threshold increases with increasing signal-to-noise ratio. Still using the peak-to-average ratio of the received signal at the lowest operating point as a benchmark, we set this value to 8 through simulation observations. Letting the peak-to-average ratio of the received signal calculated each time be par, the decision threshold for the power spectrum peak-to-average ratio is 256 / par.

[0025] Step S5: After the signal is captured, the peak values ​​of the power spectrum corresponding to the captured signal are calculated respectively, and the maximum value of these peak values ​​is found. The sampling point corresponding to the maximum peak value is the precise synchronization point.

[0026] After the signal is captured, only the coarse synchronization process is completed. Theoretically, it may deviate from the ideal synchronization point by one symbol. It is necessary to use this coarse synchronization point as a reference, find one symbol before and after, calculate the peak value of the corresponding power spectrum, and find the maximum value of these peak values ​​(note that the peak value is compared instead of the peak-to-average ratio at this time). The sampling point corresponding to the maximum peak value is used as the fine synchronization point.

[0027] In the embodiment, the frequency deviation value is synchronized with the coordinates of the corresponding power spectrum peak. One-to-one correspondence, when When it is less than N / 2, the carrier frequency deviation is positive and its absolute value is ,when When it is greater than N / 2, the carrier frequency deviation is negative, and its absolute value is , under QPSK (quadrature phase shift keying) modulation, the carrier frequency deviation Symbol rate Proportional to the number of FFT points and decimation factor , PMF (the size of the range of values ​​of discrete random variables) length Inversely proportional, that is: ; .

[0028] As long as the signal is captured, the peak coordinates of its corresponding power spectrum are certain, and the calculated frequency deviation is certain, which is independent of the signal-to-noise ratio. The accuracy depends on the number of FFT points. The more FFT transform sampling points there are, the closer the distance between the samples, the denser the spectrum lines, the less spectrum leakage, and the closer the frequency deviation estimate is to the true value.

[0029] Step S6: Through the above steps, fast frame synchronization, precise symbol synchronization, and initial frequency offset estimation are performed on the signal.

[0030] Test the capture performance under QPSK (quadrature phase shift keying) modulation The test conditions are: 128-bit synchronization code, 4 sampling points per modulation symbol, frequency deviation of 1 / 2 relative to the symbol rate, 512-bit irrelevant signal prepended to the synchronization code, and a peak-to-average ratio threshold of 192 / par (par is the peak-to-average ratio of the received baseband signal).

[0031] The capture performance is shown in Table 1. Each SNR (signal-to-noise ratio) was tested 10,000 times.

[0032]

[0033] Table 1 Capture performance at various SNRs The FFT-based parallel search and acquisition algorithm can achieve fast frame synchronization, accurate symbol synchronization, and initial frequency offset estimation under conditions of shorter synchronization codes and low signal-to-noise ratios, thus proving that the present invention can effectively reduce system synchronization overhead.

[0034] In step S1, after the received signal undergoes digital down-conversion and before obtaining sampled data, spatial diversity technology is used as a pre-process for data transmission to improve the SNR, thereby improving transmission reliability and resisting fast fading and shadow fading, including: The spatial diversity technology uses two upper and lower receiving antennas, and adopts the maximum ratio combining method when combining at the baseband, such as Figure 3 As shown, this is to combat the shadow fading caused when one antenna is blocked.

[0035] There are three forms of spatial diversity: transmit diversity, receive diversity, and transmit-receive diversity. According to the configuration of one transmit and two receive systems, the present invention adopts the spatial diversity receive form.

[0036] Spatial diversity reception is achieved by utilizing multiple receiving antennas. The transmitter uses a single antenna for transmission, while the receiver uses multiple antennas for reception. The distance between the receiving antennas, d ≥ λ / 2 (λ is the operating wavelength), ensures that the fading characteristics of the output signals from the receiving antennas are independent of each other. (When the output signal level of one receiving antenna is low, the output levels of the other receiving antennas may not also be low at the same time.) After the corresponding signals are combined and processed, a single output signal is generated. This combined signal has a higher signal-to-noise ratio (SNR) than a single-antenna signal, significantly improving transmission reliability.

[0037] After obtaining several independent branch signals at the receiving end, diversity gain must be achieved through combining techniques. Four main combining criteria and methods are used: maximum ratio combining, equal gain combining, selective combining, and switching combining. Of these combining methods, maximum ratio combining offers the best performance. When N is large, the combining gain of equal gain combining approaches that of maximum ratio combining.

[0038] Diversity reception not only has the ability to resist fast fading, but also has the same effect on shadow fading, because fast fading and shadow fading are essentially just different in channel coherence time.

[0039] Based on the preceding analysis, this system uses two upper and lower receiving antennas, and employs maximum ratio combining at baseband to mitigate shadow fading caused by obstruction of one antenna. At the receiving end, the signal-to-noise ratio of each channel is estimated based on the pilot sequence. The maximum ratio of these two ratios is then used to perform linear processing on the two received signals. Maximum likelihood detection is then used to recover the original information at the source. This simple and easy-to-implement decoding process makes it the optimal combining method.

[0040] System anti-fast fading simulation: Simulation conditions: 1. Effective information bits: 34968 bits; 2. Modulation mode: QPSK modulation; 3. Pilot sequence: 8 64-bit Frank-Zadoff sequences; 4. Channel model: SUI5 channel model, each path delay is [0, 4, 12.0] μs, and the relative power delay is [0, -3, -5] dBW; 5. Equalization mode: frequency domain equalization, FFT block length is 2048 symbols.

[0041] When transmitting with a single antenna, the performance of receiving with a single antenna is compared with that of receiving with two antennas (performance after demodulation). The simulation results are as follows: Figure 4 shown.

[0042] System anti-shadow fading simulation: Simulation conditions: 1. Effective information bits: 1024 bits; 2. Encoding method: CTC codec with a code rate of 1 / 2; 3. Modulation mode: QPSK modulation; 4. Pilot sequence: 1 Frank-Zadoff sequence, length 64; 5. Channel model: Two Gaussian channels, assuming one of them is always blocked, set EbN0=-4dB.

[0043] When the pilot sequence estimates the signal-to-noise ratio, the performance of maximum ratio combining and equal gain combining is compared. The simulation results are as follows: Figure 5 shown.

[0044] In the case of maximum ratio merging, the performance of the ideal signal-to-noise ratio and the estimated signal-to-noise ratio are compared. The simulation results are as follows: Figure 6 shown.

[0045] From the above system simulation, we can see that under ideal channel estimation conditions, the antenna diversity gain can reach 5dB for fast fading channels and 7dB for shadow fading channels.

[0046] The diversity gain of the channel estimation based on the pilot sequence loses about 1dB compared with the performance in the ideal case, which proves that the scheme is feasible.

[0047] In summary, the antenna receive diversity technology using maximum ratio combining can effectively resist fast fading and shadow fading.

[0048] The present invention significantly improves the synchronization speed and accuracy of airborne missile groups in complex electromagnetic environments, reduces the overhead of synchronization prefixes, improves transmission efficiency, and can effectively resist fast fading and shadow fading.

[0049] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-adaptive link transmission method for an airborne swarm network, characterized in that: include: Step S1, receiving a signal and performing digital down-conversion to obtain sampled data; Step S2, after the sampled data passes through the correlator, a coherently demodulated data sequence is obtained from the sampled data; Step S3, performing N-point FFT spectrum analysis on the obtained coherently demodulated data sequence to obtain the frequency deviation value of the carrier; Step S4: After FFT spectrum analysis, detect whether there is a spectrum peak in the spectrum analysis result, make a capture decision, and then complete coarse synchronization; Step S5: After the signal is captured, the peak values ​​of the power spectrum corresponding to the captured signal are calculated respectively, and the maximum value of these peak values ​​is found. The sampling point corresponding to the maximum peak value is the precise synchronization point. Step S6: Through the above steps, fast frame synchronization, precise symbol synchronization, and initial frequency offset estimation are performed on the signal.

2. The method for self-adaptive link transmission of an airborne swarm network according to claim 1, characterized in that: In step S1, obtaining sampling data includes: Assume receiving signal for: ； ； Where, To transmit the signal, is the code width, is the transmission delay relative to the receiver, is additive white Gaussian noise, For known data, is the number of code elements.

3. The method for self-adaptive link transmission of an airborne swarm network according to claim 1, characterized in that: In step S2, for the data-assisted algorithm, the log-likelihood function is: ； ； Where, is the coefficient of the log-likelihood function, is the matched filter output.

4. The method for self-adaptive link transmission of an airborne swarm network according to claim 1, characterized in that: In step S3, the peak with the largest amplitude among the N outputs is selected as the FFT output, and it is determined whether the peak is greater than the capture threshold. If it is greater than the threshold, it means that it has been captured, and the frequency value corresponding to the peak is the frequency deviation value of the carrier.

5. The method for self-adaptive link transmission of an airborne swarm network according to claim 1, characterized in that: In step S4, the maximum value of the spectrum analysis result is compared with a threshold value. If the maximum value exceeds the threshold value, it is determined that the pseudo code has been searched.

6. The method for self-adaptive link transmission of an airborne swarm network according to claim 1, characterized in that: In step S5, the frequency deviation value is synchronized with the coordinates of the corresponding power spectrum peak. One-to-one correspondence, when When it is less than N / 2, the carrier frequency deviation is positive and its absolute value is ,when When it is greater than N / 2, the carrier frequency deviation is negative, and its absolute value is , under QPSK modulation, the carrier frequency deviation Symbol rate Proportional to the number of FFT points and decimation factor , PMF length Inversely proportional, that is: ； 。

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