An Adaptive and Variable Link Transmission Method for Airborne Missile Group Networks

Abstract

This invention discloses an adaptive link transmission method for airborne missile swarm networks, comprising: receiving a signal and then digitally down-converting it to obtain sampled data; passing the sampled data through a correlator to obtain a coherently demodulated data sequence; performing an N-point FFT spectral analysis on the obtained coherently demodulated data sequence to obtain the carrier frequency offset; after the FFT spectral analysis, detecting whether spectral peaks appear in the spectral analysis results, making an acquisition decision, and thus completing coarse synchronization; after the signal is acquired, calculating the peak values ​​of the corresponding power spectrum of the acquired signal, and finding the maximum value of these peaks, with the sampling point corresponding to this maximum peak value being the fine synchronization point; through the above steps, fast frame synchronization, precise symbol synchronization, and initial frequency offset estimation are performed on the signal. This invention achieves efficient and reliable communication of airborne missile swarms in complex electromagnetic environments by combining correlation-based FFT fast acquisition and synchronization technology and spatial diversity reception technology.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to an adaptive link transmission method for airborne missile swarm networks. Background Technology

[0002] As a crucial air strike force, the stability and efficiency of the communication network of airborne missile swarms are essential for the successful completion of combat missions. However, due to the high relative speed and acceleration of airborne missiles at both the transmitting and receiving ends, this highly dynamic environment introduces significant Doppler frequency offset and frequency offset variation rate into the signal. Ordinary 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, an adaptive link transmission method for airborne missile swarm networks is provided. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing methods and provide an adaptive link transmission method for airborne missile groups. By combining correlation-based FFT (Fast Fourier Transform) fast acquisition and synchronization technology and spatial diversity reception technology, it enables efficient and reliable communication of airborne missile groups in complex electromagnetic environments.

[0005] The technical solution to achieve the above objectives is:

[0006] An adaptive and variable link transmission method for airborne missile swarm networks includes:

[0007] Step S1: The received signal is digitally down-converted to obtain sampled data;

[0008] Step S2: After the sampled data passes through the correlator, the coherently demodulated data sequence is obtained from the sampled data;

[0009] Step S3: Perform N-point FFT spectral analysis on the acquired coherent demodulated data sequence to obtain the carrier frequency offset value;

[0010] Step S4: After FFT spectral analysis, detect whether there are spectral peaks in the spectral analysis results, make a capture decision, and then complete coarse synchronization;

[0011] Step S5: After the signal is captured, calculate the peak value of the power spectrum corresponding to the captured signal, and find the maximum value of these peak values. The sampling point corresponding to the maximum peak value is the fine synchronization point.

[0012] Step S6: Through the above steps, perform fast frame synchronization, precise symbol synchronization, and initial frequency offset estimation on the signal.

[0013] Preferably, in step S1, acquiring sampling data includes:

[0014] Assume the received signal for:

[0015] ;

[0016] ;

[0017] In the formula, In order to transmit signals, For code width, The transmission delay is relative to the receiver. It is additive white Gaussian noise. Given the data, The number of code elements.

[0018] Preferably, in step S2, for data-assisted algorithms, the log-likelihood function is:

[0019] ;

[0020] ;

[0021] In the formula, These are the coefficients of the log-likelihood function. This is the output of the matched filter.

[0022] Preferably, in step S3, the peak value with the largest amplitude among the N outputs is selected as the output of FFT, and it is determined whether the peak value 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 value is the frequency offset value of the carrier.

[0023] Preferably, in step S4, the maximum value of the spectral analysis result is compared with the threshold value. If the maximum value exceeds the threshold value, it is determined that the pseudocode has been found.

[0024] Preferably, in step S5, the frequency offset value is compared with the coordinates of the corresponding power spectrum peak value after synchronization. One-to-one correspondence, when When the value is less than N / 2, the carrier frequency offset is positive, and its absolute value is [value missing]. ,when When the value is greater than N / 2, the carrier frequency offset is negative, and its absolute value is [value missing]. Under QPSK (quad phase shift keying) modulation, the carrier frequency offset With symbol rate Proportional to the FFT points and the extraction factor MF (the range of values ​​for a discrete random variable) length Inversely proportional, that is:

[0025] ;

[0026] .

[0027] The beneficial effects of this invention are as follows: This invention uses a correlator for modulation, N-point FFT output, maximum correlation value selection, and acquisition decision. After coarse synchronization, it uses this as a base point for further modulation to complete fine synchronization, which significantly improves the synchronization speed and accuracy, enhances the signal-to-noise ratio and transmission reliability of the received signal, and realizes real-time monitoring and dynamic adjustment of the channel status, thereby improving the communication performance of the airborne missile group network. Attached Figure Description

[0028] Figure 1 This is a flowchart of an adaptive link transmission method for airborne missile swarm networks according to the present invention;

[0029] Figure 2 This is a schematic diagram of the correlation-based FFT capture principle in this invention;

[0030] Figure 3 This is a schematic diagram of the maximum ratio receiver using two receiving antennas in this invention;

[0031] Figure 4 This is a comparison chart of the receiving performance of single antenna and dual antenna in an embodiment of the present invention;

[0032] Figure 5 This is a performance comparison chart of maximum ratio merging and equal gain merging in the embodiments of the present invention;

[0033] Figure 6 This is a performance comparison chart of the ideal signal-to-noise ratio and the estimated signal-to-noise ratio in an embodiment of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings. In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are 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, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] The invention will now be further described with reference to the accompanying drawings.

[0036] like Figure 1 , 2 As shown, an adaptive link transmission method for airborne missile swarm networks includes:

[0037] Step S1: The received signal is digitally down-converted to obtain sampled data.

[0038] In this embodiment, acquiring sampling data includes:

[0039] Assume the received signal for:

[0040] ;

[0041] ;

[0042] In the formula, In order to transmit signals, For code width, The transmission delay is relative to the receiver. It is additive white Gaussian noise. Given the data, The number of code elements.

[0043] Step S2: After the sampled data is passed through the correlator, the coherent demodulated data sequence is obtained from the sampled data.

[0044] In this embodiment, for data-assisted algorithms, the log-likelihood function is:

[0045] ;

[0046] ;

[0047] In the formula, These are the coefficients of the log-likelihood function. This is the output of the matched filter.

[0048] The above analysis shows that the correlation acquisition method can achieve rapid synchronization. Considering the influence of the local oscillator frequency difference of the transceiver and the Doppler frequency shift in the system, the correlation peak in the traditional correlation acquisition method drops sharply. To overcome the influence of frequency offset, an FFT-based acquisition method is adopted. While searching for the synchronization code phase, the frequency offset estimate is obtained, thus transforming the original two-dimensional search process of frequency offset and phase into a one-dimensional phase search.

[0049] Step S3: Perform N-point FFT spectral analysis on the acquired coherent demodulated data sequence (considering the maximum frequency offset, partial FFT is sufficient) to obtain the carrier frequency offset value.

[0050] In this embodiment, the peak value with the largest amplitude among the N outputs is selected as the output of the FFT. It is then determined whether the peak value is greater than the capture threshold. If it is greater than the threshold, it means that the target has been captured. The frequency value corresponding to the peak value is the frequency offset value of the carrier.

[0051] Step S4: After FFT spectral analysis, detect whether there are spectral peaks in the spectral analysis results, make a capture decision, and then complete coarse synchronization.

[0052] In the embodiment, theoretically, after performing FFT spectral analysis, it is necessary to detect whether spectral peaks appear in the spectral analysis results. That is, the maximum value of the spectral analysis results is compared with the threshold value. If the maximum value exceeds the threshold value, it is determined that the pseudocode has been found. However, in actual systems, the amplitude of the transmitted signal is unknown, so it is not possible to judge solely based on the peak value. The ratio of the peak value of the power spectrum to the mean value after peak removal can be used as the decision criterion. This ratio (peak-to-average power ratio) is compared with the threshold value, which is unaffected by the signal amplitude.

[0053] Removing peak values ​​from the power spectrum and averaging the remaining power spectrum values ​​is essentially an estimate of the background signal power level. This level decreases rapidly with increasing signal-to-noise ratio (SNR). That is, at perfect synchronization, the peak-to-average ratio (PAR) increases rapidly with increasing SNR. Therefore, using the lowest operating point as a benchmark, we calculate the average PAR at perfect synchronization and use this as the basic PAR decision threshold. Through simulation, we set this value to 32. Since the amplitude of received signal variation effectively reflects the SNR, we calculate the PAR of the received signal and use it to adjust the PAR threshold of the power spectrum. This ensures that the PAR threshold increases with increasing SNR. Again, using the PAR of the received signal at the lowest operating point as a benchmark, we set this value to 8 through simulation. Let the PAR of the received signal calculated each time be par; then the decision threshold for the power spectrum PAR is 256 / par.

[0054] Step S5: After the signal is captured, calculate the peak value of the power spectrum corresponding to the captured signal, and find the maximum value of these peak values. The sampling point corresponding to the maximum peak value is the fine synchronization point.

[0055] 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 it, calculate the peak value of the corresponding power spectrum, and find the maximum value of these peak values ​​(note that at this time, the peak value is compared, not the peak-to-average power ratio). The sampling point corresponding to the maximum peak value is the fine synchronization point.

[0056] In the embodiment, the frequency offset value is compared with the coordinates of the corresponding power spectrum peak value after synchronization. One-to-one correspondence, when When the value is less than N / 2, the carrier frequency offset is positive, and its absolute value is [value missing]. ,when When the value is greater than N / 2, the carrier frequency offset is negative, and its absolute value is [value missing]. Under QPSK (quad phase shift keying) modulation, the carrier frequency offset With symbol rate Proportional to the FFT points and the extraction factor PMF (range of values ​​for a discrete random variable) length Inversely proportional, that is:

[0057] ;

[0058] .

[0059] Once a signal is captured, the peak coordinates of its corresponding power spectrum are fixed, and the calculated frequency offset is also fixed, regardless of the signal-to-noise ratio. The accuracy depends on the number of FFT points. The more sampling points the FFT transform has, the closer the distance between the sampling points, the denser the spectral lines, the less spectral leakage, and the closer the estimated frequency offset is to the true value.

[0060] Step S6: Through the above steps, perform fast frame synchronization, precise symbol synchronization, and initial frequency offset estimation on the signal.

[0061] Test the capture performance under QPSK (quadrature phase shift keying) modulation

[0062] The test conditions were: a 128-length synchronization code, 4 sampling points per modulation symbol, a frequency offset of 1 / 2 relative to the symbol rate, a 512-length irrelevant signal preamplified by the synchronization code, and a peak-to-average power ratio threshold of 192 / par (par is the peak-to-average power ratio of the received baseband signal).

[0063] The capture performance is shown in Table 1, with each SNR (signal-to-noise ratio) tested 10,000 times.

[0064]

[0065] Table 1. Capture performance under various SNRs

[0066] The FFT-based parallel search and capture algorithm can achieve fast frame synchronization, accurate symbol synchronization, and initial frequency offset estimation under conditions of short synchronization codes and low signal-to-noise ratio. This proves that the present invention can effectively reduce system synchronization overhead.

[0067] In step S1, after the received signal undergoes digital down-conversion, spatial diversity technology is employed as a pre-process for data transmission before acquiring sampled data. This process aims to improve the signal-to-noise ratio (SNR), thereby enhancing transmission reliability and resistance to fast fading and shadowing fading. This includes:

[0068] Spatial diversity technology uses two receiving antennas, one above the other, and employs maximum ratio combining during baseband combining, such as... Figure 3 As shown, this is to counteract shadow fading caused when an antenna is blocked.

[0069] Spatial diversity can take three forms: transmit diversity, receive diversity, and transmit-receive diversity. Based on the system's one-transmit, two-receive configuration, this invention employs spatial diversity reception.

[0070] Spatial diversity reception utilizes multiple receiving antennas. The transmitting end uses one antenna to transmit, while the receiving end uses multiple antennas to receive. The distance between the receiving antennas is d ≥ λ / 2 (λ is the operating wavelength) to ensure 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 other receiving antennas may not necessarily show a low amplitude at the same time). After appropriate signal combining processing, a single output signal is obtained. Compared to the signal received by a single antenna, this combined signal has a higher SNR, which can significantly improve transmission reliability.

[0071] After acquiring several independent tributary signals at the receiving end, diversity gain must be obtained through combining techniques. The combining criteria and methods mainly fall into four categories: maximum ratio combining, equal gain combining, selective combining, and switching combining. Among these combining methods, maximum ratio combining has the best performance. When N is large, the combining gain of equal gain combining is close to that of maximum ratio combining.

[0072] 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 terms of channel coherence time.

[0073] Based on the foregoing analysis, this system employs two receiving antennas, one above the other, and uses maximum ratio combining at the baseband level to combat shadowing fading caused by one antenna being blocked. At the receiver, the signal-to-noise ratio (SNR) of each channel is estimated based on the pilot sequence. The maximum ratio of the two SNRs is used to perform linear processing on the two received signals. Then, maximum likelihood detection is used to reconstruct the original information from the transmitter. The decoding process is simple and easy to implement, making it the optimal combining method.

[0074] System fast fading simulation:

[0075] Simulation conditions:

[0076] 1. Valid information bits: 34968 bits;

[0077] 2. Modulation method: QPSK modulation;

[0078] 3. Pilot sequences: 8 Frank-Zadoff sequences, each 64 bytes long;

[0079] 4. Channel model: SUI5 channel model, with path delays of [0, 4, 12.0] μs and relative power delays of [0, -3, -5] dBW;

[0080] 5. Equalization method: Frequency domain equalization, FFT block length is 2048 symbols.

[0081] When transmitting with a single antenna, the performance (demodulated performance) of receiving with a single antenna and receiving with a dual antenna are compared. The simulation results are as follows: Figure 4 As shown.

[0082] System anti-shadowing fading simulation:

[0083] Simulation conditions:

[0084] 1. Valid information bits: 1024 bits;

[0085] 2. Encoding method: CTC encoding / decoding with a bit rate of 1 / 2;

[0086] 3. Modulation method: QPSK modulation;

[0087] 4. Pilot sequence: 1 Frank-Zadoff sequence, length 64;

[0088] 5. Channel model: Two Gaussian channels, one of which is always blocked, and EbN0 = -4dB.

[0089] When estimating the signal-to-noise ratio using pilot sequences, the performance of maximum ratio combining and equal-gain combining is compared. The simulation results are as follows: Figure 5 As shown.

[0090] In the case of maximum ratio merging, the performance of the ideal signal-to-noise ratio and the estimated signal-to-noise ratio is compared. The simulation results are as follows: Figure 6 As shown.

[0091] As can be seen from the aforementioned system simulation, under ideal channel estimation conditions, the antenna diversity gain can reach 5dB for fast fading channels and 7dB for shadowed fading channels.

[0092] The channel estimation diversity gain based on pilot sequences suffers a performance loss of about 1 dB compared to the ideal case, proving that the scheme is feasible.

[0093] In summary, antenna receiver diversity technology using maximum ratio combining can effectively combat fast fading and shadow fading.

[0094] This 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.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 method for adaptive and variable link transmission in an airborne missile swarm network, characterized in that, include: Step S1: The received signal is digitally down-converted to obtain sampled data; Step S2: After the sampled data passes through the correlator, the coherent demodulated data sequence is obtained from the sampled data; Step S3: Perform N-point FFT spectral analysis on the acquired coherent demodulated data sequence to obtain the carrier frequency offset value; Step S4: After FFT spectral analysis, detect whether there are spectral peaks in the spectral analysis results, 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 fine synchronization point. Based on the fine synchronization point, accurate symbol synchronization is completed, and the initial frequency offset estimation is achieved by combining the carrier frequency offset value obtained in step S3, thus completing fast frame synchronization. in, In step S5, the frequency offset value is compared with the coordinates of the corresponding power spectrum peak value after synchronization. One-to-one correspondence, when When the value is less than N / 2, the carrier frequency offset is positive, and its absolute value is [value missing]. ,when When the value is greater than N / 2, the carrier frequency offset is negative, and its absolute value is [value missing]. Under QPSK modulation, carrier frequency offset With symbol rate Proportional to the FFT points and the extraction factor PMF length Inversely proportional, that is: ； 。 2. The adaptive and variable link transmission method for airborne missile swarm networks according to claim 1, characterized in that, In step S1, acquiring sampling data includes: Assume the received signal for: ； ； In the formula, In order to transmit signals, For code width, The transmission delay is relative to the receiver. It is additive white Gaussian noise. Given the data, The number of code elements.

3. The adaptive link transmission method for airborne missile swarm networks according to claim 1, characterized in that, In step S2, for data-assisted algorithms, the log-likelihood function is: ； ； In the formula, These are the coefficients of the log-likelihood function. This is the output of the matched filter.

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

5. The adaptive link transmission method for airborne missile swarm networks according to claim 1, characterized in that, In step S4, the maximum value of the spectral analysis result is compared with the threshold value. If the maximum value exceeds the threshold value, it is determined that the pseudocode has been found.

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