An improved S-mode signal demodulation method

Abstract

The present invention provides an improved S-mode signal demodulation method, including: obtaining all symbols corresponding to the ADS-B signal by using a preamble pulse detection method, and then performing a preliminary determination on all symbols by using a baseline multi-point determination method to output the symbol of each symbol and the confidence level corresponding to the symbol; sampling the symbols with low confidence levels at equal intervals, and dividing the sampling values into pre-amplitude sampling values and post-amplitude sampling values, and respectively calculating the average values of the pre-amplitude sampling values and the post-amplitude sampling values; for each symbol, determining whether both the average value of the pre-amplitude sampling values and the average value of the post-amplitude sampling values are within the determination window. If so, it is determined that both the interference and the signal energy of the symbol are within the determination window; using the symbols and confidence levels of the previous and subsequent symbols to perform a secondary determination on the symbols whose interference and signal energy are both within the determination window, which can more accurately determine the symbol of the symbol, reduce the bit error rate, and improve the performance of S-mode signal demodulation.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication signal processing, and particularly relates to an improved S-mode signal demodulation method. Background Art

[0002] ADS-B (Automatic Dependent Surveillance-Broadcast) is an air traffic monitoring and cooperative surveillance system based on automatic periodic transmission of ICAO (International Civil Aviation Organization) addresses, flight identifications, navigation and other surveillance parameters. This system extracts flight surveillance parameters from on-board systems such as the latitude, longitude, barometric altitude and speed of the aircraft. Different from radar surveillance systems, it does not require any external interrogation signals. ADS-B information can be received by ground stations, which can merge the data with data from other surveillance systems; or it can be received by aircraft equipped with ADS-B.

[0003] The transmission frequency of the S-mode ADS-B broadcast signal is 1090 MHz, which is the same as the transmission frequency of the secondary surveillance radar downlink signal. Therefore, in the case of high A / C broadcast asynchronous interference overlap, the channel occupancy rate is relatively high, which is very likely to cause error code problems in ADS-B receiving devices. Therefore, a demodulation algorithm is needed to solve this problem.

[0004] The existing demodulation algorithms are as follows:

[0005] (1) 6dB threshold method: As the main method currently adopted, this method takes the midpoint sampling value of two chips, determines the position where the sampling point with a higher amplitude appears as the position of the pulse, and thus determines whether the decoded value is "0" or "1". This method takes the leading pulse reference level 6 dB lower as the threshold. If the two sampling points are one higher and one lower compared with the threshold, the data of the pulse is decoded with high confidence. If the two midpoint sampling values are both higher or both lower compared with the threshold, it is decoded with low confidence.

[0006] (2) Midpoint decision method: Also known as the ±3dB window method. According to the regulations of ICAO (International Civil Aviation Organization), the in-pulse flatness of the S-mode pulse train is within 1 - 2 dB, and the data pulse level and the leading pulse level of the non-interfered data should be within this range, which is used as the basis for decision. This method also takes the midpoint sampling values of two chips for decision, takes the leading pulse reference level as the benchmark, and determines the ±3dB window. When one of the values of the two midpoints is within ±3dB and the other is lower than the ±3dB window, or one is within ±3dB and the other is higher than the ±3dB window, "0" or "1" is determined according to the position of the point within ±3dB, and high confidence is output.

[0007] When both are within the ±3dB window, or both are outside the ±3dB window, it is determined as low confidence.

[0008] (3) Baseline multi-point decision method: This method uses the reference level of the leading pulse detection output as the reference, determines the ±3dB window that matches the reference level, and sets the threshold level 6dB lower than the reference level. The ±3dB window and the sampling points below the threshold are weighted and counted. The edge of each chip is multiplied by 1 for the two points, and the middle point is multiplied by 2 for the three points. The weighted counts are performed in the ±3dB window in the 0.5μs before and after, and the weighted counts are performed in the 0.5μs before and after that are below the threshold.

[0009] A1: weighted count value within the ±3dB window in the first 0.5μs;

[0010] A0: weighted count value within the ±3dB window in the last 0.5μs;

[0011] B1: weighted count value below the threshold in the first 0.5 μs;

[0012] B0: Weighted count value below the threshold in the next 0.5μs.

[0013] S1 represents the degree of ideal data "1", and S0 represents the degree of ideal data "0".

[0014]

[0015] Compare the values ​​of S1 and S0 to determine the symbol. When the value of S1 or S0 is greater than or equal to 3, it is determined to be high confidence. When the values ​​of S1 and S0 are 1 and 2, it is low confidence. When the values ​​of S1 and S0 are equal, the low confidence "0" is output.

[0016] For the 6dB threshold method and the midpoint decision method, they only take two points for judgment. Although the amount of calculation is lower than that of the baseline multi-point decision method, due to too few sampling points, its bit error rate and low confidence rate are much higher than those of the baseline multi-point decision method. For the baseline multi-point decision method, it is obviously better than the midpoint decision method and the 6dB value method. However, since the pulse width of the A / C mode can reach 0.55μs, the midpoints of the two chips are about 0.5μs apart, interference may occur to raise the midpoint of the vacant chip to within the ±3dB window, which will cause the baseline multi-point decision method to fail. Summary of the invention

[0017] In order to solve the above problems existing in the prior art, the present invention provides an improved S-mode signal demodulation method. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0018] The present invention provides an improved S-mode signal demodulation method comprising:

[0019] S1. Use the leading pulse detection method to obtain all the code elements corresponding to the Automatic Dependent Surveillance - Broadcast (ADS - B) signal, and use the baseline multi - point decision method to make a preliminary decision on all the code elements, and output the code element symbols of all the code elements and the confidence levels corresponding to the code element symbols;

[0020] S2. Sample the code elements with low confidence levels according to the sampling points, and divide the sampling values into pre - amplitude sampling values and post - amplitude sampling values, and respectively calculate the average values of the pre - amplitude sampling values and the post - amplitude sampling values;

[0021] S3. For each code element, determine whether both the average value of the pre - amplitude sampling values and the average value of the post - amplitude sampling values are within the decision window. If so, it is determined that both the interference and the signal energy of this code element are within the decision window;

[0022] S4. Use the previous and subsequent code element symbols and the confidence levels to perform a secondary decision on the code elements whose interference and signal energy are both within the decision window, so as to output the code element symbols and the confidence levels corresponding to the code element symbols.

[0023] The present invention provides an improved S - mode signal demodulation method, including: using the leading pulse detection to obtain all the code elements corresponding to the ADS - B signal, and using the baseline multi - point decision method to make a preliminary decision on all the code elements, and outputting the code element symbols of all the code elements and the confidence levels corresponding to the code element symbols; sampling the code elements with low confidence levels at equal intervals, and dividing the sampling values into pre - amplitude sampling values and post - amplitude sampling values, and respectively calculating the average values of the pre - amplitude sampling values and the post - amplitude sampling values; for each code element, determining whether both the average value of the pre - amplitude sampling values and the average value of the post - amplitude sampling values are within the decision window. If so, it is determined that both the interference and the signal energy of this code element are within the decision window; using the previous and subsequent code element symbols and the confidence levels, performing bit decoding and confidence level analysis on the code elements with similar interference energy and signal energy through secondary decision, reducing the bit error rate, and at the same time improving the accuracy of signal demodulation.

[0024] The following will further elaborate on the present invention in detail with reference to the accompanying drawings and embodiments. Description of the Drawings

[0025] Figure 1 is the flowchart of an improved S - mode signal demodulation method of the present invention;

[0026] Figure 2 is the comparison chart of the bit error rates between the present invention and other demodulation methods;

[0027] Figure 3 is the comparison chart of the low confidence rates between the present invention and other demodulation methods. Detailed Embodiments

[0028] The following further describes the present invention in detail with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0029] Before introducing the details of the solution of the present invention, a brief introduction to the technical concept of the present invention will be given first.

[0030] The 6dB threshold method, the midpoint decision method, and the baseline multi-point decision method cannot solve the problem of being interfered with and having similar interference energy and signal energy. Because the pulse width of the A / C mode can reach 0.55 μs, and the midpoints of two chips are about 0.5 μs apart. It is possible that the interference raises the midpoint of the empty chip into the ±3dB window, causing the midpoint of the high level to exceed the ±3dB window range. To solve the problem that the existing ADS-B demodulation method cannot accurately judge the interference energy and signal energy which are similar, thus affecting the bit error rate. In view of the sudden characteristic of the interference, the present invention makes full use of the symbols and confidence levels of the front and rear code elements to perform a secondary decision on the basis of the baseline multi-point decision, and then judge the symbol and confidence level of the code element, which can reduce the bit error rate to a greater extent.

[0031] Once the signal preamble pulse is detected successfully, it indicates that the receiver has successfully received a frame of ADS-B message. However, to extract the information carried therein, demodulation and extraction of the position confidence are required. Since the ADS-B signal uses pulse position modulation and each code element consists of two chips, the general method of demodulation is to detect the first half position chip 1 and the second half position chip 2 of each code element respectively. If the signal strength at the position of chip 1 is higher than the signal strength at the position of chip 2, the value of this code element is represented as "1"; conversely, if the signal strength at the position of chip 1 is lower than the signal strength at the position of chip 2, the value of this code element is represented as "0".

[0032] As Figure 1 shown, the present invention provides an improved S-mode signal demodulation method, including:

[0033] S1, using the preamble pulse detection method to obtain all the code elements corresponding to the automatic dependent surveillance - broadcast ADS-B signal, and using the baseline multi-point decision method to perform a preliminary decision on all the code elements, and output the code element symbols of all the code elements and the confidence levels corresponding to the code element symbols;

[0034] Specifically, S1 of the present invention includes:

[0035] S11, using the preamble pulse detection method to obtain all the code elements corresponding to the automatic dependent surveillance - broadcast ADS-B signal;

[0036] S12, taking the reference level output by the preamble pulse detection as the benchmark, determining the ±3dB window matching the reference level, and determining the level 6dB lower than the reference level as the threshold level;

[0037] Among them, the code element is divided into two chips according to 0.5 μs before;

[0038] S13, sample the chips at equal intervals according to a predetermined sampling frequency, and determine the target sampling points located within the ±3dB window or below the threshold level;

[0039] S14, according to the different positions of the target sampling points, perform weighted counting on the target sampling points using corresponding weighted count values;

[0040] Among them, the weighted count values of the target sampling points are divided into 4 categories:

[0041] A1: The weighted count value of the target sampling points within the ±3dB window in the first 0.5μs; A0: The weighted count value of the target sampling points within the ±3dB window in the latter 0.5μs; B1: The weighted count value of the target sampling points below the threshold level in the first 0.5μs; B0: The weighted count value of the target sampling points below the threshold level in the latter 0.5μs; If the target sampling points in two chips are edge points, the weighted count value is 1, and for the center point, the weighted count value is 2;

[0042] S15, calculate the accumulated values M0 and M1;

[0043] Among them, M0 represents the degree of matching with the symbol 0, and M1 represents the degree of matching with the symbol 1; M1 = A1 - A0 + B1 - B0; M2 = A0 - A1 + B0 - B1;

[0044] S16, compare the values of M1 and M2. If M1 is larger, output the symbol of the code element as 0. If M2 is larger, output the symbol of the code element as 1; When the values of M1 and M0 are equal, output the symbol of the code element as 0;

[0045] S17, when the value of M1 or M0 is greater than or equal to 3, mark the symbol of the code element as high confidence; When the values of M1 and M0 are 1 and 2, mark the symbol of the code element as low confidence; When the values of M1 and M0 are equal, mark the symbol of the code element as low confidence.

[0046] S2, sample the code elements with low confidence according to the sampling points, and divide the sampling values into the front amplitude sampling values and the back amplitude sampling values, and respectively calculate the average values of the front amplitude sampling values and the back amplitude sampling values;

[0047] In a specific embodiment, S2 includes:

[0048] S21, select the code elements with low confidence, sample the code elements at a fixed interval to obtain the sampling values;

[0049] Among them, m is the number of sampling points for each symbol of the code element;

[0050] S22. Divide the sampled values into the front amplitude sampled values, denoted as P = {pi}, and the rear amplitude sampled values, denoted as Q = {qi}, where i = 1 to m / 2;

[0051] S23. Calculate the average value x1 of the front amplitude sampled values and the average value x2 of the rear amplitude sampled values.

[0052]

[0053]

[0054] S3. For each symbol, determine whether both the average value of the front amplitude sampled values and the average value of the rear amplitude sampled values are within the determination window. If so, determine that both the interference and signal energy of this symbol are within the determination window;

[0055] In a specific embodiment, S3 includes:

[0056] S31. Taking the reference level output by the leading pulse detection as a benchmark, determine the ±3dB window that matches the reference level, and use this window as the determination window;

[0057] S32. Determine whether the average value x1 of the front amplitude sampled values and the average value x2 of the rear amplitude sampled values are both within the determination window. If so, determine that the interference and signal energy of the symbol are within the determination window; if either is not within the determination window or both are not within the determination window, output the original symbol and confidence level.

[0058] S4. Use the symbols and confidence levels of the previous and next symbols to perform a secondary decision on the symbols whose interference and signal energy are both within the determination window, so as to output the symbol and the confidence level corresponding to the symbol.

[0059] In a specific embodiment, S4 includes:

[0060] S41. For the symbol whose interference and signal energy are within the determination window, if the previous symbol of this symbol is 0 and this symbol has a high confidence level, read the sampled points near the initial point p1 of this symbol;

[0061] S42. Determine whether there is a point lower than the reference level -3dB among the sampled points near the initial point p1. If so, output the symbol as 0 and the confidence level as high; otherwise, output the original symbol and mark the symbol as having a low confidence level;

[0062] S43. If the next symbol of the symbol is 1 and the confidence level is high, read the sampled points near the end point of this symbol;

[0063] S44. Determine whether there is a point below the reference level of -3 dB among the sampling points near the end point of the symbol. If so, output the symbol of the symbol as 1 and the confidence level as high; otherwise, output the original symbol of the symbol and mark the symbol of the symbol as low confidence.

[0064] The present invention provides an improved S-mode signal demodulation device, including:

[0065] A preliminary decision module, configured to use the preamble pulse detection method to obtain all symbols corresponding to the ADS-B signal, and use the baseline multi-point decision method to make a preliminary decision on all symbols, and output the symbol of all symbols and the confidence level corresponding to the symbol;

[0066] A sampling module, configured to sample the symbols with low confidence at equal intervals, and divide the sampling values into pre-amplitude sampling values and post-amplitude sampling values, and respectively calculate the average values of the pre-amplitude sampling values and the post-amplitude sampling values;

[0067] A mean determination module, configured to determine for each symbol whether the average value of the pre-amplitude sampling values and the average value of the post-amplitude sampling values are both within the determination window. If so, determine that the interference and signal energy of the symbol are both within the determination window;

[0068] A secondary decision module, configured to use the symbols and confidence levels of the previous and subsequent symbols to make a secondary decision on the symbols whose interference and signal energy are both within the determination window, so as to output the symbol of the symbol and the confidence level corresponding to the symbol.

[0069] The present invention provides a receiver to implement an improved S-mode signal demodulation method.

[0070] Next, the present invention will be illustrated by way of examples.

[0071] In this example, the sampling frequency of the ADS-B signal is 20 MHz, so each symbol has 20 sampling points. The reference level benchmark output by the preamble pulse is R.

[0072] S1: Taking the reference level R output by the preamble pulse detection as the benchmark, determine the ±3 dB window (i.e., R ± 3 dB) that matches the reference level, and use the level 6 dB lower than the reference level R as the threshold level, and respectively perform weighted counting on the ±3 dB window and the sampling points below the threshold. Use 2 for the middle point and 1 for the edge points for weighted counting.

[0073] Then calculate two cumulative values. M1 represents the degree of matching with the ideal data "1", and M0 represents the degree of matching with the ideal data "0".

[0074] Compare the magnitudes of M1 and M0, and output the larger value as the decision result. When the value of M1 or M0 is greater than or equal to 3, the output data is considered to have a high confidence level. When the values of M1 and M0 are 1 and 2, the confidence level is low. When the values of M1 and M0 are equal, a low confidence level is output.

[0075] S2: Since the sampling frequency of this example is 20 MHz, the number of sampling points for each symbol is 20. The front amplitude sampling values are denoted as P = {p1, p2,..., p10}, and the rear amplitude sampling values are denoted as Q = {q1, q2,..., q10}.

[0076] Calculate the mean values of the front amplitude sampling value x1 and the rear amplitude sampling value x2:

[0077]

[0078]

[0079] S3: Taking the reference level R detected by the leading pulse as a benchmark, determine the R±3dB window that matches the reference level, and judge whether both the mean value x1 of the front amplitude sampling values and the mean value x2 of the rear amplitude sampling values are within the ±3dB window:

[0080] R - 3dB ≤ x1 ≤ R + 3dB

[0081] R - 3dB ≤ x2 ≤ R + 3dB

[0082] S4: If the symbol of the previous symbol of this symbol is 0 and the confidence level is high, read the sampling points near the initial point p1 of this symbol and judge whether there are points lower than the reference level R - 3dB. If so, output that the symbol of this symbol is 0 and the confidence level is high. If the symbol of the next symbol of this symbol is 1 and the confidence level is high, read the points near the end point of this symbol and judge whether there are points lower than the reference level - 3dB. If so, output that the symbol of this symbol is 1 and the confidence level is high. Otherwise, output the original symbol and confidence level.

[0083] Reference Figure 2 And Figure 3 As shown, the present invention respectively counts the bit error rates and low confidence rates of four decoding methods: the 6dB threshold method, the midpoint decision method, the baseline multi - point determination, and the secondary decision. The signal - to - noise ratios are 0 - 20 dB. The simulation results show that the low confidence rate of the midpoint decision method is higher than that of the 6dB threshold method. The bit error rates and low confidence rates of the baseline multi - point and secondary decision methods are very low. When the signal - to - noise ratio is 6dB, the bit error rate of the secondary decision method is only 0.3%. Therefore, it can be seen that the present invention can more effectively reduce the bit error rate and improve the accuracy of signal demodulation at the same time.

[0084] The present invention provides an improved S-mode signal demodulation method, including: obtaining all symbols corresponding to ADS-B signals by using a preamble pulse detection method, and performing preliminary determination on all symbols by using a baseline multi-point determination method to output the symbol of each symbol and the confidence level corresponding to the symbol; sampling the symbols with low confidence levels at equal intervals, and dividing the sampling values into pre-amplitude sampling values and post-amplitude sampling values, and respectively calculating the average values of the pre-amplitude sampling values and the post-amplitude sampling values; for each symbol, determining whether both the average value of the pre-amplitude sampling values and the average value of the post-amplitude sampling values are within a determination window. If so, it is determined that both the interference and the signal energy of the symbol are within the determination window; using the symbols and confidence levels of the previous and subsequent symbols to perform a secondary determination on the symbols for which both the interference and the signal energy are within the determination window, which can more accurately determine the symbol and reduce the bit error rate, thereby improving the performance of S-mode signal demodulation.

[0085] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0086] Although the present application has been described in conjunction with various embodiments herein, however, in the process of implementing the claimed present application, those skilled in the art can understand and implement other variations of the disclosed embodiments by viewing the accompanying drawings, the disclosed content, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "one" does not exclude a plurality of cases.

[0087] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. An improved S-mode signal demodulation method, characterized in that, Including: S1. Obtain all symbols of the Automatic Dependent Surveillance - Broadcast (ADS - B) signal by using the leading - pulse detection method, and perform a preliminary decision on all symbols by using the baseline multi - point decision method, and output the symbol of each symbol and the confidence level corresponding to the symbol of the code element; S2. Sample the symbols with low confidence levels according to the sampling points, and divide the sampling values into the front - amplitude sampling values and the back - amplitude sampling values, and respectively calculate the average values of the front - amplitude sampling values and the back - amplitude sampling values; S3. For each symbol, determine whether both the average value of the front - amplitude sampling values and the average value of the back - amplitude sampling values are within the decision window. If so, determine that both the interference and the signal energy of this symbol are within the decision window; S4. Use the symbols and confidence levels of the previous and subsequent symbols to perform a secondary decision on the symbols whose interference and signal energy are both within the decision window, so as to output the symbol of the code element and the confidence level corresponding to the symbol of the code element.

2. The improved S-mode signal demodulation method according to claim 1, characterized in that, S1 includes: S11. Obtain all symbols corresponding to the ADS - B signal by using the leading - pulse detection method; S12. Based on the reference level output by the leading - pulse detection, determine the ±3dB window that matches the reference level, and determine the level 6dB lower than the reference level as the threshold level; Wherein, the symbol is divided into two chips according to 0.5μs before; S13. Sample the chips at equal intervals according to the predetermined sampling frequency, and determine the target sampling points located within the ±3dB window or lower than the threshold level; S14. According to the different positions of the target sampling points, perform weighted counting on the target sampling points by using the corresponding weighted count values; Wherein, the weighted count values of the target sampling points are divided into 4 categories: A1: The weighted count value of the target sampling points within the ±3dB window in the first 0.5μs; A0: The weighted count value of the target sampling points within the ±3dB window in the latter 0.5μs; B1: The weighted count value of the target sampling points lower than the threshold level in the first 0.5μs; B0: The weighted count value of the target sampling points lower than the threshold level in the latter 0.5μs; If the target sampling point in the two chips is an edge point, the weighted count value is 1, and if it is a center point, the weighted count value is 2; S15. Calculate the cumulative values M0 and M1; Wherein, M0 represents the degree of matching with the symbol of 0, and M1 represents the degree of matching with the symbol of 1; M1 = A1 - A0 + B1 - B0; M2 = A0 - A1 + B0 - B1; S16. Compare the magnitudes of the values of M1 and M2. If M1 is larger, output the symbol of the code element as 0. If M2 is larger, output the symbol of the code element as 1. When the values of M1 and M0 are equal, mark the symbol of the code element as 0; S17. When the value of M1 or M0 is greater than or equal to 3, mark the symbol of the code element as high confidence. When the values of M1 and M0 are 1 and 2, mark the symbol of the code element as low confidence. When the values of M1 and M0 are equal, mark the symbol of the code element as low confidence.

3. The improved S-mode signal demodulation method according to claim 2, characterized in that, S2 Including: S21. Select the symbols with low confidence levels, sample this symbol at a fixed interval to obtain sampling values; Wherein, m is the number of sampling points of each symbol; S22. Divide the sampling values into the front - amplitude sampling values, denoted as P = {pi}, and the back - amplitude sampling values, denoted as Q = {qi}, where i = 1~m / 2; S23, obtain the average value x1 of the previous amplitude sampling values and the average value x2 of the subsequent amplitude sampling values.

4. The improved S-mode signal demodulation method according to claim 3, characterized in that, S3 Including: S31, taking the reference level output by the preamble pulse detection as a reference, determining a ±3dB window that matches the reference level, and using this window as the decision window; S32, determining whether both the average value x1 of the previous amplitude sampling values and the average value x2 of the subsequent amplitude sampling values are within the decision window. If so, determine that the interference and signal energy of the symbol are within the decision window; if either is not within the decision window or both are not within the decision window, output the original symbol and confidence level.

5. The improved S-mode signal demodulation method according to claim 1, characterized in that, S4 Including: S41, for a symbol whose interference and signal energy are within the decision window, if the previous symbol of this symbol is 0 and this symbol has a high confidence level, read the sampling points near the initial point p1 of this symbol; S42, determining whether there is a point lower than the reference level -3dB among the sampling points near the initial point p1. If so, output the symbol as 0 and the confidence level as high; otherwise, output the original symbol and mark the symbol with a low confidence level; S43, if the subsequent symbol of the symbol is 1 and the confidence level is high, read the sampling points near the end point of this symbol; S44, determining whether there is a point lower than the reference level -3dB among the sampling points near the end point of the symbol. If so, output the symbol as 1 and the confidence level as high; otherwise, output the original symbol and mark the symbol with a low confidence level.

6. An improved S-mode signal demodulation device, characterized in that, Including: A preliminary decision module, configured to use the preamble pulse detection method to obtain all symbols corresponding to the ADS-B signal, and perform a preliminary decision on all symbols using the baseline multi-point decision method, and output the symbol and the confidence level corresponding to the symbol of all symbols; A sampling module, configured to sample the symbols with low confidence levels at equal intervals, and divide the sampling values into previous amplitude sampling values and subsequent amplitude sampling values, and respectively obtain the average values of the previous amplitude sampling values and the subsequent amplitude sampling values; An average value decision module, configured to, for each symbol, determine whether both the average value of the previous amplitude sampling values and the average value of the subsequent amplitude sampling values are within the decision window. If so, determine that the interference and signal energy of this symbol are both within the decision window; A secondary decision module, configured to use the previous and subsequent symbol and the confidence level to perform a secondary decision on the symbol whose interference and signal energy are both within the decision window, so as to output the symbol and the confidence level corresponding to the symbol.

7. A receiver, characterized in that, Implement the improved S-mode signal demodulation method according to any one of claims 1 to 5.

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