Doppler-code phase two-dimensional joint search same frequency multi-target signal detection method

Abstract

The application discloses a Doppler-code phase two-dimensional joint search same-frequency multi-target signal detection method and relates to the field of spaceflight measurement and control. The application generates a global energy matrix through two-dimensional joint correlation calculation and incoherent accumulation at a receiving end according to the Doppler frequency shift caused by satellite movement and the code phase offset caused by signal propagation time delay difference, calculates an adaptive threshold, suppresses strong signal sidelobe interference by defining a protection area, and improves weak signal detection probability to more than 90%. The application allocates tracking channels in descending order of energy, and achieves the purpose of efficient detection of multiple targets at the same time. The application is especially suitable for Doppler-code phase two-dimensional joint search same-frequency multi-target signal detection in a low-orbit satellite constellation or a dense satellite network, and solves the problems of low spectrum utilization and complex pseudo code management of traditional frequency division / code division technology.

Description

Technical Field

[0001] This invention relates to the field of aerospace telemetry and control, and in particular to a method for detecting multi-target signals at the same frequency using a two-dimensional joint Doppler-code phase search. It is applicable to low-Earth orbit satellite constellations or dense satellite networks, and solves the problems of low spectrum utilization and complex pseudo-code management in traditional frequency division / code division technologies. Background Technology

[0002] With the rapid development of low-Earth orbit satellite constellations, the number of satellites is growing exponentially. Existing satellite multi-target reception technologies mainly rely on frequency division multiple access (FDMA) or code division multiple access (CDMA). Traditional frequency division multiple access poses serious challenges to spectrum resources, pseudo-code management, and system design.

[0003] FDMA requires different satellites to transmit signals at different frequencies, resulting in low spectrum utilization; according to ITU reports, FDMA spectrum utilization is less than 30%. CDMA requires assigning a unique pseudo-random code to each satellite. Pseudo-random code resources are limited and allocation and management are complex. The number of satellites is also limited; for example, GPS only supports 32 satellites. Both onboard and ground equipment need to support multi-band or multi-pseudo-random code generation, significantly increasing hardware costs and power consumption, and resulting in high system complexity.

[0004] Existing detection technologies are typically single-dimensional (Doppler or code phase only), unable to distinguish signals at the same frequency. Traditional two-dimensional search algorithms fail to address the problem of weak signals being masked by the side lobes of strong signals. When the signal-to-noise ratio is below -15dB, the probability of weak signals being masked by the side lobes of strong signals exceeds 50%, and the lack of an efficient multi-target channel allocation mechanism leads to wasted tracking resources. Achieving high-precision separation of multiple targets under the same frequency and code conditions, suppressing strong signal side lobe interference, improving the detection probability of weak signals, and realizing real-time processing with limited hardware resources are among the key problems that urgently need to be solved for large-scale constellations. Summary of the Invention

[0005] To address the problems in the background technology, a two-dimensional joint Doppler-code phase search method for detecting multiple targets at the same frequency is proposed. By utilizing the Doppler frequency shift caused by satellite motion and the code phase shift caused by the difference in signal propagation time delay, a global energy matrix is ​​generated at the receiver through two-dimensional joint correlation calculation and incoherent accumulation. An adaptive threshold is calculated, and strong signal sidelobe interference is suppressed by defining a protection region, thereby increasing the detection probability of weak signals to over 90%. Tracking channels are allocated in descending order of energy to achieve the goal of simultaneous and efficient detection of multiple targets.

[0006] The technical solution of this invention is as follows:

[0007] A method for detecting multiple targets at the same frequency using a two-dimensional joint Doppler-code phase search includes the following steps:

[0008] (1) Receive multi-target signals with the same frequency and code, downconvert them to baseband and perform segmented sampling;

[0009] (2) Perform two-dimensional joint correlation calculation of Doppler-code phase on each segment of the sampled signal to generate a segmented energy matrix;

[0010] (3) Perform incoherent accumulation of the energy matrices of each segment to generate the global energy matrix;

[0011] (4) Calculate the adaptive threshold based on the global energy matrix;

[0012] (5) Extract all candidate peaks with energies higher than the threshold from the global energy matrix and sort them in descending order of energy value to obtain a candidate peak list;

[0013] (6) For the candidate peak with the highest energy in the candidate peak list, a protection region is defined in the two-dimensional domain of Doppler and code phase with it as the center. Only the main peak with the highest energy is retained in the protection region, and other energy peaks are removed. The retained main peak is recorded as a valid detection target and then added to the list of valid detection targets.

[0014] (7) Update the candidate peak list: Remove the candidate peaks removed in step (6) and the main peaks that are retained from the current candidate peak list;

[0015] Determine whether the updated candidate peak list is empty. If it is empty, proceed to step (8); otherwise, return to step (6) based on the updated candidate peak list.

[0016] (8) For the list of effective detection targets, the effective detection targets are sorted in descending order of energy and then assigned to the idle tracking channels in sequence until the channel resources are exhausted, thus completing the detection of multi-target signals at the same frequency by Doppler-code phase joint search.

[0017] Furthermore, the expression for the two-dimensional joint correlation calculation of the Doppler-code phase in step (2) is as follows:

[0018]

[0019] In the formula E i (f d ,τ) represents the two-dimensional joint correlation value of the i-th sampled signal, s i (t k ) represents the i-th sampled signal, t k Let c(t) represent the k-th sampling time. k -τ) represents the phase-shifted version of the local pseudocode, f d τ represents the Doppler frequency shift search value, τ represents the code phase offset search value, and N represents the segmented signal length, N = T coh ·f sf s T represents the sampling rate. coh denoted by , where j represents the coherent integration time and j represents the imaginary unit.

[0020] Furthermore, in step (3), the global energy matrix E(f) d The expression for calculating τ is:

[0021]

[0022] In the formula, S represents the number of segments.

[0023] Furthermore, the adaptive threshold Γ is calculated in step (4) as follows:

[0024] Γ=μ n +K·σ n ;

[0025] In the formula μ n σ represents the mean of the noise region in the global energy matrix. n represents the standard deviation of the noise region in the global energy matrix, and K represents the threshold coefficient.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. The present invention enables all satellites to transmit isomorphic signals with the same frequency and pseudocode, which helps to reduce the complexity of satellite design.

[0028] 2. This invention can accommodate more satellites in the same frequency band, breaking through the capacity limitations of traditional frequency division / code division and improving spectrum utilization.

[0029] 3. This invention defines a protection region to suppress strong signal sidelobe interference through Doppler-code phase joint decision, which is beneficial to improving the detection probability of weak signals. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the processing in an embodiment of the present invention.

[0031] Figure 2 The figures show the simulation performance curves of detection probability and false alarm probability in the embodiments of the present invention.

[0032] Figure 3 This is a three-dimensional schematic diagram of candidate peak detection for multi-target signals based on Doppler-code phase in an embodiment of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific implementation steps:

[0034] A method for detecting multiple targets at the same frequency using a two-dimensional joint Doppler-code phase search, referring to... Figure 1The specific steps include:

[0035] (1) Receive multi-target signals with the same frequency and code, downconvert to baseband and perform segmented sampling.

[0036] In this example, the same frequency and same code signal uses the Gold sequence, the pseudo-code period is 1023, there are 3 multi-target signals, the Doppler frequencies are 1kHz, -2kHz and 3kHz respectively, the code phases are 300, 700 and 100 chips respectively, and the signal-to-noise ratios are -10dB, -15dB and -20dB respectively.

[0037] (2) Perform two-dimensional joint correlation calculation on each signal segment to generate a segmented energy matrix;

[0038] The expression for the two-dimensional joint correlation calculation is as follows:

[0039]

[0040] In the formula E i (f d ,τ) represents the two-dimensional joint correlation value of the i-th sampled signal, s i (t k ) represents the i-th sampled signal, t k Let c(t) represent the k-th sampling time. k -τ) represents the phase-shifted version of the local pseudocode, f d τ represents the Doppler frequency shift search value, τ represents the code phase offset search value, and N represents the segmented signal length, N = T coh ·f s f s T represents the sampling rate. coh denoted by , where j represents the coherent integration time and j represents the imaginary unit.

[0041] Example, sampling rate f s = 1.023 Mbps, coherent integration time T coh =1ms, segmented signal length N=1023.

[0042] (3) Perform incoherent accumulation of the energy matrices of each segment to generate the global energy matrix;

[0043] Wherein, the global energy matrix E(f d The expression for calculating τ is:

[0044]

[0045] In the formula, S represents the number of segments.

[0046] In the example, the number of segments is 10, and each segment lasts 1ms.

[0047] (4) Calculate the adaptive threshold based on the global energy matrix; global energy matrix;

[0048] The method for calculating the adaptation threshold Γ is as follows:

[0049] Γ=μ n +K·σ n

[0050] In the formula μ n σ represents the mean of the noise region in the global energy matrix. n The standard deviation of the noise region in the global energy matrix is ​​represented by K, and the threshold coefficient is represented by K. Based on engineering experience, the threshold coefficient K is typically taken as 2.5 to 4.0. This embodiment is based on 3σ. n Criteria: Threshold coefficient K=3, false alarm rate <0.3%, detection probability >90%, refer to Figure 2 .

[0051] (5) Extract all candidate peaks with energy above the threshold and sort them in descending order of energy value;

[0052] The candidate peak illustration is referenced. Figure 3 The candidate peak list is

[0053] C = {f d ,τ,E)}

[0054] (6) For the candidate peak with the highest energy in the candidate peak list, a protection region is defined in the two-dimensional domain of Doppler and code phase with it as the center. Only the main peak with the highest energy is retained in the protection region, and other energy peaks are removed. The retained main peak is recorded as a valid detection target and then added to the list of valid detection targets.

[0055] In this embodiment, the protected regions are defined as Δf and Δτ in the two-dimensional domains of Doppler and code phase, respectively. Δf = 1 / T coh Δτ is a chip.

[0056] (7) Update the candidate peak list: Remove the candidate peaks removed in step (6) and the main peaks that are retained from the current candidate peak list;

[0057] Determine whether the updated candidate peak list is empty. If it is empty, proceed to step (8); otherwise, return to step (6) based on the updated candidate peak list.

[0058] (8) For the list of effective detection targets, the effective detection targets are sorted in descending order of energy and then assigned to the idle tracking channels in sequence until the channel resources are exhausted, thus completing the detection of multi-target signals at the same frequency by Doppler-code phase joint search.

[0059] Finally, it should be noted that 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for detecting multi-target signals in the same frequency by Doppler-code phase two-dimensional joint search, characterized in that, The method comprises the following steps: (1) receiving a multi-target signal with the same frequency and code, down-converting to baseband and segmenting sampling; (2) performing Doppler-code phase two-dimensional joint correlation calculation on each segment of the sampling signal to generate a segmented energy matrix; (3) non-coherent accumulation is performed on each segmented energy matrix to generate a global energy matrix; (4) calculating an adaptive threshold based on the global energy matrix; (5) extracting all candidate peaks with energy higher than the threshold in the global energy matrix, and arranging the candidate peaks in descending order of energy values to obtain a candidate peak list; (6) taking the candidate peak with the highest energy in the candidate peak list as the center to define a protection region in the Doppler and code phase two-dimensional domain, and only retaining the main peak with the highest energy in the protection region, eliminating other energy peaks, and recording the retained main peak as an effective detection target, and then adding the main peak to an effective detection target list; (7) updating the candidate peak list: deleting the candidate peaks eliminated in step (6) and the retained main peak from the current candidate peak list; determining whether the updated candidate peak list is empty, if the list is empty, performing step (8), otherwise returning to step (6) based on the updated candidate peak list; (8) for the effective detection target list, arranging the effective detection targets in descending order of energy, and assigning the effective detection targets to idle tracking channels in sequence until the channel resources are exhausted, and completing the Doppler-code phase joint search of the multi-target signal with the same frequency.

2. The method according to claim 1, wherein, The expression of the Doppler-code phase two-dimensional joint correlation calculation in step (2) is: where E i (f d ,τ) represents the two-dimensional joint correlation value of the i-th segment of the sampled signal, s i (t k ) represents the i-th segment of the sampled signal, t k represents the k-th sampling time, c(t k -τ) represents the phase offset version of the local pseudo-code, f d represents the Doppler shift search value, τ represents the code phase offset search value, N represents the length of the segmented signal, N=T coh ·f s , f s represents the sampling rate, T coh represents the coherent integration time, and j represents the imaginary unit.

3. The method of claim 2, wherein, In step (3), the global energy matrix E(f) d The expression for calculating τ is: wherein S represents the number of segments.

4. The method of claim 1, wherein, The adaptive threshold Γ calculation method in step (4) is: Γ = μ n + K - σ n ; where μ n denotes the mean of the noise region in the global energy matrix, σ n denotes the standard deviation of the noise region in the global energy matrix, K denotes a threshold coefficient.

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