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

Abstract

The invention discloses a same-frequency multi-target signal detection method for Doppler-code phase two-dimensional joint search, and relates to the field of spaceflight measurement and control. Through Doppler frequency shift generated by satellite motion and code phase deviation caused by signal propagation time delay difference, two-dimensional joint correlation calculation and incoherent accumulation are carried out at a receiving end to generate a global energy matrix, an adaptive threshold is calculated, strong signal side lobe interference is suppressed by defining a protection area, the weak signal detection probability is increased to 90% or above, and the detection accuracy is improved. Tracking channels are distributed according to an energy descending order, and the purpose of simultaneously and efficiently detecting multiple targets is achieved. The method is particularly suitable for same-frequency multi-target signal detection based on Doppler-code phase two-dimensional joint search in a low-orbit satellite constellation or a dense satellite network, and solves the problems of low spectrum utilization rate, complex pseudo code management and the like of the traditional frequency division / code division technology.

Description

Technical Field

[0001] The present invention relates to the field of aerospace measurement and control, and in particular to a method for detecting multiple targets at the same frequency using a two-dimensional Doppler-code phase joint search. The method is applicable to low-orbit satellite constellations or dense satellite networks, and solves problems such as low spectrum utilization and complex pseudo-code management of traditional frequency division / code division technologies. Background Art

[0002] With the rapid development of low-orbit satellite constellations, the number of satellites is growing exponentially. Existing satellite multi-target reception technologies mainly rely on traditional frequency division multiple access (FDMA) or code division multiple access (CDMA), which poses severe 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 an ITU report, FDMA spectrum utilization is less than 30%. CDMA requires each satellite to be assigned a unique pseudo-random code. Pseudo-random code resources are limited, and allocation and management are complex. The number of satellites is limited; for example, GPS only supports 32 satellites. Both onboard and ground equipment must support multi-band or multi-pseudo-code generation, significantly increasing hardware costs and power consumption, and increasing system complexity.

[0004] Existing detection technologies typically rely on a single dimension (Doppler or code phase only) and are unable to distinguish co-frequency signals. Traditional two-dimensional search algorithms fail to address the problem of weak signals being masked by the sidelobes of stronger signals. When the signal-to-noise ratio (SNR) falls below -15dB, the probability of weak signals being masked by the sidelobes of stronger signals exceeds 50%. Furthermore, they lack an efficient multi-target channel allocation mechanism, resulting in wasted tracking resources. Achieving high-precision separation of multiple targets under co-frequency and co-code conditions, suppressing strong signal sidelobe interference, improving the probability of weak signal detection, and enabling real-time processing with limited hardware resources are key challenges that must be addressed for large-scale constellations. Summary of the Invention

[0005] In order to solve the problems in the background technology, a Doppler-code phase two-dimensional joint search method for detecting multiple targets at the same frequency is proposed. The Doppler frequency shift generated by satellite movement and the code phase offset caused by the signal propagation delay difference are used to perform two-dimensional joint correlation calculation and non-coherent accumulation at the receiving end to generate a global energy matrix. The adaptive threshold is calculated, and the strong signal sidelobe interference is suppressed by defining a protection area. The probability of weak signal detection is increased to more than 90%, and tracking channels are allocated in descending order of energy to achieve the purpose of simultaneous and efficient detection of multiple targets.

[0006] The technical solution of the present invention is:

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

[0008] (1) Receive multiple target signals with the same frequency and code, down-convert to baseband and perform segmented sampling;

[0009] (2) Performing Doppler-code phase two-dimensional joint correlation calculation on each sampling signal to generate a segmented energy matrix;

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

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

[0012] (5) Extract all candidate peaks with energy higher than the threshold in the global energy matrix and arrange 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, define a protection area in the Doppler and code phase two-dimensional domain with it as the center. Only the main peak with the highest energy is retained in the protection area, and other energy peaks are eliminated. The retained main peak is recorded as a valid detection target and then added to the valid detection target list;

[0014] (7) updating the candidate peak list: deleting the candidate peaks eliminated in step (6) and the retained main peaks from the current candidate peak list;

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

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

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

[0018]

[0019] Where E i (f d ,τ) represents the two-dimensional joint correlation value of the i-th segment sampling signal, s i (t k ) represents the sampling signal of the i-th segment, t k represents the kth sampling moment, c(t k -τ) represents the phase-shifted version of the local pseudo-code, f d represents the Doppler frequency shift search value, τ represents the code phase offset search value, N represents the segment signal length, N = T coh ·f s, f s represents the sampling rate, T coh represents the coherent integration time, and j represents the imaginary unit.

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

[0021]

[0022] Where S represents the number of segments.

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

[0024] Γ=μ n +K·σ n ;

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

[0026] Compared with the background technology, the present invention has the following advantages:

[0027] 1. All satellites of the present invention transmit isomorphic signals with the same frequency and pseudo code, which helps to reduce the complexity of satellite design.

[0028] 2. The present 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. The present invention defines a protection area through Doppler-code phase joint judgment to suppress strong signal sidelobe interference, which is beneficial to improving the probability of weak signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0031] Figure 2 4 is a simulation performance curve of detection probability and false alarm probability in an embodiment of the present invention.

[0032] Figure 3 3D schematic diagram of candidate peaks for multi-target signal detection based on Doppler-code phase in an embodiment of the present invention. DETAILED DESCRIPTION

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

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

[0035] (1) Receive multiple target signals with the same frequency and code, down-convert them to baseband and perform segmented sampling.

[0036] In the embodiment, the same-frequency and same-code signal uses the Gold sequence, the pseudo code period is 1023, there are three multi-target signals, the Dopplers are 1kHz, -2kHz, and 3kHz, the code phases are 300, 700, and 100 chips, 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 segment energy matrix;

[0038] Among them, the two-dimensional joint correlation calculation expression is

[0039]

[0040] Where E i (f d ,τ) represents the two-dimensional joint correlation value of the i-th segment sampling signal, s i (t k ) represents the sampling signal of the i-th segment, t k represents the kth sampling moment, c(t k -τ) represents the phase-shifted version of the local pseudo-code, f d represents the Doppler frequency shift search value, τ represents the code phase offset search value, N represents the segment signal length, N = T coh ·f s , f s represents the sampling rate, T coh represents the coherent integration time, and j represents the imaginary unit.

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

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

[0043] Among them, the global energy matrix E(f d ,τ) calculation expression is:

[0044]

[0045] Where S represents the number of segments.

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

[0047] (4) Calculating an adaptive threshold based on a global energy matrix; global energy matrix;

[0048] Among them, the calculation method of the adaptation threshold Γ is:

[0049] Γ=μ n +K·σ n

[0050] Where μ n represents the mean of the noise region in the global energy matrix, σ n Represents the standard deviation of the noise area in the global energy matrix, and K represents the threshold coefficient. According to engineering experience, the threshold coefficient K is usually set to 2.5 to 4.0. This embodiment is based on 3σ n Criteria, threshold coefficient K = 3, false alarm rate < 0.3%, detection probability greater than 90%, refer to Figure 2 .

[0051] (5) Extract all candidate peaks whose energy is higher than the threshold and sort them in descending order of energy value;

[0052] The candidate peak diagram is shown in Figure 2. 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, define a protection area in the Doppler and code phase two-dimensional domain with it as the center. Only the main peak with the highest energy is retained in the protection area, and other energy peaks are eliminated. The retained main peak is recorded as a valid detection target and then added to the valid detection target list;

[0055] In the embodiment, the protection region is defined as Δf and Δτ in the Doppler and code phase two-dimensional domains, respectively. Δf = 1 / T coh , Δτ is one chip.

[0056] (7) updating the candidate peak list: deleting the candidate peaks eliminated in step (6) and the retained main peaks from the current candidate peak list;

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

[0058] (8) For the list of valid detection targets, the valid detection targets are sorted in descending order of energy and assigned to idle tracking channels in sequence until the channel resources are exhausted, completing the detection of multiple target signals at the same frequency using the 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 limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for detecting multiple targets at the same frequency using a two-dimensional joint search of Doppler and code phase, characterized in that: The following steps are involved: (1) Receive multiple target signals with the same frequency and code, down-convert to baseband and perform segmented sampling; (2) Performing Doppler-code phase two-dimensional joint correlation calculation on each sampling signal to generate a segmented energy matrix; (3) Perform incoherent accumulation of each segment energy matrix to generate a global energy matrix; (4) Calculating the adaptive threshold based on the global energy matrix; (5) Extract all candidate peaks with energy higher than the threshold in the global energy matrix and arrange them in descending order of energy value to obtain a candidate peak list; (6) For the candidate peak with the highest energy in the candidate peak list, define a protection area in the Doppler and code phase two-dimensional domain with it as the center. Only the main peak with the highest energy is retained in the protection area, and other energy peaks are eliminated. The retained main peak is recorded as a valid detection target and then added to the valid detection target list; (7) updating the candidate peak list: deleting the candidate peaks eliminated in step (6) and the retained main peaks from the current candidate peak list; Determine whether the updated candidate peak list is empty. If it is an empty list, execute step (8); otherwise, return to execute step (6) based on the updated candidate peak list. (8) For the list of valid detection targets, the valid detection targets are sorted in descending order of energy and assigned to idle tracking channels in sequence until the channel resources are exhausted, completing the detection of multiple target signals at the same frequency using the Doppler-code phase joint search.

2. The method for detecting multiple targets at the same frequency using a two-dimensional Doppler-code phase joint search according to claim 1, wherein: The expression for 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 sampling signal, s i (t k ) represents the sampling signal of the i-th segment, t k represents the kth sampling moment, c(t k -τ) represents the phase-shifted version of the local pseudo-code, f d represents the Doppler frequency shift search value, τ represents the code phase offset search value, N represents the segment signal length, 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 for detecting multiple targets at the same frequency using a two-dimensional Doppler-code phase joint search according to claim 2, wherein: In step (3), the global energy matrix E(f d ,τ) calculation expression is: Where S represents the number of segments.

4. The method for detecting multiple targets at the same frequency using a two-dimensional Doppler-code phase joint search according to claim 1, wherein: The calculation method of the adaptive threshold Γ in step (4) is: C = m n +K·s n ; Where μ n represents the mean of the noise region in the global energy matrix, σ n represents the standard deviation of the noise area in the global energy matrix, and K represents the threshold coefficient.

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