Orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna receiver and signal processing method thereof

Abstract

This invention discloses an orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna receiver and its signal processing method. The receiver includes two or more magnetic antennas arranged along the X-axis and two or more magnetic antennas arranged along the Y-axis. The number of magnetic antennas in the X-axis and Y-axis directions is equal. The extensions of each magnetic antenna along the X-axis intersect at the same point on the X-axis. When there are three or more magnetic antennas in the X-axis direction, the distance between adjacent magnetic antennas and the angle between their extensions along the X-axis are equal. Similarly, the extensions of each magnetic antenna along the Y-axis intersect at the same point on the Y-axis. When there are three or more magnetic antennas in the Y-axis direction, the distance between adjacent magnetic antennas and the angle between their extensions along the Y-axis are equal. The receiver disclosed in this invention employs an orthogonal combination of array-type magnetic rod antennas, resulting in high sensitivity, strong anti-interference capabilities, and an increased effective communication distance.

Description

Technical Field

[0001] This invention belongs to the field of very low frequency longwave communication, and specifically relates to an orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna receiver and its signal processing method. It can be used for national defense as well as civilian applications such as longwave radio, Loran system, deep earth communication, polar communication, and maritime communication for long-distance communication support and positioning and navigation. Background Technology

[0002] Very low frequency (VLF) longwave communication is a primary technology for long-distance aviation, maritime, and submarine communication. VLF electromagnetic waves propagate through two different channel environments: air and sea. In air, this wavelength of electromagnetic transmission can be considered as transmission in a zero-order mode (TEM wave) within a waveguide between the Earth and the ionosphere. Longwave communication exhibits stable propagation characteristics and minimal attenuation in the atmosphere. However, the extremely low radiation efficiency of the transmitting antenna necessitates very high transmission power for long-distance transmission. When longwaves propagate in a seawater channel environment, the electromagnetic energy that can penetrate the seawater is very weak. As the signal propagates downwards from the sea surface, the attenuation is 1.9–6 dB / m. Therefore, although longwave communication signals have some ability to penetrate seawater, long-distance submarine communication is ultimately a matter of weak signal communication. Furthermore, longwave transmission is susceptible to low-frequency noise from lightning (atmospheric noise) and various forms of man-made electromagnetic noise interference, especially within the communication frequency band, which has a severe negative impact on communication quality. Currently, various countries have conducted extensive research on the mechanisms and suppression of atmospheric noise and in-band electromagnetic noise, and have adopted a series of methods to improve the noise immunity of longwave communication systems. However, there is still no good solution to the problem of in-band noise interference in longwave communication. From the perspective of sources, the impact of complex electromagnetic environments on very low frequency (VLF) communication mainly comes from strong electronic countermeasures interference from both sides, natural atmospheric electromagnetic pulse interference, and electromagnetic interference from electronic equipment around the receiving equipment.

[0003] In recent years, multi-antenna reception technology and signal processing technology have undergone tremendous changes, making them among the fastest-growing technologies in information science. Especially with the rapid development of wireless communication, signal processing has made significant progress, giving rise to the new scientific field of communication signal processing. Modern signal processing has been widely applied in various scientific and technological fields. Modern signal processing methods differ from the classical Fourier transform method; they primarily study statistical mathematical methods to extract effective signals. Their content includes the description of random signals, stationary random signals, estimation of autocorrelation functions, classical power spectrum estimation, and modern power spectrum estimation. Filtering methods include Wiener filtering, Kalman filtering, adaptive filtering, higher-order cumulant statistical filtering, and multi-channel signal data fusion.

[0004] In very low frequency (VLF) long-wave communication, the transmitted signal inevitably encounters various noise interferences, especially atmospheric noise and in-band electromagnetic noise, during long-distance transmission to the receiving terminal. This is a primary problem that must be addressed to increase the effective communication distance. As the transmission distance increases, the signal becomes weaker and the signal-to-noise ratio deteriorates. Due to the inclusion of many non-stationary signals and nonlinear noise signals, such as abrupt changes and trend terms, detection and decoding become extremely difficult. Therefore, how to better recover the original signal from the noise-contaminated signal at the receiving terminal is one of the key technologies for improving VLF long-wave communication capabilities.

[0005] Existing very low frequency (VLF) longwave communication technologies primarily employ a single magnetic antenna or two mutually perpendicular orthogonal magnetic antennas to receive signals. Filtering methods utilize a hardware low-pass filter combined with an FIR digital bandpass filter to extract the effective spectrum of the signal for decoding and communication. Conventional filtering schemes can effectively decode signals within a certain communication distance, but beyond a certain distance or below a certain signal-to-noise ratio, effective communication becomes impossible. Summary of the Invention

[0006] This invention addresses the communication bottleneck problem faced by existing technologies by providing an orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna receiver and its signal processing method. From the perspective of multi-channel magnetic antenna reception fusion, it adopts an orthogonal combination of array-type magnetic antenna reception to merge and fuse multiple signals. In terms of processing method, it adopts a comprehensive technical means of signal-to-noise ratio estimation and multi-channel data merging to increase the effective communication transmission distance.

[0007] The present invention adopts the following technical solution:

[0008] An orthogonal multi-channel very low frequency omnidirectional synthesized magnetic antenna receiver is improved in that it includes two or more magnetic antennas arranged in the X-axis direction and two or more magnetic antennas arranged in the Y-axis direction. The number of magnetic antennas in the X-axis direction and the Y-axis direction are equal. The extensions of each magnetic antenna in the X-axis direction intersect at the same point on the X-axis. When the number of magnetic antennas in the X-axis direction is three or more, the distance between adjacent magnetic antennas and the angle between their extensions in the X-axis direction are equal. The extensions of each magnetic antenna along the Y-axis intersect at the same point on the Y-axis. When there are three or more magnetic antennas along the Y-axis, the distance between adjacent magnetic antennas and the angle between their extensions along the Y-axis are equal. Each magnetic antenna is electrically connected to the loop adjustment and signal synthesis module in sequence through an independent RF filtering module, AD module, and channel tuning module. The loop adjustment and signal synthesis module is electrically connected to the control module and demodulation decision module, respectively. The demodulation decision module is electrically connected to the differential decoding module. The control module outputs the control signals of each digital voltage-controlled oscillator, and the differential decoding module outputs the original bit information.

[0009] Furthermore, the magnetic antenna uses a core material with a permeability of not less than 2500, and the copper core wire wound around the core material has not less than 300 turns.

[0010] Furthermore, the distance between two adjacent magnetic antennas shall not be less than 50 cm.

[0011] Furthermore, the angle between the extensions of adjacent magnetic antennas in the X-axis direction is greater than 0° and less than or equal to 45°; the angle between the extensions of adjacent magnetic antennas in the Y-axis direction is greater than 0° and less than or equal to 45°.

[0012] Furthermore, each channel tuning module captures the carrier wave and synchronization code of the signal received by the magnetic antenna.

[0013] A signal processing method, applicable to the above-mentioned orthogonal multi-channel very low frequency omnidirectional synthesized magnetic antenna receiver, is improved by including the following steps:

[0014] First, the signal received by one magnetic antenna is selected as the reference signal. The signals received by the other magnetic antennas are cross-correlated and phase-detected with the reference signal. The phase detection error between the signals received by each magnetic antenna and the reference signal is used to control the local digital voltage-controlled oscillator to change its output frequency. This makes the other signals, except for the reference signal, gradually synchronize with the reference signal after being down-converted and low-pass filtered.

[0015] Secondly, the signals received by each magnetic antenna in the Y-axis direction are used to obtain the weight coefficients of the maximum ratio combining algorithm through a signal-to-noise ratio estimation algorithm. After being combined by the maximum ratio combining algorithm, a Y-axis combined signal is obtained. The signals received by each magnetic antenna in the X-axis direction are used to obtain the weight coefficients of the maximum ratio combining algorithm through a signal-to-noise ratio estimation algorithm. After being combined by the maximum ratio combining algorithm, a X-axis combined signal is obtained. The Y-axis combined signal and the X-axis combined signal are selected, and the one with the higher signal-to-noise ratio is selected as the output.

[0016] Furthermore, signal-to-noise ratio estimation algorithms include second-order and fourth-order moment methods, higher-order cumulant estimation methods, and power spectrum estimation methods.

[0017] The beneficial effects of this invention are:

[0018] The receiver disclosed in this invention employs an orthogonal combination of arrayed ferrite rod antennas, resulting in high sensitivity, strong anti-interference capabilities, and increased effective communication distance. It features omnidirectional reception capability, unrestricted by azimuth or space, facilitating the reception of very low frequency (VLF) long-wave signals and ensuring reliable communication. Each subsystem adopts a digital modular design, facilitating future maintenance. It can be applied to VLF long-wave communication in both defense and civilian sectors, offering broad applicability. It is not constrained by modulation and coding schemes and can utilize different types of modulation and coding schemes. It can maintain stable communication in complex electromagnetic environments and adverse weather conditions, demonstrating strong environmental adaptability.

[0019] The signal processing method disclosed in this invention employs multi-channel digital acquisition and processing technology. Each channel uses a signal-to-noise ratio estimation algorithm based on spectral analysis or second-order and fourth-order moments (M2M4). Multi-channel data synthesis uses an algorithm combining the maximum ratio combining algorithm and the selection combining algorithm. Frequency offset correction and synchronization processing are performed on multiple signals. The algorithm synthesis is implemented using a hardware data processing method based on FPGA and DSP. Attached Figure Description

[0020] Figure 1 This is a block diagram of the receiver disclosed in Embodiment 1 of the present invention;

[0021] Figure 2 This is a schematic diagram of an orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna;

[0022] Figure 3 This is a block diagram of single-channel signal synchronization reception and processing;

[0023] Figure 4 This is a schematic diagram of an orthogonal magnetic antenna;

[0024] Figure 5 This is a graph showing the relationship between the coupling coefficient and the distance between the magnets;

[0025] Figure 6 A schematic diagram of a non-orthogonal magnetic antenna;

[0026] Figure 7 This is a schematic diagram of a magnetic antenna with an included angle of 60°;

[0027] Figure 8 It is the equivalent diagram of the incoming wave direction of an orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna;

[0028] Figure 9 This is a flowchart of the multi-channel signal in-phase and in-frequency adjustment, code synchronization and signal synchronization in the method disclosed in Embodiment 1 of the present invention;

[0029] Figure 10 This is a flowchart of the signal synthesis process in the method disclosed in Embodiment 1 of the present invention;

[0030] Figure 11 This is a comparison chart showing the effects of using the maximum ratio merging algorithm in a single axis direction (X-axis or Y-axis) before and after.

[0031] Figure 12 This is a block diagram of the merging algorithm;

[0032] Figure 13 This is a block diagram showing the selection of the merging algorithm. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Very low frequency (VLF) wireless communication environments are complex electromagnetic environments, and various types of electromagnetic noise significantly interfere with the effective communication of receivers. This invention designs a multi-channel orthogonal array magnetic antenna based on a traditional single-channel magnetic antenna receiver to receive communication signals from different directions of arrival. In terminal processing, each channel is subjected to conventional low-pass + FIR digital bandpass filtering. On this basis, multi-channel fusion processing is then performed, that is, the maximum ratio combining algorithm and the selective combining algorithm are used to combine and fuse the orthogonal multi-channel data, thereby improving the terminal signal-to-noise ratio and communication capability.

[0035] Example 1, such as Figure 1 As shown, this embodiment discloses an orthogonal multi-channel very low frequency omnidirectional synthesized magnetic antenna receiver, such as... Figure 2 As shown, the system includes two or more magnetic antennas positioned along the X-axis and two or more magnetic antennas positioned along the Y-axis. The number of magnetic antennas in the X-axis and Y-axis directions is equal. The extensions of each magnetic antenna along the X-axis intersect at the same point on the X-axis. When there are three or more magnetic antennas along the X-axis, the distance between adjacent magnetic antennas and the angle between their extensions along the X-axis are equal. Similarly, the extensions of each magnetic antenna along the Y-axis intersect at the same point on the Y-axis. When there are three or more magnetic antennas along the Y-axis, the distance between adjacent magnetic antennas and the angle between their extensions along the Y-axis are equal. Each magnetic antenna is electrically connected to a loop adjustment and signal synthesis module via an independent RF filtering module, an AD module, and a channel tuning module. The loop adjustment and signal synthesis module is electrically connected to a control module and a demodulation decision module, respectively. The demodulation decision module is electrically connected to a differential decoding module. The control module outputs control signals for each digital voltage-controlled oscillator, and the differential decoding module outputs the original bit information. The instruction information is transmitted via an intermediate frequency modulated signal by the transmitting system, and then propagates through multiple paths to reach the receiver terminal. The receiver obtains the original instruction information through channel tuning, synthesis, demodulation, differential decoding, etc.

[0036] In this embodiment, the magnetic antenna uses a core material with a permeability of not less than 2500, and the copper core wire wound around the core material has not less than 300 turns. The distance between two adjacent magnetic antennas is not less than 50 cm. The angle between the extensions of adjacent magnetic antennas in the X-axis direction is greater than 0° and less than or equal to 45°; the angle between the extensions of adjacent magnetic antennas in the Y-axis direction is greater than 0° and less than or equal to 45°.

[0037] Each channel tuning module captures the carrier and synchronization code of the signal received by the magnetic antenna to achieve coarse synchronization between the local signal and the received signal, while fine synchronization is achieved through loop adjustment. The initial values ​​of the local carrier NCO (digital voltage-controlled oscillator) and code NCO are obtained from the acquisition results and are controlled by the output error of the subsequent loop adjustment and signal synthesis modules. Figure 3 This is a block diagram of single-channel signal synchronous reception and processing.

[0038] The process of designing an orthogonal multi-channel omnidirectional synthetic magnetic antenna is as follows:

[0039] First, we analyze the L-shaped orthogonal ferrite rod antenna, such as... Figure 4 As shown, the distance between the magnetic bars is r, and θ is the angle between the direction of the magnetic field and the magnetic bars.

[0040] The total impedance of the antenna circuit is R0 = 400Ω, the external magnetic field strength is H, and the antenna area is A = 20m². 2 The electromotive force of the external field on the antenna in Let H be the angle between the antenna axis and the antenna current. The near field generated by this antenna is:

[0041] Approximate processing: H0 = H ρ sinθ+H φ cosθ

[0042] Substituting, we get:

[0043] The coupling coefficient is:

[0044] The relationship between the coupling coefficient and the distance between the magnets is as follows: Figure 5 As shown, the calculated coupling coefficient for magnetic rods with a distance r greater than 40 cm is less than 0.1.

[0045] like Figure 6 As shown, if the two magnetic rods are not placed in an L-shape, but at a certain angle, then the coupling coefficient is:

[0046]

[0047] Based on this analysis, the following design was implemented: Figure 7 The ferrite rod antenna shown has an angle of 60° between the extension lines of the two ferrite rod antennas and a distance r between the ferrite rods greater than 50 cm to ensure that the coupling number is less than 0.1 and to minimize the influence of mutual coupling factors.

[0048] Furthermore, since the received signal is a very low frequency long-wave signal, within a relatively short distance, there is no phase error between the signals received by the two magnetic sensors. However, because the direction of the incoming signal is at a certain angle to the induction axis of the magnetic antenna, there is an amplitude difference between the signals received by the two magnetic sensors. For example... Figure 7 As shown, within the angle range of ∠MON = 120° and ∠M'ON' = 120°, in the incoming wave direction H1 or H2, the signals received by the two magnetic antennas have no phase difference, only an amplitude difference. Within the angle range of ∠MON' = 60° and ∠M'ON = 60°, in the incoming wave direction H3 or H4, the signals received by the two magnetic antennas have a 180° phase error. From the perspective of signal synthesis, the two signals should be weighted and synthesized under the condition of being in phase and at the same frequency as much as possible. Therefore, the incoming wave signal within the angle range of ∠MON = 120° and ∠M'ON' = 120° is an effective region for combining using the maximum ratio algorithm.

[0049] Further, orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antennas are designed in the x and y axes, such as... Figure 2 As shown, in the x-axis direction, the in-phase regions of the electromagnetic incoming signals received by magnetic antennas #3 and #4 are H3 and H4, respectively. In the y-axis direction, the in-phase regions of the electromagnetic incoming signals received by magnetic antennas #1 and #2 are H1 and H2, respectively. It should be noted that to avoid the influence of magnetic antenna coupling, the distance between the two antennas must meet certain conditions. For ease of analysis and explanation, the direction of arrival of the orthogonal multi-channel very low frequency omnidirectional synthetic magnetic antenna is equivalent to... Figure 8 For any very low frequency (VLF) long-wave signal from the direction of arrival, H1 is the in-phase synthesis region of the long-wave signal from the Y-direction magnetic antenna combination, H2 is the in-phase synthesis region of the long-wave signal from the X-direction magnetic antenna combination, and H3 is the in-phase synthesis region of the long-wave signal shared by the X and Y-direction magnetic antenna combinations. Therefore, if the signal's direction of arrival is in region H1, the maximum ratio algorithm can be used to combine the signals using the Y-axis magnetic antenna combination; if the signal's direction of arrival is in region H2, the maximum ratio algorithm can be used to combine the signals using the X-axis magnetic antenna combination; and if the signal's direction of arrival is in region H3, both the X-axis and Y-axis magnetic antenna combinations can be used for signal combining. Next, for signals from any direction of arrival, the X-axis and Y-axis combined antennas are used for combining, respectively. Then, a selective combining process is performed on the X-axis combined signal and the Y-axis combined signal, i.e., at the receiving end, the best signal is selected as the combined output from the two signals. Typically, the signal with the better signal-to-noise ratio is selected as the algorithm's output.

[0050] This embodiment also discloses a signal processing method applicable to the above-mentioned orthogonal multi-channel very low frequency omnidirectional synthesized magnetic antenna receiver, comprising the following steps:

[0051] like Figure 9As shown, assuming there are three magnetic antennas receiving signals, the signal received by one magnetic antenna is first selected as the reference signal. The signals received by the other two magnetic antennas are cross-correlated and phase-detected with the reference signal. The phase detection errors between the signals received by the two magnetic antennas and the reference signal are used to control the local digital voltage-controlled oscillator, changing its output frequency and phase, so that the other two signals, except for the reference signal, gradually become in phase and frequency with the reference signal after down-conversion and low-pass filtering.

[0052] Secondly, such as Figure 10 As shown, taking four signals as an example, the signals x1(t) and x2(t) received by the two magnetic antennas in the Y-axis direction are used to obtain the weight coefficients of the maximum ratio combining algorithm using the signal-to-noise ratio estimation algorithm. After being combined by the maximum ratio combining algorithm, a Y-axis combined signal x5(t) is obtained. The signals x3(t) and x4(t) received by the two magnetic antennas in the X-axis direction are used to obtain the weight coefficients of the maximum ratio combining algorithm using the signal-to-noise ratio estimation algorithm. After being combined by the maximum ratio combining algorithm, a X-axis combined signal x6(t) is obtained. The Y-axis combined signal x5(t) and the X-axis combined signal x6(t) are selected, and the one with the higher signal-to-noise ratio is selected as the output.

[0053] Signal-to-noise ratio (SNR) estimation algorithms include second- and fourth-order moment methods, higher-order cumulant estimation methods, and power spectrum estimation methods. The orthogonal multi-channel signals of this invention are not limited to four-channel signals; combinations of four or more orthogonal channels can also be designed, such as orthogonal six-channel and eight-channel combinations. The arrangement of magnetic sensors in orthogonal directions must meet low mutual coupling requirements.

[0054] The merging algorithm's effect is as follows Figure 11 As shown, the signal-to-noise ratios (SNRs) of each channel before merging are -26dB, -26dB, and -26dB, respectively. The SNR of the merged signal channel is -21.3dB, which is an improvement of about 4.7dB. The simulation results are in good agreement with the theoretical calculations.

[0055] The algorithm required for this invention is as follows:

[0056] Signal-to-noise ratio estimation algorithm:

[0057] Signal-to-noise ratio (SNR) estimation is a crucial component of modern communication systems and serves as reference information for many signal processing methods. For example, code division multiple access (CDMA) systems utilize SNR information for power allocation across links; the selection of switching timing between blind equalization and decision pointing (DD) algorithms requires SNR estimation to provide the necessary decision-making basis; and multi-channel signal combining algorithms presuppose a relatively accurate SNR estimate. Considering the complexity and estimation accuracy of various algorithms, the SNR estimation algorithms employed in this invention include the second-moment and fourth-moment methods (M2M4 method) and methods based on spectral analysis (or power spectrum) estimation.

[0058] The signal-to-noise ratio estimation method based on the second-order moment and fourth-order moment methods is as follows:

[0059] The i-th receiving signal S i The second moment of (n) can be expressed as:

[0060]

[0061] The fourth moment can be expressed as:

[0062]

[0063] In the above formula, S i (n) is the discrete complex signal representation of the i-th signal, i.e., S i (n)=S iI (n)+jS iQ (n), A i Let be the amplitude of the i-th signal. Let Vi be the Gaussian white noise variance of the i-th signal, then the signal-to-noise ratio can be expressed as:

[0064] From the above two equations, we can deduce that:

[0065]

[0066]

[0067] In practical engineering, the second and fourth moments are calculated by averaging the received signal over time, and their estimated values ​​can be expressed as:

[0068]

[0069]

[0070] Where L is the signal length, the signal-to-noise ratio estimate of the complex signal can be further derived as follows:

[0071]

[0072] If the signal is a real signal, then the signal-to-noise ratio estimate is:

[0073]

[0074] The signal-to-noise ratio estimation method based on power spectrum estimation is as follows:

[0075] Assuming the sampled signal is represented as y(t) = s(t) + n(t), and the power spectral density of the signal is represented as Y(f), then the total power within the useful signal bandwidth can be expressed as:

[0076]

[0077] Among them, f L and fH These represent the start and end frequencies of the useful signal bandwidth, respectively.

[0078] Similarly, the total power within the sampling bandwidth can be expressed as:

[0079]

[0080] Where f1 and f2 represent the start and end frequencies of sampling.

[0081] The estimated noise density can be obtained by averaging:

[0082]

[0083] Where B = F1 - F2 represents the sampling bandwidth, B w This indicates the bandwidth of the useful signal.

[0084] To calculate the power of the useful signal, the noise power in the channel, N = n0 * B, needs to be subtracted. w

[0085] Therefore, the estimated SNR can be expressed as:

[0086]

[0087] Note: This algorithm is typically used for random noise estimation.

[0088] II. Maximum Ratio Merging Algorithm

[0089] Maximum ratio combining (MRC) is a method that combines multiple statistically independent diversity branch signals carrying the same information at the receiver according to their signal-to-noise ratio (SNR), with the weighting coefficient w... i It is proportional to the signal-to-noise ratio of each diversity branch. For example... Figure 12 The merged output is:

[0090]

[0091] When multi-channel signals are combined using the maximum ratio combining algorithm, the weighting coefficients w1, w2, ..., w of each signal are... M Determined by the following system of equations:

[0092]

[0093] w1+w2+…+w M =1

[0094] The maximum ratio combining algorithm requires estimation of the signal-to-noise ratio (SNR) of each signal, SNR1, SNR2, ..., SNR. N The higher the accuracy of the estimation, the better the merging algorithm performs.

[0095] II. Optimal Selection Merge Algorithm

[0096] Optimal selection combining (ODB) selects the best signal from multiple statistically independent diversity branch signals carrying the same information at the receiver as the combined output. The best signal is the diversity branch signal with the highest estimated signal-to-noise ratio (SNR). Taking four signals as an example, the ODB algorithm is as follows: Figure 13 As shown.

[0097] In the optimal choice merge, the weighting coefficient w is... k The expression is:

[0098]

[0099] k=1,2,…,M; j=1,2,…,M.

Claims

1. A signal processing method applicable to an orthogonal multi-channel very low frequency omnidirectional synthesized magnetic antenna receiver, comprising two or more magnetic antennas disposed in the X-axis direction and two or more magnetic antennas disposed in the Y-axis direction, wherein the number of magnetic antennas in the X-axis direction and the number of magnetic antennas in the Y-axis direction are equal, the extensions of each magnetic antenna in the X-axis direction intersect at the same point on the X-axis, and when the number of magnetic antennas in the X-axis direction is three or more, the distance between adjacent magnetic antennas and the angle between their extensions in the X-axis direction are equal, and the extensions of each magnetic antenna in the Y-axis direction are equal. At the same point intersecting the Y-axis, when there are three or more magnetic antennas in the Y-axis direction, the distance between each adjacent magnetic antenna and the angle between the extension lines in the Y-axis direction are equal; each magnetic antenna is sequentially electrically connected to the loop adjustment and signal synthesis module through an independent RF filtering module, AD module, and channel tuning module. The loop adjustment and signal synthesis module is electrically connected to the control module and demodulation decision module, respectively. The demodulation decision module is electrically connected to the differential decoding module. The control module outputs the control signals of each digital voltage-controlled oscillator, and the differential decoding module outputs the original bit information. The angle between the extensions of adjacent magnetic antennas along the X-axis is greater than 0° and less than or equal to 45°; the angle between the extensions of adjacent magnetic antennas along the Y-axis is greater than 0° and less than or equal to 45°; the magnetic antennas use a core material with a permeability of not less than 2500, and the copper core wire wound around the core material has not less than 300 turns; the distance between two adjacent magnetic antennas is not less than 50cm; each channel tuning module acquires the carrier and synchronization code of the signal received by the magnetic antenna, characterized in that... Includes the following steps: First, the signal received by one magnetic antenna is selected as the reference signal. The signals received by the other magnetic antennas are cross-correlated and phase-detected with the reference signal. The phase detection error between the signals received by each magnetic antenna and the reference signal is used to control the local digital voltage-controlled oscillator to change its output frequency. This makes the other signals, except for the reference signal, gradually synchronize with the reference signal after being down-converted and low-pass filtered. Secondly, the signals received by each magnetic antenna in the Y-axis direction are used to obtain the weight coefficients of the maximum ratio combining algorithm by using a signal-to-noise ratio estimation algorithm. After being combined by the maximum ratio combining algorithm, a Y-axis combined signal is obtained. The signals received by each magnetic antenna along the X-axis are used to obtain the weighting coefficients of the maximum ratio combining algorithm through a signal-to-noise ratio estimation algorithm. After being combined by the maximum ratio combining algorithm, one X-axis combined signal is obtained. The Y-axis combined signal and the X-axis combined signal are selected, and the one with the higher signal-to-noise ratio is selected as the output. The signal-to-noise ratio estimation algorithm includes the second-order moment and fourth-order moment method, the higher-order cumulant estimation method, and the power spectrum estimation method.

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