A data demodulation method for a transponder

Abstract

The application discloses a data demodulation method of a transponder, and mainly solves the problem of low demodulation efficiency caused by the need of establishing symbol synchronization and tracking for implementing the demodulation of phase modulation data based on Hilbert transform. The implementation scheme is as follows: dividing the radar signal received by the transponder into two paths, performing Hilbert transform on one path to generate quadrature signals, and performing delay alignment phase on the other path to generate in-phase signals; performing the operation of the sine-cosine double-angle formula and the half-frequency processing on the quadrature signals and the in-phase signals to obtain the sine wave and the cosine wave of the carrier phase; substituting the quadrature signals, the in-phase signals, the sine wave of the carrier phase and the cosine wave of the carrier phase into the cosine two-angle difference formula to perform the operation and eliminate the carrier phase to obtain the demodulation data. The application does not need symbol synchronization for implementing the demodulation of phase modulation data based on Hilbert transform, and the establishment of symbol synchronization and the tracking of symbol synchronization are avoided, thereby saving the circuit, improving the demodulation efficiency and being applicable to the data communication of the transponder.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, and specifically relates to a data demodulation method that can be used for transponder data communication. Background Technology

[0002] The radar and transponder constitute an interrogation-response secondary radar system. The transponder is mounted on the aircraft, while the radar is located on the ground. The radar periodically transmits interrogation signals to the transponder. The transponder receives the interrogation signals, judges and processes them, generates a response signal, and sends a response signal back to the radar. Based on the arrival time and content of the response signal, the radar measures the aircraft's three-dimensional data relative to the radar, including distance, azimuth, and pitch angle. The radar modulates the data using binary phase-shift keying (BPSK) and transmits it to the transponder. The transponder receives the signal, demodulates the data, decodes the data to obtain the data information, and sends it to the aircraft to assist in its navigation and positioning.

[0003] The normalized mathematical model for the amplitude of the BPSK phase-modulated signal received by the aircraft is S(n) = cosΦ. n Existing demodulation methods typically employ orthogonal demodulation, with common methods including low-pass filter-based demodulation and Hilbert transform-based demodulation. Among these:

[0004] Demodulating BPSK phase-modulated signals using the Hilbert transform method involves two parallel paths. The first path performs a Hilbert transform on the received signal, outputting a signal with unchanged amplitude but a 90° phase shift, thus generating orthogonal signals. After delaying the received signal in the second path, the phase of the received signal is aligned to generate an in-phase signal S(n) = cosΦ. n This delay time is equal to the time required to perform the Hilbert transform on the first path. Then, the quadrature and in-phase signals are squared, summed, and square-rooted to obtain the instantaneous amplitude value of the phase-modulated signal. Based on the amplitude fluctuations, the switching point of the symbol is found, and symbol synchronization is established accordingly. Each symbol is sampled at the moment of symbol synchronization to ensure that the sampling point signal is obtained in the waveform stability region of each symbol. Then, the dot product operation is performed on the sampling point signals of two adjacent symbols to obtain the phase difference Φ between the two adjacent symbols. Δ cosine signal cosΦ Δ :

[0005]

[0006] When the phase difference Φ Δ When cosΦ = 0 Δ =1 indicates digital information 0, when the phase difference Φ Δ When cosΦ = π Δ =-1 represents the digital information 1; by performing the inverse transformation on the digital information, the binary differential phase shift keying (BPSK) phase modulation signal can be demodulated.

[0007] In demodulation methods based on Hilbert transform, after establishing symbol synchronization, tracking measures such as open-loop / closed-loop symbol synchronization are required to maintain symbol synchronization at all times. This is because the accumulation of symbol timing errors and Doppler frequency shift will cause symbol synchronization failure, resulting in demodulated data errors. Therefore, symbol synchronization needs to be re-established after symbol synchronization failure.

[0008] Existing methods, during symbol synchronization reconstruction, involve repeating the symbol synchronization establishment process described above. If a symbol switching point does not occur for an extended period, this method fails to establish symbol synchronization, resulting in the inability to demodulate data. To address this issue, researchers have proposed two solutions: a scrambling / descrambling method and a preamble-assisted method.

[0009] The scrambling and descrambling method adds white noise to the data at the transmitting end using a pseudo-random code, and removes the white noise from the demodulated data at the receiving end. Because white noise is a random signal and will not remain constant for a long time, this method can achieve symbol synchronization. However, its disadvantage is that the processing is complex and increases the demodulation time.

[0010] The preamble-assisted method adds a string of alternating 1s and 0s before the data symbols to establish symbol synchronization. However, since it also requires symbol synchronization tracking measures, it results in circuit complexity. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of the existing technology by proposing a data demodulation method for transponders based on Hilbert transform, thereby avoiding the establishment and tracking of symbol synchronization, simplifying the demodulation process of phase-modulated data signals, and improving demodulation efficiency.

[0012] The key to achieving the objective of this invention is to use trigonometric function operations to replace the establishment and tracking of symbol synchronization, simplifying the demodulation process of phase-modulated data signals and avoiding circuit complexity. The implementation steps include the following:

[0013] (1) The radar transmit signal is a binary phase shift keying (BPSK) phase modulation signal, and the transponder receives a signal with a phase difference φ from the radar transmit signal: Generate orthogonal signal M(n)sinθ n and in-phase signal M(n)cosθ n These two signals, of which θ n =ωn+φ is the carrier phase, ω is angular radians, and n represents the nth sampling point. The modulation phase takes the value 0 or π, and M(n) represents the data information. When M(n) takes the value 1, it represents the digital information 0. When M(n) takes a value of -1, it represents the digital information 1;

[0014] (2) The carrier phase θ is obtained by performing calculations on the quadrature and in-phase signals using the double-angle sinusoidal formula 2sinacosa=sin2a. n Double phase 2θ n sin2θ n Then divide the frequency by two to obtain the carrier phase θ. n sinθ n ;

[0015] (3) For quadrature and in-phase signals, apply the cosine double angle formula cos 2 a-sin 2 The carrier phase θ is obtained by performing the operation a = cos2a. n Double phase 2θ n cosine wave cos2θ n And divide it by two to obtain the carrier phase θ n cosine wave cosθ n ;

[0016] (4) Based on in-phase signal, quadrature signal, and carrier phase θ n The sine and cosine waves are obtained by substituting them into the cosine difference formula cos(a)cos(b) + sin(a)sin(b) = cos(ab) to obtain the demodulated data M(n).

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] This invention utilizes trigonometric function operations to demodulate binary phase-shift keying (PSK) signals. Specifically, it uses Hilbert transform and delays to align the phases, obtaining quadrature and in-phase signals. Then, it employs multiplication, subtraction, and frequency division to obtain the sine and cosine waves of the carrier phase. Finally, it performs multiplication and addition operations on these four signals to eliminate the carrier phase and extract the data. Therefore, it eliminates the need for symbol synchronization establishment and tracking, greatly reducing the complexity of circuit design, saving hardware resources, and improving demodulation efficiency. Attached Figure Description

[0019] Figure 1 Schematic diagram of radar and transponder operation;

[0020] Figure 2 This is a schematic diagram of the principle of the present invention;

[0021] Figure 3 This is a schematic diagram illustrating the implementation of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0023] Reference Figure 1 The radar and transponder form an interrogation-response secondary radar system. The transponder is mounted on the aircraft, while the radar is located on the ground. The radar periodically transmits interrogation signals to the transponder. The transponder receives the interrogation signals, processes and interprets them, generates a response signal, and sends it back to the radar. The radar modulates the data using binary phase-shift keying (BPSK) and transmits it to the transponder. The transponder receives the signal, demodulates the data, and sends it to the aircraft.

[0024] Reference Figure 2 The data demodulation principle of the transponder in this example is as follows:

[0025] The transponder receives signals that have a phase difference from the radar's transmitted signals. By processing the received signals differently, it obtains the received quadrature and in-phase signals. Through operations on the quadrature and in-phase signals and frequency division by two, it obtains the sine and cosine waves of the carrier phase. By operating on these four signals—the quadrature signal, the in-phase signal, the sine wave of the carrier phase, and the cosine wave of the carrier phase—it eliminates the carrier phase and extracts the demodulated data.

[0026] Reference Figure 3 The data demodulation implementation steps of the transponder in this example are as follows:

[0027] Step 1: The transponder generates quadrature and in-phase signals.

[0028] 1.1) The transponder receives the radar's transmitted signals:

[0029] The radar transmits a binary phase-shift keying (BPSK) phase-modulated signal, which is transmitted through space. The transponder receives a signal with a phase difference from the transmitted signal.

[0030] Where, θ n =ωn+φ represents the carrier phase, φ represents the phase difference between the received signal and the radar transmitted signal, ω is angular radians, and n represents the nth sampling point. The modulation phase takes the value 0 or π, and M(n) represents the data information. When M(n) takes the value 1, it represents the digital information 0. When M(n) takes a value of -1, it represents the digital information 1;

[0031] 1.2) Process the signals received by the transponder to generate two signals:

[0032] The received signal M(n)cosθ in response n The Hilbert transform is performed using a Hilbert filter, resulting in an orthogonal signal M(n)sinθ with constant amplitude and a 90° phase shift. n ;

[0033] The received signal M(n)cosθ in response n Delay by time 'a' to align the received signal M(n)cosθ n The phase of the signal generates an in-phase signal M(n)cosθ. n Where a equals the received signal M(n)cosθ n The time required to perform the Hilbert transform.

[0034] Step 2: Process the quadrature and in-phase signals separately to obtain double-phase 2θ. n Sine and cosine waves.

[0035] 2.1) Obtaining double phase 2θ n sin2θ n :

[0036] The in-phase signal M(n)cosθ n Adding them together, we get a signal M(n)cosθ that lags behind the in-phase signal. n In-phase signal 2M(n)cosθ n ;

[0037] The orthogonal signal M(n)sinθ n Adding it to 0, we get the in-phase signal 2M(n)cosθ. n Phase-aligned orthogonal signals M(n)sinθ n ;

[0038] The in-phase signal 2M(n)cosθ n Multiply by the in-phase signal 2M(n)cosθ n Phase-aligned orthogonal signals M(n)sinθ n According to the double-angle formula 2sinacosa=sin2a, the double phase 2θ can be calculated. n sin2θ n :

[0039] 2M(n)cosθ n ×M(n)sinθ n =2M 2 (n)cosθ n sinθ n =sin2θ n .

[0040] 2.2) Obtaining double phase 2θ n cosine wave cos2θ n :

[0041] The in-phase signal M(n)cosθ n Multiplying by itself yields the in-phase signal M.2 (n)cos 2 θ n ;

[0042] The orthogonal signal M(n)sinθ n Multiplying by itself yields the orthogonal signal M. 2 (n)sin 2 θ n ;

[0043] The in-phase signal M 2 (n)cos 2 θ n Subtract the quadrature signal M 2 (n)sin 2 θ n According to the double-angle cosine formula, cos 2 a-sin 2 a = cos2a, which gives the double phase 2θ. n cosine wave cos2θ n :

[0044] M 2 (n)cos 2 θ n -M 2 (n)sin 2 θ n =cos 2 θ n -sin 2 θ n =cos2θ n .

[0045] Step 3, based on double phase 2θ n Frequency division of sine and cosine waves yields the carrier phase θ. n Sine and cosine waves.

[0046] For double phase 2θ n sin2θ n A frequency divider is used to obtain the carrier phase θ. n sinθ n ;

[0047] For double phase 2θ n cosine wave cos2θ n A frequency divider is used to obtain the carrier phase θ. n cosine wave cosθ n .

[0048] Step 4, from carrier phase θ n The data M(n) is obtained by demodulating the sine and cosine waves.

[0049] The in-phase signal M(n)cosθ n Multiplied by carrier phase θ n cosine wave cosθ n The orthogonal signal M(n)sinθ n Multiplied by carrier phase θ n sinθ n Then, add the two together, and calculate the demodulated data M(n) of the phase modulation data according to the cosine difference formula cos(a)cos(b) + sin(a)sin(b) = cos(ab):

[0050] M(n)cosθ n ×cosθ n +M(n)sinθ n ×sinθ n =M(n)cos(θ) n -θ n ) = M(n).

[0051] The demodulated data is decoded to obtain data information, which is then sent to the aircraft's flight management system via a serial port to help the aircraft perform navigation and positioning.

[0052] The above description is merely a specific example of the present invention and does not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A data demodulation method for a transponder, characterized in that, include: (1) The radar transmit signal is a binary phase shift keying (BPSK) phase modulation signal, and the transponder receives a signal with a phase difference from the radar transmit signal. Signal: Generates orthogonal signals and in-phase signal These two signals specifically refer to the received signal. The orthogonal signal is obtained by performing a Hilbert transform through a Hilbert filter. As the orthogonal signal generated by the first path; for the received signal Delay for time 'a' to obtain an in-phase signal. , which is the in-phase signal generated by the second path; where a is equal to the time required for the first path to perform the Hilbert transform; in For carrier phase, It is angular radius. Indicates the first One sampling point, The modulation phase and its value or , It represents data information, when hour A value of 1 represents the digital information 0, when hour A value of -1 represents the digital information 1; (2) Apply the double-angle sine formula to quadrature and in-phase signals. Perform calculations to obtain the carrier phase. Double phase sine wave The frequency is then divided by two to obtain the carrier phase. sine wave ; (3) Apply the cosine double angle formula to quadrature and in-phase signals. Perform calculations to obtain the carrier phase. Double phase cosine wave The carrier phase is obtained by dividing it by two. cosine wave ; (4) Based on in-phase signal, quadrature signal, and carrier phase The sine and cosine waves are obtained by substituting into the cosine difference formula. Demodulated data is obtained .

2. The method according to claim 1, characterized in that: In step (2), the quadrature and in-phase signals are processed according to the sine trigonometric function formula. The calculation is performed as follows: In-phase signal When the two sides are added together, the phase of the output lags behind the sum of the two sides. In-phase signal ; orthogonal signals Add to 0, output AND Phase-aligned quadrature signals ; In-phase signal and quadrature signals Multiply, then apply the formula The sine wave was calculated. : 。 3. The method according to claim 1, characterized in that: In step (3), the quadrature and in-phase signals are processed according to the cosine trigonometric function formula. The calculation is performed as follows: In-phase signal Multiply by itself, output the in-phase signal after multiplication. ; orthogonal signals Multiply by itself, output the orthogonal signal after multiplication. ; In-phase signal Subtract orthogonal signals Then according to the formula The cosine wave was calculated. : 。 4. The method according to claim 1, characterized in that: Step (4) is implemented as follows: In-phase signal Multiplied by carrier phase cosine wave orthogonal signals Multiplied by carrier phase sine wave And add the two together; then according to the formula The demodulated data was calculated. : ； 。

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