Broadband radio frequency signal processing method and system based on multistage frequency conversion

Abstract

The invention relates to the technical field of radio frequency signal processing, in particular to a broadband radio frequency signal processing method and system based on multi-stage frequency conversion, and the method comprises the following steps: S1, inputting a radio frequency signal, mixing the radio frequency signal into a first intermediate frequency signal through a first-stage mixer, and filtering the first intermediate frequency signal through a first filter and a second filter to obtain a second intermediate frequency signal; frequency mixing is performed through a second-stage frequency mixer to obtain a second intermediate frequency signal; s2, sampling the second intermediate frequency signal to obtain a modulation signal, and extracting an in-phase component and an orthogonal component of the modulation signal; s3, performing frequency mixing on the in-phase component and the orthogonal component of the modulation signal and an orthogonal signal, and performing multi-stage decimation filtering through a filter to obtain an orthogonal baseband signal; and S4, calculating an instantaneous amplitude, an instantaneous phase and an instantaneous frequency of the orthogonal baseband signal, and completing frequency modulation signal demodulation through a phase difference algorithm to obtain a modulation signal source. The method provided by the invention has the advantages of wide frequency band coverage, high signal quality and high demodulation efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency signal processing, and in particular to a method and system for processing wide-band radio frequency signals based on multi-stage frequency conversion. Background Art

[0002] RF signal processing technology has important applications in wireless communications, radar, electronic warfare, and spectrum monitoring. As modern wireless systems increasingly demand greater frequency coverage, signal flexibility, and processing efficiency, traditional single-stage frequency conversion architectures, limited by bandwidth, interference immunity, and dynamic range, struggle to meet the high-precision processing requirements for wideband signals (e.g., 10MHz to ≥512MHz). Multi-stage frequency conversion technology, through step-by-step frequency conversion, can gradually reduce broadband input signals to an intermediate frequency (IF), effectively reducing system complexity and improving signal isolation. This technology has become a key solution to the challenges of wideband signal processing.

[0003] Signal conditioning and frequency conversion are key components of RF receiver front-end design. Traditional solutions often employ fixed attenuators and a single mixer structure, but these solutions suffer from issues such as insufficient harmonic suppression and limited dynamic range.

[0004] Digital down conversion (DDC), a core technology in software-defined radio (SDR), relies on digital mixing and decimation filtering to achieve signal basebanding and downsampling. Traditional analog down-conversion solutions suffer from high phase noise and poor flexibility. FPGA-based DDC technology generates orthogonal local oscillator signals using a numerically controlled oscillator (NCO). Combined with a multi-stage decimation architecture comprising a cascaded integrator comb filter (CIC), a half-band (HB) filter, and a FIR (Finite Impulse Response) filter, it significantly reduces computational resource consumption while improving the ability to resist adjacent channel interference. Regarding demodulation algorithms, efficient demodulation of frequency modulated (FM) signals has always been a technical challenge. Traditional methods rely on complex inverse tangent operations and phase differentiation, placing high demands on processor computing power.

[0005] In the field of RF signal processing, traditional RF receiving systems typically use analog frequency conversion technology to convert high-frequency signals into intermediate-frequency signals for processing. However, with the expansion of communication frequency bands and the increase in signal complexity, traditional methods have the following problems:

[0006] 1. Limited frequency range: Traditional systems have difficulty covering wide-band signals from 10MHz to 512MHz and above.

[0007] 2. Signal distortion: Noise and distortion are easily introduced during the multi-stage frequency conversion process, affecting signal quality.

[0008] 3. High demodulation complexity: FM signal demodulation requires complex calculations and is difficult to implement efficiently in hardware.

[0009] Therefore, there is an urgent need for a radio frequency signal processing system and method that can cover a wide frequency band, reduce signal distortion and simplify the demodulation process. Summary of the Invention

[0010] This invention proposes a wideband RF signal processing method and system based on multi-stage frequency conversion. Through multi-stage attenuation, two-stage mixing, multi-stage decimation filtering, and orthogonal mixing, it addresses the limitations of conventional technologies, such as limited frequency range, signal distortion, and high demodulation complexity. Furthermore, the use of a novel demodulation algorithm and frequency modulation demodulation method simplifies the computational process and improves the accuracy and efficiency of signal demodulation.

[0011] In order to achieve the above objectives, the following technical solutions are proposed:

[0012] A wide-band radio frequency signal processing method based on multi-stage frequency conversion includes the following steps:

[0013] S1, inputting a radio frequency signal, mixing the radio frequency signal into a first intermediate frequency signal through a first mixer, filtering the first intermediate frequency signal through a first filter and a second filter, and then mixing the first intermediate frequency signal into a second intermediate frequency signal through a second mixer;

[0014] S2. Sampling the second intermediate frequency signal to obtain a modulated signal, and extracting an in-phase component and a quadrature component of the modulated signal;

[0015] S3, mixing the in-phase component and the quadrature component of the modulated signal with the quadrature signal, and performing multi-stage decimation filtering in sequence through a CIC filter, a half-band filter, and an FIR filter to obtain an orthogonal baseband signal;

[0016] S4. Calculate the instantaneous amplitude, instantaneous phase and instantaneous frequency of the orthogonal baseband signal, and complete frequency modulation signal demodulation through a phase difference algorithm to obtain a modulated signal source.

[0017] The present invention improves the flexibility, efficiency, and reliability of signal processing through designs such as multi-stage attenuation, two-stage mixing, multi-stage decimation filtering, and orthogonal mixing. Furthermore, the use of a new demodulation algorithm and frequency modulation demodulation method simplifies the calculation process and improves the accuracy and efficiency of signal demodulation.

[0018] Preferably, the specific steps of S1 are:

[0019] S11. The RF signal is input to a first attenuator, which attenuates the signal to obtain a first attenuated signal. The first attenuated signal is input to a second attenuator, which attenuates the signal to obtain a second attenuated signal. The second attenuated signal is input to a power splitter for attenuation, and the power splitter outputs a third attenuated signal.

[0020] S12, inputting the third attenuated signal into a third attenuator to adjust the signal amplitude to obtain a first conditioned signal;

[0021] S13, the first conditioned signal passes through a first filter and is input into an amplifier, and then input into a first-stage mixer and mixed with a local oscillator signal to obtain a first intermediate frequency signal;

[0022] S14, the first intermediate frequency signal is input into the second filter and the third filter, the first intermediate frequency signal is amplified and then filtered by the fourth filter and the fifth filter, and then input into the second mixer and mixed with the second local oscillator signal to obtain a second intermediate frequency signal.

[0023] Preferably, the specific steps of extracting the orthogonal component of the modulated signal are:

[0024] A low-pass filter is used to filter signals other than the orthogonal components of the modulated signal, and the passband cutoff frequency and stopband frequency of the low-pass filter are set. The passband cutoff frequency is the highest frequency corresponding to the spectral components of the orthogonal components of the modulated signal, and the stopband frequency is less than half of the channel spacing.

[0025] Preferably, the specific steps of performing multi-stage decimation filtering by using a CIC filter, a half-band filter and an FIR filter are:

[0026] The CIC filter is used as the first stage to perform preliminary extraction of the input signal;

[0027] A half-band filter is used as the second stage for decimation;

[0028] Finally, an FIR filter is used for shaping filtering, wherein each stage of the CIC filter, half-band filter and FIR filter sets a decimation factor for multi-stage decimation.

[0029] Preferably, the total calculation formula for the extraction factor when performing multi-level extraction is:

[0030]

[0031] Where D is the total extraction factor, Dm is the extraction factor of each level, m is the number of levels, and M is a positive integer.

[0032] Preferably, the specific steps of mixing the in-phase component and the quadrature component of the modulated signal with the quadrature signal are:

[0033] The in-phase component of the modulated signal is multiplied by the in-phase component of the quadrature signal and then filtered through a low-pass filter to obtain the instantaneous in-phase component;

[0034] The quadrature components of the modulated signal are multiplied by the quadrature components of the quadrature signal and then filtered through a low-pass filter to obtain instantaneous quadrature components.

[0035] Preferably, the specific steps for calculating the instantaneous phase and instantaneous frequency are as follows:

[0036] Calculating the instantaneous phase by performing an arc tangent operation on the ratio of the instantaneous in-phase component to the instantaneous quadrature component;

[0037] performing a differential operation on the instantaneous phase to obtain a change in instantaneous frequency;

[0038] After subtracting the DC component from the instantaneous frequency change, a modulation signal is obtained.

[0039] Preferably, the formula for performing differential operation on the instantaneous phase is:

[0040]

[0041] Where f(n) is the instantaneous frequency, φ(n) is the phase of the current sampling point, φ(n-1) is the phase of the previous sampling point, φ'(n) and φ(n)-φ(n-1) are the instantaneous phase differences, and X Q is the instantaneous quadrature component, X I is the instantaneous in-phase component.

[0042] Based on the same concept, a system is also proposed, including a radio frequency front-end module, an intermediate frequency processing module, a digital signal processing module and a demodulation unit;

[0043] A radio frequency front-end module, configured to mix an input radio frequency signal into a first intermediate frequency signal through a first mixer, filter the first intermediate frequency signal through a first filter and a second filter, and then mix the first intermediate frequency signal into a second intermediate frequency signal through a second mixer;

[0044] an intermediate frequency processing module, comprising an analog-to-digital converter, the analog-to-digital converter being configured to sample the second intermediate frequency signal to obtain a modulated signal and calculate a quadrature component and an in-phase component of the modulated signal;

[0045] A digital signal processing module includes a digital down-conversion unit and a demodulation unit. The digital down-conversion unit is connected to a digitally controlled oscillator. The digitally controlled oscillator generates an orthogonal signal. After mixing the modulated signal with the orthogonal signal, the orthogonal signal is subjected to multi-stage decimation filtering through a CIC filter, a half-band filter, and an FIR filter in sequence to obtain an orthogonal baseband signal.

[0046] The demodulation unit is used to extract the instantaneous amplitude, instantaneous phase and instantaneous frequency of the orthogonal baseband signal, and complete the frequency modulation signal demodulation through the phase difference algorithm to obtain the modulated signal source.

[0047] This system significantly improves signal purity and system dynamic performance through a multi-stage attenuation, adjustable gain amplifier, and multi-stage mixing design, combined with cascaded optimization of low-pass and band-pass filters. Furthermore, a two-stage frequency conversion reduces the signal to a 31.1MHz intermediate frequency, ensuring efficient sampling by the analog-to-digital converter (ADC) while reducing the complexity of subsequent digital processing.

[0048] Preferably, the analog-to-digital converter is an AD9268 analog-to-digital converter, the first filter is a low-pass filter, and the second filter is a band-pass filter.

[0049] Compared with the existing technology, the beneficial effects of the present invention are as follows: the method of the present invention can significantly reduce the sampling rate and the amount of calculation through multi-stage frequency conversion and filtering optimization, and the multi-stage extraction filter combination can significantly reduce the sampling rate and the amount of calculation. At the same time, the system of the present invention supports high-precision processing of wide-band signals, enhances anti-interference ability, and improves the real-time performance of the system; simplifies the calculation steps through the frequency modulation demodulation algorithm, realizes real-time demodulation in FPGA, and overcomes the problem of slow processing speed of traditional radio equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a flow chart of a wide-band radio frequency signal processing method and system based on multi-stage frequency conversion in Example 1;

[0051] Figure 2 1 is a functional schematic diagram of a wide-band radio frequency signal processing method and system based on multi-stage frequency conversion in Example 1;

[0052] Figure 3 1 is a circuit diagram of the RF input broadband power test in Example 1;

[0053] Figure 4 is a circuit diagram of the radio frequency analysis frequency conversion path in Example 1;

[0054] Figure 5 is a circuit diagram of the intermediate frequency sampling analog-to-digital converter in Example 1;

[0055] Figure 6 This is a block diagram of the overall principle of digital down-conversion in Example 1;

[0056] Figure 7 is a schematic diagram of the principle of orthogonal component extraction and decimation in Example 1;

[0057] Figure 8 is a characteristic principle diagram of the low-pass filter in Example 1;

[0058] Figure 9 is a schematic diagram of the orthogonal component extraction and decimation system in Example 1;

[0059] Figure 10 Schematic diagram of the demodulation mathematical model of the software radio receiving system in Example 1;

[0060] Figure 11 This is a demodulation block diagram of the FM signal in Example 1. DETAILED DESCRIPTION

[0061] The present invention will be further described in detail below in conjunction with test examples and specific embodiments. However, this should not be understood as limiting the scope of the present invention to the following embodiments, and all technologies implemented based on the present invention fall within the scope of the present invention.

[0062] In addition, the expressions "first", "second", "third", etc. that appear in the terms are merely descriptions used to distinguish the same or similar components and should not be understood as emphasizing or implying the relative importance of specific components.

[0063] In addition, in the description of the embodiments of the present invention, "several," "plurality," and "a number" represent at least two. It can also be any number such as two, three, four, five, six, seven, eight, nine, or even more than nine.

[0064] Furthermore, in the description of the technical solution of the present invention, unless otherwise expressly specified, defined, or limited, the terms "disposed," "installed," "connected," "connected," "provided with," "laid," and "arranged" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections. They may be welded, riveted, bolted, threaded, or other commonly used connection methods in the art. Such connections may be mechanical, electrical, or communicative; they may be direct, indirect via an intermediate medium, or internally connected between two components.

[0065] Example 1

[0066] A wide-band RF signal processing method and system based on multi-stage frequency conversion is shown in the flowchart. Figure 1 As shown, the method includes the following steps:

[0067] S1, inputting a radio frequency signal, mixing the radio frequency signal into a first intermediate frequency signal through a first mixer, filtering the first intermediate frequency signal through a first filter and a second filter, and then mixing the first intermediate frequency signal into a second intermediate frequency signal through a second mixer;

[0068] S2. Sampling the second intermediate frequency signal to obtain a modulated signal, and extracting an in-phase component and a quadrature component of the modulated signal;

[0069] S3, mixing the in-phase component and the quadrature component of the modulated signal with the quadrature signal, and performing multi-stage decimation filtering in sequence through a CIC filter, a half-band filter, and an FIR filter to obtain an orthogonal baseband signal;

[0070] S4. Calculate the instantaneous amplitude, instantaneous phase and instantaneous frequency of the orthogonal baseband signal, and complete frequency modulation signal demodulation through a phase difference algorithm to obtain a modulated signal source.

[0071] This method significantly reduces FPGA resource usage by eliminating the effects of carrier frequency mismatch and simplifying multiplication and division operations. While maintaining demodulation accuracy, the algorithm also improves real-time performance, making it suitable for rapid analysis of wide-band multimode signals.

[0072] like Figure 2 As shown, the RF front end of the present invention is divided into two main functions:

[0073] The analysis part completes the frequency conversion and amplitude conditioning of the input 10MHz~≥512MHz signal, and after the second-level frequency conversion, a 31.1MHz intermediate frequency signal is generated and sent to the signal processing part for sampling;

[0074] The generation part converts the 171MHz intermediate frequency modulation signal generated by AD9910 to achieve a 10MHz to ≥512MHz signal source output.

[0075] The RF signal is input to a first attenuator, which attenuates the signal to obtain a first attenuated signal. The first attenuated signal is input to a second attenuator, which attenuates the signal to obtain a second attenuated signal. The second attenuated signal is input to a power splitter for attenuation, and the power splitter outputs a third attenuated signal.

[0076] The third attenuated signal is input into a third attenuator to adjust the signal amplitude to obtain a first conditioned signal;

[0077] The first conditioned signal passes through a first filter and is input into an amplifier, and then input into a first-stage mixer and mixed with a local oscillator signal to obtain a first intermediate frequency signal;

[0078] The first intermediate frequency signal is input into the second filter and the third filter. After being amplified, the first intermediate frequency signal is filtered through the fourth filter and the fifth filter, and then input into the second mixer and mixed with the second local oscillator signal to obtain the second intermediate frequency signal.

[0079] See Figure 3As a specific embodiment, the RF signal input to the RF board first passes through a high-power attenuator F35 to attenuate the signal by 3dB, then passes through a high-power attenuator F36 to attenuate the signal by 6dB, and then passes through a power divider composed of four resistors (R59, 60, 61, 62) to attenuate the signal by 9.54dB and split it into three signals:

[0080] One signal is sent into the RF channel through C93, passes through an RF switch (D5), and then the signal amplitude is adjusted by the RF attenuator D4;

[0081] After being attenuated by about 15dB, the signal is sent to the power detector (N13) through C110 and converted into an analog voltage signal.

[0082] After passing through C24, it is connected to the internal signal source output signal.

[0083] See Figure 4 and Figure 5 The RF channel performs frequency conversion and amplitude conditioning on the signal after RF input conditioning. The signal sent from the RF attenuator D4 is amplified after passing through a low-pass filter F9 and an RF switch D14. The amplifier N4 controlled by the FPGA (U3) amplifies the signal by about 22dB and sends it to the first-stage mixer MCA1-42+ (N3) for mixing with the local oscillator signal to obtain a 1691MHz intermediate frequency signal; the 1691MHz passes through a low-pass filter (F10), a band-pass filter CMF44C1691C10B (F7), an intermediate frequency amplifier N2, and then passes through a low-pass filter (F11), a band-pass filter CMF44C1691C10B (F8) before a second RMS-30 mixing (N6). The resulting intermediate frequency signal is a 31.1MHz intermediate frequency signal. After amplification, filtering, and intermediate frequency attenuation (D3), it is sent to the signal processing board for intermediate frequency AD sampling (U3, AD9268). By analyzing and processing the sampled digital signal, various parameters of the input signal are obtained.

[0084] Through the coordinated work of the low-pass filter, RF switch, amplifier and mixer, a stable 31.1MHz intermediate frequency signal is generated, providing a reliable foundation for subsequent signal processing.

[0085] In this embodiment, an analog-to-digital converter AD9268 with a sampling rate of 80 MHz is selected. According to the sampling theorem, the input intermediate frequency is lower than 1 / 2 of the sampling rate, and then a second intermediate frequency of 31.1 MHz is selected according to the model recommendation of the filter manufacturer.

[0086] The input frequency range of this embodiment is 10MHz to 520MHz. To avoid overlap between the input signal and the second IF frequency range, which would cause signal crosstalk, this project adopts a secondary mixing solution. The input signal is first mixed to a high-frequency first IF (1691MHz was selected based on the filter manufacturer's recommendation), and then the high-frequency first IF is mixed to a low-frequency second IF. The main advantages include:

[0087] 1. Improved selectivity: Unwanted or interfering signals can be filtered out more effectively. This is because many high-performance filters work better in a specific intermediate frequency range.

[0088] 2. Enhanced sensitivity: Using two different local oscillator frequencies to process the input signal can amplify weak signals without increasing noise, thereby improving the project's ability to capture weak signals.

[0089] 3. Reduce image interference: Single-conversion systems are susceptible to the "image frequency" problem, whereby another frequency besides the target frequency may produce the same intermediate frequency output, causing interference. Secondary mixing can avoid this problem by properly selecting the first and second intermediate frequencies, making reception more stable and reliable.

[0090] 4. Better dynamic range: Due to the use of a multi-stage frequency conversion architecture, gain distribution can be better managed, overload can be prevented, and good linearity can be maintained over a wider range.

[0091] Digital down-conversion (DDC) is a mixing method in a superheterodyne receiver that creates an intermediate frequency (IF) signal at a lower frequency than the original signal. It is a core technology in software-defined radio (SDR). The analog input signal is sampled by an analog-to-digital converter (A / D) chip to generate digitized, high-rate data. This data is then mixed with the quadrature I and Q signals output by the NCO (Non-Converter Coder) within the ZYNQ. This signal then passes through a decimation filter bank, significantly reducing the sampling rate, before being sent to the back-end digital signal processing equipment for real-time processing. Through A / D conversion, a numerically controlled oscillator, and a decimation filter bank, the IF signal is converted to baseband, reducing the sampling rate and improving signal processing efficiency and accuracy.

[0092] As a specific example, see Figure 6The signal after A / D sampling is mixed with the numerically controlled oscillator (NCO), and then sent to the first-stage decimation filter integral comb filter (CIC filter) for decimation filtering. After the first stage of decimation is completed, it is sent to the second stage of the decimation filter group. The second stage uses a half-band filter (HB filter) for secondary decimation filtering. Finally, the decimated signal is sent to the last stage shaping filter (FIR filter) for shaping filtering. The shaped signal is sent to the back-end DSP processor for processing. At the same time, the FIR filter only performs shaping filtering and does not participate in decimation and frequency reduction.

[0093] In the present invention, the RF signal from the RF input terminal is converted into a 31.1 MHz intermediate frequency signal after RF down-conversion processing. The signal is sampled by an AD converter with a sampling rate of 80 MSPS in the intermediate frequency digital processing unit and its expression is:

[0094]

[0095] Among them, S(n) is the discretized intermediate frequency signal, i.e., the modulation signal, n is the sampling point number, a(n), They are the amplitude modulation and phase modulation components of the modulated signal respectively, ω0 is the signal carrier frequency or intermediate frequency, expressed as orthogonal components, which can be written as:

[0096] S(n)=I(n)cos(ω0n)-Q(n)sin(ω0n),

[0097] I(n) and Q(n) are called the in-phase and quadrature components of the modulated signal, respectively. Since the carrier frequency ω0 contains no information, the in-phase and quadrature components can fully describe the characteristics of a given signal (the power and frequency of the carrier signal are obtained through detection and counting in the RF front-end). Extracting these two quadrature components is the key to receiving and demodulating the signal. Extracting the quadrature components I(n) and Q(n) is accomplished using digital mixing.

[0098] See Figure 7 , the implementation of digital mixing method is shown in the figure, the low-pass filter in the figure It is mainly used to filter out unnecessary signals other than the I(n) and Q(n) spectral components, so the passband cutoff frequency f of the low-pass filter is p It should be the corresponding highest frequency in the I(n) and Q(n) spectral components, and the filter stopband frequency f A It should be less than half of the channel spacing to eliminate the influence of adjacent channel interference. The characteristics of its low-pass filter are as follows: Figure 8 shown.

[0099] See Figure 9, the low-pass filter and the subsequent decimator ↓D together form a standard decimation system. If the decimation factor D is large, the required order is very high, which can be achieved by multi-stage decimation, with the decimation factor of each stage being D m (m=1,2,...,M), the total extraction factor is:

[0100]

[0101] As mentioned above, cascaded integrator comb (CIC) filters and half-band (HB) filters are highly efficient digital filters widely used in decimation systems. Since CIC filters do not require multiplication operations and can achieve high-speed filtering, they are generally used in the first stage with the highest input sampling rate. Although the half-band filter requires multiplication, it only requires half the amount of computation required by the ordinary FIR filter. Therefore, the HB filter is generally used in the second stage of the medium input sampling rate. After the first two stages of decimation filtering, the sampling rate has been significantly reduced, so the subsequent stages of decimation filters can be implemented using ordinary FIR filters.

[0102] According to the above extraction structure, a mathematical model of software radio receiving system can be realized as follows: Figure 10 As shown, each level of the filter has a decimation function, and the decimation factors of each level are D1, D2, and D3, respectively. D1 and D3 can be any positive integers, and D2 is required to be a power of 2. The total decimation factor is D = D1·D2·D3.

[0103] Furthermore, the modulated signal S(n) is subjected to orthogonal mixing and D-fold decimation filtering to obtain the orthogonal baseband signals I(n) and Q(n), which are sent to the instantaneous feature extraction unit for instantaneous amplitude a(m) and instantaneous phase. And the instantaneous frequency f(m) is calculated, and finally these three instantaneous features together with the two orthogonal baseband signals I(n) and Q(n) are sent to the subsequent demodulation analysis module to complete signal recognition, demodulation and other functions.

[0104] See Figure 11 The amplitude, phase and frequency of the orthogonal baseband signal (I and Q components) are calculated by the instantaneous feature extraction unit, and the FM signal demodulation is realized through the phase difference algorithm.

[0105] The FM signal can be expressed as:

[0106]

[0107] Where SFM(t) is the time domain expression of the frequency modulated signal, t is time, ω c is the angular frequency, m(τ) is the modulation signal, A is the amplitude of the FM signal, is the initial phase.

[0108] by The intermediate frequency sampling is performed at a rate of fs, where fs is the sampling frequency, Ts is the sampling period, and the input signal S FM (t) becomes:

[0109] S FM (n) = Acos(nω c T s +k∑m(n)+φ0)

[0110] The in-phase branch is multiplied by cos(nω L0 T s +φ L0 ), and low-pass filtering to obtain:

[0111] X I (n)=A cos[nΔωT s +Δφ+k∑m(n)]

[0112] where ω L0 is the angular frequency of the down-converted signal, is the initial phase of the down-converted signal, X I (n) is the 0 intermediate frequency in-phase branch signal, X Q (n) is the zero intermediate frequency orthogonal branch signal.

[0113] The quadrature branch is multiplied by sin(nω L0 T s +φ L0 ), and low-pass filtering to obtain:

[0114] X Q (n) = A sin[nΔωT s +Δφ+k∑m(n)]

[0115] In the above formula, Δω=ω c -ω LO ,

[0116] The phase is obtained by performing the inverse tangent operation on the ratio of the quadrature and in-phase components:

[0117]

[0118] For phase difference:

[0119] φ(n)-φ(n-1)

[0120] =[ω·n+φ+k∑m(n)]-[ω·(n-1)+φ+k∑m(n-1)]

[0121] =ω+k∑m(n)

[0122] Where ω is the DC component, K is the frequency modulation sensitivity, which represents the control coefficient of the modulation signal on the frequency change; m(n) is the modulation signal, φ(n) is the instantaneous phase of the current sampling point; φ(n-1) is the instantaneous phase of the previous sampling point;

[0123] After subtracting the DC component ω, the modulated signal m(n) is obtained. From the above analysis, we can also see that when FM signals are demodulated using the orthogonal demodulation method, they have strong immunity to carrier frequency mismatch.

[0124] In addition, since the calculation of φ n The division and inverse tangent operations are complex for non-dedicated digital signal processors, so when demodulating FM signals in an FPGA, a new method is proposed to calculate the phase difference (also known as the instantaneous frequency):

[0125]

[0126] For FM signals, the amplitude is approximately constant. Let X I 2 +X Q 2 is 1, then:

[0127] f(n) = X′ Q ·X I -X′ I .X Q

[0128] =(X Q (n)-X Q (n-1))·X I (n-1)-(X I (n)-X I (n-1))·X Q (n)

[0129] =X Q (n)·X I (n-1)-X I (n)·X Q (n-1)

[0130] Where XI and XQ are the in-phase and quadrature components of the sampling point, XI(n-1) and XQ(n-1) are the in-phase and quadrature components of the previous sampling point, respectively.

[0131] Among them, X' Q =X Q (n)-X Q (n-1); X′ I =X I (n)-X I(n-1);

[0132] The above formula is to use X I 、X Q Directly calculate the approximate formula of f(n). This method only involves multiplication and division operations, and the calculation is relatively convenient.

[0133] Through orthogonal mixing, instantaneous feature extraction and demodulation analysis, accurate demodulation of modulated signals, especially FM signals, is achieved, which improves the accuracy of signal demodulation and anti-interference ability.

[0134] Finally, it should be noted that the embodiments described in detail above are only the best practices of the invention and cannot be used to limit the scope of rights of the invention. Equivalent replacement of the technical solutions recorded in the aforementioned embodiments does not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the invention, and they should all be included in the scope of the claims and description of the invention.

Claims

1. A wide-band radio frequency signal processing method based on multi-stage frequency conversion, characterized in that: The following steps are involved: S1, inputting a radio frequency signal, mixing the radio frequency signal into a first intermediate frequency signal through a first mixer, filtering the first intermediate frequency signal through a first filter and a second filter, and then mixing the first intermediate frequency signal into a second intermediate frequency signal through a second mixer; S2. Sampling the second intermediate frequency signal to obtain a modulated signal, and extracting an in-phase component and a quadrature component of the modulated signal; S3, mixing the in-phase component and the quadrature component of the modulated signal with the quadrature signal, and performing multi-stage decimation filtering in sequence through a CIC filter, a half-band filter, and an FIR filter to obtain an orthogonal baseband signal; S4. Calculate the instantaneous amplitude, instantaneous phase and instantaneous frequency of the orthogonal baseband signal, and complete frequency modulation signal demodulation through a phase difference algorithm to obtain a modulated signal source.

2. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 1, wherein: The specific steps of S1 are: S11. The RF signal is input to a first attenuator, which attenuates the signal to obtain a first attenuated signal. The first attenuated signal is input to a second attenuator, which attenuates the signal to obtain a second attenuated signal. The second attenuated signal is input to a power splitter for attenuation, and the power splitter outputs a third attenuated signal. S12, inputting the third attenuated signal into a third attenuator to adjust the signal amplitude to obtain a first conditioned signal; S13, the first conditioned signal passes through a first filter and is input into an amplifier, and then input into a first-stage mixer and mixed with a local oscillator signal to obtain a first intermediate frequency signal; S14, the first intermediate frequency signal is input into the second filter and the third filter, the first intermediate frequency signal is amplified and then filtered by the fourth filter and the fifth filter, and then input into the second mixer and mixed with the second local oscillator signal to obtain a second intermediate frequency signal.

3. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 1, wherein: The specific steps of extracting the quadrature component of the modulated signal are: A low-pass filter is used to filter signals other than the orthogonal components of the modulated signal, and the passband cutoff frequency and stopband frequency of the low-pass filter are set. The passband cutoff frequency is the highest frequency corresponding to the spectral components of the orthogonal components of the modulated signal, and the stopband frequency is less than half of the channel spacing.

4. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 1, wherein: The specific steps of performing multi-stage decimation filtering by using a CIC filter, a half-band filter, and an FIR filter are as follows: The CIC filter is used as the first stage to perform preliminary extraction of the input signal; A half-band filter is used as the second stage for decimation; Finally, an FIR filter is used for shaping filtering, wherein each stage of the CIC filter, half-band filter and FIR filter sets a decimation factor for multi-stage decimation.

5. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 4, wherein: The total calculation formula for the extraction factor when performing multi-level extraction is: Where D is the total extraction factor, Dm is the extraction factor of each level, m is the number of levels, and M is a positive integer.

6. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 1, wherein: The specific steps of mixing the in-phase component and the quadrature component of the modulated signal with the quadrature signal are: The in-phase component of the modulated signal is multiplied by the in-phase component of the quadrature signal and then filtered through a low-pass filter to obtain the instantaneous in-phase component; The quadrature components of the modulated signal are multiplied by the quadrature components of the quadrature signal and then filtered through a low-pass filter to obtain instantaneous quadrature components.

7. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 6, wherein: The specific calculation steps of the instantaneous phase and instantaneous frequency are as follows: Calculating the instantaneous phase by performing an arc tangent operation on the ratio of the instantaneous in-phase component to the instantaneous quadrature component; performing a differential operation on the instantaneous phase to obtain a change in instantaneous frequency; After subtracting the DC component from the instantaneous frequency change, a modulation signal is obtained.

8. The method for processing wide-band radio frequency signals based on multi-stage frequency conversion according to claim 7, wherein: The formula for performing differential operation on the instantaneous phase is: Where f(n) is the instantaneous frequency, φ(n) is the phase of the current sampling point, φ(n-1) is the phase of the previous sampling point, φ'(n) and φ(n)-φ(n-1) are the instantaneous phase differences, and X Q is the instantaneous quadrature component, X I is the instantaneous in-phase component.

9. A wide-band radio frequency signal processing system based on multi-stage frequency conversion, characterized in that: It includes RF front-end module, intermediate frequency processing module, digital signal processing module and demodulation unit; A radio frequency front-end module, configured to mix an input radio frequency signal into a first intermediate frequency signal through a first mixer, filter the first intermediate frequency signal through a first filter and a second filter, and then mix the first intermediate frequency signal into a second intermediate frequency signal through a second mixer; an intermediate frequency processing module, comprising an analog-to-digital converter, the analog-to-digital converter being configured to sample the second intermediate frequency signal to obtain a modulated signal and calculate a quadrature component and an in-phase component of the modulated signal; A digital signal processing module includes a digital down-conversion unit and a demodulation unit. The digital down-conversion unit is connected to a digitally controlled oscillator. The digitally controlled oscillator generates an orthogonal signal. After mixing the modulated signal with the orthogonal signal, the orthogonal signal is subjected to multi-stage decimation filtering through a CIC filter, a half-band filter, and an FIR filter in sequence to obtain an orthogonal baseband signal. The demodulation unit is used to extract the instantaneous amplitude, instantaneous phase and instantaneous frequency of the orthogonal baseband signal, and complete the frequency modulation signal demodulation through the phase difference algorithm to obtain the modulated signal source.

10. The wide-band radio frequency signal processing system based on multi-stage frequency conversion according to claim 9, characterized in that: The analog-to-digital converter adopts an AD9268 analog-to-digital converter, the first filter adopts a low-pass filter, and the second filter adopts a band-pass filter.

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