A frequency discrimination method based on difference frequency multiplication integral linear transformation network

Abstract

The present invention provides a frequency discrimination method of a difference frequency multiplication integral linear transformation network, which belongs to the field of signal processing technology. The method comprises the following steps: setting a first preset difference frequency signal u s1 (τ) and the second preset difference frequency signal u s2 (τ), receiving FM signal u i (τ), the received FM signal u i (τ) are respectively related to the first preset difference frequency signal u s1 (τ) and the second preset difference frequency signal u s2 (τ) performs multiplication and integration operations to obtain the first operation result u n1 and the second operation result u n2 , take the first operation result u n1 and the second operation result u n2 The modulation signal is obtained by performing a linear transformation. The present invention makes the debugging of the frequency discrimination system simpler and more convenient. The preset difference frequency signal can be flexibly selected according to the actual application. The initial phase of the frequency modulation signal is eliminated during the transformation, which has no impact on the frequency discrimination accuracy. The bandwidth requirement of the frequency modulation signal is low, which can meet more special applications.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing, in particular to a frequency discrimination method of a difference frequency multiplication integral linear transformation network. Background Art

[0002] Frequency discrimination, also known as frequency detection, is the process of reproducing the modulated signal from the FM wave. It is an important means of restoring the modulated signal information during FM signal transmission. Its function is to detect the original modulated signal contained in the FM signal frequency. FM is a modulation method that changes the instantaneous frequency of the carrier according to the changing rules of the desired transmitted signal. The commonly used indirect FM process block diagram is as follows: Figure 1 Frequency modulation and frequency discrimination are widely used in FM broadcasting, television audio, microwave communications, phase-locked circuits, and frequency sweepers, and are one of the important technologies in modern microwave communications.

[0003] The slope frequency detector first sends the constant amplitude FM signal into the frequency-amplitude linear conversion network to convert it into an AM-FM signal whose amplitude changes proportionally to the frequency. Then it uses the envelope detector to detect and restore the original modulated signal. Its working model is as follows: Figure 2 (a) As shown. The phase discriminator first sends the constant amplitude frequency modulated signal into the frequency-phase linear conversion network, transforming it into a phase-frequency modulated signal whose phase changes proportionally to the instantaneous frequency, and then restores the original modulated signal through the phase detector. Its working model is as follows Figure 2 (b) shown.

[0004] The frequency discrimination methods based on waveform transformation, such as slope frequency discriminator, phase frequency discriminator, ratio frequency discriminator and crystal frequency discriminator, all require the design of a very accurate linear transformation network of the carrier center frequency, otherwise the frequency discrimination result will have a large error. The slope frequency discrimination characteristic has a certain nonlinearity between the two peaks, such as Figure 3 As shown in (a), good linearity is usually achieved only near the frequency deviation Δf = 0; the phase discriminator characteristic curve is a modulated sine curve, such as Figure 3 (b) shows that only when the difference To ensure the quality of restored modulated signals, the frequency detection method is often used, which has a low distortion and narrow bandwidth. Summary of the Invention

[0005] The purpose of the present invention is to provide a frequency discrimination method of a difference frequency multiplication integral linear transformation network, so as to solve the technical problem that distortion easily occurs in high frequency signals of traditional frequency discrimination methods.

[0006] The actual frequency of the FM signal contains the original modulation signal information. The difference frequency multiplication integral linear transformation network restores the original modulation signal by analyzing the actual frequency of the FM signal. The FM signal ui is sent to two multiplication integral transformation networks and respectively compared with the preset difference frequency signal us1 and u s2 After multiplication and integration, it is sent to the linear transformation network to accurately analyze the actual frequency of the FM signal. Since the actual frequency contains the instantaneous amplitude of the modulation signal in the FM signal, the modulation signal can be obtained through linear restoration to achieve frequency discrimination.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A frequency discrimination method using a difference frequency multiplication integral linear transformation network, comprising the following steps:

[0009] Step 1: Set the first preset difference frequency signal u s1 (τ) and the second preset difference frequency signal u s2 (τ), receiving FM signal u i (τ);

[0010] Step 2: Convert the received FM signal u i (τ) are respectively related to the first preset difference frequency signal u s1 (τ) and the second preset difference frequency signal u s2 (τ) performs multiplication and integration operations to obtain the first operation result u n1 and the second operation result u n2 ;

[0011] Step 3: Take the first operation result u n1 and the second operation result u n2 Perform linear transformation to obtain the modulated signal.

[0012] Furthermore, the specific process of step 1 is as follows: assuming that the received FM signal is Among them U cm is the amplitude of the FM signal, the first preset difference frequency signal is u s1 (τ)sin2πf1t=sin2πn1τ, the second preset difference frequency signal u s2 (τ)=sin2πf2t=sin2πn2τ,f f is the frequency of the received FM signal, f1 is the frequency of the first preset difference frequency signal, f2 is the frequency of the second preset difference frequency signal, and the first preset difference frequency signal u s1 (τ) and the second preset difference frequency signal u s2 The frequencies f1 and f2 of (τ) have a greatest common divisor f0, then f1=n1f0, f2=n2f0, n1 and n2 are positive integers, then f f =xf0, x is a positive real number, indicating that the frequency of the AM signal is a multiple of the greatest common divisor f0 with the frequencies f1 and f2, τ=f0t, t is time, is the phase difference.

[0013] Furthermore, in step 2, during the multiplication and integration operation, the integration time is set to the period corresponding to f0. That is, the integral time of τ is τ0=f0t0=1, and the first operation result u n1 The operation process is:

[0014]

[0015] The second operation result u n2 The operation process is:

[0016]

[0017] Wherein, x is a positive real number, indicating that the frequency of the AM signal is a multiple of the greatest common divisor of the sum of the frequencies.

[0018] Furthermore, the specific process of step 3 is to transform the multiplication integral transformation result u n1 and u n2 By dividing, we can get the relationship between x and n1 and n2.

[0019]

[0020] Then x is equal to: Since f f =xf0, which means that the frequency of the AM signal is a multiple of the greatest common divisor f0 with the frequencies f1 and f2. Then we can calculate f f ;

[0021] The actual frequency f of the FM signal f =xf0 is composed of two parts: the carrier center frequency and the modulation signal influence frequency, and then undergoes the following linear transformation:

[0022]

[0023]

[0024] The amplitude of the modulated signal can be obtained to achieve accurate frequency discrimination.

[0025] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0026] In the FM signal with a higher FM index, the distortion of the traditional phase frequency detection method increases with the increase of the FM index. However, the method of the present application has almost no signal distortion under various FM indices, the frequency detection bandwidth is not limited, the modulation signal restoration quality is higher, and the distortion is maintained between 0.0056% and 0.0073%. Its frequency detection distortion mainly comes from noise interference, and the carrier center frequency has a very small effect on its frequency detection quality and can be ignored. At the same time, the present application does not require accurate restoration of the carrier signal, making the debugging of the frequency detection system simpler and more convenient. The preset difference frequency signal can be flexibly selected according to the actual application scenario. The initial phase of the FM signal is eliminated during the transformation, which has no effect on the frequency detection accuracy. The bandwidth requirement for the FM signal is low, which can meet more special application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the block diagram of the traditional indirect frequency modulation model;

[0028] Figure 2 This is the block diagram of the traditional frequency discriminator model;

[0029] Figure 3 It is a traditional frequency discrimination characteristic curve;

[0030] Figure 4 This is a frequency discrimination model diagram of the difference frequency multiplication integral linear transformation network of the present invention;

[0031] Figure 5 This is a comparison chart of the frequency modulation index 0.02 discrimination results of the present invention;

[0032] Figure 6 This is a comparison chart of the frequency modulation index 0.5 discrimination results of the present invention;

[0033] Figure 7 This is a comparison chart of the frequency modulation index 2.4 discrimination results of the present invention;

[0034] Figure 8 1 is a distribution diagram of the frequency discrimination distortion of the two frequency discrimination methods of the present invention;

[0035] Figure 9 This is a characteristic diagram of the frequency discrimination distortion-carrier center frequency error of the present invention. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and by way of preferred embodiments. However, it should be noted that many of the details listed in this specification are merely provided to help the reader gain a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be practiced even without these specific details.

[0037] like Figure 1As shown, a difference frequency multiplication integral linear transformation network frequency discrimination method comprises the following steps:

[0038] Step 1: Set the first preset difference frequency signal u s1 (τ) and the second preset difference frequency signal u s2 (τ), receiving FM signal u i (τ). Preset difference frequency signal u s1 and u s2 The frequency of f1 and f2 must satisfy the greatest common divisor f0, so that f1 = n1f0, f2 = n2f0, n1 and n2 are positive integers, then f f =xf0, where x is a positive real number. Let τ = f0t, and the final actual FM signal and preset difference frequency signal are expressed as follows:

[0039] FM signal

[0040] Preset difference frequency signal u s1 (τ)=sin2πf1t=sin2πn1τ;

[0041] Preset difference frequency signal u s1 (τ)=sin2πf2t=sin2πn2τ.

[0042] In the frequency modulation process, let the carrier signal be u c (t) = U cm cosω c t,U cm is the carrier amplitude, ω c is the carrier angular frequency, and the modulation signal is u Ω (t) = U Ωm cosΩt,U Ωm is the modulation signal amplitude, Ω is the modulation signal angular frequency, and the actual angular frequency of the FM signal is

[0043] ω f =ω c +Δω(t)=ω c +k f u Ω (t) = ω c +k f U Ωm cosΩt=ω c +Δω fm cosΩt.

[0044] Δω(t) is the modulation angle frequency deviation, k f is the FM sensitivity, which indicates the frequency change caused by the unit modulation signal amplitude; the actual frequency of the FM signal is

[0045]

[0046] Among them, f c is the carrier center frequency, Δf(t) is the modulation frequency deviation; Δω fm / 2π is the maximum frequency deviation of the FM wave, which represents the swing amplitude of the FM wave frequency and is a constant in the FM signal.

[0047] Step 2: Convert the received FM signal u i (x) are respectively s1 (τ) and the second preset difference frequency signal u s2 (τ) performs multiplication and integration operations to obtain the first operation result u n1 and the second operation result u n2 .

[0048] When performing multiplication-integration transformation, the integration time is set to the period corresponding to f0 That is, the integration time of τ is τ0=f0t0=1, and the result of multiplication and integration transformation with the preset difference frequency signal is:

[0049]

[0050]

[0051] The specific process of multiplication integration is as follows:

[0052]

[0053]

[0054] Step 3: Take the first operation result u n1 and the second operation result u n2 Perform linear transformation to obtain the modulated signal.

[0055] After the multiplication and integration network, the FM signal is transformed into a quantity related to the FM signal frequency and the difference frequency signal frequency. In the linear transformation restoration network, the multiplication and integration transformation result u is first converted into n1 and u n2 By dividing, we can get the relationship between x and n1 and n2 as shown in formula (1).

[0056]

[0057] The actual frequency f of the FM signal f =xf0 is composed of two parts: the carrier center frequency and the modulation signal influence frequency. After the linear transformation shown in formula (2), the amplitude of the modulation signal can be obtained to achieve accurate frequency discrimination.

[0058]

[0059]

[0060] Tables 1 and 2 show the test data for the frequency modulation distortion of the commonly used phase frequency detection method and the difference frequency multiplication-integral linear transformation network frequency detection method for frequency modulation signals with different frequency modulation indices. It can be seen that at low frequency modulation indices, both detection methods can accurately restore the original modulated signal. However, for FM signals with higher frequency modulation indices, the distortion of the phase detection method increases with the increase of the frequency modulation index. In contrast, the difference frequency multiplication-integral linear transformation network frequency detection method achieves virtually no signal distortion regardless of the frequency modulation index, with no limitation on the detection bandwidth, resulting in higher quality modulation signal restoration. Figure 6 The demodulation results of the two methods when the FM index is 0.02 are very small. Figure 7 The demodulation results of the two methods when the frequency modulation index is 0.5 are shown. The traditional phase demodulation method has obvious even-order harmonic distortion in the demodulation signal, while the demodulation method in this paper has minimal distortion. Figure 8 Figure 3 is the demodulation result of the two methods when the frequency modulation index is 2.4. The traditional phase demodulator has higher-order even harmonic distortion in the demodulated signal, while the demodulation method in this paper has extremely small distortion.

[0061] Table 1 shows the phase discriminator test results.

[0062]

[0063]

[0064] Table 2 shows the test results of the frequency discrimination method in this method.

[0065]

[0066] Based on the experimental data, the frequency discrimination distortion distribution diagrams of the two methods are drawn as follows: Figure 8 As shown in the figure, it can be seen that the low frequency discrimination distortion range of the traditional phase discriminator is small, and the corresponding available bandwidth is narrow; the low frequency discrimination distortion range of the method in this paper is applicable to almost the entire range, and the discrimination bandwidth is wider.

[0067] Under different carrier center frequency errors, the frequency discrimination distortion and relative error of the two methods are shown in Table 3. Combining the experimental data, the frequency discrimination distortion-carrier center frequency error characteristics of the two frequency discrimination methods are plotted as follows: Figure 9 shown.

[0068] Table 3 shows the frequency discrimination distortion and relative error

[0069]

[0070] Combined with the experimental data, the frequency discrimination distortion-carrier center frequency error characteristics of the two frequency discrimination methods are plotted as follows: Figure 9As shown in the figure. When the carrier center frequency error is 0, the phase discriminator's discrimination distortion is 0.257%, while the discrimination distortion of the discrimination method studied in this paper is 0.006%. When there is an error in the carrier center frequency, the discrimination distortion of the phase discriminator shows a staged increase as the error increases. When the carrier center error is less than 0.9‰, the discrimination distortion of the phase discriminator does not exceed 2%. However, when the carrier center error exceeds 0.9‰, the discrimination distortion of the phase discriminator increases exponentially, and the discrimination quality drops sharply. Under different carrier center frequency errors, the discrimination distortion of the discrimination method in this study remains between 0.0056% and 0.0073%. Its discrimination distortion is mainly caused by noise interference, and the carrier center frequency has a very small impact on its discrimination quality and can be ignored.

[0071] The method requires that the greatest common divisor f0 of the difference frequency signals be as large as possible to improve the low-pass filtering effect of the integration link, and at least one of the two difference frequency signals is close to the center frequency of the FM signal.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A frequency discrimination method using a difference frequency multiplication-integral linear transformation network, characterized in that: The method comprises the following steps: Step 1: Set the first preset difference frequency signal and the second preset difference frequency signal Receiving FM signals Step 2: Receive the FM signal respectively with the first preset difference frequency signal and the second preset difference frequency signal Perform multiplication and integration operations to obtain the first operation result u n1 and the second operation result u n2 ; Step 3: Take the first operation result u n1 and the second operation result u n2 Perform linear transformation to obtain the modulated signal; The specific process of step 1 is as follows: assuming that the received FM signal is Among them U cm is the amplitude of the FM signal, and the first preset difference frequency signal is The second preset difference frequency signal f f is the frequency of the received FM signal, f1 is the frequency of the first preset difference frequency signal, f2 is the frequency of the second preset difference frequency signal, and the first preset difference frequency signal and the second preset difference frequency signal The frequencies f1 and f2 have a greatest common divisor f0, then f1=n1f0, f2=n2f0, n1, n2 are positive integers, then f f =xf0, x is a positive real number, indicating that the frequency of the AM signal is a multiple of the greatest common divisor f0 with the frequencies f1 and f2. t is time, is the phase difference.

2. The difference frequency multiplication-integral linear transformation network frequency discrimination method according to claim 1, characterized in that: In step 2, during the multiplication and integration operation, the integration time is set to the period corresponding to f0 Right now The integration time is The first operation result u n1 The operation process is: The second operation result u n2 The operation process is: Wherein, x is a positive real number, indicating that the frequency of the AM signal is a multiple of the greatest common divisor f0 with the frequencies f1 and f2.

3. The difference frequency multiplication-integral linear transformation network frequency discrimination method according to claim 1, characterized in that: The specific process of step 3 is to transform the multiplication integral transformation result u n1 and u n2 By dividing, we can get the relationship between x and n1 and n2. Then x is equal to: Since f f =xf0, which means that the frequency of the AM signal is a multiple of the greatest common divisor f0 with the frequencies f1 and f2. Then we can calculate f f ; The actual frequency f of the FM signal f =xf0 is composed of two parts: the carrier center frequency and the modulation signal influence frequency, and then undergoes the following linear transformation: The amplitude of the modulated signal can be obtained to achieve accurate frequency discrimination. Ω is the angular frequency of the modulated signal, f c is the carrier center frequency, is the maximum frequency deviation of the FM wave.

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