A frequency conversion signal receiving method and a frequency conversion signal receiving system

Abstract

The application belongs to the field of microwave photon signal processing, and particularly relates to a frequency conversion signal receiving method and a frequency conversion signal receiving system. The method comprises the following steps: generating an optical frequency comb, setting a time delay for the optical frequency comb; after the time delay, performing undersampling on a to-be-measured signal in an electro-optical modulator, and outputting a down-converted signal; obtaining an initial phase and a frequency of the down-converted signal; changing the time delay, and calculating a phase of the down-converted signal; calculating a ratio of an original frequency of the to-be-measured signal to a repetition frequency of the optical frequency comb by using the initial phase, the phase, the repetition frequency of the optical frequency comb and a time delay difference; and obtaining the original frequency of the to-be-measured signal according to the ratio. The time delay is set for the optical frequency comb, a mapping relationship between the original frequency of the signal and the phase of the down-converted signal is established after the time delay, the original frequency of the to-be-measured signal is solved according to the mapping relationship, the frequency information lost in the down-converted receiving of the optical frequency comb is recovered, the problem of frequency information loss in the optical frequency comb receiving process of a non-cooperative signal in a large frequency range is solved, and the receiving of the non-cooperative signal is completed.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonic signal processing, specifically relating to a frequency conversion signal receiving method and a frequency conversion signal receiving system. Background Technology

[0002] Applications such as electromagnetic environment monitoring and large-scale electromagnetic signal survey and positioning require non-cooperative reception of signals appearing in a wide frequency range. Non-cooperative reception in wireless communication refers to the process of intercepting and processing signals from the perspective of a third party. Non-cooperative reception is limited by the sampling rate of analog-to-digital conversion circuits, and the instantaneous bandwidth of a typical receiver cannot cover a very large frequency range. To meet the frequency band coverage requirements of application scenarios, common approaches include channelization, sweep heterodyne, and instantaneous frequency measurement receiver guidance. Channelized receivers essentially improve signal acquisition probability through hardware multi-path parallelism, thus resulting in larger hardware size, higher complexity, and increased cost. Sweep heterodyne receivers require changing the local oscillator frequency to cover a wide frequency range, increasing time consumption and reducing the acquisition probability of non-cooperative signals. Instantaneous frequency measurement receivers can only measure signal frequency and cannot provide other information such as amplitude and phase, making them unsuitable for standalone use. They need to be used in conjunction with a heterodyne receiver to achieve full signal reception. Instantaneous frequency measurement receivers can convert the signal frequency information into a slowly varying signal form in real time. Then, a low-speed ADC is used to collect, analyze, and calculate the signal frequency. The frequency information is then used to guide the heterodyne receiver to adjust the local oscillator frequency for accurate reception, thus increasing the size, complexity, and cost of the receiving system. Furthermore, because instantaneous frequency measurement receivers map signal frequency information to other dimensions, such as amplitude, the calculation process often becomes extremely complex or even unsolvable when multiple signals are present.

[0003] Due to the undersampling frequency conversion function of optical frequency combs, coupled with the development of microwave photonics technology, wide-range reception of electromagnetic signals over a wide frequency range has become possible. Specifically, the optical frequency comb uses undersampling to shift electromagnetic signals appearing over a wide frequency range to a lower frequency. After photoelectric conversion using low-pass characteristics, the low-frequency components carrying the original electromagnetic signal information can be acquired and received by a low-speed analog-to-digital converter. However, because signals of different frequencies are shifted to the first Nyquist zone by the optical frequency comb, the original frequency information of the electromagnetic signal is lost during reception, making non-cooperative reception of electromagnetic signals over a wide frequency range impossible. Summary of the Invention

[0004] To address the aforementioned technical problem—namely, the loss of frequency information during the down-conversion process of the original signal via the optical frequency comb, which prevents non-cooperative reception of electromagnetic signals over a wide frequency range—this invention provides the following technical solution:

[0005] A method for receiving frequency conversion signals includes the following steps:

[0006] 1) Generate an optical frequency comb and set an initial time delay for the optical frequency comb;

[0007] 2) After the initial time delay, the optical frequency comb is undersampled in the electro-optic modulator to output a down-converted signal.

[0008] 3) After photoelectric conversion of the down-conversion signal, analog-to-digital conversion is then performed;

[0009] 4) Obtain the initial phase of the down-converted signal under the initial time delay. and frequency f ls ;

[0010] 5) Change the time delay to obtain the phase of the down-converted signal.

[0011] 6) Using the initial phase, the phase of step 5), and the time delay difference Δt between the time delay of step 5) and the initial time delay of step 1), calculate the original frequency of the signal under test and the frequency repetition ratio of the optical frequency comb.

[0012] 7) Obtain the original frequency of the signal under test based on the ratio of the original frequency of the signal under test to the repetition frequency of the optical frequency comb and the frequency of the down-conversion signal.

[0013] Furthermore, the calculation method for step 6) is derived based on Formula 1.

[0014]

[0015] f0 is the known optical frequency comb repetition frequency, Δt is the time delay difference, and the ratio of the original frequency of the signal under test to the optical frequency comb repetition frequency is derived. The ratio is then rounded down to obtain the value N.

[0016] Further, step 7) the original frequency f of the signal to be measured. r The calculation method is as follows: calculate according to Formula 2.

[0017] f r =|f ls -Nf0| Formula 2.

[0018] This invention also provides another method for receiving frequency conversion signals, comprising the following steps:

[0019] S1. Divide each of the multiple signals to be tested into an upper path and a lower path;

[0020] S2. Use an optical fiber beam splitter to split the optical frequency comb into an upper and lower sampling pulse source, and set an initial time delay for one of the sampling pulse sources.

[0021] S3. The two sampling pulse sources perform undersampling on the upper and lower signals of multiple signals to be measured in their respective electro-optic modulators, and output two down-converted signals of the same frequency.

[0022] S4. Obtain the initial phase of the two down-conversion signals under the initial time delay. and frequency f k0 k0 represents the kth signal to be measured when the initial phase is measured, and a and b represent the upper and lower signals, respectively.

[0023] S5. Change the delay to obtain multiple delay differences t m Multiple phase measurements were performed to obtain the phase of multiple up-converter signals. and the phase of multiple downconverter signals t m This represents the time delay difference between the corresponding time delay and the initial time delay in step S2 when the time delay measurement is changed for the mth time, 1≤m≤MN, where MN is the maximum number of measurements; This indicates the phase of the measured uplink signal when the time delay is changed for the mth time;

[0024] S6. Using the two initial phases and the phase of step S5, construct the exponential phase factor vector for each down-conversion signal.

[0025] S7. Construct a measurement matrix, and perform an inner product operation between the row vectors of the measurement matrix and the exponential phase factor vector. When the obtained inner product value is the maximum, obtain the frequency ratio n corresponding to the components of each down-conversion signal in the first Nyquist zone. k Then, the original frequencies of each signal to be measured are obtained.

[0026] Furthermore, the exponential phase factor vector for each down-converted signal is:

[0027]

[0028] In the formula

[0029] Furthermore, the measurement matrix is

[0030]

[0031] In the formula, f0 is the optical frequency comb repetition frequency, and t1≤t m ≤t MN N max The value obtained by rounding up the ratio of the maximum frequency obtained within multiple frequency ranges of the signals under test to the optical frequency comb repetition rate, -N max ≤n≤N max , where n is an integer.

[0032] Furthermore, compare each row vector in matrix B with the exponential phase factor vector v. k The inner product of the two matrices is obtained by finding the maximum inner product. The nth element of the row vector corresponding to each down-converted signal in the B matrix is ​​then n. k Then, the original frequencies of each signal under test can be obtained.

[0033] f rk =|n k f0-f k0 Formula 5.

[0034] Furthermore, all of the phases are peak phase values ​​in the spectrum.

[0035] The present invention also provides a frequency conversion signal receiving system for implementing any of the aforementioned frequency conversion signal receiving methods, comprising a femtosecond pulsed laser, an optical fiber beam splitter, an adjustable optical fiber delay line, two electro-optic modulators, two photodetectors, a dual-channel synchronous data acquisition card, and a radio frequency signal source. The output of the femtosecond pulsed laser is connected to the input of the optical fiber beam splitter via an optical fiber. The optical fiber beam splitter includes an upper output and a lower output. The upper output of the optical fiber beam splitter is sequentially connected to the adjustable optical fiber delay line, a first electro-optic modulator, and a first photodetector. The lower output of the optical fiber beam splitter is sequentially connected to a second electro-optic modulator and a second photodetector. The first electro-optic modulator and the second electro-optic modulator are respectively connected to the radio frequency signal source. The first photodetector and the second photodetector are respectively connected to one corresponding channel of the dual-channel synchronous data acquisition card.

[0036] Furthermore, it also includes a power divider, which receives signals transmitted from a radio frequency signal source and transmits the received signals to the input of a first electro-optic modulator and a second electro-optic modulator.

[0037] Furthermore, the bandwidth of the photodetector is half the repetition frequency of the femtosecond pulse laser.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The frequency conversion signal receiving method described in this invention uses an adjustable fiber delay line to generate a known time delay, establishes a mapping relationship between the original signal frequency and the phase of the down-converted signal, and solves for the original frequency information of the signal from the down-converted signal phase and the time delay value of the adjustable fiber delay line based on the mapping relationship. On this basis, the frequency information lost during the down-conversion reception of the optical frequency comb is recovered, solving the problem of frequency information loss during the reception of non-cooperative signals in a large frequency range, thereby completing the reception of non-cooperative signals. This method can be used in applications such as electromagnetic environment monitoring and other applications involving the non-cooperative reception of multiple signals in a large frequency range.

[0040] 2. This invention can simultaneously handle the frequency recovery problem of multiple down-conversion signals. In the case of multiple signal reception, the phase of all signal components within the first half-repetition frequency interval can be obtained through a single fast Fourier transform operation, and each component's n can be calculated based on the same time delay. k The number of signals has a negligible impact on the computational load during frequency recovery. Therefore, the time and computational costs of this method hardly increase with the number of signals, making it particularly suitable for applications involving multi-signal reception.

[0041] 3. This invention uses the undersampling frequency conversion function of an optical frequency comb in conjunction with microwave photonics technology and an adjustable fiber delay line as a frequency conversion signal receiving system. It can achieve one-time reception of non-cooperative signals over a wide frequency range with a small hardware size, low power consumption, and low complexity, thereby improving the acquisition probability and reducing the cost of the receiving system. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the system composition and connection in a specific embodiment of the present invention;

[0043] Figure 2 The signal spectrum obtained by performing a fast Fourier transform on the data acquired by the dual-channel synchronous data acquisition card of the present invention;

[0044] Figure 3 This represents the relationship between signal recovery success rate and the number of measurements under different signal-to-noise power ratios (SNR). Detailed Implementation

[0045] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0046] It should be noted that the terms "center", "upper", "lower", "horizontal", "left", "right", "front", "rear", "lateral", "longitudinal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0047] This invention provides a method for receiving frequency conversion signals, as detailed below:

[0048] 1) Generate an optical frequency comb and set an initial time delay for the optical frequency comb;

[0049] 2) After time delay, the optical frequency comb is undersampled in the electro-optic modulator to output a down-converted signal.

[0050] 3) After photoelectric conversion of the down-conversion signal, analog-to-digital conversion is then performed;

[0051] 4) Obtain the initial phase of the down-converted signal under the initial time delay. and frequency f ls ;

[0052] 5) Change the time delay to obtain the phase of the down-converted signal.

[0053] 6) Using the initial phase, the phase of step 5), and the time delay difference Δt between the time delay of step 5) and the initial time delay of step 1), calculate the original frequency of the signal under test and the frequency repetition ratio of the optical frequency comb.

[0054] According to the undersampling downconversion process of the optical frequency comb, the phase expression of the downconverted signal is given by Formula 1.

[0055]

[0056] f0 is a known optical frequency comb repetition frequency, Δt is a known time delay difference, and then the value of N is derived. The value of N is the ratio of the original frequency of the signal under test to the optical frequency comb repetition frequency, and the ratio is rounded down to obtain the value.

[0057] 7) Obtain the original frequency of the signal under test based on the ratio of the original frequency of the signal under test to the repetition frequency of the optical frequency comb and the frequency of the down-conversion signal.

[0058] Substitute the value of N into Formula 2:

[0059] f r =|f ls -Nf0| Formula 2

[0060] The original frequency f of the signal to be measured is obtained. r .

[0061] The above-described frequency conversion signal receiving method can also be applied to measurement scenarios involving multiple channels, multiple signals to be measured, and multiple changes in the time delay value.

[0062] To reduce the initial phase of the signal caused by timing uncertainties To mitigate random variations and systematic errors caused by uncertainties in the measurement of the absolute length of the optical path and circuitry, this embodiment uses a two-channel measurement of relative phase to cancel out these systematic errors. The specific method for receiving the frequency conversion signal is as follows:

[0063] S1. Divide each of the multiple signals to be tested into an upper path and a lower path;

[0064] The radio frequency signal emits the signal under test, which is transmitted to the power divider. The power divider splits each signal under test into an upper and lower signal.

[0065] S2. Use an optical fiber beam splitter to split the optical frequency comb into an upper and lower sampling pulse source, and set an initial time delay for one of the sampling pulse sources.

[0066] A femtosecond pulsed laser is used to generate an optical frequency comb. The optical frequency comb is then passed through a 1:1 fiber beam splitter to split the optical frequency comb generated by the femtosecond pulsed laser into upper and lower sampling pulse sources of the same frequency. An adjustable fiber delay line is used to set the time delay of the upper sampling pulse source.

[0067] S3. The two sampling pulse sources perform undersampling on the upper and lower paths of multiple signals to be measured in their respective electro-optic modulators, and output two down-converted signals of the same frequency.

[0068] The upper-path signal emitted from the power divider is injected into the first electro-optic modulator, and the lower-path signal is injected into the second electro-optic modulator. The upper-path sampling pulse source samples the upper-path signal in the first electro-optic modulator, and the lower-path sampling pulse source samples the lower-path signal in the second electro-optic modulator. The modulated upper-path signal is transmitted to the low-speed first photodetector, and the modulated lower-path signal is transmitted to the low-speed second photodetector. The first and second photodetectors transmit the two down-converted signals to the dual-channel synchronous data acquisition card. The dual-channel synchronous data acquisition card performs synchronous acquisition and analog-to-digital conversion of the two down-converted signals, and then transmits them to the host computer for data processing.

[0069] S4. Obtain the initial phase of the two down-conversion signals under the initial time delay. and frequency f k0 k0 represents the kth signal when the initial phase is measured, and a and b represent the upper and lower signals, respectively.

[0070] The adjustable fiber optic delay line is set to zero picoseconds. The uplink and downlink signals, synchronously acquired by the dual-channel synchronous data acquisition card and converted to down-converted signals via analog-to-digital conversion, are transmitted to the host computer. The host computer performs Fast Fourier Transform analysis on the acquired down-converted signals to obtain the frequency f of each down-converted signal. k0 With peak phase In the formula, k is the index of the down-converted signal, 1≤k≤KN, and KN is the number of signals to be measured. Therefore, f k0 This represents the frequency of the k-th signal during the initial phase measurement. This represents the initial phase of the uplink signal for the k-th downconverter signal. This represents the initial phase of the down-conversion signal of the k-th down-conversion signal;

[0071] S5. Change the delay to obtain multiple delay differences t mMultiple phase measurements were performed to obtain the phase of multiple up-converter signals. and the phase of multiple downconverter signals m represents the measurement order, 1≤m≤MN, and MN represents the maximum number of measurements.

[0072] t m This represents the time delay difference between the modified time delay (after the m-th measurement) and the initial time delay in step S2. The upper and lower channels of each down-converted signal are collected, and the same Fast Fourier Transform analysis as in step S4 is used to calculate the peak phases of the multiple upper and lower channel down-converted signals of the k-th signal. Specifically, This indicates the peak phase of the up-converter signal corresponding to the first change in time delay during the first phase measurement. This indicates the peak phase of the corresponding down-converter signal under the condition of the first change in time delay during the first measurement; This represents the peak phase of the up-converter signal under the condition that the time delay value corresponding to the m-th phase change is measured for the m-th time. This represents the peak phase of the down-conversion signal corresponding to the m-th measurement, given the time delay value corresponding to the m-th change. This represents the peak phase of the up-converter signal under the condition that the time delay value corresponding to the MNth phase change is obtained when the MNth phase is measured. This represents the peak phase of the downconverter signal corresponding to the value of the time delay corresponding to the MNth change during the MNth measurement.

[0073] S6: Using the initial phases of the two paths and the phase of step S5, construct the exponential phase factor vector of each down-conversion signal;

[0074] For each down-converted signal, an exponential phase factor vector is constructed, denoted as Equation 3.

[0075]

[0076] In the formula

[0077] This represents the relative phase of the k-th down-conversion signal in the m-th measurement.

[0078] S7. Construct a measurement matrix, and perform an inner product operation between the row vectors of the measurement matrix and the exponential phase factor vector. When the obtained inner product value is the maximum, obtain the frequency ratio n corresponding to the components of each down-conversion signal in the first Nyquist zone. k Then, the original frequencies of each signal to be measured are obtained.

[0079] Specifically, construct the measurement matrix, denoted as Formula 4.

[0080]

[0081] In the formula, f0 is the optical frequency comb repetition frequency, which is a priori known condition, and N max The value obtained by rounding up the ratio of the maximum frequency obtained within multiple frequency ranges of the signals under test to the optical frequency comb repetition rate, -N max ≤n≤N max n is an integer, and since the value of n in Formula 4 is in the range [-N] max N max The integers within the range are all given. Therefore, the component of the signal under test exists in each Nyquist interval, and this component carries the full amplitude and phase information of the original signal. Therefore, only a low-speed photodetector and a dual-channel synchronous data acquisition card are needed to acquire the component in the first Nyquist interval to achieve wide-open reception of non-cooperative signals over a wide frequency range. The row vectors in the B matrix and the exponential phase factor vector v k Perform an inner product operation. When the obtained inner product value is maximized, the n corresponding to the component of the k-th down-conversion signal in the first Nyquist zone is n. k , will n k Substitute into Formula 5

[0082] f rk =|n k f0-f k0 Formula 5

[0083] Then, the original frequency f of each signal to be measured is obtained. rk .

[0084] The frequency conversion signal receiving method described in this invention uses an adjustable fiber delay line to generate a known time delay, establishes a mapping relationship between the original signal frequency and the phase of the down-converted signal, and calculates the original signal frequency from the down-converted signal phase and the time delay of the adjustable fiber delay line based on the mapping relationship. This method then recovers the frequency information lost during down-conversion reception of optical frequency combs, solving the problem of frequency information loss during the reception of non-cooperative signals over a large frequency range, thereby completing the reception of non-cooperative signals. This method can be used in applications such as electromagnetic environment monitoring and other applications involving the reception of multiple signals over a large frequency range without cooperation.

[0085] like Figure 1As shown, this invention provides a frequency conversion signal receiving system, including a femtosecond pulsed laser, a 1:1 fiber optic beam splitter, an adjustable fiber optic delay line, two electro-optic modulators, two photodetectors, a dual-channel synchronous data acquisition card, and a radio frequency (RF) signal source. The output of the femtosecond pulsed laser is connected to the input of the 1:1 fiber optic beam splitter via an optical fiber. The 1:1 fiber optic beam splitter includes an upper output and a lower output. The upper output of the 1:1 fiber optic beam splitter is sequentially connected to the adjustable fiber optic delay line, a first electro-optic modulator, and a first photodetector. The lower output of the 1:1 fiber optic beam splitter is sequentially connected to a second electro-optic modulator and a second photodetector. The first and second electro-optic modulators are respectively connected to the RF signal source. The first and second photodetectors are respectively connected to one corresponding channel of the dual-channel synchronous data acquisition card. The bandwidth of the photodetector is half the repetition frequency of the femtosecond pulsed laser.

[0086] A 1:1 fiber optic beam splitter divides the optical frequency comb generated by the femtosecond pulsed laser into two sampling pulse sources of the same frequency, an upper path and a lower path. The signal under test is also split into two paths and injected into two first electro-optic modulators and a second electro-optic modulator, respectively. Analog-to-digital conversion is performed at the back end of a low-speed photodetector using a dual-channel synchronous data acquisition card. The bandwidth of the photodetector only needs to meet half the repetition frequency of the femtosecond pulsed laser. This invention uses a femtosecond pulsed light source to undersample the high-frequency signal, converting the high-frequency electromagnetic signal to a low-frequency range for reception, reducing the requirement for the back-end sampling rate. The sampling rate only needs to meet half the repetition frequency of the femtosecond pulsed laser to complete signal reception.

[0087] Provide a specific implementation case, following the example as follows: Figure 1 The connection diagram shown illustrates the setup for the measurement system. In this case, a femtosecond pulse light source is selected as the light source to generate an optical frequency comb, and an radio frequency signal source is used to generate the signal under test.

[0088] The femtosecond pulsed laser used in this case has a repetition rate frepetition rate. k =207.76MHz, the maximum number of measurements MN is selected as 2, the number of measured signals KN is 1, and the maximum frequency range of the signal under test is 12GHz, therefore N max It is 60;

[0089] Turn on the signal source to generate the test signal with a frequency of 6GHz;

[0090] The adjustable fiber optic delay line is initially set to 0 ps. The down-converted signals (channels a and b) acquired by the dual-channel synchronous data acquisition card are processed using Fast Fourier Transform (FFT) to obtain the spectra of the two signals (channels a and b). The spectra are as follows: Figure 2 As shown, the peak phase is the down-converted signal phase. The two data streams have the same signal frequency but different amplitudes and phases, so no additional signal matching operation is required in multi-signal scenarios.

[0091] Extract the phase at the peak of the two spectrums and denot it as... (Radians), at this point, the phase difference between the two paths is caused by the inconsistency in the lengths of the upper and lower optical paths and circuits. Record the frequency f of the frequency converter signal. k0 =27.55MHz;

[0092] The first time the delay is changed, the fiber optic delay line delay is set to t1 = 280 ps. Since the initial delay is 0, the delay difference t1 is the same as t1. The two signals acquired by the dual-channel synchronous data acquisition cards a and b in the first measurement are processed by Fast Fourier Transform, and the peak phases in the spectra of the two channels are extracted and recorded as follows. (radian);

[0093] The second time delay was changed, setting the fiber optic delay line delay to t2 = 317 ps. Since the initial delay was 0, the delay difference t2 was the same as t2. The two signals acquired by the dual-channel synchronous data acquisition cards a and b in the second measurement were processed using Fast Fourier Transform, and the peak phases in the spectra of the two channels were extracted and recorded as follows. (radian);

[0094] Construct the exponential phase factor vector according to Formula 3.

[0095] v1=[-0.4055+0.9141i -0.4055+0.9141i]

[0096] Construct the measurement matrix according to Formula 4.

[0097]

[0098] By comparing the dot products of each row vector of matrix B with vector v1, the maximum dot product corresponds to n1 = 29. Substituting this into formula five, the original signal frequency f can be obtained. r1 =|n1f0-f 10 |=5.9975GHz.

[0099] The specific delay value of the adjustable fiber optic delay line can be confirmed and fixed before the specific measurement system is built. For example, using a combination of optical switch switching and fixed-length fiber optic delay line can achieve the purpose of changing the delay measurement, thereby further reducing the signal recovery time involved in this invention. The existence of non-ideal factors in the system mainly affects the measurement of the down-converted signal phase. Changing the delay value and measuring multiple times can increase the difference between the target phase values, thereby reducing the impact of phase measurement uncertainty on frequency recovery in actual scenarios. Changing the delay value and measuring multiple times improves the system's ability to withstand the impact of non-ideal factors such as system noise on the down-converted signal phase measurement.

[0100] Since the down-converted signals are independent of each other and the two acquired data streams are similar, the signal frequency recovery method involved in this invention is particularly suitable for multi-signal recovery processes. In the case of multi-signal reception, the phase of the components of all signals within the first half-repetition frequency interval can be obtained through a single fast Fourier transform operation, and each signal's n is calculated based on the same time delay. k The number of signals has a negligible impact on the computational load during frequency recovery. Assuming no aliasing occurs between the down-converted signals, this method theoretically has no upper limit on the number of signals that can be recovered. The number of signals has almost no effect on the processing time required by this method, making it particularly suitable for applications involving multi-signal reception.

[0101] Ignoring non-ideal factors such as noise, the corresponding n is obtained from the exponential phase factor vector constructed from the down-conversion signal and the measurement matrix. k The rows they belong to are equal, but under the influence of non-ideal factors in reality, their similarity will decrease. This method uses the maximum similarity principle to determine the corresponding n. k Therefore, the effectiveness of this method depends on the signal-to-noise ratio (SNR) of the receiving system. There is a corresponding relationship between the SNR, the number of measurements, and the signal recovery success rate. Figure 3 As shown, the signal recovery success rate (finding the correct n) is as follows: [Signal-to-noise ratio (SNR)] k The correspondence between the signal-to-noise ratio (SNR) and the number of measurements is explained. Different measurement counts correspond to different delay groups, and the selection of delay values ​​in each group is specific and not arbitrary. It is related to factors such as the specific measurement frequency range, the optical frequency comb repetition rate, and the size limitations of the system designed and implemented in this invention. Under the same SNR limit, a higher SNR results in a higher success rate for signal frequency recovery. Under the same SNR limit, a higher number of measurements also increases the success rate of signal frequency recovery. However, as the number of measurements further increases, the improvement in success rate becomes less significant. For typical measurement needs, 2 to 4 measurements are sufficient.

[0102] Once the measurement frequency band and the signal-to-noise ratio of the received signal are determined, they can be referenced. Figure 3 The curve in the diagram determines the number of measurements. Once the number of measurements is determined, a feasible method for determining the time delay value is to randomly select from a large number of time delays according to the principle of minimizing the correlation between column vectors in the measurement matrix.

[0103] This invention uses the undersampling frequency conversion function of an optical frequency comb in conjunction with microwave photonics technology and an adjustable fiber delay line as a frequency conversion signal receiving system. It can achieve one-time reception of non-cooperative signals over a wide frequency range with a small hardware size, low power consumption, and low complexity, thereby improving the acquisition probability and reducing the cost of the receiving system.

[0104] The above technical features constitute the preferred embodiment of the present invention, which has strong adaptability and optimal implementation effect. Non-essential technical features can be added or removed according to actual needs to meet the needs of different situations.

[0105] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for receiving frequency conversion signals, characterized in that, Includes the following steps: 1) Generate an optical frequency comb and set an initial time delay for the optical frequency comb; 2) After the initial time delay, the optical frequency comb is undersampled in the electro-optic modulator to output a down-converted signal. 3) After photoelectric conversion of the down-conversion signal, analog-to-digital conversion is then performed; 4) Obtain the initial phase of the down-converted signal under the initial time delay. and frequency ; 5) Change the time delay to obtain the phase of the down-converted signal. ; 6) Utilize the initial phase, the phase of step 5), and the time delay difference between the time delay of step 5) and the initial time delay of step 1). Calculate the ratio of the original frequency of the signal under test to the frequency repetition rate of the optical frequency comb; 7) Obtain the original frequency of the signal under test based on the ratio of the original frequency of the signal under test to the frequency repetition rate of the optical frequency comb and the frequency of the down-conversion signal; The calculation method for step 6) is derived from Formula 1. Formula 1 For known optical frequency comb repetition frequencies, The time delay difference is used to derive the ratio of the original frequency of the signal under test to the repetition frequency of the optical frequency comb, and the ratio is rounded down to obtain the value N. Step 7) Original frequency of the signal to be measured The calculation method is as follows: calculate according to Formula 2. Formula 2.

2. A method for receiving frequency conversion signals, characterized in that, Includes the following steps: S1. Divide each of the multiple signals to be tested into an upper path and a lower path; S2. Use an optical fiber beam splitter to split the optical frequency comb into an upper and lower sampling pulse source, and set an initial time delay for one of the sampling pulse sources. S3. The two sampling pulse sources perform undersampling on the upper and lower signals of multiple signals to be measured in their respective electro-optic modulators, and output two down-converted signals of the same frequency. S4. Obtain the initial phase of the two down-conversion signals under the initial time delay. , and frequency k0 represents the kth signal to be measured when the initial phase is measured, and a and b represent the upper and lower signals, respectively. S5. Change the latency to obtain multiple latency differences. Multiple phase measurements were performed to obtain the phase of multiple up-converter signals. ... ... and the phase of multiple downconverter signals ... ; This represents the delay difference between the delay measured for the m-th time and the initial delay measured in step S2. MN represents the maximum number of measurements; This indicates the phase of the measured uplink signal when the time delay is changed for the mth time; S6. Using the two initial phases and the phase of step S5, construct the exponential phase factor vector for each down-conversion signal. S7. Construct a measurement matrix, and perform an inner product operation between the row vectors of the measurement matrix and the exponential phase factor vector. When the obtained inner product value is the maximum, calculate the frequency ratio corresponding to the components of each down-converted signal in the first Nyquist zone. Then, the original frequency of each signal to be measured is obtained; The measurement matrix is Formula 4 In the formula For optical frequency comb re-frequency, ; This is the value obtained by rounding up the ratio of the maximum frequency obtained within multiple frequency ranges of the signals under test to the optical frequency comb repetition rate. n is an integer; Compare each row vector in measurement matrix B with the exponential phase factor vector. The inner product of the matrix and the matrix, when the maximum inner product is obtained, is the n of the row vector corresponding to each down-converted signal in the B matrix. Then, the original frequencies of each signal under test can be obtained. Formula 5.

3. The frequency conversion signal receiving method according to claim 2, characterized in that, The exponential phase factor vector for each down-converted signal is: Formula 3 In the formula .

4. The frequency conversion signal receiving method according to claim 2 or 3, characterized in that, All phases are peak phase values ​​in the spectrum.

5. A frequency conversion signal receiving system, used to implement the frequency conversion signal receiving method according to any one of claims 1-4, characterized in that: The system includes a femtosecond pulsed laser, an optical fiber beam splitter, an adjustable optical fiber delay line, two electro-optic modulators, two photodetectors, a dual-channel synchronous data acquisition card, and an RF signal source. The output of the femtosecond pulsed laser is connected to the input of the optical fiber beam splitter via optical fiber. The optical fiber beam splitter includes an upper output and a lower output. The upper output of the optical fiber beam splitter is sequentially connected to the adjustable optical fiber delay line, the first electro-optic modulator, and the first photodetector. The lower output of the optical fiber beam splitter is sequentially connected to the second electro-optic modulator and the second photodetector. The first and second electro-optic modulators are respectively connected to the RF signal source. The first and second photodetectors are respectively connected to one corresponding channel of the dual-channel synchronous data acquisition card.

6. The frequency conversion signal receiving system according to claim 5, characterized in that, It also includes a power divider, which receives signals transmitted from a radio frequency signal source and transmits the received signals to a first electro-optic modulator and a second electro-optic modulator.

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