Signal Processing System and Terminal Device

Abstract

The present application discloses a signal processing system and a terminal device, which are related to the field of LiDAR technology. The signal processing system includes a modulation unit and a transmission unit. The modulation unit is configured to perform at least a first modulation process on a first subcarrier signal to obtain a second subcarrier signal. The modulation unit is further configured to perform at least a second modulation process on the second subcarrier signal and the first signal light to obtain a transmission signal light. The transmission signal light includes a single-frequency optical carrier signal and an optical sideband signal, and the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not completely overlap. The transmission unit is configured to transmit the transmission signal light. The signal processing system can solve the problem of frequency band overlap between the optical sideband signal and the residual optical carrier signal obtained after the modulation process, allowing the optical sideband signal and the residual optical carrier signal to be separated.

Description

Technical Field

[0001] This application relates to the field of LiDAR technology, and in particular, to signal processing systems and terminal devices.

Background Art

[0002] The phase-coded signal is a typical pulse compression signal. When the product of the time width and the bandwidth is small, the peak sidelobe ratio of the phase-coded signal is large and the compression performance is excellent. Therefore, the phase-coded signal can effectively resolve the conflict between the operating distance and the resolution of the radar and is widely used in the latest radars.

[0003] Currently, in order to perform modulation processing on an optical carrier wave to obtain a transmission signal formed by a residual optical carrier wave and a phase-coded optical sideband signal, phase coding is usually used. Then, based on the signal reflected by the transmission signal through the target and the local oscillator optical signal, a Doppler frequency shift signal and a phase-coded signal are obtained. Based on the Doppler frequency shift signal and the phase-coded signal, the relative motion speed and the relative distance between the target and the radar system are measured.

[0004] However, the frequency bands of the residual optical carrier wave and the phase-coded optical sideband signal obtained by the above modulation processing method overlap, and the residual optical carrier wave signal and the phase-coded optical sideband signal cannot be separated. As a result, the accuracy of the Doppler frequency shift signal and the phase-coded signal is insufficient, and the accuracy of distance measurement and speed measurement is low.

Summary of the Invention

[0005] Embodiments of this application provide a signal processing system and a terminal device to solve the problem of frequency band overlap between a phase-coded optical sideband signal and a residual optical carrier wave obtained after modulation processing.

[0006] According to a first aspect, embodiments of this application provide a signal processing system. The signal processing system includes a modulation unit and a transmission unit.

[0007] The modulation unit is configured to perform at least a first modulation process on the first sub-carrier signal in order to obtain a second sub-carrier signal.

[0008] The modulation unit is further configured to perform at least a second modulation process on the second sub-carrier signal and the first optical signal in order to obtain an optical transmission signal. The optical transmission signal includes a single-frequency optical carrier signal and an optical sideband signal, and the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not completely overlap.

[0009] The transmission unit is configured to transmit the optical transmission signal.

[0010] In this embodiment of the present application, the modulation unit of the signal processing system is configured to perform at least a first modulation process on the first sub-carrier signal to obtain a second sub-carrier signal, and perform at least a second modulation process on the input first optical signal and the second sub-carrier signal to obtain an optical transmission signal. The optical transmission signal is used to detect at least one target, and the components of the optical transmission signal mainly include a single-frequency optical carrier signal and an optical sideband signal. The frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal obtained by the above modulation process do not completely overlap. Therefore, the single-frequency optical carrier signal and the optical sideband signal can be separated, and the separation effect is good.

[0011] In a possible implementation, the fact that the modulation unit is configured to perform the first modulation process includes performing phase modulation on the first sub-carrier signal by using a phase-encoded signal in order to obtain a second sub-carrier signal.

[0012] In this embodiment of the present application, a specific implementation of the first modulation process is provided. Specifically, the modulation unit performs phase modulation on the first sub-carrier signal by using a phase-encoded signal to obtain a second sub-carrier signal. The phase of the obtained second sub-carrier signal is different from the phase of the first sub-carrier signal, and there is a certain degree of phase shift. Therefore, the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal, which are obtained by subsequently performing modulation on the first optical signal by using the second sub-carrier signal, can be made not to completely overlap. Furthermore, this embodiment of the present application is not limited to performing phase modulation on the first sub-carrier signal by using a phase-encoded signal to obtain a second sub-carrier signal, and other phase compression signals, for example, a linear frequency modulation signal or a non-linear frequency modulation signal, may be used to perform phase modulation on the first sub-carrier signal. The phase modulation can be performed on the first sub-carrier signal by using a signal that enables a phase shift of the second sub-carrier signal with respect to the first sub-carrier signal.

[0013] In a possible implementation, the modulation unit being configured to perform a second modulation process includes performing modulation on the first optical signal by using the second sub-carrier signal to obtain a transmission signal light including a single-frequency optical carrier signal and an optical sideband signal.

[0014] In this embodiment of the present application, a specific implementation of the second modulation process is provided. Specifically, the modulation unit performs modulation on the first optical signal by using the second sub-carrier signal to obtain a transmission signal light including a single-frequency optical carrier signal and an optical sideband signal. The first optical signal is derived from the signal light of a laser, and the execution of modulation on the first optical signal may specifically be the execution of intensity modulation. The transmission signal light is used to detect at least one target, and the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal included in the transmission signal light do not completely overlap, thereby enabling a good separation effect to be realized.

[0015] In a possible implementation, performing modulation on the first optical signal by using a second carrier signal includes performing intensity modulation on the first optical signal by using a second sub-carrier signal.

[0016] In this embodiment of the present application, a specific implementation of the second modulation process is provided. Specifically, performing modulation on the first optical signal by using a second sub-carrier signal may specifically be performing intensity modulation on the first optical signal such that the frequency band of the obtained single-frequency optical carrier signal and the frequency band of the optical sideband signal do not completely overlap.

[0017] In a possible implementation, the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not overlap.

[0018] In this embodiment of the present application, when the phase shift of the second sub-carrier signal obtained by the first modulation process is large enough, the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal included in the transmitted optical signal obtained by the second modulation process is also large enough, whereby the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not overlap. In this case, compared with the case where the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not completely overlap, the separation effect of the single-frequency optical carrier signal and the optical sideband signal is better.

[0019] In a possible implementation, the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal is greater than or equal to the bandwidth of the frequency band of the optical sideband signal.

[0020] In this embodiment of the present application, when the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal is greater than or equal to the bandwidth of the frequency band of the optical sideband signal, it is possible to realize that the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not overlap. Therefore, the single-frequency optical carrier signal and the optical sideband signal are separated, and the separation effect is good.

[0021] In a possible implementation, the modulation unit includes a frequency mixer and a modulator.

[0022] The frequency mixer is configured to perform at least a first modulation process.

[0023] The modulator is configured to perform at least a second modulation process.

[0024] In this embodiment of the present application, a specific implementation that the modulation unit can take is provided. Specifically, the modulation unit may specifically include a frequency mixer and a modulator. The frequency mixer is configured to perform at least a first modulation process, and the modulator is configured to perform at least a second modulation process. By using the frequency mixer and the modulator, the problem of frequency band overlap between the residual optical carrier and the optical sideband signal obtained after the modulation process can be solved, whereby the residual optical carrier signal and the optical sideband signal are separated, and the separation effect is good.

[0025] In a possible implementation, the frequency mixer includes an active frequency mixer or a passive frequency mixer, and is configured to transfer a signal from one frequency range to another frequency range to generate a heterodyne signal. The modulator includes an electro-optic modulator or a thermo-optic modulator, and is configured to perform modulation on the amplitude, phase, etc. of the optical signal.

[0026] In a possible implementation, the signal processing system further includes a beat frequency unit and a processing unit.

[0027] The beat frequency unit is configured to perform at least beat frequency processing on the second signal light and the reflected signal light in order to output a Doppler frequency shift signal and a third sub-carrier signal. The second signal light and the first signal light are two channels of signal light obtained after beam splitting processing is performed on one channel of the signal light from the laser, the reflected signal light is the reflected signal light corresponding to the transmission signal light, and the frequency band of the Doppler frequency shift signal and the frequency band of the third sub-carrier signal do not overlap.

[0028] The processing unit is configured to process the Doppler frequency shift signal and the third sub-carrier signal in order to output a fourth sub-carrier signal or detection information of at least one target.

[0029] In this embodiment of the present application, the signal processing system further includes a beat frequency unit and a processing unit. Specifically, the beat frequency unit is configured to output a Doppler frequency shift signal and a third sub-carrier signal after performing at least beat processing on the second signal light and the reflected signal light. The processing unit is configured to process the Doppler frequency shift signal and the third sub-carrier signal to output a fourth sub-carrier signal or a detection signal of at least one target. The second signal light and the first signal light are two channels of signal light obtained after beat splitting processing is performed on one channel of the signal light from the laser, and at least two channels of the signal light should be obtained after beam splitting processing is performed on one channel of the signal light from the laser. Optionally, more than two channels of the signal light may be obtained. The reflected signal light is the reflected signal light corresponding to the transmitted signal light. Therefore, the reflected signal light also includes a single-frequency optical carrier signal and an optical sideband signal. The frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not overlap, and the frequency bands of the Doppler frequency shift signal and the third sub-carrier signal obtained by beat frequency processing also do not overlap. Therefore, the accuracy of the Doppler frequency shift signal and the third sub-carrier signal obtained by separation is high, and the implementation accuracy of measuring the relative motion speed and relative distance between the target and the signal processing system based on the Doppler frequency shift signal and the third sub-carrier signal is also high. The Doppler frequency shift signal is used to obtain the relative motion speed between the target and the signal processing system, and the third sub-carrier signal is used to obtain the relative distance information between the target and the signal processing system. The detection information of the target includes, but is not limited to, the relative speed information and relative distance information between the target and the signal processing system. Due to the Doppler effect caused by the relative motion between the target and the signal processing system, the third sub-carrier signal further has a specific Doppler frequency shift, and the distance measurement using the third sub-carrier signal is not accurate enough. Therefore, Doppler compensation is performed on the third sub-carrier signal by using the Doppler frequency shift signal, and a fourth sub-carrier signal is obtained.Compared with the third sub-carrier signal, the fourth sub-carrier signal removes the Doppler frequency shift caused by the Doppler effect, and the accuracy of distance measurement by using the fourth sub-carrier signal can be greatly improved.

[0030] In a possible implementation, the frequency band interval between the Doppler frequency shift signal and the third sub-carrier signal is greater than or equal to the bandwidth of the frequency band of the third sub-carrier signal.

[0031] In this embodiment of the present application, when the frequency band interval between the Doppler frequency shift signal and the third sub-carrier signal is greater than or equal to the bandwidth of the frequency band of the third sub-carrier signal, it is possible to realize that the frequency band of the Doppler frequency shift signal and the frequency band of the third sub-carrier signal do not overlap. Therefore, the Doppler frequency shift signal and the third sub-carrier signal are separated, and the separation effect is good.

[0032] In a possible implementation, the beat frequency unit includes a detector and a filter unit.

[0033] The detector is configured to perform beat frequency processing.

[0034] The filter unit is configured to perform filtering processing to output the Doppler frequency shift signal and the third sub-carrier signal.

[0035] In this embodiment of the present application, a specific implementation of the beat frequency unit is provided. That is, the beat frequency unit may specifically include a detector and a filter unit. The detector is configured to execute beat processing to obtain a signal including a Doppler frequency shift signal and a third subcarrier signal. The filter unit executes filtering processing on the signal to separate and output the Doppler frequency shift signal and the third subcarrier signal. By using the detector and the filter unit, the problem of frequency band overlap that may exist between the Doppler frequency shift signal and the third subcarrier signal obtained after beat frequency processing can be solved, so the Doppler frequency shift signal and the third subcarrier signal are separated and the separation effect is good.

[0036] In a possible implementation, the Doppler frequency shift signal is obtained based on the second signal light and a single-frequency optical carrier signal in the reflected signal light, and the third subcarrier signal is obtained based on the second signal light and an optical sideband signal in the reflected signal light.

[0037] In this embodiment of the present application, after beat frequency processing is performed on at least the second signal light and the reflected signal light, a Doppler frequency shift signal and a third subcarrier signal are output. Specifically, the Doppler frequency shift signal is obtained based on the second signal light and a single-frequency optical carrier signal in the reflected signal light, and the third subcarrier signal is obtained based on the second signal light and an optical sideband signal in the reflected signal light.

[0038] In a possible implementation, the filter unit includes a first filter and a second filter.

[0039] The first filter is configured to execute filtering processing to output the Doppler frequency shift signal.

[0040] The second filter is configured to execute filtering processing to output the third subcarrier signal.

[0041] In this embodiment of the present application, a specific implementation of the filter unit is provided. Specifically, the filter unit may include a first filter and a second filter. The first filter is configured to perform a filtering process to output a low-frequency Doppler frequency shift signal, and the second filter is configured to perform a filtering process to output a high-frequency third subcarrier signal. By using the first filter and the second filter, the problem of frequency band overlap that may exist between the Doppler frequency shift signal and the third subcarrier signal obtained after beat frequency processing Can be solved , whereby the Doppler frequency shift signal and the third subcarrier signal are separated, and the separation effect is good.

[0042] In a possible implementation, the first filter is a low-pass filter or a band-pass filter, and the second filter is a high-pass filter or a band-pass filter.

[0043] In this embodiment of the present application, the first filter may be a low-pass filter or a band-pass filter and is configured to separate a low-frequency Doppler frequency shift signal, and the second filter may be a high-pass filter or a band-pass filter and is configured to separate a high-frequency third subcarrier signal.

[0044] In a possible implementation, the filter unit further includes a power divider.

[0045] The power divider is configured to supply a signal input to the first filter and the second filter.

[0046] In this embodiment of the present application, the filter unit further includes a power distributor configured to divide one signal obtained after beat frequency processing is performed by the beat frequency unit into two signals based on a ratio. The one signal is a signal including a Doppler frequency shift signal and a third sub-carrier signal, and the two signals are respectively used as signal inputs of a first filter and a second filter, and are respectively used to subsequently separate a low-frequency Doppler frequency shift signal and a high-frequency third sub-carrier signal.

[0047] According to a second aspect, an embodiment of the present application provides a LiDAR system. The LiDAR system includes a signal processing system according to any one of the first aspect or possible implementations of the first aspect. Note that there may be a plurality of intelligent sensors integrated with the sensor. When the intelligent sensor includes a laser detection function, the intelligent sensor may also be called a LiDAR system.

[0048] According to a third aspect, an embodiment of the present application provides a terminal device. The terminal device includes a signal processing system according to any one of the first aspect or possible implementations of the first aspect, or includes a LiDAR system according to the second aspect.

[0049] In this embodiment of the present application, in order to obtain a second sub-carrier signal, modulation is performed based on a first sub-carrier signal, and by using the second sub-carrier signal, modulation is performed on the first signal light, whereby a transmission signal light including a single-frequency optical carrier signal and an optical sideband signal can be obtained. Since the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal obtained by the above modulation process do not completely overlap, the problem of frequency band overlap between the residual optical carrier and the optical sideband signal obtained after the modulation process can be successfully solved, and the residual optical carrier signal and the optical sideband signal can be separated.

[0050] To more clearly describe the technical solution in the embodiments of the present application, the following briefly explains the accompanying drawings for describing the embodiments. The accompanying drawings in the following description only show some embodiments of the present application, and it is obvious that those skilled in the art can conceive of other drawings from these accompanying drawings without creative efforts.

Brief Description of the Drawings

[0051]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 6C

Figure 6D

Figure 6E

Modes for Carrying Out the Invention

[0052] To more clearly illustrate the objectives, technical solutions, and advantages of the present application, the following describes the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application.

[0053] In the description, claims, and accompanying drawings of this application, terms such as "first", "second", etc. are intended to distinguish different objects and do not indicate a specific order. Further, terms such as "comprising" or "having", or any other variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device comprising a series of steps or units is not limited to the recited steps or units, and may optionally further include steps or units not recited, or may optionally further include other steps or units inherent to the process, method, product, or device.

[0054] As used herein, "embodiments" means that the specific features, structures, or characteristics described with reference to these embodiments may be included in at least one embodiment of this application. The phrase shown in various places in this specification may not necessarily refer to the same embodiment, and is not an exclusive, independent, or optional embodiment distinct from other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] In this application, "at least one (item)" means one or more, "a plurality of ~" means two or more, "at least two (items)" means two, three or more, and "and / or" is used to describe the association relationship between related objects, and it should be understood that there may be three relationships. For example, "A and / or B" means that only A exists, only B exists, and both A and B exist, where A and B may be singular or plural. The character " / " generally indicates the "logical sum" relationship between related objects. "At least one of the following item(s)" or similar expressions refer to any combination of these items, including a single item or any combination of multiple items. For example, at least one of a, b, or c may indicate a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c may be singular or plural.

[0056] As described in the background, currently, it is necessary to consider how to solve the problem of frequency band overlap between the residual optical carrier wave and the optical sideband signal. This application provides a signal processing system and a terminal device to effectively solve the problem of frequency band overlap between the optical carrier wave signal and the optical sideband signal, and is related to the field of LiDAR technology.

[0057] To describe the solution of this application more clearly, the following first explains some knowledge about LiDAR.

[0058] Subcarrier: A subcarrier is a carrier wave of an electronic communication signal, which is carried at the upper end of another carrier wave, so that two signals can be transmitted simultaneously. In subcarrier optical fiber communication, the signal to be transmitted is first used to modulate a radio frequency (frequency from ultra-short wave to microwave) wave, and then the radio frequency wave is used to modulate the transmission light source. At the receiving point, the photodetector converts the radio frequency wave back into a signal, and then the radio frequency detector converts the signal to be transmitted back into the original signal.

[0059] Single-frequency optical carrier wave: An optical carrier wave (OC) is an optical signal that is modulated to transmit a signal. Generally, the frequency of the optical carrier wave is much higher than that of the modulation signal. During transmission using an optical carrier wave, to implement information transmission, the data signal can be superimposed on the carrier wave signal, and the receiver receives the data signal based on the frequency of the carrier wave. A single-frequency optical carrier wave generally refers to an optical carrier wave having a single frequency or a single-frequency range.

[0060] Optical sideband: The optical sideband can be understood as the sideband of an optical signal. Generally, an optical signal is modulated. The optical sideband is classified into a single sideband and a double sideband. The double sideband is the sideband on each side of the central frequency of the optical signal. The sideband greater than the central carrier frequency is the upper sideband, and the sideband less than the central carrier frequency is the lower sideband. The single sideband generally refers to the upper sideband or the lower sideband of the optical signal.

[0061] With the rapid development of detection technologies, higher performance such as operating distance, resolution, and measurement accuracy is required for radars. To improve the detection ability of a radar, the radar is required to have a large time width, bandwidth, and energy product. However, when the peak power of the radar's transmission device is limited, a large signal energy can only be obtained by increasing the time width of the signal. Although the operating distance of the radar can be extended, the resolution deteriorates, that is, there is a conflict between the resolution and the operating distance.

[0062] Pulse compression is an important system for modern radars, which can effectively resolve the conflict between the operating distance and the resolution of a radar and is widely used in modern radars. There are three typical types of pulse compression signals, namely, linear frequency modulation signals, non-linear frequency modulation signals, and phase-coded signals. When the product of the time width and the bandwidth is small, the peak sidelobe ratio of the phase-coded signal is large and the compression performance is good. Therefore, the phase-coded signal is widely used.

[0063] Currently, in order to perform modulation processing on an optical carrier wave to obtain a transmission signal formed by a residual optical carrier wave and a phase-encoded optical sideband signal, phase encoding is usually used. Then, based on the signal reflected by the transmission signal through a target and a local oscillator optical signal, a Doppler frequency shift signal and a phase-encoded signal are obtained, and based on the Doppler frequency shift signal and the phase-encoded signal, the relative motion speed and relative distance between the target and the radar system are measured.

[0064] However, the frequency bands of the residual optical carrier wave and the phase-encoded optical sideband signal obtained by the above modulation processing method overlap, and the residual optical carrier wave signal and the phase-encoded optical sideband signal cannot be separated. As a result, the accuracy of the Doppler frequency shift signal and the phase-encoded signal is insufficient, and the accuracy of distance measurement and speed measurement is low.

[0065] Furthermore, in the process of performing pulse compression on the echo signal of the target by using the phase-encoded signal, the target and the platform on which the radar is mounted have relative motion, and the seed laser carrier frequency changes within the round-trip time of the radar signal. Therefore, the echo signal is modulated by the Doppler effect. Due to the Doppler effect, the relative distance information between the target and the platform on which the radar is mounted cannot be obtained by the phase-encoded signal through pulse compression. This has a serious impact on the performance of distance measurement.

[0066] Specifically, the Doppler effect refers to the phenomenon that when the wave source and the target have relative motion, the frequency at which the target receives the wave is different from the frequency at which the wave source transmits the wave. Specifically, when the wave source moves towards the target, the frequency of the wave received by the target increases, or when the wave source moves away from the target, the frequency of the wave received by the target decreases. The same conclusion can be obtained when the target moves. The relative motion speed and relative distance between the target and the wave source can be measured based on the Doppler frequency shift signal and the phase-encoded signal by using the Doppler effect.

[0067] Based on the technical problem of the frequency band overlap between the residual optical carrier wave obtained by the current modulation method and the phase-encoded optical sideband signal, the present application proposes a new signal processing system. The signal processing system performs modulation on a first sub-carrier signal to obtain a second sub-carrier signal, and performs modulation on a first signal light by using the second sub-carrier signal, whereby a transmission signal light including a single-frequency optical carrier wave signal and an optical sideband signal can be obtained. Since the frequency band of the single-frequency optical carrier wave signal obtained by the above modulation process and the frequency band of the optical sideband signal do not completely overlap, the problem of frequency band overlap between the residual optical carrier obtained after the modulation process and the optical sideband signal can be solved, and the residual optical carrier wave signal and the optical sideband signal can be separated.

[0068] The following describes the signal processing system provided in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application.

[0069] Please refer to FIG. 1. FIG. 1 is a schematic diagram of the structure of a signal processing system according to an embodiment of the present application.

[0070] As shown in FIG. 1, the signal processing system includes a modulation unit 10 and a transmission unit 20.

[0071] In some possible embodiments, the functions of the modulation unit 10 and the transmission unit 20 are as follows.

[0072] The modulation unit 10 performs at least a first modulation process on a first sub-carrier signal to obtain a second sub-carrier signal, and performs at least a second modulation process on the input first signal light and the second sub-carrier signal to obtain a transmission signal light.

[0073] The transmission unit 20 is configured to transmit the transmission signal light.

[0074] The transmission signal light is used to detect at least one target, and the components of the transmission signal light mainly include a single-frequency optical carrier signal and an optical sideband signal. The frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal obtained by the modulation process executed by the modulation unit 10 do not completely overlap. Since the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not completely overlap, the two signals can be separated. Therefore, the problem of frequency band overlap between the residual optical carrier and the optical sideband signal obtained after modulation processing by the current modulation processing method can be solved, so the residual optical carrier signal and the optical sideband signal are wavelength-division separated, and the separation effect is good.

[0075] In some possible embodiments, the modulation unit 10 executing at least a first modulation process on the first sub-carrier signal may specifically be: performing phase modulation on the first sub-carrier signal by using a phase-encoded signal to obtain a second sub-carrier signal. The phase of the obtained second sub-carrier signal is different from the phase of the first sub-carrier signal, and there is a certain phase shift. Therefore, the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal obtained by subsequently performing modulation on the first signal light by using the second sub-carrier signal do not completely overlap.

[0076] Furthermore, this embodiment of the present application is not limited to performing phase modulation on the first sub-carrier signal by using a phase-encoded signal to obtain a second sub-carrier signal. Phase modulation may also be performed on the first sub-carrier signal by using other phase compression signals, such as a linear frequency modulation signal or a non-linear frequency modulation signal. Phase modulation can be performed on the first sub-carrier signal by using a signal that enables a phase shift of the second sub-carrier signal with respect to the first sub-carrier signal.

[0077] In some possible embodiments, for the modulation unit 10 to perform at least a second modulation process on the input first optical signal and second sub-carrier signal, specifically: in order to obtain a transmission optical signal including a single-frequency optical carrier signal and an optical sideband signal, modulation may be performed on the first optical signal by using the second sub-carrier signal.

[0078] The first optical signal may be an optical signal from a laser, and the execution of modulation on the first optical signal may specifically be the execution of intensity modulation. The intensity modulation here refers to a laser oscillation in which the intensity (optical intensity) of the first optical signal changes regularly by a modulation signal (second sub-carrier signal). Laser modulation generally adopts an intensity modulation format. This is because the receiver generally reacts directly to the change in the intensity of the light received by the receiver. The transmission optical signal is used to detect at least one target, and the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal included in the transmission optical signal do not completely overlap, thereby realizing a good separation effect.

[0079] In some possible embodiments, after the modulation process executed by the modulation unit 10, the frequency band of the obtained single-frequency optical carrier signal and the frequency band of the optical sideband signal do not overlap. Specifically, this can be classified into several possible cases as follows.

[0080] Case 1 When the phase of the second sub-carrier signal obtained by the first modulation process shifts, there is also a specific interval between the frequency bands between the single-frequency optical carrier signal and the optical sideband signal included in the transmission optical signal obtained by the second modulation process, whereby the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not completely overlap. However, since the phase shift of the second sub-carrier signal obtained by the first modulation process is limited, the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal is also limited, and the frequency bands of the single-frequency optical carrier signal and the optical sideband signal may further partially overlap.

[0081] Case 2 When the phase shift of the second sub-carrier signal obtained by the first modulation process is sufficiently large, the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal included in the transmitted signal light obtained by the second modulation process is also sufficiently large, whereby the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not completely overlap at all. Compared with the case where the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not completely overlap in the above Case 1, the separation effect of the single-frequency optical carrier signal and the optical sideband signal is better.

[0082] Case 3 When the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal is greater than or equal to the bandwidth of the frequency band of the optical sideband signal, it is possible to realize that the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not overlap, so that the single-frequency optical carrier signal and the optical sideband signal are separated and the separation effect is good. In this case, the problem of resource waste caused by the excessively large frequency band interval between the single-frequency optical carrier signal and the optical sideband signal caused by the excessively large phase shift in the above Case 2 can be avoided, that is, the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not overlap at all as long as the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal is greater than or equal to the bandwidth of the frequency band of the optical sideband signal, and a good separation effect of the single-frequency optical carrier signal and the optical sideband signal can be achieved.

[0083] In this embodiment of the present application, in order to obtain the second sub-carrier signal, modulation is performed based on the first sub-carrier signal, and by using the second sub-carrier signal, modulation is performed on the first signal light, whereby a transmitted signal light including a single-frequency optical carrier signal and an optical sideband signal can be obtained. Since the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal obtained by the above modulation process do not completely overlap, the problem of frequency band overlap between the residual optical carrier wave and the optical sideband signal obtained after the modulation process can be successfully solved, and the residual optical carrier wave signal and the optical sideband signal can be separated.

[0084] The following describes the possible structures of the modulation unit 10 with reference to the accompanying drawings.

[0085] Please refer to FIG. 2. FIG. 2 is a schematic diagram of the structure of another signal processing system according to an embodiment of the present application.

[0086] As shown in FIG. 2, the modulation unit 10 includes a frequency mixer 101 and a modulator 102.

[0087] In some possible embodiments, the functions of the frequency mixer 101 and the modulator 102 are as follows.

[0088] The frequency mixer 101 is configured to perform at least a first modulation process, that is, to perform at least a first modulation process on a first subcarrier signal to obtain a second subcarrier signal. Specifically, phase modulation is performed on the first subcarrier signal by using a phase-encoded signal so as to obtain the second subcarrier signal. The phase of the obtained second subcarrier signal is different from the phase of the first subcarrier signal, and there is a certain degree of phase shift. Therefore, the frequency band of the single-frequency optical carrier signal obtained by subsequently performing modulation on the first optical signal by using the second subcarrier signal does not completely overlap with the frequency band of the optical sideband signal.

[0089] Here, it is not limited to performing phase modulation on the first subcarrier signal by using a phase-encoded signal to obtain the second subcarrier signal. The phase modulation may also be performed on the first subcarrier signal by using other pulse compression signals, such as a linear frequency modulation signal or a non-linear frequency modulation signal. The phase modulation can be performed on the first subcarrier signal by using a signal that enables a phase shift of the second subcarrier signal with respect to the first subcarrier signal.

[0090] The modulator 102 is configured to perform at least a second modulation process, that is, to perform at least a second modulation process on the input first signal light and the second sub-carrier signal to obtain a transmission signal light. Specifically, in order to obtain a transmission signal light including a single-frequency optical carrier signal and an optical sideband signal, modulation is performed on the first signal light by using the second sub-carrier signal.

[0091] Here, the execution of modulation on the first signal light may specifically be the execution of intensity modulation. Intensity modulation refers to laser oscillation in which the intensity (optical intensity) of the first signal light changes regularly according to a modulation signal (the second sub-carrier signal). Laser modulation generally adopts an intensity modulation format. This is because the receiver generally directly responds to the change in the intensity of the light received by the receiver.

[0092] In some possible embodiments, the frequency mixer 101 may be an active frequency mixer or a passive frequency mixer, etc., and is configured to transfer a signal from one frequency range to another frequency range to generate a heterodyne signal, and the modulator 102 may be an electro-optic modulator or a thermo-optic modulator, etc., and is configured to perform modulation on the amplitude, phase, etc. of the optical signal.

[0093] After the frequency mixer 101 and the modulator 102 perform the modulation process, the frequency band of the obtained single-frequency optical carrier signal and the frequency band of the optical sideband signal do not overlap. The specific case is the same as that obtained after the modulation process performed by the modulation unit 10, and the details are not described here again.

[0094] The following describes other possible structures of the signal processing system with reference to the accompanying drawings.

[0095] Please refer to FIG. 3. FIG. 3 is a schematic diagram of the structure of another signal processing system according to an embodiment of the present application.

[0096] As shown in FIG. 3, the signal processing system further includes a beat frequency unit 30 and a processing unit 40.

[0097] In some possible embodiments, the functions of the beat frequency unit 30 and the processing unit 40 are as follows.

[0098] The beat frequency unit 30 is configured to obtain a Doppler frequency shift signal and a third sub-carrier signal after performing at least beat processing on the second signal light and the reflected signal light.

[0099] The processing unit 40 is configured to process the Doppler frequency shift signal and the third sub-carrier signal and output a fourth sub-carrier signal or a detection signal of at least one target.

[0100] The second signal light and the first signal light are two channels of signal light obtained after beat splitting processing is performed on one channel of the signal light from the laser. At least two channels of the signal light should be obtained after beam splitting processing is performed on one channel of the signal light from the laser. The beam splitting processing may be specifically implemented by using a fiber beam splitter. Optionally, after the beam splitting processing, more than two channels of the signal light are obtained and separately supplied as signal inputs to the beat frequency unit 30 and the modulation unit 10 (modulator 102). The reflected signal light is the reflected signal light corresponding to the transmitted signal light, specifically, the signal light reflected by the transmitted signal light through at least one target, and the receiving unit can receive the reflected signal light. Therefore, the components of the reflected signal light are similar to those of the transmitted signal light and also include a single-frequency optical carrier signal and an optical sideband signal.

[0101] In some possible embodiments, after the beat frequency processing performed by the beat frequency unit 30, the frequency band of the obtained Doppler frequency shift signal and the frequency band of the third sub-carrier signal do not overlap. Specifically, this can be classified into the following several possible cases.

[0102] Case 1 When the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal included in the reflected signal light is sufficiently large and the frequency bands of the single-frequency optical carrier signal and the optical sideband signal do not overlap at all, the Doppler frequency shift signal is obtained based on the second signal light and the single-frequency optical carrier signal in the reflected signal light, and the third sub-carrier signal is obtained based on the second signal light and the optical sideband signal in the reflected signal light. In this case, the frequency bands of the obtained Doppler frequency shift signal and the third sub-carrier signal do not overlap at all. Compared with the case where the frequency bands of the Doppler frequency shift signal and the third sub-carrier signal do not completely overlap, the separation effect of the Doppler frequency shift signal and the third sub-carrier signal is better.

[0103] Case 2 When the frequency band interval between the single-frequency optical carrier signal and the optical sideband signal included in the reflected signal light is greater than or equal to the bandwidth of the frequency band of the optical sideband signal, the Doppler frequency shift signal is obtained based on the second signal light and the single-frequency optical carrier signal in the reflected signal light, and the third sub-carrier signal is obtained based on the second signal light and the optical sideband signal in the reflected signal light. In this case, the frequency band interval between the obtained Doppler frequency shift signal and the third sub-carrier signal is greater than or equal to the bandwidth of the frequency band of the third sub-carrier signal, and it can be realized that the frequency band of the Doppler frequency shift signal and the frequency band of the third sub-carrier signal do not overlap. Therefore, the Doppler frequency shift signal and the third sub-carrier signal are separated, and the separation effect is good. In this case, the problem of resource waste caused by the excessive frequency band interval between the Doppler frequency shift signal and the third sub-carrier signal caused by the excessive frequency band width interval between the single-frequency optical carrier signal and the optical sideband signal in the above case 1 can be avoided. That is, the frequency bands of the Doppler frequency shift signal and the third sub-carrier signal do not overlap at all as long as the frequency band interval between the Doppler frequency shift signal and the third sub-carrier signal is greater than or equal to the bandwidth of the frequency band of the third sub-carrier signal, and a good separation effect of the Doppler frequency shift signal and the third sub-carrier signal is achieved.

[0104] Since the frequency band of the Doppler frequency shift signal acquired by the beat frequency unit 30 through the execution of beat frequency processing and the frequency band of the third sub-carrier signal do not overlap, the accuracy of the Doppler frequency shift signal and the third sub-carrier signal acquired by separation is high, and the implementation accuracy of the measurement of the relative motion speed and relative distance between the target and the signal processing system based on the Doppler frequency shift signal and the third sub-carrier signal is also high. The Doppler frequency shift signal is used to obtain the relative motion speed between the target and the signal processing system, and the third sub-carrier signal is used to obtain the relative distance information between the target and the signal processing system. The detection information of the target includes, but is not limited to, the relative speed information and relative distance information between the target and the signal processing system. Further, due to the Doppler effect caused by the relative motion between the target and the signal processing system, the third sub-carrier signal further has a specific Doppler frequency shift, and the distance measurement by using the third sub-carrier signal is not sufficiently accurate. Therefore, Doppler compensation is performed on the third sub-carrier signal by using the Doppler frequency shift signal, and a fourth sub-carrier signal is obtained. Compared with the third sub-carrier signal, the fourth sub-carrier signal removes the Doppler frequency shift caused by the Doppler effect, and the accuracy of the distance measurement by using the fourth sub-carrier signal can be greatly improved.

[0105] In some possible embodiments, for the processing unit 40 to process the Doppler frequency shift signal and the third sub-carrier signal, specifically: Doppler compensation may be performed on the third sub-carrier signal by using the Doppler frequency shift signal to obtain a fourth sub-carrier signal, which may be to obtain the fourth sub-carrier signal. Alternatively, after the fourth sub-carrier signal is obtained, the relative distance information between the target and the signal processing system is obtained by using the fourth sub-carrier signal, and the relative motion speed between the target and the signal processing system is obtained by using the Doppler frequency shift signal, and distance information of the target including, but not limited to, the relative speed information and the relative distance information between the target and the signal processing system is output.

[0106] In this embodiment of the present application, based on the fact that the frequency bands of the single-frequency optical carrier signal and the optical sideband signal obtained by the above modulation processing do not completely overlap, the frequency bands of the obtained Doppler frequency shift signal and the third sub-carrier signal do not overlap by performing beat processing on the second signal light and the reflected signal light including the single-frequency optical carrier signal and the optical sideband signal, thereby solving the problem that the frequency bands of the signals obtained after the beat processing may overlap. Further, Doppler compensation is performed on the third sub-carrier signal by using the Doppler frequency shift signal to obtain a fourth sub-carrier signal, the relative distance information between the target and the signal processing system is obtained by using the fourth sub-carrier signal, and the relative motion speed between the target and the signal processing system is obtained by using the Doppler frequency shift signal, thereby greatly improving the accuracy of the distance measurement and speed measurement of the target.

[0107] The following will describe the possible structure of the beat frequency unit 30 with reference to the accompanying drawings.

[0108] Please refer to FIG. 4. FIG. 4 is a schematic diagram of the structure of another signal processing system according to an embodiment of the present application.

[0109] As shown in FIG. 4, the beat frequency unit 30 includes a detector 301 and a filter unit 302.

[0110] In some possible embodiments, the functions of the detector 301 and the filter unit 302 are as follows.

[0111] The detector 301 is configured to perform at least beat processing, that is, to perform at least beat processing on the second signal light and the reflected signal light to obtain a signal including a Doppler frequency shift signal and a third sub-carrier signal. Specifically, the Doppler frequency shift signal is obtained based on the second signal light and the single-frequency optical carrier signal in the reflected signal light, and the third sub-carrier signal is obtained based on the second signal light and the optical sideband signal in the reflected signal light.

[0112] The filter unit 302 is configured to perform filtering processing on the signal obtained by the detector 301 to separate and output the Doppler frequency shift signal and the third sub-carrier signal in order to implement the separation between the Doppler frequency shift signal and the third sub-carrier signal.

[0113] It can be understood that after the beat frequency processing of the detector 301, the frequency band of the obtained Doppler frequency shift signal and the frequency band of the third sub-carrier signal do not overlap. The specific situation is consistent with the situation obtained after the beat frequency processing of the beat frequency unit 30, and the details are not described here again.

[0114] The following will describe the possible structure of the filter unit 302 with reference to the accompanying drawings.

[0115] Please refer to FIG. 5. FIG. 5 is a schematic diagram of the structure of another signal processing system according to an embodiment of the present application.

[0116] As shown in FIG. 5, the filter unit 302 includes a first filter 3021 and a second filter 3022.

[0117] In some possible embodiments, the functions of the first filter 3021 and the second filter 3022 are as follows.

[0118] The first filter 3021 is configured to perform a filtering process to output a low-frequency Doppler frequency shift signal.

[0119] The second filter 3022 is configured to perform a filtering process to output a high-frequency third sub-carrier signal.

[0120] In this embodiment of the present application, by using the first filter 3021 and the second filter 3022, the Doppler frequency shift signal and the third sub-carrier signal obtained after beat frequency processing can be separated, and the separation effect is good.

[0121] In some possible embodiments, the first filter 3021 may be a low-pass filter or a band-pass filter, and is configured to separate a low-frequency Doppler frequency shift signal. The second filter 3022 may be a high-pass filter or a band-pass filter, and is configured to separate a high-frequency third sub-carrier signal.

[0122] In some possible embodiments, the filter unit 302 further includes a power divider 3023, and the function of the power divider 3023 is as follows.

[0123] The power divider 3023 is configured to divide one signal obtained after beat frequency processing into two signals based on a ratio. One signal is a signal including a Doppler frequency shift signal and a third sub-carrier signal. The two signals are respectively used as signal inputs of the first filter 3021 and the second filter 3022, and are respectively used to separate a low-frequency Doppler frequency shift signal and a high-frequency third sub-carrier signal thereafter.

[0124] In some possible embodiments, the signal processing system further includes an optical fiber coupler, and the functions of the optical fiber coupler are as follows.

[0125] The optical fiber coupler is configured to combine the input second signal light and the reflected signal light, and then transmit the second signal light and the reflected signal light to the detector 301 for subsequent beat processing.

[0126] The above has described in detail the possible structures of the signal processing system in the embodiments of the present application. The following will describe the signal processing process executed by the signal processing system with reference to FIGS. 6A to 6E.

[0127] For ease of understanding, the above signal processing system shown in FIG. 5 is used as an example for illustration.

[0128] Please refer to FIG. 6A. FIG. 6A is a schematic diagram of the angular frequency - amplitude of a signal according to an embodiment of the present application. The angular frequency - amplitude of the signal shown in FIG. 6A is the angular frequency - amplitude of the first signal light obtained by the laser corresponding to point A in FIG. 5, and can be expressed as follows: E in (t)=E0exp(iω C t)

[0129] Here, E in (t) represents the first signal light, and ω C represents the angular frequency of the first signal light.

[0130] After the first signal light is modulated by the modulator 102, a schematic diagram of the angular frequency - amplitude of the signal shown in FIG. 6B is obtained. Please refer to FIG. 6B. The angular frequency - amplitude of the signal shown in FIG. 6B is the angular frequency - amplitude of the transmitted signal light obtained by the modulator 102 corresponding to point B in FIG. 5, and can be expressed as follows:

Number

[0131] Here, E MZM (t) represents the transmitted signal light, and ω RF represents the angular frequency of the second subcarrier signal, and θ n (t) represents the phase-encoded signal, and θ n (t) has a value of 0 or π, and V π represents the half-wave voltage of the modulator 102, and V RF represents the AC drive voltage amplitude, and V b represents the DC bias voltage, and β = (π / 2)·(V RF / V π ) represents the modulation coefficient, and φ = (π / 2)·(V b / V π ) represents the phase of the modulator 102.

[0132] The transmitted signal light is transmitted by using a transmission unit and reflected by at least one target. The reflected signal corresponding to the transmitted signal light, that is, the schematic diagram of the angular frequency - amplitude of the signal shown in FIG. 6C, can be obtained by using a reception unit. See FIG. 6C. The angular frequency - amplitude of the signal shown in FIG. 6C is the angular frequency - amplitude of the reflected signal light received by the reception unit corresponding to point C in FIG. 5 and can be expressed as follows:

Equation

[0133] Here, E τ (t - τ) represents the reflected signal light, τ represents the delay time of the reflected signal light, k represents the power attenuation coefficient in the transmission process of the reflected signal light, and ω d represents the Doppler frequency shift.

[0134] The reflected signal light and the second signal light transmitted by the laser enter the detector 301 after being coupled by an optical fiber coupler so as to perform beat frequency processing. The second signal light here is also called a local oscillator optical signal and can be expressed as follows: E L0 (t)EL0 exp(iω C t)

[0135] After performing beat frequency processing on the second signal light and the reflected signal light, the detector 301 can obtain an electrical signal, that is, a schematic diagram of the angular frequency - amplitude of the signal shown in FIG. 6D. Please refer to FIG. 6D. The angular frequency - amplitude of the signal shown in FIG. 6D is the angular frequency - amplitude of the electrical signal output by the detector 301 corresponding to point D in FIG. 6, and can be expressed as follows:

Equation

[0136] Here, i BPD (t) represents the electrical signal obtained after beat frequency processing is performed on the second signal light and the reflected signal light, and includes a Doppler frequency shift signal and a third sub - carrier signal.

[0137] A two - phase code is used as an example for explanation. In the case of small - signal modulation, after the above - mentioned signal i BPD (t) is filtered by the first filter 3021 and the second filter 3022, a Doppler frequency shift signal and a third sub - carrier signal are respectively obtained and can be expressed as follows:

Equation

[0138] Here, the low - frequency signal i low (t) represents the Doppler frequency shift signal, and the high - frequency signal i high (t) represents the third sub - carrier signal.

[0139] By adjusting the bias voltage of the modulator 102, the strength of the low-frequency current signal and the strength of the high-frequency current signal can be adjusted. Since the third sub-carrier signal is a wideband signal, a high signal-to-noise ratio can generally be obtained only when high signal power is required. Therefore, in an actual signal processing system, φ usually uses a value close to π / 2. Since the Doppler frequency shift signal and the third sub-carrier signal can be well separated in the frequency domain, the Doppler frequency shift signal having a low intensity can still be measured. Further, the influence of the Doppler frequency shift signal is removed from the high-frequency signal. This helps to obtain better accuracy in distance measurement.

[0140] During distance measurement, the Doppler frequency shift signal and the third sub-carrier signal are input to the processing unit 40, and the processing unit 40 performs Doppler compensation on the third sub-carrier signal by using the Doppler frequency shift signal in order to obtain the fourth sub-carrier signal, that is, the angular frequency-amplitude schematic diagram of the signal shown in FIG. 6E. See FIG. 6E. The angular frequency-amplitude of the signal shown in FIG. 6E is the angular frequency-amplitude of the fourth sub-carrier signal output by the processing unit 40 corresponding to point E in FIG. 5 and can be expressed as follows:

Equation

[0141] Pulse compression is performed on the fourth sub-carrier signal and the original current signal v(t) = V RF cos[ω RF t+θ n t] to obtain the relative distance information and the corresponding delay information between the target and the signal processing system.

[0142] In summary, according to the signal processing system provided in the present application, in order to obtain a second sub-carrier signal, modulation is performed on the first sub-carrier signal, and by using the second sub-carrier signal, modulation is performed on the first optical signal, whereby a transmission optical signal including a single-frequency optical carrier signal and an optical sideband signal can be obtained. Since the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal obtained by the above modulation process do not completely overlap, the problem of frequency band overlap between the residual optical carrier and the optical sideband signal obtained after the modulation process can be solved, and the residual optical carrier signal and the optical sideband signal can be separated.

[0143] The present application provides a terminal device. The terminal device includes the signal processing system provided in the present application. For example, the terminal device may be a transportation means, such as a car, a truck, an airplane, a drone, a low-speed transportation vehicle, a spaceship, a ship, or any other transportation means used for any purpose, or any device equipped with a laser detection device, such as a surveying and mapping device. One or more signal processing systems provided in the present application are deployed on the terminal device.

[0144] The above description is only a specific implementation of the present application, and the protection scope of the present application is not limited thereto. Any modification or substitution that can be easily conceived by those skilled in the art within the technical scope disclosed in the present application should fall within the protection scope of the present application. Therefore, the protection scope of the present application should follow the protection scope of the claims.

Claims

1. A signal processing system having a modulation unit and a transmission unit, wherein the modulation unit is configured to perform at least a first modulation process on a first sub-carrier signal in order to obtain a second sub-carrier signal, the modulation unit is further configured to perform at least a second modulation process on the second sub-carrier signal and a first optical signal in order to obtain a transmission optical signal, the transmission optical signal includes a single-frequency optical carrier signal and an optical sideband signal, and the frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not completely overlap, and the transmission unit is configured to transmit the transmission optical signal.

2. The modulation unit is configured to perform phase modulation on the first sub-carrier signal by using a phase-encoded signal in order to obtain the second sub-carrier signal, The signal processing system according to claim 1.

3. The modulation unit is configured to perform modulation on the first optical signal by using the second sub-carrier signal in order to obtain the transmission optical signal including the single-frequency optical carrier signal and the optical sideband signal, The signal processing system according to claim 1 or 2.

4. The frequency band of the single-frequency optical carrier signal and the frequency band of the optical sideband signal do not overlap, The signal processing system according to any one of claims 1 to 3.

5. The modulation unit has a frequency mixer and a modulator, the frequency mixer is configured to perform at least the first modulation process, and the modulator is configured to perform at least the second modulation process. The signal processing system according to any one of claims 1 to 4.

6. The signal processing system further has a beat frequency unit and a processing unit, the beat frequency unit is configured to perform at least beat frequency processing on a second optical signal and a reflected optical signal in order to output a Doppler frequency shift signal and a third sub-carrier signal, the second optical signal and the first optical signal are two channels of optical signals obtained after beam splitting processing is performed on one channel of the optical signal from the laser, the reflected optical signal is the reflected optical signal corresponding to the transmission optical signal, and the frequency bands of the Doppler frequency shift signal and the third sub-carrier signal do not overlap, ​ The processing unit is configured to process the Doppler frequency shift signal and the third sub-carrier signal in order to output a fourth sub-carrier signal or detection information of at least one target. The signal processing system according to any one of claims 1 to 5.

7. The beat frequency unit includes a detector and a filter unit. The detector is configured to perform the beat frequency processing. The filter unit is configured to perform a filtering process in order to output the Doppler frequency shift signal and the third sub-carrier signal. The signal processing system according to claim 6.

8. The Doppler frequency shift signal is obtained based on the second signal light and the single-frequency optical carrier signal in the reflected signal light, and the third sub-carrier signal is obtained based on the second signal light and the optical sideband signal in the reflected signal light. The signal processing system according to claim 6 or 7.

9. The filter unit includes a first filter and a second filter. The first filter is configured to perform a filtering process in order to output the Doppler frequency shift signal. The second filter is configured to perform a filtering process in order to output the third sub-carrier signal. The signal processing system according to claim 7.

10. The filter unit further includes a power distributor. The power distributor is configured to supply a signal input to the first filter and the second filter. The signal processing system according to claim 9.

11. A terminal device having the signal processing system according to any one of claims 1 to 10.

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