CN110187350B - Laser radar ranging method and device based on spread spectrum technology - Google Patents

Abstract

The invention discloses a laser radar ranging method and device based on spread spectrum technology, belonging to the field of laser radar ranging and comprising the following steps: s1: the bit information of the transmission sequence phase-modulates the light source signal by a pair of adjacent symbol phase differences, S2: transmitting the optical signal after phase modulation to enter a space to be measured through a transmitting optical antenna, and S3: the reflected optical signal enters the delay interferometer, thereby achieving demodulation of the optical signal, S4: photoelectric conversion is performed on the demodulated optical signal by a photoelectric balance detector, and S5: the local sequence implements distance measurement in a phase-ratio manner of at least one of chip phase ratio and code clock phase ratio. The laser radar ranging method and the device are based on the spread spectrum technology, have strong interference resistance, are farther from detection, are low in price, can perform rough measurement or accurate measurement according to actual requirements, and improve the measurement speed.

Description

Laser radar ranging method and device based on spread spectrum technology

Technical Field

The invention relates to the field of laser radar ranging, in particular to a laser radar ranging method based on a spread spectrum technology.

The invention relates to the field of laser radar ranging, in particular to a laser radar ranging device based on a spread spectrum technology.

Background

As a sensor capable of acquiring information on the position and shape of an object, a laser radar is suitable for topographic mapping. The method is commonly used for indoor modeling, road and facility data acquisition and mine goaf measurement, or is carried on an aircraft to carry out large-scale power line patrol, forestry census, water conservancy survey and the like, and has wide application. At present, the application of a laser radar measurement technology presents diversified situations, and besides traditional surveying and mapping, the laser radar measurement technology has a wide market prospect in emerging industries such as unmanned driving, intelligent robots and the like.

Most of the laser radar companies on the market use TOF (time of flight) technology, i.e. calculating the time of flight from the time difference of light emission and reception, thereby determining the detection distance. However, the radar ranging method has some problems, such as interference resistance, limited performance in strong light conditions and severe weather, and limited detection distance (which cannot exceed 200 meters). For the TOF technology, the interference resistance and the strong light resistance are mainly poor, and the encoding cannot be realized; the detection range is limited in relation to the amount of power it is operating at. Theoretically, the larger the power is, the longer the transmission distance is, but the stability is difficult to control after the power is increased, and meanwhile, the potential safety hazard is increased.

There is also a range finding technique for lidar, which is a coherent lidar based on coherent technology. The coherent laser radar is mainly based on FMCW technology, an electronic module of the ordinary laser radar is replaced by an optical processing module, and the detection distance can be improved under the condition of low signal-to-noise ratio. The main disadvantages of FMCW are: firstly, the FMCW laser source is bulky and expensive, and secondly it requires more computational power and therefore is slow in generating full three-dimensional surround maps, and the measurement accuracy is very sensitive to the degree of linearity in the modulation.

The spread spectrum technology can effectively reduce the influence of noise and can improve the signal-to-noise ratio on the premise of not sacrificing the resolution. In addition, the spread spectrum technology also has very strong anti-interference capability, and the dilemma faced by the TOF scheme can be effectively overcome if the spread spectrum technology is applied to the laser radar field. Theoretically, the spread spectrum technology has good prospect when being applied to the field of laser radar. However, just as spread spectrum technology is used in the field of optical communication, spread spectrum technology for lidar also first faces the problem of how to implement bipolar coding. A method and a device for applying the spread spectrum technology to the optical fiber back scattering measurement are mentioned in a comparison Chinese patent ZL 201410491605.5. However, the measurement of the optical fiber backscattering is greatly different from the laser radar in the aspects of application field, real-time requirement, test precision requirement and requirement on the critical geometric dimension of the device, and the technical scheme in patent ZL201410491605.5 cannot be directly used in the laser radar, wherein the optical DPSK modulation scheme in patent ZL201410491605.5 is as follows: i.e. a scheme in which the transmission sequence passes through a precoder and then modulates a phase modulator in the DPSK manner, and passes through delay interferometer demodulation.

By analyzing the main difference between the technical scheme of ZL201410491605.5 and the laser Raddi technical scheme: from the application field, the technical solution of patent ZL201410491605.5 is to perform positioning measurement for scattering or reflection in the optical fiber, and the lidar is to perform positioning measurement for a target object in an open outer space; from the real-time aspect, taking the laser radar required by automatic driving as an example, the automobile has real-time requirements on the measurement of the target object in the surrounding environment when running at high speed, and the positioning measurement in the optical fiber is generally performed statically without the real-time requirements; from the view of measurement accuracy, taking a vehicle-mounted laser radar as an example, the positioning accuracy of the target object outside hundreds of meters and the positioning accuracy of the target object inside the peripheral meters have different requirements; from the critical dimension of the device, the light source, the coupler, the phase modulator, etc. used in the optical fiber are all used to process the optical signal coupled into or out of the optical fiber with a diameter of 9 or 10 microns, and the diameter of the outgoing beam of the laser radar can reach several centimeters. For example, it is very easy to select a device with a half-wave voltage of several volts for the fiber phase modulator, and if the phase modulation is performed on a light beam with a light beam diameter of centimeter level, the half-wave voltage will be increased by tens of times or even hundreds of thousands of times, which will make it difficult to use the fiber phase modulator in some cases without changing the modulation mode.

Therefore, we propose a method and apparatus for lidar ranging based on spread spectrum technology.

Disclosure of Invention

The present invention provides a method and an apparatus for laser radar ranging based on spread spectrum technology, so as to solve the problems in the background art.

In order to achieve the purpose, the invention provides the following technical scheme: a laser radar ranging method based on spread spectrum technology comprises the following steps:

s1: the method for transmitting the bit information of the sequence utilizes precoding to perform phase modulation on a light source signal so as to realize a phase difference between a pair of adjacent code elements, and specifically comprises the following steps:

a: the light transmitting unit generates a light source signal;

b: a transmission sequence generator generates a transmission sequence signal;

c: the precoder precodes the transmission sequence bit signals in the step B to generate a pair of adjacent code element phase differences;

d: the phase modulation driver converts the digital signal into a corresponding level signal to complete the driving of the phase modulator, and the first phase modulator performs phase modulation on the light source signal through the precoding obtained in the step C;

s2: transmitting the optical signal after phase modulation to enter a space to be measured through an optical transmitting antenna;

s3: the optical signal reflected by the target object in the space to be detected enters the delay interferometer through the optical receiving antenna, so that the demodulation of the optical signal is realized;

s4: performing photoelectric conversion on the demodulated optical signal through a photoelectric balance detector;

s5: the local sequence generator generates a local sequence which performs correlated despreading on the photoelectrically converted signal by using a phase ratio mode of at least one of a chip phase ratio and a code clock phase ratio.

Preferably, the method further comprises:

the light source signal is modulated into a light pulse signal;

performing phase difference modulation between a pair of adjacent symbols in one optical pulse chip by using bit information of a transmission sequence;

the delay interferometer is modulated in an orthogonal working state;

the arm length difference of the delay interferometer is equal to the distance difference between two pairs of adjacent symbols.

Preferably, the transmit sequence employs a composite code to reduce the acquisition time of the correlated despreading.

Preferably, the method further comprises: modulating the phase of the delay interferometer or modulating the optical signal before entering the delay interferometer so that the optical signal to be despread is output in a single polarity on the photoelectric balance detector to complete multiplication operation required by the signal after related despreading photoelectric conversion in advance.

Preferably, the method further comprises: firstly, the coarse measurement of the distance quantity is realized by utilizing a chip phase ratio, and further, the fine measurement of the distance quantity is realized by utilizing a code clock phase ratio.

Preferably, the method further comprises: the structure of optical path multiplexing of the optical transmitting antenna and the optical receiving antenna is adopted.

An apparatus for laser radar ranging based on spread spectrum technology, the apparatus comprising: an optical transmitting unit, a transmitting sequence generator, an optical transmitting antenna, a precoder, a first phase modulator, an optical receiving antenna, a delay interferometer, a photoelectric balance detector, a local sequence generator, a phase modulation driver, a chip-phase-ratio-dependent despreader, and a distance measurement processing unit;

an optical transmitting unit for generating a light source signal;

a transmission sequence generator for generating a transmission sequence signal;

an optical transmitting antenna, a device for emitting light waves into a space;

a precoder for precoding transmission sequence bit information to generate a pair of adjacent symbol phase differences;

a first phase modulator for phase modulating the light source signal;

an optical receiving antenna, a device for receiving the reflected light wave signal in the outer space;

a delay interferometer for demodulating the reflected optical signal;

a photoelectric balance detector for performing photoelectric conversion on the demodulated optical signal;

a chip phase ratio related despreader for performing related despreading on the photoelectrically converted signal by using the local sequence in a chip phase ratio manner;

the phase modulation driver is used for converting the digital signal into a corresponding level signal so as to complete the driving of the phase modulator;

and the distance measurement processing unit is used for further processing the related despreading result to realize distance measurement.

Preferably, the delay interferometer comprises a second phase modulator, and the phase of the delay interferometer is modulated by the second phase modulator, so that the optical signal to be despread is output in a single polarity on the photoelectric balance detector, so as to complete the multiplication required by the photoelectrically converted signal in advance.

Preferably, the apparatus further comprises a code clock phase ratio phase shift tracking loop and a code clock phase ratio correlation despreader;

the code clock phase comparison related despreader is used for performing related despreading on the photoelectrically converted signal by using a local sequence in a phase comparison mode of the code clock phase comparison;

and the code clock phase comparison and phase shift tracking loop is used for shifting the phase of the local sequence within a chip interval so as to perform related despreading by using the phase-shifted local sequence and realize the second distance measurement.

Compared with the prior art, the invention has the beneficial effects that:

the laser radar ranging method and the device have the advantages of strong interference resistance, farther distance detection and low price, and can perform rough measurement or accurate measurement according to actual requirements, thereby improving the measurement speed.

Drawings

FIG. 1 is an overall flow chart of the present invention;

FIG. 2 is a diagram of a first embodiment of the present invention;

FIG. 3 is a diagram of a second embodiment of the present invention.

FIG. 4 is an exemplary schematic diagram of phase modulation of an optical source signal using precoding in accordance with the present invention

In the figure: 1. an optical transmission unit; 2. a first phase modulator; 3. a transmit sequencer; 4. a precoder; 5. a delay interferometer; 6. a photoelectric balance detector; 7. a second phase modulator; 8. a local sequence generator; 9. an integrator; 10. an optical coupler; 11. an optical transmission/reception antenna; 11-a, an optical transmitting antenna; 11-b, an optical receiving antenna; 12. a chip phase-comparison correlation despreader; 13. a distance measurement processing unit; 14. a code clock phase comparison and phase shift tracking loop; 15. a code clock phase comparison correlation despreader; 16. an alternative switching circuit; 17. a phase modulation driver; 18. a phase unmodulated normal state; 19. a certain phase is added compared with the standard state; 20. a transmission sequence; 21. an optical pulse modulation signal; 22. a precoding sequence; 23. an optical signal in which adjacent symbols are modulated out of phase; 24. a bipolar signal.

Detailed Description

The present invention will be described in further detail below with reference to the accompanying drawings.

Aiming at the defects of the prior art, the invention aims to provide a laser radar ranging and ranging method and device based on a spread spectrum technology, and the realization cost is low.

The aim of the invention is achieved by the following technical measures:

first, bit information of a transmission sequence phase-modulates a light source signal with precoding to realize a pair of adjacent symbol phase differences, and transmits the phase-modulated light signal to a space to be measured through the optical transmission antenna 11-a.

The laser radar may use optical fiber as a main transmitting and receiving optical path device, and this laser radar is called a fiber laser radar, and when the fiber laser radar scheme is used, the phase modulation scheme may use the same scheme as the optical DPSK modulation scheme used in ZL 201410491605.5: i.e. a scheme in which the transmission sequence is passed through a differential precoder and then a phase modulator is modulated in the DPSK manner, and demodulated by thedelay interferometer 5.

Many laser radars do not include an optical fiber component, and parameters such as a light emitting area of a laser and a collimated beam diameter are also different from those of the optical fiber laser radars. The beam diameter of such a lidar reaches several millimeters or even higher, and if an electro-optical phase modulator is introduced into the optical path with such a diameter, the half-wave voltage is very high, so that the phase modulation cannot be performed in the manner of ZL 201410491605.5. FIG. 4 shows another phase modulation scheme different from the scheme ZL201410491605.5

Secondly, the optical signal reflected by the target object in the space to be measured enters thedelay interferometer 5 through the optical receiving antenna 11-b, so that the demodulation of the optical signal is realized, and the demodulated optical signal is subjected to photoelectric conversion through thephotoelectric balance detector 6.

Thirdly, the local sequence performs related despreading on the photoelectrically converted signal by using a phase ratio mode of at least one of a chip phase ratio and a code clock phase ratio so as to perform distance measurement.

The basic principle of the spread spectrum ranging method is as follows: the phase comparator compares the phases of the received pseudo code and the pseudo random code sequence transmitted first, and determines a delay from the phase difference to find a distance. The specific implementation is realized by the ratio of the local pseudo code to the received pseudo code.

The phase ratio of the pseudo code is realized by the synchronization of the spreading code, the synchronization problem of the spreading code (pseudo code) is specific to the spread spectrum ranging system, that is, only when the pseudo code of the receiving end and the transmitting end is completely the same, the information modulated by the pseudo code can be demodulated (called de-spreading), generally, the synchronization of the pseudo code can be realized by two steps: and (4) capturing and tracking. Acquisition, also known as coarse synchronization, makes the local code less than one symbol wide out of phase with the received code; tracking, also known as fine synchronization, keeps the local code phase difference from the received code to a fraction of a pseudo code symbol.

When the spread code is used for acquisition, the coarse measurement of the phase difference or the distance can be realized by using a chip ratio, which is also called integer chip phase comparison, and the chip ratio is the phase comparison of the received transmission code and the local code in integer chip unit, and the phase difference between the received pseudo code and the initially transmitted pseudo code can be obtained according to the comparison result, so that the distance measurement accuracy of 1/2 chip length can be realized.

When the spread spectrum code realizes tracking, the code-clock phase ratio, also called intra-chip phase comparison, can be used to realize phase difference or distance difference of a fraction of the width of one code element, so as to realize accurate measurement of distance.

The above technical measure is represented by fig. 1.

Preferably, the method further comprises the following steps:

firstly, the phase modulation is carried out according to the following technical measures: the light source signal is modulated into a light pulse signal; performing phase difference modulation between a pair of adjacent symbols in one optical pulse chip by using bit information of a transmission sequence; thedelay interferometer 5 is modulated in quadrature operation; the arm length difference of thedelay interferometer 5 is equal to the distance difference between two pairs of adjacent symbols.

The phase modulation scheme shown in fig. 4 converts one transmitsequence 20, indicated by 10110, into abipolar signal 24 output by thephoto balance detector 6 having a one-third duty cycle. The specific implementation scheme is as follows: first, it is assumed that the slot width of the transmission sequence is 3T and the delay length of thedelay interferometer 5 is T, and further, it is assumed that thedelay interferometer 5 operates in the quadrature operation state. Under the above assumed conditions, the specific modulation method is as follows:

modulating the light of the transmitting light source into rectangular light pulses with a duty ratio of two thirds by using a light pulse modulation mode, wherein the chip width of each light pulse is 2T and is shown as 21 in FIG. 4;

the two optical pulse chips each having a width of 2T are phase-modulated by a symbol width T, and the two symbols having a width T may be modulated to have a form in which a preceding symbol is higher or lower by a certain phase than an adjacent succeeding symbol, respectively, as represented by anoptical signal 23 in fig. 4 in which one adjacent symbol is modulated with a phase difference.

In the above-described debugging manner, bitinformation 1 in onetransmission sequence 20 is precoded to 001 in oneprecoding sequence 22, and bitinformation 0 in onetransmission sequence 20 is precoded to 010. The pre-coding sequence is a digital signal, when the electro-optical phase modulator is driven by the pre-coding sequence, a driver is required to convert the digital signal into a level signal, the drive level corresponding to 0 of the pre-coding sequence is 0, the drive level corresponding to thesequence 1 in the pre-coding is calculated and determined by the amplitude of the output voltage in thebipolar signal 24 output after the photoelectric conversion is carried out by thephotoelectric balance detector 6, and the amplitude of the phase difference between the code elements is delta phi at the moment.

Second, the transmit sequence employs a composite code to reduce the acquisition time of the correlated despreading.

The laser radar ranging, especially for unmanned laser radar, has real-time requirement, the laser radar of spread spectrum technology needs to adopt fast acquisition technology, and increasing the number of correlators is a scheme for realizing fast acquisition, but the number of correlators is increased, which makes the equipment complicated. The use of composite codes as spread spectrum ranging is a very economical solution. The composite code is composed of k short codes with mutually prime period, and the chip length of ith short code is p_iMeaning that the phase of the composite code is simply passed

This can be measured by a second trial.

For example, period p₁＝7,p₂Short code x of 15₁And x₂

x₁＝1110100；x₂＝111100010011010

Modular two and composite code x of formation₃With a period length p ═ p₁p₂105, it can be captured for up to 7+15 or 22 trials. Therefore, the capture time is greatly reduced, and the requirement of real-time property is met.

Again, an optical domain multiplier is employed. The basic principle is as follows: the delay interferometer comprises a second phase modulator, and the phase of the delay interferometer is modulated by the second phase modulator, so that the optical signal to be despread is connected with the unipolar output of theoptical balance detector 6 after the delay interferometer, and the multiplication operation required by the signal after photoelectric conversion is completed in advance.

When the optical domain multiplier needs to be used, only the phase modulation is carried out on the delay interferometer on the time slice corresponding to the output of the balanced detector with the negative polarity, so that the output of the balanced detector is inverted to the positive polarity, and the phase modulation is not carried out on the delay interferometer at other moments, thereby realizing the optical domain multiplication. Similarly, optical domain multiplication can be achieved by inverting all positive polarity outputs to negative polarity.

Finally, during the distance test, the coarse measurement of the distance quantity can be realized by using the chip phase ratio, the fine measurement of the distance quantity can be realized by further using the code clock phase ratio, and the optical path multiplexing structure of the optical transmitting antenna 11-a and the optical receiving antenna 11-b can be adopted.

By combining the above technical measures, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example one

Referring to fig. 2, the present invention provides a technical solution: a laser radar ranging method based on spread spectrum technology comprises the following steps:

s1: the method for reducing the acquisition time of the correlated despreading by using the composite code for the transmitting sequence includes the following steps:

a: theoptical transmitting unit 1 generates a light source signal;

b: the transmitting sequence generator generates 3 transmitting sequence signals;

c: a precoder 4 precodes the transmission sequence bit signals in the step B to generate a pair of adjacent symbol phase differences;

d: thephase modulation driver 17 converts the digital signal into a corresponding level signal to complete the driving of the first phase modulator 2, and the first phase modulator 2 performs phase modulation on the light source signal through the precoding obtained in the above step C;

s2: transmitting the optical signal after phase modulation to enter a space to be measured through an optical transmitting antenna 11-a;

s3: an optical signal reflected by a target object in a space to be measured enters adelay interferometer 5 through an optical receiving antenna 11-b, thedelay interferometer 5 is modulated in an orthogonal working state, and the arm length difference of thedelay interferometer 5 is equal to the distance difference between two pairs of adjacent code elements;

s4: performing photoelectric conversion on the demodulated optical signal through aphotoelectric balance detector 6;

s5: thelocal sequence generator 8 generates a local sequence, the local sequence can perform related despreading on the photoelectrically converted signal by using a phase comparison mode of at least one of a chip phase comparison and a code clock phase comparison through thealternative switch circuit 16, and the distancemeasurement processing unit 13 processes a related despreading result to realize distance measurement, wherein the specific measurement modes are divided into the following three modes:

the first measurement mode is as follows: the chip phase ratio relateddespreader 12 performs related despreading on the photoelectrically converted signal by using a local sequence in a chip phase ratio mode, the distancemeasurement processing unit 13 processes a related despreading result to realize distance measurement, and the left input of thealternative switch circuit 16 of which the output end is connected with the distancemeasurement processing unit 13 is in a gating state at the moment;

the second measurement mode is as follows: the code clock phase-comparison phase-shift tracking loop 14 shifts the phase of a local sequence in a chip interval, the code clock phase-comparison relateddespreader 15 performs related despreading on the photoelectrically converted signal by using the phase-comparison mode of the code clock phase-comparison on the phase-shifted local sequence, the distancemeasurement processing unit 13 processes the related despreading result to realize distance measurement, at this time, the right input of the two-way switch circuit 16 of which the output end is connected with the distancemeasurement processing unit 13 is in a gating state while the right input end of the two-way switch circuit 16 of the code clock phase-comparison relateddespreader 15 is in a gating state;

the third measurement mode is as follows: the distance measurement is performed in the first measurement mode and then in the second measurement mode, and at this time, the right input of the one-out-of-twoswitch circuit 16 whose output terminal is connected to the distancemeasurement processing unit 13 is in a gating state, and the left input of the one-out-of-twoswitch circuit 16 whose output terminal is connected to the code clock phaseratio correlation despreader 15 is in a gating state.

An apparatus for laser radar ranging based on spread spectrum technology, the apparatus comprising: anoptical transmission unit 1, atransmission sequencer 3, an optical transmission antenna 11-a, a precoder 4, a first phase modulator 2, an optical reception antenna 11-b, adelay interferometer 5, aphotoelectric balance detector 6, alocal sequencer 8, a chip-phase-ratio-correlation despreader 12, a distancemeasurement processing unit 13, a code-clock-phase-ratio phase-shift tracking loop 14, a code-clock-phase-ratio-correlation despreader 15, analternative switching circuit 16, and aphase modulation driver 17.

Example two

Referring to fig. 3, the present invention provides a technical solution: a laser radar ranging method based on spread spectrum technology comprises the following steps:

s1: the method comprises the following steps that the bit information of a transmitting sequence carries out phase modulation on a light source signal in a mode of a phase difference between a pair of adjacent code elements so as to realize the phase difference between the pair of adjacent code elements, and the transmitting sequence adopts a composite code so as to reduce the capturing time of related despreading:

a: theoptical transmitting unit 1 generates a light source signal;

b: the transmitting sequence generator generates 3 transmitting sequence signals;

c: a precoder 4 precodes the transmission sequence bit signals in the step B to generate a pair of adjacent symbol phase differences;

d: thephase modulation driver 17 converts the digital signal into a corresponding level signal to complete the driving of the first phase modulator 2, and the first phase modulator 2 performs phase modulation on the light source signal through the precoding obtained in the above step C;

s2: transmitting the optical signal after phase modulation to enter a space to be measured through an optical transmitting/receiving antenna 11 (multiplexing is formed by an optical transmitting antenna 11-a and an optical receiving antenna 11-b);

s3: an optical signal reflected by a target object in a space to be detected enters anoptical coupler 10 through an optical transmitting/receivingantenna 11, the optical signal is converted by theoptical coupler 10 and then enters adelay interferometer 5, thedelay interferometer 5 comprises a second phase modulator 7, alocal sequence generator 8 generates a local sequence, demodulation of the optical signal is achieved, and the specific demodulation modes are divided into the following three modes:

the first demodulation method: thelocal sequence generator 8 generates a local sequence, the local sequence can be selected by thealternative switch circuit 16 to enter the second phase modulator 7, the second phase modulator 7 is used for modulating the phase of thedelay interferometer 5, so that an optical signal to be despread is connected with the single-polarity output on theoptical balance detector 6 behind thedelay interferometer 5, the multiplication operation required by the signal after photoelectric conversion is completed in advance, thedelay interferometer 5 is modulated in an orthogonal working state, the arm length difference of thedelay interferometer 5 is equal to the distance difference between two pairs of adjacent code elements, and the demodulation of the optical signal is realized;

the second demodulation method: thelocal sequence generator 8 generates a local sequence, the code clock phase-shifts the local sequence within a chip interval than the phase-shiftingtracking loop 14, the phase-shifted local sequence can be selected by thealternative switching circuit 16 to enter the second phase modulator 7, the phase of thedelay interferometer 5 is modulated by the second phase modulator 7, so that an optical signal to be despread is connected with the unipolar output on theoptical balance detector 6 behind thedelay interferometer 5, the multiplication operation required by the signal after photoelectric conversion is completed in advance, thedelay interferometer 5 is modulated in an orthogonal working state, the arm length difference of thedelay interferometer 5 is equal to the distance difference between two pairs of adjacent code elements, and the demodulation of the optical signal is realized;

the third demodulation mode: firstly, carrying out a first demodulation mode and then carrying out a second demodulation mode to realize twice demodulation of optical signals;

s4: performing photoelectric conversion on the demodulated optical signal through aphotoelectric balance detector 6;

s5: the integrator 9 performs an integration operation on the photoelectrically converted signal, and the distancemeasurement processing unit 13 processes the integration operation result to realize distance measurement.

An apparatus for laser radar ranging based on spread spectrum technology, the apparatus comprising: the system comprises anoptical transmission unit 1, atransmission sequence generator 3, a precoder 4, a first phase modulator 2, adelay interferometer 5, aphotoelectric balance detector 6, a second phase modulator 7, alocal sequence generator 8, an integrator 9, anoptical coupler 10, an optical transmission/reception antenna 11, a distancemeasurement processing unit 13, a code clock phase-shift tracking loop 14 and analternative switching circuit 16.

Through the two embodiments, the distance measuring method and the distance measuring device of the laser radar are divided into two modes according to whether the optical receiving antenna 11-b and the optical sending antenna 11-a share the optical path, and each mode is divided into three measuring methods.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents, and the invention is not limited to the embodiments described above, and various modifications and changes may be made without departing from the spirit and scope of the invention, and it is intended that all changes and modifications that fall within the scope of the invention are embraced in the appended claims.

Claims (8)

1. A laser radar ranging method based on spread spectrum technology is characterized by comprising the following steps:

s1: the method for transmitting the bit information of the sequence utilizes precoding to perform phase modulation on a light source signal so as to realize a phase difference between a pair of adjacent code elements, and specifically comprises the following steps:

a: the light transmitting unit generates a light source signal;

b: a transmission sequence generator generates a transmission sequence signal;

c: the precoder precodes the transmission sequence bit signals in the step B to generate a pair of adjacent code element phase differences;

d: the phase modulation driver converts the digital signal into a corresponding level signal to complete the driving of the phase modulator, and the first phase modulator performs phase modulation on the light source signal through the precoding obtained in the step C;

wherein the phase modulation comprises the steps of:

the light source signal is modulated into a light pulse signal;

performing phase difference modulation between a pair of adjacent symbols in one optical pulse chip by using bit information of a transmission sequence;

the delay interferometer is modulated in an orthogonal working state;

the arm length difference of the delay interferometer is equal to the distance difference between two pairs of adjacent code elements;

s2: transmitting the optical signal after phase modulation to enter a space to be measured through an optical transmitting antenna;

s3: the optical signal reflected by the target object in the space to be detected enters the delay interferometer through the optical receiving antenna, so that the demodulation of the optical signal is realized;

s4: performing photoelectric conversion on the demodulated optical signal through a photoelectric balance detector;

s5: the local sequence performs correlated despreading on the photoelectrically converted signal by using a phase ratio mode of at least one of a chip phase ratio and a code clock phase ratio to perform distance measurement.

2. The method of claim 1, further comprising:

the transmit sequence employs a composite code to reduce the acquisition time of the correlated despreading.

3. A method of lidar ranging based on spread spectrum technology according to claim 1 or 2, characterized in that the method further comprises: modulating the phase of the delay interferometer or modulating the optical signal before entering the delay interferometer so that the optical signal to be despread is output in a single polarity on the photoelectric balance detector to complete multiplication operation required by the signal after related despreading photoelectric conversion in advance.

4. A method of lidar ranging based on spread spectrum technology according to claim 1 or 2, characterized in that the method further comprises: firstly, the coarse measurement of the distance quantity is realized by utilizing a chip phase ratio, and further, the fine measurement of the distance quantity is realized by utilizing a code clock phase ratio.

5. A method of lidar ranging based on spread spectrum technology according to claim 1 or 2, characterized in that the method further comprises: the structure of optical path multiplexing of the optical transmitting antenna and the optical receiving antenna is adopted.

6. The device of claim 1, wherein the device comprises: an optical transmitting unit, a transmitting sequence generator, an optical transmitting antenna, a precoder, a first phase modulator, an optical receiving antenna, a delay interferometer, a photoelectric balance detector, a local sequence generator, a phase modulation driver, a chip-phase-ratio-dependent despreader, and a distance measurement processing unit;

an optical transmitting unit for generating a light source signal;

a transmission sequence generator for generating a transmission sequence signal;

an optical transmitting antenna, a device for emitting light waves into a space;

a precoder for precoding transmission sequence bit information to generate a pair of adjacent symbol phase differences;

a first phase modulator for phase modulating the light source signal;

an optical receiving antenna, a device for receiving the reflected light wave signal in the outer space;

a delay interferometer for demodulating the reflected optical signal;

a photoelectric balance detector for performing photoelectric conversion on the demodulated optical signal;

a chip phase ratio related despreader for performing related despreading on the photoelectrically converted signal by using the local sequence in a chip phase ratio manner;

the phase modulation driver is used for converting the digital signal into a corresponding level signal so as to complete the driving of the phase modulator;

and the distance measurement processing unit is used for further processing the related despreading result to realize distance measurement.

7. The apparatus of claim 6, wherein: the delay interferometer comprises a second phase modulator, and the phase of the delay interferometer is modulated by the second phase modulator, so that an optical signal to be despread is output in a single polarity on the photoelectric balance detector, and multiplication required by the signal after photoelectric conversion is completed in advance.

8. The apparatus of claim 6, wherein: the device also comprises a code clock phase-comparison phase-shift tracking loop and a code clock phase-comparison correlation despreader;

the code clock phase comparison related despreader is used for performing related despreading on the photoelectrically converted signal by using a local sequence in a phase comparison mode of the code clock phase comparison;

and the code clock phase comparison and phase shift tracking loop is used for shifting the phase of the local sequence within a chip interval so as to perform related despreading by using the phase-shifted local sequence and realize the second distance measurement.

Images