CN106603149A - Integration method for high-speed laser communication method and high-precision laser ranging - Google Patents

Abstract

An integrated method of high-speed laser communication and high-precision ranging, integrating ranging technology into the laser communication system, embedding the ranging code with uniqueness, good autocorrelation and cross-correlation properties into the communication data, after encoding The ranging code and communication data are serially transmitted to realize high-speed communication; at the receiving end, the correlation operation between the received ranging code and the local ranging code is obtained to obtain the rough measurement time value of the integer multiple of the symbol width, and at the same time, the The phase difference between the local clock and the received recovered clock calculates the precise time value within one symbol of the ranging code, realizing the integration of high-speed laser communication and high-precision ranging. The invention adopts two-way one-way communication to complete the time-frequency transmission of the clock while measuring the distance; the invention can realize high-speed laser communication and high-precision distance measurement without high-speed A/D conversion.

Description

High-speed laser communication method and high-precision laser ranging integration method

technical field

The invention relates to the field of laser communication and ranging in free space, in particular to a method for integrating high-speed laser communication and high-precision laser ranging.

Background technique

Laser communication has the advantages of large capacity, strong anti-interference, good confidentiality, low power consumption, small size, etc., and can solve the high-speed bottleneck of microwave communication. It is an effective way to transmit massive and ultra-high-speed data between satellites and between satellites and ground. The integrated technology of laser communication and ranging can enable the aircraft to complete multiple tasks under the same load, thereby reducing the requirements for volume and power consumption, and improving the cost performance of the system.

Existing technology [1] (Chengdu Aerospace Communication Equipment Co., Ltd. Coherent pseudo-code ranging method based on MSK spread spectrum modulation mode: China, CN103533651[A]. 2014.1.22.) Prior art [2] (Wang Qi , Wu Bin. Analysis of pseudo-code ranging accuracy in optical aerospace measurement and control system [J]. Radio Engineering, 2009, 39(1): 39-44.) The ranging method in the pseudo-random code (ranging code) is used as communication information Carrier, the accuracy of ranging can be improved by increasing the signal bandwidth through spread-spectrum communication and increasing the symbol rate, that is, the rate of the ranging code is much higher than the rate of the communication signal to achieve high-precision ranging, but this will lead to The communication rate is too low to meet the requirements of satellite communication, and when the continuous ranging code is used to measure the satellite distance of tens of thousands of kilometers, a long ranging code is required, which will increase the code acquisition time. In addition, traditional pseudo-code ranging requires an A/D chip with a high sampling rate to buffer data, which will increase hardware costs and is not easy to implement on satellite stations.

Contents of the invention

The purpose of the present invention is to provide an integrated method of high-speed laser communication and high-precision laser ranging, which combines the characteristics of large laser communication capacity, low power consumption and pseudo-code with good autocorrelation and cross-correlation and low interception characteristics. , aiming at the shortcomings of traditional pseudo-code ranging that cannot achieve high-speed communication and requires too high sampling rate of the processing chip, it is proposed to embed the ranging code into the communication data, so that the ranging code and communication data are transmitted serially, so as to achieve high-speed communication. Communication: at the receiving end, the phase comparison between the recovered clock signal and the local clock signal can realize precise measurement within one ranging symbol. Moreover, the receiving end only needs demodulation, clock recovery, sampling judgment, and decoding, and high-precision ranging can be realized without high-speed A/D conversion. The invention can simultaneously realize high-speed laser communication and high-precision laser ranging, that is, realize the integration of high-speed laser communication and high-precision laser ranging.

Technical solution of the present invention is as follows:

A method for integrating high-speed laser communication and high-precision ranging, including a plurality of ranging communication stations, is characterized in that it includes the following steps:

Step 1: Align the transmitting end and receiving end of two ranging communication stations to be implemented in the method of integrating high-speed laser communication and high-precision ranging, hereinafter referred to as A and B stations, and at A and B stations The ranging code with uniqueness, good autocorrelation and cross-correlation characteristics and its clock signal are cached locally as the local ranging code and local clock signal, and then the ranging code is embedded into the communication data, and encoded After that, the communication ranging frame is formed, and the ranging code is used as the frame header of the communication ranging frame, and the communication ranging frame includes the frame header, communication data, and frame tail;

Step 2: Stations A and B adopt a two-way one-way communication method. The communication ranging frame of station A is used as the carrier wave of the laser light source and modulated by the optical phase modulator. Similarly, the work of station B and station A is the same, and the two stations agree on Transmitting each other at time t ₀ , due to the difference of the clocks of the two places, the transmitting time of station A is t _A0 , and the transmitting time of station B is t _B0 ;

Step 3: Station A receives the signal transmitted by Station B, Station B receives the signal transmitted by Station A, demodulates the signals received by Stations A and B, recovers the clock, samples and judges, and decodes to obtain the ranging code and communication data.

Step 4: At station A, compare the recovered clock signal with the local clock signal buffered in step 1 to obtain the phase difference between the two clock signals within one clock cycle Then obtain the precise time value within the width of a ranging code symbol of station A Among them, T is the cycle of the clock signal, which is equal to the symbol width of the ranging code. Similarly, the precise time value ΔT _B within the symbol width of a ranging code at station B can be obtained, and the obtained value after decoding at station A The ranging code is correlated with the local ranging code cached in step 1 to obtain an integer multiple of the symbol width, which is the rough measurement time value (nT) _A , where T is the symbol width of the ranging code, and n is an integer, In the same way, the roughly measured time value (nT) _B of station B can be obtained;

Step 5: Calculate the distance of A and B: T _A represents the time when station A receives the signal from station B from sending a signal, T _B represents the time from station B sending a signal to receiving the signal from station _A , TA=( nT) _A +ΔT _A , T _B =(nT) _B +ΔT _B , the transmission delay between stations A and B Calculate the distance s between A and B and the clock difference Δt _clk between the two places according to the following formula:

where c is the speed of light.

Technical effect and characteristics of the present invention:

1. The present invention uses the ranging code as the frame header of the communication data, the ranging code and the communication data are serially transmitted, and the symbol rate of the communication data is equal to the symbol rate of the ranging code, while the ranging of the traditional spread spectrum communication The method requires that the symbol rate of the ranging code is far greater than the symbol rate of the communication data to realize high-precision ranging, so the present invention can realize high-speed communication;

2. The two-way one-way communication method can be used to obtain the clock difference between the two places while measuring the distance Thus, the time-frequency transmission of the clock is completed.

3. The present invention can realize precise measurement within one ranging code symbol by restoring the relative ratio between the clock signal and the local clock signal; therefore, the present invention can realize high-precision ranging.

4. Compared with the traditional pseudo-code ranging technology, the present invention only needs demodulation, clock recovery, sampling judgment, and decoding after receiving the signal, and can realize high-precision ranging without high-speed A/D conversion.

Description of drawings

Fig. 1 is a flowchart of the present invention.

Fig. 2 is a structural diagram of an embodiment of the present invention.

FIG. 3 is a schematic diagram of composition of a communication ranging frame.

Fig. 4 is a schematic diagram of two-way one-way communication.

Fig. 5 is the schematic diagram of ranging of station A in the present invention

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

Fig. 1 is a flowchart of the present invention, as can be seen from the figure, the method for the integration of high-speed laser communication and high-precision ranging of the present invention includes five steps:

Step 1: Align the transmitting end and receiving end of two ranging communication stations to be implemented in the method of integrating high-speed laser communication and high-precision ranging, hereinafter referred to as A and B stations, and at A and B stations The ranging code with uniqueness, good autocorrelation and cross-correlation characteristics and its clock signal are cached locally as the local ranging code and local clock signal, and then the ranging code is embedded into the communication data, and encoded After that, the communication ranging frame is formed, and the ranging code is used as the frame header of the communication ranging frame, and the communication ranging frame includes the frame header, communication data, and frame tail, as shown in Figure 3;

Step 2: Stations A and B adopt a two-way one-way communication method as shown in Figure 4. The communication ranging frame of station A is used as the carrier wave of the laser light source and modulated by the optical phase modulator. Similarly, the work of station B and station A is the same , the two stations agree to transmit each other at time t ₀ , due to the clock difference between the two places, the transmission time of station A is t _A0 , and the transmission time of station B is t _B0 ;

Step 3: Station A receives the signal transmitted by Station B, Station B receives the signal transmitted by Station A, demodulates the signals received by Stations A and B, recovers the clock, samples and judges, and decodes to obtain the ranging code and communication data.

Step 4: At station A, compare the recovered clock signal with the local clock signal buffered in step 1 to obtain the phase difference between the two clock signals within one clock cycle Then obtain the precise time value within the width of a ranging code symbol of station A Among them, T is the cycle of the clock signal, which is equal to the symbol width of the ranging code. Similarly, the precise time value ΔT _B within the symbol width of a ranging code at station B can be obtained, and the obtained value after decoding at station A The ranging code is correlated with the local ranging code cached in step 1, and the integer multiple symbol width is obtained as the rough measurement time value (nT) _A , as shown in Figure 5, where T is the symbol of the ranging code Width, n is an integer, similarly can obtain the roughly measured time value (nT) B of station _B ;

Step 5: T _A represents the time from station A sending a signal to receiving a signal from station B, T _B represents the time from station B sending a signal to receiving a signal from station A, T _A = (nT) _A + ΔT _A , T _B ＝(nT) _B +ΔT _B , transmission delay between stations A and B according to Among them, c is the speed of light, and the distance s between A and B can be obtained.

Fig. 2 is a structural diagram of an embodiment of the present invention, as can be seen from the figure, the satellite station comprises the first single-frequency single-mode laser 1, the first optical fiber beam splitter 2, the first pseudo-code generator 3, the first signal generator 4. The first encoder 5, the first optical phase modulator 6, the first optical fiber circulator 7, the first optical fiber collimator 8, the first 2*2 directional coupler 9, the first photoelectric balance detector 10, the first A clock recovery circuit 11, a first pattern conversion circuit 12, a first sampling decision device 13, a first decoder 14, a first phase comparator 15, and a first analog correlator 16;

The ground station includes a second single-frequency single-mode laser 17, a second optical fiber splitter 18, a second pseudocode generator 19, a second signal generator 20, a second encoder 21, a second optical phase modulator 22, a second Two optical fiber circulators 23, a second optical fiber collimator 24, a second 2*2 directional coupler 25, a second photoelectric balance detector 26, a second clock recovery circuit 27, a second pattern conversion circuit 28, and a second sampling Decider 29, second decoder 30, second phase comparator 31, second analog correlator 32; at the satellite station, the laser light emitted by the first single-frequency single-mode laser 1 is divided into two beams through the first optical fiber beam splitter 2 For light with equal light intensity, the communication ranging frame generated by the first encoder 6 is used as the carrier of one beam of light, passes through the first optical phase modulator 7, enters the transmitting end of the first optical fiber circulator 8, that is, port 1, and then passes through the first optical phase modulator 7. The port 2 of the first circulator enters the first optical fiber collimator 9 and transmits to the ground station, and another beam of light is used as the local oscillator light of the satellite station to complete the launching process of the satellite station. The launch of the ground station is the same as that of the satellite station, and the elapsed time τ, the signal transmitted by the ground station is received by the first optical fiber collimator 9, and it enters the receiving end of the first optical fiber circulator through port 2 of the first optical fiber circulator, that is, port 3, as a receiving signal, and the receiving signal and the local oscillator light The signal is detected and received by the first photoelectric balance detector through the first directional ring coupler, and then passes through the first clock recovery circuit 12, the first pattern conversion circuit 13, the first sampling decision device 14, and the first decoder 15 in sequence ; Pass the recovered clock signal and the local clock signal of the communication ranging frame through the first phase comparator, and the decoded ranging code and the local ranging code pass through the first analog correlator to complete the acceptance process of the satellite station, and the ground station The acceptance process is the same as for satellite stations.

The specific implementation includes the following steps:

Step 1: Coding: Embed the ranging code a(t) generated by the first pseudocode generator 3 and the second pseudocode generator 19 into the first signal generator 4 and the second signal respectively at the satellite station and the ground station The communication data generated by the generator 20 is encoded by the first encoder 5 and the second encoder 21 into a communication ranging frame d(t);

The ranging code a(t) generated by the first pseudocode generator 3 and the second pseudocode generator 19 is expressed as:

Among them, T is the symbol width of the ranging code, and a _n is a pseudo-random code symbol, which is randomly selected as ±1 with equal probability;

The communication data b(t) produced by the first signal generator 4 and the second signal generator 20:

The communication ranging frame d(t) after passing through the first encoder 5 and the second encoder 21 respectively is expressed as:

Wherein, l is the length of the communication ranging frame;

The clock signal of the ranging code is used as the local clock signal, which is expressed as:

Among them, T is the period of the clock signal, which is equal to the symbol width of the ranging code.

Step 2: The satellite station and the ground station adopt a two-way one-way communication mode for transmission, as shown in Figure 4, the communication ranging frames of the two stations are respectively used as the carrier waves of the first single-frequency single-mode laser 1 and the second single-frequency single-mode laser 17 Under the first optical phase modulator 6 and the second optical phase modulator 22, binary phase shift keying modulation (abbreviated as BPSK) is carried out, and the two stations agree to launch at _t0 . The time is t _A0 , and the launch time of the ground station is t _B0 ;

The light field expression of the laser output by the first single-frequency single-mode laser 1 of the satellite station is:

Among them, A ₁ represents the amplitude of the light field, ω ₁ represents the frequency of the light wave, Indicates the initial phase of the light field. The light output by the first single-frequency single-mode laser 1 passes through the first optical fiber beam splitter 2 and is divided into two beams of light with equal intensity and the same polarization state, one of which is used as the local oscillator light of the satellite station, and its light field expression is:

The other way is used as signal light, which is BPSK-modulated by the first optical phase modulator 6, then passed through the first optical fiber circulator 7 and the first optical fiber collimator 8 and sent to the ground station at time t _A0 , and the light of the emitted signal The field expression is:

The local clock signal of the satellite station at this time is expressed as:

The light field expression of the laser light output by the second single-frequency single-mode laser 17 of the ground station is

Among them, A ₂ represents the amplitude of the light field, ω ₂ represents the frequency of the light wave, Indicates the initial phase of the light field. The light output by the second single-frequency single-mode laser 17 is divided into two beams of light with the same intensity and the same polarization state by the second beam splitter 18, one of which is used as the local oscillator light of the ground station The other way is used as signal light, after it is BPSK-modulated by the second optical phase modulator 22, it passes through the second optical fiber circulator 23 and the second optical fiber collimator 24 and is sent to the satellite station as a transmission signal at the time t _B0 , which The signal expression is:

Step 3: The transmission signal of the ground station reaches the satellite station through the propagation distance _s0 of the atmosphere, and passes through the first collimator 8 of the satellite station, the port 2 of the first optical fiber circulator 7, and the port 3 of the first optical fiber circulator 7 , and the local oscillator optical signal of the satellite station is received by the first photodetector 10 through the first 2*2 directional coupler 9, and the received signal passes through the first clock recovery circuit 11, the first code conversion circuit 12, the second A sampling decision device 13 and a first decoder 14 obtain ranging codes and communication data;

Without considering the Doppler frequency shift, the expression of the demodulated signal received by the first photodetector 10 of the satellite station is:

The clock signal at time t _A obtained after the received signal passes through the first clock recovery circuit 11 is:

The communication ranging signal at the time t _A can be obtained by the first pattern conversion circuit 12 as:

With the recovered clock signal _{cr (t rA )} at Sampling the obtained communication ranging signal d(t _rA ) at time (rising edge of the clock) to obtain:

The signal after the decision is the signal passed through the first sampling decision device 13:

The ranging code obtained after passing through the first decoder 14 is:

Decoded ranging code and local ranging code (delay ) is carried out correlation operation by the first analog correlator 16 and obtains:

The correlator has a peak value after the elapsed time T _A , because T _A =t _A -t _A0 =(nT) _A ++ΔT _A , (nT) _A is an integer multiple of the symbol period, n is an integer, and T is the ranging The symbol width of the code, ΔT _A is the time value in one symbol. Here, only an integer multiple of the symbol period (nT) _A is taken, which is used as a roughly measured time value of the time T _A of the satellite station from sending a signal to receiving a signal.

The recovered clock signal is compared with the local clock signal through the first phase comparator 15 to obtain the phase difference within one clock cycle Then the precise time value in a ranging code symbol can be obtained Wherein, T is a clock period, which is equal to the ranging code symbol width;

The transmission signal of the satellite station arrives at the ground station through the atmospheric propagation distance _s0 , and thus passes through the second optical fiber collimator 24, the port 2 of the second optical fiber circulator 23, the port 3 of the second optical fiber circulator 23, and communicates with the ground station The local oscillator optical signal is received by the second photodetector 26 at time t _B through the second 2*2 directional coupler 25, and the received signal passes through the second clock recovery circuit 27, the second pattern conversion circuit 28, the second The sampling decision unit 29 and the second decoder 30 obtain the ranging code and communication data.

The same as the working process of the satellite station, the rough time value (nT) _B and the fine time value ΔT _B of the time T B from the time T _B of the ground station from sending the signal to receiving the signal can be obtained at the ground station by the same method.

Step 4: Use T _A to represent the measurement time from the satellite station sending the signal to receiving the ground station signal, and T _B to represent the time from the ground station sending the signal to receiving the satellite station signal, and τ is the time between A and B Transmission delay, Δt _clk is the clock difference between two stations, then:

T _A =Δt _clk +τ, T _B +Δt _clk =τ

T _A =(nT) _A +ΔT _A , T _B =(nT) _B +ΔT _B

So the distance between A and B is

where c is the speed of light.

In this embodiment, the method of Fast Discrete Fourier Transform (FFT) is used to find the clock signal phase difference, the local clock signal is sampled by nT, and the number of points is N samples to do FFT. When the FFT method is used to find the phase difference, due to A The variance of the phase difference measurement error caused by /D quantization and Gaussian white noise is:

Among them, q=2- ^b is the quantization width, b is the number of digits of A/D quantization, N is the number of sampling points, A is the amplitude of the signal, and SNR is the signal-to-noise ratio of the signal.

So the accuracy of measuring the distance is:

Assuming that the symbol period T=1us of the ranging code and the communication data, a communication rate of 1GHZ can be realized, and the frequency of the down-converted clock signal is f ₀ =100MHZ, and the sampling frequency f _s =500MHZ, A=1, and the number of sampling points N= 2048, A/D is 11 bits, SNR=25dB, the accuracy of distance measurement can reach 2.98mm.

Assume that the length of the ranging code is N, the length of the communication data and the length of the frame tail are M, and the communication data is sent continuously. When the bit error rate is not considered, since the ranging code and communication data are transmitted serially, the ranging code can be measured. Maximum distance:

s _max =c(M+N)T

Where c is the speed of light, and T is the width of the symbol. The traditional ranging method uses communication data as the carrier of the ranging code, and the maximum distance that can be measured by the ranging code is:

s _max =cNT

Assuming that a 10-bit m-sequence is used as the ranging code, and the width of the symbol is 1us, the maximum distance that can be measured by the traditional ranging method is s _max =3×10 ⁸ ×(2 ¹⁰ -1)×10 ^-6 = 30.69×10 ⁴ m, while using the method of the present invention, the same distance can be measured by using 5-bit ranging codes and 5-bit communication data, which reduces the number of required ranging codes.

Claims (1)

1. a kind of high rate laser communicates and precision distance measurement integral method, including multiple range finding communication stations, it is characterised in that： The method is comprised the following steps：

Step one：By the range finding of method two communication stations of high rate laser to be performed communication and precision distance measurement integration, below The transmitting terminal and receiving terminal at referred to as two station of A, B is aligned, at two station of A, B by with uniqueness, good auto-correlation and mutually The ranging code and its clock signal of correlation properties is cached to locally, respectively as local ranging code and local clock pulses, then The ranging code is embedded in communication data, composition communication distance measuring frame after warp knit code, frame head of the ranging code as communication distance measuring frame, Communication distance measuring frame includes frame head, communication data, postamble；

Step 2：Communication mode of two station of A, B using two-way one way, carrier wave Jing of the communication distance measuring frame that A stands as LASER Light Source Optical phase modulator is modulated, and in the same manner, B stations are identical with the work at A stations, and two stations are about scheduled on t₀Moment mutually launches, during due to two places The difference of clock, the launch time at A stations is t_A0, the x time at B stations is t_B0；

Step 3：A stations receive the signal of B stations transmitting, and B stations receive the signal of A stations transmitting, the letter after two station of A, B is received Number be demodulated, clock recovery, sampling judgement, decoding obtain ranging code and communication data.

Step 4：Stand the local clock signal cached in the clock signal of recovery and step one is entered line phase to compare in A, obtain To phase contrast of two clock signals within a clock cycleAnd then try to achieve in the ranging code symbol width that A stands Accurate measurement time valueWherein, T is the cycle of clock signal, and it is equal to the symbol width of ranging code, in the same manner may be used Obtain the accurate measurement time value Δ T in a ranging code symbol width at B stations_B, the ranging code that obtains and step after A stands decoding The local ranging code cached in one carries out related operation, obtains integral multiple symbol width and is bigness scale time value (nT)_A, wherein, T For the symbol width of ranging code, n is integer, and the bigness scale time value (nT) at B stations is obtained in the same manner_B；

Step 5:Calculate the distance of A, B：T_ARepresent A stations from the time for transmitting a signal to the signal for receiving B stations, T_BRepresent B stations From the time for transmitting a signal to the signal for receiving A stations, T_A=(nT)_A+ΔT_A, T_B=(nT)_B+ΔT_B, the transmission at two station of A, B prolongs WhenThe clock difference Δ t between A, B apart from s and two places is calculated by following equation_clk：

$s=c\mathrm{\τ}=\frac{1}{2}c(T_A+T_B),$

${\mathrm{\Δt}}_{clk}=\frac{1}{2}(T_A-T_B)$ Wherein, c is the light velocity.