A frame synchronization-based laser communication and ranging integrated system

Abstract

The application discloses a frame synchronization-based laser communication and ranging integrated system, and belongs to the technical field of satellite laser communication.The system solves the problem that ranging precision is limited under the condition of low communication rate.The system comprises a sending end and a receiving end, wherein the sending end comprises a synchronization header sequence generating module, a data sequence generating module and a framing module, the receiving end comprises a synchronization sliding correlation / rough ranging calculation module, a fine ranging calculation module and a data sequence extracting module; the synchronization header sequence generating module generates a synchronization header sequence, the data sequence generating module generates a data sequence, and the framing module completes splicing of the synchronization header sequence and the data sequence; the synchronization sliding correlation / rough ranging calculation module performs frame synchronization and calculates an integer symbol period of transmission delay, the fine ranging calculation module calculates a fractional symbol period of transmission delay, and the data sequence extracting module performs frame disassembly according to a starting position of the synchronization header sequence, extracts the data sequence and completes communication reception.

Description

Technical Field

[0001] The present invention belongs to the technical field of satellite laser communications, and in particular relates to a laser communication and ranging integrated system based on frame synchronization. Background Art

[0002] The bidirectional, one-way timestamp ranging method is widely used in existing integrated laser communication and ranging technologies. However, this method requires a highly synchronized, second-pulse clock at the transmitter and receiver, and incurs additional signal overhead to transmit ranging information. The receiver can detect transmission delays using correlation detection. Pseudo-code ranging schemes modulate communication information onto a PN sequence, saving additional data overhead and effectively suppressing interference. However, this integrated ranging and communication method using pseudo-code correlation detection requires direct spread spectrum operation at the transmitter and is difficult to integrate with OOK modulation formats. Furthermore, ranging accuracy based solely on correlation calculations is limited by the chip rate. Summary of the Invention

[0003] To address the issue of limited ranging accuracy at low communication rates (less than 100 Mbps), the present invention provides an integrated laser communication and ranging system based on frame synchronization. The system includes a transmitting end and a receiving end, wherein data is transmitted and received between the transmitting end and the receiving end through modulation and demodulation. The transmitting end includes a synchronization header sequence generation module, a data sequence generation module, and a framing module, and the receiving end includes a synchronous sliding correlation / coarse ranging calculation module, a fine ranging calculation module, and a data sequence extraction module.

[0004] The synchronization header sequence generation module generates a synchronization header sequence, the data sequence generation module generates a data sequence, and the framing module completes the assembly of the synchronization header sequence and the data sequence;

[0005] The synchronous sliding correlation / coarse ranging calculation module performs frame synchronization and calculates the integer code element period of the transmission delay, the fine ranging calculation module calculates the fractional code element period of the transmission delay, and the data sequence extraction module performs frame decomposition according to the starting position of the synchronization header sequence, extracts the data sequence and completes communication reception.

[0006] Furthermore, when the synchronization header sequence generation module generates a synchronization header sequence, a specific length of N bit synchronization header sequence .

[0007] Furthermore, when the data sequence generation module generates a data sequence, it encapsulates or divides the business data to be transmitted into data sequences of equal length. .

[0008] Further, when the framing module completes the assembling of the synchronization header sequence and the data sequence, the framing is performed according to the synchronization header sequence as a frame header and the data sequence as frame payload, wherein the frame header is used to complete frame synchronization and ranging, and the data sequence is used to transmit communication information.

[0009] Further, the ranging is performed by the product of the sum of the integral symbol period of the transmission delay and the fractional symbol period of the transmission delay and the speed of light.

[0010] Further, the integral symbol period of the transmission delay calculated by the synchronization sliding correlation / coarse ranging calculation module is specifically as follows:

[0011] The synchronization header sequence known by the receiving end is used Correlation operation is performed on the received sequence to perform frame synchronization and obtain a delay correlation value , The delay correlation value The peak position of the delay correlation value corresponds to the delay , which is the integral symbol period of the transmission delay.

[0012] Further, the fractional symbol period of the transmission delay calculated by the fine ranging calculation module is specifically as follows:

[0013] The received sequence is oversampled to obtain an oversampled sequence, the integral symbol period is brought into the oversampled sequence to eliminate the delay calculated by the synchronization sliding correlation / coarse ranging calculation module, early signals and late signals are constructed from the oversampled sequence according to configuration parameters, the early correlation value is obtained by using the early signals, the late correlation value is obtained by using the late signals, and the early correlation value and the late correlation value are input into a early-late correlator to obtain the fractional symbol period of the transmission delay.

[0014] Further, the data transmission and reception between the sending end and the receiving end through modulation and demodulation is specifically as follows: a modulation module and a laser sending module are configured at the sending end, a laser receiving module and a demodulation module are configured at the receiving end, the framing module of the sending end inputs data into the modulation module, converts the electrical signal into an optical signal, and sends the optical signal into the laser sending module for sending, the laser receiving module receives laser and sends it into the demodulation module, converts the optical signal into an electrical signal, and then inputs the electrical signal into the receiving end.

[0015] The system has the following beneficial effects:

[0016] The system uses the synchronization frame header necessary in the physical frame structure to replace the PN sequence for correlation detection delay, which can reduce the additional overhead of transmission ranging information and reduce the hardware complexity of direct spread spectrum at the sending end. At the same time, combined with coarse measurement and fine measurement, the problem of limited ranging accuracy under low communication rate can be solved.

[0017] The ranging is performed by correlation detection of the synchronization sequence in the frame structure, which saves the additional frame overhead in the two-way one-way ranging method and does not need the high-precision synchronization second pulse signal of the transmitting end and the receiving end, thereby improving the data transmission efficiency. Meanwhile, compared with the pseudo code correlation method, the pseudo code multiplication operation at the transmitting end is not needed, thereby reducing the hardware complexity. The selection of the parameters and the selection of the coarse measurement or the fine measurement can be determined according to the progress requirement and the actual communication rate.

[0018] In the OOK system, the accuracy of the coarse measurement can reach ±3m, ±0.3m and ±0.03m in the communication rates of 100Mbps, 1Gbps and 10Gbps respectively. In the fine measurement, the correlation interval is 1 / 2 and the 8 times oversampling is adopted, and the ranging accuracy can reach ±4.2cm, ±0.42cm and ±0.042cm respectively in the SNR of 13dB. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The system structure diagram in the embodiment of the present application is shown in the figure.

[0020] Figure 2 The framing format diagram in the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described clearly and completely in combination with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by the ordinary skilled in the art without creative labor are within the protection scope of the present application.

[0022] Embodiment 1,

[0023] The embodiment provides a laser communication ranging integrated system based on frame synchronization, which comprises a transmitting end and a receiving end as shown in the figure. Figure 1 The specific implementation can be realized based on FPGA. The transmitting end comprises a synchronization header sequence generation module, a data sequence generation module and a framing module. The receiving end comprises a synchronization sliding correlation / coarse ranging calculation module, a fine ranging calculation module, a configurable interface and a data sequence extraction module. The synchronization header sequence generation module and the data sequence generation module can be performed in parallel, and the fine ranging calculation module and the data sequence extraction module can be performed in parallel. The functions of the modules for realizing the ranging communication integration are as follows.

[0024] Transmitting end:

[0025] Synchronization header sequence generation module: generating a synchronization header sequence;

[0026] Data sequence generation module: generating a data sequence;

[0027] Frame assembling module: complete assembling of synchronization header sequence and data sequence.

[0028] Receiving end:

[0029] Synchronization sliding correlation / coarse ranging calculation module: 1. using known local synchronization header sequence to do sliding correlation operation on received sequence; 2. finding synchronization header starting position and symbol level transmission delay.

[0030] At the same time, according to the accuracy requirement and working scene, determine whether to enable fine ranging calculation module;

[0031] Fine ranging calculation module: 1. oversampling data sequence and synchronization header sequence; 2. eliminating coarse measurement delay by bringing in coarse measurement result; 3. constructing early-late signal according to configuration parameters after oversampling; 4. using early-late signal and received signal eliminating coarse measurement result to do correlation operation; 5. according to early-late correlation operation result, calculating sub-symbol level transmission delay through early-late correlator; 6. combining coarse measurement result and fine measurement result to obtain final ranging result.

[0032] Data sequence extraction module: according to the information obtained by synchronization sliding correlation / coarse ranging calculation module, frame disassembly is performed to extract data sequence and complete communication reception.

[0033] Embodiment 2,

[0034] This embodiment is a further limitation of embodiment 1, and further describes the working process of the sending end and the receiving end.

[0035] 1. Sending end:

[0036] First step: synchronization sequence generation module generates a specific synchronization sequence with length N bits , the synchronization sequence is a sequence whose main lobe value is much larger than the side lobe value after correlation operation such as PN sequence.

[0037] Second step: encapsulate or cut the to-be-transmitted service data into equal-length data sequences .

[0038] Third step: frame according to the synchronization sequence as the frame header and the data sequence as the frame payload. The frame header is used to complete frame synchronization and ranging at the same time, and the data sequence is used to transmit communication information. After frame assembling, send to modulation module for processing, and the frame assembling format is shown as Figure 2 .

[0039] As Figure 1As shown, a modulation module and a laser sending module are configured at the transmitting end, and a laser receiving module and a demodulation module are configured at the receiving end. The framing module at the transmitting end inputs data into the modulation module, converts the electrical signal into an optical signal, and sends the optical signal to the laser sending module for transmission. The laser receiving module receives the laser and sends it to the demodulation module, which converts the optical signal into an electrical signal and then inputs it into the receiving end.

[0040] 2. Receiver:

[0041] a) Synchronous sliding correlation / coarse ranging calculation module:

[0042] The input of the synchronous sliding correlation / coarse ranging calculation module is the complete frame sequence after channel transmission and demodulation. In the synchronization operation, it is necessary to use the locally known synchronization header sequence and the received sequence to perform correlation calculation to find the matching physical frame header. It can be expressed as:

[0043] ;

[0044] Noise terms and other losses are equalized and removed in the demodulation module. It only contains the delay τ of the frame sequence transmission. The specific workflow of the synchronous sliding correlation / coarse ranging calculation module is as follows:

[0045] Step 1: Using the synchronization sequence known to the receiver Correlate with the received sequence to calculate any delay , the relevant value is: (N represents the number of relevant operation points)

[0046] ;

[0047] when The result is:

[0048] ;

[0049] when When the correlation value is much smaller than situation.

[0050] Step 2: Estimate the transmission delay by searching for the correlation peak position:

[0051] ;

[0052] The results obtained from coarse ranging The starting position of the data sequence can be determined and delay information can be provided. It is the delayed code element count, so its accuracy depends on the code element period of the transmitted sequence For low-speed communication scenarios (lower than 100 Mbps), the ranging accuracy error is large, so it is necessary to improve the ranging accuracy on the basis of coarse ranging.

[0053] b) Fine ranging calculation module:

[0054] The principle of fine ranging is as follows: the delay of the received sequence can be expressed as:

[0055] ;

[0056] Wherein represents an integer symbol period of transmission delay, represents a fractional symbol period of transmission delay, which has been obtained by the synchronous sliding correlation / coarse ranging calculation module . The purpose of the fine module is to obtain .

[0057] First step: oversample the received sequence by times, with a sampling period . The discrete sequence after oversampling is: ( 4, 8, 16 can be taken)

[0058] ;

[0059] Second step: use the integer symbol period value obtained by the synchronous sliding correlation / coarse ranging calculation module to eliminate the coarse value:

[0060] , is an index parameter.

[0061] Wherein . is the received sequence after removing the coarse delay, which only contains a delay less than a symbol period.

[0062] Third step, generate early-late signals through a fractional delay filter: , wherein is an adjustable correlation interval, which is by default, and can be configured independently through an external interface.

[0063] Fourth step, calculate the early and late correlation values:

[0064] Early correlation value ; Late correlation value ;

[0065] Fifth step, calculate the sub-symbol level delay result through the early-late correlator:​

[0066] ;

[0067] Step 6, add the fine measurement delay to the coarse measurement delay to get the final measurement result .

[0068] ;

[0069] Through the above module design, the ranging communication integration function can be completed on the basis of the original frame structure without additional frame overhead and spread spectrum operation.

[0070] c) Data sequence extraction module:

[0071] The output of the synchronous sliding correlation / coarse ranging calculation module can be used to determine the starting position of the data sequence. After removing the synchronization header, the data sequence is extracted to complete the communication reception and analysis.

Claims

1. A laser communication and ranging integrated system based on frame synchronization, characterized in that: The system includes a transmitting end and a receiving end, wherein data is transmitted and received between the transmitting end and the receiving end through modulation and demodulation. The transmitting end includes a synchronization header sequence generation module, a data sequence generation module and a framing module, and the receiving end includes a synchronization sliding correlation / coarse ranging calculation module, a fine ranging calculation module and a data sequence extraction module. The synchronization header sequence generation module generates a synchronization header sequence, which serves as a frame header. The frame header is used to complete frame synchronization and ranging. The data sequence generation module generates a data sequence. The framing module completes the assembly of the synchronization header sequence and the data sequence. The synchronous sliding correlation / coarse ranging calculation module performs frame synchronization and calculates the integer code element period of the transmission delay, the fine ranging calculation module calculates the fractional code element period of the transmission delay, and the data sequence extraction module performs frame decomposition according to the starting position of the synchronization header sequence, extracts the data sequence and completes communication reception; The fine ranging calculation module calculates the small code element period of the transmission delay by oversampling the received sequence to obtain the oversampled sequence, bringing the integer code element period into the oversampled sequence to eliminate the delay calculated by the synchronous sliding correlation / coarse ranging calculation module, constructing the early signal and the late signal according to the configuration parameters of the oversampled sequence, using the early signal to calculate the leading correlation value, using the late signal to calculate the lagging correlation value, and inputting the leading correlation value and the lagging correlation value into the leading-lagging correlator to calculate the sub-code element level delay result. : ;in, Indicates that the receiving sequence times oversampling, is an adjustable correlation interval, by default , is the advance correlation value, is the lagged correlation value, is the symbol period of the transmitted sequence.

2. The laser communication and ranging integrated system based on frame synchronization according to claim 1 is characterized in that: When the synchronization header sequence generation module generates a synchronization header sequence, it generates a specific length of bit synchronization header sequence .

3. The laser communication and ranging integrated system based on frame synchronization according to claim 2 is characterized in that: When the data sequence generation module generates a data sequence, it encapsulates or divides the business data to be transmitted into data sequences of equal length. .

4. The laser communication and ranging integrated system based on frame synchronization according to claim 3 is characterized in that: When the framing module completes the assembly of the synchronization header sequence and the data sequence, it frames the data sequence as the frame header and the data sequence as the frame payload. The data sequence is used to transmit communication information.

5. The laser communication and ranging integrated system based on frame synchronization according to claim 4 is characterized in that: The distance is measured by multiplying the product of the sum of the integer code element period of the transmission delay and the small code element period of the transmission delay and the speed of light.

6. The laser communication and ranging integrated system based on frame synchronization according to claim 5 is characterized in that: The integer symbol period for the synchronous sliding correlation / coarse ranging calculation module to perform frame synchronization and calculate the transmission delay is specifically: Using the synchronization header sequence known to the receiver Perform correlation operation with the received sequence for frame synchronization and obtain delay correlation value , Indicates delay, delay-related value The peak position corresponds to the delay That is, the integer symbol period of the transmission delay.

7. The laser communication and ranging integrated system based on frame synchronization according to claim 6, characterized in that: The sending and receiving of data between the sending end and the receiving end is carried out through modulation and demodulation. Specifically, a modulation module and a laser sending module are configured at the sending end, and a laser receiving module and a demodulation module are configured at the receiving end. The framing module at the sending end inputs the data into the modulation module, converts the electrical signal into an optical signal, and sends the optical signal into the laser sending module for transmission. The laser receiving module receives the laser and sends it into the demodulation module, which converts the optical signal into an electrical signal and then inputs it into the receiving end.

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