Laser communication and distance measurement integrated system based on frame synchronization

Abstract

The invention discloses a laser communication and distance measurement integrated system based on frame synchronization, and belongs to the technical field of satellite laser communication. The problem that the ranging precision is limited under the condition that the communication rate is low is solved. The system comprises a sending end and a receiving end, the sending end comprises a synchronous head sequence generation module, a data sequence generation module and a framing module, and the receiving end comprises a synchronous sliding correlation / coarse ranging calculation module, a fine ranging calculation module and a data sequence extraction module. The synchronization head sequence generation module generates a synchronization head sequence, the data sequence generation module generates a data sequence, and the framing module completes assembly of the synchronization head sequence and the data sequence; the synchronous sliding correlation / coarse ranging calculation module carries out frame synchronization and calculates an integer code element period of transmission delay, the fine ranging calculation module calculates a small code element period of transmission delay, and the data sequence extraction module carries out frame splitting according to the initial position of a synchronous head sequence, extracts a data sequence and completes communication receiving.

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. 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; 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.

[0004] Furthermore, when the synchronization header sequence generation module generates a synchronization header sequence, a specific length of N bit synchronization header sequence .

[0005] 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. .

[0006] Furthermore, when the framing module completes the assembly of the synchronization header sequence and the data sequence, it frames the frame with the synchronization header sequence as the frame header and the data sequence as the frame payload, wherein 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.

[0007] Furthermore, the distance is measured by multiplying the product of the sum of the integer code element period of the transmission delay and the fractional code element period of the transmission delay and the speed of light.

[0008] Furthermore, 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.

[0009] Furthermore, the precise ranging calculation module calculates the small code period of the transmission delay as follows: The received sequence is oversampled to obtain an oversampled sequence, an integer symbol period is introduced into the oversampled sequence to eliminate the delay calculated by the synchronous sliding correlation / coarse ranging calculation module, an early signal and a late signal are constructed for the oversampled sequence according to the configuration parameters, an advance correlation value is obtained by using the early signal, and a lag correlation value is obtained by using the lag signal. The advance correlation value and the lag correlation value are input into the advance-lag correlator to calculate the small symbol period of the transmission delay.

[0010] Furthermore, the sending and receiving of data between the sending end and the receiving end through modulation and demodulation are specifically as follows: 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, converts the optical signal into an electrical signal, and then inputs it into the receiving end.

[0011] The beneficial effects of the system of the present invention are: This system utilizes the synchronization frame header, a prerequisite for the physical frame structure, instead of the PN sequence for correlation detection delay. This reduces the overhead of transmitting ranging information and the hardware complexity of direct spread spectrum at the transmitter. Furthermore, by combining coarse and fine measurement, it can address the issue of limited ranging accuracy at low communication rates.

[0012] Utilizing the synchronization sequence within the frame structure for correlation detection and ranging reduces the additional frame overhead associated with bidirectional, one-way ranging methods and eliminates the need for highly synchronized pulse-per-second signals on the transmitter and receiver sides, improving data transmission efficiency. Furthermore, compared to pseudocode correlation methods, pseudocode multiplication is not required on the transmitter side, reducing hardware complexity. Parameter selection and the choice between coarse and fine measurement can be determined based on schedule requirements and actual communication rates.

[0013] At communication rates of 100Mbps, 1Gbps, and 10Gbps, respectively, using an OOK system, the theoretical coarse measurement accuracy can reach ±3m, ±0.3m, and ±0.03m. For fine measurement, taking signal noise into account, using 8x oversampling and a correlation interval of 1 / 2, the theoretical ranging accuracy can be further improved to ±4.2cm, ±0.42cm, and ±0.042cm at an SNR of 13dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A diagram showing the system structure in an embodiment of the present invention; Figure 2 Schematic diagram of the framing format in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0016] Example 1 This embodiment provides a laser communication and ranging integrated system based on frame synchronization, such as Figure 1 As shown, it includes two major parts: the transmitter and the receiver. The specific implementation can be based on FPGA. The transmitter includes a synchronization header sequence generation module, a data sequence generation module, and a framing module; the receiver includes a synchronization sliding correlation / coarse ranging calculation module, a fine ranging calculation module with a configurable interface, and a data sequence extraction module. The synchronization header sequence generation module and the data sequence generation module can be operated in parallel, and the fine ranging calculation module and the data sequence extraction module can be operated in parallel. The functions of each module to achieve the integration of ranging communication are as follows: Sending end: Synchronous header sequence generation module: generates a synchronous header sequence; Data sequence generation module: generates data sequence; Framing module: completes the assembly of synchronization header sequence and data sequence.

[0017] Receiver: Synchronous sliding correlation / coarse ranging calculation module: 1. Use the known local synchronization header sequence to perform sliding correlation operation on the received sequence; 2. Find the synchronization header starting position and code element level transmission delay.

[0018] At the same time, determine whether to enable the precise ranging calculation module based on the accuracy requirements and working scenarios; Fine ranging calculation module: 1. Oversample the data sequence and synchronization header sequence; 2. Introduce the coarse measurement result to eliminate the coarse measurement delay; 3. Construct an early-late signal for the oversampled sequence according to the configuration parameters; 4. Use the early-late signal to perform a correlation operation with the received signal that has eliminated the coarse measurement result; 5. Based on the early-late correlation operation result, calculate the sub-symbol level transmission delay through the early-late correlator; 6. Combine the coarse measurement result with the fine measurement result to obtain the final ranging result.

[0019] Data sequence extraction module: De-frames and extracts data sequences based on the information obtained by the synchronous sliding correlation / coarse ranging calculation module and completes communication reception.

[0020] Example 2 This embodiment further limits the first embodiment and further illustrates the working process of the transmitting end and the receiving end.

[0021] 1. Sending end: Step 1: The synchronization header sequence generation module generates a specific synchronization sequence of length N bits. , synchronization sequence It is a sequence in which the main lobe value is much larger than the side lobe value after correlation operation such as PN sequence.

[0022] Step 2: Encapsulate or split the business data to be transmitted into data sequences of equal length .

[0023] Step 3: Use the synchronization sequence as the frame header and the data sequence as the frame payload to form a frame. The frame header is used to complete frame synchronization and ranging, and the data sequence is used to transmit communication information. After the framing is completed, it is sent to the modulation module for processing. The framing format is as follows: Figure 2 shown.

[0024] like Figure 1 As 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.

[0025] 2. Receiver: a) Synchronous sliding correlation / coarse ranging calculation module: 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: ; 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: Step 1: Using the synchronization sequence known to the receiver Perform correlation operation with the received sequence to calculate any delay , the relevant value is: (N represents the number of relevant operation points) ; when The result is: ; when When the correlation value is much smaller than situation.

[0026] Step 2: Estimate the transmission delay by searching for the correlation peak position: ; 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 (less than 100Mbps), the ranging accuracy error is large, so it is necessary to ,improve the ranging accuracy based on coarse ranging.

[0027] b) Precision ranging calculation module: The principle of precise ranging is as follows: the delay of the receiving sequence can be expressed as: ; in represents the integer symbol period of the transmission delay, The small digital element period representing the transmission delay has been obtained through the synchronous sliding correlation / coarse ranging calculation module The purpose of the precision test module is to obtain .

[0028] Step 1: Receive sequence conduct times oversampling, sampling period , the discrete sequence after oversampling is: ( 4, 8, 16 are possible) ; Step 2: Use the integer symbol period value obtained by the synchronous sliding correlation / coarse ranging calculation module to set Eliminate rough measurements: , is the index parameter.

[0029] in, . To remove the coarse delay, the received sequence only contains delays smaller than the symbol period.

[0030] The third step is to generate early and late signals through fractional delay filters: , ,in is an adjustable correlation interval, by default ,and Can be configured independently through external interfaces.

[0031] The fourth step is to calculate the leading and lagging correlation values: Leading correlation value ; Lagged correlation value ; In the fifth step, the sub-symbol delay result is calculated by the advance-lag correlator: ; Step 6: Add the fine measurement delay and the coarse measurement delay to get the final measurement result .

[0032] ; Through the above module design, the integrated ranging and communication functions can be completed on the basis of the original frame structure without the need for additional frame overhead and spread spectrum calculation.

[0033] c) Data sequence extraction module: 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, 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; 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.

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 frame payload. The frame header is used to complete frame synchronization and ranging, and 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 fractional 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 precise ranging calculation module calculates the transmission delay of the small code period as follows: The received sequence is oversampled to obtain an oversampled sequence, an integer symbol period is introduced into the oversampled sequence to eliminate the delay calculated by the synchronous sliding correlation / coarse ranging calculation module, an early signal and a late signal are constructed for the oversampled sequence according to the configuration parameters, an advance correlation value is obtained by using the early signal, and a lag correlation value is obtained by using the lag signal. The advance correlation value and the lag correlation value are input into the advance-lag correlator to calculate the small symbol period of the transmission delay.

8. The laser communication and ranging integrated system based on frame synchronization according to claim 7 is 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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