A laser ranging and communication integration method based on baseband signal combining modulation

Abstract

This invention discloses an integrated laser ranging and communication method based on baseband signal combining modulation: Step 1: On satellite A, a laser emitter generates laser light; Step 2: The power ratio of the communication signal to the pseudocode signal is set to P; Step 3: The communication signal and the pseudocode signal are input into a microwave combiner for combining, and then enter the MZM to obtain the modulated laser; Step 4: The modulated laser light enters an optical amplifier and is then emitted; Step 5: On satellite B, an optical antenna receives the signal light; a local oscillator laser generates a light wave; Step 6: The light wave and the signal light are mixed in a coherent receiving module to generate two orthogonal intermediate frequency signals; Step 7: The signal processing module performs carrier synchronization on the two orthogonal signals and sends them to the communication demodulation unit and the pseudocode acquisition and tracking unit. This invention achieves the goal of integrating precision measurement and laser communication with minimal impact on the signal-to-noise ratio of the communication link.

Description

Technical Field

[0001] This invention belongs to the field of satellite navigation and relates to an integrated laser ranging and communication method based on baseband signal combining modulation. Background Technology

[0002] The projects related to this invention originate from the next-generation satellite navigation system and payload demonstration work. Currently, the main schemes for inter-satellite laser ranging include data frame ranging schemes, high-speed pseudocode ranging schemes, and QPSK modulation schemes that combine high-speed pseudocode and high-speed communication.

[0003] In the data frame ranging scheme, the transmitter aligns the data frame header with the on-satellite second pulse before transmitting the data frame. After completing carrier synchronization and data demodulation, the receiver recovers the data frame header and completes pseudorange measurement by measuring the code phase difference between the local second pulse and the recovered header. Through bidirectional measurement, inter-satellite ranging and clock error measurement are achieved. The data frame ranging scheme integrates ranging and communication; however, because the loop coherent integration time does not exceed the code rate, the receiver loop bandwidth is relatively wide, making it difficult to improve measurement accuracy.

[0004] The high-speed pseudocode scheme achieves higher measurement accuracy with the same receiver parameters because the receiver loop coherent integration time is much longer than that of the data frame ranging scheme. However, the inter-satellite communication rate supported by this scheme is much lower than that of the data frame ranging scheme.

[0005] The QPSK modulation scheme, which combines high-speed pseudocode and high-speed communication, achieves the integration of precise pseudocode measurement and high-speed communication through equal power allocation between the measurement and communication branches. At the same laser emission power, compared to the data frame scheme, the trade-off is a 3dB reduction in power used for communication, equivalent to a 3dB signal-to-noise ratio loss at the same communication rate. Summary of the Invention

[0006] The purpose of this invention is to provide an integrated laser ranging and communication method based on baseband signal combining modulation, so as to solve the problem of achieving and optimizing precise ranging under the premise of ensuring communication rate in existing integrated laser ranging and communication schemes.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A laser ranging and communication integration method based on baseband signal combining modulation specifically includes the following steps:

[0009] Step 1: On satellite A, a laser is emitted to generate laser light;

[0010] Step 2: Set the power ratio of the communication signal y(t) to the pseudocode signal x(t) to P, where P is much greater than 1; both the communication signal and the pseudocode signal are baseband signals.

[0011] Step 3: On satellite A, the two baseband signals, the communication signal and the pseudocode signal, are input into a microwave combiner for combining and then modulated onto the same laser carrier by MZM to obtain the modulated laser.

[0012] Step 4: On satellite A, the modulated laser is fed into an optical amplifier and then emitted through an optical antenna;

[0013] Step 5: On satellite B, the optical antenna receives the signal light; the local oscillator laser generates light waves;

[0014] Step 6: On satellite B, the light wave generated by the local oscillator laser is mixed with the signal light received by the optical antenna in the coherent receiving module to generate two orthogonal intermediate frequency signals, I and Q, which then enter the signal processing module.

[0015] Step 7: On satellite B, the signal processing module performs carrier synchronization on the I and Q quadrature signals. The carrier-synchronized I and Q signals are then sent to the communication demodulation unit for communication data demodulation to obtain communication data, thereby completing the communication function. At the same time, the carrier-synchronized I and Q signals are sent to the pseudocode acquisition and tracking unit to complete pseudocode acquisition and tracking measurement, and output the pseudocode measurement value to complete the ranging function.

[0016] Furthermore, in step 1, the typical value of P is 100.

[0017] Furthermore, in step 3, the output signal of the microwave combiner is represented as:

[0018]

[0019] Where M is the output signal of the combiner; P is the power ratio of the communication signal to the pseudo-code signal; and I is the strength of the pseudo-code signal. y(t) represents the communication signal strength; x(t) is the pseudocode signal, with a value of 1 or -1; y(t) is the communication signal, with a value of 1 or -1; the communication signal and the pseudocode signal are independent of each other, and the modulation rates of x(t) and y(t) can be the same or different.

[0020] Furthermore, in step 6, the coherent receiving module consists of a 90° mixer and a balanced detector; the coherent receiving module outputs two orthogonal photoelectric signals, I and Q, which are sampled by an ADC and then sent to the signal processing module.

[0021] Compared with the following prior art, the beneficial effects of the present invention are compared as follows:

[0022] (1) Reference 1: Patent No.: CN110233677A, Invention Title: A Laser Communication Ranging Device and Method Based on Optical Orthogonal Codes. Reference 1 discloses a method that uses optical orthogonal code encoding to time-division modulate ranging frames and communication frames on an optical carrier, realizing the integration of ranging and communication. Essentially, it belongs to an implementation of the aforementioned data frame ranging system. Compared with the pseudocode measurement accuracy in the laser ranging system based on baseband signal combining modulation of this invention, the measurement accuracy of data frame ranging is lower.

[0023] (2) Reference 2: Research on the Optimization of Laser Ranging and Communication Integrated Algorithm Based on Symbol Synchronization Loop, Telemetry and Remote Control, 2022. Reference 2 belongs to the mainstream implementation method of data frame ranging. Compared with the pseudocode measurement accuracy in the laser ranging system based on baseband signal combining modulation of this invention, the measurement accuracy of data frame ranging is lower.

[0024] (3) Reference 3: Patent No.: CN202211678385.8, Invention Title: A method for integrating laser ranging and communication based on unbalanced dual BPSK. The difference between it and the method of this invention is: (1) The modulation methods are different. In Reference 3, the pseudocode and communication signal are modulated by optical carriers through independent modulators, and then the optical carriers are combined; in this patent, the pseudocode and communication signal are combined by a microwave combiner and then enter the same modulator to modulate the optical carrier; (2) The pseudocode ranging and communication power allocation in Reference 3 is achieved by using an optical unbalanced beam splitter and beam combiner with a beam splitting ratio. The power allocation for ranging and communication is inflexible and requires changes to the optical beam combiner and beam splitter; in this invention, the two baseband signals of pseudocode and communication are combined by a microwave combiner and then modulated by an optical modulator. The power allocation is flexible and does not require changes to the optical components.

[0025] Simulation results demonstrate that this invention achieves both high-speed laser communication and pseudocode-based precision measurement by unbalancedly allocating the power ratio of the communication and ranging branches through baseband combining modulation. In summary, this invention achieves the integration of precision measurement and laser communication with minimal impact on the signal-to-noise ratio of the communication link. Attached Figure Description

[0026] Figure 1 This is a block diagram illustrating the principle of laser ranging and communication integration based on baseband signal combining modulation.

[0027] Figure 2 This is a flowchart of the digital signal processing of the present invention;

[0028] Figure 3 This is a constellation diagram of the combined baseband signals of the pseudocode signal and the communication signal;

[0029] Figure 4This is the laser intermediate frequency signal constellation diagram before entering the signal processing module;

[0030] Figure 5 This is the constellation diagram after laser open-loop BPSK carrier synchronization;

[0031] Figure 6 This describes how the pseudocode measurement error changes with the communication-to-pseudocode power ratio (P).

[0032] Figure 7 This increases the impact of pseudocode modulation signals on the signal-to-noise ratio of the communication link. Detailed Implementation

[0033] like Figure 1 As shown, the laser ranging and communication integrated method based on baseband signal combining modulation provided by this invention specifically includes the following steps:

[0034] Step 1: On satellite A, a laser is emitted to generate laser light.

[0035] Step 2: Set the power ratio of the communication signal y(t) to the pseudocode signal x(t) to P. P is much greater than 1, and a typical value of P is 100. P is determined based on the ranging and communication signal-to-noise ratio requirements. Both the communication signal and the pseudocode signal are baseband signals, and the ratio can be flexibly adjusted by changing the power of the baseband signal.

[0036] Step 3: On satellite A, the two baseband signals, the communication signal and the pseudocode signal, are input into a microwave combiner for combining, and then into an MZM (Mach-Zehnder modulator) to modulate them onto the same laser carrier to obtain the modulated laser.

[0037] In a preferred embodiment of the present invention, the output signal of the microwave combiner is expressed as follows:

[0038]

[0039] Where M is the output signal of the combiner; P is the power ratio of the communication signal to the pseudo-code signal; and I is the strength of the pseudo-code signal. Let x(t) be the communication signal strength; x(t) be the pseudocode signal, with a value of 1 or -1; and y(t) be the communication signal, with a value of 1 or -1. The communication signal and the pseudocode signal are independent of each other, and the modulation rates of x(t) and y(t) can be the same or different.

[0040] Step 4: On satellite A, the modulated laser is fed into an optical amplifier and then emitted through an optical antenna.

[0041] Step 5: On satellite B, the optical antenna receives the signal light; the local oscillator laser generates light waves;

[0042] Step 6: On satellite B, the light wave generated by the local oscillator laser is mixed with the signal light received by the optical antenna in the coherent receiving module to generate two orthogonal intermediate frequency signals, I and Q, which then enter the signal processing module.

[0043] In a preferred embodiment of the present invention, the coherent receiving module consists of a 90° mixer and a balanced detector. The coherent receiving module outputs two orthogonal photoelectric signals, I and Q, which are sampled by an ADC and then sent to a digital signal processing module.

[0044] Step 7: On planet B, such as Figure 2 As shown, the signal processing module performs carrier synchronization on the I and Q quadrature signals. The synchronized I and Q signals are then sent to the communication demodulation unit for communication data demodulation to obtain communication data, thus completing the communication function. Simultaneously, the synchronized I and Q signals are sent to the pseudo-code acquisition and tracking unit to complete pseudo-code acquisition and tracking measurement, outputting the pseudo-code measurement value to complete the ranging function. Ultimately, this achieves the goal of integrating precise ranging and high-speed communication.

[0045] In step 7, carrier synchronization is used to separate the carrier frequency and phase to obtain the baseband signal. Carrier synchronization is achieved using the traditional laser open-loop BPSK carrier synchronization algorithm.

[0046] Figure 3 This is the constellation diagram after combining the pseudocode signal and the communication signal, two baseband signals. Figure 4 This is the laser intermediate frequency signal constellation diagram before entering the signal processing module. Figure 5 It is a constellation diagram for carrier stripping after applying traditional open-loop BPSK frequency offset estimation and phase noise compensation algorithms. Compared to Figure 3 The original constellation diagram shown demonstrates that carrier synchronization effectively recovered the baseband data, achieving the goal of carrier stripping. In the simulation of this embodiment, the power ratio P between the communication signal and the pseudocode signal is 9.

[0047] In this invention, for pseudocode measurement, the communication signal is broadband interference noise. The pseudocode power is relatively small, but due to its good correlation, it can be normally acquired and tracked even under communication interference. An approximate estimate of the tracking accuracy is:

[0048]

[0049] Where T is the time width of the pseudocode chip, in seconds, and B... loop C / N0 is the pseudocode tracking loop bandwidth in Hz, and C / N0 is the pseudocode carrier-to-noise ratio in Hz (non-logarithmic). t The standard deviation of the pseudocode is measured in seconds.

[0050] For pseudocode, the communication signal is the primary noise source, and the inherent noise floor of the optical communication system is negligible. The ratio of communication signal power to pseudocode power is P; therefore, the pseudocode carrier-to-noise ratio is:

[0051] C / N0 = B PRN / P,

[0052] Among them, B PRN It is the baseband bandwidth of the pseudocode, which is equal to the pseudocode rate.

[0053] Therefore, the pseudocode ranging error is:

[0054]

[0055] Figure 6 This describes the variation of pseudocode measurement error with the communication-to-pseudocode power ratio P when the pseudocode rate is 1 Gcps. Loop bandwidth B loop The frequency is 5Hz. The measurement error is measured in ps. The measurement error reaches 0.707 ps (1σ) when P equals 100.

[0056] For communication signals, the modulation of pseudo-code signals diverts some optical power, causing a decrease in communication power. Simultaneously, pseudo-code signals also interfere with communication demodulation, increasing noise in the communication link. This reduces the original signal-to-noise ratio (SNR) of x. SNR In the case of adding a pseudocode signal, the signal-to-noise ratio of the communication signal becomes:

[0057] x′ SNR =(P / (P+1)) / (1 / x) SNR +1 / (P+1)),

[0058] Figure 7 This study describes the decrease in the communication signal-to-noise ratio (SNR) when a pseudo-code modulation signal is added, with a communication power ratio of 100:1 (i.e., P equals 100). At a typical SNR of 10dB, adding the pseudo-code signal only causes a 0.46dB SNR loss in the communication link.

Claims

1. A laser ranging and communication integrated method based on baseband signal combining modulation, characterized in that, Specifically, the steps include the following: Step 1: On satellite A, a laser is emitted to generate laser light; Step 2: Set the power ratio of the communication signal y(t) to the pseudocode signal x(t) as follows: P , P Much greater than 1; both communication signals and pseudocode signals are baseband signals; Step 3: On satellite A, the two baseband signals, the communication signal and the pseudocode signal, are input into a microwave combiner for combining and then modulated onto the same laser carrier by MZM to obtain the modulated laser. The output signal of the microwave combiner is represented as follows: in, M This is the output signal of the combiner; P The power ratio of the communication signal to the pseudocode signal; I The strength of the pseudocode signal; The strength of the communication signal; x(t) This is a pseudo-code signal, with a value of 1 or -1; y(t) This is a communication signal, with a value of 1 or -1; the communication signal and the pseudocode signal are independent of each other. x(t) and y(t) The modulation rates may be the same or different; Step 4: On satellite A, the modulated laser light enters the optical amplifier and is then emitted through the optical antenna; Step 5: On satellite B, the optical antenna receives the signal light; the local oscillator laser generates light waves; Step 6: On satellite B, the light wave generated by the local oscillator laser is mixed with the signal light received by the optical antenna in the coherent receiving module to generate two orthogonal intermediate frequency signals, I and Q, which then enter the signal processing module. Step 7: On satellite B, the signal processing module performs carrier synchronization on the I and Q quadrature signals. The carrier-synchronized I and Q signals are then sent to the communication demodulation unit for communication data demodulation to obtain communication data, thereby completing the communication function. At the same time, the carrier-synchronized I and Q signals are sent to the pseudocode acquisition and tracking unit to complete pseudocode acquisition and tracking measurement, and output the pseudocode measurement value to complete the ranging function.

2. The laser ranging and communication integrated method based on baseband signal combining modulation as described in claim 1, characterized in that, In step 2, P The typical value is 100.

3. The laser ranging and communication integrated method based on baseband signal combining modulation as described in claim 1, characterized in that, In step 6, the coherent receiving module consists of a 90° mixer and a balanced detector; the coherent receiving module outputs two orthogonal photoelectric signals, I and Q, which are sampled by an ADC and then sent to the signal processing module.

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