Pulse width compression PPM modulation method based on superconducting nanowire single photon detection

Abstract

The pulse width compression PPM modulation method based on superconducting nanowire single-photon detection belongs to the technical field of signal processing. In view of the problems that the prior art cannot reduce the communication capacity, increase the system overhead and solve the ranging accuracy when reducing the communication error rate caused by random jitter. The pulse width in the PPM symbol is compressed at the sending end, the time fluctuation range of the superconducting nanowire single-photon detector response pulse is reduced, and the ranging error caused by time fluctuation is reduced. The time range of the random appearance of photons is compressed, the crosstalk of the superconducting nanowire single-photon detector response pulse to the adjacent time slot is reduced, the symbol decision error probability is reduced, and the communication reliability is improved. The signal light power is limited in a smaller time range, the instantaneous light power in the pulse time period is improved, the light power utilization efficiency is improved at the same transmission power, and a longer transmission distance is achieved. The present application is suitable for the field of communication and is used for improving the transmission distance and the ranging accuracy.

Description

Technical Field

[0001] This invention relates to a pulse width compression (PPM) modulation method based on single-photon detection using superconducting nanowires, belonging to the field of signal processing technology. Background Technology

[0002] Deep space laser communication ranging technology combines the wide bandwidth of laser communication with the high precision of laser ranging, making it one of the current research hotspots in the field of deep space exploration. Compared to microwave communication terminals, laser communication terminals are smaller, lighter, and consume less power, while offering advantages such as large communication capacity, no need for spectrum licensing, and good directionality. Its advantages, especially in spectrum licensing and directionality, make it an effective means to alleviate the scarcity of spectrum resources in space microwave communication and achieve high-speed space communication and high-precision ranging.

[0003] The US Starlink uses inter-satellite laser communication to achieve inter-satellite networking; China's BeiDou satellites have conducted inter-satellite laser communication ranging experiments; the European Space Agency and Japan have both completed satellite-to-ground and inter-satellite laser communication experiments. In 2013, NASA successfully applied laser communication ranging technology to the Lunar Laser Communication Demonstration (LLCD) project, achieving a ranging accuracy of 3cm at a 5GHz time slot rate. China's Chang'e 5 mission considered using laser communication technology, but it was ultimately not implemented due to limitations in technology maturity.

[0004] The method of single-photon detection and reception based on pulse position modulation (PPM) and superconducting nanowires possesses extremely high energy utilization efficiency and detection sensitivity, and has great potential for application in deep space exploration missions with limited power and ultra-long transmission distances. In deep space exploration scenarios, after the laser signal attenuates over long distances, the input signal power to the receiving detector reaches the single-photon level, and atmospheric turbulence occurs when passing through the Earth's atmosphere. Power attenuation and atmospheric effects cause the received photons to randomly appear within the original modulation pulse time range, resulting in jitter in the recovered electrical signal in the time domain. This leads to inter-slot crosstalk and inter-symbol interference between adjacent pulse signals, thereby increasing ranging errors, bit error rate, and reducing communication capacity.

[0005] Existing technologies reduce the communication error rate caused by random jitter by decreasing coding efficiency and long-term data interleaving. However, this approach reduces communication capacity, increases the processing complexity at the transceiver end, increases system overhead, and cannot cope with the impact of jitter on ranging accuracy. Summary of the Invention

[0006] To address the shortcomings of existing technologies and the random distribution characteristics of photons in deep-space laser link transmission scenarios, the main objective of this invention is to disclose a pulse width compression (PPM) modulation method based on single-photon detection using superconducting nanowires. By compressing the pulse width after PPM modulation, the time range of random photon distribution is reduced, thereby decreasing the jitter of the detected signal. Reduced jitter in the detected signal leads to reduced inter-slot crosstalk and inter-symbol interference, thus reducing ranging errors and communication bit error rates. Simultaneously, pulse width compression concentrates the energy of the transmitted signal, achieving higher instantaneous power with the same average transmit power, thereby improving transmission distance and power utilization efficiency.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] This invention discloses a pulse width compression (PPM) modulation method based on superconducting nanowire single-photon detection. At the transmitting end, after generating a digital baseband signal, the high-level pulses are compressed to a width narrower than those generated by normal PPM modulation. This is then converted into an analog electrical signal by a digital-to-analog converter (DAC). A laser modulator modulates the analog electrical signal with a carrier laser to form a laser signal, which is then transmitted after passing through an optical power amplifier. At the receiving end, the received optical signal is transmitted to a superconducting nanowire single-photon detector, achieving single-photon-level photoelectric detection and conversion into an analog baseband electrical signal. An analog-to-digital converter (ADC) converts the analog baseband electrical signal into a digital baseband signal, and communication and ranging are achieved through maximum likelihood demodulation and a code loop-based ranging algorithm. This improves transmission distance and power utilization efficiency.

[0009] The pulse width compression (PPM) modulation method based on single-photon detection using superconducting nanowires disclosed in this invention includes the following steps:

[0010] Step 1: The transmitting end performs pulse position modulation on the baseband signal data frame containing a specific frame header;

[0011] Data outside the frame header consists of random binary information. Each modulated PPM symbol contains exactly one pulse, and the pulse's duration represents the duration of a time slot. A PPM symbol is composed of multiple time slots. The relationship between the PPM symbol and the binary information is as follows:

[0012] s[i]=α*rect[in];i,n=0,…,2 N -1; N = 0, 1, ...

[0013] Where α represents the pulse amplitude of the PPM symbol; N represents the number of bits contained in the PPM symbol; n represents the time slot position of the pulse within the PPM symbol, i.e., the decimal value corresponding to the N bits of binary information; rect[i] is a rectangle function:

[0014]

[0015] Step 2: Based on the sampling rate F of the digital-to-analog converter (DAC) s With PPM slot rate R slot The PPM pulse width is compressed, and the symbol of the compressed PPM is shown below:

[0016]

[0017] Where M1 = F s / R slot M1 represents the oversampling factor, i.e., the number of segments that the PPM pulse can be further divided into. M2 represents the number of high-level 1 segments in the compressed pulse width. Therefore, M2 / M1 is the compression ratio. This is the floor function.

[0018] Step 3: The digital-to-analog converter converts the pulse-width compressed digital PPM signal generated in Step 2 into an analog PPM electrical signal, and mixes it with the local oscillator to obtain a PPM modulated optical signal.

[0019] Step 4: The optical power amplifier amplifies the power of the PPM modulated optical signal.

[0020] An optical power amplifier accumulates energy when there is no optical signal input and outputs the accumulated energy when a signal is input, amplifying the low-power input signal into a high-power output signal. In other words, it accumulates energy during non-pulse periods and releases the accumulated energy during pulse periods.

[0021] Step 5: The superconducting nanowire single-photon detector at the receiving end converts the received photon signal into an analog electrical signal, which is then converted into a digital signal by an analog-to-digital converter.

[0022] Step Six: Perform frame synchronization of the digital signal using fixed frame header information to achieve PPM symbol synchronization, and demodulate and recover the binary information based on maximum likelihood decision. Simultaneously, use the fixed frame header information to estimate the frame header reception time using an early-late gate and code ring algorithm to achieve ranging. This improves transmission distance and ranging accuracy.

[0023] Beneficial effects:

[0024] 1. The pulse width compression (PPM) modulation method based on superconducting nanowire single-photon detection disclosed in this invention narrows the pulse width in the PPM symbol at the transmitting end, thereby reducing the time fluctuation range of the response pulse of the superconducting nanowire single-photon detector and reducing the ranging error caused by time fluctuation.

[0025] 2. The pulse width compression (PPM) modulation method based on superconducting nanowire single-photon detection disclosed in this invention reduces crosstalk between the response pulses of the superconducting nanowire single-photon detector and adjacent time slots by compressing the time range of random photon occurrence, thereby reducing the probability of symbol decision error and improving communication reliability.

[0026] 3. The pulse width compression (PPM) modulation method based on single-photon detection using superconducting nanowires disclosed in this invention limits the signal optical power to a smaller time range, increases the instantaneous optical power within the pulse time period, improves the optical power utilization efficiency at the same transmission power, and achieves a longer transmission distance. Attached Figure Description

[0027] Figure 1 This is the overall flowchart of the pulse width compression (PPM) modulation method based on single-photon detection of superconducting nanowires disclosed in this invention.

[0028] Figure 2 This is a schematic diagram of the 16PPM symbol before and after pulse width compression in this implementation;

[0029] Figure 3 The different signal-to-noise ratios (E) in this implementation b Simulation results of ranging error of 16PPM modulation under different compression ratios when photons are uniformly distributed ( / N0) conditions;

[0030] Figure 4 In this embodiment, different signal-to-noise ratios (E) b Simulation results of communication bit error rate of 16PPM modulation under different compression ratios when photons are uniformly distributed ( / N0) conditions. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical problems solved by the present invention and its beneficial effects are also described. It should be noted that the described embodiments are only intended to facilitate understanding of the present invention and do not constitute any limitation thereof.

[0032] With 16PPM modulation, a time slot rate of 9.72MHz, and a transmit digital-to-analog converter (DAC) sampling rate F... s Taking the following as an example, the specific implementation process of the present invention is explained: the carrier laser wavelength is 1540nm, the receiving analog-to-digital converter sampling rate is 80MHz, the fixed frame header is 0x41C1D5B7A0DE18DF, and the frame length is 2250 symbols.

[0033] This embodiment discloses a pulse width compression (PPM) modulation method based on single-photon detection using superconducting nanowires, such as... Figure 1 As shown, the specific implementation steps are as follows:

[0034] Step 1: The transmitting end combines a 16-symbol fixed frame header (0x41C1D5B7A0DE18DF) with 2234 symbol random data to form a data frame of length 2250 symbols. The frame data is then modulated using 16PPM modulation. The relationship between the modulated symbols and the original symbol information is as follows:

[0035] s[i]=rect[in];i,n=0,…,15

[0036] Step 2: The ratio of the digital-to-analog converter sampling rate to the PPM time slot rate is 8. The PPM pulse is compressed by a ratio of 1 / 8, that is, the pulse width is compressed to 1 / 8 of the original. The relationship between the compressed symbol and the original information is as follows:

[0037] s[i]=rect[i-8n]; n=0,…,15; i=0,…,127

[0038] PPM symbols before and after pulse width compression are as follows: Figure 2 As shown.

[0039] Step 3: The digital-to-analog converter converts the pulse-width compressed PPM data into an analog electrical signal at a sampling rate of 77.76MHz. The laser modulator mixes the analog electrical signal with a carrier laser with a wavelength of 1540nm to obtain the PPM modulated optical signal.

[0040] Step 4: The optical power amplifier amplifies the PPM-modulated optical signal. The optical power amplifier accumulates energy when there is no optical signal input and outputs the accumulated energy when a signal is input, amplifying the low-power input signal into a high-power output signal. In other words, it accumulates energy during non-pulse periods and releases the accumulated energy during pulse periods.

[0041] Step 5: The superconducting nanowire single-photon detector at the receiving end converts the received photon signal into an analog electrical signal, which is then converted into a digital signal by an analog-to-digital converter at a sampling rate of 80MHz.

[0042] Step Six: Perform frame synchronization on the digital signal using a fixed frame header 0x41C1D5B7A0DE18DF to achieve PPM symbol synchronization, and demodulate and recover the binary information based on the maximum likelihood decision. Simultaneously, use the frame header information to estimate the frame header reception time using an early-late gate and code ring algorithm to achieve ranging.

[0043] Figure 3 , Figure 4 The curve corresponding to a compression ratio of 1 / 8 represents the simulation results obtained in this embodiment. Simulations were also performed for the bit error rate (BER) and ranging standard deviation under different compression ratios. The results show that the relationship between the BER and ranging standard deviation and the signal-to-noise ratio (SNR) without pulse width compression exhibits a plateau effect; the BER and ranging standard deviation no longer decrease above a certain value. Furthermore, at the same SNR, a smaller compression ratio results in a smaller BER and ranging standard deviation, which can improve transmission distance and power utilization efficiency.

[0044] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A pulse width compression (PPM) modulation method based on single-photon detection using superconducting nanowires, characterized in that: Includes the following steps, Step 1: The transmitting end performs pulse position modulation on the baseband signal data frame containing a specific frame header; Data outside the frame header consists of random binary information. Each modulated PPM symbol contains exactly one pulse, and the pulse's duration represents the duration of a time slot. A PPM symbol is composed of multiple time slots. The relationship between the PPM symbol and the binary information is as follows: s[i]=α*rect[i-n];i,n=0,…,2 N -1;N=0,1, Where α represents the pulse amplitude of the PPM symbol; N represents the number of bits contained in the PPM symbol; n represents the time slot position of the pulse within the PPM symbol, i.e., the decimal value corresponding to the N bits of binary information; rect[i] is a rectangle function: Step 2: Based on the sampling rate F of the digital-to-analog converter (DAC) s With PPM slot rate R slot The PPM pulse width is compressed, and the symbol of the compressed PPM is shown below: Where M1 = F s / R slot M1 represents the oversampling factor, i.e., the number of segments that the PPM pulse can be further divided into. M2 represents the number of high-level 1 segments in the compressed pulse width. Therefore, M2 / M1 is the compression ratio. It is the floor function; Step 3: The digital-to-analog converter converts the pulse-width compressed digital PPM signal generated in Step 2 into an analog PPM electrical signal, and mixes it with the local oscillator to obtain a PPM modulated optical signal. Step 4: The optical power amplifier amplifies the power of the PPM modulated optical signal; The optical power amplifier accumulates energy when there is no optical signal input and outputs the accumulated energy when there is a signal input, amplifying the low-power input signal into a high-power output signal; that is, it accumulates energy during non-pulse periods and releases the accumulated energy during pulse periods. Step 5: The superconducting nanowire single-photon detector at the receiving end converts the received photon signal into an analog electrical signal, which is then converted into a digital signal by an analog-to-digital converter. Step 6: Perform frame synchronization of the digital signal using fixed frame header information to achieve PPM symbol synchronization, and demodulate and recover binary information based on maximum likelihood decision; at the same time, use the fixed frame header information to estimate the frame header reception time through early-late gate and code ring algorithm to achieve ranging; improve transmission distance and ranging accuracy.

Images