DRoF transmission method and system based on ds modulation combined with irregular PAM8 probability shaping

Abstract

The application discloses a DRoF transmission method and system based on DS modulation combined with irregular PAM8 probability shaping, and the method steps are as follows: in the BBU, QAM-OFDM radio frequency signal modulation is completed on bit information, and a Delta-Sigma bandpass modulator is used for bandpass sampling on the radio frequency signal to generate an NRPS-PAM8 signal; after pulse shaping of the coded PS-PAM8 symbol, a modulation signal is generated, and after electro-optical conversion, the modulation signal is transmitted to a remote antenna unit by a single-mode optical fiber; in the RRU, after signal equalization, the received signal is sent to a PAS decoder for decoding, and the symbol generated by the decoding is recovered into an OFDM radio frequency signal by a digital-to-analog converter after bandpass filtering, and finally, wireless transmission is completed through an antenna. The application realizes efficient quantization of the OFDM radio frequency signal, significantly improves the signal quantization efficiency and system spectral efficiency of the DRoF system, and makes the system applicable to future mobile front-haul architectures.

Description

Technical Field

[0001] This invention pertains to modulation and transmission technologies for analog signal digitization, and particularly relates to a DRoF transmission method and system based on DS modulation combined with irregular PAM8 probabilistic shaping. Background Technology

[0002] Fifth-generation mobile communication (5G) has reached a mature commercialization stage, thus sixth-generation mobile communication places higher demands on bandwidth and communication speed compared to 5G. Traditional radio frequency transmission suffers from problems such as high wireless spatial loss and short transmission distance. Centralized Radio Access Network (C-RAN) is a simplified base station based on the 5G transmission architecture. It is inexpensive, highly integrated, and can achieve short-range transmission of microwave / millimeter-wave signals and omnidirectional signal coverage. Digital Optical Radio over Fire (DRoF) is a key technology in the digital mobile fronthaul part of C-RAN. Its baseband unit (BBU) performs digital processing of radio frequency signals, while the remote antenna unit (RRU) is responsible for the recovery and transmission of radio frequency signals. The BBU and RRU are connected by single-mode optical fiber for transmitting digital signals. Low spectral efficiency, as a key challenge of DRoF technology, has become a focus of research in recent years.

[0003] Currently, there are two main methods to improve the spectral efficiency of DRoF: one is efficient digital compression quantization schemes, which use fewer quantization bits to achieve a higher signal-to-quantization noise ratio (SQNR), such as pulse code modulation (PCM), differential pulse code modulation (DPCM), adaptive differential pulse code modulation (ADPCM), quantization noise shaping based on Delta-Sigma, and vector quantization based on K-means clustering; the other is high-order modulation format transmission, which increases the number of bits carried by each transmission symbol to increase the system transmission capacity. Among them, OOK and PAM4, as two mature intensity modulation / direct detection schemes, have achieved great success in commercialization, but there is still room for further improvement in their transmission capacity. Summary of the Invention

[0004] Given the aforementioned application background, developing a scheme combining efficient digital compression quantization technology with a high-order modulation format is of great significance for improving the spectral efficiency of DRoF. Therefore, this invention provides a DRoF transmission method and system based on DS modulation combined with irregular PAM8 probabilistic shaping.

[0005] The present invention provides a DRoF transmission method based on DS modulation combined with irregular PAM8 probabilistic shaping, comprising the following steps:

[0006] Step S1: In the BBU, the bit information is modulated into a QAM-OFDM radio frequency signal, and the radio frequency signal is bandpass sampled by a Delta-Sigma bandpass modulator. The sampled sequence constitutes a quantized bit data sequence.

[0007] Step S2: The quantized bit data sequence enters the probability amplitude shaping encoder to complete the irregular PAM8 probability shaping, generating the NRPS-PAM8 signal.

[0008] Step S3: The NRPS-PAM8 signal enters the root-raised cosine filter to complete pulse shaping and generate a modulation signal. Then, the modulation signal is modulated onto the optical carrier by the electro-optic modulator to obtain an optical signal. The optical signal is transmitted from the single-mode fiber to the demodulation module of the remote antenna unit to complete the photoelectric conversion of the optical signal. After low-pass filtering and signal equalization, the signal processing is completed.

[0009] Step S4: The equalized signal is sent to the probability amplitude shaping decoder to complete the decoding.

[0010] Step S5: The decoded digital signal is sent to the antenna unit after passing through digital narrowband bandpass filtering and digital-to-analog conversion to complete wireless transmission.

[0011] Furthermore, step S1 specifically includes:

[0012] Step S11: Determine the four parameters of the Delta-Sigma bandpass modulator: the order of the loop filter, the oversampling rate, the resolution of the quantizer, and the maximum out-of-band gain, to obtain the Delta-Sigma noise transfer function (NTF).

[0013] Step S12: The OFDM radio frequency signal enters the Delta-Sigma bandpass modulator, and after bandpass sampling and noise shaping, the corresponding binary quantized bit data is obtained.

[0014] Furthermore, step S2 specifically involves:

[0015] Step S21: Determine the pulse amplitude order, coding rate, and LDPC coding length of the probabilistic amplitude shaping encoder.

[0016] Step S22: Set the system's shaping factor λ, with a value range of 0 to 1, to obtain the probability distribution of each symbol in NRPS-PAM8. Unlike the traditional Maxwell-Boltzmann distribution and inverse Maxwell-Boltzmann distribution, the probability distribution of irregular probability shaping is further mapped from the Maxwell-Boltzmann distribution of PAM4. According to the probability distribution formula of a one-dimensional symbol, we get:

[0017]

[0018] Among them, M PAM4 x represents the number of amplitude values ​​in the four-level pulse amplitude modulation. i For each constellation point; therefore, the information entropy after PS-PAM4 shaping is:

[0019]

[0020] In the Maxwell-Boltzmann distribution of PAM4, the probability distributions of positive and negative amplitudes (-3, -1, 1, 3) are symmetrical around the 0 point. Therefore, dividing the probability distribution of positive amplitude (1, 3) by 2 yields the probability distribution of positive amplitude in PAM8, as shown in the following formula:

[0021] P PAM8 (x1)=P PAM8 (x5)=P PAM4 (x1) / 2

[0022] P PAM8 (x3)=P PAM8 (x7)=P PAM4 (x3) / 2

[0023] Therefore, the negative amplitude of PAM8 can be directly obtained from the probability symmetric distribution. Thus, the information entropy of the irregular probability distribution NRPS-PAM8 of PAM8 is:

[0024]

[0025] Step S23: Initialize the CCDM encoder with the positive amplitude probability distribution of NRPS-PAM8; the binary quantized bits output by the Delta-Sigma bandpass modulator enter the CCDM to complete the encoding; the symbols generated by the CCDM encoding are all positive amplitude, and the symbols are interleaved and mapped into the LDPC encoder to complete the symbol allocation and obtain the NRPS-PAM8 signal.

[0026] Furthermore, step S3 specifically includes:

[0027] Step S31: After encoding, the NRPS-PAM8 undergoes root raised cosine roll-off filtering to complete pulse shaping and generate a modulation signal. The modulation signal is then electro-optically modulated and transmitted through a single-mode fiber to the demodulation module of the remote antenna unit for demodulation.

[0028] In step S32, after the optical signal is transmitted to the demodulation module, it first undergoes photoelectric conversion by a photodetector to obtain an electrical signal. Then, the electrical signal is synchronized, low-pass filtered, and equalized to obtain the corresponding symbol.

[0029] Furthermore, step S4 specifically involves:

[0030] Step S41: After the symbols enter the probability amplitude shaping decoder, the log-likelihood ratio (LLR) of each symbol is calculated, and the formula is as follows:

[0031]

[0032] Step S42: The subsequently obtained bits are fed into the LDPC decoder and CCDM decoder to complete joint decoding, resulting in the recovered OFDM radio frequency digital signal.

[0033] The present invention provides a DRoF transmission system based on DS modulation and irregular PAM8 probabilistic shaping, used to implement the aforementioned DRoF transmission method based on DS modulation and irregular PAM8 probabilistic shaping, specifically including:

[0034] Delta-Sigma bandpass modulation module: Connects the baseband signal and the RF modulation module, and is used to perform bandpass sampling on OFDM RF signals to generate digital sampling sequences.

[0035] Probability Amplitude Shaping Encoder Module: Connects to the Delta-Sigma bandpass modulation module and is used to map digital sample sequences to NRPS-PAM8 symbols.

[0036] Electro-optic conversion module: connected to the probability amplitude encoder module, used to modulate the NRPS-PAM8 symbol onto the optical carrier to obtain the optical signal.

[0037] Photoelectric conversion module: Connects to the electro-optical conversion module and is used to demodulate the optical signal to obtain the NRPS-PAM8 electrical signal.

[0038] PAM8 signal filtering and equalization module: Connects to the electro-optical conversion module and is used to perform low-pass filtering and signal equalization on NRPS-PAM8 electrical signals.

[0039] Probability Amplitude Decoder Module: Connects to the PAM8 signal filtering and equalization module, used to decode the equalized NRPS-PAM8 electrical signal and recover it into a digital sampling sequence.

[0040] OFDM RF recovery module: Connects to the probability amplitude decoder module and is used to perform narrowband filtering and digital-to-analog conversion on the digital sampling sequence to generate OFDM analog RF signals.

[0041] Antenna Transmitter Module: Connects to the OFDM RF Recovery Module and is used to transmit OFDM analog RF signals.

[0042] Furthermore, the probability amplitude shaping encoder module includes a CCDM encoder and an LDPC encoder. The digital sampled signal first passes through the CCDM encoder to generate positive amplitude probability symbols, and the positive amplitude probability symbols enter the LDPC encoder to complete symbol allocation to obtain NRPS-PAM8 symbols. The probability amplitude shaping decoder contains a decoder corresponding to the probability amplitude shaping encoder.

[0043] Furthermore, the electro-optical conversion module employs a Mach-Zehnder modulator, and the NRPS-PAM8 symbol is modulated onto the optical carrier to obtain an optical signal.

[0044] The beneficial technical effects of this invention compared to the prior art are as follows:

[0045] This invention utilizes a Delta-Sigma modulator to perform bandpass sampling and noise shaping of OFDM RF signals, avoiding the nonlinear effects of analog signals in electro-optic modulation. Simultaneously, irregular PAM8 probabilistic shaping reduces the computational complexity of probabilistic shaping while achieving highly stable and efficient transmission of digitally sampled signals, enabling high-fidelity recovery of analog signals in remote antenna elements. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the DRoF transmission method based on DS modulation and irregular PAM8 probabilistic shaping according to the present invention.

[0047] Figure 2 The zero-pole diagrams and amplitude responses of the two fourth-order Delta-Sigma bandpass modulators in step S1 are shown.

[0048] Figure 3 The time-domain and frequency-domain output diagrams of the two Delta-Sigma bandpass modulators used in step S1 for bandpass sampling of OFDM RF signals are shown.

[0049] Figure 4 The flowchart for step S2 is the irregular PAM8 probability shaping process.

[0050] Figure 5 The symbol probability distribution diagram under different information entropies in step S2.

[0051] Figure 6 This is a schematic diagram of the DRoF transmission system based on DS modulation and irregular PAM8 probabilistic shaping according to the present invention. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0053] The flow of the DRoF transmission method based on DS modulation and irregular PAM8 probabilistic shaping according to the present invention is as follows: Figure 1 As shown, the specific steps include:

[0054] Step S1: In the BBU, the bit information is modulated into a QAM-OFDM radio frequency signal, and the radio frequency signal is bandpass sampled by a Delta-Sigma bandpass modulator. The sampled sequence constitutes a quantized bit data sequence.

[0055] Step S11: Determine four parameters of the Delta-Sigma bandpass modulator: the order of the loop filter, the oversampling rate, the quantizer resolution, and the maximum out-of-band gain. (See attached instruction manual) Figure 2 The zeros, poles, and amplitude responses of two bandpass filters are shown. The first type has a loop filter order of 4, an oversampling rate of 16, a quantizer resolution of 2, and a maximum out-of-band gain of 1.9. The NTF expression is as follows:

[0056]

[0057] The second type of loop filter is set to order 4, oversampling rate factor 8, quantizer resolution 4, and maximum out-of-band gain 4. The NTF expression is as follows:

[0058]

[0059] Step S12: The OFDM RF signal enters the Delta-Sigma bandpass modulator, and after bandpass sampling and noise shaping, the corresponding binary quantized bit data is obtained. (See attached instruction manual) Figure 3 The time-domain waveforms and the spectrum after noise shaping are shown, generated by passing a 64QAM-OFDM radio frequency signal with a center frequency of 5G and a bandwidth of approximately 1GHz through two bandpass filters.

[0060] Step S2: The quantized bit data sequence enters the probability amplitude shaping encoder to complete irregular PAM8 probability shaping, generating an NRPS-PAM8 signal. (See attached instruction manual) Figure 4 The complete process of performing irregular PAM8 probabilistic shaping is shown in the figure.

[0061] Step S21: Determine the pulse amplitude order, coding rate, and LDPC coding length of the probabilistic amplitude shaping encoder. In this embodiment, the pulse amplitude shaping order is determined to be 8.

[0062] Step S22: Set the system's shaping factor λ, with a value range of 0 to 1, to obtain the probability distribution of each symbol in NRPS-PAM8. (See attached instruction manual) Figure 5 The probability distribution of NRPS-PAM8 symbols under different information entropies is shown.

[0063] Unlike the traditional Maxwell-Boltzmann distribution and the inverse Maxwell-Boltzmann distribution, the probability distribution of irregular probability shaping is further mapped from the Maxwell-Boltzmann distribution of PAM4, according to the probability distribution formula of one-dimensional sign:

[0064]

[0065] Among them, M PAM4 x represents the number of amplitude values ​​in the four-level pulse amplitude modulation. i For each constellation point; therefore, the information entropy after PS-PAM4 shaping is:

[0066]

[0067] In the Maxwell-Boltzmann distribution of PAM4, the probability distributions of positive and negative amplitudes (-3, -1, 1, 3) are symmetrical around the 0 point. Therefore, dividing the probability distribution of positive amplitude (1, 3) by 2 yields the probability distribution of positive amplitude in PAM8, as shown in the following formula:

[0068] P PAM8 (x1)=P PAM8 (x5)=P PAM4 (x1) / 2

[0069] P PAM8 (x3)=P PAM8 (x7)=P PAM4 (x3) / 2

[0070] Therefore, the negative amplitude of PAM8 can be directly obtained from the probability symmetric distribution. Thus, the information entropy of the irregular probability distribution NRPS-PAM8 of PAM8 is:

[0071]

[0072] Step S23: Initialize the CCDM encoder with the positive amplitude probability distribution of NRPS-PAM8; the binary quantized bits output by the Delta-Sigma bandpass modulator enter the CCDM to complete the encoding; the symbols generated by the CCDM encoding are all positive amplitude, and the symbols are interleaved and mapped into the LDPC encoder to complete the symbol allocation and obtain the NRPS-PAM8 signal.

[0073] Step S3: The NRPS-PAM8 signal enters the root-raised cosine filter to complete pulse shaping and generate a modulation signal. Then, the modulation signal is modulated onto the optical carrier by the electro-optic modulator to obtain an optical signal. The optical signal is transmitted from the single-mode fiber to the demodulation module of the remote antenna unit to complete the photoelectric conversion of the optical signal. After low-pass filtering and signal equalization, the signal processing is completed.

[0074] Step S31: After encoding, the NRPS-PAM8 undergoes root raised cosine roll-off filtering to complete pulse shaping and generate a modulation signal. The modulation signal is then electro-optically modulated and transmitted through a single-mode fiber to the demodulation module of the remote antenna unit for demodulation.

[0075] In step S32, after the optical signal is transmitted to the demodulation module, it first undergoes photoelectric conversion by a photodetector to obtain an electrical signal. Then, the electrical signal is synchronized, low-pass filtered, and equalized to obtain the corresponding symbol.

[0076] Step S4: The equalized signal is sent to the probability amplitude shaping decoder to complete the decoding.

[0077] Step S41: After the symbols enter the probability amplitude shaping decoder, the log-likelihood ratio (LLR) of each symbol is calculated, and the formula is as follows:

[0078]

[0079] The recovery bits for each symbol are obtained after soft decision.

[0080] Step S42: The subsequently obtained bits are fed into the LDPC decoder and CCDM decoder to complete joint decoding, resulting in the recovered OFDM radio frequency digital signal.

[0081] Step S5: The decoded digital signal is sent to the antenna unit after passing through digital narrowband bandpass filtering and digital-to-analog conversion to complete wireless transmission.

[0082] Specifically, in order to improve the high-fidelity quantization performance of the DRoF system and enhance its spectral efficiency, the Delta-Sigma bandpass modulator achieves high-fidelity digitization of the radio frequency analog signal through noise shaping technology. Furthermore, the digitized information is subjected to irregular PAM8 probabilistic shaping, which reduces the probability of large-amplitude signals and increases the probability of small-amplitude signals. This further simplifies the system complexity, reduces the average power of the signal, and thus improves the signal's tolerance to fiber nonlinear effects and channel capacity.

[0083] The present invention provides a DRoF transmission system based on DS modulation and irregular PAM8 probabilistic shaping, such as... Figure 6 As shown, the DRoF transmission method based on DS modulation and joint irregular PAM8 probabilistic shaping specifically includes:

[0084] Delta-Sigma bandpass modulation module: Connects the baseband signal and the RF modulation module, and is used to perform bandpass sampling on OFDM RF signals to generate digital sampling sequences.

[0085] Probabilistic Amplitude Shaping (PAS) encoder module: Connects to the Delta-Sigma bandpass modulation module and is used to map digital sample sequences to NRPS-PAM8 symbols.

[0086] Electro-optic conversion module: connected to the probability amplitude encoder module, used to modulate the NRPS-PAM8 symbol onto the optical carrier to obtain the optical signal.

[0087] Photoelectric conversion module: Connects to the electro-optical conversion module and is used to demodulate the optical signal to obtain the NRPS-PAM8 electrical signal.

[0088] PAM8 signal filtering and equalization module: Connects to the electro-optical conversion module and is used to perform low-pass filtering and signal equalization on NRPS-PAM8 electrical signals.

[0089] Probability Amplitude Decoder Module: Connects to the PAM8 signal filtering and equalization module, used to decode the equalized NRPS-PAM8 electrical signal and recover it into a digital sampling sequence.

[0090] OFDM RF recovery module: Connects to the probability amplitude decoder module and is used to perform narrowband filtering and digital-to-analog conversion on the digital sampling sequence to generate OFDM analog RF signals.

[0091] Antenna Transmitter Module: Connects to the OFDM RF Recovery Module and is used to transmit OFDM analog RF signals.

[0092] Furthermore, the probability amplitude shaping encoder module includes a CCDM encoder and an LDPC encoder. The digital sampled signal first passes through the CCDM encoder to generate positive amplitude probability symbols, and the positive amplitude probability symbols enter the LDPC encoder to complete symbol allocation to obtain NRPS-PAM8 symbols. The probability amplitude shaping decoder contains a decoder corresponding to the probability amplitude shaping encoder.

[0093] Furthermore, the electro-optical conversion module employs a Mach-Zehnder modulator, and the NRPS-PAM8 symbol is modulated onto the optical carrier to obtain an optical signal.

[0094] In summary, this invention proposes a DRoF transmission method based on Delta-Sigma modulation combined with irregular PAM8 probabilistic shaping. By combining a Delta-Sigma bandpass modulator and irregular PAM8 probabilistic shaping, high-fidelity quantization and high-frequency efficient transmission of RF signals can be effectively achieved. Compared with existing DRoF transmission schemes, this invention can effectively improve the signal-to-quantization noise ratio of RF signals under single-bit / double-bit quantization, thereby improving spectral efficiency. Furthermore, in optical transmission, probabilistic shaping of the higher-order modulation format reduces the nonlinear effects of the signal, achieving improved bit error rate performance and receiver sensitivity performance.

Claims

1. A DRoF transmission method based on DS modulation combined with irregular PAM8 probabilistic shaping, characterized in that, Includes the following steps: Step S1: In the BBU, the bit information is modulated into a QAM-OFDM radio frequency signal, and the radio frequency signal is sampled by a Delta-Sigma bandpass modulator. The sampled sequence constitutes a quantized bit data sequence. Step S2: The quantized bit data sequence enters the probability amplitude shaping encoder to complete the irregular PAM8 probability shaping, generating the NRPS-PAM8 signal; Step S21: Determine the pulse amplitude order, coding rate, and LDPC coding length of the probabilistic amplitude shaping encoder; Step S22: Set the system's shaping factor The value range is Thus, the probability distribution of each symbol in NRPS-PAM8 is obtained; unlike the traditional Maxwell-Boltzmann distribution and inverse Maxwell-Boltzmann distribution, the probability distribution of irregular probability shaping is further mapped from the Maxwell-Boltzmann distribution of PAM4, according to the probability distribution formula of one-dimensional symbols: ； in, This represents the number of amplitude values ​​in the four-level pulse amplitude modulation. For each constellation point; therefore, the information entropy after PS-PAM4 shaping is: ； In the Maxwell-Boltzmann distribution of PAM4, the probability distributions of positive and negative amplitudes (-3, -1, 1, 3) are symmetrical around the 0 point. Therefore, dividing the probability distribution of positive amplitude (1, 3) by 2 yields the probability distribution of positive amplitude in PAM8, as shown in the following formula: ； Therefore, the negative amplitude of PAM8 can be directly obtained from the probability symmetric distribution. Thus, the information entropy of the irregular probability distribution NRPS-PAM8 of PAM8 is: ； Step S23: Initialize the CCDM encoder with the positive amplitude probability distribution of NRPS-PAM8; the binary quantized bits output by the Delta-Sigma bandpass modulator enter the CCDM to complete the encoding; the symbols generated by the CCDM encoding are all positive amplitude, and the symbols are interleaved and mapped into the LDPC encoder to complete the symbol allocation and obtain the NRPS-PAM8 signal; Step S3: The NRPS-PAM8 signal enters the root-raised cosine filter to complete pulse shaping and generate a modulation signal. Then, the modulation signal is modulated onto the optical carrier by the electro-optic modulator to obtain an optical signal. The optical signal is transmitted from the single-mode fiber to the demodulation module of the remote antenna unit to complete the photoelectric conversion of the optical signal. After low-pass filtering and signal equalization, the signal processing is completed. Step S4: The equalized signal is sent to the probability amplitude shaping decoder to complete the decoding; Step S41: After the symbols enter the probability amplitude shaping decoder, the log-likelihood ratio (LLR) of each symbol is calculated, and the formula is as follows: ； Step S42: The subsequently obtained bits are fed into the LDPC decoder and CCDM decoder to complete joint decoding, and the recovered OFDM radio frequency digital signal is obtained; Step S5: The decoded digital signal is sent to the antenna unit after passing through digital narrowband bandpass filtering and digital-to-analog conversion to complete wireless transmission.

2. The DRoF transmission method based on DS modulation and irregular PAM8 probabilistic shaping according to claim 1, characterized in that, Step S1 specifically involves: Step S11: Determine the four parameters of the Delta-Sigma bandpass modulator: the order of the loop filter, the oversampling rate, the resolution of the quantizer, and the maximum out-of-band gain, and obtain the Delta-Sigma noise transfer function (NTF). Step S12: The OFDM radio frequency signal enters the Delta-Sigma bandpass modulator, and after bandpass sampling and noise shaping, the corresponding binary quantized bit data is obtained.

3. The DRoF transmission method based on DS modulation and irregular PAM8 probabilistic shaping according to claim 1, characterized in that, Step S3 specifically involves: Step S31: After encoding, the NRPS-PAM8 undergoes root raised cosine roll-off filtering to complete pulse shaping and generate a modulation signal. The modulation signal is then electro-optically modulated and transmitted through a single-mode fiber to the demodulation module of the remote antenna unit for demodulation. In step S32, after the optical signal is transmitted to the demodulation module, it first undergoes photoelectric conversion by a photodetector to obtain an electrical signal. Then, the electrical signal is synchronized, low-pass filtered, and equalized to obtain the corresponding symbol.

4. A DRoF transmission system based on DS modulation and irregular PAM8 probabilistic shaping, used to implement the DRoF transmission method based on DS modulation and irregular PAM8 probabilistic shaping as described in any one of claims 1-3, characterized in that, include: Delta-Sigma bandpass modulation module: Connects the baseband signal and the RF modulation module, and is used to perform bandpass sampling of OFDM RF signals to generate digital sampling sequences; Probability Amplitude Shaping Encoder Module: Connects to the Delta-Sigma bandpass modulation module and is used to map digital sampling sequences to NRPS-PAM8 symbols; Electro-optic conversion module: connected to the probability amplitude encoder module, used to modulate NRPS-PAM8 symbols onto an optical carrier to obtain the optical signal; Photoelectric conversion module: Connects to the electro-optical conversion module and is used to demodulate the optical signal to obtain the NRPS-PAM8 electrical signal; PAM8 signal filtering and equalization module: connected to the electro-optical conversion module, used to perform low-pass filtering and signal equalization on NRPS-PAM8 electrical signals; Probability Amplitude Decoder Module: Connects to the PAM8 signal filtering and equalization module, used to decode the equalized NRPS-PAM8 electrical signal and recover it into a digital sampling sequence; OFDM RF recovery module: Connects to the probability amplitude decoder module and is used to perform narrowband filtering and digital-to-analog conversion on the digital sampling sequence to generate OFDM analog RF signals; Antenna Transmitter Module: Connects to the OFDM RF Recovery Module and is used to transmit OFDM analog RF signals.

5. A DRoF transmission system based on DS modulation and irregular PAM8 probabilistic shaping according to claim 4, characterized in that, The probability amplitude shaping encoder module includes a CCDM encoder and an LDPC encoder. The digital sampled signal first passes through the CCDM encoder to generate positive amplitude probability symbols, and the positive amplitude probability symbols enter the LDPC encoder to complete symbol allocation to obtain NRPS-PAM8 symbols. The probability amplitude shaping decoder contains a decoder corresponding to the probability amplitude shaping encoder.

6. A DRoF transmission system based on DS modulation and irregular PAM8 probabilistic shaping according to claim 4, characterized in that, The electro-optic conversion module uses a Mach-Zehnder modulator, and the NRPS-PAM8 symbol is modulated onto the optical carrier to obtain an optical signal.

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