Device and method for realizing PON (Passive Optical Network) rate regulation based on Polar modulation

Abstract

The invention provides a device and method for achieving PON rate adjustment based on Polar modulation, and relates to the technical field of passive optical networks, the device comprises a first external cavity laser, a second external cavity laser, a dual-polarization phase quadrature modulator, an arbitrary waveform generator, an erbium-doped optical fiber amplifier, a single-mode optical fiber, a variable optical attenuator, a coherent receiver and an oscilloscope; the method comprises the following steps: dynamically adjusting an information bit number A, splicing check bits to form total information bits, and optimizing the distribution of the information bits and freezing bits according to an optical signal channel sorting result; the method comprises the following steps: performing polarization coding on a signal at a coding end, and mapping the signal into a 16QAM coding symbol sequence by adopting a Polar modulation technology; at a receiving end, LLR is calculated, when the list width reaches a set value, path metric values of all paths are calculated and trimming operation is executed, and after decoding is completed, CRC verification detection is used for L candidate paths. According to the invention, the transmission rates of different optical network units can be flexibly regulated and controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of passive optical networks, and in particular to a device and method for realizing PON rate adjustment based on Polar modulation. Background Art

[0002] Driven by the rapid development of services such as the Internet of Things, high-definition streaming media, and mixed reality, passive optical networks (PONs) have played a crucial role in providing the last-mile connection for end-users. With the standardization of 50G PON, the peak rate of the next-generation PON may reach 200 Gb / s, which may require coherent optical technology and advanced digital signal processing (DSP) algorithms to maintain high power budget requirements. In the current PON architecture, all optical network units (ONUs) receive the same downstream signal from the optical line terminal (OLT). The peak rate is limited by the worst-case power budget, which is mainly related to the maximum supported optical path loss (OPL). In the existing optical distribution network (ODN), it is difficult to transmit the same downstream signal to edge ONUs with a large OPL at such a high data transmission rate. At the same time, using the same data transmission rate among ONUs in the downstream link may also lead to waste of spectrum resources for ONUs with a small OPL and good channel conditions.

[0003] Currently, several methods have been proposed to adjust the information rate among ONUs. The most direct method is based on adaptive coding and modulation (ACM). The ACM method uses two-level, three-level, and four-level pulse amplitude modulation (PAM) with a fixed symbol rate, as well as low-density parity-check codes (LDPCs) derived from the mother code through shortening and puncturing. To further expand the adjustment range of the data rate, subcarrier multiplexing technology is used for both upstream and downstream signals in the coherent PON scheme. Since the coherent receiver has a fixed frequency selectivity, the ONU can select the desired subcarrier for detection. The subcarrier multiplexing scheme also helps to extract the carrier phase information, thereby reducing the requirement for the laser linewidth and the cost of the laser at the ONU end. Probability shaping (PS) and geometric shaping (GS) optimize the modulation format through different mechanisms to adjust the signal information rate and improve the channel utilization rate. However, the above schemes may all require adding a digital signal processor (DSP) or a long code block decoder at the ONU end, increasing the computational complexity or the cost per end-user. Summary of the Invention

[0004] The object of the present invention is to propose a device for realizing PON rate adjustment based on Polar modulation to solve the problem of information rate adjustment in PON systems under different transmission conditions, including: a first external cavity laser, a second external cavity laser, a dual-polarization quadrature phase modulator, an arbitrary waveform generator, an erbium-doped fiber amplifier, a single-mode fiber, a variable optical attenuator, a coherent receiver, and an oscilloscope; The first external cavity laser is used as a light source, and an optical signal is input into the optical input port of the dual-polarization quadrature modulator; an arbitrary waveform generator loads a pre-generated 16QAM coded symbol sequence offline. The analog electrical signal generated by the arbitrary waveform generator is modulated into an optical signal by the dual-polarization quadrature modulator. After being amplified by an erbium-doped fiber amplifier, the modulated optical signal is transmitted through a single-mode fiber to a variable optical attenuator for adjustment. The adjusted optical signal and the optical signal output by the second external cavity laser are input into a coherent receiver, and the signal output by the coherent receiver is sampled by an oscilloscope, and the transmitted signal is restored through offline signal processing.

[0005] Furthermore, the arbitrary waveform generator has four channels.

[0006] Furthermore, the wavelength of the first external cavity laser is 1550 nm and the line width is 100 kHz.

[0007] Furthermore, four drivers are integrated inside the dual-polarization quadrature modulator.

[0008] The present invention also proposes a method for realizing PON rate adjustment based on Polar modulation, which is realized based on the above device, and includes: Evaluating the received optical signal channels and sorting each polarization channel; Dynamically adjusting the number of signal bits A, splicing parity bits to form total information bits, and then optimizing the distribution of information bits and frozen bits according to the sorting result; Using the generating matrix Performing polarization coding on the input information, where is the reverse permutation matrix, F is the basic kernel matrix, and N is the code length; after the obtained polarization codeword is adaptively processed, it is mapped into a 16QAM coded symbol sequence by using Polar modulation technology; the arbitrary waveform generator loads the 16QAM coded symbol sequence; The signal output through the device is subjected to signal restoration through offline signal processing. Among them, the decoding process of the offline signal processing includes: calculating the log-likelihood ratio LLR of each transmitted bit. In successive cancellation list decoding, for each unfrozen bit, two different result expansion paths of 0 and 1 need to be considered. When the list width L reaches the set value, calculate and sort the path metric values PM of all paths and perform pruning operations. After decoding is completed, CRC check is performed on the L candidate paths to obtain the decoded signal.

[0009] Furthermore, Sorting each polarization channel by using the Bachmann parameter. The smaller the Bachmann parameter, the more reliable the channel.

[0010] Furthermore, the LLR is defined as: , Among them, represents the log-likelihood ratio of, represents the i-th bit of the signal, represents the probability that the i-th bit of the signal is 0, represents the probability that the i-th bit of the signal is 1, and y represents the signal.

[0011] The present invention also provides a computer-readable storage medium storing a computer program, and when the computer program is executed by a processor, it implements the above method for adjusting the PON rate based on Polar modulation.

[0012] The present invention also provides an electronic device, including a processor and a memory, the processor is interconnected with the memory, wherein the memory is used to store a computer program, the computer program includes computer-readable instructions, and the processor is configured to call the computer-readable instructions to execute the above method for adjusting the PON rate based on Polar modulation.

[0013] The present invention also provides a computer program product, including a computer program / instructions, and when the computer program / instructions are executed by a processor, it implements the steps of the above method for adjusting the PON rate based on Polar modulation.

[0014] The beneficial effects brought by the technical solution provided by the present invention are: The present invention utilizes the polarization principle to realize the channel reliability ranking, and with the help of the CRC-aided successive cancellation list (CRC-SCL) decoding algorithm, it can flexibly adjust the transmission rates of different optical network units (ONUs) on the premise of ensuring equivalent or better performance. Description of the Drawings

[0015] Figure 1 is the structural diagram of the device for adjusting the PON rate based on Polar modulation according to the embodiment of the present invention; Figure 2 is the comparison diagram of the BER of two decoding algorithms CRC-SCL and SC of Polar when the code rate is in the embodiment of the present invention; Figure 3 is the comparison diagram of the BER of two decoding algorithms CRC-SCL and SC of Polar when the code rate is in the embodiment of the present invention; Figure 4 is the block diagram of an electronic device in an exemplary embodiment of the first embodiment of the present invention. Detailed Embodiments

[0016] To make the objectives, technical solutions and advantages of the present invention clearer, the embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0017] The structural diagram of the device for implementing PON rate adjustment based on Polar modulation in the embodiments of the present invention is as Figure 1 , and specifically includes: A first external cavity laser, a second external cavity laser, a dual-polarization quadrature modulator, an arbitrary waveform generator, an erbium-doped fiber amplifier, a single-mode fiber, a variable optical attenuator, a coherent receiver, and an oscilloscope.

[0018] In the embodiments of the present invention, the working wavelength of the first external cavity laser is 1550 nm, and the line width is about 100 kHz. The arbitrary waveform generator has four channels, and the dual-polarization quadrature modulator integrates four drivers inside to achieve independent modulation of dual-polarized signals. Four different code rate configurations are preset, and their information bit rates are 100 Gb / s, 133.33 Gb / s, 150 Gb / s, and 166.67 Gb / s respectively. In addition, the device can dynamically adjust the preset rate range according to the actually measured signal-to-noise ratio of the channel and other transmission conditions, so as to achieve the optimal data transmission efficiency while ensuring the transmission performance.

[0019] The working principle of the device is as follows: The first external cavity laser is used as a light source, and the optical signal is input into the optical input port of the dual-polarization quadrature modulator; the arbitrary waveform generator loads the 16QAM coded symbol sequence generated offline in advance, and the baud rate of the 16QAM signal is set to 25 Gbaud, so that the maximum original data rate achieved on the two polarization components reaches 200 Gb / s. The analog electrical signal generated by the arbitrary waveform generator is modulated into an optical signal by the dual-polarization quadrature modulator. After being amplified by the erbium-doped fiber amplifier, the modulated optical signal is transmitted by a standard single-mode fiber of more than 48 km to the variable optical attenuator for fine adjustment (adjusted in steps of 0.3 dB) to obtain an appropriate optical power at the receiving end. The adjusted optical signal and the optical signal output by the second external cavity laser are input into the coherent receiver. The second external cavity laser is used as a local oscillator. The signal output by the coherent receiver is sampled at high speed by the oscilloscope, the transmitted signal is restored through offline signal processing, and the performance of the device is evaluated.

[0020] The traditional application of flexible forward error correction (FEC) coding to flexible rate PON combines different modulation techniques with low density parity check codes (LDPC codes). Among them, the LDPC code is obtained by shortening S bits and puncturing P bits, and the codeword length is fixed at 115,200 (i.e., information K + parity check M) bits. The net rate can be flexibly adjusted by calculating K / (K + M). However, the flexible FEC coding achieved by this method comes at the cost of sacrificing coding gain; at the same time, the wider the rate adjustment range, the more the total number of shortened and punctured bits, and the greater the coding gain loss. As a new FEC coding, Polar codes have been adopted by 5G new radio as the channel coding for control information. The present invention realizes flexible adjustment of the PON rate based on Polar modulation technology. For a Polar coding, it must satisfy , that is, N must be an integer power of 2; K is the number of signal bits A plus the number of parity check bits, and N represents the code length. By adjusting the number of signal bits A, the code rate can be varied in the range from 0 to 1. This flexible adjustment method avoids operations of reducing or increasing the codeword length, and reduces the loss of coding gain to a certain extent. The coding gain of Polar codes mainly depends on the effect of channel polarization. Usually, a lower code rate will select more high-quality channels, thereby improving the coding gain; while a higher code rate may use some lower-quality channels, resulting in a decrease in coding gain. A method for realizing PON rate adjustment based on Polar modulation implemented by the above-mentioned device of the present invention includes: Evaluating the received optical signal channel and sorting each polarization channel. In Polar coding, the received optical signal channel is evaluated by using the Bhattacharyya parameter or other channel reliability metrics. The smaller the Bhattacharyya parameter, the more reliable the channel.

[0021] Dynamically adjusting the number of signal bits A, splicing the parity check bits to form the total information bits, and then optimizing the distribution of information bits and frozen bits according to the sorting result, and using as many high-quality channels as possible to transmit the information bits, so as to improve system reliability and flexibly change the rate.

[0022] Using a generator matrix at the coding end to perform polarization coding on the input information, where is the reverse permutation matrix, F is the basic kernel matrix, and N is the code length; after the obtained polarization codeword is adaptively processed, it is mapped to a 16QAM coded symbol sequence or other high-order modulation format signals by using Polar modulation technology, so as to achieve flexible regulation at a preset information rate value (such as 100 Gb / s, 133.33 Gb / s, 150 Gb / s, 166.67 Gb / s, etc.).

[0023] The 16QAM coded symbol sequence generated by the arbitrary waveform generator is loaded. The first external cavity laser is used as the light source, and the optical signal is input into the optical input port of the dual-polarization quadrature modulator. The analog electrical signal generated by the arbitrary waveform generator is modulated into an optical signal by the dual-polarization quadrature modulator. After being amplified by the erbium-doped fiber amplifier, the modulated optical signal is transmitted by a single-mode fiber to the variable optical attenuator for adjustment. The adjusted optical signal and the optical signal output by the second external cavity laser are input into the coherent receiver. The signal output by the coherent receiver is sampled by an oscilloscope, and the transmitted signal is restored through offline signal processing.

[0024] The offline signal processing specifically includes: performing dispersion compensation on the signal, signal down-conversion, signal synchronization, signal frequency estimation, using the constant modulus algorithm (CMA) and the decision-directed least mean square error algorithm (DDLMS) for adaptive filtering, then performing quadrature amplitude modulation demapping, and finally performing forward error correction decoding.

[0025] The decoding process is as follows: At the receiving end, the log-likelihood ratio LLR of each transmitted bit is calculated, which is used for the update and iteration of the subsequent signal soft information and provides key information for soft-decision-based detection, thereby improving the overall decision accuracy. The LLR is defined as: , where represents the log-likelihood ratio of the i-th bit of the signal, represents the probability that the i-th bit of the signal is 0, represents the probability that the i-th bit of the signal is 1, and y represents the signal. In successive cancellation list decoding, for each unfrozen bit, two different result expansion paths of 0 and 1 need to be considered. When the list width L reaches the set value, the path metric values PM of all paths are calculated, sorted, and a pruning operation is performed to retain the most likely paths while keeping the complexity and delay controllable. After decoding is completed, CRC check detection is performed for the L candidate paths. This mechanism enables SCL decoding to not only rely on the path metric but also utilize the verification of the overall consistency of the codeword, thereby achieving approximate maximum likelihood (ML) decoding performance and significantly improving the overall decoding accuracy and system stability.

[0026] According to the preset adjustment strategy and real-time feedback data, the encoding, mapping, and transmission parameters in the Polar modulation process can be dynamically adjusted, so that no major changes need to be made to the decoding end. This design not only simplifies the hardware implementation but also significantly expands the applicable range and compatibility of the system. Through closed-loop control, the downstream signal can match the optimal rate according to the actual channel condition of the ONU, thereby realizing flexible information rate switching of the overall PON system under different transmission conditions.

[0027] Through simulation and experiment, the present invention conducts a comparative analysis of BLER and BER for Polar CRC-SCL algorithms with total code lengths of approximately 500 and 1000, as well as two LDPC decoding algorithms, at four preset code rates. The results show that the Polar decoder using cyclic redundancy check and successive cancellation list algorithm has better or comparable receiving sensitivity to the LDPC decoder at short code block lengths and various code rates.

[0028] Figure 2 and Figure 3 shows the comparison of BER performance between Polar CRC-SCL and Polar SC with different list widths at code rates of and respectively. Among them, SC can be regarded as the SCL algorithm with a list width of 1, without path sorting and pruning, and only decodes bit by bit through a single path. Therefore, path selection or intermediate bit decoding errors will significantly affect the decoding performance. While SCL obtains a greater improvement in algorithm performance by introducing the list width. Specifically, Figure 2 when the code rate is in , the received optical power of SCL with a list width of 8 is improved by approximately 1.65 dB compared to SC at Figure 3 when the code rate is in Figure 2 and Figure 3 , the received optical power is improved by approximately 1.08 dB. Combining the test results in , when using the code rate and cooperating with the CRC-SCL decoder (list width nL = 8), its received optical power is the lowest (the decoding performance is the best); in contrast, when using a higher code rate and the SC decoder configuration, its received optical power is higher, and the performance gap between the two is approximately 6.45 dB.

[0029] Therefore, when the channel condition is poor (such as the harsh environment at the ONU side), the Polar CRC-SCL with a code rate of and a wider list width can be allocated; while when the channel condition is good (the good environment at the ONU side), the Polar SC with a code rate of or even higher or the Polar CRC-SCL with a smaller list width can be allocated. In summary, the present invention can flexibly achieve the dynamic adjustment of the passive optical network (PON) rate and improve the spectrum resource utilization rate by adjusting the Polar decoding algorithm and the selection of the number of information bits A, providing a wider configuration combination and code rate adjustment range, showing significant technical advantages.

[0030] In an exemplary embodiment, a computer-readable storage medium is provided, which stores a computer program. When the computer program is executed by a processor, the method for realizing PON rate adjustment based on Polar modulation described above is implemented.

[0031] Please refer to Figure 4 , in an exemplary embodiment, an electronic device is further provided, which includes at least one processor, at least one memory, and at least one communication bus.

[0032] Among them, a computer program is stored on the memory. The computer program includes computer-readable instructions. The processor calls the computer-readable instructions stored in the memory through the communication bus to execute the method for realizing PON rate adjustment based on Polar modulation described above.

[0033] In an exemplary embodiment, a computer program product is proposed, which includes a computer program / instructions. When the computer program / instructions are executed by a processor, the steps of the method for realizing PON rate adjustment based on Polar modulation described above are implemented.

[0034] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A device for implementing PON rate adjustment based on Polar modulation, characterized in that: The device comprises: a first external cavity laser, a second external cavity laser, a dual polarization phase quadrature modulator, an arbitrary waveform generator, an erbium-doped fiber amplifier, a single-mode optical fiber, a variable optical attenuator, a coherent receiver, and an oscilloscope; The first external cavity laser is used as a light source to input an optical signal into the optical input port of a dual-polarization phase quadrature modulator; the arbitrary waveform generator is loaded with a 16QAM coded symbol sequence generated offline in advance, and the analog electrical signal generated by the arbitrary waveform generator is modulated into an optical signal by the dual-polarization phase quadrature modulator. The modulated optical signal is amplified by an erbium-doped fiber amplifier and then transmitted to a variable optical attenuator by a single-mode optical fiber for adjustment. The adjusted optical signal and the optical signal output by the second external cavity laser are input into a coherent receiver. The signal output by the coherent receiver is sampled by an oscilloscope, and the transmission signal is restored by offline signal processing.

2. The device for implementing PON rate adjustment based on Polar modulation according to claim 1, characterized in that: The arbitrary waveform generator has four channels.

3. The device for implementing PON rate adjustment based on Polar modulation according to claim 1, characterized in that: The first external cavity laser has a wavelength of 1550nm and a line width of 100kHz.

4. The device for implementing PON rate adjustment based on Polar modulation according to claim 1, characterized in that: The dual polarization phase quadrature modulator integrates four drivers.

5. A method for implementing PON rate adjustment based on Polar modulation, characterized in that: The device according to any one of claims 1 to 4 is implemented, comprising: Evaluate the received optical signal channels and sort the polarization channels; Dynamically adjust the number of signal bits A, splice the check bits to form the total information bits, and then optimize the distribution of information bits and frozen bits according to the sorting results; Using the generator matrix Polar encoding is performed on the input information, where is the inversion permutation matrix, F is the basic core matrix, and N is the code length; the obtained polarization codeword is mapped into a 16QAM coded symbol sequence using Polar modulation technology after adaptation processing; the arbitrary waveform generator is loaded with the 16QAM coded symbol sequence; The signal output by the device is processed offline for signal recovery, wherein the decoding process of the offline signal processing includes: calculating the log-likelihood ratio LLR of each transmitted bit, and in the continuous cancellation list decoding, two different result extension paths of 0 and 1 need to be considered for each unfrozen bit, when the list width L reaches the set value, the path metric values ​​PM of all paths are calculated and sorted and a pruning operation is performed, and after the decoding is completed, the CRC check is used for the L candidate paths to obtain a decoded signal.

6. The method for implementing PON rate adjustment based on Polar modulation according to claim 5, characterized in that: The Bachmann parameters are used to sort the polarization channels. The smaller the Bachmann parameter, the more reliable the channel.

7. The method for implementing PON rate adjustment based on Polar modulation according to claim 5, characterized in that: LLR is defined as: ， in, express The log-likelihood ratio of represents the i-th bit of the signal, represents the probability that the i-th bit of the signal is 0, represents the probability that the i-th bit of the signal is 1, and y represents the signal.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 5 to 7 is implemented.

9. An electronic device, characterized in that: It comprises a processor and a memory, wherein the processor and the memory are interconnected, wherein the memory is used to store a computer program, the computer program comprises computer-readable instructions, and the processor is configured to call the computer-readable instructions to execute the method as described in any one of claims 5-7.

10. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 5 to 7 are implemented.

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