Non-Orthogonal Multiple Access-Based Passive Optical Network Information Transmission System and Method

Abstract

The present invention discloses a passive optical network information transmission system and method based on non-orthogonal multiple access. Based on the channel conditions of different ONU users or different ONU groups, i.e., the variation of the optical path loss (OPL), the access rate of the adaptive line is achieved by adjusting the transmission power and security level between different ONU users or different ONU groups. The transmission power is achieved by digitally adjusting the Euclidean distance of the modulation format allocated to each ONU or ONU group in the OLT; the security level is achieved by digitally adjusting the code rate of the forward error correction coding (FEC) between different ONU users or different ONU groups in the OLT. Therefore, the passive optical network security method based on non-orthogonal multiple access considers the optical fiber channel state between different OLT-ONUs, and sets different power allocations and different security levels according to different channel states, so that the NG-PON significantly improves the security capacity of the system while achieving an adaptive access rate.

Description

Technical Field

[0001] The present invention belongs to the fields of optical communication technology and optical network, and particularly relates to a passive optical network information transmission system and method based on non-orthogonal multiple access. Background Art

[0002] With the increasing number of service types with various traffic patterns such as video surveillance, virtual reality, and augmented reality, network traffic has grown explosively. A large-capacity fiber access network can meet the requirements of large bandwidth in the telecommunication network. Among them, the next-generation passive optical network (NG-PON) has attracted much attention as an effective solution to the "last mile" due to its advantages such as low cost, high rate, long transmission distance, and support for multiple service types. Among them, the PON based on time-division multiplexing (TDM-PON) is a typical solution. In TDM-PON, the optical line terminal (OLT) and the optical network units (ONUs) subordinate to it are connected through an optical distribution network (ODN), which can make more effective use of the bandwidth. However, in the existing NG-PON transmission system, due to the broadcast characteristic of the downstream TDM-PON, there is a high probability that there are illegal ONUs in the network or eavesdroppers in the optical fiber who demodulate the optical signal into digital data, which are all potential security hazards. The typical security protection methods in NG-PON mainly include the physical layer encryption method using chaos technology, and the digital layer cipher implemented by encrypting data using computing resources at the second layer or higher layer, such as the Advanced Encryption Standard (AES).

[0003] On the other hand, the current NG-PON system provides the same access (guaranteed) data rate for all ONUs. However, since the PON system is naturally a point-to-multipoint (PtMP) architecture, the NG-PON system is limited by the optical network unit (ONU) with the worst performance. To solve this problem, non-orthogonal multiple access (NOMA) has been considered a new and promising multiple access technology in NG-PON in recent years. As a typical NOMA scheme, power-domain based (PD-NOMA) superimposes the signals of multiple ONU users on the same time-frequency resource at the transmitter, and can optimize the power distribution ratio (PDR) according to the quality of service (QoS) of each ONU user, and performs multi-ONU user detection at the receiver according to the successive interference cancellation (SIC) algorithm.

[0004] However, there has been no research on network security protection issues in NG-PON based on NOMA yet. Summary of the Invention

[0005] In order to achieve higher security while having a flexible access data rate in NG-PON, the present invention provides a passive optical network information transmission system based on non-orthogonal multiple access (NOMA-PON), and a passive optical network information transmission method based on the NOMA-PON system. The data protection scheme in the NG-PON based on NOMA of the present invention provides characteristics of communication systems such as high spectral efficiency, low latency, improved fairness, and high security guarantee.

[0006] The passive optical network information transmission system (NOMA-PON) based on non-orthogonal multiple access of the present invention mainly includes an optical transmitter part of the OLT, an optical fiber link part, and an optical receiver part of the ONU, which are connected in sequence.

[0007] The optical transmitter part of the OLT includes a DSP module of the OLT, a digital-to-analog converter DAC, and an electro-optical modulator connected in sequence, and a laser connected to the electro-optical modulator.

[0008] The DSP module of the OLT includes a binary data input module, different ONU coding rates set according to different security levels, and different ONU modulation mappings set according to different data rates.

[0009] The optical receiver part of the ONU includes a photodetector, an analog-to-digital converter ADC, and a DSP module of the ONU connected in sequence.

[0010] The DSP module of the ONU includes a symbol synchronization and channel equalization module, different ONU demodulation mappings set according to different data rates, different ONU decoding set according to different security levels, and a binary data output module connected in sequence.

[0011] The optical fiber link part includes an optical fiber amplifier and a common standard single-mode optical fiber.

[0012] The DSP module of the OLT adjusts the binary bit data according to different security levels and different data rates into a hybrid structure carrying flexible modulation formats and code rates. After the DSP electrical signal passes through the hybrid structure, it drives the electro-optical modulator through the DAC. The laser generates an optical carrier. Then, after being transmitted through the optical fiber amplifier and the common standard single-mode optical fiber, in the receiver of the ONU, first, the photodetector converts the optical signal into an electrical signal. Then, after passing through the ADC, the electrical signal is processed by the DSP at the ONU end. The symbol synchronization and channel equalization module synchronizes the symbols between the DAC of the OLT transmitter and the ADC of each ONU receiver. Finally, each ONU recovers its own ideal data.

[0013] Implementing NG-PON with adaptive access rate and high security performance in the operator's network also improves the overall access capacity of the telecommunications network. Naturally, PON is a quasi-static distributed network, and different ONU users are distributed in different locations, which means that some ONU users have good channel conditions and there is a surplus in the signal-to-noise ratio of the overall NG-PON.

[0014] The present invention is a passive optical network information transmission method based on the NOMA-PON system. Utilizing the surplus in the signal-to-noise ratio of NG-PON, for ONU users with relatively high signal-to-noise ratio, higher-order modulation formats and higher coding rate FEC are allocated to achieve higher data rates and security levels, and vice versa;

[0015] Specifically, according to the different requirements for access rates of different ONUs in the NOMA-PON system, for different modulation formats of different ONUs in the OLT, power-domain superposition of modulation formats is performed at the transmitter end. For example, a higher-order modulation format is sent at the transmitter end of the OLT and transmitted through the ODN; at the receiving end of the ONU, the Euclidean distance is appropriately selected for hard decision according to the channel conditions to recover its ideal signal. For example, an ONU with poor channel conditions only needs to recover the lower-order modulation format from the received higher-order modulation, while an ONU with good channel conditions regards the signals received by other ONUs as noise and recovers the higher modulation format according to its channel conditions in the total received signal;

[0016] The coding rate FEC realizes different LDPC FEC coding rates varying between 0 and 1 by shortening and puncturing the mother code based on the low-density parity-check code (LDPC) in the OLT.

[0017] The present invention uses a shortening method consistent with G.9804.2 at the end of the information part of the mother code.

[0018] The passive optical network information transmission method of the present invention, where different ONUs have different security level requirements, and the meaning of different security levels is that the difference in capacity between legitimate ONUs and eavesdropping ONUs is maximized under the optical signal-to-noise ratio (OSNR) limit that satisfies the output bit error rate, such as 1e-15.

[0019] The coding rate FEC is mainly based on LDPC codes, and the mother code uses LDPC(17664,14592) defined in IEEE 802.3ca, that is, a codeword of length 17664 consists of 14592 information bits and 3072 parity-check bits.

[0020] The LDPC codes of the coding rate FEC are all generated by the same mother parity-check matrix, and the specific method for generating different code rates is as follows:

[0021] Let the information bit positions of the LDPC mother code be M, and the parity-check bit positions be N. The mother codeword is then shortened and punctured to generate various subcodes. After shortening the information bit positions by P and puncturing the parity-check bit positions by S, the sizes of the information bits become M - P and the parity-check bits become N - S, respectively, so as to achieve adjustment between different data coding rates from 0 to 1.

[0022] The shortening of the information bit positions is achieved by reducing the number of information bits fed into the FEC encoder, while fixing the remaining bits to zero. These fixed shortened bits are not transmitted. Before sending the data to the FEC decoder, the mother code is reinserted at the receiving end. Since the values on the shortened bits are determined to be zero, a relatively large log-likelihood ratio is set, thereby improving the error-correcting ability of this shortened code.

[0023] On the other hand, the parity-check bits are punctured at the end of the mother code, and the punctured bits output by the FEC encoder are discarded before transmission. At the receiving end, these information bits are regarded as unknown erasures, so the LLR is 0 and they are recovered during the FEC decoding process.

[0024] Since all shortened LDPCs reuse the same encoding and decoding matrices, only minimal changes need to be made to the original LDPC encoder and decoder. Under the constraint of constant S + P, a family of codes with different degrees of error-correcting ability and code rate ranges can be created by adjusting their respective lengths.

[0025] In the NOMA-PON of the present invention, it is adaptively adjusted according to different modulation formats and different code rates based on the channel state of the NOMA-PON to achieve flexible access. It is compatible with the traditional TDM-PON architecture, so that the traditional TDM-PON system architecture does not need to be changed.

[0026] To ensure different access rates for different service types of different ONUs in the NG-PON, the present invention provides different powers and security levels based on different transmission channels between the OLT and ONUs in the NG-PON. Based on the channel conditions of different ONU users or different ONU groups, i.e., the change in the optical path loss (OPL), the access rate of the adaptive line is achieved by adjusting the transmit power and security level between different ONU users or different ONU groups. Specifically, the transmit power is achieved by digitally adjusting the Euclidean distance of the modulation format allocated to each ONU or ONU group in the OLT; the security level is achieved by digitally adjusting the code rate of the forward error correction coding (FEC) between different ONU users or different ONU groups in the OLT. Therefore, the security method for the passive optical network based on non-orthogonal multiple access considers the fiber channel state between different OLT-ONUs and sets different power allocations and different security levels according to different channel states, so that the NG-PON significantly improves the system's security capacity while achieving an adaptive access rate.

[0027] The passive optical network information transmission method of the present invention realizes flexible NOMA-PON coverage of different regions with large differences in fiber distance and branch ratio by using adaptive power allocation and security level coding rate. Therefore, the security based on NOMA-PON provides greater freedom and security capacity for the deployment of access networks. The present invention will play an important role and significance in constructing and promoting the development of flexible and secure NG-PON communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of a passive optical network signal transmission system based on non-orthogonal multiple access of the present invention.

[0029] Figure 2 It is a schematic diagram of a passive optical network architecture based on non-orthogonal multiple access of the present invention.

[0030] Figure 3 It is a schematic diagram of setting different coding rates according to different security levels for a passive optical network based on non-orthogonal multiple access of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] For better understanding of the technical solution of the present invention by those skilled in the art, the content of the present invention will be further described in detail below with reference to the drawings and embodiments, but it is not a limitation of the present invention. Embodiment

[0032] Referring to Figure 1 , the passive optical network information transmission system based on non-orthogonal multiple access of the present invention mainly includes a light transmitter part of the OLT, a fiber link part, and a light receiver part of the ONU connected in sequence;

[0033] The light transmitter part of the OLT includes a DSP module of the OLT, a digital-to-analog converter (DAC), and an optical modulator connected in sequence, and a laser connected to the optical modulator;

[0034] The DSP module of the OLT includes a binary data input module, different ONU coding rates set according to different security levels, and different ONU modulation mappings set according to different data rates connected in sequence;

[0035] The light receiver part of the ONU includes a photodetector, an analog-to-digital converter (ADC), and a DSP module of the ONU connected in sequence;

[0036] The DSP module of the ONU includes a symbol synchronization and channel equalization module, different ONU demodulation mappings set according to different data rates, different ONU decodings set according to different security levels, and a binary data output module connected in sequence;

[0037] The optical fiber link section includes an optical fiber amplifier and a common standard single-mode optical fiber;

[0038] The DSP module of the OLT can be designed to carry a hybrid structure with flexible modulation formats and code rates for the adjustment of binary bit data according to different security levels and different data rates. After the DSP electrical signal passes through the hybrid structure, it drives an electro-optic modulator through a digital-to-analog converter (DAC), and a laser generates an optical carrier. Then, after being transmitted through an optical fiber amplifier and a common standard single-mode optical fiber (SSMF), in the receiver of the ONU, first, a photodetector converts the optical signal into an electrical signal, and then the electrical signal undergoes DSP processing at the ONU end after passing through an analog-to-digital converter (ADC). The function of the symbol synchronization and channel equalization module is to synchronize symbols between the DAC of the OLT transmitter and the ADC of each ONU receiver, and effectively suppress the non-ideal factors of the hardware and the optical fiber link during signal transmission. Finally, each ONU recovers its own ideal data.

[0039] In the flexible NOMA-PON deployment scenario, the worst channel conditions of existing ONUs limit the access rate and security capacity of the overall PON system. To further increase the flexibility and security of NG-PON deployment, the access rate and security capacity that a group of ONUs can achieve can be flexibly configured according to the channel conditions of the ONUs. By combining modulation formats and FEC, the coding can even be dynamically adjusted to cover different ONU densities, transmission distances, reliability, and energy consumption. For example, in densely populated urban areas, using high-order QAM plus high coding rate FEC (low coding overhead) can meet the high bandwidth requirements. On the other hand, in remote low-density rural areas, a low-order QAM + low coding rate FEC (high coding overhead) approach is used to extend the optical fiber transmission distance and improve network security. Therefore, the schematic diagram of the secure passive optical network signal transmission system and method based on non-orthogonal multiple access of the present invention is as Figure 1 shown.

[0040] According to different optical fiber transmission lengths and splitting ratios, the NG-PON system deployment scenarios can be divided into regions such as urban, suburban, and rural areas. The optical access network covering urban areas has a short distance and is a dense area that needs to support a large number of service ONUs. In rural areas with long-distance coverage, the commercial density is relatively low. The suburban area between the city and the countryside has a medium coverage range and density. Under multi-scenario applications, using the traditional PON architecture will reduce the usage efficiency of network resources and limit the connection flexibility. Due to different optical fiber transmission distances and the number of passive nodes, there are significant differences in the channel state and power budget of each ONU node. Moreover, there are cases of optical fiber eavesdropping and illegal ONUs in NG-PON. Figure 2An example of NG-PON deployment in scenarios with different optical fiber transmission distances, splitting ratios, and security requirements between the OLT and ONUs.

[0041] The optical power loss (OPL) of the NG-PON system consists of two parts: transmission loss and splitting loss. Suppose there are n groups of ONUs located at different positions, and the optical power losses are different. As long as the total loss is lower than the power budget, error-free transmission can be achieved. At a certain fiber length, the higher the power budget, the larger the splitting ratio that can be supported. As shown in Figure 2 When the downstream signal is transmitted through optical fibers of L1, L2, L3 to Ln km respectively, if OPL1 < OPL2 < OPL3 < OPLn, the corresponding maximum achievable data rates are R1 > R2 > R3 > Rn. For example, through the transmission of L1 km of optical fiber, the increased power budget can support 256 ONUs. Conversely, the longer the transmission distance of the downstream signal, the fewer ONUs can be supported.

[0042] Different from the upstream burst signal form of the secure passive optical network with non-orthogonal multiple access, the downstream signal is continuous. The present invention is based on the flexibility and security concepts of the NOMA-PON signal transmission total solution concentrated in the downstream, and adopts the intensity modulation direct detection mechanism.

[0043] The present invention is an information transmission method for a passive optical network based on the NOMA-PON system. Utilizing the SNR margin of the NG-PON, for ONU users with relatively high SNR, higher-order modulation formats and higher coding rate FEC are allocated to achieve higher data rates and security levels, and vice versa;

[0044] Specifically, according to the different requirements for the access rates of different ONUs in NOMA-PON, different modulation formats for different ONUs in the OLT (such as the modulation formats adopted by ONU1 to ONUn vary from QPSK format to 32QAM format), power domain superposition of modulation formats is performed at the transmitter end. For example, a higher-order modulation format is sent at the transmitter end of the OLT and transmitted through the ODN; at the receiver end of the ONU, appropriate Euclidean distance is selected for hard decision according to the channel conditions to recover its ideal signal. ONUs with poor channel conditions, such as the ONUn link, selectively demodulate the low-order modulation format (such as QPSK format) that meets the SNR requirements of this channel from the superimposed modulation formats, while ONUs with good channel conditions, such as ONU1, regard the signals received by other ONUs as noise and recover the higher modulation format (32QAM format) according to their channel conditions in the total received signal;

[0045] The coding rate FEC realizes different LDPC FEC coding rates varying between 0 and 1 by shortening and puncturing the LDPC mother code at the OLT.

[0046] The different ONUs have different security level requirements. The meaning of different security levels is that, under the optical signal-to-noise ratio (OSNR) limit that satisfies the output bit error rate such as 1e-15, the capacity difference between the legitimate ONU and the eavesdropping ONU is maximized. Specifically, an adaptive coding scheme can be adopted according to different channel conditions to make full use of the power margin of the system.

[0047] In the present invention, the method of setting the FEC rate of different ONUs according to different security levels is based on the industry standard of NG-PON. Specifically, the mother code adopts LDPC(17664,14592) defined in IEEE 802.3ca, and this mother code is also recommended by ITU-T G.9804.2, that is, a codeword of length 17664 consists of 14592 information bits and 3072 parity check bits.

[0048] Currently, in commercial NG-PON, the FEC coding uses Reed-Solomon (RS) coding, but LDPC codes have been widely studied in NG-PON due to their significant error correction ability. Therefore, the variable FEC code rate of the present invention is mainly based on LDPC codes. The implementation of adaptive coding is highly compatible with existing PON specifications and only requires minor modifications.

[0049] Taking the traditional XG-PON standard (ITU-T G987.3) as an example, in the 125-second time window of the downstream XG-PON transmission convergence (XGTC) and physical layer (PHY) frames, only one coding method is allowed. All the encoded LDPC codes here are generated by the same mother parity check matrix, and the generation of different code rates is specifically as Figure 3 shown.

[0050] The specific method for generating different code rates is as follows: Let the information bit of the LDPC mother code be M and the parity check bit be N. This mother codeword is then shortened and punctured to generate various sub-codes as Figure 3 shown. After shortening the information bit by P and puncturing the parity check bit by S, the sizes of the M-P bit information bit and the N-S bit parity check bit are respectively formed, so as to realize the adjustment between different data coding rates of 0-1;

[0051] The shortening of the information bit is achieved by reducing the number of information bits fed into the FEC encoder, and at the same time fixing the remaining bits to zero. These fixed shortened bits are not transmitted. Before sending the data to the FEC decoder, the mother code can be reinserted at the receiving end. Since the values on the shortened bits are determined to be zero, a relatively large log-likelihood ratio can be set, thereby improving the error correction ability of this shortened code.

[0052] On the other hand, puncturing is performed on the parity check bits at the end of the mother code, and the punctured bits output by the FEC encoder are discarded before transmission; at the receiving end, these information bits are regarded as unknown erasures, so the LLR is 0 and is recovered during the FEC decoding process; since all shortened LDPCs reuse the same encoding and decoding matrices, only minimal changes need to be made to the original LDPC encoder and decoder, thereby reducing the complexity and cost of ASIC and algorithm upgrades, and under the constraint of constant S+P, by adjusting their respective lengths, a family of codewords with different degrees of error correction capabilities and code rate ranges can be created.

[0053] An information transmission system and method for a secure passive optical network based on non-orthogonal multiple access according to the present invention realizes digital superposition of different powers of ONUs through flexible modulation. Moreover, in combination with flexible FEC, different optimal codewords are set according to different security levels, and the higher the signal-to-noise ratio of the channel, the higher the set code rate. This NOMA-PON secure transmission system can be configured to operate in multiple discrete systems, making full use of the available NG-PON channel conditions and maximizing the access rate and security capacity of the ONUs.

[0054] The above is only the specific implementation manner of the present invention in the embodiments, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A passive optical network information transmission system based on non - orthogonal multiple access, characterized in that: The transmission system includes an optical transmitter part of the OLT, an optical fiber link part, and an optical receiver part of the ONU, which are connected in sequence; The optical transmitter part of the OLT includes a DSP module of the OLT, a digital - to - analog converter DAC, and an electro - optical modulator connected in sequence, and a laser connected to the electro - optical modulator; The DSP module of the OLT includes a binary data input module, different ONU coding rates set according to different security levels, and different ONU modulation mappings set according to different data rates; The optical receiver part of the ONU includes a photodetector, an analog - to - digital converter ADC, and a DSP module of the ONU connected in sequence; The DSP module of the ONU includes a symbol synchronization and channel equalization module, different ONU demodulation mappings set according to different data rates, different ONU decodings set according to different security levels, and a binary data output module; The optical fiber link part includes an optical fiber amplifier and a common standard single - mode optical fiber; The DSP module of the OLT adjusts the binary bit data according to different security levels and different data rates into a hybrid structure carrying flexible modulation formats and code rates. After the DSP electrical signal passes through the hybrid structure, it drives the electro - optical modulator through the DAC, and the laser generates an optical carrier; After that, after being transmitted through the optical fiber amplifier and the common standard single - mode optical fiber, in the receiver of the ONU, first the photodetector converts the optical signal into an electrical signal, and then the electrical signal is processed by the DSP at the ONU end after passing through the ADC. The symbol synchronization and channel equalization module synchronizes the symbols between the DAC of the OLT transmitter and the ADC of each ONU receiver. Finally, each ONU recovers its own ideal data.

2. A passive optical network information transmission method based on non - orthogonal multiple access, characterized in that, it includes the non - orthogonal multiple access - based passive optical network information transmission system NOMA - PON described in claim 1; The information transmission method: Utilize the SNR margin of NG - PON. For ONU users with relatively high SNR, allocate higher - order modulation formats and higher coding rates FEC to achieve higher data rates and security levels, and vice versa; Specifically, according to the different requirements of different ONU access rates in the NOMA - PON system, for different modulation formats of different ONUs in the OLT, power - domain superposition of modulation formats is performed at the transmitter end. A higher - order modulation format is transmitted at the transmitter end of the OLT and transmitted through the ODN; At the receiving end of the ONU, the Euclidean distance is appropriately selected for hard decision according to the channel conditions to recover its own ideal signal. The ONU with poor channel conditions only needs to recover the lower - order modulation format from the received higher - order modulation, while the ONU with good channel conditions regards the signals received by other ONUs as noise and recovers the higher - order modulation format according to its channel conditions in the total received signal. The coding rate FEC varies different LDPC FEC coding rates between 0 and 1 by shortening and puncturing based on the LDPC mother code at the OLT.

3. The passive optical network information transmission method according to claim 2, characterized in that: the different ONUs have different security level requirements, and the meaning of different security levels is that the difference in capacity between the legitimate ONU and the eavesdropping ONU is the largest under the optical signal-to-noise ratio (OSNR) limit that satisfies the output bit error rate of 1e-15.

4. The passive optical network information transmission method according to claim 2, characterized in that: the coding rate FEC is based on the LDPC code, and the mother code uses LDPC(17664,14592) defined in IEEE 802.3ca, that is, a codeword of length 17664 consists of 14592 information bits and 3072 parity check bits.

5. The passive optical network information transmission method according to claim 4, characterized in that: the LDPC codes of the coding rate FEC are all generated by the same mother parity check matrix, and the specific method for generating different code rates is as follows: Let the information bit of the LDPC mother code be M, and the parity check bit be N. The mother codeword is then shortened and punctured to generate various sub-codes. After shortening the information bit to P and puncturing the parity check bit to S, the sizes of the M - P bit information bits and the N - S bit parity check bits are formed respectively, so as to realize the adjustment between different data coding rates of 0 - 1; the shortening of the information bit is achieved by reducing the number of information bits fed into the FEC encoder, and at the same time fixing the remaining bits to zero. These fixed shortened bits are not transmitted. Before sending the data to the FEC decoder, the mother code is reinserted at the receiving end. Since the values on the shortened bits are determined to be zero, a larger log-likelihood ratio is set, thus improving the error correction ability of this shortened code; On the other hand, the parity check bits are punctured at the end of the mother code, and the punctured bits output by the FEC encoder are discarded before transmission; at the receiving end, these information bits are regarded as unknown erasures, so the LLR is 0 and recovered during the FEC decoding process; Since all shortened LDPCs reuse the same encoding and decoding matrices, only minimal changes need to be made to the original LDPC encoder and decoder, and under the constraint of constant S + P, a family of codewords with different degrees of error correction ability code rate ranges can be created by adjusting their respective lengths.

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