Research On Non-orthogonal Optical Access Technology Based On Multi-carrier Coded Modulation

With the continuous development of high-bandwidth services,the global demand for Internet traffic is increasing sharply,which makes future optical access networks need to support larger data capacity,higher spectral efficiency,more access numbers,and more secure data transmission.Passive optical network technology,with its advantages of low cost,wide service range,and high access bandwidth,has been an important development direction in current access networks.Multicarrier modulation technologies such as orthogonal frequency division multiplexing have the advantages of high frequency spectral efficiency and strong dispersion tolerance.Passive optical networks based on multicarrier modulation technologies can not only combine available orthogonal physical dimensions,such as time,wavelength,mode,fiber core,etc.,but also further utilize the power dimension to build non-orthogonal optical access systems that support resource reuse,thereby effectively improving the spectral efficiency of access network systems.In this way,the important performance of the access network system such as spectral efficiency,data capacity and access number can be effectively improved.However,in practical applications,orthogonal frequency division multiplexing technology will deteriorate the transmission performance of access networks due to problems such as peak-to-average power ratio and frequency fading.Therefore,it is crucial to ensure transmission performance while achieving access network upgrades.In addition,the continuous growth of data capacity and access numbers will also cause access networks to face serious user information security issues.Using chaotic encryption technology to encrypt the information in modulation process at the transmitter can effectively ensure user information security in access networks,but how to implement low-cost user key distribution remains to be studied.The main research content of this thesis is as follows:（1）This thesis first studies orthogonal optical access systems based on orthogonal frequency division multiplexing and wavelength division multiplexing.To solve the problem of peak-to-average power ratio and user information security in the system,a chaotic set-partitioned selective mapping method is proposed.With the implementation of a three-dimensional chaotic system,peak-to-average power ratio reduction and chaotic encryption are simultaneously realized on the process of OFDM signal modulation,compared to traditional selective mapping methods,chaotic set-partitioned selective mapping method can provide a peak-to-average power ratio gain of 1.3 d B and a bit error rate gain of 0.8 d B for the access system,and provide 10⁹⁸ key space,effectively ensuring user information security.（2）To solve the problem that resources cannot be reused in orthogonal access systems,this thesis subsequently proposes a high security non-orthogonal optical access scheme based on chaotic power division multiplexing in a few-mode fiber link.The few-mode fiber link provides additional spatial mode channels for data transmission in access systems,and have a stronger nonlinear tolerance that enables the system to have a higher power budget.Chaotic power division multiplexing technology can achieve multiplexing of OFDM signals with multiple overlapping spectrums at different power ratios,which can improve the spectral efficiency of the system and the number of access users without increasing additional time-frequency resources.At the same time,the introduction of chaotic encryption technology also ensures that the information of high-power users is not leaked during the decoding process using successive interference cancellation technology.The proposed scheme has been experimentally verified in a 5 km weakly coupled few-mode fiber link,demonstrating the potential to improve the spectral efficiency,access number,and data security of the access system.Then,this thesis proposes a key distribution scheme based on noise-masking to solve the problem of key distribution in chaotic systems.For the decimal key in a chaotic system,the decimal to binary conversion is performed first,and then the binary key information is modulated into a multi-carrier signal through digital processing.By adjusting the signal power,the key’s signal with the same power level of channel noise is superimposed with the encrypted data signal for synchronization transmission.Through the proposed mechanism,even if the system’s key is constantly updated,the legitimate receiver can achieve uninterrupted key authentication and signal decryption,with the advantage of not changing the communication link and reliable communication.The proposed scheme has been verified by 124.4 Gb/s high security transmission experiments in a 2 km 7-core fiber link,which proves that it can achieve low-cost key synchronization transmission without significant bit error rate damage.（4）To solve the problem that the transmission performance of non-orthogonal access systems needs to be improved,this thesis proposes a non-orthogonal optical access scheme based on orthogonal chirp multiplexing technology.Orthogonal chirp multiplexing technology can expand information and equalize damage to the entire spectrum.Compared to traditional non-orthogonal optical access schemes based on OFDM,the proposed scheme can enhance the overall anti-interference ability of power division multiplexing signals by virtue of the advantages of chirp spread spectrum.The non-orthogonal optical access scheme based on orthogonal chirp multiplexing is experimentally demonstrated in a 25 km single mode optical fiber link.Compared with the non-orthogonal optical access scheme based on OFDM and precoded OFDM,the proposed scheme can achieve 1.3 d B and 0.5 d B receiver sensitivity improvements for high-power users,and 1.4 d B and 0.6 d B receiver sensitivity improvements for low-power users,respectively.It is proved that the proposed scheme can effectively improve the transmission performance of non-orthogonal access systems.