| With the rapid growth of the global Internet traffic, the demand for network capacity is increasing. Coded Modulation technology can achieve the high spectral efficiency while ensure the reliable transmission of the system, by jointly designing coding and modulation, which makes the Coded Modulation technology become one of the most efficient ways to improve the capacity of the optical communication system. Recently, it has been widely studied in academic circles. First of all, coded modulation can improve the spectral efficiency of the system by the use of higher order modulation. Secondly, the Forward Error Correction coding is introduced to ensure the reliabilityof the system. At the same time, the joint design of coding and modulation could obtain extra coding gain without sacrificing spectral efficiency and power efficiency. Hence,Coded Modulation technology can resolve the contradiction between validity and reliability, which will be conducive to the upgrade of system capacity. It is very important for the development and construction of the optical communication system with large capacity and long distance transmission.This dissertation focuses on the key technologies of Coded Modulation technology, especially for the optical communication system.The main contents and the thesis of the dissertation are as follows:1. Based on the High Speed Optical Transmission system, we propose a design method for high order multilevel coded modulation system. It mainly includes the design of the basic structure of the MLC system and the design of the component code rate for sub-channels. At the same time, we build a simulation platform for 16 Quadrature Amplitude Modulation (16QAM) Multilevel Coded Modulation based on MATLAB simulation tool, and simulate the performance of the proposed system design method. The simulation results show that the coding gain of the Multilevel Coded Modulation system mainly depends on the design of component code rate, the performance of the component codes used in the system, and the receiver structure which should retain the information between subchannels.2. Aiming at the situation that some subchannels' capacities would approach to '1' when Multilevel Coded Modulation system under commonly used mapping shcemes, which would improve the difficulty of the component codes design and affect the overall performance of the system, we put forward an Equal Equivalent-channel Capacity Partition design method to reduce the system design difficulty and implementation complexity. The rationality and validity of the proposed algorithm is verified based on the simulation platform for 16QAM Multilevel Coded Modulation. We can use the proposed algorithm to reduce the system design difficulty and complexity without affecting the system performance.In addition, we propose an algorithm for optimizing the multistage decoding structure, which remove the unnecessary auxiliary structure of the multistage decoding structure, to solve the problem that the traditional multistage decoding algorithm would lead to high implementation complexity and large decoding delay, without loss of system performance.The rationality and validity of the proposed algorithm is verified based on the simulation platform for 16QAM Multilevel Coded Modulation. We can use the proposed algorithm to reduce the system design difficulty and complexity without affecting the system performance.3. Since the signal average transmit power is limited in the actualsystem, the prior probability distribution of the input signal is not the equal distribution of the hypothesis in theoretical research, there will be a loss of the channel capacity of the actual system. Thus, we present a scheme of probabilistic shaping to ensure that the prior probability of the input signal of the system is changed into the optimal Gauss distribution,so as to enhance the capacity of the system. Based on the 16QAM validity of the proposed probabilistic shaping scheme is verified. The optimal Gauss distribution will be ensured through the method of adding redundancy, which will lead to an increase of the channel capacity of the actual system, and an improvement of the encoding gain. |
PDF Full Text Request