The Applications Of Multi-Carrier Modulation Technique In Passive Optical Network

With the rapid development of Internet technology in modern society, a variety of media with new forms are constantly emerging. The current situation led to the rapidly increasing the amount of information, and mankind has entered a new era of information technology. People’s requirements for information bandwidth have largely increased. Certainly, the access network bandwidth requires meeting the needs of such a large capacity.Optical fiber communication has many characteristics like large capacity, long distance, so the fiber has become a logical transmission medium used in the access network.. Fiber to the home (FTTH) becomes the ultimate wired access network solutions. Passive Optical Network (PON) consists of three parts:the Optical Line Terminal (OLT), the Optical Network Unit (ONU) and an Optical Distribution Network (ODN). Since there are no powered devices in ODN, it can reduce the cost of network operation.Nowadays, EPON and GPON are used widely which support10G bandwidth. They are part of TDM-PON. Next generation PON (NG-PON2) requires the system capacity of at least40Gbit/s even to100Gbit/s, which TDM-PON is hard to achieve.OFDM has many advantages using in PON. By using high level modulation format, the capacity of OFDM and the spectrum efficiency can be increased. In OFDMA-PON system, OFDM is not only a modulation technique, but also an access method. Thus, the bandwidth allocation can improve the flexibility of the system. Discrete multi-tone (DMT) technique can be considered a special OFDM. It can dynamically adjust the transmission modulation format and the power of every sub-channel based on channel quality of transmission. DMT can theoretically reach the capacity limit of Shannon’s theorem and further improved transmission capacity on the basis of OFDM. Main contributions and researches of the thesis are presented as below:1) By doing a serial of reading, the thesis presents the background of the application based on multi-carrier modulation system in passive optical network. Meanwhile it summarizes the basic principles of PON technology and the future development of PON.2) The thesis presents the basic theory of multi-carrier modulation in PON system. It details the basic theory of the multi-carrier modulation technology, including the OFDM technology, optical OFDM technology’s great advantages compare to conventional optical communication, focuses on the derivation of modulation and demodulation process of OFDM signal, and the key technique in OFDM. It also introduces DMT technology in ADSL and in optical fiber. At last, there are some key components of fibers:optical modulator and optical detector, focusing on the Mach-Zehnder modulator (MZM), and the principle of PIN photodiode.3) The thesis introduces a key technology research and simulation of OFDM-PON At first, there is a simple introduction on OFDM-PON, followed by principle derivation of the OFDM-PON receiver technologies, including coherent detection and direct detection optical OFDM. In the third section, it describes a time domain averaging algorithm channel equalization techniques used in our simulation system based on the training sequence. In the last section, it proposes a40G bit/s DD-OFDM-PON downstream transmission system. The structure of the system is introduced on the key parameters of the simulation system design. The analysis of final system performance also is presented, as well as the simulation of splitting ratio of the attenuation effects on system performance and system noise immunity.4) The thesis makes the key technology research and simulation analysis of large-capacity access network system based on DMT. The key technology of DMT is the adaptive bit and power allocation algorithm, and it highlights the algorithm procedure of P.S.Chow algorithm and Fischer algorithm. Then the thesis builds a100G bit/s with single wavelength short-distance high-capacity WDM optical access system platform based on DMT technology, and simulates the system performance. At last, a400G bit/s optical system could transmit5km standard single mode fiber (SSMF) without amplifier and dispersion compensation. Since the DMT modulation can bring excellent system performance, the bit and power allocation for each subcarrier can maximize the transmission bit rate, it will be a very effective solution applied to the large-capacity access network.