Study On The Key Technologies Of The PON Based On Spread Spectrum Encoding

Fiber-to-the-building (FTTB), fiber-to-the-curb (FTTC), and fiber-to-the-home (FTTH) is the essential means of broadband access network. The "replacement of copper with optical" is the development trend of broadband access networks. The passive optical network (PON) becomes the mainstream technology for broadband access networks with the following advantages:low investment cost, easy operation and maintenance, large capacity, wide coverage, supporting multi-service and excellent upgradeability. Therefore, the high speed and large capacity PON has become one of the focuses of the broadband access network.The main challenges of current PON includes:expanding coverage effectively, enhancing networks safety and maintenance convenience. In response to these challenges, this thesis mainly studies on the key technologies of the PON based on spread spectrum encoding. The spread spectrum encoding can improve the upstream sensitivity to expand coverage, strengthen the anti-interference ability, locate the branch fiber fault at optical line terminal (OLT) and detect malicious optical network unit (ONU) to enhance PON safety and maintenance convenience, etc. The main research work and contributions are listed as follows:1:The theoretical model of ECDMA-PON upstream is established. Then the ECDMA-PON upstream sensitivity and anti-interference ability are analyzed theoretically. The theoretical analysis and simulation results show:(a) when synchronous ECDMA-PON’s spread spectrum code length is N, the spread spectrum encoding gain can improve the receiver sensitivity by(?)N times compared with time division multiplex (TDM)-PON;(b) in asynchronous and quasi-synchronous ECDMA-PON, the receiver sensitivity improvement is influenced by multiple-access interference (MAI). We have deduced the analytical expression, which can describe the relationship of sensitivity improvement with code length, number of access users and synchronization precision. If code length and number of access users is fixed, the improvement of receiver sensitivity is proportional to synchronization precision;(c) when ECDMA-PON’s spread spectrum code length is N, the spread spectrum encoding can improve anti-DC interference and anti-broadband interference ability of ECDMA-PON upstream by y(?)N times and N times compared with TDM-PON respectively.2:To expand the coverage and enhance the anti-interference ability of the PON, a novel TDM-CDMA PON is proposed, in which the downstream is based on10Gbit/s on-off keying (OOK) TDM and the upstream is based on2.5Gbit/s ECDMA. The experiment system of TDM-CDMA PON is realized. The experimental results show that the2.5Gchip/s TDM-CDMA PON upstream receiver sensitivity can be improved-6dB by coding gain compared with traditional2.5Gbit/s TDM-PON. The anti-DC interference and anti-broadband interference ability can be improved～6dB and～10dB respectively compared with traditional2.5Gbit/s TDM PON.3:To solve the problem that traditional optical time domain reflectometry (OTDR) technology cannot locate the branch fiber fault of PON at OUT, a branch fiber fault location method based on optical code division multiple accesses (OCDMA) is proposed. The method can enhance the maintenance convenience of PON. The simulation results show that this method can accurately locate the branch fiber fault of the PON supporting20km transmission distance and1:16branching ratio. The spatial resolution of the method is～10cm.4:To solve the problem that current TDM-PON cannot detect the malicious ONU accurately, a malicious ONU detection mechanism based on the phase information of auto-correlation peak is proposed. The detection mechanism employs the passive components at optical distribution network (ODN), such as splitter, delayer and attenuator. The simulation results show that this mechanism can detect malicious ONU in PON supporting20km transmission distance and1:16branching ratio. The detection mechanism can enhance the safety of PON and maintain the passive optical division network (ODN) high reliability, low operating expense (Opex) and excellent upgradeability.