Study On The Key Technologies Of Passive Optical Networks

Passive optical network (PON) is one predominant technology in access network and will get more and more popular because of its advantages as high bandwidth, easy maintainance and wide area coverage. PON faces servral key problems because of the appearance of new services, new technological requirements, and evolution requirements for the next generation PON. First, the rapid development of P2P applications greatly increased data throughput between users in the access network and the traditional OLT-centered passive optical network has to make structural improvement to efficiently carry these services. Second, in order to use PON to bear services of wireless network using its benefits as high bandwidth, PON needs to support high accuracy clock synchronization and so we must study PON’s clock synchronization technology. Third, access network has consumed75%energy of the whole telecommunication network. PON, as a popular access technology, has to meet the worldwide requirement for cutting carbon emissions and environmental protection, and we need to study the suitable energy saving technology for PON. At last, CDMA PON got researchers’attention because of CDMA technology’s benifits in the anti-jamming, high link budget. And it meets people’s requirements for more users, further transmission distance and stronger secrecy.This thesis performed studies in PON’s architecture, PON’s high-accuracy clock synchronization, PON’s energy saving and CDMA PON. The main contributions of this thesis are as follows.1. A direct-loop type EPON with master-slave and peer-to-peer architecture was proposed and comparision between power budget of the direct-loop and the splitter-loop EPON architectures is presented. A adaptive load balancing algorithm based on realtime load detection (ALBRLD) was also proposed and its balancing performance is verified through simulation.The direct-loop type architecture connecst the upper links of the optical splitter to ONU and increased PON link budget by10Log(N) dB (N is the branching ratio of optical splitter). The direct-loop type architecture will not cause significant increase in network construction cost when the users have a concentrated distribution where the trunk fiber’s length is long and the branch fiber’s length is short. The ALBRLD algorithm can adapt to dynamic traffic flows and divide traffic equally between2PON links. The simulation results showed that the ALBRLD algorithm can provide no more than7%of the instantaneous balancing degree and4%of the long term balancing degree.2. An EPON time synchronization scheme based on IEEE1588v2was proposed and implemented and its synchronization accuracy was verified through experiment. The master-slave clock frequency deviation and link asymmetry’ affects on the accuracy of time synchronization was analyzed and this scheme is designed and implemented in an EPON system based on FPGA technology. The experimental results show that the scheme can achieve about30ns time accuracy when the distance between OLT and ONU is20Km.3. An EPON energy saving scheme based on two-way polling DBA and ONU periodic sleep was proposed and its energy saving performance and affects on servies’QOS was verified. The scheme performed traffic shaping using two-way polling DBA and increased the possibility of ONU’s entering sleep mode. It also uses periodical sleep to reduce degradation of services’QOS while reducing energy consumption. Simulation results show that using lms as the sleep period and small load the scheme’s energy saving ratio could be20%, while using medium load the energy-saving ratio could be8%, and the scheme meets requirements for services’QOS.4. A timing synchronization acquisition and tracking scheme based on parrell acquisition and closed loop adjustment was proposed and implemented in a TDM-CDMA hybrid PON system. A digital de-spreading scheme using pipeline design is also proposed and implemented in the system. This thesis verified the two schemes’ implementability through experiment. This thesis studied and compared the performance of4common synchronization capture schemes and designed the synchronous acquisition and tracking scheme on the base of parrell capture scheme and closed loop adjustment. This thesis also compared the implementability of two de-spreading schemes and implemented the digital CDMA de-spreading scheme using pipeline design. Finally, this thesis sets up a FPGA platform for the hybird PON system and performed a preliminary experiment of system throughput. The experimental results show that the synchronization scheme’s accuracy meets our expectation and the digital de-spreading scheme could work under2.5Gchip/s and meet the expected requirement for system throughput.