| With the endless innovations and rapid development of Internet technology, a largeburst of new businesses, such as High-Definition TV, Streaming-Video Media,3Dprinting, Remote Tele-medicare System and Cloud Computation have come to birth,which promotes Next-Generation Passive Optical Networks (NG-PON2) towards highspeed and broad bandwidth while supporting multiple end-users and differentiatedservices. This has also become a difficult task for NG-PON2.Passive Optical Networks outstands in two ways. Firstly, optical fiber in PON isused to provide data transmission with high quality and wide bandwidth. Secondly, withapplication of passive devices, PON is released of electric power supply andmaintenance problems caused by exposure of active components. Therefore, PONgradually takes place of traditional low-rate accessing technology, such as ADSL, andbecomes a good solution for last-mile access problem. OFDM, originally used inwireless communication, is an advanced multi-carrier modulation technique. And it is ofgreat attempt and innovation to introduce OFDM into optical communication. PONcombined with OFDM technique, has demonstrated numerous advantages in accessnetworks, such as spectral efficiency, flexible access, supporting radio-over-fiber,system cost-effective. Embedded with these advantages, OFDMA-PON has become themost competitive and representative candidate for NG-PON2.In this thesis, we undertake some research on dynamic bandwidth allocation forOFDMA-PON. After studying previous theories and methods of dynamic bandwidthallocation, we analyzed system architecture and transmission characteristics of nextgeneration OFDMA-PON, and figured out the problems to be resolved, that are how toaccess ONUs in a fair manner, and how to support differentiated services and guaranteeQoS.The main work in this thesis is as following:1, NSGA-II based DBA for next generation OFDMA-PON is proposed. Firstly, weanalyze the transmission features of the PON system and find out that withoutappropriate bandwidth allocation mechanism, QoS of downstream ONUs cannot be guaranteed thus leading to unfairness among ONUs. Secondly, we introduce twoparameters Transmission Quota Capacity (TQC) and Transmission Quota (TQ) tocoordinate bandwidth allocation and transform the DBA problem into multi-objectiveoptimization problem. Furthermore, we follow the law of ‘Survival of the fittest’ innature, and adopt Non-dominated Sorting Genetic Algorithm NSGA-II to obtainoptimal Pareto solution set, that is (TQ, TQC) combination for ONU data transmission.From simulation results, we can see the algorithm is able to provide efficient bandwidthallocation to guarantee QoS and fairness among ONUs.2, FUNS (First User Next Service) algorithm to support differentiated serviceswhile satisfying QoS requirement is proposed. After studying Two Layer BandwidthAllocation (TLBA) for supporting differentiated services, we figure out the advantagesand disvantages and propose FUNS algorithm, which is Inter-ONU layer andIntra-ONU layer. At Inter-ONU layer, OLT allocates bandwidth to users according totheir Total Weight (TW) value and Average Wright (AW) value. At Intra-ONU layer,OLT allocates bandwidth to services, first to Expediate Forwarding (EF), and thenallocates remaining bandwidth to Assured Forwarding (AF) and Best Effort (BE)according to their traffic ratio. The simulation results show that FUNS has a betterperformance in network throughput, queing delay and bandwidth utilization thanTLBA.The main contributions and innovations of this thesis are:1, Figure out the problems of upstream transmission in next generationOFDMA-PON, and introduce two parameters TQC and TQ to resolve. Transformdynamic bandwidth allocation problem into multi-objective optimization problem andemploy NSGA-II algorithm to tackle the accessing fairness issue.2, Absorb two layer allocation ideas in TLBA, and make changes according toOFDMA-PON feature to firstly allocate bandwidth to users next to services in order tosupport differentiated services. |
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