Research On Energy Saving Techniques For Opticalaccess Networks

With the further development of “information society” and the further increasing of broadband services,the energy consumption of telecommunication networks has became a critical issue.Huge amount of electricity consumed by telecommunication networks not only increases the operational expenditure for network service providers,but also hinders the implement of project “faster and cheaper networks”,which further resists the development of modern society toward “informationalized society” and “intellectual society”.Being the “last mile” of telecommunication networks,access networks consume about 80% of the total energy of telecommunication networks.Therefore,to reduce the energy consumption of telecommunication networks,it is of great importance to reduce the energy consumption of access networks.This thesis,focusing on optical access networks,reviews current progresses in reducing the energy consumption of optical access networks,and studies possible ways to further reduce the energy consumption of optical access networks.By optimizing network structure and dynamic resource allocation mechanism,and investigating the requirement of future optical access networks as well as advanced optical access network technology,several methods are proposed to decrease the energy consumption of optical access networks.The main works and innovations of this thesis are as follow.1.Energy efficiency study of electronic switch based optical access networks adopting optical network unit(ONU)grouping and interconnectionBased on optical access network using electronic switch,an ONU grouping and interconnection adopted optical access network scheme is proposed and studied.By grouping several ONUs into an ONU group and interconnecting the ONUs from a same ONU group,each ONU can communicate with any other ONU belonging to the same ONU group.Therefore,under low load scenarios,traffic of an ONU group can be aggregated,and the number of active port at electronic switch can be reduced.Investigation shows that under low load scenarios,the scheme decreases the power consumption of network effectively.Next,by adopting daily user traffic model,the daily energy saving performance of the proposed scheme is further investigated under different ONU group scales,and proper ONU group scale is discussed by jointly considering capital expenditure.Moreover,for asymmetric traffic scenarios,a stream separated-ONU grouping and interconnection adopted optical access network scheme is derived.The derived scheme optimizes the power consumption of electronic switch based optical access network under asymmetric traffic scenarios.The impacts of asymmetric traffic,upstream link rate,and ONU group scale on the power consumption of the derived scheme are investigated.2.Enhancing the energy efficiency of time division multiplexed optical access network based on dynamic resource allocationFor 10 Gbps Ethernet Passive Optical Network(10G-EPON)adopting ONU round-robin polling mechanism,two energy-efficient dynamic resource allocation schemes,namely load adaptive polling sequence arrangement(LASA)scheme and polling cycle compressing(PCC)scheme,respectively,are proposed and studied.a)In the LASA scheme,by dynamically adjusting the polling sequence of ONUs in each polling cycle according to traffic condition,total sleeping time arising from all ONUs in the time range of two consecutive polling cycles is increased.Compared to the conventional fixed polling sequence scheme,the LASA scheme enhances the energy efficiency of ONU with very small penalty on average packet delay.Further,as under low load scenarios,short polling cycle will prevent ONU from going to sleep and degrades the performance of the LASA scheme,the fixed minimal transmission time(FMT)mechanism is proposed to incorporate with the LASA scheme.Investigation shows that the incorporative scheme effectively enhances the energy saving performance of the LASA scheme under low load scenarios.b)In the PCC scheme,every several consecutive polling cycles are considered as a polling cycle reset loop.By setting a compressing coefficient and dynamically compressing and extending the lengths of polling cycles in a polling cycle reset loop according to the compressing coefficient,total ONU sleeping time arising from the time range of a polling cycle reset loop is extended.Theoretical analysis indicates that the PCC scheme could effectively improve the energy efficiency of ONU.Further,by investigating the impacts of compressing coefficient and the number of polling cycles in a polling cycle reset loop on the performance of the PCC scheme,the selection of compressing coefficient and the number of polling cycles in a polling cycle reset loop is discussed.3.Multilayer-ring structure based high survivability and high efficiency optical access networkBased on time and wavelength division multiplexed passive optical network(TWDM-PON),a multilayer-ring structure based high survivability and high efficiency optical access network scheme is proposed.In this scheme,optical access network is divided into four layers,and on the layers other than the optical line terminal(OLT)group layer,network devices from a same layer are interconnected as a ring.With this structure,nearby network devices belonging to a same layer can protect each other,and the flexibility of ONU-OLT link path is enhanced.Hence,standby network devices are reduced,and under low traffic load,ONU traffic can be highly aggregated to achieve power saving through turning off idle devices.Theoretical analysis indicates that the proposed scheme can greatly enhance the survivability of network while significantly decreasing the capital cost and operational power consumption.Moreover,benefiting from its traffic aggregation advantage,the proposed scheme can further improve its energy efficiency by cooperating with the LASA scheme.4.Study of energy-efficient optical access network based on digital filter multiple access(DFMA)technologyBased on digital filter multiple access passive optical network(DFMA-PON),an energy-efficient digital sub-band grouping and allocating scheme is proposed and theoretically analyzed.By grouping multiple digital sub-bands as a sub-band group and indicating multiple ONUs to share a sub-band group in time division mode,the scheme accelerates the transmission of each ONU and therefore,provides each ONU with extended idle time.Hence,by further adopting ONU sleep/awake energy saving mechanism,the energy consumption of ONU is effectively reduced.The impact of the number of sub-bands contained in a sub-band group on the energy saving performance of the proposed scheme is studied.Moreover,considering the power consumption reduction caused by technology improvement,future energy consumption of the proposed scheme in transmitting one bit is envisioned in comparison with that of a conventional optical access network,and the energy saving gained from network upgrading is discussed.