Research On Transmission Optimization And Resource Scheduling Mechanisms For Fiber-Wireless Access Networks

With the advent of the Internet + era,new applications such as cloud computing,big data,mobile Internet and Internet of things have emerged in endlessly,which drives the explosive growth of network data traffic,thus undoubtedly putting tremendous pressure on the communication network infrastructure,especially imposing great challenges on the construction and development of the broadband access network,i.e.,the "last mile" of the information highway.The future broadband access network needs to simultaneously provide users with the services of high-speed wired access and flexible broadband wireless access.To reduce the capital expenditure and operation expenditure while improving the overall resource utilization,operators expect to construct wireless backhaul networks using the existing Passive Optical Network(PON)infrastructure.As a result,radio and broadband can share the same set of cable resources.Moreover,Orthogonal Frequency Division Multiplexing(OFDM)-PON has the advantages of high spectral efficiency,flexible resource allocation and offering transparent transmission channels for different types of services,which provides a valuable opportunity for the converged access of heterogeneous technologies.Therefore,by making use of OFDM-PON to host various wired and wireless access technologies,the Fiber-Wireless(FiWi)access network has attracted great attentions from academia and industry.The future FiWi access network not only provides flexible high-speed access services for users,but also has to satisfy the differentiated requirements owned by various types of traffic.This development tendency puts forward more challenges for FiWi access networks from physical-layer transmission improvement to network-layer resource scheduling.Currently,some related works have studied the physical-layer transmission optimization mechanism.However,most of the works focused on point-to-point high-capacity and long-reach transmission,and few works investigated multipoint-to-point upstream transmission or well satisfied the transmission quality required by di'verse users.In particular,with the further improvement of the transmission rate,chromatic dispersion associated signal power fading will become the key factor limiting the maximum achievable transmission performance.Nevertheless,existing dispersion compensation methods were costly or complicated to implement,and they can not achieve flexible and differentiated compensation according to the transmission needs of diverse sub-channels.In addition,the existing studies of resource scheduling focused on improving the quality of service,while the subcarrier scheduling approach needs to be explored for the green survivability.Moreover,the promotion of applications such as smart city and mobile cloud computing has accelerated the development of network virtualization technology,but the Virtual Network Embedding(VNE)mechanisms tailored to specific application scenarios remain less touched.In summary,the research on transmission optimization and resource scheduling mechanisms for FiWi access networks is still in its infancy,and many key issues are urgent to address.As to the current problems and challenges mentioned above,in this dissertation,extensive explorations have been made from the following four aspects:optimization on physical-layer transmission performance,efficient and flexible dispersion compensation method,subcarrier scheduling for green survivability,and VNE mechanism applicable for specific application scenarios.A list of corresponding novel ideas and effective solutions has been proposed.The contributions and innovations of this dissertation are summarized as follows:(1)Research on transmission optimization mechanisms for FiWi access networks based on OFDM.First of all,the author improves the power efficiency of OFDM-based Intensity Modulation and Direct Detection(IMDD)PON systems,and an adaptive bit and power loading approach is proposed with the consideration of channel transfer function.Compared with the traditional power loading method,the proposed approach can effectively reduce the transmitting power while guaranteeing the system transmission performance.In the following,to reduce the high peak-to-average power ratio and to guarantee the transmission quality requirements of the users with different levels,a discrete Fourier transform-based multi-band IMDD OFDM-PON system is designed.Different users' transmission quality requirements are satisfied by flexibly assigning the modulation format and power for each band.Finally,considering that the IMDD OFDM-PON upstream transmission system suffers seriously from subcarrier-to-subcarrier intermixing interference and optical beating interference,the author proposes a Low Density Parity Check(LDPC)-coded OFDM-PON system so as to improve the system transmission performance.(2)Research on dispersion compensation mechanisms for FiWi access networks based on digital orthogonal filtering.The author firstly introduces the working principle of the IMDD PON system based on software reconfigurable digital orthogonal filtering.The influence of digital orthogonal filter parameters on the system performance is also analyzed to obtain the optimal parameter setting under given conditions.Next,to mitigate the channel fading caused by chromatic dispersion in digital orthogonal filtering IMDD PON systems,the Self-Phase Modulation(SPM)is utilized to compensate the dispersion.To verify the effectiveness of the SPM effect,a theoretical transmission model considering the effect of both chromatic dispersion and SPM is developed.Based on the abovementioned analysis,numerical simulations are undertaken to explore the maximum achievable signal transmission capacity for the whole system and individual sub-channels,respectively.It is shown that,for the sub-channel suffering most from the chromatic dispersion effect,the SPM effect can enhance its transmission capacity by the factor as large as 2,and a further 45%transmission capacity improvement is also obtainable when adaptive channel power loading is applied.(3)Research on subcarrier scheduling mechanisms focusing on green and survivability for FiWi access networks.Firstly,as to the survivability of FiWi access networks,an optimization mechanism on improving the efficiency of proactive maintaining distribution fibers is proposed.Aiming at minimizing the number of maintenance batches during an acceptable scheduling cycle,the corresponding problem model is formulated.The feasibility and lower bound of the problem are theoretically analyzed.A novel heuristic algorithm of the virtual subcarrier scheduling is designed to solve the abovementioned problem.It is shown that the number of maintenance batches obtained by the proposed heuristic algorithm can exactly match the bound.Next,as to the green FiWi access networks,an energy-saving mechanism is proposed based on joint resource scheduling.The energy-consumption model of the virtual subcarrier migration is presented,and the problem description and bound analysis are also given.To maximize the energy-saving effect,based on flexible modulation,a joint energy-efficient allocation algorithm is used for scheduling cycle and virtual subcarrier.Simulation results demonstrate that the algorithm performance is better than existing solutions,and the energy-saving effect is precisely matched with the bound.(4)Research on VNE mechanisms for FiWi access networks.First of all,to support the advertisement targeting which is an application of the mobile cloud computing service,the location-recommendation-aware VNE problem is investigated in the introduced FiWi architecture integrating optical metro access and ubiquitous wireless access.Recommendation methodologies of a stand-alone Point of Interest(POI)and a POI trajectory are both proposed,and then a location-recommendation-aware heuristic VNE algorithm is further described to minimize the energy consumption caused by lightpath establishment.Compared with the existing solution,the proposed approach can reduce 38%energy consumption while improving 20%network revenue.The revenue obtained by the proposed heuristic approach is also very close to the problem upper bound.Next,since the smart city heavily relies on the FiWi access network,the VEN problem is also investigated for the collaborative edge computing.A graph-cutting algorithm is employed to embed as many Virtual Networks(VNs)as possible onto the substrate Wireless Mesh Network(WMN)infrastructure.The VN that cannot be embedded into front-end WMNs will be collaboratively processed through the backhaul PON while ensuring the minimal bandwidth consumption.The proposed scheme can effectively reduce the total transmitting power,improve the VNE efficiency and reduce the backhaul bandwidth consumption,compared with the existing solution.To verify and evaluate the performance of proposed systems and approaches,a simulation platform is built via using VPI,MATLAB and C++ simulation software in this dissertation.Simulation results demonstrate that the proposed systems and schemes gain significant advantages in terms of improving transmission performance,increasing fiber maintenance efficiency,saving power consumption,enhancing network revenue and reducing bandwidth consumption.The research achievements of this dissertation are able to provide theoretical foundation and technical support for the construction and development of FiWi access networks.