| To cope with the increasing demand for 5G data services and reduce operating costs,the centralized radio access network(C-RAN)is regarded as a possible 5G system architecture and has received widespread attention.The fronthaul optical network,a data transmission channel between the baseband unit(BBU)pool and remote radio unit(RRH),is the key to the large-scale and industrial deployment of C-RAN in 5G.However,with the intensive development of RRHs,network operators will deploy more complex fronthaul optical networks,and put forward higher requirements for meeting the development requirements of new 5G services.The existing fronthaul optical networks have the following disadvantages:First,the fronthaul optical link is fixed and the structure is inflexible,resulting in low resource utilization;second,the expanding network scale causes more energy consumption,and the probability of link failure increases;third,the quality of service cannot be guaranteed when diversified services coexist in the same physical network;fourth,the increasing data transmission rate leads to the severe bandwidth pressure of digital forward optical network.In response to the above problems,this thesis focuses on the needs of 5G services,deeply analyzes and carries out research work on fronthaul optical networks in terms of resource scheduling,reliability,energy efficiency,diversified business coexistence and data transmission capabilities have been carried out,so as to improve the performance of the fronthaul optical network as much as possible.The main researches and innovations of this article are as follows:1.In view of the problem of low resource utilization caused by the fixed connection of the existing fronthaul optical link and the inflexible architecture,this article proposes a method of dynamic resource mapping in the fronthaul optical network based on traffic prediction.This method breaks the static configuration between BBU and RRH.Based on the prediction results of RRH traffic,this article aims at minimizing the total energy consumption of the system,including the energy consumption generated by the BBU pool performing baseband signal processing,the energy consumption of switching between the activated and closed states of the BBU board,and the energy consumption of inter-switching of RRHs between different BBUs.A dynamic resource mapping algorithm between BBU and RRH based on the minimum number of switches is proposed.The simulation results show that,compared with static configuration,the proposed dynamic resource mapping method can concentrate traffic into a few BBUs and achieve the purpose of improving resource utilization.Compared with the static configuration of the fronthaul network,the overall network energy consumption is reduced by 34%.2.In view of the problem of increasing energy consumption and increased link failure probability caused by the ever-expanding fronthaul optical network scale,this thesis proposes a network deployment strategy for the joint optimization of fronthaul optical network survivability and power utilization.First,a method for real-time resource scheduling between RRHs using in-band millimeter waves(mm-wave)is proposed to improve the reliability of the fronthaul optical network and reduce energy consumption.Considering the small coverage of millimeter waves,the deployment location of RRHs will greatly affect the ability of resource scheduling between RRHs,which in turn affects the reliability and power utilization of the fronthaul optical network.Therefore,this thesis further proposes the network deployment problem with the goal of maximizing the survivability and power utilization of the fronthaul optical network.To solve this problem,this thesis establishes an ILP model and proposes an heuristic algorithm.The simulation results show that the proposed method has a good performance in improving the survivability and power utilization of the fronthaul optical network.And this thesis evaluates the survivability and power utilization performance under different constraints,which provides references for network operators in future network construction.3.In view of the problem that the current fronthaul optical network cannot guarantee the service quality of diversified services,this thesis proposes a cost-optimized network upgrade strategy for the coexistence of diversified services.This strategy considers the differentiated requirements of eMBB and uRLLC services,and proposes a network upgrade method that combines millimeter wave RRH and fronthaul links.In the network upgrade process,using in-band mm-wave as a supplementary fronthaul method for optical fiber links helps reduce deployment costs.and for uRLLC services,a reliability-guaranteed stratrage based on dual-connectivity structure is proposed.With the goal of minimizing network upgrade cost,this thesis establishes an ILP model,and proposes a network upgrade algorithm that joint optimizes RRH and fronthaul links.The simulation results show that,compared with the other two disjoint network upgrade strategies,the cost of the joint optimization method is reduced by 43%and 20%,respectively.4.In view of the problem of severe pressure on the bandwidth of the digital fronthaul optical link caused by the increasing data rate,this thesis proposes a radio over fiber(RoF)fronthaul optical network transmission scheme based on the QAM-MPPM-RZ hybrid modulation format.Compared with the standard QAM signal,the QAM-MPPM-RZ signal concentrates the energy in the pulse time slots,which can effectively improve the signal receiving capability.In addition,QAM and MPPM signals carry baseband signal at different rates,which can provide services for differentiated user needs in the same RRH through sharing same optical fiber and radio resources,which helps reduce deployment costs in C-RAN.This thesis builds a simulation platform to analyze and verify the transmission effect of the QAM-MPPM-RZ signal.The results show that the QAM-MPPM-RZ signal has a better transmission effect when transmitting data at the same bit rate.In addition,in the simulation part,the tolerance of the QAM-MPPM-RZ signal to the line width of the laser is investigated.The simulation results show that the QAM-MPPM-RZ signal still maintains a good transmission effect when the line width is large.Therefore,low-cost high-linewidth lasers can be considered in fronthaul optical network deployment to reduce the deployment overhead of the entire system. |
