Research On Flexible Optical Technology For High Capacity Wireless Access Network

The centralized processing in cloud radio access network(C-RAN)enables cooperation between baseband processing units(BBUs)like joint resource allocation and data processing,and densification of cost and power-efficient simplified remote radio unit(RRUs)can enhance the network coverage and capacity.Fronthaul is a new segment in C-RAN architecture between BBUs and RRUs,which plays a critical role in the radio access network.Traditional fixed optical technology enabled fronthaul is not flexible,leading to low resource allocation efficiency of the fronthaul network.Besides,there is a conflict between capacity-constrained fronthaul and ever-increasing bandwidth requirement.Moreover,with the growing scale of the network,more energy is needed.Therefore,under different scenarios,this paper deeply analyzes the resource allocation,load balancing,bandwidth allocation,and energy efficiency of the optical fiber technology enabled fronthaul network.Specifically,the main research content and innovations of this paper are summarized as followings:(1)An efficient resource allocation optimization algorithm for time and wavelength division multiplexing passive optical network(TWDM-PON)enabled mobile fronthaul based on the operation modes of mall cells is proposed.Tidal effect in C-RAN is obvious.Based on the operation modes of small cells,combined with the time-division multiplexing and wavelength-division multiplexing characteristics of TWDM-PON,the proposed algorithm efficiently and dynamically adjusts the wavelength resource allocation,considering of the bandwidth requirement of the small cells and network topology constraints of the fronthaul.Besides,the load difference can be minimized with minimal topology adjustment.The simulation results show that,the variance of load fluctuation is far less than the scenario without optimization,and a 12%-87%wavelength resource can be saved with the variation of traffic and the numbers of sleeping small cells.Moreover,the proposed adaptive parallel genetic algorithm performs with slightly less optimized results than the integer nonlinear programming method with much less running time,which make it applicable for the large-scale fronthaul network optimization with fast convergence.(2)An efficient resource allocation algorithm for passive optical fronthaul-based coordinated multipoint transmission is proposed.Aiming at reducing the large amounts of the sharing data caused by the joint transmission to the cell-edge users,the redundant transmission problem in the fronthaul network is converted to virtual PON allocation for each small cell cluster in the proposed algorithm,based on the joint transmission mechanism and broadcast characteristic of TWDM-PON.Then through small cell allocation and fronthaul network topology reconstruction,the redundant data is reduced and bandwidth allocation efficiency of fronthaul is enhanced.Simulation results show that,with the growth of mobile users that is near the cell edge,the bandwidth allocation efficiency can be improved by about 65%,when the average traffic demand of cell edge users and the size of cell cluster are fixed.Besides,the bandwidth allocation efficiency has an increment of about 15%-18%,with the increasing of the size of cell cluster,under different scenarios.(3)A multimedia multicasting and asynchronous delivery oriented resource allocation algorithm is proposed.The algorithm focuses on the extra bandwidth consumption of fronthaul network caused by sending the same content to different multicast group users.Considering of the number of multimedia flows,the size of user group,the average rate of multicast flow,and broadcast characteristic of TWDM-PON,the extra bandwidth consumption can be reduced by flexible fronthaul network reconstruction.Besides,the transmission pressure can also be reduced by using asynchronous delivery mechanism,this is because that lots of delay-tolerant data is shifted from peak to off-peak periods.The simulation results show that,with the growth of the average size of user group,the bandwidth allocation efficiency can be improved by about 45%,when the the number of multimedia flows,and the average rate of multicast flow are fixed.Moreover,the maximum peak-to-average ratio(PAR),i.e.,the ratio of optical resource usage in the peak period to the average per-period usage of the fronthaul,decreases by about 32%with asynchronous delivery oriented optical resource optimization.(4)An energy efficiency enhancement algorithm for TWDM-PON enabled reconfigurable fronthaul is proposed.In response to the contradiction between the network scale expansion and energy consumption,an energy consumption model is investigated in the algorithm,considering of the operation modes and energy consumption of the active units in the fronthaul.By dynamically reconstructing the fronthaul virtual topology and adjusting the operation modes of the active units,energy efficiency of the fronthaul can be enhanced.The simulation results show that,compared to the traditional fronthaul with fixed topology,the energy efficiency can be improved by about 88%in off-peak period with the proposed algorithm.