Design And Implementation Of Synchronization Algorithm For LTE Small Cell Ultra-dense Network System

Since the concept of 5th generation of mobile communication(5G)has been proposed,5G has been in a substantial experimental stage.The key technologies introduced by 5G,such as large-scale MIMO,millimeter-wave and multi-carrier technique,have become the focus of the research.The era of 5G is the period of explosive growth of mobile data traffic,which can provide technical support for system throughput enhancement and massive user equipment access.In order to meet the rapid growth of traffic demand,the IMT-2020 organization proposed ultra-dense deployment scheme of Small Cell.However,with the continuous increase of Small Cell in the network.In ultra-dense deployment scheme,combined interference coordination and cell cooperation is need to be solved to achieve maximum network throughput upgrades.Network synchronization of the Small Cell is one of the basic conditions for the implementation of the above technologies.Therefore,Network synchronization is an important issue to be solved in ultra-dense Small Cell network.Firstly,network synchronization technologies of traditional 2G,3G and 4G mobile network sysntems is introduced in this thesis.The advantages and limitations of applications in the case of ultra-dense scene is analyzed.3GPP proposes an air interface listening solution for the indoor scenario that Small Cell can utilize the macro base station downlink signals of the common channel to get selfsynchronization.Therefore,the PSS signal commonly used for synchronization in the downlink signals of the LTE is elaborated in this thesis.Theoretical analysis of CRS signal frequency synchronization is also presented.The air interface monitoring synchronization technology scheme is also introduced by this thesis.Aiming at the above air interface interception synchronization technologies and considering the shortcomings of adopting the multi-hop mode in an ultra-dense network scenario,an air interface-based Small Cell clustering synchronization algorithm is proposed in this thesis.The network synchronization is divided into two procedures by clustering,which includes intra-cluster synchronization process and inter-cluster synchronization process.In intracluster synchronization,the macro node with low synchronization error is regarded as the cluster head.The synchronization source for other intra-cluster nodes monitoring is selected based on the synchronization level of the neighboring cells.Then,the downlink PSS and CRS signals of synchronization source are monitored.The inner network adopts multi-hop mode to satisfy the basic synchronization requirements of all Small Cells nodes.In inter-cluster synchronization,the MBSFN subframes are set to reduce the interference between clusters and improve the accuracy of the synchronization signal detection.The simulation results show that this algorithm can guarantee the synchronization precision of multiple nodes in a cluster,which is 6 to 10 ?s higher than the traditional air interface synchronization.Since the change of the channel condition of the Small Cell intercepting path would lead to the change of synchronization error,optimal synchronization path cann't get update promptly.Therefore,this thesis proposes a UE-asisted small cell synchronization update algorithm,which uses a cluster synchronization controller as a cluster control center.The weights of each small cell synchronization path are calculated by cluster synchronization controller according to the collected parameters measured by the UE.When the weight values is increased or decreased,the optimal synchronized path is obtained according to the proposed intra-cluster synchronization path update algorithm.Simulation shows that with the change of the listening paths channel,synchronization update algorithm could ensure that the synchronization error of nodes in the cluster can still be in the acceptable range.Finally,this thesis designs a communication control protocol OPENSC used between SDN controller and LTE Small Cell.The proposed protocol is used to realize control of Small Cell parameters,resource acquisition and synchronization of base station by SDN controller.A synchronization control module is designed for synchronization control specific strategies in LTE Small Cell.Test interface verifies the usability of the OPENSC protocol.Comparing the performance of the of the traditional synchronous control scheme,the actual result demonstrates the superiority of the synchronous control strategy to improve the UE rate.