Interference And Mobility Management Based On Virtual Cells In Ultra-dense Networks

Ultra-Dense Networks(UDN) technology achieves a significant improvement in network performance by densely deployed Next-Generation NodeBs(gNBs)to meet the requirements of the next-generation mobile communication systems(ultra-high transmission rate,ultra-high capacity,and ultra-low latency).The distances between users and gNBs in UDN are greatly shortened,which provides the necessary conditions for the implementation of virtual cells.By deploying virtual cells in UDN,the user's network service mode can be changed from "base station-centric" to "user-centric," thereby eliminating cell edge users and further improving network performance.Because of the irregular network topology of UDN and the user-centric network framework,traditional regular methods for network modeling are no longer applicable.We urgently need a new approach to model a large number of gNBs randomly distributed in UDN and to accurately analyze the performance of virtual cell users.Besides,virtual cell users face a more complex interference environment and more frequent handovers in UDN.The problems caused by these challenges,such as virtual cell optimization,a large amount of handover signaling overhead,high transmission delay,and high handover failure rate,etc.,will seriously affect user performance.To meet the challenges of interference and mobility management based on virtual cells in UDN,we use the stochastic geometric modeling theory to model and analyze the user-centric virtual cells in UDN in this paper.Based on virtual cells,a load-aware interference management solution and a proactive mobility management solution are also proposed to provide users in UDN with user-centric network services and efficient interference mobility management.The main contributions are as follows:1.Stochastic geometric modeling and interference analysis of virtual cells in UDNWe use stochastic geometry modeling theory and tools to model and analyze the user-centric virtual cells in UDN.Then,the Signal to Interference plus Noise Ratio(SINR)distribution of users and the "meta"distribution of SINR are derived separately.The main innovations are as follows:1)Chose the Non-Coherent Joint Transmission(NCJT)technology to construct virtual cells;2)Use two performance evaluation metrics to analyze the interference performance of users in UDN comprehensively.The SINR distribution is a spatially averaged performance metric,which reflects the average condition of communication links.The "meta" distribution of SINR gives the complete spatial distribution of the successful transmission probability of a communication link during fading.Simulation results show that the SINR distribution and the "meta" distribution of SINR can match the real value well.The accurate modeling and analysis of virtual cells provide a solid theoretical analysis foundation for subsequent researches about the interference and mobility management solutions based on virtual cells in UDN.2.Interference management solution based on virtual cells in UDNFor the complex interference environment faced by virtual cell users in UDN,a load-aware interference management scheme is proposed.The main innovations are as follows:1)Consider the impact of Channel State Information(CSI)and different resource allocation schemes on users,and model the channel estimation error caused by imperfect CSI as a new source of the interference;2)Find the optimal radius of virtual cells to maximize the user's system spectrum efficiency;3)Consider the impact of network load on the formation of virtual cells,and propose an optimal base station activation strategy based on fuzzy logic theory.The proposed interference management solution can find the optimal virtual radius for users according to different densities of gNBs,which can minimize the impact of interference on rate performance.The solution also can adjust the activation threshold and resource allocation scheme according to different network loads by the optimal base station activation strategy.Thereby,the strategy can reasonably activate serving gNBs for users to balance transmission rate performance and resource overhead.3.Mobility management solution based on virtual cells in UDNTo serve the problems in terms of frequent handovers and a large amount of handover signaling overhead faced by virtual cell users in UDN,a proactive mobility management solution assistant by the trajectory prediction is proposed.The main innovations are as follows:1)Propose an LSTM-DR trajectory prediction algorithm that integrity the advantages of Long Short-Term Memory(LSTM)neural network and Dead Reckoning(DR)technology;2)Use the real trajectory database of taxis to train the LSTM-DR algorithm and verify the prediction accuracy of the algorithm;3)Design four management modules which support the centralized controller to perform the proactive handover management based on the trajectory prediction information;4)Select an appropriate set of cooperative gNBs for users according to the user moving speed and activation preference;5)Optimize the handover signaling process for virtual cells.Simulation results show that the proposed trajectory prediction algorithm has a higher prediction accuracy and robustness than LSTM and DR methods.The proposed proactive management solution can significantly reduce the handover frequency,handover signaling overhead,and the handover failure rate for virtual cell users in UDN.