Research On Radio Resource Management In Ultra Dense Networks For 5G Communication Systems

With the rapid development of mobile Internet and intelligent terminal,the 5th Generation mobile communication technology(5G)has been brought into schedule to meet the users' great demands for high speed,low latency communication and more network capacity.Compared with traditional macro base stations deployment,ultra dense heterogeneous networks increase intensive deployment of small cells,shortening the distance between users and base station,as well as improving the spectrum efficiency and the system capacity significantly.The flexible deployment of small cells could not only solve the problem of load balancing in hot spot,but also weak coverage area of macro base station,which gives users a better service experience.As one of key technologies of 5G mobile communication system,the heterogeneous network not only brings a lot of advantages,but also bring technological challenges.In this thesis,the radio resource management technology in the ultra-dense network is discussed.Inter-cell interference mitigation in heterogeneous small cells is focused on.Aiming at the cross-link interference in 5G time division duplexing scene,an interference mitigation scheme based on beam coordination is proposed.Moreover,a new algorithm to support interactive message is proposed.On the basis of the proposed algorithm,two optimization algorithms are proposed.The main contributions of this thesis are summarized as follows:An interference mitigation scheme based on beam coordination is proposed.The algorithm takes beam direction characteristics and user's quality of service expected rates into consideration,and introduces the beam level power restriction.Beams scheduling and transmitting power are dynamically optimized through an iterative algorithm,which mitigates downlink interference of the cross-link interference and guarantees the signal quality of the uplink users.The system level simulation results demonstrate the effectiveness and superiority of the algorithm.Based on the traditional interference coordination signaling,a new interactive message-beam interference indicator between small cells is proposed which combines beam and multi-level power information to support the interference mitigation scheme effectively.New signaling is suitable for 5G multiple input and multiple output scenarios.With the predefined signaling,small cells could select beams to schedule and allocate power resource to mitigate interference.On the basis of beam coordinated interference mitigation algorithm,a water-filling power algorithm based on allowed interference power is proposed.The mechanism of power allocation is set by downlink user channel quality.Simulation results show that the algorithm improves the downlink throughputs and uplink throughputs in small cells.On the basis of above algorithm,a joint scheduling algorithm based on fairness is proposed.Compared with a water-filling power algorithm based on allowed interference power,the average throughput of overall small cells reduces by 1.0%,while the uplink throughput of edge users increases by 17.8%,which ensures the fairness of user scheduling in small cells.