Research On Interference Management Technology In Multi-tier Heterogeneous Network

In order to meet the demands for high-speed data connectivity at anytime from anywhere,the heterogeneous deployments have been introduced in 3GPP(The 3rd Generation Partnership Project)LTE(Long Term Evolution)standards since Release 8 specifications,which can effectively improve the system capacity and meet the increasing needs for mobile data traffic.However,the ICI(Inter-Cell-Interference)is more serious in heterogeneous overlapping coverage scenarios.To solve this problem,eICIC(enhanced Inter-Cell-Interference Coordination)schemes have been introduced in 3 GPP LTE standard since Release 10 specifications.With the advance of standardization,CoMP(Coordinated Multiple Point)has been supported in 3 GPP LTE standard since Release 11 specifications.CoMP is considered a promising technology to effectively solve the problem of ICIC(Inter-Cell-Interference Coordination).In this thesis,the relevant problems of CoMP uplink and downlink transmission in multi-tier heterogeneous networks have been studied.Optimized downlink cooperative resource scheduling scheme and enhanced uplink joint reception scheme as well as uplink cooperative power control scheme have been proposed.To evaluate these proposed schemes,system level simulations have been performed.Compared with conventional schemes,the optimized downlink cooperative resource scheduling scheme has improved from two aspects:transmission mode selection and proportional fairness factor calculation.In the aspect of transmission mode selection,the load of both macro and pico eNodeBs have been considered.A lightly loaded eNodeB can provide more resources for CoMP users accessed to a heavily loaded eNodeB,which has guaranteed the fairness.In the aspect of fairness proportion factor calculation,the concept of the user set has been introduced firstly.By considering the effect of multi-user mode and single-user mode on cell spectral efficiency,the proportional fairness factor can be calculated more reasonably.On the other hand,through the introduction of ? factors,the weight of resource allocation between cell edge users and cell center users can be adjusted flexibly according to the actual condition of the network.In the enhanced uplink joint reception scheme,the MMSE-SIC(Minimum Mean Square Error-Successive Interference Cancellation)receiver has been applied to cancel the strong interferences from the cooperative cells.Compared with the conventional MMSE-IRC(Minimum Mean Square Error-Interference Rejection Combining)joint reception scheme,this scheme allows different interference processing strategies for different situations.For intra-site CoMP,the MMSE-IRC joint reception scheme is applied;for inter-site CoMP,MMSE-SIC joint interference cancellation is applied.This enhanced scheme can not only reduce the amount of shared information transmitted through the X2 interface,but also have a certain performance gain in throughput.Uplink energy-saving cooperation power scheme is based on uplink CoMP as well as uplink power control strategy and it is easy to be implemented.In this proposed power control scheme,both large scale and small scale channel information are the factors which determine the transmission power of UE(User Equipment).The main idea of this scheme is based on the tradeoff between the increment of system uplink throughput due to CoMP and the decrement of UE energy consumption due to power control strategy.As a result,it can reduce uplink energy consumption so that prolong the battery lifetime of UE.