Research On Forward Technology Of Relay Based On Software Defined Radio

With the growth of LTE industry chain,the demand for mobile services is surging,and the construction of TD-LTE network is ushering in the climax.Relay technology is introduced into 3GPP LTE-A,which effectively extends the network coverage and solves the communication problem of severe shadow fading or coverage of dead ends.Distributed digital relay system not only expands the network coverage area,improves the system capacity,enhances the robustness of the system,but also has the advantages of low cost,easy expansion,flexible deployment and so on.Relay technology makes the resource consumption of network layout construction low,so it has become a research hotspot in the design of LTE network coverage scheme.This thesis mainly studies interference suppression technology and automatic gain control technology of relay node in TD-LTE relay forwarding,and the hardware design and implementation of distributed digital relay system.First,this thesis introduces the model of distributed digital relay system.According to 3GPP specification,The structure of TD-LTE signals and the channel characteristics of relay system are explained in detail.The same frequency interference problem of adjacent cells and downlink automatic gain control problem in relay nodes are also analyzed.Then,co-channel interference suppression technology for downlink of multi-antenna relay is studied in depth.First,a mathematical model of multi antenna relay amplification and forwarding under the same frequency interference of adjacent cells is established.Based on the processing of receiving and sending of relay nodes,the end to end signal to interference plus noise ratio(SINR)of the system is derived.Secondly,the end to end SINR of the system under the three interference suppression schemes: MRC/MRT,ZF/MRT and MMSE/MRT is investigated,and the interference suppression receiving vector structure is given to maximize the end to end SINR.Then,the influence of the number of relay nodes and the composition of the interference source on the performance of the relay interference suppression is simulated and analyzed.Finally,estimation methods of the covariance matrix parameters of interference with noise in the relay interference suppression is emphatically studied,including the estimation algorithm based on receiving signals,reference signals,or interference reconstruction and adaptive diagonal loading algorithm.The performance of these estimation algorithms is simulated and analyzed.Subsequently,the design of automatic gain control for downlink of TD-LTE relay system is studied.Through the research of the traditional AGC,the drawbacks of the traditional scheme are explained.The average power and peak to average power ratio of receiving signals under different user data are simulated and analyzed in TD-LTE downlink.Combined with the characteristics of relay receiving signals and channels,A design of TDLTE relay AGC using AGC slow loop and fast loop is proposed.The designs of AGC slow loop based on PSS correlation peak and CRS power respectively,and the AGC fast loop design scheme based on user data quantity estimation are given in this thesis,and their performance is simulated and analyzed.Finally,this thesis introduces the specific hardware design and implementation of the distributed digital relay platform.The overall structure design of the distributed digital relay platform is outlined,the selection and specific performance parameters of the key chips in the hardware platform are given.The design and implement by FPGA of the driving module,the digital interface module and the automatic gain control module are emphatically studied.The correctness and feasibility of the designs are proved by simulations.