Research On Synchronization And Realization Of Distributed Relay Networks

With continuous expansion of the TD-LTE industrial chain,the number of mobile users is growing rapidly,and 4G network construction has reached a climax.However,the coverage requirements make the problem of higher network construction costs becoming increasingly prominent.Distributed relay networks have significant advantages,such as cost advantage,wide coverage,good extensibility,deployment flexibility,which make it a hot research topic in the design of 4G network construction.However,its particular architecture and framework brings new challenges to the synchronization design.In this paper,synchronization technologies of distributed relay networks are researched in depth,and a quite comprehensive synchronization scheme with good performance and low complexity is proposed.Firstly,this paper introduces the system model and discusses the synchronization issues of the TD-LTE distributed relay networks.In TDD system,accurate downlink/uplink switching is the precondition for the relay devices to complete signal transmission,which points out that all the synchronization works should be designed around the realization of accurate downlink/uplink switching.The analysis shows that accurate downlink/uplink switching in distributed relay networks depends upon the collaboration between the mater equipments and the slave ones,under the condition of accurate symbol timing estimation and precise downlink/uplink configuration detection.Secondly,the design of the hardware platform and realization is introduced in detail.This paper completes the PCB design of the RF daughter board and its FPGA carrier board.And then several important performance parameters of the whole hardware platform have been tested,of which the results show that expected performance is satisfied.Then,according to the analysis of the TD-LTE distributed relay networks,different time and frequency synchronization algorithms are studied and simulated.The simulation results of the effects of AWGN,carrier frequency offset and multipath fading effect on different PSS detection algorithms show that M-correlation algorithm is applicable for our system for its good ability to make a tradeoff between suppression of carrier frequency offset and anti-noise performance.Then,based on the simulation results of the frequency synchronization algorithms,a combined method of carrier frequency and bandwidth detection with low complexity is proposed.At the same time,the simulation results of the carrier frequency offset estimation algorithm show that the PSS timing offset and the carrier frequency offset may affect each other,which leads to a new PSS detection scheme combined with carrier frequency offset estimation.Next,a new downlink/uplink configuration detection method was proposed to complete the air-interface synchronization design of the TD-LTE distributed relay networks.In order to improve the synchronization design of the whole system,this paper also proposes the frame structure of the cable interface based on CPRI.Lastly,the proposed synchronization scheme and necessary digital interfaces are designed and implemented by FPGA.The proposed synchronization scheme and the realization of the hardware platform are well-functioned with great performance,providing a significant reference for further design and development of the distributed relay networks.