System-level Simulation And Research On Low Latency Communication Technology In TD-LTE

Higher data speed and lower latency have always been the targets of wireless communication systems.They are also the significant advantages of the 4th-Generation communication system(4G)compared to the previous generation of mobile wireless communication system.Compared with 4G,the 5th Generation is clearly proposed the requirement of ultra reliability and low latency communication.TD-LTE as the transition stage between 4G TDD and 5G TDD,one of the goals is to further reduce user delay and increase system throughput on the basis of 4G,in order to pave the way for the arrival of 5G TDD.Reducing transmission delay is of great significance to speed up the response of the system and improve the average throughput.Transmission time interval and processing time of receiver are important components of the user's transmission delay.This paper proposes corresponding solutions to reduce the transmission delay aiming at two part of the delay.First,on the basis of the traditional frame structure of TD-LTE,the delay of data transmission is reduced by shortening the processing delay of the receiver.Second,the TTI is shortened by optimizing the subframe structure.Although the scheme for shortening TTI has a preliminary research conclusion,it is mainly based on the FDD model which has symmetric up-downlink frame structure.But for TDD model,which has asymmetric frame structure,it is not known in relevant fields whether the scheme to shorten TTI can effectively reduce the user transmission delay.Therefore,the research work of this paper is of great reference value.This paper introduces two kinds of low latency technologies mentioned above,and proposes a specific subframe length and structure optimization design for TTI shortening scheme.In the first stage of the study,this paper set up TD-LTE heterogeneous network simulation scenarios,and using file transfer protocol service and downlink data transmission model with finished packet throughput as performance indicators.The simulation results show that the two low latency schemes can effectively reduce the delay of data transmission and increase the throughput.And shortening the processing delay is more effective for the frame structure configured with more uplink subframe and the shortened TTI is more effective for the frame structure configured with more downlink subframe.The second research stage of this paper is mainly based on the preliminary conclusion that shortening TTI could improve the performance of the frame structure configured with higher downlink subframes.Two aspects of optimal design for the scheme of shortening TTI are carried out.In the first aspect,the design of subframe length and the optimal design of subframe structure are proposed.By changing the ratio of downlink pilot time slot(DwPTS),Guard Period(GP)and uplink pilot time slot(UpPTS)in special subframe to speed up the hybrid downlink data automatic retransmission request(HARQ)acknowledgement/Non-acknowledgement(ACK/NACK)response feedback,so as to further reduce downlink HARQ round-trip Time.In the second aspect,the paper presents that after the TTI shortening,the maximum number of HARQ processes should be increased to further upgrade the downlink data transmission capability to improve the performance of the system.And by system-level simulation,it is proved that the above two optimization schemes can bring 50.1%,59.5%,53.1%throughput gain of cell center users who configured with TDD UL-DL Configuration-5 at the system load levels were low,medium and high respectively.