Method for improving HARQ performance of mobile communication system of high-speed railway

In the case that the LTE(Long Term Evolution) wireless communication system is applied to high-speed railways, high moving speeds and complicated railway line environments impose great influence unfavourable for HARQ(Hybrid Automatic Retransmission Request) performance. In this paper, the HARQ performance in high-speed railway environments was analyzed. It shows that the system with HARQ technology has lower block error rate and higher throughput as compared to the case without it. However, the HARQ performance in high-speed environments is not as good as that in the scenario of public networks where most of the users are with low-speeds. And then, a novel HARQ scheme was proposed, which could enhance the HARQ performance in the overlapping region. In this scheme, the number of maximum retransmission is reduced when the train arrives at a predefined location, and the packets, which suffer transmission error or can not be acknowledged before handover triggering, will be saved by the system, and retransmitted by the target eNodeB(after the train accesses it), and then combined and decoded by the onboard UE(User Equipment). Performance analysis shows as follows: The error rate decreases by 55% when these packets are retransmitted in the target cell; compared to the situation with the fixed number of maximum retransmission, the proposed scheme provides more opportunities for new packets to be transmitted before handover, thus the throughput increases by about 12% when target eNodeB retransmits those forward packets.