Research On The Downlink Frequency Compensation And Hanover Performance For SFN In HST

In recent years, with the rapid development of the high-speed-trains(HSTs), companies are paying more and more attention to HST wireless communication system. To meet the high rate data transmission requirements of wireless of high-speed mobile users in HST environment,LTE has been suggested as one of the wireless transmission standards in the HST application by 3rd Generation Partnership Project (3GPP)Co-ordination Group. However, the large Doppler shift and frequent cell handover greatly degrade the performance of the data transmission in the LTE system under the HST scenario. At present, although some schemes have been proposed to enhance the system performance, there are still many challenges, e.g. high penetration loss, large Doppler shift, low data rate and so on. Therefore, single frequency network (SFN) of HST was proposed by Huawei and other companies. SFN has many advantages,including better coverage, less interference, less power, and higher reliability. However, SFN will also encounter a new set of problems,especially in HST scenario, these problems are particularly prominent.Firstly, under the SFN scenario of HST, multiple links will not only lead to different delay, but also result in different frequency offsets of data from different remote radio heads (RRHs) when the downlink signals arrive at user equipment (UE). Thus, it will be found that the legacy UE performance in the SFN scenario will degrade significantly,especially for the higher order modulation scheme. In this paper, in order to solve this issue, I proposed to adopt a dynamic 2-tap channel model and build a related simulation platform based on the channel model. In addition, I also proposed two methods to estimate and compensate the Doppler frequency shift, which are the base station (BS) frequency pre-compensation and the UE receiver enhancement. The simulation results show the significant downlink performance improvements can be achieved by the two solutions, especially for high-speed users in SFN.In addition, although HST SFN can reduce the number of handover greatly, it still has some problems such as a high rate of wireless link failure, the serious ping-pong effect and so on. So in this paper, I proposed a switching handover algorithm based on the Doppler shift. At the meanwhile, I improve the network topology. The simulation results show that these schemes can effectively improve the handover performance in HST SFN, especially when the two schemes are used together.