The Research Of Pre-Coding In High-Speed Mobile Scenario For Lte Downlink

MIMO pre-coding can gain higher peak rate, better transmission reliability and more effective spectrum effectiveness by taking advantage of multi-antenna to provide spatial multiplexing and space diversity. So it has becoming a key technology of LTE protocol. With the development of high-speed rail, it proposes new require to wireless communication in high-speed mobile scenario. In the future, LTE-R will take the place of GMS-R to one of communication schemes in high- speed rail. In this scenario, Doppler shift increases rapidly, when it adds up to 850Hz,coherence time is about 0.498ms less than the time of a subframe transmission cycle, the channel state information changes rapidly at the moment. Since the fast time-varying characteristics of channel, the channel state information which experiences feedback delay cannot describe the current channel situation accurately.Some different pre-coding schemes have been analyzed in high-speed mobile scenario for LTE protocol. And using statistical information of channel to execute pre-coding based on codebook was proposed in this thesis. First of all, closed-loop pre-coding based on codebook and non-codebook is analyzed by executing some simulation and comparison in link level simulation platform. Secondly, a pre-coding scheme based on codebook was proposed which is using statistical information of channel to improve the inaccuracy of channel estimation, enhance BER performance and decrease computation complexity. Although the performance of system is enhanced, but BER can’t still drop below 10-2. Once more, computational complexity of selecting pre-coding matrix index and feedback overhead is analyzed which is aiming at given scheme and conventional scheme. The result has been shown that pre-coding scheme based on statistical information of channel has a distinct advantage. In the end, four different schemes were came up with to the issue of high BER. They are codebook pre-coding scheme which is executing reduced-rank processing, codebook pre-coding scheme which is decreasing feedback granularity of codebook index, open-loop pre-coding scheme based on large delay CDD and closed-loop pre-coding scheme which is at the cost of pair-wise error probability based on non-codebook. Then, the given reduced-rank pre-coding scheme was sought out which has the most performance of BER and channel capacity and was also supported by LTE protocol to be a pre-coding scheme in high-speed mobile scenario by simulating and analyzing these schemes.