基于时频二维训练信息的高谱效多天线TFT-OFDM技术研究

Traditional multi-antenna OFDM systems have the technical problem of large training information overhead. In this project, based on the signal structure of the time domain synchronous OFDM (TDS-OFDM), which is the key technology of Chinese digital television terrestrial broadcasting (DTTB) standard, we propose a fundamentally distinct OFDM-based transmission scheme called time-frequency training OFDM (TFT-OFDM) for multi-antenna systems with high spectral efficiency. Unlike the sole time-domain training sequence or frequency-domain pilots in conventional OFDM systems, every TFT-OFDM symbol has training information both in the time and frequency domains. We further propose the time-frequency joint channel estimation scheme, whereby the time-domain orthogonal training sequences are utilized to merely acquire the path delay information of the channel without interference cancellation, while the path coefficients are estimated by using the small amount of frequency-domain orthogonal pilots. This scheme could decouple the mutually conditional relationship of time- and frequency-domain processings in conventional TDS-OFDM systems, and the pilot overhead could be significantly reduced. Moreover, the accuracy of channel estimation in TFT-OFDM systems could be substantially improved by the time-frequency joint processing. This project will provide the theoretical foundation and key technology for Chinese next-generation DTTB standard, which aims to outperform the most advacned internationl DTTB standards in spectral efficiency and system reliability.

针对现有多天线OFDM系统中用于信道估计的训练信息开销较大这一技术难题，本项目在继承中国地面数字电视标准的核心调制技术时域同步正交频分复用（TDS-OFDM）基本信号结构的基础上，将传统OFDM技术中时域或频域一维的训练信息扩展到时频二维, 提出时频联合信道估计方法，即在无需干扰消除的前提下先通过时域正交训练序列来获取信道的各径时延，然后仅利用极少量的频域正交导频即可获取信道的各径系数，进而建立基于时频二维训练信息的高谱效多天线TFT-OFDM（Time-Frequency Training OFDM）传输理论和技术。该技术突破了传统TDS-OFDM技术中时域和频域处理相互制约的依赖关系，并大幅降低了多天线系统中的导频开销，且通过时频联合处理提高了信道估计的精度。本项目将为我国新一代数字电视标准在高谱效、高可靠传输等关键技术指标上优于国外最先进的数字电视标准提供重要的理论基础和技术储备。

当前我国数字电视标准DTMB仅支持单天线，而代表国际先进水平的欧洲第二代数字电视标准DVB-T2最高可支持的发射天线数也仅为2。为了进一步挖掘多天线（MIMO）技术在高谱效低能耗方面的巨大潜能，本项目提出了适用于大规模MIMO系统的基于时频二维训练信息的OFDM传输技术TFT-OFDM（Time-Frequency Training OFDM），将传统多天线OFDM 技术中时域或频域一维的训练信息扩展到时频二维，并提出对应的高精度时频联合信道估计方法。该技术突破了传统TDS-OFDM技术中时域和频域处理相互制约的依赖关系，大幅降低了大规模MIMO系统中的导频开销，可支持的天线数目高达几十甚至几百，可在频谱效率、系统功耗等关键技术指标上显著超越DVB-T2标准。本项目研究成果不仅可用于我国数字电视标准，还可以用用于未来5G系统。