答案1
使用标准 LaTeX 命令(数学模式)
\underbrace{Text to be underbraced}_{Text under the brace in small print}
\documentclass{article}
\usepackage{amsmath} % for the \text command
\newcommand\ntime{n_{\mathit{time}}}
\newcommand\nbeam{n_{\mathit{beam}}}
\newcommand\nelem{n_{\mathit{elem}}}
\newcommand\round{\mathop{round}}
\begin{document}
\[ \mathit{BF}(n_{\ntime},n_{\nbeam}) =\sum_{\nelem=0}^{\nelem} \mathit{Data}(\nelem,\ntime+
\underbrace{\round(\Delta t(\nelem,\ntime,\nbeam)\cdot\mathit{fs})}_{\text{Fine time shift, interpolated Ts}}
,\nbeam)
\]
\end{document}