documentclass[twoside,headsepline,12pt,a4paper,bibliography=totoc,toc=listof,DIV=14,BCOR=2mm,]{scrbook}

usepackage{graphicx}
usepackage{amsmath}
usepackage{exscale}
usepackage{longtable}
usepackage{setspace}
usepackage{bm}
usepackage{indentfirst}
usepackage{amsfonts}
usepackage{gensymb}
usepackage{pgfplots}
usepackage{enumitem}
usepackage{siunitx}
usepackage{float}
usepackage{caption}
usepackage{subcaption}
usepackage{cases}
usepackage{amsmath,amsfonts}
usepackage{graphicx}
usepackage{makecell}
renewcommandtheadfont{itshapebfseries}
sisetup{table-number-alignment=center}
usepackage[all]{nowidow}
setcounter{tocdepth}{10}
setcounter{secnumdepth}{10}
usepackage[showframe=false]{geometry}
usepackage{amssymb}
usepackage{xr}
usepackage{multirow}
usepackage{hhline}
usepackage{ctable}
usepackage{graphicx,rotating,booktabs}
usepackage[verbose]{placeins}
usepackage{blindtext}
usepackage{titlesec}
usepackage{tabularx}
usepackage[nottoc]{tocbibind}


begin{document}
 begin{table}
           centering
           begin{subtable}{0.47linewidth}
               begin{tabular}{|l|*{4}{c|}}
        hline
        textbf{Rate} & multicolumn{4}{|c|}{$V_{out}$ in SI{}{Volts}} \
        cline{2-5}
         & textbf{$k=0.1$} & textbf{$k=0.3$} & textbf{$k=0.6$} & textbf{$k=0.8$} \
        hline
    SI{1}{bps} &  & & & \
    hline
    SI{100}{bps} &  & & & \
    hline
    SI{1}{kbps} &  & & & \
    hline
    SI{5}{kbps} &  & & & \
    hline
    SI{10}{kbps} &  & & & \
    hline
    SI{15}{kbps} &  & & & \
    hline
    SI{17}{kbps} &  & & & \
    hline
    SI{20}{kbps} &  & & & \
    hline
    SI{30}{kbps} &  & & & \
    hline
    SI{50}{kbps} &  & & & \
    hline
    SI{100}{kbps} & & & & \
    hline
    end{tabular}
               caption{A vs B}
               label{tab:a}
           end{subtable}%
           hspace*{4em}
           begin{subtable}{0.47linewidth}
               centering
               begin{tabular}{|l|*{4}{c|}}
        hline
        textbf{Rate} & multicolumn{4}{|c|}{$V_{out}$ in SI{}{Volts}} \
        cline{2-5}
         & textbf{$k=0.1$} & textbf{$k=0.3$} & textbf{$k=0.6$} & textbf{$k=0.8$} \
        hline
    SI{1}{bps} &  & & & \
    hline
    SI{100}{bps} &  & & & \
    hline
    SI{1}{kbps} &  & & & \
    hline
    SI{5}{kbps} &  & & & \
    hline
    SI{10}{kbps} &  & & & \
    hline
    SI{15}{kbps} &  & & & \
    hline
    SI{17}{kbps} &  & & & \
    hline
    SI{20}{kbps} &  & & & \
    hline
    SI{30}{kbps} &  & & & \
    hline
    SI{50}{kbps} &  & & & \
    hline
    SI{100}{kbps} & & & & \
    hline
    end{tabular}
               caption{A vs B}
               label{tab:b}
           end{subtable}%
           quad
           begin{subtable}{0.47linewidth}
               centering
               begin{tabular}{|l|*{4}{c|}}
        hline
        textbf{Rate} & multicolumn{4}{|c|}{$V_{out}$ in SI{}{Volts}} \
        cline{2-5}
         & textbf{$k=0.1$} & textbf{$k=0.3$} & textbf{$k=0.6$} & textbf{$k=0.8$} \
        hline
    SI{1}{bps} &  & & & \
    hline
    SI{100}{bps} &  & & & \
    hline
    SI{1}{kbps} &  & & & \
    hline
    SI{5}{kbps} &  & & & \
    hline
    SI{10}{kbps} &  & & & \
    hline
    SI{15}{kbps} &  & & & \
    hline
    SI{17}{kbps} &  & & & \
    hline
    SI{20}{kbps} &  & & & \
    hline
    SI{30}{kbps} &  & & & \
    hline
    SI{50}{kbps} &  & & & \
    hline
    SI{100}{kbps} & & & & \
    hline
    end{tabular}
               caption{A vs B}
               label{tab:c}
           end{subtable}%
           hspace*{4em}
           begin{subtable}{0.47linewidth}
               centering
              begin{tabular}{|l|*{4}{c|}}
        hline
        textbf{Rate} & multicolumn{4}{|c|}{$V_{out}$ in SI{}{Volts}} \
        cline{2-5}
         & textbf{$k=0.1$} & textbf{$k=0.3$} & textbf{$k=0.6$} & textbf{$k=0.8$} \
        hline
    SI{1}{bps} &  & & & \
    hline
    SI{100}{bps} &  & & & \
    hline
    SI{1}{kbps} &  & & & \
    hline
    SI{5}{kbps} &  & & & \
    hline
    SI{10}{kbps} &  & & & \
    hline
    SI{15}{kbps} &  & & & \
    hline
    SI{17}{kbps} &  & & & \
    hline
    SI{20}{kbps} &  & & & \
    hline
    SI{30}{kbps} &  & & & \
    hline
    SI{50}{kbps} &  & & & \
    hline
    SI{100}{kbps} & & & & \
    hline
    end{tabular}
               caption{A vs B}
               label{tab:d}
           end{subtable}%
           label{tab:d}
  caption{A vs B}
       end{table}

end{document}