makecell package
\documentclass{article} \usepackage{array, tabularx, caption, boldline} \usepackage{graphicx} \usepackage{cellspace} \setlength\cellspacetoplimit{4pt} \setlength\cellspacebottomlimit{4pt} \begin{document} \begin{table}[h!] \caption{Main Notations} \label{tab:table1}\centering \begin{tabularx}{9cm}{|Sl|X|} \hline \textbf{Notation} & \textbf{Meaning} \\ \hline $P_{md}$ & local probability of misdetection \\ \hline $P_{d}$ & local probability of detection \\ \hline $P_{fa}$ & probability of false alarm \\ \hline $P_{pu}$ & signal \\ \hline $P_b$ & broadcast \\ \hline $N_{gd}$ & node 1 \\ \hline $N_{ln}$ & Total number of node \\ \hline $h_{gd1}$ & {h number when majority of the nodes in a topology gives a decision `1' when PU is present} \\ \hline \end{tabularx} \end{table} \begin{table}[h!] \caption{Main Notations} \label{tab:table2}\centering \begin{tabularx}{9cm}{SlV{2}X} \textbf{Notation} & \textbf{Meaning} \\ \hlineB{1.2} $P_{md}$ & local probability of misdetection \\ $P_{d}$ & local probability of detection \\ $P_{fa}$ & probability of false alarm \\ $P_{pu}$ & signal \\ $P_b$ & broadcast \\ $N_{gd}$ & node 1 \\ $N_{ln}$ & Total number of node \\ $h_{gd1}$ & {h number when majority of the nodes in a topology gives a decision `1' when PU is present} \end{tabularx} \end{table} \end{document}
