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\documentclass[journal]{IEEEtran}
\usepackage{amsmath}
\usepackage{adjustbox}% http://ctan.org/pkg/adjustbox
\begin{document}
\begin{multline*}\label{eqn:1_1}
L_{p}(d, h_{TX}, h_{RX}) = \overbrace{L_{fs}(R,f)U(0.1-d)}^{L_{p,1}}+\clipbox{-2 0 5 0}{$\overbrace{(L_{fs}(R,f) + (1\hspace{1em}}^{L_{p,2}}$} \\[\jot]
\clipbox{100 0 -2 0}{$\overbrace{\phantom{\hspace{10em}}(+ \log_{10}(d))L^{EH}_{B}(f,h_{TX},h_{RX},1) - L_{fs}(0.1,f))(U(1-d) - }$}\\[\jot]
\clipbox{100 0 -2 0}{$\overbrace{\phantom{\hspace{10em}}U(d-0.1))}$}+\overbrace{L_{p}^{EH}(d,f,h_{TX,eff},h_{RX})(U(80-d) - U(d-1))}^{L_{p,3}}\\[\jot]
\overbrace{\phantom{\hspace{10em}}(+ L_{p}^{ITM}(f,h_{TX},h_{RX},p(d))+max\{L^{EH}(f,h_{TX},h_{RX},p(80)) - L_{med}^{ITM}(f,h_{TX},h_{RX},p(80)),0\})U(d-80)}^{L_{p,4}}
\end{multline*}
\end{document}