```tex \documentclass[10pt,twocolumn,twoside]{IEEEtran} \begin{document} \section{THO-OFDM system} Since the clipping noise of ACO-OFDM signal in first layer falls on the even subcarriers, the even subcarriers can be used to carry useful data after we removing the clipping noise on the even subcarriers. We denote the second layer \textit{N}/2-point data as $X_{\mathrm{THO}}^2=[0$, $X_1$, $0$, $X_3$, $\dots$, $X_{N/4-1}$, $0$, $X_{N/4-1}^*$, $0$, $\dots$, $X_3^*$, $0$, $X_1^*]$, also denote the third layer $N/2$-point data $X_{\mathrm{PAM}}^{(3)}$ as $j[0$, $0$, $P_2$, $0$, $P_4$, $\dots$, $P_{N/4-2}$, $0$, $0$, $0$, $-{P_{N/4-2}}$, $0$, $\dots$, $-{P_4}$, $0$, $-{P_2}$, $0]$, where $j=\sqrt{-1}$ and ${P_k}(k = 2$, $4$, $\dots$, ${N/4-2})$ is the PAM symbols. After IFFT and negative clipping operation, the $N/2$-point unipolar signals of the second and third layers, corresponding to $x_{\mathrm{ACO}}^2$ and $x_{\mathrm{PAM}}^3$ can be obtained. \end{document} ```