# LDM-Ex-FDM: A Novel Multi-Service Transmission Scheme for the ATSC 3.0 System
## 5 Conclusions  
In this paper, a multi-service transmission scheme called LDM-Ex-FDM for the ATSC 3.0 system is proposed. The proposed scheme can support simultaneous transmission of multiple services with different received SNR thresholds. First, the system's BICM capacity calculation shows that the LDM-Ex-FDM scheme can effectively increase the fixed service capacity and the overall service capacity while appropriately reducing the capacity of the mobile service. It should be noted that the reduction in the capacity of the mobile service is due to the reduction in the bandwidth used, thus the spectrum efficiency of the mobile service has not changed compared with the traditional _LDM_ scheme. Second, the computer simulation results show that the LDM-Ex-FDM scheme with EISP can improve the reception performance of the fixed service without lowering the SNR threshold of the mobile service compared with the traditional _LDM_ scheme in the ATSC 3.0 system. When the puncturing rate in the LDM-Ex-FDM scheme is configured as 1/12, the performance of the fixed service is improved by 1.8 dB, while the BER performance of the mobile service is not affected and the transmission rate is only reduced by 0.27 Mbps. In view of the _LDM_ symbols with overlapping constellations, our proposed LDM-Ex-FDM scheme with NEISP can increase the performance of the mobile service and fixed service by 0.9 dB and 1.05 dB, respectively. Thus, since the SNR threshold of the _EL_ service is improved, many _EL_ holes can be avoided, thereby improving the overall coverage effect. In addition, to facilitate the implementation of the scheme, a low complexity DIC receiver is proposed accordingly. Simulation results show that, compared to the traditional SIC scheme, when the injection level is greater than 10 dB, the BER performance of the proposed DIC scheme has almost no performance loss, and the complexity is significantly reduced. It is worth pointing out that although the transmission rate of the mobile service is appropriately reduced, when the _CL_ configuration is robust, that is, the constellation is QPSK and the LDPC code rate is 5/15, the _CL_ can still fully meet the transmission of 720p mobile service in the typical scenario. Therefore, for the proposed LDM-Ex-FDM scheme, a reasonable compromise can be achieved between the performance of the _EL_ demodulation and the _CL_ transmission rate. For further research, we will study the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Scheme** & **Transmitter** & **Receiver** & \begin{tabular}{c} **Achieved** \\ **Capacity** \\ \end{tabular} & **Complexity** \\ \hline layered division & \multirow{2}{*}{_LDM_} & \multirow{2}{*}{_LDM_} & successive & \multirow{2}{*}{low} & \multirow{2}{*}{low} \\ multiplexing (_LDM_) & & & & \\  & & & cancellation (SIC) & & \\ \hline time-layered & \multirow{2}{*}{_LDM_, time-division & \multirow{2}{*}{SIC} & \multirow{2}{*}{medium} & \multirow{2}{*}{medium} \\ division multiplexing & \multirow{2}{*}{\begin{tabular}{c} LDM, time-division \\ multiplexing (TDM) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} SIC \\ \end{tabular} } & \multirow{2}{*}{medium} & \multirow{2}{*}{medium} \\ multiplexing & \multirow{2}{*}{\
\begin{tabular}{c} LDM, \\ frequency-division \\ equal interval \\ symbol puncturing \\ (LDM-Ex-FDM) \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} SIC/ direct \\ interference \\ symbol puncturing \\ (EISP)/NEISP \\ \end{tabular} } & \multirow{2}{*}{high} & \multirow{2}{*}{medium} \\ \cline{1-1} \cline{5-5}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The comparison among several _LDM_ schemes. optimization of the DIC scheme in the case that the \(LDM\) power injection level is low and high-order modulation is adopted for the \(CL\) service. Conceptualization, X.D. and M.L. ; methodology, X.D., X.B., M.L. ; software, X.D. ; formal analysis, X.D. ; investigation, X.D., X.B., M.L. ; resources, X.D. ; data curation, X.D. ; project administration, X.D. ; writing--original draft preparation, X.D., X.B., M.L.