# Enhanced LDM for Next-Generation Digital Broadcasting Transmission
## 4 Compute and Simulation Results
### Simulation Results  
In this subsection, the transmission performance of each service of the proposed En-FDM scheme is evaluated under the AWGN and multipath channels. We perform simulation by MATLAB 2017b on the Intel(R) Xeon(R) E5-2667 CPU under a 2.9 GHz and 64-bit Windows 10 operating system. The simulation parameters used in this section are shown in Table 2, and the multipath channel model parameters are shown in Table 3.  
The throughput of the mobile service and fixed service of the proposed En-LDM system and traditional LDM system were simulated under the multipath channel. As shown in Figure 6, the En-LDM system provides higher channel capacity for both the overall service and the fixed service (working at high SNR) under the multipath channel. When the SNR is higher than 29 dB, the channel capacity of the fixed service in the En-LDM system is 1.77 Mbit/s higher than that of the traditional LDM system, and the channel capacity of the overall service in the En-LDM system is 0.97 Mbit/s higher than that of the traditional LDM system. In addition, we found that the channel capacity growth of \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline FFT Size & 16k \\ Scattered Pilot pattern & SP8\_2 \\ Cyclic Prefix (CP) & 1/16 \\ CL LDPC Code Length & 16,200 \\ CL LDPC Code Rate (\(CR_{C}\)) & 5/15 \\ CL Number of Iterations & 50 \\ CL Constellation & QPSK \\ EL LDPC Code Length & 16,200 \\ EL LDPC Code Rate (\(CR_{E}\)) & 9/15,11/15 \\ EL Number of Iterations & 50 \\ EL Constellation & NU\(-\)64 QAM \\ Puncturing Rate (PR, \(\gamma\)) & 1/13 \\ Injection Level (\(\Delta\)) & 10 dB, 12 dB, 15 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters. Figure 5: The shortfall from Shannon for the fixed service of the LDM and En-LDM systems under the AWGN and Rayleigh channels, where the parameters of the LDM and En-LDM systems were set to \(\Delta=10\) dB, \(B_{f}/B_{t}=1/8\), the CL constellation was set to QPSK, and the EL constellation was set to NU\(-\)64 QAM. the overall service of the system is less than that of the fixed service, which shows that the channel capacity of the mobile service in the En-LDM system is lower than that of the traditional LDM system. This result is consistent with the previous spectrum efficiency analysis and simulation results. The reason behind this is that the data removed by the puncturing of the fixed service occupies a small number of subcarrier transmissions of the original mobile service in the LDM. As these results show, in a typical scenario of delivering robust HDTV mobile services and high data rate UHDTV fixed services in an radio frequency (RF) channel [30], the proposed En-LDM scheme can provide more efficient spectrum usage while allowing a slight decrease in the transmission capacity for mobile service. The bit error rate (BER) simulations of mobile service and fixed service in the En-LDM system and traditional LDM system under the AWGN and multipath channels are performed, and the results are presented in Figures 7-11, respectively. \begin{table}
\begin{tabular}{c c c} \hline
**Echo** & **Power (dB)** & **Time Delay (\(\upmu\)s)** \\ \hline
1 & –3 & 0 \\
2 & 0 & 0.2 \\
3 & –2 & 0.5 \\
4 & –6 & 1.6 \\
5 & –8 & 2.3 \\
6 & –10 & 5.0 \\ \hline \end{tabular}
\end{table} 
Table 3: Profile of multipath channel model. Figure 6: Channel capacity of fixed service and total service of En-LDM and traditional LDM systems under the multipath channel, where the injection level was set to \(\Delta=10\) dB, the CL constellation was set to QPSK, the EL constellation was set to NU –64 QAM, the puncturing rate of En-LDM scheme was set to \(1/13\), and the low-density parity-check (LDPC) code rates of CL and EL were set to \(5/15\) and \(11/15\), respectively.