# Regularized Zero-Forcing Dirty Paper Precoding in a High-Throughput Satellite Communication System
## 4 Simulation Verification and Analysis  
Simulation analysis is carried out to verify the performance of several precoding algorithms described in this paper. The simulation parameters of the high throughput satellite communication system are shown in Table 1. Because the achievable rate of users is different when different precoding schemes are adopted, the maximum beam power of each feeder is defined to be 80 W, and 7 feeders are used to form 7 beams on the satellite. Currently, in the TDMA communication mode, each beam has one user communicating in the transmission time slot, and we can select a user from each beam to form a group of 7 users to design the precoding matrix. The method of selecting users in the same time slot is an important factor affecting the overall performance of the system, so the influence of user arrangement in the beam on system performance will also be considered in the simulation and analysis. Since the greatest feature of a high-throughput satellite is its high throughput, in this paper, the throughput is used to describe the performance of a high-throughput satellite system in the simulation. The throughput of the \(i\)-th beam can be expressed by SINR:  
\[C_{i}=W\log_{2}(1+SINR_{i}) \tag{13}\] \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Orbit & Geostationary orbit \\ Carrier frequency (GHz) & 20 \\ Number of beams & 7 \\ Coverage area diameter (km) & 500 km \\
3 dB angle & 0.4 \\ Mean of rainfall attenuation (dB) & 0.6 \\ Variance of rainfall attenuation (dB) & 1 \\ Polarization mode & Single-polarization \\ Maximum antenna transmitting gain (dBi) & 50 \\ User terminal receiving gain (dBi) & 45 \\ Free space loss of forward link (dB) & 210 \\ User link bandwidth (MHz) & 500 \\ Noise temperature of receivers (K) & 207 \\ Distribution of user terminals & Fixed \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters of a high throughput satellite communications system. Figure 3: Application flow chart of dirty paper regularized zero-forcing precoding. where \(SINR_{i}\) is the SINR of the \(i\)-th user at the receiving end, which is defined by Equation (2). The average throughput of the system is the average of all beam throughputs. In addition, the traditional satellite system usually selects the four-color frequency reuse scheme; therefore, the adjacent beams use different frequency bands to reduce the interference. Therefore, this scheme is also considered in the simulation to compare and show the improvement effect of the precoding algorithm on system throughput. The maximum achievable throughput of each beam under the four-color frequency reuse scheme can be expressed as:  
\[C_{i}=\frac{W}{4}\log_{2}\left(1+\frac{4p_{i}|h_{i,i}|^{2}}{N_{0}W}\right) \tag{14}\]  
Figure 4 shows the simulation of the throughput performance of three precoding schemes, including zero-forcing, regularized zero-forcing, and regularized zero-forcing dirty paper precoding, as well as the four-color frequency reuse scheme. When the regularized zero-forcing dirty paper precoding is used, the user channel corresponding to 7 beams should be sorted first, so the simulated beam number is the sequence after the channel maximum norm selection. It can be seen that although the traditional frequency reuse mode does not have serious co-frequency interference problems, its available bandwidth is only a fraction of the full spectrum reuse satellite system, and its achievable throughput is significantly lower than that of the full spectrum reuse satellite system. Three precoding algorithms, including zero-forcing, regularized zero-forcing, and regularized zero-forcing dirty paper precoding can improve the SINR and obtain the throughput at several times the available bandwidth; thus, they can better eliminate interference. Compared with the zero-forcing precoding algorithm, regularized zero-forcing precoding reduces the amplification of noise, and its achievable throughput is increased by about 5%.