## 3 5G Signal and Detection Performance Analysis
### CSI-RS Signal  
This paper uses the CSI-RS in 5G to detect rotating targets. CSI-RS [11; 12; 13; 14] is a reference signal used in 5G signals to obtain channel state information. It is similar to a pilot signal. In 4G, the cell-specific reference signal (CRS) is used to obtain the downlink channel status between the base station and the user. And CRS can be configured with 1, 2, and 4 antenna ports. Compared to 4G, the functions of CSI-RS in 5G have been expanded, including time-frequency tracking, channel state information obtaining, and more flexible configuration of CSI-RS parameters such as the number of antenna ports, signal period, and multiplexing method. Additionally, the parameter configuration of CSI-RS is very important for using it for target detection.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \(\mu\) & **Subcarrier Spacing \(\Delta\)/ = 2\({}^{\mu}\times\)15 kHz** & **The Type of Cyclic Prefix** \\ \hline
0 & 15 & Normal \\
1 & 30 & Normal \\
2 & 60 & Normal \\
2 & 60 & Extended \\
3 & 120 & Normal \\
4 & 240 & Normal \\
5 & 480 & Normal \\ \hline \hline \end{tabular}
\end{table}
Table 2: Subcarrier spacing parameters and cyclic prefix types of 5G.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \(\mu\) & **Subcarrier Spacing \(\Delta\)/ = 2\({}^{\mu}\times\)15 kHz** & \(N_{\text{slot}}^{\text{frame}}\) & \(N_{\text{slot}}^{\text{subframe},\mu}\) & \(N_{\text{sym}}^{\text{slot}}\) \\ \hline
0 & 15 & 10 & 1 & 14 \\
1 & 30 & 20 & 2 & 14 \\
2 & 60 & 40 & 4 & 12/14 \\
3 & 120 & 80 & 8 & 14 \\
4 & 240 & 160 & 16 & 14 \\
5 & 480 & 320 & 32 & 14 \\ \hline \hline \end{tabular}
\end{table}
Table 3: The quantity relationship between subframes, slots, and OFDM symbols with different parameters \(\mu\).  
The basic parameters of CSI-RS signals mainly include the number of antenna ports, period, and density. The number of antenna ports supported by a CSI-RS signal includes 1, 2, 4, 8, 12, 16, 24, and 32. The period of CSI-RS can be 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 160, 320, and 640 time slots, and the length of the time slot is related to the length of the CP. CSI-RS has three densities: 0.5, 1, and 3. This paper obtains channel response through the CSI-RS signal, so it is necessary to know the position of the CSI-RS signal in the resource grid. The position of the CSI-RS signal in this experiment is mainly determined by period, density, symbol location, and subcarrier location. The period determines the frequency of CSI-RS occurrence in the time domain. Density determines how many subcarriers CSI-RS occupies within a PRB, symbol location determines the time starting position of CSI-RS in a slot, and subcarrier location determines the subcarrier starting position of CSI-RS within a PRB. Figure 2 shows a CSI-RS RE mapping, which includes a slot in the time domain and a PRB in the frequency domain. When the subcarrier spacing is 30 kHz, a slot contains 14 OFDM symbols. The number of antenna ports is one and the density is three. Three CSI-RS symbols occupy three REs in a PRB. In Figure 2, the symbol location is five, starting from the fifth OFDM symbol, and the subcarrier location is one, starting from the first subcarrier.