# Reviews Based on the Reconfigurable Intelligent Surface Technical Issues
## 4 Conclusions  
It has been theoretically and experimentally studied that the RIS creates many potential opportunities and broad application prospects for improving the performance of communication shadow areas in B5G and future 6G networks. However, few studies have focused on the engineering aspects of the RIS-enabled wireless communication systems based on practical constraints and technical issues for real-world applications. Therefore, in this paper, the technical issues that need to be considered for the practical implementation of an RIS, such as the standardization of an RIS, types of RISs according to operation modes, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Scenario \#1**} & **Scenario \#2** & **Scenario \#3** & **Scenario \#4** & **Scenario \#5** \\ \hline \multicolumn{2}{c}{**Indoor**} & **Outdoor** & **Outdoor/Indoor** & **Outdoor/Indoor** & **Outdoor/Indoor** \\ \hline Operation frequency & 26 GHz & 26 GHz & 2.6 GHz (60 MHz) & 4.9 GHz (100 MHz) & 26 GHz (100 MHz) \\ \hline RIS size & 64 \(\times\) 64 & 32 \(\times\) 32 & 20 \(\times\) 20 (1 m \(\times\) 1 m) & 32 \(\times\) 32 (1 m \(\times\) 1 m) & 64 \(\times\) 64 \\ \hline BS-RIS & 20 m & 120 m & 206 m & 145 m & 45 m \\ \hline RIS-UE & 10 m & 20 m & 7 m & 45 m & 106 m \\ \hline \multirow{4}{*}{RSRP} & \(1\)-bit single polarization 30 dB 4-bit double polarization & 1-bit single polarization 30 dB 30 dB 15 dB 4 dB 21 dB & 4-bit dual polarization 21 dB \\ \hline Data rate & & & DL: 275\% & DL:442\% \\  & & & UL: 200\% & UL: 442\% \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Test results summary. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Ref.**} & \multicolumn{1}{c}{**Phase Resolution**} & \multicolumn{1}{c}{**Tuning Mechanism**} & \multicolumn{1}{c}{**Size No. of Elements**} & \multirow{2}{*}{**Frequency**} & \multirow{2}{*}{**Bandwidth**} & \multicolumn{1}{c}{**Scenarios**} & \multicolumn{1}{c}{**Effects on Channel Response**} \\ \hline \multirow{3}{*}{[79]} & \multirow{3}{*}{1-bit} & \multirow{3}{*}{Varactor} & 0.80 m \(\times\) 0.31 m (15.5\(\times\) \(\times\) 6\(\lambda\)) 1100 elements (55 \(\times\) 20) & & Indoor NLOS & 27 dB@50 m. 14 dB@500 m. 26 dB@indoor via a and 500 m. & 14 dB@500 m. 26 dB@indoor via a thick concrete wall. \\ \hline \multirow{3}{*}{[160]} & \multirow{3}{*}{1-bit} & \multirow{3}{*}{PIN diodes} & 0.41 m \(\times\) 0.26 m (7.9\(\times\) 5\(\lambda\)) 160 elements (16 \(\times\) 10) & & Outdoor NLOS & 6 dB SNR \\  & & & 160 elements & & via large & improvement. \\  & & & (16 \(\times\) 10) & & & occlusion. & \\ \hline \multirow{3}{*}{[77]} & \multirow{3}{*}{1-bit} & \multirow{3}{*}{RF switches} & 2.45 m \(\times\) 2.45 m (19.6\(\times\) 19.6\(\lambda\)) 3200 elements (64 \(\times\) 50) & & & Indoor office environment with mixed LOS/NLOS. & Max 9.8 dB \\  & & & & LOS/NLOS. & & Doubling of channel capacity. \\ \hline \multirow{3}{*}{[161]} & \multirow{3}{*}{1-bit} & \multirow{3}{*}{PIN diodes} & 512 elements (16 \(\times\) 32) & \multirow{3}{*}{2.64 GHz} & \multirow{3}{*}{160 MHz} & Indoor NLOS & \multirow{3}{*}{10 dB/10 Mbps.} \\  & & & (13.3\(\times\) 13.5\(\lambda\)) 2430 elements (30 \(\times\) 81) & & & & Indoor NLOS. \\ \hline \multirow{3}{*}{[159]} & \multirow{3}{*}{3-bit} & \multirow{3}{*}{PIN diodes} & 1.02 m \(\times\) 0.72 m (12.8\(\times\) 9\(\lambda\)) 2304 elements (48 \(\times\) 48) & & & Indoor mixed LOS/NLOS. 5 GHz & 16 dB. \\  & & & & & & Corridor & Up to 40 dB in \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of RIS field trial works at sub-6 GHz [159]. channel modeling, considerations for hardware implementation, differences with existing communication modules and the need to implement active RISs, noise and power characteristics to ensure the efficiency of RISs, etc. are discussed. In addition, the performance parameters of an RIS system and the results of field tests of an RIS in indoor and outdoor environments are presented.