## 5 Q4: What Are the Findings Based on the Existing Research Works?  
This section highlights the significant findings of this research by reviewing the papers concerning recent trends, technical challenges, privacy and security issues of UIoT. The analysis is provided in Tables 3-5 based on the years from 2010 to 2021, and the results are displayed in Figures 13-15.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Main Clause** & **Subclause** & **Paper Count** & **References Number** \\ \hline \multirow{6}{*}{Environmental monitoring} & Pollution monitoring & 3 & [117; 118; 119] \\ \cline{2-4}  & Water quality monitoring & 11 & [120; 121; 122; 123; 124; 125; 126; 127; 128; 129; 130] \\ \cline{2-4}  & Monitoring depth, temperature, pressure, & 9 & [131; 132; 133; 134; 135; 136; 137; 138; 139] \\ \cline{2-4}  & Fish farm and fish growth monitoring & 22 & [140; 141; 142; 143; 144; 145; 146; 147; 148; 149; 150; 151; 152; 153; 154; 155; 156; 157; 158; 159; 160; 161; 162; 163; 164; 165] \\ \hline \multirow{6}{*}{Resource exploration} & Underwater object tracking & 9 & [166; 167; 168; 169; 170; 171; 172; 173; 174; 175; 176; 177; 178; 179; 180; 181; 182; 183; 184; 185; 186] \\ \cline{2-4}  & Natural resource finding (Coral reefs, minerals, manganese, etc.) & 13 & [187; 188; 189; 180; 181; 183; 184; 185; 186] \\ \hline \multirow{2}{*}{Disaster prevention} & Earthquakes, Tsunami warning system & 7 & [187; 188; 189; 190; 191; 192; 193] \\ \cline{2-4}  & Landslide detection and prevention & 9 & [194; 195; 196; 197; 198; 199; 200; 201; 202] \\ \hline \multirow{3}{*}{Naval applications} & Submarine detection & 2 & [203; 204] \\ \cline{2-4}  & Mine detection & 4 & [205; 206; 207; 208] \\ \cline{2-4}  & Surveillance & 3 & [209; 201; 202; 203; 204; 205; 206; 207; 208] \\ \hline \multirow{6}{*}{Others} & Aquathlon (Suba-diving, underwater hockey, underwater wrestling, etc.) & 6 & [212; 213; 214; 215; 216; 217] \\ \cline{2-4}  & Navigation assistance & 9 & [218; 219; 220; 221; 222; 223; 224; 225; 226] \\ \cline{2-4}  & Localization & 15 & [85; 86; 227; 228; 229] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Systematic analysis on UIoT applications.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Problems** & **Solutions and Effective Methods** & **Paper Count** & **References Number** \\ \hline Transmission issues & Methods to preventing path loss and data & 17 & [240; 241; 242; 243; 244; 245; 246; 247; 248; 249; 250; 251; 252; 253; 254; 255; 256] \\  & loss in UIoT networks. & 10 & [257; 258; 259; 260; 261; 262; 263; 264; 265; 266] \\ \hline Environmental issues & Methods to solve unreliable channel & 10 & [257; 258; 259; 260; 261; 262; 263; 264; 265; 266] \\ \cline{2-3}  & conditions in UIoT networks. & 15 & [265; 266; 267; 268; 269] \\ \hline \multirow{3}{*}{Insecure environment issues} & Methods used to support trust management, security management, hardware protection, etc., in UIoT networks. & 19 & [42; 107; 113; 270; 285] \\ \hline \multirow{3}{*}{Cost issues} & Lost cost design approaches & \multirow{3}{*}{15} & [87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101] \\ \cline{2-3}  & for UIoT networks & & \\ \hline \multirow{3}{*}{Channel noise issues} & Methods to prevent ambient  
Figure 14: Results based on the systematic analysis of mitigation methods to overcome the technical challenges in UIoT.  
Figure 13: Results based on the systematic analysis of UIoT applications.