# Review of Indoor Positioning: Radio Wave Technology
## 2 Parameter Based Positioning
### Rssi  
The received signal strength indicator (RSSI) is a comparative measurement of the RSS which has random units and is commonly described by a single chip vendor [51]. RSSI is a commonly used metric to find an estimation of the distance between a target and the node without resorting to complicated calculations. It computes distance by power loss, the signal strength deficiency, between two nodes. Figure 2 shows the RSSI-based trilateration method. This method can work using only a couple of nodes to obtain a distance estimation [54]. The RSSI-based algorithm only requires the received signal \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Advantages** & **Disadvantages** \\ \hline \multirow{4}{*}{RSS} & No need for time synchronization and angle measurement. & \multirow{2}{*}{Prone to the noise, multipath effects and NLoS. Needs a fingerprinting database for scene analysis methods.} \\  & Easy to implement. & \\  & No need for extra hardware device. & \\  & Eliminates energy consumption. & \\ \hline \multirow{4}{*}{TOA} & No need for any fingerprinting database. & \multirow{2}{*}{Needs time synchronization. Influences multipath and additive noise. Needs extra hardware device. Difficult to implement in narrow bandwidth.} \\  & Provides high localization accuracy. & \\  & Difficult to implement in narrow bandwidth. & \\ \hline \multirow{4}{*}{TDOA} & No need for any fingerprinting database. & \multirow{2}{*}{Needs extra hardware devices. Difficult to implement in narrow bandwidth.} \\  & Does not require time synchronization among the device and received nodes. & \\  & the device and received nodes. & \\ \hline \multirow{4}{*}{RTT} & No need for clock synchronization between the nodes. & \multirow{2}{*}{Sufters multipath effects. Different processing time delays. Phase noise affects the accurate clock speed. No simultaneous response to large requests.} \\  & Reduces complexity, enhances reliability. & \\  & High range measurement and update rate. & \\  & Apply for passive RFID with proper synchronization. & \\ \hline \multirow{4}{*}{AOA} & No time synchronization between measuring units. & \multirow{2}{*}{Needs an antenna array. Requires extra hardware. Influences multipath, NLoS, and additive noise. Accuracy relies on accurate angle measurement.} \\  & Provides high accuracy. & \\ \hline \multirow{4}{*}{DOA} & Highly influenced by multipath effects. & \multirow{2}{*}{Accuracy relies on accurate angle measurement.} \\ \hline \multirow{4}{*}{ADOA} & No need for any fingerprinting database. & \multirow{2}{*}{Requires extra sensors like gyroscopes.} \\  & No need the information of angles in the variance between two AOA values. & \\ \hline \multirow{4}{*}{POA} & Easy to obtain the signal’s phase change during the prorogation. Improves the accuracy integrated with RSSI, TOF, and TDOA. & Has an infinite number of path lengths. Requires LoS for high accuracy. Phase ambiguity issue due to phase wrapping. \\ \hline \multirow{4}{*}{PDOA} & High accuracy. & \multirow{2}{*}{Ambiguities in the distance estimation. Accuracy depends on multipath effect.} \\  & Reduces multipath effects. & \\ \hline \multirow{4}{*}{CSI} & Provides more fine-grained signal characteristic information. & \multirow{2}{*}{Needs labour-intensive site survey to calibrate. Does not need to be appropriate for most situations. Needs larger storage and more operation time.} \\  & Good stability and higher accuracy than RSS. & \\ \hline \multirow{4}{*}{RSRP} & Supports greater power information. & \multirow{2}{*}{Impacts station interference and thermal noise. environment.} \\  & Reduces proneness to local disturbances in the environment. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the different localization measurement parameters. strength and does not require an auxiliary hardware apparatus and time synchronization, able to achieve higher accuracy than other methods. The RSSI technique can be classified into a range-based and range-free approach. The first approach is an RSSI based on a path loss model.