## 3 Literature Review and Related Work
### Fingerprinting-Based Positioning Implementing Fingerprint Images Processed Using CNNs
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Ref.** & **Year** & **Fingerprints** & **Discretized Positioning** & **CNN** & **Fingerprint** & **Side** \\  & & **Used** & **Area Size** & **Type** & **Image** & **Inform.** \\ \hline
[89] & 2017 & CSI: amplitude & 1.5 to 2.0 m & 2D & 30 subcarriers by 30 time samples & (Yes) 3 \\ \hline
[90] & 2017 & CSI: AoA & 1.8 m \(\times\) path width & 2D & Matrix of 60 \(\times\) 60 AoA values & (Yes) 2 \\ \hline
[91] & 2017 & CSI: AoA, amplitude & 1.8 m \(\times\) path width & 2D & 30 subcarriers by 30 time samples & (Yes) 3 \\ \hline
[92] & 2018 & CSI: amplitude & Ref. points spaced at 0.6 m & 2D & 30 subcarriers by 30 time samples & (Yes) 3 \\ \hline
[93] & 2018 & RSS and correlation coefficient & 1.0 m \(\times\) 1.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[94] & 2018 & RSS & Building/floor size. & 2D & Fingerp. arranged in a matrix & No \\ \hline
[95] & 2018 & RSS & Not specified & 2D & Fingerp. arranged in a matrix & No \\ \hline
[96] & 2018 & RSS & Building/floor (classification) & 2D & Fingerp. arranged in a matrix & No \\ \hline
[97] & 2018 & CSI & 1.0 m \(\times\) 1.0 m & 2D & From CSI wavelet transform & (Yes) 3 \\ \hline
[98] & 2019 & RSS & Ref. points spaced at 2.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[99] & 2019 & RSS and kurtosis & 2.0 m \(\times\) 2.0 m and & 2D & 3D tensor (number of access points & No \\  & from RSS & 5.0 m \(\times\) 5.0 m & & \(\times\) time \(\times\) fingerprint and kurtosis) & \\ \hline
[100] & 2019 & RSS & 50.0 m mean dist., outdoor & 2D & Fingerp. arranged in a matrix & No \\ \hline
[101] & 2019 & RSS & 2.0 m \(\times\) 2.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[102] & 2019 & RSS & 3.0 m \(\times\) 3.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[103] & 2019 & CSI: amplitude & 1.2 m \(\times\) 1.2 m & 2D & 90 subcarriers by 90 time samples & (Yes) 3 \\ \hline
[104] & 2019 & RSS with wavelet transform & 1.95 m \(\times\) 2.4 m (corridor of 50.0 m divided into 21 areas) & 2D & 2D representation of RSS via wavelet transform & No \\ \hline
[105] & 2019 & RSS & 2.0 m \(\times\) 2.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[106] & 2019 & CSI: amplitude, phase difference & Ref. points spaced at 1.8 m & 2D & 114 subcarriers by 114 time samples & (Yes) 3 \\ \hline
[107] & 2019 & CSI: amplitt., phase & Ref. points from 0.9 to 2.1 m & 3D & Fingerp. arranged in a tensor & (Yes) 3 \\ \hline
[108] & 2019 & CSI & Ref. points spaced at 1.2 m & 2D & Channel state matrix & (Yes) 3 \\ \hline
[109] & 2019 & Radio beams & From dataset; see [109] & 2D & Number of beams by time samples & (Yes) - \\ \hline
[30] & 2020 & Geomagnetic & 1.0 m \(\times\) 1.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[31] & 2020 & Geomagnetic & Room size & 2D & Fourier transform of fingerprints & No \\  & & & & arranged in a matrix & \\ \hline
[110] & 2020 & CSI: AoA & 1.8 m \(\times\) path width & 2D & 60 subcarriers by 60 time samples & (Yes) 3 \\ \hline
[111] & 2020 & CSI: amplitude, phase difference & 1.0 to 2.0 m & 2D & 30 subcarriers by 50 time samples & (Yes) 3 \\ \hline
[112] & 2020 & CSI: amplitude, phase & 1.0 m \(\times\) 1.0 m & 2D & Fingerp. arranged in a matrix of 30 & (Yes) 3 \\  & & & & subcarriers by 30 time samples & \\ \hline
[113] & 2020 & RSS and other & Reference points spaced on average from 1.6 m to 6.0 m & 2D & Fingerp. arranged in a matrix of the topology of the access points & No \\ \hline
[114] & 2020 & CSI: amplitude & Ref. points spaced at 0.6 m & 2D & Fingerp. arranged in a matrix & (Yes) 3 \\ \hline
[115] & 2020 & RSS & 1.8 m \(\times\) 1.8 m & 2D & Fingerp. arranged in a matrix & No \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fingerprinting-based positioning implementing fingerprint images processed using CNNs (downlink case).