## 3 Literature Review and Related Work
### Fingerprinting-Based Positioning Implementing Fingerprint Images Processed Using CNNs
The smallest discretized area size observed in the articles surveyed was 0.2 m \(\times\) 0.2 m. As will be explained in subsequent sections, we explore the use of different discretization area sizes, as determined by the size of the 2D sensor array, starting from 0.35 m \(\times\) 0.35 m.  
In the last column of Table 3, we indicate with _Yes_ or _No_ whether the corresponding work used spatial side information or not, respectively. A number after a _Yes_ entry indicates the maximum number of spatial points with side information associated with the fingerprints when this number was stated in the article. Some entries in the last column of Table 3 are marked in parentheses as _(Yes)_. These correspond to cases in which spatial side information is used in a positioning system based on radio signals, utilizing more than one antenna at the receiver, and differentiating between the fingerprints from each antenna. In these works, we did not observe the use of 2D spatial side information. In general, the antennas were either arranged as a linear array or there was no concrete information stating that a 2D antenna arrangement was \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
[146] & 2022 & RSS & \(1.6\) m \(\times\) 1.6 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[147] & 2022 & RSS & Ref. points spaced \(\leq\) 1.0 m & 2D & From a rasterization function & No \\ \hline
[148] & 2022 & CSI & Ref. points at 1.8 or 3.0 m & 2D & 30 subcarriers by 36 time samples & (Yes) 3 \\ \hline
[149] & 2022 & RSS & \(4.0\) m \(\times\) 4.0 m & 2D & Vector of fingerp. sampled in time & No \\  & & & & arranged as a matrix & & \\ \hline
[150] & 2022 & RSS & Ref. points spaced at 1.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline
[151] & 2022 & CSI & Ref. points at approx. 8.0 m & 2D & Not specified & No \\ \hline
[152] & 2022 & RSS & According to [87] & 2D & Fingerp. arranged in a matrix & No \\ \hline
[153] & 2022 & RSS & \(1.0\) m \(\times\) 1.0 m & 2D & Vector of fingerp. sampled in time & Yes 40 \\  & & & & and space arranged as a matrix & & \\ \hline
[154] & 2022 & RSS & \(1.0\) to 2.0 m [88] & 2D & Fingerp. arranged in a matrix & Yes 2 \\ \hline
[155] & 2022 & RSS & \(1.0\) to 2.0 m [88] & 2D & Fingerp. arranged in a matrix & No \\ \hline
[156] & 2022 & RSS & \(3.0\) m \(\times\) 3.0 m & 2D & Vector of fingerp. sampled in time & No \\  & & & & arranged as a matrix & & \\ \hline
[157] & 2023 & CSI: amplitude & Ref. points spaced at 0.3 m & 2D & 256 subcarriers by 1000 time sampl. & No \\ \hline
[158] & 2023 & RSS & \(3.0\) m \(\times\) 3.0 m & 2D & Vector of fingerp. sampled in time & No \\  & & & & arranged as a matrix & & \\ \hline
[159] & 2023 & RSS & Ref. points spaced at 0.6 m & 2D & Matrix of row vectors of fingerp. & No \\ \hline
[160] & 2023 & RSS & Not specified & 2D & Fingerp. arranged in a matrix of the vertical–horizontal topology of the & No \\  & & & & access points & \\ \hline
[161] & 2023 & CSI: amplitude & Ref. points spaced at 1.2 m & 2D & 60 subcarriers by 60 time samples & (Yes) 3 \\ \hline
[162] & 2023 & CSI: amplitude & \(0.8\) m \(\times\) 0.8 m & 2D & 30 subcarriers by 30 time samples & (Yes) 3 \\ \hline
[163] & 2023 & RSS & \(12.0\) m \(\times\) 12.0 m & 2D & Fingerp. arranged in a matrix & No \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._used. Therefore, the spatial side information that can be extracted from such antenna arrangements is considered to be side information in 1D. From all the works consulted using multiple antennas at the receiver, only a few have studied the possible gains and effects caused by varying the number of receiving antennas or, in the context of this research, the number of spatial side information points, namely [140; 148].