## 5 Conclusions
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Application Domain** & **Purpose** & **IoT Localization Approach** \\ \hline [PERSON] et al. (2019) [97] & Industry 4.0 & Harbors assets localization & Evaluate SF, number of nodes, etc. parameters \\ \hline [PERSON] et al. (2019) [98] & Industry 4.0 & Boat tracking and monitoring & RSSI with different LoRaWAN factors \\ \hline [PERSON] et al. (2020) [105] & Smart Healthcare & Elderly position monitoring & GNSS for outdoor and ToA for indoor \\ \hline [PERSON] et al. (2020) [106] & Smart Healthcare & Localization in risky outdoor & GPS with LoRaWAN \\ \hline [PERSON] et al. (2019) [107] & Smart Healthcare & Sea rescue system & GPS with LoRaWAN \\ \hline [PERSON] et al. (2018) [111] & Smart Healthcare & Phone-based ECS & GPS with LoRaWAN \\ \hline [PERSON] et al. (2020) [113] & Smart Healthcare & Mountain Search and Rescue & Pass loss model \\ \hline [PERSON] et al. (2019) [120] & Smart Transportation & Hybrid communications & RSSI level and energy consumption \\ \hline [PERSON] et al. (2020) [121] & Smart Transportation & Transit vehicle tracking & RSSI \\ \hline [PERSON] et al. (2018) [122] & Smart Transportation & Bus positioning system & GPS with LoRaWAN \\ \hline [PERSON] et al. (2018) [123] & Smart Transportation & IoT-based bus location system & using the location and delay information \\ \hline [PERSON] et al. (2020) [124] & Smart Transportation & Public vehicle tracking & GPS with LoRaWAN \\ \hline [PERSON] et al. (2020) [129] & Smart City & City assets track and localization & RSSI \\ \hline [PERSON] et al. (2019) [130] & Smart City & Bike localization system & RSSI \\ \hline [PERSON] et al. (2018) [131] & Smart City & Mobile applications localization & Network transfer protocol \\ \hline [PERSON] et al. (2020) [132] & Smart City & Ecotourism visitor assistance & GPS and RSSI \\ \hline \hline \end{tabular}
\end{table} 
Table 4: \(Cont.\)* Accuracy: there are different methods for accuracy improvement in positioning methods, but outdoor localization for resource-constrained IoT devices is still an open issue. Several IoT-based systems deployed in different environments have different error sources that should be considered to improve localization accuracy [39]. * Scalability: by increasing device density, for example, the scalability of a LoRaWAN network becomes a challenging issue. This is more important in a smart city application domain, which typically presents a dynamic and large number of end devices. Moreover, the scalability of a LoRaWAN network can be affected by different factors including co-SF interference, inter-SF interference, and the class selected during the design and implementation of the end nodes [139]. Based on the identified open issues, future work directions should focus on the improvement of the limitations of LPWAN-based localization methods without forgetting to address each application domain specificities. Conceptualization, A.K. and S.I.L. ; Methodology, A.M., A.K. and S.I.L. ; Investigation, A.M., A.K., S.I.L. ; Writing--Original Draft Preparation, A.M., A.K. and S.I.L. ; Writing--Review and Editing, H.R. and S.P. ; Supervision, A.K. and S.I.L. ; Project Administration, A.K. and S.I.L. All authors have read and agreed to the published version of the manuscript. This work has been partially supported by the TECH (Norte-01-0145-FEDER-000043) project, and the CoViS (POCI-01-02B7-FEDER-070090) project, under the PORTUGAL 2020 Partnership Agreement, funded through the European Regional Development Fund (ERDF). Not applicable. The authors declare no conflict of interest.