## 1 Introduction
[10] provide a comprehensive survey for localisation in WSN, which investigates the techniques and algorithms under diverse categories. [PERSON] et al. [13] narrowed down the review to the localisation in 3D space. [PERSON] et al. [12] present a brief overview of the localisation approaches in WSN. [PERSON] et al. [11] review the localisation for IoT under various categories of approaches. The reviews and the covered topics are compared in Table 1. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Brief Summary** & **1** & **2** & **3** & **4** \\ \hline
[9] & A survey on RF localisation for UAV with focus on technologies and performance metrics & ✓ & ✗ & ✓ & ✗ \\ \hline
[8] & A survey on IoT localisation, investigating technologies and performance metrics & ✗ & ✗ & ✓ & ✗ \\ \hline
[10] & A comprehensive survey on localisation on WSN & ✗ & ✗ & ✓ & ✗ \\ \hline
[15] & A overview of the 5G-based localisation & ✗ & ✗ & ✓ & ✗ \\ \hline
[11] & A survey on IoT localisation & ✗ & ✗ & ✓ & ✗ \\ \hline
[12] & A survey on localisation techniques on WSN & ✗ & ✗ & ✓ & ✗ \\ \hline
[13] & A survey on localisation in WSN in 3D space & ✗ & ✗ & ✓ & ✗ \\ \hline
[14] & A survey on localisation on WSN algorithm and techniques & ✗ & ✗ & ✓ & ✗ \\ \hline
[16] & A brief review on range-free localisation algorithms in WSN & ✗ & ✗ & ✓ & ✗ \\ \hline
[7] & A comprehensive survey of the indoor localisation using different technologies & ✗ & ✗ & ✓ & ✗ \\ \hline
[17] & A brief review of technologies used for UAV positioning in indoor environment & ✓ & ✗ & ✗ & ✗ \\ \hline \hline \end{tabular}  
* 1: UAV localisation; 2: UGV localisation; 3: Methods and algorithms; 4: 5G localisation.  
\end{table} 
Table 1: Comparison between existing reviews. Hence, this survey aims to address the issue that remained untouched by other state-of-the-art reviews. As mentioned, the existing studies focus on specific aspects of localisation, such as technologies, methods, IoT applications, communication perspective, and classification of the approaches. However, this review covers the full extent of RF-based localisation approaches, first by distinguishing the type of information that can be decoded from the received signal in the form of features and then by categorizing the methodologies based on the use, whether range based or fingerprinting (data-driven), of these RF features. Additionally, we address the use of RF for UAVs and UGVs applications and discuss the future potential of 5G. Therefore, the main contributions of this review paper are as follows:  
* Investigating the algorithms for RF-based localisation that are highly likely to be used for challenging UGV and UAV applications. * Reviewing the existing works considered using RF specifically for UAVs and UGVs positioning. * Discussing the new potential that 5G NR will provide to cope with the current issues in UAVs and UGVs localisation problem. * Discussing the challenges for ground and aerial robots localisation and its integration with 5G NR. The survey paper is organized as follows: After introducing the main RF features used for localisation, we briefly introduce localisation techniques and how they can be used. Then we proceed to explore the up-to-date, state-of-the-art algorithms that have been widely used in RF-based localisation. In the next section, we concentrate on the available RF-based localisation applied to UAVs and UGVs. The 5G NR potentials and benefits expected for the aerial and ground vehicles localisation are also explained. We also review the current state-of-the-art localisation based on 5G NR. Finally, the challenges and future direction are be explored.