## 5 Applications and Research Challenges  
The use of the data obtained by the vUE probes either from periodic pre-programming or from direct access through the SSH interface has many different applications, as envisaged in the evaluation section and summarized in Figure 14.  
Under the self-healing paradigm, the use of vUE probes can help in detecting problems in the network that are being unnoticed by the OSS system. An example of this is what is known as partial outage or sleeping cells that occur when there is a degradation of a  
Figure 13: PHY layer parameter–KQI correlations for NetTest. key performance indicator (KPI) without an alarm. The only way for operators to become aware of this type of problem is when the users report low performance. Furthermore, it is necessary to send a qualified technician to the site to determine the cause of the problem. The application of vUE probes would make it possible to detect the degradation process through periodic campaigns of experiments. Additionally, the availability of a temporary database of the user plane performance under normal load conditions represents a valuable input for all the ML algorithms proposed for fault management. For cell optimization, when operators make changes to the radio network configuration, it is not always feasible for them to assess the consequences. Due to the dynamism of the radio environment and the effects between network layers, it is necessary to have a view from the user end to verify the impact. Additionally, the efficient use of radio resources is another aspect of optimization in which vUEs can play a crucial role. Having a detailed map of the radio environment (with interferers affecting certain areas or parts of the spectrum underutilized in others), such time-stamped information can be leveraged for much more efficient and dynamic management. The heterogeneity of radio technologies that are likely to coexist in the future makes this an essential point to be addressed. Additionally, in relation to physical signal processing, some of the paradigms associated with the simultaneous transmission and reception of signals will have to be tackled in order to design systems capable of managing data of different nature in real time. Besides, traffic profiling using the most advanced deep learning techniques can serve as input for better resource planning. It can also get a more accurate picture of how many resources are consumed depending on the application the user gives them. Moreover, from a QoE management perspective, having a user interface integrated into the network management system makes it possible to better manage the quality of service without invading data privacy. The security of mobile networks, including identity management and privacy protection, would benefit significantly from the presence of vUE. Among the many threats that could be detected is the possible presence of rogue stations attempting to impersonate the network. Furthermore, through the use of vUEs, periodic pen-testing could be carried out to check the vulnerability of network access. In the same manner, the use of the probes could be extended to other use cases still under study by the 5G standardization bodies. For example, the vUE probes could communicate with other user devices that are out of coverage by acting as relays. Thus, some of the experimental features proposed at the forefront of standard development could be piloted to test their operational feasibility in commercial networks. Enabling these tests would result in a shorter time to market that would boost the revenue of operators and foster competition. However, as identified by the evaluation section, the present implementations of vUE probes present relevant challenges. First of all, the efforts of strategic alliances aimed at joining forces for an open mobile radio technology must converge in a solution of wide  
Figure 14: Applications, challenges and identified R&D lines. dissemination that suits all parties, as happened with the WiFi alliance.