## 5 Discussion, Conclusions and Future Work  
In this study, we investigated and developed an intelligent jamming system that works on fixed frequencies, specific technologies and downlink connections of mobile network operators. Jamming is a process that is made intentionally by a malicious person or by a mistake produced due to an equipment fault. Intentional jamming can alter the performance of the radio mobile connections, introducing the possibility of developing other types of attacks that are more destructive, with a lot of consequences for the personal data of the subscribers. Figure 16: (**a**) Downlink jamming. (**b**) QualiPock monitoring frequency. After conducting our experiments, we could conclude that an attacker can carry out a denial-of-service attack on the downlink connection with commercial instruments at accessible prices. According to our proposed objectives mentioned above, we could conclude the following. For the first objective, we determined that in the case of jamming the downlink connection, it was difficult to obtain 100% jamming results. The condition of jamming depends very much on the strength of the receiving signal level from the network operators who provide services, as measured at the radio-monitored point of interest. The limitations also encompassed the limited jamming range for smartphones. The jamming effect was only pronounced at distances of less than 8 m without any obstacles. The evaluation of the second objective brought to light that a study is required regarding the downlink frequencies available and, based on this, to calculate the uplink frequencies. Experiments were conducted to demonstrate that the feasibility of employing reactive jamming on a downlink connection hinged on a technical constraint. The last objective was achieved successfully. We developed, tested and demonstrated that an intelligent jamming system that works completely autonomously in a specific indoor area could disrupt the downlink connection based on the detection of an uplink. A new Python script was developed. The intelligent jamming solution presented in this paper has its technical limitations. The configuration of the hardware platform is not a compact one: it has individual equipment and antennas, which makes installation on site more difficult. The maximum transmitting power of the Hack-RF SDR equipment is only 22 dBm (158 mW). This limits the coverage area of the jamming; thus, for larger areas, is necessary to use two or three such pieces of equipment, increasing the risk of intermodulation interference. A feasible measure to increase the range is to use a power RF amplifier installed at the Hack-RF SDR output. With respect to the jamming technologies, there are no limitations; we can adapt this system for jamming 2G, 3G and of course 5 GSA, but the 5 GSA standard is not available in Romania yet. Limitations include the distance of the jamming effect and logistical limitations, including the disposal of the antennas, cable installation and minimal technical requirements to ensure a stable temperature for the entire system. Regarding further studies, researchers can identify methods to monitor security attacks and the areas where they occur, the possibility to limit the access for sensitive information applications and extensions for other technologies available in IoT (like WiFi and BLE). Conceptualization, C.C. and S.H. ; methodology, C.C., S.H. and M.P. ([PERSON]); software, M.P. ([PERSON]); validation, S.H., O.F. and M.P. ([PERSON]); formal analysis, C.C. ; investigation, C.C. and S.H. ; resources, E.-M.B. and O.F. ; data curation, C.C. and S.H. ; writing--original draft preparation, C.C., M.P. and E.-M.B. ; writing--review and editing, C.C., M.P. ([PERSON]) and S.H. ; visualization, O.F. ; supervision, S.H. and O.F. ; project administration, O.F. ; funding acquisition, C.C. and O.F. All authors have read and agreed to the published version of the manuscript.