## 4 Experimental Setup and Results
### Implementation of the Jammer
The Python script was used to process the data to identify and visualise the signals across various frequency bands, making it useful for tasks like frequency analysis, signal identification and identifying potential sources of interference. After scanning, the maximum level of amplitude on the frequency of 834.5 MHz was identified. In our laboratory conditions, the smartphone registered in the LTE 800 MHz band, the UL measurement revealed that the smartphone amplitude in this conditions was almost \(-68.32\) dBm [22]. After identifying this frequency, Hack-RF was tuned to the identified frequency, enabling it to emit a stronger signal in terms of the amplitude and wider bandwidth in the waterfall window, as illustrated in Figure 15. After 10 s, the jamming was stopped, and the scanning procedure started to identify another amplitude level above \(-60\) dBm. The advantage of this method of scanning only a predefined list of frequencies lies in the fact that the spectrum will be swept much faster so that the chances of an illegal phone being able to access the services are very low. Another advantage is reflected in the use of receivers and transmitters whose band does not have to cover the entire spectrum. The main disadvantage of this method consists of the fact that the spectrum must be periodically scanned to identify the changes made by mobile phone operators in the area or to be aware of the implementation of new technologies. Even if it is necessary to periodically scan the radio spectrum from the point of interest, in practice, it is known that the network operators do not make changes every day in their allocation of technologies in frequency bands. This is why we include a table (Table 1) displaying the leased bands authorised by the regulatory authority where Digi Mobil must provide services. As a result, the network operators cannot provide services in bands other than those assigned to them. In Appendix A, we present the pseudocode behind the Python code developed. Figure 15: Experimental setup for jamming the downlink. The results were determined after the distance between the Hack-RF antenna and the smartphone was reduced. After several tries, it was determined that the effect of the jamming with the power provided by Hack-RF became noticeable at 1.5 m. At 8 m, the effect of the jamming was not as clearly visible in the radio spectrum. Figure 16a presents the radio spectrum obtained with PR100, which shows the manifestation of the jamming on the downlink frequency of 793.5 MHz. Figure 16b presents the effect of the jamming device on the smartphone-received signal. As demonstrated earlier, there are several methods for jamming smartphone network connections based on the characteristics of the network availability in the area and with some commercial tools available in online markets. For a man-in-the-middle attack using denial of service, jamming devices are highly effective in indoor conditions. Therefore, an attack is most likely to occur indoors. To avoid such an attack, it is important to be careful with our smartphones, and when we notice any fluctuations in the received signal or vertical handover, it is recommended to use an application to monitor the cell parameters to discover whether it is an attack. If we discover that we are a victim of a denial-of-service attack, for our protection, it is advisable to manually activate airplane mode from the smartphone menu and leave the indoor area [3]. Fortunately, this kind of denial of service attack does not compromise subscribers' personal data or provide the ability to track their activities. However, it can affect the possibilities to communicate by altering the radio spectrum capabilities.