## 2 Downlink Connection Landscape of the Mobile Operators in Bucharest
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Nr.c.t.**} & \multirow{2}{*}{**ECI**} & \multirow{2}{*}{**Cell**} & \multirow{2}{*}{**EARFCN**} & \multirow{2}{*}{**BAND**} & \multirow{2}{*}{**PCI**} & \multicolumn{2}{c}{**Center**} & \multirow{2}{*}{**BW**} & \multirow{2}{*}{**NB**} & \multirow{2}{*}{**NB**} & \multirow{2}{*}{**NB**} & \multirow{2}{*}{**SINR**} & \multirow{2}{*}{**Delay**} \\  & & & & & & & (MHz) & & & **RSRP** & & **RSSI** & **RSRQ** & **(dB)** & **Spread** \\  & & & & & & (MHz) & & (dBm) & & (dBm) & (dB) & \\ \hline
1 & 28339794 & 82 & 6175 & 20 & 178 & 793.5 & 5 & \(-58.82\) & \(-33.43\) & \(-16.90\) & 0.17 & 12 \\ \hline
2 & 28339793 & 81 & 6175 & 20 & 177 & 793.5 & 5 & \(-62.42\) & \(-33.43\) & \(-21.47\) & \(-8.66\) & 10 \\ \hline
3 & — & 6175 & 20 & 136 & 793.5 & — & \(-72.25\) & — & \(-30.76\) & — & — \\ \hline
4 & 28339724 & 12 & 37,902 &
\begin{tabular}{c} 38 \\ (TDD) \\ \end{tabular} & 61 & 2585.2 & 20 & \(-80.51\) & \(-58.00\) & \(-13.21\) & 17.12 & 14 \\ \hline
5 & 28339804 & 92 & 3350 & 7 & 100 & 2680 & 20 & \(-81.94\) & \(-60.49\) & \(-15.83\) & \(-0.19\) & 55 \\ \hline
6 & 28339723 & 11 & 37,902 &
\begin{tabular}{c} 38 \\ (TDD) \\ \end{tabular} & 62 & 2585.2 & 20 & \(-85.29\) & \(-58.00\) & \(-17.58\) & 2.56 & 11 \\ \hline
7 & 28339734 & 22 & 78 & 1 & 100 & 2117.8 & 15 & \(-87.63\) & \(-60.44\) & \(-18.57\) & 1.17 & 10 \\ \hline
8 & 28339733 & 21 & 78 & 1 & 99 & 2127.8 & 15 & \(-88.34\) & \(-60.44\) & \(-19.87\) & \(-4.15\) & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main parameters NB-RSRP, NB-RSRQ and other data regarding Digi Mobil downlink connection at the radio monitoring point, as obtained with the Nestor monitoring platform. and in 2600 MHz band--TDD modulation, radio frequency channels 37,902, central frequency 2585.2 MHz and bandwidth 20 MHz, and TDD modulation, radio frequency channels 3350, central frequency 2680 MHz and bandwidth 20 MHz. Since the radio configuration of the Digi Mobil network provider was determined, including the uplink and downlink frequencies and the implemented technologies, the theoretical aspects of the used methods for jamming can be presented. The radio measurements conducted on downlink connections revealed the availability of the technologies in different frequency bands. Measurements on a smartphone with a special software called QualiPock, which can display the naturally chosen band and technology without any influences, were also performed. As shown in Figure 4, the smartphone was registered in band 20 at 800 MHz using FDD modulation with an RSSI of \(-\)50.4 dBm, RSRP of \(-\)79.5 dBm and RSRQ of \(-\)15.1 dB. Based on these measurements, we could conclude that the quality of the connection was not very good, despite the signal level being strong. The scenario of unavailability of LTE technology provided for the 800/2100/2600 MHz bands is frequently encountered in prisons and facilities with thick walls containing a lot of steel. When the LTE 800 band becomes unavailable or is jammed, smartphones tend to select GSM 900 MHz as an alternative. To precisely determine which GSM channel is preferred, measurements were conducted, and the results are illustrated in Figure 5. The mobile phone selected channel number 23, with a downlink frequency of 939.6 MHz, and the received signal level was \(-\)62 dBm, indicating a good connection. To perform a jamming signal on GSM channel 23, it was necessary to calculate the uplink frequency. Figure 4: Smartphone registered in LTE 800 MHz band. Considering the 45 MHz difference between the downlink and uplink frequencies, the uplink frequency was determined to be 894.6 MHz. Based on the radio measurements, it was possible to design a jamming system adapted for GSM technology in the 900 MHz band for the Digi Mobil operator. Jamming on GSM technology is not quite new in this field, as the radio spectrum used in GSM is susceptible to interference due to the vulnerabilities inherent in the technology.