## 2 Downlink Connection Landscape of the Mobile Operators in Bucharest
All available technologies and bands are displayed in Figure 1 for all network operators that provided services that covered our range of measurements. After we selected all the bands that were available, corresponding to our regulatory authority, we started measuring in automatic channel detection mode, which was provided \begin{table}
\begin{tabular}{c c c c c c c} \hline Operator & Frequency Band & 800 MHz & 900 MHz & 2100 MHz & 2600 MHz \\ \cline{2-6}  & LTE & GSM & LTE & UMTS & LTE & LTE \\ \hline \end{tabular}
\end{table} 
Table 1: Availability of technologies in downlink frequency bands provided by Digi Mobil, Romania. by the spectrum analyser. The spectrum analyser offered an overview of the available bands and decoded all the technologies that were provided. Figure 2 illustrates the estimation of the propagation of the network cell eNodeB ID 110702 installed near the measurement point marked with a yellow star at approximately 320 m from the cell. The estimation of the covered area was undertaken manually, with other measurements on the field based on the receiving signal level at different points in the yellow sector, which was corroborated with the information provided by Combain.com regarding the establishment of the cell. In LTE technologies, to better understand the performance limits of the network, the parameters NB RSRP, NB RSSI and NB RSRQ were introduced to characterise the radio link between the network and mobile devices. Network operators use these measurements to optimise their networks, ensure seamless handovers between cells and provide quality service to subscribers. RSRP stands for reference signal received power and it is used to measure the received power of the reference signals from the base station in a wireless communication system. NB RSRP is used to measure the power level of the reference signals transmitted by the base station. It is typically reported in dBm and the range of this measurement depends on the receiver's capability, but it is usually around \(-140\) dBm to \(-44\) dBm for typical cellular networks. In our case, NB RSRP was \(-58.82\) dBm, which indicates that the signal was very good when received at the level of the spectrum analyser antenna. NB RSSI means received signal strength indicator (RSSI) in LTE (long-term evolution) networks; it is typically measured in dBm and represents the power level of the received signal from the serving cell. The acceptable RSSI values can vary depending on factors such as the network configuration, deployment conditions and device sensitivity. However, there are general ranges and guidelines that can be considered. Strong signal strength (high RSSI) values above \(-50\) dBm are considered very strong signals. In our measurements, we obtained \(-33.43\) dBm, and thus, we can consider that the value obtained characterised a very strong serving cell. NB RSRQ means reference signal received quality and is used to measure the quality of the received reference signals from a base station or cell. The RSRQ values typically range from negative infinity to a positive value measured in decibels (dB). Acceptable RSRQ limits can vary depending on the specific network and deployment conditions. An RSRQ above \(-15\) dB is considered a very good indicator of the quality of the serving cell. Figure 2: The estimation of radio propagation of the network cell. In our measurements, we obtained RSRQ \(-16.90\) dB, and thus, the quality of the radio services provided was considered fair to adequate. In the Nestor menu, supplementary information regarding the measurements is available; Figure 3 illustrates the downlink connection qualities in green (for very good quality signal), yellow (for poor quality) and red (very poor quality) for the Digi Mobil operator's LTE technology. It includes all available and measured PCIs, along with the key parameters that describe the quality or signal strength of the received services.