## 2 Downlink Connection Landscape of the Mobile Operators in Bucharest
The spectrum analyser was configured to measure all bands used for LTE technology in the Europe region, with a threshold set above the noise level at \(-120\) dBm. In Table 2, line 1 presents the serving cell, which was characterised by the following:  
* The evolved cell identifier was 28339794. * The cell ID was 82. * The EARFCN was 6175. * The radio band was 20. * The physical cell identity (PCI) was 178. * The EARFCN central frequency was 793.5 MHz. * The level received for NB-RSRP was \(-58.82\) dBm. * The level received for NB-RSSI was \(-33.43\) dBm. * The NB-RSRQ was \(-16.90\) dB. * The signal-to-interference plus noise ratio (SINR) value was 0.17 dB. * The delay spread was 12 ns. Figure 3: RSRP and RSRQ levels according to different PCIs on Digi Mobil network. The radio spectrum analyser was set to \(-120\) dBm because we considered that any signal measured below that value could not be taken into consideration since it would be under the limit of mobile devices' sensitivity. The spectrum analyser sensitivity, after successful physical cell ID decoding according to the user manual, was \(-130\) dBm. Therefore, as corroborated with the mobile device sensitivity, which in LTE technology for high-end smartphones and mobile devices is typically in the range of \(-120\) dBm to \(-115\) dBm, we considered that the noise level was below \(-120\) dBm. Measurements made with the spectrum analyser were not influenced by the used antenna or by the length of the cable. The antenna we used was an omnidirectional one with a \(0.3\) m cable length, and thus, the losses on the cable length were insignificant. The PCI 178 was the serving cell in the 800 MHz band providing LTE technologies. As shown in Figure 3, the parameter NB-RSRP, displayed in green, indicated a very strong received power from the network. By comparing PCI 178 with PCI 177 (line 2 in Table 2), even though these cells were installed on the same cell tower, we can observe that the NB-RSRQ for PCI 177 was \(-21.47\) dB at the radio-monitoring point, signifying a poor service quality, as indicated in red. Lines 2-8 presented in Table 2 are considered neighbours of PCI 178. The characteristic parameters for lines 2-8 correspond with poor connection quality. These parameters presented are dynamic and subject to variations, depending on the mobile operator, as well as on the dynamics of the resources requested by subscribers, the dynamics of subscribers in the geographical area and the environment in which the transmission takes place. In conclusion, as inferred from Tables 1 and 2 and corroborated with the measurements presented in Figures 1-3, even if the Digi Mobil operator leased a wide variety of frequency bands from the Romanian authority, the implementation of technologies in different radio-covered areas primarily depended on the subscriber demands and complied with the National Communication Code. Once the downlink channels and technologies available were identified, based on those frequencies, the uplink frequencies could be calculated. The uplink frequencies based on radio measurements at the point of interest from Digi Mobil are presented below:  
* The GSMs in the 900 MHz band were the following: radio frequency channels 1-3 (UL frequency 890.2-890.6 MHz), 5-6 (UL frequency 891-891.2 MHz) and 22-23 (UL frequency 894.4-894.6 MHz). * The LTEs were the following: in the 800 MHz band--radio frequency channels 24,175, central frequency 834,5 MHz and bandwidth 5 MHz; in the 2100 MHz band--radio frequency channels 131,150, central frequency 19,278 MHz and bandwidth 15 MHz;