## 3 TVWS-DTV Coexistence: Field Measurements
### Field Tests Considering Long Distances
#### 3.2.4 Results from the First Stage of Field Tests  
The first stage of the field tests includes measuring and analyzing the coexistence of the DTV system with a TVWS system, and the second stage, addressed in Section 4, investigates the impact of the transmission power limitation applicable to TVWS systems on the coverage and quality of the secondary network link, which implemented the 5G-RANGE system. The results of the first stage were divided into initial tests and complementary tests, as presented below:  
* Initial test results for the coexistence of DTV and TVWS  
The proposed coexistence tests of DTV with the TVWS system consider the generation of the DTV signal on up to three distinct channels (DTV Channel), aiming to evaluate the demodulation and decoding of this signal in the presence of the TVWS signal (5G-RANGE in GFDM) as an interfering channel. Six initial test conditions were established, considering the TVWS system configured to deliver the total powers (\(P_{\text{TX}}\) TVWS) of 1 Wp, 2 Wp, and 4 Wp to the transmission antennas at the transmission side, while on the reception side, the LNA\({}_{\text{RX}}\) was deactivated and activated for each of the configured \(P_{\text{TX}}\) TVWS. Additionally, the field measurements included the power of the DTV signal (\(P_{\text{RX}}\) DTV) and the TVWS signal (\(P_{\text{RX}}\) TVWS) delivered to the input of the DTV STB. Through these measurements, an important parameter to be evaluated in the coexistence analysis was calculated, which refers to the power ratio between the signal of the analyzed channel (DTV) and the interfering channel (TVWS), i.e., the PR. The ACPR was also measured, indicating the power ratio between the lower adjacent (\"ACPR\({}_{\text{Lower}}\)\") or upper adjacent (\"ACPR\({}_{\text{Upper}}\)\") channels and the DTV channel under test. The values of the parameters achieved through measurements were obtained by the MT822B spectrum analyzer manufactured by Anritsu. In addition to the measurements, a subjective analysis of reception was conducted by observing the DTV STB Status for each of the three commercial DTV STBs for 60 s.  
The power of the undesirable DTV signal, i.e., the interfering signal present on channel 30 (\(P_{\text{RX}}\) INT. (CH30)), was also monitored. The test with interference present on channel \(n-2\) was executed only at the MS\({}_{\text{C}}\)_CafezalManolea location, where the \(P_{\text{RX}}\) INT. (CH30) level was lower than \(-90\) dBm, since for this test, the DTV signal should occupy channel 30. At the MS\({}_{\text{C}}\)_Ideaamento and MS\({}_{\text{D}}\)_DeltaBlack locations, the level of \(P_{\text{RX}}\) INT. (CH30) was higher than \(-90\) dBm, and the co-channel interference caused the decoding of the video signal to be impossible. It is worth mentioning that coexistence tests of DTV and TVWS were not conducted at the MS\({}_{\text{P}}\)_Delta_lva location, located 38.39 km from the BS, because the TVWS signal level \(P_{\text{RX}}\) TVWS at that location was significantly reduced (\(-83.9\) dBm for a \(P_{\text{TX}}\) TVWS of 1 Wp), causing no significant interference with the DTV signal. The results of the coexistence tests considering \(P_{\text{TX}}\) TVWS up to 4 Wp, which is a power level 6 dB higher than the currently prescribed limitation for TVWS systems, did not cause harmful interference to the DTV signals in the executed tests. The condition with the lowest PR value tested for interference on channels \(n-1\) and \(n+1\) was \(-28.3\) dB and \(-27\) dB, respectively, at the MS_Loteamento location, which is closest to the 5G-RANGE BS with a distance of 5.68 km, and in these conditions, all STBs were able to demodulate the DTV signal normally. On the other hand, the condition with the lowest PR value tested for interference on channel \(n-2\) was \(-16\) dB at the MS_CafezalManoeala location. Table 8 presents the collected measurements for the MS_Loteamento location with LNA off and on.