## 3 TVWS-DTV Coexistence: Field Measurements
### Field Tests Considering Short Distances
#### 3.1.2 Test Environment and Results  
The coexistence tests considering short distances were conducted within the premises of Inatel. For this purpose, a street on the campus near the Inatel Theater was selected, enabling the tests to be conducted with a direct line of sight and distances of up to 50 m between the stations. Figure 7a shows the test setup for a 15 m link distance. In the photograph, the interfering signal generation station is on the right, and the mobile or receiving station is on the left. In Figure 7b, there is an aerial view of the setup for the mentioned test condition. The estimated free-space attenuation for this distance is approximately 55 dB. Figure 8 shows the lateral and aerial views of the test setup with a 50 m distance between the stations. The free-space attenuation loss for this distance is approximately 66.3 dB. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**UHF Channel** & 26 & 27 & 28 & 29 & 30 \\ \hline
**Frequencies [MHz]** & 542 to 548 & 548 to 554 & 554 to 560 & 560 to 566 & 556 to 572 \\ \hline
**TVWS Transmission—5G-RANGE** & - & - & Yes & - & - \\ \hline
**DTV Transmission (One Channel at a Time)** & Yes & Yes & - & Yes & Yes \\ \hline
**Interference Test Channel** & \(n+2\) & \(n+1\) & - & \(n-1\) & \(n-2\) \\ \hline \(P_{\mathbf{RX}}\)**DTV** & & & \(\sim\!-\!77\) dBm & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Frequency allocations for short-distance field tests. Figure 6: Photograph of MS setup used in short-distance tests. The main objective established for short-distance tests was to evaluate the operational limit conditions of DTV STBs under the incidence of interfering signals in adjacent channels. Thus, the power of the interfering signal transmitter was adjusted to obtain PR values close to those identified in laboratory tests, given that the DTV signal reception power was adjusted to \(-77\) dBm. Gradually, the transmission power of the TVWS signal (\(P_{\text{TX}}\) TVWS) was increased until the demodulated and decoded test video exhibited an \"Intermittent\" or \"Not OK\" DTV STB Status in the subjective analysis. Upon reaching this condition, \(P_{\text{TX}}\) TVWS was reduced until the video was viewed without freezing or noticeable artifacts, achieving an \"OK\" DTV STB Status. When this condition was reached, the test results were registered in tables, as presented below. Therefore, the data documented in the tables consider the limit value for the \"OK\" status reception condition for each STB. Additionally, the measurements of the DTV signal power (\(P_{\text{RX}}\) DTV) and the TVWS signal power (\(P_{\text{RX}}\) TVWS) delivered to the input of the DTV STB were recorded. Through these measurements, the PR value was calculated and registered. ACPR, which indicates the power relationship between the lower (\"ACPRLower\") and upper (\"ACPRUpper\") adjacent channels and the DTV channel under test, was also measured. As described previously, the PR and ACPR parameters play a fundamental role in determining the viability of TVWS technology in practical scenarios. PR defines the minimum level of protection required for the DTV signal to be received without noticeable degradation in the reproduced video, while ACPR reflects the unwanted spectral interference in adjacent channels. In rural areas, where the distances between the transmitting station and  
Figure 8: Test photographs: (**a**) Tests employing a distance of 50 m between the stations. (**b**) Aerial view of the test setup with a distance of 50 m between the stations. Figure 7: Test photographs: (**a**) Tests employing a distance of 15 m between the stations. (**b**) Aerial view of the test setup with a distance of 15 m between the stations. the receiver may be greater, the presence of high spectral interference may compromise DTV reception, even in locations where the signal level should be sufficient to guarantee quality of service.