## 3 TVWS-DTV Coexistence: Field Measurements
### Field Tests Considering Long Distances
#### 3.2.1 Base Station and the Mobile Unit Setup
Therefore, all preparations for data collection for the coexistence tests of DTV and TVWS were performed in the same way as the tests considering short distances. In other words, the DTV signal passes through a filter, attenuator, and combiner and is adjusted to provide power around \(-77\) dBm at the input of the DTV STB (\(P_{\text{RX}}\) DTV), after the impedance adapter of 50 \(\Omega\) to 75 \(\Omega\). The TVWS signal generated by the BS is received via an antenna, filtered, and combined with the DTV signal from an RF combiner. Finally, the combined signal is operated in two ways: to evaluate the test signal, based on measurements using a spectrum analyzer, and as a signal applied to the input of the DTV STB for visualizing and assessing the video signal. Furthermore, all measurements made on the spectrum analyzer took into account the insertion loss of the impedance adapter, which is 5.7 dB. The three different DTV STBs were used again, and the subjective video quality analysis, referred to during the tests as DTV STB Status, was carried out in the same way as the short-distance tests, following the same classification mentioned earlier. Figure 11b shows the MS installed in a car. Regarding channel allocation, for the long-distance field tests, reception tests of DTV were planned under the incidence of interference applied to channels: \(n+1\), \(n-1\), and \(n-2\), where the position \(n\) refers to the channel occupied by the desired signal, which, in this case, is the DTV signal. In the laboratory tests, the DTV signal was fixed on one channel, and the interfering signals were switched to adjacent channels. On the other hand, in the field tests, the transmission frequency of 5G-RANGE, i.e., the interfering signal, was fixed to a specific channel for the field tests, which was UHF channel 28. This decision was made because the BS was located at considerable distances from the MS, making it impractical to go to the installation site of the interfering signal transmitter and modify its channel whenever there was a change in the interference condition analysis, since channel modification involves physically swapping some circuits of the transmitter. Thus, the DTV signal was adjusted to UHF channels 27, 29, or 30 to allow tests with interference on channels \(n+1\), \(n-1\), and \(n-2\), respectively. A filter was configured for  
Figure 11: (**a**) Block diagram of the MS setup for long-distance tests. (**b**) MS installed in a vehicle. each of these channels to properly filter the output signal of the DTV modulator. Despite the need to physically change the circuit of the DTV signal generation, this part of the test setup was installed in the MS, making manipulation more feasible. It is worth noting that UHF channel 26 was not used due to the availability of components needed for the construction of the TVWS Reception Station. Additionally, a request for radiofrequency spectrum licenses was made for the long-distance tests, and the license for channel 26 was not obtained. The received TVWS signal power (\(P_{\text{RX}}\) TVWS) depended on the location where the measurement was taken and the pointing of the antenna, which was fixed in a single direction for all tests. The attenuation loss related to the elements of the test setup, such as cables, adapters, filters, and RF combiner, was on the order of 15 dB. Furthermore, a low-noise amplifier (LNA) with a gain of approximately 22 dB to amplify the received signal was implemented after the reception antenna. The use of the LNA allowed for creating a second reception condition in each location, due to the practicality and simplicity of switching its state from on to off and vice versa. On the other hand, it can be understood that the gain of the LNA compensates for and exceeds the inherent attenuations in the setup of the MS.