## 1 Introduction
Ofcom defined frequency ranges from 470 MHz to 550 MHz and 614 MHz to 790 MHz, ANE specified frequencies between 400 MHz and 698 MHz, and ICASA standardized the frequency range from 470 MHz to 694 MHz, excluding the sub-band between 606 MHz and 614 MHz intended for Radio Astronomy. North American countries also included Very-High-Frequency (VHF) frequencies in their standardization. The United States set frequency ranges from 54 MHz to 72 MHz, 76 MHz to 88 MHz, and 174 MHz to 216 MHz for fixed WSDs, and from 470 MHz to 698 MHz for fixed and portable WSDs. Finally, Canada reserved the same frequency ranges as the FCC, excluding the sub-band from 608 MHz to 614 MHz allocated for Radio Astronomy [25; 27; 28; 30; 31]. In Brazil, the Agencia Nacional de Telecomunicacoes (Anatel) published a resolution that allocates frequency bands for the use of Idle Spectrum Devices, related to the TVWS regulations. The regulated frequencies resemble those defined by the FCC, excluding the bands from 76 MHz to 88 MHz and 608 MHz to 614 MHz. Another definition by Anatel is that initially, the maximum power of secondary users cannot exceed 1 W, or 30 dBm, peak, which may restrict the technology's predictions for long-range applications. However, international studies suggest that greater flexibility in this parameter could significantly expand TVWS coverage without compromising DTV reception [32]. Requirements for limits on OOBE and spurious components, as well as additional technical conditions for operation, are yet to be established [33]. Among the defined parameters aimed at protecting primary users, it is noted that power limitation most directly affects current technologies in mobile communication systems, as most of these systems employ multicarrier waveforms [34]. Modulations such as OFDM, applied in current standards like long-term evolution (LTE) [35], LTE-Advanced (LTE-A) [36], and 5G new radio (5G NR) [37], for instance, were not conceived to operate in secondary networks. More recent techniques, such as filtered orthogonal frequency division multiplexing (F-OFDM) and generalized frequency division multiplexing (GFDM) may be appropriate to better meet the boundary conditions for operation in TVWS [38; 39]. Particularly, low OOBE and the ability to control the peak-to-average power ratio (PAPR) are significant factors of interest for TVWS. The laboratory tests conducted in this paper can contribute to verifying if the regulation of using idle UHF channels for telecommunication services can ensure acceptable levels of adjacent channel leakage-power patio (ACLR) or absolute values of adjacent channel power emissions (ACPEs) while minimizing the impact of power restrictions on network coverage and capacity. This paper presents the results of tests conducted within the scope of the project \"Implementing TV White Spaces (TVWS) for Internet Access in Brazil: challenges and opportunities\", coordinated by the Brazilian Network Information Center or Nucleo de Informacao e Coordenacao do Ponto BR (NIC.br), and developed in collaboration with Instituto Nacional de Telecomunicacoes (Inatel) and the Universidade Federal do Ceara (UFC). The main objective is to evaluate the use of TVWS technology in Brazil and contribute to the process of regulation and standardization to establish an efficient and secure spectrum exploration method for broadcasters. Currently, one of the main regulatory challenges faced is the transmission power limitation of 1 Wp, which can significantly impact the feasibility of TVWS for long-range applications. Additionally, the need to ensure the harmonious coexistence of DTV and TVWS systems without mutual interference imposes technical constraints that must be experimentally evaluated. Thus, this study aims to bridge this gap through laboratory and field tests, providing concrete data to support future regulatory decisions. The conducted studies present the conditions under which DTV and TVWS systems can coexist harmoniously, operating on adjacent channels without mutual interference.