###### Abstract  
The concept of cognitive radio (CR) as a tool to optimize the obstacle of spectral coexistence has promoted the development of shared satellite-terrestrial wireless networks. Nevertheless, in some applications like Earth Exploration Satellite Services, which demand high spectral efficiency (bps/Hz) for downlink transmissions, spectral coexistence amidst interferences from cellular Base Stations is still challenging. Our research aims to mitigate these interferences on low-orbit satellite downlinks carrying imaging data received from a ground station. In order to fulfill this, we present cognitive radio approaches to enhance spectrum exploitation and introduce the adaptive modulation and coding (MODCOD) technique to increase RF power and spectral efficiencies. Therefore, we propose a combined methodology using CR and adaptive MODCOD (ACM) techniques. Afterwards, we applied the solution by monitoring the signal to interference plus noise ratio and the MODCOD strategy. Finally, we provide a real in situ case study at the Cuiaba ground station located in Brazil's central area, which receives images from an Earth observation satellite (EOS). In addition to demonstrating the strategy effectiveness in this scenario, we conducted a bench test emulating the interfering wireless communication system. In this sense, we demonstrated the proposed approach, successfully mitigating the harmful effects on the received EOS images. cognitive radio; downlink throughput; low-orbit satellite; MODCOD; spectral coexistence 20232323233232332  
employing modulation and coding (MODCOD) techniques in an ACM (adaptive MODCOD) system [14; 15]. Simultaneous transmissions of primary and secondary users will be necessary in the same spectral band at the same time and location, for example, are described in [16]: a GEOstationary satellite as the SU with a Low Earth Orbit (LEO) satellite as the PU, or in [17; 18]: a LEO satellite system as the SU. Conversely, in contrast with what is presented in [13], where the satellite and the terrestrial system operate as the primary network and the cognitive network, respectively, our work focuses on the satellite communication system and its reception of remote-sensing Earth-observation images amidst interference in a scenario where both are primary users. Investigating the performance of satellite downlinks in the presence of interfering signals plus noise becomes a crucial obstacle to be addressed. In this sense, this paper aims at verifying and mitigating the harmful effects on the received images. By the early 1970s, the leading Brazilian satellite earth station (ERG) was installed on a site far from the urban area of Cuiaba City, positioned in the geodetic center of South America. However, due to the region's fast urbanization, the new Business and Administrative Center of Cuiaba became closer to the ERG, bringing together advanced microwave FS links and inducing unbearable spectral interference at specific points. Earth Exploration Satellite Services (EESS) missions in Brazil monitor agriculture and the diverse biomes, including deforestation in the Amazon rainforest [19; 20]. Additionally, these missions aim at deploying small and medium-sized satellites (PqSats), with payloads utilizing ultra-high resolution optical sensors or Synthetic Aperture Radars (SARs) that require/produce high data rates [21] for downlink transmissions, involving the sharing of their frequency spectrum with Fixed Service (FS) systems, which are a category of the Private Limited Service-SLP regulated by the Brazilian National Telecommunication Agency (ANATEL) [22], for example, cellular Base Stations (BS) at Cuiaba, Mato Grosso, Brazil. This scenario highlights the issues of spectral efficiency (in bps/Hz) and coexistence in frequency, time, location, and polarization. Our research provides a solution to mitigate interference in the LEO satellite downlinks of Earth exploration services through CR and adaptive MODCOD techniques (ACM) based on DVB-S2X.