## 1 Introduction
According to this decision, FSS stations can be deployed anywhere but without the right of protection from interference generated by fixed service (FS) terrestrial links. DSS techniques could significantly increase the FSS spectrum usage by utilizing spatial, time, and/or frequency separation with dynamic (re)allocation of spectrum resources to protect FSS from interference by other FSS and terrestrial links. By CEPT decision ECC/DEC/(05)01 [7], a segmentation is provided between FSS and terrestrial stations in uplink Ka-band (27.5-29.5 GHz). As the terrestrial segment of this band is underutilized throughout Europe, FSS stations could maximize their spectrum utilization by dynamically exploiting the spectrum allocated to FSS and terrestrial segments of the uplink Ka-band. At the same time, the DSS techniques need to provide interference protection of terrestrial incumbent users, as well as mutual interference protection of FSS links. European Space Agency (ESA) has recognized that the current fixed spectrum sharing model is not a feasible approach for the future of SATCOM and, as a potential replacement, they have pinpointed a dynamic sharing of the spectrum. ESA made clear that this dynamic spectrum sharing research endeavor should take a clean slate approach, breaking free from the constraints that existing SATCOM regulations impose. It is aiming to be the driving force behind the adaptation of existing regulations towards a new era of dynamic spectrum management, and not a mere upgrade on the current regulatory framework that is aimed mainly towards static spectrum assignments and centralized control. To reach that goal, the benefits of applying DSS techniques in SATCOM need to be examined first and compared to the existing spectrum sharing model. If the achieved gains are sufficient, the migration from fixed to dynamic spectrum sharing can be considered, and existingregulations adapted accordingly. In order to increase spectrum utilization while still guaranteeing interference-free operation, we investigated the effects of novel DSS techniques in the Ka-band SATCOM in terms of performance gains and mitigation of interference components. Being mandated by ESA, we carried out the CODYSUN (COllaborative and DYnamic approaches to increasing Spectrum UtilizatioN) [8] study in order to investigate the current status quo of SATCOM and propose ways to enable advanced DSS techniques for solving the spectrum crunch problems in SATCOM. Therefore, in CODYSUN, we identified shortcomings of existing SATCOM solutions and proposed novel DSS techniques to avoid interference and reach the highest possible level of spectrum efficiency and reuse by exploiting all possible degrees of freedom (frequency, time, and space). This paper discloses for the first time the proposed techniques and achieved results from the CODYSUN study. The DSS techniques investigated in the CODYSUN study have been inspired during our participation in the Defense Advanced Research Projects Agency (DARPA) Spectrum Collaboration Challenge (SC2) [9], where, as part of team SCATTER [10], we designed and implemented DSS techniques for terrestrial networks. The goal of SC2 was to ensure that the exponentially growing number of military and civilian wireless devices and services would have full access to the increasingly crowded electromagnetic spectrum. By breaking the walls between isolated silos of the exclusively assigned spectrum, and offering a wider shared spectrum band to multiple independent and collaborative networks, current problems of underutilization of spectrum in exclusive spectrum bands, leading to a huge waste of spectrum, can be mitigated. By exploiting the spatial separation, the same spectrum can be simultaneously used by multiple communication entities, heavily boosting spectrum utilization efficiency. Starting from the results obtained in DARPA SC2 for terrestrial networks, the CODYSUN study has revealed that similar DSS techniques can be applied for spectrum sharing across both satellite and terrestrial deployments.