## 3 Justification of Assumptions  
In real-world scenarios, the selection of a flying object's flight profile in three dimensions is constrained by practical considerations and the capabilities of the flying system itself. Passenger aircraft typically maintain a flat trajectory for safety and mission requirements, whereas quadcopters exhibit greater agility, enabling sharp turns and rapid altitude changes. Previous studies have addressed this by focusing on sample flight profiles, such as the OH and DH profiles, which are particularly relevant for modeling the landing phase of quadcopters due to their vertical takeoff and landing capabilities [14]. To simplify the problem, it is assumed that the flying vehicle cannot rotate along its longitudinal axis. In other words, during a flight, the top of the flying vehicle is always \"up\". This assumption, which can be traced in quadcopter-like flying vehicles, guarantees the orientation of the airborne GNSS antenna's axis of radiation pattern with respect to the flight profile at any single point. Obviously, the propagation medium for this study is the Earth's atmosphere, from a few meters to a few tens of kilometers above the surface. But, as far as we know, this medium is not homogenous. Various types of clouds, dust, changes in air pressure in different regions, and changes in air density at various altitudes are time-dependent parameters and are impossible to model generally. While their effect can be modeled in LinkBudget calculations as attenuations [19], the first Best-Case Condition (BCC) assumption can be described as follows: the atmosphere is assumed to be clear and homogenous at any point and altitude. With its more than 6000 km radius, the Earth appears to be almost flat and without curvature for a few tens of kilometers, especially when the selected flight profile is just higher than a few hundred meters for 98% of the flight time. The second BCC assumption is, therefore, to consider the Earth as flat, theoretically. This flatness means that the surface is not curved; there are no mountains, hills, valleys, etc. ; and the _Source_ is always in the line of sight of the airborne GNSS receiver. The surface of the Earth is also considered to be completely reflective. Such a surface causes severe multipath fading effects. The effect of this assumption is studied in this paper, and thus it is not categorized as a BCC or a Worst-Case Condition (WCC). To reduce the complexity of this study, some propagation-related effects are neglected [20]. In real-world applications, the Interference Signal can be defined as any radio frequency signal that changes the noise level of the receiver. A _Source_ can also use various types of antennas, ranging from omni-directional to static or rotating directional antennas. This wide range of possible changes introduces complexity; to eliminate this unwanted and unnecessary complexity, an isotropic antenna pattern has been assumed as a BCC assumption. For any particular application, the actual radiation pattern of the _Source_ can be replaced in the formulation. Modeling in three dimensions makes it possible to move a _Source_ around and to locate it arbitrarily, as well as to select its altitude. These considerations are almost in compliance with what occurs in reality. A _Source_ can be carried by cars (i.e., police cars), mounted on static helium-filled balloons (i.e., airborne communication nodes [21, 22]), or placed at required altitudes using towers. The location and altitude of transmitters are, therefore, assumed to be selected arbitrarily. _Radiation Pattern of the Airborne GNSS Receiver's Antenna_  
The radiation pattern of the GNSS receiver's antenna can also be chosen arbitrarily. This uncertainty shows the necessity of solving the problem in its general form, which implies that the final algorithm should be able to accept any E-plane and H-plane radiation patterns with the desired resolution. The radiation patterns of antennas can be calculated using formulas found in textbooks [23] or using numerical calculations.