## 3 Angular Protection Methods
### Angular Protection: Fixed BS-ES Relative Location  
In the fixed BS-ES relative location technique, the following assumptions were made:  
* There is a fixed BS location true north of the ES and 15 km away from the ES;
* There is a fixed 0\({}^{\circ}\) azimuth angle of the BS regarding the ES (\(\varphi\) = 0);
* The steering beam of the antenna array (\(\varphi_{s}\)) changes from \(-180^{\circ}\) to \(180^{\circ}\) with a step size of 1.  
The BS interference was calculated in each step to compute the beam shut-off angle \(\varphi_{off}\) (i.e., the size of the beam angle that must be shut off). If the interference with the current beam sweep angle \(\varphi_{s}\) is higher than the I/N interference threshold, this beam angle must be shut off to protect the ES. The beam shut-off angle \(\varphi_{off}\) increases by 1\({}^{\circ}\), as presented in Figure 3.  
To compute the interference of each beam angle, the range of was set to [180:1:180]. The parameters of the two interferences (\(\varphi_{s}=180\), \(\varphi_{off}=0\)) were verified and initialized before the computation. The next stage was to assess the interference. If interference \(\varphi_{s}\) is less than or equal to the I/N protection threshold parameter, \(\varphi_{off}\) is assigned to \(\varphi_{off}\)  
Figure 3: Fixed base station to Earth station: (**a**) relative azimuth and (**b**) flux gram.  
if interference \(\varphi_{s}\) is more than the I/N protection threshold parameter, \(\varphi_{off}\) is specified to rise by \(1^{\circ}\). A second judgment on \(\varphi_{s}\) is required next. Iteratively 1 can be added to the initial value of \(\varphi_{s}\) until \(\varphi_{s}\) is larger than \(180^{\circ}\), finishing the operation and generating the interference \(\varphi_{s}\) and \(\varphi_{off}\).  
Figure 4 depicts the I/N from the BS to the ES for a distance of 15 km with a \(4\times 4\) antenna array, regarding the sweep angle RMa LOS, sweep angle UMa LOS, and sweep angle UMi LOS, respectively. Figure 5 presents the corresponding beam angle needed to be shut off, using a more intuitive illustration. The angle in the red area is the shut-off beam. It corresponds to the beam angle, which provides a higher I/N than the red line in Figure 4. The interference protection criterion was assumed as the threshold of interference-to-noise ratio (I/N) of \(-12.2\) dB (red line in Figure 4) was derived from [22]. The sweep angle, which provides a higher interference than the \(-12.2\) dB threshold, should be shut off. The beam shut-off range is higher for the LOS than for the NLOS because of the lower path loss, as displayed in Figure 5. Hence, the I/N values are higher for the LOS for all beam directions. Thus, more beam angles must be shut off. For the UMi NLOS, no beam angle must be shut off because the interference of all beam angles is lower than the I/N threshold.  
Figure 4: Interference/noise (I/N) from the base station (BS) to the Earth station (ES) for a distance of 15 km with a \(4\times 4\) antenna array. (**a**) Rural macrocell; (**b**) urban macrocell; (**c**) urban microcell.  
Figure 5: Beam angles that should be shut off: RMa (**a**), UMa (**b**) and UMi (**c**) LOS and NLOS.