## 3 Link Level Simulation Model for Interference Evaluation in 5G UDN with LAB
### SIR Dependence on the Angular Separation of Two gNB-UE Links in 5G UDN with LAB
#### 3.2.3 Evaluation of SIR Dependence on the Angular Separation  
From Figure 3b it can be seen, that for ranges greater than 30 m, a repeating pattern of SIR values is observed; local maxima are determined by the antenna array pattern and indicate, that for given values of \(\alpha\) and \(d\), gNB beam, directed with maximum AA gain to the neighboring UE, is directed with minimum AA gain to the UE\({}_{\text{S}}\). For values of \(d\), greater than 40 m, the pattern of SIR values stops to depend on \(d\), since the tilt angle at long ranges changes slowly. There is also an area of low SIR values at \(\alpha\) values less than 10 degrees,  
Figure 3: Simulation scenario 3: (**a**) gNB with two AA patterns and two UEs on the x-y plane; (**b**) Map of UE SIR values for a set of terrestrial and angular separation; (**c**) Map of SIR values exceeding a given threshold for a set of terrestrial and angular separation; (**d**) Map of SIR values for a set of angular separation and fixed terrestrial separation.  
regardless of the \(d\) values. The width of this region along the angle \(\alpha\) is determined by the HPBW of the main lobe of the AA pattern (see Figure 4). From Figure 3c,d it can be seen, that SIR regions, exceeding specified threshold 15 dB, are repeated with a change in \(\alpha\), that is determined by the shape of the AA pattern, in particular, by the number of side minima and maxima of the AA pattern side lobes, which in turn depends on the number of AA elements.  
Figure 4 shows SIR dependence on the angular separation \(\alpha\) for given range \(d=60\) m with URA: if \(N\) is the number of AE on one URA side, the total number of AEs is \(N^{2}\). From Figure 4 it can be seen, that with an increase in the number of AEs, the number of local SIR maxima increases in a given range of \(\alpha\). The maxima are evenly spaced in the \(\alpha\) range with a slight increase in the spacing between them, as \(\alpha\) increases; the number of local maxima is equal to \(N-1\). With an increase in the number of AEs we can observe an increase in the minimum (drops in the SIR values) and, accordingly, the average SIR values in a given \(\alpha\) range. The region of low SIR at the beginning of \(\alpha\) range decreases with an increase in the number of AEs, which is caused by a decrease in the beam width of the main lobe of the AA pattern. For a threshold value of SIR = 10 dB, the width of the low SIR region is about 23, 11, 7, 5 degrees for the number \(N\) equal to 2, 4, 6, 8, respectively. For a URA there is a linear relationship between the increase in the number \(N\) and decrease in the angular width of the region of low SIR: increasing \(N\) by \(k\) times reduces the angular width by \(k\) times. The width of this region can serve as a criterion for the minimum allowable UE angular separation, when working with an array with a given number of AEs. A decrease in SIR is also observed, when \(\alpha\) tends to 90 degrees, which is caused by an increase in the level of the AA side lobes at large deviation angles of the maximum of the URA beam pattern. This decrease in SIR can serve as a criterion for the maximum allowable angular separation, which is about 38, 57, 65, 70 degrees for the number \(N\) equal to 2, 4, 6, 8, respectively, with a threshold value of SIR = 10 dB. Similar conclusions are also valid for ULA with the number of AEs equal to \(N\), when operating at ranges, at which the elevation angle changes slightly.