# Deployment Protection for Interference of 5G Base Stations with Aeronautical Radio Altimeters
## 2 Methodology
### Deployment Protection Methods
#### 2.3.2 Interference Mitigation Methods  
Interference mitigation methods can help reduce the size of the prohibited zone by implementing technical measures during base station deployment to minimize interference with radio altimeters. These methods involve employing techniques such as power control and angle shutoff using beamforming technology. By adjusting the power levels and directing the beams appropriately, interference with radio altimeters can be reduced [26]. We propose two methods for interference mitigation. Algorithm 2 illustrates the steps involved in the power control method. Within the prohibited zone, a total of \(N\) points are unsuitable for base station deployment, with all base station coordinates recorded in \(BS_{list}\). First, the transmit power (\(P_{i}\)) of the \(i\)-th base station is reduced by 1 dB. Then, a calculation is performed to determine whether the interference (\(I_{i}\)) generated by this base station is less than the interference threshold (\(Th\)). If so, the counter is incremented using \(q_{j}\). This process is repeated until \(P_{i}<0\). Second, calculations are performed for all base stations in \(BS_{list}\) to obtain the proportion (\(P_{TxCon}\)) of base stations with power reduction values of 1 dB, 2 dB,..., and j dB using \(\frac{q_{1}}{N},\frac{q_{2}}{N},\ldots,\frac{q_{j}}{N}\). ```
0:\(BS_{list},N\)
0:\(P_{TxCon}\)
1:repeat
2:repeat
3:\(P_{i}=P_{i}-1\)
4:if\(I_{i}<Th\)then\(q_{j}=q_{j}+1\)
5:\(j=j+1\)
6:else
7:\(q_{j}=q_{j}\)
8:endif
9:until\(P_{i}<0\)
10:\(i=i+1\)
11:until\(i=N\)
12:\(P_{TxCon}=\{\frac{q_{1}}{N},\frac{q_{2}}{N},\ldots,\frac{q_{j}}{N}\}\)
```  
**Algorithm 3** PageRank Shutoff Method  
Algorithm 3 presents the angle shutoff method, which takes advantage of the benefits of beamforming technology. In the context of interference mitigation, it is essential to analyze the angles at which the beams may cause interference and selectively them off. In the horizontal plane, the angle \(\varphi_{h}\) in Figure 9 is from \(1^{\circ}\) to \(360^{\circ}\). In the vertical plane, \(\varphi_{v}\) in Figure 10 is from \(0^{\circ}\) to \(90^{\circ}\). Algorithm 3 is applicable to both \(\varphi_{v}\) and \(\varphi_{h}\) but with different calculation ranges. First, \(\varphi_{v}\) or \(\varphi_{h}\) is initialized at 0, and the horizontal distance (\(d\)) between the base station and the aircraft is defined, as shown in Figure 10. Then, a calculation is performed to determine whether the interference (\(I(\varphi_{h}\backslash\varphi_{v})\)) generated by the base station is less than the interference threshold (\(Th\)). If so, the counter is incremented using \(\varphi_{off}(\varphi_{h}\backslash\varphi_{v})\). This process is repeated to obtain the proportion (\(An_{Shutth}\)) of base stations with \(\varphi_{off}(\varphi_{h})\) values ranging from \(1^{\circ}\) to \(360^{\circ}\) using \(\frac{\varphi_{off}(1)}{360},\frac{\varphi_{off}(2)}{360},\ldots,\frac{\varphi_ {off}(360)}{360}\) to similarly obtain \(An_{Shutv}\). ```
0:\(\varphi_{h}\backslash\varphi_{v}=0,d\)
0:\(An_{Shutth}\backslash An_{Shutv}\)
1:repeat
2:if\(I(\varphi_{h}\backslash\varphi_{v})>Th\)then\(\varphi_{off}(\varphi_{h}\backslash\varphi_{v})=\varphi_{off}(\varphi_{h} \backslash\varphi_{v})+1\)
3:\(\varphi_{h}\backslash\varphi_{v}=\varphi_{h}\backslash\varphi_{v}+1\)
4:else
5:\(\varphi_{off}(\varphi_{h}\backslash\varphi_{v})=\varphi_{off}(\varphi_{h} \backslash\varphi_{v})\)
6:endif
7:until\(\varphi_{h}=360\)\(\backslash\varphi_{v}=90\)
8:\(An_{Shutth}=\{\frac{\varphi_{off}(1)}{360},\frac{\varphi_{off}(2)}{360},\ldots,\frac{\varphi_{off}(360)}{360}\}\)\(\backslash An_{Shutv}=\{\frac{\varphi_{off}(1)}{90},\frac{\varphi_{off}(2)}{90}, \ldots,\frac{\varphi_{off}(90)}{90}\}\)
```  
**Algorithm 2** Power Control Method  
To better understand the concept of angle shutoff, we represented it in both Cartesian and polar coordinate systems, as shown in Figure 10(a),b. Figure 10(a) illustrates the relationship between angle shutoff and azimuth.