# Optimization of Coverage and Capacity Using Smart Antennae
## 2 Small-Cell Interference  
In a traditional omni-directional antenna base station network environment, when user equipment (UE) is located within the overlapping coverage areas of two base stations, as shown in Figure 1, it will receive transmission signals from both Base Station 1 (BS1) and Base Station 2 (BS2). This situation leads to signal interference issues for UE1, as it receives signals from both BS1 and BS2 while being within the coverage range of both base stations. The same applies to UE2. One approach to address this type of interference is illustrated in Figure 2. By adjusting the transmission power of the traditional omni-directional antenna, the transmission power of BS2 can be reduced. As a result, the overlapping coverage area between BS1 and BS2 will be decreased, effectively resolving the interference problems experienced by UE1 and UE2. Reducing the power of the base station can effectively shrink the overlapping coverage area between base stations, resolving interference issues for user equipment (UE), as illustrated in Figure 3a. Prior to adjusting the transmission power of Base Station 2 (BS2), all UEs, including UE1, UE2,..., and UE6, were within the coverage areas of both Base Station 1 (BS1) and BS2, resulting in a 100% overall network coverage rate. However, due to the interference between UE1 and UE2, lowering the transmission power of BS2(as shown in Figure 3b) effectively resolved the interference problem for UE1 and UE2. Nevertheless, this action also led to a decrease in the coverage rate, as UE5 was no longer within the coverage range of BS2 and, thus, could not receive signals. Consequently, the overall network coverage rate dropped to 83%. Figure 1: Interference caused to terminals by traditional omnidirectional antennae. Figure 3: Adjusting the power reduces interference, but reduces UE coverage. Figure 2: Adjusting the power of omnidirectional antennae to reduce interference. Many scholars have proposed innovative smart antenna designs based on antenna theory. These designs enable signals to be utilized more effectively during both reception and transmission, thereby achieving communication or sensing objectives [13; 14], In order to simultaneously maintain a high base station coverage rate and effectively reduce UE interference issues, this study employed intelligent adaptive directional antennas for the base stations. Unlike traditional omni-directional antennas, where the antenna gain remained the same at different angles, intelligent adaptive directional antennas can control the signal strength in different directions, resulting in varying antenna gains for terminal devices at different angles. Figure 4 represents the intelligent adaptive directional antenna used in this study. The antenna with only a degree zero sector was activated. This represents the radiation pattern of the base station's transmitted signal. Taking the degree zero direction as an example, it is evident from the diagram that the emission intensity in the degree zero direction was greater than in the other directions. Figure 5 illustrates the solution using intelligent adaptive directional antennas. In Figure 5a, the traditional omni-directional antenna architecture shows that UE1, UE2, \(\ldots\), and UE6 were all within the coverage areas of BS1 and BS2, resulting in an overall network coverage rate of 100%. However, interference issues occurred between UE1 and UE2. By adopting the intelligent adaptive directional antenna architecture shown in Figure 5b, the transmission power of BS1 and BS2 could be adjusted along with the directional antennas. This not only resolved the interference problem for UE1 and UE2, but also maintained the overall network coverage rate at 100%. Each directional antenna can be adjusted to be on or off, enabling various radiation patterns. In this study, there were five antenna directions, each of which could be activated or deactivated. This allowed for a total of \(2^{5}=32\) possibilities.