## 4 Handover and Mobility Process in 5G HetNet
### Key HO Parameters in 5G HetNet
#### 4.1.1 HO Decision Parameters  
HO decision is a critical step in the HO initialization process in a communication system. Making perfect and appropriate HO decisions can enhance the performance of 5G HetNet in terms of reliability and seamless connectivity. In 5G HetNet, the HO decision is based on various parameters such as reference signal received power (RSRP), reference signal received quality (RSRQ), received signal strength indicator (RSSI), UE location, UE speed and direction (mobility pattern), cell load, SINR value, radio resources availability, UE battery level, RAT, HO priority (user behavior), and channel state information (CSI). \begin{table}
\begin{tabular}{l l l} \hline \hline
**S. No** & **Event Occurrence** & **Entering Condition/Rule** \\ \hline
1 & A\({}_{1}\) & When the S-gNB RSS exceeds the threshold level. \\
2 & A\({}_{2}\) & When the S-gNB RSS drops below the threshold level. \\
3 & A\({}_{3}\) & When the T-gNB RSS is stronger than that of S-gNB. \\
4 & A\({}_{4}\) & When the RSS from the T-gNB exceeds the threshold level. \\
5 & A\({}_{5}\) & When the RSS from the S-gNB drops below Threshold 1 and the T-gNB RSS exceeds Threshold 2. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Various HO events and entry regulations. Figure 6: HO and mobility process in three-tier 5G HetNet. These parameters are crucial in making the HO decision process more efficient, effective, optimal, and secure. RSRP measures the power level of the reference signal received by the UE without noise and interference. It is used to specify the quality of the connection between the UE and BS and is usually measured in dBm. A higher RSRP value indicates that the received signal quality is strong and vice versa. RSSI measures the cellular signal strength, i.e., the total received power, including noise and interference, while RSRQ is the ratio between RSRP and RSSI, which is used to measure the quality of the reference signal received by the UE. These three HODPs are mostly used together to detect the best cell for HO in 5G HetNet environments. The location of the UE can also be used to determine the best target cell for HO based on factors such as signal strength (RSSI) and coverage. The mobility patterns of the users, such as their speed and direction of travel, can be used to predict future HO requirements and optimize the HO process accordingly. If the UE is moving toward the target cell at high speed, its connection with the source cell becomes weaker while its connection with the target cell becomes stronger, and frequent HO will be performed. Based on the cell load or traffic, the UE from the heavily loaded cell can be switched to a less-loaded neighbor cell (load balancing) to perform secure and timely HO. SINR of the UE is also essential to consider in the HO process. A UE, particularly at the cell edge, has low SINR because of the large distance from the BS, and the high interference value will cause HO to the appropriate neighbor cell. The availability of resources, such as bandwidth or processing power, at the current and target cells can be used to determine the optimal time for the HO in HetNet. The battery level of a UE is an important parameter that can be used to determine whether the device has sufficient power to complete the HO process. In a 5G HetNet environment, which aims to provide services to MC and SCs UEs, the deployment of different RATs requires consideration of the serving and target cell's RAT as a parameter in the HO decision process for optimal target-cell selection. The behavior of the users, such as the types of applications they are using or the amount of data they are transmitting, can also be used for HO decisions. For example, if users are streaming HD video, they may require a high-quality connection with low latency, and the network may need to prioritize their HO requests accordingly.