# Mobility Management of Unmanned Aerial Vehicles in Ultra-Dense Heterogeneous Networks
## 3 Mobility with UAV Technology
### Handover Concept  
HO is the process of preserving connection in wireless mobile networks, this includes numerous scenarios in which the user maintains a connection while moving from one location to another. The method involves changing the BS that was previously servicing the moving user to one that has a better connection at the moment. This modification occurs through various scientific and technological procedures [45; 46; 47]. The HO method was developed to manage wireless mobile connections while users are traveling to provide highly dependable and smooth communication. In reality, HO is intended to boost user throughput while decreasing radio link failure (RLF) and interruption time. The dependability and quality of the serving network will improve if the HO management strategy is enhanced [48]. To complete the transfer, three activities must be accomplished. The mobile station may easily locate the surrounding BS in the first phase since the BS broadcasts a mobile neighbor advertisement control (MOB NBR-ADV) that identifies the radio channel and media access control (MAC) address. The target wireless network with HO timing is selected in the second step after scanning for surrounding BSs. Initially, the mobile station sends a scanning request (MOB SCN-REQ). The BS then receives the scanning response (MOB SCN-RSP) to provide a search time to the mobile station, which contains the list of target BSs. The HO decision is initiated by a mobile station HO request (MOB MSHO-REQ). The transition to the new wireless network is completed in the third step. The main HO procedures are listed in Table 1[35; 49]. Several HO methods are used to promote user mobility to define when and how the UE should undergo the process of performing HO. Various optimization options are available, such as selecting the routing protocols and suitable objectives for any access point/base station (AP/BS). The availability of mm-waves in modern wireless technologies (5G and 6G) further complicates the selection of an adequate HO. The latest technologies allow for faster mobility, reaching speeds of up to 350 km/h in 4G and 500 km/h in 5G. HO is well known for assessing wireless communication performance. Various requirements and indicators were developed to represent network performance during HO operations. The first requirement is that the relationship between the BS and the UE must be kept as stable as possible during the eNB transition. The second requirement is the HO interruption time, which is defined as the time when the UE is not permitted to deliver user plane packets to the BS. To ensure a smooth UE experience, the interruption time should be extremely short, such as less than 1 mm. The third requirement is the HO cost, which is computed by multiplying the mobility interruption time per HO by the number of HOs in the trajectory of a specific UE. The fourth requirement is the HO failure rate, which is calculated as the number of HO failures divided by the number of times the UE processes the HO. The fifth requirement is the signaling overhead, which is defined as data generated during HO processing to simplify the method. Another issue is load balancing between BS cells. If the cell connection for the same BS is blocked, other UEs would have to move to a different cell. Another benefit of using