# Handover Decisions for Ultra-Dense Networks in Smart Cities: A Survey
## 3 Related Works
### Conventional Handover Approaches
Additionally, they examined how different prioritization schemes impact handover frequency, network load balance, and blocking probability. The study was conducted using MATLAB simulations, modeling a heterogeneous network environment with varied mobility speeds and traffic types. Performance evaluation was based on handover count, balance index, and blocking probability. The mobile-priority strategy achieved the highest reduction in handovers (90.41%), while the network-priority method enhanced network load balance (18.03%) and reduced blocking probability (20.23%). However, the study did not account for real-time implementation complexities, such as energy efficiency and the impact of fluctuating network congestion, which should be explored in future research. In 2015, [PERSON] et al. [47] presented an SDN-based vertical handover decision (VHD) scheme for 5G networks. The authors proposed a VHD scheme utilizing software-defined networking (SDN). The approach separates the control and data planes, allowing handover decisions to be made at the SDN controller (SDN-C). The SDN-C evaluates handover decisions based on multiple criteria, including RSS, bandwidth, delay, block error rate, jitter, user speed, and application type. The study compared the SDN-based QoS solution with traditional RSS-based handover mechanisms. The methodology involved simulations using the NS3 network simulator, where different handover strategies were tested under varying network conditions. Performance was measured based on handover frequency, signaling overhead, handover delay, and user throughput. The proposed approach significantly reduced the number of handovers by 60%, decreased signaling overhead by 44%, minimized handover delay by 58%, and improved user throughput by 203% compared to conventional methods. However, the study did not consider real-world deployment complexities, such as interoperability with existing network infrastructures and energy efficiency, which should be addressed in future research. In 2022, [PERSON] and [PERSON] worked on the development of a user-centric cooperative transmissions-enabled handover scheme for ultra-dense 5G networks. This study [48] addresses the challenge of frequent handovers in UDNs, which are exacerbated by the increasing number of base stations (BSs) and the limitations of conventional handover strategies, such as the Xn-based method. These traditional schemes fail to efficiently accommodate the dynamic and irregular topology of dense networks. Moreover, existing literature lacks analytical frameworks that comprehensively address handover dynamics in user-centric cooperative scenarios, particularly under varying BS densities and user mobility. To resolve this, the authors proposed a Group-Cell Handover (GCHO) scheme, where multiple BSs cooperate dynamically, forming a \"group-cell\" around each piece of UE, coordinated by a software-defined networking (SDN) controller. They also introduced an enhancement called GCHO-Skipping (GCHO-S), which enables UE to skip certain handovers to reduce signaling overhead and delay. The study developed a stochastic geometry-based analytical model, where BS positions follow a homogeneous Poisson point process (PPP). A dual-slope path-loss model was adopted for realistic propagation modeling, and both handover rate and coverage probability were analytically derived. The system was evaluated using extensive simulations under varying user velocities,group-cell sizes, and BS densities. However, the study did not consider the computational complexity and response time implications of the GCHO/GCHO-S schemes as the group-cell size increases. Furthermore, while the dual-slope path loss improves realism, real-world constraints such as backhaul latency and energy consumption of BS cooperation were not addressed, which could impact the feasibility of large-scale deployments. In 2025, [PERSON] et al. developed an adaptive handover management algorithm designed for high-mobility environments in 5G networks, specifically within the context of smart cities.