# A Survey of Handover Management in Mobile HetNets: Current Challenges and Future Directions
## 4 Handover Decision Techniques
### RSRP-Based HO Decision Approaches  
UE performs periodic or event-triggered measurements and reporting for handovers to get signal quality and power level. 3 GPP defined a few measurement parameters, and RSRP is one of them. RSRP-based handover procedures are more practical and can perform better in conjunction with other measurements or decision parameters to adjust user requirements. RSRP is the average received power of a single reference signals resource element. An illustration of the RSRP-based handover process is shown in Figure 7. In this section, we included some literature related to RSRP-based HO decisions. For the 4G and 5G HetNets scenario, the authors of article [92] developed a dynamic HO control technique to optimize the HCP values and decrease HOPP and RLF. The proposed algorithm was based on the type of HOF. They employed three types of HOFs named too-early-HO, too-late-HO and wrong-cell-HO and justified that these HOFs occur due to different speed scenarios. However, one criterion for these failures is the UE's speed, and other factors that contribute to HOFs include RSRP, SINR, and aberrant HCP changes. These need to be adjusted dynamically to efficiently cover different speed scenarios and RSRP levels. According to the proposed algorithm, the system will initially monitor input parameters like RSRP, SINR, UE speed, etc. Following HOF occurrence, they classified HOFs into three types and adjusted HCP parameters based on HOF type. Without taking HOF into account, the results showed improvements in HOP, HOPP, RLF, and IT when compared to earlier papers. Similarly, in [37], the same authors proposed an auto-tuning optimization algorithm with the similar approach based on RSRP and UE speed to tune HCP values. The objective of the algorithm was to reduce HOF and HOPP, and its performance was measured using HOPP, RLF, CDR, HOF, HOD, and IT. In article [68], a penalized HO load balancing algorithm was proposed for cell edge users in LTE HetNets. The technique was based on the optimization of the MLB algorithm by cooperative UE selection and target cell selection along with Handover parameter optimization to achieve  
Figure 7: Basic illustration of RSRP based Handovers in HetNets. the objective of efficient load balancing along with better QoS. They used RSRP, cell load and SINR to optimize HCPs and the comparison of the results shows a reduction in the number of unwanted switching between UE and BS, thus increasing the throughput and QoS of the system. In [153], the authors developed an efficient HO algorithm for load balancing in the LTE HetNets scenario. They created a list of possible femtocells using RSRP from neighboring cells and SINR. This possible femtocell list is divided into three categories of neighbor cells based on the RSRP, expected RSRP, and number of free resource blocks (RB), respectivily. To begin, the algorithm will select the femtocell with the highest number of available resources in order to achieve the maximum possible throughput. In the event that a candidate femtocell is unavailable, the algorithm forces users to connect to a macro cell with adequate resource blocks. They tested the algorithm in a variety of scenarios with varying numbers of users and UE velocity for throughput and HOPP. To address HOPP and HOF, [154] proposed a method for adjusting the start of the handover process using the TTT value based on the prediction of SINR in LTE HetNets. A predictive method based on the recursive least squares algorithm was used to forecast SINR value. The handover process selects the most appropriate triggering time with the help of the monitoring of decay in SINR value. The results showed an improvement in the quantity of HOF and HOPPs. Frequent HOs degrade system performance and can be brought on by factors including channel fading, static users, and slow-moving users. Within a small cell network, high-speed UE are more likely to encounter HOs than low-speed users. These recurrent HOs require adequate detection and prevention measures.