# Mobility Management Based on Beam-Level Measurement Report in 5G Massive MIMO Cellular Networks
## 5 Numerical Results
### Performance Evaluation  
We compare the performance of the proposed scheme with the conventional inter-beam-handover (IBH) scheme [25] and beam management (BM) scheme [18; 43; 44]. We consider that the period of CSI-RS report in the conventional BM scheme is four slots. We show the performance result in single-gNB and UDN environments, respectively. First, we show uplink overhead performance by the PUCCH, PUSCH, and total uplink overhead. Total uplink overhead is the sum of PUCCH and PUSCH overhead. PUCCH and PUSCH overhead is calculated by (16) and (17). Furthermore, we show the downlink overhead performance, and the results of the successful mobility attempts. That is, downlink overhead performance is obtained by \(M_{\text{BS}}\times\text{number of BS attempts}\times(1-\text{BSF rate})+M_{\text{HO}}\times\text{number of HO attempts}\times(1-\text{HOF rate})\). In addition, we show the 3-dB loss probability calculated by (18). The beam switching failure (BSF), HOF, RLF rates are counted by the result of the scenarios in Figure 3. We show the SINR results calculated based on (8). In the single-gNB case, there is no cell-level mobility but beam-level mobility. Figure 4 shows the results of the overhead, the number of mobility attempts, and the number of mobility failure under the single-gNB scenario for three schemes. Because there is no cell-level mobility, all results are presented in terms of intra-cell and inter-beams performance. The result shows that the total uplink overhead in the proposed scheme and the conventional IBH scheme is smaller than that in the conventional BM scheme. This is because the proposed scheme and the conventional IBH scheme send MR only after TTT expiry, whereas the conventional BM scheme sends the CSI-RS report every 4 ms. Users with the proposed scheme use PUSCH to send the MR while users with the conventional BM use PUCCH to send the periodic CSI-RS report. The PUCCH load is more significant than the PUSCH load in terms of uplink overhead because each user requires PUCCS independently while PUSCH can be shared by users and this. This fact is a significant factor for the overhead usage for densely deployed users, which is another advantage of the proposed scheme, particularly for the 5G NR systems. Due to the considerably high number of beam reports, there are many occurrences of beam switching in the conventional BM case that results in significant downlink overhead requirements. This indicates that the proposed scheme has a better performance in downlink overheads compared to that of the conventional BM scheme. We find that the 3-dB loss probability performance with the proposed scheme is slightly lower than that with the conventional BM case. This is because the BM scheme's frequent periodic report makes it easier for refined TRP compared to event-triggered MR. However, it may lead to a mobility failure caused by early-beam switching, and the RLF and BSF rates are worse than those of the proposed scheme. In Figure 5a, the proposed scheme shows considerable performance improvement compared to the conventional schemes in the practical environment system of the UDN scenario. Owing to the massive number of the measurement targets (cell and beams) and the environment where both cell-level and beam-level mobilities occur, there are two main differences between the single-gNB and UDN environments. First, overall overhead and mobility attempts are increased in UDN environments compared to the single-gNB environments as shown in Figure 5a,b. Second, the proposed scheme significantly outperforms the conventional IBH scheme in practical UDN environments in terms of the overhead and RLF rate performance. Furthermore, the proposed scheme also clearly outperforms the other two conventional schemes in terms of the mobility attempts performance. If there are many adjacent cells and available beams and if the system can provide a better channel status with beam switching, the BS is considered as a better solution than the handover because of the overhead saving.