模擬結果顯示，相較於傳統以 RSRP 為主要判斷依據的換手機制，本研究所提出的策略可有效降低換手次數，減少不必要換手的發生次數，並延長 UE 與單一服務衛星之平均連線時間，減少因頻繁換手所產生的信令開銷。研究結果顯示，都卜勒頻率特徵可作為 LEO NTN 移動性管理的重要輔助資訊，有助於提升換手決策的穩定性。;In non-terrestrial network (NTN) systems， low Earth orbit (LEO) satellites have emerged as an important technology for next-generation mobile communication networks because of their relatively low propagation delay and potential for wide-area coverage. However， the high relative motion between LEO satellites and terrestrial user equipment (UE) requires frequent handovers (HOs) to maintain connection continuity and stability. Conventional 5G New Radio (NR) handover mechanisms are primarily designed for terrestrial network environments and typically rely on reference signal received power (RSRP) as the main decision criterion. However， in LEO satellite network scenarios， the spatial variation in RSRP may be relatively gradual， making accurate handover timing decisions difficult and potentially resulting in premature， repeated， or improperly timed handovers.
To address these issues， this study proposes a Doppler-frequency-based handover strategy. The proposed strategy exploits the predictable variations in Doppler shift and Doppler rate resulting from changes in the relative geometry between the satellites and the ground. These Doppler characteristics are used to determine whether the serving satellite is approaching or moving away from the UE and to estimate the expected service time of candidate satellites. The estimated information is then incorporated into the handover decision process.
Simulation results demonstrate that， compared with conventional handover mechanisms that primarily rely on RSRP， the proposed strategy can effectively reduce the number of handovers and unnecessary handovers while extending the average duration for which a UE remains connected to a single serving satellite. Consequently， the signaling overhead associated with frequent handovers can be reduced. These results indicate that Doppler-frequency characteristics can serve as important auxiliary information for mobility management in LEO NTN systems and contribute to improving the stability of handover decisions.
