## 6 Conclusions  
In UDN, handover faces severe problems such as large interference and high ping -pong rate. This paper starts with the optimization problem of effective handover rate and proposes a dynamic DQN algorithm based on signal fading condition. This method has a good backward compatibility and can provide parameter optimization suggestions for the mobile communication system as an independent module. In order to improve the efficiency and performance of the ordinary DQN method, this paper proposes a digital-twin-enhanced DQN based on the LSTM network. Taking advantage of potential handover parameters before actual handover is triggered and corresponding RSRP sequences, handover failure rate, ping-pong rate, and corresponding reward value are estimated in LSTM-based digital twin. The proposed digital twin could increase the exploration efficiency of the DQN algorithm. The simulation results show that the two DQN methods mentioned in this article have significantly promoted effective handover rate, while the DTe-DQN has better convergence efficiency and robustness than the DQN, and eventually could achieve higher effective handover rate. Methodology, J.H. ; Software, T.X. and Y.W. ; Investigation, J.H. ; Resources, H.R. ; Writing--original draft  
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