For many URLLC services, mobility is a key requirement together with latency and reliability. 3GPP has defined the target of MIT as 0 ms, and a general URLLC reliability requirement as 1 - 10-5 within a latency of 1 ms for 5G. In this article, we analyzed the impact of MIT and handover failure (HOF) rate on the reliability performance. From the analysis, at 120 km/h, with MIT of 0 ms, the required HOF rate to achieve 1 - 10-5 reliability is only 0.52 percent. Therefore, to achieve the reliability for URLLC, we need to minimize not only the MIT but also the HOF rate as close to zero as possible. Hence, we propose conditional make-before- break handover to target zero MIT and zero HOF rate simultaneously. The solution can achieve zero MIT by not releasing the connection to the source cell until the first or some downlink receptions from the target cell. It can achieve the zero HOF rate, by receiving an HO Command message when the radio link to the source cell is still stable, and by executing the handover when the connection to the target cell is preferable. Simulation results show that our proposed solution can achieve almost zero HOF rate even at 120 km/h.

中文翻译：

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NR 中用于超可靠低延迟通信的切换机制


对于许多 URLLC 服务，移动性以及延迟和可靠性是一个关键要求。 3GPP定义了5G MIT的目标为0毫秒，通用URLLC可靠性要求为1毫秒延迟内的1-10-5。在本文中，我们分析了 MIT 和切换失败（HOF）率对可靠性性能的影响。经分析，在120公里/小时时，MIT为0毫秒时，实现1-10-5可靠性所需的HOF率仅为0.52%。因此，为了实现 URLLC 的可靠性，我们不仅需要使 MIT 最小化，而且还需要使 HOF 率尽可能接近于零。因此，我们提出有条件先通后断切换，以同时实现零 MIT 和零 HOF 率的目标。该解决方案可以通过在来自目标小区的第一次或一些下行链路接收之前不释放到源小区的连接来实现零MIT。通过在到源小区的无线链路仍然稳定时接收HO命令消息，并在到目标小区的连接更好时执行切换，可以实现零HOF速率。仿真结果表明，我们提出的解决方案即使在 120 km/h 的速度下也能实现几乎为零的 HOF 率。