This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section.
For reliable and efficient communication in a wireless system, a UE is required to continuously monitor its downlink radio link conditions and determine whether it is in out-of-sync or in in-sync status when a UE is in the connected state. The procedure is commonly called Radio Link Monitoring (RLM). For legacy E-UTRAN systems, all UEs work under the same cell coverage level, which is normally predetermined by careful cell-planning during the feature deployment. Conventional RLM is Thus designed and implemented to support one cell coverage level.
3GPP introduced enhanced machine type communication (eMTC) and narrow-band Internet of Things (NB-IoT), which are believed to be the baseline, or at least used as input, for 5G massive machine type communication (mMTC) and 5G Internet of Things (5G-IoT). Unlike legacy E-UTRAN systems, where there is only one cell coverage level and the cell coverage level is predetermined by careful cell-planning during the feature deployment, eMTC and NB-IoT features support multiple coverage levels. It is expected that multiple coverage levels will also be supported for mMTC and 5G-IoT features.
According to similar principles as for LTE, eMTC and NB-IoT devices are required to monitor the downlink radio link quality and determine their In-sync and Out-of-sync status. That is, if the DL quality falls below predefined threshold Qout, UE is expected to declare it is in out-of-sync status, which may eventually trigger Radio Link Failure (RLF). For a UE already in out-of-sync status, it is expected to declare it comes back to in-sync status, if the DL quality exceeds another predefined threshold Qin to avoid unnecessarily triggering RLF. Since eMTC and NB-IoT support multiple coverage levels, the RLM for eMTC and NB-IoT is therefore required to support multiple cell coverage levels.
The current invention moves beyond these techniques and materials.
Abbreviations that may be found in the specification and/or the drawing figures are defined below, after the detailed description section.