Tuesday, 13 September 2011

CELL_FACH to LTE Mobility

At the moment, transition from RRC states from UMTS to LTE can happen from CELL_DCH to E-UTRA_RRC_CONNECTED state via Handover or from UTRA_IDLE to E-UTRA_RRC_IDLE via Cell Reselection. There is a study ongoing to transition from CELL_FACH to LTE. The state has not been specified but my guess is that it would probably be E-UTRA_RRC_CONNECTED. The following is the reasoning based on RP-111208:

It is our understanding that some of the Cell_FACH enhancement proposals for Release 11 are targeted to make it more attractive to keep UEs longer in the Cell_FACH state than is expected with pre-Rel-11 devices. This expectation that the UEs may stay longer in the Cell_FACH state is in turn motivating the mobility from Cell_FACH state to LTE proposal.

For instance, as the network can already today release the Cell_FACH UE’s RRC Connection with redirection, network may want to redirect UE to the correct RAT and frequency based on the UE measurement. Specifically if the network strategy is to keep the UEs long time in Cell_FACH state, it would make sense to provide the network the tools to manage the UEs’ mobility in that state. In addition, the needs for mobility to LTE are somewhat different from mobility to e.g. GERAN, as the former would be typically priority based while the latter would happen for coverage reasons. Thus, if introduced, the network controlled mobility from UMTS Cell_FACH would be specifically interesting for the UMTS to LTE case.

Will update once I have more info.

1 comment:

Breno said...

Hello, 36.331 Rel11 already specified this. Is there any special parameter in UE side that need to be informed to network, or this is a Rel11 feature as is? I know that some changes in SIB19 are neede, but not sure what.

Thanks and regards,