Mobility State Estimation in LTE

28 Aug

As part of the HetNet mobility enhancements for LTE, one of the topics being discussed in RAN2 is the accuracy of mobility state estimation (MSE) mechanism. I came across a nice description of the existing MSE scheme in a RAN2 doc (R2-115919). The 3GPP TS36.331 (RRC specification) describes MSE for UEs in RRC_CONNECTED mode as follows:

Step 1: The UE counts handovers during time period t-Evaluation and t-HystNormal.

Note: The UE shall not count consecutive handovers between same two cells.

Step 2: The UE detects its own mobility state based on the number of handovers:

  • If the number of handovers during the time period t-Evaluation exceeds n-CellChangeHigh

–            the UE enters the High-mobility state

  • If the number of handovers during the time period t-Evaluation exceeds n-CellChangeMedium but does not exceed n-CellChangeHigh

–            the UE enters the Medium-mobility state

  • else if criteria for either Medium- or High-mobility state is not detected during the time period t-HystNormal

–            the UE enters the Normal-mobility state

Step 3: The UE scales the timeToTrigger (TTT) based on its mobility state:

  • if the High-mobility state is detected:

–            use the TTT value multiplied by sf-High

  • else if the Medium-mobility state is detected:

–            use the TTT value multiplied by sf-Medium

  • else

–            no scaling is applied

 

Source: http://allabout4g.wordpress.com/2013/08/28/mobility-state-estimation-in-lte/

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