Entering condition for Event A1 Serving becomes better than threshold:
Inequality A1-1 (Entering condition)
Ms - Hys > Thresh
Inequality A1-2 (Leaving condition)
Ms + Hys < Thresh
The variables in the formula are defined as follows:
- Ms is the measurement result of the serving cell, not taking into account any offsets.
- Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within reportConfigEUTRA for this event).
- Thresh is the threshold parameter for this event (i.e. a1-Threshold as defined within reportConfigEUTRA for this event)
The reason is very clear. You might have observed it when you go just down the Ground based tower and will make the call. Your voice quality will get disturbed and there will be lots of noise distortion. Threshold means it has some quality level say example -95dbm and if it getting -96dbm it means it is getting unwanted resources which is not required so it can reduce the frequency tuning to decrease it.