Hi,
Ericsson document tell us:
In general the following cases occur:
If the MS and the cell support AMR HR and the number of idle FR TCH:s divided by the total number of de-blocked FR TCH:s is equal or above DTHAMR FR TCH:s will have precedence over HR TCH:s. If the number of idle FR TCH:s divided by the total number of de-blocked FR TCH:s is less than DTHAMR HR TCH:s will have precedence over FR TCH:s
If the MS or the cell do not support AMR HR and the number of idle FR TCH:s divided by the total number of de-blocked FR TCH:s is equal or above DTHNAMR FR TCH:s will have precedence over HR TCH:s. If the number of idle FR TCH:s divided by the total number of de-blocked FR TCH:s is less than DTHNAMR HR TCH:s will have precedence over FR TCH:s
so if your threshold for DTHNAMR be 70% so the traffic will start with FR channel.
example:
4 TRXs (1 BCCH & 2 SDCCHs & 29 TCHs)
%70 * 29 = 21
the BSC assigns FR channel in the begining until 8th channel assignment, for 9th MS assigning HR channel will be start.
Limitations:
1- some MSs can not support HR, so BSC assigns FR channel to them.
2- sometimes incoming HO parameters forces BSC to assign FR channel to MS.
Hi pix, Ericsson has only 1 threshold for Half Rate. Nokia has 2 threshold (FRL and FRU) for Half Rate (Hysteresis).