for 1 PDCH coded in MCS-9, there is a need of 4.5GCH
1 MS using 4PDCH in DL @ MCS9, it needs 4*4.5GCH = 18GCH
in UL, a MS can use more than 1 PDCH. It can use 2 PDCH without any special feature… (2+2 or 3+2)
There is also the new feature “extended dynamic allocation”, which allow the following configuration : 1+2, 1+3, 1+4, 1+5, 2+3, 2+4, 3+3
Anyway, the dimensioning of the GCH is always done in DL. When you got your result, for example the link needs “50 GCH”… then you design an ABIS link with 50GCH. There will be 50GCH in DL and 50GCH in UL. 1 GCH is always defined symetrically.