05.083GPPRadio subsystem link controlTS
In order to achieve the best performance the power control should be quality based. The algorithm must also consider the path loss for stability. The algorithm is not specified, it is the responsibility of the manufacturer and/or the operator.
An example of a quality based power control algorithm is:
Pn+1 = Pmax – ((C/In – C/Imin) – (Pn – Pmax)) = Pref – (C/In – Pn)
where P is the output power from the MS. C/I is the received carrier to interference value at the BTS. Pmax ,C/Imin and Pref are reference values. is a weighting factor. n is the iteration index.
In the closed loop case, this formula determines CH: CH = 0 – Pn+1 .
For the open loop case, we rewrite the formula. The carrier to interference can be written: C/I = CBTS – IBTS = P – L – IBTS
where CBTS is the received signal level at the BTS. IBTS is the received interference level at the BTS.
thus Pn+1 = Pref – (Pn – Ln – IBTS,n – Pn) = Pref + (Ln + IBTS,n)
As shown above, the path loss is: L = PBTS – C
The formula can therefore be written as (dropping the iteration index):
P = Pref + (PBTS – C + IBTS) = 0 – CH – (C – 48)
Thus, for the open loop case: CH = 0 – Pref – (PBTS + IBTS – 48)
The interference level IBTS is measured in the BTS. The parameter CH is estimated based on these measurements, considering the appropriate weighting factor , and the known parameters Pref and PBTS. The CH values are transferred to the MS in the Power Control Parameters (see 3GPP TS 04.60).