B.3 Quality based control.

3GPP45.008GSM/EDGE Radio 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:

P_n+1 = P_max –  ((C/I_n – C/I_min) – (P_n – P_max)) = P_ref –  (C/I_n – P_n)

where P is the output power from the MS.
C/I is the received carrier to interference value at the BTS.
P_max ,C/I_min and P_ref are reference values.
 is a weighting factor.
n is the iteration index.

In the closed loop case, this formula determines _CH:
_CH = ₀ – P_n+1 .

For the open loop case, we rewrite the formula. The carrier to interference can be written:
C/I = C_BTS – I_BTS = P – L – I_BTS

where C_BTS is the received signal level at the BTS.
I_BTS is the received interference level at the BTS.

thus P_n+1 = P_ref –  (P_n – L_n – I_BTS,n – P_n) = P_ref +  (L_n + I_BTS,n)

As shown above, the path loss is:
L = P_BTS – C

The formula can therefore be written as (dropping the iteration index):

P = P_ref +  (P_BTS – C + I_BTS) = ₀ – _CH –  (C – 48)

Thus, for the open loop case:
_CH = ₀ – P_ref –  (P_BTS + I_BTS – 48)

The interference level I_BTS is measured in the BTS. The parameter _CH is estimated based on these measurements, considering the appropriate weighting factor , and the known parameters P_ref and P_BTS. The _CH values are transferred to the MS in the Power Control Parameters (see 3GPP TS 44.060).