B.6 Interworking between normal and fast power control for ECSD

3GPP45.008GSM/EDGE Radio subsystem link controlTS

Interworking between normal and fast power control in the ECSD mode is done so that the normal power control may be running even if fast power control is activated. This means that both the BSS and the MS shall, at all times when in dedicated ECSD mode, estimate the radio link quality plus send power level commands and link quality reports respectively based on the cycle of the reporting period of length 104 TDMA frames (as specified in subclause 8.4). When FPC is activated though, the power level commands sent via SACCH are ignored by the MS.

Through this, a switch back to normal power control can be done very easily since the MS always knows what power level to use immediately after a switch. Switching between normal and fast power control always takes place at the beginning of a reporting period.

The figure below illustrates the simultaneous operation of the two power control mechanisms and their respective functional blocks.

The BSC has the control over which power control loop is in use. This is signalled with one control bit on the Abis interface to the BTS, which in turn informs the MS, when the fast power control loop shall be used. When FPC is not activated, there is no requirement for either the BTS nor the MS to perform quality estimations or sending commands/reports via E-IACCH.

The specific power control algorithm to be used for fast power control is, as is the case for normal power control, implementation dependent and is thus not standardised.