6.5.8 Power control procedure

03.643GPPGeneral Packet Radio Service (GPRS)Overall description of the GPRS radio interfaceStage 2TS

Power control shall be supported in order to improve the spectrum efficiency and to reduce the power consumption in the MS.

For the uplink, the MS shall follow a flexible power control algorithm, which the network can optimise through a set of parameters. It can be used for both open loop and closed loop power control.

For the downlink, the power control is performed in the BTS. Therefore, there is no need to specify the actual algorithms, but information about the downlink performance is needed. Therefore the MSs have to transfer Channel Quality Reports to the BTS.Power control is not applicable to point-to-multipoint multicast services.

For the detailed specification of power control see GSM 05.08 [15].

6.5.8.1 MS output power

The MS shall calculate the RF output power value, PCH, to be used on each individual uplink PDCH assigned to the MS:

PCH = min((0 – CH –  * (C + 48), PMAX)

where

CH is an MS and channel specific power control parameter. It is sent to the MS in any resource assigning message. Further, the network can, at any time during a packet transfer, send new CH values to the MS on the downlink PACCH.

0 is a frequency band dependent constant.

0,1 is a system parameter. Its default value is broadcast on the PBCCH. Further, MS and channel specific values can be sent to the MS together with CH.

C is the received signal level at the MS.

PMAX is the maximum allowed output power in the cell.

All power values are expressed in dBm.

PCH is not used to determine the output power when accessing the cell on PRACH or RACH , in which case PMAX shall be used.

6.5.8.2 BTS output power

The BTS shall use constant power on those PDCH radio blocks which contain PBCCH or which may contain PPCH. This power may be lower than the output power used on BCCH. The difference shall be broadcast on PBCCH.

On the other PDCH radio blocks, downlink power control may be used. Thus, a procedure may be implemented in the network to control the power of the downlink transmission based on the Channel Quality Reports.

The network shall ensure that the output power is sufficient for the MS for which the RLC block is intended as well as the MS(s) for which the USF is intended, and that for each MS in packet transfer mode, at least one downlink RLC block per multiframe is transmitted with an output power that is sufficient for that MS, on a block monitored by that MS.

6.5.8.3 Measurements at MS side

A procedure shall be implemented in the MS to monitor periodically the downlink Rx signal level and quality from its serving cell.

6.5.8.3.1 Deriving the C value

This subclause comprises information about how the MS shall derive the C value in the power control equation.

The MS shall periodically measure the received signal strength.

In packet idle mode, the MS shall measure the signal strength of the PCCCH or, if PCCCH is not existing, the BCCH.

In packet transfer mode, the MS shall measure the signal strength on BCCH. The same measurements as for cell re-selection are used (see 6.5.6.1.). Alternatively, if indicated by a broadcast parameter, the MS shall measure the signal strength on one of the PDCHs where the MS receives PACCH. This method is suitable in the case where BCCH is in another frequency band than the used PDCHs. It requires that constant output power is used on all downlink PDCH blocks.

The MS shall measure the signal strength of each radio block monitored by the MS. The C value is achieved by filtering the signal strength with a running average filter. The filtering shall normally be continuous between the packet modes. The different filter parameters for the packet modes are broadcast on PBCCH or, if PBCCH does not exist, on BCCH.

The variance of the received signal level within each block shall also be calculated. The filtered value SIGN_VAR shall be included in the channel quality report.

An MS transferring a packet in the uplink with fixed assignment is not required to make signal strength measurements and shall thus update PCH only when it receives new CH values.

6.5.8.3.2 Derivation of Channel Quality Report

The channel quality is measured as the interference signal level during the idle frames of the multiframe, when the serving cell is not transmitting.

In packet transfer mode, the MS shall measure the interference signal strength of all eight channels (slots) on the same carrier as the assigned PDCHs.

In packet idle mode, the MS shall measure the interference signal strength on certain channels which are indicated on the PBCCH or, if PBCCH does not exist, on BCCH. If no channels are indicated the MS shall not perform these measurements.

Some of the idle frames and PTCCH frames shall be used for this, while the others are required for BSIC identification and the timing advance procedure, see subclause 6.5.9.

The MS may not be capable of measuring all eight channels when allocated some configurations of channels. The MS shall measure as many channels as its allocation allows considering its multislot capability.

The slots that the MS measures on can be either idle or used by SACCH or PTCCH, depending on the channel type (TCH or PDCH).. The MS shall therefore, for each slot, take the minimum signal strength of one idle frame and one PTCCH frame. Thus the SACCH frames are avoided (except for a TCH/H with two MSs) and only the interference is measured.

The interference, CH , is achieved by filtering the measured interference in a running average filter. The filtering shall be continuous between the packet modes for channels measured in both modes. The different filter parameters for the packet modes are broadcast on PBCCH or, if PBCCH does not exist, on BCCH.

In packet transfer mode the MS shall transfer the 8 CH values and the RXQUAL, SIGN_VAR and C values (see subclause 6.5.8.3.1) to the network in the Channel Quality Report included in the PACKET DOWNLINK ACK/NACK message.

6.5.8.4 Measurements at BSS side

A procedure shall be implemented in the BSS to monitor the uplink Rx signal level and quality on each uplink PDCH, active as well as inactive.

The BSS shall also measure the Rx signal level and the quality of a specific MS packet transfer.