RF 功率控制

1概述

采用RF 功率控制来使MS或BTS所需的发射功率最小而仍然保持无线链路质量。通过使发射功率电平最小，可以减小同信道用户间的干扰。

4.2        MS implementation

RF power control shall be implemented in the MS.

The power control level to be employed by the MS on each uplink channel, except PDCH , is indicated by means of the power control information sent either in the layer 1 header of each SACCH message block (see GSM 04.04) on the corresponding downlink channel, or in a dedicated signalling block (see GSM 04.08). Power control for PDCH is defined in subclause 10.2 .

The MS shall employ the most recently commanded power control level appropriate to each channel for all transmitted bursts on either a TCH (including handover access burst), FACCH, SACCH or SDCCH.

The MS shall confirm the power control level that it is currently employing in the SACCH L1 header on each uplink channel. The indicated value shall be the power control level actually used by the mobile for the last burst of the previous SACCH period.

In the E-TCH mode, the MS shall, if so indicated by the BSS in the SACCH L1 header (see GSM 04.04) or Assignment command (see GSM 04.18), use FPC (fast power control). The MS shall employ the most recently commanded fast power control level on each uplink E-TCH channel. The power control level to be employed by the MS is indicated by means of the power control information sent via fast inband signalling once every FPC reporting period (see subclause 4.7). If FPC is in use, the MS shall report, in the SACCH L1 header, the power control level used at the end of the normal power control reporting period.

In the E.TCH mode and channel coding asymmetry configuration using 8 PSK for uplink, the MS shall use the fast inband signalling in uplink for fast measurement repoting.

NOTE:    The term "normal power control" is used in this specification only for clarification and is otherwise only referred to as "power control".

In case of a multislot configuration, each bi?directional channel shall be power controlled individually by the corresponding SACCH or fast inband signalling link, whichever is applicable. Power control information on downlink unidirectional channels shall be neglected.

When accessing a cell on the RACH (random access) and before receiving the first power command during a communication on a DCCH or TCH (after an IMMEDIATE ASSIGNMENT), all GSM and class 1 and class 2 DCS 1 800 MS shall use the power level defined by the MS_TXPWR_MAX_CCH parameter broadcast on the BCCH of the cell. The class 3 DCS 1 800 MS shall use the power level defined by MS TXPWR MAX CCH plus the value POWER OFFSET also broadcast on the BCCH of the cell.

If a power control level defined in GSM 05.05 is received but the level is not supported by the MS, the MS shall use the supported output power which is closest to the output power indicated by the received power control level.

4.3        MS power control range

The range over which a MS shall be capable of varying its RF output power shall be from its maximum output down to its minimum, in steps of nominally 2 dB.

GSM 05.05 gives a detailed definition of the RF power level step size and tolerances.

The fast power control scheme for ECSD is based on differential control to adjust the employed RF power level. The possible DL power control commands are listed in the following table.

Codeword

Power control command

0

Not used

1

Increase output power by four power control levels

2

Increase output power by three power control levels

3

Increase output power by two power control levels

4

Increase output power by one power control level

5

No  output power level change

6

Decrease output power by one power control level

7

Decrease output power by two power control levels

If a power control command is received but the requested output power is not supported by the MS, the MS shall use the supported output power which is closest to the requested output power.