Power ControlAlgorithm & Parameters

By:By:Anuj Kumar DasAnuj Kumar Das

By : Anuj Kumar Das

DefinitionThis is a feature of the GSM air interface which allows the network provider to not only

compensate for the distance from MS to BTS as regards timing, but can also cause the

BTS and MS to adjust their power output to take account of that distance also.

The closer the MS is to the BTS, the less the power it and the BTS will be required to transmit.

This feature saves radio battery power at the MS, and helps to reduce co-channel and adjacent channel interference.

Both uplink and downlink power settings can be controlled independently and individually at the discretion of the network provider.

Initial power setting for the MS is set by the information provided on the Broadcast Control Channel (BCCH) for a particular cell.

The BSS controls the transmit power of both the MS and the BTS. The received MS power is monitored by the BSS and the receive BTS power is monitored by the MS and then reported to the BSS. Using these measurements the power of both MS and BTS can be adjusted accordingly

Note:

GSM Recommendations state that uplink power control is mandatory, whereas downlink

power control is optional.

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ms_power_control_allowed

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bts_power_control_allowed

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Flow Diagram

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Power Control Thresholds

UL DL UL DLu_rxlev_ul_p u_rxlev_dl_p u_rxqual_ul_p u_rxqual_dl_p

40 40 28 28

UL DL UL DLl_rxlev_ul_p l_rxlev_dl_p l_rxqual_ul_p l_rxqual_dl_p

30 30 225 256

PC Thresholds

Upper Rx lev Rx Qual

LowerRx lev Rx Qual

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l/u_rxlev_dl_p

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l/u_rxlev_ul_p

u_rxlev_ul_p

l_rxlev_ul_p

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l/u_rxqual_dl_p

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l/u_rxqual_ul_p

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alt_qual_procDescriptionThe alt_qual_proc parameter specifies whether receive quality processing is performed using Bit Error Rate (BER) values or Quality Band (QBand) units.

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Power inc/dec step size

pow_inc_step_size_dl

pow_inc_step_size_ul

pow_red_step_size_dl

pow_red_step_size_ul

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Power Control - BSSThe MS provides averaged RSSI measurement samples on the downlink radio path to the RSS. The RSS then performs its own averaging and these values are compared against the power control thresholds. All, or a proportion of the averaged values being considered must exceed the threshold value before any action will be taken.

The proportion of averaged values that must exceed the threshold is determined by two database fields, decision_1_n1 and decision_1_p1 for increasing the output power and decision_1_n2 and decision_1_p2 for decreasing the output power. The “n” parameters represent the number of previously averaged values to be considered and the “p” parameters are the proportion of those averages that must exceed the threshold value. If “p” and “n” were set to the same value then all averaged values considered by the RSS must exceed the threshold value.

Two threshold values are required, one to determine when the BSS output power level should be increased and another to determine when the BSS output power level should be decreased. These thresholds are set in the l_rxlev_dl_p (power increase required) and u_rxlev_dl_p (power decrease required).

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Power Control – BSS Contd..

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Decision MakingDecision Makinghreqave – Total no. of measurements (SACCH frames) required to calculate One average

hreqt (N) – No. of averages required for initiating decision process for power adjustment.

P – Minimum no. of averages required out of “N” for power adjustment

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N1/P1-Increase UL/DL power on Rx Lev

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N2/P2- Decrease UL/DL power on Rx Lev

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N3/P3- Increase UL/DL power on RxQual

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N4/P4- Decrease UL/DL power on RxQual

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decision_alg_type

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bts_p_con_interval

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bts_p_con_ack

Note : Only after expiry of this timer bts_p_con_interval timer begins

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ms_p_con_interval

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ms_p_con_ack

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Optimized Power Control

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Optimized Power Control - parameters

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dyn_step_adj_fmpr

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