Friday, November 6, 2009

UMTS Power Control

Two types : Open Loop power control and Outer loop power control

Open Loop Power Control : Transmitting entity estimates the required power level by itself from the received signal. UE will have open loop power control feature. Means : UE adjusts the power level based on the received power and the further estimation
This is not feedback mechanism and it is done by self.

Closed Loop Power Control : It has inner loop : Adjusts SIR-target
It also has Outer loop : Sets the SIR-Target (Signal to Interference)

RNC sets value for NodeB , which is called Outer loop. The NodeB sends the SIR target to UE and it adjusts by itself.

The power adjustment happens with TPC commands. (Transmit power command). When TPC bit is 1 menas UE should increase the power. when TPC bit is 0 means decrease the power.

This works on feedback mechanism through TPC command.

*UE will have both inner loop and outer loop implemented.
*InNodeB, innerloop is between UE and NodeB and Outerloop is between NodeB and RNC.

*If NodeB is serving 20 UEs, in NodeB there will be 20 closed-loop control entities.

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