Open/Closed Loop Power Control

[fahmi]

Hi experts,
could please explain these 2 concepts the easiest way :

Open Loop Power Control
Closed Loop Power Control

what are their meanings and differences ?
many thks

[wahaha]

Open loop PC: MS adjust the transmit power by themselves

Closed loop PC: MS transmit power level is controlled by BS

[bigyan90]

Maybe the following figure will help you get a clear view.

[bigyan90]

Please find the figure in the attachment.

[Kirill Kucherov]

If talking about UMTS, there are three types of Power Control (PC).

To simplify their ideas, I would describe them as following:

1. Closed Loop PC - it optimises the instantaneous transmitted power: UE monitors instantaneous recieved power of DL and can ask BTS to decrease/increase DL transmitted power.
2. Outer Loop PC - it optimises the average transmitted power: UE reports measurements to RNC, based on which RNC can decide to decrease/increase BTS tranmitted power.
3. Open Loop PC: RNCs optimises random access transmitted power (UE UL) - it ensures that UE uses the lowest possible power through RACH