Power Control

 

What is power control and why do we need it?

 

Power control is the process of controlling the uplink and downlink power to the minimum level while ensuring/ maintaining good QoS (Quality of Service). It can be done both by UE or UTRAN (NodeB & RNC).

 

The mechanism is to adjust and control the power of transmit signals according to the changes of radio environment and the quality of receive signals.

Improve the system capacity & ensures the QoS.

 

 

There are four types of power control.

 

• Open-loop power control:
• Applicable in both UL and DL.
• It sets the initial uplink and downlink transmit power.
• Open-loop power control is used on physical channel such as PRACH (Physical Random Access Channel), DPCH (Dedicated Physical Channel).
• Inner-loop power control:
• Applicable in both UL and DL.
• It directly adjusts the uplink and downlink transmit power using power control commands.
• The inner loop power control is performed by each UE and NodeB with the frequency of 1500 times per second (1.5 kHz).
• Outer-loop power control:
• Applicable in UL and DL.
• It indirectly controls the uplink and downlink transmit power by increasing or decreasing the target SIR value.
• DL power balance:
• It is used to reduce the downlink power drifting of a given UE during soft handover.

*** 

1. In the uplink, if a UE near the NodeB has too large a transmit power, it may cause great interference to other UEs on the edge of the cell or even block the whole cell. This is called near-far effect. In that case, uplink power control is needed.
2. In the downlink, the system capacity is determined by the total required code power for each connection. Therefore, it is necessary to keep the transmit power at the lowest level while ensuring signal quality at the receiving end for each UE. In that case, the downlink power control is needed.
3. Power control can be used against shadow fading and fast fading.
4. Power control can increase system capacity.
5. Power control for power drifting can improve the soft handover performance in
   the downlink.

 

Later will explain in what type of scenario we use each of them.