3G Layer 1 Inner Loop Power Control Internals

Overview:

The purpose of power control in WCDMA systems is to achieve the following objectives:

· Removes near-far effect
· Mitigates fading
· Compensâtes changes in propagation conditions.

At the system level

• Decrease interference from other users
• Increase the network capacity

There are two types of power control

· Uplink (UL) Power Control: Power control in uplink must make signal powers from different users nearly equal in order to maximize the total capacity of the cell.

· Downlink (DL) Power Control: Downlink power control ensures that node B keeps the signal to the minimum level in order to decrease the interference to the users in other cells.

Inner Loop Power Control also known as (Fast closed loop power control) is based on the feedback information. There is one PC (Power control) command per timeslot. The SIR _target for fast closed loop PC is set by the outer loop PC. The three special cases of power control are radio link re-configuration, compressed mode and soft-handover (SHO).

The figure below shows inner loop downlink and uplink power control overview.

Downlink Power Control

The downlink (DL) power control is used to decrease interference to the users in other cells. The transmit power of the DL channels is determined by the network. The UE generates TPC commands to control the network transmit power and send them in the TPC field of the uplink DPCCH. Upon receiving the TPC commands UTRAN adjusts its downlink DPCCH/DPDCH power accordingly. DL power control is always applied at the pilot bits of every timeslot. The assumption here is that there is no radio-link reconfiguration (RL_RECONF), compressed mode or SHO.

Power Leveling and Output to HCP from Tx Service for power update

Abbreviations:

3GPP: 3rd Generation Partnership Project
COD: Codec
DEM: Demodulation SC
DPCCH: Dedicated Physical control channel
DPDCH: Dedicated Physical data channel
DL: downlink
DTX: discontinued transmission
GLO: Global Handler
HSDPA: High speed downlink packet access
HSM: Handler shared memory
HSUPA: High speed uplink packet access
MDM: Modem
P-CCPCH: Primary Common Control Physical Channel
S-CCPCH: Secondary common control physical channel
SHO: Soft handover
SIR: Signal to interference ratio
Tc: Chip period (1/Fc = 1/3.84 MHz)
TFCI: Transport Format Combination Indicator
Ts: Timeslot
Ue: User Equipment
UL: Uplink