41389209-09-power-control-rev-a-libre.pdf

Power Control

Christofer LindheimerWRAN System Management

Commercial in confidence Power Control 2005-09-262

Outline

Why is Power Control important in WCDMA? How different channels are Power Controlled Power Control for Dedicated Channels in up- and

downlink– Open Loop Power Control / Initial Power Setting– Outer Loop Power Control– Inner Loop Power Control

Power Balancing in SHO


Why Power Control

Maintain quality of connection– Maintain acceptable quality throughout a coverage area – Avoid excessive quality

Limit transmitted power – Minimize interference in the system=maximizing capacity

Battery/Energy Consumption– UE and Battery backups

L1 >> L2 ⇒ PRX,2 >> PRX,1

PTX,2 PTX,1L2

PRX,2 L1

PRX,1if PTX,2 = PTX,1

PowerControl !


Outline





Mapping of transport channels to physical channels

Physical Channels Logical ChannelsTransport Channels

CCCHCommon Control Channel

DCCHDedicated Control Channel

PCCHPaging Control Channel

BCCHBroadcast Control Channel

DTCHDedicated Traffic Channel

PCH (DL)Paging Channel

FACH (DL)Forward Access Channel

BCH (DL)Broadcast Channel

RACH (UL)Random Access

Channel

DCH (DL/UL)Dedicated Channel

Common Transport Channels

PRACH (UL)Physical Random Access Channel

AICHAcquisition Indication Channel

P-CCPCH (DL)Primary Common Control Physical Channel

S-CCPCH (DL)Secondary Common Control Physical Channel

PICH (DL)Paging Indication Channel

DPDCH (UL/DL)Dedicated Physical Data Channel

DPCCH (UL/DL)Dedicated Physical Control Channel

DPCH - Dedicated Physical Channel

POWER CONTROL

Primary CPICH

Primary SCH

Secondary SCH


Power control ”type” dependent on channel type Common Channels - Fixed power

– P-CPICH, P-SCH, S-SCH, P-CCPCH (BCH), S-CCPCH (PCH, FACH), AICH, PICH

– Several UEs anywhere in the cell simultaneously use these channels Maintain quality throughout coverage area

– All (DL) common channels set relative to P-CPICH

Dedicated Channels – Dynamic Power control– One UE per DPCH channel– Optimize power for each individual link– All dedicated channels have an absolute-valued maximum

power (both in UL and DL)


Common Uplink Channel-PRACH Open Loop Power Control

-Hello!

-Hello!

-Hello!

• RACH preamble is sent with a stepwise increase in powerP_PRACH=L_PCPICH (@UE) + RTWP (UL @ RBS) + constantValueCprach (+ powerOffsetP0)

•Once detected, AICH in DL respond, (powerOffsetPpm added)

• Preamble power increases interrupted after maximum number of reattempts


Outline





Power Control of Dedicated Channels -Overview

CRC = Cyclic Redundancy Check

SIR = Signal to Interference Ratio

TPC = Transmit Power Commands

Initial Power Setting in UL and DL uses Open Loop . It ensures reliable connection setup, minimal impact on existing connections (UL) and avoids excessive power (DL).

RNC

P(Start value)

Open loop

P(SIR-Target,UL)

SIR-Target,UL

CRC-Error,UL

UL-Outer loop

The RNC and UE use Outer Loop power control to calculate UL and DL quality targets to which the UE and RNC shall adjust its transmitted power.

DL-Outer loop UE specific

P(SIR-Target, DL)

Inner loop

DL-TPCUL-TPC

The RBS and UE use Inner Loop to send UL and DL TPC’s(transmit power commands).

1500 Hz!


Power Control of Dedicated Channels –Downlink, Initial Power Setting, Open Loop DL Initial Power dependent on

– CPICH Power primaryCpichPower

– Ec/No reported by UE Ec/No_PCPICH

– SIR Target dlInitSirTarget

– Spreading Factor SF_DL_DPDCH

– An offset to control initial output power level cBackOff

P_DL_DPDCH=primaryCpichPower + (dlInitSirTarget-Ec/No_PCPICH) + cBackOff + 10 log (2/SF_DL_DPDCH)


Power Control of Dedicated Channels –Downlink, Inner Loop Power Control

DPDCH/DPCCH

Present slot power P(k) = P(k-1) + P TPC(k) dBm

PTPC(k) = + 0.5 dB for ‘UP’or – 0.5 dB for ‘down’

P(k-1) = Previous slot power

DPCCH: TPC Command = ‘Up or Down’

DPDCH


Power Control of Dedicated Channels –Uplink initial power setting, Open Loop

UL Initial Power dependent on– CPICH Power

primaryCpichPower

– RTWP measured in RBS RTWP

– SIR Target (dependent on SF of DPDCH) ulInitSirTarget

– Spreading Factor SF_DPCCH

– An offset to control initial output power level cPO

– RSCP of PCPICH as measured in the UE

P_UL_DPCCH_INIT=primaryCpichPower + RTWP+ulInitSirtarget+ cPO - 10 log (SF_DPCCH) - RSCP_PCPICH


Power Control of Dedicated Channels –Uplink, Outer Loop Power Control

Increases UL SIR target whenever a transport block is erroneously received and decreases the UL SIR target whenever a transport block is correctly received

SIR target adjustments äå BLER requirements

JUMP Algorithm


Power Control of Dedicated Channels –Uplink, Inner Loop Power Control

RBS estimates the SIR of the pilot symbols (SIR_UL_RLS) and compares it to the SIR_TARGET.

If SIR_UL_RLS ≥SIR_TARGET ⇒ TPC Command =‘down’

If SIR_UL_RLS < SIR_TARGET ⇒ TPC Command =‘up’

DPDCH/DPCCH

TPC Command = ‘Up or Down’

DPCCH/DPDCH determined by gain-factors

Present slot power P(k) = P(k-1) + PTPC(k) dBm


Outline





Power Control of Dedicated Channels –Downlink, Power Control in SHO Initial Power Setting

– Aim to equalize the power transmission from different RBS’s (considering differences in PCPICH power and handover margin)

Up

TPC = Up TPC = Down

Node-B power drift is likely– Independent BER per link ⇒ different interpretations of received

TPC in different cells can occur


Power Control of Dedicated Channels –Downlink, Power Balancing

Prevents different radio links involved in a connection from transmitting different DL power.

Preference

Power

Power adjustment

Time

Cell 1

Cell 2


Power Control of Dedicated Channels –Uplink, Power Control in SHO

TPC = Up

TPC = Up & Down

TPC from cell to UE

One inner loop in respective Node-B One separate TPC from each cell in the active set

– All “increase” ⇒ increase UE power– ≥ 1 “decrease” ⇒ decrease UE power

TPC = Down


Summary

Inner loop PC– Fast PC included in every timeslot– 1500 Hz– Measure the actual SIR & Compare with SIR-target– SIR ≥ SIR-target ⇒ Decrease power – SIR < SIR-target ⇒ Increase power

Outer loop PC– Adjust SIR-target based on BLER performance– Slower, per TTI basis updates– UL: Jump algorithm

Open loop PC– Initial power setting

In SHO: Power balancing (DL)

RNC

P(Start value)

Open loop

P(SIR-Target,UL)

SIR-Target,UL

CRC-Error,UL

UL-Outer loop

DL-Outer loop UE specific

P(SIR-Target, DL)

Inner loop

DL-TPCUL-TPC

1500 Hz!

Questions and Answers

41389209-09-power-control-rev-a-libre.pdf

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