WCDMA Power Control PrincipleISSUE 1.0

Huawei Confidential. All Rights Reserved

Chapter 1 Power Overview Chapter 2 Power Control Algorithm

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Internal Use

Purpose of power controlPurpose of power controlUplink channel To overcome the near-far effect. channel: Downlink channel : Overcome fast fading and the interferences of adjacent cells.

Power control must be used in CDMA system to ensure every user transmits at minimum power, thus maximizing network capacity

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Internal Use

Power control classificationPower control classificationOpen loop Power control Closed loop Power control

> Uplink inner power control > Downlink inner-power control > Uplink outer power control > Downlink outer power controlThe purpose of inner loop power control in WCDMA system is to maintain a certain signal-to-interference ratio of transmission signal power when the signals reach the receiving end. However, for different multi-path environments, even if the mean signal-tointerference ratio is kept above a certain threshold, the communication quality requirement (BER) can not always be satisfied .4

Internal Use

The Relationship between Transmitted Power and Received Power after Power Control Methods Introduced

20 Channel 15 10 Transmitted power Received power

Relative power (dB)

5 0 -5 -10 -15 -20 0 200 400 600 800

Time (ms)5

Internal Use

Benefit of Power Control

Benefit of power controlOvercome uplink near-far problem Ensure good communication quality in uplink and downlink by adjust transmission power Overcome the influences of unfavorable factors such as fast fading, slow fading on radio channels Decrease network interference, increase the capacity and quality of network In other word, the purpose of power control is to ensure the QoS with minimum power in the CDMA system.

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Internal Use

Power control methods adopted for various physical channels

Power control methods adopted for various physical channels "X" can be applied, "" not applied

Physical channel DPDCH DPCCH PCCPCH SCCPCH PRACH AICH PICH

Open loop power control

Inner loop power control

Outer loop power Control

No power control process, power is specified by upper layers.

; ; ;

; ; ; ;

; ; ;

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Internal Use

Chapter 1 Power Overview Chapter 2 Power Control Algorithm

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Internal Use

Chapter 2 Power Control Algorithm1.Open loop power control2.Inner2.Inner-loop power control 3.Outer loop power control

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Internal Use

Open Loop Power Control OverviewPurposeUE estimates the power loss of signals on the propagation path by measuring the downlink channel signals, then calculate the transmission power of the uplink channel. Mainly used for initial connection setup.

Under the FDD mode, fast fading of the uplink channel is unrelated to fast fading of the downlink channel.

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Internal Use

Open Loop Power Control OverviewDisadvantage of open loop power controlThis power control method is rather vague

Application scenarios of open loop power controlIn the range of a cell, signal fading caused by fast fading is usually more serious than that caused by propagation loss. Therefore, open loop power control is applied only at the beginning of connection setup, generally in setting the initial power value.

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Internal Use

Open Loop Power Control of PRACHOne access slot AICH access slots RX at UE X PRACH access slots TX at UE Preamble Preamble Acq. Ind.

p-a Message part

X p-p

X p-m

Random access procedure of PRACH :-

UE transmit a preamble using the selected uplink access slot, signature, and preamble transmission power. - Then ,UTARN response by sending AI if the preamble is received. - Next, UE transmit the message part if the AI is received. - But, if UE does not receive the AI from UTRAN in p-p period, a next preamble will be transmitted.12

Internal Use

Open Loop Power Control of PRACHThe initial value of PRACH power is set through open loop power control Preamble_Initial_Power = PCPICH DL TX power CPICH_RSCP + UL

Interference + Constant Value ParametersPCPICH DL TX power, UL interference and Constant are given in system information. The value of CPICH_RSCP is measured by UE PCPICH DL TX power is very closed to the downlink coverage ability, which is already given in cell setup. UL interference can be measured by NodeB, then it will be reported to RNC. Constant Value is the threshold of preamble message. This value has to be analysed very carefully.

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Internal Use

Open loop power control of PRACHPpm Power Ramp Step

Preable_Initial_ power 10ms/20ms

NO.1 2 3 4

ParameterPower Offset Pp-m Constant Value PRACH Power Ramp Step Preamble Retrans Max

Parameter meaningThe power offset of the last access preamble and message control part. This value plus the access preamble power is the power of the control part This parameter is the correction constant used for the UE to estimate the initial transmission power of PRACH according to the open loop power This parameter is the ramp step of the preamble power when the UE has not received the capture indication from NodeB This parameter is the permitted maximum preamble repeat times of the UE within a preamble ramp cycle

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Internal Use

Open loop power control of PRACHDifferent Constant Values for different stage of WCDMA network lifecycle. Take the beginning stage for example:Constant Value can be greater (-16dB or -15dB) so that the preamble message can be received easier by UTRAN The power ramp step could be greater so that the possibility which the preamble message can be received correctly will be higher

With the development of network, the number of users increased very fast. On this stage, the Constant value could be less 1dB.

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Internal Use

Open loop power control of PRACHApplication scenariosUE Node B Serving RNS1. CCCH : RRC Connection Request RRC RRC Allocate RNTI Select L1 and L2 parameters 2. Radio Link Setup Request NBAP Start RX description 3. Radio Link Setup Response NBAP NBAP NBAP

Serving RNC

Open loop power control of PRACH

4. ALCAP Iub Data Transport Bearer Setup 5. Downlink Synchronisation 6. Uplink Synchronisation

DCH - FP DCH - FP Start TX description

DCH - FP DCH - FP

7. CCCH : RRC Connection Set up RRC 8. Radio Link Restore Indication NBAP 9. DCCH : RRC Connection Setup Complete

RRC NBAP

RRC

RRC

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Internal Use

Open loop power control of DL DPCCHThe DL DPCCH open loop power control can be calculated by the following formula: P = Ec/Io)Req - CPICH_Ec/Io + PCPICH Parameters(Ec/Io)req is the required Ec/Io, which should be satisfied for UE to be able to received the message from dedicated channel correctly CPICH_Ec/Io is measured by UE, then it is given to UTRAN by RACH PCPICH is the transmission power of CPICH Comments Similar to UL, the (Ec/Io)Req value should be considered very carefully Because there is no power ramp in the initial DL DPCCH, the initial power should be satisfied with the requirements. Therefore, this value can be greater than the one from simulation to ensure the success ratio17

Internal Use

Open loop power control of DL DPCCHApplication scenariosUE Node B Serving RNS1. CCCH : RRC Connection Request RRC RRC Allocate RNTI Select L1 and L2 parameters 2. Radio Link Setup Request NBAP Start RX description 3. Radio Link Setup Response NBAP NBAP NBAP

Serving RNC

4. ALCAP Iub Data Transport Bearer Setup

Open loop power control of DPCCH

DCH - FP DCH - FP Start TX description

5. Downlink Synchronisation 6. Uplink Synchronisation

DCH - FP DCH - FP

RRC

7. CCCH : RRC Connection Set up 8. Radio Link Restore Indication NBAP 9. DCCH : RRC Connection Setup Complete

RRC NBAP

RRC

RRC

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Internal Use

Open loop power control of UL DPCCHThe UL DPCCH open loop power control can be calculated by the following formula: DPCCH_Initial_power PCPICH DL TX power - CPICH_RSCP + UL interference + DPCCH_SIRtarget ParameterPCPICH DL TX power is the transmission power of CPICH CPICH_RSCP can be measured by UE UL interference can be measured by NodeB

CommentsThe DPCCH_SIRtarget value should be considered very carefully. It reflects the lowest requirement for decoding the DPCCH in a certain multiple path environment

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Internal Use

Open loop power control of UL DPCCHApplication scenariosUE Node B Serving RNS1. CCCH : RRC Connection Request RRC RRC Allocate RNTI Select L1 and L2 parameters 2. Radio Link Setup Request NBAP Start RX description 3. Radio Link Setup Response NBAP NBAP NBAP

Serving RNC

4. ALCAP Iub Data Transport Bearer Setup

Open loop power control of DPCCH

DCH - FP DCH - FP Start TX description

5. Downlink Synchronisation 6. Uplink Synchronisation

DCH - FP DCH - FP

7. CCCH : RRC Connection Set up RRC 8. Radio Link Restore Indication NBAP 9. DCCH : RRC Connection Setup Complete

RRC NBAP

RRC

RRC

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Internal Use

Chapter 2 Power Control Algorithm1.Open loop power control 2.Inner2.Inner-loop power control 3.Outer loop power control

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Internal Use

Close loop power controlWhy the close loop power control is needed Weakness of open loop power controlOpen loop power control can decided the initial power, but it is not accurate For WCDMA-FDD system, the uplink fading is not related to the downlink one because of the big frequency interval of them Therefore, the path loss and interference estimated by downlink can not reflect the one in uplink completely. But, the close loop power control can solve this problem

The advantages of close loop power controlCan control the transmission power of uplink and downlink very fast, and decrease interference in system. Maintains a higher quality of service

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Internal Use

Inner-loop power control nnerThe principle for Inner-loop power control InnerThe receivers calculate the SIR by estimating the power strength and the current interference. Then, compare this one to SIRtargetIf SIRmeasured < SIRtarget send TPC = 1 to inform receivers increase SIRtarget, its transmission power If SIRmeasured > SIRtarget send TPC = 0 to inform receivers decrease SIRtarget, transmission power

The receiver that receives the TPC will adjust the transmission power by algorithms. The inner loop power control can convergence the estimated SIR to SIR target

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Internal Use

Inner-loop power control nnerInner-loop power control Algorithm nnerIn 3GPP protocol, two algorithms are adopted in the inner-loop power control of uplink DPCCHPCA1 : uplink power control step is PCA2 : uplink power control step is tpc=1 tpc=1dB or 2dB tpc=1 tpc=1dB

The power control adjustment range in DPCCH is DPCCH= tpcTPC_cmd tpcTPC_cmd is achieved by different algorithm

The power offset shows the difference of transmission power of UL DPCCH and UL DPDCH The adjustment range of DPDCH is the same as the DPCCH. The power offset is decided by the signaling from higher layer

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Internal Use

UplinkUplink-inner loop power controlNodeB compares SIRmeasured with the preset target signal-to-interference ratio (SIRtarget).

1500Hz

Inner-loop

Transmit TPC set SIRtar

UE

NodeBEach UE has own loop

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Internal Use

UplinkUplink-inner loop power controlDPDCH/DPCCH structure

Data DPDCH T N data bits = 2560 chips, N = 10*2 k bits (k=0..6) slot data TFCI N TFCI bits T FBI N FBI bits TPC N TPC bits

DPCCH

Pilot N pilot bits

= 2560 chips, 10 bits slot

Slot #0

Slot #1

Slot #i 1 radio frame: T = 10 ms f

Slot #14

The power ratio of DPCCH to DPDCH is

F c2 F d2Internal Use

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UplinkUplink-inner loop power controlTPC The uplink DPCCH SIR should be estimated by different serving cells. In each time slot, the TPC can be generated by the following rules:No soft handover

> If SIR estimation > SIR target,then TPC = 0 to decrease the transmission power

> If SIR estimation < SIR target,then TPC = 1 to increase the transmission power Soft handover

> In one time slot, UE received several TPC, then combine then.

CommentsIn the last situation, the PCA decides how TPC_cmd are combined. The PCA has two methods. UTRAN decides which one is used.27

Internal Use

UplinkUplink-inner loop power controlUE can adjust the UL DPCCH transmission power with tpc step according to the received TPC_cmd The step tpc can be 1dB or 2dB, which is decided by UTRANIf the TPC_cmd = 1 the UL DPCCH and UL DPDCH transmission tpc power should be increased If the TPC_cmd = -1

the UL DPCCH and UL DPDCH transmission

power should be decreased tpc If the TPC_cmd = 0 the UL DPCCH and UL DPDCH transmission

power should be decreased tpc

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Internal Use

UplinkUplink-inner loop power controlPCA1 PCA1

UE in Non - Soft handover case UE receives only one TPC> If TPC = 0, TPC_cmd = -1 > If TPC = 1, TPC_cmd = 1

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Internal Use

UplinkUplink-inner loop power controlPCA1 PCA1 UE in Soft handoverUE receives several TPCs in one time slot and combine them to get one TPC_cmd by the following two steps:

> First, combine the TPCs from one RLS > Then, combine the TPCs from different RLS

Comments The TPC from RLSi is Wi

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Internal Use

UplinkUplink-inner loop power controlPCA1 PCA1 Wi can be achieved by the following rulesIf the TPC = 0, Wi=0 If the TPC = 1, Wi 1 N TPC can be obtained after

Assume UE has N RLSs

combination, W1 W2WN. The combination method for these N TPCs from N RLSes can be described as following formula TPC_cmd = (W1, W2, WN)

function should satisfied:If one Wi = 0, TPC_cmd = -1 If all Wi are 1 TPC_cmd = 1

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Internal Use

UplinkUplink-inner loop power controlPCA2 PCA2 UE in non-soft handover mode nonOnly one TPC is received in one time slot. The power control can be done once by each 5 time slots. Each frame is divided 3 groups of 5 time slots. In the first 4 time slots, the TPC_cmds are 0, which means the power does not change. In the 5th time slot, the TPC_cmd can be achieved by the following rules:

> If all TPC are 0, the TPC_cmd is -1 and the transmission will decrease 1dB; > If all TPC are 1, the TPC_cmd is 1 and the transmission will increase 1dB; > Otherwise, TPC_cmd=0.TPC RX TPC_cmd 0000 -1 0000 1 0000 0

0000 0 1111 1 else

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Internal Use

UplinkUplink-inner loop power controlPCA2 PCA2 UE in soft handover TPC_cmd can be achieved by the following two stepsFirst, combine the TPC from the same RLS

> N TPCi (i = 1,2......N) obtained from N RLSs in each time slot > The N TPC_cmds from different RLS can be achieved by the above mentioned rules. > Assume each final TPC_cmd from N RLS are TPC_tempi i = 1,2......NTPC_cmd in the fifth time slot can be obtain by the following rules TPC_cmd (5 slot) = (TPC_temp1, TPC_temp2, , TPC_tempN) where is defined as follows:N 1 TPC _ tempi " 0.5, TPC _ cmd ! 1 N i !1

th

orN 1 TPC _ tempi N i !1

0.5, TPC _ cmd ! 1

otherwise, TPC_cmd = 0.33

Internal Use

UplinkUplink-inner loop power controlComparison between PCA1 and PCA2 PCA1 PCA2 The control frequencyPCA1, the power control frequency is 1500Hz PCA2, the power control frequency is 300Hz

Application scenariosWhen UE is moving with high speed (80Km/h), the fast inner-loop power control can not catch up with the fast fading, but will produce negative gain. In this situation, PCA2 is preferred.

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Internal Use

Downlink Inner-loop power control Inner-

Transmit TPC

Inner-loop Measure SIR and compare

NodeB

1500Hz

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Internal Use

Downlink inner-loop power control innerTimeslot structure of Downlink DPCH : PO3 defines the power offset of the TFCI bit in the downlink DPCCH to DPDCH. PO2 defines the power offset of the TPC bit in the downlink DPCCH to DPDCH. PO1 defines the power offset of the Pilot bit in the downlink DPCCH to DPDCH. The values of PO1 PO2 and PO3 are defined by RNC.

Inner-loop power control of downlink DPCCH include two types: - Inner-loop power control in compressed mode, - Inner-loop power control in non-compressed mode.

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Internal Use

Downlink inner-loop power control innerFirst, UE should estimate the downlink DPDCH/DPCCH power and the current SIR Then, UE can generate TPC by comparing SIRestimated to SIRtargetIf SIRestimated > SIRtarget ; TPC = 0 (decrease power) If SIRestimated < SIRtarget ; TPC = 1 (increase power)

The step of DL inner-loop power control could be 0.5, 1, 1.5 or 2dB

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Internal Use

Downlink inner-loop power control innerPower control in different state When UE is not in soft handoverTPC generated by UE is transmitted in TPC domain of UL channel

When UE in soft handover, two power control modes can be used, which is decided by DPC_mode:DPC_MODE DPC_MODE 0 1 UE will transmit TPC in every slot UE will transmit the same TPC in every three time slot

When the downlink channel is out of synchronization, UE will transmit TPC=1 because UE can not measure the downlink SIR Upon reception of TPC, UTRAN will adjust the downlink power of DPCCH/DPDCH. But the transmission power can not higher than Maximum_DL_Power and not less than Minimum_DL_Power neither.Internal Use

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Chapter 2 Power Control Algorithm1.Open loop power control 2.Inner2.Inner-loop power control 3.Outer loop power control

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Internal Use

Outer-loop power control uterThe limitation of inner loop power controlThe purpose of inner loop power control of the WCDMA system is to maintain a certain signal-to-interference ratio of transmission signal power when the signals reach the receiving end.

The character of outer-loop power controlThe Qos which NAS provide to CN is BLER, not SIR

The relationship between inner-loop power control and outer-loop power controlSIR target should be satisfied to be able to decoding receive signal correctly. But different radio path radio environment has different requirement on SIR Therefore, the outer-loop power control can adjust the SIR to get a stable BLER in the changeable radio environmentInternal Use

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Uplink outer loop power control

get the good quality service data

Measure received data and compare BLER

Measure and compare SIR

Out loop

Inner-loop

Set BLERtarget

Set SIRtarget 10-100Hz

Transmit TPC

RNC

NodeB

UE

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Internal Use

Downlink outer loop power control

Measure and compare BLER1500Hz Outer loop Transmit TPC

L3 10-100Hz set SIRtar

Inner loop

L1

NodeB

Measure and compare SIR

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Internal Use

Outer loop power controlSIR target adjustment step

BLERmeas BLERt arg et (SIRtar ! SIRAdjustcoefficient * SIRAdjustStep * BLERt arg et

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Internal Use

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Internal Use