WCDMA RAN13 Power Control Algorithm and Parameters

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Confidential Information of Huawei. No Spreading Without Permission

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The WCDMA system is an interference-limited system, and the most

important way to restrain system interference is power control. The core

purpose of power control is to minimized the power of transmitting

signals while ensuring Quality of Service (QoS).

In the uplink, a UE emitting too high power will cause unacceptable

competing interference on the NodeB in comparison to signals coming

from UEs at the cell edge. This is called near-far effect. To avoid near-far

effect, uplink power control is required.

In the downlink, the system capacity is determined by the total code

power. Therefore, it is necessary to keep the transmit power at the lowest

possible level while still ensuring signal quality at the UE.

At open loop power control, the initial transmit power is calculated. This

method is rather inaccurate and it is only applied at the beginning of a

connection setup.

At closed loop power control, the transmitter dynamically adjusts its

transmit power according to the feedback from the receiver of the other

side. Closed loop power control is further classified into the following

types:

Inner loop power control directly adjusts the transmit power of the

transmitter by using power control commands.

Outer loop power control indirectly controls the transmit power of

the transmitter.

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CDMA system have the embedded characteristics of self-interference, for

uplink one user’s transmission power become interference to others.

The more connected users, the higher interference. Generally the capacity

is limited by interference level.

WCDMA suffer from Near-far effect, which means if all UE use the same

transmission power, the one close to the NodeB may block the entire cell.

Uplink power control can guarantee the service quality and minimize the

required transmission power. It will resolve the near-far effect and resist

fading of signal propagation. By lowering the uplink interference level,

the system capacity will be increased.

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The downlink has different characteristics from the uplink, for downlink

interference is caused by multi-path, part of one user’s power also become

interference to others.

Downlink power from adjacent cells also is one part of interference to the

own cell.

Transmission power of NodeB is shared by all users channels, so downlink

capacity usually is considered to be limited by transmission power.

Downlink power control also can guarantee the service quality and

minimize the required transmission power, so the capacity is maximized in

case that interference is lowered.

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Because of channel fading in mobile communication system, the radio

signal is deteriorated and fluctuated, the fast power control become one

key technology to resist this phenomenon.

In this figure, the channel fading is compensated by the transmitting power,

which is adjusted by the fast power control, so the receiving power is

almost constant and the radio propagation condition is improved.

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In WCDMA system, power control includes open loop and closed loop

power control.

Open loop power control is used to determine the initial transmission

power, and the closed loop power control adjusts the transmission power

dynamically and continuously during the connection.

For uplink, the UE’s transmission power is adjusted; and for downlink,

the NodeB’s transmission power is adjusted.

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Open loop power control is used in two cases:

1. to decide the initial transmission power of PRACH;

2. to decide the initial transmission power of DPCCH / DPDCH.

Closed loop power control is only applied on DPCCH and DPDCH.

For other common channels, power control is not applied, they will use

fixed transmission power:

The PCPICH power is defined by the PCPICHPower parameter as an

absolute value in dBm.

All other common channels power is defined in relation with the

PCPICHPower parameter, and measured in dB.

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MaxTxPower

Content: The sum of the maximum transmit power of all DL

channels in a cell.

Value range: 0 to 500

Physical value range: 0 to 50; step: 0.1

Physical unit: dBm

Set this parameter through ADD UCELLSETUP and modify it through

MOD UCELL.

PCPICHPower

Content: This parameter should be set based on the actual

environment and the downlink coverage should be guaranteed

firstly. If PCPICH transmit power is configured too big, the cell

capacity will be decreased, for power resources is occupied by

common channel and the interference to traffic channels is also

increased.

Value range: -100 to 500

Physical value range: -10 to 50; step: 0.1

Physical unit: dBm

Set this parameter through ADD UPCPICH, query it through LST

UPCPICH and modify it through MOD UCELL.

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PSCHPower and SSCHPower

Content: The offset of the PSCH/SSCH transmit power from the

PCPICH transmit power in a cell .



Physical unit: dB

For PSCH Power, set it through ADD UPSCH, and query it through

LST UPSCH; for SSCH Power, set it through ADD USSCH, and query

it through LST USSCH. And modify them through MOD UCELL.

BCHPower

Content: The offset of the BCH transmit power from the PCPICH

transmit power in a cell.



Physical unit: dB

Set this parameter through ADD UBCH, query it through LST UBCH,

and modify it through MOD UCELL.

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MaxFachPower

Content: The offset between the FACH transmit power and PCPICH




Physical unit: dB

Set this parameter through ADD UFACH, query it through LST

UFACH.

PCHPower

Content: The Offset of the PCH transmit power from the PCPICH




Physical unit: dB

Set this parameter through ADD UPCH, query it through LST UPCH,

and modify it through MOD USCCPCH.

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AICHPowerOffset

Content: The difference between the transmit power of AICH and

that of PCPICH.


Physical value range: -22 to 5; step: 1

Physical unit: dB

Set this parameter through ADD UCHPWROFFSET, query it through

LST UCHPWROFFSET, and modify it through MOD

UAICHPWROFFSET.

PICHPowerOffset

Content: The difference between the transmit power of PICH and

that of PCPICH.



Physical unit: dB

Set this parameter through ADD UCHPWROFFSET, query it through

LST UCHPWROFFSET, and modify it through MOD

UPICHPWROFFSET.

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In downlink open loop power control, the initial transmission power is

calculated according to the downlink path loss between NodeB and UE.

In uplink, since the uplink and downlink frequencies of WCDMA are in the

same frequency band, a significant correlation exists between the average

path loss of the two links. This make it possible for each UE to calculate

the initial transmission power required in the uplink based on the

downlink path loss.

However, there is 90MHz frequency interval between uplink and

downlink frequencies, the fading between the uplink and downlink is

uncorrelated, so the open loop power control is not absolutely accurate.

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In access procedure, the first signaling “RRC CONNECTION REQUEST” is

transmitted in message part on PRACH.

Before PRACH message part transmission, UE will transmit PRACH

preamble, and the transmission power of first preamble is calculated by

this PRACH open loop power control.

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After UE transmit the first Preamble on PRACH, it will wait for the corresponding AI (Acquisition Indicator) on the AICH.

If no positive or negative AI on AICH is received after p-a time,

UE shall increase preamble power by PowerRampStep, and retransmit preamble.

A preamble ramping procedure consists of several preamble ramping cycles, which cannot exceed Mmax. In each cycle, the UE retransmits preamble until the UE receives the acquisition indicator or the number of retransmissions has reached PreambleRetransMax.

If a negative AI on AICH is received by the UE after p-a time,

which indicates rejection of the preamble, the UE shall wait for a certain “Back-off Delay” and re-initiate a new random access process. The parameters NB01min and NB01max define the lower and upper limits of the back-off delay. If the value of NB01min is equal to that of NB01max, it means that the retransmission period of the preamble part is fixed.

When a positive AI on AICH is received by UE after p-a time,

it will transmit the random access message after the uplink access slot of the last preamble.

The message part consists of two parts: the control part and the data part. The power of the control part is the same as the power of the last transmitted preamble plus a value defined by the PowerOffsetPpm parameter. PowerOffsetPpm must be set for each instance of PRACH TFC.

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In this formula, where

PCPICHPower defines the PCPICH transmit power in a cell. It is

broadcast in SIB5.

CPICH_RSCP means received signal code power, the received

power measured on the PCPICH. The measurement is performed

by the UE.

UL interference is the UL RTWP measured by the NodeB. It is

broadcast in SIB7.

Constantvalue compensates for the RACH processing gain. It is

broadcast in SIB5.

The initial value of PRACH power is set through open loop power control.

UE operation steps are as follows:

1. Read “Primary CPICH DL TX power”, “UL interference” and

“Constant value” from system information;

2. Measure the value of CPICH_RSCP;

3. Calculate the Preamble_Initial_Power of PRACH.

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Constantvalue

Content: It is used to calculate the transmit power of the first

preamble in the random access process.

Value range: -35 to -10

Physical value range: -35 to -10; step: 1

Physical unit: dB

Set this parameter through ADD UPRACHBASIC, query it through

LST UPRACH, and modify it through MOD UPRACHUUPARAS.

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After UE transmit the first Preamble on PRACH, it will wait for the

corresponding AI (Acquisition Indicator) on the AICH. The timing

relationship of PRACH and AICH is as follow:

There will be 3 parameters used to define the timing relationship:

p-p: time interval between two PRACH preambles. p-p is not

a fixed value, it is decided by selecting access slot of PRACH

preambles.

Here p-p has one restriction, it must be longer than a

minimum value p-p min, namely p-p p-p min.

p-a: time interval between PRACH preamble and AICH

Acquisition Indicator. If UE sends the PRACH preamble, it will

detect the responding AI after p-a time.

p-m: time interval between PRACH preamble and PRACH

message part. If UE sends the PRACH preamble and receives

positive AI from the AICH, it will send the message part after

p-m time.

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PowerRampStep

Content: The power increase step of the random access preambles

transmitted before the UE receives the acquisition indicator in the

random access process.

Value range: 1 to 8

Physical value range: 1 to 8; step: 1

Physical unit: dB



PreambleRetransMax

Content: The maximum number of preambles transmitted in a

preamble ramping cycle.





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Mmax

Content: Maximum number of random access preamble loops.



Set this parameter through ADD URACH, query it through LST

URACH, and modify it first de-activated the cell through DEA UCELL,

then MOD URACH, finally ACT UCELL.

NB01min / NB01max

Content: Lower/Upper limit of random access back-off delay.



Physical unit: frame

Set this parameter through ADD URACH, query it through LST

URACH, and modify it first de-activated the cell through DEA UCELL,

then MOD URACH, finally ACT UCELL.

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PowerOffsetPpm

Content: The power offset between the last access preamble and

the message control part. The power of the message control part

can be obtained by adding the offset to the access preamble power.



Physical unit: dB

Set this parameter through ADD UPRACHTFC, query it through LST

UPRACH, and modify it de-activated the cell through DEA UCELL .

After the old configuration of PRACH is deleted through RMV

UPRACHTFC , a new parameters can be established through ADD

UPRACHTFC.

The power of the data part is calculated with the following formula:

Pcontrol is the power for the control part.

βd is the power gain factor for the data part. The value is defined

by the GainFactorBetaD parameter.

βc is the power gain factor for the control part. The value is defined

by the GainFactorBetaC parameter.

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MaxAllowedUlTxPower

Content: The maximum allowed uplink transmit power of a UE in

the cell, which is related to the network planning. The power

limitation just impact the UEs in idle mode.



Physical unit: dBm

Set this parameter through ADD UCELLSELRESEL, query it through

LST UCELLSELRESEL, and modify it through MOD UCELLSELRESEL.

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According to the RRC connection establishment procedure, after RNC

received the “RRC CONNECTION REQUEST” message, if the RNC decided to

use Dedicated Channel to bear the RRC connection, and the RNC told

NodeB to set up the radio link for UE, then Iub interface resources is

established between NodeB and RNC.

When DCH-FP of Iub interface finished downlink and uplink

synchronization, the downlink DPCH starts to transmit, and DPCH initial

transmission power is calculated through open loop power control.

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In this formula, where:

Pinit is initial transmit code power for downlink DPDCH.

PCPICH is the PCPICH power in a cell. The value is configured by

the PCPICHPower parameter on the RNC.

R is the traffic rate requested by the UE and W is the chip rate

(3.84 Mcps).

(Eb/No)DL is the Eb/No target of the downlink DPDCH used to

ensure the service quality. Eb is the energy of a signal information

bit and No is the noise spectral density. The RNC estimates a value

of Eb/No target dynamically based on cell environment type and

BLER target. We can consider Eb/No target as SIR Target.

(Ec/No)CPICH is the ratio of received energy per chip to noise spectral

density of the CPICH received by the UE, UE sends the

measurement value to RNC in RRC connection request message.

α is the orthogonal factor in the downlink. The value is fixed to 0.

Ptotal is the downlink transmitted carrier power measured on the

NodeB and reported to the RNC.

Based on the above description for parameters in formula, we can

change formula to the following, the change help us to understand

how to calculate the downlink DPDCH initial power:

Pinit

RW ( Eb/No )DL

=×

PCPICH

( Ec/No )CPICH

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The downlink DPCCH consists of three fields: TFCI, TPC, and pilot. Their

power is set as the offset reference to the power of the downlink DPDCHs.

The downlink power on the DPCCH and its associated DPDCHs is

simultaneously regulated. Therefore, power control adjusts the power of

the DPCCH and DPDCHs with the same step, and the power offset between

the DPCCH and the DPDCH keeps constant.

Power offsets between the DPCCH and the DPDCH in the downlink are

identical for all TFCs in the TFCS, whereas in the uplink the power offsets

are TFC-dependent.

The power offsets of TFCI, TPC and pilot fields of the DPCCH reference to

the power of DPDCHs are fixed to 0 dB, 3 dB, and 3 dB respectively.

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RlMaxDlPwr

Content: This parameter should fulfill the coverage requirement of

the network planning, and the value is relative to PCPICH transmit

power.



Physical unit: dB

Set this parameter through ADD UCELLRLPWR , query it through

LST UCELLRLPWR, and modify it through MOD UCELLRLPWR.

RlMinDlPwr

Content: This parameter should consider the maximum downlink

transmit power and the dynamic range of power control, and the

value is relative to PCPICH transmit power.



Physical unit: dB

Set this parameter through ADD UCELLRLPWR, query it through LST

UCELLRLPWR, and modify it through MOD UCELLRLPWR.

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Both downlink open loop and close loop power control will be limited by

these parameters in table.

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According to the RRC connection establishment procedure, after RNC sent

the “RRC CONNECTION SETUP” message, UE will try to synchronize with

NodeB, and the uplink DPCCH starts to transmit, here DPCCH initial

transmission power is calculated through open loop power control.

The power of the uplink DPDCH is set as a power offset (βd/βc) reference

to the uplink DPCCH. The uplink DPCCH and DPDCHs are transmitted

through different channel codes. To meet a given QoS requirement on the

transport channels, different TFCs use different power offsets.

The RNC has a set of reference values (βc,ref and βd,ref) that are stored for

each predefined Radio Access Bearer (RAB) or Signaling Radio Bearer (SRB).

βc,ref and βd,ref can be configured by BETAC and BETAD on the RNC.

The RNC calculates a new power offset for each TFC based on the

reference values dynamically and sends the power offset to the UE.

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RNC use the following formula to calculate DPCC_Power_Offset :

DPCCH_Power_Offset = PCPICHPower + UL Interference

+ DefaultConstantValue

Based on the upper formula, the initial power calculation formula for the

uplink DPCCH can be changed to the following , it’s similar to the formula

for PRACH :

DPCCH_Initial_Power = PCPICHPower – CPICH_RSCP

+ UL Interference + DefaultConstantValue

Where :

The DefaultConstantValue parameter reflects the target Ec/No of

the uplink DPCCH.

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DefaultConstantValue

Content: This parameter specifies the constant that is used by the

RNC to compute the DPCCH_Power_Offset which is further used by

the UE to calculate the UL DPCCH_Initial_Power during the open-

loop power control.

Value range: -35 to -10

Physical value range: -35 to -10; step: 1

Physical unit: dB

Set this parameter through SET UFRC, query it through LST UFRC,

and modify it through SET UFRC.

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MaxUlTxPowerforConv

MaxUlTxPowerforStr

MaxUlTxPowerforInt

MaxUlTxPowerforBac

Content: The maximum UL transmit power for specific services in a

cell. It is based on the UL coverage requirement of the specific

services designed by the network planning. These power limitation

just impact on the UEs in connected mode.



Physical unit: dBm

Set this parameter through ADD UCELLCAC, query it through LST

UCELLCAC, and modify it through MOD UCELLCAC.

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Inner Loop Power Control:

The receiver compares SIRmea (measured SIR) with SIRtar (target SIR), and

decide the TPC to send:

If SIRmea is greater than SIRtar, the TPC is set as “0” to decrease

transmission power;

Otherwise the TPC is set as “1” to increase transmission power.

TPC is sent to the transmitter in DPCCH, the transmitter will adjust the

power according to the value of received TPC.

Through inner loop power control, the SIRmea can be ensured to approach

SIRtar.

Outer Loop Power Control:

The receiver compares BLERmea (measured BLER) with BLERtar (target BLER),

and decide how to set the SIRtar:

If BLERmea is greater than BLERtar, the SIRtar is increased;

If BLERmea is less than BLERtar, the SIRtar is decreased.

The adjusted SIRtar is sent for the inner loop power control, then it will be

used in previous process to guide the transmitter power adjustment.

Through outer loop power control, the BLERmea can be ensured to

approach BLERtar.

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RNC sends SIRtar (target SIR) to NodeB and then NodeB compares SIRmea

(measured SIR) with SIRtar:

If the estimated SIR is greater than the target SIR, NodeB sends TPC

“0” to UE on downlink DPCCH TPC field;

Otherwise, NodeB sends TPC “1” to UE.

After reception of one or more TPC, UE shall derive a single TPC_cmd (TPC

command, with value among -1, 0, 1):

Two algorithms could be used by the UE for deriving the TPC_cmd,

those are PCA1 and PCA2 (PCA means Power Control Algorithm).

For UE is in soft handover state, more than one TPC is received, so

firstly multiple TPC_cmd is combined.

When deriving the combined TPC_cmd, UE shall adjust the transmit power

of uplink DPCCH with a step “UL Closed Loop Power Control Step Size“, as

following:

△DPCCH =△TPC × TPC_cmd

Where :

△DPCCH is power increment/reduction on DPCCH

TPC_cmd is calculated by the PCA1 or PCA2 according to the

TPC

△TPC is the step of power control. For PCA1, it’s determined

by UlTpcStepSize. For PCA2, the step size is fixed to 1dB.

This adjustment is executed on the DPCCH, then associated DPDCH

transmit power is calculated according to DPDCH / DPCCH power ratio d /

c.

Pdpdch = Pdpcch × (d / c)2

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When UE has single radio link, only one TPC will be received in each slot. In

this case, the value of TPC_cmd shall be derived by PCA1 as follows:

If the received TPC is equal to 0, then TPC_cmd for that slot is -1;

If the received TPC is equal to 1, then TPC_cmd for that slot is 1.

According to DPCCH channel structure, there are 15 time slots in a 10ms

radio frame, and the control is performed once in each time slot, so the

frequency of uplink inner loop PCA1 is 1500Hz.

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When UE has single radio link, only one TPC will be received in each slot. In

this case, the value of TPC_cmd shall be derived by PCA2 as follows:

For the first 4 slots of a set, TPC_cmd = 0.

For the fifth slot of a set, UE make the decisions on as follows:

If all 5 TPCs within a group are 1, then TPC_cmd = 1 in the

5th slot;

If all 5 TPCs within a group are 0, then TPC_cmd = -1 in the

5th slot;

Otherwise, TPC_cmd = 0 in the 5th slot.

According to DPCCH channel structure, there are 15 time slots in a 10ms

radio frame, and the control is performed once in each 5-slot group, so the

frequency of uplink inner loop PCA2 is 300Hz.

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On the NodeB side, there are two phases during the soft handover state:

Uplink synchronization phase

The NodeB should send durative “TPC = 1” to the newly-added RL

before successful uplink synchronization.

Multi-radio link phase

Each cell will estimate the SIR individually and the generate

TPC individually.

Especially , when UE is in softer handover state, it means UE

has radio links to the same NodeB, in this case these

RLs(Radio Link) belong to the same RLS(Radio Link Set), and

the all TPCs are the same from each RL.

Therefore , when UE enters soft handover state, the UE may receive

different TPC from different RLS, and the UE should combine these TPCs

before deriving TPC_CMD.

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When UE is in soft handover state, multiple TPC will be received in each

slot from different cells in the active set. UE will generate the TPC_cmd by

PCA1 as follows:

1. Combine the TPCs from the same RLS and derive the Wi

When the RLs (Radio Link) are in the same RLS (Radio Link Set), they

will transmit the same TPC in a slot. In this case, the TPCs from the

same RLS shall be combined into one.

After combination, UE will obtain a soft symbol decision Wi for each

RLSi.

2. Combine the TPCs from different RLSs and derive the TPC_cmd

UE derives TPC_cmd, it is based on a function and all the N soft

symbol decisions Wi:

TPC_cmd = (W1, W2, … WN),

Where TPC_cmd can only take the values 1 or -1.

In Huawei implementation, the function shall fulfil the following

criteria:

If the TPCs from all RLSs are “1”, the output of shall be equal to

“1”;

If one TPC from any RLS is “0”, the output of shall be equal to “-1”.

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When UE is in soft handover state, multiple TPC will be received in each

slot from different cells in the active set. UE will generate the TPC_cmd by

PCA2 as follows:

1. Combine the TPC from the same RLS

When the RLs are in the same RLS, they will transmit the same TPC

in a slot. In this case, the TPCs from the same RLS shall be combined

into one.

2. Calculate the TPC_tempi for each RLS

UE derives TPC_tempi through the same way in the last slide, as

follows:

For the first 4 slots of a group, TPC_tempi = 0.

For the 5th slot of a group:

If all 5 TPCs within a group are 1, then TPC_tempi = 1 in the

5th slot;

If all 5 TPCs within a group are 0, then TPC_tempi = -1 in the

5th slot;

Otherwise, TPC_tempi = 0 in the 5th slot.

3. Calculate the TPC_cmd

UE derives TPC_cmd through the following criteria:

If any TPC_tempi is equal to -1, TPC_cmd is set to -1;

If , TPC_cmd = 1;

Otherwise, TPC_cmd = 0.

5.0_1

1

N

i

itempTPCN

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The example of the uplink inner loop PCA2 in soft handover state.

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PwrCtrlAlg

Content: This parameter is used to inform the UE of the method for

translating the received Transmit Power Control (TPC) commands. In

other words, it is used to select UL power control algorithm.

Value range: ALGORITHM1, ALGORITHM2

Physical value range: ALGORITHM1, ALGORITHM2



UlTpcStepSize

Content: The step size of the closed loop power control performed

on UL DPDCH. This parameter is mandatory when the parameter

“PwrCtrlAlg” is set as ALGORITHM1.

Value range: 1 to 2


Physical unit: dB



For PCA2, the step is fixed to 1 dB.

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Basically the downlink inner loop power control process is similar with

uplink, UE L3 sends SIRtar to UE L1 and then UE L1 compares SIRmea with

SIRtar:

If the SIRmea is greater than the SIRtar, UE sends TPC “0” to NodeB

on uplink DPCCH TPC field;

Otherwise, UE sends TPC “1” to the NodeB.

The UE shall check the downlink power control mode before generating

the TPC, two algorithm DPC_MODE 0 and DPC_MODE 1 could be used by

UE to derive the TPC.

Upon receiving the TPC, if the DPC_MODE is 0 , the NodeB shall use the

TPC to generate the TPCest(k). If the DPC_MODE is 1, the NodeB shall use

the three continuous TPCs received to generate the TPCest(k).

Then The NodeB will use TPCest(k) to calculate PTPC(k), PTPC(k) is the

downlink power adjustment.

In the end, the NodeB shall adjust the current downlink power P(k-1) to a

new downlink power P(k), and adjust the power of the DPCCH and DPDCH

with the same amount, since power difference between them is fixed.

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The DPC_MODE parameter is a UE specific parameter controlled by the

UTRAN.

The UE shall check the DPC_MODE (Downlink Power Control Mode) before

generating the TPC, and upon receiving the TPC, the NodeB shall adjust its

downlink DPCH power accordingly.

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DpcMode

Content: This parameter specifies the downlink power control mode.

- SINGLE_TPC, a fast power control mode, indicates that a unique

TPC command is sent in each timeslot on the UL DPCCH.

- TPC_TRIPLET_IN_SOFT, a slow power control mode, indicates that

the same TPC command is sent over three timeslots. It is applicable

to soft handover, and it can decrease the power deviation.

- TPC_AUTO_ADJUST, an automatic adjustment mode, indicates that

the value of DPC_MODE can be modified by sending the ACTIVE SET

UPDATE message to the UE.

Value range: SINGLE_TPC (DPC_MODE = 0), TPC_TRIPLET_IN_SOFT

(DPC_MODE = 1), TPC_AUTO_ADJUST

Physical recommended value: SINGLE_TPC



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If PC_DOWNLINK_POWER_BALANCE_SWITCH is OFF, then Pbal(k) equals 0.

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From the definition above, sum(k) indicates the sum of downlink power

adjustment in the latest DL_Power_Average_Window_Size .

Power_Raise_Limit is set to 10dB.

DL_Power_Averaging_Window_Size is set to 20.

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PC_INNER_LOOP_LMTED_PWR_INC_SWITCH

This is one switch in PcSwitch (Power control switch) parameter.

Content: When the switch is on, the limited power increase function

is used for DL inner loop power control.

Value range: 1, 0

Physical value range: ON, OFF

Set this parameter through SET UCORRMALGOSWITCH, query it

through LST UCORRMALGOSWITCH, and modify it through SET

UCORRMALGOSWITCH.

FddTpcDlStepSize

Content: This parameter specifies the step size of the closed-loop

power control performed on DL DPCH in Frequency Division Duplex

(FDD) mode.

Value range: STEPSIZE_0.5DB, STEPSIZE_1DB, STEPSIZE_1.5DB,

STEPSIZE_2DB

Physical value range: 0.5, 1, 1.5, 2; step: 1

Physical unit: dB



Course Name


P-61

During soft handover, the UL TPC is demodulated in each RLS, then due to

demodulation errors, the DL transmit power of the each branch in soft

handover will drift separately, which causes loss to the macro-diversity

gain.

During softer handover, the power among all radio links may drift because

of initial power difference.

The DL Power Balance (DPB) algorithm is introduced to reduce the power

drift between links during the soft handover or softer handover.

Course Name


P-62

PC_DOWNLINK_POWER_BALANCE_SWITCH


Content: When the switch is on, the RNC supports DL power

balancing. During soft handover, TPC bit errors may cause DL power

drift. DL power balancing is enabled to balance the DL power

between radio links, thus achieving the optimal gain of soft

handover.

Value range: 1, 0




UCORRMALGOSWITCH.

Course Name


P-63

Course Name


P-64

The main reason of outer loop power control:

The QoS of Signaling or Traffic is BLER, not SIR.

The purpose of outer loop power control:

The aim is to maintain the communication quality at the level

required by the service through adjustment of SIR target.

The relationship between inner loop power control and outer loop power

control:

SIRtar should be satisfied with the requirement of decoding correctly.

But different multi-path radio environments request different SIRtar.

Therefore, the outer loop power control can adjust the SIRtar to get

a stable BLER in the changeable radio environment.

Course Name


P-65

Uplink outer-loop power control is performed in the SRNC. The SRNC

measures the received BLER and compares it with the BLERtar :

If the BLERmea is greater than the BLERtar, the SRNC increases the

SIRtar.

If the BLERmea is smaller than the BLERtar, the SRNC decreases the

SIRtar.

After adjusting the SIRtar, the SRNC sends the new SIRtar to the NodeBs for

uplink inner loop power control through Frame Protocol (FP) frames.

Course Name


P-66

The initial SIR target value is transmitted to the NodeB by using NBAP

signaling of each RADIO LINK SETUP or RADIO LINK RECONFIGURATION

PREPARE messages.

Course Name


P-67

According to the formula above,

SIRtar(n) is the target SIR used for the n:th adjustment period.

MAX means the maximum value among the total i transmission

channels.

BLERmeas,i (n) is measured for the i:th transmission channel in the

n:th adjustment period.

BLERtar,i is the target BLER of the i:th transmission channel.

Stepi is the adjustment step of the i:th transmission channel.

Factor is the adjustment factor.

In case of multi-service:

The maximum value of the SIR target among multiple services is

used for the SIR target adjustment.

If one of the services requires increase in the SIR target, the

reconfigured SIR target cannot exceed that maximum value.

The maximum value can be decreased only when all the services

require decrease in the SIR target.

Course Name


P-68

Where,

SIRtar is the adjustment of SIRtar, and SIRtar = SIRtar (n+1) - SIRtar (n).

ABS (SIRtar) means absolute value of SIRtar.

Course Name


P-69

Where,

I/B: Interactive and Background.

Set the BLERtarget of Service through ADD UTYPRABOLPC, query it through

LST UTYPRABOLPC, and modify it through MOD UTYPRABOLPC.

Course Name


P-70

PC_OLPC_SWITCH


Comments: When the switch is on, the RNC updates the UL SIR

TARGET of radio links on the NodeB side through IUB DCH FP in-

band signaling.

Value range: 1, 0




UCORRMALGOSWITCH.

Course Name


P-71

In an optimal condition, the BER target is the average BER after filtering

within the adjustment period. The BER target is obtained before the DTX

period starts during the outer-loop power control period. During soft

handover, the BER target is the minimum value among all the links. When

the BLER is a constant, the BER on the DPCCH can vary within a limited

range.

If the UE is in DTX, the NodeB measures the BER on the UL DPCCH and

send it to RNC through IUB DCH FP Frame.

Upon receiving the BER, the RNC compares it with the BER target.

If the measured BER is greater than the BER target, the OLPC

increases the SIR target.

If the measured BER is smaller than the BER target, the OLPC

decreases the SIR target.

Course Name


P-72

The downlink outer loop power control is implemented inside the UE.

Therefore, this algorithm is specified by UE manufacturer.

The information signaled to the UE by the RNC is a quality target for each

radio bearer, expressed as a BLER target. Then, depending on the

manufacturer specific outer-loop power control algorithm, an initial SIR

target value can be deduced from this BLER value.

Generally, the UE L3(RRC Layer) measures the received BLER and compares

it with the BLERtar :

If the BLERmea is greater than the BLERtar, the L3 increases the SIRtar

and send it to UE L1(Physical Layer).

If the BLERmea is smaller than the BLERtar, the L3 decreases the SIRtar.

Course Name


P-73

Documents

WCDMA RAN13 Power Control Algorithm and Parameters