017 WCDMA Power Control

WCDMA Power Control

Huawei Technologies Co., Ltd.

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WCDMA Power Control Confidentiality level: Customer

Mexico Training Center Confidential information of Huawei. No spreading

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Revision Record

Date Version Change description Author

07-01-2008 1A Victor Toledo



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Table of Contents

1 Purpose of Power contol .......................................................................................................7

Benefit from power control ................................................................................................8 Power contol classification ...............................................................................................8

2 Power control algorithms .....................................................................................................10

Open loop power control overview .................................................................................10 Open loop power control for PRACH...............................................................................11 Open loop power control for DPCCH ..............................................................................14 Closed loop power control ...............................................................................................16 Uplink inner loop power control .......................................................................................18 Downlink inner loop power control ..................................................................................24 Downlink power balance .................................................................................................29 Outer loop power control..................................................................................................30



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Objectives

Upon completion of this module, the student will be able to:

� Understand the basic principle of power control

� Understand the setting of different parameters used in power control

� Explain the Open and Closed loop power control algorithms



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1 Purpose of power control

� Purpose of power control

� Power control of the uplink channel is mainly to overcome the near-far effect.

� Downlink channel power control is to overcome fast fading and the interferences of adjacent cells.

� Power control must be used in CDMA system to ensure every user transmits by minimum power and the network capacity can get maximum.

� The 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.

� However, in different multi-path environments, even if the mean signal-to-interference ratio is kept above a certain threshold, the communication quality requirement (BER or FER or BLER) can not be always satisfied.

Figure 1.- The Relationship between Transmitted Power and Received Power after Power Control Methods Introduced.

Because of fading in mobile communication system, the radio channel environment is deteriorated, many technologies are used to solve this problem, and the fast power control is one of them. So the fading is compensated by fast power control, and the received power is almost constant, the radio transmission condition is improved.

0 200 400 600 800-20

-15

-10

-5

0

5

10

15

20

Tim e (m s)

Re

lati

ve

po

we

r(d

B)

C hanne l

Transm itted pow er

R eceived p ower

0 200 400 600 800-20

-15

-10

-5

0

5

10

15

20

Tim e (m s)

Re

lati

ve

po

we

r(d

B)

C hanne l

Transm itted pow er

R eceived p ower



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Benefit from Power Control

� Power control is known to be essential in a CDMA-based system due to the uplink near-far problem.

� Adjust transmission power to ensure communication quality of uplink and downlink.

� Power control can well 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 a word, the purpose of power control is to ensure the QoS with minimum power in the CDMA system.

Power control classification

In WCDMA system, power control includes open loop power control and closed loop power control, open loop power control is used to calculate the initial transmission power, and the closed loop power control technology adjusts the transmission power dynamically and continuously during connection.

For uplink power control, the UE’s transmission power is adjusted, for downlink power control, the NodeB’s transmission power is adjusted.

� Open loop Power control

� Closed loop Power control

− Uplink inner power control

− Downlink inner-power control

− Uplink outer power control

− Downlink outer power control

Open loop power control is used in two cases, the first one is on PRACH to decide the initial transmission power of PRACH preamble, and the second case is on DPCCH to decide the initial transmission power of DPCCH power control preamble.



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Closed loop power control is applied on DPCCH and DPDCH.

For other common channels, power control is not applied.

Power control methods adopted for various physical channels

Table 1.- Power control methods adopted for different physical channels.

XXXX－－－－－－－－－－－－PICH

XXXX－－－－－－－－－－－－AICH

－－－－－－－－－－－－XXXXPRACH

XXXX－－－－－－－－－－－－SCCPCH

XXXX－－－－－－－－－－－－PCCPCH

－－－－XXXXXXXXXXXXDPCCH

－－－－XXXXXXXX－－－－DPDCH

No power control process,

power is specified by upper

layers.

Outer loop

power

Control

Inner loop

power

control

Open loop

power

control

Physical

channel

XXXX－－－－－－－－－－－－PICH

XXXX－－－－－－－－－－－－AICH

－－－－－－－－－－－－XXXXPRACH

XXXX－－－－－－－－－－－－SCCPCH

XXXX－－－－－－－－－－－－PCCPCH

－－－－XXXXXXXXXXXXDPCCH

－－－－XXXXXXXX－－－－DPDCH

No power control process,

power is specified by upper

layers.

Outer loop

power

Control

Inner loop

power

control

Open loop

power

control

Physical

channel



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2 Power Control Algorithms

Open Loop Power Control Overview

In open loop power control, the initial transmission power is calculated according to the path loss between UE and NodeB. That means, if the UE is very far away from the NodeB, the calculated transmission power should be very high and vice versa.

Since the uplink and downlink frequencies of WCDMA are within the same frequency band, a significant correlation exists between the average path loss of the two links. This make it possible for each UE, before accessing the network, and for each NodeB, when the radio link is set up, to calculate the initial transmission power required in the uplink and downlink based on the path loss calculations in the downlink direction.

� Purpose

� the UE 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

� The open loop power control principal

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

� the disadvantage of open loop power control

� This power control method is rather vague

� Application scenarios of open loop power control

� In 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.

How to estimate the initial transmission power? Take the uplink as an example, firstly, UE will measure the path loss according to RSCP of PCPICH channel, then calculate the required uplink initial transmission power.



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That means, the uplink transmission power is calculated according to the downlink path loss, but in the 2.1 GHz band there is 90MHZ frequency interval between uplink frequencies and downlink frequencies, the fading between the uplink and downlink is un-correlated, so the calculated transmission power of open loop power control is not absolutely accurate.

Open Loop Power Control of PRACH

Figure 2.- Power Control for PRACH.

The random access procedure of PRACH is shown in above figure: UE transmits a preamble using the selected uplink access slot, signature, and preamble transmission power. After that, UTRAN will response AI if the preamble is received. Then the UE will transmit the message part if the AI is received. But, if UE does not

receive the AI from UTRAN in τp-p period, a next preamble will be transmitted. The

process won’t stop until the AI received by UE or the maximum preamble retransmission number or the maximum transmission power is reached.

� The 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

� Parameters explanation

� The values of PCPICH DL TX power、UL interference and Constant

Value are given in system information.

AICH accessslots RX at UE

PRACH accessslots TX at UE

One access slot

ττττ p-a

ττττp-mττττp-p

Pre-amble

Pre-amble

Message part

Acq.Ind.AICH access

slots RX at UE

PRACH accessslots TX at UE

One access slot

ττττ p-a

ττττp-mττττp-p

Pre-amble

Pre-amble

Message part

Acq.Ind.



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� 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, and then it will be reported to RNC.

� Constant Value is the threshold of preamble message. This value has to be analysed very carefully.

The initial value of PRACH power is set through outer loop power control. UE operation steps are as follows:

(1) Read IE “Primary CPICH DL TX power”, “UL interference” and “Constant value” from system information.

(2) Measure the value of CPICH_RSCP;

Figure 3.- Parameter definition for power control.

The power control of the Message part of PRACH has the following

characteristics: the values of βc and βd are set by the upper layer. The ratio between the control part and the data part is the same as for other uplink channel.

This parameter is the permitted maximum preamble repeat times of the UE

within a preamble ramp cycle

Preamble Retrans Max 4

This parameter is the ramp step of the preamble power when the UE has not

received the capture indication from NodeB

PRACH Power Ramp Step 3

This parameter is the correction constant used for the UE to estimate the initial

transmission power of PRACH according to the open loop power

Constant Value 2

The 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

Power Offset Pp-m 1

Parameter meaningParameterNO.

This parameter is the permitted maximum preamble repeat times of the UE

within a preamble ramp cycle

Preamble Retrans Max 4

This parameter is the ramp step of the preamble power when the UE has not

received the capture indication from NodeB

PRACH Power Ramp Step 3

This parameter is the correction constant used for the UE to estimate the initial

transmission power of PRACH according to the open loop power

Constant Value 2

The 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

Power Offset Pp-m 1

Parameter meaningParameterNO.

Power Ramp Step

Pp-m

10ms/20ms

Preable_Initial_power

Power Ramp Step

Pp-m

10ms/20ms

Preable_Initial_power



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� Different Constant Values for different stage of WCDMA network lifecycle. Take the beginning stage for example:

� Constant Value could 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 than 1dB.

Figure 4.- PRACH Application scenarios.

RRC Connection Request is transmitted on PRACH, so this is considered as an access procedure. Before RRC Connection Request transmission, UE will transmit PRACH preamble, and the first preamble power is calculated by open loop power control.



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Open loop power control of DPCCH

At the beginning of the dedicated channel setup, there is only DPCCH in the uplink dedicated channel but there is no DPDCH. DPCCH during this time is called UL DPCCH power control preamble. The specific length of a preamble is 0 to 7 frames. It is set on UE by the RRC protocol and the parameter name is “PC Preamble”. The initial transmission power of DPCCH is obtained through the open loop power control.

Open loop power control of DL DPCCH

� The DL DPCCH open loop power control can be calculated by the following formula:

P=（Ec/Io）Req-CPICH_Ec/Io+PCPICH

� Parameters explanation

� (Ec/Io)req is the required Ec/Io, which should satisfied UE can receive the message from the 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

Similar to UL, the (Ec/Io)Req value should be considered very carefully. Because there is not 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 ratio. With PO1, PO2 and PO3, initial transmission power for DPCCH can be calculated.

Figure 5. - DL DPCCH Application scenarios.



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According to the RRC connection establishment procedure, firstly, NodeB will set up the RL resource, and then Iub resource is established between NodeB and RNC. At last, DPCCH is transmitted with initial transmission power calculated by open loop power control.

Open loop power control of UL DPCCH

� The UL DPCCH open loop power control can be calculated by the following formula:

DPCCH_Initial_Power = DPCCH_Power_Offset - CPICH_RSCP

UE calculates the initial power of uplink DPCCH according to the received IE “DPCCH_Power_offset” and the measured value of CPICH_RSCP.

Parameters explanation:

DPCCH_Power_Offset: Uplink DPCCH power offset, which is configured by RNC and is delivered to UE in RRC Connection Setup.

DPCCH_Power_Offset = PCPICH DL TX Power+UL interference+ DPCCH_SIRtarget

CPICH_RSCP: Measured by UE

PCPICH DL TX power: PCPICH downlink transmission power

UL interference: NodeB uplink interference

DPCCH_SIRtarget: DPCCH demodulation threshold requirement



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Figure 6.- UL DPCCH Application scenarios.

In the RRC connection establishment procedure, when the UE have received RRC Connection Setup message, the UE will try to synchronize with the NodeB by transmitting uplink DPCCH with the initial transmission power calculated by open loop power control.

Closed loop power control

After DCH is setup, closed loop power control always take effects, which will control the transmission power dynamically.

The closed loop power includes the inner loop power control and the outer loop power control. And according to the transmission direction, closed loop power control is also divided into the uplink power control and the downlink power control. For uplink power control, the UE’s transmission power is controlled by the network, and for downlink, the NodeB’s transmission power is controlled by the UE.

� The characteristics of open loop power control

� The results from open loop power control are not accurate enough

� open loop power control can only decide the initial power

� The advantages of closed loop power control

� Guarantee the QoS

� Decrease the interference

� Increase the system capacity



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For WCDMA-FDD system, the uplink fading is not related to the downlink one because of the great frequency interval between them. Therefore, the path loss and interference estimated by downlink can not reflect the one in uplink completely.

The closed loop power control can solve this problem. Through closed loop power control, the transmission power can be controlled dynamically and quickly according to the feedback of the controller.

Figure 7.- Closed loop power control.

• Inner loop power control

The receivers calculate the SIR and compare it with SIRtarget.

If less than SIRtarget, the TPC is set as 1 to increase transmission power.

If greater than SIRtarget, the TPC is set as 0 to decrease transmission power.

TPC is delivered to the transmitter in DPCCH; the transmitter will adjust the power according to the value of received TPC.

The inner loop power control can be done 1500 times per second, then the SIR can be ensured to the level of target SIR.

• Outer loop power control

Through adjusting the SIR target value, BLER can be ensured.



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Uplink Inner-loop power control

For uplink inner loop power control, UE is the control object and NodeB is the controller.

The uplink inner loop power control adjusts the UE transmission power in order to maintain the received uplink signal-to-interference ratio (SIR) at a given SIR target, SIRtarget.

Figure 8.- Uplink inner loop power control.

The serving cells (cells in the active set) should estimate SIRmeas of the received uplink DPCH. The serving cells should then generate TPC commands and transmit the commands once per slot according to the following rule: if SIRmeas > SIRtar then the TPC command to transmit is "0", while if SIRmeas < SIRtar then the TPC command to transmit is "1".

Upon reception of one or more TPC commands in a slot, the UE shall derive a single TPC command, TPC_cmd, for each slot, combining multiple TPC commands if more than one is received in a slot. Two algorithms shall be supported by the UE for deriving a TPC_cmd, those are PCA1 and PCA2. Which of these two algorithms is used is determined by a UE-specific higher-layer parameter.

The step size DTPC is a layer 1 parameter which is derived from the UE-specific higher-layer parameter "TPC-StepSize" which is under the control of the UTRAN. If "TPC-StepSize" has the value "dB1", then the layer 1 parameter DTPC shall take the value 1 dB and if "TPC-StepSize" has the value "dB2", then DTPC shall take the value 2 dB. The parameter "TPC-StepSize" only applies to Algorithm 1. For Algorithm 2 DTPC shall always take the value 1 dB.

� NodeB compares the measured SIR to the preset target SIR

NodeB

UE

Transmit TPC

Inner-loop

set SIRtar

1500Hz1500Hz

Each UE has its own loop


NodeB

UE

Transmit TPC

Inner-loop

set SIRtar

1500Hz1500Hz



TPC Decision(0，，，，1)

TPC_CMD（（（（-1, 0, 1））））Adjust DPCCH Tx△△△△DPCCH=△△△△tpc××××TPC_cmd

PCA1

PCA2

Adjust DPDCH Tx

(ββββc,ββββd)

Compare SIRmeas with SIRtar

SIRmea>SIRtar→→→→TPC=0SIRmea<SIRtar→→→→ TPC=1



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After deriving of the combined TPC command TPC_cmd using one of the two supported algorithms, the UE shall adjust the transmit power of the uplink DPCCH with a step of DDPCCH (in dB) which is given by:

DDPCCH = DTPC * TPC_cmd

Uplink inner-loop PCA1 without soft handover

Figure 9.- Uplink inner loop power control without soft handover.

When a UE is not in soft handover, only one TPC command will be received in each slot. In this case, the value of TPC_cmd shall be derived as follows:

- If the received TPC command is equal to 0 then TPC_cmd for that slot is –1.

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

� UE gets one TPC in each time slot

� If TPC=0, TPC_cmd= -1

� If TPC=1, TPC_cmd= 1

This control is done in each time slot

Power control frequency is 1500HZ

0110110110 0110110110…… ……

…… ……TPC_CMD

TPC

-111-111-111-1 -111-111-111-1



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Uplink inner-loop PCA1 with soft handover

Figure 10.- Uplink inner loop power control with soft handover.

When a UE is in soft handover, multiple TPC commands may be received in each slot from different cells in the active set.

1. Combine the TPC commands from the same RLS.

In some cases, the UE has the knowledge that some of the transmitted TPC commands in a slot are the same. This is the case when the radio links are in the same radio link set. For these cases, the TPC commands from the same radio link set shall be combined into one TPC command, to be further combined with other TPC commands.

2. Combine the TPC commands from different RLSs.

First, the UE shall conduct a soft symbol decision Wi on each of the power control commands TPCi, where i = 1, 2, …, N, where N is greater than 1 and is the number of TPC commands from radio links of different radio link sets.

3. The UE derives a combined TPC command, TPC_cmd, as a function γ of all the N soft symbol decisions Wi:

TPC_cmd = γ (W1, W2, … WN), where TPC_cmd can take the values 1 or -1.

0110110110 0110110110…… ……

RLS1-TPC (W1)

…… ……RLS2-TPC (W2) 1010101101 1010101101

…… ……

…… ……TPC_CMD

1101100100 1101100100

0000100100 0000100100

Each time slot, combine TPC from different RLS，，，，then get W i

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3

RLS3-TPC (W3)

Get TPC_cmd based on

TPC_cmd = γγγγ (W1, W2, … WN)



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The function γ shall fulfil the following criteria:

If the N TPCi commands are random and uncorrelated, with equal probability of

being transmitted as "0" or "1", the probability that the output of γ is equal to 1 shall

be greater than or equal to 1/(2^N), and the probability that the output of γ is equal to

-1 shall be greater than or equal to 0.5. Further, the output of γ shall equal 1 if the

TPC commands from all the radio link sets are reliably “1”, and the output of γ shall equal –1 if a TPC command from any of the radio link sets is reliably “0”.

Uplink inner-loop PCA2 Without soft handover

Figure 11.- Uplink inner loop PCA2 without soft handover.

When a UE is not in soft handover, only one TPC command will be received in each slot. In this case, the UE shall process received TPC commands on a 5-slot cycle, where the sets of 5 slots shall be aligned to the frame boundaries and there shall be no overlap between each set of 5 slots.

The value of TPC_cmd shall be derived as follows:

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

For the fifth slot of a set, the UE uses hard decisions on each of the 5 received TPC commands as follows:

If all 5 hard decisions within a set are 1 then TPC_cmd = 1 in the 5th slot.

If all 5 hard decisions within a set are 0 then TPC_cmd = -1 in the 5th slot. Otherwise, TPC_cmd = 0 in the 5th slot.

110111111100000

TS14TS13TS12TS11TS10TS9TS8TS7TS6TS5TS4TS3TS2TS1TS0

110111111100000


10ms/frame

Group 2Group 1 Group 3

…… ……

-1000010000-10000 -1000010000-10000

TPC

TPC_CMD

Transmission power will be controlled in each 5 time slots

The frequency is 300HZ

…… ……



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Uplink inner-loop PCA2 With soft handover

Figure 12.- Uplink inner loop PCA2 with soft handover.

When a UE is in soft handover, multiple TPC commands may be received in each slot from different cells in the active set.

1. Combine the TPC commands from the same RLS.

In some cases, the UE has the knowledge that some of the transmitted TPC commands in a slot are the same. This is the case when the radio links are in the same radio link set. For these cases, the TPC commands from radio links of the same radio link set shall be combined into one TPC command.

2. Calculate the TPC_tempi of each RLS

The UE shall make a hard decision on the value of each TPCi, where i = 1, 2, …, N and N is the number of TPC commands from radio links of different radio link sets.

The UE shall follow this procedure for 5 consecutive slots, resulting in N hard decisions for each of the 5 slots.

The sets of 5 slots shall be aligned to the frame boundaries and there shall be no overlap between each set of 5 slots.

Combine TPC from same

RLS in each time slot

Calculate TPC_cmd

TPC_CMD=1

TPC_CMD=-1

Otherwise TPC_CMD=0

Calculate TPC_tempi for each RLS

�If 5 TPC are all 1, TPC_tempi=1

�If 5 TPC are all 0, TPC_tempi=-1

�Otherwise, TPC_tempi =0

5.0_1

1

>∑=

N

i

itempTPCN

5.0_1

1

−<∑=

N

i

itempTPC

N

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3

CELL1 CELL2

CELL4CELL3

RL11 RL12

RLS1

RLS2 RLS3



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The UE first determines one temporary TPC command, TPC_tempi, for each of the N sets of 5 TPC commands as follows:

- If all 5 hard decisions within a set are "1", TPC_tempi = 1.

- If all 5 hard decisions within a set are "0", TPC_tempi = -1.

- Otherwise, TPC_tempi = 0.

Calculate the TPC_CMD of each timeslot

The value of TPC_cmd is zero for the first 4 slots. After 5 slots have elapsed, the UE shall determine the value of TPC_cmd for the fifth slot in the following way:

A combined TPC command for the fifth slot, TPC_cmd, as a function γ of all the N temporary power control commands TPC_tempi:

TPC_cmd(5th slot) = γ (TPC_temp1, TPC_temp2, …, TPC_tempN), where

TPC_cmd(5th slot) can take the values 1, 0 or –1, and the definition of γ is shown in figure 13.

Figure 13.- Result of γ function for uplink inner loop PCA2 with soft handover.

Application scenarios:

When UE is moving with high speed (80Km/h), the fast inner loop power control can not catch up with the fast fading. In this situation fast power control PCA1 produces negative gain, so PCA2 is preferred.

RLS3

RLS2

RLS1 100100000000100

100110000011111

111111011111111


RLS3

RLS2

RLS1 100100000000100

100110000011111

111111011111111


…… ……

10ms/frame

Group 1 Group 2 Group 3

RLS3

RLS2

RLS1 00000-1000000000

00000-1000010000

100000000010000


RLS3

RLS2

RLS1 00000-1000000000

00000-1000010000

100000000010000


…… ……

TPC

TPC_tempi

00000-1000010000


00000-1000010000


…… ……

TPC_CMD

Power is controlled in each 5 time slots

The power control frequency is 300HZ



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� The control frequency

� TPC1, the power control frequency is 1500Hz

� TPC2, the power control frequency is 300Hz

Downlink inner loop power control

The downlink transmit power control procedure controls simultaneously the power of a DPCCH and its corresponding DPDCHs. The power control loop adjusts the power of the DPCCH and DPDCHs with the same amount, i.e. the relative power difference between the DPCCH and DPDCHs is not changed.

The relative transmit power offset between DPCCH fields and DPDCHs is determined by the network, The TFCI, TPC and pilot fields of the DPCCH are offset relative to the DPDCHs power by PO1, PO2 and PO3 dB respectively.

Downlink closed loop power control

Figure 14.- Downlink closed loop power control.

The same as uplink power control, the downlink power control includes inner loop power control and outer loop power control. Inner loop power control is between UE and NodeB, but outer loop power control is between L1 and L3 of UE.



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Downlink Inner loop power control

Figure 15.- Downlink inner loop power control.

Firstly, UE should estimate the downlink DPDCH/DPCCH power and the SIR, then UE can generate TPC by comparing the estimated SIR to target SIR:

If the estimated SIR is greater than the target SIR, TPC is 0 (decrease power)

If the estimated SIR is less than the target one, TPC is 1 (increase power)

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

How to generate TPC

� When UE is not in soft handover

� The TPC which is generated by UE is transmitted in TPC domain of UL channel

� When UE is in soft handover, two power control modes can be used, which is decided by DPC_mode:

� DPC_MODE＝0，UE will transmit TPC in every slot

� DPC_MODE＝1，UE will transmit the same TPC in every three time

slot



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� When the downlink channel is in out of synchronization, UE will transmit TPC 1 because UE can not measure the downlink SIR

The UE shall generate TPC commands to control the network transmit power and send them in the TPC field of the uplink DPCCH. The UE shall check the downlink power control mode (DPC_MODE) before generating the TPC command:

- If DPC_MODE = 0 : the UE sends a unique TPC command in each slot and the TPC command generated is transmitted in the first available TPC field in the uplink DPCCH;

- If DPC_MODE = 1 : the UE repeats the same TPC command over 3 slots and the new TPC command is transmitted such that there is a new command at the beginning of the frame.

The DPC_MODE parameter is a UE specific parameter controlled by the UTRAN.

How to adjust power

� Downlink power adjustment:

Where

P(k-1) is power of previous

PTPC(k) is the adjustment

Pbal(k) is correction value

� The transmission power can not higher than Maximum_DL_Power, and not less than Minimum_DL_Power neither.

Upon receiving the TPC commands UTRAN shall adjust its downlink DPCCH/DPDCH power accordingly.

For DPC_MODE = 0, UTRAN shall estimate the transmitted TPC command TPCest to be 0 or 1, and shall update the power every slot. If DPC_MODE = 1, UTRAN shall estimate the transmitted TPC command TPCest over three slots to be 0 or 1, and shall update the power every three slots.



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After estimating the k:th TPC command, UTRAN shall adjust the current downlink power P(k-1) [dB] to a new power P(k) [dB] according to the following formula:

P(k) = P(k - 1) + PTPC(k) + Pbal(k),

Where PTPC(k) is the k:th power adjustment due to the inner loop power control, and Pbal(k) [dB] is a correction according to the downlink power control procedure for balancing radio link powers towards a common reference power.

� PTPC(k)

� Without “Limited Power Raise Used”

Where

PTPC(k) is the adjustment value

TPCest(k) is uplink TPC value

△TPC is downlink power adjustment step(0.5, 1, 1.5 or 2dB)

If the value of Limited Power Raise Used parameter is 'Not used', then PTPC (k) is calculated according to the above formula. That means, the transmission power is changed only according to TPC. If the value of TPC is 1, increase the downlink transmission power, and if the value of TPC is 0, decrease the downlink transmission power, and the step size can be 0.5, 1, 1.5 or 2dB which is decided by the UTRAN.

� PTPC(k)

� With “Limited Power Raise Used”



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Where

PTPC(k) is the adjustment value

TPCest(k) is uplink TPC value

△TPC is downlink power adjustment step(0.5, 1, 1.5 or 2dB)

Power_Raise_Limit: the limited value for Power ramping in a timer

DL_power_averaging_window_size：timer for power ramping (TS)

If the value of Limited Power Raise Used parameter is 'used', the power increase can be controlled to a certain extent.

Where, the values of Power_Raise_Limit and L_power_averaging_window_size are set by RNC and sent to NodeB through NBAP protocol when the cell is set up. They are uniform in the whole cell. The value of is set through IE “FDD TPC DL Step Size”. Power_Raise_Limit is the upper limit of power increase within the specified time. DL_power_averaging_window_size specifies the number of timeslots during this time.

Figure 16.- Power offsets for DPDCH and DPCCH.

Timeslot structure of Downlink DPCH:

-PO1 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.

-PO3 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.



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Downlink Power Balance

� Downlink power balance process

� SRNC can monitor every single NodeB’s transmission. If SRNC found the power offset in soft handover is excessive, it will initiate the DPB process

� The initiation and stop of DPB

� The power offset of two RLs is greater than the DPB initial threshold, the DPB process is initiated

� The power offset of two RLs is less than the DPB stop threshold, the DPB process is stopped

Figure 17.- Downlink power balance.

Downlink power balance (DPB) is mainly to resist the power offset between different downlink radio links caused by TPC bit errors during soft handover, and the power offset will be more serious when the fast power control is used in downlink. When downlink power balance is enabled, SRNC can request all NodeBs in the active set to transmit the same power or to keep a certain deviation between them, so as to ensure the power balance between the downlink radio links in the active set.



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Outer loop power control

Outer loop power control happens between NodeB and RNC for uplink, and between L1and L3 in UE for downlink. The function is to guarantee QoS by adjusting the SIRtar which is guaranteed by inner loop power control.

� The character of outer loop power control

� The QoS which NAS provides to CN is BLER, not SIR

� 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 SIR

� Therefore, the outer loop power control can adjust the SIR to get a stable BLER in the changeable radio environment

The purpose of inner loop power control of the WCDMA system is to maintain a certain SIR of transmission signal power when the signals reach the receiving end. However, in different multi-path environments, even if the mean SIR is kept above a certain threshold, it is likely that the communication quality requirement (BER or FER or BLER) is not satisfied. So a kind of outer loop power control mechanism is required to adjust the threshold of inner loop power control dynamically in order to meet the communication quality requirements.

Uplink outer loop power control

Figure 18.- Uplink outer loop power control.



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For uplink, the RNC will estimate Bit Error Rate (BER) or Block Error Rate (BLER), and adjust the SIRtar in inner loop power control to accomplish the goal of power control. Since this kind of power control is accomplished through upper layer, it is called outer loop power control. When the measured BLER becomes bad, the RNC will increase the SIRtar to improve the quality of received signals; on the other hand, if the measured BLER is too good, the RNC will decrease the SIRtar.

Downlink outer loop power control

Figure 19.- Downlink outer loop power control.

For downlink, the upper layer of UE will estimate BER or BLER, and adjust the SIRtar in inner loop power control to accomplish the goal of power control. When the measured BLER becomes bad, the upper layer of UE will increase the SIRtar to improve the quality of received signals; on the other hand, if the measured BLER is too good, the upper layer of UE will decrease the SIRtar.



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SIR target adjustment step

Where

SirAdjustStep: Outer loop power control adjustment step

SirAdjustFactor: Coefficient for outer loop power control

BLERest: Estimated BLER

BLERtar: Target BLER

In an SIR adjustment conversation, the adjustment amplitude should not be too great. The increased amplitude should be smaller than or equal to the maximum stepup (MaxSirStepUp) and the decreased amplitude should be smaller than or equal to maximum stepdown (MaxSirStepDown). In connection admission, the maximum and minimum SIRtar will be given, and the actual SIRtar should be between the maximum and minimum value.

� Uplink outer loop power control command transmit to NodeB through DCH-FP of Iub interface

When the actual SIR is higher than the SIRtar without convergence, do not further decrease the SIRtar; when the actual SIR is lower than the SIR value without convergence, do not further increase the SIRtar.



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017 WCDMA Power Control

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