Post on 07-Apr-2018
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Power Control WCDMA
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Power control methods adopted for various physical channels
Power control methods adopted for various physical channels "X" can be applied, "" not applied
Physical
channel
Open loop
power
control
Inner loop
power
control
Outer loop
power
Control
No power control process,
power is specified by upper
layers.
DPDCH X X DPCCH X X X PCCPCH XSCCPCH XPRACH X AICH XPICH X
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Power Control Classification
UE NodeB RNC
SIR Target
Bler/BerSIR
TPC Command
Outer Loop Power Control
Inner Loop Power Control
Open Loop Power Control
Open Loop Power ControlOpen loop power control is used to determine UEs initial uplink transmit power in PRACH and
NodeBs initial downlink transmit power in DPDCH. It is used to set initial power reference values for
power control.
Outer Loop power controlOuter loop power control is used to maintain the quality of communication at the level of bearer servicequality requirement, while using as low power as possible.
Inner loop power control (also called fast closed loop power control)
Inner loop power control is used toadjustUEs uplink / NodeBs downlink Dpch Power every one slotin accordance with TPC commands. Inner loop power control frequency is 1500Hz.
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Chapter 2 Power Control Algorithm
2.1 Open loop power control
2.2 Inner-loop power control
2.3 Outer loop power control
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Open Loop Power Control Overview
Purpose the UE estimates the power loss of signals on the
propagation path by measuring the downlinkchannel 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.
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Open Loop Power Control Overview
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 moreserious than that caused by propagation loss. Therefore,open loop power control is applied only at the beginningof connection setup, generally in setting the initial powervalue.
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Open loop power control of PRACH
Application scenarios
1. CCCH: RRC Connection Request
Open loop powercontrol of PRACH
5. Downlink Synchronisation
UENode B
Serving RNS
Serving
RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRCRRC
NBAPNBAP
3. Radio Link Setup Response
NBAPNBAP
2. Radio Link Setup Request
RRCRRC7. CCCH: RRC Connection Set up
Start RXdescription
Start TXdescription
4. ALCAP Iub Data Transport Bearer Setup
RRCRRC9. DCCH: RRC Connection Setup Complete
6. Uplink Synchronisation
NBAPNBAP
8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
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Open loop power control of DL DPCCH
Application scenarios
1. CCCH: RRC Connection Request
Open loop power
control of DPCCH5. Downlink Synchronisation
UENode B
Serving RNS
Serving
RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRCRRC
NBAPNBAP
3. Radio Link Setup Response
NBAPNBAP
2. Radio Link Setup Request
RRCRRC7. CCCH: RRC Connection Set up
Start RXdescription
Start TXdescription
4. ALCAP Iub Data Transport Bearer Setup
RRCRRC9. DCCH: RRC Connection Setup Complete
6. Uplink Synchronisation
NBAPNBAP
8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
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Open loop power control of UL DPCCH
Application scenarios
1. CCCH: RRC Connection Request
Open loop power
control of DPCCH
5. Downlink Synchronisation
UE Node B
Serving RNS
Serving
RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRCRRC
NBAPNBAP
3. Radio Link Setup Response
NBAPNBAP
2. Radio Link Setup Request
RRCRRC7. CCCH: RRC Connection Set up
Start RXdescription
Start TXdescription
4. ALCAP Iub Data Transport Bearer Setup
RRCRRC9. DCCH: RRC Connection Setup Complete
6. Uplink Synchronisation
NBAPNBAP
8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
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Chapter 2 Power Control Algorithm
2.1 Open loop power control
2.2 Inner-loop power control
2.3 Outer loop power control
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Close loop power control
The deficiencies of open loop power control
the open loop power control can decided the initial power, but its still
inaccurate
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 control
Can convergence the transmission power of uplink and downlink very fast, and
decrease interference in system.
Maintains a higher quality of service
Why the close loop power control is needed
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Inner-loop power control
The receivers calculate the SIR by estimating the power strengthen
and the current interference. Then, compare this one to SIRtarget,
If less than SIRtarget, the TPC is 1 to tell receivers increase
transmission power
If greater than SIRtarget, the TPC is 0 to tell receivers decrease
transmission power
The receiver which get the TPC will adjust the transmission power
by algorithms. The inner loop power control can convergence the
estimated SIR to SIR target
The principle for Inner-loop power control
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Uplink-inner loop power control
NodeB compares the measured signal-to-interference ratioto the preset target signal-to-interference ratio (SIRtarget).
NodeB
UETransmit TPC
Inner-loop
set SIRtar
1500Hz
Each UE has own loop
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Uplink-inner loop power control
UE can adjust the UL DPCCH
transmission power withtpc step
according to the received TPC_cmd
The steptpc can be 1dB or 2dB,
which is decided by UTRAN If the TPC_cmd is 1the UL DPCCH and UL DPDCH transmission
power should be increasedtpc
If the TPC_cmd is -1the UL DPCCH and UL DPDCH transmissionpower should be decreasedtpc
If the TPC_cmd is 0the UL DPCCH and UL DPDCH transmission
power should be decreasedtpc
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Uplink-inner loop power control
NodeB compares the measured signal-to-interference ratioto the preset target signal-to-interference ratio (SIRtarget).
NodeB
UETransmit TPC
Inner-loop
set SIRtar
1500Hz
Each UE has own loop
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Chapter 2 Power Control Algorithm
2.1 Open loop power control
2.2 Inner-loop power control
2.3 Outer loop power control
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Outer-loop power control
The limitation of inner loop power control
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.
The character of outer-loop power control
The Qos which NAS provide to CN is BLER, not SIR
The relationship between inner-loop power control and outer-loop power control
SIR target should be satisfied with the requirement of decoding correctly. But
different multiple path radio environment request different SIR
Therefore, the outer-loop power control can adjust the SIR to get a stable BLER in
the changeable radio environment
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Uplink outer loop power control
NodeB UE
Transmit TPC
Measure and compare SIR
Inner-loop
Set SIRtar
get the good quality
service data
Out loop
RNC
Measure receiveddata and compareBLER in the TrCH
Set BLERtar
10-100Hz
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NodeB
set SIRtar
Transmit TPC
Measure and compare SIR
Measure and compare BLER
Outer loop
Inner loop L1
L3
10-100Hz1500Hz
Downlink outer loop power control
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UMTS Power Control
Open loop power control is the ability of the UE transmitter to sets its output power to a specific value. It is used for settinginitial uplink and downlink transmission powers when a UE is accessing the network. The open loop power control tolerance is 9 dB (normal conditions) or 12 dB (extreme conditions)
Inner loop power control (also called fast closed loop power control) in the uplink is the ability of the UE transmitter to adjust its
output power in accordance with one or more Transmit Power Control (TPC) commands received in the downlink, in order to keepthe received uplink Signal-to-Interference Ratio (SIR) at a given SIR target. The UE transmitter is capable of changing the outputpower with a step size of 1, 2 and 3 dB, in the slot immediately after the TPC_cmd can be derived. Inner loop power controlfrequency is 1500Hz.
The serving cells estimate SIR of the received uplink DPCH, generate TPC commands (TPC_cmd) and transmit the commands onceper slot according to the following rule: if SIRest > SIRtarget then the TPC command to transmit is "0", while if SIRest < SIRtarget thenthe TPC command to transmit is "1". Upon reception of one or more TPC commands in a slot, the UE derives a single TPCcommand for each slot, combining multiple TPC commands if more than one is received in a slot. Two algorithms are supportedby the UE for deriving a TPC_cmd. Which of these two algorithms is used, is determined by a UE-specific higher-layer parameter,"PowerControlAlgorithm".
Algorithm 1:The power control step is the change in the UE transmitter output power in response to a single TPC command
Algorithm 2:If all five estimated TPC command are "down" the transmit power is reduced by 1 dBIf all five estimated TPC command are "up" the transmit power is increased by 1 dBOtherwise the transmit power is not changed
The transmit power of the downlink channels is determined by the network. The power control step size can take four values: 0.5,1, 1.5 or 2 dB. It is mandatory for UTRAN to support step size of 1 dB, while support of other step sizes is optional. The UE
generates TPC commands to control the network transmit power and send them in the TPC field of the uplink DPCCH. Uponreceiving the TPC commands UTRAN adjusts its downlink DPCCH/DPDCH power accordingly.
Outer loop power control is used to maintain the quality of communication at the level of bearer service quality requirement,while using as low power as possible. The uplink outer loop power control is responsible for setting a target SIR in the Node B foreach individual uplink inner loop power control. This target SIR is updated for each UE according to the estimated uplink quality(BLock Error Ration, Bit Error Ratio) for each Radio Resource Control connection. The downlink outer loop power control is theability of the UE receiverto converge to required link quality (BLER) set by the network (RNC) in downlink.