Post on 02-Jun-2018
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Huawei Confidential. All Rights Reserved
WCDMA Power Control Principle
ISSUE 1.0
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Internal Use2
Chapter 1 Power Overview
Chapter 2 Power Control Algorithm
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Internal Use3
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 transmitby 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 .
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Internal Use4
The Relationship between Transmitted Power and
Received Power after Power Control Methods Introduced
0 200 400 600 800-20
-15
-10
-5
0
5
10
15
20
Time (ms)
Relativepower
(dB)
Channel
Transmitted power
Received power
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Internal Use5
Benefit from Power Control
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.
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Internal Use6
Power control classification
Power control classification
Open loop Power control
Closed loop Power control
Uplink inner power control
Downlink inner-power control
Uplink outer power control
Downlink outer power control
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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
powercontrol
Inner loop
powercontrol
Outer loop
powerControl
No power control process,
power is specified by upperlayers.
DPDCH
DPCCH
PCCPCH
SCCPCH
PRACH
AICH
PICH
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Chapter 1 Power Overview
Chapter 2 Power Control Algorithm
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1.Open loop power control
2.Inner-loop power control
3.Outer loop power control
Chapter 2 Power Control Algor ithm
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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 downlink channel signals, then calculate the transmission
power of the uplink channel
The open loop power control principle
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 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 Use12
Open Loop Power Control of PRACH
The random access procedure of PRACH is shown in above figure: UE transmit apreamble using the selected uplink access slot, signature, and preamble transmission
power. After that ,UTARN 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 p-p period, a next preamble will be transmitted. The process wont stop until
the AI received by UE.
AICH access
slots RX at UE
PRACH accessslots TX at UE
One access slot
p-a
p-mp-p
Pre-
amble
Pre-
ambleMessage part
Acq.Ind.
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Internal Use13
Open Loop Power Control of PRACH
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 powerUL interference and Constant
Value 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 Use14
Open loop power control of PRACH
NO. Parameter Parameter meaning
1 Power Offset Pp-m 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
2 Constant Value This parameter is the correction constant used for the UE to estimate the
initial transmission power of PRACH according to the open loop power
3 PRACH Power Ramp Step This parameter is the ramp step of the preamble power when the UE has not
received the capture indication from NodeB
4 Preamble Retrans Max This parameter is the permitted maximum preamble repeat times of the UE
within a preamble ramp cycle
Power Ramp Step
Pp-m
10ms/20ms
Preable_Initial_
power
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Internal Use15
Open loop power control of PRACH
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 1dB.
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Internal Use16
Open loop power control of PRACH
Appl ication scenar ios
1. CCCH: RRC Connection Request
Open loop powercontrol of PRACH
5. Downlink Synchronisation
UE Node BServing RNS
ServingRNC
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
NBAPNBAP8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
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Internal Use17
Open loop power control of DL DPCCH
The DL DPCCH open loop power control can be calculated by the
following formula:
P=Ec/IoReq-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
Comments
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
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Internal Use18
Open loop power control of DL DPCCH
Appl ication scenar ios
1. CCCH: RRC Connection Request
Open loop power
control of DPCCH5. Downlink Synchronisation
UE Node BServing RNS
ServingRNC
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
NBAPNBAP8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
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Internal Use19
Open loop power control of UL DPCCH
The UL DPCCH open loop power control can be calculated by the
following formula:DPCCH_Initial_powerPCPICH DL TX power-CPICH_RSCP
+UL interference+ DPCCH_SIRtarget
References explanation PCPICH DL TX power is the transmission power of CPICH
CPICH_RSCP can be measured by UE UL interference can be measured by NodeB
Comments The 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 Use20
Open loop power control of UL DPCCH
Appl ication scenar ios
1. CCCH: RRC Connection Request
Open loop power
control of DPCCH
5. Downlink Synchronisation
UE Node BServing RNS
ServingRNC
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
NBAPNBAP8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
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Internal Use21
1.Open loop power control
2.I nner-loop power control
3.Outer loop power control
Chapter 2 Power Control Algor ithm
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Internal Use22
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, anddecrease interference in system.
Maintains a higher quality of service
Why the close loop power control is needed
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Internal Use23
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 I nner-loop power control
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Internal Use24
Inner-loop power control
In 3GPP protocol, two algorithms are adopted in the inner-loop
power control of uplink DPCCH
PCA1uplink power control step istpc=1dB or 2dB
PCA2uplink power control step is tpc=1dB
The power control adjustment range in DPCCH is
DPCCH=tpcTPC_cmd
TPC_cmd is achieved by different algorithm
The power offset shows the difference of transmission power of UL
DPDCH 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
I nner-loop power control Algor ithm
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Internal Use25
Uplink-inner loop power control
NodeB compares the measured signal-to-interference ratio
to the preset target signal-to-interference ratio (SIRtarget).
NodeB
UETransmit TPC
Inner-loop
set SIRtar
1500Hz
Each UE has own loop
U li k i l t l
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Internal Use26
Uplink-inner loop power control
2
2
d
c
DPDCH/DPCCH structure
The power ratio of DPCCH to DPDCH is
Pilot
N pilot bits
TPC
NTPCbits
Data
Ndata bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot
= 2560 chips, 10 bits
1 radio frame: Tf
= 10 ms
DPDCH
DPCCHFBI
N
FBI
bitsTFCI
N
TFCI
bits
Tslot
= 2560 chips, Ndata
= 10*2 kbits (k=0..6)
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Internal Use27
Uplink-inner loop power control
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 is greater than SIR target, the TPC is 0 to
decrease the transmission power
If SIR estimation is less than SIR target, the TPC is 1 to
increase the transmission power
Soft handover
In one time slot, UE received several TPC, then combine then.
Comments
in the last situation, the PCA decides how the TPC_cmd are combined.
The PCA has two methods. UTRAN decides which one is used.
TPC
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Internal Use28
Uplink-inner loop power control
UE can adjust the UL DPCCH transmission power with tpc 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 transmission
power should be decreasedtpc
If the TPC_cmd is 0the UL DPCCH and UL DPDCH transmission
power should be decreasedtpc
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Internal Use29
Uplink-inner loop power control
UE only can receive one TPC in non-soft handover situation,
If TPC0TPC_cmd= -1
If TPC1TPC_cmd= 1
PCA1
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Internal Use30
Uplink-inner loop power control
When UE is in soft handover
UE can receive 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
PCA1
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Internal Use31
Uplink-inner loop power control
Wi can be achieved by the following rules
If the TPC is 0, Wi=0
If the TPC is 1, Wi1
Assume UE has N RLSesN TPC can be obtained after
combination, W1W2WN. 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 is 0, TPC_cmd is -1
If all Wi are 1TPC_cmd is 1
PCA1
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Internal Use32
Uplink-inner loop power control
If UE is not in soft handover
Only 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 with 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 the TPC are 0, the TPC_cmd is -1 and the transmission will decrease 1dB;
If all the TPC are 1, the TPC_cmd is 1 and the transmission will increase 1dB;
Otherwise, TPC_cmd=0.
TPC RX
TPC_cmd
0000 0 0000 -1
1111 1 0000 1
else 0000 0
PCA2
U li k i l l
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Internal Use33
Uplink-inner loop power control
When UE is in soft handover, the TPC_cmd can be achieved by thefollowing two steps
First, combine the TPC from a same RLS
N TPCi (i = 1,2......N) can be achieved from N RLSes in each time slot
The N TPC_cmds from different RLS can be achieved by the abovementioned rules. So the first 4 time slot, the TPC_cmd is 0. And the
each final TPC_cmd is decided in the 5th time slot
Assume the each final TPC_cmd from N RLS are TPC_tempii = 1,2......N
The first 4 time slots, all TPC_tempi = 0
the TPC_cmd in fifth time slot can get by the following ruls
Mathematic average for N TPC_temps. If it is greater than 0.5,
TPC_cmd=1. If it is less than -0.5, TPC_cmd=-1, otherwise TPC_cmd=0
PCA2
U li k i l t l
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Internal Use34
Uplink-inner loop power control
The control frequency
TPC1, the power control frequency is 1500Hz
TPC2, the power control frequency is 300Hz
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, which produce
negative gain. In this situation, PCA2 is prefered.
Compari son between PCA1 and PCA2
D li k I l t l
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Internal Use35
Downlink Inner-loop power control
NodeB
Set SIRtar
Transmit TPC
Measure SIR and compare
Inner-loop
1500Hz
D li k i l t l
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Internal Use36
Downlink inner-loop power control
The inner-loop power control of downlink DPCCH include two typies: one is the
inner-loop power control in compressed mode, the other is the inner-loop power
control in non-compressed mode.
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 PO1PO2 and PO3 are defined by RNC.
D li k i l t l
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Internal Use37
Downlink inner-loop power control
Firstly, UE should estimate the downlink DPDCH/DPCCH power and the
current SIR
Then, UE can generate TPC by comparing the estimated SIR to target SIR
If the estimated SIR is greater than the target one, TPC is 0 (decrease power)
If the estimated SIR is less than the target one, TPC is 1 (increase power)
The step of DL inner-loop power control could be 0.511.5 or 2dB
D li k i l t l
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Internal Use38
Downlink inner-loop power control
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_MODE0UE will transmit TPC in every slot
DPC_MODE1UE will transmit the same TPC in every three time slot
When the downlink channel is in out of synchronization, UE will transmit
TPC 1 because UE can not measure the downlink SIR
As for responding to the receiving 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.
Power control in di ff erent state
Do nlink Po er Balance
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Internal Use39
Downlink Power Balance
Downlink power balance process
SRNC can monitor every single NodeBs
transmission. If SRNC found the power
offset in soft handover is too much, it will
command the DPB process
The initiation and stop of DPB
The power offset of two RL is greater
than the DPB initial threshold, the DPB
process is initiated
The power offset of two RL is less than
the DPB stop threshold, the DPB process
is stopped
NodeBNodeB
Initiate the DPB
process
DPB process
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Internal Use40
1.Open loop power control
2.Inner-loop power control
3.Outer loop power control
Chapter 2 Power Control Algor ithm
Outer loop power control
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Internal Use41
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
Uplink outer loop power control
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Internal Use42
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
compare BLER inthe TrCH
Set BLERtar
10-100Hz
Downlink outer loop power control
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Internal Use43
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
outer loop power control
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Internal Use44
outer loop power control
SIR target adjustment step
etBLERt
etBLERtBLERmeastepSIRAdjustSoefficientSIRAdjustcSIRtar
arg
arg**
Outer loop power control
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Internal Use45
Outer loop power control
Uplink outer loop power control command transmit to NodeB through DCH-FP
Node B SRNC
OUTER LOOP PC
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