08-wcdma rno power control_20051214
DESCRIPTION
Power control classification:Open loop Power controlClosed loop Power control is divided into two main parts:Inner power control UE-Node BOuter power control Node B-RNCUplink inner power controlDownlink inner-power controlUplink outer power controlDownlink outer power controlTRANSCRIPT
Huawei Confidential
WCDMA Power Control Principle
WCDMA Power Control Principle
23/4/18 2
Chapter 1 Power OverviewChapter 1 Power Overview
Chapter 2 Power Control AlgorithmChapter 2 Power Control Algorithm
23/4/18 3
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 transmit by minimum power and
the network capacity can get maximum.
• The purpose of inner loop power control (in the UL UE
to Node B) of the WCDMA system is to maintain a
certain signal-to-interference ratio (SIR target) 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 .
23/4/18 4
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)
Rel
ati
ve
po
wer
(d
B)
Channel
Transmitted power
Received power
23/4/18 5
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.
23/4/18 6
Power control classification
Power control classification :• Open loop Power control
• Closed loop Power control is divided into two main parts:
• Inner power control UE-Node B
• Outer power control Node B-RNC
– Uplink inner power control
– Downlink inner-power control
– Uplink outer power control
– Downlink outer power control
UE NodeB RNC
SIR Target
Bler/BerSIR
TPC Command
Outer Loop Power Control
Inner Loop Power Control
Open Loop Power Control
23/4/18 7
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 - - - X
SCCPCH - - - X
PRACH X - - -
AICH - - - X
PICH - - - X
23/4/18 8
Chapter 1 Power OverviewChapter 1 Power Overview
Chapter 2 Power Control AlgorithmChapter 2 Power Control Algorithm
23/4/18 9
1.Open loop power control1.Open loop power control
2.Inner-loop power control2.Inner-loop power control
3.Outer loop power control3.Outer loop power control
Chapter 2 Power Control AlgorithmChapter 2 Power Control Algorithm
23/4/18 10
Open Loop Power Control Overview
• Purpose the UE estimates the power loss of signals on the propagation
path by measuring the downlink channel signals (CPICH-Tx
power), 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.
23/4/18 11
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.
23/4/18 12
Open Loop Power Control of PRACH
The random access procedure of PRACH is shown in above
figure: UE transmit a preamble 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 τp-p period, a next
preamble will be transmitted. The process won’t stop until the AI
received by UE. Set as 8 times
AICH accessslots RX at UE
PRACH accessslots TX at UE
One access slot
p-a
p-mp-p
Pre-amble
Pre-amble
Message part
Acq.Ind.
23/4/18 13
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 power 、 UL 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.
23/4/18 14
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
Preamble_Initial_power
23/4/18 15
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.
23/4/18 16
Open loop power control of PRACH Open loop power control of PRACH
Application scenariosApplication scenarios1. CCCH : RRC Connection Request
Open loop power control of PRACH
5. Downlink Synchronisation
UE Node BServing RNS
Serving RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRC RRC
NBAP NBAP
3. Radio Link Setup Response
NBAP NBAP
2. Radio Link Setup Request
RRC RRC
7. CCCH : RRC Connection Set up
Start RX description
Start TX description
4. ALCAP Iub Data Transport Bearer Setup
RRC RRC
9. DCCH : RRC Connection Setup Complete
6. Uplink Synchronisation
NBAP NBAP
8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
23/4/18 17
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
• 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
23/4/18 18
Open loop power control of DL DPCCH Open loop power control of DL DPCCH
Application scenariosApplication scenarios
1. CCCH : RRC Connection Request
Open loop power control of DPCCH
5. Downlink Synchronisation
UE Node BServing RNS
Serving RNC
DCH - FP
Allocate RNTISelect L1 and L2 parameters
RRC RRC
NBAP NBAP
3. Radio Link Setup Response
NBAP NBAP
2. Radio Link Setup Request
RRC RRC
7. CCCH : RRC Connection Set up
Start RX description
Start TX description
4. ALCAP Iub Data Transport Bearer Setup
RRC RRC
9. DCCH : RRC Connection Setup Complete
6. Uplink Synchronisation
NBAP NBAP
8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
23/4/18 19
Open loop power control of UL DPCCH
• The UL DPCCH open loop power control can be
calculated by the
following formula:
DPCCH_Initial_power = PCPICH DL TX power - CPICH_RSCP
+ UL interference + DPCCH_SIRtarget
• 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_SIR target value should be considered very carefully.
It reflects the lowest requirement for decoding the DPCCH in a
certain multiple path environment
23/4/18 20
Open loop power control of UL DPCCH Open loop power control of UL DPCCH
Application scenariosApplication scenarios
1. CCCH : RRC Connection Request
Open loop power control of DPCCH
5. Downlink Synchronisation
UE Node BServing RNS
Serving RNC
DCH - FP
Allocate RNTISelect L1 and L2parameters
RRC RRC
NBAP NBAP
3. Radio Link Setup Response
NBAP NBAP
2. Radio Link Setup Request
RRC RRC
7. CCCH : RRC Connection Set up
Start RX description
Start TX description
4. ALCAP Iub Data Transport Bearer Setup
RRC RRC
9. DCCH : RRC Connection Setup Complete
6. Uplink Synchronisation
NBAP NBAP
8. Radio Link Restore Indication
DCH - FP
DCH - FP
DCH - FP
23/4/18 21
1.Open loop power control1.Open loop power control
2.Inner-loop power control2.Inner-loop power control
3.Outer loop power control3.Outer loop power control
Chapter 2 Power Control AlgorithmChapter 2 Power Control Algorithm
23/4/18 22
Close loop power control
• The deficiencies of open loop power control
the open loop power control can decided the initial power, but it’s 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 neededWhy the close loop power control is needed
23/4/18 23
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
• TPC is sent in each time slot that means the
frequency of TCP is 1500 repetition per second
15/10ms
The principle for Inner-loop power controlThe principle for Inner-loop power control
23/4/18 24
Inner-loop power control
• In 3GPP protocol, two algorithms are adopted in the
inner-loop
power control of uplink DPCCH
PCA1(Power Control Algorithm) , uplink power control step is
tpc=△ 1dB or 2dB
PCA2 , uplink power control step is tpc=△ 1dB
• The power control adjustment range in DPCCH is
△ DPCCH= tpc× TPC_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
IInner-loop power control Algorithmnner-loop power control Algorithm
23/4/18 25
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 1500Hz
Each UE has own loop Each UE has own loop
23/4/18 26
Uplink-inner loop power control
2
2
d
c
DPDCH/DPCCH structureDPDCH/DPCCH structure
The power ratio of DPCCH to DPDCH is
Pilot N pilot bits
TPC NTPC bits
DataNdata bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 10 bits
1 radio frame: T f = 10 ms
DPDCH
DPCCHFBI
N FBI bitsTFCI
N TFCI bits
Tslot = 2560 chips, N data = 10*2 k bits (k=0..6)
23/4/18 27
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.
TPCTPC
23/4/18 28
Uplink-inner loop power control
• UE can adjust the UL DPCCH transmission
power with △ tpc step
according to the received TPC_cmd
• The step △ tpc can be 1dB or 2dB, which is
decided by UTRAN
If the TPC_cmd is 1 , the UL DPCCH and UL
DPDCH transmission power should be increased
△ tpc
If the TPC_cmd is -1 , the UL DPCCH and UL
DPDCH transmission power should be decreased
△ tpc
If the TPC_cmd is 0 , the UL DPCCH and UL
DPDCH transmission power should be decreased
△ tpc
23/4/18 29
Uplink-inner loop power control
• UE only can receive one TPC in non-soft handover
situation,
If TPC = 0 , TPC_cmd= -1
If TPC = 1 , TPC_cmd= 1
PCA1PCA1
23/4/18 30
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
PCA1PCA1
23/4/18 31
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, Wi = 1
Assume UE has N RLSes , N TPC can be obtained after
combination, W1 、 W2…WN. The combination method for these
N TPCs from N RLSes can be described as following formula
TPC_cmd = γ (W1, W2, … WN)
• γ function should satisfied:
If one Wi is 0, TPC_cmd is -1
If all Wi are 1 , TPC_cmd is 1
PCA1PCA1
23/4/18 32
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
PCA2PCA2
23/4/18 33
Uplink-inner loop power control
• When UE is in soft handover, the TPC_cmd can be
achieved by the
following 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 above
mentioned 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_tempi ( i =
1,2......N )
• The first 4 time slots, all TPC_tempi = 0
• Take the average.
• 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
PCA2PCA2
23/4/18 34
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 preferred.
Comparison between PCA1 and PCA2Comparison between PCA1 and PCA2
23/4/18 35
Downlink Inner-loop power control
NodeB
Set SIRtar
Transmit TPC
Measure SIR and compare
Inner-loop
1500Hz
23/4/18 36
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 PO1 、 PO2 and PO3 are defined by RNC.
23/4/18 37
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
0.5 、 1 、 1.5 or 2dB
23/4/18 38
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_MODE = 0 , UE will transmit TPC in every slot
DPC_MODE = 1 , UE 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 different statePower control in different state
23/4/18 39
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 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
NodeB
NodeB
Initiate the DPB process
DPB process
23/4/18 40
1.Open loop power control1.Open loop power control
2.Inner-loop power control2.Inner-loop power control
3.Outer loop power control3.Outer loop power control
Chapter 2 Power Control AlgorithmChapter 2 Power Control Algorithm
23/4/18 41
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
23/4/18 42
Uplink outer loop power control
NodeB UE
Transmit TPC
Measure and compare SIR
Inner-loop
Set SIRtar
get the good quality service data get the good quality service data
Out loop
RNC
Measure received data and
compare BLER in the TrCH
Set BLERtar
10-100Hz
23/4/18 43
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
23/4/18 44
outer loop power control
SIR target SIR target adjustment step adjustment step
etBLERt
etBLERtBLERmeastepSIRAdjustSoefficientSIRAdjustcSIRtar
arg
arg**
23/4/18 45
Outter loop power control
Uplink outer loop power control command transmit to
NodeB through DCH-FP
Node B SRNC
……
OUTER LOOP PC
23/4/18 46
Thank You