08-WCDMA RNO Power Control_20051214

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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 control

Transcript of 08-WCDMA RNO Power Control_20051214

WCDMA*
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 .
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The Relationship between Transmitted Power and Received Power after Power Control Methods Introduced
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200
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600
800
-20
-15
-10
-5
0
5
10
15
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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
*
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
"X" – can be applied, "–" – not applied
Physical channel
No power control process, power is specified by upper layers.
DPDCH
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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
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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
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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 access
p-a = 7680 chips
AICH_Transmission_Timing 1
p-a = 12800 chips
AICH_Transmission_Timing
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.
PCPICH DL TX POWERSIB5UL interference SIB7Constant ValueSIB5
PRACHmessageβcβdPRACH
NO.
Parameter
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
21 p-p  p-p,min 2 p-p,minSFNRACH
p-pp-p,min
p-a = 7680 chips
AICH_Transmission_Timing1
p-a = 12800 chips
AICH_Transmission_Timing
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.
Constant Value
UE

Application scenarios
Open loop power
control of PRACH
5. Downlink Synchronisation
NBAP
NBAP
RRC
RRC
Start RX
RRC
RRC
6. Uplink Synchronisation
DCH - FP
DCH - FP
DCH - FP
Open loop power control of DL DPCCH
The DL DPCCH open loop power control can be calculated by the
following formula:
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
“” RLTPCDPCCH
CPICH_EcNo=CPICH_Power-PL-interference…… ;X_EcNo=X_Power-PL-interference……;DPCCH

(Eb/No)dl=(W/R)×[(Ptx initial)/pathloss]/[(1-a)Ptx total/pathloss+i×Ior+PN]…1=======>Ptx initial=(Eb/No)dl×(R/W)×[(1-a)Ptx total +pathloss(i×Ior+PN)]…2 =======>Ptx initial=(Eb/No)dl×(R/W)×[(1-a)Ptx total +A]…(5)
(Ec/No)cpich=RSCP/RSSI=(CPICH-tx-power/pathloss)/[(Ptx total/pathloss)+i×IorPN]…(3) =======>Ptxtotal=
CPICH-tx-power/(Ec/No)cpich-A…(4)(A=pathloss×i×Ior+PN)
45Pinitial=(Eb/No) / (W/R)×[(CPICH_TX_Power) / (CPICH_Ec/No)-aPtxtotal],a; Pinitial=[(Eb/No) / (W/R)]×[(CPICH_TX_Power) / (CPICH_Ec/No)]
DPCCHRNC
P=Ec/IoReq-CPICH_Ec/Io+PCPICH
DPCCHdB
*
Application scenarios
Open loop power
control of DPCCH
5. Downlink Synchronisation
NBAP
NBAP
RRC
RRC
Start RX
RRC
RRC
6. Uplink Synchronisation
DCH - FP
DCH - FP
DCH - FP
Open loop power control of UL DPCCH
The UL DPCCH open loop power control can be calculated by the
following formula:
+ UL interference + DPCCH_SIRtarget
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
Application scenarios
Open loop power
control of DPCCH
5. Downlink Synchronisation
NBAP
NBAP
RRC
RRC
Start RX
RRC
RRC
6. Uplink Synchronisation
DCH - FP
DCH - FP
DCH - FP
*
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 needed
TPC: Transmitted power control. in each time slot
*
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 control
DPCHDPCCHDPCCHDPCCH
TPC10
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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
Inner-loop power control Algorithm
to the preset target signal-to-interference ratio (SIRtarget).
NodeB
UE
NodeBRNCSIRtarUEDPCCHpilotSIRestUMTSP129
Pilot
N
pilot
bits
TPC
N
TPC
bits
Data
N
data
bits
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
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 1the UL DPCCH and UL DPDCH transmission power should be increased tpc
If the TPC_cmd is -1the UL DPCCH and UL DPDCH transmission power should be decreased tpc
If the TPC_cmd is 0the UL DPCCH and UL DPDCH transmission power should be decreased tpc
UETPC_cmdP28RRC“Power Control Algorithm”
WCDMA RNOP15
UE only can receive one TPC in non-soft handover situation,
If TPC0TPC_cmd= -1
If TPC1TPC_cmd= 1
PCA1
“UETPC”RAKETPCTPC
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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
PCA1
If the TPC is 0, Wi=0
If the TPC is 1, Wi1
Assume UE has N RLSesN TPC can be obtained after
combination, W1W2…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:
PCA1
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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.
TPCUENodeBTPC_cmdUETPCUE
P11
R4
DPCCHTPCdummy"1"UEDPDCHDPCCHDPCCHdummydummyNDSdummyTPC"1"
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_tempii = 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
PCA2
PCA2
1TSNRLSTPC
5“1”TPC-tempi=1
5“0” TPC-tempi=-1
4TSTPC-tem
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 PCA2
UMTSP129
1.5k1dBDoppler55Hz30km/hRayleigh
3km/h1dBPCA25slot
*
*
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.
POpower offset,
UTRANTPCPK
Pk=Pk-1+Ptpc(k)+Pbal(k); Pk-1Ptpc(k)Pbal(k)
1058.unknown
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
UEUEUE↑UMTSP131
*
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 different state
NodeBTPCTPCNodeBTPC
*
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
*
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


NodeB
UE
Out loop
Set BLERtar
NodeB
*
Outter loop power control
……