LTE systems use the Orthogonal Frequency Division Multiple Access (OFDMA) technique on the downlink and the Single Carrier Frequency Division Multiple Access (SC-FDMA)
technique on the uplink. With these techniques, the subcarriers of UEs in a cell are
orthogonal. Power control compensates for path loss and shadow fading and counteracts interference between cells. In LTE systems, power control is performed on eNodeBs and UEs.
Ensure quality of service
Power control adjusts the transmit power to the optimal level to provide services of
a certain quality level that meets the requirement for the BLER. Reduce interference
Power control reduces interference in a cell, which mainly comes from neighboring
cells.
Lower power consumption
Uplink power control lowers the power consumption of UEs, and downlink power
control lowers the power consumption of eNodeBs. Expand coverage and capacity
Downlink power control allocates different power to different UEs to meet
requirements for coverage. In addition, downlink power control reduces the transmit power allocated to each UE to a minimum, so that the allocated power meets the requirement for the signal-to-interference-and-noise ratio (SINR). In this way, downlink power control expands system capacity.
Interference to neighboring cells mainly comes from UEs on cell edges. To reduce
Downlink power control is achieved through fixed power assignment or dynamic power control.
Fixed power assignment
Fixed power assignment is applicable to the cell-specific reference signal,
synchronization signal, PBCH, PCFICH, and the PDCCH and PDSCH that carry common information of the cell. Users configure fixed power based on channel quality. The configured power must meet the requirements for the downlink coverage of the cell.
Dynamic power control
Dynamic power control is applicable to the PHICH and the PDCCH and PDSCH that
carry dedicated information sent to UEs. Dynamic power control lowers
interference, expands cell capacity, and increases coverage while meeting users' QoS requirements. However, these channels can also support fix power assignment, and in fact, this is our recommendation because the AMC function can also meet the requirement of QoS
The cell-specific reference signal is transmitted in all downlink subframes. The signal serves as a basis for downlink channel estimation, which is used for data demodulation.
The power for the cell-specific reference signal is set through the ReferenceSignalPwr parameter, which indicates the Energy Per Resource Element (EPRE) of the cell-specific reference signal.
Related command: MOD PDSCHCFG LTE Power Control Feature
The synchronization signal is used for cell search and system synchronization. There are two types of synchronization signals, the Primary Synchronization Channel (P-SCH) and the Secondary Synchronization Channel (S-SCH).
The offset of the power for the P-SCH and S-SCH against the power for the cell-specific reference signal is set through the SchPwr parameter.
On the PBCH, broadcast messages are sent in each frame. The messages carry the basic system information of the cell, such as the cell bandwidth, antenna configuration, and frame number.
The offset of the power for the PBCH against the power for the cell-specific reference signal is set through the PbchPwr parameter.
The PCFICH carries the number of OFDM symbols used for PDCCH transmission in a subframe. The PCFICH is always mapped to the first OFDM symbol of each subframe. The power for the PCFICH is set through the PcfichPwr parameter, which indicates an
offset of the power for the PCFICH against the power for the cell-specific reference signal. LTE Power Control Feature
Related command: MOD CELLCHPWRCFG LTE Power Control Feature
Power control for the PHICH is set through the DlPcAlgoSwitch parameter
. When the switches PhichPcSwitch and PhichInnerLoopPcSwitch under the DlPcAlgoSwitch parameter are set to ON, the transmit power for the PHICH is
periodically adjusted to adapt to change in path loss and shadow shading according to the difference between the estimated SINRRSand SINRTarget.
When the switches PhichPcSwitch and PhichInnerLoopPcSwitch under the DlPcAlgoSwitch parameter are set to OFF, the power for PHICH is set through the PhichPcOff parameter, which indicates an offset of the power for the PHICH related to the RS power
When PDCCH carry the following dedicate info, power control should be performed to ensure the receive reliability
Uplink scheduling information (DCI format 0)
Downlink scheduling information (DCI format 1/1A/1B/2/2A) PUSCH/PUCCH TPC commands (DCI format 3/3A)
Power control for the PDCCH is set through the PdcchBndPcSw parameter
When the PdcchBndPcSw parameter is set to ON, the transmit power for the PDCCH is periodically adjusted according to the difference between the measured BLER and BLERTarget. If the measured BLER is greater than BLERTarget, transmit power is increased. Otherwise, transmit power is decreased.
When the PdcchBndPcSw parameter is set to OFF, the PDCCH uses fixed power
assignment. In this case, the offset of the power for the PDCCH against the power for the cell-specific reference signal is set through the PdcchPwrDedi parameter.
The presentation of PDCCH power
Regarding power control for the PDSCH, the OFDM symbols on one slot can be
classified into two types. Above table shows the OFDM symbol indexes within a slot where the ratio of the EPRE to the EPRE of RS is denoted by ρAor ρB. Power control for the PDSCH determines the EPREs of different OFDM symbols using ρA
and ρB. ρAdetermines the power offset against the power for the RS when there is no reference signal on the PDSCH, and ρBdetermines the power offset against the power for the cell-specific reference signal when there is a reference signal on the PDSCH.
The transmit power for the two types of OFDM symbols used on the PDSCH is defined by PPDSCH_Aand PPDSCH_B. The calculation formulas are as follows:
PPDSCH_A= ρA+ ReferenceSignalPwr PPDSCH_B= ρB+ ReferenceSignalPwr
ρA = PA. PAis sent to the UE through RRC signaling for PDSCH demodulation.
ρBis determined by the power factor ratio ρB/ρAof the EPRE on the PDSCH. Above
table lists the values of the cell-specific ratio ρB/ρAfor different PBvalues and quantities of antenna ports. PBcorresponds to the ρB/ρAon the PDSCH. PBis set through the command MOD PDCHCFG
In fact, Power control for the PDSCH is performed to determine PA for each UE. LTE Power Control Feature
Pb ρB/ρA
1 ANT port 2 or 4 ANT ports
0 1 5/4
1 4/5 1
2 3/5 3/4
Power control mechanism for the PDSCH is related with the following 2 switchs DlIcicAlgoSwitch: switch for the downlink inter-cell interference coordination (ICIC). DlPcAlgoSwitch: switch for the PDSCH power control
If :
DLIcicAlgoSwith is on, then the PDSCH power control is disabled, and PDSCH
power is setting by the follow command
DLIcicAlgoSwith is off, and PdschPcSwitch is on, system perform power control DLIcicAlgoSwith is Off, and PdschPcSwitch is off, PDSCH power is setting by the
follow command LTE Power Control Feature
The power for the PDSCH is determined and dynamically adjusted based on PA when the PdschPaAdjSwitch parameter is set to ON. PPDSCH_Aand PPDSCH_B, the initial transmit power for the PDSCH, are calculated as follows:
The eNodeB receive the CQI report to estimate the SINRRSof the cell-specific
reference signal. If no CQI is reported, the default SINRRS_Initialvalue of the system is used.
The transmission block (TB) size of the UE is estimated based on the QoS
information related to the UE, including the Guaranteed Bit Rate (GBR) and Aggregate Maximum Bit Rate (AMBR).
Under the precondition that the service requirements of the UE are met and a
balance is achieved between the power usage efficiency and RB usage efficiency in the system, the initial CQITargetis calculated based on the estimated SINRRSand the TB size.
The initial power offset for the PDSCH, namely, PO_PDSCH, is calculated based on the
estimated SINRRSand CQITarget. LTE Power Control Feature
The power control interacts with the other RRM algorithm
The downlink CQI adjustment algorithm adjusts the CQI reported by the UE,
thereby adjusting the selected MCS and ensuring that the IBLER of the PDSCH converges to IBLERTarget. In addition, the downlink CQI adjustment algorithm provides the adjusted CQI for the downlink power control algorithm to adjust the transmit power for the PDSCH.
The downlink ICIC algorithm informs the downlink power control algorithm of the
user type, which can be either CCU or CEU. The power control algorithm calculates the PAbased on the user type.
The downlink scheduling algorithm informs the downlink power control algorithm
of the PDCCH DCI. The power control algorithm performs power control based on the DCI format.
Description of each parameters:
PCMAX: The maximum transmit power of UE, 23dBm is the default value that
designed in specification
Po_pre: The target power expected by the eNodeB when the requirements for the
preamble detection performance are met and the PRACH preamble format is 0. The initial value of is set through the PreambInitRcvTargetPwr parameter.
PL: The downlink path loss estimated by the UE. This value is obtained based on
the Reference Signal Received Power (RSRP) measurement value and the transmit power for the cell-specific reference signal. The Alpha filtering factor for filtering the RSRP measurement values is set through the FilterRsrp parameter.
: The offset of the power for the current preamble format against
preamble format 0.
Npre: Number of times that the preamble of the UE is sent before the random access
procedure is successfully completed.
: The ramping step in power ramping of the preamble. This value is set
through the PwrRampingStep parameter. LTE Power Control Feature
preamble
Description of each parameters
i: The subframe number
PCMAX: The maximum transmit power of UE, 23dBm is the default value that
designed in specification
: The PUSCH transmission bandwidth(RB number) for the this subframe : The receive power expected by the eNodeB. It is determined by the
eNodeB and reflects the receive power expected by the eNodeB when the requirements for the PUSCH demodulation performance are met. The calculation formula is as follows:
: is the transmit power for the PUSCH expected by the eNodeB
when the correct PUSCH demodulation is ensured. It is set through the P0NominalPUSCH parameter.
: is the offset of the power for the UE against . This value reflects the
impact of the UE level, service type, and channel quality on the transmit power for the PUSCH.
: is the path loss compensation factor. It is set through the Alpha parameter. LTE Power Control Feature
)
(i
M
PUSCH PUSCH o P_ PUSCH UE o PUSCH NOMINAL o PUSCH oP
P
P
_
_ _
_ _ PUSCH NOMINAL o P_ _ PUSCH UE o P _ _ :is the offset of the power for the current MCS format against the reference
MCS format. If the DeltaMcsEnabled parameter is set to 0, ΔTF(i) is 0. Otherwise, the impact of ΔTF(i) is considered.
: is the adjustment of the PUSCH transmit power of the UE. This value is
obtained based on the TPC information on the PDCCH. LTE Power Control Feature
)
(i
TF
) (i f When the switch InnerLoopPuschSwitch under the UlPcAlgoSwitch parameter is set to ON, the transmit power for the PUSCH is periodically adjusted to adapt to change in the
channel environment based on the difference between the measured SINR and SINRTarget. If the measured SINR is greater than SINRTarget, the eNodeB sends a TPC command, ordering a decrease in the transmit power. If the measured SINR is smaller than SINRTarget, the
eNodeB sends a TPC command, ordering an increase in the transmit power. LTE Power Control Feature
When the switch PhSinrTarUpdateSwitch under the UlPcAlgoSwitch parameter is set to ON, SINRTargetis periodically adjusted according to the power headroom (PH) information of the current UE, and the number of RBs scheduled for the current UE.
When the switch OiSinrTarUpdateSwitch under the UlPcAlgoSwitch parameter is set to ON, SINRTarget is periodically adjusted according to the OI information of the neighboring cell and the number of RBs scheduled for the current UE. The adjustment adapts to change in the channel environment and the interference to neighboring cell.
SINR adjustment is related with many factors, such as power headroom, RB number and system load. Suppose the UL link is getting worse and worse, the following mechanism can be used to maintain the BLER with prior
Perform inner loop power control to increase UE power
When the UE power reach the maximum value, the scheduling mechanism perform
the RB decreasing to reduce data rate, but SINR is still maintained.
When the RB number gets the minimum, namely only 1 RB, then eNodeB reduce
the SINR target to maintain the BLER. LTE Power Control Feature
Description of each parameters
: is the receive power expected by the eNodeB. It s determined by the
eNodeB and is the receive power expected by the eNodeB when the requirements for the PUCCH demodulation performance are met. The calculation formula is as follows:
: is determined by the PUCCH format. nCQIis the number of
information bits of the CQI, and it reflects the impact of the number of CQI bits of the PUCCH on the power. nHARQis the number of information bits of HARQ, and it reflects the impact of the number of HARQ signaling bits of the PUCCH on the power. It is defined in protocol.
: reflects the transmission format of the PUCCH on the transmit
power. It is set through the DeltaFPUCCHFormat1, DeltaFPUCCHFormat1b, DeltaFPUCCHFormat2, DeltaFPUCCHFormat2a, and DeltaFPUCCHFormat2b parameters.
: is the adjustment of the transmit power of the UE's PUCCH, and it is LTE Power Control Feature
PUCCH P0_ PUCCH UE o PUCCH NOMINAL o PUCCH o
P
P
P
_
_ _
_ _
n ,nHARQ
h CQI ) ( _PUCCH F F ) (i g PDCCH power control configuration use the same command as PDSCH configuration. LTE Power Control Feature
Parameters Description
: is the transmission bandwidth of the SRS
: is the offset of the SRS power against the PUSCH power. This value is
set through the PsrsOffsetDeltaMcsDisable or PSrsOffsetDeltaMcsEnable parameters based on different DeltaMcsEnabled values.
LTE Power Control Feature
SRS
M
OFFSET SRS
The uplink power control algorithm informs the uplink scheduling algorithm of the current UE's power headroom. The uplink scheduling algorithm determines the UE's MCS and number of RBs based on the UE's power headroom. System throughput is maximized while meeting the user's QoS requirements. The uplink scheduling algorithm informs the uplink power control algorithm of the TB size and allocated RBs, so that the uplink power control algorithm can determine the UE's power.
The random access control algorithm informs the uplink power control algorithm of the number of times that a UE's preamble is sent. In this way, the transmit power during the random access process is determined.