OEO100030 LTE Power Control Feature ISSUE1.00

LTE Power Control Feature

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LTE Power Control Feature

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LTE Power Control Feature

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LTE Power Control Feature

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LTE Power Control Feature

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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.

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LTE Power Control Feature

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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.

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Reduce interference 

Power control reduces interference in a cell, which mainly comes from neighboring cells.

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Lower power consumption 

Uplink power control lowers the power consumption of UEs, and downlink power control lowers the power consumption of eNodeBs.

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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.

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Interference to neighboring cells mainly comes from UEs on cell edges. To reduce interference, uplink power control uses a technique known as Fractional Power Control (FPC) to lower the interference to neighboring cells, thereby increasing network capacity.

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LTE Power Control Feature

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LTE Power Control Feature

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LTE Power Control Feature

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Downlink power control is achieved through fixed power assignment or dynamic power control.

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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.

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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

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LTE Power Control Feature

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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.

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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.

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Related command: MOD PDSCHCFG

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LTE Power Control Feature

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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).

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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.

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LTE Power Control Feature

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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.

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The offset of the power for the PBCH against the power for the cell-specific reference signal is set through the PbchPwr parameter.

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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.

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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.

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LTE Power Control Feature

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Related command: MOD CELLCHPWRCFG

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LTE Power Control Feature

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Power control for the PHICH is set through the DlPcAlgoSwitch parameter

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. 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 SINRRS and SINRTarget.

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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

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LTE Power Control Feature

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When PDCCH carry the following dedicate info, power control should be performed to ensure the receive reliability 

Uplink scheduling information (DCI format 0)

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Downlink scheduling information (DCI format 1/1A/1B/2/2A)

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PUSCH/PUCCH TPC commands (DCI format 3/3A)

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Power control for the PDCCH is set through the PdcchBndPcSw parameter

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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.

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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.

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LTE Power Control Feature

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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 ρA or ρB.

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Power control for the PDSCH determines the EPREs of different OFDM symbols using ρA and ρB. ρA determines the power offset against the power for the RS when there is no reference signal on the PDSCH, and ρB determines the power offset against the power for the cell-specific reference signal when there is a reference signal on the PDSCH.

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The transmit power for the two types of OFDM symbols used on the PDSCH is defined by PPDSCH_A and PPDSCH_B. The calculation formulas are as follows: 

PPDSCH_A = ρA + ReferenceSignalPwr

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PPDSCH_B = ρB + ReferenceSignalPwr

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ρA = PA. PA is sent to the UE through RRC signaling for PDSCH demodulation.

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LTE Power Control Feature

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ρB is determined by the power factor ratio ρB/ρA of the EPRE on the PDSCH. Above table lists the values of the cell-specific ratio ρB/ρA for different PB values and quantities of antenna ports. PB corresponds to the ρB/ρA on the PDSCH. PB is set through the command MOD PDCHCFG Pb

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ρB /ρA 1 ANT port

2 or 4 ANT ports

0

1

5/4

1

4/5

1

2

3/5

3/4

3

2/5

1/2

In fact, Power control for the PDSCH is performed to determine PA for each UE.

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LTE Power Control Feature

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Power control mechanism for the PDSCH is related with the following 2 switchs DlIcicAlgoSwitch: switch for the downlink inter-cell interference coordination (ICIC).

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DlPcAlgoSwitch: switch for the PDSCH power control

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If : 

DLIcicAlgoSwith is on, then the PDSCH power control is disabled, and PDSCH power is setting by the follow command

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DLIcicAlgoSwith is off, and PdschPcSwitch is on, system perform power control

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DLIcicAlgoSwith is Off, and PdschPcSwitch is off, PDSCH power is setting by the follow command

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LTE Power Control Feature

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The power for the PDSCH is determined and dynamically adjusted based on PA when the PdschPaAdjSwitch parameter is set to ON. PPDSCH_A and PPDSCH_B, the initial transmit power for the PDSCH, are calculated as follows: 

The eNodeB receive the CQI report to estimate the SINRRS of the cell-specific reference signal. If no CQI is reported, the default SINRRS_Initial value of the system is used.

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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).

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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 CQITarget is calculated based on the estimated SINRRS and the TB size.

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The initial power offset for the PDSCH, namely, PO_PDSCH, is calculated based on the estimated SINRRS and CQITarget.

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The initial transmit power for the PDSCH, namely, PPDSCH_A and PPDSCH_B, is calculated based on PA.

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LTE Power Control Feature

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LTE Power Control Feature

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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.

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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 PA based on the user type.

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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.

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LTE Power Control Feature

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LTE Power Control Feature

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LTE Power Control Feature

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Description of each parameters: 

PCMAX : The maximum transmit power of UE, 23dBm is the default value that designed in specification

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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.

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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

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preamble format 0. 

Npreamble pre: 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

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through the PwrRampingStep parameter.

 step

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LTE Power Control Feature

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LTE Power Control Feature

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Description of each parameters  

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i: The subframe number PCMAX : The maximum transmit power of UE, 23dBm is the default value that designed in specification

M PUSCH (i) : The PUSCH transmission bandwidth(RB number) for the this subframe : The receive power expected by the eNodeB. It is determined by the Po _ PUSCHand reflects the receive power expected by the eNodeB when the eNodeB requirements for the PUSCH demodulation performance are met. The calculation formula is as follows:

Po _ PUSCH  Po _ NOMINAL _ PUSCH  Po _ UE _ PUSCH 

: is the transmit power for the PUSCH expected by the eNodeB

Po _ NOMINAL when the correct _ PUSCHPUSCH demodulation is ensured. It is set through the P0NominalPUSCH parameter. 

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: 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 Po _ UE _ PUSCH the PUSCH. : is the path loss compensation factor. It is set through the Alpha parameter.

PL: same meaning & setting as PRACH power control

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LTE Power Control Feature

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TF (i) :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.

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f (i ): is the adjustment of the PUSCH transmit power of the UE. This value is obtained based on the TPC information on the PDCCH.

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LTE Power Control Feature

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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.

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LTE Power Control Feature

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When the switch PhSinrTarUpdateSwitch under the UlPcAlgoSwitch parameter is set to ON, SINRTarget is periodically adjusted according to the power headroom (PH) information of the current UE, and the number of RBs scheduled for the current UE.

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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.

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LTE Power Control Feature

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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

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When the UE power reach the maximum value, the scheduling mechanism perform the RB decreasing to reduce data rate, but SINR is still maintained.

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When the RB number gets the minimum, namely only 1 RB, then eNodeB reduce the SINR target to maintain the BLER.

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LTE Power Control Feature

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LTE Power Control Feature

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Description of each parameters 

P0 _ PUCCH : 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:

Po _ PUCCH  Po _ NOMINAL _ PUCCH  Po _ UE _ PUCCH 

h n CQI , n HARQ  : is determined by the PUCCH format. nCQI is 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. nHARQ is 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.

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 F _ PUCCH ( F ) : reflects the transmission format of the PUCCH on the transmit power. It is set through the DeltaFPUCCHFormat1, DeltaFPUCCHFormat1b, DeltaFPUCCHFormat2, DeltaFPUCCHFormat2a, and DeltaFPUCCHFormat2b parameters.

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g (i ) : is the adjustment of the transmit power of the UE's PUCCH, and it is obtained based on the TPC information on the PDCCH.

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LTE Power Control Feature

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PDCCH power control configuration use the same command as PDSCH configuration.

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LTE Power Control Feature

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Parameters Description  

M SRS : is the transmission bandwidth of the SRS PSRS _ OFFSET : 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.

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LTE Power Control Feature

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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.

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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.

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LTE Power Control Feature

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