5.1 Transmitter power control

25.2243GPPPhysical layer procedures (TDD)TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

The basic purpose of power control is to limit the interference level within the system thus reducing the intercell interference level and to reduce the power consumption in the UE.

The main characteristics of power control are summarized in the following table.

Table 2: Transmit Power Control characteristics

	Uplink	Downlink
Power control rate	Variable Closed loop: 0-200 cycles/sec. Open loop: (about 200us – 3575us delay )	Variable Closed loop: 0-200 cycles/sec.
Step size	1,2,3 dB (closed loop)	1,2,3 dB (closed loop)
Remarks	All figures are without processing and measurement times

Note: All codes within one timeslot allocated to the same CCTrCH use the same transmission power in case they have the same Spreading Factor.

5.1.1 Uplink control

5.1.1.1 General limits

By means of higher layer signalling, the Maximum_Allowed_UL_TX_ power for uplink may be set to a value lower than what the terminal power class is capable of. Uplink power control shall be performed while the total UE transmit power is below the maximum allowed output TX power. In some cases the total requested UE transmit power in a timeslot after uplink power control calculation might exceed the maximum allowed output power. In these cases the calculated transmit power of all uplink physical channels in this timeslot shall be scaled by the same amount in dB before transmission in order that the total UE transmission power used shall be the maximum allowed output power.

The UTRAN may not expect the UE to be capable of reducing its total transmit power below the minimum level specified in [2].

5.1.1.2 UpPCH

The transmit power for the UpPCH is set by higher layers based on open loop power control as described in [15]

5.1.1.3 PRACH

The transmit power for the PRACH is set by higher layers based on open loop power control as described in [15].

5.1.1.4 DPCH and PUSCH

The initial transmission power for uplink DPCH and PUSCH is set by higher layers based on open loop power control as described in [15]. The UE then transits into closed loop power control. The node B shall generate TPC commands according to a quality target set by higher layers in order to instruct an increase or decrease in the level of transmission power from the UE and send them either in the TPC field of associated downlink CCTrCHs (see [8] for a description of the mapping between DL associated TPC symbols and UL controlled CCTrCH/timeslots) or on PLCCH (see [8] 5A.3.13). If the physical channel power should be increased, the TPC command is set to "up", whereas if the power should be reduced the command is set to "down". A TPC command sent in a downlink CCTrCH or via PLCCH controls all uplink DPCHs and PUSCHs in the associated uplink CCTrCH and timeslot. An example of SIR based UL power control is given in annex A2

If signalled by higher layers, the UE must follow the received TPC commands only. In this case, at the UE when the TPC command is judged as ‘down’, the mobile transmit power shall be reduced by one power control step, whereas if it is judged as ‘up’, the mobile transmit power shall be raised by one power control step.

If indicated as allowed by higher layers, the UE may optionally take into account pathloss estimated from beacon function physical channels in addition to the TPC commands when calculating the transmit power. In this case, the mobile transmit power is first modified as described above by the received TPC command and is then further modified based upon the pathloss estimated on recent beacon transmissions. Modifications based upon pathloss shall only be applied when the UE estimates that the pathloss on the uplink transmission timeslot and the pathloss on the beacon timeslots used to derive the modification value are likely to be similar.

The closed loop power control procedure for UL DPCH and PUSCH is not affected by the use of TSTD.

In the event of no associated uplink data being transmitted between two related downlink TPC commands, the UE shall ignore the resulting TPC command. The transmit power for the next instance of the timeslot/CCTrCH pair shall then be set:

i) to the power level of the previous uplink transmission, optionally modified to compensate for the change in pathloss observed during the uplink transmission pause or,

ii) using the open loop procedure as for initial transmissions.

The UE shall select which of the above methods to apply. For short transmission pauses method (i) should be used.

5.1.1.4.1 Gain factors

Same as that of 3.84 Mcps TDD, cf. [4.2.2.3.1 Gain factors].

5.1.1.4.2 Out of synchronization handling

In the case that uplink DPCH is controlled by TPC commands carried on downlink DPCH, out of synchronisation handling is the same as that of 3.84 Mcps TDD, cf.[ 4.2.2.3.2 Out of synchronisation handling].

In the case that uplink DPCH is controlled by TPC commands carried on PLCCH, the UE shall shut off the transmission of an UL CCTrCH if the following criteria are fulfilled for the PLCCH carrying its TPC commands:

– The UE estimates the received PLCCH quality over the last 160 ms period to be worse than a threshold Q_out. Q_out is defined implicitly by the relevant tests in [2].

The UE shall subsequently resume the uplink transmission of the CCTrCH if the following criteria are fulfilled:

– The UE estimates the received PLCCH reception quality over the last 160 ms period to be better than a threshold Q_in. Q_in is defined implicitly by the relevant tests in [2].

5.1.1.5 HS-SICH

If the UE is not configured in MIMO mode, the transmit power of the HS-SICH shall be set by the UE according to the procedures described below. In the case that an ACK is being transmitted on the HS-SICH, the UE shall apply a power offset to the transmit power of the entire HS-SICH. This power offset shall be signalled by higher layers.

For the transmissions on the semi-persistent HS-PDSCH resources without an HS-SCCH, the TPC command for HS-SICH can be conveyed in HS-PDSCH.

On receipt of a TPC command in the HS-SCCH or HS-PDSCH, the UE shall adjust the HS-SICH transmit power according to the power control step size specified by higher layers. The UE shall ignore the TPC command transmitted on an HS-SCCH order which is an uplink synchronization establishment command. An example of SIR based UL power control is given in annex A5.

i) However, for the first HS-SICH transmission following the first detected HS-SCCH transmission, the UE shall use open loop power control to set the HS-SICH transmit power for that transmission. In this case, the transmission power for HS-SICH is set by higher layers based on open loop power control as described in [15].

ii) When the transmission interval of HS-SICHs, which are in the same time slot, is less than a certain threshold, which is signalled by higher layers, UE shall adjust the transmit power according to received TPC command in HS-SCCH or HS-PDSCH during HS-SICH transmission pause based on transmission power of last instance. When receipt of TPC commands in HS-PDSCH and in HS-SCCH is in the same sub-frame, UE shall treat one single TPC command if they are identical and discard them if they are different. If indicated by higher layers, UE should take into account the pathloss compensation by means of beacon channel estimation in addition to the TPC command when calculating HS-SICH transmit power.

iii) When the transmission interval of HS-SICHs, which are in the same time slot, is equal or larger than a certain threshold, for the next instance of HS-SICH, UE shall use open loop power control described above for the initial transmission.

If the UE is configured in MIMO mode, the transmit power of the HS-SICH shall be set by the UE according to the procedures described below.

The procedure for MIMO single stream transmission is the same as that the UE is not configured in MIMO mode.

For MIMO dual stream transmission, in the case that two ACKs are being transmitted on the HS-SICH, the UE shall apply a power offset to the transmit power of the entire HS-SICH. This power offset shall be signalled by higher layers.

On receipt of a TPC command in the HS-SCCH or HS-PDSCH, the UE shall adjust the HS-SICH transmit power according to the power control step size specified by higher layers. An example of SIR based UL power control is given in annex A5.

i) However, for the first HS-SICH transmission following the first detected HS-SCCH transmission, the UE shall use open loop power control to set the HS-SICH transmit power for that transmission. In the case of dual stream transmission, a delta is applied to the HS-SICH transmission power. The delta implies the required power offset of the HS-SICH transmission for the different number of the data streams under the limit of SIR target. This transmission power is set by higher layers based on open loop power control as described in [15].

ii) When the transmission interval of HS-SICHs, which are in the same time slot, is less than a certain threshold，which is signalled by higher layers, UE shall adjust the transmit power according to received TPC command during HS-SICH transmission pause based on transmission power of last instance. In the case of dual stream transmission, a delta is applied to the HS-SICH transmission power. If indicated by higher layers, UE should take into account the pathloss compensation by means of beacon channel estimation in addition to the TPC command when calculating HS-SICH transmit power.

5.1.1.6 E-PUCH

For multi-carrier E-DCH transmission, the open-loop and closed-loop power control of E-PUCH on each carrier is independent from each other. The power of E-PUCH in each timeslot on each carrier is set as follows. Note that the power of E-PUCH in the timeslots with same spreading factor is the same.

The power of E-PUCH in each timeslot is set following the same principle used for DPCH/PUSCH in R4/5/6[15] and in 5.1.1.4, i.e., the combination of open-loop power control and traditional closed-loop power control:

– the initial transmit power of E-PUCH is set based on an open-loop power control scheme, then

– the transmission power control transits into closed-loop power control using TPC commands carried on E-AGCH or on E-HICH on the same carrier. For non-scheduled transmission, the TPC commands are carried on E-HICH only. Both TPC commands carried on E-AGCH and E-HICH are used on E-PUCH

The transmit power for E-PUCH set in each timeslot is calculated as follows:

… where:

– is the transmit power of the E-DCH physical channel E-PUCH in each timeslot.

– is a closed-loop quantity maintained by the UE and NodeB for each carrier, and which is incremented or decremented by a value Δ_e-base upon each receipt of a TPC command on E-AGCH for scheduled transmission or on E-HICH for non-scheduled transmission on the same carrier. On receipt of a TPC "up" command, P_e-base is incremented by Δ_e-base. On receipt of a TPC "down" command, P_e-base is decremented by Δ_e-base. The TPC step size Δ_e-base is configured by higher layers [15].

where, is the reference Desired E-PUCH RX power signalled by RRC signalling for each carrier according to [15], which is set to the average value of the interference signal power level over the timeslots configured for E-DCH use.

is the power control step size Δ_e-base configured by higher layers, and is a closed-loop control command.

– is a pathloss term derived from beacon function physical channels. The same as that in 5.1.1.4, if indicated as allowed by higher layers, the UE may optionally take into account pathloss modification which is estimated from the most recently received beacon function physical channel transmission, in addition to the TPC commands when calculating the transmit power.

– is the gain factor for the selected E-TFC transport block size, the allocated E-PUCH physical resources, and the Modulation type and HARQ power offset according to subclause 5.1.1.6.1. If the smallest E-TFC is selected, equals to the sum of absolute grant value and a_e.

Higher layers in the UE shall use the current calculated E-PUCH power in conjunction with the current absolute grant (power) value in order to determine the set of E-TFC’s available.

UE maintains a closed-loop quantity Pe-base for both scheduled transmission and non-scheduled transmission. is incremented or decremented by a value Δ_e-base upon each receipt of a TPC command on E-AGCH and on E-HICH on the same carrier. When receipt of TPC commands on E-AGCH and on E-HICH is in the same sub-frame, UE shall treat one single TPC command if they are identical and discard them if they are different.

When following an extended pause, which is signalled by higher layers, in the reception of TPC commands on E-AGCH and on E-HICH, the UE shall set equal to the reference Desired E-PUCH RX power. When receipt of TPC commands on E-AGCH or on E-HICH recommences, the TPC commands shall be used to modify from its previously set value.

5.1.1.6.1 Gain factors for E-PUCH

A beta factor shall be derived by the UE as a function of:

– the selected E-TFC transport block size

– the E-PUCH resource occupation in the E-DCH TTI

– the modulation type (QPSK/16-QAM)

– the HARQ power offset

Higher layers shall provide a mapping table containing a set of reference points, which defines the relationship between the coderate of E-DCH transmission (_e) and the relative reference power per resource unit (b_l dB). The mapping table is provided separately for each of QPSK and 16-QAM modulation.

The coderate of E-DCH transmission _e for the selected E-TFC, physical resource allocation and modulation type is defined as:

… in which S_e is the transport block size of the selected E-TFC and R_e is the number of physical channel bits output from the physical channel mapping stage of E-DCH transport channel processing as described in [9]. The precision requirement for _e is 1×10^-4 and the quantization mode is truncation.

The maximum and minimum values of  are the maximum and minimum values of Reference Code Rate respectively, which are signalled by higher layers for the appropriate modulation type [15], and are denoted _max and _min respectively. For a given _e there exist a ₀ and a ₁ such that:

– If _min≤_e<_max

– ₀ is the largest  signalled by higher layers for the appropriate modulation type and for which ≤_e

– ₁ is the smallest  signalled by higher layers for the appropriate modulation type and for which >_e

– Else

– If _e<_min then ₀ = _min and ₁ is the smallest signalled  for which >_min.

– If _e≥_max then ₀ is the largest signalled  for which <_max and ₁ = _max

Associated with ₀ and ₁ are the corresponding _0 and _1 which define the reference points signalled by higher layers. The normalised (per-resource-unit) beta value for the selected E-TFC and E-PUCH resource set is denoted _0,e and is:

The precision requirement for _0,e is 1×10^-3 and the quantization mode is truncation.

is a logarithmic value set as a function of the E-PUCH spreading factor (SF_E-PUCH) according to table 2a.

Table 2a: Tabulated _e values

SF_E-PUCH	(dB)
1	12
2	9
4	6
8	3
16	0

_e is then derived as

Δ_harq is set by higher layers ( see [18] ).

5.1.1.7 E-RUCCH

The transmit power for the E-RUCCH is set following the same formula used for PRACH based on open loop power control as described in [15].

5.1.1.8 Standalone midamble channel

If the UE is configured in MIMO mode, the transmit power for the standalone midamble channel shall be the same as that used for the associated HS-SICH in the same subframe.

If the UE is configured in MU-MIMO mode, the transmit power for the standalone midamble channel shall make reference to the last transmitted HS-SICH or E-PUCH. When the last transmitted uplink channel is HS-SICH, the transmit power of the standalone midamble channel shall be the same as the last transmitted HS-SICH.When the last transmitted uplink channel is E-PUCH, the transmit power of the standalone midamble channel shall be calculated as follows:

… where:

– is the desired receiving power of E-PUCH.

– is the gain factor for standalone midamble channel, and should be configured by high layer.

– is a pathloss term derived from beacon function physical channels.

5.1.2 Downlink control

The total downlink transmission power at the Node B within one timeslot shall not exceed the Maximum Transmission Power set by higher layer signalling.

5.1.2.1 P-CCPCH

Same as that of 3.84 Mcps TDD, cf.[4.2.3.1 P-CCPCH].

5.1.2.2 The power of the FPACH

The transmit power for the FPACH is set by the higher layer signalling [16].

5.1.2.3 S-CCPCH, PICH

Same as that of 3.84 Mcps TDD, cf.[4.2.3.2 S-CCPCH , PICH].

5.1.2.3A MICH

Same as that of 3.84 Mcps TDD, cf.[4.2.3.2A MICH].

5.1.2.4 DPCH, PDSCH

The initial transmission power of the downlink Dedicated Physical Channel is signalled by higher layers. After the initial transmission, the node B transits into closed-loop TPC. The UE shall generate TPC commands according to a quality target set by higher layers in order to control the level of transmission power from the node B and send them in the TPC field of associated uplink CCTrCHs (see [8] for a description of the mapping between UL associated TPC symbols and DL controlled CCTrCH/timeslots) or in the Non-scheduled E-PUCH when the associated uplink CCTrCHs do not exist. If the physical channel power should be increased, the TPC command is set to "up", whereas if the power should be reduced the command is set to "down". A TPC command sent in an uplink CCTrCH or in the Non-scheduled E-PUCH when the associated uplink CCTrCH does not exist controls all downlink DPCHs or PDSCHs in the associated downlink CCTrCH and timeslot.

UTRAN may decide how to adjust the transmit power in response to the received TPC command

When TSTD is applied, the UE can use two consecutive measurements of the received SIR in two consecutive sub-frames to generate the power control command. An example implementation of DL power control procedure for 1.28 Mcps TDD when TSTD is applied is given in Annex A.3.

The transmission power of one DPCH or PDSCH shall not exceed the limits set by higher layer signalling by means of Maximum_DL_Power (dB) and Minimum_DL_Power (dB). The transmission power is defined as the average power over one timeslot of the complex QPSK (or 8PSK respectively) symbols of a single DPCH or PDSCH before spreading relative to the power of the P-CCPCH.

Each TPC command shall be based on all associated downlink transmissions since the previous related TPC command.

In the event of no associated downlink data being transmitted between two related TPC commands, the UTRAN should ignore the resulting TPC command.

5.1.2.4.1 Out of synchronisation handling

Same as that of 3.84 Mcps TDD, cf.[4.2.3.4.1 Out of synchronisation handling].

5.1.2.5 HS-PDSCH

The power control for HS-PDSCH for 1.28 Mcps TDD is the same as for 3.84 Mcps, see section 4.2.3.5

5.1.2.6 HS-SCCH

Higher layers shall indicate the maximum transmit power of the HS-SCCH. The Node-B shall not exceed this maximum power when setting the HS-SCCH power.

The initial power of the HS-SCCH is at the discretion of the Node-B. Following the initial transmission, the NodeB may optionally power control the HS-SCCH. This may be done using TPC commands sent by the UE in the HS-SICH. When the transmission interval of HS-SCCHs, which are in the same time slot, is more than or equal to a certain threshold, which is signalled by higher layers, NodeB shall use initial transmit power for the next HS-SCCH transmission.

The UE shall set the TPC commands in the HS-SICH in order to control the transmit power of the HS-SCCH. The TPC commands shall be set in order to meet the HS-SCCH target BLER.

The accuracy of the received HS-SCCH BLER estimate made by the UE may be enhanced by a suitable use of the HCSN field received within the HS-SCCH itself [9]. This field shall initially be set to zero and shall be incremented by the NodeB each time an HS-SCCH is transmitted to the UE. UE without a dedicated UE identity in CELL_FACH state and UE in CELL_PCH state shall ignore the value of HCSN.

5.1.2.7 PLCCH

The initial transmission power of the downlink PLCCH is signalled by higher layers. After the initial transmission, the transmission power of PLCCH is under the control of Node-B. The Node-B may optionally adjust the transmission power of PLCCH according to the received TPC commands which are carried by the PLCCH-controlled UL CCTrCH(s). The UE shall generate TPC commands according to a PLCCH quality target set by higher layers. If the PLCCH power should be increased, the TPC command is set to "up", whereas if the power should be reduced the command is set to "down". UTRAN may decide how to adjust the transmit power in response to the received TPC commands. The average power of transmitted PLCCH symbols over one timeslot shall not exceed the limits set by higher layers. The transmission power is defined as the average power over one timeslot of the complex QPSK symbols of a single PLCCH before spreading relative to the power of the P-CCPCH.

5.1.2.8 E-AGCH

For multi-carrier E-DCH transmission, the power control of E-AGCH on each carrier is independent from each other and described as follows.

Higher layers shall indicate the maximum transmit power of the E-AGCH. The Node-B shall not exceed this maximum power when setting the E-AGCH power.

The initial power of the E-AGCH is at the discretion of the Node-B. Following the initial transmission, the NodeB may optionally power control the E-AGCH. This may be done using TPC commands sent by the UE in the scheduled E-PUCH on the same carrier.

The UE shall set the TPC commands in the Scheduled E-PUCH on the same carrier in order to control the transmit power of the E-AGCH. The TPC commands shall be set in order to meet the E-AGCH target BLER.

The accuracy of the received E-AGCH BLER estimate made by the UE shall be enhanced by a suitable use of the ECSN field received within the E-AGCH itself [9]. This field shall initially be set to zero and shall be incremented by the Node-B each time an E-AGCH is transmitted to the UE. For each carrier in multi-carrier E-DCH transmission, the ECSN shall initially be set to zero and shall be incremented by the Node-B each time an E-AGCH is transmitted on the carrier to the UE.

5.1.2.9 E-HICH

The power of the E- HICH is under the control of the Node B.