4.2 Transmitter power control

25.2243GPPPhysical layer procedures (TDD)TS

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

4.2.1 General parameters

Power control is applied for the TDD mode to limit the interference level within the system thus reducing the intercell interference level and to reduce the power consumption in the UE.

All codes within one timeslot allocated to the same CCTrCH use the same transmission power, in case they have the same spreading factor.

Table 1: Transmit Power Control characteristics

	Uplink	Downlink
Power control rate	Variable 1-7 slots delay (2 slot SCH) 1-14 slots delay (1 slot SCH)	Variable, with rate depending on the slot allocation.
TPC Step size	—	1dB or 2 dB or 3 dB
Remarks	All figures are without processing and measurement times

4.2.2 Uplink control

4.2.2.1 General limits

During the operation of the uplink power control procedure the UE transmit power shall not exceed a maximum allowed value which is the lower out of the maximum output power of the terminal power class and a value which may be set by higher layer signalling.

Uplink power control shall be performed while the total UE transmit power is below the maximum allowed output power. In some cases the total 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. 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].

4.2.2.2 PRACH

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

4.2.2.3 DPCH, PUSCH and HS-SICH

The transmit power for DPCH, PUSCH and HS-SICH is set by higher layers based on open loop power control as described in [15].

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.

4.2.2.3.1 Gain factors

Two or more transport channels may be multiplexed onto a CCTrCH as described in [9]. These transport channels undergo rate matching which involves repetition or puncturing. This rate matching affects the transmit power required to obtain a particular E_b/N₀. Thus, the transmission power of the CCTrCH shall be weighted by a gain factor .

There are two ways of controlling the gain factors for different TFC’s within a CCTrCH transmitted in a radio frame:

–  is signalled for the TFC, or

–  is computed for the TFC, based upon the signalled settings for a reference TFC.

Combinations of the two above methods may be used to associate  values to all TFC’s in the TFCS for a CCTrCH. The two methods are described in sections 4.2.2.3.1.1 and 4.2.2.3.1.2 respectively. Several reference TFC’s for several different CCTrCH’s may be signalled from higher layers.

The weight and gain factors may vary on a radio frame basis depending upon the current SF and TFC used. The setting of weight and gain factors is independent of any other form of power control. That means that the transmit power P_UL is calculated according to the formula given in [15] and then the weight and gain factors are applied on top of that, cf. [10].

4.2.2.3.1.1 Signalled gain factors

When the gain factor _j is signalled by higher layers for a certain TFC, the signalled values are used directly for weighting DPCH or PUSCH within a CCTrCH. Exact values are given in [10].

4.2.2.3.1.2 Computed gain factors

The gain factor_j may also be computed for certain TFCs, based on the signalled settings for a reference TFC:

Let _ref denote the signalled gain factor for the reference TFC. Further, let _j denote the gain factor used for the j-th TFC.

Define the variable:

where RM_i is the semi-static rate matching attribute for transport channel i, N_i is the number of bits output from the radio frame segmentation block for transport channel i and the sum is taken over all the transport channels i in the reference TFC.

Similarly, define the variable

where the sum is taken over all the transport channels i in the j-th TFC.

Moreover, define the variable

where SF_i is the spreading factor of DPCH or PUSCH i and the sum is taken over all DPCH or PUSCH i used in the reference TFC.

Similarly, define the variable

where the sum is taken over all DPCH or PUSCH i used in the j-th TFC.

The gain factors _j for the j-th TFC are then computed as follows:

No quantisation of _j is performed and as such, values other than the quantised _j given in [10] may be used.

4.2.2.3.2 Out of synchronisation handling

As stated in 4.2.3.4 , the association between TPC commands sent on uplink DPCH and PUSCH, with the power controlled downlink DPCH and PDSCH is signaled by higher layers. In the case of multiple DL CCTrCHs it is possible that an UL CCTrCH will provide TPC commands to more than one DL CCTrCH.

In the second phase of synchronisation evaluation, as defined in 4.4.2.1.2, the UE shall shut off the transmission of an UL CCTrCH if the following criteria are fulfilled for any one of the DL CCTrCHs commanded by its TPC:

– The UE estimates the received dedicated channel burst quality over the last 160 ms period to be worse than a threshold Q_out, and in addition, no special burst, as defined in 4.5, is detected with quality above a threshold, Q_sbout. Q_out and Q_sbout are defined implicitly by the relevant tests in [2]. If the UE detects the beacon channel reception level [10 dB] above the handover triggering level, then the UE shall use a 320 ms estimation period for the burst quality evaluation and for the Special Burst detection window.

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

– The UE estimates the received dedicated CCTrCH burst reception quality over the last 160 ms period to be better than a threshold Q_in or the UE detects a burst with quality above threshold Q_sbin and TFCI decoded to be that of the Special Burst. Q_in and Q_sbin are defined implicitly by the relevant tests in [2]. If the UE detects the beacon channel reception level [10 dB] above the handover triggering level, then the UE shall use a 320 ms estimation period for the burst quality evaluation and for the Special Burst detection window.

4.2.2.4 E-PUCH

The power of E-PUCH is set based upon the sum of:

1. An open loop component based upon beacon channel pathloss and on the E-PUCH constant value signalled by higher layers (K_E-PUCH).

2. A closed-loop TPC component. One TPC bit is signalled to the UE within each E-AGCH. The TPC command is derived by Node-B.

3. An adjustment factor (_e) accounting for the E-TFC selected by the UE and the HARQ offset.

The transmit power of the E-PUCH is calculated in the UE as follows:

… where:

– P_e-base is a closed-loop quantity maintained by the UE and which is incremented or decremented by a value Δ_e-base upon each receipt of a TPC command on E-AGCH. 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].

– L is a pathloss term derived by higher layers from beacon function physical channel measurements. It may comprise a weighted sum of the instantaneous (L_PCCPCH) and filtered (L₀) pathloss measurements (as described in [15])

– _e is the gain factor derived for the selected E-TFC transport block size, E-PUCH physical resource size, E-PUCH modulation type and HARQ offset according to subclause 4.2.2.4.1.

– K_E-PUCH is the E-PUCH constant value signalled by higher layers [15].

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 (see [18]).

When setting the initial transmit power for E-PUCH or following an extended pause in the reception of TPC commands on E-AGCH, the UE shall set P_e-base equal to the average of the I_BTS values (see [15]) over the timeslots configured for E-DCH use. When receipt of TPC commands on E-AGCH recommences, the TPC commands shall be used to modify P_e-base from its previously set value.

4.2.2.4.1 Gain factors for E-PUCH

A beta factor _e 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 (see [18])

Higher layers shall provide a set of reference points defining the relationship between the coderate of E-DCH transmission (_e) and the relative reference power per resource unit (_ dB). A set of reference points 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 maximum and minimum values of  signalled by higher layers for the appropriate modulation type are denoted _max and _min respectively. For a given _e there exists a ₀ and a ₁such 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:

is a logarithmic value set as a function of the E-PUCH spreading factor (SF_E-PUCH) according to table 1a.

Table 1a: 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]).

4.2.2.5 E-RUCCH

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

4.2.3 Downlink control

4.2.3.1 P-CCPCH

The Primary CCPCH transmit power is set by higher layer signalling and can be changed based on network conditions on a slow basis. The reference transmit power of the P-CCPCH is broadcast on BCH or individually signalled to each UE.

4.2.3.2 S-CCPCH, PICH

The relative transmit power of the Secondary CCPCH and the PICH compared to the P-CCPCH transmit power are set by higher layer signalling. The PICH power offset relative to the P-CCPCH reference power is signalled on the BCH.

4.2.3.2A MICH

The relative transmit power of the MICH compared to the P-CCPCH transmit power is set by higher layer signalling.

4.2.3.3 SCH

The SCH transmit power is set by higher layer signalling [16]. The value is given relative to the power of the P-CCPCH.

4.2.3.3A PNBSCH

The PNBSCH transmit power is set by higher layer signalling [16]. The value given is relative to the power of the P-CCPCH

4.2.3.4 DPCH, PDSCH

The initial transmission power of the downlink DPCH and the PDSCH shall be set by higher layer signalling. If associated uplink CCTrCHs for TPC commands are signalled to the UE by higher layers (mandatory for a DPCH), the network shall transit into inner loop power control after the initial transmission. The UE shall then generate TPC commands to control the network transmit power and send them in the TPC field of the associated uplink CCTrCHs. If the physical channel power should be increased, the TPC command is set to "up" whereas if the power should be reduced the TPC command is set to "down". An example on how to derive the TPC commands and the definition of the inner loop power control are given in Annex A.1. A TPC command sent in an uplink CCTrCH controls all downlink DPCHs or PDSCHs to which the associated downlink CCTrCH is mapped to.

If a PDSCH does not have associated uplink CCTrCHs configured for TPC power control, its power shall be controlled by higher layer signalling.

In the case that no associated downlink data is scheduled within 15 timeslots before the transmission of a TPC command then this is regarded as a transmission pause. The TPC commands in this case shall be derived from measurements on beacon function physical channels. An example solution for the generation of the TPC command for this case is given in Annex A 1.

When not in a transmission pause each TPC command shall always be based on all associated downlink transmissions received since the previous related TPC command. Related TPC commands are defined as TPC commands associated with the same downlink CCTrCHs. If there are no associated downlink transmissions (or equivalently no beacon transmissions when in a transmission pause) between two or more uplink transmissions carrying related TPC commands, then these TPC commands shall be identical and they shall be regarded by the UTRAN as a single TPC command.

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

The UTRAN may apply an individual offset to the transmission power in each timeslot according to the downlink interference level at the UE.

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 symbols of a single DPCH or PDSCH before spreading relative to the power of the P-CCPCH.

During a downlink transmission pause, both UE and Node B shall use the same TPC step size which is signalled by higher layers. The UTRAN may accumulate the TPC commands received during the pause. TPC commands that shall be regarded as identical may only be counted once. The initial UTRAN transmission power for the first data transmission after the pause may then be set to the sum of transmission power before the pause and a power offset according to the accumulated TPC commands. Additionally this sum may include a constant set by the operator and a correction term due to uncertainties in the reception of the TPC bits. The total downlink transmission power at the Node B within one timeslot shall not exceed Maximum Transmission Power set by higher layer signalling. If the total transmit power of all channels in a timeslot exceeds this limit, then the transmission power of all downlink DPCHs and PDSCHs shall be reduced by the same amount in dB. The value for this power reduction is determined, so that the total transmit power of all channels in this timeslot is equal to the maximum transmission power.

4.2.3.4.1 Out of synchronisation handling

When the dedicated physical channel out of sync criteria based on the received burst quality is as given in the subclause 4.4.2 then the UE shall set the uplink TPC command = "up". The CRC based criteria shall not be taken into account in TPC bit value setting.

4.2.3.5 HS-PDSCH

The HS-PDSCH power control is under the control of the NodeB.

4.2.3.6 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.

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.

4.2.3.7 E-AGCH

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 E-PUCH.

The UE shall set the TPC commands in the E-PUCH 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.

4.2.3.8 E-HICH

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