An5xter73GPP TSG-RAN WG1 #50
`Athens, Greece.
`August 20 - 24, 2007
`Agenda item:
`7.3
`Source:
`Qualcomm Europe
`Rate matching details for control and data multiplexing
`Title:
`Document for: Discussion and Decision
`
`R1-073269
`
`Introduction
`1
`The UL of E-UTRA is based on SC-FDM and this waveform is to be respected irrespective of whether control only,
`data only, or control and data are both transmitted in a given subframe.
`
`It was agreed in RAN1#46bis (Oct. 2006) as a working assumption the multiplexing of control and data prior to DFT,
`however more details on how to do it have not been agreed to date.
`
`This contribution covers two aspects:
`
`1. Impact on the PUSCH coding chain when control information is multiplexed
`
`2. Transmission strategy for the control when embedded within the PUSCH transmission
`
`This document is written under the premise that the CQI reporting by the UE is configured by the network and therefore
`the UL scheduler residing in the eNB knows when to expect CQI transmissions. The same happens with the sounding
`reference signal (SRS) transmissions from the UE. However, the ACK/NAK transmissions by the UE depend on the
`correct detection of a DL grant (if it exists) and a subsequent decoding result of the data transmission.
`
`2
`
`Background
`
`CQI transmission
`2.1
`The transmission of the CQI by the UE is configured by the eNB. The reporting cycle is configured through L3
`signalling and is periodic.
`
`Therefore, the eNB knows when to expect a CQI transmission by the UE. As a result, once the eNB receiver determines
`that there is data transmission on the PUSCH it will unambiguously know that the CQI is embedded into the PUSCH
`transmission.
`
`ACK transmission
`2.2
`The ACK/NAK transmissions by the UE are the response of a DL reception. Time asynchronous and adaptive DL
`transmissions require a PDCCH with each (re-)transmission.
`
`
`
`
`
`
`
`The UE transmits “ACK” if the PDCCH and the subsequent PDSCH are both correctly received
`
`The UE transmits “NAK” if the CRC of the PDCCH checks and the PDSCH decoding fails. The PDCCH CRC
`checks if the PDCCH is correctly received or if there is an undetected CRC-pass event.
`
`The UE “transmits” DTX if the CRC of the PDCCH does not check, i.e., if the PDCCH is missed or received
`in error.
`
`In case of DL persistent assignments, the UE will “transmit” DTX if the PDSCH CRC does not pass, while it will
`transmit “ACK” if the PDSCH CRC checks.
`
`1/6
`
`APPLE 1007
`
`

`

`Control-Data Multiplexing Alternatives
`3
`This section presents control-data multiplexing alternatives when they are both transmitted over the PUSCH:
` Alternative 1: multiplexes control and data at the coded symbol level. The coding of the control information
`depends on the data MCS. The stream with the control and data multiplexed is scrambled and modulated
`together, and the power gain on the PUSCH transmission is agnostic of whether control or data modulation
`symbols are transmitted. This alternative is fully compatible with the current functional partition of the
`relevant PHY layer specifications, i.e., 36.211 and 36.212.
` Alternative 2: multiplexes control and data at the modulation symbol level. Fixed coding and modulation is
`used for the control part. Different protection levels for the control information are achieved by way of power
`offsetting the control information transmission with respect to the data part.
`
`Alternative 1 (coded symbol level multiplexing)
`3.1
`Figure 1 shows a block diagram for the control and data multiplexing transmission chain for Alternative 1.
`
`Data TrBlk
`
`Code Block
`Segmentation
`
`for each code block
`
`Encoder
`Encoder
`
`CQI
`
`SRS
`
`RM
`RM
`
`CQI
`
`ACK(s)
`
`Code Block
`Concatenation
`
`Encoder
`
`Encoder(s)
`
`UL grant
`
`Time mapper
`
`Channel
`Interleaver
`
`LFDM symbol
`Mapper
`
`LFDM symbol
`Mapper
`
`Control present in every
`LFDM symbol in subframe
`
`for each LFDM symbol
`
`Data & Control
`Multiplexing
`
`ACK(s) puncture(s)
`data locations
`
`1
`
`Scrambling
`
`Modulator
`
`DFTNalloc
`
`Frequency
`Mapper
`
`IDFTN
`
`Gain
`
`1
`
`
`
`Figure 1. Block diagram for control and data multiplexing in PUSCH – Alternative 1
`The most salient features of this alternative include:
` Rate matching of UL-SCH depending on transmission of CQI and SRS.
`o UL-SCH is rate matched around the CQI and SRS transmission
`o ACK/NAK transmissions do not affect the rate matching of UL-SCH
` The CQI and ACK/NAK coding depends on the UL grant. Note that the varying coding protection will provide
`different protection levels to the control information when embedded into the PUSCH transmission.
`
`2/6
`
`

`

` The data and control multiplexing is such that the control information is placed in all the LFDM symbols used
`for PUSCH transmission. Note that the transmission of the control information in LFDM symbols of the two
`slots in the subframe is critical to benefit from the frequency diversity that could be available for a hopped
`transmission.
` The transmission of the CQI does not compete with the data transmission as the UL-SCH has been rate
`matched around it. The ACK/NAK transmission punctures the data in the control-data multiplexing stage to
`facilitate the turn around of the ACK transmission keeping it separate from the RM stage.
` The multiplexed stream of control and data coded and interleaved symbols undergoes the same transmit chain:
`o Common scrambling
`o Common modulation
`o Common SC-FDMA transmission (DFT precoding followed by frequency mapping and IDFT
`operations)
`o Single gain stage for the PUSCH transmission
`
`Note that this transmission strategy is fully compatible with the current functional partitioning of the relevant PHY layer
`specifications, namely, TS 36.211 and TS 36.212.
`
`Alternative 2 (modulation symbol level multiplexing)
`3.2
`Figure 2 shows a block diagram for the control and data multiplexing transmission chain for Alternative 2.
`
`3/6
`
`

`

`1
`
`DFTNalloc
`
`Frequency
`Mapper
`
`IDFTN
`
`Gain
`
`Data TrBlk
`
`Code Block
`Segmentation
`
`for each code block
`
`Encoder
`Encoder
`
`CQI
`
`SRS
`
`RM
`RM
`
`Can be a function of
`the size of UL grant
`
`CQI
`
`ACK(s)
`
`Code Block
`Concatenation
`
`Encoder
`
`Encoder(s)
`
`Fixed coding
`
`Time mapper
`
`Channel
`Interleaver
`
`[Scrambling]
`
`[Scrambling]
`
`Alternatively, one could have a single
`scrambling if done at the modulation
`symbol level (after MUX block)
`
`Scrambling
`
`Modulator
`
`Modulator
`
`Fixed modulation
`
`UL grant
`
`Modulator
`
`Gain
`
`Gain
`
`UL grant
`
`[Gain]
`
`LFDM symbol
`Mapper
`
`LFDM symbol
`Mapper
`
`Control present in every
`LFDM symbol in subframe
`
`for each LFDM symbol
`
`Data & Control
`Multiplexing
`
`ACK(s) punctures
`data locations
`
`1
`
`
`
`Figure 2. Block diagram for control and data multiplexing in PUSCH – Alternative 2
`The most salient features of this alternative include:
` Rate matching of UL-SCH depending on transmission of CQI and SRS.
`o Note that this is common with Alternative 1
`o UL-SCH is rate matched around the CQI and SRS transmission
` ACK/NAK transmissions do not affect the rate matching of UL-SCH
` Fixed CQI and ACK/NAK coding irrespective of the PUSCH transmission format (MCS)
`
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`
`

`

` Fixed CQI and ACK/NAK modulation format irrespective of the PUSCH transmission format (PUSCH)
`o Effectively this signifies that different modulation symbols may use different modulation schemes
`(control and data)
` Multiplexing of control and data at the modulation-symbol level
`o Gain applied to control information prior to multiplexing with the data – this is providing the different
`protection levels for the control information
` Note that this gain stage depends on the UL grant
`o Gain application for the data information may occur before the control-data multiplexing (in which
`case there is no need of another gain stage later in the transmit chain) or could be done after SC-FDM
`modulation (applying to control and data)
` Scrambling
`o
`
`If applied at the coded symbol level: the scrambling of data and control are independent (as data and
`control are multiplex at the modulation symbol level)
` Note that scrambling of control information may not be necessary
`
`o
`
`If applied at the modulation symbol level:
` Note that TS 36.211 currently specifies scrambling at the coded-symbol level
` The data and control multiplexing is such that the modulation symbols for control information is placed in all
`the LFDM symbols used for PUSCH transmission. Note that the transmission of the control information in
`LFDM symbols of the two slots in the subframe is critical to benefit from the frequency diversity that could be
`available for a hopped transmission.
`o Note that this is common with Alternative 1 with the caveat that the multiplexing now is at the
`modulation-symbol level
` The transmission of the CQI does not compete with the data transmission as the UL-SCH has been rate
`matched around it. The ACK/NAK transmission punctures the data in the control-data multiplexing stage.
`o Note that this is common with Alternative 1 with the caveat that the multiplexing now is at the
`modulation-symbol level
` The multiplexed stream of control and data coded and interleaved symbols undergoes the same SC-FDMA
`transmission (DFT precoding followed by frequency mapping and IDFT operations)
` Gain stage after the SC-FDM modulator for the PUSCH transmission if the data transmission has not
`undergone its own gain stage prior to the multiplexing
`
`Note that this transmission strategy violates in multiple instances the current partitioning of the relevant PHY layer
`specifications, namely, TS 36.211 and TS 36.212.
`
`Conclusions
`4
`This document has presented and discussed two control and data multiplexing strategies for the case when the control is
`embedded as part of the PUSCH transmission.
`
`The different protection levels for the control information are provided by different means in both alternatives.
`Alternative 1 exploits variable coding and fixed power level, while alternative 2 exploits different power settings with
`fixed coding.
`
`It is important to consider the eNB receiver complexity in conjunction with the overall reliability in the reception of the
`control information.
`
`In regards to the rate-matching and de-rate matching both alternatives are the same. In other aspects:
`
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`

`

`Alternative 1
`PROS
` No PAPR impact
` Fully compatible with current PHY layer specifications structure
` Link budget limited situations can be overcome with a lower code rate, which, in turn, will yield a
`transmission over a larger number of REs.
`
`CONS
` Different coding depending on the UL grant
`o Reception without blind decodes can be possible if there is an implicit mapping from MCS for
`PUSCH to control information transmission format
`
`Alternative 2
`PROS
` Same coding irrespective of the MCS – no blind decode necessary
`CONS
` PAPR impact from different power setting for control and data, and for different modulation orders for
`control and data
` Link budget limited situations cannot be overcome with a larger gain since the SC-FDM waveform maps
`virtual subcarriers to “chips” in the time domain and therefore the gain adjustment once the max power is
`achieved cannot increase the coverage of the control information.
`
`
`
`Incompatible with current PHY layer specifications structure
`
`In conclusion and based on the analysis presented in this document we recommend adopting Alternative 1 for the
`specification of the control and data multiplexing when they are transmitted in the same subframe.
`
`6/6
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`