`3GPP TSG RAN WG1 #88
`Athens, Greece 13th - 17th February 2017
`
`8.1.3.2.3
`Agenda item:
`Samsung
`Source:
`Resource Allocation for PUCCH
`Title:
`Document for: Discussion and Decision
`
` R1-1702983
`
`1. Introduction
`UL control channel design is one of the fundamental works in NR, including the structure of long and short PUCCH
`format, the PUCCH resource allocation and also how to multiplex UCI with data. This contribution discusses several
`aspects of the PUCCH resource allocation, while the PUCCH structure and UCI transmission in PUSCH are treated in
`our companion contributions [1] ~ [5].
`
`Up to RAN1 NR ad-hoc meeting, following agreements related to PUCCH resource allocation were made:
`
`Agreements (updating RAN1 #87 agreements):
`•
`A combination of semi-static configuration and (at least for some types of UCI information) dynamic signaling
`is used to determine the PUCCH resource both for the ‘long and short PUCCH formats’
`•
`The PUCCH resource includes time, frequency and, when applicable, code domains.
`•
`FFS details e.g., if the time in the PUCCH resource includes both slot and symbol, or only
`symbol in a slot
`
`Agreements:
` At least semi-static configuration for the following is supported.
` A PUCCH resource of a given UE within a slot.
` i.e., short-PUCCHs of different UEs can be TDM’ed within the given duration in a slot.
` The PUCCH resource includes time, frequency and, when applicable, code domains.
` FFS details e.g., if the time in the PUCCH resource includes both slot and symbol, or only symbol in a
`slot
`
`•
`
`•
`
`•
`
`Agreements:
`•
`Timing between DL assignment and corresponding DL data transmission is indicated by a field in the DCI
`from a set of values
`•
`The set of values is configured by higher layer
`Timing between UL assignment and corresponding UL data transmission is indicated by a field in the DCI
`from a set of values
`•
`The set of values is configured by higher layer
`Timing between DL data reception and corresponding acknowledgement is indicated by a field in the DCI
`from a set of values
`•
`The set of values is configured by higher layer
`Timing(s) is (are) defined at least for the case where the timing(s) is (are) unknown to the UE
`•
`FFS the value for the timing
`2. Discussion
`2.1 Multiple PUCCH formats
`To enable more flexible operation and dynamic slot structure, NR will support flexible/configurable HARQ-ACK
`timing. Due to flexible HARQ-ACK timing, the number of DL slots with PDSCH(s) corresponding to one
`PUCCH/PUSCH for HARQ-ACK transmission can be variable and UE-specific. In some cases, the DL slot of PDSCH
`reception and the corresponding HARQ-ACK feedback can have a one-to-one mapping (similar to LTE FDD) while in
`other cases, there can be a many-to-one mapping (similar to LTE TDD). Thus, the HARQ-ACK payload may vary with
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`APPLE 1010
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`the bundling window size (note: it depends on HARQ-ACK codebook determination [6]). If more than one bit per TB
`such as CBG-based feedback is to be supported in NR, the HARQ-ACK payload also changes with CBG/TB-level
`feedback. Furthermore, same as LTE, the UCI payload also varies with the UCI contents (i.e., HARQ-ACK/CSI/SR)
`and the number of configured/scheduled DL cells in CA.
`Therefore, similar to the LTE PUCCH formats 1~5 which are designed to optimally support different UCI payloads,
`different PUCCH formats in NR are also needed for the same reason. Considering the maximum payload of different
`PUCCH duration (long or short PUCCH) is different, the supported PUCCH formats for short and long PUCCH would
`be different. To avoid a large number of combination of PUCCH formats and PUCCH durations, it is desirable fewer
`PUCCH formats than in LTE be supported in NR.
`A PUCCH format determination can be either explicit by DCI or, similar to LTE, implicit based on the HARQ-ACK
`payload.
`Proposal 1: NR supports multiple PUCCH formats for HARQ-ACK transmission based on HARQ-ACK payload.
`Consider down-selection from LTE PUCCH format based structures.
`
`2.2 PUCCH resource indication
`UEs with different HARQ-ACK timing can transmit HARQ-ACK in a same slot while associated PDSCHs can be
`received in same or different slots. Then, the implicit determination of PUCCH resources (implicit link between a
`lowest CCE index of the PDCCH and PUCCH resource) in LTE can lead to collisions.
`One way to avoid the collision is fully explicit indication (from a set of configured PUCCH resources) similar to ARI in
`LTE as was agreed in RAN1#87. The other possible way is the implicit indication complemented by explicit signaling
`in DCI. In LTE, 2 bits ARO indicative of one of four offsets on top of PUCCH resource derived by CCE index is
`introduced to alleviate the PUCCH resource collision between UEs with same CCE index within respective EPDCCH
`search space or one in EPDCCH search space while the other in PDCCH search space. In NR, ARO could still be an
`effective way to resolve the PUCCH resource collisions from UEs with PDSCH(s) transmitted in different DL slots. It
`can be considered at least for small HARQ-ACK payloads as in LTE to reduce the PUCCH resource reservation
`overhead.
`
`
`un PDSCH
`(low capa bility)
`
`UE2 PDSCH
`_ _ _ _ _ (high capability )
`
`DL
`
`UL
`
`
`Figure 1 ACK/NACK collision between UEs with different ACK/NACK timing
`
`PUCCH for UE1
`PUCCH for UE2
`
`Proposal 2: Further study the combination of implicit and ARO-like explicit indication of PUCCH resource in
`terms of DCI overhead and UL resource efficiency.
`It is clarified in RAN1 NR ad-hoc meeting that the PUCCH resource consists of a time-domain component and
`frequency/code-domain component. Regarding the time-domain component, the granularity of time resource for long
`and short PUCCH is different. For the long PUCCH, the unit of time resource is UL slot, while the unit of time resource
`is UL symbol for short PUCCH.
`Both separate indication of PUCCH time resource and frequency/code-domain resource or joint indication of all
`resources can be considered in terms of efficient UL resource utilization and reduced DL signaling overhead. In the case
`of separate indication of time and frequency/code resource, the set of HARQ-ACK timing values is configured by
`higher-layer and one of values is dynamically indicated by HARQ-ACK timing bit in DCI, and meanwhile, the set of
`frequency/code resource is configured by a separate higher-layer signaling and one of values is indicated by ARI/ARO-
`like bit in DCI. For long PUCCH, PUCCH time resource can be fully derived from the slot-level HARQ-ACK timing
`indication. For the short PUCCH, in addition to HARQ-ACK timing indication, semi-static configuration or dynamic
`indication in DCI is needed to identify the UL symbol index. In the case of beamformed system, UL symbols within
`one UL slot may be associated with receiving beams at gNB. The UL symbol to transmit short PUCCH could be
`implicitly derived from the gNB-side Rx beam indication. On the other hand, if there is no determinate relation between
`Rx beam and PUCCH transmission, explicit indication of UL symbol index should be applied. In the case of joint
`indication, for long PUCCH format, the UL slot is configured together with frequency/code resource in the PUCCH
`resource set, i.e., by a single higher-layer signaling. Then, the HARQ-ACK timing bit field can be omitted. For short
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`PUCCH format, UL symbol index and UL slot can be configured together with frequency/code resource in PUCCH
`resource set, or UL slot is configured in PUCCH resource set while UL symbol index is implicitly derived from beam
`indication or explicitly indicated by additional bit field in DCI, or the UL symbol is configured in PUCCH resource set
`and UL slot is derived by HARQ-ACK timing in DCI.
`Proposal 3: Consider both separate indication of PUCCH time resource and frequency/code-domain resource or
`joint indication of all resources.
`
`2.3 PUCCH duration indication
`
`Multiple PUCCH duration (long and short PUCCH) is supported in NR to cope with different transmission latency,
`different link budget and probably for the different UCI payload. Since the link budget may change slowly and the
`latency of a certain service type is pre-defined, it seems sufficient to semi-statically configure the PUCCH duration. For
`the UCI payload, it may vary dynamically with number of DL slots/scheduled DL cells (with dynamic HARQ-ACK
`codebook determination). It might be beneficial to enable dynamic switching between long PUCCH and short PUCCH,
`at least for UEs with relatively good link budget. For example, when there is only one or few HARQ-ACK bits reported
`by a cell center UE, short PUCCH can still meet the performance requirement and improve scheduling flexibility by
`enabling either full UL/UL centric or DL centric slot. The dynamic switching could be implemented by either explicit
`indication in DCI (i.e., adding one bit) or ARI-like indication wherein long/short PUCCH is included in PUCCH
`resource set configuration.
`
`Proposal 4: Further study the dynamic switching between long and short PUCCH in addition to semi-static
`configuration.
`
`3. Conclusion
`This contribution considered the design aspects for PUCCH resource allocation, and proposes the following.
`Proposal 1: NR supports multiple PUCCH formats for HARQ-ACK transmission based on HARQ-ACK payload.
`Consider down-selection from LTE PUCCH format based structures.
`
`Proposal 2: Further study the combination of implicit and explicit indication of PUCCH resource in terms of
`DCI overhead and UL resource utilization efficiency.
`
`Proposal 3: Consider both separate indication of PUCCH time resource and frequency/code-domain resource or
`joint indication of all resources.
`
`Proposal 4: Further study the dynamic switching between long and short PUCCH in addtion to semi-static
`configuration.
`
`Reference
`
`[1] R1-1702979, UL Control Channel Design: Short Format, Samsung.
`[2] R1-1702981, UL Control Channel Design: Long Format, Samsung.
`[3] R1-1702980, Multiplexing Short NR-PUCCH with Data or SRS, Samsung.
`[4] R1-1702982, Consideration of Variable Slot Length, Samsung.
`[5] R1-1702984, On UCI Multiplexing in PUSCH, Samsung.
`[6] R1-1700957, HARQ-ACK feedback with flexible timing, Samsung.
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