1. WF on pre-DFT PT-RS pattern for DFTsOFDM
RAN1#90b, Prague, Czech Republic, October 2017
Agenda item:
R1-171XXXX
WF on pre-DFT PT-RS pattern for DFTsOFDM
Mitsubishi Electric, Ericsson, Nokia, NSB, IITH, IITM, CeWit, Tejas Networks, Reliance Jio, Spreadtrum, Sony, CMCC, Interdigital, Huawei, HiSilicon, AT&T, Samsung, ZTE, Sanechips, Sharp [DoCoMo, Vodafone]

2. Background The following agreements were made in the past meetings:
[RAN1#89] Uplink PTRS for DFT-s-OFDM waveform is supported.
Presence of PTRS for DFT-s-OFDM is UE-specifically configurable
Multiple pattern/density of PTRS for DFT-s-OFDM is supported
FFS: implicit or explicit signaling
[RAN1 NR AH#02] Support at least full symbol-level time density for time-domain PT-RS for DFT-S-OFDM (every PUSCH carrying symbol)
FFS: whether to support configurable symbol-level time density for time-domain PT-RS density reduction for DFT-S- OFDM
Note: If supported, the configuration can be implicit (associated with scheduled MCS and/or BW and/or DM-RS port(s)/position) or explicit, which is to be decided in next meeting
[RAN1#90] Confirm WA: Support Pre-DFT PT-RS insertion for UL DFT-S-OFDM.

3. Background
Concerning the exact pre-DFT pattern, the following was agreed [RAN1 NR AH#03]
For chunk-based pre-DFT PTRS insertion for DFTsOFDM, support the following
The supported values for K (chunk size) are 2 and 4
Implicit configuration depending on MCS/BW
The supported values for X (number of chunks/DFTsOFDM symbol) are at least 2 and 4
X implicitly depends on allocated bandwidth and/or MCS and/or K value
Implicit configuration can be subcarrier spacing dependent
FFS if K=1 is also supported and exact mechanism
When X=2 is configured, downselect among the following:
Alt. 1: chunks are placed head/tail of DFTsOFDM symbols containing PTRS
Alt. 2: chunks are placed middle/tail of the DFTsOFDM symbols containing PTRS
Alt. 3: chunks are placed head/middle of the DFTsOFDM symbols containing PTRS
Alt. 4: chunks are placed middle of each of the X equally-sized parts of the DFTsOFDM symbols containing PTRS
For PTRS sequence, downselect from the following options:
Option 1:
pi/2 BPSK PTRS is used for pi/2 BPSK PUSCH
[FFS] PTRS sequence consists of the outermost points of the PUSCH constellation
Option 2
Reuse the same sequence as PTRS or DMRS sequence for UL CP-OFDM
FFS: Time-domain PTRS density reduction is supported at least for allocated bands below N RB and/or some MCS
Time-domain pattern depends on DM-RS positions (DFTsOFDM positions near DMRS do not contain PTRS)
FFS: N value
FFS: every other DFTsOFDM symbol not neighbouring DM-RS positions does not contain PTRS
For RB allocation larger than N, PTRS density reduction is configured by RRC

4. Proposals
For chunk-based pre-DFT PTRS insertion for DFTsOFDM with X chunks of size K>1, support the following
For K=2, the samples in DFT domain are divided in X intervals, and the chunks are located in the first K samples of each interval
For K=4, the samples in DFT domain are divided in X intervals, where in the first interval the chunk is placed in the Head (first K samples), in the last interval the chunk is placed in the Tail (last K samples), and in the rest of intervals the chunk is placed in the middle of the interval
For PTRS for DFT-s-OFDM, support RRC-configured association between chunk-size/chunk-number and scheduled BW according to the table below
FFS default UE behaviour before RRC configuration
FFS value of Y (if different than 4)
FFS whether thersholds are MCS and/or subcarrier spacing dependent
Note: NRB0 can be equal to 0; when NRB0 is superior to 0, no PTRS is present for allocations less or equal to NRB0
Possible PTRS presence/absence is configured through RRC
Time-domain PTRS density is configured by RRC between every symbol and every other symbol
Time-domain pattern depends on DM-RS positions (DFTsOFDM positions after and/or before DMRS do not contain PTRS)
Scheduled BW
X x K
NRB0<NRB ≤NRB1
2x2
NRB1 <NRB≤NRB2
2x4
NRB2<NRB≤NRB3
4x2
NRB3<NRB≤NRB4
4x4
NRB > NRB4
Yx4

5. References
The following documents relating to pre-DFT PTRS pattern were submitted to RAN1#90b
R Further details of PTRS Huawei, HiSilicon
R Remaining details on PT-RS Intel Corporation
R Discussion on the remaining details on PT-RS vivo
R Discussion on PT-RS Samsung
R Remaining issues on PT-RS Spreadtrum
R On chunk-based for UL DFTsOFDM waveform Mitsubishi Electric
R Discussion on PT-RS design CMCC
R PT-RS support for pi/2 BPSK PUSCH IITH
R Remaining details on PT-RS NTT DOCOMO, INC.
R Details on PT-RS design Ericsson
R Remaining issues on PT-RS InterDigital, Inc.
R On remaining details of PT-RS design Nokia, Nokia Shanghai Bell
R PTRS considerations Qualcomm Incorporated