1. Summary of offline discussion for PDCCH structure
3GPP TSG RAN WG1 Meeting 90bis
Prague, CZ, 9th – 13th, October 2017
Agenda item:
R1-17xxxxx
Summary of offline discussion for PDCCH structure
NTT DOCOMO, INC.

2. Highlights Following are identified as key discussion topics:
Issue 0: Wideband RS (working assumption)
Let’s focus on whether to conform the working assumption
Issue 1: Interleaver design
Let’s focus on discussion on 1-step interleaver vs 2-step interleaver
Issue 2: Details on DMRS design
Let’s discuss after making progress on issue 0 and issue 1

3. Issue 0: Wideband RS - Background
Whether to conform the working assumption?
For a CORESET, precoder granularity in frequency domain is:
Configurable between i) equal to the REG bundle size in the frequency domain; or ii) equal to the number of contiguous RBs in the frequency domain within the CORESET
For ii), DMRS is mapped over all REGs within the CORESET.
Situation on Monday online:
Cannot see the performance benefit (ZTE and Ericsson)
0.7 – 1.5dB performance gain showed (Qualcomm, Samsung, and CATT)

4. Issue 0: Wideband RS - Discussions
Parameter
Value
Carrier Frequency
4 GHz
Control Resource Set Bandwidth
18 MHz
Sub-carrier Spacing
15 kHz
DCI Payload Size
20 bits + CRC
Modulation
QPSK
Channel Coding
Polar code with CRC-aided list-8 decoder; 19bit CRC
Aggregation Level 8
REG bundle size
6 REGs per bundle
Number of OFDM symbols for NR-PDCCH 1
Channel Model
TDL-A 30ns; TDL-B 300ns; TDL-C 30ns; TDL-C 300ns; 3kmph UE speed
gNB antenna configuration
2Tx
UE antenna configuration
2Rx
Channel Estimation
Practical with MRC
Noise Estimation
Ideal
Transmission Diversity Scheme
1-port precoder cycling for ’inband RS’
S-CDD for ’wideband RS (65ns delay)
Resource mapping
Distributed transmission
DMRS density
1/4
R (Ericsson)

5. Issue 0: Wideband RS - Discussions
R (ZTE)
Item
Value
Channel
TDL-A
DS = 300ns, 1000ns
Speed = 3kmph
Antenna
2*2
Frequency
4GHz
Numerology
BW = 10MHz(50RB)
SCS = 15kHz
DMRS overhead
1/4
Aggregation level 8
CCE size
6 REGs per CCE
Bundle size
3/6
Payload size
20+16(CRC)
Transmit scheme
sCDD
Mapping scheme
Interleaving
CORESET duration
3OFDM symbol(s)
Coding
TBCC
Channel estimation
MMSE

6. Issue 0: Wideband RS - Discussions
R (CATT)
Parameter
Value NR
LTE
Channel
TDL-C-1000ns
System BW (RBs)
10 MHz
CORESET BW 50
CORESET duration 2
CFI = 2
Number of TX ports 1
2 CRS ports
Tx Diversity
1 port with precoder cycling
SFBC
Antenna configuration
2Tx 2Rx AL
2,4,8
CCE-to-REG mapping
Time-first mapping, LTE PDCCH interleaver
DCI size
60bits+16bits CRC
DMRS density
1/4
REG bundling size 6
For 6 BS: 3 in freq, 2 in time
Precoder granularity
REG Bundle size in frequency domain;
Wideband RS

7. Issue 0: Wideband RS - Discussions
ZTE comments:
1: SINR of -6dB is achievable even without wideband RS
2: Wideband RS consumes more energy
3: Wideband RS creates more inter-cell interference
4: Wideband RS makes resource sharing b/w PDCCH and PDSCH more difficult
5: Wideband RS makes beam-forming/multiplexing more difficult

8. Issue 0: Wideband RS - Proposals
Whether to conform the working assumption?
For a CORESET, precoder granularity in frequency domain is:
Configurable between i) equal to the REG bundle size in the frequency domain; or ii) equal to the number of contiguous RBs in the frequency domain within the CORESET
For ii), DMRS is mapped over all REGs within the CORESET.

9. Issue 1: Interleaver design - Background
1-step interleaver vs 2-step interleaver
1-step interleaver is supported by: Ericsson, ZTE, Intel, Samsung, OPPO, InterDigital, Nokia, Motorola Mobility, Lenovo, CATT (10)
2-step interleaver is supported by: Huawei, vivo, LG, DOCOMO, MediaTek, Qualcomm (6)

10. Issue 1: Interleaver design - Discussions
Considering the current situation, it would be better to consider 1- step interleaver; following are questions to 2-step interleaver camps
Q1: What problem is found on 1-step interleaver?
If it is the blocking probability in case of overlapped CORESET, how much 2-step interleaver can reduce it?
Q2: What 1-step interleaver design is acceptable for 2-step interleaver supporting companies?

11. Issue 1: Interleaver design - Discussions
1-step vs 2-step
1-step interleaver:
Firstly, no strong motivation for overlapping CORESETs are found (Samsung)
If the number of columns/rows is configurable, and by choosing proper values for overlapping CORESETs, it is possible to achieve the same/similar benefit as 2-step interleaver (Samsung, Nokia)
2-step interleaver:
As long as the second step interleaver is common among overlapping CORESETs, the blocking can be suppressed simply, which is also beneficial for operators. Configuring proper settings for 1-step interleaver is complicated (Qualcomm, Huawei)
The value of X affects how much frequency-diversity order is obtained. According to the preliminary simulation results, diversity order of 2 would offer similar performance with full distribution of 1-step interleaver. Therefore, the value of X can be fixed to 12 – Try to obtain the results within the day (Huawei)
If no consensus is made by Friday, we will define LTE based interleaver with a specific design with the interleaver unit as a REG bundle

12. Annex – RS aspects Wideband RS DMRS pattern DMRS sequence/scrambling
Confirm the WA (Intel, Samsung, CATT, ITRI, DOCOMO, MediaTek, Qualcomm)
Use wideband RS for CORESET configured MIB (Samsung)
Do not confirm the WA (ZTE, Nokia, Ericsson)
Confirm the part of the WA (only precoder-granularity) (Ericsson)
Modify the WA such that DMRS is mapped over all REGs within the PDCCH only when AL=8 (FFS: AL=4) (Nokia)
DMRS pattern
Conform the WA that DMRS are evenly distributed (Ericsson, Intel, vivo, CMCC, DOCOMO, Nokia)
#2, #6, #10 (Ericsson, ITRI)
#1, #5, #10 (Nokia)
VCID-based cyclic-shift position (Intel)
No cyclic-shift with possible time-domain OCC (CMCC)
DMRS sequence/scrambling
Gold sequence as in LTE (Ericsson, Intel)
VCID-based initialization for RRC connected case (Intel, Samsung, MediaTek, Qualcomm)
Cell-ID based initialization for CSS during initial access (Samsung, LGE, MediaTek, Qualcomm)

13. Annex – Interleaver aspects
1-step interleaver (Ericsson, ZTE, Intel, Samsung, OPPO, InterDigital, Nokia, Motorola Mobility, Lenovo, CATT)
𝑓(𝑖)= 𝑖 𝑚𝑜𝑑 𝑁 𝑆𝐸𝐺 𝐶𝑆 𝑁 𝑅𝐵 𝑆𝐸𝐺 𝐿/ 𝑁 𝑆𝑌𝑀 𝐶𝑆 + 𝑖/ 𝑁 𝑆𝐸𝐺 𝐶𝑆 where L is the number of REGs in a REG bundle, N_SEG is the number of segments in the CORESET, N_SYM is the number of OFDM symbols in the CORESET, and N_RB is the number of contiguous RBs in a segment (Ericsson)
A block interleaver with configurable rows with the interleaving unit as a REG bundle (ZTE, Intel)
The interleaving function is LTE sub-block interleaver (Intel)
A block interleaver with configurable number of columns and with configurable inter-column permutation and cyclic-shift based on cell-ID for interleaver input (Samsung)
LTE sub-block interleaver (OPPO, InterDigital, Nokia)
With cyclic REG bundle randomization with number of rows being determined by REG bundle size and possible inter-column permutation and cell-ID based cyclic shift (Nokia)
2-step interleaver (Huawei, vivo, LG, DOCOMO, MediaTek, Qualcomm)
First step is an interleaver I1 within X logical REG bundles with the interleaving unit equal to a REG bundle (Huawei, vivo, LG, DOCOMO, Qualcomm)
Interleaver I1 is EPDCCH interleaver based (Huawei)
Interleaver I1 is PDCCH or EPDCCH interleaver (vivo)
Interleaver I1 is a block interleaver (LG)
The value of X is configurable (DOCOMO)
X=12 (Qualcomm)
Second step is an interleaver I2 within the CORESET with the interleaving unit equal to M RBs (Huawei, vivo, LG, DOCOMO, Qualcomm)
Interleaver I2 is a block interleaver (Huawei, vivo)
Interleaver I2 is the sub-block interleaver (LG)
M is 6 (Huawei, Qualcomm?)