1. Single Stream Pilots in UL MU MIMO
January, 2016
Single Stream Pilots in UL MU MIMO
Date:
Authors:
Name
Affiliation
Address
Phone
Ron Porat
Broadcom
Feng Jiang
Sriram Venkateswaran
Matthew Fischer
Mingyue Ji
Leo Montreuil
Andrew Blanksby
Vinko Erceg
Ron Porat, Broadcom, et. al.

2. 2111 NE 25th Ave, Hillsboro OR 97124, USA
January, 2016
Authors (continued)
Robert Stacey
Intel
2111 NE 25th Ave, Hillsboro OR 97124, USA     
Shahrnaz Azizi
Po-Kai Huang
Qinghua Li
Xiaogang Chen
Chitto Ghosh
Laurent Cariou
Yaron Alpert
Assaf Gurevitz
Ilan Sutskover
Ron Porat, Broadcom, et. al.

3. Authors (continued) January, 2016 Hongyuan Zhang Marvell
Name
Affiliation
Address
Phone
Hongyuan Zhang
Marvell
5488 Marvell Lane, Santa Clara, CA, 95054
Yakun Sun
Lei Wang
Liwen Chu
Jinjing Jiang
Yan Zhang
Rui Cao
Sudhir Srinivasa
Bo Yu
Saga Tamhane
Mao Yu
Xiayu Zheng
Christian Berger
Niranjan Grandhe
Hui-Ling Lou
Ron Porat, Broadcom, et. al.

4. Authors (continued) January, 2016 Alice Chen Albert Van Zelst
Name
Affiliation
Address
Phone
Alice Chen
Qualcomm
5775 Morehouse Dr. San Diego, CA, USA
Albert Van Zelst
Straatweg 66-S Breukelen, 3621 BR Netherlands
Alfred Asterjadhi
Arjun Bharadwaj
Bin Tian
Carlos Aldana
1700 Technology Drive San Jose, CA 95110, USA
George Cherian
Gwendolyn Barriac
Hemanth Sampath
Lin Yang
Menzo Wentink
Naveen Kakani
2100 Lakeside Boulevard Suite 475, Richardson TX 75082, USA
Raja Banerjea
1060 Rincon Circle San Jose CA 95131, USA
Richard Van Nee
Ron Porat, Broadcom, et. al.

5. Authors (continued) January, 2016 Rolf De Vegt Sameer Vermani Qualcomm
Name
Affiliation
Address
Phone
Rolf De Vegt
Qualcomm
1700 Technology Drive San Jose, CA 95110, USA
Sameer Vermani
5775 Morehouse Dr. San Diego, CA, USA
Simone Merlin
Tao Tian
Tevfik Yucek  
VK Jones
Youhan Kim
Ron Porat, Broadcom, et. al.

6. Authors (continued) January, 2016 James Yee Mediatek
Name
Affiliation
Address
Phone
James Yee
Mediatek
No. 1 Dusing 1st Road, Hsinchu, Taiwan  
Alan Jauh
Chingwa Hu
Frank Hsu
Thomas Pare
USA
2860 Junction Ave, San Jose, CA 95134, USA
ChaoChun Wang
James Wang
Jianhan Liu
Tianyu Wu
Zhou Lan
Russell Huang
Joonsuk Kim
Apple
Aon Mujtaba  
Guoqing Li
Eric Wong
Chris Hartman
Ron Porat, Broadcom, et. al.

7. Authors (continued) January, 2016 Peter Loc Le Liu Jun Luo Yi Luo
Name
Affiliation
Address
Phone
Peter Loc
Huawei
Le Liu
F1-17, Huawei Base, Bantian, Shenzhen
Jun Luo
5B-N8, No.2222 Xinjinqiao Road, Pudong, Shanghai
Yi Luo
Yingpei Lin
Jiyong Pang
Zhigang Rong
10180 Telesis Court, Suite 365, San Diego, CA  NA
Rob Sun
303 Terry Fox, Suite 400 Kanata, Ottawa, Canada
David X. Yang
Yunsong Yang
Junghoon Suh
Jiayin Zhang
Edward Au
Teyan Chen
Yunbo Li
Ron Porat, Broadcom, et. al.

8. Authors (continued) January, 2016 Jinmin Kim LG Electronics
Name
Affiliation
Address
Phone
Jinmin Kim
LG Electronics
19, Yangjae-daero 11gil, Seocho-gu, Seoul , Korea
Kiseon Ryu
Jinyoung Chun
Jinsoo Choi
Jeongki Kim
Dongguk Lim
Suhwook Kim
Eunsung Park
JayH Park
HanGyu Cho
Thomas Derham
Orange
Bo Sun
ZTE
#9 Wuxingduan, Xifeng Rd., Xi'an, China
Kaiying Lv
Yonggang Fang
Ke Yao
Weimin Xing
Brian Hart
Cisco Systems
170 W Tasman Dr, San Jose, CA 95134
Pooya Monajemi
Ron Porat, Broadcom, et. al.

9. Authors (continued) January, 2016 Fei Tong Samsung Hyunjeong Kang
Name
Affiliation
Address
Phone
Fei Tong
Samsung
Innovation Park, Cambridge CB4 0DS (U.K.)
Hyunjeong Kang
Maetan 3-dong; Yongtong-Gu Suwon; South Korea
Kaushik Josiam
1301, E. Lookout Dr, Richardson TX 75070
(972)
Mark Rison
Rakesh Taori
(972)
Sanghyun Chang
Yasushi Takatori
NTT
1-1 Hikari-no-oka, Yokosuka, Kanagawa Japan  
Yasuhiko Inoue  
Shoko Shinohara
Yusuke Asai  
Koichi Ishihara  
Junichi Iwatani  
Akira Yamada
NTT DOCOMO
3-6, Hikarinooka, Yokosuka-shi, Kanagawa, , Japan
 3759
Ron Porat, Broadcom, et. al.

10. Authors (continued) January, 2016 Ron Porat, Broadcom, et. al. Name
Affiliation
Address
Phone
Masahito Mori
Sony Corp.
Yusuke Tanaka
Yuichi Morioka
Kazuyuki Sakoda
William Carney
Ron Porat, Broadcom, et. al.

11. January, 2016
Introduction
The current SFD supports single stream pilots for SU, DL/UL OFDMA and DL MU-MIMO transmissions
In this contribution we investigate the performance of single stream pilots for UL MU-MIMO, show that it performs well and propose to add support for this option
Ron Porat, Broadcom, et. al.

12. January, 2016
Proposal
Support single stream pilots in UL MU MIMO transmissions also
Apply pilot modulation during HE-LTF exactly as in UL MU-MIMO payload
Same implementation at the STA
Same implementation at the AP for UL MU-MIMO LTF and payload
CFO Estimation high level
Step 1: Estimate channel on pilot tones
On each pilot, interpolate channel estimates from neighboring tones
Step 2: Use channel estimate on pilots to estimate the phases on two HE-LTF symbols. Difference in phases is an estimate of the CFO.
More details in appendix
AP uses 1 bit in the trigger frame to indicate its preference between single stream pilots and orthogonal masking sequences for CFO estimation
No additional implementation burden at STA over today: spec framework mandates transmission of both masking sequences (for UL MU) and single stream pilots (for SU, DL/UL OFDMA, DL MU MIMO)
Ron Porat, Broadcom, et. al.

13. Simulation scenario January, 2016 AP: 8 antennas
STA: 6 STAs with CFO = ± 400 Hz
Channel: 11nD
Timing offset: uniformly from [0, 800] ns
CSD: [ ] ns
RF Impairments
LTFs: 2X & 4X
MCS: 7 & 9
Ron Porat, Broadcom, et. al.

14. January, 2016
Results: 2X LTF
Correction with single stream pilots is very close to the ideal case of zero CFO
Ron Porat, Broadcom, et. al.

15. January, 2016
Results: 4X LTF
Correction with single stream pilots is very close to the ideal case of zero CFO
Ron Porat, Broadcom, et. al.

16. January, 2016
Conclusion
Propose to add single stream pilots in UL MU MIMO transmissions
STA already supports single stream pilots
Performs well in challenging scenarios
AP uses 1 bit in the trigger frame to indicate its preference between single stream pilots and orthogonal masking sequences for CFO estimation
No additional implementation burden relative to today
STA needs to transmit masking sequences on LTFs (UL MU) and pilots (for SU, DL/UL OFDMA, DL MU)
AP needs to handle single stream pilots even in UL MU during payload decoding
Ron Porat, Broadcom, et. al.

17. January, 2016
SP #1
Do you support the following change/additions to the SFD:
For UL MU MIMO transmissions, support of single stream pilots and masking the LTF sequence of each spatial stream by a distinct orthogonal code is mandatory at the transmitter side (non AP STA).
The trigger frame shall use 1 bit to indicate whether the UL MU MIMO transmission following it uses single stream pilots or a mask on each spatial stream of the LTF sequence by a distinct orthogonal code.
Yes No
Abs
Ron Porat, Broadcom, et al.

18. Appendix 1: Algorithm January, 2016
For a single subcarrier, the received signal for channel estimation is
𝒀 𝑡 =𝑯 𝑷 𝒔+ 𝒏 𝑡 , (1)
and the channel estimation is
𝑯 = 1 𝑁 𝒀 𝒕 𝑷 𝑯 𝒔 ∗ ≈ 1 𝑁 𝑯 𝑷 𝑷 𝑯 =𝑯𝑴 , (2) where 𝒏 𝑡 is the additive noise on the HE-LTF and 𝒔 is the symbol in LTF sequence, 𝑴= 1 𝑁 𝑷 𝑷 𝐻 and 𝑷 is P-matrix (𝑷 𝑷 𝐻 =𝑁𝑰), and 𝑷 is the CFO polluted matrix, as shown in the following, e.g., for 4x4 P matrix, and ,
where 𝜃 𝑖 is 𝑖 th user’s phase shift during a single LTF symbol.
Ron Porat, Broadcom, et al.

19. Appendix 1: Algorithm January, 2016
After the last HE-LTF symbol, get CFO corrupted channel estimate
𝑯 =𝑯𝑴
For a pilot at tone k, interpolate neighboring tones to get a channel estimate. Eg. Linear interpolation:
𝑯 𝑝𝑖𝑙𝑜𝑡, 𝑘 = 𝑯 𝑘 𝑯 𝑘−1
On the k-th pilot tone of l-th HE-LTF symbol, do phase estimation for all the users using the interpolated channel:
𝜽 𝑙,𝑘 = 𝑠 𝑙,𝑘 ∗ × 𝑯 𝑝𝑖𝑙𝑜𝑡,𝑘 𝐻 𝑯 𝑝𝑖𝑙𝑜𝑡,𝑘 −1 𝑯 𝑝𝑖𝑙𝑜𝑡,𝑘 𝐻 𝒚 𝑙,𝑘
On the k-th pilot tone calculate the phase difference between the first and last HE-LTF symbols to estimate CFO:
𝜽 𝑒𝑠𝑡,𝑘 = 1 𝑁−1 𝑎𝑛𝑔𝑙𝑒 𝜽 𝑁,𝑘 − 𝑎𝑛𝑔𝑙𝑒( 𝜽 1,𝑘 )
Average the CFO estimation over all the K pilot tones:
𝜽 𝑎𝑣𝑒 = 1 𝐾 𝑘=1 𝐾 𝜽 𝑒𝑠𝑡,𝑘
Use CFO estimation 𝜽 𝑎𝑣𝑒 to build modified ZF or LMMSE receiver to detect data symbols and generate the corrected input for phase tracking during data payload:
𝑾 𝐿𝑀𝑀𝑆𝐸 =𝑴 𝑯 𝑯 𝑯 + 𝜎 𝑛 2 𝑰 −1 𝑯 𝑯
Ron Porat, Broadcom, et al.