Doc.: IEEE 802.11-15/0099 Submission Payload Symbol Size for 11ax January 2015 Ron Porat,...

doc.: IEEE 802.11-15/0099

Submission

Payload Symbol Size for 11ax

January 2015

Ron Porat, BroadcomSlide 1

Date: 2015-01-12

Authors:

Robert Stacey

Intel

2111 NE 25th Ave, Hillsboro OR 97124, USA

+1-503-724-893 [email protected]

Eldad Perahia [email protected]

Shahrnaz Azizi [email protected]

Po-Kai Huang [email protected]

Qinghua Li [email protected]

Xiaogang Chen [email protected]

Chitto Ghosh [email protected]

Rongzhen Yang [email protected]

1

Ron Porat

Broadcom

[email protected]

Matthew Fischer [email protected]

Sriram Venkateswaran

Tu Nguyen

Vinko Erceg

1

Name Affiliation Address Phone email

1

doc.: IEEE 802.11-15/0099

Submission

January 2015


Authors (continued)

Fei Tong

Samsung

Innovation Park, Cambridge CB4 0DS (U.K.)

+44 1223 434633 [email protected]

Hyunjeong Kang Maetan 3-dong; Yongtong-Gu

Suwon; South Korea +82-31-279-9028 [email protected]

m

Kaushik Josiam 1301, E. Lookout Dr, Richardson TX 75070

(972) 761 7437 [email protected]

Mark Rison Innovation Park,

Cambridge CB4 0DS (U.K.) +44 1223 434600 [email protected]

Rakesh Taori 1301, E. Lookout Dr, Richardson TX 75070

(972) 761 7470 [email protected]

Sanghyun Chang Maetan 3-dong; Yongtong-Gu

Suwon; South Korea +82-10-8864-

1751 [email protected]

1


1

Lei Wang

Marvell

5488 Marvell Lane, Santa Clara, CA, 95054

858-205-7286 [email protected]

Hongyuan Zhang 5488 Marvell Lane,

Santa Clara, CA, 95054 [email protected]

Yakun Sun 5488 Marvell Lane,


Liwen Chu 5488 Marvell Lane,


Mingguan Xu 5488 Marvell Lane,


Jinjing Jiang 5488 Marvell Lane,


Yan Zhang 5488 Marvell Lane,


1

doc.: IEEE 802.11-15/0099

Submission

January 2015


Authors (continued)


1 Rui Cao

Marvell

5488 Marvell Lane, Santa Clara, CA, 95054

[email protected]

Sudhir Srinivasa 5488 Marvell Lane,


Saga Tamhane 5488 Marvell Lane,


Mao Yu 5488 Marvell Lane,


Edward Au 5488 Marvell Lane,


Hui-Ling Lu 5488 Marvell Lane,


1 Yasushi Takatori

NTT

1-1 Hikari-no-oka, Yokosuka, Kanagawa 239-0847 Japan

[email protected]

Yasuhiko Inoue [email protected]

Yusuke Asai [email protected]

Koichi Ishihara [email protected]

Akira Kishida [email protected]

Akira Yamada

NTT DOCOMO

3-6, Hikarinooka, Yokosuka-shi, Kanagawa, 239-8536,

Japan [email protected]

m

Fujio Watanabe 3240 Hillview Ave, Palo

Alto, CA 94304 watanabe@docomoinnovatio

ns.com

Haralabos Papadopoulos

[email protected]

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Submission

January 2015


Authors (continued)Name Affiliation Address Phone email

1 Phillip Barber

Huawei

The Lone Star State, TX [email protected]

Peter Loc [email protected]

Le Liu F1-17, Huawei Base, Bantian,

Shenzhen +86-18601656691 [email protected]

Jun Luo 5B-N8, No.2222 Xinjinqiao

Road, Pudong, Shanghai [email protected]

Yi Luo F1-17, Huawei Base, Bantian,

Shenzhen +86-18665891036 [email protected]

Yingpei Lin 5B-N8, No.2222 Xinjinqiao


Jiyong Pang 5B-N8, No.2222 Xinjinqiao


Zhigang Rong 10180 Telesis Court, Suite 365, San Diego, CA 92121

NA [email protected]

Rob Sun 303 Terry Fox, Suite 400 Kanata, Ottawa, Canada

[email protected]

David X. Yang F1-17, Huawei Base, Bantian,

Shenzhen [email protected]

Yunsong Yang 10180 Telesis Court, Suite 365, San Diego, CA 92121

NA [email protected]

Zhou Lan F1-17, Huawei Base, Bantian,

SHenzhen +86-18565826350 [email protected]

Junghoon Suh 303 Terry Fox, Suite 400 Kanata, Ottawa, Canada

[email protected]

Jiayin Zhang 5B-N8, No.2222 Xinjinqiao

Road, Pudong, Shanghai +86-18601656691 [email protected]

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doc.: IEEE 802.11-15/0099

Submission

January 2015


Authors (continued)

Laurent cariou Orange

[email protected]

Thomas Derham [email protected]

1 Wookbong Lee

LG Electronics

19, Yangjae-daero 11gil, Seocho-gu, Seoul 137-130,

Korea [email protected]

Kiseon Ryu [email protected]

Jinyoung Chun [email protected]

Jinsoo Choi [email protected]

Jeongki Kim [email protected]

Giwon Park [email protected]

Dongguk Lim [email protected]

Suhwook Kim [email protected]

Eunsung Park [email protected]

HanGyu Cho [email protected]

1 Albert Van Zelst

Qualcomm

Straatweg 66-S Breukelen, 3621 BR Netherlands

[email protected]

Alfred Asterjadhi

5775 Morehouse Dr. San Diego, CA, USA

[email protected]

Bin Tian 5775 Morehouse Dr. San

Diego, CA, USA [email protected]

Carlos Aldana 1700 Technology Drive San

Jose, CA 95110, USA [email protected]

George Cherian 5775 Morehouse Dr. San


Gwendolyn Barriac


[email protected]

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1

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Submission

January 2015


Hemanth Sampath

Qualcomm


[email protected]

Menzo Wentink Straatweg 66-S Breukelen,

3621 BR Netherlands [email protected]

m

Richard Van Nee Straatweg 66-S Breukelen,

3621 BR Netherlands [email protected]

Rolf De Vegt 1700 Technology Drive San


Sameer Vermani 5775 Morehouse Dr. San


m

Simone Merlin 5775 Morehouse Dr. San


Tevfik Yucek 1700 Technology Drive San


VK Jones 1700 Technology Drive San


Youhan Kim 1700 Technology Drive San


m

1


1

Authors (continued)

doc.: IEEE 802.11-15/0099

Submission

January 2015


James Yee

Mediatek

No. 1 Dusing 1st Road, Hsinchu, Taiwan


Alan Jauh [email protected]

Chingwa Hu [email protected]

Frank Hsu [email protected]

` 1 Thomas Pare

Mediatek USA

2860 Junction Ave, San Jose, CA 95134, USA


ChaoChun Wang [email protected]

James Wang [email protected]

Jianhan Liu [email protected]

Tianyu Wu [email protected]

Russell Huang [email protected]

` 1


1

Authors (continued)

doc.: IEEE 802.11-15/0099

Submission

Outline

• The need for larger symbol size for 11ax payloads has been discussed previously– Eg: [1] investigated the impact of CFO estimation on symbols with larger FFT sizes

(256 and 512 FFT)

• We have investigated several symbol durations for the payload and propose a new symbol duration

• We also follow up with a proposal for the choices of CP

• The proposals are verified via simulations that show– Significant Goodput gains over 11ac symbol and CP lengths of 3.2 us and 0.8 us

respectively– Robust performance in outdoor UL OFDMA

January 2015


doc.: IEEE 802.11-15/0099

Submission

Payload Symbol & CP Sizes

• We propose to replace the current payload symbol duration (3.2 us) with longer symbol duration 12.8 us in order to meet the following 11ax requirements– Robustness in outdoor channels– Greater tolerance to timing jitter across users in UL MU/OFDMA– Higher indoor efficiency (by lowering CP overhead)

• We also propose the three following CP sizes – 0.8 us: 11ac long GI, targeting improved efficiency in indoor settings– 1.6 us: percent-wise 11ac short GI, targeting high efficiency in outdoor channels and

indoor UL MU-MIMO/OFDMA– 3.2 us: percent-wise 11ac long GI, targeting robustness in the more demanding case of

outdoor UL MU-MIMO/OFDMA

January 2015


doc.: IEEE 802.11-15/0099

Submission

Channel models & implications

January 2015


• Outdoor channels– UMi-LoS, UMi-NLoS, UMa-NLoS

• NLoS channels have large delay spreads with significant probability • Intersymbol interference leads to high error floors

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 50

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1ITU RMS Delay Spread CDF

[uS]

UMi NLOS

UMi LOSUMa NLOS

UMa LOS

0.8 us CP leads to error floors Need longer CPs

doc.: IEEE 802.11-15/0099

Submission

Spectral efficiency

January 2015


• Assume a fixed transmission bandwidth and choose an MCS• R = code rate, bps = bits/sample (in the frequency domain. Eg. 256 QAM, bps = 8)• Nfft = symbol FFT size, Ndata = #data tones/symbol, Ncp = #CP samples

Tone utilization

Depends only on MCSDecreases as Ncp increases

Unless we increase Nfft

Increases as Ncp increases

As PER decreases for ISI channels

For a given Ncp (dictated by channel length), increase Nfft for smaller overheads and greater spectral efficiency

Spectral Efficiency

doc.: IEEE 802.11-15/0099

Submission

Simulation setup

January 2015

Ron Porat, Broadcom?

Slide 12

• Packet structure– Payload

• 1000 bytes• FFT sizes: 64, 128, 256 FFT• Data tones as defined for corresponding FFT sizes in 11ac• CP sizes: 0.8 us, 1.6 us

– 11ax-LTF: 1 symbol, same (FFT size, GI) as payload– 11ax-Preamble: 3 symbols, 64 FFT (precise structure undecided now, but # guided by 11ac)– How is the preamble relevant?

• Pilots used for phase tracking, reduce CFO estimation error

• 20MHz bandwidth, SISO, BCC • Real processing

– Channel estimation, timing, frequency offset estimation, phase tracking, phase noise: all real

L-STF L-LTF L-SIG11ax

Preamble 11ax-LTF Payload

doc.: IEEE 802.11-15/0099

Submission

UMi-LoS: PER for MCS 0-4

January 2015


PERs with 1.6 us GI (right figure) smaller than PERs with 0.8 us GI (left figure)

Even for a given GI, increasing FFT size reduces PER (ICI corrupted samples is a smaller fraction of the total number of samples)

doc.: IEEE 802.11-15/0099

Submission

UMi-LoS: PER for MCS 5-9

January 2015




doc.: IEEE 802.11-15/0099

Submission

UMi-NLoS: PER for MCS 0-4

January 2015




doc.: IEEE 802.11-15/0099

Submission

UMi-NLoS: PER for MCS 5-9

January 2015




doc.: IEEE 802.11-15/0099

Submission

Goodput metric used for comparison

January 2015


• Goodput = max spectral efficiency obtained by picking the best MCS (for each SNR)

• For a given CP size Ncp, choose largest possible Nfft • CP overhead decreases

• For a given FFT size Nfft , there is a tradeoff in choosing Ncp • Small Ncp : small overhead, but PER may be large

• Large Ncp : PER is small, but overhead large

• Choose the sweet spot for Ncp

Spectral Efficiency

doc.: IEEE 802.11-15/0099

Submission

Goodput: AWGN

January 2015


• For best results, pick as large an FFT as possible and then pick the smallest CP• Increasing CP has no PER benefit in AWGN, increasing FFT reduces overhead

• Using (256 FFT, 0.8 us CP) gives 1.32x goodput of (64 FFT, 0.8 us CP)

Absolute Goodput Goodput relative to (64 FFT, 0.8 us CP)

doc.: IEEE 802.11-15/0099

Submission

Goodput: 11nD

January 2015


• Using (256 FFT, 0.8 us CP) gives ~1.3x goodput of (64 FFT, 0.8 us CP)

• Since channels have small delay spreads, 0.8 us CP has 6-7% better throughput than 1.6 us CP (256 FFT, around 15-20 dB)


doc.: IEEE 802.11-15/0099

Submission

Goodput: UMi-LoS

January 2015


• At high SNR• Best to use large FFT with longer CP (256 FFT, 1.6 us CP)• (256 FFT, 1.6 us CP) gives nearly 2.2x goodput of (64 FFT, 0.8 us CP)

• At small SNR• Thermal noise dominates ISI: increasing CP doesn’t give substantial PER gains• Stick to smaller CPs, but use larger FFTs: (256 FFT, 0.8 us CP) works best


doc.: IEEE 802.11-15/0099

Submission

Goodput: UMi-NLoS

January 2015


• Large delay spreads leads to high ISI• Best to use large FFT with longer CP (256 FFT, 1.6 us)• (256 FFT, 1.6 us CP) gives ~2.5x goodput of (64 FFT, 0.8 us CP) at 25 dB SNR


doc.: IEEE 802.11-15/0099

Submission

Challenge of UL-OFDMA

• Timing jitter across users on the UL effectively increases channel delay spread. What is the impact on performance?– Impact of intended user delay on himself– Impact of delay of interfering users on intended user

• Sources of timing jitter– Different round trip delay– Different timing acquisition points due to different channel delay spreads

and noise– Net timing jitter ~1.3 us (details in Appendix)

January 2015


doc.: IEEE 802.11-15/0099

Submission

Simulation setup

• UL OFDMA with 4 users• Each user has one antenna, AP has 4 Rx antenna• 20MHz, 256 FFT

– Each user is allocated a contiguous block of 56 tones.– User allocations are fixed, and the second user (middle one) is the desired user (PER/Goodput

are calculated for this user)• GI values considered: 1.6us, 3.2us • ITU UMi NLOS channel • 1000 bytes packets• Real channel estimation from one LTF

January 2015


doc.: IEEE 802.11-15/0099

Submission

Results

January 2015


Interfering users have no jitterFor intended user delay of 1.2 usGoodput with 3.2 us GI = 1.16x

Goodput with 1.6 us GI

doc.: IEEE 802.11-15/0099

Submission

Discussion

January 2015


• Summary– 256 FFT consistently outperforms 11ac symbol duration– Goodput gains range from 1.3x-2.5x depending on channel– Use 0.8 us CP with 256 FFT for high efficiency in indoor channels– Use 1.6 us CP with 256 FFT for greater robustness to long outdoor channels and indoor UL

OFDMA/MU-MIMO– Use 3.2 us CP with 256 FFT for robust performance in outdoor UL OFDMA/MU-MIMO

• Why not even higher FFT sizes, say 512 FFT over 20 MHz?– Implementation complexities increase with increasing FFT sizes and bandwidths– Tones are more narrowly spaced , CFO correction needs to be very precise: challenging task [1]– Incremental gain over 256 FFT (3-6% depending on CP size) too small for increased complexity– 256 FFT size in 20 MHz seems to be the sweet spot between performance and implementation

complexities

doc.: IEEE 802.11-15/0099

Submission

Proposal

January 2015


• We propose that 11ax shall have one longer payload symbol size of duration 12.8 us based on a 256 FFT in 20 MHz– And correspondingly 512 FFT in 40 MHz, 1024 FFT in 80 MHz/80+80 MHz and 2048

FFT in 160 MHz

• We also propose to use the following CP sizes: 0.8 us, 1.6 us and 3.2 us

doc.: IEEE 802.11-15/0099

Submission

References

[1] 11-14-0801-00-00ax-envisioning-11ax-phy-structure-part-ii

January 2015


doc.: IEEE 802.11-15/0099

Submission

Straw Poll #1

• Do you agree to add to the TG Specification Framework:

– 3.y.z. Data symbols in an HE PPDU shall use DFT period of 12.8 us and subcarrier spacing of 78.125 kHz.

• Yes• No• Abstain

January 2015


doc.: IEEE 802.11-15/0099

Submission

Straw Poll #2

• Do you agree to add to the TG Specification Framework:

– 3.y.z. Data symbols in an HE PPDU shall support guard interval durations of 0.8 us, 1.6 us and 3.2 us.

• Yes• No• Abstain

January 2015


doc.: IEEE 802.11-15/0099

Submission

Appendix

January 2015


doc.: IEEE 802.11-15/0099

Submission

UMa-NLoS: PER for MCS 0-4

January 2015


doc.: IEEE 802.11-15/0099

Submission

Goodput: UMa-NLoS

January 2015



doc.: IEEE 802.11-15/0099

Submission

Sources of timing jitter

• Different round trip delays can contribute 0.6 us (~ 200 m)

• Timing acquisition on DL can contribute 0.7 us jitter in UMi-NLoS channels. For example, at 10 dB in figure below, 14 samples @ 20 MHz = 0.7 us

January 2015


AP has 4 antennas, STA has 1 antennaTiming acquired from L-LTF

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