Post on 21-Dec-2015
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 robert.stacey@intel.com
Eldad Perahia eldad.perahia@intel.com
Shahrnaz Azizi shahrnaz.azizi@intel.com
Po-Kai Huang po-kai.huang@intel.com
Qinghua Li quinghua.li@intel.com
Xiaogang Chen xiaogang.c.chen@intel.com
Chitto Ghosh chittabrata.ghosh@intel.com
Rongzhen Yang rongzhen.yang@intel.com
1
Ron Porat
Broadcom
rporat@broadcom.com
Matthew Fischer mfischer@broadcom.com
Sriram Venkateswaran
Tu Nguyen
Vinko Erceg
1
Name Affiliation Address Phone email
1
doc.: IEEE 802.11-15/0099
Submission
January 2015
Ron Porat, BroadcomSlide 2
Authors (continued)
Fei Tong
Samsung
Innovation Park, Cambridge CB4 0DS (U.K.)
+44 1223 434633 f.tong@samsung.com
Hyunjeong Kang Maetan 3-dong; Yongtong-Gu
Suwon; South Korea +82-31-279-9028 hyunjeong.kang@samsung.co
m
Kaushik Josiam 1301, E. Lookout Dr, Richardson TX 75070
(972) 761 7437 k.josiam@samsung.com
Mark Rison Innovation Park,
Cambridge CB4 0DS (U.K.) +44 1223 434600 m.rison@samsung.com
Rakesh Taori 1301, E. Lookout Dr, Richardson TX 75070
(972) 761 7470 rakesh.taori@samsung.com
Sanghyun Chang Maetan 3-dong; Yongtong-Gu
Suwon; South Korea +82-10-8864-
1751 s29.chang@samsung.com
1
Name Affiliation Address Phone email
1
Lei Wang
Marvell
5488 Marvell Lane, Santa Clara, CA, 95054
858-205-7286 Leileiw@marvell.com
Hongyuan Zhang 5488 Marvell Lane,
Santa Clara, CA, 95054 hongyuan@marvell.com
Yakun Sun 5488 Marvell Lane,
Santa Clara, CA, 95054 yakunsun@marvell.com
Liwen Chu 5488 Marvell Lane,
Santa Clara, CA, 95054 liwenchu@marvell.com
Mingguan Xu 5488 Marvell Lane,
Santa Clara, CA, 95054 mxu@marvell.com
Jinjing Jiang 5488 Marvell Lane,
Santa Clara, CA, 95054 jinjing@marvell.com
Yan Zhang 5488 Marvell Lane,
Santa Clara, CA, 95054 yzhang@marvell.com
1
doc.: IEEE 802.11-15/0099
Submission
January 2015
Ron Porat, BroadcomSlide 3
Authors (continued)
Name Affiliation Address Phone email
1 Rui Cao
Marvell
5488 Marvell Lane, Santa Clara, CA, 95054
ruicao@marvell.com
Sudhir Srinivasa 5488 Marvell Lane,
Santa Clara, CA, 95054 sudhirs@marvell.com
Saga Tamhane 5488 Marvell Lane,
Santa Clara, CA, 95054 sagar@marvell.com
Mao Yu 5488 Marvell Lane,
Santa Clara, CA, 95054 my@marvel..com
Edward Au 5488 Marvell Lane,
Santa Clara, CA, 95054 edwardau@marvell.com
Hui-Ling Lu 5488 Marvell Lane,
Santa Clara, CA, 95054 hlou@marvell.com
1 Yasushi Takatori
NTT
1-1 Hikari-no-oka, Yokosuka, Kanagawa 239-0847 Japan
takatori.yasushi@lab.ntt.co.jp
Yasuhiko Inoue inoue.yasuhiko@lab.ntt.co.jp
Yusuke Asai asai.yusuke@lab.ntt.co.jp
Koichi Ishihara ishihara.koichi@lab.ntt.co.jp
Akira Kishida kishida.akira@lab.ntt.co.jp
Akira Yamada
NTT DOCOMO
3-6, Hikarinooka, Yokosuka-shi, Kanagawa, 239-8536,
Japan yamadaakira@nttdocomo.co
m
Fujio Watanabe 3240 Hillview Ave, Palo
Alto, CA 94304 watanabe@docomoinnovatio
ns.com
Haralabos Papadopoulos
hpapadopoulos@docomoinnovations.com
1
doc.: IEEE 802.11-15/0099
Submission
January 2015
Ron Porat, BroadcomSlide 4
Authors (continued)Name Affiliation Address Phone email
1 Phillip Barber
Huawei
The Lone Star State, TX pbarber@broadbandmobiletech.com
Peter Loc peterloc@iwirelesstech.com
Le Liu F1-17, Huawei Base, Bantian,
Shenzhen +86-18601656691 liule@huawei.com
Jun Luo 5B-N8, No.2222 Xinjinqiao
Road, Pudong, Shanghai jun.l@huawei.com
Yi Luo F1-17, Huawei Base, Bantian,
Shenzhen +86-18665891036 Roy.luoyi@huawei.com
Yingpei Lin 5B-N8, No.2222 Xinjinqiao
Road, Pudong, Shanghai linyingpei@huawei.com
Jiyong Pang 5B-N8, No.2222 Xinjinqiao
Road, Pudong, Shanghai pangjiyong@huawei.com
Zhigang Rong 10180 Telesis Court, Suite 365, San Diego, CA 92121
NA zhigang.rong@huawei.com
Rob Sun 303 Terry Fox, Suite 400 Kanata, Ottawa, Canada
Rob.Sun@huawei.com
David X. Yang F1-17, Huawei Base, Bantian,
Shenzhen david.yangxun@huawei.com
Yunsong Yang 10180 Telesis Court, Suite 365, San Diego, CA 92121
NA yangyunsong@huawei.com
Zhou Lan F1-17, Huawei Base, Bantian,
SHenzhen +86-18565826350 Lanzhou1@huawei.com
Junghoon Suh 303 Terry Fox, Suite 400 Kanata, Ottawa, Canada
Junghoon.Suh@huawei.com
Jiayin Zhang 5B-N8, No.2222 Xinjinqiao
Road, Pudong, Shanghai +86-18601656691 zhangjiayin@huawei.com
1
doc.: IEEE 802.11-15/0099
Submission
January 2015
Ron Porat, BroadcomSlide 5
Authors (continued)
Laurent cariou Orange
Laurent.cariou@orange.com
Thomas Derham thomas.derham@orange.com
1 Wookbong Lee
LG Electronics
19, Yangjae-daero 11gil, Seocho-gu, Seoul 137-130,
Korea wookbong.lee@lge.com
Kiseon Ryu kiseon.ryu@lge.com
Jinyoung Chun jiny.chun@lge.com
Jinsoo Choi js.choi@lge.com
Jeongki Kim jeongki.kim@lge.com
Giwon Park giwon.park@lge.com
Dongguk Lim dongguk.lim@lge.com
Suhwook Kim suhwook.kim@lge.com
Eunsung Park esung.park@lge.com
HanGyu Cho hg.cho@lge.com
1 Albert Van Zelst
Qualcomm
Straatweg 66-S Breukelen, 3621 BR Netherlands
allert@qti.qualcomm.com
Alfred Asterjadhi
5775 Morehouse Dr. San Diego, CA, USA
aasterja@qti.qualcomm.com
Bin Tian 5775 Morehouse Dr. San
Diego, CA, USA btian@qti.qualcomm.com
Carlos Aldana 1700 Technology Drive San
Jose, CA 95110, USA caldana@qca.qualcomm.com
George Cherian 5775 Morehouse Dr. San
Diego, CA, USA gcherian@qti.qualcomm.com
Gwendolyn Barriac
5775 Morehouse Dr. San Diego, CA, USA
gbarriac@qti.qualcomm.com
1
Name Affiliation Address Phone email
1
doc.: IEEE 802.11-15/0099
Submission
January 2015
Ron Porat, BroadcomSlide 6
Hemanth Sampath
Qualcomm
5775 Morehouse Dr. San Diego, CA, USA
hsampath@qti.qualcomm.com
Menzo Wentink Straatweg 66-S Breukelen,
3621 BR Netherlands mwentink@qti.qualcomm.co
m
Richard Van Nee Straatweg 66-S Breukelen,
3621 BR Netherlands rvannee@qti.qualcomm.com
Rolf De Vegt 1700 Technology Drive San
Jose, CA 95110, USA rolfv@qca.qualcomm.com
Sameer Vermani 5775 Morehouse Dr. San
Diego, CA, USA svverman@qti.qualcomm.co
m
Simone Merlin 5775 Morehouse Dr. San
Diego, CA, USA smerlin@qti.qualcomm.com
Tevfik Yucek 1700 Technology Drive San
Jose, CA 95110, USA tyucek@qca.qualcomm.com
VK Jones 1700 Technology Drive San
Jose, CA 95110, USA vkjones@qca.qualcomm.com
Youhan Kim 1700 Technology Drive San
Jose, CA 95110, USA youhank@qca.qualcomm.co
m
1
Name Affiliation Address Phone email
1
Authors (continued)
doc.: IEEE 802.11-15/0099
Submission
January 2015
Ron Porat, BroadcomSlide 7
James Yee
Mediatek
No. 1 Dusing 1st Road, Hsinchu, Taiwan
+886-3-567-0766 james.yee@mediatek.com
Alan Jauh alan.jauh@mediatek.com
Chingwa Hu chinghwa.yu@mediatek.com
Frank Hsu frank.hsu@mediatek.com
` 1 Thomas Pare
Mediatek USA
2860 Junction Ave, San Jose, CA 95134, USA
+1-408-526-1899 thomas.pare@mediatek.com
ChaoChun Wang chaochun.wang@mediatek.com
James Wang james.wang@mediatek.com
Jianhan Liu Jianhan.Liu@mediatek.com
Tianyu Wu tianyu.wu@mediatek.com
Russell Huang russell.huang@mediatek.com
` 1
Name Affiliation Address Phone email
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
Ron Porat, BroadcomSlide 8
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
Ron Porat, BroadcomSlide 9
doc.: IEEE 802.11-15/0099
Submission
Channel models & implications
January 2015
Ron Porat, BroadcomSlide 10
• 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
Ron Porat, BroadcomSlide 11
• 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
Ron Porat, BroadcomSlide 13
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
Ron Porat, BroadcomSlide 14
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-NLoS: PER for MCS 0-4
January 2015
Ron Porat, BroadcomSlide 15
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-NLoS: PER for MCS 5-9
January 2015
Ron Porat, BroadcomSlide 16
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
Goodput metric used for comparison
January 2015
Ron Porat, BroadcomSlide 17
• 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
Ron Porat, BroadcomSlide 18
• 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
Ron Porat, BroadcomSlide 19
• 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)
Absolute Goodput Goodput relative to (64 FFT, 0.8 us CP)
doc.: IEEE 802.11-15/0099
Submission
Goodput: UMi-LoS
January 2015
Ron Porat, BroadcomSlide 20
• 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
Absolute Goodput Goodput relative to (64 FFT, 0.8 us CP)
doc.: IEEE 802.11-15/0099
Submission
Goodput: UMi-NLoS
January 2015
Ron Porat, BroadcomSlide 21
• 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
Absolute Goodput Goodput relative to (64 FFT, 0.8 us CP)
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
Ron Porat, BroadcomSlide 22
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
Ron Porat, BroadcomSlide 23
doc.: IEEE 802.11-15/0099
Submission
Results
January 2015
Ron Porat, BroadcomSlide 24
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
Ron Porat, BroadcomSlide 25
• 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
Ron Porat, BroadcomSlide 26
• 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
Ron Porat, BroadcomSlide 27
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
Ron Porat, BroadcomSlide 28
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
Ron Porat, BroadcomSlide 29
doc.: IEEE 802.11-15/0099
Submission
Appendix
January 2015
Ron Porat, BroadcomSlide 30
doc.: IEEE 802.11-15/0099
Submission
UMa-NLoS: PER for MCS 0-4
January 2015
Ron Porat, BroadcomSlide 31
doc.: IEEE 802.11-15/0099
Submission
Goodput: UMa-NLoS
January 2015
Ron Porat, BroadcomSlide 32
Absolute Goodput Goodput relative to (64 FFT, 0.8 us CP)
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
Ron Porat, BroadcomSlide 33
AP has 4 antennas, STA has 1 antennaTiming acquired from L-LTF