doc.:ieee 802.11-10/0070r5 submission march 2010 hongyuan zhang et al.slide 1 802.11ac preamble...
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Hongyuan Zhang et al.Slide 1
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Slide 1
802.11ac Preamble
Authors: Date: 2010-03-15
Name Company Address Phone email Hongyuan Zhang Marvell 5488 Marvell Lane, Santa
Clara CA, 95054 [email protected]
Raja Banerjea Marvell 5488 Marvell Lane, Santa Clara CA, 95054
Vinko Erceg Broadcom San Diego, CA [email protected]
Joonsuk Kim Broadcom 190 Mathilda Place Sunnyvale, California 94086
Eldad Perahia Intel 2111 NE 25th Ave, Hillsboro, OR 97124
Ning Zhang Atheros 5480 Great America Parkway, Santa Clara, CA 95054, USA
Richard Van Nee Qualcomm Netherlands [email protected]
Youngsoo Kim Samsung Mt. 14-1 Nongseo-Ri, Giheung-Eup, Yongin-Si, Gyeonggi-Do, Korea 449-712
+82-31-280-9614 [email protected]
Hongyuan Zhang et al.Slide 2
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Abstract
• Changes from r1 (with italic font in slides)– Remove duration field in VHT-SIGA for bit allocation
consideration– Remove SU/MU bit in VHT-SIGA for bit allocation consideration– Combine “Field/Bits consideration slides for SU and MU” into a
single slide– Update comparison slide for AutoDetection– Update references with revision number– Minor editorial changes– Add a couple of strawpolls at the end
• Changes from r2/r3– Modify strawpolls
Hongyuan Zhang et al.Slide 3
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
I. Numerology
Hongyuan Zhang et al.Slide 4
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Proposed Basic Numerology(previously presented to TGac)
• Max number of transmit (Tx) antennas sounded: 8– Reasonable complexity, cost, and preamble length trade-off
• Max number of Nss (spatial streams) in the SU case: 8– Given that 8 Tx antennas are proposed to be sounded, then there is inherent support
for up to 8 spatial streams
• Max number of Nss per user in the MU case: 4– Given that multiple users will share spatial streams, it is natural to make this
number smaller than 8– Fits VHT-SIG size limitations, reduces number of representation bits required
• Maximum number of Nss summed over users in the MU case: 8– Given that 8 Tx antennas are proposed to be sounded, then there is inherent support
for up to 8 spatial streams
• Max number of MU users: 4– Larger number significantly increases MAC/PHY complexity– Fits VHT-SIG size limitations, reduces number of representation bits required
Hongyuan Zhang et al.Slide 5
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Maximum number of transmit antennas sounded = 8
• Meets PAR requirements– For single user case 8 antenna with Nss=8 allows for > 500Mbps
throughput
– For multi user case 8 antenna sounding allows for > 1 Gbps throughput
• Physical limitation on AP and STAs to put more than 8 antennas
• Going to 16 antenna sounding increases preamble length– Number of bits required to indicate number of antennas sounded also
increases – limited number of bits available in preamble
Hongyuan Zhang et al.Slide 6
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Max number of Nss (spatial streams) in the SU case = 8
• Meets PAR requirements– For single user case 8 spatial stream allows for > 500Mbps
throughput
• Maximum number of Nss <= Maximum number of Antennas sounded
Hongyuan Zhang et al.Slide 7
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Max number of Nss per user in the MU case: 4
• Meets PAR requirements– For multi user transmission two transmissions of Nss=4 allows for
> 1Gbps throughput
• Given that multiple users will share spatial streams, it is natural to make this number smaller than 8
• Fits VHT-SIG size limitations, reduces number of representation bits required– 3 bits required to define Nsts per user for MU transmission– For resolvable LTFs these bits have to be in VHT-SIGA
Hongyuan Zhang et al.Slide 8
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Maximum number of Nss summed over users in the MU case: 8
• Meets PAR requirements– For multi user transmission sum of Nss equal to 8 leads to
throughput > 1Gbps
• Given that 8 Tx antennas are proposed to be sounded, then there is inherent support for up to 8 spatial streams
Hongyuan Zhang et al.Slide 9
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Max number of MU users: 4
• Meets PAR requirements– For multi user transmission 4 users with 2 streams per user > 1Gbps
throughput
• Larger number significantly increases MAC/PHY complexity– Each users stream has to be separately encrypted and modulated
• Fits VHT-SIG size limitations, reduces number of representation bits required– Nss bits have to be pre-allocated for each user in VHT-SIGA.
– Even with 4 MU users, most of the VHT-SIGA bits are already allocated
Hongyuan Zhang et al.Slide 10
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
II. Preamble Comparisons
Hongyuan Zhang et al.Slide 11
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
TGac Preamble Proposals
• Two proposals in TGac on preamble: (1) our proposal 10/070r1, and (2) 10/130r0 (Tu, et al).
• Major differences:– Auto detection:
• (1) 90-deg rotation on 2nd VHTSIG symbol, • (2) Manipulate constellation of 1st VHTSIG symbol, e.g. alternative 90-deg
rotate, or 45-deg rotate.
– Modulation of VHT-SIG:• (1) Same as 11n/a: BPSK r=1/2• (2) Allows QPSK from 2nd VHTSIG symbol
– Green Field:• (1) A single preamble for SU/MU, no GF.• (2) Allow GF
Hongyuan Zhang et al.Slide 12
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Preamble Structure in (1)-0070r0
VHT-STF VHT-LTFsL-STF L-LTF L-SIG VHTSIGA VHTSIGB VHTData
2 symbols 1 symbol
T
VHT auto-detection
Rate=6MbpsLength determined by T
Hongyuan Zhang et al.Slide 13
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Preamble Structure in (2)-0130r0
• Or the “90-deg Orthogonal shift” may be replaced by +-45-deg shift.
HT-SIG2HT-SIG1L-SIG
DATA2DATA1L-SIG11aLegacy
11nMM HT-STF HT-LTF HT-DATA1
VHT-SIGn VHT-STF VHT-LTFVHT-SIG1L-SIGVHTMM
VHT-DATA1
90 degreerotation
90 degreeAlternate
subcarriers
Hongyuan Zhang et al.Slide 14
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Comparisons—Auto Detection• Proposal (1) is more reliable than (2):
– Guarantees the most reliable spoofing of existing 11n receivers (as 11a packet), regardless of what 11n auto-detect algorithm was implemented.
– Guarantees the most reliable 11ac auto detection, largest Euclidean Distance (BPSK vs QBPSK).
• It is risky to manipulate modulation of the 1st VHTSIG symbol.– Given various existing implementations of 11n auto-detections.
• Not fair to pre-assume any 11n auto-detect approach as in proposal (2)
– More likely that an 11n device false-detects HTSIG, and goes into ED-CCA stage.
• On timing issue for detection– VHT-STF AGC may be deferred by approximate FFT processing time (before VHT
detection). – 11ac will most likely run faster clock to support higher throughput; therefore AGC
computation is faster than HT devices. – May use partial GI of VHTLTF1 for AGC computation. – There are much more complex functions (e.g. DLMU, faster decoder, etc) required
for 11ac. VHT AGC enhancement is trivial. – A reliable legacy spoofing is more important than the extra complexity of AGC
enhancement.
Hongyuan Zhang et al.Slide 15
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Comparisons—VHTSIG Modulation
• Preferable to keep using the lowest possible MCS to modulate VHTSIG fields:– MCS0 is still necessary to guarantee the longest range.
– Make sure header is not worse than Data.
Hongyuan Zhang et al.Slide 16
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Comparisons—Green Field
• Preferable not to define the second preamble format (GF):– 11n GF has seen limited usage so far.
– One of the arguments in favor of GF in 11n was the existence of green space in 5 GHz due to the limited use of 11a• If there are no 5 GHz deployments of 11n, then there is no point to
TGac
• The assumption should be that there will be 5 GHz deployments of 11n.
– Like in 11n, multiple preamble types compounds the difficulty of auto-detection for small PHY efficiency improvement.• GF protection exchanges offsets the PHY improvement.
Hongyuan Zhang et al.Slide 17
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
III. Re-present of Our Preamble Proposal (1)
Hongyuan Zhang et al.Slide 18
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Preamble Design Goals
• Backward compatibility– Robust legacy 11a deferral
– Robust legacy 11n deferral
• Reliable auto-detection among 11a, 11n (MM and GF), and VHT preambles
• Single preamble structure in SU and MU
• Signaling of VHT PHY information by VHTSIG.
• Training for wider channels, and detection and deferral in each sub-channel.
• Low PAPR
• Minimize overall preamble length
Hongyuan Zhang et al.Slide 19
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Spoofing and Auto-detection
• Use L-SIG spoofing for both 11a and 11n receivers:– As 11n spoofing for 11a/g receivers.
– Rate=6Mbps, Length/Rate indicates duration.
• Use 90-deg rotated BPSK (QBPSK) on VHTSIG symbol for VHT auto-detection.– 11n receiver will treat the packet as 11a packet (L-SIG spoofing).
Hongyuan Zhang et al.Slide 20
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Preamble Structure
VHT-STF VHT-LTFsL-STF L-LTF L-SIG VHTSIGA VHTSIGB VHTData
2 symbols 1 symbol
T
VHT auto-detection
Rate=6MbpsLength determined by T
Hongyuan Zhang et al.Slide 21
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Aggregation bit in VHT-SIGs for MU Packets?
• There is no need to indicate the duration of the packet in VHT-SIG again– Length information can be obtain from L-SIG
• Use A-MPDU structure to provide length information for individual MPDUs– Require that A-MPDU always be used with VHT frame
• MAC provides an A-MPDU that fills the frame up to the last byte for each per-user stream, and PHY provides 0-7 bits of padding.
• Same padding scheme also defined in SU packets.• “Aggregation” bit in VHTSIG is then not needed.• Details refer to document 11-10-0064r1 (VHT frame padding).
L-TFs L-SIG
VHT A-MPDU
VHTSIGA
PHY Pad TailService
Last Symbol
VHT A-MPDU
VHT A-MPDU
Service
Service
PHY Pad Tail
PHY Pad Tail
A-MPDU subframe 1
A-MPDU subframe 2
Null subframe
Null subframe
A-MPDU subframe n
Last byte boundary
Less than 8-bit
MPDU Length = 0
MPDU Length = 0
MAC Pad
0-3 octets
VHT-TFsVHTSIG
B
Hongyuan Zhang et al.Slide 22
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Summary on VHT-SIGs• In MU, VHT-SIGA contains the “common” bits for all clients.
– Indicates number of space-time streams (NSTS) for each user.– Need prior multiuser group and user ID assignment frame exchanges before
DL-MU packets (e.g. by sounding and/or management frames).• Each user will be able to get its own NSTS information from VHTSIGA..
• Details refer to document 11-10-0073r2 (Group ID Concept for Downlink MU-MIMO Transmission).
• VHT-SIGB contains user-specific information (e.g. modulation and coding rate) and is spatially multiplexed for different clients.
– It is placed after all the VHT-LTFs to enable better receiver side interference mitigation in DL-MU before decoding VHT-SIGB.
– This requires each client getting as many LTFs as needed to train the total number of spatial streams across all users—named as “resolvable VHT-LTF”.
– “Non-resolvable VHT-LTF” may be selected if all clients do not support receiver side interference mitigation, or if interference mitigation is not required .
– Rx interference mitigation in DL-MU refer to document 11-09-1234r1 (Interference Cancellation for Downlink MU-MIMO).
Hongyuan Zhang et al.Slide 23
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
VHT-SIG Fields Considerations
• Bandwidth• Short GI• Group ID Field• MCS• STBC• Sounding• Smoothing• Coding Type• CRC & Tail
• For further investigation– Full/partial MAC ID– Number of Extension Streams– Resolvable/Non-resolvable LTF Indication
Details of bit allocation are subject to change if necessary
Hongyuan Zhang et al.Slide 24
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Straw Poll on Numerology
• Do you support adding a basic guideline on the numerology for 11ac device described as in Section I of 11-10/0070r4, excluding slide 9 (max Number of users for MU remains TBD), to the spec framework document, 11-09-0992?– Yes: 79
– No: 0
– Abs: 3
Agreed to pass it to TGac
Hongyuan Zhang et al.Slide 25
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Straw Poll on Preamble Structure
• Do you support adding the 11ac preamble structure with two SIGNAL fields (VHT-SIGA located before VHT-STF and VHT-SIGB located after VHT-LTFs) as in Section III (Slide 22) of 11-10/0070r4 to the spec framework document, 11-09-0992?– Yes: 70
– No: 0
– Abs: 16
Agreed to pass it to TGac
Hongyuan Zhang et al.Slide 26
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Follow-up Straw Poll on Preamble Structure
• Do you support to have 2 OFDM symbols for VHT-SIGA and a single OFDM symbol for VHT-SIGB, and to edit the spec framework document, 11-09-0992, accordingly?– Yes: 54
– No: 22
– Abs: 13
Hongyuan Zhang et al.Slide 27
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Straw Poll on Spoofing
• Do you support to have BPSK on the 1st VHT-SIGA symbol and 90-deg rotated BPSK (QBPSK) on the 2nd VHT-SIGA symbol for VHT auto-detection as in Section III (Slide 20) of 11-10/0070r4, and to edit the spec framework document, 11-09-0992, accordingly?– Yes: 54
– No: 24
– Abs: 8
Hongyuan Zhang et al.Slide 28
doc.:IEEE 802.11-10/0070r5
Submission
March 2010
Straw Poll on Spoofing II
• Do you support to have BPSK on the 1st VHT-SIGA symbol and TBD on the 2nd VHT-SIGA symbol for VHT auto-detection, and to edit the spec framework document, 11-09-0992, accordingly?– Yes: 71
– No: 1
– Abs: 11
Agreed to pass it to TGac