1. 802.11ac Preamble Date: 2010-01-18 Authors: Month Year Month Year
doc.: IEEE yy/xxxxr0
doc.: IEEE yy/xxxxr0
802.11ac Preamble
Date:
Authors:
Slide 1
Hongyuan Zhang, Vinko Erceg et al.
Page 1
John Doe, Some Company
John Doe, Some Company

2. Outlines Numerology Preamble Structure VHTSIG field considerations
Conclusions
Hongyuan Zhang, Vinko Erceg et al.

3. Proposed Basic Numerology
Month Year
doc.: IEEE yy/xxxxr0
Proposed Basic Numerology
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
Max number of MU users: 4
Larger number significantly increases MAC/PHY complexity
Hongyuan Zhang, Vinko Erceg et al.
John Doe, Some Company

4. 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, Vinko Erceg et al.

5. 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, Vinko Erceg et al.

6. Preamble Structure T Rate=6Mbps Length determined by T 2 symbols
L-STF
L-LTF
L-SIG
VHTSIGA
VHT-STF
VHT-LTFs
VHTSIGB
VHTData T
VHT auto-detection
Hongyuan Zhang, Vinko Erceg et al.

7. MU Packets
VHT-SIG indicates PPDU duration only (number of OFDM symbols)
No per user length indication in preamble
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 r0 (VHT frame padding).
Hongyuan Zhang, Vinko Erceg et al.

8. Further Discussions on VHTSIG
In MU, VHTSIGA 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 r0 (Group ID Concept for Downlink MU-MIMO Transmission).
VHTSIGB contains user-specific information (e.g. modulation and coding rate) and is spatially multiplexed for different clients.
It is placed after all the VHTLTFs to enable better receiver side interference mitigation in DL-MU before decoding VHTSIGB.
This requires each client getting as many LTFs as needed to train the total number of spatial streams across all users—named as “resolvable VHTLTF”.
“Non-resolvable VHTLTF” 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 r0 (Interference Cancellation for Downlink MU-MIMO).
Hongyuan Zhang, Vinko Erceg et al.

9. VHTSIG Fields Considerations (SU)
Duration
Bandwidth
Short GI
MU/SU Indication (=SU)
MCS
STBC
Coding Type
Smoothing
Sounding
CRC & Tail
For further investigations:
Number of Extension Streams
MAC ID
Hongyuan Zhang, Vinko Erceg et al.

10. VHTSIG Fields Considerations (MU)
Duration
Bandwidth
Short GI
MU/SU Indication (=MU)
Group ID
Indication of Number of Space-Time Streams for each user
Mod/Coding per user
STBC
Coding Type
CRC & Tail
For further investigations:
Sounding
Number of Extension Streams
Smoothing
Resolvable/Non-resolvable LTF Indication
Hongyuan Zhang, Vinko Erceg et al.

11. Conclusions Basic PHY numerology is proposed.
Tradeoff between performance and complexity.
A common preamble structure for both MU and SU is proposed:
Use L-SIG spoofing, and auto-detection with QBPSK in VHT-SIG.
Minimum preamble length for DL-MU.
Considerations for some of the subfields in VHTSIG.
Hongyuan Zhang, Vinko Erceg et al.