1. Bits Consideration for SIGNAL fields
Month Year
Month Year
doc.: IEEE yy/xxxxr0
doc.: IEEE /0382r0
Bits Consideration for SIGNAL fields
Date:
Authors:
Slide 1
Joonsuk Kim, et. al..
Page 1
John Doe, Some Company
Joonsuk Kim

2. Preamble Structure [1] 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
Joonsuk Kim, et. al..

3. Different Natures for VHT-SIGs in MU
VHT-SIGA contains the “common” bits for all clients.
Bits/Fields that deliver common information for all users need to be located in VHT-SIGA
Information on the number of VHT-LTFs to follow also need to be located in VHT-SIGA
Better to indicate the number of spatial streams earlier for a receiver to be prepared for decoding DATA
Bandwidth indication also needs to be informed earlier before VHT-STF.
VHT-SIGB contains user-specific information (e.g. modulation and coding rate) and is spatially multiplexed for different clients.
Typically, VHT-STF,VHT-LTFs and VHT-SIGB are being beamformed in order to minimize the interference terms for other users
It is placed after all the VHT-LTFs to enable better receiver side interference mitigation in DL-MU before decoding VHT-SIGB.
Joonsuk Kim, et. al..

4. Bits/Fields to Consider in VHT-SIGs
Bandwidth  VHT-SIGA
Needs to be informed early before VHT-STF
Group ID Field  VHT-SIGA
It indicates the number of VHT-LTFs and the stream numbers to decode for each STA
MCS  VHT-SIGB
MCS is a user-specific information
STBC  VHT-SIGA
If Nsts is not the same as Nss with STBC encoded symbols, it needs to be informed early for a recipient to be prepared to decode symbols correctly.
Short GI
Sounding
Smoothing
Coding Type
CRC & Tail: Located at both VHT-SIGA and SIGB.
Bits in Italic font are not covered in this presentation
Other new bits/fields are possible to consider if necessary, for example, MAC ID, Number of Extension Streams and Resolvable/Non-resolvable LTF Indication
Joonsuk Kim, et. al..

5. GroupID Field in VHT-SIG A [2]
VHT-SIG A tells the number of columns of Qk (steering matrix for user k) in the order of assigned user number in the group-definition-field.
All STAs can listen to VHT-SIG A, so each participating user knows when to start to detect its own stream.
VHT-SIG A includes following field (called GroupID field)
Some of these bits may be reused for SU-MIMO packet
Usage scenario of GroupID
If it is non–zero
The receiving STA(s) use the GroupID as described above
If it is zero (Only the first 3 bits out of x bits in Nsts field are sufficient to indicate the number of streams), the packet can be either
Single user transmission (SU-MIMO packet)
A transmission when the group membership between the transmitter and the receiving STA(s) is not established yet.
A transmission that needs to bypass a group (for example, a broadcast packet)
y bits
x bits
Group ID
# of columns of Qk (Nsts_k) for k=1,2,3,4
Qk is the steering matrix for user k
x>0, y >0
x bits indicate the number of columns of Nsts for user 1,2,3 and 4. Details are TBD
It is possible Nsts_k = 0 for certain k if STA k is not a recipient of MU-MIMO packet.
Joonsuk Kim, et. al..

6. MCS Field in VHT-SIG B
For n, we have 77 MCS sets to cover many combinations for up to 4 streams with unequal modulations.
For ac, we’re talking about 256 QAM and up to 8 streams, which may end up with too many combinations.
For testing purpose, we have too many modes.
With simpler design for MCS table, we don’t need a giant LUT for implementation.
We propose not to allow unequal modulation for 11ac MCS set.
Joonsuk Kim, et. al..

7. STBC Bits in VHT-SIG A
Spatial
Mapping
STBC . . .
Nss
Nsts
Ntx
802.11n has a hybrid mode of SDM and STBC (for example, Nss=3 and Nsts=4)
If we allow this with up to 8 streams for 11ac, it also causes a lot of STBC modes (testing issue)
We propose only one bit for STBC mode (Almouti scheme)
If Nsts is even, Nsts = 2*Nss
If Nsts is odd, Nsts = 2*Nss – 1 (only one stream is not STBC encoded)
Whether or not we allow this case (Nsts is odd) is TBD
If it is allowed, the position of spatial-stream that is not encoded by STBC is TBD
Joonsuk Kim, et. al..

8. Reference [1] 11-10/0070r5 “802.11ac Preamble.ppt”
[2] 11-10/0073r2 “GroupID Concept for Downlink MU-MIMO Transmission.ppt”
Joonsuk Kim, et. al..

9. Straw Poll on Bit Allocation in VHT-SIGs
Do you support including bits for Bandwidth, STBC and GroupID field in VHT-SIGA and including MCS field in VHT-SIGB, and editing the spec framework document, , accordingly?
Yes:
No:
Abs:
Joonsuk Kim, et. al..

10. Straw Poll on MCS field
Do you support allowing only equal modulation MCS across all streams per user and stating this in the spec framework document, ?
Yes:
No:
Abs:
Joonsuk Kim, et. al..

11. Straw Poll on STBC bit
Do you support to have one bit to indicate STBC mode and to edit the spec framework document, , accordingly?
Yes:
No:
Abs:
Joonsuk Kim, et. al..

12. Straw Poll on GroupID
Do you support adopting the value of GroupID (whether it is zero or not) as a method as described in Slide 5 of r0 and editing the spec framework document, , accordingly?
Yes:
No:
Abs:
Joonsuk Kim, et. al..