doc.:IEEE 802.11-10/1281r0
Nov. 2010
Bandwidth Indication and Static/Dynamic
Indication within Legacy
Date: 2010-11-06
Name
Company Address
Phone
email
Brian Hart
Cisco Systems
170 W Tasman Dr, San Jose,
CA, 95134, USA
+1-408-5253346
[email protected]
V. K. Jones
Qualcomm
Youhan Kim
Atheros
Eldad Perahia
Intel
Vinko Erceg
Broadcom
Minho Cheong
ETRI
Daewon Lee
LG Electronics
Hongyuan Zhang
Marvell
Uikun Kwon
Samsung
5775 Morehouse Dr. San Diego,
CA
1700 Technology Drive
San Jose, CA 95110
2111 NE 25th Ave, Hillsboro OR
97124, USA
16340 West Bernardo Dr., San
Diego, CA 92127
161 Gajeong-dong, Yuseong-gu,
Daejeon, Korea
LG R&D Complex 533, Hogye1dong, Dongan-Gu, AnyangShi, Kyungki-Do, 431-749,
Korea
5488 Marvell Lane, Santa Clara
CA, 95054
San #14-1, Nongseo-dong,
Giheung-gu, Yongin-si,
Gyeonggi-do, 449-712, Korea
Sean Coffey
Vish Ponnampalam
George Vlantis
Realtek
MediaTek
ST-Ericsson
Submission
[email protected]
+1-408-830-5835
[email protected]
[email protected]
858-521-5885
[email protected]
+82 42 860 5635
[email protected]
+82-31-450-7897
[email protected]
+1-408-222-1837
[email protected]
+82-10-280-9513
[email protected]
[email protected]
[email protected]
[email protected]
Slide 1
Brian Hart, Cisco Systems
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Outline
• Bandwidth and Static/Dynamic Indications are needed in non-HT PPDUs
• Inserting a new indication in a non-HT PPDU is complicated
• How to insert Bandwidth and Static/Dynamic Indications into the First 7
Bits in Scrambling Sequence
• How to indicate that the First 7 Bits in Scrambling Sequence are modified
• Pre-Motion
Submission
Slide 2
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Bandwidth and Static/Dynamic Indications are
Needed in non-HT PPDUs
• E.g. Send RTS/CTS duplicated across 80 MHz
• Sending RTS/CTS in a non-HT PPDU ensures that all nearby STAs can
set their NAV
• Using an RTS rather than a new control frame preserves the NAV
cancellation feature unique to RTS
• RTS + no CTS + no Data => clear NAV
• In 11n, the duplication of a frame (e.g. RTS) is not explicitly signaled
• Receivers should perform extra, error-prone processing
• This gets still more unreliable and expensive with 20/40/80/160/80+80 MHz
operation
• Static/Dynamic indication in an RTS is needed since it affects CTS
behavior.
• See 10/1289 RTS/CTS Operation for Wider Bandwidth for a description of Static/Dynamic
Submission
Slide 3
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Inserting a New Indication in a non-HT PPDU is
Complicated
• Three bits (2 bits of Bandwidth Indication and 1 bit of Static/Dynamic
Indication) need to be inserted
• Plus an indication that these bits have actually been inserted (i.e. this is
not a pre-VHT non-HT PPDU)
• The selected method should have the broadest compatibility with the
range of devices already deployed at 5 GHz
• Deployed receivers may require that Reserved fields have particular
values, else a frame is discarded
• Diminishes the purpose of sending an RTS/CTS
• A range of options was considered and rejected. For instance:
• There is little opportunity to change bits within a) the RTS/CTS MPDU, b) the
one Reserved bit in the L-SIG field or c) the nine Reserved bits of the Service
field without a reduction in legacy-compatibility
• Some important control frames have only 2 Pad bits, and these Pad bits would
lack a Tail
Submission
Slide 4
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Properties of the OFDM Scrambler
L-STF, L-LTF, L-SIG
DATA
SERVICE
Scrambler Init (0000000)
PSDU, Tail, Pad
9 Reserved Zeros
XOR
Scrambler Seed =
7 random bits (1-127)
Scrambling Sequence
First 7 Bits in Scrambling Seq
=
Scrambled DATA
First 7 Bits in Scrambling Seq
• Crucially, the mapping between Scrambler Seed and First 7 Bits in
Scrambling Sequence is one-to-one
• So, defining the First 7 Bits in Scrambling Sequence is equivalent
to defining the Scrambler Seed
• In the following, we define the scrambler via the First 7 Bits in
Scrambling Sequence, instead of via the Scrambler Seed
Submission
Slide 5
doc.:IEEE 802.11-10/1281r0
Nov. 2010
How to Insert Bandwidth & S/D Indications into
First 7 Bits in Scrambling Sequence (1/2)
Bits
0-3
4
5-6
RTS
scramblingSequenceStart4
IsDynamic
Bandwidth
CTS etc
scramblingSequenceStart5
• scramblingSequenceStart4 is randomly chosen from 1-15
• scramblingSequenceStart5 is randomly chosen from 1-31
• Ensures First 7 Bits in Scrambling Sequence is non-zero (and so the
Scrambler Seed is non-zero)
• Provides reduced yet still good protection against sequences with
pathologically poor PAPRs
• IsDynamic: 0 (Static), 1 (Dynamic)
• Bandwidth: 0 (20 MHz), 1 (40 MHz), 2 (80 MHz), 3 (160 or
80+80 MHz)
• Very high compatibility since this First 7 Bits in Scrambling
Sequence can arise from a valid Scrambler Seed
Submission
Slide 6
doc.:IEEE 802.11-10/1281r0
Nov. 2010
How to Insert Bandwidth and S/D Indications
into First 7 Bits in Scrambling Sequence (2/2)
INDICATED_CH_BANDWIDTH
is present and within first 7 bits
First 7 Bits in
Scrambling Sequence
1
Data In
0
X 7 X6 X5
X4 X 3 X 2 X 1
Scrambled
Data Out
• Since the first 7 bits of Data In are all-zeros, therefore the shift register
input is the same as Scrambled Data Out, and therefore the state of the
shift register after 7 bits equals the first 7 Scrambled Data Out bits
• Thus the Scrambler Sequence for the remainder of the DATA field is
generated by setting the Scrambler State to First 7 Scrambled Bits after 7
bits, and then continuing to run the scrambler as shown above
Submission
Slide 7
doc.:IEEE 802.11-10/1281r0
Nov. 2010
How To Indicate that the First 7 Bits in
Scrambling Sequence are modified by VHT
VHT Initiator
RTS(TA with M/U=M, RA=Responder)
CTS (no TA)
VHT Responder
Third Party
•
A MAC Address comprises 48 bits with a Unicast/Multicast bit and 47 other bits
• The Unicast/Multicast bit in the TA has heretofore been set to Unicast
•
•
To indicate that the First 7 Scrambled Bits are modified by VHT, a VHT Initiator sets the
Unicast/Multicast bit to Multicast in the TA of a TBD non-response (e.g. RTS) frame carried
in a non-HT PPDU sent to a VHT recipient
The VHT Responder doesn’t signal anything explicitly in the response (e.g. CTS) frame – the
signaling behavior is inherited from the frame that solicited the response frame
• When a VHT Recipient receives a TBD (e.g. RTS) frame with the Unicast/Multicast bit of the TA set
to Multicast, the recipient needs to copy the TA and change the Unicast/Multicast bit to Unicast before
inserting it as the RA of the response (e.g. CTS) frame
•
This should have high legacy compatibility
• Unchanged response (e.g. CTS) frame
• Slightly modified TA in the soliciting frame (e.g. RTS frame), but the RA never matches a pre-VHT
STA’s MAC address
•
No known devices that use the Multicast/Unicast bit of a TA at 5 GHz
Submission
Slide 8
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Pre-Motion
• Do you support adding to the Specification Frame Work document,
the insertion of the Bandwidth and Static/Dynamic indications into
the First 7 Bits in Scrambling Sequence as per Slides 6 and 7, with
the insertion signaled by the Multicast/Unicast bit of the TA as per
Slide 8
• Y/N/A
Submission
Slide 9
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Backup Slides
Submission
Slide 10
doc.:IEEE 802.11-10/1281r0
Nov. 2010
Existing Scrambler
Submission
Slide 11