doc.: ieee 802.11-10/0130r0 submission january 2010 yung-szu tu, et al., ralink tech.slide 1...
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January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 1
doc.: IEEE 802.11-10/0130r0
Submission
Proposed TGac Preamble
Date: 2010-01-20
Name Company Address Phone email Yung-Szu Tu yungszu_tu@ralinktech.com.tw
Yen-Chin Liao julia_liao@ralinktech.com.tw
Cheng-Hsuan Wu
5F., No.36, Taiyuan St., Jhubei City, Hsinchu County 302, Taiwan
+886-3-560-0868
cs_wu@ralinktech.com.tw
Peter Loc +1-408- 807-0868 peterloc@gmail.com
Tom Pare tpare@ralinktech.com
Kiran Uln
Ralink Technology 20833 Stevens Creek
Blvd, Suite 200., Cupertino CA 95014
+1-408-725-8070 kiran@ralinktech.com
Leonardo Lanante leonardo@dsp.cse.kyutech.ac.jp
Yuhei Nagao nagao@dsp.cse.kyutech.ac.jp
Wahyul Amien Syafei
Kyushu Institute of Technology
Kawazu 680-4, Iizuka, JAPAN
+81-948-29-7692
wasyafei@dsp.cse.kyutech.ac.jp
Hiroshi Ochi ochi@cse.kyutech.ac.jp
Thet Htun Khine Radrix Corp. Kawazu 680-4, Iizuka, JAPAN
+81-948-29-7692 thet@radrix.com
Shin Chon Park Korea Advanced Institute of Science and Technology
2201 Creation Hall, KAIST-ICC, 103-6, Munji-Dong, Yuseong-Gu, KOREA
+82-42-350-6921
scpark@icu.ac.kr
Authors:
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 2
doc.: IEEE 802.11-10/0130r0
Submission
Outline
• PPDU format• VHT-SIG• Legacy Rx state machine for VHT-SIG• VHT-LTF
– 2 options
• Conclusion and future work
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 3
doc.: IEEE 802.11-10/0130r0
Submission
PPDU Format
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 4
doc.: IEEE 802.11-10/0130r0
Submission
VHT PPDU Format Design Considerations
• Immediate (no symbol delay) detection• Reliable• Backward compatibility with 11a/n• Low PAPR
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 5
doc.: IEEE 802.11-10/0130r0
Submission
Possible VHT PPDU Formats
• All packet types present in MM-VHT network– Support for VHT-GF is optional
HT-SIG2HT-SIG1L-SIG
DATA2DATA1L-SIG
VHT-SIGn VHT-STF VHT-LTFVHT-SIG1L-SIG
11aLegacy
11nMM
11acMM
VHT-DATA1
HT-STF HT-LTF HT-DATA1
HT-SIG2HT-SIG111nGF HT-LTF HT-DATA1
11a Legacy Packet
VHT-SIGn VHT-LTFVHT-SIG111acGF
VHT-DATA1
11n Packet Types
11ac Packet Types
L-LTFL-STF
L-LTFL-STF
HT-LTF1HT-GF-STF
L-LTFL-STF
VHT-LTF1VHT-GF-STF
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 6
doc.: IEEE 802.11-10/0130r0
Submission
Phase Rotation
• 09/1174r0 [2] mentioned phase rotation over 4 sub-bands is required for low PAPR
• Our simulation result on phase rotation agrees with 09/0847r1 [3] by Leonardo et al., i.e. 1 j 1 -j
• We also found other sets of rotation that yield low PAPR
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 7
doc.: IEEE 802.11-10/0130r0
Submission
VHT-SIG
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 8
doc.: IEEE 802.11-10/0130r0
Submission
VHT Signal Field
• Challenges for VHT-SIG design• Immediate and Reliable detection on first symbol after L-SIG
– Minimize false detection• Backward compatibility
– With 11a/n• Efficiency
– Support enhanced features of TGac with no unnecessary fields
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 9
doc.: IEEE 802.11-10/0130r0
Submission
Previously Proposed VHT Preamble Format
• Proposed Signaling scheme allows MM/GF structure identical to 11n• Alternating subcarriers get 90-degree shift
– “Orthogonal shift” compared to 0-degree and 90-degree
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
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 10
doc.: IEEE 802.11-10/0130r0
Submission
11n HT-SIG Field detection using 90 degree BPSK
• 90 degree detector– Operate on 1st symbol following L-SIG– Detection:
• Measure FEQ output • Compare I vs Q energy levels: High Q energy HT packet• Legacy data symbols: low Q, or equal I and Q components
-1 +1
L-SIG
-j
+j
HT-SIG
Q
DATA(QPSK e.g.)
I
Q
I
Q
I
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 11
doc.: IEEE 802.11-10/0130r0
Submission
Previously Proposed VHT-SIG modified 90 degree BPSK
• Alternate 0/90 degree BPSK symbols on odd/even subcarriers
• Will not be detected as 11n HT-SIG field
-1 +1
VHT-SIG
-j
+jQ
I
Q
I
OddSC’s
EvenSC’s
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 12
doc.: IEEE 802.11-10/0130r0
Submission
Previously Proposed VHT-SIG MM Detection Scheme
xHT-SIGn xHT STF xHT-LTFxHT-SIG1L-SIG xHT-DATA1
2 2
1
Nsc
i ii
I Q
2 2 2 2
, ,
Nsc Nsc
i i k ki even k odd
I Q I Q
11n Detection
11ac Detection
nS
acS
Metric Data Symbol 11a L-SIG 11n HT-SIG 11ac VHT-SIG
11n 0 S -S 0
11ac 0 0 0 -S
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 13
doc.: IEEE 802.11-10/0130r0
Submission
Newly Proposed VHT-SIG with +45/+135 degree BPSK
• Rotate VHT BPSK symbols +45 degrees– Alternate +45/-45 (+135) degree BPSK symbols on odd/even
subcarriers– Will not be detected as 11n HT-SIG field
• Even just a few subcarriers would detect equal I/Q energy
VHT-SIG
(1-j)
(-1+j)Q
I
Q
I
OddSC’s
EvenSC’s
(1+j)
(-1-j)
45.0°
45.0°
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 14
doc.: IEEE 802.11-10/0130r0
Submission
Newly Proposed VHT-SIG MM Detection with Rotation
xHT-SIGn xHT STF xHT-LTFxHT-SIG1L-SIG xHT-DATA1
2 2
1
Nsc
i ii
I Q
2 2 2 2
, ,
Nsc Nsc
i i k ki even k odd
I Q I Q
11n Detection
VHT Detection
nS
acS-45-deg rotation
4je
• Detection metrics unchanged• More robust 11n spoofing
• All subcarriers appear as QPSK to 11n detector (i.e., data symbol)• VHT detection on de-rotated symbols
– Recovers original orthogonal 90-degree BPSK shift
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 15
doc.: IEEE 802.11-10/0130r0
Submission
Orthogonal shift provides better backward compatibility
• Both VHT-SIG1, 2 appear as QPSK data to 11n detector– All subcarriers contain both I/Q energy– Both VHT-SIG fields appear as data symbols under 11n detection
• Delayed-90 shift could result in “false positive” 11n detection – Certain 11n implementations could trigger off either HT-SIG field
to declare 11n packet• More efficient SIG field design
– Open possibility to QPSK VHT-SIG2– No need for VHT-SIG3– Or, pack twice as much VHT descriptor info. by employing higher-
order Modulation and Code Rate
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 16
doc.: IEEE 802.11-10/0130r0
Submission
Detection Timeline with and without Rotation of VHT-SIG1
• With VHT-SIG1 rotation, 11ac devices can recognize 11ac packets at FEQ output
immediately after VHT-SIG1
VHT-SIG3 VHT-STF VHT-LTFVHT-SIG1L-SIG11acMM
VHT-DATA1L-LTFL-STF
No rotation of
VHT-SIG1
VHT-SIG2
with rotation of
VHT-SIG1
11ac detectedStart VHT processing
11ac detectedStart VHT processing
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 17
doc.: IEEE 802.11-10/0130r0
Submission
Straightforward Extension to Greenfield
• Allows highly efficient all-GF operation– Eventual phase-out of 11a devices: all 11n/ac network
HT-SIG2HT-SIG1L-SIG11nMM HT-STF HT-LTF HT-
DATA1
HT-SIG2HT-SIG111nGF HT-STF HT-LTF HT-
DATA1
VHT-SIGn VHT-STF VHT-LTFVHT-SIG1NewVHTGF
VHT-DATA1
Orthogonal Shift0-degree shift 90-degree shiftSHIFT DEFINITIIONS
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 18
doc.: IEEE 802.11-10/0130r0
Submission
Rx State Machine
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 19
doc.: IEEE 802.11-10/0130r0
Submission
11a PLCP Rx State Machine
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 20
doc.: IEEE 802.11-10/0130r0
Submission
11n PLCP Rx State Machine
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 21
doc.: IEEE 802.11-10/0130r0
Submission
Legacy Rx State Machine
• 11a devices can recognize L-SIG but not the following VHT-SIG, so it will wait LENGTH indicated in L-SIG
• 11n devices cannot recognize VHT-SIG, so three ways at “RX HT-SIG” are all possible1. Carrier lost2. HT-SIG, but CRC will fail3. Claimed as 11a/g, but can’t be decoded wait LENGTH– 1 and 2 will return to IDLE state when the PPDU is over, just as
invalid and corrupted 11n PPDU
All legacy devices are not affected
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 22
doc.: IEEE 802.11-10/0130r0
Submission
Summary
• Use “orthogonal shift” to signal new VHT packet format– Take advantage of OFDM property to expand signaling space– More robust detection VHT-SIG1,2 appear as QPSK to 11n detector
• More efficient SIG field design– Open possibility to QPSK VHT-SIG2
• No need for VHT-SIG3 • Additional user data
• GF compatibility– Extends gracefully to VHT-GF operation
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 23
doc.: IEEE 802.11-10/0130r0
Submission
VHT-LTF
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 24
doc.: IEEE 802.11-10/0130r0
Submission
Channel Estimation by P Matrix
28:28
28:28
28:28
28:28
Tx1= * 1 1 1 1
Tx2= * 1 1 1 1
Tx3= * 1 1 1 1
Tx4= * 1 1 1 1
HTLTF
HTLTF
HTLTF
HTLTF
CSD Q IFFT
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 25
doc.: IEEE 802.11-10/0130r0
Submission
Generation of the New P matrixfor More Tx Antenna
• Requirement of generating P– P must be a unitary matrix ( )– The element of P must be +1 or -1
• Ensures the Tx and Rx power the same as payload. – The 2x2 P must be a sub-matrix of 3x3 P
1 TP P
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 26
doc.: IEEE 802.11-10/0130r0
Submission
Compatible with 11n P Matrix• The size of the P matrix must be even.• There exists no 6x6 P matrix which is also compatible with the 11n P
matrix(4x4)
1 -1 1 1 1 -1 1 1 1 1 -1 1 1 1 -1 1 1 1 1 -1 1 1 1 -1-1 1 1 1 -1 1 1 1 1 1 1 1 -1 -1 -1 -1 1 -1 1 -1 -1 1 -1 1 1 1 -1 -1 -1 -1 1 1 1 -1 -1 1 -1 1 1 -1
88
87
86
85
44
43
22
11
NDLTFNSTS
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 27
doc.: IEEE 802.11-10/0130r0
Submission
MIMO Channel Estimation by FDM LTF (1)
LTF1
LTF2
LTF6
IFFT
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 28
doc.: IEEE 802.11-10/0130r0
Submission
MIMO Channel Estimation by FDM LTF (2)
LTF1 LTF2 LTF3 LTF4 LTF5 LTF6 Data
LTF2 LTF3 LTF4 LTF5 LTF6 LTF1 Data
LTF3 LTF4 LTF5 LTF6 LTF1 LTF2 Data
LTF4 LTF5 LTF6 LTF1 LTF2 LTF3 Data
LTF5 LTF6 LTF1 LTF2 LTF3 LTF4 Data
LTF6 LTF1 LTF2 LTF3 LTF4 LTF5 Data
Tx1
Tx6
Tx2
Tx3
Tx4
Tx5
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 29
doc.: IEEE 802.11-10/0130r0
Submission
Mean Square Error for 6x6
• Channel B • Channel D
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 30
doc.: IEEE 802.11-10/0130r0
Submission
Mean Square Error for 6x8
• Channel B • Channel D
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 31
doc.: IEEE 802.11-10/0130r0
Submission
Mean Square Error for 8x8
• Channel B • Channel D
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 32
doc.: IEEE 802.11-10/0130r0
Submission
Comparison
• FDM is more efficiency– For FDM, No. of symbols = No. of streams– For P matrix, No. of symbols = 8 for 5~7 streams– At the expense of worse MSE
• P matrix method is compatible with 11n and has lower MSE
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 33
doc.: IEEE 802.11-10/0130r0
Submission
Conclusion and Future Work
• VHT-SIG is refined with extra 45 degree rotation, compared with 09/1258r0
• VHT-SIG is backward compatible with legacy Rx state machine
• Two options of VHT-LTF are proposed• Future work:
– Simulation of VHT-SIG– More PHY designs
January 2010
Yung-Szu Tu, et al., Ralink Tech.
Slide 34
doc.: IEEE 802.11-10/0130r0
Submission
References
• [1] Yug-Szu Tu, et. al., Proposal for TGac VHT Format , IEEE 802.11-09/1258r0, Nov. 19, 2009
• [2] Hongyuan Zhang , et. al., 802.11ac Preamble, IEEE 802.11-10/0070r0, Jan. 19, 2010
• [3] Leonardo Lanante , et. al., IEEE802.11ac Preamble with Legacy 802.11a/n Backward Compatibility, IEEE 802.11-09/0847r1, Nov. 16, 2009
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