submission doc.: ieee 802.11-14/1208r1 september 2014 jinsoo ahn, yonsei universityslide 1 mac...
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Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 1
MAC considerations on802.11ax OFDMA
Date: 2014-09-17
Name Affiliations Address Phone email Jinsoo Ahn Yonsei Univ. [email protected]
c.kr Woojin Ahn Yonsei Univ. [email protected]
c.kr
Ronny Yongho Kim
Korea National University of Transportation
Authors:
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 2
Introduction
• In IEEE 802.11ax PAR [1], IEEE 802.11ax should provide methods for ef-ficient use of spectrum resources in dense STAs per BSS.
− Make more efficient use of spectrum resources in scenarios with a high density of STAs per BSS.
− Significantly increase spectral frequency reuse and manage interference between neighboring overlapping BSS (OBSS) in scenarios with a high density of both STAs and BSSs.
• OFDMA could be one of solutions to provide efficient spectrum resource utilization• In IEEE 802.11-10/0317r1[2] DL-OFDMA increase AP utilization and throughput dramati-
cally.
• At the same time, OFDMA should be designed to provide interference management under a high density of both STAs and OBSSs.
• Since dense wideband STAs and OBSSs scenarios may cause severe sys-tem degradation by contentions, OFDMA with guaranteed TXOP should be studied in 802.11ax
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 3
OFDMA operation
• OFDMA without RTS/CTS– New Preamble is only way to support OFDMA without RTS/CTS ex-
cept full scanning case• Full scanning means STAs are always listening and decoding all the possi-
ble channels
– A parameter indicating group allocation is required (e.g., Group ID of MU-MIMO)
– Resource indicator for user-resource assignment is also required– However, OFDMA w/o RTS/CTS suffers from severe interference due
to a high density of STAs and OBSSs
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 4
Considerations on OFDMA with RTS/CTS
• Requirements for OFDMA operation with RTS/CTS– Protection from interference caused by legacy devices as well as
802.11ax devices should be provided• Collisions should be minimized
– Using legacy control frames is recommended• Modification on control frames for OFDMA should be minimized
– Power consumption & complexity should be reduced• Operational overhead should be minimized
– When OFDMA is unusable, 802.11ax devices should be able to act like non-OFDMA devices• Procedure overhead for OFDMA transmission should be minimized
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 5
OFDMA under high density of STAs and OB-SSs (CTS-to-Self)
• OFDMA CTS-to-Self CTS-to-self
Area
Hidden terminal Area
for CH#1
Hidden terminal Area
for CH#2
Hidden terminal Area
for CH#3
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 6
OFDMA under high density of STAs and OB-SSs (CTS-to-Self)
• OFDMA CTS-to-Self[3]
– Disadvantage• CTS-to-Self cannot solve Hidden terminal problem (severe interference)
– Advantage• Primary channel based simple scanning
AP
STA1
AP
STA2
CTS-to-Self
ACK
AP SIFS
DIF
S
PIF
S CTS-to-Self
SIFS
SIFS
STA3
PIF
S CTS-to-Self
ACKSI
FS
SIFS
ACK
SIFS
SIFS
Data1
SIFS
SIFS
Data3
Data2
ACK1
ACK3
ACK2
CH #1
CH #2
CH #3
Control frame for Channel assign
Control frame for Channel assign
Control frame for Channel assign
(Primary channel)
SIFS
SIFS
SIFS
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 7
OFDMA under high density of STAs and OB-SSs (RTS/CTS)
• OFDMA RTS/CTSRTS Area
CTS Area for CH#1
CTS Area for CH#2
CTS Area for CH#3
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 8
OFDMA under high density of STAs and OB-SSs (RTS/CTS)
• Example protocol of Full Scanning OFDMA RTS/CTS
– Channel extended form of legacy RTS/CTS– Each STAs are scanning all the possible channel always– Large operational overhead but similar to ideal form
• Does not satisfy the requirement of operational overhead reduction
AP
STA1
AP
STA2
RTS1
CTS1
AP SIFS
DIF
S
PIF
S
RTS3
SIFS
SIFS
STA3
PIF
S
RTS2
CTS3
SIFS
SIFS
CTS2SI
FS
SIFS
Data1
SIFS
SIFS
Data3
Data2
ACK1
ACK3
ACK2
CH #1
CH #2
CH #3
(Primary channel)
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 9
OFDMA under high density of STAs and OB-SSs (RTS/CTS)
• OFDMA modified RTS/CTS
– All the transmitted modified RTS frames are exactly identical– Legacy STAs recognize the modified RTS as a normal RTS
(Same frame format as a legacy RTS frame, but different use of re-ceiver address)
– User and channel assignment information is not included in RTS
AP
STA1
AP
STA2
ModifiedRTS
CTS1
AP SIFS
DIF
S
PIF
S ModifiedRTS
SIFS
SIFS
STA3
PIF
S ModifiedRTS
CTS3SI
FS
SIFS
CTS2
SIFS
SIFS
Data1
SIFS
SIFS
Data3
Data2
ACK1
ACK3
ACK2
CH #1
CH #2
CH #3
(Primary channel)
Control frame for Channel assign
Control frame for Channel assign
Control frame for Channel assign
SIFS
SIFS
SIFS
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 10
Summary
Pros Cons
Without RTS/CTS
Full ScanningUsing Legacy procedure and frame Large operational overhead
New PreamblesMinimizing operational overhead Modification on preamble
With RTS/CTS
Full ScanningUsing Legacy procedure and control frame Large operational overhead
CTS-to-SelfUsing Legacy control frame Hidden terminal problem
Modified RTSGuarantee of TXOP with low operational overhead Control frame modification
Submission
doc.: IEEE 802.11-14/1208r1September 2014
Jinsoo Ahn, Yonsei UniversitySlide 11
Conclusion
• Full scanning method makes OFDMA channel access pro-tocol simple, however, it requires high operational over-head
• OFDMA operation w/o RTS/CTS relies on preamble of its data frame
• CTS-to-self technique requires small operational overhead, but cannot solve hidden terminal problem
• Modified RTS does not cause hidden terminal problem• Since using OFDMA with RTS/CTS provides good per-
formance in dense STAs and OBSS scenario, it is recom-mended to study more in 802.11ax