Transcript 11-14/1208

September 2014
doc.: IEEE 802.11-14/1208r1
MAC considerations on
802.11ax OFDMA
Date: 2014-09-17
Authors:
Name
Affiliations
Jinsoo Ahn
Yonsei Univ.
Woojin Ahn
Yonsei Univ.
Ronny Yongho
Kim
Korea National
University of
Transportation
Submission
Address
Phone
email
[email protected]
c.kr
[email protected]
c.kr
[email protected]
Slide 1
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
Introduction
•
In IEEE 802.11ax PAR [1], IEEE 802.11ax should provide methods for
efficient use of spectrum resources in dense STAs per BSS.
−
−
•
OFDMA could be one of solutions to provide efficient spectrum resource
utilization
•
•
•
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.
In IEEE 802.11-10/0317r1[2] DL-OFDMA increase AP utilization and throughput dramatically.
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
system degradation by contentions, OFDMA with guaranteed TXOP
should be studied in 802.11ax
Submission
Slide 2
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
OFDMA operation
• OFDMA without RTS/CTS
– New Preamble is only way to support OFDMA without RTS/CTS
except full scanning case
• Full scanning means STAs are always listening and decoding all the
possible 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
Slide 3
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
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
Slide 4
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
OFDMA under high density of STAs and
OBSSs (CTS-to-Self)
• OFDMA CTS-to-Self
CTS-to-self
Area
Hidden
terminal Area
for CH#3
Hidden
terminal Area
for CH#2
Hidden
terminal Area
for CH#1
Submission
Slide 5
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
OFDMA under high density of STAs and
OBSSs (CTS-to-Self)
ACK
CH #3
ACK
STA3
ACK3
Data3
SIFS
SIFS
PIFS
AP
Control frame for
Channel assign
ACK2
Data2
STA2
CTSto-Self
SIFS
Control frame for
Channel assign
SIFS
SIFS
AP
CTSto-Self
SIFS
CH #2
PIFS
STA1
ACK1
SIFS
ACK
(Primary channel)
SIFS
CH #1
SIFS
Data1
SIFS
Control frame for
Channel assign
SIFS
AP
CTSto-Self
SIFS
DIFS
• OFDMA CTS-to-Self[3]
– Disadvantage
• CTS-to-Self cannot solve Hidden terminal problem (severe interference)
– Advantage
• Primary channel based simple scanning
Submission
Slide 6
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
OFDMA under high density of STAs and
OBSSs (RTS/CTS)
• OFDMA RTS/CTS
RTS Area
CTS Area for
CH#3
CTS Area for
CH#2
CTS Area for
CH#1
Submission
Slide 7
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
OFDMA under high density of STAs and
OBSSs (RTS/CTS)
CH #3
CTS3
STA3
ACK3
Data3
SIFS
PIFS
STA2
RTS3
SIFS
CTS2
AP
ACK2
Data2
SIFS
PIFS
RTS2
SIFS
CH #2
AP
ACK1
SIFS
CTS1
STA1
SIFS
CH #1
(Primary channel)
SIFS
Data1
SIFS
RTS1
SIFS
AP
DIFS
• 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
Submission
Slide 8
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
OFDMA under high density of STAs and
OBSSs (RTS/CTS)
CH #3
CTS3
STA3
ACK3
Data3
SIFS
SIFS
AP
PIFS
STA2
Control frame for
Channel assign
ACK2
Data2
CTS2
Modified
RTS
SIFS
Control frame for
Channel assign
SIFS
SIFS
PIFS
Modified
RTS
SIFS
CH #2
AP
ACK1
SIFS
CTS1
STA1
SIFS
CH #1
(Primary channel)
SIFS
Data1
SIFS
Control frame for
Channel assign
SIFS
Modified
RTS
SIFS
AP
DIFS
• 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
receiver address)
– User and channel assignment information is not included in RTS
Submission
Slide 9
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
Summary
Pros
Cons
Full Scanning
Using Legacy procedure
and frame
Large operational overhead
New Preambles
Minimizing operational
overhead
Modification on preamble
Full Scanning
Using Legacy procedure
and control frame
Large operational overhead
CTS-to-Self
Using Legacy control
frame
Hidden terminal problem
Modified RTS
Guarantee of TXOP with
low operational overhead
Control frame modification
Without
RTS/CTS
With
RTS/CTS
Submission
Slide 10
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
Conclusion
• Full scanning method makes OFDMA channel access
protocol simple, however, it requires high operational
overhead
• 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
performance in dense STAs and OBSS scenario, it is
recommended to study more in 802.11ax
Submission
Slide 11
Jinsoo Ahn, Yonsei University
September 2014
doc.: IEEE 802.11-14/1208r1
References
• [1] IEEE 802.11-14/0165r1 “802.11 HEW SG Proposed
PAR”
• [2] IEEE 802.11-10/0317r1 “DL-OFDMA for Mixed Clients”
• [3] IEEE 802.11-09/0138r3 “OFDMA Related Issues in
VHTL6”
Submission
Slide 12
Jinsoo Ahn, Yonsei University