submission doc.: ieee 802.11-14/1208r1 september 2014 jinsoo ahn, yonsei universityslide 1 mac...

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

[email protected]

Authors:

Submission



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



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



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



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


for CH#2


for CH#3

Submission



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



(Primary channel)

SIFS

SIFS

SIFS

Submission



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




• 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




• 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)




SIFS

SIFS

SIFS

Submission



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



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

Submission



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 doc.: ieee 802.11-14/1208r1 september 2014 jinsoo ahn, yonsei universityslide 1 mac...

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