Submission doc.: IEEE 802.11-15/0091r1 January 2015 Woojin Ahn, Yonsei UniversitySlide 1 UL-OFDMA procedure in IEEE 802.11ax Date: 2015-01-14 Authors:

Submission

doc.: IEEE 802.11-15/0091r1January 2015

Woojin Ahn, Yonsei UniversitySlide 1

UL-OFDMA procedure in IEEE 802.11ax• Date: 2015-01-14

Name Affiliations Address Phone email Woojin Ahn Yonsei Univ. [email protected]

Jinsoo Ahn Yonsei Univ. [email protected]

Ronny Yongho Kim

Korea National University Transportation

[email protected]

Authors:

Submission

doc.: IEEE 802.11-15/0091r1

Woojin Ahn, Yonsei University

Introduction

• UL-OFDMA is included in Spec Framework Document for 11ax [1],[2]− UL-OFDMA is a key enabling technique to meet the requirement of throughput

enhancement

− Number of problem statement and solutions have been discussed in TGax [3], [4], [5], [6], [7]

• 11ax is aiming to enhance the spectral efficiency− Finer granularity of bandwidth usage (2.5/5 MHz BW)

− Aggressive wideband operation

• In this contribution, issues on UL-OFDMA procedure in 802.11ax, as well as possible solutions will be discussed

− With finer sub-channels, wideband operation, dense OBSS environment

Slide 2

January 2015

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doc.: IEEE 802.11-15/0091r1


Issues on UL-OFDMA in 802.11

• lack of multiple transmission control mechanism− When and who to initiate UL-OFDMA?

− Which STA to participate or to be selected?• Scheduling

− How to protect data transmission(NAV) from multiple groups of hidden nodes

− How to finish the whole procedure• ACK procedure

• How do we support UL-OFMDA in wideband and dense OBSS environment?

Slide 3

January 2015

Submission

doc.: IEEE 802.11-15/0091r1


When and who to initiate UL-OFDMA

• Timing/power/frequency Synchronization− AP can calculate the timing/power/frequency differences among STAs

• AP centralized initiation− AP indicates each STA to adjust time/frequency/power differences[5]

− Trigger frame[3]

• Periodic or scheduling− Following beacon period

− Whenever scheduling status meets UL-OFDMA trigger condition

− Depends on target situation, procedure development

Slide 4

January 2015

Submission

doc.: IEEE 802.11-15/0091r1


Which STA to participate• AP doesn’t have any information on STAs’ buffer status

• Conventional polling mechanism

− Simple, stable, rich information/Large overhead

− UL-request frame[3]

• Each STA sends UL request frame independently to indicate its buffer status to AP

• Buffer status feedback− Buffer status indication with ongoing tx/rx

• Reusing duplicated or reserved field of preamble/header• Ex) group ID, NSTS, partial AID of UL transmission

• More data, more fragment bit

• Less overhead / limited informationSlide 5

January 2015

STA4 UL DataAccess req

uest

STA

4)

Access req

uest

poll STA2 UL Data

STA3 UL Data

STA1 UL DataAccess req

uest

(STA

1)

Req

uest A

CK

Req

uest A

CK

Poll co

llision

Access req

uest

(STA

2)

Req

uest A

CK

Medium access polling

Access req

uest

poll

Prim

ary

AP

STAs

Reso

urce

allocatio

n

Submission

doc.: IEEE 802.11-15/0091r1


NAV Protection

• Each STA has different hidden nodes group

• In order to set NAV for every hidden nodes group, each UL-tx STA must transmit at least one RTS or CTS− RTS/CTS with 802.11a format

− Legacy STAs cannot read Data frame

Slide 6

January 2015

STA1

Submission

doc.: IEEE 802.11-15/0091r1


NAV Protection

• Serial RTS transmission

− Large overhead

− CTS time out• Reset NAV if no PHY-RXSTART.indication with a duration of (2 ×

aSIFSTime) + (CTS_Time) + aPHY-RX-START-Delay + (2 × aSlot-Time)

• The hidden nodes group of STA1 won't receive any RXstart. indication within the time limit

Slide 7

January 2015

STA1

STA4 UL Data

RTS(STA

3)

STA2 UL Data

STA3 UL Data

STA1 UL Data

RTS(STA

1)

CTS

Reso

urce allo

cation

Sched

ulin

g

RTS(STA

2)

RTS(STA

4)

NAV

ACK p

roced

ures

First RXSTART.indicator

CTS Timeout

NAV reset!

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r1


NAV setting using common CTS

• ① CTS-to-STA group− Using CTS to prevent hidden nodes group from resetting NAV

− CTS doesn’t have condition for resetting NAV

− Assign a dedicated multicast address for 11ax UL-OFDMA

• ② Common CTS[3]− Every UL-OFDMA participants send CTS with identical waveform

• E.g., DA: AP, SA: multicast address for 11ax UL-OFDMA

− Resource allocation acknowledgement might follow

Slide 8

January 2015

Reso

urce

allocatio

n

STA4 UL Data

CTS

-to-ST

A g

roup

STA2 UL Data

STA3 UL Data

STA1 UL DataCom

mon C

TS

¢

£

or

Reso

urce

allocatio

n

CTS

-to-ST

A g

roup

Com

mon C

TS

RA ACK

RA ACK

RA ACK

RA ACKSch

edulin

g

Prim

ary

AP

STAs

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doc.: IEEE 802.11-15/0091r1


ACK procedure

• Serial ACK transmission− Large overhead

• Sub-channel based ACK − Less overhead

− Unfairness between Legacy and ax STAs• STA that received erroneous frame previously has to defer EIFS

• The STA having the shorter EIFS parameter has the higher channel access probability[8]

Slide 9

January 2015

STA4 UL Data

STA2 UL Data

STA3 UL Data

STA1 UL Data ACK(ST

A2)

ACK(ST

A1)

ACK(ST

A3)

ACK duration

ACK(ST

A4)

ACK(ST

A1)

Prim

ary

AP

STAs STA4 UL Data

DIFS

STA2 UL Data

STA3 UL Data

STA1 UL Data

sACK

sACK

sACK

sACK

EIFS

Prim

ary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r1


ACK procedure using common ACK

• Sub-channel based ACK − Acknowledgement of received data

• Common ACK− Preventing legacy STAs from waiting for EIFS

− Identical waveform

Slide 10

January 2015

STA4 UL Data

STA2 UL Data

STA3 UL Data

STA1 UL Data

sACK

sACK

sACK

sACK

AP & STAs

Prim

ary

AP

STAsCom

mon A

CK

Submission

doc.: IEEE 802.11-15/0091r1


UL-OFDMA in wideband operation

• In dense OBSS environment− STAs might belong to different OBSSs

• AP initiates UL-OFDMA after CCA− The snapshot of CCA results

could be different from each other

− Channel availability

− Which band should be assigned towhich STAs?

Slide 11

January 2015

Secondary1

Secondary2

Secondary3

Secondary4

Secondary5

Secondary6

Secondary7

Primary

Submission

doc.: IEEE 802.11-15/0091r1


UL-OFDMA in wideband operation

• STAs should inform AP of both their buffer status and channel availabil-ity

• Channel availability feedback might also introduce massive overhead

Slide 12

January 2015

Reso

urce allo

cation

CTS-to

-STA g

roup STA2 UL Data

STA1 UL Data

Duplicated

CTS

Reso

urce allo

cation

CTS-to

-STA g

roup STA4 UL Data

STA3 UL Data

Duplicated

CTS

AP STA1 STA2 STA3 STA4

Sched

ulin

g

STA1, STA2 -> primarySTA3, STA4 -> secondary 1

Primary

Secondary 1

AP

STAs

AP

STAs

CTS-to

-STA g

roup

CCA

feedback

(STA1)

CTS-to

-STA g

roup

CCA

feedback

(STA1)

CTS-to

-STA g

roup

CTS-to

-STA g

roup

CCA

feedback

(STA2)

CCA

feedback

(STA3)

CCA

feedback

(STA4)

CCA

feedback

(STA2)

CCA

feedback

(STA3)

CCA

feedback

(STA1)

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

CCA

feedback

request

CCA

feedback

request

CCA

feedback

request

CCA

feedback

request

Sched

ulin

g

Primary

Secondary 1

Secondary 2

Secondary 3

AP

STAs

AP

STAs

AP

STAs

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r1


Code based access

• Pseudo random code− Enhancing CSMA/CA performance via introducing code based contention mecha-

nism[9], [10]

− PRACH, PUCCH, PUSCH in LTE

− CAZAC sequence (Zadoff-chu)

• Code access could play a role both for channel availability feedback and buffer status indication

− Every 11ax STA that has uplink data simultaneously sends a chosen code to clear-assessed channels after CTS-to-STA group

• Code assignment− Randomly chosen from code set

− Unique code for each STA

Slide 13

January 2015

CTS-to

-STA g

roup

4

3

2

1

Reso

urce allo

cation

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r1


Comparison of channel availability feedback

Slide 14

January 2015

AP STA1 STA2 STA3 STA4

CTS-to

-STA g

roup

CTS-to

-STA g

roup

CTS-to

-STA g

roup

CTS-to

-STA g

roup

4

3

2

1

2

1

3

1

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

CTS-to

-STA g

roup

CCA

feedback

(STA1)

CTS-to

-STA g

roup

CCA

feedback

(STA1)

CTS-to

-STA g

roup

CTS-to

-STA g

roup

CCA

feedback

(STA2)

CCA

feedback

(STA3)

CCA

feedback

(STA4)

CCA

feedback

(STA2)

CCA

feedback

(STA3)

CCA

feedback

(STA1)

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

CCA

feedback

request

CCA

feedback

request

CCA

feedback

request

CCA

feedback

request

Conventional round robin Code based

Sched

ulin

g

Primary

Secondary 1

Secondary 2

Secondary 3

AP

STAs

AP

STAs

AP

STAs

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r1


Expected form of UL-OFDMA procedure

Slide 15

January 2015

Access code

STA2

STA3

STA4

STA5

STA6

STA7

STA8

STA1STA5 UL Data sACK

Primary

Secondary 1

Secondary 2

Secondary 3

Com

mon C

TS

CTS-to

-STA g

roup

CTS-to

-STA g

roup

CTS-to

-STA g

roup

CTS-to

-STA g

roup

Com

mon C

TSCom

mon C

TSCom

mon C

TS

STA4 UL Data

STA6 UL Data

STA7 UL Data

STA3 UL Data

STA8 UL Data

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK

sACK Com

mon A

CK

Com

mon A

CK

Com

mon A

CK

Com

mon A

CK

8

7

6

5

4

3

2

1

7

5

3

2

1

8

7

6

2

1

6

2

1

STA2 UL Data

STA1 UL Data

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

Reso

urce allo

cation

AP

STAs

AP

STAs

AP

STAs

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r1


Conclusion

• In this contribution, we discussed issues on UL-OFDMA proce-dure in 802.11ax, as well as possible solutions

• UL-OFDMA might cause massive control overhead, and unstable transmission protection− Due to lack of multiple transmission control mechanism

− Developments or modifications on Scheduling, NAV setting, ACK proce-dure, channel availability feedback are necessary

• We introduced several possible solutions to the discussed issues− Common CTS/ACK(identical wave form) transmission

• NAV setting, ACK procedure

− Code based access • Scheduling, CCA feedback

Slide 16

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Submission

doc.: IEEE 802.11-15/0091r1


Reference

• [1][14/1453/r2] Spec Framework Proposal

• [2][14/1447/r1] Proposed Spec Framework Document for 11ax considering potential tech features

• [3][14/1431/r1] Issues on UL-OFDMA

• [4][14/1446/r0] Analysis of frequency and power requirements for UL-OFDMA

• [5][14/0802/r0] Consideration on UL MU transmission

• [6][14/1190/r2] Frame Exchange Control for Uplink Multi-user transmission

• [7][14/1232/r1] On Multi-STA Aggregation Mechanism in 11ax

• [8][14/1211/r0] Ack Procedure for OFDMA

• [9][14/0616/r0] CSMA/CA enhancements

• [10][14/1681/r1] 802.11 Tgax PHY Frame Structure Discussion for Enabling New Contention Mechanism

Slide 17

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doc.: IEEE 802.11-15/0091r1


Straw Poll 1

• Do you agree to add to the TG Specification Frame-work:

x.y.z AP shall indicate UL OFDMA initiation.

• Y

• N

• ABS

January 2015

Slide 18

Submission

doc.: IEEE 802.11-15/0091r1


Straw Poll 2


x.y.z UL OFDMA uplink channels shall be allocated considering STAs’ channel status.

• Y

• N

• ABS

January 2015

Slide 19

Submission

doc.: IEEE 802.11-15/0091r1


Straw Poll 3


x.y.z UL OFDMA shall provide NAV setting mechanism for allocated channels.

• Y

• N

• ABS

January 2015

Slide 20

Documents

Submission doc.: IEEE 802.11-15/0091r1 January 2015 Woojin Ahn, Yonsei UniversitySlide 1 UL-OFDMA procedure in IEEE 802.11ax Date: 2015-01-14 Authors: