Submission doc.: IEEE 802.11-15/0091r0 January 2015 Woojin Ahn, Yonsei Univ.Slide 1 UL-OFDMA...

Submission

doc.: IEEE 802.11-15/0091r0January 2015

Woojin Ahn, Yonsei Univ.Slide 1

UL-OFDMA procedure in IEEE 802.11ax• Date: 2015-01-12

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

Jinsoo Ahn Yonsei Univ. [email protected]

Ronny Yonho Kim

KNUT [email protected]

Authors:

Submission

doc.: IEEE 802.11-15/0091r0

Introduction

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

put 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-channel, wideband operation, dense OBSS environment

Slide 2 Woojin Ahn, Yonsei Univ.

January 2015

Submission

doc.: IEEE 802.11-15/0091r0

Issues on UL-OFDMA in 802.11

• Lack of 1:N 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?


January 2015

Submission

doc.: IEEE 802.11-15/0091r0

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


January 2015

Submission

doc.: IEEE 802.11-15/0091r0

Which STA should participate

• AP doesn’t have any information on STAs’ buffer status

• Conventional polling mechanism

− Simple, stable, rich information• Unrestricted STA selection, data duration

− Large overhead• The more STA, the longer delay

• UL-request frame[3]• Each STA sends UL request frame independently to indicate its buffer status to AP


January 2015

STAAP

STA4 UL Data

Access req

uest

STA4)

Access req

uest

poll STA2 UL Data

STA3 UL Data

STA1 UL DataAccess req

uest

(STA1)

Req

uest A

CK

Req

uest A

CK

Poll co

llision

Access req

uest

(STA2)

Req

uest A

CK

Medium access polling

Access req

uest

poll

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r0

Which STA should participate

• 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

− Small overhead, limited information, restricted STA selection


January 2015

Submission

doc.: IEEE 802.11-15/0091r0

NAV Protection

• Each STA has different 3rd party STAs− 3rd party: STAs those only belong to tx STA’s (eg., Fig. 1’s STA1)

radio range

• In order to set NAV for every 3rd party, each UL-tx STA must transmit at least one RTS or CTS− RTS/CTS with 802.11a format

− Legacy STAs cannot read Data frame


January 2015

STA1

Submission

doc.: IEEE 802.11-15/0091r0

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)

− CTS doesn’t have condition for resetting NAV


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 802.11-15/0091r0

NAV setting using common CTS

• ① CTS-to-STA group− Using CTS to prevent 3rd party STAs from 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 can be followed


January 2015

Reso

urce allo

cation

STA4 UL Data

CTS-to

-STA g

roup

STA2 UL Data

STA3 UL Data

STA1 UL DataCom

mon C

TS

¢

£

or

Reso

urce allo

cation

CTS-to

-STA g

roup

Com

mon C

TS

RA ACK

RA ACK

RA ACK

RA ACK

Sched

ulin

g

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r0

ACK procedure

• Serial ACK transmission− Large overhead

• Sub-channel based ACK − Less overhead

− Unfairness between Legacy and ax STAs[8]• The STA having the shorter EIFS parameter has the higher channel

access probability


January 2015

STA4 UL Data

STA2 UL Data

STA3 UL Data

STA1 UL Data

ACK(STA

2)

ACK(STA

1)

ACK(STA

3)

ACK duration

ACK(STA

4)

ACK(STA

1)

Primary

AP

STAsSTA4 UL Data

DIFS

STA2 UL Data

STA3 UL Data

STA1 UL Data

sACK

sACK

sACK

sACK

EIFS

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r0

ACK procedure using common ACK

• Sub-channel based ACK − Acknowledgement of received data

• Common ACK− Preventing legacy STAs from waiting for EIFS

− Identical waveform


January 2015

Com

mon A

CKSTA4 UL Data

STA2 UL Data

STA3 UL Data

STA1 UL Data

sACK

sACK

sACK

sACK

AP

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r0

UL-OFDMA in wideband operation

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

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

could be different from each other

− Which band should be assigned towhich STAs?


January 2015

Secondary1

Secondary2

Secondary3

Secondary4

Secondary5

Secondary6

Secondary7

Primary

Submission

doc.: IEEE 802.11-15/0091r0

UL-OFDMA in wideband operation

• STAs should inform AP of both their buffer and CCA status

• CCA feedback might also introduce massive overhead


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 802.11-15/0091r0

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 assignment− Randomly chosen from code set

− Unique code for each STA

• Code access could play a role both for CCA 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

− Unrestricted STA selection, no data durationSlide 14 Woojin Ahn, Yonsei Univ.

January 2015

CTS-to

-STA g

roup

4

3

2

1

Reso

urce allo

cation

Primary

AP

STAs

Submission

doc.: IEEE 802.11-15/0091r0

Comparison of CCA feedback


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 802.11-15/0091r0

Expected form of UL-OFDMA procedure


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 802.11-15/0091r0

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

− Scheduling, 3rd party NAV setting, ACK procedure, CCA feedback

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

− Code based access


January 2015

Submission

doc.: IEEE 802.11-15/0091r0

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


January 2015

Submission doc.: IEEE 802.11-15/0091r0 January 2015 Woojin Ahn, Yonsei Univ.Slide 1 UL-OFDMA...

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