September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 1

doc.: IEEE 802.11-01/536r0

Submission

Proposal to Add Link Margin Field in IEEE 802.11h

A. Soomro and S. ChoiPHILIPS Research, USA

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 2

doc.: IEEE 802.11-01/536r0

Submission

Introduction

• Review of current Path Loss Estimation mechanism in IEEE 802.11h draft

• Benefits of TX Power and/or Rate Adaptation

• Proposed changes

• Conclusions

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 3

doc.: IEEE 802.11-01/536r0

Submission

Path Loss Estimation

RATE4 bits

Reserved1 bit

LENGTH12 bits

Parity1 bit

Tail6 bits

SERVICE16 bits

PSDUTail

6 bitsPad Bits

PLCP Header

SIGNALOne OFDM Symbol

DATAVariable Number of OFDM Symbols

PLCP Preamble12 Symbols

Coded OFDMBPSK, r = 1/2

Coded OFDMRATE is indicated in SIGNAL

• PPDU frame format

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 4

doc.: IEEE 802.11-01/536r0

Submission

• TX Power contains the power used to transmit the PPDU– Relative to the max TX Power Level

Path Loss Estimation

• SERVICE field frame format

Scrambler Initialization TX Power Reserved

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 0 0 0 0 0 0 T1 T2 T3 T4 0 0 0 0 0BitValue

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 5

doc.: IEEE 802.11-01/536r0

Submission

Path Loss Estimation

Transmitted PowerT1 T2 T3 T4

Power difference[dB]

1111 0

1110 -3

1101 -6

1100 -9

1011 -12

1010 -15

1001 -18

1000 -21

Transmitted PowerT1 T2 T3 T4

Power difference[dB]

0111 -24

0110 -27

0101 -30

0100 -33

0011 -36

0010 -39

0001 -42

0000 Unknown

• TX Power field encoding

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 6

doc.: IEEE 802.11-01/536r0

Submission

Path Loss Estimation Process

• TX STA encodes the TX power level of PPDU in SERVICE field

• RX STA measures the RX power level of PPDU

• Path Loss = Encoded TX Level - RX Power Level

• Assuming reverse symmetry, path loss in reverse direction is estimated

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 7

doc.: IEEE 802.11-01/536r0

Submission

Benefits

• Contention Period (CP)– Better adaptation of TX rate

• Contention Free Period– Better TX Power and/or TX Rate control

• Results in– Increased throughput

– Lower interference

– Longer battery life

– More reliable communication

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 8

doc.: IEEE 802.11-01/536r0

Submission

However…

• Could be improved further, due to – Implementation-dependent receiver

performance– Local noise/interference levels– Channel characteristics

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 9

doc.: IEEE 802.11-01/536r0

Submission

The Link Margin

• The difference in signal level in dB, from the level of the immediately prior frame received from the STA (that is the current PPDU’s destination STA) that could be tolerated by this STA without affecting its correct reception at that rate.

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 10

doc.: IEEE 802.11-01/536r0

Submission

Proposed Changes

• Use bits 12-15 to convey Link Margin

Scrambler Initialization TX Power R Link Margin

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

0 0 0 0 0 0 0 T1 T2 T3 T4 0 L1 L2 L3 L4

Bit

Value

Range: +9 dB to -5 dB

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 11

doc.: IEEE 802.11-01/536r0

Submission

Proposed Changes

• Margin encoding

Link MarginL1 L2 L3 L4

Margin(dB)

0000 Unknown

0001 < -5

0010 -4

0011 -3

0100 -2

0101 -1

0110 0

0111 +1

Link MarginL1 L2 L3 L4

Margin(dB)

1000 +2

1001 +3

1010 +4

1011 +5

1100 +6

1101 +7

1110 +8

1111 > +9

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 12

doc.: IEEE 802.11-01/536r0

Submission

Proposed Changes

• Transmission of Link Margin by a STA is optional

• Usage of this information by a receiving STA is optional– A STA could choose to ignore this information– Or, it could utilize this information to

intelligently control TX power and/or TX rate for future transmissions

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 13

doc.: IEEE 802.11-01/536r0

Submission

An Example

AP STA 1STA 1 sends one MPDU to APwith TX Power field set

AP sends ACK with TX powerand Link Margin fields set

STA 1 adjusts TX Powerand/or TX rateSTA 1 sends next MPDU to AP

with adjusted power and/or rate

The current channel/receiverinformation could be an inputfactor to select TX power/ratefor subsequent transmissionsto the AP

AP sends ACK with TX powerand Link Margin fields set

September 2001

A. Soomro and S. Choi, Philips Research, USA Slide 14

doc.: IEEE 802.11-01/536r0

Submission

Conclusions

• Enhances network performance– Increased network throughput

– More reliable communications

– Lower interference

– Longer battery life

• Backward compatible• Little additional complexity• Optional Features