Short story of 802.11ax, SNR

& 1024-QAM

#WLPC Prague 2019

About me

Troy Martin

ECSE-Troubleshooting #007

Scotch Malt Whisky Society #36

@troymart

26

52

106

242

52

52

26

52 52

26 26

26 26

26 26 26 2626

11ax Resource Unit (RU) Distribution

20 MHz

Guard Subcarriers

Null Subcarriers

PHY Preamble

Pilot

Data

RU 26

78.125 kHz

78.125 kHz

RU 52

78.125kHz * 26 = 2.031MHz

78.125kHz * 52 = 4.063MHz

11ax Tone Distribution

64-QAM 1024-QAM256-QAM

Modulation Techniques

Bits per tone

• BPSK 1

• QPSK 2

• 16-QAM 4

• 64-QAM 6

• 256-QAM 8

• 1024-QAM 10

MCS

IndexModulation

Coding

Rate

Relative constellation

error (dB)

0 BPSK 1/2 -5

1 QPSK 1/2 -10

2 QPSK 3/4 -13

3 16-QAM 1/2 -16

4 16-QAM 3/4 -19

5 64-QAM 1/2 -22

6 64-QAM 3/4 -25

7 64-QAM 5/6 -27

8 256-QAM 3/4 -30

9 256-QAM 5/6 -32

10 1024-QAM 3/4 -35

11 1024-QAM 5/6 -35

Moduation RateMin Sensitivity

@ 20 MHz

(dBm)

Min Sensitivity

@ 40 MHz (dBm)

Min Sensitivity

@ 80 MHz (dBm)

Min Sensitivity

@ 160 MHz

(dBm)BPSK 1/2 -82 -79 -76 -73

QPSK 1/2 -79 -76 -73 -70

QPSK 3/4 -77 -74 -71 -68

16-QAM 1/2 -74 -71 -68 -65

16-QAM 3/4 -70 -67 -64 -61

64-QAM 2/3 -66 -63 -60 -57

64-QAM 3/4 -65 -62 -59 -56

64-QAM 5/6 -64 -61 -58 -55

256-QAM 3/4 -59 -65 -53 -50

256-QAM 5/6 -57 -54 -51 -48

1024-QAM 3/4 -54 -51 -48 -45

1024-QAM 5/6 -52 -49 -46 -43

Modulation Techniques

Background Noise

• Thermal Noise

• Black Body Noise

• Cosmic Noise

• Atmospheric Noise

-115

-110

-105

-100

-95

-90

ThermalNoiseFloorvsBandwidth

160MHz @ -92dBm

80MHz @ -95dBm

40MHz @ -98dBm

20MHz @ -101dBm

1MHz @ -114dBm

2MHz @ -111dBm

4MHz @ -108dBm

8MHz @ -105dBm

Thermal Noise

PdBm=10log10(kBTBx1000)

kB=BoltzmannConstant(J/K)

T=temperature(K)

B=bandwidth(Hz)

dBm

} 3dB

BSS Operating Channel Width

BSS Operating

Channel Width

field

HR/DSS, OFDM, ERP, HT, VHT, HE BSS

operating channel width

0 20 MHz or 22 MHz

1 40 MHz

2 80 MHz

3 160 MHz or 80+80 MHz

4-7 Reserved

Take Away

• 11ax Rx radio “listens” to 20MHz (or 40/80/160/80+80 MHz) wide

channel

• Receives ALL tones/subcarriers across BSS channel width

• Processes ALL tones assigned to destination

• NO SNR gain with smaller RUs due to narrower Bandwidth

• Potential for SNR gain by sending individual RUs at higher Tx power