RUCKUS WIRELESS PROPRIETARY AND CONFIDENTIAL

Layman’s Guide to TxBF, MIMO and MU-MIMO

GT HillChief Big Dog

Ruckus Wireless

gt@ruckuswireless.com

@gthill

◦ Poor adoption with 802.11n◦ 802.11ac focuses on one implementation

◦ Universal industry focus

◦ NDP Sounding with explicit immediate compressed feedback

2x2

Access Point 1x1

Client

Signal

Quality

TxBF

3

4

+3dB

5

+4.7dB

6

+6dB

7

12

8

12

9

12

10

12

o 3 / 4.7 / 6 dB gain vs. additional spatial streamoEach antenna can either

reinforce the signal (TxBF) or

add more data (spatial

multiplexing) but never both at

the same time.

oEach additional spatial stream

adds significantly more speed

o3dB adds <10% more speed

oRequires client feedbackoDoes not work with 11a/b/g/n

and only some 11ac clients

11

Problem

AP

Conventional 11ac

TxBF Pattern

(symmetric)

How to optimize signal

for client location?

Client Direction

TxBF

Client

1 B

itCan you hit this target?

2 B

its

How about one of these?

4 B

its

6 B

its

8 B

its

o Improves efficiency by 33%

oAdds complexity, requires higher

SNR

oEfficiency gain from modulation

does not increase linearly

256-

QAM64-QAM16-QAM

QPSKBPSK

0 1

01 11

00 10

100% gain (2x)

100% gain (2x) 50% gain (1.5x) 33% gain (1.3x)

18

Uses only ONE antenna for transmit and receive

802.11a/b/g

Go Get Certified!

19

802.11n/ac

Can use multiple antennas for transmit and receive

Go

Get

Certified!Tx Rx : SS

3 x 3 : 3

20

802.11n/ac

Can use multiple antennas for transmit and receive

Go

Get

Certified!Tx Rx : SS

3 x 3 : 3

21

oIncreasing the difference in “perspective” between each stream

oHorizontal vs. vertical polarization

oMultipath

22

oRequires 11ac client(s) with TxBF feedback/support

oCreates new challenges related to signal steering and isolation

4x4:4

Access Point

4x4:4

Access Point

Multi-User MIMOmultiple clients at the same time

Single-User MIMOone client at a time

oPeak to Average Power Ratio

oTransmit power equalization

oRate selection

oDelayed Acknowledgment (block ack)

oData Queuing

oSelecting MU groups

oMaking the process efficientoSame size frames

oSame data rate clients