Marketing v. Reality in Multi-Antenna Wi-Fi

Guide to Beamforming March 2011

Scott Reeves

Technical Director EMEA

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Summary

Wi-Fi vendors are marketing chip-based beamforming more heavily

They gloss over limitations, naturally

Mutually-exclusive chip-based beamforming and spatial multiplexing

Zero gain from implicit beamforming, minimal (2 dB) from explicit

Zero client support today for explicit

Customers are easily confused, since all beamforming sounds the same to any non-specialist

A back-to-the-basics view (focusing on simple but technically accurate descriptions how multi-antenna techniques really work) can cut through the confusion

...and illustrate why Ruckus BeamFlex remains the superior approach

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Conventional Wi-Fi: omni Tx pattern

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BeamFlex Smart Antennas

Auto

RF signal

optimizer (Optimises RF coverage based on device

orientation)

Horizontally-

polarized

antenna

elements

Vertically -polarized

antenna

elements

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Automatic Interference Mitigation (AIM)

Chip-based beamforming has no mechanism to reject interference

Omni-directional antennas can’t ignore interference

BeamFlex mitigates interference by positioning antenna nulls in specific directions

Negating interference can be more beneficial than signal gain

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Interference Rejection is Essential

-10db

interference

rejection

7 dBi signal gain

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Key concepts: combination and phase

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How chip-based beamforming works

Understanding the narrow definition of the term “beamforming”

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Beamforming: only one signal allowed

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Chip Based Beamforming Limitations

Generates unwanted

interference and

wastes energy

No way to cope with

real-time interference

at the client

Beams predicated on

antenna separation

Optimal beamforming (5GHz) calls

for .5” antenna separation

Optimal spatial multiplexing

“requires” antenna separation at

inches (5GHz)

!

Client

Client

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Not All Beams Are Created Equal

Client

Client

Client

Client

AP AP

AP AP

Antenna Pattern Example:

Chip-based beamforming

Antenna Pattern Example:

Antenna-based beamforming

Wasted

RF energy

Added

interference

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Spatial multiplexing is essential Speeds in the 802.11 protocols

1

10

100

1,000

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 23 31

802.11n >1stream, 40 MHz, 400ns GI

802.11n 1stream, 40 MHz, 400ns GI

802.11n >1stream, 20 MHz, 800ns GI

802.11n 1stream, 20 MHz, 800ns GI

802.11a/g

802.11b

Peak bit rate, Mbps

MCS number

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How spatial multiplexing works

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Why 3 radio chains don’t help

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Tx 1

In Phase

Tx 2

2x signal strength

Same waveform

Rx

Tx 1

Tx 2

Different coded waveforms (on same frequency)

Data stream split

and cross-encoded for Tx

...0010

...1011

...1101001101

SM and chip BF are mutually exclusive

Chip-based beamforming

Spatial multiplexing

(With 1 radio chain per stream)

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BeamFlex + spatial multiplexing

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A proper multi-antenna taxonomy

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BeamFlex Antenna Advantages

BeamFlex smart antenna:

Beamforming focuses the RF energy ensuring multipath arrives in phase and provides maximum signal density = extended range and superior performance

Horizontally and vertically polarised elements offer 4000+ unique antenna patterns automatically selected on a per packet/per client basis

Attenuate interference from adjacent APs, clients and other RF sources

Cause significantly less interference to adjacent APs

Omni-directional antenna:

Cannot control interference to neighbouring APs

Multipath phasing can be a significant issue

No interference rejection

Make bad RF neighbors

Signal Gain

Up to 9dBi

Rejected Interference

Up to -17dB

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BeamFlex™: Interference Resistance

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60

iPhone 3G Client Throughput Comparison

Vendor C Ruckus Vendor B

0.3

8.7

5.5

0.1

6.7

8.3

Test House Baseline (low interference)

High Interference Location (191 active APs in 3,000m² facility)

Throughput, Mbps

Average

Time, Seconds

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SmartMesh:

Meshing with Adaptive antenna beamforming

Mesh-APs contiunously announce their link capacity

Each Accesspoint selects the best path to Root-AP

BeamFlex optimizes the signal quality to clients & mesh-APs

Self-healing in case of an outage of a mesh-node

(also to an alternate Root AP possible)

Root AP

ZoneDirector controller

300 Mbps

150 Mbps 150 Mbps 75 Mbps Mesh AP

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Performance varies significantly

Note: 2.4 GHz, 800 ns GI, ETSI EIRP, 15 dB fading margin for interference

and obstructions

Sources: Ruckus testing, experience.

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30 35 40 45 50

[1] .11n 1x1:1 omni

[2] .11n + Explicit Beamforming (1 stream)

[3] .11n 2x2:2 omni

[4] .11n 3x3:3 omni

[5] .11n 1x1:1 + BeamFlex

[6] .11n 2x2:2 + BeamFlex

RF Technology Comparison

Peak Throughput, Mbps

Range, m

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Net result: BeamFlex 70% better

Ruckus 3x3:2 APwith BeamFlex

4-Year Aggregate Client Throughput per AP, Terabytes

Generic 3x3:3 APwith ExplicitBeamforming

440

more capacity for client servicewith Ruckus

260

70%

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Case Study

Wireless Broadband Deployment

Tikona India

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The World’s Largest Wireless Mesh

Mesh Access Point

Began build out in 2009

40,000 smart mesh APs now deployed and operational (50k by 2011)

Hundreds of smart WLAN controllers

Central management through FlexMaster

Hundreds of thousands of users

Based on Ruckus Wireless Product and Technology End-to-End

0

2

4

6

8

10

12

14

16

18

0% 20% 40% 60% 80% 100%

802.11g outdoor AP to indoor CPE data rates 1,670 samples on live Tikona network

Mbps

% of CPE

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Tikona footprint

• 40,000 AP live

• 45,000AP

deployed

(approximately)

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Large-Scale Mesh Deployment

ZoneFlex 7731 Point-to-point

802.11n backhaul

FlexMaster Remote Management

ZoneDirector WLAN Controller

MediaFlex 2211 Bridge/Repeater

Outdoor Mesh AP

50 Mbps at 10km 100 Mbps at

2km

20 Mbps at 300m/1000 ft

Backhaul POP

NOC

WBA

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End-to-end visibility and control One NOC

Multiple cities

Tens of Thousands of access points

Hundreds of Thousands of clients

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Active Antenna Beamforming Wi-Fi Portfolio

I N D O O R O U T D O O R

802.11n Bridge

802.11 n AP

802.11g

Single-band 802.11n

2X2 dual-band 802.11n

3X3 dual-band 802.11n

802.11g outdoor mesh

Dual-band 802.11n outdoor

802.11g outdoor mesh

Dual-band 802.11n outdoor

Strand-Mounted 802.11n 5GHz 802.11n PtP/PtMP

Autonomous, Controller-Based or Remotely Managed

802.11n wall switch

Sectorized dual-band 802.11n

Smart Wi-Fi

controllers for RF

and AP

management

Network and Subscriber Management

Highly-scalable centralized

network and element

management

ZoneDirector™ FlexMaster™

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Thank You

Scott Reeves

Technical Director EMEA

Ruckus Wireless

Scott@ruckuswireless.com