Wireless LAN & 802.11ac Wi-Fi Fundamentals #AirheadsConf Italy

802.11ac Wi-Fi Fundamentals

Eric Johnson

June 2014

CONFIDENTIAL

© Copyright 2014. Aruba Networks, Inc.

All rights reserved2 #AirheadsConf

Agenda

11ac Standards Physical Layer Overview

11ac Data Rates

Radio Realities

Receivers

Antennas

11ac Beamforming

11ac Products

3CONFIDENTIAL


All rights reserved#AirheadsConf

802.11ac Technology Overview

Think of 11ac as an extension of 11n

• 11n specification introduced/leveraged:• 2.4 and 5 GHz supported

• Wider channels (40 MHz)

• Better modulation (64-QAM)

• Additional streams (up to 4 streams)

• Beam forming (explicit and implicit)

• Backwards compatibility with 11a/b/g

11ac introduces• 5 GHz supported

• Even wider channels (80 MHz and 160 MHz)

• Better modulation (256-QAM)

• Additional streams (up to 8)

• Beam forming (explicit)

• Backwards compatibility with 11a/b/g/n

• Refer to http://www.802-11.ac.net for in-depth information

4CONFIDENTIAL



Wider Channels

• 80 MHz channel widths supported in first

generation

– 80 MHz is 4.5x faster than 20 MHz

– 80 MHz is contiguous

– Per packet dynamic channel width decisions

• Future releases will allow for 160 MHz

channel widths

– 160 MHz can be either contiguous or in two non-

contiguous 80 MHz slices

5CONFIDENTIAL



Channel Allocations

6CONFIDENTIAL



802.11ac Channels (ETSI)

Channel

Freq (MHz)

UNII I and UNII II

2x 80 MHz

4x 40 MHz

8x 20 MHz

Channel

Freq (MHz)

UNII II extended

2x 80 MHz

5x 40 MHz

11x 20 MHz

36 4844 5240 56 6460 Band

Edge

5180 5200 5220 5240 5260 5280 5300 5320 5350

Band

Edge

5150

100 112108 116104 120 128124

5500 5520 5540 5560 5580 5600 5620 5640

Band

Edge

5470

136 140 Band

Edge

5680 5700 5725

132

5660

7CONFIDENTIAL



802.11ac Channels (FCC)

Channel

Freq (MHz)

UNII I and UNII II

2x 80 MHz

4x 40 MHz

8x 20 MHz

Band

EdgeChannel

Freq (MHz) 5850

US UNII III

1x 80 MHz

2x 40 MHz

5x 20 MHz

Channel

Freq (MHz)

UNII II extended

3x 80 MHz

6x 40 MHz

12x 20 MHz

36 4844 5240 56 6460 Band

Edge

5180 5200 5220 5240 5260 5280 5300 5320 5350

Band

Edge

5150

149 161157153

5745 5765 5785 5805

Band

Edge

5725

165

5825

100 112108 116104 120 128124

5500 5520 5540 5560 5580 5600 5620 5640

Band

Edge

5470

136 140 Band

Edge

5680 5700 5725

132

5660

144

5720

Weather

Radar

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Dynamic Bandwidth Management:Channel Usage with Two APs

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Wave 2

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Wave 2 of 11ac

• What will wave 2 802.11ac deliver?• MU-MIMO

• Use AP MIMO resources more effectively

• Transmit data to multiple devices simultaneously: for example 4SS AP streaming data to four 1SS clients simultaneously

• 4x4:4SS

• Benefit of additional stream mostly for MU-MIMO

• Not anticipating any 4x4:4SS client devices

• Adds 33% to max datarate

• VHT160

• Doubles max datarate

• Practical problem: only 2 VHT160 channels available in entire 5GHz band

• Max 5GHz radio throughput triples again!• 450 (11n 3x3 HT40), 1,300 (11ac 3x3 VHT80), 3,467 (11ac 4x4 VHT160)

• When will it be available?• Radio chipsets available late 2014

• Products in 2015

13CONFIDENTIAL



Reasons not to wait for Wave 2

• Unlikely to see any 4x4:4SS client devices

• Use of VHT160 not practical for typical enterprise deployment

• MU-MIMO is a nice-to-have optimization.• How well it will work and what the real benefits are is still not entirely

clear

• Requires new client devices (Wave 1 clients also not FW upgradeable)

• Wave 1 is here now (technology, products, market momentum), offering huge advantages over 11n. Wave 2 is the expected next step in the evolution of the technology.

• In general: the next wave in technology is always around the corner, something better is always coming Once Wave 2 is available, we’ll for sure be talking about Wave 3.

• No different from when 11n 2x2 products were introduced and it was clear that 3x3 products would be available within 18 months.

14CONFIDENTIAL



11ad and what it means

• 60GHz band, three channels in most countries (each 2.16GHz wide), each providing up to 6.8Gbps PHY datarate

• No MIMO

• Challenges: Non-Line of Sight (NLOS) connections, range, penetrating obstacles (and people)

• Targeted to clean up a cluttered desk or TV cabinet

• Likely not appropriate for traditional AP use. But can be interesting for related applications like wireless docking, high-capacity WLAN hotspots, AP backhaul/aggregation, etc.

• It is being investigated (but no product plans as of yet)

• Standard is available, certification program in place

• Wi-Fi Alliance WiGig Alliance

15CONFIDENTIAL



Understanding 11ac Data Rates

16CONFIDENTIAL



Terminology

• Symbol: basic element containing 1 to 8 bits of information

• Tone/Sub-Carriers: OFDM is made up of many tones. Each symbol is mapped to a tone.

• Cyclic Extension: technique used in OFDM to protect against multipath interference– You need cyclic extension but it is dead air and consumes transmit time

• Guard Band: Space between channels. In these regions tones have a constant value of zero amplitude

• Pilot Tones: Used to train the receiver and estimate the channel

• Radio Channel: For Wi-Fi 20, 40, 80, or 160 MHz of spectrum

• Propagation Channel: everything that happens between the transmitter and receiver

• FEC: Forward Error Correction. Redundant information that is sent to assist the receiver in decoding the bits.

17CONFIDENTIAL



Sub-carriers

52 subcarriers (48 usable) for a 20 MHz non-HT

mode (legacy 802.11a/g) channel

fc +10MHz-10MHz

26 carriers 26 carriers

56 subcarriers (52 usable) for a 20 MHz HT

mode (802.11n) channel

fc


114 subcarriers (108 usable) for a 40 MHz HT mode (802.11n) channel

fc +10MHz-20MHz


+20MHz-10MHz

242 subcarriers (234 usable) for a 80 MHz VHT mode (802.11ac) channel

An 80+80MHz or 16MHz channel is exactly two 80MHz channels, for 484 subcarriers (468 usable)


fc +10MHz-20MHz +20MHz-10MHz-40MHz -30MHz +30MHz +40MHz

OFDM subcarriers used in 802.11a, 802.11n and 802.11ac

+10MHz-10MHz

Guard Tones

18CONFIDENTIAL



QAM constellations

Amplitude +1

Amplitude -1

Quadra

ture

-1

Quadra

ture

+1

Amplitude +1

Amplitude -1Q

uadra

ture

-1

Quadra

ture

+1

Amplitude +1

Amplitude -1

Quadra

ture

-1

Quadra

ture

+1

16-QAM constellation 64-QAM constellation 256-QAM constellation

Constellation diagrams for 16-, 64-, 256-QAM

19CONFIDENTIAL



How do I get to the data rate for a given MCS?

• Basic Symbol Rate

– 312.5 KHz

– 3.2 ms

• Cyclic Extension

– t/4 0.8 ms

– t/8 0.4 ms

• Bits Per Tone

– BPSK 1

– QPSK 2

– 16 QAM 4

– 64 QAM 6

– 256 QAM 8

19

20CONFIDENTIAL



Raw Data Rates

• #Tones * Bits per Tone * Symbol Rate

– 16 QAM, 20 MHz

– 52 * 4 * 0.3125 = 65 Mbps

20

21CONFIDENTIAL



Correct for Cyclic Extension

21

22CONFIDENTIAL



Apply FEC Coding

22

31CONFIDENTIAL



Receivers

32CONFIDENTIAL



Receiver Line Up

32

ADCSymbol

DecodeDown

ConvertLNA

33CONFIDENTIAL



Receiver Impairments

• Analog Compression

– Modern LNAs have very effective input power tolerance

• Digital Compression

– This is where a high power signal hits the Automatic Gain

Control (AGC) Circuit. Gain drops and receiver sensitivity

degrades

– The radio can be totally blocked if the power hits the Analog

to Digital Converter (ADC) and consumes all the bits

• Intermodulation

– Again, the effective linearity of modern LNAs reduces the

impact of this

33

34CONFIDENTIAL



DAS Interference: Example

• Without filtering any signal that hits the receiver

above -45 dBm will cause a reduction of

sensitivity

• The degradation continues until about -15 dBm

at which point the signal is totally blocked

• With a 100 mW (20 dBm) DAS system at 2100

MHz

– Tx 20 dBm

– Effective rx antenna gain 3 dBi

– 1st meter at 2100 MHz -39 dB

• Power at 1m -19 dBm

– No impact distance 40 meters

34

35CONFIDENTIAL



Advanced Cellular Coexistence

• Proliferation of DAS and new LTE bands at 2.6

GHz are creating issue for Wi-Fi solution

• All new APs introduced by Aruba in the last 12

months and going forward have implemented

significant filtering into the 2.4 GHz radio portion

to combat this

• Design solution

– Use high-linear LNA followed with a high-rejection filter to achieve

rejection target and little sensitivity degradation;

– Design target: Minimal Sensitivity degradation with -10dBm interference

from 3G/4G networks (theoretical analysis).

41CONFIDENTIAL



Antennas

42CONFIDENTIAL



Reading Antenna Pattern Plots -Omni

42

Azimuth Elevation

Omnidirectional Antenna (Linear View)

-3 dB

Sidelobes

43CONFIDENTIAL



Reading Antenna Pattern Plots -Sector

43

Azimuth Elevation

Sector Antenna (Logarithmic View)

-3 dB

-3 dB

SidelobesBacklobe

Front

Back

Side

44CONFIDENTIAL



44

ANT-2x2-5010

Heat Maps

45CONFIDENTIAL



Ant-2x2-5010 Antenna Patterns

45

• Model

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a

a 5 dB per division

• Measured

46CONFIDENTIAL



Ant-2x2-5010 Simple projection

46

0

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a

a 5 dB per division

Assuming 20m install height

0m20m

50m100 m200 m

47CONFIDENTIAL



Analysis

• The heatmaps are shown across 100m by 100m

and 1000m by 1000m areas

• These are flat earth models and the antenna is

straight up above the plane

• 2 ray propagation effects are not included

47

48CONFIDENTIAL



C/I Contours

CI dBm

C/I Contours

CI dBm

Heat Map: Antenna at 5 m height

48

100 m 1000 m

49CONFIDENTIAL



C/I Contours

CI dBm

C/I Contours

CI dBm


49

100 m 1000 m

50CONFIDENTIAL



C/I Contours

CI dBm


50

100 m 1000 m

C/I Contours

CI dBm

51CONFIDENTIAL



C/I Contours

CI dBm

C/I Contours

CI dBm


51

100 m 1000 m

52CONFIDENTIAL



Antenna Basic Physics

• When the charges oscillate the

waves go up and down with the

charges and radiate away

• With a single element the energy

leaves uniformly.

• Also known as omni-directionally

52

53CONFIDENTIAL



Building Arrays: 2 Elements

• By introducing additional antenna elements we

can control the way that the energy radiates

• 2 elements excited in phase

53

l/2

0

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Linear Plot

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dB Plot

54CONFIDENTIAL



0

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• By introducing additional antenna elements we

can control the way that the energy radiates


– Equal amplitude

54

Linear Plot

dB Plot

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55CONFIDENTIAL



0

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• By shaping the amplitude we can control

sidelobes


– Amplitude 1, 3, 3, 1

55

Linear Plot

dB Plot

56CONFIDENTIAL



0

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Building Arrays: 4 Elements Phase

• By altering phase we can alter the direction that the energy

travels

• 4 elements excited with phase slope

– Even amplitude

56

Linear Plot

dB Plot

57CONFIDENTIAL



802.11ac Beamforming

58CONFIDENTIAL



Beamforming: Notes

• AP 22x series has 11ac beamforming support in 2.4 and 5 GHz bands

• Works with clients that support 11ac beamforming function

– This is at a minimum all 11ac client devices using Broadcom chipsets

– Support will have to come to all devices to compete with Broadcom offering

• 11ac beamforming is standards based

– first standard that is doing this the “right” way

– 11ac beamforming represents the consensus view of the 1000’s of contributors to the standards process

• 11ac beamforming is implemented in baseband.

– It works with all antenna subsystems

– The total number of beamforming combinations is effectively infinite

• 11ac actively tracks users so has a recent channel estimate between the AP and client that is updated frequently

58

59CONFIDENTIAL



Channel state information, implicit and explicit beamforming estimation

59

Explicit feedback for beamforming (802.11n and 802.11ac)

1 (Beamformer) Here’s a sounding frame

2 (Beamformee) Here’s how I heard the sounding frame

3 Now I will pre-code to match how you heard me

sounding frames

Beamformed frames

feedback from sounding

Explicit feedback for beamforming

Beamformer Beamformee

Actual

CSI

60CONFIDENTIAL



5- 4- 3- 2- 1- 0 1 2 3 4 51 10

4-

1 103-

0.01Antenna 1

Antenna 2

Antenna 3

Wavelengths

E F

ield

Am

plitu

de

Client Antennas

h11

h21

h31

#airheadsconf61

Practical Example: Beamforming

62CONFIDENTIAL



Line of Sight

• 3 stream AP

• Smartphone

– 1 Antenna/1 Stream

Client

AP

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8090100110

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63CONFIDENTIAL



Simple Reflection

• Let’s introduce two

reflection surfaces

and look at the

impact of one bounce

on each side

Client

AP

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Virtual

Antenna Pattern

64CONFIDENTIAL



Multi Stream Client

• The reflections allow

beamforming to send

different streams

with different

antenna pattern

through the system

Client

AP

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Str

eam

1

Str

ea

m 2

Str

eam

3

65CONFIDENTIAL



Beamforming

• Stream 3 now appears on all three antenna

– Here is how each transmitted component shows up at the

client

65

5- 4- 3- 2- 1- 0 1 2 3 4 51 10

3-

0.01

0.1

1

10Antenna 1

Wavelengths

E F

ield

Am

plitu

de

Now add them!

66CONFIDENTIAL



Similarly Stream 1 and 2

66

Stream 1

Stream 2

67CONFIDENTIAL



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11ac Beamforming across an 80 MHz channel

• The standards based algorithm actually works out patterns

for each sub carrier

• Below is the pattern for stream 1 at 5460, 5500, 5540 MHz

68CONFIDENTIAL



Aruba 11ac Solutions

69CONFIDENTIAL



AP-224/225 802.11ac 3x3 AP

• Enterprise class 3x3 802.11ac

• Aggregate TCP platform throughput performance >1Gbps

• Two platform models:

– AP-224: external antennas (3x, dual band)

– AP-225: integrated antennas

– “Advanced Cellular Coexistence” support

• Dual radio:

– 802.11n 3x3:3 HT40 2.4GHz(450Mbps), support for “TurboQAM”

– 802.11ac 3x3:3 HT80 5GHz (1.3Gbps)

– 11ac beamforming supported in both bands

• Wired interfaces

– Network: 2x 10/100/1000Base-T Ethernet, with MACSec support

– USB 2.0 host interface, console port, DC power

• Will require 802.3at PoE (or DC power) for full functional operation

– Functional, but capabilities reduced when powered from 802.3af POE

• Enterprise temperature range, plenum rated, TPM

70CONFIDENTIAL



Indoor 802.11ac Needs an Outdoor Complement

• Fully ruggedized for extreme environments

• Gigabit performance

• Simplified installation

• Inconspicuous design

• Designed for indoor-use

• Gigabit performance

71CONFIDENTIAL



AP-270 Series – Detailed Overview

Antenna Gain: 5 dBi

2G: 3x3:3 11ac (2.4 GHz)

5G: 3x3:3 11ac (5.15 to 5.875 GHz)

11ac Beamforming

Conducted Tx Power

2G: 23 dBm per branch (28 aggregate)

MAX EIRP = 36 dBm

5G: 23 dBm per branch (28 aggregate)

MAX EIRP = 36 dBm

Power Interface: AC and 802.3at (PoE+)

Power Consumption: 25 W

Gigabit Ethernet WAN + LAN Port

Advanced Cellular Coexistence

Designed to Both IP66 and IP67

-40 to +65°CNo Heater. Start and operate.

72 @arubanetworks

What 11ac can Deliver

73CONFIDENTIAL



Performance: 3 Stream 11ac outdoors!

850 Mbps

TCP!

74CONFIDENTIAL



Performance: Samsung GS4

75CONFIDENTIAL



76

Thank You

#AirheadsConfCONFIDENTIAL


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