shanghai breakout: 802.11ac wi-fi fundamentals

802.11ac Wi-Fi Fundamentals

Eric Johnson

December 2014

CONFIDENTIAL

© Copyright 2014. Aruba Networks, Inc.

All rights reserved2 #AirheadsConf

Agenda

11ac Standards Physical Layer Overview

11ac Data Rates

Antennas

11ac Beamforming

Field Results

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



Understanding 11ac Data Rates

6CONFIDENTIAL



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

7CONFIDENTIAL



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.

8CONFIDENTIAL



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

9CONFIDENTIAL



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

9

10CONFIDENTIAL



Raw Data Rates

• #Tones * Bits per Tone * Symbol Rate

– 16 QAM, 20 MHz

– 52 * 4 * 0.3125 = 65 Mbps

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11CONFIDENTIAL



Correct for Cyclic Extension

11

12CONFIDENTIAL



Apply FEC Coding

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13CONFIDENTIAL



Receivers

14CONFIDENTIAL



Receiver Line Up

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ADCSymbol

DecodeDown

ConvertLNA

15CONFIDENTIAL



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

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16CONFIDENTIAL



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

16

17CONFIDENTIAL



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).

18CONFIDENTIAL



Antennas

19CONFIDENTIAL



Reading Antenna Pattern Plots -Omni

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Azimuth Elevation

Omnidirectional Antenna (Linear View)

-3 dB

Sidelobes

20CONFIDENTIAL



Reading Antenna Pattern Plots -Sector

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Azimuth Elevation

Sector Antenna (Logarithmic View)

-3 dB

-3 dB

SidelobesBacklobe

Front

Back

Side

21CONFIDENTIAL



21

ANT-2x2-5010

Heat Maps

22CONFIDENTIAL



Ant-2x2-5010 Antenna Patterns

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• Model

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a

a 5 dB per division

• Measured

23CONFIDENTIAL



Ant-2x2-5010 Simple projection

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a

a 5 dB per division

Assuming 20m install height

0m20m

50m100 m200 m

24CONFIDENTIAL



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

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25CONFIDENTIAL



C/I Contours

CI dBm

C/I Contours

CI dBm

Heat Map: Antenna at 5 m height

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100 m 1000 m

26CONFIDENTIAL



C/I Contours

CI dBm

C/I Contours

CI dBm


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100 m 1000 m

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C/I Contours

CI dBm


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100 m 1000 m

C/I Contours

CI dBm

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C/I Contours

CI dBm

C/I Contours

CI dBm


28

100 m 1000 m

29CONFIDENTIAL



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

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30CONFIDENTIAL



Building Arrays: 2 Elements

• By introducing additional antenna elements we

can control the way that the energy radiates

• 2 elements excited in phase

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l/2

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Linear Plot

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dB Plot

31CONFIDENTIAL



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• By introducing additional antenna elements we

can control the way that the energy radiates


– Equal amplitude

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Linear Plot

dB Plot

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32CONFIDENTIAL



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• By shaping the amplitude we can control

sidelobes


– Amplitude 1, 3, 3, 1

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Linear Plot

dB Plot

33CONFIDENTIAL



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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

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Linear Plot

dB Plot

34CONFIDENTIAL



802.11ac Beamforming

35CONFIDENTIAL



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

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36CONFIDENTIAL



Channel state information, implicit and explicit beamforming estimation

36

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

37CONFIDENTIAL



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

38CONFIDENTIAL



Practical Example: Beam forming

39CONFIDENTIAL



Line of Sight

• 3 stream AP

• Smartphone

– 1 Antenna/1 Stream

Client

AP

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40CONFIDENTIAL



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

41CONFIDENTIAL



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

eam

2S

tre

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3

42CONFIDENTIAL



Beamforming

• Stream 3 now appears on all three antenna

– Here is how each transmitted component shows up at the

client

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

3-

0.01

0.1

1

10Antenna 1

Wavelengths

E F

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Am

plitu

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Now add them!

43CONFIDENTIAL



Similarly Stream 1 and 2

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Stream 1

Stream 2

44CONFIDENTIAL



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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

45CONFIDENTIAL



Aruba 11ac Solutions

46CONFIDENTIAL



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

47CONFIDENTIAL



Indoor 802.11ac Needs an Outdoor Complement

• Fully ruggedized for extreme environments

• Gigabit performance

• Simplified installation

• Inconspicuous design

• Designed for indoor-use

• Gigabit performance

48CONFIDENTIAL



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.

49CONFIDENTIAL



What 11ac can Deliver

50CONFIDENTIAL



Performance: 3 Stream 11ac outdoors!

850 Mbps

TCP!

51CONFIDENTIAL



Performance: Samsung GS4

52CONFIDENTIAL

