Wireless LAN & 802.11ac Wi-Fi Fundamentals

802.11ac Wi-Fi Fundamentals Eric Johnson March 2014

CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved

2 #AirheadsConf

Agenda

11ac Standards Physical Layer Overview 11ac Data Rates Radio Realities

Transmitters Receivers

Antennas 11ac Beamforming 11ac Products

3 CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved

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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)

•  Be?er modulaAon (256-‐QAM) •  AddiAonal streams (up to 8) •  Beam forming (explicit) •  Backwards compaAbility with 11a/b/g/n

•  Refer to h?p://www.802-‐11.ac.net for in-‐depth informaAon


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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


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802.11ac Channels (FCC)

Channel

Freq (MHz)

UNII I and UNII II 2x 80 MHz 4x 40 MHz 8x 20 MHz

Band Edge Channel

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 48 44 52 40 56 64 60 Band Edge

5180 5200 5220 5240 5260 5280 5300 5320 5350

Band Edge 5150

149 161 157 153

5745 5765 5785 5805

Band Edge

5725

165

5825

100 112 108 116 104 120 128 124

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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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 48 44 52 40 56 64 60 Band Edge

5180 5200 5220 5240 5260 5280 5300 5320 5350

Band Edge 5150

100 112 108 116 104 120 128 124

5500 5520 5540 5560 5580 5600 5620 5640

Band Edge 5470

136 140 Band Edge

5680 5700 5725

132

5660


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Understanding 11ac Data Rates


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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.


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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


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QAM constellations

Amplitude +1

Amplitude -1

Qua

drat

ure

-1

Quadrature +1

Amplitude +1

Amplitude -1 Q

uadr

atur

e -

1 Q

uadrature +1

Amplitude +1

Amplitude -1

Qua

drat

ure

-1

Quadrature +1

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

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


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

•  Basic Symbol Rate –  312.5 KHz –  3.2 µs

•  Cyclic Extension –  t/4 0.8 µs –  t/8 0.4 µs

•  Bits Per Tone –  BPSK 1 –  QPSK 2 –  16 QAM 4 –  64 QAM 6 –  256 QAM 8

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Raw Data Rates

•  #Tones * Bits per Tone * Symbol Rate –  16 QAM, 20 MHz –  52 * 4 * 0.3125 = 65 Mbps

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Correct for Cyclic Extension

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Apply FEC Coding

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Transmitters


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Transmitter Line Up

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DAC Symbol Generation

Up Convert PA


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Transmitter Terms

•  Conducted Power –  This is the power that leaves the connectors

•  EIRP: Effective Isotropic Radiated Power –  This is the conducted power (dBm) + antenna gain (dBi) in

the direction of interest – cable losses (dB)

•  Peak EIRP –  This is what is regulated –  It is the conducted power + peak gain – cable losses

•  dBm: log power ratio to milliwatt •  dBi: antenna gain relative to isotropic •  dBr: relative power eg:used with describing

transmit mask

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802.11 Symbol Stream

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0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 6415−

11.25−

7.5−

3.75−

0

3.75

7.5

11.25

15

Time (symbols)

Line

ar A

mpl

itude


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802.11n Signal Frequency Domain

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0 5 10 15 20 25 30 35 4060−

50−

40−

30−

20−

10−

0

Frequency (MHz)

Am

plitu

de (d

B)

Digital Domain

After DAC

PA Non Linearity

0 5 10 15 20 25 30 35 4060−

50−

40−

30−

20−

10−

0

a


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Transmitter Non-Idealities

•  DAC Quantization: this is due to the limited number of bits in a practical Digital to Analog Converter –  This noise source is not affected when the power is reduced

•  PA Non Linearity: OFDM has a high Peak to Average Ratio. The peaks in the OFDM signal cause distortions which manifest as noise like shoulders –  Known as spectral regrowth –  For every one 1 dB drop in tx power the regrowth drops by 3 dB

•  2 dB net

•  The in channel noise is referred to as EVM –  Error Vector Magnitude

•  The out of channel noise interferes with other Wi-Fi channels and determines how close we can space antennas

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EVM

•  As the depth of modulation increase the number of bits per symbol increases

•  The in-band noise introduces uncertainty wrt to the actual symbol position

•  Higher order modulations decrease the space between code points

•  To make higher order modulations work the tx power needs to be reduced

•  The EVM noise will add with interference and background noise

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16 QAM


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BPSK 1/2 -‐5 -‐5QPSK 1/2 -‐10 -‐10QPSK 3/4 -‐13 -‐1316QAM 1/2 -‐16 -‐1616QAM 3/4 -‐19 -‐1964QAM 2/3 -‐22 -‐2264QAM 3/4 -‐25 -‐2564QAM 5/6 -‐28 -‐27256QAM 3/4 N/A -‐30256QAM 5/6 N/A -‐32

802.11n EVM (dB)

802.11ac EVM (dB)

Modulation Coding Rate

EVM Specfication and 22x tx table

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Receivers


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Receiver Line Up

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ADC Symbol Decode

Down Convert LNA


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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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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

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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).


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Coverage Example

1.  Sample coverage for 3x3 11n AP (or 3x3 11ac AP with 11n clients) in HT40 mode

• Coverage area sustains MCS5 and up

360 405

450


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Coverage Example

2.  Upgrade to 3x3 11ac AP with 11ac clients, still using 40Mhz channels (VHT40)

• Radius for 600Mbps (MCS9) area is 1/4 of that for 450Mbps (MCS7)

360 405

450 540

600


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Coverage Example

3.  Equivalent range for clients using 80MHz channels (VHT80)

– Rates roughly double, relative range for each of the MCS rates does not change, but 80MHz range is ~70% of equivalent (same MCS) 40MHz range

780 878 975 1170 1300

585


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Relative Range 802.11ac Rates

Datarate 40MHz 80MHz

MCS0 45 97.5 MCS1 90 195 MCS2 135 292.5 MCS3 180 390 MCS4 270 585 MCS5 360 780 MCS6 405 877.5 MCS7 450 975 MCS8 540 1,170 MCS9 600 1,300

Signal level and rela@ve range -‐dB r

MCS0 87 63 MCS1 85 50 MCS2 83 40 MCS3 79 25 MCS4 76 18 MCS5 71 10 MCS6 66 5.6 MCS7 63 4.0 MCS8 58 2.2 MCS9 51 1.0


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Pros and Cons of 802.11ac

•  Pros 1.  APs can accommodate more users/devices

•  Increased capacity 2.  Standards based Explicit Beam-forming increases SNR

•  Higher data rates over longer distances 3.  256-QAM

•  Increased throughput at high SNRs •  Improved modulation and coding techniques

4.  Multi-User MIMO (future generations) •  Improved utilization of RF capacity

5.  Use of 5 GHz spectrum •  More non-overlapping channels •  Quieter RF environment


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Pros and Cons of 802.11ac

•  Caveats 1.  Hardware update required to support 802.11ac

•  Some features will not be available on legacy devices 2.  Increased product cost

•  Small premium for 3x performance •  Prices will come down

3.  Supporting 802.11ac will result in increased load on the infrastructure

4.  AP-225 requires 802.3at (PoE+) for full functionality & performance

•  However, no restrictions on 11ac radio with 802.3af POE •  USB disabled, second Ethernet port disabled, 2.4GHz radio in

1x3:1SS mode


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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


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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.


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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


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Antennas


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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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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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•  By introducing additional antenna elements we can control the way that the energy radiates

•  4 elements excited in phase –  Equal amplitude

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Linear Plot

dB Plot

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•  By shaping the amplitude we can control sidelobes

•  4 elements excited in phase –  Amplitude 1, 3, 3, 1

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Linear Plot

dB Plot


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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


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Reading Antenna Pattern Plots - Omni

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Azimuth Elevation

Omnidirectional Antenna (Linear View)

-3 dB

Sidelobes


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Reading Antenna Pattern Plots - Sector

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Azimuth Elevation

Sector Antenna (Logarithmic View)

-3 dB

-3 dB

Sidelobes Backlobe

Front

Back Side


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802.11ac Beamforming


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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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Channel state information, implicit and explicit beamforming estimation

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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


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5− 4− 3− 2− 1− 0 1 2 3 4 51 10 4−×

1 10 3−×

0.01Antenna 1Antenna 2Antenna 3

Wavelengths

E Fi

eld

Am

plitu

de

Client Antennas

h11 h21

h31


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Line of Sight

•  3 stream AP •  Smartphone –  1 Antenna/1 Stream

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Simple Reflection

•  Let’s introduce two reflection surfaces and look at the impact of one bounce on each side

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Virtual Antenna Pattern


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Multi Stream Client

•  The reflections allow beamforming to send different streams with different antenna pattern through the system

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Stre

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tream

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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


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Aruba 11ac Solutions


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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

$1,295 U.S. List


Thank You

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