The document provides an in-depth analysis of the 802.11ac Wi-Fi standard, detailing its features such as channel width, QAM encoding, beamforming, and multi-user MIMO (MU-MIMO), which collectively enhance throughput and efficiency. It emphasizes the benefits of frame aggregation and forward error correction while advocating for increased availability of 5 GHz channels. Additionally, it presents several case studies and performance expectations to illustrate the practical applications and advantages of these technologies.

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802.11ac Feature Deep Dive
MatthewSMullin
RAFerruolo
Blog.airtightnetworks.com@MatthewSMullin
@RAFerruolo

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Agenda
• 11ac Feature/Benefit Review
• Dear FCC, etc. - More 5 GHz Channels Please
• What the heck is QAM?
• Beamforming Demystified
• Good Old Fashion MIMO
• MU-MIMO Magic
• Frame Aggregation Broken Down
• Forward Error Correction
• Tres Dynamic Channel Width
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11ac Features and Benefits
Feature Benefits 11ac
Channel Width Quadruple Throughput 20, 40, 80, 80+80, 160 MHz
QAM Encoding More Bits/MHz 16, 64, 256 QAM
Spatial Streams Double Throughput 8
Beamforming Higher Data Rates & Range (Standardized) Explicit
Multi User MIMO Switch-like Wi-Fi MU-MIMO
Frame Aggregation Greater MAC Efficiency
A-MSDU size 11,426 Bytes
A-MPDU size 1,048,576 Bytes
Forward Error Correction
Signal Strength Gain
1 – 2 dB for LDPC
BCC
LDPC
Dynamic Channel Width Use Widest Channel Possible RTS/CTS Enhancements
Bands Supported
More Channels & Less
Cluttered Spectrum
5 GHz Only

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Dear FCC - More 5 GHz Channels Please
• Channels shown as red may become available in not too distant future.
Image source: http://www.samsung.com/global/business/enterprise-communications/news/latest-
news/upcoming-new-wi-fi-technologies-ieee802-11ac

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Channel Width Australia
& US
Brazil China Europe Japan Korea
20 MHz 9 17 12 4 8 25
40 MHz 4 8 5 2 4 12
80 MHz 2 4 2 1 1 6
160 or 80+80 MHz 1 2 1 0 0 3
Channel Availability without DFS Channels
Includes TDWR (Terminal Doppler Weather Radar) channels 120, 124 and 128.

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Channel Width Australia
& US
Brazil China Europe Japan Korea
20 MHz 25 28 16 19 23 25
40 MHz 12 14 8 9 11 12
80 MHz 6 7 3 4 5 6
160 or 80+80 MHz 3 3 1 2 2 3
Channel Availability with DFS Channels
Includes TDWR (Terminal Doppler Weather Radar) channels 120, 124 and 128.

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Quadrature Amplitude Modulation
Source: Wikipedia - http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation
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Amplitude Modulation and Phase (Time) Shift
Constellation Diagram

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More Bits per MHz: 64-QAM vs. 256-QAM
As constellations become denser higher signal strength and SNR
are required to decode the data properly.
Constellation Diagrams

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QAM Analogy
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64-QAM
256-QAM
Phase and amplitude steer the dart.

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Explicit Beamforming: Higher Client Data Rates
• Uses NDP (Null Data Packets) sounding
frames
• Clients respond with channel state
• Channel state includes DSP, antenna
and RF properties
• AP uses channel state to calculate
steering matrix
• Steering matrix is used to determine
amplitude and phase (time) parameters
of the transmission
• Single spatial stream is transmitted over
multiple antennas
• Objective is to create constructive
interference at the receiver
SNR

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Explicit Beamforming: Potential Gains
Client type Spatial Streams Potential Gain
Phone
e.g. Galaxy S5
1 Up to 7 dB
Tablet
e.g. Galaxy Tab Pro
1 Up to 7 dB
Tablet
e.g. Surface Pro 3
2 Up to 3 dB
Laptop
e.g. MacBook Air
2 Up to 3 dB
Laptop
e.g. MacBook Pro
3 Negligible
Potential Gains for a 3 Spatial Stream AP

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Beamforming Analogy
Waves crests combining
resulting in a stronger wave

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Beamforming Oversimplified
Dark blue wave is transmitted at
the same time as the light blue
wave.
Dark blue wave is transmitted
before the light blue wave.
Antenna 2Antenna 1 Antenna 1 Antenna 2

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MIMO Example 1
• With an 80 MHz channel the max data rate is 1.733 Gbps, with
an expected max throughput rate of approximately 1 Gbps
• Puts all 4ss of the AP to good use
• Enables full capacity of the AP and channel

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MIMO Example 2
• With an 80 MHz channel the max data rate is 433 Mbps, with an
expected max throughput rate of approximately 260 Mbps
• Uses only 1ss of the AP’s 4ss
• Effectively only use ¼ of the AP’s throughput potential

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MU-MIMO: Efficient Use of AP Radio/Channel
• With an 80 MHz channel the aggregate max date rate is 1.733 Gbps
• However, the max aggregate throughput is expected to be somewhere
between 400 – 600 Mbps
• Enables AP to be used more efficiently and supports greater channel
capacity when clients support fewer spatial streams than the AP

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MU-MIMO Magic
• Downstream only
• Supports up to 4 clients
simultaneously
• AP uses channel state from
individual beamformees to
calculate a composite steering
matrix
• Composite steering matrix is
used to determine amplitude and
phase parameters of the MU-
MIMO transmission
• Relies on APs ability to create
beams (constructive interference)
in combination with null beams
Null Beam
Beam

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MU-MIMO Considerations
• AP transmit power is shared amongst the group in a MU-MIMO
transmission.
• Null beams raise the noise floor.
• Sustaining high per client data rate is more challenging with MU-
MIMO.
• Clients need to be spatially differentiated
• Channel state measurements consume airtime
• Unlikely the 256-QAM enabled MCS rates (MCS-8 and MCS-9) will
be used that often with MU-MIMO.

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Frame Aggregation Broken Down
MAC Layer Aggregation
• Frame aggregation is a technique of combining multiple MPDUs or
MSDUs.
• Makes 802.11 more efficient by minimizing the time lost to 802.11
protocol overheads, such as:
• Contention process
• Interframe spacing
• PHY level headers (Preamble + PLCP)
• Acknowledgment frames
• A key difference between A-MSDU aggregation and A-MPDU
aggregation is that A-MPDU aggregation happens after the MAC
header encapsulation process.

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A-MPDU Aggregation
Image source: EE Times - http://www.eetimes.com/document.asp?doc_id=1278239
A-MPDU - Aggregated MAC Protocol
Data Unit
• Multiple MPDUs into a single
aggregated MAC frame
• Uses block acknowledgements or
BlockAcks
• Retransmissions are limited to
specific subframes that were not
received.
• 802.11ac specifies that every
802.11ac transmission to be sent as
an A-MPDU aggregate.

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A-MSDU Aggregation
Image source: EE Times - http://www.eetimes.com/document.asp?doc_id=1278239
A-MSDU - Aggregated Multi Service
Data Unit
• Multiple MSDUs destined for the
same receiver are concatenated
in a single MPDU.
• Each original frame becomes a
subframe within the aggregated
MAC frame.
• Only MSDUs of the same Access
Class can be aggregated.
• Cannot be used for broadcast &
multicast.

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Frame Aggregation Analogy
Without Aggregation
With Aggregation

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Forward Error Correction
BCC - Binary Convolutional Code
• Required
LDPC – Low Density Parity Check
• Optional
• Potential Benefits:
• Effective gain of 1 – 2 dB over BCC
• Enable MCS-8 and MCS-9 (256-QAM rates) at greater distances
• Increase data rates
• Reduce transmission times
• Improve power savings
• Low density refers to the relatively fewer 1s, compared to 0s needed for
the parity check matrix.

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Dynamic Channel Width
• Objective is to use widest possible channel to transmit.
• RTS/CTS is used to determine when channel bandwidth is clear.
• 802.11a transmissions (20 MHz) are replicated as needed (e.g. 80 MHz
channel would require 4 separate RTSs)
• Devices addressed by the RTSs respond with CTSs for the free/usable
20 MHz channels.

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Staggered Primary Channels
20 MHz
Primary AP1
40 MHz 40 MHz
80 MHz 80 MHz
160 MHz
20 MHz
Primary AP2
AP1 AP2
Channels
100 104 108 112 116 120 124 128

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Dynamic Bandwidth - Transmissions Over Time
40 40
4040
80 80
20
20
80
20
20
t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 t13
Ch. 40
Ch. 44
Primary
Ch. 48
Ch. 36
Primary
AP1
AP2

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AirTight Networks 802.11ac APs
Dual radios
• Radio 1—802.11a/n/ac, 3x3:3, 5 GHz
• Radio 2—802.11b/g/n, 3x3:3, 2.4 GHz
Connectors
• LAN 1—GigE/802.3af PoE
• LAN 2—GigE/Wired Backhaul
• Power—12 VDC
• Console—RJ45
• Antenna—6 RSMA (Model C-75-E only)
Benefits
• Best price/performance
• Industry’s only 11ac WIPS solution
• Low power consumption (No feature sacrifice using 802.3af PoE)
• Uses existing infrastructure (No costly upgrades to 802.3at required)
Model C-75-E
External antennas
Model C-75
Internal antennas
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#11acDeepDive

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Additional Resources
www.airtightnetworks.com/11ac
802.11ac Data Sheets
For C-75 and C-75-E Access
Points
802.11ac White Paper
Essential Considerations
802.11ac Migration
Qualifying and Planning Questions
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29. © 2014 AirTight Networks, Inc. All rights reserved.
Session 1: Intro to 11ac
Session 2: 11ac Feature Deep Dive
Session 3: Is 11ac Right for Your Network?
Session 4: 11ac Deployment Best Practices
Session 5: 11ac Channel Capacity Planning
Session 6: 11ac Network Optimization
11ac Webinar Series

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Thank You!
Send inquiries to Ask@airtightnetworks.com
Next webinar: Tuesday, July 23rd, 8am & 6pm Pacific.
“Is 802.11ac Right for your Network.”
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