Advanced RF Design & Troubleshooting #AirheadsConf Italy

1. Advanced RF Design & Troubleshooting
Blake Krone
June 2014

2. CONFIDENTIAL
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2 #AirheadsConf
Agenda
Who Am I?
Past and Present Design Goals
Design, Design, Design
Love Thy Patch
Demystifying RF With Tools

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Who Am I?

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Who Am I?
Blake Krone
blake.krone@nostringsattachedshow.com
@blakekrone
http://NSAShow.com
All around tech junkie, programmer, RC junkie
CWNA, CCIE #31229 (Wireless)

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Past & Present Design Goals

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Pre #GenMobile Design Goals
Green = Good = Coverage
• Designed for Coverage
– Full bars, devices were connected
• Large cells, high power
• Less than 2 devices per person
– Laptop
– Smartphone

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#GenMobile Design Goals
Green = Good = Coverage – no longer applicable!
• Designed for Capacity
– I’m connected, but can I send/receive with 100 other
devices?
• Small cells, lower power
• More than 4 devices per person
– Laptop
– Smartphone
– Tablet
– Wearables

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How To Reach the Goals?
RF is like Black Magic, the Dark Arts, etc…
Or Is it?
• Design, Design, Design
• Troubleshooting Accordingly

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Design, Design, Design

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About RF Design
Key to a Great Design
• Airtime
– Be fair and play fair
• SNR
– Not just RSSI!
• Frequency & Channel Reuse
– Clients are like 2 year olds, their way or the high way!
• Don’t Forget the Backbone
– It’s never the RF, it’s those pesky servers!

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Airtime
Basic Design
• RSSI Good
• Legacy Data Rates
On
• Longer Waits to Get
On
• Longer Time On
Great Design
• RSSI Great
• Legacy Data Rates
Off
• Get On and Off
Quickly

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Airtime Example
Download/Upload 1Mb File
• 6Mbps Client – 1.33s
• 36Mbps Client – 0.22s
How Many Users per 5 Minute?
• 6Mbps – 230
• 36Mbps - 1363

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Airtime Calculations
Mode
(20Mhz, 1ss – 3ss)
Receive Sensitivity per
Chain (dBm)
SNR (dB) @ -95 dBm
Noise Floor
Legacy 802.11a/g 54
Mbps
-75 20
802.11n HT20 MCS7/15
65 – 216 Mbps
-71 24
802.11ac VHT20 87 –
289 Mbps
-65 30
Great Resource for Calculating Device Airtime:
http://www.revolutionwifi.net/p/downloads.html - WLAN
Capacity Planning Overview and Worksheets.pdf

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SNR
SNR is More Important Than RSSI!
• RSSI is how strong I hear AP
– Doesn’t imply quality
• SNR is relationship to noise floor
– Changes per site per area per day per environment etc

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SNR Example
Take datasheet values for AP-220
• 802.11n HT20
• MCS7/15
• 65 – 216 Mbps
• 24 SNR
Perfect world with -95 dB noise floor says -71
dBm RSSI. Reality says more like -65 dBm or
better!

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Frequency & Channel Reuse
Use As Much Frequency As You Can
• 2.4GHz
– Yes it’s dirty and bloated, but we need it
• 5.0GHz
– Don’t be shy, client adoption increasing rapidly
– Just watch out for DFS channels
• 20MHz Channels Might Make More Sense
– We don’t always need insane speed but we do need
channels

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Frequency & Channel Reuse
• Lower the Power
– Just cause an AP does 200mW doesn’t mean you should
allow it
– Reduce the cell size to allow more channel reuse
• Steer When You Can - Client Ultimately Calls the
Shots
– If it thinks 2.4GHz is better it’ll join there
– Always assume a roaming issue will occur

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Don’t Forget Backbone
RF Still Needs Wires & Core Services
• DHCP
– Active clients vs Associated clients. Makes no difference,
they still use an IP if just associated.
– Short lease times for guest – example football game is 3
hours, use 3 – 4 hours for lease
• AAA Scaling
– Account for Web/RADIUS server calls per second for portals
– Better yet, forget about the portal!

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Love Thy Patch

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Love Thy Patch
Learn From Interior Lighting Engineers
• Flood or Spotlight?
– While a floodlight might work is it the right solution?
– Paint the area with RF like you would light.
• Omni or Patch?
– Same rules apply here as they do with lights.
– More precisely control signal spread

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Patch Example
How would you cover a
long corridor that never
seems to end and provide
density coverage?

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Patch Example
Absolutely Not! Omnis Maybe

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Patch Example
Use patch antennas
alternating down a
hallway.
Signal goes where
you want, antennas
accessible.

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Demystifying RF With Tools

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Demystifying RF
A screwdriver makes a decent hammer, but a
hammer is better.
• Survey Tools
– Site Survey Software
– Spectrum Analysis Software
• Packet Tools
• Testing Devices

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Survey Tools
Ekahau Site Survey
• Predictive Design
• Active (AP on Stick)
Survey
• Post Validation
Survey
• Proxim 8494
Adapters

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Spectrum Analyzer
Metageek Chanalyzer
Pro
• USB Form Factor
• 2 x Wi-Spy DBx for
2.4 & 5GHz
simultaneous
• Easy to Use
• Report Builder

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Packet Capture
Metageek Eye P.A
• Compatible with
pcap files
• AirPcap direct
capture
• Visualizes the
packet flows

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Testing Devices
Fluke AirCheck
• Rugged handheld
test device
• Consistent
readings
• Fast startup
• Auto Test tool
• Import / Export data

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Testing Devices
Fluke LinkSprinter 200
• Extremely portable
• PoE, Link, VLAN,
DHCP, Internet
testing device
• WiFi hotspot for
advanced mobile
display

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Questions

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Thank You
#AirheadsConf
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