hostile environments: wireless lan design for warehouse wlpc
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CONFIDENTIAL
© Copyright 2014. Aruba Networks, Inc.
All rights reserved
CONFIDENTIAL
© Copyright 2014. Aruba Networks, Inc.
All rights reserved
Hostile Environments
Wireless LAN Design for Warehouses
Charlie Clemmer
Consulting Systems Engineer
Twitter: @charlieclemmer
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Agenda
• Characteristics of a Warehouse
• Planning for Deployment
• RF Fundamentals
• Troubleshooting
• Q&A
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Characteristics of a Warehouse
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How Are Warehouses Unique?
The Good, The Bad, and The Ugly
• Typically low bandwidth requirements
– Usually handheld scanner or forklift mounted terminal
• High ceilings
• Tall shelving packed with goods of varying density
• Potentially hostile temperatures (both extremes)
• Seasonal variability with stock levels
• Frequent layout changes
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Characteristics of a Warehouses
• Physical
– Tall metal shelving, limited LOS to ceiling
– Long aisles, limited AP installation options
– Freezers, firewalls, building additions
• Technical
– Incorrect antenna aiming
– Tend to be older clients
• Outdated OS/firmware
• Limited protocol support (LEAP/802.11b?)
• Operational
– Product pickers incented based on speed
– Varying stock levels/rack configuration
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Planning for Deployment
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Planning for Deployment
• Inventory wireless devices
• Quantify facility requirements
• Develop coverage and client density model
• Perform RF plan and spectrum clearing
walkthrough
• Perform passive site survey post deployment to
verify coverage
• Perform client testing to verify operations
• Fine tune plan/documentation for next site
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Inventory Wireless Devices
• Identify all client device make/models/apps
• Capture all device limitations (TX
power/Encryption)
• Capture best firmware level
• Worksheets used for RF and Security designs
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Quantify Facility Requirements
• Intended use(s)
• Ceiling height / building square footage
• Unique coverage areas? Freezers?
• WAN backhaul/redundancy
• Local compute resources
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Selecting a Target Cell Edge Data Rate
• Manufacturers of
some voice and data
devices recommend
“minimum SNR”
• Applications typically
determine data rate
• Each 802.11 data rate
requires a minimum
SNR to demodulate
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Match AP Output Power to Clients
• Match AP output power to least capable client device
• Reasons why this is important
– If the AP transmits at higher power than the client, the client may
hear the AP, but may not have sufficient transmit power so the AP
can hear the client
– APs have greater receive sensitivity than do clients
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AP Location & Antenna Selection
• Vertical coverage is especially important in
warehouse environments to get coverage in between
shelving to ensure that intended signals reach the
clients
• Low gain, downtilt omnidirectional antennas are
ideal for warehouse and high-ceiling environments
because:
– Low gain limits range to a predictable area around the AP and
reduces AP-AP interference
– Low gain limits users per AP to a controlled area
– Downtilt omni pattern provides users at ground level a higher
signal than Aps see from each other
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AP Location – Adjust for High Shelves
• As shelving gets higher, place Aps more closely
together to overcome attenuation from shelving
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AP Guidelines for Warehouses
• For general dry goods, overhead mounting is
recommended
• For cold/frozen storage, wall mount strategy is more
typical and every row should have 1 AP with clear
line of sight
• Use down-tilt omnidirectional antennas when
ceilings are above 25 feet
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RF Fundamentals
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RF Fundamentals – Design Considerations
• The Goods Stored
• Coverage vs Coverage Reliability
• Antennas and Antenna Patterns
• Managing AP to AP Interference
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Characterizing Goods: Absorption
Microwave Absorption Analysis
• Goods are placed in a reverberation chamber and
excited simultaneously by multiple modes and random
incidence wave fronts of varying frequency
• During the test, the specific absorption rate is
monitored to determine the absorption characteristic
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Characterizing Goods: Absorption
Alternatively, if limited to 2.4GHz studies, this
reverberation chamber is usually more accessible
• Check the break room
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The Goods: Absorption & Reflection
• All products have different RF characteristics and
can be thought of in relative terms with respect to
their Absorption and Reflection characteristics
– Absorption Goods
• Low Absorption – Air, low density paper goods, apparel
• Higher Absorption – Rubber, plastics, general dry goods
• Highest Absorption – Liquids, frozen goods, butter
– Reflection Goods
• Metal parts and machinery/handling equipment
• In general, High Absorption goods affect RF much
more than High Reflection goods
• In stacks of goods, waves propagate in both the
materials and spaces of air. Variations can have
significant effects
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Coverage Vs Coverage Reliability
• Most warehouses contain goods of varying
absorption characteristics
– Coverage affected differently in different areas of the
warehouse
– Coverage varies day to day due to changing in stock levels
• The ability of an RF coverage design to survive
these changes is called “Coverage Reliability”
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Coverage Reliability Basics
• Reliable Coverage requires the following:
– Actual AP or Client Power minimum
– Actual antenna gain in the direction of clients
– Loss due to materials and walls/racks
– Higher minimum desired SNR for day to day variation in stock
• Because dB is a logarithmic scale, small changes
can make a big difference on the end result
• Coverage Reliability must be a DESIGN
requirement and not exclusively a survey
validation
• Typical Site Survey is only one snapshot in time
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Design Considerations - Antennas
• Radiation Pattern
– All antennas radiate in 3 dimensions
– Antennas do not create or destroy
power
– Antennas focus energy into a tighter
region of 3D space
• Gain
– Higher gain = more tightly focused
– Higher gain typically focuses in the
vertical direction
– High gain antennas are typically no
appropriate where both horizontal
and vertical coverage is needed
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Omni-directional Antenna Patterns
Azimuth (H-plane) Elevation (E-plane)
High Gain Antenna
10 dBi
Vert BW: 8o
Max Range: 500m
Lower Gain Antenna
5dBi
Vert BW: 18o
Max Range: 285m
Down Tilt Antenna
3dBi
Vert BW: 60o
Centered at -45
Max Range: 226m
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Wall Mounted Antennas
• The antenna on the
left is 13 dBi, on the
right is a 5 dBi
antenna
• The darker area is a
coverage hole close
to the AP, caused by
the high gain antenna
pattern
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Wall Mounted Antennas – 3D View
High Gain Antenna Pattern
(narrow vertical beamwidth)Low Gain Antenna Pattern
(wide vertical beamwidth)
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Antennas (Summary)
• Vertical coverage is critical in high ceiling
environments
• Low gain, down-tilt omni-directional antennas are
ideal
– Low gain limits range to a predictable area
– Reduces AP-AP interference
– Focuses signal towards users at ground level
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Troubleshooting
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Troubleshooting User Issues
• What symptoms are being reported?
• Where in the network flow is the problem
occurring?
– Can the client establish an association with the AP?
– Can the client authentication if 802.1X is being used?
– Did the client get an IP address?
– Does the problem happen while the client is stationary, or while
the client is roaming?
– What is the SNR between the client and the AP?
– Did any network events occur at the time of the problem?
– Is there any interference on the RF spectrum?
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Troubleshooting Roaming Issues
• Are all APs on a consistent power level?
• How many APs can a client hear?
– Does AP power setting match the EIRP of the client?
– Are Aps a mix of legacy a/b/g and 802.11n?
– Do clients support 802.11k? Is it enabled?
– Can a probe response threshold be used on the AP?
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Troubleshooting Installation Issues
• Has the AP power level(s) changed?
- Are APs at full power?
• Are antennas aimed correctly?
- Are the correct antennas being used?
• Has stock levels changed dramatically?
• Has the warehouse layout been reconfigured?
• Has a new wireless service been introduced?
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Q&A
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Thank You
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