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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
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved 2
Agenda
• Characteristics of a Warehouse • Planning for Deployment • RF Fundamentals • Troubleshooting • Q&A
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
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• Technical – Incorrect antenna aiming – Tend to be older clients • Outdated OS/firmware • Limited protocol support (LEAP/802.11b?)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
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
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
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
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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CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
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?
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
Q&A
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