Hostile Environments Wireless LAN Design for...

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 2

Agenda

•  Characteristics of a Warehouse •  Planning for Deployment •  RF Fundamentals •  Troubleshooting •  Q&A



Characteristics of a Warehouse


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


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•  Technical –  Incorrect antenna aiming –  Tend to be older clients •  Outdated OS/firmware •  Limited protocol support (LEAP/802.11b?)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



Planning for Deployment


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


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


Quantify Facility Requirements

•  Intended use(s) •  Ceiling height / building square footage •  Unique coverage areas? Freezers? •  WAN backhaul/redundancy •  Local compute resources


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


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


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


AP Location – Adjust for High Shelves

•  As shelving gets higher, place Aps more closely together to overcome attenuation from shelving


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



RF Fundamentals


RF Fundamentals – Design Considerations

•  The Goods Stored •  Coverage vs Coverage Reliability •  Antennas and Antenna Patterns •  Managing AP to AP Interference


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


Characterizing Goods: Absorption

Alternatively, if limited to 2.4GHz studies, this reverberation chamber is usually more accessible •  Check the break room


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


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”


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


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


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


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


Wall Mounted Antennas – 3D View

High Gain Antenna Pattern (narrow vertical beamwidth)

Low Gain Antenna Pattern (wide vertical beamwidth)


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



Troubleshooting


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?


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?


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?



Q&A



Thank You

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