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  • Hi guys,

    I have A LOT of warehouses to predicatively design wireless for as they aren't yet constructed but need the design confirmed and issued so they can have cablers run their cables etc... So site surveys etc are out of the question, everything must be done predicatively via a planner tool like Ekahau/Airmagnet.

    The one part that really gets me is how are you supposed to calculate dB loss on shelves with different products?

    No where on the internet can I find dB loss of RF going through the actual product on the shelves and the generic -27dB for a warehouse shelf or -18dB value for a warehouse rack attenuation area on Ekahau is far too vague/approximate of a value to use.

    For instance, some racks are full of engine parts, they could stack up to 3 engines on the width of 1 row of shelves while on the other shelf there could be a bunch of car tyres. I know for a fact that the dB loss between an engine and a car tyre is no where near similar in value.

    In addition, there are so many gaps and holes around the products on the shelves which is also not factored in as all planner tools assume the obstruction is constant, uniform and no gaps/holes. Based on the planner results putting a omnidirectional AP less than 8M high in the middle of 2 shelves is guaranteed to have 0 spill over to the next aisle of shelves but I'm 100% sure theres going to be A LOT of random spill over and co-channel interference is going to kill my design.

    Directional Antennas have the same problem as the omni-directional APs as the lobe is far too large for a long/narrow shelf design without MASSIVE co-channel interference.

    How does an RF engineer predicatively calculate dB loss per object on the shelves? 

    What have the rest of you done to get warehouse designs that is 100% reliant on wifi work via a predictive with the client expecting less than 1% room for error?

    Any advice is greatly appreciated.

  • There is no way to accurately predict a changing environment. The predictive tools will only give you an estimate based on the values you give it.

    Best practice for warehouses:

    • Mount directional antennas at the ends of isles alternating the end. So every second AP is at the south end pointing north and every other the other way. For narrow beams you can use sector antennas mounted horizontally. 
    • As throughput requirements aren't that high in warehouses keep the channel width to 20MHz. That will give you more 5GHz channels to cycle through to minimize CCI. You might be able to make it work with 2.4GHz with 1-6-11 as the next AP on the same channel will be two isles away and at the other end.
    • Try to keep the transmit power low to minimize CCI. Often the AP doesn't need to cover the whole isle to the end as there are two APs with side lobes in the adjacent isles. If the shelves leak sufficiently they adjacent isle APs will cover the end of the isle. It depends what is on the shelves. Engines, concrete slabs, oil barrels are the best/worst blockers. You may need to know if some types of goods are in static locations. In hub terminal warehouses you don't have that luxury.

  • By Howard - edited: February 22

    I will second Petri's answers.   In addition, I'll add:

    1.   Don't dismiss directional antennas - they are your friends !  

    2.   Don't place AP's too high.  Use side walls, instead of ceilings wherever possible.   Keep them at safe level off the ground, you don't want equipment (fork lifts) running into  them.  See companies like Ventev for semi-indestructable wall and ceiling mounts.

    2.5   Don't forget that antennas can be found with "downtilt" built-in.

    3.0  Try to use RF barriers to your advantage where you can.   This can be a life-saver for some designs.

    3.1  Design for roll up/down doors to be in unexpected, up or down,  positions.   If you are using one for an intentional RF barrier, the customer may be very unhappy if it has to be opened frequently 

    3.2  Watch out for unexpected RF ducting, as through HVAC vents etc.  You might find signals hundreds of feet away from where you expect them.   Especially if the duct work is hidden above ceilings.   Don't laugh, I've seen it.

    3.3.   There are companies (e.g. ETS-Lindgren)  that make RF barriers for the interior of duct work, but it's unlikely you'll need any except for secure facilities.

    4.   Keep expected roaming speeds reasonable.   This can affect your AP spacing.  There is almost no way a floor plan designed for typical  walking speeds will keep up with much faster forklifts.  Especially if drivers have lax supervision at night.  

    4.5  (note) Search on for "forklift drifting" for interesting/funny/scary  videos.

    5.   Make sure any client devices attached to forklifts are not buried in metal enclosures, like tin cans attached to their frames.  Devices need to roam even when the operators aren't using them in their hands.

    6.   Design for adequate battery charging station placement (for clients, not forklifts).

    6.5  Check out Zebra Technologies for solutions that may help  you.

    7.   Be VERY leery of RRM !   Especially, set realistic min/max output power levels.

    8.  Typical warehouse devices like bar code scanners and printers do not require high wireless rates (no matter what anyone's marketing department tells you).  

    Good luck

  • Thanks guys for you reply,

    I've already factored in the advised suggestion but my issue is with the inaccuracy of the planner tools Ekahau and Airmagnet.

    Essentially as soon as I put an attenuation area or wall above 10dB of loss (surveyor recommends warehouse shelves to be 27dB and racks 18dB) I get no bleed.

    However in a different client's existing environment which is somewhat similar I did a post survey for, there was clearly bleed, lots of bleed. If I shoot down 1 AP per isle based on the bleed I saw using ant2566p4w, they would cause a lot of co channel interference on the 2.4GHz which is mandatory for this client's end user devices as some are doing 2.4GHz only.

    My dilemma is if I use the planner tool of the surveyor there will be way too much co channel interference as it is telling me I get 0 bleed with any AP/antenna as soon as I put a 10dB loss or more on the wall/shelves but my post survey results of similar environments show varying degrees of bleed, in some cases it can bleed across 3-4 isles but doesn't get all the way to the end meaning lots of co-channel interference.

    Unfortunately I can't do a survey on a stick as the warehouse is operational 24/7 and I cannot obstruct the forklifts etc... Also some of the warehouses I am to design aren't even built yet. Financially speaking a survey on the stick method was not budgeted for (I was not involved in the RFP, but given the work to complete).

    I have to get this right the first time round as this client is overseas and they won't pay for my travel more than once. They also have this expectation of having flawless wifi under 1 site visit and predicatively designed due to the promises stated on the RFP which I was not involved in so my ass on the line regardless of how unreasonable.

    With the directional antenna per isle approach using 1 down every isle but placed North/South/North/South, my issue with that is that the isles don't go all the way to the ends of the warehouse, there is a considerable distance between where the shelf ends and where the wall is so if the isles are horizontally oriented, then the vertical walkway will have co-channel interference from all the directional antennas.

    My second idea was to go with the directional antennas ant2566p4w but using a spotlight method like a stadium design due to the ceiling being very high (over 12 meters) and AP + antenna obviously cannot be placed much lower due to forklift clearance. However this method is essentially giving off an omni-directional pattern.

    On the planner tool this looks all hunky dory showing 0 bleed but I am worried about co-channel interference as looking at the post site surveys I've done, an omni-directional antenna showed A LOT of bleed across 3-4 isles and covering a really terrible circular area in other warehouse environments.

    What do you guys think about spotlight vs directional and what are your thoughts on the co-channel interference where the isles don't continue all the way to the wall? Has anyone done a warehouse environment and discovered that their post survey showed completely different bleed results to what the planner showed etc?

  • The antenna you propose are NOT that directional, it has a 60 degree beam width,   I'd suggest a more narrow beam.

    You also talk about being limited to 2.4 GHz, but this is a dual band antenna - What are you planning ?

    As far (No Pun Intended) as the end wall being well away from the ends of the racks, use a drop-down support (pole ?) at that end, to bring the AP's down to a lower value, and closer to the ends.

    It's no wonder you're getting so much bleed over, when the AP's are so far away from the ends of the aisles.  

    How high are you planning to mount the AP's on the (close-to-the racks) back wall ?

    I would plan on a longer visit, on  site, than you are probably planning on.  At least in that way you won't have to travel so much.

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