Why the Wi-Fi drops in the warehouse and not in the front office

An office is drywall, ceilings nine feet up, and laptops that sit still. A warehouse is thirty-foot ceilings, aisles of steel racking that block and reflect radio, inventory whose height changes with the season, and scanners that move at forklift speed through a dozen coverage cells in a minute. The access points that cover an office from the ceiling cannot see down a racked aisle from the roof, and a scanner that changes cells every few seconds is doing the hardest thing a wireless client can do, which is roam.

The complaint arrives as 'the Wi-Fi drops', but the scanner rarely loses signal. It holds on to an access point it has left behind, or the picking application's session times out during a hand-off that took two seconds too long. Those are design problems, and they have known fixes.

1. Access points mounted at the roof over the aisles, with racking between them and the scanner; the fix is lower mounting on the racking or the columns, or directional antennas aimed down the aisles
2. Old scanners that only speak 2.4 GHz, and the network still allowing the slowest legacy data rates, which lets a distant scanner cling to a far access point at a crawl; raise the minimum rate, put the scanners that can on 5 GHz, and retire the ones that cannot
3. Sticky roaming: transmit power turned up to fill the gaps, which makes every scanner hear a distant access point loudly enough to stay on it; turn power down, add access points, and turn on the fast-roaming standards only after checking the scanners support them
4. Too few access points for the device count, so a shift change or a receiving wave saturates one radio while the next sits idle
5. Interference from the building: microwave ovens in the break room, the neighbour's network on the same channel, wireless cameras, and in some plants the motors and welders on the floor

A survey done in July when the racks are half empty describes a different building from the one in November. Radio that passed through an empty bay is absorbed by a full one, especially by paper, liquids, and anything dense. Design for full racks, survey at both ends of the year if you can, and expect the fourth quarter to be the test.

Two things. A predictive design, from the floor plan and the racking layout, that says where the access points go and how many. Then a validation walk with the scanner model you actually use, not a laptop, because scanners have weaker radios and their own roaming habits. The output is a heat map at scanner height, a list of access points with their locations and names on a drawing, and the channel and power plan. Label the access points so the drawing stays true.

A survey is also what settles the argument between the WMS vendor, who says it is the network, and the network provider, who says it is the application. The heat map and the roam log say which.

• Scanners on their own VLAN, separated from the office, the cameras, and the guest network, with the WMS reachable and nothing else
• A DHCP scope sized for every scanner, tablet, and printer on the floor with room to spare, and a lease long enough that a scanner does not renew mid-shift
• Switch ports with enough power budget for the access points, and current firmware on the controller
• The application's session timeout raised to cover a normal roam, after the roam has been fixed, not instead of fixing it
• Label printers on the floor on a cable where there is one, because a printer roaming is a printer offline

• A consumer range extender in the back corner, which doubles the airtime every packet costs
• A second network name for the warehouse on the same access points
• Transmit power set to maximum, which makes the sticky-client problem worse in every aisle
• Replacing the scanners before surveying the building, which produces newer scanners with the same complaint

The survey and the redesign are the network, firewall, and Wi-Fi work on our Enterprise IT services page, and the floor it lands on is described on the 3PL and warehouse software page; the label printer case study is what the printers on the same floor needed.