Warehouse Wi-Fi With 80 MHz Channels and Roaming Voice Clients
A 12,000 m² automated warehouse uses 12 ceiling-mounted 5 GHz access points, all configured for 80 MHz channels and 30 dBm EIRP. Sixty handheld scanners, 25 AGVs, and 10 voice-over-Wi-Fi headsets share the network. During peak picking, the voice clients report 300–800 ms one-way latency and occasional disconnects; scanners show retries above 40%, and AGV telemetry misses its 100 ms deadline. A site survey shows each AP hears at least four others above -70 dBm, and only two 80 MHz channels are usable without DFS. The operations team asks whether to add more APs, raise power, or change channel width, and whether to force all clients to 5 GHz. The building has metal racking and changing stock levels, so the survey is noisy.
1. Evaluate the proposed remedies and recommend a channel and width plan, justifying it with airtime and co-channel reasoning.
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Adding APs or raising power will worsen the problem. With 80 MHz channels, only two non-DFS channels exist, so 12 APs reuse each channel about six times; each AP already hears four others above -70 dBm. An 80 MHz channel consumes four 20 MHz channels, reducing reuse and spreading energy over a wider band. Raising EIRP to 30 dBm enlarges cells and increases co-channel interference. Move scanners and AGVs to 20 MHz channels, which provide more non-overlapping channels and lower airtime per frame. Use 40 MHz only for voice if the channel plan has enough clean spectrum, and lower EIRP to shrink cells. Add APs only where coverage holes exist, not for capacity. Forcing all clients to 5 GHz is risky; keep 2.4 GHz as fallback where scanners need coverage, but steer capable clients when RSSI is adequate.
2. Design roaming and client-band policy for the voice and AGV clients. Include thresholds and practices to avoid.
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Enable 802.11k and 802.11v where clients support them, and 802.11r only if all voice devices interoperate with it. Set a minimum RSSI around -70 dBm with about 6 dB hysteresis; voice should roam before -67 dBm. Avoid a single aggressive threshold that causes ping-pong roaming. Disable low legacy rates on 5 GHz to reduce airtime, but do not disable rates that distant scanners still need. For AGVs, prefer deterministic coverage and redundant APs over aggressive roaming, because a roam during a control cycle can miss the 100 ms deadline. Do not force every client to 5 GHz; use band steering with a probe suppression or minimum RSSI policy, and verify that scanners still associate. Test handover while stock levels change.
3. What measurements would prove the change worked, and what failure modes could remain?
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Collect per-AP channel utilization, retry rate, airtime consumed by each client class, latency percentiles, packet loss, and roam time during peak picking. Compare voice one-way latency and AGV deadline misses before and after. Validate that 20 MHz channels are actually non-overlapping in the deployed plan and that EIRP changes did not create coverage holes. Remaining failure modes include DFS radar events forcing channel changes, metal racking producing deep nulls, sticky clients that ignore 802.11k/v, uplink congestion at the AP, and increasing stock levels changing multipath. A post-change survey should include the worst-case aisle and a failover test.