5 GHz Channel Width and Power Plan for a High-Density Auditorium
A 1,200-seat auditorium has 30 ceiling APs deployed for a keynote with 1,500 simultaneous devices. The current 5 GHz plan uses 80 MHz channels and 25 dBm transmit power on every AP. Attendees report video stalls; Mist shows a 35% retry rate, 70% channel utilization, and median per-client throughput of 8 Mbps. The 2.4 GHz band is enabled with 20 MHz channels and is carrying 400 devices. There are only six non-overlapping 80 MHz channels in the venue's allowed UNII bands, and the RF design shows four APs per 80 MHz channel. The customer wants maximum throughput per client and is reluctant to lower channel width because '80 MHz is faster.' The event starts in 48 hours. The venue also has a real-time location tracking use case for staff badges.
1. Recommend the 5 GHz channel width and channel plan. Justify the choice against the customer's 80 MHz preference.
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Use 20 MHz channels on 5 GHz in the auditorium, not 80 MHz. With 30 APs and only six 80 MHz channels, four APs share each channel; that is co-channel interference, not capacity. 20 MHz gives roughly 24 non-overlapping channels in the allowed bands and much better reuse; 40 MHz is a compromise only if the channel plan can keep reuse low. The customer's '80 MHz is faster' is true only for a single client with clean RF; here it lowers per-client throughput because airtime is shared and retries rise. Design a 20 MHz plan, keep 5 GHz as the primary band, and use 2.4 GHz only for legacy/IoT with low power. Reserve 80 MHz for isolated low-density areas, not the hall.
2. Recommend transmit power, band steering, and client steering settings. What should be validated with a walk test?
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Lower transmit power from 25 dBm to a level that gives a consistent cell edge, typically 14-17 dBm for ceiling APs in a dense hall, and balance power with channel reuse. Enable band steering so 5 GHz-capable clients are moved off 2.4 GHz; set a minimum RSSI/roam threshold so clients do not stay at -72 dBm. Disable 2.4 GHz on some APs or reduce 2.4 GHz power to shrink its coverage. Use 20 MHz on 2.4 GHz. Confirm that APs are not all on max power, which creates a large overlap and sticky clients. Validate with a walk test: SNR, retries, channel utilization, and the percentage of clients on 5 GHz.
3. How should Wi-Fi 6 features and the BLE location use case influence the design? How would you verify the result?
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Enable Wi-Fi 6 features that help density: OFDMA for small packets, BSS coloring with a well-planned color map, and TWT only where it does not harm latency-sensitive video. Do not rely on them to fix a bad channel plan. Keep the staff location badges on BLE or a separate IoT radio; do not widen 5 GHz channels for location. Before the event, run a validation: per-AP client count, 5 GHz utilization below about 60%, retry below 10%, and median throughput target. After the event, compare SLEs (Capacity, Throughput, Coverage) and adjust power/color map. If throughput still stalls, add APs or use 40 MHz in low-reuse zones, not 80 MHz everywhere.