Wi-Fi 6E Coverage in a Dense Lecture Hall
A 300-seat lecture hall needs Wi-Fi 6E. The room is 30 m x 20 m with a 6 m ceiling, concrete walls, and a metal ceiling grid. Current 5 GHz design uses 6 APs on the ceiling at 20 dBm with 40 MHz channels; users report good signal but poor throughput when 250 clients are present. The customer wants 6 GHz added with 80 MHz channels and high density. Spectrum analysis shows strong co-channel overlap with adjacent rooms and a nearby elevator shaft.
1. Evaluate the proposed 6 GHz 80 MHz design and recommend channel/width and power changes.
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Problem with the proposal. 80 MHz channels in 6 GHz cut the available non-overlapping channels roughly in half and, combined with 20 dBm and 6 APs in a 30x20 room, create co-channel interference and high airtime contention - the same failure mode as the current 5 GHz design. High density is about airtime per client, not raw channel width.
Recommendation.
- Use 40 MHz (or 20 MHz for highest density) in 6 GHz for the lecture hall; reserve 80/160 MHz for low-density areas. More, narrower channels give more reuse and lower contention.
- Lower transmit power (e.g., 11–14 dBm) and enable ARM/auto RF so power and channel adapt to neighbors. High power in a dense room increases co-channel overlap and sticky clients.
- Stagger channels across the 6 APs so no two adjacent APs share a channel; use the 6 GHz clean spectrum to your advantage.
- Consider more APs at lower power if 250 clients is the design target; 6 APs at 250 clients is ~42 clients/AP, which is high for 80 MHz.
Validate with a post-deployment survey focused on airtime utilization and retries, not just RSSI.
2. The metal ceiling grid and elevator shaft cause issues. How do they affect the design and what do you do?
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Metal ceiling grid. Acts as a partial shield/reflector: it can attenuate signals above the ceiling (where APs are mounted) and create multipath/null patterns below. Mount APs below the grid with appropriate brackets, or use the grid as a mounting plane with antennas oriented downward. Verify with a survey; do not assume ceiling-mounted = good coverage.
Elevator shaft. A large metal mass causes shadowing and reflections. Expect a coverage hole on the far side and possible multipath. Place an AP to cover the shadowed zone and avoid aiming through the shaft. Do not place an AP adjacent to the shaft where it radiates into metal.
Actions.
- Do a predictive survey with the grid and shaft modeled, then a validation survey with APs mounted as intended.
- Check 6 GHz coverage specifically; 6 GHz penetrates walls less than 5 GHz, so room-to-room leakage may actually be lower - confirm adjacent-room overlap is acceptable.
- Adjust AP placement and power based on measured results, not the plan.
Avoid over-powering to punch through metal; fix placement instead.
3. Users report good signal but poor throughput at 250 clients. What metrics and design levers matter most?
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Metrics that matter.
- Channel utilization / airtime per AP and per channel (target well under ~50% busy at peak).
- Retry rate and PHY rate distribution (are clients stuck at low MCS?).
- Client count and per-client throughput; number of clients per radio.
- Co-channel interference and adjacent-channel overlap.
- SSID count (each SSID adds beacon/airtime overhead).
Design levers.
- Reduce channel width (80 → 40/20 MHz) to cut contention and raise reuse.
- Lower power + more APs to spread clients and shrink cells.
- Band steering / 6 GHz preferred so capable clients move off 5 GHz; disable legacy rates where safe.
- Limit SSIDs and disable unnecessary broadcast/multicast (e.g., mDNS flooding) - big airtime saver in dense rooms.
- Enable client match/load balancing so clients aren't sticky on one AP.
- QoS/WMM to protect latency-sensitive traffic.
RSSI being "good" is expected - the problem is airtime, so measure utilization and retries, then reduce width and power and add capacity.