Best practices for WiFi AP channel, power and layout

Here are the starting points I use for WiFi networks.

  • 5 GHz AP transmit power: 18 dBm
  • 2.4 GHz: only 1/4 of APs 2.4 GHz enabled.
  • 2.4 GHz AP transmit power: 13 dBm
  • manually pick channels for least overlap
  • consider DFS channels for interior locations where best performance (clearest channels) are desired
  • 40 MHz channel (VHT40) on 5 GHz, 20 MHz channel (HT20) on 2.4 GHz

Wifi AP transmit power

Commercial Wifi systems have automatic power adjustment routines that estimate the optimum power levels for best handoff while avoiding co-channel interference. You might choose to set your Wifi AP transmit power manually to get better control of your network. This can really help mobile users where devices try to hang on to the more distant Wifi AP instead of roaming.

The exact Wifi AP transmit power level depends on the devices you prioritize. For mobile phones, Wifi AP transmit power in the 18-20 dBm range is a good starting point. Increasing power increases download data bandwidth, but if it causes your phone to hang on too long, upload errors increase dramatically and you will experience bad two-way video connections. As network density increases to commercial level (hotels, schools), it’s even more important to use 5 GHz only and lower Wifi AP transmit power.

Large Rooms

In the extreme case of several hundred person lecture hall, you may need:

  • two to four 5 GHz Wifi AP (as traffic demands). Note that excessive AP density causes problems from too much channel reuse.
  • 40 MHz channels
  • transmit power: 10-13 dBm
  • APs high on wall or tripod, facing down on crowd, in farthest corners of room for least overlap.

Hotels

  • Business hotels: Wifi AP in each room (or one per pair of adjoining rooms), 5 GHz, 6-10 dBm transmit power.
  • Casual hotels: might serve 4-8 rooms with a 10-15 dBm transmit power 5 GHz Wifi AP.

Wifi network planning

SSID

Do NOT pick different SSIDs for each AP, floor, room, etc. This limits the ability of the device to pick the best AP. Put all the guests/customers on one Hotspot 2.0 SSID, and using VLAN put internal stuff (sensors, control, admin) on another SSID. Two or three SSIDs (public/private) should be adequate. Complicated networks like hospitals may need to partition users into 3 VLANs/SSIDs. Do not use more than 4 SSIDs to avoid wasting data bandwidth on SSID broadcasts.

Channel selection

  • Maximize physical distance between co-channel APs.
  • Only 1 of every 4 or 8 Wifi APs might have 2.4 GHz enabled with 20 MHz bandwidth on channel 1, 6 or 11 ONLY.
  • Auto-channel Wifi APs will act based on what they can hear, which may be very different than what your clients can hear. High end professional systems from Cisco and Meraki do a better job than the average AP at guessing the right channel since they use more sophisticated measurement and analysis.
  • Site survey: Consider InSSIDer or AirSpy.
  • Set the APs on lower floors and middle of the building to channels that are more in use in adjacent (not controlled by you) Wifi APs. Set the APs in busier traffic areas to the clearest channels.
  • You can play tricks like reusing channels from low-traffic APs (say a loading dock–manual bar code scanners don’t take that much bandwidth) more closely physically spaced than usual.

Channel width

  • Use only 20 or 40 MHz channels on 5 GHz. Increased interference on 80 MHz or 160 MHz in urban areas leads to ineffectiveness.
  • Because of the difference between raw channel rate and throughput, even if you have a 100 Mbps throughput connection to the AP (such as via MoCA 2.0/2.5 or Powerline Ethernet AV2/G.hn) 40 MHz channels can still more than double your Wifi throughput vs. 20 MHz channels on 5 GHz
  • 20 MHz ONLY on 2.4 GHz

The only time I could think of using 40 MHz on 2.4 GHz is on a farm in a barn or shed, away from other buildings and with one AP serving the whole building.

The only place I would consider 80 MHz for 5 GHz is for single-room service in a rural home office or personal “cave”, isolated from neighbors and the rest of the home, with lowest power 10 dBm for just that room.

For home entertainment or gaming systems the ultimate networking performance comes from either:

  • having a 5 GHz AP in the same room
  • having a wired Ethernet connection (or MoCA or Powerline Ethernet)

Notes

Ubiquiti routers with DFS

Ubiquiti AP DFS
UniFi AP-AC v1 No
UniFi AP-AC v2 No
UniFi AP-AC-Pro Yes
UniFi AP HD Wave 2 Yes

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