WiFi AP setting channel, power, and SSID: best practices

tl;dr

Unless you have top-end Cisco/Meraki gear with channel optimization software:

  • set Wifi AP power to 18 dBm
  • no more than 1 of 4 APs with 2.4 GHz enabled, set 2.4 GHz AP power to 13 dBm
  • manually pick channels for least overlap
  • 40 MHz channel (VHT40) on 5 GHz, 20 MHz channel (HT20) on 2.4 GHz

choose Wifi AP power level

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, especially if you’re having coverage issues 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. If it’s mobile phones, setting your 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.

School/College Wifi AP power level dBm

In the extreme case of a school in a large few hundred person lecture hall, you may need four 5 GHz Wifi AP, set to 40 MHz channels, using low transmit power say 10-13 dBm so that you reduce bleedover into adjacent rooms or outdoors.

Hotel Wifi AP power level dBm

In the case of a hotel, the number of APs depends on the customer profile. Business hotels may want a Wifi AP in each room (for rooms at least one step above basic) set to 5 GHz, 6-10 dBm transmit power. Casual traveler hotels might serve adjacent rooms with a 10-15 dBm transmit power 5 GHz Wifi AP every other room.

Wifi SSID plan

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 SSIDs (public/private) should be all you need, unless in a complicated network like hospitals you may need to partition users into 3 VLANs/SSIDs. Do not use more than 4 SSIDs as you’re wasting bandwidth on SSID broadcasts.

Wifi Channel plan

  • Make a plan maximizing physical distance between APs on the same channel.
  • 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.

There are two philosophies on manual vs. automatic channel plans for 5 GHz, based on whether your AP has DFS or not.

Ubiquiti routers with DFS

This list is best I can determine at time of writing using Firmware 3.7.21. Check yourself before making decisions!

Ubiquiti AP DFS
UniFi AP-AC v1 No
UniFi AP-AC v2 No
UniFi AP-AC-Pro Yes
UniFi AP HD Wave 2 Yes (beta tester access to UniFi AP HD November 2016)

Non-DFS Wifi AP channel plan

If you don’t have an AP capable of DFS (basically year 2015 and older APs) do not put APs on Auto channel. Auto-channel Wifi APs will act based on what they can hear, which may be very different than what your clients can hear.

  • It’s best to do a site survey yourself. If you’re doing this as a hobby, get an app like InSSIDer. If you’re a professional or prosumer, get something like 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–bar code scanners don’t take that much bandwidth) more closely physically spaced than usual.

DFS Wifi AP channel plan

If you have a DFS-capable router (many but not all professional and prosumer Wifi APs from 2016 forward) than use Auto channel; your router should prefer DFS channels unless you’re near airport radar.

You might deliberately “clear the air” for DFS by setting lower data traffic APs to manual channels, even if they are new APs, and only setting Auto channel for APs in the primary use areas (conference rooms, common work areas).

High end professional systems from Cisco and Meraki et al do a better job than the average AP at guessing the right channel since they use more sophisticated measurement and analysis.

optimizing WiFi AP channel width

  • Do not use more than 40 MHz channels on 5 GHz, the increased interference and lack of today’s clients capable of 80 MHz or 160 MHz make those settings a waste and network clogger.
  • 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)

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