iPad Pro Wi-Fi 6E Preference of 5 GHz over 6 GHz

You may have read my 6 GHz discovery test of the new Wi-Fi 6E iPad Pro. This time we ask the “Hey Siri, what is iPad Pro’s favourite band?” question.

Since Apple hasn’t published any documentation that would cover this subject, I configured a tri-band SSID on Catalyst 9136 AP. The SSID name is the same for all 2.4 GHz, 5 GHz and 6 GHz bands. Now, what band does iPad prefer?

Setup

  • Wi-Fi 6E iPad Pro 11-inch (4th generation) running iPadOS 16.1
  • Catalyst 9136 Wi-Fi 6E AP
  • C9800-CL cloud controller running 17.9.2

Max transmit power and 80 MHz wide 5 GHz channel

All 3 bands are enabled with manual Power Level 1 (PL1), which forces the AP to use highest permitted Transmit Power.

In this case, the 6 GHz SSID had the strongest absolute signal strength (RSSI) of the 3 bands.

  • 2.4 GHz enabled, PL1
  • 5 GHz channel 36, 80 MHz wide, PL1
  • 6 GHz channel 5, 80 MHz wide, PL1

The iPad prefers the 5 GHz band and joins using this band.

Reduce transmit power on 5 GHz radio

Let’s use the exact same configuration as above and reduce 5 GHz radio’s transmit power to the lowest, Power Level 8 (PL8). Will that make it prefer 6 GHz?

  • 2.4 GHz enabled, PL1 (RSSI on the iPad -31 dBm)
  • 5 GHz channel 36, 80 MHz wide, PL8 (RSSI on the iPad -55 dBm)
  • 6 GHz channel 5, 80 MHz wide, PL1 – strongest absolute RSSI (RSSI on the iPad -30 dBm)

Yes! The iPad Pro prefers 6 GHz every single time. As you can see, the 6 GHz RSSI is 25 dB stronger than the 5 GHz one, which is why (as far as I can tell).

Narrower 5 GHz channel

We are using the the same configuration as in our very first scenario, but 40 MHz we will reduce 5 GHz channel width to 40 MHz.

  • 2.4 GHz enabled, PL1
  • 5 GHz channel 36, 40 MHz wide, PL1
  • 6 GHz channel 5, 80 MHz wide, PL1

Using narrower 5 GHz channel makes the iPad connect using 6 GHz instead.

Disable 5 GHz radio

This time we disable 5 GHz radio and see if 2.4 GHz or 6 GHz wins. I have high hopes for 6 GHz, you?

  • 2.4 GHz enabled, PL1
  • 5 GHz disabled
  • 6 GHz channel 5, 80 MHz wide, PL1 – strongest absolute RSSI

Indeed, the iPad prefers 6 GHz.

Now, let forcefully shut the 6 GHz radio on the AP. iPad moves to its only available option, the 2.4 GHz radio and happily lives there. We now reenable the 6 GHz radio. The iPad doesn’t automatically jump back to 6 GHz, although 6 GHz has stronger RSSI. When we disabled iPad’s Wi-Fi radio, and reenable, it connected on 6 GHz.

Make 2.4 GHz stronger than 6 GHz and disable 5 GHz

Can we make 2.4 GHz appealing enough to the iPad so that it would prefer it over 6 GHz? Let’s disable 5 GHz radio, keep max transmit power on 2.4 GHz, and reduce 6 GHz transmit power to the lowest Power Level 8 (PL8).

  • 2.4 GHz enabled, PL1
  • 5 GHz disabled
  • 6 GHz channel 5, 80 MHz wide, PL8

The 6 GHz RSSI (-45 dBm) is now weaker than the 2.4 GHz RSSI (-33 dBm) by 12 dB. Is it good enough reason for the iPad to prefer 2.4 GHz?

Not really. It connected on 6 GHz 2 times out of 3. Once it connected on 2.4 GHz.

Summary

When 80 MHz wide 5 GHz channel is used, the iPad prefers 5 GHz. If 5 GHz drops below a certain threshold, and is much weaker than 6 GHz, it then prefers 6 GHz.

It prefers 6 GHz over 40 MHz wide 5 GHz channel.

It doesn’t use 2.4 GHz unless it has no other option.

Please take these tests with a pinch of salt. Ideally I would repeat each of them 10 or so times. Time is of the essence and I only repeated each test 3 times.

Published by

Jiri Brejcha

Jiri is passionate about mobility ranging from Wi-Fi to folding bikes;-) He is a Wi-Fi Technical Solutions Architect at Cisco UK, proud member of the Cisco Live Network Operations Center deployment team, and WLAN Pi development team. If he is not working, he is most likely riding his Brompton bike.

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