802.11ax PHY changes
Last Post: January 3, 2018:
I just watched a webinar on 802.11ax presented by NI (National Instruments).
There are some very interesting changes from a PHY perspective that will require substantially better electronics (oscillators, etc.) and it will have have 3 dB tighter than /ac EVM limits - i.e. it will also have higher SNR requirements.
Sub-carriers will be spaced at 1/4 the spacing of /a/g/n/ac, but symbol duration's will be longer. Protection for /a/g/n/ac frames will be provided by using the existing Training and Signalling fields using the current sub-carrier spacing, followed by /ax Training/SIG fields with its close-in spacing.
Phase errors will limited to 1/10 PPM, and PHY test equipment will require non-signalling test methods requiring chip-set based Firmware in every device. As a side note I should mention that test instruments usually need to be better by a factor of 10 than the DUT's they are testing - so in this case we would expect 1/100 PPM accuracy as a minimum in the test gear for 802.11ax.
From my own experience I can tell you that these requirements will make PHY level testing even more expensive than it already is - Very much more expensive. IMO small radio manufacturers may have a hard time staying in business. Expect fewer choices, both in test gear and in radios, in the future.
NI has a Whitepaper on the /ax PHY and MAC changes at:
Here is a good one from WLAP Pros in Phoenix too:
Can you share the webinar link with NI or was it private?
The webinar will supposedly be available publicly tomorrow.
I will put up the link when they email it to me.
Excellent. Thank you sir. The whitepaper already has some of the best printed info I've seen so far.
I just watched Chucks presentation. It was excellent, and a fine complement to the NI webinar.
Actually, Chucks presentation was a great overview of the technology, whereas the NI webinar was (almost) totally related to the PHY - which is where the majority of my interest lies.
I found Chucks talk regarding the lack of any /ax Broadcast frames, its requirement for multiple NAV's on each device, and the new 2 MHz Channel widths especially interesting.
During the NI webinar, I almost asked a question about whether there were new CCA thresholds - regrettably I didn't. I just found it talked about in the white paper though.
As an aside, I have been making 802.11 PHY tests for almost 9 years and Receive Sensitivity measurements have been slowly, if not steadily, improving. They are now almost 20 dBm higher for the same PHY, than they used to be - but CCA requirements have really not changed much, if at all. BTW, neither have the 802 standards minimum Sensitivity Levels, except when a new PHY is introduced e.g. /n/ac.
I guess with the new "colored" BSSID's they just about had to change the CCA values..
Sorry, I didn't get the link until today.
Here it is:
Hope you find it useful.
Here is another white paper on 802.11ax from (R&S) - Rohde & Schwarz.
Great info. Thanks Howard.