Re: Is the data rate estimation for 5GHz channels overly pessimistic?

[Denis Kenzior <denkenz@gmail.com>]

Hi Simonas,

>>
>> Me or James can walk you through all this if needed.
> 
> Thanks for offering. I have cracked open the file, and just started playing 
> around by adding a new `he_test_data` structure. Alas, I’m really hazy on what I 
> ought to be filing into the `capabilities` and `he_capabilities` fields. My 
> initial guess is something like this, based on one of the other tests around:
> 
> +/* 5GHz, 40MHz, MCS 11, NSS 1 */
> +const struct he_test_data he_test_5_40mhz_mcs_5_nss_1 = {
> +    .freq = BAND_FREQ_5_GHZ,
> +    .rssi = -76,
> +    .expected_rate = 275200000ULL,
> +    .capabilities = {
> +        .he_mcs_set = { HE_MCS_SET(MCS11, 1), MCS_UNSUP },
> +        .he_phy_capa = { HE_PHY_CAPA(0x00) },
> +        .iftypes = 1 << NETDEV_IFTYPE_STATION,
> +    },
> +    .he_capabilities = {
> +        22, IE_TYPE_HE_CAPABILITIES - 256, HE_MAC_CAPA,
> +        HE_PHY_CAPA(0x00), MCS_UNSUP, HE_MCS_SET(MCS11, 1)
> +    },
> +};
> 
> This computes a rate of `25800000`, which I’m guessing corresponds to 25.8Mbps, 

Yes, sounds about right.  This is for a single NSS.  If NSS==2, then use 
HE_MCS_SET(MCS11, 2)

> perhaps? That’s fair I guess, since the only thing I really really changed in 
> there compared to the other tests is the `MCS11` (that’s supported by AX201) and 
> the `rssi`. There clearly are plenty of other fields that I should be filling in 
> here, I feel, if I wanted to accurately represent my hardware.

Right.  Easiest is to look at this with wireshark or iwmon:
https://rowelldionicio.com/identifying-802-11ax-support-wireshark/

> 
> I think I managed to grab the capabilities of both the AP and the client using 
> your instructions, but I’m really unclear on how to go from the output from 
> `iwmon` to fields in this struct. My best guess right now is to actually run 
> `iwd` under a gdb and place some breakpoints in the scanning code to extract the 
> capabilities. Would that make sense, or is there a better way to fill in these 
> fields?

Having the IE format from the spec would be easiest, but I can't find a public 
reference just now.

> 
> (As I’m writing this mail, I realize now that I probably want to somehow specify 
> NSS=2 for `2x2` MIMO…?)
> 

Yes.

> Another thing that confuses me a great deal is the fact that the scan results 
> with my APs don’t actually show any of the HE capabilities, only the HT and VHT 

Hmm, that would explain the low estimate.

> ones (see attached sample from the `iwmon` output.) I also tried scanning an 
> Android hotspot on a reasonably recent phone, and although the set of MCS 
> supported were different, the output still contains only HT and VHT 
> capabilities. I would love to attach my pcap here, but unfortunately I also have 
> no clue how to sanitize it, so I’m going to attach an excerpt from `iwmon`’s 
> output for the time being. Is this expected, or could this perhaps be at least 
> part of the problem I’m seeing? Is it possible that an AP could not advertise HE 
> capabilities at scan time, but for HE to still be used after authentication occurs?

Yes, HE Capabilities would be included during Association, so this indeed could 
happen.

Regards,
-Denis