This is a third attempt at a RADIOTAP header for S1G captures.

Aaron Lee did the work in creating these definitions. I simply transcribed them.

The attached patch defines changes to the Channel field, 0-length-MPDU
field and a new S1G field.

There is also the associated definitions of the S1G NDP field which is
defined in 802.11ah-2016 Section 9.9.

1. Channel field:

3 new values for Mask: 0x0002 for 700 MHz, 0x0004 for 800 MHz and
0x0008 for 900 MHz spectrum channels respectively.

2. 0-length MPDU field:

1 new value: 0x02 in the type value: 2 indicates that this is an S1G
NDP frame and that an S1G field is included in the Radiotap header..

3. The new S1G frame.

It consists of three 16-bit fields, an 8-bit field and a 40-bit field:

U16 known, U16 data1, U16 data2, U8 ndp_type, U8 ndp_data[5]

Known:
0x0001 S1G PPDU format known
0x0002 Response indication known
0x0004 Guard Interval known
0x0008 NSS known
0x0010 Bandwidth known
0x0020 MCS known
0x0040 Color known
0x0080 Is NDP
0x0100 NDP known
0xFE00 Reserved

Data1:
0x0003: S1G PPDU Format: 0=S1G_1M, 1=S1G_SHORT, 2=S1G_LONG
0x000C: Response indication: 0=NO_RESPONSE, 1=NDP_RESPONSE,
2=NORMAL_RESPONSE, 3=LONG_RESPPNSE
0x0010: Reserved
0x0020: Guard interval: 0=Long GI, 1=Short GI
0x00C0: Number spatial streams: 0=1 Spatial stream, 1=2, .. 3=4 Spatial streams
0x0F00: Bandwidth: 0=1MHz, 1=2MHz, 2=4MHz, 3=8MHz, 4=16MHz, 5-15 reserved
0xF000:  MCS (MCS rate index, 0-10, 11-15 reserved)

Data2:
0x000F: Color: 0-7
0xFFF0: Reserved

NDP type:
0x00: NDP Control frame
0x01: NDP Management frame
0x02-0xFF: Reserved

NDP data:

These are as defined in 802.11ah-2016 Section 9.9 except that the top
two bits of data[4] are:

0x00: 1MHz
0x01: 2MHz
0x02-0x03: Reserved

The S1G NPD format is essentially from section 9.9 of 802.11ah-2016
with some additional syntactic sugar:

It is a 40-bit field.

In between, a 1MHz NDP CMAC frame contains 26 used bits and 13 unused
bits. The used bits are defined in section 9.9 of 802.11ah-2016. A
2MHz NDP CMAC frame contains 37 used bits and one unused bit. Again,
the used bits are defined in 802.11ah-2016.

-- 
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)(传说杜康是酒的发明者)