==
They are never reseted and will just increase monotonic.

Maybe:

These four data items monotonically increase for entire duration of the connection; they are never reset.

==
The first Data Item (Radio Channel Active) announces ...

I think (?) this would be better as a bulleted list or some such, rather than paragraph text.

==
... the channels livetime of the radio channel ..

I think this means something like:

... the total time this channel has been used by the radio for any purpose (i.e., the total amount of time the radio has transmitted on this channel) ...

==
A radio that doesn't track the time for receiving and transmitting data explicitly can just add all times the radio channel is not free into the Radio Channel Busy Data Item

I think this might be clearer something like:

If a radio does not track its send or receive times explicitly, it SHOULD still calculate and advertise the Radio Channel Busy Time data item.

==
The router can calculate statistics on the channel usage ...

Maybe:

The router can calculate channel usage statistics ...

==
Is there a potential need for these calculations to apply to either spread spectrum or beam forming systems? I suppose these calculations could be "per reachable neighbor" in that case, but the document doesn't say anything about these situations, so I thought I'd ask.

==
Radio Channel Active Item contains information how long the radio channel has been active.

The diagram is a little confusing (?) ... it seems to imply there could be multiple "active time" sections in the TLV. Maybe something like:

0                   1                   2                   3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Item Type                | Length                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Active Time                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          ...........                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

...and then explain the "active time" is one field?

==
Same thing for the busy and rx data item, etc. fields.

==
Active Time: Time in nanoseconds since the channel has been active.

This could be read two different ways:

- How long has it been since the last transmission on this channel
- The total amount of time this channel has been in use

From the text, the latter is what's wanted, but the text above allows for either. Maybe:

Active Time: Time in nanoseconds this channel has been in use.

==
... Time in nanoseconds the local radio was receiving data ...

Maybe:

... Time in nanoseconds the local radio has received data ...