On 29 Aug 2013, at 17:04, Benjamin A. Rolfe
<[email protected]<mailto:[email protected]>> wrote:
I too was confused by this, and *think* I have figured it out (perhaps
incorrectly):
"Unavailable" means the channel is not indicated as available at the specific
location and time of the query. Thus intentional radiation by a whitespace
device is not allowed. In real RF systems, a device transmitting in an
available channel near the unavailable channel will have some energy "spill"
outside the boundaries of the channel. The white space issued and proposed
regulations I have reviewed have different definitions of what is allowed to
"spill". I assume (dangerous word alert) that the intention is to allow
communication of these different regulatory requirements.
Hmm, ok...
FCC regulations do not define "unavailable" but do specify limits on emissions
by TVWS devices outside of the TV channel being used, whether it is indicated
as "available" or not. This is specified as a level relative to transmit signal
level, not absolute dBm (" 72.8 dB below the highest average power in the TV
channel in which the device is operating."). For frequencies beyond the TV
channel adjacent to channel being used, maximum emissions are defined as field
strength (15.209). Representing the later is in dBm requires defining the
parameters for conversion; Note FCC received multiple comments suggesting
changing the adjacent channel requirement to an absolute level and not relative
to an actual level. I don't see how the FCC requirements as issued can be
expressed in this format.
The draft ETSI spec has a table (ยง4.2.4.2.2, Table 3) giving permitted adjacent
frequency leakage ratios. They also appear to be relative to the in-block
power rather than absolute values.
In any event, how would this data model support the perfectly feasible scenario
where a device is offered two adjacent channels, and therefore has "full power"
available in either, but only choses to use one, and therefore must limit its
OOB transmissions in the other?
If what you've described above is the real rationale (and other messages I've
seen suggest it is) then it seems to me that mixing together in-block power
levels and out-of-block power limits in the same frequency table is a big
mistake. There appears to be no way to encode the frequency parameters to say
"you may use 30 dBm in this channel if you're using it, but only leak -30 dBm
into it if you use the adjacent channel instead".
kind regards,
Ray
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