Re: [PATCH] ath: support new FCC DFS Radar Type 1

[Peter Oh <poh@codeaurora.org>]

On 02/27/2015 02:45 AM, Zefir Kurtisi wrote:
> On 02/25/2015 11:17 PM, Peter Oh wrote:
>> Add support for new FCC DFS rules released on August 14, 2014.
>> FCC has added a new radar type named Radar Type 1 and original
>> Radar Type 1 is renamed to Radar Type 0 in consequence.
>> In fact, the type ID does nothing to functionalities.
>> In other words, even if we re-order the IDs, DFS detection will
>> work as well, but we give the ID with matching to FCC doc.
>>
>> By adding this support, the drivers using this DFS function are
>> able to support both of old and new FCC DFS rules simultaneously
>> without any other changes.
>>
>> [...]
> Peter,
>
> while trying to solve detection of the special FCC type 1 radar pattern
> with the
> pri_detector at hand is a valid approach, it is neither suitable nor
> effective.
>
> It is not suitable because in the way you do, it will not reach the
> required
> detection probability required to pass certification. This is because you
> take the
> very first pri to configure its detector specs, which is way too
> optimistic. You
> have to consider that the detector must be able to detect properly with
> only 50%
> of the pulses seen. In this particular case, you would ignore a lot of
> type 1
> patterns, since the resulting visibility gap causes temporary false PRIs
> that
> won't be considered. You might want to have a look on my slides 15ff in
> [1] for an
> idea what needs to be handled.
>
> Generally, to reach the detection probability requirements, the design of
> the
> PRI-detector at hand follows a full-coverage search with fast cancellation
> approach. For that, it allows collecting potential pattern candidates and
> a
> posteriori correction of initial assumptions. It is specifically targeting
> at
> radar patterns defined through PRI-ranges, where constant PRI-ranges are
> supported
> as special cases by setting the same values for pri_min and pri_max (as is
> done
> for pattern 0). With support for PRI-ranges and unique PRIs, everything
> needed to
> detect pattern 1 is there, but defining it as a PRI-range over all the
> unique 23
> PRIs is the wrong way.
>
> The correct approach is more simple, robust, and efficient: define all
> those 23
> unique PRIs as sub-patterns for type 1 with individual specs. Would look
> like:
>
> #define TYPE1_PPB(X) ((19 * 100000) / (36 * X))
> static const struct radar_detector_specs fcc_radar_ref_types[] = {
> 	FCC_PATTERN(0, 0, 1, 1428, 1428, 1, 18, false),
> 	FCC_PATTERN(101, 0, 1, 518, 518, 1, TYPE1_PPB(518), false),
> 	FCC_PATTERN(102, 0, 1, ..., ..., 1, ..., false),
> 	[...],
> 	FCC_PATTERN(123, 0, 1, 3066, 3066, 1, TYPE1_PPB(3066), false),
> 	FCC_PATTERN(2, 0, 5, 150, 230, 1, 23, false),
> 	FCC_PATTERN(3, 6, 10, 200, 500, 1, 16, false),
> 	FCC_PATTERN(4, 11, 20, 200, 500, 1, 12, false),
> 	FCC_PATTERN(5, 50, 100, 1000, 2000, 1, 1, true),
> 	FCC_PATTERN(6, 0, 1, 333, 333, 1, 9, false),
> };
>
>
> Hope it helps, and sorry I didn't do myself, but so far we are only
> working in
> ETSI domains and ignored FCC completely.
Thank you Zefir for the advice and I'll review and update the code based 
on your comment.
>
> Cheers,
> Zefir
>
> [1]
> http://linuxwireless.sipsolutions.net/attachments/en/developers/DFS/Vancou
> ver2011-Slides-DFS.pdf
>
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Thanks,
Peter