Re: [Discuss-gnuradio] PFB mapping: M < N?

Thanks, Michael. It's always reassuring to find out "it's not me..."

Although I don't currently need the M < N capability (I was mainly
trying to make sure I understood the docs), I'd like to get your blocks
if you don't mind.

Thanks!
John
----
On 12/06/2017 08:11 PM, Michael Dickens wrote:
> Hi John - You are certainly correct that the documentation could be more
> clear. I recall from reviewing the GR-core provided PFB blocks just a
> few months ago that either a synthesizer or channelizer existed that
> correctly handled the M < N and a mapping, but that the other version
> didn't exist and/or didn't work as advertised. I ended up writing my own
> Python heir blocks for both PFB versions that did the minimum required
> for both PFB channels and mapping. They are not complex scripts, and
> they do what you seem to be looking for: 1 input -> M < N outputs with
> mapping, and the reverse. I'm happy to share if you'd like to try them
> out. Cheers! - MLD
>
> On Mon, Dec 4, 2017, at 10:54 AM, John Ackermann N8UR wrote:
>> I find the documentation about PFB channel mapping to be confusing.
>> I've extracted it below.
>>
>> The first paragraph seems to say the channel map has to have as many
>> elements "M" as the number of outputs "N".
>>
>> But the second and third paragraphs talk about cases where M < N, and
>> only "M out of N channels are driven to an output stream." This seems
>> to contradict the first paragraph.
>>
>> GRC allows me to make a channel map with M elements where M < N, but it
>> still requires me to connect all N ports to a sink. If that's so, why
>> would one ever want map less than N elements? There seems to be no
>> benefit to doing so.
>>
>> Is this documentation contradictory, or confusing, or am I missing
>> something?
>>
>> Thanks,
>> John
>>
>> From https://gnuradio.org/doc/sphinx-3.7.0/filter/channelizers_blk.html:
>> "
>> The map should have the same number of elements as the number of output
>> connections from the block. The minimum value of the map is 0 (for the
>> 0th channel) and the maximum number is N-1 where N is the number of
>> channels.
>>
>> We specify M as the number of output connections made where M <= N, so
>> only M out of N channels are driven to an output stream. The number of
>> items in the channel map should be at least M long. If there are more
>> channels specified, any value in the map over M-1 will be ignored. If
>> the size of the map is less than M the behavior is unknown (we don't
>> wish to check every entry into the work function).
>>
>> This means that if the channelizer is splitting the signal up into N
>> channels but only M channels are specified in the map (where M <= N),
>> then M output streams must be connected and the map and the channel
>> numbers used must be less than N-1. Output channel number can be reused,
>> too. By default, the map is [0...M-1] with M = N."

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