Re: [Discuss-gnuradio] Questions regarding hierarchical polyphase channelizer

[Sylvain Munaut]

Hi,


> For example for 13e6 GSM band I can extract all channels by setting
> Channels parameter of the channelizer to 65 (13e6/0.2e6).
> Then I can get output signal that is sampled with 4*gsm_symbol_rate by
> setting oversampling to 65/12.
>
> It would be great to have something like this in your block because it
> is more efficient than the regular one. I can look into this if I will
> find some time.

Unfortunately that's not so simple.

If you want to have channel width that's wider that the channel
spacing, that means that in the hierarchy, your first layer will need
to have oversampling as well. (else the channels at the 'border'
between two first layer band would be cut).

So that means the input of the second layer will be oversampled,
meaning that at the output of the second layer, some channels will be
useless (because they'll correspond to the 'sideband' of the
oversampled first layer output) and you'll need to drop them. Also
means your second layer will run at a higher rate, using more CPU. So
your computational overhead becomes much higher and the benefits of
the hierarchical version decreases.


Cheers,

    Sylvain