On Mon, Sep 5, 2011 at 11:55 AM, Tom Rondeau <[email protected]> wrote:
> On Sun, Sep 4, 2011 at 11:33 AM, Ryan Pape <[email protected]> wrote: > >> >> We are successfully using the PFB filterbank to channelize 1-6mhz into a >> variety of channel widths (25K, 50K etc). >> >> In one application, we have 25K channels which are then resampled using >> PFB resampler to 19.2K fed into gmsk_demod @ 9600bps with 2sps. >> >> In this case, we may have 20-40 ports "active" (not null sink) with pfb >> resamplers connected to each. >> >> Is there way to perform this resampling in the filterbank to avoid the >> need for many separate resampler blocks in an effort to improve performance? >> >> We are pushing the limits of hardware already, so any efficiencies are >> helpful. We will consider a hierarchical filterbank structure if necessary, >> but our first goal is to do it with one filterbank, if possible. >> > > Ryan, > What you are talking about is possible, but not with the current > implementation of the GNU Radio channelizer. fred harris has recently > published a few papers on doing arbitrary channel / arbitrary bandwidth > channelizers that should meet your needs, but it would have to be programmed > up. > > Now, that having been said, there is a way to handle this. If you have a > 9600 bps signal in a 25 ksps channel, you can switch to using the > gr_pfb_clock_resampler_fff block, which allows you to specify a real number > for the number of samples per symbol (2.6042 in this case) instead of > integers. That should do the trick. > > > Tom, Thank you. To be clear I'm not looking for arbitrary channel size channelizer, when I said 25K/50K etc, I was just referring to the fact that we are using channelizers of various sizes. the gr_pfb_clock_resampler looks like exactly what I need. Will give it a shot. Also, in our case where we are actively using 20% of channels from the channelizer, it is more advantagous to provide the filterbank with the least computationally intensive channel filter and add a more selective filter on only the channels we are using (but do so with N separate filter blocks), or is the filterbank implementation efficient enough to worry about it and we should design the channel filter to best fit the ultimate need?
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