Channelizer And Matlab

Re: [Discuss-gnuradio] DDC and Polyphase Channelizer

Hi, Tom:

Please see my comments below.

Thanks

On 12/29/2010 12:58 AM, Tom Rondeau wrote:
> On Mon, Dec 27, 2010 at 3:48 AM, Jimmy Richardson< jmmrchrdsn@gmail.com > wrote:
>> Hi,:
>>
>> I'm learning about polyphase channelizer, and I have been reading fred
>> harris' paper "Digital Receivers and Transmitters Using Polyphase Filter
>> Banks for Wireless Communications". I have also played with the Matlab
>> programs at the end of the paper. What I'm trying to do next is to use
>> GNURadio to do the channelization. I made two attempts, one uses
>> freq_xlating_fir_filter_ccf to implement a DDC channelizer, another uses
>> pfb_channelizer_ccf, running against the data in appendix III of harris'
>> paper. I'm hoping the channelizer result from GNURadio code would match the
>> result from Matlab, but I failed on both, I wonder if someone could help me
>> spot the problem.
>>
>> 1. DDC Channelizer:
>
> Using the frequency xlating filters here is not recommended. You'll
> need to use much longer filters than when using the channelizer. That

Could you clarify? Does this mean I need to change the parameter to
gr.firdes.low_pass, maybe reduce _cutoff_freq?

> said, I'm not sure what would cause the problem you identified below.
> In my opinion, it's not worth doing it this way.

Ok, the reason I did this is because I want a way to verify the result
from pfb channelizer is correct, since I'm not sure if I'm using it
correctly.

>
>> 1.1 Code: The following is the core part of the code (input parsing and
>> various other stuff are omitted), the value for the variables can be found
>> in 1.2
>> self._filter_taps = gr.firdes.low_pass(1, self._input_rate,
>> self._cutoff_freq, self._trans_width,
>>
>> window=gr.firdes.WIN_BLACKMAN_hARRIS)
>> print "Number of taps: _filter_taps = ", len(self._filter_taps)
>>
>> # Blocks
>> self.ddc_filter = list()
>> # i = 0 to M-1
>> for i in xrange(self._M):
>> offset = self._channel_bandwidth * (float(self.

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