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Re: [Discuss-gnuradio] Best Resample Method For Resampling LTE Data

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Best Resample Method For Resampling LTE Data
Date: Tue, 2 Dec 2014 10:19:50 -0500

On Mon, Dec 1, 2014 at 5:34 PM, Paul Creaser <address@hidden> wrote:
I've used both the Fractional Resampler and the Rational Resampler so far
with reasonable results. At this stage in the case of the Rational
Resampler, I simply use the Interpolation setting and decimation setting to
form a ratio (taps:None, Fractional BW:0), which then generates the required
output sample rate.

One interesting point. When for example resampling from 30.72MHz to
30.72002MHz, I had a look at the FFTs using the QT Gui Frequency Sink. One
thing that struck me was, the rational resampler was acting as a low pass
filter. At both ends of the spectrum I could see a roll off.

I am also looking at trying the Polyphase resampler. Well actually I have
tried it, just I haven't figured out, how to choose the parameters yet!

Yes, all of the resamplers are filters. You need to filter whenever you resample a signal. The rational resampler and PFB resampler both try and find a good default filter such that the signal in the original passband is not distorted but and aliasing or images are properly attenuated. However, Bug #745 on our issue tracker suggests that the default RR taps are not correct. I'm planning on looking into that this week.


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