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Re: [Discuss-gnuradio] Resampling with USRP

From: Dincer Beken
Subject: Re: [Discuss-gnuradio] Resampling with USRP
Date: Tue, 8 Oct 2013 14:28:40 +0000

I just mixed up things I guess.


After searching a bit more, I saw that the taps below whre for the frac. Resampler. I again looked at python in the NONE case and saw the def design_filter function and implemented it in C++. Did not reached my ultimate goal yet but I think that this is the real solution for the taps in C++ code.


Von: Dincer Beken [mailto:address@hidden
Gesendet: Dienstag, 8.
Oktober 2013 14:55
An: address@hidden
Cc: address@hidden
Betreff: Re: [Openlte-discuss] Resampling with USRP


Interpolator_taps.h in include file solves my issue I guess. Could not see it before.


For the LTE Part, I still am not sure if this is ok for the openLTE project as resampling taps.



Von: Dincer Beken
Gesendet: Dienstag, 8.
Oktober 2013 14:32
An: Dincer Beken;
Betreff: AW: Resampling with USRP


I found the folder: General interpolator Taps (over 3.6). That Is probably my answer…

Though I don’t know if I have to separately install it…


Von: Dincer Beken [mailto:address@hidden]
Gesendet: Dienstag, 8. Oktober 2013 10:00
Betreff: [Openlte-discuss] Resampling with USRP


Hi all,


I want to implement a low pass for the resampler. I am going to use not a polyphase filterbank, because I don’t know its details.


My USRP output is configured to 10Msps. I want to catch a 10Mhz LTE carrier. I want to use a normal resampler with decimation 1000 and interpolation 1536. I guess, need to fill in the taps part with an appropriate low pass filter (H(ejw)).




Since I never implemented in practice a resampler, according to the DSP books, I need to have a low pass filter with gain of L(1536), if I want to use a resampler with non-integer rate (1,536). The low pass filter will have a gain of 1536.  



So I have to following questions:


1-      Can I use the rational_resampler_base_ccc ­or rational_resampler_base_ccf? I am tending more towards the ccc, sing H(ejw) is usually complex. Or do I need to use a PFB filter?

2-      Is a gain with 1536 really necessary? I fear of destroying the Daughterboard.

3-      For the low pass filter, I want to use the gr::filter::firdes::low_pass (1). The sampling rate is L (15,36M). No idea about cutoff frequency and transition with. Can anyone please, please help me with those parameter..

a.       http://gnuradio.org/doc/doxygen/classgr_1_1filter_1_1firdes.html#a772eb5c542093d65518a6d721483aace

I would be very happy, if I could get some help. Especially from anyone who tried to implement openLTE on the USRP.





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