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From: | Anderson, Douglas J. |
Subject: | Re: [Discuss-gnuradio] Filter bank and massive “DDD” messages |
Date: | Wed, 24 Jun 2015 14:47:57 +0000 |
I recently faced a similar problem with my USRP N210 with a resampler chewing up my CPU. These steps helped a lot:
1) Design a filter with less taps (as Marcus recommended)
2) Build the latest GNURadio and UHD from git, and flash the N210 with the recently released FPGA update.
Not sure if the recent FGPA image update affects the N200 as well, but if it does, take advantage of it.
-Doug
From: discuss-gnuradio-bounces+address@hidden [discuss-gnuradio-bounces+address@hidden on behalf of Marcus Müller address@hidden
Sent: Wednesday, June 24, 2015 1:38 AM To: address@hidden Subject: Re: [Discuss-gnuradio] Filter bank and massive “DDD” messages Hi Luis,
I guess the idea was to look whether your CPU was really your bottleneck; filter banks are one of the most CPU-hungry signal processing steps one can think of, and hence, your "D"ropped packets could be caused by that. If I understand correctly, with the null sink (and/or the file_sink) you don't get that behaviour? If that's the case, your PC can't keep up to both the calculations needed for the filters and receiving the data from your USRP. I think your polyphase filter bank approach has the brightest future (basically because I think polyphase filter banks are cool, and because they are really quite efficient), but your filter parameters are frightening: A transition bandwidth of 10kHz at a sampling rate of 25MHz is 0.04% transition width, which leads to a filter of more than 8000 taps. Relax that transition width! I'd say: start gr_filter_design, and design a filter there, playing around with the parameters until things look better. Generally, you don't even closely seem to need the full 25MS/s you get from the USRP in your flow graphs, but you select different subbands in each flow graph (and in your original mail). What is the real span you need from lower edge of your lowest channel to upper edge of your highest channel? You should let the USRP do as much decimation for you as possible. It's its job! Best regards, Marcus On 06/24/2015 08:34 AM, Luis Grajales wrote:
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