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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Filter bank and massive “DDD” messages |
Date: | Wed, 24 Jun 2015 21:22:02 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 |
Hi Luis,I mean in order to sect an appropriate PC hardware requirements. (sorry if it is an obvious question) .No, that's a very valid question. Generally, the computational load of a filter is basically (n_taps x sampling rate). So, the computational load for the *same* filter scales linearly with rate. BUT: The sharper, measured in 1/sampling rate, a filter is, the more taps it needs. There are approximate formulas for filters where the passband ripple gets designed to be equal to the stoppband ripple; I've learned that with , the stoppband attenuation and the relative transition with () the length N of the filter amounts to: That approximation is "pretty good" in my experience. Now, since N is proportional to the sampling rate, and since the computational load is both proportional to sampling rate and N, you get quadratic dependency on sampling rate for a fixed transition width. Back to your original question: The USRP doesn't really care about the sampling rate. It can, without a problem produce the 25MS/s (or even 50MS/s with 8bit samples), the only limit here is the bandwidth of gigabit ethernet. Everything that can go wrong happens on your PC. Generally, "D" is the worst form of failure, because it means that even your Operating System didn't have enough time to process all the samples. So considering requirements for your PC: With your 8000 real taps filter, you probably won't be able to find a computer that can deal with that like it is. Without taking advantage of polyphase technologies, that would be 16000 real multiplications and 16000 additions per sample -- that's a whopping 16000 FMAC/S * 25MS/s = 400GFMAC/s. GNU Radio has pretty good optimization for filters, so you might get considerable speed up. It's pretty hard hence to say what you need, because it depends so much on what you want to do. Exactly, I don't need to process the full 25 MHz of bandwidth but the problem is that my different subbands are into this spectrum. For example:Yeah, but how much bandwidth do you **really** need at once? Now, the question is: multiplex USRP those 125 channel and will be the new rate 200 Ksps?Sorry, I don't really understand your question. Best regards, Marcus On 06/24/2015 07:41 PM, Luis Grajales
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