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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Recover the signal |
Date: | Fri, 23 Oct 2015 15:34:06 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 |
Hi Maksim,I sent a lot of different signals using USRP + gnu radio "specially with flat characteristic in frequency domain" but I notice some strange behavior, that the received signals has some spikes. For example, I attached OFDM signal mentioned this behavior in red. I believe what we're looking at is the time domain magnitude of an OFDM signal in complex baseband, right? In that case, I'm not surprised -- OFDM classically has what is typically called a Peak-Average-Power-Ratio (PAPR) problem . Since you know how OFDM works: Assume you feed it a symbol vector of all the same symbols. What does the time domain signal look like? Considering that, these spikes aren't even really high; eyeballing the average power during OFDM transmissionto be around digital 0.15, a maximum peak of three times that isn't really what I'd even consider a spike -- it's not even 5dB higher than the avarage; and considering the noise floor seems to be somewhere around 0.005, your receiver doesn't even need 20dB of dynamic range. Is it because of some properties of USRP?I doubt that; unless you're driving your USRP's frontend's amplifier very hard, you should have 20dB spurious-free dynamic range without problem. Best regards, Marcus On 23.10.2015 15:19, scott tiger wrote:
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