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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Question regarding correlating output and IQ samples in a reciever |
Date: | Wed, 27 Jan 2016 09:38:32 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
Hi Abhinav, On 01/27/2016 03:17 AM, abhinav narain
wrote:
That "exact sample position" cannot exist, because if it did, you wouldn't need timing recovery. So for example, your timing recovery might implicitely figure out (it won't give you that number, usually; you'd have to integrate over the timing error estimate to get an actual timing offset estimate) that your symbols have duration of 2.236472 samples and start with a sample offset of 114.060072; I don't see how knowing that would map the end of a preamble to any "exact" sample. So what's your modulation scheme? Generally, is only really a useful measure if you either have
Usually, even when you have 1., you do 2.. If you measure SNR based on a subset of bits that actually have
energy, you're biasing your measurement, and it won't have any
meaning for your real transmission, unless you've done the math
and know that these bits represent a certain percentage of the
power of an actual transmission. But as soon as you do the math,
and figure out that some bits have higher Energy per bit , you'd
try to minimize the average , so
that you can just increase the signal amplitude without breaking
your specifications, and get a higher average SNR; this implies
spreading the energy over different bits more evenly, and that
just leads to the whitening mentioned above. Best regards,
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