|Subject:||Re: [Discuss-gnuradio] BER over air|
|Date:||Mon, 29 Dec 2014 14:22:41 +0100|
|User-agent:||Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0|
On 12/29/2014 01:58 PM, Mostafa Alizadeh wrote:
it's totally ok to use that model, but only if your application indicates that this is the right model to use. By the way, *all* components in your equation have time dependency (t), so this alone doesn't justify assuming time-invariance.
Estimation h is called gaining channel state information, to give you some hints on what to look for in literature.
convolution with the channel is exactly identical to "applying a filter". This implies your channel is not flat.
If I understand you correctly, then you state exactly what I'm saying: everything you calculate is but an estimate, and the things you can say about SNR are thus only estimates. Whether or not that estimate is a good representation for the reality depends on the way you estimate, and how well your assumptions match reality. This demands a high level of understanding for the underlying concepts!
There's two key words in this paragraph: 1. "channel model" and 2. "acquire".
1. "channel model": this implies you model the channel, ie. you make justified assumptions on what the channel is. in the y(t) = h(t)*x(t)+n(t), it's implied the channel is linear and might have a time dependence.
2. acquiring channel state information usually is done by transmitting something that you already know (e.g. a preamble) or using redundancy (ie. coding); if you're being honest, you would have to say "ok, now that I have information about h, I can actually transmit data, but since it took energy and time to get that information, I must account for this effort (==energy) when considering the effort I have sending the data (==bit energy)". That's a strong argument for not using SNR but E_b/N.
All in all, I think I should stop participating in this thread, since I feel that I'm repeating myself. I'd very very humble suggest that you take a few days with the appropriate theoretical literature on digital communications , as you seem to be about to write something with a very strong theoretical aspect. None of these mails related in any kind to GNU Radio or even SDR, just basic digital communication theory.
Best regards, and all the best,
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