|Subject:||Re: [Discuss-gnuradio] diminishing returns with increasing frequency offset|
|Date:||Mon, 21 Mar 2016 03:42:22 +0100|
I didn’t set them and am not an expert, but I think there is no justification for this particular parameter set, i.e., there is no easy formula for calculating ideal parameters. I guess someone started with an educated guess and made simulations to find parameters that worked reasonably well.
Anyhow, I don’t think that the parameters of the MM block are the problem (once you adapted omega of course). As far as I see
- the gain parameters are independent from the sample rate as the error/feedback is calculated once per symbol
- mu is the initial phase and doesn’t matter
- omega relative limit could be cut in half (when using 8MHz). IIRC, it’s the maximum frequency deviation normalised with the sample rate.
What you could try is to adapt alpha of the single pole IIR, to get the same averaging with the increased sample rate.
When this transceiver was implemented, the polyphase clock sync block was not available yet. You are right, it should improve performance. If you switch to that block and see performance improvements, it would be great if you made a pull request.
I think there is no reason why that shouldn’t work. It would be helpful if you could upload your flow graph, maybe there is a mistake somewhere (the picture you posted did not show the USRP and xlating filters, for example).
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