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Re: [Discuss-gnuradio] diminishing returns with increasing frequency off

From: tom x
Subject: Re: [Discuss-gnuradio] diminishing returns with increasing frequency offset
Date: Sat, 19 Mar 2016 12:08:41 +0100



I tried doubling both, the sample rate to 8MHz and Omega to 4, but still no progress. The setup is simply the 802.15.4 PHY block connected to a USRP source, listening for an over the air transmission. Can you give some insight on how you picked the other MM Clock Recovery params? Is there any other dependence in the PHY block? The papers and guides I looked at explain what the MM params are but don't give much intuition for choosing them.

Additionally, based on posts in this thread: https://lists.gnu.org/archive/html/discuss-gnuradio/2015-07/msg00585.html ,
 I thought it would be better to replace the MM CR block with a polyphase clock sync block, as "M&M block isn't great in fading environments", and I would like to receive possibly weak signals,
 Again, works for 4 MHz sample rate and 2 samples per symbol, but not 8 MHz rate and 4 samples per signal. What do you think?

Thanks for reading,

On Sat, Mar 19, 2016 at 12:57 AM, Bastian Bloessl <address@hidden> wrote:

> On 18 Mar 2016, at 20:01, tom x <address@hidden> wrote:
> Maybe there is an implicit dependence on 4MHz, in the parameters set by the Clock Recovery block? I am not sure.
> If there's any other relevant info I can give, let me know.

The omega parameter of the MM Clock Recovery defines the samples per symbol (here samples per chip). With a  chip rate of 2Mcps and a sample rate of 4MHz, it is currently set to 2. You will have to adjust this.


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