Re: [Discuss-gnuradio] GnuRadio: Clock Recovery MM: imu out of bounds

On Thu, Aug 20, 2015 at 3:09 AM, Michael B <miboe60@hotmail.com> wrote:

Hi Tom,

Thanks for your answer. That's indeed something that I need to think about more. However, as I understand it, the samples per symbol rate is equal to (samp_rate / data_rate). My sample rate is 500k, and my data rate (i think) is only around 100 or 200. See this figure of my (cleaned) signal:

http://imgur.com/8pNqCop

You see that it takes approximately 10 ms to transmit one symbol. This means 100 symbols per second. As I have 500k samples per second, this means 5k samples per symbol, right?

However, I have tried setting the samples per symbol to 4, just to try, and the 'out of bounds' error still persists.

Regards,
Michael

Decimate decimate decimate. You should down sample your signal as soon as possible to something reasonable. You want your sample rate to be large enough to hold the information, but not too large that you're just wasting cycles. Take your input signal down to reasonably represent the slow data rate so that the actual sps is correct. You can just set these numbers arbitrarily.

Tom

 

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From: tom@trondeau.com
Date: Wed, 19 Aug 2015 09:41:19 -0400
Subject: Re: [Discuss-gnuradio] GnuRadio: Clock Recovery MM: imu out of bounds
To: miboe60@hotmail.com
CC: discuss-gnuradio@gnu.org

On Wed, Aug 19, 2015 at 2:51 AM, Michael B <miboe60@hotmail.com> wrote:

I have created a flowgraph, based on an example of Michael Ossmann, which takes in a signal, and should output bits.

I need to use the clock recovery MM block, which I do not fully understand yet. However, after reading some blogposts, I am quite sure that I can leave most of the settings default, except for the Omega one. Here's my flowgraph:

http://imgur.com/pHRXnZu

When running this flowgraph, it gives me the following error:

thread[thread-per-block[5]:<block clock_recovery_mm_ff (9)>]: mmse_fir_interpolator_ff: imu out of bounds.



While searching, I stumbled upon this piece of code in the source of GnuRadio:


int imu = (int)rint(mu * NSTEPS);  
  if((imu < 0) || (imu > NSTEPS)) {
    throw std::runtime_error("mmse_fir_interpolator_ff: imu out of bounds.\n");
  }

So, I suspect it is not due to my Omega setting (which might be wrong, I have to play with that setting), but that it is due to my Mu setting, which is just the default (0.5). However, I understand that Mu needs to be between 0 and 1, so I do not really understand what the problem is. Anyone who does?

Environment details:

• GNU Radio Companion 3.7.7.1
• Running a GNU Radio live DVD in a virtual machine (VirtualBox 4.2.12) on Windows 7.
• Using Volk machine: ssse3_64

Michael,

I don't have an answer, but I can say where you're doing something wrong. You're samples/symbol (samp_per_sym) is definitely /not/ 2.5k. That's a massively oversampled signal and can't be right. You need to think what's the sampling rate of the system? What's the symbol rate of my signal? That will tell you the samples/symbol you need. It should small, like 2 or 4.

Tom