[USRP-users] Bandwidth of USRP N201 with daughterboard LFTX and LFRX

Mike McLernon Mike.McLernon at mathworks.com
Wed Sep 10 13:53:01 EDT 2014

Hi Antoun,

Here is a list of performance improvements you can make in your Simulink models to approach, if not achieve, real-time:

  1.  In the Configuration Parameters → Data Import/Export dialog, turn off all logging.
  2.  Make sure that the model is single-rate. If the model requires resampling, then choose rational coefficients that will keep the model single-rate. For instance, the FM demos in the Communications Blockset use a native frame size of 358, with an initial sample rate of roughly 195 kHz. The signal is eventually piped to an output audio device, which runs at 48 kHz. The model then uses a resampling factor of 44/179 to get close to 48 kHz, and results in good quality audio. (To get to those demos, type ‘demo toolbox commblks’ at the MATLAB command prompt, then navigate in the help browser to Simulink Demos -> SDR Hardware.)
  3.  Do not add any Buffer blocks to the model. Although it's tempting to create friendlier frame lengths than the default, doing so by using a Buffer will severely degrade performance.
  4.  You should try to run with Rapid Accelerator instead of Normal mode. Be aware that some scopes do not plot data when run in Rapid Accelerator mode, but scopes inevitably slow down a model in any case. (See point 6.)
  5.  Try to avoid feedback loops. Typically, such loops imply scalar processing, which will slow down the model considerably.
  6.  Do not use scopes unless absolutely necessary. To visualize your data, send it to a workspace variable and post-process it.
  7.  If you are using Accelerator or Rapid Accelerator, set the Configuration Parameters → Optimization → Compiler optimization level to 'Optimizations on (faster runs)'.
  8.  If the model has lots of Constant blocks, it could help slightly if Configuration Parameters → Optimization (Signals and Parameters) → Inline parameters is checked on. This will cause the sample time of those Constant blocks to truly become inf -- Simulink will get the values once and only once during a run.
  9.  If the model generates code, the Solver setting should be Fixed-step/discrete. The tasking mode should be SingleTasking.

This information should be in the documentation of your USRP support package.


From: USRP-users [mailto:usrp-users-bounces at lists.ettus.com] On Behalf Of FIXED-TERM Ghobrial Antoun (CR/AEH4) via USRP-users
Sent: Wednesday, September 10, 2014 11:40 AM
To: usrp-users at lists.ettus.com
Subject: [USRP-users] Bandwidth of USRP N201 with daughterboard LFTX and LFRX

Hello ,

I am using USRP N210 with daughter boards LFTX and LFRX (operating frequency range is 30 Mhz) using Simulink model. I set the Symbol rate to be 50 KHz .  I need higher data rate .
When I increase the symbol rate more than 50 Khz , it introduces UnderRun messages

Any suggestions please

Mit freundlichen Grüßen / Best regards


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