Hello Ann,
This question might be best addressed in the [USRP-users] list, as it might be device specific, and you are not explicitly stating if you are using GNURadio for your application.
Before moving your post there, have the following questions in consideration:
* Are you still seeing this problem or have you solved it already?
If you already solved it:
* Could you please share what was the reason behind the unwanted behaviour, and how you overcame it?
If you are still seeing the issue?
* Could you please explain better what the problem really is? Are you seeing Underruns (U)? are you seeing Overruns (O)? or are you having a packet error calculation in your receiver?
The reason why it might be causing problems at higher sample rate might be because your host machine is not keeping up with the generation of samples for transmission and/or processing of received samples (in that case, U's or O's would be shown in terminal). You have to check if it is really a performance issue, being it either that your application is not optimized enough, or that your host machine doesn't really have the computational power to deal with the task. Either way, a better description of the problem is required in order to dig into it.
Regards,
- Nicolas