SOURCEFORGE » RALF » 2015 Quantitative analysis of RF signals

1. Synchronisation issues for digital measurements¶

Usually, the USRP does not abide the “IQ sampling rate” that has been entered as an input parameter, and forces a value that is close to it. This “actual IQ sampling rate” is displayed on the user interface. As a result, there is a continuous drift of the sampling time instant regarding the optimal sampling time instant: at a given time, the optimal sampling time instant is reached and the constellation appears, later, the sampling time instant falls between two adjacent symbols and the constellation vanished. This phenomenon can be witnessed on the following video.

Video: Illustration of the continuous drift of the sampling time instant regarding the optimal sampling time instant