We introduce Xampling, a design methodology for sub-Nyquist sampling of
continuous-time analog signals. The main principles underlying this framework
are the ability to capture a broad signal model, low sampling rate, efficient
analog and digital implementation and lowrate baseband processing. The main
hypothesis of Xampling is that in order to break through the Nyquist barrier,
one has to combine classic methods and results from sampling theory together
with recent developments from the literature of compressed sensing.

The sensing matrix of a compressive system impacts the stability of the
associated sparse recovery problem. In this paper, we study the sensing matrix
of the modulated wideband converter, a recently proposed system for sub-Nyquist
sampling of analog sparse signals. Attempting to quantify the conditioning of
the converter sensing matrix with existing approaches leads to unreasonable
rate requirements, due to the relatively small size of this matrix.