On quasi-isometry of threshold-based sampling

• Bernhard A. Moser
• M. Lunglmayr

The problem of isometry for threshold-based sampling such as integrate-and-fire (IF) or send-on-delta (SOD) is addressed. While for uniform sampling the Parseval theorem provides isometry and makes the Euclidean metric canonical, there is no analogy for threshold-based sampling. The relaxation of the isometric postulate to quasi-isometry, however, allows the discovery of the underlying metric structure of threshold-based sampling. This paper characterizes this metric structure making Hermann Weyl's discrepancy measure canonical for threshold-based sampling. The usefulness of the approach is demonstrated by means of a novel adaptive threshold-based sampling scheme, which, applied on electrocardiography (ECG) signals, allows a substantial reduction of the number of samples while maintaining nearly the same SNR after reconstruction.