ECG RECORDER SAMPLING AT THE VARIABLE RATE
Piotr Augustyniak, A. Wrzesniowski · 2001
This paper discusses practical aspects of implementation of the signal-dependent adjustable subband coding in a real-world portable long-term digital recorder. Various dependency rules for the local sampling frequency are considered. The most sophisticated one consists in the on-line detection of QRS complexes and adjusting the effective sampling rate to the expected signal bandwidth. The recorded signal is digitized at a constant maximum rate, but immediately afterwards it is split into the mandatory coarse approximation and the facultative, ruledependant upper-band details. Regardless the algorithm uses orthogonal time-frequency decomposition, it is feasible to implement it in the recorder's hardware. The only difference for the hardware using the fixed-point arithmetic is the mandatory use of wavelets that maps integers to integers. The methodological consequences of the use of the fixed-point data representation are focused on in the closing chapter of this paper.