A New Real-time Lossless Data Compression Algorithm for ECG and PPG Signals

Objective: Data compression is a useful process in tele-monitoring applications, in which lesser number of bits are needed to represent the same data. In this work, a run-time lossless compression of single channel Electrocardiogram (ECG) and Photoplethysmogram (PPG) signal is proposed, maintaining all dominant features. Methods: The single channel data are first quantized using optimal quantization level, so that lesser number of bits are needed to represent it, maintaining low quantization error. Then second order delta encoding and run-length encoding (RLE) based data compression are proposed in this work. A new approach of using ‘buffer array’ along with RLE is also introduced, so that minimum bits are needed to store. Results: This algorithm was tested on various single lead ECG and PPG signals available in Physionet. An average compression ratio (CR) was achieved of 6.52, 3.82, and 2.49 for 547 PTBDB ECG records, 48 MITDB ECG records, and 53 MIMIC-II PPG records, respectively. This algorithm was also performed on single channel ECG, collected from 10 healthy volunteers using AD8232 ECG module, with 125 Hz sampling frequency and 10-bit data resolution, which resulted in average CR of 2.34. Discussion: This algorithm was also performed on a smartphone device that provided user-friendly operation. The low computational complications and standalone operation of data collection, compression, and transmission encouraged its implementation for run-time operation. Significance: A comparative study of proposed work with previously published works proved this fact that this algorithm provided better performance in the area of run-time patient health monitoring applications.