Hardware-assisted lossless ECG coder

This paper describes an implementation of a lossless digital waveform coder as a soft-core CPU custom instruction for use in portable electrocardiogram (ECG) recording systems. Holter monitors are portable ECG recorders that are designed to be worn by the patient for a typical period of 24~48 hours. Such systems can generate large quantities of data, necessitating some form of coding to reduce the size of the stored data. Traditionally, ECG coding methods employ lossy approaches. While such methods can attain better compression than a lossless method, the reduction in signal fidelity may obscure important details in the signal. The coding algorithm implemented consists of a linear decorrelator selected from analysis of a block of samples, followed by entropy coding of the residual using Golomb-Rice codes. The implementation is designed as a custom instruction for the Altera Nios CPU, and when tested on signals from real ECG libraries, performed approximately seven times faster than a software implementation written in C and running on the same CPU