ECG COMPRESSION USING FFT

ECG

The ECG (electrocardiogram)is a diagnostic tool that is routinely used to assess the electrical and muscular functions of the heart.

Sometimes it is required to send the ECG signals from one place to another place. The ECG signals are compressed at first to reduce the amplitude and frequency and then transferred.

FFT

• ECG signals are compressed by using many techniques. One of the most important technique is FFT.

• FFT (Fast Fourier Transform) is a technique used to convert analog signal to digital signal.

FFT

Five Stages

In FFT, The total process takes five steps:-1) Input signal 2) Compression (counter A)3) Compression (counter B)4) Recovery of the original signal by using IFFT5) Error checking

First stageThe input signal (ECG SIGNAL) IS TAKEN

Compression stage (counter A)

There are two stages for compression. In first stage of compression there is a counter A. It identifies the non-zero values of the signal before compression.

After compression length of the compressed signal is compared with the length of the actual signal.

ZERO PADDING

• If the length of the compressed signal is less than the length of the actual signal, then zero padding is done to make equal the lengths of compressed and actual signal.

ZERO PADDING

COMPRESSION STAGE(COUNTER B)

• Now the signal is passed through the counter B. It identifies the non-zero values after the compression of the signal.

• After compression length of the compressed signal is compared with the length of the actual signal

TRUNCATION

Now after compression if the length of the compressed signal is greater than the length of the actual signal, then TRUNCATION of the signal is done.

TRUNCATION

COMPRESSED ECG SIGNAL

Recovery of the original signal by using IFFT

Now by applying IFFT

(Inverse Fast Fourier Transform) the original ECG signal is recovered.

Recovery of the original signal by using IFFT

ERROR CHECKING STAGE

The recovered signal y’(t) is compared with the original signal y(t).

Error is given by e(t)=y(t)-y’(t) e(t)=error in the recovered signal y(t)= original signal y’(t)=recovered signal

ERROR CHECKING STAGE

The compressed signal contains only positive values

Compression Ratio

• Compression ratio is given by• CR=((B-A)/B) *100• CR-Compression ratio• A-compression in counter A• B-compression in counter B • Compression ratio is a major factor to

determine how much compression the signal undergoes.

Applications

It finds application in hospitals,

when a patient’s report is to be send to another doctor in prenominal place.