Efficient compression and communication of ECG signals is required for the doctors to remotely monitor the patient in some emergency cases. We investigate the performances of the different signal compression, encoding and communication techniques. We proposed modified run length encoding (MRLE) with the FFT compression of ECG signal. Run length coding is the lossless technique of compression proposed by number of authors. We modified this algorithm for simplification and to increase the system complexity. And then it is applied to the FFT based compressed ECG signal for the purpose of encoding. Overall compression ratio found to be about 6:1. Decompression of the same produces the original ECG with percentage Root mean square Difference of about 1.2%. AWGN is considered in finding the performance of different communication techniques. Performance comparison satisfactorily proves demanding performance through PSK (M-2) modulation scheme of OFDM technique.
Keywords ECG, Fast Fourier Transform, Run Length Encoding, Communication, OFDM, PSK, DPSK, QAM and AWGN channel.
[...] MRLE and Inverse Modified Run Length Encoding (IMRLE) are designed for coding and decoding purpose PROPOSED SYSTEM Figure 1 shows the block diagram of encoder and decoder used in our proposed system ECG Compression Model ECG signal to be transmitted is passed through the FFT calculation. After applying FFT to it, we propose removal of noise in low amplitude levels and then applied MRLE algorithm to encode those FFT coefficients. Encoded signal is digitized and send through the OFDM link. [...]
[...] Logically and practically we concluded that searching of two * in MRLE increases the complexity than searching large number of * in RLE OFDM LINK Compressed ECG signal is transmitted using OFDM link. Various components of OFDM link are shown in Figure 2. First the serial data bit stream is converted into parallel form using Bit to integer Converter for transmitting over multiple subcarriers. Each sub-carrier is modulated using a particular modulation (PSK/DPSK/QAM). Next processing is through OFDM base-band Modulation, Inverse Fast Fourier Transform (IFFT), add cyclic Prefix and parallel to serial conversion to get signal to be transmitted over the channel. [...]
[...] Post-processing checks the 17th bit for assigning positive and negative value and bits to integer converter (16 bit) is used to get the integer value of decoded ECG data stream. = X(k)exp( n N MRLE- Modified Run Length Encoding Run Length Encoding (RLE) is a very simple technique of loss-less data compression. It takes advantages of repetitive data. Its performance depends heavily on the input data statistics. It is FFT- Fast Fourier Transform FFTENCODER is the discrete Fourier transform (DFT) of vector input. [...]
[...] Figure Reconstructed ECG1 signal PSK M-2 QAM M-2 DPSK M-2 PSK M-4 QAM Bit Error Rate SNR in dB Figure Error Signal Figure Comparison curves of various Modulation schemes using OFDM Figure 7 shows the reconstructed ECG signals and error signal between original and reconstructed ECG1 signal is shown in Figure 8. Performance of OFDM with QAM and PSK are found best as compared to others modulating schemes. Compression ratio is the ratio of original size of the ECG to the compressed size (encoded size) of the ECG It is expressed as CR = Original size in bytes Encoded size in bytes Algorithm The distortion between the original and reconstructed signal is measured by Percent Root mean square Difference (PRD).The Percent RMS Difference (PRD) is used to compare how well the re-constructed waveform matches the original data. [...]
[...] We successfully used the OFDM link with various modulation schemes and concluded QAM and PSK modulation schemes with OFDM as a best ECG transmission schemes REFERENCES Zhitao Lu, Dong Youn Kim, William A. Pearlman,” Wavelet Compression of ECG Signals by the Set Partitioning in Hierarchical Trees (SPIHT) Algorithm”, IEEE transactions on Biomedical Engineering, January S. Jalaleddine, C. Hutchens, R. Strattan and W. Coberly, Table PRD and CR comparison of Different Algorithms data compression techniques - A unified approach”, IEEE Trans. [...]
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